Initial Concentration Of Oxalic Acid Research Articles

Catalytic Ozonation by Copper Modified Sepiolite for the Degradation of Oxalic Acid in Water

ABSTRACT Copper modified sepiolite (Cu-SEP) with high catalytic activity was successfully prepared and used in ozonation to remove oxalic acid from water. The influence of Cu-SEP dosage, initial pH, ozone dosage and initial oxalic acid concentration on the removal of oxalic acid in heterogeneous catalytic ozonation was investigated, and XRD, FTIR, SEM, TEM and XPS were employed to characterize the Cu-SEP to clarify its working mechanism in ozonation. The experimental results showed that under the optimal condition, the removal of oxalic acid could reach 95.8%. Cu element successfully replaced Mg in the sepiolite lattice to form the Cu-SEP, it existed mainly in the form of Cu2+. Cu-SEP contained abundant surface hydroxyl groups, which played an important role in the catalytic ozonation process. With the combination of free radical quenching experiment, the possible mechanism of Cu-SEP catalyzed ozonation to degrade oxalic acid was proposed. After ozonation, Cu-SEP retained the original structure, and exhibited excellent stability and reusability.

Influence of reaction parameters on oxalic acid crystallization using conventional and ultrasonication: Doehlert matrix

The present work aims to optimize the yield of crystallization using conventional and ultrasonic irradiation by using surface response methodology. The experiments were designed with the help of a Doehlert matrix which has not been previously reported. Initially, the solubility curve, induction time estimation and the metastable zone width have been thoroughly investigated. Later, using surface response obtained from statistics software, the effects of initial concentration and saturation temperature, stirring speed and initial concentration, and cooling temperature and stirring speed on yield of crystallization were compared using the conventional method and ultrasound- assisted crystallization. When compared to conventional methods, ultrasound-assisted crystallization has been shown to minimize the maximum reduction of MSZW and induction time. In ultrasound-assisted crystallization, the initial concentration, saturation temperature and stirring speed have been found to have a significant effect on the yield of crystallization than cooling temperature. The maximum yield of crystallization was 96.8% using ultrasound and 75.0% using conventional methods, respectively at an optimal condition of 1200 rpm, 15 °C cooling temperature, 80 °C saturation temperature and initial concentration of oxalic acid 75 g/50 mL of water. In comparison to the ultrasound method, the conventional method produced twice the average crystal size and irregular shape. Overall, the work has clearly established that ultrasound- assisted crystallization gives significant results as compared to the conventional method in terms of yield, metastable zone width, induction time and crystal characteristics.

Band gap tuning of g-C3N4 via decoration with AgCl to expedite the photocatalytic degradation and mineralization of oxalic acid

A series of functional organic–metal AgCl-decorated graphitic carbon nitride (AgCl-CNx) composites were synthesized and applied for the degradation of oxalic acid (OA) under visible light. The highest photocatalytic activity was achieved with AgCl decoration ratio of 1.0 (denoted as AgCl-CN1.0). The pseudo-first-order constant for OA degradation was 0.0722 min−1 with the mineralization efficiency of 90.80% after 60 min reaction in the photocatalytic process with AgCl-CN1.0. A variety of characterization techniques including Brunauer–Emmett–Teller, X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, ultraviolet–visible diffuse reflectance spectra, photoluminescence, and Mott–Schottky were utilized to elucidate the physicochemical, microstructure, and optical properties contributing to the improvement of the photocatalytic performance. The results showed that AgCl-CN1.0 had an oblate flaky erythrocyte-like structure with a moderate band gap energy of ~3.00 eV. In addition, the effects of the key parameters (i.e., AgCl-CN1.0 dosage, initial OA concentration, solution pH, and presence of natural organic matter) on OA degradation were systematically investigated. Radical scavenger experiments indicated that photogenerated holes, electrons, superoxide anion radicals, and hydroxyl radicals were the dominant reactive species. Moreover, AgCl-CN1.0 exhibited excellent stability and reusability for OA degradation without detectable Ag+ release in the solution over multiple reaction cycles. The efficient OA mineralization could be mainly ascribed to the moderate specific surface area, increased numbers of active sites, and effective interfacial charge transfer of AgCl-CN1.0. Overall, the AgCl-CN1.0 composite was demonstrated to be a highly efficient, stable, and recoverable photocatalyst.

Photodegradation of Methylene Blue in Fe<sub>2</sub>O<sub>3</sub>–Oxalate Suspension Under UV Light Irradiation

The aim of this study was to investigate the photodegradation of organic pollutants in natural environment with co-existence of iron oxides and oxalic acid. Methylene Blue (MB) was selected as a model pollutant while Fe₂O₃ was selected as iron oxide. Commercial Fe₂O₃ was calcined at 300°C, 400°C and 500°C and was used to degrade MB in oxalate solutions of different concentration under UV radiation. Adsorption of MB on the surface of calcined Fe₂O₃ was studied and 30 minutes was required to reach the adsorption equilibrium. The effect of the initial concentration of oxalic acid, initial concentration of MB and calcined temperature of Fe₂O₃ on photodegradation of MB in the Fe₂O₃–oxalate suspension under UV light irradiation was investigated. Oxalic acid plays a very important role, no significant degradation of MB was found in absence of oxalic acid in the suspension. But excess concentration of oxalic acid decreases the degradation. Photodegradation of MB increases with increasing calcined temperature of Fe₂O₃ and decreases with increase in MB concentration. Since this process does not require the addition of hydrogen peroxide and shows good efficiency under UV irradiation, it is an economically viable method for pre-treating wastewater containing dye.

Detailed modeling of oxalic acid degradation by UV-TiO2 nanoparticles: Importance of light scattering and photoreactor scale-up

A detailed computational fluid dynamics model is presented that integrates reactor hydrodynamics with advanced light models and UV-TiO2 advanced oxidation kinetics to yield the degradation of oxalic acid in a dispersed-phase photoreactor. Model predictions were first compared against experimental data obtained from the literature and subsequently used in a parametric study for investigating scale-up effects associated with both process and photoreactor variables. Investigated variables included: TiO2 concentration (5–400 mg L−1), initial oxalic acid concentration (0.9–32 mg L−1), lamp irradiance (100–10,000 W m−2), background fluid absorbance (0-30 m−1), reactor size (1/4-4 as relative scaling factor), lamp orientation (0-360°) and flowrate (2.5–10 m3 h−1). The analysis revealed that an optimum in oxalic acid degradation is observed when the TiO2 concentration was controlled in the 20–40 mg L−1 range (depending on lamp irradiance). While lamp orientation showed minimal impact, reactor size and flowrate emerged as key variables for photoreactor design. Moreover, an increase in initial oxalic acid concentration substantially reduced oxalic acid degradation performance observed at high loadings. Also, TiO2 activation and photoreactor degradation performance were impacted negatively by light competition with background fluid absorbance.

Equilibrium and kinetics of biosorption of oxalic acid by wheat straw

Biosorption equilibrium and kinetics of oxalic acid on wheat straw, Triticum aestivum, in an aqueous solution was investigated. Among the models tested, namely the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms, the biosorption equilibrium was best described by Freundlich model. It was also found the biosorption of oxalic acid by wheat straw followed second-order kinetics. The equilibrium amount of oxalic acid adsorbed onto the wheat straw increased with increasing the initial oxalic acid concentration and decreasing adsorbent weight. On the other hand, an increase of temperature decreased the biosorption of oxalic acid. Mean free energy of biosorption (10 kJ/mole) indicates that biosorotion of oxalic acid by wheat straw might follow a chemisorptions mechanism.

Catalytic Photodegradation of Rhodamine B in the Presence of Natural Iron Oxide and Oxalic Acid under Artificial and Sunlight Radiation

AbstractNatural iron oxide was used as catalyst for a heterogeneous photo-Fenton-like process and it was characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, scanning electron microscopy and N2adsorption volumetry measurement. Natural iron oxide consists mainly of hematite (76 %). Rhodamine B was mineralized by iron oxide/oxalic acid/UV system, involving creation of dissolved Fe-oxalate and adsorption of Fe-oxalate on the iron oxide surface. The effects of the initial concentration of oxalic acid and pH value, amount of natural iron oxide and concentration of dye, temperature and sunlight irradiation on the kinetics of photodegradation of rhodamine B were investigated. Excellent degradation rate was achieved with 5 mmol.L−1of oxalic acid at a pH around 2–4. During the process, the formation of Fe2+, H2O2and the pH of the solution were strongly dependent on the initial concentration of oxalic acid. Use oft-butanol (2.0 %) confirms that hydroxyl radicals are the entities responsible for the rhodamine B photodegradation. The use of the natural iron oxide as a catalyst in wastewater treatment is very interesting; because it is an abundant mineral and easy to separate from the solution in the end of treatment.

Electrochemical Incineration of Oxalic Acid at Manganese Dioxide Rotating Cylinder Anode: Role of Operative Parameters in the Presence of NaCl

A detailed experimental study was devoted to the anodic oxidation of oxalic acid using manganese dioxide rotating cylinder anode with the objective to evaluate in a systematic way the effect on the oxalic acid oxidation process of several relevant parameters, including the presence of sodium chloride, the current density (J), the rotation speed, the temperature, and the initial concentration of oxalic acid. Thin manganese dioxide film on graphite substrate has been prepared by electrochemical oxidation from MnSO4-H2SO4 electrolyte. The morphology of this electrode was investigated by XRD, SEM, EDS and AFM techniques. The results show that a firm γ-structure of MnO2 film on graphite rod can be obtained successfully. The results indicate that the presence of NaCl has a vital role on the performance of the oxalic acid incineration process. Also current density has the major effect on the removal and current efficiencies. Positive effect of temperature on the removal and current efficiencies and negative effect of rotation speed were observed. The best adopted operative conditions were T = 50°C, J = 40 mA/cm2 and 200 rpm in the presence of 1g/l NaCl where a conversion of about 97% and a current efficiency close to 55% with energy consumption less than 28 kWh(kg of COD)−1 were obtained after four hours of electrolysis time. The findings of the present research validate that incineration of oxalic acid can be carried out successfully on MnO2 anode.

The effect of oxalic acid activation on the bleaching properties of a bentonite from Milos Island, Greece

AbstractA bentonite from Milos, Greece, was activated with oxalic acid and the effect of acid activation conditions on bleaching of sunflower oil was investigated. The activation parameters studied were temperature, retention time and oxalic acid to bentonite mass ratio. The activated materials produced had good bleaching properties and were suitable for industrial use as bleaching earths. Optimum bleaching properties could be achieved using a variety of combinations of acid to bentonite ratios and activation times. Bleaching efficiency tests indicated that 24 h activation at 100°C with 1m oxalic acid and 25% pulp density (w/v) gave results equivalent to that of a commercial bleaching earth (Tonsil Optimum 210 FF). The combination that is likely to be more preferable on an industrial scale was 100°C, 25% pulp density (w/v), 1m initial oxalic acid concentration, 60% recycling of the oxalate solution (making up an acid to bentonite ratio 0.2 w/w) and 6 h activation time. The materials produced under these conditions have acceptable bleaching properties, corresponding to bleaching capacity greater than 78% compared to commercial Tonsil, and colour index (in red and yellow units) equal or even better than Tonsil.

Adsorption and photodegradation of methylene blue by iron oxide impregnated on granular activated carbons in an oxalate solution

The photocatalytic adsorbents BAU-OA, BAU-CL and BAU-HA with varying iron oxide content (9–10 mass%) were prepared by heat treatment at 250°C from commercial activated carbon (BAU) impregnated with iron oxalate, chloride, tris-benzohydroxamate, respectively. The XRD patterns showed amorphous structure in the BAU-CL sample (SBET 50m2/g) and low crystallinity (as FeOOH and Fe2O3 phases) in the BAU-HA and BAU-OA samples (SBET 4 and 111m2/g, respectively). The methylene blue adsorption capacities was decreased in order of BAU-OA<BAU-CL<BAU-HA sample and the adsorption followed Langmuir model. The apparent MB photodegradation rate constant (kapp) was increased in same order BAU-HA<BAU-CL<BAU-OA under the standard experimental conditions (initial MB concentrations 0.015–0.025mM; sample content – 10mg/l; initial oxalic acid concentration – 0.43mM; pH 3–4; UV illumination). The process included high efficiency combination of adsorption, heterogeneous and homogeneous catalysis under UV and solar lights illumination without addition of hydrogen peroxide. The detoxification of water sample containing organic dyes was confirmed after combined sorption-photocatalytic treatment.

Oxidative Degradation of Oxalic Acid in Aqueous Medium Using Manganese Oxide as Catalyst at Ambient Temperature and Pressure

Manganese oxide was prepared by mechano chemical process in solid phase and was characterized by physical (surface area, particle size, XRD and FTIR analyses) and chemical (surface and total oxygen content) techniques. Prepared manganese oxide was used as catalyst for oxidation/degradation of oxalic acid in aqueous medium in an agitated slurry batch reactor, where molecular oxygen was used as an oxidant. Influence of different reaction parameters like time of reaction, speed of agitation, initial concentration of oxalic acid, temperature and partial pressure of oxygen on oxidation/degradation of oxalic acid was investigated. About 71.5% of oxalic acid (20 mL of 0.017 M) was degraded with in 1 h. The oxidation/degradation reaction followed the Langmuir–Hinshelwood type of mechanism. Curve Expert software was used for kinetic analysis.

Photodegradation kinetics of 2,6-dimetylphenol by natural iron oxide and oxalate in aqueous solution

Abstract Heterogeneous photodegradation of 2,6-dimethylphenol (2,6-DMP) in the natural iron oxide (NIO) system with oxalic acid under UV irradiation was investigated. The NIO was characterized by X-ray diffraction (XRD), X-ray fluorescence and Brunauer–Emmett–Teller (BET) methods. The XRD pattern of NIO showed a mixed crystal structure. In order to show the effect of temperature on the structure of NIO, the last one was calcined at 800 °C and 1000 °C. The XRD patterns of calcined iron oxides at 800 °C (NIO/800) and 1000 °C (NIO/1000) depict the conversion from mixed crystalline hematite to completely pure crystalline hematite. The experiments showed that the most effective catalyst for degradation of 2,6-DMP is NIO in presence of oxalate. The dependence of 2,6-DMP degradation was attributable to the formation of the dissolved Fe–oxalate in the solution and the adsorbed Fe–oxalate on the surface of natural iron oxide. The photodegradation of 2,6-DMP depends also on the oxalate and pH. The optimal initial concentration of oxalic acid was found to be 5 × 10 −3 M. The results demonstrated that the optimal pH value should be in the range of 3–4. The use of 2.0% of isopropanol as a scavenger confirmed the intervention of hydroxyl radicals in the photodegradation of 2,6-DMP. Furthermore, an important effect of oxygen was observed.

Photodecolourization of orange II with iron corrosion products and oxalic acid in aqueous solution

Iron corrosion products (ICPs) were tested as heterogeneous catalysts to decolourize orange II (OII) in the presence of oxalic acid under simulated natural light or solar light. ICPs were collected from the cast iron pipes used in a wastewater treatment plant, and characterized with energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD) and N2 adsorption/desorption isotherm analyses. The photodecolourization efficiency depends significantly on various factors including the ICPs dosage, initial concentration of oxalic acid and the initial pH value. Under the optimal conditions (ICPs dosage 0.40g/L, initial concentration of oxalic acid 1.6mM and pH 3.0), the photodecolourization efficiency for a solution of 25mL containing 10mg/L OII reaches 83% and 44%, respectively, under simulated natural light (I=14mW/cm2) and solar light (I=1.2mW/cm2) for 30min. Tartaric or citric acid is also efficient for ICPs to photodecolourize OII under simulated natural light. Since this system directly uses ICPs as heterogeneous catalysts and does not require the addition of hydrogen peroxide and shows good efficiency even under solar light, it is an economically viable method for decolourization of wastewaters containing dyes.

Catalytic Wet Air Oxidation of Oxalic Acid Using Ceria-promoted Pt/Al2O3

Catalytic wet air oxidation of oxalic acid using ceria-promoted Pt/Al2O3 catalyst was studied in a glass reactor operated at atmospheric pressure. The catalyst was prepared by the excess solution impregnation method and the catalyst characterization was performed using scanning electron microscopy, nitrogen adsorption, hydrogen chemisorption and thermogravimetric analysis techniques. The effect of initial concentration of oxalic acid, air flow rate, reaction temperature and ceria loading on oxidation of oxalic acid was investigated. The activation energy was found to be 42 kJ/mol and a rate equation was proposed for the oxidation of oxalic acid. Catalyst deactivation and regeneration were studied. It was noticed that the presence of ceria reduced the deactivation of the Pt/Al2O3 catalyst.

Degradation of oxalic acid in a photocatalytic ozonation system by means of Pilkington Active™ glass

This study aims to present the effect of combined ozone and immobilized TiO2 in the form of a well-known commercial product, Pilkington Active™, as a photocatalyst for the degradation of oxalic acid in aqueous solutions which is refractory to conventional ozonation treatments. Inclusive results on the influence of experimental variables such as temperature, pH value and initial concentration of oxalic acid on the rate of oxalic acid degradation and ozone consumption are demonstrated. Total organic carbon analyses were performed to investigate the mineralization of oxalic acid. Due to the enhanced photogeneration of hydroxyl radicals as a consequence of a synergistic interaction between the photo-activated TiO2 and ozone, the O3/Pilkington Active™/UVA system showed excellent potential for the oxidation and removal of oxalic acid contaminants in water.

Photodegradation of Sulfadiazine by Goethite−Oxalate Suspension under UV Light Irradiation

Sulfadiazine, a potent antibacterial agent belonging to the group of antibiotics called sulfonamides, has been reported to be present in surface and groundwater. This study investigated the degradation of sulfadiazine in a goethite (α-FeOOH)−oxalate Fenton-like system under UV irradiation. The results showed that sulfadiazine could be effectively photodegraded by the goethite−oxalate Fenton-like system as a result of the formation of the highly oxidizing hydroxyl radicals, •OH. Among the iron oxides tested (α-FeOOH, γ-Fe2O3, γ-FeOOH, and α-Fe2O3), α-FeOOH was found to be the most effective. Degradation of sulfadiazine depended significantly on the pH and initial concentration of oxalic acid in the system, with optimal values of 3.5 and 4.0 mM, respectively, under UV irradiation. Five intermediate products of sulfadiazine degradation were identified using high-performance liquid chromatography−mass spectrometry (HPLC−MS), gas chromatography−mass spectrometry (GC−MS), and ion chromatography (IC), and a poss...

Heterogeneous photodegradation of pentachlorophenol and iron cycling with goethite, hematite and oxalate under UVA illumination

Heterogeneous photodegradation of pentachlorophenol (PCP) in the goethite (α-FeOOH) and hematite (α-Fe 2O 3) systems with oxalate under UVA illumination was investigated. The PCP degradation, dechlorination and detoxification, in terms of Microtox acute toxicity, were all achieved to the higher efficiency in the hematite suspension than in the goethite suspension. The optimal initial concentration of oxalic acid ( C ox 0 ) for the PCP degradation with goethite and hematite under the experimental conditions was found to be 1.2 mM, since sufficient Fe(III) as Fe(C 2O 4) 3 3− and Fe(II) as Fe(C 2O 4) 2 2− can be formed at C ox 0 ≥ 1 .2 mM . The main intermediates of PCP degradation were identified by GC–MS, HPLC and IC analyses. It was found that the cycling process between Fe(III) and Fe(II) in both the goethite and hematite systems occurred more vigorously at the initial stage and gradually became gentle, while the rate of PCP photodegradation varied from fast to slow during the reaction time. Furthermore, the formation of H 2O 2 during photoreaction was studied to explore its relationship with the photodegradation efficiency and the iron cycling process.

CuCr 2O 4/TiO 2 heterojunction for photocatalytic H 2 evolution under simulated sunlight irradiation

CuCr 2O 4/TiO 2 heterojunction has been successfully synthesized via a facile citric acid (CA)-assisted sol–gel method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectrum (UV–vis DRS) have been employed to characterize the as-synthesized nanocomposites. Furthermore, photocatalytic activities of the as-obtained nanocomposites have been evaluated based on the H 2 evolution from oxalic acid solution under simulated sunlight irradiation. Factors such as CuCr 2O 4 to TiO 2 molar ratio in the composites, calcination temperature, photocatalyst mass concentration, and initial oxalic acid concentration affecting the photocatalytic hydrogen producing have been studied in detail. The results showed that the nanocomposite of CuCr 2O 4/TiO 2 is more efficient than their single part of CuCr 2O 4 or TiO 2 in producing hydrogen. The optimized composition of the nanocomposites has been found to be CuCr 2O 4·0.7TiO 2. And the optimized calcination temperature and photocatalyst mass concentration are 500 °C and 0.8 g l −1, respectively. The influence of initial oxalic acid concentration is consistent with the Langmuir model.

Heterogeneous Photodegradation of Pentachlorophenol with Maghemite and Oxalate under UV Illumination

The degradation of pentachlorophenol (PCP) in a heterogeneous system with maghemite (gamma-Fe2O3) and oxalate under UV illumination was investigated in this study. The results of adsorption experiments demonstrated competitive adsorption between PCP and oxalic acid on the surface of gamma-Fe2O3. The results of photodegradation experiments showed that the rate of PCP degradation strongly relied on the oxalic acid concentration and that an optimal tested initial concentration of oxalic acid (Cox(0)) of 0.8 mM was obtained under our experimental conditions. It was observed that a sufficient amount of oxalic acid can be adsorbed on the gamma-Fe2O3 to form various Fe(III)-oxalate complexes at Cox(o) = 0.8 mM. During the photoreaction, Fe(C2O4)2- and Fe(C2O4)3(3-) were found to be the dominant Fe(III)-oxalate complexes at different Cox(0), while Fe(C2O4)2(2-) was the dominant Fe(II)-oxalate complex at Cox(0) > or = 0.8 mM. The mechanism of H2O2 formation and consumption in the UV-irradiated gamma-Fe2O3/oxalate system was proposed and evaluated. Furthermore, six intermediates of PCP degradation were identified by GC/MS, HPLC, and IC analyses, respectively, and a possible pathway of PCP degradation in such a system was proposed.

Removal of Decontaminating Agent from Aqueous Solution Using Microporous and Mesoporous Materials: Activated Carbon as an Effective Adsorbent

Wastewater from nuclear plants contains oxalic acid, a chelating compound used to remove surface activity. This forms complexes with radioactive cations, thereby impeding their removal by conventional techniques. In this study, oxalic acid was removed by adsorption techniques using commercial activated carbon and various synthesised mesoporous materials, viz. Al-MCM-41 (Si/Al = 50), Al-MCM-41 (Si/Al = 100) and Si-MCM-41, as adsorbents, all of which were characterised by XRD, N2 sorption and TEM analysis. The extent of oxalic acid removal was increased by optimising parameters such as the adsorbent employed, the contact time, the initial concentration of oxalic acid, the pH value of the aqueous solution and the temperature. Activated carbon removed a higher percentage of oxalic acid than any of the other adsorbents studied. The experimental data obtained could be fitted by the Langmuir adsorption model and also followed first-order kinetics. In addition, the negative value of the enthalpy obtained indicate...