Showing papers on "Oxalic acid published in 2006"
TL;DR: In this article, two analytical methods for extracting vitamin C ( l -ascorbic and l -dehydroasorbic acids) in tropical fruits [banana, papaya, mango (at three maturity stages) and pineapple] were evaluated.
343 citations
TL;DR: In this article, aqueous phase photochemical reactions of pyruvic acid and hydrogen peroxide at pH values typical of clouds were conducted and demonstrated that photochemical oxidation yields glyoxylic, oxalic, acetic and formic acids.
Abstract: [1] Aqueous-phase oxidation (in clouds and aerosols) is a potentially important source of organic aerosol and could explain the atmospheric presence of oxalic acid. Methylglyoxal, a water-soluble product of isoprene, oxidizes further in the aqueous phase to pyruvic acid. Discrepancies in the literature regarding the aqueous-phase oxidation of pyruvic acid create large uncertainties in the in-cloud yields of secondary organic aerosol (SOA) and oxalic acid. Resolving the fate of aqueous-phase pyruvic acid is critical to understanding SOA formation through cloud processing of water-soluble products of isoprene, other alkenes and aromatics. In this work, aqueous-phase photochemical reactions of pyruvic acid and hydrogen peroxide at pH values typical of clouds were conducted and demonstrated that photochemical oxidation of pyruvic acid yields glyoxylic, oxalic, acetic and formic acids. Oxalic and glyoxylic acids remain mostly in the particle phase upon droplet evaporation. Thus isoprene is an important precursor of in-cloud SOA formation.
322 citations
TL;DR: A Fe on activated carbon catalyst has been prepared and tested for phenol oxidation with H 2 O 2 in aqueous solution at low concentration (100mg/L) as discussed by the authors.
Abstract: A Fe on activated carbon catalyst has been prepared and tested for phenol oxidation with H 2 O 2 in aqueous solution at low concentration (100 mg/L). Working at 50 °C, initial pH 3 and a dose of H 2 O 2 corresponding to the stoichiometric amount (500 mg/L) complete removal of phenol and a high TOC reduction (around 85%) has been reached. Oxidation of phenol gives rise to highly toxic aromatic intermediates which finally disappear completely evolving to short-chain organic acids. Some of these last showed to be fairly resistant to oxidation being responsible for the residual TOC. In long-term continuous experiments the catalyst undergoes a significant loss of activity in a relatively short term (20–25 h) due to Fe leaching, this being related with the amount of oxalic acid produced. Deactivation may also be caused by active sites blockage due to polymeric deposits on whose formation some evidences were found. Washing with 1N NaOH solution allows to recover the activity although complete restoration was not achieved.
299 citations
TL;DR: In this article, the degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles.
Abstract: The commercially available TiO2-catalyst (Degussa P25) was modified with nanosized platinum and silver particles by the photoreduction method to obtain different noble metal loading (0.5 and 1 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, XPS, TEM and the adsorption of the model pollutant. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles. The photocatalytic activity of TiO2, modified with noble metal, is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content 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 Schottky barriers on the metal–semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.
222 citations
TL;DR: In this paper, the effect of oxalic acid on pericarp browning of litchi (Litchi chinensis Sonn.) fruit during postharvest storage was investigated.
203 citations
TL;DR: In this paper, the relative contributions of two aqueous-phase routes responsible for oxalic acid formation were examined; the oxidation of glyoxylic acid was predicted to dominate over the decay of longer-chain dicarboxylic acids.
Abstract: inorganic ions (including SO4� ) and five organic acid ions (including oxalate) were measured on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter research aircraft by a particle-into-liquid sampler (PILS) during flights over Ohio and surrounding areas. Five local atmospheric conditions were studied: (1) cloud-free air, (2) power plant plume in cloud-free air with precipitation from scattered clouds overhead, (3) power plant plume in cloud-free air, (4) power plant plume in cloud, and (5) clouds uninfluenced by local pollution sources. The aircraft sampled from two inlets: a counterflow virtual impactor (CVI) to isolate droplet residuals in clouds and a second inlet for sampling total aerosol. A strong correlation was observed between oxalate and SO4� when sampling through both inlets in clouds. Predictions from a chemical cloud parcel model considering the aqueous-phase production of dicarboxylic acids and SO4� show good agreement for the relative magnitude of SO4� and oxalate growth for two scenarios: power plant plume in clouds and clouds uninfluenced by local pollution sources. The relative contributions of the two aqueous-phase routes responsible for oxalic acid formation were examined; the oxidation of glyoxylic acid was predicted to dominate over the decay of longer-chain dicarboxylic acids. Clear evidence is presented for aqueous-phase oxalic acid production as the primary mechanism for oxalic acid formation in ambient aerosols.
187 citations
TL;DR: In this study, citric acid or acetic acid at higher concentrations had the greatest improvement of Pb(2+) desorption, followed by malic acid; and the smallest was oxalic acid.
180 citations
TL;DR: In this article, the drug paracetamol was treated with ozone alone and catalyzed with Fe 2+, Cu 2+ and/or UVA light at 25.0°C.
Abstract: Acid solutions containing up to 1 g l −1 of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe 2+ , Cu 2+ and/or UVA light at 25.0 °C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be efficiently destroyed by the combined action of generated H 2 O 2 and UVA light. In the presence of Fe 2+ and UVA light, the process is accelerated due to the production of oxidant hydroxyl radical ( OH) and the photodecomposition of Fe 3+ complexes. The highest oxidizing power is achieved by combining Fe 2+ , Cu 2+ and UVA light, because complexes of final acids with Cu 2+ are more quickly degraded than those competitively formed with Fe 3+ . For all catalyzed methods, the initial mineralization rate is enhanced and the percent of degradation generally drops with increasing drug concentration. The paracetamol decay always follows a pseudo-first-order reaction with slightly higher rate constant for catalyzed systems than direct ozonation. Aromatic products such as hydroquinone, p -benzoquinone and 2-hydroxy-4-( N -acetyl)aminophenol are identified by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Acetamide is generated when hydroquinone is produced. These products are degraded to oxalic and oxamic acids as ultimate carboxylic acids, as detected by GC–MS and ion-exclusion chromatography. Oxalic acid is generated via glycolic, glyoxylic, tartronic, ketomalonic and maleic acids. While Fe 3+ -oxalato complexes are photolyzed by UVA light, Cu 2+ -oxalato, Fe 3+ -oxamato and Cu 2+ -oxamato complexes are oxidized with OH. NH 4 + and NO 3 − ions are produced during mineralization.
173 citations
TL;DR: The present work investigates the use of simple additives such as salt and carbon tetrachloride as process intensifying parameters with an aim of reduction in the treatment times and hence the cost of operation.
160 citations
TL;DR: In this paper, the effect of solvents on particle size and morphology of nano ZnO was investigated, and the optical properties of nano-ZnO were studied extensively, which revealed different nature of surfaces and microstructures for zinc oxide obtained in aqueous and organic solvENTS.
157 citations
TL;DR: In this article, the effect of pH, apparent current density, temperature and metabolite concentration on the degradation rate, consumed specific charge and mineralization current efficiency has been investigated, and a reaction pathway for clofibric acid degradation involving all these intermediates is proposed.
TL;DR: In this paper, the authors investigated the characteristics of dissolution of iron oxides in oxalic acid and found that the dissolution rate increases with increasing oxalate concentration at the constant pH values set within the optimum range of pH2.5-3.0.
TL;DR: It is concluded that coupling visible irradiation and hydroquinone could be a strong and universal driving force in the Fenton reaction for the complete degradation and mineralization of organic pollutants, even in the presence of LMWOAs.
Abstract: The influence of low-molecular-weight organic acids (LMWOAs), such as malonic acid, ethylenediaminetetraacetic acid, and oxalic acid, on the Fenton degradation of organic pollutants was examined under visible irradiation (λ > 450 nm). The Fenton degradation of malachite green in the dark was completely blocked in the presence of LMWOAs. It was found that either visible light irradiation or the addition of hydroquinone could initiate the dye degradation, but the mineralization yield was almost zero. An important result was that the dye mineralization in the presence of LMWOAs could be achieved when both visible irradiation and hydroquinone were introduced. Similar results were obtained with colorless pollutants, such as benzyltrimethylammonium chloride and 2,4,5-trichlorophenol. We concluded that coupling visible irradiation and hydroquinone could be a strong and universal driving force in the Fenton reaction for the complete degradation and mineralization of organic pollutants, even in the presence of LMWOAs.
TL;DR: In this article, the dihydrate of oxalic acid (OAD) acts as a heterogeneous ice nucleus, with an increase in freezing temperature between 2 and 5 K depending on solution composition.
Abstract: . Heterogeneous ice freezing points of aqueous solutions containing various immersed solid dicarboxylic acids (oxalic, adipic, succinic, phthalic and fumaric) have been measured with a differential scanning calorimeter. The results show that only the dihydrate of oxalic acid (OAD) acts as a heterogeneous ice nucleus, with an increase in freezing temperature between 2 and 5 K depending on solution composition. In several field campaigns, oxalic acid enriched particles have been detected in the upper troposphere with single particle aerosol mass spectrometry. Simulations with a microphysical box model indicate that the presence of OAD may reduce the ice particle number density in cirrus clouds by up to ~50% when compared to exclusively homogeneous cirrus formation without OAD. Using the ECHAM4 climate model we estimate the global net radiative effect caused by this heterogeneous freezing to result in a cooling as high as −0.3 Wm−2.
TL;DR: In this article, anode material Li4Ti5O12 for lithium-ion batteries has been prepared by a sol-gel method with oxalic acid as a chelating agent and Li2CO3 and tetrabutyl titanate [Ti(OC4H9)4] as starting materials.
TL;DR: Hydrogen-terminated diamonds exhibited well-defined peaks of oxalic acid oxidation in a wide pH range, and surface termination contributed highly to the control of the oxidation reaction.
Abstract: Electrochemical oxidation of oxalic acid has been investigated at bare, highly boron-doped diamond electrodes. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. Hydrogen-terminated diamonds exhibited well-defined peaks of oxalic acid oxidation in a wide pH range. A good linear response was observed for a concentration range from 50 nM to 10 μM, with an estimated detection limit of ∼0.5 nM (S/N = 3). In contrast, oxygen-terminated diamonds showed no response for oxalic acid oxidation inside the potential window, indicating that surface termination contributed highly to the control of the oxidation reaction. An investigation with glassy carbon electrodes was conducted to confirm the surface termination effect on oxalic acid oxidation. Although a hydrogen-terminated glassy carbon electrode showed an enhancement of signal-to-background ratio in comparison with untreated glassy carbon, less stability of the current responses was observed...
TL;DR: Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO(2-x)N(x) surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes.
Abstract: We report the photooxidation of toluene over nitrogen doped TiO2 (TiO2−xNx) under visible light irradiation. The photocatalytic oxidation of toluene in air over TiO2−xNx powders was studied using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), gas chromatography (GC), ion chromatography (IC), and gas chromatography mass spectrometry (GC-MS), focusing on the photocatalytic decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO2−xNx surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. No gaseous intermediates were detected during the photooxidation. Major intermediates adsorbed at the catalyst surface were oxalic acid, (COOH)2, acetic acid, CH3COOH, formic acid, HCOOH, and pyruvic acid, CH3COCOOH, whereas more complicated carboxylic species, including propionic acid, CH3CH2COOH, isovaleric acid, (CH3)2CHCH2COOH, and succinic acid, (CH2COOH)2, were also found in the early stage of the photooxidation. These intermediate products were gradually photodegraded to CO2 and H2O under visible light irradiation.
TL;DR: In this article, a nanosized zinc aluminate spinel has been obtained by the thermal decomposition of Zn-Al gel prepared by sol-gel technique using oxalic acid as a chelating agent.
TL;DR: The adsorption and photoreaction of oxalic acid on the surface of anatase and rutile TiO2 nanoparticles have been studied using a combined experimental and theoretical approach and can be described as a mixture of adsorbed water and oxAlic acid molecules.
Abstract: The adsorption and photoreaction of oxalic acid on the surface of anatase and rutile TiO2 nanoparticles have been studied using a combined experimental and theoretical approach. In the dark, the experimental adsorption reaches an equilibrium state that can be described as a mixture of adsorbed water and oxalic acid molecules, with the latter forming two different surface complexes on anatase and one on rutile particles. When the system is subsequently illuminated with UV(A) light, the surface becomes enriched with absorbed oxalic acid, which replaces photo-desorbed water molecules, and one of the adsorbed oxalic acid structures on anatase is favoured over the other.
TL;DR: The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.
TL;DR: Ozone in combination with oxalic or citric acid could be a partial alternative to sulphur dioxide fumigation as a control of postharvest decay and browning of longan fruit cv.
TL;DR: In this paper, the hydrophobic and physical properties of tetraethoxysilane (TEOS) based silica aerogels were compared by two-step sol-gel process followed by supercritical drying.
TL;DR: In this article, carbon aerogels were prepared by polymerization of a resorcinol-formaldehyde mixture using different polymerization catalysts such as: sodium or potassium carbonates, oxalic acid or para -toluenesulfonic acid.
TL;DR: Results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.
Abstract: Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.
TL;DR: In this paper, the degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO 2, modified with nanosized gold particles.
Abstract: The commercially available TiO 2 -catalyst (Degussa P25) was supported by spray pyrolysis deposition method on the outer surface of the quartz tubes, incorporated in photocatalytic reactor. The crystal structure and the morphology of the films were studied. The immobilized TiO 2 is modified with nanosized gold particles by the photoreduction method to obtain different noble metal loading (0.05–0.4 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, X-ray photoelectron spectroscopy (XPS), SEM, TEM and the adsorption of the model pollutant was determined. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO 2 , modified with nanosized gold particles. The presence of low amounts of gold on the TiO 2 surface leads to an increase of its photocatalytic activity. The maximum value of the photocatalytic activity was registered with the ≈0.16 wt.% Au on TiO 2 sample. At this concentration the activity of the Au-modified TiO 2 is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content 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.
TL;DR: In this article, the degradation of PbEDTA in aqueous solution by a H 2 O 2 /UV process was studied and the effect of pH, pH of the solution and the presence of nitrate were investigated.
TL;DR: Although bubbling nitrogen gave higher degradation than that for bubbling air, both gases could not help to enhance the degradation of oxalic acid when compared with the degradation without gas passage and there was an optimum concentration of NaCl for enhancing the degradation degree of oxAlic acid.
TL;DR: In this article, it was shown that MnO2 yields a range of reactivity that is nearly 20 times greater than that of MnOOH, indicating that ligand-assisted dissolution took place.
TL;DR: In this article, the effect of iron oxides and oxalate on photodegradation of 2-mercaptobenzothiazole (MBT) was investigated by X-ray diffractograms (XRD) and Brunauer-Emmett-Teller (BET) methods.
Abstract: γ-FeOOH was prepared by hydrothermal process and went through the phase transformation from lepidocrocite to maghemite firstly and then to hematite with the increase of sintering temperature. The iron oxides sintered at 250, 320, 420 and 520 °C for 2 h were named as IO-250, IO-320, IO-420 and IO-520, respectively, and characterized by X-ray diffractograms (XRD) and Brunauer–Emmett–Teller (BET) methods. XRD results showed that IO-250 and IO-320 had a mixed crystal structure of maghemite and hematite while IO-420 and IO-520 were pure hematite. BET results showed that the specific surface area decreased significantly with the increase of sintering temperature. The effect of iron oxides and oxalate on the photodegradation of 2-mercaptobenzothiazole (MBT) was investigated. The degradation of MBT depended strongly on the dosage of iron oxides and the initial concentration of oxalic acid ( C ox 0 ). The optimal dosages of iron oxides were 0.40, 0.35, 0.30, 0.25 and 0.25 g/L for γ-FeOOH, IO-250, IO-320, IO-420 and IO-520, respectively, and the optimal C ox 0 was 1.0 mM for all the five iron oxides. The results showed that MBT photodegradation could be enhanced greatly in the presence of oxalic acid. The first-order kinetic constants k for MBT degradation was ranked the order as IO-320 > IO-250 > IO-420 > IO-520 > γ-FeOOH in the presence of oxalate with the optimal C ox 0 of 1.0 mM. The oxalate photodegradation, the pH value in the solution and the concentration of Fe2+ and Fe3+ along with the reaction time were also investigated. The results showed that they also depended on iron oxides and C ox 0 . IO-420 and IO-520 with hematite structure and higher stability had a lower activity for oxalate adsorption and photodegradation, and then less formation of Fe3+ and Fe2+, while γ-FeOOH and IO-250 with a lower stability had much higher activity for oxalate adsorption and photodegradation, and then much more Fe3+ and Fe2+ formed in the solution. The excessive Fe3+ inhibited the formation of H2O2 while the much less Fe2+/3+ led to a much less Fe2+/3+-oxalate complex on the surface of iron oxides or in the solution. Therefore, IO-320 had the most photoactivity among them because of the mixed crystal structure and the suitable concentration of Fe3+ and Fe2+.
TL;DR: The higher oxalate content in whole grain than in refined grain cereals suggests that oxalic acid is primarily located in the outer layers of cereal grains.
Abstract: Detailed knowledge of food oxalate content is of essential importance for dietary treatment of recurrent calcium oxalate urolithiasis. Dietary oxalate can contribute considerably to the amount of urinary oxalate excretion. Because cereal foods play an important role in daily nutrition, the soluble and total oxalate contents of various types of cereal grains, milling products, bread, pastries, and pasta were analyzed using an HPLC-enzyme-reactor method. A high total oxalate content (>50 mg/100 g) was found in whole grain wheat species Triticum durum (76.6 mg/100 g), Triticum sativum (71.2 mg/100 g), and Triticum aestivum (53.3 mg/100 g). Total oxalate content was comparably high in whole grain products of T. aestivum, that is, wheat flakes and flour, as well as in whole grain products of T. durum, that is, couscous, bulgur, and pasta. The highest oxalate content was demonstrated for wheat bran (457.4 mg/100 g). The higher oxalate content in whole grain than in refined grain cereals suggests that oxalic acid is primarily located in the outer layers of cereal grains. Cereals and cereal products contribute to the daily oxalate intake to a considerable extent. Vegetarian diets may contain high amounts of oxalate when whole grain wheat and wheat products are ingested. Recommendations for prevention of recurrence of calcium oxalate stone disease have to take into account the oxalate content of these foodstuffs.