Electro-oxidation Behavior Research Articles

Evidence for Independent Glycerol Electrooxidation Behavior on Different Ordered Domains of Polycrystalline Platinum

AbstractWe investigate the electrooxidation of glycerol (GlOH) on polycrystalline Pt. The results obtained in the presence of GlOH were compared with those of fresh and disturbed low‐index Pt single crystals [(111), (100) and (110)]. Monitoring of the oxidation currents of GlOH by cyclic voltammetry on the different surfaces revealed that the electrooxidation of GlOH is highly sensitive to the order of the polycrystalline Pt atoms. Interestingly, after being disturbed by the application of voltammetric cycles, the combined responses of the disordered single crystals become similar to that of polycrystalline Pt. The changes in the current values associated with the specific potentials at which each oxidation peak takes place suggest that different ordered domains of Pt oxidize GlOH independently. This simple approach can clearly assist in our understanding of the effect of the order of surface atoms in a given reaction, not only in electrochemical reactions.

Electro-oxidation of anthracene on polyanilino-graphene composite electrode

A novel graphenated-polyaniline (GR-PANI) nanocomposite sensor was constructed and used for the determination of anthracene. The direct electro-oxidation behavior of anthracene on the GR-PANI modified glassy carbon electrode (GCE) was used as the sensing principle. The results indicate that the response profile of the oxidation of anthracene on GR-PANI-modified GCE provides for the construction of sensor systems based on amperometric and voltammetric signal transductions. A dynamic linear range of 0.012–1000μM anthracene and a detection limit of 0.0044μM anthracene were established for the sensor system.

The fabrication of a Co (II) complex and multi-walled carbon nanotubes modified glass carbon electrode, and its application for the determination of dopamine

An electrochemical biosensor based on [Co(phen)3]2+ (phen=1,10-phenanthroline) and multi-walled carbon nanotubes (MWCNTs) was developed for the determination of dopamine (DA) by using a glassy carbon electrode (GCE). The electrochemistry properties of the composite film were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the electrooxidation behavior of DA on [Co(phen)3]2+/MWCNTs/GCE was studied by amperometry. Under the optimum experimental conditions, the linear calibration curve was obtained in the range from 5 to 453μmolL−1 with a low detection limit of 1.76μmolL−1 (at a signal-to-noise ratio of 3). The experimental results also proved that several co-existing substances, including K+, Na+, etc., had no significant interference on the determination of DA. The validity of using this modified electrode to determine DA in dopamine hydrochloride injection was also demonstrated.

Electrooxidative Behavior of Arylazo Pyridone Dyes and Their Inclusion Complexes on Gold Electrode in 0.1 M NaOH

The electrochemical behavior of six arylazo pyridone dyes classified to the substituents present at the phenylazo and 2-pyridone moiety and their 1:1 inclusion complexes with (2-hydroxypropyl)-β-cyclodextrin was studied using cyclic and square wave voltammetry in 0.1M NaOH on a gold electrode. The formation of the inclusion complexes of the dyes was confirmed using UV-Vis and FTIR spectroscopy measurements. Among the studied dyes, according to potentiodynamic measurements, the most active is the dye 1. The inclusion complexes of the dyes exhibited improved electrochemical activity in comparison to the pure dyes. The results obtained by square wave voltammetry show the apparent activity of the dyes with a methoxy group as a substituent at the phenylazo moiety and ethyl and hydroxyethyl groups in the 2-pyridone moiety, and their inclusion complexes. The electrooxidation mechanism of the investigated arylazo pyridone dyes was also proposed.

Roles of nitric acid treatment on PtRu catalyst supported on graphite nanofibers and their methanol electro-oxidation behaviors

In the present study, the effect of chemical treatment on graphite nanofiber supports (GNFs) with various concentrations of nitric acid was investigated for methanol electro-oxidation. To optimize the electrocatalytic activity, PtRu catalysts were deposited on GNF supports by the impregnation method. The surface and structural properties of the GNF supports were characterized by X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), and X-ray diffraction (XRD). The morphology of the catalysts was characterized by transmission electron microscopy (TEM). The electrocatalytic activity of PtRu/GNF catalysts was investigated by cyclic voltammetry. Oxygen functional groups were introduced on the GNF supports by the addition of nitric acid. Increasing the concentration of nitric acid caused a subsequent increase in the presence of oxygen functional groups, which resulted in smaller catalyst particle size and a higher loading of the catalyst. The electrocatalytic activity of the catalysts for methanol oxidation was also improved with these treatments. Consequently, it was found that chemical treatments could influence the surface properties of the carbon supports, resulting in enhanced electrocatalytic activity of the catalysts for direct methanol fuel cells (DMFCs).

Graphenated polyaniline-doped tungsten oxide nanocomposite sensor for real time determination of phenanthrene

A graphenated polyaniline/tungsten oxide (PANI/WO3/GR) nanocomposite sensor was prepared by electropolymerisation of a mixture of aniline monomer and tungsten oxide on a graphene-modified glassy carbon electrode (GCE). The PANI/WO3/GR/GCE nanocomposite electrode was tested as a sensor for the determination of phenanthrene. The direct electro-oxidation behaviour of phenanthrene on the PANI/WO3/GR modified GCE was carefully investigated by cyclic voltammetry. The results indicated that the PANI/WO3/GR/GCE sensor was more sensitive to phenanthrene (with a dynamic linear range of 1.0 - 6.0 pM and a detection limit of 0.123 pM.) than GCE, PANI/GCE or PANI/WO3/GCE. The sensor exhibited excellent reproducibility and long-term stability. The sensor exhibits lower detection sensitivity than the WHO permissible level of 1.12nM phenanthrene in wastewater.

Electro-oxidation Behaviour and Passivation Potential of Natural Oil as Corrosion Inhibitor in Hydrochloric Acid Environment

Electro-oxidation Behaviour and Passivation Potential of Natural Oil as Corrosion Inhibitor in Hydrochloric Acid Environment

Direct Electro-oxidation of Toluene Derivations on Graphite Electrode

Direct electro-oxidation behaviors of toluene derivations(p-methoxy methylbenzene,p-xylene,p-chloro methylbenzene,p-tert-butyl methylbenzene) were studied by cyclic voltammetry(CV),in situ Fourier transform infrared spectroscopy(in situ FTIR),and constant potential electrolysis on graphite electrode in sulfuric acid and acetone solutions.The direct electro-oxidation behaviors of the four toluene derivations were similar.The negative-going band at 1710 cm-1is the stretching vibration peak of carboxyl group of aromatic aldehydes,and the positive-going band at 1130 cm-1shows the consumption peak of methyl of toluene derivations.The main electro-oxidation products are aromatic aldehydes detected by gas chromatography-mass spectrometry(GC-MS).The yield of p-methoxy benzaldehyde could reach up to 70.9% in the sulfuric acid system at 40 ℃.

Electro-oxidation of carbamazepine metabolites: Characterization and influence in the voltammetric determination of the parent drug

The electro-oxidation behavior of five important metabolites of carbamazepine (CBZ) and their potential influence on the voltammetric determination of the parent drug in biological fluids was investigated for the first time. This investigation was performed using cyclic voltammetry, in combination with controlled potential electrolysis and HPLC-DAD-MS analysis of oxidation products of these compounds. Using a sensitive glassy carbon electrode modified with multi-walled carbon nanotubes it was found that each metabolite produces a voltammetric response, that differs from the parent molecule and which can be used in its identification and to gain some insight about the electro-oxidation mechanisms of this class of molecules. Taking into account the HPLC-DAD-MS data, these electro-oxidation mechanisms were advanced and discussed. A voltammetric procedure for the determination of CBZ in human fluids was also been tested. Selecting the most appropriate experimental conditions was verified that the interference of each metabolite and their oxidation products on the voltammetric signal of CBZ may be neglected. The analytical performance of the proposed voltammetric procedure, as well as the correlation of its results with the results obtained from LC–MS, were very good.

Electroanalytical Characterization of Levodropropizine and its Voltammetric Determination in Pharmaceuticals

Levodropropizine is a cough suppressant and easily oxidizable at the carbon-base electrodes. The electrooxidative behavior and determination of levodropropizine on glassy carbon and boron-doped diamond electrodes were investigated using cyclic, linear sweep, differential pulse, and square wave voltammetric methods. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. In this study, also simple and fully validated reverse phase-liquid chromatography (RP-LC) method for the assay of levodropropizine in syrup dosage form has been developed using X-Select RP-18 column (250x4.60 mm ID x 5μ) at 25 ºC with the mobile phase (containing 15 mM o-phosphoric acid) of acetonitrile:water (30:70, v/v) adjusted to pH 8.0. The proposed methods allow a number of cost and time saving benefits. Levodropropizine was also exposed to thermal, photolytic, oxidative stress, acid and base hydrolysis conditions, and the stressed samples were detected by the proposed LC method. The proposed methods were successfully applied for the determination of levodropropizine from pharmaceutical dosage forms.

Electrooxidation Behavior and Amperometric Determination of Sotalol on a Graphene Oxide Nanosheets-modified Glassy Carbon Electrode

The electrochemical behavior of sotalol was investigated on a graphene oxide nanosheets-modified glassy carbon electrode in a phosphate buffer solution, pH 7.4. Cyclic voltammetry and chronoamperometry were employed to obtain information about the electrooxidation process. During the electrooxidation of sotalol, one irreversible anodic peak appeared in the voltammograms. Some kinetic parameters, such as the diffusion and charge transfer coefficients were obtained. An amperometric procedure was developed for the determination of sotalol, a detection limit of 7.57 μM, a linear dynamic range of 0.1 to 2.24 mM, and a calibration sensitivity of 0.945 mA M-1 were obtained. The method was applied to the analysis of sotalol tablets, and applicability of the method to direct assays of spiked human serum and urine fluids was investigated. Keywords: Graphene, sotalol, modified electrode, electrocatalysis, nanosensor.

Hierarchical Layered Double Hydroxide Microspheres with Largely Enhanced Performance for Ethanol Electrooxidation

AbstractHierarchical MgFe‐layered double hydroxide (LDH) microspheres with tunable interior structure are synthesized by a facile and cost‐effective surfactant‐templated method. Scanning and transmission electron microscopy images reveal that the obtained microspheres display a three‐dimensional architecture with hollow, yolk−shell and solid interior structure, respectively, with continuous changes in specific surface area and pore‐size distribution. Moreover, the hollow MgFe‐LDH microspheres exhibit excellent electrocatalytic oxidation of ethanol in alkaline fuel cell, including high activity, long‐term durability and cycling stability, owing to the significantly improved faradaic redox reaction and mass transport. Therefore, this work provides a promising approach for the design and synthesis of structure tunable materials with largely enhanced ethanol electrooxidation behavior, which can be potentially used in noble metal‐free alkaline fuel cells.

Simultaneous electrochemical determination of guanosine and adenosine with graphene–ZrO2 nanocomposite modified carbon ionic liquid electrode

In this paper an ionic liquid 1-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was fabricated and used as the basal electrode, which was further modified by graphene (GR) and ZrO2 nanoparticle with chitosan (CTS) film to immobilize the nanocomposite. The modified electrode was denoted as CTS–GR–ZrO2/CILE and further used for the simultaneous detection of adenosine and guanosine. Electrochemical performances of the modified electrode were greatly enhanced due to the presence of GR–ZrO2 nanocomposite, and the direct electro-oxidation behaviors of adenosine and guanosine were carefully investigated. Both adenosine and guanosine exhibited an increase of the oxidation peak currents with the negative shift of the oxidation peak potentials on the modified electrode, which indicated the electrocatalytic activity of GR–ZrO2 nanocomposite on the electrode surface. Electrochemical parameters of adenosine and guanosine on CTS–GR–ZrO2/CILE were calculated respectively, and a new electroanalytical method for the simultaneous determination of adenosine and guanosine was further established with the peak-to-peak separation (ΔEp) as 0.225V. The proposed method was successfully applied to detect adenosine and guanosine in human urine samples with satisfactory results.

Electrochemical degradation of ethidium bromide using boron-doped diamond electrode

Ethidium bromide (EtBr), a DNA intercalating pollutant, is widely disposed in aqueous solutions by most biomedical laboratories. The release of EtBr in the ecosystem may cause serious environmental problems like water pollution, eutrophication and perturbation in aquatic life. In this study, the degradation behavior of EtBr on boron-doped diamond (BDD) electrode was investigated under galvanostatic conditions. The electro-oxidation behavior of EtBr at BDD electrode was firstly examined by means of cyclic voltammetric technique. Such operating parameters as applied current density, types of electrolyte, temperature and initial concentration of EtBr were then varied in order to determine their effects on this oxidation process. The degradation of EtBr was mainly monitored by UV–vis spectrophotometer. The experimental results revealed the suitability of electrochemical processes employing BDD electrode for removing EtBr completely from the solution. The kinetics for EtBr degradation followed a pesudo-first order reaction in most cases, indicating the process was under mass transport control. Moreover, the better performance of BDD anode was proved on a comparative study with PbO2 anode under similar experimental conditions. As a result, the BDD technology could be considered as a nice solution to the treatment of EtBr-polluted wastewater.

Electrooxidative behavior and determination of trifluoperazine at multiwalled carbon nanotube-modified glassy carbon electrode

The mechanism of electrochemical oxidation of trifluoperazine has been proposed on the basis of cyclic and differential pulse voltammetry at a multiwalled carbon nanotube-modified glassy carbon electrode. The modified electrode exhibits catalytic activity, high sensitivity, and stability. The oxidation process exhibited an adsorption-controlled behavior. Also, depending on this adsorption control, a sensitive electroanalytical method for the determination of trifluoperazine has been investigated by adsorptive stripping differential pulse voltammetry. Under the optional conditions, the anodic peak current was linear to the trifluoperazine concentration over the range of 2.08 10−8 M to 1.67 10−6 M, and the limit of detection was 7.49 10−10 M. The modified electrode had good stability and repeatability, and it was successfully applied to the determination of trifluoperazine in pharmaceuticals.

Simultaneous determination of guanine, adenine and thymine using a modified carbon paste electrode by TiO2 nanoparticles-magnesium(II) doped natrolite zeolite

A novel, simple and reliable electrochemical method for simultaneous determination and direct electro-oxidation behaviors of guanine (G), adenine (A) and thymine (T) was developed at a TiO2 nanoparticles-magnesium doped zeolite Y modified carbon paste electrode (TiO2NPs-MgY/ZMCPE). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to examine the structure of the TiO2NPs-MgY/ZMCPE. The measurements were carried out using cyclic voltammetry in phosphate buffer solution with pH 7.2. This modified electrode exhibits potent and persistent electro-oxidation behavior followed by well-separated oxidation peaks toward G, A and T with increasing the oxidation current. The electrochemical behaviors of guanine, adenine and thymine on the modified electrode were carefully studied by cyclic voltammetry and the electrochemical parameters such as the area of the electrode (A), the electron transfer number (n), the electron transfer coefficient (α), the electrode reaction standard rate constant (ks), and the surface coverage (ГT) were calculated. Differential pulse voltammetry (DPV) was proposed for simultaneous determination of three DNA bases. Under the selected conditions the oxidation peak currents were proportional to guanine, adenine and thymine concentrations in the range from 0.1 to 100μM, 0.1 to 100μM and 8 to 1000μM respectively with the detection limit as 0.013, 0.02 and 0.878μM (3σ) and relative standard deviation (RSD%) 5.25%, 6.5% and 8.63% (n=10 for guanine, adenine and thymine respectively). The proposed method showed good selectivity to the G, A and T detection without the interferences of coexisting substances.

Electrooxidation behavior and electrochemistry determination method of the xanthophylls: Lutein in nonaqueous media

The electrooxidation behavior and determination of lutein, which is an important botanical pigment and antioxidant, were investigated by electrochemical method in nonaqueous media for the first time. The electrooxidation of lutein is a diffusion-controlled irreversible reaction. The electrochemical method shows some selectivity for lutein and lutein esters due to their different end structures, and can be applied to discrimination and qualitative detection of the two, which cannot be achieved by the spectrophotometry. Besides, using differential pulse voltammetry, anodic currents of lutein are linear with their concentration in the range of 0.5–76μM, with detection limits of 0.1μM. The proposed determination method has been successfully applied in the real sample analysis with good sensitivity and reproducibility, confirming it should be a useful addition to the analytical methodology available for monitoring the concentrates of lutein.

Direct electrochemistry of adenine on multiwalled carbon nanotube–ionic liquid composite film modified carbon paste electrode and its determination in DNA

A novel, simple and reliable sensor based on multiwalled carbon nanotube–ionic liquid (1-ethyl-3-methylimidazolium hexafluorophosphate, EMIMPF6) composite film modified carbon paste electrode (MWCNT–IL/CPE) was proposed for direct electrooxidation behavior and determination of adenine. Compared with unmodified electrode, the modified electrode not only significantly enhanced the oxidation peak current but also lowered its oxidation peak potential. The electrochemical behavior of adenine on the modified electrode was carefully studied by cyclic voltammetry and the electrochemical parameters such as the electron transfer coefficient (α), the electrode reaction standard rate constant (ks), the area of the electrode (A), the electron transfer number (n) and the concentration of the electroactive adenine (ГT) were calculated with the results of 0.36, 3.65×10−6s−1, 1.4×10−3cm2, 2.04 and 7.43×10−9molcm−2 respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the adenine concentration in the range from 5.0×10−7 to 7.5×10−5molL−1 with the detection limit of 1.089×10−9molL−1 (3σ) and the relative standard deviation (RSD) 6.5% (n=7) of 5×10−5molL−1 for adenine. The common coexisting substances showed no interferences to the adenine detection and the modified electrode showed good ability to distinguish the electrochemical response of adenine.

Comparison of ethanol electro-oxidation on Pt/C and Pd/C catalysts in alkaline media

The ethanol electro-oxidation behaviors of Pt/C and Pd/C in alkaline media were compared using potentiodynamic and potentiostatic methods. Various ethanol and alkaline concentrations were studied. In addition, the temperature effect of ethanol oxidation was investigated. The Pd/C showed a higher activity toward ethanol oxidation than the Pt/C, especially in the potentiostatic measurement. This is mainly due to the higher oxyphilic characteristics of the Pd/C and the relatively inert nature of the Pd/C on C–C bond cleavage. The apparent activation energies of the ethanol oxidation on the Pd/C in alkaline media varied from 26.6 to 30.4 kJ mol−1, depending on the potentials. The Tafel slopes could be divided into two parts on both catalysts: at low overpotentials, the Tafel slope on both the Pt/C and the Pd/C was close to 120 mV dec−1 at all temperatures; at high overpotentials, the Tafel slope was ca. 260 mV dec−1 on the Pd/C at all temperatures, but was much higher on the Pt/C, especially at high temperatures. Based on these results, it is concluded that Pd/C has less poisoning effect and higher activity than Pt/C for selective oxidation of ethanol to acetate.

Electrochemical oxidation of 6-hydroxyquinoline on a glassy carbon paste electrode: Voltammetric and computational study

Experimental study of the electro-oxidation behavior of 6-hydroxyquinoline (6HQ) has been performed using cyclic voltammetry (CV) on a glassy carbon paste electrode (GCPE). The theoretical study of the 6HQ electrochemical oxidation mechanism, based on the AM1 semi-empirical quantum chemical computations of the heats of formation and ionization energy of reaction intermediates, taking into account influence of pH and solvation effects, has also been conducted. It was established that a two-electron, irreversible process, controlled by diffusion of electroactive species, is responsible for an oxidation peak of 6HQ that appears in all cyclic voltammograms recorded on a clean electrode, in solutions of pH range 2–12, with a supporting electrolyte of Britton–Robinson buffer/methanol. A single-electron oxidation of 6HQ leads, depending on pH, to the formation of various free radical species that combine to make C5–C5 coupled 6HQ dimers which, after being oxidized once more, give quinonoid-type compounds. The irreversible electrochemical oxidation of 6HQ does not stop after the dimerization step but proceeds further to the formation of oligo/poly(6HQ). The optimum conditions for Differential Pulse Voltammetry (DPV) determinations were established and it was shown that for more sensitive quantitative determinations Adsorptive Stripping Differential Pulse Voltammetry (AdSDPV) can be used.