Electrocatalytic reduction of hydrogen peroxide and its determination in antiseptic and soft-glass cleaning solutions at phosphotungstate-doped-glutaraldehyde-cross-linked poly-l-lysine film electrodes

The present work describes the electrocatalytic behavior of phosphotungstate-doped glutaraldehyde-cross-linked poly-l-lysine (PLL-GA-PW) film electrode towards reduction of hydrogen peroxide (H₂O₂) in acidic medium. The modified electrode was prepared by means of electrostatically trapping the phosphotungstate anion into the cationic PLL-GA coating on glassy carbon electrode. The PLL-GA-PW film electrode showed excellent electrocatalytic activity towards H₂O₂ reduction in 0.1 M H₂SO₄. Under the optimized conditions, the electrochemical sensor exhibited a linear response for H₂O₂ concentration over the range 2.5 × 10⁻⁶ to 6.85 × 10⁻³ M with a sensitivity of 1.69 μA mM⁻¹. The curvature in the calibration curve at high concentration is explained in terms of Michaelis-Menten (MM) saturation kinetics, and the kinetics parameters calculated by three different methods were compared. The PLL-GA-PW film electrode did not respond to potential interferents such as dopamine, ascorbic acid and uric acid. This unique feature of PLL-GA-PW film electrode allowed selective determination of H₂O₂. Finally, the proposed electrochemical sensor was successfully applied to determine H₂O₂ in commercially available antiseptic solution and soft-contact lenses cleaning solution and the method has been validated using independent estimation by classical potassium permanganate titration method. Major advantages of the method are simple electrode fabrication, stability and high selectivity towards hydrogen peroxide.     

Characterisation and corrosion studies of steel electrodes covered by polypyrrole/phosphotungstate using Electrochemical Impedance Spectroscopy

Polypyrrole/PW₁₂O₄₀³⁻ hybrid material was electrosynthesised on carbon steel electrodes in acetonitrile medium. The coatings obtained were characterised by Electrochemical Impedance Spectroscopy (EIS). On free-standing polypyrrole films the electrical response was mainly due to ion–ion charge transfer resistance, with a value of 175 Ω cm². A value of 2 × 10⁻⁵ S/cm was determined for the hybrid material conductivity. A charge transfer resistance about 7000 Ω cm² was obtained due to steel/oxide interface. Corrosion tests showed an important improvement in the protection against corrosion when the carbon steel electrodes were coated by these polymeric films.     

Novel electrocatalytic system for the oxidation of methyl jasmonate based on layer-by-layer assembling of montmorillonite and phosphotungstic acid nanohybrid on graphite electrode

In this work, a novel phosphotungstic acid/neutral red intercalated montmorillonite composite (PTA/NR–MMT) film was prepared by layer-by-layer assembling on a graphite electrode (GE). The PTA/NR–MMT/GE exhibited excellent electrocatalytic effect for the oxidation of alkylene group in methyl jasmonate (MeJA). The synergistic effect of the good conductivity and high adsorption capacity of MMT and the solid super-acidity of PTA was believed responsible for the high electrocatalytic activity of this nanohybrid. Under optimal working conditions, MeJA showed a wide calibration range of 5.0 × 10⁻⁷ to 8.0 × 10⁻⁵ M with a low detection limit of 2.0 × 10⁻⁷ M by using the derivative differential pulse voltammetry. This novel electrocatalytic system can be applied to the determination of MeJA in spikelet samples of rice.     

磷钨酸盐催化选择性氧化苯甲醇合成苯甲醛的研究

通过两步法合成了两种磷钨酸盐催化剂,并利用13CNMR、1HNMR、IR、XRD等技术对催化剂进行了表征.表征结果显示,磷钨酸盐均具有磷钨酸的Keggin型结构.将该催化剂用于催化氧化苯甲醇的反应,以30%H2O2为氧化剂,分别考察了含不同阳离子的磷钨酸盐、反应时间、反应温度、催化剂用量和H2O2用量对反应的影响.结果...     

Electrochemical and chemical characterization of polypyrrole/phosphotungstate coatings electrosynthesized on carbon steel electrodes in acetonitrile medium

Hybrid material polypyrrole/PW₁₂O₄₀³⁻ was potentiostatically electrosynthesized on carbon steel electrodes in acetonitrile medium. The obtained coatings were characterized by cyclic voltammetry, FTIR-ATR, XPS, SEM and EDX techniques. Phosphotungstate as dopant agent, Fe oxides and polypyrrole chains are the compounds that form the hybrid material structure. The influence of the electrosynthesis potential was analysed. Oxidized and reduced state of the coatings was also studied. When the electrosynthesis potential is increased up to 2.00 V and the polymeric coatings are in reduced state, the covering degree is very high and the coatings present a very homogenous and uniform surface.     

PVC Membrane Sensor for Potentiometric Determination of Atropine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of atropine has been developed. It is based on the formation of the ion association complex of the atropinium cation with phosphotungstate counter anion as electroactive material dispersed in a PVC matrix, β‐Cyclodextrin and o‐nitrophenyl octyl ether serve as a plasticizer. The sensor shows a fast, stable, near Nernstian response for 1×10^?2 M to 1×10^?6 M atropine at 25°C over the pH range of 3–8 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 8×10^?7 M and the response time is 20–45 sec. Selectivity coefficients of atropine, relative to a number of interfering substances, were investigated. There are negligible interferences caused by most of the studied cations, anions, and pharmaceutical excipients. The direct determination of atropine shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.6% at 100 µg/mL. The results obtained by determination of atropine in some formulations (atropine injection and eye drops) are favorably comparable with those obtained by the British Pharmacopoeia method. The developed membrane electrode has been used as end point indicator electrode for some potentiometric titrations.     

Highly conductive, methanol resistant fuel cell membranes fabricated by layer-by-layer self-assembly of inorganic heteropolyacid

Layer-by-layer (LBL) self-assembly is a simple and elegant method of constructing organic-inorganic composite thin films from environmentally benign aqueous solutions. In this paper, we utilize this method to develop proton-exchange membranes for fuel cells. The multilayer film is constructed onto the surface of sulfonated poly(arylene ether ketone) (SPAEK-COOH) membrane by LBL self-assembly of polycation chitosan (CTS) and negatively charged inorganic particle phosphotungstic acid (PTA). The highly conductive inorganic nanoparticles ensure SPAEK-COOH-(CTS/PTA)_n membranes to maintain high proton conductivity values up to 0.086 S cm⁻¹ at 25 °C and 0.24 S cm⁻¹ at 80 °C, which are superior than previous LBL assembled electrolyte systems. These multilayer systems also exhibit extremely low water swelling ratio and methanol permeability. The selectivity of SPAEK-COOH-(CTS/PTA)₈ is 2 orders of more than Nafion^® 117, which is attractive in direct methanol fuel cells (DMFCs).