Oxidation Of Oxalic Acid Research Articles

Evaluation of Pt Alloys as Electrocatalysts for Oxalic Acid Oxidation: A Combined Experimental and Computational Study

In this study we combined experimental approaches and density functional theory to evaluate novel platinum-based materials as electrocatalysts for oxalic acid oxidation. Several Pt alloys, PtSn (1:1), PtSn (19:1), PtRu (1:4), PtRuSn (5:4:1), and PtRhSn (3:1:4), were synthetized using sacrificial support method and tested for oxidation of oxalic acid at pH 4. It was shown that PtSn (1:1) and PtRu (1:4) have higher mass activity relative to Pt. These two materials along with Pt and one of the least active alloys, PtSn (19:1), were further analyzed for the oxidation of oxalic acid at different pHs. The results show that all samples tested followed an identical trend of decreased onset potential with increased pH and increased catalytic activity with decreased pH. Density functional theory was further utilized to gain a fundamental knowledge about the mechanism of oxalic acid oxidation on Pt, PtSn (1:1), and PtRu (1:4). The results of the calculations along with the experimentally observed dependence of generated currents on the oxalic acid concentration indicate that the mechanism of oxalic acid oxidation on Pt proceeds without the participation of surface oxidizing species, while on Pt alloys it involves their participation.

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.

A one-pot gold seed-assisted synthesis of gold/platinum wire nanoassemblies and their enhanced electrocatalytic activity for the oxidation of oxalic acid.

Three-dimensional (3D) noble metal nanoassemblies composed of one-dimensional (1D) nanowires have been attracting much interest due to the unique physical and chemical properties of 1D nanowires as well as the particular interconnected open-pore structure of 3D nanoassemblies. In this work, well-defined Au/Pt wire nanoassemblies were synthesized by using a facile NaBH4 reduction method in the presence of a branched form of polyethyleneimine (PEI). A study of the growth mechanism indicated the morphology of the final product to be highly related to the molecular structure of the polymeric amine. Also, the preferred Pt-on-Pt deposition contributed to the formation of the 1D Pt nanowires. The Au/Pt wire nanoassemblies were functionalized with PEI at the same time that these nanoassemblies were synthesized due to the strong N-Pt bond. The chemically functionalized Au/Pt wire nanoassemblies exhibited better electrocatalytic activity for the electro-oxidation of oxalic acid than did commercial Pt black.

Electrocatalytic Oxidation of Oxalic Acid Using a Multielectrolytic Modified Glassy Carbon Electrodes

Electrocatalytic oxidation activity of oxalic acid can be observed by using a multielectrolytic modified glassy carbon electrode (MMGCE). The MMGCE was fabricated by using the following electrolytic-oxidation/reduction processes. First, the functional groups containing nitrogen atoms such as amino group are introduced by the electrode oxidation of a bare glassy carbon electrode in an ammonium carbamate aqueous solution, and next, this electrode was electroreduced in sulfuric acid, and it was found that the reduction current gradually increased as the electrolysis time increased. This suggests that functional groups containing nitrogen atoms contributing the catalytic electron transfer of hydrogen ion are introduced. To observe the electrode oxidation wave of oxalic acid, the voltammmetric measurements of oxalic acid was carried out by using MMGCE in an acidic medium. The oxidation wave of oxalic acid at low potential range was appeared in the linear sweep voltammograms. The MMGCE exhibited well-defined peak of oxalic acid oxidation in acidic medium.

Promoting the oxidative removal rate of oxalic acid on gold-doped CeO2/TiO2 photocatalysts under UV and visible light irradiation

Abstract The photooxidation of oxalic acid, catalyzed by nanosized TiO 2 , CeO 2 , CeO 2 /TiO 2 and the respective gold-doped samples has been studied under irradiation with UV and visible light. UV–vis DRS, XRD, TEM, SEM, XPS techniques have been applied to the characterization of prepared photocatalysts. The photocatalytic mineralization of oxalic acid, catalyzed by CeO 2 /TiO 2 or Au/CeO 2 /TiO 2 , proceeded at a significantly higher rate under UV-A light irradiation than that under visible light. This is due to the low content of the CeO 2 (5 wt.%) in the composite catalyst. Doping the semiconductor materials with gold nanoparticles increases more than twice the rates of mineralization of oxalic acid, compared to non-doped samples. The higher rate constants of oxalic acid decomposition under UV or visible light irradiation over the CeO 2 /TiO 2 and Au/CeO 2 /TiO 2 catalysts, in comparison to those measured over the individual oxides, are due to the more efficient separation of the electron–hole pairs generated under irradiation. Especially efficient is the charge separation in the case of the Au/CeO 2 /TiO 2 photocatalyst under irradiation with UV light, when the rate constants of oxalic acid oxidation are approximately 1.6 times higher than the values when the process is catalyzed by Au/TiO 2 and 3.1 times higher than that over pure TiO 2 .

Characterization and application of the hetero-junction ZnFe2O4/TiO2 for Cr(VI) reduction under visible light

The spinel ZnFe2O4 prepared by nitrate route is used as dispersed photons collector capable to sensitize TiO2 under visible light and to reduce Cr(VI) into trivalent state. The transport properties, optical and photo-electrochemical characterizations are correlated, to build the energetic diagram of the hetero-system ZnFe2O4/TiO2/CrO4− solution. A gap of 1.97 eV is obtained for the spinel from the diffuse reflectance. The conduction band of ZnFe2O4 (−1.47 VSCE) favors the electrons injection into TiO2, permitting a physical separation of the charge carriers. The oxidation of oxalic acid by photoholes prevents the corrosion of the spinel. The best configuration ZnFe2O4 (75 %)/TiO2 (25 %) is used to catalyze the downhill reaction (2HCrO4− + 3C2H4O4 + 1.5O2 + 8H+ → 2Cr3+ + 6CO2 + 11 H2O, ∆G° = −557 kcal mol−1). 60 % of Cr(VI) are reduced after 3 h of visible light illumination and the photoactivity follows a first-order kinetic with a half-life of 70 min. The water reduction competes with the HCrO4− reduction which is the reason in the regression of the photoactivity; a hydrogen evolution rate of 24 µmol mg−1 h−1 is obtained.

Thermodynamics of the formation of intermediate complexes in the oxidation of oxalic acid by cerium(IV) and kinetics of their intramolecular redox decomposition

The thermodynamic and kinetic characteristics of the intermediate cerium(IV) oxalate complex formed at the first stage of the oxidation of oxalic acid (H2Ox) by cerium(IV) are studied by spectrophotometry and pH potentiometry at an ionic strength I = 2, pH 0.4–1.1 of a sulfuric acid medium, and temperatures of 281.65–298.35 K. The composition, the form of organic ligands, the thermodynamic parameters of formation, and the kinetic parameters of intramolecular redox decomposition are established for this complex. A detailed scheme of the initial stages in the redox process that occurs in the Ce4+-SO 4 2- -H2Ox system is considered, and the law behind its rate and the reaction mechanism associated with this law are established.

Biocompatible laponite ionogels based non-enzymatic oxalic acid sensor

An enzyme-free oxalic acid (OA) electrochemical sensor was assembled on indium tin oxide (ITO) plate on which a film of laponite ionogel was coated that resulted in an L/IL/ITO electrode. This ionogel electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV–Vis spectroscopy techniques. Electrochemical oxidation of OA on the electrode surface was investigated by cyclic voltammetry. Further this electrode exhibited high electrochemical activity that yielded well-defined peaks of OA oxidation, and a notably suppressed over-potential compared to the laponite–ITO (L/ITO) electrode. Under optimized conditions, a good linear response (anodic current) was observed for the OA concentration in the 1–20mM range with a detection limit of 3μM. Furthermore, this electrochemical strip sensor presented good characteristics in terms of stability, and reproducibility offering promise of applicability of this green sensor platform.

Hybrid Biotic/Abiotic Catalysts for Oxidation of Complex Biofuels

The electrochemical oxidation of oxalic acid on platinum is one of the main methods explored so far in the design of amperometric sensors for quantitative determination of oxalate and a commonly used approach for wastewater purification and energy production. Apart from that, herein we report the application of various platinum alloys and platinum nanoclusters as catalyst for oxidation of oxalic acid as a final step in the multistep oxidation of various organic compounds, such as fructose, glycerol, glyceric acid, glyceraldehyde, etc. This multistep oxidation processes can involve purely biotic or abiotic catalysts or a hybrid organo/metalo/enzyme catalysts, where the latter along with traditional electrocatalysis takes advantage of bioelectrocatalysis as well. Various PtSn and PtRu alloys were electrochemically evaluated towards the oxidation of oxalic acid in neutral and acidic media (Fig. 1). The onset potential of oxalate oxidation was significantly shifted towards lower potentials for all platinum alloys tested indicating decreased activation energy for the rate-limiting step especially at low pH. Along with the improved thermodynamics of the process, the kinetic of oxalate oxidation was also enhanced when PtSn (1:1) was employed. Density Functional Theory (DFT) calculations were explored to gain a better understanding of the reactivity of the platinum alloys [1]. The mechanism in which two electrons are transferred directly from oxalic acid molecule to the catalyst surface was considered: C2O4H2→*C2O4H + H+ + e-→*CO2H+CO2+H++e-→2CO2+2H++2e- where * represents the active site on the catalyst’s surface. Other mechanisms were also considered, which involve participation of adsorbed species such as OH or O. The free energy diagrams for the oxidation of oxalic acid on Pt based on these mechanisms were calculated using Perdew-Burke-Ernzerhof functional [1]. The results indicate that the adsorption of oxalic acid, which is accompanied by the release of H+and transfer of one electron to the electrode, requires the largest change in the free energy and can be considered as thermodynamically limiting step. Since the adsorption of oxalic acid is the potential-limiting step, an increase in the adsorption energy of oxalic acid on the different platinum alloys can explain the differences in the overpotential observed during the electrochemical evaluation. Based on the DFT calculations it was established that the presence of Sn and/or Ru increases oxalate adsorption and leads to decrease in the overpotential of oxalate oxidation in accordance to the experimentally observed results. DFT also predicted that oxalate oxidation is highly sensitive to the size of the Pt clusters used as a catalyst, imposing the conclusion that decreasing the size of Pt would provide higher activity. Thus, platinum nanoclusters were synthesized using DNA as a template that provides improved cluster stability and were evaluated towards oxidation of oxalic acid. These nanoclusters could be further assembled with aldehyde dehydrogenase to provide multistep catalysis of glyoxalic acid to CO2. In addition, Pt alloys were explored in combination with TEMPO for the subsequent and complete oxidation of glycerol. [1] I. Matanovic, S. Babanova, A. Perry III, A. Serov, K. Artyushkova and P. Atanassov, Bio-inspired design of electrcatalysis for oxalate oxidation: a combined experimental and computational study of Mn-N-C catalyst, Phys. Chem. Chem. Phys., 2015, DOI: 10.1039/C5CP00676G Figure 1

Adsorption and oxidation of oxalic acid on anatase TiO2 (0 0 1) surface: A density functional theory study

Anatase TiO2 (001) surfaces have attracted great interest for photo-degradation of organic species recently due to their high reactivity. In this work, adsorption properties and oxidation mechanisms of oxalic acid on the anatase TiO2 (001) surface have been theoretically investigated using the first-principles density functional theory. Various possible adsorption configurations are considered by diversifying the connectivity of carboxylic groups with the surface. It is found that the adsorption of oxalic acid on the anatase (001) surface prefer the dissociative states. A novel double-bidentate configuration has been found due to the structural match between oxalic acid and the (001) surface. More charge is transferred from the adsorbed oxalic acid to the surface with the double-bidentate configuration when comparing with other adsorption structures. Thus, there is a positive correlation relationship between the transferred charge amount and the interfacial bond numbers when oxalic acid adsorbs on the anatase TiO2 (001) surface. The adsorption energies with dispersion corrections have demonstrated that the van der Waals interactions play an important role in the adsorption, especially when adsorbates are close to the surface.

Synthesis, characterization, scale-up and catalytic behaviour of Co3O4 nanoparticles

Highly uniform cobalt oxide (Co3O4) nanoparticles were synthesized via thermal decomposition of cobalt hydroxy carbonates with particle size around 16 ± 1 nm. The process gives reproducible results in batches of 1–5 kg. The particles show good catalytic activity for the oxidation of oxalic acid and benzaldehyde under mild temperature conditions. The characterization was performed by X-ray diffractometry (XRD), Transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectrum and Nuclear magnetic resonance (NMR). The XRD measurements show cubic spinel phase and Debye–Scherrer relation was used to measure average particle size. The convenience of the production of catalyst can be exploited for its large-scale production and use in laboratories, R&Ds and industries.

Graphene-supported PtPd Bimetallic Gathered Nanocrystals for Non-enzymatic Sensing of Oxalic Acid.

A novel non-enzymatic oxalic acid (OA) sensor was developed using a nanocrystal PtPd loaded reduced graphene nanosheets (PtPdNCs/RGO)-modified electrode. PtPdNCs/RGO were successfully achieved by a facile, one-step and template-free method, in which PtPd nanoparticles with 100 nm-scale were assembled from polyhedral PtPd nanocrystals of various shapes and dispersed on the graphene nanosheets. Resulting PtPdNCs/RGO were characterized and used for PtPdNCs/RGO-modified electrodes. Electrochemical oxidation of OA on the modified electrode was investigated by cyclic voltammetry and differential pulse voltammetry (DPV). Well-defined peaks of OA oxidation could be obtained using an electrode that indicated its high electrochemical activity. The concentration of OA and the current responses could be obtained in the ranges of 0.5 - 10 and 10 - 35 mM with correlation coefficients of 0.9994 and 0.9952; the detection limit (S/N = 3) was found to be 0.05 mM. The modified electrode presented good characteristics in terms of both stability and reproducibility, promising its applicability in practical analysis.

Photocatalytic reduction of nitrate over Ag–TiO2 in the presence of oxalic acid

This study investigates the UV assisted reduction of nitrate using Ag–TiO2 composite photocatalyst in the presence of oxalic acid as hole scavenger. Ag–TiO2 composite was prepared by photodeposition method and its physico-chemical properties were determined by HRTEM with EDAX, XRD, XPS, BET Surface area and FTIR studies. Nitrite and ammonium should not be formed as by-products during the reduction of nitrate as both are more toxic than nitrate. Hence, experimental conditions like UV irradiation time, nitrate concentration, oxalate concentration and dose of photocatalyst were optimized to convert nitrate completely into nitrogen have been scrutinized. Effective nitrate reduction with 100% nitrogen selectivity was attained within 1h. Effect of common anions present in water like Cl−, SO42− and HCO3− on the photocatalytic reduction of nitrate was investigated. The kinetic data of oxalic acid oxidation obeyed the pseudo-first order equation. The applicability of this system for the reduction of nitrate from drinking water has been tested.

Zinc Oxide Nanopillar: Preparation, Characterization and Its Photoelectrocatalytic Activity

Zinc oxide nanopillar was synthesized by simple and cost-effective wet chemical method and characterized by several techniques. The XRD confirmed hexagonal wurtzite phase and the crystal quality of the nanostructure. The band gap was calculated using Tauc’s plot from reflectance spectra. The morphology of ZnO nanostructure was studied using SEM analysis. The prepared ZnO nanopillar shows photoelectrocatalytic activity against oxalic acid oxidation.

Sensitive electrochemical determination of oxalic acid in spinach samples by a graphene-modified carbon ionic liquid electrode

In this paper, a new electrochemical oxalic acid (OA) sensor based on graphene (GR)-modified carbon ionic liquid electrode (CILE) was proposed. The GR nanosheets were deposited on the surface of CILE by electroreduction with graphene oxide as precursor and electrocatalytic oxidation of OA on GR/CILE was further investigated. As compared with that of bare CILE, the oxidation peak current of OA on GR/CILE were greatly improved with the decrease of the oxidation potential. Electrochemical parameters of the electrooxidation of OA were calculated. Under the selected conditions, the oxidation peak currents increased with OA concentration in the range from 8.0 μM to 6.0 mM with the detection limit as 0.48 μM (3σ). The proposed method exhibited higher sensitivity and wider linear range, which was applied to determination of OA concentration in spinach samples with satisfactory results.

Tungsten carbide nanotubes supported platinum nanoparticles as a potential sensing platform for oxalic acid.

Supported tungsten carbide is an efficient and vital nanomaterial for the development of high-performance, sensitive, and selective electrochemical sensors. In this work, tungsten carbide with tube-like nanostructures (WC NTs) supported platinum nanoparticles (PtNPs) are synthesized and explored as an efficient catalyst toward electrochemical oxidation of oxalic acid for the first the time. The WC NTs supported PtNPs modified glassy carbon (GC) electrode is highly sensitive toward the electrochemical oxidation of oxalic acid. A large decrease in the oxidation overpotential (220 mV) and significant enhancement in the peak current compared to unmodified and Pt/C modified GC electrodes have been observed without using any redox mediator. Moreover, WC NTs supported PtNPs modified electrode possessed wide linear concentration ranges from 0 to 125 nM and a higher sensitivity toward the oxidation of oxalic acid (80 nA/nM) achieved by the amperometry method. The present modified electrode showed an experimentally determined lowest detection limit (LOD) of 12 nM (S/N = 3). Further, WC NTs supported PtNPs electrode can be demonstrated to have an excellent selectivity toward the detection of oxalic acid in the presence of a 200-fold excess of major important interferents. The practical application of WC NTs supported PtNPs has also been demonstrated in the detection of oxalic acid in tomato fruit sample, by differential pulse voltammetry under optimized conditions.

Nitrogen-doped carbon xerogels as catalysts for advanced oxidation processes

Nitrogen-doped carbon xerogels were tested as metal-free catalysts for the mineralization of oxalic acid by ozonation and by wet air oxidation. Oxalic acid was completely mineralized in less than 45min in wet air oxidation, but complete conversion was never achieved with ozone. Some general trends were observed, and correlations between the catalytic activity and the surface chemistry of the carbon materials were established. In particular, the apparent reaction rate constants for both processes correlate with the concentration of surface nitrogen. The effect of N-doping is particularly effective in CWAO, the rate constants increasing by two orders of magnitude in comparison with the nitrogen-free material. With ozone, oxidation of oxalic acid may occur both in the liquid phase (homogeneous reaction) and on the catalyst surface, while wet air oxidation appears to proceed mainly on the carbon surface.

Ceria promoted γ-Al2O3 supported platinum catalyst for catalytic wet air oxidation of oxalic acid: kinetics and catalyst deactivation

Alumina-supported platinum catalysts were prepared for catalytic wet air oxidation of oxalic acid.

Photocatalytic Degradation of Water Contaminants in Multiple Photoreactors and Evaluation of Reaction Kinetic Constants Independent of Photon Absorption, Irradiance, Reactor Geometry, and Hydrodynamics

The literature on photocatalytic oxidation of water pollutants often reports reaction kinetic constants, which cannot be unraveled from photoreactor type and experimental conditions. This study addresses this challenging aspect by presenting a general and simple methodology for the evaluation of fundamental "intrinsic" reaction kinetic constants of photocatalytic degradation of water contaminants, which are independent of photoreactor type, catalyst concentration, irradiance levels, and hydrodynamics. The degradation of the model contaminant, oxalic acid (OA) on titanium dioxide (TiO2) aqueous suspensions, was monitored in two annular photoreactors (PR1 and PR2). The photoreactors with significantly different geometries were operated under different hydrodynamic regimes (turbulent batch mode and laminar flow-through recirculation mode), optical thicknesses, catalyst and OA concentrations, and photon irradiances. The local volumetric rate of photon absorption (LVRPA) was evaluated by the six-flux radiation absorption-scattering model (SFM). The SFM was further combined with a comprehensive kinetic model for the adsorption and photodecomposition of OA on TiO2 to determine local reaction rates and, after integration over the reactor volume, the intrinsic reaction kinetic constants. The model could determine the oxidation of OA in both PR1 and PR2 under a wide range of experimental conditions. This study demonstrates a more meaningful way for determining reaction kinetic constants of photocatalytic degradation of water contaminants.

Mesoporous Thin Films of TiO2 on Attenuated Total Reflection Crystals. An In Situ Fourier-Transform Infrared Study of the Kinetics and Equilibrium of Adsorption and Photocatalysis of Carboxylic Acids

Highly organized titanium dioxide (TiO2) mesoporous thin films were deposited directly on silicon attenuated total reflection (ATR) crystals by dip-coating, submitted to two different thermal treatments, and characterized by ellipsometric porosimetry analysis (EPA), X-ray diffraction, and electron microscopy. The kinetics and equilibrium of the adsorption of oxalic acid as well as their photocatalytic efficiency were studied in situ by Fourier transformed infrared spectroscopy (FTIR-ATR). The spectral properties and the Langmuir constants of the detected surface complexes resemble those previously found in TiO2 Degussa P25 and anatase particulate films. The photocatalytic activity for the oxidation of oxalic acid was found to be similar to the corresponding one for Degussa P25. The kinetics of adsorption of oxalic acid follows a pseudo-first-order behavior. The pseudo-first-order rate constants show a linear relationship with the oxalic acid concentration. Adsorption (ka) and desorption rate constants (kd) were obtained. The ka values were analyzed in relation to the pore and neck sizes, accessible volume, thickness, and film area. The film area affects strongly the kinetic parameters, while no clear dependence on the thickness value was observed. When the film area is taken into account, adsorption rates on mesoporous films are appreciably larger than on particulate films. Thus, enhanced adsorption rates make mesoporous films better candidates as photocatalysts. The difference is interpreted in terms of a reduced tortousity in the ordered mesoporous films, probably due to their regular spatial order. It is also concluded that sensors and catalysts based on mesoporous films should respond faster than those based on conventional films.