Linear Sweep Voltammetric Techniques Research Articles

Remarkable energy storage and photocatalytic remediation potential of novel graphene oxide loaded bi-metal sulphide Ba4Fe2S6-GO nanocomposite thin film

A novel hybrid Barium–Iron sulphide combined with graphene oxide (Ba4Fe2S6-GO) thin film was prepared. The newly synthesized bi-metal composite was synthesized in situ by diethyldithiocarbamate ligand. Deposition of pure BaFe–S and hybrid [BaFe]S-GO on FTO substrate was performed through electron-beam deposition system. The hybrid thin films exhibited enhanced electrical and photocatalytic properties. Characterization was performed by UV–vis spectrophotometry, FTIR, XRD, XPS, SEM-EDX. Direct band gaps 5.48 and 5.8 eV were observed for Ba4Fe2S6-GO and Ba4Fe2S6, respectively, calculated through Tauc's plot. X-ray diffraction revealed anorthic crystal arrangement possessing crystal lattices 9 (a), 6.7 (b) and 24.6 (c) Å. SEM displayed a cloud-like spherical morphology. The energy storage potential of thin film was explored by cyclic voltammetric and linear sweep voltammetric techniques. A specific capacitance of 248 F g−1 presented it as a potential energy storage supercapacitor electrode material. Redox reaction displayed by Ba4Fe2S6-GO electrode exhibited that it is electrochemically active. Thin films were also investigated for their potentiality to remove organic contaminants. Ba4Fe2S6-GO thin films clearly displayed an enhanced photocatalytic activity for the removal of toxic pollutants owing to the presence GO in its structure. The use of films for decontamination presents it to be utilized as a remediation tool.

Development of a spiramycin sensor based on adsorptive stripping linear sweep voltammetry and its application for the determination of spiramycin in chicken egg samples.

Herein, an adsorptive stripping linear sweep voltammetric technique was described to determine spiramycin, a macrolide antibiotic, using a carboxylic multiwalled glassy carbon electrode modified with carbon nanotubes. The main principle of the analytical methodology proposed was based on the preconcentration of spiramycin by open-circuit accumulation of the macrolide onto the modified electrode surface. As a result of the adsorption affinity of spiramycin to the modified surface, the sensitivity of the glassy carbon electrode was significantly increased for the determination of spiramycin. The electrochemical behavior of spiramycin was evaluated by cyclic voltammetry and the irreversible anodic peak observed was measured as an analytical signal in the methodology. The proposed electrochemical sensing platform was quite linear in the range of 0.100–40.0 µM of spiramycin concentration with a correlation coefficient of 0.9993. The limit of detection and the limit of quantification were 0.028 and 0.094 µM, respectively. The intra- and interday repeatability of the proposed sensor was within acceptable limits. Finally, the applicability of the electrochemical methodology was examined by determining the drug content of chicken egg samples spiked with spiramycin standard. A rapid and easy extraction technique was performed to extract spiked spiramycin from the egg samples. The extraction technique followed had good recovery values between 85.3 ± 4.0% and 93.4 ± 1.9%.

SYNTHESIS, CHARACTERIZATION AND ORR ACTIVITY OF METAL-N4-NANOCOMPOSITES

Inspired by nature, Metal-N4-complexes have been utilized as potential models to catalyze the sluggish oxygen reduction reaction (ORR) at cathode in fuel cells. Herein, we designed and synthesized dibenzo-N4-[14]annulene metal complexes of FeII and CoII metal ions and their nanocomposites with carbon black and characterized by various techniques. Computational and spectroscopic results suggested that the prepared complexes have saddle octahedral geometry. Further, the electrocatalytic activity of prepared nanocomposites towards ORR was investigated by using cyclic and linear sweep voltammetric techniques. The results exhibited that these nanocomposites are significantly ORR active; however, Fe-nanocomposite showed high ORR activity as compared to Co-composite. Theoretical studies indicated that the HOMO of Fe-complex was very near to the antibonding LUMO orbitals of dioxygen as compared to Co-complex, endowing high ORR activity.

Introduction of a thrombin sensor based on its interaction with dabigatran as an oral direct thrombin inhibitor

Dabigatran (DAB) is a direct thrombin inhibitor used for preventing blood clots and emboli after orthopedic surgery. The DAB - thrombin interaction was followed by fluorescence and UV–Vis spectroscopic methods. The binding of DAB to thrombin was also modeled by the molecular docking method. The obtained experimental results were consistent with theoretical results. The voltammetric method was also tested for DAB - thrombin interaction. Based on voltammetric findings, carbon paste electrode containing graphite powder, paraffin oil, MWCNTs, and DAB was constructed and used for thrombin monitoring after investigation of the DAB oxidation mechanism for the first time. The decrease in the linear sweep voltammetric (LSV) peak current of DAB in the presence of thrombin was utilized for the thrombin analysis. The calibration plot was linear in the concentration range of 1 to 70 nM (R2 = 0.9992) by LSV technique with a detection limit of 0.3 nM. The applicability of the proposed sensor was evaluated by the determination of thrombin in human serum as a real sample.

Voltammetric detection of anticancer drug Doxorubicin at pencil graphite electrode: A voltammetric study

In this work, focused on the characteristic of a pencil graphite electrode (PGE) as a voltammetric study to the electroanalysis of anticancer drug Doxorubicin (DOX) has been investigated. For PGE, detection sensitivity was determined by using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and linear sweep voltammetric (LSV) techniques. In addition, the morphological structural feature of the PGE was characterized by scanning electron microscopy (SEM). Some of the most important effective parameters such as pH, sweep rate, and concentration of DOX were optimized at PGE by using CV, DPV and LSV techniques. A Plausible electrooxidation mechanism of DOX was proposed and successful selective separation of dopamine (DA) and DOX were achieved by using the above mentioned techniques. The applicability of the suggested method was illustrated by the investigation of DOX present in real sample analysis and the method can also be used in clinical analysis, quality control and routine verification of drugs in pharmaceutical formulations.

Applications of zinc oxide nanoparticles as an electrode modifier for ambroxol

Abstract In the present work, zinc oxide (ZnO) nanoparticles were used as an electrode modifier for ambroxol. The electrochemical behaviour of ambroxol was studied at cyclic voltammetric and linear sweep voltammetric techniques in phosphate buffer solutions. The impact of parameters such as amount of ZnO modifier, accumulation time, pH, scan rate and concentration of the drug was studied. Based on the obtained results, number of protons/electrons involved in the process and rate constant were calculated. Limit of detection and limit of quantification were calculated from of peak current versus concentration plot and both values are better as compared with the reported values. The applicability of the proposed electrode was tested by analyzing pharmaceutical and urine samples.

Characterization of the binding and conformational changes of bovine serum albumin upon interaction with antihypertensive olmesartan medoxomil

The interaction of bovine serum albumin (BSA) with the olmesartan medoxomil (OLM) was investigated by different spectroscopic and linear sweep voltammetric techniques under experimentally optimised physiological conditions. The alteration of functional properties of BSA when quenched by OLM was illustrated by the continuous decrease of the fluorescence intensity of BSA upon addition of OLM. The quenching constants (Ksv) obtained were 0.71 × 104, 1.3 × 104 and 2.1 × 104 Lmol−1 at 288, 298 and 308 K respectively. The binding mechanism was dynamic type quenching. The value of K is of the order of 104, indicating that a long-lasting interaction exists between OLM and BSA. The positive values of ΔH0 and ΔS0 suggested the hydrophobic interactions play the major roles in the binding reaction. The conformational change of BSA after binding with OLM was demonstrated by the synchronous, FTIR and 3-D fluorescence spectral results. The effects of some common metal ions and site probes on binding of BSA– OLM were also investigated.

2D and 3D Silica‐Template‐Derived MnO2 Electrocatalysts towards Enhanced Oxygen Evolution and Oxygen Reduction Activity

AbstractIn this work, a hard‐template‐based nano‐replication process is employed to prepare mesoporous MnO2 materials. We adopted four silica materials, namely, SBA‐15, KIT‐6, MCM‐41, and MCM‐48 as templates to prepare MnO2 materials by using a nanocasting route. The structural characteristics of the resultant MnO2 materials were thoroughly investigated by using XRD, BET, FESEM, HR‐TEM, XPS, and Raman techniques. All studies confirmed the replication of porous MnO2 nanostructures from silica supports in β‐crystallographic form. By employing X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS), we identified the existence of Mn and oxygen vacancies in the developed MnO2 material. The hydrodynamic linear sweep voltammetric technique was employed to demonstrate the efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity of the catalyst in 0.1 M KOH solution. The KIT‐6‐derived MnO2 nanostructure displayed equal activity to the benchmark catalyst RuO2. This work lays a foundation to prepare and employ ordered mesoporous MnO2 materials as OER/ORR catalysts, which have potential applications in electrochemical energy conversion and storage devices.

Polarographic determination of DNA based on its interaction with the phenanthroline-zinc(II) complex

By using the linear sweep voltammetric technique, a phenanthroline (Phen) and zinc(II) (Phen-Zn(II)) complex was used as the electrochemical probe for the determination of double-stranded (ds) DNA. In pH 9.0 Britton- -Robinson (B-R) buffer solution, Phen can interact with Zn(II) to form a stable electroactive [Phen-Zn(II)] complex, which had a sensitive second order derivative polarographic reductive peak at -1.300 V (vs. SCE). After the addition of dsDNA into a solution of Phen-Zn(II) complex, the reduction peak current decreased with a negative shift of the reduction peak potential and without the appearance of new peaks. The results showed that a new supramolecular complex was formed via interaction of the Phen-Zn(II) complex with dsDNA. The conditions of interaction and the electrochemical detection were carefully investigated. Under the optimum conditions, the decrease in the reduction peak current was directly proportional to the dsDNA concentration in the range of 0.4-18.0 mg L-1 with the linear regression equation: ?Ip?/nA = 349.48 + + 84.647(c/mg L-1) (n = 13, ? = 0.991) and a determination limit of 0.20 mg L-1 (3?). The relative standard deviation (RSD) for 10 parallel determinations of 10.0 mg L-1 dsDNA was found to be 2.03 %. The method was successfully applied to the detection of synthetic samples with satisfactory results.

Carboxyl-functionalized graphene oxide-modified electrode for the electrochemical determination of nonsteroidal anti-inflammatory drug diclofenac

A simple and sensitive electrochemical method was proposed for the quantitative determination of nonsteroidal anti-inflammatory drug diclofenac (DCF). For the first time, carboxyl-functionalized graphene oxide (GO-COOH)-modified glassy carbon electrode (GCE) was employed for the determination of DCF by cyclic voltammetry (CV) and linear sweep voltammetric (LSV) techniques. The proposed modified electrode showed strong electrocatalytic activity toward DCF with higher anodic peak enhancement than that of the unmodified electrode. The practicality of the proposed electrode for the detection of DCF in human urine and blood serum samples was successfully demonstrated using LSV techniques. The obtained results were satisfactory. The detection limit and sensitivity of the proposed method were of 0.09 μM and 0.532 μA μM−1 cm−2, respectively (by LSV). Applicability of the proposed method was verified with commercially available pharmaceutical tablets, and the obtained results were in good agreement with the claimed label amounts of the tablets. In addition, this method could be used for the accurate detection of DCF in clinical and pharmaceutical industries in the future.

Electrodeposition of Sb(III) in alkaline solutions containing xylitol

The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique. Initial stages of antimony electrocrystallization were determined by chronoamperometry. Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from −1.20 V to +0.60 V (vs Hg/HgO). There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of −1.75 V to 1.25 V (vs Hg/HgO) while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than −1.70 V (vs Hg/HgO). Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol, 0.64 and 4.40×10−6 A/m2, respectively. The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation. The average diffusion coefficient of antimony was calculated to be 1.53×10−6 cm2/s.

Simultaneous Voltammetric Determination of Ascorbic Acid and Sulfite in Beverages Employing a Glassy Carbon Electrode Modified with Carbon Nanotubes within a Poly(Allylamine Hydrochloride) Film

AbstractA glassy carbon electrode modified with functionalized multiwalled carbon nanotubes within a poly(allylamine hydrochloride) film was used for the simultaneous voltammetric determination of ascorbic acid and sulfite. The anodic peak potentials of ascorbic acid and sulfite oxidation at a MWCNTs‐PAH/GCE were found to be 0.005 V and 0.327 V (vs. Ag/AgCl (3.0 M KCl)), respectively by cyclic voltammetry, whereas at a GCE were 0.278 V and 0.722 V. Using linear sweep voltammetric technique, the obtained analytical curves were linear in the ascorbic acid and sulfite concentration range from 5.0 to 200.0 µM, with detection limits of 3.0 and 3.5 µM for ascorbic acid and sulfite, respectively. The proposed method was successfully used for the simultaneous determination of ascorbic acid and sulfite in fruit juices.

Electrodics of methanol oxidation on Pt-f-multiwalled carbon nanotube composite, prepared by γ-radiolysis

We report the electrodics of methanol oxidation on Pt-multiwalled carbon nanotube composites (Pt-f-MWCNTs), prepared by γ-radiolysis of K2PtCl6 in the presence of HOOC-functionalized multiwalled carbon nanotubes. The electrocatalytic activity for the methanol oxidation was studied using cyclic and linear sweep voltammetric techniques on the stationary indium tin oxide and rotating gold disc electrodes, respectively. Higher values of oxidative (anodic) current were obtained using Pt-f-MWCNTs compared to the polycrystalline Pt electrode. This phenomenon is attributed to the synergistic effect of oxy groups on MWCNTs, which alleviate CO poisoning. The electrodics of the reaction at various temperatures was studied using linear sweep voltammetry (LSV) on a rotating disc gold electrode, modified with the composite. From the Koutecky-Levich plots, the standard rate constant (k0) was determined to be 7.9±1.9×10−8cms−1.

Electrodeposition and characterization of undoped and nitrogen-doped ZnSe films

Semiconducting films of (n-type) ZnSe and (p-type) nitrogen-doped ZnSe were electrodeposited by a linear-sweep voltammetric technique on to a substrate of fluorine–tin oxide (FTO) glass ceramics. The films were characterized by scanning electron microscopy, energy-dispersive X-ray analysis and grazing-incidence X-ray diffraction. The results indicated that the material was deposited uniformly over the substrate, forming clusters when the Zn content of the bath was 0.1 mol L −1 and a film when it was 0.2 or 0.3 mol L −1. The effectiveness of doping the films with nitrogen by adding ammonium sulfate to the deposition solution was assessed by measuring the film–electrolyte interface capacitance ( C) at various applied potentials ( E ap) and plotting Mott–Schottky curves ( C −2 vs E ap), whose slope sign was used to identify p-type ZnSe.

Computational electrochemistry: Lattice Boltzmann simulations of voltammetry at microelectrodes

This paper describes the development of a two-dimensional lattice Boltzmann method for the simulation of mass transport at a range of microelectrode geometries using potential step and linear sweep voltammetric techniques. The simulations of the current response for microband and micro hemicylinder geometries were compared with previously published analytical solutions. Excellent agreement between the numerical models and the analytical solutions was observed for a series of experimental parameters. To illustrate the flexibility of the lattice Boltzmann method the simulation of the current response for a range of electrode geometries, distorted from microband electrode geometry to micro hemicylinder electrode, is also described.

Voltammetric studies on the electrochemical determination of methylmercury in chloride medium at carbon microelectrodes

Electroanalytical techniques have been used to determine methylmercury at low levels in environmental matrices. The electrochemical behaviour of methylmercury at carbon microelectrodes in a hydrochloric acid medium using cyclic, square wave and fast-scan linear-sweep voltammetric techniques has been investigated. The analytical utility of the methylmercury reoxidation peak has been explored, but the recorded peak currents were found to be poorly reproducible. This is ascribed to two factors: the adsorption of insoluble chloromercury compounds on the electrode surface, which appears to be an important contribution to hinder the voltammetric signal of methylmercury; and the competition between the reoxidation of the methylmercury radical and its dimerization reaction, which limits the reproducibility of the methylmercury peak. These problems were successfully overcome by adopting the appropriate experimental conditions. Fast-scan rates were employed and an efficient electrochemical regeneration procedure of the electrode surface was achieved, under potentiostatic conditions in a mercury-free solution containing potassium thiocyanate—a strong complexing agent. The influence of chloride ion concentration was analysed. Interference by metals, such as lead and cadmium, was considered. Calibration plots were obtained in the micromolar and submicromolar concentration ranges, allowing the electrochemical determination of methylmercury in trace amounts. An estuarine water sample was analysed using the new method with a glassy carbon microelectrode.

A Linear Sweep Voltammetric Determination of DNA with Methyl Violet

A new quantitative method for the determination of DNA in aqueous solution based on the interaction of methyl violet (MV) with fsDNA by linear sweep voltammetric technique is proposed in this paper. The interaction of MV with fsDNA caused the decrease of the reductive peak current of MV at −0.650 V (vs. SCE) on a mercury electrode in pH 1.5 Britton-Robinson (B-R) buffer solution. Factors including the acidity of the buffer, the reaction time, the optimal concentration of MV, the reaction temperature, the influences of the foreign substances, etc. were all carefully investigated. Under the optimal conditions, the decrease of the reductive peak current of MV was proportional to the concentration of fsDNA in the linear range of 0.90∼20.0 mg/L and the detection limit for fsDNA was 0.25 mg/L with the RSD of 4.00%. Synthetic samples were determined with satisfactorily results. The stoichiometry of MV with DNA was calculated by voltammetric data and the results showed that the binding ratio of DNA:MV was 1:2 with the binding constant β as 7.36 × 108.

Study of electrochemical oxidation and determination of albendazole using a glassy carbon-rotating disk electrode

In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E 1/2 = 0.99 V vs. Ag/AgCl sat, when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51 ± 0.07) × 10 –5 cm s –1, with a αn a value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 × 10 –5 to 1.0 × 10 –2 mol l –1 range, being obtained a detection limit of 2.4 × 10 –5 mol l –1. Proposed methodology was applied to ABZ quantification in pharmaceutical formulations.

Impedance Analysis for Oxygen Reduction in a Lithium Carbonate Melt: Effects of Partial Pressure of Carbon Dioxide and Temperature

Effects of partial pressure of carbon dioxide and temperature on oxygen reduction kinetics on a gold electrode in a lithium carbonate melt were examined using electrochemical impedance spectroscopic (EIS) and linear sweep voltammetric techniques. The impedance spectra were analyzed by a complex nonlinear least squares method, using the Randles‐Ershler equivalent circuit model, to determine the electrode‐kinetic and the mass‐transfer parameters such as the charge‐transfer resistance and the Warburg coefficient. The cyclic voltammetric measurements indicated that the oxygen reduction process in lithium carbonate melt is “reversible” up to 200 mV/s. The product determined by cyclic voltammetry agreed well with those estimated by the EIS method. The reaction order with respect to carbon dioxide and the activation energy for the exchange current density were determined to be −0.52 and 132 kJ/mol, respectively. Also, the reaction order with respect to carbon dioxide and the activation energy for were calculated to be −0.8 and 185 kJ/mol, respectively.

Studies on the electroreduction of dialdehyde starch on mercury electrode in alkaline solutions

The electroreduction of dialdehyde starch (DAS) on a DME in lithium hydroxide and sodium hydroxide solutions has been studied in detail at temperatures in the range 35–55°C. The polarographic wave has been found to be mainly diffusion controlled. The adsorption of DAS on mercury in lithium hydroxide has been studied with an a.c. bridge. The DAS has been found to be adsorbed in the potential range −0.30 to −1.50 V (vs. SCE). It has also been found that the dissolution of mercury in the potential region −0.3 to −0.1 is reduced in the presence of DAS. The electro-reduction of DAS on a rotating amalgamated gold disc electrode in 1 M NaOH has also been studied by the linear sweep voltammetric technique. The linear sweep voltammograms (l.s.v.) show that the limiting current of the step observed at −1.51 V increases with increasing sweep rate and decreasing rotation speed. The DAS is known to undergo alkaline degradation. The results of the present study indicate that the polarographic wave and the well-defined step in the l.s.v. are due to the reduction of DAS and not due to the reduction of any of the degradation products of DAS such as glycolaldehyde, glyoxylic acid or glyoxal. The increase of the limiting current of the step in the l.s.v. with increasing sweep rate as well as decreasing rotation speed has been explained. The l.s.v.'s obtained after an initial oxidation of Hg at ±0.0 V (vs. SCE) show two well-defined peaks in the potential region where a wide peak due to the reduction of mercuric oxide (in the absence of DAS) is observed. The appearance of these peaks as well as a small peak and a well-defined step at −1.30 V (vs. SCE) in addition to the reduction step due to DAS in the l.s.v. have been explained.