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Sample records for quartz manganese oxide

  1. Tellurium content of marine manganese oxides and other manganese oxides

    USGS Publications Warehouse

    Lakin, H.W.; Thompson, C.E.; Davidson, D.F.

    1963-01-01

    Tellurium in amounts ranging from 5 to 125 parts per million was present in all of 12 samples of manganese oxide nodules from the floor of the Pacific and Indian oceans. These samples represent the first recognized points of high tellurium concentration in a sedimentary cycle. The analyses may lend support to the theory that the minor-element content of seafloor manganese nodules is derived from volcanic emanations.

  2. Manganese oxidation by Leptothrix discophora.

    PubMed Central

    Boogerd, F C; de Vrind, J P

    1987-01-01

    Cells of Leptothrix discophora SS1 released Mn2+-oxidizing factors into the medium during growth in batch culture. Manganese was optimally oxidized when the medium was buffered with HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) at pH 7.5. Manganese-oxidizing activity in the culture medium in which this strain had been grown previously was sensitive to heat, phosphate, Tris, NaN3, HgCl2 NaCl, sodium dodecyl sulfate, and pronase; 0.5 mol of O2 was consumed per mol of MnO2 formed. During Mn2+ oxidation, protons were liberated. With sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two protein-containing bands were detected in the spent culture medium. One band had an apparent molecular weight of 110,000 and was predominant in Mn2+-oxidizing activity. The second product (Mr 85,000) was only detected in some cases and probably represents a proteolytic breakdown moiety of the 110,000-Mr protein. The Mn2+-oxidizing factors were associated with the MnO2 aggregates that had been formed in spent culture medium. After solubilization of this MnO2 with ascorbate, Mn2+-oxidizing activity could be recovered. Images PMID:3804969

  3. Biomimetic Water-Oxidation Catalysts: Manganese Oxides.

    PubMed

    Kurz, Philipp

    2016-01-01

    The catalytic oxidation of water to molecular oxygen is a key process for the production of solar fuels. Inspired by the biological manganese-based active site for this reaction in the enzyme Photosystem II, researchers have made impressive progress in the last decades regarding the development of synthetic manganese catalysts for water oxidation. For this, it has been especially fruitful to explore the many different types of known manganese oxides MnOx. This chapter first offers an overview of the structural, thermodynamic, and mechanistic aspects of water-oxidation catalysis by MnOx. The different test systems used for catalytic studies are then presented together with general reactivity trends. As a result, it has been possible to identify layered, mixed Mn (III/IV)-oxides as an especially promising class of bio-inspired catalysts and an attempt is made to give structure-based reasons for the good performances of these materials. In the outlook, the challenges of catalyst screenings (and hence the identification of a "best MnOx catalyst") are discussed. There is a great variety of reaction conditions which might be relevant for the application of manganese oxide catalysts in technological solar fuel-producing devices, and thus catalyst improvements are currently still addressing a very large parameter space. Nonetheless, detailed knowledge about the biological catalyst and a solid experimental basis concerning the syntheses and water-oxidation reactivities of MnOx materials have been established in the last decade and thus this research field is well positioned to make important contributions to solar fuel research in the future. PMID:25980320

  4. Environmental Controls of Biological Manganese Oxidation

    NASA Astrophysics Data System (ADS)

    Belz, A. P.; Ahn, C. C.; Nealson, K. H.

    2001-12-01

    Biological catalysis of manganese oxidation represents an important contribution to global manganese cycling; biological oxidation rates are several orders of magnitude higher than those of abiotic processes. Despite recent genetics advances, ongoing behavioral studies, and a large pool of knowledge regarding manganese chemistry, the links between biology and environmental chemistry remain unresolved. We have performed experiments on batch cultures of Leptothrix discophora SS-1 to explore the physiology of biological manganese oxidation. We have further conducted spectroscopic and microscopic studies of the mechanism as manganese proceeds from the soluble Mn2+ species to the insoluble Mn(III) and Mn(IV) phases. These investigations suggest roles for aqueous chemistry, mineralogy, and microbial physiology in controlling manganese fluxes in metal-rich environments.

  5. Synthesis, characterization, optical and sensing property of manganese oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Manigandan, R.; Suresh, R.; Giribabu, K.; Vijayalakshmi, L.; Stephen, A.; Narayanan, V.

    2014-01-01

    Manganese oxide nanoparticles were prepared by thermal decomposition of manganese oxalate. Manganese oxalate was synthesized by reacting 1:1 mole ratio of manganese acetate and ammonium oxalate along with sodium dodecyl sulfate (SDS). The structural characterization of manganese oxalate and manganese oxide nanoparticles was analyzed by XRD. The XRD spectrum confirms the crystal structure of the manganese oxide and manganese oxalate. In addition, the average grain size, lattice parameter values were also calculated using XRD spectrum. Moreover, the diffraction peaks were broadened due to the smaller size of the particle. The band gap of manganese oxide was calculated from optical absorption, which was carried out by DRS UV-Visible spectroscopy. The morphology of manganese oxide nanoparticles was analyzed by SEM images. The FT-IR analysis confirms the formation of the manganese oxide from manganese oxalate nanoparticles. The electrochemical sensing behavior of manganese oxide nanoparticles were investigated using hydrogen peroxide by cyclic voltammetry.

  6. Synthesis, characterization, optical and sensing property of manganese oxide nanoparticles

    SciTech Connect

    Manigandan, R.; Suresh, R.; Giribabu, K.; Narayanan, V.; Vijayalakshmi, L.; Stephen, A.

    2014-01-28

    Manganese oxide nanoparticles were prepared by thermal decomposition of manganese oxalate. Manganese oxalate was synthesized by reacting 1:1 mole ratio of manganese acetate and ammonium oxalate along with sodium dodecyl sulfate (SDS). The structural characterization of manganese oxalate and manganese oxide nanoparticles was analyzed by XRD. The XRD spectrum confirms the crystal structure of the manganese oxide and manganese oxalate. In addition, the average grain size, lattice parameter values were also calculated using XRD spectrum. Moreover, the diffraction peaks were broadened due to the smaller size of the particle. The band gap of manganese oxide was calculated from optical absorption, which was carried out by DRS UV-Visible spectroscopy. The morphology of manganese oxide nanoparticles was analyzed by SEM images. The FT-IR analysis confirms the formation of the manganese oxide from manganese oxalate nanoparticles. The electrochemical sensing behavior of manganese oxide nanoparticles were investigated using hydrogen peroxide by cyclic voltammetry.

  7. Contaminant Transformation by a Biogenic Manganese Oxide

    NASA Astrophysics Data System (ADS)

    Toner, B. M.; Sposito, G.

    2001-12-01

    Biomineralization of manganese by Pseudomonas putida strain MnB1 produces tetravalent manganese oxides that surround the exterior of the bacterial cell. The manganese oxides produced by P. putida transform the herbicide atrazine, a widespread environmental contaminant, by dechlorination, dealkylation and deamination reactions. The transformation reactions catalyzed by biogenic manganese oxide surfaces create a suite of transformation intermediates whose properties, such as aqueous solubility, toxicity and biodegradability, differ dramatically from those of the parent compound. The rates and products of atrazine transformation by biogenic manganese oxide surfaces were examined as functions of temperature and water potential. Air-dry samples of hydrous manganese oxide (δ -MnO2) and biogenic manganese oxide were isopiestically equilibrated to -3.10, -0.50 and -0.04 MPa at 40 degrees Celsius and to -0.04 MPa at 20 and 30 degrees Celcius. The concentrations of atrazine and eight transformation intermediates were determined by HPLC. Our results suggest that biogenic manganese oxides may contribute greatly to the detoxification and immobilization of organic contaminants in the environment because of their nanoparticle size, large surface area and high chemical reactivity.

  8. Manganese oxidation model for rivers

    USGS Publications Warehouse

    Hess, Glen W.; Kim, Byung R.; Roberts, Philip J.W.

    1989-01-01

    The presence of manganese in natural waters (>0.05 mg/L) degrades water-supply quality. A model was devised to predict the variation of manganese concentrations in river water released from an impoundment with the distance downstream. The model is one-dimensional and was calibrated using dissolved oxygen, biochemical oxygen demand, pH, manganese, and hydraulic data collected in the Duck River, Tennessee. The results indicated that the model can predict manganese levels under various conditions. The model was then applied to the Chattahoochee River, Georgia. Discrepancies between observed and predicted may be due to inadequate pH data, precipitation of sediment particles, unsteady flow conditions in the Chattahoochee River, inaccurate rate expressions for the low pH conditions, or their combinations.

  9. Silver manganese oxide electrodes for lithium batteries

    DOEpatents

    Thackeray, Michael M.; Vaughey, John T.; Dees, Dennis W.

    2006-05-09

    This invention relates to electrodes for non-aqueous lithium cells and batteries with silver manganese oxide positive electrodes, denoted AgxMnOy, in which x and y are such that the manganese ions in the charged or partially charged electrodes cells have an average oxidation state greater than 3.5. The silver manganese oxide electrodes optionally contain silver powder and/or silver foil to assist in current collection at the electrodes and to improve the power capability of the cells or batteries. The invention relates also to a method for preparing AgxMnOy electrodes by decomposition of a permanganate salt, such as AgMnO4, or by the decomposition of KMnO4 or LiMnO4 in the presence of a silver salt.

  10. Manganese

    SciTech Connect

    Major-Sosias, M.A.

    1996-10-01

    Manganese (Mn) is a hard, brittle, gray-white transition metal, with the most numerous oxidation states of the elements in the first series of the Periodic Table. Since the manganese atom can donate up to seven electrons from its outer two shells, manganese compounds exist with valences from -3 to +7, the most common being +2, +4, and +7. Due to its sulfur-fixing, deoxidizing, and alloying properties, as well as its low cost, the principal commercial application for manganese is in iron and steel production. Manganese is also employed in non-ferrous metallurgy, batteries and chemical processes. Although potentially harmful to the respiratory and nervous systems, manganese is an essential element for animals and humans, and a micronutrient for plants.

  11. Sol-gel synthesis of manganese oxides

    NASA Astrophysics Data System (ADS)

    Bach, S.; Henry, M.; Baffier, N.; Livage, J.

    1990-10-01

    Transparent and stable manganese dioxide gels are obtained upon reduction of permanganate aqueous solutions AMnO 4 [ A = Li, Na, K, NH 4, N(CH 3) 4] by fumaric acid. All xerogels are amorphous when dried at room temperature. Their thermal behavior however depends on the nature of the counter cation A+. Ammonium permanganates lead to the formation of ?- or ?-Mn 2O 3 while AMnO 2 mixed oxides are obtained at high temperature when A = Li, Na, K. Other crystalline phases such as LiMn 2O 4 or Na 0.7MnO 2 are also formed at lower temperature around 500C. Oxidation of these mixed oxides into sulfuric acid lead to the formation of ?- or ?-MnO 2 while A+ and Mn 2+ ions are released into the solution. Such manganese dioxides could be good candidates for making reversible cathodes in nonaqueous lithium batteries.

  12. Oxidative decarboxylation of diclofenac by manganese oxide bed filter.

    PubMed

    Huguet, Mélissa; Deborde, Marie; Papot, Sébastien; Gallard, Hervé

    2013-09-15

    Diclofenac (DCF) was eliminated by fast chemical oxidation on natural manganese oxide in a column reactor. Identification of transformation by-products of DCF by HPLC-UV-MS(n) gave evidence of decarboxylation, iminoquinone formation and dimerization. The fast oxidation of DCF is also accompanied by a strong adsorption of organic carbon that was explained by the sorption of dimer products on the surface of manganese oxide. Decarboxylation and dimerization increased the hydrophobic interactions with manganese oxide and reduced the presence of potentially toxic by-products in the effluent. The rate of oxidation was first order with respect to DCF and was slowed down by the presence of organic buffer MOPS (3-morpholinopropane-1-sulfonic acid). The first order rate constant in absence of MOPS was extrapolated by considering a surface site-binding model and MOPS as a co-adsorbate. The rate constant was 0.818 min(-1) at pH 7 and 10 mM NaCl corresponding to empty bed residence time of 50 s only for 50% removal of DCF. Rate constants increased when pH decreased from pH 8.0 to 6.5 and when ionic strength increased. Manganese oxide bed filter can be considered as an alternative treatment for polishing waste water effluent or for remediation of contaminated groundwater. PMID:23850215

  13. Oxidation state of marine manganese nodules

    USGS Publications Warehouse

    Piper, D.Z.; Basler, J.R.; Bischoff, J.L.

    1984-01-01

    Analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98% of the Mn in deep ocean nodules is present as Mn(IV). The samples were collected from three quite different areas: the hemipelagic environment of the Guatemala Basin, the pelagic area of the North Pacific, and seamounts in the central Pacific. Results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry: (K, Na, Ca, Ba).33(Mg, Cu, Ni).76Mn5O22(H2O)3.2. ?? 1984.

  14. Manganese Dependent Anaerobic Oxidation of Methane

    NASA Astrophysics Data System (ADS)

    Beal, E.; House, C.

    2007-12-01

    Understanding the anaerobic oxidation is not only important for understanding hydrocarbon degradation but it also important for understanding the global carbon cycle. The anaerobic oxidation of methane (AOM) is a large sink for methane consuming 5-20% of today's methane flux (Valentine and Reeburgh, 2000), yet the requirements for this process are not well understood. It has been suggested that no other electron acceptors other than sulfate can be used in the AOM (Nauhaus, 2005). However, our new data suggests that manganese, in the form of birnessite, can be used as an electron acceptor instead of sulfate (Beal et al., in prep). Methane seep sediment from the Eel River Basin, CA was incubated with methane, 13C-labeled methane, and carbon dioxide. Because the net result of the AOM is the production of carbon dioxide from methane, the rate of the AOM in each of the incubations can be determined by measuring the incorporation of 13C in the carbon dioxide. Using this method, it was found that cultures incubated with nitrate showed inhibition of the AOM, while cultures incubated with iron gave inconclusive results. The only positive results that were found for alternate electron acceptors are the incubations that were given manganese and no sulfate, which showed methane oxidation. Further, when more manganese was injected into these incubations, the rate of AOM increased. Preliminary analysis of the microbial population using terminal restriction fragment length polymorphism (TRFLP) targeting the mcr gene showed an unidentified organism in these cultures. Future work with TRFLP, as well as clone libraries, will help to identify the organisms responsible for this process. Nauhaus, K., 2005, Environmental regulation of the anaerobic oxidation of methane: a comparison of ANME-I and ANME-II communities: Environmental microbiology, v. 7, p. 98. Valentine, D.L., and Reeburgh, W.S., 2000, New perspectives on anaerobic methane oxidation: Environmental Microbiology, v. 2, p. 477-484.

  15. 40 CFR 721.10201 - Cobalt lithium manganese nickel oxide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cobalt lithium manganese nickel oxide... Specific Chemical Substances § 721.10201 Cobalt lithium manganese nickel oxide. (a) Chemical substance and... nickel oxide (PMN P-04-269; CAS No. 182442-95-1) is subject to reporting under this section for...

  16. 40 CFR 721.10201 - Cobalt lithium manganese nickel oxide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cobalt lithium manganese nickel oxide... Specific Chemical Substances § 721.10201 Cobalt lithium manganese nickel oxide. (a) Chemical substance and... nickel oxide (PMN P-04-269; CAS No. 182442-95-1) is subject to reporting under this section for...

  17. 40 CFR 721.10201 - Cobalt lithium manganese nickel oxide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Cobalt lithium manganese nickel oxide... Specific Chemical Substances § 721.10201 Cobalt lithium manganese nickel oxide. (a) Chemical substance and... nickel oxide (PMN P-04-269; CAS No. 182442-95-1) is subject to reporting under this section for...

  18. Thermochemistry of iron manganese oxide spinels

    SciTech Connect

    Guillemet-Fritsch, Sophie; Navrotsky, Alexandra . E-mail: anavrotsky@ucdavis.edu; Tailhades, Philippe; Coradin, Herve; Wang Miaojun

    2005-01-15

    Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} at 298K from the oxides, tetragonal Mn{sub 3}O{sub 4} (hausmannite) and cubic Fe{sub 3}O{sub 4} (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.670.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation-reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. {delta}S{sub mix}, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4.

  19. Sol-gel synthesis of manganese oxides

    SciTech Connect

    Bach, S.; Henry, M.; Baffier, N.; Livage, J. )

    1990-10-01

    Transparent and stable manganese dioxide gels are obtained upon reduction of permanganate aqueous solutions AMnO{sub 4} (A = Li, Na, K, NH{sub 4}, N(CH{sub 3}){sub 4}) by fumaric acid. All xerogels are amorphous when dried at room temperature. Their thermal behavior however depends on the nature of the counter cation A{sup +}. Ammonium permanganates lead to the formation of {alpha}- or {gamma}-Mn{sub 2}O{sub 3} while AMnO{sub 2} mixed oxides are obtained at high temperature when A = Li, Na, K. Other crystalline phases such as LiMn{sub 2}O{sub 4} or Na{sub 0.7}MnO{sub 2} are also formed at lower temperature around 500{degree}C. Oxidation of these mixed oxides into sulfuric acid lead to the formation of {lambda}- or {delta}-MnO{sub 2} while A{sup +} and Mn{sup 2+} ions are released into the solution. Such manganese dioxides could be good candidates for making reversible cathodes in nonaqueous lithium batteries.

  20. Rates of manganese oxidation in aqueous systems

    USGS Publications Warehouse

    Hem, J.D.

    1981-01-01

    The rate of crystal growth of Mn3O4 (hausmannite) and ??MnOOH (feitknechtite) in aerated aqueous manganous perchlorate systems, near 0.01 M in total manganese, was determined at pH levels ranging from 7.00 to 9.00 and at temperatures from 0.5 to 37.4??C. The process is autocatalytic, but becomes psuedo first-order in dissolved Mn2+ activity when the amount of precipitate surface is large compared to the amount of unreacted manganese. Reaction rates determined by titrations using an automated pH-stat were fitted to an equation for precipitate growth. The rates are proportional to surface area of oxide and degree of supersaturation with respect to Mn2+. The oxide obtained at the higher temperature was Mn3O4, but at 0.5?? C only ??MnOOH was formed. At intermediate temperatures, mixtures of these solids were formed. The rate of precipitation of hausmannite is strongly influenced by temperature, and that of feitknechtite much less so. The difference in activation energy may be related to differences in crystal structure of the oxides and the geometry of polymeric hydroxy ion precursors. ?? 1981.

  1. Manganese oxide nanowires, films, and membranes and methods of making

    DOEpatents

    Suib, Steven Lawrence (Storrs, CT); Yuan, Jikang (Storrs, CT)

    2011-02-15

    Nanowires, films, and membranes comprising ordered porous manganese oxide-based octahedral molecular sieves and methods of making the same are disclosed. A method for forming nanowires includes hydrothermally treating a chemical precursor composition in a hydrothermal treating solvent to form the nanowires, wherein the chemical precursor composition comprises a source of manganese cations and a source of counter cations, and wherein the nanowires comprise ordered porous manganese oxide-based octahedral molecular sieves.

  2. Biological Superoxide In Manganese Oxide Formation

    NASA Astrophysics Data System (ADS)

    Hansel, C.; Learman, D.; Zeiner, C.; Santelli, C. M.

    2011-12-01

    Manganese (Mn) oxides are among the strongest sorbents and oxidants within the environment, controlling the fate and transport of numerous elements and the degradation of recalcitrant carbon. Both bacteria and fungi mediate the oxidation of Mn(II) to Mn(III/IV) oxides but the genetic and biochemical mechanisms responsible remain poorly understood. Furthermore, the physiological basis for microbial Mn(II) oxidation remains an enigma. We have recently reported that a common marine bacterium (Roseobacter sp. AzwK-3b) oxidizes Mn(II) via reaction with extracellular superoxide (O2-) produced during exponential growth. Here we expand this superoxide-mediated Mn(II) oxidation pathway to fungi, introducing a surprising homology between prokaryotic and eukaryotic metal redox processes. For instance, Stibella aciculosa, a common soil Ascomycete filamentous fungus, precipitates Mn oxides at the base of asexual reproductive structures (synnemata) used to support conidia (Figure 1). This distribution is a consequence of localized production of superoxide (and it's dismutation product hydrogen peroxide, H2O2), leading to abiotic oxidation of Mn(II) by superoxide. Disruption of NADPH oxidase activity using the oxidoreductase inhibitor DPI leads to diminished cell differentiation and subsequent Mn(II) oxidation inhibition. Addition of Cu(II) (an effective superoxide scavenger) leads to a concentration dependent decrease in Mn oxide formation. We predict that due to the widespread production of extracellular superoxide within the fungal and likely bacterial kingdoms, biological superoxide may be an important contributor to the cycling of Mn, as well as other metals (e.g., Hg, Fe). Current and future explorations of the genes and proteins involved in superoxide production and Mn(II) oxidation will ideally lend insight into the physiological and biochemical basis for these processes.

  3. [Ferrous-manganese oxidizing bacteria from the nature water].

    PubMed

    Qin, Song-yan; Ma, Fang; Huang, Peng

    2008-06-01

    Glass slides were hanged into a canal to acquire the ferrous-manganese oxidizing bacteria settled bio-film. Two isolated methods for ferrous-manganese oxidizing bacteria with special iron-manganese oxidizing matrix from the bio-film were tested. Element component of bacteria product and sheath structure of bacteria were analyzed. With two methods, plate cultivation and the novel semi-solid in situ cultivation method, strains belong to Family Leptothrix were isolated. XRF showed that the amorphous iron and manganese were two major metal elements of the precipitation formed by one strain of Leptothrix spp.. Through the microscope observation, one strain of Family Leptothrix was determined to form branch-like structured sheath, while another strain formed spider web-like structured sheath. Those isolated bacteria provide model strains for future testing of FISH probe and PCR primer of ferrous-manganese oxidizing bacteria. PMID:18763517

  4. Electrochromic reactions in manganese oxides I. Raman analysis

    SciTech Connect

    Bernard, M.C.; Hugot-Le Goff, A.; Thi, B.V. . UPR 15 du CNRS Physique des Liquides et Electrochimie); Cordoba de Torresi, S. . Dept. de Fisica Aplicada)

    1993-11-01

    Like nickel oxide, manganese oxide is a widely studied material in the primary batteries field. The reactions taking place during voltametric cycling of manganese oxides can be determined using in situ Raman spectroscopy. The main difficulty for the oxide identification is to obtain relevant Raman reference spectra because of the many possible compounds and, for some of these compounds, of their instability in the laser beam. As a consequence, several modifications of different tetra-, tri- and divalent manganese oxides and oxyhydroxides were carefully studied. The electrochromic behavior of three types of manganese oxides, two prepared by thermal oxidations and the other by electrochemical deposition, were then compared. The presence of nonstoichiometry in the pristine material was necessary to obtain a reversible electrochromic effect. The reaction during electrochromic cycling is more complicated than a simple passage from MnO[sub 2] to MnOOH.

  5. Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor

    NASA Technical Reports Server (NTRS)

    Myers, Charles R.; Nealson, Kenneth H.

    1988-01-01

    Microbes that couple growth to the reduction of manganese could play an important role in the biogeochemistry of certain anaerobic environments. Such a bacterium, Alteromonas putrefaciens MR-1, couples its growth to the reduction of manganese oxides only under anaerobic conditions. The characteristics of this reduction are consistent with a biological, and not an indirect chemical, reduction of manganese, which suggest that this bacterium uses manganic oxide as a terminal electron acceptor. It can also utilize a large number of other compounds as terminal electron acceptors; this versatility could provide a distinct advantage in environments where electron-acceptor concentrations may vary.

  6. 40 CFR 721.10011 - Barium calcium manganese strontium oxide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Barium calcium manganese strontium... Specific Chemical Substances § 721.10011 Barium calcium manganese strontium oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium...

  7. 40 CFR 721.10011 - Barium calcium manganese strontium oxide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Barium calcium manganese strontium... Specific Chemical Substances § 721.10011 Barium calcium manganese strontium oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium...

  8. 40 CFR 721.10011 - Barium calcium manganese strontium oxide.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Barium calcium manganese strontium... Specific Chemical Substances § 721.10011 Barium calcium manganese strontium oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium...

  9. 40 CFR 721.10011 - Barium calcium manganese strontium oxide.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Barium calcium manganese strontium... Specific Chemical Substances § 721.10011 Barium calcium manganese strontium oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium...

  10. 40 CFR 721.10011 - Barium calcium manganese strontium oxide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Barium calcium manganese strontium... Specific Chemical Substances § 721.10011 Barium calcium manganese strontium oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium...

  11. Metal Doped Manganese Oxide Thin Films for Supercapacitor Application.

    PubMed

    Tung, Mai Thanh; Thuy, Hoang Thi Bich; Hang, Le Thi Thu

    2015-09-01

    Co and Fe doped manganese oxide thin films were prepared by anodic deposition at current density of 50 mA cm(-2) using the electrolyte containing manganese sulfate and either cobalt sulfate or ferrous sulfate. Surface morphology and crystal structure of oxides were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD). Chemical composition of materials was analyzed by X-ray energy dispersive spectroscope (EDS), iodometric titration method and complexometric titration method, respectively. Supercapacitive behavior of Co and Fe doped manganese oxide films were characterized by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The results show that the doped manganese oxides are composed of nano fiber-like structure with radius of 5-20 nm and remain amorphous structure after heat treatment at 100 degrees C for 2 hours. The average valence of manganese increases from +3.808 to +3.867 after doping Co and from +3.808 to +3.846 after doping Fe. The doped manganese oxide film electrodes exhibited preferably ideal pseudo-capacitive behavior. The specific capacitance value of deposited manganese oxide reaches a maximum of 175.3 F/g for doping Co and 244.6 F/g for doping Fe. The thin films retained about 84% of the initial capacity even after 500 cycles of charge-discharge test. Doping Co and Fe decreases diffusion and charge transfer resistance of the films. The electric double layer capacitance and capacitor response frequency are increased after doping. PMID:26716267

  12. Manganese superoxide dismutase and oxidative stress modulation.

    PubMed

    Bresciani, Guilherme; da Cruz, Ivana Beatrice Mnica; Gonzlez-Gallego, Javier

    2015-01-01

    Oxidative stress is characterized by imbalanced reactive oxygen species (ROS) production and antioxidant defenses. Two main antioxidant systems exist. The nonenzymatic system relies on molecules to directly quench ROS and the enzymatic system is composed of specific enzymes that detoxify ROS. Among the latter, the superoxide dismutase (SOD) family is important in oxidative stress modulation. Of these, manganese-dependent SOD (MnSOD) plays a major role due to its mitochondrial location, i.e., the main site of superoxide (O(2)(-)) production. As such, extensive research has focused on its capacity to modulate oxidative stress. Early data demonstrated the relevance of MnSOD as an O(2)(-) scavenger. More recent research has, however, identified a prominent role for MnSOD in carcinogenesis. In addition, SOD downregulation appears associated with health risk in heart and brain. A single nucleotide polymorphism which alters the mitochondria signaling sequence for the cytosolic MnSOD form has been identified. Transport into the mitochondria was differentially affected by allelic presence and a new chapter in MnSOD research thus begun. As a result, an ever-increasing number of diseases appear associated with this allelic variation including metabolic and cardiovascular disease. Although diet and exercise upregulate MnSOD, the relationship between environmental and genetic factors remains unclear. PMID:25858870

  13. Microbial Manganese Oxidation in Saltmarsh Surface Sediments Using a Leuco Crystal Violet Manganese Oxide Detection Technique

    NASA Astrophysics Data System (ADS)

    Spratt, Henry G.; Siekmann, Ellen C.; Hodson, Robert E.

    1994-01-01

    Microbial manganese (Mn) oxide production in surface sediments of a Georgia saltmarsh was directly measured using an assay involving the oxidation of 4,4',4?-methylidynetris (N,N-dimethylaniline), leuco crystal violet (LCV), by Mn oxides to produce crystal violet. The assay exhibits high specificity for Mn oxides without interference by Mn(II) and is sufficiently sensitive to determine rates of Mn oxidation in surface sediment or saltmarsh creek water suspensions. Sample salinity affects crystal violet absorbance in the 0-25 salinity range and must be corrected for in Mn oxide determinations for estuarine samples of variable salinity. Other oxidants found to oxidize LCV slowly included Cl(I), Cr(III), I(V), Fe(III), and Mn(III), although the sensitivity of the assay for Mn(IV) oxides was found to be seven times greater than for Mn(III), and at least 100 times greater than for any of the other oxidants. Rates of abiotic Mn oxide production in sediment suspensions treated with either sodium azide or formalin, or autoclaved, were much slower than rates determined for untreated sediments. Sodium azide (77 mM) inhibited Mn oxide production in these sediment suspensions to rates between 5 and 10% of the rates of Mn oxidation determined for unamended suspensions. Manganese oxidation was highly temperature dependent, with maximal rates on a dry weight basis (89 nmol mg dwt -1 h -1), occurring at 60C, and negligible activity at 100 and 0C. Rates were also dependent on sample pH, with maximal rates at pH 67, decreasing to near 0 as the pH was lowered to approximately 30. For Mn(II) concentrations ranging from 9 to 91 ?M, rates of Mn oxide production were independent of Mn(II) concentration, while Mn oxide production was inhibited at concentrations greater than 91 ?M (e.g. by 25-40% at 450 ?M). Rates of microbial Mn oxide production in surface sediment/saltmarsh creek water suspensions incubated under natural conditions of temperature, pH, and Mn(II) concentration ranged from 049 to 27 nmol mg dwt -1 h -1 and were nearly four times higher in surface sediments from creek banks than in sediments from the high marsh. The microorganisms associated with saltmarsh creek water particulate matter oxidized Mn(II) at rates intermediate to the values obtained for the two types of surface sediments, averaging 098 nmol mg dwt -1 h -1.

  14. Three manganese oxide-rich marine sediments harbor similar communities of acetate-oxidizing manganese-reducing bacteria

    PubMed Central

    Vandieken, Verona; Pester, Michael; Finke, Niko; Hyun, Jung-Ho; Friedrich, Michael W; Loy, Alexander; Thamdrup, Bo

    2012-01-01

    Dissimilatory manganese reduction dominates anaerobic carbon oxidation in marine sediments with high manganese oxide concentrations, but the microorganisms responsible for this process are largely unknown. In this study, the acetate-utilizing manganese-reducing microbiota in geographically well-separated, manganese oxide-rich sediments from Gullmar Fjord (Sweden), Skagerrak (Norway) and Ulleung Basin (Korea) were analyzed by 16S rRNA-stable isotope probing (SIP). Manganese reduction was the prevailing terminal electron-accepting process in anoxic incubations of surface sediments, and even the addition of acetate stimulated neither iron nor sulfate reduction. The three geographically distinct sediments harbored surprisingly similar communities of acetate-utilizing manganese-reducing bacteria: 16S rRNA of members of the genera Colwellia and Arcobacter and of novel genera within the Oceanospirillaceae and Alteromonadales were detected in heavy RNA-SIP fractions from these three sediments. Most probable number (MPN) analysis yielded up to 106 acetate-utilizing manganese-reducing cells cm−3 in Gullmar Fjord sediment. A 16S rRNA gene clone library that was established from the highest MPN dilutions was dominated by sequences of Colwellia and Arcobacter species and members of the Oceanospirillaceae, supporting the obtained RNA-SIP results. In conclusion, these findings strongly suggest that (i) acetate-dependent manganese reduction in manganese oxide-rich sediments is catalyzed by members of taxa (Arcobacter, Colwellia and Oceanospirillaceae) previously not known to possess this physiological function, (ii) similar acetate-utilizing manganese reducers thrive in geographically distinct regions and (iii) the identified manganese reducers differ greatly from the extensively explored iron reducers in marine sediments. PMID:22572639

  15. Manganese Oxide-Based Chemically Powered Micromotors.

    PubMed

    Safdar, Muhammad; Wani, Owies M; Jänis, Janne

    2015-11-25

    Chemically powered micromotors represent an exciting research area in nanotechnology. Such artificial devices are typically driven by catalytic bubble formation, taking place at the solid-liquid interface. Platinum has been most frequently used for the fabrication of different micromotors due to its superior catalytic efficiency. Other materials typically suffer from slow speeds and require very high concentrations of chemical fuel. Here, we report preparation and characterization of fast moving micromotors based on manganese oxide (MnO2) with different geometrical shapes (tubes, rods, and spheres). On the basis of the results, the prepared micromotors reached the highest speeds (up to ∼900 μm s(-1) in 10% H2O2) reported to date for any MnO2-based micromotors. Moreover, they moved by bubble propulsion even at very low concentrations of peroxide fuel. Thus, MnO2 represents a promising material for the preparation of micromotors for various biomedical or environmental applications, where high speeds are desired. PMID:26551302

  16. Giant negative magnetoresistance in Manganese-substituted Zinc Oxide

    PubMed Central

    Wang, X. L.; Shao, Q.; Zhuravlyova, A.; He, M.; Yi, Y.; Lortz, R.; Wang, J. N.; Ruotolo, A.

    2015-01-01

    We report a large negative magnetoresistance in Manganese-substituted Zinc Oxide thin films. This anomalous effect was found to appear in oxygen-deficient films and to increase with the concentration of Manganese. By combining magnetoresistive measurements with magneto-photoluminescence, we demonstrate that the effect can be explained as the result of a magnetically induced transition from hopping to band conduction where the activation energy is caused by the sp-d exchange interaction. PMID:25783664

  17. Giant negative magnetoresistance in Manganese-substituted Zinc Oxide.

    PubMed

    Wang, X L; Shao, Q; Zhuravlyova, A; He, M; Yi, Y; Lortz, R; Wang, J N; Ruotolo, A

    2015-01-01

    We report a large negative magnetoresistance in Manganese-substituted Zinc Oxide thin films. This anomalous effect was found to appear in oxygen-deficient films and to increase with the concentration of Manganese. By combining magnetoresistive measurements with magneto-photoluminescence, we demonstrate that the effect can be explained as the result of a magnetically induced transition from hopping to band conduction where the activation energy is caused by the sp-d exchange interaction. PMID:25783664

  18. Manganese-oxidizing bacteria mediate the degradation of 17?-ethinylestradiol.

    PubMed

    Sabirova, Julia S; Cloetens, L F F; Vanhaecke, L; Forrez, I; Verstraete, Willy; Boon, N

    2008-11-01

    Manganese (II) and manganese-oxidizing bacteria were used as an efficient biological system for the degradation of the xenoestrogen 17?-ethinylestradiol (EE2) at trace concentrations. Mn(2+)-derived higher oxidation states of Mn (Mn(3+), Mn(4+)) by Mn(2+)-oxidizing bacteria mediate the oxidative cleavage of the polycyclic target compound EE2. The presence of manganese (II) was found to be essential for the degradation of EE2 by Leptothrix discophora, Pseudomonas putida MB1, P. putida MB6 and P. putida MB29. Mn(2+)-dependent degradation of EE2 was found to be a slow process, which requires multi-fold excess of Mn(2+) and occurs in the late stationary phase of growth, implying a chemical process taking place. EE2-derived degradation products were shown to no longer exhibit undesirable estrogenic activity. PMID:21261871

  19. Acetone oxidation using ozone on manganese oxide catalysts.

    PubMed

    Xi, Yan; Reed, Corey; Lee, Yong-Kul; Oyama, S Ted

    2005-09-22

    Supported manganese oxide catalysts were prepared by the impregnation of alumina foam blocks washcoated with alumina and silica. The manganese content based on the weight of the washcoats was 10 wt % calculated as MnO2. Fourier transform profiles of the Mn K-edge EXAFS spectra for these samples gave three distinctive peaks at 0.15, 0.25, and 0.32 nm and were close to the profiles of Mn3O4 and beta-MnO2. The number of surface active sites was determined through oxygen chemisorption measurements at a reduction temperature (Tred = 443 K) obtained from temperature-programmed reduction (TPR) experiments. Acetone catalytic oxidation was studied from room temperature to 573 K, and was found to be highly accelerated by the use of ozone on both catalysts with substantial reductions in the reaction temperature. The only carbon-containing product detected was CO2. The alumina-supported catalyst was found to be more active than the silica-supported catalyst in acetone and ozone conversion, with higher turnover frequencies (TOFs) for both reactions. The pressure drop through the foam was low and increased little (0.003 kPa/10 000 h(-1)) with space velocity. In situ steady-state Raman spectroscopy measurements during the acetone catalytic oxidation reaction showed the presence of an adsorbed acetone species with a C-H bond at 2930 cm(-1) and a peroxide species derived from ozone with an O-O bond at 890 cm(-1). PMID:16853250

  20. Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

    PubMed Central

    Birkner, Nancy; Nayeri, Sara; Pashaei, Babak; Najafpour, Mohammad Mahdi; Casey, William H.; Navrotsky, Alexandra

    2013-01-01

    Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn3+/Mn4+ ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states. PMID:23667149

  1. The sorption of silver by poorly crystallized manganese oxides

    USGS Publications Warehouse

    Anderson, B.J.; Jenne, E.A.; Chao, T.T.

    1973-01-01

    The sorption of silver by poorly crystallized manganese oxides was studied using synthesized samples of three members of the manganous manganite (birnessite) group, of different chemical composition and crystallinity, and a poorly organized ??-MnO2. All four oxides sorbed significant quantities of silver. The manganous manganites showed the greatest sorption (up to 0.5 moles silver/mole MnOx at pH 7) while the ??-MnO2 showed the least (0.3 moles silver/ mole MnOx at pH 7). Sorption of silver was adequately described by the Langmuir equation over a considerable concentration range. The relationship failed at low pH values and high equilibrium silver concentrations. The sorption capacity showed a direct relationship with pH. However, the rate of increase of sorption capacity decreased at the higher pH values. Silver sorption maxima. were not directly related to surface area but appeared to vary with the amount of occluded sodium and potassium present in the manganese oxide. The important processes involved in the uptake of silver by the four poorly crystallized manganese oxides ara considered to be surface exchange for manganese, potassium and sodium as well as exchange for structural manganese, potassium and sodium. ?? 1973.

  2. Synthesis of manganese oxide supported on mesoporous titanium oxide: Influence of the block copolymer

    SciTech Connect

    Schmit, F.; Bois, L.; Chiriac, R.; Toche, F.; Chassagneux, F.; Besson, M.; Descorme, C.; Khrouz, L.

    2015-01-15

    Manganese oxides supported on mesoporous titanium oxides were synthesized via a sol–gel route using block copolymer self-assembly. The oxides were characterized by X-ray diffraction, infrared spectroscopy, thermal analyses, nitrogen adsorption/desorption, electron microscopy and electronic paramagnetic resonance. A mesoporous anatase containing amorphous manganese oxide particles could be obtained with a 0.2 Mn:Ti molar ratio. At higher manganese loading (0.5 Mn:Ti molar ratio), segregation of crystalline manganese oxide occurred. The influence of block copolymer and manganese salt on the oxide structure was discussed. The evolution of the textural and structural characteristics of the materials upon hydrothermal treatment was also investigated. - Graphical abstract: One-pot amorphous MnO{sub 2} supported on mesoporous anataseTiO{sub 2}. - Highlights: • Mesoporous manganese titanium oxides were synthesized using block copolymer. • Block copolymers form complexes with Mn{sup 2+} from MnCl{sub 2}. • With block copolymer, manganese oxide can be dispersed around the titania crystallites. • With Mn(acac){sub 2}, manganese is dispersed inside titania. • MnOOH crystallizes outside mesoporous titania during hydrothermal treatment.

  3. Suppressing Manganese Dissolution from Lithium Manganese Oxide Spinel Cathodes with Single-Layer Graphene

    SciTech Connect

    Jaber-Ansari, Laila; Puntambekar, Kanan P.; Kim, Soo; Aykol, Muratahan; Luo, Langli; Wu, Jinsong; Myers, Benjamin D.; Iddir, Hakim; Russell, John T.; Saldana, Spencer J.; Kumar, Rajan; Thackeray, Michael M.; Curtiss, Larry A.; Dravid, Vinayak P.; Wolverton, Christopher M.; Hersam, Mark C.

    2015-06-24

    Spinel-structured LiMn 2 O 4 (LMO) is a desirable cathode material for Li-ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single-layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene-coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X-ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single-layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn 3+ at the LMO electrode surface, promoting an oxidation state change to Mn 4+ , which suppresses dissolution.

  4. 40 CFR 721.10010 - Barium manganese oxide (BaMnO3).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Barium manganese oxide (BaMnO3). 721... Substances 721.10010 Barium manganese oxide (BaMnO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium manganese oxide (BaMnO3) (PMN...

  5. 40 CFR 721.10010 - Barium manganese oxide (BaMnO3).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Barium manganese oxide (BaMnO3). 721... Substances 721.10010 Barium manganese oxide (BaMnO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium manganese oxide (BaMnO3) (PMN...

  6. 40 CFR 721.10010 - Barium manganese oxide (BaMnO3).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Barium manganese oxide (BaMnO3). 721... Substances 721.10010 Barium manganese oxide (BaMnO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium manganese oxide (BaMnO3) (PMN...

  7. 40 CFR 721.10010 - Barium manganese oxide (BaMnO3).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Barium manganese oxide (BaMnO3). 721... Substances 721.10010 Barium manganese oxide (BaMnO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium manganese oxide (BaMnO3) (PMN...

  8. 40 CFR 721.10010 - Barium manganese oxide (BaMnO3).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Barium manganese oxide (BaMnO3). 721... Substances 721.10010 Barium manganese oxide (BaMnO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as barium manganese oxide (BaMnO3) (PMN...

  9. 40 CFR 721.10529 - Cobalt iron manganese oxide, carboxylic acid-modified (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cobalt iron manganese oxide... Significant New Uses for Specific Chemical Substances § 721.10529 Cobalt iron manganese oxide, carboxylic acid... substance identified generically as cobalt iron manganese oxide, carboxylic acid-modified (PMN P-12-35)...

  10. 40 CFR 721.10529 - Cobalt iron manganese oxide, carboxylic acid-modified (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cobalt iron manganese oxide... Significant New Uses for Specific Chemical Substances § 721.10529 Cobalt iron manganese oxide, carboxylic acid... substance identified generically as cobalt iron manganese oxide, carboxylic acid-modified (PMN P-12-35)...

  11. 40 CFR 721.4587 - Lithium manganese oxide (LiMn204) (generic name).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Lithium manganese oxide (LiMn204... Specific Chemical Substances § 721.4587 Lithium manganese oxide (LiMn204) (generic name). (a) Chemical... as lithium manganese oxide (LiMn204) (P-96-175) is subject to reporting under this section for...

  12. 40 CFR 721.10013 - Manganese yttrium oxide (Mn2YO5).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Manganese yttrium oxide (Mn2YO5). 721... Substances 721.10013 Manganese yttrium oxide (Mn2YO5). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (Mn2YO5) (PMN...

  13. 40 CFR 721.10013 - Manganese yttrium oxide (Mn2YO5).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Manganese yttrium oxide (Mn2YO5). 721... Substances 721.10013 Manganese yttrium oxide (Mn2YO5). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (Mn2YO5) (PMN...

  14. 40 CFR 721.10013 - Manganese yttrium oxide (Mn2YO5).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Manganese yttrium oxide (Mn2YO5). 721... Substances 721.10013 Manganese yttrium oxide (Mn2YO5). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (Mn2YO5) (PMN...

  15. 40 CFR 721.10009 - Manganese yttrium oxide (MnYO3).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Manganese yttrium oxide (MnYO3). 721... Substances 721.10009 Manganese yttrium oxide (MnYO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (MnYO3) (PMN...

  16. 40 CFR 721.10009 - Manganese yttrium oxide (MnYO3).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Manganese yttrium oxide (MnYO3). 721... Substances 721.10009 Manganese yttrium oxide (MnYO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (MnYO3) (PMN...

  17. 40 CFR 721.10009 - Manganese yttrium oxide (MnYO3).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Manganese yttrium oxide (MnYO3). 721... Substances 721.10009 Manganese yttrium oxide (MnYO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (MnYO3) (PMN...

  18. 40 CFR 721.10009 - Manganese yttrium oxide (MnYO3).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Manganese yttrium oxide (MnYO3). 721... Substances 721.10009 Manganese yttrium oxide (MnYO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (MnYO3) (PMN...

  19. 40 CFR 721.10013 - Manganese yttrium oxide (Mn2YO5).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Manganese yttrium oxide (Mn2YO5). 721... Substances 721.10013 Manganese yttrium oxide (Mn2YO5). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (Mn2YO5) (PMN...

  20. 40 CFR 721.10009 - Manganese yttrium oxide (MnYO3).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Manganese yttrium oxide (MnYO3). 721... Substances 721.10009 Manganese yttrium oxide (MnYO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (MnYO3) (PMN...

  1. 40 CFR 721.10013 - Manganese yttrium oxide (Mn2YO5).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Manganese yttrium oxide (Mn2YO5). 721... Substances 721.10013 Manganese yttrium oxide (Mn2YO5). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese yttrium oxide (Mn2YO5) (PMN...

  2. Characterization of Newly-Formed Manganese (Hydr)oxides in Biofilms in Pinal Creek, Arizona

    NASA Astrophysics Data System (ADS)

    Gilbert, H.; Conklin, M.; O'Day, P.

    2003-12-01

    Active, biologically mediated precipitation of manganese (hydr)oxides (Mn-oxides) in Pinal Creek, Arizona, a stream with a history of high manganese levels due to historic mining practices, was studied to determine the identity of newly formed phases and their ability to sequester other metals. Packages of crushed grains of eight clean mineral substrates, quartz, ilmenite, microcline, rutile, magnetite, hematite and labradorite, were placed in Pinal Creek for one to three months. Glass slides were set out as well in order to characterize biofilm formation. After retrieval and drying, the coating distributions were characterized using scanning electron microscopy (SEM), energy dispersive analysis, and X-ray absorption spectroscopy. Morphologically, coating material developed on the different substrates after one month appeared similar to those developed after two and three months. Overall, the SEM images indicate poorly crystalline, aggregated particles that are small (less than a few microns in general) and lack geometric regularity, although size estimates are somewhat hindered by particle aggregation. The coatings that formed on the microscope slides are characterized as biofilms, as numerous microorganisms were observed using microscopy, both confocal and SEM. Samples were further characterized using extended x-ray absorption fine structure spectroscopy (EXAFS) on coatings that had been separated from mineral substrates. EXAFS spectra of material from rutile and quartz substrates and the biofilm were analyzed and fit, using a natural and synthetic birnessite compounds as reference spectra. This analysis suggests that the rutile, quartz, and biofilm samples are composed of a disordered Mn-oxide that is similar in local structure to a natural birnessite of low symmetry. The formation of disordered, poorly crystalline birnessite is important, as it is an extremely efficient metal scavenger and the interlayer vacancies in the birnessite structure aids in metal sequestration.

  3. Manganese

    MedlinePLUS

    Manganese is a mineral that is found in several foods including nuts, legumes, seeds, tea, whole grains, and leafy green vegetables. It is ... manganese by mouth along with other vitamins and minerals can promote growth in children who have low ...

  4. Reduction in the Band Gap of Manganese-Doped Zinc Oxide: Role of the Oxidation State

    NASA Astrophysics Data System (ADS)

    Sharma, Sonia; Ramesh, Pranith; Swaminathan, P.

    2015-12-01

    Manganese-doped zinc oxide powders were synthesized by solid state reaction of the respective oxides. The high-temperature conditions were chosen such that multiple valence states of manganese were doped in the host zinc oxide lattice. Structural characterization was carried out to confirm the doping and to find the maximum amount of manganese that can be incorporated. Diffuse reflectance spectroscopy was used to measure the optical band gap of the doped sample and the lowering with respect to pure ZnO was attributed to the presence of higher oxidation states of manganese. The presence of these oxidation states was confirmed using x-ray photoelectron spectroscopy. The study shows that a solid state reaction is a viable route for synthesizing doped metal oxides with desired optical properties.

  5. Manganese oxidation state mediates toxicity in PC12 cells

    SciTech Connect

    Reaney, S.H. . E-mail: stevereaney@hotmail.com; Smith, D.R.

    2005-06-15

    The role of the manganese (Mn) oxidation state on cellular Mn uptake and toxicity is not well understood. Therefore, undifferentiated PC12 cells were exposed to 0-200 {mu}M Mn(II)-chloride or Mn(III)-pyrophosphate for 24 h, after which cellular manganese levels were measured along with measures of cell viability, function, and cytotoxicity (trypan blue exclusion, medium lactate dehydrogenase (LDH), 8-isoprostanes, cellular ATP, dopamine, serotonin, H-ferritin, transferrin receptor (TfR), Mn-superoxide dismutase (MnSOD), and copper-zinc superoxide dismutase (CuZnSOD) protein levels). Exposures to Mn(III) >10 {mu}M produced 2- to 5-fold higher cellular manganese levels than equimolar exposures to Mn(II). Cell viability and ATP levels both decreased at the highest Mn(II) and Mn(III) exposures (150-200 {mu}M), while Mn(III) exposures produced increases in LDH activity at lower exposures ({>=}50 {mu}M) than did Mn(II) (200 {mu}M only). Mn(II) reduced cellular dopamine levels more than Mn(III), especially at the highest exposures (50% reduced at 200 {mu}M Mn(II)). In contrast, Mn(III) produced a >70% reduction in cellular serotonin at all exposures compared to Mn(II). Different cellular responses to Mn(II) exposures compared to Mn(III) were also observed for H-ferritin, TfR, and MnSOD protein levels. Notably, these differential effects of Mn(II) versus Mn(III) exposures on cellular toxicity could not simply be accounted for by the different cellular levels of manganese. These results suggest that the oxidation state of manganese exposures plays an important role in mediating manganese cytotoxicity.

  6. 40 CFR 721.10008 - Manganese strontium oxide (MnSrO3).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Manganese strontium oxide (MnSrO3... Specific Chemical Substances 721.10008 Manganese strontium oxide (MnSrO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese strontium...

  7. 40 CFR 721.10008 - Manganese strontium oxide (MnSrO3).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Manganese strontium oxide (MnSrO3... Specific Chemical Substances 721.10008 Manganese strontium oxide (MnSrO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese strontium...

  8. 40 CFR 721.10008 - Manganese strontium oxide (MnSrO3).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Manganese strontium oxide (MnSrO3... Specific Chemical Substances 721.10008 Manganese strontium oxide (MnSrO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese strontium...

  9. 40 CFR 721.10008 - Manganese strontium oxide (MnSrO3).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Manganese strontium oxide (MnSrO3... Specific Chemical Substances 721.10008 Manganese strontium oxide (MnSrO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese strontium...

  10. 40 CFR 721.10008 - Manganese strontium oxide (MnSrO3).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Manganese strontium oxide (MnSrO3... Specific Chemical Substances 721.10008 Manganese strontium oxide (MnSrO3). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as manganese strontium...

  11. Nanoscale manganese oxide within Faujasite zeolite as an efficient and biomimetic water oxidizing catalyst.

    PubMed

    Najafpour, Mohammad Mahdi; Pashaei, Babak

    2012-09-14

    Nanoscale manganese oxides within Faujasite zeolite have been synthesized with a simple method and characterized by scanning electron microscopy, X-ray diffraction spectrometry, N(2) adsorption-desorption isotherms, transmission electron microscopy, and atomic absorption spectroscopy. These oxides showed efficient water oxidizing activity in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant. PMID:22833185

  12. Kinetic patterns in the formation of nanosized manganese-manganese oxide systems

    NASA Astrophysics Data System (ADS)

    Surovoi, E. P.; Bugerko, L. N.; Surovaya, V. E.; Zaikonnikova, T. M.

    2016-03-01

    Transformations in nanosized manganese films are studied by means of optical spectroscopy, microscopy, and gravimetry at different film thicknesses ( d = 4-108 nm) and temperatures of heat treatment ( T = 373-673 K). It is found that the kinetic curves of conversion are satisfactorily described in the terms of linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference is measured for Mn and MnO films, and photo EMF is measured for Mn-MnO systems. An energy band diagram is constructed for Mn-MnO systems. A model for the thermal transformation of Mn films is proposed that includes stages of oxygen adsorption, the redistribution of charge carriers in the contact field of Mn-MnO, and manganese(II) oxide formation.

  13. Characterization of Synthetic and Natural Manganese Oxides as Martian Analogues

    NASA Technical Reports Server (NTRS)

    Fox, V. K.; Arvidson, R. E.; Jolliff, B. L.; Carpenter, P. K.; Catalano, J. G.; Hinkle, M. A. G.; Morris, R. V.

    2015-01-01

    Recent discoveries of highly concentrated manganese oxides in Gale Crater and on the rim of Endeavour Crater by the Mars Science Laboratory Curiosity and Mars Exploration Rover Opportunity, respectively, imply more highly oxidizing aqueous conditions than previously recognized. Manganese oxides are a significant environmental indicator about ancient aqueous conditions, provided the phases can be characterized reliably. Manganese oxides are typically fine-grained and poorly crystalline, making the mineral structures difficult to determine, and they generally have very low visible reflectance with few distinctive spectral features in the visible to near infrared, making them a challenge for interpretation from remote sensing data. Therefore, these recent discoveries motivate better characterization using methods available on Mars, particularly visible to near infrared (VNIR) spectroscopy, X-ray diffractometry (XRD), and compositional measurements. Both rovers have complementary instruments in this regard. Opportunity is equipped with its multispectral visible imager, Pancam, and an Alpha Particle X-ray Spectrometer (APXS), and Curiosity has the multispectral Mastcam, ChemCam (laser-induced breakdown spectroscopy and passive spectroscopy), and APXS for in situ characterization, and ChemMin (XRD) for collected samples.

  14. Microbial oxidation of manganese in a North Carolina estuary

    SciTech Connect

    Sunda, W.G.; Huntsman, S.A. )

    1987-05-01

    Experiments were conducted with Mn-54 (++) to determine the kinetics of particulate manganese formation in seawater from the lower Newport River estuary, North Carolina. Dissolved Mn was rapidly converted into particles at constant rates that ranged from 0.36 to 6.2%/h, yielding turnover times of the dissolved manganese pool of 0.7-11 d. Dissolved Mn turnover rates increased with temperature up to a maximum at 25-35 C and also increased with the ratio of particulate to dissolved Mn. These two factors explained most of the variation in the observed turnover rates. The formation of particulate Mn appeared to result primarily from the oxidation of Mn(++) to manganese oxides. However, the oxidation rates were much too rapid to be accounted for by abiotic mechanisms, and the rate was reduced by 97% following heat sterilization of the seawater. In addition, the rates conformed to the Michaelis-Menten enzyme kinetics model, providing strong evidence that oxidation of Mn in the estuarine samples is microbially catalyzed. This catalysis appears to be instrumental in the rapid redox cycling of Mn and in the scavenging of dissolved Mn onto particles in aquatic systems. 35 refs., 8 figs., 2 tabs.

  15. Distributions of Manganese, Iron, and Manganese-Oxidizing Bacteria In Lake Superior Sediments of Different Organic Carbon Content

    NASA Technical Reports Server (NTRS)

    Richardson, Laurie L.; Nealson, Kenneth H.

    1989-01-01

    Profiles of oxygen, soluble and particulate manganese and iron, organic carbon and nitrogen were examined in Lake Superior sediment cores, along with the distribution and abundance of heterotrophic and manganese oxidizing bacteria. Analyses were performed using cores collected with the submersible Johnson Sea Link II. Three cores, exhibiting a range of organic carbon content, were collected from the deepest basin in Lake Superior and the north and south ends of the Caribou trough, and brought to the surface for immediate analysis. Minielectrode profiles of oxygen concentration of the three cores were carried out using a commercially available minielectrode apparatus. Oxygen depletion to less than 1% occurred within 4 cm of the surface for two of the cores, but not until approximately 15 cm for the core from the south basin of the Caribou trough. The three cores exhibited very different profiles of soluble, as well as leachable, manganese and iron, suggesting different degrees of remobilization of these metals in the sediments. Vertical profiles of viable bacteria and Mn oxidizing bacteria, determined by plating and counting, showed that aerobic (and facultatively aerobic) heterotrophic bacteria were present at the highest concentrations near the surface and decreased steadily with depth, while Mn oxidizing bacteria were concentrations primarily at and above the oxic/anoxic interface. Soluble manganese in the pore waters, along with abundant organic carbon, appeared to enhance the presence of manganese oxidizing bacteria, even below the oxic/anoxic interface. Profiles of solid-phase leachable manganese suggested a microbial role in manganese reprecipitation in these sediments.

  16. Ionic Strength-Controlled Mn (Hydr)oxide Nanoparticle Nucleation on Quartz: Effect of Aqueous Mn(OH)2.

    PubMed

    Jung, Haesung; Jun, Young-Shin

    2016-01-01

    The early formation of manganese (hydr)oxide nanoparticles at mineral-water interfaces is crucial in understanding how Mn oxides control the fate and transport of heavy metals and the cycling of nutrients. Using atomic force microscopy, we investigated the heterogeneous nucleation and growth of Mn (hydr)oxide under varied ionic strengths (IS; 1-100 mM NaNO3). Experimental conditions (i.e., 0.1 mM Mn(2+) (aq) concentration and pH 10.1) were chosen to be relevant to Mn remediation sites. We found that IS controls Mn(OH)2 (aq) formation, and that the controlled Mn(OH)2 (aq) formation can affect the system's saturation and subsequent Mn(OH)2 (s) and further Mn3O4 (s) nanoparticle formation. In 100 mM IS system, nucleated Mn (hydr)oxide particles had more coverage on the quartz substrate than those in 1 mM and 10 mM IS systems. This high IS also resulted in low supersaturation ratio and thus favor heterogeneous nucleation, having better structural matching between nucleating Mn (hydr)oxides and quartz. The unique information obtained in this work improves our understanding of Mn (hydr)oxide formation in natural as well as engineered aqueous environments, such as groundwater contaminated by natural leachate and acid mine drainage remediation. PMID:26588858

  17. Preliminary LIBS analysis of Yucca Mountain manganese oxide minerals

    SciTech Connect

    Blacic, J.; Pettit, D.; Cremers, D.

    1996-01-01

    The licensing and performance of a potential repository at Yucca Mountain will require the characterization of radionuclide sorptive capacity of the host rock, which in turn calls for hundreds of analyses based on extensive sampling or in situ measurements. A rapid method specifically for characterizing the manganese oxide minerals occurring heterogeneously throughout the Yucca Mountain block as fracture surface coatings is needed. Our unique solution is a laser-induced breakdown spectroscopy (LIBS) surface-analysis technique that is usable in the field to produce high-resolution atomic emission spectra. In tests with manganese oxide minerals and fracture surface coatings from a few Yucca Mountain core samples, we used four spectral bands to show that qualitative measurement of all constituent elements except K and Na (in the presence of Mn) is possible with LIBS. Detailed calibration of final hardware will make the system quantitative.

  18. Manganese oxide nanowires, films, and membranes and methods of making

    DOEpatents

    Suib, Steven Lawrence; Yuan, Jikang

    2008-10-21

    Nanowires, films, and membranes comprising ordered porous manganese oxide-based octahedral molecular sieves, and methods of making, are disclosed. A single crystal ultra-long nanowire includes an ordered porous manganese oxide-based octahedral molecular sieve, and has an average length greater than about 10 micrometers and an average diameter of about 5 nanometers to about 100 nanometers. A film comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is stacked on a surface of a substrate, wherein the nanowires of each layer are substantially axially aligned. A free standing membrane comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is aggregately stacked, and wherein the nanowires of each layer are substantially axially aligned.

  19. Nano-sized manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis: a review

    PubMed Central

    Najafpour, Mohammad Mahdi; Rahimi, Fahimeh; Aro, Eva-Mari; Lee, Choon-Hwan; Allakhverdiev, Suleyman I.

    2012-01-01

    There has been a tremendous surge in research on the synthesis of various metal compounds aimed at simulating the water-oxidizing complex (WOC) of photosystem II (PSII). This is crucial because the water oxidation half reaction is overwhelmingly rate-limiting and needs high over-voltage (approx. 1 V), which results in low conversion efficiencies when working at current densities required for hydrogen production via water splitting. Particular attention has been given to the manganese compounds not only because manganese has been used by nature to oxidize water but also because manganese is cheap and environmentally friendly. The manganese–calcium cluster in PSII has a dimension of about approximately 0.5 nm. Thus, nano-sized manganese compounds might be good structural and functional models for the cluster. As in the nanometre-size of the synthetic models, most of the active sites are at the surface, these compounds could be more efficient catalysts than micrometre (or bigger) particles. In this paper, we focus on nano-sized manganese oxides as functional and structural models of the WOC of PSII for hydrogen production via water splitting and review nano-sized manganese oxides used in water oxidation by some research groups. PMID:22809849

  20. A redox-assisted supramolecular assembly of manganese oxide nanotube

    SciTech Connect

    Tao Li; Sun Chenggao; Fan Meilian; Huang Caijuan; Wu Hailong; Chao Zisheng . E-mail: zschao@yahoo.com; Zhai Hesheng . E-mail: hszhai@xmu.edu.cn

    2006-11-09

    In this paper, we report the hydrothermal synthesis of manganese oxide nanotube from an aqueous medium of pH 7, using KMnO{sub 4} and MnCl{sub 2} as inorganic precursors, polyoxyethylene (10) nonyl phenyl ether (TX-10) a surfactant and acetaldehyde an additive. The characterization of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and N{sub 2} adsorption at 77 K (BET) reveals that the synthesized manganese oxide nanotube has a mesopore size of ca. 3.65 nm and a wall thickness of ca. 12 nm, with the wall being composed of microporous crystals of monoclinic manganite. The X-ray photoelectron spectroscopy (XPS) result demonstrates a decrease of the binding energy of the Mn{sup 3+} in the manganese oxide nanotube, which may be related to both the nanotubular morphology and the crystalline pore wall. A mechanism of a redox-assisted supramolecular assembly, regulated by acetaldehyde, is postulated.

  1. The Overlapping Roles of Manganese and Cu/Zn SOD in Oxidative Stress Protection

    PubMed Central

    Reddi, Amit R.; Jensen, Laran T.; Naranuntarat, Amornrat; Rosenfeld, Leah; Leung, Edison; Shah, Rishita; Culotta, Valeria C.

    2009-01-01

    In various organisms, high intracellular manganese provides protection against oxidative damage through unknown pathways. Herein we use a genetic approach in S. cerevisiae to analyze factors that promote manganese as an anti-oxidant in cells lacking Cu/Zn superoxide dismutase (sod1?). Unlike certain bacterial systems [1], oxygen resistance in yeast correlates with high intracellular manganese without a lowering of iron. This manganese for anti-oxidant protection is provided by the Nramp transporters Smf1p and Smf2p, with Smf1p playing a major role. In fact, loss of manganese transport by Smf1p together with loss of the Pmr1p manganese pump is lethal to sod1? cells in spite of normal manganese SOD2 activity. Manganese-phosphate complexes are excellent superoxide dimustase mimics in vitro [2], yet through genetic disruption of phosphate transport and storage, we observed no requirement for phosphate in manganese suppression of oxidative damage. If anything, elevated phosphate correlated with profound oxidative stress in sod1? mutants. The efficacy of manganese as an anti-oxidant was drastically reduced in cells that hyper-accumulate phosphate without effects on MnSOD activity. Non-SOD manganese can provide a critical backup for Cu/Zn SOD1, but only under appropriate physiologic conditions. PMID:18973803

  2. Manganese oxidation induced by water table fluctuations in a sand column.

    PubMed

    Farnsworth, Claire E; Voegelin, Andreas; Hering, Janet G

    2012-01-01

    On-off cycles of production wells, especially in bank filtration settings, cause oscillations in the local water table, which can deliver significant amounts of dissolved oxygen (DO) to the shallow groundwater. The potential for DO introduced in this manner to oxidize manganese(II) (Mn(II)), mediated by the obligate aerobe Pseudomonas putida GB-1, was tested in a column of quartz sand fed with anoxic influent solution and subject to 1.3 m water table changes every 30-50 h. After a period of filter ripening, 100 ?M Mn was rapidly removed during periods of low water table and high dissolved oxygen concentrations. The accumulation of Mn in the column was confirmed by XRF analysis of the sand at the conclusion of the study, and both measured net oxidation rates and XAS analysis suggest microbial oxidation as the dominant process. The addition of Zn, which inhibited GB-1 Mn oxidation but not its growth, interrupted the Mn removal process, but Mn oxidation recovered within one water table fluctuation. Thus transient DO conditions could support microbially mediated Mn oxidation, and this process could be more relevant in shallow groundwater than previously thought. PMID:22126514

  3. Manganese ion-assisted assembly of superparamagnetic graphene oxide microbowls

    NASA Astrophysics Data System (ADS)

    Tian, Zhengshan; Xu, Chunxiang; Li, Jitao; Zhu, Gangyi; Xu, Xiaoyong; Dai, Jun; Shi, Zengliang; Lin, Yi

    2014-03-01

    A facile manganese ion Mn(II)-assisted assembly has been designed to fabricate microbowls by using graphene oxide nanosheets as basic building blocks, which were exfoliated ultrasonically from the oxidized soot powders in deionized water. From the morphology evolution observations of transmission electron microscope and scanning electron microscope, a coordinating-tiling-collapsing manner is proposed to interpret the assembly mechanism based on attractive Van der Waals forces, π-π stacking, and capillary action. It is interesting to note that the as-prepared microbowls present a room temperature superparamagnetic behavior.

  4. Manganese ion-assisted assembly of superparamagnetic graphene oxide microbowls

    SciTech Connect

    Tian, Zhengshan; Xu, Chunxiang Li, Jitao; Zhu, Gangyi; Xu, Xiaoyong; Dai, Jun; Shi, Zengliang; Lin, Yi

    2014-03-24

    A facile manganese ion Mn(II)-assisted assembly has been designed to fabricate microbowls by using graphene oxide nanosheets as basic building blocks, which were exfoliated ultrasonically from the oxidized soot powders in deionized water. From the morphology evolution observations of transmission electron microscope and scanning electron microscope, a coordinating-tiling-collapsing manner is proposed to interpret the assembly mechanism based on attractive Van der Waals forces, π-π stacking, and capillary action. It is interesting to note that the as-prepared microbowls present a room temperature superparamagnetic behavior.

  5. Manganese oxide nanosheets and a 2D hybrid of graphene-manganese oxide nanosheets synthesized by liquid-phase exfoliation

    NASA Astrophysics Data System (ADS)

    Coelho, João; Mendoza-Sánchez, Beatriz; Pettersson, Henrik; Pokle, Anuj; McGuire, Eva K.; Long, Edmund; McKeon, Lorcan; Bell, Alan P.; Nicolosi, Valeria

    2015-06-01

    Manganese oxide nanosheets were synthesized using liquid-phase exfoliation that achieved suspensions in isopropanol (IPA) with concentrations of up to 0.45 mg ml-1. A study of solubility parameters showed that the exfoliation was optimum in N,N-dimethylformamide followed by IPA and diethylene glycol. IPA was the solvent of choice due to its environmentally friendly nature and ease of use for further processing. For the first time, a hybrid of graphene and manganese oxide nanosheets was synthesized using a single-step co-exfoliation process. The two-dimensional (2D) hybrid was synthesized in IPA suspensions with concentrations of up to 0.5 mg ml-1 and demonstrated stability against re-aggregation for up to six months. The co-exfoliation was found to be a energetically favorable process in which both solutes, graphene and manganese oxide nanosheets, exfoliate with an improved yield as compared to the single-solute exfoliation procedure. This work demonstrates the remarkable versatility of liquid-phase exfoliation with respect to the synthesis of hybrids with tailored properties, and it provides proof-of-concept ground work for further future investigation and exploitation of hybrids made of two or more 2D nanomaterials that have key complementary properties for various technological applications.

  6. Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore

    USGS Publications Warehouse

    Okita, P.M.; Maynard, J.B.; Spiker, E. C.; Force, E.R.

    1988-01-01

    Unlike other marine-sedimentary manganese ore deposits, which are largely composed of manganese oxides, the primary ore at Molango (Hidalgo State, Mexico) is exclusively manganese carbonate (rhodochrosite, Mn-calcite, kutnahorite). Stable isotope studies of the carbonates from Molango provide critical new information relevant to the controversy over syngenetic and diagenetic models of stratiform manganese deposit formation. Negative ??13C values for carbonates from mineralized zones at Molango are strongly correlated with manganese content both on a whole rock scale and by mineral species. Whole rock ??13C data fall into three groups: high-grade ore = -16.4 to -11.5%.; manganese-rich, sub-ore-grade = -5.2 to 0%.; and unmineralized carbonates = 0 to +2.5%. (PDB). ??18O data show considerable overlap in values among the three groups: +4.8 to -2.8, -5.4 to -0.3%., and -7.4 to +6.2 (PDB), respectively. Isotopic data for individual co-existing minerals suggest a similar separation of ??13C values: ??13C values from calcite range from -1.1 to +0.7%. (PDB), whereas values from rhodochrosite are very negative, -12.9 to -5.5%., and values from kutnahorite or Mn-calcite are intermediate between calcite and rhodochrosite. 13C data are interpreted to indicate that calcite (i.e. unmineralized carbonate) formed from a normal marine carbon reservoir. However, 13C data for the manganese-bearing carbonates suggest a mixed seawater and organic source of carbon. The presence of only trace amounts of pyrite suggests sulfate reduction may have played a minor part in oxidizing organic matter. It is possible that manganese reduction was the predominant reaction that oxidized organic matter and that it released organic-derived CO2 to produce negative ??13C values and manganese carbonate mineralization. ?? 1988.

  7. Validation of In-Situ Iron-Manganese Oxide Coated Stream Pebbles as Sensors for Arsenic Source Monitoring

    NASA Astrophysics Data System (ADS)

    Blake, J.; Peters, S. C.; Casteel, A.

    2013-12-01

    Locating nonpoint source contaminant fluxes can be challenging due to the inherent heterogeneity of source and of the subsurface. Contaminants such as arsenic are a concern for drinking water quality and ecosystem health. Arsenic contamination can be the result of several natural and anthropogenic sources, and therefore it can be difficult to trace and identify major areas of arsenic in natural systems. Identifying a useful source indicator for arsenic is a crucial step for environmental remediation efforts. Previous studies have found iron-manganese oxide coated streambed pebbles as useful source indicators due to their high attraction for heavy metals in water. In this study, pebbles, surface water at baseflow and nearby rocks were sampled from the Pennypack Creek and its tributaries, in southwestern Pennsylvania, to test the ability of coated streambed pebbles as environmental source indicators for arsenic. Quartz pebbles, 5-7 cm in diameter, were sampled to minimize elemental contamination from rock chemistry. In addition, quartz provides an excellent substrate for iron and manganese coatings to form. These coatings were leached from pebbles using 4M nitric acid with 0.1% concentrated hydrochloric acid. Following sample processing, analyses were performed using an ICP-MS and the resulting data were spatially organized using ArcGIS software. Arsenic, iron and manganese concentrations in the leachate are normalized to pebble surface area and each location is reported as a ratio of arsenic to iron and manganese. Results suggest that iron-manganese coated stream pebbles are useful indicators of arsenic location within a watershed.

  8. Constraints on superoxide mediated formation of manganese oxides

    PubMed Central

    Learman, Deric R.; Voelker, Bettina M.; Madden, Andrew S.; Hansel, Colleen M.

    2013-01-01

    Manganese (Mn) oxides are among the most reactive sorbents and oxidants within the environment, where they play a central role in the cycling of nutrients, metals, and carbon. Recent discoveries have identified superoxide (O2?) both of biogenic and abiogenic origin as an effective oxidant of Mn(II) leading to the formation of Mn oxides. Here we examined the conditions under which abiotically produced superoxide led to oxidative precipitation of Mn and the solid-phases produced. Oxidized Mn, as both aqueous Mn(III) and Mn(III/IV) oxides, was only observed in the presence of active catalase, indicating that hydrogen peroxide (H2O2), a product of the reaction of O2? with Mn(II), inhibits the oxidation process presumably through the reduction of Mn(III). Citrate and pyrophosphate increased the yield of oxidized Mn but decreased the amount of Mn oxide produced via formation of Mn(III)-ligand complexes. While complexing ligands played a role in stabilizing Mn(III), they did not eliminate the inhibition of net Mn(III) formation by H2O2. The Mn oxides precipitated were highly disordered colloidal hexagonal birnessite, similar to those produced by biotically generated superoxide. Yet, in contrast to the large particulate Mn oxides formed by biogenic superoxide, abiotic Mn oxides did not ripen to larger, more crystalline phases. This suggests that the deposition of crystalline Mn oxides within the environment requires a biological, or at least organic, influence. This work provides the first direct evidence that, under conditions relevant to natural waters, oxidation of Mn(II) by superoxide can occur and lead to formation of Mn oxides. For organisms that oxidize Mn(II) by producing superoxide, these findings may also point to other microbially mediated processes, in particular enzymatic hydrogen peroxide degradation and/or production of organic ligand metabolites, that allow for Mn oxide formation. PMID:24027565

  9. Iron and manganese oxide mineralization in the Pacific

    USGS Publications Warehouse

    Hein, J.R.; Koschinsky, A.; Halbach, P.; Manheim, F. T.; Bau, M.; Kang, J.-K.; Lubick, N.

    1997-01-01

    Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ??REEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ??REE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.

  10. Manganese chlorins immobilized on silica as oxidation reaction catalysts.

    PubMed

    Castro, Kelly A D F; Pires, Snia M G; Ribeiro, Marcos A; Simes, Mrio M Q; Neves, M Graa P M S; Schreiner, Wido H; Wypych, Fernando; Cavaleiro, Jos A S; Nakagaki, Shirley

    2015-07-15

    Synthetic strategies that comply with the principles of green chemistry represent a challenge: they will enable chemists to conduct reactions that maximize the yield of products with commercial interest while minimizing by-products formation. The search for catalysts that promote the selective oxidation of organic compounds under mild and environmentally friendly conditions constitutes one of the most important quests of organic chemistry. In this context, metalloporphyrins and analogues are excellent catalysts for oxidative transformations under mild conditions. In fact, their reduced derivatives chlorins are also able to catalyze organic compounds oxidation effectively, although they have been still little explored. In this study, we synthesized two chlorins through porphyrin cycloaddition reactions with 1.3-dipoles and prepared the corresponding manganese chlorins (MnCHL) using adequate manganese(II) salts. These MnCHL were posteriorly immobilized on silica by following the sol-gel process and the resulting solids were characterized by powder X-ray diffraction (PXRD), UVVIS spectroscopy, FTIR, XPS, and EDS. The catalytic activity of the immobilized MnCHL was investigated in the oxidation of cyclooctene, cyclohexene and cyclohexane and the results were compared with the ones obtained under homogeneous conditions. PMID:25841060

  11. Rechargeable 3 V Li cells using hydrated lamellar manganese oxide

    SciTech Connect

    Bach, S.; Pereira-Ramos, J.P.; Baffier, N.

    1996-11-01

    The synthesis and the electrochemical features of hydrated lamellar manganese oxides are reported. The authors use the reduction of aqueous permanganate solution by fumaric acid and the oxidation of manganese hydroxide by an aqueous permanganate solution to obtain sol-gel birnessite and classical X-exchanged birnessites (X = Li, Al, Na), respectively. The high oxidation state of Mn associated with the 2D character of the hot lattice allows high specific capacities (150 to 200 Ah/kg) available in the potential range of 4 to 2 V. Interlayer water provides the structural stability of the host lattice required for long cycling. Rechargeable two-electrode Li cells using starved or flooded electrolytes were built with the cathodic materials. The batteries exhibit a satisfactory behavior with a specific capacity of 160 Ah/kg recovered after 30 cycles at the C/20 discharge-charge rate for the sol-gel birnessite. This paper demonstrates an interest in cathodic materials based on oxides containing structural water for use in secondary Li batteries.

  12. Oxidation of manganese(II) during chlorination: role of bromide.

    PubMed

    Allard, S; Fouche, L; Dick, J; Heitz, A; von Gunten, U

    2013-08-01

    The oxidation of dissolved manganese(II) (Mn(II)) during chlorination is a relatively slow process which may lead to residual Mn(II) in treated drinking waters. Chemical Mn(II) oxidation is autocatalytic and consists of a homogeneous and a heterogeneous process; the oxidation of Mn(II) is mainly driven by the latter process. This study demonstrates that Mn(II) oxidation during chlorination is enhanced in bromide-containing waters by the formation of reactive bromine species (e.g., HOBr, BrCl, Br2O) from the oxidation of bromide by chlorine. During oxidation of Mn(II) by chlorine in bromide-containing waters, bromide is recycled and acts as a catalyst. For a chlorine dose of 1 mg/L and a bromide level as low as 10 ?g/L, the oxidation of Mn(II) by reactive bromine species becomes the main pathway. It was demonstrated that the kinetics of the reaction are dominated by the adsorbed Mn(OH)2 species for both chlorine and bromine at circumneutral pH. Reactive bromine species such as Br2O and BrCl significantly influence the rate of manganese oxidation and may even outweigh the reactivity of HOBr. Reaction orders in [HOBr]tot were found to be 1.33 (0.15) at pH 7.8 and increased to 1.97 (0.17) at pH 8.2 consistent with an important contribution of Br2O which is second order in [HOBr]tot. These findings highlight the need to take bromide, and the subsequent reactive bromine species formed upon chlorination, into account to assess Mn(II) removal during water treatment with chlorine. PMID:23859083

  13. Manganese oxide composite electrodes for lithium batteries

    DOEpatents

    Johnson, Christopher S.; Kang, Sun-Ho; Thackeray, Michael M.

    2009-12-22

    An activated electrode for a non-aqueous electrochemical cell is disclosed with a precursor thereof a lithium metal oxide with the formula xLi.sub.2MnO.sub.3.(1-x)LiMn.sub.2-yM.sub.yO.sub.4 for 0.5

  14. Manganese oxide composite electrodes for lithium batteries

    DOEpatents

    Thackeray, Michael M. (Naperville, IL); Johnson, Christopher S. (Naperville, IL); Li, Naichao (Croton on Hudson, NY)

    2007-12-04

    An activated electrode for a non-aqueous electrochemical cell is disclosed with a precursor of a lithium metal oxide with the formula xLi.sub.2MnO.sub.3.(1-x)LiMn.sub.2-yM.sub.yO.sub.4 for 0

  15. Mesoporous Manganese Oxide Catalyzed Aerobic Oxidative Coupling of Anilines To Aromatic Azo Compounds.

    PubMed

    Dutta, Biswanath; Biswas, Sourav; Sharma, Vinit; Savage, Nancy Ortins; Alpay, S Pamir; Suib, Steven L

    2016-02-01

    Herein we introduce an environmentally friendly approach to the synthesis of symmetrical and asymmetrical aromatic azo compounds by using air as the sole oxidant under mild reaction conditions in the presence of cost-effective and reusable mesoporous manganese oxide materials. PMID:26749298

  16. Sol-gel route to the tunneled manganese oxide cryptomelane

    SciTech Connect

    Ching, S.; Roark, J.L.; Duan, N.; Suib, S.L.

    1997-03-01

    The sol-gel reaction between KMnO{sub 4} and fumaric acid in a 3:1 mole ratio generates a flocculant gel that serves as a precursor to the tunneled manganese oxide, cryptomelane. The elemental composition of sol-gel cryptomelane has been determined to be K{sub 0.12}MnO{sub 2.0-} (H{sub 2}O){sub 0.09}. Further characterization has been performed using powder X-ray diffraction, scanning electron microscopy, and Auger electron spectroscopy. The sol-gel process is heavily dependent on reactant concentration. Solutions that are too concentrated produce the layered manganese oxide birnessite, whereas overly dilute reactions yield mixtures of cryptomelane and Mn{sub 2}O{sub 3}. The preference for cryptomelane over birnessite correlates with low potassium content in the gel. The sol-gel procedure for synthesizing cryptomelane is not easily transferred to the preparation of analogous manganese oxides with different tunnel cations. Reactions that employ permanganates other than KMnO{sub 4} generally yield Mn{sub 2}O{sub 3}, with cryptomelane being a minor product at best. Thermal analyses of cryptomelane gels indicate that calcination proceeds through a series of stages that involve loss of water, loss of residual organics, conversion to cryptomelane, and finally degradation to Mn{sub 3}O{sub 4}. The extraction of potassium ions from sol-gel cryptomelane by various foreign cations is minimal, with the loss of K{sup +} being on the order of 10%. 49 refs., 7 figs., 3 tabs.

  17. Chemical synthesis and characterization of manganese oxide coated Ni particles

    NASA Astrophysics Data System (ADS)

    An, Jing; Xu, LiHong; He, Jun; Zhao, DongLiang; Liu, ZhongYuan

    2013-08-01

    Nanosized Ni particles with an average diameter of about 8 nm were prepared by reducing of NiCl2 with sodium borohydride (NaBH4) in aqueous solution. By moderate annealing in protective atmosphere, the composite grew up to be 15-20 nm particles. Both of the as-prepared and annealed Ni particles were coated by a layer of manganese oxide via decomposition reaction in aqueous KMnO4 solution. Hysteresis loops of as-prepared samples show a large increase in the magnetization with decreasing temperature and an unsaturated component at high magnetic field. In contrast, the ferromagnetic characteristics of annealed one are much stronger with large magnetization and coercivity. The thermomagnetic curves verified the coexistence of ferromagnetic Ni and antiferromangetic Mn oxide phases. But there exists no exchange bias behavior in the samples, even though the interface structure between the ferromagnetic Ni core and the antiferromagnetic manganese oxides has been distinctly formed. The absence of exchange bias probably originates from the weak ferromagnetic characteristic of Ni cores.

  18. Calcium manganese(IV) oxides: biomimetic and efficient catalysts for water oxidation.

    PubMed

    Najafpour, Mohammad Mahdi; Pashaei, Babak; Nayeri, Sara

    2012-04-28

    CaMnO(3) and Ca(2)Mn(3)O(8) were synthesized and characterized by SEM, XRD, FTIR and BET. Both oxides showed oxygen evolution activity in the presence of oxone, cerium(IV) ammonium nitrate and H(2)O(2). Oxygen evolution from water during irradiation with visible light (? > 400 nm) was also observed upon adding these manganese oxides to an aqueous solution containing tris(2,2'-bipyridyl) ruthenium(II), as photosensitizer, and chloro pentaammine cobalt(III) chloride, as electron acceptor, in an acetate buffer. The amounts of dissolved manganese and calcium from CaMnO(3) and Ca(2)Mn(3)O(8) in the oxygen evolving reactions were reported and compared with other (calcium) manganese oxides. Proposed mechanisms of oxygen evolution and proposed roles for the calcium ions are also considered. PMID:22382465

  19. Manganese

    Integrated Risk Information System (IRIS)

    Manganese ; CASRN 7439 - 96 - 5 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effect

  20. Manganese-Based Molecular Electrocatalysts for Oxidation of Hydrogen

    SciTech Connect

    Hulley, Elliott; Kumar, Neeraj; Raugei, Simone; Bullock, R. Morris

    2015-10-05

    Oxidation of H2 (1 atm) is catalyzed by the manganese electrocatalysts [(P2N2)MnI(CO)(bppm)]+ and [(PNP)MnI(CO)(bppm)]+ (P2N2= 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; PNP = (Ph2PCH2)2NMe); bppm = (PArF2)2CH2, and ArF = 3,5-(CF3)2C6H3). In fluorobenzene solvent using 2,6-lutidine as the exogeneous base, the turnover frequency for [(P2N2)MnI(CO)(bppm)]+ is 3.5 s-1 with an estimated overpotential of 590 mV. For [(PNP)MnI(CO)(bppm)], in fluorobenzene solvent using N-methylpyrrolidine as the exogeneous base, the turnover frequency is 1.4 s-1 with an estimated overpotential of 700 mV. Density functional theory calculations suggest that the slow step in the catalytic cycle is proton transfer from the oxidized 17-electron manganese hydride, e.g., [(P2N2)MnIIH(CO)(bppm)]+ to the pendant amine. The computed activation barrier for intramolecular proton transfer from the metal to the pendant amine is 20.4 kcal/mol in [(P2N2)MnIIH(CO)(bppm)]+ and 21.3 kcal/mol in [(PNP)MnI(CO)(bppm)]. The high barrier appears to result from both the unfavorability of metal-to-nitrogen proton transfer (thermodynamically uphill by 6.6 pKa units, 9 kcal/mol), as well as the relatively long manganese-nitrogen separation in the MnIIH complexes.

  1. Population Structure of Manganese-Oxidizing Bacteria in Stratified Soils and Properties of Manganese Oxide Aggregates under ManganeseComplex Medium Enrichment

    PubMed Central

    Zhang, Zhongming; Chen, Hong; Liu, Jin; Ali, Muhammad; Liu, Fan; Li, Lin

    2013-01-01

    Manganese-oxidizing bacteria in the aquatic environment have been comprehensively investigated. However, little information is available about the distribution and biogeochemical significance of these bacteria in terrestrial soil environments. In this study, stratified soils were initially examined to investigate the community structure and diversity of manganese-oxidizing bacteria. Total 344 culturable bacterial isolates from all substrata exhibited Mn(II)-oxidizing activities at the range of 1 M to 240 M of the equivalent MnO2. The high Mn(II)-oxidizing isolates (>50 mM MnO2) were identified as the species of phyla Actinobacteria, Firmicutes and Proteobacteria. Seven novel Mn(II)-oxidizing bacterial genera (species), namely, Escherichia, Agromyces, Cellulomonas, Cupriavidus, Microbacterium, Ralstonia, and Variovorax, were revealed via comparative phylogenetic analysis. Moreover, an increase in the diversity of soil bacterial community was observed after the combined enrichment of Mn(II) and carbon-rich complex. The phylogenetic classification of the enriched bacteria represented by predominant denaturing gradient gel electrophoresis bands, was apparently similar to culturable Mn(II)-oxidizing bacteria. The experiments were further undertaken to investigate the properties of the Mn oxide aggregates formed by the bacterial isolates with high Mn(II)-oxidizing activity. Results showed that these bacteria were closely encrusted with their Mn oxides and formed regular microspherical aggregates under prolonged Mn(II) and carbon-rich medium enrichment for three weeks. The biotic oxidation of Mn(II) to Mn(III/IV) by these isolates was confirmed by kinetic examinations. X-ray diffraction assays showed the characteristic peaks of several Mn oxides and rhodochrosite from these aggregates. Leucoberbelin blue tests also verified the Mn(II)-oxidizing activity of these aggregates. These results demonstrated that Mn oxides were formed at certain amounts under the enrichment conditions, along with the formation of rhodochrosite in such aggregates. Therefore, this study provides insights into the structure and diversity of soil-borne bacterial communities in Mn(II)-oxidizing habitats and supports the contribution of soil-borne Mn(II)-oxidizing bacteria to Mn oxide mineralization in soils. PMID:24069232

  2. Oxidation of organic contaminants by manganese oxide geomedia for passive urban stormwater treatment systems.

    PubMed

    Grebel, Janel E; Charbonnet, Joseph A; Sedlak, David L

    2016-01-01

    To advance cost-effective strategies for removing trace organic contaminants from urban runoff, the feasibility of using manganese oxides as a geomedia amendment in engineered stormwater infiltration systems to oxidize organic contaminants was evaluated. Ten representative organic chemicals that have previously been detected in urban stormwater were evaluated for reactivity in batch experiments with birnessite. With respect to reactivity, contaminants could be classified as: highly reactive (e.g., bisphenol A), moderately reactive (e.g., diuron) and unreactive (e.g., tris(2-chloro-1-propyl)phosphate). Bisphenol A and diuron reacted with birnessite to produce a suite of products, including ring-cleavage products for bisphenol A and partially dechlorinated products for diuron. Columns packed with manganese oxide-coated sand were used evaluate design parameters for an engineered infiltration system, including necessary contact times for effective treatment, as well as the impacts of stormwater matrix variables, such as solution pH, concentration of natural organic matter and major anions and cations. The manganese oxide geomedia exhibited decreased reactivity when organic contaminants were oxidized, especially in the presence of divalent cations, bicarbonate, and natural organic matter. Under typical conditions, the manganese oxides are expected to retain their reactivity for 25 years. PMID:26521218

  3. Dimensionality dependent water splitting mechanisms on free manganese oxide clusters.

    PubMed

    Lang, Sandra M; Fleischer, Irene; Bernhardt, Thorsten M; Barnett, Robert N; Landman, Uzi

    2013-01-01

    The interaction of ligand-free manganese oxide nanoclusters with water is investigated, aiming at uncovering phenomena which could aid the design of artificial water-splitting molecular catalysts. Gas phase measurements in an ion trap in conjunction with first-principles calculations provide new mechanistic insight into the water splitting process mediated by bi- and tetra-nuclear singly charged manganese oxide clusters, Mn2O2(+) and Mn4O4(+). In particular, a water-induced dimensionality change of Mn4O4(+) is predicted, entailing transformation from a two-dimensional ring-like ground state structure of the bare cluster to a cuboidal octa-hydroxy-complex for the hydrated one. It is further predicted that the water splitting process is facilitated by the cluster dimensionality crossover. The vibrational spectra calculated for species occurring along the predicted pathways of the reaction of Mn4O4(+) with water provide the impetus for future explorations, including vibrational spectroscopic experiments. PMID:24164444

  4. Occurrence of manganese-oxidizing microorganisms and manganese deposition during biofilm formation on stainless steel in a brackish surface water.

    PubMed

    Kielemoes, Jan; Bultinck, Isabelle; Storms, Hedwig; Boon, Nico; Verstraete, Willy

    2002-01-01

    Abstract Biofilm formation on 316L stainless steel was investigated in a pilotscale flow-through system fed with brackish surface water using an alternating flow/stagnation/flow regime. Microbial community analysis by denaturing gradient gel electrophoresis and sequencing revealed the presence of complex microbial ecosystems consisting of, amongst others, Leptothrix-related manganese-oxidizing bacteria in the adjacent water, and sulfur-oxidizing, sulfate-reducing and slime-producing bacteria in the biofilm. Selective plating of the biofilm indicated the presence of high levels of manganese-oxidizing microorganisms, while microscopic and chemical analyses of the biofilm confirmed the presence of filamentous manganese-precipitating microorganisms, most probably Leptothrix species. Strong accumulation of iron and manganese occurred in the biofilm relative to the adjacent water. No evidence of selective colonization of the steel surface or biocorrosion was found over the experimental period. The overall results of this study highlight the potential formation of complex microbial biofilm communities in flow-through systems thriving on minor concentrations of manganese. PMID:19709183

  5. The mechanism of water oxidation catalyzed by nanolayered manganese oxides: New insights.

    PubMed

    Najafpour, Mohammad Mahdi; Abbasi Isaloo, Mohsen

    2015-11-01

    Herein we consider the mechanism of water oxidation by nanolayered manganese oxide in the presence of cerium(IV) ammonium nitrate. Based on membrane-inlet mass spectrometry results, the rate of H2((18))O exchange of ?-O groups on the surface of the nanolayered Mn-K oxide, and studies on water oxidation in the presence of different ratios of acetonitrile/water we propose a mechanism for water oxidation by nanolayered Mn oxides in the presence of cerium(IV) ammonium nitrate. PMID:25666103

  6. Manganese sulfide formation via concomitant microbial manganese oxide and thiosulfate reduction

    SciTech Connect

    Lee, Ji-Hoon; Kennedy, David W.; Dohnalkova, Alice; Moore, Dean A.; Nachimuthu, Ponnusamy; Reed, Samantha B.; Fredrickson, Jim K.

    2011-12-13

    The dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 produced {gamma}-MnS (rambergite) nanoparticles during the concurrent reduction of MnO{sub 2} and thiosulfate coupled to H{sub 2} oxidation. To investigate effect of direct microbial reduction of MnO{sub 2} on MnS formation, two MR-1 mutants defective in outer membrane c-type cytochromes ({Delta}mtrC/{Delta}omcA and {Delta}mtrC/{Delta}omcA/{Delta}mtrF) were also used and it was determined that direct reduction of MnO{sub 2} was dominant relative to chemical reduction by biogenic sulfide generated from thiosulfate reduction. Although bicarbonate was excluded from the medium, incubations of strain MR-1 with lactate as the electron donor produced MnCO{sub 3} (rhodochrosite) as well as MnS in nearly equivalent amounts as estimated by micro X-ray diffraction (micro-XRD) analysis. It was concluded that carbonate released from lactate metabolism promoted MnCO{sub 3} formation and that Mn(II) mineralogy was strongly affected by carbonate ions even in the presence of abundant sulfide and weakly alkaline conditions expected to favor the precipitation of MnS. Formation of MnS, as determined by a combination of micro-XRD, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction analyses was consistent with equilibrium speciation modeling predictions. Biogenic manganese sulfide may be a manganese sink in the Mn biogeochemical cycle in select environments such as deep anoxic marine basins within the Baltic Sea.

  7. Chromite oxidation by manganese oxides in subseafloor basalts and the presence of putative fossilized microorganisms

    PubMed Central

    2011-01-01

    Chromite is a mineral with low solubility and is thus resistant to dissolution. The exception is when manganese oxides are available, since they are the only known naturally occurring oxidants for chromite. In the presence of Mn(IV) oxides, Cr(III) will oxidise to Cr(VI), which is more soluble than Cr(III), and thus easier to be removed. Here we report of chromite phenocrysts that are replaced by rhodochrosite (Mn(II) carbonate) in subseafloor basalts from the Koko Seamount, Pacific Ocean, that were drilled and collected during the Ocean Drilling Program (ODP) Leg 197. The mineral succession chromite-rhodochrosite-saponite in the phenocrysts is interpreted as the result of chromite oxidation by manganese oxides. Putative fossilized microorganisms are abundant in the rhodochrosite and we suggest that the oxidation of chromite has been mediated by microbial activity. It has previously been shown in soils and in laboratory experiments that chromium oxidation is indirectly mediated by microbial formation of manganese oxides. Here we suggest a similar process in subseafloor basalts. PMID:21639896

  8. Nickel and Lead Sequestration in Manganese Oxide-coated Montmorillonite

    SciTech Connect

    Boonfueng,T.; Axe, L.; Xu, Y.; Tyson, T.

    2006-01-01

    Amorphous hydrous manganese oxide (HMO) is an important mineral in soils and sediments influencing the mobility and bioavailability of metal contaminants. In this study, nickel and lead sorption to discrete HMO and HMO-coated montmorillonite was investigated mechanistically. The effect of pH and concentration revealed that when normalized to the mass of oxide present, the HMO-coated montmorillonite behaved similarly to the discrete Mn oxide, where both ions sorbed onto HMO-coated montmorillonite as inner-sphere complexes. Ni coordinated to the vacancy sites in the Mn oxide structure, while Pb formed bidentate corner-sharing complexes. These coordination environments were observed not only as a function of loading, pH, and ionic strength, but also in long-term studies where sorption increased by as much as 100% (from 6 x 10{sup -4} to 1.2 x 10{sup -3} mol Ni/g HMO-coated montmorillonite). In this slower sorption process, intraparticle diffusion, the internal surface sites along microporous walls appear to be no different than external ones. Best fit diffusivities ranged from 10{sup -12} to 10{sup -13} cm{sup 2}/s for Ni and 10{sup -17} to 10{sup -20} cm{sup 2}/s for Pb. The significant difference in the diffusivities for the two ions is consistent with site activation theory, where theoretical surface diffusivities were predicted and given their error were in agreement with experimental results. Mn oxides sequester heavy metals in the environment.

  9. Manganese oxide minerals: Crystal structures and economic and environmental significance

    PubMed Central

    Post, Jeffrey E.

    1999-01-01

    Manganese oxide minerals have been used for thousands of yearsby the ancients for pigments and to clarify glass, and today as ores of Mn metal, catalysts, and battery material. More than 30 Mn oxide minerals occur in a wide variety of geological settings. They are major components of Mn nodules that pave huge areas of the ocean floor and bottoms of many fresh-water lakes. Mn oxide minerals are ubiquitous in soils and sediments and participate in a variety of chemical reactions that affect groundwater and bulk soil composition. Their typical occurrence as fine-grained mixtures makes it difficult to study their atomic structures and crystal chemistries. In recent years, however, investigations using transmission electron microscopy and powder x-ray and neutron diffraction methods have provided important new insights into the structures and properties of these materials. The crystal structures for todorokite and birnessite, two of the more common Mn oxide minerals in terrestrial deposits and ocean nodules, were determined by using powder x-ray diffraction data and the Rietveld refinement method. Because of the large tunnels in todorokite and related structures there is considerable interest in the use of these materials and synthetic analogues as catalysts and cation exchange agents. Birnessite-group minerals have layer structures and readily undergo oxidation reduction and cation-exchange reactions and play a major role in controlling groundwater chemistry. PMID:10097056

  10. Oxidation reactions catalyzed by manganese peroxidase isoenzymes from Ceriporiopsis subvermispora.

    PubMed

    Urza, U; Fernando Larrondo, L; Lobos, S; Larran, J; Vicua, R

    1995-09-01

    A total of 11 manganese peroxidase isoenzymes (MnP1-MnP11) with isoelectric points (pIs) in the range of 4.58-3.20 were isolated from liquid- and solid-state cultures of the basidiomycete Ceriporiopsis subvermispora. In the presence of hydrogen peroxide, these isoenzymes showed different requirements for Mn(II) in the oxidation of vanillylacetone, o-dianisidine, p-anisidine and ABTS, whereas oxidation of guaiacol by any isoenzyme did not take place when this metal was omitted. Km values for o-dianisidine and p-anisidine in the absence of Mn(II) are in the range of 0.5-1.0 mM and 4.5-42.0 mM, respectively. Oxalate and citrate, but not tartrate, accelerate the oxidation of o-dianisidine, both in the presence and in the absence of Mn(II). MnPs from this fungus are able to oxidize kojic acid without externally added hydrogen peroxide, indicating that they can also act as oxidases. In this reaction, however, the requirement for Mn(II) is absolute. PMID:7672112

  11. Manganese(III) binding to a pyoverdine siderophore produced by a manganese(II)-oxidizing bacterium

    NASA Astrophysics Data System (ADS)

    Parker, Dorothy L.; Sposito, Garrison; Tebo, Bradley M.

    2004-12-01

    The possible roles of siderophores (high affinity chelators of iron(III)) in the biogeochemistry of manganese remain unknown. Here we investigate the interaction of Mn(III) with a pyoverdine-type siderophore (PVD MnB1) produced by the model Mn(II)-oxidizing bacterium Pseudomonas putida strain MnB1. PVD MnB1 confirmed typical pyoverdine behavior with respect to: (a) its absorption spectrum at 350-600 nm, both in the absence and presence of Fe(III), (b) the quenching of its fluorescence by Fe(III), (c) the formation of a 1:1 complex with Fe(III), and (d) the thermodynamic stability constant of its Fe(III) complex. The Mn(III) complex of PVD MnB1 had a 1:1 Mn:pvd molar ratio, showed fluorescence quenching, and exhibited a light absorption spectrum (A max = 408-410 nm) different from that of either PVD MnB1-Fe(III) or uncomplexed PVD MnB1. Mn(III) competed strongly with Fe(III) for binding by PVD MnB1 in culture filtrates (pH 8, 4C). Equilibration with citrate, a metal-binding ligand, did not detectably release Mn from its PVD MnB1 complex at a citrate/PVD MnB1 molar ratio of 830 (pH 8, 4C), whereas pyrophosphate under the same conditions removed 55% of the Mn from its PVD MnB1 complex. Most of the PVD MnB1-complexed Mn was released by reaction with ascorbate, a reducing agent, or with EDTA, a ligand that is also oxidized by Mn(III). Data on the competition for binding to PVD MnB1 by Fe(III) vs. Mn(III) were used to determine a thermodynamic stability constant (nominally at 4C) for the neutral species MnHPVD MnB1 (log K = 47.5 0.5, infinite dilution reference state). This value was larger than that determined for FeHPVD MnB1 (log K = 44.6 0.5). This result has important implications for the metabolism, solubility, speciation, and redox cycling of manganese, as well as for the biologic uptake of iron.

  12. Manganese Oxide Nanoarray-Based Monolithic Catalysts: Tunable Morphology and High Efficiency for CO Oxidation.

    PubMed

    Chen, Sheng-Yu; Song, Wenqiao; Lin, Hui-Jan; Wang, Sibo; Biswas, Sourav; Mollahosseini, Mehdi; Kuo, Chung-Hao; Gao, Pu-Xian; Suib, Steven L

    2016-03-30

    A generic one-pot hydrothermal synthesis route has been successfully designed and utilized to in situ grow uniform manganese oxide nanorods and nanowires onto the cordierite honeycomb monolithic substrates, forming a series of nanoarray-based monolithic catalysts. During the synthesis process, three types of potassium salt oxidants have been used with different reduction potentials, i.e., K2Cr2O7, KClO3, and K2S2O8, denoted as HM-DCM, HM-PCR, and HM-PSF, respectively. The different reduction potentials of the manganese source (Mn(2+)) and oxidants induced the formation of manganese oxide nanoarrays with different morphology, surface area, and reactivity of carbon monoxide (CO) oxidation. K2Cr2O7 and KClO3 can induce sharp and long nanowires with slow growth rates due to their low reduction potentials. In comparison, the nanoarrays of HM-PSF presented shorter nanorods but displayed an efficient 90% CO oxidation conversion at 200 °C (T90) without noble-metal loading. Reducibility tests for the three monolithic catalysts by hydrogen temperature-programmed reduction revealed an activation energy order of HM-PSF > HM-DCM > HM-PCR for CO oxidation. The characterizations of oxygen temperature-programmed desorption and X-ray photoelectron spectroscopy indicated the abundant surface-adsorbed oxygen and lattice oxygen contributing to the superior reactivity of HM-PSF. The straightforward synthetic process showed a scalable, low-cost, and template-free method to fabricate manganese oxide nanoarray monolithic catalysts for exhaust treatment. PMID:26954301

  13. Thermodynamics of Manganese Oxides at Bulk and Nanoscale: Phase Formation, Transformation, Oxidation-Reduction, and Hydration

    NASA Astrophysics Data System (ADS)

    Birkner, Nancy R.

    Natural manganese oxides are generally formed in surficial environments that are near ambient temperature and water-rich, and may be exposed to wet-dry cycles and a variety of adsorbate species that influence dramatically their level of hydration. Manganese oxide minerals are often poorly crystalline, nanophase, and hydrous. In the near-surface environment they are involved in processes that are important to life, such as water column oxygen cycling, biomineralization, and transport of minerals/nutrients through soils and water. These processes, often involving transformations among manganese oxide polymorphs, are governed by a complex interplay between thermodynamics and kinetics. Manganese oxides are also used in technology as catalysts, and for other applications. The major goal of this dissertation is to examine the energetics of bulk and nanophase manganese oxide phases as a function of particle size, composition, and surface hydration. Careful synthesis and characterization of manganese oxide phases with different surface areas provided samples for the study of enthalpies of formation by high temperature oxide melt solution calorimetry and of the energetics of water adsorption on their surfaces. These data provide a quantitative picture of phase stability and how it changes at the nanoscale. The surface energy of the hydrous surface of Mn3O4 is 0.96 +/- 0.08 J/m2, of Mn2O3 is 1.29 +/- 0.10 J/m2, and of MnO2 is 1.64 +/- 0.10 J/m2. The surface energy of the anhydrous surface of Mn3O4 is 1.62 +/- 0.08 J/m 2, of Mn2O3 is 1.77 +/- 0.10 J/m 2, and of MnO2 is 2.05 +/- 0.10 J/m2. Supporting preliminary findings (Navrotsky et al., 2010), the spinel phase (Mn3O4) has a lower surface energy (more stabilizing) than bixbyite, while the latter has a smaller surface energy than pyrolusite. These differences significantly change the positions in oxygen fugacity---temperature space of the redox couples Mn3O4-Mn2O 3 and Mn2O3-MnO2 favoring the lower surface enthalpy phase (the spinel Mn3O4) for smaller particle size and in the presence of surface hydration. Chemisorption of water onto anhydrous nanophase Mn2O 3 surfaces promotes rapidly reversible redox phase changes at room temperature as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Water adsorption microcalorimetry (in situ) at room temperature measured the strongly exothermic integral enthalpy of water adsorption (-103.5 kJ/mol) and monitored the energetics of the redox phase transformation. Hydration-driven redox transformation of anhydrous nanophase Mn(III) 2O3, (high surface enthalpy of anhydrous surfaces 1.77 +/- 0.10 J/m2) to Mn(II,III)3O4 (lower surface enthalpy 0.96 +/- 0.08 J/m2) occurred during the first few doses of water vapor. Surface reduction of nanoparticle bixbyite (Mn 2O3) to hausmannite (Mn3O4) occurs under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Layered structure manganese oxides contain alkali or alkaline earth cations and water, are generally fine-grained, and have considerable thermodynamic stability. The surface enthalpies (SE) of layered and tunnel structure complex manganese oxides are significantly lower than those of the binary manganese oxide phases. The SE for hydrous surfaces and overall manganese average oxidation state (AOS) (value in parentheses) are: cryptomelane 0.77 +/- 0.10 J/m 2 (3.78), sodium birnessite 0.69 +/- 0.13 J/m2 (3.56), potassium birnessite 0.55 +/- 0.11 J/m2 (3.52), and calcium birnessite 0.41 +/- 0.11 J/m2 (3.50). Surface enthalpies of hydrous surfaces of the calcium manganese oxide nanosheets are: deltaCa 0.39MnO2.3nH2O 0.75 +/- 0.10 J/m2 (3.89) and deltaCa0.43MnO2.3nH2O 0.57 +/- 0.12 J/m2 (3.68). The surface enthalpy of the complex manganese oxides appears to decrease with decreasing manganese average oxidation state, that is, with greater mixed valence manganese (Mn 3+/4+). Low surface energy suggests loose binding of H2O on the internal and external surfaces and may be critical to catalysis in both natural and technological settings.

  14. Sol-gel synthesis and characterization of mesoporous manganese oxide

    SciTech Connect

    Hong Xinlin; Zhang Gaoyong; Zhu Yinyan; Yang Hengquan

    2003-10-30

    Mesoporous manganese oxide (MPMO) from reduction of KMnO{sub 4} with maleic acid, was obtained and characterized in detail. The characterization of the material was confirmed by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffractometry (XRD) and N{sub 2} sorptometry. The results showed that MPMO is a pseudo-crystalline material with complex network pore structure, of which BET specific surface area is 297 m{sup 2}/g and pore size distribution is approximately in the range of 0.7-6.0 nm. The MPMO material turns to cryptomelane when the calcinating temperature rises to 400 deg. C. The optimum sol-gel reaction conditions are KMnO{sub 4}/C{sub 4}H{sub 4}O{sub 4} molar ratio=3, pH=7 and gelation time>6 h.

  15. Monte Carlo study of double exchange interaction in manganese oxide

    NASA Astrophysics Data System (ADS)

    Naa, Christian Fredy; Suprijadi, Viridi, Sparisoma; Fasquelle, Didier; Djamal, Mitra

    2015-09-01

    In this paper we study the magnetoresistance properties attributed by double exchange (DE) interaction in manganese oxide by Monte Carlo simulation. We construct a model based on mixed-valence Mn3+ and Mn4+ on the general system of Re2/3Ae1/3MnO3 in two dimensional system. The conduction mechanism is based on probability of eg electrons hopping from Mn3+ to Mn4+. The resistivity dependence on temperature and the external magnetic field are presented and the validity with related experimental results are discussed. We use the resistivity power law to fit our data on metallic region and basic activated behavior on insulator region. On metallic region, we found our result agree well with the quantum theory of DE interaction. From general arguments, we found our simulation agree qualitatively with experimental results.

  16. Uncovering structure-activity relationships in manganese-oxide-based heterogeneous catalysts for efficient water oxidation.

    PubMed

    Indra, Arindam; Menezes, Prashanth W; Driess, Matthias

    2015-03-01

    Artificial photosynthesis by harvesting solar light into chemical energy could solve the problems of energy conversion and storage in a sustainable way. In nature, CO2 and H2 O are transformed into carbohydrates by photosynthesis to store the solar energy in chemical bonds and water is oxidized to O2 in the oxygen-evolving center (OEC) of photosystem II (PS II). The OEC contains CaMn4 O5 cluster in which the metals are interconnected through oxido bridges. Inspired by biological systems, manganese-oxide-based catalysts have been synthesized and explored for water oxidation. Structural, functional modeling, and design of the materials have prevailed over the years to achieve an effective and stable catalyst system for water oxidation. Structural flexibility with eg(1) configuration of Mn(III) , mixed valency in manganese, and higher surface area are the main requirements to attain higher efficiency. This Minireview discusses the most recent progress in heterogeneous manganese-oxide-based catalysts for efficient chemical, photochemical, and electrochemical water oxidation as well as the structural requirements for the catalyst to perform actively. PMID:25641823

  17. Multiple-scattering EXAFS analysis of tetraalkylammonium manganese oxide colloids

    SciTech Connect

    Ressler, T.; Wong, J.; Brock, S.L.; Suib, S.L.

    1999-08-05

    X-ray absorption spectroscopy at the Mn K edge was employed to elucidate the structure of colloidal tetraalkylammonium (TAA) manganese oxides in sols and gels obtained by different preparation and heat treatment procedures. Two series of colloidal TAA MnO{sub x} prepared with tetrapropylammonium (TPA) and tetraethylammonium (TEA) cations were studied. Several manganese oxides, birnessite, and feitknechtite were also measured and served as model compounds for structural refinements. Near edge structure (XANES) analysis revealed different average valences of the colloidal systems. As synthesized and heat-treated, TAA colloids exhibited an average valence of 3.6--3.7, whereas gelled TAA colloids showed a lower average valence of {approximately} 3.5. Extended absorption fine structure (EXAFS) analysis was carried out to distances of {approximately} 6.0 {angstrom} around the central Mn atom using theoretical backscattering phases and amplitudes calculated from the ab initio FEFF code. All multiple-scattering (MS) paths with a weight of 2% and more with respect to the main Fourier transform peak were included in the refinement. It is found that, except for gelled TAA samples, no significant amount of corner-shared MnO{sub 6} units was detected in the colloidal systems. Theoretical EXAFS phases and amplitudes were derived for a monoclinic birnessite MnO{sub x} layer structure consisting of edge-shared MnO{sub 6} octahedra. EXAFS refinements utilizing these phases and amplitudes resulted in good agreement with experimental data. Differences in the refined scattering shell distances between the TPA and TEA series suggest a structure influencing effect of the two ammonium ions. Bond angles between neighboring MnO{sub 6} octahedra were determined from the amplitude dependence of a collinear Mn-Mn-Mn MS path on deviations from 180{degree} (focusing effect). On the basis of the bond angles, and with use of the average valence to define the distribution of tri- and tetravalent manganese in the MnO{sub x} layers, three distinct 2D structures are proposed: one for birnessite, one for TAA sols, and one for TAA gels.

  18. Water exchange in manganese-based water-oxidizing catalysts in photosynthetic systems: from the water-oxidizing complex in photosystem II to nano-sized manganese oxides.

    PubMed

    Najafpour, Mohammad Mahdi; Isaloo, Mohsen Abbasi; Eaton-Rye, Julian J; Tomo, Tatsuya; Nishihara, Hiroshi; Satoh, Kimiyuki; Carpentier, Robert; Shen, Jian-Ren; Allakhverdiev, Suleyman I

    2014-09-01

    The water-oxidizing complex (WOC), also known as the oxygen-evolving complex (OEC), of photosystem II in oxygenic photosynthetic organisms efficiently catalyzes water oxidation. It is, therefore, responsible for the presence of oxygen in the Earth's atmosphere. The WOC is a manganese-calcium (Mn?CaO?(H?O)?) cluster housed in a protein complex. In this review, we focus on water exchange chemistry of metal hydrates and discuss the mechanisms and factors affecting this chemical process. Further, water exchange rates for both the biological cofactor and synthetic manganese water splitting are discussed. The importance of fully unveiling the water exchange mechanism to understand the chemistry of water oxidation is also emphasized here. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy. PMID:24685431

  19. Vanadia supported on nickel manganese oxide nanocatalysts for the catalytic oxidation of aromatic alcohols

    NASA Astrophysics Data System (ADS)

    Adil, Syed F.; Alabbad, Saad; Kuniyil, Mufsir; Khan, Mujeeb; Alwarthan, Abdulrahman; Mohri, Nils; Tremel, Wolfgang; Tahir, Muhammad Nawaz; Siddiqui, Mohammed Rafiq Hussain

    2015-02-01

    Vanadia nanoparticles supported on nickel manganese mixed oxides were synthesized by co-precipitation method. The catalytic properties of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as oxidant. It was observed that the calcination temperature and the size of particles play an important role in the catalytic process. The catalyst was evaluated for its oxidation property against aliphatic and aromatic alcohols, which was found to display selectivity towards aromatic alcohols. The samples were characterized by employing scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, thermogravimetric analysis, and X-ray photoelectron spectroscopy.

  20. Towards a mechanistic understanding of carbon stabilization in manganese oxides

    PubMed Central

    Johnson, Karen; Purvis, Graham; Lopez-Capel, Elisa; Peacock, Caroline; Gray, Neil; Wagner, Thomas; März, Christian; Bowen, Leon; Ojeda, Jesus; Finlay, Nina; Robertson, Steve; Worrall, Fred; Greenwell, Chris

    2015-01-01

    Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems. PMID:26194625

  1. Nature of Activated Manganese Oxide for Oxygen Evolution.

    PubMed

    Huynh, Michael; Shi, Chenyang; Billinge, Simon J L; Nocera, Daniel G

    2015-12-01

    Electrodeposited manganese oxide films (MnOx) are promising stable oxygen evolution catalysts. They are able to catalyze the oxygen evolution reaction in acidic solutions but with only modest activity when prepared by constant anodic potential deposition. We now show that the performance of these catalysts is improved when they are "activated" by potential cycling protocols, as measured by Tafel analysis (where lower slope is better): upon activation the Tafel slope decreases from ?120 to ?70 mV/decade in neutral conditions and from ?650 to ?90 mV/decade in acidic solutions. Electrochemical, spectroscopic, and structural methods were employed to study the activation process and support a mechanism where the original birnessite-like MnOx (?-MnO2) undergoes a phase change, induced by comproportionation with cathodically generated Mn(OH)2, to a hausmannite-like intermediate (?-Mn3O4). Subsequent anodic conditioning from voltage cycling or water oxidation produces a disordered birnessite-like phase, which is highly active for oxygen evolution. At pH 2.5, the current density of activated MnOx (at an overpotential of 600 mV) is 2 orders of magnitude higher than that of the original MnOx and begins to approach that of Ru and Ir oxides in acid. PMID:26574923

  2. Synthesis and characterization of cobalt-manganese oxides

    NASA Astrophysics Data System (ADS)

    Valencia, J.; Arias, N. P.; Giraldo, O.; Rosales-Rivera, A.

    2012-08-01

    Cobalt doped/un-doped manganese oxides materials were synthesized at various doping rates by soft chemical reactions, oxidation-reduction method, which allows generating a metal-mixed oxide. The synthesized materials were characterized using several techniques including chemical analysis, X-rays diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The chemical analysis confirmed the presence of cobalt in the samples. XRD patterns reveal mainly a spinel-like structure and SEM micrographs exhibited morphology with fine aggregate of particles. TGA profiles showed weight loss due to loss of water in a first step, followed by a loss of oxygen from the lattice associated with partial reduction of Mn4+ to Mn3+. VSM was used to measure the magnetization as a function of the applied magnetic field at temperatures T=50 and 300 K. Different magnetic behaviors were observed when cobalt percentage changed in the samples. These behaviors are considered to be related to the size of the particles and composition of the materials. Higher coercive field and lesser magnetization were observed for the sample with higher cobalt content.

  3. Towards a mechanistic understanding of carbon stabilization in manganese oxides.

    PubMed

    Johnson, Karen; Purvis, Graham; Lopez-Capel, Elisa; Peacock, Caroline; Gray, Neil; Wagner, Thomas; März, Christian; Bowen, Leon; Ojeda, Jesus; Finlay, Nina; Robertson, Steve; Worrall, Fred; Greenwell, Chris

    2015-01-01

    Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems. PMID:26194625

  4. Unilamellar nanosheet of layered manganese cobalt nickel oxide and its heterolayered film with polycations.

    PubMed

    Oh, Eun-Jin; Kim, Tae Woo; Lee, Kyung Min; Song, Min-Sun; Jee, Ah-Young; Lim, Seung Tae; Ha, Hyung-Wook; Lee, Minyung; Choy, Jin-Ho; Hwang, Seong-Ju

    2010-08-24

    The exfoliation of layered Li[Mn(1/3)Co(1/3)Ni(1/3)]O(2) into individual monolayers could be achieved through the intercalation of quaternary tetramethylammonium (TMA(+)) ions into protonated metal oxide. An effective exfoliation occurred when the TMA(+)/H(+) ratio was 0.5-50. Reactions outside this range produced no colloidal suspension, but all the manganese cobalt nickel oxides precipitated. Atomic force microscopy and transmission electron microscopy clearly demonstrated that exfoliated manganese cobalt nickel oxide nanosheets have a nanometer-level thickness, underscoring the formation of unilamellar nanosheets. The maintenance of the hexagonal atomic arrangement of the manganese cobalt nickel oxide layer upon the exfoliation was confirmed by selected area electron diffraction analysis. According to diffuse reflectance ultraviolet--visible spectroscopy, the exfoliated manganese cobalt nickel oxides displayed distinct absorption peaks at approximately 354 and approximately 480 nm corresponding to the d-d transitions of octahedral metal ions, which contrasted with the featureless spectrum of the pristine metal oxide. In the light of zeta potential data showing the negative surface charge of manganese cobalt nickel oxide nanosheets, a heterolayered film of manganese cobalt nickel oxide and conductive polymers could be prepared through the successive coating process with colloidal suspension and polycations. The UV--vis and X-ray diffraction studies verified the layer-by-layer ordered structure of the obtained heterolayered film, respectively. PMID:20731429

  5. Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study.

    PubMed

    Frey, Carolin E; Kurz, Philipp

    2015-10-12

    Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnOx ) with various solid-state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnOx was then investigated with Ce(4+) as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\\rm{mmol}}_{{\\rm{O}}_{\\rm{2}} } }$?${{\\rm{mol}}_{{\\rm{Mn}}}^{ - 1} }$ h(-1) or about 50 ?molO2 m(-2) h(-1) . In comparison, catalytic rates per mole of Mn of oxides characterised by well-defined 3D networks were rather low (e.g., ca. 90 ${{\\rm{mmol}}_{{\\rm{O}}_{\\rm{2}} } }$?${{\\rm{mol}}_{{\\rm{Mn}}}^{ - 1} }$ h(-1) for bixbyite, Mn2 O3 ), but impressive if normalised per unit surface area (>100 ${{\\rm{{\\rm \\mu} mol}}_{{\\rm{O}}_{\\rm{2}} } }$ m(-2) h(-1) for marokite, CaMn2 O4 ). Thus, two groups of MnOx emerge from this screening as hot candidates for manganese-based WOC materials: 1) amorphous oxides with tunnelled structures and the well-established layered oxides; 2) crystalline Mn(III) oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass. PMID:26332508

  6. Photochemical water oxidation by crystalline polymorphs of manganese oxides: structural requirements for catalysis.

    PubMed

    Robinson, David M; Go, Yong Bok; Mui, Michelle; Gardner, Graeme; Zhang, Zhijuan; Mastrogiovanni, Daniel; Garfunkel, Eric; Li, Jing; Greenblatt, Martha; Dismukes, G Charles

    2013-03-01

    Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ? ?-MnO2, where the latter is derived from spinel LiMn2O4 following partial Li(+) removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and ?-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration e(g)(1) which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface. PMID:23391134

  7. Manganese peroxidase-catalyzed oxidative degradation of vanillylacetone.

    PubMed

    Hwang, Sangpill; Lee, Chang-Ha; Ahn, Ik-Sung; Park, Kwangyong

    2008-06-01

    When 4-(4-hydroxy-3-methoxy-phenyl)-2-butanone (vanillylacetone) was tested for manganese peroxidase (MnP)-catalyzed oxidation, it was found to be degraded with the cleavage of an aromatic ring. Among numerous products of vanillylacetone oxidation, four major ones were purified by thin-layer chromatography and identified using mass spectroscopy (MS) and nuclear magnetic resonance (NMR) analysis. Three of them maintained the aromatic ring structure and were identified as 4-[6,2'-dihydroxy-5,3'-dimethoxy-5'-(3-oxo-butyl)-biphenyl]-butan-2-one, 4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-one, and 4-[6,2'-dihydroxy-5,3'-dimethoxy-5'-(3-oxo-butyl)-biphenyl]-3-buten-2-one. Even though the fourth product could not be purified to a single compound, data from infrared spectroscopy showed that it did not have a benzene ring. From MS and NMR analysis, 3-(3-oxo-butyl)-hexa-2,4-dienedioic acid-1-methyl ester was tentatively suggested as the dominant species. The reaction mechanism was suggested on the basis of the structural information of these products. To our knowledge, this paper is the first report on aromatic ring cleavage of the phenolic compound by MnP. PMID:18472135

  8. Sodium perxenate permits rapid oxidation of manganese for easy spectrophotometric determination

    NASA Technical Reports Server (NTRS)

    Bane, R. W.

    1967-01-01

    Sodium perxenate oxidizes manganese to permanganate almost instantaneously in dilute acid solution and without a catalyst. A solution is prepared by dissolving 200 mg of sodium perxenate in distilled water and diluting to 100 ml.

  9. Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

    PubMed Central

    Birkner, Nancy; Navrotsky, Alexandra

    2014-01-01

    Chemisorption of water onto anhydrous nanophase manganese oxide surfaces promotes rapidly reversible redox phase changes as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Surface reduction of bixbyite (Mn2O3) to hausmannite (Mn3O4) occurs in nanoparticles under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Additionally, transformation does not occur on nanosurfaces passivated by at least 2% coverage of what is likely an amorphous manganese oxide layer. The transformation is due to thermodynamic control arising from differences in surface energies of the two phases (Mn2O3 and Mn3O4) under wet and dry conditions. Such reversible and rapid transformation near room temperature may affect the behavior of manganese oxides in technological applications and in geologic and environmental settings. PMID:24733903

  10. Electrochromic properties of manganese oxide thin films prepared by chemical vapor deposition

    SciTech Connect

    Maruyama, Toshiro; Osaki, Yoshinori

    1995-09-01

    Electrochromic manganese oxide thin films were prepared by chemical vapor deposition. The source material was manganese (III) acetylacetonate. Transparent Mn{sub 3}O{sub 4} thin films were obtained at a substrate temperature above 250 C. Oxidation and reduction of the films in a 0.3 M LiClO{sub 4} propylene carbonate solution resulted in desirable changes in optical absorption. Coulometry indicated that the coloration efficiency was 6.03 cm{sup 2}/C.

  11. Bi-template assisted synthesis of mesoporous manganese oxide nanostructures: Tuning properties for efficient CO oxidation.

    PubMed

    Roy, Mouni; Basak, Somjyoti; Naskar, Milan Kanti

    2016-02-10

    A simple soft bi-templating process was used for the synthesis of mesoporous manganese oxide nanostructures using KMnO4 as a precursor and polyethylene glycol and cetyltrimethylammonium bromide as templates in the presence of benzaldehyde as an organic additive in alkaline media, followed by calcination at 400 °C. X-ray diffraction and Raman spectroscopic analysis of the calcined products confirmed the existence of stoichiometric (MnO2 and Mn5O8) and non-stoichiometric mixed phases (MnO2 + Mn5O8) of Mn oxides obtained by tuning the concentration of the additive and the synthesis time. The surface properties of the prepared Mn oxides were determined by X-ray photoelectron spectroscopy. The mesoporosity of the samples was confirmed by N2 adsorption-desorption. Different synthetic conditions resulted in the formation of different morphologies of the Mn oxides (α-MnO2, Mn5O8, and α-MnO2 + Mn5O8), such as nanoparticles, nanorods, and nanowires. The synthesized mesoporous Mn oxide nanostructures were used for the catalytic oxidation of the harmful air pollutant carbon monoxide. The Mn5O8 nanoparticles with the highest Brunauer-Emmett-Teller surface area and the non-stoichiometric manganese oxide (α-MnO2 + Mn5O8) nanorods with a higher Mn(3+) concentration had the best catalytic efficiency. PMID:26815335

  12. Oxidative damage and neurodegeneration in manganese-induced neurotoxicity

    SciTech Connect

    Milatovic, Dejan; Yu, Yingchun

    2009-10-15

    Exposure to excessive manganese (Mn) levels results in neurotoxicity to the extrapyramidal system and the development of Parkinson's disease (PD)-like movement disorder, referred to as manganism. Although the mechanisms by which Mn induces neuronal damage are not well defined, its neurotoxicity appears to be regulated by a number of factors, including oxidative injury, mitochondrial dysfunction and neuroinflammation. To investigate the mechanisms underlying Mn neurotoxicity, we studied the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates (HEP), neuroinflammation mediators and associated neuronal dysfunctions both in vitro and in vivo. Primary cortical neuronal cultures showed concentration-dependent alterations in biomarkers of oxidative damage, F{sub 2}-isoprostanes (F{sub 2}-IsoPs) and mitochondrial dysfunction (ATP), as early as 2 h following Mn exposure. Treatment of neurons with 500 {mu}M Mn also resulted in time-dependent increases in the levels of the inflammatory biomarker, prostaglandin E{sub 2} (PGE{sub 2}). In vivo analyses corroborated these findings, establishing that either a single or three (100 mg/kg, s.c.) Mn injections (days 1, 4 and 7) induced significant increases in F{sub 2}-IsoPs and PGE{sub 2} in adult mouse brain 24 h following the last injection. Quantitative morphometric analyses of Golgi-impregnated striatal sections from mice exposed to single or three Mn injections revealed progressive spine degeneration and dendritic damage of medium spiny neurons (MSNs). These findings suggest that oxidative stress, mitochondrial dysfunction and neuroinflammation are underlying mechanisms in Mn-induced neurodegeneration.

  13. Visible and near-infrared spectra of manganese oxides: Detecting high manganese phases in Curiosity Mastcam multispectral images

    NASA Astrophysics Data System (ADS)

    Hardgrove, C. J.; Lanza, N.; Bell, J. F., III; Wiens, R. C.; Johnson, J. R.; Morris, R. V.

    2014-12-01

    The Mars Science Laboratory Curiosity rover's Chemcam instrument has identified manganese in relatively high abundance on several rock surfaces. The manganese abundances are several orders of magnitude greater than has been previously identified on Mars, indicating the presence of a manganese-rich phase. Although the specific phase has yet to be identified, these results suggest that the martian surface may have been much more highly oxidizing than has previously been recognized. The presence of a manganese-rich phase could provide an additional indicator of habitable aqueous environments. Given the importance of manganese for understanding past habitability, and the high abundances identified with Chemcam, we investigate the utility of using Mastcam multispectral imaging surveys to identify areas for subsequent detailed analysis with Chemcam. Vempati et al. showed that Mn3+ affect the reflectance spectra of Mn-bearing minerals. Specifically, relatively weak features due to electronic transitions and crystal field effects are observed in Mn-enriched hematites and geothites at 454, 554, 596 and 700 nm. The Mastcam-34 medium angle camera has filter band-passes at 550, 675 and 750nm, and we will explore the utility of using these bands (or combinations thereof) to determine if there is a contribution of Mn-bearing phases on spectra, specifically those that have been identified as having elevated Mn with Chemcam. The most common Mn-bearing mineral phase in terrestrial varnishes, Birnessite, has charge-transfer features that are similar to Fe-oxides but are centered at slightly longer wavelength band positions. Longer wavelength features are also common for other Mn-oxides, and this could be used to distinguish these phases from other Fe-oxide components. In this study we will present visible to near-infrared (0.4 - 3 µm) reflectance spectra on a suite of Mn-oxide laboratory standards. The set of standards includes Mn-oxide abundances that vary from less than 1 up to ~75 wt.%. Spectra will be downsampled to Mastcam bandpasses to determine if the effects of Mn-bearing phases could be identified from Mastcam multispectral observations in Gale Crater.

  14. Photosynthetic water oxidation: insights from manganese model chemistry.

    PubMed

    Young, Karin J; Brennan, Bradley J; Tagore, Ranitendranath; Brudvig, Gary W

    2015-03-17

    Catalysts for light-driven water oxidation are a critical component for development of solar fuels technology. The multielectron redox chemistry required for this process has been successfully deployed on a global scale in natural photosynthesis by green plants and cyanobacteria using photosystem II (PSII). PSII employs a conserved, cuboidal Mn4CaOX cluster called the O2-evolving complex (OEC) that offers inspiration for artificial O2-evolution catalysts. In this Account, we describe our work on manganese model chemistry relevant to PSII, particularly the functional model [Mn(III/IV)2(terpy)2(?-O)2(OH2)2](NO3)3 complex (terpy = 2,2';6',2?-terpyridine), a mixed-valent di-?-oxo Mn dimer with two terminal aqua ligands. In the presence of oxo-donor oxidants such as HSO5(-), this complex evolves O2 by two pathways, one of which incorporates solvent water in an O-O bond-forming reaction. Deactivation pathways of this catalyst include comproportionation to form an inactive Mn(IV)Mn(IV) dimer and also degradation to MnO2, a consequence of ligand loss when the oxidation state of the complex is reduced to labile Mn(II) upon release of O2. The catalyst's versatility has been shown by its continued catalytic activity after direct binding to the semiconductor titanium dioxide. In addition, after binding to the surface of TiO2 via a chromophoric linker, the catalyst can be oxidized by a photoinduced electron-transfer mechanism, mimicking the natural PSII process. Model oxomanganese complexes have also aided in interpreting biophysical and computational studies on PSII. In particular, the ?-oxo exchange rates of the Mn-terpy dimer have been instrumental in establishing that the time scale for ?-oxo exchange of high-valent oxomanganese complexes with terminal water ligands is slower than O2 evolution in the natural photosynthetic system. Furthermore, computational studies on the Mn-terpy dimer and the OEC point to similar Mn(IV)-oxyl intermediates in the O-O bond-forming mechanism. Comparison between the OEC and the Mn-terpy dimer indicates that challenges remain in the development of synthetic Mn water-oxidation catalysts. These include redox leveling to couple multielectron reactions with one-electron steps, avoiding labile Mn(II) species during the catalytic cycle, and protecting the catalyst active site from undesired side reactions. As the first example of a functional manganese O2-evolution catalyst, the Mn-terpy dimer exemplifies the interrelatedness of biomimetic chemistry with biophysical studies. The design of functional model complexes enriches the study of the natural photosynthetic system, while biology continues to provide inspiration for artificial photosynthetic technologies to meet global energy demand. PMID:25730258

  15. In situ synthesis of mixed-valent manganese oxide nanocrystals: an in situ synchrotron X-ray diffraction study.

    PubMed

    Shen, Xiong-Fei; Ding, Yun-Shuang; Hanson, Jonathan C; Aindow, Mark; Suib, Steven L

    2006-04-12

    Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. However, most reported in situ synchrotron XRD studies focus on solid state/gel systems by measuring phase/structure changes during application of pressure or heat. Phase transformations during material synthesis and their applications, especially in wet chemistry processes with different media, have not drawn much attention. Here, using manganese oxides as examples, we report the successful characterization of phase transformations in in situ hydrothermal synthesis conditions by the in situ synchrotron XRD method using a quartz/sapphire capillary tube as the synthesis reactor. The results were used for better design of materials with controlled structures and properties. This method can be generally used for synthesis of manganese oxides as well as for in situ characterization of other material syntheses using hydrothermal, sol-gel, and other methods. In addition, catalytic processes in liquid-solid, gas-solid, and solid-solid systems can also be studied in such an in situ way so that catalytic mechanisms can be better understood and catalyst synthesis and catalytic processes can be optimized. PMID:16594683

  16. Bismuth oxide coated amorphous manganese dioxide for electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Li, Xiaofeng; Zhang, Linsen; Dong, Huichao; Xia, Tongchi; Huang, Zhigang

    2015-05-01

    With MnSO4, NaOH and K2S2O8 as the raw materials, the amorphous and ?-type manganese dioxide (MnO2) is separately prepared by using different chemical precipitation-oxidation methods. The results of charge-discharge and electrochemical impedance spectroscopy (EIS) tests show that (i) the specific capacitance of the amorphous MnO2 reaches to 301.2 F g-1 at a current density of 200 mA g-1 and its capacitance retention rate after 2000 cycles is 97%, which is obviously higher than 250.8 F g-1 and 71% of the ?-type one, respectively; (ii) good electrochemical capacitance properties of the amorphous MnO2 should be contributed to easy insertion/extraction of ions within the material; (iii) when 5 wt% Bi2O3 is coated on the amorphous MnO2, its specific capacitance increases to 352.8 F g-1 and the capacitance retention rate is 90% after 2000 cycles.

  17. Surfactant-mediated electrodeposition of a water-oxidizing manganese oxide.

    PubMed

    Osowiecki, Wojciech T; Sheehan, Stafford W; Young, Karin J; Durrell, Alec C; Mercado, Brandon Q; Brudvig, Gary W

    2015-10-14

    Splitting water into hydrogen and oxygen is one of the most promising ways of storing energy from intermittent, renewable sources in the future. Toward this goal, development of inexpensive, stable, and non-toxic catalysts for water oxidation is crucial. We report that the electrodeposition of manganese oxide in the presence of sodium dodecyl sulfate (SDS) produces a material that is highly active for electrocatalytic water oxidation at pH near 7 and remains stable for over 24 hours of sustained electrolysis. Clark electrode measurements demonstrate more than 95% Faradaic efficiency for oxygen evolution after an initial charging period. We found that catalytic performance was optimized in films prepared by electrodeposition using a precursor solution containing moderate concentration of substrates, namely 25 mM Mn(2+) and 25 mM SDS. Microstructure and elemental analyses revealed that the deposited material, a mixed-phase manganese oxide, is structurally similar to materials used for electrochemical capacitors and batteries, drawing a parallel between highly studied cathode materials for rechargeable batteries and heterogeneous catalysts for water oxidation. PMID:26350519

  18. Role of manganese in protection against oxidative stress under iron starvation in cyanobacterium Anabaena 7120.

    PubMed

    Kaushik, Manish Singh; Srivastava, Meenakshi; Verma, Ekta; Mishra, Arun Kumar

    2015-06-01

    The cyanobacterium Anabaena sp. PCC 7120 was grown in presence and absence of iron to decipher the role of manganese in protection against the oxidative stress under iron starvation and growth, manganese uptake kinetics, antioxidative enzymes, lipid peroxidation, electrolyte leakage, thiol content, total peroxide, proline and NADH content was investigated. Manganese supported the growth of cyanobacterium Anabaena 7120 under iron deprived conditions where maximum uptake rate of manganese was observed with lower K(m) and higher V(max) values. Antioxidative enzymes were also found to be elevated in iron-starved conditions. Estimation of lipid peroxidation and electrolyte leakage depicted the role of manganese in stabilizing the integrity of the membrane which was considered as the prime target of oxygen free radicals in oxidative stress. The levels of total peroxide, thiol, proline and NADH content, which are the representative of oxidative stress response in Anabaena 7120, were also showed increasing trends in iron starvation. Hence, the results discerned, clearly suggested the role of manganese in protection against the oxidative stress in cyanobacterium Anabaena 7120 under iron starvation either due to its antioxidative properties or involvement as cofactor in a number of antioxidative enzymes. PMID:25572501

  19. Distribution of manganese species in an oxidative dimerization reaction of a bis-terpyridine mononuclear manganese (II) complex and their heterogeneous water oxidation activities.

    PubMed

    Takahashi, Kosuke; Sato, Taisei; Yamazaki, Hirosato; Yagi, Masayuki

    2015-11-01

    Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of [Mn(II)(terpy)2](2+) (terpy=2,2':6',2?-terpyridine) (1') with various oxidants in water was revealed. 1' was stoichiometrically oxidized to form di-?-oxo dinuclear manganese complex, [(OH2)(terpy)Mn(III)(?-O)2Mn(IV)(terpy)(OH2)](3+) (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to [(OH2)(terpy)Mn(IV)(?-O)2Mn(IV)(terpy)(OH2)](4+) (2) was observed after the oxidative dimerization reaction of 1'. The mica adsorbates with various composition of 1', 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1' (1'ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce(3+) cations (generated in oxidative dimerization of 1') co-adsorbed with 1ads. PMID:25935510

  20. Iron and manganese oxide mineralization in the Pacific

    USGS Publications Warehouse

    Hein, J. R., (Edited By); Koschinsky, A.; Halbach, P.; Manheim, F. T., (Edited By); Bau, M.; Jung-Keuk, Kang; Lubick, N.

    1997-01-01

    Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. These processes are discussed.

  1. Prophylactic use of polyvinylpyridine-N-oxide (PVNO) in baboons exposed to quartz dust

    SciTech Connect

    Goldstein, B.; Rendall, R.E.G.

    1987-04-01

    Twelve baboons were exposed to a quartz dust cloud. Four of these were also given polyvinylpyridine-N-oxide (PVNO) by aerosol and four received PVNO by aerosol and injection. A prophylactic effect was demonstrated during the course of treatment, but when treatment stopped the silicosis progressed to the same degree of severity as in the untreated animals.

  2. Alcohol-assisted room temperature synthesis of different nanostructured manganese oxides and their pseudocapacitance properties in neutral electrolyte

    NASA Astrophysics Data System (ADS)

    Subramanian, V.; Zhu, Hongwei; Wei, Bingqing

    2008-03-01

    Different nanostructured manganese oxides have been synthesized by a simple precipitation technique using KMnO4 and different alcohols. The synthesized manganese oxides were extensively studied using TEM, XRD, XPS, surface area measurements and electrochemical studies. TEM observations showed a range of nanostructures from nanowiskers to nanoparticles. This synthesis method promises the tuning of electronic and structural properties of the nanostructured manganese oxides by simply varying the alcohols used in the reactions. MnO2 shows more whisker-like morphology while the Mn2O3 shows particle morphology. The nanostructured manganese oxides showed excellent performance as a pseudocapacitor electrode in a neutral electrolyte.

  3. Water oxidation catalysed by manganese compounds: from complexes to 'biomimetic rocks'.

    PubMed

    Wiechen, Mathias; Berends, Hans-Martin; Kurz, Philipp

    2012-01-01

    One of the most fundamental processes of the natural photosynthetic reaction sequence is the light-driven oxidation of water to molecular oxygen. In vivo, this reaction takes place in the large protein ensemble Photosystem II, where a ?-oxido-Mn(4)Ca- cluster, the oxygen-evolving-complex (OEC), has been identified as the catalytic site for the four-electron/four-proton redox reaction of water oxidation. This Perspective presents recent progress for three strategies which have been followed to prepare functional synthetic analogues of the OEC: (1) the synthesis of dinuclear manganese complexes designed to act as water-oxidation catalysts in homogeneous solution, (2) heterogeneous catalysts in the form of clay hybrids of such Mn(2)-complexes and (3) the preparation of manganese oxide particles of different compositions and morphologies. We discuss the key observations from the studies of such synthetic manganese systems in order to shed light upon the catalytic mechanism of natural water oxidation. Additionally, it is shown how research in this field has recently been motivated more and more by the prospect of finding efficient, robust and affordable catalysts for light-driven water oxidation, a key reaction of artificial photosynthesis. As manganese is an abundant and non-toxic element, manganese compounds are very promising candidates for the extraction of reduction equivalents from water. These electrons could consecutively be fed into the synthesis of "solar fuels" such as hydrogen or methanol. PMID:22068958

  4. Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water.

    PubMed

    Wang, Jinlong; Zhang, Pengyi; Li, Jinge; Jiang, Chuanjia; Yunus, Rizwangul; Kim, Jeonghyun

    2015-10-20

    Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 C, 100 C, 200 C, 300 C, and 500 C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials. PMID:26426569

  5. Effect of oxide formation mechanisms on lead adsorption by biogenic manganese (hydr)oxides, iron (hydr)oxides, and their mixtures.

    PubMed

    Nelson, Yarrow M; Lion, Leonard W; Shuler, Michael L; Ghiorse, William C

    2002-02-01

    The effects of iron and manganese (hydr)oxide formation processes on the trace metal adsorption properties of these metal (hydr)oxides and their mixtures was investigated by measuring lead adsorption by iron and manganese (hydr)oxides prepared by a variety of methods. Amorphous iron (hydr)oxide formed by fast precipitation at pH 7.5 exhibited greater Pb adsorption (gamma(max) = 50 mmol of Pb/mol of Fe at pH 6.0) than iron (hydr)oxide formed by slow, diffusion-controlled oxidation of Fe(II) at pH 4.5-7.0 or goethite. Biogenic manganese(III/IV) (hydr)oxide prepared by enzymatic oxidation of Mn(II) by the bacterium Leptothrix discophora SS-1 adsorbed five times more Pb (per mole of Mn) than an abiotic manganese (hydr)oxide prepared by oxidation of Mn(II) with permanganate, and 500-5000 times more Pb than pyrolusite oxides (betaMnO2). X-ray crystallography indicated that biogenic manganese (hydr)oxide and iron (hydr)oxide were predominantly amorphous or poorly crystalline and their X-ray diffraction patterns were not significantly affected by the presence of the other (hydr)oxide during formation. When iron and manganese (hydr)oxides were mixed after formation, or for Mn biologically oxidized with iron(III) (hydr)oxide present, observed Pb adsorption was similar to that expected for the mixture based on Langmuir parameters for the individual (hydr)oxides. These results indicate that interactions in iron/manganese (hydr)oxide mixtures related to the formation process and sequence of formation such as site masking, alterations in specific surface area, or changes in crystalline structure either did not occur or had a negligible effect on Pb adsorption by the mixtures. PMID:11871557

  6. Porous manganese oxide synthesized through organic-electrolyte templates and their catalytic applications

    SciTech Connect

    Zhang Wei; Li Jiangying; Du Xuemin; Zhang Zhicheng

    2009-11-15

    We report a facile approach to the preparation of porous manganese oxide materials by the organic-electrolyte templates based on strategy. The final products are thoroughly characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Brunauer-Emmett-Teller (BET) techniques. The results reveal that porosity (pore size and distribution, surface area) of these manganese oxides has strong relationship with the templates used, which implies a simple way to obtain a series of porous materials. By comparing the catalytic effects of these manganese oxides in oxidation of indene and benzyl alcohol, we find that the pore size and distribution are also crucial to the catalytic properties of these porous materials.

  7. Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures.

    PubMed

    Najafpour, Mohammad Mahdi; Renger, Gernot; Hołyńska, Małgorzata; Moghaddam, Atefeh Nemati; Aro, Eva-Mari; Carpentier, Robert; Nishihara, Hiroshi; Eaton-Rye, Julian J; Shen, Jian-Ren; Allakhverdiev, Suleyman I

    2016-03-01

    All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn-Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25-90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn-Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn complexes decomposing to Mn oxide. We then provide a detailed assessment of the chemistry of Mn oxides by considering how their bulk and nanoscale properties contribute to their effectiveness as water-oxidizing catalysts. PMID:26812090

  8. Early diagenetic quartz formation at a deep iron oxidation front in the Eastern Equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Meister, Patrick; Chapligin, Bernhard; Picard, Aude; Meyer, Hanno; Fischer, Cornelius; Rettenwander, Daniel; Amthauer, Georg; Vogt, Christoph; Aiello, Ivano

    2015-04-01

    The mechanisms of early diagenetic quartz formation under low-temperature conditions are still poorly understood. We studied lithified cherts consisting of microcrystalline quartz recovered from ODP Site 1226 in the Eastern Equatorial Pacific. The cherts occur near the base of a 420-m-thick Miocene-Holocene sequence within unlithified nannofossil and diatom ooze. Palaeo-temperatures reconstructed from ?18O values in the cherts are near to present porewater temperatures and a sharp depletion in dissolved silica occurs around 385 mbsf indicating that silica precipitation is still ongoing. Also a deep iron oxidation front occurs at the same depth, which is caused by upward diffusing nitrate from an oxic seawater aquifer in the underlying basaltic crust. Sequential iron extraction and analysis of the X-ray absorption near-edge structure (XANES) revealed that iron in the cherts predominantly occurs as illite and amorphous iron oxide, whereas iron in the nannofossil and diatom ooze occurs mainly as smectites. Mssbauer spectroscopy confirmed that the illite iron in the cherts is largely oxidized. A possible mechanisms that may be operative is quartz precipitation initiated by adsorption of silica to freshly precipitated iron oxides. The decrease in porewater silica concentration below opal-A and opal-CT saturation then allows for the precipitation of the thermodynamically more stable phase: quartz. We suggest that the formation of early-diagenetic chert at iron oxidation fronts is an important process in suboxic zones of silica-rich sediments. The largest iron oxidation front ever occurred during the great oxidation event ca. 2.5 Ga ago, when large amounts of iron and chert beds were deposited.

  9. EFFECTS OF SOLAR RADIATION ON MANGANESE OXIDE REACTIONS WITH SELECTED ORGANIC COMPOUNDS

    EPA Science Inventory

    The effects of sunlight on aqueous redox reactions between manganese oxides (MnOx) and selected organic substances are reported. o sunlight-induced rate enhancement was observed for the MnOx oxidation of substituted phenols, anisole, o-dichlorobenzene, or p-chloroaniline. n the o...

  10. Quartz and Hydrous Iron Oxides from the Bee Bluff Structure of South Texas

    NASA Astrophysics Data System (ADS)

    Graham, R. A.; Martin, M.; Thadhani, N. N.; Morosin, B.

    2006-07-01

    There is substantial information showing that the Bee Bluff structure is an impact site and that a residual crater can be identified. The thin hard cap of Carrizo Sandstone, Indio fm calcareous silt and a thin layer of iron-rich siltstone leads to impact processes in which the high pressure release wave proceeds promptly upward leading to a trapping of metamorphic products at the impact interface, a `bottom-up' pressure release. Release of water from goethite binder in the sandstone and from the iron-rich siltstone results in supersaturated steam in mixtures with iron and quartz compounds. Samples with quartz and hydrous iron oxide features are examined with optical microscopy, SEM, EDX and XRD. A quartz grain is found with a well defined PDF set. There is widespread amorphous quartz including lechatleriete. Nanocrystals of α-goethite in the acicular form are common. A condensation sphere from the `Uvalde Crater Rosetta Stone' shows a complex mixture of hematite, goethite, and alpha quartz with a trace of trydimite. Numerous samples are yet to be analyzed. The crater appears to have features that can serve as an Earth analog to Mars craters. A companion paper in the present proceedings summarizes prior work, adds new site detail, reports impact-loading analysis, and describes overall features of impactite samples from the site.

  11. Determination of uranyl incorporation into biogenic manganese oxides using X-ray absorption spectroscopy and scattering

    USGS Publications Warehouse

    Webb, S.M.; Fuller, C.C.; Tebo, B.M.; Bargar, J.R.

    2006-01-01

    Biogenic manganese oxides are common and an important source of reactive mineral surfaces in the environment that may be potentially enhanced in bioremediation cases to improve natural attenuation. Experiments were performed in which the uranyl ion, UO22+ (U(VI)), at various concentrations was present during manganese oxide biogenesis. At all concentrations, there was strong uptake of U onto the oxides. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) studies were carried out to determine the molecular-scale mechanism by which uranyl is incorporated into the oxide and how this incorporation affects the resulting manganese oxide structure and mineralogy. The EXAFS experiments show that at low concentrations (2 mol % U, >4 ??M U(VI) in solution), the presence of U(VI) affects the stability and structure of the Mn oxide to form poorly ordered Mn oxide tunnel structures, similar to todorokite. EXAFS modeling shows that uranyl is present in these oxides predominantly in the tunnels of the Mn oxide structure in a tridentate complex. Observations by XRD corroborate these results. Structural incorporation may lead to more stable U(VI) sequestration that may be suitable for remediation uses. These observations, combined with the very high uptake capacity of the Mn oxides, imply that Mn-oxidizing bacteria may significantly influence dissolved U(VI) concentrations in impacted waters via sorption and incorporation into Mn oxide biominerals. ?? 2006 American Chemical Society.

  12. Experimental evaluation of the effects of quench rate and quartz surface area on homogeneous mercury oxidation

    SciTech Connect

    Andrew Fry; Brydger Cauch; Geoffrey D. Silcox; JoAnn S. Lighty; Constance L. Senior

    2007-07-01

    This paper presents a mercury oxidation data set suitable for validation of fundamental kinetic models of mercury chemistry and for mechanism development. Experimental facilities include a mercury reactor fitted with a 300-W, quartz-glass burner and a quartz reaction chamber. While operated with a temperature profile representative of a typical boiler, a residence time of 6 s was achieved. Participating reacting species (chlorine, mercury) were introduced through the burner to produce a radical pool representative of real combustion systems. Speciated mercury measurements were performed using a Tekran 2537A Analyzer coupled with a conditioning system. Homogeneous mercury reactions involving chlorine have been investigated under two different temperature profiles producing quench rates of -210 K/s and -440 K/s. The larger quench rate produced 52% greater total oxidation than the lower quench at chlorine concentrations of 200 ppm. The effect of reactor surface area on oxidation was also investigated. The quartz surfaces interacted with mercury only in the presence of chlorine and their overall effect was to weakly inhibit oxidation. The extent of oxidation was predicted using a detailed kinetic model. The model predicted the effects of quench rate and chlorine concentration shown in experimentation. 12 refs., 5 figs., 3 tabs.

  13. Manganese and Iron Oxidation During Benthic Oxygenic Photosynthesis

    NASA Astrophysics Data System (ADS)

    Epping, E. H. G.; Schoemann, V.; de Heij, H.

    1998-12-01

    The effect of benthic oxygenic photosynthesis on sediment-water fluxes of manganese and iron was studied for an intertidal sediment. Undisturbed sediments were incubated at an incident surface irradiance of 250 ?E m-2 s-1at 26 C. Oxygenic photosynthesis was selectively inhibited by adding [3-(3,4-dichloro)-1,1-dimethyl-urea] (DCMU). Benthic fluxes were determined experimentally from the change in manganese and iron concentrations in the overlying water, and were predicted from the pore water concentration gradients at the sediment-water interface assuming molecular diffusion as the transport mechanism. The experimental fluxes of manganese and iron in DCMU-treated cores amounted to -084 and -059 mmol m-2day-1, respectively, and were directed from the sediment towards the overlying water. In the control cores, showing high rates of benthic oxygenic photosynthesis, the fluxes of manganese and iron were directed towards the sediment, 006 and 001 mmol m-2day-1, respectively. Mass balances for the 01-014 cm thick oxic zone, calculated from the experimental fluxes and the predicted fluxes, suggest a minimum areal reoxidation of 06 mmol m-2day-1for manganese and of 048 mmol m-2day-1for iron in cores showing benthic photosynthesis. The estimated turnover times for dissolved Mn2+and dissolved Fe2+in the oxic surface layer during benthic photosynthesis were 08 and 025 h, respectively. Sediment oxygen microprofiles and the sediment pH profiles suggest that chemical precipitation and reoxidation dominates the retention of manganese and iron during benthic oxygenic photosynthesis in shallow intertidal sediments.

  14. Sol-gel synthesis and adsorption properties of mesoporous manganese oxide

    NASA Astrophysics Data System (ADS)

    Ivanets, A. I.; Kuznetsova, T. F.; Prozorovich, V. G.

    2015-03-01

    Sol-gel synthesis of mesoporous xerogels of manganese oxide with different phase compositions has been performed. The manganese oxide sols were obtained by redox reactions of potassium permanganate with hydrogen peroxide or manganese(II) chloride in aqueous solutions. The isotherms of the low-temperature adsorption-desorption of nitrogen with manganese oxide xerogels treated at 80, 200, 400, and 600°C were measured. The samples were studied by electron microscopy and thermal and XRD analysis. The phase transformation and the changes in the adsorption and capillary-condensation properties of manganese oxide were shown to depend on the sol synthesis conditions and the temperature of the thermal treatment of the gel. The X-ray amorphous samples heated at 80°C were shown to have low values of the specific surface; at higher temperatures, the xerogel crystallized into mixed phases with various compositions and its surface area increased at 200-400°C and decreased at 600°C.

  15. Catalytic ozonation of sulfosalicylic acid over manganese oxide supported on mesoporous ceria.

    PubMed

    Xing, Shengtao; Lu, Xiaoyang; Liu, Jia; Zhu, Lin; Ma, Zichuan; Wu, Yinsu

    2016-02-01

    Manganese oxide supported on mesoporous ceria was prepared and used as catalyst for catalytic ozonation of sulfosalicylic acid (SA). Characterization results indicated that the manganese oxide was mostly incorporated into the pores of ceria. The synthesized catalyst exhibited high activity and stability for the mineralization of SA in aqueous solution by ozone, and more than 95% of total organic carbon was removed in 30 min under various conditions. Mechanism studies indicated that SA was mainly degraded by ozone molecules, and hydroxyl radical reaction played an important role for the degradation of its ozonation products (small molecular organic acids). The manganese oxide in the pores of CeO2 improved the adsorption of small molecular organic acids and the generation of hydroxyl radicals from ozone decomposition, resulting in high TOC removal efficiency. PMID:26344143

  16. Strontium and Actinides Removal from Savannah River Site Actual Waste Samples by Freshly Precipitated Manganese Oxide

    SciTech Connect

    Barnes, M.J.

    2002-10-18

    The authors investigated the performance of freshly precipitated manganese oxide and monosodium titanate (MST) for the removal of strontium (Sr) and actinides from actual high-level waste. Manganese oxide precipitation occurs upon addition of a reductant such as formate (HCO2-) or peroxide (H2O2) to a waste solution containing permanganate (MnO4-). An addition of non-radioactive strontium typically precedes the MnO4- and reductant addition, which serves primarily to isotopically dilute the strontium-90 (90Sr) present in the waste. Tests utilized a Tank 37H/44F composite waste solution. Personnel significantly increased the concentration of actinides in the waste by the addition of acidic americium/curium solution (F-Canyon Tank 17.1 solution), which contained a significant quantity of plutonium (Pu), and neptunium-237 (237Np) stock solution. Initial tests examined three manganese oxide treatment options.

  17. Sorption of lead ions on diatomite and manganese oxides modified diatomite.

    PubMed

    Al-Degs, Y; Khraisheh, M A; Tutunji, M F

    2001-10-01

    Naturally occurring diatomaceous earth (diatomite) has been tested as a potential sorbent for Pb(II) ions. The intrinsic exchange properties were further improved by modification with manganese oxides. Modified adsorbent (referred to as Mn-diatomite) showed a higher tendency for adsorbing lead ions from solution at pH 4. The high performance exhibited by Mn-diatomite was attributed to increased surface area and higher negative surface charge after modification. Scanning electron microscope pictures revealed a birnessite structure of manganese oxides, which was featured by a plate-like-crystal structure. Diatomite filtration quality was improved after modification by manganese oxides. Good filtration qualities combined with high exchange capacity emphasised the potential use of Mn-diatomite in filtration systems. PMID:11561635

  18. Synthesis and Characterization of a Layered Manganese Oxide: Materials Chemistry for the Inorganic or Instrumental Methods Lab

    ERIC Educational Resources Information Center

    Ching, Stanton; Neupane, Ram P.; Gray, Timothy P.

    2006-01-01

    A three-week laboratory project involving synthesis and characterization of a layered manganese oxide provides an excellent vehicle for teaching important concepts of inorganic chemistry and instrumental methods related to non-molecular systems. Na-birnessite is an easily prepared manganese oxide with a 7 A interlayer spacing and Na[superscript +]

  19. Some derivatives of polyvinylpyridine 1-oxides and their effect on the cytotoxicity of quartz in macrophage cultures

    PubMed Central

    Holt, P. F.; Lindsay, H.; Beck, E. G.

    1970-01-01

    1. Poly(2-vinylpyridine 1-oxide) counteracts the pathogenic effects normally produced when quartz is injected into or inhaled by animals and the cytotoxic effects when quartz is added to macrophage cultures. The protective action of this polymer has been attributed variously to the formation of an adsorbed layer on the quartz particles, complex formation with monosilicic acid produced by the dissolution of quartz, and strengthening of the membranes or microstructures of the cells. 2. Stereoregular forms of poly(2-vinylpyridine 1-oxide), some alkyl derivatives of poly(2-vinylpyridine 1-oxide), poly(3-vinylpyridine 1-oxide) and poly(4-vinylpyridine 1-oxide), a copolymer of 2-vinylpyridine 1-oxide and 2-n-propenylpyridine 1-oxide, some poly(1-methyl-2-vinylpyridinium) quaternary salts, and poly(1-methoxy-2-vinylpyridinium iodide), which had previously been synthesized and studied with respect to their viscosities and interaction with silicic acid, were tested for their ability to counteract the cytotoxic effects of quartz in macrophage cultures. The tests were effected both by pretreating the quartz with polymers, and by pretreating the cells. 3. Every polymer proved active in one or other of these conditions, but several were active in one test but inactive in the other. Some polymer quaternary salts, which do not contain the N-oxide group, were found to be active. A remarkable difference in activity was found between the two stereoregular forms of poly(2-vinylpyridine 1-oxide). Pretreatment of the quartz with some of the polymers increased its cytotoxicity significantly. 4. Most of the results could be interpreted on the hypothesis that the polymers form an adsorbed layer on the quartz surface, but it is difficult to apply this explanation to two polymers which are inactive when used to pretreat the macrophages but are active when adsorbed on quartz. PMID:4312930

  20. Manganese oxide helices, rings, strands, and films, and methods for their preparation

    DOEpatents

    Suib, Steven L. (Storrs, CT); Giraldo, Oscar (Storrs, CT); Marquez, Manuel (Wheeling, IL); Brock, Stephanie (Detroit, MI)

    2003-01-07

    Methods for the preparation of mixed-valence manganese oxide compositions with quaternary ammonium ions are described. The compositions self-assemble into helices, rings, and strands without any imposed concentration gradient. These helices, rings, and strands, as well as films having the same composition, undergo rapid ion exchange to replace the quaternary ammonium ions with various metal ions. And the metal-ion-containing manganese oxide compositions so formed can be heat treated to form semi-conducting materials with high surface areas.

  1. Oxidation and dechlorination of chlorophenols in dilute aqueous suspensions of manganese oxides: Reaction products

    SciTech Connect

    Ukrainczyk, L.; McBride, M.B. . Dept.of Soil, Crop, and Atmospheric Sciences)

    1993-11-01

    Some monomeric and dimeric oxidation products of para- and/or ortho-chlorinated phenols in dilute (1 mmol/L phenol), acidified, aqueous suspensions of manganese oxide (Na-buserite) were identified by MS, Fourier-transform IR spectroscopy and UV/visible spectroscopy. The para-chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-chloro-2-methylphenol) gave corresponding p-benzoquionones (benzoquinone, 2-chlorobenzoquinone, 2,6-dichlorobenzoquinone, 2-methylbenzoquinone) as the detectable water-soluble oxidation products. Dimeric products were present in the extracts obtained by washing the oxide with methylene chloride. Michael addition of phenolate to quinone seems to be the predominant mode of coupling. Chlorinated phenols without chlorine in the para-position (2-chlorophenol, 2,6-dichlorophenol) were more difficult to oxidize and afforded diphenoquinones as the only detectable water-soluble products. For all studied phenols, with the exception of 2,4,6-trichlorophenol, the amount of water-soluble products accounts only for a small fraction of oxidized phenol. The quinone and diphenoquinone products readily couple with phenols into humus like materials.

  2. Growth and Dissolution of Iron and Manganese Oxide Films

    SciTech Connect

    Scot T. Martin

    2008-12-22

    Growth and dissolution of Fe and Mn oxide films are key regulators of the fate and transport of heavy metals in the environment, especially during changing seasonal conditions of pH and dissolved oxygen. The Fe and Mn are present at much higher concentrations than the heavy metals, and, when Fe and Mn precipitate as oxide films, heavy metals surface adsorb or co-precipitate and are thus essentially immobilized. Conversely, when the Fe and Mn oxide films dissolve, the heavy metals are released to aqueous solution and are thus mobilized for transport. Therefore, understanding the dynamics and properties of Fe and Mn oxide films and thus on the uptake and release of heavy metals is critically important to any attempt to develop mechanistic, quantitative models of the fate, transport, and bioavailablity of heavy metals. A primary capability developed in our earlier work was the ability to grow manganese oxide (MnO{sub x}) films on rhodochrosite (MnCO{sub 3}) substrate in presence of dissolved oxygen under mild alkaline conditions. The morphology of the films was characterized using contact-mode atomic force microscopy. The initial growth began by heteroepitaxial nucleation. The resulting films had maximum heights of 1.5 to 2 nm as a result of thermodynamic constraints. Over the three past years, we have investigated the effects of MnO{sub x} growth on the interactions of MnCO{sub 3} with charged ions and microorganisms, as regulated by the surface electrical properties of the mineral. In 2006, we demonstrated that MnO{sub x} growth could induce interfacial repulsion and surface adhesion on the otherwise neutral MnCO{sub 3} substrate under environmental conditions. Using force-volume microscopy (FVM), we measured the interfacial and adhesive forces on a MnO{sub x}/MnCO{sub 3} surface with a negatively charged silicon nitride tip in a 10-mM NaNO3 solution at pH 7.4. The interfacial force and surface adhesion of MnOx were approximately 40 pN and 600 pN, respectively, whereas those of MnCO{sub 3} were essentially zero. The force differences between MnO{sub x} and MnCO{sub 3} suggest that oxide film growth can focus adsorbates to certain parts of the surface and thereby templating a heterogeneous layout of them. We suspected that the force differences were in part due to the differences in surface electrical properties. In 2007, we investigated two important electrical properties of MnO{sub x} and MnCO{sub 3} surfaces, namely surface potential and ion mobility. Surface potential is a composite quantity that can be linked to the local lattice structure of the reconstructed surface and the adsorption of water layers. The mobile surface ions formed by dissolution can also contribute to surface potential. Using Kelvin probe force microscopy (KPFM) and scanning polarization force microscopy (SPFM), we found that MnOx possessed excess surface potentials of over +200 mV in humid nitrogen and the excess surface potential decreased with increasing relative humidity (i.e., increasing adsorbed water layers on the mineral surface). The dependence of the excess surface potential was attributed to the change of the contributions from mobile ions. These results supported our earlier hypothesis that MnO{sub x} and MnCO{sub 3} had different surface electrical properties. In the third year, we systematically characterized that the change of the electrical double layer (EDL) structure of MnCO{sub 3} surface due to MnO{sub x} growth in aqueous solution and its dependence on pH. The structure of the electrical double layer determines the electrostatic interactions between the mineral surface and charged adsorbates. As described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the electrostatic force, together with van der Waals interaction, regulates surface adsorption and bacterial attachment. Once adsorbates establish contact with the surface, they must resist hydraulic shear forces through surface adhesion. The adhesion of mineral surfaces is also affected by their electrostatic interactions with adsorbates. To probe the EDL structure, we applied force-volume microscopy coupled with physical and chemical models of the SPM system.

  3. Processes of nickel and cobalt uptake by a manganese oxide forming sediment in Pinal Creek, Globe mining district, Arizona

    USGS Publications Warehouse

    Kay, J.T.; Conklin, M.H.; Fuller, C.C.; O'Day, P. A.

    2001-01-01

    A series of column experiments was conducted using manganese oxide coated sediments collected from the hyporheic zone in Pinal Creek (AZ), a metal-contaminated stream, to study the uptake and retention of Mn, Ni, and Co. Experimental variables included the absence (abiotic) and presence (biotic) of active Mn-oxidizing bacteria, the absence and presence of dissolved Mn, and sediment manganese oxide content. Uptake of Mn under biotic conditions was between 8 and 39% higher than under abiotic conditions. Continuous uptake of Mn due to biotic oxidation was evident from extraction of column sediments. Manganese uptake is hypothesized to initially occur as adsorption, which led to subsequent surface and/or microbial oxidation. Complete breakthrough of Ni within 100 pore volumes indicated no process of continuous uptake and was modeled as an equilibrium adsorption process. Nickel uptake in the presence of dissolved Mn was 67-100% reversible. Sediment extractions suggest that Ni uptake occurred through weak and strong adsorption. Continuous uptake of cobalt increased with sediment manganese oxide content, and Co uptake was up to 75% greater under biotic than abiotic conditions. Cobalt uptake was controlled by both existing and newly formed manganese oxides. Only a small amount of Co uptake was reversible (10-25%). XANES spectral analysis indicated that most Co(II) was oxidized to Co(III) and probably incorporated structurally into manganese oxides. Although manganese oxides were the primary phase controlling uptake and retention of Mn, Ni, and Co, the mechanisms varied among the metals.

  4. Reactivity of biogenic manganese oxide for metal sequestration and photochemistry: Computational solid state physics study

    SciTech Connect

    Kwon, K.D.; Sposito, G.

    2010-02-01

    Many microbes, including both bacteria and fungi, produce manganese (Mn) oxides by oxidizing soluble Mn(II) to form insoluble Mn(IV) oxide minerals, a kinetically much faster process than abiotic oxidation. These biogenic Mn oxides drive the Mn cycle, coupling it with diverse biogeochemical cycles and determining the bioavailability of environmental contaminants, mainly through strong adsorption and redox reactions. This mini review introduces recent findings based on quantum mechanical density functional theory that reveal the detailed mechanisms of toxic metal adsorption at Mn oxide surfaces and the remarkable role of Mn vacancies in the photochemistry of these minerals.

  5. The scavenging of silver by manganese and iron oxides in stream sediments collected from two drainage areas of Colorado

    USGS Publications Warehouse

    Chao, T.T.; Anderson, B.J.

    1974-01-01

    Stream sediments of two well-weathered and aerated drainage areas of Colorado containing anomalous amounts of silver were allowed to react by shaking with nitric acid of different concentrations (1-10M). Silver, manganese, and iron simultaneously dissolved were determined by atomic absorption. The relationship between silver dissolution and the dissolution of manganese and/or iron was evaluated by linear and multiple regression analyses. The highly significant correlation coefficient (r = 0.913) between silver and manganese dissolution suggests that manganese oxides are the major control on the scavenging of silver in these stream sediments, whereas iron oxides only play a secondary role in this regard. ?? 1974.

  6. Size and morphology controlled lithium manganese oxide on silica sphere with core-shell structure.

    PubMed

    Ryu, Seong-Hyeon; Ju, Jeong-Hun; Cho, Sung-Woo; Ryu, Kwang-Sun

    2012-02-01

    Core-shell structures were prepared from synthesized SiO2-LiMn2O4 with manganese oxide as shell on the silica core by a precipitation method, which allowed control of core structure in terms of thickness and particle size. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), field emission-transmission electron microscopy (FE-TEM), and energy dispersive spectroscopy (EDS) were used to characterize the SiO2-LiMn2O4. According to FE-SEM images, particle growth was controlled by controlling the amount of manganese precursor and the temperature. The synthesized core-shell structure was composed of silica, lithium silicate, Mn2O3, and the spinel phase of lithium manganese oxide. Electrochemical measurements show that the synthesized core-shell structure has poorer electrochemical performance than that of LiMn2O4. PMID:22629996

  7. Impact of interactions between metal oxides to oxidative reactivity of manganese dioxide.

    PubMed

    Taujale, Saru; Zhang, Huichun

    2012-03-01

    Manganese oxides typically exist as mixtures with other metal oxides in soil-water environments; however, information is only available on their redox activity as single oxides. To bridge this gap, we examined three binary oxide mixtures containing MnO(2) and a secondary metal oxide (Al(2)O(3), SiO(2) or TiO(2)). The goal was to understand how these secondary oxides affect the oxidative reactivity of MnO(2). SEM images suggest significant heteroaggregation between Al(2)O(3) and MnO(2) and to a lesser extent between SiO(2)/TiO(2) and MnO(2). Using triclosan and chlorophene as probe compounds, pseudofirst-order kinetic results showed that Al(2)O(3) had the strongest inhibitory effect on MnO(2) reactivity, followed by SiO(2) and then TiO(2). Al(3+) ion or soluble SiO(2) had comparable inhibitory effects as Al(2)O(3) or SiO(2), indicating the dominant inhibitory mechanism was surface complexation/precipitation of Al/Si species on MnO(2) surfaces. TiO(2) inhibited MnO(2) reactivity only when a limited amount of triclosan was present. Due to strong adsorption and slow desorption of triclosan by TiO(2), precursor-complex formation between triclosan and MnO(2) was much slower and likely became the new rate-limiting step (as opposed to electron transfer in all other cases). These mechanisms can also explain the observed adsorption behavior of triclosan by the binary oxide mixtures and single oxides. PMID:22309023

  8. Influence of synthesis conditions on the electrochemical properties of nanostructured amorphous manganese oxide cryogels

    NASA Astrophysics Data System (ADS)

    Yang, Jingsi; Xu, Jun John

    Amorphous manganese oxides have received increasing attention in recent years as intercalation cathodes for rechargeable lithium batteries. The sol-gel method is a versatile method for achieving nanostructured amorphous oxides. In this paper, two different sol-gel routes are investigated, where nanostructured amorphous manganese oxide cryogels are obtained via freeze drying Mn(IV) oxide hydrogels formed in situ. In one route the hydrogels are formed by reaction between a solution of sodium permanganate and a solution of disodium fumarate, and in the other route by reaction between a solution of sodium permanganate and solid fumaric acid. Highly homogeneous monolithic manganese oxide hydrogels are obtained from both synthesis routes with precursor concentrations between 0.1 and 0.2 M. The freeze drying method proves to be an efficient method for obtaining nanostructured amorphous manganese oxide cryogels out of the hydrogels. Depending on the synthesis conditions of the hydrogels, the resultant cryogels can yield very high specific capacities for lithium intercalation and excellent rate performance. The cryogel with the best performance exhibits 289 mAh/g at a C/100 rate and 174 mAh/g at a 2 C rate. Strong dependence of electrochemical properties of the cryogels on the synthesis conditions of the parent hydrogels has been observed. The different electrochemical properties are believed to be due to different surface areas and local structures of the cryogels derived from hydrogels synthesized under different conditions. This strong dependence gives rise to the possibility of achieving promising intercalation materials through tailoring the surface area and the local structure of amorphous manganese oxides by adjusting sol-gel synthesis conditions.

  9. The kinetics of iodide oxidation by the manganese oxide mineral birnessite

    USGS Publications Warehouse

    Fox, P.M.; Davis, J.A.; Luther, G. W., III

    2009-01-01

    The kinetics of iodide (I-) and molecular iodine (I2) oxidation by the manganese oxide mineral birnessite (??-MnO2) was investigated over the pH range 4.5-6.25. I- oxidation to iodate (IO3-) proceeded as a two-step reaction through an I2 intermediate. The rate of the reaction varied with both pH and birnessite concentration, with faster oxidation occurring at lower pH and higher birnessite concentration. The disappearance of I- from solution was first order with respect to I- concentration, pH, and birnessite concentration, such that -d[I-]/dt = k[I-][H+][MnO2], where k, the third order rate constant, is equal to 1.08 ?? 0.06 ?? 107 M-2 h-1. The data are consistent with the formation of an inner sphere I- surface complex as the first step of the reaction, and the adsorption of I- exhibited significant pH dependence. Both I2, and to a lesser extent, IO3- sorbed to birnessite. The results indicate that iodine transport in mildly acidic groundwater systems may not be conservative. Because of the higher adsorption of the oxidized I species I2 and IO3-, as well as the biophilic nature of I2, redox transformations of iodine must be taken into account when predicting I transport in aquifers and watersheds.

  10. Low-temperature nitridation of manganese and iron oxides using NaNH2 molten salt.

    PubMed

    Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro

    2013-10-21

    Manganese and iron nitrides are important functional materials, but their synthesis processes from oxides often require high temperatures. Herein, we show a novel meta-synthesis method for manganese and iron nitrides by low-temperature nitridation of their oxides using NaNH2 molten salt as the nitrogen source in an autoclave at 240 °C. With this method, nitridation of micrometer-sized oxide particles kept their initial morphologies, but the size of the primary particles decreased. The thermodynamic driving force is considered to be the conversion of oxides to sodium hydroxide, and the kinetic of nitridation is improved by the decrease of particle size and the low melting point of NaNH2. This technique as developed here has the advantages of low reaction temperature, reduced consumption of ammonia, employing nonspecialized equipment, and providing facile control of the reactions for producing nitrides from oxides. PMID:24074443

  11. High-performance hybrid oxide catalyst of manganese and cobalt for low-pressure methanol synthesis

    NASA Astrophysics Data System (ADS)

    Li, Cheng-Shiuan; Melaet, Grme; Ralston, Walter T.; An, Kwangjin; Brooks, Christopher; Ye, Yifan; Liu, Yi-Sheng; Zhu, Junfa; Guo, Jinghua; Alayoglu, Selim; Somorjai, Gabor A.

    2015-03-01

    Carbon dioxide capture and use as a carbon feedstock presents both environmental and industrial benefits. Here we report the discovery of a hybrid oxide catalyst comprising manganese oxide nanoparticles supported on mesoporous spinel cobalt oxide, which catalyses the conversion of carbon dioxide to methanol at high yields. In addition, carbon-carbon bond formation is observed through the production of ethylene. We document the existence of an active interface between cobalt oxide surface layers and manganese oxide nanoparticles by using X-ray absorption spectroscopy and electron energy-loss spectroscopy in the scanning transmission electron microscopy mode. Through control experiments, we find that the catalysts chemical nature and architecture are the key factors in enabling the enhanced methanol synthesis and ethylene production. To demonstrate the industrial applicability, the catalyst is also run under high conversion regimes, showing its potential as a substitute for current methanol synthesis technologies.

  12. Manganese deposits on Mars suggest a highly oxidized past

    NASA Astrophysics Data System (ADS)

    Rosen, Julia

    2014-11-01

    As the Curiosity rover picks its way across the Martian surface, sampling rocks and snapping photos, it searches for signs that the dusty craters and ridges under its treads may once have supported life or, at least, that they might have been habitable. Now, using measurements of manganese abundances in Martian rocks, Lanza et al. provide new evidence that Mars may have hosted liquid water and a more strongly oxygenated atmosphere at some point in its past.

  13. X-ray photoelectron spectroscopic studies on initial oxidation of iron and manganese mono-silicides

    NASA Astrophysics Data System (ADS)

    Ohtsu, Naofumi; Oku, Masaoki; Nomura, Akiko; Sugawara, Takamasa; Shishido, Toetsu; Wagatsuma, Kazuaki

    2008-03-01

    Initial oxidation of iron and manganese mono-silicides (FeSi and MnSi) surfaces was studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these silicides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa. For the clean FeSi surface, positive chemical shifts of the Fe 2p 3/2 and Si 2p peaks from elemental Fe and Si were 0.5 eV and 0.1 eV, respectively. For the clean MnSi surface, a negative chemical shift of the Si 2p peak from elemental Si was 0.1 eV. Iron on the FeSi surface was oxidized at an oxygen pressure of 1.3 Pa, whereas the silicon was oxidized under the pressure of 1.3 × 10 -6 Pa, indicating that oxidation of silicon occurred prior to that of iron. Manganese and silicon on the MnSi were simultaneously oxidized in the range from 1.3 × 10 -6 Pa to 1.3 × 10 -3 Pa; however, over the pressure of 1.3 Pa, the oxidation of manganese occurs prior to that of silicon. These oxidation behaviors at low oxygen pressures were similar to those of the FeSi and MnSi fractured in air.

  14. Organ weight changes in mice after long-term inhalation exposure to manganese oxides nanoparticles

    NASA Astrophysics Data System (ADS)

    Zeman, T.; Buchtová, M.; Dočekal, B.; Míšek, I.; Navrátil, J.; Mikuška, P.; Šerý, O.; Večeřa, Z.

    2015-05-01

    Recently, it has been proven that manganese from inhaled particles of manganese compounds can accumulate in the internal organs of laboratory animals. Nevertheless, there were only a few researches dealing with changes in body morphology induced by inhalation of these particles, even though results of some studies indicate existence of such changes. The aim of our research was to assess the effect of inhaled manganese oxides nanoparticles on weight of internal organs. For this purpose a long-term inhalation experiment on laboratory mice was performed, during which the mice were exposed to MnO.Mn2O3 nanoparticles in concentration 2 × 106 particles/cm3 for 17 weeks, 24 hours a day, 7 days a week. Manganese oxides nanoparticles were synthesized continuously via aerosol route in a hot wall tube flow reactor using thermal decomposition of metal organic precursor manganese(II)acetylacetonate in the flow tube reactor at temperature 750 °C in the presence of 30 vol% of oxygen. It was proven that inhaled nanoparticles can influence the weight of internal organs of mice. Moreover, it was discovered that the resulting change in weight of selected organs is disproportional. The mice from the experimental group had statistically significantly lighter kidneys, liver and spleen and heavier pancreas compared to the mice from the control group.

  15. Plasma-electrolytic formation, composition and catalytic activity of manganese oxide containing structures on titanium

    NASA Astrophysics Data System (ADS)

    Rudnev, V. S.; Vasilyeva, M. S.; Kondrikov, N. B.; Tyrina, L. M.

    2005-12-01

    In the present work, we report the data about formation of TiO 2-rutile or TiO 2 and Mn 2O 3, Mn 3O 4 containing oxide structures on titanium in aqueous electrolytes by means of plasma-electrolytic deposition. The layers formed are characterized by X-ray diffraction, electron probe microanalysis and scanning electron microscopy methods. The PEO coatings on titanium formed in sodium tetraborate solution contain the TiO 2 stabile rutile modification that is important when utilizing such a structure as a catalyst carrier. Manganese acetate adding into the electrolyte leads to formation of layers that contain Mn 2O 3, Mn 3O 4 and TiO 2-rutile in outer region. The manganese content in the surface layer depends on the formation conditions as well as on manganese acetate concentration in the electrolyte. Catalytic activity of the layers in CO ? CO 2 reaction is studied in the static and flow conditions. The manganese-containing layers obtained possess the catalytic activity in CO ? CO 2 oxidation reaction at the temperature range of 250-350 C. The catalytic activity depends on the concentration and surface distribution of manganese as well as on the layers morphology.

  16. Spinel coatings for solid oxide fuel cell interconnects and crystal structure of copper manganese oxide

    NASA Astrophysics Data System (ADS)

    Wei, Ping

    Long-term stability and chromium (Cr) contamination are two major concerns for application of chromium-bearing metallic materials as interconnects of solid oxide fuel cells (SOFCs) at intermediate temperature (800C). Copper-manganese (Cu-Mn) and cobalt-manganese (Co-Mn) spinel can be promising coating materials for the metallic interconnects as they show high electrical conductivities. The first objective of this research is to develop an economical and convenient method through which the spinel coatings can be applied to the metallic substrates. The investigations on the crystal structure of Cu xMn3-xO4 spinel, e.g., structure symmetry and cation distributions, have always been controversial, which hinders the total understanding of the detailed structure of the material. In order to resolve the inconsistency, in-situ neutron and X-ray diffraction were employed to determine the structure of the spinel. A novel method was developed to obtain high quality manganese coating without any additives (sulphur or selenium compounds). Cu-Mn and Co-Mn spinel coatings were applied to metallic coupons by electrodeposition and subsequent annealing. The method is convenient and easy to control. The performance testing showed that the area specific resistances (ASRs) of the coated samples (0.003 Ocm 2) are much lower than that of the uncoated UNS 430 (0.189 Ocm 2) after oxidation at 750C for 1500 hours. Moreover, both spinel coatings can effectively suppress the outward diffusion of Cr, which resulted in reduction of Cr contamination significantly. The oxidation studies of Cu-Mn coating revealed the transformation mechanisms of Cu-Mn coating to the spinel. In-situ neutron and X-ray diffraction analysis clarified the crystal symmetry of CuxMn3-xO4 spinel and CuMnO2 at high temperatures. Rietveld refinement revealed the cation distribution of Cu and Mn ions on tetrahedral and octrahedral sites of CuxMn 3-xO4 spinel, which was compared to values in the literatures.

  17. Endowing manganese oxide with fast adsorption ability through controlling the manganese carbonate precursor assembled in ionic liquid.

    PubMed

    Ge, X; Gu, C D; Wang, X L; Tu, J P

    2015-01-15

    Manganese oxides with desired structure are controllably obtained through annealing MnCO3 precursors with required structures. The structures of MnCO3 precursors are determined by a "mesocrystal formation" process in an ionic liquid system of a choline chloride/urea (CU) mixture. Without addition of surfactants, only CU solvent and manganese chloride are needed in the reaction system, in which the CU acts as reaction medium as well as control agent for particle growth. A shape transformation of MnCO3 particles from well-defined rhombohedral mesocrystals to ellipsoidal polycrystal ensembles, and to nanoparticulate aggregates is observed when heating the reaction system for 4 h at 120, 150, and 180 C, respectively. With a longer aging time at 120 C, etching and disassembly of MnCO3 mesocrystals happened. The correlation between the microstructure and the underlying formation mechanism is highlighted. Porous and nanowire-like MnO(x) nanostructures are obtained through a facile thermal conversion process from the diverse MnCO3 precursors, which are demonstrated as effective and efficient adsorbents to remove organic waste (e.g. Congo red) from water. Significantly, the nanowire-like MnO(x) nanostructures obtained by annealing the MnCO3 mesocrystals at 300 C for 4 h can remove about 95% Congo red in waste water at room temperature in only one minute, which is superior to the reported hierarchical hollow nanostructured MnO2. PMID:25454437

  18. IMPACT OF WATER CHEMISTRY ON MANGANESE REMOVAL DURING OXIDATION/FILTRATION TREATMENT

    EPA Science Inventory

    This is a poster showing the purpose and setup of our pilot plant experiments with manganese filtration. The focus is on the differences, effectiveness, and problems with using chlorine and potassium permanganate in oxidation/filtration. The poster will show the results and findi...

  19. Diclofenac and 2-anilinophenylacetate degradation by combined activity of biogenic manganese oxides and silver.

    PubMed

    Meerburg, Francis; Hennebel, Tom; Vanhaecke, Lynn; Verstraete, Willy; Boon, Nico

    2012-05-01

    The occurrence of a range of recalcitrant organic micropollutants in our aquatic environment has led to the development of various tertiary wastewater treatment methods. In this study, biogenic manganese oxides (Bio-MnOx), biogenic silver nanoparticles (Bio-Ag(0)) and ionic silver were used for the oxidative removal of the frequently encountered drug diclofenac and its dechlorinated form, 2-anilinophenylacetate (APA). Diclofenac was rapidly degraded during ongoing manganese oxidation by Pseudomonas putida MnB6. Furthermore, whereas preoxidized Bio-MnOx, Bio-Ag(0) and Ag(+) separately did not show any removal capacity for diclofenac, an enhanced removal occurred when Bio-MnOx and silver species were combined. Similar results were obtained for APA. Finally, a slow removal of diclofenac but more rapid APA degradation was observed when silver was added to manganese-free P. putida biomass. Combining these results, three mechanisms of diclofenac and APA removal could be distinguished: (i) a co-metabolic removal during active Mn(2+) oxidation by P. putida; (ii) a synergistic interaction between preoxidized Bio-MnOx and silver species; and (iii) a (bio)chemical process by biomass enriched with silver catalysts. This paper demonstrates the use of P. putida for water treatment purposes and is the first report of the application of silver combined with biogenic manganese for the removal of organic water contaminants. PMID:22221449

  20. Nanostructural evolution from nanosheets to one-dimensional nanoparticles for manganese oxide

    SciTech Connect

    Pan, Hongmei; Kong, Xingang; Wen, Puhong; Kitayama, Tomonori; Feng, Qi

    2012-09-15

    Highlights: ? Nanosheets were transformed to other one-dimensional nanoparticles. ? Nanofibers, nanotubes, nanoribbons, and nanobelts were obtained. ? Nanoparticle morphology can be controlled with organic amines. ? Organic amines act as morphology directing agent. -- Abstract: This paper introduces a novel hydrothermal soft chemical synthesis process for manganese oxide nanostructured particles using two-dimensional manganese oxide nanosheets as precursor. In this process, a birnessite-type manganese oxide with a layered structure was exfoliated into its elementary layer nanosheets, and then the nanosheets were hydrothermally treated to transform the two-dimensional morphology of the nanosheets to one-dimensional nanoparticles. The manganese oxide nanofibers, nanotubes, nanobelts, nanoribbons, and fabric-ribbon-like particles constructed from nanofibers or nanobelts were obtained using this hydrothermal soft chemical process. The nanostructural evolution from the two-dimensional nanosheets to the one-dimensional nanoparticles was characterized by XRD, SEM, TEM, and TG-DTA analysis. The morphology and nanostructure of the products are strongly dependent on the molecular dimension of organic amine cations added in the reaction system. The organic amine cations act as a morphology directing agent in the nanostructural evolution process.

  1. Synthesis of nanostructured manganese oxides based materials and application for supercapacitor

    NASA Astrophysics Data System (ADS)

    Dung Dang, Trung; Le, Thi Thu Hang; Bich Thuy Hoang, Thi; Mai, Thanh Tung

    2015-01-01

    Manganese oxides are important materials with a variety of applications in different fields such as chemical sensing devices, magnetic devices, field-emission devices, catalysis, ion-sieves, rechargeable batteries, hydrogen storage media and microelectronics. To open up new applications of manganese oxides, novel morphologies or nanostructures are required to be developed. Via sol—gel and anodic electrodeposition methods, M (Co, Fe) doped manganese oxides were prepared. On the other hand, nanostructured (nanoparticles, nanorods and hollow nanotubes) manganese oxides were synthesized via a process including a chemical reaction with carbon nanotubes (CNTs) templates followed by heat treatment. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and impedance spectroscopy (EIS) were used for characterization of the prepared materials. The influence of chemical reaction conditions, heat treatment and template present on the morphology, structure, chemical and electrochemical properties of the prepared materials were investigated. Chronopotentiometry (CP) and CV results show high specific capacitance of 186.2 to 298.4 F g-1 and the charge/discharge stability of the prepared materials and the ideal pseudocapacitive behaviors were observed. These results give an opening and promising application of these materials in advanced energy storage applications.

  2. SERUM CHEMISTRIES OF COTURNIX JAPONICA GIVEN DIETARY MANGANESE OXIDE (MN3O4)

    EPA Science Inventory

    Plasma creatinine and inorganic phosphorus were increased in manganese oxide (Mn3O4)-treated adult male Coturnix quail, but BUN, BUN/creatinine ratio, uric acid, and total calcium were decreased. 2. Serum enzymes (alkaline phosphatase glutamic oxaloacetic transaminase, glutamic p...

  3. The effect of lanthanum(III) and cerium(III) ions between layers of manganese oxide on water oxidation.

    PubMed

    Najafpour, Mohammad Mahdi; Isaloo, Mohsen Abbasi; Hołyńska, Małgorzata; Shen, Jian-Ren; Allakhverdiev, Suleyman I; Allakhverdiev, Suleyman

    2015-12-01

    Manganese oxide structure with lanthanum(III) or cerium(III) ions between the layers was synthesized by a simple method. The ratio of Mn to Ce or La in samples was 0.00, 0.04, 0.08, 0.16, 0.32, 0.5, 0.82, or 1.62. The compounds were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction studies, and atomic absorption spectroscopy. The compounds show efficient catalytic activity of water oxidation in the presence of cerium(IV) ammonium nitrate with a turnover frequency of 1.6 mmol O2/mol Mn.s. In contrast to the water-oxidizing complex in Photosystem II, calcium(II) has no specific role to enhance the water-oxidizing activity of the layered manganese oxides and other cations can be replaced without any significant decrease in water-oxidizing activities of these layered Mn oxides. Based on this and previously reported results from oxygen evolution in the presence of H 2 (18) O, we discuss the mechanism and the important factors influencing the water-oxidizing activities of the manganese oxides. PMID:25701552

  4. Determining the Oxidation States of Manganese in NT2 Cells and Cultured Astrocytes

    SciTech Connect

    Gunter,K.; Aschner, M.; Miller, L.; Eliseev, R.; Salter, J.; Andersen, K.; Gunter, T.

    2006-01-01

    Excessive brain manganese (Mn) can produce a syndrome called 'manganism', which correlates with loss of striatal dopamine and cell death in the striatum and globus pallidus. The prevalent hypothesis for the cause of this syndrome has been oxidation of cell components by the strong oxidizing agent, Mn{sup 3+}, either formed by oxidation of intracellular Mn{sup 2+} or transported into the cell as Mn{sup 3+}. We have recently used X-ray absorption near edge structure spectroscopy (XANES) to determine the oxidation states of manganese complexes in brain and liver mitochondria and in nerve growth factor (NGF)-induced and non-induced PC12 cells. No evidence was found for stabilization or accumulation of Mn{sup 3+} complexes because of oxidation of Mn{sup 2+} by reactive oxygen species in these tissues. Here we extend these studies of manganese oxidation state to cells of brain origin, human neuroteratocarcinoma (NT2) cells and primary cultures of rat astrocytes. Again we find no evidence for stabilization or accumulation of any Mn{sup 3+} complex derived from oxidation of Mn{sup 2+} under a range of conditions.

  5. Coexistence of electrical conductivity and ferromagnetism in a hybrid material formed from reduced graphene oxide and manganese oxide.

    PubMed

    Murashima, Yusuke; Ohtani, Ryo; Matsui, Takeshi; Takehira, Hiroshi; Yokota, Ryotaro; Nakamura, Masaaki; Lindoy, Leonard F; Hayami, Shinya

    2015-03-21

    The coexistence of electrical conductivity and ferromagnetism has been achieved in a reduced graphene oxide/manganese oxide hybrid (rGO-Mn) synthesized by chemical reduction of a graphene oxide and Mn(2+) (as its GO-Mn(2+) complex) using hydrazine. The rGO-Mn and GO-Mn(2+) complexes were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). In rGO-Mn the Mn was present as manganese oxide nanoparticles located on the rGO nanosheets. This rGO-Mn exhibits both electrical conductivity and ferromagnetism. The synthesis of hybrids incorporating rGO and metal oxides is proposed as a useful strategy for generation of new multifunctional nano-composite materials. PMID:25697449

  6. Amperometric Biosensors Based on Carbon Paste Electrodes Modified with Nanostructured Mixed-valence Manganese Oxides and Glucose Oxidase

    SciTech Connect

    Cui, Xiaoli; Liu, Guodong; Lin, Yuehe

    2005-06-01

    Nanostructured multivalent manganese oxides octahedral molecular sieve (OMS), including cryptomelane-type manganese oxides and todorokite-type manganese oxides, were synthesized and evaluated for chemical sensing and biosensing at low operating potential. Both cryptomelane-type manganese oxides and todorokite-type manganese oxides are nanofibrous crystals with sub-nanometer open tunnels that provide a unique property for sensing applications. The electrochemical and electrocatalytic performance of OMS for the oxidation of H2O2 have been compared. Both cryptomelane-type manganese oxides and todorokite-type manganese oxides can be used to fabricate sensitive H2O2 sensors. Amperometric glucose biosensors are constructed by bulk modification of carbon paste electrodes (CPEs) with glucose oxidase as a biocomponent and nanostructured OMS as a mediator. A Nafion thin film was applied as an immobilization/encapsulation and protective layer. The biosensors were evaluated as an amperometric glucose detector at phosphate buffer solution with a pH 7.4 at an operating potential of 0.3 V (vs. Ag/AgCl). The biosensor is characterized by a well-reproducible amperometric response, linear signal-to-glucose concentration range up to 3.5 mM and 1.75 mM, and detection limits (S/N = 3) of 0.1 mM and 0.05 mM for todorokite-type manganese oxide and cryptomelane-type manganese oxide modified electrodes, respectively. The biosensors based on OMS exhibit considerable good reproducibility and stability, and the construction and renewal are simple and inexpensive.

  7. Activation of Manganese Oxidants with Bisulfite for Enhanced Oxidation of Organic Contaminants: The Involvement of Mn(III).

    PubMed

    Sun, Bo; Guan, Xiaohong; Fang, Jingyun; Tratnyek, Paul G

    2015-10-20

    MnO4(-) was activated by HSO3(-), resulting in a process that oxidizes organic contaminants at extraordinarily high rates. The permanganate/bisulfite (PM/BS) process oxidized phenol, ciprofloxacin, and methyl blue at pHini 5.0 with rates (kobs ? 60-150 s(-1)) that were 5-6 orders of magnitude faster than those measured for permanganate alone, and ?5 to 7 orders of magnitude faster than conventional advanced oxidation processes for water treatment. Oxidation of phenol was fastest at pH 4.0, but still effective at pH 7.0, and only slightly slower when performed in tap water. A smaller, but still considerable (?3 orders of magnitude) increase in oxidation rates of methyl blue was observed with MnO2 activated by HSO3(-) (MO/BS). The above results, time-resolved spectroscopy of manganese species under various conditions, stoichiometric analysis of pH changes, and the effect of pyrophosphate on UV absorbance spectra suggest that the reactive intermediate(s) responsible for the extremely rapid oxidation of organic contaminants in the PM/BS process involve manganese(III) species with minimal stabilization by complexation. The PM/BS process may lead to a new category of advanced oxidation technologies based on contaminant oxidation by reactive manganese(III) species, rather than hydroxyl and sulfate radicals. PMID:26421879

  8. Significantly improved cyclability of lithium manganese oxide under elevated temperature by an easily oxidized electrolyte additive

    NASA Astrophysics Data System (ADS)

    Zhu, Yunmin; Rong, Haibo; Mai, Shaowei; Luo, Xueyi; Li, Xiaoping; Li, Weishan

    2015-12-01

    Spinel lithium manganese oxide, LiMn2O4, is a promising cathode for lithium ion battery in large-scale applications, because it possesses many advantages compared with currently used layered lithium cobalt oxide (LiCoO2) and olivine phosphate (LiFePO4), including naturally abundant resource, environmental friendliness and high and long work potential plateau. Its poor cyclability under high temperature, however, limits its application. In this work, we report a significant cyclability improvement of LiMn2O4 under elevated temperature by using dimethyl phenylphonite (DMPP) as an electrolyte additive. Charge/discharge tests demonstrate that the application of 0.5 wt.% DMPP yields a capacity retention improvement from 16% to 82% for LiMn2O4 after 200 cycles under 55 °C at 1 C (1C = 148 mAh g-1) between 3 and 4.5 V. Electrochemical and physical characterizations indicate that DMPP is electrochemically oxidized at the potential lower than that for lithium extraction, forming a protective cathode interphase on LiMn2O4, which suppresses the electrolyte decomposition and prevents LiMn2O4 from crystal destruction.

  9. A kinetic study of the enhancement of solution chemiluminescence of glyoxylic acid oxidation by manganese species.

    PubMed

    Otamonga, Jean-Paul; Abdel-Mageed, Amal; Agater, Irena B; Jewsbury, Roger A

    2015-08-01

    In order to study the mechanism of the enhancement of solution chemiluminescence, the kinetics of the decay of the oxidant and the chemiluminescence emission were followed for oxidations by permanganate, manganese dioxide sol and Mn(3+) (aq) of glyoxylic acid, using stopped-flow spectrophotometry. Results are reported for the glyoxylic acid oxidized under pseudo first-order conditions and in an acidic medium at 25?C. For permanganate under these conditions, the decay is sigmoidal, consistent with autocatalysis, and for manganese dioxide sol and Mn(3+) it is pseudo first order. The effects of the presence of aqueous formaldehyde and Mn(2+) were observed and a fit to a simple mechanism is discussed. It is concluded that chemiluminescent enhancement in these systems is best explained by reaction kinetics. PMID:25223402

  10. An Electrochemical Sensor Based on Nanostructured Hollandite-type Manganese Oxide for Detection of Potassium Ions

    PubMed Central

    Lima, Alex S.; Bocchi, Nerilso; Gomes, Homero M.; Teixeira, Marcos F. S.

    2009-01-01

    The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. A sensor based on a nanostructured hollandite-type manganese oxide was investigated for voltammetric detection of potassium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and the subsequent extraction of the potassium ions into the hollandite structure. In this work, an amperometric procedure at an operating potential of 0.80 V (versus SCE) is exploited for amperometric monitoring. The current signals are linearly proportional to potassium ion concentration in the range 4.97 10?5 to 9.05 10?4 mol L?1, with a correlation coefficient of 0.9997. PMID:22399969

  11. Manganese oxides supported on gold nanoparticles: new findings and current controversies for the role of gold.

    PubMed

    Najafpour, Mohammad Mahdi; Hosseini, Seyedeh Maedeh; Hołyńska, Małgorzata; Tomo, Tatsuya; Allakhverdiev, Suleyman I

    2015-12-01

    We synthesized manganese oxides supported on gold nanoparticles (diameter <100 nm) by the reaction of KMnO4 with gold nanoparticles under hydrothermal conditions. In this green method Mn oxide is deposited on the gold nanoparticles. The compounds were characterized by scanning electron microscopy, energy-dispersive spectrometry, high-resolution transmission electron microscopy, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In the next step, the water-oxidizing activities of these compounds in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant were studied. The results show that these compounds are good catalysts toward water oxidation with a turnover frequency of 1.0 ± 0.1 (mmol O2/(mol Mn·s)). A comparison with other previously reported Mn oxides and important factors influencing the water-oxidizing activities of Mn oxides is also discussed. PMID:26076756

  12. Electrodeposition of layered manganese oxide nanocomposites intercalated with strong and weak polyelectrolytes.

    PubMed

    Nakayama, Masaharu; Tagashira, Hiroki

    2006-04-11

    Multilayered manganese oxide nanocomposites intercalated with strong (poly(diallyldimethylammonium) chloride, PDDA) and weak (poly(allylamine hydrochloride), PAH) polyelectrolytes can be produced on polycrystalline platinum electrode in a thin film form by a simple, one-step electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn2+ ions at around +1.0 V (vs Ag/AgCl) in the presence of polyelectrolytes. Fully charged PDDA polycations are accommodated tightly in the interlayer space by electrostatic interaction with negative charges on the manganese oxide layers, leading to an interlayer distance of 0.97 nm. The layered film prepared with PAH has a larger polymer content (PAH/Mn molar ratio of 0.98) than that (PDDA/Mn molar ratio of 0.43) made with PDDA because of the smaller charging degree of PAH, exhibiting a larger interlayer distance (1.19 nm). The interlayer PAH contains neutral (-NH2) and positively charged (-NH3(+)) amine groups, and the -NH3(+) groups are associated with Cl- (to generate -NH3(+) Cl- ion pairs) as well as the negatively charged manganese oxide layers. Both polyelectrolytes once incorporated were not ion exchanged with small cations in solution. The layered structure of PDDA/MnO(x) was collapsed during the reduction process in a KCl electrolyte solution, accompanying an expansion of the interlayer as a result of incorporation of K+ ions for charge neutrality. On the contrary, the layered PAH/MnO(x) film showed a good electrochemical response due to the redox reaction of Mn3+/Mn4+ couple with no change in the structure. X-ray photoelectron spectroscopy revealed that, in this case, excess negative charges generated on the manganese oxide layers upon reduction can be balanced by the protons being released from the -NH3(+) Cl- sites in the interlayer PAH; the Cl- anions becoming unnecessary are inevitably excluded from the interlayer, and vice versa upon oxidation. PMID:16584268

  13. Improved manganese-oxidizing activity of DypB, a peroxidase from a lignolytic bacterium

    PubMed Central

    Singh, Rahul; Grigg, Jason C.; Qin, Wei; Kadla, John F.; Murphy, Michael E.P.; Eltis, Lindsay D.

    2013-01-01

    DypB, a dye-decolorizing peroxidase from the lignolytic soil bacterium Rhodococcus jostii RHA1, catalyzes the peroxide-dependent oxidation of divalent manganese (Mn2+), albeit less efficiently than fungal manganese peroxidases. Substitution of Asn246, a distal heme residue, with alanine, increased the enzymes apparent kcat and kcat/Km values for Mn2+ by 80- and 15-fold, respectively. A 2.2 resolution X-ray crystal structure of the N246A variant revealed the Mn2+ to be bound within a pocket of acidic residues at the heme edge, reminiscent of the binding site in fungal manganese peroxidase and very different to that of another bacterial Mn2+-oxidizing peroxidase. The first coordination sphere was entirely comprised of solvent, consistent with the variants high Km for Mn2+ (17 2 mM). N246A catalyzed the manganese-dependent transformation of hard wood kraft lignin and its solvent-extracted fractions. Two of the major degradation products were identified as 2,6-dimethoxybenzoquinone and 4-hydroxy-3,5-dimethoxybenzaldehyde, respectively. These results highlight the potential of bacterial enzymes as biocatalysts to transform lignin. PMID:23305326

  14. Electroless preparation and ASAXS microstructural analysis of pseudocapacitive carbon manganese oxide supercapacitor electrodes.

    PubMed

    Weber, Christian; Reichenauer, Gudrun; Pflaum, Jens

    2015-01-20

    Anomalous small angle X-ray scattering (ASAXS) has been utilized as a noninvasive, integral tool to access the structural properties of carbon xerogel-manganese oxide electrodes with nanometer resolution. As these electrodes constitute the elementary functional units in supercapacitors and as their microstructure governs the macroscopic electrical performance, it is essential to gain a detailed morphological understanding of the underlying carbon particle scaffold coated with manganese oxide. We demonstrate that, in this regard, ASAXS provides a powerful technique and in combination with a theoretical core-shell model enables a quantitative estimation of the relevant structural parameters. As a result, we determined the thicknesses of the solution deposited MnO2 shells to range between 3 and 26 nm depending on the carbon particle size and thus on their effective surface area. By our core-shell modeling we conclude the revealed manganese oxide coatings on the carbon support to be rather thick, but nevertheless to show a high uniformity in thickness. At 1.8 0.2 to 2.2 0.1 g/cm(3) the related effective MnO2 densities of the shells are about 30% lower than the corresponding bulk density of 3.0 g/cm(3). This mainly originates from a substructure within the shell, whose growth is controlled by a pronounced reduction of the manganese precursor during layer formation. Finally, the presented ASAXS data are complemented by SEM and N2 sorption measurements, proving not only qualitatively the proposed flake-like MnO2 surface morphology but also confirming quantitatively the manganese shell thickness, complementary, on a local scale. PMID:25453192

  15. Tailoring structural, optical and magnetic properties of spinel type cobalt oxide (Co3O4) by manganese doping

    NASA Astrophysics Data System (ADS)

    Naveen, A. Nirmalesh; Selladurai, Subramanian

    2015-01-01

    To study the effects of manganese doping on structural, optical and magnetic properties of spinel type cobalt oxide (Co3O4) system, manganese ions were doped at different concentrations (5-20%) using co-precipitation method. Crystalline nature and phase purity of the prepared materials were investigated using XRD, FTIR and XPS measurements. Manganese ions played a major role in reducing crystallite size and introducing macro/micro-strains in the doped compounds. Surface morphology of the materials examined using FESEM images confirmed the role played by manganese ion in restraining particle growth. Manganese doping was further confirmed using EDS and XPS elemental analysis. From the XPS studies, manganese concentration in the doped samples were identified to be close to the initial doping percentage (MnxCo3-xO4; x=4.61%, 8.25%, 14.13% and 18.10%). Presence of three types of manganese ions was revealed from the XPS study. Pair of absorption bands centered at 440 nm and 720 nm characteristic of spinel type cobalt oxide was observed for all the prepared materials. Micro- and macro-strains induced by manganese doping have created localized density of states reducing band energy gaps in the doped materials. Mn2+ ions replacing Co2+ ions in the tetrahedral site have enhanced the weak ferromagnetism observed for pristine cobalt oxide. Saturation magnetization, coercivity and remanent magnetization was found to increase with Mn2+ concentration.

  16. Uraninite oxidation and dissolution induced by manganese oxide: A redox reaction between two insoluble minerals

    NASA Astrophysics Data System (ADS)

    Wang, Zimeng; Lee, Sung-Woo; Kapoor, Pratyul; Tebo, Bradley M.; Giammar, Daniel E.

    2013-01-01

    The longevity of subsurface U(IV) produced by reduction of U(VI) during in situ bioremediation can be limited by reoxidation to more mobile U(VI) species. Coupling of the biogeochemical cycles of U and Mn may affect the fate and transport of uranium. Manganese oxides can act as a powerful oxidant that accelerates the oxidative dissolution of UO2. This study investigated the physical and chemical factors controlling the interaction between UO2 and MnO2, which are both poorly soluble minerals. A multi-chamber reactor with a permeable membrane was used to eliminate direct contact of the two minerals while still allowing transport of aqueous species. The oxidation of UO2 was not significantly enhanced by MnO2 if the two solids were physically separated. Complete mixing of MnO2 with UO2 led to a much greater extent and rate of U oxidation. When direct contact is not possible, the reaction slowly progresses through release of soluble U(IV) with its adsorption and oxidation on MnO2. Continuously-stirred tank reactors (CSTRs) were used to quantify the steady-state rates of UO2 dissolution induced by MnO2. MnO2 dramatically promoted UO2 dissolution, but the degree of promotion leveled off once the MnO2:UO2 ratio exceeded a critical value. Substantial amounts of U(VI) and Mn(II) were retained on MnO2 surfaces. The total production of Mn(II) was less than that of U(VI), indicating that the fate of Mn products and their impact on UO2-MnO2 reaction kinetics were complicated and may involve formation of Mn(III) phases. At higher dissolved inorganic carbon concentrations, UO2 oxidation by MnO2 was faster and less U(VI) was adsorbed to MnO2. Such an inverse relationship suggested that U(VI) may passivate MnO2 surfaces. A conceptual model was developed to describe the oxidation rate of UO2 by MnO2. This model is potentially applicable to a broad range of water chemistry conditions and is relevant to other environmental redox processes involving two poorly soluble minerals.

  17. Controllable Synthesis of Formaldehyde Modified Manganese Oxide Based on Gas-Liquid Interfacial Reaction and Its Application of Electrochemical Sensing.

    PubMed

    Bai, Wushuang; Sheng, Qinglin; Nie, Fei; Zheng, Jianbin

    2015-12-30

    Controllable synthesis of manganese oxides was performed via a simple one-step synthetic method. Then obtained manganese oxides which exhibit flower-like, cloud-like, hexagon-like, and rod-like morphologies were modified by formaldehyde based on a simple self-made gas-liquid reaction device respectively and the modified manganese oxides with coral-like, scallop-like and rod-like morphology were synthesized accordingly. The obtained materials were characterized and the formation mechanism was also researched. Then the modified manganese oxides were used to fabricate electrochemical sensors to detect H2O2. Comparison of electrochemical properties between three kinds of modified manganese oxides was investigated and the best one has been successfully employed as H2O2 sensor which shows a low detection limit of 0.01 ?M, high sensitivity of 162.69 ?A mM(-1) cm(-2), and wide linear range of 0.05 ?M-12.78 mM. The study provides a new method for controllable synthesis of metal oxides, and electrochemical application of formaldehyde modified manganese oxides will provides a new strategy for electrochemical sensing with high performance, low cost, and simple fabrication. PMID:26647786

  18. Diclofenac and 2‐anilinophenylacetate degradation by combined activity of biogenic manganese oxides and silver

    PubMed Central

    Meerburg, Francis; Hennebel, Tom; Vanhaecke, Lynn; Verstraete, Willy; Boon, Nico

    2012-01-01

    Summary The occurrence of a range of recalcitrant organic micropollutants in our aquatic environment has led to the development of various tertiary wastewater treatment methods. In this study, biogenic manganese oxides (Bio‐MnOx), biogenic silver nanoparticles (Bio‐Ag0) and ionic silver were used for the oxidative removal of the frequently encountered drug diclofenac and its dechlorinated form, 2‐anilinophenylacetate (APA). Diclofenac was rapidly degraded during ongoing manganese oxidation by Pseudomonas putida MnB6. Furthermore, whereas preoxidized Bio‐MnOx, Bio‐Ag0 and Ag+ separately did not show any removal capacity for diclofenac, an enhanced removal occurred when Bio‐MnOx and silver species were combined. Similar results were obtained for APA. Finally, a slow removal of diclofenac but more rapid APA degradation was observed when silver was added to manganese‐free P. putida biomass. Combining these results, three mechanisms of diclofenac and APA removal could be distinguished: (i) a co‐metabolic removal during active Mn2+ oxidation by P. putida; (ii) a synergistic interaction between preoxidized Bio‐MnOx and silver species; and (iii) a (bio)chemical process by biomass enriched with silver catalysts. This paper demonstrates the use of P. putida for water treatment purposes and is the first report of the application of silver combined with biogenic manganese for the removal of organic water contaminants. PMID:22221449

  19. Protective role of silymarin against manganese-induced nephrotoxicity and oxidative stress in rat.

    PubMed

    Chtourou, Yassine; Garoui, El mouldi; Boudawara, Tahia; Zeghal, Najiba

    2014-10-01

    Metal toxicity may occur after exposure from many sources. Oxidative stress is thought to be involved in manganese-induced toxicity and leads to various health disorders. Silymarin (SIL), a natural flavonoid, has been reported to have many benefits and medicinal properties. The aim of this study was to assess the toxicity of manganese (Mn) on oxidative stress and DNA damage in the kidney of rats and its alleviation by SIL. Manganese was given orally in drinking water (20 mg MnCl2 /mL) with or without SIL administration (100 mg /kg intraperitoneally) for 30 days. Our data showed that SIL significantly prevented Mn induced nephrotoxicity, indicated by both diagnostic indicators of kidney injury like plasma urea, uric acid and creatinine and urinary electrolyte levels and by histopathological analysis. Moreover, Mn-induced profound elevation of the production of reactive oxygen species (ROS) and altered the levels of oxidative stress related biomarkers in kidney tissue. This is evidenced by the increase of lipid peroxidation, protein carbonylation, DNA fragmentation and urinary hydrogen peroxide, while, the activities of enzymatic antioxidant and glutathione level were decreased. Treatment with SIL reduced the alterations in the renal and urine markers, decreasing lipid peroxidation markers, increasing the antioxidant cascade and decreasing the Mn-induced damage. All these changes were supported by histopathological observations. These findings suggested that the inhibition of Mn-induced damage by SIL was due at least in part to its antioxidant activity and its capacity to modulate the oxidative damage. PMID:23339144

  20. Interactions between manganese oxides and multiple-ringed aromatic compounds

    SciTech Connect

    Whelan, G.; Sims, R.C.

    1992-08-01

    Objective is to determine whether Mn reductive dissolution can oxidize multiple-ringed aromatics, such as PAHs, in an oxic environment? Research indicated that certain PAHs (eg, dihydrodiols and diones that form free-radical intermediates) are susceptible to oxidation and polymerization. Over 14 days, 83, 76, 54, 70, and 20% of the Mn was reduced by 2,3-, 1,3-, and 1,4-naphthalenediol, quinizarin, and 1,4-naphthoquinone, respectively. 100, 100, and 65% of the first three PAHs were oxidized, respectively. Aromatics with diol functional groups were more easily oxidized than those with only dione groups. Relatively insoluble compounds like quinizarin can be oxidized; insoluble ``humic-like`` material precipitated, indicating a polymerization-humification process. Results suggest that electron transfer/organic release from the oxide surface is the rate-limiting step.

  1. Interactions between manganese oxides and multiple-ringed aromatic compounds

    SciTech Connect

    Whelan, G. ); Sims, R.C. . Dept. of Civil and Environmental Engineering)

    1992-08-01

    Objective is to determine whether Mn reductive dissolution can oxidize multiple-ringed aromatics, such as PAHs, in an oxic environment Research indicated that certain PAHs (eg, dihydrodiols and diones that form free-radical intermediates) are susceptible to oxidation and polymerization. Over 14 days, 83, 76, 54, 70, and 20% of the Mn was reduced by 2,3-, 1,3-, and 1,4-naphthalenediol, quinizarin, and 1,4-naphthoquinone, respectively. 100, 100, and 65% of the first three PAHs were oxidized, respectively. Aromatics with diol functional groups were more easily oxidized than those with only dione groups. Relatively insoluble compounds like quinizarin can be oxidized; insoluble ''humic-like'' material precipitated, indicating a polymerization-humification process. Results suggest that electron transfer/organic release from the oxide surface is the rate-limiting step.

  2. Searching for biosignatures using electron paramagnetic resonance (EPR) analysis of manganese oxides.

    PubMed

    Kim, Soon Sam; Bargar, John R; Nealson, Kenneth H; Flood, Beverly E; Kirschvink, Joseph L; Raub, Timothy D; Tebo, Bradley M; Villalobos, Mario

    2011-10-01

    Manganese oxide (Mn oxide) minerals from bacterial sources produce electron paramagnetic resonance (EPR) spectral signatures that are mostly distinct from those of synthetic simulants and abiogenic mineral Mn oxides. Biogenic Mn oxides exhibit only narrow EPR spectral linewidths (?500 G), whereas abiogenic Mn oxides produce spectral linewidths that are 2-6 times broader and range from 1200 to 3000 G. This distinction is consistent with X-ray structural observations that biogenic Mn oxides have abundant layer site vacancies and edge terminations and are mostly of single ionic species [i.e., Mn(IV)], all of which favor narrow EPR linewidths. In contrast, abiogenic Mn oxides have fewer lattice vacancies, larger particle sizes, and mixed ionic species [Mn(III) and Mn(IV)], which lead to the broader linewidths. These properties could be utilized in the search for extraterrestrial physicochemical biosignatures, for example, on Mars missions that include a miniature version of an EPR spectrometer. PMID:21970705

  3. The oxidation of As(III) in groundwater using biological manganese removal filtration columns.

    PubMed

    Yang, Hong; Sun, Wenyong; Ge, Huoqing; Yao, Renda

    2015-01-01

    Arsenic is known as a toxic element to humans, and has been reported to co-exist with iron and manganese in groundwater worldwide. The typical method for arsenic removal from groundwater is to oxidize trivalent (As(III)) to pentavalent (As(V)) followed by the As(V) removal. This study aims to evaluate the oxidization efficiency of As(III) in a mature biological manganese (Mn(2+)) removal filtration system with different elevated influent As(III) concentrations. The effects of influent Mn(2+) concentrations, influent As(III) concentrations, filtration rates and dissolved oxygen (DO) levels on the efficiency of As(III) oxidation were assessed. The results showed that As(III) oxidation can be simultaneously achieved with removing Mn(2+) in the filtration system. The oxidation efficiency was not impacted by increasing the influent As(III) concentration up to nearly 2500?g?L(-1), but the filtration rate was limited at 11?m?h(-1) for maintaining the effluent As(III) concentration below 10?g?L(-1). The oxidation process followed first-order kinetics with the constant reaching 0.56-0.61?min(-1). The As(III) oxidation process was most likely to be mediated by the bacterial community initially developed for Mn(2+) removal in the filtration system, which performed the catalytic oxidation for As(III). PMID:26056846

  4. Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH.

    PubMed

    Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

    2014-01-01

    Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH. PMID:24977746

  5. Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

    2014-06-01

    Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH.

  6. Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH

    PubMed Central

    Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

    2014-01-01

    Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH. PMID:24977746

  7. Coordination compounds of manganese(II) with polyamines - catalysts of the oxidation of organic dyes by hydrogen peroxide

    SciTech Connect

    Batyr, D.G.; Isak, V.G.; Kirienko, A.A.; Kharitonov, Yu.Ya.

    1987-02-01

    The peroxidase activity of complexes of manganese(II) with polyamines has been characterized. A comparison of the original and literature data has led to the conclusion that the oxidation of organic substrates having some complexing ability with respect to Manganese(II) in Mn(II)-ligand-H/sub 2/O/sub 2/-S systems takes place according to an inner-sphere ion-molecule mechanism. In cases in which the substrate does not have any complexing ability with respect to Manganese(II), the oxidation process takes place according to an outer-sphere mechanism.

  8. CHROMIUM TRANSPORT, OXIDATION, AND ADSORPTION IN MANGANESE-COATED SAND

    EPA Science Inventory

    We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (P-MnO$-coated sand. We find that P-Mn02 effectively oxidizes Cr@I) to Cr(VI) and that the extent of oxida...

  9. Strong antiferromagnetic exchange between manganese phthalocyanine and ferromagnetic europium oxide.

    PubMed

    Wckerlin, Christian; Donati, Fabio; Singha, Aparajita; Baltic, Romana; Uldry, Anne-Christine; Delley, Bernard; Rusponi, Stefano; Dreiser, Jan

    2015-08-21

    We report on the antiferromagnetic exchange coupling between a submonolayer of Mn(II)-phthalocyanine molecules and a ferromagnetic Eu(II)-oxide thin film. The exchange energy is larger by nearly two orders of magnitude compared to previous studies involving oxidic substrates. PMID:26171839

  10. Enhanced mercury removal from fix-bed reactor by lamella manganese oxide sorbents

    NASA Astrophysics Data System (ADS)

    Cheng, H. W.; Yu, C. T.

    2015-12-01

    Mercury (Hg) is an extremely hazardous metal and attracted more concern because of its high toxicity and bioaccumulation. Several manganese-oxide-containing sorbents prepared by co-precipitation method could exhibit the mercury removal activities toward Hg0. The mercury removal test at the temperature of 300°C has the highest removal efficiency. Under this temperature, the maximum absorption equivalent of Mg-Al-Mn and Mn-Al were up to 90.9 and 247 μg/g, then gradually decreased at 400°C. The mercury removal efficiency declined in the following sequence: Mn-Al > Mg-Al-Mn > Mg-Al-Mn/ACA = Mn/AC(p)> Mn/AC(g), due to the manganese-oxide content formed on the sorbents.

  11. Studies on microbiologically influenced corrosion of SS304 by a novel manganese oxidizer, Bacillus flexus.

    PubMed

    Anandkumar, B; George, R P; Tamilvani, S; Padhy, N; Mudali, U Kamachi

    2011-01-01

    A manganese oxidizing bacterium was isolated from the surface of steel scraps and biochemical tests and 16S rRNA sequencing analysis confirmed the isolate as Bacillus flexus. Potentiodynamic polarization curves showed ennoblement of open circuit potential, increased passive current, a lowering of breakdown potential, active re-passivation potential and enhanced cathodic current in the presence of B. flexus. Adhesion studies with B. flexus on SS304 specimens with different surface treatments demonstrated decreased adhesion on passivated and FeCl(3) treated specimens due to the removal of MnS inclusions. The present study provides evidence that surface treatment of stainless steels can reduce adhesion of this manganese oxidizing bacterium and decrease the probability of microbiologically influenced corrosion. PMID:21749279

  12. Phase stability and properties of manganese oxide polymorphs: Assessment and insights from diffusion Monte Carlo

    NASA Astrophysics Data System (ADS)

    Schiller, Joshua A.; Wagner, Lucas K.; Ertekin, Elif

    2015-12-01

    We present an analysis of the polymorphic energy ordering and properties of the rocksalt and zinc-blende structures of manganese oxide using fixed node diffusion Monte Carlo (DMC). Manganese oxide is a correlated, antiferromagnetic material that has proven to be challenging to model from first principles across a variety of approaches. Unlike conventional density functional theory and some hybrid functionals, fixed node diffusion Monte Carlo finds the rocksalt structure to be more stable than the zinc-blende structure, and thus recovers the correct energy ordering. Analysis of the site-resolved charge fluctuations of the wave functions according to DMC and other electronic structure descriptions gives insights into elements that are missing in other theories. While the calculated band gaps within DMC are in agreement with predictions that the zinc-blende polymorph has a lower band gap, the gaps themselves overestimate reported experimental values.

  13. Low-temperature, manganese oxide-based, thermochemical water splitting cycle

    PubMed Central

    Xu, Bingjun; Bhawe, Yashodhan; Davis, Mark E.

    2012-01-01

    Thermochemical cycles that split water into stoichiometric amounts of hydrogen and oxygen below 1,000?C, and do not involve toxic or corrosive intermediates, are highly desirable because they can convert heat into chemical energy in the form of hydrogen. We report a manganese-based thermochemical cycle with a highest operating temperature of 850?C that is completely recyclable and does not involve toxic or corrosive components. The thermochemical cycle utilizes redox reactions of Mn(II)/Mn(III) oxides. The shuttling of Na+ into and out of the manganese oxides in the hydrogen and oxygen evolution steps, respectively, provides the key thermodynamic driving forces and allows for the cycle to be closed at temperatures below 1,000?C. The production of hydrogen and oxygen is fully reproducible for at least five cycles. PMID:22647608

  14. Effect of enhanced manganese oxidation in the hyporheic zone on basin-scale geochemical mass balance

    USGS Publications Warehouse

    Harvey, J.W.; Fuller, C.C.

    1998-01-01

    We determined the role of the hyporheic zone (the subsurface zone where stream water and shallow groundwater mix) in enhancing microbially mediated oxidation of dissolved manganese (to form manganese precipitates) in a drainage basin contaminated by copper mining. The fate of manganese is of overall importance to water quality in Pinal Creek Basin, Arizona, because manganese reactions affect the transport of trace metals. The basin-scale role of the hyporheic zone is difficult to quantify because stream-tracer studies do not always reliably characterize the cumulative effects of the hyporheic zone. This study determined cumulative effects of hyporheic reactions in Pinal Creek basin by characterizing manganese uptake at several spatial scales (stream-reach scale, hyporheicflow-path scale, and sediment-grain scale). At the stream-reach scale a one-dimensional stream-transport model (including storage zones to represent hyporheic flow paths) was used to determine a reach-averaged time constant for manganese uptake in hyporheic zones, 1/??(s), of 1.3 hours, which was somewhat faster but still similar to manganese uptake time constants that were measured directly in centimeter-scale hyporheic flow paths (1/??(h) = 2.6 hours), and in laboratory batch experiments using streambed sediment (1/?? = 2.7 hours). The modeled depths of subsurface storage zones (d(s) = 4-17 cm) and modeled residence times of water in storage zones (t(s) = 3-12 min) were both consistent with direct measurements in hyporheic flow paths (d(h) = 0-15 cm, and t(h) = 1-25 min). There was also good agreement between reach-scale modeling and direct measurements of the percentage removal of dissolved manganese in hyporheic flow paths (f(s) = 8.9%, and f(h) = 9.3%). Manganese uptake experiments in the laboratory using sediment from Pinal Creek demonstrated (through comparison of poisoned and unpoisoned treatments) that the manganese removal process was enhanced by microbially mediated oxidation. The cumulative effect of hyporheic exchange in Pinal Creek basin was to remove approximately 20% of the dissolved manganese flowing out of the drainage basin. Our results illustrate that the cumulative significance of reactive uptake in the hyporheic zone depends on the balance between chemical reaction rates, hyporheic porewater residence time, and turnover of streamflow through hyporheic flow paths. The similarity between the hyporheic reaction timescale (1??(s) ??? 1.3 hours), and the hyporheic porewater residence timescale (t(s) ??? 8 min) ensured that there was adequate time for the reaction to progress. Furthermore, it was the similarity between the turnover length for stream water flow through hyporheic flow paths (L(s) = stream velocity/storage-zone exchange coefficient ??? 1.3 km) and the length of Pinal Creek (L ??? 7 km), which ensured that all stream water passed through hyporheic flow paths several times. As a means to generalize our findings to other sites where similar types of hydrologic and chemical information are available, we suggest a cumulative significance index for hyporheic reactions, R(s) = ??(s)t(s)L/L(s) (dimensionless); higher values indicate a greater potential for hyporheic reactions to influence geochemical mass balance. Our experience in Pinal Creek basin suggests that values of R(s) > 0.2 characterize systems where hyporheic reactions are likely to influence geochemical mass balance at the drainage-basin scale.

  15. Oxidative Transformation of Controlled Substances by Manganese Dioxide

    PubMed Central

    Lai, Webber Wei-Po; Lin, Angela Yu-Chen; Yang, Sheng-Yao; Huang, Ching-Hua

    2015-01-01

    This study investigated the oxidative transformation of four controlled substances (ketamine, methamphetamine, morphine, and codeine) by synthesized MnO2 (?-MnO2) in aqueous environments. The results indicated that ketamine and methamphetamine were negligibly oxidized by MnO2 and, thus, may be persistent in the aqueous environment. However, morphine and codeine were able to be oxidized by MnO2, which indicated that they are likely naturally attenuated in aqueous environments. Overall, lower solution pH values, lower initial compound concentrations, and higher MnO2 loading resulted in a faster reaction rate. The oxidation of morphine was inhibited in the presence of metal ions (Mn2+, Fe3+, Ca2+, and Mg2+) and fulvic acid. However, the addition of Fe3+ and fulvic acid enhanced codeine oxidation. A second-order kinetics model described the oxidation of morphine and codeine by MnO2; it suggested that the formation of a surface precursor complex between the target compound and the MnO2 surface was the rate-limiting step. Although the target compounds were degraded, the slow TOC removal indicated that several byproducts were formed and persist against further MnO2 oxidation. PMID:26078991

  16. Chemical fluxes and origin of a manganese carbonate-oxide-silicate deposit in bedded chert

    USGS Publications Warehouse

    Huebner, J.S.; Flohr, M.J.K.; Grossman, J.N.

    1992-01-01

    Lens-like rhodochrosite-rich bodies within interbedded chert and shale are associated with basalt and/or graywacke in ophiolitic and orogenic zones. The Buckeye manganese mine in the Franciscan Complex of the California Coast Ranges is associated with metagraywacke. Despite blueschist-facies metamorphism, this deposit preserves the compositions and some textural features of its sedimentary protoliths. For this reason, it is a suitable deposit with which to compare more intensely altered deposits, or deposits originating in different paleoenvironments. Six Mn-rich and three Mn-poor minerals form monomineralic layers and mixtures: rhodochrosite, gageite, Mn-oxides (hausmannite, braunite), divalent Mn-silicates (caryopilite, taneyamalite), chlorite, quartz (metachert) and aegirine-augite. The Mn-rich protoliths have high Mn/Fe combined with relatively low concentrations of Ca, Al, Ti, Co, Ni, Cu, Th and REE. REE patterns of various protoliths are distinct. Rhodochrosite and gageite layers are depleted (seawater ?? 5 ?? 104) and flat, whereas patterns of metachert and the Mn-silicate-rich layers mimic the patterns of metashale and metagraywacke (seawater ?? 106). Hausmannite layers have flat patterns (seawater ?? 7 ?? 104) whereas braunite-rich layers are more enriched (seawater ?? 2 ?? 105) and show a distinct positive Ce anomaly. Factor analysis reveals components and fluxes attributed to sub-seafloor fluids (Ni, As, Zn, Sb, W, Mn), seawater (Mg, Au, V, Mo), detritus and veins (Ca, Ba, Sr). Silica is negatively correlated with the sub-seafloor factor. The observed variances indicate that water from the sediment column mixed with seawater, that deposition occurred near the sediment-seawater interface before mixtures of subsurface fluid and seawater homogenized, and that the system was not entirely closed during metamorphism. The variations in REE enrichment can be related to kinetics of deposition: rhodochrosite and gageite were precipitated most rapidly, and therefore were the protoliths that most effectively diluted the REE-rich background resulting from fine clastic material (derived from distal turbidites). The variation of the Ce anomaly and U/Th among diverse lithologies and the differences in Mn oxidation states are consistent with progressive dilution of reduced subsurface fluids with oxidized seawater. By this scheme, rhodochrosite, gageite and hausmannite were deposited from the most reduced fluids, braunite from intermediate mixtures, and Mn-silicates from the sub-seafloor fluids most diluted with fresh seawater. Comparison of the Buckeye with other lens-like and sheet-like deposits having high Mn/Fe and containing Mn3+ and/or Mn2+ suggests that each had three essential fluxes: a sub-seafloor source of Mn, a local source of very soluble silica and a source of relatively fresh, oxygenated water. Additional fluxes, such as clastics, appear to be more characteristic of the paleoenvironment than the three essential fluxes. ?? 1992.

  17. Synthesis and Electrochemical Analyses of Manganese Oxides for Super-Capacitors.

    PubMed

    Kim, Taewoo; Hwang, Hyein; Jang, Jaeyong; Park, Inyeong; Shim, Sang Eun; Baeck, Sung-Hyeon

    2015-11-01

    δ-Phase and α-phase manganese oxides were prepared using a hydrothermal method and their electrochemical properties were characterized. The influence of calcination temperature on the properties of manganese oxides was studied. Crystallinities were studied by X-ray diffraction, and scanning and transmission electron microscopy were utilized to examine morphologies. Average pore sizes and specific surface areas of samples were analyzed using the Barret-Joyner-Halenda and Brunauer-Emmett-Teller methods, respectively. After calcination in the range 300 degrees C to 600 degrees C, changes in morphology and crystallinity were observed. The flower-like shape of as synthesized samples became nanorod-like and the δ-phase changed to the α-phase. These changes may have been due to the removal of water during calcination. Furthermore, a transition stage in which the two phases coexisted was observed. Synthesized manganese oxides were mixed with carbon by sonification, to increase electric conductivity and to induce a synergistic effect between pseudo-capacitor and electric double layer capacitor (EDLC). Specific capacitances and rate durability of each composite were investigated by cyclic voltammetry in 1 M Na2SO4 electrolyte at different scan rates. MnO2 calcined at 400 degrees C exhibited the highest capacitance, probably due to its high surface area and more porous structure. PMID:26726613

  18. Catalytic Role of Manganese Oxides in Prebiotic Nucleobases Synthesis from Formamide.

    PubMed

    Bhushan, Brij; Nayak, Arunima; Kamaluddin

    2016-06-01

    Origin of life processes might have begun with the formation of important biomonomers, such as amino acids and nucleotides, from simple molecules present in the prebiotic environment and their subsequent condensation to biopolymers. While studying the prebiotic synthesis of naturally occurring purine and pyrimidine derivatives from formamide, the manganese oxides demonstrated not only good binding for formamide but demonstrated novel catalytic activity. A novel one pot manganese oxide catalyzed synthesis of pyrimidine nucleobases like thymine is reported along with the formation of other nucleobases like purine, 9-(hydroxyacetyl) purine, cytosine, 4(3 H)-pyrimidinone and adenine in acceptable amounts. The work reported is significant in the sense that the synthesis of thymine has exhibited difficulties especially under one pot conditions and also such has been reported only under the catalytic activity of TiO2. The lower oxides of manganese were reported to show higher potential as catalysts and their existence were favored by the reducing atmospheric conditions prevalent on early Earth; thereby confirming the hypothesis that mineral having metals in reduced form might have been more active during the course of chemical evolution. Our results further confirm the role of formamide as a probable precursor for the formation of purine and pyrimidine bases during the course of chemical evolution and origin of life. PMID:26758444

  19. Catalytic Role of Manganese Oxides in Prebiotic Nucleobases Synthesis from Formamide

    NASA Astrophysics Data System (ADS)

    Bhushan, Brij; Nayak, Arunima; Kamaluddin

    2016-01-01

    Origin of life processes might have begun with the formation of important biomonomers, such as amino acids and nucleotides, from simple molecules present in the prebiotic environment and their subsequent condensation to biopolymers. While studying the prebiotic synthesis of naturally occurring purine and pyrimidine derivatives from formamide, the manganese oxides demonstrated not only good binding for formamide but demonstrated novel catalytic activity. A novel one pot manganese oxide catalyzed synthesis of pyrimidine nucleobases like thymine is reported along with the formation of other nucleobases like purine, 9-(hydroxyacetyl) purine, cytosine, 4(3 H)-pyrimidinone and adenine in acceptable amounts. The work reported is significant in the sense that the synthesis of thymine has exhibited difficulties especially under one pot conditions and also such has been reported only under the catalytic activity of TiO2. The lower oxides of manganese were reported to show higher potential as catalysts and their existence were favored by the reducing atmospheric conditions prevalent on early Earth; thereby confirming the hypothesis that mineral having metals in reduced form might have been more active during the course of chemical evolution. Our results further confirm the role of formamide as a probable precursor for the formation of purine and pyrimidine bases during the course of chemical evolution and origin of life.

  20. Manganese-oxidizing photosynthesis before the rise of cyanobacteria.

    PubMed

    Johnson, Jena E; Webb, Samuel M; Thomas, Katherine; Ono, Shuhei; Kirschvink, Joseph L; Fischer, Woodward W

    2013-07-01

    The emergence of oxygen-producing (oxygenic) photosynthesis fundamentally transformed our planet; however, the processes that led to the evolution of biological water splitting have remained largely unknown. To illuminate this history, we examined the behavior of the ancient Mn cycle using newly obtained scientific drill cores through an early Paleoproterozoic succession (2.415 Ga) preserved in South Africa. These strata contain substantial Mn enrichments (up to ?17 wt %) well before those associated with the rise of oxygen such as the ?2.2 Ga Kalahari Mn deposit. Using microscale X-ray spectroscopic techniques coupled to optical and electron microscopy and carbon isotope ratios, we demonstrate that the Mn is hosted exclusively in carbonate mineral phases derived from reduction of Mn oxides during diagenesis of primary sediments. Additional observations of independent proxies for O2--multiple S isotopes (measured by isotope-ratio mass spectrometry and secondary ion mass spectrometry) and redox-sensitive detrital grains--reveal that the original Mn-oxide phases were not produced by reactions with O2, which points to a different high-potential oxidant. These results show that the oxidative branch of the Mn cycle predates the rise of oxygen, and provide strong support for the hypothesis that the water-oxidizing complex of photosystem II evolved from a former transitional photosystem capable of single-electron oxidation reactions of Mn. PMID:23798417

  1. Chromium transport, oxidation, and adsorption in manganese-coated sand.

    PubMed

    Guha, H; Saiers, J E; Brooks, S; Jardine, P; Jayachandran, K

    2001-06-01

    We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (beta-MnO2)-coated sand. We find that beta-MnO2 effectively oxidizes Cr(III) to Cr(VI) and that the extent of oxidation is sensitive to changes in pH, pore water velocity, and influent concentrations of Cr(III). Cr(III) oxidation rates, although initially high, decline well before the supply of beta-MnO2 is depleted, suggesting that a reaction product inhibits the conversion of Cr(III) to Cr(VI). Rate-limited reactions govern the weak adsorption of each chromium species, with Cr(III) adsorption varying directly with pH and Cr(VI) adsorption varying inversely with pH. The breakthrough data on chromium transport can be matched closely by calculations of a simple model that accounts for (1) advective-dispersive transport of Cr(III), Cr(VI), and dissolved oxygen, (2) first-order kinetics adsorption of the reduced and oxidized chromium species, and (3) nonlinear rate-limited oxidation of Cr(III) to Cr(VI). Our work supplements the limited database on the transport of redox-sensitive metals in porous media and provides a means for quantifying the coupled processes that contribute to this transport. PMID:11411402

  2. Manganese-oxidizing photosynthesis before the rise of cyanobacteria

    PubMed Central

    Johnson, Jena E.; Webb, Samuel M.; Thomas, Katherine; Ono, Shuhei; Kirschvink, Joseph L.; Fischer, Woodward W.

    2013-01-01

    The emergence of oxygen-producing (oxygenic) photosynthesis fundamentally transformed our planet; however, the processes that led to the evolution of biological water splitting have remained largely unknown. To illuminate this history, we examined the behavior of the ancient Mn cycle using newly obtained scientific drill cores through an early Paleoproterozoic succession (2.415 Ga) preserved in South Africa. These strata contain substantial Mn enrichments (up to ∼17 wt %) well before those associated with the rise of oxygen such as the ∼2.2 Ga Kalahari Mn deposit. Using microscale X-ray spectroscopic techniques coupled to optical and electron microscopy and carbon isotope ratios, we demonstrate that the Mn is hosted exclusively in carbonate mineral phases derived from reduction of Mn oxides during diagenesis of primary sediments. Additional observations of independent proxies for O2—multiple S isotopes (measured by isotope-ratio mass spectrometry and secondary ion mass spectrometry) and redox-sensitive detrital grains—reveal that the original Mn-oxide phases were not produced by reactions with O2, which points to a different high-potential oxidant. These results show that the oxidative branch of the Mn cycle predates the rise of oxygen, and provide strong support for the hypothesis that the water-oxidizing complex of photosystem II evolved from a former transitional photosystem capable of single-electron oxidation reactions of Mn. PMID:23798417

  3. Manganese sulfide formation via concomitant microbial manganese oxide and thiosulfate reduction.

    SciTech Connect

    Lee, Ji-Hoon; Kennedy, David W.; Dohnalkova, Alice; Moore, Dean A.; Nachimuthu, Ponnusamy; Reed, Samantha B.; Fredrickson, Jim K.

    2011-12-27

    The dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 produced ?-MnS (rambergite) nanoparticles under the concurrent reduction of synthetic MnO2 and thiosulfate coupled to H2 oxidation. Using two MR-1 mutants defective in outer membrane c-type cytochromes (?mtrC/?omcA and ?mtrC/?omcA/?mtrF) to eliminate the direct reduction pathway for solid electron acceptors, it was determined that respiratory reduction of MnO2 was dominant relative to chemical reduction by biogenic sulfide generated from bacterial thiosulfate reduction. Although bicarbonate was excluded from the medium, incubations of MR-1 using lactate as the sole electron donor produced MnCO3 (rhodochrosite) as well as MnS in nearly equivalent amounts as estimated by micro X-ray diffraction (micro-XRD) analysis. It was concluded that carbonate released from lactate metabolism promoted MnCO3 formation and that Mn(II) mineralogy was strongly affected by carbonate ions even in the presence of abundant sulfide and weakly alkaline conditions that favor the precipitation of MnS. Formation of the biogenic MnS, as determined by a combination of micro-XRD, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction analyses was consistent with equilibrium speciation modeling predictions. Although biogenic MnS likely only forms and is stable over a relatively narrow range of conditions, it may be a significant sink for Mn in anoxic marine basins and terrestrial subsurface sediments where Mn and sulfur compounds are undergoing concurrent reduction.

  4. [Synthesis of manganese oxide octahedral molecular sieve and their application in catalytic oxidation of benzene].

    PubMed

    Li, Dong-Yan; Liu, Hai-Di; Chen, Yun-Fa

    2011-12-01

    Manganese oxide octahedral molecular sieves (OMS-2) for VOCs catalytic combustion were synthesized by refluxing method. The crystal structure, particle morphology, pore structure and H2-reduction ability were characterized by XRD, SEM, N2 adsorption-desorption and H2-TPR techniques. The catalytic activities of the OMS-2 calcined at different temperatures in benzene combustion and the stability of the sample calcined at 300 degrees C were evaluated. The results indicated that the effect of calcinations temperature on the surface characters of catalysts was remarkable. With higher calcination temperature, the samples showed lower surface area and pore volume, but larger average pore size. At the same time, high calcination temperature leaded to low activity. The benzene conversion of the sample calcined at 300 degrees C was 50% degrees C at 200 degrees C and 90% at 250 degrees C, respectively. The catalytic activity exhibited only 5% reduction after reaction at 260 degrees C for 70 h, which indicated that the as-made catalysts were very stable after calcination at 300 degrees C. PMID:22468535

  5. Adsorption of ribose nucleotides on manganese oxides with varied mn/o ratio: implications for chemical evolution.

    PubMed

    Bhushan, Brij; Shanker, Uma; Kamaluddin

    2011-10-01

    Manganese exists in different oxidation states under different environmental conditions with respect to redox potential. Various forms of manganese oxides, namely, Manganosite (MnO), Bixbyite (Mn(2)O(3)), Hausmannite (Mn(3)O(4)) and Pyrolusite (MnO(2)) were synthesized and their possible role in chemical evolution studied. Adsorption studies of ribose nucleotides (5'-AMP, 5'-GMP, 5'-CMP and 5'-UMP) on these manganese oxides at neutral pH, revealed a higher binding affinity to manganosite (MnO) compared to the other manganese oxides. That manganese oxides having a lower Mn-O ratio show higher binding affinity for the ribonucleotides indirectly implies that such oxides may have provided a surface onto which biomonomers could have been concentrated through selective adsorption. Purine nucleotides were adsorbed to a greater extent compared to the pyrimidine nucleotides. Adsorption data followed Langmuir adsorption isotherms, and X( m ) and K( L ) values were calculated. The nature of the interaction and mechanism was elucidated by infrared spectral studies conducted on the metal-oxide and ribonucleotide-metal-oxide adducts. PMID:21626404

  6. Manganese (Mn) Oxidation Increases Intracellular Mn in Pseudomonas putida GB-1

    PubMed Central

    Banh, Andy; Chavez, Valarie; Doi, Julia; Nguyen, Allison; Hernandez, Sophia; Ha, Vu; Jimenez, Peter; Espinoza, Fernanda; Johnson, Hope A.

    2013-01-01

    Bacterial manganese (Mn) oxidation plays an important role in the global biogeochemical cycling of Mn and other compounds, and the diversity and prevalence of Mn oxidizers have been well established. Despite many hypotheses of why these bacteria may oxidize Mn, the physiological reasons remain elusive. Intracellular Mn levels were determined for Pseudomonas putida GB-1 grown in the presence or absence of Mn by inductively coupled plasma mass spectrometry (ICP-MS). Mn oxidizing wild type P. putida GB-1 had higher intracellular Mn than non Mn oxidizing mutants grown under the same conditions. P. putida GB-1 had a 5 fold increase in intracellular Mn compared to the non Mn oxidizing mutant P. putida GB-1-007 and a 59 fold increase in intracellular Mn compared to P. putida GB-1 ?2665 ?2447. The intracellular Mn is primarily associated with the less than 3 kDa fraction, suggesting it is not bound to protein. Protein oxidation levels in Mn oxidizing and non oxidizing cultures were relatively similar, yet Mn oxidation did increase survival of P. putida GB-1 when oxidatively stressed. This study is the first to link Mn oxidation to Mn homeostasis and oxidative stress protection. PMID:24147089

  7. Manganese oxide phases and morphologies: A study on calcination temperature and atmospheric dependence

    PubMed Central

    Fenske, Daniela; Bardenhagen, Ingo; Westphal, Anne; Knipper, Martin; Plaggenborg, Thorsten; Kolny-Olesiak, Joanna; Parisi, Jrgen

    2015-01-01

    Summary Manganese oxides are one of the most important groups of materials in energy storage science. In order to fully leverage their application potential, precise control of their properties such as particle size, surface area and Mnx + oxidation state is required. Here, Mn3O4 and Mn5O8 nanoparticles as well as mesoporous ?-Mn2O3 particles were synthesized by calcination of Mn(II) glycolate nanoparticles obtained through an economical route based on a polyol synthesis. The preparation of the different manganese oxides via one route facilitates assigning actual structureproperty relationships. The oxidation process related to the different MnOx species was observed by in situ X-ray diffraction (XRD) measurements showing time- and temperature-dependent phase transformations occurring during oxidation of the Mn(II) glycolate precursor to ?-Mn2O3 via Mn3O4 and Mn5O8 in O2 atmosphere. Detailed structural and morphological investigations using transmission electron microscopy (TEM) and powder XRD revealed the dependence of the lattice constants and particle sizes of the MnOx species on the calcination temperature and the presence of an oxidizing or neutral atmosphere. Furthermore, to demonstrate the application potential of the synthesized MnOx species, we studied their catalytic activity for the oxygen reduction reaction in aprotic media. Linear sweep voltammetry revealed the best performance for the mesoporous ?-Mn2O3 species. PMID:25671151

  8. Characterization of Manganese Oxide Precipitates from Appalachian Coal Mine Mine Drainage Treatment Systems

    SciTech Connect

    Tan, H.; Zhang, G; Heaney, P; Webb, S; Burgos, W

    2010-01-01

    The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnO{sub x}). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20-150 mg/L), system construction ({+-}inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnO{sub x} precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnOx precipitates from all sites was coarse and 'sponge-like' composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnO{sub x} precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnOx mineral assemblages in CMD treatment systems.

  9. Tailor-made ultrathin manganese oxide nanostripes: magic widths on Pd(1 1 N) terraces

    NASA Astrophysics Data System (ADS)

    Franchini, C.; Li, F.; Surnev, S.; Podloucky, R.; Allegretti, F.; Netzer, F. P.

    2012-02-01

    The growth of ultrathin two-dimensional manganese oxide nanostripes on vicinal Pd(1 1 N) surfaces leads to particular stable configurations for certain combinations of oxide stripe and substrate terrace widths. Scanning tunneling microscopy and high-resolution low-energy electron diffraction measurements reveal highly ordered nanostructured surfaces with excellent local and long-range order. Density functional theory calculations provide the physical origin of the stabilization mechanism of magic width stripes in terms of a finite-size effect, caused by the significant relaxations observed at the stripe boundaries.

  10. Microbial reduction of manganese oxides - Interactions with iron and sulfur

    NASA Technical Reports Server (NTRS)

    Myers, Charles R.; Nealson, Kenneth H.

    1988-01-01

    Alteromonas putrefaciens (strain MR-1) is capable of rapid Mn(IV) reduction under conditions of neutral pH and temperatures characteristic of the Oneida Lake, New York, sediments from which it was isolated. MR-1 also reduces Fe(3+) to Fe(2+), and disproportionates thiosulfate to sulfide and sulfite; independently, the Fe(2+) and sulfide act as rapid reductants of Mn. The addition of Fe(3+) or thiosulfate to cultures of MR-1 in the presence of oxidized Mn increases the rate and the extent of Mn reduction relative to that observed in the absence of Fe(3+) or thiosulfate. Furthermore, when Fe(3+) and Mn oxides are present conjointly, Fe(2+) does not appear until the reduction of the oxidized Mn is complete. These results demonstrate that the observed rates of Fe(2+) and sulfide production may underestimate the total rates of Fe and sulfate reduction in those environments containing oxidized Mn. These results also demonstrate the potential impact that a single microbe can exert on sediment geochemistry, and provide the basis for preliminary models of the complexity of microbial and geochemical interactions that occur.

  11. c-Type cytochromes and manganese oxidation in Pseudomonas putida MnB1

    SciTech Connect

    Caspi, R.; Tebo, B.M.; Haygood, M.G.

    1998-10-01

    Pseudomonas putida MnB1 is an isolate from an Mn oxide-encrusted pipeline that can oxidize Mn(II) to Mn oxides. The authors used transposon mutagenesis to construct mutants of strain MnB1 that are unable to oxidize manganese, and they characterized some of these mutants. The mutants were divided into three groups: mutants defective in the biogenesis of c-type cytochromes, mutants defective in genes that encode key enzymes of the tricarboxylic acid cycle, and mutants defective in the biosynthesis of tryptophan. The mutants in the first two groups were cytochrome c oxidase negative and did not contain c-type cytochromes. Mn(II) oxidation capability could be recovered in a c-type cytochrome biogenesis-defective mutant by complementation of the mutation.

  12. Oxide Formation Mechanisms in High Manganese Steel Welds

    NASA Astrophysics Data System (ADS)

    Kim, Dooyoung; Han, Kyutae; Lee, Bongkeun; Han, Ilwook; Park, Joo Hyun; Lee, Changhee

    2014-04-01

    Oxide inclusions in high-Mn steel welds were analyzed and almost all of which were found to belong to the MnO-Al2O3-SiO2 system. In this study, the inclusions were categorized based on MnS morphology into the following two types: (1) aluminosilicate with a MnS patch, or (2) aluminosilicate with a MnS shell. The most frequently detected was type 1, the formation mechanism of which was investigated using commercially available thermochemical computing software, FactSage (ver. 6.3). The thermodynamic calculations predicted that galaxite (MnAl2O4), tephroite (Mn2SiO4), and MnS could precipitate during solidification. However, because of the fast cooling rate in welding processes, galaxite and tephroite phases were unable to fully crystallize, but rather were supercooled as glassy phases. In order to confirm the validity of the thermodynamic calculations, the composition of the observed inclusions was compared with the MnO-SiO2-Al2O3 ternary phase diagram, resulting in remarkably good agreement. Furthermore, it was found that the type of the oxide inclusions was dependent on their location ( i.e., MnS shell- and MnS patch-type oxides were detected at the dendritic core and interdendritic boundary, respectively). Both types of oxides were occasionally found in one oxide, near the interdendritic boundary. This indicates that the morphology variation originates from the redistribution of solute due to fast solidification.

  13. Photoelectrochemical And Structural Behavior Of Manganese Oxide/N-Si Photoanodes

    NASA Astrophysics Data System (ADS)

    Kainthla, R. C.; Zelenay, B.; Bockris, J. O.

    1985-12-01

    N-silicon photoanodes have been protected against photocorrosion, for use in photo-assisted water electrolysis photoelectrochemical cells, by chemically depositing a thin film of manganese oxide on the surface. Current-potential characteristics of the electrodes have been measured in 0.5 M K2SO4 solution and in 0.2 M NaOH solutions. The onset potential for photocurrent in these electrolytes occur at + 1.1 V and + 0.56 V (vs NHE), respectively. The occurrence of photocurrent due to the photoevolution of oxygen was confirmed by pH dependence of onset potential and the appearance of gas bubbles on the electrode surface. When used in 0.5 M K2SO4 solution, at ~ 1.1 mA.cm-2 photocurrent density, the electrode has shown complete stability, for continuous illumination of ~ 650 hours. The surface analysis of the electrode surface shows that manganese in the manganese oxide is present in + 3 state. The use of electrode for oxygen evolution in aqueous solution changes the Mn203 to MnO (OH) on the surface without affecting the bulk composition.

  14. Secondary cell with orthorhombic alkali metal/manganese oxide phase active cathode material

    DOEpatents

    Doeff, Marca M. (Hayward, CA); Peng, Marcus Y. (Cupertino, CA); Ma, Yanping (Albany, CA); Visco, Steven J. (Berkeley, CA); DeJonghe, Lutgard C. (Lafayette, CA)

    1996-01-01

    An alkali metal manganese oxide secondary cell is disclosed which can provide a high rate of discharge, good cycling capabilities, good stability of the cathode material, high specific energy (energy per unit of weight) and high energy density (energy per unit volume). The active material in the anode is an alkali metal and the active material in the cathode comprises an orthorhombic alkali metal manganese oxide which undergoes intercalation and deintercalation without a change in phase, resulting in a substantially linear change in voltage with change in the state of charge of the cell. The active material in the cathode is an orthorhombic structure having the formula M.sub.x Z.sub.y Mn.sub.(1-y) O.sub.2, where M is an alkali metal; Z is a metal capable of substituting for manganese in the orthorhombic structure such as iron, cobalt or titanium; x ranges from about 0.2 in the fully charged state to about 0.75 in the fully discharged state, and y ranges from 0 to 60 atomic %. Preferably, the cell is constructed with a solid electrolyte, but a liquid or gelatinous electrolyte may also be used in the cell.

  15. Secondary cell with orthorhombic alkali metal/manganese oxide phase active cathode material

    DOEpatents

    Doeff, M.M.; Peng, M.Y.; Ma, Y.; Visco, S.J.; DeJonghe, L.C.

    1996-09-24

    An alkali metal manganese oxide secondary cell is disclosed which can provide a high rate of discharge, good cycling capabilities, good stability of the cathode material, high specific energy (energy per unit of weight) and high energy density (energy per unit volume). The active material in the anode is an alkali metal and the active material in the cathode comprises an orthorhombic alkali metal manganese oxide which undergoes intercalation and deintercalation without a change in phase, resulting in a substantially linear change in voltage with change in the state of charge of the cell. The active material in the cathode is an orthorhombic structure having the formula M{sub x}Z{sub y}Mn{sub (1{minus}y)}O{sub 2}, where M is an alkali metal; Z is a metal capable of substituting for manganese in the orthorhombic structure such as iron, cobalt or titanium; x ranges from about 0.2 in the fully charged state to about 0.75 in the fully discharged state, and y ranges from 0 to 60 atomic %. Preferably, the cell is constructed with a solid electrolyte, but a liquid or gelatinous electrolyte may also be used in the cell. 11 figs.

  16. Manganese-oxidizing photosynthesis before the rise of cyanobacteria

    NASA Astrophysics Data System (ADS)

    Johnson, J. E.; Webb, S.; Thomas, K. S.; Ono, S.; Kirschvink, J. L.; Fischer, W. W.

    2012-12-01

    The evolution of oxygenic photosynthesis was a singularity that fundamentally transformed our planet's core biogeochemical cycles and changed the redox structure of Earth's surface, crust, and mantle. To date, understanding the evolution of this molecular machinery has largely been derived from comparative biology. Several biochemical innovations enabled water-splitting, including a central photosynthetic pigment with a higher redox potential and coupled photosystems. However the critical photochemical invention was the water oxidizing complex (WOC) of photosystem II, a cubane cluster of four redox-active Mn atoms and a Ca atom bound by oxo bridges, that couple the single electron photochemistry of the photosystem to the four-electron oxidation of water to O2. Transitional forms of the WOC have been postulated, including an Mn-containing catalase-like peptide using an H2O2 donor, or uptake and integration of environmental Mn-oxides. One attractive hypothesis from the perspective of modern photo-assembly of the WOC posits an initial Mn(II)-oxidizing photosystem as a precursor to the WOC (Zubay, 1996; Allen and Martin, 2007). To test these hypotheses, we studied the behavior of the ancient Mn cycle captured by 2415 ± 6 Ma scientific drill cores retrieved by the Agouron Drilling Project through the Koegas Subgroup in Griqualand West, South Africa. This succession contains substantial Mn-enrichments (up to 17 wt.% in bulk). To better understand the petrogenesis and textural context of these deposits, we employed a novel X-ray absorption spectroscopy microprobe to make redox maps of ultra-thin sample sections at a 2μm scale. Coupled to light and electron microscopy and C isotopic measurements, we observe that all of the Mn is present as Mn(II), contained within carbonate minerals produced from early diagenetic reduction of Mn-oxide phases with organic matter. To assay the environmental oxidant responsible for the production of the Mn-oxides we examined two independent techniques sensitive to low levels of environmental O2—multiple sulfur isotopes analyzed using whole-rock IRMS and texture-specific SIMS techniques, and the presence of redox-sensitive detrital grains. Despite the conspicuous oxidation of Mn, both proxies reveal a lack of significant molecular oxygen present in the environment at this time (O2 << 1 ppm). These results provide strong geological support for the idea that an early Mn-oxidizing photosystem once existed as a transitional form prior to the evolution of the WOC of photosystem II and oxygenic photosynthesis. [Refs: Zubay J (1996) Origins of Life on the Earth and in the Cosmos, Academic Press: San Diego. Allen JF, Martin W (2007) Evolutionary biology: Out of thin air, Nature, 445, 610-612.

  17. Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

    USGS Publications Warehouse

    Buss, H.L.; Sak, P.B.; Webb, S.M.; Brantley, S.L.

    2008-01-01

    In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2-2 m thick zone of partially weathered rock layers (???2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive ??V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 A??, forming 'altered biotite'. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 ?? 10-14 mol biotite m-2 s-1. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 ??m resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet-saprolite interface, hornblende dissolves to completion at a rate of 6.3 ?? 10-13 mol hornblende m-2 s-1: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O2 at the bedrock-saprolite interface. ?? 2008 Elsevier Ltd. All rights reserved.

  18. Weathering of the Rio Blanco Quartz Diorite, Luquillo Mountains, Puerto Rico: Coupling Oxidation, Dissolution, And Fracturing

    SciTech Connect

    Buss, H.L.; Sak, P.B.; Webb, S.M.; Brantley, S.L.

    2009-05-12

    In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2-2 m thick zone of partially weathered rock layers ({approx}2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive {Delta}V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 {angstrom}, forming 'altered biotite'. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 x 10{sup -14} mol biotite m{sup -2} s{sup -1}. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 {micro}m resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet-saprolite interface, hornblende dissolves to completion at a rate of 6.3 x 10{sup -13} mol hornblende m{sup -2} s{sup -1}: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O{sub 2} at the bedrock-saprolite interface.

  19. Facile synthesis of manganese oxide loaded hollow silica particles and their application for methylene blue degradation.

    PubMed

    Meng, Qingnan; Xiang, Siyuan; Cheng, Wei; Chen, Qiaonan; Xue, Pengfei; Zhang, Kai; Sun, Hongchen; Yang, Bai

    2013-09-01

    A facile poly acrylic acid (PAA) soft templating method was developed to fabricate manganese oxide loaded hollow silica particles (MHSPs). The synthesis involves PAA-Mn aggregation to form spherical particles and silica coating layer formation on the outer surface of the particles. Subsequent calcination in air at 500 C removes the polymer inside the particles, and hollow silica spheres with trapped metal oxide particles are thus formed. The PAA traps the Mn ions and forms aggregates which template the silica shell formation in this process. The Mn content and the structure of the MHSPs can be tuned by changing doses of the Mn salt initially added. Moreover, decomposition of PAA during calcination endows high surface areas of the MHSPs. Catalytic oxidation of methylene blue (MB) with H2O2 was tested on the MHSPs. The results show that the MHSPs with hollow structure and high surface areas enhance the catalytic activity compare to the corresponding manganese oxide solid particles (MSPs). This strategy can also be used to synthesize other metal oxides (such as MgO and NiO) loaded hollow silica particles. PMID:23777863

  20. Graphene oxide thin film coated quartz crystal microbalance for humidity detection

    NASA Astrophysics Data System (ADS)

    Yao, Yao; Chen, Xiangdong; Guo, Huihui; Wu, Zuquan

    2011-06-01

    In this paper, we demonstrated that chemically derived graphene oxide (GO) thin film as a humidity sensitive coating deposited on quartz crystal microbalances (QCMs) for humidity detection. By exposing GO thin film coated QCMs to various relative humidity (RH) environments at room temperature, the humidity sensing characteristics of the QCMs such as sensitivity and linearity, response and recovery, humidity hysteresis were investigated. The experiment results show that GO thin film coated QCMs exhibit an excellent humidity sensing performance. Moreover, the possible humidity sensing mechanism of GO thin film coated QCMs was also investigated by monitoring the crystal's motional resistance change. It is suggested that the frequency response of the QCMs is dependent on water molecules adsorbed/desorbed masses on GO thin film in the low RH range, and on both water molecules adsorbed/desorbed masses on GO thin film and variations in interlayer expansion stress of GO thin film derived from swelling effect in the high RH range.

  1. Significant role of Mn(III) sites in e(g)(1) configuration in manganese oxide catalysts for efficient artificial water oxidation.

    PubMed

    Indra, Arindam; Menezes, Prashanth W; Schuster, Felix; Driess, Matthias

    2015-11-01

    Development of efficient bio-inspired water oxidation system with transition metal oxide catalyst has been considered as the one of the most challenging task in the recent years. As the oxygen evolving center of photosystem II consists of Mn4CaO5 cluster, most of the water oxidation study was converged to build up manganese oxide based catalysts. Here we report the synthesis of efficient artificial water oxidation catalysts by transferring the inactive manganese monooxide (MnO) under highly oxidizing conditions with ceric ammonium nitrate (CAN) and ozone (O3). MnO was partially oxidized to form mixed-valent manganese oxide (MnOx) with CAN whereas completely oxidized to mineral phase of ?-MnO2 (Akhtenskite) upon treatment of O3 in acidic solution, which we explore first time as a water oxidation catalyst. Chemical water oxidation, as well as the photochemical water oxidation in the presence of sacrificial electron acceptor and photosensitizer with the presented catalysts were carried out that followed the trends: MnOx>MnO2>MnO. Structural and activity correlation reveals that the presence of larger extent of Mn(III) in MnOx is the responsible factor for higher activity compared to MnO2. Mn(III) species in octahedral system with eg(1) configuration furnishes and facilitates the Mn-O and Mn-Mn bond enlargement with required structural flexibility and disorder in the manganese oxide structure which indeed facilitates water oxidation. PMID:25542875

  2. Manganese oxides: parallels between abiotic and biotic structures.

    PubMed

    Saratovsky, Ian; Wightman, Peter G; Pastn, Pablo A; Gaillard, Jean-Franois; Poeppelmeier, Kenneth R

    2006-08-30

    A large number of microorganisms are responsible for the oxidation of Mn(2+)((aq)) to insoluble Mn(3+/4+) oxides (MnO(x)()) in natural aquatic systems. This paper reports the structure of the biogenic MnO(x)(), including a quantitative analysis of cation vacancies, formed by the freshwater bacterium Leptothrix discophora SP6 (SP6-MnO(x)()). The structure and the morphology of SP6-MnO(x)() were characterized by transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), including full multiple-scattering analysis, and powder X-ray diffraction (XRD). The biogenic precipitate consists of nanoparticles that are approximately 10 nm by 100 nm in dimension with a fibrillar morphology that resembles twisted sheets. The results dem-onstrate that this biogenic MnO(x)() is composed of sheets of edge-sharing of Mn(4+)O(6) octahedra that form layers. The detailed analysis of the EXAFS spectra indicate that 12 +/- 4% of the Mn(4+) layer cation sites in SP6-MnO(x)() are vacant, whereas the analysis of the XANES suggests that the average oxidation state of Mn is 3.8 +/- 0.3. Therefore, the average chemical formula of SP6-MnO(x)() is M(n)()(+)(y)()Mn(3+)(0.12)[ square(0.12)Mn(4+)(0.88)]O(2).zH(2)O, where M(n)()(+)(y)() represents hydrated interlayer cations, square(0.12) represents Mn(4+) cation vacancies within the layer, and Mn(3+)(0.12) represents hydrated cations that occupy sites above/below these cation vacancies. PMID:16925437

  3. Nanocrystalline todorokite-like manganese oxide produced by bacterial catalysis.

    PubMed

    Kim, Hack-Sung; Pastn, Pablo A; Gaillard, Jean-Franois; Stair, Peter C

    2003-11-26

    We describe the characterization of an unknown and difficult to identify but geochemically and environmentally significant MnOx structure produced by a freshwater bacterium, Leptothrix discophora SP-6, using combined transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), and UV Raman spectroscopy. The large surface-to-volume ratio of the needle-shaped nanocrystalline MnO2 formed around the bacterial cells coupled to the porous, zeolite-like structure has the potential to catalyze reactions and oxidize and adsorb metals. PMID:14624570

  4. Relationship between external and internal parameters of exposure to manganese in workers from a manganese oxide and salt producing plant

    SciTech Connect

    Roels, H.; Lauwerys, R.; Genet, P.; Sarhan, M.J.; de Fays, M.; Hanotiau, I.; Buchet, J.P.

    1987-01-01

    In a plant producing manganese (Mn) oxides and salts, 11 different workplaces were identified. The current exposure to airborne Mn (total dust, personal sampling, n = 80) varied from 0.07 to 8.61 mg/m3. The geometric mean and median values amounted approximately to 1 mg/m3 and the 95th percentile was 3.30 mg/m3. The concentration of Mn in blood (Mn-B) in a group of 141 Mn-exposed male workers ranged from 0.10-3.59 micrograms/100 ml compared to 0.04-1.31 micrograms/100 ml in a group of 104 control subjects. The ranges of the concentrations of Mn in urine (Mn-U) were 0.06-140.6 and 0.01-5.04 micrograms/g creatinine for the exposed and control groups, respectively. The average level of Mn-B in the Mn group was more than twice as high as in the control group (arithmetic mean, 1.36 vs 0.57 microgram/100 ml) and that of Mn-U was ten times higher in the Mn group (geometric mean, 1.56 vs 0.15 microgram/g creatinine). The Mn-B level did not change significantly after 8 h of Mn exposure, whereas the Mn-U level dropped rapidly when exposure ceased (half-life less than 30 h). On an individual basis, neither Mn-B nor Mn-U correlated with the current levels of Mn-air or duration of Mn exposure. There was also no relationship between Mn-B and Mn-U. On a group basis, there was no correlation between the mean Mn-B levels and the current levels of Mn-air at each workplace.

  5. Effects of solar radiation on manganese oxide reactions with selected organic compounds

    SciTech Connect

    Bertino, D.J.; Zepp, R.G. )

    1991-07-01

    The effects of sunlight on aqueous redox reactions between manganese oxides (MnO{sub x}) and selected organic substances are reported. No sunlight-induced rate enhancement was observed for the MnO{sub x} oxidation of substituted phenols, anisole, o-dichlorobenzene, or p-chloroaniline. On the other hand, solar radiation did accelerate the reduction of manganese oxides by dissolved organic matter (DOM) from aquatic environments. The photoreduction of MnO{sub x} by DOM was little affected by molecular oxygen in air-saturated water (250 {mu}M), but was inhibited by 2,6-dichloroindophenol (0.5-6 {mu}M), and excellent electron acceptor. MnO{sub x} reduction also was photosensitized by anthraquinone-2-sulfonate. These results indicate that the photoreduction probably involves electron transfer from excited states of sorbed DOM to the oxide surface. Wavelength studies indicated that ultraviolet-B radiation (280-320 nm) plays an important role in this photoreduction.

  6. Scalable Synthesis of Efficient Water Oxidation Catalysts: Insights into the Activity of Flame-Made Manganese Oxide Nanocrystals.

    PubMed

    Liu, Guanyu; Hall, Jeremy; Nasiri, Noushin; Gengenbach, Thomas; Spiccia, Leone; Cheah, Mun Hon; Tricoli, Antonio

    2015-12-01

    Chemical energy storage by water splitting is a promising solution for the utilization of renewable energy in numerous currently impracticable needs, such as transportation and high temperature processing. Here, the synthesis of efficient ultra-fine Mn3 O4 water oxidation catalysts with tunable specific surface area is demonstrated by a scalable one-step flame-synthesis process. The water oxidation performance of these flame-made structures is compared with pure Mn2 O3 and Mn5 O8 , obtained by post-calcination of as-prepared Mn3 O4 (115?m(2) ?g(-1) ), and commercial iso-structural polymorphs, probing the effect of the manganese oxidation state and synthetic route. The structural properties of the manganese oxide nanoparticles were investigated by XRD, FTIR, high-resolution TEM, and XPS. It is found that these flame-made nanostructures have substantially higher activity, reaching up to 350?% higher surface-specific turnover frequency (0.07??molO2 ?m(-2) ?s(-1) ) than commercial nanocrystals (0.02??molO2 ?m(-2) ?s(-1) ), and production of up to 0.33?mmolO2 ?molMn (-1) ?s(-1) . Electrochemical characterization confirmed the high water oxidation activity of these catalysts with an initial current density of 10?mA?cm(-2) achieved with overpotentials between 0.35 and 0.50?V in 1?m NaOH electrolyte. PMID:26601653

  7. Metal Inhibition of Growth and Manganese Oxidation in Pseudomonas putida GB-1

    NASA Astrophysics Data System (ADS)

    Pena, J.; Sposito, G.

    2009-12-01

    Biogenic manganese oxides (MnO2) are ubiquitous nanoparticulate minerals that contribute to the adsorption of nutrient and toxicant metals, the oxidative degradation of various organic compounds, and the respiration of metal-reducing bacteria in aquatic and terrestrial environments. The formation of these minerals is catalyzed by a diverse and widely-distributed group of bacteria and fungi, often through the enzymatic oxidation of aqueous Mn(II) to Mn(IV). In metal-impacted ecosystems, toxicant metals may alter the viability and metabolic activity of Mn-oxidizing organisms, thereby limiting the conditions under which biogenic MnO2 can form and diminishing their potential as adsorbent materials. Pseudomonas putida GB-1 (P. putida GB-1) is a model Mn-oxidizing laboratory culture representative of freshwater and soil biofilm-forming bacteria. Manganese oxidation in P. putida GB-1 occurs via two single-electron-transfer reactions, involving a multicopper oxidase enzyme found on the bacterial outer membrane surface. Near the onset of the stationary phase of growth, dark brown MnO2 particles are deposited in a matrix of bacterial cells and extracellular polymeric substances, thus forming heterogeneous biomineral assemblages. In this study, we assessed the influence of various transition metals on microbial growth and manganese oxidation capacity in a P. putida GB-1 culture propagated in a nutrient-rich growth medium. The concentration-response behavior of actively growing P. putida GB-1 cells was investigated for Fe, Co, Ni, Cu and Zn at pH ≈ 6 in the presence and absence of 1 mM Mn. Toxicity parameters such as EC0, EC50 and Hillslope, and EC100 were obtained from the sigmoidal concentration-response curves. The extent of MnO2 formation in the presence of the various metal cations was documented 24, 50, 74 and 104 h after the metal-amended medium was inoculated. Toxicity values were compared to twelve physicochemical properties of the metals tested. Significant correlations were found between EC50 values and reduction potential, electronegativity and the covalent index. Thus, metal toxicity in P. putida GB-1 appears to be modulated by the metals’ propensity to participate in covalent interactions and generate oxidative stress. This study provides a quantitative measure of metal tolerance in P. putida GB-1, as well as operational limits for Mn oxidation in this model system, both of which have important implications for the reactivity of P. putida-MnO2 assemblages formed in metal-impacted ecosystems.

  8. The ability of oxidative stress to mimic quartz-induced chemokine responses is lung cell line-dependent.

    PubMed

    Ovrevik, Johan; Refsnes, Magne; Schwarze, Per; Lg, Marit

    2008-09-26

    Oxidative stress induced by surface-generated radicals has been a dominating hypothesis to explain how mineral particles and fibers trigger cellular responses. However, conflicting studies suggest that the importance of particle-derived formation of reactive oxygen species (ROS) requires further examination. The present study focuses on whether oxidative stress in the form of H(2)O(2)-exposure may mimic the effects of quartz particles on chemokine responses in epithelial lung cells. The results show that H(2)O(2) and quartz exposure induced almost identical levels of CXCL8 (interleukin-8) release in the alveolar epithelial cell line A549, but in the bronchial epithelial cell line BEAS-2B, H(2)O(2)-exposure did not affect CXCL8 release significantly, whereas quartz induced a 16-fold increase. Among 17 different cytokine and chemokine genes H(2)O(2) induced up-regulation of only IL-5 in BEAS-2B cells, while quartz increased the expression of 8 different cytokines and chemokines. In A549 cells, however, there was a moderate but significant correlation between the cytokine/chemokine gene-expression profiles induced by the two agents. Thus, the response to oxidative stress may vary considerably between different lung cell lines. Moreover, the results from the BEAS-2B cells strengthen the notion that non-oxidant initiation mechanisms may also be important to the effects of mineral particles and fibers. PMID:18662758

  9. The Role of High Molecular Weight Polyethylene Oxide in Reducing Quartz Gangue Entrainment in Chalcopyrite Flotation by Xanthate Collectors

    NASA Astrophysics Data System (ADS)

    Gong, Jihua

    Fine particles pose two challenging problems to all mineral processors around the world today. The problems are the inefficient collection of hydrophobic particles (low recovery), and mechanical/hydraulic entrainment of hydrophilic gangue particles (low concentrate grade). Extensive research has been conducted to improve the flotation recovery of fine hydrophobic particles. However, much less effort was made to lower the mechanical/hydraulic entrainment of fine gangue mineral particles. In this study, polyethylene oxide (PEO) was used to flocculate and depress fine quartz particles. Batch flotation results indicated that the addition of low dosages of PEO improved value mineral recovery and concentrate grade in the flotation of artificial mixtures of chalcopyrite/quartz and a commercial Au-Cu sulfide ore sample. It was found that PEO adsorbed on both minerals mainly through hydrogen bonding and caused non-selective flocculation of quartz and chalcopyrite, forming large hetero-aggregates. However, the addition of potassium amyl xanthate (KAX), a specific sulfide mineral collector, adsorbed on chalcopyrite through chemical interaction, replaced PEO and caused the chalcopyrite particles to break away from the hetero-aggregates, forming separate homo-aggregates of quartz and chalcopyrite. The flotation of the chalcopyrite and the depression of the quartz were thus both improved due to the larger sizes of the homo-aggregates compared to the discrete particles. It was also observed that a completely solubilized PEO solution could not flocculate quartz, while a partially solubilized PEO solution was most effective. This was attributed to the better “bridging” functions of the undissolved PEO aggregates when it was partially solubilized. When the PEO was fully solubilized, the individual PEO molecules were probably too flexible and tended to flatten on the adsorbed solid surface and thus could not function as an effective bridging flocculant. Furthermore, it was found that PEO could function as a “collector” for quartz due to its affinity to air-water interface and quartz, and it could increase quartz entrainment when used at high dosages. Selective flocculation and depression of the quartz gangue during chalcopyrite flotation could only be achieved at low PEO dosages. The implication of these observations on how to utilize the polyethylene oxide in industrial flotation was discussed.

  10. Manganese(II)-oxidizing Bacillus spores in Guaymas Basin hydrothermal sediments and plumes.

    PubMed

    Dick, Gregory J; Lee, Yifan E; Tebo, Bradley M

    2006-05-01

    Microbial oxidation and precipitation of manganese at deep-sea hydrothermal vents are important oceanic biogeochemical processes, yet nothing is known about the types of microorganisms or mechanisms involved. Here we report isolation of a number of diverse spore-forming Mn(II)-oxidizing Bacillus species from Guaymas Basin, a deep-sea hydrothermal vent environment in the Gulf of California, where rapid microbially mediated Mn(II) oxidation was previously observed. mnxG multicopper oxidase genes involved in Mn(II) oxidation were amplified from all Mn(II)-oxidizing Bacillus spores isolated, suggesting that a copper-mediated mechanism of Mn(II) oxidation could be important at deep-sea hydrothermal vents. Phylogenetic analysis of 16S rRNA and mnxG genes revealed that while many of the deep-sea Mn(II)-oxidizing Bacillus species are very closely related to previously recognized isolates from coastal sediments, other organisms represent novel strains and clusters. The growth and Mn(II) oxidation properties of these Bacillus species suggest that in hydrothermal sediments they are likely present as spores that are active in oxidizing Mn(II) as it emerges from the seafloor. PMID:16672456

  11. Manganese(II)-Oxidizing Bacillus Spores in Guaymas Basin Hydrothermal Sediments and Plumes

    PubMed Central

    Dick, Gregory J.; Lee, Yifan E.; Tebo, Bradley M.

    2006-01-01

    Microbial oxidation and precipitation of manganese at deep-sea hydrothermal vents are important oceanic biogeochemical processes, yet nothing is known about the types of microorganisms or mechanisms involved. Here we report isolation of a number of diverse spore-forming Mn(II)-oxidizing Bacillus species from Guaymas Basin, a deep-sea hydrothermal vent environment in the Gulf of California, where rapid microbially mediated Mn(II) oxidation was previously observed. mnxG multicopper oxidase genes involved in Mn(II) oxidation were amplified from all Mn(II)-oxidizing Bacillus spores isolated, suggesting that a copper-mediated mechanism of Mn(II) oxidation could be important at deep-sea hydrothermal vents. Phylogenetic analysis of 16S rRNA and mnxG genes revealed that while many of the deep-sea Mn(II)-oxidizing Bacillus species are very closely related to previously recognized isolates from coastal sediments, other organisms represent novel strains and clusters. The growth and Mn(II) oxidation properties of these Bacillus species suggest that in hydrothermal sediments they are likely present as spores that are active in oxidizing Mn(II) as it emerges from the seafloor. PMID:16672456

  12. Simulation of the surface structure of lithium manganese oxide spinel

    NASA Astrophysics Data System (ADS)

    Benedek, R.; Thackeray, M. M.

    2011-05-01

    Simulations of the surface structure of low-index surfaces of LiMn2O4 (LMO), a candidate Li-ion battery electrode material, have been performed within the GGA+U approximation, using the VASP code. Surfaces of (001), (110), and (111) orientation were considered, with at least two terminations treated in each case. A slab geometry was employed, with termination-layer vacancies introduced to remove the bulk dipole moment while maintaining ideal stoichiometry. To complement static-structure relaxation calculations, molecular-dynamics simulations were performed to explore the phase space of possible surface reconstructions. A reconstruction is predicted for the Mn-terminated (111) surface, in which the top layers mix in stoichiometric proportions to form an LMO termination layer with square-planar-coordinated Mn. Average surface Mn oxidation states are reduced, relative to the bulk, for all surfaces considered, as a consequence of the lower-energy cost of Jahn-Teller distortion at the surface. Threefold-coordinated surface Mn, found for two terminations, is divalent, which may enhance its vulnerability to dissolution. The Li-terminated (001) surface is lowest in energy, consistent with previous classical-potential simulations for MgAl2O4 that showed the Mg-terminated (001) surface to be lowest in energy.

  13. Metalloradical complexes of manganese and chromium featuring an oxidatively rearranged ligand.

    PubMed

    Celenligil-Cetin, Remle; Paraskevopoulou, Patrina; Lalioti, Nikolia; Sanakis, Yiannis; Staples, Richard J; Rath, Nigam P; Stavropoulos, Pericles

    2008-12-01

    Redox events involving both metal and ligand sites are receiving increased attention since a number of biological processes direct redox equivalents toward functional residues. Metalloradical synthetic analogues remain scarce and require better definition of their mode of formation and subsequent operation. The trisamido-amine ligand [(RNC6H4)3N]3-, where R is the electron-rich 4-t-Bu Ph, is employed in this study to generate redox active residues in manganese and chromium complexes. Solutions of [(L1)Mn(II)-THF]- in THF are oxidized by dioxygen to afford [(L1re-1)Mn(III)-(O)2-Mn(III)(L1 re-1)]2-as the major product. The rare dinuclear manganese (III,III) core is stabilized by a rearranged ligand that has undergone an one-electron oxidative transformation, followed by retention of the oxidation equivalent as a pi radical in ano-diiminobenzosemiquinonate moiety. Magnetic studies indicate that the ligand-centered radical is stabilized by means of extended antiferromagnetic coupling between the S ) 1/2 radical and the adjacent S ) 2 Mn(III) site, as well as between the two Mn(III) centers via the dioxo bridge. Electrochemical and EPR data suggest that this system can store higher levels of oxidation potency. Entry to the corresponding Cr(III) chemistry is achieved by employing CrCl3 to access both[(L1)Cr(III)-THF] and [(L1re-1)Cr(III)-THF(Cl)], featuring the intact and the oxidatively rearranged ligands, respectively. The latter is generated by ligand-centered oxidation of the former compound. The rearranged ligand is perceived to be the product of an one-electron oxidation of the intact ligand to afford a metal-bound aminyl radical that subsequently mediates a radical 1,4-(N-to-N) aryl migration. PMID:18937446

  14. Metalloradical Complexes of Manganese and Chromium Featuring an Oxidatively Rearranged Ligand

    PubMed Central

    Çelenligil-Çetin, Remle; Paraskevopoulou, Patrina; Lalioti, Nikolia; Sanakis, Yiannis; Staples, Richard J.; Rath, Nigam P.; Stavropoulos, Pericles

    2009-01-01

    Redox events involving both metal and ligand sites are receiving increased attention since a number of biological processes direct redox equivalents toward functional residues. Metalloradical synthetic analogs remain scarce and require better definition of their mode of formation and subsequent operation. The trisamido-amine ligand [(RNC6H4)3N]3−, where R is the electron-rich 4-t-BuPh, is employed in this study to generate redox active residues in manganese and chromium complexes. Solutions of [(L1)Mn(II)–THF]− in THF are oxidized by dioxygen to afford [(L1re–1)Mn(III)–(O)2–Mn(III)(L1re–1)]2− as the major product. The rare dinuclear manganese (III,III) core is stabilized by a rearranged ligand that has undergone an one-electron oxidative transformation, followed by retention of the oxidation equivalent as a π radical in an o-diiminobenzosemiquinonate moiety. Magnetic studies indicate that the ligand-centered radical is stabilized by means of extended antiferromagnetic coupling between the S = ½ radical and the adjacent S = 2 Mn(III) site, as well as between the two Mn(III) centers via the dioxo bridge. Electrochemical and EPR data suggest that this system can store higher levels of oxidation potency. Entry to the corresponding Cr(III) chemistry is achieved by employing CrCl3 to access both [(L1)Cr(III)–THF] and [(L1re–1)Cr(III)–THF(Cl)], featuring the intact and the oxidatively rearranged ligands, respectively. The latter is generated by ligand-centered oxidation of the former compound. The rearranged ligand is perceived to be the product of an one-electron oxidation of the intact ligand to afford a metal-bound aminyl radical that subsequently mediates a radical 1,4-(N-to-N) aryl migration. PMID:18937446

  15. Coprecipitation and redox reactions of manganese oxides with copper and nickel

    USGS Publications Warehouse

    Hem, J.D.; Lind, Carol J.; Roberson, C.E.

    1989-01-01

    Open-system, continuous-titration experiments have been done in which a slow flux of ???0.02 molar solution of Mn2+ chloride, nitrate, or perchlorate with Cu2+ or Ni2+ in lesser concentrations was introduced into an aerated reactor solution held at constant temperature and at constant pH by a pH-stat titrator that added dilute NaOH. The resulting mixtures of metal oxyhydroxides and their native solutions were aged for periods as long as 2 1/2 years. Fresh and aged precipitates were characterized by chemical analysis, oxidation state determinations, X-ray and electron diffraction, and electron microscopy. The precipitates can be described as mixtures of oxide and oxyhydroxide species, using concepts of equilibrium and nonequilibrium chemical thermodynamics. The metal-ion content of the aged precipitates in systems that contained copper is distributed among three principal components. One of these is a mixed oxide Cu2Mn3O8 in which all Mn is in the 4+ oxidation state. A major component in all precipitates is feitknechtite, ??MnOOH. These forms are supplemented by CuO or by birnessite or ramsdellite forms of MnO2 where stoichiometry and thermodynamic calculations predict them. In systems that contained nickel and manganese, identifiable components included ??MnOOH, Ni(OH)2, and the same two forms of MnO2. The oxidation number of the precipitated manganese increased during aging, and the pH of the supernatant solution decreased. The maximum Mn oxidation number observed was 3.55 in an Mn + Cu precipitate aged for 18 months. Concentrations of Cu2+ and Ni2+ generally decreased to values substantially below those predicted by oxide or hydroxide equilibrium. Scavenging effects of this type are common in natural aqueous systems. ?? 1989.

  16. Illumina sequencing of fungi associated with manganese oxide deposits in cave systems

    NASA Astrophysics Data System (ADS)

    Zorn, B. T.; Santelli, C. M.; Carmichael, S. K.; Pepe-Ranney, C. P.; Roble, L.; Carmichael, M.; Bräuer, S.

    2013-12-01

    The environmental cycling of manganese (Mn) remains relatively poorly characterized when compared with other metals such as iron. However, fungi have been observed to produce Mn(III/IV) oxides resembling buserite, birnessite, and todorokite on the periphery of vegetative hyphae, hyphal branching points and at the base of fruiting bodies. Recent studies indicate that some of these oxides may be generated by a two-stage reaction with soluble Mn(II) and biogenic reactive oxygen species for some groups of fungi, in particular the Ascomycota. These oxides can provide a versatile protective barrier or aid in the capture of trace metals in the environment, although the exact evolutionary function and trigger is unclear. In this study, two caves in the southern Appalachians, a pristine cave and an anthropogenically impacted cave, were compared by analyzing fungal community assemblages in manganese oxide rich deposits. Quantitative PCR data indicated that fungi are present in a low abundance (<1%) in all locations sampled within the caves. Among amplified DNA sequences retrieved in an 18S rDNA clone library, over 88% were representative of the phylum Basidiomycota (predominantly Agaricomycetes), 2.74% of Ascomycota, 2.28% of Blastocladiomycota and Chytridiomycota, 0.46% of Zygomycota, and 3.65% of Eukarya or Fungi incertae sedis. Using Illumina's MiSeq to sequence amplicons of the fungal ITS1 gene has yielded roughly 100,000-200,000 paired-end reads per sample. These data are currently being analyzed to compare fungal communities before and after induced Mn oxidation in the field. In addition, sites within the pristine cave are being compared with analogous sites in the impacted cave. Culturing efforts have thus far yielded Mn oxide producing members of the orders Glomerales and Pleosporales as well as two Genus incertae sedis (Fungal sp. YECT1, and Fungal sp. YECT3, growing on discarded electrical tape) that do not appear to be closely related to any other known Mn oxidizing fungi.

  17. The Structure and Properties of Plasma Sprayed Iron Oxide Doped Manganese Cobalt Oxide Spinel Coatings for SOFC Metallic Interconnectors

    NASA Astrophysics Data System (ADS)

    Puranen, Jouni; Lagerbom, Juha; Hyvärinen, Leo; Kylmälahti, Mikko; Himanen, Olli; Pihlatie, Mikko; Kiviaho, Jari; Vuoristo, Petri

    2011-01-01

    Manganese cobalt oxide spinel doped with Fe2O3 was studied as a protective coating on ferritic stainless steel interconnects. Chromium alloying causes problems at high operation temperatures in such oxidizing conditions where chromium compounds evaporate and poison the cathode active area, causing the degradation of the solid oxide fuel cell. In order to prevent chromium evaporation, these interconnectors need a protective coating to block the chromium evaporation and to maintain an adequate electrical conductivity. Thermal spraying is regarded as a promising way to produce dense and protective layers. In the present work, the ceramic Mn-Co-Fe oxide spinel coatings were produced by using the atmospheric plasma spray process. Coatings with low thickness and low amount of porosity were produced by optimizing deposition conditions. The original spinel structure decomposed because of the fast transformation of solid-liquid-solid states but was partially restored by using post-annealing treatment.

  18. Chemical and optical properties of thermally evaporated manganese oxide thin films

    SciTech Connect

    Al-Kuhaili, M. F.

    2006-09-15

    Manganese oxide thin films were deposited using thermal evaporation from a tungsten boat. Films were deposited under an oxygen atmosphere, and the effects of thickness, substrate temperature, and deposition rate on their properties were investigated. The chemical properties of the films were studied using x-ray photoelectron spectroscopy and x-ray fluorescence. The optical properties were determined from normal-incidence transmittance and reflectance. Based on the chemical and optical characterizations, the optimum conditions for the deposition of the films were investigated. Subsequently, the optical properties (refractive index, extinction coefficient, and band gap) of these films were determined.

  19. Dual Effect of Manganese Oxide Micromotors: Catalytic Degradation and Adsorptive Bubble Separation of Organic Pollutants.

    PubMed

    Wani, Owies M; Safdar, Muhammad; Kinnunen, Niko; Jnis, Janne

    2016-01-01

    Manganese oxide (MnO2 ) based micromotors exhibiting a dual effect, that is, catalytic degradation and adsorptive bubble separation, were employed for water remediation. The dual effect of MnO2 microparticles led to a greater than 90?% of decolorization of non-biodegradable organic dyes in just 1?h, without the need for external agitation or bubble generation. These findings suggest high potential of MnO2 micromotors for decontamination of organic pollutants from wastewaters or natural water reserves. PMID:26604046

  20. Nanostructured and layered lithium manganese oxide and method of manufacturing the same

    NASA Technical Reports Server (NTRS)

    Singhal, Amit (Inventor); Skandan, Ganesh (Inventor)

    2005-01-01

    Nanostructured and layered lithium manganese oxide powders and methods of producing same. The powders are represented by the chemical formula, LixMn1-yMyO2, where 0.5

  1. Heterogeneous catalytic ozonation of ciprofloxacin in water with carbon nanotube supported manganese oxides as catalyst.

    PubMed

    Sui, Minghao; Xing, Sichu; Sheng, Li; Huang, Shuhang; Guo, Hongguang

    2012-08-15

    Carbon nanotube-supported manganese oxides (MnOx/MWCNT) were used as catalysts to assist ozone in degrading ciprofloxacin in water. Manganese oxides were successfully loaded on multi-walled carbon nanotube surfaces by simply impregnating the carbon nanotube with permanganate solution. The catalytic activities of MnOx/MWCNT in ciprofloxacin ozonation, including degradation, mineralization effectiveness, and antibacterial activity change, were investigated. The presence of MnOx/MWCNT significantly elevated the degradation and mineralization efficiency of ozone on ciprofloxacin. The microbiological assay with a reference Escherichia coli strain indicated that ozonation with MnOx/MWCNT results in more effective antibacterial activity inhibition of ciprofloxacin than that in ozonation alone. The effects of catalyst dose, initial ciprofloxacin concentration, and initial pH conditions on ciprofloxacin ozonation with MnOx/MWCNT were surveyed. Electron spin resonance trapping was applied to assess the role of MnOx/MWCNT in generating hydroxyl radicals (HO) during ozonation. Stronger 5,5-dimethyl-1-pyrroline-N-oxide-OH signals were observed in the ozonation with MnOx/MWCNT compared with those in ozonation alone, indicating that MnOx/MWCNT promoted the generation of hydroxyl radicals. The degradation of ciprofloxacin was studied in drinking water and wastewater process samples to gauge the potential effects of water background matrix on MnOx/MWCNT catalytic ozonation. PMID:22658829

  2. Pathogenic prion protein is degraded by a manganese oxide mineral found in soils

    USGS Publications Warehouse

    Russo, F.; Johnson, C.J.; McKenzie, D.; Aiken, Judd M.; Pedersen, J.A.

    2009-01-01

    Prions, the aetiological agents of transmissible spongiform encephalopathies, exhibit extreme resistance to degradation. Soil can retain prion infectivity in the environment for years. Reactive soil components may, however, contribute to the inactivation of prions in soil. Members of the birnessite family of manganese oxides (MnO2) rank among the strongest natural oxidants in soils. Here, we report the abiotic degradation of pathogenic prion protein (PrPTSE) by a synthetic analogue of naturally occurring birnessite minerals. Aqueous MnO2 suspensions degraded the PrPTSE as evidenced by decreased immunoreactivity and diminished ability to seed protein misfolding cyclic amplification reactions. Birnessite-mediated PrPTSE degradation increased as a solution's pH decreased, consistent with the pH-dependence of the redox potential of MnO2. Exposure to 5.6 mg MnO2 ml-1 (PrPTSE:MnO2=1 : 110) decreased PrPTSE levels by ???4 orders of magnitude. Manganese oxides may contribute to prion degradation in soil environments rich in these minerals. ?? 2009 SGM.

  3. Photocatalytic Water Oxidation Using Manganese Compounds Immobilized in Nafion Polymer Membranes

    PubMed Central

    Young, Karin J.; Gao, Yunlong; Brudvig, Gary W.

    2011-01-01

    Robust water oxidation catalysts using earth abundant metals are required as part of an overall scheme to convert sunlight into fuels. Here, we report the immobilization of [Mn4IVO5(terpy)4(H2O)2](ClO4)6 (terpy = 2,2?;6?,2?-terpyridine), [Mn4O6(tacn)4](ClO4)4 (tacn = 1,4,7-triazacyclononane), and manganese dioxide nanoparticles in Nafion on fluorine-doped tin oxide conducting glass electrodes. The electrodes are illuminated with white light in the presence of an applied potential and the resulting photocurrent is assigned to the oxidation of solvent water. Photodecomposition of the tetrameric complexes results in a material that is more active for light-driven electrooxidation of water. The reactivity, wavelength dependence, and stability of the compounds in Nafion under illumination are discussed. PMID:22140273

  4. Highly Efficient Elimination of Carbon Monoxide with Binary Copper-Manganese Oxide Contained Ordered Nanoporous Silicas.

    PubMed

    Lee, Jiho; Kim, Hwayoun; Lee, Hyesun; Jang, Seojun; Chang, Jeong Ho

    2016-12-01

    Ordered nanoporous silicas containing various binary copper-manganese oxides were prepared as catalytic systems for effective carbon monoxide elimination. The carbon monoxide elimination efficiency was demonstrated as a function of the [Mn]/[Cu] ratio and reaction time. The prepared catalysts were characterized by Brunauer-Emmett-Teller (BET) method, small- and wide-angle X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM) for structural analysis. Moreover, quantitative analysis of the binary metal oxides within the nanoporous silica was achieved by inductively coupled plasma (ICP). The binary metal oxide-loaded nanoporous silica showed high room temperature catalytic efficiency with over 98 % elimination of carbon monoxide at higher concentration ratio of [Mn]/[Cu]. PMID:26744146

  5. Highly Efficient Elimination of Carbon Monoxide with Binary Copper-Manganese Oxide Contained Ordered Nanoporous Silicas

    NASA Astrophysics Data System (ADS)

    Lee, Jiho; Kim, Hwayoun; Lee, Hyesun; Jang, Seojun; Chang, Jeong Ho

    2016-01-01

    Ordered nanoporous silicas containing various binary copper-manganese oxides were prepared as catalytic systems for effective carbon monoxide elimination. The carbon monoxide elimination efficiency was demonstrated as a function of the [Mn]/[Cu] ratio and reaction time. The prepared catalysts were characterized by Brunauer-Emmett-Teller (BET) method, small- and wide-angle X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM) for structural analysis. Moreover, quantitative analysis of the binary metal oxides within the nanoporous silica was achieved by inductively coupled plasma (ICP). The binary metal oxide-loaded nanoporous silica showed high room temperature catalytic efficiency with over 98 % elimination of carbon monoxide at higher concentration ratio of [Mn]/[Cu].

  6. Trace metal-rich Quaternary hydrothermal manganese oxide and barite deposit, Milos Island, Greece

    USGS Publications Warehouse

    Hein, J.R.; Stamatakis, G.; Dowling, J.S.

    2000-01-01

    The Cape Vani Mn oxide and barite deposit on Milos Island offers an excellent opportunity to study the three-dimensional characteristics of a shallow-water hydrothermal system. Milos Island is part of the active Aegean volcanic arc. A 1 km long basin located between two dacitic domes in northwest Milos is filled with a 35-50 m thick section of Quaternary volcaniclastic and pyroclastic rocks capped by reef limestone that were hydrothermally mineralized by Mn oxides and barite. Manganese occurs as thin layers, as cement of sandstone and as metasomatic replacement of the limestone, including abundant fossil shells. Manganese minerals include chiefly δ-MnO2, pyrolusite and ramsdellite. The MnO contents for single beds range up to 60%. The Mn oxide deposits are rich in Pb (to 3.4%), BaO (to 3.1%), Zn (to 0.8%), As (to 0.3%), Sb (to 0.2%) and Ag (to 10 ppm). Strontium isotopic compositions of the Mn oxide deposits and sulphur isotopic compositions of the associated barite show that the mineralizing fluids were predominantly sea water. The Mn oxide deposit formed in close geographical proximity to sulphide-sulphate-Au-Ag deposits and the two deposit types probably formed from the same hydrothermal system. Precipitation of Mn oxide took place at shallow burial depths and was promoted by the mixing of modified sea water (hydrothermal fluid) from which the sulphides precipitated at depth and sea water that penetrated along faults and fractures in the Cape Vani volcaniclastic and tuff deposits. The hydrothermal fluid was formed from predominantly sea water that was enriched in metals leached from the basement and overlying volcanogenic rocks. The hydrothermal fluids were driven by convection sustained by heat from cooling magma chambers. Barite was deposited throughout the time of Mn oxide mineralization, which occurred in at least two episodes. Manganese mineralization occurred by both focused and diffuse flow, the fluids mineralizing the beds of greatest porosity and filling dilatational fractures along with barite.

  7. Role of Reactive Intermediates in Manganese Oxide Formation By Filamentous Ascomycete Fungi

    NASA Astrophysics Data System (ADS)

    Zeiner, C. A.; Anderton, C.; Wu, S.; Purvine, S.; Zink, E.; Paša-Tolić, L.; Santelli, C. M.; Hansel, C. M.

    2014-12-01

    Biogenic manganese (Mn) oxide minerals are ubiquitous in the environment, and their high reactivity can profoundly impact the fate of contaminants and cycling of carbon and nutrients. In contrast to bacteria, the pathways utilized by fungi to oxidize Mn(II) to Mn(III,IV) oxides remain largely unknown. Here, we explore the mechanisms of Mn(II) oxidation by a phylogenetically diverse group of filamentous Ascomycete fungi using a combination of chemical assays and bulk and spatially-resolved mass spectrometry. We show that the mechanisms of Mn(II) oxidation vary with fungal species, over time during secretome compositional changes, and in the presence of other fungi. Specifically, our work implicates a dynamic transition in Mn(II) oxidation pathways that varies between species. In particular, while reactive oxygen species (ROS) produced via transmembrane NADPH oxidases are involved in initial oxidation, over time, secreted enzymes become important Mn(II) oxidation mediators for some species. In addition, the overall secretome oxidation capacity varies with time and fungal species. Secretome analysis reveals a surprising absence of enzymes currently considered to be Mn(II)-oxidizing enzymes in these organisms, and instead highlights a wide variety of redox-active enzymes. Furthermore, we implicate fungal cell defense mechanisms in the formation of distinct Mn oxide patterns when fungi are grown in head-to-head competition. The identification and regulation of these secreted enzymes are under current investigation within the bulk secretome and within the interaction zone of structured fungal communities. Overall, our findings illustrate that Ascomycete Mn(II) oxidation mechanisms are highly variable and are dictated by complex environmental and ecological interactions. Future work will explore the connection between Ascomycete Mn(II) oxidation and the ability to degrade cellulose, a key carbon reservoir for biofuel production.

  8. Manganese Oxide Nanoarchitectures as Broad-Spectrum Sorbents for Toxic Gases.

    PubMed

    Long, Jeffrey W; Wallace, Jean M; Peterson, Gregory W; Huynh, Kim

    2016-01-20

    We demonstrate that sol-gel-derived manganese oxide (MnOx) nanoarchitectures exhibit broad-spectrum filtration activity for three chemically diverse toxic gases: NH3, SO2, and H2S. Manganese oxides are synthesized via the reaction of NaMnO4 and fumaric acid to form monolithic gels of disordered, mixed-valent Na-MnOx; incorporated Na(+) is readily exchanged for H(+) by subsequent acid rinsing to form a more crystalline H-MnOx phase. For both Na-MnOx and H-MnOx forms, controlled pore-fluid removal yields either densified, yet still mesoporous, xerogels or low-density aerogels (prepared by drying from supercritical CO2). The performance of these MnOx nanoarchitectures as filtration media is assessed using dynamic-challenge microbreakthrough protocols. We observe technologically relevant sorption capacities under both dry conditions and wet (80% relative humidity) for each of the three toxic industrial chemicals investigated. The Na-MnOx xerogels and aerogels provide optimal performance with the aerogel exhibiting maximum sorption capacities of 39, 200, and 680 mg g(-1) for NH3, SO2, and H2S, respectively. Postbreakthrough characterization using X-ray photoelectron spectroscopy (XPS) and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms that NH3 is captured and partially protonated within the MnOx structure, while SO2 undergoes oxidation by the redox-active oxide to form adsorbed sulfate at the MnOx surface. Hydrogen sulfide is also oxidized to form a combination of sulfate and sulfur/polysulfide products, concomitant with a decrease in the average Mn oxidation state from 3.43 to 2.94 and generation of a MnOOH phase. PMID:26741498

  9. Electrochemical Sensor Based on Carbon Paste Electrode Modified with Nanostructured Crypotomelane-Type Manganese Oxides for Detection of Heavy Metals

    SciTech Connect

    Cui, Xiaoli; Liu, Guodong; Li, Liyu; Yantasee, Wassana; Lin, Yuehe

    2005-02-03

    A carbon paste electrode modified with nanostructured crypotomelane type manganese oxides was evaluated as new electrochemical sensor for the detection of heavy metal ions in aqueous media. The crypotomelane type manganese oxides are nanofibrous crystals with sub-nanometer tunnels which provide excellent sites for ion-exchanges. The adsorptive stripping voltammetry (ASV) technique involves preconcentration of the metal ions into nanostructured crypotomelane type manganese oxides under an open circuit, then electrolysis of the preconcentrated species, followed by a square-wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated using lead ion as the model analyte. The voltammetric responses increased with the preconcentration time from 2 to 30 min, and also linearly with lead ion concentrations ranging from 50 to 1200 ppb. The detection limits of target metal ion were 10 ppb after 4 min preconcentration and improved to 1 ppb after 20 min preconcentration. The potential for simultaneous detection of copper, silver and lead is also discussed.

  10. Solution Layer Deposition: A Technique for the Growth of Ultra-Pure Manganese Oxides on Silica at Room Temperature.

    PubMed

    Cure, Jérémy; Piettre, Kilian; Coppel, Yannick; Beche, Eric; Esvan, Jérôme; Collière, Vincent; Chaudret, Bruno; Fau, Pierre

    2016-02-01

    With the ever increasing miniaturization in microelectronic devices, new deposition techniques are required to form high-purity metal oxide layers. Herein, we report a liquid route to specifically produce thin and conformal amorphous manganese oxide layers on silicon substrate, which can be transformed into a manganese silicate layer. The undesired insertion of carbon into the functional layers is avoided through a solution metal-organic chemistry approach named Solution Layer Deposition (SLD). The growth of a pure manganese oxide film by SLD takes place through the decoordination of ligands from a metal-organic complex in mild conditions, and coordination of the resulting metal atoms on a silica surface. The mechanism of this chemical liquid route has been elucidated by solid-state (29) Si MAS NMR, XPS, SIMS, and HRTEM. PMID:26822812

  11. Pretreatment of algae-laden and manganese-containing waters by oxidation-assisted coagulation: Effects of oxidation on algal cell viability and manganese precipitation.

    PubMed

    Lin, Jr-Lin; Hua, Lap-Cuong; Wu, Yuting; Huang, Chihpin

    2016-02-01

    Preoxidation is manipulated to improve performance of algae and soluble manganese (Mn) removal by coagulation-sedimentation for water treatment plants (WTPs) when large amount of soluble Mn presents in algae-laden waters. This study aimed to investigate the effects of preoxidation on the performance of coagulation-sedimentation for the simultaneous removal of algae and soluble Mn, including ionic and complexed Mn. NaOCl, ClO2, and KMnO4 were used to pretreat such algae-laden and Mn containing waters. The variation of algal cell viability, residual cell counts, and concentrations of Mn species prior to and after coagulation-sedimentation step were investigated. Results show that NaOCl dosing was effective in reducing the viability of algae, but precipitated little Mn. ClO2 dosing had a strongest ability to lower algae viability and oxidize ionic and complexed soluble Mn, where KMnO4 dosing oxidized ionic and complexed Mn instead of reducing the viability of cells. Preoxidation by NaOCl only improved the algae removal by sedimentation, whereas most of soluble Mn still remained. On the other hand, ClO2 preoxidation substantially improved the performance of coagulation-sedimentation for simultaneous removal of algae and soluble Mn. Furthermore, KMnO4 preoxidation did improve the removal of algae by sedimentation, but left significant residual Mn in the supernatant. Images from FlowCAM showed changes in aspect ratio (AR) and transparency of algae-Mn flocs during oxidation-assisted coagulation, and indicates that an effective oxidation can improve the removal of most compact algae-Mn flocs by sedimentation. It suggests that an effective preoxidation for reducing algal cell viability and the concentration of soluble Mn is a crucial step for upgrading the performance of coagulation-sedimentation. PMID:26689663

  12. The simple preparation of birnessite-type manganese oxide with flower-like microsphere morphology and its remarkable capacity retention

    SciTech Connect

    Zhu, Gang; Deng, Lingjuan; Wang, Jianfang; Kang, Liping; School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062 ; Liu, Zong-Huai; School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062

    2012-11-15

    Graphical abstract: Flower-like birnessite-type manganese oxide microspheres with large specific surface area and excellent electrochemical properties have been prepared by a facile hydrothermal method. Highlights: ► Birnessite-type manganese oxide with flower-like microsphere morphology and large specific surface area. ► A facile low-temperature hydrothermal method. ► Novel flower-like microsphere consists of the thin nano-platelets. ► Birnessite-type manganese oxide exhibits an ideal capacitive behavior and excellent cycling stability. -- Abstract: Birnessite-type manganese oxide with flower-like microsphere morphology and large specific surface area has been prepared by hydrothermal treating a mixture solution of KMnO{sub 4} and (NH{sub 4}){sub 2}SO{sub 4} at 90 °C for 24 h. The obtained material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N{sub 2} adsorption–desorption. Results indicate that the birnessite-type manganese oxide shows novel flower-like microsphere morphology and a specific surface area of 280 m{sup 2} g{sup −1}, and the flower-like microsphere consists of the thin nano-platelets. Electrochemical characterization indicates that the prepared material exhibits an ideal capacitive behavior with a capacitance value of 278 F g{sup −1} in 1 mol L{sup −1} Na{sub 2}SO{sub 4} aqueous solution at a scan rate of 5 mV s{sup −1}. Moreover, the prepared manganese oxide electrode shows excellent cycle stability, and the specific capacitance can maintain 98.6% of the initial one after 5000 cycles.

  13. Manganese regulation of virulence factors and oxidative stress resistance in Neisseria gonorrhoeae

    PubMed Central

    Wu, Hsing-Ju; Seib, Kate L.; Srikhanta, Yogitha N.; Edwards, Jennifer; Kidd, Stephen P.; Maguire, Tina L .; Hamilton, Amanda; Pan, Kuan-Tin; Hsiao, He-Hsuan; Yao, Chen-Wen; Grimmond, Sean M.; Apicella, Michael A.; McEwan, Alastair G.; Wang, Andrew H-J.; Jennings, Michael P.

    2014-01-01

    Neisseria gonorrhoeae has evolved a complex and novel network of oxidative stress responses, including defense mechanisms that are dependent on manganese (Mn). We performed systematic analyses at the transcriptomic and proteomic (1D SDS-PAGE and Isotope-Coded Affinity Tag [ICAT]) levels to investigate the global expression changes that take place in a high Mn environment, which results in a Mn-dependent oxidative stress resistance phenotype. These studies revealed that 97 proteins are regulated at the post-transcriptional level under conditions of increased Mn concentration, including proteins involved in virulence (eg. Pilin, a key adhesin), oxidative stress defence (eg. superoxide dismutase), cellular metabolism, protein synthesis, RNA processing and cell division. Mn regulation of inorganic pyrophosphatase (Ppa) indicated the potential involvement of phosphate metabolism in the Mn-dependent oxidative stress defense. A detailed analysis of the role of Ppa and polyphosphate kinase (Ppk) in the gonococcal oxidative stress response revealed that ppk and ppa mutant strains showed increased resistance to oxidative stress. Investigation of these mutants grown with high Mn suggests that phosphate and pyrophosphate are involved in Mn-dependent oxidative stress resistance. PMID:20004262

  14. Recovery of manganese oxides from spent alkaline and zinc–carbon batteries. An application as catalysts for VOCs elimination

    SciTech Connect

    Gallegos, María V.; Falco, Lorena R.; Peluso, Miguel A.; Sambeth, Jorge E.; Thomas, Horacio J.

    2013-06-15

    Highlights: • Manganese oxides were synthesized using spent batteries as raw materials. • Spent alkaline and zinc–carbon size AA batteries were used. • A biohydrometallurgical process was employed to bio-lixiviate batteries. • Manganese oxides were active in the oxidation of VOCs (ethanol and heptane). - Abstract: Manganese, in the form of oxide, was recovered from spent alkaline and zinc–carbon batteries employing a biohydrometallurgy process, using a pilot plant consisting in: an air-lift bioreactor (containing an acid-reducing medium produced by an Acidithiobacillus thiooxidans bacteria immobilized on elemental sulfur); a leaching reactor (were battery powder is mixed with the acid-reducing medium) and a recovery reactor. Two different manganese oxides were recovered from the leachate liquor: one of them by electrolysis (EMO) and the other by a chemical precipitation with KMnO{sub 4} solution (CMO). The non-leached solid residue was also studied (RMO). The solids were compared with a MnO{sub x} synthesized in our laboratory. The characterization by XRD, FTIR and XPS reveal the presence of Mn{sub 2}O{sub 3} in the EMO and the CMO samples, together with some Mn{sup 4+} cations. In the solid not extracted by acidic leaching (RMO) the main phase detected was Mn{sub 3}O{sub 4}. The catalytic performance of the oxides was studied in the complete oxidation of ethanol and heptane. Complete conversion of ethanol occurs at 200 °C, while heptane requires more than 400 °C. The CMO has the highest oxide selectivity to CO{sub 2}. The results show that manganese oxides obtained using spent alkaline and zinc–carbon batteries as raw materials, have an interesting performance as catalysts for elimination of VOCs.

  15. Pulsed laser deposition of manganese oxide thin films for supercapacitor applications

    NASA Astrophysics Data System (ADS)

    Yang, Dongfang

    2011-10-01

    Thin films of manganese oxides have been grown by the pulsed laser deposition (PLD) process on silicon wafer and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of processing parameters such as temperature and oxygen pressure during the PLD process, pure crystalline phases of Mn2O3, Mn3O4 as well as amorphous phase of MnOx were successfully fabricated as identified by X-ray diffraction. The pseudo-capacitance behaviours of these different phases of manganese oxides have also been evaluated by the electrochemical cyclic voltammetry measured in 0.1 M Na2SO4 aqueous electrolyte at different scan rates. Their specific current and capacitance determined by electrochemical measurements were compared and the results show that crystalline Mn2O3 phase has the highest specific current and capacitance, while the values for crystalline Mn3O4 films are the lowest. The specific current and capacitance values of the amorphous MnOx films are lower than Mn2O3 but higher than Mn3O4. The specific capacitance of Mn2O3 films of 120 nm thick reaches 210 F g-1 at 1 mV s-1 scan rate with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for screening high performance active materials for supercapacitor applications due to its excellent flexibility and capability of easily controlling chemical composition, microstructures and phases of materials.

  16. Manganese oxide nanowires wrapped with nitrogen doped carbon layers for high performance supercapacitors.

    PubMed

    Li, Ying; Mei, Yuan; Zhang, Lin-Qun; Wang, Jian-Hai; Liu, An-Ran; Zhang, Yuan-Jian; Liu, Song-Qin

    2015-10-01

    In this study, manganese oxide nanowires wrapped by nitrogen-doped carbon layers (MnO(x)@NCs) were prepared by carbonization of poly(o-phenylenediamine) layer coated onto MnO2 nanowires for high performance supercapacitors. The component and structure of the MnO(x)@NCs were controlled through carbonization procedure under different temperatures. Results demonstrated that this composite combined the high conductivity and high specific surface area of nitrogen-doped carbon layers with the high pseudo-capacitance of manganese oxide nanowires. The as-prepared MnO(x)@NCs exhibited superior capacitive properties in 1 M Na2SO4 aqueous solution, such as high conductivity (4.16710(-3) S cm(-1)), high specific capacitance (269 F g(-1) at 10 mV s(-1)) and long cycle life (134 F g(-1) after 1200 cycles at a scan rate of 50 mV s(-1)). It is reckoned that the present novel hybrid nanowires can serve as a promising electrode material for supercapacitors and other electrochemical devices. PMID:26070189

  17. Anomalous pseudocapacitive behavior of a nanostructured, mixed-valent manganese oxide film for electrical energy storage.

    PubMed

    Song, Min-Kyu; Cheng, Shuang; Chen, Haiyan; Qin, Wentao; Nam, Kyung-Wan; Xu, Shucheng; Yang, Xiao-Qing; Bongiorno, Angelo; Lee, Jangsoo; Bai, Jianming; Tyson, Trevor A; Cho, Jaephil; Liu, Meilin

    2012-07-11

    While pseudocapacitors represent a promising option for electrical energy storage, the performance of the existing ones must be dramatically enhanced to meet today's ever-increasing demands for many emerging applications. Here we report a nanostructured, mixed-valent manganese oxide film that exhibits anomalously high specific capacitance (?2530 F/g of manganese oxide, measured at 0.61 A/g in a two-electrode configuration with loading of active materials ?0.16 mg/cm(2)) while maintaining excellent power density and cycling life. The dramatic performance enhancement is attributed to its unique mixed-valence state with porous nanoarchitecture, which may facilitate rapid mass transport and enhance surface double-layer capacitance, while promoting facile redox reactions associated with charge storage by both Mn and O sites, as suggested by in situ X-ray absorption spectroscopy (XAS) and density functional theory calculations. The new charge storage mechanisms (in addition to redox reactions of cations) may offer critical insights to rational design of a new-generation energy storage devices. PMID:22681539

  18. Development of a genetic system for a model manganese-oxidizing proteobacterium, Leptothrix discophora SS1.

    PubMed

    Bocioaga, Daniela; El Gheriany, Iman A; Lion, Leonard W; Ghiorse, William C; Shuler, Michael L; Hay, Anthony G

    2014-11-01

    Understanding the molecular underpinnings of manganese oxidation in Leptothrix discophora SS1 has been hampered by the lack of a genetic system. In this report, we describe the development of a genetic system for L. discophora SS1. The antibiotic sensitivity was characterized, and a procedure for transformation with exogenous DNA via conjugation was developed and optimized, resulting in a maximum transfer frequency of 5.210(-1) and a typical transfer frequency of the order of 110(-3) transconjugants per donor. Genetic manipulation of L. discophora SS1 was demonstrated by disrupting pyrF via chromosomal integration with a plasmid containing a R6K? origin of replication through homologous recombination. This resulted in resistance to 5-fluoroorotidine, which was abolished by complementation with an ectopically expressed copy of pyrF cloned into pBBR1MCS. This system is expected to be amenable to a systematic genetic analysis of L. discophora SS1, including those genes responsible for manganese oxidation. PMID:25149187

  19. Stress response to cadmium and manganese in Paracentrotus lividus developing embryos is mediated by nitric oxide.

    PubMed

    Migliaccio, Oriana; Castellano, Immacolata; Romano, Giovanna; Palumbo, Anna

    2014-11-01

    Increasing concentrations of contaminants, often resulting from anthropogenic activities, have been reported to occur in the marine environment and affect marine organisms. Among these, the metal ions cadmium and manganese have been shown to induce developmental delay and abnormalities, mainly reflecting skeleton elongation perturbation, in the sea urchin Paracentrotus lividus, an established model for toxicological studies. Here, we provide evidence that the physiological messenger nitric oxide (NO), formed by l-arginine oxidation by NO synthase (NOS), mediates the stress response induced by cadmium and manganese in sea urchins. When NO levels were lowered by inhibiting NOS, the proportion of abnormal plutei increased. Quantitative expression of a panel of 19 genes involved in stress response, skeletogenesis, detoxification and multidrug efflux processes was followed at different developmental stages and under different conditions: metals alone, metals in the presence of NOS inhibitor, NO donor and NOS inhibitor alone. These data allowed the identification of different classes of genes whose metal-induced transcriptional expression was directly or indirectly mediated by NO. These results open new perspectives on the role of NO as a sensor of different stress agents in sea urchin developing embryos. PMID:25181703

  20. Geology, alteration, age, and origin of iron oxide-apatite deposits in Upper Eocene quartz monzonite, Zanjan district, NW Iran

    NASA Astrophysics Data System (ADS)

    Nabatian, Ghasem; Ghaderi, Majid; Corfu, Fernando; Neubauer, Franz; Bernroider, Manfred; Prokofiev, Vsevolod; Honarmand, Maryam

    2014-02-01

    Iron oxide-apatite deposits are present in Upper Eocene pyroxene-quartz monzonitic rocks of the Zanjan district, northwestern Iran. Mineralization occurred in five stages: (1) deposition of disseminated magnetite and apatite in the host rock; (2) mineralization of massive and banded magnetite ores in veins and stockwork associated with minor brecciation and calcic alteration of host rocks; (3) deposition of sulfide ores together with potassic alteration; (4) formation of quartz and carbonate veins and sericite, chlorite, epidote, silica, carbonate, and tourmaline alteration; and (5) supergene alteration and weathering. U-Pb dating of monazite inclusions in the apatite indicates an age of 39.99 ± 0.24 Ma, which is nearly coeval with the time of emplacement of the host quartz monzonite, supporting the genetic connection. Fluid inclusions in the apatite have homogenization temperatures of about 300 °C and oxygen isotopic compositions of the magnetite support precipitation from magmatic fluids. Late-stage quartz resulted from the introduction of a cooler, less saline, and isotopically depleted fluid. The iron oxide-apatite deposits in the Tarom area of the Zanjan district are typical of a magmatic-hydrothermal origin and are similar to the Kiruna-type deposits with respect to mineral assemblages, fabric and structure of the iron ores, occurrence of the ore bodies, and wall rock alteration.

  1. Nano-sized Lithium Manganese Oxide Dispersed on Carbon Nanotubes for Energy Storage Applications

    SciTech Connect

    Bak, S.B.

    2009-08-01

    Nano-sized lithium manganese oxide (LMO) dispersed on carbon nanotubes (CNT) has been synthesized successfully via a microwave-assisted hydrothermal reaction at 200 C for 30 min using MnO{sub 2}-coated CNT and an aqueous LiOH solution. The initial specific capacity is 99.4 mAh/g at a 1.6 C-rate, and is maintained at 99.1 mAh/g even at a 16 C-rate. The initial specific capacity is also maintained up to the 50th cycle to give 97% capacity retention. The LMO/CNT nanocomposite shows excellent power performance and good structural reversibility as an electrode material in energy storage systems, such as lithium-ion batteries and electrochemical capacitors. This synthetic strategy opens a new avenue for the effective and facile synthesis of lithium transition metal oxide/CNT nanocomposite.

  2. Sodium manganese oxide thin films as cathodes for Na-ion batteries

    SciTech Connect

    Baggetto, Loic; Carroll, Kyler J; Unocic, Raymond R; Bridges, Craig A; Meng, Ying Shirley; Veith, Gabriel M

    2014-01-01

    This paper presents the fabrication and characterization of sodium manganese oxide cathode thin films for rechargeable Na-ion batteries. Layered oxide compounds of nominal compositions Na0.6MnO2 and Na1.0MnO2 have been prepared by radio frequency magnetron sputtering and post-annealing at high temperatures under various conditions. The Na0.6MnO2 thin films possess either a hexagonal or orthorhombic structure while the Na1.0MnO2 films crystallize in a monoclinic structure, as shown by X-ray diffraction and X-ray absorption spectroscopy results. The potential profiles of the film cathodes are characterized by features similar to those measured for the powders and exhibit reversible storage capacities in the range of 50-60 Ah cm-2 m-1, which correspond to about 120-140 mAh g-1, and are maintained over 80 cycles.

  3. Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts.

    PubMed

    Liang, Yongye; Wang, Hailiang; Zhou, Jigang; Li, Yanguang; Wang, Jian; Regier, Tom; Dai, Hongjie

    2012-02-22

    Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions. PMID:22280461

  4. Fully Converting Graphite into Graphene Oxide Hydrogels by Preoxidation with Impure Manganese Dioxide.

    PubMed

    Sun, Jiaojiao; Yang, Ningxin; Sun, Zhe; Zeng, Mengqi; Fu, Lei; Hu, Chengguo; Hu, Shengshui

    2015-09-30

    Potassium permanganate (KMnO4) has been proved to be an efficient oxidant for converting graphite into graphite oxide, but its slow diffusion in the interlayer of graphite seriously restricts the production of graphene oxide (GO). Here, we demonstrate that the preoxidation of graphite by impure manganese dioxide (MnO2) in a mixture of concentrated sulfuric acid (H2SO4) and phosphorus pentoxide (P2O5) can efficiently improve the synthesis of GO when KMnO4 is employed as the oxidant. The prepared honey-like GO hydrogels possess a high yield of single-layer sheets, large sizes (average lateral size up to 20 μm), wide ranges of stable dispersion concentrations (from dilute solutions, viscous hydrogels, to dry films), and good conductivity after reduction (~2.9 × 10(4) S/m). The mechanism for the improved synthesis of GO by impure MnO2 was explored. The enhanced exfoliation and oxidation of graphite by oxidative Mn ions (mainly Mn(3+)), which are synergistically produced by the reaction of impure MnO2 with H2SO4 and P2O5, are found to be responsible for the improved synthesis of such GO hydrogels. Particularly, preoxidized graphite (POG) can be partially dispersed in water with sonication, which allows the facile construction of flexible and highly conductive graphene nanosheet film electrodes with excellent electrochemical sensing properties. PMID:26352992

  5. A Highly Sensitive Immunosorbent Assay Based on Biotinylated Graphene Oxide and the Quartz Crystal Microbalance.

    PubMed

    Deng, Xudong; Chen, Mengsu; Fu, Qiang; Smeets, Niels M B; Xu, Fei; Zhang, Zhuyuan; Filipe, Carlos D M; Hoare, Todd

    2016-01-27

    A high-sensitivity flow-based immunoassay is reported based on a gold-coated quartz crystal microbalance (QCM) chip functionalized directly in the QCM without requiring covalent conjugation steps. Specifically, the irreversible adsorption of a biotinylated graphene oxide-avidin complex followed by loading of a biotinylated capture antibody is applied to avoid more complex conventional surface modification chemistries and enable chip functionalization and sensing all within the QCM instrument. The resulting immunosensors exhibit significantly lower nonspecific protein adsorption and stronger signal for antigen sensing relative to simple avidin-coated sensors. Reproducible quantification of rabbit IgG concentrations ranging from 0.1 ng/mL to 10 ?g/mL (6 orders of magnitude) can be achieved depending on the approach used to quantify the binding with simple mass changes used to detect higher concentrations and a horseradish peroxidase-linked detection antibody that converts its substrate to a measurable precipitate used to detect very low analyte concentrations. Sensor fabrication and assay performance take ?5 h in total, which is on par with or faster than other techniques. Quantitative sensing is possible in the presence of complex protein mixtures, such as human plasma. Given the broad availability of biotinylated capture antibodies, this method offers both an easy and flexible platform for the quantitative sensing of a variety of biomolecule targets. PMID:26725646

  6. Study of quartz crystal microbalance NO2 sensor coated with sputtered indium tin oxide film

    NASA Astrophysics Data System (ADS)

    Georgieva, V.; Aleksandrova, M.; Stefanov, P.; Grechnikov, A.; Gadjanova, V.; Dilova, T.; Angelov, Ts

    2014-12-01

    A study of NO2 gas sorption ability of thin indium tin oxide (ITO) deposited on 16 MHz quartz crystal microbalance (QCM) is presented. ITO films are grown by RF sputtering of indium/tin target with weight proportion 95:5 in oxygen environment. The ITO films have been characterized by X-ray photoelectron spectroscopy measurements. The ITO surface composition in atomic % is defined to be: In-40.6%, Sn-4.3% and O-55%. The thickness and refractive index of the films are determined by ellipsometric method. The frequency shift of QCM-ITO is measured at different NO2 concentrations. The QCM-ITO system becomes sensitive at NO2 concentration >= 500 ppm. The sorbed mass for each concentration is calculated according the Sauerbrey equation. The results indicated that the 1.09 ng of the gas is sorbed into 150 nm thick ITO film at 500 ppm NO2 concentration. When the NO2 concentration increases 10 times the calculated loaded mass is 5.46 ng. The sorption process of the gas molecules is defined as reversible. The velocity of sorbtion /desorption processes are studied, too. The QCM coated with thin ITO films can be successfully used as gas sensors for detecting NO2 in the air at room temperature.

  7. Transport of Sulfide-Reduced Graphene Oxide in Saturated Quartz Sand: Cation-Dependent Retention Mechanisms.

    PubMed

    Xia, Tianjiao; Fortner, John D; Zhu, Dongqiang; Qi, Zhichong; Chen, Wei

    2015-10-01

    We describe how the reduction of graphene oxide (GO) via environmentally relevant pathways affects its transport behavior in porous media. A pair of sulfide-reduced GOs (RGOs), prepared by reducing 10 mg/L GO with 0.1 mM Na2S for 3 and 5 days, respectively, exhibited lower mobility than did parent GO in saturated quartz sand. Interestingly, decreased mobility cannot simply be attributed to the increased hydrophobicity and aggregation upon GO reduction because the retention mechanisms of RGOs were highly cation-dependent. In the presence of Na(+) (a representative monovalent cation), the main retention mechanism was deposition in the secondary energy minimum. However, in the presence of Ca(2+) (a model divalent cation), cation bridging between RGO and sand grains became the most predominant retention mechanism; this was because sulfide reduction markedly increased the amount of hydroxyl groups (a strong metal-complexing moiety) on GO. When Na(+) was the background cation, increasing pH (which increased the accumulation of large hydrated Na(+) ions on grain surface) and the presence of Suwannee River humic acid (SRHA) significantly enhanced the transport of RGO, mainly due to steric hindrance. However, pH and SRHA had little effect when Ca(2+) was the background cation because neither affected the extent of cation bridging that controlled particle retention. These findings highlight the significance of abiotic transformations on the fate and transport of GO in aqueous systems. PMID:26348539

  8. In Situ X-ray Absorption Study of a Layered Manganese-chromium Oxide-based Cathode Material

    SciTech Connect

    Balasubramanian, M.; McBreen, J; Davidson, I; Whitfield, P; Kargina, I

    2010-01-01

    We have investigated the electronic and atomic structure of a manganese-chromium-based layered oxide material Li[Li{sub 0.2}Cr{sub 0.4}Mn{sub 0.4}]O{sub 2} during electrochemical cycling using in situ X-ray absorption spectroscopy. Our results indicate that charge compensation in the cathode material is achieved by the oxidation/reduction of octahedral Cr(III) ions to tetrahedral Cr(VI) ions during delithiation/lithiation. Manganese ions are present predominantly in the Mn(IV) oxidation state and do not appear to actively participate in the charge compensation process. To accommodate the large changes in coordination symmetry of the Cr(III) and Cr(VI) ions, the chromium ions have to move between the regular octahedral sites in the R{bar 3}m-like lattice to interstitial tetrahedral sites during the charge/discharge process. The highly reversible (at least after the first charge) three-electron oxidation/reductions and the easy mobility of the chromium between octahedral and tetrahedral sites are very unusual and interesting. Equally interesting is the fact that chromium is the active metal undergoing oxidation/reduction rather than manganese. Our results also suggest that in the local scale manganese and chromium ions are not evenly distributed in the as-prepared material, but are present in separate domains of Mn and Cr-rich regions.

  9. Manganese-oxide minerals in fractures of the Crater Flat Tuff in drill core USW G-4, Yucca Mountain, Nevada

    SciTech Connect

    Carlos, B.A.; Bish, D.L.; Chipera, S.J.

    1990-07-01

    The Crater Flat Tuff is almost entirely below the water table in drill hole USW G-4 at Yucca Mountain, Nevada. Manganese-oxide minerals from the Crater Flat Tuff in USW G-4 were studied using optical, scanning electron microscopic, electron microprobe, and x-ray powder diffraction methods to determine their distribution, mineralogy, and chemistry. Manganese-oxide minerals coat fractures in all three members of the Crater Flat Tuff (Prow Pass, Bullfrog, and Tram), but they are most abundant in fractures in the densely welded devitrified intervals of these members. The coatings are mostly of the cryptomelane/hollandite mineral group, but the chemistry of these coatings varies considerably. Some of the chemical variations, particularly the presence of calcium, sodium, and strontium, can be explained by admixture with todorokite, seen in some x-ray powder diffraction patterns. Other chemical variations, particularly between Ba and Pb, demonstrate that considerable substitution of Pb for Ba occurs in hollandite. Manganese-oxide coatings are common in the 10-m interval that produced 75% of the water pumped from USW G-4 in a flow survey in 1983. Their presence in water-producing zones suggests that manganese oxides may exert a significant chemical effect on groundwater beneath Yucca Mountain. In particular, the ability of the manganese oxides found at Yucca Mountain to be easily reduced suggests that they may affect the redox conditions of the groundwater and may oxidize dissolved or suspended species. Although the Mn oxides at Yucca Mountain have low exchange capacities, these minerals may retard the migration of some radionuclides, particularly the actinides, through scavenging and coprecipitation. 23 refs., 21 figs., 2 tabs.

  10. Preparation of anionic clay-birnessite manganese oxide composites by interlayer oxidation of oxalate ions by permanganate

    SciTech Connect

    Arulraj, James; Rajamathi, Michael

    2013-02-15

    Oxalate intercalated anionic clay-like nickel zinc hydroxysalt was obtained starting from nickel zinc hydroxyacetate, Ni{sub 3}Zn{sub 2}(OH){sub 8}(OAc){sub 2}{center_dot}2H{sub 2}O, by anion exchange. The intercalated oxalate species was reacted with potassium permanganate in such a way that the layered manganese oxide formed was within the interlayer region of the anionic clay resulting in a layered composite in which the negative charges on the birnessite type manganese oxide layers compensate the positive charges on the anionic clay layers. Birnessite to anionic clay ratio could be varied by varying the reaction time or the amount of potassium permanganate used. - Graphical abstract: Nickel zinc hydroxyoxalate was reacted with potassium permanganate to get nickel zinc hydroxide birnessite composites in which the positive charges on the hydroxide layers are neutralized by the negative charges on birnessite layers. Highlights: Black-Right-Pointing-Pointer Anionic and cationic layered solid composites prepared. Black-Right-Pointing-Pointer Ni-Zn hydroxyoxalate reacted with KMnO{sub 4} to deposit MnO{sub 2} in the interlayer. Black-Right-Pointing-Pointer Birnessite layers coexist with anionic clay layers in the composites. Black-Right-Pointing-Pointer Birnessite/anionic clay ratio controlled by amount of KMnO{sub 4} used and reaction time.

  11. Effect of bacterial adsorption on low frequency electrical properties of clean quartz sands and iron-oxide coated sands

    NASA Astrophysics Data System (ADS)

    Abdel Aal, Gamal; Atekwana, Estella; Radzikowski, Sylvia; Rossbach, Silvia

    2009-02-01

    Low frequency electrical measurements (0.1-1000 Hz) were conducted to investigate the adsorption effect of Pseudomonas aeruginosa cells onto clean quartz sands and iron-oxide coated sands. The clean quartz sands showed a gradual increase in the microbial adsorption to mineral grains, concurrent with an increase of 13% in the imaginary conductivity component (?''). However, iron-oxide coated sands (20-100% by weight) showed a rapid increase in microbial adsorption with ?'' reaching a maximum of 37 % for the 80-100% iron coated sands. No significant changes were observed in the real conductivity component (?') due to microbial adsorption. A power law dependency was observed between the adsorbed cells and ?''. We suggest that the polarization results from the increase in the surface roughness and surface area of the grain due to bacteria sorption. These results suggest that low frequency electrical measurements can play an important role in assessing microbial transport in subsurface environments.

  12. Manganese As a Metal Accumulator

    EPA Science Inventory

    Manganese deposits in water distribution systems accumulate metals, radionuclides and oxyanions by a combination of surface complexation, adsorption and solid substitution, as well as a combination of oxidation followed by manganese reduction and sorption of the oxidized constitu...

  13. Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report

    SciTech Connect

    Brown Jr., G. E.; Chambers, S. A.

    1999-10-31

    Many of the inorganic and organic contaminants present in sediments at DOE sites can be altered or destroyed by reduction and oxidation (redox) reactions occurring at mineral surfaces. A fundamental understanding of such redox processes provided by molecular-level studies on structurally and compositionally well-defined mineral surfaces will lead to: (i) improved models of contaminant fate and transport in geochemical systems, and (ii) optimized manipulation of these processes for remediation purposes. To contribute to this understanding, we will study, both experimentally and theoretically, redox processes involving three important contaminants - chromate ion, carbon tetrachloride, and trichloroethene TCE, on the following iron and manganese oxides - hematite, magnetite, maghemite, and pyrolusite. These oxides and their hydroxylated analogs commonly occur as coatings on minerals or as interfaces in the subsurface environment. Single-crystal surfaces of these oxides will be synthesized in carefully controlled fashion by molecular beam epitaxy. These surfaces, as well as high surface are powdered samples of these oxides, will be used in spectroscopic and kinetic experiments in both aqueous and gas phases. Our goal is to identify products and to determine the kinetics and mechanisms of surface-catalyzed redox reaction of Cr(VI) and CR(III), and the reductive dechlorination of carbon tetrachloride and TCE. The combination of theory and experiment will provide the base information needed to scale from the molecular level to the microscopic grain level minerals.

  14. Stability of manganese-oxide-modified lanthanum strontium cobaltite in the presence of chromia

    NASA Astrophysics Data System (ADS)

    Ou, Ding Rong; Cheng, Mojie

    2014-12-01

    In order to restrain the decomposition and conductivity degradation of perovskite-type conductive material in the presence of chromia, manganese oxide modification of lanthanum strontium cobaltite has been studied. La0.7Sr0.3CoO3-δ (LSC) and MnO2-modified LSC coatings are applied onto Ni-Cr alloy and exposed to long-term oxidation text to examine their chemical stability. In a LSC coating, chromium species migrating from the Ni-Cr alloy could induce the decomposition of LSC and produce SrCrO4 and Co-Cr spinel oxides. In contrast, in the MnO2-modified LSC, Sr is stable and the low-conductivity phase SrCrO4 phase is rarely seen even the coated alloy has gone through 1000 h of oxidation tests at 800 °C. It highlights that MnO2 modification could greatly improve the stability of LSC under Cr-rich conditions. The study of solid state reactions reveals that the influence of MnO2 is mainly due to the reaction between MnO2 and LSC, instead of the direct reaction between MnO2 and chromium oxides.

  15. Thiol-mediated oxidation of nonphenolic lignin model compounds by manganese peroxidase of Phanerochaete chrysosporium

    SciTech Connect

    Wariishi, Hiroyuki; Valli, K.; Renganathan, V.; Gold, M.H. )

    1989-08-25

    In the presence of Mn{sup II}, H{sub 2}O{sub 2}, and glutathione (GSH), manganese peroxidase oxidized veratryl alcohol (1) to veratraldehyde (4). Anisyl alcohol (2) and benzyl alcohol (3) were also oxidized by this system to their corresponding aldehydes, anisaldehyde (5) and benzaldehyde (6). In the presence of GSH, chemically prepared Mn{sup III} or {gamma}-irradiation also catalyzed the oxidation of 1, 2, and 3 to 4, 5, and 6, respectively. GSH and dithiothreitol rapidly reduced Mn{sup III} to Mn{sup II} in the absence of aromatic substrates and the dithiothreitol was oxidized to its disulfide (4,5-dihydroxyl-1,2-dithiane). These results indicate that the thiol is oxidized by enzyme-generated Mn{sup III} to a thiyl radical. The latter abstracts a hydrogen from the substrate , forming a benzylic radical which reacts with another thiyl radical to yield an intermediate which decomposes to the benzaldehyde product. 51 refs., 5 figs., 2 tabs.

  16. Improved photoelectrochemical water oxidation by the WO3/CuWO4 composite with a manganese phosphate electrocatalyst.

    PubMed

    Nam, Ki Min; Cheon, Eun Ah; Shin, Won Jung; Bard, Allen J

    2015-10-01

    We describe a composite of the n-type semiconductors for the photoelectrochemical oxygen evolution reaction (OER). A simple drop-casting technique of mixed precursors and a one-step annealing process were used in the synthesis of the WO3/CuWO4 composite. The composite showed improved photocurrent for water oxidation compared to either of the two compounds individually. We discuss possible electron-hole separation mechanisms in two semiconductors comprising a primary photon-absorbing semiconductor of CuWO4 with a secondary semiconductor of WO3. When the WO3/CuWO4 composite is simultaneously irradiated, the photogenerated hole from the WO3 valence band transfers to CuWO4, which results in an enhanced charge separation of CuWO4. Furthermore, the OER catalytic activity of manganese phosphate (MnPO) was compared to manganese oxide nanoparticles (Mn2O3) by electrochemical measurements, showing that the manganese phosphate was more efficient for the OER reaction. To investigate the effect of catalysts on semiconductors, manganese phosphate was deposited on the WO3/CuWO4 composite. The result demonstrates the promise of manganese phosphate for improving the photocurrent as well as the stability of the WO3/CuWO4 composite. PMID:26371544

  17. Graphene oxide/manganese ferrite nanohybrids for magnetic resonance imaging, photothermal therapy and drug delivery.

    PubMed

    Yang, Yan; Shi, Haili; Wang, Yapei; Shi, Benzhao; Guo, Linlin; Wu, Dongmei; Yang, Shiping; Wu, Huixia

    2016-01-01

    Superparamagnetic manganese ferrite (MnFe2O4) nanoparticles have been deposited on graphene oxide (GO) by the thermal decomposition of manganese (II) acetylacetonate and iron (III) acetylacetonate precursors in triethylene glycol. The resulting GO/MnFe2O4 nanohybrids show very low cytotoxicity, negligible hemolytic activity, and imperceptible in vivo toxicity. In vitro and in vivo magnetic resonance imaging experiments demonstrate that GO/MnFe2O4 nanohybrids could be used as an effective T2 contrast agent. The strong optical absorbance in the near-infrared (NIR) region and good photothermal stability of GO/MnFe2O4 nanohybrids result in the highly efficient photothermal ablation of cancer cells. GO/MnFe2O4 nanohybrids can be further loaded with doxorubicin (DOX) by π-π conjugate effect for chemotherapy. DOX release from GO/MnFe2O4 is significantly influenced by pH and can be triggered by NIR laser. The enhanced cancer cell killing by GO/MnFe2O4/DOX composites has been achieved when irradiated with near-infrared light, suggesting that the nanohybrids could deliver both DOX chemotherapy and photothermal therapy with a synergistic effect. PMID:26296777

  18. Facile synthesis and functionalization of manganese oxide nanoparticles for targeted T1-weighted tumor MR imaging.

    PubMed

    Luo, Yu; Yang, Jia; Li, Jingchao; Yu, Zhibo; Zhang, Guixiang; Shi, Xiangyang; Shen, Mingwu

    2015-12-01

    We report the polyethyleneimine (PEI)-enabled synthesis and functionalization of manganese oxide (Mn3O4) nanoparticles (NPs) for targeted tumor magnetic resonance (MR) imaging in vivo. In this work, monodispersed PEI-coated Mn3O4 NPs were formed by decomposition of acetylacetone manganese via a solvothermal approach. The Mn3O4 NPs with PEI coating were sequentially conjugated with fluorescein isothiocyanate, folic acid (FA)-linked polyethylene glycol (PEG), and PEG monomethyl ether. Followed by final acetylation of the remaining PEI surface amines, multifunctional Mn3O4 NPs were formed and well characterized. We show that the formed multifunctional Mn3O4 NPs with a mean diameter of 8.0nm possess good water-dispersibility, colloidal stability, and cytocompatibility and hemocompatibility in the given concentration range. Flow cytometry and confocal microscopic observation reveal that the multifunctional Mn3O4 NPs are able to target FA receptor-overexpressing cancer cells in vitro. Importantly, the FA-targeted Mn3O4 NPs can be used as a nanoprobe for efficient T1-weighted MR imaging of cancer cells in vitro and the xenografted tumor model in vivo via an active FA-mediated targeting pathway. With the facile PEI-enabled formation and functionalization, the developed PEI-coated Mn3O4 NPs may be modified with other biomolecules for different biomedical imaging applications. PMID:26454057

  19. ADSORPTION OF LEAD FROM A CONTAMINATED SOIL TREATED WITH PHOSPHORUS AND MANGANESE OXIDES BY APRAGUE-DAWLEY RATS

    EPA Science Inventory

    In addition to the formation of insoluble lead (Pb) compounds as a mean of reducing Pb bioavalability, adsorption is another potentially important process controlling the bioavailability of Pb in soils. Less attention has been given to manganese (Mn) oxides, even though they are ...

  20. L-DOPA-Coated Manganese Oxide Nanoparticles as Dual MRI Contrast Agents and Drug-Delivery Vehicles.

    PubMed

    McDonagh, Birgitte Hjelmeland; Singh, Gurvinder; Hak, Sjoerd; Bandyopadhyay, Sulalit; Augestad, Ingrid Lovise; Peddis, Davide; Sandvig, Ioanna; Sandvig, Axel; Glomm, Wilhelm Robert

    2016-01-01

    Manganese oxide nanoparticles (MONPs) are capable of time-dependent magnetic resonance imaging contrast switching as well as releasing a surface-bound drug. MONPs give T2/T2* contrast, but dissolve and release T1-active Mn(2+) and L-3,4-dihydroxyphenylalanine. Complementary images are acquired with a single contrast agent, and applications toward Parkinson's disease are suggested. PMID:26619158

  1. Understanding the role of manganese dioxide in the oxidation of phenolic compounds by aqueous permanganate.

    PubMed

    Jiang, Jin; Gao, Yuan; Pang, Su-Yan; Lu, Xue-Ting; Zhou, Yang; Ma, Jun; Wang, Qiang

    2015-01-01

    Recent studies have shown that manganese dioxide (MnO2) can significantly accelerate the oxidation kinetics of phenolic compounds such as triclosan and chlorophenols by potassium permanganate (Mn(VII)) in slightly acidic solutions. However, the role of MnO2 (i.e., as an oxidant vs catalyst) is still unclear. In this work, it was demonstrated that Mn(VII) oxidized triclosan (i.e., trichloro-2-phenoxyphenol) and its analogue 2-phenoxyphenol, mainly generating ether bond cleavage products (i.e., 2,4-dichlorophenol and phenol, respectively), while MnO2 reacted with them producing appreciable dimers as well as hydroxylated and quinone-like products. Using these two phenoxyphenols as mechanistic probes, it was interestingly found that MnO2 formed in situ or prepared ex situ greatly accelerated the kinetics but negligibly affected the pathways of their oxidation by Mn(VII) at acidic pH 5. The yields (R) of indicative products 2,4-dichlorophenol and phenol from their respective probes (i.e., molar ratios of product formed to probe lost) under various experimental conditions were quantified. Comparable R values were obtained during the treatment by Mn(VII) in the absence vs presence of MnO2. Meanwhile, it was confirmed that MnO2 could accelerate the kinetics of Mn(VII) oxidation of refractory nitrophenols (i.e., 2-nitrophenol and 4-nitrophenol), which otherwise showed negligible reactivity toward Mn(VII) and MnO2 individually, and the effect of MnO2 was strongly dependent upon its concentration as well as solution pH. These results clearly rule out the role of MnO2 as a mild co-oxidant and suggest a potential catalytic effect on Mn(VII) oxidation of phenolic compounds regardless of their susceptibility to oxidation by MnO2. PMID:25437924

  2. Purification and Characterization of the Manganese(II) Oxidizing Protein from Erythrobacter sp. SD-21

    NASA Astrophysics Data System (ADS)

    Nakama, K. R.; Lien, A.; Johnson, H. A.

    2013-12-01

    The manganese(II) oxidizing protein (Mop) found in the alpha-proteobacterium Erythrobacter sp. SD-21 catalyzes the formation of insoluble Mn(III/IV) oxides from soluble Mn(II). These Mn(III/IV) oxides formed are one of the strongest naturally occurring oxides, next to oxygen, and can be used to adsorb and oxidize toxic chemicals from the surrounding environment. Because of the beneficial use in the treatment of contaminated sources, the mechanism and biochemical properties of this novel enzyme are being studied. Due to low expression levels in the native host strain, purification of Mop has been problematic. To overcome this problem the gene encoding Mop, mopA, was cloned from the native host into a C-terminal histidine tag vector and expressed in Escherichia coli cells. Affinity chromatography under denaturing conditions have been applied in attempts to purify an active Mop. Western blots have confirmed that the protein is being expressed and is at the expected size of 250 kDa. Preliminary characterization on crude extract containing Mop has shown a Km and vmax value of 2453 uM and 0.025 uM min-1, respectively. Heme and pyrroloquinoline quinone can stimulate Mn(II) oxidizing activity, but hydrogen peroxide does not affect activity, despite the sequence similarity to animal heme peroxidase proteins. Research has been shown that calcium is essential for Mop activity. Purifying an active Mn(II) oxidizing protein will allow for a better understanding behind the enigmatic process of Mn(II) oxidation.

  3. Description of the first fungal dye-decolorizing peroxidase oxidizing manganese(II).

    PubMed

    Fernndez-Fueyo, Elena; Linde, Dolores; Almendral, David; Lpez-Lucendo, Mara F; Ruiz-Dueas, Francisco J; Martnez, Angel T

    2015-11-01

    Two phylogenetically divergent genes of the new family of dye-decolorizing peroxidases (DyPs) were found during comparison of the four DyP genes identified in the Pleurotus ostreatus genome with over 200 DyP genes from other basidiomycete genomes. The heterologously expressed enzymes (Pleos-DyP1 and Pleos-DyP4, following the genome nomenclature) efficiently oxidize anthraquinoid dyes (such as Reactive Blue 19), which are characteristic DyP substrates, as well as low redox-potential dyes (such as 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) and substituted phenols. However, only Pleos-DyP4 oxidizes the high redox-potential dye Reactive Black 5, at the same time that it displays high thermal and pH stability. Unexpectedly, both enzymes also oxidize Mn(2+) to Mn(3+), albeit with very different catalytic efficiencies. Pleos-DyP4 presents a Mn(2+) turnover (56 s(-1)) nearly in the same order of the two other Mn(2+)-oxidizing peroxidase families identified in the P. ostreatus genome: manganese peroxidases (100 s(-1) average turnover) and versatile peroxidases (145 s(-1) average turnover), whose genes were also heterologously expressed. Oxidation of Mn(2+) has been reported for an Amycolatopsis DyP (24 s(-1)) and claimed for other bacterial DyPs, albeit with lower activities, but this is the first time that Mn(2+) oxidation is reported for a fungal DyP. Interestingly, Pleos-DyP4 (together with ligninolytic peroxidases) is detected in the secretome of P. ostreatus grown on different lignocellulosic substrates. It is suggested that generation of Mn(3+) oxidizers plays a role in the P. ostreatus white-rot lifestyle since three different families of Mn(2+)-oxidizing peroxidase genes are present in its genome being expressed during lignocellulose degradation. PMID:25967658

  4. Redoxable nanosheet crystallites of MnO2 derived via delamination of a layered manganese oxide.

    PubMed

    Omomo, Yoshitomo; Sasaki, Takayoshi; Wang, Lianzhou; Watanabe, Mamoru

    2003-03-26

    This paper reports on the swelling and exfoliation behavior of a layered protonic manganese oxide, H(0.13)MnO(2).0.7H(2)O, in a solution of tetrabutylammonium (TBA) hydroxide and the formation and characterizations of unilamellar two-dimensional crystallites of MnO(2). At low doses of TBA ions, layered manganese oxide was observed to undergo normal intercalation, yielding a TBA intercalated phase with a gallery height of 1.25 nm. With a large excess of TBA ions, osmotic swelling occurred, giving rise to a very large intersheet separation of 3.5-7 nm. In an intermediate TBA concentration range, the sample exhibited a broad X-ray diffraction profile with superimposed diffraction features due to intercalation and osmotic swelling. The component responsible for the broad profile was isolated by centrifuging the mixture twice at different speeds, and the recovered colloid was identified as a pile of MnO(2) nanosheets, corresponding to the individual host layer of the precursor layered manganese oxide. Observations by transmission electron microscopy and atomic force microscopy revealed high two-dimensional anisotropy with a lateral dimension of submicrometers and a thickness of approximately 0.8 nm. The nanosheet exhibited broad optical absorption with a peak at 374 nm (epsilon = 1.13 x 10(4) mol(-1) dm(3) cm(-1)). The restacking process of the colloidal MnO(2) nanosheets was followed by aging the colloid at a relative humidity of 95%. The broad diffraction pattern due to the exfoliated sheets weakened with time and eventually resolved into two sharp distinct profiles attributable to a TBA intercalation compound with an intersheet spacing of 1.72 nm and an osmotically swollen hydrate with >10 nm at a very early stage. As drying progressed, the former phase became more abundant without a change in interlayer distance, while the degree of swelling of the latter phase gradually decreased to 2.7 nm that remained unchanged on further aging. Subsequent drying at a lower humidity collapsed the 2.7 nm phase. The resulting single 1.72 nm phase was dehydrated by heating at 150 degrees C to produce a phase with a contracted interlayer spacing of 1.3 nm. PMID:12643719

  5. Coprecipitation mechanisms and products in manganese oxidation in the presence of cadmium

    USGS Publications Warehouse

    Hem, J.D.; Lind, Carol J.

    1991-01-01

    Manganese oxidation products were precipitated in an aerated open-aqueous system where a continuous influx of mixed Mn2+ and Cd2+ solution was supplied and pH was maintained with an automated pH-stat adding dilute NaOH. X-ray diffraction and electron diffraction identified the solids produced as mixtures of Cd2Mn34+O8, Mn2+2Mn4+3O8, MnO2 (ramsdellite), and CdCO3. Mean oxidation numbers of the total precipitated Mn as great as 3.6 were reached during titrations. During subsequent aging in solution, oxidation numbers between 3.8 and 3.9 were reached in some precipitates in less than 40 days. Conditional oxidation rate constants calculated from a crystal-growth equation applied to titration data showed the overall precipitation rate, without considering manganese oxidation state in the precipitate, was increased by a factor of ~4 to ~7 when the mole ratio (Cd/Mn + Cd) of cadmium in the feed solution was 0.40 compared with rate constants for hausmannite (Mn2+Mn23+O4 precipitation under similar conditions but without accessory metals. Kinetic experiments were made to test effects of various Cd/Mn + Cd mole ratios and rates of addition of the feed solution, different temperatures from 5.0 to 35??C, and pH from 8.0 to 9.0. Oxidation rates were slower when the Cd mole ratio was less than 0.40. The rate increased by a factor of ~10 when pH was raised one-half unit. The effect of temperature on the rate constants was also substantial, but the meaning of this is uncertain because the rate of formation of Mn4+ oxide in the absence of Cd or other accessory metals was too slow to be measurable in titration experiments. The increased rate of Mn4+ oxide formation in the presence of Cd2+ can be ascribed to the formation of a labile adsorbed intermediate, CdMn2O4 Int, an analog of hausmannite, formed on precipitate surfaces at the beginning of the oxidation process. The increased lability of this structure, resulting from coordination-chemical behavior of Cd2+ during the titration, causes a rapid second-stage rearrangement and facilitates disproportionation of the Mn3+ ions. The Mn2+ ions thus released provide a positive feedback mechanism that couples the two steps of the conversion of Mn2+ to Mn4+ more closely than is possible when other metal ions besides manganese are not present. During aging of precipitates in contact with solutions, proportions of Cd2Mn3O8 and MnO2 increased at the expense of other precipitate components. ?? 1991.

  6. Mesoporous ironmanganese oxides for sulphur mustard and soman degradation

    SciTech Connect

    tengl, Vclav; J.E. Purkyn? University in st nad Labem, Faculty of Environment, 400 96 st nad Labem ; Grygar, Tom Matys; J.E. Purkyn? University in st nad Labem, Faculty of Environment, 400 96 st nad Labem ; Bludsk, Jana; Oplutil, Frantiek; N?mec, Tom

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ? New nanodispersive materials based on Fe and Mn oxides for degradations of warfare agents. ? The best activities for the degradation of sulphur mustard (97.9% in 64 min) and soman (97.9% in 64 min). ? One pot synthesis with friendly transformed to industrial conditions. -- Abstract: Substituted iron(III)manganese(III, IV) oxides, ammonio-jarosite and birnessite, were prepared by a homogeneous hydrolysis of potassium permanganate and iron(III) sulphate with 2-chloroacetamide and urea, respectively. Synthesised oxides were characterised using BrunauerEmmettTeller (BET) surface area and BarrettJoinerHalenda porosity (BJH), X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy and scanning electron microscopy (SEM). The oxides were taken for an experimental evaluation of their reactivity against sulphur mustard (HD) and soman (GD). When ammonio-jarosite formation is suppressed by adding urea to the reaction mixture, the reaction products are mixtures of goethite, schwertmannite and ferrihydrite, and their degradation activity against soman considerably increases. The best activities for the degradation of sulphur mustard (97.9% in 64 min) and soman (97.9% in 64 min) were observed for FeMn{sub 7}5 with 32.6 wt.% Fe (36.8 wt.% Mn) and FeMn{sub 3}7U with 60.8 wt.% Fe (10.1 wt.% Mn) samples, respectively.

  7. Bio-templated synthesis of lithium manganese oxide microtubes and their application in Li+ recovery.

    PubMed

    Yu, Qianqian; Sasaki, Keiko; Hirajima, Tsuyoshi

    2013-11-15

    Microbial transformations, a primary pathway for the Mn oxides formation in nature, provide potential for material-oriented researchers to fabricate new materials. Using Mn oxidizing fungus Paraconiothyrium sp. WL-2 as a bio-oxidizer as well as a bio-template, a special lithium ion sieve with microtube morphology was prepared through a solid-state transformation. Varying the calcination temperature from 300 to 700 C was found to influence sample properties and consequently, the adsorption of Li(+). Lithium manganese oxide microtube (LMO-MTs) calcined at different temperatures as well as their delithiated products (HMO-MTs) were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Calcination temperatures affect not only the content but also the crystal structure of LMO spinel, which is important in Li(+) adsorption. The optimized sample was obtained after calcination at 500 C for 4h, which shows higher Li(+) adsorption capacity than particulate materials. PMID:24007997

  8. THEORETICAL TECHNIQUE FOR DETERMINING THE CUMULATIVE IMPACT OF IRON AND MANGANESE OXIDATION IN STREAMS RECEIVING COAL-MINE DISCHARGE.

    USGS Publications Warehouse

    Bobay, Keith E.; Banaszak, Konrad J.

    1985-01-01

    Two U. S. Geological Survey computer programs are modified and linked to predict the cumulative impact of iron and manganese oxidation in coal-mine discharge on the dissolved-chemical quality of a receiving stream. The coupled programs calculate the changes in dissolved-iron, dissolved-manganese, and dissolved-oxygen concentrations, and the pH of surface water downstream from the discharge. The cumulative impact of representative discharges from several coal mines on stream quality in a small watershed in southwestern Indiana was simulated to determine the effectiveness and sensitivity of the coupled programs.

  9. Heterologous Expression and Characterization of the Manganese-Oxidizing Protein from Erythrobacter sp. Strain SD21

    PubMed Central

    Nakama, Katherine; Medina, Michael; Lien, Ahn; Ruggieri, Jordan; Collins, Krystle

    2014-01-01

    The manganese (Mn)-oxidizing protein (MopA) from Erythrobacter sp. strain SD21 is part of a unique enzymatic family that is capable of oxidizing soluble Mn(II). This enzyme contains two domains, an animal heme peroxidase domain, which contains the catalytic site, followed by a C-terminal calcium binding domain. Different from the bacterial Mn-oxidizing multicopper oxidase enzymes, little is known about MopA. To gain a better understanding of MopA and its role in Mn(II) oxidation, the 238-kDa full-length protein and a 105-kDa truncated protein containing only the animal heme peroxidase domain were cloned and heterologously expressed in Escherichia coli. Despite having sequence similarity to a peroxidase, hydrogen peroxide did not stimulate activity, nor was activity significantly decreased in the presence of catalase. Both pyrroloquinoline quinone (PQQ) and hemin increased Mn-oxidizing activity, and calcium was required. The Km for Mn(II) of the full-length protein in cell extract was similar to that of the natively expressed protein, but the Km value for the truncated protein in cell extract was approximately 6-fold higher than that of the full-length protein, suggesting that the calcium binding domain may aid in binding Mn(II). Characterization of the heterologously expressed MopA has provided additional insight into the mechanism of bacterial Mn(II) oxidation, which will aid in understanding the role of MopA and Mn oxidation in bioremediation and biogeochemical cycling. PMID:25172859

  10. Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

    NASA Astrophysics Data System (ADS)

    Abdel Hameed, R. M.; Fetohi, Amani E.; Amin, R. S.; El-Khatib, K. M.

    2015-12-01

    The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt-MnO2/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO2 improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt-MnO2/C towards methanol oxidation in H2SO4 solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169 mV when MnO2 is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt-MnO2/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt-MnO2/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).

  11. Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study

    SciTech Connect

    J Durand; S Senanayake; S Suib; D Mullins

    2011-12-31

    The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340-1390 cm{sup -1} are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm{sup -1} band gap between v{sub s}OCO and v{sub as}OCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K{sup +} {hor_ellipsis} OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.

  12. Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study

    SciTech Connect

    Durand, Jason; Senanayake, Sanjaya D; Mullins, David R; Suib, Steven

    2010-01-01

    The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340-1390 cm{sup -1} are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm{sup -1} band gap between v{sub s}OCO and v{sub as}OCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K{sup +} {hor_ellipsis} OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.

  13. a Manganese Oxide Contained Coating for Biodegradable AZ31B Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Yan, Tingting; Tan, Lili; Xiong, Dangsheng; Zhang, Bingchun; Yang, Ke

    A manganese oxide contained coating was prepared on biodegradable AZ31B magnesium alloy to control the degradation of AZ31B and improve its biocompatibility. Morphology, composition, and corrosion resistance of the coating were studied. The SEM observations showed that the coating was approximately 4-6 ?m in thickness with net-like microcracks. The XPS analysis indicated that the coating was mainly composed of MgO, Mg(OH)2, MnO2, Mn2O3, and Mn3O4. It was found that AZ31B with such coating showed better corrosion resistance in simulated blood plasma through electrochemical and immersion tests. The hemolytic assay indicated that the treated AZ31B had no hemolytic effect.

  14. Doubling the capacity of lithium manganese oxide spinel by a flexible skinny graphitic layer.

    PubMed

    Noh, Hyun Kuk; Park, Han-Saem; Jeong, Hu Young; Lee, Sang Uck; Song, Hyun-Kon

    2014-05-12

    By coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220?mA?h?g(-1) at a cutoff voltage of 2.5?V. The graphitic layers 1)?provided a facile electron-transfer highway without hindering ion access and, more interestingly, 2)?stabilized the structural distortion at the 3?V region reaction. The gain was won by a simple method in which microsized LMO was ball-milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10?layers and combined them together with an extremely intimate contact. Ab?initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3?V region and could be overcome by the graphitic skin strategy proposed. PMID:24706561

  15. Aerobic oxidation of anthracene in the presence of manganese porphyrinates and NaBH/sub 4/ reducing agent

    SciTech Connect

    Lukashova, E.A.; Solov'ev, A.B.; Chugreev, A.L.; Enikolopyan, N.S.

    1987-12-01

    The authors investigate the kinetics of anthracene oxidation by molecular oxygen in the presence of manganese, iron, and cobalt porphyrinate catalysts and a sodium borohydride reducing agent at room temperature in solutions of ethanol or ethanol with chloroform and benzene. Effective rate constants for the reactions are determined based on the amount of anthraquinone formed in the reaction. In all cases with the exception of cobalt tetraphenylporphyrinate the only oxidation product was anthraquinone. Its structure was verified by NMR and IR spectroscopy.

  16. Theory of chemical bonds in metalloenzymes - Manganese oxides clusters in the oxygen evolution center -

    NASA Astrophysics Data System (ADS)

    Yamaguchi, K.; Shoji, M.; Saito, T.; Isobe, H.; Yamada, S.; Nishihara, S.; Kawakami, T.; Kitagawa, Y.; Yamanaka, S.; Okumura, M.

    2012-12-01

    In early 1980 we have initiated broken-symmetry (BS) MO theoretical calculations of transition-metal oxo species M = O (M = Ti,V,Cr,Mn,Fe,Ni,Cu) to elucidate the nature of d?-p? and d?-p? bonds. It has been concluded that high-valent M = O species such as [Mn(IV) = O]2+ and [Fe(IV) = O]2+ exhibit electrophilic property in a sharp contrast with nucleophilic character of low-valent M = O bonds: [M(II)O2-]0, and closed-shell d?-p? bonds of high-valent M = O species often suffer the triplet-instability, giving rise to open-shell (BS) configurations with significant metal-diradical (MDR) character: M-O: note that these bonds are therefore regarded as typical examples of strongly correlated electron systems. Because of the MDR character, 1,4-metal diradical mechanism was indeed preferable to four-centered mechanism in the case of addition reaction of naked Mn(IV) = O to ethylene. Recently the manganese-oxo species have been receiving renewed interest in relation to catalytic cycle of oxygen evolution from water molecules in the photosynthesis II (PSII) system. Accumulated experimental results indicate that this process is catalyzed with four manganese oxide clusters coordinated with calcium ion (CaMn4O4). Past decade we have performed BS MO theoretical investigations of manganese oxide clusters related to CaMn4O4. These calculations have elucidated that high-valent Mn(X) = O (X = IV,V) bonds exhibit intermediate MDR character (y=40-60%) in the case of total low-spin (LS) configuration but the MDR character decreases with coordination of Ca2+ and water molecules. While the MDR character of the Mn-oxo bonds becomes very high at the high-spin (HS) configuration. Our computational results enabled us to propose two possible mechanisms on the theoretical ground: (A) electrophilic (EP) mechanism and (B) radical coupling (RC) mechanism. The theoretical results indicate that the EP mechanism is preferable for the low-spin (LS) state in polar media like in the protein environments (native OEC), whereas the RC mechanism is feasible at the state without such environmental stabilization: local singlet and local triplet diradical mechanisms are proposed for the OO coupling process. Possibilities of EP and RC mechanisms are examined in comparison with a lot of experimental results accumulated and theoretical results with several groups.

  17. Structure-property relationships in manganese oxide--mesoporous silica nanoparticles used for T1-weighted MRI and simultaneous anti-cancer drug delivery.

    PubMed

    Chen, Yu; Chen, Hangrong; Zhang, Shengjian; Chen, Feng; Sun, Shikuan; He, Qianjun; Ma, Ming; Wang, Xia; Wu, Huixia; Zhang, Lingxia; Zhang, Linlin; Shi, Jianlin

    2012-03-01

    The extremely low longitudinal relaxivity (r(1)) of manganese oxide has severely impeded their substitution for cytotoxic gadolinium-based contrast agents for safe clinical magnetic resonance imaging (MRI). Here, we report on a synthetic strategy of chemical oxidation/reduction reaction in-situ in mesopores, followed by hydrogen reduction, for the fabrication of non-toxic manganese oxide/MSNs-based MRI-T(1) contrast agents with highly comparable imaging performance to commercial Gd-based agents. This strategy involves a "soft-templating" process to prepare mesoporous silica nanoparticles, in-situ reduction of MnO(4)(-) by the "soft templates" in mesopores and heat treatment under reducing atmosphere, to disperse manganese oxide nanoparticles within mesopores. This special nanostructure combines the merits of nanopores for maximum manganese paramagnetic center accessibility for water molecules for enhanced MRI performance and encapsulation/sustained release/intracellular delivery of drugs. The synthesized manganese oxide/MSNs were successfully assessed as a high performance contrast agent for MRI-T(1) both in intro and in vivo, and meanwhile, was also demonstrated as an effective anti-cancer drug delivery (doxorubicin) vehicle, therefore, a family of manganese-based theranostics was successfully demonstrated based on the manganese oxide/MSNs composite. PMID:22177841

  18. Metals, Oxidative Stress and Neurodegeneration: A focus on Iron, Manganese and Mercury

    PubMed Central

    Farina, Marcelo; Avila, Daiana Silva; da Rocha, João Batista Teixeira

    2013-01-01

    Essential metals are crucial for the maintenance of cell homeostasis. Among the 23 elements that have known physiological functions in humans, 12 are metals, including iron (Fe) and manganese (Mn). Nevertheless, excessive exposure to these metals may lead to pathological conditions, including neurodegeneration. Similarly, exposure to metals that do not have known biological functions, such as mercury (Hg), also present great health concerns. This reviews focuses on the neurodegenerative mechanisms and effects of Fe, Mn and Hg. Oxidative stress (OS), particularly in mitochondria, is a common feature of Fe, Mn and Hg toxicity. However, the primary molecular targets triggering OS are distinct. Free cationic iron is a potent pro-oxidant and can initiate a set of reactions that form extremely reactive products, such as OH•. Mn can oxidize dopamine (DA), generating reactive species and also affect mitochondrial function, leading to accumulation of metabolites and culminating with OS. Cationic Hg forms have strong affinity for nucleophiles, such as –SH and –SeH. Therefore, they target critical thiol- and selenol-molecules with antioxidant properties. Finally, we address the main sources of exposure to these metals, their transport mechanisms into the brain, and therapeutic modalities to mitigate their neurotoxic effects. PMID:23266600

  19. Manganese Doping of Magnetic Iron Oxide Nanoparticles: Tailoring Surface Reactivity for a Regenerable Heavy Metal Sorbent

    SciTech Connect

    Warner, Cynthia L.; Chouyyok, Wilaiwan; Mackie, Katherine E.; Neiner, Doinita; Saraf, Laxmikant; Droubay, Timothy C.; Warner, Marvin G.; Addleman, Raymond S.

    2012-02-28

    A method for tuning the analyte affinity of magnetic, inorganic nanostructured sorbents for heavy metal contaminants is described. The manganese-doped iron oxide nanoparticle sorbents have a remarkably high affinity compared to the precursor material. Sorbent affinity can be tuned toward an analyte of interest simply by adjustment of the dopant quantity. The results show that following the Mn doping process there is a large increase in affinity and capacity for heavy metals (i.e., Co, Ni, Zn, As, Ag, Cd, Hg, and Tl). Capacity measurements were carried out for the removal of cadmium from river water and showed significantly higher loading than the relevant commercial sorbents tested for comparison. The reduction in Cd concentration from 100 ppb spiked river water to 1 ppb (less than the EPA drinking water limit of 5 ppb for Cd) was achieved following treatment with the Mn-doped iron oxide nanoparticles. The Mn-doped iron oxide nanoparticles were able to load 1 ppm of Cd followed by complete stripping and recovery of the Cd with a mild acid wash. The Cd loading and stripping is shown to be consistent through multiple cycles with no loss of sorbent performance.

  20. Evaluation of OC/EC speciation by thermal manganese dioxide oxidation and the IMPROVE method.

    PubMed

    Fung, Kochy; Chow, Judith C; Watson, John G

    2002-11-01

    Ambient particulate samples are routinely analyzed for organic and elemental carbon (OC/EC) using either thermal manganese dioxide oxidation (TMO) or thermal volatilization-pyrolysis correction methods, such as the Interagency Monitoring of PROtected Visual Environments (IMPROVE) method with correction by reflectance, or a variation of the National Institute of Occupational Safety and Health (NIOSH) Method 5040 using thermal optical transmittance (TOT). With TMO, EC is modeled after the oxidation properties of submicron graphite and needle coke by MnO2, and is the fraction of total carbon (TC) that is not oxidized at >525 degrees C. In thermal volatilization methods, EC is the fraction of TC that accounts for the light extinction properties of the sample at the start of analysis. Chow et al. (2001) compared IMPROVE and NIOSH methods implemented on the same instrument using 60 samples of various types and found that NIOSH EC was lower than IMPROVE. This study compares total, organic, and elemental carbon measurements from the TMO and IMPROVE thermal optical reflectance (TOR) methods using a sample set consisting of 60 IMPROVE nonurban, 16 Korean urban, 10 Hong Kong urban, and 14 synthetic carbon black samples. PMID:12469720

  1. Early diagenetic processes generate iron and manganese oxide layers in the sediments of Lake Baikal, Siberia.

    PubMed

    Torres, Natascha T; Och, Lawrence M; Hauser, Peter C; Furrer, Gerhard; Brandl, Helmut; Vologina, Elena; Sturm, Michael; Brgmann, Helmut; Mller, Beat

    2014-04-01

    Distinct layers of iron(III) and manganese(IV) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH? (AOM) either via the reduction of sulphate (SO?(2-)) and the subsequent generation of Fe(II) by S(-II) oxidation, or directly coupled to Fe reduction. Dissolved Fe(II) diffuses upwards to reduce particulate Mn(IV) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH?(+) observed at locations with Mn(IV). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented. PMID:24619231

  2. Manganese scavenging and oxidation at hydrothermal vents and in vent plumes

    NASA Astrophysics Data System (ADS)

    Mandernack, Kevin W.; Tebo, Bradley M.

    1993-08-01

    Hydrothermal vents provide a major source of dissolved Mn(II) to the oceans, where concentrations range from 5 mM within the 350C hot smokers to just above ambient seawater concentration in far field vent plumes. The Mn(II)-rich environments within warm vents and vent plumes provide a suitable habitat for Mn(II) oxidizing bacteria. In order to compare rates of scavenging and oxidation of Mn(II) proximally within vent fields (<30 m from venting water and temperatures <16C) and distally within vent plumes, and to determine the relative contribution of microbes, incubation experiments using 54Mn as a radiotracer were conducted in situ and on collected water samples from three hydrothermal vent locations: the Guaymas basin (GB), the Galapagos spreading center (GA), and the Endeavor Ridge of the Juan de Fuca spreading center (JDF). Both the adsorbed and oxidized fractions of the total 54Mn scavenged were determined and found to often be significant (as high as 65 and 74%, respectively). Manganese scavenging rates were generally higher in in situ incubations than in incubations conducted on board ship. Inhibition of 54Mn scavenging by sodium azide provided evidence for microbially mediated Mn(II) uptake and oxidation in waters both proximal (GA and GB) and distal to the vents (GA and JDF), even at distances as great as 17 km from the ridge axis at JDF. The highest manganese scavenging rates were observed within the vent fields (up to 2.5 nM/day). The residence times of dissolved Mn(II) were shorter in the GB and GA vent fields (26 and 28 days) than in the JDF vent field (1.4 years). This difference may be due to different mechanisms of Mn(II) precipitation in operation. At the GA vent field Mn(II) precipitation was often strongly inhibited by sodium azide and therefore apparently due to microbial activity. In contrast, Mn(II) scavenging within the JDF vent field was not significantly affected by sodium azide. Because 54Mn scavenging in the JDF vent field was dependent on the presence of oxygen and a much larger fraction of the total 54Mn scavenged was adsorbed than oxidized, manganese scavenging appears to occur primarily by an abiological mechanism, perhaps coprecipitation with iron oxyhydroxides. In comparison to the vent fields, Mn(II) scavenging rates were lower within the vent plumes (<0.6 nM/ day for GA and <0.2 nM/day for JDF), whereas residence times were not significantly different (as low as 34 days for GA and 1.0 years for JDF). The short residence times (90 and 118 days) and high microbial activity measured in bottom waters beneath the vent plumes at GA and JDF probably resulted from enhanced scavenging by manganate-coated bacteria that settled out from the vent plume and accumulated near the bottom. Therefore, bacteria not only enhance the scavenging of Mn within vent waters, but also facilitate Mn deposition to the sediments.

  3. Chemical syntheses of manganese and tantalum oxide octahedral molecular sieves and their structural characterization by powder x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Duan, Niangao

    This research consists of soft chemical synthesis and structural investigations of manganese and tantalum oxide octahedral molecular sieves. These include the use of sol-gel, hydrothermal and reflux methods for syntheses and the employment of various techniques for characterization, especially the Rietveld analysis of powder X-ray diffraction data for structural refinements. The manganese oxide cryptomelane (K-OMS-2) with a tunnel structure and birnessite layered materials (OL-1) were prepared by the sol gel method. The synthesis consists of reacting MnO4- solutions with fumaric acid or glucose to form a gel, and heating the xerogels at a temperature effective to produce the final manganese oxide materials. These sol-gel methods give many advantages, such as high thermal stabilities of products, over other preparation routes. The synthetic parameters have been optimized to prepare pure K-OMS-2 and OL-1. The crystal structure of K-OMS-2 has been refined by the Rietveld method from in-house powder X-ray diffraction data. The potassium tantalate defect pyrochlores were prepared by hydrothermal methods at a temperature of 200C. The materials were crystallized from tantalum pentoxide in a potassium hydroxide solution, with a uniform crystal size of about 1 mum. They were ion-exchanged with H+ at low temperatures in a nitric acid solution. A BET surface area of 15 m 2/g was obtained. The structure of this defect pyrochlore and its acid exchanged form were determined by Rietveld refinement from powder X-ray diffraction data. The reflux method was also employed to search for new manganese oxide microporous materials. A ramsdellite material with a 1 x 2 tunnel structure and high surface area of 70 m2/g was prepared. Catalytic oxidations of hexane and cyclohexane with tert-butyl hydroperoxide have shown good activities with this catalyst. This investigation suggests that shape selectivity plays a role in the high catalytic activities of the oxidations of these saturated hydrocarbons.

  4. Superoxide production by a manganese-oxidizing bacterium facilitates iodide oxidation.

    PubMed

    Li, Hsiu-Ping; Daniel, Benjamin; Creeley, Danielle; Grandbois, Russell; Zhang, Saijin; Xu, Chen; Ho, Yi-Fang; Schwehr, Kathy A; Kaplan, Daniel I; Santschi, Peter H; Hansel, Colleen M; Yeager, Chris M

    2014-05-01

    The release of radioactive iodine (i.e., iodine-129 and iodine-131) from nuclear reprocessing facilities is a potential threat to human health. The fate and transport of iodine are determined primarily by its redox status, but processes that affect iodine oxidation states in the environment are poorly characterized. Given the difficulty in removing electrons from iodide (I(-)), naturally occurring iodide oxidation processes require strong oxidants, such as Mn oxides or microbial enzymes. In this study, we examine iodide oxidation by a marine bacterium, Roseobacter sp. AzwK-3b, which promotes Mn(II) oxidation by catalyzing the production of extracellular superoxide (O2(-)). In the absence of Mn(2+), Roseobacter sp. AzwK-3b cultures oxidized ?90% of the provided iodide (10 ?M) within 6 days, whereas in the presence of Mn(II), iodide oxidation occurred only after Mn(IV) formation ceased. Iodide oxidation was not observed during incubations in spent medium or with whole cells under anaerobic conditions or following heat treatment (boiling). Furthermore, iodide oxidation was significantly inhibited in the presence of superoxide dismutase and diphenylene iodonium (a general inhibitor of NADH oxidoreductases). In contrast, the addition of exogenous NADH enhanced iodide oxidation. Taken together, the results indicate that iodide oxidation was mediated primarily by extracellular superoxide generated by Roseobacter sp. AzwK-3b and not by the Mn oxides formed by this organism. Considering that extracellular superoxide formation is a widespread phenomenon among marine and terrestrial bacteria, this could represent an important pathway for iodide oxidation in some environments. PMID:24561582

  5. Superoxide Production by a Manganese-Oxidizing Bacterium Facilitates Iodide Oxidation

    PubMed Central

    Li, Hsiu-Ping; Daniel, Benjamin; Creeley, Danielle; Grandbois, Russell; Zhang, Saijin; Xu, Chen; Ho, Yi-Fang; Schwehr, Kathy A.; Kaplan, Daniel I.; Santschi, Peter H.; Hansel, Colleen M.

    2014-01-01

    The release of radioactive iodine (i.e., iodine-129 and iodine-131) from nuclear reprocessing facilities is a potential threat to human health. The fate and transport of iodine are determined primarily by its redox status, but processes that affect iodine oxidation states in the environment are poorly characterized. Given the difficulty in removing electrons from iodide (I?), naturally occurring iodide oxidation processes require strong oxidants, such as Mn oxides or microbial enzymes. In this study, we examine iodide oxidation by a marine bacterium, Roseobacter sp. AzwK-3b, which promotes Mn(II) oxidation by catalyzing the production of extracellular superoxide (O2?). In the absence of Mn2+, Roseobacter sp. AzwK-3b cultures oxidized ?90% of the provided iodide (10 ?M) within 6 days, whereas in the presence of Mn(II), iodide oxidation occurred only after Mn(IV) formation ceased. Iodide oxidation was not observed during incubations in spent medium or with whole cells under anaerobic conditions or following heat treatment (boiling). Furthermore, iodide oxidation was significantly inhibited in the presence of superoxide dismutase and diphenylene iodonium (a general inhibitor of NADH oxidoreductases). In contrast, the addition of exogenous NADH enhanced iodide oxidation. Taken together, the results indicate that iodide oxidation was mediated primarily by extracellular superoxide generated by Roseobacter sp. AzwK-3b and not by the Mn oxides formed by this organism. Considering that extracellular superoxide formation is a widespread phenomenon among marine and terrestrial bacteria, this could represent an important pathway for iodide oxidation in some environments. PMID:24561582

  6. Manganese Oxidation State as a Cause of Irritant Patch Test Reactions

    PubMed Central

    Shallcross, Laurie; Ritchie, Simon; Harberts, Erin; Tammaro, Antonella; Gaitens, Joanna; Gaspari, Anthony A.

    2015-01-01

    Background Manganese chloride (MnCl2) 2.5% is included in the extended metals patch test series to evaluate patients for contact hypersensitivity to this metal salt. Objectives The objective of this study was to prospectively determine the rate of allergic and irritant patch test reactions to MnCl2 (Mn(II)), Mn2O3 (Mn(III)), and KMnO4 (Mn(VII)) in a cohort of patients undergoing patch testing. Methods Fifty-eight patients were patch tested with MnCl2, Mn2O3, and KMnO4, each at 2.5% in petrolatum. Patch readings were taken at 48, and 72 or 96 hours, and scored using standard methods. Cultured monolayers of keratinocytes (KCs) were exposed to MnCl2, Mn2O3, and KMnO4 in aqueous culture medium, and cell survival and cytokine release were studied. Conclusions MnCl2 caused irritant patch test reactions in 41% of the cohort, whereas Mn2O3 and KMnO4 caused a significantly lower rate of irritant reactions (both 3%). No allergic morphologies were observed. Similarly, in cultured KC monolayers, only MnCl2 was cytotoxic to KC and induced tumor necrosis factor ? release. The oxidation state of manganese used for patch testing affects the irritancy of this metal salt, as Mn(II) caused an unacceptably high rate of irritant reactions in a cohort of patients. In vitro studies confirmed these clinical data, as only Mn(II) was cytotoxic to cultured monolayers of KC. PMID:24603521

  7. Electrocatalytic oxidation of dopamine based on non-covalent functionalization of manganese tetraphenylporphyrin/reduced graphene oxide nanocomposite.

    PubMed

    Sakthinathan, Subramanian; Lee, Hsin Fang; Chen, Shen-Ming; Tamizhdurai, P

    2016-04-15

    In the present work, a reduced graphene oxide (RGO) supported manganese tetraphenylporphyrin (Mn-TPP) nanocomposite was electrochemically synthesized and used for the highly selective and sensitive detection of dopamine (DA). The nuclear magnetic resonance, scanning electron microscopy and elemental analysis were confirmed the successful formation of RGO/Mn-TPP nanocomposite. The prepared RGO/Mn-TPP nanocomposite modified electrode exhibited an enhanced electrochemical response to DA with less oxidation potential and enhanced response current. The electrochemical studies revealed that the oxidation of the DA at the composite electrode is a surface controlled process. The cyclic voltammetry, differential pulse voltammetry and amperometry methods were enable to detect DA. The working linear range of the electrode was observed from 0.3 to 188.8μM, limit of detection was 8nM and the sensitivity was 2.606μAμM(-1)cm(-2). Here, the positively charged DA and negatively charged porphyrin modified RGO can accelerate the electrocatalysis of DA via electrostatic attraction, while the negatively charged ascorbic acid (AA) repulsed by the negatively charged electrode surface which supported for good selectivity. The good recovery results obtained for the determination of DA present in DA injection samples and human pathological sample further revealed the good practicality of RGO/Mn-TPP nanocomposite film modified electrode. PMID:26835582

  8. In situ synthesis of manganese oxides on polyester fiber for formaldehyde decomposition at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, Jinlong; Yunus, Rizwangul; Li, Jinge; Li, Peilin; Zhang, Pengyi; Kim, Jeonghyun

    2015-12-01

    Removal of low-level formaldehyde (HCHO) is of great interest for indoor air quality improvement. Supported materials especially those with low air pressure drop are of necessity for air purification. Manganese oxides (MnOx) was in situ deposited on the surface of fibers of a non-woven fabric made of polyethylene terephthalate (PET). As-synthesized MnOx/PET were characterized by SEM, XRD, TEM, ATR-FTIR and XPS analysis. The growth of MnOx layer on PET is thought to start with partial hydrolysis of PET, followed by surface oxidation by KMnO4 and then surface-deposition of MnOx particles from the bulk phase. The MnOx particles assembled with nanosheets were uniformly coated on the PET fibers. MnOx/PET showed good activity for HCHO decomposition at room temperature which followed the Mars-van Krevelen mechanism. The removal of HCHO was kept over 94% after 10 h continuous reaction under the conditions of inlet HCHO concentration ∼0.6 mg/m3, space velocity ∼17,000 h-1 and relative humidity∼50%. This research provides a facile method to deposit active MnOx onto polymers with low air resistance, and composite MnOx/PET material is promising for indoor air purification.

  9. Nutrient input influences fungal community composition and size and can stimulate manganese (II) oxidation in caves.

    PubMed

    Carmichael, Sarah K; Zorn, Bryan T; Santelli, Cara M; Roble, Leigh A; Carmichael, Mary J; Bruer, Suzanna L

    2015-08-01

    Little is known about the fungal role in biogeochemical cycling in oligotrophic ecosystems. This study compared fungal communities and assessed the role of exogenous carbon on microbial community structure and function in two southern Appalachian caves: an anthropogenically impacted cave and a near-pristine cave. Due to carbon input from shallow soils, the anthropogenically impacted cave had an order of magnitude greater fungal and bacterial quantitative-polymerase chain reaction (qPCR) gene copy numbers, had significantly greater community diversity, and was dominated by ascomycotal phylotypes common in early phase, labile organic matter decomposition. Fungal assemblages in the near-pristine cave samples were dominated by Basidiomycota typically found in deeper soils (and/or in late phase, recalcitrant organic matter decomposition), suggesting more oligotrophic conditions. In situ carbon and manganese (II) [Mn(II)] addition over 10 weeks resulted in growth of fungal mycelia followed by increased Mn(II) oxidation. A before/after comparison of the fungal communities indicated that this enrichment increased the quantity of fungal and bacterial cells, yet decreased overall fungal diversity. Anthropogenic carbon sources can therefore dramatically influence the diversity and quantity of fungi, impact microbial community function, and stimulate Mn(II) oxidation, resulting in a cascade of changes that can strongly influence nutrient and trace element biogeochemical cycles in karst aquifers. PMID:25865809

  10. Manganese oxide/titania materials for removal of NOx and elemental mercury from flue gas

    SciTech Connect

    Lei Ji; Pavani M. Sreekanth; Panagiotis G. Smirniotis; Stephen W. Thiel; Neville G. Pinto

    2008-07-15

    A novel catalyst for low temperature selective catalytic reduction (SCR) using CO as reductant, MnOx supported on titania, has been shown to be effective for both elemental mercury capture and low temperature SCR. In low temperature (200{sup o}C) SCR trials using an industrially relevant space velocity (50 000 h{sup -1}) and oxygen concentration (2 vol %), nearly quantitative reduction of NOx was obtained using CO as the reductant. Fresh catalyst used as an adsorbent for elemental mercury from an inert atmosphere showed remarkable mercury capture capacity, as high as 17.4 mg/g at 200{sup o}C. The catalyst effectively captured elemental mercury after use in NOx reduction. Mercury capture efficiency was not affected by the presence of water vapor. Mercury capacity was reduced in the presence of SO{sub 2}. Manganese loading and bed temperature, which influence surface oxide composition, were found to be important factors for mercury capture. X-ray photoelectron spectroscopy (XPS) results reveal that the mercury is present in its oxidized form (HgO) in spent catalyst, indicating the participation of lattice oxygen of the catalyst in the reaction. These results suggest that a single-step process integrating low temperature SCR and mercury capture from flue gas might be feasible. 42 refs., 10 figs., 2 tabs.

  11. Effect of additives on electrochemical performance of lithium nickel cobalt manganese oxide at high temperature

    NASA Astrophysics Data System (ADS)

    Kang, Kyoung Seok; Choi, Suneui; Song, JunHo; Woo, Sang-Gil; Jo, Yong Nam; Choi, Jungkyu; Yim, Taeeun; Yu, Ji-Sang; Kim, Young-Jun

    2014-05-01

    Lithium-nickel-cobalt-manganese oxide, Li[NixCoyMnz]O2 (NCM) is a low-cost cathode material with a high capacity and a moderately high rate capability, however, it still suffers from poor electrochemical performance. In this study, several types of additives are attempted to enhance the surface stability of high-Ni-content (Ni ? 60%) cathodes and the most effective additive turns out to be PS. The cycle performance in the presence of 2% PS is much improved at a high temperature of 60 C: (1) 98.9% of its initial capacity is preserved, (2) the increase in thickness is only 17.9%, preventing undesired swellings, and (3) gases are not generated in large amounts with the internal pressure being 56.4 kPa. The FT-IR spectroscopy results suggest that the surface of the cathode in the presence of 2% PS is covered with a film of alkyl sulfone components (RSOSR and RSO2SR), which is possibly formed by the electrochemical oxidation of PS. The current results confirm that the electrochemical performance of Ni-rich cathodes can be improved via the appropriate use of additives. They also indicate that among the tested additive candidates in this study, PS is highly desirable for enhancing the electrochemical performance of Ni-rich cathodes.

  12. Spatially Resolved Characterization of Biogenic Manganese Oxide Production within a Bacterial Biofilm

    PubMed Central

    Toner, Brandy; Fakra, Sirine; Villalobos, Mario; Warwick, Tony; Sposito, Garrison

    2005-01-01

    Pseudomonas putida strain MnB1, a biofilm-forming bacterial culture, was used as a model for the study of bacterial Mn oxidation in freshwater and soil environments. The oxidation of aqueous Mn+2 [Mn+2(aq)] by P. putida was characterized by spatially and temporally resolving the oxidation state of Mn in the presence of a bacterial biofilm, using scanning transmission X-ray microscopy (STXM) combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Mn L2,3 absorption edges. Subsamples were collected from growth flasks containing 0.1 and 1 mM total Mn at 16, 24, 36, and 48 h after inoculation. Immediately after collection, the unprocessed hydrated subsamples were imaged at a 40-nm resolution. Manganese NEXAFS spectra were extracted from X-ray energy sequences of STXM images (stacks) and fit with linear combinations of well-characterized reference spectra to obtain quantitative relative abundances of Mn(II), Mn(III), and Mn(IV). Careful consideration was given to uncertainty in the normalization of the reference spectra, choice of reference compounds, and chemical changes due to radiation damage. The STXM results confirm that Mn+2(aq) was removed from solution by P. putida and was concentrated as Mn(III) and Mn(IV) immediately adjacent to the bacterial cells. The Mn precipitates were completely enveloped by bacterial biofilm material. The distribution of Mn oxidation states was spatially heterogeneous within and between the clusters of bacterial cells. Scanning transmission X-ray microscopy is a promising tool for advancing the study of hydrated interfaces between minerals and bacteria, particularly in cases where the structure of bacterial biofilms needs to be maintained. PMID:15746332

  13. Biogenic precipitation of manganese oxides and enrichment of heavy metals at acidic soil pH

    NASA Astrophysics Data System (ADS)

    Mayanna, Sathish; Peacock, Caroline L.; Schäffner, Franziska; Grawunder, Anja; Merten, Dirk; Kothe, Erika; Büchel, Georg

    2014-05-01

    The precipitation of biogenic Mn oxides at acidic pH is rarely reported and poorly understood, compared to biogenic Mn oxide precipitation at near neutral conditions. Here we identified and investigated the precipitation of biogenic Mn oxides in acidic soil, and studied their role in the retention of heavy metals, at the former uranium mining site of Ronneburg, Germany. The site is characterized by acidic pH, low carbon content and high heavy metal loads including rare earth elements. Specifically, the Mn oxides were present in layers identified by detailed soil profiling and within these layers pH varied from 4.7 to 5.1, Eh varied from 640 to 660 mV and there were enriched total metal contents for Ba, Ni, Co, Cd and Zn in addition to high Mn levels. Using electron microprobe analysis, synchrotron X-ray diffraction and X-ray absorption spectroscopy, we identified poorly crystalline birnessite (δ-MnO2) as the dominant Mn oxide in the Mn layers, present as coatings covering and cementing quartz grains. With geochemical modelling we found that the environmental conditions at the site were not favourable for chemical oxidation of Mn(II), and thus we performed 16S rDNA sequencing to isolate the bacterial strains present in the Mn layers. Bacterial phyla present in the Mn layers belonged to Firmicutes, Actinobacteria and Proteobacteria, and from these phyla we isolated six strains of Mn(II) oxidizing bacteria and confirmed their ability to oxidise Mn(II) in the laboratory. The biogenic Mn oxide layers act as a sink for metals and the bioavailability of these metals was much lower in the Mn layers than in adjacent layers, reflecting their preferential sorption to the biogenic Mn oxide. In this presentation we will report our findings, concluding that the formation of natural biogenic poorly crystalline birnessite can occur at acidic pH, resulting in the formation of a biogeochemical barrier which, in turn, can control the mobility and bioavailability of heavy metals in acidic soil environments.

  14. Polyvinylpyrrolidone/reduced graphene oxide nanocomposites thin films coated on quartz crystal microbalance for NO2 detection at room temperature

    NASA Astrophysics Data System (ADS)

    Huang, Junlong; Xie, Guangzhong; Zhou, Yong; Xie, Tao; Tai, HuiLing; Yang, Guangjin

    2014-08-01

    Polyvinylpyrrolidone (PVP)/reduced graphene oxide (RGO) nanocomposites are sprayed on quartz crystal microbalance (QCM) for NO2 sensing. The thin films are characterized by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-VIS). The experimental results reveal that PVP/RGO sensor exhibits higher sensitivity and shorter recovery time than those of PVP. Besides, the response to 20 ppm NO2 is higher than other gases such as CO, CO2 and NH3 even at 100ppm. When the PVP/RGO sensor is exposed to these gases, the good selectivity to NO2 makes the sensor ideal for NO2 detection.

  15. Nanogold supported on manganese oxide doped alumina microspheres as a highly active and selective catalyst for CO oxidation in a H2-rich stream.

    PubMed

    Miao, Yu-Xin; Li, Wen-Cui; Sun, Qiang; Shi, Lei; He, Lei; Wang, Jing; Deng, Gao-Ming; Lu, An-Hui

    2015-12-28

    Manganese oxide-doped Al2O3 microspheres were synthesized via a redox method, and were then deposited with Au nanoparticles using a deposition-precipitation method. The obtained catalyst is not only highly active and selective for the preferential oxidation of CO in a H2-rich stream, but also shows excellent stability in the co-presence of H2O and CO2 at 80 C. PMID:26489890

  16. A cascade approach to hetero-pentanuclear manganese-oxide clusters in polyoxometalates and their single-molecule magnet properties.

    PubMed

    Suzuki, Kosuke; Sato, Rinta; Minato, Takuo; Shinoe, Masahiro; Yamaguchi, Kazuya; Mizuno, Noritaka

    2015-08-28

    Structurally well-defined hetero-pentanuclear manganese-oxide clusters {MMn4} were successfully synthesized in TBA7Hn[MMn4(OH)2(A-?-SiW9O34)2]2H2OC2H4Cl2 (, M = Fe(iii), Co(ii), Ni(ii), Cu(ii), Ga(iii)) by sequential introduction of metal cations into the trivacant lacunary polyoxometalates (POMs). The pentanuclear manganese-oxide cluster {Mn5} showed a small spin ground state and a low energy barrier for magnetization relaxation. In contrast, the magnetic interactions in the hetero-pentanuclear clusters could be controlled by the arrangements of metals, and the clusters showed large magnetic anisotropy and single-molecule magnet behavior. In particular, the cluster {FeMn4} in (S = 11/2) showed the slowest relaxation and the highest energy barrier among the previously reported transition metal-containing POMs. PMID:26000986

  17. Translocation of Inhaled Ultrafine Manganese Oxide Particles to the Central Nervous System

    PubMed Central

    Elder, Alison; Gelein, Robert; Silva, Vanessa; Feikert, Tessa; Opanashuk, Lisa; Carter, Janet; Potter, Russell; Maynard, Andrew; Ito, Yasuo; Finkelstein, Jacob; Oberdörster, Günter

    2006-01-01

    Background Studies in monkeys with intranasally instilled gold ultrafine particles (UFPs; < 100 nm) and in rats with inhaled carbon UFPs suggested that solid UFPs deposited in the nose travel along the olfactory nerve to the olfactory bulb. Methods To determine if olfactory translocation occurs for other solid metal UFPs and assess potential health effects, we exposed groups of rats to manganese (Mn) oxide UFPs (30 nm; ~ 500 μg/m3) with either both nostrils patent or the right nostril occluded. We analyzed Mn in lung, liver, olfactory bulb, and other brain regions, and we performed gene and protein analyses. Results After 12 days of exposure with both nostrils patent, Mn concentrations in the olfactory bulb increased 3.5-fold, whereas lung Mn concentrations doubled; there were also increases in striatum, frontal cortex, and cerebellum. Lung lavage analysis showed no indications of lung inflammation, whereas increases in olfactory bulb tumor necrosis factor-α mRNA (~ 8-fold) and protein (~ 30-fold) were found after 11 days of exposure and, to a lesser degree, in other brain regions with increased Mn levels. Macrophage inflammatory protein-2, glial fibrillary acidic protein, and neuronal cell adhesion molecule mRNA were also increased in olfactory bulb. With the right nostril occluded for a 2-day exposure, Mn accumulated only in the left olfactory bulb. Solubilization of the Mn oxide UFPs was < 1.5% per day. Conclusions We conclude that the olfactory neuronal pathway is efficient for translocating inhaled Mn oxide as solid UFPs to the central nervous system and that this can result in inflammatory changes. We suggest that despite differences between human and rodent olfactory systems, this pathway is relevant in humans. PMID:16882521

  18. Removal and Recovery of Toxic Silver Ion Using Deep-Sea Bacterial Generated Biogenic Manganese Oxides

    PubMed Central

    Pei, Yuanjun; Chen, Xiao; Xiong, Dandan; Liao, Shuijiao; Wang, Gejiao

    2013-01-01

    Products containing silver ion (Ag+) are widely used, leading to a large amount of Ag+-containing waste. The deep-sea manganese-oxidizing bacterium Marinobacter sp. MnI7-9 efficiently oxidizes Mn2+ to generate biogenic Mn oxide (BMO). The potential of BMO for recovering metal ions by adsorption has been investigated for some ions but not for Ag+. The main aim of this study was to develop effective methods for adsorbing and recovering Ag using BMO produced by Marinobacter sp. MnI7-9. In addition, the adsorption mechanism was determined using X-ray photoelectron spectroscopy analysis, specific surface area analysis, adsorption kinetics and thermodynamics. The results showed that BMO had a higher adsorption capacity for Ag+ compared to the chemical synthesized MnO2 (CMO). The isothermal absorption curves of BMO and CMO both fit the Langmuir model well and the maximum adsorption capacities at 28C were 8.097 mmol/g and 0.787 mmol/g, for BMO and CMO, respectively. The change in enthalpy (?H?) for BMO was 59.69 kJ/mol indicating that it acts primarily by chemical adsorption. The change in free energy (?G?) for BMO was negative, which suggests that the adsorption occurs spontaneously. Ag+ adsorption by BMO was driven by entropy based on the positive ?S? values. The Ag+ adsorption kinetics by BMO fit the pseudo-second order model and the apparent activation energy of Ea is 21.72 kJ/mol. X-ray photoelectron spectroscopy analysis showed that 15.29% Ag+ adsorbed by BMO was transferred to Ag(0) and meant that redox reaction had happened during the adsorption. Desorption using nitric acid and Na2S completely recovered the Ag. The results show that BMO produced by strain MnI7-9 has potential for bioremediation and reutilization of Ag+-containing waste. PMID:24312566

  19. Development of optically transparent water oxidation catalysts using manganese pyrophosphate compounds.

    PubMed

    Takashima, Toshihiro; Hotori, Yuki; Irie, Hiroshi

    2015-11-01

    One challenge in artificial photosynthetic systems is the development of active oxygen evolution catalysts composed of abundant elements. The oxygen evolution activities of manganese pyrophosphate compounds were examined in electrochemical and photochemical experiments. Electrocatalysis using calcium-manganese pyrophosphate exhibited good catalytic ability under neutral pH and an oxygen evolution reaction was driven with a small overpotential (?<100mV). UV-vis diffuse reflectance measurements revealed that manganese pyrophosphates exhibit weak absorption in the visible light region while commonly used oxygen evolution catalysts exhibit intense absorption. Therefore, the efficient light absorption of a photocatalyst was retained even after surface modification with a manganese pyrophosphate, and photochemical oxygen evolution was achieved by using magnesium ferrite modified with manganese pyrophosphate nanoparticles under the illumination of visible light at wavelength of over 420nm. PMID:25648929

  20. Solar-thermal Water Splitting Using the Sodium Manganese Oxide Process & Preliminary H2A Analysis

    SciTech Connect

    Francis, Todd M; Lichty, Paul R; Perkins, Christopher; Tucker, Melinda; Kreider, Peter B; Funke, Hans H; Lewandowski, A; Weimer, Alan W

    2012-10-24

    There are three primary reactions in the sodium manganese oxide high temperature water splitting cycle. In the first reaction, Mn2O3 is decomposed to MnO at 1,500°C and 50 psig. This reaction occurs in a high temperature solar reactor and has a heat of reaction of 173,212 J/mol. Hydrogen is produced in the next step of this cycle. This step occurs at 700°C and 1 atm in the presence of sodium hydroxide. Finally, water is added in the hydrolysis step, which removes NaOH and regenerates the original reactant, Mn2O3. The high temperature solar-driven step for decomposing Mn2O3 to MnO can be carried out to high conversion without major complication in an inert environment. The second step to produce H2 in the presence of sodium hydroxide is also straightforward and can be completed. The third step, the low temperature step to recover the sodium hydroxide is the most difficult. The amount of energy required to essentially distill water to recover sodium hydroxide is prohibitive and too costly. Methods must be found for lower cost recovery. This report provides information on the use of ZnO as an additive to improve the recovery of sodium hydroxide.

  1. Facile synthesis of manganese ferrite/graphene oxide nanocomposites for controlled targeted drug delivery

    NASA Astrophysics Data System (ADS)

    Wang, Guangshuo; Ma, Yingying; Zhang, Lina; Mu, Jingbo; Zhang, Zhixiao; Zhang, Xiaoliang; Che, Hongwei; Bai, Yongmei; Hou, Junxian

    2016-03-01

    In this study, manganese ferrite/graphene oxide (MnFe2O4/GO) nanocomposites as controlled targeted drug delivery were prepared by a facile sonochemical method. It was found that GO nanosheets were fully exfoliated and decorated with MnFe2O4 nanoparticles having diameters of 5-13 nm. The field-dependent magnetization curve indicated superparamagnetic behavior of the obtained MnFe2O4/GO with saturation magnetization of 34.9 emu/g at room temperature. The in vitro cytotoxicity testing exhibited negligible cytotoxicity of as-prepared MnFe2O4/GO even at the concentration as high as 150 μg/mL. Doxorubicin hydrochloride (DOX) as an anti-tumor model drug was utilized to explore the application potential of MnFe2O4/GO for controlled drug delivery. The drug loading capacity of this nanocarrier was as high as 0.97 mg/mg and the drug release behavior showed a sustained and pH-responsive way.

  2. Layered manganese oxide intergrowth electrodes for rechargeable lithium batteries: Part 1-substitution with Co or Ni

    SciTech Connect

    Dolle, Mickael; Patoux, Sebastien; Doeff, Marca M.

    2004-09-08

    Lithium manganese oxides substituted with nickel or cobalt were characterized electrochemically in lithium cell configurations. The compounds studied were either single-phase layered structures with either primarily O2 or O3 stacking arrangements, or O2/O3 intergrowths, prepared from P2, P3 and P2/P3 sodium-containing precursors, respectively. The stacking arrangements are extremely sensitive to the Na/T. M. (T. M. = transition metal) ratios and the level of substitution. Phase diagrams showing the stability regions of the various arrangements for the Na-Ni-Mn-O system are presented. A possible correlation between vacancies and electrochemical performance is suggested. For high levels of substitution with Ni, fewer defects are possible for materials containing more O3 component and higher discharge capacities can be achieved, but spinel conversion upon cycling also occurs more rapidly as the O3 content increases. Intergrowths show intermediate behavior and represent a potential route towards designing stable, high capacity electrodes.

  3. Removal of lead ions by acid activated and manganese oxide-coated bentonite.

    PubMed

    Eren, E; Afsin, B; Onal, Y

    2009-01-30

    This paper presents the adsorption of Pb(II) from aqua solutions onto Unye (Turkey) bentonite in raw (RB), acid activated (AAB) and manganese oxide-coated (MCB) forms. Adsorption of Pb(II) by RB, AAB and MCB sample was investigated as a function of the initial Pb(II) concentration, solution pH, ionic strength, temperature and inorganic ligand (Cl(-)). Changes in the surfaces and structure were characterized by means of XRD, IR and potentiometric titration. The Langmuir monolayer adsorption capacities of RB, AAB and MCB in 0.1M KNO(3) solution were estimated as 16.70, 8.92 and 58.88 mg/g, respectively. The spontaneity of the adsorption process is established by decrease in DeltaG which varied from -21.60 to -28.60 kJ/mol (RB), -22.63 to -29.98 kJ/mol (AAB) and -19.57 to -26.22 (MCB) in temperature range 303-338 K. PMID:18501507

  4. Electrochemical deposition of silver on manganese dioxide coated reduced graphene oxide for enhanced oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Lee, Kyungmi; Ahmed, Mohammad Shamsuddin; Jeon, Seungwon

    2015-08-01

    We have prepared a reduced graphene oxide (rGO)-supported silver (Ag) and manganese dioxide (MnO2) deposited porous-like catalyst (denoted as rGO/MnO2/Ag) through a facile electrochemical deposition route and have been used as a cathode catalyst for oxygen reduction reaction (ORR) in alkaline fuel cells. The physical properties of rGO/MnO2/Ag have been investigated via several instrumental methods. This material exhibits a polycrystalline structure characterized by Ag/MnO2 microsphere formation as a result of Ostwald ripening. The X-ray diffraction and X-ray photoelectron spectroscopy data reveal that the MnO2 and Ag have been slightly alloyed and Mn presents with the dioxide form on rGO. The electrochemical properties of the electrocatalyst have been studied via several voltammetric methods. The results demonstrated that the rGO/MnO2/Ag has an excellent catalytic activity for ORR in alkaline media compared to the other tested electrodes. Particularly, it shows 1.2 times higher current density and better electron transfer rate at 0.3 V per O2 than that of 20 wt% Pt/C. The other kinetic analysis reveals that the O2 has reduced directly to H2O through a nearly four-electron pathway with better anodic fuel tolerance and duration performance than that of 20% Pt/C.

  5. The Influence of Manganese Oxide on the Sintering Behavior of Yttria Tetragonal Zirconia

    SciTech Connect

    Meenaloshini, S.; Amiriyan, M.; Sankar, U.; Tolouei, R.; Ramesh, S.

    2011-01-17

    The sintering behavior of yttria-stabilized zirconia, with the influence of small additions of MnO{sub 2}(up to 1 wt %) sintered over the temperature range from 1250 deg. C to 1500 deg. C was investigated. It was found that the mechanical properties of Y-TZP were dependent on the dopant amount and sintering temperature. The results revealed that relative densities above 97.5% of theoretical (i.e. >5.95 Mgm{sup -3}) could be obtained in Y-TZPs sintered at low temperatures, 1250 deg. C and 1300 deg. C, with the additions of {<=}0.3 wt% MnO{sub 2}. In comparison to the undoped samples, the additions of up to 1 wt%MnO{sub 2} and for sintering up to 1350 deg. C was found to be beneficial in enhancing the Vickers hardness of the ceramic. The fracture toughness of Y-TZP however, was found to increase only in the 1 wt% MnO{sub 2}-doped samples when sintered above 1400 deg. C. The relation between the measured mechanical properties is discussed with the emphasis on the role of the manganese oxide.

  6. The Influence of Manganese Oxide on the Sintering Behavior of Yttria Tetragonal Zirconia

    NASA Astrophysics Data System (ADS)

    Meenaloshini, S.; Amiriyan, M.; Sankar, U.; Tolouei, R.; Ramesh, S.

    2011-01-01

    The sintering behavior of yttria-stabilized zirconia, with the influence of small additions of MnO2 (up to 1 wt %) sintered over the temperature range from 1250 C to 1500 C was investigated. It was found that the mechanical properties of Y-TZP were dependent on the dopant amount and sintering temperature. The results revealed that relative densities above 97.5% of theoretical (i.e. >5.95 Mgm-3) could be obtained in Y-TZPs sintered at low temperatures, 1250 C and 1300 C, with the additions of ?0.3 wt% MnO2. In comparison to the undoped samples, the additions of up to 1 wt% MnO2 and for sintering up to 1350 C was found to be beneficial in enhancing the Vickers hardness of the ceramic. The fracture toughness of Y-TZP however, was found to increase only in the 1 wt% MnO2-doped samples when sintered above 1400 C. The relation between the measured mechanical properties is discussed with the emphasis on the role of the manganese oxide.

  7. Material characteristics of perovskite manganese oxide thin films for bolometric applications

    SciTech Connect

    Goyal, A.; Rajeswari, M.; Shreekala, R.; Lofland, S.E.; Bhagat, S.M.; Boettcher, T.; Kwon, C.; Ramesh, R.; Venkatesan, T.

    1997-10-01

    We are optimizing thin films of perovskite manganese oxides for bolometric applications. We have studied the relevant material characteristics of several members of this family namely, La{sub 0.7}Ba{sub 0.3}MnO{sub 3}, La{sub 0.7}Sr{sub 0.3}MnO{sub 3}, La{sub 0.7}Ca{sub 0.3}MnO{sub 3}, and Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}. Here, we discuss issues related to the choice of material, the influence of deposition parameters, and postdeposition heat treatments on the relevant characteristics such as the resistivity-peak temperature (T{sub p}) and the temperature coefficient of resistance (TCR). For a given material, a higher peak temperature implies a larger temperature coefficient of resistance. In contrast, on comparing different material systems, the TCR tends to decrease as T{sub p} increases. {copyright} {ital 1997 American Institute of Physics.}

  8. Direct and environmentally benign synthesis of manganese oxide/graphene composites from graphite for electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Hae-Min; Jeong, Gyoung Hwa; Kang, Doo Won; Kim, Sang-Wook; Kim, Chang-Koo

    2015-05-01

    We develop a direct and environmentally benign method to prepare manganese oxide (Mn3O4)/graphene composites via one-step hydrothermal synthesis from graphite without using strong acids and toxic reducing agents. Structural and morphological analyses reveals that the irregularly shaped Mn3O4 nanoparticles are well-dispersed on the graphene flakes. Cyclic voltammetry and galvanostatic charge-discharge tests indicate that the charge-storing mechanism of the Mn3O4/graphene composites is pseudocapacitive. The Mn3O4/graphene composite exhibits a specific capacitance of 367 F/g at a current density of 5 A/g. After 3000 charge-discharge cycles, the Mn3O4/graphene electrode retains 91.8% of its initial specific capacitance. From electrochemical impedance spectra, it is evident that the changes in both the equivalent series resistance and charge-transfer resistance of the Mn3O4/graphene electrode before and after 3000 charge-discharge cycles are small, indicating good cycling and electrochemical stability of the Mn3O4/graphene electrode.

  9. Effect of pH on morphology and supercapacitive properties of manganese oxide/polypyrrole nanocomposite

    NASA Astrophysics Data System (ADS)

    Gan, John Kevin; Lim, Yee Seng; Huang, Nay Ming; Lim, Hong Ngee

    2015-12-01

    In the present work, manganese oxide/polypyrrole (MnO2/PPy) nanocomposites with compact sheet, fibrous-porous, and granular morphologies were successfully synthesized using a simple, one step in situ chemical synthesis method. Their morphologies were tunable by varying the pH of the reactant's solution, which was very simple and scalable. Moreover, their electrochemical behaviors were greatly influenced by the pH of the reactant's solution. The optimum pH condition was found to be 4.0, producing an MnO2/PPy nanocomposite with high porosity. The porosity of the nanocomposite effectively improved its specific surface area, and its pore accessibility enabled the rapid intercalation/deintercalation of the electrolyte. As a result, a high specific capacitance of up to 312 F g-1 at 10 mV s-1 was obtained for the porous nanocomposite. A symmetric supercapacitor device built from the porous MnO2/PPy nanocomposite yielded a specific capacitance of 142 F g-1 per mass of one electrode and exhibited remarkable cycling stability, with 93.2% capacitance retention over 1000 charge/discharge cycles. These features show the promise of porous MnO2/PPy nanocomposite as an electrode material for high-performance supercapacitors.

  10. Complexation and redox interactions between aqueous plutonium and manganese oxide interfaces

    SciTech Connect

    Shaughnessy, Dawn A.; Nitsche, Heino; Booth, Corwin H.; Shuh, David K.; Waychunas, Glenn A.; Wilson, Richard E.; Cantrell, Kirk J.; Serne, R. Jeffrey

    2001-11-01

    The sorption of Pu(VI) and Pu(V) onto manganite (MnOOH) and Hausmannite (Mn3O4) was studied at pH 5. Manganite sorbed 21-24% from a 1x10-4 M plutonium solution and the hausmannite removed between 43-66% of the plutonium. The increased sorption by hausmannite results from its larger surface area (about twice that of manganite) plus a larger number of active surface sites. X-ray absorption near-edge structure (XANES) spectra taken at the Pu LIII edge were compared to standard spectra of plutonium in single oxidation states. Based on these spectra, it appears that both manganite and hausmannite reduce the higher valent plutonium species to Pu(IV). Between 53-59% of the plutonium was present as Pu(IV) in the manganite samples while 55-61% of the plutonium complexed to the hausmannite had also been reduced to Pu(IV). The exact mechanism behind this redox interaction between the plutonium and the manganese needs to be identified.

  11. Lattice-mismatch Strain Effects in Electron-Doped Calcium Manganese Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Hart, Cacie; Yong, Grace; Warecki, Zoey; Chaudhry, Adeel; Sharma, Prakash; Johnson, Anthony; Schaefer, David; Kolagani, Rajeswari

    2015-03-01

    Electron-doped Calcium Manganese Oxide (CaMnO3-?) thin films are of interest for use as photocatalysts and fuel cell electrodes in renewable energy applications. Oxygen stoichiometry of the films is a key parameter for the functionality in these applications. Currently, we are investigating the properties of (CaMnO3-?) films grown by pulsed laser deposition. The thin films are epitaxially grown on LaAlO3 and SrTiO3 substrates. Both of these substrates have larger in-plane lattice parameters than CaMnO3-?, which leads to bi-axial tensile strain in the thin films. We have characterized the thickness dependence of structural, electrical, and morphological properties of these films using high resolution x-ray diffraction, temperature dependent electrical resistivity measurements, and atomic force microscopy. The thickness dependence is characteristically different from what has been preciously observed in thin films of hole-doped manganites. Our results suggest that coupling between tensile strain and oxygen deficiency affect the electrical and structural properties of the material. NSF Grant ECCS1128586.

  12. Caldimonas manganoxidans gen. nov., sp. nov., a poly(3-hydroxybutyrate)-degrading, manganese-oxidizing thermophile.

    PubMed

    Takeda, Minoru; Kamagata, Yoichi; Ghiorse, William C; Hanada, Satoshi; Koizumi, Jun-ichi

    2002-05-01

    A poly(3-hydroxybutyrate) (PHB)-degrading, gram-negative, aerobic bacterium, strain HS(T), was isolated from a hot spring and chemotaxonomically and phylogenetically characterized. The oxidase-positive, weakly catalase-positive, non-pigmented cells (0.6 x 2.6 microm) exhibited a single polar flagellum and accumulated PHB granules. Strain HS(T) was capable of manganese oxidation. Highest growth rate was attained at 50 degrees C. The optimum pH for growth was 7-8. The major respiratory quinone was ubiquinone-8 and major cellular fatty acids were C16:0, C16:1 and C18:1. The G+C content of the DNA was 66.2 mol%. Comparative 16S rDNA analysis indicated that strain HS(T) is related to the Rubrivivax subgroup and the family Comamonadaceae. The nearest phylogenetic relatives were Ideonella dechloratans (92.1% similarity), Leptothrix discophora (93.6%), Roseateles depolymerans (92.4%) and Rubrivivax gelatinosus (92.2%). On the basis of its phylogenetic and phenotypic properties, it is proposed that this isolate be designated Caldimonas manganoxidans gen. nov., sp. nov.; the type strain is HS(T) (= JCM 10698T = IFO 16448T = ATCC BAA-369T). PMID:12054255

  13. Modeling sorption of divalent metal cations on hydrous manganese oxide using the diffuse double layer model

    USGS Publications Warehouse

    Tonkin, J.W.; Balistrieri, L.S.; Murray, J.W.

    2004-01-01

    Manganese oxides are important scavengers of trace metals and other contaminants in the environment. The inclusion of Mn oxides in predictive models, however, has been difficult due to the lack of a comprehensive set of sorption reactions consistent with a given surface complexation model (SCM), and the discrepancies between published sorption data and predictions using the available models. The authors have compiled a set of surface complexation reactions for synthetic hydrous Mn oxide (HMO) using a two surface site model and the diffuse double layer SCM which complements databases developed for hydrous Fe (III) oxide, goethite and crystalline Al oxide. This compilation encompasses a range of data observed in the literature for the complex HMO surface and provides an error envelope for predictions not well defined by fitting parameters for single or limited data sets. Data describing surface characteristics and cation sorption were compiled from the literature for the synthetic HMO phases birnessite, vernadite and ??-MnO2. A specific surface area of 746 m2g-1 and a surface site density of 2.1 mmol g-1 were determined from crystallographic data and considered fixed parameters in the model. Potentiometric titration data sets were adjusted to a pH1EP value of 2.2. Two site types (???XOH and ???YOH) were used. The fraction of total sites attributed to ???XOH (??) and pKa2 were optimized for each of 7 published potentiometric titration data sets using the computer program FITEQL3.2. pKa2 values of 2.35??0.077 (???XOH) and 6.06??0.040 (???YOH) were determined at the 95% confidence level. The calculated average ?? value was 0.64, with high and low values ranging from 1.0 to 0.24, respectively. pKa2 and ?? values and published cation sorption data were used subsequently to determine equilibrium surface complexation constants for Ba2+, Ca2+, Cd 2+, Co2+, Cu2+, Mg2+, Mn 2+, Ni2+, Pb2+, Sr2+ and Zn 2+. In addition, average model parameters were used to predict additional sorption data for which complementary titration data were not available. The two-site model accounts for variability in the titration data and most metal sorption data are fit well using the pKa2 and ?? values reported above. A linear free energy relationship (LFER) appears to exist for some of the metals; however, redox and cation exchange reactions may limit the prediction of surface complexation constants for additional metals using the LFER. ?? 2003 Elsevier Ltd. All rights reserved.

  14. Curcumin protects against cytotoxic and inflammatory effects of quartz particles but causes oxidative DNA damage in a rat lung epithelial cell line

    SciTech Connect

    Li Hui; Berlo, Damien van; Shi Tingming; Speit, Guenter; Knaapen, Ad M.; Borm, Paul J.A.; Albrecht, Catrin; Schins, Roel P.F.

    2008-02-15

    Chronic inhalation of high concentrations of respirable quartz particles has been implicated in various lung diseases including lung fibrosis and cancer. Generation of reactive oxygen species (ROS) and oxidative stress is considered a major mechanism of quartz toxicity. Curcumin, a yellow pigment from Curcuma longa, has been considered as nutraceutical because of its strong anti-inflammatory, antitumour and antioxidant properties. The aim of our present study was to investigate whether curcumin can protect lung epithelial cells from the cytotoxic, genotoxic and inflammatory effects associated with quartz (DQ12) exposure. Electron paramagnetic resonance (EPR) measurements using the spin-trap DMPO demonstrated that curcumin reduces hydrogen peroxide-dependent hydroxyl-radical formation by quartz. Curcumin was also found to reduce quartz-induced cytotoxicity and cyclooxygenase 2 (COX-2) mRNA expression in RLE-6TN rat lung epithelial cells (RLE). Curcumin also inhibited the release of macrophage inflammatory protein-2 (MIP-2) from RLE cells as observed upon treatment with interleukin-1 beta (IL-1{beta}) and tumour necrosis factor-alpha (TNF{alpha}). However, curcumin failed to protect the RLE cells from oxidative DNA damage induced by quartz, as shown by formamidopyrimidine glycosylase (FPG)-modified comet assay and by immunocytochemistry for 8-hydroxydeoxyguanosine. In contrast, curcumin was found to be a strong inducer of oxidative DNA damage itself at non-cytotoxic and anti-inflammatory concentrations. In line with this, curcumin also enhanced the mRNA expression of the oxidative stress response gene heme oxygenase-1 (ho-1). Curcumin also caused oxidative DNA damage in NR8383 rat alveolar macrophages and A549 human lung epithelial cells. Taken together, these observations indicate that one should be cautious in considering the potential use of curcumin in the prevention or treatment of lung diseases associated with quartz exposure.

  15. Heavy metals and manganese oxides in the genesee watershed, New York state: effects of geology and land use

    USGS Publications Warehouse

    Whitney, P.R.

    1981-01-01

    Manganese oxide coatings on gravels from 255 sites on tributary streams in the Genesee River Watershed were analyzed for Mn, Fe, Zn, Cd, Co, Ni, Pb, and Cu. The results were compared with data on bedrock geology, surficial geology and land use, using factor analysis and stepwise multiple regression. All metals except Pb show strong positive correlation with Mn. This association results from the well-known tendency of Mn oxide precipitates to adsorb and incorporate dissolved trace metals. Pb may be present in a separate phase on the gravel surfaces; alternatively Pb abundance may be so strongly influenced by environmental factors that the effect of varying abundance of the carrier phase becomes relatively unimportant. When the effects of varying Mn abundance are allowed for, Pb and to a lesser extent Zn and Cu abundances are seen to be related to commercial, industrial and residential land use. In addition to this pollution effect, all the trace metals, Cd and Ni most strongly, tend to be more abundant in oxide coatings from streams in the forested uplands in the southern part of the area. This probably reflects increased geochemical mobility of the metals in the more acid soils and groundwater of the southern region. A strong Zn anomaly is present in streams draining areas underlain by the Lockport Formation. Oxide coatings in these streams contain up to 5% Zn, originating from disseminated sphalerite in the Lockport and secondary Zn concentrations in the overlying muck soils. The same group of metals, plus calcium and loss on ignition, were determined in the silt and clay (minus 230 mesh) fraction of stream sediments from 129 of the same sites, using a hot nitric acid leach. The amounts of manganese in the sediments are low (average 1020 ppm) and manganese oxides are, at most, of relatively minor significance in the trace-metal geochemistry of these sediments. The bulk of the trace metals in sediment appears to be associated with iron oxides, clays and organic matter. ?? 1981.

  16. Photo-catalytic Degradation and Sorption of Radio-cobalt from EDTA-Co Complexes Using Manganese Oxide Materials - 12220

    SciTech Connect

    Koivula, Risto; Harjula, Risto; Tusa, Esko

    2012-07-01

    The synthesised cryptomelane-type ?-MnO{sub 2} was tested for its Co-57 uptake properties in UV-photo-reactor filled with 10 ?M Co-EDTA solution with a background of 10 mM NaNO{sub 3}. High cobalt uptake of 96% was observed after 1 hour of UV irradiation. As for comparison, a well-known TiO{sub 2} (Degussa P25) was tested as reference material that showed about 92% cobalt uptake after six hours of irradiation in identical experiment conditions. It was also noted that the cobalt uptake on cryptomelane with out UV irradiation was modest, only about 10%. Decreasing the pH of the Co-EDTA solution had severe effects on the cobalt uptake mainly due to the rather high point of zero charge of the MnO{sub 2} surface (pzc at pH ?4.5). Modifying the synthesis procedure we were able to produce a material that functioned well even in solution of pH 3 giving cobalt uptake of almost 99%. The known properties, catalytic and ion exchange, of manganese oxides were simultaneously used for the separation of EDTA complexed Co-57. Tunnel structured cryptomelane -type showed very fast and efficient Co uptake properties outperforming the well known and widely used Degussa P25 TiO{sub 2} in both counts. The layered structured manganese oxide, birnessite, reached also as high Co removal level as the reference material Degussa did but the reaction rate was considerably faster. Since the decontamination solutions are typically slightly acidic and the point of zero charge of the manganese oxides are rather high > pH 4.5 the material had to be modified. This modified material had tolerance to acidic solutions and it's Co uptake performance remained high in the solutions of lower pH (pH 3). Increasing the ion concentration of test solutions, background concentration, didn't affect the final Co uptake level; however, some changes in the uptake kinetics could be seen. The increase in EDTA/MoMO ratio was clearly reflected in the Co uptake curves. The obtained results of manganese oxide were very promising for the treatment of EDTA complexed Co solutions. The better performance values and cheaper production cost of manganese oxide, compared to titanium dioxide, is so big driving force that further studies on the material are evident. The possibilities for continuous treatment, instead of the fluidized bed -type batch experiment are investigated and the effects of other compounds affecting the de-complexation of Co-EDTA are further studied. (authors)

  17. Well-ordered organic-inorganic hybrid layered manganese oxide nanocomposites with excellent decolorization performance

    SciTech Connect

    Zhou, Junli; Yu, Lin; Sun, Ming; Ye, Fei; Lan, Bang; Diao, Guiqiang; He, Jun

    2013-02-15

    Well-ordered organic-inorganic hybrid layered manganese oxide nanocomposites (CTAB-Al-MO) with excellent decolorization performance were prepared through a two-step process. Specifically, the MnO{sub 2} nanosheets were self-assembled in the presence of CTAB, and subsequently pillared with Keggin ions. The obtained CTAB-Al-MO with the basal spacing of 1.59 nm could be stable at 300 Degree-Sign C for 2 h and also possesses high total pore volumes (0.41 cm Superscript-Three g{sup -1}) and high specific BET surface area (161 m{sup 2} g{sup -1}), which is nine times larger than that of the pristine (19 m{sup 2} g{sup -1}). Possible formation process for the highly thermal stable CTAB-Al-MO is proposed here. The decolorization experiments of methyl orange showed that the obtained CTAB-Al-MO exhibit excellent performance in wastewater treatment and the decolorization rate could reach 95% within 5 min. - Graphical Abstract: Well-ordered organic-inorganic hybrid LMO nanocomposites (CTAB-Al-MO) with excellent decolorization performance were prepared through a two-step process. Specifically, the MnO{sub 2} nanosheets were self-assembled by CTAB, and subsequently pillared with Keggin ions. Highlights: Black-Right-Pointing-Pointer A two-step synthesis method was used to prepare the CTAB-Al-MO. Black-Right-Pointing-Pointer The CTAB-Al-MO has the large basal spacing and high specific BET surface area. Black-Right-Pointing-Pointer The thermal stability of the well-ordered CTAB-Al-MO could obviously improve. Black-Right-Pointing-Pointer The CTAB-Al-MO exhibits excellent oxidation and absorption ability to remove organic pollutants.

  18. Structural Distortion of Molybdenum-Doped Manganese Oxide Octahedral Molecular Sieves for Enhanced Catalytic Performance.

    PubMed

    Chen, Chun-Hu; Njagi, Eric C; Chen, Sheng-Yu; Horvath, Dayton T; Xu, Linping; Morey, Aimee; Mackin, Charles; Joesten, Raymond; Suib, Steven L

    2015-11-01

    Due to the excellent catalytic performance of manganese oxide (K-OMS-2) in a wide range of applications, incorporation of various dopants has been commonly applied for K-OMS-2 to acquire additional functionality or activities. However, the understanding of its substitution mechanism with respect to the catalytic performance of doped K-OMS-2 materials remains unclear. Here we present the structural distortion (from tetragonal to monoclinic cell) and morphological evolution in K-OMS-2 materials by doping hexavalent molybdenum. With a Mo-to-Mn ratio of 1:20 (R-1:20) in the preparation, the resultant monoclinic K-OMS-2 shows a small equidimensional particle size (∼15 nm), a high surface area of 213 m(2) g(-1), and greatly improved catalytic activity toward CO oxidation with lower onset temperatures (40 °C) than that of pristine K-OMS-2 (above 130 °C). HR-TEM analyses reveal direct evidence of structural distortion on the cross-section of 2 × 2 tunnels with the absence of 4-fold rotation symmetry expected for a tetragonal cell, which are indexed using a monoclinic cell. Our results suggest that substitution of Mo(6+) for Mn(3+) (rather than Mn(4+)) coupled with the vacancy generation results in a distorted structure and unique morphology. The weakened Mn-O bonds and Mn vacancies associated with the structural distortion may be mainly responsible for the enhanced catalytic activity of monoclinic K-OMS-2 instead of dopant species. PMID:26451851

  19. Revisiting the coordination chemistry for preparing manganese oxide nanocrystals in the presence of oleylamine and oleic acid

    NASA Astrophysics Data System (ADS)

    Zhang, Hongwei; Jing, Lihong; Zeng, Jianfeng; Hou, Yi; Li, Zhen; Gao, Mingyuan

    2014-05-01

    By pyrolyzing manganese(ii) acetate in 1-octadecene in the presence of oleylamine and oleic acid, manganese oxide nanocrystals were prepared. It was observed that both MnO and Mn3O4 nanocrystals were simultaneously formed by quickly heating the reaction mixture up to 250 C, while a preheating procedure carried out at 100 C led to uniform MnO nanocubes that developed into eight-arm MnO nanocrystals upon prolonged reaction. To understand the mechanisms for forming these two different kinds of manganese oxide nanocrystals, i.e., Mn3O4 and MnO, the coordination between oleic acid/oleylamine and Mn2+ was investigated. The detailed investigations suggest that Mn2+-oleylamine coordination is kinetically driven and favorable for the formation of Mn3O4 nanocrystals due to the relatively low electronegativity of N from oleylamine, while Mn2+-oleate coordination is thermodynamically driven and can prevent the central metal ion (Mn2+) from being oxidized owing to the relatively high electronegativity of O from the oleate ligand. Following these new insights, by properly balancing the coordination of oleic acid and oleylamine to Mn2+, the selective synthesis of MnO and Mn3O4 nanocrystals with uniform shapes was successfully achieved.By pyrolyzing manganese(ii) acetate in 1-octadecene in the presence of oleylamine and oleic acid, manganese oxide nanocrystals were prepared. It was observed that both MnO and Mn3O4 nanocrystals were simultaneously formed by quickly heating the reaction mixture up to 250 C, while a preheating procedure carried out at 100 C led to uniform MnO nanocubes that developed into eight-arm MnO nanocrystals upon prolonged reaction. To understand the mechanisms for forming these two different kinds of manganese oxide nanocrystals, i.e., Mn3O4 and MnO, the coordination between oleic acid/oleylamine and Mn2+ was investigated. The detailed investigations suggest that Mn2+-oleylamine coordination is kinetically driven and favorable for the formation of Mn3O4 nanocrystals due to the relatively low electronegativity of N from oleylamine, while Mn2+-oleate coordination is thermodynamically driven and can prevent the central metal ion (Mn2+) from being oxidized owing to the relatively high electronegativity of O from the oleate ligand. Following these new insights, by properly balancing the coordination of oleic acid and oleylamine to Mn2+, the selective synthesis of MnO and Mn3O4 nanocrystals with uniform shapes was successfully achieved. Electronic supplementary information (ESI) available: (1) TEM image and corresponding SAED pattern of the tiny particles shown in Fig. 1b; (2) TEM images of the branched nanoparticles (Fig. 1e) showing a self-organized superstructure; (3) TEM image and the electron diffraction pattern of the particles obtained by heating the Mn(Ac)2 in oleylamine at 100 C for 540 min; (4) TEM image and the electron diffraction pattern of the particles obtained from the second reference experiment; (5) Temporal evolution of size and size distribution of manganese oxide nanocrystals shown in Fig. 5 and Fig. 6. See DOI: 10.1039/c4nr00761a

  20. Biological versus mineralogical chromium reduction: potential for reoxidation by manganese oxide.

    PubMed

    Butler, Elizabeth C; Chen, Lixia; Hansel, Colleen M; Krumholz, Lee R; Elwood Madden, Andrew S; Lan, Ying

    2015-11-01

    Hexavalent chromium (Cr(vi), present predominantly as CrO4(2-) in water at neutral pH) is a common ground water pollutant, and reductive immobilization is a frequent remediation alternative. The Cr(iii) that forms upon microbial or abiotic reduction often co-precipitates with naturally present or added iron (Fe), and the stability of the resulting Fe-Cr precipitate is a function of its mineral properties. In this study, Fe-Cr solids were formed by microbial Cr(vi) reduction using Desulfovibrio vulgaris strain RCH1 in the presence of the Fe-bearing minerals hematite, aluminum substituted goethite (Al-goethite), and nontronite (NAu-2, Clay Minerals Society), or by abiotic Cr(vi) reduction by dithionite reduced NAu-2 or iron sulfide (FeS). The properties of the resulting Fe-Cr solids and their behavior upon exposure to the oxidant manganese (Mn) oxide (birnessite) differed significantly. In microcosms containing strain RCH1 and hematite or Al-goethite, there was significant initial loss of Cr(vi) in a pattern consistent with adsorption, and significant Cr(vi) was found in the resulting solids. The solid formed when Cr(vi) was reduced by FeS contained a high proportion of Cr(iii) and was poorly crystalline. In microcosms with strain RCH1 and hematite, Cr precipitates appeared to be concentrated in organic biofilms. Reaction between birnessite and the abiotically formed Cr(iii) solids led to production of significant dissolved Cr(vi) compared to the no-birnessite controls. This pattern was not observed in the solids generated by microbial Cr(vi) reduction, possibly due to re-reduction of any Cr(vi) generated upon oxidation by birnessite by active bacteria or microbial enzymes. The results of this study suggest that Fe-Cr precipitates formed in groundwater remediation may remain stable only in the presence of active anaerobic microbial reduction. If exposed to environmentally common Mn oxides such as birnessite in the absence of microbial activity, there is the potential for rapid (re)formation of dissolved Cr(vi) above regulatory levels. PMID:26452013

  1. Iron and manganese in oxide minerals and in glasses: preliminary consideration of Eh buffering potential at Yucca Mountain, Nevada

    SciTech Connect

    Caporuscio, F.A.; Vaniman, D.T.

    1985-04-01

    The tuffs of Yucca Mountain at the Nevada Test Site are currently under investigation as a possible deep burial site for high-level radioactive waste disposal. One of the main concerns is the effect of oxidizing groundwater on the transport of radionuclides. Rock components that may affect the oxygen content of groundwater include Fe-Ti oxides, Mn oxides, and glasses that contain ferrous iron. Some phenocryst Fe-Ti oxides at Yucca Mountain are in reduced states, whereas groundmass Fe-Ti oxides have been oxidized to hematite, rutile, and pseudobrookite (Fe{sup 3+}-bearing phases) exclusively. Estimates of Fe{sup 2+}-bearing oxides indicate that less than 0.33 vol% phenocrysts is available to act as solid buffering agents of Eh. Of this percentage, significant amounts of Fe-Ti oxides are isolated from effective interaction with groundwater because they occur in densely welded, devitrified tuffs that have low interstitial permeability. Manganese oxides occur primarily along fractures in the ash-flow tuffs. Because the Mn oxides are concentrated along the same pathways (fractures) where transport has occurred in the past, these small volume percentages could act as buffers. However, the oxidation states of actual Mn-oxide phases are high (Mn{sup 4+}), and these minerals have virtually no potential for reducing groundwater Eh. Manganese oxides may even act as oxidizing agents. However, regardless of their poor capabilities as reducing agents, the Mn oxides could be important as sorbents of heavy metals at Yucca Mountain. The lack of accessible, pristine Fe-Ti oxides and the generally high oxidation states of Mn oxides seem to rule out these oxides as Eh buffers of the Yucca Mountain groundwater system. Reduction of ferrous iron within glassy tuffs may have some effect on Eh, but further study is needed. At present it is prudent to assume that minerals and glasses have little or no capacity for reducing oxygen-rich groundwater at Yucca Mountain. 25 refs., 3 figs., 12 tabs

  2. Kinetics of the catalytic oxidation of phenol over manganese oxide in supercritical water

    SciTech Connect

    Oshima, Yoshito; Tomita, Kengo; Koda, Seiichiro

    1999-11-01

    A kinetic analysis was made for the phenol disappearance rate in catalytic oxidation of phenol over MnO{sub 2} in supercritical water at a fixed temperature of 425 C and pressures between 22.7 and 27.2 MPa. The nonsupported MnO{sub 2} catalyst possessed a strong activity for promoting phenol oxidation, though the overall reaction rate was appreciably influenced by internal mass-transfer resistance. From the kinetic analysis on the reaction rate of the phenol disappearance, the global rate expression of the surface reaction was obtained, where the reaction orders with respect to phenol, oxygen, and water were almost unity, 0.7, and {minus}2.0, respectively. A Langmuir-type mechanism, in which phenol and oxygen adsorbed on the catalytic sites and water adsorbed on the same site to inhibit the phenol and oxygen adsorption, was proposed to explain the reaction orders for phenol, oxygen, and water.

  3. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation

    PubMed Central

    2015-01-01

    To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnOx, a promising OER catalyst. We conclusively demonstrate that adding Au to MnOx significantly enhances OER activity relative to MnOx in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnOx catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnOx that leads to the observed enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addition of Au or other noble metals could still represent a scalable catalyst as even trace amounts of Au are shown to lead a significant enhancement in the OER activity of MnOx. PMID:24661269

  4. Synthesis, Structure, and Magnetism of Mono- and Binuclear Manganese(II) Compounds of Nitronyl Nitroxide Substituted Phosphine Oxides.

    PubMed

    Rancurel, Corinne; Leznoff, Daniel B.; Sutter, Jean-Pascal; Golhen, Stphane; Ouahab, Lahcne; Kliava, Janis; Kahn, Olivier

    1999-10-18

    Complexes of manganese(II)-containing aminoxyl radical substituted phosphine oxide ligands are reported. The compounds [(o-nitronyl nitroxide-phenyl)diphenylphosphine oxide]bis(hexafluoroacetylacetonato)manganese(II), 3, and bis{[(p-nitronyl nitroxide-phenyl) diphenylphosphine oxide]bis(hexafluoroacetylacetonato)manganese(II)}, 4, prepared by addition of the free radical phosphine oxides to Mn(hfac)(2), were structurally characterized. Complex 3 is mononuclear, containing an O,O-chelating ortho-substituted radical phosphine oxide ligand, while in 4 the para-substituted ligands bridge two Mn(hfac)(2) units to yield a binuclear molecular rectangle. The magnetic behavior of both systems is dominated by a strong antiferromagnetic Mn(II)-aminoxyl interaction (J = -213 (3), -218 (4) cm(-)(1) with H = -JS(Mn).S(rad)) to give effective S = 2 ground state units. The S = 3 excited state is populated at high temperatures. At low temperatures a decrease in chi(M)T in both complexes is attributable primarily to inter- or intramolecular antiferromagnetic interactions rather than zero-field splitting (ZFS) of the S = 2 ground state. For the bimetallic compound, the magnetic data indicate that ligand-mediated interactions between the Mn(II) spin carriers are weak. The powder EPR spectra of both systems have been recorded and successfully simulated, giving a ZFS parameter D = 0.112 cm(-)(1). Crystals of 3 are triclinic, space group P&onemacr; with a = 10.6672(19) , b = 13.270(6) , c = 15.363(3) , alpha = 93.84(2) degrees, beta = 108.054(16) degrees, gamma = 105.69(3) degrees, and Z = 2. Crystals of 4 are monoclinic, space group P2(1)/a with a = 12.463(6) , b = 19.315(3) , c = 17.084(9) , alpha = 90 degrees, beta = 98.49(2) degrees, gamma = 90 degrees, and Z = 2. PMID:11671201

  5. Manganese-Cobalt Mixed Spinel Oxides as Surface Modifiers for Stainless Steel Interconnects of Solid Oxide Fuel Cells

    SciTech Connect

    Xia, Gordon; Yang, Z Gary; Stevenson, Jeffry W.

    2006-11-06

    Ferritic stainless steels are promising candidates for interconnect applications in low- and mid-temperature solid oxide fuel cells (SOFCs). A couple of issues however remain for the particular application, including the chromium poisoning due to chromia evaporation, and long-term surface and electrical stability of the scale grown on these steels. Application of a manganese colbaltite spinel protection layer on the steels appears to be an effective approach to solve the issues. For an optimized performance, Mn{sub 1+x}Co{sub 2-x}O{sub 4} (-1 {le} x {le} 2) spinels were investigated against properties relative for protection coating applications on ferritic SOFC interconnects. Overall it appears that the spinels with x around 0.5 demonstrate a good CTE match to ceramic cell components, a relative high electrical conductivity, and a good thermal stability up to 1,250 C. This was confirmed by a long-term test on the Mn{sub 1.5}Co{sub 1.5}O{sub 4} protection layer that was thermally grown on Crofer22 APU, indicating the spinel protection layer not only significantly decreased the contact resistance between a LSF cathode and the stainless steel interconnects, but also inhibited the sub-scale growth on the stainless steels.

  6. PROGRESS REPORT. TRANSURANIC INTERFACIAL REACTION STUDIES ON MANGANESE OXIDE HYDROXIDE MINERAL SURFACES

    EPA Science Inventory

    Several DOE sites have been contaminated by transuranic radionuclide (TRU) discharges including neptunium and plutonium. Their interaction with the surrounding geological media can affect the transport and remediation of these radionuclides in the environment. Manganese based min...

  7. Structural and optical properties of polycrystalline thin films of rare earth oxides grown on fused quartz by low pressure MOCVD

    NASA Astrophysics Data System (ADS)

    Singh, M. P.; Shivashankar, S. A.

    2005-03-01

    We report the structural and optical properties of oriented polycrystalline thin films of rare earth oxides (REO), namely Er 2O 3, Gd 2O 3, Eu 2O 3, and Yb 2O 3 grown on fused quartz by low-pressure metalorganic chemical vapour deposition (MOCVD) in the temperature range of 450-800 C, using adducted ?-diketonate complexes of rare earth metals as precursors. The films were characterized by X-ray diffraction (XRD) and UV-visible spectrophotometry. While the films grown at low temperatures (500 C) are poorly crystalline, those grown on or above 525 C display a significant (1 1 1) texture. Growth of textured cubic REO in (1 1 1) direction on amorphous substrate is interpreted in terms of minimization of surface energy at the film-substrate interface. The degree of misfit between the interatomic distances in the disordered fused quartz substrate and those in the crystalline REO is invoked to explain the presence (absence) of low-intensity reflections other than (1 1 1). The incorporation of carbon (from the precursor) into the films affects the optical properties of REO, as examined by UV-visible spectroscopy.

  8. Synthesis and characterization of novel manganese and vanadium oxides as cathodes for lithium rechargeable batteries

    NASA Astrophysics Data System (ADS)

    Chen, Rongji

    The development of advanced rechargeable lithium batteries depends on cathodes that can reversibly intercalate lithium ions. Intercalation chemistry plays a key role in the electrochemical reduction and oxidation by lithium of many solid electrodes including transition metal compounds. Intercalation compounds such as LixTiS2 and LiCoO2 exhibit some of the ideal characteristics expected of a cathode for advanced batteries. The former shows high rate capability, excellent electronic conductivity and almost perfect reversibility; the latter shows a high voltage suitable for carbon based anodes and good reversibility but an energy density no higher than that of LixTiS2, a prohibitively high cost and an environmental hazard. The spinel LiMn2O4 removes the cost issue but not the others. Thus, much effort has been directed at synthesizing new structures that exhibit enhanced electrochemical activity. Soft chemistry approaches have been applied for this purpose. One such approach is mild hydrothermal reactions which lead to the formation of new metastable transition metal oxides, not accessible by conventional high temperature methods. The nature of the reactants, the pH of the reaction medium, heating temperature and heating duration have dramatic effects on the crystal structure of the phase formed. The mild hydrothermal decomposition of aqueous permanganate solutions has been found to lead to new layered manganese oxides. In the case of alkali permanganates AMnO4, layered birnessite-type compounds are formed with the general formula AxMnO2.nH 2O (A = Li, Na, K). These compounds have R 3 m rhombohedral structures analogous to the layered disulfides. The water is reversibly lost on heating, and the compounds readily react with lithium through an intercalation mechanism. The capacity for lithium is a function of the alkali ion present, and the larger potassium ion maintains the capacity best. For the lithium compound, there is a tendency to convert to the spinel structure which leads to loss of capacity. In the case of hydrothermal decomposition of tetramethylammonium permanganate in the presence of nickel, a new structure compound Ni1-xMn1-yO 3 is formed that has a different structure from that of the known ilmenite form. The structure contains empty tunnels into which lithium ions can be intercalated. Reaction of this nickel manganese oxide with n-butyl lithium showed the uptake of 0.91 Li per formula unit. It converts into the known ilmenite form of NiMnO3 at around 400C. This compound also has interesting magnetic properties. A wide variety of vanadium oxides can be prepared using hydrothermal methods. Organic templates play an important role in directing the structures formed. Although tetramethyl ammonium hydroxide is a widely used organic template, other amines and long chain amine surfactants also yield interesting new structures many of which are layered phases. The hydrothermal reaction of vanadium pentoxide with methylamine leads to a series of new layered vanadium oxides, which differ in structure from the corresponding ones prepared in the presence of the tetramethylammonium ion because of the existence of hydrogen bonding. Methylamine is the first organic to form a double sheet vanadium oxide, (CH3NH3) 0.75V4O10.0.67H2O, with delta-AgxV2O5 structure. (CH 3NH3)V3O7 shows significant buckling of the vanadium oxide layers compared with N(CH3)4V 3O7. Both of these two compounds are monoclinic. (CH 3NH2)2V8O17 has a tetrahedral unit cell and IR shows that the lone pair electrons of nitrogen bond to vanadium. Also, vanadium coordination decreases with an increase in the pH of the reaction medium and hydrogen bonding controls the orientation of the polyhedra in the vanadium sheets, in contrast to the tetramethylammonium ion where the bonding is predominantly ionic.

  9. One-dimensional manganese-cobalt oxide nanofibres as bi-functional cathode catalysts for rechargeable metal-air batteries

    PubMed Central

    Jung, Kyu-Nam; Hwang, Soo Min; Park, Min-Sik; Kim, Ki Jae; Kim, Jae-Geun; Dou, Shi Xue; Kim, Jung Ho; Lee, Jong-Won

    2015-01-01

    Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries. PMID:25563733

  10. Lipid Peroxidation by the Manganese Peroxidase of Phanerochaete chrysosporium Is the Basis for Phenanthrene Oxidation by the Intact Fungus

    PubMed Central

    Moen, Mark A.; Hammel, Kenneth E.

    1994-01-01

    The manganese peroxidase (MnP) of Phanerochaete chrysosporium supported Mn(II)-dependent, H2O2-independent lipid peroxidation, as shown by two findings: linolenic acid was peroxidized to give products that reacted with thiobarbituric acid, and linoleic acid was peroxidized to give hexanal. MnP also supported the slow oxidation of phenanthrene to 2,2?-diphenic acid in a reaction that required Mn(II), oxygen, and unsaturated lipids. Phenanthrene oxidation to diphenic acid by intact cultures of P. chrysosporium occurred to the same extent that oxidation in vitro did and was stimulated by Mn. These results support a role for MnP-mediated lipid peroxidation in phenanthrene oxidation by P. chrysosporium. PMID:16349285

  11. Manganese superoxide dismutase protects nNOS neurons from NMDA and nitric oxide-mediated neurotoxicity.

    PubMed

    Gonzalez-Zulueta, M; Ensz, L M; Mukhina, G; Lebovitz, R M; Zwacka, R M; Engelhardt, J F; Oberley, L W; Dawson, V L; Dawson, T M

    1998-03-15

    Neuronal nitric oxide synthase (nNOS) neurons kill adjacent neurons through the action of NMDA-glutamate receptor activation, although they remain relatively resistant to the toxic effects of NMDA and NO. The molecular basis of the resistance of nNOS neurons to toxic insults is unknown. To begin to understand the molecular mechanisms of the resistance of nNOS neurons, we developed a pheochromacytoma-derived cell line (PC12) that is resistant to the toxic effects of NO. We found through serial analysis of gene expression (SAGE) that manganese superoxide dismutase (MnSOD) is enriched in the NO-resistant PC12 cell-derived line (PC12-R). Antisense MnSOD renders PC12-R cells sensitive to NO toxicity and increases the sensitivity to NO in the parental, NO-sensitive PC12 line (PC12-S). Adenoviral transfer of MnSOD protects PC12-S cells against NO toxicity. We extended these studies to cortical cultures and showed that MnSOD is enriched in nNOS neurons and that antisense MnSOD renders nNOS neurons susceptible to NMDA neurotoxicity, although it has little effect on the overall susceptibility of cortical neurons to NMDA toxicity. Overexpression of MnSOD provides dramatic protection against NMDA and NO toxicity in cortical cultures, but not against kainate or AMPA neurotoxicity. Furthermore, nNOS neurons from MnSOD -/- mice are markedly sensitive to NMDA toxicity. Adenoviral transfer of MnSOD to MnSOD-/- cultures restores resistance of nNOS neurons to NMDA toxicity. Thus, MnSOD is a major protective protein that appears to be essential for the resistance of nNOS neurons in cortical cultures to NMDA mediated neurotoxicity. PMID:9482791

  12. Electrodeposited Manganese Oxides on Three-Dimensional Carbon Nanotube Substrate: Supercapacitive Behaviour in Aqueous and Organic Electrolytes

    SciTech Connect

    Nam,K.W.; Yang,X.

    2009-03-01

    Thin amorphous manganese oxide layers with a thickness of 3-5nm are electrodeposited on a carbon nanotube (CNT) film substrate that has a three-dimensional nanoporous structure (denoted asMnO2/CNT electrode). For the purpose of comparison, manganese oxide films are also electrodeposited on a flat Pt-coated Si wafer substrate (denoted as MnO2 film electrode). The pseudocapacitive properties of the MnO2 film and MnO2/CNT electrodes are examined in both aqueous electrolyte (1.0M KCl) and nonaqueousorganic electrolyte (1.0M LiClO4 in propylene carbonate). While both types of electrode showpseudocapacitive behaviour in the aqueous electrolyte, only the MnO2/CNT electrode does so in the organic electrolyte, due to its high oxide/electrolyte interfacial area and improved electron conduction through the CNT substrate. Compared with the MnO2 film electrode, the MnO2/CNT electrode shows a much higher specific capacitance and better high-rate capability, regardless of the electrolyte used.Use of the organic electrolyte results in a ?6 times higher specific energy compared with that obtained with the aqueous electrolyte, while maintaining a similar specific power. The construction of a threedimensional nanoporous network structure consisting of a thin oxide layer on a CNT film substrate at the nm scale and the use of an organic electrolyte are promising approaches to improving the specific energyof supercapacitors.

  13. Capacity fading mechanisms and origin of the capacity above 4.5 V of spinel lithium manganese oxides

    NASA Astrophysics Data System (ADS)

    Shin, Youngjoon

    2003-06-01

    Lithium ion batteries have become attractive for portable devices due to their high operating voltage, high energy density, low self-discharge, and long cycle life. Lithium ion cells currently use the layered LiCoO 2 cathode, but cobalt is expensive and relatively toxic. In this regard, spinel LiMn2O4 has become appealing since manganese is inexpensive and environmentally benign. However, LiMn2O 4 exhibits severe capacity fade. This dissertation explores the electrochemical performances of spinel oxides derived from LiMn2O4 in a wide voltage range of 3.5 to 5.2 V to understand the capacity fading mechanisms and the origin of the high voltage capacity above 4.5 V. From a systematic investigation of a series of singly substituted LiMn 2-yMyO4 and doubly substituted LiMn 2-y-zMyLizO4 (M = Li, Al, or transition metal) oxides, the doubly substituted LiMn2-y-z NiyLizO4 oxides are found to show superior cyclability, low irreversible capacity (IRC), high rate capability, low electrode resistance, and excellent storage performance compared to LiMn2O 4 despite a similar manganese dissolution. For example, LiMn1.85 Ni0.075Li0.075O4 retains more than 99 and 97% of its initial capacity after 50 cycles at, respectively, 25 and 60C. Its excellent electrochemical performances are found to be due to the small lattice parameter difference between the two cubic phases formed in the two-phase region during cycling and the consequent low microstrain. This concept of minimizing the lattice parameter difference and microstrain could successfully enable the use of spinel lithium manganese oxides for electric vehicle applications. In contrast to the literature suggestions that other transition metal ions or excess oxygen are essential to impart the high voltage (>4.5 V) capacity, spinel lithium manganese oxides free from other transition metal ions are found to show capacity above 4.5 V even with a significant amount of oxygen deficiency if there are extractable Li+ ions in the 8a tetrahedral sites after the oxidation state of manganese reaches 4+. In the presence of other transition metals, the reversibility of the high voltage capacity depends on the element replacing Mn3+, and it decreases in the order LiMn2-yNiyO4 > LiMn2-yCoyO4 ? LiMn 2-y-zCoyLizO4 > LiMn 2-y-zNiyLizO4. Based on the results, the capacity above 4.5 V in manganese-based spinel oxides could be understood to arise from a participation of the O2-:2p band or a hybridized band involving M3+/4+:3d (or M 2+/3+:3d) and O2-:2p.

  14. Towards an understanding of thallium isotope fractionation during adsorption to manganese oxides

    NASA Astrophysics Data System (ADS)

    Nielsen, Sune G.; Wasylenki, Laura E.; Rehkmper, Mark; Peacock, Caroline L.; Xue, Zichen; Moon, Ellen M.

    2013-09-01

    We have conducted the first study of Tl isotope fractionation during sorption of aqueous Tl(I) onto the manganese oxide hexagonal birnessite. The experiments had different initial Tl concentrations, amounts of birnessite, experimental durations, and temperatures, but all of them exhibit heavy Tl isotope compositions for the sorbed Tl compared with the solution, which is consistent with the direction of isotope fractionation observed between seawater and natural ferromanganese sediments. However, the magnitude of fractionation in all experiments (? ? 1.0002-1.0015, where ?=205Tl/203Tl/205Tl/203Tl is smaller than observed between seawater and natural sediments (? ? 1.0019-1.0021; Rehkmper et al., 2002, Earth. Planet. Sci. Lett. 197, 65-81). The experimental results display a strong correlation between the concentration of Tl in the resulting Tl-sorbed birnessite and the magnitude of fractionation. This correlation is best explained by sorption of Tl to two sites on birnessite, one with large isotope fractionation and one with little or no isotope fractionation. Previous work (Peacock and Moon, 2012, Geochim. Cosmochim. Acta 84, 297-313) indicates that Tl in natural ferromanganese sediments is oxidized to Tl(III) and adsorbed over Mn vacancy sites in the phyllomanganate sheets of birnessite, and we hypothesize that this site is strongly fractionated from Tl in solution due to the change in oxidation state from aqueous Tl(I). In most experiments, which have orders of magnitude more Tl associated with the solid than in nature, these vacancy sites are probably fully saturated, so various amounts of additional Tl are likely sorbed to either edge sites on the birnessite or triclinic birnessite formed through oxidative ripening of the hexagonal starting material, with unknown oxidation state and little or no isotopic fractionation. Thus each experiment displays isotopic fractionation governed by the proportions of Tl in the fractionated and slightly fractionated sites, and those proportions are controlled by how much total Tl is sorbed per unit of birnessite. In the experiments with the lowest initial Tl concentrations in solution (0.15-0.4 ?g/g) and the lowest concentrations of Tl in the resulting Tl-sorbed birnessite (?17 ?g Tl/mg birnessite), we observed the largest isotopic fractionations, and fractionation is inversely proportional to the initial aqueous Tl concentration. Again, this correlation can be explained by the simultaneous occupation of two different sorption sites; vacancy sites that carry isotopically fractionated Tl and a second site carrying slightly fractionated Tl. The fractionation factors observed in nature exceed those in the experiments likely because the Tl concentrations in seawater and in ferromanganese sediments are three to four orders of magnitude lower than in our experiments, and therefore the second slightly fractionated sorption site is not significantly utilized. Temperature (6-40 C) and experimental duration (3 min-72 h) appear to have little or no effects on isotope behaviour in this system.

  15. Microbially-mediated thiocyanate oxidation and manganese cycling control arsenic mobility in groundwater at an Australian gold mine

    NASA Astrophysics Data System (ADS)

    Horvath, A. S.; Baldisimo, J. G.; Moreau, J. W.

    2010-12-01

    Arsenic contamination of groundwater poses a serious environmental and human health problem in many regions around the world. Historical groundwater chemistry data for a Western-Central Victorian gold mine (Australia) revealed a strong inverse correlation between dissolved thiocyanate and iron(II), supporting the interpretation that oxidation of thiocyanate, a major groundwater contaminant by-product of cyanide-based gold leaching, was coupled to reductive dissolution of iron ox(yhydrox)ides in tailings dam sediments. Microbial growth was observed in this study in a selective medium using SCN- as the sole carbon and nitrogen source. The potential for use of SCN- as a tracer of mining contamination in groundwater was evaluated in the context of biological SCN- oxidation potential in the aquifer. Geochemical data also revealed a high positive correlation between dissolved arsenic and manganese, indicating that sorption on manganese-oxides most likely controls arsenic mobility at this site. Samples of groundwater and sediments along a roughly straight SW-NE traverse away from a large mine tailings storage facility, and parallel to the major groundwater flow direction, were analysed for major ions and trace metals. Groundwater from wells approaching the tailings along this traverse showed a nearly five-fold increase (roughly 25-125 ppb) in dissolved arsenic concentrations relative to aqueous Mn(II) concentrations. Thus, equivalent amounts of dissolved manganese released a five-fold difference in the amount of adsorbed arsenic. The interpretation that reductive dissolution of As-bearing MnO2 at the mine site has been mediated by groundwater (or aquifer) microorganisms is consistent with our recovery of synthetic birnessite-reducing enrichment cultures that were inoculated with As-contaminated groundwaters.

  16. Theoretical technique for predicting the cumulative impact of iron and manganese oxidation in streams receiving discharge from coal mines

    USGS Publications Warehouse

    Bobay, Keith E.

    1986-01-01

    Two U.S. Geological Survey computer programs are modified and linked to predict the cumulative impact of iron and manganese oxidation in coal-mine discharge water on the dissolved chemical quality of a receiving stream. The coupled programs calculate the changes in dissolved iron, dissolved manganese, and dissolved oxygen concentrations; alkalinity; and, pH of surface water downstream from the point of discharge. First, the one-dimensional, stead-state stream, water quality program uses a dissolved oxygen model to calculate the changes in concentration of elements as a function of the chemical reaction rates and time-of-travel. Second, a program (PHREEQE) combining pH, reduction-oxidation potential, and equilibrium equations uses an aqueous-ion association model to determine the saturation indices and to calculate pH; it then mixes the discharge with a receiving stream. The kinetic processes of the first program dominate the system, whereas the equilibrium thermodynamics of the second define the limits of the reactions. A comprehensive test of the technique was not possible because a complete set of data was unavailable. However, the cumulative impact of representative discharges from several coal mines on stream quality in a small watershed in southwestern Indiana was simulated to illustrate the operation of the technique and to determine its sensitivity to changes in physical, chemical, and kinetic parameters. Mine discharges averaged 2 cu ft/sec, with a pH of 6.0, and concentrations of 7.0 mg/L dissolved iron, 4.0 mg/L dissolved manganese, and 8.08 mg/L dissolved oxygen. The receiving stream discharge was 2 cu ft/sec, with a pH of 7.0, and concentrations of 0.1 mg/L dissolved iron, 0.1 mg/L dissolved manganese, and 8.70 mg/L dissolved oxygen. Results of the simulations indicated the following cumulative impact on the receiving stream from five discharges as compared with the effect from one discharge: 0.30 unit decrease in pH, 1.82 mg/L increase in dissolved iron, 1.50 mg/L increase in dissolved manganese, and 0.24 mg/L decrease in dissolved oxygen concentration. (Author 's abstract)

  17. Synthesis of waste cooking oil based biodiesel via ferric-manganese promoted molybdenum oxide / zirconia nanoparticle solid acid catalyst: influence of ferric and manganese dopants.

    PubMed

    Alhassan, Fatah H; Rashid, Umer; Taufiq-Yap, Yun Hin

    2015-01-01

    The utilization of ferric-manganese promoted molybdenum oxide/zirconia (Fe-Mn- MoO3/ZrO2) (FMMZ) solid acid catalyst for production of biodiesel was demonstrated. FMMZ is produced through impregnation reaction followed by calcination at 600C for 3 h. The characterization of FMMZ had been done using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), temperature programmed desorption of NH3 (TPD-NH3), transmission electron microscopy(TEM) and Brunner-Emmett-Teller (BET) surface area measurement. The effect of waste cooking oil methyl esters (WCOME's) yield on the reactions variables such as reaction temperature, catalyst loading, molar ratio of methanol/oil and reusability were also assessed. The catalyst was used to convert the waste cooking oil into corresponding methyl esters (95.6%0.15) within 5 h at 200? reaction temperature, 600 rpm stirring speed, 1:25 molar ratio of oil to alcohol and 4% w/w catalyst loading. The reported catalyst was successfully recycled in six connective experiments without loss in activity. Moreover, the fuel properties of WCOME's were also reported using ASTM D 6751 methods. PMID:25843280

  18. Dissociation of manganese(III) oxide as part of a thermochemical water splitting cycle

    NASA Astrophysics Data System (ADS)

    Francis, Todd Michael

    A three-step thermochemical cycle to produce renewable hydrogen was proposed, which utilizes manganese(III) oxide and thermal energy to produce hydrogen. Most work on the cycle has focused on the hydrogen generating and product recovery steps with little work on the dissociation. It is essential to understand the dissociation because the feasibility of the cycle is based on this reaction having a high conversion. Because of the importance of the reduction step, this reaction has been selected as the topic of this dissertation. Additionally, because the dispersion of Mn2O3 particles into an Aerosol Flow Reactor (AFR) is important, feeding concepts were developed as well. Two powder feeding systems were developed: a Spinning Wheel Feeder (SWF) and a Fluidized Bed Feeder (FBF). Results of statistical particle size distribution studies indicated that the FBF was the better choice to disperse Mn2O3 powder. Additionally, results in an AFR demonstrated that the FBF was able to produce higher dissociation conversions. A study in a Thermogravimetric Analyzer (TGA) indicated multiple mechanisms were controlling Mn2O3 dissociation. The first half reaction of the dissociation was calculated to be controlled by an Avrami-Erofeev mechanism and had an activation energy of 106.4+/-1.9 kJ/mol. The second half reaction had a duel mechanism utilizing an Avrami-Erofeev and Order of Reaction (OOR) mechanism. The mechanisms had activation energies of 251.2+/-6.5 and 110.7+/-24.6 kJ/mol respectively. Mn2O3 dissociation investigations were done in an AFR. They revealed oxygen is a significant factor and to effectively control the dissociation with temperature and gas flow rate, the oxygen concentration must be below 0.25%. Experimental runs that had oxygen concentrations less than 0.25% were used to calculate reaction rate constants. The Avrami-Erofeev mechanisms were combined into a single mechanism. Rate constants for the Avrami-Erofeev and OOR mechanisms were 1.8E7+/-1.3E7 and 5.6E3+/-4.1E3 s -1 respectively. The results of a CFD model compared favorably with what was observed experimentally. A heavy feed concentration case predicted this as well. When the gas flow rate was higher the r-velocity was concluded to transport the more reacted powder near the wall to the center of the reactor, leading to higher conversions for the high gas flow rate.

  19. Electrical transport properties of manganese containing pyrochlore type semiconducting oxides using impedance analyses

    SciTech Connect

    Sumi, S.; Prabhakar Rao, P.; Mahesh, S.K.; Koshy, Peter

    2012-12-15

    Graphical abstract: DC conductivity variation of CaCe{sub 1?x}Mn{sub x}SnNbO{sub 7??} (x = 0, 0.2, 0.4 and 0.6) with inverse of temperature. Variation of conductivity with Mn concentration at 600 C is shown in the inset. Display Omitted Highlights: ? We have observed that the structural ordering as well as grain size increase with Mn substitution. ? Impedance analysis proved that a correlated barrier hopping type conduction mechanism is involved in the materials. ? Activation energy as well as electrical conductivity increases with increase in Mn substitution. ? Localization of electrons associated with Mn{sup 2+} and structural ordering are the key factors for the increased activation energy with Mn substitution. ? All the materials showed good NTC thermistor properties. -- Abstract: A new series of manganese containing pyrochlore type semiconducting oxides CaCe{sub 1?x}Mn{sub x}SnNbO{sub 7??} (x = 0, 0.2, 0.4 and 0.6) have been synthesized to study the effect of Mn substitution on the structure, microstructure and electrical properties of these samples. X-ray diffraction and scanning electron microscopy studies revealed an increase of structural ordering and grain size respectively with increase of Mn substitution. Rietveld analysis and Raman spectroscopy were also employed to corroborate the XRD results. The bulk resistance measurements with temperature exhibit negative temperature coefficient behavior. The impedance analysis of the samples revealed a non-Debye type relaxation existed in the materials. The ac conductivity variation with temperature and frequency indicates a correlated barrier hopping type conduction mechanism in these materials. The barrier height and the intersite separation for hopping influence the electrical conductivity of these samples and are found to be a function of localization of electrons associated with the Mn{sup 2+} ions and the unit cell volume respectively. The Mn substitution increases both electrical conductivity and activation energy contrastingly. This unusual behavior has been explained by correlating the structure, microstructure, defect states, electron localization and intersite separation with the conductivity data of the samples.

  20. The Staphylococcus aureus ABC-Type Manganese Transporter MntABC Is Critical for Reinitiation of Bacterial Replication Following Exposure to Phagocytic Oxidative Burst

    PubMed Central

    Coady, Alison; Xu, Min; Phung, Qui; Cheung, Tommy K.; Bakalarski, Corey; Alexander, Mary Kate; Lehar, Sophie M.; Kim, Janice; Park, Summer; Tan, Man-Wah; Nishiyama, Mireille

    2015-01-01

    Manganese plays a central role in cellular detoxification of reactive oxygen species (ROS). Therefore, manganese acquisition is considered to be important for bacterial pathogenesis by counteracting the oxidative burst of phagocytic cells during host infection. However, detailed analysis of the interplay between bacterial manganese acquisition and phagocytic cells and its impact on bacterial pathogenesis has remained elusive for Staphylococcus aureus, a major human pathogen. Here, we show that a mntC mutant, which lacks the functional manganese transporter MntABC, was more sensitive to killing by human neutrophils but not murine macrophages, unless the mntC mutant was pre-exposed to oxidative stress. Notably, the mntC mutant formed strikingly small colonies when recovered from both type of phagocytic cells. We show that this phenotype is a direct consequence of the inability of the mntC mutant to reinitiate growth after exposure to phagocytic oxidative burst. Transcript and quantitative proteomics analyses revealed that the manganese-dependent ribonucleotide reductase complex NrdEF, which is essential for DNA synthesis and repair, was highly induced in the mntC mutant under oxidative stress conditions including after phagocytosis. Since NrdEF proteins are essential for S. aureus viability we hypothesize that cells lacking MntABC might attempt to compensate for the impaired function of NrdEF by increasing their expression. Our data suggest that besides ROS detoxification, functional manganese acquisition is likely crucial for S. aureus pathogenesis by repairing oxidative damages, thereby ensuring efficient bacterial growth after phagocytic oxidative burst, which is an attribute critical for disseminating and establishing infection in the host. PMID:26379037

  1. Biological and Chemical Interactions with U(VI) During Anaerobic Enrichment in the Presence of Iron Oxide Coated Quartz

    SciTech Connect

    Brady D. Lee; Michelle R. Walton; Jodette L. Megio

    2005-11-01

    Microcosm experiments were performed to understand chemical and biological interactions with hexavalent uranium (U(VI)) in the presence of iron oxide bearing minerals and trichloroethylene (TCE) as a co-contaminant. Interactions of U(VI) and hydrous iron oxide moieties on the mineral oxide surfaces were studied during enrichments for dissimilatory iron reducing (DIRB) and sulfate reducing bacteria (SRB). Microbes enriched from groundwater taken from the Test Area North (TAN) site at the Idaho National Engineering and Environmental Laboratory (INEEL) were able to reduce the U(VI) in the adsorption medium as well as the iron on quartz surfaces. Early in the experiment disappearance of U(VI) from solution was a function of chemical interactions since no microbial activity was evident. Abiotic removal of U(VI) was enhanced in the presence of carbonate. As the experiment proceeded, further removal of U(VI) from solution was associated with the fermentation of lactate to propionate and acetate. During later phases of the experiment when lactate was depleted from the growth medium in the microcosm containing the DIRB enrichments, U(VI) concentrations in the solution phase increased until additional lactate was added. When lactate fermentation proceeded, U(VI) concentrations in the liquid phase again returned to near zero. Similar results were shown for the SRB enrichment but less uranium was released back into solution, while in the enrichment with carbonate uranium was not released back into solution. Chemical and biological interactions appear to be important on the mobilization/immobilization of U(VI) in an iron oxide system when TCE is present as a co-contaminant. Interestingly, TCE present in the microcosm experiments was not dechlorinated which was probably an effect of redox conditions that were unsuitable for reductive dechlorination by the microbial culture tested.

  2. Oxidant Selection for the Treatment of Manganese (II), Iron (II), and Arsenic (III) in Groundwaters

    EPA Science Inventory

    In order to comply with the United States Environmental Protection Agencys (U.S. EPAs) arsenic standard and the manganese and iron secondary maximum contaminant levels (MCLs) in water (10g/L, 50g/L, and 300g/L, respectively), many Midwestern water utilities must add a strong...

  3. Graphene-Based Hybrids with Manganese Oxide Polymorphs as Tailored Interfaces for Electrochemical Energy Storage: Synthesis, Processing, and Properties

    NASA Astrophysics Data System (ADS)

    Gupta, S.; van Meveren, M. M.; Jasinski, J.

    2015-01-01

    Technological progress is determined to a greater extent by developments of novel materials or new combinations of known materials with different dimensionality and diverse functionality. In this work, we report on the synthesis and characterization of graphene-based hybrid nanomaterials coupled with transition-metal oxide polymorphs (nano/micro-manganese oxides, i.e., β-MnO2 [Mn(IV)] and Mn3O4 [Mn(II, III)]). This lays the groundwork for high-performance electrochemical electrodes for alternative energy devices owing to their higher specific capacitance, wide operational potential window and stability through charge-discharge cycling, environmentally benignity, cost-effectiveness, easy processing, and reproducibility on a larger scale. To accomplish this, we strategically designed these hybrids by direct anchoring or physical adsorption of β-MnO2 and Mn3O4 on variants of graphene, namely graphene oxide and its reduced form, via mixing dispersions of the constituents under mild ultrasonication and drop-casting, resulting in four different combinations. This facile approach affords strong chemical/physical attachment and is expected to result in coupling between the pseudocapacitive transition-metal oxides and supercapacitive nanocarbons showing enhanced activity/reactivity and reasonable areal density of tailored interfaces. We used a range of complementary analytical characterization tools to determine the structure and physical properties, such as scanning electron microscopy combined with energy-dispersive x-ray spectroscopy, atomic force microscopy, x-ray diffraction, resonance Raman spectroscopy combined with elemental Raman mapping, and transmission electron microscopy in conjunction with selected-area electron diffraction. All of these techniques reveal surface morphology, local (lattice dynamical) and average structure, and local charge transfer due to the physically (or chemically) adsorbed manganese oxide of synthesized hybrids that helps to establish microscopic structure-property-function correlations highlighting the surface structure and interfaces to further investigate their electrochemical supercapacitor properties.

  4. Selective Alkane Oxidation by Manganese Oxide: Site Isolation of MnOx Chains at the Surface of MnWO4 Nanorods.

    PubMed

    Li, Xuan; Lunkenbein, Thomas; Pfeifer, Verena; Jastak, Mateusz; Nielsen, Pia Kjaer; Girgsdies, Frank; Knop-Gericke, Axel; Rosowski, Frank; Schlögl, Robert; Trunschke, Annette

    2016-03-14

    The electronic and structural properties of vanadium-containing phases govern the formation of isolated active sites at the surface of these catalysts for selective alkane oxidation. This concept is not restricted to vanadium oxide. The deliberate use of hydrothermal techniques can turn the typical combustion catalyst manganese oxide into a selective catalyst for oxidative propane dehydrogenation. Nanostructured, crystalline MnWO4 serves as the support that stabilizes a defect-rich MnOx surface phase. Oxygen defects can be reversibly replenished and depleted at the reaction temperature. Terminating MnOx zigzag chains on the (010) crystal planes are suspected to bear structurally site-isolated oxygen defects that account for the unexpectedly good performance of the catalyst in propane activation. PMID:26913704

  5. Manganese, Metallogenium, and Martian Microfossils

    NASA Technical Reports Server (NTRS)

    Stein, L. Y.; Nealson, K. H.

    1999-01-01

    Manganese could easily be considered an abundant element in the Martian regolith, assuming that the composition of martian meteorites reflects the composition of the planet. Mineralogical analyses of 5 SNC meteorites have revealed an average manganese oxide concentration of 0.48%, relative to the 0.1% concentration of manganese found in the Earth's crust. On the Earth, the accumulation of manganese oxides in oceans, soils, rocks, sedimentary ores, fresh water systems, and hydrothermal vents can be largely attributed to microbial activity. Manganese is also a required trace nutrient for most life forms and participates in many critical enzymatic reactions such as photosynthesis. The wide-spread process of bacterial manganese cycling on Earth suggests that manganese is an important element to both geology and biology. Furthermore, there is evidence that bacteria can be fossilized within manganese ores, implying that manganese beds may be good repositories for preserved biomarkers. A particular genus of bacteria, known historically as Metallogenium, can form star-shaped manganese oxide minerals (called metallogenium) through the action of manganese oxide precipitation along its surface. Fossilized structures that resemble metallogenium have been found in Precambrian sedimentary formations and in Cretaceous-Paleogene cherts. The Cretaceous-Paleogene formations are highly enriched in manganese and have concentrations of trace elements (Fe, Zn, Cu, and Co) similar to modern-day manganese oxide deposits in marine environments. The appearance of metallogenium-like fossils associated with manganese deposits suggests that bacteria may be preserved within the minerals that they form. Additional information is contained in the original extended abstract.

  6. Hydrothermal manganese oxide deposits from Galapagos mounds, DSDP Leg 70, hole 509B and ``Alvin'' dives 729 and 721

    NASA Astrophysics Data System (ADS)

    Lalou, Claude; Brichet, Evelyne; Jehanno, Celestine; Perez-Leclaire, Helose

    1983-04-01

    During DSDP Leg 70, a 1.60 m thick manganese oxide layer was sampled in hole 509B. This deposit is formed of alternating layers of hard plates of pure todorokite, about 2 mm thick, and of a more powdery material deeply impregnated with manganese oxide, about 3 mm thick. A SEM study of the plates and the associated powder shows that the powdery material is a transformation of a pre-existing sediment, while the plates are a direct precipitation from a hydrothermal solution. The uranium series disequilibrium method was used to determine the ages of the plates. They are found to be in good chronological sequence and in accordance with the sedimentation rate of the area (4.9 cm/10 3 years) which implies that they have been formed at the sediment-seawater interface during a pulsed injection of hydrothermal solution. The powder presents systematically an "older age" which is explained by a slowing down of the injection while the normal sediment settles; the older age is due to the 230Th excess of the sediment.

  7. Adsorption of antimony(V) onto Mn(II)-enriched surfaces of manganese-oxide and FeMn binary oxide.

    PubMed

    Liu, Ruiping; Xu, Wei; He, Zan; Lan, Huachun; Liu, Huijuan; Qu, Jiuhui; Prasai, Tista

    2015-11-01

    Manganese(IV) oxide [Mn(IV)] potentially oxidizes antimony(III) [Sb(III)] to antimony(V) [Sb(V)] and improves Sb removal by FeMn binary oxide (FMBO) through an oxidation-adsorption mechanism. This study focused on the effect of Mn(IV) reductive dissolution by potassium sulfite (K2SO3) on Sb(V) adsorption onto manganese oxide (Mn-oxide) and FMBO. The maximum Sb(V) adsorption (Qmax,Sb(V)) increased from 1.0 to 1.1 mmol g(-1) for FMBO and from 0.4 to 0.6 mmol g(-1) for Mn-oxide after pretreatment with 10 mmol L(-1) K2SO3. The addition of 2.5 mmol L(-1) Mn(2+) also significantly improved Sb(V) adsorption, and the observed Qmax,Sb(V) increased to 1.4 and 1.0 mmol g(-1) for FMBO and Mn-oxide, respectively, with pre-adsorbed Mn(2+). Neither K2SO3 nor Mn(2+) addition had any effect on Sb(V) adsorption onto iron oxide (Fe-oxide). Mn(2+) introduced by either Mn(IV) dissolution or addition tended to form outer-sphere surface complexes with hydroxyl groups on Mn-oxide surfaces (MnOOH). Mn(2+) at 2.5 mmol L(-1) shifted the isoelectric point (pHiep) from 7.5 to 10.2 for FMBO and from 4.8 to 9.2 for Mn-oxide and hence benefited Sb(V) adsorption. The adsorption of Sb(V) onto Mn(2+)-enriched surfaces contributed to the release of Mn(2+), and the X-ray photoelectron spectra also indicated increased binding energy of Mn 2p3/2 after the adsorption of Sb(V) onto K2SO3-pretreated FMBO and Mn-oxide. Sb(V) adsorption involved the formation of inner-sphere complexes and contributed to the release of Mn(2+). In the removal of Sb(III) by Mn-based oxides, the oxidation of Sb(III) to Sb(V) by Mn(IV) oxides had an effect; however, Mn(IV) dissolution and Mn(2+)-enrichment also played an important role. PMID:26218341

  8. Different Arsenate and Phosphate Incorporation Effects on the Nucleation and Growth of Iron(III) (Hydr)oxides on Quartz

    SciTech Connect

    Neil, Chelsea W.; Lee, Byeongdu; Jun, Young-Shin

    2014-10-21

    Iron(III) (hydr)oxides play an important role in the geochemical cycling of contaminants in natural and engineered aquatic systems. The ability of iron(III) (hydr)oxides to immobilize contaminants can be related to whether the precipitates form heterogeneously (e.g., at mineral surfaces) or homogeneously in solution. Utilizing grazing incidence small-angle X-ray scattering (GISAXS), we studied heterogeneous iron(III) (hydr)oxide nucleation and growth on quartz substrates for systems containing arsenate and phosphate anions. For the iron(III) only system, the radius of gyration ( R g ) of heterogeneously formed precipitates grew from 1.5 to 2.5 ( ± 1.0) nm within 1 h. For the system containing 10-5 M arsenate, R g grew from 3.6 to 6.1 ( ± 0.5) nm, and for the system containing 10-5 M phosphate, R g grew from 2.0 to 4.0 ( ± 0.2) nm. While the systems containing these oxyanions had more growth, the system containing only iron(III) had the most nucleation events on substrates. Ex situ analyses of homogeneously and heterogeneously formed precipitates indicated that precipitates in the arsenate system had the highest water content and that oxyanions may bridge iron(III) hydroxide polymeric embryos to form a structure similar to ferric arsenate or ferric phosphate. These new fi ndings are important because di ff erences in nucleation and growth rates and particle sizes will impact the number of available reactive sites and the reactivity of newly formed particles toward aqueous contaminants.

  9. Oxidation of aniline and other primary aromatic amines by manganese dioxide

    SciTech Connect

    Laha, S.; Luthy, R.G. )

    1990-03-01

    This investigation evaluated the redox reaction between a manganese dioxide, {sigma}-MnO{sub 2}, and anilines and other aromatic reductants in aqueous suspensions at pH values ranging from 3.7 to 6.5. The reaction with manganese dioxide may represent a pathway for transformation of aniline and other primary aromatic amines in acidic mineralogical and soil/water environments in the absence of oxygen and substantial microbial activity. The reaction rate with aniline is pH-dependent, increasing with decreasing pH, and first order with respect to {sigma}-MnO{sub 2} and organic solute. Aniline and p-toluidine are demonstrated to be 2-equiv reductants, as is believed to be the case for the other aromatic solutes considered in this study, including the substituted anilines, and hydroquinone and catechol and their alkyl substituents. Ring-bound nitrogen-containing aromatic solutes (methylimidazole, quinoline, and 5,5-dimethylhydantion) were unreactive with manganese dioxide at pH 6.4. The order of the reactivity of para-substituted anilines was methoxy >> methyl > chloro > carboxy >> nitro; the relative reactivity of these compounds correlated with the solute's half-wave potential and Hammett constant.

  10. Power generation using spinel manganese-cobalt oxide as a cathode catalyst for microbial fuel cell applications.

    PubMed

    Mahmoud, Mohamed; Gad-Allah, Tarek A; El-Khatib, K M; El-Gohary, Fatma

    2011-11-01

    This study focused on the use of spinel manganese-cobalt (Mn-Co) oxide, prepared by a solid state reaction, as a cathode catalyst to replace platinum in microbial fuel cells (MFCs) applications. Spinel Mn-Co oxides, with an Mn/Co atomic ratios of 0.5, 1, and 2, were prepared and examined in an air cathode MFCs which was fed with a molasses-laden synthetic wastewater and operated in batch mode. Among the three Mn-Co oxide cathodes and after 300 h of operation, the Mn-Co oxide catalyst with Mn/Co atomic ratio of 2 (MnCo-2) exhibited the highest power generation 113 mW/m2 at cell potential of 279 mV, which were lower than those for the Pt catalyst (148 mW/m2 and 325 mV, respectively). This study indicated that using spinel Mn-Co oxide to replace platinum as a cathodic catalyst enhances power generation, increases contaminant removal, and substantially reduces the cost of MFCs. PMID:21944282

  11. QUILF: A pascal program to assess equilibria among Fe?Mg?Mn?Ti oxides, pyroxenes, olivine, and quartz

    NASA Astrophysics Data System (ADS)

    Andersen, David J.; Lindsley, Donald H.; Davidson, Paula M.

    1993-10-01

    Program QUILF assesses equilibria among Ti-magnetite, ilmenite, augite, pigeonite, orthopyroxene, olivine, and quartz (or subassemblages thereof). Oxide and silicate equilibria are related through the QUIIF equilibrium: ?Depending on the assemblage, QUILF can provide information on temperature, pressure, oxygen fugacity, and the activities of SiO 2, TiO 2, and Fe o at which the phases were last in equilibrium. For many low-variance assemblages, the system is overdetermined; thus quantitative information can be extracted even if one phase is altered or has reequilibrated. QUILF equilibria can reduce the uncertainties in temperature and oxygen fugacity as determined from coexisting ilmenite and Ti-magnetite alone. QUILF is written in Turbo Pascal for IBM PC and compatibles. The compiled program is approximately 210 kbyte; it also requires two data files that total approximately 10 kbyte. The compositions of the phases first must be projected into seven-component space (CaO?MgO?MnO?FeO?Fe 2O 3TiO 2?SiO 2) before they are used in program QUILF; routines to accomplish this are included in the program, and also are available as separate BASIC programs.

  12. Bacterial removal in flow-through columns packed with iron-manganese bimetallic oxide-coated sand.

    PubMed

    Park, Seong-Jik; Lee, Chang-Gu; Kim, Song-Bae; Chang, Yoon-Young; Yang, Jae-Kyu

    2012-01-01

    The objective of this study was to investigate the performance of iron-manganese bimetallic oxide-coated sand (IMCS) in the removal of bacteria (Escherichia coli ATCC 11105) using small-scale (length = 20 cm, inner diameter = 2.5 cm) and 30-day long-term (length = 50 cm, inner diameter = 2.5 cm) column experiments. Results indicated that the bacterial removal capacity of IMCS (q(eq) = 0.66 g/g) was slightly lower than that of iron oxide-coated sand (ICS) (q(eq) = 0.69 g/g) but about two times greater than those of manganese oxide-coated sand (MCS, q(eq) = 0.30 g/g) and dual media containing ICS and MCS (q(eq) = 0.35 g/g). In IMCS, increasing the flow rate from 0.5 to 3.0 mL/min decreased the removal capacity from 1.14 to 0.64 g/g. Nitrate showed an enhancement effect on the removal capacity of IMCS at 1 and 10 mM, while phosphate and bicarbonate had both hindrance (1 mM) and enhancement (10 mM) effects, depending on their concentrations. The long-term column experiment (bacterial injection conc. = 4.2 10(6) CFU/mL) showed that IMCS could remove more than 99.9 % of bacteria within 13 days (effluent conc. = 1.6 10(2) CFU/mL). This study demonstrated that IMCS could be used as an adsorptive filter medium for bacterial removal in water treatment. PMID:22571524

  13. First evidence of manganese-nickel segregation and densification upon cycling in Li-rich layered oxides for lithium batteries.

    PubMed

    Boulineau, Adrien; Simonin, Loc; Colin, Jean-Franois; Bourbon, Carole; Patoux, Sbastien

    2013-08-14

    Lithium-rich manganese-based layered oxides Li[Li(x)Mn(y)TM(1-x-y)]O2 with TM standing for Ni, Co, or Fe are of great interest as cathode materials for lithium ion batteries. Indeed, among all of the materials, they offer the highest rechargeable capacity and energy density. However, when used, they suffer from complex evolutions that need to be understood before their practical use. Here we report on such evolutions studied using advanced transmission electron microscopy. Structural modifications are directly observed at the atomic scale using Cs corrected STEM HAADF imaging technique, and the chemical modifications are probed by the means of STEM EELS experiments. For the first time, segregation between nickel and manganese close the particle surface is pointed out. Finally, observed evolutions are correlated within a proposed mechanism that leads to the densification of the material. Our results allow understanding the link between the decrease of electrochemical performance and these evolutions occurring into the material upon cycling. PMID:23876058

  14. Structural, optical, and magnetic studies of manganese-doped zinc oxide hierarchical microspheres by self-assembly of nanoparticles

    PubMed Central

    2012-01-01

    In this study, a series of manganese [Mn]-doped zinc oxide [ZnO] hierarchical microspheres [HMSs] are prepared by hydrothermal method only using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. X-ray diffraction indicates that all of the as-obtained samples including the highest Mn (7 mol%) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). A broad Raman spectrum from as-synthesized doping samples ranges from 500 to 600 cm-1, revealing the successful doping of paramagnetic Mn2+ ions in the host ZnO. Optical absorption analysis of the samples exhibits a blueshift in the absorption band edge with increasing dopant concentration, and corresponding photoluminescence spectra show that Mn doping suppresses both near-band edge UV emission and defect-related blue emission. In particular, magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high Curie temperature exceeding 400 K, signifying that the as-formed Mn-doped ZnO HMSs will have immense potential in spintronic devices and spin-based electronic technologies. PMID:22296968

  15. Characterization of High-Velocity Solution Precursor Flame-Sprayed Manganese Cobalt Oxide Spinel Coatings for Metallic SOFC Interconnectors

    NASA Astrophysics Data System (ADS)

    Puranen, Jouni; Laakso, Jarmo; Kylmälahti, Mikko; Vuoristo, Petri

    2013-06-01

    A modified high-velocity oxy-fuel spray (HVOF) thermal spray torch equipped with liquid feeding hardware was used to spray manganese-cobalt solutions on ferritic stainless steel grade Crofer 22 APU substrates. The HVOF torch was modified in such a way that the solution could be fed axially into the combustion chamber through 250- and 300-μm-diameter liquid injector nozzles. The solution used in this study was prepared by diluting nitrates of manganese and cobalt, i.e., Mn(NO3)2·4H2O and Co(NO3)2·6H2O, respectively, in deionized water. The as-sprayed coatings were characterized by X-ray diffraction and field-emission scanning electron microscopy operating in secondary electron mode. Chemical analyses were performed on an energy dispersive spectrometer. Coatings with remarkable density could be prepared by the novel high-velocity solution precursor flame spray (HVSPFS) process. Due to finely sized droplet formation in the HVSPFS process and the use of as delivered Crofer 22 APU substrate material having very low substrate roughness ( R a < 0.5 μm), thin and homogeneous coatings, with thicknesses lower than 10 μm could be prepared. The coatings were found to have a crystalline structure equivalent to MnCo2O4 spinel with addition of Co-oxide phases. Crystallographic structure was restored back to single-phase spinel structure by heat treatment.

  16. The development of manganese oxide coated ceramic membranes for combined catalytic ozonation and ultrafiltration of drinking water

    NASA Astrophysics Data System (ADS)

    Corneal, Lindsay Marie

    A novel method for the preparation of hydrated MnO2 by the ozonation of MnCl2 in water is described. The hydrated MnO 2 was used to coat titania water filtration membranes using a layer-by-layer technique. The coated membranes were then sintered in air at 500°C for 45 minutes. Upon sintering, the MnO2 is converted to alpha-Mn 2O3 (as characterized by x-ray and electron diffraction). Atomic force microscopy (AFM) imaging showed no significant change in the roughness or height of the surface features of coated membranes, while scanning electron microscopy (SEM) imaging showed an increase in grain size with increasing number of coating layers. Energy dispersive x-ray spectroscopy (EDS) mapping and line scans revealed manganese present throughout the membrane, indicating that manganese dispersed into the porous membrane during the coating process and diffused into the titania grains during sintering. Selected area diffraction (SAD) of the coated and sintered membrane was used to index the surface layer as alpha-Mn2O3. The surface layer was uneven, although there was a trend of increasing thickness with increasing coating layers. The coating acts as a catalyst for the oxidation of organic matter when coated membranes are used in a hybrid ozonation-membrane filtration system. A trend of decreasing total organic carbon (TOC) in the permeate water was observed with increasing number of coating layers. The catalytic activity also manifests itself as improved recovery of the water flux due to oxidation of foulants on the membrane surface. Ceramic nanoparticle coatings on ceramic water filtration membranes must undergo high temperature sintering. However, this means that the underlying membrane, which has been engineered for a given molecular weight cut-off (MWCO), also undergoes a high temperature heat treatment that serves to increase pore size that have resulted in increases in permeability of titania membranes. Coating the titania membrane with manganese oxide followed by sintering in air at 500°C maintains the MWCO of the membranes, with high DI water permeability, which may be favorable in terms of membrane use. SEM micrographs of titania membrane samples sintered between 500°C to 900°C were analyzed to identify a statistically significant increase in grain size with increasing sintering temperature. The grains however, generally retain a uniform shape until the 900°C sintering temperature, where large, irregularly shaped grains were observed. AFM analysis showed a corresponding increase in the surface roughness of the membrane for the sample sintered at 900°C.

  17. Tunable T1 and T2 contrast abilities of manganese-engineered iron oxide nanoparticles through size control

    NASA Astrophysics Data System (ADS)

    Huang, Guoming; Li, Hui; Chen, Jiahe; Zhao, Zhenghuan; Yang, Lijiao; Chi, Xiaoqin; Chen, Zhong; Wang, Xiaomin; Gao, Jinhao

    2014-08-01

    In this paper, we demonstrate the tunable T1 and T2 contrast abilities of engineered iron oxide nanoparticles with high performance for liver contrast-enhanced magnetic resonance imaging (MRI) in mice. To enhance the diagnostic accuracy of MRI, large numbers of contrast agents with T1 or T2 contrast ability have been widely explored. The comprehensive investigation of high-performance MRI contrast agents with controllable T1 and T2 contrast abilities is of high importance in the field of molecular imaging. In this study, we synthesized uniform manganese-doped iron oxide (MnIO) nanoparticles with controllable size from 5 to 12 nm and comprehensively investigated their MRI contrast abilities. We revealed that the MRI contrast effects of MnIO nanoparticles are highly size-dependent. By controlling the size of MnIO nanoparticles, we can achieve T1-dominated, T2-dominated, and T1-T2 dual-mode MRI contrast agents with much higher contrast enhancement than the corresponding conventional iron oxide nanoparticles.In this paper, we demonstrate the tunable T1 and T2 contrast abilities of engineered iron oxide nanoparticles with high performance for liver contrast-enhanced magnetic resonance imaging (MRI) in mice. To enhance the diagnostic accuracy of MRI, large numbers of contrast agents with T1 or T2 contrast ability have been widely explored. The comprehensive investigation of high-performance MRI contrast agents with controllable T1 and T2 contrast abilities is of high importance in the field of molecular imaging. In this study, we synthesized uniform manganese-doped iron oxide (MnIO) nanoparticles with controllable size from 5 to 12 nm and comprehensively investigated their MRI contrast abilities. We revealed that the MRI contrast effects of MnIO nanoparticles are highly size-dependent. By controlling the size of MnIO nanoparticles, we can achieve T1-dominated, T2-dominated, and T1-T2 dual-mode MRI contrast agents with much higher contrast enhancement than the corresponding conventional iron oxide nanoparticles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02680b

  18. Chemical versus Enzymatic Digestion of Contaminated Estuarine Sediment: Relative Importance of Iron and Manganese Oxides in Controlling Trace Metal Bioavailability

    NASA Astrophysics Data System (ADS)

    Turner, A.; Olsen, Y. S.

    2000-12-01

    Chemical and enzymatic reagents have been employed to determine available concentrations of Fe, Mn, Cu and Zn in contaminated estuarine sediment. Gastric and intestinal enzymes (pepsin, pH 2, and trypsin, pH 76, respectively) removed significantly more metal than was water-soluble or exchangeable (by seawater or ammonium acetate), while gastro-intestinal fluid of the demersal teleost, Pleuronectes platessa L. (plaice), employed to operationally define a bioavailable fraction of contaminants, generally solubilized more metal than the model enzymes. Manganese was considerably more available than Fe under these conditions and it is suggested that the principal mechanism of contaminant release is via surface complexation and reductive solubilization of Mn oxides, a process which is enhanced under conditions of low pH. Of the chemical reagents tested, acetic acid best represents the fraction of Mn (as well as Cu and Zn) which is available under gastro-intestinal conditions, suggesting that the reducing tendency of acetate is similar to that of the ligands encountered in the natural digestive environment. Although the precise enzymatic and non-enzymatic composition of plaice gastro-intestinal fluid may be different to that encountered in more representative, filter-feeding or burrowing organisms, a general implication of this study is that contaminants associated with Mn oxides are significantly more bioavailable than those associated with Fe oxides, and that contaminant bioavailability may be largely dictated by the oxidic composition of contaminated sediment.

  19. Manganese, the stress reliever.

    PubMed

    Latour, J-M

    2015-01-01

    Convergent evidence has emerged over the past decade to highlight the role of manganese as a key player in the defenses that many organisms are building to fight oxidative stress. For redox processes replacing iron by manganese requires adaptation at different levels. The aim of this perspective is to summarize recent important observations and to analyze the implications of the present knowledge for resolving future issues. PMID:25434324

  20. Graphite coated with manganese oxide/multiwall carbon nanotubes composites as anodes in marine benthic microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Fu, Yubin; Yu, Jian; Zhang, Yelong; Meng, Yao

    2014-10-01

    Improving anode performance is of great significance to scale up benthic microbial fuel cells (BMFCs) for its marine application to drive oceanography instruments. In this study, manganese oxide (MnO2)/multiwall carbon nanotubes (MWCNTs) composites are prepared to be as novel anodes in the BMFCs via a direct redox reaction between permanganate ions (MnO4-) and MWCNTs. The results indicate that the MnO2/MWCNTs anode has a better wettability, greater kinetic activity and higher power density than that of the plain graphite (PG) anode. It is noted that the MnO2 (50% weight percent)/MWCNTs anode shows the highest electrochemical performance among them and will be a promising material for improving bioelectricity production of the BMFCs. Finally, a synergistic mechanism of electron transfer shuttle of Mn ions and their redox reactions in the interface between modified anode and bacteria biofilm are proposed to explain its excellent electrochemical performance.

  1. Hybrid nickel manganese oxide nanosheet-3D metallic dendrite percolation network electrodes for high-rate electrochemical energy storage.

    PubMed

    Nguyen, Tuyen; Eugnio, Snia; Boudard, Michel; Rapenne, Laetitia; Carmezim, M Joo; Silva, Teresa M; Montemor, M Ftima

    2015-08-01

    This work reports the fabrication, by electrodeposition and post-thermal annealing, of hybrid electrodes for high rate electrochemical energy storage composed of nickel manganese oxide (Ni0.86Mn0.14O) nanosheets over 3D open porous dendritic NiCu foams. The hybrid electrodes are made of two different percolation networks of nanosheets and dendrites, and exhibit a specific capacitance value of 848 F g(-1) at 1 A g(-1). The electrochemical tests revealed that the electrodes display an excellent rate capability, characterized by capacitance retention of approximately 83% when the applied current density increases from 1 A g(-1) to 20 A g(-1). The electrodes also evidenced high charge-discharge cycling stability, which attained 103% after 1000 cycles. PMID:26135715

  2. Ketjenblack carbon supported amorphous manganese oxides nanowires as highly efficient electrocatalyst for oxygen reduction reaction in alkaline solutions.

    PubMed

    Lee, Jang-Soo; Park, Gi Su; Lee, Ho Il; Kim, Sun Tai; Cao, Ruiguo; Liu, Meilin; Cho, Jaephil

    2011-12-14

    A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ?190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts. PMID:22050041

  3. Hybrid nickel manganese oxide nanosheet-3D metallic dendrite percolation network electrodes for high-rate electrochemical energy storage

    NASA Astrophysics Data System (ADS)

    Nguyen, Tuyen; Eugnio, Snia; Boudard, Michel; Rapenne, Laetitia; Carmezim, M. Joo; Silva, Teresa M.; Montemor, M. Ftima

    2015-07-01

    This work reports the fabrication, by electrodeposition and post-thermal annealing, of hybrid electrodes for high rate electrochemical energy storage composed of nickel manganese oxide (Ni0.86Mn0.14O) nanosheets over 3D open porous dendritic NiCu foams. The hybrid electrodes are made of two different percolation networks of nanosheets and dendrites, and exhibit a specific capacitance value of 848 F g-1 at 1 A g-1. The electrochemical tests revealed that the electrodes display an excellent rate capability, characterized by capacitance retention of approximately 83% when the applied current density increases from 1 A g-1 to 20 A g-1. The electrodes also evidenced high charge-discharge cycling stability, which attained 103% after 1000 cycles.

  4. Degradation of lithium ion batteries employing graphite negatives and nickel-cobalt-manganese oxide + spinel manganese oxide positives: Part 2, chemical-mechanical degradation model

    NASA Astrophysics Data System (ADS)

    Purewal, Justin; Wang, John; Graetz, Jason; Soukiazian, Souren; Tataria, Harshad; Verbrugge, Mark W.

    2014-12-01

    Capacity fade is reported for 1.5 Ah Li-ion batteries containing a mixture of Li-Ni-Co-Mn oxide (NCM) + Li-Mn oxide spinel (LMO) as positive electrode material and a graphite negative electrode. The batteries were cycled at a wide range of temperatures (10 C-46 C) and discharge currents (0.5C-6.5C). The measured capacity losses were fit to a simple physics-based model which calculates lithium inventory loss from two related mechanisms: (1) mechanical degradation at the graphite anode particle surface caused by diffusion-induced stresses (DIS) and (2) chemical degradation caused by lithium loss to continued growth of the solid-electrolyte interphase (SEI). These two mechanisms are coupled because lithium is consumed through SEI formation on newly exposed crack surfaces. The growth of crack surface area is modeled as a fatigue phenomenon due to the cyclic stresses generated by repeated lithium insertion and de-insertion of graphite particles. This coupled chemical-mechanical degradation model is consistent with the observed capacity loss features for the NCM + LMO/graphite cells.

  5. Multivariate data analysis approach to understand magnetic properties of perovskite manganese oxides

    SciTech Connect

    Imamura, N.; Mizoguchi, T.; Yamauchi, H.; Karppinen, M.

    2008-05-15

    Here we apply statistical multivariate data analysis techniques to obtain some insights into the complex structure-property relations in antiferromagnetic (AFM) and ferromagnetic (FM) manganese perovskite systems, AMnO{sub 3}. The 131 samples included in the present analyses are described by 21 crystal-structure or crystal-chemical (CS/CC) parameters. Principal component analysis (PCA), carried out separately for the AFM and FM compounds, is used to model and evaluate the various relationships among the magnetic properties and the various CS/CC parameters. Moreover, for the AFM compounds, PLS (partial least squares projections to latent structures) analysis is performed so as to predict the magnitude of the Neel temperature on the bases of the CS/CC parameters. Finally, so-called PLS-DA (PLS discriminant analysis) method is employed to find out the most influential/characteristic CS/CC parameters that differentiate the two classes of compounds from each other. - Graphical abstract: Statistical multivariate data analysis techniques are applied to detect structure-property relations in antiferromagnetic (AFM) and ferromagnetic (FM) manganese perovskites. For AFM compounds, partial least squares projections to latent structures analysis predict the magnitude of the Neel temperature on the bases of structural parameters only. Moreover, AFM and FM compounds are well separated by means of so-called partial least squares discriminant analysis method.

  6. Natural manganese oxide: Combined analytical approach for solid characterization and arsenic retention

    NASA Astrophysics Data System (ADS)

    Ouvrard, S.; de Donato, Ph.; Simonnot, M. O.; Begin, S.; Ghanbaja, J.; Alnot, M.; Duval, Y. B.; Lhote, F.; Barres, O.; Sardin, M.

    2005-06-01

    To understand the retention of As on a natural manganese sand, the structural, textural and chemical properties of the solid were first investigated by combining scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron-energy-loss spectroscopy (EELS), X-ray diffraction (XRD), BET N 2 gas adsorption, diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. Manganese sand could be mainly described as a mixture of a phyllomanganate, lithiophorite [(Al,Li)MnO 2(OH) 2], and pyrolusite (MnO 2). Iron particle, kaolinite and gibbsite type-phases were also observed. Particles organization led to the presence of a mesoporosity with pore diameters ranging from 100 to 200 and a specific surface area of 23 m 2 g -1. Contact with an As(V) solution (0.67 mmol L -1) led to an average fractional surface coverage of 0.4. Both As (V) and (III) were present on the surface of the sand in a 1:1 ratio. As(V) was sorbed on lithiophorite-type particles through surface complexation type reaction. As(III) was thought to result from As(V) reduction mechanism on iron particles.

  7. Oxidative aliphatic C-H fluorination with manganese catalysts and fluoride ion.

    PubMed

    Liu, Wei; Huang, Xiongyi; Groves, John T

    2013-12-01

    Fluorination is a reaction that is useful in improving the chemical stability and changing the binding affinity of biologically active compounds. The protocol described here can be used to replace aliphatic, C(sp(3))-H hydrogen in small molecules with fluorine. Notably, isolated methylene groups and unactivated benzylic sites are accessible. The method uses readily available manganese porphyrin and manganese salen catalysts and various fluoride ion reagents, including silver fluoride (AgF), tetrabutylammonium fluoride and triethylamine trihydrofluoride (TREATHF), as the source of fluorine. Typically, the reactions afford 50-70% yield of mono-fluorinated products in one step. Two representative examples, the fragrance component celestolide and the nonsteroidal anti-inflammatory drug ibuprofen, are described; they produced useful isolated quantities (250-300 mg, ~50% yield) of fluorinated material over periods of 1-8 h. The procedures are performed in a typical fume hood using ordinary laboratory glassware. No special precautions to rigorously exclude water are required. PMID:24177292

  8. Design, synthesis, and characterization of materials for controlled line deposition, environmental remediation, and doping of porous manganese oxide material

    NASA Astrophysics Data System (ADS)

    Calvert, Craig A.

    This thesis covers three topics: (1) coatings formed from sol-gel phases, (2) environmental remediation, and (3) doping of a porous manganese oxide. Synthesis, characterization, and application were investigated for each topic. Line-formations were formed spontaneously by self-assembly from vanadium sol-gels and other metal containing solutions on glass substrates. The solutions were prepared by the dissolution of metal oxide or salt in water. A more straightforward method is proposed than used in previous work. Analyses using optical microscopy, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, and infrared spectroscopy showed discreet lines whose deposition could be controlled by varying the concentration. A mechanism was developed from the observed results. Microwave heating, the addition of graphite rods, and oxidants, can enhance HCB remediation from soil. To achieve remediation, a TeflonRTM vessel open to the atmosphere along with an oxidant, potassium persulfate (PerS) or potassium hydroxide, along with uncoated or aluminum oxide coated, graphite rods were heated in a research grade microwave oven. Microwave heating was used to decrease the heating time, and graphite rods were used to increase the absorption of the microwave energy by providing thermal centers. The results showed that the percent HCB removed was increased by adding graphite rods and oxidants. Tungsten, silver, and sulfur were investigated as doping agents for K--OMS-2. The synthesis of these materials was carried out with a reflux method. The doping of K--OMS-2 led to changes in the properties of a tungsten doped K--OMS-2 had an increased resistivity, the silver doped material showed improved epoxidation of trans-stilbene, and the addition of sulfur produced a paper-like material. Rietveld refinement of the tungsten doped K--OMS-2 showed that the tungsten was doped into the framework.

  9. Manganese peroxidase from the basidiomycete Phanerochaete chrysosporium: spectral characterization of the oxidized states and the catalytic cycle

    SciTech Connect

    Wariishi, H.; Akileswaran, L.; Gold, M.H.

    1988-07-12

    Manganese peroxidase (MnP), an extracellular heme enzyme from the lignin-degrading fungus Phanerochaete chrysosporium, catalyzes the Mn(II)-dependent oxidation of a variety of phenols. Herein, the authors spectroscopically characterize the oxidized states of MnP compounds I, II, and III and clarify the role of Mn in the catalytic cycle of the enzyme. Addition of 1 equiv of H/sub 2/O/sub 2/ to the native ferric enzyme yields compound I, characterized by absorption maxima at 407, 558, 605, and 650 nm. Addition of 2 or 250 equiv of H/sub 2/O/sub 2/ to the native enzyme yields compound II or III, respectively, identified by absorption maxima at 420, 528, and 555 nm or at 417, 545, and 579 nm, respectively. These characteristics are very similar to those of horseradish peroxidase (HRP) and lignin peroxidase (LiP) compounds I, II, and III. Addition of 1 equiv of either Mn(II), ferrocyanide, or a variety of phenols to MnP compound I rapidly reduces it to MnP compound II. In contrast, only Mn(II) or ferrocyanide, added at a concentration of 1 equiv, reduces compound II. The Mn(III) produced by the enzymic oxidation of Mn(II) oxidizes the terminal phenolic substrates. This indicates that compounds I and II of MnP contain 2 and 1 oxidizing equiv, respectively, over the native ferric resting enzyme and that the catalytic cycle of the enzyme follows the path native enzyme ..-->.. compound I ..-->.. compound II ..-->.. native enzyme. In addition, these results indicate that Mn(II) serves as an obligatory substrate for MnP compound II, allowing the enzyme to complete its catalytic cycle. Finally, the Mn(II)/Mn(III) redox couple enables the enzyme to rapidly oxidize the terminal phenolic substrates.

  10. Novel Mode of Microbial Energy Metabolism: Organic Carbon Oxidation Coupled to Dissimilatory Reduction of Iron or Manganese

    PubMed Central

    Lovley, Derek R.; Phillips, Elizabeth J. P.

    1988-01-01

    A dissimilatory Fe(III)- and Mn(IV)-reducing microorganism was isolated from freshwater sediments of the Potomac River, Maryland. The isolate, designated GS-15, grew in defined anaerobic medium with acetate as the sole electron donor and Fe(III), Mn(IV), or nitrate as the sole electron acceptor. GS-15 oxidized acetate to carbon dioxide with the concomitant reduction of amorphic Fe(III) oxide to magnetite (Fe3O4). When Fe(III) citrate replaced amorphic Fe(III) oxide as the electron acceptor, GS-15 grew faster and reduced all of the added Fe(III) to Fe(II). GS-15 reduced a natural amorphic Fe(III) oxide but did not significantly reduce highly crystalline Fe(III) forms. Fe(III) was reduced optimally at pH 6.7 to 7 and at 30 to 35C. Ethanol, butyrate, and propionate could also serve as electron donors for Fe(III) reduction. A variety of other organic compounds and hydrogen could not. MnO2 was completely reduced to Mn(II), which precipitated as rhodochrosite (MnCO3). Nitrate was reduced to ammonia. Oxygen could not serve as an electron acceptor, and it inhibited growth with the other electron acceptors. This is the first demonstration that microorganisms can completely oxidize organic compounds with Fe(III) or Mn(IV) as the sole electron acceptor and that oxidation of organic matter coupled to dissimilatory Fe(III) or Mn(IV) reduction can yield energy for microbial growth. GS-15 provides a model for how enzymatically catalyzed reactions can be quantitatively significant mechanisms for the reduction of iron and manganese in anaerobic environments. Images PMID:16347658

  11. Protective effect of manganese in cadmium-induced hepatic oxidative damage, changes in cadmium distribution and trace elements level in mice

    PubMed Central

    Eybl, Vladislav; Kotyzová, Dana

    2010-01-01

    Oxidative tissue damage is considered an early sign of cadmium (Cd) toxicity and has been linked with carcinogenesis. Manganese(II)-at low doses, was found to act as a potent antioxidant against oxidative stress in different in vitro systems producing lipid peroxidation conditions. The present study investigates in vivo antioxidant effects of Mn2+ pretreatment in acute Cd intoxication with regard to lipid peroxidation, antioxidant defense system and cadmium distribution in the tissues of mice. Four groups of male mice (n=7–8) were used: Cd group was injected sc a single dose of CdCl2 · 2½ H2O · (7 mg/kg b.w.); Cd+Mn group was treated ip with MnCl2 · 4H2O (20 mg/kg b.w.) 24 hours before Cd intoxication; Mn group received manganese treatment only; Control group received saline only. Twenty-four hours after Cd intoxication an increased lipid peroxidation (p<0.05), depleted GSH level (p<0.01), increased activity of GSH-Px (p<0.05) and inhibited CAT activity (p<0.01) were found in Cd-treated group compared to controls. Manganese(II) pre-treatment either completely prevented (LP, GSH, GSH-Px) or significantly attenuated (CAT) these changes. Manganese(II) treatment alone decreased LP, enhanced hepatic GSH level and had no effect on antioxidant enzymes compared to control group. A significant increase of Cd concentration in the liver and decreased Cd concentration in the kidneys and testes were found in Cd+Mn treated mice compared to Cd-only treated group. The effect of manganese may result from a different metallothionein induction in particular organs. Manganese(II) pretreatment attenuated the interference of cadmium with Ca homeostasis, the alteration in Zn and Cu levels remained mostly unaffected. PMID:21217875

  12. Degradation of lithium ion batteries employing graphite negatives and nickel-cobalt-manganese oxide + spinel manganese oxide positives: Part 1, aging mechanisms and life estimation

    NASA Astrophysics Data System (ADS)

    Wang, John; Purewal, Justin; Liu, Ping; Hicks-Garner, Jocelyn; Soukazian, Souren; Sherman, Elena; Sorenson, Adam; Vu, Luan; Tataria, Harshad; Verbrugge, Mark W.

    2014-12-01

    We examine the aging and degradation of graphite/composite metal oxide cells. Non-destructive electrochemical methods were used to monitor the capacity loss, voltage drop, resistance increase, lithium loss, and active material loss during the life testing. The cycle life results indicated that the capacity loss was strongly impacted by the rate, temperature, and depth of discharge (DOD). Lithium loss and active electrode material loss were studied by the differential voltage method; we find that lithium loss outpaces active material loss. A semi-empirical life model was established to account for both calendar-life loss and cycle-life loss. For the calendar-life equation, we adopt a square root of time relation to account for the diffusion limited capacity loss, and an Arrhenius correlation is used to capture the influence of temperature. For the cycle life, the dependence on rate is exponential while that for time (or charge throughput) is linear.

  13. Rational design of coaxial structured carbon nanotube-manganese oxide (CNT-MnO2) for energy storage application.

    PubMed

    Salunkhe, Rahul R; Ahn, Heejoon; Kim, Jung Ho; Yamauchi, Yusuke

    2015-05-22

    Recently, there has been great research interest in the development of composites (core-shell structures) of carbon nanotubes (CNTs) with metal oxides for improved electrochemical energy storage, photonics, electronics, catalysis, etc. Currently, the synthetic strategies for metal oxides/hydroxides are well established, but the development of core-shell structures by robust, cost-effective chemical methods is still a challenge. The main drawbacks for obtaining such electrodes are the very complex synthesis methods which ultimately result in high production costs. Alternatively, the solution based method offers the advantages of simple and cost effective synthesis, as well as being easy to scale up. Here, we report on the development of multi-walled carbon nanotube-manganese oxide (CNT-MnO2) core-shell structures. These samples were directly utilized for asymmetric supercapacitor (ASC) applications, where the CNT-MnO2 composite was used as the positive electrode and ZIF-8 (zeolitic imidazolate framework, ZIF) derived nanoporous carbon was used as the negative electrode. This unconventional ASC shows a high energy density of 20.44 W h kg(-1) and high power density of 16 kW kg(-1). The results demonstrate that these are efficient electrodes for supercapacitor application. PMID:25927162

  14. Anthocyanin-rich aa (Euterpe oleracea Mart.) extract attenuates manganese-induced oxidative stress in rat primary astrocyte cultures.

    PubMed

    da Silva Santos, Vivian; Bisen-Hersh, Emily; Yu, Yingchun; Cabral, Ingridy Simone Ribeiro; Nardini, Viviani; Culbreth, Megan; Teixeira da Rocha, Joo Batista; Barbosa, Fernando; Aschner, Michael

    2014-01-01

    Manganese (Mn) is an essential element for human health. However, at high concentrations Mn may be neurotoxic. Mn accumulates in astrocytes, affecting their redox status. In view of the high antioxidant and anti-inflammatory properties of the exotic Brazilian fruit aa (Euterpe oleracea Mart.), its methanolic extract was obtained by solid-phase extraction (SPE). This aa extract showed considerable anthocyanins content and direct antioxidant capacity. The aa extract scavenged 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH) with an EC?? of 19.1 ppm, showing higher antioxidant activity compared to butylated hydroxytoluene (BHT), but lower than ascorbic acid and quercetin. This obtained aa extract also attenuated Mn-induced oxidative stress in primary cultured astrocytes. Specifically, the aa extract at an optimal and nutritionally relevant concentration of 0.1 ?g/ml prevented Mn-induced oxidative stress by (1) restoring GSH/GSSG ratio and net glutamate uptake, (2) protecting astrocytic membranes from lipid peroxidation, and (3) decreasing Mn-induced expression of erythroid 2-related factor (Nrf2) protein. A larger quantity of aa extract exacerbated the effects of Mn on these parameters except with respect to lipid peroxidation assessed by means of F?-isoprostanes. These studies indicate that at nutritionally relevant concentration, anthocyanins obtained from aa protect astrocytes against Mn neurotoxicity, but at high concentrations, the "pro-oxidant" effects of its constituents likely prevail. Future studies may be profitably directed at potential protective effects of aa anthocyanins in nutraceutical formulations. PMID:24617543

  15. Acclimation of a marine microbial consortium for efficient Mn(II) oxidation and manganese containing particle production.

    PubMed

    Zhou, Hao; Pan, Haixia; Xu, Jianqiang; Xu, Weiping; Liu, Lifen

    2016-03-01

    Sediment contamination with metals is a widespread concern in the marine environment. Manganese oxidizing bacteria (MOB) are extensively distributed in various environments, but a marine microbial community containing MOB is rarely reported. In this study, a consortium of marine metal-contaminated sediments was acclimated using Mn(II). The shift in community structure was determined through high-throughput sequencing. In addition, the consortium resisted several harsh conditions, such as toxic metals (1mM Cu(II) and Fe(III)), and exhibited high Mn(II) oxidation capacities even the Mn(II) concentration was up to 5mM. Meanwhile, biogenic Mn containing particles were characterized by scanning electron microscope (SEM), X-ray powder diffraction (XRD), and N2 adsorption/desorption. Dye removal performance of the Mn containing particles was assayed using methylene blue, and 20.8mgg(-1) adsorption capacity was obtained. Overall, this study revealed several new genera associated with Mn(II) oxidation and rare biogenic Na3MnPO4CO3. Results suggested the complexity of natural microbe-mediated Mn transformation. PMID:26606462

  16. Tunable T1 and T2 contrast abilities of manganese-engineered iron oxide nanoparticles through size control.

    PubMed

    Huang, Guoming; Li, Hui; Chen, Jiahe; Zhao, Zhenghuan; Yang, Lijiao; Chi, Xiaoqin; Chen, Zhong; Wang, Xiaomin; Gao, Jinhao

    2014-09-01

    In this paper, we demonstrate the tunable T1 and T2 contrast abilities of engineered iron oxide nanoparticles with high performance for liver contrast-enhanced magnetic resonance imaging (MRI) in mice. To enhance the diagnostic accuracy of MRI, large numbers of contrast agents with T1 or T2 contrast ability have been widely explored. The comprehensive investigation of high-performance MRI contrast agents with controllable T1 and T2 contrast abilities is of high importance in the field of molecular imaging. In this study, we synthesized uniform manganese-doped iron oxide (MnIO) nanoparticles with controllable size from 5 to 12 nm and comprehensively investigated their MRI contrast abilities. We revealed that the MRI contrast effects of MnIO nanoparticles are highly size-dependent. By controlling the size of MnIO nanoparticles, we can achieve T1-dominated, T2-dominated, and T1-T2 dual-mode MRI contrast agents with much higher contrast enhancement than the corresponding conventional iron oxide nanoparticles. PMID:25079966

  17. One-step through-mask electrodeposition of a porous structure composed of manganese oxide nanosheets with electrocatalytic activity for oxygen reduction

    SciTech Connect

    Fukuda, Masaki; Iida, Chihiro; Nakayama, Masaharu

    2009-06-03

    Potentiostatic electrolysis of a mixed aqueous solution of Bu{sub 4}NBr and MnSO{sub 4} at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br{sup -} and Mn{sup 2+} ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu{sub 4}N{sup +} and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO{sub x}-modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode.

  18. Degradation of aqueous and soil-sorbed estradiol using a new class of stabilized manganese oxide nanoparticles.

    PubMed

    Han, Bing; Zhang, Man; Zhao, Dongye; Feng, Yucheng

    2015-03-01

    Manganese oxide (MnO?) was reported to be effective for degrading aqueous pharmaceutical chemicals. However, little is known about its potential use for degrading soil-sorbed contaminants. To bridge this knowledge gap, we synthesized, for the first time, a class of stabilized MnO? nanoparticles using carboxymethyl celluloses (CMC) as a stabilizer, and tested their effectiveness for degrading aqueous and soil-sorbed estradiol. The most desired particles (highest reactivity and soil deliverability) were obtained at a CMC/MnO? molar ratio of 1.39 10(-3), which yielded a mean hydrodynamic size of 39.5 nm and a narrow size distribution (SD = 0.8 nm). While non-stabilized MnO? particles rapidly aggregated and were not transportable through a soil column, CMC-stabilized nanoparticles remained fully dispersed in water and were soil deliverable. At typical aquatic pH (6-7), CMC-stabilized MnO? exhibited faster degradation kinetics for oxidation of 17?-estradiol than non-stabilized MnO?. The reactivity advantage becomes more evident when used for treating soil-sorbed estradiol owing to the ability of CMC to complex with metal ions and prevent the reactive sites from binding with inhibitive soil components. A retarded first-order rate model was able to interpret the oxidation kinetics for CMC-stabilized MnO?. When used for degrading soil-sorbed estradiol, several factors may inhibit the oxidation effectiveness, including desorption rate, soil-MnO? interactions, and soil-released metals and reductants. CMC-stabilized MnO? nanoparticles hold the potential for facilitating in situ oxidative degradation of various emerging contaminants in soil and groundwater. PMID:25543239

  19. Melatonin inhibits manganese-induced motor dysfunction and neuronal loss in mice: involvement of oxidative stress and dopaminergic neurodegeneration.

    PubMed

    Deng, Yu; Jiao, Congcong; Mi, Chao; Xu, Bin; Li, Yuehui; Wang, Fei; Liu, Wei; Xu, Zhaofa

    2015-02-01

    Excessive manganese (Mn) induces oxidative stress and dopaminergic neurodegeneration. However, the relationship between them during Mn neurotoxicity has not been clarified. The purpose of this study was to investigate the probable role of melatonin (MLT) against Mn-induced motor dysfunction and neuronal loss as a result of antagonizing oxidative stress and dopaminergic neurodegeneration. Mice were randomly divided into five groups as follows: control, MnCl2, low MLT?+?MnCl2, median MLT?+?MnCl2, and high MLT?+?MnCl2. Administration of MnCl2 (50 mg/kg) for 2 weeks significantly induced hypokinesis, dopaminergic neurons degeneration and loss, neuronal ultrastructural damage, and apoptosis in the substantia nigra and the striatum. These conditions were caused in part by the overproduction of reactive oxygen species, malondialdehyde accumulation, and dysfunction of the nonenzymatic (GSH) and enzymatic (GSH-Px, superoxide dismutase, quinone oxidoreductase 1, glutathione S-transferase, and glutathione reductase) antioxidative defense systems. Mn-induced neuron degeneration, astrocytes, and microglia activation contribute to the changes of oxidative stress markers. Dopamine (DA) depletion and downregulation of DA transporter and receptors were also found after Mn administration, this might also trigger motor dysfunction and neurons loss. Pretreatment with MLT prevented Mn-induced oxidative stress and dopaminergic neurodegeneration and inhibited the interaction between them. As a result, pretreatment with MLT significantly alleviated Mn-induced motor dysfunction and neuronal loss. In conclusion, Mn treatment resulted in motor dysfunction and neuronal loss, possibly involving an interaction between oxidative stress and dopaminergic neurodegeneration in the substantia nigra and the striatum. Pretreatment with MLT attenuated Mn-induced neurotoxicity by means of its antioxidant properties and promotion of the DA system. PMID:24969583

  20. Daily Manganese Intake Status and Its Relationship with Oxidative Stress Biomarkers under Different Body Mass Index Categories in Korean Adults

    PubMed Central

    Bu, So-Young

    2012-01-01

    Manganese (Mn) is an essential micronutrient for human and plays an important role as a cofactor for several enzymes involving fatty acid synthesis, hepatic gluconeogenesis, and oxidative stresses. Also, Mn intake status has been reported to have beneficial effects in reversing metabolic dysfunction including obesity and nonalcoholic steatosis which is linked to mitochondrial dysfunction and oxidative stresses, however, information on dietary Mn intake in Koreans are limited. Hence we investigated the relationship between dietary Mn intake and antioxidant defense factors in healthy and obese subjects. Total of 333 healthy subjects were recruited in the study and were assigned to one of three study groups: a normal group (18.5-22.9), a overweight group (23-24.9), and a obesity group (>25) according to their body mass index (BMI). We assessed Mn intakes (24-hr recall method) and several indicators for antioxidative defenses such as glutathione (GSH), glutathione peroxidase (GPx) and urinary malonaldehyde (MDA). Results showed that body weight and blood pressure of study subjects were increased in dependent of their BMI (p < 0.01). However dietary Mn intakes and oxidative stress biomarkers (GSH, GPx, and MDA) were not significantly different by groups defined by BMI. In correlation analysis adjusting for age, sex and energy intake, dietary Mn intake of the subjects in different BMI categories were not significantly correlated with GSH, GPx, MDA and showed a weak or no association with these oxidative stress markers. In conclusion dietary Mn intake at least in this study has a little or no influence on markers of oxidative status in both healthy and obese subjects. PMID:23431039

  1. Multifunctional nanosheets based on folic acid modified manganese oxide for tumor-targeting theranostic application

    NASA Astrophysics Data System (ADS)

    Hao, Yongwei; Wang, Lei; Zhang, Bingxiang; Zhao, Hongjuan; Niu, Mengya; Hu, Yujie; Zheng, Cuixia; Zhang, Hongling; Chang, Junbiao; Zhang, Zhenzhong; Zhang, Yun

    2016-01-01

    It is highly desirable to develop smart nanocarriers with stimuli-responsive drug-releasing and diagnostic-imaging functions for cancer theranostics. Herein, we develop a reduction and pH dual-responsive tumor theranostic platform based on degradable manganese dioxide (MnO2) nanosheets. The MnO2 nanosheets with a size of 20–60 nm were first synthesized and modified with (3-Aminopropyl) trimethoxysilane (APTMS) to get amine-functionalized MnO2, and then functionalized by NH2-PEG2000-COOH (PEG). The tumor-targeting group, folic acid (FA), was finally conjugated with the PEGylated MnO2 nanosheets. Then, doxorubicin (DOX), a chemotherapeutic agent, was loaded onto the modified nanosheets through a physical adsorption, which was designated as MnO2-PEG-FA/DOX. The prepared MnO2-PEG-FA/DOX nanosheets with good biocompatibility can not only efficiently deliver DOX to tumor cells in vitro and in vivo, leading to enhanced anti-tumor efficiency, but can also respond to a slightly acidic environment and high concentration of reduced glutathione (GSH), which caused degradation of MnO2 into manganese ions enabling magnetic resonance imaging (MRI). The longitudinal relaxation rate r 1 was 2.26 mM‑1 s‑1 at pH 5.0 containing 2 mM GSH. These reduction and pH dual-responsive biodegradable nanosheets combining efficient MRI and chemotherapy provide a novel and promising platform for tumor-targeting theranostic application.

  2. Nanolayered manganese oxide/C(60) composite: a good water-oxidizing catalyst for artificial photosynthetic systems.

    PubMed

    Najafpour, Mohammad Mahdi; Abasi, Mahnaz; Tomo, Tatsuya; Allakhverdiev, Suleyman I

    2014-08-21

    For the first time, we considered Mn oxide/C60 composites as water-oxidizing catalysts. The composites were synthesized by easy and simple procedures, and characterized by some methods. The water-oxidizing activities of these composites were also measured in the presence of cerium(iv) ammonium nitrate. We found that the nanolayered Mn oxide/C60 composites show promising activity toward water oxidation. PMID:24984108

  3. Manganese oxide-based multifunctionalized mesoporous silica nanoparticles for pH-responsive MRI, ultrasonography and circumvention of MDR in cancer cells.

    PubMed

    Chen, Yu; Yin, Qi; Ji, Xiufeng; Zhang, Shengjian; Chen, Hangrong; Zheng, Yuanyi; Sun, Yang; Qu, Haiyun; Wang, Zheng; Li, Yaping; Wang, Xia; Zhang, Kun; Zhang, Linlin; Shi, Jianlin

    2012-10-01

    Nano-biotechnology has been introduced into cancer theranostics by engineering a new generation of highly versatile hybrid mesoporous composite nanocapsules (HMCNs) for manganese-based pH-responsive dynamic T(1)-weighted magnetic resonance imaging (MRI) to efficiently respond and detect the tumor acidic microenvironment, which was further integrated with ultrasonographic function based on the intrinsic unique hollow nanostructures of HMCNs for potentially in vitro and in vivo dual-modality cancer imaging. The manganese oxide-based multifunctionalization of hollow mesoporous silica nanoparticles was achieved by an in situ redox reaction using mesopores as the nanoreactors. Due to the dissolution nature of manganese oxide nanoparticles under weak acidic conditions, the relaxation rate r(1) of manganese-based mesoporous MRI-T(1) contrast agents (CAs) could reach 8.81 mM(-1)s(-1), which is a 11-fold magnitude increase compared to the neutral condition, and is almost two times higher than commercial Gd(III)-based complex agents. This is also the highest r(1) value ever reported for manganese oxide nanoparticles-based MRI-T(1) CAs. In addition, the hollow interiors and thin mesoporous silica shells endow HMCNs with the functions of CAs for efficient in vitro and in vivo ultrasonography under both harmonic- and B-modes. Importantly, the well-defined mesopores and large hollow interiors of HMCNs could encapsulate and deliver anticancer agents (doxorubicin) intracellularly to circumvent the multidrug resistance (MDR) of cancer cells and restore the anti-proliferative effect of drugs by nanoparticle-mediated endocytosis process, intracellular drug release and P-gp inhibition/ATP depletion in cancer cells. PMID:22789722

  4. One-pot synthesis of ultrathin manganese dioxide nanosheets and their efficient oxidative degradation of Rhodamine B

    NASA Astrophysics Data System (ADS)

    Sun, Hang; Xu, Kongliang; Huang, Majia; Shang, Yinxing; She, Ping; Yin, Shengyan; Liu, Zhenning

    2015-12-01

    Ultrathin manganese dioxide (MnO2) nanosheets have been synthesized in aqueous solution by a facile one-step method. MnO2 nanosheets show a typical 2D lamellar morphology, possessing an average lateral dimension of 100-300 nm, and a typical thickness of 3.1-7.5 nm, corresponding to 4-10 layers of δ-MnO2. The resultant MnO2 nanosheets have been demonstrated to possess superior oxidative degradation ability to Rhodamine B (RhB) by investigating the decomposition rate and comparing the results with the commercial MnO2 powder. Typically, ultrathin MnO2 nanosheets have shown a high oxidation degradation performance of RhB solution (97.9% removed within 30 min) in acid solution (pH 2.0), which can be attributed to special lamellar morphology and the large surface area of the layered MnO2 nanosheets. It is believed that such a convenient approach for the cost-effective and environmentally friendly synthesis of ultrathin MnO2 nanosheets holds great promise for the degradation of complex and various dye wastewater in practical application.

  5. Synthesis of magnetic core/shell carbon nanosphere supported manganese catalysts for oxidation of organics in water by peroxymonosulfate.

    PubMed

    Wang, Yuxian; Sun, Hongqi; Ang, Ha Ming; Tad, Moses O; Wang, Shaobin

    2014-11-01

    Magnetic separation is more cost-effective than conventional separation processes in heterogeneous catalysis, especially for ultrafine nanoparticles. Magnetic core/shell nanospheres (MCS, Fe3O4/carbon) were synthesized by a hydrothermal method and their supported manganese oxide nanoparticles (Mn/MCS) were obtained by redox reactions between MCS and potassium permanganate at a low temperature. The materials were analyzed by a variety of characterization techniques such as powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N2 adsorption/desorption. The Mn/MCS catalysts were able to effectively activate Oxone for phenol degradation in aqueous solutions. Nitrogen treated MCS supported Mn achieved 100% conversion within 120min. Kinetic studies showed that phenol degradation over supported Mn catalysts follows the first order kinetics. It was also found that the catalysts can be easily separated from the aqueous solutions by an external magnetic field. The Oxone activation mechanism by Mn/MCS catalysts was discussed and sulfate radicals were suggested to be the primary reactive species generated from peroxymonosulfate (PMS) for phenol catalytic oxidation. PMID:25112914

  6. Preparation of graphene oxide-manganese dioxide for highly efficient adsorption and separation of Th(IV)/U(VI).

    PubMed

    Pan, Ning; Li, Long; Ding, Jie; Li, Shengke; Wang, Ruibing; Jin, Yongdong; Wang, Xiangke; Xia, Chuanqin

    2016-05-15

    Manganese dioxide decorated graphene oxide (GOM) was prepared via fixation of crystallographic MnO2 (α, γ) on the surface of graphene oxide (GO) and was explored as an adsorbent material for simultaneous removal of thorium/uranium ions from aqueous solutions. In single component systems (Th(IV) or U(VI)), the α-GOM2 (the weight ratio of GO/α-MnO2 of 2) exhibited higher maximum adsorption capacities toward both Th(IV) (497.5mg/g) and U(VI) (185.2mg/g) than those of GO. In the binary component system (Th(IV)/U(VI)), the saturated adsorption capacity of Th(IV) (408.8mg/g)/U(VI) (66.8mg/g) on α-GOM2 was also higher than those on GO. Based on the analysis of various data, it was proposed that the adsorption process may involve four types of molecular interactions including coordination, electrostatic interaction, cation-pi interaction, and Lewis acid-base interaction between Th(IV)/U(VI) and α-GOM2. Finally, the Th(IV)/U(VI) ions on α-GOM2 can be separated by a two-stage desorption process with Na2CO3/EDTA. Those results displayed that the α-GOM2 may be utilized as an potential adsorbent for removing and separating Th(IV)/U(VI) ions from aqueous solutions. PMID:26878706

  7. Preparation of highly active manganese oxides supported on functionalized MWNTs for low temperature NOx reduction with NH3

    NASA Astrophysics Data System (ADS)

    Pourkhalil, Mahnaz; Moghaddam, Abdolsamad Zarringhalam; Rashidi, Alimorad; Towfighi, Jafar; Mortazavi, Yadollah

    2013-08-01

    Manganese oxide catalysts (MnOx) supported on functionalized multi-walled carbon nanotubes (FMWNTs) for low temperature selective catalytic reduction (LTSCR) of nitrogen oxides (NOx) with NH3 in the presence of excess O2 were prepared by the incipient wetness impregnation method. These catalysts were characterized by N2 adsorption, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and H2-temperature programmed reduction (H2-TPR) methods. The effects of reaction temperature, MnOx loading, calcination temperature and calcination time were investigated. The presence of surface nitrate species under moderate calcination conditions may play a favorable role in the LTSCR of NOx with NH3. Under the reaction conditions of 200 C, 1 bar, NO = NH3 = 900 ppm, O2 = 5 vol%, GHSV = 30,000 h-1 and 12 wt% MnOx, NOx conversion and N2 selectivity were 97% and 99.5%, respectively. The SCR activity was reduced in the presence of 100 ppm SO2 and 2.5 vol% H2O from 97% to 92% within 6 h at 200 C, however such an effect was shown to be reversible by exposing the catalyst to a helium flow for 2 h at 350 C due to thermal decomposition of ammonium sulphate salts.

  8. Characterization of a mitochondrial manganese superoxide dismutase gene from Apis cerana cerana and its role in oxidative stress.

    PubMed

    Jia, Haihong; Sun, Rujiang; Shi, Weina; Yan, Yan; Li, Han; Guo, Xingqi; Xu, Baohua

    2014-01-01

    Mitochondrial manganese superoxide dismutase (mMnSOD) plays a vital role in the defense against reactive oxygen species (ROS) in eukaryotic mitochondria. In this study, we isolated and identified a mMnSOD gene from Apis cerana cerana, which we named AccSOD2. Several putative transcription factor-binding sites were identified within the 5'-flanking region of AccSOD2, which suggests that AccSOD2 may be involved in organismal development and/or environmental stress responses. Quantitative real-time PCR analysis showed that AccSOD2 is highly expressed in larva and pupae during different developmental stages. In addition, the expression of AccSOD2 could be induced by cold (4 °C), heat (42 °C), H2O2, ultraviolet light (UV), HgCl2, and pesticide treatment. Using a disc diffusion assay, we provide evidence that recombinant AccSOD2 protein can play a functional role in protecting cells from oxidative stress. Finally, the in vivo activities of AccSOD2 were measured under a variety of stressful conditions. Taken together, our results indicate that AccSOD2 plays an important role in cellular stress responses and anti-oxidative processes and that it may be of critical importance to honeybee survival. PMID:24269344

  9. Effects of Cobalt on Manganese Oxidation by Pseudomonas putida MnB1

    NASA Astrophysics Data System (ADS)

    Pena, J.; Bargar, J.; Sposito, G.

    2005-12-01

    The oxidation of Mn(II) in the environment is thought to occur predominantly through biologically mediated pathways. During the stationary phase of growth, the well-characterized freshwater and soil bacterium Pseudomonas putida MnB1 oxidizes soluble Mn(II) to a poorly crystalline layer type Mn(IV) oxide. These Mn oxide particles (2 - 5 nm thickness) are deposited in a matrix of extracellular polymeric substances (EPS) surrounding the cell, creating a multi-component system distinct from commonly studied synthetic Mn oxides. Accurate characterization of the reactivity of these biomineral assemblages is essential to understanding trace metal biogeochemistry in natural waters and sediments. Moreover, these biogenic oxides may potentially be used for the remediation of surface and ground waters impacted by mining, industrial pollution, and other anthropogenic activities. In this study, we consider the interactions between Co, P. putida MnB1, and its biogenic Mn oxide. Cobalt is a redox-active transition metal which exists in the environment as Co(II) and Co(III). While Co is not generally found in the environment at toxic concentrations, it may be released as a byproduct of mining activities (e.g. levels of up to 20 μM are found in Pinal Creek, AZ, a stream affected by copper mining). In addition, the radionuclide 60Co, formed by neutron activation in nuclear reactors, is of concern at Department of Energy sites, such as that at Hanford, and has several industrial applications, including radiotherapy. We address the following questions: Do high levels of Co inhibit enzymatic processes such as Mn(II) oxidation? Can the multicopper oxidase enzyme involved in Mn(II) oxidation facilitate Co(II) oxidation? Lastly, does the organic matter surrounding the oxides affect Co or Mn oxide reactivity? These issues were approached via wet chemical analysis, synchrotron radiation X-ray diffraction (SR-XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy. In the presence of both Mn (1 mM) and Co (10-40 μM), Mn oxidation proceeded as it does in the absence of Co; SR-XRD data did not indicate the formation of a separate Co oxide phase, and EXAFS data showed that Co is incorporated into the biooxide structure as Co(III). In the absence of Mn, Co oxide formation was not observed; EXAFS data showed that Co remains as Co(II) and is complexed to cells or EPS. While it cannot be ascertained that Co(II) oxidation and incorporation into the bioxides is completely abiotic, Co(II) is not oxidized by P. putida MnB1 in the absence of Mn.

  10. Interleukin-6 counteracts therapy-induced cellular oxidative stress in multiple myeloma by up-regulating manganese superoxide dismutase.

    PubMed

    Brown, Charles O; Salem, Kelley; Wagner, Brett A; Bera, Soumen; Singh, Neeraj; Tiwari, Ajit; Choudhury, Amit; Buettner, Garry R; Goel, Apollina

    2012-06-15

    IL (interleukin)-6, an established growth factor for multiple myeloma cells, induces myeloma therapy resistance, but the resistance mechanisms remain unclear. The present study determines the role of IL-6 in re-establishing intracellular redox homoeostasis in the context of myeloma therapy. IL-6 treatment increased myeloma cell resistance to agents that induce oxidative stress, including IR (ionizing radiation) and Dex (dexamethasone). Relative to IR alone, myeloma cells treated with IL-6 plus IR demonstrated reduced annexin/propidium iodide staining, caspase 3 activation, PARP [poly(ADP-ribose) polymerase] cleavage and mitochondrial membrane depolarization with increased clonogenic survival. IL-6 combined with IR or Dex increased early intracellular pro-oxidant levels that were causally related to activation of NF-?B (nuclear factor ?B) as determined by the ability of N-acetylcysteine to suppress both pro-oxidant levels and NF-?B activation. In myeloma cells, upon combination with hydrogen peroxide treatment, relative to TNF (tumour necrosis factor)-?, IL-6 induced an early perturbation in reduced glutathione level and increased NF-?B-dependent MnSOD (manganese superoxide dismutase) expression. Furthermore, knockdown of MnSOD suppressed the IL-6-induced myeloma cell resistance to radiation. MitoSOX Red staining showed that IL-6 treatment attenuated late mitochondrial oxidant production in irradiated myeloma cells. The present study provides evidence that increases in MnSOD expression mediate IL-6-induced resistance to Dex and radiation in myeloma cells. The results of the present study indicate that inhibition of antioxidant pathways could enhance myeloma cell responses to radiotherapy and/or chemotherapy. PMID:22471522

  11. Low power loss and field-insensitive permeability of Fe-6.5%Si powder cores with manganese oxide-coated particles

    SciTech Connect

    Li, Junnan E-mail: rzhgong@hust.edu.cn; Wang, Xian; Xu, Xiaojun; Gong, Rongzhou E-mail: rzhgong@hust.edu.cn; Feng, Zekun; Chen, Yajie; Harris, V. G.

    2015-05-07

    Fe-6.5%Si alloy powders coated with manganese oxides using an innovative in situ process were investigated. The in-situ coating of the insulating oxides was realized with a KMnO{sub 4} solution by a chemical process. The insulating manganese oxides with mixed valance state were verified by X-ray photoelectron spectroscopy analysis. The thickness of the insulating layer on alloy particles was determined to be in a range of 20–210 nm, depending upon the KMnO{sub 4} concentration. The powder core loss and the change in permeability under a DC-bias field were measured at frequencies ranging from 50 to 100 kHz. The experiments indicated that the Fe-6.5%Si powder cores with a 210 nm-thick manganese oxide layer not only showed a low core loss of 459 mW/cm{sup 3} at 100 kHz but also showed a small reduction in permeability (μ(H)/μ(0) = 85% for μ = 42) at a DC-bias field of 80 Oe. This work has defined a novel pathway to realizing low core loss and field-insensitive permeability for Fe-Si powder cores.

  12. Oxidation Of Manganese At Kimberley, Gale Crater: More Free Oxygen In Mars' Past?

    NASA Technical Reports Server (NTRS)

    Lanza, N. L.; Wiens, R. C.; Arvidson, R. E.; Clark, B. C.; Fischer, W. W.; Gellert, R.; Grotzinger, J. P.; Hurowitz, J. A.; McLennan, S. M.; Morris, R. V.; Rice, M. S.; Bell, J. F., III; Berger, J. A.; Blaney, D. L.; Bridges, N. T.; Calef, F., III; Campbell, J. L.; Clegg, S. M.; Cousin, A.; Edgett, K. S.; Fabre, C.; Fisk, M. R.; Forni, O.; Frydenvang, J.; Ming, D. W.

    2015-01-01

    High Mn concentrations provide unique indicators of water-rich environments and their redox state. Very high-potential oxidants are required to oxidize Mn to insoluble, high-valence oxides that can precipitate and concentrate Mn in rocks and sediments; these redox potentials are much higher than those needed to oxidize Fe or S. Consequently, Mn-rich rocks on Earth closely track the rise of atmospheric oxygen. Given the association between Mn-rich rocks and the redox state of surface environments, observations of anomalous Mn enrichments on Mars raise similar questions about redox history, solubility and aqueous transport, and availability as a metabolic substrate. Our observations suggest that at least some of the high Mn present in Gale crater occurs in the form of Mn-oxides filling veins that crosscut sand-stones, requiring post-depositional precipitation as highly oxidizing fluids moved through the fractured strata after their deposition and lithification.

  13. One-step sonochemical synthesis of a graphene oxide-manganese oxide nanocomposite for catalytic glycolysis of poly(ethylene terephthalate)

    NASA Astrophysics Data System (ADS)

    Park, Gle; Bartolome, Leian; Lee, Kyoung G.; Lee, Seok Jae; Kim, Do Hyun; Park, Tae Jung

    2012-06-01

    Ultrasound-assisted synthesis of a graphene oxide (GO)-manganese oxide nanocomposite (GO-Mn3O4) was conducted without further modification of GO or employing secondary materials. With the GO nanoplate as a support, potassium permanganate oxidizes the carbon atoms in the GO support and gets reduced to Mn3O4. An intensive ultrasound method could reduce the number of reaction steps and temperature, enhance the reaction rate and furthermore achieve a Mn3O4 phase. The composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The coverage and crystallinity of Mn3O4 were controlled by changing the ratio of permanganate to GO dispersion. The synthesized nanocomposite was used as a catalyst for poly(ethylene terephthalate) (PET) depolymerization into its monomer, bis(2-hydroxylethyl) terephthalate (BHET). The highest monomer yield of 96.4% was obtained with the nanocomposite containing the lowest amount of Mn3O4, while PET glycolysis with the Mn3O4 without GO yielded 82.7% BHET.Ultrasound-assisted synthesis of a graphene oxide (GO)-manganese oxide nanocomposite (GO-Mn3O4) was conducted without further modification of GO or employing secondary materials. With the GO nanoplate as a support, potassium permanganate oxidizes the carbon atoms in the GO support and gets reduced to Mn3O4. An intensive ultrasound method could reduce the number of reaction steps and temperature, enhance the reaction rate and furthermore achieve a Mn3O4 phase. The composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The coverage and crystallinity of Mn3O4 were controlled by changing the ratio of permanganate to GO dispersion. The synthesized nanocomposite was used as a catalyst for poly(ethylene terephthalate) (PET) depolymerization into its monomer, bis(2-hydroxylethyl) terephthalate (BHET). The highest monomer yield of 96.4% was obtained with the nanocomposite containing the lowest amount of Mn3O4, while PET glycolysis with the Mn3O4 without GO yielded 82.7% BHET. Electronic supplementary information (ESI) available: XPS spectra of GO-Mn3O4 A and B, EDS mapping images of GO-Mn3O4 C, AFM analysis and TEM image of Mn3O4. See DOI: 10.1039/c2nr30168g

  14. In-situ X-Ray Absorption Spectroscopy (XAS) Investigation of a Bifunctional Manganese Oxide Catalyst with High Activity for Electrochemical Water Oxidation and Oxygen Reduction

    PubMed Central

    Benck, Jesse D.; Gul, Sheraz; Webb, Samuel M.; Yachandra, Vittal K.; Yano, Junko; Jaramillo, Thomas F.

    2013-01-01

    In-situ x-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in-situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs. RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs. RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS and electrochemical characterization of two thin film catalysts with different MnOx thicknesses reveals no significant influence of thickness on the measured oxidation states, at either ORR or OER potentials, but demonstrates that the OER activity scales with film thickness. This result suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film. As the portion of the catalyst film that is most likely to be oxidized at the high potentials necessary for the OER is that which is closest to the electrolyte interface, we hypothesize that the MnIII,IV oxide, rather than Mn3II,III,IIIO4, is the phase pertinent to the observed OER activity. PMID:23758050

  15. PerR-Regulated Manganese Ion Uptake Contributes to Oxidative Stress Defense in an Oral Streptococcus

    PubMed Central

    Wang, Xinhui; Dong, Xiuzhu

    2014-01-01

    Metal homeostasis plays a critical role in antioxidative stress. Streptococcus oligofermentans, an oral commensal facultative anaerobe lacking catalase activity, produces and tolerates abundant H2O2, whereas Dpr (an Fe2+-chelating protein)-dependent H2O2 protection does not confer such high tolerance. Here, we report that inactivation of perR, a peroxide-responsive repressor that regulates zinc and iron homeostasis in Gram-positive bacteria, increased the survival of H2O2-pulsed S. oligofermentans 32-fold and elevated cellular manganese 4.5-fold. perR complementation recovered the wild-type phenotype. When grown in 0.1 to 0.25 mM MnCl2, S. oligofermentans increased survival after H2O2 stress 2.5- to 23-fold, and even greater survival was found for the perR mutant, indicating that PerR is involved in Mn2+-mediated H2O2 resistance in S. oligofermentans. Mutation of mntA could not be obtained in brain heart infusion (BHI) broth (containing ∼0.4 μM Mn2+) unless it was supplemented with ≥2.5 μM MnCl2 and caused 82 to 95% reduction of the cellular Mn2+ level, while mntABC overexpression increased cellular Mn2+ 2.1- to 4.5-fold. Thus, MntABC was identified as a high-affinity Mn2+ transporter in S. oligofermentans. mntA mutation reduced the survival of H2O2-pulsed S. oligofermentans 5.7-fold, while mntABC overexpression enhanced H2O2-challenged survival 12-fold, indicating that MntABC-mediated Mn2+ uptake is pivotal to antioxidative stress in S. oligofermentans. perR mutation or H2O2 pulsing upregulated mntABC, while H2O2-induced upregulation diminished in the perR mutant. This suggests that perR represses mntABC expression but H2O2 can release the suppression. In conclusion, this work demonstrates that PerR regulates manganese homeostasis in S. oligofermentans, which is critical to H2O2 stress defenses and may be distributed across all oral streptococci lacking catalase. PMID:24487543

  16. Determining the Role of Multicopper Oxidases in Manganese(II) Oxidation by Marine Bacillus Spores

    NASA Astrophysics Data System (ADS)

    Dick, G. J.; Tebo, B. M.

    2005-12-01

    Bacteria play an important role in the environmental cycling of Mn by oxidizing soluble Mn(II) and forming insoluble Mn(III/IV) oxides. These biogenic Mn oxides are renowned for their strong sorptive and oxidative properties, which control the speciation and availability of many metals and organic compounds. A wide variety of bacteria are known to catalyze the oxidation of Mn(II); one of the most frequently isolated types are Bacillus species that oxidize Mn(II) only as metabolically dormant spores. We are using genetic and biochemical methods to study the molecular mechanisms of this process in these organisms. mnxG, a gene related to the multicopper oxidase (MCO) family of enzymes, is required for Mn(II) oxidation in the model organism, Bacillus sp. strain SG-1. Mn(II)-oxidizing activity can be detected in crude protein extracts of the exosporium and as a discrete band in SDS-PAGE gels, however previous attempts to purify or identify this Mn(II)-oxidizing enzyme have failed. A direct link between the Mn(II)-oxidizing enzyme and the MCO gene suspected to encode it has never been made. We used genetic and biochemical methods to investigate the role of the MCO in the mechanism of Mn(II) oxidation. Comparative analysis of the mnx operon from several diverse Mn(II)-oxidizing Bacillus spores revealed that mnxG is the most highly conserved gene in the operon, and that copper binding sites are highly conserved. As with Mn(II) oxidases from other organisms, heterologous expression of the Bacillus mnxG in E. coli did not yield an active Mn(II) oxidase. Purifying sufficient quantities of the native Mn(II) oxidase from Bacillus species for biochemical characterization has proven difficult because the enzyme does not appear to be abundant, and it is highly insoluble. We were able to partially purify the Mn(II) oxidase, and to analyze the active band by in-gel trypsin digestion followed by tandem mass spectrometry (MS/MS). MS/MS spectra provided a conclusive match to mnxG, suggesting that this MCO directly catalyzes the oxidation of Mn(II) and the precipitation of Mn(IV) oxide, which represents a novel reaction for a MCO. MS/MS analysis of bands identified by in-gel activity assays is a powerful method of identifying novel enzymes responsible for geochemical processes.

  17. Kinetics and mechanism of benzene oxidation by peroxymonosulfate catalyzed with a binuclear manganese(IV) complex in the presence of oxalic acid

    NASA Astrophysics Data System (ADS)

    Shul'pina, L. S.; Kozlov, Yu. N.; Strelkova, T. V.; Shul'pin, G. B.

    2013-03-01

    It is established that Oxone (peroxymonosulfate, 2KHSO5 KHSO4 K2SO4) oxidizes benzene to p-quinone very efficiently and selectively in a homogeneous solution in aqueous acetonitrile in the presence of a catalyst, i.e., dimeric manganese(IV) complex [LMn(O)3MnL](PF6)2 where L is 1,4,7-trimethyl-1,4,7-triazacyclononane, and a cocatalyst, i.e., oxalic acid. The dependences of the maximum rate of quinone accumulation on the initial concentrations of reagents are studied. It is proposed that benzene is oxidized by the manganyl particle containing the Mn(V)=O fragment that forms upon the reaction of the reduced form of the starting dimeric manganese complex with Oxone.

  18. Design and analysis of triangle phase diagram for preparation of new lithium manganese oxide solid solutions with stable layered crystal structure

    NASA Astrophysics Data System (ADS)

    Park, Ki Soo; Cho, Myung Hun; Jin, Sung Jang; Song, Chi Hoon; Nahm, Kee Suk

    A new phase diagram of AB(CD) 1/2 system, where A, B, C, and D represent Li 2MnO 3, LiMO 2 (M = Co, Al, Cr, etc.), LiMnO 2, and LiM'O 2 (M' = Ni, Cu, Fe, etc.), respectively, was developed to express all compositions of solid solutions with layered manganese oxides. The phase diagram satisfied the theoretical manganese oxidation state of +4 over the whole triangle plane of the diagram and was expressed with a new design equation of Li[M(Mn)y(Mn)1-x-y]O. Solid solutions whose compositions were randomly chosen from the phase diagram were experimentally prepared using a direct synthetic method and were subjected to the examination of the structural and electrochemical properties. All the synthesized solid solutions had layered structure with maintaining +4 and showed one-step monotonous discharge curve shape without structural transformation during charge/discharge processes.

  19. An anionic N-donor ligand promotes manganese-catalyzed water oxidation

    PubMed Central

    Young, Karin J.; Takase, Michael K.; Brudvig, Gary W.

    2014-01-01

    Four manganese complexes of pentadentate ligands have been studied for their ability to act as oxygen-evolution catalysts in the presence of Oxone or hydrogen peroxide. The complexes [Mn(PaPy3)(NO3)](ClO4), 1 (PaPy3H = N,N-bis(2-pyridylmethyl)-amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy3)(?-O)(PaPy3)Mn](ClO4)2, 2 feature an anionic carboxamido ligand trans to the labile sixth coordination site, while [Mn(N4Py)OTf](OTf), 3 (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and [Mn(PY5)(OH2)](ClO4)2, 4 (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)-pyridine) have neutral ligands of varying flexibility. 1 and 2 are shown to evolve oxygen in the presence of either Oxone or hydrogen peroxide, but 3 evolves oxygen only in the presence of hydrogen peroxide and 4 is inactive. The activity of 1 and 2 with Oxone suggests that the presence of an anionic N-donor ligand plays a role in stabilizing putative high-valent intermediates. Anionic N-donor ligands may be viewed as an alternative to ?-oxo ligands that are prone to protonation in low-valent Mn species formed during a catalytic cycle, resulting in loss of catalyst structure. PMID:23777320

  20. Cation distribution, structure and magnetic properties of lithium manganese iron oxide spinel solid solutions

    SciTech Connect

    Wende, C.; Olimov, Kh.; Modrow, H.; Wagner, F.E.; Langbein, H. . E-mail: Hubert.Langbein@chemie.tu-dresden.de

    2006-08-10

    Single phase cubic spinel compounds Li {sub x}Mn{sub 1+x}Fe{sub 2-2x}O{sub 4} (x = 0, ..., 1) were obtained by thermal decomposition of freeze-dried formate solutions of appropriate composition. The samples were characterized by X-ray powder diffraction and Rietveld refinement, XANES, {sup 57}Fe Moessbauer spectroscopy and magnetization measurements. The combination of these methods provides useful conclusions concerning the structure, cation distribution and properties of the spinel solid solutions. The Li {sub x}Mn{sub 1+x}Fe{sub 2-2x}O{sub 4} samples contain Mn(II) and Mn(III) or Mn(III) and Mn(IV) for x < 0.5 or x > 0.5, respectively. With the increase of x the portion of Li ions occupying tetrahedral sites increases and becomes 100% at about x = 4/7. In spite of the preferred occupation of octahedral sites by manganese(III), the experimental results can only be explained by a partial occupation also of tetrahedral sites by Mn(III). An increase of M {sub S} with the increase of x (expected for a preferred substitution of magnetic ions in tetrahedral sites by non-magnetic Li ions) is not observed. It should be prevented by the decreasing cooperative coupling effects due to the reduction of the iron content.

  1. [Removal Kinetics and Mechanism of Aniline by Manganese-oxide-modified Diatomite].

    PubMed

    Xiao, Shao-dan; Liu, Lu; Jiang, Li-ying; Chen, Jian-meng

    2015-06-01

    A novel rapid green one-step method was developed for the preparation of manganese modified diatomite (Mn-D) by treating roasted diatomite with an acidic permanganate solution. The effects of calcination temperature and mass ratio of KMnO4 and diatomite (p) on aniline removal efficiency of Mn-D were investigated. The removal kinetics and mechanism of aniline by Mn-D were also discussed. The results showed that when the optimal calcination temperature was 450 degrees C, p was 1.6, and the loading amounts of δ-MnO2 was 0.82 g x g(-1), Mn-D had a great performance for aniline removal, and more than 80% of aniline was adsorbed within 10 minutes, accompanied with the release of Mn2+. In acidic conditions, the adsorption process on Mn-D followed pseudo-second-order and was mainly controlled by intra-particle diffusion. The best fitting of the experimental adsorption data was given by the Freundlich equation. Gas chromatograph-mass spectrometer was applied to identify the reaction intermediates at different times, and azobenzene was found to be the main reaction intermediate in the degradation system. Based on the above observations, the possible degradation pathway of aniline by Mn-D was proposed. PMID:26387323

  2. Biodiesel synthesis catalyzed by transition metal oxides: ferric-manganese doped tungstated/molybdena nanoparticle catalyst.

    PubMed

    Alhassan, Fatah Hamid; Rashid, Umer; Taufiq-Yap, Yun Hin

    2015-01-01

    The solid acid Ferric-manganese doped tungstated/molybdena nananoparticle catalyst was prepared via impregnation reaction followed by calcination at 600C for 3 h. The characterization was done using X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis (TGA), temperature programmed desorption of NH3 (TPD-NH3), X-ray fluorescence (XRF), Transmission electron microscope (TEM) and Brunner-Emmett-Teller surface area measurement (BET). Moreover, dependence of biodiesel yield on the reaction variables such as the reaction temperature, catalyst loading, as well as molar ratio of methanol/oil and reusability were also appraised. The catalyst was reused six times without any loss in activity with maximum yield of 92.3% 1.12 achieved in the optimized conditions of reaction temperature of 200C; stirring speed of 600 rpm, 1:25 molar ratio of oil to alcohol, 6 % w/w catalyst loading as well as 8 h as time of the reaction. The fuel properties of WCOME's were evaluated, including the density, kinematic viscosity, pour point, cloud point and flash point whereas all properties were compared with the limits in the ASTM D6751 standard. PMID:25492234

  3. Mesoporous manganese oxide nanowires for high-capacity, high-rate, hybrid electrical energy storage.

    PubMed

    Yan, Wenbo; Ayvazian, Talin; Kim, Jungyun; Liu, Yu; Donavan, Keith C; Xing, Wendong; Yang, Yongan; Hemminger, John C; Penner, Reginald M

    2011-10-25

    Arrays of mesoporous manganese dioxide, mp-MnO(2), nanowires were electrodeposited on glass and silicon surfaces using the lithographically patterned nanowire electrodeposition (LPNE) method. The electrodeposition procedure involved the application, in a Mn(ClO(4))(2)-containing aqueous electrolyte, of a sequence of 0.60 V (vs MSE) voltage pulses delineated by 25 s rest intervals. This "multipulse" deposition program produced mp-MnO(2) nanowires with a total porosity of 43-56%. Transmission electron microscopy revealed the presence within these nanowires of a network of 3-5 nm diameter fibrils that were X-ray and electron amorphous, consistent with the measured porosity values. mp-MnO(2) nanowires were rectangular in cross-section with adjustable height, ranging from 21 to 63 nm, and adjustable width ranging from 200 to 600 nm. Arrays of 20 nm 400 nm mp-MnO(2) nanowires were characterized by a specific capacitance, C(sp), of 923 24 F/g at 5 mV/s and 484 15 F/g at 100 mV/s. These C(sp) values reflected true hybrid electrical energy storage with significant contributions from double-layer capacitance and noninsertion pseudocapacitance (38% for 20 nm 400 nm nanowires at 5 mV/s) coupled with a Faradaic insertion capacity (62%). These two contributions to the total C(sp) were deconvoluted as a function of the potential scan rate. PMID:21942449

  4. Oxidation state of manganese in zinc pyrophosphate: Probed by luminescence and EPR studies

    NASA Astrophysics Data System (ADS)

    Gupta, Santosh K.; Kadam, R. M.; Natarajan, V.; Godbole, S. V.

    2014-04-01

    Zn2P2O7: Mn was synthesized by wet chemical route and characterized by X-ray diffraction (XRD), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. Photoluminescence spectrum shows two bands, one at 500 nm (green emission), which is attributed to the 4T1(4G)-6A1(6S) transition of Mn2+ and other centered at 686 nm (red emission) is attributed to the electronic transition between 2E and 4A2 of Mn4+ accompanied with vibronic transitions. EPR spectroscopic studies also confirmed the presence of both Mn2+ and Mn4+ ions in zinc pyrophosphate with difference in the number of fine transitions and g values (Mn4+, S=3/2, three fine transitions and g < 2.00; Mn2+ S=5/2, five fine transitions and g=2.00).Mn2+ is attributed to presence of Mn at 6-ccordinated Zn2+ site whereas Mn4+ is due to presence substitution of Mn4+ at Zn2+ site thereby invoking charge compensation by presence of interstitial oxygen ions around Mn4+ ion or due to substitution of manganese at distorted 5-coordinated zinc site.

  5. Oxidation state of manganese in zinc pyrophosphate: Probed by luminescence and EPR studies

    SciTech Connect

    Gupta, Santosh K. Kadam, R. M. Natarajan, V. Godbole, S. V.

    2014-04-24

    Zn{sub 2}P{sub 2}O{sub 7}: Mn was synthesized by wet chemical route and characterized by X-ray diffraction (XRD), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. Photoluminescence spectrum shows two bands, one at 500 nm (green emission), which is attributed to the {sup 4}T{sub 1}({sup 4}G)-{sup 6}A{sub 1}({sup 6}S) transition of Mn{sup 2+} and other centered at 686 nm (red emission) is attributed to the electronic transition between {sup 2}E and {sup 4}A{sub 2} of Mn{sup 4+} accompanied with vibronic transitions. EPR spectroscopic studies also confirmed the presence of both Mn2+ and Mn4+ ions in zinc pyrophosphate with difference in the number of fine transitions and g values (Mn{sub 4+}, S=3/2, three fine transitions and g < 2.00; Mn{sup 2+} S=5/2, five fine transitions and g=2.00).Mn{sup 2+} is attributed to presence of Mn at 6-ccordinated Zn{sup 2+} site whereas Mn{sup 4+} is due to presence substitution of Mn{sup 4+} at Zn{sup 2+} site thereby invoking charge compensation by presence of interstitial oxygen ions around Mn{sup 4+} ion or due to substitution of manganese at distorted 5-coordinated zinc site.

  6. Manganese Intoxication

    PubMed Central

    Hine, Charles H.; Pasi, Aurelio

    1975-01-01

    We have reported two cases of chronic manganese poisoning. Case 1 followed exposure to manganese fumes in cutting and burning manganese steel. Case 2 resulted from exposure to dusts of manganese dioxide, an ingredient used in glazing of ceramics. There were initial difficulties in establishing the correct diagnosis. Prominent clinical features were severe and persistent chronic depressive psychosis (Case 1), transient acute brain syndrome (Case 2) and the presence of various extrapyramidal symptoms in both cases. Manganese intoxication has not previously been reported as occurring in California. With increasing use of the metal, the disease should be considered in the differential diagnosis of neurologic and psychiatric disease. Our observations were made in the period 1964 through 1968. Recently the prognosis of victims of manganese poisoning has been improved dramatically by the introduction of levodopa as a therapeutic agent. PMID:1179714

  7. Partial purification and characterization of manganese-oxidizing factors of Pseudomonas fluorescens GB-1.

    PubMed Central

    Okazaki, M; Sugita, T; Shimizu, M; Ohode, Y; Iwamoto, K; de Vrind-de Jong, E W; de Vrind, J P; Corstjens, P L

    1997-01-01

    The Mn(2+)-oxidizing bacterium Pseudomonas fluorescens GB-1 deposits Mn oxide around the cell. During growth of a culture, the Mn(2+)-oxidizing activity of the cells first appeared in the early stationary growth phase. It depended on the O2 concentration in the culture during the late logarithmic growth phase. Maximal activity was observed at an oxygen concentration of 26% saturation. The activity could be recovered in cell extracts and was proportional to the protein concentration in the cell extracts. The specific activity was increased 125-fold by ammonium sulfate precipitation followed by reversed-phase and gel filtration column chromatographies. The activity of the partly purified Mn(2+)-oxidizing preparation had a pH optimum of circa 7 and a temperature optimum of 35 degrees C and was lost by heating. The Mn(2+)-oxidizing activity was sensitive to NaN3 and HgCl2. It was inhibited by KCN, EDTA, Tris, and o-phenanthroline. Although most data indicated the involvement of protein in Mn2+ oxidation, the activity was slightly stimulated by sodium dodecyl sulfate at a low concentration and by treatment with pronase and V8 protease. By polyacrylamide gel electrophoresis, two Mn(2+)-oxidizing factors with estimated molecular weights of 180,000 and 250,000 were detected. PMID:9406397

  8. The cytochrome c maturation operon is involved in manganese oxidation in Pseudomonas putida GB-1

    SciTech Connect

    Vrind, J.P.M. de; Brouwers, G.J.; Corstijens, P.L.A.M.; Dulk, J. den; Vrind-de Jong, E.W. de

    1998-10-01

    A Pseudomonas putida strain, strain GB-1, oxidizes Mn{sup 2+} to Mn oxide in the early stationary growth phase. It also secretes a siderophore (identified as pyoverdine) when it is subjected to iron limitation. After transposon (Tn5) mutagenesis several classes of mutants with differences in Mn{sup 2+} oxidation and/or secretion of the Mn{sup 2+}-oxidizing activity were identified. Preliminary analysis of the Tn5 insertion site in one of the nonoxidizing mutants suggested that a multicopper oxidase-related enzyme is involved in Mn{sup 2+} oxidation. The insertion site in another mutant was preliminarily identified as a gene involved in the general protein secretion pathway. Two mutants defective in Mn{sup 2+}-oxidizing activity also secreted porphyrins into the medium and appeared to be derepressed for pyoverdine production. These strains were chosen for detailed analysis. Both mutants were shown to contain Tn5 insertions in the ccmF gene, which is part of the cytochrome c maturation operon. They were cytochrome oxidase negative and did not contain c-type cytochromes. Complementation with part of the ccm operon isolated from the wild type restored the phenotype of the parent strain. These results indicate that a functional ccm operon is required for Mn{sup 2+} oxidation in P. putida GB-1. A possible relationship between porphyrin secretion resulting from the ccm mutation and stimulation of pyoverdine production is discussed.

  9. Manganese oxidation in pH and O2 microenvironments produced by phytoplankton

    NASA Technical Reports Server (NTRS)

    Richardson, Laurie L.; Aguilar, Carmen; Nealson, Kenneth H.

    1988-01-01

    This paper reports on the oxidation of Mn(II) by pure cultures of Chlorella. It is shown that these cultures establish strong microgradients of pH and O2 concentration due to their photosynthetic activity, and it is demonstrated that Mn oxidation in the pelagic zone of Oneida Lake, New York, is limited to a microzone of high pH and O2 associated with the near-surface aggregates of phytoplankton cells. The data suggest that visible light is important in catalyzing Mn oxidation by driving the photosynthetic removal of CO2 with concomitant increases in pH.

  10. Manganese Oxide Biomineralization by Spores of the Marine Bacillus sp. Strain SG-1

    NASA Astrophysics Data System (ADS)

    Bargar, J. R.; Tebo, B. M.; Pecher, K. H.; McCubbery, D.; Chiu, V.; Tonner, B. P.

    2001-12-01

    Biogenic Mn oxides are ubiquitous in natural waters, have high sorptive capacities for metal ions, and oxidize organic and inorganic substances such as aromatic hydrocarbons, Cr(III), and hydrogen sulfide. In this fashion, Mn(II)-oxidizing bacteria impact the biogeochemical cycling of essential nutrients and toxic trace constituents of natural waters. In spite of their importance, the molecular mechanisms, intermediates, and products of Mn oxide biomineralization are poorly understood. Similarly, the relationship between biotic and abiotic Mn oxidation mechanisms is not well documented. We have studied Mn oxide biomineralization by spores of the marine Bacillus sp. strain SG-1 as functions of reaction time (10 min to 77 d), Mn(II) concentration (0.01 to 1 mM), major ion composition (50 mM NaCl to sea water), O2 partial pressure, and temperature. SG-1 spores are an ideal subject because they are dormant, Mn-oxidation is not inactivated by the x-rays utilized, and they previously have been extensively studied. Reaction products and Mn oxidation state evolution were directly observed in order to infer mechanisms and phase dominance. To obtain this information, a combination of Mn(II) uptake measurements, K-edge x-ray absorption spectroscopy (XAS), L-edge scanning transmission x-ray microspectroscopy (STXM, 60 nm nominal spot size), and synchrotron-based x-ray diffraction measurements were performed. All samples were measured under fully hydrated conditions to prevent dehydration of reaction products. This set of techniques provides chemical and structural information on Mn in amorphous and crystalline states in the samples. Mn oxide biomineralization products were sensitive to [Mn(II)]. At 0.01 mM [Mn(II)], biogenic Mn oxides were found to contain highly oxidized Mn (80-85% Mn(IV)) as observed after 48 hr. reaction. The dominant phase is identified as an amorphous Mn(IV) oxide similar to d-MnO2. K-edge XAS measurements suggest this phase forms within minutes of reaction onset and dominates after 6 hr. reaction, without detection of Mn(III). In contrast, L-edge STXM suggests that Mn(III) is important throughout the 6 - 48 hr interval and Mn(IV) is a minor component. At [Mn(II)] = 1 mM, crystalline b-MnOOH was observed as a dominant abiotic reaction product, likely formed on biogenic am. MnO2 surfaces. We will discuss important aspects of K- and L-edge spectroscopy and their application on microscopic scales and demonstrate how these aspects account for each set of observations. Implications for reaction mechanisms will be presented.

  11. Thermal chemistry of Mn{sub 2}(CO){sub 10} during deposition of thin manganese films on silicon oxide and on copper surfaces

    SciTech Connect

    Qin Xiangdong; Sun Huaxing; Zaera, Francisco

    2012-01-15

    The surface chemistry of dimanganese decacarbonyl on the native oxide of Si(100) wafers was characterized with the aid of x-ray photoelectron spectroscopy. Initial experiments in a small stainless-steel reactor identified a narrow range of temperatures, between approximately 445 and 465 K, in which the deposition of manganese could be achieved in a self-limiting fashion, as is desirable for atomic layer deposition. Deposition at higher temperatures leads to multilayer growth, but the extent of this Mn deposition reverses at even higher temperatures (about 625 K), and also ifhydrogen is added to the reaction mixture. Extensive decarbonylation takes place below room temperature, but limited C-O bond dissociation and carbon deposition are still seen after high exposures at 625 K. The films deposited at low ({approx}450 K) temperatures are mostly in the form of MnO, but at 625 K that converts to a manganese silicate, and upon higher doses a manganese silicide forms at the SiO{sub 2}/Si(100) interface as well. No metallic manganese could be deposited with this precursor on either silicon dioxide or copper surfaces.

  12. Redox processes at surfaces of manganese oxide and their effects on aqueous metal ions

    USGS Publications Warehouse

    Hem, J.D.

    1978-01-01

    Mn oxides precipitated from aerated solutions of Mn2+ by raising the pH are reported in various publications to have the approximate composition Mn3O4 or MnOOH. These oxyhydroxides in turn can disproportionate to Mn2+ and MnO2 resulting in a substantial decrease in equilibrium Mn solubility. The disproportionation can catalyze the oxidation of Mn2+ and other metals by facilitating electron-transfer processes. Diversion of some electron transfers from Mn species to other metal ions can greatly decrease the equilibrium solubility of Co, Pb, Ni and some other elements in the presence of mixed-valence Mn oxides. Some scavenging and coprecipitation effects involving Mn oxides may be attributable to redox processes. Equilibrium solubilities for Mn, Co and Pb are summarized in four graphs. ?? 1978.

  13. Effects of NOM on oxidative reactivity of manganese dioxide in binary oxide mixtures with goethite or hematite.

    PubMed

    Zhang, Huichun; Taujale, Saru; Huang, Jianzhi; Lee, Gang-Juan

    2015-03-10

    MnO2 typically coexists with iron oxides as either discrete particles or coatings in soils and sediments. This work examines the effect of Aldrich humic acid (AHA), alginate, and pyromellitic acid (PA) as representative natural organic matter (NOM) analogues on the oxidative reactivity of MnO2, as quantified by pseudo-first-order rate constants of triclosan oxidation, in mixtures with goethite or hematite. Adsorption studies showed that there was low adsorption of the NOMs by MnO2, but high (AHA and alginate) to low (PA) adsorption by the iron oxides. Based on the ATR-FTIR spectra obtained for the adsorbed PA on goethite or goethite + MnO2, the adsorption of PA occurred mainly through formation of outer-sphere complexes. The Fe oxides by themselves inhibited MnO2 reactivity through intensive heteroaggregation between the positively charged Fe oxides and the negatively charged MnO2; the low solubility of the iron oxides limited surface complexation of soluble Fe(3+) with MnO2. In ternary mixtures of MnO2, Fe oxides, and NOM analogues, the reactivity of MnO2 varied from inhibited to promoted as compared with that in the respective MnO2 + NOM binary mixtures. The dominant interaction mechanisms include an enhanced extent of homoaggregation within the Fe oxides due to formation of oppositely charged patches within the Fe oxides but an inhibited extent of heteroaggregation between the Fe oxide and MnO2 at [AHA] < 2-4 mg-C/L or [alginate/PA] < 5-10 mg/L, and an inhibited extent of heteroaggregation due to the largely negatively charged surfaces for all oxides at [AHA] > 4 mg-C/L or [alginate/PA] > 10 mg/L. PMID:25652230

  14. Distribution and speciation of trace elements in iron and manganese oxide cave deposits

    SciTech Connect

    Frierdich, Andrew J.; Catalano, Jeffrey G.

    2012-10-24

    Fe and Mn oxide minerals control the distribution and speciation of heavy metals and trace elements in soils and aquatic systems through chemical mechanisms involving adsorption, incorporation, and electron transfer. The Pautler Cave System in Southwest Illinois, an analog to other temperate carbonate-hosted karst systems, contains Fe and Mn oxide minerals that form in multiple depositional environments and have high concentrations of associated trace elements. Synchrotron-based micro-scanning X-ray fluorescence ({mu}-SXRF) shows unique spatial distributions of Fe, Mn, and trace elements in mineral samples. Profile maps of Mn oxide cave stream pebble coatings show Fe- and As-rich laminations, indicating dynamic redox conditions in the cave stream. {mu}-SXRF maps demonstrate that Ni, Cu, and Zn correlate primarily with Mn whereas As correlates with both Mn and Fe; As is more enriched in the Fe phase. Zn is concentrated in the periphery of Mn oxide stream pebble coatings, and may be an indication of recent anthropogenic surface activity. X-ray absorption fine structure spectroscopy measurements reveal that As(V) occurs as surface complexes on Mn and Fe oxides whereas Zn(II) associated with Mn oxides is adsorbed to the basal planes of phyllomanganates in a tetrahedral coordination. Co(III) and Se(IV) are also observed to be associated with Mn oxides. The observation of Fe, Mn, and trace element banding in Mn oxide cave stream pebble coatings suggests that these materials are sensitive to and document aqueous redox conditions, similar to ferromanganese nodules in soils and in marine and freshwater sediments. Furthermore, speciation and distribution measurements indicate that these minerals scavenge trace elements and limit the transport of micronutrients and contaminants in karst aquifer systems while also potentially recording changes in anthropogenic surface activity and land-use.

  15. Distribution and speciation of trace elements in iron and manganese oxide cave deposits

    NASA Astrophysics Data System (ADS)

    Frierdich, Andrew J.; Catalano, Jeffrey G.

    2012-08-01

    Fe and Mn oxide minerals control the distribution and speciation of heavy metals and trace elements in soils and aquatic systems through chemical mechanisms involving adsorption, incorporation, and electron transfer. The Pautler Cave System in Southwest Illinois, an analog to other temperate carbonate-hosted karst systems, contains Fe and Mn oxide minerals that form in multiple depositional environments and have high concentrations of associated trace elements. Synchrotron-based micro-scanning X-ray fluorescence (μ-SXRF) shows unique spatial distributions of Fe, Mn, and trace elements in mineral samples. Profile maps of Mn oxide cave stream pebble coatings show Fe- and As-rich laminations, indicating dynamic redox conditions in the cave stream. μ-SXRF maps demonstrate that Ni, Cu, and Zn correlate primarily with Mn whereas As correlates with both Mn and Fe; As is more enriched in the Fe phase. Zn is concentrated in the periphery of Mn oxide stream pebble coatings, and may be an indication of recent anthropogenic surface activity. X-ray absorption fine structure spectroscopy measurements reveal that As(V) occurs as surface complexes on Mn and Fe oxides whereas Zn(II) associated with Mn oxides is adsorbed to the basal planes of phyllomanganates in a tetrahedral coordination. Co(III) and Se(IV) are also observed to be associated with Mn oxides. The observation of Fe, Mn, and trace element banding in Mn oxide cave stream pebble coatings suggests that these materials are sensitive to and document aqueous redox conditions, similar to ferromanganese nodules in soils and in marine and freshwater sediments. Furthermore, speciation and distribution measurements indicate that these minerals scavenge trace elements and limit the transport of micronutrients and contaminants in karst aquifer systems while also potentially recording changes in anthropogenic surface activity and land-use.

  16. The autophagic- lysosomal pathway determines the fate of glial cells under manganese- induced oxidative stress conditions.

    PubMed

    Gorojod, R M; Alaimo, A; Porte Alcon, S; Pomilio, C; Saravia, F; Kotler, M L

    2015-10-01

    Manganese (Mn) overexposure is frequently associated with the development of a neurodegenerative disorder known as Manganism. The Mn-mediated generation of reactive oxygen species (ROS) promotes cellular damage, finally leading to apoptotic cell death in rat astrocytoma C6 cells. In this scenario, the autophagic pathway could play an important role in preventing cytotoxicity. In the present study, we found that Mn induced an increase in the amount and total volume of acidic vesicular organelles (AVOs), a process usually related to the activation of the autophagic pathway. Particularly, the generation of enlarged AVOs was a ROS- dependent event. In this report we demonstrated for the first time that Mn induces autophagy in glial cells. This conclusion emerged from the results obtained employing a battery of autophagy markers: a) the increase in LC3-II expression levels, b) the formation of autophagic vesicles labeled with monodansylcadaverine (MDC) or LC3 and, c) the increase in Beclin 1/ Bcl-2 and Beclin 1/ Bcl-X(L) ratio. Autophagy inhibition employing 3-MA and mAtg5(K130R) resulted in decreased cell viability indicating that this event plays a protective role in Mn- induced cell death. In addition, mitophagy was demonstrated by an increase in LC3 and TOM-20 colocalization. On the other hand, we proposed the occurrence of lysosomal membrane permeabilization (LMP) based in the fact that cathepsins B and D activities are essential for cell death. Both cathepsin B inhibitor (Ca-074 Me) or cathepsin D inhibitor (Pepstatin A) completely prevented Mn- induced cytotoxicity. In addition, low dose of Bafilomycin A1 showed a similar effect, a finding that adds evidence about the lysosomal role in Mn cytotoxicity. Finally, in vivo experiments demonstrated that Mn induces injury and alters LC3 expression levels in rat striatal astrocytes. In summary, our results demonstrated that autophagy is activated to counteract the harmful effect caused by Mn. These data is valuable to be considered in future research concerning Manganism therapies. PMID:26163003

  17. Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

    1989-01-01

    The ability of Alteromonas putrefaciens to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory Fe(III) or Mn(IV) reduction was investigated. A. putrefaciens grew with hydrogen, formate, lactate, or pyruvate as the sole electron donor and Fe(III) as the sole electron acceptor. Lactate and pyruvate were oxidized to acetate, which was not metabolized further. With Fe(III) as the electron acceptor, A. putrefaciens had a high affinity for hydrogen and formate and metabolized hydrogen at partial pressures that were 25-fold lower than those of hydrogen that can be metabolized by pure cultures of sulfate reducers or methanogens. The electron donors for Fe(III) reduction also supported Mn(IV) reduction. The electron donors for Fe(III) and Mn(IV) reduction and the inability of A. putrefaciens to completely oxidize multicarbon substrates to carbon dioxide distinguish A. putrefaciens from GS-15, the only other organism that is known to obtain energy for growth by coupling the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). The ability of A. putrefaciens to reduce large quantities of Fe(III) and to grow in a defined medium distinguishes it from a Pseudomonas sp., which is the only other known hydrogen-oxidizing, Fe(III)-reducing microorganism. Furthermore, A. putrefaciens is the first organism that is known to grow with hydrogen as the electron donor and Mn(IV) as the electron acceptor and is the first organism that is known to couple the oxidation of formate to the reduction of Fe(III) or Mn(IV). Thus, A. putrefaciens provides a much needed microbial model for key reactions in the oxidation of sediment organic matter coupled to Fe(III) and Mn(IV) reduction.

  18. The effects of iron(II) on the kinetics of arsenic oxidation and sorption on manganese oxides.

    PubMed

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-01

    In this study, As(III) oxidation kinetics by a poorly-crystalline phyllomanganate (?-MnO2) in the presence and absence of dissolved Fe(II) was investigated using stirred-flow and batch experiments. Chemically synthetic ?-MnO2 was reacted with four influent solutions, containing the same As(III) concentration but different Fe(II) concentrations, at pH 6. The results show an initial rapid As(III) oxidation by ?-MnO2, which is followed by an appreciably slow reaction after 8h. In the presence of Fe(II), As(III) oxidation is inhibited due to the competitive oxidation of Fe(II) as well as the formation of Fe(III)-(hydr)oxides on the ?-MnO2 surface. However, the sorption of As(III), As(V) and Mn(II) are increased, for the newly formed Fe(III)-(hydr)oxides provide additional sorption sites. This study suggests that the competitive oxidation of Fe(II) and consequently the precipitation of Fe(III) compounds on the ?-MnO2 surface play an important role in As(III) oxidation and As sequestration. Understanding these processes would be helpful in developing in situ strategies for remediation of As-contaminated waters and soils. PMID:26196715

  19. In Situ XAS and XRD Studies of Substituted Spinel Lithium Manganese Oxides in the 4-5 V Region

    SciTech Connect

    McBreen, J.; Mukerjee, S.; Yang, X. Q.; Sun, X.; Ein-Eli, Y.

    1998-11-01

    Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the phase behavior of the cathode. Substitution with either metal or with a combination of both shortens the 4.2 V plateau and results in higher voltage plateaus. In situ x-ray absorption (XAS) studies indicate that the higher voltage plateaus are related to redox processes on the substituents. In situ x-ray diffraction (XRD) on LiCu{sub 0.5}Mn{sub 1.5}O{sub 4} shows single phase behavior during the charge and discharge process. Three phases are observed for LiNi{sub 0.5}Mn{sub 1.5}O{sub 4} and two phases are observed in the case of LiNi{sub 0.25}Cu{sub 0.25}Mn{sub 1.5}O{sub 4}. The electrolyte stability is dependent on both the operating voltage and the cathode composition. Even though Ni substituted materials have lower voltages, the electrolyte is more stable in cells with the Cu substituted materials.

  20. Catalytic degradation of Acid Orange 7 by manganese oxide octahedral molecular sieves with peroxymonosulfate under visible light irradiation.

    PubMed

    Duan, Lian; Sun, Binzhe; Wei, Mingyu; Luo, Shilu; Pan, Fei; Xu, Aihua; Li, Xiaoxia

    2015-03-21

    In this paper, the photodegradation of Acid Orange 7 (AO7) in aqueous solutions with peroxymonosulfate (PMS) was studied with manganese oxide octahedral molecular sieves (OMS-2) as the catalyst. The activities of different systems including OMS-2 under visible light irradiation (OMS-2/Vis), OMS-2/PMS and OMS-2/PMS/Vis were evaluated. It was found that the efficiency of OMS-2/PMS was much higher than that of OMS-2/Vis and could be further enhanced by visible light irradiation. The catalyst also exhibited stable performance for multiple runs. Results from ESR and XPS analyses suggested that the highly catalytic activity of the OMS-2/PMS/Vis system possible involved the activation of PMS to sulfate radicals meditated by the redox pair of Mn(IV)/Mn(III) and Mn(III)/Mn(II), while in the OMS-2/PMS system, only the redox reaction between Mn(IV)/Mn(III) occurred. Several operational parameters, such as dye concentration, catalyst load, PMS concentration and solution pH, affected the degradation of AO7. PMID:25528234

  1. Electrochemical and structural characterization of titanium-substituted manganese oxides based on Na0.44MnO2

    SciTech Connect

    Doeff, Marca M.; Richardson, Thomas J.; Hwang, Kwang-Taek

    2004-03-01

    A series of titanium-substituted manganese oxides, Li{sub x}Ti{sub y}Mn{sub 1-y}O{sub 2} (y = 0.11, 0.22, 0.33, 0.44, and 0.55) with the Na{sub 0.44}MnO{sub 2} structure were prepared from Na{sub x}Ti{sub y}Mn{sub 1-y}O{sub 2} (x {approx} 0.44) precursors. The electrochemical characteristics of these compounds, which retain the unique double-tunnel structure during ion exchange, were examined in lithium/polymer electrolyte cells operating at 85 C. All of the substituted cathode materials intercalated lithium reversibly, with Li{sub x}Ti{sub 0.22}Mn{sub 0.78}O{sub 2} exhibiting the highest capacity in polymer cells, about 10-20% greater than that of unsubstituted Li{sub x}MnO{sub 2} made from Na{sub 0.44}MnO{sub 2}. In common with Li{sub x}MnO{sub 2}, the Ti-substituted materials exhibited good capacity retention over one hundred or more cycles, with some compositions exhibiting a fade rate of less than 0.03% per cycle.

  2. Silica-F127 nanohybrid-encapsulated manganese oxide nanoparticles for optimized T1 magnetic resonance relaxivity.

    PubMed

    Wei Hsu, Benedict You; Wang, Miao; Zhang, Yu; Vijayaragavan, Vimalan; Wong, Siew Yee; Yuang-Chi Chang, Alex; Bhakoo, Kishore Kumar; Li, Xu; Wang, John

    2014-01-01

    To properly engineer MnO nanoparticles (MONPs) of high r1 relaxivity, a nanohybrid coating consisting of silica and F127 (PEO106PPO70PEO106) is designed to encapsulate MONPs. Achieved by an interfacial templating scheme, the nanohybrid encapsulating layer is highly permeable and hydrophilic to allow for an optimal access of water molecules to the encapsulated manganese oxide core. Hence, the efficacy of MONPs as MRI contrast agents is significantly improved, as demonstrated by an enhancement of the MR signal measured with a pre-clinical 7.0 T MRI scanner. The nanohybrid encapsulation strategy also confers high colloidal stability to the hydrophobic MONPs by the surface decoration of PEO chains and a small overall diameter (<100 nm) of the PEO-SiO2 nanohybrid-encapsulated MONPs (PEOMSNs). The PEOMSNs are not susceptible to Mn-ion leaching, and their biocompatibility is affirmed by a low toxicity profile. Moreover, these hybrid nanocapsules exhibit a nano-rattle structure, which would favor the facile loading of various therapeutic reagents for theranostic applications. PMID:24193096

  3. In situ growth of manganese oxide on 3D graphene by a reverse microemulsion method for supercapacitors

    NASA Astrophysics Data System (ADS)

    Wei, Bing; Wang, Lidong; Wang, Yang; Yuan, Yinan; Miao, Qinghua; Yang, Ziyue; Fei, Weidong

    2016-03-01

    In this study, a new, effective strategy is reported for the fabrication of composites using manganese oxide (MnO2) grown in situ on three-dimensional (3D) graphene by the reverse microemulsion (water-in-oil) method. A uniform coating of nanoscale MnO2 layers can be observed on the internal surface of 3D graphene, which could benefit rapid ionic and electronic transport. The electrochemical performance of the MnO2/3D graphene composites is optimized by the control of the composite structure and mass loading of MnO2. The MnO2/3D graphene composite thus prepared exhibits a significantly high specific capacitance of 659.7 F g-1 at 0.3 A g-1 and an excellent retention life of 106% after 1000 cycles. The facile synthesis and excellent electrochemical performance of the MnO2/3D graphene composites indicate that the developed method demonstrates potential applications for the fabrication of novel electrode materials for use in energy storage devices.

  4. Removal of arsenic from water using manganese (III) oxide: Adsorption of As(III) and As(V).

    PubMed

    Babaeivelni, Kamel; Khodadoust, Amid P

    2016-03-20

    Removal of arsenic from water was evaluated with manganese (III) oxide (Mn2O3) as adsorbent. Adsorption of As(III) and As(V) onto Mn2O3 was favorable according to the Langmuir and Freundlich adsorption equilibrium equations, while chemisorption of arsenic occurred according to the Dubinin-Radushkevich equation. Adsorption parameters from the Langmuir, Freundlich, and Temkin equations showed a greater adsorption and removal of As(III) than As(V) by Mn2O3. Maximum removal of As(III) and As(V) occurred at pH 3-9 and at pH 2, respectively, while removal of As(V) in the pH range of 6-9 was 93% (pH 6) to 61% (pH 9) of the maximum removal. Zeta potential measurements for Mn2O3 in As(III) was likely converted to As(V) solutions indicated that As(III) was likely converted to As(V) on the Mn2O3 surface at pH 3-9. Overall, the effective Mn2O3 sorbent rapidly removed As(III) and As(V) from water in the pH range of 6-9 for natural waters. PMID:26745439

  5. Manganese hexacyanoferrate derived Mn3O4 nanocubes-reduced graphene oxide nanocomposites and their charge storage characteristics in supercapacitors.

    PubMed

    Subramani, K; Jeyakumar, D; Sathish, M

    2014-03-14

    Mn3O4-reduced graphene oxide (RGO) nanocomposites were prepared by chemical decomposition of the manganese hexacyanoferrate (MnHCF) complex directly on the graphene surface. XRD studies revealed the formation of crystalline hausmannite Mn3O4 nanocubes in the as-prepared nanocomposites without any heat treatment. The FE-SEM images showed the formation of Mn3O4 nanocubes on the graphene surface in the as-prepared nanocomposites. HR-TEM studies confirmed the homogeneous dispersion of ?25 nm Mn3O4 nanocubes on graphene nanosheets. The amount of Mn3O4 nanocubes and graphene in the nanocomposites was estimated using TGA analysis from room temperature to 800 C in air. The FT-IR and Raman spectroscopic analysis confirmed the functional groups in the nanocomposites and defects in graphene nanosheets in the nanocomposites. Cyclic voltammetry and galvanostatic charge-discharge experiments demonstrated a high specific capacitance of 131 F g(-1) in 1 M Na2SO4 electrolyte at a current density of 0.5 A g(-1) for the RGM-0.5 nanocomposite. A capacitance retention of 99% was observed for 500 charge-discharge cycles at a current density of 5 A g(-1), which conformed the excellent stability of the RGM electrodes. The prepared Mn3O4-RGO nanocomposites are promising for electrochemical energy storage. PMID:24477791

  6. Manganese Oxide-Coated Carbon Nanotubes As Dual-Modality Lymph Mapping Agents for Photothermal Therapy of Tumor Metastasis.

    PubMed

    Wang, Sheng; Zhang, Qin; Yang, Peng; Yu, Xiangrong; Huang, Li-Yong; Shen, Shun; Cai, Sanjun

    2016-02-17

    Lymph node (LN) status is a major indicator of stage and survival of lung cancer patients. LN dissection is a primary option for lung cancer LN metastasis; however, this strategy elicits adverse effects and great trauma. Therefore, developing a minimally invasive technique to cure LN metastasis of lung cancer is desired. In this study, multiwalled carbon nanotubes (MWNTs) coated with manganese oxide (MnO) and polyethylene glycol (PEG) (namely MWNTs-MnO-PEG) was employed as a lymphatic theranostic agent to diagnose and treat metastatic LNs. After single local injection and lymph drainage were performed, regional LNs were clearly mapped by T1-weighted magnetic resonance (MR) of MnO and dark dye imaging of MWNTs. Meanwhile, metastatic LNs could be simultaneously ablated by near-infrared (NIR) irradiation under the guidance of dual-modality mapping. The excellent result was obtained in mice bearing LNs metastasis models, showing that MWNTs-MnO-PEG as a multifunctional theranostic agent was competent for dual-modality mapping guided photothermal therapy of metastatic LNs. PMID:26653008

  7. Mobilization of manganese by basalt associated Mn(II)-oxidizing bacteria from the Indian Ridge System.

    PubMed

    Sujith, P P; Mourya, B S; Krishnamurthi, S; Meena, R M; Loka Bharathi, P A

    2014-01-01

    The Indian Ridge System basalt bearing Mn-oxide coatings had todorokite as the major and birnesite as the minor mineral. We posit that microorganisms associated with these basalts participate in the oxidation of Mn and contribute to mineral deposition. We also hypothesized that, the Mn-oxidizing microbes may respond reversibly to pulses of fresh organic carbon introduced into the water column by mobilizing the Mn in Mn-oxides. To test these two hypotheses, we enumerated the number of Mn-oxidizers and -reducers and carried out studies on the mobilization of Mn by microbial communities associated with basalt. In medium containing 100 ?M Mn(2+), 10(3) colony forming units (CFU) were recovered with undetectable number of reducers on Mn-oxide amended medium, suggesting that the community was more oxidative. Experiments were then conducted with basalt fragments at 42 C in the presence 'G(+)' and absence 'G(-)' of glucose (0.1%). Controls included set-ups, some of which were poisoned with 15 mM azide and the others of which were heat-killed. The mobilization of Mn in the presence of glucose was 1.76 ?g g(-1) d(-1) and in the absence, it was 0.17 ?g g(-1) d(-1) after 150 d. Mn mobilization with and without added glucose was 13 and 4 times greater than the corresponding azide treated controls. However, rates in 'G(+)' were 16 times and 'G(-)' 24 times more than the respective heat killed controls. The corresponding total counts in the presence of added glucose increased from 1.6310(6) to 6.7110(7) cells g(-1) and from 1.4110(7) to 3.5210(7) cells g(-1) in its absence. Thus, the addition of glucose as a proxy for organic carbon changed the community's response from Mn(II)-oxidizing to Mn(IV)-reducing activity. The results confirm the participation of Mn oxidizing bacteria in the mobilization of Mn. Identification of culturable bacteria by 16S rRNA gene analysis showed taxonomic affiliations to Bacillus, Exiguobacterium, Staphylococcus, Brevibacterium and Alcanivorax sp. PMID:24183631

  8. Protective effects of antioxidants and anti-inflammatory agents against manganese-induced oxidative damage and neuronal injury

    SciTech Connect

    Milatovic, Dejan; Gupta, Ramesh C.; Yu, Yingchun; Zaja-Milatovic, Snjezana; Aschner, Michael; Pharmacology and the Kennedy Center for Research on Human Development, Nashville, TN

    2011-11-15

    Exposure to excessive manganese (Mn) levels leads to neurotoxicity, referred to as manganism, which resembles Parkinson's disease (PD). Manganism is caused by neuronal injury in both cortical and subcortical regions, particularly in the basal ganglia. The basis for the selective neurotoxicity of Mn is not yet fully understood. However, several studies suggest that oxidative damage and inflammatory processes play prominent roles in the degeneration of dopamine-containing neurons. In the present study, we assessed the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates and associated neuronal dysfunctions both in vitro and in vivo. Results from our in vitro study showed a significant (p < 0.01) increase in biomarkers of oxidative damage, F{sub 2}-isoprostanes (F{sub 2}-IsoPs), as well as the depletion of ATP in primary rat cortical neurons following exposure to Mn (500 {mu}M) for 2 h. These effects were protected when neurons were pretreated for 30 min with 100 of an antioxidant, the hydrophilic vitamin E analog, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), or an anti-inflammatory agent, indomethacin. Results from our in vivo study confirmed a significant increase in F{sub 2}-IsoPs levels in conjunction with the progressive spine degeneration and dendritic damage of the striatal medium spiny neurons (MSNs) of mice exposed to Mn (100 mg/kg, s.c.) 24 h. Additionally, pretreatment with vitamin E (100 mg/kg, i.p.) or ibuprofen (140 {mu}g/ml in the drinking water for two weeks) attenuated the Mn-induced increase in cerebral F{sub 2}-IsoPs? and protected the MSNs from dendritic atrophy and dendritic spine loss. Our findings suggest that the mediation of oxidative stress/mitochondrial dysfunction and the control of alterations in biomarkers of oxidative injury, neuroinflammation and synaptodendritic degeneration may provide an effective, multi-pronged therapeutic strategy for protecting dysfunctional dopaminergic transmission and slowing of the progression of Mn-induced neurodegenerative processes. -- Research highlights: Black-Right-Pointing-Pointer Mn exposure leads to neurotoxicity in vitro and in vivo. Black-Right-Pointing-Pointer Antioxidants and anti-inflammatory agents attenuate Mn-induced oxidative injury. Black-Right-Pointing-Pointer These agents also protect the striatal neurons from dendritic atrophy and spine loss. Black-Right-Pointing-Pointer These prophylactic strategies may be effective against Mn neurotoxicity.

  9. Nanostructured dimagnesium manganese oxide (Spinel): Control of size, shape and their magnetic and electro catalytic properties

    NASA Astrophysics Data System (ADS)

    Garg, Neha; Menaka; Ramanujachary, Kandalam V.; Lofland, Samuel E.; Ganguli, Ashok K.

    2013-01-01

    Tetravalent Mn based ternary oxides are of interest as they are important electrode materials. Dimagnesium manganate (Mg2MnO4) is one Mn(IV) containing oxide which has been of interest. Nanostructures of the above oxide (spinel) have been obtained by the thermal decomposition of nanostructured metal oxalate precursor at 500 C. The size and anisotropy of the oxide nanostructures was controlled by choosing appropriate decomposition temperature of the oxalate precursor. Mg2MnO4 nanorods were obtained at low temperature (500 C), formed by aligned nanoparticles of size8-10 nm. These nanoparticles show Curie-Weiss behavior with Weiss constant (14 K). Below 50 K there is a small deviation resulting in a negative Weiss constant (-7.36 K) indicating exchange cross over (from ferromagnetic like interactions to antiferromagnetic interactions). The high temperature magnetic moment corresponds to Mn (IV). Electrochemical experiments show that nanostructured Mg2MnO4 is an efficient anode material for oxygen evolution reaction with a current density of 14 mA/cm2. The stability of the anode over several cycles of oxidation and reduction is highly encouraging.

  10. Relationship of manganese-iron oxides and associated heavy metals to grain size in stream sediments

    USGS Publications Warehouse

    Whitney, P.R.

    1975-01-01

    The distribution of ammonium citrate-leachable lead, zinc and cadmium among size fractions in stream sediments is strongly influenced by the presence of hydrous Mn-Fe oxides in the form of coatings on sediment grains. Distribution curves showing leachable metals as a function of particle size are given for eight samples from streams in New York State. These show certain features in common; in particular two concentrations of metals, one in the finest fractions, and a second peak in the coarse sand and gravel fraction. The latter can be explained as a result of the increasing prevalence and thickness of oxide coatings with increasing particle size, with the oxides serving as collectors for the heavy metals. The distribution of Zn and Cd in most of the samples closely parallels that of Mn; the distribution of Pb is less regular and appears to be related to Fe in some samples and Mn in others. The concentration of metals in the coarse fractions due to oxide coatings, combined with the common occurrence of oxide deposition in streams of glaciated regions, raises the possibility of using coarse materials for geochemical surveys and environmental heavy-metal studies. ?? 1975.

  11. YREE sorption on hydrous manganese oxide (MnOx) in 0.5 M NaCl

    NASA Astrophysics Data System (ADS)

    Marshall, K. S.; Schijf, J.

    2010-12-01

    Cerium is the only member of the yttrium and rare earth element (YREE) series that can be oxidized in natural waters from Ce(III) to less soluble Ce(IV), causing anomalous sorption behavior with respect to its strictly trivalent YREE neighbors. Sedimentary Ce anomaly records have been interpreted in terms of episodic shifts in the bottom water oxygenation of the paleo-ocean. However, Ce anomalies also form due to catalytic Ce oxidation on certain sorbent surfaces regardless of ambient redox conditions, thus creating a preformed signal that may instead reflect variations in the composition of settling particles. We investigate YREE sorption in 0.5 M NaCl on mixtures of three major components of marine particulate matter: Fe and Mn oxides, and algal debris. Here we report our results for one pure endmember, hydrous manganese oxide (MnOx). Batch experiments with freshly prepared MnOx were conducted under nitrogen atmosphere, to prevent aerobic Ce oxidation and YREE complexation with carbonate, over a range of pH (4-8) at 25.00.1C. After at least 6 hours of equilibration at each pH, solution samples were filtered to 0.22 ?m and dissolved YREE concentrations analyzed by ICP-MS to determine their solid/solution distribution coefficient, K. Under the same experimental conditions, log K increases less steeply with pH for MnOx than for hydrous ferric oxide (HFO). This may result from the lower pHzpc of MnOx as well as its higher tendency than HFO to form bidentate edge-sharing YREE surface complexes, as determined by others using X-ray Absorption Fine Structure (XAFS) spectroscopy. A non-electrostatic surface complexation model is being developed to further elucidate these findings. Preferential Ce sorption, implying catalytic Ce oxidation at the mineral-water interface, was observed on MnOx but never on HFO or organic surfaces, in agreement with prior research. This may be related to the generally higher Gibbs free energy gain associated with oxidation reactions in which MnOx is the electron acceptor, although some large organic ligands, such as siderophores, have also been reported to catalyze Ce(III) oxidation. The enhanced Ce removal in anoxic 0.5 M NaCl solutions increases with pH from about 10- to 100-fold relative to the other YREEs, which show comparatively little fractionation among themselves. Sedimentary Ce anomalies are therefore unlikely to provide a reliable and lasting record of bottom water oxygenation when Mn oxides are an important constituent of settling particles and their interpretation as a proxy of paleo-redox conditions should be undertaken with appropriate caution.

  12. Removal of multi-heavy metals using biogenic manganese oxides generated by a deep-sea sedimentary bacterium - Brachybacterium sp. strain Mn32.

    PubMed

    Wang, Wenming; Shao, Zongze; Liu, Yanjun; Wang, Gejiao

    2009-06-01

    A deep-sea manganese-oxidizing bacterium, Brachybacterium sp. strain Mn32, showed high Mn(II) resistance (MIC 55 mM) and Mn(II)-oxidizing/removing abilities. Strain Mn32 removed Mn(II) by two pathways: (1) oxidizing soluble Mn(II) to insoluble biogenic Mn oxides - birnessite (delta-MnO(2) group) and manganite (gamma-MnOOH); (2) the biogenic Mn oxides further adsorb more Mn(II) from the culture. The generated biogenic Mn oxides surround the cell surfaces of strain Mn32 and provide a high capacity to adsorb Zn(II) and Ni(II). Mn(II) oxidation by strain Mn32 was inhibited by both sodium azide and o-phenanthroline, suggesting the involvement of a metalloenzyme which was induced by Mn(II). X-ray diffraction analysis showed that the crystal structures of the biogenic Mn oxides were different from those of commercial pyrolusite (beta-MnO(2) group) and fresh chemically synthesized vernadite (delta-MnO(2) group). The biogenic Mn oxides generated by strain Mn32 showed two to three times higher Zn(II) and Ni(II) adsorption abilities than commercial and fresh synthetic MnO(2). The crystal structure and the biogenic MnO(2) types may be important factors for the high heavy metal adsorption ability of strain Mn32. This study provides potential applications of a new marine Mn(II)-oxidizing bacterium in heavy metal bioremediation and increases our basic knowledge of microbial manganese oxidation mechanisms. PMID:19383675

  13. Understanding the capacity fade mechanisms of spinel manganese oxide cathodes and improving their performance in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Choi, Won Chang

    Lithium ion batteries have been successful in portable electronics market due to their high energy density, adopting the layered LiCoO2 as the cathode material in commercial lithium ion cells. However, increasing interest in lithium ion batteries for electric vehicle and hybrid electric vehicle applications requires alternative cathode materials due to the high cost, toxicity, and limited power capability of the layered LiCoO2 cathode. In this regard, spinel LiMn2O4 has become appealing as manganese is inexpensive and environmentally benign, but LiMn2O 4 is plagued by severe capacity fade at elevated temperatures. This dissertation explores the factors that control and limit the electrochemical performance of spinel LiMn2O4 cathodes and focuses on improving the performance parameters such as the capacity, cyclability, and rate capability of various spinel cathodes derived from LiMn2O 4. From a systematic investigation of a number of cationic and anionic (fluorine) substituted spinel oxide compositions, the improvements in electrochemical properties and performances are found to be due to the reduced manganese dissolution and suppressed lattice parameter difference between the two cubic phases formed during the charge-discharge process. Investigations focused on fluorine substitution reveal that spinel LiMn 2-y-zLiyZnzO4-etaFeta oxyfluoride cathodes synthesized by solid-state reactions at 800°C employing ZnF2 as a raw material and spinel LiMn2-y-zLiy NizO4-etaFeta oxyfluoride cathodes synthesized by firing the cation-substituted LiMn2-y-zLiy NizO4 oxides with NH4HF2 at a moderate temperature of 450°C show superior cyclability, increased capacity, reduced Mn dissolution, and excellent storage performance compared to the corresponding oxide analogs and the conventional LiMn2O 4. Spinel-layered composite cathodes are found to exhibit better electrochemical performance with graphite anode when charged to 4.7 V in the first cycle followed by cycling at 4.3--3.5 V compared to the normal cycling at 4.3--3.5 V. The improved performance is explained to be due to the trapping of trace amounts of protons that may be present in the electrolyte within the layered oxide lattice during the first charge to 4.7 V and the consequent reduction in Mn dissolution. Electrochemical performances of 3 V spinel Li4Mn5O 12 cathodes are also improved by fluorine substitution due to the suppression of the disproportionation of Li4Mn5O12 during synthesis and the formation of the Li2MnO3 phase.

  14. Manganese-exposed developing rats display motor deficits and striatal oxidative stress that are reversed by Trolox.

    PubMed

    Cordova, Fabiano M; Aguiar, Aderbal S; Peres, Tanara V; Lopes, Mark W; Gonalves, Filipe M; Pedro, Daniela Z; Lopes, Samantha C; Pilati, Clso; Prediger, Rui D S; Farina, Marcelo; Erikson, Keith M; Aschner, Michael; Leal, Rodrigo B

    2013-07-01

    While manganese (Mn) is essential for proper central nervous system (CNS) development, excessive Mn exposure may lead to neurotoxicity. Mn preferentially accumulates in the basal ganglia, and in adults it may cause Parkinson's disease-like disorder. Compared to adults, younger individuals accumulate greater Mn levels in the CNS and are more vulnerable to its toxicity. Moreover, the mechanisms mediating developmental Mn-induced neurotoxicity are not completely understood. The present study investigated the developmental neurotoxicity elicited by Mn exposure (5, 10 and 20mg/kg; i.p.) from postnatal day 8 to PN27 in rats. Neurochemical analyses were carried out on PN29, with a particular focus on striatal alterations in intracellular signaling pathways (MAPKs, Akt and DARPP-32), oxidative stress generation and cell death. Motor alterations were evaluated later in life at 3, 4 or 5weeks of age. Mn exposure (20mg/kg) increased p38(MAPK) and Akt phosphorylation, but decreased DARPP-32-Thr-34 phosphorylation. Mn (10 and 20mg/kg) increased caspase activity and F2-isoprostane production (a biological marker of lipid peroxidation). Paralleling the changes in striatal biochemical parameters, Mn (20mg/kg) also caused motor impairment, evidenced by increased falling latency in the rotarod test, decreased distance traveled and motor speed in the open-field test. Notably, the antioxidant Trolox reversed the Mn (20mg/kg)-dependent augmentation in p38(MAPK) phosphorylation and reduced the Mn (20mg/kg)-induced caspase activity and F2-isoprostane production. Trolox also reversed the Mn-induced motor coordination deficits. These findings are the first to show that long-term exposure to Mn during a critical period of neurodevelopment causes motor coordination dysfunction with parallel increment in oxidative stress markers, p38(MAPK) phosphorylation and caspase activity in the striatum. Moreover, we establish Trolox as a potential neuroprotective agent given its efficacy in reversing the Mn-induced neurodevelopmental effects. PMID:23385959

  15. Activated carbon doped with biogenic manganese oxides for the removal of indigo carmine.

    PubMed

    Hu, Yichen; Chen, Xiao; Liu, Zhiqiang; Wang, Gejiao; Liao, Shuijiao

    2016-01-15

    Indigo carmine (IC) is one of the oldest, most important, and highly toxic dyes which is released from the effluents of many industries and results in serious pollution in water. In this study, the biogenic Mn oxides were activated by NaOH and then heated for 3h at 350C to produce activated carbon doped with Mn oxide (Bio-MnOx-C), which were produced by culturing Mn (II)-oxidizing bacterial strain MnI7-9 in liquid A medium at 28C with 10mmol/L MnCl2. Bio-MnOx-C was characterized by SEM, TEM, IR, XPS, XRD, etc. It contained C, O, and Mn which comprised Mn (IV) and Mn (III) valence states at a ratio of 3.81:1. It had poorly crystalline ?-MnO2 with a specific surface area of 130.94m(2)/g. A total of 0.1g Bio-MnOx-C could remove 45.95g IC from 500mg/L IC solution after 0.5h contact time. IC removal by Bio-MnOx-C included a rapid oxidation reaction and the removal reaction followed second-order kinetic equation. These results confirmed that Bio-MnOx-C could be a potential material for wastewater remediation. PMID:26595178

  16. ROLE OF IRON AND MANGANESE OXIDES IN BIOSOLIDS AND BIOSOLIDS-AMENDED SOILS ON METAL BINDING

    EPA Science Inventory

    Biosolids contain high levels of Fe, Mn, and Al. Surfaces of freshly precipitated metal oxides, especially Fe and Mn, are known to be highly active sites for most dissolved metal ion species. We nw have metal sorption/desorption data that illustrate the importance of Fe and Mn fr...

  17. Enhancement Effect of Noble Metals on Manganese Oxide for the Oxygen Evolution Reaction.

    PubMed

    Seitz, Linsey C; Hersbach, Thomas J P; Nordlund, Dennis; Jaramillo, Thomas F

    2015-10-15

    Developing improved catalysts for the oxygen evolution reaction (OER) is key to the advancement of a number of renewable energy technologies, including solar fuels production and metal air batteries. In this study, we employ electrochemical methods and synchrotron techniques to systematically investigate interactions between metal oxides and noble metals that lead to enhanced OER catalysis for water oxidation. In particular, we synthesize porous MnOx films together with nanoparticles of Au, Pd, Pt, or Ag and observe significant improvement in activity for the combined catalysts. Soft X-ray absorption spectroscopy (XAS) shows that increased activity correlates with increased Mn oxidation states to 4+ under OER conditions compared to bare MnOx, which exhibits minimal OER current and remains in a 3+ oxidation state. Thickness studies of bare MnOx films and of MnOx films deposited on Au nanoparticles reveal trends suggesting that the enhancement in activity arises from interfacial sites between Au and MnOx. PMID:26722794

  18. Patterns of sheath elongation, cell proliferation, and manganese(II) oxidation in Leptothrix cholodnii.

    PubMed

    Takeda, Minoru; Kawasaki, Yuta; Umezu, Takuto; Shimura, Shoichi; Hasegawa, Makoto; Koizumi, Jun-ichi

    2012-08-01

    Leptothrix cholodnii is a Mn(II)-oxidizing and sheath-forming member of the class ?-Proteobacteria. Its sheath is a microtube-like filament that contains a chain of cells. From a chemical perspective, the sheath can be described as a supermolecule composed of a cysteine-rich polymeric glycoconjugate, called thiopeptidoglycan. However, the mechanism that controls the increase in sheath length is unknown. In this study, we attempted to detect sheath elongation through microscopic examination by using conventional reagents. Selective fluorescent labeling of preexisting or newly formed regions of the sheath was accomplished using combinations of biotin-conjugated maleimide, propionate-conjugated maleimide, and a fluorescent antibiotin antibody. Epifluorescence microscopy indicated that the sheath elongates at the terminal regions. On the bases of this observation, we assumed that the newly secreted thiopeptidoglycan molecules are integrated into the preexisting sheath at its terminal ends. Successive phase-contrast microscopy revealed that all cells proliferate at nearly the same rate regardless of their positions within the sheath. Mn(II) oxidation in microcultures was also examined with respect to cultivation time. Results suggested that the deposition of Mn oxides is notable in the aged regions. The combined data reveal the spatiotemporal relationships among sheath elongation, cell proliferation, and Mn oxide deposition in L. cholodnii. PMID:22392226

  19. In situ control of the oxide layer on thermally evaporated titanium and lysozyme adsorption by means of electrochemical quartz crystal microbalance with dissipation.

    PubMed

    Van De Keere, Isabel; Svedhem, Sofia; Hgberg, Hans; Vereecken, Jean; Kasemo, Bengt; Hubin, Annick

    2009-02-01

    Electrochemical (EC) quartz crystal microbalance with dissipation monitoring (ECQCM-D) is a new and powerful technique for the in situ study of adsorption phenomena, e.g., as a function of the potential of the substrate. When titanium (Ti) is employed as the substrate, its oxidation behavior needs to be taken into account. Ti is always covered with a native oxide layer that can grow by, e.g., thermal oxidation or under anodic polarization. For biomolecular adsorption studies on oxidized Ti under applied potential, a stable oxide layer is desired in order to be able to distinguish the adsorption phenomena and the oxide growth. Therefore, the oxidation of thermally evaporated Ti films was investigated in phosphate-buffered saline by means of ECQCM-D, using a specially designed EC flow cell. Upon stepping the potential applied to Ti up to 2.6 V vs standard hydrogen electrode (SHE), a fast increase of the mass was observed initially for each potential step, evolving slowly to an asymptotic mass change after several hours. The oxide layer thickness increased as a quasi-linear function of the oxidation potential for potentials up to 1.8 V vs SHE. The growth rate of the oxide was around 2.5-3 nm/V. No changes in the dissipation shift were observed for potentials up to 1.8 V vs SHE. The composition of the oxide layer was analyzed by X-ray photoelectron spectroscopy (XPS). It was mainly composed of TiO(2), with a small percentage of suboxides (TiO and Ti(2)O(3)) primarily at the inner metal/oxide interface. The amount of TiO(2) increased, and that of TiO and Ti(2)O(3) decreased, with increasing oxidation potential. For each oxidation potential, the calculated thickness obtained from ECQCM-D correlated well with the thickness obtained by XPS depth profiling. A procedure to prepare Ti samples with a stable oxide layer was successfully established for investigations on the influence of an electric field on the adsorption of biomolecules. As such, the effect of an applied potential on the adsorption behavior of lysozyme on oxidized Ti was investigated. It was observed that the adsorption of lysozyme on oxidized Ti was not influenced by the applied potential. PMID:20353217

  20. The inhibitory effect of manganese on acetylcholinesterase activity enhances oxidative stress and neuroinflammation in the rat brain

    PubMed Central

    Santos, Dinamene; Milatovic, Dejan; Andrade, Vanda; Camila, Batoreu M.; Aschner, Michael; Marreilha dos Santos, A.P.

    2011-01-01

    Background Manganese (Mn) is a naturally occurring element and an essential nutrient for humans and animals. However, exposure to high levels of Mn may cause neurotoxic effects. The pathological mechanisms associated with Mn neurotoxicity are poorly understood, but several reports have established it is mediated, at least in part, by oxidative stress. Objectives The present study was undertaken to test the hypothesis that a decrease in acetylcholinesterase (AChE) activity mediates Mn-induced neurotoxicity. Methods Groups of 6 rats received 4 or 8 intraperitoneal (i.p.) injections of 25 mg MnCl2/kg/day, every 48 hours. Twenty-four hours after the last injection, brain AChE activity and the levels of F2-isoprostanes (F2-IsoPs) and F4-neuroprostanes (F4-NPs) (biomarkers of oxidative stress), as well as prostaglandin E2 (PGE2) (biomarker of neuroinflammation) were analyzed. Results The results showed that after either 4 or 8 Mn doses, brain AChE activity was significantly decreased (p<0.05), to 60 ± 16 % and 55 ± 13 % of control levels, respectively. Both treated groups exhibited clear signs of neurobehavioral toxicity, characterized by a significant (p<0.001) decrease in ambulation and rearings in open-field. Furthermore, Mn treatment caused a significant increase (p<0.05) in brain F2-IsoPs and PGE2 levels, but only after 8 doses. In rats treated with 4 Mn doses, a significant increase (p<0.05) in brain F4-NPs levels was found. To evaluate cellular responses to oxidative stress, we assessed brain nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) and Mn-superoxide dismutase (Mn-SOD, SOD2) protein expression levels. A significant increase in Mn-SOD protein expression (p<0.05) and a trend towards increased Nrf2 protein expression was noted in rat brains after 4 Mn doses vs. the control group, but the expression of these proteins was decreased after 8 Mn doses. Taken together, these results suggest that the inhibitory effect of Mn on AChE activity promotes increased neuronal oxidative stress and neuroinflammatory biomarkers. PMID:22154916

  1. Protective effects of antioxidants and anti-inflammatory agents against manganese-induced oxidative damage and neuronal injury

    PubMed Central

    Milatovic, Dejan; Gupta, Ramesh C.; Yu, Yingchun; Zaja-Milatovic, Snjezana; Aschner, Michael

    2011-01-01

    Exposure to excessive manganese (Mn) levels leads to neurotoxicity, referred to as manganism, which resembles Parkinsons disease (PD). Manganism is caused by neuronal injury in both cortical and subcortical regions, particularly in the basal ganglia. The basis for the selective neurotoxicity of Mn is not yet fully understood. However, several studies suggest that oxidative damage and inflammatory processes play prominent roles in the degeneration of dopamine-containing neurons. In the present study, we assessed the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates and associated neuronal dysfunctions both in vitro and in vivo. Results from our in vitro study showed a significant (P<0.01) increase in biomarkers of oxidative damage, F2-isoprostanes (F2-IsoPs), as well as the depletion of ATP in primary rat cortical neurons following exposure to Mn (500 M) for 2 hours. These effects were protected when neurons were pretreated for 30 min with 100 M of an antioxidant, the hydrophilic vitamin E analog, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), or an anti-inflammatory agent, indomethacin. Results from our in vivo study confirmed a significant increase in F2-IsoPs levels in conjunction with the progressive spine degeneration and dendritic damage of the striatal medium spiny neurons (MSNs) of mice exposed to Mn (100 mg/kg, s.c.) 24 hours. Additionally, pretreatment with vitamin E (100 mg/kg, i.p.) or ibuprofen (140 g/ml in the drinking water for two weeks) attenuated the Mn-induced increase in cerebral F2-IsoPs and protected the MSNs from dendritic atrophy and dendritic spine loss. Our findings suggest that the mediation of oxidative stress/mitochondrial dysfunction and the control of alterations in biomarkers of oxidative injury, neuroinflammation and synaptodendritic degeneration may provide an effective, multi-pronged therapeutic strategy for protecting dysfunctional dopaminergic transmission and slowing of the progression of Mn-induced neurodegenerative processes. PMID:21684300

  2. Occupational exposure to welding fume among welders: alterations of manganese, iron, zinc, copper, and lead in body fluids and the oxidative stress status.

    PubMed

    Li, Guojun Jane; Zhang, Long-Lian; Lu, Ling; Wu, Ping; Zheng, Wei

    2004-03-01

    Welders in this study were selected from a vehicle manufacturer; control subjects were from a nearby food factory. Airborne manganese levels in the breathing zones of welders and controls were 1.45 +/- SD1.08 mg/m and 0.11 +/- 0.07 microg/m, respectively. Serum levels of manganese and iron in welders were 4.3-fold and 1.9-fold, respectively, higher than those of controls. Blood lead concentrations in welders increased 2.5-fold, whereas serum zinc levels decreased 1.2-fold, in comparison with controls. Linear regression revealed the lack of associations between blood levels of five metals and welder's age. Furthermore, welders had erythrocytic superoxide dismutase activity and serum malondialdehyde levels 24% less and 78% higher, respectively, than those of controls. These findings suggest that occupational exposure to welding fumes among welders disturbs the homeostasi