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Zinc doped Cerium oxide nanoparticles are prepared by a facile single step co-precipitation method. The synthesis method involves co-precipitation of the precursor salts using a non-toxic, green reagent oxalic acid, followed by annealing process at reliable low temperature. The effect of Zn doping on cerium nanoparticles are clearly investigated by the different characterization techniques such as X-Ray Diffraction, Scanning electron microscopy for morphological study, Fourier Transform Infra-Red studies to study the functional groups present and UV–Vis spectroscopy for optical study. The micro-structural and optical studies exhibit remarkable variation in the structural, optical, and morphological properties.

In this study we report a facile, cost effective one step preparation method for the synthesis of Mn doped cerium oxide (CeO2) nanoparticles (NPs) through co-precipitation technique. The synthesis was performed at relatively low temperature using a green reagent oxalic acid as reducing agent. The structural and optical attributes of the samples were characterized by X-Ray Diffraction spectroscopy (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV–Visible spectroscopy and SEM (Scanning electron microscopy). The XRD and FTIR results show the formation of Mn doped ceria NPs having a cubic fluorite structure. The morphology and chemical composition of the prepared sample was realized using SEM and EDX spectrum. The synthesized Mn doped ceria NPs shows greater absorption in the visible region and reduced particle size compared to pure ceria NPs.

In this study, Mg–6.0Zn–3.0Sn–0.5Mn (ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid, and a phosphate conversion coating (PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid, exhibited excellent corrosion resistance and behavior.

Electrochemical degradation performances of three non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen (ACT), aspirin (ASP) and ibuprofen (IBP), were investigated and compared in their alone and mixture conditions using Ti/SnO2-Sb/La-PbO2. The pseudo-first-order degradation kinetics (k) order was kIBP-A (0.110 min−1) ˃ kASP-A (0.092 min−1) ˃ kACT-A (0.066 min−1) in their alone condition, while that was kACT-M (0.088 min−1) ˃ kASP-M (0.063 min−1) ˃ kIBP-M (0.057 min−1) in their mixture condition. The •OH apparent production rate constant of 5.23 mmol L−1 min−1 m−2 and an electrical energy per order (EEO) value of 6.55 Wh/L could ensure the synchronous degradation of the NSAIDs mixture. The mineralization efficiency of NSAIDs mixture was 86.9% at 240 min with a mineralization current efficiency of 1.67%. Acetic acid and oxalic acid were the main products in the mineralization process for the both conditions. In the mixture condition, there were higher k values at lower initial concentrations and higher current density, while the presence of carbonate and humic acid inhibited their degradation. The results indicated electrochemical advanced oxidation process can effectively and synchronously mineralize NSAIDs mixture in wastewater.

This study investigated the best pretreatment conditions for olive tree biomass (OTB) to produce bio-hydrogen. The pretreatment conditions were optimized with response surface methodology for the dark fermentative hydrogen production to achieve maximum reducing sugar recovery and the independent variables were residence time (30–90min), temperature (100–140 °C), and acid concentration (0.5–3 %w/w for sulfuric and 5–10 %w/w for oxalic acid). Maximum reducing sugar obtained after sulfuric acid pretreatment and oxalic acid pretreatment at optimal pretreatment conditions were 37 g/L and 28 g/L, respectively. An approximately 20-fold increase in sugar concentration was achieved in pretreatment with sulfuric acid compared to the untreated control. The highest hydrogen yield was 0.83 and 0.91 mol H2/mol reducing sugar for oxalic acid pretreatment and sulfuric acid pretreatment, respectively. The results show that OTB has the potential to be used in bioenergy production.

Efficient conversion of straw cellulose to chemicals or fuels is an attracting topic today for the utilization of biomass to substitute for fossil resources. The development of catalysts is of vital importance. In this work, a composite catalyst Metal-organic frameworks (MOFs) immobilized on three-dimensional reduced graphene oxide (3D-rGO) were synthesized by in situ growth of the MIL-101(Cr) within the 3D-rGO matrix. The supporting of 3D-rGO guaranteed the dispersion and acid site density of MIL-101(Cr). The MIL-101(Cr)@3D-rGO nanocomposite possesses excellent catalytic activity, stability, recyclability and is an idea catalyst for the efficient degradation of straw cellulose into formic acid (FA), acetic acid (AA) and oxalic acid (OA). A maximum FA conversion rates of 95.36% was obtained by using MIL-101(Cr)@3D-rGO(1:1) as catalyst and hydrothermal reaction at mild conditions of 200 °C for 1h in alkaline aqueous medium. The MIL-101(Cr)@3D-rGO nanocomposite can be reused with high catalytic activity without any collapse of structure or leaching of chromium.

Dye desalination is a challenge in the treatment of textile wastewater with high salt concentration. It is imperative to develop salt resistance membrane that is from sustainable materials to effectively treat dye/salt mixtures. And most polymer membrane materials are non-renewable petrochemical resources. In this paper, a green hydrogel membrane (CMCS-OA-NaAlg) was prepared by non-metallic ions of oxalic acid (OA) cross-linking of two natural macromolecules of sodium alginate (NaAlg) and carboxymethyl chitosan (CMCS). The membrane showed excellent anti-swelling at high salt concentration (swelling rate less than 8.0% in 10.0 wt% NaCl solution) and good anti-fouling performance. The membrane exhibited a rejection higher than 95.0% for dyes (bright blue, direct black, direct red, and Congo red) and lower than 7.0% for NaCl, which can achieve better dye/NaCl separation performance. This study provides a promising membrane material for high salt textile wastewater treatment only using water and carbohydrates as raw materials without any organic solvents.

Due to the progressive shortage of primary resources and growing environmental concerns over industrial and household residues, proper management of electronic wastes is of great importance in addressing sustainability issues. Spent batteries are considered as important secondary sources of their constituting components. In this study, the co-recycling of used zinc-carbon and lithium-ion batteries was performed aiming at the recovery of their manganese and lithium contents as compounds which can be used as precursors for the synthesis of spinel LiMn2O4. Manganese was recovered in the form of amorphous, submicron, spherical nodules of MnO2 after acid leaching of zinc-carbon battery pastes. Lithium was obtained from nickel-manganese-cobalt (NMC) batteries as its monohydrate oxalate (C2HLiO4.H2O) through selective leaching in oxalic acid followed by crystallization. Lithium carbonate was also prepared by subsequent calcination of the oxalate. The synthesis of LiMn2O4 spinel cathode was carried out using the recycled Li- and Mn-containing compounds via solid-state synthesis method. The effect of such parameters as type of reactants (C2HLiO4.H2O, Li2CO3, Mn2O3, and MnO2), temperature (750, 800, and 850 °C), and time (8 and 10 h) on the synthesis of LiMn2O4 was investigated. The products were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The crystallographic parameters used to predict the electrochemical behavior of synthesized cathode materials were derived from XRD patterns. Based on these, the spinel powder synthesized at 850 °C for 10 h was determined as the sample with the best potential electrochemical properties among the synthesized samples. The galvanostatic charge/discharge characterization within the voltage range of 2.5–4.3 V showed the specific capacity of the 850°C-10 h sample to be 127.87 mAhg−1.

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

The recovery of rare earths elements (REEs) from NdFeB slurry by traditional hydrometallurgy has been limited becuase a large number of REEs are lost during separation together with iron. In this paper, a simple and sustainable method is proposed to efficiently separate and recover REEs and iron from NdFeB slurry. REEs were recovered by one-step selective precipitation in phosphoric acid, and the dissolved iron was recovered by oxalic acid. Phosphoric acid leaching results show that under the conditions of 4 mol/L phosphoric acid, 80 °C, L/S of 30:1 and 90 min, the leaching efficiencies of Fe and REEs reach 98.76% and 1.09%, respectively. While the rest of REEs remained in the leaching residue in the form of REEPO4·nH2O precipitation. Subsequently, the mixed rare earth oxide (rare earth oxalate roasted at 800 °C) and FeC2O4·2H2O are obtained by oxalic acid precipitation with purities of 99.49% and 97.17% from the REEPO4·nH2O dissolving solution and the phosphoric acid leaching solution. Moreover, the phosphoric acid is regenerated while recovering iron, and it can be reused in the phosphoric acid leaching step after removing the impurity C2O42−. In summary, this work provides an efficient and environmentally friendly method for recovering REEs and iron from NdFeB slurry waste.

A novel methodology for the preparation of nanostructured layers of mechanically processed carbon nanotubes (CNT) on macro-structured supports was investigated as a means to prepare macro-structured composite catalysts consisting of a variety of different ceria – CNT combinations as ozonation catalysts. Two different synthesis routes were used for the preparation of the ceria: precipitation and sol-gel. The composite materials were prepared using different approaches: introduction of ball-milled CNT during the synthesis procedure; ball-milling the pure ceria together with as-received CNT; and decoration of ball-milled CNT with well-dispersed ceria through incipient wetness impregnation. The powder composite catalysts were then transferred onto macro-structured supports by using the aforementioned novel methodology for the preparation of slurries suitable to be used in the dip-coating of the macro-structures. A further structured composite catalyst was also prepared using a two-step approach by dipping a previously prepared CNT structured catalyst in a ceria solution. The powder and structured composite catalysts were then tested as ozonation catalysts in semi-batch and continuous experiments. It was found that the different ceria synthesis routes and the composite preparation methods affected both the catalytic performance of the powder composites and also the characteristics of the slurry used for dip-coating of the macro-structured supports. The ball-milling of sol-gel ceria together with CNT resulted in the most active powder catalyst, but the impregnated CNT with well-dispersed ceria was found to be the most active structured catalyst prepared from coating with the powder composites. The two-step structured catalyst prepared by dipping in a ceria-sol was able to achieve the highest removal of oxalic acid (85 % at steady-state continuous operation); however, due to the more energy intensive preparation procedure, its use in practical applications might not be the most recommendable.

Owing to the ease of synthesis and the unique luminescence characteristics for the applications of white light emitting diodes (WLEDs), the red-emitting fluoride phosphors activated by Mn4+ ions are critical to achieving WLEDs with ideal color rendering index (CRI). In this work, a new type of Mn4+ doped phosphor KRb3Ge2F12:Mn4+ (KRGF:Mn) has been synthesized by a simple ion-exchange method in atmosphere. A strategy of surface modification by using a weak reducing agent oxalic acid (OA) is proposed, which can essentially improve the moisture stability of phosphor KRGF:Mn. Moreover, the modified phosphors can still maintain bright red light after being completely immersed in water for more than 100 days. A group of LEDs combined with the as-synthesized phosphor KRGF:Mn as a light source can be well applied to artificial lighting for the growth of tomatoes and Chinese cabbage plants. Additionally, the luminescence efficiency of KRGF:Mn has been optimized with high thermal stability. This work will provide high-quality red phosphor for LED lighting sources that being required for indoor plant growth.

This work sheds light on the development of new low-cost ceramic ultrafiltration (UF) membrane based on Moroccan clay and zirconia. The ceramic support with a pore diameter of 1.95 µm was prepared by uniaxial pressing of clay powder and corn starch followed by sintering at temperature of 950 °C. To prepare the zirconia membrane layer on the clay support, zirconyl oxalate sol was prepared through an aqueous sol–gel route using zirconium oxychloride as a zirconia source and oxalic acid as a peptizing agent. The clay support was coated with resulting zirconyl oxalate particles using dip-coating technique and then sintered at temperature of 600 °C. The prepared zirconia UF membrane has a pore diameter of 80 nm and a permeability of 36 L h−1m−2bar−1. Finally, the performance of prepared zirconia UF membrane was assessed by the filtration of acid orange 74 dye. It was confirmed that the membrane could be effective for removal of soluble dye solution. Furthermore, it was shown that the rejection remarkably increases when the feed concentration increases from 50 to 150 ppm. On the other hand, the applied pressure does not significantly affect dye rejection (about 98%) in the range from 1 to 3 bar.

Nanocellulose from oil palm mesocarp fiber (OPMF) was isolated using hydrothermal treatment at a pressure of 150 kPa and 120 °C coupled with hydrolysis of low concentration of weak acid i.e. oxalic acid dihydrate (OAD). Two different concentrations of OAD i.e. 11 and 13 wt% were introduced in the acid hydrolysis process. Crystallinity index of the raw fiber increased from 39.5 to 70.4 and 70% for 11 and 13 wt% OAD, respectively. The average particles sizes of nanocellulose measured using TEM was approximately 25 nm for both concentrations of OAD which approximately equivalent to the one measured using dynamic light scattering (DLS). The values of zeta potential of the nanocellulose suspension isolated using 11 and 13 wt% OAD were −26 and −27.5 mV respectively. Isolation technique which is hydrothermal treatment coupled with low concentration of OAD was effective in producing OPMF nanocellulose at high crystallinity index, less than 100 nm size distribution, and it is a stable suspension.

CO2 is one of the leading greenhouse gases, so studies that turn this gas into higher value-added products, that function as simpler and cheaper hydrogen stores, as an alcohols, are extremely important. In this work we using a polymeric Electrolyte Reactor– fuel cell type supplied with H2 on platinum anode and dry CO2 in the cathode with a copper-carbon electrocatalyst. Copper nanoparticles supported on carbon Vulcan XC72 were produced by the sodium borohydride reduction method. The XRD revealed the presence of two different phases, CuO and Cu2O. In addition, the TEM images revealed agglomerates presence. The water, formaldehyde, methanol, methane, formic acid, dimethyl ether, oxalic acid, dimethyl carbonate, and ethylene-glycol were observed by differential mass spectroscopy on line with the reaction and the onset potential for each product and these results were confirmed by infrared spectroscopy – ATR-FTIR setup. This work showed the mapping CO2 reduced compounds for onset potential proposing some contributions to the literature.

Polyanilines doped with different concentrations of oxalic acid have been synthesized by oxidative chemical polymerization using potassium perdisulfate as oxidizing agent. The effect of dopant on the kinetics of polymerization has been studied by UV–VIS spectroscopy. The presence of oxalic acid in the polymer has been studied by FTIR, and morphology by SEM and TEM. The thermal stability of the polymer was investigated by TGA and degree of crystallinity of polyaniline was studied by XRD. The electrochemical behaviour has been studied by cyclic voltammetry (CV) and the phenomenon of charge transport and capacitance was examined by Electrochemical Impedance Spectroscopy (EIS). The morphological study shows the particles to be of nanosize and EIS studies show that these samples have significant double layer capacitance (Cdl) and can be used as capacitors.

Molecular level behavior is the key factor for the behavior of a material. The molecular level is governed by the role of sub atomic particles present in it. The performance of particles is better studied through quantum mechanics. This work is the molecular level quantum mechanical study of semiconductor silica and its composites of electron deficient inorganic acid boric acid, organic dicorboxylic acid oxalic acid and organic base emeraldine. The quantum studies were performed using density function theory employing B3LYP and 631G** basis set. The order of capacitance may be; S-BA > S-OA > S-EB. Composites have NLO properties. Cologne structure can have better capacitance than helix.

An effective method comprising the immersion in dilute sulfuric acid and the leaching in a mixture of sulfuric acid and oxalic acid under ultrasonic irradiation is provided to improve the removal effect of harmful metals in spent FCC catalyst without destroying the zeolite Y framework and the microstructure of spent catalyst particle. The influence of different experimental conditions on the regeneration effect of spent catalyst is studied by using SEM, EPMA-EDX, XRD, ICP, N2 adsorption, and particle size analysis techniques. The experimental results show that immersion in sulfuric acid can effectively restore blocked pores and increase the specific surface area of spent catalyst by 51.7% compared with the untreated spent catalyst, which is beneficial to the subsequent acid leaching. After leaching in a mixture of 0.5 mol/L oxalic acid and 2 wt.% sulfuric acid for 30 min at 70 °C with an ultrasonic power of 250 W, the regenerated catalyst with complete particle structure and zeolite Y framework is obtained with the removing rates of Fe, V, and Ni being 36.2, 43.8 and 30.1 %, respectively, whereas Al loss is only 7.9 %. Compared with conventional leaching, ultrasonic assisted leaching only needs 1/4 of the time to achieve much the same harmful metal removal effect and has superior advantages in retaining the integrity of particles.

Efficient recycling of high-value metals from spent cathode materials is important in that it not only alleviates the severe shortage of raw material supply but also addresses the environmental and safety issues associated with the disposal of these materials. Here, we report a selective leaching strategy by virtue of the defect-induced lattice instability. In contrast to the traditional “primary leaching – multistep separation” process, this technique enables simultaneous recovery and separation of value metals from the waste cathode by selective dissolution. The feasibility of this technique was first demonstrated by density functional theory (DFT) calculations, and then confirmed by laboratory studies in which a spent LiNi1/3Co1/3Mn1/3O2 material was successfully recycled, where the recoveries of Li, Ni/Co and Mn reached close to 100%, 99.5%/98.2% and 100%, respectively, without the need for a separation step. The recovery of Li, Ni/Co and Mn uses oxalic acid, phosphoric acid and sulfuric acid as leaching agents, respectively. We believe that this work has both practical and theoretical significance, in that the strategy has the potential to be expanded to the recovery/recycling of many other spent materials, and that the atomic-scale insight on the relation between vacancies and lattice stability offers new perspective for developing advanced recycling strategies.

Surface functionalization of piezoelectric greatly determines its piezo-catalytic activity and selectivity in that functional group affect specific reactants’ surface adsorption and activation abilities. Herein, we propose chemical functionalization on the surface of nano-scaled BaTiO3 piezoelectric via a one-pot hydrothermal process using polyethylene glycol as surfactant, and evaluate its piezo-catalytic activity and selectivity by degrading model antibiotic and dye reactants under ultrasonic vibrations. Acetate or/and oxalic unidentate ligands on the surface of BaTiO3 nanobelts can be formed by controlling precursor and hydrothermal parameters. Particularly, oxalic acid functionalized BaTiO3 nanobelts presented a high piezo-catalytic rate constant of 0.068 min−1 for Rhodamine B solution and maintained >87% degradation efficiency within 30 min under the condition of ultrasonic bath with 40 kHz and 100 W, which was mainly ascribed to piezo-sensitization effect. This work provides references for the preparation of chemical functionalized catalysts and also contributes to the development of novel catalysts for special applications.

The preparation of α-Al2O3 powders with equiaxed architecture for the fabrication of advanced ceramics is of great importance but still challenging. A new and facile approach for the fabrication of equiaxed α-Al2O3 adopting alumina hydroxide and oxalic acid as the raw materials was reported in this paper for the first time. The current work demonstrated that the adding 0.16 mol/L oxalic acid solution made α-Al2O3 heterogeneously nucleate at a temperature as low as 800 °C, and the amount of nucleation was high enough to remove the vermicular microstructures during the morphology evolution of α-Al2O3, resulting in the formation of equiaxed α-Al2O3 particles with an average size of 205.72 nm at 1300 °C.

Converting the γ phase into the α phase completely is necessary in the presintering stage of industrial alumina (Al2O3), which requires high temperature and energy consumption. To reduce the presintering temperature, γ-Al2O3 was activated by oxalic acid. XRD, 27Al-MAS-NMR and TG-DSC were used to characterize the γ - alumina before and after activation, and the phase transformation was studied. The formation temperature of α-Al2O3 decreased to 1029 °C for oxalic acid activated γ-Al2O3, and the α-fraction was 100% for activated γ-Al2O3 at 1300 °C. After oxalic acid activation, the diffraction peak intensity of γ-Al2O3 decreased significantly; the results of 27Al-MAS-NMR suggested that octahedral [AlO6] in γ-Al2O3 was easier than tetrahedral [AlO4] to be attacked by oxalic acid, and the formation of pentavalent [AlO5] with higher reaction activity, which was in favour of the lowering formation temperature of α-Al2O3. The dissolution concentration of Al increased after oxalic acid activation, and the dissolution process was controlled by surface reactions. Oxalic acid mainly attacked the octahedral aluminium in γ-Al2O3 and extracted Al as three complexes of [Al(C2O4)]+, [Al(C2O4)2]- and [Al(C2O4)3]3-. Oxalic acid activated γ - Al2O3 with a lower phase transformation temperature has broad application prospects in the alumina industry.

Phosphate doped bis-urea oxalic acid (PBUO) crystals were grown using the aqueous solution by slow evaporation technique. Single crystal XRD study indicates that the sample crystallizes in monoclinic structure. The mechanical parameters like hardness, yield strength and stiffness constant of the crystal were determined by using the Vickers hardness tester. UV-visible spectral studies were done to determine the various linear optical parameters. Second harmonic generation (SHG) efficiency was measured for the grown crystal of PBUO to understand the nonlinear optical activity. TG/DTA analysis shows that the PBUO crystal is thermally stable upto 170 °C. Energy dispersive X-ray analysis (EDAX) was carried out by recording the EDAX spectrum of the grown crystal to identify elements in the sample. The grown PBUO crystals were also characterized by FTIR, SEM, PL, LDT and impedance studies.

Background Oxalic acid (OA) existing widely in animal, plants, and factory processes may affect human health and result in environmental pollution. It is highly desired to develop a rapid fluorescent sensing for accurate determination of OA content in food and wastewater. Methods We are the first to design an easy-to-prepare rhodamine-6G based zinc complex as a fluorescent probe for the selective detection of OA and explore the sensing mechanism between zinc complex and OA. The zinc complex presents the coordination with two Zn2+ and both of rapid color and linear fluorescent response toward OA in the range of 0-10 μM. Findings The detection limit of the probe for OA can reach to 1.20 μM, which is superior to those reported in the literature. Compared with other dicarboxylic acids, the binuclear zinc complex probe displays rapid detection and high selectivity for OA over a wide pH range due to the steric hindrance and ring strains. The recycling of the probe can be achieved by the treatment with sodium sulfide to form zinc sulfide and regenerate the intermediate.

The extraction of tungsten from scheelite was carried out using a sulfuric acid solution with oxalic acid as the chelating agent. Tungsten was obtained in the form of highly soluble hydrogen aqua oxalato tungstate (H2[WO3(C2O4)·H2O]) during the leaching process, while calcium remained in the residue as calcium sulfate dihydrate (CaSO4·2H2O). About 99.2% of the tungsten was leached at 70 °C, 1.5 mol/L sulfuric acid, 1 mol/L oxalic acid, a liquid/solid ratio of 25:1 (mL/g), an oxalic acid to sulfuric acid molar ratio of 1:1, a stirring speed of 300 r/min and a leaching time of 2 h. H2[WO3(C2O4)·H2O] was thermally decomposed into tungstic acid (H2WO4), and tungsten trioxide (WO3) was directly produced by calcining H2WO4 at 700 °C for 2 h. The surface chemical reaction was determined to be the controlling step during tungsten leaching, and the apparent activation energy was calculated to be 51.43 kJ/mol.

The selective dissolution of V and Fe from spent denitrification catalyst (SDC) with oxalic acid was investigated to minimise their environmental effects. The dissolution kinetics of different elements from SDC by using 0.1–1.5 mol L−1 oxalic acid concentration was studied at 60 °C–90 °C. V and Fe were preferentially released (65% and 81%) compared with Al, Ti and W within 5 min due to the redox reactions of oxalic acid. The dissolved fractions of Fe, V, Al, W and Ti increased with the increase of oxalic acid concentration and reaction temperature. The dissolution kinetic experiments were analysed and controlled diffusion with n 0.92). The Arrhenius parameters of the Ea values of Ti, W, V, Fe and Al from SDC with oxalic acid were 30, 26, 20, 19 and 11 kJ mol−1, respectively. The obtained Avrami equation of V and Fe was successfully used to predict their leaching behaviour in oxalic acid. Toxicity characteristic leaching procedure revealed that the toxicity risk of V and Fe metals from SDC after leaching with oxalic acid decreased to below 5 mg kg−1 residua. Overall, the leaching residua by oxalic acid indicated its safety for the environment.

Selective catalytic reduction using NH3 (NH3-SCR) is a chemical process that is used for the elimination of NOx (NO and NO2). Although current vanadia-based catalysts need a high reaction temperature, which leads to deactivation of the catalysts, bulk vanadium oxide showed the potential for NH3-SCR at a low temperature below 150 °C. We investigated a method for synthesis of vanadium oxide with a large surface area using an organic acid to enhance its NH3-SCR activity. Vanadium oxide catalysts were synthesized from ammonium metavanadate (NH4VO3) and organic acids (oxalic acid, succinic acid, malic acid and citric acid). When carboxylic acids (oxalic acid and succinic acid) were used as the organic acid source, the surface area of the catalysts increased up to 41 cm2 g−1, which was larger than that of vanadium oxide synthesized without an organic acid and with hydroxy acid. SEM and TEM measurements showed that vanadium oxide catalysts synthesized by the calcination of vanadyl oxalate at 300 °C (V2O5-OX_300) formed a pore structure that contributed to the increase in surface area. An increase in the number of acid sites and redox sites, which is important for NH3-SCR to proceed, was confirmed from NH3-TPD and H2-TPR measurements for V2O5-OX_300. The NO conversion of V2O5-OX_300 (47 % at 100 °C) was higher than that of the catalysts synthesized from only NH4VO3 (19 % at 100 °C), indicating that vanadium oxide catalysts synthesized using carboxylic acid have the low-temperature NH3-SCR activity due to the increase in their surface area.

Perovskite oxides have emerged as promising alternatives for the supported Platinum group metal catalysts for total oxidation of propane and other volatile organic compounds (VOC). Here, we report a surface modification method to improve propane oxidation activity of La0.8Sr0.2CoO3 monolithic catalysts using diluted oxalic acid etching. The oxalic acid treatment decreases the light-off temperatures of propane oxidation by 30–40 °C. Experimental and DFT investigations reveal that the treatment selectively etches Sr cations and slightly reduces LSCO surface, leading to an increased population of low-valence Co2+ Lewis acid sites, which promotes activation of lattice oxygen and adsorbed oxygen species and facilitates propane adsorption and dissociation. Our work offers a rapid strategy to activate perovskite monolithic catalysts and will inspire the research on surface modification of perovskite catalyst.

Deep eutectic solvents (DES), a new class of alternative solvents, have recently been used in the pre-treatment of lignocellulosic biomass. Due to the ability to dissolve phenolic compounds, they have been efficiently applied as delignification agents. However, to extend DES application to bioprocesses, such as Anaerobic Digestion (AD), their toxicity to microbial consortia must be evaluated. In this work, an effective delignifying DES, composed of choline chloride (ChCl) and oxalic acid (OA) (1:1) was prepared and its effect evaluated, for the first time, in biogas production. Results show that the presence of DES had both beneficial and detrimental effects on the anaerobic consortium, depending on its concentration. In the concentration range of 0.3–12.5 g/L, the presence of DES led to a lag-phase of 1 to 8 d as the DES concentration increased. However, after the lag-phase has been surpassed, DES up to a concentration of 12.5 g/L improved the biogas production, reaching an accumulated biogas volume three times higher than the control assay for the concentration of 12.5 g/L. For the highest DES concentrations (19.8–78.1 g/L), the biogas production was inhibited. The assays performed with DES components alone have indicated that OA at 3.2 g/L was the main responsible for the inhibition of biogas production (50% less biogas produced than the control). ChCl at 4.9 g/L has not presented a lag-phase and produced an accumulated biogas volume like the control assay (1200 mL for 30 d incubation). This work points out that ChCl:OA DES may be used in the delignification of biomass further submitted to AD, provided the inhibitory concentrations of OA are not achieved.

Encapsulation and controlled release of volatile molecules such as fragrances in a designed manner is important but challenging for the flavor and fragrance industry. Here, we report the tuning release of volatile molecules by postsynthetic modification of an amine-terminated metal-organic framework (MOF) MIL-101-NH2. By amidation, we obtained three MIL-101 MOFs, the trimethylacetamide-terminated TC-MIL-101, the benzamide-terminated BC-MIL-101, and the oxalic acid monoamide-terminated OC-MIL-101. All the MOFs can efficiently encapsulate volatile molecules. Moreover, we demonstrate that the release profile of volatiles can be widely tuned to sustain the release in several days to months and even over a year using different modified MIL-101 MOFs. We show that the release profiles are correlated with the binding energies between the guest volatiles and pores in MOFs. The pore diffusion and the synergistic transport are the rate-limiting step of the guest molecules from the modified MOFs.

In this study, a core-shell design of Fe3O4@SnO2 was prepared, doped with silver nanoparticles (Fe3O4@SnO2/Ag) and later laden into three-dimensional graphene oxide hydrogel (rGH) forming 10% rGH-Fe3O4@SnO2/Ag, which was synthesized using chemical reduction methods and utilized in the degradation of 2,4 dichlorophenol as a target pollutant in the solution. Fourier Transform Infrared Spectroscopy/FTIR spectra, Raman spectroscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, X-ray diffraction, Photoluminescence spectra, Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy were some of the standardized characterization techniques utilized. 2,4 dichlorophenol (2,4-DCP) was quickly adsorbed by three-dimensional 10% rGH-Fe3O4@SnO2/Ag composite and rapidly degraded by Fe3O4@SnO2/Ag nanoparticles under sunlight irradiation, indicating that superb synergies between adsorption-photocatalysis degradation could significantly improve the pollutant degradation performance. The maximum adsorption capacity of 10% rGH-Fe3O4@SnO2/Ag was 14.90 mg/g after 30 min. According to the results, the percent degradation efficiency of 2,4-DCP in Fe3O4@SnO2/Ag-rGH was not only high i.e. 93.8% via the synergy amongst adsorption-photocatalytic degradation, but also the percent degradation efficiency of 2,4-DCP was 85% after 5 repetitive cycles, which signified a high synergistic effect between Fe3O4@SnO2/Ag nanoparticles and 3D graphene. A corresponding pathway for 2,4-DCP photodegradation was suggested, such as 2,4 -dichlorophenol, formic, acetic, or oxalic acid as the main intermediate compounds. The experimental results of radical species trapping showed the photo-generated holes exhibiting an important role in promoting both direct oxidation of 2,4-DCP and production of ·O2 radicals. Therefore, 10% rGH-Fe3O4@SnO2/Ag composite revealed that it has a photocatalyst with high degradation activity, facile recyclability and easy magnetic separation for its potential wide application in the water treatment.

In recent years, transition-metal oxides (TMOs) have been long employed for aerobic oxidative desulfurization. However, the inherent bottlenecks, such as the low explosion of active sites, limit the application of bulk TMOs catalyst. In this study, V2O5 nanoparticles with oxygen vacancies were prepared in large-scale via facile ball milling strategy with adding oxalic acid as a reducing agent. The as-prepared catalysts exhibit remarkable sulfur removal for oils with different initial S-concentrations and different substrates. Sulfur removal could reach up to 99.7% (< 2 ppm) under the optimized reaction conditions. This work provides a feasible desulfurization strategy for fuel oils.

Star fruit (Averrhoa carambola) is a popular fruit in many tropical countries, including Sri Lanka. It is rich in oxalic acid, which is nephrotoxic in higher concentrations. The development of both acute (AKI) and chronic kidney injury after oxalate nephropathy is often underrecognized. Here we discuss the risk factors, clinical features, treatment, and outcomes of 4 patients who developed AKI after star fruit ingestion. Baseline clinical characteristics, the amount of star fruit ingested, clinical presentation, investigation, and outcome of the patients (ages 28, 50, 54, and 55 y; all male) were traced. More common symptoms of acute star fruit intoxication were nausea, vomiting, and abdominal and back pain, followed by low urine output and high serum creatinine over hours to days. Urinary analysis of all patients demonstrated oxalate crystals. Histopathologic examination of renal tissues of all 4 patients revealed acute tubular damage with calcium oxalate crystals, interstitial edema, and inflammatory cellular infiltration. The presence of calcium oxalate crystals was further confirmed with the brilliant birefringence seen under polarized light. Two patients needed intermittent hemodialysis over a week owing to oliguria and uremia. The other 2 patients did not require hemodialysis and had improvement of renal function with supportive treatment. All had high renal function on discharge but were back to normal within a month. This study highlights AKI as a serious complication of star fruit ingestion. The type and quantity of star fruit ingested and some patient factors may play a role in the pathogenesis of AKI. Public education about this serious uncommon complication is important.

A series of carboxylic acid-functionalized deep eutectic solvents(DES) wereconstructed by a natural organic dicarboxylic acid, oxalic acid (OA), as the hydrogen bond donor and the polyethylene glycol (PEG)with different polymerization degrees as the hydrogen bond acceptors, which are used in the hydration of α-pineneto produce α-terpineol. Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), and thermogravimetric analysis (TGA) were used to prove the hydrogen bonding between OA and PEG. It is found that the presence of PEG has a less impact on the acid strength of DES. However, an increase in both molecular weight and dosage of PEG results in a decrease in total acidity and catalytic activity.Among them, OA/0.6PEG200, a DES catalyst prepared by PEG with the smallest molecular weight, exhibits a favorable catalytic performance. Under an optimal reaction condition with 0.03 mol of DES (based on OA), 0.06 molof α-pinene, 0.3 mol of water,at 75°C for 8 h, anα-pinene conversion of 81.5% and an α-terpineol selectivity of 51.2% are obtained. The catalyst phase can be separated by refrigerating overnight after reaction and reused directly with relatively stable catalytic performance. Thus, OA/0.6PEG200, as a DES catalyst prepared by a simple and highly atom economical process, will offer a clean catalytic route for the one-step production of α-terpineol.

Advanced methods to design biocompatible mesoporous superparamagnetic nanoparticles are required for various healthcare applications. This work was designated to synthesize superparamagnetic mesoporous hydroxyapatite (HAp) nanorods (NRs) with the intrinsic pure phase through the doping of cobalt ions inside it. This nanoparticle was synthesized using a black Scallop seashell as a low cost calcium source using oxalic acid as a strong chelating agent via microwave synthesis. The prepared magnetic HAp NRs are analyzed by diverse methods to understand the clarity of phase and its nanostructural features. XRD and EDX results prove that Co is distributed well in the HAp nanoparticles without affecting its structure. The BET surface areas of CoHAp-1, CoHAp-2, and pristine HAp NRs were found to be 69, 126, and 97 m2 g−1, correspondingly. Further, evaluated pore volume of CoHAp-1, CoHAp-2, and pristine HAp NRs are identified to be 0.0275, 0.0349, and 0.0368 cm3 g−1 and also pore diameters were found as 3.02, 4.67, and 4.71 nm. Hence, the HAp mesoporous NRs with higher surface area were achieved with the incorporation of Co in the HAp system. The superparamagnetic characteristics were identified only in the Co-doped HAp samples. The high saturation magnetization of 0.20 Am2 kg−1 was observed with the high doping of Co ions. Toxicity of the pristine and the Co-incorporated HAp samples were evaluated using zebrafish. The toxicity result reveals that Co incorporations in HAp do not affect significantly the biocompatible nature compared to the pristine HAp sample. Antibacterial test shows excellent antibacterial activities for Co-HAp samples among different pathogens. Hence, the approach of oxalic acid-associated microwave mediated synthesis of intrinsic mesoporous superparamagnetic HAp NRs from naturally occurring seashells as a precursor can be a superior method for obtaining nanomaterials towards various applications like magnetic resonance imaging, targeting of drug, hyperthermia, and cancer treatments.

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).

Amides, a series of significant atmospheric nitrogen-containing volatile organic compounds (VOCs), can participate in new particle formation (NPF) throught interacting with sulfuric acid (SA) and organic acids. In this study, we investigated the molecular interactions of formamide (FA), acetamide (AA), N-methylformamide (MF), propanamide (PA), N-methylacetamide (MA), and N,N-dimethylformamide (DMF) with SA, acetic acid (HAC), propanoic acid (PAC), oxalic acid (OA), and malonic acid (MOA). Global minimum of clusters were obtained through the association of the artificial bee colony (ABC) algorithm and density functional theory (DFT) calculations. The conformational analysis, thermochemical analysis, frequency analysis, and topological analysis were conducted to determine the interactions of hydrogen-bonded molecular clusters. The heterodimers formed a hepta or octa membered ring through four different types of hydrogen bonds, and the strength of the bonds are ranked in the following order: SOH•••O > COH•••O > NH•••O > CH•••O. We also evaluated the stability of the clusters and found that the stabilization effect of amides with SA is weaker than that of amines with SA but stronger than that of ammonia (NH3) with SA in the dimer formation of nucleation process. Additionally, the nucleation capacity of SA with amides is greater than that of organic acids with amides.

The morphology effect of tungsten oxide on the NH3-SCR activity of the supported CeO2 catalyst was experimentally investigated by comparing the catalytic performance of WO3 in different morphologies. Nanoparticles (W-NP), nanorods (W-NR) and microspheres self-assembled by nanorods (W-MP) of WO3 were synthesized by using different carboxylic acid structure-directing agents. Based on this, the impregnation method was adopted to form the composite catalysts including the Ce/W-NP, the Ce/W-NR and the Ce/W-MP. After the impregnation of Ce species, a new redox cycle of Ce4++W5+↔Ce3++W6+ is formed due to the interaction of W and Ce ions, which significantly facilitates the redox reaction on the composite catalyst. However, compared with nanorods (W-NR) and microspheres self-assembled by nanorods (W-MP), WO3 nanoparticles (W-NP) enclosed with (0 0 1) facets of the hexagonal WO3 shows the best redox ability due to the largest molar ratio of W5+/(W5++W6+) and the highest concentration of Ce4+ on the surface of Ce/W-NP, which was proven by the results of XPS. As a consequence, the Ce/W-NP presents the strongest surface redox properties and the largest molar ratio of Oα/(Oα+Oβ), which is beneficial to promote the NH3-SCR activity of the catalyst. It is worth mentioning that the morphology of tungsten oxide that remarkably affects the activity of the catalyst is determined by tartaric acid, citric acid and oxalic acid, indicating the significance of the structure-directing agents for improving the NH3-SCR activity of the impregnated Ce/W catalyst.

Oil palm trunk biomass (OPTB) is a promising lignocellulosic resource for bioconversion due to its abundant availability, low cost and high carbohydrates content. In the present work, oxalic acid was used to pretreat OPTB under different pretreatment conditions. We maintained the same pretreatment severity value by manipulating the reaction time over a range of oxalic acid concentrations. The impact of oxalic acid pretreatment was evaluated in terms of xylose recovery, enzymatic digestibility as well as fermentability of Actinobacillus succinogenes 130Z for the production of industrially valuable succinic acid. Our findings demonstrated that oxalic acid at 4% (w/v) concentration showed superior effectiveness in solubilising hemicellulose from OPTB, achieving 60.3% xylose recovery. During enzymatic hydrolysis, again, the OPTB pretreated with 4% (w/v) oxalic acid exhibited the highest enzymatic digestibility of 63.4% yielding 39.1 g of sugar per 100 g OPTB. However, it was found that high concentration of oxalic acid (3–4%, w/v) inhibited A. succinogenes 130Z fermentation. The results reported herein suggest that the pretreatment using low oxalic acid (1%, w/v), though requiring longer reaction time, is preferable for an improved succinic acid production from OPTB.

This study investigated the dissolution behavior of metals from chalcopyrite concentrate in a pressure reactor system in the presence of hydrogen peroxide by oxalic acid leaching. The fact that the compounds formed by copper and iron with oxalic acid had different dissolution coefficients showed that metals could be selectively extracted based on the leaching temperature. The effects of various leaching parameters on metal extraction in the autoclave system were investigated at different H2O2 concentrations (1-5 M), H2C2O4 concentrations (25-125 g/L), leaching temperatures (318-443 K) and leaching times (15-180 min). While iron and copper extraction as a result of 180 min of leaching with 5 M H2O2, 318 K and 100 g/L H2C2O4 was respectively 90.6% and 1.73%, 88.5% of copper and 2.11% of iron could be extracted as a result of 180 min of leaching with 3 M H2O2, 443 K and 100 g/L H2C2O4. The reversal of the copper and iron extraction dissolution behavior started after the leaching temperature of 378 K. In the XRD analysis of leach residues obtained at low leaching temperatures, CuC2O4 peaks were dominant, while at high temperature conditions, Fe2O3 peaks were dominant. (c) 2020 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Austenitic stainless steel is one among the most commonly adopted materials for various engineering applications such as nuclear reactors, internals of vessels and valve body due to exceptional characteristics. Welding is an important process in manufacturing which helps to join the material in an effective manner, especially with help of laser welding. Corrosion is a phenomenon which huge contribution on environmental destruction also influences the all the metallic materials. It is a common issue for all the manufacturing industries such as petroleum, aerospace and marine. This present investigation an endeavor has been taken to analyze the corrosion rate with different mediums such as ferric chloride, nitric acid and Oxalic acid. The rate of corrosion has been assessed by weight loss method. The outcome of this experimentation witnessed that the rate of corrosion is increased with respect to temperature and time. Increase in temperature makes considerable chemical reactions which consequences significantly on the rate of corrosion. A comparison has been done to corrosion behavior of laser beam welded 304L Stainless steel samples and results are presented. The composition existing in the selected material contributes for reducing the corrosion rate especially in acidic environments.

Allopurinol is considered to be one of the most effective medications, which is regularly prescribed to reduce urate level and treat chronic gout. The drug belongs to biopharmaceutics Classification System (BCS) class IV category with poor aqueous solubility and permeability. High-throughput solid-form screening of the active pharmaceutical ingredient for new binary solid forms was carried out in order to improve drug properties. Multicomponent solids with oxalic acid and maleic acid were obtained during liquid assisted grinding of equivalent stoichiometry. The novel binary systems were characterized by PXRD, FT-IR, DSC, TGA and SEM images. Vibrational spectroscopy was exploited to confirm the ionization states of the multicomponent systems. Thermal analysis indicates the new solid phases with the possibility of hydrates in the oxalate and maleate salts, which degraded to allopurinol after melting. Powder dissolution experiment was carried out on the drug and the salts in pH-1.2 (acidic) and pH-7 (phosphate buffer, neutral) medium, which suggests that salts improved dissolution up to 4 fold compared to the native drug. In both the aqueous medium, maleate salt exhibited higher dissolution rate compared to the oxalate salt, which is correlated with its (former) lower melting point and higher crystal surface area.

The influence of HCl and NaOH activation on kaolinite to synthesize acid and base activated kaolinite (AAK and BAK) as catalyst supports for nickel oxalate precursor synthesized via oxalic acid functionalization (OAF) was explored in the study. For comparison, another catalyst was synthesized via incorporation of nickel nitrate salt into the activated supports and the catalysts were calcined at 700 °C. The characterization results confirmed that while acid treatment reduced the crystallinity of Kaol, base treatment transformed Kaol into sodalite-zeolite according to the XRD and FESEM results. The Ni nanoparticle (NP) sizes on nickel supported on AAK (Ni/AAK-700) were nine times larger than Ni particle sizes on nickel supported on BAK (Ni/BAK-700) which itself is 1.42 times smaller than the Ni NP in oxalic acid-functionalized Ni supported on BAK (NiOL/BAK-700). The XPS Ni2p peak of Ni/BAK-700 was observed to shift towards higher binding energy signifying a higher degree of metal-support interaction with increased H2 reduction difficulty. A reversed phenomenon was observed for NiOL/BAK-700. The samples basicity followed the order Ni/BAK-700 > NiOL/BAK-700 > NiOL/BAK-800 > Ni/AAK-700, while the acidity followed the reverse. These results provide insights into modified Kaol supported Ni catalysis for various applications based on the required physicochemical properties.

MicroRNAs are key regulators of the normal kidney function and development, and altered in acute kidney injury (AKI). However, there is a lack of studies comparing serum and urine miRNA expression in toxic AKI in humans. We aimed to compare the global signature of urinary and serum microRNAs, with and without kidney injury, after human oxalic acid poisoning. We profiled urinary microRNAs in patients who ingested oxalic acid and developed no injury (No AKI n = 3), moderate injury (AKIN2 n = 3) or severe injury (AKIN3 n = 3) and healthy controls (n = 3). We validated a signature of 30 urinary microRNAs identified in the discovery profiling, in a second cohort of individuals exposed to oxalic acid (No AKI n = 15, AKIN2 n=11 & AKIN3 n= 18) and healthy controls (n=-27) and we compared the results with previously published serum data. Global profiling in toxic AKI patients showed a higher expression of urinary microRNAs and lower expression of serum microRNAs. Most urine microRNA in the validation cohort were significantly upregulated (25/30, fold change >2.8 and p < 0.05) in AKIN2/3 patients compared to No AKI. Four urinary microRNAs (miR-191, miR-19b, miR-20a and miR-30b) had good diagnostic performance (AUC greater than 0.8) to predict AKIN2/3 between 4-8 hours post ingestion. Poisoning irrespective of AKI led to significantly lower expression of many microRNAs in serum but relatively few changes in urinary miRNA expression. In conclusion, urinary microRNA signature provides a stronger measure of AKI in oxalic acid poisoning compared to serum microRNA. Kidney injury has the greatest impact on urinary microRNA, while poisoning itself was better reflected in serum miRNA. Plasma and urinary microRNAs signatures provide complementary information in toxic kidney injury.

Fructose was converted to 5-hydroxymethylfurfural (HMF), an important biomass-derived platform chemical, under mild conditions (100–130 °C) with several organic acids including p-toluene sulfonic (pTSA), oxalic, maleic, malonic and succinic acids as the catalysts. The process kinetics was compared considering fructose dehydration to HMF as the objective reaction and condensation of fructose and HMF to humin and rehydration of HMF as the main side reactions. DMSO was found to be the most effective solvent reaction medium to obtain high fructose conversion and HMF yield. Observed kinetic modeling illustrated that the rehydration and condensation of HMF in DMSO actually could be neglected, especially for the oxalic acid catalyzed system. The determined observed activation energy for fructose conversion to HMF and humin in DMSO medium was 33.75 and 24.94 kJ/mol for pTSA catalyzed system, and 96.51 and 78.39 kJ/mol for oxalic acid-catalyzed system, respectively. HMF yields of 90.2% and 84.1% were obtained for pTSA and oxalic acid catalyzed systems, respectively.

Thermochromic materials have attracted the attention of scientific and technological researchers due to their ability to change color depending on the temperature. Vanadium dioxide (VO2) is capable of considerable polymorphs and has aroused interest mainly because its metal–insulator transition (MIT) presents a thermochromic characteristic at a relatively low temperature. This work aimed to obtain vanadium oxide nanostructures using hydrothermal synthesis to tune the MIT temperature. Ammonium metavanadate or vanadium pentoxide was used as a precursor of vanadium, oxalic acid as a reducing agent, and sodium molybdate as an additive. The starting materials were homogenized and inserted in a hydrothermal reactor at 180 °C. After 24 h of synthesis, part of the resulting product was heat-treated at 400 °C for 3 h. The powders obtained were characterized by their structure, morphology, and thermal properties. The results showed a fiber/rod-shaped VO2 (M) morphology. Distinct strategies were used to obtain the crystalline phase of interest (VO2(M)), and the presence of a reversible change occurring at ~68 °C was evaluated according to the parameters from the VO2 phase transition. The addition of sodium molybdate favored a 22% reduction in the MIT temperature when the precursor used was vanadium pentoxide, indicating possible doping in the structure increased the effects of smaller crystallite size and the presence of crystalline phases. This work opens new perspectives for applications of the vanadium oxides obtained, such as in thermal sensors and/or intelligent materials.

The extraction of Sc by acid leaching with CaF2 and solvent extraction with P507 from red mud was proposed. The influence of acid leaching and solvent extraction on recovery of Sc was investigated. The CaF2 can obviously improve the leaching efficiency of Sc and reduce the acid consumption. The leaching efficiency of Sc increases from 74% to 92% and the dosage of acid reduces under suitable conditions by adding 5% CaF2. The minerals in red mud can easily be decomposed and leached into the acid solution with CaF2 through analysis of XRD pattern. The particles of red mud become smaller and multihole. The Sc can be selectively extracted with 10% P507 at the pH value of 0.1 from the acid leaching solution. More than 98% of Sc and less than 10% of Al and Fe are extracted. The Sc2O3 with purity of 99% is obtained after the process of reverse extraction with NaOH, H2SO4 dissolution, precipitation by oxalic acid and roasting at 750 °C.

Chitosan/aroylhydrazine composite were synthesized in hydrogel form in which aroylhyrazines, heteroaroylhydrazines as well as p-tolylsulphonylhydrazine embedded in the cross linked Chitosan/oxalic acid network. Their structures were characterized by (elemental analysis, FT-IR, 1H NMR, and XRD). Antimicrobial behavior and Cytotoxicity screening of the examined compounds against breast, colon and hepatocellular cancer were investigated. The obtained data revealed that the examined compounds have promising cell growth inhibitory effect on the cell lines as compared to standard. Also, some of the newly synthesized derivatives had shown better antibacterial and antifungal activities, comparing with that of the parent chitosan.

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.