Electrocatalytic properties of [Ru(bpy)(tpy)Cl]PF6 at carbon ceramic electrode modified with nafion sol-gel composite: application to amperometric detection of l-cysteine

A two-step sol-gel technique was used here to prepare a carbon ceramic electrode modified with nafion and [Ru(bpy)(tpy)Cl]PF₆. This involves two steps: first, forming a bulk-modified carbon ceramic electrode with nafion, and then immersing the electrode into a Ru-complex solution (electroless deposition) for a short period of time (5-25 s). Cyclic voltammograms of the resulting surface-modified carbon ceramic electrode show stable and a well-defined redox couple due to Ru(II)/Ru(III) system with surface-confined characteristic. l-Cysteine (CySH) has been chosen as a model to elucidate the electrocatalytic ability of Ru-complex nafion sol-gel composite electrode. Not only the modified electrode shows excellent catalytic activity toward l-cysteine electrooxidation in pH range 3-9, but the antifouling effect of nafion film also increases the reproducibility of results in comparison with CCE modified with homogeneous mixing of graphite powder and Ru-complex (one step sol-gel method). Under the optimized conditions in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.1-100 μM, 20 nM and 50 nA/μM, respectively. The advantages of this modified electrode are good reproducibility, excellent catalytic activity, simplicity of preparation and especially its antifouling properties towards l-cysteine and its oxidation products. Additionally, it is promising as a detector in flow system or chromatography systems.     

Electrochemical Pretreatment of Amino‐Carbon Nanotubes on Graphene Support as a Novel Platform for Bilirubin Oxidase with Improved Bioelectrocatalytic Activity towards Oxygen Reduction

The electrochemical conditioning of amino‐carbon nanotubes (CNTs) on a graphene support in an alkaline solution is used to produce ?NHOH as hydrophilic functional groups for the efficient immobilization of bilirubin oxidase enzyme. The application of the immobilized enzyme for the direct electrocatalytic reduction of O₂ is investigated. The onset potential of 0.81 V versus NHE and peak current density of 2.3 mA cm^?2 for rotating modified electrode at 1250 rpm, indicate improved biocatalytic activity of the proposed system for O₂ reduction.     

NaHSO4·H2O as a Heterogeneous Acidic Reagent for Mild and Convenient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives

One-pot cyclocondensation reaction of aromatic aldehydes, 1,3-dicarbonyl compounds and urea/thiourea in the presence of NaHSO₄·H₂O produced 4-aryl substituted 3,4-dihydropyrimidin-2(1H)-ones and their sulfur analogs in high to excellent yields. The reactions were carried out in refluxing n-hexane and were completed within 2.5–11 h.     

The effect of basecoat pigmentation on mechanical properties of an automotive basecoat/clearcoat system during weathering

The aim of this study is to elucidate the effect of basecoat pigmentation on mechanical aspects of an automotive basecoat/clearcoat (BC/CC) system during artificial weathering exposures. A silver basecoat as the most reflective and a black basecoat as the most absorptive basecoat were selected. These two extreme behaviored basecoats were chosen with hopes that other basecoats would behave somewhere between the silver and the black extremes. The structural and mechanical properties of the coatings were investigated after various weathering exposure times (0, 150, 300, 450, 600 h). Dynamic mechanical thermal analysis (DMTA) was carried out to study variations in structure and basic characteristics of the system such as cross-linking density and T_g during weathering. In order to investigate variations in mechanical properties of the system, nano indentation, nano scratch, and tensile tests were also utilized.It was found that although both silver and black systems experienced post-curing reactions (dominant at earlier stages of weathering) and degradation reactions (dominant at later stages of weathering), but basecoat pigmentation affected the post-curing and degradation reaction rates of the BC/CC system, leading to variations in mechanical properties. It was concluded that post-curing occurred to a greater extent in the black pigmented system whilst in the silver pigmented system weathering degradation was much more sever.     

Simultaneous Investigation of the Laser Intensity and Magnetic Field Effects on Laser-Induced Plasma Spectroscopy

Journal of Russian Laser Research - In this paper, we use laser-induced breakdown spectroscopy (LIBS) to investigate the laser-induced copper plasma with and without an external magnetic field,...     

On the Thermal Degradation of a Novel Epoxy-Based Nanocomposite Cured With Tryptophan as an Environment-Friendly Curing Agent

The thermal degradation kinetics of diglycidyl ether of bisphenol-A (DGEBA) cured with tryptophan (Trp) in the presence of silica nanoparticles (SiNP) was investigated by thermogravimetry analysis. The activation energies of the solid-state decomposition process were evaluated using the advanced isoconversional method. The dependence of conversion (degradation) on the temperature and activation energy was determined allowing the calculation of master plots. The experimental master plots agreed with the first-order (F1) kinetic function for both neat epoxy and nanocomposite in the conversion range of 0.45–0.85. Using the kinetic model and the calculated kinetic parameters, the times at half conversion (α = 0.5) were computed for different degradation temperatures. The kinetic analysis showed that the degradation rate of the epoxy nanocomposite was lower than that of the neat epoxy for conversions between 0.45 and 0.85. Therefore, we concluded that adding SiNP to DGEBA/Trp can improve the thermal stability in the conversion range of 0.45–0.85.