Nickel/Poly(o‐aminophenol) Film Prepared in Presence of Sodium Dodecyl Sulfate: Application for Electrocatalytic Oxidation of Carbohydrates

Poly(o‐aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode (CPE). Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Electrochemical study of this modified electrode shows a good redox behavior of the Ni(III)/Ni(II) couple. The electrocatalytic oxidations of glucose and other carbohydrates at the surface of the Ni/SDS‐POAP/CPE were studied in a 0.1 M NaOH solution. Compared to POAP/CPE, the SDS‐POAP/CPE significantly enhanced the catalytic efficiency of Ni ions for carbohydrates oxidation. Finally, using chronoamperometric method, the catalytic rate constants (k) for carbohydrates were calculated.     

Electrocatalytic Oxidation of Hydrogen Peroxide on Poly(m‐toluidine)‐Nickel Modified Carbon Paste Electrode in Alkaline Medium

The poly(m‐toluidine) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 0.2 M NiSO₄, also the electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. The electrocatalytic ability of Ni(II)/poly(m‐toluidine)/modified carbon paste electrode (Ni/PMT/MCPE) was demonstrated by electrocatalytic oxidation of hydrogen peroxide with cyclic voltammetry and chronoamperometry methods in the alkaline solution. The effects of scan rate and hydrogen peroxide concentration on the anodic peak height of hydrogen peroxide oxidation were also investigated. The catalytic oxidation peak current showed two linear ranges with different slopes dependent on the hydrogen peroxide concentration and the lower detection limit was 6.5 μM (S/N=3). The catalytic reaction rate constant, (k_h), was calculated 5.5×10² M^?1 s^?1 by the data of chronoamperometry. This modified electrode has many advantages such as simple preparation procedure, good reproducibility and high catalytic activity toward the hydrogen peroxide oxidation. This method was also applied as a simple method for routine control and can be employed directly without any pretreatment or separation for analysis cosmetics products.     

Electrocatalytic Oxidation of Folic Acid on Carbon Paste Electrode Modified by Nickel Ions Dispersed into Poly(o‐anisidine) Film

Poly(o‐anisidine) (POA) was formed by successive cyclic voltammetry in monomer solution containing sodium dodecyl sulfate (SDS) at the surface of carbon paste electrode. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed. The capability of this modified electrode for catalytic oxidation of folic acid was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for folic acid oxidation were calculated. The catalytic oxidation peak current of folic acid was linearly dependent on its concentration and a linear calibration curve was obtained in the range of 0.1 to 5 mM with a correlation coefficient of 0.9994. The limit of detection (3σ) was determined as 0.091 mM. This electrocatalytic oxidation was used as simple, selective and precise voltammetric method for determination of folic acid in pharmaceutical preparations.     

Nickel–poly(o-aminophenol)-modified carbon paste electrode; an electrocatalyst for methanol oxidation

In this work, a modified carbon paste electrode consisting of Nickel dispersed in poly(ortho-aminophenol) was used for electrocatalytic oxidation of methanol in alkaline solution. A carbon paste electrode bulk modified with o-aminophenol was used for polymer preparation by cyclic voltammetry method; then, Ni(II) ions were incorporated by immersion of the modified electrode in 1 M Ni(II) ion solution at open circuit. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)–Ni(II) couple. Electrocatalytic oxidation of methanol on the surface of modified electrode was investigated with cyclic voltammetry and chronoamperometry methods, and the dependence of the oxidation current and shape of cyclic voltammograms on methanol concentration and scan rate were discussed. Also, long-term stability of modified electrode for electrocatalytic oxidation of methanol was investigated.     

A novel and low cost electrochemical sensor for ceftazidime and cefazoline as antibiotic drugs based on nickel/SDS-poly(o-aminophenol) modified electrode

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode (CPE). Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Electrochemical study of this modified electrode shows a good redox behavior of the Ni(III)/Ni(II) couple. The electrocatalytic oxidations of ceftazidim and cefazolin at the surface of the Ni/SDS-POAP/CPE were studied in a 0.1 M NaOH solution. Finally, using chronoamperometric method, the catalytic rate constants (k) for ceftazidim and cefazolin were calculated. Electrode was successfully applied for determination of ceftazidim and cefazolin in pharmaceutical preparations.     

聚邻氨基酚/Ni2+修饰碳糊电极的制备及其对葡萄糖的电催化氧化

以循环伏安法在碳糊电极(CPE)表面上修饰聚邻氨基酚膜(P-OAP),再以浸泡吸附法在此膜中嵌入金属离子Ni2 ,制成Ni/P-OAP/CPE。该电极在0.09mol/LNaOH溶液中通过90圈扫描活化后,在-0.15至0.65V区间出现一对峰形良好且稳定的氧化还原峰。循环伏安实验发现,Ni/P-OAP/CPE对葡萄糖的电氧化有良好的催化特性,催化活性受薄膜的厚度、薄膜中Ni2 的浓度、电极的活化时间以及电解液组成的影响。实验结果表明:该电极是一种良好的无酶葡萄糖传感器。     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols at Ni(II)–quercetin complex modified multi-wall carbon nanotube paste electrode

A modified electrode Ni(II)–Qu–MWCNT-PE has been fabricated by electrodepositing nickel(II)–quercetin [Ni(II)–Qu] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. Ni(II)–Qu–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–MWCNT-PE and Ni(II)–Qu-carbon paste electrode. It also shows electrocatalytic activity toward the oxidation of methanol and other short chain aliphatic alcohols, such as ethanol, 1-propanol, and 1-butanol. The catalytic peak current and peak potential decrease in exponential form with the increase of carbon number of the chains. Kinetic parameters such as the electron transfer coefficient, α, rate constant, k _s, of the electrode reaction, and the catalytic rate constant, k _cat, for oxidation of methanol are determined. The stability and reproducibility of the Ni(II)–Qu–MWCNT-PE are good for practical applications.     

Ni/ZSM‐5 Zeolite Modified Carbon Paste Electrode as an Efficient Electrode for Electrocatalytic Oxidation of Formaldehyde

In this study, we prepared a modified carbon paste electrode consisting of Nickel entrapped in synthesized ZSM‐5 zeolite (Ni/ZMCPE). Then Ni(II) ions were incorporated to electrode by immersion of modified electrode in 1 M Ni(II) ion solution. Cyclic voltammetry and chronoamperometry experiments were used for electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the excellent capability of this modified electrode for catalytic oxidation of formaldehyde was demonstrated during the anodic potential sweep in alkaline solution. The amount of transfer coefficient (α), surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for formaldehyde were evaluated. Thus, it can be a candidate as an anode for fuel cell application.     

Promotion Effect of Bismuth on Nickel Electrodeposition and Its Electrocatalysis to Glucose Oxidation

Metallic Bi and Ni were co‐deposited onto the surface of glass carbon electrode (GCE) from the electrolyte solution containing their respective nitrate to fabricate a Bi/Ni alloy modified GCE (Bi/Ni‐GCE). The purpose is to study the influence of Bi³⁺ on the deposition of Ni and that of deposited Bi on the electrocatalytic performance of Ni to glucose in alkali solution. The results show that both redox signal of Ni(OH)₂/NiOOH and Ni(OH)₂/NiOOH mediated electrocatalysis to glucose is remarkably increased in the presence of Bi. It seems that there is a synergistic effect between Bi and Ni on each other’s redox electrochemistry. It’s possible that the firstly deposited Bi on GCE surface helps to the following nucleation and growth of Ni, leading to the deposition of more metallic Ni on GCE surface. An extremely attractive feature of Bi/Ni‐GCE is reflected by the fast response time to the electrocatalytic oxidation of glucose. The electrode nearly responses immediately after glucose is added and it reaches a steady‐state level within only 2 seconds, demonstrating a good electrocatalytic property of Bi/Ni‐GCE. The calibration plot is linear over the wide concentration range of 0–5.8 mM with a sensitivity of 33.96 µA/mM and a correlation coefficient of 0.9985. The detection limit of the glucose was found to be 0.59 µM at a signal‐to‐noise ratio of 3. The fabricated Bi/Ni‐GCE was successfully employed to analyze the glucose level in blood samples, exhibiting high accuracy, strong resistance against inference and good reliability in the practical applications.     

Electrocatalytic Oxidation of Methanol at Lower Potentials on Glassy Carbon Electrode Modified by Platinum and Platinum Alloys Incorporated in Poly(o‐Aminophenol) Film

The electrocatalytic oxidation of methanol at a glassy carbon electrode modified by a thin film of poly(o‐aminophenol) (PoAP) containing Pt, Pt‐Ru and Pt‐Sn microparticles has been investigated using cyclic voltammetry as analytical technique and 0.10 M perchloric acid as supporting electrolyte. It has been shown that the presence of PoAP film increases considerably the efficiency of deposited Pt microparticles toward the oxidation of methanol. The catalytic activity of Pt particles is further enhanced when Ru or specially Sn is co‐deposited in the polymer film. The effects of various parameters such as the thickness of polymer film, concentration of methanol, medium temperature as well as the long term stability of modified electrodes have also been investigated.     

Carbon paste electrode modified by cobalt ions dispersed into poly (N-methylaniline) preparing in the presence of SDS: application in electrocatalytic oxidation of hydrogen peroxide

Conducting and stable poly (N-methylaniline) film was prepared by using the repeated potential cycling technique in aqueous solution containing N-methylaniline, sulfuric acid, and sodium dodecyl sulfate (SDS) at the surface of carbon paste electrode (CPE). The transition metal ions of Co(ІІ) were incorporated to the polymer by immersion of the modified electrode in 0.1 M cobalt chloride solution for 10 min. The electrochemical characterization of this modified electrode exhibits stable redox behavior of Co(ІІ)→Co(ІІІ) and formation of insoluble oxide/hydroxide cobalt species on the CPE surface. The modified electrode showed well-defined and stable redox couples in alkaline aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response of modified electrode toward the H₂O₂ oxidation was examined using cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and chronoamperometry. This modified electrode has many advantages such as simple preparation procedure, good reproducibility, and high catalytic activity toward the hydrogen peroxide oxidation. Such characteristics were explored for the specific determination of hydrogen peroxide in cosmetics product sample, giving results in excellent agreement with those obtained by standard method.     

Electrocatalytic Determination of 6‐Tioguanine at a p‐Aminophenol Modified Carbon Paste Electrode

A p‐aminophenol modified carbon paste electrode (p‐APMCPE) was constructed for determination of an anticancer drug 6‐thioguanine (6‐TG). The cyclic voltammogram showed that the electrocatalytic oxidation of 6‐TG at the surface of p‐APMCPE occurs at a potential about 840 mV less positive than at an unmodified electrode. Square‐wave voltammetry results presented that the electrocatalytic oxidation peak currents of 6‐TG in pH 9.0 had two linear dynamic ranges in the range of 0.2 to 8.0 and 8.0 to 350.0 μM 6‐TG with a detection limit of 0.08 μM. The kinetic parameters such as electron transfer coefficient (α) and rate constant were determined for the chemical reaction between 6‐TG and p‐aminophenol. Finally, this method was evaluated for the determination of 6‐TG in 6‐thioguanine tablets and urine samples.     

Electrochemical Quartz Crystal Impedance Study of Glucose Oxidation on a Nickel Hydroxide Modified Au Electrode in Alkaline Solution

The electrochemical quartz crystal impedance (EQCI) technique has been applied to investigate glucose oxidation on bare and Ni(OH)₂‐modified Au electrodes in 0.2 mol L^?1 KOH aqueous solution. The EQCI responses suggest different contributions of H⁺‐release and OH^?‐incorporation reactions of the Ni(OH)₂‐film redox process in 0.2 mol L^?1 aqueous KOH at different potentials. Glucose adsorption on the Ni(OH)₂‐modified Au electrode was studied. A mechanism for potential cyclic redox process of glucose at Ni(OH)₂‐modified Au electrode is suggested, mainly based on a comparative EQCI analysis with direct glucose oxidation on bare gold and glucose ad‐/desorption on Ni(OH)₂ film.     

Electrocatalytic Oxidation of Carbohydrates Mediated by Nitroxyl Radical‐modified Electrodes in Aqueous Solution

The electrocatalytic activity of a 2,2,6,6‐tetramethylpipridine‐N‐oxyl (TEMPO)‐modified electrode toward the oxidation of carbohydrates in phosphate buffer solution was investigated under neutral aqueous solution conditions at 25 °C. The modified electrode was prepared on the surface of a glassy carbon electrode by the electrochemical polymerization of a TEMPO precursor containing a pyrrole side chain. Cyclic voltammetric studies showed that the anodic peak current increased with the concentration of carbohydrates in a dose‐dependent manner.     

Preparation and characterization of Ni(II)/polyacrylonitrile and carbon nanotube composite modified electrode and application for carbohydrates electrocatalytic oxidation

A nickel(II) into porous polyacrylonitrile–carbon nanotubes composite modified glassy carbon electrode (Ni/PAN-CNT/GCE) was fabricated by simple drop-casting and immersing technique. The unique electrochemical activity of Ni/PAN-CNT composite modified glassy carbon electrode was illustrated in 0.10?M NaOH using cyclic voltammetry. The Ni/PAN-CNT/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni/PAN/GCE and Ni/CNT/GCE. The results of electrochemical impedance spectroscopy and scanning electron microscopy indicated the successful immobilization for PAN-CNT composite film. Kinetic parameters such as the electron transfer coefficient, α, and rate constant, k _s, of the electrode reaction were determined. Ni/PAN-CNT/GCE also shows good electrocatalytic activity toward the oxidation of carbohydrates (glucose, sucrose, fructose, and sorbitol). The electrocatalytic response showed a wide linear range (10–1,500, 12–3,200, 7–3,500, and 16–4,200?μM for glucose, sucrose, fructose, and sorbitol, respectively) as well as its experimental limit of detection can be achieved 6, 7, 5, and 11?μM for glucose, sucrose, fructose, and sorbitol, respectively. The modified electrode for carbohydrates determination is of the property of simple preparation, good stability, and high sensitivity.     

Nanostructured Base Electrochemical Sensor for Simultaneous Quantification and Voltammetric Studies of Levodopa and Carbidopa in Pharmaceutical Products and Biological Samples

A novel carbon paste electrode modified with carbon nanotubes and 5‐amino‐2′‐ethyl‐biphenyl‐2‐ol (5AEB) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of levodopa (LD) and carbidopa (CD), is described. Cyclic voltammetry (CV) was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, k_s, and transfer coefficient, a, for electron transfer between 5AEB and CPE were calculated as 17.3 s^?1 and 0.5, respectively. Square wave voltammetry (SWV) exhibits a linear dynamic range from 2.5×10^?7 to 2.0×10^?4 M and a detection limit of 9.0×10^?8 M for LD.     

A New and Simple Electrocatalyst for Formaldehyde Oxidation; Nickel/poly(o‐Anisidine)/Film Modified Ionic Liquid Carbon Paste Electrode

In present work, the ionic liquid, 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl) imide was incorporated in the carbon paste electrode as the binder (IL‐CPE). O‐anisidine (OA) monomer is electropolymerized in the presence of an aqueous acidic solution onto IL‐CPE (POA/IL‐CPE). The as‐prepared substrate is used as a porous matrix for dispersion of Ni(II) ions by immersing the modified electrode in a nickel(II) nitrite solution. The modified electrodes are characterized by scanning electron microscopy (SEM) and electrochemical methods. The POA/IL‐CPE was applied successfully to highly efficient (current density of 18.2 mA cm^?2) electrocatalytic oxidation of formaldehyde in alkaline medium. Finally, the rate constant for chemical reaction between formaldehyde and redox sites of the electrode was calculated.     

Cu and Ni Nanoparticles Deposited on ITO Electrode for Nonenzymatic Electrochemical Carbohydrates Sensor Applications

A novel non‐enzymatic carbohydrates sensor which was an indium tin oxide (ITO) glass electrode modified by nickel and copper nanoparticles (Cu/Ni/ITO) was developed by an electrochemical method. The crystallinity, morphology, electrochemical measurements and amperometric response of the as‐prepared ITO modified electrode were examined by the X‐ray diffraction (XRD), scanning electron microscopic (SEM), cyclic voltammetry (CV) and chronoamperometry, respectively. The Cu/Ni/ITO electrode had better electroactivity for glucose oxidation than that obtained using Cu/ITO, Ni/ITO, and Ni/Cu/ITO. The logistic regression equation, I_pa = (A ₁ – A ₂)/[1 + (C_glucose /x ₀)^p ] + A ₂, was used to fit the calibration curves of glucose aqueous solution concentrations and responsive current intensity. In research of other saccharides, such as fructose, lactose, sucrose, and maltose, which were detected by the Cu/Ni/ITO electrode, it was obvious that the Cu/Ni/ITO electrode was more sensitive to monosaccharides than disaccharides. Monosaccharides and disaccharides can be detected because the saccharides themselves had aldehyde group or be isomerized to an isomer having an aldehyde group in alkaline environment, and then aldehyde group produced carboxylic acid in the catalytic oxidation of the electrode, which lead to the change of electrode surface conductivity and the appearance of oxidation peak, and the alkaline environment further promotes the above reaction.     

Direct Electrochemistry of Hemoglobin and its Electrocatalysis Based on a Carbon Nanotube Paste Electrode

A new hemoglobin (Hb) and carbon nanotube (CNT) modified carbon paste electrode was fabricated by simply mixing the Hb, CNT with carbon powder and liquid paraffin homogeneously. To prevent the leakage of Hb from the electrode surface, a Nafion film was further applied on the surface of the Hb‐CNT composite paste electrode. The modified electrode was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Direct electrochemistry of hemoglobin in this paste electrode was easily achieved and a pair of well‐defined quasi‐reversible redox peaks of a heme Fe(III)/Fe(II) couple appeared with a formal potential (E^0′) of ?0.441 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The electrochemical behaviors of Hb in the composite electrode were carefully studied. The fabricated modified bioelectrode showed good electrocatalytic ability for reduction of H₂O₂ and trichloroacetic acid (TCA), which shows potential applications in third generation biosensors.     

Ni(II)-baicalein complex modified multi-wall carbon nanotube paste electrode toward electrocatalytic oxidation of hydrazine

A modified electrode Ni(II)-BA-MWCNT-PE has been fabricated by electrodepositing nickel(II)-baicalein [Ni(II)-BA] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. The Ni(II)-BA-MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-BA-CPE. It also shows good electrocatalytic activity toward the oxidation of hydrazine. Kinetic parameters such as the electron transfer coefficient α, rate constant k_s of the electrode reaction, the diffusion coefficient D of hydrazine and the catalytic rate constant k_cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of hydrazine from 2.5 μM to 0.2 mM by amperometry. The detection limit and sensitivity are 0.8 μM and 69.9 μA mM⁻¹, respectively. The modified electrode for hydrazine determination is of the property of simple preparation, good stability, fast response and high sensitivity.