Electrochemical Oxidation and Determination of Oxalic Acid at an Exfoliated Graphite-Polystyrene Composite Electrode

Electrochemical corrosion study of chitosan-hydroxyapatite coated dental implant

Chitosan (Ch) is a naturally occurring biocompatible and bio-degradable material with high corrosion protective capacities for metals in various corrosive media. Hydroxyapatite (HA) is a significant biodegradable and bioactive material. In the present work, chitosan-hydroxyapatite (Ch-HA) composite coatings with various concentrations of chitosan were made on 316L stainless steel (316L SS) using sol-gel dip coating technique. The coatings were characterized by X-ray diffraction (XRD), FTIR, SEM, and electrochemical measurements. The surface morphology results (SEM) of coated implants exposed the fairly dense microstructures having uniformity without cracks and pores indicating that coating was successfully deposited. From electrochemical analyses, it was observed that the value of corrosion current density and the corrosion rate decreased from 6.03 to 0.15 and 5.56-0.13 respectively indicating that 1.5gCh-HA is the best coating concentration. The electrochemical results demonstrated an improvement in the corrosion resistance of 316L SS than the bare one. The decrease in slope and loop area of cyclic voltammograms reveals about improvement in corrosion resistance. This increment in corrosion resistance of the Ch-HA coated SS implant in the artificial saliva is as 1.5gCh-HA > 2gCh-HA >1gCh-HA >0.5gCh-HA. Furthermore, Ch-HA coatings revealed appropriate adhesion with 316L SS substrate for its use in dental implants.

Carbon dots derived from peptone as "off-on" fluorescent probes for the detection of oxalic acid

A simple and rapid microwave heating approach was reported for the preparation of water soluble carbon dots (CDs) using peptone as carbon source with the assistance of ethylenediamine. Several characterization techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were employed to analyze CDs. The optical properties of synthesized CDs were examined by UV-vis and fluorescence spectroscopy. The CDs exhibit strong blue emission under 365 nm UV lamp and have the excitation and pH (2.0-12.0) dependent emission behavior. The fluorescence intensity of CDs can be selectively quenched by Co²⁺ via dynamic mechanism, while the addition of oxalic acid (OA) results in a remarkable recovery of the fluorescence intensity due to the strong coordination binding between oxalic acid and Co²⁺. Hence, the prepared CDs can conveniently serve as "off-on" fluorescent probes for highly sensitive determination of oxalic acid. The wide linear range is 0.5-70 mg/L with a low detection limit of 0.288 mg/L. Furthermore, the probes were successfully applied to detect oxalic acid in tomato and cherry tomato samples with the recovery of 96.4 %-106.4 % and the relative standard deviation lower than 0.25 %.

Electrochemical Enzyme-free Sensing of Oxalic Acid Using an Amine-mediated Synthesis of CuS Nanosphere

Copper sulfide nanospheres (CuS NS) were prepared by a solvothermal method with the support of p-phenylene diamine as a structure direct agent. The formation of CuS NS was evaluated using XRD, FE-SEM, HR-TEM, XPS, and electrochemical methods. The CuS NS modified electrode demonstrated excellent electro-catalytic behavior for the electro-oxidation of oxalic acid (OA). The modified electrode showed a good linear range (50 to 700 μM), high sensitivity (0.0353 μA μM^-1 cm^-2), a low detection limit (35.6 μM), long term stability and good anti-interference behavior.

Graphite/Ag/AgCl nanocomposite as a new and highly efficient electrocatalyst for selective electroxidation of oxalic acid and its assay in real samples

Herein, graphite/Ag/AgCl nanocomposite is introduced as a new electrocatalyst material for the electrocatalytic oxidation of oxalic acid. Graphite/Ag/AgCl was synthesized by electroless deposition of nano-sized metallic silver and then silver chloride on graphite powder. The material obtained was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy. The nanocomposite was mixed with n-eicosane as binder and used as carbon paste electrode for electrocatalytic oxidation of oxalic acid (OA). The graphite/Ag/AgCl nanocomposite electrode showed good catalytic activity for the electroxidation of oxalic acid in H₃PO₄ solution (0.05 mol L^-1), leading to a distinct decrease in anodic overpotential (100 mV) and a substantial increase in anodic peak current (about 10 times), in comparison with the unmodified carbon paste electrode. Using the developed nanocomposite electrode and differential pulse voltammetry method, it became possible to determine oxalic acid in the concentration range of 0.01-0.75 mmol L^-1 with detection limit of 3.7 × 10^-6 mol L^-1. The electrode showed very high sensitivity of 1341.3 μA mM^-1 cm^-2 which is remarkably better than the previously reported oxalic acid sensors. Thanks to high sensitivity and good selectivity of the electrode, the proposed method was successfully applied for the determination of OA in human urine and spinach samples. The satisfactory results obtained, confirmed the applicability of this sensor in the practical analysis.

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.