Benzene oxidation coupled to sulfate reduction

USGS Publications Warehouse

Lovley, D.R.; Coates, J.D.; Woodward, J.C.; Phillips, E.J.P.

1995-01-01

Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to I ??M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [14C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14CO2. Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14CO2 from [14C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [14C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p-hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O2, with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

Molecular Modeling of Environmentally Important Processes: Reduction Potentials

ERIC Educational Resources Information Center

Lewis, Anne; Bumpus, John A.; Truhlar, Donald G.; Cramer, Christopher J.

2004-01-01

The increasing use of computational quantum chemistry in the modeling of environmentally important processes is described. The employment of computational quantum mechanics for the prediction of oxidation-reduction potential for solutes in an aqueous medium is discussed.

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.

Voltage-induced reduction of graphene oxide

NASA Astrophysics Data System (ADS)

Faucett, Austin C.

Graphene Oxide (GO) is being widely researched as a precursor for the mass production of graphene, and as a versatile material in its own right for flexible electronics, chemical sensors, and energy harvesting applications. Reduction of GO, an electrically insulating material, into reduced graphene oxide (rGO) restores electrical conductivity via removal of oxygen-containing functional groups. Here, a reduction method using an applied electrical bias, known as voltage-induced reduction, is explored. Voltage-induced reduction can be performed under ambient conditions and avoids the use of hazardous chemicals or high temperatures common with standard methods, but little is known about the reduction mechanisms and the quality of rGO produced with this method. This work performs extensive structural and electrical characterization of voltage-reduced GO (V-rGO) and shows that it is competitive with standard methods. Beyond its potential use as a facile and eco-friendly processing approach, V-rGO reduction also offers record high-resolution patterning capabilities. In this work, the spatial resolution limits of voltage-induced reduction, performed using a conductive atomic force microscope probe, are explored. It is shown that arbitrary V-rGO conductive features can be patterned into insulating GO with nanoscale resolution. The localization of voltage-induced reduction to length scales < 10 nm allows studies of reduction reaction kinetics, using electrical current obtained in-situ, with statistical robustness. Methods for patterning V-rGO nanoribbons are then developed. After presenting sub-10nm patterning of V-rGO nanoribbons in GO single sheets and films, the performance of V-rGO nanoribbon field effect transistors (FETs) are demonstrated. Preliminary measurements show an increase in electrical current on/off ratios as compared to large-area rGO FETs, indicating transport gap modulation that is possibly due to quantum confinement effects.

Direct electrochemical reduction of solid uranium oxide in molten fluoride salts

NASA Astrophysics Data System (ADS)

Gibilaro, Mathieu; Cassayre, Laurent; Lemoine, Olivier; Massot, Laurent; Dugne, Olivier; Malmbeck, Rikard; Chamelot, Pierre

2011-07-01

The direct electrochemical reduction of UO 2 solid pellets was carried out in LiF-CaF 2 (+2 mass.% Li 2O) at 850 °C. An inert gold anode was used instead of the usual reactive sacrificial carbon anode. In this case, oxidation of oxide ions present in the melt yields O 2 gas evolution on the anode. Electrochemical characterisations of UO 2 pellets were performed by linear sweep voltammetry at 10 mV/s and reduction waves associated to oxide direct reduction were observed at a potential 150 mV more positive in comparison to the solvent reduction. Subsequent, galvanostatic electrolyses runs were carried out and products were characterised by SEM-EDX, EPMA/WDS, XRD and microhardness measurements. In one of the runs, uranium oxide was partially reduced and three phases were observed: nonreduced UO 2 in the centre, pure metallic uranium on the external layer and an intermediate phase representing the initial stage of reduction taking place at the grain boundaries. In another run, the UO 2 sample was fully reduced. Due to oxygen removal, the U matrix had a typical coral-like structure which is characteristic of the pattern observed after the electroreduction of solid oxides.

Stabilized tin-oxide-based oxidation/reduction catalysts

NASA Technical Reports Server (NTRS)

Watkins, Anthony Neal (Inventor); Oglesby, Donald M. (Inventor); Gulati, Suresh T. (Inventor); Summers, Jerry C. (Inventor); Schryer, David R. (Inventor); Davis, Patricia P. (Inventor); Leighty, Bradley D. (Inventor); Jordan, Jeffrey D. (Inventor); Schryer, Jacqueline L. (Inventor)

2008-01-01

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

Oxidation-reduction potential and lipid oxidation in ready-to-eat blue mussels in red sauce: criteria for package design.

PubMed

Bhunia, Kanishka; Ovissipour, Mahmoudreza; Rasco, Barbara; Tang, Juming; Sablani, Shyam S

2017-01-01

Ready-to-eat in-package pasteurized blue mussels in red sauce requires refrigerated storage or in combination with an aerobic environment to prevent the growth of anaerobes. A low barrier packaging may create an aerobic environment; however, it causes lipid oxidation in mussels. Thus, evaluation of the oxidation-reduction potential (Eh) (aerobic/anaerobic nature of food) and lipid oxidation is essential. Three packaging materials with oxygen transmission rate (OTR) of 62 (F-62), 40 (F-40) and 3 (F-3) cm 3 m -2 day -1 were selected for this study. Lipid oxidation was measured by color changes in thiobarbituric acid reactive substances (TBARS) at 532 nm (TBARS@532) and 450 nm (TBARS@450). Significantly higher (P < 0.05) TBARS@532 was found in mussels packaged in higher OTR film. TBARS@450 in mussels packaged with F-62 and F-40 gradually increased during refrigerated storage (3.5 ± 0.5 °C), but remained constant after 20 days of storage for mussels packaged with F-3. The Eh of pasteurized sauce was not significantly affected (P > 0.05) by OTR and remained negative (< -80 mV) during storage. Negative Eh values can support the growth of anaerobes such as Clostridium botulinum. The headspace oxygen concentration was reduced by about 50% from its initial value during pasteurization, and then further declined during storage. The headspace oxygen concentration was higher in trays packaged with higher OTR film. Mussels packed with high OTR film showed higher lipid oxidation, indicating that high barrier film is required for packaging of mussels. Pasteurized mussels must be kept in refrigerated storage to prevent growth of anaerobic proteolytic C. botulinum spores under temperature abuse. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

Reduction of aqueous transition metal species on the surfaces of Fe(II) -containing oxides

NASA Astrophysics Data System (ADS)

White, Art F.; Peterson, Maria L.

1996-10-01

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25°C. For an aqueous transition metal m, such reactions are 3[FeFe23+]O+2/nm→4[Fe23+]O+Fe+2/nm and 3[FeTi]O+→Fe23+TiO+Fe+2/nm, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] → [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe 2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 × 10 -10 mol m -2 s -1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe 2+ is oxidized homogeneously in solution to Fe 3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show

A review on photocatalytic CO2 reduction using perovskite oxide nanomaterials

NASA Astrophysics Data System (ADS)

Zeng, Sheng; Kar, Piyush; Thakur, Ujwal Kumar; Shankar, Karthik

2018-02-01

As the search for efficient catalysts for CO2 photoreduction continues, nanostructured perovskite oxides have emerged as a class of high-performance photocatalytic materials. The perovskite oxide candidates for CO2 photoreduction are primarily nanostructured forms of titanates, niobates, tantalates and cobaltates. These materials form the focus of this review article because they are much sought-after due to their nontoxic nature, adequate chemical stability, and tunable crystal structures, bandgaps and surface energies. As compared to conventional semiconductors and nanomaterial catalysts, nanostructured perovskite oxides also exhibit an extended optical-absorption edge, longer charge carrier lifetimes, and favorable band-alignment with respect to reduction potential of activated CO2 and reduction products of the same. While CO2 reduction product yields of several hundred μmol-1 h-1 are observed with many types of perovskite oxide nanomaterials in stand-alone forms, yield of such quantities are not common with semiconductor nanomaterials of other types. In this review, we present current state-of-the-art synthesis methods to form perovskite oxide nanomaterials, and procedures to engineer their bandgaps. This review also presents a comprehensive summary and discussion on crystal structures, defect distribution, morphologies and electronic properties of the perovskite oxides, and correlation of these properties to CO2 photoreduction performance. This review offers researchers key insights for developing advanced perovskite oxides in order to further improve the yields of CO2 reduction products.

Oxidation-Reduction Resistance of Advanced Copper Alloys

NASA Technical Reports Server (NTRS)

Greenbauer-Seng, L. (Technical Monitor); Thomas-Ogbuji, L.; Humphrey, D. L.; Setlock, J. A.

2003-01-01

Resistance to oxidation and blanching is a key issue for advanced copper alloys under development for NASA's next generation of reusable launch vehicles. Candidate alloys, including dispersion-strengthened Cu-Cr-Nb, solution-strengthened Cu-Ag-Zr, and ODS Cu-Al2O3, are being evaluated for oxidation resistance by static TGA exposures in low-p(O2) and cyclic oxidation in air, and by cyclic oxidation-reduction exposures (using air for oxidation and CO/CO2 or H2/Ar for reduction) to simulate expected service environments. The test protocol and results are presented.

Effects of oxidation reduction potential in the bypass micro-aerobic sludge zone on sludge reduction for a modified oxic-settling-anaerobic process.

PubMed

Li, Kexun; Wang, Yi; Zhang, Zhongpin; Liu, Dongfang

2014-01-01

Batch experiments were conducted to determine the effect of oxidation reduction potential (ORP) on sludge reduction in a bypass micro-aerobic sludge reduction system. The system was composed of a modified oxic-settling-anaerobic process with a sludge holding tank in the sludge recycle loop. The ORPs in the micro-aerobic tanks were set at approximately +350, -90, -150, -200 and -250 mV, by varying the length of aeration time for the tanks. The results show that lower ORP result in greater sludge volume reduction, and the sludge production was reduced by 60% at the lowest ORP. In addition, low ORP caused extracellular polymer substances dissociation and slightly reduced sludge activity. Comparing the sludge backflow characteristics of the micro-aerobic tank's ORP controlled at -250 mV with that of +350 mV, the average soluble chemical oxygen (SCOD), TN and TP increased by 7, 0.4 and 2 times, median particle diameter decreased by 8.5 μm and the specific oxygen uptake rate (SOUR) decreased by 0.0043 milligram O2 per gram suspended solids per minute. For the effluent, SCOD and TN and TP fluctuated around 30, 8.7 and 0.66 mg/L, respectively. Therefore, the effective assignment of ORP in the micro-aerobic tank can remarkably reduce sludge volume and does not affect final effluent quality.

Oxidative shift in tissue redox potential increases beat-to-beat variability of action potential duration.

PubMed

Kistamás, Kornél; Hegyi, Bence; Váczi, Krisztina; Horváth, Balázs; Bányász, Tamás; Magyar, János; Szentandrássy, Norbert; Nánási, Péter P

2015-07-01

Profound changes in tissue redox potential occur in the heart under conditions of oxidative stress frequently associated with cardiac arrhythmias. Since beat-to-beat variability (short term variability, SV) of action potential duration (APD) is a good indicator of arrhythmia incidence, the aim of this work was to study the influence of redox changes on SV in isolated canine ventricular cardiomyocytes using a conventional microelectrode technique. The redox potential was shifted toward a reduced state using a reductive cocktail (containing dithiothreitol, glutathione, and ascorbic acid) while oxidative changes were initiated by superfusion with H2O2. Redox effects were evaluated as changes in "relative SV" determined by comparing SV changes with the concomitant APD changes. Exposure of myocytes to the reductive cocktail decreased SV significantly without any detectable effect on APD. Application of H2O2 increased both SV and APD, but the enhancement of SV was the greater, so relative SV increased. Longer exposure to H2O2 resulted in the development of early afterdepolarizations accompanied by tremendously increased SV. Pretreatment with the reductive cocktail prevented both elevation in relative SV and the development of afterdepolarizations. The results suggest that the increased beat-to-beat variability during an oxidative stress contributes to the generation of cardiac arrhythmias.

Oxide reduction during triggered-lightning fulgurite formation

NASA Astrophysics Data System (ADS)

Jones, B. E.; Jones, K. S.; Rambo, K. J.; Rakov, V. A.; Jerald, J.; Uman, M. A.

2005-03-01

In this study triggered-lightning induced fulgurites were formed in 99.9% pure binary oxides of manganese (MnO) and nickel (NiO) in order to study oxide reduction mechanisms. The fulgurite formation process involved packing the oxide in PVC holders and using the standard rocket-and-wire technique to trigger a lightning strike through the oxide at the International Center for Lightning Research and Testing in Camp Blanding, Florida. These two oxides were chosen from the thermodynamic extrapolation of the oxide stability using the Ellingham Diagram. This diagram indicates that NiO is significantly less stable than MnO. Fulgurites from the pure oxides were analyzed in a scanning electron microscope (SEM); secondary electron images, backscattered images and energy dispersive spectroscopy (EDS) were used to determine the microstructure and composition of the fulgurites. SEM/EDS analysis of the NiO and MnO prior to fulgurite formation confirmed they were pure binary oxides with no metallic contamination. After fulgurite formation, it was found that the nickel oxide fulgurite contained metallic nickel particles; the manganese oxide fulgurite showed no metallic phase formation. Transmission electron microscopy (TEM) examination confirmed that the MnO was a pure oxide with no sign of metallic phase formation. However, TEM results of the NiO showed that approximately 50% of the NiO was reduced to metallic face-centered cubic Ni. The Ni and NiO were observed to be coherent with the [1 0 0]Ni//[1 0 0]NiO and [1 1 0]Ni//[1 1 0]NiO. These results are consistent with the aforementioned thermodynamic stability calculations and show that the presence of carbonaceous material or mixtures of oxides is not necessary for oxide reduction during fulgurite formation. These studies do not rule out the possibility that electrolysis plays a role in oxide reduction. However, these fulgurites were made simultaneously during the same lightning strike and therefore were subjected to the same

Analysis of flow decay potential on Galileo. [oxidizer flow rate reduction by iron nitrate precipitates

NASA Technical Reports Server (NTRS)

Cole, T. W.; Frisbee, R. H.; Yavrouian, A. H.

1987-01-01

The risks posed to the NASA's Galileo spacecraft by the oxidizer flow decay during its extended mission to Jupiter is discussed. The Galileo spacecraft will use nitrogen tetroxide (NTO)/monomethyl hydrazine bipropellant system with one large engine thrust-rated at a nominal 400 N, and 12 smaller engines each thrust-rated at a nominal 10 N. These smaller thrusters, because of their small valve inlet filters and small injector ports, are especially vulnerable to clogging by iron nitrate precipitates formed by NTO-wetted stainless steel components. To quantify the corrosion rates and solubility levels which will be seen during the Galileo mission, corrosion and solubility testing experiments were performed with simulated Galileo materials, propellants, and environments. The results show the potential benefits of propellant sieving in terms of iron and water impurity reduction.

Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides

USGS Publications Warehouse

White, A.F.; Peterson, M.L.

1996-01-01

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25??C. For an aqueous transition metal m, such reactions are 3[Fe2+Fe3+2]O4(magnetite) + 2/nmz ??? 4[Fe3+2]O3(maghemite) + Fe2+ + 2/nmz-n and 3[Fe2+Ti]O3(ilmenite) + 2/nmz ??? Fe3+2Ti3O9(pseudorutile) + Fe2+ + 2/nmz-n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] ??? [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 ?? 10-10 mol m-2 s-1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe2+ is oxidized homogeneously in solution to Fe3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental

Reconstructing metabolic pathways of a member of the genus Pelotomaculum suggesting its potential to oxidize benzene to carbon dioxide with direct reduction of sulfate.

PubMed

Dong, Xiyang; Dröge, Johannes; von Toerne, Christine; Marozava, Sviatlana; McHardy, Alice C; Meckenstock, Rainer U

2017-03-01

The enrichment culture BPL is able to degrade benzene with sulfate as electron acceptor and is dominated by an organism of the genus Pelotomaculum. Members of Pelotomaculum are usually known to be fermenters, undergoing syntrophy with anaerobic respiring microorganisms or methanogens. By using a metagenomic approach, we reconstructed a high-quality genome (∼2.97 Mbp, 99% completeness) for Pelotomaculum candidate BPL. The proteogenomic data suggested that (1) anaerobic benzene degradation was activated by a yet unknown mechanism for conversion of benzene to benzoyl-CoA; (2) the central benzoyl-CoA degradation pathway involved reductive dearomatization by a class II benzoyl-CoA reductase followed by hydrolytic ring cleavage and modified β-oxidation; (3) the oxidative acetyl-CoA pathway was utilized for complete oxidation to CO2. Interestingly, the genome of Pelotomaculum candidate BPL has all the genes for a complete sulfate reduction pathway including a similar electron transfer mechanism for dissimilatory sulfate reduction as in other Gram-positive sulfate-reducing bacteria. The proteome analysis revealed that the essential enzymes for sulfate reduction were all formed during growth with benzene. Thus, our data indicated that, besides its potential to anaerobically degrade benzene, Pelotomaculum candidate BPL is the first member of the genus that can perform sulfate reduction. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Phyto-reduction of graphene oxide using the aqueous extract of Eichhornia crassipes (Mart.) Solms

NASA Astrophysics Data System (ADS)

Firdhouse, M. Jannathul; Lalitha, P.

2014-10-01

The aqueous extract of Eichhornia crassipes was used as reductant to produce graphene from graphene oxide by refluxing method. The complete reduction of graphene oxide was monitored using UV-Vis spectrophotometer. Characterization of graphene was made through FTIR, XRD, and Raman spectroscopy analysis. The stability of graphene was studied by thermal gravimetric analysis and zeta potential measurements. The nature and surface morphology of the synthesized graphene was analyzed by transmission electron microscopy. The production of graphene using phytoextract as reductant emphasizes on the facile method of synthesis and greener nanotechnology.

Influence on the oxidative potential of a heavy-duty engine particle emission due to selective catalytic reduction system and biodiesel blend.

PubMed

Godoi, Ricardo H M; Polezer, Gabriela; Borillo, Guilherme C; Brown, Andrew; Valebona, Fabio B; Silva, Thiago O B; Ingberman, Aline B G; Nalin, Marcelo; Yamamoto, Carlos I; Potgieter-Vermaak, Sanja; Penteado Neto, Renato A; de Marchi, Mary Rosa R; Saldiva, Paulo H N; Pauliquevis, Theotonio; Godoi, Ana Flavia L

2016-08-01

Although the particulate matter (PM) emissions from biodiesel fuelled engines are acknowledged to be lower than those of fossil diesel, there is a concern on the impact of PM produced by biodiesel to human health. As the oxidative potential of PM has been suggested as trigger for adverse health effects, it was measured using the Electron Spin Resonance (OP(ESR)) technique. Additionally, Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF) was employed to determine elemental concentration, and Raman Spectroscopy was used to describe the amorphous carbon character of the soot collected on exhaust PM from biodiesel blends fuelled test-bed engine, with and without Selective Catalytic Reduction (SCR). OP(ESR) results showed higher oxidative potential per kWh of PM produced from a blend of 20% soybean biodiesel and 80% ULSD (B20) engine compared with a blend of 5% soybean biodiesel and 95% ULSD (B5), whereas the SCR was able to reduce oxidative potential for each fuel. EDXRF data indicates a correlation of 0.99 between concentration of copper and oxidative potential. Raman Spectroscopy centered on the expected carbon peaks between 1100cm(-1) and 1600cm(-1) indicate lower molecular disorder for the B20 particulate matter, an indicative of a more graphitic carbon structure. The analytical techniques used in this study highlight the link between biodiesel engine exhaust and increased oxidative potential relative to biodiesel addition on fossil diesel combustion. The EDXRF analysis confirmed the prominent role of metals on free radical production. As a whole, these results suggest that 20% of biodiesel blends run without SCR may pose an increased health risk due to an increase in OH radical generation. Copyright © 2015 Elsevier B.V. All rights reserved.

Reduction Rates for Higher Americium Oxidation States in Nitric Acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grimes, Travis Shane; Mincher, Bruce Jay; Schmitt, Nicholas C

The stability of hexavalent americium was measured using multiple americium concentrations and nitric acid concentrations after contact with the strong oxidant sodium bismuthate. Contrary to our hypotheses Am(VI) was not reduced faster at higher americium concentrations, and the reduction was only zero-order at short time scales. Attempts to model the reduction kinetics using zero order kinetic models showed Am(VI) reduction in nitric acid is more complex than the autoreduction processes reported by others in perchloric acid. The classical zero-order reduction of Am(VI) was found here only for short times on the order of a few hours. We did show thatmore » the rate of Am(V) production was less than the rate of Am(VI) reduction, indicating that some Am(VI) undergoes two electron-reduction to Am(IV). We also monitored the Am(VI) reduction in contact with the organic diluent dodecane. A direct comparison of these results with those in the absence of the organic diluent showed the reduction rates for Am(VI) were not statistically different for both systems. Additional americium oxidations conducted in the presence of Ce(IV)/Ce(III) ions showed that Am(VI) is reduced without the typical growth of Am(V) observed in the systems sans Ce ion. This was an interesting result which suggests a potential new reduction/oxidation pathway for Am in the presence of Ce; however, these results were very preliminary, and will require additional experiments to understand the mechanism by which this occurs. Overall, these studies have shown that hexavalent americium is fundamentally stable enough in nitric acid to run a separations process. However, the complicated nature of the reduction pathways based on the system components is far from being rigorously understood.« less

Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens

PubMed Central

Levar, Caleb E; Hoffman, Colleen L; Dunshee, Aubrey J; Toner, Brandy M; Bond, Daniel R

2017-01-01

Geobacter sulfurreducens uses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of –0.10 V vs the standard hydrogen electrode, whereas the ImcH-dependent pathway operates only above this value. Here, we provide evidence that G. sulfurreducens also requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)-(oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high-potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment. PMID:28045456

Lithium metal reduction of plutonium oxide to produce plutonium metal

DOEpatents

Coops, Melvin S.

1992-01-01

A method is described for the chemical reduction of plutonium oxides to plutonium metal by the use of pure lithium metal. Lithium metal is used to reduce plutonium oxide to alpha plutonium metal (alpha-Pu). The lithium oxide by-product is reclaimed by sublimation and converted to the chloride salt, and after electrolysis, is removed as lithium metal. Zinc may be used as a solvent metal to improve thermodynamics of the reduction reaction at lower temperatures. Lithium metal reduction enables plutonium oxide reduction without the production of huge quantities of CaO--CaCl.sub.2 residues normally produced in conventional direct oxide reduction processes.

In-situ sequential laser transfer and laser reduction of graphene oxide films

NASA Astrophysics Data System (ADS)

Papazoglou, S.; Petridis, C.; Kymakis, E.; Kennou, S.; Raptis, Y. S.; Chatzandroulis, S.; Zergioti, I.

2018-04-01

Achieving high quality transfer of graphene on selected substrates is a priority in device fabrication, especially where drop-on-demand applications are involved. In this work, we report an in-situ, fast, simple, and one step process that resulted in the reduction, transfer, and fabrication of reduced graphene oxide-based humidity sensors, using picosecond laser pulses. By tuning the laser illumination parameters, we managed to implement the sequential printing and reduction of graphene oxide flakes. The overall process lasted only a few seconds compared to a few hours that our group has previously published. DC current measurements, X-Ray Photoelectron Spectroscopy, X-Ray Diffraction, and Raman Spectroscopy were employed in order to assess the efficiency of our approach. To demonstrate the applicability and the potential of the technique, laser printed reduced graphene oxide humidity sensors with a limit of detection of 1700 ppm are presented. The results demonstrated in this work provide a selective, rapid, and low-cost approach for sequential transfer and photochemical reduction of graphene oxide micro-patterns onto various substrates for flexible electronics and sensor applications.

Direct observation of spatially heterogeneous single-layer graphene oxide reduction kinetics.

PubMed

McDonald, Matthew P; Eltom, Ahmed; Vietmeyer, Felix; Thapa, Janak; Morozov, Yurii V; Sokolov, Denis A; Hodak, Jose H; Vinodgopal, Kizhanipuram; Kamat, Prashant V; Kuno, Masaru

2013-01-01

Graphene oxide (GO) is an important precursor in the production of chemically derived graphene. During reduction, GO's electrical conductivity and band gap change gradually. Doping and chemical functionalization are also possible, illustrating GO's immense potential in creating functional devices through control of its local hybridization. Here we show that laser-induced photolysis controllably reduces individual single-layer GO sheets. The reaction can be followed in real time through sizable decreases in GO's photoluminescence efficiency along with spectral blueshifts. As-produced reduced graphene oxide (rGO) sheets undergo additional photolysis, characterized by dramatic emission enhancements and spectral redshifts. Both GO's reduction and subsequent conversion to photobrightened rGO are captured through movies of their photoluminescence kinetics. Rate maps illustrate sizable spatial and temporal heterogeneities in sp(2) domain growth and reveal how reduction "flows" across GO and rGO sheets. The observed heterogeneous reduction kinetics provides mechanistic insight into GO's conversion to chemically derived graphene and highlights opportunities for overcoming its dynamic, chemical disorder.

Fluctuation Analysis of Redox Potential to Distinguish Microbial Fe(II) Oxidation.

PubMed

Enright, A M L; Ferris, F G

2016-11-01

We developed a novel method for distinguishing abiotic and biological iron oxidation in liquid media using oxidation-reduction (redox) potential time series data. The instrument and processing algorithm were tested by immersing the tip of a Pt electrode with an Ag-AgCl reference electrode into an active iron-oxidizing biofilm in a groundwater discharge zone, as well as in two abiotic systems: a killed sample and a chemical control from the same site. We used detrended fluctuation analysis to characterize average root mean square fluctuation behavior, which was distinct in the live system. The calculated α value scaling exponents determined by detrended fluctuation analysis were significantly different at p < 0.001. This indicates that time series of electrode response data may be used to distinguish live and abiotic chemical reaction pathways. Due to the simplicity, portability, and small size, it may be suitable for characterization of extraterrestrial environments where water has been observed, such as Mars and Europa. Key Words: Oxidation-reduction potential-Detrended fluctuation analysis-Iron-oxidizing bacteria. Astrobiology 16, 846-852.

Simultaneous reduction and nitrogen functionalization of graphene oxide using lemon for metal-free oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Begum, Halima; Ahmed, Mohammad Shamsuddin; Cho, Sung; Jeon, Seungwon

2017-12-01

Inspire by the vision of finding a simple and green method for simultaneous reduction and nitrogen (N)-functionalization of graphene oxide (GO), a N-rich reduced graphene oxide (rGO) has been synthesized through a facile and ecofriendly hydrothermal strategy while most of the existing methods are involving with multiple steps and highly toxic reducing agents that are harmful to human health and environment. In this paper, the simultaneous reduction and N-functionalization of GO using as available lemon juice (denoted as Lem-rGO) for metal-free electrocatalysis towards oxygen reduction reaction (ORR) is described. The proposed method is based on the reduction of GO using of the reducing and the N-precursor capability of ascorbic acid and citric acid as well as the nitrogenous compounds, respectively, that containing in lemon juice. The resultant Lem-rGO has higher reduction degree, higher specific surface area and better crystalline nature with N-incorporation than that of well investigated ascorbic acid and citric acid treated rGO. As a result, it shows better ORR electrocatalytic activity in respect to the improved onset potential, electron transfer rate and kinetics than those typical rGO catalysts. Moreover, it shows a significant tolerance to the anodic fuels and durability than the Pt/C during ORR.

Oxidation-reduction catalyst and its process of use

NASA Technical Reports Server (NTRS)

Schryer, Jacqueline L. (Inventor); Oglesby, Donald M. (Inventor); Jordan, Jeffrey D. (Inventor); Watkins, Anthony Neal (Inventor)

2008-01-01

This invention relates generally to a ruthenium stabilized oxidation-reduction catalyst useful for oxidizing carbon monoxide, and volatile organic compounds, and reducing nitrogen oxide species in oxidizing environments, substantially without the formation of toxic and volatile ruthenium oxide species upon said oxidizing environment being at high temperatures.

Investigation of iron oxide reduction by TEM

NASA Astrophysics Data System (ADS)

Rau, Mann-Fu; Rieck, David; Evans, James W.

1987-03-01

An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction; during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite; at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction in the hydrogen-argon mixture was slower than in pure hydrogen.

Reduction of metal oxides through mechanochemical processing

DOEpatents

Froes, Francis H.; Eranezhuth, Baburaj G.; Senkov, Oleg N.

2000-01-01

The low temperature reduction of a metal oxide using mechanochemical processing techniques. The reduction reactions are induced mechanically by milling the reactants. In one embodiment of the invention, titanium oxide TiO.sub.2 is milled with CaH.sub.2 to produce TiH.sub.2. Low temperature heat treating, in the range of 400.degree. C. to 700.degree. C., can be used to remove the hydrogen in the titanium hydride.

Nitrous oxide production kinetics during nitrate reduction in river sediments.

PubMed

Laverman, Anniet M; Garnier, Josette A; Mounier, Emmanuelle M; Roose-Amsaleg, Céline L

2010-03-01

A significant amount of nitrogen entering river basins is denitrified in riparian zones. The aim of this study was to evaluate the influence of nitrate and carbon concentrations on the kinetic parameters of nitrate reduction as well as nitrous oxide emissions in river sediments in a tributary of the Marne (the Seine basin, France). In order to determine these rates, we used flow-through reactors (FTRs) and slurry incubations; flow-through reactors allow determination of rates on intact sediment slices under controlled conditions compared to sediment homogenization in the often used slurry technique. Maximum nitrate reduction rates (R(m)) ranged between 3.0 and 7.1microg Ng(-1)h(-1), and affinity constant (K(m)) ranged from 7.4 to 30.7mg N-NO(3)(-)L(-1). These values were higher in slurry incubations with an R(m) of 37.9microg Ng(-1)h(-1) and a K(m) of 104mg N-NO(3)(-)L(-1). Nitrous oxide production rates did not follow Michaelis-Menten kinetics, and we deduced a rate constant with an average of 0.7 and 5.4ng Ng(-1)h(-1) for FTR and slurry experiments respectively. The addition of carbon (as acetate) showed that carbon was not limiting nitrate reduction rates in these sediments. Similar rates were obtained for FTR and slurries with carbon addition, confirming the hypothesis that homogenization increases rates due to release of and increasing access to carbon in slurries. Nitrous oxide production rates in FTR with carbon additions were low and represented less than 0.01% of the nitrate reduction rates and were even negligible in slurries. Maximum nitrate reduction rates revealed seasonality with high potential rates in fall and winter and low rates in late spring and summer. Under optimal conditions (anoxia, non-limiting nitrate and carbon), nitrous oxide emission rates were low, but significant (0.01% of the nitrate reduction rates). Copyright 2009 Elsevier Ltd. All rights reserved.

Mechanistic investigation of Fe(III) oxide reduction by low molecular weight organic sulfur species

NASA Astrophysics Data System (ADS)

Eitel, Eryn M.; Taillefert, Martial

2017-10-01

Low molecular weight organic sulfur species, often referred to as thiols, are known to be ubiquitous in aquatic environments and represent important chemical reductants of Fe(III) oxides. Thiols are excellent electron shuttles used during dissimilatory iron reduction, and in this capacity could indirectly affect the redox state of sediments, release adsorbed contaminants via reductive dissolution, and influence the carbon cycle through alteration of bacterial respiration processes. Interestingly, the reduction of Fe(III) oxides by thiols has not been previously investigated in environmentally relevant conditions, likely due to analytical limitations associated with the detection of thiols and their oxidized products. In this study, a novel electrochemical method was developed to simultaneously determine thiol/disulfide pair concentrations in situ during the reduction of ferrihydrite in batch reactors. First order rate laws with respect to initial thiol concentration were confirmed for Fe(III) oxyhydroxide reduction by four common thiols: cysteine, homocysteine, cysteamine, and glutathione. Zero order was determined for both Fe(III) oxyhydroxide and proton concentration at circumneutral pH. A kinetic model detailing the molecular mechanism of the reaction was optimized with proposed intermediate surface structures. Although metal oxide overall reduction rate constants were inversely proportional to the complexity of the thiol structure, the extent of metal reduction increased with structure complexity, indicating that surface complexes play a significant role in the ability of these thiols to reduce iron. Taken together, these results demonstrate the importance of considering the molecular reaction mechanism at the iron oxide surface when investigating the potential for thiols to act as electron shuttles during dissimilatory iron reduction in natural environments.

Analysis of long-term bacterial vs. chemical Fe(III) oxide reduction kinetics

NASA Astrophysics Data System (ADS)

Roden, Eric E.

2004-08-01

Data from studies of dissimilatory bacterial (10 8 cells mL -1 of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L -1) were analyzed in relation to a generalized rate law for mineral dissolution (J t/m 0 = k'(m/m 0) γ, where J t is the rate of dissolution and/or reduction at time t, m 0 is the initial mass of oxide, and m/m 0 is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher γ values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher γ values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to

Oxidation and Reduction Reactions in Organic Chemistry

ERIC Educational Resources Information Center

Shibley, Ivan A., Jr.; Amaral, Katie E.; Aurentz, David J.; McCaully, Ronald J.

2010-01-01

A variety of approaches to the concept of oxidation and reduction appear in organic textbooks. The method proposed here is different than most published approaches. The oxidation state is calculated by totaling the number of heterogeneous atoms, [pi]-bonds, and rings. A comparison of the oxidation states of reactant and product determine what type…

Effects of Borax on the Reduction of Pre-oxidized Panzhihua Ilmenite

NASA Astrophysics Data System (ADS)

Guo, Yufeng; Zheng, Fuqiang; Jiang, Tao; Chen, Feng; Wang, Shuai; Qiu, Guanzhou

2018-01-01

The effects of borax (sodium borate) on the enhancement reduction of pre-oxidized Panzhihua ilmenite were investigated. The effects of borax on the mineral phase transformation, microstructures, crystal cell parameter, melting point and Mg distribution were studied to reveal the mechanism of enhancement reduction. Under the constant reduction conditions, the borax could reduce the reduction activation energy of pre-oxidized ilmenite. The reduction kinetics analysis indicated that the reduction rate was controlled by interfacial chemical reaction. The reduction activation energy of the pre-oxidized ilmenite with 4% borax was 80.263 kJ/mol, which was 28.585 kJ/mol less than that of the pre-oxidized ilmenite without borax. Borax could eliminate the migration of Mg into the reduced particle center. The crystal cell parameter of the reduced product was increased by adding borax. Borax could improve the growth of dendritic crystals in the pre-oxidized ilmenite.

Reduction of nitric oxide catalyzed by hydroxylamine oxidoreductase from an anammox bacterium.

PubMed

Irisa, Tatsuya; Hira, Daisuke; Furukawa, Kenji; Fujii, Takao

2014-12-01

The hydroxylamine oxidoreductase (HAO) from the anammox bacterium, Candidatus Kuenenia stuttgartiensis has been reported to catalyze the oxidation of hydroxylamine (NH2OH) to nitric oxide (NO) by using bovine cytochrome c as an oxidant. In contrast, we investigated whether the HAO from anammox bacterium strain KSU-1 could catalyze the reduction of NO with reduced benzyl viologen (BVred) and the NO-releasing reagent, NOC 7. The reduction proceeded, resulting in the formation of NH2OH as a product. The oxidation rate of BVred was proportional to the concentration of BVred itself for a short period in each experiment, a situation that was termed quasi-steady state. The analyses of the states at various concentrations of HAO allowed us to determine the rate constant for the catalytic reaction, (2.85 ± 0.19) × 10(5) M(-1) s(-1), governing NO reduction by BVred and HAO, which was comparable to that reported for the HAO from the ammonium oxidizer, Nitrosomonas with reduced methyl viologen. These results suggest that the anammox HAO functions to adjust anammox by inter-conversion of NO and NH2OH depending on the redox potential of the physiological electron transfer protein in anammox bacteria. Copyright © 2014 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity

PubMed Central

Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.

2013-01-01

Nanosize platinum clusters with small diameters of 2–4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

Reduced graphene oxide supported gold nanoparticles for electrocatalytic reduction of carbon dioxide

NASA Astrophysics Data System (ADS)

Saquib, Mohammad; Halder, Aditi

2018-02-01

Electrochemical reduction of carbon dioxide is one of the methods which have the capability to recycle CO2 into valuable products for energy and industrial applications. This research article describes about a new electrocatalyst "reduced graphene oxide supported gold nanoparticles" for selective electrochemical conversion of carbon dioxide to carbon monoxide. The main aim for conversion of CO2 to CO lies in the fact that the latter is an important component of syn gas (a mixture of hydrogen and carbon monoxide), which is then converted into liquid fuel via well-known industrial process called Fischer-Tropsch process. In this work, we have synthesized different composites of the gold nanoparticles supported on defective reduced graphene oxide to evaluate the catalytic activity of reduced graphene oxide (RGO)-supported gold nanoparticles and the role of defective RGO support towards the electrochemical reduction of CO2. Electrochemical and impedance measurements demonstrate that higher concentration of gold nanoparticles on the graphene support led to remarkable decrease in the onset potential of 240 mV and increase in the current density for CO2 reduction. Lower impedance and Tafel slope values also clearly support our findings for the better performance of RGOAu than bare Au for CO2 reduction.

In situ spectroscopic monitoring of CO2 reduction at copper oxide electrode.

PubMed

Wang, Liying; Gupta, Kalyani; Goodall, Josephine B M; Darr, Jawwad A; Holt, Katherine B

2017-04-28

Copper oxide modified electrodes were investigated as a function of applied electrode potential using in situ infrared spectroscopy and ex situ Raman and X-ray photoelectron spectroscopy. In deoxygenated KHCO 3 electrolyte bicarbonate and carbonate species were found to adsorb to the electrode during reduction and the CuO was reduced to Cu(i) or Cu(0) species. Carbonate was incorporated into the structure and the CuO starting material was not regenerated on cycling to positive potentials. In contrast, in CO 2 saturated KHCO 3 solution, surface adsorption of bicarbonate and carbonate was not observed and adsorption of a carbonato-species was observed with in situ infrared spectroscopy. This species is believed to be activated, bent CO 2 . On cycling to negative potentials, larger reduction currents were observed in the presence of CO 2 ; however, less of the charge could be attributed to the reduction of CuO. In the presence of CO 2 CuO underwent reduction to Cu 2 O and potentially Cu, with no incorporation of carbonate. Under these conditions the CuO starting material could be regenerated by cycling to positive potentials.

Proton translocation coupled to trimethylamine N-oxide reduction in anaerobically grown Escherichia coli.

PubMed Central

Takagi, M; Tsuchiya, T; Ishimoto, M

1981-01-01

Proton translocation coupled to trimethylamine N-oxide reduction was studied in Escherichia coli grown anaerobically in the presence of trimethylamine N-oxide. Rapid acidification of the medium was observed when trimethylamine N-oxide was added to anaerobic cell suspensions of E. coli K-10. Acidification was sensitive to the proton conductor 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF6847). No pH change was shown in a strain deficient in trimethylamine N-oxide reductase activity. The apparent H+/trimethylamine N-oxide ratio in cells oxidizing endogenous substrates was 3 to 4 g-ions of H+ translocated per mol of trimethylamine N-oxide added. The addition of trimethylamine N-oxide and formate to ethylenediaminetetraacetic acid-treated cell suspension caused fluorescence quenching of 3,3'-dipropylthiacarbocyanine [diS-C3-(5)], indicating the generation of membrane potential. These results indicate that the reduction of trimethylamine N-oxide in E. coli is catalyzed by an anaerobic electron transfer system, resulting in formation of a proton motive force. Trimethylamine N-oxide reductase activity and proton extrusion were also examined in chlorate-resistant mutants. Reduction of trimethylamine N-oxide occurred in chlC, chlG, and chlE mutants, whereas chlA, chlB, and chlD mutants, which are deficient in the molybdenum cofactor, could not reduce it. Protons were extruded in chlC and chlG mutants, but not in chlA, chlB, and chlD mutants. Trimethylamine N-oxide reductase activity in a chlD mutant was restored to the wild-type level by the addition of 100 microM molybdate to the growth medium, indicating that the same molybdenum cofactor as used by nitrate reductase is required for the trimethylamine N-oxide reductase system. PMID:7031034

Linking Thermodynamics to Pollutant Reduction Kinetics by Fe2+ Bound to Iron Oxides.

PubMed

Stewart, Sydney M; Hofstetter, Thomas B; Joshi, Prachi; Gorski, Christopher A

2018-05-15

Numerous studies have reported that pollutant reduction rates by ferrous iron (Fe 2+ ) are substantially enhanced in the presence of an iron (oxyhydr)oxide mineral. Developing a thermodynamic framework to explain this phenomenon has been historically difficult due to challenges in quantifying reduction potential ( E H ) values for oxide-bound Fe 2+ species. Recently, our group demonstrated that E H values for hematite- and goethite-bound Fe 2+ can be accurately calculated using Gibbs free energy of formation values. Here, we tested if calculated E H values for oxide-bound Fe 2+ could be used to develop a free energy relationship capable of describing variations in reduction rate constants of substituted nitrobenzenes, a class of model pollutants that contain reducible aromatic nitro groups, using data collected here and compiled from the literature. All the data could be described by a single linear relationship between the logarithms of the surface-area-normalized rate constant ( k SA ) values and E H and pH values [log( k SA ) = - E H /0.059 V - pH + 3.42]. This framework provides mechanistic insights into how the thermodynamic favorability of electron transfer from oxide-bound Fe 2+ relates to redox reaction kinetics.

Removal of oxides from alkali metal melts by reductive titration to electrical resistance-change end points

DOEpatents

Tsang, Floris Y.

1980-01-01

Alkali metal oxides dissolved in alkali metal melts are reduced with soluble metals which are converted to insoluble oxides. The end points of the reduction is detected as an increase in electrical resistance across an alkali metal ion-conductive membrane interposed between the oxide-containing melt and a material capable of accepting the alkali metal ions from the membrane when a difference in electrical potential, of the appropriate polarity, is established across it. The resistance increase results from blocking of the membrane face by ions of the excess reductant metal, to which the membrane is essentially non-conductive.

Nox control for high nitric oxide concentration flows through combustion-driven reduction

DOEpatents

Yeh, James T.; Ekmann, James M.; Pennline, Henry W.; Drummond, Charles J.

1989-01-01

An improved method for removing nitrogen oxides from concentrated waste gas streams, in which nitrogen oxides are ignited with a carbonaceous material in the presence of substoichiometric quantities of a primary oxidant, such as air. Additionally, reductants may be ignited along with the nitrogen oxides, carbonaceous material and primary oxidant to achieve greater reduction of nitrogen oxides. A scrubber and regeneration system may also be included to generate a concentrated stream of nitrogen oxides from flue gases for reduction using this method.

Fe(III) oxides accelerate microbial nitrate reduction and electricity generation by Klebsiella pneumoniae L17.

PubMed

Liu, Tongxu; Li, Xiaomin; Zhang, Wei; Hu, Min; Li, Fangbai

2014-06-01

Klebsiella pneumoniae L17 is a fermentative bacterium that can reduce iron oxide and generate electricity under anoxic conditions, as previously reported. This study reveals that K. pneumoniae L17 is also capable of dissimilatory nitrate reduction, producing NO2(-), NH4(+), NO and N2O under anoxic conditions. The presence of Fe(III) oxides (i.e., α-FeOOH, γ-FeOOH, α-Fe2O3 and γ-Fe2O3) significantly accelerates the reduction of nitrate and generation of electricity by K. pneumoniae L17, which is similar to a previous report regarding another fermentative bacterium, Bacillus. No significant nitrate reduction was observed upon treatment with Fe(2+) or α-FeOOH+Fe(2+), but a slight facilitation of nitrate reduction and electricity generation was observed upon treatment with L17+Fe(2+). This result suggests that aqueous Fe(II) or mineral-adsorbed Fe(II) cannot reduce nitrate abiotically but that L17 can catalyze the reduction of nitrate and generation of electricity in the presence of Fe(II) (which might exist as cell surface-bound Fe(II)). To rule out the potential effect of Fe(II) produced by L17 during microbial iron reduction, treatments with the addition of TiO2 or Al2O3 instead of Fe(III) oxides also exhibited accelerated microbial nitrate reduction and electricity generation, indicating that cell-mineral sorption did account for the acceleration effect. However, the acceleration caused by Fe(III) oxides is only partially attributed to the cell surface-bound Fe(II) and cell-mineral sorption but may be driven by the iron oxide conduction band-mediated electron transfer from L17 to nitrate or an electrode, as proposed previously. The current study extends the diversity of bacteria of which nitrate reduction and electricity generation can be facilitated by the presence of iron oxides and confirms the positive role of Fe(III) oxides on microbial nitrate reduction and electricity generation by particular fermentative bacteria in anoxic environments. Copyright �

Oxidation of aromatic contaminants coupled to microbial iron reduction

USGS Publications Warehouse

Lovley, D.R.; Baedecker, M.J.; Lonergan, D.J.; Cozzarelli, I.M.; Phillips, E.J.P.; Siegel, D.I.

1989-01-01

THE contamination of sub-surface water supplies with aromatic compounds is a significant environmental concern1,2. As these contaminated sub-surface environments are generally anaerobic, the microbial oxidation of aromatic compounds coupled to nitrate reduction, sulphate reduction and methane production has been studied intensively1-7. In addition, geochemical evidence suggests that Fe(III) can be an important electron acceptor for the oxidation of aromatic compounds in anaerobic groundwater. Until now, only abiological mechanisms for the oxidation of aromatic compounds with Fe(III) have been reported8-12. Here we show that in aquatic sediments, microbial activity is necessary for the oxidation of model aromatic compounds coupled to Fe(III) reduction. Furthermore, a pure culture of the Fe(III)-reducing bacterium GS-15 can obtain energy for growth by oxidizing benzoate, toluene, phenol or p-cresol with Fe(III) as the sole electron acceptor. These results extend the known physiological capabilities of Fe(III)-reducing organisms and provide the first example of an organism of any type which can oxidize an aromatic hydrocarbon anaerobically. ?? 1989 Nature Publishing Group.

Prediction of Reduction Potentials of Copper Proteins with Continuum Electrostatics and Density Functional Theory

PubMed Central

Fowler, Nicholas J.; Blanford, Christopher F.

2017-01-01

Abstract Blue copper proteins, such as azurin, show dramatic changes in Cu2+/Cu+ reduction potential upon mutation over the full physiological range. Hence, they have important functions in electron transfer and oxidation chemistry and have applications in industrial biotechnology. The details of what determines these reduction potential changes upon mutation are still unclear. Moreover, it has been difficult to model and predict the reduction potential of azurin mutants and currently no unique procedure or workflow pattern exists. Furthermore, high‐level computational methods can be accurate but are too time consuming for practical use. In this work, a novel approach for calculating reduction potentials of azurin mutants is shown, based on a combination of continuum electrostatics, density functional theory and empirical hydrophobicity factors. Our method accurately reproduces experimental reduction potential changes of 30 mutants with respect to wildtype within experimental error and highlights the factors contributing to the reduction potential change. Finally, reduction potentials are predicted for a series of 124 new mutants that have not yet been investigated experimentally. Several mutants are identified that are located well over 10 Å from the copper center that change the reduction potential by more than 85 mV. The work shows that secondary coordination sphere mutations mostly lead to long‐range electrostatic changes and hence can be modeled accurately with continuum electrostatics. PMID:28815759

THE RELATION OF THE BACTERIOSTATIC ACTION OF CERTAIN DYES TO OXIDATION-REDUCTION PROCESSES

PubMed Central

Dubos, René

1929-01-01

Oxidized indophenols and methylene blue are bacteriostatic for Pneumococcus and hemolytic streptococci of human and bovine origin, while the indigoes, malachite green and litmus are not toxic. 2-Chloroindophenol, the most positive of the indicators of oxidation-reduction potentials used, is also the only one to have a bacteriostatic action on cheese strains of Streptococcus hæmolyticus. Methylene blue and the indophenols are no longer bacteriostatic when present in a reduced form in a medium capable of maintaining them in such a condition. A comparison of these results with the growth in plain broth of the organisms studied suggests that the "inhibiting" dyes "poise" the medium at an oxidation potential outside the range in which the inhibited organisms can grow. PMID:19869565

Improvement in gold grade from iron-oxide mineral using reduction roasting and magnetic separation

NASA Astrophysics Data System (ADS)

Kim, Hyun-soo; On, Hyun-sung; Lim, Dae-hack; Myung, Eun-ji; Park, Cheon-young

2017-04-01

Microwave has a wide range of applications in mineral technology, metallurgy, etc. It is an established fact that microwave energy has potential for the speedy and efficient heating of minerals and in a commercial context may provide savings in both time and energy. Microwave heating is being developed as a potential thermal pre-treatment process, because of its unique advantages over the differences of ore minerals in absorbing microwaves. The aim of this study was to investigate the improvement in Au grade from iron-oxide mineral using reduction roasting and magnetic separation. The characteristics of iron-oxide mineral were analyzed using chemical, XRD and reflected light microscopy. The reduction roasting using microwave and magnetic separation experiments were examined under various conditions (reducing agent and chemical additive). The results of XRD and reflected light microscopy showed that the iron-oxide mineral mainly composed of illite, quartz and hematite. The iron-oxide mineral had an Au, Ag, Fe contents of 6.4, 35.1 and 155,441.1 mg/kg, respectively. The results demonstrated that the improvement in Au by reduction roasting using microwave (frequency of 2.45GHz, intensity of 5kW) and magnetic separation (magnetic field intensity of 9,000 Gauss) were effective processes. The Au content in iron-oxide mineral from 6.4 mg/kg to 14.2 mg/kg was achieved within microwave exposure time of 10min (reducing agent(PAC) ratio = 50 : 50, 5% of chemical additive(Soda ash)). Acknowledgment : This subject is supported by Korea Ministry of Environment as "Advanced Technology Program for Environmental Industry"

X-ray Crystal Truncation Rod Studies of Surface Oxidation and Reduction on Pt(111)

DOE PAGES

Liu, Yihua; Barbour, Andi; Komanicky, Vladimir; ...

2016-02-26

Here, we present X-ray crystal truncation rods measurements of Pt(111) surface under electrochemical conditions. Analyses of crystal truncation rods reveal that surface oxide formation buckles the top surface layer of platinum to two different heights at the potential (0.95 V vs RHE) below the so-called place-exchange potential. While the anti-Bragg intensity, sensitive to the top surface layer, drops in response to the anodic charge transfers, its responses to the cathodic charge transfers are significantly delayed. Implications to the surface oxidation and reduction behaviors are discussed.

Production and reduction of nitrous oxide in agricultural and forest soils.

PubMed

Yu, K; Chen, G; Struwe, S; Kjøller, A

2000-06-01

A soil-water slurry experiment was conducted to study the potentials of N2O production and reduction in denitrification of agricultural and beech forest soils in Denmark. The effects of nitrate and ammonium additions on denitrification were also investigated. The forest soil showed a higher denitrification potential than the agricultural soil. However, N2O reduction potential of the agricultural soil was higher than the beech forest soil, shown by the ratio of N2O/N2 approximately 0.11 and 3.65 in the agricultural and the beech forest soils, respectively. Both nitrate and ammonium additions stimulated the N2O production in the two soils, but reduced the N2O reduction rates in the agricultural soil slurries. In contrast to the effect on the agricultural soil, nitrate reduced the N2O reduction rate in the beech forest soil, while ammonium showed a stimulating effect on the N2O reduction activity. After one week incubation, all of the N2O produced was reduced to N2 in the agricultural soil when nitrate was still present. Nitrous oxide reduction in the beech forest soil occurred only when nitrate almost disappeared. The different nitrate inhibitory effect on the N2O reduction activity in the two soils was due to the difference in soil pH. Inhibition of nitrate on N2O reduction was significant under acidic condition. Consequently, soil could serve as a sink of atmospheric N2O under the conditions of anaerobic, pH near neutral and low nitrate content.

Investigation on the Oxidation and Reduction of Titanium in Molten Salt with the Soluble TiC Anode

NASA Astrophysics Data System (ADS)

Wang, Shulan; Wan, Chaopin; Liu, Xuan; Li, Li

2015-12-01

To reveal the oxidation process of titanium from TiC anode and the reduction mechanism of titanium ions in molten NaCl-KCl, the polarization curve of TiC anode in molten NaCl-KCl and cyclic voltammograms of the molten salt after polarization were studied. Investigation on the polarization curve shows that titanium can be oxidized and dissociated from the TiC anode at very low potential. The cyclic voltammograms demonstrated that the reduction reaction of titanium ions in the molten salt is a one-step process. By potentiostatic electrolysis, dendritic titanium is obtained on the steel plate. The work promotes the understanding on the process of electrochemical oxidization/dissociation of titanium from TiC anode and the reduction mechanism of titanium ions in molten salt.

Prediction of Reduction Potentials of Copper Proteins with Continuum Electrostatics and Density Functional Theory.

PubMed

Fowler, Nicholas J; Blanford, Christopher F; Warwicker, Jim; de Visser, Sam P

2017-11-02

Blue copper proteins, such as azurin, show dramatic changes in Cu 2+ /Cu + reduction potential upon mutation over the full physiological range. Hence, they have important functions in electron transfer and oxidation chemistry and have applications in industrial biotechnology. The details of what determines these reduction potential changes upon mutation are still unclear. Moreover, it has been difficult to model and predict the reduction potential of azurin mutants and currently no unique procedure or workflow pattern exists. Furthermore, high-level computational methods can be accurate but are too time consuming for practical use. In this work, a novel approach for calculating reduction potentials of azurin mutants is shown, based on a combination of continuum electrostatics, density functional theory and empirical hydrophobicity factors. Our method accurately reproduces experimental reduction potential changes of 30 mutants with respect to wildtype within experimental error and highlights the factors contributing to the reduction potential change. Finally, reduction potentials are predicted for a series of 124 new mutants that have not yet been investigated experimentally. Several mutants are identified that are located well over 10 Å from the copper center that change the reduction potential by more than 85 mV. The work shows that secondary coordination sphere mutations mostly lead to long-range electrostatic changes and hence can be modeled accurately with continuum electrostatics. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Thermodynamic Versus Surface Area Control of Microbial Fe(III) Oxide Reduction Kinetics

NASA Astrophysics Data System (ADS)

Roden, E. E.

2003-12-01

Recent experimental studies of synthetic and natural Fe(III) oxide reduction permit development of conceptual and quantitative models of enzymatic Fe(III) oxide reduction at circumneutral pH that can be compared to and contrasted with established models of abiotic mineral dissolution. The findings collectively support a model for controls on enzymatic reduction that differs fundamentally from those applied to abiotic reductive dissolution as a result of two basic phenomena: (1) the relatively minor influence of oxide mineralogical and thermodynamic properties on surface area-normalized rates of enzymatic reduction compared to abiotic reductive dissolution; and (2) the major limitation which sorption and/or surface precipitation of biogenic Fe(II) on residual oxide and Fe(III)-reducing bacterial cell surfaces poses to enzymatic electron transfer in the presence of excess electron donor. Parallel studies with two major Fe(III)-reducing bacteria genera (Shewanella and Geobacter) lead to common conclusions regarding the importance of these phenomena in regulating the rate and long-term extent of Fe(III) oxide reduction. Although the extent to which these phenomena can be traced to underlying kinetic vs. thermodynamic effects cannot be resolved with current information, models in which rates of enzymatic reduction are limited kinetically by the abundance of "available" oxide surface sites (as controlled by oxide surface area and the abundance of surface-bound Fe(II)) provide an adequate macroscopic description of controls on the initial rate and long-term extent of oxide reduction. In some instances, thermodynamic limitation posed by the accumulation of aqueous reaction end-products (i.e. Fe(II) and alkalinity) must also be invoked to explain observed long-term patterns of reduction. In addition, the abundance of Fe(III)-reducing microorganisms plays an important role in governing rates of reduction and needs to be considered in models of Fe(III) reduction in nonsteady

Reduced Graphene Oxides: Influence of the Reduction Method on the Electrocatalytic Effect towards Nucleic Acid Oxidation

PubMed Central

Báez, Daniela F.; Pardo, Helena; Laborda, Ignacio; Marco, José F.; Yáñez, Claudia; Bollo, Soledad

2017-01-01

For the first time a critical analysis of the influence that four different graphene oxide reduction methods have on the electrochemical properties of the resulting reduced graphene oxides (RGOs) is reported. Starting from the same graphene oxide, chemical (CRGO), hydrothermal (hTRGO), electrochemical (ERGO), and thermal (TRGO) reduced graphene oxide were produced. The materials were fully characterized and the topography and electroactivity of the resulting glassy carbon modified electrodes were also evaluated. An oligonucleotide molecule was used as a model of DNA electrochemical biosensing. The results allow for the conclusion that TRGO produced the RGOs with the best electrochemical performance for oligonucleotide electroanalysis. A clear shift in the guanine oxidation peak potential to lower values (~0.100 V) and an almost two-fold increase in the current intensity were observed compared with the other RGOs. The electrocatalytic effect has a multifactorial explanation because the TRGO was the material that presented a higher polydispersity and lower sheet size, thus exposing a larger quantity of defects to the electrode surface, which produces larger physical and electrochemical areas. PMID:28677654

Effects of Low-temperature Pre-oxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in a Fluidized Bed

NASA Astrophysics Data System (ADS)

Adetoro, Ajala Adewole; Sun, Haoyan; He, Shengyi; Zhu, Qingshan; Li, Hongzhong

2018-04-01

With respect to high efficient utilization of low-grade iron ore resource, the behavior of low-temperature "973 K to 1123 K (700 °C to 850 °C)" oxidation, on the phase transition of SA TTM ore (South African titanomagnetite), and its effect on subsequent reduction was investigated. The results showed that hematite and rutile are the oxidation product below 1048 K (775 °C), while pseudobrookite is the stable phase above 1073 K (800 °C). With the increase in temperature and oxidation time, there is a competitive relationship between the amount of hematite and pseudobrookite generated. The reduction efficiency of SA TTM was significantly improved by oxidation pretreatment, primarily due to the dissociation of titania-ferrous oxides to more easily reducible hematite. But the generation of pseudobrookite phase decreases the amount of free hematite available for reduction, which weakens the improvement effect of pre-oxidation. The equilibrium relationship between the metallization degree and the gas reduction potential for TTM ore with pre-oxidation treatment has been built. Finally, the reduction metallization degree for the first and second step can be improved averagely by 16.67 and 3.45 pct, respectively, for sample pre-oxidized at 1098 K (825 °C) for 15 and 90 minutes, while 26.96 and 7.4 pct, improvement is achieved for sample pre-oxidized at a lower temperature of 1048 K (775 °C) for 120 minutes.

Influences of top electrode reduction potential and operation ambient on the switching characteristics of tantalum oxide resistive switching memories

NASA Astrophysics Data System (ADS)

Ding, Tse-Ming; Chen, Yi-Ju; Jeng, Jiann-Shing; Chen, Jen-Sue

2017-12-01

Modulation of the oxygen distribution is liable for the electrical performance of oxide-based devices. When the top electrode (TE) is deposited on the active layer, an oxygen exchange layer (OEL) may be formed at the interface. Oxygen ions can be absorbed and offered in OEL to assist resistive switching (RS). In this study, the impact of different TEs (Al, Zr, Ta and Au) on the active layer TaOx is investigated. TEs are chosen based on the reduction potential (E0Al=-2.13V, E0Zr=-1.55V, E0Ta=-0.75V, E0Au=1.52V), which determines whether OEL is formed. Based on TEM micrographs, as the difference of TE reduction potential to E0Ta becomes more negative, a thicker OEL exists. We find that Zr TE device has the most stable I-V characteristic and data retention, while Al TE device suffers from the reset failure, and Au TE device fails to switch. Moreover, we fabricate two different thicknesses (20 nm and 120 nm) of Zr TE and alter the operation ambient to vacuum (10-5 Torr) to study the influence on RS. The magnitude of reset voltage becomes larger when the devices are measured in vacuum ambient. According to these findings, the RS mechanism with different TE materials, thicknesses and at the different operation ambient is established.

Aggregate-scale heterogeneity in iron (hydr)oxide reductive transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tufano, K.J.; Benner, S.G.; Mayer, K.U.

There is growing awareness of the complexity of potential reaction pathways and the associated solid-phase transformations during the reduction of Fe (hydr)oxides, especially ferrihydrite. An important observation in static and advective-dominated systems is that microbially produced Fe(II) accelerates Ostwald ripening of ferrihydrite, thus promoting the formation of thermodynamically more stable ferric phases (lepidocrocite and goethite) and, at higher Fe(II) surface loadings, the precipitation of magnetite; high Fe(II) levels can also lead to green rust formation, and with high carbonate levels siderite may also be formed. This study expands this emerging conceptual model to a diffusion-dominated system that mimics an idealizedmore » micropore of a ferrihydrite-coated soil aggregate undergoing reduction. Using a novel diffusion cell, coupled with micro-x-ray fluorescence and absorption spectroscopies, we determined that diffusion-controlled gradients in Fe{sup 2+}{sub (aq)} result in a complex array of spatially distributed secondary mineral phases. At the diffusive pore entrance, where Fe{sup 2+} concentrations are highest, green rust and magnetite are the dominant secondary Fe (hydr)oxides (30 mol% Fe each). At intermediate distances from the inlet, green rust is not observed and the proportion of magnetite decreases from approximately 30 to <10%. Across this same transect, the proportion of goethite increases from undetectable up to >50%. At greater distances from the advective-diffusive boundary, goethite is the dominant phase, comprising between 40 and 95% of the Fe. In the presence of magnetite, lepidocrocite forms as a transient-intermediate phase during ferrihydrite-to-goethite conversion; in the absence of magnetite, conversion to goethite is more limited. These experimental observations, coupled with results of reactive transport modeling, confirm the conceptual model and illustrate the potential importance of diffusion-generated concentration

A micro-nano porous oxide hybrid for efficient oxygen reduction in reduced-temperature solid oxide fuel cells

PubMed Central

Da Han; Liu, Xuejiao; Zeng, Fanrong; Qian, Jiqin; Wu, Tianzhi; Zhan, Zhongliang

2012-01-01

Tremendous efforts to develop high-efficiency reduced-temperature (≤ 600°C) solid oxide fuel cells are motivated by their potentials for reduced materials cost, less engineering challenge, and better performance durability. A key obstacle to such fuel cells arises from sluggish oxygen reduction reaction kinetics on the cathodes. Here we reported that an oxide hybrid, featuring a nanoporous Sm0.5Sr0.5CoO3−δ (SSC) catalyst coating bonded onto the internal surface of a high-porosity La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) backbone, exhibited superior catalytic activity for oxygen reduction reactions and thereby yielded low interfacial resistances in air, e.g., 0.021 Ω cm2 at 650°C and 0.043 Ω cm2 at 600°C. We further demonstrated that such a micro-nano porous hybrid, adopted as the cathode in a thin LSGM electrolyte fuel cell, produced impressive power densities of 2.02 W cm−2 at 650°C and 1.46 W cm−2 at 600°C when operated on humidified hydrogen fuel and air oxidant. PMID:22708057

Green reduction of graphene oxide by ascorbic acid

NASA Astrophysics Data System (ADS)

Khosroshahi, Zahra; Kharaziha, Mahshid; Karimzadeh, Fathallah; Allafchian, Alireza

2018-01-01

Graphene, a single layer of sp2-hybridized carbon atoms in a hexagonal (two-dimensional honey-comb) lattice, has attracted strong scientific and technological interest due to its novel and excellent optical, chemical, electrical, mechanical and thermal properties. The solution-processable chemical reduction of Graphene oxide (GO is considered as the most favorable method regarding mass production of graphene. Generally, the reduction of GO is carried out by chemical approaches using different reductants such as hydrazine and sodium borohydride. These components are corrosive, combustible and highly toxic which may be dangerous for personnel health and the environment. Hence, these reducing agents are not promising choice for reducing of graphene oxide (GO). As a consequence, it is necessary for further development and optimization of eco-friendly, natural reducing agent for clean and effective reduction of GO. Ascorbic acid, an eco-friendly and natural reducing agents, having a mild reductive ability and nontoxic property. So, the aim of this research was to green synthesis of GO with ascorbic acid. For this purpose, the required amount of NaOH and ascorbic acid were added to GO solution (0.5 mg/ml) and were heated at 95 °C for 1 hour. According to the X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrochemical results, GO were reduced with ascorbic acid like hydrazine with better electrochemical properties and ascorbic acid is an ideal substitute for hydrazine in the reduction of graphene oxide process.

Methodology for the effective stabilization of tin-oxide-based oxidation/reduction catalysts

NASA Technical Reports Server (NTRS)

Jordan, Jeffrey D. (Inventor); Schryer, David R. (Inventor); Leighty, Bradley D. (Inventor); Watkins, Anthony N. (Inventor); Summers, Jerry C. (Inventor); Davis, Patricia P. (Inventor); Oglesby, Donald M. (Inventor); Schryer, Jacqueline L. (Inventor); Gulati, Suresh T. (Inventor)

2011-01-01

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

Tuning spontaneous polarization to alter water oxidation/reduction activities of LiNbO3

NASA Astrophysics Data System (ADS)

Fu, Hongwei; Song, Yan; Wu, Yangqing; Huang, Huiting; Fan, Guozheng; Xu, Jun; Li, Zhaosheng; Zou, Zhigang

2018-02-01

Here, we investigated the effects of spontaneous polarization on photoreactivities by using a ferroelectric material n-type congruent LiNbO3 single crystal as a model. It was found that c+ LiNbO3 was superior to c- LiNbO3 in photocatalytic water reduction, while c- LiNbO3 exhibited better performances for photoelectrochemical water oxidation than c+ LiNbO3. Using Kelvin probe force microscopy and open circuit potential methods, we observed that c- LiNbO3 generated a higher photovoltage and had a slower charge-recombination rate than c+ LiNbO3. The results of electrochemical impedance spectroscopy measurements indicated that c- LiNbO3 may favor the hole transport from the bulk to the surface compared with c+ LiNbO3, leading to the anisotropic performances of c+ and c- LiNbO3 in water oxidation/reduction. Therefore, tuning the direction of the polarization may be a strategy to dramatically prompt the photoreactivities of water oxidation or reduction.

Biological Oxidation of Fe(II) in Reduced Nontronite Coupled with Nitrate Reduction by Pseudogulbenkiania sp. Strain 2002

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Linduo; Dong, Hailiang; Kukkadapu, Ravi K.

Nitrate contamination in soils, sediments, and water bodies is a significant issue. Although much is known about nitrate degradation in these environments, especially via microbial pathways, a complete understanding of all degradation processes, especially in clay mineral-rich soils, is still lacking. The objective of this study was to study the potential of removing nitrate contaminant using structural Fe(II) in clay mineral nontronite. Specifically, the coupled processes of microbial oxidation of Fe(II) in microbially reduced nontronite (NAu-2) and nitrate reduction by Pseudogulbenkiania species strain 2002 was investigated. Bio-oxidation experiments were conducted in bicarbonate-buffered medium under both growth and nongrowth conditions. Themore » extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57Fe-Mössbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in nontronite. The bio-oxidation extent under growth and nongrowth conditions reached 93% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N2), via an intermediate product nitrite. Magnetite was a mineral product of nitrate-dependent Fe(II) oxidation, as evidenced by XRD data and TEM diffraction patterns. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in soils.« less

Progress of reduction of graphene oxide by ascorbic acid

NASA Astrophysics Data System (ADS)

De Silva, K. Kanishka H.; Huang, Hsin-Hui; Yoshimura, Masamichi

2018-07-01

Graphene oxide (GO) and reduced graphene oxide (RGO) are in greater demand in many research fields. As a result, the synthesis of these materials on a large scale in a costeffective manner is more concerned for numerous applications. In the present work, GO was synthesized by oxidizing natural graphite and reduced by ascorbic acid (AA), which is a green reductant. The reduced products obtained at different time periods were in detail characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results showed that the oxidation of graphite has given highly oxidized GO with a 9.30 Å interlayer space and about 33% of oxygen atomic percentage. Until 50 min of the reduction, both GO and RGO coexist. The reduction rate is fast within the first 30 min. In addition, the suitability of natural graphite over synthetic graphite for the synthesis of GO is shown. The findings of this work pave the way to select GO and RGO for applications of interest in a cheap, green and efficient manner.

Contrasting dual (C, Cl) isotope fractionation offers potential to distinguish reductive chloroethene transformation from breakdown by permanganate.

PubMed

Doğan-Subaşı, Eylem; Elsner, Martin; Qiu, Shiran; Cretnik, Stefan; Atashgahi, Siavash; Shouakar-Stash, Orfan; Boon, Nico; Dejonghe, Winnie; Bastiaens, Leen

2017-10-15

cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors ε C (‰), but starkly contrasting dual element isotope slopes Δδ 13 C/Δδ 37 Cl for permanganate oxidation (ε C =-26‰±6‰, Δδ 13 C/Δδ 37 Cl≈-125±47) compared to reductive dechlorination (ε C =-18‰±4‰, Δδ 13 C/Δδ 37 Cl≈4.5±3.4). The difference can be tracked down to distinctly different chlorine isotope fractionation: an inverse isotope effect during chemical oxidation (ε Cl =+0.2‰±0.1‰) compared to a large normal isotope effect in reductive dechlorination (ε Cl =-3.3‰±0.9‰) (p≪0.05). A similar trend was observed for TCE. The dual isotope approach was evaluated in the field before and up to 443days after a pilot scale permanganate injection in the subsurface. Our study indicates, for the first time, the potential of the dual element isotope approach for distinguishing cis-DCE (and TCE) concentration drops caused by dilution, oxidation by permanganate and reductive dechlorination both at laboratory and field scale. Copyright © 2017. Published by Elsevier B.V.

The influence of oxidation reduction potential and water treatment processes on quartz lamp sleeve fouling in ultraviolet disinfection reactors.

PubMed

Wait, Isaac W; Johnston, Cliff T; Blatchley, Ernest R

2007-06-01

Ultraviolet (UV) disinfection systems are incorporated into drinking water production facilities because of their broad-spectrum antimicrobial capabilities, and the minimal disinfection by-product formation that generally accompanies their use. Selection of an optimal location for a UV system within a drinking water treatment facility depends on many factors; a potentially important consideration is the effect of system location on operation and maintenance issues, including the potential for fouling of quartz surfaces. To examine the effect of system location on fouling, experiments were conducted at a groundwater treatment facility, wherein aeration, chlorination, and sand filtration were applied sequentially for treatment. In this facility, access to the water stream was available prior to and following each of the treatment steps. Therefore, it was possible to examine the effects of each of these unit operations on fouling dynamics within a UV system. Results indicated zero-order formation kinetics for the fouling reactions at all locations. Increases in oxidation reduction potential, caused by water treatment steps such as aeration and chlorination, increased the rate of sleeve fouling and the rate of irradiance loss within the reactor. Analysis of metals in the sleeve foulant showed that calcium and iron predominate, and relative comparisons of foulant composition to water chemistry highlighted a high affinity for incorporation into the foulant matrix for both iron and manganese, particularly after oxidizing treatment steps. Fouling behavior was observed to be in qualitative agreement with representations of the degree of saturation, relative to the metal:ligand combinations that are believed to comprise a large fraction of the foulants that accumulate on the surfaces of quartz jackets in UV systems used to treat water.

Promotion of Iron Oxide Reduction and Extracellular Electron Transfer in Shewanella oneidensis by DMSO

PubMed Central

Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Dao-Bo; Chen, Jie-Jie; Li, Wen-Wei; Tong, Zhong-Hua; Wu, Chao; Yu, Han-Qing

2013-01-01

The dissimilatory metal reducing bacterium Shewanella oneidensis MR-1, known for its capacity of reducing iron and manganese oxides, has great environmental impacts. The iron oxides reducing process is affected by the coexistence of alternative electron acceptors in the environment, while investigation into it is limited so far. In this work, the impact of dimethyl sulphoxide (DMSO), a ubiquitous chemical in marine environment, on the reduction of hydrous ferric oxide (HFO) by S. oneidensis MR-1 was investigated. Results show that DMSO promoted HFO reduction by both wild type and ΔdmsE, but had no effect on the HFO reduction by ΔdmsB, indicating that such a promotion was dependent on the DMSO respiration. With the DMSO dosing, the levels of extracellular flavins and omcA expression were significantly increased in WT and further increased in ΔdmsE. Bioelectrochemical analysis show that DMSO also promoted the extracellular electron transfer of WT and ΔdmsE. These results demonstrate that DMSO could stimulate the HFO reduction through metabolic and genetic regulation in S. oneidensis MR-1, rather than compete for electrons with HFO. This may provide a potential respiratory pathway to enhance the microbial electron flows for environmental and engineering applications. PMID:24244312

In-Situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes

DTIC Science & Technology

2010-12-28

DATES COVERED (From - To) 1/29/10-9/30/10 4. TITLE AND SUBTITLE In situ optical studies of oxidation/reduction kinetics on SOFC cermet anodes 5a...0572 In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Department of Chemistry and Biochemistry Montana State University...of Research In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Principal Investigator Robert Walker Organization

Mechanisms for chelator stimulation of microbial Fe(III) -oxide reduction

USGS Publications Warehouse

Lovley, D.R.; Woodward, J.C.

1996-01-01

The mechanisms by which nitrilotriacetic acid (NTA) stimulated Fe(III) reduction in sediments from a petroleum-contaminated aquifer were investigated in order to gain insight into how added Fe(III) chelators stimulate the activity of hydrocarbon-degrading, Fe(III)-reducing microorganisms in these sediments, and how naturally occurring Fe(III) chelators might promote Fe(III) reduction in aquatic sediments. NTA solubilized Fe(III) from the aquifer sediments. NTA stimulation of microbial Fe(III) reduction did not appear to be the result of making calcium, magnesium, potassium, or trace metals more available to the microorganisms. Stimulation of Fe(III) reduction could not be attributed to NTA serving as a source of carbon or fixed nitrogen for Fe(III)-reducing bacteria as NTA was not degraded in the sediments. Studies with the Fe(III)-reducing microorganism, Geobacter metallireducens, and pure Fe(III)-oxide forms, demonstrated that NTA stimulated the reduction of a variety of Fe(III) forms, including highly crystalline Fe(III)-oxides such as goethite and hematite. The results suggest that NTA solubilization of insoluble Fe(III)-oxide is an important mechanism for the stimulation of Fe(III) reduction by NTA in aquifer sediments.

Geochemical control of microbial Fe(III) reduction potential in wetlands: Comparison of the rhizosphere to non-rhizosphere soil

USGS Publications Warehouse

Weiss, J.V.; Emerson, D.; Megonigal, J.P.

2004-01-01

We compared the reactivity and microbial reduction potential of Fe(III) minerals in the rhizosphere and non-rhizosphere soil to test the hypothesis that rapid Fe(III) reduction rates in wetland soils are explained by rhizosphere processes. The rhizosphere was defined as the area immediately adjacent to a root encrusted with Fe(III)-oxides or Fe plaque, and non-rhizosphere soil was 0.5 cm from the root surface. The rhizosphere had a significantly higher percentage of poorly crystalline Fe (66??7%) than non-rhizosphere soil (23??7%); conversely, non-rhizosphere soil had a significantly higher proportion of crystalline Fe (50??7%) than the rhizosphere (18??7%, P<0.05 in all cases). The percentage of poorly crystalline Fe(III) was significantly correlated with the percentage of FeRB (r=0.76), reflecting the fact that poorly crystalline Fe(III) minerals are labile with respect to microbial reduction. Abiotic reductive dissolution consumed about 75% of the rhizosphere Fe(III)-oxide pool in 4 h compared to 23% of the soil Fe(III)-oxide pool. Similarly, microbial reduction consumed 75-80% of the rhizosphere pool in 10 days compared to 30-40% of the non-rhizosphere soil pool. Differences between the two pools persisted when samples were amended with an electron-shuttling compound (AQDS), an Fe(III)-reducing bacterium (Geobacter metallireducens), and organic carbon. Thus, Fe(III)-oxide mineralogy contributed strongly to differences in the Fe(III) reduction potential of the two pools. Higher amounts of poorly crystalline Fe(III) and possibly humic substances, and a higher Fe(III) reduction potential in the rhizosphere compared to the non-rhizosphere soil, suggested the rhizosphere is a site of unusually active microbial Fe cycling. The results were consistent with previous speculation that rapid Fe cycling in wetlands is due to the activity of wetland plant roots. ?? 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.

Photoactivity of N-doped ZnO nanoparticles in oxidative and reductive reactions

NASA Astrophysics Data System (ADS)

Oliveira, Jéssica A.; Nogueira, André E.; Gonçalves, Maria C. P.; Paris, Elaine C.; Ribeiro, Caue; Poirier, Gael Y.; Giraldi, Tania R.

2018-03-01

N-doped ZnO is a prospective material for photocatalytic reactions. However, only oxidative paths are well investigated in the literature. This paper describes a comparative study about ZnO and ZnO:N potential for oxidative and reductive reactions, probed by rhodamine B dye photodegradation and CO2 photoreduction. The materials were prepared by the polymeric precursor method, using urea as a nitrogen source, and different heat treatments were used to observe their effects on surface decontamination, crystallinity, particle sizes and shapes, and photocatalytic performance. ZnO and ZnO:N presented a wurtzite crystalline structure and nanometric-scale particles. Samples submitted to higher temperatures showed lower specific surface areas, but higher crystallinity and lower contents of species adsorbed on their surfaces. On the other hand, the photocatalysts annealed in shorter times presented smaller crystallite sizes and lower crystallinity. These factors influenced the photoactivity in both conditions, i.e., oxidation and reduction reactions, under the ultraviolet and visible light, indicating that structural factors influenced the adequate charge separation and consequent photocatalytic activity since the as-synthesized samples were versatile photocatalysts in both redox reactions.

REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON

EPA Science Inventory

Fenton oxidation and Fenton oxidation preceded by reduction solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration of the carbon coul...

Global Emissions of Nitrous Oxide: Key Source Sectors, their Future Activities and Technical Opportunities for Emission Reduction

NASA Astrophysics Data System (ADS)

Winiwarter, W.; Höglund-Isaksson, L.; Klimont, Z.; Schöpp, W.; Amann, M.

2017-12-01

Nitrous oxide originates primarily from natural biogeochemical processes, but its atmospheric concentrations have been strongly affected by human activities. According to IPCC, it is the third largest contributor to the anthropogenic greenhouse gas emissions (after carbon dioxide and methane). Deep decarbonization scenarios, which are able to constrain global temperature increase within 1.5°C, require strategies to cut methane and nitrous oxide emissions on top of phasing out carbon dioxide emissions. Employing the Greenhouse gas and Air pollution INteractions and Synergies (GAINS) model, we have estimated global emissions of nitrous oxide until 2050. Using explicitly defined emission reduction technologies we demonstrate that, by 2030, about 26% ± 9% of the emissions can be avoided assuming full implementation of currently existing reduction technologies. Nearly a quarter of this mitigation can be achieved at marginal costs lower than 10 Euro/t CO2-eq with the chemical industry sector offering important reductions. Overall, the largest emitter of nitrous oxide, agriculture, also provides the largest emission abatement potentials. Emission reduction may be achieved by precision farming methods (variable rate technology) as well as by agrochemistry (nitrification inhibitors). Regionally, the largest emission reductions are achievable where intensive agriculture and industry are prevalent (production and application of mineral fertilizers): Centrally Planned Asia including China, North and Latin America, and South Asia including India. Further deep cuts in nitrous oxide emissions will require extending reduction efforts beyond strictly technological solutions, i.e., considering behavioral changes, including widespread adoption of "healthy diets" minimizing excess protein consumption.

1. West facade of Plutonium Concentration Facility (Building 233S), ReductionOxidation ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. West facade of Plutonium Concentration Facility (Building 233-S), Reduction-Oxidation Building (REDOX-202-S) to the right. Looking east. - Reduction-Oxidation Complex, Plutonium Concentration Facility, 200 West Area, Richland, Benton County, WA

Insights on Microbial Activity from Reduction Potential: Electrochemical Noise Analysis of a Pristine Aquifer

NASA Astrophysics Data System (ADS)

Enright, A. M.; Shirokova, V.; Ferris, G.

2012-12-01

Reduction potential was measured in a shallow, till-hosted, pristine aquifer. A previous study* characterized the microbial community of the aquifer, and geochemical analysis of water from the aquifer from 2010, 2011, and 2012 indicates persistent localized geochemical gradients of ferrous, ferric, sulphate, and sulphide ions. The chemical plume changes oxidation state from a reduced centre to oxidized outer boundaries, and microbial activity is responsible for the shift in redox state. Analysis of reduction potential as electrochemical noise in both the frequency and time domains provides insight into the manipulation of dissolved ions by the microbial community. Analysis of electrochemical noise is sensitive enough to distinguish the rates and magnitude of influence of the mechanisms which contribute to the redox state of a system. Self-similarity has been suggested to arise in any system where electrochemical noise is the result of a multitude of contributory processes, and this type of noise signature has been reported for many biological and abiotic natural processes. This observed ubiquity is not well understood. Reduction potential data is analyzed using detrended fluctuation analysis in the frequency domain and detrended moving average analysis in the time domain to characterize the Hurst exponent and fractal dimension of this physiological time series. *V.L. Shirokova and F.G. Ferris. (2012). Microbial Diversity and Biogeochemistry of a Pristine Canadian Shield Groundwater System. Geomicrobiology Journal.

Evolution of thermal stress and failure probability during reduction and re-oxidation of solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Wang, Yu; Jiang, Wenchun; Luo, Yun; Zhang, Yucai; Tu, Shan-Tung

2017-12-01

The reduction and re-oxidation of anode have significant effects on the integrity of the solid oxide fuel cell (SOFC) sealed by the glass-ceramic (GC). The mechanical failure is mainly controlled by the stress distribution. Therefore, a three dimensional model of SOFC is established to investigate the stress evolution during the reduction and re-oxidation by finite element method (FEM) in this paper, and the failure probability is calculated using the Weibull method. The results demonstrate that the reduction of anode can decrease the thermal stresses and reduce the failure probability due to the volumetric contraction and porosity increasing. The re-oxidation can result in a remarkable increase of the thermal stresses, and the failure probabilities of anode, cathode, electrolyte and GC all increase to 1, which is mainly due to the large linear strain rather than the porosity decreasing. The cathode and electrolyte fail as soon as the linear strains are about 0.03% and 0.07%. Therefore, the re-oxidation should be controlled to ensure the integrity, and a lower re-oxidation temperature can decrease the stress and failure probability.

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment

PubMed Central

Marzocchi, Ugo; Trojan, Daniela; Larsen, Steffen; Louise Meyer, Rikke; Peter Revsbech, Niels; Schramm, Andreas; Peter Nielsen, Lars; Risgaard-Petersen, Nils

2014-01-01

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4–6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed. PMID:24577351

Dissimilatory nitrate reduction to nitrate, nitrous oxide, and ammonium by Pseudomonas putrefaciens.

PubMed

Samuelsson, M O

1985-10-01

The influence of redox potential on dissimilatory nitrate reduction to ammonium was investigated on a marine bacterium, Pseudomonas putrefaciens. Nitrate was consumed (3.1 mmol liter-1), and ammonium was produced in cultures with glucose and without sodium thioglycolate. When sodium thioglycolate was added, nitrate was consumed at a lower rate (1.1 mmol liter-1), and no significant amounts of nitrite or ammonium were produced. No growth was detected in glucose media either with or without sodium thioglycolate. When grown on tryptic soy broth, the production of nitrous oxide paralleled growth. In the same medium, but with sodium thioglycolate, nitrous oxide was first produced during growth and then consumed. Acetylene caused the nitrous oxide to accumulate. These results and the mass balance calculations for different nitrogen components indicate that P. putrefaciens has the capacity to dissimilate nitrate to ammonium as well as to dinitrogen gas and nitrous oxide (denitrification). The dissimilatory pathway to ammonium dominates except when sodium thioglycolate is added to the medium.

Oxidation-reduction potentials of molybdenum, flavin and iron-sulphur centres in milk xanthine oxidase.

PubMed Central

Cammack, R; Barber, M J; Bray, R C

1976-01-01

1. The mid-point reduction potentials of the various groups in xanthine oxidase from bovine milk were determined by potentiometric titration with dithionite in the presence of dye mediators, removing samples for quantification of the reduced species by e.p.r. (electron-paramagnetic-resonance) spectroscopy. The values obtained for the functional enzyme in pyrophosphate buffer, pH8.2, are: Fe/S centre I, -343 +/- 15mV; Fe/S II, -303 +/- 15mV; FAD/FADH-; -351 +/- 20mV; FADH/FADH2, -236 +/-mV; Mo(VI)/Mo(V) (Rapid), -355 +/- 20mV; Mo(V) (Rapid)/Mo(IV), -355 +/- 20mV. 2. Behaviour of the functional enzyme is essentially ideal in Tris but less so in pyrophosphate. In Tris, the potential for Mo(VI)/Mo(V) (Rapid) is lowered relative to that in pyrophosphate, but the potential for Fe/S II is raised. The influence of buffer on the potentials was investigated by partial-reduction experiments with six other buffers. 3. Conversion of the enzyme with cyanide into the non-functional form, which gives the Slow molybdenum signal, or alkylation of FAD, has little effect on the mid-point potentials of the other centres. The potentials associated with the Slow signal are: Mo(VI)/Mo(V) (Slow), -440 +/- 25mV; Mo(V) (Slow)/Mo(IV), -480 +/- 25 mV. This signal exhibits very sluggish equilibration with the mediator system. 4. The deviations from ideal behaviour are discussed in terms of possible binding of buffer ions or anti-co-operative interactions amongst the redox centres. PMID:183752

Integration of graphene onto silicon through electrochemical reduction of graphene oxide layers in non-aqueous medium

NASA Astrophysics Data System (ADS)

Marrani, Andrea Giacomo; Coico, Anna Chiara; Giacco, Daniela; Zanoni, Robertino; Scaramuzzo, Francesca Anna; Schrebler, Ricardo; Dini, Danilo; Bonomo, Matteo; Dalchiele, Enrique A.

2018-07-01

Wafer-scale integration of reduced graphene oxide with H-terminated Si(1 1 1) surfaces has been accomplished by electrochemical reduction of a thin film of graphene oxide deposited onto Si by drop casting. Two reduction methods have been assayed and carried out in an acetonitrile solution. The initial deposit was subjected either to potential cycling in a 0.1 M TBAPF6/CH3CN solution at scan rates values of 20 mV s-1 and 50 mV s-1, or to a potentiostatic polarization at Eλ,c = -3 V for 450 s. The resulting interface has been characterized in its surface composition, morphology and electrochemical behavior by X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy and electrochemical measurements. The results evidence that few-layer graphene deposits on H-Si(1 1 1) were obtained after reduction, and use of organic instead of aqueous medium led to a very limited surface oxidation of the Si substrate and a very low oxygen-to-carbon ratio. The described approach is fast, simple, economic, scalable and straightforward, as one reduction cycle is already effective in promoting the establishment of a graphene-Si interface. It avoids thermal treatments at high temperatures, use of aggressive chemicals and the presence of metal contaminants, and enables preservation of Si(1 1 1) surface from oxidation.

Green reduction of graphene oxide via Lycium barbarum extract

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hou, Dandan, E-mail: houdandan114@163.com; Liu, Qinfu, E-mail: lqf@cumtb.edu.cn; Cheng, Hongfei, E-mail: h.cheng@cumtb.edu.cn

The synthesis of graphene from graphene oxide (GO) usually involves toxic reducing agents that are harmful to human health and the environment. Here, we report a facile approach for effective reduction of GO, for the first time, using Lycium barbarum extract as a green and natural reducing agent. The morphology and de-oxidation efficiency of the reduced graphene were characterized and results showed that Lycium barbarum extract can effectively reduce GO into few layered graphene with a high carbon to oxygen ratio (6.5), comparable to that of GO reduced by hydrazine hydrate (6.6). The possible reduction mechanism of GO may bemore » due to the active components existing in Lycium barbarum fruits, which have high binding affinity to the oxygen containing groups to form their corresponding oxides and other by-products. This method avoided the use of any nocuous chemicals, thus facilitating the mass production of graphene and graphene-based bio-materials. - Graphical abstract: Schematic illustration of the preparation of reduced graphene by Lycium barbarum extract. - Highlights: • The Lycium barbarum extract was used for the reduction of graphene oxide. • The obtained few layered graphene exhibited high carbon to oxygen ratio. • This approach can be applied in the preparation of graphene-based bio-materials.« less

Patterning and reduction of graphene oxide using femtosecond-laser irradiation

NASA Astrophysics Data System (ADS)

Kang, SeungYeon; Evans, Christopher C.; Shukla, Shobha; Reshef, Orad; Mazur, Eric

2018-07-01

Graphene has emerged as one of the most versatile materials ever discovered due to its extraordinary electronic, optical, thermal, and mechanical properties. However, device fabrication is a well-known challenge and requires novel fabrication methods to realize the complex integration of graphene-based devices. Here, we demonstrate direct laser writing of reduced graphene oxide using femtosecond-laser irradiation at λ = 795 nm. We perform a systematic study of the reduction process of graphene oxide to graphene by varying both the laser fluence and the pulse repetition rate. Our observations show that the reduction has both thermal and non-thermal features, and suggest that we can achieve better resolution and conductivity using kHz pulse trains than using MHz pulse trains or a continuous wave laser. Our reduced graphene oxide lines written at 10-kHz exhibit a 5 order-of-magnitude decrease in resistivity compared to a non-irradiated control sample. This study provides new insight into the reduction process of graphene oxide and opens doors to achieving a high degree of flexibility and control in the fabrication of graphene layers.

Electrolytic oxide reduction system

DOEpatents

Wiedmeyer, Stanley G; Barnes, Laurel A; Williamson, Mark A; Willit, James L; Berger, John F

2015-04-28

An electrolytic oxide reduction system according to a non-limiting embodiment of the present invention may include a plurality of anode assemblies, a plurality of cathode assemblies, and a lift system configured to engage the anode and cathode assemblies. The cathode assemblies may be alternately arranged with the anode assemblies such that each cathode assembly is flanked by two anode assemblies. The lift system may be configured to selectively engage the anode and cathode assemblies so as to allow the simultaneous lifting of any combination of the anode and cathode assemblies (whether adjacent or non-adjacent).

Anaerobic Methane Oxidation Driven by Microbial Reduction of Natural Organic Matter in a Tropical Wetland

PubMed Central

Valenzuela, Edgardo I.; Prieto-Davó, Alejandra; López-Lozano, Nguyen E.; Hernández-Eligio, Alberto; Vega-Alvarado, Leticia; Juárez, Katy; García-González, Ana Sarahí; López, Mercedes G.

2017-01-01

ABSTRACT Wetlands constitute the main natural source of methane on Earth due to their high content of natural organic matter (NOM), but key drivers, such as electron acceptors, supporting methanotrophic activities in these habitats are poorly understood. We performed anoxic incubations using freshly collected sediment, along with water samples harvested from a tropical wetland, amended with 13C-methane (0.67 atm) to test the capacity of its microbial community to perform anaerobic oxidation of methane (AOM) linked to the reduction of the humic fraction of its NOM. Collected evidence demonstrates that electron-accepting functional groups (e.g., quinones) present in NOM fueled AOM by serving as a terminal electron acceptor. Indeed, while sulfate reduction was the predominant process, accounting for up to 42.5% of the AOM activities, the microbial reduction of NOM concomitantly occurred. Furthermore, enrichment of wetland sediment with external NOM provided a complementary electron-accepting capacity, of which reduction accounted for ∼100 nmol 13CH4 oxidized · cm−3 · day−1. Spectroscopic evidence showed that quinone moieties were heterogeneously distributed in the wetland sediment, and their reduction occurred during the course of AOM. Moreover, an enrichment derived from wetland sediments performing AOM linked to NOM reduction stoichiometrically oxidized methane coupled to the reduction of the humic analogue anthraquinone-2,6-disulfonate. Microbial populations potentially involved in AOM coupled to microbial reduction of NOM were dominated by divergent biota from putative AOM-associated archaea. We estimate that this microbial process potentially contributes to the suppression of up to 114 teragrams (Tg) of CH4 · year−1 in coastal wetlands and more than 1,300 Tg · year−1, considering the global wetland area. IMPORTANCE The identification of key processes governing methane emissions from natural systems is of major importance considering the global

Anaerobic Methane Oxidation Driven by Microbial Reduction of Natural Organic Matter in a Tropical Wetland.

PubMed

Valenzuela, Edgardo I; Prieto-Davó, Alejandra; López-Lozano, Nguyen E; Hernández-Eligio, Alberto; Vega-Alvarado, Leticia; Juárez, Katy; García-González, Ana Sarahí; López, Mercedes G; Cervantes, Francisco J

2017-06-01

Wetlands constitute the main natural source of methane on Earth due to their high content of natural organic matter (NOM), but key drivers, such as electron acceptors, supporting methanotrophic activities in these habitats are poorly understood. We performed anoxic incubations using freshly collected sediment, along with water samples harvested from a tropical wetland, amended with 13 C-methane (0.67 atm) to test the capacity of its microbial community to perform anaerobic oxidation of methane (AOM) linked to the reduction of the humic fraction of its NOM. Collected evidence demonstrates that electron-accepting functional groups (e.g., quinones) present in NOM fueled AOM by serving as a terminal electron acceptor. Indeed, while sulfate reduction was the predominant process, accounting for up to 42.5% of the AOM activities, the microbial reduction of NOM concomitantly occurred. Furthermore, enrichment of wetland sediment with external NOM provided a complementary electron-accepting capacity, of which reduction accounted for ∼100 nmol 13 CH 4 oxidized · cm -3 · day -1 Spectroscopic evidence showed that quinone moieties were heterogeneously distributed in the wetland sediment, and their reduction occurred during the course of AOM. Moreover, an enrichment derived from wetland sediments performing AOM linked to NOM reduction stoichiometrically oxidized methane coupled to the reduction of the humic analogue anthraquinone-2,6-disulfonate. Microbial populations potentially involved in AOM coupled to microbial reduction of NOM were dominated by divergent biota from putative AOM-associated archaea. We estimate that this microbial process potentially contributes to the suppression of up to 114 teragrams (Tg) of CH 4 · year -1 in coastal wetlands and more than 1,300 Tg · year -1 , considering the global wetland area. IMPORTANCE The identification of key processes governing methane emissions from natural systems is of major importance considering the global warming

Microbial oxidation and reduction of manganese: consequences in groundwater and applications.

PubMed

Gounot, A M

1994-08-01

In the natural environment, manganese is found as reduced soluble or adsorbed Mn(II) and insoluble Mn(III) and Mn(IV) oxides. Mn oxidation has been reported in various microorganisms. Several possible pathways, indirect or direct, have been proposed. A wider variety of Mn-reducing microorganisms, from highly aerobic to strictly anaerobic, has been described. The mechanisms of Mn reduction can be either an indirect process resulting from interactions with organic or inorganic compounds, or a direct enzymatic (electron-transfer) reaction. The role of microorganisms in Mn cycle is now well demonstrated by various methods in superficial natural environments, and research has been initiated on subsurface sediments. Observations in vivo (Rhône valley) and under in vitro suggested that bacterial activities are the main processes that promote manganese evolution and migration in shallow aquifers. After the building of hydroelectric dams, the stream of the Rhône was modified, giving rise to mud deposition on the bank. In the mud, bacteria are stimulated by the high organic content and consume oxygen. The redox potential drops. The manganese oxides previously formed under aerobic conditions are reduced and soluble manganese (Mn(II)) migrates into the aquifer. If the subsurface sediments are coarse-grained, the aquifer is well aerated, allowing the re-oxidation of Mn(II) by the oligotrophic attached bacteria in aquifer sediments. If the aquifer is confined, aeration is not sufficient for Mn-reoxidation. Mn(II) remains in a reduced state and migrates to the wells. Furthermore, the presence of organic matter in subsurface sediments results in the reduction of previously formed Mn oxides. Pseudo-amorphous manganese oxides, which were probably recently formed by bacteria, are more readily reduced than old crystalline manganese oxides. Although the concentrations of soluble manganese found in groundwaters are not toxic, it still is a problem since its oxidation results in

Thermogravimetric, Calorimetric, and Structural Studies of the Co3 O4 /CoO Oxidation/Reduction Reaction

NASA Astrophysics Data System (ADS)

Unruh, Karl; Cichocki, Ronald; Kelly, Brian; Poirier, Gerald

2015-03-01

To better assess the potential of cobalt oxide for thermal energy storage (TES), the Co3O4/CoO oxidation/reduction reaction has been studied by thermogravimetric (TGA), calorimetric (DSC), and x-ray diffraction (XRD) measurements in N2 and atmospheric air environments. TGA measurements showed an abrupt mass loss of about 6.6% in both N2 and air, consistent with the stoichiometric reduction of Co3O4 to CoO and structural measurements. The onset temperature of the reduction of Co3O4 in air was only weakly dependent on the sample heating rate and occurred at about 910 °C. The onset temperature for the oxidation of CoO varied between about 850 and 875 °C for cooling rates between 1 and 20 °C/min, but complete re-conversion to Co3O4 could only be achieved at the slowest cooling rates. Due to the dependence of the rate constant on the oxygen partial pressure, the oxidation of Co3O4 in a N2 environment occurred at temperatures between about 775 and 825 °C for heating rates between 1 and 20 °C/min and no subsequent re-oxidation of the reduced Co3O4 was observed on cooling to room temperature. In conjunction with a measured transition heat of about 600 J/g of Co3O4, these measurements indicate that cobalt oxide is a viable TES material.

Change of Cu+ species and synergistic effect of copper and cerium during reduction-oxidation treatment for preferential CO oxidation

NASA Astrophysics Data System (ADS)

Zhang, Hao; Zhao, Xiaozhou; Wang, Shuang; Zeng, Shanghong; Su, Haiquan

2018-05-01

The CuO-CeO2@SiO2 catalyst with flower-sphere morphology was prepared by the impregnation method and then experienced the reduction-oxidation treatment at different temperatures. The multi-technique characterization shows that the reduction-oxidation treatment can remodel CuO, improve textural and surface properties and change Cu+ content and synergistic effect of copper and cerium. The importance of this work lies in the fact that the decrease of Cu+ content and synergistic effect of copper and cerium that occurs in the reduction-oxidation process results in the decrease of catalytic activity over the CuO-CeO2@SiO2 catalyst for preferential CO oxidation. The process of reaction in rich-hydrogen streams is equivalent to a reduction procedure which decreases Cu+ content and synergistic effect of copper and cerium.

Heterogeneous oxidation of SO2 by O3-aged black carbon and its dithiothreitol oxidative potential.

PubMed

Xu, Weiwei; Li, Qian; Shang, Jing; Liu, Jia; Feng, Xiang; Zhu, Tong

2015-10-01

Ozone (O3) is an important atmospheric oxidant. Black carbon (BC) particles released into the atmosphere undergo an aging process via O3 oxidation. O3-aged BC particles may change their uptake ability toward trace reducing gases such as SO2 in the atmosphere, leading to different environmental and health effects. In this paper, the heterogeneous reaction process between O3-aged BC and SO2 was explored via in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Combined with ion chromatography (IC), DRIFTS was used to qualitatively and quantitatively analyze the sulfate product. The results showed that O3-aged BC had stronger SO2 oxidation ability than fresh BC, and the reactive species/sites generated on the surface had an important role in the oxidation of SO2. Relative humidity or 254nm UV (ultraviolet) light illumination enhanced the oxidation uptake of SO2 on O3-aged BC. The oxidation potentials of the BC particles were detected via dithiothreitol (DTT) assay. The DTT activity over BC was decreased in the process of SO2 reduction, with the consumption of oxidative active sites. Copyright © 2015. Published by Elsevier B.V.

Microbial reduction of graphene oxide by Escherichia coli: a green chemistry approach.

PubMed

Gurunathan, Sangiliyandi; Han, Jae Woong; Eppakayala, Vasuki; Kim, Jin-Hoi

2013-02-01

Graphene and graphene related materials are an important area of research in recent years due to their unique properties. The extensive industrial application of graphene and related compounds has led researchers to devise novel and simple methods for the synthesis of high quality graphene. In this paper, we developed an environment friendly, cost effective, simple method and green approaches for the reduction of graphene oxide (GO) using Escherichia coli biomass. In biological method, we can avoid use of toxic and environmentally harmful reducing agents commonly used in the chemical reduction of GO to obtain graphene. The biomass of E. coli reduces exfoliated GO to graphene at 37°C in an aqueous medium. The E. coli reduced graphene oxide (ERGO) was characterized with UV-visible absorption spectroscopy, particle analyzer, high resolution X-ray diffractometer, scanning electron microscopy and Raman spectroscopy. Besides the reduction potential, the biomass could also play an important role as stabilizing agent, in which synthesized graphene exhibited good stability in water. This method can open up the new avenue for preparing graphene in cost effective and large scale production. Our findings suggest that GO can be reduced by simple eco-friendly method by using E. coli biomass to produce water dispersible graphene. Copyright © 2012 Elsevier B.V. All rights reserved.

Self-propagating solar light reduction of graphite oxide in water

NASA Astrophysics Data System (ADS)

Todorova, N.; Giannakopoulou, T.; Boukos, N.; Vermisoglou, E.; Lekakou, C.; Trapalis, C.

2017-01-01

Graphite Oxide (GtO) is commonly used as an intermediate material for preparation of graphene in the form of reduced graphene oxide (rGO). Being a semiconductor with tunable band gap rGO is often coupled with various photocatalysts to enhance their visible light activity. The behavior of such rGO-based composites could be affected after prolonged exposure to solar light. In the present work, the alteration of the GtO properties under solar light irradiation is investigated. Water dispersions of GtO manufactured by oxidation of natural graphite via Hummers method were irradiated into solar light simulator for different periods of time without addition of catalysts or reductive agent. The FT-IR analysis of the treated dispersions revealed gradual reduction of the GtO with the increase of the irradiation time. The XRD, FT-IR and XPS analyses of the obtained solid materials confirmed the transition of GtO to rGO under solar light irradiation. The reduction of the GtO was also manifested by the CV measurements that revealed stepwise increase of the specific capacitance connected with the restoration of the sp2 domains. Photothermal self-propagating reduction of graphene oxide in aqueous media under solar light irradiation is suggested as a possible mechanism. The self-photoreduction of GtO utilizing solar light provides a green, sustainable route towards preparation of reduced graphene oxide. However, the instability of the GtO and partially reduced GO under irradiation should be considered when choosing the field of its application.

Dissimilatory perchlorate reduction linked to aerobic methane oxidation via chlorite dismutase

NASA Astrophysics Data System (ADS)

Oremland, R. S.; Baesman, S. M.; Miller, L. G.

2013-12-01

The presence of methane (CH4) in the atmosphere of Mars is controversial yet the evidence has aroused scientific interest, as CH4 could be a harbinger of extant or extinct microbial life. There are various oxidized compounds present on the surface of Mars that could serve as electron acceptors for the anaerobic oxidation of CH4, including perchlorate (ClO4-). We examined the role of perchlorate, chlorate (ClO3-) and chlorite (ClO2-) as oxidants linked to CH4 oxidation. Dissimilatory perchlorate reduction begins with reduction of ClO4- to ClO2- and ends with dismutation of chlorite to yield chloride (Cl-) and molecular oxygen (O2). We explored the potential for aerobic CH4 oxidizing bacteria to couple with oxygen derived from chlorite dismutation during dissimilatory perchlorate reduction. Methane (0.2 kPa) was completely removed within several days from the N2-flushed headspace above cell suspensions of methanotrophs (Methylobacter albus strain BG8) and perchlorate reducing bacteria (Dechloromonas agitata strain CKB) in the presence of 5 mM ClO2-. Similar rates of CH4 consumption were observed for these mixed cultures whether they were co-mingled or segregated under a common headspace, indicating that direct contact of cells was not required for methane consumption to occur. We also observed complete removal of 0.2 kPa CH4 in bottles containing dried soil (enriched in methanotrophs by CH4 additions over several weeks) and D. agitata CKB and in the presence of 10 mM ClO2-. This soil (seasonally exposed sediment) collected from the shoreline of a freshwater lake (Searsville Lake, CA) demonstrated endogenous CH4 uptake as well as perchlorate, chlorate and chlorite reduction/dismutation. However, these experiments required physical separation of soil from the aqueous bacterial culture to allow for the partitioning of O2 liberated from chlorite dismutation into the shared headspace. Although dissimilatory reduction of ClO4- and ClO3- could be inferred from the

Comparative studies on single-layer reduced graphene oxide films obtained by electrochemical reduction and hydrazine vapor reduction

NASA Astrophysics Data System (ADS)

Wang, Zhijuan; Wu, Shixin; Zhang, Juan; Chen, Peng; Yang, Guocheng; Zhou, Xiaozhu; Zhang, Qichun; Yan, Qingyu; Zhang, Hua

2012-02-01

The comparison between two kinds of single-layer reduced graphene oxide (rGO) sheets, obtained by reduction of graphene oxide (GO) with the electrochemical method and hydrazine vapor reduction, referred to as E-rGO and C-rGO, respectively, is systematically studied. Although there is no morphology difference between the E-rGO and C-rGO films adsorbed on solid substrates observed by AFM, the reduction process to obtain the E-rGO and C-rGO films is quite different. In the hydrazine vapor reduction, the nitrogen element is incorporated into the obtained C-rGO film, while no additional element is introduced to the E-rGO film during the electrochemical reduction. Moreover, Raman spectra show that the electrochemical method is more effective than the hydrazine vapor reduction method to reduce the GO films. In addition, E-rGO shows better electrocatalysis towards dopamine than does C-rGO. This study is helpful for researchers to understand these two different reduction methods and choose a suitable one to reduce GO based on their experimental requirements.

Bacteria-mediated arsenic oxidation and reduction in the growth media of arsenic hyperaccumulator Pteris vittata.

PubMed

Wang, Xin; Rathinasabapathi, Bala; de Oliveira, Letuzia Maria; Guilherme, Luiz R G; Ma, Lena Q

2012-10-16

Microbes play an important role in arsenic transformation and cycling in the environment. Microbial arsenic oxidation and reduction were demonstrated in the growth media of arsenic hyperaccumulator Pteris vittata L. All arsenite (AsIII) at 0.1 mM in the media was oxidized after 48 h incubation. Oxidation was largely inhibited by antibiotics, indicating that bacteria played a dominant role. To identify AsIII oxidizing bacteria, degenerate primers were used to amplify ∼500 bp of the AsIII oxidase gene aioA (aroA) using DNA extracted from the media. One aioA (aroA)-like sequence (MG-1, tentatively identified as Acinetobacter sp.) was amplified, exhibiting 82% and 91% identity in terms of gene and deduced protein sequence to those from Acinetobacter sp. 33. In addition, four bacterial strains with different arsenic tolerance were isolated and identified as Comamonas sp.C-1, Flavobacterium sp. C-2, Staphylococcus sp. C-3, and Pseudomonas sp. C-4 using carbon utilization, fatty acid profiles, and/or sequencing 16s rRNA gene. These isolates exhibited dual capacity for both AsV reduction and AsIII oxidation under ambient conditions. Arsenic-resistant bacteria with strong AsIII oxidizing ability may have potential to improve bioremediation of AsIII-contaminated water using P. vittata and/or other biochemical strategies.

Biogenic iron oxide transformation by hyperthermophiles: spectral and physiological potentials

NASA Astrophysics Data System (ADS)

Kashyap, S.; Sklute, E.; Dyar, M. D.; Holden, J. F.

2017-12-01

It is likely that any putative life in our Solar System beyond Earth, extinct or extant, is microbial. However, to detect such life, distinct organic or mineral biosignatures need to be established. Microbe-mineral interactions and mineral transformations deserve further examination in this regard. This study focused on hyperthermophilic iron oxide-reducing archaea and addressed the types of iron-oxide minerals that are favored for growth, the kinetics of such reactions, and the mineral transformations that occur depending upon the electron acceptor. Two hyperthermophilic archaea (Pyrodictium delaneyi and Pyrobaculum islandicum) and six laboratory-synthesized nanophase iron oxide minerals (2-line ferrihydrite, lepidocrocite, akaganéite, goethite, hematite and maghemite) were tested for cell growth and Fe(II) production. The mineral end-products were further characterized by examining the spectral signatures associated with these transformations using reflectance, Raman, and Mössbauer spectroscopies and electron diffraction patterns. Additionally, we critically examined how sample preparation techniques influence the end products of these transformations by comparing freeze-dried samples against those still in solution. Results showed that both organisms utilize all six nanophase iron oxides, although with varying success. The best candidates for microbial reduction were ferrihydrite, akaganéite, and lepidocrocite. The mineral transformation products and the extent of reduction varied and showed subtle differences based on organism and the type of iron oxide used. The subtle spectral differences were best characterized using combined spectroscopy techniques. This research provides new insights into microbe-mineral interactions and the discrimination of potential biosignatures in the search for life beyond Earth.

Oxidation-Reduction Potential of Saturated Forest Soils

Treesearch

F. T. Bonner; C. W. Ralston

1968-01-01

Large decreases in redox potentials of saturated soil over a 25-day incubation period were favored by high temperature and the addition of sucrose, loblolly pine needles (Pinus taeda L. ), or yellow-poplar leaves (Liriodendron tulipifera L.). The addition of a complete nutrient solution had no effect in soils incubated with sucrose, but it reduced the drop in potential...

Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the Carson River, Nevada

USGS Publications Warehouse

Oremland, R.S.; Miller, L.G.; Dowdle, P.; Connell, T.; Barkay, T.

1995-01-01

Sediments from mercury-contaminated and uncontaminated reaches of the Carson River, Nevada, were assayed for sulfate reduction, methanogenesis, denitrification, and monomethylmercury (MeHg) degradation. Demethylation of [14C]MeHg was detected at all sites as indicated by the formation of 14CO2 and 14CH4. Oxidative demethylation was indicated by the formation of 14CO2 and was present at significant levels in all samples. Oxidized/reduced demethylation product ratios (i.e., 14CO2/14CH4 ratios) generally ranged from 4.0 in surface layers to as low as 0.5 at depth. Production of 14CO2 was most pronounced at sediment surfaces which were zones of active denitrification and sulfate reduction but was also significant within zones of methanogenesis. In a core taken from an uncontaminated site having a high proportion of oxidized, coarse-grain sediments, sulfate reduction and methanogenic activity levels were very low and 14CO2 accounted for 98% of the product formed from [14C]MeHg. There was no apparent relationship between the degree of mercury contamination of the sediments and the occurrence of oxidative demethylation. However, sediments from Fort Churchill, the most contaminated site, were most active in terms of demethylation potentials. Inhibition of sulfate reduction with molybdate resulted in significantly depressed oxidized/reduced demethylation product ratios, but overall demethylation rates of inhibited and uninhibited samples were comparable. Addition of sulfate to sediment slurries stimulated production of 14CO2 from [14C]MeHg, while 2-bromoethanesulfonic acid blocked production of 14CH4. These results reveal the importance of sulfate-reducing and methanogenic bacteria in oxidative demethylation of MeHg in anoxic environments.

Reduction-oxidation Enabled Glass-ceramics to Stainless Steel Bonding Part I: screening of doping oxidants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Steve Xunhu

Lithium silicate-based glass-ceramics with high coefficients of thermal expansion, designed to form matched hermetic seals in 304L stainless steel housing, show little evidence of interfacial chemical bonding, despite extensive inter-diffusion at the glass-ceramic-stainless steel (GC-SS) interface. A series of glass-ceramic compositions modified with a variety of oxidants, AgO, FeO, NiO, PbO, SnO, CuO, CoO, MoO 3 and WO 3, are examined for the feasibility of forming bonding oxides through reduction-oxidation (redox) at the GC-SS interface. The oxidants were selected according to their Gibbs free energy to allow for oxidation of Cr/Mn/Si from stainless steel, and yet to prevent a reductionmore » of P2O5 in the glass-ceramic where the P 2O 5 is to form Li 3PO 4 nuclei for growth of high expansion crystalline SiO 2 phases. Other than the CuO and CoO modified glass-ceramics, bonding from interfacial redox reactions were not achieved in the modified glass-ceramics, either because of poor wetting on the stainless steel or a reduction of the oxidants at the surface of glass-ceramic specimens rather than the GC-SS interface.« less

Tuning the nonlinear optical absorption of reduced graphene oxide by chemical reduction.

PubMed

Shi, Hongfei; Wang, Can; Sun, Zhipei; Zhou, Yueliang; Jin, Kuijuan; Redfern, Simon A T; Yang, Guozhen

2014-08-11

Reduced graphene oxides with varying degrees of reduction have been produced by hydrazine reduction of graphene oxide. The linear and nonlinear optical properties of both graphene oxide as well as the reduced graphene oxides have been measured by single beam Z-scan measurement in the picosecond region. The results reveal both saturable absorption and two-photon absorption, strongly dependent on the intensity of the pump pulse: saturable absorption occurs at lower pump pulse intensity (~1.5 GW/cm2 saturation intensity) whereas two-photon absorption dominates at higher intensities (≥5.7 GW/cm2). Intriguingly, we find that the two-photon absorption coefficient (from 1.5 cm/GW to 4.5cm/GW) and the saturation intensity (from 1 GW/cm2 to 2 GW/cm2) vary with chemical reduction, which is ascribed to the varying concentrations of sp2 domains and sp2 clusters in the reduced graphene oxides. Our results not only provide an insight into the evolution of the nonlinear optical coefficient in reduced graphene oxide, but also suggest that chemical engineering techniques may usefully be applied to tune the nonlinear optical properties of various nano-materials, including atomically thick graphene sheets.

Liquid-phase and solid-phase microwave irradiations for reduction of graphite oxide

NASA Astrophysics Data System (ADS)

Zhao, Na; Wen, Chen-Yu; Zhang, David Wei; Wu, Dong-Ping; Zhang, Zhi-Bin; Zhang, Shi-Li

2014-12-01

In this paper, two microwave irradiation methods: (i) liquid-phase microwave irradiation (MWI) reduction of graphite oxide suspension dissolved in de-ionized water and N, N-dimethylformamide, respectively, and (ii) solid-phase MWI reduction of graphite oxide powder have been successfully carried out to reduce graphite oxide. The reduced graphene oxide products are thoroughly characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectral analysis, Raman spectroscopy, UV-Vis absorption spectral analysis, and four-point probe conductivity measurements. The results show that both methods can efficiently remove the oxygen-containing functional groups attached to the graphite layers, though the solid-phase MWI reduction method can obtain far more efficiently a higher quality-reduced graphene oxide with fewer defects. The I(D)/I(G) ratio of the solid-phase MWI sample is as low as 0.46, which is only half of that of the liquid-phase MWI samples. The electrical conductivity of the reduced graphene oxide by the solid method reaches 747.9 S/m, which is about 25 times higher than that made by the liquid-phase method.

Effectiveness of acidic oxidative potential water in preventing bacterial infection in islet transplantation.

PubMed

Miyamoto, M; Inoue, K; Gu, Y; Hoki, M; Haji, S; Ohyanagi, H

1999-01-01

At a number of points in the current procedures of islet isolation and islet culture after the harvesting of donor pancreata, microorganisms could potentially infect the islet preparation. Furthermore, the use of islets from multiple donors can compound the risks of contamination of individual recipients. Acidic oxidative potential water (also termed electrolyzed strong acid solution, function water, or acqua oxidation water), which was developed in Japan, is a strong acid formed on the anode in the electrolysis of water containing a small amount of sodium chloride. It has these physical properties: pH, from 2.3 to 2.7; oxidative-reduction potential, from 1,000 to 1,100 mV; dissolved chlorine, from 30 to 40 ppm; and dissolved oxygen, from 10 to 30 ppm. Because of these properties, acidic oxidative potential water has strong bactericidal effects on all bacteria including methicillin-resistant Staphylococcus aureus (MRSA), viruses including HIV, HBV, HCV, CMV, and fungi as a result of the action of the active oxygen and active chlorine that it contains. We conducted this study to evaluate the effect of acidic oxidative potential water irrigation on bacterial contamination on the harvesting of porcine pancreata from slaughterhouses for islet xenotransplantation by counting the number of pancreatic surface bacteria using the Dip-slide method, and on the results of islet culture; and to evaluate the direct effect on isolated islets when it is used to prevent bacterial contamination by the static incubation test and by morphological examination. Direct irrigation of the pancreas by acidic oxidative potential water was found to be very effective in preventing bacterial contamination, but direct irrigation of isolated islets slightly decreased their viability and function.

Studies toward the oxidative and reductive activation of C-S bonds in 2'-S-aryl-2'-thiouridine derivatives.

PubMed

Rayala, Ramanjaneyulu; Giuglio-Tonolo, Alain; Broggi, Julie; Terme, Thierry; Vanelle, Patrice; Theard, Patricia; Médebielle, Maurice; Wnuk, Stanislaw F

2016-04-21

Studies directed toward the oxidative and reductive desulfurization of readily available 2'- S -aryl-2'-thiouridine derivatives were investigated with the prospect to functionalize the C2'-position of nucleosides. The oxidative desulfurization-difluorination strategy was successful on 2-(arylthio)alkanoate surrogates, while extension of the combination of oxidants and fluoride sources was not an efficient fluorination protocol when applied to 2'- S -aryl-2'-thiouridine derivatives, resulting mainly in C5-halogenation of the pyrimidine ring and C2'-monofluorination without desulfurization. Cyclic voltammetry of 2'-arylsulfonyl-2'-deoxyuridines and their 2'-fluorinated analogues showed that cleavage of the arylsulfone moiety could occur, although at relatively high cathodic potentials. While reductive-desulfonylation of 2'-arylsulfonyl-2'-deoxyuridines with organic electron donors (OEDs) gave predominantly base-induced furan type products, chemical (OED) and electrochemical reductive-desulfonylation of the α-fluorosulfone derivatives yielded the 2'-deoxy-2'-fluorouridine and 2',3'-didehydro-2',3'-dideoxy-2'-fluorouridine derivatives. These results provided good evidence of the generation of a C2'-anion through carbon-sulfur bond cleavage, opening new horizons for the reductive-functionalization approaches in nucleosides.

Studies toward the oxidative and reductive activation of C-S bonds in 2'-S-aryl-2'-thiouridine derivatives

PubMed Central

Rayala, Ramanjaneyulu; Giuglio-Tonolo, Alain; Broggi, Julie; Terme, Thierry; Vanelle, Patrice; Theard, Patricia; Médebielle, Maurice; Wnuk, Stanislaw F.

2016-01-01

Studies directed toward the oxidative and reductive desulfurization of readily available 2'-S-aryl-2'-thiouridine derivatives were investigated with the prospect to functionalize the C2'-position of nucleosides. The oxidative desulfurization-difluorination strategy was successful on 2-(arylthio)alkanoate surrogates, while extension of the combination of oxidants and fluoride sources was not an efficient fluorination protocol when applied to 2'-S-aryl-2'-thiouridine derivatives, resulting mainly in C5-halogenation of the pyrimidine ring and C2'-monofluorination without desulfurization. Cyclic voltammetry of 2'-arylsulfonyl-2'-deoxyuridines and their 2'-fluorinated analogues showed that cleavage of the arylsulfone moiety could occur, although at relatively high cathodic potentials. While reductive-desulfonylation of 2'-arylsulfonyl-2'-deoxyuridines with organic electron donors (OEDs) gave predominantly base-induced furan type products, chemical (OED) and electrochemical reductive-desulfonylation of the α-fluorosulfone derivatives yielded the 2'-deoxy-2'-fluorouridine and 2',3'-didehydro-2',3'-dideoxy-2'-fluorouridine derivatives. These results provided good evidence of the generation of a C2'-anion through carbon-sulfur bond cleavage, opening new horizons for the reductive-functionalization approaches in nucleosides. PMID:27019535

Green reduction of graphene oxide via Lycium barbarum extract

NASA Astrophysics Data System (ADS)

Hou, Dandan; Liu, Qinfu; Cheng, Hongfei; Zhang, Hao; Wang, Sen

2017-02-01

The synthesis of graphene from graphene oxide (GO) usually involves toxic reducing agents that are harmful to human health and the environment. Here, we report a facile approach for effective reduction of GO, for the first time, using Lycium barbarum extract as a green and natural reducing agent. The morphology and de-oxidation efficiency of the reduced graphene were characterized and results showed that Lycium barbarum extract can effectively reduce GO into few layered graphene with a high carbon to oxygen ratio (6.5), comparable to that of GO reduced by hydrazine hydrate (6.6). The possible reduction mechanism of GO may be due to the active components existing in Lycium barbarum fruits, which have high binding affinity to the oxygen containing groups to form their corresponding oxides and other by-products. This method avoided the use of any nocuous chemicals, thus facilitating the mass production of graphene and graphene-based bio-materials.

High-Quality Reduced Graphene Oxide by a Dual-Function Chemical Reduction and Healing Process

PubMed Central

Some, Surajit; Kim, Youngmin; Yoon, Yeoheung; Yoo, HeeJoun; Lee, Saemi; Park, Younghun; Lee, Hyoyoung

2013-01-01

A new chemical dual-functional reducing agent, thiophene, was used to produce high-quality reduced graphene oxide (rGO) as a result of a chemical reduction of graphene oxide (GO) and the healing of rGO. Thiophene reduced GO by donation of electrons with acceptance of oxygen while it was converted into an intermediate oxidised polymerised thiophene that was eventually transformed into polyhydrocarbon by loss of sulphur atoms. Surprisingly, the polyhydrocarbon template helped to produce good-quality rGOC (chemically reduced) and high-quality rGOCT after thermal treatment. The resulting rGOCT nanosheets did not contain any nitrogen or sulphur impurities, were highly deoxygenated and showed a healing effect. Thus the electrical properties of the as-prepared rGOCT were superior to those of conventional hydrazine-produced rGO that require harsh reaction conditions. Our novel dual reduction and healing method with thiophene could potentially save energy and facilitate the commercial mass production of high-quality graphene. PMID:23722643

Rate Dependency of Silver Vanadium Phosphorous Oxide Reduction

NASA Astrophysics Data System (ADS)

Cheng, Po-Jen

2011-12-01

The silver vanadium phosphorus oxide (Ag2VO2PO 4) is a high-capacity and good-compatibility material for the cathode in the battery. Due to their innovative properties, they are used as cathode in lithium batteries. Therefore, when the lithium batteries begin to discharge, the anodes of the cell perform an electrochemical oxidation and release electrons. In the mean time, the cathodes in the cells perform the electrochemical reduction and catch the electrons. For reduction of Ag2VO2PO 4, two silver ions (Ag+) catch two electrons to form silver particles, and the vanadium ions (V5+) catch two electrons to form V3+. It means that four electrons will be released by lithium anode. We call this four electrons discharge as 100% discharge. In my most of the projects, the Ag2VO2PO4 material is tested by differential scanning calorimetry (DSC) to check purity. My study is based on the discharge of batteries, and I focus on the morphology and the intensity of silver particles on the cathode after discharge. Depending on different adjustment of factors, such as discharge time, discharge rate, storage time, storage temperature, I try to investigate the silver intensity, conductivity as a function of DOD (Depth of Discharge). The silver particles could be examined by optical microscope, and scanning electron microscope (SEM). Moreover, I do some x-ray diffraction analysis to quantify the silver particles after discharge. Also, I perform magnetic susceptibility measurement to check the mechanism of the reduction of vanadium ions. Under the research on silver ions and vanadium ions, I will know a big frame of reduction process on silver vanadium phosphorous oxide and the time effect on this cathode material.

Predictive tests to evaluate oxidative potential of engineered nanomaterials

NASA Astrophysics Data System (ADS)

Ghiazza, Mara; Carella, Emanuele; Oliaro-Bosso, Simonetta; Corazzari, Ingrid; Viola, Franca; Fenoglio, Ivana

2013-04-01

Oxidative stress constitutes one of the principal injury mechanisms through which particulate toxicants (asbestos, crystalline silica, hard metals) and engineered nanomaterials can induce adverse health effects. ROS may be generated indirectly by activated cells and/or directly at the surface of the material. The occurrence of these processes depends upon the type of material. Many authors have recently demonstrated that metal oxides and carbon-based nanoparticles may influence (increasing or decreasing) the generation of oxygen radicals in a cell environment. Metal oxide, such as iron oxides, crystalline silica, and titanium dioxide are able to generate free radicals via different mechanisms causing an imbalance within oxidant species. The increase of ROS species may lead to inflammatory responses and in some cases to the development of cancer. On the other hand carbon-based nanomaterials, such as fullerene, carbon nanotubes, carbon black as well as cerium dioxide are able to scavenge the free radicals generated acting as antioxidant. The high numbers of new-engineered nanomaterials, which are introduced in the market, are exponentially increasing. Therefore the definition of toxicological strategies is urgently needed. The development of acellular screening tests will make possible the reduction of the number of in vitro and in vivo tests to be performed. An integrated protocol that may be used to predict the oxidant/antioxidant potential of engineered nanoparticles will be here presented.

Note: Rapid reduction of graphene oxide paper by glow discharge plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bo, Zheng; Qian, Jiajing; Duan, Liangping

2015-05-15

This note reports on a novel method for the rapid reduction of graphene oxide (GO) paper using a glow discharge plasma reactor. Glow discharge is produced and sustained between two parallel-plate graphite electrodes at a pressure of 240 mTorr. By exposing GO paper at the junction of negative-glow and Faraday-dark area for 4 min, the oxygen-containing groups can be effectively removed (C/O ratio increases from 2.6 to 7.9), while the material integrality and flexibility are kept well. Electrochemical measurements demonstrate that the as-obtained reduced GO paper can be potentially used for supercapacitor application.

Ceruloplasmin copper induces oxidant damage by a redox process utilizing cell-derived superoxide as reductant

NASA Technical Reports Server (NTRS)

Mukhopadhyay, C. K.; Fox, P. L.

1998-01-01

Oxidative damage by transition metals bound to proteins may be an important pathogenic mechanism. Ceruloplasmin (Cp) is a Cu-containing plasma protein thought to be involved in oxidative modification of lipoproteins. We have previously shown that Cp increased cell-mediated low-density lipoprotein (LDL) oxidation by a process requiring cell-derived superoxide, but the underlying chemical mechanism(s) is (are) unknown. We now show that superoxide reduction of Cp Cu is a critical reaction in cellular LDL oxidation. By bathocuproine disulfonate (BCS) binding and by superoxide utilization, we showed that exogenous superoxide reduces a single Cp Cu atom, the same Cu required for LDL oxidation. The Cu atom remained bound to Cp during the redox cycle. Three avenues of evidence showed that vascular cells reduce Cp Cu by a superoxide-dependent process. The 2-fold higher rate of Cp Cu reduction by smooth muscle cells (SMC) compared to endothelial cells (EC) was consistent with their relative rates of superoxide release. Furthermore, Cp Cu reduction by cells was blocked by Cu,Zn superoxide dismutase (SOD1). Finally, the level of superoxide produced by EC and SMC was sufficient to cause the amount of Cu reduction observed. An important role of Cp Cu reduction in LDL oxidation was suggested by results showing that SOD1 inhibited Cp Cu reduction and LDL oxidation by SMC with equal potency, while tumor necrosis factor-alpha stimulated both processes. In summary, these results show that superoxide is a critical cellular reductant of divalent transition metals involved in oxidation, and that protein-bound Cu is a substrate for this reaction. The role of these mechanisms in oxidative processes in vivo has yet to be defined.

Control of oxidation-reduction potential during Cheddar cheese ripening and its effect on the production of volatile flavour compounds.

PubMed

Caldeo, Veronica; Hannon, John A; Hickey, Dara-Kate; Waldron, Dave; Wilkinson, Martin G; Beresford, Thomas P; McSweeney, Paul L H

2016-11-01

In cheese, a negative oxidation-reduction (redox) potential is required for the stability of aroma, especially that associated with volatile sulphur compounds. To control the redox potential during ripening, redox agents were added to the salted curd of Cheddar cheese before pressing. The control cheese contained only salt, while different oxidising or reducing agents were added with the NaCl to the experimental cheeses. KIO3 (at 0·05, 0·1 and 1%, w/w) was used as the oxidising agent while cysteine (at 2%, w/w) and Na2S2O4 (at 0·05 and 0·1%, w/w) were used as reducing agents. During ripening the redox potential of the cheeses made with the reducing agents did not differ significantly from the control cheese (E h ≈ -120 mV) while the cheeses made with 0·1 and 0·05% KIO3 had a significantly higher and positive redox potential in the first month of ripening. Cheese made with 1% KIO3 had positive values of redox potential throughout ripening but no starter lactic acid bacteria survived in this cheese; however, numbers of starter organisms in all other cheeses were similar. Principal component analysis (PCA) of the volatile compounds clearly separated the cheeses made with the reducing agents from cheeses made with the oxidising agents at 2 month of ripening. Cheeses with reducing agents were characterized by the presence of sulphur compounds whereas cheeses made with KIO3 were characterized mainly by aldehydes. At 6 month of ripening, separation by PCA was less evident. These findings support the hypothesis that redox potential could be controlled during ripening and that this parameter has an influence on the development of cheese flavour.

Reduction of Iron-Oxide-Carbon Composites: Part III. Shrinkage of Composite Pellets during Reduction

NASA Astrophysics Data System (ADS)

Halder, S.; Fruehan, R. J.

2008-12-01

This article involves the evaluation of the volume change of iron-oxide-carbon composite pellets and its implications on reduction kinetics under conditions prevalent in a rotary hearth furnace (RHF) that were simulated in the laboratory. The pellets, in general, were found to shrink considerably during the reduction due to the loss of carbon and oxygen from the system, sintering of the iron-oxide, and formation of a molten slag phase at localized regions inside the pellets due to the presence of binder and coal/wood-charcoal ash at the reduction temperatures. One of the shortcomings of the RHF ironmaking process has been the inability to use multiple layers of composite pellets because of the impediment in heat transport to the lower layers of a multilayer bed. However, pellet shrinkage was found to have a strong effect on the reduction kinetics by virtue of enhancing the external heat transport to the lower layers. The volume change of the different kinds of composite pellets was studied as a function of reduction temperature and time. The estimation of the change in the amount of external heat transport with varying pellet sizes for a particular layer of a multilayer bed was obtained by conducting heat-transfer tests using inert low-carbon steel spheres. It was found that if the pellets of the top layer of the bed shrink by 30 pct, the external heat transfer to the second layer increases by nearly 6 times.

Dominance of sulfur-fueled iron oxide reduction in low-sulfate freshwater sediments.

PubMed

Hansel, Colleen M; Lentini, Chris J; Tang, Yuanzhi; Johnston, David T; Wankel, Scott D; Jardine, Philip M

2015-11-01

A central tenant in microbial biogeochemistry is that microbial metabolisms follow a predictable sequence of terminal electron acceptors based on the energetic yield for the reaction. It is thereby oftentimes assumed that microbial respiration of ferric iron outcompetes sulfate in all but high-sulfate systems, and thus sulfide has little influence on freshwater or terrestrial iron cycling. Observations of sulfate reduction in low-sulfate environments have been attributed to the presumed presence of highly crystalline iron oxides allowing sulfate reduction to be more energetically favored. Here we identified the iron-reducing processes under low-sulfate conditions within columns containing freshwater sediments amended with structurally diverse iron oxides and fermentation products that fuel anaerobic respiration. We show that despite low sulfate concentrations and regardless of iron oxide substrate (ferrihydrite, Al-ferrihydrite, goethite, hematite), sulfidization was a dominant pathway in iron reduction. This process was mediated by (re)cycling of sulfur upon reaction of sulfide and iron oxides to support continued sulfur-based respiration--a cryptic sulfur cycle involving generation and consumption of sulfur intermediates. Although canonical iron respiration was not observed in the sediments amended with the more crystalline iron oxides, iron respiration did become dominant in the presence of ferrihydrite once sulfate was consumed. Thus, despite more favorable energetics, ferrihydrite reduction did not precede sulfate reduction and instead an inverse redox zonation was observed. These findings indicate that sulfur (re)cycling is a dominant force in iron cycling even in low-sulfate systems and in a manner difficult to predict using the classical thermodynamic ladder.

Dominance of sulfur-fueled iron oxide reduction in low-sulfate freshwater sediments

PubMed Central

Hansel, Colleen M; Lentini, Chris J; Tang, Yuanzhi; Johnston, David T; Wankel, Scott D; Jardine, Philip M

2015-01-01

A central tenant in microbial biogeochemistry is that microbial metabolisms follow a predictable sequence of terminal electron acceptors based on the energetic yield for the reaction. It is thereby oftentimes assumed that microbial respiration of ferric iron outcompetes sulfate in all but high-sulfate systems, and thus sulfide has little influence on freshwater or terrestrial iron cycling. Observations of sulfate reduction in low-sulfate environments have been attributed to the presumed presence of highly crystalline iron oxides allowing sulfate reduction to be more energetically favored. Here we identified the iron-reducing processes under low-sulfate conditions within columns containing freshwater sediments amended with structurally diverse iron oxides and fermentation products that fuel anaerobic respiration. We show that despite low sulfate concentrations and regardless of iron oxide substrate (ferrihydrite, Al-ferrihydrite, goethite, hematite), sulfidization was a dominant pathway in iron reduction. This process was mediated by (re)cycling of sulfur upon reaction of sulfide and iron oxides to support continued sulfur-based respiration—a cryptic sulfur cycle involving generation and consumption of sulfur intermediates. Although canonical iron respiration was not observed in the sediments amended with the more crystalline iron oxides, iron respiration did become dominant in the presence of ferrihydrite once sulfate was consumed. Thus, despite more favorable energetics, ferrihydrite reduction did not precede sulfate reduction and instead an inverse redox zonation was observed. These findings indicate that sulfur (re)cycling is a dominant force in iron cycling even in low-sulfate systems and in a manner difficult to predict using the classical thermodynamic ladder. PMID:25871933

Oxidation and reduction in irradiated binary crystals of resorcinol and progesterone

NASA Astrophysics Data System (ADS)

Box, Harold C.; Budzinski, Edwin E.

1985-12-01

The binary single crystals of resorcinol and progesterone were x-irradiated at 4.2 K. The semiquinone of resorcinol was generated by radiation induced oxidation. The oxidation and reduction products were identified from ESR and ENDOR measurements. (AIP)

Single-step treatment of 2,4-dinitrotoluene via zero-valent metal reduction and chemical oxidation.

PubMed

Thomas, J Mathew; Hernandez, Rafael; Kuo, Chiang-Hai

2008-06-30

Many nitroaromatic compounds (NACs) are considered toxic and potential carcinogens. The purpose of this study was to develop an integrated reductive/oxidative process for treating NACs contaminated waters. The process consists of the combination of zero-valent iron and an ozonation based treatment technique. Corrosion promoters are added to the contaminated water to minimize passivation of the metallic species. Water contaminated with 2,4-dinitrotoluene (DNT) was treated with the integrated process using a recirculated batch reactor. It was demonstrated that addition of corrosion promoters to the contaminated water enhances the reduction of 2,4-DNT with zero-valent iron. The addition of corrosion promoters resulted in 62% decrease in 2,4-DNT concentration to 2,4-diaminotoluene. The data shows that iron reduced the 2,4-DNT and ozone oxidized these products resulting in a 73% removal of TOC and a 96% decrease in 2,4-DNT concentration.

Effect of oxidation and catalytic reduction of trace organic contaminants on their activated carbon adsorption.

PubMed

Schoutteten, Klaas V K M; Hennebel, Tom; Dheere, Ellen; Bertelkamp, Cheryl; De Ridder, David J; Maes, Synthia; Chys, Michael; Van Hulle, Stijn W H; Vanden Bussche, Julie; Vanhaecke, Lynn; Verliefde, Arne R D

2016-12-01

The combination of ozonation and activated carbon (AC) adsorption is an established technology for removal of trace organic contaminants (TrOCs). In contrast to oxidation, reduction of TrOCs has recently gained attention as well, however less attention has gone to the combination of reduction with AC adsorption. In addition, no literature has compared the removal behavior of reduction vs. ozonation by-products by AC. In this study, the effect of pre-ozonation vs pre-catalytic reduction on the AC adsorption efficiency of five TrOCs and their by-products was compared. All compounds were susceptible to oxidation and reduction, however the catalytic reductive treatment proved to be a slower reaction than ozonation. New oxidation products were identified for dinoseb and new reduction products were identified for carbamazepine, bromoxynil and dinoseb. In terms of compatibility with AC adsorption, the influence of the oxidative and reductive pretreatments proved to be compound dependent. Oxidation products of bromoxynil and diatrizoic acid adsorbed better than their parent TrOCs, but oxidation products of atrazine, carbamazepine and dinoseb showed a decreased adsorption. The reductive pre-treatment showed an enhanced AC adsorption for dinoseb and a major enhancement for diatrizoic acid. For atrazine and bromoxynil, no clear influence on adsorption was noted, while for carbamazepine, the reductive pretreatment resulted in a decreased AC affinity. It may thus be concluded that when targeting mixtures of TrOCs, a trade-off will undoubtedly have to be made towards overall reactivity and removal of the different constituents, since no single treatment proves to be superior to the other. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reduced-graphene-oxide supported tantalum-based electrocatalysts: Controlled nitrogen doping and oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Yang, Xiaoyun; Mo, Qijie; Guo, Yulin; Chen, Nana; Gao, Qingsheng

2018-03-01

Controlled N-doping is feasible to engineer the surface stoichiometry and the electronic configuration of metal-oxide electrocatalysts toward efficient oxygen reduction reactions (ORR). Taking reduced graphene oxide supported tantalum-oxides (TaOx/RGO) for example, this work illustrated the controlled N-doping in both metal-oxides and carbon supports, and the contribution to the improved ORR activity. The active N-doped TaOx/RGO electrocatalysts were fabricated via SiO2-assisted pyrolysis, in which the amount and kind of N-doping were tailored toward efficient electrocatalysis. The optimal nanocomposites showed a quite positive half-wave potential (0.80 V vs. RHE), the excellent long-term stability, and the outstanding tolerance to methanol crossing. The improvement in ORR was reasonably attributed to the synergy between N-doped TaOx and N-doped RGO. Elucidating the importance of controlled N-doping for electrocatalysis, this work will open up new opportunities to explore noble-metal-free materials for renewable energy applications.

Reduction potentials of heterometallic manganese–oxido cubane complexes modulated by redox-inactive metals

PubMed Central

Tsui, Emily Y.; Agapie, Theodor

2013-01-01

Understanding the effect of redox-inactive metals on the properties of biological and heterogeneous water oxidation catalysts is important both fundamentally and for improvement of future catalyst designs. In this work, heterometallic manganese–oxido cubane clusters [MMn3O4] (M = Sr2+, Zn2+, Sc3+, Y3+) structurally relevant to the oxygen-evolving complex (OEC) of photosystem II were prepared and characterized. The reduction potentials of these clusters and other related mixed metal manganese–tetraoxido complexes are correlated with the Lewis acidity of the apical redox-inactive metal in a manner similar to a related series of heterometallic manganese–dioxido clusters. The redox potentials of the [SrMn3O4] and [CaMn3O4] clusters are close, which is consistent with the observation that the OEC is functional only with one of these two metals. Considering our previous studies of [MMn3O2] moieties, the present results with more structurally accurate models of the OEC ([MMn3O4]) suggest a general relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidities of incorporated cations that applies to diverse structural motifs. These findings support proposals that one function of calcium in the OEC is to modulate the reduction potential of the cluster to allow electron transfer. PMID:23744039

Dual passivation of intrinsic defects at the compound semiconductor/oxide interface using an oxidant and a reductant.

PubMed

Kent, Tyler; Chagarov, Evgeniy; Edmonds, Mary; Droopad, Ravi; Kummel, Andrew C

2015-05-26

Studies have shown that metal oxide semiconductor field-effect transistors fabricated utilizing compound semiconductors as the channel are limited in their electrical performance. This is attributed to imperfections at the semiconductor/oxide interface which cause electronic trap states, resulting in inefficient modulation of the Fermi level. The physical origin of these states is still debated mainly because of the difficulty in assigning a particular electronic state to a specific physical defect. To gain insight into the exact source of the electronic trap states, density functional theory was employed to model the intrinsic physical defects on the InGaAs (2 × 4) surface and to model the effective passivation of these defects by utilizing both an oxidant and a reductant to eliminate metallic bonds and dangling-bond-induced strain at the interface. Scanning tunneling microscopy and spectroscopy were employed to experimentally determine the physical and electronic defects and to verify the effectiveness of dual passivation with an oxidant and a reductant. While subsurface chemisorption of oxidants on compound semiconductor substrates can be detrimental, it has been shown theoretically and experimentally that oxidants are critical to removing metallic defects at oxide/compound semiconductor interfaces present in nanoscale channels, oxides, and other nanostructures.

Two-electron Reduction versus One-electron Oxidation of the Type 3 Pair in the Multicopper Oxidases

PubMed Central

Kjaergaard, Christian H.; Jones, Stephen M.; Gounel, Sébastien; Mano, Nicolas; Solomon, Edward I.

2015-01-01

Multicopper Oxidases (MCOs) utilize an electron shuttling Type 1 Cu (T1) site in conjunction with a mononuclear Type 2 (T2) and a binuclear Type 3 (T3) site, arranged in a trinuclear copper cluster (TNC), to reduce O2 to H2O. Reduction of O2 occurs with limited overpotential indicating that all the coppers in the active site can be reduced via high-potential electron donors. Two forms of the resting enzyme have been observed in MCOs: the Alternative Resting form (AR), where only one of the three TNC Cu’s is oxidized, and the Resting Oxidized form (RO), where all three TNC Cu’s are oxidized. In contrast to the AR form, we show that in the RO form of a high-potential MCO, the binuclear T3 Cu(II) site can be reduced via the 700 mV T1 Cu. Systematic spectroscopic evaluation reveals that this proceeds by a two-electron process, where delivery of the first electron, forming a high energy, meta-stable half reduced T3 state, is followed by the rapid delivery of a second energetically favorable electron to fully reduce the T3 site. Alternatively, when this fully reduced binuclear T3 site is oxidized via the T1 Cu, a different thermodynamically favored half oxidized T3 form, i.e. the AR site, is generated. This behavior is evaluated by DFT calculations, which reveal that the protein backbone plays a significant role in controlling the environment of the active site coppers. This allows for the formation of the meta-stable, half reduced state and thus the complete reductive activation of the enzyme for catalysis. PMID:26075678

Direct chemical reduction of neptunium oxide to neptunium metal using calcium and calcium chloride

DOE PAGES

Squires, Leah N.; Lessing, Paul

2016-01-13

A process of direct reduction of neptunium oxide to neptunium metal using calcium metal as the reducing agent is discussed. After reduction of the oxide to metal, the metal is separated by density from the other components of the reaction mixture and can easily removed upon cooling. Furthermore, the direct reduction technique consistently produces high purity (98%–99% pure) neptunium metal.

Biomineralization associated with microbial reduction of Fe3+ and oxidation of Fe2+ in solid minerals

USGS Publications Warehouse

Zhang, G.; Dong, H.; Jiang, H.; Kukkadapu, R.K.; Kim, J.; Eberl, D.; Xu, Z.

2009-01-01

Iron-reducing and oxidizing microorganisms gain energy through reduction or oxidation of iron, and by doing so play an important role in the geochemical cycling of iron. This study was undertaken to investigate mineral transformations associated with microbial reduction of Fe3+ and oxidation of Fe2+ in solid minerals. A fluid sample from the 2450 m depth of the Chinese Continental Scientific Drilling project was collected, and Fe3+-reducing and Fe2+-oxidizing microorganisms were enriched. The enrichment cultures displayed reduction of Fe3+ in nontronite and ferric citrate, and oxidation of Fe2+ in vivianite, siderite, and monosulfide (FeS). Additional experiments verified that the iron reduction and oxidation was biological. Oxidation of FeS resulted in the formation of goethite, lepidocrocite, and ferrihydrite as products. Although our molecular microbiological analyses detected Thermoan-aerobacter ethanolicus as a predominant organism in the enrichment culture, Fe3+ reduction and Fe2+ oxidation may be accomplished by a consortia of organisms. Our results have important environmental and ecological implications for iron redox cycling in solid minerals in natural environments, where iron mineral transformations may be related to the mobility and solubility of inorganic and organic contaminants.

Effects of oxidants and reductants on the efficiency of excitation transfer in green photosynthetic bacteria

NASA Technical Reports Server (NTRS)

Wang, J.; Brune, D. C.; Blankenship, R. E.

1990-01-01

The efficiency of energy transfer in chlorosome antennas in the green sulfur bacteria Chlorobium vibrioforme and Chlorobium limicola was found to be highly sensitive to the redox potential of the suspension. Energy transfer efficiencies were measured by comparing the absorption spectrum of the bacteriochlorophyll c or d pigments in the chlorosome to the excitation spectrum for fluorescence arising from the chlorosome baseplate and membrane-bound antenna complexes. The efficiency of energy transfer approaches 100% at low redox potentials induced by addition of sodium dithionite or other strong reductants, and is lowered to 10-20% under aerobic conditions or after addition of a variety of membrane-permeable oxidizing agents. The redox effect on energy transfer is observed in whole cells, isolated membranes and purified chlorosomes, indicating that the modulation of energy transfer efficiency arises within the antenna complexes and is not directly mediated by the redox state of the reaction center. It is proposed that chlorosomes contain a component that acts as a highly quenching center in its oxidized state, but is an inefficient quencher when reduced by endogenous or exogenous reductants. This effect may be a control mechanism that prevents cellular damage resulting from reaction of oxygen with reduced low-potential electron acceptors found in the green sulfur bacteria. The redox modulation effect is not observed in the green gliding bacterium Chloroflexus aurantiacus, which contains chlorosomes but does not contain low-potential electron acceptors.

Extraction of copper from an oxidized (lateritic) ore using bacterially catalysed reductive dissolution.

PubMed

Nancucheo, Ivan; Grail, Barry M; Hilario, Felipe; du Plessis, Chris; Johnson, D Barrie

2014-01-01

An oxidized lateritic ore which contained 0.8 % (by weight) copper was bioleached in pH- and temperature-controlled stirred reactors under acidic reducing conditions using pure and mixed cultures of the acidophilic chemolithotrophic bacterium Acidithiobacillus ferrooxidans. Sulfur was provided as the electron donor for the bacteria, and ferric iron present in goethite (the major ferric iron mineral present in the ore) acted as electron acceptor. Significantly more copper was leached by bacterially catalysed reductive dissolution of the laterite than in aerobic cultures or in sterile anoxic reactors, with up to 78 % of the copper present in the ore being extracted. This included copper that was leached from acid-labile minerals (chiefly copper silicates) and that which was associated with ferric iron minerals in the lateritic ore. In the anaerobic bioreactors, soluble iron in the leach liquors was present as iron (II) and copper as copper (I), but both metals were rapidly oxidized (to iron (III) and copper (II)) when the reactors were aerated. The number of bacteria added to the reactors had a critical role in dictating the rate and yield of copper solubilised from the ore. This work has provided further evidence that reductive bioprocessing, a recently described approach for extracting base metals from oxidized deposits, has the potential to greatly extend the range of metal ores that can be biomined.

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.

Electrocatalytic CO2 reduction near the theoretical potential in water using Ru complex supported on carbon nanotubes

NASA Astrophysics Data System (ADS)

Sato, Shunsuke; Arai, Takeo; Morikawa, Takeshi

2018-01-01

We successfully developed a highly efficient electrode for CO2 reduction using a Ru-complex catalyst ([Ru]) supported on carbon paper coated with multi-walled carbon nanotubes (CPCNT/[Ru]). The CPCNT/[Ru] electrode promoted the CO2 reduction reaction in aqueous solution near the theoretical potential, and produced formate linearly with a current density of greater than 0.9 mA cm-2 at -0.15 V (versus RHE) for at least 24 h. Due to the outstandingly low overpotential, a monolithic tablet-shaped photo-device was realized by coupling the CPCNT/[Ru] catalyst with amorphous SiGe-jn as a light absorber and IrO x as a water oxidation catalyst, and the device produced formate from CO2 and water in a single-compartment reactor. The nanotubes enhanced the rate for CO2 reduction at [Ru], and accordingly a solar-to-chemical conversion efficiency of 4.3% for formate production was achieved when the CO2 reduction and H2O oxidation sites had the same area.

Surface-Potential-Based Metal-Oxide-Silicon-Varactor Model for RF Applications

NASA Astrophysics Data System (ADS)

Miyake, Masataka; Sadachika, Norio; Navarro, Dondee; Mizukane, Yoshio; Matsumoto, Kenji; Ezaki, Tatsuya; Miura-Mattausch, Mitiko; Mattausch, Hans Juergen; Ohguro, Tatsuya; Iizuka, Takahiro; Taguchi, Masahiko; Kumashiro, Shigetaka; Miyamoto, Shunsuke

2007-04-01

We have developed a surface-potential-based metal-oxide-silicon (MOS)-varactor model valid for RF applications up to 200 GHz. The model enables the calculation of the MOS-varactor capacitance seamlessly from the depletion region to the accumulation region and explicitly considers the carrier-response delay causing a non-quasi-static (NQS) effect. It has been observed that capacitance reduction due to this non-quasi-static effect limits the MOS-varactor application to an RF regime.

Potential role of punicalagin against oxidative stress induced testicular damage.

PubMed

Rao, Faiza; Tian, Hui; Li, Wenqing; Hung, Helong; Sun, Fei

2016-01-01

Punicalagin is isolated from pomegranate and widely used for the treatment of different diseases in Chinese traditional medicine. This study aimed to evaluate the effect of Punicalagin (purity ≥98%) on oxidative stress induced testicular damage and its effect on fertility. We detected the antioxidant potential of punicalagin in lipopolysaccharide (LPS) induced oxidative stress damage in testes, also tried to uncover the boosting fertility effect of Punicalagin (PU) against oxidative stress-induced infertility. Results demonstrated that 9 mg kg-1 for 7 days treatment significantly decreases LPS induced oxidative damage in testes and nitric oxide production. The administration of oxidative stress resulted in a significant reduction in testes antioxidants GSH, T-SOD, and CAT raised LPO, but treatment with punicalagin for 7 days increased antioxidant defense GSH, T-SOD, and CAT by the end of the experiment and reduced LPO level as well. PU also significantly activates Nrf2, which is involved in regulation of antioxidant defense systems. Hence, the present research categorically elucidates the protective effect of punicalagin against LPS induced oxidative stress induced perturbation in the process of spermatogenesis and significantly increased sperm health and number. Moreover, fertility success significantly decreased in LPS-injected mice compared to controls. Mice injected with LPS had fertility indices of 12.5%, while others treated with a combination of PU + LPS exhibited 75% indices. By promoting fertility and eliminating oxidative stress and inflammation, PU may be a useful nutrient for the treatment of infertility.

Potential role of punicalagin against oxidative stress induced testicular damage

PubMed Central

Rao, Faiza; Tian, Hui; Li, Wenqing; Hung, Helong; Sun, Fei

2016-01-01

Punicalagin is isolated from pomegranate and widely used for the treatment of different diseases in Chinese traditional medicine. This study aimed to evaluate the effect of Punicalagin (purity ≥98%) on oxidative stress induced testicular damage and its effect on fertility. We detected the antioxidant potential of punicalagin in lipopolysaccharide (LPS) induced oxidative stress damage in testes, also tried to uncover the boosting fertility effect of Punicalagin (PU) against oxidative stress-induced infertility. Results demonstrated that 9 mg kg−1 for 7 days treatment significantly decreases LPS induced oxidative damage in testes and nitric oxide production. The administration of oxidative stress resulted in a significant reduction in testes antioxidants GSH, T-SOD, and CAT raised LPO, but treatment with punicalagin for 7 days increased antioxidant defense GSH, T-SOD, and CAT by the end of the experiment and reduced LPO level as well. PU also significantly activates Nrf2, which is involved in regulation of antioxidant defense systems. Hence, the present research categorically elucidates the protective effect of punicalagin against LPS induced oxidative stress induced perturbation in the process of spermatogenesis and significantly increased sperm health and number. Moreover, fertility success significantly decreased in LPS-injected mice compared to controls. Mice injected with LPS had fertility indices of 12.5%, while others treated with a combination of PU + LPS exhibited 75% indices. By promoting fertility and eliminating oxidative stress and inflammation, PU may be a useful nutrient for the treatment of infertility. PMID:26763544

Humin as an electron donor for enhancement of multiple microbial reduction reactions with different redox potentials in a consortium.

PubMed

Zhang, Dongdong; Zhang, Chunfang; Xiao, Zhixing; Suzuki, Daisuke; Katayama, Arata

2015-02-01

A solid-phase humin, acting as an electron donor, was able to enhance multiple reductive biotransformations, including dechlorination of pentachlorophenol (PCP), dissimilatory reduction of amorphous Fe (III) oxide (FeOOH), and reduction of nitrate, in a consortium. Humin that was chemically reduced by NaBH4 served as an electron donor for these microbial reducing reactions, with electron donating capacities of 0.013 mmol e(-)/g for PCP dechlorination, 0.15 mmol e(-)/g for iron reduction, and 0.30 mmol e(-)/g for nitrate reduction. Two pairs of oxidation and reduction peaks within the humin were detected by cyclic voltammetry analysis. 16S rRNA gene sequencing-based microbial community analysis of the consortium incubated with different terminal electron acceptors, suggested that Dehalobacter sp., Bacteroides sp., and Sulfurospirillum sp. were involved in the PCP dechlorination, dissimilatory iron reduction, and nitrate reduction, respectively. These findings suggested that humin functioned as a versatile redox mediator, donating electrons for multiple respiration reactions with different redox potentials. Copyright © 2014 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Nitric oxide alleviates wheat yield reduction by protecting photosynthetic system from oxidation of ozone pollution.

PubMed

Li, Caihong; Song, Yanjie; Guo, Liyue; Gu, Xian; Muminov, Mahmud A; Wang, Tianzuo

2018-05-01

Accelerated industrialization has been increasing releases of chemical precursors of ozone. Ozone concentration has risen nowadays, and it's predicted that this trend will continue in the next few decades. The yield of many ozone-sensitive crops suffers seriously from ozone pollution, and there are abundant reports exploring the damage mechanisms of ozone to these crops, such as winter wheat. However, little is known on how to alleviate these negative impacts to increase grain production under elevated ozone. Nitric oxide, as a bioactive gaseous, mediates a variety of physiological processes and plays a central role in response to biotic and abiotic stresses. In the present study, the accumulation of endogenous nitric oxide in wheat leaves was found to increase in response to ozone. To study the functions of nitric oxide, its precursor sodium nitroprusside was spayed to wheat leaves under ozone pollution. Wheat leaves spayed with sodium nitroprusside accumulated less hydrogen peroxide, malondialdehyde and electrolyte leakage under ozone pollution, which can be accounted for by the higher activities of superoxide dismutase and peroxidase than in leaves treated without sodium nitroprusside. Consequently, net photosynthetic rate of wheat treated using sodium nitroprusside was much higher, and yield reduction was alleviated under ozone fumigation. These findings are important for our understanding of the potential roles of nitric oxide in responses of crops in general and wheat in particular to ozone pollution, and provide a viable method to mitigate the detrimental effects on crop production induced by ozone pollution, which is valuable for keeping food security worldwide. Copyright © 2018 Elsevier Ltd. All rights reserved.

Phosphine-functionalized graphene oxide, a high-performance electrocatalyst for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Ensafi, Ali A.; Golbon Haghighi, Mohsen; Jafari-Asl, Mehdi

2018-01-01

Here, a new approach for the synthesis of phosphine-functionalized graphene oxide (GO-PPh2) was developed. Using a simple method, diphenylphosphine group was linked to the hydroxyl group of OH-functionalized graphene that existing at the graphene surface. The electrochemical activity of GO-PPh2 for electrochemical oxygen reduction was checked. The results demonstrated that the new carbon hybrid material has a powerful potential for electrochemical oxygen reduction reaction (ORR). Moreover, GO-PPh2 as an electrocatalyst for ORR exhibited tolerance for methanol or ethanol as a result of crossover effect. In comparison with commercial Pt/C and Pt/rGO electrocatalysts, results showed that GO-PPh2 has a much higher selectivity, better durability, and much better electrochemical stability towards the ORR. The proposed method based on GO-PPh2 introduce an efficient electrocatalyst for further application in fuel cells.

Removal of PCBs in contaminated soils by means of chemical reduction and advanced oxidation processes.

PubMed

Rybnikova, V; Usman, M; Hanna, K

2016-09-01

Although the chemical reduction and advanced oxidation processes have been widely used individually, very few studies have assessed the combined reduction/oxidation approach for soil remediation. In the present study, experiments were performed in spiked sand and historically contaminated soil by using four synthetic nanoparticles (Fe(0), Fe/Ni, Fe3O4, Fe3 - x Ni x O4). These nanoparticles were tested firstly for reductive transformation of polychlorinated biphenyls (PCBs) and then employed as catalysts to promote chemical oxidation reactions (H2O2 or persulfate). Obtained results indicated that bimetallic nanoparticles Fe/Ni showed the highest efficiency in reduction of PCB28 and PCB118 in spiked sand (97 and 79 %, respectively), whereas magnetite (Fe3O4) exhibited a high catalytic stability during the combined reduction/oxidation approach. In chemical oxidation, persulfate showed higher PCB degradation extent than hydrogen peroxide. As expected, the degradation efficiency was found to be limited in historically contaminated soil, where only Fe(0) and Fe/Ni particles exhibited reductive capability towards PCBs (13 and 18 %). In oxidation step, the highest degradation extents were obtained in presence of Fe(0) and Fe/Ni (18-19 %). The increase in particle and oxidant doses improved the efficiency of treatment, but overall degradation extents did not exceed 30 %, suggesting that only a small part of PCBs in soil was available for reaction with catalyst and/or oxidant. The use of organic solvent or cyclodextrin to improve the PCB availability in soil did not enhance degradation efficiency, underscoring the strong impact of soil matrix. Moreover, a better PCB degradation was observed in sand spiked with extractable organic matter separated from contaminated soil. In contrast to fractions with higher particle size (250-500 and <500 μm), no PCB degradation was observed in the finest fraction (≤250 μm) having higher organic matter content. These findings

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

Localized conductive patterning via focused electron beam reduction of graphene oxide

NASA Astrophysics Data System (ADS)

Kim, Songkil; Kulkarni, Dhaval D.; Henry, Mathias; Zackowski, Paul; Jang, Seung Soon; Tsukruk, Vladimir V.; Fedorov, Andrei G.

2015-03-01

We report on a method for "direct-write" conductive patterning via reduction of graphene oxide (GO) sheets using focused electron beam induced deposition (FEBID) of carbon. FEBID treatment of the intrinsically dielectric graphene oxide between two metal terminals opens up the conduction channel, thus enabling a unique capability for nanoscale conductive domain patterning in GO. An increase in FEBID electron dose results in a significant increase of the domain electrical conductivity with improving linearity of drain-source current vs. voltage dependence, indicative of a change of graphene oxide electronic properties from insulating to semiconducting. Density functional theory calculations suggest a possible mechanism underlying this experimentally observed phenomenon, as localized reduction of graphene oxide layers via interactions with highly reactive intermediates of electron-beam-assisted dissociation of surface-adsorbed hydrocarbon molecules. These findings establish an unusual route for using FEBID as nanoscale lithography and patterning technique for engineering carbon-based nanomaterials and devices with locally tailored electronic properties.

Nitrous oxide reduction in nodules: denitrification or N/sub 2/ fixation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coyne, M.S.; Focht, D.D.

1987-05-01

Detached cowpea nodules that contained a nitrous oxide reductase-positive (Nor/sup +/) rhizobium strain (8A55) and a nitrous oxide reductase-negative (Nor/sup -/) rhizobium strain (32H1) were incubated with 1% /sup 15/N/sub 2/O (95 atom% /sup 15/N) in the following three atmospheres: aerobic with C/sub 2/H/sub 2/ (10%), aerobic without C/sub 2/H/sub 2/, and anaerobic (argon atmosphere) without C/sub 2/H/sub 2/. The greatest production of /sup 15/N/sub 2/ occurred anaerobically with 8A55, yet very little was formed with 32H1. Although acetylene reduction activity was slightly higher with 32H1, about 10 times more /sup 15/N/sub 2/ was produced aerobically by 8A55 than bymore » 32H1 in the absence of acetylene. The major reductive pathway of N/sub 2/O reduction by denitrifying rhizobium strain 8A55 is by nitrous oxide reductase rather than nitrogenase.« less

Investigation of the reduction process of dopamine using paired pulse voltammetry

PubMed Central

Kim, Do Hyoung; Oh, Yoonbae; Shin, Hojin; Blaha, Charles D.; Bennet, Kevin E.; Lee, Kendall H.; Kim, In Young; Jang, Dong Pyo

2014-01-01

The oxidation of dopamine (DA) around +0.6V potential in anodic sweep and its reduction around −0.1V in cathodic sweep at a relatively fast scanning rate (300 V/s or greater) have been used for identification of DA oxidation in fast-scan cyclic voltammetry (FSCV). However, compared to the oxidation peak of DA, the reduction peak has not been fully examined in analytical studies, although it has been used as one of the representative features to identify DA. In this study, the reduction process of DA was investigated using paired pulse voltammetry (PPV), which consists of two identical triangle-shaped waveforms, separated by a short interval at the holding potential. Especially, the discrepancies between the magnitude of the oxidation and reduction peaks of DA were investigated based on three factors: (1) the instant desorption of the DA oxidation product (dopamine-o-quinone: DOQ) after production, (2) the effect of the holding potential on the reduction process, and (3) the rate-limited reduction process of DA. For the first test, the triangle waveform FSCV experiment was performed on DA with various scanrates (from 400 to 1000 V/s) and durations of switching potentials of the triangle waveform (from 0.0 to 6.0 ms) in order to vary the duration between the applied oxidation potential at +0.6V and the reduction potential at −0.2V. As a result, the ratio of reduction over oxidation peak current response decreased as the duration became longer. To evaluate the effect of holding potentials during the reduction process, FSCV experiments were conducted with holding potential from 0.0V to −0.8V. We found that more negative holding potentials lead to larger amount of reduction process. For evaluation of the rate-limited reduction process of DA, PPV with a 1Hz repetition rate and various delays (2, 8, 20, 40 and 80ms) between the paired scans were utilized to determine how much reduction process occurred during the holding potential (−0.4V). These tests showed that

Isothermal Oxidation of Magnetite to Hematite in Air and Cyclic Reduction/Oxidation Under Carbon Looping Combustion Conditions

NASA Astrophysics Data System (ADS)

Simmonds, Tegan; Hayes, Peter C.

2017-12-01

In the carbon looping combustion process the oxygen carrier is regenerated through oxidation in air; this process has been simulated by the oxidation of dense synthetic magnetite for selected temperatures and times. The oxidation of magnetite in air is shown to occur through the formation of dense hematite layers on the particle surface. This dense hematite forms through lath type shear transformations or solid-state diffusion through the product layer. Cyclic reduction in CO-CO2/oxidation in air of hematite single crystals has been carried out under controlled laboratory conditions at 1173 K (900 °C). It has been shown that the initial reduction step is critical to determining the product microstructure, which consists of gas pore dendrites in the magnetite matrix with blocky hematite formed on the pore surfaces. The progressive growth of the magnetite layer with the application of subsequent cycles appears to continue until no original hematite remains, after which physical disintegration of the particles takes place.

MiOXSYS: a novel method of measuring oxidation reduction potential in semen and seminal plasma.

PubMed

Agarwal, Ashok; Sharma, Rakesh; Roychoudhury, Shubhadeep; Du Plessis, Stefan; Sabanegh, Edmund

2016-09-01

To measure oxidative reduction potential (ORP) in semen and seminal plasma and to establish their reference levels. ORP levels were measured in semen and seminal plasma. Tertiary hospital. Twenty-six controls and 33 infertile men. None. Static ORP (sORP) and capacitance ORP (cORP) were measured in semen and seminal plasma at time 0 and 120 minutes. Correlation of ORP was assessed between [1] semen and seminal plasma and [2] time 0 and 120 minutes. The association with sperm parameters was studied in (a) controls and (b) infertile patients, and a receiver operating characteristic curve was generated to establish the sORP cutoff. Semen sORP and cORP levels were associated with seminal plasma levels at time 0 and time 120 minutes. In controls and infertile patients, an inverse relationship of sORP levels was established with concentration and total sperm count in semen as well as seminal plasma at time 0 and 120 minutes. Classification of subjects based on sperm motility showed that subjects with abnormal motility present with poor concentration, total count, morphology, and elevated levels of semen and seminal plasma sORP at time 120 minutes. The sORP cutoff of 1.48 in semen and 2.09 in seminal plasma based on motility was able to distinguish subjects with normal semen quality from those with abnormal semen quality. The MiOXSYS System can reliably measure ORP levels in semen and seminal plasma. ORP levels are not affected by semen age, making this new technology easy to employ in a clinical setting. Copyright © 2016 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.

INFLUENCE OF PH AND OXIDATION-REDUCTION POTENTIAL (EH) ON THE DISSOLUTION OF MERCURY-CONTAINING MINE WASTES FROM THE SULFUR BANK MERCURY MINE

EPA Science Inventory

This study was undertaken as a part of developing treatment alternatives for waste materials, primarily waste rock and roaster tailings, from sites contaminated with mercury (Hg) mining wastes. Leaching profiles of waste rock over a range of different pH and oxidation-reduction (...

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.

Cell oxidation-reduction imbalance after modulated radiofrequency radiation.

PubMed

Marjanovic, Ana Marija; Pavicic, Ivan; Trosic, Ivancica

2015-01-01

Aim of this study was to evaluate an influence of modulated radiofrequency field (RF) of 1800 MHz, strength of 30 V/m on oxidation-reduction processes within the cell. The assigned RF field was generated within Gigahertz Transversal Electromagnetic Mode cell equipped by signal generator, modulator, and amplifier. Cell line V79, was irradiated for 10, 30, and 60 min, specific absorption rate was calculated to be 1.6 W/kg. Cell metabolic activity and viability was determined by MTT assay. In order to define total protein content, colorimetric method was used. Concentration of oxidised proteins was evaluated by enzyme-linked immunosorbent assay. Reactive oxygen species (ROS) marked with fluorescent probe 2',7'-dichlorofluorescin diacetate were measured by means of plate reader device. In comparison with control cell samples, metabolic activity and total protein content in exposed cells did not differ significantly. Concentrations of carbonyl derivates, a product of protein oxidation, insignificantly but continuously increase with duration of exposure. In exposed samples, ROS level significantly (p < 0.05) increased after 10 min of exposure. Decrease in ROS level was observed after 30-min treatment indicating antioxidant defence mechanism activation. In conclusion, under the given laboratory conditions, modulated RF radiation might cause impairment in cell oxidation-reduction equilibrium within the growing cells.

Nanoscale reduction of graphene oxide thin films and its characterization

NASA Astrophysics Data System (ADS)

Lorenzoni, M.; Giugni, A.; Di Fabrizio, E.; Pérez-Murano, Francesc; Mescola, A.; Torre, B.

2015-07-01

In this paper, we report on a method to reduce thin films of graphene oxide (GO) to a spatial resolution better than 100 nm over several tens of micrometers by means of an electrochemical scanning probe based lithography. In situ tip-current measurements show that an edged drop in electrical resistance characterizes the reduced areas, and that the reduction process is, to a good approximation, proportional to the applied bias between the onset voltage and the saturation thresholds. An atomic force microscope (AFM) quantifies the drop of the surface height for the reduced profile due to the loss of oxygen. Complementarily, lateral force microscopy reveals a homogeneous friction coefficient of the reduced regions that is remarkably lower than that of native graphene oxide, confirming a chemical change in the patterned region. Micro Raman spectroscopy, which provides access to insights into the chemical process, allows one to quantify the restoration and de-oxidation of the graphitic network driven by the electrochemical reduction and to determine characteristic length scales. It also confirms the homogeneity of the process over wide areas. The results shown were obtained from accurate analysis of the shift, intensity and width of Raman peaks for the main vibrational bands of GO and reduced graphene oxide (rGO) mapped over large areas. Concerning multilayered GO thin films obtained by drop-casting we have demonstrated an unprecedented lateral resolution in ambient conditions as well as an improved control, characterization and understanding of the reduction process occurring in GO randomly folded multilayers, useful for large-scale processing of graphene-based material.

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

NASA Astrophysics Data System (ADS)

Halder, S.; Fruehan, R. J.

2008-12-01

A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO2 and wüstite reduction by CO by isolating them from the influence of heat- and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wüstite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coal-char. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wüstite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wüstite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

Sulfur doped reduced graphene oxides with enhanced catalytic activity for oxygen reduction via molten salt redox-sulfidation.

PubMed

Gu, Yuxing; Chen, Zhigang; Tang, Juanjuan; Xiao, Wei; Mao, Xuhui; Zhu, Hua; Wang, Dihua

2016-12-07

A spontaneous redox reaction of reduced graphene oxide (rGO) in molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 with a small amount of Li 2 SO 4 at 550 °C was applied to synthesize sulfur and sulfur-cobalt doped rGOs (S-rGO/S-Co-rGO). The obtained S-rGOs and S-Co-rGOs show enhanced catalytic activity for the oxygen reduction reaction (ORR) in alkaline aqueous solutions. The onset reduction potential and the half-wave potential of S-Co-rGO are 60 and 40 mV more positive than those of the original rGO, respectively. The reduction current density of S-Co-rGO increases by nearly five times. This study provides a green and continuous molten salt doping approach for the fabrication of heteroatom-doped graphene with excellent catalytic activity for the ORR.

In vitro enzymatic reduction kinetics of mineral oxides by membrane fractions from Shewanella oneidensis MR-1

NASA Astrophysics Data System (ADS)

Ruebush, Shane S.; Icopini, Gary A.; Brantley, Susan L.; Tien, Ming

2006-01-01

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite/pyrolusite using formate. In contrast, nicotinamide adenine dinucleotide (NADH) and succinate cannot function as electron donors. The significant implications of observations related to this cell-free system are: (i) both iron and manganese mineral oxides are reduced by the TM fraction, but aqueous U(VI) is not; (ii) TM fractions from anaerobically grown, but not aerobically grown, cells can reduce the mineral oxides; (iii) electron shuttles and iron chelators are not needed for this in vitro reduction, documenting conclusively that reduction can occur by direct contact with the mineral oxide; (iv) electron shuttles and EDTA stimulate the in vitro Fe(III) reduction, documenting that exogenous molecules can enhance rates of enzymatic mineral reduction; and (v) multiple membrane components are involved in solid-phase oxide reduction. The membrane fractions, consisting of liposomes of cytoplasmic and outer membrane segments, contain at least 100 proteins including the enzyme that oxidizes formate, formate dehydrogenase. Mineral oxide reduction was inhibited by the addition of detergent Triton X-100, which solubilizes membranes and their associated proteins, consistent with the involvement of multiple electron carriers that are disrupted by detergent addition. In contrast, formate dehydrogenase activity was not inhibited by Triton X-100. The addition of anthraquinone-2,6-disulfonate (AQDS) and menaquinone-4 was unable to restore activity; however, menadione (MD) restored 33% of the activity. The addition of AQDS and MD to reactions without added detergent increased the rate of goethite

Descriptors and Thermodynamic Limitations of Electrocatalytic Carbon Dioxide Reduction on Rutile Oxide Surfaces.

PubMed

Bhowmik, Arghya; Vegge, Tejs; Hansen, Heine A

2016-11-23

A detailed understanding of the electrochemical reduction of CO 2 into liquid fuels on rutile metal oxide surfaces is developed by using DFT calculations. We consider oxide overlayer structures on RuO 2 (1 1 0) surfaces as model catalysts to elucidate the trends and limitations in the CO 2 reduction reaction (CO2RR) based on thermodynamic analysis. We aim to specify the requirements for CO2RR catalysts to establish adsorbate scaling relations and use these to derive activity volcanoes. Computational results show that the OH* binding free energy is a good descriptor of the thermodynamic limitations and it defines the left leg of the activity volcano for CO2RR. HCOOH* is a key intermediate for products formed through further reduction, for example, methanediol, methanol, and methane. The surfaces that do not bind HCOOH* are selective towards formic acid (HCOOH) production, but hydrogen evolution limits their suitability. We determine the ideal binding free energy for H* and OH* to facilitate selective CO2RR over H 2 /CO evolution to be ΔG B [H]>0.5 eV and -0.5 eV<ΔG B [OH]<0.1 eV. The Re-containing overlayers considered in this work display excellent promise for selectivity, although they are active at a highly reducing potential. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficient Reduction of Antibacterial Activity and Cytotoxicity of Fluoroquinolones by Fungal-Mediated N-Oxidation.

PubMed

Rusch, Marina; Spielmeyer, Astrid; Meißner, Jessica; Kietzmann, Manfred; Zorn, Holger; Hamscher, Gerd

2017-04-19

Extensive usage of fluoroquinolone antibiotics in livestock results in their occurrence in manure and subsequently in the environment. Fluoroquinolone residues may promote bacterial resistance and are toxic to plants and aquatic organisms. Moreover, fluoroquinolones may enter the food chain through plant uptake, if manure is applied as fertilizer. Thus, the presence of fluoroquinolones in the environment may pose a threat to human and ecological health. In this study, the biotransformation of enrofloxacin, marbofloxacin, and difloxacin by the fungus X. longipes (Xylaria) was investigated. The main metabolites were unequivocally identified as the respective N-oxides by mass spectrometry and nuclear magnetic resonance spectroscopy. Fungal-mediated N-oxidation of fluoroquinolones led to a 77-90% reduction of the initial antibacterial activity. In contrast to their respective parent compounds, N-oxides showed low cytotoxic potential and had a reduced impact on cell proliferation. Thus, biotransformation by X. longipes may represent an effective method for inactivating fluoroquinolones.

Harm Reduction Agencies as a Potential Site for Buprenorphine Treatment.

PubMed

Fox, Aaron D; Chamberlain, Adam; Frost, Taeko; Cunningham, Chinazo O

2015-01-01

Harm reduction agencies complement addiction treatment by providing diverse services that improve the health of people who use drugs. Buprenorphine maintenance treatment (BMT) is an effective opioid addiction treatment that may be provided from flexible settings, potentially including harm reduction agencies. This study investigated attitudes toward different potential sites for BMT (harm reduction agencies, general medical clinics, and drug treatment programs) among harm reduction clients. Using computer-based interviews, participants indicated preferred potential site for BMT (harm reduction agency, drug treatment program, or general medical clinic), interest in BMT by potential site, motivation for treatment, and barriers to BMT. Multivariable logistic regression was used to determine factors associated with harm reduction agency preference. Of 102 opioid users, the most preferred potential site for BMT was a harm reduction agency (51%), whereas fewer preferred general medical clinics (13%), drug treatment programs (12%), or were not interested in BMT (25%). In multivariable analysis, experiencing ≥1 barrier to BMT was strongly associated with preferring harm reduction agencies (adjusted odds ratio [aOR] = 3.39, 95% confidence interval [CI]: 1.00-11.43). The potential to initiate BMT at harm reduction agencies is highly favorable among harm reduction clients, especially among those experiencing barriers to BMT. Offering BMT at harm reduction agencies could improve access to treatment, but studies are needed to determine safety and efficacy of this approach.

Potential role of green tea catechins in the management of oxidative stress-associated infertility.

PubMed

Roychoudhury, Shubhadeep; Agarwal, Ashok; Virk, Gurpriya; Cho, Chak-Lam

2017-05-01

Reactive oxygen species (ROS) are present in low concentrations in the genital tracts of males and females. Excessive ROS lead to oxidative stress, which damages DNA, lipids and proteins. Such molecular changes result in compromised vitality, increased morphological defects and decreased sperm motility in the male. In the female, oxidative stress interferes with oocyte maturation, and may inhibit in-vitro maturation of the oocyte. Recently, green tea supplementation has been reported to possess properties that may improve the quality of male and female gametes largely due to the ability of catechin polyphenols to quench ROS. Epigallocatechin-3-gallate (EGCG) is considered the most promising bioactive compound in green tea due to its strong antioxidant activity. The unique property of green tea catechins may potentially improve reproductive health and pose an important research area. We present a comprehensive overview on the effects and potential roles of green tea catechins on oxidative stress in male and female reproduction and fertility. In this review, possible mechanisms of action are highlighted to better understand the potential use of green tea catechins in the reduction of oxidative stress and its associated beneficial effects in the clinical setting. Copyright © 2017 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.

Mechanism of sodium chloride in promoting reduction of high-magnesium low-nickel oxide ore

PubMed Central

Zhou, Shiwei; Wei, Yonggang; Li, Bo; Wang, Hua; Ma, Baozhong; Wang, Chengyan

2016-01-01

Sodium chloride has been proved that it is an effective promoter for the reduction of high-magnesium, low-nickel oxide ore. The aim of current work is to clarify the promotion behavior of sodium chloride in the roasting reduction process. The influence of moisture on the reduction of ore in the presence of sodium chloride is studied to get clear comprehension of promotion process. In the presence of moisture, the HCl is produced by pyrohydrolysis of sodium chloride for chlorinating nickel and iron oxides, moreover, interactions between metallic oxides and sodium chloride are also a way for chlorination at high temperature (>802 °C); subsequently, the metal chloride would be reduced by reductant. In the absence of moisture, the magnetic separation results show that the recoveries of iron and nickel have a significant increase; moreover, olivine structure would be destroyed gradually with the increase of roasting temperature in the action of sodium chloride, and the sodium chloride existed in high-magnesium, low-nickel oxide ore could make the NiO isolate from NiO-bearing minerals. The NiO reacts with Fe2O3 at high temperature to form NiFe2O4, which is conductive to the formation of Ni-Fe alloy during the reduction process. PMID:27374991

Mechanism of sodium chloride in promoting reduction of high-magnesium low-nickel oxide ore.

PubMed

Zhou, Shiwei; Wei, Yonggang; Li, Bo; Wang, Hua; Ma, Baozhong; Wang, Chengyan

2016-07-04

Sodium chloride has been proved that it is an effective promoter for the reduction of high-magnesium, low-nickel oxide ore. The aim of current work is to clarify the promotion behavior of sodium chloride in the roasting reduction process. The influence of moisture on the reduction of ore in the presence of sodium chloride is studied to get clear comprehension of promotion process. In the presence of moisture, the HCl is produced by pyrohydrolysis of sodium chloride for chlorinating nickel and iron oxides, moreover, interactions between metallic oxides and sodium chloride are also a way for chlorination at high temperature (>802 °C); subsequently, the metal chloride would be reduced by reductant. In the absence of moisture, the magnetic separation results show that the recoveries of iron and nickel have a significant increase; moreover, olivine structure would be destroyed gradually with the increase of roasting temperature in the action of sodium chloride, and the sodium chloride existed in high-magnesium, low-nickel oxide ore could make the NiO isolate from NiO-bearing minerals. The NiO reacts with Fe2O3 at high temperature to form NiFe2O4, which is conductive to the formation of Ni-Fe alloy during the reduction process.

Use of ion conductors in the pyrochemical reduction of oxides

DOEpatents

Miller, W.E.; Tomczuk, Z.

1994-02-01

An electrochemical process and electrochemical cell for reducing a metal oxide are provided. First the oxide is separated as oxygen gas using, for example, a ZrO[sub 2] oxygen ion conductor anode and the metal ions from the reduction salt are reduced and deposited on an ion conductor cathode, for example, sodium ion reduced on a [beta]-alumina sodium ion conductor cathode. The generation of and separation of oxygen gas avoids the problem with chemical back reaction of oxygen with active metals in the cell. The method also is characterized by a sequence of two steps where an inert cathode electrode is inserted into the electrochemical cell in the second step and the metallic component in the ion conductor is then used as the anode to cause electrochemical reduction of the metal ions formed in the first step from the metal oxide where oxygen gas formed at the anode. The use of ion conductors serves to isolate the active components from chemically reacting with certain chemicals in the cell. While applicable to a variety of metal oxides, the invention has special importance for reducing CaO to Ca[sup o] used for reducing UO[sub 2] and PuO[sub 2] to U and Pu. 2 figures.

Use of ion conductors in the pyrochemical reduction of oxides

DOEpatents

Miller, William E.; Tomczuk, Zygmunt

1994-01-01

An electrochemical process and electrochemical cell for reducing a metal oxide are provided. First the oxide is separated as oxygen gas using, for example, a ZrO.sub.2 oxygen ion conductor anode and the metal ions from the reduction salt are reduced and deposited on an ion conductor cathode, for example, sodium ion reduced on a .beta.-alumina sodium ion conductor cathode. The generation of and separation of oxygen gas avoids the problem with chemical back reaction of oxygen with active metals in the cell. The method also is characterized by a sequence of two steps where an inert cathode electrode is inserted into the electrochemical cell in the second step and the metallic component in the ion conductor is then used as the anode to cause electrochemical reduction of the metal ions formed in the first step from the metal oxide where oxygen gas formed at the anode. The use of ion conductors serves to isolate the active components from chemically reacting with certain chemicals in the cell. While applicable to a variety of metal oxides, the invention has special importance for reducing CaO to Ca.degree. used for reducing UO.sub.2 and PuO.sub.2 to U and Pu.

Elevated acetate concentrations in the rhizosphere of Spartina alterniflora and potential influences on sulfate reduction

NASA Technical Reports Server (NTRS)

Hines, Mark E.; Tugel, Joyce B.; Giblin, A. E.; Banta, G. T.; Hobbie, J. E.

1992-01-01

Acetate is important in anaerobic metabolism of non-vegetated sediments but its role in salt marsh soils was not investigated thoroughly. Acetate concentrations, oxidation (C-14) and SO4(2-) reduction (S-35) were measured in S. alterniflora soils in NH and MA. Pore water from cores contained greater than 0.1 mM acetate and in some instances greater than 1.0 mM. Non-destructive samples contained less than 0.01 mM. Acetate was associated with roots and concentrations were highest during vegetative growth and varied with changes in plant physiology. Acetate turnover was very low whether whole core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of SO4(2-) reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a significant percentage of SO4(2-) reduction. These results differ markedly from data for non-vegetated coastal sediments where acetate levels are low, oxidation rate constants are high and acetate oxidation rates greatly exceed rates of SO4(2-) reduction. The discrepancy between rates of acetate oxidation and SO4(2-) reduction in marsh soils may be due either to the utilization of substrates other than acetate by SO4(2-) reducers or artifacts associated with measurements of organic utilization by rhizosphere bacteria.

Electrochemical CO 2 Reduction on Oxide-Derived Cu Surface with Various Oxide Thicknesses

DOE PAGES

Liang, Zhixiu; Fu, Jie; Vukmirovic, Miomir B.; ...

2018-03-26

Here, cuprous oxide on copper foil electrodes prepared via electrochemical deposition and thermal annealing are investigated towards CO 2 electrochemical reduction at low overpotential. The thickness of the electrochemical deposited Cu 2O was controlled by varying the constant-current deposition time. The surface morphology and roughness were examined with SEM and CV respectively. The electrode fabricated by cuprous oxide deposited for 20 min demonstrated the best faradic efficiency (7.02%) and specific activity (0.123 mA/cm 2) towards format/formic acid formation at -0.5 V vs. RHE in CO 2 saturated 0.5 M K 2CO 3 among studied samples.

Electrochemical CO 2 Reduction on Oxide-Derived Cu Surface with Various Oxide Thicknesses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Zhixiu; Fu, Jie; Vukmirovic, Miomir B.

Here, cuprous oxide on copper foil electrodes prepared via electrochemical deposition and thermal annealing are investigated towards CO 2 electrochemical reduction at low overpotential. The thickness of the electrochemical deposited Cu 2O was controlled by varying the constant-current deposition time. The surface morphology and roughness were examined with SEM and CV respectively. The electrode fabricated by cuprous oxide deposited for 20 min demonstrated the best faradic efficiency (7.02%) and specific activity (0.123 mA/cm 2) towards format/formic acid formation at -0.5 V vs. RHE in CO 2 saturated 0.5 M K 2CO 3 among studied samples.

Electrochemically reduced graphene-oxide supported bimetallic nanoparticles highly efficient for oxygen reduction reaction with excellent methanol tolerance

NASA Astrophysics Data System (ADS)

Yasmin, Sabina; Cho, Sung; Jeon, Seungwon

2018-03-01

We report a simple and facile method for the fabrication of bimetallic nanoparticles on electrochemically reduced graphene oxide (ErGO) for electrocatalytic oxygen reduction reaction (ORR) in alkaline media. First, reduced graphene oxide supported palladium and manganese oxide nanoparticle (rGO/Pd-Mn2O3) catalyst was synthesized via a simple chemical method at room temperature; then, it was electrochemically reduced for oxidation reduction reaction (ORR) in alkaline media. The chemical composition and morphological properties of ErGO/Pd-Mn2O3 was characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The TEM images reveals that, nano-sized Pd and Mn2O3 particles were disperse on the ErGO sheet without aggregation. The as-prepared ErGO/Pd-Mn2O3 was employed for ORR in alkaline media which shows higher ORR activity with more positive onset and half-wave potential, respectively. Remarkably, ErGO/Pd-Mn2O3 reduced oxygen via four-electron transfer pathway with negligible amount of intermediate peroxide species (HO2-). Furthermore, the higher stability and excellent methanol tolerance of the ErGO/Pd-Mn2O3 compared to commercial Pt/C (20 wt%) catalyst, indicating its suitability for fuel cells.

Anion exchange membranes for electrochemical oxidation-reduction energy storage system

NASA Technical Reports Server (NTRS)

Odonnell, P. M.; Sheibley, D. W.; Gahn, R. F.

1977-01-01

Oxidation-reduction couples in concentrated solutions separated by appropriate ion selective membranes were considered as an attractive approach to bulk electrical energy storage. A key problem is the development of the membrane. Several promising types of anionic membranes are discussed which were developed and evaluated for redox energy storage systems. The copolymers of ethyleneglycoldimethacrylate with either 2-vinylpyridine or vinylbenzl chloride gave stable resistance values compared to the copolymer of vinylbenzlchloride and divinylbenzene which served as the baseline membrane. A polyvinylchloride film aminated with tetraethylenepentamine had a low resistance but a high ion transfer rate. A slurry coated vinylpyridine had the lowest ion transfer rate. All these membranes functioned well in laboratory cells at ambient temperatures with the acidic chloride oxidant/reductant system, Fe 3, Fe 2/Ti 3, Ti 4.

Tuning electronic properties by oxidation-reduction reactions at graphene-ruthenium interface

DOE PAGES

Kandyba, Viktor; Al-Mahboob, Abdullah; Giampietri, Alessio; ...

2018-06-06

Mass production of graphene is associated with the growth on catalysts used also in other chemical reactions. In this study, we exploit the oxidation-reduction to tailor the properties of single layer graphene domains with incorporated bi-layer patches on ruthenium. Using photoelectron spectromicroscopy techniques, we find that oxygen, intercalating under single layer and making it p-doped by the formation of Ru-O x, does not intercalate under the bilayer patches with n-doped upper layer, but decorates them under single layer surrounding creating lateral p-n junctions with chemical potential difference of 1.2 eV. O-reduction by thermal treatment in vacuum results in C-vacancy defectsmore » enhancing electronic coupling of remained graphene to Ru, whereas in H 2, vacancy formation is suppressed. Also, for the domains below 15–25 μm size, after O-reduction in H 2, graphene/Ru coupling is restored, while wrinkle pattern produced by O-intercalation is irreversible and can trap reaction products between the wrinkles and Ru surface step edges. In fact, in certain regions of bigger domains, the products, containing H 2O and/or its fragments, remain at the interface, making graphene decoupled and undoped.« less

Enhanced reduction of Fe(III) oxides and methyl orange by Klebsiella oxytoca in presence of anthraquinone-2-disulfonate.

PubMed

Yu, Lei; Wang, Shi; Tang, Qing-Wen; Cao, Ming-Yue; Li, Jia; Yuan, Kun; Wang, Ping; Li, Wen-Wei

2016-05-01

Klebsiella oxytoca GS-4-08 is capable of azo dye reduction, but its quinone respiration and Fe(III) reduction abilities have not been reported so far. In this study, the abilities of this strain were reported in detail for the first time. As the biotic reduction of Fe(III) plays an important role in the biogeochemical cycles, two amorphous Fe(III) oxides were tested as the sole electron acceptor during the anaerobic respiration of strain GS-4-08. For the reduction of goethite and hematite, the biogenic Fe(II) concentrations reached 0.06 and 0.15 mM, respectively. Humic acid analog anthraquinone-2-disulfonate (AQS) was found to serve as an electron shuttle to increase the reduction of both methyl orange (MO) and amorphous Fe(III) oxides, and improve the dye tolerance of the strain. However, the formation of Fe(II) was not accelerated by biologically reduced AQS (B-AH2QS) because of the high bioavailability of soluble Fe(III). For the K. oxytoca strain, high soluble Fe(III) concentrations (above 1 mM) limit its growth and decolorization ability, while lower soluble Fe(III) concentrations produce an electron competition with MO initially, and then stimulate the decolorization after the electron couples of Fe(III)/Fe(II) are formed. With the ability to respire both soluble Fe(III) and insoluble Fe(III) oxides, this formerly known azo-reducer may be used as a promising model organism for the study of the interaction of these potentially competing processes in contaminated environments.

Reduced graphene oxide as photocatalyst for CO2 reduction reaction(Conference Presentation)

NASA Astrophysics Data System (ADS)

Chang, Yu-Chung

2016-10-01

Photocatalytic conversion of carbon dioxide (CO2) to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO2 reduction. Our previous work is using graphene oxide (GO) as a promising photocatalyst for photocatalytic conversion of CO2 to methanol[1].When using graphene oxide as photocatalyst, the photocatalytic efficiency is 4-flod higher than TiO2 powder. GO has a lot of defects on the surface and those defects make sp2 carbon structure become sp3 carbon structure. The carbon structure change cause the GO has large energy gap about 2.7 eV to 3.2 eV. In order to remove the defect and reduce the energy gap of GO, Zhao et al. try to annealing GO powder in the nitrogen atmosphere at 900oC, the GO structure can be reduced to near graphene structure[2]. Zhu et al. do some low temperature annealing, it can control the structure and energy bandgap of GO by control annealing temperature. If the annealing temperature increase the bandgap of GO will be reduce[3]. So, we can using this annealing process to reduce the bandgap of the GO. In the varying temperature thermal reduction process, as the temperature increases from 130oC to 170oC, the functional groups of the graphene oxide will be reduced and band gap of graphene oxide will be narrowed at same time. The characteristic of thermal reduced graphene oxide were analyzed by SEM, XRD and Raman measurements. The band position was determined by UV/Vis. The reduction of functional groups correlates to red shift in light absorption and eventual quenching in the PL signal of RGOs. Combining hydrophobicity, light harvesting and PL quench, we get the highest yield of RGO150 (0.31 μmole g-1 -cat hr-1) is 1.7-fold higher than that of GO (0.18μmole g-1 -cat hr-1). This work investigates a modified method for using a thermal reduction process to reduce the energy gap of graphene oxide.

Complexation facilitated reduction of aromatic N-oxides by aqueous Fe(II)-tiron complex: reaction kinetics and mechanisms.

PubMed

Chen, Yiling; Zhang, Huichun

2013-10-01

Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom.

WORKSHOP ON MONITORING OXIDATION-REDUCTION PROCESSES FOR GROUND-WATER RESTORATION

EPA Science Inventory

Redox conditions are among the most important parameters for controlling contaminant transport and fate in ground-water systems. Oxidation-reduction (redox) reactions mediate the chemical behavior of both inorganic and organic chemical constituents by affecting solubility, rea...

New rare earth hafnium oxynitride perovskites with photocatalytic activity in water oxidation and reduction.

PubMed

Black, Ashley P; Suzuki, Hajime; Higashi, Masanobu; Frontera, Carlos; Ritter, Clemens; De, Chandan; Sundaresan, A; Abe, Ryu; Fuertes, Amparo

2018-02-06

RHfO 2 N perovskites with R = La, Nd and Sm show a GdFeO 3 -type structure and are semiconductors with band gaps of 3.35, 3.40 and 2.85 eV and relative dielectric constants of 30, 16 and 28 respectively. These compounds have adequate reduction and oxidation potentials to conduct the overall water splitting reaction, and the analogous perovskite LaZrO 2 N with a band gap of 2.8 eV shows photocatalytic activity under visible light irradiation for O 2 evolution.

Anoxic nitrate reduction coupled with iron oxidation and attenuation of dissolved arsenic and phosphate in a sand and gravel aquifer

NASA Astrophysics Data System (ADS)

Smith, Richard L.; Kent, Douglas B.; Repert, Deborah A.; Böhlke, J. K.

2017-01-01

Nitrate has become an increasingly abundant potential electron acceptor for Fe(II) oxidation in groundwater, but this redox couple has not been well characterized within aquifer settings. To investigate this reaction and some of its implications for redox-sensitive groundwater contaminants, we conducted an in situ field study in a wastewater-contaminated aquifer on Cape Cod. Long-term (15 year) geochemical monitoring within the contaminant plume indicated interacting zones with variable nitrate-, Fe(II)-, phosphate-, As(V)-, and As(III)-containing groundwater. Nitrate and phosphate were derived predominantly from wastewater disposal, whereas Fe(II), As(III), and As(V) were mobilized from the aquifer sediments. Multiple natural gradient, anoxic tracer tests were conducted in which nitrate and bromide were injected into nitrate-free, Fe(II)-containing groundwater. Prior to injection, aqueous Fe(II) concentrations were approximately 175 μM, but sorbed Fe(II) accounted for greater than 90% of the total reactive Fe(II) in the aquifer. Nitrate reduction was stimulated within 1 m of transport for 100 μM and 1000 μM nitrate additions, initially producing stoichiometric quantities of nitrous oxide (>300 μM N). In subsequent injections at the same site, nitrate was reduced even more rapidly and produced less nitrous oxide, especially over longer transport distances. Fe(II) and nitrate concentrations decreased together and were accompanied by Fe(III) oxyhydroxide precipitation and decreases in dissolved phosphate, As(III), and As(V) concentrations. Nitrate N and O isotope fractionation effects during nitrate reduction were approximately equal (ε15N/ε18O = 1.11) and were similar to those reported for laboratory studies of biological nitrate reduction, including denitrification, but unlike some reported effects on nitrate by denitrification in aquifers. All constituents affected by the in situ tracer experiments returned to pre-injection levels after several weeks

Stability of Residual Oxides in Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction Investigated with 18 O Labeling.

PubMed

Lum, Yanwei; Ager, Joel W

2018-01-08

Oxide-derived (OD) Cu catalysts have high selectivity towards the formation of multi-carbon products (C 2 /C 3 ) for aqueous electrochemical CO 2 reduction (CO 2 R). It has been proposed that a large fraction of the initial oxide can be surprisingly resistant to reduction, and these residual oxides play a crucial catalytic role. The stability of residual oxides was investigated by synthesizing 18 O-enriched OD Cu catalysts and testing them for CO 2 R. These catalysts maintain a high selectivity towards C 2 /C 3 products (ca. 60 %) for up to 5 h in 0.1 m KHCO 3 at -1.0 V vs. RHE. However, secondary-ion mass spectrometry measurements show that only a small fraction (<1 %) of the original 18 O content remains, showing that residual oxides are not present in significant amounts during CO 2 R. Furthermore, we show that OD Cu can reoxidize rapidly, which could compromise the accuracy of ex situ methods for determining the true oxygen content. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plasma in-liquid method for reduction of zinc oxide in zinc nanoparticle synthesis

NASA Astrophysics Data System (ADS)

Amaliyah, Novriany; Mukasa, Shinobu; Nomura, Shinfuku; Toyota, Hiromichi; Kitamae, Tomohide

2015-02-01

Metal air-batteries with high-energy density are expected to be increasingly applied in electric vehicles. This will require a method of recycling air batteries, and reduction of metal oxide by generating plasma in liquid has been proposed as a possible method. Microwave-induced plasma is generated in ethanol as a reducing agent in which zinc oxide is dispersed. Analysis by energy-dispersive x-ray spectrometry (EDS) and x-ray diffraction (XRD) reveals the reduction of zinc oxide. According to images by transmission electron microscopy (TEM), cubic and hexagonal metallic zinc particles are formed in sizes of 30 to 200 nm. Additionally, spherical fiber flocculates approximately 180 nm in diameter are present.

Evidence for single metal two electron oxidative addition and reductive elimination at uranium.

PubMed

Gardner, Benedict M; Kefalidis, Christos E; Lu, Erli; Patel, Dipti; McInnes, Eric J L; Tuna, Floriana; Wooles, Ashley J; Maron, Laurent; Liddle, Stephen T

2017-12-01

Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations. However, these reactions have never been observed together in the f-block because these metals exhibit irreversible one- or multi-electron oxidation or reduction reactions. Here we report that azobenzene oxidises sterically and electronically unsaturated uranium(III) complexes to afford a uranium(V)-imido complex in a reaction that satisfies all criteria of a single-metal two-electron oxidative addition. Thermolysis of this complex promotes extrusion of azobenzene, where H-/D-isotopic labelling finds no isotopomer cross-over and the non-reactivity of a nitrene-trap suggests that nitrenes are not generated and thus a reductive elimination has occurred. Though not optimally balanced in this case, this work presents evidence that classical d-block redox chemistry can be performed reversibly by f-block metals, and that uranium can thus mimic elementary transition metal reactivity, which may lead to the discovery of new f-block catalysis.

Reduction reactions and densification during in situ TEM heating of iron oxide nanochains

NASA Astrophysics Data System (ADS)

Bonifacio, Cecile S.; Das, Gautom; Kennedy, Ian M.; van Benthem, Klaus

2017-12-01

The reduction reactions and densification of nanochains assembled from γ-Fe2O3 nanoparticles were investigated using in situ transmission electron microscopy (TEM). Morphological changes and reduction of the metal oxide nanochains were observed during in situ TEM annealing through simultaneous imaging and quantitative analysis of the near-edge fine structures of Fe L2,3 absorption edges acquired by spatially resolved electron energy loss spectroscopy. A change in the oxidation states during annealing of the iron oxide nanochains was observed with phase transformations due to continuous reduction from Fe2O3 over Fe3O4, FeO to metallic Fe. Phase transitions during the in situ heating experiments were accompanied with morphological changes in the nanochains, specifically rough-to-smooth surface transitions below 500 °C, neck formation between adjacent particles around 500 °C, and subsequent neck growth. At higher temperatures, coalescence of FeO particles was observed, representing densification.

Electron transfer of Pseudomonas aeruginosa CP1 in electrochemical reduction of nitric oxide.

PubMed

Zhou, Shaofeng; Huang, Shaobin; He, Jiaxin; Li, Han; Zhang, Yongqing

2016-10-01

This study reports catalytic electro-chemical reduction of nitric oxide (NO) enhanced by Pseudomonas aeruginosa strain CP1. The current generated in the presence of bacteria was 4.36times that in the absence of the bacteria. The strain was able to catalyze electro-chemical reduction of NO via indirect electron transfer with an electrode, revealed by a series of cyclic voltammetry experiments. Soluble electron shuttles secreted into solution by live bacteria were responsible for the catalytic effects. The enhancement of NO reduction was also confirmed by detection of nitrous oxide; the level of this intermediate was 46.4% higher in the presence of bacteria than in controls, illustrated that the electron transfer pathway did not directly reduce nitric oxide to N2. The findings of this study may offer a new model for bioelectrochemical research in the field of NO removal by biocatalysts. Copyright © 2016 Elsevier Ltd. All rights reserved.

Remote fabrication and irradiation test of recycled nuclear fuel prepared by the oxidation and reduction of spent oxide fuel

NASA Astrophysics Data System (ADS)

Jin Ryu, Ho; Chan Song, Kee; Il Park, Geun; Won Lee, Jung; Seung Yang, Myung

2005-02-01

A direct dry recycling process was developed in order to reuse spent pressurized light water reactor (LWR) nuclear fuel in CANDU reactors without the separation of sensitive nuclear materials such as plutonium. The benefits of the dry recycling process are the saving of uranium resources and the reduction of spent fuel accumulation as well as a higher proliferation resistance. In the process of direct dry recycling, fuel pellets separated from spent LWR fuel rods are oxidized from UO2 to U3O8 at 500 °C in an air atmosphere and reduced into UO2 at 700 °C in a hydrogen atmosphere, which is called OREOX (oxidation and reduction of oxide fuel). The pellets are pulverized during the oxidation and reduction processes due to the phase transformation between cubic UO2 and orthorhombic U3O8. Using the oxide powder prepared from the OREOX process, the compaction and sintering processes are performed in a remote manner in a shielded hot cell due to the high radioactivity of the spent fuel. Most of the fission gas and volatile fission products are removed during the OREOX and sintering processes. The mini-elements fabricated by the direct dry recycling process are irradiated in the HANARO research reactor for the performance evaluation of the recycled fuel pellets. Post-irradiation examination of the irradiated fuel showed that microstructural evolution and fission gas release behavior of the dry-recycled fuel were similar to high burnup UO2 fuel.

Oxidation and reduction behaviors of a prototypic MgO-PuO2-x inert matrix fuel

NASA Astrophysics Data System (ADS)

Miwa, Shuhei; Osaka, Masahiko

2017-04-01

Oxidation and reduction behaviors of prototypic MgO-based inert matrix fuels (IMFs) containing PuO2-x were experimentally investigated by means of thermogravimetry. The oxidation and reduction kinetics of the MgO-PuO2-x specimen were determined. The oxidation and reduction rates of the MgO-PuO2-x were found to be low compared with those of PuO2-x. It is note that the changes in O/Pu ratios of MgO-PuO2-x from stoichiometry were smaller than those of PuO2-x at high oxygen partial pressure.

Effect of applied voltage, initial concentration and natural organic matter on sequential reduction/oxidation of nitrobenzene by graphite electrodes

PubMed Central

Sun, Mei; Reible, Danny D.; Lowry, Gregory V.; Gregory, Kelvin B.

2012-01-01

Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H2 at the cathode and oxidizing conditions and O2 at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (kNB) and NSB (kNSB) increased with applied voltage between 2V and 3.5 V (when the initial NB concentration was 100 µM, kNB=0.3 d−1 and kNSB=0.04 d−1at 2V; kNB=1.6 d−1 and kNSB=0.64 d−1at 3.5 V) but stopped increasing beyond the threshold of 3.5V. When initial NB concentration decreased from 100 to 5 µM, kNB and kNSB became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased kNB while slightly increased kNSB, but only to a limited extent (~factor of 3) for dissolved organic carbon content up to 100 mg/l. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation. PMID:22571797

Study on the influences of reduction temperature on nickel-yttria-stabilized zirconia solid oxide fuel cell anode using nickel oxide-film electrode

NASA Astrophysics Data System (ADS)

Jiao, Zhenjun; Ueno, Ai; Suzuki, Yuji; Shikazono, Naoki

2016-10-01

In this study, the reduction processes of nickel oxide at different temperatures were investigated using nickel-film anode to study the influences of reduction temperature on the initial performances and stability of nickel-yttria-stabilized zirconia anode. Compared to conventional nickel-yttria-stabilized zirconia composite cermet anode, nickel-film anode has the advantage of direct observation at nickel-yttria-stabilized zirconia interface. The microstructural changes were characterized by scanning electron microscopy. The reduction process of nickel oxide is considered to be determined by the competition between the mechanisms of volume reduction in nickel oxide-nickel reaction and nickel sintering. Electrochemical impedance spectroscopy was applied to analyze the time variation of the nickel-film anode electrochemical characteristics. The anode performances and microstructural changes before and after 100 hours discharging and open circuit operations were analyzed. The degradation of nickel-film anode is considered to be determined by the co-effect between the nickel sintering and the change of nickel-yttria-stabilized zirconia interface bonding condition.

Regioselective electrochemical reduction of 2,4-dichlorobiphenyl - Distinct standard reduction potentials for carbon-chlorine bonds using convolution potential sweep voltammetry

NASA Astrophysics Data System (ADS)

Muthukrishnan, A.; Sangaranarayanan, M. V.; Boyarskiy, V. P.; Boyarskaya, I. A.

2010-04-01

The reductive cleavage of carbon-chlorine bonds in 2,4-dichlorobiphenyl (PCB-7) is investigated using the convolution potential sweep voltammetry and quantum chemical calculations. The potential dependence of the logarithmic rate constant is non-linear which indicates the validity of Marcus-Hush theory of quadratic activation-driving force relationship. The ortho-chlorine of the 2,4-dichlorobiphenyl gets reduced first as inferred from the quantum chemical calculations and bulk electrolysis. The standard reduction potentials pertaining to the ortho-chlorine of 2,4-dichlorobiphenyl and that corresponding to para chlorine of the 4-chlorobiphenyl have been estimated.

Study on emission characteristics and reduction strategy of nitrous oxide during wastewater treatment by different processes.

PubMed

Sun, Shichang; Bao, Zhiyuan; Sun, Dezhi

2015-03-01

Given the inexorable increase in global wastewater treatment, increasing amounts of nitrous oxide are expected to be emitted from wastewater treatment plants and released to the atmosphere. It has become imperative to study the emission and control of nitrous oxide in the various wastewater treatment processes currently in use. In the present investigation, the emission characteristics and the factors affecting the release of nitrous oxide were studied via full- and pilot-scale experiments in anoxic-oxic, sequencing batch reactor and oxidation ditch processes. We propose an optimal treatment process and relative strategy for nitrous oxide reduction. Our results show that both the bio-nitrifying and bio-denitrifying treatment units in wastewater treatment plants are the predominant sites for nitrous oxide production in each process, while the aerated treatment units are the critical sources for nitrous oxide emission. Compared with the emission of nitrous oxide from the anoxic-oxic (1.37% of N-influent) and sequencing batch reactor (2.69% of N-influent) processes, much less nitrous oxide (0.25% of N-influent) is emitted from the oxidation ditch process, which we determined as the optimal wastewater treatment process for nitrous oxide reduction, given the current technologies. Nitrous oxide emissions differed with various operating parameters. Controlling the dissolved oxygen concentration at a proper level during nitrification and denitrification and enhancing the utilization rate of organic carbon in the influent for denitrification are the two critical methods for nitrous oxide reduction in the various processes considered.

Pyrite oxidation and reduction - Molecular orbital theory considerations. [for geochemical redox processes

NASA Technical Reports Server (NTRS)

Luther, George W., III

1987-01-01

In this paper, molecular orbital theory is used to explain a heterogeneous reaction mechanism for both pyrite oxidation and reduction. The mechanism demonstrates that the oxidation of FeS2 by Fe(3+) may occur as a result of three important criteria: (1) the presence of a suitable oxidant having a vacant orbital (in case of liquid phase) or site (solid phase) to bind to the FeS2 via sulfur; (2) the initial formation of a persulfido (disulfide) bridge between FeS2 and the oxidant, and (3) an electron transfer from a pi(asterisk) orbital in S2(2-) to a pi or pi(asterisk) orbital of the oxidant.

Direct printing and reduction of graphite oxide for flexible supercapacitors

NASA Astrophysics Data System (ADS)

Jung, Hanyung; Ve Cheah, Chang; Jeong, Namjo; Lee, Junghoon

2014-08-01

We report direct printing and photo-thermal reduction of graphite oxide (GO) to obtain a highly porous pattern of interdigitated electrodes, leading to a supercapacitor on a flexible substrate. Key parameters optimized include the amount of GO delivered, the suitable photo-thermal energy level for effective flash reduction, and the substrate properties for appropriate adhesion after reduction. Tests with supercapacitors based on the printed-reduced GO showed performance comparable with commercial supercapacitors: the energy densities were 1.06 and 0.87 mWh/cm3 in ionic and organic electrolytes, respectively. The versatility in the architecture and choice of substrate makes this material promising for smart power applications.

Pre-converted nitric oxide gas in catalytic reduction system

DOEpatents

Hsiao, Mark C.; Merritt, Bernard T.; Penetrante, Bernardino M.; Vogtlin, George E.

1999-01-01

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO.sub.2 in the presence of O.sub.2. The second stage serves to convert NO.sub.2 to environmentally benign gases that include N2, CO2, and H.sub.2 O. By preconverting NO to NO.sub.2 in the first stage, the efficiency of the second stage for NO.sub.x reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO.sub.2 in the presence of O.sub.2 and includes platinum/alumina, e.g., Pt/Al.sub.2 O.sub.3 catalyst. A flow of hydrocarbons (C.sub.x H.sub.y) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO.sub.2 from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO.sub.2 to N2, CO2, and H.sub.2 O, and includes a gamma-alumina .gamma.-Al.sub.2 O.sub.3. The hydrocarbons and NO.sub.x are simultaneously reduced while passing through the second catalyst.

Pre-converted nitric oxide gas in catalytic reduction system

DOEpatents

Hsiao, M.C.; Merritt, B.T.; Penetrante, B.M.; Vogtlin, G.E.

1999-04-06

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO{sub 2} in the presence of O{sub 2}. The second stage serves to convert NO{sub 2} to environmentally benign gases that include N{sub 2}, CO{sub 2}, and H{sub 2}O. By preconverting NO to NO{sub 2} in the first stage, the efficiency of the second stage for NO{sub x} reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO{sub 2} in the presence of O{sub 2} and includes platinum/alumina, e.g., Pt/Al{sub 2}O{sub 3} catalyst. A flow of hydrocarbons (C{sub x}H{sub y}) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO{sub 2} from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO{sub 2} to N{sub 2}, CO{sub 2}, and H{sub 2}O, and includes a {gamma}-Al{sub 2}O{sub 3}. The hydrocarbons and NO{sub x} are simultaneously reduced while passing through the second catalyst. 9 figs.

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

DOE PAGES

Chen, Sheng-Yu; Song, Wenqiao; Lin, Hui-Jan; ...

2016-03-08

In this work, 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., K 2Cr 2O 7, KClO 3, and K 2S 2O 8, 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 reactivitymore » of carbon monoxide (CO) oxidation. K 2Cr 2O 7 and KClO 3 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. Finally, the straightforward synthetic process showed a scalable, low-cost, and template-free method to fabricate manganese oxide nanoarray monolithic catalysts for exhaust treatment.« less

Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation

NASA Astrophysics Data System (ADS)

Paneva, D.; Dimitrov, M.; Velinov, N.; Kolev, H.; Kozhukharov, V.; Tsoncheva, T.; Mitov, I.

2010-03-01

La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state.

XPS study of graphene oxide reduction induced by (100) and (111)-oriented Si substrates

NASA Astrophysics Data System (ADS)

Priante, F.; Salim, M.; Ottaviano, L.; Perrozzi, F.

2018-02-01

The reduction of graphene oxide (GO) has been extensively studied in literature in order to let GO partially recover the properties of graphene. Most of the techniques proposed to reduce GO are based on high temperature annealing or chemical reduction. A new procedure, based on the direct reduction of GO by etched Si substrate, was recently proposed in literature. In the present work, we accurately investigated the Si-GO interaction with x-ray photoelectron spectroscopy. In order to avoid external substrate oxidation factors we used EtOH as the GO solvent instead of water, and thermal annealing was carried out in UHV. We investigated the effect of Si(100), Si(111) and Au substrates on GO, to probe the role played by both the substrate composition and substrate orientation during the reduction process. A similar degree of GO reduction was observed for all samples but only after thermal annealing, ruling out the direct reduction effect of the substrate.

Myeloperoxidase potentiates nitric oxide-mediated nitrosation.

PubMed

Lakshmi, Vijaya M; Nauseef, William M; Zenser, Terry V

2005-01-21

Nitrosation is an important reaction elicited by nitric oxide (NO). To better understand how nitrosation occurs in biological systems, we assessed the effect of myeloperoxidase (MPO), a mediator of inflammation, on nitrosation observed during NO autoxidation. Nitrosation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ; 10 mum) to 2-nitrosoamino-3-methylimidazo[4,5-f]quinoline (N-NO-IQ) was monitored by HPLC. Using the NO donor spermine NONOate at pH 7.4, MPO potentiated N-NO-IQ formation. The minimum effective quantity of necessary components was 8.5 nm MPO, 0.25 mum H(2)O(2)/min, and 0.024 mum NO/min. Autoxidation was only detected at >/=1.2 mum NO/min. MPO potentiation was not affected by a 40-fold excess flux of H(2)O(2) over NO or less than a 2.4-fold excess flux of NO over H(2)O(2). Potentiation was due to an 8.8-fold increased affinity of MPO-derived nitrosating species for IQ. Autoxidation was inhibited by azide, suggesting involvement of the nitrosonium ion, NO(+). MPO potentiation was inhibited by NADH, but not azide, suggesting oxidative nitrosylation with NO(2)(.) or an NO(2)(.)-like species. MPO nonnitrosative oxidation of IQ with 0.3 mm NO(2)(-) at pH 5.5 was inhibited by azide, but not NADH, demonstrating differences between MPO oxidation of IQ with NO compared with NO(2)(-). Using phorbol ester-stimulated human neutrophils, N-NO-IQ formation was increased with superoxide dismutase and inhibited by catalase and NADH, but not NaN(3). This is consistent with nitrosation potentiation by MPO, not peroxynitrite. Increased N-NO-IQ formation was not detected with polymorphonuclear neutrophils from two unrelated MPO-deficient patients. Results suggest that the highly diffusible stable gas NO could initiate nitrosation at sites of neutrophil infiltration.

Material and system for catalytic reduction of nitrogen oxide in an exhaust stream of a combustion process

DOEpatents

Gardner, Timothy J.; Lott, Stephen E.; Lockwood, Steven J.; McLaughlin, Linda I.

1998-01-01

A catalytic material of activated hydrous metal oxide doped with platinum, palladium, or a combination of these, and optionally containing an alkali or alkaline earth metal, that is effective for NO.sub.X reduction in an oxidizing exhaust stream from a combustion process is disclosed. A device for reduction of nitrogen oxides in an exhaust stream, particularly an automotive exhaust stream, the device having a substrate coated with the activated noble-metal doped hydrous metal oxide of the invention is also provided.

Single Platinum Atoms Electrocatalysts: Oxygen Reduction and Hydrogen Oxidation Reactions

DOE PAGES

Vukmirovic, Miomir B.; Teeluck, Krishani M.; Liu, Ping; ...

2017-08-08

We prepared atomically dispersed catalyst consisting of Pt atoms arranged in a c(2 × 2) array on RuO2(110) substrate. A large interatomic distance of Pt atoms in a c(2 × 2) phase precludes the reactants to interact with more than one Pt atoms. A strong bond of Pt atoms with RuO2 prevents agglomeration of Pt atoms to form 2D-islands or 3D-clusters. The activities of single Pt atom catalyst for the oxygen reduction and hydrogen oxidation reactions were determined and compared with those of bulk Pt. It has lower catalytic activity for the oxygen reduction reaction and similar activity for hydrogenmore » oxidation reaction compared to Pt(111). This was explained by a large calculated up-shift of the dband center of Pt atoms and larger Pt-Pt interatomic distance than that of Pt(111). Our information is of considerable interest for further development of electrocatalysis.« less

Direct printing and reduction of graphite oxide for flexible supercapacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Hanyung; Ve Cheah, Chang; Jeong, Namjo

2014-08-04

We report direct printing and photo-thermal reduction of graphite oxide (GO) to obtain a highly porous pattern of interdigitated electrodes, leading to a supercapacitor on a flexible substrate. Key parameters optimized include the amount of GO delivered, the suitable photo-thermal energy level for effective flash reduction, and the substrate properties for appropriate adhesion after reduction. Tests with supercapacitors based on the printed-reduced GO showed performance comparable with commercial supercapacitors: the energy densities were 1.06 and 0.87 mWh/cm{sup 3} in ionic and organic electrolytes, respectively. The versatility in the architecture and choice of substrate makes this material promising for smart powermore » applications.« less

Particulate matter oxidative potential from waste transfer station activity.

PubMed

Godri, Krystal J; Duggan, Sean T; Fuller, Gary W; Baker, Tim; Green, David; Kelly, Frank J; Mudway, Ian S

2010-04-01

Adverse cardiorespiratory health is associated with exposure to ambient particulate matter (PM). The highest PM concentrations in London occur in proximity to waste transfer stations (WTS), sites that experience high numbers of dust-laden, heavy-duty diesel vehicles transporting industrial and household waste. Our goal was to quantify the contribution of WTS emissions to ambient PM mass concentrations and oxidative potential. PM with a diameter < 10 microm (PM10) samples were collected daily close to a WTS. PM10 mass concentrations measurements were source apportioned to estimate local versus background sources. PM oxidative potential was assessed using the extent of antioxidant depletion from a respiratory tract lining fluid model. Total trace metal and bioavailable iron concentrations were measured to determine their contribution to PM oxidative potential. Elevated diurnal PM10 mass concentrations were observed on all days with WTS activity (Monday-Saturday). Variable PM oxidative potential, bioavailable iron, and total metal concentrations were observed on these days. The contribution of WTS emissions to PM at the sampling site, as predicted by microscale wind direction measurements, was correlated with ascorbate (r = 0.80; p = 0.030) and glutathione depletion (r = 0.76; p = 0.046). Increased PM oxidative potential was associated with aluminum, lead, and iron content. PM arising from WTS activity has elevated trace metal concentrations and, as a consequence, increased oxidative potential. PM released by WTS activity should be considered a potential health risk to the nearby residential community.

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

PubMed

Kaspar, H F; Tiedje, J M

1981-03-01

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat.

Reduction of mixed Mn-Zr oxides: in situ XPS and XRD studies.

PubMed

Bulavchenko, O A; Vinokurov, Z S; Afonasenko, T N; Tsyrul'nikov, P G; Tsybulya, S V; Saraev, A A; Kaichev, V V

2015-09-21

A series of mixed Mn-Zr oxides with different molar ratios Mn/Zr (0.1-9) have been prepared by coprecipitation of manganese and zirconium nitrates and characterized by X-ray diffraction (XRD) and BET methods. It has been found that at concentrations of Mn below 30 at%, the samples are single-phase solid solutions (MnxZr1-xO2-δ) based on a ZrO2 structure. X-ray photoelectron spectroscopy (XPS) measurements showed that manganese in these solutions exists mainly in the Mn(4+) state on the surface. An increase in Mn content mostly leads to an increase in the number of Mn cations in the structure of solid solutions; however, a part of the manganese cations form Mn2O3 and Mn3O4 in the crystalline and amorphous states. The reduction of these oxides with hydrogen was studied by a temperature-programmed reduction technique, in situ XRD, and near ambient pressure XPS in the temperature range from 100 to 650 °C. It was shown that the reduction of the solid solutions MnxZr1-xO2-δ proceeds via two stages. During the first stage, at temperatures between 100 and 500 °C, the Mn cations incorporated into the solid solutions MnxZr1-xO2-δ undergo partial reduction. During the second stage, at temperatures between 500 and 700 °C, Mn cations segregate on the surface of the solid solution. In the samples with more than 30 at% Mn, the reduction of manganese oxides was observed: Mn2O3 → Mn3O4 → MnO.

Oxidative Addition and Reductive Elimination at Main-Group Element Centers.

PubMed

Chu, Terry; Nikonov, Georgii I

2018-04-11

Oxidative addition and reductive elimination are key steps in a wide variety of catalytic reactions mediated by transition-metal complexes. Historically, this reactivity has been considered to be the exclusive domain of d-block elements. However, this paradigm has changed in recent years with the demonstration of transition-metal-like reactivity by main-group compounds. This Review highlights the substantial progress achieved in the past decade for the activation of robust single bonds by main-group compounds and the more recently realized activation of multiple bonds by these elements. We also discuss the significant discovery of reversible activation of single bonds and distinct examples of reductive elimination at main-group element centers. The review consists of three major parts, starting with oxidative addition of single bonds, proceeding to cleavage of multiple bonds, and culminated by the discussion of reversible bond activation and reductive elimination. Within each subsection, the discussion is arranged according to the type of bond being cleaved or formed and considers elements from the left to the right of each period and down each group of the periodic table. The majority of results discussed in this Review come from the past decade; however, earlier reports are also included to ensure completeness.

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

PubMed Central

Kaspar, H F; Tiedje, J M

1981-01-01

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat. PMID:7224631

Anoxic nitrate reduction coupled with iron oxidation and attenuation of dissolved arsenic and phosphate in a sand and gravel aquifer

USGS Publications Warehouse

Smith, Richard L.; Kent, Douglas B.; Repert, Deborah A.; Böhlke, J.K.

2017-01-01

Nitrate has become an increasingly abundant potential electron acceptor for Fe(II) oxidation in groundwater, but this redox couple has not been well characterized within aquifer settings. To investigate this reaction and some of its implications for redox-sensitive groundwater contaminants, we conducted an in situ field study in a wastewater-contaminated aquifer on Cape Cod. Long-term (15 year) geochemical monitoring within the contaminant plume indicated interacting zones with variable nitrate-, Fe(II)-, phosphate-, As(V)-, and As(III)-containing groundwater. Nitrate and phosphate were derived predominantly from wastewater disposal, whereas Fe(II), As(III), and As(V) were mobilized from the aquifer sediments. Multiple natural gradient, anoxic tracer tests were conducted in which nitrate and bromide were injected into nitrate-free, Fe(II)-containing groundwater. Prior to injection, aqueous Fe(II) concentrations were approximately 175 μM, but sorbed Fe(II) accounted for greater than 90% of the total reactive Fe(II) in the aquifer. Nitrate reduction was stimulated within 1 m of transport for 100 μM and 1000 μM nitrate additions, initially producing stoichiometric quantities of nitrous oxide (>300 μM N). In subsequent injections at the same site, nitrate was reduced even more rapidly and produced less nitrous oxide, especially over longer transport distances. Fe(II) and nitrate concentrations decreased together and were accompanied by Fe(III) oxyhydroxide precipitation and decreases in dissolved phosphate, As(III), and As(V) concentrations. Nitrate N and O isotope fractionation effects during nitrate reduction were approximately equal (ε15N/ε18O = 1.11) and were similar to those reported for laboratory studies of biological nitrate reduction, including denitrification, but unlike some reported effects on nitrate by denitrification in aquifers. All constituents affected by the in situ tracer experiments returned to pre-injection levels after several

Reduction of Iron-Oxide-Carbon Composites: Part II. Rates of Reduction of Composite Pellets in a Rotary Hearth Furnace Simulator

NASA Astrophysics Data System (ADS)

Halder, S.; Fruehan, R. J.

2008-12-01

A new ironmaking concept is being proposed that involves the combination of a rotary hearth furnace (RHF) with an iron-bath smelter. The RHF makes use of iron-oxide-carbon composite pellets as the charge material and the final product is direct-reduced iron (DRI) in the solid or molten state. This part of the research includes the development of a reactor that simulated the heat transfer in an RHF. The external heat-transport and high heating rates were simulated by means of infrared (IR) emitting lamps. The reaction rates were measured by analyzing the off-gas and computing both the amount of CO and CO2 generated and the degree of reduction. The reduction times were found to be comparable to the residence times observed in industrial RHFs. Both artificial ferric oxide (PAH) and naturally occurring hematite and taconite ores were used as the sources of iron oxide. Coal char and devolatilized wood charcoal were the reductants. Wood charcoal appeared to be a faster reductant than coal char. However, in the PAH-containing pellets, the reverse was found to be true because of heat-transfer limitations. For the same type of reductant, hematite-containing pellets were observed to reduce faster than taconite-containing pellets because of the development of internal porosity due to cracking and fissure formation during the Fe2O3-to-Fe3O4 transition. This is, however, absent during the reduction of taconite, which is primarily Fe3O4. The PAH-wood-charcoal pellets were found to undergo a significant amount of swelling at low-temperature conditions, which impeded the external heat transport to the lower layers. If the average degree of reduction targeted in an RHF is reduced from 95 to approximately 70 pct by coupling the RHF with a bath smelter, the productivity of the RHF can be enhanced 1.5 to 2 times. The use of a two- or three-layer bed was found to be superior to that of a single layer, for higher productivities.

Compositional engineering of perovskite oxides for highly efficient oxygen reduction reactions.

PubMed

Chen, Dengjie; Chen, Chi; Zhang, Zhenbao; Baiyee, Zarah Medina; Ciucci, Francesco; Shao, Zongping

2015-04-29

Mixed conducting perovskite oxides are promising catalysts for high-temperature oxygen reduction reaction. Pristine SrCoO(3-δ) is a widely used parent oxide for the development of highly active mixed conductors. Doping a small amount of redox-inactive cation into the B site (Co site) of SrCoO(3-δ) has been applied as an effective way to improve physicochemical properties and electrochemical performance. Most findings however are obtained only from experimental observations, and no universal guidelines have been proposed. In this article, combined experimental and theoretical studies are conducted to obtain fundamental understanding of the effect of B-site doping concentration with redox-inactive cation (Sc) on the properties and performance of the perovskite oxides. The phase structure, electronic conductivity, defect chemistry, oxygen reduction kinetics, oxygen ion transport, and electrochemical reactivity are experimentally characterized. In-depth analysis of doping level effect is also undertaken by first-principles calculations. Among the compositions, SrCo0.95Sc0.05O(3-δ) shows the best oxygen kinetics and corresponds to the minimum fraction of Sc for stabilization of the oxygen-vacancy-disordered structure. The results strongly support that B-site doping of SrCoO(3-δ) with a small amount of redox-inactive cation is an effective strategy toward the development of highly active mixed conducting perovskites for efficient solid oxide fuel cells and oxygen transport membranes.

Tetraalykylammonium polyoxoanionic oxidation catalysts

DOEpatents

Ellis, Paul E.; Lyons, James E.; Myers, Jr., Harry K.; Shaikh, Shahid N.

1998-01-01

Alkanes are catalytically oxidized in air or oxygen using iron-substituted polyoxoanions (POAs) of the formula: H.sub.e-z ›(n-C.sub.4 H.sub.9).sub.4 N!.sub.z (XM.sub.11 M'O.sub.39).sup.-e The M' (e.g., iron(III)/iron(II)) reduction potential of the POAs is affected by selection of the central atom X and the framework metal M, and by the number of tetrabutyl-ammonium groups. Decreased Fe(III)/Fe(II) reduction potential has been found to correlate to increased oxidation activity.

Bonding Cu to Al2O3 with Bi-B-Zn Oxide Glass Via Oxidation-Reduction Reaction

NASA Astrophysics Data System (ADS)

Chen, Jianqiang; Li, Yufeng; Miao, Weiliang; Mai, Chengle; Li, Mingyu

2018-01-01

Bonding Cu on Al2O3 is a key and difficult technology applied in high-power semiconductor devices. A method proposed in this work investigates bonding with a kind of Bi-B-Zn oxide glass powder paste as a solder. Oxidation-reduction reactions between the Cu plate and the solder took place and generated Bi metal during the joining procedure. With an increase in the joining temperature, the tensile strength increased due to the increase of Bi metal formation. The Bi metal played an important role in joining Cu and Al2O3 because of its much better wettability on Cu than that of the oxides. A compound ZnAl2O4 was observed to form between the Al2O3 ceramic and oxide layer, which strengthened the bond.

Evidence of alloy formation during reduction of platinized tin oxide surfaces

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1989-01-01

Ion scattering spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis have been used to examine a platinized tin oxide catalyst surface before, during, and after reduction by annealing under vacuum at 250 to 450 C. These techniques were then used to examine the reduced surface after a room-temperature, low-pressure oxygen exposure. The spectral results and the behavior of the reduced surface toward oxygen exposure both indicate that a Pt/Sn alloy is produced during reduction.

Catalyst for reduction of nitrogen oxides

DOEpatents

Ott, Kevin C.

2010-04-06

A Selective Catalytic Reduction (SCR) catalyst was prepared by slurry coating ZSM-5 zeolite onto a cordierite monolith, then subliming an iron salt onto the zeolite, calcining the monolith, and then dipping the monolith either into an aqueous solution of manganese nitrate and cerium nitrate and then calcining, or by similar treatment with separate solutions of manganese nitrate and cerium nitrate. The supported catalyst containing iron, manganese, and cerium showed 80 percent conversion at 113 degrees Celsius of a feed gas containing nitrogen oxides having 4 parts NO to one part NO.sub.2, about one equivalent ammonia, and excess oxygen; conversion improved to 94 percent at 147 degrees Celsius. N.sub.2O was not detected (detection limit: 0.6 percent N.sub.2O).

Coupled Mercury–Cell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA

DOE PAGES

Lin, Hui; Morrell-Falvey, Jennifer L.; Rao, Balaji; ...

2014-09-30

G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), in this paper we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62).more » These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell–SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10 –19 to 25 × 10 –19 moles-Hg/cell (equivalent to Hg/cell–SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn 2+ leads to increased Hg reduction and decreased methylation. Finally, these results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.« less

Landscape planning for agricultural nonpoint source pollution reduction III: Assessing phosphorus and sediment reduction potential

USGS Publications Warehouse

Diebel, M.W.; Maxted, J.T.; Robertson, Dale M.; Han, S.; Vander Zanden, M. J.

2009-01-01

Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable following the implementation of riparian buffers; then we estimated load reduction potential for a set of 1598 watersheds (average 54 km2) in Wisconsin. Our results indicate that land cover is generally the most important driver of constituent loads in Wisconsin streams, but its influence varies among pollutants and according to the scale at which it is measured. Physiographic (drainage density) variation also influenced sediment and phosphorus loads. The effect of historical land use on present-day channel erosion and variation in soil texture are the most important sources of phosphorus and sediment that riparian buffers cannot attenuate. However, in most watersheds, a large proportion (approximately 70%) of these pollutants can be eliminated from streams with buffers. Cumulative frequency distributions of load reduction potential indicate that targeting pollution reduction in the highest 10% of Wisconsin watersheds would reduce total phosphorus and sediment loads in the entire state by approximately 20%. These results support our approach of geographically targeting nonpoint source pollution reduction at multiple scales, including the watershed scale. ?? 2008 Springer Science+Business Media, LLC.

The Reduction of Aqueous Metal Species on the Surfaces of Fe(II)-Containing Oxides: The Role of Surface Passivation

USGS Publications Warehouse

White, A.F.; Peterson, M.L.

1998-01-01

The reduction of aqueous transition metal species at the surfaces of Fe(II)- containing oxides has important ramifications in predicting the transport behavior in ground water aquifers. Experimental studies using mineral suspensions and electrodes demonstrate that structural Fe(II) heterogeneously reduces aqueous ferric, cupric, vanadate and chromate ions on magnetite and ilmenite surfaces. The rates of metal reduction on natural oxides is strongly dependent on the extent of surface passivation and redox conditions in the weathering environment. Synchrotron studies show that surface oxidation of Fe(II)-containing oxide minerals decreases their capacity for Cr(VI) reduction at hazardous waste disposal sites.

Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table.

PubMed

Toh, Rou Jun; Sofer, Zdeněk; Pumera, Martin

2015-11-16

Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microbial Fe(III) Oxide Reduction in Chocolate Pots Hot Springs, Yellowstone National Park

NASA Astrophysics Data System (ADS)

Fortney, N. W.; Roden, E. E.; Boyd, E. S.; Converse, B. J.

2014-12-01

Previous work on dissimilatory iron reduction (DIR) in Yellowstone National Park (YNP) has focused on high temperature, low pH environments where soluble Fe(III) is utilized as an electron acceptor for respiration. Much less attention has been paid to DIR in lower temperature, circumneutral pH environments, where solid phase Fe(III) oxides are the dominant forms of Fe(III). This study explored the potential for DIR in the warm (ca. 40-50°C), circumneutral pH Chocolate Pots hot springs (CP) in YNP. Most probable number (MPN) enumerations and enrichment culture studies confirmed the presence of endogenous microbial communities that reduced native CP Fe(III) oxides. Enrichment cultures demonstrated sustained DIR coupled to acetate and lactate oxidation through repeated transfers over ca. 450 days. Pyrosequencing of 16S rRNA genes indicated that the dominant organisms in the enrichments were closely affiliated with the well known Fe(III) reducer Geobacter metallireducens. Additional taxa included relatives of sulfate reducing bacterial genera Desulfohalobium and Thermodesulfovibrio; however, amendment of enrichments with molybdate, an inhibitor of sulfate reduction, suggested that sulfate reduction was not a primary metabolic pathway involved in DIR in the cultures. A metagenomic analysis of enrichment cultures is underway in anticipation of identifying genes involved in DIR in the less well-characterized dominant organisms. Current studies are aimed at interrogating the in situ microbial community at CP. Core samples were collected along the flow path (Fig. 1) and subdivided into 1 cm depth intervals for geochemical and microbiological analysis. The presence of significant quantities of Fe(II) in the solids indicated that DIR is active in situ. A parallel study investigated in vitro microbial DIR in sediments collected from three of the coring sites. DNA was extracted from samples from both studies for 16S rRNA gene and metagenomic sequencing in order to obtain a

Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

DOE PAGES

Eilert, Andre; Cavalca, Filippo; Roberts, F. Sloan; ...

2016-12-16

Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO 2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stablemore » under the strongly reducing conditions found in CO 2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.« less

Interim glycol flowsheet reduction/oxidation (redox) model for the Defense Waste Processing Facility (DWPF)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jantzen, C. M.; Williams, M. S.; Zamecnik, J. R.

Control of the REDuction/OXidation (REDOX) state of glasses containing high concentrations of transition metals, such as High Level Waste (HLW) glasses, is critical in order to eliminate processing difficulties caused by overly reduced or overly oxidized melts. Operation of a HLW melter at Fe +2/ΣFe ratios of between 0.09 and 0.33, a range which is not overly oxidizing or overly reducing, helps retain radionuclides in the melt, i.e. long-lived radioactive 99Tc species in the less volatile reduced Tc 4+ state, 104Ru in the melt as reduced Ru +4 state as insoluble RuO 2, and hazardous volatile Cr 6+ in themore » less soluble and less volatile Cr +3 state in the glass. The melter REDOX control balances the oxidants and reductants from the feed and from processing additives such as antifoam. Currently, the Defense Waste Processing Facility (DWPF) is running a formic acid-nitric acid (FN) flowsheet where formic acid is the main reductant and nitric acid is the main oxidant. During decomposition formate and formic acid releases H 2 gas which requires close control of the melter vapor space flammability. A switch to a nitric acid-glycolic acid (GN) flowsheet is desired as the glycolic acid flowsheet releases considerably less H 2 gas upon decomposition. This would greatly simplify DWPF processing. Development of an EE term for glycolic acid in the GN flowsheet is documented in this study.« less

Oxidation of N-nitrosodimethylamine (NDMA) precursors with ozone and chlorine dioxide: kinetics and effect on NDMA formation potential.

PubMed

Lee, Changha; Schmidt, Carsten; Yoon, Jeyong; von Gunten, Urs

2007-03-15

The oxidation of N-nitrosodimethylamine (NDMA) precursors chlorine dioxide (ClO2). Second-order rate constants for the reactions of model NDMA precursors (dimethylamine (DMA) and 7 tertiary amines) with ozone (kapp at pH 7 = 2.4 x 10(-1) to 2.3 x 10(9) M(-1) s(-1)), ClO2 (kapp at pH 7 = 6.7 x 10(-3) to 3.0 x 10(7) M(-1) s(-1)), and hydroxyl radical (*OH) (kapp at pH 7 = 6.2 x 10(7) to 1.4 x 10(10) M(-1) s(-1)) were determined, which showed that the selected NDMA precursors, with the exception of dimethylformamide (DMFA) can be completely transformed via their direct reaction with ozone. During ozonation, DMFA may be partially transformed through oxidation by the secondary oxidant *OH. ClO2 was also shown to effectively transform most of the precursors, with the exceptions of DMA and DMFA. In the second part of the study, the NDMA formation potentials (NDMA-FP) in synthetic and natural waters were measured with and without pre-oxidation with ozone and ClO2. A significant reduction in the NDMA-FPs was observed after complete transformation of the model NDMA precursors. Ozonation generally led to more effective reduction of the NDMA-FP than ClO2. For most of the precursors, the formation of DMA could account for the NDMA-FPs remaining after complete transformation of the model NDMA precursors. In contrast, dimethylethanolamine and dimethyldithiocarbamate yielded other NDMA precursors (not DMA) as their oxidation products. Pre-oxidation by ozone and ClO2 of several natural waters showed behavior similar to that of the oxidation of model NDMA precursors with a reduction of the NDMA-FP by 32-94% for various natural water sources.

Recent progress and perspectives in the photocatalytic CO2 reduction of Ti-oxide-based nanomaterials

NASA Astrophysics Data System (ADS)

Sohn, Youngku; Huang, Weixin; Taghipour, Fariborz

2017-02-01

The conversion of CO2 with H2O to valuable chemicals and fuels is a new solution to current environmental and energy problems, and the high energy barrier of these reactions can be overcome by the input of solar and electrical energy. However, the reduction efficiencies and selectivities of these reactions are insufficient for practical use, and significant effort and strategy are required to overcome the many obstacles preventing the large-scale application of photocatalytic CO2 reduction. This article reviews recent progress in CO2 reduction using titanium oxide-based materials and various strategic factors for increasing photocatalytic efficiency. This article also highlights non-titanium-oxide catalysts, the photoelectrocatalytic reduction of CO2, and other recent review articles concerning the recycling of CO2 to value-added carbon compounds.

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO 2 Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lum, Yanwei; Yue, Binbin; Lobaccaro, Peter

Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO 2 and better selectivity toward C 2 and C 3 (C 2+) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO 2 reduction, with particular attention given to the selectivity to C 2+ products. All catalysts were tested for CO 2 reduction in 0.1 M KHCO 3 and 0.1 M CsHCO 3 at applied voltagesmore » in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C 2+ products and only ~3% selectivity to C 1 products at –1.0 V vs RHE when CsHCO 3 is used as the electrolyte. In contrast, the selectivity to C 2+ products decreases to ~56% for the same catalysts tested in KHCO 3. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C 2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO 2. On the basis of recent theoretical studies, a high pH suppresses the formation of C 1 relative to C 2+ products. At the same time, however, a high local CO 2 concentration is necessary for the formation of C 2+ products.« less

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO 2 Reduction

DOE PAGES

Lum, Yanwei; Yue, Binbin; Lobaccaro, Peter; ...

2017-07-06

Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO 2 and better selectivity toward C 2 and C 3 (C 2+) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO 2 reduction, with particular attention given to the selectivity to C 2+ products. All catalysts were tested for CO 2 reduction in 0.1 M KHCO 3 and 0.1 M CsHCO 3 at applied voltagesmore » in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C 2+ products and only ~3% selectivity to C 1 products at –1.0 V vs RHE when CsHCO 3 is used as the electrolyte. In contrast, the selectivity to C 2+ products decreases to ~56% for the same catalysts tested in KHCO 3. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C 2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO 2. On the basis of recent theoretical studies, a high pH suppresses the formation of C 1 relative to C 2+ products. At the same time, however, a high local CO 2 concentration is necessary for the formation of C 2+ products.« less

Effects of surface chemistry and microstructure of electrolyte on oxygen reduction kinetics of solid oxide fuel cells

DOE PAGES

Park, Joong Sun; An, Jihwan; Lee, Min Hwan; ...

2015-11-01

In this study, we report systematic investigation of the surface properties of yttria-stabilized zirconia (YSZ) electrolytes with the control of the grain boundary (GB) density at the surface, and its effects on electrochemical activities. The GB density of thin surface layers deposited on single crystal YSZ substrates is controlled by changing the annealing temperature (750-1450 °C). Higher oxygen reduction reactions (ORR) kinetics is observed in samples annealed at lower temperatures. The higher ORR activity is ascribed to the higher GB density at the YSZ surface where 'mobile' oxide ion vacancies are more populated. Meanwhile, oxide ion vacancies concurrently created withmore » yttrium segregation at the surface at the higher annealing temperature are considered inactive to oxygen incorporation reactions. Our results provide additional insight into the interplay between the surface chemistry, microstructures, and electrochemical activity. They potentially provide important guidelines for engineering the electrolyte electrode interfaces of solid oxide fuel cells for higher electrochemical performance.« less

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan J.; Sookhakian, Mehran; Baradaran, Saeid; Mahmoudian, Mohammad R.; Ebadi, Mehdi

2013-09-01

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.

Oxidation-Reduction Calculations in the Biochemistry Course

ERIC Educational Resources Information Center

Feinman, Richard D.

2004-01-01

Redox calculations have the potential to reinforce important concepts in bioenergetics. The intermediacy of the NAD[superscript +]/NADH couple in the oxidation of food by oxygen, for example, can be brought out by such calculations. In practice, students have great difficulty and, even when adept at the calculations, frequently do not understand…

Tetraalklylammonium polyoxoanionic oxidation catalysts

DOEpatents

Ellis, P.E.; Lyons, J.E.; Myers, H.K. Jr.; Shaikh, S.N.

1998-10-06

Alkanes are catalytically oxidized in air or oxygen using iron-substituted polyoxoanions (POAs) of the formula: H{sub e{minus}z}[(n-C{sub 4}H{sub 9}){sub 4}N]{sub z}(XM{sub 11}M{prime}O{sub 39}){sup {minus}e}. The M{prime} (e.g., iron(III)/iron(II)) reduction potential of the POAs is affected by selection of the central atom X and the framework metal M, and by the number of tetrabutyl-ammonium groups. Decreased Fe(III)/Fe(II) reduction potential has been found to correlate to increased oxidation activity.

The Simulation of an Oxidation-Reduction Titration Curve with Computer Algebra

ERIC Educational Resources Information Center

Whiteley, Richard V., Jr.

2015-01-01

Although the simulation of an oxidation/reduction titration curve is an important exercise in an undergraduate course in quantitative analysis, that exercise is frequently simplified to accommodate computational limitations. With the use of readily available computer algebra systems, however, such curves for complicated systems can be generated…

Reduction and Oxidation of the Active Site Iron in Tyrosine Hydroxylase: Kinetics and Specificity†

PubMed Central

Frantom, Patrick A.; Seravalli, Javier; Ragsdale, Stephen W.; Fitzpatrick, Paul F.

2006-01-01

Tyrosine hydroxylase (TyrH) is a pterin-dependent enzyme that catalyzes the hydroxylation of tyrosine to form dihydroxyphenylalanine. The oxidation state of the active site iron atom plays a central role in the regulation of the enzyme. The kinetics of reduction of ferric TyrH by several reductants were determined by anaerobic stopped-flow spectroscopy. Anaerobic rapid freeze–quench EPR confirmed that the change in the near-UV absorbance of TyrH upon adding reductant corresponded to iron reduction. Tetrahydrobiopterin reduces wild-type TyrH following a simple second-order mechanism with a rate constant of 2.8 ± 0.1 mM−1 s−1. 6-Methyltetrahydropterin reduces the ferric enzyme with a second-order rate constant of 6.1 ± 0.1 mM−1 s−1 and exhibits saturation kinetics. No EPR signal for a radical intermediate was detected. Ascorbate, glutathione, and 1,4-benzoquinone all reduce ferric TyrH, but much more slowly than tetrahydrobiopterin, suggesting that the pterin is a physiological reductant. E332A TyrH, which has an elevated Km for tetrahydropterin in the catalytic reaction, is reduced by tetrahydropterins with the same kinetic parameters as those of the wild-type enzyme, suggesting that BH4 does not bind in the catalytic conformation during the reduction. Oxidation of ferrous TyrH by molecular oxygen can be described as a single-step second-order reaction, with a rate constant of 210 mM−1 s−1. S40E TyrH, which mimics the phosphorylated state of the enzyme, has oxidation and reduction kinetics similar to those of the wild-type enzyme, suggesting that phosphorylation does not directly regulate the interconversion of the ferric and ferrous forms. PMID:16475826

Synthesis of flower-like gold nanoparticles and their electrocatalytic activity towards the oxidation of methanol and the reduction of oxygen.

PubMed

Jena, Bikash Kumar; Raj, C Retna

2007-03-27

This article describes the synthesis of branched flower-like gold (Au) nanocrystals and their electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Gold nanoflowers (GNFs) were obtained by a one-pot synthesis using N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid (HEPES) as a reducing/stabilizing agent. The GNFs have been characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical measurements. The UV-visible spectra show two bands corresponding to the transverse and longitudinal surface plasmon (SP) absorption at 532 and 720 nm, respectively, for the colloidal GNFs. The GNFs were self-assembled on a sol-gel-derived silicate network, which was preassembled on a polycrystalline Au electrode and used for electrocatalytic applications. The GNFs retain their morphology on the silicate network; the UV-visible diffuse reflectance spectra (DRS) of GNFs on the silicate network show longitudinal and transverse bands as in the case of colloidal GNFs. The GNFs show excellent electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Oxidation of methanol in alkaline solution was observed at approximately 0.245 V, which is much less positive than that on an unmodified polycrystalline gold electrode. Reduction of oxygen to H2O2 and the further reduction of H2O2 to water in neutral pH were observed at less negative potentials on the GNFs electrode. The electrocatalytic activity of GNFs is significantly higher than that of the spherically shaped citrate-stabilized Au nanoparticles (SGNs).

The light-induced reduction of horizontal cell receptive field size in the goldfish retina involves nitric oxide.

PubMed

Daniels, Bryan A; Baldridge, William H

2011-03-01

Horizontal cells of the vertebrate retina have large receptive fields as a result of extensive gap junction coupling. Increased ambient illumination reduces horizontal cell receptive field size. Using the isolated goldfish retina, we have assessed the contribution of nitric oxide to the light-dependent reduction of horizontal cell receptive field size. Horizontal cell receptive field size was assessed by comparing the responses to centered spot and annulus stimuli and from the responses to translated slit stimuli. A period of steady illumination decreased the receptive field size of horizontal cells, as did treatment with the nitric oxide donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (100 μM). Blocking the endogenous production of nitric oxide with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (1 mM), decreased the light-induced reduction of horizontal cell receptive field size. These findings suggest that nitric oxide is involved in light-induced reduction of horizontal cell receptive field size. Copyright © Cambridge University Press, 2011

Enzymatic versus nonenzymatic mechanisms for Fe(III) reduction in aquatic sediments

USGS Publications Warehouse

Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

1991-01-01

The potential for nonenzymatic reduction of Fe(III) either by organic compounds or by the development of a low redox potential during microbial metabolism was compared with direct, enzymatic Fe(III) reduction by Fe(III)-reducing microorganisms. At circumneutral pH, very few organic compounds nonenzymatically reduced Fe(III). In contrast, in the presence of the appropriate Fe(IH)-reducing microorganisms, most of the organic compounds examined could be completely oxidized to carbon dioxide with the reduction of Fe(III). Even for those organic compounds that could nonenzymatically reduce Fe(III), microbial Fe(III) reduction was much more extensive. The development of a low redox potential during microbial fermentation did not result in nonenzymatic Fe(III) reduction. Model organic compounds were readily oxidized in Fe(III)-reducing aquifer sediments, but not in sterilized sediments. These results suggest that microorganisms enzymatically catalyze most of the Fe(III) reduction in the Fe(III) reduction zone of aquatic sediments and aquifers.

Reduction of Vanadium Oxide (VOx) under High Vacuum Conditions as Investigated by X-Ray Photoelectron Spectroscopy

NASA Astrophysics Data System (ADS)

Chourasia, A.

2015-03-01

Vanadium oxide thin films were formed by depositing thin films of vanadium on quartz substrates and oxidizing them in an atmosphere of oxygen. The deposition was done by the e-beam technique. The oxide films were annealed at different temperatures for different times under high vacuum conditions. The technique of x-ray photoelectron spectroscopy has been employed to study the changes in the oxidation states of vanadium and oxygen in such films. The spectral features in the vanadium 2p, oxygen 1s, and the x-ray excited Auger regions were investigated. The Auger parameter has been utilized to study the changes. The complete oxidation of elemental vanadium to V2O5 was observed to occur at 700°C. At any other temperature, a mixture of oxides consisting of V2O5 and VO2 was observed in the films. Annealing of the films resulted in the gradual loss of oxygen followed by reduction in the oxidation state from +5 to 0. The reduction was observed to depend upon the annealing temperature and the annealing time. Organized Research, TAMU-Commerce.

Role of tartaric and malic acids in wine oxidation.

PubMed

Danilewicz, John C

2014-06-04

Tartaric acid determines the reduction potential of the Fe(III)/Fe(II) redox couple. Therefore, it is proposed that it determines the ability of Fe to catalyze wine oxidation. The importance of tartaric acid was demonstrated by comparing the aerial oxidation of 4-methylcatechol (4-MeC) in model wine made up with tartaric and acetic acids at pH 3.6. Acetic acid, as a weaker Fe(III) ligand, should raise the reduction potential of the Fe couple. 4-MeC was oxidized in both systems, but the mechanisms were found to differ. Fe(II) readily reduced oxygen in tartrate model wine, but Fe(III) alone failed to oxidize the catechol, requiring sulfite assistance. In acetate model wine the reverse was found to operate. These observations should have broad application to model systems designed to study the oxidative process in foods and other beverages. Consideration should be given to the reduction potential of metal couples by the inclusion of appropriate ligands.

Reduction of nitrogen oxides with catalytic acid resistant aluminosilicate molecular sieves and ammonia

DOEpatents

Pence, Dallas T.; Thomas, Thomas R.

1980-01-01

Noxious nitrogen oxides in a waste gas stream such as the stack gas from a fossil-fuel-fired power generation plant or other industrial plant off-gas stream is catalytically reduced to elemental nitrogen and/or innocuous nitrogen oxides employing ammonia as reductant in the presence of a zeolite catalyst in the hydrogen or sodium form having pore openings of about 3 to 10 A.

The anaerobic degradation of organic matter in Danish coastal sediments - Iron reduction, manganese reduction, and sulfate reduction

NASA Technical Reports Server (NTRS)

Canfield, Donald E.; Thamdrup, BO; Hansen, Jens W.

1993-01-01

A combination of porewater and solid phase analysis as well as a series of sediment incubations are used to quantify organic carbon oxidation by dissimilatory Fe reduction, Mn reduction, and sulfate reduction, in sediments from the Skagerrak (located off the northeast coast of Jutland, Denmark). Solid phase data are integrated with incubation results to define the zones of the various oxidation processes. At S(9), surface Mn enrichments of up to 3.5 wt pct were found, and with such a ready source of Mn, dissimilatory Mn reduction was the only significant anaerobic process of carbon oxidation in the surface 10 cm of the sediment. At S(4) and S(6), active Mn reduction occurred; however, most of the Mn reduction may have resulted from the oxidation of acid volatile sulfides and Fe(2+) rather than by a dissimilatory sulfate. Dissolved Mn(2+) was found to completely adsorb onto sediment containing fully oxidized Mn oxides.

Roles of Cationic and Elemental Calcium in the Electro-Reduction of Solid Metal Oxides in Molten Calcium Chloride

NASA Astrophysics Data System (ADS)

Qiu, Guohong; Jiang, Kai; Ma, Meng; Wang, Dihua; Jin, Xianbo; Chen, George Z.

2007-06-01

Previous work, mainly from this research group, is re-visited on electrochemical reduction of solid metal oxides, in the form of compacted powder, in molten CaCl2, aiming at further understanding of the roles of cationic and elemental calcium. The discussion focuses on six aspects: 1.) debate on two mechanisms proposed in the literature, i. e. electro-metallothermic reduction and electro-reduction (or electro-deoxidation), for the electrolytic removal of oxygen from solid metals or metal oxides in molten CaCl2; 2.) novel metallic cavity working electrodes for electrochemical investigations of compacted metal oxide powders in high temperature molten salts assisted by a quartz sealed Ag/AgCl reference electrode (650 ºC- 950 ºC); 3.) influence of elemental calcium on the background current observed during electrolysis of solid metal oxides in molten CaCl2; 4.) electrochemical insertion/ inclusion of cationic calcium into solid metal oxides; 5.) typical features of cyclic voltammetry and chronoamperometry (potentiostatic electrolysis) of metal oxide powders in molten CaCl2; and 6.) some kinetic considerations on the electrolytic removal of oxygen.

Creating rigorous pathways to monetize methane and nitrous oxide emission reductions at small scale rice farms in three states of semi-arid peninsular India

NASA Astrophysics Data System (ADS)

Kritee, K.; Tiwari, R.; Nair, D.; Adhya, T. K.; Rudek, J.

2014-12-01

As a part of a joint undertaking by Environmental Defense Fund and the Fair Climate Network, we have measured reduction in methane and nitrous oxide emissions due to alternate "low carbon" rice cultivation practices for three ago-ecological zones in India for the past two years. Sampling for nitrous oxide and methane emissions was done on approximately 60-80% of the total number of days in a growing season and was based on modified GRACEnet protocol. In recognition of farmer's economic interest and global food security demands, we also measured the effect of rice cultivation practices on farm economics and yields. Our data from three agro-ecological zones for 2012-2014 suggest that, for semi-arid peninsular India, low-carbon rice cultivation practices offer large range of emission reduction potential (0.5-5 metric tons CO2e/acre/year). The regions with sandy soils (Alfisols) had high rates of nitrous oxide emissions even under baseline "flooded" rice cultivation regimes and, thus, the Tier 1 IPCC emissions factors grossly underestimate both the amount of nitrous oxide emission from conventional rice cultivation practices, and the extent to which it can be reduced through better fertilizer management. Also, the IPCC factors overestimate the methane emission reduction possible due to water management for rice paddies. Therefore, it is crucial to customize N and water management to each region such that yields and net GHG emission reduction are maximized. These practices also have the potential to decrease water use by 10-30% and improve long term soil health by optimizing organic matter and increasing water-holding capacity. In addition, through GPS based demarcation of farmer plots, recording baseline practices through extensive surveys, documenting the parameters required to aggregate and prove implementation of low carbon rice farming practices, and to model the GHG emission reduction over large scales, we have put forward a path for better monetization of GHG

Anaerobic oxidation of methane coupled to thiosulfate reduction in a biotrickling filter.

PubMed

Cassarini, Chiara; Rene, Eldon R; Bhattarai, Susma; Esposito, Giovanni; Lens, Piet N L

2017-09-01

Microorganisms from an anaerobic methane oxidizing sediment were enriched with methane gas as the substrate in a biotrickling filter (BTF) using thiosulfate as electron acceptor for 213days. Thiosulfate disproportionation to sulfate and sulfide were the dominating sulfur conversion process in the BTF and the sulfide production rate was 0.5mmoll -1 day -1 . A specific group of sulfate reducing bacteria (SRB), belonging to the Desulforsarcina/Desulfococcus group, was enriched in the BTF. The BTF biomass showed maximum sulfate reduction rate (0.38mmoll -1 day -1 ) with methane as sole electron donor, measured in the absence of thiosulfate in the BTF. Therefore, a BTF fed with thiosulfate as electron acceptor can be used to enrich SRB of the DSS group and activate the inoculum for anaerobic oxidation of methane coupled to sulfate reduction. Copyright © 2017 Elsevier Ltd. All rights reserved.

Oxidative dissolution potential of biogenic and abiogenic TcO 2 in subsurface sediments

NASA Astrophysics Data System (ADS)

Fredrickson, James K.; Zachara, John M.; Plymale, Andrew E.; Heald, Steve M.; McKinley, James P.; Kennedy, David W.; Liu, Chongxuan; Nachimuthu, Ponnusamy

2009-04-01

Technetium-99 (Tc) is an important fission product contaminant associated with sites of nuclear fuels reprocessing and geologic nuclear waste disposal. Tc is highly mobile in its most oxidized state [Tc(VII)O4-] and less mobile in the reduced form [Tc(IV)O 2· nH 2O]. Here we investigate the potential for oxidation of Tc(IV) that was heterogeneously reduced by reaction with biogenic Fe(II) in two sediments differing in mineralogy and aggregation state; unconsolidated Pliocene-age fluvial sediment from the upper Ringold (RG) Formation at the Hanford Site and a clay-rich saprolite from the Field Research Center (FRC) background site on the Oak Ridge Site. Both sediments contained Fe(III) and Mn(III/IV) as redox active phases, but FRC also contained mass-dominant Fe-phyllosilicates of different types. Shewanella putrefaciens CN32 reduced Mn(III/IV) oxides and generated Fe(II) that was reactive with Tc(VII) in heat-killed, bioreduced sediment. After bioreduction and heat-killing, biogenic Fe(II) in the FRC exceeded that in RG by a factor of two. More rapid reduction rates were observed in the RG that had lower biogenic Fe(II), and less particle aggregation. EXAFS measurements indicated that the primary reduction product was a TcO 2-like phase in both sediments. The biogenic redox product Tc(IV) oxidized rapidly and completely in RG when contacted with air. Oxidation, in contrast, was slow and incomplete in the FRC, in spite of similar molecular scale speciation of Tc compared to RG. X-ray microprobe, electron microprobe, X-ray absorption spectroscopy, and micro X-ray diffraction were applied to the whole sediment and isolated Tc-containing particles. These analyses revealed that non-oxidizable Tc(IV) in the FRC existed as complexes with octahedral Fe(III) within intra-grain domains of 50-100 μm-sized, Fe-containing micas presumptively identified as celadonite. The markedly slower oxidation rates in FRC as compared to RG were attributed to mass

Candida parapsilosis: A versatile biocatalyst for organic oxidation-reduction reactions.

PubMed

Chadha, Anju; Venkataraman, Sowmyalakshmi; Preetha, Radhakrishnan; Padhi, Santosh Kumar

2016-10-01

This review highlights the importance of the biocatalyst, Candida parapsilosis for oxidation and reduction reactions of organic compounds and establishes its versatility to generate a variety of chiral synthons. Appropriately designed reactions using C. parapsilosis effect efficient catalysis of organic transformations such as deracemization, enantioselective reduction of prochiral ketones, imines, and kinetic resolution of racemic alcohols via selective oxidation. This review includes the details of these biotransformations, catalyzed by whole cells (wild type and recombinant strains), purified enzymes (oxidoreductases) and immobilized whole cells of C. parapsilosis. The review presents a bioorganic perspective as it discusses the chemo, regio and stereoselectivity of the biocatalyst along with the structure of the substrates and optical purity of the products. Fermentation scale biocatalysis using whole cells of C. parapsilosis for several biotransformations to synthesize important chiral synthons/industrial chemicals is included. A comparison of C. parapsilosis with other whole cell biocatalysts for biocatalytic deracemization and asymmetric reduction of carbonyl and imine groups in the synthesis of a variety of enantiopure products is presented which will provide a basis for the choice of a biocatalyst for a desired organic transformation. Thus, a wholesome perspective on the present status of C. parapsilosis mediated organic transformations and design of new reactions which can be considered for large scale operations is provided. Taken together, C. parapsilosis can now be considered a 'reagent' for the organic transformations discussed here. Copyright © 2016 Elsevier Inc. All rights reserved.

Selective reduction of N-oxides to amines: application to drug metabolism.

PubMed

Kulanthaivel, Palaniappan; Barbuch, Robert J; Davidson, Rita S; Yi, Ping; Rener, Gregory A; Mattiuz, Edward L; Hadden, Chad E; Goodwin, Lawrence A; Ehlhardt, William J

2004-09-01

Phase I oxidative metabolism of nitrogen-containing drug molecules to their corresponding N-oxides is a common occurrence. There are instances where liquid chromatography/tandem mass spectometry techniques are inadequate to distinguish this pathway from other oxidation processes, including C-hydroxylations and other heteroatom oxidations, such as sulfur to sulfoxide. Therefore, the purpose of the present study was to develop and optimize an efficient and practical chemical method to selectively convert N-oxides to their corresponding amines suitable for drug metabolism applications. Our results indicated that efficient conversion of N-oxides to amines could be achieved with TiCl(3) and poly(methylhydrosiloxane). Among them, we found TiCl(3) to be a facile and easy-to-use reagent, specifically applicable to drug metabolism. There are a few reports describing the use of TiCl(3) to reduce N-O bonds in drug metabolism studies, but this methodology has not been widely used. Our results indicated that TiCl(3) is nearly as efficient when the reductions were carried out in the presence of biological matrices, including plasma and urine. Finally, we have shown a number of examples where TiCl(3) can be successfully used to selectively reduce N-oxides in the presence of sulfoxides and other labile groups.

Reduction and functionalization of graphene oxide sheets using biomimetic dopamine derivatives in one step.

PubMed

Kaminska, Izabela; Das, Manash R; Coffinier, Yannick; Niedziolka-Jonsson, Joanna; Sobczak, Jonusz; Woisel, Patrice; Lyskawa, Joel; Opallo, Marcin; Boukherroub, Rabah; Szunerits, Sabine

2012-02-01

An easy and environmentally friendly chemical method for the simultaneous reduction and noncovalent functionalization of graphene oxide (GO) using dopamine derivatives is described. The reaction takes place at room temperature under ultrasonication of an aqueous suspension of GO and a dopamine derivative. X-ray photoelectron spectroscopy, FT-IR spectroscopy, and cyclic voltammetry characterizations revealed that the resulting material consists of graphene functionalized with the dopamine derivative. This one-step protocol is applied for simultaneous reduction and functionalization of graphene oxide with a dopamine derivative bearing an azide function. The chemical reactivity of the azide function was demonstrated by a postfunctionalization with ethynylferrocene using the Cu(I) catalyzed 1,3-dipolar cyloaddition.

Facile one-pot synthesis of platinum nanoparticles decorated nitrogen-graphene with high electrocatalytic performance for oxygen reduction and anodic fuels oxidation

NASA Astrophysics Data System (ADS)

Navaee, Aso; Salimi, Abdollah; Soltanian, Saeid; Servati, Peyman

2015-03-01

Due to exceptional electronic properties of graphene (Gr) and nitrogen doped graphene (N-Gr), they are considered as superior supporting platforms for novel metal nanoparticle decorations. Here, we report, a novel one-step electrochemical method for synthesis of Nitrogen-doped graphene sheets uniformly decorated with platinum nanoparticles (Pt/N-Gr). A graphite rod and platinum wire are respectively used for graphene and platinum nanoparticles production. The potential is cycled from -3V to +3V in acetonitrile solution as a nitrogen dopant source. By increasing the number of cycles the nitrogen-doped graphene/platinum nanoparticles composite is generated. After heat-treating the composite is characterized with various techniques such as FTIR, Raman, XPS, SEM and TEM. The electrocatalytic activity of the prepared composite toward the reduction of O2 and the oxidation of usual anodic fuels such as methanol, ethanol, hydrazine and formic acid is investigated using cyclic voltammetry technique. In comparison to commercial platinum/carbon, the onset potentials and the current densities for both O2 reduction and fuels oxidation are remarkably improved. Furthermore, the modified electrode by this composite shows good long-term stability and poisoning tolerance.

Dual path mechanism in the thermal reduction of graphene oxide.

PubMed

Larciprete, Rosanna; Fabris, Stefano; Sun, Tao; Lacovig, Paolo; Baraldi, Alessandro; Lizzit, Silvano

2011-11-02

Graphene is easily produced by thermally reducing graphene oxide. However, defect formation in the C network during deoxygenation compromises the charge carrier mobility in the reduced material. Understanding the mechanisms of the thermal reactions is essential for defining alternative routes able to limit the density of defects generated by carbon evolution. Here, we identify a dual path mechanism in the thermal reduction of graphene oxide driven by the oxygen coverage: at low surface density, the O atoms adsorbed as epoxy groups evolve as O(2) leaving the C network unmodified. At higher coverage, the formation of other O-containing species opens competing reaction channels, which consume the C backbone. We combined spectroscopic tools and ab initio calculations to probe the species residing on the surface and those released in the gas phase during heating and to identify reaction pathways and rate-limiting steps. Our results illuminate the current puzzling scenario of the low temperature gasification of graphene oxide.

Chemical potential of oxygen in (U, Pu) mixed oxide with Pu/(U+Pu) = 0.46

NASA Astrophysics Data System (ADS)

Dawar, Rimpi; Chandramouli, V.; Anthonysamy, S.

2016-05-01

Chemical potential of oxygen in (U,Pu) mixed oxide with Pu/(U + Pu) = 0.46 was measured for the first time using H2/H2O gas equilibration combined with solid electrolyte EMF technique at 1073, 1273 and 1473 K covering an oxygen potential range of -525 to -325 kJ mol-1. The effect of oxygen potential on the oxygen to metal ratio was determined. Increase in oxygen potential increases the O/M. In this study the minimum O/M obtained was 1.985 below which reduction was not possible. Partial molar enthalpy ΔHbar O2 and entropy ΔSbar O2 of oxygen were calculated from the oxygen potential data. The values of -752.36 kJ mol-1 and 0.25 kJ mol-1 were obtained for ΔHbar O2 and ΔSbar O2 respectively.

Oxidative stress protection by newly synthesized nitrogen compounds with pharmacological potential.

PubMed

Silva, João P; Areias, Filipe M; Proença, Fernanda M; Coutinho, Olga P

2006-02-09

In this study we used new nitrogen compounds obtained by organic synthesis whose structure predicted an antioxidant potential and then an eventual development as molecules of pharmacological interest in diseases involving oxidative stress. The compounds, identified as FMA4, FMA5, FMA7 and FMA8 differ in the presence of hydroxyl groups located in the C-3 and/or C-4 position of a phenolic unit, which is possibly responsible for their free radicals' buffering capacity. Data from the DPPH discoloration method confirm the high antiradical efficiency of the compounds. The results obtained with cellular models (L929 and PC12) show that they are not toxic and really protect from membrane lipid peroxidation induced by the ascorbate-iron oxidant pair. The level of protection correlates with the drug's lipophilic profile and is sometimes superior to trolox and equivalent to that observed for alpha-tocopherol. The compounds FMA4 and FMA7 present also a high protection from cell death evaluated in the presence of a staurosporine apoptotic stimulus. That protection results in a significant reduction of caspase-3 activity induced by staurosporine which by its turn seems to result from a protection observed in the membrane receptor pathway (caspase-8) together with a protection observed in the mitochondrial pathway (caspase-9). Taken together the results obtained with the new compounds, with linear chains, open up perspectives for their use as therapeutical agents, namely as antioxidants and protectors of apoptotic pathways. On the other hand the slight pro-oxidant profile obtained with the cyclic structures suggests a different therapeutic potential that is under current investigation.

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

DOE PAGES

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei; ...

2018-05-12

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO

NASA Technical Reports Server (NTRS)

Drawdy, Jean E.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1990-01-01

Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

Nitric-glycolic flowsheet reduction/oxidation (redox) model for the defense waste processing facility (DWPF)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jantzen, C. M.; Williams, M. S.; Edwards, T. B.

Control of the REDuction/OXidation (REDOX) state of glasses containing high concentrations of transition metals, such as High Level Waste (HLW) glasses, is critical in order to eliminate processing difficulties caused by overly reduced or overly oxidized melts. Operation of a HLW melter at Fe +2/ΣFe ratios of between 0.09 and 0.33, retains radionuclides in the melt and thus the final glass. Specifically, long-lived radioactive 99Tc species are less volatile in the reduced Tc 4+ state as TcO 2 than as NaTcO 4 or Tc 2O 7, and ruthenium radionuclides in the reduced Ru 4+ state are insoluble RuO 2 inmore » the melt which are not as volatile as NaRuO 4 where the Ru is in the +7 oxidation state. Similarly, hazardous volatile Cr 6+ occurs in oxidized melt pools as Na 2CrO 4 or Na 2Cr 2O 7, while the Cr +3 state is less volatile and remains in the melt as NaCrO 2 or precipitates as chrome rich spinels. The melter REDOX control balances the oxidants and reductants from the feed and from processing additives such as antifoam.« less

Hydrogen peroxide-induced reduction of delayed rectifier potassium current in hippocampal neurons involves oxidation of sulfhydryl groups.

PubMed

Hasan, Sonia M K; Redzic, Zoran B; Alshuaib, Waleed B

2013-07-03

This study examined the effect of H2O2 on the delayed rectifier potassium current (IKDR) in isolated hippocampal neurons. Whole-cell voltage-clamp experiments were performed on freshly dissociated hippocampal CA1 neurons of SD rats before and after treatment with H2O2. To reveal the mechanism behind H2O2-induced changes in IKDR, cells were treated with different oxidizing and reducing agents. External application of membrane permeable H2O2 reduced the amplitude and voltage-dependence of IKDR in a concentration dependent manner. Desferoxamine (DFO), an iron-chelator that prevents hydroxyl radical (OH) generation, prevented H2O2-induced reduction in IKDR. Application of the sulfhydryl-oxidizing agent 5,5 dithio-bis-nitrobenzoic acid (DTNB) mimicked the effect of H2O2. Sulfhydryl-reducing agents dithiothreitol (DTT) and glutathione (GSH) alone did not affect IKDR; however, DTT and GSH reversed and prevented the H2O2-induced inhibition of IKDR, respectively. Membrane impermeable agents GSH and DTNB showed effects only when added intracellularly identifying intracellular sulfhydryl groups as potential targets for hydroxyl-mediated oxidation. However, the inhibitory effects of DTNB and H2O2 at the positive test potentials were completely and partially abolished by DTT, respectively, suggesting an additional mechanism of action for H2O2, that is not shared by DTNB. In summary, this study provides evidence for the redox modulation of IKDR, identifies hydroxyl radical as an intermediate oxidant responsible for the H2O2-induced decrease in current amplitude and identifies intracellular sulfhydryl groups as an oxidative target. Copyright © 2013 Elsevier B.V. All rights reserved.

Portable Nitric Oxide (NO) Generator Based on Electrochemical Reduction of Nitrite for Potential Applications in Inhaled NO Therapy and Cardiopulmonary Bypass Surgery.

PubMed

Qin, Yu; Zajda, Joanna; Brisbois, Elizabeth J; Ren, Hang; Toomasian, John M; Major, Terry C; Rojas-Pena, Alvaro; Carr, Benjamin; Johnson, Thomas; Haft, Jonathan W; Bartlett, Robert H; Hunt, Andrew P; Lehnert, Nicolai; Meyerhoff, Mark E

2017-11-06

A new portable gas phase nitric oxide (NO) generator is described for potential applications in inhaled NO (INO) therapy and during cardiopulmonary bypass (CPB) surgery. In this system, NO is produced at the surface of a large-area mesh working electrode by electrochemical reduction of nitrite ions in the presence of a soluble copper(II)-ligand electron transfer mediator complex. The NO generated is then transported into gas phase by either direct purging with nitrogen/air or via circulating the electrolyte/nitrite solution through a gas extraction silicone fiber-based membrane-dialyzer assembly. Gas phase NO concentrations can be tuned in the range of 5-1000 ppm (parts per million by volume for gaseous species), in proportion to a constant cathodic current applied between the working and counter electrodes. This new NO generation process has the advantages of rapid production times (5 min to steady-state), high Faraday NO production efficiency (ca. 93%), excellent stability, and very low cost when using air as the carrier gas for NO (in the membrane dialyzer configuration), enabling the development of potentially portable INO devices. In this initial work, the new system is examined for the effectiveness of gaseous NO to reduce the systemic inflammatory response (SIR) during CPB, where 500 ppm of NO added to the sweep gas of the oxygenator or to the cardiotomy suction air in a CPB system is shown to prevent activation of white blood cells (granulocytes and monocytes) during extracorporeal circulation with cardiotomy suction conducted with five pigs.

The Nernst equation applied to oxidation-reduction reactions in myoglobin and hemoglobin. Evaluation of the parameters.

PubMed

Saroff, Harry A

Analyses of the binding of oxygen to monomers such as myoglobin employ the Mass Action equation. The Mass Action equation, as such, is not directly applicable for the analysis of the binding of oxygen to oligomers such as hemoglobin. When the binding of oxygen to hemoglobin is analyzed, models incorporating extensions of mass action are employed. Oxidation-reduction reactions of the heme group in myoglobin and hemoglobin involve the binding and dissociation of electrons. This reaction is described with the Nernst equation. The Nernst equation is applicable only to a monomeric species even if the number of electrons involved is greater than unity. To analyze the oxidation-reduction reaction in a molecule such as hemoglobin a model is required which incorporates extensions of the Nernst equation. This communication develops models employing the Nernst equation for oxidation-reduction reactions analogous to those employed for hemoglobin in the analysis of the oxygenation (binding of oxygen) reaction.

Oxidation Potentials in Matte Smelting of Copper and Nickel

NASA Astrophysics Data System (ADS)

Matousek, Jan W.

2014-09-01

The oxidation potential, given as the base-ten logarithm of the oxygen partial pressure in bars and the temperature [log pO2/ T, °C], defines the state of oxidation of pyrometallurgical extraction and refining processes. This property varies from copper making, [-6/1150]; to lead/zinc smelting, [-10/1200]; to iron smelting, [-13/1600]. The current article extends the analysis to the smelting of copper and nickel/copper sulfide concentrates to produce mattes of the type Cu(Ni)FeS(O) and iron silicate slags, FeOxSiO2—with oxidation potentials of [-7.5/1250].

Sequential reductive and oxidative conditions used to biodegradation of organochlorine pesticides by native bacteria.

NASA Astrophysics Data System (ADS)

Kopytko, M.; Correa-Torres, S. N.; Plata, A.

2016-07-01

Despite restrictions and bans on the use of many organochlorine pesticides in the 1970s and 1980s, they continue to persist in the environment today. This is the case of Agustin Codazzi, Cesar where the organochlorine pesticides were buried without control in the soil in 1999, after being banned their use. Nowadays is necessary to find the best method, which allows remediation of this soils. Reductive dechlorination is the first and limiting step in the metabolism of many organochlorine pesticides by anaerobic bacteria. In this study the reductive conditions were enhanced by addition of biogas as an auxiliary electron donors.The soil sample was taken from the zone at Agustin Codazzi, Cesar, and their characteristics correspond to a loam soil with low nutrient and slight compaction. The experimental tests were performed by varying the exposure time of a reducer to oxidative environment. Reductive conditions were enhanced by methane from biogas and oxidative environment was generated by air blown to stimulate a metabolic process of the soil native bacteria. Removals between 70 and 78.9% of compounds such as 4,4'-DDT, 4, 4'-DDD, 4,4'-DDE, Endrin and Trans- Chlordane, detected by gas chromatography analysis, were achieved under reductive/oxidative conditions during 120 days. Furthermore, bacterial strains capable of degrading organochlorine pesticides were selected from the native bacteria, and identified by the purified and identified based on its morphological characteristics and 16S rDNA sequencing.

Oxidant production from source-oriented particulate matter - Part 1: Oxidative potential using the dithiothreitol (DTT) assay

NASA Astrophysics Data System (ADS)

Charrier, J. G.; Richards-Henderson, N. K.; Bein, K. J.; McFall, A. S.; Wexler, A. S.; Anastasio, C.

2014-09-01

Recent epidemiological evidence supports the hypothesis that health effects from inhalation of ambient particulate matter (PM) are governed by more than just the mass of PM inhaled. Both specific chemical components and sources have been identified as important contributors to mortality and hospital admissions, even when these endpoints are unrelated to PM mass. Sources may cause adverse health effects via their ability to produce reactive oxygen species, possibly due to the transition metal content of the PM. Our goal is to quantify the oxidative potential of ambient particle sources collected during two seasons in Fresno, CA using the dithiothreitol (DTT) assay. We collected PM from different sources or source combinations into different ChemVol (CV) samplers in real time using a novel source-oriented sampling technique based on single particle mass spectrometry. We segregated the particles from each source-oriented mixture into two size fractions - ultrafine (Dp ≤ 0.17 μm) and submicron fine (0.17 μm ≤ Dp ≤ 1.0 μm) - and measured metals and the rate of DTT loss in each PM extract. We find that the mass-normalized oxidative potential of different sources varies by up to a actor of 8 and that submicron fine PM typically has a larger mass-normalized oxidative potential than ultrafine PM from the same source. Vehicular Emissions, Regional Source Mix, Commute Hours, Daytime Mixed Layer and Nighttime Inversion sources exhibit the highest mass-normalized oxidative potential. When we apportion the volume-normalized oxidative potential, which also accounts for the source's prevalence, cooking sources account for 18-29% of the total DTT loss while mobile (traffic) sources account for 16-28%. When we apportion DTT activity for total PM sampled to specific chemical compounds, soluble copper accounts for roughly 50% of total air-volume-normalized oxidative potential, soluble manganese accounts for 20%, and other unknown species, likely including quinones and other

Establishment of a Method for Measuring Antioxidant Capacity in Urine, Based on Oxidation Reduction Potential and Redox Couple I2/KI

PubMed Central

Cao, Tinghui; He, Min; Bai, Tianyu

2016-01-01

Objectives. To establish a new method for determination of antioxidant capacity of human urine based on the redox couple I2/KI and to evaluate the redox status of healthy and diseased individuals. Methods. The method was based on the linear relationship between oxidation reduction potential (ORP) and logarithm of concentration ratio of I2/KI. ORP of a solution with a known concentration ratio of I2/KI will change when reacted with urine. To determine the accuracy of the method, both vitamin C and urine were reacted separately with I2/KI solution. The new method was compared with the traditional method of iodine titration and then used to measure the antioxidant capacity of urine samples from 30 diabetic patients and 30 healthy subjects. Results. A linear relationship was found between logarithm of concentration ratio of I2/KI and ORP (R 2 = 0.998). Both vitamin C and urine concentration showed a linear relationship with ORP (R 2 = 0.994 and 0.986, resp.). The precision of the method was in the acceptable range and results of two methods had a linear correlation (R 2 = 0.987). Differences in ORP values between diabetic group and control group were statistically significant (P < 0.05). Conclusions. A new method for measuring the antioxidant capacity of clinical urine has been established. PMID:28115919

Unified interatomic potential and energy barrier distributions for amorphous oxides.

PubMed

Trinastic, J P; Hamdan, R; Wu, Y; Zhang, L; Cheng, Hai-Ping

2013-10-21

Amorphous tantala, titania, and hafnia are important oxides for biomedical implants, optics, and gate insulators. Understanding the effects of oxide doping is crucial to optimize performance in these applications. However, no molecular dynamics potentials have been created to date that combine these and other oxides that would allow computational analyses of doping-dependent structural and mechanical properties. We report a novel set of computationally efficient, two-body potentials modeling van der Waals and covalent interactions that reproduce the structural and elastic properties of both pure and doped amorphous oxides. In addition, we demonstrate that the potential accurately produces energy barrier distributions for pure and doped samples. The distributions can be directly compared to experiment and used to calculate physical quantities such as internal friction to understand how doping affects material properties. Future analyses using these potentials will be of great value to determine optimal doping concentrations and material combinations for myriad material science applications.

Oxygen potential of uranium--plutonium oxide as determined by controlled- atmosphere thermogravimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swanson, Gerald C.

1975-10-01

The oxygen-to-metal atom ratio, or O/M, of solid solution uranium- plutonium oxide reactor fuel is a measure of the concentration of crystal defects in the oxide which affect many fuel properties, particularly, fuel oxygen potential. Fabrication of a high-temperature oxygen electrode, employing an electro-active tip of oxygen-deficient solid-state electrolyte, intended to confirm gaseous oxygen potentials is described. Uranium oxide and plutonium oxide O/M reference materials were prepared by in situ oxidation of high purity metals in the thermobalance. A solid solution uranium-plutonium oxide O/M reference material was prepared by alloying the uranium and plutonium metals in a yttrium oxide cruciblemore » at 1200°C and oxidizing with moist He at 250°C. The individual and solid solution oxides were isothermally equilibrated with controlled oxygen potentials between 800 and 1300°C and the equilibrated O/ M ratios calculated with corrections for impurities and buoyancy effects. Use of a reference oxygen potential of -100 kcal/mol to produce an O/M of 2.000 is confirmed by these results. However, because of the lengthy equilibration times required for all oxides, use of the O/M reference materials rather than a reference oxygen potential is recommended for O/M analysis methods calibrations.« less

Electrostatic force spectroscopy revealing the degree of reduction of individual graphene oxide sheets.

PubMed

Shen, Yue; Wang, Ying; Zhou, Yuan; Hai, Chunxi; Hu, Jun; Zhang, Yi

2018-01-01

Electrostatic force spectroscopy (EFS) is a method for monitoring the electrostatic force microscopy (EFM) phase with high resolution as a function of the electrical direct current bias applied either to the probe or sample. Based on the dielectric constant difference of graphene oxide (GO) sheets (reduced using various methods), EFS can be used to characterize the degree of reduction of uniformly reduced one-atom-thick GO sheets at the nanoscale. In this paper, using thermally or chemically reduced individual GO sheets on mica substrates as examples, we characterize their degree of reduction at the nanoscale using EFS. For the reduced graphene oxide (rGO) sheets with a given degree of reduction (sample n), the EFS curve is very close to a parabola within a restricted area. We found that the change in parabola opening direction (or sign the parabola opening value) indicates the onset of reduction on GO sheets. Moreover, the parabola opening value, the peak bias value (tip bias leads to the peak or valley EFM phases) and the EFM phase contrast at a certain tip bias less than the peak value can all indicate the degree of reduction of rGO samples, which is positively correlated with the dielectric constant. In addition, we gave the ranking of degree for reduction on thermally or chemically reduced GO sheets and evaluated the effects of the reducing conditions. The identification of the degree of reduction of GO sheets using EFS is important for reduction strategy optimization and mass application of GO, which is highly desired owing to its mechanical, thermal, optical and electronic applications. Furthermore, as a general and quantitative technique for evaluating the small differences in the dielectric properties of nanomaterials, the EFS technique will extend and facilitate its nanoscale electronic devices applications in the future.

Developing Investigation Skills in an Introductory Multistep Synthesis Using Fluorene Oxidation and Reduction

ERIC Educational Resources Information Center

Stocksdale, Mark G; Pointer, Roy D; Benson, Barret W.; Fletcher, Steven E. S.; Henry, Ian; Ogren, Paul J.; Berg, Michael A. G.

2004-01-01

A two-step oxidation-reduction sequence that incorporates several important aspects of synthesis into introductory organic chemistry laboratories is described. This experiment is an excellent vehicle for introducing elements of discovery and intermediate yield improvement strategies.

Controlled, Stepwise Reduction and Band Gap Manipulation of Graphene Oxide.

PubMed

Mathkar, Akshay; Tozier, Dylan; Cox, Paris; Ong, Peijie; Galande, Charudatta; Balakrishnan, Kaushik; Leela Mohana Reddy, Arava; Ajayan, Pulickel M

2012-04-19

Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.

Oxidative Polyoxometalates Modified Graphitic Carbon Nitride for Visible-Light CO2 Reduction.

PubMed

Zhou, Jie; Chen, Weichao; Sun, Chunyi; Han, Lu; Qin, Chao; Chen, Mengmeng; Wang, Xinlong; Wang, Enbo; Su, Zhongmin

2017-04-05

Developing a photocatalysis system for converting CO 2 to valuable fuels or chemicals is a promising strategy to address global warming and fossil fuel consumption. Exploring photocatalysts with high-performance and low-cost has been two ultimate goals toward photoreduction of CO 2 . Herein, noble-metal-free polyoxometalates (Co4) with oxidative ability was first introduced into g-C 3 N 4 resulted in inexpensive hybrid materials (Co4@g-C 3 N 4 ) with staggered band alignment. The staggered composited materials show a higher activity of CO 2 reduction than bare g-C 3 N 4 . An optimized Co4@g-C 3 N 4 hybrid sample exhibited a high yield (107 μmol g -1 h -1 ) under visible-light irradiation (λ ≥ 420 nm), meanwhile maintaining high selectivity for CO production (94%). After 10 h of irradiation, the production of CO reached 896 μmol g -1 . Mechanistic studies revealed the introduction of Co4 not only facilitate the charge transfer of g-C 3 N 4 but greatly increased the surface catalytic oxidative ability. This work creatively combined g-C 3 N 4 with oxidative polyoxometalates which provide novel insights into the design of low-cost photocatalytic materials for CO 2 reduction.

[Reduction of nitrobenzene by iron oxides bound Fe(II) system at different pH values].

PubMed

Luan, Fu-Bo; Xie, Li; Li, Jun; Zhou, Qi

2009-07-15

Batch tests were conducted to investigate the reductive transformation of nitrobenzene by goethite, hematite, magnetite and steel converter slag bound Fe(II) system. And the reduction mechanism was explored at different pH values. Experimental results showed that hematite, magnetite and steel converter slag could adsorb Fe(II) on surfaces and form iron oxides bound Fe(II) system at pH from 6.5 to 7.0. The systems had strong reductive capacity and could reduce nitrobenzene to aniline. The reduction efficiency of nitrobenzene in surface bound Fe(II) system followed the sequence of magnetite, hematite and steel converter slag from high to low. The reduction efficiency of hematite and magnetite system increased with pH increasing. While it was almost pH independent in steel converter slag system. Although goethite adsorbed most of Fe(II) in solution, the adsorbed Fe(II) had no reductive activity for nitrobenzene. At pH 6.0, small amount of Fe(II) was adsorbed on magnetite and hematite and the systems did not show reductive activity for nitrobenzene. However, steel converter slag could adsorb Fe(II) at pH 6.0 and reduction efficiency almost equaled to the value at pH 7.0. When pH was above 7.5, dissolved Fe(II) could be converted to Fe(OH)2 and the newly formed Fe(OH)2 became the main redactor in the system. Under alkali condition, the presence of iron oxides inhibited the reduction capacity of system.

Anaerobic oxidation of methane associated with sulfate reduction in a natural freshwater gas source

PubMed Central

Timmers, Peer HA; Suarez-Zuluaga, Diego A; van Rossem, Minke; Diender, Martijn; Stams, Alfons JM; Plugge, Caroline M

2016-01-01

The occurrence of anaerobic oxidation of methane (AOM) and trace methane oxidation (TMO) was investigated in a freshwater natural gas source. Sediment samples were taken and analyzed for potential electron acceptors coupled to AOM. Long-term incubations with 13C-labeled CH4 (13CH4) and different electron acceptors showed that both AOM and TMO occurred. In most conditions, 13C-labeled CO2 (13CO2) simultaneously increased with methane formation, which is typical for TMO. In the presence of nitrate, neither methane formation nor methane oxidation occurred. Net AOM was measured only with sulfate as electron acceptor. Here, sulfide production occurred simultaneously with 13CO2 production and no methanogenesis occurred, excluding TMO as a possible source for 13CO2 production from 13CH4. Archaeal 16S rRNA gene analysis showed the highest presence of ANME-2a/b (ANaerobic MEthane oxidizing archaea) and AAA (AOM Associated Archaea) sequences in the incubations with methane and sulfate as compared with only methane addition. Higher abundance of ANME-2a/b in incubations with methane and sulfate as compared with only sulfate addition was shown by qPCR analysis. Bacterial 16S rRNA gene analysis showed the presence of sulfate-reducing bacteria belonging to SEEP-SRB1. This is the first report that explicitly shows that AOM is associated with sulfate reduction in an enrichment culture of ANME-2a/b and AAA methanotrophs and SEEP-SRB1 sulfate reducers from a low-saline environment. PMID:26636551

Oxidant production from source-oriented particulate matter - Part 1: Oxidative potential using the dithiothreitol (DTT) assay

NASA Astrophysics Data System (ADS)

Charrier, J. G.; Richards-Henderson, N. K.; Bein, K. J.; McFall, A. S.; Wexler, A. S.; Anastasio, C.

2015-03-01

Recent epidemiological evidence supports the hypothesis that health effects from inhalation of ambient particulate matter (PM) are governed by more than just the mass of PM inhaled. Both specific chemical components and sources have been identified as important contributors to mortality and hospital admissions, even when these end points are unrelated to PM mass. Sources may cause adverse health effects via their ability to produce reactive oxygen species in the body, possibly due to the transition metal content of the PM. Our goal is to quantify the oxidative potential of ambient particle sources collected during two seasons in Fresno, CA, using the dithiothreitol (DTT) assay. We collected PM from different sources or source combinations into different ChemVol (CV) samplers in real time using a novel source-oriented sampling technique based on single-particle mass spectrometry. We segregated the particles from each source-oriented mixture into two size fractions - ultrafine Dp ≤ 0.17 μm) and submicron fine (0.17 μm ≤ Dp ≤ 1.0 μm) - and measured metals and the rate of DTT loss in each PM extract. We find that the mass-normalized oxidative potential of different sources varies by up to a factor of 8 and that submicron fine PM typically has a larger mass-normalized oxidative potential than ultrafine PM from the same source. Vehicular emissions, regional source mix, commute hours, daytime mixed layer, and nighttime inversion sources exhibit the highest mass-normalized oxidative potential. When we apportion DTT activity for total PM sampled to specific chemical compounds, soluble copper accounts for roughly 50% of total air-volume-normalized oxidative potential, soluble manganese accounts for 20%, and other unknown species, likely including quinones and other organics, account for 30%. During nighttime, soluble copper and manganese largely explain the oxidative potential of PM, while daytime has a larger contribution from unknown (likely organic) species.

Effect of plasma power on reduction of printable graphene oxide thin films on flexible substrates

NASA Astrophysics Data System (ADS)

Banerjee, Indrani; Mahapatra, Santosh K.; Pal, Chandana; Sharma, Ashwani K.; Ray, Asim K.

2018-05-01

Room temperature hydrogen plasma treatment on solution processed 300 nm graphene oxide (GO) films on flexible indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates has been performed by varying the plasma power between 20 W and 60 W at a constant exposure time of 30 min with a view to examining the effect of plasma power on reduction of GO. X-ray powder diffraction (XRD) and Raman spectroscopic studies show that high energy hydrogen species generated in the plasma assist fast exfoliation of the oxygenated functional groups present in the GO samples. Significant decrease in the optical band gap is observed from 4.1 eV for untreated samples to 0.5 eV for 60 W plasma treated samples. The conductivity of the films treated with 60 W plasma power is estimated to be six orders of magnitude greater than untreated GO films and this enhancement of conductivity on plasma reduction has been interpreted in terms of UV-visible absorption spectra and density functional based first principle computational calculations. Plasma reduction of GO/ITO/PET structures can be used for efficiently tuning the electrical and optical properties of reduced graphene oxide (rGO) for flexible electronics applications.

Alternative Anodes for the Electrolytic Reduction of Uranium Dioxide

NASA Astrophysics Data System (ADS)

Merwin, Augustus

Reprocessing of spent nuclear fuel is an essential step in closing the nuclear fuel cycle. In order to consume current stockpiles, ceramic uranium dioxide spent nuclear fuel will be subjected to an electrolytic reduction process. The current reduction process employs a platinum anode and a stainless steel alloy 316 cathode in a molten salt bath consisting of LiCl-2wt% Li 2O and occurs at 700°C. A major shortcoming of the existing process is the degradation of the platinum anode under the severely oxidizing conditions encountered during electrolytic reduction. This work investigates alternative anode materials for the electrolytic reduction of uranium oxide. The high temperature and extreme oxidizing conditions encountered in these studies necessitated a unique set of design constraints on the system. Thus, a customized experimental apparatus was designed and constructed. The electrochemical experiments were performed in an electrochemical reactor placed inside a furnace. This entire setup was housed inside a glove box, in order to maintain an inert atmosphere. This study investigates alternative anode materials through accelerated corrosion testing. Surface morphology was studied using scanning electron microscopy. Surface chemistry was characterized using energy dispersive spectroscopy and Raman spectroscopy. Electrochemical behavior of candidate materials was evaluated using potentiodynamic polarization characteristics. After narrowing the number of candidate electrode materials, ferrous stainless steel alloy 316, nickel based Inconel 718 and elemental tungsten were chosen for further investigation. Of these materials only tungsten was found to be sufficiently stable at the anodic potential required for electrolysis of uranium dioxide in molten salt. The tungsten anode and stainless steel alloy 316 cathode electrode system was studied at the required reduction potential for UO2 with varying lithium oxide concentrations. Electrochemical impedance spectroscopy

Streaming potential method for characterizing interaction of electrical double layers between rice roots and Fe/Al oxide-coated quartz in situ.

PubMed

Liu, Zhao-Dong; Wang, Hai-Cui; Li, Jiu-Yu; Xu, Ren-Kou

2017-10-01

The interaction between rice roots and Fe/Al oxide-coated quartz was investigated through zeta potential measurements and column leaching experiments in present study. The zeta potentials of rice roots, Fe/Al oxide-coated quartz, and the binary systems containing rice roots and Fe/Al oxide-coated quartz were measured by a specially constructed streaming potential apparatus. The interactions between rice roots and Fe/Al oxide-coated quartz particles were evaluated/deduced based on the differences of zeta potentials between the binary systems and the single system of rice roots. The zeta potentials of the binary systems moved in positive directions compared with that of rice roots, suggesting that there were overlapping of diffuse layers of electric double layers on positively charged Fe/Al oxide-coated quartz and negatively charged rice roots and neutralization of positive charge on Fe/Al oxide-coated quartz with negative charge on rice roots. The greater amount of positive charges on Al oxide led to the stronger interaction of Al oxide-coated quartz with rice roots and the more shift of zeta potential compared with Fe oxide. The overlapping of diffuse layers on Fe/Al oxide-coated quartz and rice roots was confirmed by column leaching experiments. The greater overlapping of diffuse layers on Al oxide and rice roots led to more simultaneous adsorptions of K + and NO 3 - and greater reduction in leachate electric conductivity when the column containing Al oxide-coated quartz and rice roots was leached with KNO 3 solution, compared with the columns containing rice roots and Fe oxide-coated quartz or quartz. When the KNO 3 solution was replaced with deionized water to flush the columns, more K + and NO 3 - were desorbed from the binary system containing Al oxide-coated quartz and rice roots than from other two binary systems, suggesting that the stronger electrostatic interaction between Al oxide and rice roots promoted the desorption of K + and NO 3 - from the binary

Highly Selective TiN-Supported Highly Dispersed Pt Catalyst: Ultra Active toward Hydrogen Oxidation and Inactive toward Oxygen Reduction.

PubMed

Luo, Junming; Tang, Haibo; Tian, Xinlong; Hou, Sanying; Li, Xiuhua; Du, Li; Liao, Shijun

2018-01-31

The severe dissolution of the cathode catalyst, caused by an undesired oxygen reduction reaction at the anode during startup and shutdown, is a fatal challenge to practical applications of polymer electrolyte membrane fuel cells. To address this important issue, according to the distinct structure-sensitivity between the σ-type bond in H 2 and the π-type bond in O 2 , we design a HD-Pt/TiN material by highly dispersing Pt on the TiN surface to inhibit the unwanted oxygen reduction reaction. The highly dispersed Pt/TiN catalyst exhibits excellent selectivity toward hydrogen oxidation and oxygen reduction reactions. With a Pt loading of 0.88 wt %, our catalyst shows excellent hydrogen oxidation reaction activity, close to that of commercial 20 wt % Pt/C catalyst, and much lower oxygen reduction reaction activity than the commercial 20 wt % Pt/C catalyst. The lack of well-ordered Pt facets is responsible for the excellent selectivity of the HD-Pt/TiN materials toward hydrogen oxidation and oxygen reduction reactions. Our work provides a new and cost-effective solution to design selective catalysts toward hydrogen oxidation and oxygen reduction reactions, making the strategy of using oxygen-tolerant anode catalyst to improve the stability of polymer electrolyte membrane fuel cells during startup and shutdown more affordable and practical.

Oxidative stress in uremia: nature, mechanisms, and potential consequences.

PubMed

Vaziri, Nosratola D

2004-09-01

Oxidative stress has emerged as a constant feature of chronic renal failure (CRF). The presence of oxidative stress in CRF is evidenced by an overabundance of lipid, carbohydrate, and protein oxidation products in the plasma and tissues of uremic patients and animals. We recently have shown that oxidative stress in CRF animals is associated with and, in part, owing to up-regulation of superoxide-producing enzyme, nicotinamide-adenine dinucleotide phosphate (NAD(P)H) oxidase, and down-regulation of superoxide dismutase (SOD). The functional significance of these findings was confirmed by favorable response to administration of the cell-permeable SOD-mimetic agent, tempol, in CRF rats. Oxidative stress in CRF plays an important role in the pathogenesis of the associated hypertension (oxidation of NO and arachidonic acid and vascular remodeling), cardiovascular disease (oxidation of lipoproteins, atherogenesis), neurologic disorders (nitration of brain proteins, oxidation of myelin), anemia (reduction of erythrocyte lifespan), inflammation (nuclear factor kappa B activation), fibrosis, apoptosis, and accelerated aging. The CRF-induced oxidative stress is aggravated by diabetes, uncontrolled hypertension, and autoimmune diseases, which independently increase production of reactive oxygen intermediates, and frequently are associated with CRF. In addition, dialysis treatment (blood interaction with dialyzer membrane and dialysate impurities), acute and chronic infections (blood access infection, hepatitis, and so forth), and excessive parenteral iron administration intensify CRF-associated oxidative stress and its adverse consequences in patients with end-stage renal disease. The problem is compounded by limited intake of fresh fruits and vegetables (K(+) restriction), which contain numerous natural phytochemicals and antioxidant vitamins.

The potential for iron reduction in upland soils in Calhoun Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Thompson, A.; Chen, C.; Noor, N.; Hodges, C. A.; Barcellos, D.; Richter, D. D., Jr.

2017-12-01

Fe redox cycling plays an important role in organic matter preservation and degradation, and the fate of nutrients and contaminants. Despite its importance, Fe redox cycling in non-flooded upland soils has been underappreciated, although many upland terrestrial ecosystems have episodes of low redox events and an abundance of anoxic microsites. Soil Fe reduction is generally constrained by C availability, the reactivity of Fe(III) oxyhydroxides, and the abundance of Fe reducing bacteria. The goal of this study was to determine the potential for Fe reduction in upland soils under varying land-uses (Hardwood, Pine and Cultivated soils) from Calhoun Critical Zone Observatory. Fresh field soils from multiple depths were incubated in the lab without amendments under anoxic conditions for 3 weeks to determine the native potential for soil Fe reduction and to assess the limiting factors, the soils were amended with factorial mixtures of the following: (1) organic substrates (glucose and alanine); (2) bioavailable Fe (ferrihydrite); and (3) Fe reducing bacteria (Shewanella oneidensis strain MR-1). Results showed that Fe reduction potential generally decreased with soil depth. Fe reduction potential is very minimal below 1m of soil profile. The availability of Fe(III) minerals did not constrain pine and hardwood soil Fe reduction potential. Fe(III) availability only slightly limited the potential for Fe reduction the cultivated soils, which have the lowest extractable Fe by ascorbate-citrate. Labile C constrained Fe reduction in the hardwood and cultivated soils, but not in the pine soils, which had the highest extractable C by K2SO4. In addition, we found the more energetic C source (glucose) facilitated more Fe reduction in the subsurface soil than did Alanine. Finally, the abundance of Fe-reducing bacteria limited Fe reduction potential in almost all of these soils, particularly the pine soils.

Direct Reduction of Ferrous Oxides to form an Iron-Rich Alternative Charge Material

NASA Astrophysics Data System (ADS)

Ünal, H. İbrahim; Turgut, Enes; Atapek, Ş. H.; Alkan, Attila

2015-12-01

In this study, production of sponge iron by direct reduction of oxides and the effect of reductant on metallization were investigated. In the first stage of the study, scale formed during hot rolling of slabs was reduced in a rotating furnace using solid and gas reductants. Coal was used as solid reductant and hydrogen released from the combustion reaction of LNG was used as the gas one. The sponge iron produced by direct reduction was melted and solidified. In the second stage, Hematite ore in the form of pellets was reduced using solid carbon in a furnace heated up to 1,100°C for 60 and 120 minutes. Reduction degree of process was evaluated as a function of time and the ratio of Cfix/Fetotal. In the third stage, final products were examined using scanning electron microscope and microanalysis was carried out by energy dispersive x-ray spectrometer attached to the electron microscope. It is concluded that (i) direct reduction using both solid and gas reductants caused higher metallization compared to using only solid reductant, (ii) as the reduction time and ratio of Cfix/Fetotal increased %-reduction of ore increased.

Kinetic determinations of accurate relative oxidation potentials of amines with reactive radical cations.

PubMed

Gould, Ian R; Wosinska, Zofia M; Farid, Samir

2006-01-01

Accurate oxidation potentials for organic compounds are critical for the evaluation of thermodynamic and kinetic properties of their radical cations. Except when using a specialized apparatus, electrochemical oxidation of molecules with reactive radical cations is usually an irreversible process, providing peak potentials, E(p), rather than thermodynamically meaningful oxidation potentials, E(ox). In a previous study on amines with radical cations that underwent rapid decarboxylation, we estimated E(ox) by correcting the E(p) from cyclic voltammetry with rate constants for decarboxylation obtained using laser flash photolysis. Here we use redox equilibration experiments to determine accurate relative oxidation potentials for the same amines. We also describe an extension of these experiments to show how relative oxidation potentials can be obtained in the absence of equilibrium, from a complete kinetic analysis of the reversible redox kinetics. The results provide support for the previous cyclic voltammetry/laser flash photolysis method for determining oxidation potentials.

Reduction of antibiotic resistance genes in municipal wastewater effluent by advanced oxidation processes.

PubMed

Zhang, Yingying; Zhuang, Yao; Geng, Jinju; Ren, Hongqiang; Xu, Ke; Ding, Lili

2016-04-15

This study investigated the reduction of antibiotic resistance genes (ARGs), intI1 and 16S rRNA genes, by advanced oxidation processes (AOPs), namely Fenton oxidation (Fe(2+)/H2O2) and UV/H2O2 process. The ARGs include sul1, tetX, and tetG from municipal wastewater effluent. The results indicated that the Fenton oxidation and UV/H2O2 process could reduce selected ARGs effectively. Oxidation by the Fenton process was slightly better than that of the UV/H2O2 method. Particularly, for the Fenton oxidation, under the optimal condition wherein Fe(2+)/H2O2 had a molar ratio of 0.1 and a H2O2 concentration of 0.01molL(-1) with a pH of 3.0 and reaction time of 2h, 2.58-3.79 logs of target genes were removed. Under the initial effluent pH condition (pH=7.0), the removal was 2.26-3.35 logs. For the UV/H2O2 process, when the pH was 3.5 with a H2O2 concentration of 0.01molL(-1) accompanied by 30min of UV irradiation, all ARGs could achieve a reduction of 2.8-3.5 logs, and 1.55-2.32 logs at a pH of 7.0. The Fenton oxidation and UV/H2O2 process followed the first-order reaction kinetic model. The removal of target genes was affected by many parameters, including initial Fe(2+)/H2O2 molar ratios, H2O2 concentration, solution pH, and reaction time. Among these factors, reagent concentrations and pH values are the most important factors during AOPs. Copyright © 2016 Elsevier B.V. All rights reserved.

General Solvent-dependent Strategy toward Enhanced Oxygen Reduction Reaction in Graphene/Metal Oxide Nanohybrids: Effects of Nitrogen-containing Solvent

NASA Astrophysics Data System (ADS)

Kao, Wei-Yao; Chen, Wei-Quan; Chiu, Yu-Hsiang; Ho, Yu-Hsuan; Chen, Chun-Hu

2016-11-01

A general solvent-dependent protocol directly influencing the oxygen reduction reaction (ORR) in metal oxide/graphene nanohybrids has been demonstrated. We conducted the two-step synthesis of cobalt oxide/N-doped graphene nanohybrids (CNG) with solvents of water, ethanol, and dimethylformamide (DMF), representing tree typical categories of aqueous, polar organic, and organic N-containing solvents commonly adopted for graphene nanocomposites preparation. The superior ORR performance of the DMF-hybrids can be attributed to the high nitrogen-doping, aggregation-free hybridization, and unique graphene porous structures. As DMF is the more effective N-source, the spectroscopic results support a catalytic nitrogenation potentially mediated by cobalt-DMF coordination complexes. The wide-distribution of porosity (covering micro-, meso-, to macro-pore) and micron-void assembly of graphene may further enhance the diffusion kinetics for ORR. As the results, CNG by DMF-synthesis exhibits the high ORR activities close to Pt/C (i.e. only 8 mV difference of half-wave potential with electron transfer number of 3.96) with the better durability in the alkaline condition. Additional graphene hybrids comprised of iron and manganese oxides also show the superior ORR activities by DMF-synthesis, confirming the general solvent-dependent protocol to achieve enhanced ORR activities.

General Solvent-dependent Strategy toward Enhanced Oxygen Reduction Reaction in Graphene/Metal Oxide Nanohybrids: Effects of Nitrogen-containing Solvent

PubMed Central

Kao, Wei-Yao; Chen, Wei-Quan; Chiu, Yu-Hsiang; Ho, Yu-Hsuan; Chen, Chun-Hu

2016-01-01

A general solvent-dependent protocol directly influencing the oxygen reduction reaction (ORR) in metal oxide/graphene nanohybrids has been demonstrated. We conducted the two-step synthesis of cobalt oxide/N-doped graphene nanohybrids (CNG) with solvents of water, ethanol, and dimethylformamide (DMF), representing tree typical categories of aqueous, polar organic, and organic N-containing solvents commonly adopted for graphene nanocomposites preparation. The superior ORR performance of the DMF-hybrids can be attributed to the high nitrogen-doping, aggregation-free hybridization, and unique graphene porous structures. As DMF is the more effective N-source, the spectroscopic results support a catalytic nitrogenation potentially mediated by cobalt-DMF coordination complexes. The wide-distribution of porosity (covering micro-, meso-, to macro-pore) and micron-void assembly of graphene may further enhance the diffusion kinetics for ORR. As the results, CNG by DMF-synthesis exhibits the high ORR activities close to Pt/C (i.e. only 8 mV difference of half-wave potential with electron transfer number of 3.96) with the better durability in the alkaline condition. Additional graphene hybrids comprised of iron and manganese oxides also show the superior ORR activities by DMF-synthesis, confirming the general solvent-dependent protocol to achieve enhanced ORR activities. PMID:27853187

A One-Step, Solvothermal Reduction Method for Producing Reduced Graphene Oxide Dispersions in Organic Solvents

PubMed Central

Dubin, Sergey; Gilje, Scott; Wang, Kan; Tung, Vincent C.; Cha, Kitty; Hall, Anthony S.; Farrar, Jabari; Varshneya, Rupal; Yang, Yang; Kaner, Richard B.

2014-01-01

Refluxing graphene oxide (GO) in N-methyl-2-pyrrolidinone (NMP) results in deoxygenation and reduction to yield a stable colloidal dispersion. The solvothermal reduction is accompanied by a color change from light brown to black. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images of the product confirm the presence of single sheets of the solvothermally reduced graphene oxide (SRGO). X-ray photoelectron spectroscopy (XPS) of SRGO indicates a significant increase in intensity of the C=C bond character, while the oxygen content decreases markedly after the reduction is complete. X-ray diffraction analysis of SRGO shows a single broad peak at 26.24° 2θ (3.4 Å), confirming the presence of graphitic stacking of reduced sheets. SRGO sheets are redispersible in a variety of organic solvents, which may hold promise as an acceptor material for bulk heterojunction photovoltaic cells, or electromagnetic interference shielding applications. PMID:20586422

On the Significance of a Carbon-Rich Background in Plasma-Based Graphene Oxide Reduction

DTIC Science & Technology

2016-06-02

can lead to the formation of defects and vacancies. We find that methane provides not only hydrogen but also the carbon necessary to restore the...Graphene oxide Reduction Plasma Argon Hydrogen Methane Office of Naval Research One Liberty Center 875 North Randolph Street, Suite 1425 Arlington, VA...electron-beam generated plasmas produced in argon/ methane (Ar/CH4) backgrounds. However, unlike other reduction approaches [14] the process was found to

Natural printed silk substrate circuit fabricated via surface modification using one step thermal transfer and reduction graphene oxide

NASA Astrophysics Data System (ADS)

Cao, Jiliang; Huang, Zhan; Wang, Chaoxia

2018-05-01

Graphene conductive silk substrate is a preferred material because of its biocompatibility, flexibility and comfort. A flexible natural printed silk substrate circuit was fabricated by one step transfer of graphene oxide (GO) paste from transfer paper to the surface of silk fabric and reduction of the GO to reduced graphene oxide (RGO) using a simple hot press treatment. The GO paste was obtained through ultrasonic stirring exfoliation under low temperature, and presented excellent printing rheological properties at high concentration. The silk fabric was obtained a surface electric resistance as low as 12.15 KΩ cm-1, in the concentration of GO 50 g L-1 and hot press at 220 °C for 120 s. Though the whiteness and strength decreased with the increasing of hot press temperature and time slowly, the electric conductivity of RGO surface modification silk substrate improved obviously. The surface electric resistance of RGO/silk fabrics increased from 12.15 KΩ cm-1 to 18.05 KΩ cm-1, 28.54 KΩ cm-1 and 32.53 KΩ cm-1 after 10, 20 and 30 washing cycles, respectively. The results showed that the printed silk substrate circuit has excellent washability. This process requires no chemical reductant, and the reduction efficiency and reduction degree of GO is high. This time-effective and environmentally-friendly one step thermal transfer and reduction graphene oxide onto natural silk substrate method can be easily used to production of reduced graphene oxide (RGO) based flexible printed circuit.

Nitrate Reduction Functional Genes and Nitrate Reduction Potentials Persist in Deeper Estuarine Sediments. Why?

PubMed Central

Papaspyrou, Sokratis; Smith, Cindy J.; Dong, Liang F.; Whitby, Corinne; Dumbrell, Alex J.; Nedwell, David B.

2014-01-01

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are processes occurring simultaneously under oxygen-limited or anaerobic conditions, where both compete for nitrate and organic carbon. Despite their ecological importance, there has been little investigation of how denitrification and DNRA potentials and related functional genes vary vertically with sediment depth. Nitrate reduction potentials measured in sediment depth profiles along the Colne estuary were in the upper range of nitrate reduction rates reported from other sediments and showed the existence of strong decreasing trends both with increasing depth and along the estuary. Denitrification potential decreased along the estuary, decreasing more rapidly with depth towards the estuary mouth. In contrast, DNRA potential increased along the estuary. Significant decreases in copy numbers of 16S rRNA and nitrate reducing genes were observed along the estuary and from surface to deeper sediments. Both metabolic potentials and functional genes persisted at sediment depths where porewater nitrate was absent. Transport of nitrate by bioturbation, based on macrofauna distributions, could only account for the upper 10 cm depth of sediment. A several fold higher combined freeze-lysable KCl-extractable nitrate pool compared to porewater nitrate was detected. We hypothesised that his could be attributed to intracellular nitrate pools from nitrate accumulating microorganisms like Thioploca or Beggiatoa. However, pyrosequencing analysis did not detect any such organisms, leaving other bacteria, microbenthic algae, or foraminiferans which have also been shown to accumulate nitrate, as possible candidates. The importance and bioavailability of a KCl-extractable nitrate sediment pool remains to be tested. The significant variation in the vertical pattern and abundance of the various nitrate reducing genes phylotypes reasonably suggests differences in their activity throughout the sediment column. This

Gold Decorated Graphene for Rapid Dye Reduction and Efficient Electro Catalytic Oxidation of Ethanol

NASA Astrophysics Data System (ADS)

Siddhardha, R. S.; Kumar v, Lakshman; Kaniyoor, A.; Podila, R.; Kumar, V. S.; Venkataramaniah, K.; Ramaprabhu, S.; Rao, A.; Ramamurthy, S. S.; Clemson University Team; Sri Sathya Sai Institute of Higher Learning Team; IITMadras Team

2013-03-01

A well known disadvantage in fabrication of metal-graphene composite is the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. Here, we demonstrate a novel one pot synthesis of gold nanoparticles (AuNPs) by laser ablation of gold strip and simultaneous decoration of these on functionalized graphene derivatives. Not only the impregnation of AuNPs was linker free, but also the synthesis by itself was surfactant free. This resulted in in-situ decoration of pristine AuNPs on functionalized graphene derivatives. These materials were well characterized and tested for catalytic applications pertaining to dye reduction and electrooxidation. The catalytic reduction rates are 1.4 x 102 and 9.4x102 times faster for Rhodamine B and Methylene Blue dyes respectively, compared to earlier reports. The enhanced rate involves synergistic interplay of electronic relay between AuNPs and the dye, also charge transfer between the graphene system and dye. In addition, the onset potential for ethanol oxidation was found to be more negative ~ 100 mV, an indication of its promising application in direct ethanol fuel cells.

A rapid room temperature chemical route for the synthesis of graphene: metal-mediated reduction of graphene oxide.

PubMed

Dey, Ramendra Sundar; Hajra, Saumen; Sahu, Ranjan K; Raj, C Retna; Panigrahi, M K

2012-02-07

A rapid and facile route for the synthesis of reduced graphene oxide sheets (rGOs) at room temperature by the chemical reduction of graphene oxide using Zn/acid in aqueous solution is demonstrated. This journal is © The Royal Society of Chemistry 2012

Direct reduction processes for titanium oxide in molten salt

NASA Astrophysics Data System (ADS)

Suzuki, Ryosuke O.

2007-02-01

Molten salt electrolysis using CaCl2 is employed to produce pure titanium and its alloys directly from TiO2 and a mixture of elemental oxides, respectively, as an alternate to the Kroll process. This is because CaO, which is a reduction by-product, is highly soluble in CaCl2. Good-quality titanium containing only a small amount of residual oxygen has been successfully produced and scaled to industrial levels. Thermochemical and electrochemical bases are reviewed to optimize the process conditions. Several processes using molten salt are being examined for future progress in titanium processing.

Nitrous oxide emission reduction in temperate biochar-amended soils

NASA Astrophysics Data System (ADS)

Felber, R.; Hüppi, R.; Leifeld, J.; Neftel, A.

2012-01-01

Biochar, a pyrolysis product of organic residues, is an amendment for agricultural soils to improve soil fertility, sequester CO2 and reduce greenhouse gas (GHG) emissions. In highly weathered tropical soils laboratory incubations of soil-biochar mixtures revealed substantial reductions for nitrous oxide (N2O) and carbon dioxide (CO2). In contrast, evidence is scarce for temperate soils. In a three-factorial laboratory incubation experiment two different temperate agricultural soils were amended with green waste and coffee grounds biochar. N2O and CO2 emissions were measured at the beginning and end of a three month incubation. The experiments were conducted under three different conditions (no additional nutrients, glucose addition, and nitrate and glucose addition) representing different field conditions. We found mean N2O emission reductions of 60 % compared to soils without addition of biochar. The reduction depended on biochar type and soil type as well as on the age of the samples. CO2 emissions were slightly reduced, too. NO3- but not NH4+ concentrations were significantly reduced shortly after biochar incorporation. Despite the highly significant suppression of N2O emissions biochar effects should not be transferred one-to-one to field conditions but need to be tested accordingly.

Mediated electrochemical oxidation (MEO) process: a study on nonylphenol ethoxylates (NPE) oxidation in batch mode using cerium (IV) oxidant

NASA Astrophysics Data System (ADS)

Setiyanto, H.; Adyatmika, I. M.; Syaifullah, M. M.; Zulfikar, M. A.; Buchari

2018-05-01

Nonylphenol ethoxylate (NPE-10) is one type of non-ionic surfactants from the class of alkylphenol ethoxylate (APE). This compound is already tightened their use in European Union countries. However, these surfactants are still used widely in Indonesia because the price is relatively cheap. Consequently, these compounds can accumulate in aquatic environments. NPE-10 can disrupt aquatic ecosystems. This study aimed to describe the electro-oxidation process of NPE-10 based on the parameters of a potential difference, concentration of NPE-10, concentration of Ce (III), and oxidation time. The result of oxidation NPE-10 was measured by the amount of current generated from voltammetry technique. Studies of cyclic voltammetry using carbon paste electrodes illustrates the potential value of the oxidation of Ce (III) / Ce (IV) of 1.25 V and the reduction potential value of Ce (IV) / Ce (III) of 1.192 V. NPE-10 are electroactive irreversible because it only provides the potential value of oxidation at 1.44 V. Percent of total degradation of 84.96% was obtained at electro-oxidation of 500 ppm NPE-10 by the addition of 0.015 M Ce (III) for 90 minutes at 0.2 M H2SO4and the use of potential of 6 V.

In vitro toxicity of particulate matter (PM) collected at different sites in the Netherlands is associated with PM composition, size fraction and oxidative potential - the RAPTES project

PubMed Central

2011-01-01

Background Ambient particulate matter (PM) exposure is associated with respiratory and cardiovascular morbidity and mortality. To what extent such effects are different for PM obtained from different sources or locations is still unclear. This study investigated the in vitro toxicity of ambient PM collected at different sites in the Netherlands in relation to PM composition and oxidative potential. Method PM was sampled at eight sites: three traffic sites, an underground train station, as well as a harbor, farm, steelworks, and urban background location. Coarse (2.5-10 μm), fine (< 2.5 μm) and quasi ultrafine PM (qUF; < 0.18 μm) were sampled at each site. Murine macrophages (RAW 264.7 cells) were exposed to increasing concentrations of PM from these sites (6.25-12.5-25-50-100 μg/ml; corresponding to 3.68-58.8 μg/cm2). Following overnight incubation, MTT-reduction activity (a measure of metabolic activity) and the release of pro-inflammatory markers (Tumor Necrosis Factor-alpha, TNF-α; Interleukin-6, IL-6; Macrophage Inflammatory Protein-2, MIP-2) were measured. The oxidative potential and the endotoxin content of each PM sample were determined in a DTT- and LAL-assay respectively. Multiple linear regression was used to assess the relationship between the cellular responses and PM characteristics: concentration, site, size fraction, oxidative potential and endotoxin content. Results Most PM samples induced a concentration-dependent decrease in MTT-reduction activity and an increase in pro-inflammatory markers with the exception of the urban background and stop & go traffic samples. Fine and qUF samples of traffic locations, characterized by a high concentration of elemental and organic carbon, induced the highest pro-inflammatory activity. The pro-inflammatory response to coarse samples was associated with the endotoxin level, which was found to increase dramatically during a three-day sample concentration procedure in the laboratory. The underground samples

Nitric oxide reduction in coal combustion: role of char surface complexes in heterogeneous reactions.

PubMed

Arenillas, Ana; Rubiera, Fernando; Pis, José J

2002-12-15

Nitrogen oxides are one of the major environmental problems arising from fossil fuel combustion. Coal char is relatively rich in nitrogen, and so this is an important source of nitrogen oxides during coal combustion. However, due to its carbonaceous nature, char can also reduce NO through heterogeneous reduction. The objectives of this work were on one hand to compare NO emissions from coal combustion in two different types of equipment and on the other hand to study the influence of char surface chemistry on NO reduction. A series of combustion tests were carried out in two different scale devices: a thermogravimetric analyzer coupled to a mass spectrometer and an FTIR (TG-MS-FTIR) and a fluidized bed reactor with an on line battery of analyzers. The TG-MS-FTIR system was also used to perform a specific study on NO heterogeneous reduction reactions using chars with different surface chemistry. According to the results obtained, it can be said that the TG-MS-FTIR system provides valuable information about NO heterogeneous reduction and it can give good trends of the behavior in other combustion equipments (i.e., fluidized bed combustors). It has been also pointed out that NO-char interaction depends to a large extent on temperature. In the low-temperature range (<800 degrees C), NO heterogeneous reduction seems to be controlled by the evolution of surface complexes. In the high-temperature range (>800 degrees C), a different mechanism is involved in NO heterogeneous reduction, the nature of the carbon matrix being a key factor.

Shifts in oxidation states of cerium oxide nanoparticles detected inside intact hydrated cells and organelles

PubMed Central

Szymanski, Craig J.; Munusamy, Prabhakaran; Mihai, Cosmin; Xie, Yumei; Hu, Dehong; Gilles, Mary K.; Tyliszczak, Tolek; Thevuthasan, Suntharampillai; Baer, Donald R.; Orr, Galya

2015-01-01

Cerium oxide nanoparticles (CNPs) have been shown to induce diverse biological effects, ranging from toxic to beneficial. The beneficial effects have been attributed to the potential antioxidant activity of CNPs via certain redox reactions, depending on their oxidation state or Ce3+/Ce4+ ratio. However, this ratio is strongly dependent on the environment and age of the nanoparticles and it is unclear whether and how the complex intracellular environment impacts this ratio and the possible redox reactions of CNPs. To identify any changes in the oxidation state of CNPs in the intracellular environment and better understand their intracellular reactions, we directly quantified the oxidation states of CNPs outside and inside intact hydrated cells and organelles using correlated scanning transmission x-ray and super resolution fluorescence microscopies. By analyzing hundreds of small CNP aggregates, we detected a shift to a higher Ce3+/Ce4+ ratio in CNPs inside versus outside the cells, indicating a net reduction of CNPs in the intracellular environment. We further found a similar ratio in the cytoplasm and in the lysosomes, indicating that the net reduction occurs earlier in the internalization pathway. Together with oxidative stress and toxicity measurements, our observations identify a net reduction of CNPs in the intracellular environment, which is consistent with their involvement in potentially beneficial oxidation reactions, but also point to interactions that can negatively impact the health of cells. PMID:26056725

Shifts in oxidation states of cerium oxide nanoparticles detected inside intact hydrated cells and organelles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szymanski, Craig J.; Munusamy, Prabhakaran; Mihai, Cosmin

2015-09-01

Cerium oxide nanoparticles (CNPs) have been shown to induce diverse biological effects, ranging from toxic to beneficial. The beneficial effects have been attributed to the potential antioxidant activity of CNPs via certain redox reactions, depending on their oxidation state or Ce3+/Ce4+ ratio. However, this ratio is strongly dependent on the environment and age of the nanoparticles and it is unclear whether and how the complex intracellular environment impacts this ratio and the possible redox reactions of CNPs. To identify any changes in the oxidation state of CNPs in the intracellular environment and better understand their intracellular reactions, we directly quantifiedmore » the oxidation states of CNPs outside and inside intact hydrated cells and organelles using correlated scanning transmission x-ray and super resolution fluorescence microscopies. By analyzing hundreds of small CNP aggregates, we detected a shift to a higher Ce3+/Ce4+ ratio in CNPs inside versus outside the cells, indicating a net reduction of CNPs in the intracellular environment. We further found a similar ratio in the cytoplasm and in the lysosomes, indicating that the net reduction occurs earlier in the internalization pathway. Together with oxidative stress and toxicity measurements, our observations identify a net reduction of CNPs in the intracellular environment, which is consistent with their involvement in potentially beneficial oxidation reactions, but also point to interactions that can negatively impact the health of cells.« less

Anode shroud for off-gas capture and removal from electrolytic oxide reduction system

DOEpatents

Bailey, James L.; Barnes, Laurel A.; Wiedmeyer, Stanley G.; Williamson, Mark A.; Willit, James L.

2014-07-08

An electrolytic oxide reduction system according to a non-limiting embodiment of the present invention may include a plurality of anode assemblies and an anode shroud for each of the anode assemblies. The anode shroud may be used to dilute, cool, and/or remove off-gas from the electrolytic oxide reduction system. The anode shroud may include a body portion having a tapered upper section that includes an apex. The body portion may have an inner wall that defines an off-gas collection cavity. A chimney structure may extend from the apex of the upper section and be connected to the off-gas collection cavity of the body portion. The chimney structure may include an inner tube within an outer tube. Accordingly, a sweep gas/cooling gas may be supplied down the annular space between the inner and outer tubes, while the off-gas may be removed through an exit path defined by the inner tube.

Anaerobic Oxidation of Methane Coupled to Nitrite Reduction by Halophilic Marine NC10 Bacteria.

PubMed

He, Zhanfei; Geng, Sha; Cai, Chaoyang; Liu, Shuai; Liu, Yan; Pan, Yawei; Lou, Liping; Zheng, Ping; Xu, Xinhua; Hu, Baolan

2015-08-15

Anaerobic oxidation of methane (AOM) coupled to nitrite reduction is a novel AOM process that is mediated by denitrifying methanotrophs. To date, enrichments of these denitrifying methanotrophs have been confined to freshwater systems; however, the recent findings of 16S rRNA and pmoA gene sequences in marine sediments suggest a possible occurrence of AOM coupled to nitrite reduction in marine systems. In this research, a marine denitrifying methanotrophic culture was obtained after 20 months of enrichment. Activity testing and quantitative PCR (qPCR) analysis were then conducted and showed that the methane oxidation activity and the number of NC10 bacteria increased correlatively during the enrichment period. 16S rRNA gene sequencing indicated that only bacteria in group A of the NC10 phylum were enriched and responsible for the resulting methane oxidation activity, although a diverse community of NC10 bacteria was harbored in the inoculum. Fluorescence in situ hybridization showed that NC10 bacteria were dominant in the enrichment culture after 20 months. The effect of salinity on the marine denitrifying methanotrophic culture was investigated, and the apparent optimal salinity was 20.5‰, which suggested that halophilic bacterial AOM coupled to nitrite reduction was obtained. Moreover, the apparent substrate affinity coefficients of the halophilic denitrifying methanotrophs were determined to be 9.8 ± 2.2 μM for methane and 8.7 ± 1.5 μM for nitrite. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Catalyst and method for reduction of nitrogen oxides

DOEpatents

Ott, Kevin C [Los Alamos, NM

2008-05-27

A Selective Catalytic Reduction (SCR) catalyst was prepared by slurry coating ZSM-5 zeolite onto a cordierite monolith, then subliming an iron salt onto the zeolite, calcining the monolith, and then dipping the monolith either into an aqueous solution of manganese nitrate and cerium nitrate and then calcining, or by similar treatment with separate solutions of manganese nitrate and cerium nitrate. The supported catalyst containing iron, manganese, and cerium showed 80 percent conversion at 113 degrees Celsius of a feed gas containing nitrogen oxides having 4 parts NO to one part NO.sub.2, about one equivalent ammonia, and excess oxygen; conversion improved to 94 percent at 147 degrees Celsius. N.sub.2O was not detected (detection limit: 0.6 percent N.sub.2O).

Catalyst and method for reduction of nitrogen oxides

DOEpatents

Ott, Kevin C [Los Alamos, NM

2008-08-19

A Selective Catalytic Reduction (SCR) catalyst was prepared by slurry coating ZSM-5 zeolite onto a cordierite monolith, then subliming an iron salt onto the zeolite, calcining the monolith, and then dipping the monolith either into an aqueous solution of manganese nitrate and cerium nitrate and then calcining, or by similar treatment with separate solutions of manganese nitrate and cerium nitrate. The supported catalyst containing iron, manganese, and cerium showed 80 percent conversion at 113 degrees Celsius of a feed gas containing nitrogen oxides having 4 parts NO to one part NO.sub.2, about one equivalent ammonia, and excess oxygen; conversion improved to 94 percent at 147 degrees Celsius. N.sub.2O was not detected (detection limit: 0.6 percent N.sub.2O).

Nitrate Reduction to Nitrite, Nitric Oxide and Ammonia by Gut Bacteria under Physiological Conditions

PubMed Central

Tiso, Mauro; Schechter, Alan N.

2015-01-01

The biological nitrogen cycle involves step-wise reduction of nitrogen oxides to ammonium salts and oxidation of ammonia back to nitrites and nitrates by plants and bacteria. Neither process has been thought to have relevance to mammalian physiology; however in recent years the salivary bacterial reduction of nitrate to nitrite has been recognized as an important metabolic conversion in humans. Several enteric bacteria have also shown the ability of catalytic reduction of nitrate to ammonia via nitrite during dissimilatory respiration; however, the importance of this pathway in bacterial species colonizing the human intestine has been little studied. We measured nitrite, nitric oxide (NO) and ammonia formation in cultures of Escherichia coli, Lactobacillus and Bifidobacterium species grown at different sodium nitrate concentrations and oxygen levels. We found that the presence of 5 mM nitrate provided a growth benefit and induced both nitrite and ammonia generation in E.coli and L.plantarum bacteria grown at oxygen concentrations compatible with the content in the gastrointestinal tract. Nitrite and ammonia accumulated in the growth medium when at least 2.5 mM nitrate was present. Time-course curves suggest that nitrate is first converted to nitrite and subsequently to ammonia. Strains of L.rhamnosus, L.acidophilus and B.longum infantis grown with nitrate produced minor changes in nitrite or ammonia levels in the cultures. However, when supplied with exogenous nitrite, NO gas was readily produced independently of added nitrate. Bacterial production of lactic acid causes medium acidification that in turn generates NO by non-enzymatic nitrite reduction. In contrast, nitrite was converted to NO by E.coli cultures even at neutral pH. We suggest that the bacterial nitrate reduction to ammonia, as well as the related NO formation in the gut, could be an important aspect of the overall mammalian nitrate/nitrite/NO metabolism and is yet another way in which the microbiome

Metabolic potential of fatty acid oxidation and anaerobic respiration by abundant members of Thaumarchaeota and Thermoplasmata in deep anoxic peat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Xueju; Handley, Kim M.; Gilbert, Jack A.

2015-12-01

To probe the metabolic potential of abundant Archaea in boreal peats, we reconstructed two near-complete archaeal genomes, affiliated with Thaumarchaeota group 1.1c (bin Fn1, 8% abundance), which was a genomically unrepresented group, and Thermoplasmata (bin Bg1, 26% abundance), from metagenomic data acquired from deep anoxic peat layers. Each of the near-complete genomes encodes the potential to degrade long-chain fatty acids (LCFA) via β-oxidation. Fn1 has the potential to oxidize LCFA either by syntrophic interaction with methanogens or by coupling oxidation with anaerobic respiration using fumarate as a terminal electron acceptor (TEA). Fn1 is the first Thaumarchaeota genome without an identifiablemore » carbon fixation pathway, indicating that this mesophilic phylum encompasses more diverse metabolisms than previously thought. Furthermore, we report genetic evidence suggestive of sulfite and/or organosulfonate reduction by Thermoplasmata Bg1. In deep peat, inorganic TEAs are often depleted to extremely low levels, yet the anaerobic respiration predicted for two abundant archaeal members suggests organic electron acceptors such as fumarate and organosulfonate (enriched in humic substances) may be important for respiration and C mineralization in peatlands.« less

Reduction and shaping of graphene-oxide by laser-printing for controlled bone tissue regeneration and bacterial killing

NASA Astrophysics Data System (ADS)

Palmieri, Valentina; Barba, Marta; Di Pietro, Lorena; Gentilini, Silvia; Chiara Braidotti, Maria; Ciancico, Carlotta; Bugli, Francesca; Ciasca, Gabriele; Larciprete, Rosanna; Lattanzi, Wanda; Sanguinetti, Maurizio; De Spirito, Marco; Conti, Claudio; Papi, Massimiliano

2018-01-01

Graphene and graphene oxide (GO) are capable of inducing stem cells differentiation into bone tissue with variable efficacy depending on reductive state of the material. Thus, modulation of osteogenic process and of bone mineral density distribution is theoretically possible by controlling the GO oxidative state. In this study, we laser-printed GO surfaces in order to obtain both a local photo-thermal GO reduction and the formation of nano-wrinkles along precise geometric pattern. Initially, after cells adhered on the surface, stem cells migrated and accumulated on the reduced and wrinkled surface. When the local density of the stem cells on the reduced stripes was high, cells started to proliferate and occupy the oxidized/flat area. The designed surfaces morphology guided stem cell orientation and the reduction accelerated differentiation. Furthermore the reduced sharp nano-wrinkles were able to enhance the GO antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), a common cause of prosthetic joints infections. This strategy can offer a revolution in present and future trends of scaffolds design for regenerative medicine.

Comparative Study of Exchange-Correlation Functional and Potential for Evaluating Thermoelectric Transport Properties in d0 Perovskite Oxides

NASA Astrophysics Data System (ADS)

Ohkubo, Isao; Mori, Takao

2017-07-01

The influence of two different types of exchange-correlation functional/potential, namely, the generalized gradient approximation Perdew-Burke-Ernzerhof (GGA-PBE) functional and the modified Becke-Johnson (mBJ) potential, on the thermoelectric transport properties of d0 perovskite oxides (SrTiO3 and KTaO3) was investigated. The reduction of band dispersion induced by the mBJ scheme allows the improved prediction of band gap values by thelocal density approximation (LDA) and GGA, which increases the resolution of the increases in the density of states (DOS), carrier concentration, and effective mass near the conduction band edge. A comparison of the experimental effective mass values of d0 perovskite oxides shows that the effective mass values provided by the mBJ potential are similar to those provided by the GGA-PBE functional. Comparative analysis of the data obtained from Boltzmann theory calculations using the electronic structures determined with the GGA-PBE functional and the mBJ potential shows a difference in the transport coefficients owing to the increases in the DOS, carrier concentration, and effective mass induced by the mBJ scheme.

Formation of Green Rust and Immobilization of Nickel in Response to Bacterial Reduction of Hydrous Ferric Oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parmar, N.; Gorby, Yuri A.; Beveridge, Terrance J.

This investigation documents the formation of Green Rust (GR) and immobilization of Ni2+ in response to bacterial reduction of hydrous ferric oxide (HFO) reduction experiments provided evidence that the solid-phase partitioning of Ni2+ in GR extended from equilibrium solid-solution behavior.

Reduction of Salmonella enterica on alfalfa seeds with acidic electrolyzed oxidizing water and enhanced uptake of acidic electrolyzed oxidizing water into seeds by gas exchange.

PubMed

Stan, Silvia D; Daeschel, Mark A

2003-11-01

Alfalfa sprouts have been implicated in several salmonellosis outbreaks in recent years. The disinfectant effects of acidic electrolyzed oxidizing (EO) water against Salmonella enterica both in an aqueous system and on artificially contaminated alfalfa seeds were determined. The optimum ratio of seeds to EO water was determined in order to maximize the antimicrobial effect of EO water. Seeds were combined with EO water at ratios (wt/vol) of 1:4, 1:10, 1:20, 1:40, and 1:100, and the characteristics of EO water (pH, oxidation reduction potential [ORP], and free chlorine concentration) were determined. When the ratio of seeds to EO water was increased from 1:4 to 1:100, the pH decreased from 3.82 to 2.63, while the ORP increased from +455 to +1,073 mV. EO water (with a pH of 2.54 to 2.38 and an ORP of +1,083 to +1,092 mV) exhibited strong potential for the inactivation of S. enterica in an aqueous system (producing a reduction of at least 6.6 log CFU/ml). Treatment of artificially contaminated alfalfa seeds with EO water at a seed-to-EO water ratio of 1:100 for 15 and 60 min significantly reduced Salmonella populations by 2.04 and 1.96 log CFU/g, respectively (P < 0.05), while a Butterfield's buffer wash decreased Salmonella populations by 0.18 and 0.23 log CFU/g, respectively. After treatment, EO water was Salmonella negative by enrichment with or without neutralization. Germination of seeds was not significantly affected (P > 0.05) by treatment for up to 60 min in electrolyzed water. The uptake of liquid into the seeds was influenced by the internal gas composition (air, N2, or O2) of seeds before the liquid was added.

IMPACTS OF ANTIFOAM ADDITIONS AND ARGON BUBBLING ON DEFENSE WASTE PROCESSING FACILITY REDUCTION/OXIDATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jantzen, C.; Johnson, F.

2012-06-05

During melting of HLW glass, the REDOX of the melt pool cannot be measured. Therefore, the Fe{sup +2}/{Sigma}Fe ratio in the glass poured from the melter must be related to melter feed organic and oxidant concentrations to ensure production of a high quality glass without impacting production rate (e.g., foaming) or melter life (e.g., metal formation and accumulation). A production facility such as the Defense Waste Processing Facility (DWPF) cannot wait until the melt or waste glass has been made to assess its acceptability, since by then no further changes to the glass composition and acceptability are possible. therefore, themore » acceptability decision is made on the upstream process, rather than on the downstream melt or glass product. That is, it is based on 'feed foward' statistical process control (SPC) rather than statistical quality control (SQC). In SPC, the feed composition to the melter is controlled prior to vitrification. Use of the DWPF REDOX model has controlled the balanjce of feed reductants and oxidants in the Sludge Receipt and Adjustment Tank (SRAT). Once the alkali/alkaline earth salts (both reduced and oxidized) are formed during reflux in the SRAT, the REDOX can only change if (1) additional reductants or oxidants are added to the SRAT, the Slurry Mix Evaporator (SME), or the Melter Feed Tank (MFT) or (2) if the melt pool is bubble dwith an oxidizing gas or sparging gas that imposes a different REDOX target than the chemical balance set during reflux in the SRAT.« less

The potential of household solid waste reduction in Sukomanunggal District, Surabaya

NASA Astrophysics Data System (ADS)

Warmadewanthi, I. D. A. A.; Kurniawati, S.

2018-01-01

The rapid population growth affects the amount of waste generated. Sukomanunggal Subdistrict is the densest area in West Surabaya which has a population of 100,602 inhabitants with a total area of 11.2 km2. The population growth significantly affects the problem of limited land for landfill facilities (final processing sites). According to the prevailing regulations, solid waste management solutions include the solid waste reduction and management. This study aims to determine the potential reduction of household solid waste at the sources. Household solid waste samplings were performed for eight consecutive days. The samples were then analyzed to obtain the generation rate, density, and composition so that the household solid waste reduction potential for the next 20 years could be devised. Results of the analysis showed that the value of waste is 0.27 kg/person/day, while the total household solid waste generation amounted to 27,162.58 kg/day or 187.70 m3/day. Concerning the technical aspects, the current solid waste reduction in Sukomanunggal Subdistrict has reached 2.1% through the application of waste bank, composting, and scavenging activities at the dumping sites by the garbage collectors. In the year of 2036, the potential reduction of household solid waste in Sukomanunggal Subdistrict has been estimated to reach 28.0%.

Manganese oxide/poly(3,4-ethylenedioxythiophene) hybrid electrocatalysts for the oxygen reduction reaction in alkaline fuel cells

DOE PAGES

Lambert, Timothy N.; Vigil, Julian A.

2016-08-22

Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO x/PEDOT provided improvements over MnO x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO x/PEDOTmore » also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO x with PEDOT and due to the increase in Mn 3+ content at the surface of the oxide.« less

Manganese oxide/poly(3,4-ethylenedioxythiophene) hybrid electrocatalysts for the oxygen reduction reaction in alkaline fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lambert, Timothy N.; Vigil, Julian A.

Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO x/PEDOT provided improvements over MnO x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO x/PEDOTmore » also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO x with PEDOT and due to the increase in Mn 3+ content at the surface of the oxide.« less

Anaerobic ammonium oxidation mediated by Mn-oxides: from sediment to strain level.

PubMed

Javanaud, Cedric; Michotey, Valerie; Guasco, Sophie; Garcia, Nicole; Anschutz, Pierre; Canton, Mathieu; Bonin, Patricia

2011-11-01

Nitrite and (29)N(2) productions in slurry incubations of anaerobically sediment after (15)NO(3) or (15)NH(4) labelling in the presence of Mn-oxides suggested that anaerobic Mn-oxides mediated nitrification coupled with denitrification in muddy intertidal sediments of Arcachon Bay (SW Atlantic French coast). From this sediment, bacterial strains were isolated and physiologically characterized in terms of Mn-oxides and nitrate reduction as well as potential anaerobic nitrification. One of the isolated strain, identified as Marinobacter daepoensis strain M4AY14, was a denitrifier. Nitrous oxide production by this strain was demonstrated in the absence of nitrate and with Mn-oxides and NH(4) amendment, giving indirect proof of anaerobic nitrate or nitrite production. Anaerobic Mn-oxide-mediated nitrification was confirmed by (29)N(2) production in the presence of (15)NO(3) and (14)NH(4) under denitrifying conditions. Anaerobic nitrification by M4AY14 seemed to occur only in the absence of nitrate, or at nitrate levels lower than that of Mn-oxides. Most of the other isolates were affiliated with the Shewanella genus and were able to use both nitrate and Mn-oxides as electron acceptors. When both electron acceptors were present, whatever their concentrations, nitrate and Mn-oxide reduction co-occurred. These data indicate that bacterial Mn-oxide reduction could be an important process in marine sediments with low oxygen concentrations, and demonstrate for the first time the role of bacteria in anaerobic Mn-mediated nitrification. Copyright © 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

Interfacial Reduction-Oxidation Mechanisms Governing Fate and Transport of Contaminants in the Vadose Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Principal Investigator: Baolin Deng, University of Missouri, Columbia, MO; Co-Principal Investigator: Silvia Sabine Jurisson, University of Missouri, Columbia, MO; Co-Principal Investigator: Edward C. Thornton, Pacific Northwest National Laboratory Richland, WA

2008-05-12

primary objective of this project was to understand the complex interactions among the contaminants (i.e., Cr, Tc, and U), H{sub 2}S, and various soil constituents. The reaction with iron sulfide is also the focus of the research, which could be formed from iron oxide reduction by hydrogen sulfide. Factors controlling the reductive immobilization of these contaminants were identified and quantified. The results and fundamental knowledge obtained from this project shall help better evaluate the potential of in situ gaseous treatment to immobilize toxic and radioactive metals examined.« less

Selective inhibition of extracellular oxidants liberated from human neutrophils--A new mechanism potentially involved in the anti-inflammatory activity of hydroxychloroquine.

PubMed

Jančinová, Viera; Pažoureková, Silvia; Lucová, Marianna; Perečko, Tomáš; Mihalová, Danica; Bauerová, Katarína; Nosáľ, Radomír; Drábiková, Katarína

2015-09-01

Hydroxychloroquine is used in the therapy of rheumatoid arthritis or lupus erythematosus. Although these diseases are often accompanied by activation of neutrophils, there are still few data relating to the impact of hydroxychloroquine on these cells. We investigated the effect of orally administered hydroxychloroquine on neutrophil oxidative burst in rats with adjuvant arthritis. In human neutrophils, extra- and intracellular formation of oxidants, mobilisation of intracellular calcium and the phosphorylation of proteins regulating NADPH oxidase assembly were analysed. Administration of hydroxychloroquine decreased the concentration of oxidants in blood of arthritic rats. The inhibition was comparable with the reference drug methotrexate, yet it was not accompanied by a reduction in neutrophil count. When both drugs were co-applied, the effect became more pronounced. In isolated human neutrophils, treatment with hydroxychloroquine resulted in reduced mobilisation of intracellular calcium, diminished concentration of external oxidants and in decreased phosphorylation of Ca(2+)-dependent protein kinase C isoforms PKCα and PKCβII, which regulate activation of NADPH oxidase on plasma membrane. On the other hand, no reduction was observed in intracellular oxidants or in the phosphorylation of p40(phox) and PKCδ, two proteins directing the oxidase assembly to intracellular membranes. Hydroxychloroquine reduced neutrophil-derived oxidants potentially involved in tissue damage and protected those capable to suppress inflammation. The observed effects may represent a new mechanism involved in the anti-inflammatory activity of this drug. Copyright © 2015 Elsevier B.V. All rights reserved.

In-Situ Chemical Reduction and Oxidation of VOCs in Groundwater: Groundwater Treatability Studies

NASA Technical Reports Server (NTRS)

Keith, Amy; Glasgow, Jason; McCaleh, Rececca C. (Technical Monitor)

2001-01-01

This paper presents NASA Marshall Space Flight Center's treatability studies for volatile organic compounds in groundwater. In-Situ groundwater treatment technologies include: 1) Chemical Reduction(Ferox); 2) Chemical Oxidation (Fenton Reagents, Permanganate, and Persulfate); and 3) Thermal (Dynamic Underground Stripping, Six-Phase Heating). This paper is presented in viewgraph form.

RP-UHPLC-UV-ESI-MS/MS analysis of LPMO generated C4-oxidized gluco-oligosaccharides after non-reductive labeling with 2-aminobenzamide.

PubMed

Frommhagen, Matthias; van Erven, Gijs; Sanders, Mark; van Berkel, Willem J H; Kabel, Mirjam A; Gruppen, Harry

2017-08-07

Lytic polysaccharide monooxygenases (LPMOs) are able to cleave recalcitrant polysaccharides, such as cellulose, by oxidizing the C1 and/or C4 atoms. The analysis of the resulting products requires a variety of analytical techniques. Up to now, these techniques mainly focused on the identification of non-oxidized and C1-oxidized oligosaccharides. The analysis of C4-oxidized gluco-oligosaccharides is mostly performed by using high pressure anion exchange chromatography (HPAEC). However, the alkaline conditions used during HPAEC analysis lead to tautomerization of C4-oxidized gluco-oligosaccharides, which limits the use of this technique. Here, we describe the use of reverse phase-ultra high performance liquid chromatography (RP-UHPLC) in combination with non-reductive 2-aminobenzamide (2-AB) labeling. Non-reductive 2-AB labeling enabled separation of C4-oxidized gluco-oligosaccharides from their non-oxidized counterparts. Moreover, RP-UHPLC does not require buffered mobile phases, which reduce mass spectrometry (MS) sensitivity. The latter is seen as an advantage over other techniques such as hydrophilic interaction liquid chromatography and porous graphitized carbon coupled to MS. RP-UHPLC coupled to UV detection and mass spectrometry allowed the identification of both labeled non-oxidized and C4-oxidized oligosaccharides. Non-reductive labeling kept the ketone at the C4-position of LPMO oxidized oligosaccharides intact, while selective reducing agents such as sodium triacetoxyborohydride (STAB) reduced this ketone group. Our results show that RP-UHPLC-UV-ESI-MS in combination with non-reductively 2-AB labeling is a suitable technique for the separation and identification of LPMO-generated C4-oxidized gluco-oligosaccharides. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Ammonia oxidation, denitrification and dissimilatory nitrate reduction to ammonium in two US Great Basin hot springs with abundant ammonia-oxidizing archaea.

PubMed

Dodsworth, Jeremy A; Hungate, Bruce A; Hedlund, Brian P

2011-08-01

Many thermophiles catalyse free energy-yielding redox reactions involving nitrogenous compounds; however, little is known about these processes in natural thermal environments. Rates of ammonia oxidation, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in source water and sediments of two ≈ 80°C springs in the US Great Basin. Ammonia oxidation and denitrification occurred mainly in sediments. Ammonia oxidation rates measured using (15)N-NO(3)(-) pool dilution ranged from 5.5 ± 0.8 to 8.6 ± 0.9 nmol N g(-1) h(-1) and were unaffected or only mildly stimulated by amendment with NH(4) Cl. Denitrification rates measured using acetylene block ranged from 15.8 ± 0.7 to 51 ± 12 nmol N g(-1) h(-1) and were stimulated by amendment with NO(3)(-) and complex organic compounds. The DNRA rate in one spring sediment measured using an (15)N-NO(3)(-) tracer was 315 ± 48 nmol N g(-1) h(-1). Both springs harboured distinct planktonic and sediment microbial communities. Close relatives of the autotrophic, ammonia-oxidizing archaeon 'Candidatus Nitrosocaldus yellowstonii' represented the most abundant OTU in both spring sediments by 16S rRNA gene pyrotag analysis. Quantitative PCR (qPCR) indicated that 'Ca. N. yellowstonii'amoA and 16S rRNA genes were present at 3.5-3.9 × 10(8) and 6.4-9.0 × 10(8) copies g(-1) sediment. Potential denitrifiers included members of the Aquificales and Thermales. Thermus spp. comprised <1% of 16S rRNA gene pyrotags in both sediments and qPCR for T. thermophilus narG revealed sediment populations of 1.3-1.7 × 10(6) copies g(-1) sediment. These data indicate a highly active nitrogen cycle (N-cycle) in these springs and suggest that ammonia oxidation may be a major source of energy fuelling primary production. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Oxidation of ultrathin GaSe

DOE PAGES

Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; ...

2015-10-26

Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga 2Se 3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

Catalytic reduction of carbonyl groups in oxidized PAPC by Kvβ2 (AKR6)

PubMed Central

Xie, Zhengzhi; Barski, Oleg A.; Cai, Jian; Bhatnagar, Aruni; Tipparaju, Srinivas M.

2011-01-01

The β-subunits of the voltage-gated potassium channel (Kvβ) belong to the aldo-keto reductase superfamily. The Kvβ-subunits dock with the pore-forming Kv α-subunits and impart or accelerate the rate of inactivation in Kv channels. Inactivation of Kv currents by Kvβ is differentially regulated by oxidized and reduced pyridine nucleotides. In mammals, AKR6 family is comprised of 3 different genes Kvβ1-3. We have shown previously that Kvβ2 catalyzes the reduction of a broad range of carbonyls including aromatic carbonyls, electrophilic aldehydes and prostaglandins. However, the endogenous substrates for Kvβ have not been identified. To determine whether products of lipid oxidation are substrates of Kvβs, we tested the enzymatic activity of Kvβ2 with oxidized phospholipids generated during the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC). Electrospray ionization mass spectrometric analysis showed that Kvβ2 catalyzed the NADPH-dependent reduction of several products of oxPAPC, including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC), 1-palmitoyl-2-(epoxycyclopentenone)-sn-glycero-3-phosphorylcholine (PECPC), 1-palmitoyl-2-(5,6)- epoxyisoprostane E2-sn-glycero-3-phosphocholine (PEIPC). These results were validated using high resolution mass spectrometric analysis. Time course analysis revealed that the reduced products reached significant levels for ions at m/z 594/596 (POVPC/PHVPC), 810/812 (PECPC/2H-PECPC) and 828/830 (PEIPC/2H-PEIPC) in the oxPAPC + Kvβ2 mixture (p < 0.01). These results suggest that Kvβ could serve as a sensor of lipid oxidation via its catalytic activity and thereby alter Kv currents under conditions of oxidative stress. PMID:21296056

Synthesis of high intrinsic loss power aqueous ferrofluids of iron oxide nanoparticles by citric acid-assisted hydrothermal-reduction route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behdadfar, Behshid, E-mail: bbehdadfar@ma.iut.ac.ir; Kermanpur, Ahmad; Sadeghi-Aliabadi, Hojjat

Monodispersed aqueous ferrofluids of iron oxide nanoparticle were synthesized by hydrothermal-reduction route. They were characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy and dynamic light scattering. The results showed that certain concentrations of citric acid (CA) are required to obtain only magnetic iron oxides with mean particle sizes around 8 nm. CA acts as a modulator and reducing agent in iron oxide formation which controls nanoparticle size. The XRD, magnetic and heating measurements showed that the temperature and time of hydrothermal reaction can affect the magnetic properties of obtained ferrofluids. The synthesized ferrofluids weremore » stable at pH 7. Their mean hydrodynamic size was around 80 nm with polydispersity index (PDI) of 0.158. The calculated intrinsic loss power (ILP) was 9.4 nHm{sup 2}/kg. So this clean and cheap route is an efficient way to synthesize high ILP aqueous ferrofluids applicable in magnetic hyperthermia. - Graphical abstract: Monodispersed aqueous ferrofluids of iron oxide nanoparticles were synthesized by hydrothermal-reduction method with citric acid as reductant which is an efficient way to synthesize aqueous ferrofluids applicable in magnetic hyperthermia. Highlights: Black-Right-Pointing-Pointer Aqueous iron oxide ferrofluids were synthesized by hydrothermal-reduction route. Black-Right-Pointing-Pointer Citric acid acted as reducing agent and surfactant in the route. Black-Right-Pointing-Pointer This is a facile, low energy and environmental friendly route. Black-Right-Pointing-Pointer The aqueous iron oxide ferrofluids were monodispersed and stable at pH of 7. Black-Right-Pointing-Pointer The calculated intrinsic loss power of the synthesized ferrofluids was very high.« less

Mechanisms for Fe(III) oxide reduction in sedimentary environments

USGS Publications Warehouse

Nevin, Kelly P.; Lovely, Derek R.

2002-01-01

Although it was previously considered that Fe(III)-reducing microorganisms must come into direct contact with Fe(III) oxides in order to reduce them, recent studies have suggested that electron-shuttling compounds and/or Fe(III) chelators, either naturally present or produced by the Fe(III)-reducing microorganisms themselves, may alleviate the need for the Fe(III) reducers to establish direct contact with Fe(III) oxides. Studies with Shewanella alga strain BrY and Fe(III) oxides sequestered within microporous beads demonstrated for the first time that this organism releases a compound(s) that permits electron transfer to Fe(III) oxides which the organism cannot directly contact. Furthermore, as much as 450 w M dissolved Fe(III) was detected in cultures of S. alga growing in Fe(III) oxide medium, suggesting that this organism releases compounds that can solublize Fe(III) from Fe(III) oxide. These results contrast with previous studies, which demonstrated that Geobacter metallireducens does not produce electron-shuttles or Fe(III) chelators. Some freshwater aquatic sediments and groundwaters contained compounds, which could act as electron shuttles by accepting electrons from G. metallireducens and then transferring the electrons to Fe(III). However, other samples lacked significant electron-shuttling capacity. Spectroscopic studies indicated that the electron-shuttling capacity of the waters was not only associated with the presence of humic substances, but water extracts of walnut, oak, and maple leaves contained electron-shuttling compounds did not appear to be humic substances. Porewater from a freshwater aquatic sediment and groundwater from a petroleum-contaminated aquifer contained dissolved Fe(III) (4-16 w M), suggesting that soluble Fe(III) may be available as an electron acceptor in some sedimentary environments. These results demonstrate that in order to accurately model the mechanisms for Fe(III) reduction in sedimentary environments it will be necessary

Oxidative and reductive metabolism of lipid-peroxidation derived carbonyls

PubMed Central

Singh, Mahavir; Kapoor, Aniruddh; Bhatnagar, Aruni

2015-01-01

Extensive research has shown that increased production of reactive oxygen species (ROS) results in tissue injury under a variety of pathological conditions and chronic degenerative diseases. While ROS are highly reactive and can incite significant injury, polyunsaturated lipids in membranes and lipoproteins are their main targets. ROS-triggered lipid peroxidation reactions generate a range of reactive carbonyl species (RCS), and these RCS spread and amplify ROS-related injury. Several RCS generated in oxidizing lipids, such as 4-hydroxy trans-2-nonenal (HNE), 4-oxo-2-(E)-nonenal (ONE), acrolein, malondialdehyde (MDA) and phospholipid aldehydes have been shown to be produced under conditions of oxidative stress and contribute to tissue injury and dysfunction by depleting glutathione and other reductants leading to the modification of proteins, lipids, and DNA. To prevent tissue injury, these RCS are metabolized by several oxidoreductases, including members of the aldo-keto reductase (AKR) superfamily, aldehyde dehydrogenases (ALDHs), and alcohol dehydrogenases (ADHs). Metabolism via these enzymes results in RCS inactivation and detoxification, although under some conditions, it can also lead to the generation of signaling molecules that trigger adaptive responses. Metabolic transformation and detoxification of RCS by oxidoreductases prevent indiscriminate ROS toxicity, while at the same time, preserving ROS signaling. A better understanding of RCS metabolism by oxidoreductases could lead to the development of novel therapeutic interventions to decrease oxidative injury in several disease states and to enhance resistance to ROS-induced toxicity. PMID:25559856

Development of molecular electrocatalysts for CO2 reduction and H2 production/oxidation.

PubMed

Rakowski DuBois, M; DuBois, Daniel L

2009-12-21

The conversion of solar energy to fuels in both natural and artificial photosynthesis requires components for both light-harvesting and catalysis. The light-harvesting component generates the electrochemical potentials required to drive fuel-generating reactions that would otherwise be thermodynamically uphill. This Account focuses on work from our laboratories on developing molecular electrocatalysts for CO(2) reduction and for hydrogen production. A true analog of natural photosynthesis will require the ability to capture CO(2) from the atmosphere and reduce it to a useful fuel. Work in our laboratories has focused on both aspects of this problem. Organic compounds such as quinones and inorganic metal complexes can serve as redox-active CO(2) carriers for concentrating CO(2). We have developed catalysts for CO(2) reduction to form CO based on a [Pd(triphosphine)(solvent)](2+) platform. Catalytic activity requires the presence of a weakly coordinating solvent molecule that can dissociate during the catalytic cycle and provide a vacant coordination site for binding water and assisting C-O bond cleavage. Structures of [NiFe] CO dehydrogenase enzymes and the results of studies on complexes containing two [Pd(triphosphine)(solvent)](2+) units suggest that participation of a second metal in CO(2) binding may also be required for achieving very active catalysts. We also describe molecular electrocatalysts for H(2) production and oxidation based on [Ni(diphosphine)(2)](2+) complexes. Similar to palladium CO(2) reduction catalysts, these species require the optimization of both first and second coordination spheres. In this case, we use structural features of the first coordination sphere to optimize the hydride acceptor ability of nickel needed to achieve heterolytic cleavage of H(2). We use the second coordination sphere to incorporate pendant bases that assist in a number of important functions including H(2) binding, H(2) cleavage, and the transfer of protons between

REDUCTION OF ALDOSTERONE PRODUCTION IMPROVES RENAL OXIDATIVE STRESS AND FIBROSIS IN DIABETIC RATS

PubMed Central

Matavelli, Luis C.; Siragy, Helmy M.

2012-01-01

SUMMARY Aldosterone is increased in diabetes and contributes to the development of diabetic nephropathy. We hypothesized that reduction in aldosterone production in diabetes by amlodipine or aliskiren improves diabetic kidney disease by attenuating renal oxidative stress and fibrosis. Normoglycemic and streptozotocin-induced diabetes Sprague-Dawley rats were given vehicle, amlodipine or aliskiren individually and combined for six weeks. At the end of study, we evaluated BP, 24h urinary sodium (UNaV) and aldosterone excretion rates, renal interstitial fluid (RIF) levels of nitric oxide (NO), cGMP and 8-isoprostane, and renal morphology. BP was not significantly different between any of experimental groups. UNaV increased in diabetic animals and was not affected by different treatments. Urinary aldosterone excretion increased in diabetic rats receiving vehicle and decreased with amlodipine and aliskiren individually or combined. RIF NO and cGMP levels were reduced in vehicle treated diabetic rats and increased with amlodipine or aliskiren given individually and combined. RIF 8-isoprostane levels and renal immunostaining for PAS and fibronectin were increased in vehicle treated diabetic rats and decreased with aliskiren individually or combined with amlodipine. We conclude that inhibition of aldosterone by amlodipine or aliskiren ameliorates diabetes induced renal injury via improvement of NO-cGMP pathway, and reduction in oxidative stress and fibrosis, independent of BP changes. PMID:23011470

Simultaneous Surface Modification and Chemical Reduction of Graphene Oxide Using Glucose.

PubMed

Pan, Hui; Liu, Ruiqi; Li, Guanglong; Wang, Xiaodong; Ding, Tao

2018-05-01

In this paper, we develop a simple and facile approach to prepare graphene nanosheets through chemical reduction with glucose as reducing agent and modification agent. The reduced and modified graphene by glucose (denoted as g-rGO) was characterized with techniques of Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), etc. It is found that, besides the desired reduction capability to graphene oxide (denoted as GO), glucose plays an important role as a modifying reagent in stabilizing the as-prepared graphene nanosheets simultaneously and the g-rGO exhibits good dispersibility and stability in water and waterborne polyurethane matrix (denoted as WPU). Moreover, the g-rGO can improve evidently the mechanical properties, weather ability and water resistance of WPU.

Two Oxidation Sites for Low Redox Potential Substrates

PubMed Central

Morales, María; Mate, María J.; Romero, Antonio; Martínez, María Jesús; Martínez, Ángel T.; Ruiz-Dueñas, Francisco J.

2012-01-01

Versatile peroxidase shares with manganese peroxidase and lignin peroxidase the ability to oxidize Mn2+ and high redox potential aromatic compounds, respectively. Moreover, it is also able to oxidize phenols (and low redox potential dyes) at two catalytic sites, as shown by biphasic kinetics. A high efficiency site (with 2,6-dimethoxyphenol and p-hydroquinone catalytic efficiencies of ∼70 and ∼700 s−1 mm−1, respectively) was localized at the same exposed Trp-164 responsible for high redox potential substrate oxidation (as shown by activity loss in the W164S variant). The second site, characterized by low catalytic efficiency (∼3 and ∼50 s−1 mm−1 for 2,6-dimethoxyphenol and p-hydroquinone, respectively) was localized at the main heme access channel. Steady-state and transient-state kinetics for oxidation of phenols and dyes at the latter site were improved when side chains of residues forming the heme channel edge were removed in single and multiple variants. Among them, the E140G/K176G, E140G/P141G/K176G, and E140G/W164S/K176G variants attained catalytic efficiencies for oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) at the heme channel similar to those of the exposed tryptophan site. The heme channel enlargement shown by x-ray diffraction of the E140G, P141G, K176G, and E140G/K176G variants would allow a better substrate accommodation near the heme, as revealed by the up to 26-fold lower Km values (compared with native VP). The resulting interactions were shown by the x-ray structure of the E140G-guaiacol complex, which includes two H-bonds of the substrate with Arg-43 and Pro-139 in the distal heme pocket (at the end of the heme channel) and several hydrophobic interactions with other residues and the heme cofactor. PMID:23071108

Noise and Fuel Burn Reduction Potential of an Innovative Subsonic Transport Configuration

NASA Technical Reports Server (NTRS)

Guo, Yueping; Nickol, Craig L.; Thomas, Russell H.

2014-01-01

A study is presented for the noise and fuel burn reduction potential of an innovative double deck concept aircraft with two three-shaft direct-drive turbofan engines. The engines are mounted from the fuselage so that the engine inlet is over the main wing. It is shown that such an aircraft can achieve a cumulative Effective Perceived Noise Level (EPNL) about 28 dB below the current aircraft noise regulations of Stage 4. The combination of high bypass ratio engines and advanced wing design with laminar flow control technologies provide fuel burn reduction and low noise levels simultaneously. For example, the fuselage mounted engine position provides more than 4 EPNLdB of noise reduction by shielding the inlet radiated noise. To identify the potential effect of noise reduction technologies on this concept, parametric studies are presented to reveal the system level benefits of various emerging noise reduction concepts, for both engine and airframe noise reduction. These concepts are discussed both individually to show their respective incremental noise reduction potential and collectively to assess their aggregate effects on the total noise. Through these concepts approximately about 8 dB of additional noise reduction is possible, bringing the cumulative noise level of this aircraft to 36 EPNLdB below Stage 4, if the entire suite of noise reduction technologies would mature to practical application. In a final step, an estimate is made for this same aircraft concept but with higher bypass ratio, geared, turbofan engines. With this geared turbofan propulsion system, the noise is estimated to reach as low as 40-42 dB below Stage 4 with a fuel burn reduction of 43-47% below the 2005 best-in-class aircraft baseline. While just short of the NASA N+2 goals of 42 dB and 50% fuel burn reduction, for a 2025 in service timeframe, this assessment shows that this innovative concept warrants refined study. Furthermore, this design appears to be a viable potential future passenger

Biological reduction of uranium coupled with oxidation of ammonium by Acidimicrobiaceae bacterium A6 under iron reducing conditions.

PubMed

Gilson, Emily R; Huang, Shan; Jaffé, Peter R

2015-11-01

This study investigated the possibility of links between the biological immobilization of uranium (U) and ammonium oxidation under iron (Fe) reducing conditions. The recently-identified Acidimicrobiaceae bacterium A6 (ATCC, PTA-122488) derives energy from ammonium oxidation coupled with Fe reduction. This bacterium has been found in various soil and wetland environments, including U-contaminated wetland sediments. Incubations of Acidimicrobiaceae bacteria A6 with nontronite, an Fe(III)-rich clay, and approximately 10 µM U indicate that these bacteria can use U(VI) in addition to Fe(III) as an electron acceptor in the presence of ammonium. Measurements of Fe(II) production and ammonium oxidation support this interpretation. Concentrations of approximately 100 µM U were found to entirely inhibit Acidimicrobiaceae bacteria A6 activity. These results suggest that natural sites of active ammonium oxidation under Fe reducing conditions by Acidimicrobiaceae bacteria A6 could be hotspots of U immobilization by bioreduction. This is the first report of biological U reduction that is not coupled to carbon oxidation.

A potential biomarker for fatigue: Oxidative stress and anti-oxidative activity.

PubMed

Fukuda, Sanae; Nojima, Junzo; Motoki, Yukari; Yamaguti, Kouzi; Nakatomi, Yasuhito; Okawa, Naoko; Fujiwara, Kazumi; Watanabe, Yasuyoshi; Kuratsune, Hirohiko

2016-07-01

We sought to determine whether oxidative stress and anti-oxidative activity could act as biomarkers that discriminate patients with chronic fatigue syndrome (CFS) from healthy volunteers at acute and sub-acute fatigue and resting conditions. We calculated the oxidative stress index (OSI) from reactive oxygen metabolites-derived compounds (d-ROMs) and the biological antioxidant potential (BAP). We determined changes in d-ROMs, BAP, and OSI in acute and sub-acute fatigue in two healthy groups, and compared their values at rest between patients with CFS (diagnosed by Fukuda 1994 criteria) and another group of healthy controls. Following acute fatigue in healthy controls, d-ROMs and OSI increased, and BAP decreased. Although d-ROMs and OSI were significantly higher after sub-acute fatigue, BAP did not decrease. Resting condition yielded higher d-ROMs, higher OSI, and lower BAP in patients with CFS than in healthy volunteers, but lower d-ROMs and OSI when compared with sub-acute controls. BAP values did not significantly differ between patients with CFS and controls in the sub-acute condition. However, values were significantly higher than in the resting condition for controls. Thus, measured of oxidative stress (d-ROMS) and anti-oxidative activity (BAP) might be useful for discriminating acute, sub-acute, and resting fatigue in healthy people from patients with CFS, or for evaluating fatigue levels in healthy people. Copyright © 2016 Elsevier B.V. All rights reserved.

Identifying external nutrient reduction requirements and potential in the hypereutrophic Lake Taihu Basin, China.

PubMed

Peng, Jiao-Ting; Zhu, Xiao-Dong; Sun, Xiang; Song, Xiao-Wei

2018-04-01

Reducing external nutrient loads is the first step for controlling eutrophication. Here, we identified external nutrient reduction requirements and potential of strategies for achieving reductions to remediate a eutrophic water body, Lake Taihu, China. A mass balance approach based on the entire lake was used to identify nutrient reduction requirements; an empirical export coefficient approach was introduced to estimate the nutrient reduction potential of the overall program on integrated regulation of Taihu Lake Basin (hereafter referred to as the "Guideline"). Reduction requirements included external total nitrogen (TN) and total phosphorus (TP) loads, which should be reduced by 41-55 and 25-50%, respectively, to prevent nutrient accumulation in Lake Taihu and to meet the planned water quality targets. In 2010, which is the most seriously polluted calendar year during the 2008-2014 period, the nutrient reduction requirements were estimated to be 36,819 tons of N and 2442 tons of P, and the potential nutrient reduction strategies would reduce approximately 25,821 tons of N and 3024 tons of P. Since there is a net N remaining in the reduction requirements, it should be the focus and deserves more attention in identifying external nutrient reduction strategies. Moreover, abatement measures outlined in the Guideline with high P reduction potential required large monetary investments. Achieving TP reduction requirement using the cost-effective strategy costs about 80.24 million USD. The design of nutrient reduction strategies should be enacted according to regional and sectoral differences and the cost-effectiveness of abatement measures.

The effect of oxidizing water on metallic restorations in the mouth: in vitro reduction behavior of oxidizing water.

PubMed

Nishida, T

1997-03-01

Mouth-rinsing with oxydized water which contains electrolytically generated chlorine is known to hinder dental plaque formation and growth, but it also accelerates the deterioration of metallic restorations in the mouth. The present work consists of an in vitro study to elucidate the electrochemical reactions involved in the reduction of oxydized water on dental alloys through a systematic investigation of the potentiostatic polarization behavior of dental alloy electrodes. The five dental alloys selected for investigation were gold alloy, gold alloy containing platinum, silver-palladium-gold alloy, conventional amalgam and high copper amalgam. The corrosion potentials of all dental alloy electrodes were shown to be more noble in oxydized water than in 0.1N sodium chloride solution. The potential differences between the corrosion potentials were relatively small in the case of amalgam electrodes. The polarization curves for all of the dental alloy electrodes in oxydized water revealed reduction currents of chlorine, hypochlorous acid, dissolved oxygen and oxonium ion. The reduction of chlorine and hypochlorous acid started at a more noble potential than that of dissolved oxygen. The dental alloys studied, except the amalgams, did not dissolve excessively at the corrosion potentials in oxydized water.

Simulation of reduction of iron-oxide-carbon composite pellets in a rotary hearth furnace

NASA Astrophysics Data System (ADS)

Halder, Sabuj

The primary motivation of this work is to evaluate a new alternative ironmaking process which involves the combination of a Rotary Hearth Furnace (RHF) with an iron bath smelter. This work is concerned primarily, with the productivity of the RHF. It is known that the reduction in the RHF is controlled by chemical kinetics of the carbon oxidation and wustite reduction reactions as well as by heat transfer to the pellet surface and within the pellet. It is heat transfer to the pellet which limits the number of layers of pellets in the pellet bed in the RHF and thus, the overall productivity. Different types of carbon like graphite, coal-char and wood charcoal were examined. Part of the research was to investigate the chemical kinetics by de-coupling it from the influence of heat and mass transfer. This was accomplished by carrying out reduction experiments using small iron-oxide-carbon powder composite mixtures. The reaction rate constants were determined by fitting the experimental mass loss with a mixed reaction model. This model accounts for the carbon oxidation by CO2 and wustite reduction by CO, which are the primary rate controlling surface-chemical reactions in the composite system. The reaction rate constants have been obtained using wustite-coal-char powder mixtures and wustite-wood-charcoal mixtures. The wustite for these mixtures was obtained from two iron-oxide sources: artificial porous analytical hematite (PAH) and hematite ore tailings. In the next phase of this study, larger scale experiments were conducted in a RHF simulator using spherical composite pellets. Measurement of the reaction rates was accomplished using off-gas analysis. Different combinations of raw materials for the pellets were investigated. These included artificial ferric oxide as well as naturally existing hematite and taconite ores. Graphite, coal-char and wood-charcoal were the reductants. Experiments were conducted using a single layer, a double layer and a triple layer of

Impacts of halogen additions on mercury oxidation, in a slipstream selective catalyst reduction (SCR), reactor when burning sub-bituminous coal.

PubMed

Cao, Yan; Gao, Zhengyang; Zhu, Jiashun; Wang, Quanhai; Huang, Yaji; Chiu, Chengchung; Parker, Bruce; Chu, Paul; Pant, Wei-Ping

2008-01-01

This paper presents a comparison of impacts of halogen species on the elemental mercury (Hg(0)) oxidation in a real coal-derived flue gas atmosphere. It is reported there is a higher percentage of Hg(0) in the flue gas when burning sub-bituminous coal (herein Powder River Basin (PRB) coal) and lignite, even with the use of selective catalytic reduction (SCR). The higher Hg(0)concentration in the flue gas makes it difficult to use the wet-FGD process for the mercury emission control in coal-fired utility boilers. Investigation of enhanced Hg(0) oxidation by addition of hydrogen halogens (HF, HCl, HBr, and HI) was conducted in a slipstream reactor with and without SCR catalysts when burning PRB coal. Two commercial SCR catalysts were evaluated. SCR catalyst no. 1 showed higher efficiencies of both NO reduction and Hg(0) oxidation than those of SCR catalyst no. 2. NH3 addition seemed to inhibit the Hg(0) oxidation, which indicated competitive processes between NH3 reduction and Hg(0) oxidation on the surface of SCR catalysts. The hydrogen halogens, in the order of impact on Hg(0) oxidation, were HBr, HI, and HCl or HF. Addition of HBr at approximately 3 ppm could achieve 80% Hg(0) oxidation. Addition of HI at approximately 5 ppm could achieve 40% Hg(0) oxidation. In comparison to the empty reactor, 40% Hg(0) oxidation could be achieved when HCl addition was up to 300 ppm. The enhanced Hg(0) oxidation by addition of HBr and HI seemed not to be correlated to the catalytic effects by both evaluated SCR catalysts. The effectiveness of conversion of hydrogen halogens to halogen molecules or interhalogens seemed to be attributed to their impacts on Hg(0) oxidation.

Ion Association, Solubilities, and Reduction Potentials in Aqueous Solution.

ERIC Educational Resources Information Center

Russo, Steven O.; Hanania, George I. H.

1989-01-01

Incorporates the combined effects of ionic strength and ion association to show how calculations involving ionic equilibria are carried out. Examines the variability of reduction potential data for two aqueous redox systems. Provides several examples. (MVL)

Surface Selective Oxide Reduction During the Intercritical Annealing of Medium Mn Steel

NASA Astrophysics Data System (ADS)

Jo, Kyoung Rae; Cho, Lawrence; Oh, Jong Han; Kim, Myoung Soo; Kang, Ki Cheol; De Cooman, Bruno C.

2017-08-01

Third generation advanced high-strength steels achieve an excellent strength-ductility balance using a cost-effective alloy composition. During the continuous annealing of medium Mn steel, the formation of an external selective oxide layer of MnO has a negative impact on the coating quality after galvanizing. A procedure to reduce the selective oxide was therefore developed. It involves annealing in the temperature range of 1073 K to 1323 K (800 °C to 1050 °C) in a HNx gas atmosphere. Annealing at higher temperatures and the use of larger H2 volume fractions are shown to make the gas atmosphere reducing with respect to MnO. The reduction of the surface MnO layer was observed by SEM, GDOES, and cross-sectional TEM analysis.

Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria

PubMed Central

Klueglein, Nicole; Zeitvogel, Fabian; Stierhof, York-Dieter; Floetenmeyer, Matthias; Konhauser, Kurt O.; Obst, Martin

2014-01-01

Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic conditions. While most of the mixotrophic nitrate-reducing Fe(II)-oxidizing bacteria become encrusted with Fe(III)-rich minerals, photoautotrophic and microaerophilic Fe(II) oxidizers avoid cell encrustation. The Fe(II) oxidation mechanisms and the reasons for encrustation remain largely unresolved. Here we used cultivation-based methods and electron microscopy to compare two previously described nitrate-reducing Fe(II) oxidizers ( Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002) and two heterotrophic nitrate reducers (Paracoccus denitrificans ATCC 19367 and P. denitrificans Pd 1222). All four strains oxidized ∼8 mM Fe(II) within 5 days in the presence of 5 mM acetate and accumulated nitrite (maximum concentrations of 0.8 to 1.0 mM) in the culture media. Iron(III) minerals, mainly goethite, formed and precipitated extracellularly in close proximity to the cell surface. Interestingly, mineral formation was also observed within the periplasm and cytoplasm; intracellular mineralization is expected to be physiologically disadvantageous, yet acetate consumption continued to be observed even at an advanced stage of Fe(II) oxidation. Extracellular polymeric substances (EPS) were detected by lectin staining with fluorescence microscopy, particularly in the presence of Fe(II), suggesting that EPS production is a response to Fe(II) toxicity or a strategy to decrease encrustation. Based on the data presented here, we propose a nitrite-driven, indirect mechanism of cell encrustation whereby nitrite forms during heterotrophic denitrification and abiotically oxidizes Fe(II). This work adds to the known assemblage of Fe(II)-oxidizing bacteria in nature and complicates our ability to delineate microbial Fe(II) oxidation in ancient microbes preserved as fossils in the geological record. PMID:24271182

Control of Sulfidogenesis Through Bio-oxidation of H 2S Coupled to (per)chlorate Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gregoire, Patrick; Engelbrektson, Anna; Hubbard, Christopher G.

2014-04-04

Here, we investigate H 2S attenuation by dissimilatory perchlorate-reducing bacteria (DPRB). All DPRB tested oxidized H 2S coupled to (per)chlorate reduction without sustaining growth. H 2S was preferentially utilized over organic electron donors resulting in an enriched (34S)-elemental sulfur product. Electron microscopy revealed elemental sulfur production in the cytoplasm and on the cell surface of the DPRB Azospira suillum. We also propose a novel hybrid enzymatic-abiotic mechanism for H 2S oxidation similar to that recently proposed for nitrate-dependent Fe(II) oxidation. The results of this study have implications for the control of biosouring and biocorrosion in a range of industrial environments.

Efficient photocatalytic selective nitro-reduction and C-H bond oxidation over ultrathin sheet mediated CdS flowers.

PubMed

Pahari, Sandip Kumar; Pal, Provas; Srivastava, Divesh N; Ghosh, Subhash Ch; Panda, Asit Baran

2015-06-28

We report here a visible light driven selective nitro-reduction and oxidation of saturated sp(3) C-H bonds using ultrathin (0.8 nm) sheet mediated uniform CdS flowers as catalyst under a household 40 W CFL lamp and molecular oxygen as oxidant. The CdS flowers were synthesized using a simple surfactant assisted hydrothermal method.

Limitations in Using Chemical Oxidative Potential to Understand Oxidative Stress from Particulate Matter

NASA Astrophysics Data System (ADS)

Chan, A. W. H.; Wang, S.; Wang, X.; Kohl, L.; Chow, C. W.

2017-12-01

Particulate matter (PM) in the atmosphere is known to cause adverse cardiorespiratory health effects. It has been suggested that the ability of PM to generate oxidative stress leads to a proinflammatory response. In this work, we study the biological relevance of using a chemical oxidative potential (OP) assay to evaluate proinflammatory response in airway epithelial cells. Here we study the OPs of laboratory secondary organic aerosol (SOA) and metal mixtures, ambient PM from India, ash from the 2016 Alberta wildfires, and diesel exhaust particles. We use SOA derived from naphthalene and from monoterpenes as model systems for SOA. We measure OP using the dithiothreitol (DTT) assay, and cytosolic reactive oxygen species (ROS) production in BEAS-2B cell culture was measured using CellROX assay. We found that both SOA and copper show high OPs individually, but the OP of the combined SOA/copper mixture, which is more atmospherically relevant, was lower than either of the individual OPs. The reduced activity is attributed to chelation between metals and organic compounds using proton nuclear magnetic resonance. There is reasonable association between DTT activity and cellular ROS production within each particle type, but weak association across different particle types, suggesting that particle composition plays an important role in distinguishing between antioxidant consumption and ROS production. Our results highlight that while oxidative potential is a useful metric of PM's ability to generate oxidative stress, the chemical composition and cellular environment should be considered in understanding health impacts of PM.

In Situ Scanning Tunneling Microscopy Topography Changes of Gold (111) in Aqueous Sulfuric Acid Produced by Electrochemical Surface Oxidation and Reduction and Relaxation Phenomena

NASA Astrophysics Data System (ADS)

Pasquale, M. A.; Nieto, F. J. Rodríguez; Arvia, A. J.

The electrochemical formation and reduction of O-layers on gold (111) films in 1 m sulfuric acid under different potentiodynamic routines are investigated utilizing in situ scanning tunneling microscopy. The surface dynamics is interpreted considering the anodic and cathodic reaction pathways recently proposed complemented with concurrent relaxation phenomena occurring after gold (111) lattice mild disruption (one gold atom deep) and moderate disruption (several atoms deep). The dynamics of both oxidized and reduced gold topographies depends on the potentiodynamic routine utilized to form OH/O surface species. The topography resulting from a mild oxidative disruption is dominated by quasi-2D holes and hillocks of the order of 5 nm, involving about 500-600 gold atoms each, and their coalescence. A cooperative turnover process at the O-layer, in which the anion ad-layer and interfacial water play a key role, determines the oxidized surface topography. The reduction of these O-layers results in gold clusters, their features depending on the applied potential routine. A moderate oxidative disruption produces a surface topography of hillocks and holes several gold atoms high and deep, respectively. The subsequent reduction leads to a spinodal gold pattern. Concurrent coalescence appears to be the result of an Ostwald ripening that involves the surface diffusion of both gold atoms and clusters. These processes produce an increase in surface roughness and an incipient gold faceting. The dynamics of different topographies can be qualitatively explained employing the arguments from colloidal science theory. For 1.1 V ≤ E ≅ Epzc weak electrostatic repulsions favor gold atom/cluster coalescence, whereas for E < Epzc the attenuated electrostatic repulsions among gold surfaces stabilize small clusters over the substrate producing string-like patterns.

Role of nitric oxide in long-term potentiation of the rat medial vestibular nuclei.

PubMed

Grassi, S; Pettorossi, V E

2000-01-01

In rat brainstem slices, we investigated the role of nitric oxide in long-term potentiation induced in the ventral portion of the medial vestibular nuclei by high-frequency stimulation of the primary vestibular afferents. The nitric oxide scavenger [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide ] and the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester were administered before and after induction of potentiation. Both drugs completely prevented long-term potentiation, whereas they did not impede the potentiation build-up, or affect the already established potentiation. These results demonstrate that the induction, but not the maintenance of vestibular long-term potentiation, depends on the synthesis and release into the extracellular medium of nitric oxide. In addition, we analysed the effect of the nitric oxide donor sodium nitroprusside on vestibular responses. Sodium nitroprusside induced long-term potentiation, as evidenced through the field potential enhancement and unit peak latency decrease. This potentiation was impeded by D, L-2-amino-5-phosphonopentanoic acid, and was reduced under blockade of synaptosomal platelet-activating factor receptors by ginkgolide B and group I metabotropic glutamate receptors by (R,S)-1-aminoindan-1, 5-dicarboxylic acid. When reduced, potentiation fully developed following the washout of antagonist, demonstrating an involvement of platelet-activating factor and group I metabotropic glutamate receptors in its full development. Potentiation induced by sodium nitroprusside was also associated with a decrease in the paired-pulse facilitation ratio, which persisted under ginkgolide B, indicating that nitric oxide increases glutamate release independently of platelet-activating factor-mediated presynaptic events. We suggest that nitric oxide, released after the activation of N-methyl-D-aspartate receptors, acts as a retrograde messenger leading to an enhancement of glutamate release to a

Xylary pH and Reduction Potential Levels of Iron-stressed Silver Maple (Acer saccharinum L.) 1

PubMed Central

Morris, Robert L.; Swanson, Bert T.

1980-01-01

Xylary fluid pH and reduction potentials were measured on silver maple (Acer saccharinum L.) grown under Fe and pH stress. Although pH and reduction potential (millivolt/59.2) varied significantly in the nutrient solution, xylary pH and reduction potential remained constant. It was concluded that changes in the pH and reduction potential in the xylary fluid of silver maple are not responsible for iron chlorosis. PMID:16661196

Age-related alterations of plasma glutathione and oxidation of redox potentials in chimpanzee (Pan troglodytes) and rhesus monkey (Macaca mulatta).

PubMed

Paredes, Jamespaul; Jones, Dean P; Wilson, Mark E; Herndon, James G

2014-04-01

Chimpanzee (Pan troglodytes) and rhesus macaque (Macaca mulatta) and humans (Homo sapiens) share physiological and genetic characteristics, but have remarkably different life spans, with chimpanzees living 50-60 % and the rhesus living 35-40 % of maximum human survival. Since oxidative processes are associated with aging and longevity, we might expect to see species differences in age-related oxidative processes. Blood and extracellular fluid contain two major thiol redox nodes, glutathione (GSH)/glutathione-disulfide (GSSG) and cysteine (Cys)/cystine (CySS), which are subject to reversible oxidation-reduction reactions and are maintained in a dynamic non-equilibrium state. Disruption of these thiol redox nodes leads to oxidation of their redox potentials (EhGSSG and EhCySS) which affects cellular physiology and is associated with aging and the development of chronic diseases in humans. The purpose of this study was to measure age-related changes in these redox thiols and their corresponding redox potentials (Eh) in chimpanzees and rhesus monkeys. Our results show similar age-related decreases in the concentration of plasma GSH and Total GSH as well as oxidation of the EhGSSG in male and female chimpanzees. Female chimpanzees and female rhesus monkeys also were similar in several outcome measures. For example, similar age-related decreases in the concentration of plasma GSH and Total GSH, as well as age-related oxidation of the EhGSSG were observed. The data collected from chimpanzees and rhesus monkeys corroborates previous reports on oxidative changes in humans and confirms their value as a comparative reference for primate aging.

Wet air oxidation pretreatment of biomethanated distillery effluent: mapping pretreatment efficiency in terms color, toxicity reduction and biogas generation.

PubMed

Sarat Chandra, T; Malik, S N; Suvidha, G; Padmere, M L; Shanmugam, P; Mudliar, S N

2014-04-01

The effluents from molasses-based distilleries after biomethanation are beset with problems of intensified dark brown color, high residual COD, low biodegradability index (BOD/COD ratio <0.2) and toxicity issues for possible land application as a potential fertilizer. Wet air oxidation (WAO) pretreatment of biomethanated distillery effluent resulted in substantial enhancement in the biodegradability index (BI) (up to 0.8). WAO pretreated effluent on anaerobic digestion indicated favorable biogas generation with methane content up to 64% along with concomitant COD reduction up to 54.75%. The HPLC analysis indicated that the pretreatment facilitated degradation of major color containing compounds-namely melanoidins, up to 97.8%. The pretreated effluent with enhanced biodegradability along with substantially reduced color also indicated positive effect on seed germination (up to 100%), implying toxicity reduction of the effluent post WAO pretreatment. Copyright © 2014 Elsevier Ltd. All rights reserved.

Increasing Stability and Activity of Core-Shell Catalysts by Preferential Segregation of Oxide on Edges and Vertexes: Oxygen Reduction on Ti-Au@Pt/C

DOE PAGES

Hu, J.; Wu, L.; Kuttiyiel, K.; ...

2016-06-30

We describe a new class of core-shell nanoparticle catalysts having edges and vertexes covered by refractory metal oxide that preferentially segregates onto these catalyst sites. The monolayer shell is deposited on the oxidefree core atoms. The oxide on edges and vertexes induces high catalyst’s stability and activity. The catalyst and synthesis are exemplified by fabrication of Au nanoparticles doped by Ti atoms that segregate as oxide onto low–coordination sites of edges and vertexes. Pt monolayer shell deposited on Au sites has the mass and specific activities for the oxygen reduction reaction about 13 and 5 times higher than those ofmore » commercial Pt/C catalysts. The durability tests show no activity loss after 10000 potential cycles from 0.6 to 1.0V. The superior activity and durability of the Ti-Au@Pt catalyst originate from protective Ti oxide located at the most dissolution-prone edge and vertex sites, and Au-supported active and stable Pt shell.« less

Metal and Metal Oxide Interactions and Their Catalytic Consequences for Oxygen Reduction Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Qingying; Ghoshal, Shraboni; Li, Jingkun

2017-06-01

Many industrial catalysts are composed of metal particles supported on metal oxides (MMO). It is known that the catalytic activity of MMO materials is governed by metal and metal oxide interactions (MMOI), but how to optimize MMO systems via manipulation of MMOI remains unclear, due primarily to the ambiguous nature of MMOI. Herein, we develop a Pt/NbOx/C system with tunable structural and electronic properties via a modified arc plasma deposition method. We unravel the nature of MMOI by characterizing this system under reactive conditions utilizing combined electrochemical, microscopy, and in situ spectroscopy. We show that Pt interacts with the Nbmore » in unsaturated NbOx owing to the oxygen deficiency in the MMO interface, whereas Pt interacts with the O in nearly saturated NbOx, and further interacts with Nb when the oxygen atoms penetrate into the Pt cluster at elevated potentials. While the Pt–Nb interactions do not benefit the inherent activity of Pt toward oxygen reduction reaction (ORR), the Pt–O interactions improve the ORR activity by shortening the Pt–Pt bond distance. Pt donates electrons to NbOx in both Pt–Nb and Pt–O cases. The resultant electron efficiency stabilizes low-coordinated Pt sites, hereby stabilizing small Pt particles. This determines the two characteristic features of MMO systems: dispersion of small metal particles and high catalytic durability. These findings contribute to our understandings of MMO catalytic systems.« less

Selective CO2 reduction conjugated with H2O oxidation utilizing semiconductor/metal-complex hybrid photocatalysts

NASA Astrophysics Data System (ADS)

Morikawa, T.; Sato, S.; Arai, T.; Uemura, K.; Yamanaka, K. I.; Suzuki, T. M.; Kajino, T.; Motohiro, T.

2013-12-01

We developed a new hybrid photocatalyst for CO2 reduction, which is composed of a semiconductor and a metal complex. In the hybrid photocatalyst, ΔG between the position of conduction band minimum (ECBM) of the semiconductor and the CO2 reduction potential of the complex is an essential factor for realizing fast electron transfer from the conduction band of semiconductor to metal complex leading to high photocatalytic activity. On the basis of this concept, the hybrid photocatalyst InP/Ru-complex, which functions in aqueous media, was developed. The photoreduction of CO2 to formate using water as an electron donor and a proton source was successfully achieved as a Z-scheme system by functionally conjugating the InP/Ru-complex photocatalyst for CO2 reduction with a TiO2 photocatalyst for water oxidation. The conversion efficiency from solar energy to chemical energy was ca. 0.04%, which approaches that for photosynthesis in a plant. Because this system can be applied to many other inorganic semiconductors and metal-complex catalysts, the efficiency and reaction selectivity can be enhanced by optimization of the electron transfer process including the energy-band configurations, conjugation conformations, and catalyst structures. This electrical-bias-free reaction is a huge leap forward for future practical applications of artificial photosynthesis under solar irradiation to produce organic species.

Magnesiothermic reduction for direct synthesis of Ti-Nb alloy at 1073 K (800 °C)

NASA Astrophysics Data System (ADS)

Choi, Kyunsuk; Lee, Kwang Hee; Ali, Basit; Choi, Sang-Hoon; Park, Kyoung-Tae; Sohn, Il

2017-09-01

Direct fabrication of titanium (Ti) and niobium (Nb) alloys by direct magnesiothermic reduction from the respective initial metal oxides and complex oxides has been studied. TiO2, Nb2O5, and complex TiNb2O7 oxides were used as raw materials with Mg used as a reductant. To ensure a high chemical potential of the reactants to drive the spontaneous magnesiothermic reduction of the oxide mixtures, excess Mg five times higher than the required stoichiometric molar ratio was added. Samples were heated in a glove box under recycled and purified Ar atmosphere at 1073 K (800 °C) for 10 h. After the reduction of TiO2, intermediate oxide phases of Ti6O could still be observed, but reduction of Nb2O5 and TiNb2O7 showed metallic Nb and Ti-Nb to be present with negligible oxides according to the scanning electron microscope-energy dispersive spectroscopy and x ray diffraction analysis. This indicated that direct fabrication of Ti-Nb alloys through a complex TiNb2O7 oxide is possible and can be more efficient than alloying pure metallic elements of Ti and Nb.

Factors Driving Potential Ammonia Oxidation in Canadian Arctic Ecosystems: Does Spatial Scale Matter?

PubMed Central

Banerjee, Samiran

2012-01-01

Ammonia oxidation is a major process in nitrogen cycling, and it plays a key role in nitrogen limited soil ecosystems such as those in the arctic. Although mm-scale spatial dependency of ammonia oxidizers has been investigated, little is known about the field-scale spatial dependency of aerobic ammonia oxidation processes and ammonia-oxidizing archaeal and bacterial communities, particularly in arctic soils. The purpose of this study was to explore the drivers of ammonia oxidation at the field scale in cryosols (soils with permafrost within 1 m of the surface). We measured aerobic ammonia oxidation potential (both autotrophic and heterotrophic) and functional gene abundance (bacterial amoA and archaeal amoA) in 279 soil samples collected from three arctic ecosystems. The variability associated with quantifying genes was substantially less than the spatial variability observed in these soils, suggesting that molecular methods can be used reliably evaluate spatial dependency in arctic ecosystems. Ammonia-oxidizing archaeal and bacterial communities and aerobic ammonia oxidation were spatially autocorrelated. Gene abundances were spatially structured within 4 m, whereas biochemical processes were structured within 40 m. Ammonia oxidation was driven at small scales (<1m) by moisture and total organic carbon, whereas gene abundance and other edaphic factors drove ammonia oxidation at medium (1 to 10 m) and large (10 to 100 m) scales. In these arctic soils heterotrophs contributed between 29 and 47% of total ammonia oxidation potential. The spatial scale for aerobic ammonia oxidation genes differed from potential ammonia oxidation, suggesting that in arctic ecosystems edaphic, rather than genetic, factors are an important control on ammonia oxidation. PMID:22081570

Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets

EIA Publications

2012-01-01

Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets is an update to a previous Energy Information Administration (EIA) report, Reductions in Northeast Refining Activity: Potential Implications for Petroleum Product Markets, released in December 2011. This update analyzes possible market responses and impacts in the event Sunoco's Philadelphia refinery closes this summer, in addition to the recently idled refineries on the East Coast and in the U.S. Virgin Islands.

Ce-Sn binary oxide catalyst for the selective catalytic reduction of NOx by NH3

NASA Astrophysics Data System (ADS)

Liu, Zhiming; Feng, Xu; Zhou, Zizheng; Feng, Yongjun; Li, Junhua

2018-01-01

Ce-Sn binary oxide catalysts prepared by the hydrothermal method have been investigated for the selective catalytic reduction (SCR) of NOx with NH3. Compared with pure CeO2 and SnO2, Ce-Sn binary oxide catalyst showed significantly higher NH3-SCR activity. Moreover, Ce-Sn catalyst showed high resistance against H2O and SO2. The high catalytic performance of Ce-Sn binary oxide is attributed to the synergetic effect between Ce and Sn species, which not only enhances the redox property of the catalyst but also increases the Lewis acidity, thus promoting the adsorption and activation of NH3 species, which contributes to improving the NH3-SCR performance.

2,3-diaminopyridine functionalized reduced graphene oxide-supported palladium nanoparticles with high activity for electrocatalytic oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Yasmin, Sabina; Joo, Yuri; Jeon, Seungwon

2017-06-01

The electrochemical deposition of Pd nanoparticles (Pd NPs) on 2,3 diamino pyridine functionalized reduced graphene oxide (2,3 DAP-rGO/Pd) has been investigated for the oxygen reduction reaction (ORR) in alkaline media. First, 2,3 diaminopyridine functionalized graphene oxide (2,3 DAP-rGO) has been synthesized via simple hydrothermal method. Then, palladium is directly incorporated into the 2,3 DAP-rGO by electrochemical deposition method to generate 2,3 DAP-rGO/Pd composites. The as-prepared material 2,3 DAP-rGO/Pd has been characterized by various instrumental methods. The morphological analysis shows the cluster-like Pd nanoparticles are dispersed onto the 2,3 diamino pyridine functionalized reduced graphene oxide (2,3 DAP-rGO). The electrocatalytic activities have been verified using cyclic voltammetry (CV) and hydrodynamic voltammetry and chronoamperometry techniques in 0.1 M KOH electrolyte. The as-synthesized 2,3 DAP-rGO/Pd shows higher catalytic activity toward ORR with more positive onset potential and cathodic current density, superior methanol/ethanol tolerance and excellent stability in alkaline medium. It is also noteworthy that the 2,3 DAP-rGO/Pd exhibits a four-electron transfer pathway for ORR with lower H2O2 yield.

Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R.

2015-09-05

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than - 0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poisedmore » at - 0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ΔcbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below - 0.1 V vs. SHE.« less

Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens.

PubMed

Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R

2016-02-01

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than -0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poised at -0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ∆cbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below -0.1 V vs. SHE. Copyright © 2015. Published by Elsevier B.V.

Monte Carlo simulations of safeguards neutron counter for oxide reduction process feed material

NASA Astrophysics Data System (ADS)

Seo, Hee; Lee, Chaehun; Oh, Jong-Myeong; An, Su Jung; Ahn, Seong-Kyu; Park, Se-Hwan; Ku, Jeong-Hoe

2016-10-01

One of the options for spent-fuel management in Korea is pyroprocessing whose main process flow is the head-end process followed by oxide reduction, electrorefining, and electrowining. In the present study, a well-type passive neutron coincidence counter, namely, the ACP (Advanced spent fuel Conditioning Process) safeguards neutron counter (ASNC), was redesigned for safeguards of a hot-cell facility related to the oxide reduction process. To this end, first, the isotopic composition, gamma/neutron emission yield and energy spectrum of the feed material ( i.e., the UO2 porous pellet) were calculated using the OrigenARP code. Then, the proper thickness of the gammaray shield was determined, both by irradiation testing at a standard dosimetry laboratory and by MCNP6 simulations using the parameters obtained from the OrigenARP calculation. Finally, the neutron coincidence counter's calibration curve for 100- to 1000-g porous pellets, in consideration of the process batch size, was determined through simulations. Based on these simulation results, the neutron counter currently is under construction. In the near future, it will be installed in a hot cell and tested with spent fuel materials.

Sequential reductive and oxidative biodegradation of chloroethenes stimulated in a coupled bioelectro-process.

PubMed

Lohner, Svenja T; Becker, Dirk; Mangold, Klaus-Michael; Tiehm, Andreas

2011-08-01

This article for the first time demonstrates successful application of electrochemical processes to stimulate sequential reductive/oxidative microbial degradation of perchloroethene (PCE) in mineral medium and in contaminated groundwater. In a flow-through column system, hydrogen generation at the cathode supported reductive dechlorination of PCE to cis-dichloroethene (cDCE), vinyl chloride (VC), and ethene (ETH). Electrolytically generated oxygen at the anode allowed subsequent oxidative degradation of the lower chlorinated metabolites. Aerobic cometabolic degradation of cDCE proved to be the bottleneck for complete metabolite elimination. Total removal of chloroethenes was demonstrated for a PCE load of approximately 1.5 μmol/d. In mineral medium, long-term operation with stainless steel electrodes was demonstrated for more than 300 days. In contaminated groundwater, corrosion of the stainless steel anode occurred, whereas DSA (dimensionally stable anodes) proved to be stable. Precipitation of calcareous deposits was observed at the cathode, resulting in a higher voltage demand and reduced dechlorination activity. With DSA and groundwater from a contaminated site, complete degradation of chloroethenes in groundwater was obtained for two months thus demonstrating the feasibility of the sequential bioelectro-approach for field application.

A case study of the relative effects of power plant nitrogen oxides and sulfur dioxide emission reductions on atmospheric nitrogen deposition.

PubMed

Vijayaraghavan, Krish; Seigneur, Christian; Bronson, Rochelle; Chen, Shu-Yun; Karamchandani, Prakash; Walters, Justin T; Jansen, John J; Brandmeyer, Jo Ellen; Knipping, Eladio M

2010-03-01

The contrasting effects of point source nitrogen oxides (NOx) and sulfur dioxide (SO2) air emission reductions on regional atmospheric nitrogen deposition are analyzed for the case study of a coal-fired power plant in the southeastern United States. The effect of potential emission reductions at the plant on nitrogen deposition to Escambia Bay and its watershed on the Florida-Alabama border is simulated using the three-dimensional Eulerian Community Multiscale Air Quality (CMAQ) model. A method to quantify the relative and individual effects of NOx versus SO2 controls on nitrogen deposition using air quality modeling results obtained from the simultaneous application of NOx and SO2 emission controls is presented and discussed using the results from CMAQ simulations conducted with NOx-only and SO2-only emission reductions; the method applies only to cases in which ambient inorganic nitrate is present mostly in the gas phase; that is, in the form of gaseous nitric acid (HNO3). In such instances, the individual effects of NOx and SO2 controls on nitrogen deposition can be approximated by the effects of combined NOx + SO2 controls on the deposition of NOy, (the sum of oxidized nitrogen species) and reduced nitrogen species (NHx), respectively. The benefit of controls at the plant in terms of the decrease in nitrogen deposition to Escambia Bay and watershed is less than 6% of the overall benefit due to regional Clean Air Interstate Rule (CAIR) controls.

Oxide_Oxide Ceramic Matrix Composite (CMC) Exhaust Mixer Development in the NASA Environmentally Responsible Aviation (ERA) Project

NASA Technical Reports Server (NTRS)

Kiser, J. Douglas; Bansal, Narottam P.; Szelagowski, James; Sokhey, Jagdish; Heffernan, Tab; Clegg, Joseph; Pierluissi, Anthony; Riedell, Jim; Wyen, Travis; Atmur, Steven;

Plasma Jet Printing and in Situ Reduction of Highly Acidic Graphene Oxide.

PubMed

Dey, Avishek; Krishnamurthy, Satheesh; Bowen, James; Nordlund, Dennis; Meyyappan, M; Gandhiraman, Ram P

2018-05-23

Miniaturization of electronic devices and the advancement of Internet of Things pose exciting challenges to develop technologies for patterned deposition of functional nanomaterials. Printed and flexible electronic devices and energy storage devices can be embedded onto clothing or other flexible surfaces. Graphene oxide (GO) has gained much attention in printed electronics due its solution processability, robustness, and high electrical conductivity in the reduced state. Here, we introduce an approach to print GO films from highly acidic suspensions with in situ reduction using an atmospheric pressure plasma jet. Low-temperature plasma of a He and H 2 mixture was used successfully to reduce a highly acidic GO suspension (pH < 2) in situ during deposition. This technique overcomes the multiple intermediate steps required to increase the conductivity of deposited GO. X-ray spectroscopic studies confirmed that the reaction intermediates and the concentration of oxygen functionalities bonded to GO have been reduced significantly by this approach without any additional steps. Moreover, the reduced GO films showed enhanced conductivity. Hence, this technique has a strong potential for printing conducting patterns of GO for a range of large-scale applications.

Copper increases the ability of 6-hydroxydopamine to generate oxidative stress and the ability of ascorbate and glutathione to potentiate this effect: potential implications in Parkinson's disease.

PubMed

Cruces-Sande, Antón; Méndez-Álvarez, Estefanía; Soto-Otero, Ramón

2017-06-01

Copper is an essential metal for the function of many proteins related to important cellular reactions and also involved in the synaptic transmission. Although there are several mechanisms involved in copper homeostasis, a dysregulation in this process can result in serious neurological consequences, including degeneration of dopaminergic neurons. 6-Hydroxydopamine is a dopaminergic neurotoxin mainly used in experimental models of Parkinson's disease, whose neurotoxicity has been related to its ability to generate free radicals. In this study, we examined the effects induced by copper on 6-OHDA autoxidation. Our data show that both Cu + and Cu 2+ caused an increase in • OH production by 6-OHDA autoxidation, which was accompanied by an increase in the rate of both p-quinone formation and H 2 O 2 accumulation. The presence of ascorbate greatly enhanced this process by establishing a redox cycle which regenerates 6-OHDA from its p-quinone. However, the presence of glutathione did not change significantly the copper-induced effects. We observed that copper is able to potentiate the ability of 6-OHDA to cause both lipid peroxidation and protein oxidation, with the latter including a reduction in free-thiol content and an increase in carbonyl content. Ascorbate also increases the lipid peroxidation induced by the action of copper and 6-OHDA. Glutathione protects against the copper-induced lipid peroxidation, but does not reduce its potential to oxidize free thiols. These results clearly demonstrate the potential of copper to increase the capacity of 6-OHDA to generate oxidative stress and the ability of ascorbate to enhance this potential, which may contribute to the destruction of dopaminergic neurons. © 2017 International Society for Neurochemistry.

Effect of Precursor Selection on the Photocatalytic Performance of Indium Oxide Nanomaterials for Gas-Phase CO 2 Reduction

DOE PAGES

Hoch, Laura B.; He, Le; Qiao, Qiao; ...

2016-06-01

Nonstoichiometric indium oxide nanoparticles, In 2O 3–x(OH)y, have been shown to function as active photocatalysts for gas-phase CO 2 reduction under simulated solar irradiation. We demonstrate that the choice of starting material has a strong effect on the photocatalytic activity of indium oxide nanoparticles. We also examine three indium oxide materials prepared via the thermal decomposition of either indium(III) hydroxide or indium(III) nitrate and correlate their stability and photocatalytic activity to the number and type of defect present in the material. Furthermore, we use 13CO 2 isotope-tracing experiments to clearly identify the origins of the observed carbon-containing products. Significantly, wemore » find that the oxidizing nature of the precursor anion has a substantial impact on the defect formation within the sample. Our study demonstrates the importance of surface defects in designing an active heterogeneous photocatalyst and provides valuable insight into key parameters for the precursor design, selection, and performance optimization of materials for gas-phase CO 2 reduction.« less

Copper-substituted perovskite compositions for solid oxide fuel cell cathodes and oxygen reduction electrodes in other electrochemical devices

DOEpatents

Rieke, Peter C [Pasco, WA; Coffey, Gregory W [Richland, WA; Pederson, Larry R [Kennewick, WA; Marina, Olga A [Richland, WA; Hardy, John S [Richland, WA; Singh, Prabhaker [Richland, WA; Thomsen, Edwin C [Richland, WA

2010-07-20

The present invention provides novel compositions that find advantageous use in making electrodes for electrochemical cells. Also provided are electrochemical devices that include active oxygen reduction electrodes, such as solid oxide fuel cells, sensors, pumps and the like. The compositions comprises a copper-substituted ferrite perovskite material. The invention also provides novel methods for making and using the electrode compositions and solid oxide fuel cells and solid oxide fuel cell assemblies having cathodes comprising the compositions.

Efficient control of ultrafast optical nonlinearity of reduced graphene oxide by infrared reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattachraya, S.; Maiti, R.; Das, A. C.

Simultaneous occurrence of saturable absorption nonlinearity and two-photon absorption nonlinearity in the same medium is well sought for the devices like optical limiter and laser mode-locker. Pristine graphene sheet consisting entirely of sp{sup 2}-hybridized carbon atoms has already been identified having large optical nonlinearity. However, graphene oxide (GO), a precursor of graphene having both sp{sup 2} and sp{sup 3}-hybridized carbon atom, is increasingly attracting cross-discipline researchers for its controllable properties by reduction of oxygen containing groups. In this work, GO has been prepared by modified Hummers method, and it has been further reduced by infrared (IR) radiation. Characterization of reducedmore » graphene oxide (RGO) by means of Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-Visible absorption measurements confirms an efficient reduction with infrared radiation. Here, we report precise control of non-linear optical properties of RGO in femtosecond regime with increased degrees of IR reduction measured by open aperture z-scan technique. Depending on the intensity, both saturable absorption and two-photon absorption effects are found to contribute to the non-linearity of all the samples. Saturation dominates at low intensity (∼127 GW/cm{sup 2}) while two-photon absorption becomes prominent at higher intensities (from 217 GW/cm{sup 2} to 302 GW/cm{sup 2}). The values of two-photon absorption co-efficient (∼0.0022–0.0037 cm/GW for GO, and ∼0.0128–0.0143 cm/GW for RGO) and the saturation intensity (∼57 GW/cm{sup 2} for GO, and ∼194 GW/cm{sup 2} for RGO) increase with increasing reduction, indicating GO and RGO as novel tunable photonic devices. We have also explained the reason of tunable nonlinear optical properties by using amorphous carbon model.« less

Iron Recovery from Copper Slag Through Oxidation-Reduction Magnetic Concentration at Intermediate Temperature

NASA Astrophysics Data System (ADS)

Wu, Zhiwen; Chen, Chen; Feng, Yahui; Hong, Xin

Large amounts of copper slag containing about 40 wt% iron is generated during the process of producing copper. Recovery of iron from the copper slag is very essential not only for recycling the valuable metals and mineral resources but also for protecting the environment. The purpose of this study was to investigate the possibility of separating fayalite by oxidation-reduction process into Magnetite and silicate phases in intermediate temperature condition. Experimental results show that when the oxidation reaction at 1000°C for 120min and the oxygen flow is 0.1L/min, most fayalite decompose to hematite, less part of magnetite and silica. And then, the mixture of carbon and oxidation product is pressed into blocks and reduced to magnetite and silica at 900°C for 90min. A magnetic product containing about 57.9wt% iron was obtained from the magnetic separation under a magnetic field strength of 100 mT.

The role of iron-oxide aerosols and sunlight in the atmospheric reduction of Hg(II) species: A DFT+ U study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tacey, Sean A.; Szilvasi, Tibor; Xu, Lang

Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl 2 and HgBr 2 undergo reduction to elemental mercury (Hg°), which remains in the atmosphere longer than oxidized mercury species due to its higher volatility. We performed density functional theory (DFT, PW91+U) calculations to elucidate the reduction mechanism for atmospheric HgCl 2 and HgBr 2 to Hg° on several iron-oxide aerosol surfaces relevant in the troposphere. On the OH-Fe-R-terminated α-Fe 2O 3(0001) surface, predicted to be most prevalent under ambient conditions, we show that: (1) the first Hg-Xmore » bond is broken via either thermal or photolytic activation depending on the ambient temperature; (2) photons with an energy of 2.69 eV (461 nm) are required to break the second Hg-X bond; and (3) a photo-induced surface-to-adsorbate charge-transfer process can promote Hg° desorption with an excitation energy of 2.59 eV (479 nm). All the calculated excitation energies are below the threshold value of 3.9 eV (320 nm) for photons in the troposphere, suggesting that sunlight can facilitate mercury reduction on iron-oxide aerosol surfaces. In contrast, the gas-phase reduction of HgCl 2 (HgBr 2) involves photoexcitation requiring an energy of 4.98 (4.45) eV (249 (279) nm); therefore, the energy range of sunlight is not suitable for gas-phase reduction. Our computational results provide the first evidence on the detailed mechanism for the combined role of aerosols and photons in the reduction of HgCl 2 and HgBr 2. In conclusion, our methodology can be adapted to study other photochemical heterogeneous processes in the atmosphere.« less

The role of iron-oxide aerosols and sunlight in the atmospheric reduction of Hg(II) species: A DFT+ U study

DOE PAGES

Tacey, Sean A.; Szilvasi, Tibor; Xu, Lang; ...

2018-04-22

Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl 2 and HgBr 2 undergo reduction to elemental mercury (Hg°), which remains in the atmosphere longer than oxidized mercury species due to its higher volatility. We performed density functional theory (DFT, PW91+U) calculations to elucidate the reduction mechanism for atmospheric HgCl 2 and HgBr 2 to Hg° on several iron-oxide aerosol surfaces relevant in the troposphere. On the OH-Fe-R-terminated α-Fe 2O 3(0001) surface, predicted to be most prevalent under ambient conditions, we show that: (1) the first Hg-Xmore » bond is broken via either thermal or photolytic activation depending on the ambient temperature; (2) photons with an energy of 2.69 eV (461 nm) are required to break the second Hg-X bond; and (3) a photo-induced surface-to-adsorbate charge-transfer process can promote Hg° desorption with an excitation energy of 2.59 eV (479 nm). All the calculated excitation energies are below the threshold value of 3.9 eV (320 nm) for photons in the troposphere, suggesting that sunlight can facilitate mercury reduction on iron-oxide aerosol surfaces. In contrast, the gas-phase reduction of HgCl 2 (HgBr 2) involves photoexcitation requiring an energy of 4.98 (4.45) eV (249 (279) nm); therefore, the energy range of sunlight is not suitable for gas-phase reduction. Our computational results provide the first evidence on the detailed mechanism for the combined role of aerosols and photons in the reduction of HgCl 2 and HgBr 2. In conclusion, our methodology can be adapted to study other photochemical heterogeneous processes in the atmosphere.« less

Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts

DOE PAGES

Verdaguer-Casadevall, Arnau; Li, Christina W.; Johansson, Tobias P.; ...

2015-07-30

CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H 2 reduction of Cu 2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 °C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changesmore » are accompanied by a reduction in the proportion of strong CO binding sites. Here, we propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.« less

Fumaric acid production in Saccharomyces cerevisiae by simultaneous use of oxidative and reductive routes.

PubMed

Xu, Guoqiang; Chen, Xiulai; Liu, Liming; Jiang, Linghuo

2013-11-01

In this study, the simultaneous use of reductive and oxidative routes to produce fumaric acid was explored. The strain FMME003 (Saccharomyces cerevisiae CEN.PK2-1CΔTHI2) exhibited capability to accumulate pyruvate and was used for fumaric acid production. The fum1 mutant FMME004 could produce fumaric acid via oxidative route, but the introduction of reductive route derived from Rhizopus oryzae NRRL 1526 led to lower fumaric acid production. Analysis of the key factors associated with fumaric acid production revealed that pyruvate carboxylase had a low degree of control over the carbon flow to malic acid. The fumaric acid titer was improved dramatically when the heterologous gene RoPYC was overexpressed and 32 μg/L of biotin was added. Furthermore, under the optimal carbon/nitrogen ratio, the engineered strain FMME004-6 could produce up to 5.64 ± 0.16 g/L of fumaric acid. These results demonstrated that the proposed fermentative method is efficient for fumaric acid production. Copyright © 2013 Elsevier Ltd. All rights reserved.

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides

PubMed Central

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-01-01

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG. PMID:24717290

The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.

PubMed

Chuang, C-H; Wang, Y-F; Shao, Y-C; Yeh, Y-C; Wang, D-Y; Chen, C-W; Chiou, J W; Ray, Sekhar C; Pong, W F; Zhang, L; Zhu, J F; Guo, J H

2014-04-10

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp(2) bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

Potential for microbial oxidation of ferrous iron in basaltic glass.

PubMed

Xiong, Mai Yia; Shelobolina, Evgenya S; Roden, Eric E

2015-05-01

Basaltic glass (BG) is an amorphous ferrous iron [Fe(II)]-containing material present in basaltic rocks, which are abundant on rocky planets such as Earth and Mars. Previous research has suggested that Fe(II) in BG can serve as an energy source for chemolithotrophic microbial metabolism, which has important ramifications for potential past and present microbial life on Mars. However, to date there has been no direct demonstration of microbially catalyzed oxidation of Fe(II) in BG. In this study, three different culture systems were used to investigate the potential for microbial oxidation of Fe(II) in BG, including (1) the chemolithoautotrophic Fe(II)-oxidizing, nitrate-reducing "Straub culture"; (2) the mixotrophic Fe(II)-oxidizing, nitrate-reducing organism Desulfitobacterium frappieri strain G2; and (3) indigenous microorganisms from a streambed Fe seep in Wisconsin. The BG employed consisted of clay and silt-sized particles of freshly quenched lava from the TEB flow in Kilauea, Hawaii. Soluble Fe(II) or chemically reduced NAu-2 smectite (RS) were employed as positive controls to verify Fe(II) oxidation activity in the culture systems. All three systems demonstrated oxidation of soluble Fe(II) and/or structural Fe(II) in RS, whereas no oxidation of Fe(II) in BG material was observed. The inability of the Straub culture to oxidize Fe(II) in BG was particularly surprising, as this culture can oxidize other insoluble Fe(II)-bearing minerals such as biotite, magnetite, and siderite. Although the reason for the resistance of the BG toward enzymatic oxidation remains unknown, it seems possible that the absence of distinct crystal faces or edge sites in the amorphous glass renders the material resistant to such attack. These findings have implications with regard to the idea that Fe(II)-Si-rich phases in basalt rocks could provide a basis for chemolithotrophic microbial life on Mars, specifically in neutral-pH environments where acid-promoted mineral dissolution and

Theophylline-assisted, eco-friendly synthesis of PtAu nanospheres at reduced graphene oxide with enhanced catalytic activity towards Cr(VI) reduction.

PubMed

Hu, Ling-Ya; Chen, Li-Xian; Liu, Meng-Ting; Wang, Ai-Jun; Wu, Lan-Ju; Feng, Jiu-Ju

2017-05-01

Theophylline as a naturally alkaloid is commonly employed to treat asthma and chronic obstructive pulmonary disorder. Herein, a facile theophylline-assisted green approach was firstly developed for synthesis of PtAu nanospheres/reduced graphene oxide (PtAu NSs/rGO), without any surfactant, polymer, or seed involved. The obtained nanocomposites were applied for the catalytic reduction and removal of highly toxic chromium (VI) using formic acid as a model reductant at 50°C, showing the significantly enhanced catalytic activity and improved recyclability when compared with commercial Pt/C (50%) and home-made Au nanocrystals supported rGO (Au NCs/rGO). It demonstrates great potential applications of the catalyst in wastewater treatment and environmental protection. The eco-friendly route provides a new platform to fabricate other catalysts with enhanced catalytic activity. Copyright © 2016 Elsevier Inc. All rights reserved.

Reduction of Mn-oxides by ferrous iron in a flow system: column experiment and reactive transport modeling

NASA Astrophysics Data System (ADS)

Postma, D.; Appelo, C. A. J.

2000-04-01

The reduction of Mn-oxide by Fe2+ was studied in column experiments, using a column filled with natural Mn-oxide coated sand. Analysis of the Mn-oxide indicated the presence of both Mn(III) and Mn(IV) in the Mn-oxide. The initial exchange capacity of the column was determined by displacement of adsorbed Ca2+ with Mg2+. Subsequently a FeCl2 solution was injected into the column causing the reduction of the Mn-oxide and the precipitation of Fe(OH)3. Finally the exchange capacity of the column containing newly formed Fe(OH)3 was determined by injection of a KBr solution. During injection of the FeCl2 solution into the column, an ion distribution pattern was observed in the effluent that suggests the formation of separate reaction fronts for Mn(III)-oxide and Mn(IV)-oxide travelling at different velocities through the column. At the proximal reaction front, Fe2+ reacts with MnO2 producing Fe(OH)3, Mn2+ and H+. The protons are transported downstream and cause the disproportionation of MnOOH at a separate reaction front. Between the two Mn reaction fronts, the dissolution and precipitation of Fe(OH)3 and Al(OH)3 act as proton buffers. Reactive transport modeling, using the code PHREEQC 2.0, was done to quantify and analyze the reaction controls and the coupling between transport and chemical processes. A model containing only mineral equilibria constraints for birnessite, manganite, gibbsite, and ferrihydrite, was able to explain the overall reaction pattern with the sequential appearance of Mn2+, Al3+, Fe3+, and Fe2+ in the column outlet solution. However, the initial breakthrough of a peak of Ca2+ and the observed pH buffering indicated that exchange processes were of importance as well. The amount of potential exchangers, such as birnessite and ferrihydrite, did vary in the course of the experiment. A model containing surface complexation coupled to varying concentrations of birnessite and ferrihydrite and a constant charge exchanger in addition to mineral equilibria

Evidence of a reduction reaction of oxidized iron/cobalt by boron atoms diffused toward naturally oxidized surface of CoFeB layer during annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Soshi, E-mail: sato.soshi@cies.tohoku.ac.jp; Honjo, Hiroaki; Niwa, Masaaki

2015-04-06

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer.more » The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO{sub 2}, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram.« less

The variations of Oxidation-Reduction Potential in paddy soil and effects on the methane emission from a periodically irrigated paddy field.

NASA Astrophysics Data System (ADS)

Yagi, K.; Iwata, T.; Wakikuromaru, N.

2014-12-01

Paddy fields are one of the most important eco-system in monsoon Asia and one of the largest source of CH4 emission. CH4 has significant contribution to the global warming next to CO2 and its greenhouse effect is about 21 times as large as same amount of CO2. CH4 is generated by decomposition of organic matter in soil under anaerobic condition. Oxidation-Reduction Potential (ORP) is the most suitable index representing soil aerobic condition. Or, CH4 is more generated under lower ORP conditions. In this study, ORP in paddy soil was measured during rice cultivated season at a periodically irrigated paddy field, and some effects on the methane flux from the paddy soil was investigated. 3-days flood and 4-days drained condition were regularly repeated at the site from late-June to early October. ORP under flooded condition was measured during irrigated term in 2013 at two mode; regular interval measurement every 2 weeks and intensive measurements during two flooded periods. Methane flux was also measured by the aerodynamic gradient technique. ORP showed rapid decrease when irrigation water was introduced in the paddy field, and lower ORP was shown under the longer flooded condition. From the seasonal-term point of view, lower ORP was shown in later rice season. ORP was suitably modeled as a function of irrigation time. During an irrigation period for four days, higher methane emissions were shown under lower OPR conditions as shown in Fig.1. From the seasonal-term point of view, however, no significant relationship between ORP and methane fluxes. Rapid rise of CH4 flux in early August and gradual decrease between late August and September were shown. It is suggested that seasonal change of methane flux is affected by seasonal changes of soil temperature or the growth level of rice plants.

Chemoselective reduction and oxidation of ketones in water through control of the electron transfer pathway

PubMed Central

Kim, Sun Min; Yoo, Ho Sung; Hosono, Hideo; Yang, Jung Woon; Kim, Sung Wng

2015-01-01

The selective synthesis of different products from the same starting materials in water, which is the most abundant solvent in nature, is a crucial issue as it maximizes the utilization of materials. Realizing such reactions for ketones is of considerable importance because numerous organic functionalities can be obtained via nucleophilic addition reactions. Herein, we report chemoselective reduction and oxidation reactions of 1,2-diketones in water, which initiates anionic electron transfer from the inorganic electride [Ca24Al28O64]4+·4e−, through controlling the pathway of the electrons to substrates. The generation of different radical species for transient intermediates was the key process required to control the reaction selectivity, which was achieved by reacting the anionic electrons with either diketones or O2, leading to the formation of ketyl dianion and superoxide radicals in the reduction and oxidation reactions, respectively. This methodology that utilizes electrides may provide an alternative to the pulse radiolysis of water in synthetic chemistry. PMID:26020413

Predicting Reduction Rates of Energetic Nitroaromatic Compounds Using Calculated One-Electron Reduction Potentials

DOE PAGES

Salter-Blanc, Alexandra; Bylaska, Eric J.; Johnston, Hayley; ...

2015-02-11

The evaluation of new energetic nitroaromatic compounds (NACs) for use in green munitions formulations requires models that can predict their environmental fate. The susceptibility of energetic NACs to nitro reduction might be predicted from correlations between rate constants (k) for this reaction and one-electron reduction potentials (E1NAC) / 0.059 V, but the mechanistic implications of such correlations are inconsistent with evidence from other methods. To address this inconsistency, we have reevaluated existing kinetic data using a (non-linear) free-energy relationship (FER) based on the Marcus theory of outer-sphere electron transfer. For most reductants, the results are inconsistent with rate limitation bymore » an initial, outer-sphere electron transfer, suggesting that the strong correlation between k and E1NAC is justified only as an empirical model. This empirical correlation was used to calibrate a new quantitative structure-activity relationship (QSAR) using previously reported values of k for non-energetic NAC reduction by Fe(II) porphyrin and newly reported values of E1NAC determined using density functional theory at the B3LYP/6-311++G(2d,2p) level with the COSMO solvation model. The QSAR was then validated for energetic NACs using newly measured kinetic data for 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,4-dinitroanisole (DNAN). The data show close agreement with the QSAR, supporting its applicability to energetic NACs.« less

Mercury oxidation promoted by a selective catalytic reduction catalyst under simulated Powder River Basin coal combustion conditions.

PubMed

Lee, Chun W; Serre, Shannon D; Zhao, Yongxin; Lee, Sung Jun; Hastings, Thomas W

2008-04-01

A bench-scale reactor consisting of a natural gas burner and an electrically heated reactor housing a selective catalytic reduction (SCR) catalyst was constructed for studying elemental mercury (Hg(o)) oxidation under SCR conditions. A low sulfur Powder River Basin (PRB) subbituminous coal combustion fly ash was injected into the entrained-flow reactor along with sulfur dioxide (SO2), nitrogen oxides (NOx), hydrogen chloride (HCl), and trace Hg(o). Concentrations of Hg(o) and total mercury (Hg) upstream and downstream of the SCR catalyst were measured using a Hg monitor. The effects of HCl concentration, SCR operating temperature, catalyst space velocity, and feed rate of PRB fly ash on Hg(o) oxidation were evaluated. It was observed that HCl provides the source of chlorine for Hg(o) oxidation under simulated PRB coal-fired SCR conditions. The decrease in Hg mass balance closure across the catalyst with decreasing HCl concentration suggests that transient Hg capture on the SCR catalyst occurred during the short test exposure periods and that the outlet speciation observed may not be representative of steady-state operation at longer exposure times. Increasing the space velocity and operating temperature of the SCR led to less Hg(o) oxidized. Introduction of PRB coal fly ash resulted in slightly decreased outlet oxidized mercury (Hg2+) as a percentage of total inlet Hg and correspondingly resulted in an incremental increase in Hg capture. The injection of ammonia (NH3) for NOx reduction by SCR was found to have a strong effect to decrease Hg oxidation. The observations suggest that Hg(o) oxidation may occur near the exit region of commercial SCR reactors. Passage of flue gas through SCR systems without NH3 injection, such as during the low-ozone season, may also impact Hg speciation and capture in the flue gas.

Giant refractive-index modulation by two-photon reduction of fluorescent graphene oxides for multimode optical recording.

PubMed

Li, Xiangping; Zhang, Qiming; Chen, Xi; Gu, Min

2013-10-02

Graphene oxides (GOs) have emerged as precursors offering the potential of a cost-effective and large-scale production of graphene-based materials. Despite that their intrinsic fluorescence property has already brought interest of researchers for optical applications, to date, refractive-index modulation as one of the fundamental aspects of optical properties of GOs has received less attention. Here we reported on a giant refractive-index modulation on the order of 10(-2) to 10(-1), accompanied by a fluorescence intensity change, through the two-photon reduction of GOs. These features enabled a mechanism for multimode optical recording with the fluorescence contrast and the hologram-encoded refractive-index modulation in GO-dispersed polymers for security-enhanced high-capacity information technologies. Our results show that GO-polymer composites may provide a new material platform enabling flexible micro-/nano-photonic information devices.

The Effect of Reduction Potential on the Generation of the Perylene Diimide Radical Anions

NASA Astrophysics Data System (ADS)

Zhao, Y. Z.; Li, K. X.; Ding, S. Y.; Zhu, M.; Ren, H. P.; Ma, Q.; Guo, Z.; Tian, S. P.; Zhang, H. Q.; Miao, Z. C.

2018-07-01

Perylene diimide derivatives (PDIs) with different substituents in the bay positions (Un-PDI, DFPDI and THBPDI) were chosen in this report to investigate the effect of potential on the reduction of PDIs through base (hydrazine, 1,2-ethanediamine and triethylamine)-driven keto-enol anion tautomerism. The reduction potentials (PDI/PDI•-) of these compounds determined via cyclic voltammetry are -0.51, ‒0.34, and -0.098 V for Un-PDI, DFPDI, and THBPDI, respectively. The reduction of Un-PDI, DFPDI and THBPDI by hydrazine can produce corresponding radical anions and dianions, but the volume of hydrazine added at which the radicals started to appear is different and depends on their reduction potential. The similar phenomenon was observed using 1,2-ethylenediamine and triethylamine. However, only the radical anion was obtained even in a large excess of 1,2-ethanediamine or triethylamine. Moreover, the reduction of these PDIs with different bases added in the same amount was investigated, and the correlation with their basicity was shown.

Reduction Potentials of [FeFe]-Hydrogenase Accessory Iron-Sulfur Clusters Provide Insights into the Energetics of Proton Reduction Catalysis.

PubMed

Artz, Jacob H; Mulder, David W; Ratzloff, Michael W; Lubner, Carolyn E; Zadvornyy, Oleg A; LeVan, Axl X; Williams, S Garrett; Adams, Michael W W; Jones, Anne K; King, Paul W; Peters, John W

2017-07-19

An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H 2 activation. In addition to the catalytic H-cluster, CpI contains four accessory iron-sulfur [FeS] clusters in a branched series that transfer electrons to and from the active site. In this work, potentiometric titrations have been employed in combination with electron paramagnetic resonance (EPR) spectroscopy at defined electrochemical potentials to gain insights into the role of the accessory clusters in catalysis. EPR spectra collected over a range of potentials were deconvoluted into individual components attributable to the accessory [FeS] clusters and the active site H-cluster, and reduction potentials for each cluster were determined. The data suggest a large degree of magnetic coupling between the clusters. The distal [4Fe-4S] cluster is shown to have a lower reduction potential (∼ < -450 mV) than the other clusters, and molecular docking experiments indicate that the physiological electron donor, ferredoxin (Fd), most favorably interacts with this cluster. The low reduction potential of the distal [4Fe-4S] cluster thermodynamically restricts the Fd ox /Fd red ratio at which CpI can operate, consistent with the role of CpI in recycling Fd red that accumulates during fermentation. Subsequent electron transfer through the additional accessory [FeS] clusters to the H-cluster is thermodynamically favorable.

Melanoma Inhibition by Anthocyanins Is Associated with the Reduction of Oxidative Stress Biomarkers and Changes in Mitochondrial Membrane Potential.

PubMed

Diaconeasa, Zoriţa; Ayvaz, Huseyin; Ruginǎ, Dumitriţa; Leopold, Loredana; Stǎnilǎ, Andreea; Socaciu, Carmen; Tăbăran, Flaviu; Luput, Lavinia; Mada, Diana Carla; Pintea, Adela; Jefferson, Andrew

2017-12-01

Anthocyanins are water soluble pigments which have been proved to exhibit health benefits. Several studies have investigated their effects on several types of cancer, but little attention has been given to melanoma. The phytochemical content of nine different berry samples was assessed by liquid chromatography followed by electrospray ionization mass spectrometry (LC-ESI + -MS). Twenty-six anthocyanins were identified, after a previous C 18 Sep-pak clean-up procedure. Chokeberry and red grape anthocyanins rich extracts (C-ARE and RG-ARE) were selected to be tested on normal and melanoma cell lines, due to their different chemical pattern. C-ARE composition consists of cyanidin aglycone glycosylated with different sugars; while RG-ARE contains glucosylated derivatives of five different aglycones. Both C-ARE and RG-ARE anthocyanins reduced proliferation, increased oxidative stress biomarkers and diminished mitochondrial membrane potential in melanoma cells, having no negative influence on normal cells. A synergistic response may be attributed to the five different aglycones present in RG-ARE, which proved to exert greater effects on melanoma cells than the mixture of cyanidin derivatives with different sugars (C-ARE). In conclusion, C-ARE and RG-ARE anthocyanins may inhibit melanoma cell proliferation and increase the level of oxidative stress, with opposite effect on normal cells. Therefore, anthocyanins might be recommended as active ingredients for cosmetic and nutraceutical industry. Graphical Abstract ᅟ.

Fatty Acid Biosynthesis Inhibition Increases Reduction Potential in Neuronal Cells under Hypoxia.

PubMed

Brose, Stephen A; Golovko, Svetlana A; Golovko, Mikhail Y

2016-01-01

Recently, we have reported a novel neuronal specific pathway for adaptation to hypoxia through increased fatty acid (FA) biosynthesis followed by esterification into lipids. However, the biological role of this pathway under hypoxia remains to be elucidated. In the presented study, we have tested our hypothesis that activation of FA synthesis maintains reduction potential and reduces lactoacidosis in neuronal cells under hypoxia. To address this hypothesis, we measured the effect of FA synthesis inhibition on [Formula: see text]/NAD + and [Formula: see text]/NADP + ratios, and lactic acid levels in neuronal SH-SY5Y cells exposed to normoxic and hypoxic conditions. FA synthesis inhibitors, TOFA (inhibits Acetyl-CoA carboxylase) and cerulenin (inhibits FA synthase), increased [Formula: see text]/NAD + and [Formula: see text]/NADP + ratios under hypoxia. Further, FA synthesis inhibition increased lactic acid under both normoxic and hypoxic conditions, and caused cytotoxicity under hypoxia but not normoxia. These results indicate that FA may serve as hydrogen acceptors under hypoxia, thus supporting oxidation reactions including anaerobic glycolysis. These findings may help to identify a radically different approach to attenuate hypoxia related pathophysiology in the nervous system including stroke.

Fatty Acid Biosynthesis Inhibition Increases Reduction Potential in Neuronal Cells under Hypoxia

PubMed Central

Brose, Stephen A.; Golovko, Svetlana A.; Golovko, Mikhail Y.

2016-01-01

Recently, we have reported a novel neuronal specific pathway for adaptation to hypoxia through increased fatty acid (FA) biosynthesis followed by esterification into lipids. However, the biological role of this pathway under hypoxia remains to be elucidated. In the presented study, we have tested our hypothesis that activation of FA synthesis maintains reduction potential and reduces lactoacidosis in neuronal cells under hypoxia. To address this hypothesis, we measured the effect of FA synthesis inhibition on NADH2+/NAD+ and NADPH2+/NADP+ ratios, and lactic acid levels in neuronal SH-SY5Y cells exposed to normoxic and hypoxic conditions. FA synthesis inhibitors, TOFA (inhibits Acetyl-CoA carboxylase) and cerulenin (inhibits FA synthase), increased NADH2+/NAD+ and NADPH2+/NADP+ ratios under hypoxia. Further, FA synthesis inhibition increased lactic acid under both normoxic and hypoxic conditions, and caused cytotoxicity under hypoxia but not normoxia. These results indicate that FA may serve as hydrogen acceptors under hypoxia, thus supporting oxidation reactions including anaerobic glycolysis. These findings may help to identify a radically different approach to attenuate hypoxia related pathophysiology in the nervous system including stroke. PMID:27965531

Oxidative potential of subway PM2.5