Electrochemical properties of Meldola's Blue immobilized on silica-titania phosphate prepared by the sol-gel method

The mixed oxide phosphate (≡SiO)₂Ti(O₃POH)₂ having a specific surface area of S_BET= 595 m² g⁻¹ and an average pore volume of 0.43 mL g⁻¹ was prepared by the sol-gel processing method. The material showed the following characteristics: Ti=11.6 wt% and P=10.5 wt%; ion exchange capacity of 0.60 mmol g⁻¹. Meldola's Blue (MLB) dye was adsorbed, by an ion exchange reaction, from an aqueous solution in a quantity of 0.62 mmol g⁻¹. The dye was strongly retained and was not easily leached from the matrix even in presence of 0.5 M electrolyte solution. Changing the solution pH between 2.5 and 7.0, the midpoint potential of the dye-adsorbed (≡SiO)₂ Ti(O₃POMLB)₂ matrix carbon paste electrode remained practically constant, i.e. about 20 mV vs. SCE. This is not the usual behaviour of MLB since its midpoint potential changes considerably in solution phase as the pH is changed. The modified electrode has proved to be stable and electrocatalytically active for hydrazine oxidation at pH 6. Received: 22 June 1999 / Accepted: 7 September 1999     

Voltammetric determination of malachite green in fish samples based on the enhancement effect of anionic surfactant

In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of malachite green over the range from 8.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol l⁻¹, and the detection limit is 4.0 × 10⁻⁹ mol l⁻¹ after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024. The text was submitted by the authors in English.     

Studies on the Synthesis and Characterization of Pd?TiO2?SiO2 Nanocomposite for Electroanalytical Applications

A nanocomposite of Pd? TiO₂? SiO₂ is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO₂? SiO₂. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0).     

Flow Injection Analysis of Phenolic Compounds with Carbon Paste Electrodes Modified with Tyrosinase Purchased from Different Companies

Abstract

Tyrosinase-modified carbon paste electrodes were prepared using lyophilised powder of the enzyme purchased from different companies. The selectivity of these electrodes for nine phenolic compounds, including six substituted catechols, has been studied. The signals obtained for catechol were always higher than those found for other phenolic compounds. Cyclic voltammetry and flow injection measurements indicated that the response of the tyrosinase-modified carbon paste electrodes was limited by the rate of the enzymatic oxidation of catechols. Different approaches of paste electrode preparation have been studied and compared. Direct mixing of enzyme into the graphite powder doped with the osmium based mediator, resulted in the highest sensitivity for the studied substrates. However, substrate selectivity was found to be dependent on the source of enzyme used for electrode preparation.     

茜素紫修饰碳糊电极阳极溶出伏安法测定痕量锡

研究了利用茜素紫修饰碳糊电极测定痕量锡的阳极溶出伏安法。在 0 1 5mol/L醋酸盐缓冲溶液 (pH 4 .8)中 ,通过开路富集 ,Sn 和茜素紫形成络合物富集于电极表面 ,然后经过介质交换至 3 0mol/L的盐酸溶液中 ,于 -0 .80V还原后再进行阳极化扫描 ,于 -0 .68V左右获得一灵敏的锡的溶出峰。二次导数峰电流与Sn 浓度在 8.4× 1 0 -9～ 1 .4× 1 0 -6mol/L范围内呈良好的线性关系。检出限达 4×1 0 -9mol/L ,同时对电极反应机理进行了讨论。     

颜料体积浓度对水在醇酸涂层中传输行为的影响

水、离子和氧气是导致涂层下金属发生腐蚀的三个重要因素,它们在涂层中的传输过程对其下面金属的腐蚀会产生较大的影响,研究它们在涂层中的传输过程对于弄清涂层下金属发生腐蚀的机制至关重要 .研究表明 [1－ 8], 水在涂层中的传输是一个扩散过程,分起始和饱和两个阶段;在起始阶段,随研究体系和实验条件的不同,水在涂层中的扩散过程遵循不同的规律,可能满足菲克第二扩散定律,也可能会发生较大的偏差 .　　颜料与基料界面间的孔隙是水在涂层中传输的主要通道,调整颜料体积浓度（ PVC）可以改变涂层中这种孔隙的数量和分布,从而…     

Copper nanoclusters conjugated silica nanoparticles modified on carbon paste as an electrochemical sensor for the determination of dopamine

An electrochemical sensor based on modification of carbon paste electrode by glutathione‐capped copper nanoclusters silica nanoparticles (CuNCs/SiO₂NPs) composite for determination of dopamine in the presence of ascorbic acid was presented. Transmission electron microscopy, scanning electron microscopy, energy dispersive X‐Ray analysis, X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, X‐ray diffraction and electrochemical impedance spectroscopy were used for characterization of the developed electrode. The electrochemical behavior of dopamine on CuNCs/SiO₂NPs/carbon paste electrode was investigated by cyclic voltammetry and differential pulse voltammetry. Dopamine was determined in the range of 10.0 – 900.0 μM, and the limit of detection was obtained as 0.43 μM. The electrochemical behaviors of the coexisting electroactive species, which often cause interference with the determination of dopamine, were investigated. The results show that the developed electrode does not show any interference with respect to coexisting species, even in the presence of ascorbic acid. The developed electrochemical sensor was further employed for the determination of dopamine in human blood plasma, with a good recovery.     

Application of Carbon Paste Electrode Modified with Carbon Nanofibres/Polyaniline/Platinum Nanoparticles as an Electrochemical Sensor for the Determination of Bezafibrate

The present study deals with the development of an electrochemical sensor for quantitative determination of Bezafibrate (BZF) based on carbon nanofibers/polyaniline/platinum nanoparticles modified carbon paste electrode (CNF/PANI/Pt/CPE). BZF is a fibric acid derivative and is used largely in the treatment of lipid disorders. The nanocomposite was synthesized by in situ polymerization of aniline using ammonium persulphate and platinum nanoparticles were uniformly decorated on the CNF/PANI surface by reducing hexachloroplatinic acid using sodium borohydride. The electrochemical response of BZF at CNF/PANI/Pt/CPE was studied using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The above study resulted into significant improvement of the electrochemical signal towards the oxidation of BZF, revealing that the oxidation process is highly favorable at the surface of modified electrode. The anodic peak current I_p (μA) is found to be linearly dependent on BZF concentration in the range of 0.025 μM to 100 μM with a detection limit of 2.46 nM. The practical analytical utilities of the sensor were investigated by performing the experiments on synthetic pharmaceutical formulations, human blood serum and urine samples which offered good recovery, suggesting the high efficacy and authenticity of CNF/PANI/Pt/CPE sensor for BZF determination.     

Investigation of Methanol Behavior at the Designed Electrochemical Sensor based on Ni(II) Complex and Graphene Nanosheets

In this work, the electrochemical oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with (N‐5‐methoxysalicylaldehyde, N´‐2‐hydroxyacetophenon‐1, 2 phenylenediimino nickel(II) complex (Ni(II)–MHP) and reduced graphene oxide (RGO), which is named Ni(II)‐MHP/RGO/CPE, in an alkaline solution. This modified electrode was found to be efficient for the oxidation of methanol. It was found that methanol was oxidized by the NiOOH groups generated by further electrochemical oxidation of nickel(II) hydroxide on the surface of the modified electrode. Under optimum conditions, some parameters of the analyte (MeOH), such as the electron transfer coefficient (α), the electron transfer rate constant) k_s), and the diffusion coefficient of species in a 0.1 M solution (pH = 13), were determined. The designed sensor showed a linear dynamic range of 2.0–100.0 and 100.0–1000.0 μM and a detection limit of 0.68 μM for MeOH determination. The Ni(II)‐MHP/RGO/CPE sensor was used in the determination of MeOH in a real sample.     

“金属的电化学腐蚀”教学设计创新

以学科理解为基础,注重创设真实的教学情境,创新实验设计,使学生在探究暖贴发热原理和钢铁腐蚀原理的过程中获得金属电化学腐蚀的知识,拓展认知结构,学习科学方法,发展科学探究能力。