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Sample records for aqueous acidic solution

  1. Unusual hydrophobic interactions in acidic aqueous solutions.

    PubMed

    Chen, Hanning; Xu, Jianqing; Voth, Gregory A

    2009-05-21

    Hydrophobic interaction, which is believed to be a primary driving force for many fundamental chemical and biological processes such as nanostructure self-assembly, micelle formation, and protein folding, is different in acidic aqueous solutions compared to salt solutions. In this study, the aggregation/dispersion behavior of nonpolar hydrophobic molecules in aqueous solutions with varying acid (HCl) concentrations is investigated using novel molecular dynamics simulations and compared to the hydrophobic behavior in corresponding salt (NaCl) solutions. The formation of unusual weakly bound hydrophobe-hydrated proton solvation structures is observed and can be attributed to the unique "amphiphilic" characteristic of hydrated protons. This molecular-level mechanism for the acid-enhanced dissolution of hydrophobic particles also provides a novel interpretation for the apparent anomaly of the hydronium cation in the Hofmeister series.

  2. NIR spectroscopic properties of aqueous acids solutions.

    PubMed

    Omar, Ahmad Fairuz; Atan, Hanafi; Matjafri, Mohd Zubir

    2012-06-15

    Acid content is one of the important quality attributes in determining the maturity index of agricultural product, particularly fruits. Despite the fact that much research on the measurement of acidity in fruits through non-destructive spectroscopy analysis at NIR wavelengths between 700 to 1,000 nm has been conducted, the same response towards individual acids is not well known. This paper presents NIR spectroscopy analysis on aqueous citric, tartaric, malic and oxalic solutions through quantitative analysis by selecting a set of wavelengths that can best be used to measure the pH of the solutions. The aquaphotomics study of the acid solutions has generated R² above 0.9 for the measurement of all acids. The most important wavelengths for pH are located at 918-925 nm and 990-996 nm, while at 975 nm for water.

  3. Speciation in aqueous solutions of nitric acid.

    PubMed

    Hlushak, S; Simonin, J P; De Sio, S; Bernard, O; Ruas, A; Pochon, P; Jan, S; Moisy, P

    2013-02-28

    In this study, speciation in aqueous solutions of nitric acid at 25 °C was assessed in two independent ways. First, Raman experiments were carried out and interpreted in terms of free nitrate ions, ion pairs and neutral HNO(3) molecules. In parallel, a model was developed to account for the formation of these two kinds of pairs. It was based on an extension of the binding mean spherical approximation (BiMSA), or associative MSA (AMSA), in which the size and the charge of the ions in the chemical pair may differ from those of the free ions. A simultaneous fit of the osmotic coefficient and of the proportion of free ions (obtained from Raman spectroscopy experiments) led to an estimation of the speciation in nitric acid solutions. The result obtained using this procedure was compared with the estimation obtained from the Raman experiments.

  4. Uranyl fluoride luminescence in acidic aqueous solutions

    SciTech Connect

    Beitz, J.V.; Williams, C.W.

    1996-08-01

    Luminescence emission spectra and decay rates are reported for uranyl species in acidic aqueous solutions containing HF or added NaF. The longest luminescence lifetime, 0.269 {+-} 0.006 ms, was observed from uranyl in 1 M HF + 1 M HClO{sub 4} at 296 K and decreased with increasing temperature. Based on a luminescence dynamics model that assumes equilibrium among electronically excited uranyl fluoride species and free fluoride ion, this long lived uranyl luminescence in aqueous solution is attributed primarily to UO{sub 2}F{sub 2}. Studies on the effect of added LiNO{sub 3} or Na{sub 2}WO{sub 4}{center_dot}2H{sub 2}O showed relatively weak quenching of uranyl fluoride luminescence which suggests that high sensitivity determination of the UF{sub 6} content of WF{sub 6} gas should be feasible via uranyl luminescence analysis of hydrolyzed gas samples of impure WF{sub 6}.

  5. RECOVERY OF ACTINIDES FROM AQUEOUS NITRIC ACID SOLUTIONS

    DOEpatents

    Ader, M.

    1963-11-19

    A process of recovering actinides is presented. Tetravalent actinides are extracted from rare earths in an aqueous nitric acid solution with a ketone and back-extracted from the ketone into an aqueous medium. The aqueous actinide solution thus obtained, prior to concentration by boiling, is sparged with steam to reduce its ketone to a maximum content of 3 grams per liter. (AEC)

  6. Acidities of Water and Methanol in Aqueous Solution and DMSO

    ERIC Educational Resources Information Center

    Gao, Daqing

    2009-01-01

    The relative acidities of water and methanol have been a nagging issue. In gas phase, methanol is more acidic than water by 36.0 kJ/mol; however, in aqueous solution, the acidities of methanol and water are almost identical. The acidity of an acid in solution is determined by both the intrinsic gas-phase ionization Gibbs energy and the solvent…

  7. Acidities of Water and Methanol in Aqueous Solution and DMSO

    ERIC Educational Resources Information Center

    Gao, Daqing

    2009-01-01

    The relative acidities of water and methanol have been a nagging issue. In gas phase, methanol is more acidic than water by 36.0 kJ/mol; however, in aqueous solution, the acidities of methanol and water are almost identical. The acidity of an acid in solution is determined by both the intrinsic gas-phase ionization Gibbs energy and the solvent…

  8. Polymerization of beta-amino acids in aqueous solution

    NASA Technical Reports Server (NTRS)

    Liu, R.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    1998-01-01

    We have compared carbonyl diimidazole (CDI) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) as activating agents for the oligomerization of negatively-charged alpha- and beta-amino acids in homogeneous aqueous solution. alpha-Amino acids can be oligomerized efficiently using CDI, but not by EDAC. beta-Amino acids can be oligomerized efficiently using EDAC, but not by CDI. Aspartic acid, an alpha- and beta-dicarboxylic acid is oligomerized efficiently by both reagents. These results are explained in terms of the mechanisms of the reactions, and their relevance to prebiotic chemistry is discussed.

  9. Polymerization of beta-amino acids in aqueous solution

    NASA Technical Reports Server (NTRS)

    Liu, R.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    1998-01-01

    We have compared carbonyl diimidazole (CDI) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) as activating agents for the oligomerization of negatively-charged alpha- and beta-amino acids in homogeneous aqueous solution. alpha-Amino acids can be oligomerized efficiently using CDI, but not by EDAC. beta-Amino acids can be oligomerized efficiently using EDAC, but not by CDI. Aspartic acid, an alpha- and beta-dicarboxylic acid is oligomerized efficiently by both reagents. These results are explained in terms of the mechanisms of the reactions, and their relevance to prebiotic chemistry is discussed.

  10. Solubility of uranous sulfate in aqueous sulfuric acid solution

    NASA Astrophysics Data System (ADS)

    Suzuki, Shigeru; Hirono, Shuichiro; Awakura, Yasuhiro; Majima, Hiroshi

    1990-10-01

    To provide important thermodynamic data for use in uranium hydrometallurgy, solubilities of uranous sulfate were determined as a function of free acid concentration and temperature. Two sets of experiments were performed in this study. One set was the precipitation experiments of uranous sulfate crystals, in which concentrated uranous sulfate solution was mixed with sulfuric acid solution of suitable concentration. The other set was the dissolution experiments of uranous sulfate crystals in aqueous sulfuric acid solutions. It is noteworthy that good agreement exists between the solubilities determined by the two methods. At elevated temperatures, say, 363 K, the presence of free sulfuric acid is required to avoid precipitation of uranous hydroxide resulting from the hydrolysis of uranous sulfate. Generally speaking, however, an increase in free sulfuric acid concentration results in a slight decrease in uranous sulfate solubility. The elevation of solution temperature causes a decrease in solubility of uranous sulfate. It should be noted that the solid uranous sulfates equilibrated with saturated solutions at 298 K were U(SO4)2 2H2O in dilute sulfuric acid solution and U(SO4)2 4H2O in concentrated sulfuric acid solution, while those at 333 K and 363 K were mainly U(SO4)2 4H2O.

  11. Dephosphorization of Steelmaking Slag by Leaching with Acidic Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Qiao, Yong; Diao, Jiang; Liu, Xuan; Li, Xiaosa; Zhang, Tao; Xie, Bing

    2016-09-01

    In the present paper, dephosphorization of steelmaking slag by leaching with acidic aqueous solution composed of citric acid, sodium hydroxide, hydrochloric acid and ion-exchanged water was investigated. The buffer solution of C6H8O7-NaOH-HCl system prevented changes in the pH values. Kinetic parameters including leaching temperature, slag particle size and pH values of the solution were optimized. The results showed that temperature has no obvious effect on the dissolution ratio of phosphorus. However, it has a significant effect on the dissolution ratio of iron. The dephosphorization rate increases with the decrease of slag particle size and the pH value of the solution. Over 90% of the phosphorus can be dissolved in the solution while the corresponding leaching ratio of iron was only 30% below the optimal condition. Leaching kinetics of dephosphorization follow the unreacted shrinking core model with a rate controlled step by the solid diffusion layer, the corresponding apparent activation energy being 1.233 kJ mol-1. A semiempirical kinetic equation was established. After leaching, most of the nC2S-C3P solid solution in the steelmaking slag was selectively dissolved in the aqueous solution and the iron content in the solid residue was correspondingly enriched.

  12. Methanol Uptake by Low Temperature Aqueous Sulfuric Acid Solutions

    NASA Technical Reports Server (NTRS)

    Iraci, L. T.; Essin, A. M.; Golden, D. M.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    The global methanol budget is currently unbalanced, with source terms significantly larger than the sinks terms. To evaluate possible losses of gaseous methanol to sulfate aerosols, the solubility and reactivity of methanol in aqueous sulfuric acid solutions representative of upper tropospheric and lower stratospheric aerosols is under investigation. Methanol will partition into sulfate aerosols according to its Henry's law solubility. Using standard uptake techniques in a Knudsen cell reactor, we have measured the effective Henry's law coefficient, H*, for cold (196 - 220 K) solutions ranging between 45 and 70 wt % H2SO4. We have found that methanol solubility ranges from approx. 10(exp 5) - 10(exp 7) M/atm for UT/LS conditions. Solubility increases with decreasing temperature and with increasing sulfuric acid content. Although methanol is slightly more soluble than are acetone and formaldehyde, current data indicate that uptake by clean aqueous sulfuric acid particles will not be a significant sink for methanol in the UT/LS. These solubility measurements include uptake due to physical solvation and any rapid equilibria which are established in solution. Reaction between primary alcohols and sulfuric acid does occur, leading to the production of alkyl sulfates. Literature values for the rate of this reaction suggest that formation of CH3OSO3H is not significant over our experimental time scale for solutions below 80 wt % H2SO4. To confirm this directly, results obtained using a complementary equilibrium measurement technique will also be presented.

  13. Decomposition Studies of Triphenylboron, Diphenylborinic Acid and Phenylboric Acid in Aqueous Alkaline Solutions Containing Copper

    SciTech Connect

    Crawford, C.L.; Peterson, R. A.

    1997-02-11

    This report documents the copper-catalyzed chemical kinetics of triphenylboron, diphenylborinic acid and phenylboric acid (3PB, 2PB and PBA) in aqueous alkaline solution contained in carbon-steel vessels between 40 and 70 degrees C.

  14. γ-Irradiation of malic acid in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Negron-Mendoza, Alicia; Graff, Rebecca L.; Ponnamperuma, Cyril

    1980-12-01

    The γ-irradiation of malic acid in aqueous solutions was studied under initially oxygenated and oxygen-free conditions in an attempt to determine the possible interconversion of malic acid into other carboxylic acids, specifically those associated with Krebs cycle. The effect of dose on product formation of the system was investigated. Gas-liquid chromatography combined with mass spectrometry was used as the principal means of identification of the non-volatile products. Thin layer chromotography and direct probe mass spectroscopy were also employed. The findings show that a variety of carboxylic acids are formed, with malonic and succinic acids in greatest abundance. These products have all been identified as being formed in the γ-irradiation of acetic acid, suggesting a common intermediary. Since these molecules fit into a metabolic cycle, it is strongly suggestive that prebiotic pathways provided the basis for biological systems.

  15. Irradiation stability of folic Acid in powder and aqueous solution.

    PubMed

    Araújo, Michel M; Marchioni, Eric; Bergaentzle, Martine; Zhao, Minjie; Kuntz, Florent; Hahn, Emeline; Villavicencio, Anna Lucia C H

    2011-02-23

    This study attempts to examine the folic acid stability after irradiation treatment, under different physical states, pH values, and atmosphere conditions. Aqueous folic acid samples, folic acid in powder, and wheat flour fortified with folic acid were irradiated by an electron beam (E-beam) between 0 (control) and 10.0 kGy. It was realized that the physical state of folic acid plays an important role on its stability toward E-beam processing, being largely unstable in solution, no matter the pH and atmosphere conditions assayed. Otherwise, folic acid in powder showed huge irradiation stability, even when mixed in a dry food matrix, such as fortified wheat flour samples.

  16. Polymerization of Pu(IV) in aqueous nitric acid solutions

    SciTech Connect

    Toth, L.M.; Friedman, H.A.; Osborne, M.M.

    1980-10-01

    The polymerization of Pu(IV) in aqueous nitric acid solutions has been studied spectrophotometrically both to establish the influence of large UO{sub 2}(NO{sub 3}){sub 2} concentrations on the polymerization rates and, more generally, to review the influence of the major parameters on the polymer reaction. Typically, experiments have been performed at 50{sup 0}C and with 0.05 M Pu in nitric acid solutions that vary in acidity from 0.07 to 0.4 M. An induction period usually precedes the polymer growth stage during which time nucleation of primary hydrolysis products occurs. Uranyl nitrate retards the polymerization reaction by approximately 35% in spite of the counteracting influence of the nitrate ions associated with this solute. The rate of polymer formation, expressed as d(percent polymer)/dt, has been shown to depend on the total plutonium concentration in reactions where the Pu(IV) concentration remained constant; and it is therefore suggested that the polymer reaction rate is not first order with respect to the concentration of plutonium as was previously thought. It has been shown further that accurate acid determinations on stock reagents are essential in order to obtain reliable polymerization experiments. Satisfactory procedures for these analyses did not exist, so appropriate modifications to the iodate precipitation methods were developed. The most ideal plutonium reagent material has been shown to be crystalline Pu(IV) nitrate because it can be added directly to acid solutions without the occurrence of unintentional hydrolysis reactions.

  17. Methanol Uptake By Low Temperature Aqueous Sulfuric Acid Solutions

    NASA Technical Reports Server (NTRS)

    Iraci, Laura T.; Essin, Andrew M.; Golden, David M.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    To evaluate the role of upper tropospheric and lower stratospheric aerosols in the global budget of methanol, the solubility and reactivity of CH3OH in aqueous sulfuric acid solutions are under investigation. Using standard uptake techniques in a Knudsen cell reactor, we have measured the effective Henry's law coefficient, H(*), for methanol dissolution into 45 to 70 percent by weight H2SO4. We find that methanol solubility ranges from 10(exp 5) to 10(exp 8) M/atm and increases with decreasing temperature and with increasing sulfuric acid content. These solubility measurements include uptake due to physical solvation and all rapid equilibria which are established in solution. Our data indicate that simple uptake by aqueous sulfuric acid particles will not be a significant sink for methanol in the UT/LS. These results differ from those recently reported in the literature, and an explanation of this disparity will be presented. In addition to solvation, reaction between primary alcohols and sulfuric acid does occur, leading to the production of alkyl sulfates. Literature values for the rate of this reaction suggest that formation of CH3OSO3H may proceed in the atmosphere but is not significant under our experimental conditions. Results obtained using a complementary equilibrium measurement technique confirm this directly. In addition, the extent of methanol sequestration via formation of mono- and dimethylsulfate will be evaluated under several atmospheric conditions.

  18. Adsorption of citric acid from dilute aqueous solutions by hydroxyapatite.

    PubMed

    Vega, Enrique D; Narda, Griselda E; Ferretti, Ferdinando H

    2003-12-01

    The role of citric acid in the demineralization of dental enamel, which is mainly constituted by hydroxyapatite, is important for periodontal regeneration and in the conditioning of enamel or dentin for bonding restorative resins. The adsorption of citric acid from aqueous solutions onto synthetic hydroxyapatite at 278, 288, 298, and 308 K and pH 4.8 has been studied by means of UV spectroscopy. The adsorption reaction, which takes place by an interaction between phosphate groups and citrate anions at the solid-solution interface, yields an adsorbate-adsorbent complex of high stability. The adsorption isotherms fit the Langmuirian shape. The proposed adsorption model, where citrate species interact in a bidentate manner (one citrate ion links two phosphate sites), is coherent with the experimental data. The activation standard heat and activation standard entropy were calculated. All the thermodynamic and kinetic parameters were in concordance with the adsorption reaction proposed in this work.

  19. Reversible absorption of SO2 by amino acid aqueous solutions.

    PubMed

    Deng, Renpan; Jia, Lishan; Song, Qianqian; Su, Shuai; Tian, Zhongbiao

    2012-08-30

    Six water-soluble amino acids (glycine, l-α-alanine, dl-alanine, β-alanine, proline and arginine) aqueous solutions were applied to remove SO(2) from SO(2)-N(2) system in this report. All the tested amino acids solutions were found to be excellent absorbents for SO(2) removal, and SO(2) saturation uptake of β-alanine solution was the highest under the same experimental conditions. The effects of amino acid concentration, SO(2) concentration, absorption temperature, desorption temperature and initial pH value of the absorbent on the removal of SO(2) were investigated with β-Ala solution. The experimental results showed that SO(2) saturation uptake increased with the increase in β-alanine solution and SO(2) concentration. Room temperature (20-30°C) was found to be optimal for SO(2) absorption. Additionally the SO(2) desorption capacity increased with increasing desorption temperature. The neutral environment pH value of 6.8 was found to be optimal for SO(2) removal. Ten continuous absorption-desorption cycles showed that the absorbent had an excellent regeneration performance. (13)C NMR and ultraviolet analyses offer ample evidence to speculate that the bonding between SO(2) and β-alanine was not covalent but some weak interactive forces, such as dispersion force, induction force, dipole-dipole force and hydrogen bond. Copyright © 2012 Elsevier B.V. All rights reserved.

  20. UV photolysis of perfluorooctanoic acid (PFOA) in dilute aqueous solution.

    PubMed

    Giri, R R; Ozaki, H; Morigaki, T; Taniguchi, S; Takanami, R

    2011-01-01

    Perfluorooctanoic acid (PFOA) is very persistent in the environment and widely detected in the water environment. Only some advanced methods with extreme reaction conditions are shown to be capable of degrading the compound efficiently, and almost all the earlier investigations used very high PFOA concentrations. The compound is detected normally at very low concentrations in the water environment, while mild reaction conditions for its degradation are preferable. This article aimed to elucidate photodegradation of PFOA in dilute aqueous solutions by combined UV wavelengths (185 nm+254 nm) and 254 nm using a newly designed UV jacket. PFOA degradation was greatly enhanced with the combined wavelengths with almost one hundred percent PFOA removals in four-hour reaction. The removals were well described by the first-order reaction kinetic. The removal efficiencies and rate values significantly decreased with smaller initial PFOA concentrations. But defluorination was greatly enhanced with smaller PFOA concentrations possibly due to accelerated decomposition of fluorinated intermediates of PFOA. Formic acid and acetic acid were two tentatively identified intermediates of PFOA photolysis while the former was a major intermediate predominantly controlling solution pH during the oxidation. The results demonstrated that PFOA photolysis by the combined wavelengths with mild reaction conditions can be greatly enhanced by proper design of UV jacket and reactor system.

  1. A method for calculating the acid-base equilibria in aqueous and nonaqueous electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Tanganov, B. B.; Alekseeva, I. A.

    2017-06-01

    Concentrations of particles in acid-base equilibria in aqueous and nonaqueous solutions of electrolytes are calculated on the basis of logarithmic charts, activity coefficients, and equilibrium constants.

  2. Conformation of poly(γ-glutamic acid) in aqueous solution.

    PubMed

    Muroga, Yoshio; Nakaya, Asami; Inoue, Atsuki; Itoh, Daiki; Abiru, Masaya; Wada, Kaori; Takada, Masako; Ikake, Hiroki; Shimizu, Shigeru

    2016-04-01

    Local conformation and overall conformation of poly(γ-DL-glutamic acid) (PγDLGA) and poly(γ-L-glutamic acid) (PγLGA) in aqueous solution was studied as a function of degree of ionization ε by (1) H-NMR, circular dichroism, and potentiometric titration. It was clarified that their local conformation is represented by random coil over an entire ε range and their overall conformation is represented by expanded random-coil in a range of ε > ε(*) , where ε(*) is about 0.3, 0.35, 0.45, and 0.5 for added-salt concentration of 0.02M, 0.05M, 0.1M, and 0.2M, respectively. In a range of ε < ε(*) , however, ε dependence of their overall conformation is significantly differentiated from each other. PγDLGA tends to aggregate intramolecularly and/or intermolecularly with decreasing ε, but PγLGA still behaves as expanded random-coil. It is speculated that spatial arrangement of adjacent carboxyl groups along the backbone chain essentially affects the overall conformation of PγGA in acidic media.

  3. Optical properties of chitosan in aqueous solution of L- and D-ascorbic acids

    NASA Astrophysics Data System (ADS)

    Malinkina, Olga N.; Shipovskaya, Anna B.; Kazmicheva, Olga F.

    2016-04-01

    The optical properties of aqueous chitosan solutions in L- and D-ascorbic acids were studied by optical rotatory dispersion and spectrophotometry. The specific optical rotation [α] of all chitosan solutions tested was positive, in contrast to aqueous solutions of the ascorbic acid enantiomers, which exhibit an inverse relationship of [α] values. Significant differences in the absolute values of [α] of the chitosan solutions at polymer-acid ratios exceeding the equimolar one were found.

  4. 49 CFR 173.195 - Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (hydrocyanic acid, aqueous solution). 173.195 Section 173.195 Transportation Other Regulations Relating to... (hydrocyanic acid, aqueous solution). (a) Hydrogen cyanide, anhydrous, stabilized, must be packed in... 3A480, 3A480X, 3AA480, or 3A1800 metal cylinders of not over 126 kg (278 pounds) water capacity (nominal...

  5. 49 CFR 173.195 - Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... (hydrocyanic acid, aqueous solution). 173.195 Section 173.195 Transportation Other Regulations Relating to... (hydrocyanic acid, aqueous solution). (a) Hydrogen cyanide, anhydrous, stabilized, must be packed in... 3A480, 3A480X, 3AA480, or 3A1800 metal cylinders of not over 126 kg (278 pounds) water capacity (nominal...

  6. 49 CFR 173.195 - Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (hydrocyanic acid, aqueous solution). 173.195 Section 173.195 Transportation Other Regulations Relating to... (hydrocyanic acid, aqueous solution). (a) Hydrogen cyanide, anhydrous, stabilized, must be packed in... 3A480, 3A480X, 3AA480, or 3A1800 metal cylinders of not over 126 kg (278 pounds) water capacity (nominal...

  7. Population and size distribution of solute-rich mesospecies within mesostructured aqueous amino acid solutions.

    PubMed

    Jawor-Baczynska, Anna; Moore, Barry D; Lee, Han Seung; McCormick, Alon V; Sefcik, Jan

    2013-01-01

    Aqueous solutions of highly soluble substances such as small amino acids are usually assumed to be essentially homogenous systems with some degree of short range local structuring due to specific interactions on the sub-nanometre scale (e.g. molecular clusters, hydration shells), usually not exceeding several solute molecules. However, recent theoretical and experimental studies have indicated the presence of much larger supramolecular assemblies or mesospecies in solutions of small organic and inorganic molecules as well as proteins. We investigated both supersaturated and undersaturated aqueous solutions of two simple amino acids (glycine and DL-alanine) using Dynamic Light Scattering (DLS), Brownian Microscopy/Nanoparticles Tracking Analysis (NTA) and Cryogenic Transmission Electron Microscopy (Cryo-TEM). Colloidal scale mesospecies (nanodroplets) were previously reported in supersaturated solutions of these amino acids and were implicated as intermediate species on non-classical crystallization pathways. Surprisingly, we have found that the mesospecies are also present in significant numbers in undersaturated solutions even when the solute concentration is well below the solid-liquid equilibrium concentration (saturation limit). Thus, mesopecies can be observed with mean diameters ranging from 100 to 300 nm and a size distribution that broadens towards larger size with increasing solute concentration. We note that the mesospecies are not a separate phase and the system is better described as a thermodynamically stable mesostructured liquid containing solute-rich domains dispersed within bulk solute solution. At a given temperature, solute molecules in such a mesostructured liquid phase are subject to equilibrium distribution between solute-rich mesospecies and the surrounding bulk solution.

  8. Raman spectroscopic study of the conformation of dicarboxylic acid salts in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Fukushima, Kunio; Watanabe, Toshiaki; Umemura, Matome

    1986-08-01

    It is already known that the molecules of long chain monocarboxylic acid salts have a tendency to form micelles in aqueous solutions, the molecular chain taking the all- trans zigzag structure. However it is considered difficult for dicarboxylic acid salts to adopt the same structure as the monocarboxylic acid salts as they have two carboxyl groups, one on each end of the molecular chain. Therefore, a special structure is expected to exist for dicarboxylic acid salts in aqueous solution. In order to examine this, Raman spectra of suberic acid salt and azelaic acid salt in aqueous solution were measured and the normal vibrational calculation carried out, showing that dicarboxylic acid salts have a helical structure in aqueous solution.

  9. Near infrared photochemistry of pyruvic acid in aqueous solution.

    PubMed

    Larsen, Molly C; Vaida, Veronica

    2012-06-21

    Recent experimental and theoretical results have suggested that organic acids such as pyruvic acid, can be photolyzed in the ground electronic state by the excitation of the OH stretch vibrational overtone. These overtones absorb in the near-infrared and visible regions of the spectrum where the solar photons are plentiful and could provide a reaction pathway for the organic acids and alcohols that are abundant in the earth's atmosphere. In this paper the overtone initiated photochemistry of aqueous pyruvic acid is investigated by monitoring the evolution of carbon dioxide. In these experiments CO(2) is being produced by excitation in the near-infrared, between 850 nm and ∼1150 nm (11,765-8696 cm(-1)), where the second OH vibrational overtone (Δν = 3) of pyruvic acid is expected to absorb. These findings show not only that the overtone initiated photochemical decarboxylation reaction occurs but also that in the aqueous phase it occurs at a lower energy than was predicted for the overtone initiated reaction of pyruvic acid in the gas phase (13,380 cm(-1)). A quantum yield of (3.5 ± 1.0) × 10(-4) is estimated, suggesting that although this process does occur, it does so with a very low efficiency.

  10. Phosphorylation of Glyceric Acid in Aqueous Solution Using Trimetaphosphate

    NASA Technical Reports Server (NTRS)

    Kolb, Vera; Orgel, Leslie E.

    1996-01-01

    The phosphorylation of glyceric acid is an interesting prebiotic reaction because it converts a simple, potentially prebiotic organic molecule into phosphate derivatives that are central to carbohydrate metabolism. We find that 0.05 M glyceric acid in the presence of 0.5 M trimetaphosphate in alkaline solution gives a mixture of 2- and 3-phosphoglyceric acids in combined yields of up to 40%.

  11. Phosphorylation of glyceric acid in aqueous solution using trimetaphosphate

    NASA Astrophysics Data System (ADS)

    Kolb, Vera; Orgel, Leslie E.

    1996-02-01

    The phosphorylation of glyceric acid is an interesting prebiotic reaction because it converts a simple, potentially prebiotic organic molecule into phosphate derivatives that are central to carbohydrate metabolism. We find that 0.05 M glyceric acid in the presence of 0.5 M trimetaphosphate in alkaline solution gives a mixture of 2- and 3-phosphoglyceric acids in combined yields of up to 40%.

  12. [Sorption of amino acids from aqueous solutions on activated charcoal].

    PubMed

    Nekliudov, A D; Tsibanov, V V

    1985-03-01

    Various methods for quantitative description of amino acid sorption from solutions for parenteral nutrition on activated charcoal were studied under dynamic and static conditions. With the use of the well-known Freindlich and Langmuir absorption isotherms it was shown to be possible to describe in a simplified way the complex multicomponent process of sorption of the amino acids and to estimate their loss at the filtration stage.

  13. Radiolysis of aqueous solutions of 2-aminoethanethiosulfuric acid. [Gamma radiation

    SciTech Connect

    Grachev, S.A.; Koroleva, I.K.; Kropachev, E.V.; Litvyakova, G.I.

    1982-07-10

    In the radiolysis products of aerated and deaerated solutions of the 2-aminoethanethiosulfuric acid the authors have identified cystamine monoxide, cystamine, taurine, mercamine, the sulfate ion, the sulfite ion, and the dithionate ion. The yields of these products under different conditions have been determined. Results indicated that the sulfate ion is formed both from the divalent and the hexavalent sulfur atom of the 2-aminoethanethiosulfuric acid moelcule. A possible radiolysis mechanism is discussed.

  14. Thermodynamics of the complexation of arabinogalactan with salicylic and p-aminobenzoic acids in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Mudarisova, R. Kh.; Badykova, L. A.

    2016-03-01

    The thermodynamics of complexation of arabinogalactan with salicylic and p-aminobenzoic acids in aqueous solutions is studied by means spectroscopy. The standard thermodynamic characteristics (Δ H°; Δ G°; Δ S°) of complexation are calculated.

  15. Behaviors of acrylamide/itaconic acid hydrogels in uptake of uranyl ions from aqueous solutions

    SciTech Connect

    Karadag, E.; Saraydin, D.; Gueven, O.

    1995-12-01

    In this study, adsorptions of uranyl ions from two different aqueous uranyl solutions by acrylamide-itaconic acid hydrogels were investigated by a spectroscopic method. The hydrogels were prepared by irradiating with {gamma}-radiation. In the experiment of uranyl ions adsorption, Type II adsorption was found. One gram of acrylamide-itaconic acid hydrogels sorbed 178-219 mg uranyl ions from the solutions of uranyl acetate, 42-76 mg uranyl ions from the aqueous solutions of uranyl nitrate, while acrylamide hydrogel did not sorb any uranyl ion. For the hydrogel containing 40 mg of itaconic acid and irradiated to 3.73 kGy, swelling of the hydrogels was observed in water (1660%), in the aqueous solution of uranyl acetate (730%), and in the aqueous solution of uranyl nitrate (580%). Diffusions of water onto hydrogels were a non-Fickian type of diffusion, whereas diffusions of uranyl ions were a Fickian type of diffusion.

  16. Molecular Diffusivities of Silicic and Gernamic Acids in Aqueous Solutions

    NASA Astrophysics Data System (ADS)

    Cummins, K. M.; Hammond, D. E.

    2001-12-01

    Germanium and silicon have many similarities in their water column behaviors, but these elements may be fractionated by diagenetic reactions in iron-rich, reducing sediments. Pore water profiles can constrain the magnitude of this fractionation, but diffusion coefficients for both silicic and germanic acid are required to quantitatively determine their transport. The objective of this study was to experimentally determine these diffusivities, using a diaphragm cell in the laboratory. A porous frit was filled with solutions containing KCl, silicic acid, and germanic acid (as a 68Ge tracer). These solutes were allowed to diffuse into a reservoir of well-mixed deionized water at 25 C. Samples were drawn from the reservoir over time, and a numerical simulation was used to estimate the diffusivity required to best fit the resulting concentration change over a 4-6 day period. Results (in 10e-6 cm2 s-1) for silicic acid averaged 8.86 +/- 0.42 and 7.83 +/- 0.66 for silicic acid concentrations of 350 uM and 910 uM respectively. These are significantly smaller than previously published results of Applin (1987), but show a similar dependence on silicic acid concentration. These results in fresh water are comparable to results of Wollast and Garrels (1970) in sea water. Results for germanic acid averaged 8.92 +/- 0.82, indistinguishable from results for silicic acid, and they did not exhibit a strong dependence on the silicic acid concentration. Additional experiments are underway using a sea water medium.

  17. Acid gas absorption in aqueous solutions of mixed amines

    SciTech Connect

    Rinker, E.B.; Ashour, S.S.; Sandall, O.C.

    1996-12-31

    A mass transfer model has been developed to describe the rate of absorption (or desorption) of H{sub 2}S and CO{sub 2} in aqueous blends of a tertiary and a secondary or a primary amine. The model is based on penetration theory, and all significant chemical reactions are incorporated in the model. The reactions are taken to be reversible, with reactions involving only a proton transfer considered to be at equilibrium. The particular amines studied in this research were methyldiethanolamine (MDEA), a tertiary amine, and diethanolamine (DEA), a secondary amine. Key physicochemical data needed in the model, such as diffusion coefficients, kinetic rate constants, and gas solubilities, were measured. Experimental absorption rates of CO{sub 2} and H{sub 2}S were measured in a model gas-liquid contacting device and were compared with model predictions. Experiments were carried out for single amine solutions (both MDEA and DEA) and for amine blends.

  18. Adsorption of organic acids from dilute aqueous solution onto activated carbon

    SciTech Connect

    Wang, S.W.

    1980-06-01

    The radioisotope technique was used to study the removal of organic acid contaminants from dilute aqueous solutions onto activated carbon. Acetic acid, propionic acid, n-butyric acid, n-hexanoic acid and n-heptanoic acid were studied at 278, 298, and 313/sup 0/K. Three bi-solute acid mixtures (acetic and propionic acids, acetic and butanoic acids, and propionic and butanoic acids) were studied at 278 and 298/sup 0/K. Isotherms of the single-solute systems were obtained at three different temperatures in the very dilute concentration region (less than 1% by weight). These data are very important in the prediction of bi-solute equilibrium data. A Polanyi-based competitive adsorption potential theory was used to predict the bi-solute equilibrium uptakes. Average errors between calculated and experimental data ranges from 4% to 14%. It was found that the competitive adsorption potential theory gives slightly better results than the ideal adsorbed solution theory.

  19. Micro-organization of humic acids in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Klučáková, Martina; Věžníková, Kateřina

    2017-09-01

    The methods of dynamic light scattering and micro-rheology were used to investigate the molecular organization of humic acids in solutions. The obtained results were supplemented by ultraviolet/visible spectrometry and measurement of the zeta potential. Particle tracking micro-rheology was used for the first time as a novel method in humic research. Solutions of humic acids were prepared in three different mediums: NaOH, NaCl, and NaOH neutralized by HCl after dissolution of the humic sample. The molecular organization of humic acids was studied over a wide concentration range (0.01-10 g dm-3). Two breaks were detected in the obtained concentration dependencies. The rearrangements were observed at concentrations around 0.02 g dm-3 and 1 g dm-3. Changes in the measured values observed at around 0.02 g dm-3 were less noticeable and were related to the formation of particles between 100 and 1000 nm in size and the strong bimodal character of humic systems diluted by NaCl. The ;switch-over point; at around 1 g dm-3 indicated changes in the secondary structure of humic acids connected with the increase in colloidal stability (decrease of zeta potential), the decrease in polydispersity, and minimal values of viscosity.

  20. Treatment of infectious skin defects or ulcers with electrolyzed strong acid aqueous solution.

    PubMed

    Sekiya, S; Ohmori, K; Harii, K

    1997-01-01

    A chronic ulcer with an infection such as methicillin-resistant Staphylococcus aureus is hard to heal. Plastic and reconstructive surgeons often encounter such chronic ulcers that are resistant to surgical or various conservative treatments. We applied conservative treatment using an electrolyzed strong acid aqueous solution and obtained satisfactory results. The lesion was washed with the solution or soaked in a bowl of the solution for approximately 20 min twice a day. Fresh electrolyzed strong acid aqueous solution is unstable and should be stored in a cool, dark site in a sealed bottle. It should be used within a week after it has been produced. Here we report on 15 cases of infectious ulcers that were treated by electrolyzed strong acid aqueous solution. Of these cases, 7 patients were healed, 3 were granulated, and in 5, infection subsided. In most cases the lesion became less reddish and less edematous. Discharge or foul odor from the lesion was decreased. Electrolyzed strong acid aqueous solution was especially effective for treating a chronic refractory ulcer combined with diabetes melitus or peripheral circulatory insufficiency. This clinically applied therapy of electrolyzed strong acid aqueous solution was found to be effective so that this new therapeutic technique for ulcer treatment can now be conveniently utilized.

  1. The solvent effect on the acidities of haloacetic acids in aqueous solution. A RISM-SCF study

    NASA Astrophysics Data System (ADS)

    Kawata, Masaaki; Ten-no, Seiichiro; Kato, Shigeki; Hirata, Fumio

    1995-06-01

    The acidities of acetic, fluoracetic and chloroacetic acids in aqueous solution are calculated by means of the ab initio method combined with the reference interaction site method in the statistical mechanics of molecular liquids (the RISM-SCF method). The inversion in the order of acidities experimentally observed when a series of haloacetic acids is immersed into aqueous solution is reproduced. It is shown that the inversion is caused by competition between substitution and solvation effects. The solvation effect is discussed in molecular detail in terms of the charge distribution of the solute and the solute-solvent radial distribution functions.

  2. Reduction of hexavalent chromium by ascorbic acid in aqueous solutions.

    PubMed

    Xu, Xiang-Rong; Li, Hua-Bin; Li, Xiao-Yan; Gu, Ji-Dong

    2004-11-01

    Hexavalent chromium is a priority pollutant in the USA and many other countries. Reduction of Cr(VI) to Cr(III) is environmentally favorable as the latter species is not toxic to most living organisms and also has a low mobility and bioavailability. Reduction of Cr(VI) by ascorbic acid (vitamin C) as a reductant was studied using potassium dichromate solution as the model pollutant. Effects of concentration of vitamin C, pH, temperature, irradiation and reaction time on the reduction of Cr(VI) were examined. Cr(VI) might be reduced by vitamin C not only in acidic conditions but also in weakly alkaline solutions. The reduction of Cr(VI) by vitamin C might occur not only under irradiation but also in the dark. Vitamin C is an important biological reductant in humans and animals, and not toxic. It is water-soluble and can easily permeate through various types of soils. The results indicate that vitamin C could be used in effective remediation of Cr(VI)-contaminated soils and groundwater in a wide range of pH, with or without sunlight. copyright 2004 Elsevier Ltd.

  3. The standard enthalpies of formation of crystalline N-(carboxymethyl)aspartic acid and its aqueous solutions

    NASA Astrophysics Data System (ADS)

    Lytkin, A. I.; Chernyavskaya, N. V.; Volkov, A. V.; Nikol'Skii, V. M.

    2007-07-01

    The energy of combustion of N-(carboxymethyl)aspartic acid (CMAA) was determined by bomb calorimetry in oxygen. The standard enthalpies of combustion and formation of crystalline N-(carboxymethyl)aspartic acid were calculated. The heat effects of solution of crystalline CMAA in water and a solution of sodium hydroxide were measured at 298.15 K by direct calorimetry. The standard enthalpies of formation of CMAA and its dissociation products in aqueous solution were determined.

  4. Aqueous solutions of acidic ionic liquids for enhanced stability of polyoxometalate-carbon supercapacitor electrodes

    NASA Astrophysics Data System (ADS)

    Hu, Chenchen; Zhao, Enbo; Nitta, Naoki; Magasinski, Alexandre; Berdichevsky, Gene; Yushin, Gleb

    2016-09-01

    Nanocomposites based on polyoxometalates (POMs) nanoconfined in microporous carbons have been synthesized and used as electrodes for supercapacitors. The addition of the pseudocapacitance from highly reversible redox reaction of POMs to the electric double-layer capacitance of carbon lead to an increase in specific capacitance of ∼90% at 1 mV s-1. However, high solubility of POM in traditional aqueous electrolytes leads to rapid capacity fading. Here we demonstrate that the use of aqueous solutions of protic ionic liquids (P-IL) as electrolyte instead of aqueous sulfuric acid solutions offers an opportunity to significantly improve POM cycling stability. Virtually no degradation in capacitance was observed in POM-based positive electrode after 10,000 cycles in an asymmetric capacitor with P-IL aqueous electrolyte. As such, POM-based carbon composites may now present a viable solution for enhancing energy density of electrical double layer capacitors (EDLC) based on pure carbon electrodes.

  5. Uptake of Hypobromous Acid (HOBr) by Aqueous Sulfuric Acid Solutions: Low-Temperature Solubility and Reaction

    NASA Technical Reports Server (NTRS)

    Iraci, Laura T.; Michelsen, Rebecca R.; Ashbourn, Samatha F. M.; Rammer, Thomas A.; Golden, David M.

    2005-01-01

    Hypobromous acid (HOBr) is a key species linking inorganic bromine to the chlorine and odd hydrogen chemical families. We have measured the solubility of HOBr in 45 - 70 wt% sulfuric acid solutions representative of upper tropospheric and lower stratospheric aerosol composition. Over the temperature range 201 - 252 K, HOBr is quite soluble in sulfuric acid, with an effective Henry's law coefficient, H* = 10(exp 4) - 10(exp 7) mol/L/atm. H* is inversely dependent on temperature, with Delta H = -46.2 kJ/mol and Delta S = -106.2 J/mol/K for 55 - 70 wt% H2SO4 solutions. Our study includes temperatures which overlap both previous measurements of HOBr solubility. For uptake into aqueous 45 wt% H2SO4, the solubility can be described by log H* = 3665/T - 10.63. For 55 - 70 wt% H2SO4, log H* = 2412/T - 5.55. At temperatures colder than approx. 213 K, the solubility of HOBr in 45 wt% H2SO4 is noticeably larger than in 70 wt% H2SO4. The solubility of HOBr is comparable to that of HBr, indicating that upper tropospheric and lower stratospheric aerosols should contain equilibrium concentrations of HOBr which equal or exceed those of HBr. Our measurements indicate chemical reaction of HOBr upon uptake into aqueous sulfuric acid in the presence of other brominated gases followed by evolution of gaseous products including Br2O and Br2, particularly at 70 wt% H2SO4.

  6. Biosorption of acidic textile dyestuffs from aqueous solution by Paecilomyces sp. isolated from acidic mine drainage.

    PubMed

    Çabuk, Ahmet; Aytar, Pınar; Gedikli, Serap; Özel, Yasemin Kevser; Kocabıyık, Erçin

    2013-07-01

    Removal of textile dyestuffs from aqueous solution by biosorption onto a dead fungal biomass isolated from acidic mine drainage in the Çanakkale Region of Turkey was investigated. The fungus was found to be a promising biosorbent and identified as Paecilomyces sp. The optimal conditions for bioremediation were as follows: pH, 2.0; initial dyestuff concentration, 50 mg l(-1) for Reactive Yellow 85 and Reactive Orange 12, and 75 mg l(-1) for Reactive Black 8; biomass dosage, 2 g l(-1) for Reactive Yellow 85, 3 g l(-1) for Reactive Orange 12, 4 g l(-1) for Reactive Black 8; temperature, 25 °C; and agitation rate, 100 rpm. Zeta potential measurements indicated an electrostatic interaction between the binding sites and dye anions. Fourier transform infrared spectroscopy showed that amine, hydroxyl, carbonyl, and amide bonds were involved in the dyestuff biosorption. A toxicity investigation was also carried out before and after the biosorption process. These results showed that the toxicities for the reactive dyestuffs in aqueous solutions after biosorption studies decreased. The Freundlich and Langmuir adsorption models were used for the mathematical description of the biosorption equilibrium, and isotherm constants were evaluated for each dyestuff. Equilibrium data of biosorption of RY85 and RO12 dyestuffs fitted well to both models at the studied concentration and temperature.

  7. Extraction of steroidal glucosiduronic acids from aqueous solutions by anionic liquid ion-exchangers

    PubMed Central

    Mattox, Vernon R.; Litwiller, Robert D.; Goodrich, June E.

    1972-01-01

    A pilot study on the extraction of three steroidal glucosiduronic acids from water into organic solutions of liquid ion-exchangers is reported. A single extraction of a 0.5mm aqueous solution of either 11-deoxycorticosterone 21-glucosiduronic acid or cortisone 21-glucosiduronic acid with 0.1m-tetraheptylammonium chloride in chloroform took more than 99% of the conjugate into the organic phase; under the same conditions, the very polar conjugate, β-cortol 3-glucosiduronic acid, was extracted to the extent of 43%. The presence of a small amount of chloride, acetate, or sulphate ion in the aqueous phase inhibited extraction, but making the aqueous phase 4.0m with ammonium sulphate promoted extraction strongly. An increase in the concentration of ion-exchanger in the organic phase also promoted extraction. The amount of cortisone 21-glucosiduronic acid extracted by tetraheptylammonium chloride over the pH range of 3.9 to 10.7 was essentially constant. Chloroform solutions of a tertiary, a secondary, or a primary amine hydrochloride also will extract cortisone 21-glucosiduronic acid from water. The various liquid ion exchangers will extract steroidal glucosiduronic acid methyl esters from water into chloroform, although less completely than the corresponding free acids. The extraction of the glucosiduronic acids from water by tetraheptylammonium chloride occurs by an ion-exchange process; extraction of the esters does not involve ion exchange. PMID:5075264

  8. High-Yield Production of Levulinic Acid from Pretreated Cow Dung in Dilute Acid Aqueous Solution.

    PubMed

    Su, Jialei; Shen, Feng; Qiu, Mo; Qi, Xinhua

    2017-02-14

    Agricultural waste cow dung was used as feedstock for the production of a high value-added chemical levulinic acid (LA) in dilute acid aqueous solutions. A high LA yield of 338.9 g/kg was obtained from the pretreated cow dung, which was much higher than that obtained from the crude cow dung (135 g/kg), mainly attributed to the breakage of the lignin fraction in the lignocellulose structure of the cow dung by potassium hydroxide (KOH) pretreatment, and thus enhanced the accessibility of cow dung to the acid sites in the catalytic reaction. Meanwhile, another value-added chemical formic acid could be obtained with a yield of ca. 160 g/kg in the process, implying a total production of ca. 500 g/kg yield for LA and formic acid from the pretreated cow dung with the proposed process. The developed process was shown to be tolerant to high initial substrate loading with a satisfied LA yield. This work provides a promising strategy for the value-increment utilization of liglocellulosic agricultural residues.

  9. Ultrasonic Studies of 4-Aminobutyric Acid in Aqueous Metformin Hydrochloride Solutions at Different Temperatures

    NASA Astrophysics Data System (ADS)

    Rajagopal, K.; Jayabalakrishnan, S. S.

    2010-12-01

    Ultrasonic speeds and density data of 4-aminobutyric acid in 0.05 M, 0.10 M, and 0.15 M aqueous metformin hydrochloride (MFHCl) solutions are measured at 308.15 K, 313.15 K, and 318.15 K. The isentropic compressibility ( k S ), the change in isentropic compressibility (Δ k S ), the relative change in isentropic compressibility ({Δ k_S/k_S^0}), the apparent molal compressibility ({k_φ}), the limiting apparent molal compressibility ({k_φ^0 }), the transfer limiting apparent molal compressibility ({Δ k_φ^0}), the hydration number ( n H), and the pair and triplet interaction parameters ( k AH, k AHH) are estimated. The above parameters are used to interpret the solute-solute and solute-solvent interactions of 4-aminobutyric acid in aqueous MFHCl solutions.

  10. 49 CFR 173.195 - Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Hydrogen cyanide, anhydrous, stabilized... Hazardous Materials Other Than Class 1 and Class 7 § 173.195 Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution). (a) Hydrogen cyanide, anhydrous, stabilized, must be packed...

  11. 49 CFR 173.195 - Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 2 2011-10-01 2011-10-01 false Hydrogen cyanide, anhydrous, stabilized... Hazardous Materials Other Than Class 1 and Class 7 § 173.195 Hydrogen cyanide, anhydrous, stabilized (hydrocyanic acid, aqueous solution). (a) Hydrogen cyanide, anhydrous, stabilized, must be packed...

  12. SOLVENT EXTRACTION PROCESS FOR SEPARATING URANIUM AND PLUTONIUM FROM AQUEOUS ACIDIC SOLUTIONS OF NEUTRON IRRADIATED URANIUM

    DOEpatents

    Bruce, F.R.

    1962-07-24

    A solvent extraction process was developed for separating actinide elements including plutonium and uranium from fission products. By this method the ion content of the acidic aqueous solution is adjusted so that it contains more equivalents of total metal ions than equivalents of nitrate ions. Under these conditions the extractability of fission products is greatly decreased. (AEC)

  13. Arsenous acid ionisation in aqueous solutions from 25 to 300 °C

    NASA Astrophysics Data System (ADS)

    Zakaznova-Herzog, V. P.; Seward, T. M.; Suleimenov, O. M.

    2006-04-01

    The ultraviolet spectra of dilute, aqueous arsenic (III)-containing solutions have been measured from 25 to 300 °C at the saturated vapour pressure. From these measurements, the equilibrium constant was obtained for the reaction H3AsO3⇄H++H2AsO3-; for which p K1 (arsenous acid) decreases from 9.25 to 7.11 over a temperature range from 25 to 300 °C. In addition, electrospray mass spectrometric measurements support the conclusion that the arsenous acid moeities in low density aqueous media are HAsO 2 and AsO 2-.

  14. Composition and process for separating cesium ions from an acidic aqueous solution also containing other ions

    DOEpatents

    Dietz, M.L.; Horwitz, E.P.; Bartsch, R.A.; Barrans, R.E. Jr.; Rausch, D.

    1999-03-30

    A crown ether cesium ion extractant is disclosed as is its synthesis. The crown ether cesium ion extractant is useful for the selective purification of cesium ions from aqueous acidic media, and more particularly useful for the isolation of radioactive cesium-137 from nuclear waste streams. Processes for isolating cesium ions from aqueous acidic media using the crown ether cesium extractant are disclosed as are processes for recycling the crown ether cesium extractant and processes for recovering cesium from a crown ether cesium extractant solution. 4 figs.

  15. Composition and process for separating cesium ions from an acidic aqueous solution also containing other ions

    DOEpatents

    Dietz, Mark L.; Horwitz, E. Philip; Bartsch, Richard A.; Barrans, Jr., Richard E.; Rausch, David

    1999-01-01

    A crown ether cesium ion extractant is disclosed as is its synthesis. The crown ether cesium ion extractant is useful for the selective purification of cesium ions from aqueous acidic media, and more particularly useful for the isolation of radioactive cesium-137 from nuclear waste streams. Processes for isolating cesium ions from aqueous acidic media using the crown ether cesium extractant are disclosed as are processes for recycling the crown ether cesium extractant and processes for recovering cesium from a crown ether cesium extractant solution.

  16. Interfacial structures of acidic and basic aqueous solutions

    SciTech Connect

    Tian, C.; Ji, N.; Waychunas, G.; Shen, Y.R.

    2008-10-20

    Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the spectrum. We found clear evidence that hydronium ions prefer to emerge at interfaces. Their OH stretches contribute to the 'ice-like' band in the spectrum. Their charges create a positive surface field that tends to reorient water molecules more loosely bonded to the topmost water layer with oxygen toward the interface, and thus enhances significantly the 'liquid-like' band in the spectrum. Iodine ions in solution also like to appear at the interface and alter the positive surface field by forming a narrow double-charge layer with hydronium ions. In NaOH solution, the observed weak change of the 'liquid-like' band and disappearance of the 'ice-like' band in the spectrum indicates that OH{sup -} ions must also have excess at the interface. How they are incorporated in the interfacial water structure is however not clear.

  17. The dissolution of quartz in dilute aqueous solutions of organic acids at 25 degree C

    SciTech Connect

    Bennett, P.C.; Melcer, M.E.; Siegel, D.I.; Hassett, J.P. )

    1988-06-01

    The dissolution of quartz in dilute aqueous solutions of organic acids at 25{degree}C and standard pressure was investigated by the batch dissolution method. The bulk dissolution rate of quartz in 20 mmole/Kg citrate solutions at pH 7 was 8 to 10 times faster than that in pure water. After 1750 hours the concentration of dissolved silica in the citrate solution was 167 {mu}mole/Kg compared to 50 {mu}mole/Kg in water and a 20 mmole/Kg solution of acetate at pH 7. Solutions of salicylic, oxalic, and humic acids also accelerated the dissolution of quartz in aqueous solution at pH 7. The rate of dissolution in organic acids decreased sharply with decreasing pH. The possibility of a silica-organic acid complex was investigated using UV-difference spectroscopy. Results suggest that dissolved silica is complexed by citrate, oxalate and pyruvate at pH 7 by an electron-donor acceptor complex, whereas no complexation occurs between silica and acetate, lactate, malonate, or succinate. Three models are proposed for the solution and surface complexation of silica by organic acid which result in the accelerated dissolution and increased solubility of quartz in organic rich water.

  18. The dissolution of quartz in dilute aqueous solutions of organic acids at 25°C

    USGS Publications Warehouse

    Bennett, P.C.; Melcer, M.E.; Siegel, D.I.; Hassett, J.P.

    1988-01-01

    The dissolution of quartz in dilute aqueous solutions of organic acids at 25° and standard pressure was investigated by the batch dissolution method. The bulk dissolution rate of quartz in 20 mmole/Kg citrate solutions at pH 7 was 8 to 10 times faster than that in pure water. After 1750 hours the concentration of dissolved silica in the citrate solution was 167 μmole/Kg compared to 50 μmole/Kg in water and a 20 mmole/Kg solution of acetate at pH 7. Solutions of salicylic, oxalic, and humic acids also accelerated the dissolution of quartz in aqueous solution at pH 7. The rate of dissolution in organic acids decreased sharply with decreasing pH.The possibility of a silica-organic acid complex was investigated using UV-difference spectroscopy. Results suggest that dissolved silica is complexed by citrate, oxalate and pyruvate at pH 7 by an electron-donor acceptor complex, whereas no complexation occurs between silica and acetate, lactate, malonate, or succinate. Three models are proposed for the solution and surface complexation of silica by organic acid anions which result in the accelerated dissolution and increased solubility of quartz in organic rich water.

  19. Ab initio aqueous thermochemistry: application to the oxidation of hydroxylamine in nitric acid solution.

    PubMed

    Ashcraft, Robert W; Raman, Sumathy; Green, William H

    2007-10-18

    Ab initio molecular orbital calculations were performed and thermochemical parameters estimated for 46 species involved in the oxidation of hydroxylamine in aqueous nitric acid solution. Solution-phase properties were estimated using the several levels of theory in Gaussian03 and using COSMOtherm. The use of computational chemistry calculations for the estimation of physical properties and constants in solution is addressed. The connection between the pseudochemical potential of Ben-Naim and the traditional standard state-based thermochemistry is shown, and the connection of these ideas to computational chemistry results is established. This theoretical framework provides a basis for the practical use of the solution-phase computational chemistry estimates for real systems, without the implicit assumptions that often hide the nuances of solution-phase thermochemistry. The effect of nonidealities and a method to account for them is also discussed. A method is presented for estimating the solvation enthalpy and entropy for dilute aqueous solutions based on the solvation free energy from the ab initio calculations. The accuracy of the estimated thermochemical parameters was determined through comparison with (i) enthalpies of formation in the gas phase and in solution, (ii) Henry's law data for aqueous solutions, and (iii) various reaction equilibria in aqueous solution. Typical mean absolute deviations (MAD) for the solvation free energy in room-temperature water appear to be ~1.5 kcal/mol for most methods investigated. The MAD for computed enthalpies of formation in solution was 1.5-3 kcal/mol, depending on the methodology employed and the type of species (ion, radical, closed-shell) being computed. This work provides a relatively simple and unambiguous approach that can be used to estimate the thermochemical parameters needed to build detailed ab initio kinetic models of systems in aqueous solution. Technical challenges that limit the accuracy of the estimates are

  20. Comparison of XAD macroporous resins for the concentration of fulvic acid from aqueous solution

    USGS Publications Warehouse

    Aiken, G.R.

    1979-01-01

    Five macroreticular, nonlonlc AmberlHe XAD resins were evaluated for concentration and Isolation of fulvlc acid from aqueous solution. The capacity of each resin for fulvlc acid was measured by both batch and column techniques. Elution efficiencies were determined by desorptlon with 0.1 N NaOH. Highest recoveries were obtained with the acrylic ester resins which proved to be most efficient for both adsorption and elution of fulvlc acid. Compared to the acrylic ester resins, usefulness of the styrene dvlnybenzene resins to remove fulvlc acid is limited because of slow diffusion-controlled adsorption and formation of charge-transfer complexes, which hinders elution. ?? 1979 American Chemical Society.

  1. [Efficient killing of anthrax spores using aqueous and alcoholic peracetic acid solutions].

    PubMed

    Nattermann, H; Becker, S; Jacob, D; Klee, S R; Schwebke, I; Appel, B

    2005-08-01

    We analysed the sporicidal effect of different concentrations of aqueous and alcoholic peracetic acid (PAA) solutions on anthrax spores in suspension and germ carrier tests. In activation of anthrax spores in suspension assays was achieved in less than 2 min using 1% PAA solution and in less than 3 min using 0.5% PAA solution, respectively. In contrast, in germ carrier as says, a test under practical conditions, spores on 38% of the germ carriers survived treatment with 1% PAA solution for 15 min. The use of PAA in 80% ethyl alcohol outclassed the sporicidal effect of aqueous PAA solutions in both suspension and germ carrier assays. Anthrax spores on 14% of germ carriers tested survived 30 min of treatment with a 1% aqueous PAA solution. In contrast anthrax spores were reliably inactivated under the same test procedure using a 1% alcoholic PAA solution for 30 min. The proven enhancement of the sporicidal effect of alcoholic PAA solutions should be kept in mind when using disinfectants in practice. In further surveys we will optimise the test conditions.

  2. Mechanistic study of fulvic acid assisted propranolol photodegradation in aqueous solution.

    PubMed

    Makunina, Maria P; Pozdnyakov, Ivan P; Chen, Yong; Grivin, Vyacheslav P; Bazhin, Nikolay M; Plyusnin, Victor F

    2015-01-01

    Laser flash (355 nm) and stationary (365 nm) photolysis were used to study the mechanisms of propranolol photolysis in the presence of fulvic acid in aqueous solutions. The FA-assisted photodegradation of propranolol was observed using UV-A irradiation (where propranolol is stable). Direct evidence indicated that the photodegradation resulted from the static quenching of the FA triplet state by propranolol via the electron transfer mechanism. The triplet state yield (ϕT≈0.6%) and the T-T absorption coefficient (ɛT(620 nm)≈5×10(4) M(-1) cm(-1)) were estimated for the first time by modeling the yields of the FA triplet state in the presence of propranolol. Thus, fulvic acid is a promising agent for accelerating propranolol photodegradation in aqueous solutions under UV-A light irradiation.

  3. Enhanced removal of Hg(II) from acidic aqueous solution using thiol-functionalized biomass.

    PubMed

    Chai, Liyuan; Wang, Qingwei; Li, Qingzhu; Yang, Zhihui; Wang, Yunyan

    2010-01-01

    Spent grain, the low-cost and abundant biomass produced in the brewing industry, was functionalized with thiol groups to be used as an adsorbent for Hg(II) removal from acidic aqueous solution. The adsorbents were characterized by the energy-dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectroscopy. Optimum pH for Hg(II) adsorption onto the thiol-functionalized spent grain (TFSG) was 2.0. The equilibrium and kinetics of the adsorption of Hg(II) onto TFSG from acidic aqueous solution were investigated. From the Langmuir isotherm model the maximum adsorption capacity of TFSG for Hg(II) was found to be 221.73 mg g(-1), which was higher than that of most various adsorbents reported in literature. Moreover, the adsorption of Hg(II) onto TFSG followed pseudo-second-order kinetic model.

  4. Removal of transition metals from dilute aqueous solution by carboxylic acid group containing absorbent polymers

    USDA-ARS?s Scientific Manuscript database

    A new carboxylic acid group containing resin with cation exchange capacity, 12.67 meq/g has been used to remove Cu2+, Co2+ and Ni2+ ions from dilute aqueous solution. The resin has Cu2+, Co2+ and Ni2+ removal capacity, 216 mg/g, 154 mg/g and 180 mg/g, respectively. The selectivity of the resin to ...

  5. [Catalytic ozonation by ceramic honeycomb for the degradation of oxalic acid in aqueous solution].

    PubMed

    Zhao, Lei; Sun, Zhi-Zhong; Ma, Jun

    2007-11-01

    Comparative experiments for the degradation of oxalic acid in aqueous solution were carried out in the three processes of ozonation alone, ceramic honeycomb-catalyzed ozonation and ceramic honeycomb adsorption. The results show that the degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation, ozonation alone and ceramic honeycomb adsorption systems are 37.6%, 2.2% and 0.4%, and the presence of ceramic honeycomb catalyst significantly improves the degradation rate of oxalic acid compared to the results from non-catalytic ozonation and adsorption. With the addition of tert-butanol, the degradation rates of oxalic acid in catalytic ozonation system decrease by 24.1%, 29.0% and 30.1%, respectively, at the concentration of 5, 10 and 15 mg x L(-1). This phenomenon indicates that ceramic honeycomb-catalyzed ozonation for the degradation of oxalic acid in aqueous solution follows the mechanism of *OH oxidation, namely the heterogeneous surface of catalyst enhances the initiation of *OH. The results of TOC analysis demonstrate that the process of ceramic honeycomb-catalyzed ozonation can achieve the complete mineralization level without the formation of intermediary degradation products. The experimental results suggest that the reaction temperature has positive relationship with the degradation rate of oxalic acid. The degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation system are 16.4%, 37.6%, 61.3% and 68.2%, at the respective reaction temperature of 10, 20, 30 and 40 degrees C.

  6. Gamma-irradiation of malic acid in aqueous solutions. [prebiotic significance

    NASA Technical Reports Server (NTRS)

    Negron-Mendoza, A.; Graff, R. L.; Ponnamperuma, C.

    1980-01-01

    The gamma-irradiation of malic acid in aqueous solutions was studied under initially oxygenated and oxygen-free conditions in an attempt to determine the possible interconversion of malic acid into other carboxylic acids, specifically those associated with Krebs cycle. The effect of dose on product formation of the system was investigated. Gas-liquid chromatography combined with mass spectrometry was used as the principal means of identification of the nonvolatile products. Thin layer chromatography and direct probe mass spectroscopy were also employed. The findings show that a variety of carboxylic acids are formed, with malonic and succinic acids in greatest abundance. These products have all been identified as being formed in the gamma-irradiation of acetic acid, suggesting a common intermediary. Since these molecules fit into a metabolic cycle, it is strongly suggestive that prebiotic pathways provided the basis for biological systems.

  7. Gamma-irradiation of malic acid in aqueous solutions. [prebiotic significance

    NASA Technical Reports Server (NTRS)

    Negron-Mendoza, A.; Graff, R. L.; Ponnamperuma, C.

    1980-01-01

    The gamma-irradiation of malic acid in aqueous solutions was studied under initially oxygenated and oxygen-free conditions in an attempt to determine the possible interconversion of malic acid into other carboxylic acids, specifically those associated with Krebs cycle. The effect of dose on product formation of the system was investigated. Gas-liquid chromatography combined with mass spectrometry was used as the principal means of identification of the nonvolatile products. Thin layer chromatography and direct probe mass spectroscopy were also employed. The findings show that a variety of carboxylic acids are formed, with malonic and succinic acids in greatest abundance. These products have all been identified as being formed in the gamma-irradiation of acetic acid, suggesting a common intermediary. Since these molecules fit into a metabolic cycle, it is strongly suggestive that prebiotic pathways provided the basis for biological systems.

  8. Chapter 21 Architecture of Hydrates and Local Structure of Acetic Acid Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Pu, Liang; Wang, Qing; Zhang, Yong; Miao, Qiang; Kim, Yang-Soo; Zhang, Zhibing

    The protonation and deprotonation phenomena and molecular association of solute molecule with water via intermolecular hydrogen bonding forming various hydration compounds are very common in aqueous solution and in biological cell in nature. In the aqueous solution, more complicated type of hydrogen bond, hydrogen-bonding rings, various kinds of hydration compounds (hydrates), and even hydrogen-bonding network can be expected. The nature of hydrogen bonding, the bonds networking, the rule in architecture of larger hydration compounds, deprotonation of acetic acid in solution, stability of the hydrated proton, and the local structure of its aqueous solution are the most fundamental problems to understanding solute molecule living style in aqueous solution. Hydrogen-bonding rings and network in the multi-hydrates of acetic acid monomer have been investigated by ab initio calculations, and ab initio molecular dynamics (CPMD) simulations on acetic acid monomer-water system were also performed to explore the local structure of acetic acid aqueous solution. More than hundreds of multi-hydrates have been selected as candidates during our calculations. The structural optimizations and energy calculations have been performed at the MP2/6-31+g (d, p) and MP4/6-31+g (d, p) levels which are adequate for our large hydrates calculations with reliable results and reasonable cost as we stated in the Section 2. The most stable structure of the smallest hydration compound of acetic acid monomer, i.e., acetic acid water dimer, has a four-membered head-on ring with the smallest dipole moment. To verify the existence of it, the infrared spectra experiment data were collected in the dilute CCl4/HAc and CCl4/H2O ratio condition. The hydroxyl (O-H) stretching vibrations in molecules of water, acetic acid, and the dimer are distinguished, for the dissolved species are isolated from each other by surrounded solvent molecules CCl4. The calculated and measured vibration frequencies are almost

  9. Adsorptions of some heavy metal ions in aqueous solutions by acrylamide/maleic acid hydrogels

    SciTech Connect

    Saraydin, D.; Karadag, E.; Gueven, O.

    1995-10-01

    In this study, acrylamide-maleic acid (AAm/MA) hydrogels in the form of rod have been prepared by {gamma}-radiation. They have been used for adsorption of some heavy metal ions such as uranium, iron, and copper. For the hydrogel containing 40 mg of maleic acid and irradiated at 3.73 kGy, maximum and minimum swellings in the aqueous solutions of the heavy metal ions have been observed with water (1480%) and the aqueous solution of iron(III) nitrate (410%), respectively. Diffusions of water and heavy metal ions onto hydrogels have been found to be of the non-Fickian type of diffusion. In experiments of uranyl ions adsorption, Type II adsorption has been found. One gram of AAa/MA hydrogels sorbed 14-86 mg uranyl ions from solutions of uranyl acetate, 14-90 mg uranyl ions from solutions of uranyl nitrate, 16-39 mg iron ions from solutions of iron(IV) nitrate, and 28-81 mg copper ions from solutions of copper acetate, while acrylamide hydrogel did not sorb any heavy metals ions.

  10. Leaching of lead from zinc leach residue in acidic calcium chloride aqueous solution

    NASA Astrophysics Data System (ADS)

    Wang, Le; Mu, Wen-ning; Shen, Hong-tao; Liu, Shao-ming; Zhai, Yu-chun

    2015-05-01

    A process with potentially reduced environmental impacts and occupational hazards of lead-bearing zinc plant residue was studied to achieve a higher recovery of lead via a cost-effective and environmentally friendly process. This paper describes an optimization study on the leaching of lead from zinc leach residue using acidic calcium chloride aqueous solution. Six main process conditions, i.e., the solution pH value, stirring rate, concentration of CaCl2 aqueous solution, liquid-to-solid (L/S) ratio, leaching temperature, and leaching time, were investigated. The microstructure and components of the residue and tailing were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). On the basis of experimental results, the optimum reaction conditions were determined to be a solution pH value of 1, a stirring rate of 500 r·min-1, a CaCl2 aqueous solution concentration of 400 g·L-1, a liquid-to-solid mass ratio of 7:1, a leaching temperature of 80°C, and a leaching time of 45 min. The leaching rate of lead under these conditions reached 93.79%, with an iron dissolution rate of 19.28%. Silica did not take part in the chemical reaction during the leaching process and was accumulated in the residue.

  11. Effective Removal of Tetracycline from Aqueous Solution by Organic Acid-Coated Magnetic Nanoparticles.

    PubMed

    Guo, Liang; Liang, Yuyan; Chen, Xuelan; Xu, Wei; Wu, Kesheng; Wei, Hua; Xiong, Yonghua

    2016-03-01

    Self-assembled iron oxide nanocomposites are good magnetic nano-adsorbents that can be prepared using simple methods. Four types of organic acid-functionalised (oleic acid, undecenoic acid, caprylic acid or hexanoic acid) magnetic nanoparticles (MNPs) were synthesised through a one-pot chemisorption method for the removal of tetracycline (TC) from aqueous solution. The undecenoic acid-coated MNPs (UA-MNPs) exhibited the highest adsorption efficiency and can be easily retrieved with a low-gradient magnetic separator (0.4 Tesla) at pH 5.0 aqueous solution. The TC adsorption process on the UA-MNPs followed the Langmuir isotherm and the maximum adsorption capacities increased from 86.96 mg g(-1) to 222.2 mg g(-1) with the increase in temperature from 288 K to 318 K. The kinetics of adsorption fits pseudo-second-order model perfectly with a rate constant, 5.946 g mg(-1) min(-1) at 298 K. The positive values of the enthalpy (AH) and the negative value of the free energy (AG) indicated an endothermic and spontaneous adsorption process of TC on the UA-MNPs. Moreover, the UA-MNPs possessed excellent ability to adsorb the other three major types of TC antibiotics, including chlortetracycline, oxytetracycline and doxycycline.

  12. Superhydrophobic copper surfaces fabricated by fatty acid soaps in aqueous solution for excellent corrosion resistance

    NASA Astrophysics Data System (ADS)

    Xu, Wenlong; Hu, Yuanyuan; Bao, Wenda; Xie, Xiaoyu; Liu, Yiran; Song, Aixin; Hao, Jingcheng

    2017-03-01

    A simple and safe one-step immersion method was developed to obtain the stable superhydrophobic copper surfaces with excellent corrosion resistance ability using fatty acids in water-medium instead of ethanol. An organic alkali, N,N-dimethylcyclohexylamine (DMCHA), was chosen to solve the poor solubility of fatty acids in water and the high Krafft point of carboxylate salts with inorganic counterions. The superhydrophobic property can be realized in a much quicker process (7.5 min) in aqueous solution than in ethanol (more than 2 d), which is universally feasible for the fabrication of superhydrophobic metal surfaces in industry scale, thereby greatly increasing the safety in industrial manufacture.

  13. Removal of MCPA from aqueous solutions by acid-activated spent bleaching earth.

    PubMed

    Mahramanlioglu, Mehmet; Kizilcikli, Irfan; Biçer, I Ozlem; Tuncay, Melda

    2003-11-01

    The removal of MCPA (4-chloro-2-methyl phenoxyacetic acid) from aqueous solutions by activated spent bleaching earth (SBE) was studied as a function of time, initial concentration, adsorbent concentration, and temperature. The Langmuir and Freundlich isotherms were fitted by the adsorption data obtained. The values of Langmuir and Freundlich constants were determined. The adsorption kinetics was described by the Lagergren equation. Mass transfer coefficient and thermodynamic parameters were also calculated. Column experiments were conducted and brekthrough capacities were found for different concentrations and different flow rates. The study demonstrates that acid-treated SBE could be used as an efficient adsorbent for the removal of MCPA-bearing wastewater effluents.

  14. Influence of Acidity on Uranyl Nitrate Association in Aqueous Solutions: A Molecular Dynamics Simulation Study

    SciTech Connect

    de Almeida, Valmor F; Cui, Shengting; Khomami, Bamin; Ye, Xianggui; Smith, Rodney Bryan

    2010-01-01

    Uranyl ion complexation with water and nitrate is a key aspect of the uranium/plutonium extraction process. We have carried out a molecular dynamics simulation study to investigate this complexation process, including the molecular composition of the various complex species, the corresponding structure, and the equilibrium distribution of the complexes. The observed structures of the complexes suggest that in aqueous solution, uranyls are generally hydrated by 5 water molecules in the equatorial plane. When associating with nitrate ions, a water molecule is replaced by a nitrate ion, preserving the five-fold coordination and planar symmetry. Analysis of the pair correlation function between uranyl and nitrate suggests that nitrates bind to uranyl in aqueous solution mainly in a monodentate mode, although a small portion of bidentates occur. Dynamic association and dissociation between uranyls and nitrates take place in aqueous solution with a substantial amount of fluctuation in the number of various uranyl nitrate species. The average number of the uranyl mononitrate complexes shows a dependence on acid concentration consistent with equilibrium-constant analysis, namely, the concentration of [UO2NO3]+ increases with nitric acid concentration.

  15. Methylene blue adsorption from aqueous solution by activated carbon: effect of acidic and alkaline solution treatments.

    PubMed

    Ijagbemi, Christianah O; Chun, Ji I; Han, Da H; Cho, Hye Y; O, Se J; Kim, Dong S

    2010-01-01

    The removal of Methylene Blue (MB) from aqueous solution using activated carbon (AC) has been investigated. Adsorption experiments were conducted and the maximum adsorption capacity was determined. The effect of experimental parameters such as pH, dye concentration and temperature were studied on the adsorption process. Equilibrium data were mathematically modeled using the Langmuir and Freundlich adsorption models to describe the equilibrium isotherms at different dye concentrations and temperature. Parameters of best-fit model were calculated and discussed. To understand the mechanism of adsorption, kinetic models were employed to follow the adsorption processes; the pseudo-first-order best described the adsorption of MB onto AC. It was found that pH plays a major role in the adsorption process; adsorption capacity was influenced by the physical and surface chemical properties of carbon and the pH of the solution. 99.0% MB removal was achieved at equilibrium.

  16. The infrared optical constants of sulfuric acid at 250 K. [spectral reflectance measurement of aqueous solutions

    NASA Technical Reports Server (NTRS)

    Pinkley, L. W.; Williams, D.

    1976-01-01

    Results are presented for measurements of the IR spectral reflectance at near-normal incidence of aqueous solutions of sulfuric acid with acid concentrations of 75% and 95.6% by weight. Kramers-Kronig analyses of the reflectance data are employed to obtain values of the optical constants n(nu) and k(nu) in the spectral range from 400 to 6000 cm to the -1 power. The optical constants of these solutions at 250 K and 300 K are compared. It is found that in spectral regions remote from strong absorption bands, the values of the n(nu) indices obtained at 250 K agree with the values given by Lorentz-Lorenz correction of the same indices at 300 K. All absorption bands observed at 300 K are found to be present at 250 K with slight shifts in frequency and with significant differences in the k(nu) indices at the band maxima. Based on these results, it is concluded that the clouds of Venus probably consist of droplets of aqueous solutions of sulfuric acid with acid concentrations of about 75% by weight.

  17. Self-assembling of poly(aspartic acid) with bovine serum albumin in aqueous solutions.

    PubMed

    Nita, L E; Chiriac, A P; Bercea, M; Asandulesa, M; Wolf, Bernhard A

    2017-02-01

    Macromolecular co-assemblies built up in aqueous solutions, by using a linear polypeptide, poly(aspartic acid) (PAS), and a globular protein, bovine serum albumin (BSA), have been studied. The main interest was to identify the optimum conditions for an interpenetrated complex formation in order to design materials suitable for biomedical applications, such as drug delivery systems. BSA surface possesses several amino- and carboxylic groups available for covalent modification, and/or bioactive substances attachment. In the present study, mixtures between PAS and BSA were investigated at 37°C in dilute aqueous solution by viscometry, dynamic light scattering and zeta potential determination, as well as in solid state by AFM microscopy and dielectric spectroscopy. The experimental data have shown that the interpolymer complex formation occurs for a PAS/BSA molar ratio around 0.541.

  18. Determination of hydroxyl radicals with salicylic acid in aqueous nitrate and nitrite solutions.

    PubMed

    Yang, Xi; Zhan, Man-jun; Kong, Ling-ren; Wang, Lian-sheng

    2004-01-01

    The qualitative and quantitative analyses of reactive oxygen species are essential to determine their steady-state concentration and related reaction mechanisms in environmental aquatic systems. In this study, salicylic acid was employed as an innovative molecular probe of hydroxyl radical(OH) generated in aqueous nitrate and nitrite solutions through photochemical reactions. Kinetic studies showed that the steady-state concentrations of OH in aqueous NO3- (10 mmol/L, pH = 5) and NO2- (10 mmol/L, pH = 5) solutions under ultraviolet irradiation were at a same magnitude, 10(-15) mol/L. Apparent quantum yields of OH at 313 nm were measured as 0.011 and 0.07 for NO3- and NO2- respectively, all comparable to the results of previous studies.

  19. Adipic and malonic acid aqueous solutions: surface tensions and saturation vapor pressures.

    PubMed

    Riipinen, Ilona; Koponen, Ismo K; Frank, Göran P; Hyvärinen, Antti-Pekka; Vanhanen, Joonas; Lihavainen, Heikki; Lehtinen, Kari E J; Bilde, Merete; Kulmala, Markku

    2007-12-20

    The surface tension of adipic aqueous solutions was measured as a function of temperature (T=278-313 K) and adipic acid mole fraction (X=0.000-0.003) using the Wilhelmy plate method. A parametrization fitted to these data is presented. The evaporation rates of binary water-malonic and water-adipic acid droplets were measured with a TDMA technique at different temperatures (T=293-300 K) and relative humidities (58-80%), and the saturation vapor pressures of subcooled liquid malonic and adipic acids were derived from the data using a binary evaporation model. The temperature dependence of the vapor pressures was obtained as least-squares fits to the derived vapor pressures: ln(Psat,l) (Pa)=220.2389-22634.96/T (K)-26.66767 ln T (K) for malonic acid and ln(Psat,l) (Pa)=140.6704-18230.97/T (K)-15.48011 ln T (K) for adipic acid.

  20. Influence of Nitric Acid on the Helium Ion Radiolysis of Aqueous Butanal Oxime Solutions.

    PubMed

    Costagliola, A; Venault, L; Deroche, A; Vermeulen, J; Duval, F; Blain, G; Vandenborre, J; Fattahi-Vanani, M; Vigier, N

    2017-07-13

    Samples of butanal oxime in aqueous nitric acid solutions have been irradiated with the helium ion ((4)He(2+)) beam of the CEMHTI (Orléans, France) cyclotron. The consumption yield of butanal oxime has been measured by gas chromatography coupled with mass spectrometry. Gaseous products (mainly H2 and N2O) have also been monitored by micro-gas chromatography. Yields of liquid phase products (hydrogen peroxide and nitrous acid) have been determined by colorimetric methods. The influence of nitric acid on the radiation chemical behavior of butanal oxime depends on the nitric acid concentration. For a low concentration (≤0.5 mol L(-1)) butanal oxime is protected by the nitrate ions, which can efficiently scavenge the water radiolysis radicals. For higher concentrations, nitrous acid can accumulate in the medium, therefore leading to a strong increase of the butanal oxime degradation. The associated mechanism is an autocatalytic oxidation of butanal oxime by HNO2.

  1. Thermochemical study of the reactions of acid-base interaction in an aqueous solution of α-aminobutyric acid

    NASA Astrophysics Data System (ADS)

    Lytkin, A. I.; Chernikov, V. V.; Krutova, O. N.; Skvortsov, I. A.; Korchagina, A. S.

    2017-01-01

    The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO3 and KOH are measured by means of calorimetry in different ranges of pH at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO3). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δr H 0, Δr G 0, and Δr S 0) of the reactions of acid-base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.

  2. Removal of Pb(ii) from aqueous/acidic solutions by using bentonite as an adsorbent.

    PubMed

    Naseem, R; Tahir, S S

    2001-11-01

    The ability of bentonite clay to remove Pb(II) from aqueous solutions and from nitric acid, hydrochloric acid and perchloric acid solutions (1.0-1 x 10(-5)) has been studied at different optimized conditions of concentrations, amount of adsorbent, temperature, concentration of electrolyte and pH. Maximum adsorption of Pb(II), i.e. > 98% has been achieved in aqueous solutions, while 86% is achieved from 1.0 x 10(-5) M HCl using 0.5 g of bentonite. The adsorption decreases by increasing the concentration of electrolytes. Flame atomic absorption spectrometer was used for measuring lead concentration. Isotherm analysis of adsorption data obtained at 25 degrees C, 30 degrees C, 40 degrees C and 50 degrees C showed that the adsorption pattern of lead on bentonite followed the langmuir isotherm and freundlich isotherm, respectively. DeltaH(o) and deltaS(o) were calculated from the slope and intercept of ln K(D) vs. I/T plots.

  3. EXAFS study of the speciation of protactinium(V) in aqueous hydrofluoric acid solutions.

    PubMed

    De Sio, Stéphanie M; Wilson, Richard E

    2014-12-01

    The speciation of protactinium(V) in hydrofluoric acid (HF) solutions was studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure measurements were performed on an aqueous solution of 0.05 M protactinium(V) with various HF concentrations ranging from 0.5 to 27 M in order to probe the protactinium coordination sphere with respect to the identity and number of coordinating ligands. The resulting fits to the spectra suggest the presence of an eight-coordinate homoleptic fluoro complex in highly concentrated fluoride solutions (27 M), with equilibrium between seven- and eight-coordinate fluoro complexes at moderate acidities, and in more dilute solutions, results indicate that one water molecule is likely to replace a fluoride in the first coordination sphere, at a distance of 2.54-2.57 Å. Comparisons of this chemistry with group V metals, niobium and tantalum, are presented, and the potential implications for these results on the hydrolytic behavior of protactinium in aqueous systems are discussed.

  4. An EXAFS study of the speciation of protactinium(V) in aqueous hydrofluoric acid solution

    SciTech Connect

    De Sio, Stephanie M.; Wilson, Richard E.

    2014-12-01

    The speciation of protactinium(V) in hydrofluoric acid (HF) solutions was studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure measurements were performed on an aqueous solution of 0.05 M protactinium(V) with various HF concentrations ranging from 0.5 to 27 M in order to probe the protactinium coordination sphere with respect to the identity and number of coordinating ligands. The resulting fits to the spectra suggest the presence of an eight-coordinate homoleptic fluoro complex in highly concentrated fluoride solutions (27 M), with equilibrium between seven- and eight-coordinate fluoro complexes at moderate acidities, and in more dilute solutions, results indicate that one water molecule is likely to replace a fluoride in the first coordination sphere, at a distance of 2.54-2.57 angstrom. Comparisons of this chemistry with group V metals, niobium and tantalum, are presented, and the potential implications for these results on the hydrolytic behavior of protactinium in aqueous systems are discussed.

  5. Uptake of isoprene, methacrylic acid and methyl methacrylate into aqueous solutions of sulfuric acid and hydrogen peroxide.

    PubMed

    Liu, Ze; Ge, Maofa; Wang, Weigang

    2012-01-01

    Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol formation from isoprene and its gas-phase oxidation products, but the lack of kinetics data significantly limited the evaluation of this process in the atmosphere. Here we report the first measurement of the uptake of isoprene, methacrylic acid and methyl methacrylate into aqueous solutions of sulfuric acid and hydrogen peroxide. Isoprene cannot readily partition into the solution because of its high volatility and low solubility, which hinders its further liquid-phase oxidation. Both methacrylic acid and methyl methacrylate can enter the solutions and be oxidized by hydrogen peroxide, and steady-state uptake was observed with the acidity of solution above 30 wt.% and 70 wt.%, respectively. The steady-state uptake coefficient of methacrylic acid is much larger than that of methyl methacrylate for a solution with same acidity. These observations can be explained by the different reactivity of these two compounds caused by the different electron-withdrawing conjugation between carboxyl and ester groups. The atmospheric lifetimes were estimated based on the calculated steady-state uptake coefficients. These results demonstrate that the multiphase acid-catalyzed oxidation of methacrylic acid plays a role in secondary organic aerosol formation, but for isoprene and methyl methacrylate, this process is not important in the troposphere.

  6. Radiolysis of aqueous solutions of acetic acid in the presence of Na-montmorillonite

    NASA Technical Reports Server (NTRS)

    Navarro-Gonzalez, R.; Negron-Mendoza, A.; Ramos, S.; Ponnamperuma, C.

    1990-01-01

    The gamma-irradiation of 0.8 mol dm-3 aqueous, oxygen-free acetic acid solutions was investigated in the presence or absence of Na-montmorillonite. H2, CH4, CO, CO2, and several polycarboxylic acids were formed in all systems. The primary characteristics observed in the latter system were: (1) Higher yield of the decomposition of acetic acid; (2) Lower yield of the formation of polycarboxylic acids; (3) No effect on the formation of methane; (4) Higher yield of the formation of carbon dioxide; and (5) The reduction of Fe3+ in the octahedral sites of Na-montmorillonite. A possible reaction scheme was proposed to account for the observed changes. The results are important in understanding heterogeneous processes in radiation catalysis and might be significant to prebiotic chemistry.

  7. Radiolysis of aqueous solutions of acetic acid in the presence of Na-montmorillonite

    NASA Technical Reports Server (NTRS)

    Navarro-Gonzalez, R.; Negron-Mendoza, A.; Ramos, S.; Ponnamperuma, C.

    1990-01-01

    The gamma-irradiation of 0.8 mol dm-3 aqueous, oxygen-free acetic acid solutions was investigated in the presence or absence of Na-montmorillonite. H2, CH4, CO, CO2, and several polycarboxylic acids were formed in all systems. The primary characteristics observed in the latter system were: (1) Higher yield of the decomposition of acetic acid; (2) Lower yield of the formation of polycarboxylic acids; (3) No effect on the formation of methane; (4) Higher yield of the formation of carbon dioxide; and (5) The reduction of Fe3+ in the octahedral sites of Na-montmorillonite. A possible reaction scheme was proposed to account for the observed changes. The results are important in understanding heterogeneous processes in radiation catalysis and might be significant to prebiotic chemistry.

  8. Radiation-induced degradation of cyclohexanebutyric acid in aqueous solutions by gamma ray irradiation

    NASA Astrophysics Data System (ADS)

    Jia, Wenbao; He, Yanquan; Ling, Yongsheng; Hei, Daqian; Shan, Qing; Zhang, Yan; Li, Jiatong

    2015-04-01

    The radiation-induced degradation of cyclohexanebutyric acid under gamma ray irradiation was investigated. Degradation experiments were performed with 100 mL sealed Pyrex glass vessels loaded with 80 mL of cyclohexanebutyric acid solutions at various initial concentrations of 10, 20, and 40 mg L-1. The absorbed doses were controlled at 0, 0.65, 1.95, 3.25, 6.5, 9.75, and 13 kGy. The results showed that gamma ray irradiation could effectively degrade cyclohexanebutyric acid in aqueous solutions. The removal rate of cyclohexanebutyric acid increased significantly with the increase of absorbed dose and the decrease of its initial concentration. At the same time, the removal of chemical oxygen demand (COD) was as effective as that of cyclohexanebutyric acid. The kinetic studies showed that the degradation of cyclohexanebutyric acid followed pseudo first-order reaction. Above all, the proposed mechanism obtained when NaNO2, NaNO3 and tert-butanol were added showed that the •OH radical played a major role in the gamma degradation process of cyclohexanebutyric acid, while •H and eaq- played a minor role in the gamma degradation process. The degradation products were identified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectrometry (GC/MS) during cyclohexanebutyric acid degradation.

  9. [Studies on carbonization of saccharides by using aqueous solution of various acids].

    PubMed

    Zhang, Xin; He, An-Qi; Kang, Ting-Guo; Xia, Jin-Ming; Weng, Shi-Fu; Xu, Yi-Zhuang; Wu, Jin-Guang

    2014-09-01

    The authors tried to establish an approach to use acids to convert biomass into a fuel with higher carbon content and lower oxygen content in a zero-energy-consumption fashion. Considering that biomass is composed of monosaccharide, we used aqueous solutions of variation acids including hydrochloric acid, sulfuric acid and perchloric acid to treat 2-deoxy-ribose and fructose at ambient temperature and pressure. Black substances were produced after a period of time when 2-deoxy-ribose and fructose were mixed with aqueous solutions containing 8 mol · L(-1) acids. The black substance was collected and characterized by using elemental analysis, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Elemental analysis results indicate that the contents of carbon increases significantly in the black substances in comparison with 2-deoxy-ribose and fructose. Moreover, XPS results indicate that the content of oxygen in the black substance undergoes a significant decrease compared with pure 2-deoxy-ribose and fructose. In the XPS spectra, the is peaks of 2-deoxy-ribose, strong sub peak at 286. 05 eV, which is assigned to carbon linked to oxygen directly, dominate in the C is peak envelop. After treatment by HClO4, the peak decreased dramatically. This result also supports the conclusion that the content of oxygen in mono-saccharide is significantly reduced after treatment by acids. In the FTIR spectra of the black substances, strong peaks can be observed around 1 600 cm(-1), indicating that C==C bond is formed in the product. The above results suggest that treatments with acids may be developed as a new zero-energy-consumption approach to convert biomass in a new fuel with improved energy output efficiency.

  10. Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution

    NASA Astrophysics Data System (ADS)

    Lytkin, A. I.; Chernikov, V. V.; Krutova, O. N.; Skvortsov, I. A.; Korchagina, A. S.

    2016-09-01

    Heat effects of the dissolution of crystalline γ-aminobutyric acid in water and potassium hydroxide solutions are determined by direct colorimetry at 298.15 K. Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution are calculated.

  11. Experimental Shock Chemistry of Aqueous Amino Acid Solutions and the Cometary Delivery of Prebiotic Compounds

    NASA Astrophysics Data System (ADS)

    Blank, Jennifer G.; Miller, Gregory H.; Ahrens, Michael J.; Winans, Randall E.

    2001-02-01

    A series of shock experiments were conducted to assess the feasibility of the delivery of organic compounds to the Earth via cometary impacts. Aqueous solutions containing near-saturation levels of amino acids (lysine, norvaline, aminobutyric acid, proline, and phenylalanine) were sealed inside stainless steel capsules and shocked by ballistic impact with a steel projectile plate accelerated along a 12-m-long gun barrel to velocities of 0.5-1.9 km sec^-1. Pressure-temperature-time histories of the shocked fluids were calculated using 1D hydrodynamical simulations. Maximum conditions experienced by the solutions lasted 0.85-2.7 μs and ranged from 5.1-21 GPa and 412-870 K. Recovered sample capsules were milled open and liquid was extracted. Samples were analyzed using high performance liquid chromatography (HPLC) and mass spectrometry (MS). In all experiments, a large fraction of the amino acids survived. We observed differences in kinetic behavior and the degree of survivability among the amino acids. Aminobutyric acid appeared to be the least reactive, and phenylalanine appeared to be the most reactive of the amino acids. The impact process resulted in the formation of peptide bonds; new compounds included amino acid dimers and cyclic diketopiperazines. In our experiments, and in certain naturally occurring impacts, pressure has a greater influence than temperature in determining reaction pathways. Our results support the hypothesis that significant concentrations of organic material could survive a natural impact process.

  12. Competitive adsorption of boric acid and chromate onto alumina in aqueous solutions.

    PubMed

    Demetriou, A; Pashalidis, I

    2014-01-01

    The competitive adsorption of boric acid and chromate from aqueous solutions by alumina has been investigated by spectrophotometry at pH 8, ionic strength = 0.0, 0.1 and 1.0 M NaClO4, T = 22 ± 3 °C and under normal atmospheric conditions. The experimental data show that addition of excess boric acid in the system leads to the increase of Cr(VI) concentration in solution, indicating the replacement of adsorbed chromate by boron on the alumina surface. Data evaluation results in the determination of the competition reaction constant and the formation constant of the Cr(VI) surface complexes, which are logKCr(VI)-B(III) = -3.5 ± 0.2 and logβ*Cr = 7.6 ± 0.3, respectively.

  13. Separation of glycols from dilute aqueous solutions via complexation with boronic acids

    SciTech Connect

    Randel, L.A.; King, C.J.

    1991-07-01

    This work examines methods of separating low molecular weight glycols from dilute aqueous solution. Extraction into conventional solvents is generally not economical, since, in the literature reviewed, distribution ratios for the two- to four-carbon glycols are all less than one. Distribution ratios can be increased, however, by incorporating into the organic phase an extracting agent that will complex with the solute of interest. The extracting agent investigated in this work is 3-nitrophenylboronic acid (NPBA). NPBA, a boric acid derivative, reversibly complexes with many glycols. The literature on complexation of borate and related compounds with glycols, including mechanistic data, measurement techniques, and applications to separation processes, provides information valuable for designing experiments with NPBA and is reviewed herein. 88 refs., 15 figs., 24 tabs.

  14. Regeneration of basic sorbents used in the recovery of acetic acid from dilute aqueous solution

    SciTech Connect

    Ng, M.; King, C.J.

    1988-10-01

    The regeneration of basic sorbents used in the recovery of dilute aqueous acetic acid was explored. The regeneration methods studied were solvent leaching and vaporization. The resins used were weak base anion exchange resins, Dow Chemical Company's Dowex MWA-1 (tertiary amine resin) and Celanese Corporation's Aurorez (polybenzimidazole resin). The equilibrium between the aqueous acetic acid solution and the resins was measured in batch experiments. The composite isotherms calculated from these data wee comparable to those of other researchers. Methanol was used as the solvent to leach acetic acid from the resin. The equilibrium data from the batch experiments were used in the local-equilibrium theory of fixed-bed devices to model the desorption behavior of acetic acid in methanol. Both sorption and desorption equilibrium data were used in chemical complexation models to obtain sorption affinities and capacities of the resin for acetic acid. However, the amount of methanol needed to achieve a high degree of regeneration was too large to be economical. 15 refs., 25 figs., 3 tabs.

  15. Statistical mechanics of hydrophobic amino acids in aqueous solution: A joint experimental scattering and computational study

    NASA Astrophysics Data System (ADS)

    Song, Lingshuang; Yang, Lin; Huang, Wei; Meng, Jie; Yang, Sichun

    How hydrophobic amino acids interact with each other is still a fundamental question in understanding protein dynamics and folding. Here, we describe an integrative experimental-computational approach of combining x-ray solution scattering and atomistic molecular simulations to determine the molecular properties of a hydrophobic leucine amino acid in an aqueous solution. First, scattering data were acquired at a series of amino acid and salt concentrations and these scattering profiles were further used to calibrate atomistic molecular simulations via a single parameter for solute-solvent interaction. Second, these accurate data of atomistic leucine simulations were used to quantify the effective interacting potentials via a structural simplification of one-bead-per-residue and two-bead-per-residue representations. Third, comparative energetic analyses between the one-bead and two-bead representations were performed to reach a simple picture of residue-residue interactions with an accurate energy function. Taken together, this joint experimental-computational study provides critical insights into microscopic interactions of hydrophobic amino acids in solution with a profound application for studying molecular dynamics of, e.g., intrinsically disordered proteins and their folding.

  16. Solution properties and taste behavior of lactose monohydrate in aqueous ascorbic acid solutions at different temperatures: Volumetric and rheological approach.

    PubMed

    Sarkar, Abhijit; Sinha, Biswajit

    2016-11-15

    The densities and viscosities of lactose monohydrate in aqueous ascorbic acid solutions with several molal concentrations m=(0.00-0.08)molkg(-1) of ascorbic acid were determined at T=(298.15-318.15)K and pressure p=101kPa. Using experimental data apparent molar volume (ϕV), standard partial molar volume (ϕV(0)), the slope (SV(∗)), apparent specific volumes (ϕVsp), standard isobaric partial molar expansibility (ϕE(0)) and its temperature dependence [Formula: see text] the viscosity B-coefficient and solvation number (Sn) were determined. Viscosity B-coefficients were further employed to obtain the free energies of activation of viscous flow per mole of the solvents (Δμ1(0≠)) and of the solute (Δμ2(0≠)). Effects of molality, solute structure and temperature and taste behavior were analyzed in terms of solute-solute and solute-solvent interactions; results revealed that the solutions are characterized predominantly by solute-solvent interactions and lactose monohydrate behaves as a long-range structure maker.

  17. Removal of lead from aqueous solutions by a poly(acrylic acid)/bentonite nanocomposite

    NASA Astrophysics Data System (ADS)

    Rafiei, H. R.; Shirvani, M.; Ogunseitan, O. A.

    2016-11-01

    We synthesized a novel poly acrylic acid-organobentonite (PAA-Bent) nanocomposite by successive intercalation of cetyltrimethylammonium (CTA) surfactant and polyacrylic acid (PAA) into the bentonite (Bent) interlayer spaces. The surfactant-modified clay (CTA-Bent) and PAA-Bent nanocomposite were characterized by XRD and FT-IR techniques and used for removal of Pb(II) from aqueous solution. The XRD results confirmed the intercalation of CTA and PAA into the interlayer spaces of the bentonite increasing the d 001 spacing of the clay from 12.2 up to 38.9 Å. FT-IR analysis of the modified clay samples revealed the functional groups of CTA and PAA constituents alighted on the bentonite surfaces. Maximum Pb sorption capacity of the Bent and PAA-Bent predicted by Langmuir model were 52.3 and 93.0 mg g-1, respectively, showing that the synthesized nanocomposite superiorly adsorbed Pb from the solution as compared to the Bent. The maximum Pb removal efficiency of 99.6 % was achieved by the nanocomposite at 25 °C with <30 min contact time for a 7.5 g L-1 solid-to-liquid ratio and an initial metal concentration of 400 mg L-1. The results indicated that PAA-Bent nanocomposite can be efficiently used as a superadsorbent for the removal of Pb(II) from aqueous solution.

  18. Pretreatment of sugarcane bagasse by acid-catalysed process in aqueous ionic liquid solutions.

    PubMed

    Zhang, Zhanying; O'Hara, Ian M; Doherty, William O S

    2012-09-01

    A biomass pretreatment process was developed using acidified ionic liquid (IL) solutions containing 10-30% water. Pretreatment of sugarcane bagasse at 130°C for 30 min by aqueous 1-butyl-3-methylimidazolium chloride (BMIMCl) solution containing 1.2% HCl resulted in a glucan digestibility of 94-100% after 72 h of enzymatic hydrolysis. HCl was found to be a more effective catalyst than H(2)SO(4) or FeCl(3). Increasing acid concentration (from 0.4% to 1.2%) and reaction temperature (from 90 to 130°C) increased glucan digestibility. The glucan digestibility of solid residue obtained with the acidified BMIMCl solution that was re-used for three times was >97%. The addition of water to ILs for pretreatment could significantly reduce IL solvent costs and allow for increased biomass loadings, making the pretreatment by ILs a more economic proposition. Copyright © 2012 Elsevier Ltd. All rights reserved.

  19. Acid-catalysed autoreduction of ferrylmyoblobin in aqueous solution studied by freeze quenching and ESR spectroscopy.

    PubMed

    Kröger-Ohlsen, M V; Andersen, M L; Skibsted, L H

    1999-04-01

    Decay of the hypervalent muscle pigment ferrylmyoglobin, formed by activation of metmyoglobin by hydrogen peroxide, was found, when studied by a combination of ESR and UV/VIS spectroscopy in aqueous solution at physiological pH, to proceed by parallel second- and first-order kinetics. At pH below 6.5 a sharp ESR signal (g = 2.003) with an increasing intensity for decreasing pH were observed in solutions frozen in liquid nitrogen, and a broad signal (g = 2.005) was seen throughout the studied pH range also in frozen solutions. The g = 2.005 signal is suggested to arise from an intermediate formed in an intramolecular rate-determining electron-transfer in ferrylmyoglobin, whereas the g 2.003 signal is caused by a radical formed in a proton-assisted electron-transfer initiating the specific acid-catalysed autoreduction.

  20. Thermosensitivity of bile acid-based oligo(ethylene glycol) stars in aqueous solutions.

    PubMed

    Strandman, Satu; Le Dévédec, Frantz; Zhu, X X

    2011-08-03

    Amphiphilic star-shaped oligo(ethylene glycol)s with a hydrophobic bile acid core and varying number of hydrophilic arms have been made. Their thermal behavior in aqueous solutions depends on the number rather than the length of the arms. The two-armed lithocholate derivative showed the strongest tendency for association and exhibited the lowest cloud point (79 °C) of the oligomers made, as well as another phase separation at a lower temperature (31 °C). The "double thermosensitivity" arising both from the salt-dependent LCST of the oligo(ethylene glycol) segments and the temperature-responsive self-assembly of amphiphilic bile acid derivative provides an interesting path in the design of bile acid-based smart materials. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. [Adsorption of acid orange II from aqueous solution onto modified peat-resin particles].

    PubMed

    Sun, Qing-Ye; Yang, Lin-Zhang

    2007-06-01

    The adsorption of acid orange II onto modified peat-resin particles was examined in aqueous solution in a batch system. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The pseudo-first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data. The results showed that both Langmuir and Freundlich adsorption models could be used to describe the adsorption of acid orange II onto modified peat-resin particles. The maximum adsorption capacity was 71.43 mg x g(-1). The data analysis indicated that the intraparticle diffusion model could fit the results of kinetic experiment well. The adsorption rate of acid orange II onto modified peat-resin particles is affected by the initial dye concentrations, sizes and doses of modified peat-resin particles and agitation rates. The surface of modified peat-resin particle is the major adsorption area.

  2. Removal of fluoride ion from aqueous solution by a cerium-poly(hydroxamic acid) resin complex.

    PubMed

    Haron, M J; Yunus, W M

    2001-05-01

    A cerium-loaded poly(hydroxamic acid) chelating ion exchanger was used for fluoride ion removal from aqueous solution. The resin was effective in decreasing the fluoride concentration from 5 mM down to 0.001 mM in acidic pH between 3 and 6. The sorption followed a Langmuir model with a maximum capacity of 0.5 mmol/g. The removal is accomplished by an anion exchange mechanism. The rate constant for the sorption was found to be 9.6 x 10(-2) min-1. A column test shows that the fluoride ion was retained on the column until breakthrough point and the fluoride sorbed in the column can be eluted with 0.1 M NaOH. The column can be reused after being condition with hydrochloric acid at pH 4. The resin was tested and found to be effective for removal of fluoride from actual industrial wastewater.

  3. CESIUM RECOVERY FROM AQUEOUS SOLUTIONS

    DOEpatents

    Goodall, C.A.

    1960-09-13

    A process is given for precipitating cesium on zinc ferricyanide (at least 0.0004 M) from aqueous solutions containing mineral acid in a concentration of from 0.2 N acidity to 0.61 N acid-deficiency and advantageously, but not necessarily, also aluminum nitrate in a concentration of from l to 2.5 M.

  4. Interaction of Atmospheric-Pressure Air Microplasmas with Amino Acids as Fundamental Processes in Aqueous Solution

    PubMed Central

    Zhou, Renwu; Zhou, Rusen; Zhuang, Jinxing; Zong, Zichao; Zhang, Xianhui; Liu, Dongping; Bazaka, Kateryna; Ostrikov, Kostya

    2016-01-01

    Plasma medicine is a relatively new field that investigates potential applications of cold atmospheric-pressure plasmas in bioengineering, such as for bacterial inactivation and degradation of organic molecules in water. In order to enunciate mechanisms of bacterial inactivation at molecular or atomic levels, we investigated the interaction of atmospheric-pressure air microplasmas with amino acids in aqueous solution by using high-resolution mass spectrometry (HRMS). Results show that the oxidation effect of plasma-induced species on the side chains of the amino acids can be categorized into four types, namely hydroxylation, nitration, dehydrogenation and dimerization. In addition, relative activities of amino acids resulting from plasma treatment come in descending order as follows: sulfur-containing carbon-chain amino acids > aromatic amino acids > five-membered ring amino acids > basic carbon-chain amino acids. Since amino acids are building blocks of proteins vital to the growth and reproduction of bacteria, these results provide an insight into the mechanism of bacterial inactivation by plasma. PMID:27183129

  5. Interaction of Atmospheric-Pressure Air Microplasmas with Amino Acids as Fundamental Processes in Aqueous Solution.

    PubMed

    Zhou, Renwu; Zhou, Rusen; Zhuang, Jinxing; Zong, Zichao; Zhang, Xianhui; Liu, Dongping; Bazaka, Kateryna; Ostrikov, Kostya

    2016-01-01

    Plasma medicine is a relatively new field that investigates potential applications of cold atmospheric-pressure plasmas in bioengineering, such as for bacterial inactivation and degradation of organic molecules in water. In order to enunciate mechanisms of bacterial inactivation at molecular or atomic levels, we investigated the interaction of atmospheric-pressure air microplasmas with amino acids in aqueous solution by using high-resolution mass spectrometry (HRMS). Results show that the oxidation effect of plasma-induced species on the side chains of the amino acids can be categorized into four types, namely hydroxylation, nitration, dehydrogenation and dimerization. In addition, relative activities of amino acids resulting from plasma treatment come in descending order as follows: sulfur-containing carbon-chain amino acids > aromatic amino acids > five-membered ring amino acids > basic carbon-chain amino acids. Since amino acids are building blocks of proteins vital to the growth and reproduction of bacteria, these results provide an insight into the mechanism of bacterial inactivation by plasma.

  6. Removal of Se(IV) from aqueous solution using sulphuric acid-treated peanut shell.

    PubMed

    El-Shafey, E I

    2007-09-01

    A carbonaceous sorbent was prepared from peanut shell via sulphuric acid treatment. Se(IV) removal from aqueous solution on the sorbent was studied varying time, pH, Se(IV) concentration, temperature and sorbent status (wet and dry). Se(IV) removal was faster using the wet sorbent than the dry sorbent following a pseudo-first-order model. Se(IV) removal increases at low pH values, and decreases as pH increases until pH 7. Sorption was found to fit the Langmuir equation and sorption capacity for the wet sorbent was higher than that for the dry one. Both sorbents showed an increased selenium sorption by rising the temperature. Redox processes between Se(IV) and the carbon sorbent are involved. Analysis by scanning electron microscope and X-ray powder diffraction for the sorbent after the reaction with acidified Se(IV) confirmed the availability of elemental selenium as particles on the sorbent surface as a result of Se(IV) reduction. Physicochemical tests showed an increase in sorbent acidity, cation exchange capacity (CEC) and surface functionality after the reaction with acidified Se(IV), indicating the oxidation processes occurring on the sorbent surface. Due to its reduction properties, the sorbent seems efficient for Se(IV) removal from aqueous solution.

  7. Terahertz microfluidic chips for detection of amino acids in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Su, Bo; Zhang, Cong; Fan, Ning; Zhang, Cunlin

    2016-11-01

    Microfluidic technology can control the fluidic thickness accurately in less than 100 micrometers. So the combination of terahertz (THz) and microfluidic technology becomes one of the most interesting directions towards biological detection. We designed microfluidic chips for terahertz spectroscopy of biological samples in aqueous solutions. Using the terahertz time-domain spectroscopy (THz-TDS) system, we experimentally measured the transmittance of the chips and the THz absorption spectra of L-threonine and L-arginine, respectively. The results indicated the feasibility of performing high sensitivity THz spectroscopy of amino acids solutions. Therefore, the microfluidic chips can realize real-time and label-free measurement for biochemistry samples in THz-TDS system.

  8. Fixed bed adsorption of 2-naphthalenesulfonic acid from aqueous solution by composite resin.

    PubMed

    Jia, Dong M; Li, Ya P; Li, Yue J; Li, Yong G; Li, Chang H

    2014-02-01

    Adsorption behavior of the iron impregnated, weakly basic resin D301 (Fe-D301) for removal of 2-naphthalenesulfonic acid (2-NSA) from aqueous solution was studied by using a fixed-bed column. The effects of process variables such as bed height, flow rate, and coexisting ions were investigated. The results indicated that the breakpoint and exhaustion point increased with increasing bed height and decreased with increasing 2-NSA flowrate. Experimental data showed a strong fit to the Bed Depth Service Time model. The coexisting ions in the 2-NSA solution had a clear effect on the breakthrough volume. The high extent of recovery of 2-NSA with good reproducibility provided an effective method for the separation of 2-NSA by the adsorbent Fe-D301.

  9. Electrodeposited Films from Aqueous Tungstic Acid-Hydrogen Peroxide Solutions for Electrochromic Display Devices

    NASA Astrophysics Data System (ADS)

    Yamanaka, Kazusuke

    1987-11-01

    Electrodeposited tungsten oxide films from aqueous tungstic acid-hydrogen peroxide solutions were investigated for applications to electrochromic devices. These films exhibited electrochromism in aprotic electrolyte solutions containing Li-salts. When the films were heat-treated for an hour at temperatures between 100 and 200°C, the electrochromic reactions were rich in reversibility. The coloring efficiency and response rate for the films were favorable and comparable to those for tungsten trioxide evaporated films. A cell life-test was performed on several clock-size cells by applying a 1.2-V, 1-Hz, continuous square wave. The typical amount of charge required for coloration was about 50 C / m2 and remained unchanged even after 107 coloration-bleaching cycles.

  10. Action of combined magnetic fields on aqueous solution of glutamic acid: the further development of investigations.

    PubMed

    Giuliani, Livio; Grimaldi, Settimio; Lisi, Antonella; D'Emilia, Enrico; Bobkova, Natalia; Zhadin, Mikhail

    2008-01-25

    In the present work the results of the known investigation of the influence of combined static (40 microT) and alternating (amplitude of 40 nT) parallel magnetic fields on the current through the aqueous solution of glutamic acid, were successfully replicated. Fourteen experiments were carried out by the application of the combined magnetic fields to the solution placed into a Plexiglas reaction vessel at application of static voltage to golden electrodes placed into the solution. Six experiments were carried out by the application of the combined magnetic fields to the solution placed in a Plexiglas reaction vessel, without electrodes, within an electric field, generated by means of a capacitor at the voltage of 27 mV. The frequency of the alternating field was scanned within the bounds of 1.0 Hz including the cyclotron frequency corresponding to a glutamic acid ion and to the applied static magnetic field. In this study the prominent peaks with half-width of approximately 0.5 Hz and with different heights (till 80 nA) were registered at the alternating magnetic field frequency equal to the cyclotron frequency (4.2 Hz). The general reproducibility of the investigated effects was 70% among the all solutions studied by us and they arose usually after 40-60 min. after preparation of the solution. In some made-up solutions the appearance of instability in the registered current was noted in 30-45 min after the solution preparation. This instability endured for 20-40 min. At the end of such instability period the effects of combined fields action appeared practically every time. The possible mechanisms of revealed effects were discussed on the basis of modern quantum electrodynamics.

  11. Sorption of As(V) from aqueous solution using acid modified carbon black.

    PubMed

    Borah, Dipu; Satokawa, Shigeo; Kato, Shigeru; Kojima, Toshinori

    2009-03-15

    The sorption performance of a modified carbon black was explored with respect to arsenic removal following batch equilibrium technique. Modification was accomplished by refluxing the commercial carbon black with an acid mixture comprising HNO(3) and H(2)SO(4). Modification resulted in the substantial changes to the inherent properties like surface chemistry and morphology of the commercial carbon black to explore its potential as sorbent. The suspension pH as well as the point of zero charge (pH(pzc)) of the material was found to be highly acidic. The material showed excellent sorption performance for the removal of arsenic from a synthetic aqueous solution. It removed approximately 93% arsenic from a 50mg/L solution at equilibration time. The modified carbon black is capable of removing arsenic in a relatively broad pH range of 3-6, invariably in the acidic region. Both pseudo-first-order and second-order kinetics were applied to search for the best fitted kinetic model to the sorption results. The sorption process is best described by the pseudo-second-order kinetic. It has also been found that intra-particle diffusion is the rate-controlling step for the initial phases of the reaction. Modelling of the equilibrium data with Freundlich and Langmuir isotherms revealed that the correlation coefficient is more satisfactory with the Langmuir model although Freundlich model predicted a good sorption process. The sorption performance has been found to be strongly dependent on the solution pH with a maximum display at pH of 5.0. The temperature has a positive effect on sorption increasing the extent of removal with temperature up to the optimum temperature. The sorption process has been found to be spontaneous and endothermic in nature, and proceeds with the increase in randomness at the solid-solution interface. The spent sorbent was desorbed with various acidic and basic extracting solutions with KOH demonstrating the best result ( approximately 85% desorption).

  12. Aromatic ionene topology and counterion-tuned gelation of acidic aqueous solutions.

    PubMed

    Bachl, Jürgen; Bertran, Oscar; Mayr, Judith; Alemán, Carlos; Díaz Díaz, David

    2017-04-19

    Unusual gelation of acidic solutions was achieved using polycations bearing quaternary ammonium moieties. These ionene polymers are based on a disubstituted phenylene dibenzamide core, which allows the construction of different topomers (i.e. ortho-1, meta-2 and para-3). The topology of the polymers was found to play a key role on their aggregation behaviour both in pure water and in a variety of aqueous acidic solutions leading to the formation of stable acidic gels. Specifically, ortho-1 showed superior gelation ability than the analogues meta-2 and para-3 in numerous solutions of different pH and ionic strengths. Lower critical gelation concentrations, higher gel-to-sol transition temperatures and faster gelation were usually observed for ortho-1 regardless the solvent system. Detailed computational molecular dynamic simulations revealed a major role of the counterion (Cl(-)) and specific polymerpolymer interactions. In particular, hydrogen bonds, N-Hπ interactions and intramolecular π-π stacking networks are distinctive in ortho-1. In addition, counterions located at internal hydration regions also affect to such polymerpolymer interactions, acting as binders and, therefore, providing additional stability.

  13. Cesium recovery from aqueous solutions

    DOEpatents

    Goodhall, C. A.

    1960-09-13

    A process for recovering cesium from aqueous solutions is given in which precipitation on zinc ferricyanide is used. The precipitation is preferably carried out in solutions containing at least 0.0004M zinc ferricyanide, an acidity ranging from 0.2N mineral acid to 0.61N acid deficiency, and 1 to 2.5M aluminum nitrate. (D.L.C.)

  14. Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Bajuk-Bogdanović, D.; Uskoković-Marković, S.; Hercigonja, R.; Popa, A.; Holclajtner-Antunović, I.

    2016-01-01

    Micro Raman spectroscopy was applied to investigate the speciation of heteropoly and isopoly molybdates in 0.05 and 0.005 M aqueous solutions of 12-molybdophosphoric acid at pH values between 1 and 6. For comparative purposes, 31P NMR spectroscopy was applied too. It is shown that stability of Keggin anion is influenced both by pH and concentration of solution. The Keggin structure is stable in acidic solutions (pH < 1.6) while defective Keggin structures are formed with further alkalization (up to pH 5.6). Monolacunary anion PMo11O397 - is the main component in the pH region from 1.6 to 3.4. Further removal of molybdenyl species causes the appearance of other vacant Keggin structures such as PMo9O31(OH)36 - and PMo6O259 - at about pH 4. At pH 5.0, anion PMo6O259 - is the main species. In solutions with pH greater than 5.0, heteropolymolybdates disappear completely and isopolymolybdates Mo7O246 - and MoO42 - are formed in higher amounts. In more diluted solution of 0.005 M, the decomposition scheme of 12-molybdophosphoric acid solution with increasing of pH takes place without observation of significant amounts of Mo7O246 - species. If alkalinization is performed with 0.5 M instead of 5 M NaOH, there are no significant changes in the Raman spectra of solutions. It is shown that the spectra of evaporated samples may be used for the identification of molecular species in corresponding concentrated solutions. However, Raman spectra of dry residues of more diluted solutions differ from spectra of corresponding solutions due to the reactions performed during the process of drying and cannot be used for unambiguous identification of species in solution. Acidification of 0.05 M solution of Na2MoO4 shows that at pH > 5.6, molybdate anion MoO42 - dominates, while in the pH range between 5.6 and 1, heptamolybdate anion Mo7O246 - is preferentially formed.

  15. Uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide.

    PubMed

    Liu, Ze; Wu, Ling-Yan; Wang, Tian-He; Ge, Mao-Fa; Wang, Wei-Gang

    2012-01-12

    Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol (SOA) formation from isoprene and its gas-phase oxidation products, but the kinetics and chemical mechanism remain largely uncertain. Here we report the first measurement of uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide in the temperature range of 253-293 K. The steady-state uptake coefficients were acquired and increased quickly with increasing sulfuric acid concentration and decreasing temperature. Propyne, acetone, and 2,3-dihydroxymethacrylic acid were suggested as the products. The chemical mechanism is proposed to be the oxidation of carbonyl group and C═C double bonds by peroxide hydrogen in acidic environment, which could explain the large content of polyhydroxyl compounds in atmospheric fine particles. These results indicate that multiphase acid-catalyzed oxidation of methacrolein by hydrogen peroxide can contribute to SOA mass in the atmosphere, especially in the upper troposphere.

  16. Adsorption of naphthalene from aqueous solution onto fatty acid modified walnut shells.

    PubMed

    Zhu, Mijia; Yao, Jun; Dong, Lifu; Sun, Jingjing

    2016-02-01

    The removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous solution is challenging to environmental technologists. Agricultural waste is apparently the most attractive materials in removing PAHs because of its abundance, renewability, and economic advantage. The adsorption of PAHs (e.g., naphthalene) onto walnut shell (WNS) and its fatty acid (e.g., capric acid, lauric acid, palmitic acid, and oleic acid)-modified equivalent were investigated in this work to develop low-cost biosorbents for hydrophobic organic compounds. Compared with other modified sorbents, oleic acid graftted walnut shell (OWNS) showed the maximum partition coefficient (4330 ± 8.8 L kg(-1)) because of its lowest polarity and highest aromaticity. The adsorption capacity (7210 μg g(-1)) of OWNS at the temperature of 298 K was observed for an initial naphthalene concentration of 25 mg L(-1) with contact time of 40 h, sorbent dosage of 1 g L(-1), and in neutral condition. Furthermore, the regeneration capability of OWNS implied that it was a promising biosorbent for naphthalene removal. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. ''Pulling'' Nanoparticles into Water: Phase Transfer of Oleic Acid Stabilized Monodisperse Nanoparticles into Aqueous Solutions of alpha-Cyclodextrin

    SciTech Connect

    Wang, Y.; Wong, J.F.; Teng, X.; Lin, X.Z.; Yang, H.

    2003-10-18

    (B204)This paper describes a general method to drastically improve the disparity of oleic acid stabilized nanoparticles in aqueous solutions. We use oleic acid stabilized monodisperse nanoparticles of iron oxides and silver as model systems, and have modified the surface properties of these nanoparticles through the formation of an inclusion complex between surface-bound surfactant molecules and alpha-cyclodextrin (alpha-CD). After the modification, the nanoparticles of both iron oxide and Ag can transfer from hydrophobic solvents, such as hexane, to alpha-CD aqueous phase. The efficiency of the phase transfer to the aqueous solutions depend son the initial alpha-CD concentration. The alpha-CD/oleic acid complex stabilized nanoparticles can be stable for long periods of time in aqueous phase under ambient atmospheric conditions. Transmission electron microscopy (TME), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, and colorimetric methods have been used in the characterization of these nanoparticles.

  18. Aquatic photolysis: photolytic redox reactions between goethite and adsorbed organic acids in aqueous solutions

    USGS Publications Warehouse

    Goldberg, M.C.; Cunningham, K.M.; Weiner, Eugene R.

    1993-01-01

    Photolysis of mono and di-carboxylic acids that are adsorbed onto the surface of the iron oxyhydroxide (goethite) results in an oxidation of the organic material and a reduction from Fe(III) to Fe(II) in the iron complex. There is a subsequent release of Fe2+ ions into solution. At constant light flux and constant solution light absorption, the factors responsible for the degree of photolytic reaction include: the number of lattice sites that are bonded by the organic acid; the rate of acid readsorption to the surface during photolysis; the conformation and structure of the organic acid; the degree of oxidation of the organic acid; the presence or absence of an ??-hydroxy group on the acid, the number of carbons in the di-acid chain and the conformation of the di-acid. The ability to liberate Fe(III) at pH 6.5 from the geothite lattice is described by the lyotropic series: tartrate>citrate> oxalate > glycolate > maleate > succinate > formate > fumarate > malonate > glutarate > benzoate = butanoate = control. Although a larger amount of iron is liberated, the series is almost the same at pH 5.5 except that oxalate > citrate and succinate > maleate. A set of rate equations are given that describe the release of iron from the goethite lattice. It was observed that the pH of the solution increases during photolysis if the solutions are not buffered. There is evidence to suggest the primary mechanism for all these reactions is an electron transfer from the organic ligand to the Fe(III) in the complex. Of all the iron-oxyhydroxide materials, crystalline goethite is the least soluble in water; yet, this study indicates that in an aqueous suspension, iron can be liberated from the goethite lattice. Further, it has been shown that photolysis can occur in a multiphase system at the sediment- water interface which results in an oxidation of the organic species and release of Fe2+ to solution where it becomes available for further reaction. ?? 1993.

  19. Photocatalytic hydrogen generation from hydriodic acid using methylammonium lead iodide in dynamic equilibrium with aqueous solution

    NASA Astrophysics Data System (ADS)

    Park, Sunghak; Chang, Woo Je; Lee, Chan Woo; Park, Sangbaek; Ahn, Hyo-Yong; Nam, Ki Tae

    2017-01-01

    The solar-driven splitting of hydrohalic acids (HX) is an important and fast growing research direction for H2 production. In addition to the hydrogen, the resulting chemicals (X2/X3-) can be used to propagate a continuous process in a closed cycle and are themselves useful products. Here we present a strategy for photocatalytic hydrogen iodide (HI) splitting using methylammonium lead iodide (MAPbI3) in an effort to develop a cost-effective and easily scalable process. Considering that MAPbI3 is a water-soluble ionic compound, we exploit the dynamic equilibrium of the dissolution and precipitation of MAPbI3 in saturated aqueous solutions. The I- and H+ concentrations of the aqueous solution are determined to be the critical parameters for the stabilization of the tetragonal MAPbI3 phase. Stable and efficient H2 production under visible light irradiation was demonstrated. The solar HI splitting efficiency of MAPbI3 was 0.81% when using Pt as a cocatalyst.

  20. Surface characterisation of ethylene propylene diene rubber upon exposure to aqueous acidic solution

    NASA Astrophysics Data System (ADS)

    Mitra, Susanta; Ghanbari-Siahkali, Afshin; Kingshott, Peter; Hvilsted, Søren; Almdal, Kristoffer

    2006-07-01

    Two types of pure ethylene propylene diene rubbers were exposed to two different acids for varying period of time. Surface characterisation was carried out using X-ray photoelectron spectroscopy (XPS). Two EPDM rubbers selected for this study were comparable in co-monomer compositions but significantly different with respect to molar mass and the presence of long chain branching. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were exposed in two different acidic solutions, viz. chromosulphuric (Cr (VI)/H 2SO 4) and sulphuric acid (H 2SO 4) (20%, v/v) at ambient temperature from 1 to 12 weeks. XPS analysis indicated that several oxygenated species were formed on the surface of both rubbers after exposure. It was postulated from the XPS analyses that both aqueous acidic solutions attacked the olefinic double bonds (C dbnd C) of ENB. Furthermore, 20% Cr (VI)/H 2SO 4 also attacked the allylic carbon-hydrogen (C sbnd H) bonds of ENB resulting in more oxygenated species on the surface compared to 20% H 2SO 4 under identical conditions. Cr (VI) in the 20% Cr (VI)/H 2SO 4 was found to play an important role in alteration of surface chemistry. Studies using a model system consisting of EPDM mixed with Cr (VI) and Cr (III) salts revealed that the change of oxidation state from Cr (VI) to Cr (III) as a consequence of direct involvement of Cr (VI) in the chemical alteration of EPDM surfaces. Interestingly, the presence of long chain branching and molar mass did not significantly influence the chemical processes owing to the acid treatment.

  1. Biosorption of methyl blue onto tartaric acid modified wheat bran from aqueous solution

    PubMed Central

    2012-01-01

    Tartaric acid modified wheat bran was utilized as adsorbent to remove methyl blue, a basic dye from aqueous solution. Batch experiments were carried out to study the effect of various experimental parameters such as initial solution pH, contact time, initial dye concentration and adsorbent dosage, on dye adsorption. The results showed that the modification of wheat bran by tartaric acid significantly improved its adsorption capacity, and made this material a suitable adsorbent to remove methyl blue. The adsorption capacity of modified wheat bran was about 1.6 times higher than that of unmodified one. The amount of methyl blue adsorbed was found to vary with initial solution pH, adsorbent dosage, contact time and initial methyl blue concentration. Kinetics study showed that the overall adsorption rate of methyl blue was illustrated by pseudo-second-order kinetic model. The applicability of the Langmuir and Freundlich models for the data was tested. Both models adequately described the experimental data of the biosorption of methyl blue. The maximum adsorption capacity for methyl blue calculated from Langmuir model was 25.18 mg/g. The study has shown the effectiveness of modified wheat bran in the removal of methyl blue, and that it can be considered as an attractive alternative to the more expensive technologies used in wastewater treatment. PMID:23369295

  2. Biosorption of methyl blue onto tartaric acid modified wheat bran from aqueous solution.

    PubMed

    Yao, Shuhua; Lai, Hong; Shi, Zhongliang

    2012-12-05

    Tartaric acid modified wheat bran was utilized as adsorbent to remove methyl blue, a basic dye from aqueous solution. Batch experiments were carried out to study the effect of various experimental parameters such as initial solution pH, contact time, initial dye concentration and adsorbent dosage, on dye adsorption. The results showed that the modification of wheat bran by tartaric acid significantly improved its adsorption capacity, and made this material a suitable adsorbent to remove methyl blue. The adsorption capacity of modified wheat bran was about 1.6 times higher than that of unmodified one. The amount of methyl blue adsorbed was found to vary with initial solution pH, adsorbent dosage, contact time and initial methyl blue concentration. Kinetics study showed that the overall adsorption rate of methyl blue was illustrated by pseudo-second-order kinetic model. The applicability of the Langmuir and Freundlich models for the data was tested. Both models adequately described the experimental data of the biosorption of methyl blue. The maximum adsorption capacity for methyl blue calculated from Langmuir model was 25.18 mg/g. The study has shown the effectiveness of modified wheat bran in the removal of methyl blue, and that it can be considered as an attractive alternative to the more expensive technologies used in wastewater treatment.

  3. Enhanced copper surface protection in aqueous solutions containing short-chain alkanoic acid potassium salts.

    PubMed

    Abelev, Esta; Starosvetsky, David; Ein-Eli, Yair

    2007-10-23

    The ability of dissolved potassium monocarboxylate salts to produce surface passivation and to inhibit aqueous corrosion of copper was studied. The electrochemical measurements indicate that the inhibiting efficiency of these compounds, with a general formula Cn-1H2n-1COOK or CnK (n=3...12), is dependent on the hydrocarbon chain length. The inhibiting efficiency was higher for a longer hydrocarbon chain of n-alkanoic acid. The degree of copper protection was found to increase with an increase in n-alkanoic acid potassium salt concentration; the optimum concentration of potassium dodecanoate (C12K) in sulfate solutions was found to be 0.07 M. The protective layers formed at the copper surface subsequent to exposure in various n-alkanoic acid potassium salt solutions were characterized by contact angle measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared reflection spectroscopy. Pronounced copper protection was attributed to the growth of a protective film on the copper surface, containing both copper oxides and copper carboxylate compounds. It is suggested that the organic molecules enhance copper protection by covering copper oxides with a thin and dense organic layer, which prevents water molecules or aggressive anions from interacting with the copper surface.

  4. CESIUM RECOVERY FROM AQUEOUS SOLUTIONS

    DOEpatents

    Schneider, R.A.

    1961-06-20

    Cesium may be precipitated from an aqueous solution whose acidity ranges between a pH of 1.5 and a molarity of 5 on cobaltous, zinc, cadmium, nickel, or ferrous cobalticyanide. This precipitation brings about a separation from most fission products. Ruthenium which coprecipitates to a great degree can be removed by dissolving in sulfuric acid and boiling the solution in the presence of periodic acid for volatilization; other coprecipitated fission products can then be precipitated from the sulfuric acid solution with a ferric hydroxide carrier.

  5. Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal-Organic Frameworks.

    PubMed

    Jonckheere, Dries; Steele, Julian A; Claes, Birgit; Bueken, Bart; Claes, Laurens; Lagrain, Bert; Roeffaers, Maarten B J; De Vos, Dirk E

    2017-09-06

    Metal-organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids l-phenylalanine (l-Phe), l-tryptophan (l-Trp), and l-tyrosine (l-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr-MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for l-Trp and 20 wt % for l-Phe. These uptakes are 5-10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for l-Phe and l-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5-7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of l-Trp to form hydrogen bonds favor the uptake of l-Trp with its larger indole moiety compared to the smaller phenyl side group of l-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded l-Trp within the MIL-140C framework are evidenced by red- and blue-shifted -NH vibrations (3400 cm(-1)) in Fourier transform infrared spectroscopy, which were attributed to types N-Hl-Trp···πMIL-140C and N-Hl-Trp···OMIL-140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids l-glutamate and l-aspartate (l-Glu and l-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids l-Tyr, l-Phe, and l-Trp and of l-Glu and l-Asp from waste protein hydrolysates.

  6. Reflectance of aqueous solutions

    NASA Technical Reports Server (NTRS)

    Querry, M. R.

    1972-01-01

    The optical properties and optical constants of water and aqueous solutions were studied to develop an accurate tabulation of graphical representations of the optical constants through a broad spectrum. Manuscripts of articles are presented concerning extinction coefficients, relative specular reflectance, and temperature effect on the water spectrum. Graphs of absolute reflectance, phase shifts, index of refraction, and extinction coefficients for water, heavy water and aqueous solutions are included.

  7. Characterization of potassium bromide crystals grown in the aqueous solution of picric acid

    NASA Astrophysics Data System (ADS)

    Maheswari, J. Uma; Krishnan, C.; Kalyanaraman, S.; Selvarajan, P.

    2016-12-01

    Potassium bromide crystals were grown in the aqueous solution of picric acid by slow evaporation technique at room temperature. X-ray Diffraction (XRD) analysis ensures that the grown sample is in Fm3m space group and FCC structure. Energy Dispersive X-ray Spectroscopy (EDX) reveals the presence of elements in the title compound. UV-Vis-NIR spectrum reveals that the grown sample is a promising nonlinear optical (NLO) material. FTIR analysis confirms the functional groups present in the sample. The thermogravimetric (TG) and differential thermogravimetric (DTA) analyses ensure that the sample material is thermally stable up to 160 °C. The second harmonic efficiency of the sample is 1.3 times greater than that of standard KDP. The mechanical strength of the grown sample is estimated by Vickers microhardness tester. The electrical properties were investigated by impedance analysis and the results of various studies of the grown crystals are discussed.

  8. The aqueous photolysis of α-pinene in solution with humic acid

    USGS Publications Warehouse

    Goldberg, Marvin C.; Cunningham, Kirkwood M.; Aiken, George R.; Weiner, Eugene R.; ,

    1992-01-01

    Terpenes are produced abundantly by environmental processes but are found in very low concentrations in natural waters. Aqueous photolysis of solutions containing α-pinene, a representative terpene, in the presence of humic acid resulted in degradation of the pinene. Comparison of this reaction to photolysis of α-pinene in the presence of methylene blue leads to the conclusion that the reactive pathway for the abiotic degradation of α-pinene is due to reaction with singlet oxygen produced by irradiation of the humic material. The initial product of single oxygen and α-pinene is a hydroperoxide. Since humic materials are prevalent in most natural waters, this mechanism of photodecomposition for α-pinene probably also applies to other terpenes in surface waters and may be reasonably considered to contribute to their low environmental concentration.

  9. Removal of Basic Violet 14 from aqueous solution using sulphuric acid activated materials.

    PubMed

    Suresh, S

    2016-01-01

    In this study the adsorption of Basic Violet, 14 from aqueous solution onto sulphuric acid activated materials prepared from Calophyllum inophyllum (CS) and Theobroma cacao (TS) shells were investigated. The experimental data were analysed by Langmuir, Freundlich and Temkin isotherm models. The results showed that CS has a superior adsorption capacity compared to the TS. The adsorption capacity was found to be 1416.43 mg/g for CS and 980.39 mg/g for TS. The kinetic data results at different concentrations were analysed using pseudo first-order and pseudo-second order model. Boyd plot indicates that the dye adsorption onto CS and TS is controlled by film diffusion. The adsorbents were characterised by scanning electron microscopy. The materials used in this study were economical waste products and hence can be an attractive alternative to costlier adsorbents for dye removal in industrial wastewater treatment processes.

  10. Studies on equilibrium of anthranilic acid in aqueous solutions and in two-phase systems: aromatic solvent-water.

    PubMed

    Zapała, Lidia; Kalembkiewicz, Jan; Sitarz-Palczak, Elzbieta

    2009-03-01

    The acid-base equilibria of anthranilic acid have been characterized in terms of macro- and microdissociation constants (dissociation constants K(a1), K(a2) and tautomeric constant K(z)). On the basis of spectrophotometric investigations the values of the distribution ratio D of anthranilic acid in the two-phase systems: aromatic solvent (benzene, ethylbenzene, toluene, chlorobenzene, bromobenzene)-aqueous solution were obtained. Employing the results of potentiometric titration in the two-phase systems: aromatic solvent-aqueous solution the distribution constant K(D) and dimerization constant K(dim) values were calculated. The influence of organic solvent polarity and pH of the aqueous phase on the contents of the particular forms of the acid in the two-phase systems were analyzed.

  11. Acid-activated spent bleaching earth as a sorbent for chromium (VI) in aqueous solution.

    PubMed

    Low, K S; Lee, C K; Lee, T S

    2003-02-01

    Spent bleaching earth, an industrial waste produced after the bleaching of crude palm oil, was investigated for its potential in removing Cr(VI) from aqueous solution. The earth was treated with different amounts of sulfuric acid and under different activation temperatures. Results show that the optimum treatment process involved 10% sulfuric acid at 350 degrees C. The effects of contact time, pH, initial concentration, sorbent dosage, temperature, sorption isotherms and the presence of other anions on its sorption capacity were studied. Isotherm data could be fitted into a modified Langmuir isotherm model implying monolayer coverage of Cr(VI) on acid activated spent bleaching earth. The maximum sorption capacity derived from the Langmuir isotherm was 21.2 mg g(-1). This value was compared with those of some other low cost sorbents. Studies of anion effect on the uptake of Cr(VI) on acid activated spent bleaching earth provided the following order of suppression: EDTA >PO4(3-)>SO4(2-)>NO3(-)>Cl(-).

  12. Removal of fluoride in aqueous solution by adsorption on acid activated water treatment sludge

    NASA Astrophysics Data System (ADS)

    Vinitnantharat, Soydoa; Kositchaiyong, Sriwilai; Chiarakorn, Siriluk

    2010-06-01

    This paper reports the use of a pellet of adsorbent made from water treatment sludge (S) and acid activated water treatment sludge (SH) for removal of fluoride in the batch equilibration technique. The influence of pH, adsorbent dosage, temperature and effect of other ions were employed to find out the feasibility of acid activated adsorbent to remove fluoride to the permissible concentration of 0.7 mg/L. The results from the adsorption isotherm followed both Langmuir and Freundlich models and the highest fluoride removal was found for adsorbent activated with acetic acid at 2.0 mol/L. The optimum adsorbent dosage was found at 40 g/L, 0.01 mol/L acid activated adsorbent which was able to adsorb fluoride from 10 down to 0.11 mg/L. The adsorption capacity was decreased when the temperature increased. This revealed that the adsorption of fluoride on SH was exothermic. In the presence of nitrate and carbonate ions in the aqueous solution, fluoride removal efficiency of SH decreased from 94.4% to 86.6% and 90.8%, respectively. However, there is no significant effect in the presence of sulfate and chloride ions.

  13. Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite.

    PubMed

    Zhan, Yanhui; Zhu, Zhiliang; Lin, Jianwei; Qiu, Yanling; Zhao, Jianfu

    2010-01-01

    Natural zeolite was modified by loading cetylpyridinium bromide (CPB) to create more efficient sites for humic acid (HA) adsorption. The natural and CPB modified zeolites were characterized with X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and elemental analysis. The effects of various experimental parameters such as contact time, initial HA concentration, solution pH and coexistent Ca2+, upon HA adsorption onto CPB modified zeolites were evaluated. The results showed that natural zeolite had negligible affinity for HA in aqueous solutions, but CPB modified zeolites exhibited high adsorption efficiency for HA. A higher CPB loading on natural zeolites exhibited a larger HA adsorption capacity. Acidic pH and coexistent Ca2+ were proved to be favorable for HA adsorption onto CPB modified zeolite. The kinetic process was well described by pseudo second-order model. The experimental isotherm data fitted well to Langmuir and Sips models. The maximum monolayer adsorption capacity of CPB modified zeolite with surfactant bilayer coverage was found to be 92.0 mg/g.

  14. The adsorption of cationic dye from aqueous solution onto acid-activated andesite.

    PubMed

    Tsai, Wen-Tien; Hsu, Hsin-Chieh; Su, Ting-Yi; Lin, Keng-Yu; Lin, Chien-Ming; Dai, Tzong-Hung

    2007-08-25

    The adsorption of cationic dye (i.e., methylene blue) onto acid-activated andesite in aqueous solution was studied in a batch system with respect to its kinetics as a function of agitation speed, initial adsorbate concentration, pH, and adsorbent mass. It was found that the resulting acid-activated adsorbent possessed a mesoporous structure with BET surface areas at around 60m(2)/g. The surface characterization of acid-activated andesite was also performed using the zeta-potential measurements, indicating that the charge sign on the surface of the andesite should be negative in a wide pH range (i.e., 3-11). Furthermore, a simplified kinetic model, pseudo-second-order, was tested to investigate the adsorption behaviors of methylene blue onto the clay samples treated under different process conditions. It was found that the adsorption process could be well described with the model. The adsorption capacity parameter of the model obtained in the present work was significantly in line with the process parameters.

  15. Removal of boron from aqueous solution using magnetic carbon nanotube improved with tartaric acid

    PubMed Central

    2014-01-01

    Boron removal capacity of multi-walled carbon nanotubes (MWCNTs) modified with tartaric acid was investigated in this study. Modification of MWCNTs with tartaric acid was confirmed by Boehm surface chemistry method and fourier transform infra-red (FT-IR) spectroscopy. Experiments were performed to determine the adsorption isotherm and adsorption thermodynamic parameters of boron adsorption on tartaric acid modified MWCNTs (TA-MWCNTs). The effect of variables including initial pH, dosage of adsorbent, contact time and temperature was investigated. Analysis of data showed that adsorption equilibrium could be better described by Freundlich isotherm and the maximum adsorption capacities obtained at the pH of 6.0 was 1.97 mg/g. The estimated thermodynamic values of free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) indicated a spontaneous and an endothermic process. Furthermore, the TA-MWCNTs was magnetized for separation of boron-contaminated adsorbent from aqueous solution by applying magnetic field. The results showed that magnetic TA-MWCNTs particles were separated effectively after adsorption from contaminated water. PMID:24393401

  16. Effects of ultrasonic processing on degradation of salvianolic acid B in aqueous solution.

    PubMed

    Guo, Y X; Zhang, L; Lu, L; Liu, E H; Shi, C Z

    2016-09-10

    To evaluate the stability of salvianolic acid B (Sal B) under ultrasound-assisted extraction in the pharmaceutical industry, degradation of Sal B under ultrasonic irradiation was investigated as the function of buffer concentration, pH, and temperature. With regard to Sal-B concentration, a first-order degradation process was determined, with 10% change in assay from its initial concentration as t90=4.81h, under maximum stability acidic conditions (pH 2.0) and at 25°C. The logkpH-pH profile described by specific acid-base catalysis and water molecules supported the experimental results. Liquid chromatography-mass spectrometry (LC-MS) analyses revealed 7 major degradation products whose structures were characterized by electrospray ionization/mass spectrometry. A primary degradation pathway involved cleavage of the ester bond and ring-opening of benzofuran in Sal B was proposed. The complete degradation pathway of Sal B was also proposed. Results showed that ultrasonic irradiation leads to degradation of Sal B in aqueous solution.

  17. Isolation and separation of transplutonium elements from other actinides on ion exchange resins from aqueous and aqueous ethanol solutions of sulfuric acid

    SciTech Connect

    Guseva, L.I.; Tikhomirova, G.S.; Stepushkina, V.V.

    1987-11-01

    The behavior of Am, Cm, Bk, Cf, Es, and other actinides, as well as Zr, on an anion exchange resin and a cation exchange resin in aqueous and aqueous alcohol solutions of sulfuric acid was investigated as a function of the concentration of various components of the solution. It was found that the presence of alcohol in sulfuric acid solutions leads to an increase in the distribution coefficients both on cation exchange resins and on anion exchange resins. The possibility of using ion exchange resins for the concentration and separation of transplutonium elements from U, Np, Pu, Zr, and other elements that form strong complexes with sulfate ions in a wide range of sulfuric acid concentrations was demonstrated.

  18. Adsorption of chloridazon from aqueous solution on heat and acid treated sepiolites.

    PubMed

    González-Pradas, E; Socías-Viciana, M; Ureña-Amate, M D; Cantos-Molina, A; Villafranca-Sánchez, M

    2005-05-01

    The adsorption of chloridazon on heat treated sepiolite samples at 110 degrees C (S-110), 200 degrees C (S-200), 400 degrees C (S-400), 600 degrees C (S-600) and acid treated samples with H2SO4 solutions of two different concentrations (0.25 and 1.0M) (S-0.25 and S-1.0, respectively) from pure water at 25 degrees C has been studied by using batch experiments. In addition, column experiments were carried out with the natural (S-110) and 600 degrees C (S-600) heat treated samples, using a 10.30 mg l-1 aqueous solution of chloridazon. The adsorption experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 2.89 mg kg-1 for the S-1.0 sample up to 164 mg kg-1 for the S-600 sample; so, the heat treatment given to the sepiolite greatly increases its adsorption capacity for the herbicide chloridazon whereas the acid treatment produces a clear decrease in the amount of chloridazon adsorbed. The removal efficiency (R) has also been calculated; R values ranging from 5.08% for S-1.0 up to 60.9% for S-600. The batch experiments showed that the strongest heat treatment is more effective than the natural and acid treated sepiolite in relation to adsorption of chloridazon. The column experiments also showed that 600 degrees C heat treated sepiolite might be reasonably used in removing chloridazon from water. Thus, as this type of clay is relatively plentiful, these activated samples might be reasonably used in order to remove chloridazon from water.

  19. Nitrogen dioxide radicals mediated mineralization of perfluorooctanoic acid in aqueous nitrate solution with UV irradiation.

    PubMed

    Li, Aimin; Zhang, Zhe; Li, Peifeng; Cai, Lejuan; Zhang, Lizhi; Gong, Jingming

    2017-09-03

    Effective decomposition of perfluorooctanoic acid (PFOA) has received increasing attention in recent years because of its global occurrence and resistance to most conventional treatment processes. In this study, the complete mineralization of PFOA was achieved by the UV-photolysis of nitrate aqueous solution (UV/Nitrate), where the in-situ generated nitrogen dioxide radicals (NO2) efficiently mediated the degradation of PFOA. In particular, when the twinborn hydroxyl radicals were scavenged, the production of more NO2 radicals realized the complete mineralization of PFOA. DFT calculations further confirm the feasibility of PFOA removal with NO2. Near-stoichiometric equivalents of fluoride released rather than the related intermediates were detected in solution after decomposition of PEOA, further demonstrating the complete degradation of PFOA. Possible PFOA degradation pathways were proposed on the basis of experimental results. This work offers an efficient strategy for the complete mineralization of perfluorinated chemicals, and also sheds light on the indispensable roles of nitrogen dioxide radicals for environmental pollutants removal. Copyright © 2017. Published by Elsevier Ltd.

  20. Adsorption removal of tannic acid from aqueous solution by polyaniline: Analysis of operating parameters and mechanism.

    PubMed

    Sun, Chencheng; Xiong, Bowen; Pan, Yang; Cui, Hao

    2017-02-01

    Polyaniline (PANI) prepared by chemical oxidation was studied for adsorption removal of tannic acid (TA) from aqueous solution. Batch adsorption studies were carried out under different adsorbent dosages, pH, ionic strength, initial TA concentration and coexisting anions. Solution pH had an important impact on TA adsorption onto PANI with optimal removal in the pH range of 8-11. TA adsorption on PANI at three ionic strength levels (0.02, 0.2 and 2molL(-1) NaCl) could be well described by Langmuir model (monolayer adsorption process) and the maximum adsorption capacity was 230, 223 and 1023mgg(-1), respectively. Kinetic data showed that TA adsorption on PANI fitted well with pseudo-second-order model (controlled by chemical process). Among the coexisting anions tested, PO4(3-) significantly inhibited TA adsorption due to the enhancement of repulsive interaction. Continuous flow adsorption studies indicated good flexibility and adaptability of the PANI adsorbent under different flow rates and influent TA concentrations. The mechanism controlling TA adsorption onto PANI under different operating conditions was analyzed with the combination of electrostatic interactions, hydrogen bonding, π-π interactions and Van der Waals interactions.

  1. Adsorption of copper ions from aqueous solution by citric acid modified soybean straw.

    PubMed

    Zhu, Bo; Fan, Tongxiang; Zhang, Di

    2008-05-01

    The objectives of the present study were to convert soybean straw to a metal ion adsorbent and further to investigate the potential of using the adsorbent for the removal of Cu(2+) from aqueous solution. The soybean straw was water or base washed and citric acid (CA) modified to enhance its nature adsorption capacity. The morphological and chemical characteristics of the adsorbent were evaluated by spectroscopy and N(2)-adsorption techniques. The porous structure, as well as high amounts of introduced free carboxyl groups of CA modified soybean straw makes the adsorbent be good to retain Cu(2+). The adsorption capacities increased when the solution pH increased from 2 to 6 and reached the maximum value at pH 6 (0.64 mmol g(-1) for the base washed, CA modified soybean straw (CA-BWSS)). The Cu(2+) uptake increased and percentage adsorption of the Cu(2+) decreased with the increase in initial Cu(2+) concentration from 1 mM to 20 mM. Both the Langmuir and Freundlich adsorption isotherms were tested, and the Freundlich model fited much better than the Langmuir model. It was found that CA-BWSS have the highest adsorption capacity of the four kinds of pretreated soybean straw.

  2. Photo-induced coupling reactions of tetrazoles with carboxylic acids in aqueous solution: application in protein labelling.

    PubMed

    Zhao, Shan; Dai, Jianye; Hu, Mo; Liu, Chang; Meng, Rong; Liu, Xiaoyun; Wang, Chu; Luo, Tuoping

    2016-03-28

    The photo-induced reactions of diaryltetrazoles with carboxylic acids in aqueous solution were investigated. Besides measuring the apparent second-order rate constant and evaluating the functional group compatibility of these reactions, we further incorporated the tetrazoles into SAHA, leading to a new active-site-directed probe for labelling HDACs in both cell lysates and living cells.

  3. The role of hydrogen bonds in an aqueous solution of acetylsalicylic acid: a molecular dynamics simulation study.

    PubMed

    Donnamaria, Maria Cristina; de Xammar Oro, Juan Roberto

    2011-10-01

    This work focuses on the role of the dynamic hydrogen bonds (HB) formed in an aqueous solution of aspirin using molecular dynamics simulation. The statistics reveal the existence of internal HB that inhibit the rotational movements of the acetyl and the carboxylic acid groups, forcing the molecule to adopt a closed conformer structure in water, and playing an important role in stabilizing this conformation.

  4. Solute-enhanced production of gamma-valerolactone (GVL) from aqueous solutions of levulinic acid

    DOEpatents

    Dumesic, James A.; Wettstein, Stephanie G.; Alonso, David Martin; Gurbuz, Elif Ispir

    2016-06-28

    A method to produce levulinic acid (LA) and gamma-valerolactone (GVL) from biomass-derived cellulose or lignocellulose by selective extraction of LA using GVL and optionally converting the LA so isolated into GVL, with no purifications steps required to yield the GVL.

  5. Solute-enhanced production of gamma-valerolactone (GVL) from aqueous solutions of levulinic acid

    DOEpatents

    Dumesic, James A; Wettstein, Stephanie G; Alonso, David Martin; Gurbuz, Elif Ispir

    2015-02-24

    A method to produce levulinic acid (LA) and gamma-valerolactone (GVL) from biomass-derived cellulose or lignocellulose by selective extraction of LA using GVL and optionally converting the LA so isolated into GVL, with no purifications steps required to yield the GVL.

  6. Novel Regenerated Solvent Extraction Processes for the Recovery of Carboxylic Acids or Ammonia from Aqueous Solutions Part I. Regeneration of Amine-Carboxylic Acid Extracts

    SciTech Connect

    Poole, Loree Joanne; King, C. Judson

    1990-03-01

    Two novel regenerated solvent extraction processes are examined. The first process has the potential to reduce the energy costs inherent in the recovery of low-volatility carboxylic acids from dilute aqueous solutions. The second process has the potential for reducing the energy costs required for separate recovery of ammonia and acid gases (e.g. CO2 and H2S) from industrial sour waters. The recovery of carboxylic acids from dilute aqueous solution can be achieved by extraction with tertiary amines. An approach for regeneration and product recovery from such extracts is to back-extract the carboxylic acid with a water-soluble, volatile tertiary amine, such as trimethylamine. The resulting trimethylammonium carboxylate solution can be concentrated and thermally decomposed, yielding the product acid and the volatile amine for recycle. Experimental work was performed with lactic acid, succinic acid, and fumaric acid. Equilibrium data show near-stoichiometric recovery of the carboxylic acids from an organic solution of Alamine 336 into aqueous solutions of trimethylamine. For fumaric and succinic acids, partial evaporation of the aqueous back extract decomposes the carboxylate and yields the acid product in crystalline form. The decomposition of aqueous solutions of trimethylammonium lactates was not carried out to completion, due to the high water solubility of lactic acid and the tendency of the acid to self-associate. The separate recovery of ammonia and acid gases from sour waters can be achieved by combining steam-stripping of the acid gases with simultaneous removal of ammonia by extraction with a liquid cation exchanger. The use of di-2,4,4-trimethylpentyl phosphinic acid as the liquid cation exchanger is explored in this work. Batch extraction experiments were carried out to measure the equilibrium distribution ratio of ammonia between an aqueous buffer solution and an organic solution of the phosphinic acid (0.2N) in Norpar 12. The

  7. Adsorption of Benzoic Acid in Aqueous Solution by Bagasse Fly Ash

    NASA Astrophysics Data System (ADS)

    Suresh, S.

    2012-09-01

    This paper reports the studies on the benzoic acid (BA) onto bagasse fly ash (BFA) was studied in aqueous solution in a batch system. Physico-chemical properties including surface area, surface texture of the GAC before and after BA adsorption onto BFA were analysed using X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The optimum initial pH for the adsorption of BA was found to be 5.56. The adsorbent dose was 10 g/l for BFA and the equilibrium time 8 h of reaction. Pseudo first and second order models were used to find the adsorption kinetics. It was found that intraparticle diffusion played important role in the adsorption mechanisms of BA and the adsorption kinetics followed pseudo-second order kinetic model rather than the pseudo first order kinetic model. Isotherm data were generated for BA solution having initial concentrations of BA in the range of 10-200 mg/l for the BFA dosage of 10 g/l at temperatures of 288, 303, and 318 K. The adsorption of BA onto BFA was favorably influenced by an increase in temperature. Equilibrium data were well represented by the Redlich-Peterson isotherm model. Values of the change in entropy ( ΔS 0), heat of adsorption ( ΔH 0) for adsorption of BA on BFA was found to be 120.10 and 19.61 kJ/mol respectively. The adsorption of BA onto BFA was an endothermic reaction. Desorption of BA from BFA was studied by various solvents method. Acetic acid was found to be a better eluant for desorption of BA with a maximum desorption efficiency of 55.2 %. Owing to its heating value, spent BFA can be used as a co-fuel for the production of heat in boiler furnaces.

  8. Extraction and isolation of TPE from other elements on ion exchangers in aqueous and aqueous-organic solutions of phosphoric acid

    SciTech Connect

    Guseva, L.I.; Tikhomirova, G.S.; Stepushkina, V.V.

    1988-07-01

    The behavior of Am-Es and other actinides on anion and cation exchange resins in aqueous and aqueous-organic solutions of phosphoric acid has been studied in a wide range of concentration of various components of the solution. The sorptivity of transplutonium elements (TPE) on anion exchangers from dilute H/sub 3/PO/sub 4/ with a concentration less than or equal to 1 M in presence of organic solvents (alcohols, ketones, etc.) and on cation exchangers from concentrated H/sub 3/PO/sub 4/ has been found to be significant. The possibility of use of phosphoric acid solutions for isolation of TPE from Th, Pa, U, Np, Pu, and Zr and separation of TPE in different oxidation states in presence of a high-purity oxidant has been shown.

  9. Simultaneous determination of nitric acid and uranium concentrations in aqueous solution from measurements of electrical conductivity, density, and temperature

    SciTech Connect

    Spencer, B.B.

    1991-01-01

    Nuclear fuel reprocessing plants handle aqueous solutions of nitric acid and uranium in large quantities. Automatic control of process operations requires reliable measurements of these solutes concentration, but this is difficult to directly measure. Physical properties such as solution density and electrical conductivity vary with solute concentration and temperature. Conductivity, density and temperature can be measured accurately with relatively simple and inexpensive devices. These properties can be used to determine solute concentrations will good correlations. This paper provides the appropriate correlations for solutions containing 2 to 6 Molar (M) nitric acid and 0 to 300 g/L uranium metal at temperatures from 25--90{degrees}C. The equations are most accurate below 5 M nitric acid, due to a broad maximum in the conductivity curve at 6 M. 12 refs., 9 figs., 6 tabs.

  10. UV – INDUCED SYNTHESIS OF AMINO ACIDS FROM AQUEOUS STERILIZED SOLUTION OF AMMONIUM FORMATE AND AMMONIA UNDER HETROGENEOUS CONDITIONS

    PubMed Central

    Bisht, G.; Bisht, L. S.

    1990-01-01

    Irradiation of sterilized aqueous solution of ammonium formate and ammonia with UV light in the presence and or absence of certain inorganic sensitizers for 25 hrs. gave six ninhydrin positive products in appreciable amounts. Out of the six products observed fiver were characterized as lysine, serine, glutemic acid, n-amino butyric acid and leucine. The sensitizing effect of additives on ammonium formate was observed in the order; uranium oxide > ammonium formate > ferric oxide > arsenic oxide. PMID:22556511

  11. Synthesis, characterization and adsorption properties of diethylenetriamine-modified hypercrosslinked resins for efficient removal of salicylic acid from aqueous solution.

    PubMed

    Huang, Jianhan; Jin, Xiaoying; Mao, Jinglin; Yuan, Bin; Deng, Rujie; Deng, Shuguang

    2012-05-30

    We report an effective approach for tailoring the pore textural properties and surface polarity of a hypercrosslinked resin to enhance its adsorption capacity and selectivity for removing salicylic acid from aqueous solution. Four hypercrosslinked resins were synthesized by controlling the reaction time of the self Friedel-Crafts reaction of chloromethylated polystyrene-co-divinylbenzene, and then modified with diethylenetriamine to adjust their surface polarity. The resins were characterized with N(2) adsorption for pore textural properties, Fourier transform infrared spectroscopy (FT-IR) for surface functional groups, chemical analysis for residual chlorine content and weak basic exchange capacity. Adsorption equilibrium, kinetics and breakthrough performance were determined for the removal of salicylic acid from aqueous solution on a selected resin HJ-M01. The equilibrium adsorption capacity of salicylic acid on HJ-M01 is significantly higher than that on its precursor HJ-11 and a few commercial adsorbents including AB-8, XAD-4 and XAD-7. The dynamic adsorption capacity of salicylic acid on HJ-M01 was found to be 456.4 mg/L at a feed concentration of 1000 mg/L and 294 K. The used resin could be fully regenerated with 1% sodium hydroxide solution. The hypercrosslinked resins being developed were promising alternatives to commercial adsorbents for removing salicylic acid and other volatile organic compounds (VOCs) from aqueous solution.

  12. Formation of an 8-hydroxyguanine moiety in deoxyribonucleic acid on gamma-irradiation in aqueous solution

    SciTech Connect

    Dizdaroglu, M.

    1985-07-30

    Isolation and characterization of a novel radiation-induced product, i.e., the 8-hydroxyguanine residue, produced in deoxyribonucleic acid (DNA), 2'-deoxyguanosine, and 2'-deoxyguanosine 5'-monophosphate by gamma-irradiation in aqueous solution, are described. For this purpose, gamma-irradiated DNA was first hydrolyzed with a mixture of four enzymes, i.e., DNase I, spleen and snake venom exonucleases, and alkaline phosphatase. Analysis of the resulting mixture by capillary gas chromatography-mass spectrometry after trimethylsilylation revealed the presence of a product, which was identified as 8-hydroxy-2'-deoxyguanosine on the basis of the typical fragment ions of its trimethylsilyl (Me3Si) derivative. This product was then isolated by using reversed-phase high-performance liquid chromatography. The UV and proton nuclear magnetic resonance spectra taken from the isolated product confirmed the structure suggested by the mass spectrum of its Me3Si derivative. The yield of 8-hydroxyguanine was also measured. Its mechanism of formation is believed to involve OH radical addition to the C-8 position of guanine followed by oxidation of the radical adduct.

  13. [Mechanism of action of combined extremely weak magnetic field on aqueous solution of amino acid].

    PubMed

    Zhadin, M N; Bakharev, B V; Bobkova, N V

    2014-01-01

    The fundamental physical mechanisms of resonance action of an extremely weak (40 nT) alternating magnetic field at the cyclotron frequency combined with a weak (40 μT) static magnetic field, on living systems are analyzed in the present work. The experimental effects of such sort of magnetic fields were described in different papers: the very narrow resonant peaks in electrical conductivity of the aqueous solutions in the in vitro experiments and the biomedical in vivo effects on living animals of magnetic fields with frequencies tuned to some amino acids. The existing experimental in vitro data had a good repeatability in different laboratories and countries. Unfortunately, for free ions such sort of effects are absolutely impossible because the dimensions of an ion rotation radius should be measured by meters at room temperature and at very low static magnetic fields used in all the above experiments. Even for bound ions these effects should be also absolutely impossible from the positions of classic physics because of rather high viscosity of biological liquid media (blood plasma, cerebrospinal liquid, cytoplasm). Only modern quantum electrodynamics of condensed media opens the new ways for solving these problems. The proposed article is devoted to analysis of quantum mechanisms of these effects.

  14. Laccase-mediated transformation of triclosan in aqueous solution with metal cations and humic acid.

    PubMed

    Sun, Kai; Kang, Fuxing; Waigi, Michael Gatheru; Gao, Yanzheng; Huang, Qingguo

    2017-01-01

    Triclosan (TCS) is a broad-spectrum antimicrobial agent that is found extensively in natural aquatic environments. Enzyme-catalyzed oxidative coupling reactions (ECOCRs) can be used to remove TCS in aqueous solution, but there is limited information available to indicate how metal cations (MCs) and natural organic matter (NOM) influence the environmental fate of TCS during laccase-mediated ECOCRs. In this study, we demonstrated that the naturally occurring laccase from Pleurotus ostreatus was effective in removing TCS during ECOCRs, and the oligomerization of TCS was identified as the dominant reaction pathway by high-resolution mass spectrometry (HRMS). The growth inhibition studies of green algae (Chlamydomonas reinhardtii and Scenedesmus obliquus) proved that laccase-mediated ECOCRs could effectively reduce the toxicity of TCS. The presence of dissolved MCs (Mn(2+), Al(3+), Ca(2+), Cu(2+), and Fe(2+) ions) influenced the removal and transformation of TCS via different mechanisms. Additionally, the transformation of TCS in systems with NOM derived from humic acid (HA) was hindered, and the apparent pseudo first-order kinetics rate constants (k) for TCS decreased as the HA concentration increased, which likely corresponded to the combined effect of both noncovalent (sorption) and covalent binding between TCS and humic molecules. Our results provide a novel insight into the fate and transformation of TCS by laccase-mediated ECOCRs in natural aquatic environments in the presence of MCs and NOM. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Synthesis of S-linked glycosyl amino acids in aqueous solution with unprotected carbohydrates.

    PubMed

    Cohen, S B; Halcomb, R L

    2001-02-08

    [figure: see text] The cyclic sulfamidate 5 was synthesized in 60% overall yield from L-serine benzyl ester. Compound 5 reacted cleanly with the sodium thiolate salt of a variety of unprotected 1-thio sugars in aqueous buffer to afford the corresponding S-linked amino acid glycoconjugates in good yields after hydrolysis of the N-sulfates.

  16. Oxidation of hydroxyurea with oxovanadium(V) ions in acidic aqueous solution.

    PubMed

    Gabricević, Mario; Besić, Erim; Birus, Mladen; Zahl, Achim; Eldik, Rudi van

    2006-10-01

    Hydroxyurea (HU) effectively reduces vanadium(V) into vanadium(IV) species (hereafter V(V) and V(IV) species, respectively) in acidic aqueous solution via the formation of a transient complex followed by an electron transfer process that includes the formation and subsequent fading out of a free radical, U* (U* identical with H(2)N-C(=O)N(H)O*). The electron paramagnetic resonance (EPR) spectra of U* in H(2)O/D(2)O solutions suggest that the unpaired electron is located predominantly on the hydroxamate hydroxyl-oxygen atom. Visible and V(IV)-EPR spectroscopic data reveal HU as a two-electron donor, whereas formation of U*, which reduces a second V(V), indicates that electron transfer occurs in two successive one-electron steps. At the molarity ratio [V(V)]/[HU]=2, the studied reaction can be formulated as: 2 V(V)+HU-->2 V(IV)+0.98 CO(2)+0.44 N(2)O+1.1 NH(3)+0.1 NH(2)OH. Lack of evidence for the formation of NO is suggested to be a consequence of the slow oxidation of HNO due to the too low reduction potential of the V(V)/V(IV) couple under the experimental conditions used. The nuclear magnetic resonance ((51)V-NMR) spectral data indicate protonation of (H(2)O)(4)V(V)O(2)(+), and the protonation equilibrium constant was determined to be K=0.7 M(-1). Spectrophotometric titration data for the V(V)-HU system reveal formation of (H(2)O)(2)V(V)O(OH)U(+) and (H(2)O)(3)V(V)OU(2+). Their stability constants were calculated as K(110)=5 M(-1) and K(111)=22 M(-2), where the subscript digits refer to (H(2)O)(4)V(V)O(2)(+), HU and H(+), respectively.

  17. Drin pesticides removal from aqueous solutions using acid-treated date stones.

    PubMed

    El Bakouri, H; Usero, J; Morillo, J; Rojas, R; Ouassini, A

    2009-05-01

    This work describes the potential applicability of chemically and thermally treated date stones for removing drin pesticides (aldrin, dieldrin and endrin) from aqueous solutions. The effect of several parameters, such as sorbent particle size, adsorbent dose, shaking speed, shaking time, concentration of pesticide solution and temperature, was evaluated by batch experiments. Pesticide determination was carried out using stir bar sorptive extraction and gas chromatography coupled with mass spectroscopy. Maximum removal efficiency (93%) was reached using 0.1 g of acid-treated date stones (ATDS) (63-100 microm) and 100 mL of aldrin (0.5 mg L(-1)). The removal efficiency of drin pesticides decreased in the order of aldrin, dieldrin and endrin, and decreased as the temperature rose. Adsorption data were processed according to various kinetic models. Lagergren and Morris-Weber equations were applied to fit the kinetic results. The second order model was the most suitable on the whole, and intra-particle diffusion was found to be the rate-controlling the adsorption process. According to adsorption kinetic data, 3.5h were considered as the equilibrium time for determining adsorption isotherms. Adsorption data were analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich adsorption approaches. Experimental results showed that the Freundlich isotherm model best described the adsorption process. In addition, thermodynamic parameters such as DeltaH, DeltaS and DeltaG were calculated. Negative values of DeltaH and DeltaG indicate the exothermic and spontaneous nature of pesticide adsorption on ATDS.

  18. Sulfonated methyl esters of fatty acids in aqueous solutions: Interfacial and micellar properties.

    PubMed

    Danov, Krassimir D; Stanimirova, Rumyana D; Kralchevsky, Peter A; Basheva, Elka S; Ivanova, Veronika I; Petkov, Jordan T

    2015-11-01

    The interest to sulfonated methyl esters of fatty acids (SME) has been growing during the last decade, because these surfactants are considered as an environmentally friendly and renewable alternative of the linear alkyl-benzene sulfonates (LAS). Here, we present a quantitative study on the properties of aqueous SME solutions, and especially on their surface tension isotherms, critical micelle concentration (CMC) and its dependence on the concentration of added NaCl. It is demonstrated that the CMC of an ionic surfactant determined by electrical conductivity is insensitive to the presence of a small nonionic admixture, so that the CMC values determined by conductivity represent the CMC of the pure surfactant. Using SME as an example, we have demonstrated the application of a new and powerful method for determining the physicochemical parameters of the pure ionic surfactant by theoretical data analysis ("computer purification") if the used surfactant sample contains nonionic admixtures, which are present as a rule. This method involves fits of the experimental data for surface tension and conductivity by a physicochemical model based on a system of mass-balance, chemical-equilibrium and electric-double-layer equations, which allows us to determine the adsorption and micellization parameters of C12-, C14-, C16- and C18-SME, as well the fraction of nonionic admixtures (if any). Having determined these parameters, we can further predict the interfacial and micellization properties of the surfactant solutions, such as surface tension, adsorption, degree of counterion binding, and surface electric potential at every surfactant, salt and co-surfactant concentrations. Copyright © 2015 Elsevier Inc. All rights reserved.

  19. Photocatalytic degradation of perfluorooctanoic acid with beta-Ga2O3 in anoxic aqueous solution.

    PubMed

    Zhao, Baoxiu; Lv, Mou; Zhou, Li

    2012-01-01

    Perfluorooctanoic acid (PFOA) is a new-found hazardous persistent organic pollutant, and it is resistant to decomposition by hydroxyl radical (HO*) due to its stable chemical structure and the high electronegativity of fluorine. Photocatalytic reduction of PFOA with beta-Ga2O3 in anoxic aqueous solution was investigated for the first time, and the results showed that the photoinduced electron (e(cb-)) coming from the beta-Ga2O3 conduction band was the major degradation substance for PFOA, and shorter-chain perfluorinated carboxylic acids (PFCAs, CnF2n+i1COOH, 1 < or = n < or = 6) were the dominant products. Furthermore, the concentration of F- was measured by the IC technique and defluorination efficiency was calculated. After 3 hr, the photocatalytic degradation efficiency was 98.8% and defluorination efficiency was 31.6% in the presence of thiosulfate and bubbling N2. The degradation reaction followed first-order kinetics (k = 0.0239 min(-1), t1/2 = 0.48 hr). PFCAs (CnF2n+1COOH, 1 < or = n < or = 7) were detected and measured by LC-MS and LC-MS/MS methods. It was deduced that the probable photocatalytic degradation mechanism involves e(cb-) attacking the carboxyl of CnF2n+1COOH, resulting in decarboxylation and the generation of CnF2n+1*. The produced CnF2n+1* reacted with H2O, forming CnF2n+1OH, then CnF2n+1OH underwent HF loss and hydrolysis to form CnF2n+1COOH.

  20. Regeneration of an aqueous solution from an acid gas absorption process by matrix stripping

    DOEpatents

    Rochelle, Gary T [Austin, TX; Oyenekan, Babatunde A [Katy, TX

    2011-03-08

    Carbon dioxide and other acid gases are removed from gaseous streams using aqueous absorption and stripping processes. By replacing the conventional stripper used to regenerate the aqueous solvent and capture the acid gas with a matrix stripping configuration, less energy is consumed. The matrix stripping configuration uses two or more reboiled strippers at different pressures. The rich feed from the absorption equipment is split among the strippers, and partially regenerated solvent from the highest pressure stripper flows to the middle of sequentially lower pressure strippers in a "matrix" pattern. By selecting certain parameters of the matrix stripping configuration such that the total energy required by the strippers to achieve a desired percentage of acid gas removal from the gaseous stream is minimized, further energy savings can be realized.

  1. Raman spectra and structures of 1-methyl-4-(4-diethylaminophenylazo)-pyridinium iodide in neutral and acidic aqueous solutions

    NASA Astrophysics Data System (ADS)

    Iwase, Akitaka; Ueda, Atsushi; Kuwae, Akio; Hanai, Kazuhiko; Kunimoto, Ko-Ki

    2013-09-01

    Fourier transform (FT) and resonance Raman spectra of 1-methyl-4-(4-diethylaminophenylazo)-pyridinium iodide (MDP) and its four deuterated and three 15N stable isotopic compounds have been measured in neutral and acidic aqueous solutions, and the molecular structures have been discussed on the basis of detailed vibrational assignments using the isotope shifts. No Raman band due to the azo Ndbnd N group is observed in a neutral aqueous solution and also in the solid state of MDP; therefore, this finding suggests that double bond character of the azo group becomes weak and, consequently, the structures of both benzene and pyridinium rings are close to that of a quinoid. The Raman and the 15N NMR spectra indicate that the Nβ of the azo group is protonated in an acidic solution of MDP. Comparison of the spectra of the two solutions suggests that the benzene ring has more quinoid character in the acidic than in the neutral solution. The chromophore structures have been revealed in each of the neutral (purple) and the acidic (yellow) solution.

  2. Partial molar volumes of some alpha-amino acids in aqueous sodium acetate solutions at 308.15 K.

    PubMed

    Wang, J; Yan, Z; Zhuo, K; Lu, J

    1999-08-30

    The apparent molar volumes V(2,phi) have been determined for glycine, DL-alpha-alanine, DL-alpha-amino-n-butyric acid, DL-valine and DL-leucine in aqueous solutions of 0.5, 1.0, 1.5 and 2.0 mol kg(-1) sodium acetate by density measurements at 308.15 K. These data have been used to derive the infinite dilution apparent molar volumes V(0)(2,phi) for the amino acids in aqueous sodium acetate solutions and the standard volumes of transfer, Delta(t)V(0), of the amino acids from water to aqueous sodium acetate solutions. It has been observed that both V(0)(2,phi) and Delta(t)V(0) vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. These linear correlations have been utilized to estimate the contributions of the charged end groups (NH(3)(+), COO(-)), CH(2) group and other alkyl chains of the amino acids to V(0)(2,phi) and Delta(t)V(0). The results show that V(0)(2,phi) values for (NH(3)(+), COO(-)) groups increase with sodium acetate concentration, and those for CH(2) are almost constant over the studied sodium acetate concentration range. The transfer volume increases and the hydration number of the amino acids decreases with increasing electrolyte concentrations. These facts indicate that strong interactions occur between the ions of sodium acetate and the charged centers of the amino acids. The volumetric interaction parameters of the amino acids with sodium acetate were calculated in water. The pair interaction parameters are found to be positive and decreased with increasing alkyl chain length of the amino acids, suggesting that sodium acetate has a stronger dehydration effect on amino acids which have longer hydrophobic alkyl chains. These phenomena are discussed by means of the co-sphere overlap model.

  3. Coefficient of ozone mass transfer during its interaction with an aqueous solution of formic acid in a bubble column reactor

    NASA Astrophysics Data System (ADS)

    Levanov, A. V.; Isaikina, O. Ya.; Gasanova, R. B.; Lunin, V. V.

    2017-08-01

    A way of determining the coefficient of ozone mass transfer between the gas phase and liquid aqueous phase using a test compound (formic acid) is described. The values of ozone mass transfer coefficient (in aqueous solutions of 0.1-0.55 M HClO4 and 0-1 M HCOOH, and in 0.75 M H2SO4, 0.125 M KHSO4, and 0-2 M HCOOH) are determined along with the rate constants of the reaction of O3 with undissociated HCOOH molecules and formate ions at 21 ± 1°C.

  4. Calculating the acidity of silanols and related oxyacids in aqueous solution

    NASA Astrophysics Data System (ADS)

    Tossell, John A.; Sahai, Nita

    2000-12-01

    Ab initio molecular orbital theory was used to calculate deprotonation energies and enthalpies (ΔE d, ΔH d) of oxyacid monomers and oligomers. Results were interpreted with reference to current phenomenological models for estimating metal-oxide surface acidities. The ultimate goal is to predict surface acidities using the ab initio method. We evaluated contributions to ΔE d and ΔH d from the electrostatic potential at the proton, electronic relaxation, geometric relaxation, solvation, and polymerization for the neutral-charge gas-phase molecules H 2O, CH 3OH, HCOOH, SiH 3OH, Si(OH) 4, Si 2O 7H 6, H 3PO 4, P 2O 7H 4, H 2SO 3, H 2SO 4, HOCl, HClO 4, Ge(OH) 4, As(OH) 3, and AsO(OH) 3. ΔE d, gas calculated at the modest 6-31G∗ HF of theory level correlates well with experimental pK a in solution, because hydration enthalpies for the acid anions (ΔH hyd, A-) are closely proportional to ΔE d, gas. That is, anion interaction energies with water in aqueous solution and with H + in the gas phase are closely correlated. Correction for differential hydration between an acid and its conjugate base permits generalization of the ΔE d, gas - pK a correlation to deprotonation reactions involving charged acids. Thus, stable protonated, neutral, and deprotonated species Si(OH) 3(OH 2) 1+, Si(OH) 40, Si(OH) 3O 1-, and Si(OH) 2O 22- have been characterized, and solution pK a's for Si(OH) 3(OH 2) 1+ and Si(OH) 3O 1- were estimated, assuming that the charged species (Si(OH) 3(OH 2) 1+, Si(OH) 3O -1) fit into the same ΔE d, gas - pK a correlation as do the neutral acids. The correlation yields a negative pK a (˜ -5) for Si(OH) 3(OH 2) +1. Calculated ΔE d, gas also correlates well with the degree of O under-bonding evaluated using Brown's bond-length based approach. ΔE d, gas increases along the series HClO 4 - Si(OH) 4 mainly because of increasingly negative potential at the site of the proton, not because of differing electronic or geometric relaxation energies. Thus, pK a

  5. Study of monoprotic acid-base equilibria in aqueous micellar solutions of nonionic surfactants using spectrophotometry and chemometrics.

    PubMed

    Babamoradi, Hamid; Abdollahi, Hamid

    2015-10-05

    Many studies have shown the distribution of solutes between aqueous phase and micellar pseudo-phase in aqueous micellar solutions. However, spectrophotometric studies of acid-base equilibria in these media do not confirm such distribution because of the collinearity between concentrations of chemical species in the two phases. The collinearity causes the number of detected species to be equal to the number of species in a homogenous solution that automatically misinterpreted as homogeneity of micellar solutions, therefore the collinearity is often neglected. This interpretation is in contradiction to the distribution theory in micellar media that must be avoided. Acid-base equilibrium of an indicator was studied in aqueous micellar solutions of a nonionic surfactant to address the collinearity using UV/Visible spectrophotometry. Simultaneous analysis (matrix augmentation) of the equilibrium and solvation data was applied to eliminate the collinearity from the equilibrium data. A model was then suggested for the equilibrium that was fitted to the augmented data to estimate distribution coefficients of the species between the two phases. Moreover, complete resolution of concentration and spectral profiles of species in each phase was achieved.

  6. Removal of Pb(II) ions from aqueous solutions by sulphuric acid-treated wheat bran.

    PubMed

    Ozer, A

    2007-03-22

    Sulphuric acid-treated wheat bran (STWB) was used as an adsorbent to remove Pb(II) ions from aqueous solution. It was observed that the adsorption yield of Pb(II) ions was found to be pH dependent. The equilibrium time for the process was determined as 2h. STWB gave the highest adsorption yield at around pH 6.0. At this pH, adsorption percentage for an initial Pb(II) ions concentration of 100mg/L was found to be 82.8 at 25 degrees C for contact time of 2h. The equilibrium data obtained at different temperatures fitted to the non-linear form of Langmuir, Freundlich and Redlich-Peterson and linear form of Langmuir and Freundlich models. Isotherm constants were calculated and compared for the models used. The maximum adsorption capacity (q(max)) which was obtained linear form of Langmuir model increased from 55.56 to 79.37mg/g with increasing temperature from 25 to 60 degrees C. Similar trend was observed for other isotherm constants related to the adsorption capacity. Linear form of Langmuir isotherm data was evaluated to determine the thermodynamic parameters for the process. Thermodynamic parameters show that adsorption process of Pb(II) ions is an endothermic and more effective process at high temperatures. The pseudo nth order kinetic model was successfully applied to the kinetic data and the order (n) of adsorption reaction was calculated at the range from 1.711 to 1.929. The values of k(ad) were found to be 5.82x10(-4) and 21.81x10(-4)(min(-1))(mg/g)(1-n) at 25 and 60 degrees C, respectively. Activation energy was determined as 29.65kJ/mol for the process. This suggest that the adsorption Pb(II) ions by STWB is chemically controlled.

  7. Volatility of organic aerosol: evaporation of ammonium sulfate/succinic acid aqueous solution droplets.

    PubMed

    Yli-Juuti, Taina; Zardini, Alessandro A; Eriksson, Axel C; Hansen, Anne Maria K; Pagels, Joakim H; Swietlicki, Erik; Svenningsson, Birgitta; Glasius, Marianne; Worsnop, Douglas R; Riipinen, Ilona; Bilde, Merete

    2013-01-01

    Condensation and evaporation modify the properties and effects of atmospheric aerosol particles. We studied the evaporation of aqueous succinic acid and succinic acid/ammonium sulfate droplets to obtain insights on the effect of ammonium sulfate on the gas/particle partitioning of atmospheric organic acids. Droplet evaporation in a laminar flow tube was measured in a Tandem Differential Mobility Analyzer setup. A wide range of droplet compositions was investigated, and for some of the experiments the composition was tracked using an Aerosol Mass Spectrometer. The measured evaporation was compared to model predictions where the ammonium sulfate was assumed not to directly affect succinic acid evaporation. The model captured the evaporation rates for droplets with large organic content but overestimated the droplet size change when the molar concentration of succinic acid was similar to or lower than that of ammonium sulfate, suggesting that ammonium sulfate enhances the partitioning of dicarboxylic acids to aqueous particles more than currently expected from simple mixture thermodynamics. If extrapolated to the real atmosphere, these results imply enhanced partitioning of secondary organic compounds to particulate phase in environments dominated by inorganic aerosol.

  8. Volatility of Organic Aerosol: Evaporation of Ammonium Sulfate/Succinic Acid Aqueous Solution Droplets

    PubMed Central

    2013-01-01

    Condensation and evaporation modify the properties and effects of atmospheric aerosol particles. We studied the evaporation of aqueous succinic acid and succinic acid/ammonium sulfate droplets to obtain insights on the effect of ammonium sulfate on the gas/particle partitioning of atmospheric organic acids. Droplet evaporation in a laminar flow tube was measured in a Tandem Differential Mobility Analyzer setup. A wide range of droplet compositions was investigated, and for some of the experiments the composition was tracked using an Aerosol Mass Spectrometer. The measured evaporation was compared to model predictions where the ammonium sulfate was assumed not to directly affect succinic acid evaporation. The model captured the evaporation rates for droplets with large organic content but overestimated the droplet size change when the molar concentration of succinic acid was similar to or lower than that of ammonium sulfate, suggesting that ammonium sulfate enhances the partitioning of dicarboxylic acids to aqueous particles more than currently expected from simple mixture thermodynamics. If extrapolated to the real atmosphere, these results imply enhanced partitioning of secondary organic compounds to particulate phase in environments dominated by inorganic aerosol. PMID:24107221

  9. Stabilized aqueous hydrogen peroxide solution

    SciTech Connect

    Malin, M.J.; Sciafani, L.D.

    1988-05-17

    This patent describes a stabilized aqueous hydrogen peroxide solution having a pH below 7 and an amount of Ferric ion up to about 2 ppm comprising hydrogen peroxide, acetanilide having a concentration which ranges between 0.74 M Mol/L and 2.22 mMol/L, and o-benzene disulfonic acid or salt thereof at a concentration between about 0.86 mMol/L to about 1.62 mMol/L.

  10. Extraction of nitric acid, uranyl nitrate, and bismuth nitrate from aqueous nitric acid solutions with CMPO

    SciTech Connect

    Spencer, B.B.

    1995-08-01

    DOE sponsored development of the transuranium extraction (TRUEX) process for removing actinides from radioactive wastes. The solvent is a mixture of CMPO and TBP. Since the extraction characteristics of CMPO are not as well understood as those of TBP, the extraction of nitric acid, uranyl nitrate, and bismuth nitrate with CMPO (dissolved in n-dodecane) were studied. Results indicate that CMPO extracts nitric acid with a 1:1 stoichiometry; equilibrium constant is 2. 660{plus_minus}0.092 at 25 C, and extraction enthalpy is -5. 46{plus_minus}0.46 kcal/mol. Slope analysis indicates that uranyl nitrate extracts with a mixed equilibria of 1:1 and 2:1 stoichiometries in nearly equal proportion. Equil. constant of the 2: 1 extraction was 1.213 {times} 10{sup 6}{plus_minus}3.56 {times} 10{sup 4} at 25 C; reaction enthalpy was -9.610{plus_minus}0.594 kcal/mol. Nitration complexation constant is 8.412{plus_minus}0.579, with an enthalpy of -10.72{plus_minus}1.87 kcal/mol. Bismuth nitrate also extracts with a mixed equilibria of (perhaps) 1:1 and 2:1 stoichiometries. A 2:1 extraction equilibrium and a nitrate complexation adequately model the data. Kinetics and enthalpies were also measured.

  11. Concentration effects in the nucleophilic reactions of tertiary amines in aqueous solutions: Alkylation of amines with chloroacetic acid

    NASA Astrophysics Data System (ADS)

    Kazantsev, O. A.; Baruta, D. S.; Shirshin, K. V.; Sivokhin, A. P.; Kamorin, D. M.

    2011-03-01

    In alkylations of tertiary amines with chloroacetic acid in aqueous solutions, an increase in the initial concentrations of reagents to a certain level led to an abrupt increase in the initial rates and conversions attained during the control time. Viscosimetric and refractometric data showed that association with reagents occurred in these systems. The structures of associates that determine the character of the concentration effects of the Menschutkin reaction in water were suggested.

  12. Long-term degradation study of hyaluronic acid in aqueous solutions without protection against microorganisms.

    PubMed

    Simulescu, Vasile; Kalina, Michal; Mondek, Jakub; Pekař, Miloslav

    2016-02-10

    The degradation of hyaluronan (HA) of different molecular weights (Mw 14.3, 267.2 and 1160.6 kDa, measured for fresh solutions, before degradation) was studied in aqueous solutions by SEC-MALLS determination of molecular mass, polydispersity and conformation parameters. The solutions were stored either at laboratory or refrigerator temperatures for two months. After this period the weight average molecular weight decreased by 90% for 14.3 kDa, 95% for 267.2 kDa and 71% for 1160.6 kDa hyaluronan (room temperature) or 5.6% for 14.3 kDa, 6.2% for 267.2 kDa and 7.7% for 1160.6 kDa hyaluronan (refrigerator temperature). The hyaluronan aqueous solutions studied did not contain sodium azide or other protectants against microorganisms, because the aim of our study was to assess the degradation in solutions to be used in medicine or cosmetics (without any compounds that are poisonous or toxic for the human body). The solvent used to prepare the samples was pure water. The polydispersity of all the samples remained unaltered during the entire degradation at both temperatures. This indicates a non-random mechanism of degradation.

  13. Thermodynamic and ultrasonic properties of ascorbic Acid in aqueous protic ionic liquid solutions.

    PubMed

    Singh, Vickramjeet; Sharma, Gyanendra; Gardas, Ramesh L

    2015-01-01

    In this work, we report the thermodynamic and ultrasonic properties of ascorbic acid (vitamin C) in water and in presence of newly synthesized ammonium based protic ionic liquid (diethylethanolammonium propionate) as a function of concentration and temperature. Apparent molar volume and apparent molar isentropic compression, which characterize the solvation state of ascorbic acid (AA) in presence of protic ionic liquid (PIL) has been determined from precise density and speed of sound measurements at temperatures (293.15 to 328.15) K with 5 K interval. The strength of molecular interactions prevailing in ternary solutions has been discussed on the basis of infinite dilution partial molar volume and partial molar isentropic compression, corresponding volume of transfer and interaction coefficients. Result has been discussed in terms of solute-solute and solute-solvent interactions occurring between ascorbic acid and PIL in ternary solutions (AA + water + PIL).

  14. Thermodynamic and Ultrasonic Properties of Ascorbic Acid in Aqueous Protic Ionic Liquid Solutions

    PubMed Central

    Singh, Vickramjeet; Sharma, Gyanendra; Gardas, Ramesh L.

    2015-01-01

    In this work, we report the thermodynamic and ultrasonic properties of ascorbic acid (vitamin C) in water and in presence of newly synthesized ammonium based protic ionic liquid (diethylethanolammonium propionate) as a function of concentration and temperature. Apparent molar volume and apparent molar isentropic compression, which characterize the solvation state of ascorbic acid (AA) in presence of protic ionic liquid (PIL) has been determined from precise density and speed of sound measurements at temperatures (293.15 to 328.15) K with 5 K interval. The strength of molecular interactions prevailing in ternary solutions has been discussed on the basis of infinite dilution partial molar volume and partial molar isentropic compression, corresponding volume of transfer and interaction coefficients. Result has been discussed in terms of solute-solute and solute-solvent interactions occurring between ascorbic acid and PIL in ternary solutions (AA + water + PIL). PMID:26009887

  15. Biosorption of formic and acetic acids from aqueous solution using activated carbon from shea butter seed shells

    NASA Astrophysics Data System (ADS)

    Adekola, Folahan A.; Oba, Ismaila A.

    2016-10-01

    The efficiency of prepared activated carbon from shea butter seed shells (SB-AC) for the adsorption of formic acid (FA) and acetic acid (AA) from aqueous solution was investigated. The effect of optimization parameters including initial concentration, agitation time, adsorbent dosage and temperature of adsorbate solution on the sorption capacity were studied. The SB-AC was characterized for the following parameters: bulk density, moisture content, ash content, pH, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The optimal conditions for the adsorption were established and the adsorption data for AA fitted Dubinin-Radushkevich (D-R) isotherm well, whereas FA followed Langmuir isotherm. The kinetic data were examined. It was found that pseudo-second-order kinetic model was found to adequately explain the sorption kinetic of AA and FA from aqueous solution. It was again found that intraparticle diffusion was found to explain the adsorption mechanism. Adsorption thermodynamic parameters were estimated and the negative values of ∆G showed that the adsorption process was feasible and spontaneous in nature, while the negative values of ∆H indicate that the adsorption process was exothermic. It is therefore established that SB-AC has good potential for the removal of AA and FA from aqueous solution. Hence, it should find application in the regular treatment of polluted water in aquaculture and fish breeding system.

  16. Recovery of transplutonium elements from aqueous and water-ethanol solutions of sulfuric acid and their separation from other actinides

    SciTech Connect

    Guseva, L.I.; Tikhomirova, G.S.; Stepushkina, V.V.

    1988-05-01

    The behavior of Am, Cm, Bk, Cf, Es, and other actinides, as well as Zr, on anion and cation exchangers in aqueous and water-ethanol solutions of sulfuric acid as a function of the various components of the solution has been investigated. It has been discovered that the presence of ethanol in sulfuric acid solutions causes an increase in the distribution coefficients both on cation exchangers and on anion exchangers. The possibility of the use of ion exchangers for the preconcentration and separation of transplutonium elements from U, Np, Pu, Zr, and other elements which form strong complexes with sulfate ions over a broad range of concentrations of sulfuric acid has been demonstrated.

  17. Amino acid tautomerization reactions in aqueous solution via concerted and assisted mechanisms using free energy curves from MD simulation.

    PubMed

    Tolosa, Santiago; Hidalgo, Antonio; Sansón, Jorge A

    2012-11-01

    A theoretical study is described of chemical reactions in solution by means of molecular dynamics simulations, with solute-solvent interaction potentials derived from AMBER van der Waals parameters and QM/MM electrostatic charges in solution. The solvent is used as the reaction coordinate, and the free energy curves to calculate the properties related to the reaction mechanism. The proposed scheme is applied to the tautomerization process in aqueous solution for some amino acids H(2)NCHR-COOH (with R = H being glycine, R = CH(3) alanine, R = CH(2)OH serine, and R = CH(2)COOH aspartic acid), focusing on the role of the solvent in the reaction (assisted versus unassisted mechanisms) and on the effect of the hydrophilic/hydrophobic character of the radical R on the activation and reaction energies.

  18. Quantitative extraction and concentration of synthetic water-soluble acid dyes from aqueous media using a quinine-chloroform solution

    SciTech Connect

    Kobayashi, F.; Ozawa, N.; Hanai, J.; Isobe, M.; Watabe, T.

    1986-12-01

    Twenty-one water-soluble acid dyes, including eleven azo, five triphenylmethane four xanthene, one naphthol derivatives, used at practical concentrations for food coloration, were quantitatively extracted from water and various carbonated beverages into a 0.1 M quinine-chloroform solution in the presence of 0.5 M boric acid by brief shaking. Quantitative extraction of these dyes was also accomplished by the 0.1 M quinine-chloroform solution made conveniently from chloroform, quinine hydrochloride, and sodium hydroxide added successively to water or beverages containing boric acid. Quinine acted as a countercation on the dyes having sulfonic and/or carboxylic acid group(s) to form chloroform-soluble ion-pair complexes. The diacidic base alkaloid interacted with each acid group of mono-, di-, tri-, and tetrasulfonic acid dyes approximately in the ratio 0.8-0.9 to 1. The dyes in the chloroform solution were quantitatively concentrated into a small volume of sodium hydroxide solution also by brief shaking. The convenient quinine-chloroform method was applicable to the quantitative extraction of a mixture of 12 dyes from carbonated beverages, which are all currently used for food coloration. A high-pressure liquid chromatographic method is also presented for the systematic separation and determination of these 12 dyes following their concentration into the aqueous alkaline solution. The chromatogram was monitored by double-wavelength absorptiometry in the visible and ultraviolet ray regions.

  19. Aspartic acid interaction with cobalt(II) in dilute aqueous solution: A 57Co emission Mössbauer spectroscopic study

    NASA Astrophysics Data System (ADS)

    Kamnev, Alexander A.; Tugarova, Anna V.; Kovács, Krisztina; Homonnay, Zoltan; Kuzmann, Erno; Vértes, Attila

    2012-03-01

    Emission (57Co) Mössbauer spectra of the aspartic acid—57CoCl2 system were measured at T = 80 K in frozen aqueous solution and in the form of a dried residue of this solution. The Mössbauer spectra, besides a weak contribution from after-effects, showed two Fe2 + /Co2 + components which were ascribed to octahedrally and tetrahedrally coordinated 57CoII microenvironments in the Asp-cobalt(II) complex. This dual coordination mode may be due to the involvement of the second terminal carboxylic group of aspartic acid in the coordination sphere of Co.

  20. Intermolecular interactions in aqueous solutions of gallic acid at 296-306 K according to spectrofluorimetry and densimetry data

    NASA Astrophysics Data System (ADS)

    Grigoryan, K. R.; Sargsyan, L. S.

    2015-12-01

    Features of intermolecular interactions in aqueous solutions of gallic acid (GA) are studied by means of densimetry and fluorescence spectroscopy (intrinsic fluorescence, 2D spectra, and excitation/ emission matrix fluorescence spectra, 3D) at 296.15, 301.15, and 306.15 K in the concentration range of 5.88 × 10-4-5.88 × 10-2 mol L-1. It is shown by analyzing the concentration and temperature dependences of the apparent molar volumes and fluorescence parameters of GA that the equilibrium between nonassociated and associated species in the solution and the hydration of these species undergo changes.

  1. Synthesis, spectra, and electron-transfer reaction of aspartic acid-functionalized water-soluble perylene bisimide in aqueous solution.

    PubMed

    Zhong, Lina; Xing, Feifei; Shi, Wei; Yan, Liuming; Xie, Liqing; Zhu, Shourong

    2013-04-24

    An aspartic acid-functionalized water-soluble perylene bisimide, N,N'-di(2-succinic acid)-perylene-3,4,9,10-tetracarboxylic bisimide (PASP) was synthesized and characterized. It has absorbance maximum A(0-0) and A(0-1) at 527 and 498 nm (ε ≈ 1.7 × 10(4) L cm(-1) mol(-1)) respectively in pH 7.20 HEPES buffer. Two quasi-reversible redox processes with E1/2 at -0.17 and -0.71 V (vs Ag/AgCl) respectively in pH 7-12.5 aqueous solutions. PASP can react with Na2S in pure aqueous solution to form monoanion radical and dianion species consecutively. PASP(-•) has EPR signal with g = 1.998 in aqueous solution, whereas PASP(2-) is EPR silent. The monoanion radical formation is a first-order reaction with k = 8.9 × 10(-2) s(-1). Dianion species formation is a zero-order reaction and the rate constant is 4.3 × 10(-8) mol L(-1) s(-1). The presence of H2O2 greatly increases the radical formation rate constant. PASP as a two-electron transfer reagent is expected to be used in the water photolysis.

  2. Characterization of Solid Dispersion of Itraconazole Prepared by Solubilization in Concentrated Aqueous Solutions of Weak Organic Acids and Drying.

    PubMed

    Parikh, Tapan; Sandhu, Harpreet K; Talele, Tanaji T; Serajuddin, Abu T M

    2016-06-01

    The purpose of this study was to develop an amorphous solid dispersion (SD) of an extremely water-insoluble and very weakly basic drug, itraconazole (ITZ), by interaction with weak organic acids and then drying that would enhance dissolution rate of drug and physical stability of formulation. Aqueous solubility of ITZ in concentrated solutions of weak organic acids, such as glutaric, tartaric, malic and citric acid, was determined. Solutions with high drug solubility were dried using vacuum oven and the resulting SDs having 2 to 20% drug load were characterized by differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The dissolution of SDs was initially studied in 250 mL of 0.1 N HCl (pH 1.1), and any undissolved solids were collected and analyzed by PXRD. The pH of the dissolution medium was then changed from 1.1 to 5.5, particle size of precipitates were measured, and drug concentrations in solution were determined by filtration through membrane filters of varying pore sizes. The aqueous solubility of ITZ was greatly enhanced in presence of weak acids. While the solubility of ITZ in water was ~4 ng/ mL, it increased to 25-40 mg per g of solution at 25°C and 200 mg per g of solution at 65°C at a high acid concentration leading to extremely high solubilization. PXRD of SDs indicated that ITZ was present in the amorphous form, wherein the acid formed a partially crystalline matrix. ATR-FTIR results showed possible weak interactions, such as hydrogen bonding, between drug and acid but there was no salt formation. SDs formed highly supersaturated solutions at pH 1.1 and had superior dissolution rate as compared to amorphous drug and physical mixtures of drug and acids. Following the change in pH from 1.1 to 5.5, ITZ precipitated as mostly nanoparticles, providing high surface area for relatively rapid redissolution. A method of highly solubilizing an

  3. Free energy surface for Brønsted acid-catalyzed glucose ring-opening in aqueous solution.

    PubMed

    Qian, Xianghong

    2013-10-03

    Car-Parrinello-based molecular dynamics coupled with metadynamics simulations were used to determine the mechanism and associated free energy surface for opening the ring structure of cyclic glucopyranose in acidic aqueous solutions. The ring-opening process is initiated by the protonation of the ring oxygen atom and the breakage of the C1-O5 bond. The barrier for this process is about 25 kcal/mol, in good agreement with experimental measurements. Moreover, the glucose cyclic conformation is found to be more stable than the open chain form. The barrier for proton-catalyzed ring-opening in aqueous solution appears to be largely solvent induced due to the high affinity of water molecules for protons.

  4. Thermodynamic studies of ionic hydration and interactions for amino acid ionic liquids in aqueous solutions at 298.15 K.

    PubMed

    Dagade, Dilip H; Madkar, Kavita R; Shinde, Sandeep P; Barge, Seema S

    2013-01-31

    Amino acid ionic liquids are a special class of ionic liquids due to their unique acid-base behavior, biological significance, and applications in different fields such as templates in synthetic chemistry, stabilizers for biological macromolecules, etc. The physicochemical properties of these ionic liquids can easily be altered by making the different combinations of amino acids as anion along with possible cation modification which makes amino acid ionic liquids more suitable to understand the different kinds of molecular and ionic interactions with sufficient depth so that they can provide fruitful information for a molecular level understanding of more complicated biological processes. In this context, volumetric and osmotic coefficient measurements for aqueous solutions containing 1-ethyl-3-methylimidazolium ([Emim]) based amino acid ionic liquids of glycine, alanine, valine, leucine, and isoleucine are reported at 298.15 K. From experimental osmotic coefficient data, mean molal activity coefficients of ionic liquids were estimated and analyzed using the Debye-Hückel and Pitzer models. The hydration numbers of ionic liquids in aqueous solutions were obtained using activity data. Pitzer ion interaction parameters are estimated and compared with other electrolytes reported in the literature. The nonelectrolyte contribution to the aqueous solutions containing ionic liquids was studied by calculating the osmotic second virial coefficient through an application of the McMillan-Mayer theory of solution. It has been found that the second osmotic virial coefficient which includes volume effects correlates linearly with the Pitzer ion interaction parameter estimated independently from osmotic data as well as the hydrophobicity of ionic liquids. The enthalpy-entropy compensation effect, explained using the Starikov-Nordén model of enthalpy-entropy compensation, and partial molar entropy analysis for aqueous [Emim][Gly] solutions are made by using experimental Gibb

  5. Surface properties of aqueous amino acid solutions. I. Surface tension of hydrochloric acid-glycine and glycine-sodium hydroxide systems.

    PubMed

    Matubayasi, Norihiro; Namihira, Junji; Yoshida, Masao

    2003-11-01

    The surface tensions of aqueous solutions of four mixtures (hydrochloric acid-glycine hydrochloride, glycine hydrochloride-glycine, glycine-sodium glycinate, and sodium glycinate-sodium hydroxide) were measured as a function of total molality and mole fraction. The measurements correspond to the change in surface tension with variation of pH. The contribution of glycine hydrochloride to the increments in surface tension is equivalent to that observed for the aqueous solution of glycine, while the contribution of sodium glycinate is much larger than that of glycine. The variations in surface tension on mixing in the surface region are discussed using comparisons with mixtures of simple salts.

  6. Behavior of transplutonium elements on ion-exchange materials in mixed aqueous-organic solutions of mineral acids

    SciTech Connect

    Guseva, L.I.; Tikhomirov, G.S.; Stepushkina, V.V.

    1987-03-01

    Systematic studies are reported on the behavior of transplutonium elements (TPE) on cation-exchange and anion-exchange materials in mixed aqueous-organic solutions of mineral acids (HClO/sub 4/, HCl, HNO/sub 3/, H/sub 2/SO/sub 4/, H/sub 3/PO/sub 4/) as affected by solution composition, nature of acid, and nature of organic solvent. With all these acids, replacing most of the water by alcohol increases the TPE uptake on the ion exchangers, and the effect occurs for the cation exchangers at lower contents of the organic component. Optimum conditions have been identified for concentrating and separating TPE from numerous elements. The most effective system consists of anion exchanger with HNO/sub 3/ and alcohol.

  7. Removal characteristics of As(III) and As(V) from acidic aqueous solution by steel making slag.

    PubMed

    Oh, Chamteut; Rhee, Sungsu; Oh, Myounghak; Park, Junboum

    2012-04-30

    This study focused on the environmental risk of steel making slag itself, arsenic removal mechanism and re-leaching possibility of arsenic to aqueous state after the adsorption. The purpose of the study is to promote the use of steel making slag as a low-cost adsorbent for arsenic in aqueous system. Calcium was easily dissolved out from the slag and become the dominant substance in the leachate. Some of the calcium could form amorphous calcium carbonate in alkaline condition, and arsenic in the aqueous solution would be removed by being co-precipitated with or adsorbed onto the amorphous calcium carbonate. Most of the amorphous calcium carbonate containing arsenic would be bound to amorphous iron oxide of the slag. When the slag was used as an adsorbent for arsenic removal, a little amount of toxic chemicals were leached from the slag itself under pH 0.8 to 13.6. Also, 70-80% of arsenic laden on the slag was bound to amorphous iron oxide which would not easily desorb unless given a reducing and complexing condition. Showing 95-100% removal efficiency near initial pH 2, the slag, therefore, could be used as an appropriate adsorbent for eliminating arsenic in acidic aqueous solution.

  8. REDUCTION OF PLUTONIUM VALUES IN AN ACIDIC AQUEOUS SOLUTION WITH FORMALDEHYDE

    DOEpatents

    Olson, C.M.

    1959-06-01

    A method is given for reducing Pu to the tetravalent state and lowering the high acidity of dissolver solutions containing U and Pu. Formaldehyde is added to the HNO/sub 3/ solution of U and Pu to effect a formaldehyde to HNO/sub 3/ molar ratio of 0.375:1 to 1.5:1. The Pu can then be removed from the solution by carrier precipitation using BiPO/sub 4/ or by ion exchange. (T.R.H.)

  9. Investigation of the role of protonation of benzophenone and its derivatives in acidic aqueous solutions using time-resolved resonance Raman spectroscopy: how are ketyl radicals formed in aqueous solutions?

    PubMed

    Li, Ming-De; Huang, Jinqing; Liu, Mingyue; Li, Songbo; Ma, Jiani; Phillips, David Lee

    2015-02-12

    The formation mechanism of ketyl radicals and several other selective photoreactions of benzophenone and its derivatives are initiated by the protonation of their triplet state and have been investigated using nanosecond time-resolved resonance Raman spectroscopy (ns-TR(3)) in solutions of varying conditions. Evidence is found that the ketyl radical is generated by the combined action of a ketone protonation and a subsequent electron transfer based on the results from previous studies on the photochemistry and photophysics of benzophenone and the ns-TR(3) results reported here for benzophenone, 1,4-dibenzoylbenzene, 3-(hydroxymethyl)benzophenone, and ketoprofen in neutral and acidic solution. In order to better understand the role of the protonated ketone, results are summarized for some selective photochemical reactions of benzophenone and its derivatives induced by protonation in acidic solutions. For the parent benzophenone, the protonation of the ketone leads to the photohydration reactions at the ortho- and meta-positions of the benzene ring in acidic aqueous solutions. For 3-(hydroxymethyl)benzophenone, the protonation promotes an interesting photoredox reaction to become very efficient and the predominant reaction in a pH = 2 aqueous solution. While for ketoprofen, the protonation can initiate a solvent-mediated excited-state intramolecular proton transfer (ESIPT) from the carboxyl group to the carbonyl group that then leads to a decarboxylation reaction in a pH = 0 acidic aqueous solution. We briefly discuss the key role of the protonation of the ketone in the photochemistry of these aromatic ketones.

  10. Trivalent chromium removal from aqueous solutions by a sol–gel synthesized silica adsorbent functionalized with sulphonic acid groups

    SciTech Connect

    Gomez-Gonzalez, Sergio Efrain; Carbajal-Arizaga, Gregorio Guadalupe; Manriquez-Gonzalez, Ricardo; De la Cruz-Hernandez, Wencel; Gomez-Salazar, Sergio

    2014-11-15

    Highlights: • Corpuscular sulphonic acid-functionalized silica holds improved uptake of chromium. • Mesopores on adsorbent facilitate (CH{sub 3}COO){sub 2}Cr{sup +} ion uptake on sulphonate sites. • Formation of chromium acetate sulphonate complex proposed from XPS results. • Fixed bed chromium uptake results suggest potential industrial use. - Abstract: A high capacity hybrid silica adsorbent was synthesized via sol–gel processing with sulphonic acid groups as trivalent chromium complex ions chelators from aqueous solutions. The synthesis included co-condensation of tetraethoxysilane (TEOS) with 3-(mercaptopropyl)trimethoxysilane (MPS), and oxidation of thiol to sulphonic acid groups. Chromium uptake kinetic, batch and fixed-bed experiments were performed to assess the removal of this metal from aqueous solutions. {sup 13}C, {sup 29}Si CPMAS NMR, FTIR, XPS were used to characterize the adsorbent structure and the nature of chromium complexes on the adsorbent surface. Chromium maximum uptake was obtained at pH 3 (72.8 mg/g). Elemental analysis results showed ligand density of 1.48 mmol sulphonic groups/g. About 407 mL of Cr(III) solution (311 mg/L) were treated to breakthrough point reaching ≤0.06 mg/L at the effluent. These results comply with USEPA regulation for chromium concentration in drinking water (≤0.1 mg/L). The adsorbent shows potential to be used in chromium separations to the industrial level.

  11. Interaction of model aryl- and alkyl-boronic acids and 1,2-diols in aqueous solution.

    PubMed

    Marinaro, William A; Prankerd, Richard; Kinnari, Kaisa; Stella, Valentino J

    2015-04-01

    The goal of this work was to quantitate ester formation between alkyl and aryl boronic acids and vicinal-diols or 1,2-diols in aqueous solution. As used here, 1,2-diols includes polyols with one or more 1,2-diol pairs. Multiple techniques were used including apparent pKa shifts of the boronic acids using UV spectrophotometry (for aryl acids) and titration (for aryl and alkyl acids). Isothermal microcalorimetry was also used, with all reactions being enthalpically favored. For all the acids and 1,2-diols and the conditions studied, evidence only supported 1:1 ester formation. All the esters formed were found to be significantly more acidic, as Lewis acids, by 3-3.5 pKa units than the corresponding nonesterified boronic acid. The equilibrium constants for ester formation increased with increasing number of 1,2-diol pairs but stereochemistry may also play a role as sorbitol with five possible 1,2-diol pairs and five isomers (taking into account the stereochemistry of the alcohol groups) was twice as efficient at ester formation compared with mannitol, also with five possible 1,2-diol pairs but only three isomers. Alkyl boronic acids formed esters to a greater extent than aryl acids. Although some quantitative differences were seen between the various techniques used, rank ordering of the structure/reactivity was consistent. Formulation implications of ester formation between boronic acids and 1,2-diols are discussed.

  12. Mass spectroscopic approach to amino acids formation processes by UV irradiation to simple organic molecules in aqueous solution.

    PubMed

    Morita, Masaki; Harada, Yoshie; Iseki, Kunihiro; Izumi, Shunsuke; Hiraya, Atsunari

    2005-09-01

    We have studied amino acid formation by UV (193 nm) irradiation to organic molecules (amines, alcohols and amides) in aqueous solution. Among several types of detected amino acids, small aliphatic amino acids (Gly and alpha-, beta-Ala and alpha-, beta-, gamma-ABA) were quantitatively identified. Among these small aliphatic amino acids, certain amino acids were formed in its free form, even before hydrolysis, contrary to the results of UV irradiation to a gas mixture of CO, NH3, and H2O, where amino acids were hardly detected before hydrolysis. The species distribution of identified amino acids showed a dependence on the starting organic molecules, and also on the presence of ammonia. The formation processes of the identified small aliphatic amino acids were investigated with the aid of electrospray ionization (ESI) MS and MS/MS measurements of photoproducts. Possible formation processes of these amino acid precursors from each starting molecules are proposed. By identifying the amino acid precursor, which has a chiral carbon atom, a new possibility is suggested for asymmetric photosynthesis of amino acid from achiral organic molecules.

  13. An improved synthesis of 1,3,5-triaryl-2-pyrazolines in acetic acid aqueous solution under ultrasound irradiation.

    PubMed

    Li, Ji-Tai; Zhang, Xiao-Hui; Lin, Zhi-Ping

    2007-03-21

    Pyrazoline derivatives have been found to possess a broad spectrum of biological activities. Among various pyrazoline derivatives, 2-pyrazolines seem to be the most frequently studied. A variety of methods have been reported for the preparation of this class of compound. However, in spite of their potential utility, some of the reported methods suffer from drawbacks such as long reaction times, cumbersome product isolation procedures and environmental concerns. Organic reactions in aqueous media have attracted increasing interest recently because of environmental issues and the understanding of biochemical processes. Ultrasound has increasingly been used in organic synthesis in the last three decades. A large number of organic reactions can be carried out in higher yields, shorter reaction time or milder conditions under ultrasound irradiation. Preparation of a series of 1,3,5-triaryl-2-pyrazolines through the reaction of chalcones and phenylhydrazine hydrochloride was carried out in 83-96% yield within 1.5-2 h in sodium acetate-acetic acid aqueous solution under ultrasound irradiation. We have described a practical and convenient procedure for the synthesis of 1,3,5-triaryl-2-pyrazolines in sodium acetate-acetic acid aqueous solution at room temperature under ultrasound irradiation.

  14. The effect of nanoparticles and humic acid on technology critical element concentrations in aqueous solutions with soil and sand.

    PubMed

    Stepka, Zane; Dror, Ishai; Berkowitz, Brian

    2017-08-23

    As a consequence of their growing use in electronic and industrial products, increasing amounts of technology critical elements (TCEs) are being released to the environment. Currently little is known about the fate of many of these elements. Initial research on their potential environmental impact identifies TCEs as emerging contaminants. TCE movement in the environment is often governed by water systems. Research on "natural" waters so far demonstrates that TCEs tend to be associated with suspended particulate matter (SPM), which influences TCE aqueous concentrations (here: concentration of TCEs in dissolved form and attached to SPM) and transport. However, the relative potential of different types of SPM to interact with TCEs is unknown. Here we examine the potential of various types of particulate matter, namely different nanoparticles (NPs; Al2O3, SiO2, CeO2, ZnO, montmorillonite, Ag, Au and carbon dots) and humic acid (HA), to impact TCE aqueous concentrations in aqueous solutions with soil and sand, and thus influence TCE transport in soil-water environments. We show that a combination of NPs and HA, and not NPs or HA individually, increases the aqueous concentrations of TCEs in soil solutions, for all tested NPs regardless of their type. TCEs retained on SPM, however, settle with time. In solutions with sand, HA alone is as influential as NPs+HA in keeping TCEs in the aqueous phase. Among NPs, Ag-NPs and Au-NPs demonstrate the highest potential for TCE transport. These results suggest that in natural soil-water environments, once TCEs are retained by soil, their partitioning to the aqueous phase by through-flowing water is unlikely. However, if TCEs are introduced to soil-water environments as part of solutions rich in NPs and HA, it is likely that NP and HA combinations can increase TCE stability in the aqueous phase and prevent their retention on soil and sand, thus facilitating TCE transport. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Effective removal of phosphate from aqueous solution using humic acid coated magnetite nanoparticles.

    PubMed

    Rashid, Mamun; Price, Nathaniel T; Gracia Pinilla, Miguel Ángel; O'Shea, Kevin E

    2017-10-15

    Effective removal of excess phosphate from water is critical to counteract eutrophication and restore water quality. In this study, low cost, environmentally friendly humic acid coated magnetite nanoparticles (HA-MNP) were synthesized and applied for the remediation of phosphate from aqueous media. The HA-MNPs, characterized by FTIR, TEM and HAADF-STEM showed the extensive coating of humic acid on the magnetite surface. The magnetic nanoparticles with diameters of 7-12 nm could be easily separated from the reaction mixture by using a simple hand held magnet. Adsorption studies demonstrate the fast and effective separation of phosphate with maximum adsorption capacity of 28.9 mg/g at pH 6.6. The adsorption behavior follows the Freundlich isotherm suggesting the formation of non-uniform multilayers of phosphate on the heterogeneous surface of HA-MNP. The adsorption kinetic fits the pseudo-second order model well with rate constants of 0.206 ± 0.003, 0.073 ± 0.002 and 0.061 ± 0.003 g mg(-1)min(-1) for phosphate (P) concentrations of 2, 5 and 10 mg/L respectively. The removal of phosphate was found higher at acidic and neutral pH compared to basic conditions. The nanoparticles exhibit good selectivity and adsorption efficiency for phosphate in presence of co-existing ions such as Cl(-), SO4(2-)and NO3(-) with some inhibition effect by CO3(2-). The effect of temperature on the adsorption reveals that the process is endothermic and spontaneous. HA-MNPs are promising, simple, environmentally friendly materials for the removal of phosphate from aqueous media. Copyright © 2017. Published by Elsevier Ltd.

  16. Spectrophotometric Study of the Interaction Np(VI) with Orthosilicic Acid and Polymeric Silicic Acids in Aqueous Solutions

    SciTech Connect

    Yusov, A. B.; Shilov, V. P.; Fedoseev, A. M.; Astafurova, L. N.; Delegard, Calvin H.

    2005-07-15

    Spectrophotometric methods were used to investigate the interaction of the NpO22+ ion with orthosilicic acid, Si(OH)4, and polymeric silicic acids (PSA) in aqueous solutions. At рН ≤ 4.5, the interaction is described by the reaction NpO22+ + Si(OH)4 = NpO2OSi(OH)3+ + H+ with an equilibrium constant of lg K = -2.88 ± 0.12 (ionic strength I = 0.1-0.2). Recalculation to I = 0 gives lg K0 =-2.61 ± 0.12; the stability constant of the complex NpO2OSi(OH)3+ is lg β0 = 7.20 ± 0.12. Polymerization of Si(OH)4 does not lead to an apparent increase in the constant K. In solutions with рН higher than 5, and with silicate concentration more than 0.02 mole/l, leads to formation of a second complex, whose structure probably is described by the formula NpO2(≡SiO)2(≡SiOH)m-2, where (≡SiOH)m designates the PSA molecule with superficial Si-OH groups. The factors influencing the apparent equilibrium constants in forming of complexes NpO2OSi(OH)3+ and NpO2(≡SiO)2(≡SiOH)m-2 are considered upon polymerization of Si(OH)4. Absorption spectra of complexes NpO2OSi(OH)3+ and NpO2(≡SiO)2(≡SiOH)m-2 were obtained. Molar extinction coefficients at the maxima (500-600 nanometers) are much higher than those of the Np(VI) aquo ion and are about 25-30 l/mol∙cm. The stabilities of silicate complexes of all types - MO2OSi(OH)3+, MO2(≡SiO)2(≡SiOH)m-2, or MO2SiO3 (M = U, Np, or Pu) - decrease in order U> Np> Pu with the greatest difference occurring between Np and Pu.

  17. RECOVERY OF TETRAVALENT CATIONS FROM AQUEOUS SOLUTIONS

    DOEpatents

    Moore, R.L.

    1958-05-01

    The recovery of plutonium, zirconium, and tetravalent cerium values from aqueous solutions is described. It consists of adding an alkyl phosphate to a nnineral acid aqueous solution containing the metal to be recovered, whereby a precipitate forms with the tetravalent values, and separating the precipitate from the solution. All alkyl phosphates, if water-soluble, are suitable for the process; however, monobutyl phosphate has been found best.

  18. Determination of acidity constants of curcumin in aqueous solution and apparent rate constant of its decomposition.

    PubMed

    Bernabé-Pineda, Margarita; Ramírez-Silva, María Teresa; Romero-Romo, Mario; González-Vergara, Enrique; Rojas-Hernández, Alberto

    2004-04-01

    The stability of curcumin (H3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur3- species of 1.39 (10(-9)) Mmin(-1). There were three acidity constants measured for the curcumin as follows: pKA3 = 10.51 +/- 0.01 corresponding to the equilibrium HCur2- = Cur3- + H+, a pKA2 = 9.88 +/- 0.02 corresponding to the equilibrium H2Cur- = HCur-(2) + H+. These pKA values were attributed to the hydrogen of the phenol part of the curcumin, while the pKA1 = 8.38 +/- 0.04 corresponds to the equilibrium H3Cur = H2Cur- + H+ and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.

  19. Poly (vinylsulfonic acid) assisted synthesis of aqueous solution stable vaterite calcium carbonate nanoparticles.

    PubMed

    Nagaraja, Ashvin T; Pradhan, Sulolit; McShane, Michael J

    2014-03-15

    Calcium carbonate nanoparticles of the vaterite polymorph were synthesized by combining CaCl2 and Na2CO3 in the presence of poly (vinylsulfonic acid) (PVSA). By studying the important experimental parameters we found that controlling PVSA concentration, reaction temperature, and order of reagent addition the particle size, monodispersity, and surface charge can be controlled. By increasing PVSA concentration or by decreasing temperature CCNPs with an average size from ≈150 to 500 nm could be produced. We believe the incorporation of PVSA into the reaction plays a dual role to (1) slow down the nucleation rate by sequestering calcium and to (2) stabilize the resulting CCNPs as the vaterite polymorph, preventing surface calcification or aggregation into microparticles. The obtained vaterite nanoparticles were found to maintain their crystal structure and surface charge after storage in aqueous buffer for at least 5 months. The aqueous stable vaterite nanoparticles could be a useful platform for the encapsulation of a large variety of biomolecules for drug delivery or as a sacrificial template toward capsule formation for biosensor applications. Copyright © 2013 Elsevier Inc. All rights reserved.

  20. Spectrofluorimetric study of the interaction of ciprofloxacin with amino acids in aqueous solution following solvatochromic studies

    NASA Astrophysics Data System (ADS)

    Alizadeh, Kamal; Mobarrez, Mahsa; Ganjali, Mohammad Reza; Norouzi, Parviz; Chaichi, Mohammad Javad

    Complexation of a fluoroquinolone derivative (ciprofloxacin), L, and some amino acids has been studied using spectrofluorimetric method. Results indicated that ciprofloxacin have a greater tendency to form a 1:1 complex with aspartic acid and arginine than the other tested molecules. The fluorescence of ciprofloxacin exhibits quenching process while it has been titrated with these amino acids. Formation constant values (Kf) for complex formed between ciprofloxacin and amino acids were also calculated. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were studied too. Possible reasons for the observed stability sequence were discussed based on the structures proposed for the resulting complexes. Besides the solution studies, solvatochromic properties of the ciprofloxacin are discussed by studying its spectra in a selection of different solvents.

  1. Photocatalytic decomposition of humic acids in anoxic aqueous solutions producing hydrogen, oxygen and light hydrocarbons.

    PubMed

    Klauson, Deniss; Budarnaja, Olga; Beltran, Ignacio Castellanos; Krichevskaya, Marina; Preis, Sergei

    2014-01-01

    Photocatalytic water splitting for hydrogen and oxygen production requires sacrificial electron donors, for example, organic compounds. Titanium dioxide catalysts doped with platinum, cobalt, tungsten, copper and iron were experimentally tested for the production of hydrogen, oxygen and low molecular weight hydrocarbons from aqueous solutions of humic substances (HS). Platinum-doped catalyst showed the best results in hydrogen generation, also producing methane, ethene and ethane, whereas the best oxygen production was exhibited by P25, followed by copper--and cobalt-containing photocatalysts. Iron-containing photocatalyst produced carbon monoxide as a major product. HS undergoing anoxic photocatalytic degradation produce hydrogen with minor hydrocarbons, and/or oxygen. It appears that better hydrogen yield is achieved when direct HS splitting takes place, as opposed to HS acting as electron donors for water splitting.

  2. Water- and acid-mediated excited-state intramolecular proton transfer and decarboxylation reactions of ketoprofen in water-rich and acidic aqueous solutions.

    PubMed

    Li, Ming-De; Yeung, Chi Shun; Guan, Xiangguo; Ma, Jiani; Li, Wen; Ma, Chensheng; Phillips, David Lee

    2011-09-19

    We present an investigation of the decarboxylation reaction of ketoprofen (KP) induced by triplet excited-state intramolecular proton transfer in water-rich and acidic solutions. Nanosecond time-resolved resonance Raman spectroscopy results show that the decarboxylation reaction is facile in aqueous solutions with high water ratios (water/acetonitrile ≥50%) or acidic solutions with moderate and strong acid concentration. These experimental results are consistent with results from density functional theory calculations in which 1) the activation energy barriers for the triplet-state intramolecular proton transfer and associated decarboxylation process become lower when more water molecules (from one up to four molecules) are involved in the reaction system and 2) perchloric acid, sulfuric acid, and hydrochloric acid can shuttle a proton from the carboxyl to carbonyl group through an initial intramolecular proton transfer of the triplet excited state, which facilitates the cleavage of the C-C bond, thus leading to the decarboxylation reaction of triplet state KP. During the decarboxylation process, the water molecules and acid molecules may act as bridges to mediate intramolecular proton transfer for the triplet state KP when KP is irradiated by ultraviolet light in water-rich or acidic aqueous solutions and subsequently it generates a triplet-protonated carbanion biradical species. The faster generation of triplet-protonated carbanion biradical in acidic solutions than in water-rich solutions with a high water ratio is also supported by the lower activation energy barrier calculated for the acid-mediated reactions versus those of water-molecule-assisted reactions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. The effect of high-energy radiation on aqueous solution of Acid Red 1 textile dye

    NASA Astrophysics Data System (ADS)

    Földváry, Cs. M.; Wojnárovits, L.

    2007-08-01

    The effect of high-energy radiation on Acid Red 1 (AR1) azo-dye solution was investigated by UV-Vis spectroscopy and chemical oxygen demand (COD) measurements. Doses in the order of 10 kGy cause complete decolouration of the 10 -3-10 -4 mol dm -3 solutions; however, for complete mineralization doses higher by 1-2 order of magnitude are needed. Hydrated electrons and H rad atom are more effective in fading reaction, while the rad OH radicals have higher efficiency in mineralization. The HO 2•/O 2•- radical-radical anion pair is rather inefficient in fading reaction.

  4. Formulation and make-up of simulated acidic concentrated water (SAW), high ionic content aqueous solution

    SciTech Connect

    Gdowski, G.

    1996-09-30

    This procedure describes the formulation and make-up of Simulated Acidified Water (SAW), a high-ionic-content water to be used for Activity E-20-50 ''Long-Term Corrosion Studies.'' Acidic solutions at the repository may result as a consequence of microbial activity. In formulating the ionic composition of the SAW, it was attempted to simulate the acidification of high ionic content water contacting a waste package. Therefore, the composition of this water is based on the acidification of the Simulated Concentrated Water (SCW), which is described in TIP-CM-07. The pH of the solution will be controlled at a nominal value of 2.

  5. Unexpectedly Enhanced Solubility of Aromatic Amino Acids and Peptides in an Aqueous Solution of Divalent Transition-Metal Cations

    NASA Astrophysics Data System (ADS)

    Shi, Guosheng; Dang, Yaru; Pan, Tingting; Liu, Xing; Liu, Hui; Li, Shaoxian; Zhang, Lijuan; Zhao, Hongwei; Li, Shaoping; Han, Jiaguang; Tai, Renzhong; Zhu, Yiming; Li, Jichen; Ji, Qing; Mole, R. A.; Yu, Dehong; Fang, Haiping

    2016-12-01

    We experimentally observed considerable solubility of tryptophan (Trp) in a CuCl2 aqueous solution, which could reach 2-5 times the solubility of Trp in pure water. Theoretical studies show that the strong cation-π interaction between Cu2 + and the aromatic ring in Trp modifies the electronic distribution of the aromatic ring to enhance significantly the water affinity of Trp. Similar solubility enhancement has also been observed for other divalent transition-metal cations (e.g., Zn2 + and Ni2 + ), another aromatic amino acid (phenylalanine), and three aromatic peptides (Trp-Phe, Phe-Phe, and Trp-Ala-Phe).

  6. Experimental and theoretical evaluation on the microenvironmental effect of dimethyl sulfoxide on adrenaline in acid aqueous solution

    NASA Astrophysics Data System (ADS)

    Yu, Zhang-Yu; Liu, Tao; Guo, Dao-Jun; Liu, Yong-Jun; Liu, Cheng-Bu

    2010-12-01

    The microenvironmental effect of dimethyl sulfoxide (DMSO) on adrenaline was studied by several approaches including the cyclic voltammetry (CV) of adrenaline at a platinum electrode in acid aqueous solution, the chemical shift of 1H nuclear magnetic resonance ( 1H NMR) of adrenaline, and the change of diffusion coefficient of adrenaline. The experimental results demonstrated that DMSO has significant microenvironmental effect on adrenaline, which was confirmed by the density functional theory (DFT) study on the hydrogen bond (H-bond) complexes of adrenaline with water and DMSO.

  7. Biosorption of hexavalent chromium by raw and acid-treated green alga Oedogonium hatei from aqueous solutions.

    PubMed

    Gupta, V K; Rastogi, A

    2009-04-15

    The hexavalent chromium, Cr(VI), biosorption by raw and acid-treated Oedogonium hatei were studied from aqueous solutions. Batch experiments were conducted to determine the biosorption properties of the biomass. The optimum conditions of biosorption were found to be: a biomass dose of 0.8 g/L, contact time of 110 min, pH and temperature 2.0 and 318 K respectively. Both Langmuir and Freundlich isotherm equations could fit the equilibrium data. Under the optimal conditions, the biosorption capacities of the raw and acid-treated algae were 31 and 35.2 mg Cr(VI) per g of dry adsorbent, respectively. Thermodynamic parameters showed that the adsorption of Cr(VI) onto algal biomass was feasible, spontaneous and endothermic under studied conditions. The pseudo-first-order kinetic model adequately describe the kinetic data in comparison to second-order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The physical and chemical properties of the biosorbent were determined and the nature of biomass-metal ions interactions were evaluated by FTIR analysis, which showed the participation of -COOH, -OH and -NH(2) groups in the biosorption process. Biosorbents could be regenerated using 0.1 M NaOH solution, with up to 75% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of chromium bearing aqueous solutions.

  8. Evidence for a Morin Type Intramolecular Cyclization of an Alkene with a Phenylsulfenic Acid Group in Neutral Aqueous Solution

    PubMed Central

    Keerthi, Kripa; Sivaramakrishnan, Santhosh; Gates, Kent S.

    2009-01-01

    Sulfenic acids (RSOH) are among the most common sulfur-centered reactive intermediates generated in biological systems. Given the biological occurrence of sulfenic acids, it is important to explore the reactivity of these intermediates under physiological conditions. The Morin rearrangement is a synthetic process developed for the conversion of penicillin derivatives into cephalosporins that proceeds via nucleophilic attack of an alkene on a sulfenic acid intermediate. In its classic form, the Morin reaction involves initial elimination of a sulfenic acid from a cyclic sulfoxide, followed by intramolecular cyclization of the resulting alkene and sulfenic acid groups to generate an episulfonium ion intermediate that undergoes further reaction to yield ring-expanded products. On the basis of the existing literature, it is difficult to assess whether the reaction between an alkene and a sulfenic group can occur under mild conditions because the conditions required to generate the sulfenic acid from the sulfoxide precursor in the Morin reaction typically involve high temperatures and strong acid. In the work described here, β-sulfinylketone precursors were used to generate a “Morin type” sulfenic acid intermediate under mild conditions. This approach made it possible to demonstrate that the intramolecular cyclization of an alkene with a phenylsulfenic acid to generate an episulfonium ion intermediate can occur in neutral aqueous solution at room temperature. PMID:18500784

  9. A systematic investigation and insight into the formation mechanism of bilayers of fatty acid/soap mixtures in aqueous solutions.

    PubMed

    Xu, Wenlong; Song, Aixin; Dong, Shuli; Chen, Jingfei; Hao, Jingcheng

    2013-10-08

    Vesicles are the most common form of bilayer structures in fatty acid/soap mixtures in aqueous solutions; however, a peculiar bilayer structure called a "planar sheet" was found for the first time in the mixtures. In the past few decades, considerable research has focused on the formation theory of bilayers in fatty acid/soap mixtures. The hydrogen bond theory has been widely accepted by scientists to explain the formation of bilayers. However, except for the hydrogen bond, no other driving forces were proposed systematically. In this work, three kinds of weak interactions were investigated in detail, which could perfectly demonstrate the formation mechanism of bilayer structures in the fatty acid/soap mixtures in aqueous solutions. (i) The influence of hydrophobic interaction was detected by changing the chain length of fatty acid (C(n)H(2n+1)COOH), in which n = 10 to 18, the phase behavior was investigated, and the phase region was presented. With the help of cryogenic transmission electron microscopy (cryo-TEM) observations, deuterium nuclear magnetic resonance ((2)H NMR), and X-ray diffraction (XRD) measurements, the vesicles and planar sheets were determined. The chain length of C(n)H(2n+1)COOH has an important effect on the physical state of the hydrophobic chain, resulting in an obvious difference in the viscoelasticity of the solution samples. (ii) The existence of hydrogen bonds between fatty acids and their soaps in aqueous solutions was demonstrated by Fourier transform infrared (FT-IR) spectroscopy and molecule dynamical simulation. From the pH measurements, the pH ranges of the bilayer formation were at the pKa values of fatty acids, respectively. (iii) Counterions can be embedded in the stern layer of the bilayers and screen the electrostatic repulsion between the COO(-) anionic headgroups. FT-IR characterization demonstrated a bidentate bridging coordination mode between counterions and carboxylates. The conductivity measurements provided the degree

  10. Visible-light photoconversion of carbon dioxide into organic acids in an aqueous solution of carbon dots.

    PubMed

    Sahu, Sushant; Liu, Yamin; Wang, Ping; Bunker, Christopher E; Fernando, K A Shiral; Lewis, William K; Guliants, Elena A; Yang, Fan; Wang, Jinping; Sun, Ya-Ping

    2014-07-22

    Carbon "quantum" dots (or carbon dots) have emerged as a new class of optical nanomaterials. Beyond the widely reported bright fluorescence emissions in carbon dots, their excellent photoinduced redox properties that resemble those found in conventional semiconductor nanostructures are equally valuable, with photon-electron conversion applications from photovoltaics to CO2 photocatalytic reduction. In this work we used gold-doped carbon dots from controlled synthesis as water-soluble catalysts for a closer examination of the visible-light photoconversion of CO2 into small organic acids, including acetic acid (for which the reduction requires many more electrons than that for formic acid) and, more interestingly, for the significantly enhanced photoconversion with higher CO2 pressures over an aqueous solution of the photocatalysts. The results demonstrate the nanoscale semiconductor-equivalent nature of carbon dots, with excellent potential in energy conversion applications.

  11. Fast removal of copper ions from aqueous solution by chitosan-g-poly(acrylic acid)/attapulgite composites.

    PubMed

    Wang, Xiaohuan; Zheng, Yian; Wang, Aiqin

    2009-09-15

    Novel chitosan-g-poly(acrylic acid)/attapulgite (CTS-g-PAA/APT) composites were applied as adsorbents for the removal of Cu(II) from aqueous solution. The effects of the initial pH value (pH(0)) of Cu(II) solution, contact time (t), APT content (wt%) and the initial concentration of Cu(II) solution (C(0)) on the adsorption capacity of the composites were investigated. Results from kinetic experimental data showed that the Cu(II) adsorption rate on the composites with 10, 20 and 30 wt% APT was fast and more than 90% of the maximum adsorption capacity for Cu(II) occurred within the initial 15 min. The adsorption kinetics was better described by the pseudo-second order equation, and their adsorption isotherms were better fitted for the Langmuir equation. The results of the five-time consecutive adsorption-desorption studies showed that the composites had high adsorption and desorption efficiencies, which implies that the composites may be used as quite effective adsorbents for the removal of Cu(II) from aqueous solution.

  12. Influence of trace elements on stabilization of aqueous solutions of ascorbic acid.

    PubMed

    Dolińska, Barbara; Ostróżka-Cieślik, Aneta; Caban, Artur; Rimantas, Klimas; Leszczyńska, Lucyna; Ryszka, Florian

    2012-12-01

    Together with vitamin C, zinc, selenium, manganese, and magnesium play a vital role in the preservation of organs scheduled for transplantation. In the present study, it is shown that addition of 1 mg/l of these elements influences the stability of 0.3 mM ascorbic acid solutions. The solution's stability was estimated using an accelerated stability test. The concentration of vitamin C was measured using a validated spectrophotometric method, which uses the reduction of 2,6-dichlorophenoloindophenol by ascorbic acid. Elevated temperatures, the factor accelerating substances' decomposition reaction rate, were used in the tests. The research was conducted at two temperatures at intervals of 10 °C: 80 ± 0.1 and 90 ± 0.1 °C. It was stated that the studied substances' decomposition occurred in accordance with the equation for first-order reactions. The function of the logarithmic concentration (log%C) over time was revealed to be rectilinear. This dependence was used to determine the kinetics of decomposition reaction rate parameters. The stabilization of vitamin C solutions was measured as the time in which 10 % of the substance decomposed at 20 and 0 °C. Addition of Se(IV) or Mg(II) ions significantly increase the stability of ascorbic acid solution (∼34 and ∼16 %, respectively), but Zn(II) causes a significant decrease in stability by ∼23 %. Addition of Mn(II) has no significant influence on vitamin C stability.

  13. Novel Regenerated Solvent Extraction Processes for the Recovery of Carboxylic Acids or Ammonia from Aqueous Solutions Part II. Recovery of Ammonia from Sour Waters

    SciTech Connect

    Poole, L.J.; King, C.J.

    1990-03-01

    Two novel regenerated solvent extraction processes are examined. The first process has the potential to reduce the energy costs inherent in the recovery of low-volatility carboxylic acids from dilute aqueous solutions. The second process has the potential for reducing the energy costs required for separate recovery of ammonia and acid gases (e.g. CO{sub 2} and H{sub 2}S) from industrial sour waters. The recovery of carboxylic acids from dilute aqueous solution can be achieved by extraction with tertiary amines. An approach for regeneration and product recovery from such extracts is to back-extract the carboxylic acid with a water-soluble, volatile tertiary amine, such as trimethylamine. The resulting trimethylammonium carboxylate solution can be concentrated and thermally decomposed, yielding the product acid and the volatile amine for recycle. Experimental work was performed with lactic acid, SUCCiOlC acid, and fumaric acid. Equilibrium data show near-stoichiometric recovery of the carboxylic acids from an organic solution of Alamine 336 into aqueous solutions of trimethylamine. For fumaric and succinic acids, partial evaporation of the aqueous back extract decomposes the carboxylate and yields the acid product in crystalline form. The decomposition of aqueous solutions of trimethylammonium lactates was not carried out to completion, due to the high water solubility of lactic acid and the tendency of the acid to self-associate. The separate recovery of ammonia and acid gases from sour waters can be achieved by combining steam-stripping of the acid gases with simultaneous removal of ammonia by extraction with a liquid cation exchanger. The use of di-2,4,4-trimethylpentyl phosphinic acid as the liquid cation exchanger is explored in this work. Batch extraction experiments were carried out to measure the equilibrium distribution ratio of ammonia between an aqueous buffer solution and an organic solution of the phosphinic acid (0.2N) in Norpar 12. The concentration

  14. Formation of specific amino acid sequences during carbodiimide-mediated condensation of amino acids in aqueous solution, and computer-simulated sequence generation

    NASA Astrophysics Data System (ADS)

    Hartmann, Jürgen; Nawroth, Thomas; Dose, Klaus

    1984-12-01

    Carbodiimide-mediated peptide synthesis in aqueous solution has been studied with respect to self-ordering of amino acids. The copolymerisation of amino acids in the presence of glutamic acid or pyroglutamic acid leads to short pyroglutamyl peptides. Without pyroglutamic acid the formation of higher polymers is favoured. The interactions of the amino acids and the peptides, however, are very complex. Therefore, the experimental results are rather difficult to explain. Some of the experimental results, however, can be explained with the aid of computer simulation programs. Regarding only the tripeptide fraction the copolymerisation of pyroGlu, Ala and Leu, as well as the simulated copolymerisation lead to pyroGlu-Ala-Leu as the main reaction product. The amino acid composition of the insoluble peptides formed during the copolymerisation of Ser, Gly, Ala, Val, Phe, Leu and Ile corresponds in part to the computer-simulated copolymerisation data.

  15. Mechanism of polyol-induced protein stabilization: solubility of amino acids and diglycine in aqueous polyol solutions.

    PubMed

    Gekko, K

    1981-12-01

    The solubilities of several amino acids and diglycine have been measured in water and at several concentrations of methanol and various polyols (glycerol, erythritol, xylitol, sorbitol, and inositol). The solubility data were used to calculate the free energy of transfer of amino acid side chains and peptide group from water to the aqueous alcohol solutions. The results for methanol systems were similar to those reported for ethanol and dioxane systems. The free energy of transfer to aqueous solutions of linear polyols was positive for most nonpolar side chains and peptide group, but high concentrations of the polyols may disrupt the hydrophobic interactions of large nonpolar side chains. Moreover, the linear polyols appeared to stabilize the hydrophobic interaction more effectively and the peptide-peptide hydrogen bond less effectively with increasing hydroxymethyl chain length of polyols. A cyclic polyol, inositol, had a very strong stabilizing ability on hydrophobic interactions of nonpolar side chains, but it may act as a destabilizing reagent for peptide-peptide hydrogen bonds. From these results, it was concluded that the protein stabilization by polyols is a manifestation of polyol-induced strengthening of the hydrophobic interaction of protein molecules.

  16. Copper (II) ion adsorption from aqueous solution onto fatty hydroxamic acid - Immobilized zeolyte

    NASA Astrophysics Data System (ADS)

    Muhsinun, Sugita, Purwantiningsih; Purwaningsih, Henny

    2017-01-01

    Separation of Cu (II) ion from a mixture containing Zn (II) ion was conducted by solid-liquid extraction method through column chromatography. The column was filled with FHA-ZEO resin. This resin is the result of immobilized fatty hydroxamic acid (FHA) into activated natural zeolite (ZEO) involving as solid phase. Parameters becoming variable were resin mass to concentration ratio and pH of Cu (II) ion solution. The research result shows that optimum condition of Cu (II) ion adsorption was 1 gram resin mass FHA-ZEO to ion Cu (II) solution concentration of 100 ppm with pH value of 5. This Cu (II) ion separation from its mixture containing Zn (II) ion gives Cu(II) ion adsorption capacity of 162.39 mg/g FHA-ZEO in that optimum condition, 4 times higher than Zn (II) ion adsorption with Cu (II) ion recovery of 93,88%.

  17. The use of raw and acid-pretreated bivalve mollusk shells to remove metals from aqueous solutions.

    PubMed

    Liu, Yang; Sun, Changbin; Xu, Jin; Li, Youzhi

    2009-08-30

    Heavy metal removal from industrial wastewater is not only to protect living organisms in the environment but also to conserve resources such as metals and water by enabling their reuse. To overcome the disadvantage of high cost and secondary pollution by the conventional physico-chemical treatment techniques, environmentally benign and low-cost adsorbents are in demand. In this study, the use of raw and acid-pretreated bivalve mollusk shells (BMSs) to remove metals from aqueous solutions with single or mixed metal was evaluated at different BMSs doses, pH and temperatures in batch shaking experiments in laboratory conditions. When the BMSs were used to treat CuSO(4)x5H(2)O solution, the copper sorption capacities of the raw and acid-pretreated BMSs were approximately 38.93 mg/g and 138.95 mg/g, respectively. The copper removal efficiency (CRE) of the raw BMSs became greatly enhanced with increasing initial pH, reaching 99.51% at the initial pH 5. Conversely, the CRE of the acid-pretreated BMSs was maintained at 99.48-99.52% throughout the pH range of 1-5. Furthermore, the CRE values of the raw and acid-pretreated BMSs were not greatly changed when the temperature was varied from 15 degrees C to 40 degrees C. In addition, the CRE value of the raw BMSs was maintained for 12 cycles of sorption-desorption with a CRE of 98.4% being observed in the final cycle. Finally, when the BMSs were used to treat electroplating wastewater, the removal efficiencies (REs) of the raw BMSs were 99.97%, 98.99% and 87% for Fe, Zn and Cu, respectively, whereas the REs of the acid-pretreated BMSs were 99.98%, 99.43% and 92.13%, respectively. Ion exchange experiments revealed that one of mechanisms for metal sorption by the BMSs from aqueous solution is related to ion exchange, especially between the metal ions in the treated solution and Ca(2+) from BMSs. Infrared absorbance spectra analysis indicated that the acid pretreatment led to occurrence of the groups (i.e. -OH, -NH, C=O and S

  18. Acid-base equilibria in aqueous solutions of meta-cresolsulfophthalein in the temperature range of 25 to 200°C

    NASA Astrophysics Data System (ADS)

    Stepanchikova, S. A.; Galay, G. I.

    2017-01-01

    Values of the second thermodynamic ionization constant of pH indicator m-Cresol Purple are determined spectrophotometrically in slightly alkaline aqueous solutions in the temperature range of 25 to 200°C at saturated vapor pressure. Data required for studies on acid-base equilibria in weakly alkaline aqueous solution of rare-earth elements at elevated temperatures are obtained to characterize their behavior in geochemical systems.

  19. Chemisorption of Perfluorooctanoic Acid on Powdered Activated Carbon Initiated by Persulfate in Aqueous Solution.

    PubMed

    Sun, Bo; Ma, Jun; Sedlak, David L

    2016-07-19

    Perfluorooctanoic acid (PFOA) is a perfluorocarboxylic acid that is difficult to treat by most conventional methods. As a result, it is often removed from solution by adsorption on powdered activated carbon (PAC), followed by incineration of the spent carbon. To provide a new approach for treatment, PFOA was exposed to sulfate radicals (SO4(-•)) produced by thermolysis of persulfate (S2O8(2-)) in the presence of PAC. Under acidic conditions, thermal activation of persulfate resulted in transformation of PFOA to shorter-chain-length perfluorinated compounds, as previously reported. However, when thermolysis of persulfate occurred under circumneutral pH conditions in the presence of PAC, a new removal pathway for PFOA was observed. Under these conditions, the removal of PFOA was attributable to chemisorption, a process in which PAC catalyzed persulfate decomposition and reacted with the transformation products to produce covalently bound PFOA. At PAC concentrations between 200 and 1000 mg/L and an initial PFOA concentration of 0.5 μM, covalent bonding resulted in removal of 10-40% of the PFOA. Under these conditions, the process resulted in removal of more than half of a more hydrophilic perfluoroalkyl acid (i.e., perfluorobutanoic acid, PFBA), which was greater than the amount of PFBA removed by physical adsorption on PAC. Although the high reaction temperatures (i.e., 80 °C) and relatively high doses of PAC used in this study may be impractical for drinking water treatment, this process may be applied to the treatment of these recalcitrant compounds in industrial wastewater, reverse osmosis concentrate, and other waters that contain high concentrations of PFOA and other perfluorocarboxylic acids.

  20. Interaction of some metals between marine-origin humic acids and aqueous solutions

    SciTech Connect

    Huljev, D.J.

    1986-08-01

    The interaction of metal ions (carrier-free form) in aquatic medium with humic acids is a complicated process depending on the properties of humic acids (elementary, chemical, and trace element composition), metals studied (valence, charge, chemical form, concentration), and medium used (pH, ionic strength). The use of radionuclides was found to be very suitable for a rapid and precise determination of the distribution coefficient K/sub d/ (ratio of the concentration of a certain trace metal association with a gram of humic acid over the concentration of the same trace metal per milliliter of solution) of the investigated system. Isolated humic acids from offshore sediments from the North Adriatic (Lim channel, near Rovinj, Yugoslavia) were characterized according to their elementary composition, the amount of products of hydrolysis, and the trace elements bound. All experiments were carried out between pH 3 and 5. It was found that conditions usually present at the site where humic acid interacts with metal ions (anaerobic conditions, H/sub 2/S) in brackish (21% S) and standard seawater (38% S) are determined in the pH range 3 to 5. The results of the pick-up (uptake) and replacement (release) experiments are presented as a distribution coefficient (K/sub d/), as a function of contact time. Processes of pick-up and replacement of a number of metals under various physicochemical conditions were investigated and special attention was paid to the influence of salinity. With the increase in NaCl concentration and pH in the system, the fixation of ruthenium, zinc, cobalt, and mercury by humic acids decreased.

  1. Complete mineralization of perfluorooctanoic acid (PFOA) by γ-irradiation in aqueous solution

    PubMed Central

    Zhang, Ze; Chen, Jie-Jie; Lyu, Xian-Jin; Yin, Hao; Sheng, Guo-Ping

    2014-01-01

    Decomposition of perfluorooctanoic acid (C7F15COOH, PFOA) has been gaining increasing interests because it is a ubiquitous environmental contaminant and resistant to the most conventional treatment processes. In this work, the rapid and complete mineralization of PFOA and simultaneous defluorination were achieved by γ-ray irradiation with a 60Co source. The degradation rate of PFOA by γ-ray irradiation would be high, and a pseudo-first-order kinetic rate constant of 0.67 h−1 could be achieved in the N2 satured condition at pH 13.0. The experimental results and quantum chemical calculation confirmed that two radicals, i.e., hydroxyl radical (·OH) and aqueous electrons (eaq−), were responsible for the degradation of PFOA, while only either eaq− or ·OH might not be able to accomplish complete mineralization of PFOA. The synergistic effects of ·OH and eaq− involved in the cleavage of C-C and C-F bonds, and therefore complete mineralization of PFOA were achieved. The intermediate products were identified and the degradation pathway was also proposed. The results of this study may offer a useful, high-efficient approach for complete mineralizing fluorochemicals and other persistent pollutants. PMID:25492109

  2. Complete mineralization of perfluorooctanoic acid (PFOA) by γ-irradiation in aqueous solution

    NASA Astrophysics Data System (ADS)

    Zhang, Ze; Chen, Jie-Jie; Lyu, Xian-Jin; Yin, Hao; Sheng, Guo-Ping

    2014-12-01

    Decomposition of perfluorooctanoic acid (C7F15COOH, PFOA) has been gaining increasing interests because it is a ubiquitous environmental contaminant and resistant to the most conventional treatment processes. In this work, the rapid and complete mineralization of PFOA and simultaneous defluorination were achieved by γ-ray irradiation with a 60Co source. The degradation rate of PFOA by γ-ray irradiation would be high, and a pseudo-first-order kinetic rate constant of 0.67 h-1 could be achieved in the N2 satured condition at pH 13.0. The experimental results and quantum chemical calculation confirmed that two radicals, i.e., hydroxyl radical (.OH) and aqueous electrons (eaq-), were responsible for the degradation of PFOA, while only either eaq- or .OH might not be able to accomplish complete mineralization of PFOA. The synergistic effects of .OH and eaq- involved in the cleavage of C-C and C-F bonds, and therefore complete mineralization of PFOA were achieved. The intermediate products were identified and the degradation pathway was also proposed. The results of this study may offer a useful, high-efficient approach for complete mineralizing fluorochemicals and other persistent pollutants.

  3. Impact of humic/fulvic acid on the removal of heavy metals from aqueous solutions using nanomaterials: a review.

    PubMed

    Tang, Wang-Wang; Zeng, Guang-Ming; Gong, Ji-Lai; Liang, Jie; Xu, Piao; Zhang, Chang; Huang, Bin-Bin

    2014-01-15

    Nowadays nanomaterials have been widely used to remove heavy metals from water/wastewater due to their large surface area and high reactivity. Humic acid (HA) and fulvic acid (FA) exist ubiquitously in aquatic environments and have a variety of functional groups which allow them to complex with metal ions and interact with nanomaterials. These interactions can not only alter the environmental behavior of nanomaterials, but also influence the removal and transportation of heavy metals by nanomaterials. Thus, the interactions and the underlying mechanisms involved warrant specific investigations. This review outlined the effects of HA/FA on the removal of heavy metals from aqueous solutions by various nanomaterials, mainly including carbon-based nanomaterials, iron-based nanomaterials and photocatalytic nanomaterials. Moreover, mechanisms involved in the interactions were discussed and potential environmental implications of HA/FA to nanomaterials and heavy metals were evaluated.

  4. A kinetic and mechanistic study of the amino acid catalyzed aldol condensation of acetaldehyde in aqueous and salt solutions.

    PubMed

    Nozière, Barbara; Córdova, Armando

    2008-04-03

    The amino acid catalyzed aldol condensation is of great interest in organic synthesis and natural environments such as atmospheric particles. However, kinetic and mechanistic information on these reactions is limited. In this work the kinetics of the aldol condensation of acetaldehyde in water and aqueous salt solutions (NaCl, CaCl2, Na2SO4, MgSO4) catalyzed by five amino acids (glycine, alanine, serine, arginine, and proline) at room temperature (295 +/- 2 K) has been studied. Monitoring the formation of three products, crotonaldehyde, 2,4-hexadienal, and 2,4,6-octatrienal, by UV-vis absorption over 200-1100 nm revealed two distinct kinetic regimes: at low amino acid concentrations (in all cases, below 0.1 M), the overall reaction was first-order with respect to acetaldehyde and kinetically limited by the formation of the enamine intermediate. At larger amino acid concentrations (at least 0.3 M), the kinetics was second order and controlled by the C-C bond-forming step. The first-order rate constants increased linearly with amino acid concentration consistent with the enamine formation. Inorganic salts further accelerated the enamine formation according to their pKb plausibly by facilitating the iminium or enamine formation. The rate constant of the C-C bond-forming step varied with the square of amino acid concentration suggesting the involvement of two amino acid molecules. Thus, the reaction proceeded via a Mannich pathway. However, the contribution of an aldol pathway, first-order in amino acid, could not be excluded. Our results show that the rate constant for the self-condensation of acetaldehyde in aqueous atmospheric aerosols (up to 10 mM of amino acids) is identical to that in sulfuric acid 10-15 M (kI approximately 10-7-10-6 s-1) clearly illustrating the potential importance of amino acid catalysis in natural environments. This work also demonstrates that under usual laboratory conditions and in natural environments aldol condensation is likely to be

  5. Steric structure and thermodynamic aspects of the complexes of dysprosium (III) with aminobenzoic acids in aqueous solutions

    SciTech Connect

    Kondrashina, Yu, G.; Mustafina, A.R.; Vul`fson, S.G.

    1994-10-01

    Steric structures of dysprosium (III) aminobenzoate complexes with the 1:1 and 1:2 molar ratio in aqueous solutions were determined on the basis of pH-metric and paramagnetic birefringence data. An increase in conjugation observed for the series of the acids, viz., benzoic, meta-, ortho-, and para-aminobenzoic acids, results in the increased stability of the complexes with the 1:1 and 1:2 composition. In the case of para-aminobenzoic acid, the polyhedra [DyL(H{sub 2}O){sub 6}]{sup 2+} and [DyL{sub 2}(H{sub 2}O){sub 4}]{sup +} are cubes with the ligands coordinated to one and two edges, respectively. In the case of meta-aminobenzoic acid, the polyhedra [DyL(H{sub 2}O){sub 6}]{sup 2+} and [DyL{sub 2}(H{sub 2}O){sub 4}]{sup +} are a dodecahedron with the ligand coordinated to one edge and a square anti-prism with the ligands coordinated to two edges, respectively. In the case of ortho-aminobenzoic acid, both the 1:1 and 1:2 complexes have structures that are intermediate between the structures of meta- and para-aminobenzoic acids.

  6. Use of oxalic acid as inducer in photocatalytic oxidation of cresol red in aqueous solution under natural and artificial light.

    PubMed

    Seraghni, N; Ghoul, I; Lemmize, I; Reguig, A; Debbache, N; Sehili, T

    2017-08-30

    This work was carried out in the field of water treatment using advanced oxidation processes (AOPs), especially photolysis of carboxylic acid that leads to the formation in situ of hydroxyl radical (·OH). Cresol red (CR) degradation induced by organic acids/UV system was investigated in aqueous solution. The preliminary study of CR-organic acid mixture in the dark and at room temperature allowed confirming the absence of interaction under our experimental conditions. However, upon irradiation at 365 nm, the proportion of elimination of CR was 89% after 5 h of irradiation. Indeed, the CR degradation efficiency depends on the acid concentration and the pH of the medium. The concentration of acid is optimized to the 5 × 10(-3) M. pH 2.39 was the optimal one when C2HO(-)4 was the most important species at this pH. The use of i-PrOH as (·)OH confirmed the involvement of (·)OH in photodegradation of CR induced by Ox. The addition of metal ions including Zn(2+) and Cu(2+) to the CR-organic acid mixture slowed the CR degradation unlike Fe(2+), hence an improvement of its disappearance was observed. The results showed a faster degradation of the pollutant under excitation by sunlight. This environmentally friendly method appears to be very effective in the treatment of wastewater.

  7. Enhanced catalytic performance of Pd catalyst for formic acid electrooxidation in ionic liquid aqueous solution

    NASA Astrophysics Data System (ADS)

    Feng, Yuan-Yuan; Yin, Qian-Ying; Lu, Guo-Ping; Yang, Hai-Fang; Zhu, Xiao; Kong, De-Sheng; You, Jin-Mao

    2014-12-01

    A protic ionic liquid (IL), n-butylammonium nitrate (N4NO3), is prepared and employed as the electrolyte for formic acid electrooxidation reaction (FAOR) on Pd catalysts. The oxidation peak potential of FAOR in the IL solution shows about a 200 mV negative shift as compared with those in traditional H2SO4/HClO4 electrolytes, suggesting that FAOR can be more easily carried out on Pd catalysts in IL media. The catalytic properties of Pd toward FAOR are not only dependent on the concentration of IL, as a consequence of the varied electronic conductivity of the IL solution, but also on the high potential limit of the cyclic voltammograms. When the Pd catalyst is cycled up to 1.0 V (vs. SCE), which induces a significant oxidation of Pd, it shows ca. 4.0 times higher activity than that not subjected to the Pd oxidation (up to 0.6 V). The Pd oxides, which are more easily formed in IL solution than in traditional H2SO4/HClO4 electrolytes, may play a crucial role in increasing the catalytic activities of Pd toward FAOR. Our work would shed new light on the mechanism of FAOR and highlight the potential applications of IL as green and environment-friendly electrolytes in fuel cells and other technologies.

  8. Adsorption of methyl violet in aqueous solutions by poly(acrylamide-co-acrylic acid) hydrogels

    NASA Astrophysics Data System (ADS)

    Şolpan, D.; Duran, S.; Saraydin, D.; Güven, O.

    2003-02-01

    In this study, Acrylamide(AAm)/Acrylic Acid(AAc) monomer mixtures which contain different quantities of acrylic acid have been irradiated to form hydrogels with γ-radiation. Acrylamide/Acrylic Acid (AAm/AAc) monomer mixtures which contain 15%, 20%, 30% AAm and irradiated with 8.0 kGy were used for swelling and diffusion studies in water and solutions of methyl violet. Diffusions of water and methyl violet within the hydrogels were found to be non-Fickian in character. In experiments on the adsorption of methyl violet, Type-S adsorption was found. Poly(AAm-co-AAc) hydrogel adsorbed methyl violet, while poly(AAm) hydrogel did not adsorb any dye. (Δ H) Heat of adsorption, (Δ G) Free energy of adsorption, (Δ S) Entropy of adsorption were calculated. These results show that poly(AAm-co-AAc) hydrogels can be used as a sorbent for water pollutants such as dyes and treatment of these organic contaminants from wastewater.

  9. SEPARATION OF RUTHENIUM FROM AQUEOUS SOLUTIONS

    DOEpatents

    Callis, C.F.; Moore, R.L.

    1959-09-01

    >The separation of ruthenium from aqueous solutions containing uranium plutonium, ruthenium, and fission products is described. The separation is accomplished by providing a nitric acid solution of plutonium, uranium, ruthenium, and fission products, oxidizing plutonium to the hexavalent state with sodium dichromate, contacting the solution with a water-immiscible organic solvent, such as hexone, to extract plutonyl, uranyl, ruthenium, and fission products, reducing with sodium ferrite the plutonyl in the solvent phase to trivalent plutonium, reextracting from the solvent phase the trivalent plutonium, ruthenium, and some fission products with an aqueous solution containing a salting out agent, introducing ozone into the aqueous acid solution to oxidize plutonium to the hexavalent state and ruthenium to ruthenium tetraoxide, and volatizing off the ruthenium tetraoxide.

  10. Thermodynamic characteristics of acid-base equilibria of DL-α-alanyl-DL-norleucine in aqueous solutions at 298 K

    NASA Astrophysics Data System (ADS)

    Lytkin, A. I.; Chernikov, V. V.; Krutova, O. N.; Bychkova, S. A.; Skvortsov, I. A.

    2015-09-01

    Protolytic equilibria in aqueous solutions of DL-α-alanyl-DL-norleucine are studied via potentiometry and calorimetry. Measurements are made at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (against a background of potassium nitrate). The thermodynamic characteristics (p K, Δ G, Δ H, Δ S) of the stepwise dissociation of the dipeptide both in aqueous-salt solutions and in standard solution are obtained for the first time.

  11. Structural and vibrational investigation on species derived from the cyclamic acid in aqueous solution by using HATR and Raman spectroscopies and SCRF calculations

    NASA Astrophysics Data System (ADS)

    Brizuela, Alicia B.; Raschi, Ana B.; Castillo, María V.; Davies, Lilian; Romano, Elida; Brandán, Silvia A.

    2014-09-01

    In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HATR (Horizontal Attenuated Total Reflectance) and Raman spectroscopies. The theoretical structures of cyclamate ion, the zwitterionic and neutral forms of the cyclamic acid and its dimer were optimized in gas and aqueous solution phases by using the hybrid B3LYP/6-31G* method. The solvent effects for the four species in aqueous solutions were simulated by using self-consistent reaction field (SCRF) calculations employing the integral equation formalism variant (IEFPCM) model. The complete assignments of the vibrational spectra of all the forms of cyclamic acid were performed taking into account the factor group analysis with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The existence of the zwitterionic and neutral forms of the cyclamic acid and its dimer in a solution of cyclamate in water is evidenced by characteristic bands in the HATR and Raman spectra. The dimerization of cyclamate in aqueous solution was previously reported by conductimetric method. The natural population analysis (NPA) and Merz-Kollman (MK) charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) calculations predict for all the species the principal donor and acceptor sites for the H bonds formation in aqueous solution. The SQM force fields for the cyclamate ion, the zwitterionic and neutral species of the cyclamic acid were obtained and their corresponding force constants in both phases were reported. Additionally, the solvation energies for those species were reported.

  12. ADSORPTION OF CERIUM VALUES FROM AQUEOUS SOLUTIONS

    DOEpatents

    Roberts, F.P.

    1963-08-13

    Cerium can be removed from aqueous nitric acid (2 to 13 M) solutions by passing the latter over a PbO/sub 2/-containing anion exchange resin. The cerium is taken up by the resin, while any lanthanides, yttrium, and strontium present remain in the solution. (AEC)

  13. Sonocatalytic degradation of humic acid by N-doped TiO2 nano-particle in aqueous solution.

    PubMed

    Kamani, Hossein; Nasseri, Simin; Khoobi, Mehdi; Nabizadeh Nodehi, Ramin; Mahvi, Amir Hossein

    2016-01-01

    Un-doped and N-doped TiO2 nano-particles with different nitrogen contents were successfully synthesized by a simple sol-gel method, and were characterized by X-ray diffraction, field emission scanning electron microscopy, Energy dispersive X-ray analysis and UV-visible diffuse reflectance spectra techniques. Then enhancement of sonocatalytic degradation of humic acid by un-doped and N-doped TiO2 nano-particles in aqueous environment was investigated. The effects of various parameters such as initial concentration of humic acid, N-doping, and the degradation kinetics were investigated. The results of characterization techniques affirmed that the synthesis of un-doped and N-doped TiO2 nano-particles was successful. Degradation of humic acid by using different nano-particles obeyed the first-order kinetic. Among various nano-particles, N-doped TiO2 with molar doping ratio of 6 % and band gap of 2.92 eV, exhibited the highest sonocatalytic degradation with an apparent-first-order rate constant of 1.56 × 10(-2) min(-1). The high degradation rate was associated with the lower band gap energy and well-formed anatase phase. The addition of nano-catalysts could enhance the degradation efficiency of humic acid as well as N-doped TiO2 with a molar ratio of 6 %N/Ti was found the best nano-catalyst among the investigated catalysts. The sonocatalytic degradation with nitrogen doped semiconductors could be a suitable oxidation process for removal of refractory pollutants such as humic acid from aqueous solution.

  14. Freezing and glass transitions upon cooling and warming and ice/freeze-concentration-solution morphology of emulsified aqueous citric acid.

    PubMed

    Bogdan, Anatoli; Molina, Mario J; Tenhu, Heikki

    2016-12-01

    Although freeze-induced phase separation and the ice/FCS (freeze-concentration solution) morphology of aqueous solutions play an important role in fields ranging from life sciences and biotechnology to geophysics and high-altitude ice clouds, their understanding is far from complete. Herein, using differential scanning calorimetry (DSC) and optical cryo-microscope (OC-M), we have studied the freezing and glass transition behavior and the ice/FCS morphology of emulsified 10-60wt% CA (citric acid) solutions in the temperature region of ∼308and153K. We have obtained a lot of new result which are understandable and unclear. The most essential understandable results are as follows: (i) similar to bulk CA/H2O, emulsified CA/H2O also freezes upon cooling and warming and (ii) the ice/FCS morphology of frozen drops smaller than ∼3-4μm is less ramified than that of frozen bulk solutions. Unclear results, among others, are as follows: (i) in contrast to bulk solutions, which produce one freezing event, emulsified CA/H2O produces two freezing events and (ii) in emulsions, drop concentration is not uniform. Our results demonstrate that DSC thermograms and OC-M images/movies are mutually supplementary and allow us to extract important information which cannot be gained when DSC and OC-M techniques are used alone. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Extraction of electrolytes from aqueous solutions and their spectrophotometric determination by use of acid-base chromoionophores in lipophylic solvents.

    PubMed

    Barberi, Paola; Giannetto, Marco; Mori, Giovanni

    2004-04-01

    The formation of non-absorbing complexes in an organic phase has been exploited for the spectrophotometric determination of ionic analytes in aqueous solutions. The method is based on liquid-liquid extraction of aqueous solution with lipophylic organic phases containing an acid-base chromoionophore, a neutral lypophilic ligand (neutral carrier) selective to the analyte and a cationic (or anionic) exchanger. The method avoids all difficulties of the preparation of the very thin membranes used in optodes, so that it can advantageously be used for the study of the role physical-chemical parameters of the system in order to optimize them and to prepare, if necessary, an optimized optode. Two lipophylic derivatives of Nile Blue and 4',5-dibromofluorescein have been synthesized, in order to ensure their permanence within organic phase. Two different neutral carriers previously characterized by us as ionophores for liquid-membrane Ion Selective Electrodes have been employed. Three different ionic exchangers have been tested. Furthermore, a model allowing the interpolation of experimental data and the determination of the thermodynamic constant of the ionic-exchange equilibrium has been developed and applied.

  16. Nitrilotriacetic acid functionalized Adansonia digitata biosorbent: Preparation, characterization and sorption of Pb (II) and Cu (II) pollutants from aqueous solution.

    PubMed

    Adewuyi, Adewale; Pereira, Fabiano Vargas

    2016-11-01

    Nitrilotriacetic acid functionalized Adansonia digitata (NFAD) biosorbent has been synthesized using a simple and novel method. NFAD was characterized by X-ray Diffraction analysis technique (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analyzer, Fourier Transform Infrared spectrometer (FTIR), particle size dispersion, zeta potential, elemental analysis (CHNS/O analyzer), thermogravimetric analysis (TGA), differential thermal analysis (DTA), derivative thermogravimetric analysis (DTG) and energy dispersive spectroscopy (EDS). The ability of NFAD as biosorbent was evaluated for the removal of Pb (II) and Cu (II) ions from aqueous solutions. The particle distribution of NFAD was found to be monomodal while SEM revealed the surface to be heterogeneous. The adsorption capacity of NFAD toward Pb (II) ions was 54.417 mg/g while that of Cu (II) ions was found to be 9.349 mg/g. The adsorption of these metals was found to be monolayer, second-order-kinetic, and controlled by both intra-particle diffusion and liquid film diffusion. The results of this study were compared better than some reported biosorbents in the literature. The current study has revealed NFAD to be an effective biosorbent for the removal of Pb (II) and Cu (II) from aqueous solution.

  17. Preparation and utilization of wheat straw bearing amine groups for the sorption of acid and reactive dyes from aqueous solutions.

    PubMed

    Xu, Xing; Gao, Bao-Yu; Yue, Qin-Yan; Zhong, Qian-Qian

    2010-10-15

    Removal of Acid Red 73 (AR 73) and Reactive Red 24 (RR 24) onto modified wheat straw (MWS) from aqueous solutions was investigated. Sorption experiments were carried out as function of MWS dosage, contact time, initial concentration, pH and temperature. Characterizations of MWS were measured and a mass of amine groups were observed in the framework of MWS. The equilibrium sorption data were well represented by the Langmuir isotherm equation, and the calculated thermodynamic parameters indicated a spontaneous and endothermic nature for sorption process. It was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. More over, the high maximum sorption capacity (q(e max), 714.3 mg g(-1) for AR 73 and 285.7 mg g(-1) for RR 24) and low cost (1.24 US$ kg(-1)) of MWS provided strong evidence of the potential of MWS for the technological applications of anionic dyes removal from aqueous solutions. 2010 Elsevier B.V. All rights reserved.

  18. Mapping the conformational free energy of aspartic acid in the gas phase and in aqueous solution.

    PubMed

    Comitani, Federico; Rossi, Kevin; Ceriotti, Michele; Sanz, M Eugenia; Molteni, Carla

    2017-04-14

    The conformational free energy landscape of aspartic acid, a proteogenic amino acid involved in a wide variety of biological functions, was investigated as an example of the complexity that multiple rotatable bonds produce even in relatively simple molecules. To efficiently explore such a landscape, this molecule was studied in the neutral and zwitterionic forms, in the gas phase and in water solution, by means of molecular dynamics and the enhanced sampling method metadynamics with classical force-fields. Multi-dimensional free energy landscapes were reduced to bi-dimensional maps through the non-linear dimensionality reduction algorithm sketch-map to identify the energetically stable conformers and their interconnection paths. Quantum chemical calculations were then performed on the minimum free energy structures. Our procedure returned the low energy conformations observed experimentally in the gas phase with rotational spectroscopy [M. E. Sanz et al., Phys. Chem. Chem. Phys. 12, 3573 (2010)]. Moreover, it provided information on higher energy conformers not accessible to experiments and on the conformers in water. The comparison between different force-fields and quantum chemical data highlighted the importance of the underlying potential energy surface to accurately capture energy rankings. The combination of force-field based metadynamics, sketch-map analysis, and quantum chemical calculations was able to produce an exhaustive conformational exploration in a range of significant free energies that complements the experimental data. Similar protocols can be applied to larger peptides with complex conformational landscapes and would greatly benefit from the next generation of accurate force-fields.

  19. Mapping the conformational free energy of aspartic acid in the gas phase and in aqueous solution

    NASA Astrophysics Data System (ADS)

    Comitani, Federico; Rossi, Kevin; Ceriotti, Michele; Sanz, M. Eugenia; Molteni, Carla

    2017-04-01

    The conformational free energy landscape of aspartic acid, a proteogenic amino acid involved in a wide variety of biological functions, was investigated as an example of the complexity that multiple rotatable bonds produce even in relatively simple molecules. To efficiently explore such a landscape, this molecule was studied in the neutral and zwitterionic forms, in the gas phase and in water solution, by means of molecular dynamics and the enhanced sampling method metadynamics with classical force-fields. Multi-dimensional free energy landscapes were reduced to bi-dimensional maps through the non-linear dimensionality reduction algorithm sketch-map to identify the energetically stable conformers and their interconnection paths. Quantum chemical calculations were then performed on the minimum free energy structures. Our procedure returned the low energy conformations observed experimentally in the gas phase with rotational spectroscopy [M. E. Sanz et al., Phys. Chem. Chem. Phys. 12, 3573 (2010)]. Moreover, it provided information on higher energy conformers not accessible to experiments and on the conformers in water. The comparison between different force-fields and quantum chemical data highlighted the importance of the underlying potential energy surface to accurately capture energy rankings. The combination of force-field based metadynamics, sketch-map analysis, and quantum chemical calculations was able to produce an exhaustive conformational exploration in a range of significant free energies that complements the experimental data. Similar protocols can be applied to larger peptides with complex conformational landscapes and would greatly benefit from the next generation of accurate force-fields.

  20. Photochemical Formation of Nitrite and Nitrous Acid (HONO) upon Irradiation of Nitrophenols in Aqueous Solution and in Viscous Secondary Organic Aerosol Proxy.

    PubMed

    Barsotti, Francesco; Bartels-Rausch, Thorsten; De Laurentiis, Elisa; Ammann, Markus; Brigante, Marcello; Mailhot, Gilles; Maurino, Valter; Minero, Claudio; Vione, Davide

    2017-07-05

    Irradiated nitrophenols can produce nitrite and nitrous acid (HONO) in bulk aqueous solutions and in viscous aqueous films, simulating the conditions of a high-solute-strength aqueous aerosol, with comparable quantum yields in solution and viscous films (10(-5)-10(-4) in the case of 4-nitrophenol) and overall reaction yields up to 0.3 in solution. The process is particularly important for the para-nitrophenols, possibly because their less sterically hindered nitro groups can be released more easily as nitrite and HONO. The nitrophenols giving the highest photoproduction rates of nitrite and HONO (most notably, 4-nitrophenol and 2-methyl-4-nitrophenol) could significantly contribute to the occurrence of nitrite in aqueous phases in contact with the atmosphere. Interestingly, dew-water evaporation has shown potential to contribute to the gas-phase HONO levels during the morning, which accounts for the possible importance of the studied process.

  1. Enhanced adsorption of Methylene Blue from aqueous solution by chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites.

    PubMed

    Liu, Yi; Zheng, Yian; Wang, Aiqin

    2010-01-01

    A series of chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites were synthesized and used as adsorbents for the investigation of the effect of process parameters such as vermiculite content, pH of dye solution, contact time, initial concentration of dye solution, temperature, ionic strength and concentration of surfactant sodium dodecyl sulfate on the removal of Methylene Blue (MB) from aqueous solution. The results showed that the adsorption capacity for dye increased with increasing pH, contact time and initial dye concentration, but decreased with increasing temperature, ionic strength and sodium dodecyl sulfate concentration in the present of the surfactant. The adsorption kinetics of MB onto the hydrogel composite followed pseudo second-order kinetics and the adsorption equilibrium data obeyed Langmuir isotherm. By introducing 10 wt.% vermiculite into chitosan-g-poly (acrylic acid) polymeric network, the obtaining hydrogel composite showed the highest adsorption capacity for MB, and then could be regarded as a potential adsorbent for cationic dye removal in a wastewater treatment process.

  2. Spectroscopic study of Mg(II) ion influence on the autoxidation of gallic acid in weakly alkaline aqueous solutions

    NASA Astrophysics Data System (ADS)

    Nikolić, G. M.; Veselinović, A. M.; Nikolić, R. S.; Mitić, S. S.

    2011-12-01

    Gallic acid autoxidation in weakly alkaline aqueous solutions was studied by UV-Vis spectrophotometry and ESR spectroscopy under various conditions. Lowering the pH value from 10 to 8.5 probably changes the mechanism of the autoxidation reaction as evidenced by the different time variations of UV-Vis spectra of solutions. The presence of Mg(II) ions greatly influences the autoxidation reaction at pH 8.5. Although the UV-Vis spectral changes with time follow the similar pattern during the gallic acid autoxidation at pH 10 and at pH 8.5 in the presence of Mg(II) ions, some small differences indicate that Mg(II) ions not only affect the electron density of absorbing species but also influence the overall mechanism of the autoxidation reaction. ESR spectra of free radials formed during the initial stage of gallic acid autoxidation at pH 8.5 in the presence of Mg(II) ions were recorded. Computer simulation of ESR spectra allows partial characterization of these free radicals.

  3. Effect of rat pretreatment with aqueous solutions of stevioside and bile acids on the action of certain cardioactive drugs.

    PubMed

    Vasović, Velibor; Vukmirović, Sasa; Posa, Mihalj; Mikov, Momir; Rasković, Aleksandar; Jakovljević, Vida

    2006-01-01

    The interaction of aqueous solutions of stevioside and bile acids with cardioactive drugs was studied in rats by registering changes in their electrocardiograms (ECG). Wistar rats of both sexes received daily doses of 20 mg/kg (i.p.) of an aqueous solution of stevioside or physiological solution (controls), then were narcotized with urethane and connected to the ECG apparatus for the first recording. The jugular vein was prepared and connected to an infusion pump to administer one of the drugs: adrenaline (0.1 mg/ml), verapamil (2.5 mg/ml) or metoprolol (1 mg/ml) to rats in both groups, while recording their ECGs. In the second part of the study, the animals were treated in the same way but instead of the stevioside solution received a single dose of 4 mg/kg of monoketocholic acid methyl ester (ME) or sodium salt of the same bile acid (MKHNa), 30 minutes before cardioactive drug infusion. The infusion rate of cardioactive drugs was 0.2 ml/min, except for verapamil (0.1 ml/min). The events observed on ECG recordings were the first myocardial reaction to drug infusion, the second longer-lasting reaction (observed as more extended extrasystoles, decrease in intensity of the QRS complex, or changes in heart rate frequency), and toxicity effect. In the control animals, adrenaline induced a decrease in heart rate frequency at a dose of 0.094 mg/kg, while with stevioside-pretreated rats this effect appeared significantly earlier (at a dose of 0.018 mg/kg). No toxic effect of adrenaline was observed, either in control or stevioside-pretreated group. Bile acids caused no changes in myocardial reaction to adrenaline. Only in the group of animals that received MKHNa, a significant decrease in the QRS complex was observed. Finally, the infusion of stevioside to intact animals at doses of 45 and 55 mg/kg caused no significant changes in the ECG patterns. The myocardial reaction to metoprolol remained unchanged in rats of all groups when compared with controls except for a mild

  4. Superlubricity of a Mixed Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Ma, Zhi-Zuo; Zhang, Chen-Hui; Luo, Jian-Bin; Lu, Xin-Chun; Wen, Shi-Zhu

    2011-05-01

    A super-low friction coefficient of 0.0028 is measured under a pressure of 300 MPa when the friction pair (the silicon nitride ball sliding on the silicate glass) is lubricated by the mixed aqueous solution of glycerol and boric acid. The morphorlogies of the hydroxylated glass plate are observed by an atomic force microscope (AFM) in deionized water, glycerol, boric acid and their mixed aqueous solution. Bonding peaks of the retained liquids adhered on the surface of the sliding track are detected by an infrared spectrum apparatus and a Raman spectrum apparatus. The mechanism of the superlubricity of the glycerol and boric acid mixed aqueous solution is discussed. It is deduced that the formation of the lubricant film has enough strength to support higher loads, the hydration effect offering the super lower shear resistance. Key words: superlubricity, water based lubricant, ultra-low friction

  5. Formation of Amino Acids on the Sonolysis of Aqueous Solutions Containing Acetic Acid, Methane, or Carbon Dioxide, in the Presence of Nitrogen Gas.

    PubMed

    Dharmarathne, Leena; Grieser, Franz

    2016-01-21

    The sonolysis of aqueous solutions containing acetic acid, methane, or carbon dioxide in the presence of nitrogen gas was found to produce a number of different amino acids at a rate of ∼1 to 100 nM/min, using ultrasound at an operating power of 70 W and 355 kHz. Gas-phase elementary reactions are suggested, and discussed, to account for the formation of the complex biomolecules from the low molar mass solutes used. On the basis of the results, a new hypothesis is presented to explain the formation of amino acids under primitive atmospheric conditions and how their formation may be linked to the eventual abiotic genesis of life on Earth.

  6. Removal of humic acid from aqueous solution by magnetically separable polyaniline: adsorption behavior and mechanism.

    PubMed

    Wang, Jiahong; Bi, Lijuan; Ji, Yanfen; Ma, Hongrui; Yin, Xiaolong

    2014-09-15

    Magnetically separable polyaniline (Fe3O4@SiO2-PANI) was prepared by in situ chemical polymerization of aniline on the surface of silica-coated Fe3O4 nanoparticles, and characterized by FTIR spectroscopy, powder X-ray diffraction, elemental analysis, transmission electron microscopy, vibrating sample magnetometry and X-ray photoelectron spectroscopy. Characterization results showed that Fe3O4@SiO2-PANI with amino groups of 1.78 mmol/g and the average diameter of 21.6 nm are superparamagnetic. Adsorption behavior of Fe3O4@SiO2-PANI nanoparticles for humic acid (HA) was investigated by batch experiments and adsorption kinetic tests. HA adsorption amount on the adsorbent decreased with increasing solution pH and the presence of Ca(2+) resulted in the enhanced HA adsorption. HA adsorption on Fe3O4@SiO2-PANI could be well described by Langmuir model and the maximum adsorption amount of the adsorbent for HA at 25°C was 36.36 mg/g. HA adsorption process on the adsorbent obey pseudo-second-order kinetics and the adsorption rates decrease with increasing initial HA concentration. The XPS analysis verified that HA adsorption over the adsorbent could be attributed to the surface complexation between the disassociated HA molecules and the protonated nitrogen of polyaniline on the adsorbent. HA loaded adsorbent could be magnetically separated and easily desorbed in 0.01 mol/L NaOH solution. Regeneration tests indicated that Fe3O4@SiO2-PANI could be used repeatedly. Copyright © 2014 Elsevier Inc. All rights reserved.

  7. Development of tannic acid/chitosan/pullulan composite nanofibers from aqueous solution for potential applications as wound dressing.

    PubMed

    Xu, Fenghua; Weng, Baicheng; Gilkerson, Robert; Materon, Luis Alberto; Lozano, Karen

    2015-01-22

    This study presents the successful development of biocompatible tannic acid (TA)/chitosan (CS)/pullulan (PL) composite nanofibers (NFs) with synergistic antibacterial activity against the Gram-negative bacteria Escherichia coli. The NFs were developed utilizing the forcespinning(®) (FS) technique from CS-CA aqueous solutions to avoid the usage of toxic organic solvents. The ternary nanofibrous membranes were crosslinked to become water stable for potential applications as wound dressing. The morphology, structure, water solubility, water absorption capability and thermal properties of the NFs were characterized. The ternary composite membrane exhibits good water absorption ability with rapid uptake rate. This novel membrane favors fibroblast cell attachment and growth by providing a 3D environment which mimics the extracellular matrix (ECM) in skin and allows cells to move through the fibrous structure resulting in interlayer growth throughout the membrane, thus favoring potential for deep and intricate wound healing.

  8. Hollow-fiber membrane extraction of copper(II) from aqueous ethylenediaminetetraacetic acid solutions with Aliquat 336

    SciTech Connect

    Juang, R.S.; Huang, I.P.

    2000-05-01

    The extraction of Cu(II) from an equimolar EDTA ethylenediaminetetraacetic acid (EDTA) solution across microporous hollow fibers to an organic phase containing Aliquat 336 (a quaternary amine) was studied. It was shown that the resistance of interfacial chemical reaction could be neglected. A mass-transfer model was proposed considering aqueous-layer diffusion, membrane diffusion, and organic-layer diffusion on the basis of knowledge of extraction chemistry and the transport properties of the relevant geometry. The calculated time profiles of Cu(II) concentrations were in reasonable agreement with the measured ones (average standard deviation, 12%). The mass-transfer mechanism of this membrane extraction process was finally identified and discussed.

  9. Morphological and phase evolution of TiO 2 nanocrystals prepared from peroxotitanate complex aqueous solution: Influence of acetic acid

    NASA Astrophysics Data System (ADS)

    Chang, Jeong Ah; Vithal, Muga; Baek, In Chan; Seok, Sang Il

    2009-04-01

    Nanosized anatase and rutile TiO 2 having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H 2O 2) in water/isopropanol media by a facile sol-gel process. The TiO 2 nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO 2 are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given.

  10. Equilibrium and kinetics study on the adsorption of perfluorooctanoic acid from aqueous solution onto powdered activated carbon.

    PubMed

    Qu, Yan; Zhang, Chaojie; Li, Fei; Bo, Xiaowen; Liu, Guangfu; Zhou, Qi

    2009-09-30

    Powdered activated carbon (PAC) was applied to remove perfluorooctanoic acid (PFOA) from the aqueous PFOA solution in this study. Contact time, adsorbent dose and temperature were analyzed as the effect factors in the adsorption reaction. The contact time of maximum PFOA uptake was around 1h while the sorption removal efficiency increased with the PAC concentrations. And the process of adsorption increased from 303 K to 313 K and then decreased from 313 K to 323 K. Among four applied models, the experimental isotherm data were discovered to follow Langmuir isotherm model more closely. Thermodynamically, adsorption was endothermic because enthalpy, entropy and Gibbs constants were 198.5 kJ/mol, 0.709 kJ/mol/K and negative, respectively, which also indicated that the adsorption process was spontaneous and feasible. From kinetic analysis, the adsorption was suggested to be pseudo-second-order model. The adsorption of PFOA on the PAC was mainly controlled by particle diffusion.

  11. Removal of fluoride from aqueous solution using granular acid-treated bentonite (GHB): batch and column studies.

    PubMed

    Ma, Yuxin; Shi, Fengmei; Zheng, Xilai; Ma, Jun; Gao, Congjie

    2011-01-30

    Removal of fluoride from aqueous solution using granular acid-treated bentonite (GHB) was studied by batch and column adsorption experiments. The results of the batch adsorption experiments demonstrated that the maximum fluoride removal was obtained at pH of 4.95 and it took 40 min to attain equilibrium. Kinetics data fitted pseudo-second-order model. Batch adsorption data was better described by Redlich-Peterson and Freundlich isotherm models than Langmuir isotherm model. The adsorption type of GHB was ion exchange. Column experiments were carried out at different influent fluoride concentrations and different flow rates. The capacities of the breakthrough and exhaustion points increased with the decrease of flow rate and the increase of initial fluoride concentration. The experimental results were well fitted with Thomas model. Exhausted GHB was regenerated by alkali/alum treatment. The total sorption capacity of GHB was increased after regeneration and activation. Copyright © 2010 Elsevier B.V. All rights reserved.

  12. Simultaneous removal of acid green 25 and mercury ions from aqueous solutions using glutamine modified chitosan magnetic composite microspheres.

    PubMed

    Tao, Xue; Li, Kun; Yan, Han; Yang, Hu; Li, Aimin

    2016-02-01

    In this current work, the magnetic composite microsphere containing glutamine modified chitosan and silica coated Fe3O4 nanoparticles (CS-Gln-MCM) has been successfully prepared and extensively characterized, which is a kind of biodegradable materials. CS-Gln-MCM shows enhanced removal efficiency for both acid green 25 (AG25), an amphoteric dye, and mercury ions (Hg(2+)) from water in the respective while measured pH range compared with chitosan magnetic composite microsphere (CS-MCM) without modification. It is due to the fact that the grafted amino acid provides a variety of additional adsorption active sites and diverse adsorption mechanisms are involved. In AG25 and Hg(2+) aqueous mixture, the modified adsorbents bear preferential adsorption for AG25 over Hg(2+) in strong acidic solutions ascribed to multiple interactions between AG25 and CS-Gln-MCM, such as hydrogen bonding and electrostatic interactions. While, in weak acidic conditions, an efficient simultaneous removal is observed for different adsorption effects involved in aforementioned two pollutants. Besides, CS-Gln-MCM illuminates not only short equilibrium time for adsorption of each pollutant less than 20.0 min but also rapid magnetic separation from water and efficient regeneration after saturated adsorption. Therefore, CS-Gln-MCM bears great application potentials in water treatment.

  13. An In Silico study of TiO2 nanoparticles interaction with twenty standard amino acids in aqueous solution

    NASA Astrophysics Data System (ADS)

    Liu, Shengtang; Meng, Xuan-Yu; Perez-Aguilar, Jose Manuel; Zhou, Ruhong

    2016-11-01

    Titanium dioxide (TiO2) is probably one of the most widely used nanomaterials, and its extensive exposure may result in potentially adverse biological effects. Yet, the underlying mechanisms of interaction involving TiO2 NPs and macromolecules, e.g., proteins, are still not well understood. Here, we perform all-atom molecular dynamics simulations to investigate the interactions between TiO2 NPs and the twenty standard amino acids in aqueous solution exploiting a newly developed TiO2 force field. We found that charged amino acids play a dominant role during the process of binding to the TiO2 surface, with both basic and acidic residues overwhelmingly preferred over the non-charged counterparts. By calculating the Potential Mean Force, we showed that Arg is prone to direct binding onto the NP surface, while Lys needs to overcome a ~2 kT free energy barrier. On the other hand, acidic residues tend to form “water bridges” between their sidechains and TiO2 surface, thus displaying an indirect binding. Moreover, the overall preferred positions and configurations of different residues are highly dependent on properties of the first and second solvation water. These molecular insights learned from this work might help with a better understanding of the interactions between biomolecules and nanomaterials.

  14. Quaternary Ammonium Polyamidoamine Dendrimer Modified Quantum Dots as Fluorescent Probes for p-Fluorophenoxyacetic Acid Detection in Aqueous Solution.

    PubMed

    Xu, Xiao; Cao, Yuan-Cheng; Liu, Jun'An; Lin, Yongjun

    2017-09-11

    The wide use of pesticide p-fluorophenoxyacetic acid has caused the serious environmental contaminant. A novel fluorescent probe for sensitive detection of p-fluorophenoxyacetic acid in aqueous solutions based on 3.0G quaternary ammonium polyamidoamine (PAMAM) dendrimer modified quantum dots (QDs) (PAMAM@QDs) was reported. Through the solvent-evaporation method, quaternary ammonium PAMAM was employed to modify the QDs. Poloxamer 188 was used to improve the solubility and stability. The resultant PAMAM@QDs dispersed well in water. Fluorescence (FL) spectroscopic study showed that the FL intensity of the PAMAM@QDs was enhanced in the presence of p-fluorophenoxyacetic acid. Under optimal conditions, the enhanced FL intensity as a function of concentration matched very well in the range of 1 ~ 200 µg/mL of p-fluorophenoxyacetic acid, while the lower limits of detection were found to be 0.16 µg/mL. These results show that PAMAM@QDs is a promising luminescent probe for the detection of pesticides.

  15. An In Silico study of TiO2 nanoparticles interaction with twenty standard amino acids in aqueous solution

    PubMed Central

    Liu, Shengtang; Meng, Xuan-Yu; Perez-Aguilar, Jose Manuel; Zhou, Ruhong

    2016-01-01

    Titanium dioxide (TiO2) is probably one of the most widely used nanomaterials, and its extensive exposure may result in potentially adverse biological effects. Yet, the underlying mechanisms of interaction involving TiO2 NPs and macromolecules, e.g., proteins, are still not well understood. Here, we perform all-atom molecular dynamics simulations to investigate the interactions between TiO2 NPs and the twenty standard amino acids in aqueous solution exploiting a newly developed TiO2 force field. We found that charged amino acids play a dominant role during the process of binding to the TiO2 surface, with both basic and acidic residues overwhelmingly preferred over the non-charged counterparts. By calculating the Potential Mean Force, we showed that Arg is prone to direct binding onto the NP surface, while Lys needs to overcome a ~2 kT free energy barrier. On the other hand, acidic residues tend to form “water bridges” between their sidechains and TiO2 surface, thus displaying an indirect binding. Moreover, the overall preferred positions and configurations of different residues are highly dependent on properties of the first and second solvation water. These molecular insights learned from this work might help with a better understanding of the interactions between biomolecules and nanomaterials. PMID:27883086

  16. Poly(hydroxyethyl methacrylate-co-methacryloylglutamic acid) nanospheres for adsorption of Cd2+ ions from aqueous solutions

    NASA Astrophysics Data System (ADS)

    Esen, Cem; Şenay, Raziye Hilal; Feyzioğlu, Esra; Akgöl, Sinan

    2014-02-01

    Poly(2-hydroxyethyl methacrylate-co- N-methacryloyl-( l)-glutamic acid) p(HEMA-MAGA) nanospheres have been synthesized, characterized, and used for the adsorption of Cd2+ ions from aqueous solutions. Nanospheres were prepared by surfactant free emulsion polymerization. The p(HEMA-MAGA) nanospheres were characterized by SEM, FTIR, zeta size, and elemental analysis. The specific surface area of nanospheres was found to be 1,779 m2/g. According to zeta size analysis results, average size of nanospheres is 147.3 nm with poly-dispersity index of 0.200. The goal of this study was to evaluate the adsorption performance of p(HEMA-MAGA) nanospheres for Cd2+ ions from aqueous solutions by a series of batch experiments. The Cd2+ concentration was determined by inductively coupled plasma-optical emission spectrometer. Equilibrium sorption experiments indicated a Cd2+ uptake capacity of 44.2 mg g-1 at pH 4.0 at 25 °C. The adsorption of Cd2+ ions increased with increasing pH and reached a plateau value at around pH 4.0. The data were successfully modeled with a Langmuir equation. A series of kinetics experiments was then carried out and a pseudo-second order equation was used to fit the experimental data. Desorption experiments which were carried out with nitric acid showed that the p(HEMA-MAGA) nanospheres could be reused without significant losses of their initial properties in consecutive adsorption and elution operations.

  17. Sorption study of an acid dye from an aqueous solutions using modified clays.

    PubMed

    Bouberka, Z; Kacha, S; Kameche, M; Elmaleh, S; Derriche, Z

    2005-03-17

    The removal of the pollutant Supranol Yellow 4GL (S.Y.4GL) was studied by using different clays: clay exchanged with sodium (BNa+) and hydroxyaluminic polycation pillared clays in the presence or absence of non-ionic surfactant. While decomposing the surfactant at 500 degrees C, the surface of the clay changed significantly. The study of the behaviour of the three clays with respect to coloring solutions, allowed to determine the equilibrium time and the rate-determining step of the dye S.Y.4GL adsorption. Two simplified kinetic models, were tested to investigate the adsorption mechanisms in terms of pseudo-first order and pseudo-second order equations. Besides, the adsorption capacity data were fitted to Langmuir and Freundlich equations as well. A better fixation was obtained with an acidic pH. The effect of temperature on the adsorption of dye has been also studied and the thermodynamic parameters DeltaG degrees , DeltaH degrees and DeltaS degrees were determined.

  18. Fast and highly-efficient removal of methylene blue from aqueous solution by poly(styrenesulfonic acid-co-maleic acid)-sodium-modified magnetic colloidal nanocrystal clusters

    NASA Astrophysics Data System (ADS)

    Song, Yu-Bei; Lv, Shao-Nan; Cheng, Chang-Jing; Ni, Guo-Li; Xie, Xiao-Wa; Huang, Wei; Zhao, Zhi-Gang

    2015-01-01

    Magnetic colloidal nanocrystal clusters (MCNCs) modified with different amounts of poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSMA) have been prepared through simple one-step solvothermal method for removal of methylene blue (MB) from aqueous solution. The prepared MCNCs are characterized by Fourier transform infrared (FT-IR) spectra, scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), nitrogen adsorption-desorption technique and dynamic light scattering (DLS). Moreover, effects of the solution pH, contact time, adsorbent dosage, ionic strength and initial dye concentration on MB adsorption onto the MCNCs are systematically investigated. The PSSMA-modified MCNCs show fast and highly-efficient MB removal capacity, which dramatically depends on the immobilization amounts of PSSMA, solution pH and adsorbent dosage. Their adsorption kinetics and isotherms exhibit that the kinetics and equilibrium adsorptions can be well-described by pseudo-second-order kinetic and Langmuir model, respectively. These magnetic nanocomposites, with high separation efficiency, low production cost and recyclable property, are promising as functional adsorbents for efficient removal of cationic organic pollutants from aqueous solution.

  19. Removal of Cu(II) and Ni(II) from aqueous solution by lignite-based humic acids

    SciTech Connect

    Arslan, G.; Cetin, S.; Pehlivan, E.

    2007-07-01

    The removal of Cu(II) and Ni(II) metal ions from an aqueous solution were investigated by using humic acids (HAs) in a batch arrangement. HAs were prepared by using alkaline extraction, following sedimentation and acidic precipitation from three Turkish lignites: Ilgin, Beysehir, and Ermenek. The interactions of Cu(II) and Ni(II) with solid HAs and influence of three parameters (initial metal concentration, solution pH and temperature) on the removal of metals were studied. Adsorption equilibrium was achieved in about 120 min for Cu(II) and Ni(II) ions. The sorption of Cu(II) and Ni(II) on the surface of HAs depended strongly on the pH, and increased with increasing pH and the initial concentration of metal. The sorption of Cu(II) was higher than that of Ni(II) for HAs. The equilibrium relationship between adsorbent and adsorbate is described by adsorption isotherms at a fixed temperature 35 {sup o}C, at pH about 4.0. The Langmuir adsorption isotherm was used to describe observed sorption phenomena. Adsorption isotherms and kinetics data of Cu(II) and Ni(II) ions removed by HAs are presented and discussed.

  20. Study of the dose response of the system ferrous ammonium sulfate-sucrose-xylenol orange in acid aqueous solution

    NASA Astrophysics Data System (ADS)

    Juarez-Calderon, J. M.; Negron-Mendoza, A.; Ramos-Bernal, S.

    2014-11-01

    An aqueous solution of ammonium ferrous sulfate-sucrose-xylenol orange in sulfuric acid (FSX) is proposed as a dosimetric system for the processes of gamma irradiation in a range between 0.3 and 6 Gy. This system is based on the indirect oxidation of ferrous ion by an organic compound (sucrose) to ferric ion and on the formation of a color complex of Fe3+ in an acidic medium with xylenol orange (a dye). After gamma radiation, an observable change occurs in the color of the system. Irradiation was executed at three different temperatures (13 °C, 22 °C, and 40 °C). A spectrometric readout method at 585 nm was employed to evaluate the system's dose response. In all of the cases analyzed, the responses had a linear behavior, and a slight effect of irradiation temperature was observed. Post-irradiation response was also evaluated and showed the stability of the solutions 24 h after the irradiation. The results obtained suggest that FSX might be used as a dosimeter for low doses of gamma irradiation because it provides a stable signal, good reproducibility, and an accessible technique for analysis.

  1. Electrocatalytic and photocatalytic hydrogen production from acidic and neutral-pH aqueous solutions using iron phosphide nanoparticles.

    PubMed

    Callejas, Juan F; McEnaney, Joshua M; Read, Carlos G; Crompton, J Chance; Biacchi, Adam J; Popczun, Eric J; Gordon, Thomas R; Lewis, Nathan S; Schaak, Raymond E

    2014-11-25

    Nanostructured transition-metal phosphides have recently emerged as Earth-abundant alternatives to platinum for catalyzing the hydrogen-evolution reaction (HER), which is central to several clean energy technologies because it produces molecular hydrogen through the electrochemical reduction of water. Iron-based catalysts are very attractive targets because iron is the most abundant and least expensive transition metal. We report herein that iron phosphide (FeP), synthesized as nanoparticles having a uniform, hollow morphology, exhibits among the highest HER activities reported to date in both acidic and neutral-pH aqueous solutions. As an electrocatalyst operating at a current density of -10 mA cm(-2), FeP nanoparticles deposited at a mass loading of ∼1 mg cm(-2) on Ti substrates exhibited overpotentials of -50 mV in 0.50 M H2SO4 and -102 mV in 1.0 M phosphate buffered saline. The FeP nanoparticles supported sustained hydrogen production with essentially quantitative faradaic yields for extended time periods under galvanostatic control. Under UV illumination in both acidic and neutral-pH solutions, FeP nanoparticles deposited on TiO2 produced H2 at rates and amounts that begin to approach those of Pt/TiO2. FeP therefore is a highly Earth-abundant material for efficiently facilitating the HER both electrocatalytically and photocatalytically.

  2. Ion segregation in aqueous solutions.

    PubMed

    Bian, Hongtao; Li, Jiebo; Zhang, Qiang; Chen, Hailong; Zhuang, Wei; Gao, Yi Qin; Zheng, Junrong

    2012-12-13

    Microscopic structures and dynamics of aqueous salt solutions were investigated with the ultrafast vibrational energy exchange method and anisotropy measurements. In KSCN aqueous solutions of various concentrations, the rotational time constants of SCN(-) anions are proportional to the viscosities of the solutions. However, the reorientation dynamics of the water molecules are only slightly affected by the solution viscosity. With the addition of strongly hydrated F(-) anions, the rotations of both SCN(-) anions and water molecules slow down. With the addition of weakly hydrated I(-) anions, only the rotation of SCN(-) anions slows down with that of water molecules unaffected. Vibrational energy exchange measurements show that the separation among SCN(-) anions decreases with the addition of F(-) and increases with the addition of I(-). The series of experiments clearly demonstrate that both structures and dynamics of ion and water are segregated in the strong electrolyte aqueous solutions.

  3. MTBE Hydrolysis in Dilute Aqueous Solution Using Heterogeneous Strong Acid Catalysts

    NASA Astrophysics Data System (ADS)

    Rixey, W. G.

    2003-12-01

    The objective of this research has been the development of a potential in situ catalytic process for the hydrolysis of methyl tertiary butyl ether (MTBE) to tertiary butyl alcohol (TBA) and methanol in ground water. Bench-scale batch reactor studies were conducted over a temperature range of 23 deg C to 50 deg C with several heterogeneous strong acid catalysts to obtain rates of hydrolysis of MTBE to TBA and methanol at dilute concentrations in water. Continuous flow experiments were then conducted to obtain kinetic data over a temperature range of 15 deg C to 50 deg C for various flow rates for the most active catalysts. It was found that the batch and continuous flow experiments yielded similar intrinsic kinetic rate constants when sorption of MTBE to the catalyst was accounted for. Additional fixed-bed experiments were conducted with deionized water and 0.005 M CaCl2 feed solutions containing 100 mg/L MTBE, respectively, to assess the deactivation of the catalyst, and deactivation was found to be controlled by ion exchange of H+ in the catalyst with Ca+2 in the feed. Our results indicate that, for low to moderate groundwater velocities and cation concentrations at ambient temperatures, an in situ reactive barrier process using the most active catalysts studied in this research could be a viable process in terms of both suitable conversion of MTBE and catalyst life. Although application to in situ remediation is emphasized, the results of this research are also applicable to ex-situ groundwater treatment.

  4. Trace level uranyl complexation with phenylphosphonic acid in aqueous solution: direct speciation by high resolution mass spectrometry.

    PubMed

    Galindo, Catherine; Del Nero, Mirella

    2013-04-15

    The complexation of U(VI) by organic P-containing ligands in humic substances (HS) is an important issue of uranyl mobility in soil. We have investigated the complexation of uranyl by a model ligand for aromatic phosphorus functionalities in HS, phenylphosphonic acid, by using ultrahigh resolution electrospray ionization-mass spectrometry (ESI-MS). The high sensitivity permitted to investigate the complexation of trace level uranyl and to explore directly in the native aqueous solutions the nature of the uranyl-phenylphosphonate complexes. Positive identification of the complexes coexisting in solutions with low pH and varying ligand-to-metal ratio was achieved thanks to the high resolving power, high mass accuracy, and reliability of ion abundance of the technique. The positively charged and neutral uranyl species were detected simultaneously on negative ion mass spectra, evidencing formation of three types of U(VI)-phenylphosphonate complexes. Two complexes with a metal-to-ligand stoichiometry of 1:1 (in the monoprotonated and nonprotonated forms) existed in solutions at pH 3-5, and a 1:2 complex was additionally formed at relatively high ligand-to-metal ratio. A strategy based on the use of uranyl-phosphate solution complexes as internal standards was developed to determine from the ESI(-)MS results the stability constants of the complexes, which were calculated to be log K111 = 3.4 ± 0.2 for UO2(HPhPO3)(+), log K101 = 7.1 ± 0.1 for UO2PhPO3, and log K112 = 7.2 ± 0.2 for UO2(HPhPO3)2. The speciation model presented here suggests that organic P existing at low concentration in HS is involved significantly in binding by humic and fulvic acids of trace level uranyl in soil.

  5. SEPARATION OF PLUTONIUM FROM AQUEOUS SOLUTIONS BY ION-EXCHANGE

    DOEpatents

    Schubert, J.

    1958-06-01

    A process is described for the separation of plutonium from an aqueous solution of a plutonium salt, which comprises adding to the solution an acid of the group consisting of sulfuric acid, phosphoric acid, and oxalic acid, and mixtures thereof to provide an acid concentration between 0.0001 and 1 M, contacting the resultant solution with a synthetic organic anion exchange resin, and separating the aqueous phase and the resin which contains the plutonium.

  6. Oxidation of clofibric acid in aqueous solution using a non-thermal plasma discharge or gamma radiation.

    PubMed

    Madureira, Joana; Ceriani, Elisa; Pinhão, Nuno; Marotta, Ester; Melo, Rita; Cabo Verde, Sandra; Paradisi, Cristina; Margaça, Fernanda M A

    2017-11-01

    In this work, we study degradation of clofibric acid (CFA) in aqueous solution using either ionizing radiation from a(60)Co source or a non-thermal plasma produced by discharges in the air above the solution. The results obtained with the two technologies are compared in terms of effectiveness of CFA degradation and its by-products. In both cases the CFA degradation follows a quasi-exponential decay in time well modelled by a kinetic scheme which considers the competition between CFA and all reaction intermediates for the reactive species generated in solution as well as the amount of the end product formed. A new degradation law is deduced to explain the results. Although the end-product CO2 was detected and the CFA conversion found to be very high under the studied conditions, HPLC analysis reveals several degradation intermediates still bearing the aromatic ring with the chlorine substituent. The extent of mineralization is rather limited. The energy yield is found to be higher in the gamma radiation experiments. Copyright © 2017 Elsevier Ltd. All rights reserved.

  7. Preparation and characterization of irradiated carboxymethyl sago starch-acid hydrogel and its application as metal scavenger in aqueous solution.

    PubMed

    Basri, Sri Norleha; Zainuddin, Norhazlin; Hashim, Kamaruddin; Yusof, Nor Azah

    2016-03-15

    Carboxymethyl sago starch-acid hydrogel was prepared via irradiation technique to remove divalent metal ions (Pb, Cu and Cd) from their aqueous solution. The hydrogel was characterized by using Fourier Transform Infrared (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The removal of these metal ions was analyzed by using inductively coupled plasma-optic emission spectra (ICP-OES) to study the amount of metal uptake by the hydrogel. Parameters of study include effect of pH, amount of sample, contact time, initial concentration of metal solution and reaction temperature. FTIR spectroscopy shows the CMSS hydrogel absorption peaks at 1741cm(-1), 1605cm(-1) and 1430cm(-1) which indicates the substitution of carboxymethyl group of modified sago starch. The degradation temperature of CMSS hydrogel is higher compared to CMSS due to the crosslinking by electron beam radiation and formed a porous hydrogel. From the data obtained, about 93.5%, 88.4% and 85.5% of Pb, Cu and Cd ions has been respectively removed from their solution under optimum condition.

  8. Investigation of a Cu(II)-poly(gamma-glutamic acid) complex in aqueous solution and its insulin-mimetic activity.

    PubMed

    Karmaker, Subarna; Saha, Tapan K; Sakurai, Hiromu

    2007-04-10

    The complexation between cupric ions (Cu(II)) and poly(gamma-glutamic acid) (gamma-PGA) in aqueous solutions (pH 3-11) has been studied by UV-visible absorption and electron spin resonance (ESR) techniques. Formation of the Cu(II)-gamma-PGA complex is confirmed by the observation of the blue shift of the absorption band in the visible region, anisotropic line shapes in the ESR spectrum at room temperature, and a computer simulation of the visible absorption spectrum of the complex. The structure of the Cu(II)-gamma-PGA complex, depending on the pH, has been determined. The in vitro insulin-mimetic activity of the Cu(II)-gamma-PGA complex is examined by determining both inhibition of free fatty acid release and glucose uptake in isolated rat adipocytes treated with epinephrine, in which the concentration of the Cu(II)-gamma-PGA complex for 50% inhibition of free fatty acid release is very similar to that of CuSO4. However, it is significantly lower than that of a previously reported insulin-mimetic bis(3-hydroxypicolinato)copper(II), [Cu(3hpic)2], complex.

  9. 4-Carboxybenzophenone-sensitized photooxidation of sulfur-containing amino acids in alkaline aqueous solutions. Secondary photoreactions kinetics

    SciTech Connect

    Bobrowski, K.; Hug, G.L. ); Marciniak, B. A. Mickiewicz Univ., Poznan ); Kozubek, H. )

    1994-01-13

    Sulfur-containing amino acids and alanine were oxidized via photosensitization by 4-carboxybenzophenone (CB) in alkaline aqueous solutions. The mechanism of this reaction was examined using steady-state and laser flash photolysis techniques. The rate constants were determined for the quenching of the CB triplet state by five sulfur-containing amino acids and alanine and were found to be approximately 10[sup 9] and 1.8 x 10[sup 8] M[sup [minus]1] s[sup [minus]1], respectively. The observation of the (S therefore S)[sup +] radical cations of some of the amino acids showed that the quenching process involves an electron transfer from the sulfur atom to the triplet state of CB. A show process of formation of the ketyl radical anion occurring on the microsecond time scale was assigned to the one-electron reduction of CB by the [alpha]-aminoalkyl radicals that were formed earlier as a result of an intramolecular electron transfer from the carboxyl group to the sulfur-centered radical cation followed by decarboxylation. For thiaproline, the pseudo-first-order rate constant, k[prime][sub obs], which characterizes the slow process of secondary ketyl radical anion formation, is linearly dependent on the CB concentration over the pH region 9.4-13.4. A detailed mechanism for the primary and the secondary photoreduction of CB is proposed and discussed. 32 refs., 7 figs., 5 tabs.

  10. RECOVERY OF PROTACTINIUM FROM AQUEOUS SOLUTIONS

    DOEpatents

    Elson, R.E.

    1959-07-14

    The recovery of fluoride complexed protactinium from aqueous acidic solutions by solvent extraction is described. Generally the prccess of the invention com rises mixing an aqueous solution containing protactinium in a complexed form with an organic solvent which is specific for protactinium, such as diisopropyl carbinol, then decomposing the protactinium complex by adjusting the acidity of the aqueous solution to between 0-3 to 0-9 M in hydrogen ion concentration, and introducing a source of aluminum ions in sufficient quantity to establish a concentration of 0.5 to 1.2 M aluminum ion, whereupon decomposition of the protactinium fluoride complex takes place and the protactinium ion is taken up by the organic solvent phase.

  11. Gamma irradiation of isocitric and citric acid in aqueous solution: Relevance in prebiotic chemistry

    SciTech Connect

    Negrón-Mendoza, A. Ramos-Bernal, S.

    2015-07-23

    The radiation chemistry of hydroxy acids like citric and isocitric acids is rather scarce, even though they are crucial compounds in biological systems and for food irradiation. The aim of this work is to study the radiolytic behavior of these acids focused on the interconversion induced by radiation of citric and isocitric acid into other members of the Krebs cycle. The results showed that among the products formed were succinic, malonic, malic and other acids related to metabolic pathways, and these results are correlated with its possible role in chemical evolution processes.

  12. Gamma irradiation of isocitric and citric acid in aqueous solution: Relevance in prebiotic chemistry

    NASA Astrophysics Data System (ADS)

    Negrón-Mendoza, A.; Ramos-Bernal, S.

    2015-07-01

    The radiation chemistry of hydroxy acids like citric and isocitric acids is rather scarce, even though they are crucial compounds in biological systems and for food irradiation. The aim of this work is to study the radiolytic behavior of these acids focused on the interconversion induced by radiation of citric and isocitric acid into other members of the Krebs cycle. The results showed that among the products formed were succinic, malonic, malic and other acids related to metabolic pathways, and these results are correlated with its possible role in chemical evolution processes.

  13. Polyacrylic acid brushes grafted from P(St-AA)/Fe3O4 composite microspheres via ARGET-ATRP in aqueous solution for protein immobilization.

    PubMed

    Xie, Liqin; Lan, Fang; Li, Wenliao; Liu, Ziyao; Ma, Shaohua; Yang, Qi; Wu, Yao; Gu, Zhongwei

    2014-11-01

    Recently, the atom transfer radical polymerization (ATRP) of acrylic monomers in many reaction systems has been successfully accomplished. However, its application in aqueous solution is still a challenging task. In this work, polyacrylic acid (PAA) brushes with tunable length were directly grafted from P(St-AA)/Fe3O4 composite microspheres in aqueous solution via an improved method, activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP). This reaction was carried out in environment-friendly solvent. As well, this method overcame the sensitivity of the catalyst. Due to the strong coordination interaction of carboxyl groups, PAA brushes were employed for immobilizing gold nanoparticles, which were prepared via the in situ reduction of chloroauric acid. The PAA brushes modified magnetic composite microspheres decorating with gold nanoparticles were efficient for specific immobilization and separation of bovine serum albumin (BSA) from aqueous solution under the external magnetic field. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. Thermodynamics of DL-α-aminobutyric acid induced solvation mechanism in aqueous KCl solutions at 288.15-308.15 K

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Ghosh, S.; Hossain, A.; Mahali, K.; Roy, S.; Dolui, B. K.

    2016-09-01

    The solubilities of DL-α-aminobutyric acid in KCl solutions of different concentrations are measured at 288.15-308.15 K. Gibbs energies and entropies have been determined for transfer of α-aminobutyric acid form water to aqueous KCl solution at 298.15 K. The cavity, dipole-dipole and other interactions affecting the solubility, as well as stability of the amino acid in solution are also evaluated. Gibbs energy and entropy of transfer due to interactions are computed to create the model of the complex solute-solvent and solventsolvent interactions. Molar volume, densities, dipole moment of solvent and diameter of co-solvent in aqueous potassium chloride are also evaluated.

  15. A study of effects of acid activated saw dust on the removal of different dissolved tannery dyes (acid dye) from aqueous solutions.

    PubMed

    Dhar, N R; Khoda, A K M B; Khan, A H; Bala, P; Karim, M F

    2005-04-01

    The effectiveness of acid activated sawdust in absorbing D-Brown EGP and Lurazol Brown PM dyes from aqueous solutions was studied as a function of agitation time and initial dye concentration. The experimental data were fitted to Langmuir and Freundlich isotherm and found that adsorption process follows both the isotherms. The values of Langmuir and Freundlich constants indicate favorable and beneficial adsorption. Saw dust is an excellent low cost adsorbent of colored organic anions and may have significant potential as a color removal from tannery wastewater.

  16. Efficiency of natural and acid-activated clays in the removal of Pb(II) from aqueous solutions.

    PubMed

    Eloussaief, Mabrouk; Benzina, Mourad

    2010-06-15

    The adsorption of Pb(2+) ions onto Tunisian clay in aqueous solution was studied in a batch system. Four samples of clay (RGC, RRC, AGC, and ARC) were used. The raw RGC and RRC clays were sampled in jebel Tejera-Esghira in Medenine area (Southeast of Tunisia). AGC and ARC corresponds respectively to RGC and RRC activated by 6M sulphuric acid. The adsorbents employed were characterized by X-Ray Diffraction, chemical analysis, and the specific surface area was also estimated. The ability of clay samples to remove Pb(2+) ions from aqueous solutions has been studied at different operating conditions: temperature and pH. The optimum pH for lead ions retention was found 7.0 for the four clay samples. The effect of temperature on adsorption phenomenon was also investigated. The results indicated that adsorption is an exothermic process for lead ions removal. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The adsorption capacities (X(m)) for RRC, RGC, ARC and AGC were found 17.84, 25.44, 27.15 and 40.75 mg g(-1), respectively. The performance of the red clay after activation was compared to that of silica gel, which has maximum adsorption of 20 mg g(-1). On the other hand, although the performance of activated carbon (88.3 mg g(-1)) is by far higher than that of the green clay after activation, the latter seems to have better performance than that of the silica gel.

  17. Side-chain conformational thermodynamics of aspartic acid residue in the peptides and achatin-I in aqueous solution.

    PubMed

    Kimura, Tomohiro; Matubayasi, Nobuyuki; Nakahara, Masaru

    2004-02-01

    Sequence-position dependence of the side-chain conformational equilibrium of aspartic acid (Asp) residue is investigated for both model Asp peptides (di- to tetra-) and neuropeptide achatin-I (Gly--Phe-Ala-Asp) in aqueous solution. The trans-to-gauche conformational changes on the dihedral angle of C-C(alpha)-C(beta)-C are analyzed in terms of the standard free energy DeltaG(0), enthalpy DeltaH(0), and entropy -TDeltaS(0). The thermodynamic quantities are obtained by measuring the dihedral-angle-dependent vicinal (1)H-(1)H coupling constants in nuclear magnetic resonance over a wide temperature range. When the carboxyl groups of Asp are ionized, DeltaG(0) in the aqueous phase depends by approximately 1-2 kJ mol(-1) on the sequence position, whereas the energy change in the gas phase (absence of solvent) depends by tens of kJ mol(-1). Therefore, the weak position dependence of DeltaG(0) is a result of the compensation for the intramolecular effect by the hydration (= DeltaG(0)-). The DeltaH(0) and -TDeltaS(0) components, on the other hand, exhibit a notable trend at the C-terminus. The C-terminal DeltaH(0) is larger than the N- and nonterminal DeltaH(0) values due to the intramolecular repulsion between alpha- and beta-. The C-terminal -TDeltaS(0) is negative and larger in magnitude than the others, and an attractive solute-solvent interaction at the C-terminus serves as a structure breaker of the water solvent.

  18. Interaction Between Some Monosaccharides and Aspartic Acid in Dilute Aqueous Solutions

    PubMed Central

    Kulikova, Galina A.

    2008-01-01

    Interaction between aspartic acid and d-glucose, d-galactose, and d-fructose has been studied by isothermal titration calorimetry, calorimetry of dissolution, and densimetry. It has been found that d-glucose and d-fructose form thermodynamically stable associates with aspartic acid, in contrast to d-galactose. The selectivity in the interaction of aspartic acid with monosaccharides is affected by their stereochemical structures. PMID:19669542

  19. REMOVAL OF CHLORIDE FROM AQUEOUS SOLUTIONS

    DOEpatents

    Hyman, M.L.; Savolainen, J.E.

    1960-01-01

    A method is given for dissolving reactor fuel elements in which the uranium is associated with a relatively inert chromium-containing alloy such as stainless steel. An aqueous mixture of acids comprising 2 to 2.5 molar hydrochloric acid and 4 to 8 molar nitric acid is employed in dissolving the fuel element. In order io reduce corrosion in subsequent processing of the resulting solution, chloride values are removed from the solution by contacting it with concentrated nitric acid at an elevated temperature.

  20. Experimental and Theoretical Studies of the Acid-Catalyzed Conversion of Furfuryl Alcohol to Levulinic Acid in Aqueous Solution

    SciTech Connect

    Gonzalez Maldonado, Gretchen M.; Assary, Rajeev S.; Dumesic, James A.; Curtiss, Larry A.

    2012-02-14

    The conversion of furfuryl alcohol (FAL) to levulinic acid over Amberlyst TM 15 in aqueous media was investigated using a combination of liquid chromatography-mass spectrometry (LC-MS) measurements, isotopic labeling studies, nuclear magnetic resonance (NMR) spectroscopy, and ab initio quantum chemical calculations using the G4MP2 method. The results of these combined studies showed that one of the major reaction pathways takes place via a geminal diol species (4,5,5- trihydroxypentan-2-one, denoted as intermediate A), formed by the addition of two water molecules to FAL, where two of the oxygen atoms from FAL are retained. This geminal diol species can also be produced from another intermediate found to be a dimer-like species, denoted as intermediate B. This dimer-like species is formed at the early stages of reaction, and it can also be converted to intermediate A, indicating that intermediate B is the product of the reaction of FAL with another early intermediate. Quantum chemical calculations suggested this to be a protonated acyclic species. Reaction of this early intermediate with water produces intermediate A, while reaction with FAL produces intermediate B.

  1. Experimental and Theoretical Studies of the Acid-Catalyzed Conversion of Furfuryl Alcohol to Levulinic Acid in Aqueous Solution

    SciTech Connect

    González Maldonado, Gretchen M.; Assary, Rajeev S.; Dumesic, James; Curtiss, Larry A.

    2012-01-01

    The conversion of furfuryl alcohol (FAL) to levulinic acid over AmberlystTM 15 in aqueous media was investigated using a combination of liquid chromatography-mass spectrometry (LC-MS) measurements, isotopic labeling studies, nuclear magnetic resonance (NMR) spectroscopy, and ab initio quantum chemical calculations using the G4MP2 method. The results of these combined studies showed that one of the major reaction pathways takes place via a geminal diol species (4,5,5-trihydroxypentan-2-one, denoted as intermediate A), formed by the addition of two water molecules to FAL, where two of the oxygen atoms from FAL are retained. This geminal diol species can also be produced from another intermediate found to be a dimer-like species, denoted as intermediate B. This dimer-like species is formed at the early stages of reaction, and it can also be converted to intermediate A, indicating that intermediate B is the product of the reaction of FAL with another early intermediate. Quantum chemical calculations suggested this to be a protonated acyclic species. Reaction of this early intermediate with water produces intermediate A, while reaction with FAL produces intermediate B.

  2. Controlled radical fluorination of poly(meth)acrylic acids in aqueous solution.

    PubMed

    Dong, Yucheng; Wang, Zhentao; Li, Chaozhong

    2017-08-17

    Fluorinated alkenes exhibit very poor reactivity in copolymerization with non-fluorinated polar monomers such as acrylates. Herein we describe a convenient method for the synthesis of poly(vinyl fluoride-co-acrylic acid) and poly(2-fluoropropene-co-methacrylic acid) copolymers. Thus, the silver-catalyzed decarboxylative radical fluorination of poly(acrylic acid) with Selectfluor in water at room temperature affords poly(vinyl fluoride-co-acrylic acid) copolymers in high yields with well-defined molecular weights and polydispersities. A linear correlation is observed between the extent of fluorination and the amount of Selectfluor, indicating that the copolymer of virtually any monomer ratio can be readily accessed by controlling the amount of Selectfluor. This controlled decarboxylative fluorination is extended to poly(methacrylic acid), leading to well-defined poly(2-fluoropropene-co-methacrylic acid) copolymers.Fluorinated alkenes have very poor reactivity in copolymerizations with non-fluorinated polar monomers. Here the authors show silver-catalyzed decarboxylative radical fluorination of poly(acrylic acid) with Selectfluor in water at room temperature to form poly(vinyl fluoride-co-acrylic acid) copolymers.

  3. Structures of polynuclear complexes of palladium(II) and platinum(II) formed by slow hydrolysis in acidic aqueous solution.

    PubMed

    Torapava, Natallia; Elding, Lars I; Mändar, Hugo; Roosalu, Kaspar; Persson, Ingmar

    2013-06-07

    The aqua ions of palladium(II) and platinum(II) undergo extremely slow hydrolysis in strongly acidic aqueous solution, resulting in polynuclear complexes. The size and structures of these species have been determined by EXAFS and small angle X-ray scattering, SAXS. For palladium(II), the EXAFS data show that the Pd-O and Pd···Pd distances are identical to those of crystalline palladium(II) oxide, but the intensities of the Pd···Pd distances in the Fourier transform at 3.04 and 3.42 Å are significantly lower compared to those of crystalline PdO. Furthermore, no Pd···Pd distances beyond 4 Å are observed. These observations strongly indicate that the polynuclear palladium(II) complexes are oxido- and hydroxido-bridged species with the same core structure as solid palladium(II) oxide. Based on the number of Pd···Pd distances, as derived from the EXAFS data, their size can be estimated to be approximately two unit cells, or ca. 1.0 nm(3). For platinum(II), EXAFS data of the polynuclear species formed in the slow hydrolysis process show Pt-O and Pt···Pt distances identical to those of amorphous platinum(II) oxide, precipitating from the solution studied. The Pt···Pt distances are somewhat different from those reported for crystalline platinum(II) oxide. The polynuclear platinum(II) complexes have a similar structure to the palladium ones, but they are somewhat larger, with an estimated diameter of 1.5-3.0 nm. It has not been possible to precipitate any of these species by ultracentrifugation. They are detectable by SAXS, indicating diameters between 0.7 and 2 nm, in excellent agreement with the EXAFS observations. The number of oxido- relative to hydroxido bridges will increase with increasing size of the complex. The charge of the complexes will remain about the same, +4, at growth, with approximate formulas [Pd10O4(OH)8(H2O)12](4+) and [Pt14O8(OH)8(H2O)12](4+) for complexes with a size of 2 and 3 unit cells of the corresponding solid metal oxide

  4. Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions.

    PubMed

    Ashraf, Anam; Bibi, Irshad; Niazi, Nabeel Khan; Ok, Yong Sik; Murtaza, Ghulam; Shahid, Muhammad; Kunhikrishnan, Anitha; Li, Dongwei; Mahmood, Tariq

    2017-07-03

    In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L(-1) and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g(-1), respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R(2) = 0.97) and O-mont (R(2) = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the -OH, -COOH, -NH2, and for O-mont intercalated amines and -OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.

  5. Removal of dicyclohexyl acetic acid from aqueous solution using ultrasound, ozone and their combination.

    PubMed

    Kumar, Pardeep; Headley, John; Peru, Kerry; Bailey, Jon; Dalai, Ajay

    2014-01-01

    Naphthenic acids are a complex mixture of organic components, some of which include saturated alkyl-substituted cycloaliphatic carboxylic acids and acyclic aliphatic acids. They are naturally found in hydrocarbon deposits like oil sand, petroleum, bitumen and crude oil. In this study, the oxidation of a relatively high molecular weight naphthenic acid (Dicyclohexyl acetic acid) was investigated using ozonation, ultrasonication and hydrogen peroxide alone and their combinations. Effects on oxidation of dicyclohexyl acetic acid (DAA) were measured for different concentrations of ozone ranging between 0.7 to 3.3 mg L(-1) and pH in the range 6 to 10. Ultrasonication and hydrogen peroxide alone were not effective to oxidize dicyclohexyl acetic acid, but combining ultrasonication with H2O2 had a significant effect on oxidation of dicyclohexyl acetic acid with maximum removal reaching to 84 ± 2.2% with 81 ± 2.1% reduction in chemical oxygen demand (COD). Synergistic effects were observed for combining ultrasonication with ozonation and resulted in 100% DAA removal with 98 ± 0.8% reduction in COD within 15 min at 3.3 mg L(-1) ozone concentration and 130 Watts ultrasonication power. The reaction conditions obtained for the maximum oxidation of DAA and COD removal were used for the degradation of naphthenic acids mixture extracted from oil sands process water (OSPW). The percentage oxidation of NAs mixture extracted from OSPW was 89.3 ± 1.1% in ozonation and combined ozonation and ultrasonication, but COD removal observed was 65 ± 1.2% and 78 ± 1.4% for ozonation and combined ozonation and ultrasonication treatments, respectively.

  6. Degradation of Acid Orange 7 in aqueous solution by dioxygen activation in a pyrite/H₂O/O₂ system.

    PubMed

    Hao, Feifei; Guo, Weilin; Lin, Xin; Leng, Yanqiu; Wang, Anqi; Yue, Xinxin; Yan, Liangguo

    2014-05-01

    Increasing attention has been paid to pyrite due to its ability to generate hydroxyl radicals in air-saturated solutions. In this study, the mineral pyrite was studied as a catalyst to activate molecular oxygen to degrade Acid Orange 7 (AO7) in aqueous solution. A complete set of control experiments were conducted to optimize the reaction conditions, including the dosage of pyrite, the AO7 concentration, as well as the initial pH value. The role of reactive oxygen species (ROS) generated by pyrite in the process was elucidated by free radical quenching reactions. Furthermore, the concentrations of Fe(II) and total Fe formed were also measured. The mechanism for the production of ROS in the pyrite/H2O/O2 system was that H2O2 was formed by hydrogen ion and superoxide anion (O2(·-)) which was produced by the reaction of pyrite activating O2 and then reacted with Fe(II) dissolved from pyrite to produce (·)OH through Fenton reaction. The findings suggest that pyrite/H2O/O2 system is potentially practical in pollution treatment. Moreover, the results provide a new insight into the understanding of the mechanism for degradation of organic pollutants by pyrite.

  7. Efficient photocatalytic degradation of acid fuchsin in aqueous solution using separate porous tetragonal-CuFe2O4 nanotubes.

    PubMed

    Jing, Panpan; Li, Jianan; Pan, Lining; Wang, Jianbo; Sun, Xiaojun; Liu, Qingfang

    2015-03-02

    To develop a new promising magnetic photocatalyst, homogeneous tetragonal-CuFe2O4 (t-CuFe2O4) nanotubes were successfully synthesized via the electrospinning technique followed by heating treatment. The detailed investigation of chemical phase and microstructure reveals that the obtained samples are inversely spinel CuFe2O4 nanotubes with an average diameter of about 272±2nm, which are assembled by numerous CuFe2O4 single crystal nanoparticles with regular polyhedron structure and possess a very outstanding porous feature. Furthermore, element mapping, UV-vis adsorption spectrum, N2 adsorption-desorption isotherm, and magnetic hysteresis loop indicate that these t-CuFe2O4 nanotubes have uniform component distribution, strong light response in the range of 200 nm-800 nm, considerable specific surface area of 12.8 m(2)/g and porosity of 15.5 nm, and enough magnetization of about 18 emu/g. Therefore, the t-CuFe2O4 nanotubes show an excellent catalytic activity and durability for the photodecomposition of acid fuchsin dye in aqueous solution under a simulated sunlight source. Furthermore, these CuFe2O4 nanotubes could be acted as an eco-friendly and recyclable photocatalyst because they can be efficiently separated from the residual solution. Finally, a mechanism is presented for the significant photocatalytic performance of the porous CuFe2O4 nanotubes.

  8. Universal reaction mechanism of boronic acids with diols in aqueous solution: kinetics and the basic concept of a conditional formation constant.

    PubMed

    Furikado, Yuki; Nagahata, Tomomi; Okamoto, Takuya; Sugaya, Tomoaki; Iwatsuki, Satoshi; Inamo, Masahiko; Takagi, Hideo D; Odani, Akira; Ishihara, Koji

    2014-10-06

    To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (Ka(BL)) of boronic acid diol esters (HBLs) were determined based on the well-established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4-difluorophenylboronic acid and chromotropic acid, 3-nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K', based on the main reaction: RB(OH)2 + H2L (K1)⇌ RB(L)(OH)(-) + H3O(+) instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B') with uncomplexed diol species (L') to form boronic acid diol complex species (esters, BL') in aqueous solution at pH 5-11: B' + L' (K')⇌ BL'. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution.

  9. Removal of copper ions from aqueous solution by the sodium salt of the maleic acid-allylpropionate-styrene terpolymer.

    PubMed

    Akperov, Elchin; Akperov, Oktay; Jafarova, Elnara; Gafarova, Sabahiye

    2016-09-01

    The sodium salt of the maleic acid-allylpropionate-styrene terpolymer was used for recovery of copper ions from aqueous solution. Effects of contact time, sorbent weight and initial Cu(2+) ion concentrations on removal efficiency were tested. The maximum experimental sorption capacity of the sorbent for copper ions is 0.71 g g(-1). The sorption isotherm of copper ions onto a prepared polymer sorbent has been studied and the equilibrium data were analyzed using Langmuir and Freundlich isotherm models. The adsorption isotherm data showed that copper ions adsorption on the sorbent was better fitted to the Langmuir isotherm model. The Lagergren pseudo-first- and pseudo-second-order kinetic models were applied to examine the kinetics of the copper ions sorption by the synthesized sorbent. The kinetic data are best described by the pseudo-second-order model. The calculated value of the maximum sorption capacity by the pseudo-second-order equation (0.62 g g(-1)) corresponds well with its experimentally found value (0.71 g g(-1)). Considering the obtained kinetic data, and the Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectra of the sorbent after the sorption, it is possible to come to the conclusion that during the sorption process Cu(2+) ions enter a complex with the carboxylic groups of the maleic acid units of the sorbent.

  10. Contact ion pair formation between hard acids and soft bases in aqueous solutions observed with 2DIR spectroscopy.

    PubMed

    Sun, Zheng; Zhang, Wenkai; Ji, Minbiao; Hartsock, Robert; Gaffney, Kelly J

    2013-12-12

    The interaction of charged species in aqueous solution has important implications for chemical, biological, and environmental processes. We have used 2DIR spectroscopy to study the equilibrium dynamics of thiocyanate chemical exchange between free ion (NCS(-)) and contact ion pair configurations (MNCS(+)), where M(2+) = Mg(2+) or Ca(2+). Detailed studies of the influence of anion concentration and anion speciation show that the chemical exchange observed with the 2DIR measurements results from NCS(-) exchanging with other anion species in the first solvation shell surrounding Mg(2+) or Ca(2+). The presence of chemical exchange in the 2DIR spectra provides an indirect, but robust, determinant of contact ion pair formation. We observe preferential contact ion pair formation between soft Lewis base anions and hard Lewis acid cations. This observation cannot be easily reconciled with Pearson's acid-base concept or Collins' Law of Matching Water Affinities. The anions that form contact ion pairs also correspond to the ions with an affinity for water and protein surfaces, so similar physical and chemical properties may control these distinct phenomena.

  11. Preparation of novel magnetic chitosan nanoparticle and its application for removal of humic acid from aqueous solution

    NASA Astrophysics Data System (ADS)

    Dong, Changlong; Chen, Wei; Liu, Cheng

    2014-02-01

    A novel magnetic chitosan nanoparticle (MCNP) with a BET surface area of 108.32 m2/g was prepared using a time and energy saving method at mild condition. MCNP exhibits an excellent ability to adsorb humic acid (HA) from aqueous solution in a wide range of initial HA concentration. The rate of HA adsorption is rapid with more than 50% of HA can be adsorbed in initial 10 min, and the equilibrium state can be reached in 60 min. The adsorption kinetics data fits well to the pseudo-second-order model, and the adsorption process is transport-limited at low initial HA concentration and attachment-limited at high initial HA concentration. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model, indicating that the adsorption of HA onto MCNP is a monolayer adsorption. Based on the Langmuir isotherm model, the maximum adsorption capacity of HA is 32.6 mg/g at 25 °C. Thermodynamic parameters presents that the adsorption of HA onto MCNP is spontaneous and endothermic in nature. The mechanism for the adsorption of HA onto MCNP involves electrostatic interaction and hydrogen bonding. Regeneration studies indicate that MCNP can be recyclable for a long term. All the experimental results suggest that MCNP is a promising adsorbent for treating water that is contaminated with humic acid.

  12. Sorption of benzoic acid from aqueous solution by cetyltrimethylammonium bromide modified birnessite.

    PubMed

    Wang, Nan-Hui; Lo, Shang-Lien

    2012-01-01

    Layered manganese oxide (birnessite) has been studied for its use as catalytic materials. The research presented in this study investigates the sorption of benzoic acid from water on synthesized cetyltrimethylammonium bromide modified birnessite (CTAB-birnessite). The synthesized CTAB-birnessite was characterized by X-ray powder diffraction (XRD). The experimental results of sorption kinetic were well fitted to the pseudo-second-order equation. The sorption isotherms were linear at different pH values, and it indicates a partition mechanism. Up to about 53% of the dissolved benzoic acid was sorbed by CTAB-birnessite; in contrast, only 16% of the dissolved benzoic acid was sorbed by birnessite. These results indicate that CTAB-birnessite can be a potential sorbent for benzoic acid removal.

  13. Adsorption characteristics of malic acid from aqueous solutions by weakly basic ion-exchange chromatography.

    PubMed

    Gao, Qiang; Pan, Chaoqiang; Liu, Fabao; Lu, Fuping; Wang, Depei; Zhang, Jian; Zhu, Yan

    2012-08-17

    In this study, we reported the effects of temperature, malic acid loading concentration, and resin dose on malic acid adsorption by IRA-67 in batch experiments. The kinetic data well fitted the pseudo-second-order kinetic model. Both the equilibrium and ultimate adsorption slightly decreased with increased temperature from 303 to 323 K at 74.7 g/L malic acid loading concentration. The malic acid adsorption was revealed as a homogeneous adsorbent process by the Langmuir model and film diffusion process at loading concentrations of 18.2-94.5 g/L malic acid by the Boyd plot. The values of effective diffusion coefficient D(i) also increased with the temperature. Based on Eq. (15), the negative values of ΔG° and ΔH° revealed that the adsorption process was spontaneous and exothermic. The negative value of ΔS° also indicated the decrease in the solid-liquid interface randomness at this interface when malic acid is adsorbed by IRA-67.

  14. Removal of 8-quinolinecarboxylic acid pesticide from aqueous solution by adsorption on activated montmorillonites.

    PubMed

    Mekhloufi, M; Zehhaf, A; Benyoucef, A; Quijada, C; Morallon, E

    2013-12-01

    Sodium montmorillonite (Na-M), acidic montmorillonite (H-M), and organo-acidic montmorillonite (Org-H-M) were applied to remove the herbicide 8-quinolinecarboxylic acid (8-QCA). The montmorillonites containing adsorbed 8-QCA were investigated by transmission electron microscopy, FT-IR spectroscopy, X-ray diffraction analysis, X-ray fluorescence thermogravimetric analysis, and physical adsorption of gases. Experiments showed that the amount of adsorbed 8-QCA increased at lower pH, reaching a maximum at pH 2. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The Langmuir model provided the best correlation of experimental data for adsorption equilibria. The adsorption of 8-QCA decreased in the order Org-H-M > H-M > Na-M. Isotherms were also used to obtain the thermodynamic parameters. The negative values of ΔG indicated the spontaneous nature of the adsorption process.

  15. Synergistic effects of citric acid and polyethyleneimine to remove copper from aqueous solutions.

    PubMed

    Maketon, W; Ogden, K L

    2009-04-01

    Citric acid and copper are often found in the waste streams from semiconductor manufacturing. They are likely to form complexes, which modify copper speciation. This can lead to changes in sorption mechanisms and the sorption capacity. PEI-agarose adsorbents in a packed bed column are capable of removing these anionic complexes, but the competitive binding between these organic ligands and PEI for copper is not well understood and needs to be explored. The current work focuses on investigating copper sorption by PEI-agarose adsorbent in the presence of citrate ions. Copper binding capacity and copper breakthrough curves are compared and contrasted to results without additional chelator present. The presence of citric acid at the molar ratios of 0.5, 1, and 2 to copper enhances the total copper uptake in a continuous column by 175%, 100% and 75%, respectively. This is a great advantage when wastewater streams contain either low or high amounts of citric acid ligand.

  16. Enthalpy changes upon dilution and ionization of poly(L-glutamic acid) in aqueous solutions.

    PubMed

    Godec, Andrej; Skerjanc, Joze

    2005-07-14

    The enthalpy changes accompanying the dilution and ionization of poly(L-glutamic acid) in water have been measured at 25 degrees C for two degrees of polymerization (DP = 115 and DP = 480) at various degrees of ionization, alpha, for a concentration range from about 0.2 to 0.002 monomol/L. The heat of dilution displays an unusual dependence on the degree of ionization, which is in sharp contrast to the behavior of other weak carboxylic polyelectrolytes, such as poly(acrylic acid). The exothermic heat effects observed at low values of alpha become endothermic for the region where the helix-coil transition is most pronounced, and for high degrees of ionization, they are exothermic again. Evidently, an endothermic heat effect, produced by an additional conformational transition in the dilution process, is superimposed on the exothermic enthalpy of dilution, and it overweighs the latter in the region of alpha where the conformational transition is prevailing. The calorimetric titration curve, which gives the dependence of the heat of ionization, deltaH(i), on alpha, has a maximum and is typical for poly(carboxylic acids) which undergo pH-induced conformational transition, such as poly(methacrylic acid). The values of deltaH(i) obtained at two polymer concentrations indicate that the enthalpy of ionization depends on the polypeptide concentration.

  17. SEPARATION OF SCANDIUM FROM AQUEOUS SOLUTIONS

    DOEpatents

    Peppard, D.F.; Nachtman, E.S.

    1958-02-25

    This patent relates to a process for the separation of scandium from yttrium, thorium, and trivalent rare earths and with their separation from each other. It has been found that scandium and yttrium can be separated from trivalent rare earths in acidic solution, for example, a solution 6 M in HCl, by contacting with tributyl phosphate, whereupon the scandum is preferentially extracted into the organic phase, leaving the yttrium and trivalent rare earths in the aqueous phase.

  18. Characterisation of weak magnetic field effects in an aqueous glutamic acid solution by nonlinear dielectric spectroscopy and voltammetry

    PubMed Central

    Pazur, Alexander

    2004-01-01

    Background Previous reports indicate altered metabolism and enzyme kinetics for various organisms, as well as changes of neuronal functions and behaviour of higher animals, when they were exposed to specific combinations of weak static and alternating low frequency electromagnetic fields. Field strengths and frequencies, as well as properties of involved ions were related by a linear equation, known as the formula of ion cyclotron resonance (ICR, abbreviation mentioned first by Liboff). Under certain conditions already a aqueous solution of the amino acid and neurotransmitter glutamate shows this effect. Methods An aqueous solution of glutamate was exposed to a combination of a static magnetic field of 40 μT and a sinusoidal electromagnetic magnetic field (EMF) with variable frequency (2–7 Hz) and an amplitude of 50 nT. The electric conductivity and dielectric properties of the solution were investigated by voltammetric techniques in combination with non linear dielectric spectroscopy (NLDS), which allow the examination of the dielectric properties of macromolecules and molecular aggregates in water. The experiments target to elucidate the biological relevance of the observed EMF effect on molecular level. Results An ion cyclotron resonance (ICR) effect of glutamate previously reported by the Fesenko laboratory 1998 could be confirmed. Frequency resolution of the sample currents was possible by NLDS techniques. The spectrum peaks when the conditions for ion cyclotron resonance (ICR) of glutamate are matched. Furthermore, the NLDS spectra are different under ICR- and non-ICR conditions: NLDS measurements with rising control voltages from 100–1100 mV show different courses of the intensities of the low order harmonics, which could possibly indicate "intensity windows". Furthermore, the observed magnetic field effects are pH dependent with a narrow optimum around pH 2.85. Conclusions Data will be discussed in the context with recent published models for the

  19. Kinetics and mechanism of adsorption of methylene blue from aqueous solution by nitric-acid treated water-hyacinth.

    PubMed

    El-Khaiary, Mohammad I

    2007-08-17

    Kinetics adsorption experiments were conducted to evaluate the adsorption characteristics of a cationic dye (methylene blue, MB) onto nitric-acid treated water-hyacinth (N-WH). Results showed that N-WH can remove MB effectively from aqueous solution. The loading of MB onto N-WH was found to increase significantly with increasing the initial MB concentration, but the residual concentration of MB in solution also increased. A complete removal of MB from solution was only achieved at the lower range of initial MB concentration (less than 286 mg/L). Temperature had a slight effect on the amount adsorbed at equilibrium. The adsorption rate was fast and more than half of the adsorbed-MB was removed in the first 15 min at room temperature, which makes the process practical for industrial application. The adsorption kinetics at room temperature could be expressed by the pseudo second order model, while at higher temperatures (45-80 degrees C) and low MB concentration (97 mg/L) both Lagergren's model and the pseudo second order model can be used to predict the kinetics of adsorption. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of adsorption, then gradually changed to intraparticle diffusion control at a later stage. The initial period where external mass transfer is the rate controlling step was found to increase with increasing initial MB concentration and decrease with increasing temperature. The increase in temperature was also found to increase the rate of adsorption and reduce the time required to reach equilibrium. The initial rate of adsorption, h(o), was calculated, it was found to increase with increasing temperature, while the increase in MB concentration decreased h(o) at the lower concentration range then increased h(o) again at high concentration. The value of the activation coefficient, E, was found to be 8.207 kJ/mol, which indicates a diffusion controlled process.

  20. Acidity of the amidoxime functional group in aqueous solution. A combined experimental and computational study

    SciTech Connect

    Mehio, Nada; Lashely, Mark A.; Nugent, Joseph W.; Tucker, Lyndsay; Correia, Bruna; Do-Thanh, Chi-Linh; Dai, Sheng; Hancock, Robert D.; Bryantsev, Vyacheslav S.

    2015-01-26

    Poly(acrylamidoxime) adsorbents are often invoked in discussions of mining uranium from seawater. It has been demonstrated repeatedly in the literature that the success of these materials is due to the amidoxime functional group. While the amidoxime-uranyl chelation mode has been established, a number of essential binding constants remain unclear. This is largely due to the wide range of conflicting pKa values that have been reported for the amidoxime functional group in the literature. To resolve this existing controversy we investigated the pKa values of the amidoxime functional group using a combination of experimental and computational methods. Experimentally, we used spectroscopic titrations to measure the pKa values of representative amidoximes, acetamidoxime and benzamidoxime. Computationally, we report on the performance of several protocols for predicting the pKa values of aqueous oxoacids. Calculations carried out at the MP2 or M06-2X levels of theory combined with solvent effects calculated using the SMD model provide the best overall performance with a mean absolute error of 0.33 pKa units and 0.35 pKa units, respectively, and a root mean square deviation of 0.46 pKa units and 0.45 pKa units, respectively. Finally, we employ our two best methods to predict the pKa values of promising, uncharacterized amidoxime ligands. Hence, our study provides a convenient means for screening suitable amidoxime monomers for future generations of poly(acrylamidoxime) adsorbents used to mine uranium from seawater.

  1. Acidity of the amidoxime functional group in aqueous solution. A combined experimental and computational study

    DOE PAGES

    Mehio, Nada; Lashely, Mark A.; Nugent, Joseph W.; ...

    2015-01-26

    Poly(acrylamidoxime) adsorbents are often invoked in discussions of mining uranium from seawater. It has been demonstrated repeatedly in the literature that the success of these materials is due to the amidoxime functional group. While the amidoxime-uranyl chelation mode has been established, a number of essential binding constants remain unclear. This is largely due to the wide range of conflicting pKa values that have been reported for the amidoxime functional group in the literature. To resolve this existing controversy we investigated the pKa values of the amidoxime functional group using a combination of experimental and computational methods. Experimentally, we used spectroscopicmore » titrations to measure the pKa values of representative amidoximes, acetamidoxime and benzamidoxime. Computationally, we report on the performance of several protocols for predicting the pKa values of aqueous oxoacids. Calculations carried out at the MP2 or M06-2X levels of theory combined with solvent effects calculated using the SMD model provide the best overall performance with a mean absolute error of 0.33 pKa units and 0.35 pKa units, respectively, and a root mean square deviation of 0.46 pKa units and 0.45 pKa units, respectively. Finally, we employ our two best methods to predict the pKa values of promising, uncharacterized amidoxime ligands. Hence, our study provides a convenient means for screening suitable amidoxime monomers for future generations of poly(acrylamidoxime) adsorbents used to mine uranium from seawater.« less

  2. [Surface organic modification of acid vermiculite and its adsorption of hydrophobic micro pollutants in aqueous solutions].

    PubMed

    Jiang, Zheng-Ming; Yu, Xu-Biao; Hu, Yun; Ren, Yuan; Li, Xue-Hui; Wei, Chao-Hai

    2013-07-01

    To solve the problems of intercalated organoclay such as low surface area and inhomogeneous organic loading, natural vermiculite was activated by acid leaching and then modified by trimethylchlorosilane (CTMS) and triethylchlorosilane (CTES). The modified materials were characterized by FTIR, BET, SEM and TG. Experimental results indicated that the surface area of the modified acid vermiculite (361.0 m2 x g(-1)) was much larger than that of the intercalated organovermiculite (6.0 m2 x g(-1)), moreover, the organic groups were grafted onto the surface covalently. Diethyl phthalate (DEP), a typical hydrophobic micro-organic pollutant, was used to test the adsorption capacity of different adsorbents. The adsorption amounts of DEP were 63.7, 51.2 and 15.7 mg x g(-1) for CTES, CTMS and intercalated organovermiculite in this study, respectively. The high organic affinity of modified acid vermiculite was due to both the bigger surface area and the homogeneous organic loading. The adsorption kinetics was found to follow the pseudosecond-order model. The isotherms exhibited linear characteristics and could be described by Henry and Freundlich equations, indicating that the partition process is the main control mechanism of the removal of DEP.

  3. Revisiting the carboxylic acid dimers in aqueous solution: interplay of hydrogen bonding, hydrophobic interactions, and entropy.

    PubMed

    Chen, Jianhan; Brooks, Charles L; Scheraga, Harold A

    2008-01-17

    Carboxylic acid dimers are useful model systems for understanding the interplay of hydrogen bonding, hydrophobic effects, and entropy in self-association and assembly. Through extensive sampling with a classical force field and careful free energy analysis, it is demonstrated that both hydrogen bonding and hydrophobic interactions are indeed important for dimerization of carboxylic acids (except formic acid). The dimers are only weakly ordered, and the degree of ordering increases with stronger hydrophobic interactions between longer alkyl chains. Comparison of calculated and experimental dimerization constants reveals a systematic tendency for excessive self-aggregation in current classical force fields. Qualitative and quantitative information on the thermodynamics of hydrogen bonding and hydrophobic interactions derived from these simulations is in excellent agreement with existing results from experiment and theory. These results provide a verification from first principles of previous estimations based on two statistical mechanical hydrophobic theories. We also revisit and clarify the fundamental statistical thermodynamics formalism for calculating absolute binding constants, external entropy, and solvation entropy changes upon association from detailed free energy simulations. This analysis is believed to be useful for a wide range of applications including computational studies of protein-ligand and protein-protein binding.

  4. In-situ spectroscopic investigations of the redox behavior of poly(indole-5-carboxylic-acid) modified electrodes in acidic aqueous solutions.

    PubMed

    Talbi, H; Billaud, D; Louarn, G; Pron, A

    2001-03-01

    The oxidation of electrochemically grown poly(indole-5-carboxylic-acid) (P5CO2H) and its spectroscopic properties have been studied by in-situ spectroelectrochemical techniques. The purpose of this paper is to characterize the different modifications on the P5CO2H backbone, induced by the electrochemical oxidation in aqueous acidic solution. We have identified, on the basis of Raman spectra, the vibrational modes associated with neutral and oxidized segments of polymer. It was shown that at least three chemically and optically different species (perhaps other products too) are produced in different potential regimes upon oxidation of this polymer. The results obtained also indicate that the molecular properties of this conducting polymer are better revealed by in-situ resonant spectra than by ex-situ infrared and Raman studies.

  5. Acid-base interactions and complex formation while recovering copper(II) ions from aqueous solutions using cellulose adsorbent in the presence of polyvinylpyrrolidone

    NASA Astrophysics Data System (ADS)

    Nikiforova, T. E.; Kozlov, V. A.; Islyaikin, M. K.

    2012-12-01

    The sorption properties of nontreated cotton cellulose and cellulose modified with polyvinylpyrrolidone with respect to copper(II) ions are investigated. It is established that modified cellulose adsorbents have high sorption capability associated with the formation of new sorption centers during treatment with nitrogen-containing polymer. A mechanism is proposed for acid-base interactions in aqueous solutions of acids, bases, and salts during copper(II) cation recovery using cellulose adsorbent with the participation of polyvinylpyrrolidone.

  6. A mechanistic analysis of the increase in the thermal stability of proteins in aqueous carboxylic acid salt solutions.

    PubMed Central

    Kaushik, J. K.; Bhat, R.

    1999-01-01

    The stability of proteins is known to be affected significantly in the presence of high concentration of salts and is highly pH dependent. Extensive studies have been carried out on the stability of proteins in the presence of simple electrolytes and evaluated in terms of preferential interactions and increase in the surface tension of the medium. We have carried out an in-depth study of the effects of a series of carboxylic acid salts: ethylene diamine tetra acetate, butane tetra carboxylate, propane tricarballylate, citrate, succinate, tartarate, malonate, and gluconate on the thermal stability of five different proteins that vary in their physico-chemical properties: RNase A, cytochrome c, trypsin inhibitor, myoglobin, and lysozyme. Surface tension measurements of aqueous solutions of the salts indicate an increase in the surface tension of the medium that is very strongly correlated with the increase in the thermal stability of proteins. There is also a linear correlation of the increase in thermal stability with the number of carboxylic groups in the salt. Thermal stability has been found to increase by as much as 22 C at 1 M concentration of salt. Such a high thermal stability at identical concentrations has not been reported before. The differences in the heat capacities of denaturation, deltaCp for RNase A, deduced from the transition curves obtained in the presence of varying concentrations of GdmCl and that of carboxylic acid salts as a function of pH, indicate that the nature of the solvent medium and its interactions with the two end states of the protein control the thermodynamics of protein denaturation. Among the physico-chemical properties of proteins, there seems to be an interplay of the hydrophobic and electrostatic interactions that lead to an overall stabilizing effect. Increase in surface free energy of the solvent medium upon addition of the carboxylic acid salts appears to be the dominant factor in governing the thermal stability of proteins

  7. Supercooling behavior in aqueous solutions.

    PubMed

    Kimizuka, Norihito; Suzuki, Toru

    2007-03-08

    Using the emulsion method, we measured the homogeneous nucleation temperature depression, DeltaT(f,hom), and equilibrium melting points depression, DeltaT(m), of various aqueous solutions and then calculated lambda for each solute using the linear relationship DeltaT(f,hom) = lambdaDeltaT(m). We defined lambda as the solute-specific supercooling capacity and examined its correlation with some known hydration characteristics. The results showed that lambda is correlated with D0, the self-diffusion coefficient of solute molecules in infinite dilution.

  8. Removal of hexavalent chromium from acidic aqueous solutions using rice straw-derived carbon.

    PubMed

    Hsu, Nai-Hua; Wang, Shan-Li; Liao, Yi-Huei; Huang, Shiuh-Tsuen; Tzou, Yu-Min; Huang, Yuh-Ming

    2009-11-15

    This study evaluates the removal of Cr(VI) from water by carbon derived from the burning of rice straw. Rice straw was burned in the air to obtain rice carbon (RC), and then the removal of Cr(VI) by RC was investigated under various pHs and ionic strengths. After the experiments, the oxidation state of Cr bound to RC was analyzed using X-ray photoelectron spectroscopy, which revealed that Cr bound to RC was predominately in the trivalent form. The results showed that upon reacting with RC, Cr(VI) was reduced to Cr(III), which was either adsorbed on RC or released back into solution. The extent and rate of Cr(VI) removal increased with decreasing solution pH because the Cr(VI) adsorption and the subsequent reduction of adsorbed Cr(VI) to Cr(III) both occur preferentially at low pH. The minimal effect of ionic strength on the rates of Cr(VI) removal and Cr(III) adsorption indicated specific interactions between Cr(VI)/Cr(III) and their surface binding sites on RC. These results suggest that rice straw-based carbon may be effectively used at low pH as a substitute for activated carbon for the treatment of Cr(VI) contaminated water.

  9. Selective Chemical Conversion of Sugars in Aqueous Solutions without Alkali to Lactic Acid Over a Zn-Sn-Beta Lewis Acid-Base Catalyst

    NASA Astrophysics Data System (ADS)

    Dong, Wenjie; Shen, Zheng; Peng, Boyu; Gu, Minyan; Zhou, Xuefei; Xiang, Bo; Zhang, Yalei

    2016-05-01

    Lactic acid is an important platform molecule in the synthesis of a wide range of chemicals. However, in aqueous solutions without alkali, its efficient preparation via the direct catalysis of sugars is hindered by a side dehydration reaction to 5-hydroxymethylfurfural due to Brønsted acid, which originates from organic acids. Herein, we report that a previously unappreciated combination of common two metal mixed catalyst (Zn-Sn-Beta) prepared via solid-state ion exchange synergistically promoted this reaction. In water without a base, a conversion exceeding 99% for sucrose with a lactic acid yield of 54% was achieved within 2 hours at 190 °C under ambient air pressure. Studies of the acid and base properties of the Zn-Sn-Beta zeolite suggest that the introduction of Zn into the Sn-Beta zeolite sequentially enhanced both the Lewis acid and base sites, and the base sites inhibited a series of side reactions related to fructose dehydration to 5-hydroxymethylfurfural and its subsequent decomposition.

  10. Selective Chemical Conversion of Sugars in Aqueous Solutions without Alkali to Lactic Acid Over a Zn-Sn-Beta Lewis Acid-Base Catalyst.

    PubMed

    Dong, Wenjie; Shen, Zheng; Peng, Boyu; Gu, Minyan; Zhou, Xuefei; Xiang, Bo; Zhang, Yalei

    2016-05-25

    Lactic acid is an important platform molecule in the synthesis of a wide range of chemicals. However, in aqueous solutions without alkali, its efficient preparation via the direct catalysis of sugars is hindered by a side dehydration reaction to 5-hydroxymethylfurfural due to Brønsted acid, which originates from organic acids. Herein, we report that a previously unappreciated combination of common two metal mixed catalyst (Zn-Sn-Beta) prepared via solid-state ion exchange synergistically promoted this reaction. In water without a base, a conversion exceeding 99% for sucrose with a lactic acid yield of 54% was achieved within 2 hours at 190 °C under ambient air pressure. Studies of the acid and base properties of the Zn-Sn-Beta zeolite suggest that the introduction of Zn into the Sn-Beta zeolite sequentially enhanced both the Lewis acid and base sites, and the base sites inhibited a series of side reactions related to fructose dehydration to 5-hydroxymethylfurfural and its subsequent decomposition.

  11. Selective Chemical Conversion of Sugars in Aqueous Solutions without Alkali to Lactic Acid Over a Zn-Sn-Beta Lewis Acid-Base Catalyst

    PubMed Central

    Dong, Wenjie; Shen, Zheng; Peng, Boyu; Gu, Minyan; Zhou, Xuefei; Xiang, Bo; Zhang, Yalei

    2016-01-01

    Lactic acid is an important platform molecule in the synthesis of a wide range of chemicals. However, in aqueous solutions without alkali, its efficient preparation via the direct catalysis of sugars is hindered by a side dehydration reaction to 5-hydroxymethylfurfural due to Brønsted acid, which originates from organic acids. Herein, we report that a previously unappreciated combination of common two metal mixed catalyst (Zn-Sn-Beta) prepared via solid-state ion exchange synergistically promoted this reaction. In water without a base, a conversion exceeding 99% for sucrose with a lactic acid yield of 54% was achieved within 2 hours at 190 °C under ambient air pressure. Studies of the acid and base properties of the Zn-Sn-Beta zeolite suggest that the introduction of Zn into the Sn-Beta zeolite sequentially enhanced both the Lewis acid and base sites, and the base sites inhibited a series of side reactions related to fructose dehydration to 5-hydroxymethylfurfural and its subsequent decomposition. PMID:27222322

  12. 2010 Water & Aqueous Solutions

    SciTech Connect

    Dor Ben-Amotz

    2010-08-13

    Water covers more than two thirds of the surface of the Earth and about the same fraction of water forms the total mass of a human body. Since the early days of our civilization water has also been in the focus of technological developments, starting from converting it to wine to more modern achievements. The meeting will focus on recent advances in experimental, theoretical, and computational understanding of the behavior of the most important and fascinating liquid in a variety of situations and applications. The emphasis will be less on water properties per se than on water as a medium in which fundamental dynamic and reactive processes take place. In the following sessions, speakers will discuss the latest breakthroughs in unraveling these processes at the molecular level: Water in Solutions; Water in Motion I and II; Water in Biology I and II; Water in the Environment I and II; Water in Confined Geometries and Water in Discussion (keynote lecture and poster winners presentations).

  13. Kinetics and mechanism of the oxidation of bromide by periodate in aqueous acidic solution.

    PubMed

    Szél, Viktor; Csekő, György; Horváth, Attila K

    2014-11-13

    The periodate–bromide reaction has been studied spectrophotometrically mainly in excess of bromide ion, monitoring the formation of the total amount of bromine at 450 nm at acidic buffered conditions and at a constant ionic strength in the presence of a phosphoric acid/dihydrogen phosphate buffer. The stoichiometry of the reaction was established to be strictly IO4(–) + 2Br(–) + 2H(+) → Br2 + IO3(–) + H2O. The formal kinetic order of the reactants was found to be perfectly one and two in the cases of periodate and bromide, respectively, but that of the hydrogen ion lies between one and two. We have also provided experimental evidence that dihydrogen phosphate accelerates the formation of bromine, suggesting the appearance of strong buffer assistance. On the basis of the experiments, a simple two-step kinetic model is proposed involving BrIO3 as a key intermediate that perfectly explains all of the experimental findings. Furthermore, we have also shown that in huge excess of bromide, the apparent rate coefficient obtained from the individual curve fitting method of the absorbance–time series is necessarily independent of the initial periodate concentration that may falsely be interpreted as the rate of bromine formation is also independent of the concentration of periodate.

  14. Adsorption of acids and bases from aqueous solutions onto silicon dioxide particles.

    PubMed

    Zengin, Huseyin; Erkan, Belgin

    2009-12-30

    The adsorption of acids and bases onto the surface of silicon dioxide (SiO(2)) particles was systematically studied as a function of several variables, including activation conditions, contact time, specific surface area, particle size, concentration and temperature. The physical properties of SiO(2) particles were investigated, where characterizations were carried out by FT-IR spectroscopy, and morphology was examined by scanning electron microscopy (SEM). The SEM of samples showed good dispersion and uniform SiO(2) particles with an average diameter of about 1-1.5 microm. The adsorption results revealed that SiO(2) surfaces possessed effective interactions with acids and bases, and greatest adsorption capacity was achieved with NaOH, where the best fit isotherm model was the Freundlich adsorption model. The adsorption properties of raw SiO(2) particles were further improved by ultrasonication. Langmuir monolayer adsorption capacity of NaOH adsorbate at 25 degrees C on sonicated SiO(2) (182.6 mg/g) was found to be greater than that of the unsonicated SiO(2) (154.3mg/g). The spontaneity of the adsorption process was established by decreases in DeltaG(ads)(0), which varied from -10.5 to -13.6 kJ mol(-1), in the temperature range 283-338K.

  15. Interaction of polycyclic aromatic hydrocarbons with a soil humic acid in aqueous solution

    SciTech Connect

    Jones, K.D.; Tiller, C.L.

    1996-10-01

    The effects of pH, ionic strength, and cation type on the interactions of several polycyclic aromatic hydrocarbons (PAHs) with a well-characterized soil humic acid were investigated. Binding coefficients (K{sub oc}) for anthracene, phenanthrene, pyrene, and triphenylene were determined by fluorescence quenching. At low ionic strength (as NaNO{sub 3}), K{sub oc}, for each of the PAHs increased with pH in the range 4 to 10; at high ionic strength this trend was less apparent. At a given pH, the effect of ionic strength was small, but K{sub oc} was highest at the lowest ionic strength. When pH and ionic strength were held constant but different electrolytes were used, binding of phenanthrene by the humic acid was greatest in the presence of (monovalent) sodium, followed by (bivalent) calcium, and lowest in the presence of (trivalent) aluminum. The results of this investigation are consistent with the view that interactions of hydrophobic organic compounds with natural organic matter (NOM) can be dependent on the conformational behavior of the NOM.

  16. Chemical aspects of radiosensitization. Reaction of sensitizers with radicals produced in the radiolysis of aqueous solutions of nucleic acid components.

    PubMed Central

    Asmus, K. D.; Deeble, D. J.; Garner, A.; Ali, K. M.; Scholes, G.

    1978-01-01

    The effects of oxidants (sensitizers) in the radiolysis of aqueous solutions of pyrimidine and purine bases have been investigated. Their influence on the nature of the permanent radiolysis products and on the kinetics of disappearance of transient intermediates is reported. Particular attention has been paid to the chemical fates of carbocationic intermediates which can be produced from radical-sensitizer interaction. PMID:277256

  17. Coarse-grained modeling of the titration and conductance behavior of aqueous fullerene hexa malonic acid (FHMA) solutions.

    PubMed

    Allison, Stuart A; Wu, Hengfu; Moyher, Avery; Soegiarto, Linda; Truong, Bi; Nguyen, Duy; Nguyen, Tam; Park, Donghyun

    2014-03-20

    The coarse-grained continuum primitive model is developed and used to characterize the titration and electrical conductance behavior of aqueous solutions of fullerene hexa malonic acid (FHMA). The spherical FHMA molecule, a highly charged electrolyte with an absolute valence charge as large as 12, is modeled as a dielectric sphere in Newtonian fluid, and electrostatics are treated numerically at the level of the non-linear Poisson-Boltzmann equation. Transport properties (electrophoretic mobilities and conductances) of the various charge states of FHMA are numerically computed using established numerical algorithms. For reasonable choices of the model parameters, good agreement between experiment (published literature) and modeling is achieved. In order to accomplish this, however, a moderate degree of specific binding of principal counterion and FHMA must be included in the modeling. It should be emphasized, however, that alternative explanations are possible. This comparison is made at 25 °C for both Na(+) and Ca(2+) principal counterions. The model is also used to characterize the different charge states and degree of counterion binding to those charge states as a function of pH.

  18. Rhodamine-modified upconversion nanophosphors for ratiometric detection of hypochlorous acid in aqueous solution and living cells.

    PubMed

    Zhou, Yi; Pei, Wenbo; Wang, Chenyuan; Zhu, Jixin; Wu, Jiansheng; Yan, Qinyu; Huang, Ling; Huang, Wei; Yao, Cheng; Loo, Joachim Say Chye; Zhang, Qichun

    2014-09-10

    Hypochlorous acid (HOCl), a reactive oxygen species (ROS) produced by myeloperoxidase (MPO) enzyme-mediated peroxidation of chloride ions, acts as a key microbicidal agent in immune systems. However, misregulated production of HOCl could damage host tissues and cause many inflammation-related diseases. Due to its biological importance, many efforts have been focused on developing fluorescent probes to image HOCl in living system. Compared with those conventional fluorescent probes, up-conversion luminescence (UCL) detection system has been proven to exhibit a lot of advantages including no photo-bleaching, higher light penetration depth, no autofluorescence and less damage to biosamples. Herein, we report a novel water-soluble organic-nano detection system based on rhodamine-modified UCNPs for UCL-sensing HOCl. Upon the interaction with HOCl, the green UCL emission intensity in the detection system were gradually decreased, but the emissions in the NIR region almost have no change, which is very important for the ratiometric UCL detection of HOCl in aqueous solution. More importantly, RBH1-UCNPs could be used for the ratiometric UCL visualization of HOCl released by MPO-mediated peroxidation of chloride ions in living cells. This organic-nano system could be further developed into a novel next-generation imaging technique for bio-imaging HOCl in living system without background noise.

  19. Impact of feed water pH and membrane material on nanofiltration of perfluorohexanoic acid in aqueous solution.

    PubMed

    Zeng, Chenghui; Tanaka, Shuhei; Suzuki, Yuji; Fujii, Shigeo

    2017-09-01

    Nanofiltration was thought to be a good option for the recovery of perfluorohexanoic acid (PFHxA) from industrial wastewater. In this study, two commercially available nanofiltration (NF) membranes (NF 270 and NTR-7450) were tested to concentrate the PFHxA in aqueous solution. Filtration test was conducted in crossflow filtration mode. Membrane flux and PFHxA rejection rate were monitored throughout the filtration test. The impact of initial feed water pH on membrane performance was investigated. Results demonstrated that the two NF membranes showed different response to the change of initial feed water pH, which was caused by the intrinsic properties of membrane material. The flux performance of NF 270 was stable, while its rejection rate of PFHxA was very sensitive to the change of initial feed water pH. Opposite result was obtained with NTR-7450. It had a very good stability on rejection rate, while its flux was very sensitive to the change of initial feed water pH. The mechanisms behind these phenomena were also discussed. The results obtained in this study should be very useful for the process design in practical engineering. Copyright © 2017 Elsevier Ltd. All rights reserved.

  20. Fe-based MOFs for efficient adsorption and degradation of acid orange 7 in aqueous solution via persulfate activation

    NASA Astrophysics Data System (ADS)

    Li, Xianghui; Guo, Weilin; Liu, Zhonghua; Wang, Ruiqin; Liu, Hua

    2016-04-01

    Fe-based metal-organic frameworks (MOFs) including MIL-101(Fe), MIL-100(Fe), MIL-53(Fe), and MIL-88B(Fe) prepared via a facile solvothermal process were introduced as both adsorbents and catalysts to generate powerful radicals from persulfate for acid orange 7 (AO7) removal in aqueous solution. Various catalysts were described and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectra. Because of the high specific surface area of the materials, we studied the adsorption isotherms of the four MILs by the fitting of Langmuir adsorption isotherm. Meanwhile, the catalytic activities in persulfate oxidation system were investigated. The results showed that the sequence of the materials ability in the combination of adsorption and degradation was MIL-101(Fe) > MIL-100(Fe) > MIL-53(Fe) > MIL-88B(Fe), which had a close connection with the activity of metal ion in active site of the catalysts and their different cages in size. Moreover, the reactive species in MILs/persulfate system were identified as sulfate radicals and hydroxyl radicals. The reaction mechanism for persulfate activation over MILs was also studied.

  1. Surface modification of activated carbon for enhanced adsorption of perfluoroalkyl acids from aqueous solutions.

    PubMed

    Zhi, Yue; Liu, Jinxia

    2016-02-01

    The objective of the research was to examine the effect of increasing carbon surface basicity on uptake of perfluorooctane sulfonic (PFOS) and carboxylic acids (PFOA) by activated carbon. Granular activated carbons made from coal, coconut shell, wood, and phenolic-polymer-based activated carbon fibers were modified through high-temperature and ammonia gas treatments to facilitate systematical evaluation of the impact of basicity of different origins. Comparison of adsorption isotherms and adsorption distribution coefficients showed that the ammonia gas treatment was more effective than the high-temperature treatment in enhancing surface basicity. The resultant higher point of zero charges and total basicity (measured by total HCl uptake) correlated with improved adsorption affinity for PFOS and PFOA. The effectiveness of surface modification to enhance adsorption varied with carbon raw material. Wood-based carbons and activated carbon fibers showed enhancement by one to three orders of magnitudes while other materials could experience reduction in adsorption towards either PFOS or PFOA.

  2. Enhanced removal of 8-quinolinecarboxylic acid in an activated carbon cloth by electroadsorption in aqueous solution.

    PubMed

    López-Bernabeu, S; Ruiz-Rosas, R; Quijada, C; Montilla, F; Morallón, E

    2016-02-01

    The effect of the electrochemical treatment (potentiostatic treatment in a filter-press electrochemical cell) on the adsorption capacity of an activated carbon cloth (ACC) was analyzed in relation with the removal of 8-quinolinecarboxylic acid pollutant from water. The adsorption capacity of an ACC is quantitatively improved in the presence of an electric field (electroadsorption process) reaching values of 96% in comparison to 55% in absence of applied potential. In addition, the cathodic treatment results in higher removal efficiencies than the anodic treatment. The enhanced adsorption capacity has been proved to be irreversible, since the removed compound remains adsorbed after switching the applied potential. The kinetics of the adsorption processes is also improved by the presence of an applied potential. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. RECOVERY OF PLUTONIUM FROM AQUEOUS SOLUTIONS

    DOEpatents

    Reber, E.J.

    1959-09-01

    A process is described for recovering plutonium values from aqueous solutions by precipitation on bismuth phosphate. The plutonium is secured in its tetravalent state. bismuth salt is added to the solution, and ant excess of phosphoric acid anions is added to the solution in two approximately equal installments. The rate of addition of the first installment is about two to three times as high as the rate of addition of the second installment, whereby a precipitate of bismuth phosphate forms, the precipitate carrying the plutonium values. The precipitate is separated from the solution.

  4. Electrospray mass spectrometry of some proteins and the aqueous solution acid/base equilibrium model in the negative ion detection mode

    NASA Astrophysics Data System (ADS)

    Le Blanc, J. C. Y.; Guevremont, R.; Siu, K. W. M.

    1993-06-01

    Basic solutions of myoglobin, [beta]-lactoglobulin, pepsin and ubiquitin have been examined by means of electrospray mass spectrometry in the negative ion detection mode. The distribution of protein ions in the mass spectra was found to correlate well with the distribution of protein species in solution calculated from published titration data. These results lend further credibility to an earlier proposed aqueous solution acid/base equilibrium model, which relates the "bellshape" ion distribution observed in the electrospray mass spectrometry of proteins to the distribution of protein ions in solution.

  5. Sequence dependent N-terminal rearrangement and degradation of peptide nucleic acid (PNA) in aqueous solution

    NASA Technical Reports Server (NTRS)

    Eriksson, M.; Christensen, L.; Schmidt, J.; Haaima, G.; Orgel, L.; Nielsen, P. E.

    1998-01-01

    The stability of the PNA (peptide nucleic acid) thymine monomer inverted question markN-[2-(thymin-1-ylacetyl)]-N-(2-aminoaminoethyl)glycine inverted question mark and those of various PNA oligomers (5-8-mers) have been measured at room temperature (20 degrees C) as a function of pH. The thymine monomer undergoes N-acyl transfer rearrangement with a half-life of 34 days at pH 11 as analyzed by 1H NMR; and two reactions, the N-acyl transfer and a sequential degradation, are found by HPLC analysis to occur at measurable rates for the oligomers at pH 9 or above. Dependent on the amino-terminal sequence, half-lives of 350 h to 163 days were found at pH 9. At pH 12 the half-lives ranged from 1.5 h to 21 days. The results are discussed in terms of PNA as a gene therapeutic drug as well as a possible prebiotic genetic material.

  6. Adsorption of chromium from aqueous solutions using crosslinked chitosan-diethylenetriaminepentaacetic acid.

    PubMed

    Bhatt, Ronak; Sreedhar, B; Padmaja, P

    2015-03-01

    Chitosan (CH) and its derivatives have been the focus of attention for researchers as potential adsorbents for heavy metal removal. The adsorption potential of chitosan cross-linked with diethylenetriaminepentaacetic acid (CD) for Cr6+ was investigated. CD was characterized by FTIR, XRD, TGA, XPS and ESR techniques. Batch experiments were conducted to optimize the parameters affecting the adsorption of chromium. The optimum pH was found to be 3 and the adsorption process was found to be exothermic. Adsorption isotherms were determined and the maximum adsorption capacity of CD for chromium was found to be 192.3 mg/g which was higher than the adsorption capacity of the adsorbents reported in literature. The thermodynamic parameters, such as Gibbs free energy, changes in enthalpy and changes in entropy change were also evaluated. XPS and ESR studies revealed that Cr6+ adsorbed onto CD was reduced to Cr3+. The efficacy of CD for removal of Cr6+ from chrome plating effluent was demonstrated.

  7. Kinetics and thermodynamic studies for removal of acid blue 129 from aqueous solution by almond shell

    PubMed Central

    2014-01-01

    Efficiency and performance of Almond shell (AS) adsorbent for the removal and recovery of Acid Blue 129 (AB129) from wastewater is presented in this report. The influence of variables including pH, initial dye concentration, adsorbent dosage, particle size, contact time and temperature on the dye removal have been investigated in batch method by one at a time optimization method. The experimental equilibrium data were tested by four widely used isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich (D–R). It was found that adsorption of AB129 on AS well with the Langmuir isotherm model, implying monolayer coverage of dye molecules onto the surface of the adsorbent. More than 98% removal efficiency was obtained within 14 min at adsorbent dose of 0.4 g for initial dye concentration of 40 mg/L at pH 2. Kinetics of the adsorption process was tested by pseudo-first-order and pseudo-second-order kinetics, and intraparticle diffusion mechanism. Pseudo-second-order kinetic model provided a better correlation for the experimental data studied in comparison to the pseudo-first-order model. Calculation of various thermodynamic parameters such as, Gibb’s free energy, entropy and enthalpy of the on-going adsorption process indicate feasibility and endothermic nature of AB129 adsorption on all adsorbents. This work can be used in design of adsorption columns for dyes removal. PMID:24620822

  8. Sequence dependent N-terminal rearrangement and degradation of peptide nucleic acid (PNA) in aqueous solution

    NASA Technical Reports Server (NTRS)

    Eriksson, M.; Christensen, L.; Schmidt, J.; Haaima, G.; Orgel, L.; Nielsen, P. E.

    1998-01-01

    The stability of the PNA (peptide nucleic acid) thymine monomer inverted question markN-[2-(thymin-1-ylacetyl)]-N-(2-aminoaminoethyl)glycine inverted question mark and those of various PNA oligomers (5-8-mers) have been measured at room temperature (20 degrees C) as a function of pH. The thymine monomer undergoes N-acyl transfer rearrangement with a half-life of 34 days at pH 11 as analyzed by 1H NMR; and two reactions, the N-acyl transfer and a sequential degradation, are found by HPLC analysis to occur at measurable rates for the oligomers at pH 9 or above. Dependent on the amino-terminal sequence, half-lives of 350 h to 163 days were found at pH 9. At pH 12 the half-lives ranged from 1.5 h to 21 days. The results are discussed in terms of PNA as a gene therapeutic drug as well as a possible prebiotic genetic material.

  9. Synthesis and evaluation of molecularly imprinted silica gel for 2-hydroxybenzoic Acid in aqueous solution.

    PubMed

    Raof, Siti Farhana Abdul; Mohamad, Sharifah; Abas, Mhd Radzi

    2013-03-14

    A molecularly imprinted silica gel sorbent for selective removal of 2-Hydroxybenzoic acid (2-HA) was prepared by a surface imprinting technique with a sol-gel process. The 2-HA molecularly imprinted silica gel (2-HA-MISG) sorbent was evaluated by various parameters, including the influence of pH, static, kinetic adsorption and selectivity experiments. The optimum adsorption capacity to the 2-HA appeared to be around pH 2 by the polymer. Morevoer, the imprinted sorbent displayed fast uptake kinetics, obtained within 20 min. The adsorption capacity of the 2-HA-MISG (76.2 mg g-1) was higher than that of the non-imprinted silica gel (NISG) (42.58 mg g-1). This indicates that the 2-HA-MISG offers a higher affinity for 2-HA than the NISG. The polymer displays good selectivity and exhibits good reusability. Experimental results show the potential of molecularly imprinted silica sorbent for selective removal of 2-HA.

  10. Synthesis and Evaluation of Molecularly Imprinted Silica Gel for 2-Hydroxybenzoic Acid in Aqueous Solution

    PubMed Central

    Abdul Raof, Siti Farhana; Mohamad, Sharifah; Abas, Mhd Radzi

    2013-01-01

    A molecularly imprinted silica gel sorbent for selective removal of 2-Hydroxybenzoic acid (2-HA) was prepared by a surface imprinting technique with a sol-gel process. The 2-HA molecularly imprinted silica gel (2-HA-MISG) sorbent was evaluated by various parameters, including the influence of pH, static, kinetic adsorption and selectivity experiments. The optimum adsorption capacity to the 2-HA appeared to be around pH 2 by the polymer. Morevoer, the imprinted sorbent displayed fast uptake kinetics, obtained within 20 min. The adsorption capacity of the 2-HA-MISG (76.2 mg g−1) was higher than that of the non-imprinted silica gel (NISG) (42.58 mg g−1). This indicates that the 2-HA-MISG offers a higher affinity for 2-HA than the NISG. The polymer displays good selectivity and exhibits good reusability. Experimental results show the potential of molecularly imprinted silica sorbent for selective removal of 2-HA. PMID:23493059

  11. Determination of acidity constants of sparingly soluble drugs in aqueous solution by the internal standard capillary electrophoresis method.

    PubMed

    Cabot, Joan Marc; Fuguet, Elisabet; Rosés, Martí

    2014-12-01

    A set of 33 drugs with different solubilities, ranging from soluble to very insoluble, has been chosen in order to evaluate the performance of the internal standard CE method to determine acidity constants of compounds with limited solubility. The set of drugs tested in this work has been chosen as a function of their intrinsic solubility. For the most insoluble compounds, several analytical conditions to overcome the insolubility in aqueous buffers have been tested. This paper assesses the compound solubility limits for the IS-CE method in aqueous pKa determinations, and also compares the determined pKa s with the results from the literature data obtained by other methods. It is proved that IS-CE method determines acidity constants of sparingly soluble drugs in aqueous media (compounds with logS down to around -6), whereas other reference methods require the use of aqueous-organic solvent buffers and extrapolation procedures to obtain the aqueous pKa for the same compounds.

  12. Selective removal of Cr(VI) from aqueous solution by polypyrrole/2,5-diaminobenzene sulfonic acid composite.

    PubMed

    Kera, Nazia H; Bhaumik, Madhumita; Ballav, Niladri; Pillay, Kriveshini; Ray, Suprakas Sinha; Maity, Arjun

    2016-08-15

    A polypyrrole/2,5-diaminobenzenesulfonic acid (PPy/DABSA) composite, synthesised by the in situ oxidative polymerization of pyrrole in the presence of DABSA, was studied as an adsorbent for the removal of Cr(VI) from aqueous solution. The structure and morphology of the composite were investigated by ATR-FTIR, FE-SEM, EDX, TGA, XRD and XPS studies. The adsorption of Cr(VI) by PPy/DABSA composite was highly pH dependent and optimum removal was achieved at pH 2. Adsorption of Cr(VI) was confirmed by EDX and XPS studies. The isotherm data fitted the linear Langmuir model well, with a maximum adsorption capacity of 303mg/g at 25°C. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) were calculated using isotherm data and confirmed that the adsorption process was spontaneous and endothermic. Adsorption kinetics was best described by the pseudo-second-order model. The activation energy of the adsorption process suggested that Cr(VI) was chemisorbed by PPy/DABSA composite. PPy/DABSA composite could be used for three consecutive adsorption-desorption cycles without loss of its original adsorption capacity. Highly selective removal of Cr(VI) was observed even when co-existing ions such as Cu(2+), Zn(2+), Ni(2+), Cl(-), SO4(2)(-) and NO3(-) were present in the solution. In summary, the potential of PPy/DABSA composite for remediating industrial wastewater contaminated by Cr(VI) has been demonstrated. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. Cd(II) removal from aqueous solution by adsorption on α-ketoglutaric acid-modified magnetic chitosan

    NASA Astrophysics Data System (ADS)

    Yang, Guide; Tang, Lin; Lei, Xiaoxia; Zeng, Guangming; Cai, Ye; Wei, Xue; Zhou, Yaoyu; Li, Sisi; Fang, Yan; Zhang, Yi

    2014-02-01

    The present study developed an α-ketoglutaric acid-modified magnetic chitosan (α-KA-Fe3O4/CS) for highly efficient adsorption of Cd(II) from aqueous solution. Several techniques, including transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and vibrating sample magnetometer (VSM), were applied to characterize the adsorbent. Batch tests were conducted to investigate the Cd(II) adsorption performance of α-KA-Fe3O4/CS. The maximum adsorption efficiency of Cd(II) appeared at pH 6.0 with the value of 93%. The adsorption amount was large and even reached 201.2 mg/g with the initial Cd(II) concentration of 1000 mg/L. The adsorption equilibrium was reached within 30 min and commendably described by pseudo-second-order model, and Langmuir model fitted the adsorption isotherm better. Furthermore, thermodynamic parameters, free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) of Cd(II) adsorption were also calculated and showed that the overall adsorption process was endothermic and spontaneous in nature because of positive ΔH values and negative ΔG values, respectively. Moreover, the Cd(II)-loaded α-KA-Fe3O4/CS could be regenerated by 0.02 mol/L NaOH solution, and the cadmium removal capacity could still be kept around 89% in the sixth cycle. All the results indicated that α-KA-Fe3O4/CS was a promising adsorbent in environment pollution cleanup.

  14. Removal of metal ions from aqueous solution

    DOEpatents

    Jackson, Paul J.; Delhaize, Emmanuel; Robinson, Nigel J.; Unkefer, Clifford J.; Furlong, Clement

    1990-11-13

    A method of removing heavy metals from aqueous solution, a composition of matter used in effecting said removal, and apparatus used in effecting said removal. One or more of the polypeptides, poly (.gamma.-glutamylcysteinyl)glycines, is immobilized on an inert material in particulate form. Upon contact with an aqueous solution containing heavy metals, the polypeptides sequester the metals, removing them from the solution. There is selectivity of poly (.gamma.-glutamylcysteinyl)glycines having a particular number of monomer repeat unit for particular metals. The polypeptides are easily regenerated by contact with a small amount of an organic acid, so that they can be used again to remove heayv metals from solution. This also results in the removal of the metals from the column in a concentrated form.

  15. Removal of metal ions from aqueous solution

    DOEpatents

    Jackson, Paul J.; Delhaize, Emmanuel; Robinson, Nigel J.; Unkefer, Clifford J.; Furlong, Clement

    1990-01-01

    A method of removing heavy metals from aqueous solution, a composition of matter used in effecting said removal, and apparatus used in effecting said removal. One or more of the polypeptides, poly (.gamma.-glutamylcysteinyl)glycines, is immobilized on an inert material in particulate form. Upon contact with an aqueous solution containing heavy metals, the polypeptides sequester the metals, removing them from the solution. There is selectivity of poly (.gamma.-glutamylcysteinyl)glycines having a particular number of monomer repeat units for particular metals. The polypeptides are easily regenerated by contact with a small amount of an organic acid, so that they can be used again to remove heavy metals from solution. This also results in the removal of the metals from the column in a concentrated form.

  16. Sucrose diffusion in aqueous solution

    PubMed Central

    Murray, Benjamin J.

    2016-01-01

    The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes–Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle. PMID:27364512

  17. Sorption of estrogens and pesticides from aqueous solution by a humic acid and raw and processed plant materials

    NASA Astrophysics Data System (ADS)

    Loffredo, Elisabetta; Taskin, Eren

    2016-04-01

    The huge number of organic contaminants released in water as a consequence of anthropogenic activities have detrimental effects to environmental systems and human health. Industrial products and byproducts, pharmaceuticals, pesticides, detergents and so on impose increasing costs for wastewater decontamination. Adsorption techniques can be successfully used for the treatment of wastewaters to remove contaminants of various nature. Humic acids (HA) have well-known adsorptive capacities towards hydrophilic and, especially, hydrophobic compounds. In the recent years, alternative low-cost adsorbents, especially originated from agricultural wastes and food industries residues, such as wood chips, almond and coconut shells, peanut and rice husks, are under investigation. Biochar is also considered a promising and relatively low-cost adsorbent, even if there are still knowledge gaps about the influence of feedstock type, pyrolysis conditions, physical and chemical properties on its potential and safe use. In the present work, a HA from a green compost was used along with three other materials of plant origin to remove two estrogens, 4-tert-octylphenol and 17-β-estradiol, and two pesticides, carbaryl and fenuron, from an aqueous solution. The four molecules were spiked in water each at a concentration of 1 mg L-1. The materials were: a biochar obtained from 100% red spruce pellet pyrolysed at 550 °C, spent coffee grounds and spent tea leaves. Kinetics curves and adsorption isotherms studies were performed using a batch equilibrium method. Adsorption data obtained for each compound were fitted to a linear equation and non-linear Freundlich and Langmuir models. Kinetics data of the four compounds onto all adsorbents showed an initial very rapid adsorption which was completed in few hours when it reached equilibrium. The two estrogens were adsorbed onto all materials more quickly than the two less hydrophobic pesticides. Significant differences among adsorbents and the

  18. Formic acid enhanced effective degradation of methyl orange dye in aqueous solutions under UV-Vis irradiation.

    PubMed

    Wang, Jingjing; Bai, Renbi

    2016-09-15

    Developing efficient technologies to treat recalcitrant organic dye wastewater has long been of great research and practical interest. In this study, a small molecule, formic acid (FA), was applied as a process enhancer for the degradation of methyl orange (MO) dye as a model recalcitrant organic pollutant in aqueous solutions under the condition of UV-Vis light irradiation and air aeration at the ambient temperature of 25 °C. It was found that the decolouration of the dye solutions can be rapidly achieved, reducing the time, for example, from around 17.6 h without FA to mostly about less than 2 h with the presence of FA. The mineralization rate of MO dye reached as high as 81.8% in 1.5 h in the case of initial MO dye concentration at 25 mg L(-1), which is in contrast to nearly no mineralization of the MO dye for a similar system without the FA added. The study revealed that the generation of the H2O2 species in the system was enhanced and the produced OH radicals effectively contributed to the degradation of the MO dye. Process parameters such as the initial concentration of MO dye, FA dosage and solution pH were all found to have some effect on the degradation efficiency under the same condition of UV-Vis light irradiation and air aeration. The MO dye degradation performance was found to follow a first-order reaction rate to the MO dye concentration in most cases and there existed a positive correlation between the reaction rate constant and the initial FA concentration. Compared to the traditional H2O2/UV-Vis oxidation system, the use of FA as a process-enhancing agent can have the advantages of low cost, easy availability, and safe to use. The study hence demonstrates a promising approach to use a readily available small molecule of FA to enhance the degradation of recalcitrant organic pollutants, such as MO dye, especially for their pre-treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. Extraction of formic and acetic acids from aqueous solution by dynamic headspace-needle trap extraction temperature and pH optimization.

    PubMed

    Lou, Da-Wei; Lee, Xinqing; Pawliszyn, Janusz

    2008-08-08

    A combined method of dynamic headspace-needle trap sample preparation and gas chromatography for the determination of formic and acetic acids in aqueous solution was developed in this study. A needle extraction device coupled with a gas aspirating pump was intended to perform sampling and preconcentration of target compounds from aqueous sample before gas chromatographic analysis. The needle trap extraction (NTE) technique allows for the successful sampling of short chain fatty acids under dynamic conditions while keeping the headspace (HS) volume constant. Two important parameters, including extraction temperature and effect of acidification, have been optimized and evaluated using the needle trap device. The method detection limits for the compounds estimated were 87.2microg/L for acetic acid and 234.8microg/L for formic acid in spite of the low flame ionization detection response for formic acid and its low Henry's law constant in aqueous solution. Precision was determined based on the two real samples and ranged between 4.7 and 10.7%. The validated headspace-needle trap extraction method was also successfully applied to several environmental samples.

  20. Specular reflectance of aqueous solutions.

    NASA Technical Reports Server (NTRS)

    Querry, M. R.; Waring, R. C.; Holland, W. E.; Mansell, G. R.

    1971-01-01

    Description of two laboratory instruments for measuring the specular reflectance of aqueous solutions. The instruments are an organic-dye-laser spectrophotometer for the 360- to 650-nm wavelength region and a reflectometer accessory for a Perkin-Elmer E-system spectrophotometer which will operate in the 0.2- to 20-micron wavelength region. The reflectometer accessory has been used to measure the relative infrared specular reflectance in limited spectral regions for aqueous solutions of NaCl, K2SO4, ZnSO4, (NH4)2SO4, and NH4H2PO4 with radiant flux incident at about 70 deg and polarized perpendicular to the plane of incidence. The laser spectrometer has been used to measure the absolute reflectance of aqueous solutions of NaCl in the wavelength region from 575 to 610 nm for light incident at angles of about 60, 65, and 70 deg and polarized parallel to the plane of incidence.

  1. Specular reflectance of aqueous solutions.

    NASA Technical Reports Server (NTRS)

    Querry, M. R.; Waring, R. C.; Holland, W. E.; Mansell, G. R.

    1971-01-01

    Description of two laboratory instruments for measuring the specular reflectance of aqueous solutions. The instruments are an organic-dye-laser spectrophotometer for the 360- to 650-nm wavelength region and a reflectometer accessory for a Perkin-Elmer E-system spectrophotometer which will operate in the 0.2- to 20-micron wavelength region. The reflectometer accessory has been used to measure the relative infrared specular reflectance in limited spectral regions for aqueous solutions of NaCl, K2SO4, ZnSO4, (NH4)2SO4, and NH4H2PO4 with radiant flux incident at about 70 deg and polarized perpendicular to the plane of incidence. The laser spectrometer has been used to measure the absolute reflectance of aqueous solutions of NaCl in the wavelength region from 575 to 610 nm for light incident at angles of about 60, 65, and 70 deg and polarized parallel to the plane of incidence.

  2. Efficient degradation of Acid Orange 7 in aqueous solution by iron ore tailing Fenton-like process.

    PubMed

    Zheng, Jianming; Gao, Zhanqi; He, Huan; Yang, Shaogui; Sun, Cheng

    2016-05-01

    An effective method based on iron ore tailing Fenton-like process was studied for removing an azo dye, Acid Orange 7 (AO7) in aqueous solution. Five tailings were characterized by X-ray fluorescence spectroscope (XFS), Brunner-Emmet-Teller (BET) measurement, and Scanning Electron Microscope (SEM). The result of XFS showed that Fe, Si and Ca were the most abundant elements and some toxic heavy metals were also present in the studied tailings. The result of BET analysis indicated that the studied tailings had very low surface areas (0.64-5.68 m(2) g(-1)). The degradation efficiencies of AO7 were positively correlated with the content of iron oxide and cupric oxide, and not related with the BET surface area of the tailings. The co-existing metal elements, particularly Cu, might accelerate the heterogeneous Fenton-like reaction. The effects of other parameters on heterogeneous Fenton-like degradation of AO7 by a converter slag iron tailing (tailing E) which contains highest iron oxide were also investigated. The tailing could be reused 10 times without significant decrease of the catalytic capacity. Very low amount of iron species and almost undetectable toxic elements were leached in the catalytic degradation of AO7 by the tailing E. The reaction products were identified by gas chromatography-mass spectrometry and a possible pathway of AO7 degradation was proposed. This study not only provides an effective method for removing azo dyes in polluted water by employing waste tailings as Fenton-like catalysts, but also uses waste tailings as the secondary resource.

  3. Removal of Mefenamic acid from aqueous solutions by oxidative process: Optimization through experimental design and HPLC/UV analysis.

    PubMed

    Colombo, Renata; Ferreira, Tanare C R; Ferreira, Renato A; Lanza, Marcos R V

    2016-02-01

    Mefenamic acid (MEF) is a non-steroidal anti-inflammatory drug indicated for relief of mild to moderate pain, and for the treatment of primary dysmenorrhea. The presence of MEF in raw and sewage waters has been detected worldwide at concentrations exceeding the predicted no-effect concentration. In this study, using experimental designs, different oxidative processes (H2O2, H2O2/UV, fenton and Photo-fenton) were simultaneously evaluated for MEF degradation efficiency. The influence and interaction effects of the most important variables in the oxidative process (concentration and addition mode of hydrogen peroxide, concentration and type of catalyst, pH, reaction period and presence/absence of light) were investigated. The parameters were determined based on the maximum efficiency to save time and minimize the consumption of reagents. According to the results, the photo-Fenton process is the best procedure to remove the drug from water. A reaction mixture containing 1.005 mmol L(-1) of ferrioxalate and 17.5 mmol L(-1) of hydrogen peroxide, added at the initial reaction period, pH of 6.1 and 60 min of degradation indicated the most efficient degradation, promoting 95% of MEF removal. The development and validation of a rapid and efficient qualitative and quantitative HPLC/UV methodology for detecting this pollutant in aqueous solution is also reported. The method can be applied in water quality control that is generated and/or treated in municipal or industrial wastewater treatment plants.

  4. Thermodynamic and spectroscopic study of Al(3+) interaction with glycine, l-cysteine and tranexamic acid in aqueous solution.

    PubMed

    Cardiano, Paola; Giacobello, Fausta; Giuffrè, Ottavia; Sammartano, Silvio

    2017-08-08

    In this paper a thermodynamic and spectroscopic study on the interaction between Al(3+) and glycine (Gly), l-cysteine (Cys), tranexamic acid (Tranex) is reported. Speciation models have been obtained by processing potentiometric titration data to determine stability constants of the species formed in aqueous solution at T=298.15K, 0.15≤I/molL(-1)≤1 in NaCl. Thermodynamic formation parameters have been obtained from calorimetric titration data, at T=298.15K, I=0.15molL(-1) using NaCl as ionic medium. Al(3+)-Cys system was also investigated by spectrophotometric and (1)H NMR measurements. (1)H NMR experiments were performed on Al(3+)-Tranex system as well. Different speciation models have been observed for the three systems. The results showed the formation of MLH, ML and M2L2(OH)2 species for Gly, ML, M2L and MLOH for Cys, MLH and MLOH for Tranex. The formed species are quite stable, i.e. for ML, logβ=7.18, 11.91 for Gly and Cys, respectively, at I=0.15molL(-1) and T=298.15K. For all the systems the dependence of formation constants on ionic strength over the range 0.1-1molL(-1) is reported. The sequestering ability of the ligands under study was also evaluated by pL0.5 empiric parameter. For Gly, Cys and Tranex, pL0.5=2.51, 3.74, 3.91 respectively, at pH=5, I=0.15molL(-1) and T=298.15K. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Thermosensitive aqueous solutions of polyvinylacetone

    NASA Astrophysics Data System (ADS)

    Wu, Wei-Tai; Wang, Yusong; Shi, Lei; Zhu, Qingren; Pang, Wenmin; Xu, Guoyong; Lu, Fei

    2006-04-01

    The dimethylketals of poly(vinyl alcohol), termed polyvinylacetone (PVKA), of moderate ketalization degree in the range from 0.28 to 0.6 exhibited temperature-induced phase transition in aqueous solution, as revealed by cloud point measurements and electron micrographs, which was then further investigated on molecular level using solution-state 1H NMR measurements. The present phase transition is caused by the amphiphilic characteristics in the polymer chain. Moreover, this finding could be further applied as a novel strategy in the syntheses of thermosensitive polymer by the hydrophobic functionalities of linear polyol.

  6. Effect of medium acidity on the thermodynamics and kinetics of the reaction of pyridoxal 5'-phosphate with isoniazid in an aqueous solution

    NASA Astrophysics Data System (ADS)

    Gamov, G. A.; Zavalishin, M. N.; Usacheva, T. R.; Sharnin, V. A.

    2017-05-01

    Thermodynamic characteristics of the formation of the Schiff base between isoniazid and pyridoxal 5'-phosphate in an aqueous solution at different pH values of a medium are determined by means of spectrophotometry and calorimetric titration. The process kinetics is studied spectrophotometrically, and the reaction rate constants for the formation of the imine at different acidities of a medium are determined. Biochemical aspects of the binding of pyridoxal 5'-phosphate into stable compounds are discussed.

  7. Cation-exchange behavior of berkelium in aqueous-organic solutions of nitric acid, containing trioctylphosphine oxide

    SciTech Connect

    Guseva, L.I.; Tikhomirova, G.S.; Korovaikov, P.A.

    1995-07-01

    Behavior of transplutonium elements (TPEs), Eu, and Zr on Dowex-50 cation-exchange resin in aqueous-organic solutions of HNO{sub 3} containing trioctylphosphine oxide (TOPO) has been studied as influenced by the nature of the solvent (H{sub 2}O, CH{sub 3}OH, C{sub 2}H{sub 5}OH, CH{sub 3}COOH, CH{sub 3}CN), the composition and concentration of various components of the solution, and the presence of an oxidant (PbO{sub 2}) in the resin phase. The authors found that the factors of Bk distribution between the PbO{sub 2}-containing resin and CH{sub 3}CN-HNO{sub 3}-TOPO solutions are considerably lower than the distribution factors of other TPEs, which is due to oxidation of Bk(III) into Bk(IV). This fact can be used for separation of Bk(IV) from other TPEs with a cation-exchange column containing an oxidant. The optimal conditions of separation (elution with solutions containing 1.0-2.5 M HNO{sub 3}, 0.1 M TOPO, and 80-90% CH{sub 3}CN) have been determined. A mechanism is proposed for TPE sorption on the cation-exchange resin from aqueous-organic solutions of HNO{sub 3} containing TOPO. The analogy between behavior of TPEs in ion-exchange and extraction processes in these systems is discussed.

  8. Degradation of 17beta-estradiol in aqueous solution by ozonation in the presence of manganese(II) and oxalic acid.

    PubMed

    Jiang, Liying; Zhang, Lu; Chen, Jianmeng; Ji, Hong

    2013-01-01

    Natural estrogens, such as 17beta-estradiol (E2), are the main substances responsible for estrogenic activity found in domestic sewage. In the work described herein, the degradation of E2 has been investigated by single ozonation and catalytic ozonation in the presence of manganese ion (Mn2+) and oxalic acid. The presence of Mn2+ and oxalic acid in the ozonation processes significantly improved the E2 degradation and, hence, the reduction of estrogenic activity in aqueous solution. The addition of Mn2+ and oxalic acid produced many more hydroxyl radicals in the catalytic ozonation system than in the single ozonation system. Oxidation products formed during ozonation of E2 have been identified by means of gas chromatography-mass spectrometry (GC-MS), on the basis of which a possible reaction pathway for E2 degradation by ozonation is proposed. E2 was first oxidized to hydroxyl-semiquinone isomers, and these were subsequently degraded to low molecular weight compounds such as oxalic acid and malonic acid. The latter were easily oxidized by ozone to form carbon dioxide (CO2). The results demonstrate that the ozonation-Mn(2+)-oxalic acid system may serve as a powerful tool for removing E2, and the addition of Mn2+ and oxalic acid is favourable for the complete removal of estrogenic activity induced by steroid estrogens in aqueous solution.

  9. 15N nuclear magnetic resonance studies of acid-base properties of pyridoxal-5'-phosphate aldimines in aqueous solution.

    PubMed

    Sharif, Shasad; Huot, Monique Chan; Tolstoy, Peter M; Toney, Michael D; Jonsson, K Hanna M; Limbach, Hans-Heinrich

    2007-04-19

    By use of 15N NMR spectroscopy, we have measured the pKa values of the aldimines 15N-(pyridoxyl-5'-phosphate-idine)-methylamine (2a), N-(pyridoxyl-5'-phosphate-15N-idine)-methylamine (2b), and 15N-(pyridoxyl-idine)-methylamine (3). These aldimines model the cofactor pyridoxal-5'-phosphate (PLP, 1) in a variety of PLP-dependent enzymes. The acid-base properties of the aldimines differ substantially from those of the free cofactor in the aldehyde form 1a or in the hydrated form 1b, which were also investigated using 15N NMR for comparison. All compounds contain three protonation sites, the pyridine ring, the phenol group, and the side chain phosphate (1, 2) or hydroxyl group (3). In agreement with the literature, 1a exhibits one of several pKas at 2.9 and 1b at 4.2. The 15N chemical shifts indicate that the corresponding deprotonation occurs partially in the pyridine and partially in the phenolic site, which compete for the remaining proton. The equilibrium constant of this ring-phenolate tautomerism was measured to be 0.40 for 1a and 0.06 for 1b. The tautomerism is essentially unaltered above pH 6.1, where the phosphate group is deprotonated to the dianion. This means that the pyridine ring is more basic than the phenolate group. Pyridine nitrogen deprotonation occurs at 8.2 for 1a and at 8.7 for 1b. By contrast, above pH 4 the phosphate site of 2 is deprotonated, while the pyridine ring pKa is 5.8. The Schiff base nitrogen does not deprotonate below pH 11.4. When the phosphate group is removed, the pKa of the Schiff base nitrogen decreases to 10.5. The phenol site cannot compete for the proton of the Schiff base nitrogen and is present in the entire pH range as a phenolate, preferentially hydrogen bonded to the solvent. The intrinsic 15N chemical shifts provide information about the hydrogen bond structures of the protonated and unprotonated species involved. Evidence is presented that the intramolecular OHN hydrogen bond of PLP aldimines is broken in aqueous

  10. Side-Chain Conformational Thermodynamics of Aspartic Acid Residue in the Peptides and Achatin-I in Aqueous Solution

    PubMed Central

    Kimura, Tomohiro; Matubayasi, Nobuyuki; Nakahara, Masaru

    2004-01-01

    Sequence-position dependence of the side-chain conformational equilibrium of aspartic acid (Asp) residue is investigated for both model Asp peptides (di- to tetra-) and neuropeptide achatin-I (Gly-𝒟-Phe-Ala-Asp) in aqueous solution. The trans-to-gauche conformational changes on the dihedral angle of C–Cα–Cβ–C are analyzed in terms of the standard free energy ΔG0, enthalpy ΔH0, and entropy −TΔS0. The thermodynamic quantities are obtained by measuring the dihedral-angle-dependent vicinal 1H-1H coupling constants in nuclear magnetic resonance over a wide temperature range. When the carboxyl groups of Asp are ionized, ΔG0 in the aqueous phase depends by ∼1–2 kJ mol−1 on the sequence position, whereas the energy change \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\Delta}E_{{\\mathrm{gas}}}^{0}\\end{equation*}\\end{document} in the gas phase (absence of solvent) depends by tens of kJ mol−1. Therefore, the weak position dependence of ΔG0 is a result of the compensation for the intramolecular effect \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\Delta}E_{{\\mathrm{gas}}}^{0}\\end{equation*}\\end{document} by the hydration \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\Delta}G_{{\\mathrm{hyd}}}^{0}\\end{equation*}\\end{document} (= ΔG0–\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage

  11. Unexpected formation of a copper(II) 12-metallacrown-4 with (S)-glutamic-gamma-hydroxamic acid: a thermodynamic and spectroscopic study in aqueous solution.

    PubMed

    Tegoni, Matteo; Dallavalle, Francesco; Belosi, Barbara; Remelli, Maurizio

    2004-05-07

    The equilibria of copper(II) with (S)-glutamic-gamma-hydroxamic acid (H2L) were investigated in aqueous solution by different techniques: glass electrode potentiometry; calorimetry; VIS and CD spectrophotometry; and ES-MS. An unexpected pentacopper(II) 12-metallacrown-4 [Cu5L4H(-4)](2-) was detected, analogous to those well known formed by alpha- and beta-aminohydroxamic acids, but of lower stability. Another five species were found: [CuLH]+; [CuL2H2]; [Cu2L2]; [CuL2H]-; and [CuL2]2-. Their structures are proposed based on both spectroscopic and calorimetric data.

  12. Reusable nanocomposite of CoFe2O4/chitosan-graft-poly(acrylic acid) for removal of Ni(II) from aqueous solution

    NASA Astrophysics Data System (ADS)

    Nguyen, Van Cuong; Huynh, Thi Kim Ngoc

    2014-06-01

    In this paper, CoFe2O4/chitosan-graft-poly(acrylic acid) (CoFe2O4/CS-graft-PAA) nanocomposites were prepared successfully by coprecipitation of the compounds in alkaline solution and were used for removal of nickel (II) ions from aqueous solution. The sorption rate was affected significantly by the initial concentration of the solution, sorbent amount, and pH value of the solution. Batch experiments were conducted to investigate the adsorption capacity under different initial concentration (ranging from 25 to 150 mg L-1), solution pH (4.1, 5.3, 6.4 and 7.6), and contact time. These nanocomposites can be recycled conveniently from water with the assistance of an external magnet because of their exceptional properties. The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), x-ray powder diffraction (XRD), and thermogravimetric analysis (TGA).

  13. Oxidative photodegradation of herbicide fenuron in aqueous solution by natural iron oxide α-Fe2O3, influence of polycarboxylic acids.

    PubMed

    Kribéche, Mohamed El Amine; Mechakra, Hind; Sehili, Tahar; Brosillon, Stephan

    2016-01-01

    The photodegradation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by using a natural iron oxide (NIO), α-Fe2O3, in aqueous solution at acidic pH has been undertaken. The NIO was characterized by the Raman spectroscopy method. The degradation pathways and the formation of degradation products were studied. A high-pressure mercury lamp and sunlight were employed as light source. Fenuron photodegradation using NIO with oxalic acid followed the pseudo-first-order kinetics, the optimal experimental conditions were [oxalic acid]0 = 10(-3) M and [NIO] = 0.1 g L(-1) at pH 3. A UVA/NIO/oxalic acid system led to a low fenuron half-life (60 min). The results were even better when solar light is used (30 min). The variables studied were the doses of iron oxide, of carboxylic acids, the solution pH and the effect of sunlight irradiation. The effects of four carboxylic acids, oxalic, citric, tartaric and malic acids, on the fenuron photodegradation with NIO have been investigated, oxalic acid was the most effective carboxylic acid used at pH 3. A similar trend was observed for the removal of total organic carbon (TOC), 75% of TOC was removed. The analytical study showed many aromatic intermediates, short-chain carboxylic acids and inorganic ion.

  14. Instrumental Characterization Of Coir PITH By XRD, FTIR and SEM After Radium Adsorption From Aqueous Solution Under The Presence Of Humic Acids

    NASA Astrophysics Data System (ADS)

    Laili, Zalina; Omar, Muhamat; Yasir, Muhamad Samudi; Ibrahim, Mohd Zaidi; Yahaya, Mohd Yusri; Murshidi, Julie Andrianny

    2010-01-01

    Adsorption interactions of radium (Ra) ions onto coir pith (CP) under the presence of humic acid (HA) in the aqueous solution were investigated using X-ray diffraction (XRD), Fourier Transform Infrared Spectrophotometer (FTIR) and Scanning Electron Microscopy (SEM) techniques. XRD, IR and SEM characterization of the CP has revealed differences in the native CP and Ra ions loaded CP under the presence of HA in the aqueous solution. The X-Ray patterns showed that crystalline structure of the loaded CP exhibited a decrease in crystalline structure at around 49°-51° compared with unloaded CP. Characterization by IR revealed that participation of some surface functional groups during the Ra adsorption. SEM images for the morphological studies showed that there were slightly changes of the CP surfaces after the adsorption process.

  15. Modelling of the acid-base properties of natural and synthetic adsorbent materials used for heavy metal removal from aqueous solutions.

    PubMed

    Pagnanelli, Francesca; Vegliò, Francesco; Toro, Luigi

    2004-02-01

    In this paper a comparison about kinetic behaviour, acid-base properties and copper removal capacities was carried out between two different adsorbent materials used for heavy metal removal from aqueous solutions: an aminodiacetic chelating resin as commercial product (Lewatit TP207) and a lyophilised bacterial biomass of Sphaerotilus natans. The acid-base properties of a S. natans cell suspension were well described by simplified mechanistic models without electrostatic corrections considering two kinds of weakly acidic active sites. In particular the introduction of two-peak distribution function for the proton affinity constants allows a better representation of the experimental data reproducing the site heterogeneity. A priori knowledge about resin functional groups (aminodiacetic groups) is the base for preliminary simulations of titration curve assuming a Donnan gel structure for the resin phase considered as a concentrated aqueous solution of aminodiacetic acid (ADA). Departures from experimental and simulated data can be interpreted by considering the heterogeneity of the functional groups and the effect of ionic concentration in the resin phase. Two-site continuous model describes adequately the experimental data. Moreover the values of apparent protonation constants (as adjustable parameters found by non-linear regression) are very near to the apparent constants evaluated by a Donnan model assuming the intrinsic constants in resin phase equal to the equilibrium constants in aqueous solution of ADA and considering the amphoteric nature of active sites for the evaluation of counter-ion concentration in the resin phase. Copper removal outlined the strong affinity of the active groups of the resin for this ion in solution compared to the S. natans biomass according to the complexation constants between aminodiacetic and mono-carboxylic groups and copper ions.

  16. REMOVAL OF CHLORIDE FROM AQUEOUS SOLUTIONS

    DOEpatents

    Schulz, W.W.

    1959-08-01

    The removal of chlorides from aqueons solutions is described. The process involves contacting the aqueous chloride containing solution with a benzene solution about 0.005 M in phenyl mercuric acetate whereby the chloride anions are taken up by the organic phase and separating the organic phase from the aqueous solutions.

  17. Exclusion of Nitrate from Frozen Aqueous Solutions

    NASA Astrophysics Data System (ADS)

    Marrocco, H. A.; Michelsen, R. R.

    2013-12-01

    Reactions occurring at the surface of ice, sea ice, and snow in Earth's cryosphere have an impact on the composition of the overlying atmosphere. In order to elucidate reaction mechanisms and model their contributions to atmospheric processes, the morphology of frozen aqueous surfaces and amounts of reactants contained therein must be determined. To this end, the exclusion of nitrate ions to the surface of frozen aqueous solutions has been studied by attenuated total reflection infrared spectroscopy (ATR-IR). In this technique the near-surface region of the frozen films are interrogated to a depth of a few hundred nanometers from the film-crystal interface. Aqueous solutions (0.001 to 0.01 M) of sodium nitrate (NaNO3), magnesium nitrate (Mg(NO3)2), and nitric acid (HNO3) were quickly frozen on the germanium ATR crystal and observed at a constant temperature of about -18°C. In addition to ice and the solutes, liquid water in varying amounts was observed in the spectra. The amount of nitrate in the surface liquid is three to four orders of magnitude higher than in the unfrozen solution. While all the nitrate salts exhibit exclusion to the unfrozen surface, the dynamics are different for different counter-ions. Results are compared to freezing point depression data and the predictions of equilibrium thermodynamics.

  18. Boric acid, “carbonic” acid, and N-containing oxyacids in aqueous solution: Ab initio studies of structure, pKa, NMR shifts, and isotopic fractionations

    NASA Astrophysics Data System (ADS)

    Tossell, J. A.

    2005-12-01

    B(OH) 3 and CO 2 are acidic species of considerable geochemical importance, yet the microscopic nature of the acid dissociation reactions for these B and C species is not well understood. Quantum mechanical methods have recently been applied to the direct ab initio calculation of p Ka values for many organic and inorganic weak acids, but the B and C acids have not yet been considered in detail. In the present study, p Ka values are calculated quantum mechanically for the oxyacids B(OH) 3, H 2CO 3 and HNO 3, which have experimental first p Ka values of 9.2, 6.4 and -1.3, respectively. We calculate the gas-phase reaction free energies at the highly accurate CBS-QB3 ab initio quantum mechanical level and reaction free energies of hydration using a polarizable continuum method. Using a thermodynamic cycle corresponding to the simple dissociation process HA A - + H +, in aqueous solution, we calculate p Ka values of 21.6, 3.8 to 2.2 and -0.8 for the three oxyacids mentioned above, closely matching experiment only for HNO 3. The discrepancies with experiment arise from the more complex nature of the acid dissociation process for B(OH) 3, which involves the addition of H 2O to B(OH) 3 and formation of the B(OH) 4- anion, and from the instability of hypothetical H 2CO 3 compared to the proper hydrated reactant complex CO 2. . . H 2O. When the proper microscopic description of the reactants and products is used the calculated p Ka values for the three acids become 11.1, 7.2 and -0.8, in considerably better agreement with experiment for B(OH) 3 and CO 2. . . H 2O. Thus p Ka calculations using this approach are accurate enough to give information on the actual acid species present in solution and the details of their acid dissociation processes at the microscopic level. 11B and 13C-NMR chemical shifts are also calculated for the various species and compared to experiment. By comparison of our calculations with experiment it is apparent that the 13C-NMR chemical shift has

  19. Rheological Properties of Aqueous Acid Solutions of Chitosan: Experiment and Calculations of the Viscometric Functions on the Basis of a Mesoscopic Model

    NASA Astrophysics Data System (ADS)

    Shipovskaya, A. B.; Abramov, A. Yu.; Pyshnograi, G. V.; Aziz, Al Joda Hyder Nadom

    2016-05-01

    The rheological properties of chitosan solutions in acetic acid at 20°C in the range of polymer concentrations from 0.5 to 8 mass% and acid concentrations from 2 to 70% have been investigated. With the use of a modified Vinogradov-Pokrovskii model based on the microstructural approach to the description of polymer fluid dynamics, numerical solutions of gradient dependences of viscometric functions of aqueous acid solutions of chitosan have been obtained. It has been established that the numerical solution describes with good accuracy the experimental viscosity rheograms. The values of the highest Newton viscosity ηmax have been calculated. The concentration modes of semidiluted and concentrated solutions have been determined by the dependence of ηmax on the polymer concentration, and the range of concentrations in which the mass transfer mechanism changes and a fluctuation network is formed has been found. It has been shown that the concentration of acetic acid practically does not influence the structure and character of flow of chitosan solutions, the formation concentration of a network, and the efficiency of its labile nodes.

  20. Synthesis of walnut shell modified with titanium dioxide and zinc oxide nanoparticles for efficient removal of humic acid from aqueous solutions.

    PubMed

    Naghizadeh, Ali; Shahabi, Habibeh; Ghasemi, Fatemeh; Zarei, Ahmad

    2016-12-01

    The main aim of this research was to study the efficiency of modified walnut shell with titanium dioxide (TiO2) and zinc oxide (ZnO) in the adsorption of humic acid from aqueous solutions. This experimental study was carried out in a batch condition to determine the effects of factors such as contact time, pH, humic acid concentration, dose of adsorbents (raw walnut shell, modified walnut shell with TiO2 and ZnO) on the removal efficiency of humic acid. pHzpc of raw walnut shell, walnut shell modified with TiO2 and walnut shell modified with ZnO were 7.6, 7.5, and 8, respectively. The maximum adsorption capacity of humic acid at concentration of 30 mg/L, contact time of 30 min at pH = 3 in an adsorbent dose of 0.02 g of walnut shell and ZnO and TiO2 modified walnut shell were found to be 35.2, 37.9, and 40.2 mg/g, respectively. The results showed that the studied adsorbents tended to fit with the Langmuir model. Walnut shell, due to its availability, cost-effectiveness, and also its high adsorption efficiency, can be proposed as a promising natural adsorbent in the removal of humic acid from aqueous solutions.

  1. Radiation- and photo-induced formation of salicylic acid from phenol and CO{sub 2} in aqueous solution

    SciTech Connect

    Krapfenbauer, K.; Getoff, N.

    1996-12-31

    The concentration of CO{sub 2} in the atmosphere is steady increasing because of the combustion of fossil fuels and the industrial pollution. As a result, global warming has occurred. In the present study the formation of the salicylic acid and other products, originating from the carboxylation of phenol is investigated. It has been found that the formation of salicylic acid strongly depend on several experimental conditions: pH of the solution, concentration of phenol and CO{sub 2}, and absorbed dose. The formation of salicylic acid was also studied in the presence of catalysts. Photo-induced carboxylation of phenol to salicylic acid will be also reported. Probable reaction mechanisms for the salicylic acid formation are suggested. Finally, a comparison is made between the well known industrial Kolbe-Schmitt process for salicylic acid production and the aspects of the present new method for CO{sub 2} utilization.

  2. PROCESS FOR RECOVERING URANIUM FROM AQUEOUS PHOSPHORIC ACID LIQUORS

    DOEpatents

    Schmitt, J.M.

    1962-09-01

    A liquid-liquid extraction method is given for recovering uranium values from aqueous solutions. An acidic aqueous solution containing uranium values is contacted with an organic phase comprising an organic diluent and the reaction product of phosphorous pentoxide and a substantially pure dialkylphosphoric acid. The uranium values are transferred to the organic phase even from aqueous solutions containing a high concentration of strong uranium complexing agents such as phosphate ions. (AEC)

  3. SOLVENT EXTRACTION OF THORIUM VALUES FROM AQUEOUS SOLUTIONS

    DOEpatents

    Warf, J.C.

    1959-04-21

    The separation of thorium values from rare earth metals contained ln aqueous solutions by means of extraction with a water immiscible alkyl phosphate diluted with a hydrocarbon such as hexane is described. While the extraction according to this invention may be carried out from any aqueous salt solution, it is preferred to use solutions containing free mineral acid. Hydrochloric acid and in particular nitric acid are sultable in a concentration ranging from 0.1 to 7 normal. The higher acid concentration results in higher extraction values.

  4. Solubilities and Glass Formation in Aqueous Solutions of the Sodium Salts of Malonic Acid With and Without Ammonium Sulfate.

    PubMed

    Kissinger, Jared A; Buttke, Lukas G; Vinokur, Anastasiya I; Guzei, Ilia A; Beyer, Keith D

    2016-06-02

    The solubility of sodium hydrogen malonate and sodium malonate in water both with and without ammonium sulfate present has been studied using differential scanning calorimetry and infrared spectroscopy. The crystals that form from sodium hydrogen malonate/water solutions were determined to be sodium hydrogen malonate monohydrate by single-crystal X-ray diffractometry. The crystals formed in sodium malonate/water solutions were determined to be sodium malonate monohydrate, a compound whose structure had not been previously known. When ammonium sulfate is added to these respective aqueous systems, the precipitation solids contain sodium sulfate decahydrate under low to moderate ammonium concentrations and lecontite (NaNH4SO4·2H2O) under high ammonium concentrations, which can be found under dry atmospheric conditions. Thus, it appears the presence of malonate and hydrogen malonate ions does not significantly affect the precipitation of inorganic salts in these systems. The glass transition temperatures of all solutions were also determined, and it was observed that the addition of ammonium sulfate slightly lowers the glass transition temperature in these solutions.

  5. Selected ion flow tube mass spectrometry of 3-hydroxybutyric acid, acetone and other ketones in the headspace of aqueous solution and urine

    NASA Astrophysics Data System (ADS)

    Wang, Tianshu; Spanel, Patrik; Smith, David

    2008-04-01

    A study has been carried out of the reactions of three isomers of hydroxybutyric acid, giving special attention to 3-hydroxybutyric acid, 3-HBA, with H3O+ and NO+ ions to acquire the required kinetic data for a selected ion flow tube mass spectrometry, SIFT-MS, search for 3-HBA in the headspace of urine since it is known to be one of the "ketone bodies" important in the diagnosis of ketoacidosis. Thus, the product ions formed in the reactions of the H3O+ and NO+ precursor ions with the three hydroxy acids were established by sampling the headspace above the pure compounds over a range of absolute humidities from 1.5% (ambient air) to 6% (liquid headspace at 37 C and exhaled breath). Then these data, together with the rate coefficients for the reactions estimated by calculation, were used to detect and quantify 3-HBA in the headspace of an aqueous solution of this compound of known concentration and above urine donated by two volunteers. The level of 3-HBA above the urine samples after they were acidified with hydrochloric acid was seen to be typically 40 parts-per-billion, ppb, which is much lower than that for acetone seen to be typically 800 ppb. Exploiting the aqueous solution data as a reference, the 3-HBA concentration in the urine samples was estimated to be about 1-2 mmol/L, which is typical of the urine from healthy individuals.

  6. Comparison of the influence of polyaspartic acid and polylysine functional groups on the adsorption at the Cr2O3-Aqueous polymer solution interface

    NASA Astrophysics Data System (ADS)

    Ostolska, Iwona; Wiśniewska, Małgorzata

    2014-08-01

    Polyamino acids are a group of synthesized polymers obtained by polymerization of a given kind of amino acid monomer. Because of high biodegradability of this class of polymers, they can be used as flocculation or stabilization agents in the environmental aspects. Therefore determination of their influence on the stability of the aqueous suspension of metal oxides is important. An influence of different functional groups of polyamino acids, their molecular weight and concentration on the adsorption at the chromium (III) oxide (Cr2O3)-aqueous solution interface was determined. Experiments were carried out for four values of solution pH varying from 3 to 10 (3, 4, 7.6 and 10, respectively). Two polymers were used: anionic polyaspartic acid (ASP) of 6800 and 27,000 as well as polylysine (LYS) of 4900 and 33,000 molecular weights. Changes of surface charge density of colloidal Cr2O3 in the presence and in the absence of macromolecular substances were determined using potentiometric titration. In these studies the influence of the concentration and molecular weight of the ionic polymers on the pHpzc value was determined. Additionally, due to the lack of appropriate literature data, potentiometric titration of the selected polymers was performed to determine pKa values.

  7. Sorption of carboxylic acid from carboxylic salt solutions at pHs close to or above the pK[sub a] of the acid, with regeneration with an aqueous solution of ammonia or low-molecular-weight alkylamine

    DOEpatents

    King, C.J.; Tung, L.A.

    1992-07-21

    Carboxylic acids are sorbed from aqueous feedstocks at pHs close to or above the acids' pH[sub a] into a strongly basic organic liquid phase or onto a basic solid adsorbent or moderately basic ion exchange resin. The acids are freed from the sorbent phase by treating it with aqueous alkylamine or ammonia thus forming an alkylammonium or ammonium carboxylate which dewatered and decomposed to the desired carboxylic acid and the alkylamine or ammonia. 8 figs.

  8. Sorption of carboxylic acid from carboxylic salt solutions at PHS close to or above the pK.sub.a of the acid, with regeneration with an aqueous solution of ammonia or low-molecular-weight alkylamine

    DOEpatents

    King, C. Judson; Tung, Lisa A.

    1992-01-01

    Carboxylic acids are sorbed from aqueous feedstocks at pHs close to or above the acids' pH.sub.a into a strongly basic organic liquid phase or onto a basic solid adsorbent or moderately basic ion exchange resin. the acids are freed from the sorbent phase by treating it with aqueous alkylamine or ammonia thus forming an alkylammonium or ammonium carobxylate which dewatered and decomposed to the desired carboxylic acid and the alkylamine or ammonia.

  9. Interactions of L-Aspartic Acid with Aqueous Solution of 1,2-Propanediol at Different Temperatures: A Volumetric, Compressibility and Viscometric Approach.

    PubMed

    Rani, Ruby; Kumar, Ashwani; Sharma, Tanu; Saini, Balwinder; Bamezai, Rajinder Kumar

    2016-01-01

    The volumetric, acoustic and viscometric methods are used for investigating the interactions of L-aspartic acid (Asp) in aqueous solution of 1,2-propanediol (PD) over a temperature of (298.15, 303.15 and 308.15) K at atmospheric pressure. Using the experimental results, the apparent molar volume, Vφ, limiting apparent molar volume, V0φ, the slope, Sv, and partial molar volume of transfer, V0φ,tr, have been calculated from density data. The apparent molar isentropic compressibility, K φ,s, limiting apparent molar isentropic compressibility, K0φ,s, its slope, Sk, and partial molar compressibility of transfer, K0φ,s, tr, have been calculated from speed of sound data. These values are also used for calculating the number of water molecules hydrated, nH, to the Asp. The viscosity data has also been used to determine relative viscosity ηr, viscosity B-coefficients, temperature derivative of B-coefficients, dB/dT and viscosity B-coefficients of transfer, Btr. The calculated parameters have been discussed in terms of various solute-solute and solute-solvent interactions prevailing in these solutions. Further, a detailed insight into the physicochemical interactions between Asp and aqueous PD, e.g., ion-hydrophilic and hydrophilic-hydrophilic interactions along with the structure-making tendency have been retrieved through the perusal of these calculated parameters.

  10. Chemical Composition and Properties of the Liquid-Vapor Interface of Aqueous C1 to C4 Monofunctional Acid and Alcohol Solutions.

    PubMed

    Lee, Ming-Tao; Orlando, Fabrizio; Artiglia, Luca; Chen, Shuzhen; Ammann, Markus

    2016-12-15

    The liquid-vapor interface is playing an important role in aerosol and cloud chemistry in cloud droplet activation by aerosol particles and potentially also in ice nucleation. We have employed the surface sensitive and chemically selective X-ray photoelectron spectroscopy (XPS) technique to examine the liquid-vapor interface for mixtures of water and small alcohols or small carboxylic acids (C1 to C4), abundant chemicals in the atmosphere in concentration ranges relevant for cloud chemistry or aerosol particles at the point of activation into a cloud droplet. A linear correlation was found between the headgroup carbon 1s core-level signal intensity and the surface excess derived from literature surface tension data with the offset being explained by the bulk contribution to the photoemission signal. The relative interfacial enhancement of the carboxylic acids over the carboxylates at the same bulk concentration was found to be highest (nearly 20) for propionic acid/propionate and still about 5 for formic acid/formate, also in fair agreement with surface tension measurements. This provides direct spectroscopic evidence for high carboxylic acid concentrations at aqueous solution-air interfaces that may be responsible for acid catalyzed chemistry under moderately acidic conditions with respect to their bulk aqueous phase acidity constant. By assessing the ratio of aliphatic to headgroup C 1s signal intensities XPS also provides information about the orientation of the molecules. The results indicate an increasing orientation of alcohols and neutral acids toward the surface normal as a function of chain length, along with increasing importance of lateral hydrophobic interactions at higher surface coverage. In turn, the carboxylate ions exhibit stronger orientation toward the surface normal than the corresponding neutral acids, likely caused by the stronger hydration of the charged headgroup.

  11. Calcium Binding to Amino Acids and Small Glycine Peptides in Aqueous Solution: Toward Peptide Design for Better Calcium Bioavailability.

    PubMed

    Tang, Ning; Skibsted, Leif H

    2016-06-01

    Deprotonation of amino acids as occurs during transfer from stomach to intestines during food digestion was found by comparison of complex formation constants as determined electrochemically for increasing pH to increase calcium binding (i) by a factor of around 6 for the neutral amino acids, (ii) by a factor of around 4 for anions of the acidic amino acids aspartic and glutamic acid, and (iii) by a factor of around 5.5 for basic amino acids. Optimized structures of the 1:1 complexes and ΔHbinding for calcium binding as calculated by density functional theory (DFT) confirmed in all complexes a stronger calcium binding and shorter calcium-oxygen bond length in the deprotonated form. In addition, the stronger calcium binding was also accompanied by a binding site shift from carboxylate binding to chelation by α-amino group and carboxylate oxygen for leucine, aspartate, glutamate, alanine, and asparagine. For binary amino acid mixtures, the calcium-binding constant was close to the predicted geometric mean of the individual amino acid binding constants indicating separate binding of calcium to two amino acids when present together in solution. At high pH, corresponding to conditions for calcium absorption, the binding affinity increased in the order Lys < Arg < Cys < Gln < Gly ∼ Ala < Asn < His < Leu < Glu< Asp. In a series of glycine peptides, calcium-binding affinity was found to increase in the order Gly-Leu ∼ Gly-Gly < Ala-Gly < Gly-His ∼ Gly-Lys-Gly < Glu-Cys-Gly < Gly-Glu, an ordering confirmed by DFT calculations for the dipeptides and which also accounted for large synergistic effects in calcium binding for up to 6 kJ/mol when compared to the corresponding amino acid mixtures.

  12. Thermodynamics of the dissociation of aminomethanesulfonic acid and its N-substituted derivatives in aqueous solutions at 293-313 K

    NASA Astrophysics Data System (ADS)

    Khoma, R. E.

    2017-01-01

    Δ G, Δ H, and Δ S of the second dissociation step of aminomethanesulfonic acid and its N-methyl, N-hydroxyethyl, N-( tert-butyl), N-benzyl derivatives in aqueous solutions (at the isoelectric point where the ionic strength is 4.75 × 10-4 M) are determined on basis of pH measurements at 293-313 K. It is found that an increase of the electron-acceptor properties of the substituents at nitrogen atom reduces the effect temperature has on the thermodynamic functions of dissociation. Enthalpy-enthropy compensation at an isothermodynamic temperature of 303 K is recorded.

  13. Benign methodology and improved synthesis of 5-(2-chloroquinolin-3-yl)-3-phenyl-4,5-dihydroisoxazoline using acetic acid aqueous solution under ultrasound irradiation.

    PubMed

    Tiwari, Vandana; Parvez, Ali; Meshram, Jyotsna

    2011-09-01

    In the present paper, we have executed the synthesis of substituted 5-(2-chloroquinolin-3-yl)-3-phenyl-4,5-dihydroisoxazolines via the reactions of substituted 3-(2-chloroquinolin-3-yl)-1-phenylprop-2-en-1-ones with hydroxylamine hydrochloride and sodium acetate in aqueous acetic acid solution in 72-90% yields at room temperature under ultrasound irradiation. This method provides several advantages such as operational simplicity, higher yield, safety and environment friendly protocol. The resulting substituted isoxazolines were characterized on the basis of (1)H NMR, (13)C NMR, IR, elemental analysis, and mass spectral data. Copyright © 2010 Elsevier B.V. All rights reserved.

  14. Bisphenol-A modified hyper-cross-linked polystyrene resin for salicylic acid removal from aqueous solution: adsorption equilibrium, kinetics and breakthrough studies.

    PubMed

    Hu, Huanxiao; Wang, Xiaomei; Li, Shengyong; Huang, Jianhan; Deng, Shuguang

    2012-04-15

    In this study, a series of bisphenol-A modified hyper-cross-linked polystyrene resins labeled as HJ-L00, HJ-L02, HJ-L04, HJ-L06 and HJ-L08 were synthesized, characterized and evaluated for adsorptive removal of salicylic acid from aqueous solutions. The structural characterization results indicated that the resins possessed predominant micropores/mesopores, moderate specific surface area and a few bisphenol-A groups on the surface. All the bisphenol-A modified hyper-cross-linked resins were effective for removing salicylic acid from aqueous solutions, and sample HJ-L02 had the largest adsorption capacity. The adsorption equilibrium data were correlated by the Freundlich isotherm model, and a positive adsorption enthalpy was obtained. The kinetic data were analyzed with two diffusion models and indicated that the intra-particle diffusion was the sole rate-controlling step in the first stage. The dynamic experimental results showed that the breakthrough point of the HJ-L02 adsorbent was at 90.2 BV (bed volume, 1 BV=10 mL) for a feed concentration of 500.0mg/L of salicylic acid, and 14.0 BV of 1% of sodium hydroxide could completely regenerate the HJ-L02 adsorbent column.

  15. Study of diatoms/aqueous solution interface. I. Acid-base equilibria and spectroscopic observation of freshwater and marine species

    NASA Astrophysics Data System (ADS)

    Gélabert, A.; Pokrovsky, O. S.; Schott, J.; Boudou, A.; Feurtet-Mazel, A.; Mielczarski, J.; Mielczarski, E.; Mesmer-Dudons, N.; Spalla, O.

    2004-10-01

    This work reports on a concerted study of diatom-water interfaces for two marine planktonic ( Thalassiosira weissflogii= TW, Skeletonema costatum= SC) and two freshwater periphytic species ( Achnanthidium minutissimum= AMIN, Navicula minima= NMIN). Proton surface adsorption was measured at 25°C, pH of 3 to 11 and ionic strength of 0.001 to 1.0 M via potentiometric titration using a limited residence time reactor. Electrophoretic mobility of living cells and their frustules was measured as a function of pH and ionic strength. Information on the chemical composition and molecular structure of diatoms surfaces was obtained using FT-IR (in situ attenuated total reflectance) and X-ray Photoelectron Spectroscopy (XPS). The surface area of living cells and their frustules in aqueous solutions was quantified using Small Angle X-ray Scattering Spectroscopy (SAXS). These observations allowed us to identify the nature and to determine the concentration of the major surface functional groups (carboxyl, amine and silanol) responsible for the amphoteric behavior of cell surfaces in aqueous solutions. Taking into account the relative proportion of surface sites inferred from XPS and FT-IR measurements, a surface complexation model of diatom-solution interfaces was generated on the basis of surface titration results. The cell-normalized ratios of the three major surface sites {>COOH}: {>NH 3}: {>SiOH} are 1:1:0.1, 1:10:0, 1:1:0.4 and 1:1:0.3 for TW, SC, AMIN and NMIN, respectively. The total amount of proton/hydroxyl active surface sites for investigated species ranges from 1 (NMIN) to 9 (SC) mmol/g dry weight. Normalization of these site densities to the area of siliceous skeleton yields values between 0.3 (NMIN) and 0.9 mmol/m 2 (SC) which are an order of magnitude higher than corresponding values for organic-free frustules or amorphous silica. This suggests that the amphoteric properties and possibly the affinity for metal adsorption of diatom cultures are essentially

  16. Photochemistry of aqueous pyruvic acid

    PubMed Central

    Griffith, Elizabeth C.; Carpenter, Barry K.; Shoemaker, Richard K.; Vaida, Veronica

    2013-01-01

    The study of organic chemistry in atmospheric aerosols and cloud formation is of interest in predictions of air quality and climate change. It is now known that aqueous phase chemistry is important in the formation of secondary organic aerosols. Here, the photoreactivity of pyruvic acid (PA; CH3COCOOH) is investigated in aqueous environments characteristic of atmospheric aerosols. PA is currently used as a proxy for α-dicarbonyls in atmospheric models and is abundant in both the gas phase and the aqueous phase (atmospheric aerosols, fog, and clouds) in the atmosphere. The photoreactivity of PA in these phases, however, is very different, thus prompting the need for a mechanistic understanding of its reactivity in different environments. Although the decarboxylation of aqueous phase PA through UV excitation has been studied for many years, its mechanism and products remain controversial. In this work, photolysis of aqueous PA is shown to produce acetoin (CH3CHOHCOCH3), lactic acid (CH3CHOHCOOH), acetic acid (CH3COOH), and oligomers, illustrating the progression from a three-carbon molecule to four-carbon and even six-carbon molecules through direct photolysis. These products are detected using vibrational and electronic spectroscopy, NMR, and MS, and a reaction mechanism is presented accounting for all products detected. The relevance of sunlight-initiated PA chemistry in aqueous environments is then discussed in the context of processes occurring on atmospheric aerosols. PMID:23821751

  17. Photochemistry of aqueous pyruvic acid.

    PubMed

    Griffith, Elizabeth C; Carpenter, Barry K; Shoemaker, Richard K; Vaida, Veronica

    2013-07-16

    The study of organic chemistry in atmospheric aerosols and cloud formation is of interest in predictions of air quality and climate change. It is now known that aqueous phase chemistry is important in the formation of secondary organic aerosols. Here, the photoreactivity of pyruvic acid (PA; CH3COCOOH) is investigated in aqueous environments characteristic of atmospheric aerosols. PA is currently used as a proxy for α-dicarbonyls in atmospheric models and is abundant in both the gas phase and the aqueous phase (atmospheric aerosols, fog, and clouds) in the atmosphere. The photoreactivity of PA in these phases, however, is very different, thus prompting the need for a mechanistic understanding of its reactivity in different environments. Although the decarboxylation of aqueous phase PA through UV excitation has been studied for many years, its mechanism and products remain controversial. In this work, photolysis of aqueous PA is shown to produce acetoin (CH3CHOHCOCH3), lactic acid (CH3CHOHCOOH), acetic acid (CH3COOH), and oligomers, illustrating the progression from a three-carbon molecule to four-carbon and even six-carbon molecules through direct photolysis. These products are detected using vibrational and electronic spectroscopy, NMR, and MS, and a reaction mechanism is presented accounting for all products detected. The relevance of sunlight-initiated PA chemistry in aqueous environments is then discussed in the context of processes occurring on atmospheric aerosols.

  18. GC/MS method for determining carbon isotope enrichment and concentration of underivatized short-chain fatty acids by direct aqueous solution injection of biogas digester samples.

    PubMed

    Mulat, Daniel Girma; Feilberg, Anders

    2015-10-01

    In anaerobic digestion of organic matter, several metabolic pathways are involved during the simultaneous production and consumption of short-chain fatty acids (SCFA) in general and acetate in particular. Understanding the role of each pathway requires both the determination of the concentration and isotope enrichment of intermediates in conjunction with isotope labeled substrates. The objective of this study was to establish a rapid and simple GC/MS method for determining the isotope enrichment of acetate and concentration of underivatized short-chain fatty acids (SCFA) in biogas digester samples by direct liquid injection of acidified aqueous samples. Sample preparation involves only acidification, centrifugation and filtration of the aqueous solution followed by direct injection of the aqueous supernatant solution onto a polar column. With the sample preparation and GC/MS conditions employed, well-resolved and sharp peaks of underivatized SCFA were obtained in a reasonably short time. Good recovery (96.6-102.3%) as well as low detection (4-7 µmol/L) and quantification limits (14-22 µmol/L) were obtained for all the 6 SCFA studied. Good linearity was achieved for both concentration and isotope enrichment measurement with regression coefficients higher than 0.9978 and 0.9996, respectively. The method has a good intra- and inter-day precision with a relative standard deviation (RSD) below 6% for determining the tracer-to-tracee ratio (TTR) of both [2-(13)C]acetate and [U-(13)C]acetate. It has also a good intra- and inter-day precision with a RSD below 6% and 5% for determining the concentration of standard solution and biogas digester samples, respectively. Acidification of biogas digester samples with oxalic acid provided the low pH required for the protonation of SCFA and thus, allows the extraction of SCFA from the complex sample matrix. Moreover, oxalic acid was the source of formic acid which was produced in the injector set at high temperature. The produced

  19. SEPARATION OF RUTHENIUM FROM AQUEOUS SOLUTIONS

    DOEpatents

    Beederman, M.; Vogler, S.; Hyman, H.H.

    1959-07-14

    The separation of rathenium from a rathenium containing aqueous solution is described. The separation is accomplished by adding sodium nitrite, silver nitrate and ozone to the ruthenium containing aqueous solution to form ruthenium tetroxide and ihen volatilizing off the ruthenium tetroxide.

  20. ENGINEERING BULLETIN: AIR STRIPPING OF AQUEOUS SOLUTIONS

    EPA Science Inventory

    Air striding is a means to transfer contaminants from aqueous solutions to air. ontaminants are not destroyed by air stripping but are physically separated from the aqueous solutions. ontaminant vapors are transferred into the air stream and, if necessary, can be treated by incin...

  1. ENGINEERING BULLETIN: AIR STRIPPING OF AQUEOUS SOLUTIONS

    EPA Science Inventory

    Air striding is a means to transfer contaminants from aqueous solutions to air. ontaminants are not destroyed by air stripping but are physically separated from the aqueous solutions. ontaminant vapors are transferred into the air stream and, if necessary, can be treated by incin...

  2. Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions.

    PubMed

    Dávila-Jiménez, Martín M; Elizalde-González, María P; Hernández-Montoya, Virginia

    2009-12-01

    In this study the husk of mango seed and two carbonaceous adsorbents prepared from it were used to study the adsorption behavior of eight acid dyes. The adsorbed amount in mmol m(-2) decayed asymptotically as the molecular volume and area increased. The interaction between the studied dyes and the mesoporous carbon was governed by the ionic species in solution and the acidic/basic groups on the surface. Less than 50% of the external surface of the microporous carbon became covered with the dyes molecules, though monolayer formation demonstrating specific interactions only with active sites on the surface and the adsorption magnitudes correlated with the shape parameter of the molecule within a particular dye group. The adsorption behavior in mixtures was determined by the molecular volume of the constituents; the greater the molecular volume difference, the greater the effect on the adsorbed amount. We also demonstrated that the raw husk of the mango seed can be used to remove up to 50% from model 50 mg l(-1) solutions of the studied acid dyes.

  3. Stability of cefozopran hydrochloride in aqueous solutions.

    PubMed

    Zalewski, Przemysław; Skibiński, Robert; Paczkowska, Magdalena; Garbacki, Piotr; Talaczyńska, Alicja; Cielecka-Piontek, Judyta; Jelińska, Anna

    2016-01-01

    The influence of pH on the stability of cefozopran hydrochloride (CZH) was investigated in the pH range of 0.44-13.00. Six degradation products were identified with a hybrid ESI-Q-TOF mass spectrometer. The degradation of CZH as a result of hydrolysis was a pseudo-first-order reaction. As general acid-base hydrolysis of CZH was not occurred in the solutions of hydrochloric acid, sodium hydroxide, acetate, borate and phosphate buffers, kobs = kpH because specific acid-base catalysis was observed. Specific acid-base catalysis of CZH consisted of the following reactions: hydrolysis of CZH catalyzed by hydrogen ions (kH+), hydrolysis of dications (k1H2O), monocations (k2H2O) and zwitter ions (k3H2O) and hydrolysis of zwitter ions (k1OH-) and monoanions (k2OH-) of CZH catalyzed by hydroxide ions. The total rate of the reaction was equal to the sum of partial reactions: [Formula: see text]. CZH similarly like other fourth generation cephalosporin was most stable at slightly acidic and neutral pH and less stable in alkaline pH. The cleavage of the β-lactam ring resulting from a nucleophilic attack on the carbonyl carbon in the β-lactam moiety is the preferred degradation pathway of β-lactam antibiotics in aqueous solutions.

  4. Acid titrations of poly(dG-dC).poly(dG-dC) in aqueous solution and in a w/o microemulsion.

    PubMed

    Airoldi, Marta; Boicelli, C Andrea; Gennaro, Guiseppe; Giomini, Marcello; Giuliani, Anna Maria; Giustini, Mauro

    2006-02-01

    The model polynucleotide poly(dG-dC).poly(dG-dC) (polyGC) was titrated with a strong acid (HCl) in aqueous unbuffered solutions and in the quaternary w/o microemulsion CTAB/n-pentanol/n-hexane/water. The titrations, performed at several concentrations of NaCl in the range 0.005 to 0.600 M, were followed by recording the modifications of the electronic absorption and of the CD spectra (210< or = lambda < or =350 nm) upon addition of the acid. In solution, the polynucleotide undergoes two acid-induced transitions, neither of which corresponds to denaturation of the duplex to single coil. The first transition leads to the Hoogsteen type synG.C+ duplex, while the second leads to the C+.C duplex. The initial B-form of polyGC was recovered by back-titration with NaOH. The apparent pKa values were obtained for both steps of the titration, at all salt concentrations. A reasonably linear dependence of pKa1 and pKa2 from p[NaCl] was obtained, with both pKa values decreasing with increasing ionic strength. In microemulsion, at salt concentrations < or = 0.300 M, an acid-induced transition was observed, matching the first conformational transition recorded also in solution. However, further addition of acid led to denaturation of the protonated duplex. Renaturation of polyGC was obtained by back-titration with NaOH. At salt concentrations > 0.300 M, polyGC is present as a mixture of B-form and psi- aggregates, that slowly separate from the microemulsion. The acid titration induces at first a conformational transition similar to the one observed at low salt or in solution, then denaturation occurs, which is however preceded by the appearance of a transient conformation, that has been tentatively classified as a left-handed Z double helix.

  5. Dissociative Binding of Carboxylic Acid Ligand on Nanoceria Surface in Aqueous Solution: A Joint in Situ Spectroscopic Characterization and First-Principles Study

    SciTech Connect

    Lu, Zhou; Karakoti, Ajay S.; Velarde Ruiz Esparza, Luis A.; Wang, Weina; Yang, Ping; Thevuthasan, Suntharampillai; Wang, Hongfei

    2013-11-21

    Carboxylic acid is a common ligand anchoring group to functionalize nanoparticle surfaces. Its binding structures and mechanisms as a function of the oxidation states of metal oxide nanoparticle surfaces are not well characterized experimentally. We present an in situ sum frequency generation vibrational spectroscopy (SFG-VS) study on the binding of deuterated acetic acid on ceria nanoparticles in the aqueous solution. In the SFG experiment, ceria nanoparticles were deposited on the flat surface of a CaF2 hemisphere in contact with acetic acid solutions. While the ceria nanoparticle deprotonated the acetic acid, the CaF2 surface could not. Thus, the binding of the deprotonated acetic acid on ceria can be selectively probed. SFG spectra revealed that the binding modes of the carboxylate group depend on the oxidation states of the ceria surfaces. SFG polarization analysis suggested that the bidentate chelating and bridging binding modes co-exist on the reduced ceria surfaces, while the oxidized ceria surfaces are dominated by the bidentate bridging mode. The direct spectroscopic evidence helps to clarify the binding structures and mechanisms on the ceria nanoparticles. Furthermore, the middle-infrared (IR) transparent CaF2 and its chemical inertness make CaF2 and similar substrate materials good candidates for direct SFG-VS measurement of nanoparticle surface reactions and binding chem-istry.

  6. Structural, optical and electrical properties of ZnTe thin films electrochemically deposited from a citric acid aqueous solution

    NASA Astrophysics Data System (ADS)

    Ishizaki, Takahiro; Ohtomo, Takeshi; Fuwa, Akio

    2004-01-01

    ZnTe thin films were electrodeposited onto Au-coated Cu substrates from an electrolytic solution containing ZnSO4, TeO2, citric acid and sodium citrate, and the dependence of structure, composition and surface morphology on the solution's Zn concentration were investigated. Results of examinations for resistivity and optical absorption demonstrated, respectively, that as the Zn concentration in the electrolyte was reduced over the range of 5-50 mmol dm-3, the resistivity of the films obtained continuously decreased and their band gap increased. Quantative analysis of energy dispersive x-ray analysis and inductively coupled plasma results indicated that the composition ratio (Zn : Te) was approximately stoichiometric under all conditions in this study. X-ray diffraction results revealed that all the ZnTe thin films obtained showed a preferred (111) orientation with cubic structure. ZnTe thin films we transferred onto nonconductive epoxy resin also showed the same structure.

  7. Bupivacaine salts of diflunisal and other aromatic hydroxycarboxylic acids: aqueous solubility and release characteristics from solutions and suspensions using a rotating dialysis cell model.

    PubMed

    Østergaard, Jesper; Larsen, Susan W; Parshad, Henrik; Larsen, Claus

    2005-11-01

    In the search for poorly soluble bupivacaine salts potentially enabling prolonged postoperative pain relief after local joint administration in the form of suspensions the solubility of bupivacaine salts of diflunisal and other aromatic hydroxycarboxylic acids were investigated together with the release characteristics of selected 1:1 salts from solutions and suspensions using a rotating dialysis cell model. The poorest soluble bupivacaine salts were obtained from the aromatic ortho-hydroxycarboxylic acids diflunisal, 5-iodosalicylic acid, and salicylic acid (aqueous solubilities: 0.6-1.9 mM at 37 degrees C). Diffusant appearance rates in the acceptor phase upon instillation of solutions of various salts in the donor cell applied to first-order kinetics. Calculated permeability coefficients for bupivacaine and the counterions diflunisal, 5-iodosalicylic acid, and mandelic acid were found to be correlated with the molecular size of the diffusants. Release experiments at physiological pH involving suspensions of the bupivacaine-diflunisal salt revealed that at each sampling point the diflunisal concentration exceeded that of bupivacaine in the acceptor phase. However, after an initial lag period, a steady state situation was attained resulting in equal and constant fluxes of the two diffusants controlled by the permeability coefficients in combination with the solubility product of the salt. Due to the fact that the saturation solubility of the bupivacaine-salicylic acid salt in water exceeded that of bupivacaine at pH 7.4, suspensions of the latter salt were unable to provide simultaneous release of the cationic and anionic species at pH 7.4. The release profiles were characterised by a rapid release of salicylate accompanied by a much slower appearance of bupivacaine in the acceptor phase caused by precipitation of bupivacaine base from the solution upon dissolution of the salt in the donor cell.

  8. Functionalized polymers for binding to solutes in aqueous solutions

    DOEpatents

    Smith, Barbara F.; Robison, Thomas W.

    2006-11-21

    A functionalized polymer for binding a dissolved molecule in an aqueous solution is presented. The polymer has a backbone polymer to which one or more functional groups are covalently linked. The backbone polymer can be such polymers as polyethylenimine, polyvinylamine, polyallylamine, and polypropylamine. These polymers are generally water-soluble, but can be insoluble when cross-linked. The functional group can be for example diol derivatives, polyol derivatives, thiol and dithiol derivatives, guest-host groups, affinity groups, beta-diphosphonic acids, and beta-diamides

  9. Terahertz absorption of dilute aqueous solutions.

    PubMed

    Heyden, Matthias; Tobias, Douglas J; Matyushov, Dmitry V

    2012-12-21

    Absorption of terahertz (THz) radiation by aqueous solutions of large solutes reports on the polarization response of their hydration shells. This is because the dipolar relaxation of the solute is dynamically frozen at these frequencies, and most of the solute-induced absorption changes, apart from the expulsion of water, are caused by interfacial water. We propose a model expressing the dipolar response of solutions in terms of a single parameter, the interface dipole moment induced in the interfacial water by electromagnetic radiation. We apply this concept to experimental THz absorption of hydrated sugars, amino acids, and proteins. None of the solutes studied here follow the expectations of dielectric theories, which predict a negative projection of the interface dipole on the external electric field. We find that this prediction is not able to describe the available experimental data, which instead suggests a nearly zero interface dipole for sugars and a more diverse pattern for amino acids. Hydrophobic amino acids, similarly to sugars, give rise to near zero interface dipoles, while strongly hydrophilic ones are best described by a positive projection of the interface dipole on the external field. The sign of the interface dipole is connected to the slope of the absorption coefficient with the solute concentration. A positive slope, implying an increase in the solution polarity relative to water, mirrors results frequently reported for protein solutions. We therefore use molecular dynamics simulations of hydrated glucose and lambda repressor protein to calculate the interface dipole moments of these solutes and the concentration dependence of the THz absorption. The absorption at THz frequencies increases with increasing solute concentration in both cases, implying a higher polarity of the solution compared to bulk water. The structure of the hydration layer, extracted from simulations, is qualitatively similar in both cases, with spatial correlations

  10. Metallacrowns of Ni(II) with α-aminohydroxamic acids in aqueous solution: beyond a 12-MC-4, an unexpected (vacant?) 15-MC-5.

    PubMed

    Bacco, Dimitri; Bertolasi, Valerio; Dallavalle, Francesco; Galliera, Lorenzo; Marchetti, Nicola; Marchiò, Luciano; Remelli, Maurizio; Tegoni, Matteo

    2011-03-21

    Growing attention has been devoted in the recent years to a class of metallamacrocycles known as metallacrowns (MCs). They are structural analogues of crown ethers where the methylene bridges have been substituted by coordinative bonds formed by a transition metal ion ("ring" metal) and a nitrogen atom. The cavity of the metallacrown can accommodate an additional metal ion ("core" metal) either identical or different from the ring metal, thus forming a homo- or hetero-metallic MC. The most studied ring metal ion is certainly Cu(2+) and the aminohydroxamic acids have proved to be very suitable ligands to form MCs. The behavioural analogies between Cu(2+) and Ni(2+) in forming complexes, along with recent literature data in the solid state, prompted us to investigate the possible MC formation between Ni(2+) and both (S)-α-alaninehydroxamic acid and (S)-valinehydroxamic acid, in aqueous solution. Two metallacrowns, a 12-MC-4 and an unexpected 15-MC-5 have been detected by potentiometry and confirmed by ESI-MS results. Their structures are discussed on the basis of potentiometric, calorimetric, spectroscopic data and DFT calculations. The existence of a vacant 15-MC-5 species in solution can be put forward for the first time, making the present metal/ligand systems very interesting for their potential applications in cation recognition and separation. Finally, the crystal structure of the binary complex K[NiL(2)H(-1)]·5/3 H(2)O of (S)-α-alaninehydroxamic acid (LH) is also reported.

  11. Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: effect of citric acid.

    PubMed

    Gan, Weibing; Liu, Qi

    2008-08-01

    Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca(2+) and Mg(2+) on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing 10(-3)mol/L of Ca(2+), Mg(2+) and Fe(3+) with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of 5 x 10(-4)mol/L citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of 10(-3)mol/L Ca(2+) and Mg(2+) cations at pH approximately 10, and at pH approximately 8 for Fe(3+). It was found that hydrolyzable metal cations enhanced bitumen-kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal-citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.

  12. Rapid degradation of p-arsanilic acid with simultaneous arsenic removal from aqueous solution using Fenton process.

    PubMed

    Xie, Xiande; Hu, Yuanan; Cheng, Hefa

    2016-02-01

    Although banned in some developed countries, p-arsanilic acid (p-ASA) is still used widely as a feed additive for swine production in many countries. With little uptake and transformation in animal bodies, nearly all the p-ASA administered to animals is excreted chemically unchanged in animal wastes, which can subsequently release the more toxic inorganic arsenic species upon degradation in the environment. For safe disposal of the animal wastes laden with p-ASA, we proposed a method of leaching the highly water-soluble p-ASA out of the manure first, followed by treatment of the leachate using the Fenton process to achieve fast oxidation of p-ASA and removal of the inorganic arsenic species released (predominantly arsenate) from solution simultaneously. The effects of solution pH, dosages of H2O2 and Fe(2+), and the presence of dissolved organic matter (DOM) on the treatment efficiency were systematically investigated. Under the optimum treatment conditions (0.53 mmol L(-1) Fe(2+), 2.12 mmol L(-1) H2O2, and initial pH of 3.0), p-ASA (10 mg-As L(-1)) could be completely oxidized to As(V) within 30 min in pure water and 4 natural water samples, and at the final pH of 4.0, the residual arsenic levels in solution phase were as low as 1.1 and 20.1-43.4 μg L(-1) in the two types of water matrixes, respectively. The presence of humic acid significantly retarded the oxidation of p-ASA by scavenging HO, and inhibited the As(V) removal through competitive adsorption on ferric hydroxide. Due to the high contents of DOM in the swine manure leachate samples (TOC at ∼500 mg L(-1)), much higher dosages of Fe(2+) (10.0 mmol L(-1)) and H2O2 (40.0 mmol L(-1)) and a longer treatment time (120 min) were required to achieve near complete oxidation of p-ASA (98.0%), while maintaining the levels of residual arsenic in the solution at <70.0 μg L(-1). The degradation pathway of p-ASA in the Fenton process was proposed based on the major degradation products detected

  13. Catalyzed reduction of nitrate in aqueous solutions

    SciTech Connect

    Haas, P.A.

    1994-08-01

    Sodium nitrate and other nitrate salts in wastes is a major source of difficulty for permanent disposal. Reduction of nitrate using aluminum metal has been demonstrated, but NH{sub 3}, hydrazine, or organic compounds containing oxygen would be advantageous for reduction of nitrate in sodium nitrate solutions. Objective of this seed money study was to determine minimum conditions for reduction. Proposed procedure was batchwise heating of aqueous solutions in closed vessels with monitoring of temperatures and pressures. A simple, convenient apparatus and procedure were demonstrated for observing formation of gaseous products and collecting samples for analyses. The test conditions were 250{degree}C and 1000 psi max. Any useful reduction of sodium nitrate to sodium hydroxide as the primary product was not found. The nitrate present at pHs < 4 as HNO{sub 3} or NH{sub 4}NO{sub 3} is easily decomposed, and the effect of nitromethane at these low pHs was confirmed. When acetic acid or formic acid was added, 21 to 56% of the nitrate in sodium nitrate solutions was reduced by methanol or formaldehyde. With hydrazine and acetic acid, 73 % of the nitrate was decomposed to convert NaNO{sub 3} to sodium acetate. With hydrazine and formic acid, 36% of the nitrate was decomposed. If these products are more acceptable for final disposal than sodium nitrate, the reagents are cheap and the conversion conditions would be practical for easy use. Ammonium acetate or formate salts did not significantly reduce nitrate in sodium nitrate solutions.

  14. REMOVAL OF CESIUM BY SORPTION FROM AQUEOUS SOLUTIONS

    DOEpatents

    Ames, L.L.

    1962-01-16

    ABS>A process is given for selectively removing cesium from acid aqueous solutions containing cesium in microquantities and other cations in macroquantities by absorption on clinoptilolite. The cesium can be eluted from the clinoptilolite with a solution of ammonia, potassium hydroxide, or rubidium hydroxide. (AEC)

  15. Thermodynamics of aqueous borate solutions I. Mixture of boric acid with sodium or potassium borate and chloride

    SciTech Connect

    Simonson, J.M.; Roy, R.N.; Roy, L.N.; Johnson, D.A.

    1987-10-01

    Potentials for the cell without liquid junction H/sub 2/, Ptlt. slashB(OH)/sub 3/(m/sub 1/),MB(OH)/sub 4/(m/sub 2/),MCl(m/sub 3/)lt. slashAgCl,Ag where M is sodium or potassium are reported over a range of ionic strength to I = 3 mol-kg/sup -1/ at 5 to 55/sup 0/C. Total boron concentration in the solutions was restricted to low levels to minimize formation of polynuclear boron species. Cell potentials are treated with the Pitzer ion interaction treatment for mixed electrolytes, with linear ionic strength dependence assumed for the activity coefficient of undissociated boric acid. Trace activity coefficients of sodium and potassium borates in chloride media are calculated at various temperatures.

  16. Structure of the complex of beta-cyclodextrin with beta-naphthyloxyacetic acid in the solid state and in aqueous solution.

    PubMed

    Kokkinou, A; Yannakopoulou, K; Mavridis, I M; Mentzafo, D

    2001-05-08

    The structure of the complex of beta-cyclodextrin (cyclomaltoheptaose) with beta-naphthyloxyacetic acid was studied in solid state by X-ray diffraction and in aqueous solution by 1H NMR spectroscopy. The complex crystallizes in the channel mode, space group C2, with a stoichiometry of 2:1; two beta-cyclodextrin molecules related by a twofold crystal axis form dimers, in the cavity of which one guest molecule is found on average. The above stoichiometry indicates one guest per beta-CD dimer statistically oriented over two positions or two guest molecules in pi-pi interactions in half of the beta-CD dimers and the rest of the beta-CD dimers empty. In addition, occupancy of 0.5 for the guest per every beta-CD dimer is in accord with the occupancy of the two disordered primary hydroxyls. These two hydroxyl groups, to which the carboxylic oxygen atoms of the guest are hydrogen bonded, point towards the interior of the beta-CD cavity. In aqueous solution, the 1H NMR spectroscopic study indicated that there is a mixture of complexes with host-guest stoichiometries both 1:1 and 2:1.

  17. Preparation of chitosan/poly(acrylic acid) magnetic composite microspheres and applications in the removal of copper(II) ions from aqueous solutions.

    PubMed

    Yan, Han; Yang, Lingyun; Yang, Zhen; Yang, Hu; Li, Aimin; Cheng, Rongshi

    2012-08-30

    In this current work, the magnetic composite microspheres (MCM), consisting of Fe(3)O(4) nanoparticles and poly(acrylic acid) (PAA) blended chitosan (CS), were prepared successfully by a simple method, co-precipitation of the compounds in alkaline solution. SEM, FTIR and TG techniques have been applied to investigate the structures of the MCM materials. The vibrating-sample magnetometer (VSM) measurement illustrated a paramagnetic property as well as a fast magnetic response, which indicated the significant separability of the MCM in the aqueous suspensions. Then, the MCM materials were employed as absorbents for removal of copper(II) (Cu(II)) ions from aqueous solutions. The fundamental adsorption behaviors of MCM were studied also. Experimental results revealed that the CS/PAA-MCM had greater adsorption capacity than CS-MCM, and PAA played an important role for the adsorption of Cu(II) ions. Moreover, the adsorption isotherms were all well described by the Langmuir model, while the adsorption kinetics followed the pseudo-second order equation. Furthermore, the adsorbent could be easily regenerated at lower pH and reused almost without any loss of adsorption capacity. On the contrary, the Cu(II) ions loaded CS-MCM and CS/PAA-MCM were stable enough at pH higher than 4.0, and both exhibited efficient phosphate removal with maximal uptakes around 63.0 and 108.0 mg Pg(-1), respectively. Copyright © 2012 Elsevier B.V. All rights reserved.

  18. Indian jujuba seed powder as an eco-friendly and a low-cost biosorbent for removal of acid blue 25 from aqueous solution.

    PubMed

    Krishna, L Sivarama; Reddy, A Sreenath; Zuhairi, W Y Wan; Taha, M R; Reddy, A Varada

    2014-01-01

    Indian jujuba seed powder (IJSP) has been investigated as a low-cost and an eco-friendly biosorbent, prepared for the removal of Acid Blue 25 (AB25) from aqueous solution. The prepared biomaterial was characterized by using FTIR and scanning electron microscopic studies. The effect of operation variables, such as IJSP dosage, contact time, concentration, pH, and temperature on the removal of AB25 was investigated, using batch biosorption technique. Removal efficiency increased with increase of IJSP dosage but decreased with increase of temperature. The equilibrium data were analyzed by the Langmuir and the Freundlich isotherm models. The data fitted well with the Langmuir model with a maximum biosorption capacity of 54.95 mg g(-1). The pseudo-second-order kinetics was the best for the biosorption of AB25 by IJSP, with good correlation. Thermodynamic parameters such as standard free energy change (ΔG(0)), standard enthalpy changes (ΔH(0)), and standard entropy changes (ΔS(0)) were analyzed. The removal of AB25 from aqueous solution by IJSP was a spontaneous and exothermic adsorption process. The results suggest that IJSP is a potential low-cost and an eco-friendly biosorbent for the AB25 removal from synthetic AB25 wastewater.

  19. Indian Jujuba Seed Powder as an Eco-Friendly and a Low-Cost Biosorbent for Removal of Acid Blue 25 from Aqueous Solution

    PubMed Central

    Krishna, L. Sivarama; Reddy, A. Sreenath; Zuhairi, W. Y. Wan; Taha, M. R.; Reddy, A. Varada

    2014-01-01

    Indian jujuba seed powder (IJSP) has been investigated as a low-cost and an eco-friendly biosorbent, prepared for the removal of Acid Blue 25 (AB25) from aqueous solution. The prepared biomaterial was characterized by using FTIR and scanning electron microscopic studies. The effect of operation variables, such as IJSP dosage, contact time, concentration, pH, and temperature on the removal of AB25 was investigated, using batch biosorption technique. Removal efficiency increased with increase of IJSP dosage but decreased with increase of temperature. The equilibrium data were analyzed by the Langmuir and the Freundlich isotherm models. The data fitted well with the Langmuir model with a maximum biosorption capacity of 54.95 mg g−1. The pseudo-second-order kinetics was the best for the biosorption of AB25 by IJSP, with good correlation. Thermodynamic parameters such as standard free energy change (ΔG0), standard enthalpy changes (ΔH0), and standard entropy changes (ΔS0) were analyzed. The removal of AB25 from aqueous solution by IJSP was a spontaneous and exothermic adsorption process. The results suggest that IJSP is a potential low-cost and an eco-friendly biosorbent for the AB25 removal from synthetic AB25 wastewater. PMID:25383360

  20. Removal of 2,4-dichlorophenoxyacetic acid in aqueous solution by pulsed corona discharge treatment: Effect of different water constituents, degradation pathway and toxicity assay.

    PubMed

    Singh, Raj Kamal; Philip, Ligy; Ramanujam, Sarathi

    2017-10-01

    A multiple pin-plane corona discharge reactor was used to generate plasma for the degradation of 2,4 dichlorophenoxyacetic acid (2,4-D) from the aqueous solution. The 2,4-D of concentration 1 mg/L was completely removed within 6 min of plasma treatment. Almost complete mineralization was achieved after the treatment time of 14 min for a 2,4-D concentration of 10 mg/L. Effects of different water constituents such as carbonates, nitrate, sulphate, chloride ions, natural organic matter (humic acids) and pH on 2,4-D degradation was studied. A significant antagonistic effect of carbonate and humic acid was observed, whereas, the effects of other ions were insignificant. A higher first order rate constant of 1.73 min(-1) was observed, which was significantly decreased in the presence of carbonate ions and humic acids. Also, a higher degradation of 2,4-D was observed in acidic pH conditions. Different 2,4-D intermediates were detected and the degradation pathway of 2,4-D in plasma treatment process was suggested. The toxicity of 10 mg/L 2,4-D was completely eradicated after 10 min of plasma treatment. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. Effects of reactive oxygen and nitrogen species induced by ammonium dinitramide decomposition in aqueous solutions of deoxyribose nucleic acid.

    PubMed

    Steel-Goodwin, L; Kuhlman, K J; Miller, C; Pace, M D; Carmichael, A J

    1997-01-01

    Ammonium dinitramide (ADN), a potential rocket fuel, decomposes in water forming NO2. The chemistry of this ADN-released NO2 in oxygenated biological systems is complex both in the number of potential chemical species and in the number of parallel and consecutive reactions that can theoretically occur. High-pressure liquid chromatography (HPLC) studies revealed ADN fragmented deoxyribose nucleic acid (DNA). Damage to DNA standard solutions was caused by at least two major pathways, one arising from reactions of NO2 with oxygen and one arising from a reaction with superoxide (O2-.). The radical species generated when ADN is incubated with standard solutions of DNA, pH 7.5, in the presence of the spin trap agent n-tert-butyl-alpha-nitrone (PBN) was compared with the PBN-radical adducts generated in the presence of ADN and O2-. or of ADN and hydrogen peroxide (H2O2). The ADN-induced PBN radical adducts increased linearly over the 90-minute study period. The values of peak intensity in the presence of O2-. and in the presence of H2O2, were 828% and 7.08%, respectively, of the ADN-induced radicals alone. The synergistic effect of ADN with O2- may provide an understanding of the sensitivity of the rat blastocyst to aDN at the preimplantation stage of development and the lack of toxicity in in vivo studies in tissues high in catalase.

  2. Photocatalytic discoloration of Acid Red 14 aqueous solution using titania nanoparticles immobilized on graphene oxide fabricated plate.

    PubMed

    Akerdi, Abdollah Gholami; Bahrami, S Hajir; Arami, Mokhtar; Pajootan, Elmira

    2016-09-01

    Textile industry consumes remarkable amounts of water during various operations. A significant portion of the water discharge to environment is in the form of colored contaminant. The present research reports the photocatalytic degradation of anionic dye effluent using immobilized TiO2 nanoparticle on graphene oxide (GO) fabricated carbon electrodes. Acid Red 14 (AR 14) was used as model compound. Graphene oxide nanosheets were synthesized from graphite powder using modified Hummer's method. The nanosheets were characterized with field emission scanning electron microscope (FESEM) images, X-ray diffraction (XRD) and FTIR spectrum. The GO nanoparticles were deposited on carbon electrode (GO-CE) by electrochemical deposition (ECD) method and used as catalyst bed. TiO2 nanoparticles were fixed on the bed (GO-CE- TiO2) with thermal process. Photocatalytic processes were carried out using a 500 ml solution containing dye in batch mode. Each photocatalytic treatment were carried out for 120 min. Effect of dye concentration (mg/L), pH of solution, time (min) and TiO2 content (g/L) on the photocatalytic decolorization was investigated. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Aqueous thermal degradation of gallic acid

    SciTech Connect

    Boles, J.S.; Crerar, D.A.; Grissom, G.; Key, T.C.

    1988-02-01

    Aqueous thermal degradation experiments show gallic acid, a naturally occurring aromatic carboxylic compound, decomposes rapidly at temperatures between 105/sup 0/ and 150/sup 0/C, with an activation energy of 22.9 or 27.8 kcal/mole, depending on pH of the starting solution. Pyrogallol is the primary product identified, indicating degradation via decarboxylation and a carbanion transition state. Relatively rapid degradation of vanillic, phthalic, ellagic and tannic acids has also been observed,suggesting that these and perhaps other aromatic acids could be short-lived in deep formation waters.

  4. Aqueous thermal degradation of gallic acid

    NASA Astrophysics Data System (ADS)

    Snow Boles, Jennifer; Crerar, David A.; Grissom, Grady; Key, Tonalee C.

    1988-02-01

    Aqueous thermal degradation experiments show gallic acid, a naturally occurring aromatic carboxylic compound, decomposes rapidly at temperatures between 105° and 150°C, with an activation energy of 22.9 or 27.8 kcal/ mole, depending on pH of the starting solution. Pyrogallol is the primary product identified, indicating degradation via decarboxylation and a carbanion transition state. Relatively rapid degradation of vanillic, phthalic, ellagic and tannic acids has also been observed, suggesting that these and perhaps other aromatic acids could be short-lived in deep formation waters.

  5. A single-stranded amphipathic alpha-helix in aqueous solution: design, structural characterization, and its application for determining alpha-helical propensities of amino acids.

    PubMed

    Zhou, N E; Kay, C M; Sykes, B D; Hodges, R S

    1993-06-22

    In order to investigate the positional effect of alpha-helical propensities of amino acids in an amphipathic alpha-helix, an amphipathic alpha-helical model peptide (Ac-Glu-Ala-Glu-Lys-Ala-Ala-Lys-Glu-Ala-Glu-Lys-Ala-Ala-Lys-Glu-Ala-Glu-Lys- amide) was designed and characterized by circular dichroism and 2D-NMR spectroscopies. This peptide contains 65% alpha-helical structure in solution, and its monomeric molecular weight in aqueous solution was determined by size-exclusion chromatography. The independence of alpha-helical structure and stability on peptide concentration demonstrates that helix formation of this peptide is a monomolecular process. To compare the effect of substitutions in the hydrophobic and hydrophilic face of the helix on structure and stability, a leucine, alanine, or glycine was individually substituted in the hydrophobic face (position 9) or hydrophilic face (position 7) of the model peptide. The change in helix content and stability upon substitution was measured by circular dichroism studies in the absence and presence of TFE or urea. The results indicate that each amino acid has a different helix propensity when it is located in the hydrophobic face versus hydrophilic face and the effect of substitution is more significant in the hydrophobic face. This single-stranded amphipathic alpha-helical peptide provides an appropriate model system to determine helix propensities of amino acids on both hydrophobic and hydrophilic faces.

  6. Adsorption of dyestuff from aqueous solutions through oxalic acid-modified swede rape straw: adsorption process and disposal methodology of depleted bioadsorbents.

    PubMed

    Feng, Yanfang; Dionysiou, Dionysios D; Wu, Yonghong; Zhou, Hui; Xue, Lihong; He, Shiying; Yang, Linzhang

    2013-06-01

    Swede rape straw (Brassica napus L.) was modified by oxalic acid under mild conditions producing an efficient dye adsorbent (SRSOA). This low-cost and environmental friendly bioadsorbent was characterized by various techniques and then applied to purify dye-contaminated aqueous solutions. Equilibrium study showed that the Langmuir model demonstrated the best fit to the equilibrium data and the methylene blue (MB) adsorption capacity calculated by this model was 432mgg(-1). The adsorption process and mechanism is also discussed. To properly deal with the dye-loaded bioadsorbents, the disposal methodology is discussed and a biochar based on depleted bioadsorbents was for the first time produced and examined. This method both solved the disposal problem of contaminant-loaded bioadsorbents and produced an useful adsorbent thereafter. The study indicates that SRSOA is a promising substitute for ACs in purifying dye-contaminated wastewater and that producing biochars from contaminant-loaded bioadsorbents maybe a feasible disposal method.

  7. Oxidation by-products and ecotoxicity assessment during the photodegradation of fenofibric acid in aqueous solution with UV and UV/H2O2.

    PubMed

    Santiago, Javier; Agüera, Ana; del Mar Gómez-Ramos, María; Fernández Alba, Amadeo R; García-Calvo, Eloy; Rosal, Roberto

    2011-10-30

    The degradation of an aqueous solution of fenofibric acid was investigated using ultraviolet (UV) photolysis and UV/H(2)O(2) with a low-pressure mercury lamp. We obtained quantum yields at different temperatures and the rate constant for the reaction of fenofibric acid with hydroxyl radicals. The maximum radical exposure per fluence ratio obtained was 1.4 × 10(-10)ML(-1)mW(-1). Several reaction intermediates were detected by means of exact mass measurements performed by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (LC-ESI-QTOF-MS). UV and UV/H(2)O(2) pathways involve the decarboxylation of fenofibric acid to 4-chloro-4'-(1-hydroxy-1-methylethyl)benzophenone and other minor products, predominantly chlorinated aromatics. We detected several intermediates from reactions with hydroxyl radicals and some lower molecular weight products from the scission of the carbonyl carbon-to-aromatic-carbon bond. We recorded high toxicity in UV irradiated samples for the growth of Pseudokirchneriella subcapitata even after the total depletion of fenofibric acid; this was probably due to the presence of chlorinated aromatics. A degree of toxicity reappeared in highly irradiated UV/H(2)O(2) samples, probably because of the formation of ring-opening products. The degree of mineralization was closely related to that of dechlorination and reached values of over 50% after 3-4 min before stabilizing thereafter. Copyright © 2011 Elsevier B.V. All rights reserved.

  8. Polar modified post-cross-linked resin and its adsorption toward salicylic acid from aqueous solution: Equilibrium, kinetics and breakthrough studies.

    PubMed

    Fu, Zhenyu; He, Chunlian; Huang, Jianhan; Liu, You-Nian

    2015-08-01

    A novel polar modified post-cross-linked resin PDMPA was synthesized, characterized and evaluated for adsorption of salicylic acid from aqueous solution. PDMPA was prepared by a suspension polymerization of methyl acrylate (MA) and divinylbenzene (DVB), a Friedel-Crafts reaction and an amination reaction. After characterization of the chemical and pore structure of PDMPA, the adsorption behaviors of salicylic acid on PDMPA were determined in comparison with the precursor resins. The equilibrium adsorption capacity of salicylic acid on PDMPA was much larger than the precursor resins and the equilibrium data were correlated by both of the Langmuir and Freundlich models. The pseudo-second-order rate equation fitted the kinetic data better than the pseudo-first-order rate equation, and the micropore diffusion model could characterize the kinetic data very well. The dynamic experimental results showed that the breakthrough point and saturated point of salicylic acid on PDMPA were 40.3 and 92.4BV (1BV=10mL) at a feed concentration of 995.8mg/L and a flow rate of 1.4mL/min, and the resin column could be regenerated by 16.0BV of a mixture desorption solvent containing 0.01mol/L of NaOH (w/v) and 50% of ethanol (v/v).

  9. Thermodynamic properties of potassium chloride aqueous solutions

    NASA Astrophysics Data System (ADS)

    Zezin, Denis; Driesner, Thomas

    2017-04-01

    Potassium chloride is a ubiquitous salt in natural fluids, being the second most abundant dissolved salt in many geological aqueous solutions after sodium chloride. It is a simple solute and strong electrolyte easily dissociating in water, however the thermodynamic properties of KCl aqueous solutions were never correlated with sufficient accuracy for a wide range of physicochemical conditions. In this communication we propose a set of parameters for a Pitzer-type model which allows calculation of all necessary thermodynamic properties of KCl solution, namely excess Gibbs free energy and derived activity coefficient, apparent molar enthalpy, heat capacity and volume, as well as osmotic coefficient and activity of water in solutions. The system KCl-water is one of the best studied aqueous systems containing electrolytes. Although extensive experimental data were collected for thermodynamic properties of these solutions over the years, the accurate volumetric data became available only recently, thus making possible a complete thermodynamic formulation including a pressure dependence of excess Gibbs free energy and derived properties of the KCl-water liquids. Our proposed model is intended for calculation of major thermodynamic properties of KCl aqueous solutions at temperatures ranging from freezing point of a solution to 623 K, pressures ranging from saturated water vapor up to 150 MPa, and concentrations up to the salt saturation. This parameterized model will be further implemented in geochemical software packages and can facilitate the calculation of aqueous equilibrium for reactive transport codes.

  10. Preparation and characterization of trihydroxamic acid functionalized carbon materials for the removal of Cu(II) ions from aqueous solution

    NASA Astrophysics Data System (ADS)

    Godino-Salido, M. Luz; Santiago-Medina, Antonio; López-Garzón, Rafael; Gutiérrez-Valero, María D.; Arranz-Mascarós, Paloma; López de la Torre, M. Dolores; Domingo-García, María; López-Garzón, F. Javier

    2016-11-01

    The main objective of this study is to prepare and characterize two functionalizated carbon materials with enhanced adsorptive properties for Cu(II). Thus, two novel hybrid materials have been prepared by a non-covalent functionalization method based on the adsorption of a pyrimidine-desferrioxamine-B conjugate compound (H4L) on two activated carbons, ACs (labelled Merck and F). The adsorption of H4L on the ACs is pH-dependent and highly irreversible. This is due to strong π-π interactions between the arene centers of the ACs and the pyrimidine moiety of H4L. The textural characterization of the AC/H4L hybrids shows large decreases of their surface areas. Thus the values of Merck and F are 1031 and 1426 m2/g respectively, while these of Merck/H4L and F/H4L hybrids are 200 and 322 m2/g. An important decrease in the micropore volumes is also found, due to the blockage of narrow porosity produced by the adsorption of H4L molecules. The ACs/H4L hybrids show larger adsorption capacities for Cu(II) (0.105(4) and 0.13(2) mmol/g, at pH 2.0, and 0.20(3) and 0.242(9) mmol/g, at pH 5.5, for Merck/H4L and F/H4L, respectively) than those of the ACs (0.024(6) and 0.096(9) mmol/g, at pH 2.0, and 0.10(2) and 0.177(8) mmol/g, at pH 5.5, for Merck and F respectively), which is explained on the basis of the complexing ability of the trihydroxamic acid functions. The desorption of Cu(II) from the ACs/H4L/Cu(II) materials in acid solution allows the regeneration of most active sites (78.5% in the case of Merck/H4L/Cu(II) and 83.0% in the case of F/H4L/Cu(II)).

  11. Process for decomposing nitrates in aqueous solution

    DOEpatents

    Haas, Paul A.

    1980-01-01

    This invention is a process for decomposing ammonium nitrate and/or selected metal nitrates in an aqueous solution at an elevated temperature and pressure. Where the compound to be decomposed is a metal nitrate (e.g., a nuclear-fuel metal nitrate), a hydroxylated organic reducing agent therefor is provided in the solution. In accordance with the invention, an effective proportion of both nitromethane and nitric acid is incorporated in the solution to accelerate decomposition of the ammonium nitrate and/or selected metal nitrate. As a result, decomposition can be effected at significantly lower temperatures and pressures, permitting the use of system components composed of off-the-shelf materials, such as stainless steel, rather than more costly materials of construction. Preferably, the process is conducted on a continuous basis. Fluid can be automatically vented from the reaction zone as required to maintain the operating temperature at a moderate value--e.g., at a value in the range of from about 130.degree.-200.degree. C.

  12. Decontamination of aqueous glyphosate, (aminomethyl)phosphonic acid, and glufosinate solutions by electro-fenton-like process with Mn2+ as the catalyst.

    PubMed

    Balci, Beytul; Oturan, Mehmet A; Oturan, Nihal; Sirés, Ignasi

    2009-06-10

    The ability of the modified electro-Fenton-like (EF-like) process to degrade aqueous solutions of glyphosate, which is the most widely used herbicide in the world, has been assessed with Mn(2+) and other metal ions as catalysts to overcome the problems posed by some stable metal ion complexes of phosphonate herbicides. Bulk electrolyses with a carbon-felt cathode and Pt anode were performed in an undivided cell under galvanostatic conditions to study the effect of the applied current as well as Mn(2+) and glyphosate concentrations. The herbicide was completely destroyed in all cases following a pseudofirst-order kinetics, and the second-order rate constant for its reaction with (*)OH was determined. The decay trends obtained by high-performance liquid chromatography-fluorometric detection (HPLC-FL) and ion chromatography analysis were similar. AMPA [(aminomethyl)phosphonic acid] was the major reaction intermediate and showed slower pseudofirst-order destruction kinetics. The high mineralization degree obtained for glyphosate solutions confirmed the great performance of the EF-like process with Mn(2+), which promotes the C-N cleavage by (*)OH attack as the first oxidation step and the C-P cleavage in a further step. High-level decontamination achieved for AMPA and glufosinate solutions corroborated the benefits of this oxidation process.

  13. Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: equilibrium, thermodynamic, kinetics, mechanism and process design.

    PubMed

    Dawood, Sara; Sen, Tushar Kanti

    2012-04-15

    Pine cone a natural, low-cost agricultural by-product in Australia has been studied for its potential application as an adsorbent in its raw and hydrochloric acid modified form. Surface study of pine cone and treated pine cone was investigated using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The modification process leads to increases in the specific surface area and decreases mean particle sizes of acid-treated pine cone when compared to raw pine cone biomass. Batch adsorption experiments were performed to remove anionic dye Congo red from aqueous solution. It was found that the extent of Congo red adsorption by both raw pine cone biomass and acid-treated biomass increased with initial dye concentration, contact time, temperature but decreased with increasing solution pH and amount of adsorbent of the system. Overall, kinetic studies showed that the dye adsorption process followed pseudo-second-order kinetics based on pseudo-first-order and intra-particle diffusion models. The different kinetic parameters including rate constant, half-adsorption time, and diffusion coefficient were determined at different physico-chemical conditions. Equilibrium data were best represented by Freundlich isotherm model among Langmuir and Freundlich adsorption isotherm models. It was observed that the adsorption was pH dependent and the maximum adsorption of 32.65 mg/g occurred at pH of 3.55 for an initial dye concentration of 20 ppm by raw pine cone, whereas for acid-treated pine cone the maximum adsorption of 40.19 mg/g for the same experimental conditions. Freundlich constant 'n' also indicated favourable adsorption. Thermodynamic parameters such as ∆G(0), ∆H(0), and ∆S(0) were calculated. A single-stage batch absorber design for the Congo red adsorption onto pine cone biomass also presented based on the Freundlich isotherm model equation.

  14. Kinetic and mechanism of the oxidation of chromium(III) complex with anthranil- N, N-diacetic acid by periodate ion in acidic aqueous solutions

    NASA Astrophysics Data System (ADS)

    Ali, Ismat H.

    2015-06-01

    The kinetics of oxidation of [CrIII(atda)(H2O)2] (atda = anthranil- N, N-diacetato) complex by IO{4/-} was studied spectrophotometrically in aqueous solutions with pH range 2.20-3.34, 0.30 M ionic strength and in 20.0-40.0°C temperature range. The rate law of the reaction exhibited saturation kinetics. Values of the rate constant for the electron transfer process, the equilibrium constant for dissociation of [CrIII (atda)(H2O)2] to [CrIII (atda) (H2O)OH]+ + H+ and the pre-equilibrium formation constant were calculated. The thermodynamic activation parameters are reported. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of the IVII to chromium(III).

  15. Kinetics of nitrobenzene hydrogenation on spongy nickel and catalyst with supported palladium in 2-propanol aqueous solutions with acid or base additives

    NASA Astrophysics Data System (ADS)

    Thu Ha, Nguen Thi; Latypova, A. R.; Efremov, E. V.; Lefedova, O. V.; Filippov, D. V.

    2017-04-01

    The effect acetic acid and sodium hydroxide additives in a 2-propanol aqueous solution of azeotrope composition have on the rate of nitrobenzene (NB) hydrogenation over spongy nickel and supported palladium catalysts is studied. Analysis of the experimental data indicates that adding acid slows the rate more than adding a base during NB hydrogenation on spongy nickel. The observed rate for spongy nickel falls in a series of solvents: 2-propanol-water (0.68 mole fraction) > 2-propanol-water (0.68 mole fraction) + NaOH (0.01M) > 2-propanol-water (0.68 mole fraction) + CH3COOH (0.01 M). When a palladium catalyst is used, the addition of acid has less of an effect on slowing the rate of the reaction than that of the base: 2-propanol-water (0.68 mole fraction) > 2-propanol-water (0.68 mole fraction) + CH3COOH (0.01 M) > 2-propanol-water (0.68 mole fraction) + NaOH (0.01 M).

  16. Spatial structure of heptapeptide Glu-Ile-Leu-Asn-His-Met-Lys, a fragment of the HIV enhancer prostatic acid phosphatase, in aqueous and SDS micelle solutions

    NASA Astrophysics Data System (ADS)

    Bloсhin, Dmitri S.; Aganova, Oksana V.; Yulmetov, Aidar R.; Filippov, Andrei V.; Gizatullin, Bulat I.; Afonin, Sergii; Antzutkin, Oleg N.; Klochkov, Vladimir V.

    2013-02-01

    Prostatic acid phosphatase (PAP) is a protein abundantly present in human seminal fluid. PAP plays important role in fertilization. Its 39-amino-acid fragment, PAP(248-286), is effective in enhancing infectivity of HIV virus. In this work, we determined the spatial structure in aqueous solution of a heptapeptide within the PAP fragment, containing amino acid residues 266-272 (Glu-Ile-Leu-Asn-His-Met-Lys). We also report the structure of the complex formed by this heptapeptide with sodium dodecyl sulfate micelles, a model of a biological membrane, as determined by 1H NMR spectroscopy and 2D NMR (TOCSY, HSQC-HECADE, NOESY) spectroscopy. Complex formation was confirmed by chemical shift alterations in the 1H NMR spectra of the heptapeptide, as well as by the signs and values of NOE effects. We also present a comparison of the spatial structure of Glu-Ile-Leu-Asn-His-Met-Lys in water and in complex with sodium dodecyl sulfate.

  17. An NMR and ab initio quantum chemical study of acid-base equilibria for conformationally constrained acidic alpha-amino acids in aqueous solution.

    PubMed

    Nielsen, P A; Jaroszewski, J W; Norrby, P O; Liljefors, T

    2001-03-07

    The protonation states of a series of piperidinedicarboxylic acids (PDAs), which are conformationally constrained acidic alpha-amino acids, have been studied by (13)C NMR titration in water. The resulting data have been correlated with theoretical results obtained by HF/6-31+G calculations using the polarizable continuum model (PCM) for the description of water. The PDAs are highly ionizable and contain one or two possible internal hydrogen bonds. In the present study, we show that the PCM model is able to reproduce the relative stabilities of the different protonation states of the PDAs. Furthermore, our results show that prediction of relative pK(a) values for two different types of ionizable functional groups covering a pK(a) range from 1.6 to 12.1 is possible with a high degree of accuracy.

  18. Radiolysis of aqueous solutions of thiamine

    NASA Astrophysics Data System (ADS)

    Chijate, C.; Albarran, G.; Negron-Mendoza, A.

    1998-06-01

    The results of the radiolysis of aqueous solutions of thiamine (vitamin B 1) are presented. The yields for decomposition of thiamine and the product of radiolytic products were determined. The G values decrease as the dose increases. Some radiolytic products were identified. Decomposition of thiamine was slightly dependent on the presence of oxygen and on the pH of the solution. At pH 4.4 with a concentration of 2.5 × 10 -4 mol L -1 of thiamine in an oxygen free aqueous solution, the G 0 value for decomposition is 5.0.

  19. Separation of metal ions from aqueous solutions

    DOEpatents

    Almon, Amy C.

    1994-01-01

    A process and apparatus for quantitatively and selectively separating metal ions from mixtures thereof in aqueous solution. The apparatus includes, in combination, a horizontal electrochemical flow cell containing flow bulk electrolyte solution and an aqueous, metal ion-containing solution, the cell containing a metal mesh working electrode, a counter electrode positioned downstream from the working electrode, an independent variable power supply/potentiostat positioned outside of the flow cell and connected to the electrodes, and optionally a detector such as a chromatographic detector, positioned outside the flow cell. This apparatus and its operation has significant application where trace amounts of metal ions are to be separated.

  20. Effect of ascorbic acid on the degradation of cyanocobalamin and hydroxocobalamin in aqueous solution: a kinetic study.

    PubMed

    Ahmad, Iqbal; Qadeer, Kiran; Zahid, Saima; Sheraz, Muhammad Ali; Ismail, Tehmina; Hussain, Waqar; Ansari, Izhar Ahmad

    2014-10-01

    The degradation kinetics of 5 × 10(-5) M cyanocobalamin (B12) and hydroxocobalamin (B12b) in the presence of ascorbic acid (AH2) was studied in the pH range of 1.0-8.0. B12 is degraded to B12b which undergoes oxidation to corrin ring cleavage products. B12b alone is directly oxidized to the ring cleavage products. B12 and B12b in degraded solutions were simultaneously assayed by a two-component spectrometric method at 525 and 550 nm without interference from AH2. Both degrade by first-order kinetics and the values of the rate constants at pH 1.0-8.0 range from 0.08 to 1.05 × 10(-5) s(-1) and 0.22-7.62 × 10(-5) s(-1), respectively, in the presence of 0.25 × 10(-3) M AH2. The t 1/2 values of B12 and B12b range from 13.7 to 137.5 h and 2.5-87.5 h, respectively. The second-order rate constants for the interaction of AH2 with B12 and B12b are 0.05-0.28 × 10(-2) and 1.10-30.08 × 10(-2) M(-1) s(-1), respectively, indicating a greater effect of AH2 on B12b compared to that of B12. The k obs-pH profiles for both B12 and B12b show the highest rates of degradation around pH 5. The degradation of B12 and B12b by AH2 is affected by the catalytic effect of phosphate ions on the oxidation of AH2 in the pH range 6.0-8.0.

  1. Multiple-path dissociation mechanism for mono- and dinuclear tris(hydroxamato)iron(III) complexes with dihydroxamic acid ligands in aqueous solution.

    PubMed

    Boukhalfa, H; Crumbliss, A L

    2000-09-18

    Linear synthetic dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln) with short (n = 2) and long (n = 8) hydrocarbon-connecting chains form mono- and dinuclear complexes with Fe(III) in aqueous solution. At conditions where the formation of Fe2(Ln)3 is favored, complexes with each of the two ligand systems undergo [H+]-induced ligand dissociation processes via multiple sequential and parallel paths, some of which are common and some of which are different for the two ligands. The pH jump induced ligand dissociation proceeds in two major stages (I and II) where each stage is shown to be comprised of multiple components (Ix, where x = 1-3 for L2 and L8, and IIy, where y = 1-3 for L2 and y = 1-4 for L8). A reaction scheme consistent with kinetic and independent ESI-MS data is proposed that includes the tris-chelated complexes (coordinated H2O omitted for clarity) (Fe2(Ln)3, Fe2(L2)2(L2H)2, Fe(LnH)3, Fe(L8)(L8H)), bis-chelated complexes (Fe2(Ln)2(2+), Fe(LnH)2+, Fe(L8)+), and monochelated complexes (Fe(LnH)2+). Analysis of kinetic data for ligand dissociation from Fe2(Ln)(LnH)3+ (n = 2, 4, 6, 8) allows us to estimate the dielectric constant at the reactive dinuclear Fe(III) site. The existence of multiple ligand dissociation paths for the dihydroxamic acid complexes of Fe(III) is a feature that distinguishes these systems from their bidentate monohydroxamic acid and hexadentate trihydroxamic acid counterparts and may be a reason for the biosynthesis of dihydroxamic acid siderophores, despite higher environmental molar concentrations necessary to completely chelate Fe(III).

  2. Oxidation of Purine Nucleotides by Triplet 3,3′,4,4′-Benzophenone Tetracarboxylic Acid in Aqueous Solution: pH-Dependence

    PubMed Central

    2014-01-01

    The photo-oxidation of purine nucleotides adenosine-5′-monophosphate (AMP) and guanosine-5′-monophosphate (GMP) by 3,3′,4,4′-benzophenone tetracarboxylic acid (TCBP) has been investigated in aqueous solutions using nanosecond laser flash photolysis (LFP) and time-resolved chemically induced dynamic nuclear polarization (CIDNP). The pH dependences of quenching rate constants and of geminate polarization are measured within a wide range of pH values. As a result, the chemical reactivity of reacting species in different protonation states is determined. In acidic solution (pH < 4.9), the quenching rate constant is close to the diffusion-controlled limit: kq = 1.3 × 109 M–1 s–1 (GMP), and kq = 1.2 × 109 M–1 s–1 (AMP), whereas in neutral and basic solutions it is significantly lower: kq = 2.6 × 108 M–1 s–1 (GMP, 4.9 < pH < 9.4), kq = 3.5 × 107 M–1 s–1 (GMP, pH > 9.4), kq = 1.0 × 108 M–1 s–1 (AMP, pH > 6.5). Surprisingly, the strong influence of the protonation state of the phosphoric group on the oxidation of adenosine-5′-monophosphate is revealed: the deprotonation of the AMP phosphoric group (6.5) decreases the quenching rate constant from 5.0 × 108 M–1 s–1 (4.9 < pH < 6.5) to 1.0 × 108 M–1 s–1 (pH > 6.5). PMID:24926567

  3. Probing the General Time Scale Question of Boronic Acid Binding with Sugars in Aqueous Solution at Physiological pH

    PubMed Central

    Ni, Nanting; Laughlin, Sarah; Wang, Yingji; Feng, You; Zheng, Yujun

    2012-01-01

    The boronic acid group is widely used in chemosensor design due to its ability to reversibly bind diol-containing compounds. The thermodynamic properties of the boronic acid-diol binding process have been investigated extensively. However, there are few studies of the kinetic properties of such binding processes. In this report, stopped-flow method was used for the first time to study the kinetic properties of the binding between three model arylboronic acids, 4-, 5-, and 8-isoquinolinylboronic acids, and various sugars. With all the boronic acid-diol pair sexamined, reactions were complete within seconds. The kon values with various sugars follow the order of D-fructose >D-tagatose>D-mannose >D-glucose. This trend tracks the thermodynamic binding affinities for these sugars and demonstrates that the “on” rate is the key factor determining the binding constant. PMID:22464680

  4. Degradation of the herbicide 2, 4-dichlorophenoxyacetic acid (2,4-D) dimethylamine salt by gamma radiation from cobalt-60 in aqueous solution containing humic acid

    NASA Astrophysics Data System (ADS)

    Campos, Sandro X.; Vieira, Eny M.; Cordeiro, Paulo J. M.; Rodrigues-Fo, Edson; Murgu, Michael

    2003-12-01

    In this study, gamma radiation from cobalt-60 was used to degrade the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) dimethylamine salt in water in the presence of humic acid. The 2,4-D dimethylamine salt 1.13×10 -4 mol dm -3 solution was irradiated with different doses. HPLC was used as an analytical technique to determine the degradation rate of herbicide studied. The results showed that the herbicide was completely degraded at an absorbed dose of 3 kGy. Degradation decreased when humic acid was added to all the doses. ESI/MS and MS/MS were used to identify the radiolytic degradation products. A fragmentation path for production of 4.6-dichlororesorcinol, is suggested. The radiolytic yields ( G) were calculated.

  5. EXTRACTION OF URANYL NITRATE FROM AQUEOUS SOLUTIONS

    DOEpatents

    Furman, N.H.; Mundy, R.J.

    1957-12-10

    An improvement in the process is described for extracting aqueous uranyl nitrate solutions with an organic solvent such as ether. It has been found that the organic phase will extract a larger quantity of uranyl nitrate if the aqueous phase contains in addition to the uranyl nitrate, a quantity of some other soluble nitrate to act as a salting out agent. Mentioned as suitable are the nitrates of lithium, calcium, zinc, bivalent copper, and trivalent iron.

  6. Precipitation of neptunium dioxide from aqueous solution

    SciTech Connect

    Roberts, K E

    1999-12-01

    Tens of thousands of metric tons of highly radioactive, nuclear waste have been generated in the US. Currently, there is no treatment or disposal facility for these wastes. Of the radioactive elements in high-level nuclear waste, neptunium (Np) is of particular concern because it has a long half-life and may potentially be very mobile in groundwaters associated with a proposed underground disposal site at Yucca Mountain, Nevada. Aqueous Np concentrations observed in previous, short-term solubility experiments led to calculated potential doses exceeding proposed long-term regulatory limits. However, thermodynamic data for Np at 25 C showed that these observed aqueous Np concentrations were supersaturated with respect to crystalline NpO{sub 2}. It was hypothesized that NpO{sub 2} is the thermodynamically stable solid phase in aqueous solution, but it is slow to form in an aqueous solution of NpO{sub 2}{sup +} on the time scale of previous experiments. The precipitation of NpO{sub 2} would provide significantly lower aqueous Np concentrations leading to calculated doses below proposed regulatory limits. To test this hypothesis, solubility experiments were performed at elevated temperature to accelerate any slow precipitation kinetics. Ionic NpO{sub 2}{sup +} (aq) was introduced into very dilute aqueous solutions of NaCl with initial pH values ranging from 6 to 10. The reaction vessels were placed in an oven and allowed to react at 200 C until steady-state aqueous Np concentrations were observed. In all cases, aqueous Np concentrations decreased significantly from the initial value of 10{sup {minus}4} M. The solids that formed were analyzed by x-ray powder diffraction, x-ray absorption spectroscopy, and scanning electron microscopy. The solids were determined to be high-purity crystals of NpO{sub 2}. This is the first time that crystalline NpO{sub 2} has been observed to precipitate from NpO{sub 2}{sup +}(aq) in near-neutral aqueous solutions. The results obtained

  7. Photochemistry of norharmane in aqueous solution.

    PubMed

    Gonzalez, M Micaela; Salum, M Laura; Gholipour, Yousef; Cabrerizo, Franco M; Erra-Balsells, Rosa

    2009-08-01

    The photochemistry of norharmane (9H-pyrido[3,4-b]indole) in acidic (pH 5.0+/-0.1) and alkaline (pH 10.0+/-0.1) aqueous solutions was studied. The photochemical reactions were monitored by TLC, UV/VIS absorption spectroscopy, high-performance liquid chromatography (HPLC), electronic ionization-mass spectrometry (EI-MS), UV-laser desorption/ionization-time of flight-mass spectrometry (UV-LDI-TOF-MS) and an enzymatic method for H2O2 determination. The neutral (nHoN) and the protonated (nHoH+) forms of norharmane irradiated under Ar atmosphere were photostable, but they suffered a photochemical transformation in the presence of O2, yielding as photoproducts norharmane dimers, trimers and tetramers. nHoN shown to be more photostable than nHoH+. The nHoH+ and nHoN consumption quantum yields were 1.82x10(-3) and 0.51x10(-3), respectively, and the mechanisms involved in its photochemistry are discussed. H2O2 and singlet oxygen (1O2) were also detected and quantified in irradiated solutions of norharmane, and their role in the photochemistry of norharmane is discussed.

  8. Equilibrium and kinetic studies on the removal of Acid Red 114 from aqueous solutions using activated carbons prepared from seed shells.

    PubMed

    Thinakaran, N; Panneerselvam, P; Baskaralingam, P; Elango, D; Sivanesan, S

    2008-10-01

    The use of low-cost and ecofriendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. This paper deals with the removal of Acid Red 114 (AR 114) from aqueous solutions using activated carbons prepared from agricultural waste materials such as gingelly (sesame) (Sp), cotton (Cp) and pongam (Pp) seed shells. Optimum conditions for AR 114 removal were found to be pH 3, adsorbent dosage=3g/L of solution and equilibrium time=4h. Higher removal percentages were observed at lower concentrations of AR 114. The adsorption isotherm data were fitted to Langmuir and Freundlich equation, and the adsorption capacity of the studied adsorbents was in the order Sp>Cp>Pp. Kinetic studies showed that the adsorption followed both pseudo-second-order and Elovich equation. The thermodynamics parameters such as DeltaG degrees, DeltaH degrees, DeltaS degrees were also evaluated. The activated carbons prepared were characterized by FT-IR, SEM and BET analysis.

  9. Synthesis and application of reduced graphene oxide and molecularly imprinted polymers composite in chemo sensor for trichloroacetic acid detection in aqueous solution

    NASA Astrophysics Data System (ADS)

    Kibechu, Rose W.; Mamo, Messai A.; Msagati, Titus A. M.; Sampath, S.; Mamba, Bhekie B.

    This work presents the fabrication of a simple, cheap and fast thin film chemo sensor for detection of trichloroacetic acid (TCAA) in aqueous solutions. Reduced graphene oxide (RGO) based molecular imprinted polymers (MIP) chemo-sensor has been developed. The recognition of TCAA was achieved by imprinted polymers synthesized by copolymerization of 4-vinylpyridine (4-VP) and a crosslinking monomer ethylene glycol dimethacrylate (EDGMA) in acetonitrile using bulk polymerization method. Adsorption studies to determine the rebinding properties of the MIP with the template were conducted using UV Visible spectrophotometer. The fabricated sensor exhibited high recognition ability and affinity for HAA in comparison with the non-imprinted one which was employed as a control, this indicated that the MIP could selectively rebind with TCAA. Reduced graphene oxide (RGO) was used to improve conductivity of the sensor; RGO was obtained from reduction of graphene oxide (GO) synthesized using modified Stauddmer and Hummers method. Polysulphone was used in solution blending of MIP and RGO to form a hybrid which was deposited between two gold plated electrodes by spin coating to form a thin film. The performance of the imprinted sensor was studied using a homemade circuit. The results demonstrate that the sensor based on TCAA-imprinted polymer is fast, cheap and sensitive screening method of TCAA in drinking water.

  10. The enhanced PC and PEC oxidation of formic acid in aqueous solution using a Cu-TiO2/ITO film.

    PubMed

    He, Chun; Li, Xiangzhong; Xiong, Ya; Zhu, Xihai; Liu, Shaorong

    2005-01-01

    The photocatalytic (PC) and photoelectrocatalytic (PEC) activity of Cu-TiO2/ITO films for degrading formic acid in aqueous solution was investigated in this study. Compared with a TiO2/ITO film, the degradation efficiency of formic acid on the Cu-TiO2 films increased markedly in both the PC and PEC oxidation processes. However, it was found that the photodeposited Cu metal on the Cu-TiO2 films could electrochemically dissolute during the PEC reaction, while an electrical bias with the voltage higher than 1.48 V was applied. It is believed this is a common problem occurred for several metals deposition on the TiO2 films, which results in a poor stability of the metal-deposited TiO2 electrode in PEC processes. To improve the stability of the Cu-TiO2 electrode, an alternative process between PC and PEC reactions was investigated. It was found that the dissolute Cu metal during the PEC process was re-deposited on the Cu-TiO2 film again during the PC process. The experiments with repeated runs demonstrated that this alternative process could not only overcome the loss of Cu, but also enhance the PEC oxidation efficiency of the Cu-TiO2 films.

  11. Morphological and phase evolution of TiO{sub 2} nanocrystals prepared from peroxotitanate complex aqueous solution: Influence of acetic acid

    SciTech Connect

    Chang, Jeong Ah; Vithal, Muga; Baek, In Chan; Seok, Sang Il

    2009-04-15

    Nanosized anatase and rutile TiO{sub 2} having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H{sub 2}O{sub 2}) in water/isopropanol media by a facile sol-gel process. The TiO{sub 2} nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO{sub 2} are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given. - Graphical abstract: The morphology of TiO{sub 2} depends on the sequence of addition of AcOH and H{sub 2}O{sub 2} from the system of titanium isopropoxide and acetic acid (AcOH) in the presence of H{sub 2}O{sub 2}.

  12. Iminodiacetic acid functionalized cation exchange resin for adsorptive removal of Cr(VI), Cd(II), Ni(II) and Pb(II) from their aqueous solutions.

    PubMed

    Misra, R K; Jain, S K; Khatri, P K

    2011-01-30

    Iminodiacetic acid functionality has been introduced on styrene-divinyl benzene co-polymeric beads and characterized by FT-IR in order to develop weak acid based cation exchange resin. This resin was evaluated for the removal of different heavy metal ions namely Cd(II), Cr(VI), Ni(II) and Pb(II) from their aqueous solutions. The results showed greater affinity of resin towards Cr(VI) for which 99.7% removal achieved in optimal conditions following the order Ni(II)>Pb(II)>Cd(II) with 65%, 59% and 28% removal. Experiments were also directed towards kinetic studies of adsorption and found to follow first order reversible kinetic model with the overall rate constants 0.3250, 0.2393, 0.4290 and 0.2968 for Cr(VI), Ni(II), Pb(II) and Cd(II) removal respectively. Detailed studies of Cr(VI) removal has been carried out to see the effect of pH, resin dose and metal ion concentration on adsorption and concluded that complexation enhanced the chromium removal efficacy of resin drastically, which is strongly pH dependent. The findings were also supported by the comparison of FT-IR spectra of neat resin with the chromium-adsorbed resin.

  13. Adsorption of humic acid from aqueous solutions on crosslinked chitosan-epichlorohydrin beads: kinetics and isotherm studies.

    PubMed

    Wan Ngah, W S; Hanafiah, M A K M; Yong, S S

    2008-08-01

    The adsorption of humic acid on crosslinked chitosan-epichlorohydrin (chitosan-ECH) beads was investigated. Chitosan-ECH beads were characterized by Fourier transform infrared spectroscopy (FTIR), surface area and pore size analyses, and scanning electron microscopy (SEM). Batch adsorption experiments were carried out and optimum humic acid adsorption on chitosan-ECH beads occurred at pH 6.0, agitation rate of 300 rpm and contact time of 50 min. Adsorption equilibrium isotherms were analyzed by Langmuir and Freundlich models. Freundlich model was found to show the best fit for experimental data while the maximum adsorption capacity determined from Langmuir model was 44.84 mg g(-1). The adsorption of humic acid on chitosan-ECH beads was best described with pseudo-first-order kinetic model. For desorption study, more than 60% of humic acid could be desorbed from the adsorbent using 1.0M HCl for 180 min.

  14. Removal of Acid Orange 7 dye from aqueous solutions by adsorption onto Kenya tea pulps; granulated shape

    PubMed Central

    Naraghi, Behnaz; Zabihi, Fahimeh; Narooie, Mohammad Reza; Saeidi, Mahdi; Biglari, Hamed

    2017-01-01

    Background and Aim Water resources pollution control is one of the main challenges of our time for researchers. Colored wastewater discharges caused by textile industry activities has added to the concern. In this study, removal of Acid Orange 7 dye (AO7) using Kenya Tea residue absorbent (granular) has been studied. Methods This cross-sectional study was conducted in 2016. In this work, initially, tea residue was prepared in three forms of raw, treated with concentrated phosphoric acid, and carbonated, at temperatures of 350, 450 and 500 °C in the chemistry laboratory of Gonabad University of Medical Sciences. Then, efficiency of the above absorbents in the removal of Acid Orange 7 dye in initial concentrations of dye as 50–500 mg/l from water samples in terms of pH 2–10 and 1–10 g/l of adsorbent dose within 20 to 300 minutes was investigated. In addition, their subordination from Langmuir and Freundlich absorption isotherms was also determined. Concentration changes in Acid Orange 7 dye at a wavelength of 483 nm was determined by spectrophotometry and results were reported using descriptive statistics. Results Results showed that efficiency of Acid Orange 7 dye removal is higher in acidic pH and higher adsorbent dosage. The highest efficiency of Acid Orange 7 dye removal was 98.41% by raw tea residue absorbent at pH 2, reaction time was 120 minutes and initial concentration of dye was 50 mg/l, which was obtained at adsorbent dosage of 10 g/l. It was determined that the mechanism of absorption acceptably follows Freundlich absorption isotherm (R2=0.97). Conclusion Due to the availability and very low price, optimal performance of Kenya tea raw residue (granular) in Acid Orange 7 dye removal, it can be used as an efficient surface absorber in an absorber from colored wastewater. PMID:28713501

  15. Double Hydrogen Bonding between Side Chain Carboxyl Groups in Aqueous Solutions of Poly (β-L-Malic Acid): Implication for the Evolutionary Origin of Nucleic Acids

    PubMed Central

    Francis, Brian R.; Watkins, Kevin; Kubelka, Jan

    2017-01-01

    The RNA world hypothesis holds that in the evolutionary events that led to the emergence of life RNA preceded proteins and DNA and is supported by the ability of RNA to act as both a genetic polymer and a catalyst. On the other hand, biosynthesis of nucleic acids requires a large number of enzymes and chemical synthesis of RNA under presumed prebiotic conditions is complicated and requires many sequential steps. These observations suggest that biosynthesis of RNA is the end product of a long evolutionary process. If so, what was the original polymer from which RNA and DNA evolved? In most syntheses of simpler RNA or DNA analogs, the D-ribose phosphate polymer backbone is altered and the purine and pyrimidine bases are retained for hydrogen bonding between complementary base pairs. However, the bases are themselves products of complex biosynthetic pathways and hence they too may have evolved from simpler polymer side chains that had the ability to form hydrogen bonds. We hypothesize that the earliest evolutionary predecessor of nucleic acids was the simple linear polyester, poly (β-D-malic acid), for which the carboxyl side chains could form double hydrogen bonds. In this study, we show that in accord with this hypothesis a closely related polyester, poly (β-L-malic acid), uses carboxyl side chains to form robust intramolecular double hydrogen bonds in moderately acidic solution.

  16. Thermodynamic Properties of Aqueous Solution of Ammonia

    NASA Astrophysics Data System (ADS)

    Kitamura, Hiroshi; Oguchi, Kosei

    Present status on the thermodynamic properties of experimental data and their correlations of both ammonia and aqueous solution of ammonia was introduced in this paper. The aqueous solution of ammonia is used for not only a working fluid in absorption refrigerator cycles but also working fluids in bottoming cycles of steam power plants and other heat recovering systems. Therefore, the thermodynamic properties of this substance are required in a wide range of temperatures, pressures and compositions. The experimental results of pVTx properties for ammonia and aqueous solution of ammonia and their comparisons with a formulation by Tillner-Roth and Friend1) were critically surveyed. The “Guideline on the IAPWS Formulation 2000 for the Thermodynamic Properties of Ammonia-Water Mixtures”, correlated by Tillner-Roth and Friend1), was approved on September, 2001, by the International Association for the Properties of Water and Steam (IAPWS) 2).

  17. Removal of uranium from aqueous HF solutions

    DOEpatents

    Pulley, Howard; Seltzer, Steven F.

    1980-01-01

    This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separting the solution from the settled particulates. The CaF.sub.2 is selected to have a nitrogen surface area in a selected range and is employed in an amount providing a calcium fluoride/uranium weight ratio in a selected range. As applied to dilute HF solutions containing 120 ppm uranium, the method removes at least 92% of the uranium, without introducing contaminants to the product solution.

  18. Aqueous Solution Chemistry of Plutonium

    SciTech Connect

    Clark, David L.

    2014-01-28

    Things I have learned working with plutonium: Chemistry of plutonium is complex; Redox equilibria make Pu solution chemistry particularly challenging in the absence of complexing ligands; Understanding this behavior is key to successful Pu chemistry experiments; There is no suitable chemical analog for plutonium.

  19. Hydrophobic Solvation: Aqueous Methane Solutions

    ERIC Educational Resources Information Center

    Konrod, Oliver; Lankau, Timm

    2007-01-01

    A basic introduction to concept of a solvation shell around an apolar solute as well as its detection is presented. The hydrophobic solvation of toluene is found to be a good teaching example which connects macroscopic, phenomenological thermodynamic results with an atomistic point of view.

  20. Hydrophobic Solvation: Aqueous Methane Solutions

    ERIC Educational Resources Information Center

    Konrod, Oliver; Lankau, Timm

    2007-01-01

    A basic introduction to concept of a solvation shell around an apolar solute as well as its detection is presented. The hydrophobic solvation of toluene is found to be a good teaching example which connects macroscopic, phenomenological thermodynamic results with an atomistic point of view.

  1. Kinetics and mechanism of oxidation of chondroitin-4-sulfate polysaccharide by chromic acid in aqueous perchlorate solutions.

    PubMed

    Hassan, Refat; Ibrahim, Samia; Dahy, Abdel Rahman; Zaafarany, Ishaq; Tirkistani, Fahd; Takagi, Hideo

    2013-02-15

    The kinetics of chromic acid oxidation of chondroitin-4-sulfate polysaccharide as sulfated carbohydrates at a constant ionic strength of 4.0 mol dm(-3) has been investigated, spectrophotometrically. The reaction kinetics showed a first-order dependence in chromic acid and fractional-first-order kinetics with respect to the chondroitin-4-sulfate concentration. The influence of [H(+)] on the reaction rates showed that the oxidation process is acid-catalyzed. Added Mn(2+) ions indicated the formation of Cr(IV) as intermediate species. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The kinetic parameters have been evaluated and a tentative reaction mechanism in good consistent with the kinetic results obtained is discussed.

  2. Freezing temperatures of aqueous iron(III) sulfate solutions and crystallization of a new acidic water-rich sulfate

    NASA Astrophysics Data System (ADS)

    Hennings, E.; Zürner, P.; Schmidt, H.; Voigt, W.

    2013-09-01

    An important question concerning the possibility of life under martian conditions is the existence of liquid water at low temperatures. On the martian surface, the existence of iron(III) sulfate is expected. The influence of iron(III) sulfate salt on ice deposits in respect to the formation of liquid salt brines was not investigated in the past. In this contribution, the investigation of the phase diagram of the system iron(III) sulfate-water and the influence of sulfuric acid to this system are presented. A new crystalline acidic iron(III) sulfate hydrate has been found in the ternary system iron(III) sulfate-water-sulfuric acid, which represents the most water-rich iron salt phase ever detected.

  3. Coupled diffusion in aqueous weak acid + alkanolamine absorbents

    SciTech Connect

    Leaist, D.G.; Li, Y.; Poissant, R.

    1998-11-01

    Taylor dispersion and differential refractometry are used to measure ternary interdiffusion coefficients (D{sub ik}) for aqueous solutions of acetic acid + triethanolamine (TEA) and aqueous solutions of oxalic acid + TEA at 25 C. The D{sub ik} coefficients give the coupled fluxes of acid and TEA driven by the gradient in the concentration of each solute. Ternary Fick equations with variable D{sub ik} coefficients are integrated numerically to calculate accurate concentration profiles and the moving reaction front produced by the interdiffusion of TEA and acetic or oxalic acid. Ternary diffusion coefficients are also used to predict the rate of dissolution of oxalic acid in 1.00 mol/dm{sup 3} aqueous TEA, a process analogous to the absorption of a diprotic acid gas by an alkanolamine absorbent. The diffusion of oxalic acid drives a significant counterflow of TEA. The resulting buildup of TEA at the surface of the dissolving acid increases the interfacial concentration of TEA from 1.00 to 1.20 mol/dm{sup 3}, which in turn increases the solubility of the acid by 0.20 mol/dm{sup 3}. Nernst-Planck equations are used to predict D{sub ik} coefficients for aqueous weak acid + alkanolamine solutions. The fluxes of these solutes are shown to be strongly coupled by the electric field that is generated by the diffusing ions.

  4. Salinity, water hardness, and dissolved organic carbon modulate degradation of peracetic acid (PAA) compounds in aqueous solutions

    USDA-ARS?s Scientific Manuscript database

    Peracetic acid (PAA) is used in aquaculture under different conditions for disinfection purposes. However, there is a lack of information about its environmental fate, particularly its persistence in aquatic systems with different chemistries. Therefore, the impact of water hardness, salinity, and d...

  5. Reorientation and Allied Dynamics in Water and Aqueous Solutions

    NASA Astrophysics Data System (ADS)

    Laage, Damien; Stirnemann, Guillaume; Sterpone, Fabio; Rey, Rossend; Hynes, James T.

    2011-05-01

    The reorientation of a water molecule is important for a host of phenomena, ranging over—in an only partial listing—the key dynamic hydrogen-bond network restructuring of water itself, aqueous solution chemical reaction mechanisms and rates, ion transport in aqueous solution and membranes, protein folding, and enzymatic activity. This review focuses on water reorientation and related dynamics in pure water, and for aqueous solutes with hydrophobic, hydrophilic, and amphiphilic character, ranging from tetra-methylurea to halide ions and amino acids. Attention is given to the application of theory, simulation, and experiment in the probing of these dynamics, in usefully describing them, and in assessing the description. Special emphasis is placed on a novel sudden, large-amplitude jump mechanism for water reorientation, which contrasts with the commonly assumed Debye rotational diffusion mechanism, characterized by small-amplitude angular motion. Some open questions and directions for further research are also discussed.

  6. Electrochemical, HPLC and electrospray ionization mass spectroscopic analyses of peroxycitric acid coexisting with citric acid and hydrogen peroxide in aqueous solution.

    PubMed

    Ferdousi, Begum Nadira; Islam, Md Mominul; Okajima, Takeyoshi; Ohsaka, Takeo

    2008-02-15

    We successfully determined the molecular structure of peroxycitric acid (PCA) coexisting in the aqueous equilibrium mixture with citric acid (CA; 1,2,3-tricarboxylic-2-hydroxy propane) and hydrogen peroxide (H(2)O(2)) by a combined use of reversed-phase HPLC (RP-HPLC), potentiometric, hydrodynamic chronocoulometric (HCC) and electrospray ionization mass spectroscopic (ESI-MS) methods. Firstly, the RP-HPLC was employed to separate CA, PCA and H(2)O(2) coexisting in the equilibrium mixture and the concentration of CA consumed (DeltaC(CA)) in the formation of PCA that was evidenced to be fairly stable during the RP-HPLC measurement was quantitatively measured based on the standard calibration curve of CA. Secondly, the total oxidant concentration (C(Ox)) corresponding to peroxycarboxylic (-COOOH) group in PCA in the equilibrium mixture was determined using potentiometric measurement. The ratio of C(Ox)/DeltaC(CA) was found to be 1.07, which indicates that only one -COOH group in CA molecule is oxidized to the corresponding -COOOH group in PCA molecule. Thirdly, using the HCC technique the diffusion coefficient of PCA, which could be electroreduced at a more positive potential by 1.0 V than the coexisting H(2)O(2), was independently measured as 0.3 x 10(-5)cm(2)s(-1) and at the same time, by considering DeltaC(CA) as the concentration of PCA, the number of electrons (n) required for the reduction of PCA was determined to be 2. The result obtained from RP-HPLC and HCC, i.e., n=2 which is equivalent to one -COOOH group in PCA, is in agreement with that obtained from the combination of RP-HPLC and potentiometric measurements. Finally, the structure of PCA was proposed to contain one -COOOH group with a molecular mass of 208 confirmed by negative ion ESI-MS method. A probable molecular structure of PCA was discussed.

  7. Nitric acid recovery from waste solutions

    DOEpatents

    Wilson, A. S.

    1959-04-14

    The recovery of nitric acid from aqueous nitrate solutions containing fission products as impurities is described. It is desirable to subject such solutions to concentration by evaporation since nitric acid is regenerated thereby. A difficulty, however, is that the highly radioactive fission product ruthenium is volatilized together with the nitric acid. It has been found that by adding nitrous acid, ruthenium volatilization is suppressed and reduced to a negligible degree so that the distillate obtained is practically free of ruthenium.

  8. Layered double hydroxide intercalated with aromatic acid anions for the efficient capture of aniline from aqueous solution.

    PubMed

    Yu, Shujun; Wang, Xiangxue; Chen, Zhongshan; Wang, Jian; Wang, Suhua; Hayat, Tasawar; Wang, Xiangke

    2017-01-05

    Aniline is toxic and hard to be degraded, and thereby causes the environmental pollution seriously. Herein, a practical and green hydrothermal method was applied to fabricate terephthalic acid and pyromellitic acid intercalated layered double hydroxides (LDH) (named as TAL and PAL) for aniline efficient removal. The sorption of aniline on LDH-based materials were investigated at different experimental conditions, and the results indicated that aniline sorption on LDH, TAL and PAL were strongly dependent on pH and independent of ionic strength. The maximum sorption capacities of aniline on TAL and PAL at pH 5.0 and 293K were 90.4 and 130.0mg/g, respectively, which were significantly higher than that of aniline on LDH (52.6mg/g). Based on the BET, FTIR and XPS analysis, the higher sorption capacities of TAL and PAL were mainly due to high surface area and basal spacing as well as the abundant functional groups (e.g. -COO(-)). The interactions of aniline with TAL and PAL were mainly dominated by hydrogen bonds and electrostatic interactions. Such a facile synthesis method, efficient removal performance and superior reusability indicated that the aromatic acid modified LDH materials had potential application for efficient treatment of organic pollutants in environmental pollution cleanup.

  9. Comparison of hydroxyl radical formation in aqueous solutions at different ultrasound frequencies and powers using the salicylic acid dosimeter.

    PubMed

    Milne, Louise; Stewart, Isobel; Bremner, David H

    2013-05-01

    Ultrasonic frequencies of 20kHz, 382kHz, 584kHz, 862kHz (and 998kHz) have been compared with regard to energy output and hydroxyl radical formation utilising the salicylic acid dosimeter. The 862kHz frequency inputs 6 times the number of Watts into water, as measured by calorimetry, with the other frequencies having roughly the same value under very similar conditions. A plausible explanation involving acoustic fountain formation is proposed although enhanced coupling between this frequency and water cannot be discounted. Using the salicylic acid dosimeter and inputting virtually the same Wattages it is established that 862kHz is around 10% more efficient at generating hydroxyl radicals than the 382kHz but both of these are far more effective than the other frequencies. Also, it is found that as temperature increases to 42°C then the total dihydroxybenzoic acid (Total DHBA) produced is virtually identical for 382kHz and 862kHz, though 582kHz is substantially lower, when the power levels are set at approximately 9W for all systems. An equivalent power level of 9W could not be obtained for the 998kHz transducer so a direct comparison could not be made in this instance. These results have implications for the optimum frequencies chosen for both Advanced Oxidation Processes (AOPs) and organic synthesis augmented by ultrasound.

  10. Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution II: Solvent Coordinate-Dependent Reaction Path.

    PubMed

    Daschakraborty, Snehasis; Kiefer, Philip M; Miller, Yifat; Motro, Yair; Pines, Dina; Pines, Ehud; Hynes, James T

    2016-03-10

    The protonation of methylamine base CH3NH2 by carbonic acid H2CO3 within a hydrogen (H)-bonded complex in aqueous solution was studied via Car-Parrinello dynamics in the preceding paper (Daschakraborty, S.; Kiefer, P. M.; Miller, Y.; Motro, Y.; Pines, D.; Pines, E.; Hynes, J. T. J. Phys. Chem. B 2016, DOI: 10.1021/acs.jpcb.5b12742). Here some important further details of the reaction path are presented, with specific emphasis on the water solvent's role. The overall reaction is barrierless and very rapid, on an ∼100 fs time scale, with the proton transfer (PT) event itself being very sudden (<10 fs). This transfer is preceded by the acid-base H-bond's compression, while the water solvent changes little until the actual PT occurrence; this results from the very strong driving force for the reaction, as indicated by the very favorable acid-protonated base ΔpKa difference. Further solvent rearrangement follows immediately the sudden PT's production of an incipient contact ion pair, stabilizing it by establishment of equilibrium solvation. The solvent water's short time scale ∼120 fs response to the incipient ion pair formation is primarily associated with librational modes and H-bond compression of water molecules around the carboxylate anion and the protonated base. This is consistent with this stabilization involving significant increase in H-bonding of hydration shell waters to the negatively charged carboxylate group oxygens' (especially the former H2CO3 donor oxygen) and the nitrogen of the positively charged protonated base's NH3(+).

  11. Aqueous Solution Chemistry on Mars

    NASA Astrophysics Data System (ADS)

    Quinn, R.; Hecht, M.; Kounaves, S.; Young, S.; West, S.; Fisher, A.; Grunthaner, P.

    2007-12-01

    Currently en route to Mars, the Phoenix mission carries four wet chemistry cells designed to perform basic solution chemistry on martian soil. The measurement objectives are typical of those that would be performed on an unknown sample on Earth, including detection of common anions and cations, total conductivity, pH, redox potential, cyclic voltammetry (CV), etc. Both the challenge and the novelty arise from the necessity to perform these measurements with severely constrained resources in a harsh and (literally) alien environment. Sensors for all measurements are integrated into a common "beaker," with the ability to perform a two-point calibration of some sensors using a pair of low-concentration solutions. Sulfate measurement is performed with a crude titration. While most measurements use ion selective electrodes, halide interferences are resolved by independent chronopotentiometry (CP) measurements. No preconditioning of the soil-water mixture is possible, nor is any physical characterization of the introduced soil sample beyond coarse visual inspection. Among the idiosyncrasies of the measurement is the low external pressure, which requires that the analysis be performed close to the boiling point of water under an atmosphere consisting almost entirely of water vapor. Despite these liabilities, however, extensive laboratory characterization has validated the basic approach, and protocols for both CV and CP have been developed and tested. Enhancing the value of the measurement is the suite of coordinated observations, such as microscopy and evolved gas analysis, to be performed by other Phoenix instruments.

  12. Electrochemical efficacy of a carboxylated multiwalled carbon nanotube filter for the removal of ibuprofen from aqueous solutions under acidic conditions.

    PubMed

    Bakr, Ahmed Refaat; Rahaman, Md Saifur

    2016-06-01

    This study provides insight into the efficiency of a functionalized multiwalled carbon nanotube filter for the removal of an anti-inflammatory drug, ibuprofen, through conventional filtration and electrochemical filtration processes. A comparison was made between carboxylated multiwalled carbon nanotubes (MWNTs-COOH) and pristine multiwalled carbon nanotubes (MWNTs) in order to emphasize the enhanced performance of MWNTs-COOH for the removal of ibuprofen using an electrochemical filtration process under acidic conditions. Ibuprofen-removal trials were evaluated based on absorbance values obtained using a UV/Vis spectrophotometer, and possible degradation products were identified using liquid chromatography mass spectrometry (LC-MS). The results exhibited near complete removal of ibuprofen by MWNTs-COOH at lower applied potentials (2 V), at lower flow rates, and under acidic conditions, which can be attributed to the generation of superoxides and their active participation in simultaneous degradation of ibuprofen, and its by-products, under these conditions. At higher applied potential (3 V), the possible participation of both bulk indirect oxidation reactions, and direct electron transfer were hypothesized for the removal behavior over time (breakthrough). At 3 V under acidic conditions, near 100% removal of the target molecule was achieved and was attributed to the enhanced generation of electroactive species toward bulk chemical reactions and a possible contribution from direct electron transfer under these conditions. The degradation by-products of ibuprofen were effectively removed by allowing longer residence time during the filtration process. Moreover, the effect of temperature was studied, yet showed a non-significant effect on the overall removal process.

  13. Protonation of Excited State Pyrene-1-Carboxylate by Phosphate and Organic Acids in Aqueous Solution Studied by Fluorescence Spectroscopy

    PubMed Central

    Zelent, Bogumil; Vanderkooi, Jane M.; Coleman, Ryan G.; Gryczynski, Ignacy; Gryczynski, Zygmunt

    2006-01-01

    Pyrene-1-carboxylic acid has a pK of 4.0 in the ground state and 8.1 in the singlet electronic excited state. In the pH range of physiological interest (pH ∼5–8), the ground state compound is largely ionized as pyrene-1-carboxylate, but protonation of the excited state molecule occurs when a proton donor reacts with the carboxylate during the excited state lifetime of the fluorophore. Both forms of the pyrene derivatives are fluorescent, and in this work the protonation reaction was measured by monitoring steady-state and time-resolved fluorescence. The rate of protonation of pyrene-COO− by acetic, chloroacetic, lactic, and cacodylic acids is a function of ΔpK, as predicted by Marcus theory. The rate of proton transfer from these acids saturates at high concentration, as expected for the existence of an encounter complex. Trihydrogen-phosphate is a much better proton donor than dihydrogen- and monohydrogen-phosphate, as can be seen by the pH dependence. The proton-donating ability of phosphate does not saturate at high concentrations, but increases with increasing phosphate concentration. We suggest that enhanced rate of proton transfer at high phosphate concentrations may be due to the dual proton donating and accepting nature of phosphate, in analogy to the Grotthuss mechanism for proton transfer in water. It is suggested that in molecular structures containing multiple phosphates, such as membrane surfaces and DNA, proton transfer rates will be enhanced by this mechanism. PMID:16920831

  14. Protonation of excited state pyrene-1-carboxylate by phosphate and organic acids in aqueous solution studied by fluorescence spectroscopy.

    PubMed

    Zelent, Bogumil; Vanderkooi, Jane M; Coleman, Ryan G; Gryczynski, Ignacy; Gryczynski, Zygmunt

    2006-11-15

    Pyrene-1-carboxylic acid has a pK of 4.0 in the ground state and 8.1 in the singlet electronic excited state. In the pH range of physiological interest (pH approximately 5-8), the ground state compound is largely ionized as pyrene-1-carboxylate, but protonation of the excited state molecule occurs when a proton donor reacts with the carboxylate during the excited state lifetime of the fluorophore. Both forms of the pyrene derivatives are fluorescent, and in this work the protonation reaction was measured by monitoring steady-state and time-resolved fluorescence. The rate of protonation of pyrene-COO(-) by acetic, chloroacetic, lactic, and cacodylic acids is a function of DeltapK, as predicted by Marcus theory. The rate of proton transfer from these acids saturates at high concentration, as expected for the existence of an encounter complex. Trihydrogen-phosphate is a much better proton donor than dihydrogen- and monohydrogen-phosphate, as can be seen by the pH dependence. The proton-donating ability of phosphate does not saturate at high concentrations, but increases with increasing phosphate concentration. We suggest that enhanced rate of proton transfer at high phosphate concentrations may be due to the dual proton donating and accepting nature of phosphate, in analogy to the Grotthuss mechanism for proton transfer in water. It is suggested that in molecular structures containing multiple phosphates, such as membrane surfaces and DNA, proton transfer rates will be enhanced by this mechanism.

  15. The molecular velocity of sound. [aqueous solutions

    NASA Technical Reports Server (NTRS)

    Auslaender, D.; Onitiu, L.

    1974-01-01

    The molecular velocity of sound was calculated according to Rao's formula and the temperature and concentration dependences of this value were studied in aqueous solutions of alkali and alkaline-earth halides. Study of relative association brought to light characteristic effects of ions. The variation of the relative association can be explained by a breaking of hydrogen bonds by ions and thermal agitation.

  16. Water & Aqueous Solutions. Final Progress Report

    SciTech Connect

    2002-08-09

    The Gordon Research Conference (GRC) on Water & Aqueous Solutions was held at Holderness School, New Hampshire, 8/4/02 thru 8/9/02. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  17. PHOTOREACTION OF VALEROPHENONE IN AQUEOUS SOLUTION

    EPA Science Inventory

    Kinetics and products of the photoreaction of the phenyl ketone valerophenone were investigated as a function of temperature, pH, and wavelength in aqueous solution. Under these conditions (<10-4M), the photoreactions are pseudo-first-order with respect to valerophenone concentra...

  18. The molecular velocity of sound. [aqueous solutions

    NASA Technical Reports Server (NTRS)

    Auslaender, D.; Onitiu, L.

    1974-01-01

    The molecular velocity of sound was calculated according to Rao's formula and the temperature and concentration dependences of this value were studied in aqueous solutions of alkali and alkaline-earth halides. Study of relative association brought to light characteristic effects of ions. The variation of the relative association can be explained by a breaking of hydrogen bonds by ions and thermal agitation.

  19. PHOTOREACTION OF VALEROPHENONE IN AQUEOUS SOLUTION

    EPA Science Inventory

    Kinetics and products of the photoreaction of the phenyl ketone valerophenone were investigated as a function of temperature, pH, and wavelength in aqueous solution. Under these conditions (<10-4M), the photoreactions are pseudo-first-order with respect to valerophenone concentra...

  20. Dopamine functionalized tannic-acid-templated mesoporous silica nanoparticles as a new sorbent for the efficient removal of Cu2+ from aqueous solution

    PubMed Central

    Gao, Junkai; Lei, Hao; Han, Zhi; Shi, Qian; Chen, Yan; Jiang, Yanjun

    2017-01-01

    A simple, environmentally friendly and cost-effective nonsurfactant template method was used to synthesize tannic-acid-templated mesoporous silica nanoparticles (TMSNs), and then dopamine functionalized TMSNs (Dop-TMSNs) which was synthesized by a facile and biomimetic coating strategy, was developed as a new sorbent for the removal of Cu2+ from aqueous solution. The Dop-TMSNs were thoroughly characterized by SEM, TEM, BET, FT-IR and TGA, and the effects of contact time, initial pH, K+ and Na+ concentrations, co-existing polyvalent metal ions and adsorption-desorption cycle times on the sorption capacity of Dop-TMSNs were studied. It was demonstrated that the maximum adsorption capacity of Cu2+ by Dop-TMSNs was 58.7 mg/g at pH 5.5, and the sorption reached equilibrium within 180 min. Moreover, the K+ and Na+ concentrations had a very slight influence on the sorption process and the adsorption capacity of the Dop-TMSNs still remained 89.2% after recycling for four times. All the results indicated that the Dop-TMSNs could be utilized as an excellent sorbent for the sequestration of Cu2+. PMID:28327600

  1. Solubility and modeling acid-base properties of adrenaline in NaCl aqueous solutions at different ionic strengths and temperatures.

    PubMed

    Bretti, Clemente; Cigala, Rosalia Maria; Crea, Francesco; De Stefano, Concetta; Vianelli, Giuseppina

    2015-10-12

    Solubility and acid-base properties of adrenaline were studied in NaCl aqueous solutions at different ionic strengths (0

  2. Application of L-Aspartic Acid-Capped ZnS:Mn Colloidal Nanocrystals as a Photosensor for the Detection of Copper (II) Ions in Aqueous Solution

    PubMed Central

    Heo, Jungho; Hwang, Cheong-Soo

    2016-01-01

    Water-dispersible ZnS:Mn nanocrystals (NCs) were synthesized by capping the surface with polar L-aspartic acid (Asp) molecules. The obtained ZnS:Mn-Asp NC product was optically and physically characterized using the corresponding spectroscopic methods. The ultra violet-visible (UV-VIS) absorption spectrum and photoluminescence (PL) emission spectrum of the NCs showed broad peaks at 320 and 590 nm, respectively. The average particle size measured from the obtained high resolution-transmission electron microscopy (HR-TEM) image was 5.25 nm, which was also in accordance with the Debye-Scherrer calculations using the X-ray diffraction (XRD) data. Moreover, the surface charge and degree of aggregation of the ZnS:Mn-Asp NCs were determined by electrophoretic and hydrodynamic light scattering methods, respectively. These results indicated the formation of agglomerates in water with an average size of 19.8 nm, and a negative surface charge (−4.58 mV) in water at ambient temperature. The negatively-charged NCs were applied as a photosensor for the detection of specific cations in aqueous solution. Accordingly, the ZnS:Mn-Asp NCs showed an exclusive luminescence quenching upon addition of copper (II) cations. The kinetic mechanism study on the luminescence quenching of the NCs by the addition of the Cu2+ ions proposed an energy transfer through the ionic binding between the two oppositely-charged ZnS:Mn-Asp NCs and Cu2+ ions. PMID:28335210

  3. Static and dynamic investigations of poly(aspartic acid) and Pluronic F127 complex prepared by self-assembling in aqueous solution

    NASA Astrophysics Data System (ADS)

    Nita, Loredana E.; Chiriac, Aurica P.; Bercea, Maria; Nistor, Manuela T.

    2015-12-01

    The present investigation is focused on evaluation of self-assembling ability in aqueous solutions of two water soluble polymers: poly(aspartic acid) (PAS) and Pluronic F127 (PL). The intermolecular complexes, realized between polyacid and neutral copolymer surfactant in different ratios, have been studied by combining various characterization techniques as rheology, DLS, spectroscopy, microscopy, chemical imaging, and zeta potential determination, measurements performed in static and/or dynamic conditions. In static conditions, when the equilibrium state between PAS/PL polymeric pair was reached, and depending on the polymers mixture composition, and of experimental rheological conditions, positive or negative deviations from the additive rule are registered. Conformational changes of the macromolecular chains and correspondingly physical interactions are generated between PL and PAS for self-assembly and the formation of interpolymer complex as suprastructure with micellar configuration. The phenomenon was better evidenced in case of 1/1 wt ratio between the two polymers. In dynamic conditions of determination, during "in situ" evaluation of the hydrodynamic diameter, zeta potential and conductivity, when the equilibrium state is not reached and as result either the intermolecular bonds are not achieved, the self-assembling process is not so obvious evidenced.

  4. Dopamine functionalized tannic-acid-templated mesoporous silica nanoparticles as a new sorbent for the efficient removal of Cu2+ from aqueous solution

    NASA Astrophysics Data System (ADS)

    Gao, Junkai; Lei, Hao; Han, Zhi; Shi, Qian; Chen, Yan; Jiang, Yanjun

    2017-03-01

    A simple, environmentally friendly and cost-effective nonsurfactant template method was used to synthesize tannic-acid-templated mesoporous silica nanoparticles (TMSNs), and then dopamine functionalized TMSNs (Dop-TMSNs) which was synthesized by a facile and biomimetic coating strategy, was developed as a new sorbent for the removal of Cu2+ from aqueous solution. The Dop-TMSNs were thoroughly characterized by SEM, TEM, BET, FT-IR and TGA, and the effects of contact time, initial pH, K+ and Na+ concentrations, co-existing polyvalent metal ions and adsorption-desorption cycle times on the sorption capacity of Dop-TMSNs were studied. It was demonstrated that the maximum adsorption capacity of Cu2+ by Dop-TMSNs was 58.7 mg/g at pH 5.5, and the sorption reached equilibrium within 180 min. Moreover, the K+ and Na+ concentrations had a very slight influence on the sorption process and the adsorption capacity of the Dop-TMSNs still remained 89.2% after recycling for four times. All the results indicated that the Dop-TMSNs could be utilized as an excellent sorbent for the sequestration of Cu2+.

  5. Rapid and efficient removal of Pb(II) from aqueous solutions using biomass-derived activated carbon with humic acid in-situ modification.

    PubMed

    Guo, Zizhang; Zhang, Jian; Kang, Yan; Liu, Hai

    2017-11-01

    This study developed an humic acid (HA) in-situ modified activated carbon adsorbent (AC-HA) for the rapid and efficient removal of Pb(II) from aqueous media, and adsorption mechanisms are discussed. The physicochemical characteristics of activated carbons (AC) were investigated via N2 adsorption/desorption, scanning electron microscopy (SEM), Boehm's titration method and Fourier transform infrared spectroscopy (FTIR). AC-HA exhibited richer oxygen-containing functional groups than the original AC. In addition, the removal performance of AC-HA (250.0mg/g) toward Pb(II) was greatly improved compared with the original AC (166.7mg/g). The batch adsorption study results revealed that the Pb(II) adsorption data were best fit by the pseudo-second-order model of kinetics and Langmuir isotherm of isothermals, and therefore, the effect of the solution pH was studied. The superior performance of AC-HA was attributed to the HA modification, which contains numbers of groups and has a strong π-π interaction binding energy with AC and Pb(II) species. The adsorption mechanisms were confirmed via the XPS study. More importantly, the modified method is simple and has a low cost of production. Copyright © 2017 Elsevier Inc. All rights reserved.

  6. Ultrasound assisted reduction of graphene oxide to graphene in L-ascorbic acid aqueous solutions: kinetics and effects of various factors on the rate of graphene formation.

    PubMed

    Abulizi, Abulikemu; Okitsu, Kenji; Zhu, Jun-Jie

    2014-05-01

    The reduction of graphene oxide (GO) to graphene (rGO) was achieved by using 20 kHz ultrasound in L-ascorbic acid (L-AA, reducing agent) aqueous solutions under various experimental conditions. The effects of ultrasound power, ultrasound pulse mode, reaction temperature, pH value and L-AA amount on the rates of rGO formation from GO reduction were investigated. The rates of rGO formation were found to be enhanced under the following conditions: high ultrasound power, long pulse mode, high temperature, high pH value and large amount of L-AA. It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment. The pseudo rate and pseudo activation energy (Ea) of rGO formation were determined to discuss the reaction kinetics under both treatment. The Ea value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition. We proposed that physical effects such as shear forces, microjets and shock waves during acoustic cavitation enhanced the mass transfer and reaction of L-AA with GO to form rGO as well as the change in the surface morphology of GO. In addition, the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.

  7. Removal of Acid Black 1 and Basic Red 2 from aqueous solutions by electrocoagulation/Moringa oleifera seed adsorption coupling in a batch system.

    PubMed

    de Carvalho, Helder Pereira; Huang, Jiguo; Ni, Jiaheng; Zhao, Meixia; Yang, Xinyu; Wang, Xiansheng

    2015-01-01

    The removal of Acid Black 1 (AB1) and Basic Red 2 (BR2) from aqueous solutions via an electrocoagulation (EC)/Moringa oleifera seeds (MOS) adsorption coupling process by using aluminum and stainless steel electrode in a batch reactor is described in this study. The influences of the operational parameters, i.e. current density, MOS dosage, and dye initial concentration, on degree of color removal were studied, and the unit energy demand, the unit electrode material demand, and the charge loading were calculated and discussed. The amounts of adsorbent and energy consumption were considered as main criteria of process evaluation, and ideal conditions were chosen. The addition of an appropriate MOS dosage (0.6 g/L for AB1 and 5 g/L for BR2) resulted in faster decolorization of dyes especially at lower current densities and was simultaneously accompanied by a significant reduction in contact time compared to the conventional simple EC process. The coupling process achieved degree of removals above 99.3% and 94% for AB1 and BR2, respectively. The EC/MOS coupling technique could be recommended to replace the conventional simple EC because of its high degree of removal, short contact time, and low energy consumption.

  8. Rapid removal of Pb(II) from aqueous solution by chitosan-g-poly(acrylic acid)/attapulgite/ sodium humate composite hydrogels.

    PubMed

    Zhang, Junping; Jin, Yeling; Wang, Aiqin

    2011-04-01

    A series of novel granular chitosan-g-poly(acrylic acid)/attapulgite/sodium humate (CTS-g-PAA/APT/SH) composite hydrogels were successfully prepared by one-step free radical graft polymerization and applied as adsorbents for the removal of Pb(II) from aqueous solution. The effects of adsorbent composition (including the contents of APT, SH and CTS) on adsorption capacity and adsorption rate were investigated in detail. Results from kinetic experiments showed that the rate of Pb(II) adsorption on the composite hydrogels was quite fast, that more than 90% of the equilibrium adsorption capacity occurs within two minutes and that the adsorption equilibrium could be achieved within 10 minutes. The adsorption kinetics fit well with the pseudo-second order equation. The introduced SH is helpful for both adsorption capacity and adsorption rate. The -COOH and -COO of PAA, -NH2 of CTS, Ph-O and -COO- of SH, as well as cation exchange and Si-OH of APT, participate in adsorption of Pb(II). The synergistic effect of these groups is responsible for the high adsorption capacity and rate.

  9. Swelling and gel/sol formation of perchlorate-type layered double hydroxides in concentrated aqueous solutions of amino acid-related zwitterionic compounds.

    PubMed

    Iyi, Nobuo; Ishihara, Shinsuke; Kaneko, Yoshiro; Yamada, Hirohisa

    2013-02-26

    ClO(4)(-)MgAl-LDH3, a MgAl (Mg/Al = 3) layered double hydroxide (LDH) containing perchlorate, swells and forms colloidal suspensions (sols) via the gel state in concentrated aqueous solutions of zwitterionic compounds related to amino acids. In total, 36 zwitterionic compounds with different molecular structures and additional functional groups were examined at various concentrations, and the sol-formation ability was judged by the transmittance (at λ = 589 nm) of the resulting suspensions. At low concentration, the obtained suspensions were turbid, with transmittances of ~0%. However, above the threshold concentration (0.3-1.0 M), osmotic swelling occurred and the transmittances of the suspensions increased sharply with increases in concentration to reach maximum values of 70-95%. The threshold concentration and maximum transmittance value depended on the structure and the location of the functional groups. The enhancement of the permittivity of water by the zwitterions and the formation of H-bond networks were assumed to be the reasons for the swelling phenomenon. Similar gel/sol formation was observed for ClO(4)(-)LDHs with Mg/Al = 2, Ni/Al = 2, 3, and Co/Al = 2 and some NO(3)(-)LDHs. Large ClO(4)(-)LDH films could be prepared by filtration of the colloidal suspensions followed by washing and drying processes.

  10. Kinetic, equilibrium and thermodynamic studies on sorption of uranium and thorium from aqueous solutions by a selective impregnated resin containing carminic acid.

    PubMed

    Rahmani-Sani, Abolfazl; Hosseini-Bandegharaei, Ahmad; Hosseini, Seyyed-Hossein; Kharghani, Keivan; Zarei, Hossein; Rastegar, Ayoob

    2015-04-09

    In this work, the removal of uranium and thorium ions from aqueous solutions was studied by solid-liquid extraction using an advantageous extractant-impregnated resin (EIR) prepared by loading carminic acid (CA) onto Amberlite XAD-16 resin beads. Batch sorption experiments using CA/XAD-16 beads for the removal of U(VI) and Th(IV) ions were carried out as a function of several parameters, like equilibration time, metal ion concentration, etc. The equilibrium data obtained from the sorption experiments were adjusted to the Langmuir isotherm model and the calculated maximum sorption capacities in terms of monolayer sorption were in agreement with those obtained from the experiments. The experimental data on the sorption behavior of both metal ions onto the EIR beads fitted well in both Bangham and intra-particle diffusion kinetic models, indicating that the intra-particle diffusion is the rate-controlling step. The thermodynamic studies at different temperatures revealed the feasibility and the spontaneous nature of the sorption process for both uranium and thorium ions.

  11. Removal of Acid Violet 17 from aqueous solutions by adsorption onto activated carbon prepared from sunflower seed hull.

    PubMed

    Thinakaran, N; Baskaralingam, P; Pulikesi, M; Panneerselvam, P; Sivanesan, S

    2008-03-01

    The adsorption of Acid Violet 17 (AV17) was carried out using various activated carbons prepared from sunflower seed hull (SSH), an agricultural solid waste by-product. The effect of parameters such as agitation time, initial dye concentration, adsorbent dosage, pH and temperature were studied. The Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to best report the equilibrium isotherm data. Langmuir adsorption capacity was found to be 116.27 mg/g. Kinetic data followed pseudo-second-order kinetics. Maximum colour removal was observed at pH 2.0. It was observed that the rate of adsorption improves with increasing temperature and the process is endothermic. The adsorbent surface was analysed with a scanning electron microscope. The results indicate that activated sunflower seed hull could be an attractive option for colour removal from dilute industrial effluents.

  12. Adsorption of phthalic acid esters (PAEs) by amphiphilic polypropylene nonwoven from aqueous solution: the study of hydrophilic and hydrophobic microdomain.

    PubMed

    Zhou, Xiangyu; Wei, Junfu; Zhang, Huan; Liu, Kai; Wang, Han

    2014-05-30

    A kind of amphiphilic polypropylene nonwoven with hydrophilic and hydrophobic microdomain was prepared through electron beam induced graft polymerization and subsequent ring opening reaction and then utilized in the adsorption of phthalic acid esters (PAEs). To elucidate the superiority of such amphiphilic microdomain, a unique structure without hydrophilic part was constructed as comparison. In addition, the adsorption behaviors including adsorption kinetics, isotherms and pH effect were systematically investigated. The result indicated that the amphiphilic structure and the synergy between hydrophilic and hydrophobic microdomain could considerably improve the adsorption capacities, rate and affinity. Particularly the existence of hydrophilic microdomain could reduce the diffusion resistance and energy barrier in the adsorption process. These adsorption results showed that the amphiphilic PP nonwoven have the potential to be used in environmental application. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Rational design of interfacial properties of ferric (hydr)oxide nanoparticles by adsorption of fatty acids from aqueous solutions.

    PubMed

    Ponnurangam, Sathish; Chernyshova, Irina V; Somasundaran, Ponisseril

    2012-07-24

    Notwithstanding the great practical importance, still open are the questions how, why, and to what extent the size, morphology, and surface charge of metal (hydr)oxide nanoparticles (NPs) affect the adsorption form, adsorption strength, surface density, and packing order of organic (bio)molecules containing carboxylic groups. In this article, we conclusively answer these questions for a model system of ferric (hydr)oxide NPs and demonstrate applicability of the established relationships to manipulating their hydrophobicity and dispersibility. Employing in situ Fourier transform infrared (FTIR) spectroscopy and adsorption isotherm measurements, we study the interaction of 150, 38, and 9 nm hematite (α-Fe(2)O(3)) and ∼4 nm 2-line ferrihydrite with sodium laurate (dodecanoate) in water. We discover that, independent of morphology, an increase in size of the ferric (hydr)oxide NPs significantly improves their adsorption capacity and affinity toward fatty acids. This effect favors the formation of bilayers, which in turn promotes dispersibility of the larger NPs in water. At the same time, the local order in self-assembled monolayer (SAM) strongly depends on the morphological compatibility of the NP facets with the geometry-driven well-packed arrangements of the hydrocarbon chains as well as on the ratio of the chemisorbed to the physically adsorbed carboxylate groups. Surprisingly, the geometrical constraints can be removed, and adsorption capacity can be increased by negatively polarizing the NPs due to promotion of the outer-sphere complexes of the fatty acid. We interpret these findings and discuss their implications for the nanotechnological applications of surface-functionalized metal (hydr)oxide NPs.

  14. RECOVERY OF URANIUM FROM AQUEOUS PHOSPHATE-CONTAINING SOLUTIONS

    DOEpatents

    Igelsrud, I.; Stephen, E.F.

    1959-08-11

    ABS>A method is presented for recovering hexavalent uranium from an acidic phosphaie solution. A high molecular weight amine, such as a mixture of cccoanut oil amines, is added to the solution in such amount as to give a ratio of about 2000 parts by weight of amine to 1 part by weight of uranium. The uranium is precipitated with the amines and the whole filtered from the solution. The uranium is leached from the amine mass by washing with aqueous sodium carbonate solution; and the amine mixture is available for reuse.

  15. Efficacy of chlorine, acidic electrolyzed water and aqueous chlorine dioxide solutions to decontaminate Escherichia coli O157:H7 from lettuce leaves

    USDA-ARS?s Scientific Manuscript database

    This study compared the efficacy of chlorine (20 – 200 ppm), acidic electrolyzed water (50 ppm chlorine, pH 2.6), acidified sodium chlorite (20 – 200 ppm chlorite ion concentration, Sanova), and aqueous chlorine dioxide (20 – 200 ppm chlorite ion concentration, TriNova) washes in reducing population...

  16. UV-vis and Raman spectroelectrochemical investigation of the redox behavior of poly(5-cyanoindole) in acidic aqueous solutions

    NASA Astrophysics Data System (ADS)

    Talbi, H.; Billaud, D.; Louarn, G.; Pron, A.

    2000-03-01

    Spectroelectrochemical properties of conducting poly(5-cyanoindole) films deposited on indium tin oxide (ITO) and platinum electrodes are investigated using UV-vis and resonant Raman spectroscopies. The transitions from undoped to semi-conducting state of P5CN require the partial oxidation of the polymer to create radical-cations by insertion of charge-neutralizing anions into the polymer. In order to obtain detailed structural information from the vibrational spectra, it is necessary to know the vibrational modes of oxidation-sensitive bands. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The drastic changes in optical absorption and Raman spectra observed at various stage of oxidation were explained by the conversions between at least three different structures. On the basis of the Raman spectra, we have identified the vibrational modes associated with neutral and polaronic segments. The perturbation associated with the coexistence of these polaronic segments has been described as a quinoid structure growing on the expense of the benzoid one. The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in-situ Raman spectra than by ex-situ studies.

  17. UV-vis and Raman spectroelectrochemical investigation of the redox behavior of poly(5-cyanoindole) in acidic aqueous solutions.

    PubMed

    Talbi, H; Billaud, D; Louarn, G; Pron, A

    2000-03-01

    Spectroelectrochemical properties of conducting poly(5-cyanoindole) films deposited on indium tin oxide (ITO) and platinum electrodes are investigated using UV-vis and resonant Raman spectroscopies. The transitions from undoped to semi-conducting state of P5CN require the partial oxidation of the polymer to create radical-cations by insertion of charge-neutralizing anions into the polymer. In order to obtain detailed structural information from the vibrational spectra, it is necessary to know the vibrational modes of oxidation-sensitive bands. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The drastic changes in optical absorption and Raman spectra observed at various stage of oxidation were explained by the conversions between at least three different structures. On the basis of the Raman spectra, we have identified the vibrational modes associated with neutral and polaronic segments. The perturbation associated with the coexistence of these polaronic segments has been described as a quinoid structure growing on the expense of the benzoid one. The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in-situ Raman spectra than by ex-situ studies.

  18. An 17O NMR Study of Hydrolyzed Nb(V) in Weakly Acidic and Basic Aqueous Solution

    PubMed Central

    Marek, Keith A.

    2013-01-01

    Time-dependent 17O NMR spectra of basified decaniobate (Nb10O286−) solutions displayed intense resonances assigned to the well-known protonated hexaniobate anion (Nb6O198−) and two other species identified as heptaniobate (Nb7O229−) and protonated tetracosaniobate (Nb24O7224−) anions. The decaniobate ion showed no sign of protonation from pH 6 – 10, in contrast with the hexaniobate ion which was protonated at doubly-bridging oxygen sites at pH 10–13. Most (> 90%) of the heptaniobate formed 1 h after basification was transformed into other species after 3 weeks. Tetracosaniobate was formed reversibly from decaniobate, but only when KOH, NaOH and [(CH3)4N]OH were employed; none was observed after basification with [(n-C4H9)4N]OH. Moreover, far more tetracosaniobate was formed from KOH than from [(CH3)4N]OH. This effect was attributed to a tetracosaniobate cation binding site that binds K+ more readily than (CH3)4N+ but is too small to accommodate (n-C4H9)4N+. PMID:23585727

  19. Hydroxyl radical induced degradation of salicylates in aerated aqueous solution

    NASA Astrophysics Data System (ADS)

    Szabó, László; Tóth, Tünde; Homlok, Renáta; Rácz, Gergely; Takács, Erzsébet; Wojnárovits, László

    2014-04-01

    Ionizing radiation induced degradation of acetylsalicylic acid, its hydrolysis product salicylic acid and a salicylic acid derivative 5-sulpho-salicylic acid, was investigated in dilute aqueous solutions by UV-vis spectrophotometry, HPLC separation and diode-array or MS/MS detection, chemical oxygen demand, total organic carbon content and by Vibrio fischeri toxicity measurements. Hydroxyl radicals were shown to degrade these molecules readily, and first degradation products were hydroxylated derivatives in all cases. Due to the by-products, among them hydrogen peroxide, the toxicity first increased and then decreased with the absorbed dose. With prolonged irradiation complete mineralization was achieved.

  20. Mutual effects of Pb(II) and humic acid adsorption on multiwalled carbon nanotubes/polyacrylamide composites from aqueous solutions.

    PubMed

    Yang, Shubin; Hu, Jun; Chen, Changlun; Shao, Dadong; Wang, Xiangke

    2011-04-15

    This paper examines the adsorption of Pb(II) and a natural organic macromolecular compound (humic acid, HA) on polyacrylamide (PAAM) -grafted multiwalled carbon nanotubes (denoted as MWCNTs/PAAM), prepared by an N(2)-plasma-induced grafting technique. The mutual effects of HA/Pb(II) on Pb(II) and HA adsorption on MWCNTs/PAAM, as well as the effects of pH, ionic strength, HA/Pb(II) concentrations, and the addition sequences of HA/Pb(II) were investigated. The results indicated that Pb(II) and HA adsorption were strongly dependent on pH and ionic strength. The presence of HA led to a strong increase in Pb(II) adsorption at low pH and a decrease at high pH, whereas the presence of Pb(II) led to an increase in HA adsorption. The adsorbed HA contributed to modification of adsorbent surface properties and partial complexation of Pb(II) with the adsorbed HA. Different effects of HA/Pb(II) concentrations and addition sequences on Pb(II) and HA adsorption were observed, indicating different adsorption mechanisms. After adsorption of HA on MWCNTs/PAAM, the adsorption capacity for Pb(II) was enhanced at pH 5.0; the adsorption capacity for HA was also enhanced after Pb(II) adsorption on MWCNTs/PAAM. These results are important for estimating and optimizing the removal of metal ions and organic substances by use of MWCNT/PAAM composites.

  1. Potentiometric and Conductometric Study of Aqueous Solutions of Lithium and Sodium Salts of Poly(thiophen-3-ylacetic acid).

    PubMed

    Hostnik, Gregor; Vlachy, Vojko; Bondarev, Dmitrij; Jiří, Vohlídal; Cerar, Janez

    2012-09-01

    The title polymer, PTAA, practically free of ester groups was obtained by oxidative polymerization of methyl thiophen-3-ylacetate and subsequent basic hydrolysis of primary polymer. Poly(thiophen-3-ylacetic acid) has been thoroughly characterized by NMR, IR, Raman, and UV/Vis spectroscopy. The polyacid behavior during neutralization titrations with lithium and sodium hydroxides, carried out under nitrogen atmosphere, has been studied by conductometry and potentiometry. Henderson-Hasselbach plots of potentiometric titration curves show a break point at pH around 6, where the curve slope drops from 1.8 (at lower pH) to a value from 1.05 to 1.3 (at higher pH values). The UV/Vis spectra monitored during back titration show: (i) monotonous decrease of both λmax and εmax as pH decreases, (ii) the presence of the isosbestic point at 401 nm that can be ascribed to conformational transition of PTAA chains, and (iii) absence of the isosbestic point at 392 nm reported previously by other authors.

  2. Ibuprofen photodegradation in aqueous solutions.

    PubMed

    Iovino, Pasquale; Chianese, Simeone; Canzano, Silvana; Prisciandaro, Marina; Musmarra, Dino

    2016-11-01

    The advanced treatment of polluted liquid streams containing traces of pharmaceutical compounds is a major issue, since more and more effluents from pharma labs and wastewaters containing the excretions of medically treated humans and animals are discharged in the conventional wastewater treatment plants without previous effective treatments. Ibuprofen is a widely used non-steroidal anti-inflammatory drug (NSAID), which explains why it is found in wastewaters so often. In this paper, the removal of IBP from simulated water streams was investigated by using a lab-scale experimental device, consisting of a batch reactor equipped with a lamp emitting monochromatic UV light at a fixed wavelength (254 nm) and various intensities. Three sets of experiments were carried out: the first to study IBP concentration as a function of time, at different volumes of treated solutions (V = 10-30 mL); the second to explore the effect of pH on IBP degradation as a function of time (pH = 2.25-8.25) and the third to evaluate the effect of different UV light intensities on IBP degradation (E = 100-400 mJ m(-2)). The IBP initial concentration (IBP 0) was varied in the range 30-60 mg L(-1). The results obtained show that the concentration of IBP decreases along with treatment time, with a negative effect of the treated volume, i.e. smaller volumes, such as lower liquid heights, are more easily degraded. Moreover, the higher the pH, the better the IBP degradation; actually, when pH increases from 2.25 to 6.6 and 8.25, the IBP concentration, after an hour of treatment, decreases respectively to 45, 34 and 27 % of its initial value. In addition, as the intensity of light increases from 100 to 400 mJ m(-2), the IBP concentration decreases to 34 % of its initial value. A reaction scheme is put forward in the paper, which well describes the effects of volume, pH and light intensity on the IBP degradation measured experimentally. Moreover, the IBP degradation by-products have

  3. Copper removal from aqueous solutions by sugar beet pulp treated by NaOH and citric acid.

    PubMed

    Altundogan, H Soner; Arslan, N Ezgi; Tumen, Fikret

    2007-10-22

    Sugar beet pulp was converted into effective copper sorption material by treating subsequently with NaOH and citric acid. Compared with the untreated sugar beet pulp, the cation exchange capacity of the modified sugar beet pulp increased from 0.86 to 3.21 mequiv.g(-1). Swelling capacity and COD values of modified sugar beet pulp were found to be decreased in the ratio of 38% and 61%, respectively, compared to the corresponding values of native sugar beet pulp, meaning that modification causes stabilization. Sorption characteristics of the modified sugar beet pulp towards copper ions were studied with batch experiments. Pseudo-first, pseudo-second-order and intraparticle kinetic models were applied to the kinetic data and it was found that the sorption processes followed the pseudo-second-order rate kinetics with activation energy of 16.34 kJ mol(-1). The equilibration data fit best with the Langmuir isotherm the maximum copper sorption capacity of which is 119.43 mgg(-1). The mean free energy of copper sorption process calculated from Dubinin-Radushkevich model and the Polanyi potential concept was found to be in the range of 10.91-11.95 kJ mol(-1) showing that the main mechanism governing the sorption process is ion exchange. The negative values found for enthalpy change (-14.797 kJ mol(-1) over the range of 25-55 degrees C) and free energy change (-19.361 kJ mol(-1) for 25 degrees C) indicate that the sorption process is exothermic and spontaneous in nature.

  4. Photodecomposition of an acaricide, fenazaquin, in aqueous alcoholic solution.

    PubMed

    Bhattacharyya, Jayati; Banerjee, Hemanta; Bhattacharyya, Anjan

    2003-07-02

    Fenazaquin (I) is a new acaricide of the quinazoline class. The photodecomposition of I was studied in aqueous methanolic and 2-propanolic solution under UV light (30 h) and sunlight (70 h) separately. The photolytic half-lives in aqueous methanolic solution were found to be 17.1 h (UV) and 38.1 h (sunlight), whereas these were 12.9 h (UV) and 29.2 h (sunlight) for aqueous 2-propanolic solution; all followed a first-order reaction kinetics. Six photoproducts were obtained: beta-phenyl (p-tert-butyl) ethyl alcohol (II), 4-hydroxyquinazoline (III), p-tert-butyl vinyl benzene (IV), 2,4-dihydroxyquinazoline (V), phenyl (p-tert-butyl) acetic acid (VI), and 2-methyl-2-[4'-(2' '-hydroxyethyl)phenyl]propanoic acid (VII). Compounds VI and VII could be isolated only from aqueous 2-propanolic solution under sunlight irradiation. The major degradation products are formed as a result of cleavage of the ether bridge linking the quinazoline and phenyl ring systems of the molecule, oxidation of the tert-butyl substituent, and oxidation of the heterocyclic portion of the quinazoline ring. A probable mechanism of formation of the photoproducts is also suggested.

  5. Structure of Hydronium (H3O+)/Chloride (Cl-) Contact Ion Pairs in Aqueous Hydrochloric Acid Solution: A Zundel-like Local Configuration

    SciTech Connect

    Fulton, John L.; Balasubramanian, Mahalingam

    2010-09-15

    Details of the H3O+ and H2O structure in the first solvation shell about Cl- in aqueous HCl solutions are reported from x-ray absorption fine structure (XAFS) measurements. Results show increasing degrees of contact ion pairing between Cl- and H3O+ as the HCl concentration increases from 6.0 m, 10.0 m and finally 16.1 m HCl (concentrated acid). At the highest acid concentration there are on average, approximately 1.6 H3O+ ions and 4.2 H2O’s in the first shell about Cl-. The structure of the Cl-/H3O+ contact ion pair is distinctly different than that of the H2O structure about Cl-. The Cl-O bond length (2.98Å) for Cl-/H3O+ is approximately 0.16 Å shorter than the Cl-/H2O bond. The bridging proton resides at an intermediate position between Cl and O at 1.60 Å from the Cl- and approximately 1.37 Å from the O of the H3O+. The bridging-proton structure of this contact ion pair, [Cl-H-OH2], is similar to structure of the water Zundel ion, [H2O-H-OH2]+. In both cases there is a shortened Cl-O or O-O bond and the intervening proton bond distances are substantially longer than for the covalent bonds of either HCl or H2O. The results further our understanding of the interaction H3O+ with Cl- that is of interest to fundamental physical chemistry and that has consequences in biochemical, geochemical and atmospheric processes.

  6. Complexation of NpO2+ with (2-Hydroxyethyl)ethylenediaminetriacetic Acid (HEDTA) in Aqueous Solutions: Thermodynamic Studies and Structural Analysis

    SciTech Connect

    Li, Xingliang; Zhang, Zhicheng; Martin, Leigh R; Luo, Shunzhong; Rao, Linfeng

    2016-12-02

    Complexation of Np(V) with N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) was studied in aqueous solution (I = 1.0 mol L-1 NaClO4, t = 25 °C) by spectrophotometry, microcalorimetry and Extended X-ray absorption fine structure (EXAFS) spectroscopy. Equilibrium constants for the formation of three complexes, NpO2L2-, NpO2(HL)-, and (NpO2)2(OH)2L26-, were determined to be (6.91 ± 0.06), (4.28 ± 0.03) and -(4.93 ± 0.03), respectively. The enthalpies of complexation were determined to be -(8.0 ± 2.0) kJ mol-1 for NpO2L2- and -(2.2 ± 2.0) kJ mol-1 for NpO2(HL)-. Thermodynamic data of the complexation of Np(V) with HEDTA were compared to those of Np(V) with other aminopolycarboxylic acids, gaining insight into the possible coordination modes of the complexes. The EXAFS studies provided further structural information on those modes. In both NpO2L2- and NpO2(HL)- complexes, HEDTA coordinates to Np(V) in a tridentate mode through two oxygens of two carboxylic groups and one nitrogen of the amine group. In the (NpO2)2(OH)2L26- complex, two Np(V) atoms are bridged by two hydroxides and each HEDTA maintains the tridentate coordination mode.

  7. Adsorption behavior of levulinic acid onto microporous hyper-cross-linked polymers in aqueous solution: Equilibrium, thermodynamic, kinetic simulation and fixed-bed column studies.

    PubMed

    Lin, Xiaoqing; Huang, Qianlin; Qi, Gaoxiang; Xiong, Lian; Huang, Chao; Chen, Xuefang; Li, Hailong; Chen, Xinde

    2017-03-01

    The recovery of levulinic acid (LA) from aqueous solution and actual biomass hydrolysate by a microporous hyper-cross-linked polymer, SY-01, was investigated for the first time under batch and fixed-bed column conditions. The results showed that the optimum pH should be in the acidic range (pH < 3.0) without adjusting the pH. In the single-component system equilibrium study, the Langmuir isotherm model fits the LA adsorption onto SY-01 resin better than the Freundlich isotherm model, indicating that LA adsorption onto SY-01 resin under the concentration range studied is a monolayer homogeneous adsorption process. The maximum adsorption capacity of LA onto SY-01 resin decreased with increasing temperature, ranging from 103.74 to 95.70 mg/g. The obtained thermodynamic parameters suggested that the adsorption of LA on SY-01 was spontaneous (ΔG(0)<-3.788 kJ/mol), and exothermic (ΔH(0) = -11.764 kJ/mol). For kinetic study, the adsorption of LA onto SY-01 resin at various operating conditions follows the pore diffusion model and the intraparticle diffusion is the rate-limiting step for the adsorption of LA onto SY-01 resin. The effective pore diffusivity was dependent upon temperature, but independent of initial LA concentration, and were 3.306 × 10(-10), 5.274 × 10(-10) and 7.707 × 10(-10) m(2)/s at 298, 318 and 338 K, respectively. In desorption process, the recovery efficiency of LA from SY-01 resin was 99.39%, and LA concentration in the eluent was raised 2.97-fold. In conclusion, our results show that the SY-01 resin has potential application in product recovery of LA from biomass hydrolysate.

  8. Polyacrylamido-2-methyl-1-propane sulfonic acid-grafted-natural rubber as bio-adsorbent for heavy metal removal from aqueous standard solution and industrial wastewater.

    PubMed

    Phetphaisit, Chor Wayakron; Yuanyang, Siriwan; Chaiyasith, Wipharat Chuachuad

    2016-01-15

    Bio-adsorbent modified natural rubber (modified NR) was prepared, by placing the sulfonic acid functional group on the isoprene chain. This modification was carried out with the aim to prepare material capable to remove heavy metals from aqueous solution. The structures of modified NR materials were characterized by FT-IR and NMR spectroscopies. Thermal gravimetric analysis of modified NR showed that the initial degradation temperature of rubber decreases with increasing amount of polyacrylamido-2-methyl-1-propane sulfonic acid (PAMPS) in the structure. In addition, water uptake of the rubber based materials was studied as a function of time and content of PAMPS. The influence of the amount of PAMPS grafted onto NR, time, pH, concentration of metal ions, temperature, and regeneration were studied in terms of their influence on the adsorption of heavy metals (Pb(2+), Cd(2+) and Cu(2+)). The adsorption isotherms of Pb(2+) and Cd(2+) were fitted to the Freundlich isotherm model, while Cu(2+) was fitted to the Langmuir isotherm. However, the results from these two isotherms resulted in a similar behavior. The adsorption capacity of the modified NR for the various heavy metals was in the following order: Pb(2+)∼Cd(2+)>Cu(2+). The maximum adsorption capacities of Pb(2+), Cd(2+), and Cu(2+) were 272.7, 267.2, and 89.7 mg/g of modified rubber, respectively. Moreover, the modified natural rubber was used for the removal of metal ions in real samples of industrial effluents where the efficiency and regeneration were also investigated.

  9. Complexation of NpO2+ with (2-Hydroxyethyl)ethylenediaminetriacetic Acid (HEDTA) in Aqueous Solutions: Thermodynamic Studies and Structural Analysis

    DOE PAGES

    Li, Xingliang; Zhang, Zhicheng; Martin, Leigh R; ...

    2016-12-02

    Complexation of Np(V) with N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) was studied in aqueous solution (I = 1.0 mol L-1 NaClO4, t = 25 °C) by spectrophotometry, microcalorimetry and Extended X-ray absorption fine structure (EXAFS) spectroscopy. Equilibrium constants for the formation of three complexes, NpO2L2-, NpO2(HL)-, and (NpO2)2(OH)2L26-, were determined to be (6.91 ± 0.06), (4.28 ± 0.03) and -(4.93 ± 0.03), respectively. The enthalpies of complexation were determined to be -(8.0 ± 2.0) kJ mol-1 for NpO2L2- and -(2.2 ± 2.0) kJ mol-1 for NpO2(HL)-. Thermodynamic data of the complexation of Np(V) with HEDTA were compared to those of Np(V) with othermore » aminopolycarboxylic acids, gaining insight into the possible coordination modes of the complexes. The EXAFS studies provided further structural information on those modes. In both NpO2L2- and NpO2(HL)- complexes, HEDTA coordinates to Np(V) in a tridentate mode through two oxygens of two carboxylic groups and one nitrogen of the amine group. In the (NpO2)2(OH)2L26- complex, two Np(V) atoms are bridged by two hydroxides and each HEDTA maintains the tridentate coordination mode.« less

  10. Electrochemical and FTIR studies of the mutual influence of lead(II) or iron(III) and phenol on their adsorption from aqueous acid solution by modified activated carbons.

    PubMed

    Pakuła, M; Walczyk, M; Biniak, S; Swiatkowski, A

    2007-09-01

    Cyclic voltammetry and spectral FTIR studies of the influence of activated carbon surface modification on the co-adsorption of metal cation (lead or iron) and phenol from aqueous acidic solution were carried out. The diversity in surface chemical structure was achieved by applying different procedures of inorganic matter removal and by modifying the carbon samples in various ways: heating under vacuum, aminoxidation in an ammonia-oxygen atmosphere, oxidation with concentrated nitric acid. The quantities of adsorbed metal ions (Pb(2+) or Fe(3+)) and phenol from solutions containing cation or phenol separately or in a mixture were determined. The adsorption capacity from acidic aqueous acidic solution depends on the chemical properties of the activated carbon surface (e.g., decrease in phenol adsorption with relative lower basicity of the adsorbent). The electrochemical parameters of electrodes made from the carbon samples were estimated, and some possible electrochemical reactions were determined from voltammograms recorded in acid electrolyte solution containing adsorbed species (separately or as a mixture). Relationships were found between metal ion adsorption and electrochemical behavior of Pb(2+)/Pb(4+) and Fe(3+)/Fe(2+) couples on the one hand, and the presence of phenol in the solutions tested and the influence of surface chemistry of the carbon electrodes on electrochemical processes on the other. The changes in adsorption capacity with respect to the adsorbates used and the changes in FTIR spectra of the carbons as a result of adsorption and/or coupling phenol molecules are discussed.

  11. Preparation of thin ceramic films via an aqueous solution route

    DOEpatents

    Pederson, Larry R.; Chick, Lawrence A.; Exarhos, Gregory J.

    1989-01-01

    A new chemical method of forming thin ceramic films has been developed. An aqueous solution of metal nitrates or other soluble metal salts and a low molecular weight amino acid is coated onto a substrate and pyrolyzed. The amino acid serves to prevent precipitation of individual solution components, forming a very viscous, glass-like material as excess water is evaporated. Using metal nitrates and glycine, the method has been demonstrated for zirconia with various levels of yttria stabilization, for lanthanum-strontium chromites, and for yttrium-barium-copper oxide superconductors on various substrates.

  12. Critical Heat Flux of Butanol Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Shotaro; Shoji, Masahiro

    It is known that the addition of small amount of alcohol such as butanol to water enhances the CHF. Such aqueous solution is actively applied to heat transfer devices such as heat pipes and microchannel cooling systems, however, the fundamental characters of boiling have not been fully understood. In the present research, the experiment of boiling heat transfer is performed on a heated wire by employing butanol aqueous solution as a typical test solution and by changing concentration 1-butanol and subcooling in a wide range. Bubbling aspects were observed using high-speed video camera. It is found from the experiment that CHF is 2 to 3 times higher than that of pure water and generating bubbles are tiny even at the saturated condition. The dependence of CHF on subcooling is found to be curious showing that CHF decreases first, takes a minimum, and then increases with increasing subcooling. These results suggest that the butanol aqueous solution is a promising liquid for the application of boiling to a small-scaled cooling device.

  13. Hydroxide ion hydration in aqueous solutions.

    PubMed

    Smiechowski, Maciej; Stangret, Janusz

    2007-04-19

    Hydroxide ion hydration was studied in aqueous solutions of selected alkali metal hydroxides by means of Fourier transform infrared (FTIR) spectroscopy of HDO isotopically diluted in H2O. The quantitative difference spectra procedure was applied for the first time to investigate such systems. It allowed removal of bulk water contribution and separation of the spectra of solute-affected HDO. The obtained spectral data were confronted with ab initio calculated structures of small gas-phase and polarizable continuum solvation model (PCM) solvated aqueous clusters, OH-(H2O)n, n = 1-7, to establish the structural and energetic states of hydration spheres of the hydrated hydroxide anion. This was achieved by comparison of the calculated optimal geometries with the interatomic distances derived from HDO band positions. The energetic state of water in OH- hydration shells, as revealed by solute-affected HDO spectra, is similar to that of an isoelectronic F- anion. No evidence was found for the existence of stable hydroxide dimer, H3O2-, in an aqueous solution. Spectral data do confirm, however, existence of a weak interaction with a single water molecule at the hydrogen site of OH-.

  14. Infrared titration of aqueous sulfuric acid

    SciTech Connect

    Max, J.J.; Menichelli, C.; Chapados, C.

    2000-03-30

    This paper presents the infrared (IR) titration of aqueous sulfuric acid solutions (0.50 M) obtained by the attenuated total reflection (ATR) sampling technique. After subtracting the water spectra, the spectra of the ionic species of H{sub 2}SO{sub 4} in the 0--14 pH range were separated by factor analysis (FA) which also gave their abundance. The results were in agreement with the theoretical calculation of the distribution of the species. Three sulfate species were found: HSO{sub 4}{sup {minus}}, SO{sub 4}{sup 2{minus}}, and HSO{sub 4}{sup {minus}}/HCl. The latter stands for the bisulfate--hydronium complex formed by the addition of HCl to obtain measurements in the 0--0.47 pH range. For 0.50 M sulfuric acid, the comparison between the experimentally IR-determined quantities and the theoretical values gave a mean activity coefficient of 0.12 {+-} 0.04, a value comparable to that from electrochemical measurements. Three types of water were quantitatively determined in the solutions: acidic water, basic water, and neutral water. The latter is always present while the two others are present in the low and high pH range, respectively. Another type of water strongly associated with the sulfates is also present. Moreover, knowledge of the behavior of the different types of water as the titration proceeded permitted us to give the details of the neutralization reactions of aqueous sulfuric acid by sodium hydroxide.

  15. Aqueous solution dispersement of carbon nanotubes

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Woo (Inventor); Park, Cheol (Inventor); Choi, Sang H. (Inventor); Lillehei, Peter T. (Inventor); Harrison, Joycelyn S. (Inventor)

    2011-01-01

    Carbon nanotubes (CNTs) are dispersed in an aqueous buffer solution consisting of at least 50 weight percent water and a remainder weight percent that includes a buffer material. The buffer material has a molecular structure defined by a first end, a second end, and a middle disposed between the first and second ends. The first end is a cyclic ring with nitrogen and oxygen heteroatomes, the middle is a hydrophobic alkyl chain, and the second end is a charged group.

  16. Optimization of aqueous degassing of rubber solutions

    SciTech Connect

    Rotenberg, E.B.; Slutsman, N.N.

    1983-02-01

    The optimality criterion of the aqueous degassing process of rubber solutions is proposed. The limitation system for the variables of the process is formulated. The problems of determination of the optimal temperature and average residence time of a rubber crumb in each degasifier, the number of degasifiers, and the total average residence time of a rubber crumb in the system at the planning and control stages are solved.

  17. Effect of acidity on the equilibria of formation of mixed Co2+ complexes with heparin and arginine in aqueous solutions at 37°C

    NASA Astrophysics Data System (ADS)

    Feofanova, M. A.; Frantseva, Yu. V.; Semenov, A. N.; Baranova, N. V.; Zhuravlev, E. V.

    2014-02-01

    Results from studying interactions in the heparin-Co2+ ion-arginine system are presented. The constants of formation of mixed Co2+ complexes with heparin and arginine in aqueous solutions in a broad pH range at 37°C are determined potentiometrically. The chemical equilibria in the system are simulated and the stoichiometry of formation of the complex forms is determined.

  18. Pressure Dependence of the Acid/Base Equilibria of Methyl Orange in Aqueous Solutions to 1000 bars at 20°C

    SciTech Connect

    Suleimenov, Oleg M; Boily, Jean F

    2006-07-31

    The pressure dependence on the acid/base equilibria of methyl orange in aqueous solution was measured at 20°C in the 1-1000 bar range with a newly designed flow-through spectrophotometric cell. Combined chemometric and thermodynamic analyses of uv-vis spectrophotometric data were used to extract the dissociation constants as well as the changes in molar volume and isothermal compressibility of methyl orange as a function of pressure. The results show increasing pressure promotes the deprotonation of the methyl orange, with pK values ranging from 3.505 at 1 bar to 3.445 (0.002) at 1000 bars. Increasing pressure also yields small values of negative changes in the molar volume ranging from –6.9 cm3∙mol-1 at 1 bar to –1.7 cm3∙mol-1 at 1000 bars. The isothermal compressibility of methyl orange in this pressure range was estimated using the 2nd derivative of 2nd and 3rd order polynomial fits to the constants and gave rise to a constant value of –48.4x 10-4 cm3∙mol-1∙bar-1 in the former case, and increasing values from -107×10-4 cm3∙mol-1∙bar-1 at 1 bar to 3.43×10-4 cm3∙mol-1∙bar-1 at 1000 bars in the latter case. Molar absorption coefficients for the protonated and deprotonated species were also shown to be only slightly affected by pressure changes and can be used to accurately predict the absorption spectra of methyl orange as a function of pressure.

  19. Cationic gemini surfactant as a dual linker for a cholic acid-modified polysaccharide in aqueous solution: thermodynamics of interaction and phase behavior.

    PubMed

    Bai, Guangyue; Wu, Hui; Lou, Pengxiao; Wang, Yujie; Nichifor, Marieta; Zhuo, Kelei; Wang, Jianji; Bastos, Margarida

    2017-01-04

    Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (ΔHobs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.

  20. Experimental and theoretical vibrational spectroscopy studies of acetohydroxamic acid and desferrioxamine B in aqueous solution: Effects of pH and iron complexation

    NASA Astrophysics Data System (ADS)

    Edwards, David C.; Nielsen, Steen B.; Jarzęcki, Andrzej A.; Spiro, Thomas G.; Myneni, Satish C. B.

    2005-07-01

    The deprotonation and iron complexation of the hydroxamate siderophore, desferrioxamine B (desB), and a model hydroxamate ligand, acetohydroxamic acid (aHa), were studied using infrared, resonance Raman and UV-vis spectroscopy. The experimental spectra were interpreted by a comparison with DFT calculated spectra of aHa (partly hydrated) and desB (reactive groups of unhydrated molecule) at the B3LYP/6-31G* level of theory. The ab initio models include three water molecules surrounding the deprotonation site of aHa to account for partial hydration. Experiments and calculations were also conducted in D 2O to verify spectral assignments. These studies of aHa suggest that the cis-keto-aHa is the dominant form, and its deprotonation occurs at the oxime oxygen atom in aqueous solutions. The stable form of iron-complexed aHa is identified as Fe(aHa) 3 for a wide range of pH conditions. The spectral information of aHa and an ab initio model of desB were used to interpret the chemical state of different functional groups in desB. Vibrational spectra of desB indicate that the oxime and amide carbonyl groups can be identified unambiguously. Vibrational spectral analysis of the oxime carbonyl after deprotonation and iron complexation of desB indicates that the conformational changes between anion and the iron-complexed anion are small. Enhanced electron delocalization in the oxime group of Fe-desB when compared to that of Fe(aHa) 3 may be responsible for higher stability constant of the former.