Showing papers on "Oxalic acid published in 2007"
TL;DR: In this paper, an expanded aqueous phase oxidation mechanism for glyoxal is proposed that reasonably explains the concentration dynamics of formic and oxalic acids and includes larger multifunctional compounds.
463 citations
TL;DR: In this article, the catalytic behavior of the Fe3+/Fe2+ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O-2-diffusion cathode have been used.
Abstract: The catalytic behavior of the Fe3+/Fe2+ System in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O-2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na2SO4 as supporting electrolyte and Fe3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical ((OH)-O-center dot) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe2+ + H2O2, both of them generated at the cathode). The catalytic behavior of the Fe3+/Fe2+ system mainly depends on the cathode tested. In the cells with an O-2-diffusion cathode, H2O2 is largely accumulated and the Fe3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe3+ concentration, because this leads to a higher quantity of Fe2+ regenerated at the cathode and, subsequently, to a greater (OH)-O-center dot production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H2O2 is electrogenerated in small extent, whereas Fe2+ is largely accumulated because the regeneration of this ion from Fe3+ reduction at the cathode is much faster than its oxidation to Fe3+ at the anode. In this case, an Fe3+ concentration as low as 0.2 mM is required to obtain the maximum (OH)-O-center dot generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O-2 diffusion cell because the final Fe3+-oxalate complexes are difficult to oxidize with (OH)-O-center dot. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of (OH)-O-center dot generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe3+, because oxalic acid and its Fe2+ complexes are directly oxidized with (OH)-O-center dot in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution. (c) 2006 Elsevier B.V. All rights reserved.
376 citations
TL;DR: In this paper, the antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O2 diffusion cathode.
249 citations
TL;DR: In this article, the effect of oxalic acid and HEDTA complexant on the extraction of actinides (III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from a high active raffinate (HAR) has been evaluated.
Abstract: The extractant, N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) has been evaluated for the separation of actinides(III) and lanthanides(III) from a high active raffinate (HAR). The effect of oxalic acid and HEDTA complexant on the extraction of actinides(III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from synthetic HAR has been studied with 0.2 mol/L TODGA in TPH. With an extractant mixture of TODGA and tributyl phosphate (TBP) the amount of oxalic acid can be reduced to less than 0.3 mol/L for the effective complexation of zirconium, whereas the distribution ratios of actinides(III) and lanthanides(III) are still high for the separation from HAR. Furthermore the maximum loading of lanthanides (e.g. Nd) can be significantly increased by adding TBP to the extractant. However, the extraction of oxalic acid and nitric acid also increased by the addition of TBP, which can lead to problems during back extraction of the loaded extractant. Extraction studies after radio...
210 citations
TL;DR: In this article, a one-step flame spray pyrolysis (FSP) technique was used to synthesize Fe-doped TiO2 photocatalyst with high temperature annealing.
191 citations
TL;DR: In this article, the characteristics of NaOH-, KOH- and NH 4 OH-oxalic acid mixtures were also determined in the presence of oxalate concentration, solution pH and temperature.
181 citations
TL;DR: In this paper, the degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles.
Abstract: The commercially available TiO2-photocatalyst (Degussa P25) was modified with nanosized gold particles by the photoreduction method at four different values of the pH factor of the medium. The characterization of the synthesized catalysts was carried out by the BET method, X-ray photoelectron spectroscopy (XPS), TEM and the adsorption of the model pollutant. A remarkable influence of the pH on the particle size of Au was registered upon investigating the catalysts by XPS and TEM methods. The size of the gold nanoparticles on the TiO2 surface decreases with increase in the pH of the medium. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles. The photocatalytic activity of TiO2, modified with gold, was found to increase with the decrease of the size of the gold nanoparticles on the surface of the photocatalytic material. The maximal value of the photocatalytic activity (twice higher than that of the semiconducting support) is registered in the case of gold photoreduction at pH 7. The adsorption properties of the catalysts, as well as the size of the noble metal nanoparticles on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schotky barriers on the metal-semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.
164 citations
TL;DR: The ultimate product is oxalic acid, which forms very stable Fe(3+)-oxalato complexes under electro-Fenton conditions, which is viable for treating acidic wastewaters containing this pollutant.
156 citations
Abstract: This work shows that aqueous solutions of clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid), the bioactive metabolite of various lipid-regulating drugs, up to saturation at pH 3.0 are efficiently and completely degraded by electrochemical advanced oxidation processes such as electro-Fenton and photoelectro-Fenton with Fe2+ and UVA light as catalysts using an undivided electrolytic cell with a boron-doped diamond (BDD) anode and an O2-diffusion cathode able to electrogenerate H2O2. This is feasible in these environmentally friendly methods by the production of oxidant hydroxyl radical at the BDD surface from water oxidation and in the medium from Fenton's reaction between Fe2+ and electrogenerated H2O2. The degradation process is accelerated in photoelectro-Fenton by additional photolysis of Fe3+ complexes under UVA irradiation. Comparative treatments by anodic oxidation with electrogenerated H2O2, but without Fe2+, yield much slower decontamination. Chloride ion is released and totally oxidized to chlorine at the BDD surface in all treatments. The decay kinetics of clofibric acid always follows a pseudo-first-order reaction. 4-Chlorophenol, 4-chlorocatechol, hydroquinone, p-benzoquinone and 2-hydroxyisobutyric, tartronic, maleic, fumaric, formic and oxalic acids, are detected as intermediates. The ultimate product is oxalic acid, which is slowly but progressively oxidized on BDD in anodic oxidation. In electro-Fenton this acid forms Fe3+–oxalato complexes that can also be totally destroyed at the BDD anode, whereas in photoelectro-Fenton the mineralization rate of these complexes is enhanced by its parallel photodecarboxylation with UVA light.
140 citations
TL;DR: The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter participated in the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) mission during August-September 2006 as mentioned in this paper.
Abstract: The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter participated in the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) mission during August–September 2006. A particle-into-liquid sampler (PILS) coupled to ion chromatography was used to characterize the water-soluble ion composition of aerosol and cloud droplet residual particles (976 5-min PM_(1.0) samples in total). Sulfate and ammonium dominated the water-soluble mass (NH_4+ + SO_4^(2−) = 84 ± 14%), while organic acids contributed 3.4 ± 3.7%. The average NH_4^+:SO_4^(2−) molar ratio was 1.77 ± 0.85. Particulate concentrations of organic acids increased with decreasing carbon number from C_9 to C_2. Organic acids were most abundant above cloud, presumably as a result of aqueous phase chemistry in cloud droplets, followed by subsequent droplet evaporation above cloud tops; the main product of this chemistry was oxalic acid. The evolution of organic acids with increasing altitude in cloud provides evidence for the multistep nature of oxalic acid production; predictions from a cloud parcel model are consistent with the observed oxalate:glyoxylate ratio as a function of altitude in GoMACCS cumuli. Suppressed organic acid formation was observed in clouds with relatively acidic droplets, as determined by high particulate nitrate concentrations (presumably high HNO_3 levels too) and lower liquid water content, as compared to other cloud fields probed. In the Houston Ship Channel region, an area with significant volatile organic compound emissions, oxalate, acetate, formate, benzoate, and pyruvate, in decreasing order, were the most abundant organic acids. Photo-oxidation of m-xylene in laboratory chamber experiments leads to a particulate organic acid product distribution consistent with the Ship Channel area observations.
134 citations
TL;DR: This study provided guidance for the selection of organic acids to enhance the electrokinetic (EK) remediation of copper and cadmium from contaminated soils.
TL;DR: The results show that deliquescence can transform API to cocrystal or reverse the reaction given the right conditions and the interplay between moisture uptake and dissolution determines the liquid phase composition, supersaturation, and cocystal formation rates.
Abstract: The purpose of this study is to determine the mechanisms by which moisture can generate cocrystals when solid particles of cocrystal reactants are exposed to deliquescent conditions (when moisture sorption forms an aqueous solution). It is based on the hypothesis that cocrystallization behavior during water uptake can be derived from solution chemistry using models that describe cocrystal solubility and reaction crystallization of molecular complexes. Cocrystal systems were selected with active pharmaceutical ingredients (APIs) that form hydrates and include carbamazepine, caffeine, and theophylline. Moisture uptake and crystallization behavior were studied by gravimetric vapor sorption, X-ray powder diffraction, and on-line Raman spectroscopy. Results indicate that moisture uptake generates cocrystals of carbamazepine−nicotinamide, carbamazepine−saccharin, and caffeine or theophylline with dicarboxylic acid ligands (oxalic acid, maleic acid, glutaric acid, and malonic acid) when solid mixtures with cocry...
TL;DR: A method for the preparation of anatase TiO2, which is stable to a temperature as high as 900 °C, without using any complex cationic dopants is presented in this article.
Abstract: A method for the preparation of anatase TiO2, which is stable to a temperature as high as 900 °C, without using any complex cationic dopants is presented. The synthetic procedure involves the reaction of titanium tetraisopropoxide (TTIP) with trifluoroacetic acid (TFA) followed by hydrolysis and sol−gel conversion to the xerogel and further calcination. The retention of the anatase phase to high temperatures can be attributed to the presence of small amounts of fluorine in the lattice, which is gradually removed between 500 and 900 °C as confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopic analysis. Samples prepared with a 1:16 TTIP/TFA composition calcined at 900 °C showed significantly higher photocatalytic activity compared to the control sample, standard commercial photocatalyst Degussa P25, and samples prepared using acetic acid and oxalic acid. The high-temperature anatase phase stability, determined by X-ray diffraction and Raman spectroscopy, coupled with its ...
TL;DR: In this article, a reductive acid leaching with sulphuric acid in the presence of oxalic acid as reductant was used to extract zinc and manganese from alkaline and zinc-carbon spent batteries.
TL;DR: The results showed that some useful chemicals and biofuels could be obtained by this process and the Higher Heating Value of the residue and the acetone-soluble fractions were higher than that of bagasse.
TL;DR: The results demonstrated that the photodegradation of BPA depends strongly on the properties of iron oxides and oxalate, and pH, and that the optimal pH value should be in the range of 3-4.
TL;DR: In this paper, the performance of the grinding-derived catalysts is investigated in the steam reforming of methanol (SRM), and the results show that they exhibit superior performance to their conventional counterparts obtained by wet-chemical methods.
TL;DR: The properties of copper-based pillared clays (Cu-PILC) have been studied and compared with those of the analogous iron-based clays in the wet hydrogen peroxide catalytic oxidation (WHPCO) of model phenolic compounds (p-coumaric and p-hydroxybenzoic acids) and real olive oil milling wastewater (OMW) as discussed by the authors.
Abstract: The properties of copper-based pillared clays (Cu-PILC) have been studied and compared with those of the analogous iron-based clays (Fe-PILC) in the wet hydrogen peroxide catalytic oxidation (WHPCO) of model phenolic compounds (p-coumaric and p-hydroxybenzoic acids) and real olive oil milling wastewater (OMW). These two catalysts show comparable performances in all these reactions, although they show some differences in the rates of the various steps of reaction. In particular, Cu-PILC shows a lower formation of oxalic acid (main reaction intermediate) with respect to Fe-PILC. Both catalysts show no leaching of the transition metal differently from other copper-based catalysts prepared by wetness impregnation on oxides (alumina, zirconia) or ion-exchange of clays (bentonite) or zeolite ZSM-5. No relationship was observed between copper reducibility in the catalyst and the performance in WHPCO, as well as between the rate of copper leaching and catalytic behavior. Cu-PILC shows a comparable activity to dissolved Cu2+ ions, although the turnover number is lower assuming that all copper ions in Cu-PILC are active. Cu-PILC shows a high resistance to leaching and a good catalytic performance, which was attributed to the presence of copper essentially in the pillars of the clay. A high efficiency in H2O2 use in the first hour of reaction with the participation of dissolved O2 in solution was also shown. For longer reaction times, however, the efficiency of H2O2 use considerably decreases.
TL;DR: In this paper, two fungal isolates (Aspergillus niger 1B and 6A) displaying superior phosphate solubilization and hydrolytic enzyme secretion were studied using P forms of calcium (Ca-P), iron (Fe-P) and aluminum (Al-P).
Abstract: Two of 187 fungal isolates (Aspergillus niger 1B and 6A) displaying superior phosphate (P) solubilization and hydrolytic enzyme secretion were studied using P forms of calcium (Ca-P), iron (Fe-P), and aluminum (Al-P). Phosphate solubilization in a sucrose-basal salt (SB) broth was increased and pH decreased by both isolates. In Ca-P medium, solubilization for 6A was approximately 322 μg P mL−1 and pH decreased by 4.2 units to 2.3 in 72 h. However, when pH value of the SB broth was lowered to 2.5 using HCl, 65.3 ± 0.4 μg mL−1 of P was released from Ca-P, whereas trace amounts of P were released from Fe-P and Al-P. Both isolates displayed enhanced Al-P solubilization using NH4Cl rather than KNO3 as the N source; final pH values were not significantly different. With Ca-P, gluconic acid was predominantly produced by 1B and 6A, whereas oxalic acid predominated with Fe-P and Al-P. Addition of gluconic acid (final concentration of 8.5 μmol mL−1) to Ca-P-supplemented SB lowered pH (2.9) and solubilized phosphate (146.0 ± 1.0 μg mL−1). Similarly, addition of oxalic acid (final concentration 6.6 μmol mL−1) to Ca-P- and Fe-P-amended media solubilized P (60.2 ± 0.9 and 21.6 ± 2.1 μg mL−1, respectively), although these quantities were significantly lower than those detected in unamended SB. The presence of unidentified P solubilized compound(s) in the dialyzed (MW>500) supernatant warrants further study. In pot experiments, significant increases in plant (Brassica chinensis Linn.) dry weight and N and P contents were observed with the addition of isolate 6A, when a small amount of organic fertilizer together with either rock phosphate (South African apatite) or Ca-P served as the main P sources.
TL;DR: In this article, the chemistry of formic, acetic and oxalic acids was studied at four sites representing the urban and rural conditions in Beijing from March 2002 to October 2003.
TL;DR: In this paper, the formation of spinel compound ZnCo2O4 has been confirmed by thermogravimetry (TGA) and X-ray powder diffraction (XRD) and Infra-red spectra (IR).
TL;DR: It is proved that oxalic acid could improve the photocatalytic efficiency in the solar-Fenton process and the effect of pH value and the concentration of dye, Fe(2+), H(2)O(2), and oxAlic acid on Eosin Y degradation efficiency were investigated.
TL;DR: In this paper, a mango fruit (Mangifera indica L. cv. Zill) was dipped in 5 mM oxalic acid solution for 10 min at 25 °C to investigate effects on ripening and decay incidence during storage at room temperature.
TL;DR: Results indicate that components producing relatively soluble ACP are more likely to reduce P stability and precipitation rate of Ca phosphate in soils and sediments than are components that have less effect on the crystallinity.
TL;DR: The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory and the rate constant predicted for the formation of CO2 and HOCOH agrees well with available experimental data.
Abstract: The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decomposition of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate constants for the dehydration and decarboxylation reactions are in good agreement with the experimental data. The calculated CO/CO2 ratio, 13.6−13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured experimentally by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramolecular hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decomposition channels of oxalic acid producing CO2 + HO...
TL;DR: It was found that the presence of nano-TiO2 more or less improved the efficiency of the photo-induced chemical/cold vapor generation (photo-CVG) with most of the organic reductants.
Abstract: With UV irradiation, Hg(2+) in aqueous solution can be converted into Hg(0) cold vapor by low molecular weight alcohols, aldehydes, or carboxylic acids, e.g., methanol, formaldehyde, acetaldehyde, glycol, 1,2-propanediol, glycerol, acetic acid, oxalic acid, or malonic acid. It was found that the presence of nano-TiO(2) more or less improved the efficiency of the photo-induced chemical/cold vapor generation (photo-CVG) with most of the organic reductants. The nano-TiO(2)-enhanced photo-CVG systems can be coupled to various analytical atomic spectrometric techniques for the determination of ultratrace mercury. In this work, we evaluated the application of this method to the atomic fluorescence spectrometric (AFS) determination of mercury in cold vapor mode. Under the optimized experimental conditions, the instrumental limits of detection (based on three times the standard deviation of 11 measurements of a blank solution) were around 0.02-0.04 microg L(-1), with linear dynamic ranges up to 15 microg L(-1). The interference of transition metals and the mechanism of the photo-CVG are briefly discussed. Real sample analysis using the photo-CVG-AFS method revealed that it was promising for water and geological analysis of ultralow levels of mercury.
TL;DR: The first uranyl tartrate to be crystallographically characterized was described in this paper, where each tartrate ligand bridges three uranyl ions, one of them in chelating fashion through proximal carboxylate and hydroxyl groups, resulting in two-dimensional assemblages with the uranyl pentagonal bipyramidal coordination polyhedra separated from one another.
TL;DR: The effects of methanol as HO scavenger demonstrated that the relative contribution of HO-based reactions to the decomposition of phenol in UV/VUV-irradiated solutions decreased strongly with increase of the initial phenol concentration as discussed by the authors.
Abstract: The UV (254 nm) and UV/VUV (254/185 nm) photolysis of phenol and the distribution of the products in solutions saturated with oxygen or nitrogen were investigated and compared. The initial rate of degradation of phenol in UV/VUV-irradiated solutions exceeded that determined in UV-irradiated solutions, but the difference decreased dramatically with increase of the initial phenol concentration. The effects of methanol as HO scavenger demonstrated that the relative contribution of the HO -based reactions to the decomposition of phenol in UV/VUV-irradiated solutions decreased strongly with increase of the initial phenol concentration. The same aromatic (1,2- and 1,4-dihydroxybenzene) and aliphatic (maleic, malic, tartaric and oxalic acids) intermediates were detected in UV- and UV/VUV-irradiated solutions saturated with oxygen. The decompositions of 1,2- and 1,4-dihydroxybenzene, 1,4-benzoquinone and oxalic acid were also investigated both in UV/VUV- and in UV-irradiated solutions.
TL;DR: In this article, the growth of porous anodic films in malonic and oxalic acid electrolytes has been investigated using transmission electron microscopy, Rutherford backscattering spectroscopy and nuclear reaction analysis.
TL;DR: The photoluminescence of PAA films prepared by high-field anodization shows remarkable redshift of the peak position and decrease of the intensity compared to that of pAA films formed by conventional low field anodisation as discussed by the authors.
Abstract: Highly ordered porous anodic alumina (PAA) films are fabricated with high efficiency by stable high-field anodization in oxalic acid/ethanol/water electrolytes at 100–180V and sulfuric acid/oxalic acid/ethanol/water electrolytes at 30–80V, giving interpore distances in the range of 225–450nm and 70–140nm, respectively. The photoluminescence of PAA films prepared by high-field anodization shows remarkable redshift of the peak position and decrease of the intensity compared to that of PAA films formed by conventional low-field anodization.