Preparation of highly water-selective mordenite membranes via post-synthetic treatment with oxalic acid

The effect of post-synthetic treatment with oxalic acid was investigated on the pervaporation performance of mordenite membranes for the separation of a water/ethanol mixture. It was demonstrated that the water/ethanol separation factors were enhanced from 6–44 to higher than 10,000 after as-synthesized mordenite membranes were hydrothermally treated in an oxalic acid solution under appropriate conditions. The change in the pervaporation performance of mordenite membranes upon post-treatment with oxalic acid was discussed.     

A Phase Study of the System: Oxalic Acid/Acetic Acid/Water; Its Significance in Oxalic Acid Crystal Growth

The presence of limited amounts of water appears to improve the quality of anhydrous oxalic acid single crystals grown from acetic acid solutions. Water concentrations in the saturated solutions which allow crystallization of the anhydrous acid have been determined from the phase study of this ternary system. Near 50 °C the anhydrous acid crystallizes from solutions containing up to 5.2 weight percent water, while the dihydrate appears when water is in excess of this amount.The phase diagram shows a minimum content of oxalic acid in solution at a solvent composition near 83 percent acetic acid, 17 percent water. The solubility increases with increased acetic acid to the isothermal invariant point, found experimentally at a measured temperature of 50.21 °C to have the composition 20.94 percent oxalic acid, 73.89 percent acetic acid, 5.17 percent water. Decreasing solubility occurs at higher acetic acid concentrations. The maximum water content which allows crystallization of anhydrous acid increases with increasing crystallization temperature. The solubility of oxalic acid in acetic acid/water mixtures at 40° and 50 °C is reported.     

Effect of relative amount of complexing agents on the properties of Sb2S3 precipitated powders

Powders of Sb₂S₃ are obtained by a bulk preparation technique using aqueous solutions of antimony trichloride and thioacetamide for two different complexing agents, namely, oxalic acid and tartaric acid. The concentration of solution is kept constant at 0.1 M and only the concentration of complexing agent is varied. The effect of concentration of the complexing agents on the properties of precipitated powder is studied. The powders precipitated using oxalic acid are grey, whereas the powders precipitated using tartaric acid are orange in colour. X-ray diffraction studies reveal that the powders are polycrystalline in nature. Crystallinity using the former acid is relatively higher than that with the latter. It has been observed that the crystallinity goes on decreasing as the concentration of complexing agents increases. Infrared spectroscopy studies indicate the presence of carbon and absorbed water in the powders complexed with oxalic acid. Optical absorption studies show that the direct bandgap energy of the precipitated powders prepared using oxalic acid varies from 1.59 to 1.98 eV and it is found to be higher (1.98 eV) for powder prepared using 0.25 M oxalic acid, while for powders prepared using tartaric acid, it varies from 1.92 to 2.02 eV and is found to be higher (2.02 eV) for the powder prepared using 0.75 M tartaric acid. Electrical resistivity study reveals that the room-temperature electrical resistivity of the powders prepared using oxalic acid is relatively lower (10⁴–10⁶ Ω cm) than that of tartaric-acid-complexed powders (10⁵–10⁷ Ω cm).     

Comparative study of oxidation of dye-Reactive Black B by different advanced oxidation processes: Fenton, electro-Fenton and photo-Fenton

This study makes a comparison between photo-Fenton and a novel electro-Fenton called Fered-Fenton to study the mineralization of 10,000 mg/L of dye-Reactive Black B (RBB) aqueous solution, which was chosen as the model dye contaminant. Results indicate that the traditional Fenton process only yields 70% mineralization. This result can be improved by using Fered-Fenton to yield 93% mineralization resulting from the action of ferrous ion regenerated on the cathode. Furthermore, photo-Fenton allows a fast and more complete destruction of dye solutions and as a result of the action of ferrous ion regenerated by UV irradiation yields more than 98% mineralization. In all treatments, the RBB is rapidly decayed to some carboxylic acid intermediates. The major intermediates found are formic acid and oxalic acid. This study finds that formic acid can be completely mineralized by photo-Fenton, but its destruction is problematic using the Fenton method. Oxalic acid is much more difficult to treat than other organic acids. It could get further mineralization with the use of the Fered-Fenton process.     

A kinetics study on the biodegradation of synthetic wastewater simulating effluent from an advanced oxidation process using Pseudomonas putida CECT 324

Bacterial growth on mixed substrates is employed for wastewater treatment. Biodegradation kinetics of Pseudomonas putida CECT 324 growth on formic acid, vanillin, phenol and oxalic acid mixtures is described. The experiments were carried out in a stirred-tank fermentor in batch mode at different temperatures (25, 30 and 35 degrees C) and pH (5, 6 and 7). The four compounds selected are typical intermediates in pesticide-contaminated water treated by advanced oxidation processes (AOPs). The toxicity of intermediates was investigated for a combined AOP-biological treatment, and the minimum DOC inhibitory concentration of the intermediate mixture was 175 ppm. The resulting biodegradation and growth kinetics were best described by the sum kinetics with interaction parameters (SKIP) model. Phenol and oxalic acid inhibit P. putida growth, and formic acid consumption strongly affects the biodegradation of oxalic acid. At all the temperatures tested and at pH between 5 and 7, P. putida CECT 324 was able to degrade the four substrates after culture times of 30 h at 30 degrees C and pH 7, which were the best conditions, and after 70 h, under the worst, at 35 degrees C.     

Application of several advanced oxidation processes for the destruction of terephthalic acid (TPA)

Terephthalic acid (TPA) is widely applied as a raw material in making polyester fiber, polyethylene terephthalate (PET) bottles, polyester films, etc. TPA is toxic and is known to act as endocrine disruptor. TPA wastewater is traditionally treated by biological process and this study aims to evaluate the effectiveness of several advanced oxidation processes on TPA removal. The oxidation processes studied were: UV-TiO(2), UV-H(2)O(2), UV-H(2)O(2)-Fe, O(3), O(3)/Fe, O(3)/TiO(2), UV-O(3)-H(2)O(2)-Fe and UV-O(3)-H(2)O(2)-Fe-TiO(2). The results indicate that the time required for the complete destruction of 50 ppm of TPA can be minimized from 10h using UV-TiO(2) system, to less than 10 min by UV-H(2)O(2)-Fe-O(3) system. Some of the likely organic intermediates identified during TPA destruction include, benzoquinone, benzene, maleic acid and oxalic acid. Possible destruction pathway of TPA has been proposed. TPA degradation by various systems was also analyzed based on the reaction kinetics and operating costs.     

AAO模板受热失重及发光机理的研究

为了深入理解草酸溶液中制备的阳极氧化铝(AAO)模板受热失重以及草酸根对模板发光性能的影响,利用程序升温脱附与质谱联用(TPD-MS)、热重分析(TGA)、差热分析(DTA)以及光致发光(PL)等技术对AAO模板进行了系统研究.热失重分析结果表明,当温度低于402.2℃时,发生H2O、CO以及CO2分子的脱附以及掺杂草酸的分解,其中H2O的脱附为失重的主要原因;在402.2~866.7℃范围内,主要是草酸盐分解放出CO和CO2引起失重,CO为主要产物;碳酸盐以及残余的草酸盐的剧烈分解发生在866.7~1022.9℃范围内,主要放出CO2,并且引起大量失重.由热重结果及脱附产物中CO的摩尔比得到草酸根残余量随处理温度的变化趋势.最后,对模板PL强度、草酸根含量以及氧空位缺陷(F+)浓度三者随处理温度的变化趋势进行了关联,对AAO模板发光的原因进行了分析.     

The effect of the presence of Ag nanoparticles on the photocatalytic degradation of oxalic acid adsorbed on TiO2 nanoparticles monitored by ATR-FTIR

Photocatalytic degradation of oxalic acid adsorbed on the Ag/P25 TiO₂ composite nanoparticle films were investigated using ATR-FTIR technique under UV irradiation. Ag/P25 TiO₂ composite nanoparticle films with various Ag content were tested. Topography and chemical structure/composition of the composite nanoparticle films were analyzed by AFM and XPS respectively. It was found that in the degradation reaction of the oxalic acid, the presence of only 2% Ag nanoparticles leads to six times more oxalic acid degradation compared to that degraded in the presence of pure P25 TiO₂ nanoparticles. The degradation rate of the oxalic acid is three times higher in the case of Ag/TiO₂ composite nanoparticle film than in the case of pure TiO₂ nanoparticles. It was observed that both the rate of oxalic acid degradation and the degraded amount of the oxalic acid were significantly affected by Ag incorporation.     

高岭土除铁增白的实验研究

采用硫酸作酸浸剂、Na2S2O4作还原剂的方法对高岭土进行了除铁增白实验,考察硫酸的质量分数、温度、浸出时间、Na2S2O4的用量、草酸用量等因素对除铁增白效果的影响,得出最佳除铁增白方案。最佳除铁增白方案为:在矿浆中高岭土与水的质量比为20∶100时,硫酸的质量分数为20%、温度为80℃、浸出时间为2h、Na2S2O4用量为0.5g、草酸用量为1.0g。经除铁增白后,高岭土中的Fe2O3的质量分数由原来的2.098%降为0.35%,白度由原来的56.4%提高到81.5%。     

Thermodynamic and Kinetic Studies of Uranium and REEs Leaching by Oxalic Acid from Abu-Tartur Phosphate Rock,Western Desert,Egypt

Radiochemistry - Leaching of uranium and REEs with oxalic acid from the Egyptian Abu-Tartur phosphate rock (PR) was studied. The effect exerted on the leaching process by oxalic acid concentration,...     

Oxidation of acidic dye Eosin Y by the solar photo-Fenton processes

Oxidation of acidic dye Eosin Y has been investigated with Fenton process and photo-Fenton process (solar light or artificial light source). With UV-Fenton process and Fenton, 42.5% and 21.3% of dye could be removed from the water, respectively. However, 94.1% of dye was removed in solar-Fenton in 90min. Based on solar-Fenton process, the effect of pH value and the concentration of dye, Fe(2+), H(2)O(2) as well as oxalic acid concentration on Eosin Y degradation efficiency were investigated. In 60min, 96% of Eosin Y was degraded when the pH value was 3.5 and the concentration of Fe(2+), H(2)O(2) and oxalic acid was 10mol/L, 600mg/L and 300mg/L, respectively. The Eosin Y degradation was dependent on the dye concentration. That is higher Eosin Y concentration resulted in lower degradation efficiency. Under the conditions of pH 3.5, the Eosin Y apparent kinetics equation was -dC/dt=0.000249[Eosin Y](0.78)[Fe(2+)](1.14)[H(2)O(2)](1.26). Meanwhile, this research also proved that oxalic acid could improve the photocatalytic efficiency in the solar-Fenton process.     

草酸、水杨酸、茉莉酸甲酯处理对甜樱桃采后贮藏品质的影响

目的 探究草酸、水杨酸、茉莉酸甲酯处理对甜樱桃品质及抗氧化特性的影响。方法 分别使用5 mmol/L草酸、1 mmol/L水杨酸、0.15 mmol/L茉莉酸甲酯浸泡甜樱桃10 min,测定果实贮藏期间的颜色、硬度、呼吸强度、总酚含量、类黄酮含量、谷胱甘肽含量、抗氧化相关酶活性等多项指标。结果 草酸能够有效保持贮藏末期的果实硬度,水杨酸能够最大程度地抑制果实的呼吸强度,茉莉酸甲酯对保持果实亮度的效果最佳,同时3种处理均可维持总酚、类黄酮和谷胱甘肽等含量,调控抗氧化相关酶活性。结论 采用草酸、水杨酸、茉莉酸甲酯处理均可以诱导甜樱桃在贮藏过程中的抗氧化能力,从而减缓果实衰老,延长果实的货架期。     

Electrochemical oxidation of oxalic acid at highly boron-doped diamond electrodes

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 microM, with an estimated detection limit of approximately 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 than that at hydrogen-terminated diamond.     

多孔氧化铝模板的制备研究

以草酸为电解液,采用二次阳极氧化法制备多孔有序氧化铝模板,研究了氧化电压、电解液浓度、去一次氧化膜时间和二次阳极氧化时间对多孔氧化铝膜结构的影响。结果表明,退火后在60V电压、0.6mol/L的草酸溶液中、去一次阳极氧化膜5h、二次阳极氧化15h制备的膜结构孔洞均匀有序、孔径达80nm、孔密度达8.2×109个/cm2。     

Effect of different extracting solutions on the electrodialytic remediation of CCA-treated wood waste Part I. Behaviour of Cu and Cr

Removal of Cu and Cr from chromated copper arsenate (CCA)-treated wood waste under batch electrodialytic conditions was studied. The effect of different types of extracting solutions, such as deionised water or aqueous solutions of NaCl, formic acid, oxalic acid, and EDTA, on the magnitude and direction of the fluxes of Cu- and Cr-containing species in the electrodialytic cell was investigated. Oxalic acid was found to have the best performance if simultaneous removal of the two elements is required (removal efficiencies of 80.5% for Cu and 87.4% for Cr, respectively). A mixture of oxalic acid and formic acid also led to similar removal efficiencies. In these experiments, the target elements were accumulated in both the anode and cathode compartments of the electrodialytic cell due to the formation of negatively charged complexes with the organic acids used besides the free cationic forms. The latter were not present if EDTA was the extracting solution resulting in directing the Cu and Cr fluxes to the anode compartment. Contrary, these fluxes were exclusively to the cathode compartment if deionised water or an aqueous solution of NaCl were used. These extracting solutions proved suitable for solubilising (re-mobilisation) of Cu but were less efficient for Cr removal (less than 20% removal). Overall, the results obtained show the important role of the proper selection of the type and composition of the extracting solution for the success of subsequent electrodialytic removal of Cu and Cr from CCA-treated wood waste.     

溶胶-凝胶法制备SiC前驱体

为了尽量减少硫、氯等有害元素的含量,本文用不含有害元素的草酸和六次甲基四胺（HMTA）为催化剂,正硅酸乙酯（TEOS）为硅源,酚醛树脂为碳源,成功探索出了制备SiC前驱体的两步法溶胶-凝胶工艺．第一步TEOS在草酸的催化下预水解,第二步用HMTA加速凝胶．实验得出了草酸含量、预水解时间、预水解温度等因素对凝胶形成的影响规律,进而讨论了水解和缩合的机理．所得SiC前驱体为黄色透明的玻璃态,由纳米级的颗粒组成,结构均匀而精细．     

溶胶-凝胶法制备 SiC前驱体

为了尽量减少硫、氯等有害元素的含量,本文用不含有害元素的草酸和六次甲基四胺（HMTA）为催化剂,正硅酸乙酯（TEOS）为硅源,酚醛树脂为碳源,成功探索出了制备SiC前驱体的两步法溶胶-凝胶工艺．第一步TEOS在草酸的催化下预水解,第二步用HMTA加速凝胶．实验得出了草酸含量、预水解时间、预水解温度等因素对凝胶形成的影响规律,进而讨论了水解和缩合的机理．所得SiC前驱体为黄色透明的玻璃态,由纳米级的颗粒组成,结构均匀而精细．     

Photocatalytic decomposition of perfluorooctanoic acid (PFOA) by TiO2 in the presence of oxalic acid

Heterogeneous photocatalytic decomposition of perfluoroocatanoic acid (PFOA) by TiO(2) under 254 nm UV light was investigated. Adding oxalic acid as a hole-scavenger significantly accelerated PFOA decomposition under nitrogen atmosphere. Fluoride ion, formic acid and six shorter-chain perfluorinated carboxylic acids (PFCAs) bearing C(2)-C(7) were identified as intermediates. When using perchloric acid (HClO(4)) as a replacement of oxalic acid to maintain the same pH of the reaction solution, PFOA did not decomposition efficiently. Compared with oxalic acid, potassium iodide (KI, another hole-scavenger) also led to a slower PFOA decomposition, while the addition of an electron acceptor (potassium persulfate, K(2)S(2)O(8)) obviously inhibited PFOA decomposition. This suggested that oxalic acid played more than one role in PFOA decomposition rather than simply providing acidity and acting as a hole-scavenger. The electron paramagnetic resonance (EPR) measurements confirmed the existence of carboxyl anion radicals (CO(2)(-)) in the photocatalytic process, which was a result of the reaction between oxalic acid and photogenerated hole. These findings indicated that PFOA decomposition was primarily induced by CO(2)(-) radicals, although photogenerated electron was also conducive to PFOA decomposition. A possible mechanism for PFOA decomposition was proposed.     

草酸-聚苯乙烯对化学光源发光效率的影响研究

以双(2,4,5-三氯-6-正丁烷氧羰基苯基)草酸酯(简称CPPO)和红色荧光剂罗丹明B为研究体系,分别讨论了抑制剂草酸、聚合物添加剂聚苯乙烯以及二者共同作用对过氧草酸酯类体系发光效率的影响.结果表明,加入草酸和聚苯乙烯的复合添加剂后,体系的发光寿命显著延长,发光强度接近于标准体系,发光效率最高.     

Nanoporous ZnO thin films deposited by electrochemical anodization: effect of UV light

Nanoporous ZnO thin films were deposited by electrochemical anodization of high purity Zn at room temperature using Pt counter electrode, calomel reference electrode and oxalic acid as the electrolyte. The crystallinity and the surface morphology were studied by X-ray diffraction (XRD) and Field emission scanning electron microscope (FESEM). The variation in molar concentration of oxalic acid during anodization had significant effect on the crystal size and the pore size particularly in the presence of UV light. An increase in room temperature band gap from 3.25 to 3.87 eV of ZnO film grown in 0.3 M oxalic acid indicates a quantum confinement effect and it was further confirmed by a blue shift of the photoluminescence (PL) spectra. A possible mechanism of the anodization and the photoetching in the presence of UV light of the ZnO film have been suggested.