Electrocatalytic Oxidation of Some Carbohydrates by Nickel/Poly(o‐Aminophenol) Modified Carbon Paste Electrode

This study investigates the electrocatalytic oxidation of glucose and some other carbohydrates on nickel/poly(o‐aminophenol) modified carbon paste electrode as an enzyme free electrode in alkaline solution. Poly(o‐aminophenol) was prepared by electropolymerization using a carbon paste electrode bulk modified with o‐aminophenol and continuous cyclic voltammetry in HClO₄ solution. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 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 glucose and other carbohydrates was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for each carbohydrate were calculated. Also, the electrocatalytic oxidation peak currents of all tested carbohydrates exhibit a good linear dependence on concentration and their quantification can be done easily.     

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.     

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.     

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.     

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.     

Preparation of Ni/poly(1,5-diaminonaphthalene)-modified carbon paste electrode; application in electrocatalytic oxidation of formaldehyde for fuel cells

This paper deals with electrochemical oxidation of formaldehyde in alkaline solution with a new electrocatalytic system composed of carbon paste electrode coated with poly(1,5-diaminonaphthalene) (P-1,5-DAN) film containing incorporated Ni(II)/Ni(III) redox ions. The modifier layer of (P-1,5-DAN-Ni)(OH)₂ at the electrode surface acts as a catalyst for the oxidation of formaldehyde in 0.1-M NaOH solution. Cyclic voltammetric and chronoamperometric experiments showed that the formaldehyde can be oxidized at the surface of Ni/P-1,5-DAN-modified carbon paste electrode. In cyclic voltammetry studies, the peak current of the oxidation of nickel hydroxide in the presence of formaldehyde increases and is followed by a decrease in the corresponding cathodic current. The rate constant (k) for the chemical reaction between the formaldehyde and nickel hydroxide has been evaluated by chronoamperometry method. This polymeric-modified electrode can oxidize the formaldehyde with high current density (over 7 mA cm⁻²). Thus, it can be a candidate as an anode for fuel cell applications.     

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.     

The Determination of Methanol Using an Electrolytically Fabricated Nickel Microparticle Modified Boron Doped Diamond Electrode

A nickel modified boron doped diamond (Ni‐BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni‐BDD electrode was electrodeposited from a 1 mM Ni(NO₃)₂ solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)₂/NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni‐BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni‐BDD to be modified by a quasi‐random microparticle array.     

Voltammetric Characterization of Grafted Polymer Modified with ZnO Nanoparticles on Glassy Carbon Electrode

In this study, a grafted polymer (GP) with ZnO nanoparticles (GP/ZnO NPs) was attached on the surface of glassy carbon electrode (GCE), in order to produce a new modified electrode (GP/ZnO NPs-GCE). The gamma irradiation method was used to grafted polystyrene (polymer) with acrylonitrile (monomer), while slow evaporation process was used to prepare the new modified electrode. The cyclic voltammetry (CV) of K₄[Fe(CN)₆] was used to study the electrochemical properties GP/ZnO NPs-GCE. The peak separation (ΔE_pa-c) was 500 mV between the redox peaks of Fe(II)/Fe(III) in an aqueous solution of 1 M KCl and the current ratio of redox current peaks (I_pa/I_pc) was ≈ 1 for the modified electrode. This indicated that the modified electrode has s good reversibility and conductivity, wherefore; it was applied in the voltammetric filed. It was found that the modified electrode GP/ZnO NPs-GCE have a reasonable solubility and stability at various pH medium. Additionally, the sensitivity of the electrochemical analysis by cyclic voltammetric (CV) method is extensively subjected to the pH medium and the scan rate (SR). A couple of redox current peaks of K₄[Fe(CN)₆] in KCl solution was observed with a reversible process: Fe³⁺/Fe²⁺. Finally a good diffusion coefficient of electroactive species (D) for the new modified electrode was found in this study by chronoamperometry method using Cottrell equation.     

Renewable Surface Sol‐Gel Derived Carbon Ceramic Electrode Modified with [Ru(NH3)5Cl](PF6)2 Complex : Application to Amperometric Detection of Chlorate

A novel modified carbon ceramic electrode (CCE ) containing [Ru(NH₃)₅ Cl](PF₆)₂ complex was fabricated by sol‐gel technique. The cyclic voltammograms of the modified electrodes show a well defined redox couple due to Ru(III)/Ru(II) system with surface confined characteristics. The stability of the modified CCE modified with ruthenium complex was checked over several days, obtaining reproducible results. Chlorate has been chosen as a model to elucidate the electrocatalytic ability of modified CCE. The modified electrode showed excellent electrocatalytic activity toward chlorate electroreduction in acidic medium. Chlorate was determined amperometrically at the surface of this modified electrode in pH 2 solution. Under the optimized conditions the calibration curve is linear in the concentration range 10 μM?5 mM chlorate. The detection limit and sensitivity are 1 μM and 0.43 nA/μM respectively. The advantages of the modified CCE is its good stability and reproducibility of surface renewal by simple polishing, excellent catalytic activity and simplicity of preparation. This sensor can be used as an amperometric detector in flow systems. or chromatographic instruments.     

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.     

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 Investigations of Cu(II) and Fe(III) Complexes of Salophen Derivative Schiff Bases on the Pencil Graphite Electrode

This present study describes a pencil graphite electrode surface covered with Cu(II) and Fe(III) complexes based on Salophen derivative Schiff bases in acetonitrile solution containing LiClO₄ as a supporting electrolyte. Cyclic voltammetry method was used for the surface modification procedure with 25 cycle at a sweep rate of 50 mV s^?1. Some characterization methods were used to identify of the prepared modified surfaces including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Ultraviolet‐visible Spectroscopy (UV‐Vis), and Scanning Electron Microscopy/Energy Dispersive X‐ray Spectroscopy (SEM/SEM‐EDX). The catalytic activity of these modified surfaces on the electrochemical oxidation of catechol (CC) was investigated and they compared with each other. The results demonstrated that these modified electrodes showed perfect electrocatalytic activity on the catechol determination, however the modified electrode prepared with the Cu(II) complex has higher catalytic activity than this prepared with the Fe(III) complex thanks to its the lower detection limit.     

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.     

Electrocatalytic Oxidation of Sulfur Containing Amino Acids at Renewable Ni‐Powder Doped Carbon Ceramic Electrode: Application to Amperometric Detection L‐Cystine,L‐Cysteine and L‐Methionine

A sol‐gel technique was used here to prepare a renewable carbon ceramic electrode modified with nickel powder. Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple due to Ni(II)/Ni(III) system with surface confined characteristics. The modified electrode shows excellent catalytic activity toward L ‐cystine, L ‐cysteine and L ‐methionine oxidation at reduced overpotential in alkaline solutions. In addition the antifouling properties at the modified electrode toward the above analytes and their oxidation products increases the reproducibility of results. L ‐cystine, L ‐cysteine and L ‐methionine were determined chronoamperometricaly at the surface of this modified electrode at pH range 9–13. Under the optimized conditions the calibration curves are linear in the concentration range 1–450 μM, 2–90 μM and 0.2–75 μM for L ‐cystine, L ‐methionine and L ‐cysteine determination, respectively. The detection limit and sensitivity were 0.64 μM, 3.8 nA/ μM for L ‐cystine, 2 μM, 5.6 nA/ μM for L ‐methionine and 0.2 μM and 8.1 nA/μM for L ‐cysteine. The advantageous of this modified electrode is high response, good stability and reproducibility, excellent catalytic activity for oxidation inert molecules at reduced overpotential and possibility of regeneration of the electrode surface by potential cycling for 5 minutes. Furthermore, the modified electrode has been prepared without using specific reagents. This sensor can be used as an amperometric detector for disulfides detection in chromatographic or flow systems.     

Hemoglobin Modified Carbon Paste Electrode: Direct Electrochemistry and Electrocatalysis

Abstract

A new hemoglobin (Hb) modified carbon paste (CP) electrode was fabricated by simply mixing the hemoglobin with carbon powder and paraffin homogeneously. To prevent the leakage of Hb from the electrode surface, a Nafion film was further applied on the surface of Hb-carbon composite paste electrode. Direct electrochemistry of hemoglobin in the paste electrode was easily achieved, and a pair of well-defined quasi-reversible redox peak of heme Fe(III)/Fe(II) couple appeared with the formal potential (E^0′) as ?0.335 V (vs. Saturated calomel electrode; CE) in pH 7.0 phosphate buffer solution (PBS). The fabricated Hb modified electrode showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) and H₂O₂.     

Renewable Surface Sol‐gel Derived Carbon Ceramic Electrode Modified with Copper Complex and Its Application as an Amperometric Sensor for Bromate Detection

A sol‐gel technique was used for the preparation of a three dimensional carbon composite electrode modified with [Cu(bpy)₂]Br₂ complex. A reversible redox couple of Cu(II)/Cu(I) is observed at the electrode surface. The electrochemical behavior and stability of the modified electrode was characterized by cyclic voltammetry. The charge transfer coefficient (α) and charge transfer rate constant (K_s) for the modified electrode were determined by cyclic voltammetry, which were found to be 0.46 and 14.2 s^?1, respectively. The modified electrode showed excellent catalytic activity toward bromate reduction at significantly reduced overpotentials and can be used successfully for amperometric detection of bromate. Under the optimized conditions, the calibration plots are linear in the concentration range 0.5 μM ?200μM. Detection limit (signal to noise is 3) and sensitivity were found to be 0.1 μM and 20 nA / μM, respectively. These analytical parameters compare favorably with those obtained with modern analytical techniques. The modified carbon ceramic electrode doped with Cu‐Complex shows a good reproducibility, a short response time (t<2 s), remarkable long term stability (>4 months) and especially good surface renewability by simple mechanical polishing (RSD for 6 successive polishing is 1.5%).     

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.     

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.     

Electropolymerization of N,N-dimethylaniline in presence of sodium dodecyl sulfate and its electrochemical properties

Poly(N,N-dimethylaniline) (PDMA) 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. The polymerization behavior of N,N-dimethylaniline in the presence of SDS is quite different from that of N,N-dimethylaniline in the absence of SDS. The effect of varying amount of SDS on the rate of polymerization of N,N-dimethylaniline was investigated. The electrochemical behavior of the SDS-PDMA carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M H₂SO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. The synthesized PDMA was characterized by FT-IR and scanning electron microscopy (SEM). 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. The electro catalytic oxidations of methanol at the surface of the Ni/SDS-PDMA electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and PDMA-modified carbon paste electrodes; the SDS-PDMA electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation.