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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, 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.

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.

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.

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.

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.

In this study, expanded graphite (EG) was prepared by the oxidation and intercalation of the natural flake graphite using perchloric acid and potassium permanganate at different expansion temperatures (300, 400, 500, and 600°C), and were characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). EG prepared at 500°C was found to be highly effective for the mineralization of oxalic acid aqueous solution during ozonation at pH 3, which was ascribed to the formation of hydroxyl radicals from the surface reaction of surface hydroxyl groups on EG with ozone. The performance of expanded graphite in this catalytic system was basically unchanged after three repeated use. The presence of Cl−, SO42−, HPO42−/H2PO4− and NO3− could inhibit the degradation of oxalic acid in catalytic ozonation with EG. Degradations of oxamic acid and pyruvic acid in catalytic ozonation with EG were pH-dependent, which were lower than that of oxalic acid. The degradations of oxalic acid and oxamic acid were identified as mineralization process by the determination of TOC, while pyruvic acid may transform into organic products such as acetic acid by O3/EG. Manganese ion (Mn2+) could promote the degradation of oxalic acid by O3/EG at pH 3 because permanganate was produced by O3/EG in oxalic acid solution and then reacted with oxalic acid readily at acidic pH. Catalytic ozonation by EG exhibited great application potential for the destruction of refractory organic compounds.

The increase of harmful carbon monoxide (CO) caused by incomplete combustion can affect human health even lead to suffocation. Therefore reducing the CO discharged by vehicles or factories is urgent to improve the air quality. The spinel cobalt (II, III) oxide (Co3O4) is an active catalyst for CO abatement. In this study, we tried to fabricate dispersing Co3O4 via the dispersion-precipitation method with acetic acid, formic acid, and oxalic acid as the chelating dispersants. Then, the asprepared samples were calcined at 300 ºC for 4 h to obtain active catalysts, and assigned as Co(A), Co(F) and Co(O) respectively, the amount of the dispersants used are labeled as I (0.12 mole), II (0.03 mole) and III (0.01 mole). For comparison, another CoAP sample was prepared via alkaliinduced precipitation and calcined at 300 ºC. All samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), scanning electron microscope (SEM), and nitrogen adsorption/desorption system, and the catalytic activity focused on the CO oxidation. The influence of chelating dispersant on the performance of abatement of CO was pursued in this study. Apparently, the results showed that the chelating dispersant can influence the catalytic activity of CO abatement. An optimized ratio of dispersant can improve the performance, while excess dispersant lessens the surface area and catalytic performance. The series of Co(O) samples can easily donate the active oxygen since the labile Co–O bonding and indicated the preferential performance than both Co(A) and Co(F) samples. The nanorod Co(O)-II showed preferential for CO oxidation, T50 and T90 approached 96 and 127 ºC, respectively. Also, the favorable durability of Co(O)-II sample maintains 95% conversion still for 50 h at 130 ºC and does not emerge deactivation.

Batch adsorption experiments were carried out to eliminating Congo red (CR) and methylene blue (MB) from aqueous solution using oxalic acid-modified jujube shells of Ziziphus lotus (OA-JS)/ZnFe2O4(OA-JS@ZnFe2O4) nanocomposite as a high efficient adsorbent. The Fourier transform infrared (FTIR), Brunauer Emmett Teller, thermogravimetric analysis–differential scanning calorimetry, scanning electron microscope, transition electron microscope, and X-ray diffraction techniques were used to characterize the OA-JS@ZnFe2O4. The equilibrium data fitted to Langmuir isotherm and the maximum adsorption capacities were determined as 980.39 mg g−1 and 476.18 mg g−1 for CR and MB, respectively. The pseudo-second-order model could be best described the sorption kinetics. The calculated thermodynamic suggests that the CR and MB adsorption on OA-JS@ZnFe2O4 is spontaneous and endothermic. The OA-JS@ZnFe2O4 recycled, and the removal CR and MB were 82.08% and 76.59% after seven cycles, respectively. The synthesis of OA-JS@ZnFe2O4 nanocomposite showed excellent potential adsorbent for dye removal from wastewaters.

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.

Mesoporous SBA-15-type silica, with cylindrical pores hexagonally ordered, was obtained and modified with niobium oxide in a highly dispersed way. Subsequently, a further modification with cobalt hematoporphyrin was performed. The ordered pore structure of the SBA-15 was preserved after successive modifications, maintaining its textural properties. The material was used to modify a carbon paste electrode that was successfully applied to the individual and simultaneous detection of both oxalic acid and uric acid, by using cyclic voltammetry and differential pulse voltammetry. For individual evaluation, the obtained detection limits for oxalic acid and uric acid were 9.94 and 0.17 μmol∙L−1, respectively. However, for the simultaneous evaluation of both analytes, the detection limits were 2.83 and 0.14 μmol∙L−1, for oxalic acid and uric acid, respectively.

Amides were synthesized in 1:1 and 1:2 molar ratios of amber and oxalic acid with monoethanolamine. IR-spectra of the obtained substances were drawn, the structures were determined and confirmed, physicochemical properties were studied. 10% aqueous solutions of these substances were prepared, physicochemical properties were determined and bactericidal properties were studied. Bactericidal efficacy of amber acid N-mono­ethanolamide was 82.9% at 25 mg/l of concentration, 88% at 50 mg/l and 95% at 100 mg/l of concentrations. Bactericidal efficacy of amber acid N1, N2 - bis-monoethanolamide was 69% at 25 mg/l of concentration, 83.2% at 50 mg/l and 90% at 100 mg/l of concentrations. The bactericidal effect of oxalic acid has also been studied N-mono­ethanolamide was 82% at 25 mg/l of concentration, 91% at 50 mg/l and 97% at 100 mg/l of concentrations. Bactericidal efficacy of amber acid N1, N2 - bis-monoethanolamide was 85% at 25 mg/l of concentration, 94% at 50 mg/l and 97.6 at 100 mg/l of concentrations. Key words: amber acid, oxalic acid, bactericidal efficacy, N-monoethanolamide, N1,N -bis-monoethanolamide

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.

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 production of oxalic acid from sawdust using a mixture of strong nitric acid and concentrated sulphuric acid with coal fly ash as a catalyst has been explored. Operating parameters affecting the reaction were determined to be temperature, mesh size and amount of fly ash catalyst, time and the $${\text{HNO}}_{3} :{\text{H}}_{2} {\text{SO}}_{4}$$ HNO 3 : H 2 SO 4 ratio. A maximum oxalic acid yield of 84% was obtained using a mixture of 60% $${\text{HNO}}_{3} {\text{ and }}40 \%{\text{ H}}_{2} {\text{SO}}_{4}$$ HNO 3 and 40 % H 2 SO 4 at 70 °C and a reaction time of 150 minutes. Coal fly ash with particle size of 50–100 μm proved to be a suitable and efficient catalyst, and the optimum quantity of catalyst employed was 5g of fly ash for every 100g of sawdust.

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.

A search is initiated for new solvents for liquid–liquid extraction (LLE) chemistry of actinides for future separations. Of late, reports on deep eutectic solvents (DES), which resemble ionic liquids, are on the rise. Two hydrophobic DES based on tri–n-octylphosphine oxide (TOPO) and simple dicarboxylic acids, namely, oxalic acid and its higher homologue, malonic acid are prepared and characterized by FT-IR, UV–Vis, water content, density and viscosity measurements. The LLE chemistry of U(VI) and Am(III) is carried out using the above DES as a function of a few parameters and UV–Vis and IR spectra of the extracted phases were also recorded. The results are discussed with appropriate explanations in this report.

In this research, Zn, Ni, and Cu recovery from mobile phone printed circuit boards was investigated. The initial pH and pulp density using Aspergillus niger or Penicillium simplicissimum fungi were optimized to improve the recovery of Zn, Ni, and Cu using a central composite design. Fungi were able to recover 97% of Cu. Often for Ni recovery, A. niger was more effective, but in low pulp densities and low pH, P. simplicissimum was preferred. For recovery of Zn, A. niger is more appropriate at pH lower than 6, but P. simplicissimum outperforms at pH higher than 6. Under the optimum conditions (pulp density of 4 gL−1 and initial pH 10), the respective recovery of Cu, Ni, and Zn was determined as 94%, 100%, and 100% using A. niger as well as 100%, 95%, and 87% using P. simplicissimum. At alkaline conditions, oxalic acid, citric acid, and gluconic acid are the main acids produced by A. niger; the main acid produced by P. simplicissimum is oxalic acid. Similarly, FTIR and chemical characteristics of the metabolites (the organic acid produced) were analyzed under optimal conditions using HPLC. A. niger in alkaline and acidic conditions produces more acids which lead to higher recovery.

To co-extract vanadium, titanium, and chromium from vanadium slag, a cleaner process featuring oxalic acid hydrothermal leaching with synergy of Fe powder was proposed in this paper. With the leaching temperature of 125 °C, oxalic acid concentration of 25 wt pct, liquid-to-solid mass ratio of 8:1, leaching time of 90 minutes, and iron powder addition of 3.2 wt pct, the leaching extents of vanadium, titanium, and chromium can reach up to 97.9, 98.4, and 93.3 pct, respectively. The non-toxic residue is mainly composed of FeC2O4·2H2O, MnC2O4·2H2O, and amorphous SiO2. Compared with the traditional sodium roasting-water leaching and calcification roasting-acid leaching processes, this novel process is possessed of two prominent advantages. Firstly, without the roasting step, the process is simplified significantly and the energy consumption is reduced greatly. Secondly, the valuable components titanium and chromium which cannot be extracted by the traditional processes are leached synchronously and efficiently.

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.

Актуальность исследования обоснована целесообразностью создания благоприятных условий при проведении термохимической обработки топливных фрагментов с целью обеспечения одновременной трансформации керамического топлива в порошкообразный материал и полного высвобождения продукта реакции из оболочки, а также удаления из топливной композиции перед гидрометаллургическими операциями летучих продуктов деления (тритий, иод-129, углерод-14, радиоактивные благородные газы). Цель: определить основные технологические параметры процесса получения окислительной смеси NxOy-O2-СО2-Н2О(пар), пригодной для использования на операции термохимической обработки фрагментов оболочечного топлива на основе диоксида урана керамического качества. Объекты: раствор смеси азотной и щавелевой кислот, окислительная смесь NxOy-O2-СО2-Н2О(пар), образец необлученного твэл на основе диоксида урана. Методы: экспериментальные исследования, кондуктометрическое и потенциометрическое титрование, гравиметрический и рентгенофазовый анализ, морфологические исследования, газовая хроматография. Результаты. Исследованы основные физико-химические закономерности процесса получения окислительной смеси NxOyO2-СО2-Н2О(пар) для термохимической обработки топлива на основе диоксида урана. Установлено, что при пропускании раствора смеси кислот (азотная кислота - 380 г/л, щавелевая кислота - 80 г/л) со скоростью 5 колон. об/час через слой катализатора Pt/Cr2O3/ZrO2 при температуре 368-373 К происходит образование газового потока, содержащего 26 об. % диоксида азота, 20 об. % монооксида азота, 44 об. % диоксида углерода, 10 об % паров воды. Доокисление монооксида азота и каталитическую активацию полученного газового потока предпочтительно проводить на насадке Pt/Cr2O3/ZrO2 при температуре 413 К и соотношении высоты насадочного слоя к диаметру колонны 5:1, в результате чего полученная окислительная смесь соответствует следующему составу: 41 об. % диоксида азота, 6 об. % монооксида азота, 42 об. % диоксида углерода, 6 об. % паров воды, 5 об % кислорода. Показана принципиальная возможность трансформации керамического топлива на основе необлученного диоксида урана, заключенного в циркониевую оболочку, в порошкообразный октаоксид триурана с использованием в качестве окислителя каталитически активированной смеси NxOy-O2-СО2-Н2О(пар). Получен порошкообразный материал, полностью отделенный от циркониевой оболочки, который по результатам рентгенофазового и гравиметрического анализа (соотношение O/U=2,67) соответствовал брутто-формуле U3O8. The relevance of the research is based on the rationale for creating suitable environment for fuel thermochemical treatment to ensure simultaneous ceramic fuel conversion into powder-like material, complete recladding of reaction product, and volatile fission products entrapment (tritium, iodine-129, carbon-14, radioactive noble gases) from fuel composition prior to hydrometallurgical processes. The main aim is to find main process parameters of NxOy-O2-CO2-H2O(steam) oxidizing mixture which can be used for thermochemical treatment of cladded fuel containing ceramic uranium dioxide. Subjects: solution of nitric acid and oxalic acid composition, NxOy-O2-CO2-H2O(steam) oxidizing mixture, sample of new fuel element containing uranium dioxide. Methods: investigational studies, conductometric and potentiometric titration, gravimetric and and X-ray phase analysis, morphological studies, gas chromatography. The results. The main physical and chemical rules of fabricating NxOy-O2-CO2-H2O(steam) oxidizing mixture were studied for thermochemical treatment of fuel containing uranium dioxide. It was found that generation of gas bearing nitrogen dioxide (26 vol. %), nitrogen monoxide (20 vol. %), carbon dioxide (44 vol. %) and water vapor (10 vol. %) was the result of passing acids mixture (nitric acid - 380 g/l, oxalic acid - 80 g/l) at the rate of 5 column volumes per hour through Pt/Cr2O3/ZrO2 catalyst layer at 368-373 K. It is preferable to implement nitrogen monoxide full oxidation and gas catalytic activation by means of Pt/Cr2O3/ZrO2 packing at 413 K and height of packed bed to column diameter ratio as 5:1. Upon doing that, oxidizing mixture has the following composition: nitrogen dioxide (41 vol. %), nitrogen monoxide (6 vol. %), carbon dioxide (42 vol. %), water vapor (6 vol. %) and oxygen (5 vol. %). Ability in principle to convert ceramic fuel containing nonirradiated uranium dioxide in zirconium cladding into powder-like triuranium octoxide was proven by using NxOy-O2-CO2-H2O(steam) mixture as an oxidizing agent following catalytic activation. We made powder-like material separated from zirconium cladding in full which corresponds to molecular formula U3O8 from X-ray phase and gravimetric analyses, O/U=2,67.

The valorization of hemicellulose isolated from lignocellulosic biomass (wheat straw, rice husk, and bagasse) to furfural was achieved by pH-controlled acid catalysis using choline-based Brønsted acidic (BA) and natural acidic (NA) deep eutectic solvents (DES) serving both as catalyst and solvent. The effect of pH variation on the catalytic activity of various BADES and NADES prepared in 1 : 1 molar ratio was observed, and choline chloride/p-toluene sulfonic acid (ChCl/p-TSA) was found to be the best with lower pH value of 1.0. The yield of furfural decreased from 85 to 51 % with increase in pH from 1.0 to 3.0. The molar ratio of hydrogen bond donor to acceptor components was varied from 1 : 1 to 1 : 9 to achieve the lowest possible pH values of the DESs and to increase the furfural yield. Further optimization of reaction conditions was also done in terms of DES loading, time of reaction, and temperature using the model DES to achieve higher furfural yield. The best results were obtained using 5 mmol DES at pH 1.0 in 1.5 h at 120 °C. ChCl/p-TSA and ChCl/oxalic acid among BADES and ChCl/levulinic acid among NADES investigated in this work yielding 85 % furfural were found to be most efficient. The reported methodology is advantageous in terms of using bio-based green solvents, mild reaction conditions, and efficient scale-up of the reaction. The DESs were found to be efficiently recyclable up to five consecutive runs for the process.

Red mud is a polymetallic waste generated during Bayer's process of alumina production. High alkalinity (pH > 11), multiple elements, and micron-sized particles make red mud recycling energy-intensive and challenging. The following work presents a hydrometallurgical flowsheet for separation of different red mud elements and recovery of high purity Fe (II) product using cost-effective reagents, energy-efficient processes, and minimal waste generation. Red mud preprocessing was carried out by mild hydrochloric acid wash (1 M, 13 pct pulp density, 40 °C 15 minutes), followed by leaching of hematite from neutralized red mud in oxalic acid (2 M, 10 pct pulp density, 95 °C, 2.5 hours). UV light-assisted photochemical reduction of oxalic leach solution of red mud separated more than 98 pct Fe in the form of ferrous oxalate (purity more than 99 pct) within 5 hours. The process's material balance shows a overall recovery of more than 85 pct Fe value as solid ferrous oxalate of high purity and concentrating titanium oxide in the residue and aluminum in the leaching solution.

An efficient and simple process was developed to extract valuable metals from monazite ore. Monazite was subjected to acidic digestion. Then isopropyl alcohol as a miscible solvent was added in different ratios. The produced REEs were purified with Dowex 50 cation-exchange resin. 4 M HCl was used for the complete REEs elution. Thorium was separated by precipitation with 20% oxalic acid. Uranium was separated using Dowex 1 anion-exchange resin, eluted with acidified sodium chloride (1 M NaCl + 0.15 M H2SO4), and precipitated at pH 7.5.

A great amount of poultry feathers wastes are produced every year in the world, leading to the discard of keratin resources and causing environmental pollution. The recycling of poultry feathers keratin is of great significance to the protection of environment and utilization of resource. In this work, poultry feathers were dissolved in a dissolution system composed of deep eutectic solvent (choline chloride (ChCl) and oxalic acid (OA) mixed in a certain molar ratio) and deionized water. After dissolution, dialysis, and filtration, the water soluble and insoluble extraction fractions were obtained and separated. The effects of dissolution system composition, dissolution temperature, and dissolution time on the dissolution of poultry feathers and keratin extraction were evaluated. Under the dissolution conditions of ChCl/OA=1:2, mwater=30 wt%, 80 °C×6 h, the dissolution rate of poultry feathers reached more than 90 %, and the total extraction yield was nearly 30 %. The results of SEM, FTIR, Raman spectra, and XRD data showed that the secondary structure of poultry feathers’ macromolecules changed obviously during the process of dissolution and extraction. The results of TGA and DTG showed that insoluble extraction fraction had better thermal stability than soluble extraction fraction.

A biocomposite system was developed and tested for the removal of the azo dye Reactive Red (RR195) from wastewater. The biocomposite was synthesized using ceramic particles containing 75% alumina which were coated using chitosan cross-linked with oxalic acid. The biocomposite showed high performance at low pH (maximum adsorption capacity = 345.3mg.g−1 at pH=2.0). The physicochemical and structure characteristics of the matrix were evaluated by Z-potential, FTIR-ATR, SEM-EDS, XRD, and porosity. Langmuir sorption isotherm and pseudosecond-order model gave the best fit. The electrostatic interaction between RR195 (due to the sulfonate groups) and the free amino groups of chitosan, enabled successive desorption/regeneration cycles. The maximum removal percentage (>80%) occurred at pH=2.0 due to the cross-linking effect. Experiments at different temperatures allowed the calculation of thermodynamic parameters (ΔG, ΔS, ΔH); adsorption was spontaneous, exothermic, and enthalpy controlled. The presence of inorganic ions ( $$ {\mathrm{SO}}_4^{2-}>\mathrm{N}{\mathrm{O}}_3^{-}>{\mathrm{Cl}}^{-} $$ ) was analyzed during the adsorption process. This novel biocomposite can be applied as a cost-effective and environmentally friendly adsorbent for anionic azo dye removal from wastewater. The application of chitosan cross-linked with oxalic acid as a coating of the ceramic support enhanced the adsorption capacity and enabled its use under acidic conditions without solubilization.

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.

A procedure is developed for the separate determination of the Sn(II) and Sn(IV) in the range of 0.05–0.25 M in acidic aqueous and ethylene glycol solutions in the presence of Ni(II), Cu(II), F–, a surfactant (OS-20), and citric or oxalic acids. The direct iodatometric titration of Sn(II) is used before and after the reduction of Sn(IV) with aluminum. The procedure is applicable to the analysis of electrolytes for the deposition of tin and Ni–Sn and Cu–Sn alloys and can be used to monitor changes in the concentrations of Sn(II and IV) as a result of redox processes in electrolytes and the hydrolysis of tin compounds. The interfering effect of copper consists in the interaction of Cu(II) with Sn(II) and Al with the formation of Cu(I) ions, reacting with iodate ions, and is eliminated by the introduction of oxalic acid. The relative error in determining the concentration of tin in the absence of copper(II) ions and in the presence of other components does not exceed 2.2%, and in the presence of Cu(II) the error is 4.3%.

Manganese nodules from ocean bed are potential resources of Cu, Ni, and Co for which land-based deposits are scarce in India. The present work describes a novel approach of using glycerol, a nontoxic biomass-derived reductant, for the reductive acid leaching of manganese nodules. Parameters such as acid concentration, time, temperature, and pulp density were optimized for leaching. The optimal leaching conditions were found to be 10% (w/v) pulp density and 10% (v/v) H2SO4 at 80 °C with 1% (v/v) glycerol yielding >95% of Ni and >98% Cu, Co, and Mn extraction within an hour. Kinetic analysis of the data based on the initial rate method showed that the leaching process was chemical reaction-controlled with an apparent activation energy of 55.47 kJ/mol. Various oxidation intermediates of glycerol formed during leaching were identified using mass spectrometry and Raman spectroscopy, and a probable oxidation pathway of glycerol during the leaching process has been elucidated based on the analysis. Glycerol was oxidized to glyceraldehyde, glyceric acid, tartronic acid, dihydroxyacetone, hydroxy pyruvic acid, glyoxalic acid, oxalic acid, and finally converted to CO2 during leaching. The fast reaction kinetics, near-complete dissolution of manganese, and other associated metals in the nodule can be attributed to the participation of all intermediate products of glycerol oxidation in redox reactions with MnO2, enhancing the overall reduction leaching efficiency.

This work reports a study of the extraction of iron (III) deeply from the chromium sulphate solution in which most of the iron was precipitated with oxalic acid. Di(2-ethylhexyl)phosphoric acid (P2...

The article presents the results of studies on preparation of amorphous zirconium dioxide from zirconium nitrate by its hydrolysis in the presence of oxalic acid. It is determined that the balance of reagents taken for synthesis (1 ml 0,025 M ZrO(NO3)2 is 1.35 ml 4 M HOOC-COOH), and the optimum temperature of the received gel drying, which is 230 ̊С, is established, too. Morphology of the obtained ZrO2 samples was explored. It has been found that the calcining temperature is independent of the size and shape forming irregular agglomerates, consisting of smaller spherical particles, whose diameter varies between 50 and 300 nm. The X-ray analysis of the sample is represented, which showed a low degree of crystallinity of the substance. IR spectroscopy data showed the presence of zirconium dioxide-characteristic peaks on the IR spectrum. The same spectrum reflects the presence of a large amount of sorbed water in the obtained sample, as well as peaks characteristic of the gas adsorbed by the sample from the environment.

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.

Phase-pure alpha-iron-oxide (α-Fe2O3) nano-powders were obtained via Pechini gel-combustion using iron nitrates as an oxidant and different organic compounds (L-alanine, glycine, citric acid, oxalic acid, tartaric acid and urea) as fuels. The complex precursors isolated before the system's combustion were characterized by thermal analysis (TGA). After combustion, the as-synthesized powders were calcined at 600°C to obtain the α-Fe2O3 phase and eliminate the residual carbon. The powders prepared using different fuels were characterized using x-ray diffraction and field emission scanning electron microscopy. n-type gas sensitivity of thick film resistive sensors fabricated by using α-Fe2O3 powders was investigated in detail and it was observed that amongst the different fuels, citric acid-derived α-Fe2O3 is methane selective at 120°C operating temperature, examined in the presence of other similar types of resistive gas analyses of the same concentrations.

Hydrometallurgical extraction of strategic metals from exhausted Li-ion batteries has been explored using sequential application of biodegradable oxalic acid and sulfuric acid solutions. Following L25 orthogonal design of experiment (DoE), optimized extraction of > 99% Li and Cu with organic acid was achieved using a H2C2O4 concentration of 0.25 mol L−1, solid–liquid ratio of 10%, H2O2 at 0.5%, temperature of 80°C, and duration of 90 min. Subsequently, leaching of the residual mass in mineral acid yielded 99% efficiency of Ni, Co, and Mn at the optimal condition of H2SO4 concentration of 3.0 mol L−1, solid–liquid ratio of 6%, H2O2 at 2%, temperature of 60°C, and duration of 120 min. Fitting of the kinetic data using a logarithmic rate law revealed that, except for Cu that followed an intermediate-controlled mechanism with Ea = 27.6 kJ mol–1, all the other metals exhibited a diffusion-controlled mechanism with Ea < 12 kJ mol–1. Not only does this study demonstrate selectivity that will be beneficial to downstream processing, but the use of DoE also makes it applicable industrially.

In the preparation process of magnesium-cobalt nano-ferrite powder (Mg0.1Co0.9Fe2O4) by sol–gel self-propagation method, the effect of complexing agent on the nanostructure and magnetic properties of ferrite is studied by changing the type of complexing agent (the complexing agent includes citric acid, oxalic acid, tartaric acid, glucose, and egg white). The XRD pattern of each sample has eight distinct characteristic peaks, and the number of the strongest peak in each map is one [i.e., (311) peak]. All these evidences can preliminarily indicate that the sample has a spinel structure. In addition, in the FTIR of the sample, it can be seen that there are several distinct characteristic peaks at 580 cm−1 (i.e., Fe–O peak, etc.) which can also prove the structural characteristics of the sample. In the SEM map, the sample can be seen to have an elliptical shape with a crystalline grain size between 28 and 50 nm. From this, we can guess that the complexing agent participates in the reaction and has a certain influence on the particle size of the sample. Elemental analysis showed that all the six samples prepared contained magnesium, cobalt, iron, and oxygen, and then we quantitatively analyzed the sample to find that the prepared sample was the target product. The BET test shows that a sample is prepared with glucose as the complexing agent, the specific surface area of it can be increased. The VSM data show that magnesium–cobalt ferrite powder with high saturation magnetization, residual magnetization, and coercivity can be prepared by selecting glucose as the complexing agent.

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...

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.

Organic acids such as citric acid, itaconic acid and oxalic acid synthesised by Aspergillus niveus were used for the bioleaching of metals from waste printed circuit boards. Bioleaching of valuable metals was performed in one‐step, two‐steps and spent medium approaches using A. niveus. In the absence of waste printed circuit boards (WPCBs), the dry cell weight of A. niveus was higher when compared with the presence of WPCBs. Variations in the dry cell weight were observed for the presence of different particle sizes. The increase in itaconic acid and oxalic acid synthesis was found at a reduced particle size (60–80 mesh) and reached the maximum titre of itaconic acid (22.35 ± 0.87 mM) and oxalic acid (12.75 ± 0.54 mM) in 12 days during the two‐step bioleaching. The maximum recovery of 75.66% Zn, 73.58% Ni and 80.25% Cu from WPCBs was achieved in 15 days in two‐step leaching with particle sizes of the mesh being 60–80.

Anodic Alumina Oxide (AAO) is one of the nanomaterials that have developed as a template in the nanowires, nanodots and nanotubes. This research focuses on synthesizing AAO by two different electrolytic solutions which are using sulfuric acid (H2SO4) and oxalic acid (C2H2O4) by electrochemical anodization method. Two parameters were influencing the anodization process in the experiment; the type and the concentration of the electrolytic solution. The effects of the different type of electrolytic solutions produced different size of pores. When the voltage used is 25 V in H2SO4, the optimum reading size of the nanopores is in the range of 16-22 nm, whereas the AAO pores in C2H2O4 are in the range of 100-200 nm. Meanwhile, the concentration of H2SO4 and C2H2O4 is set to be 0.3 M, 0.4 M and 0.5 M., The results in 0.3 M H2SO4 and C2H2O4, show the optimum concentration of electrolytic solutions which is the key parameter affecting the morphological structure of porous membranes in AAO. The optimum value for these two acidic solutions has produced such highly ordered arrangement of nanopores which are from the average size of nanopores that anodized in sulfuric acid is 19 nm while 120 nm in oxalic acid. The morphological structure properties of AAO templates include the diameter of nanopores, the thickness of membrane and density of nanopores would be examined by Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray (EDX). Also, Fourier-transmittance infrared spectroscopy (FTIR) detected the chemical functional group of bonds in AAO. In conclusion, AAO templates have a big potential to be the major contributor in the future for the development of new electronic devices.

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.

In this study, oxalic acid has been successfully loaded on Fe3O4/PEG-400 under ultrasonic irradiation and Fe3O4/PEG/oxalic acid as a new nanomagnetic catalyst has been synthesized. The chemical structure of the catalyst has been investigated by FT-IR spectrum, XRD, EDX and SEM methods. The catalyst has been used for the synthesis of 3-acyl-5-hydroxy-3-pyrrolin-2-one derivatives from the corresponding aldehydes, anilines and dimethyl acetylenedicarboxylate (DMAD) by one-pot and three-component the MCR reaction in the excellent yields (90-95 %) of products within 24 hours at room temperature. The fourteen samples are available. The recovered catalyst could be satisfactorily used for the second and third run without regeneration. This method has green and eco-friendly profile. Also, this research introduces an improvement mechanism for the types of this reaction. The chemical structures of new compounds have been characterized by FT-IR, 1H-NMR, 13C-NMR, and Mass spectra.

In this study we used a chemical solution method from oxalic acid (OX. acid) and zinc acetate (ZnAc) to prepare Zinc Oxide nanoparticles (ZnONPs) and Zinc Oxide nanoparticles doped with Chlorine (Cl:ZnONPs). The characterizations (FTIR, X-ray, SEM, TEM) of ZnONPs and Cl:ZnONPs were determined. Amylase inhibitors of ZnONPs and Cl:ZnONPs also were determined. SEM indicated that the ZnONPs and Cl:ZnONPs have an average particle size of 46.65 - 74.64 nm. TEM images of the ZnONPs and Cl:ZnONPs showed the round shaped. Compounds b, d and e exhibited significant inhibitory activity against amylase enzyme (from 69.21 ± 1.44 to 76.32 ± 0.78), respectively, and were comparable with that of acarbose (86.32 ± 0.63) at 1000 μg, thereby, projecting ZnONPs and Cl:ZnONPs as α-amylase inhibitors.

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.

In this work, COF-LZU1@PEI@Fe3O4 was synthesized by immobilization of COF-LZU1 onto the surface of polyethyleneimine-functionalized Fe3O4 nanoparticles (PEI@Fe3O4) and employed as an adsorbent for magnetic dispersive micro-solid phase extraction of tetracyclines (TCs). COF-LZU1@PEI@Fe3O4 was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and nitrogen adsorption–desorption isotherms analysis. The optimal extraction and desorption conditions were as follows: 15.00 mL sample solution (pH 7.0) extracted with 5.0 mg of adsorbent for 30 min at 30 °C, and then desorbed with 1.50 mL methanol/acetonitrile/0.02 mol L−1 oxalic acid solution (v/v, 1 : 2 : 7). Good linearities were obtained between the peak area and TC concentration ranging from 5–500 μg L−1 with correlation coefficients (R2) higher than 0.9992 and limits of detection lower than 0.51 μg L−1. The relative standard deviations (RSDs) of intra-day and inter-day were less than 5.7% and 7.4%, respectively. The developed method was successfully applied to the determination of TCs in environmental water samples with recoveries in the range of 87.0–113.8% and RSDs less than 5.1%, suggesting great potential of COF-LZU1@PEI@Fe3O4 for efficient extraction and analysis of trace TCs in water samples.