Single-crystal growth and solid-state characterization of two new 2-methylimidazolium oxalate salts

Wood treated with CCB (chromated copper borate) has an expected service life of 20–50 years, depending on conditions of service and method of treatment. After this period, treated wood is discarded as special waste. Due to toxic elements (Cu, Cr, and B) in such treated wood, burning and landfill disposal are not considered as environmentally sound solutions. Chemical extraction seems more promising. The principle of the method is to convert fixed biocides in wood into soluble form and leach them out of the wood. In order to elucidate this process, copper(II) sulfate, potassium dichromate, and CCB-treated samples were leached using five different agents, namely, water, an aqueous solution of oxalic or acetic acid, and an aqueous solution of oxalic or acetic acid with ammonia. Afterwards, the amounts of leached copper and chromium were determined. In a parallel experiment, electron paramagnetic resonance measurements of wet- and dry-leached and unleached samples were performed in order to determine the paramagnetic complexes that were formed. The highest chromium leaching was achieved with the aqueous solution of oxalic acid, as chromium was converted into water-soluble chromium oxalate. While the mixture of oxalic acid and ammonia resulted in the highest copper leaching, EPR observation revealed that in this case water-soluble complexes of copper, oxalic acid, and ammonia were formed. We found out that oxalates formation is not the only mechanism responsible for copper or chromium leaching. High acidity may play an important role too.

We report a simple, facile, surfactant-free chemical route to fabricate morphologically different Cu2O nanoparticles such as octahedron, truncated octahedron, hollow octahedron, cube, and sphere by varying the hydrolyzing agents, complexing agent, and reducing agents. Then the componential and morphological evolution of Cu2O nanoparticles have been studied independently, employing different etching agents such as aqueous NaOH, triethylamine (TEA), and oxalic acid solution. Particles of varied shapes and compositions resulted from the etching, and those particles were characterized by different physical methods. The oxidative dissolution of morphologically different Cu2O nanoparticles with different etching agents depends on the exposed crystal planes. During oxidative dissolution in aqueous oxalic acid solution, it is realized that the stability of the (100) crystal plane is higher than that of the (111) crystal plane. Among all the etching reagents used, only oxalic acid exhibits shape transformation of the as-prepared Cu2O nanoparticles. Oxalic acid etching causes the formation of cubes and hollow cubes as etching products with a 50% reduction of edge length compared to that of octahedral, truncated octahedral, and hollow octahedral Cu2O nanoparticles. But ill-defined cubes are always obtained as the etching products with a 40% reduction of size compared to that of Cu2O cubes and spheres. As-prepared Cu2O nanoparticles and chemically etched products exhibit facet-dependent photocatalytic activity under visible light irradiation where mineralization of congo red takes place. Experimentally it has been concluded that photocatalytic activity of different particles bears a close relationship with exposed crystal planes, surface area, and particle size for congo red degradation. Interestingly, NaOH-etched product with hollow octahedral morphology bearing many (111) facets demonstrates the highest photocatalytic activity.

Memory effect-enhanced catalytic ozonation of aqueous phenol and oxalic acid over supported Cu catalysts derived from hydrotalcite

Synthesis, crystal structure and Hirshfeld surface analysis of Mn(II) coordination compounds with ONO-donor ligands derived from ampyrone

Dissolution kinetics of iron oxides in clay in oxalic acid solutions

A study of the oxidation of aqueous solutions of oxalic acid in various supporting electrolytes, at an Ebonex® anode is reported. From data obtained by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry, controlled potential coulometry and gas chramatography it has been shown that oxalic acid oxidation at an Ebonex® anode, does not proceed, to any significant extent. Data collected using different electrolytes showed that sulphuric acid supported higher current densities at similar electrode potentials. Ebonex® is essentially a selective oxygen evolver and is thus a suitable anode for the electroreduction of oxalic acid to glyoxylic acid in an undivided cell. The behaviour of a platinized titanium anode is also reported and this material has similar electrochemical characteristics to Ebonex® in aqueous oxalic acid solutions.

A kinetic study was conducted experimentally for the precipitation of ferrous oxalate. The ferrous oxalate, in the form of dihydrate (FeC2O4·2H2O), was produced by the acidic dissolution of ferrous ammonium sulfate (Fe(NH4)2(SO4)2) in an aqueous solution of oxalic acid, and then precipitated by nucleation and particle growth from supersaturated solution. The effect of the concentration of ferrous ammonium sulfate and oxalic acid as raw materials was investigated on the kinetics of the ferrous oxalate precipitation. Temperature was kept constant at 25 °C. The surface morphology, atomic compositions, and crystal phase were characterized for the ferrous oxalate precipitate collected. As the initial concentration of ferrous ammonium sulfate increased, the initial precipitation of ferrous oxalate occurred faster. The concentration of oxalic acid did not significantly affect the rate of precipitation of ferrous oxalate. The experimental behavior of ferrous oxalate precipitation was modeled with first-order models of reaction kinetics.

CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter

Single crystals of semi-organic nonlinear optical material potassium hydrogen oxalate are grown from the aqueous solutions of potassium hydroxide and oxalic acid in 1:1 stoichiometric ratio by slow evaporation solution growth method at room temperature. The grown crystals are subjected to various characterization techniques to explore their structural explication, thermal, linear and nonlinear optical perspectives for optoelectronic device applications. The monoclinic structure with non-centrosymmetric space group P21/c of the titular compound has been confirmed by single-crystal X-ray diffraction. The crystal packing is ruled by extensive networks of hydrogen bonds revealed by the detailed study of the refinement of the crystal structure. Optical transparency of the crystal in the entire visible region has been confirmed by ultraviolet–visible-near infrared (UV–Vis-NIR) analysis. The robust thermal stability of the grown crystal is ensured by thermogravimetric–differential thermal analysis. The presence of expected functional groups in the grown crystal has been confirmed by Fourier transform infrared spectroscopic studies. Second-harmonic generation efficiency has been calculated by Kurtz powder method.

Chemical mechanical planarization of copper using abrasive-free solutions of oxalic acid and hydrogen peroxide

Nature of the carboxylate species incorporated in anodic alumina films formed in oxalic acid solution

When choosing metal packaging for canned vegetables, it is advisable to take into account the corrosion aggressiveness, because corrosion of the inner surface is one of the factors affecting the products quality during storage. The main corrosion-aggressive substances in canned vegetables are organic acids and their salts. To rationalize the corrosion tests of metal-packaging materials, it is advisable to replace food with model media – solutions of organic acids. The objective of this work was to study the kinetics of corrosion of electrolytic tinplate in model media – aqueous solutions of oxalic acid with the concentration of 0.25–1.00 %. The rate of uniform corrosion was measured by the linear polarization resistance method, and of pitting corrosion – by zero resistance amperometry method. The experiments were carried out using Ekspert-004 corrosion-meter, according to a two-electrode scheme. For oxalic acid solutions with the concentration of 0.25 and 0.50 %, at the beginning of the experiment the maximum values of the uniform and pitting corrosion rates are observed, which drop to a steady value within 4–16 hours. The process is characterized as uniform corrosion, because the stationary pitting rate is 7–8 times less than the uniform corrosion rate (2.54–3.53 and 19.87–23.83 µm / year, respectively). For solutions with the concentration of 0.75 and 1.00% for 4–12 hours from the beginning of the experiment, the uniform corrosion and pitting rates values are set at 48–51 and 5–7 µm / year, respectively. Then, after 48–72 hours, the uniform corrosion rate reaches a minimum value of 1.04–2.95 μm / year, and then increases to a steady value (10.71–12.56 μm/year). The pitting rate after 96–104 hours increases to a steady value (21.26–32.8 µm/year). According to the results of research, it was found that oxalic acid solutions with the concentration of 0.25 and 0.50 % are the most corrosion-aggressive against tinplate - they should be used as components of model media for corrosion tests.

Microcrystalline zirconium phosphate (ZrP) has been synthesized by precipitating a Zr(IV) salt (i.e., zirconium propionate, chloride, or oxide chloride) with H(3)PO(4) from aqueous solutions of oxalic acid (H(2)C(2)O(4)) at 80 °C. Independent of the Zr(IV) salt, crystalline materials have been obtained with reaction yields >90% and reaction time of one day for the following molar ratios: H(3)PO(4)/Zr = 6 and H(2)C(2)O(4)/Zr = 10. The material prepared from Zr propionate (ZrP(prop)) has been further investigated by scanning electron microscopy, thermogravimetry, and ion exchange titrations. Structural characterization has been performed by X-ray powder diffraction and solid state (1)H-(31)P 2D correlation NMR experiments. Structural parameters obtained by Rietveld analysis of powder diffraction data agree with those reported in the literature for single crystal determinations. Moreover, NMR data show that the closest proton environment of the phosphorus atom in ZrP(prop) is the same as in ZrP samples of similar crystallinity prepared according to literature methods.

Electrochemical measurements during irradiation can be made in studying chemical changes in an irradiated solution. Several papers (1-3) have shown that the changes can be measured quantitatively; the reduction products of radiolysis react predominantly on the platinum electrode, whereas the oxidation products react on the gold and mercury electrodes. In this work we have used the dropping mercury and rotating platinum electrodes for a direct and continuous measurement of the radiolysis products during the irradiation of aqueous solutions of oxalic acid, in order to check some aspects of the previously suggested mechanism of radiolysis (4). The measurement of the oxygen consumption was of particular interest, because it should be a measure of free radical yield, and its determination by standard gas analysis is possible only with considerable error. As the participation of short-lived products of radiolysis in electrochemical measurements is still a subject of some doubt (2, 3, 5), it was interesting to see to what extent the results obtained under our standard working conditions could be explained merely by the molecular products of radiolysis (H2 and H202) and the molecular oxygen. Investigations were done in air-saturated oxalic acid solutions (50 mM) in acid (pH 1.6 and 3.6), neutral (pH -7), and alkaline (pH -9) media.

Induction periods during anodic polarization of zinc in aqueous oxalic acid solutions