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Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements (Ce3+, Nd3+, and Y3+) using oxalic acid as a precipitant. Trivalent metal ions, Al3+ and Fe3+, were found to considerably affect the precipitation efficiency of REEs. When Al3+ and Fe3+ concentrations were increased by 1 × 10−4 mol/L, in order to achieve an acceptable cerium recovery of 93% from solutions containing 1 × 10−4 mol/L Ce3+, oxalate dosage needed to increase by 1.2 × 10−4 and 1.68 × 10−4 mol/L, respectively. Such great impacts on the required oxalate dosage were also observed for Nd3+ and Y3+, which indicates that oxalic acid consumption and cost will be largely increased when the trivalent metal ions exist in REE-concentrated solutions. Effects of the divalent metal ions on the oxalate dosage is minimal. Furthermore, solution equilibrium calculation results showed that the precipitation of Fe3+ and Ca2+ (e.g., hematite and Ca(C2O4)∙H2O(s)) likely occurs during the oxalate precipitation of REEs at relatively high pH (e.g., pH 2.5), which will reduce rare earth oxalate product purity. In addition to the metal ions, anionic species, especially SO42−, were also found to negatively affect the precipitation recovery of REEs. For example, when 0.1 mol/L SO42− occurs in a solution containing 1 × 10−4 mol/L Ce3+ and 4 × 10−4 mol/L oxalate, the pH needed to be elevated from 2.0 to 3.3 to achieve the acceptable recovery. Overall, findings from this study provide guidance for the obtainment of high-purity rare earth products from solutions containing a considerable amount of contaminant metal ions by means of oxalic acid precipitation. Accepted version

Understanding the reactions taking place in the hematite-oxalic acid system is important in order to clean iron oxides from filters and to remove iron from mineral concentrates. Previous studies reported the formation of an unwanted solid phase during this process. The objective of the current work, therefore, was to visualize and rationalize the iron dissolution steps taking place in the hematite–oxalic acid reaction by combining density functional theory (DFT) calculations and experimental data. The results of DFT calculations indicated that a precipitate was formed in this reaction; XRD analysis of the solid phase after the dissolution experiment revealed the formation of humboldtine as the precipitate. The attachment of oxalate on the hematite surface and the reduction of Fe(III) to Fe(II) were key steps for humboldtine formation. Both simulations and the experimental results showed that greater oxalic acid concentrations yielded more precipitate, suggesting a simple and novel route to synthesize humboldtine, a material which is relevant to the demand for clean energy.

In this work, we proposed to combine oxalic acid and ferric ions in very low concentrations to create new, economic, and effective homogeneous photo-Fenton catalytic systems for the degradation of methylene blue. The effects of ferric concentration, H2C2O4 concentration, pH, and tert-butanol on the catalytic activity were also investigated. According to the experimental results, Fe3+ ions exhibited impressive catalytic performances in the presence of H2C2O4 at concentrations below type B (5.0 mg.l–1) from the Vietnam National Technical Regulation on Industrial Wastewater. Specifically, a ferric concentration of 3.0 mg.l–1, H2C2O4 concentration of 10–3 mol.l–1, and pH value of 3 were found to be the best conditions for MB degradation under UVA light. Furthermore, owing to a very low concentration of ferric ions, iron sludge formation can be avoided after wastewater treatment, which makes the photo-Fenton process suitable for practical applications.

In manufacturing C-N bond-containing compounds, it is important challenge to alternate the conventional methodologies that utilize reactive substrates, toxic reagents and organic solvents. In this study, we developed an electrochemical method to synthesize a C-N bond-containing molecule avoiding the use of cyanides and amines by harnessing nitrate (NO 3 - ) as a nitrogen source in an aqueous electrolyte. In addition, we utilized oxalic acid as a carbon source which can be obtained from electrochemical conversion of CO 2 , so that our approach can provide a route for the utilization of anthropogenic CO 2 and nitrate wastes which cause serious environmental problems including global warming and eutrophication. Interestingly, the coreduction of oxalic acid and nitrate generated reactive intermediates, which led to C-N bond formation followed by further reduction to an amino acid, namely, glycine. By carefully controlling this multireduction process with a fabricated Cu-Hg electrode, we demonstrated the efficient production of glycine with a faradaic efficiency (F.E.) of up to 43.1% at -1.4 V vs. Ag/AgCl (current density = ~90 mA cm -2 ).

In the past 10 years, the treatment and restoration of soil and water bodies contaminated by mercury and other heavy metals have received unprecedented attention and support from China's environmental protection authorities. The search for low-cost and high-efficiency adsorbents has become one of the research hotspots in this field. In this paper, a simple and environment-friendly method was used to graft 3-mercaptopropyl trimethoxysilane on the surface of palygorskite. The synthesized mercaptofunctionalized palygorskite (M-PAL) was characterized by XRD, FT-IR, BET and SEM-EDS, respectively, and its adsorption conditions, adsorption models and thermodynamic parameters for Hg2+ were systematically investigated. The experimental results indicated that the saturated adsorption capacity of Hg2+ on the M-PAL could reach 203.4 mg·g-1, within 120 min at pH 4 and 298 K. By analyzing the experimental data of adsorption kinetics and thermodynamics, it was found that the adsorption process of Hg2+ conformed to the pseudo-second-order kinetic model, which belonged to chemical adsorption of the rate-controlled step; the Langmuir model better described the adsorption isotherm. The thermodynamic parameters obtained (ΔH=29.95 kJ·mol-1, ΔS=103.09 J·mol-1·K-1 and ΔG

Recent advances in high-tech applications have highlighted the growing demand on highly pure silicates like quartz. Therefore, purification of quartz ore was determined as the subject of this study performed by pyrometallurgical followed by hydrometallurgical processes. In this research, the effect of thermal treatment (TT) followed by oxalic acid (OA) bleaching of quartz was examined to have a better understanding on the relationship between Fe remaining in concentrate and colour response. The level of TT temperature was found to have a significant effect on the purification of quartz by OA. The maximum Fe rejection rate was observed to occur both for non-treated and TT quartz up to 250°C. TT between 400°C and 900°C showed poor purification performance: decreasing L* value, and increasing a* and b* values. It is important to note that further increase in TT temperature to 1100°C resulted in the poorest bleaching: Fe rejection rate decreased, but colour response improved providing the highest L* value and the lowest a* and b* values. This finding was explained by the formation of dissolution resistant iron silicates. Moreover, the rate of Fe removal from quartz ore and differences observed in its colour response by OA bleaching were explained by changes in crystalline structure and formation of microcracks.

The yields of oxidation of substances in aqueous solutions under the action of a corona electric discharge were studied. The possibilities of reducing the energy consumption for the oxidation of organic compounds by hydroxyl radicals by initiating and maintaining chain reactions are considered. Hydroxyl radicals were generated in a corona electric discharge on a point solid electrode located above the surface of an aqueous solution. Under the experimental conditions, an ozone-hydroxyl mixture is formed, in which the lifetime of hydroxyl radicals increases to 0.2 s. The conditions for the development of a chain reaction were analysed. Experiments were carried out for aqueous solutions of phenol with COD values from 710 to 2900 mg O/L, oxalic acid with a COD of 2000 mg O/L and 0.1 M solution KI for treated liquid volumes from 2.5 to 35 L. Oxalic acid was used as a detector of hydroxyl radicals, KI solution – detector OH• + O3. At a low concentration of dissolved organic substances (COD ~ 700 mgO/L), initiation of a chain reaction is impossible. It is shown that there are conditions, when take place the inhibition of chain oxidative reactions of phenol. The reasons for inhibition are a decrease in the pH of the medium, the transformation of primary radicals into inactive secondary ones, and the occurrence of reverse reactions. The yield of hydroxyl radicals is ~ 0.2 (100 eV)−1, while the oxidation yield reaches ~ 7.5 (100 eV)−1 and increases with an increase in the volume of the treated liquid.

Fe(II)-driven transformation of schwertmannite can strongly impact the transport and redistribution of coprecipitated As in reducing acid sulfate soil (ASS)/acid mine drainage (AMD)-contaminated en...

The photocatalytic activity of titania supported bimetallic Cu-Ni photocatalysts were assessed for hydrogen production from water and also a mixture of glycerol-water system under visible light illumination. Addition of 2.0 mL glycerol to 8.0 mL water enhanced the solar hydrogen production from 6.1 mL to 9.5 mL. If metal was not incorporated onto TiO2 , the hydrogen production was minimal, 2.0 mL after 2 hr reaction. The band gap for bimetallic Cu-Ni/TiO2 was 2.78 eV compared to 3.16 eV for TiO2 . Photooxidation of glycerol produced glyceraldehyde, glycolic acid and oxalic acid.

Two ionic liquid (IL) thermomorphic systems were designed. The thermoregulated property exhibited by the IL systems was utilized for the recovery of Au(III) from acidic medium. The cloud point order of the two ILs was proposed and evidenced via a combination of experimental measurements and quantum chemical calculations. The impacts of salt ions and acid on the thermomorphic phase behavior of the IL–H₂O binary mixture system were investigated. After comprehensive comparison, a systematic study of Au(III) extraction by the [Suc][Tf₂N]₂ (succinyl bis(trifluoromethylsulfonyl)imide) system was carried out because of its outstanding hydrophobicity and extraction ability. Then, a comparison between traditional liquid–liquid extraction (TLLE) and homogeneous liquid–liquid extraction (HLLE) was made during the process of optimization of various extraction parameters. In addition, the anion-exchange mechanism in the extraction process was revealed. The thermoregulated [Suc][Tf₂N]₂ system presented an excellent selectivity for Au(III) in a solution of coexisting multimetallic ions. Finally, Au(III) was almost completely stripped from the loaded IL phase by oxalic acid. The extraction efficiency of Au(III) using regenerated IL still maintains a surprising stability after five turns of cycling experiments. Hence, the dicationic IL [Suc][Tf₂N]₂ was regarded as a potential extractant for the recovery of gold.

Iron coordination polymer, Fe(ox)(H2O)2 (H2ox = oxalic acid) nanorods were grown on a nickel foam (NF) collector via a one-step electrodeposition method, which can be directly used as a freestandin...

This study was formulated to synthesize the ZnO nanoparticles through acetate-based zinc salts with NaOH (ZnO-I) and Oxalic acid (ZnO-II) as reactants; sodium dodecyl sulfate (SDS) used as a stabil...

The present study evaluates the reductive leaching of indium from indium-bearing zinc ferrite using oxalic acid as a reducer in sulfuric acid solution. The effect of main factors affecting the process rate, including the oxalic-acid-to-sulfuric-acid ratio, stirring rate, grain size, temperature, and the initial concentration of synergic acid, was precisely evaluated. The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid. The shrinking-core model with a chemical-reaction-controlled step can correctly describe the kinetics of indium dissolution. On the basis of an apparent activation energy of 44.55 kJ/mol and a reaction order with respect to the acid concentration of 1.14, the presence of oxalic acid was found to reduce the sensitivity to temperature changes and to increase the effect of changes in acid concentration. Finally, the equation of the kinetic model based on the factors under study is presented.

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process. In this study, a new method for leaching NdFeB waste with oxalic acid was developed. The high-efficiency, simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit. Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90 °C for 6 h in the aqueous solution of oxalic acid (2 mol/L) with a liquid–solid ratio of 60 mL/g, the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%, respectively. Rare earth oxalate and Fe(C2O4)33− were left in the residue and the leaching solution, respectively. The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model, and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction. The leaching residue was calcined at 850 °C for 3 h and then decomposed into rare earth oxide, which can be directly used to prepare rare earth alloy via molten salt electrolysis. For the leaching solution, ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate (FeC2O4·2H2O).

The quest for developing next-generation non-precious electrocatalysts has risen in recent times. Herein, we have designed and developed a low cost electrocatalyst by a ligand-assisted synthetic strategy in an aqueous medium. An oxalate ligand-assisted non-oxide electrocatalyst was developed by a simple wet-chemical technique for alkaline water oxidation application. The synthetic parameters for the preparation of nickel–cobalt oxalate (Ni2.5Co5C2O4) were optimized, such as the metal precursor (Ni/Co) ratio, oxalic acid amount, reaction temperature, and time. Microstructural analysis revealed a mesoporous block-like architecture for nickel–cobalt oxalate (Ni2.5Co5C2O4). The required overpotential of Ni2.5Co5C2O4 for the alkaline oxygen evolution reaction (OER) was found to be 330 mV for achieving 10 mA cmgeo−2, which is superior to that of NiC2O4, CoC2O4, NiCo2O4 and the state-of-the-art RuO2. The splendid performance of Ni2.5Co5C2O4 was further verified by its low charge transfer resistance, impressive stability performance, and 87% faradaic efficiency in alkaline medium (pH = 14). The improved electrochemical activity was further attributed to double layer capacitance (Cdl), which indefinitely divulged the inferiority of NiCo2O4 compared to Ni2.5Co5C2O4 for the alkaline oxygen evolution reaction (OER). The obtained proton reaction order (ρRHE) was about 0.80, thus indicating the proton decoupled electron transfer (PDET) mechanism for OER in alkaline medium. Post-catalytic investigation revealed the formation of a flake-like porous nanostructure, indicating distinct transformation in morphology during the alkaline OER process. Further, XPS analysis demonstrated complete oxidation of Ni2+ and Co2+ centres into Ni3+ and Co3+, respectively under high oxidation potential, thereby indicating active site formation throughout the microstructural network. Additionally, from BET-normalised LSV investigation, the intrinsic activity of Ni2.5Co5C2O4 was also found to be higher than that of NiCo2O4. Finally, Ni2.5Co5C2O4 delivered a TOF value of around 3.28 × 10−3 s−1, which is 5.56 fold that of NiCo2O4 for the alkaline OER process. This report highlights the unique benefit of Ni2.5Co5C2O4 over NiCo2O4 for the alkaline OER. The structure–catalytic property relationship was further elucidated using density functional theory (DFT) study. To the best of our knowledge, nickel–cobalt oxalate (Ni2.5Co5C2O4) was introduced for the first time as a non-precious non-oxide electrocatalyst for alkaline OER application.

A new metal–organic framework (MOF) showed excellent recognition ability toward five toxic oxo-anions, namely arsenate (HAsO42−), phosphate (PO43−), permanganate (MnO4−), chromate (CrO42−), and dichromate (Cr2O72−) in aqueous medium upon irradiation with UV light. The MOF [Y(tp)(ox)0.5(H2O)2]·H2O, 1 and a 20% Tb-doped MOF [Y0.8Tb0.2(tp)(ox)0.5(H2O)2]·H2O, 1a were synthesized by the self-assembly of Y(III)/Tb(III), terephthalic acid (H2tp), and oxalic acid (H2ox) under hydrothermal conditions. The crystal structure of 1 demonstrated three-dimensional structures with water occupying a one-dimensional channel. Upon UV light exposure, an aqueous suspension of 1a exhibited strong green luminescence. This luminescence showed a colour change when water was contaminated by the said anions. Several other interfering anions were also tested to establish its selectivity as a chemosensor toward the aforementioned anions. The estimated limit of detection (LOD) of 1a for these anions was 41.7, 33.5, 19.6, 40.8, and 43.9 nM for HAsO42−, PO43−, MnO4−, CrO42−, and Cr2O72−, respectively, which were significantly lower than the levels recommended for these anions in the aqueous environment. The root of the luminescence quenching of 1a in the presence of such a low concentration of aforementioned anions was due to the interruption of the sensitization process of the Tb centre. Anions HAsO42−, PO43−, and MnO4− entered the channel of MOF and interacted with Y3+/Tb3+ centres at the molecular-level, which hampered the energy flow from the ligand to the metal centre through a weakening of Tb–O bonds of carboxylates, resulting in a quenching of the Tb centre emission with a concomitant enhancement of the ligand centre emission. Additionally, in the case of the MnO4− ion, an inner filter effect also contributed to the quenching of the Tb centre emission, but to a smaller extent. For CrO42− and Cr2O72− anions, the inner filter effect is the key mechanism for the luminescence intensity reduction. Besides, these analytes could also reduce the energy flow from the ligand to the lanthanide ion, which led to the luminescence quenching.

Electrochemical CO2 reduction to oxalic acid in aprotic solvents could be a potential pathway to produce carbon-neutral oxalic acid. One of the challenges in aprotic CO2 reduction are the limited achievable current densities under standard conditions, despite the increased CO2 solubility compared to aqueous applications. The application of aprotic solvents can reduce CO2 rather selectively to oxalate, and faradaic efficiencies (FEs) of up to 80% were achieved in this study with a Pb catalyst in acetonitrile, the FE being mainly dictated by the local CO2 concentration at the electrode. This process was integrated into a flow cell employing a two-layered carbon-free lead (Pb) gas diffusion electrode (GDE) and a sacrificial zinc (Zn) anode. With the application of this GDE the applicable current densities could be improved up to a current density of j = 80 mA cm−2 at a FE(oxalate) = 53%, which is within the range of the highest j reported in the literature. In addition, we provide an explanation for the deactivation mechanism of metal catalysts observed in the aprotic CO2 reduction literature. The deactivation is not related to a mass transport limitation but to cathodic corrosion observed at highly negative potential when employing quaternary ammonium supporting electrolyte cations, promoting catalyst leaching.

Paracetamol (PCA) has two well-known polymorphic forms, monoclinic (form I) and orthorhombic (form II). The parallel packing of flat hydrogen bonded layers in the metastable form II results in compaction properties superior to the thermodynamic stable form I which contains corrugated hydrogen bonded layers of molecules. In this study, the structure of Paracetamol (PCA)-Oxalic acid (OXA) co-crystal has been analyzed and found layered structure similar to PCA form II which enhance ability to form tablet. The Density Functional Theory (DFT) has been conducted to find some physicochemical properties of co-crystal. It was observed that the lattice energy of co-crystal is more than that of PCA form II showing more stability on co-crystal. The energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gap) in co-crystal was found less than PCA form II showing bigger enhancement of reactivity.

Two lanthanide coordination polymers (CPs) with the chemical formulae of [Pr(HPIDC)(C2O4)0.5(H2O)]n (1, H3PIDC = 2-(pyridine-2-yl)-1H-imidazole-4,5-dicarboxylic acid and H2C2O4 = oxalic acid) and [...

We reported a low cost, high efficiency hydrogen generation method from NaBH4 hydrolysis promoted by oxalic acid. NaBH4 and H2C2O4 were premixed and hydrogen generation was initiated by adding water into the solid mixture. H2C2O4 was selected as the acid promotor due to its solid state and low mass per proton. The effect of reactant ratio on the hydrogen yield and hydrogen storage density was investigated. With optimized reactant ratio, high gravimetric hydrogen storage up to 4.4wt% based on all the reactants can be achieved with excellent hydrogen generation kinetics.

Schwertmannite (Sch), a common metastable ferric sulfate secondary mineral in acidic mine drainage (AMD) matrix, can be transformed under solar irradiation, thus playing a significant role in eleme...

The dissolution of iron oxides in mixtures of acids is fairly uncommon but can result in a more efficient dissolution process. The objective in this work was to investigate the dissolution of synthetic hematite powder in mixtures of oxalic and sulfuric acid. Experiments were done at different acid ratios and temperatures. An increase in temperature from 15 to 35 °C increased solubility, whereas an increase from 35 to 50 °C did not change the solubility but had a profound effect on the kinetics. An important finding was that oxalic acid advanced the dissolution process since increasing the amount of oxalic acid in the system resulted in faster kinetics and higher solubilities. The dissolution kinetics were well described with the Kabai model, which was the only studied model able to describe the whole reaction time. However, the solid specific constant a varied for the different acid ratios and this is argued to be a result of changes in the solid phase. The changes in the constant a were not in line with the original study of Kabai, which indicates that a cannot be the solid specific constant but it can be the constant connected to dissolving media describing the changes in the dissolution mechanism.

So far, studies on the conversion of stereochemistry under photo-Fenton conditions and their atmospheric implication are still rare. Here, we found that the biomass burning marker, the chiral compound levoglucosan (L), undergoes oxidative degradation under photo-Fenton conditions and can be isomerized into mannosan (M) and galactosan (G) simultaneously. Among the formic acid, acetic acid, and oxalic acid in the degradation products of levoglucosan, it was found that the yield of formation of formic acid in the photo-Fenton pathway can be as high as 86%. It is worth noting that both levoglucosan and its isomers are present in the atmosphere and their concentrations are strongly correlated. At the same time, the range of their concentration ratios, L/(G + M), measured in the photo-Fenton experiments in the laboratory was found to agree well with that measured in atmospheric PM2.5 samples. However, the sources of L, G, and M in the atmosphere are complex, and the photo-Fenton reaction may be an essential pathway for the distribution of L, G, and M in the atmosphere.

Structural modification of alumina was carried out by the decomposition of the products of the reaction of aluminum hydroxide with the organic acid used simultaneously as a peptizer and a “burnable” additive. The modification changes the acidity of the support surface and induces the formation of pentacoordinate Al3+ cations interacting with platinum, which increases the fraction of platinum atoms with electron deficiency. The alumina-platinum catalyst based on the support treated with oxalic acid shows an enhanced selectivity to aromatization in n-heptane reforming.

Anodic oxidation based on PbO2 anode has been demonstrated as the feasible approach for the decontamination of organic pollutants; however, the performance of this process is hindered by its ordinary electrochemical activity and relatively low stability. In this study, we fabricated an efficient Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND electrode with electrochemically reduced TiO2 nanotubes as the interlayer and nano-diamond as the dopant. As compared with other electrodes, the constructed Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND exhibited higher oxygen evolution overpotential, larger active area and less charge transfer resistance. Thus, the average current efficiency of 30% could be attained at 120 min with TiO2-NTs/Sb-SnO2/PbO2, which was 1.5 times higher in comparison with the typical Ti/Sb-SnO2/PbO2 electrode. It was found that the removal efficiency of COD could be increased from 49% to 69% after 120 min treatment in the presence of 10 mM Cl−1 in the electrolyte. After 6 h of electrolysis, 74% of TOC was removed and 31% and 22% of initial N was transformed into NH4+ and NO3− ions, respectively. And oxalic acid, glyoxylic acid, malonic acid and acetic acid were identified quantitatively as the intermediate products. Finally, it was estimated that the accelerated service life of Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND electrode was approximately three times of Ti/Sb-SnO2/PbO2 electrode. Generally, this study is of great interest for the engineering community to design an efficient electrode material for the wastewater treatment.

Oxalic acid (OA), naturally available in vegetables and foodstuffs derived from them, easily combines with calcium and iron to form insoluble oxalates. Their chelation will result in various renal diseases; thus, the accurate determination of OA is quite significant in the evaluation of food quality and healthcare settings. Here, we developed an electrochemically induced alcohol-free sol-gel method to obtain platinum nanoparticles (PtNPs) adhered with porous silica on glassy carbon electrode (PSiO2-PtNPs/GCE) by a one-step process, which can be potentially used as an excellent catalyst towards electrochemical oxidation of OA for the first time. Without any redox mediator, PSiO2-PtNPs/GCE exhibited a low oxidation overpotential and a significantly high current signal, achieving a wide linear range of concentration from 0 to 45 μM and a detection limit as low as to 25 nM for OA detection. Moreover, this present alcohol-free sol-gel approach towards OA determination was verified in real samples, which is promising for foodstuff analysis and clinical diagnosis.

The separation of sulfur from the wet limestone fuel gas desulfurization (FGD) gypsum using oxalic acid solution was studied. Optimal separation conditions and a separation mechanism of sulfur were investigated. The obtained results indicate that the sulfur in FGD gypsum can be separated efficiently by oxalic acid solution. When separating under the optimal experimental conditions of 0.3 mol/L oxalic acid solution, 30 °C, and a 5/150 g/mL solid to liquid ratio for 8 min, the separation rate reached 97.0 wt %. Besides, the Avrami equation is more suitable for the kinetic analysis of the sulfur separation reaction than the unreacted shrinking core model. When the reaction temperature is less than or equal to 20 °C, the mechanism of the sulfur separation process is chemical-reaction-controlled; otherwise, it is diffusion-controlled. The activation energy E a of the sulfur separation reaction is 34.84 kJ/mol. During the separation process, the pH of the solution gradually decreased due to the conversion of oxalic acid to sulfuric acid, so the liquid obtained after the sulfur separation of FGD gypsum can be recycled as industrial sulfuric acid. Nearly 1 mol of sulfuric acid can be obtained for every mole of oxalic acid consumption.

This study explored whether MXene (Ti3C2Tx) could remove radioactive Cs+ from model nuclear wastewater. Various adsorption tests were performed and the physical aspects of the interaction were investigated. We varied the MXene dosage, Cs+ initial concentration, solution pH, solution temperature and exposure time. MXene adsorption exhibited very fast kinetics, based on the fact that equilibrium was achieved within 1 h. MXene exhibited an outstanding adsorption capacity (148 mg g−1) at adsorbent and adsorbate concentrations of 5 and 2 mg L−1, respectively, at neutral pH condition (i.e., pH 7). We explored Cs+ adsorption by MXene in the presence of four different ions (NaCl, KCl, CaCl2 and MgCl2) and three different organic acids (sodium oleate, oxalic acid, and citric acid). The Cs+ removal rate changed in the presence of these components; adsorption of Cs+ by MXene thus involved ion exchange, supported by both Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. We confirmed that MXene was re-usable for at least four cycles. MXene is cost-effective and practical when used to adsorb radionuclides (e.g., Cs+) in nuclear wastewater.

Methylglyoxal (CH3COCHO, MG), which is one of the most abundant α-dicarbonyl compounds in the atmosphere, has been reported as a major source of secondary organic aerosol (SOA). In this work, the reaction of MG with hydroxyl radicals was studied in a 500 L smog chamber at (293 ± 3) K, atmospheric pressure, (18 ± 2)% relative humidity, and under different NOx and SO2. Particle size distribution was measured by using a scanning mobility particle sizer (SMPS) and the results showed that the addition of SO2 can promote SOA formation, while different NOx concentrations have different influences on SOA production. High NOx suppressed the SOA formation, whereas the particle mass concentration, particle number concentration and particle geometric mean diameter increased with the increasing NOx concentration at low NOx concentration in the presence of SO2. In addition, the products of the OH-initiated oxidation of MG and the functional groups of the particle phase in the MG/OH/SO2 and MG/OH/NOx/SO2 reaction systems were detected by gas chromatography mass spectrometry (GC-MS) and attenuated total reflection fourier transformed infrared spectroscopy (ATR-FTIR) analysis. Two products, glyoxylic acid and oxalic acid, were detected by GC-MS. The mechanism of the reaction of MG and OH radicals that follows two main pathways, H atom abstraction and hydration, is proposed. Evidence is provided for the formation of organic nitrates and organic sulfate in particle phase from IR spectra. Incorporation of NOx and SO2 influence suggested that SOA formation from anthropogenic hydrocarbons may be more efficient in polluted environment.

The demand for lithium-ion batteries (LiBs) is significantly increasing leading to a shortage in supply for critical metals, such as lithium and cobalt. Recycling LiCoO2 cathodes can provide a seco...

Oxalic acid and sulfate salts are major components of aerosol particles. Here, we explore the potential for their respective precursor species, glyoxal and SO2, to form atmospheric brown carbon via aqueous-phase reactions in a series of bulk aqueous and flow chamber aerosol experiments. In bulk aqueous solutions, UV- and visible-light-absorbing products are observed at pH 3-4 and 5-6, respectively, with small but detectable yields of hydroxyquinone and polyketone products formed, especially at pH 6. Hydroxymethanesulfonate (HMS), C2, and C3 sulfonates are major products detected by electrospray ionization mass spectrometry (ESI-MS) at pH 5. Past studies have assumed that the reaction of formaldehyde and sulfite was the only atmospheric source of HMS. In flow chamber experiments involving sulfite aerosol and gas-phase glyoxal with only 1 min residence times, significant aerosol growth is observed. Rapid brown carbon formation is seen with aqueous aerosol particles at >80% relative humidity (RH). Brown carbon formation slows at 50-60% RH and when the aerosol particles are acidified with sulfuric acid but stops entirely only under dry conditions. This chemistry may therefore contribute to brown carbon production in cloud-processed pollution plumes as oxidizing volatile organic compounds (VOCs) interact with SO2 and water.

Binary copolymers possessing thermal stability up to 290°C and suitable for the formation of ion-exchange membranes have been obtained by free radical copolymerization of sodium p-styrene sulfonate and 1-vinylimidazole with subsequent conversion to the H-form. The composition and structure of the copolymers are confirmed by elemental analysis and IR and NMR spectroscopy. Multicomponent membranes based on the copolymers of sodium p-styrene sulfonate and 1-vinylimidazole have been obtained using poly(vinyl alcohol) crosslinked by oxalic acid as a film-forming agent. It is shown by scanning electron microscopy that the surface and cut of the membranes have a uniform structure. The specific electric conductivity of the membranes with different concentrations of styrene sulfonic acid (20 to 80 mol % in the copolymer) increases with an increase in the fraction of styrene sulfonic acid and is 29.5 to 52.0 mS cm−1 at 80°C. The activation energy of proton transport of the membranes is 12.5 to 15.5 kJ mol−1. The water uptake of the membranes decreases with the increase in the concentration of the basic (imidazole) component in them, which may be associated with the increase in the density of ionic crosslinking due to the acid–base interaction of the sulfo groups and pyridine nitrogen atoms of the imidazole cycle. The formation of acid–base pairs results in the formation of continuous proton transport channels in addition to the sulfonic acid channels, which is confirmed by the high values of specific electric conductivity even in the case of a decrease in the concentration of sulfostyrene in the composition of the membrane. Increasing the concentration of 1‑vinylimidazole in the composition of the copolymer from 20 to 80 mol % leads to an increase in the relative elongation at break from 3 to 6%, an increase in the tensile strength at break from 4 to 7 MPa, a decrease in the Young modulus of the membranes from 127 to 102 MPa, and a decrease in the water uptake from 45 to 15.

In this study, a new Co(II)-containing coordination polymer with the chemical formula [Co(ox)(dimb)] (1, ox = oxalic acid, dimb = 1,4-di(1H-imidazol-1-yl)butane) is successfully prepared by the reaction of Co(NO3)2·6H2O, oxalic acid, and 1,4-di(1H-imidazol-1-yl)butane in a mixed solvent of DMF and water under the solvothermal conditions. As-prepared crystalline complex 1 is characterized by the elemental analysis and single crystal X-ray diffraction. Furthermore, the mechanical grinding method is used to produce nanostructured 1 with the average size distribution of around 326 nm. To detect the in vivo protective effect of nano 1 on CVB3-induced myocarditis, the histopathology evaluation is performed. To reveal the underlying relationship between the cell inflammatory response and the mechanism of the compound protective activity, the level of IL-1 and TNF-α in the myocardial tissue is measured by ELISA.

The electrophoretic behavior of twenty anions has been studied on silica gel-G, titanium (IV) tungstate and silica gel-G- titanium (IV) tungstate admixture layers using 0.1 M solutions of oxalic acid, citric acid, tartaric acid, succinic acid and acetic acid as background electrolyte. The mechanism of migration is explained in terms of adsorption and the solubility of various sodium or potassium salts of the anions in water. Titanium (IV) tungstate behaves only as an adsorbent and not as an ion exchanger. Being a cation exchanger, there is no exchange phenomenon occurring with anions. The migration of halides increase linearly with an increase in the bare ion radii of these ions. Differential migration of the anions on silica gel-G layers led to binary, ternary and quaternary separations of similar anions such as F− – Cl− – Br− – I−, I− – IO3− – IO4−, BrO3− – IO3− and Fe(CN)63− – Fe(CN)64−. The two cyanoferrate ions are separated from industrial waste water and from fixer and bleach solutions. The migration of anions has also been found to be in accordance with their lyotropic numbers.

Electrochemical conversion of CO2 to value added chemicals is a promising route for its utilization and mitigation from atmosphere. Nevertheless, an industrial process involving CO2 electroreduction is yet to be a reality and requires further studies on improving the existing processes. In the present work, we report new insights into the electrochemical conversion of CO2 to zinc oxalate at SS 304 L cathode in acetonitrile in the presence of a sacrificial Zn anode. The influence of current density, water content in the electrolyte solution and pressure on product selectivity were evaluated. In addition, oxalic acid synthesis from zinc oxalate was studied using ester hydrolysis process. Our results showed that the product yield is affected due to CO2 reduction to carbonate, decomposition of acetonitrile to cyanide and glycolate formed due to partial reduction of oxalate. Experiments performed in a batch reactor at 2 bar pressure showed that an average Faradaic efficiency of 73.9% can be obtained for zinc oxalate. A yield of 58.1% was obtained for the extraction of oxalic acid. Both zinc oxalate and oxalic acid obtained from this process were compared with commercially available products to confirm its purity.

As a promising hydrogen evolution reaction (HER) electrocatalyst, molybdenum carbide materials have attracted great attention owing to their Pt-like electronic structure. The morphology control of Mo2C usually involves complicated procedures, and porous structures are desirable for electrocatalytic applications. Herein, we present a facile acid-directed synthesis strategy for β-Mo2C nanoparticles embedded in a nitrogen doped carbon matrix (β-Mo2C/NC) with controllable morphologies through heat treatment of Mo–melamine complexes for electrocatalytic HER applications. It is found that the applied acid can effectively tune the morphology of Mo–melamine complexes, and thus the final β-Mo2C/NC materials. With oxalic acid, the as-prepared β-Mo2C/NC materials possess a porous structure and high surface area (23.3 m2 g−1), leading to distinguished electrocatalytic HER activities in both acidic and alkaline media, requiring low overpotentials of 152 and 135 mV vs. reversible hydrogen electrode (RHE) to reach a current density of −10 mA cm−2, with a Tafel slope of 58 and 56 mV dec−1, respectively. The synthetic route proposed in this work may offer a new thinking for the morphology-controllable synthesis of transition metal carbide materials for heterogeneous (electro)catalysis applications.

The main objective of the study was to derive an appropriate ligand in sulfidized nanoscale zero-valent iron-persulfate (S-nZVI-PS) system for the efficient and rapid degradation of recalcitrant organic pollutants. In this aspect, we have compared the efficiency of three ligands (L) such as ethylenediaminetetraacetic acid (EDTA), oxalic acid (OA) and citric acid (CA) for the degradation of benzoic acid (BA). Complete degradation of BA was achieved within 10 min in S-nZVI-L-PS system. In order to investigate the controlling factors in ligand assisted degradation, Fe dissolution, the thermodynamic feasibility of Fenton reactions and adsorption of ligands on the material surface has been studied. It is found that CA and OA caused more Fe dissolution and there by a more feasible Fenton condition compared to other ligands. Whereas EDTA has high affinity for the Fe surface and it attracts the PS after adsorption. Thus, we confirmed that heterogeneous Fenton like reactions are more favorable in the presence of EDTA and homogeneous Fenton like reaction is more favorable in presence of CA and OA. All these reactions produce OH and SO4 − (confirmed by electron spin resonance (EPR) measurements). However, for used S-nZVI the adsorption possibility is less and only CA is the choice in this case. Thus our study concluded that S-nZVI-CA-PS system would be the conclusive solution for field remediation.

For the removal of volatile organic compounds (VOCs) from environmental systems, gaseous benzene, a model VOC, was adsorbed on naturally Fe-containing activated carbon and subsequently, decomposed in the presence of de-ionized water, and low (0.03%, pH 6.5) and high (30%, pH 2.5) concentration H2O2 solutions. The intermediates produced during benzene decomposition were analyzed and compared using gas chromatography-mass spectrometry. After the decomposition process, the activated carbon sample was air dried. Three cycles were carried out with de-ionized water and low and high concentration H2O2 solutions as oxidants. The adsorption capacity of the activated carbon sample treated with DI water gradually decreased as the number of cycles increased. On the other hand, the benzene adsorption capacity of the activated carbon samples treated with the H2O2 solutions was improved due to the relatively higher specific surface areas of these samples. After treatment with the low-concentration H2O2 solution, intermediates such as glyoxylic acid, oxalic acid, phenol, malonic acid, and pyrocatechol were observed. After treatment with high-concentration H2O2 solution, intermediates such as glyoxylic acid, formic acid, and acetic acid were formed. With increasing H2O2 concentration, the number and the molecular weight of the intermediate formed by the oxidative degradation of benzene, simultaneously decreased. The Fenton reaction induced by naturally Fe-containing activated carbon and H2O2 could lead to more efficient decomposition of benzene.

It is shown that the rate of oxidation of oxalic acid H2C2O4 during the ozonation of its solutions grows considerably if sodium chloride is added to the solution. Based on the kinetics of evolution of molecular chlorine during ozone treatment of solutions of H2C2O4 and NaCl, the mechanism of reaction of oxalic acid with chlorine is clarified, and the rate constant of this reaction is determined.

Two families of lanthanide(III) metal–organic frameworks (Ln-MOFs) constructed from a 2-(4-pyridyl)-terephthalic acid (H2pta) ligand, namely [Ln4(pta)5(Hpta)2(H2O)4]·xH2O (1-Eu, 2-Gd) and [Ln(Hpta)(C2O4)]·3H2O (3-Tb, 4-Dy, 5-Er and 6-Ho) (C2O4 = oxalic acid), have been discovered using the solvothermal method. On the basis of thermodiffractometry, all MOFs retain their crystallinity and main structure below 370 °C. Utilizing their excellent water stability and chemical stability, luminescence studies have been carried out. Notably, the Eu-metal organic framework (MOF) and Tb-MOF demonstrate pronounced luminescence, as well as high stability in water and other organic solvents. The luminescence explorations reveal that the Eu-MOF possesses good selectivity for testing Fe3+ in the aqueous phase via fluorescence quenching, while the Tb-MOF behaves as a multifunctional chemical sensor for the detection of Fe3+ cations and Cr2O72− anions in aqueous media and the recognition of nitrofuran (NIF) in DMF solvent. The recyclability and stability of Eu-MOF and Tb-MOF after the sensing experiments were observed to be adequate. By virtue of the superior stability, detection efficiency, applicability and reusability, Eu-MOF and Tb-MOF could be promising fluorescent materials for practical sensing applications.

Crystals of organic salts can be grown by sublimation in two systems: succinic acid with hexamethylenetetramine, and oxalic acid with 4,4′-bipyridine. Both systems also form co-crystals by sublimation. Additionally, salts and co-crystals are able to re-sublime once formed, allowing the separation of different multicomponent crystal forms using sublimation. Preliminary experiments indicate that ion pairs may be present in the gas phase during the sublimation of salts. Crystallisation by sublimation is compared to solution crystallisation and mechanochemical methods.

The most abundant rare earth metals in the Earth's crust have received considerable recent attention as efficient electrocatalysts for full water splitting, but it is highly desired to explore a new strategy to improve their catalytic activity. In this communication, we report the development of nanoporous CeO2 nanowire array on Ti mesh (np-CeO2/TM) derived from MnO2–CeO2/TM via an acid etching strategy, and MnO2 acts as a pore-forming agent through selective etching with oxalic acid. As a rare earth metal catalyst, np-CeO2/TM needs an overpotential of 91 mV for the hydrogen evolution reaction (HER) and 279 mV for the oxygen evolution reaction (OER) to drive a current density of 10 mV cm−2 in 1.0 M KOH, 93 mV and 101 mV less than that needed by MnO2–CeO2/TM, respectively. We also demonstrate the use of np-CeO2/TM to make a two-electrode electrolyzer capable of driving 10 mV cm−2 at a cell voltage of 1.57 V.

A novel water-stable Tb-based metal–organic framework (Tb-MOF), namely {[Tb(CA)(OA)0.5(H2O)2]·H2O}n (H2CA = chelidonic acid; H2OA = oxalic acid), was synthesized via a solvothermal method. Tb-MOF was studied for its highly sensitive detection towards nitrite, which is a hazardous chemical in water and food. As a luminescent sensor, Tb-MOF displays a linear detection range between 0 and 15.6 μM, with a limit of detection of 28.25 nM. Dynamic quenching process was observed in this system and was studied in detail. A mechanism study revealed that the fluorescence response of Tb-MOF towards nitrite was due to the energy transfer from the sensitized Tb3+ ion to the nitrite.

Cyclohexane oxidation by H2O2 to cyclohexanol, cyclohexanone, and cyclohexylhydroperoxide under mild (40 °C, 1 atm) conditions is significantly enhanced in the system composed of VO(acac)2 (starting catalyst) and small additives of oxalic acid (process promoter). In corroboration of this, several times higher yield of the desired products was obtained compared to that obtained in the acid-free process. The revealed advantage was addressed to elevate the electrical conductance G (or vice versa, decreasing the resistance, 1/G) of the reaction medium. On the other hand, the content of oxalic acid (20–30 mM) was compulsory to optimize the process parameters. The last value of concentration affords, besides the lowest 1/G, the utmost impact on pH, redox potential, and current–voltage relationships. Exceeding this level leads to an increase in 1/G of the reaction solution, ceases the impact on pH, ORP, and CV profiles, and is detrimental for the product yield. The putative mechanism of the revealed effects has been envisaged.

Due to the increasing criticality of rare earth elements (REEs), it has become essential to recover REEs from alternative resources. In this study, systematic REEs leaching tests were performed on the calcination product of a coal coarse refuse using hydrochloric acid and different types of organic acid as lixiviants. Experimental results show that the recovery of REEs, especially heavy REEs (HREEs) and scandium (Sc), is improved by using selected organic acids. Citric acid and dl -malic acid afford the best leaching performances; whereas, malonic acid, oxalic acid, and dl -tartaric acid are inferior to hydrochloric acid. Results of zeta potential measurements and solution chemical equilibrium calculations show that malonic acid is more likely adsorbed on the surface of the calcined material compared with citric acid and dl -malic acid. The adsorption may reduce the effective concentration of malonic species in solution and/or increase the amount of REEs adsorbed on the surface, thereby impairing the leaching recovery. Compared with light REEs (LREEs), a stronger adsorption of the HREEs on the surface is observed from electro-kinetic test results. This finding explains why organic acids impose a more positive impact on the leaching recovery of HREEs. By complexing with the HREEs, organic acids can keep the metal ions in solution and improve the leaching recovery. The adsorption of Sc3+ on the surface is the lowest compared with other REEs. Therefore, rather than complexing, the organic anionic species likely play a function of solubilizing Sc from the solid, which is similar to that of hydrogen ions.

With our consistent aim to further expand the solid-state landscape via molecular recognition and regulate solubility of tetrahydroberberine (THB), charge-assisted hydrogen bond (CAHB) recognitions and solubility regulation of pharmaceutical salts/cocrystals of THB are comprehensively investigated through exploring four pharmaceutical salts/cocrystals of THB. Four pharmaceutical salts/cocrystals of THB with oxalic acid, malonic acid, maleic acid and fumaric acid were obtained with solution evaporation approach. Comprehensive crystal structures and Hirshfeld surface analyses reveal CAHB recognitions between THBs and coformers are dominant intermolecular interactions to stabilize crystal packing. As expected, solubilities of four pharmaceutical salts/cocrystals of THB have been improved by dicarboxylic acids. Importantly, the dicarboxylic acid with higher solubility can modulate solubility of THB to become higher. The enthalpy of hydration for four pharmaceutical salts/cocrystals is greater than that for neutral pure THB when CAHBs (with electrostatic interactions) exist, which effectively improve solubility of THB. Solvent molecules can disrupt interactions of pharmaceutical salts/cocrystals by solvent···solute interactions when dicarboxylic acids are highly soluble thereby leading to enhancement of dissolution. Research results inspirationally enlightens that the solubility of insoluble APIs could be effectively regulated by utilizing gradient solubility coformers with simultaneously forming CAHBs between active pharmaceutical ingredients and coformers.

A UVC photo-Fenton advanced oxidation process (AOP) was studied to develop a process for the decomposition of oxalic acid waste generated in the chemical decontamination of nuclear power plants. The oxalate decomposition behavior was investigated by using a UVC photo-Fenton reactor system with a recirculation tank. The effects of the three operational variables―UVC irradiation, H2O2 and Fenton reagent―on the oxalate decomposition behavior were experimentally studied, and the behavior of the decomposition product, CO2, was observed. UVC irradiation of oxalate resulted in vigorous CO2 bubbling, and the irradiation dose was thought to be a rate-determining variable. Based on the above results, the oxalate decomposition kinetics were investigated from the viewpoint of radical formation, propagation, and termination reactions. The proposed UVC irradiation density model, expressed by the first-order reaction of oxalate with the same amount of H2O2 consumption, satisfactorily predicted the oxalate decomposition behavior, irrespective of the circulate rate in the reactor system within the experimental range. Keywords: AOP, UVC photo-Fenton, Chemical decontamination waste, Oxalic acid

The simultaneous photocatalytic H2 evolution with environmental remediation over semiconducting metal oxides is a fascinating process for sustainable fuel production. However, most of the previously reported photocatalytic reforming showed nonstoichiometric amounts of the evolved H2 when organic substrates were used. To explain the reasons for this phenomenon, a careful analysis of the products and intermediates in gas and aqueous phases upon the photocatalytic hydrogen evolution from oxalic acid using Pt/TiO2 was performed. A quadrupole mass spectrometer (QMS) was used for the continuous flow monitoring of the evolved gases, while high performance ion chromatography (HPIC), isotopic labeling, and electron paramagnetic resonance (EPR) were employed to understand the reactions in the solution. The entire consumption of oxalic acid led to a ~30% lower H2 amount than theoretically expected. Due to the contribution of the photo-Kolbe reaction mechanism, a tiny amount of formic acid was produced then disappeared shortly after the complete consumption of oxalic acid. Nevertheless, a much lower concentration of formic acid was generated compared to the nonstoichiometric difference between the formed H2 and the consumed oxalic acid. Isotopic labeling measurements showed that the evolved H2, HD, and/or D2 matched those of the solvent; however, using D2O decreased the reaction rate. Interestingly, the presence of KI as an additional hole scavenger with oxalic acid had a considerable impact on the reaction mechanism, and thus the hydrogen yield, as indicated by the QMS and the EPR measurements. The added KI promoted H2 evolution to reach the theoretically predictable amount and inhibited the formation of intermediates without affecting the oxalic acid degradation rate. The proposed mechanism, by which KI boosts the photocatalytic performance, is of great importance in enhancing the overall energy efficiency for hydrogen production via photocatalytic organic reforming.