Potential-triggered adsorption of CdSe nanoparticles on glassy carbon electrode for generation of electrochemiluminescence

In this work we discovered the potential-triggered adsorption of the thioglycerol stabilized CdSe nanoparticles on the glassy carbon electrode (GCE), which induced the electrochemiluminescence (ECL) of the nanoparticles coreacted with triethylamine. The increasing ECL emission was controlled by the applied potential of the electric field, with an optimized potential of +1.0 V. The adsorption event of the nanoparticles on the GCE was quantitatively identified by the stripping voltammetric analysis of Cd²⁺ ions, etc. The ECL emission was also found to be notably enhanced after the removal of the interference from the dissolved oxygen. These results would be helpful to make the full understanding of the ECL processes by the CdSe nanoparticles-tertiary amines system and promote the design of the high-sensitive bioelectronic sensors.     

Electrochemical oxidation of benzene at a glassy carbon electrode

Benzene oxidation in sulfuric acid at a glassy carbon electrode was investigated using voltammetric, chronoamperometric, and spectroscopic methods. The results are compared with those at a Pt electrode. Benzene was observed to be oxidized to benzoquinone presumably by active oxygen that was adsorbed on the GC electrode in the oxygen evolution region. It is concluded that oxidation at glassy carbon can produce benzoquinone or quinone-like compounds from an aqueous benzene solution. The applied potential for benzene oxidation should be less than 2.1 V vs RHE in order to prevent glassy carbon electrode damage by oxidation during long operation.     

Oxygen and hydrogen peroxide reduction catalyses in neutral aqueous media using copper ion loaded glassy carbon electrode electrolyzed in ammonium carbamate solution

An aminated glassy carbon electrode (AGCE) can be obtained by the electrode oxidation of glassy carbon electrode in ammonium carbamate solution. In the cyclic voltammetric experiments, the electrode reduction of the dissolved oxygen began from −0.15 V vs. Ag/AgCl in neutral aqueous media when the aminated glassy carbon electrode was used as a working electrode although it began from −0.40 V vs. Ag/AgCl when a polished GCE was used. The nitrogen containing groups introduced by the electrode oxidation of carbamic acid must be related with the acceleration of the electron transfer rate of oxygen. Moreover, the new reduction wave of the dissolved oxygen appeared at +0.15 V vs. Ag/AgCl when copper (II) ion was coordinated to AGCE surface. This reduction potential of oxygen coincided with that of copper (II) ion and this fact suggests that the coordinated copper ion to the aminated carbon surface works as a redox mediator of oxygen. The reduction product of oxygen was monitored by rotating platinum ring - aminated glassy carbon disk electrode, and it was found that most of oxygen was reduced to water in a potential range negative than −0.4 V vs. Ag/AgCl. By using AGCE, it was recognized that the catalytic reduction of hydrogen peroxide was also taken place as well as oxygen reduction.     

The potential-resolved electrochemiluminescent behavior of calcein in aqueous alkaline solutions at a glassy carbon electrode

In aqueous alkaline solutions, the potential-resolved electrochemiluminescent (ECL) behavior of calcein at a glassy carbon electrode was investigated. A sharp ECL light emission peak appeared near 0.8 V (vs. Ag/AgCl) under cyclic voltammogram (CV) conditions. In order to obtain a better understanding of the light emission, we investigated the effects of supporting electrolytes, the pH value, the presence of O₂ or N₂, and the concentration of calcein. The oxidative form of calcein reacted with hydroxyl radicals and oxygen, producing singlet excited oxygen that was identified as the emitter using the ECL, UV-vis absorption and fluorescence spectra. A possible mechanism for the behavior of calcein in this system was also proposed.     

Pt/PAn/GC电极的制备及对甲酸电催化氧化性能的研究

利用循环伏安法电聚合导电高分子聚苯胺，并制备了Pt／PAn／GC电极和Pt／GC电极，优化了苯胺在玻碳电极上的聚合条件，用在H2SO4中的循环伏安曲线对其进行了表征，Pt／PAn／GC电极的制备提高了Pt的分散度，增加了催化剂Pt的利用率。实验结果表明Pt／PAn／GC电极对甲酸电氧化的催化活性明显高于Pt／GC电极和Pt电极，正向扫描和反向扫描时对应的氧化峰电位分别是0．68V、0．45V。峰电流为54．23mA／cm^2和84．23mA／cm^2，为Pt／GC电极的修饰电极1．7倍和1．9倍，为Pt片电极的3．8倍和4．9倍，有效地提高了铂微粒的催化活性，并得到聚合苯胺的最佳条件为扫描速度50mV／s、扫描上限1．2V。     

玻碳电极上碘仿电解合成的机理

本文采用循环伏安法研究了在Na2CO3溶液介质中KI在金电极和玻碳电极上的电化学行为.在0.2V～1.2V电位范围内玻碳电极上仅发生I-被氧化为I2的反应,而在金电极上除了I-被氧化为I2外,还发生生成IO3-的氧化反应.同时通过不同电位扫描速度下的循环伏安行为分析发现电极过程为传质控制步骤.     

Electrochemical studies of kerosene-pyrolysedcarbon films

Polycrystalline thin films of conducting carbon are deposited on alumina substrates by the pyrolysis of kerosene vapour at 1000C for 2h in argon atmosphere. Preliminary structural analysis is done by XRD, laser-Raman, FTIR and SEM studies. The electrochemical behaviour of as-grown conducting carbon films was investigated in various electrolytes at different pH and the performance was compared with that of platinum and glassy electrodes. The electrochemical window of the kerosene carbon electrode in 100mm H2SO4 was found to be 2.91V which is greater than that of glassy carbon (2.79V) and platinum (2.02V). Cyclic voltammetry reveals that Pt electrode has almost an equal tendency towards hydrogen and oxygen evolution, whereas glassy carbon favours hydrogen evolution and kerosene carbon favours oxygen evolution. It is suggested that the kerosene carbon electrode can be used as an oxygen electrode more efficiently. Unlike diamond films or glassy electrodes, kerosene carbon thin films are of low cost and good stability; they are also easy to grow on various ceramic substrates of any size. Moreover, these electrodes are very economical and promising for application in chlor-alkali industry.     

Electrochemical studies on [M(diars)<Subscript>2</Subscript>X<Subscript>2</Subscript>]<Superscript>+</Superscript> where [X = Cl,Br; M = Os,Re, Ru,Rh; diars = <Emphasis Type="Italic">o</Emphasis>-phenylenebis (dimethylarsine)] at bare and Nafion modified electrodes

The voltammetric behaviour of the M(III/II) redox couple of the complexes of the general formula [M(diars)₂X₂]⁺ where M = Os, Re, Ru, Rh and diars = o-phenylenebis-(dimethylarsine) has been investigated in aqueous and aqueous/ethanol solvents at bare and Nafion modified electrodes. The formal reduction potential falls within the range of 0.097–0.0920 V and increases with the dielectric constant of the solvent. In acertonitrile, both the oxidized and reduced forms of the complex showed no adsorption at the surface of the glassy carbon electrode as shown by cyclic voltammetry. The electrochemistry is consistent with a quasireversible one electron transfer between the di and tri cationic forms of the complexes. A current-enhancement of ∼2 was observed at Nafion-modified glassy carbon over the bare electrode. Well defined voltammograms were obtained at Nafion-modified glassy carbon with a detectable signal down to 10⁻⁹ M range by differential pulse voltammetry. Electrochemical detection of dopamine in presence of [Os(4-mediars)₂Cl₂]⁺ at Nafion modified electrode indicates an increase in peak current. This shows that this complex acts as biochemical-sensor for dopamine.     

Enhanced electrochemiluminescence of CdTe quantum dots with carbon nanotube film and its sensing of methimazole

A novel analytical method was reported based on electrochemiluminescence (ECL) of CdTe quantum dots (QDs) using carbon nanotube (CNT) modified glass carbon (GC) electrode. It was found that the CNT film on the GC electrode could greatly enhance the ECL intensity of CdTe QDs dispersed in aqueous solution, and the ECL peak potential and ECL onset potential both shifted positively. Influences of some factors on the ECL intensity were investigated using CNT modified GC electrode, and a high sensitive method for the determination of methimazole was developed under the optimal conditions. The ECL intensity decreased linearly in the concentration range of 1.0 × 10⁻⁹ to 4.0 × 10⁻⁷ M for methimazole with the relative coefficient of 0.995, which showed finer sensitivity than that at bare electrode. Thus, CNT modified electrode would have a great merit to expand the application of QD ECL.     

Direct electrochemiluminescence of CdTe quantum dots based on room temperature ionic liquid film and high sensitivity sensing of gossypol

A new method with high sensitivity was developed to determine gossypol content using CdTe quantum dot (QD) electrochemiluminescence (ECL) with a room temperature ionic liquid (RTIL) modified glassy carbon (GC) electrode. It was found that use of RTIL film on the GC electrode can greatly enhance the ECL intensity of CdTe QDs, and the ECL peak potential and ECL onset potential were both shifted positively. Under optimal conditions, the quenching effect of gossypol on the ECL emission of CdTe QDs was observed, and ECL intensity showed a good linear relationship in the gossypol concentration range of 5.0 × 10⁻⁷ to 5.0 × 10⁻⁹ M with a detection limit of 5.0 × 10⁻⁹ M. The proposed method was used to detect gossypol in cottonseed oil with satisfactory results. As a result, the introduction of an RTIL-modified electrode can extend the analytical applications of QD ECL systems.     

Second-order data obtained from differential pulse voltammetry: Determination of tryptophan at a gold nanoparticles decorated multiwalled carbon nanotube modified glassy carbon electrode

Three-way data obtained from different pulse heights of differential pulse voltammetry (DPV) was analyzed using multivariate curve resolution by alternating least squares (MCR-ALS) algorithm. Differential pulse voltammograms of tryptophan were recorded at a gold nanoparticles decorated multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNTs-nanoAu). The determination of tryptophan was performed even in the presence of unexpected electroactive interference(s). Both the simulated and experimental data were non-bilinear. Therefore a potential shift algorithm was used to correct the observed shift in the data. After correction, the data was augmented and MCR-ALS was applied to the augmented data. A relative error of prediction of less than 8% for the determination of the simulated analyte of interest and tryptophan in synthetic samples indicated that the methodology employing voltammetry and second-order calibration could be applied to complex analytical systems.     

Electrode kinetics in non-aqueous vanadium acetylacetonate redox flow batteries

Three electrode materials (glassy carbon, gold, and platinum) were investigated for application in a non-aqueous single-metal redox flow battery based on vanadium (III) acetylacetonate, supported by tetraethylammonium tetrafluoroborate in acetonitrile. Redox couples associated with the one-electron disproportionation of V(acac)₃ were observed in voltammetry for each metal tested. An elementary kinetic model was created and used to determine rates for oxidation or reduction of the vanadium complex. The oxidation rates for V(acac)₃ were mass-transfer limited on all electrode materials, suggesting reversible kinetics. For the V(acac)₃ reduction reaction, exchange-current densities of 1.3, 3.8, and 8.4 A m⁻² were observed on glassy carbon, platinum, and gold electrodes, respectively.     

The effect of platinum on carbon corrosion behavior in polymer electrolyte fuel cells

To assess the catalytic effect of platinum on the corrosion of the high surface area carbon support, single triangular potential sweeps with various upper and lower limits were applied to fuel cells comprising electrodes having different Pt/C compositions. Carbon loss rates in H₂/N₂ and air/air mode were determined by integration of the resulting CO₂ concentration peaks in the exhaust gas of the positive electrode. Generally, the contribution of platinum catalyzed carbon corrosion to total CO₂ evolution was found to decrease with increasing upper potential limit. Similar carbon loss rates obtained for Pt/C and pure carbon electrodes in case of lower potential limits of 1.0 V indicate that the catalytic activity of platinum is substantially lowered by the formation of a passivating oxide layer on the platinum particles. Changes in corrosion behavior in the potential range below 0.6 V, which cannot be attributed to platinum effects, are suggested to originate from modifications in carbon surface oxide composition. Due to the high oxygen equilibrium potential of approximately 1 V, carbon corrosion in air/air mode is significantly influenced by platinum oxide formation. However, the polarization of the negative electrode and the influence of platinum oxidation on the equilibrium potential results in a passivating effect that is less pronounced than expected from measurements in H₂/N₂ mode.     

Endeavor toward competitive electrochlorination by comparing the performance of easily affordable carbon electrodes with platinum

Kinetics of chloride ion oxidation was studied on graphite, glassy carbon (GC), and platinum electrodes. The performance of the electrodes was monitored using the cumulative productivity and current efficiency of the cell as indicators. It was seen that the performance of the working electrode improved with repeated uses, the current efficiency increased from 22% in the third use to about 46% in the tenth use. The study also revealed that the role of diffusion to the total anodic current was insignificant and chloride ions were transported at the electrode surface only by conduction. The hypochlorite production in case of platinum was about 3.66 times than that of graphite and GC with the current efficiency of 75% in contrast to 46% found in graphite and GC. But platinum undergoes passivation to a significant extent unlike the graphite and GC electrodes. Chronopotentiometry experiments confirmed the passivation process in platinum electrodes, showed a steep rise in potential from 1.2 to 2?V while the electrode potential was uniformly maintained at 1.7?V in carbon electrodes. The highest i_o, exchange current density value was observed at 0.45?mA/cm² in 0.5?M electrolyte, which is an indication of improved electrocatalytic activity with increased molar concentration. After continuous uses the corrosion rate studies revealed that platinum and GC electrodes were corrosion resistant whereas graphite underwent corrosion at the rate of 0.006?mm/h. The study dictated that carbon electrodes has great potential to be used as an alternatives to platinum electrodes, however, further investigations are required to assess its practical applicability in the public water supply system.     

Electrochemical deposition of platinum nanoparticles on different carbon supports and conducting polymers

Electrodeposition of Pt nanoparticles under potentiostatic conditions was performed on several types of carbon electrode supports: commercial macroporous carbon (a three-dimensional electrode), glassy carbon and graphite. Conducting polymers (poly-aniline and poly-o-aminophenol) were also used. The platinum nanoparticles were obtained by different Potential Step Deposition (PSD) methods in 5 mM H₂PtCl₆ + 0.5 M H₂SO₄ aqueous solutions. The effect of the final potential, time and number of steps on the quantity, distribution and size of the platinum nanoparticles was analysed. The mechanism of the electrochemical deposition of platinum was studied through the application of theoretical modelling. The progressive nucleation mechanism provided the closest agreement with the results obtained. In addition, the chemical state and morphology of the electrodeposited materials were determined by means of SEM, TEM and XPS. The results show that the carbon material structure has a strong influence on the Pt particle structure and this, in turn, affects the catalytic activity.     

Poly(taurine)/MWNT-modified glassy carbon electrodes for the detection of acetaminophen

A novel dye-polymer/CNT, poly(taurine)/MWNT-modified glassy carbon electrode was fabricated. This electrode is based on an electrochemically polymerized taurine layer coated on a MWNT film. The application of this electrode for voltammetric detection of acetaminophen is described. The electroactive surface area of the modified electrode was calculated to be 0.37 cm². Acetaminophen is oxidized at 0.38 V and then reduced at 0.27 V on the modified electrode. The irreversible oxidation process is due to the conversion of acetaminophen into imidogenquinone; the reduction process is ascribed to the reverse electrode reaction. The adsorption-controlled anodic peak current is proportional to the acetaminophen concentration (from 1.0 μM to 0.1 mM) with a detection limit of 0.5 μM. The detection of acetaminophen in drugs was conducted.     

Enhanced electrochemiluminescence quenching of CdS:Mn nanocrystals by CdTe QDs-doped silica nanoparticles for ultrasensitive detection of thrombin

This work reports an aptasensor for ultrasensitive detection of thrombin based on remarkably efficient energy-transfer induced electrochemiluminescence (ECL) quenching from CdS:Mn nanocrystals (NCs) film to CdTe QDs-doped silica nanoparticles (CdTe/SiO(2) NPs). CdTe/SiO(2) NPs were synthesized via the St?ber method and showed black bodies' strong absorption in a wide spectral range without excitonic emission, which made them excellent ECL quenchers. Within the effective distance of energy scavenging, the ECL quenching efficiency was dependent on the number of CdTe QDs doped into the silica NPs. Using ca. 200 CdTe QDs doped silica NPs on average of 40 nm in diameter as ECL quenching labels, attomolar detection of thrombin was successfully realized. The protein detection involves a competition binding event, based on thrombin replacing CdTe/SiO(2) NPs labeled probing DNA which is hybridized with capturing aptamer immobilized on a CdS:Mn NCs film modified glassy carbon electrode surface by specific aptamer-protein affinity interactions. It results in the displacement of ECL quenching labels from CdS:Mn NCs film and concomitant ECL signal recovery. Owing to the high-content CdTe QDs in silica NP, the increment of ECL intensity (ΔI(ECL)) and the concentration of thrombin showed a double logarithmic linear correlation in the range of 5.0 aM～5.0 fM with a detection limit of 1aM. And, the aptasensor hardly responded to antibody, bovine serum albumin (BSA), haemoglobin (Hb) and lysozyme, showing good detection selectivity for thrombin. This long-distance energy scavenging could have a promising application perspective in the detection of biological recognition events on a molecular level.     

甲醇在聚苯胺载铂电极上的电催化氧化

用循环伏安法在玻碳电极上电聚合导电高分子聚苯胺用于附载Pt,提高了Pt的分散度。发现甲醇在Pt／PAN／GC电极和Pt／GC电极上均能自发解离出强吸附中间体CO,证实聚苯胺膜的存在有利于提高电极对甲醇的电催化氧化活性,CO在Pt／PAN／GC电极上的氧化峰电流明显高于Pt／GC电极。通过比较甲醇的电催化氧化活性可知,Pt/PAN／GC电极催化氧化甲醇的峰电流为58．68mA/cm^2和50．00mA／cm^2,是Pt／GC电极氧化峰电流的1．6倍和1．7倍。     

甲醇在碳载纳米Pt电极上的电化学研究

应用循环伏安法制备了nano-Pt/GC修饰电极,优化了铂微粒在电极表面的沉积条件,并用扫描电子显微镜(SEM)和在硫酸中的循环伏安曲线对其进行了表征。结果表明铂微粒较为均匀地分散在玻碳电极表面,粒径约为140nm,电极具有很大的比表面积。循环伏安实验结果表明nano-Pt/GC电极对甲醇电氧化的催化活性明显高于铂片电极,在该修饰电极上甲醇正向扫描和反向扫描时的氧化峰电位分别是0.67V和0.49V,峰电流为61.00mA/cm2和50.50mA/cm2,分别是铂片电极上的3.13倍和3.10倍,有效地提高了金属铂的利用率,铂微粒在电极表面的最佳沉积条件是循环次数为100次和沉积速度为5mV/s。     

Cathodic electrochemiluminescence behavior of norfloxacin/peroxydisulfate system in purely aqueous solution

A novel cathodic electrochemiluminescence (ECL) behavior of the norfloxacin (NFLX)/peroxydisulfate (S₂O₈²⁻) system in purely aqueous solution at a glassy carbon electrode (GCE) was firstly reported in this paper. The NFLX/S₂O₈²⁻ system could produce a very strong ECL signal under the potential scan from 0 to −1.8 V in 0.1 M phosphate buffer solution (pH 7.0) containing 0.24 mg/mL NFLX and 10 mM S₂O₈²⁻, which was about 350 times higher than that of S₂O₈²⁻ alone, while NFLX did not produce ECL in the absence of S₂O₈²⁻. The effects of pH value, S₂O₈²⁻ and NFLX concentration on the ECL intensity were investigated and the possible mechanism for the ECL behavior of NFLX/S₂O₈²⁻ system was proposed.