Showing papers on "Oxalic acid published in 2012"

The Effects of Carboxylic Acids on the Aqueous Dispersion and Electrophoretic Deposition of ZrO2

Abstract: The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability.

Synthesis of graphene nanosheets via oxalic acid-induced chemical reduction of exfoliated graphite oxide

Abstract: Preparing high-quality graphene through reduction of graphene oxide (GO) by oxalic acid is demonstrated in this paper. Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectrometry, X-ray diffraction and Raman spectrometry were taken to confirm the reduction of GO and the formation of graphene under these mild conditions. Thermogravimetric analysis and conductivity measurements further testify the excellent thermal stability and conductivity of the obtained graphene. A possible mechanism for the reduction process was also proposed. Furthermore, a Pt–graphene composite was fabricated on a glassy carbon electrode and excellent electrocatalytic activity towards methanol oxidation was observed. With advantages of low toxicity, simple purification process and high quality of the product, oxalic acid provides a feasible route to prepare graphene from GO under mild conditions, thus facilitating the use of graphene-based materials for large-scale applications.

Crystal engineering of stable temozolomide cocrystals.

Abstract: The antitumor prodrug temo-zolomide (TMZ) decomposes in aque-ous medium of pH 7 but is relativelystable under acidic conditions. PureTMZ is obtained as a white powderbut turns pink and then brown, whichis indicative of chemical degradation.Pharmaceutical cocrystals of TMZwere engineered with safe coformerssuch as oxalic acid, succinic acid, sali-cylic acid, d,l-malic acid, and d,l-tarta-ric acid, to stabilize the drug as a coc-rystal. All cocrystals were character-ized by powder X-ray diffraction(PXRD), single crystal X-ray diffrac-tion, and FT-IR as well as FT-Ramanspectroscopy. Temozolomide cocrystalswith organic acids (pK a 2–6) werefound to be more stable than the refer-ence drug under physiological condi-tions. The half-life (T 1/2 ) of TMZ–oxalic and TMZ–salicylic acid mea-sured by UV/Vis spectroscopy in pH 7buffer is two times longer than that ofTMZ (3.5 h and 3.6 h vs. 1.7 h); TMZ–succinic acid, TMZ–tartaric acid, andTMZ–malic acid also exhibiteda longer half-life (2.3, 2.5, and 2.8 h, re-spectively). Stability studies at 408Cand 75% relative humidity (ICH con-ditions) showed that hydrolytic degra-dation of temozolomide in the solidstate started after one week, as deter-mined by PXRD, whereas its cocrystalswith succinic acid and oxalic acid wereintact at 28 weeks, thus confirming thegreater stability of cocrystals comparedto the reference drug. The intrinsic dis-solution rate (IDR) profile of TMZ–oxalic acid and TMZ–succinic acid coc-rystals in buffer of pH 7 is comparableto that of temozolomide. Among thetemozolomide cocrystals examined,those with succinic acid and oxalic acidexhibited both an improved stabilityand a comparable dissolution rate tothe reference drug.Keywords: crystal engineering ·cocrystals · stability · temozolo-mide · X-ray diffraction2274

Catalytic ozonation of toxic pollutants over magnetic cobalt-doped Fe3O4 suspensions

Abstract: Magnetic cobalt-doped Fe3O4 (FeCo) was prepared using a co-precipitation method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The catalyst showed high, stable catalytic activity for the degradation and mineralization of toxic persistent organic pollutants, as demonstrated with the herbicides 2,4-dichlorophenoxyacetic acid, 2,4-dichlorophenol, and 2,4,6-trichlorophenol and pharmaceutical phenazone in aqueous solution with ozone. FeCo was very effective at the mineralization of refractory oxalic acid produced in the degradation of organic compounds. The ozone was adsorbed on the surface of FeCo competing with water molecules in the aqueous phase, and converted into hydroxyl radical, meanwhile the catalyst surface underwent oxidation and reduction as demonstrated by in situ ATR-FTIR, CV and other experimental data obtained. Furthermore, the characterization studies indicated that the introduction of Co increased the rate of FeCo oxidation and reduction during the decomposition of ozone, enhancing the activity and stability of Fe3O4. (c) 2012 Elsevier B.V. All rights reserved.

Electrocatalytic oxidation of ethylene glycol (EG) on supported Pt and Au catalysts in alkaline media: Reaction pathway investigation in three-electrode cell and fuel cell reactors

Abstract: Carbon supported Pt and Au nanoparticles with small sizes (2.4 nm for Pt/C, and 3.5 nm for Au/C) and narrow size distributions were prepared though a modified solution-phase reduction method, and served as the working catalysts for an investigation of electrocatalytic oxidation of EG in alkaline media. Our three-electrode cell with an on-line sample collection system showed that with applied potential increasing, glycolic acid, oxalic acid and formic acid were sequentially produced from EG oxidation on Pt/C, while only glycolic acid and formic acid were detected on Au/C. Oxalic acid is a fairly stable product, and Pt/C is inactive to its further oxidation reaction. On Au/C, glycolic acid is the primary product, and no oxalic acid was found at specified test conditions. We clarified that formic acid was produced preferably from direct C C bond cleavage of EG not glycolic acid on both Pt/C and Au/C catalysts. The single anion exchange membrane-direct EG fuel cell (AEM-DEGFC) with Pt/C and Au/C anode catalysts showed consistent results with the three-electrode cell tests. The AEM-DEGC with Pt/C anode catalyst demonstrated a peak power density of 71.0 mW cm−2, which is much higher than that with the Au/C (only 7.3 mW cm−2) at 50 °C. With the fuel cell operation voltage decreasing (anode overpotential increasing), deeper-oxidized products oxalic acid and formic acid were generated in the Pt/C anode AEM-DEGFC with higher selectivity. No formic acid was detected in the Pt anode AEM-DEGFC when glycolic acid was employed as fuel. On Au/C anode catalyst, very high selectivity to glycolic acid (>98%) was achieved. The AEM-DEGFC results confirmed the EG electro-oxidation pathways proposed by using an on-line sample collection system.

Green synthesis of gold-chitosan nanocomposites for caffeic acid sensing.

Abstract: In this work, colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix were prepared using a green route. The synthesis was carried out by reducing AuIII to Au0 in an aqueous solution of chitosan and different organic acids (i.e., acetic, malonic, or oxalic acid). We have demonstrated that by varying the nature of the acid it is possible to tune the reduction rate of the gold precursor (HAuCl4) and to modify the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a large number of amino and hydroxyl functional groups, enables the simultaneous synthesis and surface modification of AuNPs in one pot. Because of the excellent film-forming capability of this polymer, AuNPs–chitosan solutions were used to obtain hybrid nanocomposite films that combine highly conductive AuNPs with a large number of organic functional groups. Herein, Au–chitosan nanocomposites are successfully proposed as sensitive and selective electrochemical sensors...

Bioconversion of giant reed (Arundo donax L.) hemicellulose hydrolysate to ethanol by Scheffersomyces stipitis CBS6054

Abstract: The objective of this study was to evaluate the production of ethanol by Scheffersomyces ( Pichia ) stipitis CBS6054, a native xylose fermenting yeast, from sugars contained in the giant reed ( Arundo donax L.) hemicellulosic hydrolysate. A response surface methodology with two input parameters, severity factor and oxalic acid concentration ranging from 2.87 to 4.05 and from 2 to 8 (% w oxalic acid/w solid dry matter), respectively, was employed to minimize degradation products and maximize sugar release. However, at the optimum condition for sugar release (43.8 g l −1 ), levels of toxic degradation products (acetic acid, furfural, HMF and phenolic compounds) were considered too high for yeast fermentation. The condition to minimize degradation products and maximize sugar yields was judged to be 2.87 severity factor and 5.0% oxalic acid concentration. At this condition 26.0 g l −1 xylose, 5.0 g l −1 glucose and 2.4 g l −1 arabinose were recovered in giant reed hydrolysate fraction. Adjustment of pH to 5.0 with Ca(OH) 2 decreased xylose, glucose and acetic acid, 22%, 8% and 27% respectively. Increasing the initial pH from 5.0 to 5.5, 6.0 and 6.5, respectively, significantly improved the fermentability of the giant reed hemicelluloses hydrolysate; no fermentation was observed at pH 5.0 after 96 h, while 8.20 g l −1 of ethanol was obtained at pH 6.0 after 48 h, with an ethanol yield of 0.33 ( g e / g s ) and a productivity of 0.17 g l −1 h −1 . The optimum pH of acid hydrolysate fermentation for ethanol production was 6.0–6.5.

Comparative Studies on Structural, Optical, and Textural Properties of Combustion Derived ZnO Prepared Using Various Fuels and Their Photocatalytic Activity

Abstract: Pure mesoporous nanosized ZnO samples have been synthesized by combustion synthesis method using different type of fuels such as citric acid, dextrose, glycine, oxalyl dihydrazide, oxalic acid, and urea. All these samples were found to have the standard hexagonal wurtzite structure with the lattice constants a and c having values 3.25 A and 5.21 A, respectively. The diffuse reflectance spectra of the prepared samples have shown the maximum absorption of light in the UV region stating that these catalysts can be used as photocatalysts. The BET surface area measurements of the prepared catalysts were found to vary according to the equivalence ratio. The presence of pronounced hysteresis in N2 adsorption–desorption isotherm curves indicated the three-dimensional network arrangement of pores in the ZnO samples prepared using dextrose and urea as fuels. The photodegradation ability of the various synthesized photocatalysts was tested for the photodegradation of an azo dye, namely, orange G dye solution. ZnO ph...

Crystal engineering approach to improve the solubility of mebendazole

Abstract: An anthelmintic drug, mebendazole, shows a very low bioavailability (less than 10%) due to its poor aqueous solubility (0.035 mg/mL at 25 °C for form C). To improve its solubility, we combined a group of dicarboxylic acids with mebendazole via liquid-assisted grinding and reaction crystallization methods, and two salts with oxalic and maleic acids, as well as two co-crystals with malonic and glutaric acids, were obtained. These novel multi-component complexes were characterized by powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analyses and infrared spectra. The single-crystal structures of mebendazole-maleate salt, mebendazole-glutaric acid co-crystal, and mebendazole-monomethyl oxalate salt, in which one of the carboxyl groups of oxalic acid was esterified during the single-crystal growth in methanol, were determined. It was observed that mebendazole combines dicarboxylic acid/ester via a R22(8) hydrogen-bonding motif that involves a carbamyl benzimidazole and a carboxyl group, resulting in the 1:1 stoichiometry. The powder dissolution studies revealed that the apparent solubility of the complexes was significantly increased after the formation of co-crystals and salts.

Synthesis of vanillin in water by TiO2 photocatalysis

Abstract: The photoproduction of vanillin is studied in aqueous medium starting from trans-ferulic acid, isoeugenol, eugenol or vanillyl alcohol by using both commercial and home prepared TiO2 samples as photocatalysts and batch Pyrex photoreactors. The photo-oxidation at room temperature of these compounds produces vanillin with a selectivity ranging from 1.4 to 21 mol% with respect to the converted substrate. An investigation on the intermediates was performed in the case of trans-ferulic acid; for this substrate the most important intermediates were homovanillic acid, vanillyl mandelic acid, trans-caffeic acid, formic acid, acetic acid, and oxalic acid. The carbon mass balance, including CO2 derived from the mineralization, was made for all of the substrates at irradiation times corresponding to the highest selectivity to vanillin. High closure of the carbon balance was obtained with vanillyl alcohol (ca. 90%) and trans-ferulic acid (ca. 80%).

One‐Step Hydrothermal Synthesis of Carboxyl‐Functionalized Upconversion Phosphors for Bioapplications

Abstract: In this paper, we report a facile one-step hydrothermal method to synthesize phase-, size-, and shape-controlled carboxyl-functionalized rare-earth fluorescence upconversion phosphors by using a small-molecule binary acid, such as malonic acid, oxalic acid, succinic acid, or tartaric acid as capping agent. The crystals, from nano- to microstructures with diverse shapes that include nanospheres, microrods, hexagonal prisms, microtubes, microdisks, polygonal columns, and hexagonal tablets, can be obtained with different reaction times, reaction temperatures, molar ratios of capping agent to sodium hydroxide, and by varying the binary acids. Fourier transform infrared, thermogravimetric analysis, and upconversion luminescence spectra measurements indicate that the synthesized NaYF(4):Yb/Er products with hydrophilic carboxyl-functionalized surface offer efficient upconversion luminescent performance. Furthermore, the antibody/secondary antibody conjugation can be realized by the carboxyl-functionalized surfaces of the upconversion phosphors, thus indicating the potential bioapplications of these kinds of materials.

Effective enhancement of the degradation of oxalic acid by catalytic ozonation with TiO2 by exposure of {001} facets and surface fluorination

Abstract: Heterogeneous catalytic ozonation is a promising advanced oxidation technology for water treatment. In the present work, the surface fluorination of TiO2 catalysts with a high percentage of exposed {001} facets (F-TiO2) were synthesized through a hydrothermal method using tetrabutyl titanate as the precursor and HF as the shape controlling agent. The structural properties of the catalysts were characterized by X-ray diffraction, the Brunauer–Emmett–Teller method, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The sheetlike TiO2 is pure anatase, with ∼75% of highly reactive {001} facets. The surface fluoride of the F-TiO2 nanosheets can be removed by washing with dilute NaOH solution (abbreviated here as OH-TiO2), resulting in a decrease of Ti3+ content and an increase of the specific surface area. The catalytic activity of the samples was evaluated by degradation of oxalic acid in aqueous solution in the presence of ozone. It was found that F-TiO2 facilitated the cataly...