Oxalate In Aqueous Solution Research Articles

Bipolar membrane crystallization enables near zero-waste production of high-purity oxalic acid crystals

The sodium formate method is currently the predominant route for oxalic acid production but is environmentally harmful. Water splitting in bipolar membranes provides the possibility for clean production of oxalic acid. However, bipolar membrane electrodialysis(BMED) also suffers from the major drawbacks of low concentrations and low purity products. Herein, we propose the use of bipolar membrane crystallization (BMC) to achieve synergistic conversion and crystallization of oxalic acid dihydrate. The dissolution of oxalate in aqueous solution and the electromigration of oxalate through the membrane were precisely tuned under different current densities. The consecutive electromigration of oxalate could boost the dissolution of oxalate. The morphology of the H2C2O4·H2O crystals is related to the current density: a plate-like shape is obtained at 5 mA/cm2, while a needle-shaped crystal is obtained at 10 mA/cm2. The intermittent crystallization of five batches of BMC demonstrated the robustness of bipolar membrane crystallization for the near zero-waste production of oxalic acid.

The primary photolysis dynamics of oxalate in aqueous solution: decarboxylation.

We study the primary reaction dynamics of aqueous oxalate following photo-excitation of the nO → πCO* transition at λ = 200 nm. After the excitation, some of the oxalate molecules return to the electronic ground state on two very different time scales: a fast component of τ = 1.1 ± 0.5 ps comprising 40% of the excited molecules and a much slower component of τ = 0.28 ± 0.05 ns accounting for 15% of the excited molecules. The remaining 45% of the excited molecules do not return to the ground state during the first 500 ps, because they either detach an electron, dissociate or stay excited for hundreds of picoseconds. Dissociation and electron detachment of oxalate predominantly produces CO2 molecules with only minor yields of CO2˙- radical anions. The CO2 formation is accompanied by the ejection of electrons.

Large Magneto-Current Effect in the Electrochemical Detection of Oxalate in Aqueous Solution

Herein, we first report an interesting observation of a large magneto-current (MC) of nearly 30% based on the electrochemical oxidation of oxalate in aqueous solution at room temperature. The large MC is ascribed to spin-dependent oxidation of oxalate. Both singlet and triplet radical pairs are generated during the electrochemical oxidation of oxalate. An applied magnetic field could accelerate the spin evolution of a singlet radical pair into its triplet state. The triplet radical pair has a much larger dissociation probability than the singlet radical pair because of the Pauli exclusion principle. Thus, enhancing the triplet yield could largely increase the oxidation rate of oxalate and generate significant MC. The significant MC effect provides a new approach to study spin evolution of radical pairs in electrochemical cells. Furthermore, an effective analytical method for oxalate determination can be developed based on the significant MC effect.

Precipitation of Amorphous Calcium Oxalate in Aqueous Solution

Inspired by the observation that crystalline calcium carbonate and calcium phosphate biominerals frequently form via amorphous precursors, a wide range of studies have been performed which demonstrate that many inorganic crystals can precipitate from solution via amorphous phases. This article considers the crystallization mechanism of calcium oxalate, which is a significant biomineral in many plants and the primary constituent of kidney stones in vertebrates, and shows that this can also precipitate via an amorphous precursor phase from aqueous solution. A range of approaches were employed to study calcium oxalate formation, including precipitation in bulk solution in the presence and absence of additives and in the spatially confined volumes offered by track etched membranes and a crossed cylinders apparatus. A freeze concentration method was also used to generate sufficient quantities of amorphous calcium oxalate (ACO) for analysis. The results show that amorphous calcium oxalate crystallizes rapidly in bulk solution but can be significantly stabilized through the concerted activity of additives and confinement. We also demonstrate that ACO has a composition of ≈CaC2O4:H2O. These data suggest that calcium oxalate biominerals, in common with their carbonate and phosphate counterparts, may also precipitate via amorphous phases.

The Complexation of Cm(III) with Oxalate in Aqueous Solution at T = 20–90 °C: A Combined TRLFS and Quantum Chemical Study

The complexation of Cm(III) with oxalate is studied in aqueous solution as a function of the ligand concentration, the ionic strength (NaCl), and the temperature (T = 20–90 °C) by time-resolved laser fluorescence spectroscopy (TRLFS) and quantum chemical calculations. Four complex species ([Cm(Ox)n](3–2n), n = 1, 2, 3, 4) are identified, and their molar fractions are determined by peak deconvolution of the emission spectra. The conditional log K′n(T) values of the first three complexes are calculated and extrapolated to zero ionic strength with the specific ion interaction theory approach. The [Cm(Ox)4](5–) complex forms only at high temperatures. Thus, the log K4(0)(T) value was determined at T > 60 °C. The log K1(0)(25 °C) = 6.86 ± 0.02 decreases by 0.1 logarithmic units in the studied temperature range. The log K2(0)(25 °C) = 4.68 ± 0.09 increases by 0.35, and log K3(0)(25 °C) = 2.11 ± 0.05 increases by 0.37 orders of magnitude. The log Kn(0)(T) (n = 1, 2, 3) values are linearly correlated with the reciprocal temperature. Thus, their temperature dependencies are fitted with the linear Van’t Hoff equation yielding the standard reaction enthalpy (ΔrHm(0)) and standard reaction entropy (ΔrSm(0)) of the stepwise formation of the [Cm(Ox)n](3–2n) species (n = 1, 2, 3). Furthermore, the binary ion–ion interaction coefficients of the four Cm(III) oxalate species with Cl(–)/Na(+) are determined. The binding energies, bond lengths, and bond angles of the different Cm(III) oxalate complexes are calculated in the gas phase as well as in a box containing 1000 H2O molecules by ab inito calculations and molecular dynamics simulations, respectively.

Study of the photocatalytic and sensor properties of ZnO/SiO2 nanocomposite layers

ZnO/SiO2 nanocomposite layers are deposited onto glass substrates by the sol-gel method. The fraction of SiO2 is 20%. The layers are produced by single or double deposition and sol centrifugation. To study the photocatalytic properties of the samples, experiments are performed on the decomposition of Malachite Green oxalate in aqueous solutions under the action of light in the ultra-violet and visible (UV/VIS) spectral ranges. The gas-sensitive properties of the layers are examined by impedance spectroscopy in various gas atmospheres. In all experiments, double-layer ZnO/SiO2 nanocomposites exhibit a higher efficiency, compared with the rest of the samples, irrespective of the irradiation type. The double-layer samples also show the best sensitivity to acetone and isopropanol vapors.

Enthalpies of reaction of calcium chloride and sodium oxalate in aqueous solution of Tween 80

The heats of mixing of dilute calcium chloride and sodium oxalate solutions in water and aqueous solutions of a nonionogenic surfactant, namely, polyoxyethylene (20) sorbitan monooleate (Tween 80) containing 1–5 wt % of the dissolved substance were measured at 298.15 K. The heats of dilution of calcium chloride solutions were determined, and the enthalpies of precipitation of calcium oxalate in water and surfactant solutions were calculated. The surfactant concentration was found to have almost no effect on the enthalpies of the processes under study; rather, it modifies the shape of the resultant deposit by preventing the agglomeration of calcium oxalate particles.

Thermodynamics of the complexation of uranium(vi) with oxalate in aqueous solution at 10–70 °C

The protonation reactions of oxalate (ox) and the complex formation of uranium(vi) with oxalate in 1.05 mol kg(-1) NaClO(4) were studied at variable temperatures (10-70 degrees C). Three U(vi)/ox complexes (UO(2)ox(j)((2-2j)+) with j = 1, 2, 3) were identified in this temperature range. The formation constants and the molar enthalpies of complexation were determined by spectrophotometry and calorimetry. The complexation of uranium(vi) with oxalate ion is exothermic at lower temperatures (10-40 degrees C) and becomes endothermic at higher temperatures (55-70 degrees C). In spite of this, the free energy of complexation becomes more negative at higher temperatures due to increasingly more positive entropy of complexation that exceeds the increase of the enthalpy of complexation. The thermodynamic parameters at different temperatures, in conjunction with the literature data for other dicarboxylic acids, provide insight into the relative strength of U(vi) complexes with a series of dicarboxylic acids (oxalic, malonic and oxydiacetic) and rationalization for the highest stability of U(vi)/oxalate complexes in the series. The data reported in this study are of importance in predicting the migration of uranium(vi) in geological environments in the case of failure of the engineering barriers, which protect waste repositories.

Piperazinium aquabis(oxalato)oxidovanadate(IV) dihydrate

The title compound, (C4H12N2)[V(C2O4)2O(H2O)]·2H2O, has been obtained by the reaction of vanadium(III) chloride with piperazinediium oxalate in aqueous solution. It shows distorted octahedral geometry [V=O = 1.6010 (12) Å and V—O = 1.9932 (12)–2.2176 (12) Å]]. The structure exhibits intermolecular N—H⋯O and C—H⋯O hydrogen bonds. The uncoordinated water mol­ecules contribute to the formation of the supra­molecular structure via O—H⋯O hydrogen bonds.

One-step formation of ultra-thin chemically functionalized redox-active Langmuir-Schaefer Nafion films.

A novel "one-step procedure" to incorporate different cationic redox-active species within ultra-thin Nafion films is reported. Ultra-thin films of Nafion containing trimethylammonioferrocene (FA), tris(2,2'-bipyridyl)ruthenium(), Ru(bpy), and hexaaminoruthenium(), [Ru(NH)], were prepared using the Langmuir-Schaefer (LS) technique. The morphology and thickness of the films were evaluated with atomic force microscopy (AFM). Film thicknesses were 1.9 ± 0.7, 1.8 ± 0.9, 1.5 ± 0.9 nm per layer for Nafion-FA, Nafion-Ru(bpy)and Nafion-[Ru(NH)], respectively. Electrochemical data confirmed the successful incorporation of the mediators into the films and proved that the redox activity was maintained during extensive voltammetric cycling. Key parameters such as surface coverage, concentration of the mediator within the films and apparent diffusion coefficients were extracted using cyclic voltammetry. To demonstrate the utility of the redox-active films for sensing applications, films with Ru(bpy) incorporated were utilized for the electrocatalysis of oxalate in aqueous solution.

Effect of Various Kinds of Carboxylates on Phases Compositions of Calcium Oxalate in Aqueous Solutions

Effect of Various Kinds of Carboxylates on Phases Compositions of Calcium Oxalate in Aqueous Solutions

Morphological Control of Calcium Oxalate Dihydrate by a Double-Hydrophilic Block Copolymer

The crystallization of calcium oxalate in aqueous solutions of a double-hydrophilic block copolymer poly(ethyleneglycol)-block-poly(methacrylic acid) (PEG-b-PMAA) has been investigated, focusing on morphological control of the calcium oxalate dihydrate (COD) crystals. It has been shown that with increasing polymer concentration, the morphology of the obtained COD crystals gradually changed from tetragonal bipyramids dominated by the {101} faces to rodlike tetragonal prisms dominated by the {100} faces, which is a morphology adopted by some plant COD crystals but not obtained in vitro previously. The concentration of calcium oxalate and the [Ca2+]/[C2O42-] ratio were also found to show considerable effects on the morphology of the obtained COD crystals. Seed growth experiments further demonstrated the drastic effect of the polymer on the COD crystal morphology. This effect was preliminarily discussed in terms of possible structural correlation between the short PMAA chain of the polymer and the COD {100} p...

XPS study of dissolution of birnessite by humate with constraints on reaction mechanism

The present study is an investigation into the surface reactions of synthetic birnessite [Mn(II) 0.05Mn(III) 0.25Mn(IV) 0.7O 1.7(OH) 0.25] when reacted with dilute (5 × 10 −4 M) Na-humate solution using X-ray Photoelectron Spectroscopy (XPS). Mn2p 3/2, C1s and O1s spectra of reacted surfaces reveal that Mn(IV) of birnessite is reduced to Mn(III) while humate is oxidized to CO 2. Initial rapid production of CO 2 results in accumulation of CO 2 at the reaction interface. After approximately 15 min, the reaction rate decreases to the point where desorption keeps pace with accumulation until after 5 h of reaction, when CO 2 is no longer detected at the reaction surface. Reduction of Mn(IV) of birnessite to Mn(III) indicates that the MnO 2-oxalate redox reaction proceeds as a transfer of one electron per metal centre. There is no XPS evidence for reduction of Mn(III) of the solid to Mn(II) in the presence of humate. The carboxyl group of humate apparently inhibits this step, most likely through formation of strong Mn(III)-carboxyl surface complexes. This postulate is consistent with Mn 3+(aq) stabilization by oxalate in aqueous solutions. Further study using X-ray absorption spectroscopy (XAS) is required for a better understanding of the structure of the surface complexes. The rate of release of soluble Mn(II) into dilute humate solutions (5 × 10 −4 M) is lower by more than two orders of magnitude compared with rate of release to aerated, distilled water at similar pH. The process of proton promoted dissolution of the soluble Mn(II) component of birnessite in distilled water would appear to be impeded by the addition of humate. This could be attributed to the formation of strong, multinuclear surface complexes between Mn(II, III) and the adsorbed carboxyl groups.

XPS study of reductive dissolution of birnessite by oxalate: rates and mechanistic aspects of dissolution and redox processes

Reductive dissolution of synthetic 7Å-birnessite [MnO1.7(OH)0.25 or MnO1.95] by Na-oxalate produces a Mn(III) intermediate reaction product (here represented as MnOOH∗) which subsequently reacts with sorbed (COO)2−2 to form an unreactive Mn(III)-oxalate surface complex at the solution-mineral interface according to the reactions: 2MnO2+(COO)2−2+2H+=2MnOOH∗+2CO2↑ (1)2MnOOH∗+(COO)2−2=2[MnOOH-COO]−(2) X-ray Photoelectron Spectroscopy (XPS) results from Mn2p3/2, C1s and O1s spectra of reacted surfaces reveal that initially rapid production of CO2 via Eqn. (1) results in accumulation of CO2 at the reaction interface. After about 15 min, the reaction rate decreases to the point where CO2 desorption keeps pace with accumulation. Surface concentrations of CO2 suggest that the rate of CO2 production decreases with time, until after 10 hr of reaction, it is undetectable. Reduction of Mn(IV) to Mn(III) suggests that the MnO2-oxalate redox reaction proceeds as a transfer of one electron per metal centre.There is no XPS evidence for reduction of Mn(III) from birnessite to Mn(II) in the presence of oxalate. Although this reaction proceeds in presence of arsenite, it is inhibited by oxalate, probably through formation of a strong Mn(III)-oxalate surface complex (either monodentate or bidentate). This hypothesis is consistent with Mn3+(aq) stabilization by oxalate in aqueous solutions. Further study using X-ray absorption spectroscopy (XAS) is required for a better understanding of the structure of the surface complexes.Rate of release of soluble Mn(II) to dilute oxalate solutions (5 × 10−4 M) is lower by an order of magnitude than the rate of release to aerated, distilled water at similar pH. Apparently, the process of proton-promoted dissolution of the soluble Mn(II) component of birnessite in distilled water is impeded by the addition of oxalate, probably by formation of a binuclear, bidentate surface complex between Mn(II, III) and adsorbed oxalate ions.

シュウ酸による含Ｃｏ有機相からの晶析逆抽出への超音波の利用

The precipitation stripping phenomena of cobalt oxalate from cobalt-loaded D2EHPA solution were investigated with and without ultrasound irradiation. Morphological variation of precipitated cobalt oxalate was examined with processing factors such as pH value and C2H2O4 concentration under three kinds of mixing modes encountered in crystallization operation ; 1) precipitation synthesis of cobalt oxalate in aqueous solution mixed with an impeller, 2) precipitation stripping from cobalt-loaded organic solution and 3) precipitation stripping from cobalt-loaded organic solution under ultrasound irradiation. The shape of precipitate was rod-like and not significantly influenced by any mixing mode. The size of cobalt oxalate particles obtained without ultrasound irradiation was at most 10μm in major axis. The aspect ratio of rod-like particles, moreover, tended to increase with increasing in H+ and C2H2O4 concentrations in the stripping solutions. Meanwhile, the ultrasound irradiation significantly decreased particle size of cobalt oxalate. It was less than 1μm in major axis, when the [C2H2O4]a concentration was lower. On the other hand, ultrasound irradiation induced fibriform precipitation when the [C2H2O4]a concentration was higher.

Triamterene and renal stone formation: the influence of triamterene and triamterene stones on calcium oxalate crystallization.

A constant composition method has been used to compare the effects of triamterene renal stone material, synthetic triamterene precipitates, and soluble triamterene on the nucleation and crystallization kinetics of calcium oxalate in aqueous solution in vitro. Crystallization studies have been carried out with the concentrations of calcium and oxalate ions maintained constant by the potentiometrically controlled addition of concentrated reagent solutions containing these ions. Triamterene renal stones were found to be much less effective than synthetic triamterene towards promoting the nucleation and crystallization of calcium oxalate from supersaturated solution. Renal stones composed of triamterene and matrix did not significantly enhance the deposition of calcium oxalate compared to nonseeded controls. The triamterene stones were also found to be ineffective in promoting calcium oxalate crystallization compared to other precipitates thought to be involved in the etiology of stone disease such as calcium hydroxyapatite. For stones of mixed triamterene/calcium oxalate composition, the enhancement of the nucleation and crystallization of calcium oxalate was directly related to the calcium oxalate content of the stone seed material. The presence of soluble triamterene or its metabolites in solution did not influence the crystallization kinetics of pure calcium oxalate seed materials. The results of this study indicate that triamterene in stones does not significantly contribute to further stone development through the enhancement of calcium oxalate crystallization processes.

Spectrophotometric determination of oxalate in aqueous solution

A simple, rapid, and reliable spectrophotometric method for the determination of oxalate in aqueous solution has been developed. The decomposition produced by oxalate on the quercetin-zirconium complex allows the oxalate determination by an indirect method, at 430 nm, or a direct method at 370 nm. The decrease or increase in absorbance is linear within the oxalate range of 0–50 μg, with a detection limit of 2.5 μg in a final volume of 10 ml.

Chiral metal complexes. 9. Changes in tetradentate stereochemistry involving a Λ-α to Δ-α rearrangement: a new form of octahedral inversion

When Λ-α-[Co(R-picpn)Cl 2)]Cl) 4 (R-picpn = (3R)3-methyl 1,6-di(2-pyridyl)-2,5-diazahexane) is reacted with sodium oxalate in aqueous solution, the complex Λ-α[Co(R-picpn)(ox)]ClO 4 is obtained. This reaction represents a total inversion of absolute configuration with respect to the metal centre. When isolated as the iodide salt, [Co(R-picpn)(ox)]I·1.5H 2O, the cationic product is obtained as a mixture of Δ-α and Λ-β diastereoisomers with a minor quantity of the Λ-αform. These isomeric ratios appear to be influenced by differences in reaction conditions, including exposure to light.

Darstellung und spektroskopische Charakterisierung von Tetrachloro- und Tetrabromo-Oxalatoiridaten(IV) / Preparation and Spectroscopical Characterization of Tetrachloro- and Tetrabromoiridates(IV)

On treatment of [IrX6]2- with oxalate in aqueous solution at first [IrX4OX]3- (X = Cl, Br) is formed, which after extraction with pentylammonium ions into CH2Cl2 can be oxidised by X2 to give the corresponding pure Ir(IV) complexes [IrX4OX]2-. The IR and Raman spectra are assigned according to point group C2V- The UV/VIS absorption spectra show strong CT bands of transitions from "(π + σ)tlu"- and "πt2U"-ligand niveaus to t2g 5 (IrIV). These are split into three components by spin-orbit coupling and corresponding to the different groups of ligands: Xtr 2, Xc 2, ox. The spectrum of (TBA)2[IrBr4OX] recorded at 10 K is highly resolved, showing a splitting of the Brtr 2 → Ir(IV) and Bc 2 → Ir(IV) transitions by 1000-1400 cm-1. In the NIR-region two d-d-transitions are observed superimposed with a fine structure by coupling with vibration modes

Reactive ion-exchange precipitation procedure for the determination of trace amounts of oxalate

The feasibility of using reactive ion-exchange for the determination of oxalate in aqueous solution has been demonstrated. The procedure consists of pH adjustment of the analyte solution, concentration of oxalate on a lead(II)-loaded cation exchange mini-column in the form of lead oxalate precipitate, reactive elution of oxalate by sulphuric acid dissolution and analysis of the concentrated eluate by permanganate titration. Almost quantitative yields of oxalate are obtained for concentrations typically found in human urine. The procedure represents a simple and reliable technique to concentrate oxalate for determination by classical methods.