Aqueous Solution Of Oxalic Acid Research Articles

The synergistic effect of attapulgite in the highly enhanced photoreduction of Cr(VI) by oxalic acid in aqueous solution

Attapulgite (ATP), a widely existed clay in nature, was firstly and successfully applied to enhance the photoreduction of highly toxic Cr(VI) by oxalic acid (Ox). In ATP + Ox + UV system, batch effects (Ox concentration, initial Cr(VI) concentration, ATP dosage, and reusability of ATP) were investigated. By studying the impact of the initial pH in the solution, the change of pH and Fe species concentration as well as Ox concentration during the reaction, the free radical scavenging test, and the role of ATP, the mechanism of Cr(VI) removal by ATP + Ox + UV system was revealed. The methyl orange (MO) removal of ATP + Ox + UV system was also inspected. The results indicated that ATP showed the obvious enhancement in efficient photoreduction of Cr(VI) by Ox in water. The Fe and Si components in ATP played an important role in Cr(VI) removal by ATP + Ox + UV system: most of Cr(VI) was reduced by Fe(II) and CO2•‒ produced by the Fe(III)-Ox complex from the dissolved Fe component in ATP under UV irradiation. Some of Cr(VI) was reduced by e− and CO2•‒ from the oxidation of Ox by h+ generated by the photocatalyzed SiO2 in ATP. Furthermore, ATP + Ox + UV system also showed excellent MO removal performance, indicating the great potential in practical applications.

Room temperature electrosynthesis of TinO2n-1 film and its bilayer with PNMPy on mild steel for corrosion protection in sulphuric acid

The low-temperature electrosynthesis of titanium suboxide (TinO2n-1) is carried out cathodically on mild steel (MS) in acetonitrile solution containing TiO(ClO4)2•6H2O. A bilayer coating of TinO2n-1 and poly(N-methyl pyrrole) (PNMPy) is also performed to combine the protective and hydrophobic properties of metal oxide and conductive polymer, respectively. PNMPy top layer is deposited anodically on the TinO2n-1-coated MS electrode in an aqueous oxalic acid solution containing NMPy monomer. The parameters affecting the experimental conditions for the synthesis are optimized according to their resistances obtained from EIS. XRD, XPS, and SEM-EDX studies reveal that the homogeneously dispersed TinO2n-1 is obtained with phases containing different amounts of oxygen, such as Ti3O5, Ti4O7, and Ti5O9 simultaneously, together with Fe2O3 at room temperature. The co-deposition of some Fe2O3 on MS surface contributes to the protective property of the TinO2n-1 coating due to providing the rough surface. Besides, the formation of the Fe2TiO5 intermetallic phase on the surface could be an important factor for the quality of TinO2n-1 deposition. The corrosion performances of the coatings are evaluated by Tafel, long term OCP and EIS measurements. According to the EIS results, the TinO2n-1/PNMPy bilayer coating improves the corrosion resistance of the bare MS by about 50 times (702 ohm.cm2) in 0.5 M H2SO4 and enhances the protection efficiency up to about 98%. This is because hydrophobic PNMPy fills the pores of the TinO2n-1 undercoating layer; thus, not only conductive but also lower porosity and better protective properties are achieved.

Thermal-assisted back-extraction of inert platinum group metals from [Hbet][Tf2N] ionic liquid phase to oxalic acid aqueous solution

ABSTRACT Temperature-dependency of back-extraction behavior of inert platinum group metals (PGMs) like Ru(III) and Rh(III) has been investigated in a biphasic system consisting of H2C2O4(aq) and betainium bis(trifluoromethylsulfonyl)amide ([Hbet][Tf2N]) after extracting these PGMs as well as that of non-inert Pd(II). At 298 K, Pd(II) in [Hbet][Tf2N] phase was stripped high efficiency (78.8%) by 0.1 M H2C2O4 within 2 min. In contrast, back-extraction of Rh(III) and Ru(III) did not proceed at all in practice under the same condition, demonstrating the inertness of these PGMs. When the sample temperature was risen up to 353 K, the stripping of Rh(III) was promoted, and completed within 300 min at 353 K. The stripping efficiency of Ru(III) was still as low as 24.2% at 300 min and 353 K, and took 48 h in use of 1 M H2C2O4(aq) for completion. Further mechanistic studies by means of UV-vis absorption spectroscopy clarified that the complexation of these PGMs and oxalate ion (C2O4 2-) is rate-determining in their stripping, and is successfully accelerated and enhanced by elevating the temperature and increasing the concentration of the stripping agent.

Electrochemical Synthesis, Characterization and Corrosion Properties of POA−MoO42- Coating in 3.5% NaCl

Polyanisidine (POA) and polyanisidine-molybdate (POA−MoO42-) coatings have been successfully synthesized on steel grade СТ3 from aqueous solutions of oxalic acid by electrochemical method using cyclic voltammetry. The morphology and composition of these films were characterized by scanning electron microscopy (SEM) and energydispersive X-ray (EDAX) methods. It was proven that the introduction of MoO42- into the polyanisidine matrix raised the corrosion resistance of the POA coating and also improved its adhesion properties. The protective properties of steel grade CT3 with POA and POA-MoO42- films were studied using potentiodynamic polarization in 3.5% NaCl solution. The results showed that ions improve anti-corrosion properties of POA films.

Reduction behavior of chromium(VI) with oxalic acid in aqueous solution

The direct Cr(VI) reduction process by oxalic acid was conducted. The existence of Cr(VI) in the reaction medium was measured by software Visual MINTEQ and the concentration of Cr(VI) was measured by ICP-OES. The results showed that the Cr(VI) was efficiently reduced by oxalic acid at high reaction temperature and high dosage of oxalic acid. The reduced product, Cr(III), was easily generated stable complex compounds (Cr(HC2O4)3) with oxalate, which displayed a negative effect on the reduction process. The high reaction temperature and high acidic medium could destroy the stable structure of a complex compound to release oxalate, and facilitate the reduction of Cr(VI). Generally, the results showed in this paper provided a versatile strategy for Cr(VI) reduction and exhibited a bright application future for real wastewater treatment.

Physicochemical interaction of CdTe and ZnxCd1–xTe single crystals with K2Cr2O7–HBr–oxalic acid aqueous solutions

Physicochemical interaction of CdTe and ZnxCd1–xTe single crystals with K2Cr2O7–HBr–oxalic acid aqueous solutions

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

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).

Growth, structural, optical and thermal studies of semi-organic nonlinear optical potassium hydrogen oxalate single crystal

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.

Formation of ordered anodic alumina nanofibers during aluminum anodizing in oxalic acid at high voltage and electrical power

In this study, we modified the synthesis modes of aluminum anodizing in an aqueous solution of oxalic acid and suggested quick, one-step and convenient method for porous alumina surface modification to increase largely its surface area. Anodic alumina nanofibers consisting of pure aluminum oxide were formed by high field anodizing with evolving of Joule heating of aluminum foil of 60 and 100 μm thickness in 0.3 M aqueous solution of oxalic acid. It was shown that nanofibers formed on the surface of the films for an anodizing voltage of 90 V and a power range of 13.5–31.5 W cm−2. The thickness of the Al foil has proved to be responsible for the formation of the alumina nanofibers, which cannot be obtained in the same electrolyte and for similar current densities on 25 μm thick aluminum foil. We could show that during anodizing of 60 μm thick Al foil, regardless of anodic current density value, alumina nanofibers uniformly covered the entire surface of the films. However, during 100 μm Al foil anodizing, the pores were etched and the nanofibers partially dissolved and separated from the surface with increasing anodizing current density. Auger electron spectroscopy measurements showed that porous anodic alumina containing carbon impurities was obtained during anodizing of the 25 μm Al foil. Alternatively, the surface of the nanofibers formed on 60 and 100 μm Al foil consisted of pure alumina.

Investigation on Ag‐containing compound generated in manufacturing of low‐temperature polycrystalline Si active matrix organic light‐emitting diode

AbstractIn this work, we report a systematic investigation on Ag‐containing compound widely generated in anode wet etching process of low‐temperature polycrystalline Si active matrix organic light‐emitting diode (LTPS‐AMOLED). The formation mechanism of the aforementioned compound was proposed and confirmed by sufficient evidence. The relevant test results show that, unlike traditional metal compounds, this compound cannot be removed by aqueous oxalic acid solution. Furthermore, the reported Ag‐containing compounds grow and migrate in response to electric fields in high‐temperature and high‐humidity environment (85°C, 85% humidity) to short neighboring integrated circuit pads, causing severe product reliability failure. Spectra test results indicate that products with reliability failure are characterized by reduced display brightness and shifted color coordinates. To improve the reliability failure caused by Ag‐containing compounds, five potential schemes are presented, and most of them are conducted in this study.

Polypyrrole/graphene oxide composite coating on Ti implants: a promising material for biomedical applications

Advanced materials can be developed by the combination of synthetic polymer and nanomaterial for biomedical application. Polypyrrole/graphene oxide (PPy/GO) composite coating on Ti metal was developed through electropolymerization of pyrrole by varying the amount of GO in aqueous oxalic acid solution. The influence of GO in the PPy matrix was confirmed by scanning electron microscopy studies. Structural interactions between PPy and GO in the composite coating were studied using ATR-FTIR, solid 13C NMR and Raman spectroscopy. The higher surface roughness and the lower wettability of the composite-coated Ti favor biocompatibility. The increase in adhesion strength of the composite coating was analyzed by the cross-hatch adhesion test. Potentiodynamic polarization studies showed a higher polarization resistance (Rp) and lower corrosion rates for composite coatings. Dynamic electrochemical impedance spectroscopy studies confirmed the PPy/GO composite coating exhibited a higher impedance from − 0.55 to 1.25 V in SBF solution. Bode impedance and Bode phase angle results revealed a higher resistance for PPy/GO composite-coated Ti. Immersion studies of PPy/GO composite coating in SBF solution revealed the growth of dense hydroxyapatite (Hap.) over Ti metal. Further, in vitro cell culture studies were carried out by MG-63 cells to assess the biocompatibility of PPy/GO composite coating on the substrate. Improved corrosion protection and biocompatibility behavior of PPy/GO composite-coated Ti suggests the potential candidate for biomedical applications.

Mixed oxides CuO-NiO fabricated for selective detection of 2-Aminophenol by electrochemical approach

New heterometallic complex [NiCu(NO3)2(H2O)2] (1) was prepared via the reaction of aqueous solutions of (oxalic acid, nickel nitrate and copper nitrate). Mixed oxide CuO-NiO was successfully obtained with different morphological structures (2) and (3) through the annealing of 1 at different temperature 300°C and 600°C, respectively. The materials were characterized using FT-IR, TGA, XRD and SEM. As showed from XRD data, with increasing the calcination temperature the crystallinity of CuO-NiO in sample 3 was improved and the diffraction peaks exhibited narrower and stronger than CuO-NiO in sample 2. The average size of CuO-NiO crystals obtained was calculated from Debye-Scherrer equation and found to be 16.65nm. To assemble the working electrode of 2-aminophenol (2-AP) chemical sensor, a thin layer of CuO-NiO NPs was deposited on glassy carbon electrode (GCE) with conducting binder and used to detect 2-AP in aqueous medium successfully. The chemical sensor is exhibited the higher stability, good sensitivity (20.2729μAmM−1cm−2) and enhanced electrochemical activity at room conditions. Therefore, the fabricated chemical sensor with active CuO-NiO NPs may be an effective and sensitive sensor for detection of hazardous materials by reliable I–V method for broad scales environmental safety of and healthcare sectors.

Solubility of Ozone in Aqueous Solutions of Oxalic Acid and Potassium and Sodium Nitrates: Determination of the Anion-Specific Parameter for the Oxalate Ion in a Model for the Solubility of Gases in Electrolyte Solutions

The solubility of ozone in solutions of oxalic acid H2C2O4 and potassium nitrate at concentrations up to 1 and 2 M, respectively, is studied at 25°C. The Sechenov constants for these electrolyte solutions are found: 0.081 ± 0.010 and 0.082 ± 0.004 M–1, respectively. The anion-specific parameter in the Weisenberger–Schumpe gas solubility model for oxalate ion is determined: $${{h}_{{{{{\text{C}}}_{2}}{\text{O}}_{4}^{{2 - }}}}}$$ = 0.1266 M–1. A set of coefficients is determined using the experimental data from various sources to calculate the density of H2C2O4 solutions as a function of temperature in the range of 5–100°C at solution concentrations up to the saturated concentration at a given temperature.

Development of a solvometallurgical process for the separation of yttrium and europium by Cyanex 923 from ethylene glycol solutions

Recycling of critical raw materials such as rare-earth elements (REEs) is increasingly crucial in the development of a sustainable economy. Separation of individual REEs (mainly yttrium and europium) from lamp phosphor waste has become essential due to the substantial stockpiling of end-of-life fluorescent lamps. The mutual separation of Y(III) and Eu(III) from aqueous chloride solutions with solvating extractants by conventional extraction methods is highly inefficient. Hence, separation of Y(III) and Eu(III) was investigated using a novel technique called “non-aqueous solvent extraction”. Unlike conventional solvent extraction, the new approach uses two immiscible organic phases (more polar (MP) and less polar (LP)) instead of an aqueous and an organic phase. The present work describes a new solvometallurgical process for the separation of Y(III) and Eu(III) from ethylene glycol solutions using the solvating extractant Cyanex 923 in an aliphatic diluent. This extraction system exhibits improved separation compared to extraction from aqueous solutions. Following predictions based on a McCabe-Thiele diagram, a three-stage counter-current extraction simulation was carried out to extract Y(III) quantitatively, with 7% co-extraction of Eu(III) at a volume phase ratio of MP:LP of 1.5:1. The co-extracted Eu(III) was selectively scrubbed in two stages using an Y(III) scrub solution. Y(III) was recovered from the loaded less polar organic phase by precipitation stripping with an aqueous oxalic acid solution and a subsequent calcination step. Y2O3 with a purity of more than 99.9% was obtained. A complete process flow sheet, comprising extraction, scrubbing and stripping steps for the separation of Y(III) and Eu(III) is reported. The feasibility of the developed process was successfully demonstrated in continuous mode using a battery of mixer-settlers.

Electrocopolymerization, Characterization and Anticorrosive Properties of Nanostructure Poly (aniline-co-4-hydroxy phenyl acetic acid)

In this study electrochemical deposition of nanostructure poly (aniline-co-4-hydroxy phenyl acetic acid) (PAHPA), polyaniline (PANI) and poly (4-hydroxy phenyl acetic acid) (PHPA) were carried out using cyclic voltammetry (CV) in aqueous solution of oxalic acid 0.3 M as reaction medium to achieve a protective coating for ferritic and economic 430SS in high corrosive solutions as 3.5% NaCl. In the electropolymerization of PAHPA, the monomer ratio was 1 : 1 (mol/mol). FT-IR and CV techniques were applied to characterize electrodeposited coatings. The morphological and structure analyses of the deposited films were done using scanning electron microscopy (SEM). Anticorrosive behaviors of coated steels were investigated by two techniques, potentiodynamic polarization and EIS (Electrochemical Impedance Spectroscopy) and were compared with protection efficiencies of PANI and PHPA. Our results showed that PAHPA coatings provided a noticeable better corrosion protection than homopolymers. The protection efficiency value for the PAHPA coated 430SS electrode was 97%, that it was higher than protection efficiencies of the hompolymers. Also effect of long immersion times on the protective films and their corrosion behaviors was studied. The PAHPA protection efficiency decreased about %3 when immersion time increased to 10 days. These results demonstrated the copolymer film can be highly corrosion resistant coating for 430SS in corrosive solutions that have chloride ions.

Kinetics of celestite conversion to acidic strontium oxalate hydrate in aqueous solution of oxalic acid

Abstract Conversion of SrSO 4 to acidic strontium oxalate hydrate (H[Sr(C 2 O 4 ) 1.5 (H 2 O)]) in aqueous H 2 C 2 O 4 solutions proceeds as a consecutive reaction. In the first step of the consecutive reaction, SrSO 4 reacts with H 2 C 2 O 4 and pseudomorphic conversion to SrC 2 O 4 ·H 2 O occurs. In the second step, SrC 2 O 4 ·H 2 O reacts with H 2 C 2 O 4 to form H[Sr(C 2 O 4 ) 1.5 (H 2 O)]. Sr(HC 2 O 4 )(C 2 O 4 ) 0.5 ·H 2 O crystallizes during cooling of the reaction mixture to room temperature if the solution reaches the saturation concentration of H[Sr(C 2 O 4 ) 1.5 (H 2 O)]. The aims of this study are the derivation of reaction rate equations and the determination of the kinetic parameters such as pre-exponential factor, apparent activation energy and order of H 2 C 2 O 4 concentration for each reaction step. Fractional conversions of SrSO 4 were calculated using the quantitative amounts of dissolved S and Sr. It was determined that the reaction rate increased at the initial time of reaction by increasing the temperature using solutions with approximately same H 2 C 2 O 4 concentrations. The reaction extends very slowly after a certain time in solutions with low H 2 C 2 O 4 concentration and ends by the formation of a protective layer of SrC 2 O 4 ·H 2 O around the surfaces of solid particles. Fractional conversion of SrSO 4 is increased by increasing concentration of H 2 C 2 O 4 at constant temperature. Kinetic model equations were derived using shrinking core model for each step.

Fabrication of a superconducting YBa2Cu4O8 film via coprecipitation

We have successfully synthesized the c-axis oriented YBa2Cu4O8 (Y-124) film on a SrTiO3 (1 0 0) substrate via a coprecipitation and dip-coating method. The precipitations including Y, Ba and Cu ions were obtained using their metal nitrates solution and the aqueous solution of sodium hydroxide and oxalic acid. Superconducting transition of the synthesized film was observed at 64–70 K corresponding to bulk Y-124 in the magnetization and resistance measurement. The developed method is suitable to synthesize superconducting Y-124 films for technological applications.

Electrochemical degradation of oxalic acid over highly reactive nano-textured γ- and α-MnO2/carbon electrode fabricated by KMnO4 reduction on loofah sponge-derived active carbon.

Manganese dioxide incorporated activated carbon (MnO2/AC) was synthesized and used to electrochemically degrade oxalic acid in aqueous solutions. The highly porous carbon provided reactive sites for the electro-sorption of oxalic acid and MnO2, with a specific polymorphism efficiently mediating the electron transfer between the electrode and organic pollutants. The activated carbon, made from the pyrolysis of dry loofah sponge using ZnCl2 as activating agent, exhibited a high double-layer capacitance dependent upon the heating temperature (100 F/g at 800 °C). The γ-MnO2 was in-situ deposited over the microporous structure of activated carbon through the redox reaction between KMnO4 and carbon. Simple further calcination converted γ-MnO2 to α-MnO2 nano-whisker at temperatures above 500 °C. Cyclic voltammetry showed that oxalic acid significantly improved the anodic current of the Mn(III)/Mn(IV) redox couple on the MnO2/AC electrode at an electrode potential around + 0.6 V (vs. Ag/AgCl). About 95% of oxalic acid degradation was achieved at pH < 4; meanwhile, 80% of the mineralization (total organic carbon removal) was attained independent of pH. Calcination converted γ-MnO2 to α-MnO2 which had higher electrochemical stability and inhibited the dissolution of Mn(II) from the electrode.

Solvometallurgical route for the recovery of Sm, Co, Cu and Fe from SmCo permanent magnets

A solvometallurgical recycling route for the recovery of samarium, cobalt, copper and iron from SmCo magnets was developed. The SmCo magnets were first crushed and milled to powder size and then leached in a 2 mol L−1 hydrochloric acid solution in ethylene glycol. Afterwards, cobalt, copper and iron were extracted from the leachate with 50 wt% Aliquat 336® in toluene, which was pre-saturated with 37 wt% HCl. The non-aqueous solvent extraction system improved the extraction efficiency of cobalt. The extraction was optimized by evaluating the extraction rates, the effects of temperature, feed/solvent ratio and the hydrochloric acid concentration. Through the construction of a McCabe-Thiele diagram it was possible to calculate the number of stages required for continuous extraction. Cobalt was recovered from the loaded solvent by stripping with a 0.5 mol L−1 aqueous hydrochloric acid solution. Copper was recovered by stripping with a 5 vol% aqueous ammonia solution, whereas iron precipitated under these conditions. The solvent could be reused after regeneration, i.e. evaporation of water and ammonia and reintegration of toluene and HCl. The samarium left in the raffinate was extracted by 20 vol% Cyanex 272 in n-dodecane. Finally, samarium was recovered from the loaded Cyanex 272 by precipitation stripping with a 0.2 mol L−1 aqueous oxalic acid solution. The purity of the recovered cobalt chloride was 98.3 wt% and that of samarium oxalate was 99.4 wt%.

Leaching and Selective Extraction of Indium and Tin from Zinc Flue Dust Using an Oxalic Acid-Based Deep Eutectic Solvent

Deep eutectic solvents have previously been used as cost-effective and readily available alternatives to conventional ionic liquids. Due to their versatile complexation properties, they are potential lixiviants for selective metal processing. In this study, we investigate the leaching behavior of three choline chloride-based deep eutectic solvents to selectively separate indium and tin from an oxide flue dust material. Ethylene glycol, urea, and oxalic acid dihydrate were used as hydrogen bond donors in the eutectic mixtures. The highest leaching yields were observed in the oxalic acid system Oxaline. A two-step precipitation procedure was developed for the leachate solution to separate the target metals indium and tin from the main flue dust components, i.e., iron, zinc, lead, and copper. This ionometallurgical approach was compared to equivalent leaching experiments using aqueous oxalic acid solutions and other deep eutectic solvents.