Modified Graphite Electrode Research Articles

A comparative study of the electrooxidation of C1 to C3 aliphatic alcohols on Ni modified graphite electrode

Nickel modified graphite electrodes (G/Ni) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol, ethanol, 1-propanol and 2-propanol in alkaline solutions. The methods of cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, the electrochemical response, peak current varied in the order of MeOH > EtOH > 1-PrOH > 2-PrOH. Under the CA regime, a higher catalytic rate constant obtained for methanol oxidation was in agreement with CV measurements. Lower charge transfer resistance was obtained for low carbon alcohols oxidation and significantly higher exchange current density was obtained for methanol oxidation.

Simultaneous Decolorization and Bioelectricity Generation in a Dual Chamber Microbial Fuel Cell Using Electropolymerized-Enzymatic Cathode

Effect of cathodic enzymatic decolorization of reactive blue 221 (RB221) on the performance of a dual-chamber microbial fuel cell (MFC) was investigated. Immobilized laccase on the surface of a modified graphite electrode was used in the cathode compartment in order to decolorize the azo dye and enhance the oxygen reduction reaction. First, methylene blue which is an electroactive polymer was electropolymerized on the surface of a graphite bar to prepare the modified electrode. Utilization of the modified electrode with no enzyme in the MFC increased the power density up to 57% due to the reduction of internal resistance from 1000 to 750 Ω. Using the electropolymerized-enzymatic cathode resulted in 65% improvement of the power density and a decolorization efficiency of 74%. Laccase could act as a biocatalyst for oxygen reduction reaction along with catalyzing RB221 decolorization. Treatment of RB221 with immobilized laccase reduced its toxicity up to 5.2%. Degradation products of RB221 were identified using GC-MS, and the decomposition pathway was proposed. A discussion was also provided as to the mechanism of dye decolorization on the enhancement of the MFC performance.

An amperometric bienzymatic cholesterol biosensor based on functionalized graphene modified electrode and its electrocatalytic activity towards total cholesterol determination

Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been covalently immobilized onto functionalized graphene (FG) modified graphite electrode. Enzymes modified electrodes were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). FG accelerates the electron transfer from electrode surface to the immobilized ChOx, achieving the direct electrochemistry of ChOx. A well defined redox peak was observed, corresponding to the direct electron transfer of the FAD/FADH2 of ChOx. The electron transfer coefficient (α) and electron transfer rate constant (Ks) were calculated and their values are found to be 0.31 and 0.78s−1, respectively. For the free cholesterol determination, ChOx-FG/Gr electrode exhibits a sensitive response from 50 to 350μM (R=−0.9972) with a detection limit of 5μM. For total cholesterol determination, co-immobilization of ChEt and ChOx on modified electrode, i.e. (ChEt/ChOx)-FG/Gr electrode showed linear range from 50 to 300μM (R=−0.9982) with a detection limit of 15μM. Some common interferents like glucose, ascorbic acid and uric acid did not cause any interference, due to the use of a low operating potential. The FG/Gr electrode exhibits good electrocatalytic activity towards hydrogen peroxide (H2O2). A wide linear response to H2O2 ranging from 0.5 to 7mM (R=−0.9967) with a sensitivity of 443.25μAmM−1cm−2 has been obtained.

Electrosynthesis of polypyrrole composite film and electrocatalytic oxidation of ethanol

Nickel oxide (NiOx) and polypyrrole (PPy) were electrodeposited from NiSO4 and pyrrole through cyclic voltammetry scans to afford PPy–NiOx composite film at controlled pH environment. Surface morphology of the composite was studied by surface microscopy techniques (SEM). The presence of Nickel in the composite films was confirmed by XRD analysis. Modified graphite electrodes (G/NiPPy) were examined for their redox process and electrocatalytic activities towards the oxidation of ethanol in alkaline solutions. The methods of cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) were employed. In CV studies, in the presence of ethanol G/NiPPy modified electrode shows a significantly higher response for ethanol oxidation. A mechanism based on the electro-chemical generation of Ni (III) active sites and their subsequent consumptions by ethanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In addition, G/NiPPy electrode shows a considerably lower onset potential than that of G/Ni in ethanol electrooxidation.

Electrocatalysis of free glycerol at a nanonickel modified graphite electrode and its determination in biodiesel

This study reports the success of using an electrosynthesized nanocrystalline hexagonal close-packed (hcp) nickel (Ni) modified composite graphite (CG) electrode for the electrocatalytic oxidation of glycerol in alkaline medium (0.1 M KOH). The hcp-nano Ni modified CG had an improved response and remarkable electrocatalytic oxidation of glycerol over the bare CG. The electrocatalysis was the result of the formation of NiOOH during the oxidation process. The process was influenced by the scan rate and concentration of glycerol. A linear relationship between the concentrations of glycerol with the current was obtained over a range of 0.5–12.0 mM glycerol, with a limit of detection (S/N = 3) at 0.033 mM glycerol. The hcp-nano Ni modified CG electrode was applied to directly determine the free glycerol concentration in the biodiesel samples. As a glycerol sensor, the hcp-nano Ni modified CG is quite stable.

Non-enzymatic Reduction of Hydrogen Peroxide Sensor Based on (Polyaniline-polystyrene Sulphonate) - Carboxylated Graphene Modified Graphite Electrode

A modified electrode is fabricated by the electrodeposition of polyaniline-polystyrene sulphonate composite onto the carboxylated graphene modified graphite electrode for the detection of hydrogen peroxide (H 2O2). The modified electrode displayed excellent catalytic response to the reduction of hydrogen peroxide in neutral pH. It was found that the presence of carboxylated graphene in the sensor system could effectively increase the electron transfer rate and stability. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. Chronoamperometric studies showed the linear relationship between the reduction peak current and the concentration of H 2O2 in the range 25 to 350 µM ( R = 0.995) with the detection limit of 1×10 -6 mol/L ( S/N =3). Further, electrochemical analysis of H 2O2 in the presence of common interferents such as dopamine, uric acid and ascorbic acid with the modified electrode reveals that there is no overlapping signal from the interferents.

Anodic stripping determination of Pt(IV) based on the anodic oxidation of In from electrochemically deposited Pt–In alloy phases

A simple, rapid, and sensitive anodic stripping voltammetric method for the determination of Pt (IV) is described. It is based on depositing an intermetallic indium–platinum alloy phase on the surface of a modified graphite electrode, and recording the oxidation peak of indium from that alloy phase with the help of linear scan voltammetry. A systematic study of the behavior of different In–Pt phases revealed that the peak potential of indium oxidation from the different phases can be explained on the basis of simple thermodynamic considerations. Different alloy phases have characteristic peak potentials. For the purpose of analysis, it is possible to choose such conditions that only one specific alloy phase forms, viz. PtIn. This is the case for a concentration (milligrams per liter) ratio of In(III)/Pt(IV) = 50,000:1, at least.

A Biosensor Using Poly(4-Aminophenol)/acetylcholinesterase modified graphite electrode for the detection of dichlorvos

The properties of poly(4-aminophenol) modified graphite electrode as material for the immobilization of acetylcholinesterase were investigated by the Cyclic Voltammetry, Electrochemical Impedance Spectroscopy and Atomic Force Microscopy. The polymer was deposited on graphite electrode surface by the oxidation of 4-aminophenol and then acetylcholinesterase was immobilized on the surface of the electrode. The biosensor coupled in the continuous flow system was employed for the detection of dichlorvos. The detection and quantification limits were 0.8 and 2.4 μmol L-1 dichlorvos, respectively. Graphite electrodes modified with the poly(4-aminophenol) showed to be an efficient and promising material for immobilization of acetylcholinesterase enzyme. The proposed method requires simple parts which are easy to build, involves only one biosensor and the potentiometric detection is simple.

MWNT-modified electrodes for voltammetric determination of lipophilic vitamins

Multi-walled carbon nanotube modified graphite electrodes (MWNT-GEs) have been created for the voltammetric determination of α-tocopherol and retinol. The electrode surface was characterized by atomic force microscopy. The MWNT-GEs presented structured surfaces and a significant (26-fold) increase in roughness over unmodified graphite electrodes (8.2 vs. 0.32 nm for MWNT-GEs and GEs, respectively). Their surfaces consisted of aggregates with a highly regular “thorn-like” structure. α-Tocopherol and retinol were oxidized on the bare GEs and the MWNT-GEs in 0.1 M HClO4 in acetonitrile. Decreases in the overpotential of 0.2 and 0.04 V for α-tocopherol and retinol, respectively, and increased oxidation currents were observed on the MWNT-GEs in comparison with the unmodified electrodes. The calibration graphs were linear in the range 0.065–2.00 mM for α-tocopherol and 0.05–1.50 mM for retinol. The detection limits were found to be 0.05 and 0.04 mM for α-tocopherol and retinol, respectively. The developed electrodes were applied to determine α-tocopherol and retinol in pharmaceuticals. The results obtained agreed well with coulometric titration data.

Single-walled carbon nanotubes-polymer modified graphite electrodes for DNA hybridization

Single-walled carbon nanotubes (SWCNT)-poly(vinylferrocenium) (PVF +) modified pencil graphite electrodes (PGEs) were developed in our study for the electrochemical monitoring of a sequence-selective DNA hybridization event. Firstly, SWCNT-PVF + modified PGE, PVF + modified PGE and unmodified PGE were characterized using scanning electron microscopy (SEM). The electrochemical behavior of these electrodes was then investigated using electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The SWCNT-PVF + modified PGEs were optimized for improved DNA sensing ability by measuring the guanine oxidation signal. In order to obtain the full coverage immobilization of the DNA probe following the optimum working conditions, the effect of amino-linked, thiol-linked and, bare oligonucleotides (ODNs), and the concentration of the DNA probe on the response of the modified electrode were examined. After optimization studies, the sequence-selective DNA hybridization was evaluated in the case of hybridization between an amino-linked probe and its complementary (target), a noncomplementary (NC) sequence, calf thymus double stranded DNA (dsDNA), and target/mismatch (MM) mixtures in the ratio of 1:1. SWCNT-PVF + modified PGEs presented very effective discrimination of DNA hybridization owing to their superior selectivity and sensitivity.

Simple and reliable biosensor for determination of glucose in alcoholic beverages

The objective of this work was to determine the glucose in alcoholic beverages using the simple and reliable glucose oxidase (GOx) biosensor. Glucose oxidase was immobilized on the surface of modified graphite electrode in mixed photocurable polymeric membranes of polyacrylamide (PAA)/polyvinylpyrolidone (PVP), taking advantage of both immobilizations; higher activity due to enzyme entrapment (PVP) and longer life of biosensor due to covalent bonding of enzyme (PAA). The surface of graphite electrode was modified with electrodeposited layer of indium (III) and ruthenium (III) hexacyanoferrate films to get faster electron transfer through the surface layer of the modified electrode. Voltammetric and amperometric measurements were performed under batch conditions.The response of biosensor was measured as a function of selected organic solvents (methanol, ethanol and isopropanol) containing phosphate buffer solution (pH=6.5) at −100mV against a reference Hg∣Hg2Cl2∣3M KCl electrode. Addition of 10% of methanol and ethanol increased, while higher volume fractions decreased the biosensor response. On the other hand isopropanol (10%) decomposed the photopolymeric membrane. Therefore, the determination of glucose in alcoholic beverages has been performed in phosphate buffer with 10% of ethanol. The linear range was obtained up to 0.8mM (R2=0.9925) for mixed solvents, as well as phosphate buffer (R2=0.9996).The simple, fast and easy preparation of the biosensor, high activity and long life, if glucose was immobilized in mixed polymeric photocurable membrane, and reasonably accurate glucose determination, make the proposed procedure appropriate for quality control of the alcoholic beverages in mixed solvents.

Bioelectrochemically Reductive Dechlorination of Trichloroacetic Acid by Gel Immobilized Hemoglobin on Multiwalled Carbon Nanotubes Modified Graphite Electrode

Bioelectrochemically Reductive Dechlorination of Trichloroacetic Acid by Gel Immobilized Hemoglobin on Multiwalled Carbon Nanotubes Modified Graphite Electrode

Electrochemical detection of acetaminophen on the functionalized MWCNTs modified electrode using layer-by-layer technique

A selective electrochemical method is fabricated via layer-by-layer (LBL) method using both positively and negatively charged multi walled carbon nanotubes (MWCNTs) on poly (diallyldimetheylammonium chloride) (PDDA)/poly styrene sulfonate (PSS) modified graphite electrode, for the determination of acetaminophen (ACT) in the presence of dopamine (DA) and high concentration of ascorbic acid (AA). The modified electrode was characterized by cyclic voltammetry (CV) electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Experimental conditions such as pH, accumulation potential and time, effect of potential sweep rates and interferents were studied. In CV well defined peaks for AA, ACT and DA are obtained at 24, 186 and 374 mV, respectively. The separations of peaks were 210, 188 and 398 mV between AA and DA, DA and ACT and AA and ACT, respectively. The diffusion coefficient was calculated by chronocoulometric. Chronoamperometric studies showed the linear relationship between oxidation peak current and concentration of ACT in the range 25–400 μM ( R = 0.9991). The detection limit was 5 × 10 −7 mol/L. The proposed method gave satisfactory results in the determination of ACT in pharmaceutical and human serum samples.

Hg(II) immobilized MWCNT graphite electrode for the anodic stripping voltammetric determination of lead and cadmium

The preparation of Hg(II)-modified multi walled carbon nanotube (MWCNT) by reaction of oxidized MWCNT with aqueous HgCl2 was carried out. The Hg(II)-modified multi walled carbon nanotube (Hg(II)/MWCNT) dispersed in Nafion solution was used to coat the polished graphite electrode surface. The Hg(II)/MWCNT modified graphite electrode was held at a cathodic potential (−1.0V) to reduce the coordinated Hg(II) to Hg forming nanodroplets of Hg. The modified electrode was characterized by FESEM/EDAX which provided useful insights on the morphology of the electrode. The SEM images showed droplets of Hg in the size of around 260nm uniformly distributed on the MWCNT. Differential pulse anodic stripping voltammetry (DPASV) and electrochemical impedance spectroscopy were used to study the Hg(II) binding with MWCNT. Differential pulse anodic stripping voltammetry of ppb levels of cadmium and lead using the modified electrode yielded well-defined peaks with low background current under a short deposition time. Detection limit of 0.94 and 1.8ngL−1 were obtained following a 3min deposition for Pb(II) and Cd(II), respectively. Various experimental parameters were characterized and optimized. High reproducibility was observed from the RSD values for 20 repetitive measurements of Pb(II) and Cd(II) (1.7 and 1.9%, respectively). The determination of Pb(II) and Cd(II) in tap water and Pb(II) in human hair samples was carried out. The above method of fabrication of Hg(II)/MWCNT modified graphite electrode clearly suggests a safe route for preparing Hg immobilized electrode for stripping analysis.

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264 mV between AA–DA, DA–UA and AA–UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.

Electrochemical Behavior and Determination of Dopamine at ZnO Nanorods Intercalated Graphite Modified Electrode

Hydrothermally prepared zinc oxide nanorods were characterized by scanning electron microscopy and infrared spectroscopy.The zinc oxide nanorod modified graphite electrode was prepared by intercalation for dopamine determination.Voltammetric behavior and reaction mechanism of dopamine at the modified graphite electrode were investigated with cyclic voltammetry and differential pulse voltammetry.The results showed that there were good voltammetric responses for dopamine at the modified electrode under optimal conditions,with peak currents greatly enhanced and an negative shift of anodic peak potential by 68 mV.Kinetic properties of the electrochemical process were also obtained: the number of transfer electrons(n) is 2 and the electron transfer coefficient(α) is 0.48.The peak currents of differential pulse voltammetry of dopamine are linear in the ranges of 5.0×10-7~1.0×10-4 mol/L with a detection limit of 1.0×10-7 mol/L at the signal-to-noise of 3.Relative standard deviation(RSD) is 3.42% for eight parallel detections of 1.0×10-5 mol/L dopamine.The recoveries of this proposed method for determination of dopamine hydrochloride injection solutions are in the range of 94.83%~104.5%.

Electrocatalytic Oxidation of NADH on Functionalized Graphene Modified Graphite Electrode

AbstractGraphite electrode modified with functionalized graphene (FG) is a new family of electrocatalysts for the oxidation of nicotinamide adenine dinucleotide (NADH). A substantial decrease in the over potential of NADH oxidation is observed on functionalized graphene modified graphite electrode (FGGE). The COO− functionalized graphene is characterized by powder X‐ray diffraction and infrared spectroscopy techniques and the modified FGGE is characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy and scanning electron microscopy. The modified electrode is found to be stable and reproducible. The FGGE shows rapid and highly sensitive amperometric response to NADH.

Pseudo-Capacitive and Electrocatalytic Properties of Electrochemically Modified Graphite Electrode in Different Solutions

A graphite electrode (GE) was electrochemically modified by recurrent galvanic pulses. The pseudo-capacitive behavior in acidic and neutral solutions and the electrocatalytic property in HCl and HNO3 solutions of the modified graphite electrode (MGE) were evaluated by cyclic voltammetry (CV). We found that the MGE exhibited a considerable pseudo-capacitance (the specific capacitance was high up to 1.730 F·cm - 2 ) in H2SO4 solution and excellent pseudo-capacitive behavior was obtained in HCl solution as well except for a narrow potential window. This was due to the excellent electrocatalytic activity of the MGE toward the chlorine evolution reaction (the onset potential of chlorine evolution was negatively shifted 238 mV). However, the MGE showed no pseudo-capacitive behavior in HNO3 solution but did show electrocatalytic activity toward the reduction of nitric acid. Compared with the pseudo-capacitive behavior in acidic solutions, the potential window of the MGE in neutral solution was substantially broadened and its energy density improved greatly eventually even though the corresponding peak current density decreased.

Voltammetric Detection of Dopamine in Presence of Ascorbic Acid and Uric Acid at Poly (Xylenol Orange) Film-Coated Graphite Pencil Electrode

Poly (xylenol orange) film-coated graphite pencil electrode was fabricated for the detection of dopamine in the presence of ascorbic acid and uric acid in phosphate buffer solution of pH 7. The redox peaks obtained at modified electrode shows a good enhancement. The scan rate effect was found to be a diffusion-controlled electrode process. The electrochemical oxidation of dopamine was depended on pH, and the limit of detection was found to be 9.1×10−8 M. The simultaneous study gave and excellent result with great potential difference between dopamine and other bioactive organic molecules by using both cyclic voltammetric and differential pulse voltammetric techniques. The present modified graphite electrode was applied to the detection of dopamine in the injection samples, and the recovery obtained was satisfactory.

Electro-oxidation of alcohols on nickel dispersed in poly-o-aminophenol modified graphite electrode

Electro-oxidation of alcohols (methanol, ethanol, 1-propanol and 2-propanol) on nickel dispersed into a thick layer of poly-o-aminophenol on graphite electrode (GE/POAP–SDS/Ni) was investigated. Ni-doping into the polymeric film was achieved chemically followed by enrichment of Ni(III) through cycling the potential. The electro-oxidation of alcohols on GE/POAP–SDS/Ni were found to be dominated by direct electro-oxidation with some contribution from Ni(II)/Ni(III) couple. Rate constants for the electro-oxidation of methanol, ethanol, 1-propanol and 2-propanol as derived by chronoamperometry were 1.65 × 10 5, 1.31 × 10 5, 2.53 × 10 4 and 1.40 × 10 4 cm 3 mol −1 s −1, respectively. Impedance spectroscopy was used to shed more light on the mechanism. Equivalent circuit is proposed and kinetic parameters of the reaction as well as the electrical parameters of the doped polymeric film are obtained.