Modified Graphite Electrode Research Articles

Determination of isoniazid by a copper-based metal-organic frameworks/carbon nitride quantum dots modified pencil graphite electrode as a highly sensitive and selective sensor

Abstract In this work, a particular electrochemical sensor for analysis of isoniazid (INZ), a tuberculostatic drug, was presented. The electrotreated pencil graphite electrode (ETPGE) was modified by a nanocomposite of the copper-based metal-organic frameworks (Cu-MOFs)/carbon nitride quantum dots (CNQDs), Cu-MOFs/CNQDs/ETPGE, and was utilized for electroanalysis of INZ. Physicochemical characteristics and analytical performance of the Cu-MOFs/CNQDs/ETPGE were investigated through relevant instruments. Compared with bare PGE, ETPGE, CNQDs/ETPGE, and Cu-MOFs/ETPGE, the Cu-MOFs/CNQDs/ETPGE showed strong electrocatalytic activity for oxidation of the INZ and exhibited a well-defined anodic peak at a low potential of +0.364 V versus Ag/AgCl in pH 7.0 medium due to its high specific surface area, high conductivity and fast charge transfer ability. The experimental results demonstrated that the Cu-MOFs/CNQDs/ETPGE has a promising potential candidate as a stable and efficient electrochemical sensor for determination of INZ. Under the optimized experimental conditions, the designed sensor presented a wide linear response range for INZ concentration (0.1 μM to 65.0 μM) with a low practical detection limit (0.0675 μM), limit of quantification (LOQ) (0.225 μM), high sensitivity (1.507 A mol−1 L cm−2) and excellent repeatability in differential pulse voltammetry. Further, the suggested method was employed successfully for determination of INZ in drug and biological samples with satisfactory recovery values.

A novel electrochemical immobilization of Hg in CdSe QDs - modified graphite electrode and its improved performance in voltammetric determination of lead (II) ion

A novel metal ion sensor was fabricated through electrochemically immobilized Hg spheres on surface-unpassivated CdSe quantum dots modified paraffin wax impregnated graphite electrode. The size and surface morphology of the CdSe QDs and CdSe QDs - Hg modified electrode was characterized by transmission electron microscope and field emission scanning electron microscopy. The modified electrode was also characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode was used for the determination of trace level lead ion which was preconcentrated onto the modified electrode by differential pulse anodic stripping voltammetry (DPASV). Numerous key variables affecting the current response of lead ion have been optimized. The proposed electrode has a linear concentration range of 5.2 ng/L–4.2 µg/L with a optimized deposition time of 180 s and the detection limit is found to be 1.7 ng/L (S/N = 3). The electroanalytical performance of the modified electrode was successfully tested in a real sample of tap water and sea water spiked with Pb(II) ion. The proposed electrode shows excellent selectivity and sensitivity over other heavy metals, such as copper, zinc, manganese and tin. Hg(II) immobilized CdSe QDs modified electrode has shown great potential application in detecting metal ions at very low concentrations.

Study of Organic Sulfide Oxidation on the Modified Graphite Electrodes by Co, Fe and Ni Nano Particles

Electro-oxidation of methyl phenyl sulfide with the aim of producing sulfoxide and sulfone was investigated over Ni, Co, Fe, and their alloys on graphite electrodes in the acetic acid as a non-toxic solvent. The modified electrodes were prepared by cyclic voltammetry technique. The surface morphology of electrodes was investigated by scanning electron microscopy and the presence of metal nanoparticles on the graphite was investigated by X-ray diffraction. The catalytic treatment and synergistic effects of the modified electrodes were studied by electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). It was found the performance of all the modified electrodes is successful. In the attendance of methyl phenyl sulfide, the graphite/CoFe modified electrode (G/CoFe) showed the highest performance for electro-oxidation also there was a linear relationship between the square root of the scan rate and anodic current in low scan rates, that indicates a diffusion controlled process. The diffusion coefficient, heterogeneous electron transfer rate constant and electron transfer coefficient were determined for methyl phenyl sulfide electrochemical oxidation. Electro-oxidation of methyl phenyl sulfide by electrolysis method was investigated and its results were studied by gas chromatograph (GC). Based on GC studies, the electro-oxidation of methyl phenyl sulfide by electrolysis produced methyl phenyl sulfoxide and methyl phenyl sulfone. Also, a mechanism for electro-oxidation of sulfide was proposed. The using of non-noble metals as the electrocatalyst for the first time for the organic sulfide electro-oxidation, the very easy, affordable and fast preparation of the modified electrode, high performance of the modified electrode, no need of using oxidant and co-catalyst and designing a homogeneous media with proper conductivity for oxidation of insoluble in water compounds demonstrate important items for the use of this procedure and electrode in the subsequent investigation of sulfides.

Electrochemical Detection of Dopamine and Tyrosine using Metal oxide (MO, M=Cu and Ni) Modified Graphite Electrode: a Comparative Study

An electrochemical oxidation of dopamine (DA) and tyrosine (Tyr) by metal oxide (MO) modified electrode where M=Cu and Ni in phosphate buffer solution (PBS), pH 7.0 has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. CuO and NiO nanoparticles were prepared by sol-gel process and co-precipitation method respectively and their structure, composition and surface morphology were examined by SEM, XRD, FTIR, UV and Raman techniques. A simple drop cast method is employed for the surface modification of graphite electrode to prepare MO modified electrode and it exhibited good electrocatalytic activity towards detection of DA and Tyr. The present investigation on CV studies of DA at CuO modified electrode showed a reversible oxidation process with an anodic peak potential at +0.249V vs. SCE. However, no specific anodic oxidation peak identified with NiO modified electrode. Subsequent CV studies with Tyr at MO modified electrode (M=Cu, Ni) shows an irreversible oxidation process and both modified electrodes exhibited an anodic peak at a potential of +0.80V against very low or no anodic peak currents obtained at bare graphite electrode. Moreover, the CuO modified electrode (CMG) successfully separated the anodic signals of dopamine (DA), Ascorbic acid (AA) and Tyrosine in their ternary mixture whereas on bare graphite a single, overlapped oxidative peak was observed. In CV studies, the peak potential difference between AA-DA, DA-Tyr and AA-Tyr is 166 mV, 323 mV and 489 mV respectively and the corresponding peak potential separations are 209 mV, 400 mV and 609 mV respectively in differential pulse voltammetry (DPV). Owing to good stability, selectivity and simple low cost fabrication method, CuO modified electrode is found to be well suited for simultaneous determination of DA, AA and Tyr in their ternary mixture. Additionally, NiO modified electrode also shows good sensitivity towards the detection of tyrosine, so it acts as a good electrochemical sensor to assay tyrosine in the biological sample.

Polypyrrole‐Based Nanohybrid Electrodes: Their Preparation and Potential Use for DNA Recognition and Paclitaxel Quantification

AbstractFabrication of conducting polymer networks based on polypyrrole/multi‐walled carbon nanotubes (PPy/MWCNTs) modified graphite electrodes that were achieved with a single‐step electropolymerization and potential use of these electrodes for deoxyribonucleic acid (DNA) recognition and anticancer drug (Paclitaxel, PTX) quantification were presented in the present work. PPy/MWCNTs nanohybrid PGEs were constructed in aqueous solution of pyrrole (Py) and MWCNTs using cyclic voltammetry (CV) and constant potential electrolysis. So‐formed electrodes were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Surface morphologies of the surfaces were investigated by scanning electron microscopy (SEM) studies. Bio‐application of the PPy/MWCNTs nanohybrid modified PGEs were accomplished by subjecting them to double‐stranded DNA (dsDNA) modification for direct DNA recognition and PTX determination. For the drug determination, interaction of DNA‐based electrodes with PTX was investigated. Detection limit was found as 1.55 x 10−8 M based on the changes in the oxidation of guanine base which made the proposed electrode convenient for clinical trials.

Evaluation of human macrophage functional state by voltammetric monitoring of nitrite ions.

The method for assessing the level of nitric oxide (II) (NO) by voltammetric monitoring of nitrite ions was carried out on models M1 and M2 of polarized macrophages induced from monocytes of human peripheral blood with the addition of lipopolysaccharide (LPS) and interleukin-4 (IL-4), respectively. The model of induction of M1 and M2 macrophages was used in the work to achieve the corresponding shifts in the functional status of studied cells. Ethyl nitrite (EtONO) was used as a standard compound of nitrite ions for electrochemical measurements. Electrochemical determination of nitrite ions was performed by anodic linear sweep voltammetry in the first-order derivative mode (ALSV FOD) in Britton-Robinson (BR) buffer with pH4.02 on carbon ink modified graphite electrode. EtONO calibrations were linear over a concentration range from 2 to 9μmolL-1 with corresponding regression equation y = 0.768c - 0.048. Limit of detection (LOD) (S/N = 3) was 0.38μmolL-1. The results of the study showed the fundamental possibility of using voltammetry to assess indirectly the production of nitric oxide by cells in supernatants of the monocytic macrophage lineage. The level of nitric oxide metabolites (nitrite ions) in supernatants was associated with the functional state of macrophages.

Polyaniline-MnO2 composites prepared in-situ during oxidative polymerization of aniline for supercapacitor applications

Polyaniline-manganese dioxide (PAni-MnO2) composites of varying compositions were prepared by in situ chemical oxidative polymerization of aniline monomer in aqueous acidic medium in the presence of different amounts of MnO2 formed in situ by the reaction of MnSO4 with KMnO4. PAni was also synthesized from aniline in acidic solution using ammonium peroxydisulfate as an oxidant for use as a reference material. PAni and PAni-MnO2 composites were characterized by FT-IR spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). FT-IR spectra revealed the formation of PAni and PAni-MnO2 composites. SEM images showed different morphologies of PAni and PAni-MnO2 composites and spherical MnO2 particles were distributed in the PAni matrix. Modified graphite electrode was prepared with PAni and PAni-MnO2 composites using solvent casting technique. Supercapacitive performance of PAni and PAni-MnO2 composites in 0.5 M aqueous Na2SO4 electrolytic solution was investigated using cyclic voltammetric and chronopotentiometric techniques. The specific capacitance (Cs) of PAni-MnO2 composites as high as 242 F g−1 could be obtained which was stable up to 1000 cycles at a current density of 0.25 A g−1. Electrochemical capacitors were developed by fabricating graphite electrodes modified with PAni and PAni-MnO2 composite electrodes in the range of 0.0–0.8 V. The Cs of the materials was found to be 99 to 242 F g−1 at a current density of 0.10 A g−1 in the potential range of 0.0 to 0.8 V. These results indicate that PAni and PAni-MnO2 composites have potential for application in supercapacitors.

Determination of Heavy Metals in Herbal Food Supplements using Bismuth/Multi-walled Carbon Nanotubes/Nafion modified Graphite Electrodes sourced from Waste Batteries

An electrochemical sensor based on graphite electrode extracted from waste zinc-carbon battery is developed. The graphite electrode was modified with bismuth nanoparticles (BiNP), multi-walled carbon nanotubes (MWCNT) and Nafion via the drop coating method. The bare and modified graphite electrodes were used as the working electrode in anodic stripping voltammetry for the determination of trace amounts of cadmium (Cd2+) and lead (Pb2+). The modified electrode exhibited excellent electroanalytical performance for heavy metal detection in comparison with the bare graphite electrode. The linear concentration range from 5 parts per billion (ppb) to 1000 ppb (R2 = 0.996), as well as detection limits of 1.06 ppb for Cd2+ and 0.72 ppb for Pb2+ were obtained at optimized experimental conditions and parameters. The sensor was successfully utilized for the quantification of Cd2+ and Pb2+ in herbal food supplement samples with good agreement to the results obtained by atomic absorption spectroscopy. Thus, the BiNP/MWCNT/Nafion modified graphite electrode is a cost-effective and environment-friendly sensor for monitoring heavy metal contamination.

Carboxylated graphene-alcohol oxidase thin films modified graphite electrode as an electrochemical sensor for electro-catalytic detection of ethanol

A new enzyme-electrode is developed for the determination of ethanol by immobilizing carboxylated graphene (CG) and alcohol oxidase (AOX) on poly diallyldimethylammonium chloride (PDDA) modified graphite electrode (Gr). The biosensor showed high sensitivity and rapid detection of ethanol in the concentration range 250 μM to 1500 μM. Addition of ethanol reduced the reduction current of oxygen, which is due to the consumption of molecular oxygen for the oxidation of ethanol. The effect of temperature and pH on the performance of the biosensor has been studied. The excellent performance of the biosensor is attributed to large surface to volume ratio and high conductivity of graphene. This promotes direct electron transfer between redox enzymes and electrode surface. Low operating potential and specificity of the enzyme will restrict the interference of ascorbic acid, acetaminophen, and glucose. The biosensor was characterized by field emission scanning electron microscopy (FESEM) and cyclic voltammetry (CV) using Fe2+/Fe3+ as an electrochemical probe.

Efficient improvement of microbial fuel cell performance by the modification of graphite cathode via electrophoretic deposition of CuO/ZnO

Microbial fuel cells (MFCs) are considered renewable energy sources in recent years. Their major advantages are energy production, wastewater treatment, and application of microorganisms as available and inexpensive biocatalysts. In this study, the electrophoretic deposition of CuO/ZnO nanoparticles on the surface of graphite electrode and also the performance of the modified electrode as the cathode of an H-type MFC were investigated, for the first time. FESEM, XRD, EDX, and elemental mapping were used to characterize the nanoparticles and the modified electrode. According to the FESEM and elemental mapping analyses, the nanoparticle immobilization was homogeneous on the surface of the electrode. The ability of the modified electrode was investigated on decreasing the oxygen reduction reaction (ORR) overpotential. The MFC performance was evaluated with and without visible light irradiation. The maximum voltage of 363.5 mV was achieved by the modified graphite electrode under the irradiation after 47 h. This maximum voltage was 32.22% higher than that of the bare graphite. The maximum power density of the modified electrode was 51.84 mW m−2 at a current density of 144 mA m−2, i.e. 2.74 times of the bare graphite under visible light irradiation. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to evaluate the electrochemical behavior of the modified electrode, showing the improvement of the electrochemical activity of the modified graphite compared with the bare one.

Electrochemical determination of mercury (II) using NaPb4-xCdx(PO4)3 (0 ≤ x ≤ 2) modified graphite electrode: application in fish and seawater samples

ABSTRACT The aim of this work is the synthesis of a new series of lacunar apatite NaPb4-xCdx(PO4)3 (0 ≤ x ≤ 2) by the solid-state reaction, in which the substitution was selected between cadmium and lead. These powders were crystallised in the hexagonal system, space group P63/m. The characterisation of apatite powders was carried out using X-ray powder diffraction, Infrared and Raman spectroscopy. The prepared apatite was used as a modifier of carbon electrode for mercury (II) analysis using differential pulse anodic stripping voltammetry. The best distribution of apatite has been selected in terms of high electrochemical response of mercury oxidation. The obtained results show excellent linear calibration curves in the range of 9.0 × 10−7 – 1.0 × 10−4 mol L−1 with a detection limit of 1.35 × 10−8 mol L−1. The selectivity of this electrode was evaluated in the presence of other metal ions. Furthermore, the analytical methodology was then successfully applied to monitor mercury in fish and seawater samples.

3-Acrylamidopropyl-trimethylammoniumchloride cationic hydrogel modified graphite electrode and its superior sensitivity to hydrogen peroxide

A highly sensitive hydrogen peroxide (H2O2) sensor is fabricated by the synthesized 3-Acrylamidopropyl-trimethylammoniumchloride (p(APTMACl)) hydrogel to covered of pen- graphite (PG) electrodes. (p(APTMACl))-PG electrode is characterized using scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The electrochemical properties of these sensors are investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The CV behavior of (p(APTMACl))-PG electrode is investigated in 0.1 M PBS (pH 7, 5 mm diameter of mold). The developed sensor displays significantly enhanced electrocatalytic activity through the H2O2 detection. Linear response of the sensor to H2O2 were observed in the concentration range from 0 to 130 µM (R2 = 0.99) with a detection limit of 1.08 × 10−6 M, quantification limit of 3.62 × 10−6 M (S/N = 3) and sensitivity of 2375 µA/mMcm2. In addition, interference studies reveal that (p(APTMACl))-PG electrode is not affected by ascorbic acid (AA), uric acid (UA), and dopamine which are common interfering species. The developed sensor is also successfully applied to detect H2O2 in real commercial samples. This study describes a novel strategy to sensing characteristics to hydrogen peroxide by p(APTMACl)-PG electrode.

Polypyrrole Modified Graphite Electrode for Supercapacitor Application: The Effect of Cycling Electrolytes

Graphite electrode was modified by polypyrrole (PPy) thin film. PPy was electrodeposited potentiostatically by applying -1.5 V from acidic aqueous solution having pyrrole monomers. The waiting time of deposition solution effect the surface coverage of resulted films. PPy modified electrodes fabricated by old solution have lower surface coverage than PPy obtained from freshly prepared solution. PPy films were transferred to aqueous (acidic, neutral, alkaline) and a non-aqueous (Deep Eutectic Solvent) solutions for cycling. Capacitance performance of PPy film in a choline chloride based ionic liquid (Ethaline) was compared with that of PPy films in aqueous solutions. As PPy film in salt solution (LiClO4 and NaCl) was evolved because deposition electrolyte was different (H2SO4) than deposition electrolyte and salt ions are exchanged at the beginning of cycling. Film obtained in acidic media was transferred into alkaline solution or ionic liquid is electroinactive. PPy film is strongly electroactive in an acidic media for hundreds of cycles as acidic media can cause the highest charge which is directly related to capacitive performance. Upon increasing pH value of cycling electrolyte, current and charge value decreases. PPy film in a salt solution (NaCl or LiClO4 in water) and acidic solution (H2SO4) is electroactive and can be used for supercapacitor application. As PPy film in ionic liquids and alkaline solution cannot be electroactive, they cannot be used for supercapacitor applications. Capacity retention of PPy in KOH and Ethaline is low (around 5%). However, PPy thin film in H2SO4 has 77% of capacitance retention after 500 scans.

Mesoporous SiO2 (SBA-15) modified graphite electrode as highly sensitive sensor for ultra trace level determination of Dapoxetine hydrochloride drug in human plasma

Mesoporous silica materials are considered highly popular in electroanalysis field especially Santa Barbara Amorphous type; SBA-15. Due to its extensive properties, SBA-15 was synthesized and utilized for construction of a simple and an inexpensive modified graphite sensor. This was done by hand mixing of different percentages of as-prepared SBA-15 with graphite powder as a conductor and Nujol oil as a binder until achieving homogenous carbon paste (CP). The as-prepared SBA-15 was characterized using TEM, SEM, EDX, XRD, BET N2 sorption isotherm and FTIR. In addition, electrochemical impedance spectra (EIS) and cyclic voltammetric measurements were used to characterize modified carbon paste electrode. They indicate lowest charge transfer resistance and highest effective surface area of the constructed 10%(w/w) SBA-15/CPE. This sensor exhibited also excellent electrocatalytic activity towards electrochemical oxidation of Dapoxetine hydrochloride (DPX.HCl). The applied SW-AdASV method shows also the efficiency of this sensor for DPX.HCl determination in its formulation and human plasma. Low value of the detection limit (LOD) of 2.45×10−10M and wide linearity range (9×10−10M to 1×10−8M) in human plasma confirm the validity of the 10%(w/w) SBA-15/CPE as a sensor for quality control analysis of DPX.HCl and for pharmacokinetic study in clinical laboratories.

A Study of the Electro-Catalytic Oxidation of Methanol on a Ni-Functionalized Graphene Oxide/p-Type Conductive Polymer Modified Graphite Electrode: Experimental and Theoretical Approach

The preparation of Ni-functionalized graphene oxide/poly orthoaminophenol composites (Ni–FGO–POAP) is presented and the composites were used as graphite electrode modifier for methanol electrooxidation in NaOH. Nickel was accumulated by complex formation between Ni(II), in solution and amines sites in the polymer backbone to obtain Ni–FGO–POAP/G electrode. The electrochemical performance of Ni–FGO–POAP composite electrodes was investigated by common electrochemical techniques. The peak on the potentiodynamic curve for Ni–FGO–POAP electrode in alkaline solutions of methanol is observed which is ascribed to the methanol oxidation in alkaline medium. Under the CA regimes the reaction followed a Cottrellian behavior. The results obtained are discussed from the point of view of employment of the Ni–FGO–POAP composites for the catalytic electrodes of fuel cells. In addition, the atoms-in-molecule (AIM) theory is used to study atomic-scale charge/energy transfer in grapheme-like molecular system.

Anodic stripping voltammetry for direct determination of heavy metals in bovine seminal plasma using thick film modified graphite electrodes

The thick-film modified graphite sensors (TMGE) as working electrodes are used for determination of heavy metals in bovine seminal plasma by anodic stripping voltammetry. The technique proposed is a very simple, express and no any sample preparation such as acid deproteinization or autoclave digestion is necessary. The sample of seminal plasma is just diluted with electrolyte solution in the analysis process. The aliquot of the sample is injected in the electrochemical cell and the analytical signal is measured. The analytical signal dependences on the accumulation potential, accumulation time and sweep rate have been studied. The standard addition method is used for calculating of heavy metal concentrations in the samples. The accuracy of the developed technique is proved by comparison with the results obtained by the independent method of ICP-AES (atomic emission spectrometry with inductively coupled plasma). The detection limits (3SDblank) are found to be 3.6 μg·L−1 for Pb and 40 μg·L−1 for Cu in bovine seminal plasma (taking into account sample dilution). The relative standard deviation (RSD) obtained by the proposed technique do not exceed 13%.

Interaction of vanadium species with a functionalized graphite electrode: A combined theoretical and experimental study for flow battery applications

Vanadium redox flow battery (VRFB) is one of the most promising large-scale energy storage system; however, a widespread VRFB development is still limited by the poor electrochemical activity of graphite electrodes and a poor understanding of redox reactions occurring at electrode/electrolyte interface.In this work, DFT was performed to study the first solvation shell structure of all vanadium ions and to investigate the reactivity of modified graphite electrodes toward the V2+/V3+ redox species. The results suggest that the presence of oxygen and nitrogen functionalities at the electrode edges provides more active sites for adsorption of the V2+/V3+ redox couple, and therefore improve electron transfer kinetics.These results have been experimentally validated by means of Cyclic Voltammetry and Electrochemical Impedance Spectroscopy with carbon black electrode having different density of oxygen and nitrogen-containing surface groups.

VOLTAMETRIC DETERMINATION OF Cu IN FUEL USING CHEMICALLY MODIFIED ELECTRODE BY TETRAZOLES

This article describes an analytical procedure for the determination of copper in fuel samples using the modified graphite electrode basal pyrolysis (BPPGME) by tetrazolium salts: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2Htetrazolium (MTT) Br]. The determination of metals in fuel is an issue of environmental relevance because it believes that these elements can be released into the atmosphere causing damage to the environment and health. Fuel samples (ethanol, biodiesel and gasoline) were previously digested in a microwave oven using nitric acid and peroxides (biodiesel) and only nitric acid (alcohol and gasoline). The metal ion studied reacted on the surface of the chemically modified electrode to produce marked changes in the corresponding voltammograms. In order to determine the species of interest the best results were at pH 5.0 for copper and pH 6.0 for other species. The concentration scale for copper was 2.0x10-6 at 1.25 X 10-5 mol L-1. The limit of detection in fuels of samples (ethanol, biodiesel or gasoline), by ARV was 2.5x10-6 mol L-1. The accuracy of the proposed technique was compared by providing similar results, ie the copper concentration in the samples analyzed by both techniques at a non-statistically different 95% certainty level.

A comparative study of different electrodeposited NiCo2O4 microspheres anchored on a reduced graphene oxide platform: electrochemical sensor for anti-depressant drug venlafaxine.

Two different fabrication methods were performed and compared for preparation of binary metallic oxide microstructures supported on a reduced graphene oxide (rGO) modified graphite electrode. Nickel–Cobalt oxide microspheres (NiCo2O4 MSs) were prepared by two different deposition methods: wet chemical and in situ-electrical deposited methods. Different characterization methods were conducted, including cyclic voltammetry (CV), scanning emission microscopy (SEM), electrochemical impedance spectroscopy (EIS) and Raman spectroscopy. The deposition methods of NiCo2O4 MSs were found to affect the electrochemical behavior of the modified electrodes towards the oxidation of venlafaxine (VEN), an anti-depressant drug. The fabricated electrode showed linearity over the range 5–500 nmol L−1 and an excellent sensitivity with a limit of detection (LOD) and limit of quantitation (LOQ) of 3.4 and 10.3 nmol L−1, respectively. It was revealed that the wet-NiCo2O4@rGO modified electrode prepared by the wet chemical method showed an improved electrochemical behavior for determination of VEN in pharmaceuticals and human plasma with high recovery results in the range of 96.7–98.6% and 96.0–100.7%, respectively without any interference from the co-existing components.

Modified graphite electrodes as potential cathodic electrocatalysts for microbial electrolysis cells

Microbial electrolysis cell (MEC) is an ecologically clean and innovative technology for hydrogen production. The development of cost-effective cathodes with high catalytic activity for hydrogen evolution reaction (HER) in nearneutral electrolytes is the most critical challenge for the practical application of MEC technology. In this study, graphite electrodes, functionalized with non-noble metal oxides, were produced and after electrochemical pre-treatment investigated as potential cathodes for MEC. The morphology of the developed materials was analyzed by scanning electron microscopy (SEM). Their electrochemical performance in neutral phosphate buffer solution (PBS) was explored by means of linear sweep voltammetry (LSV) and chronoamperometry (CA). The results from both methods show that all modified electrodes exhibit higher electrocatalytic activity towards HER than that of bare graphite, which is a prerequisite for further evaluation of these materials as cathodes in real MEC.