Electro-oxidation of Ascorbic Acid on PVP-stabilized Graphene Electrode

Polyvinylpyrrolidone-stabilized graphene(PVP-graphene) was synthesized and investigated as a modifier for the determination of ascorbic acid(AA).With PVP acting as stabilizer and dispersant,the resulting PVP-graphene material could disperse well into water.And the PVP-graphene modified glassy carbon electrode(PVP-graphene-GCE) showed an obvious electrocatalytical activity toward the oxidation of AA in a phosphate buffer solution(PBS,pH=7.0) with an oxidation potential of AA at 0.052 V vs.Ag|AgCl(sat.KCl).The calibration curve for AA was linear in a concentration range from 1.0×10-5 to 5.0×10-4 mol/L with a correlation coefficient of 0.9998.And the detection limit was found to be 1μmol/L.During the oxidation of AA,the π-π interaction of graphene plane with conjugated hexenoic acid-lactone in AA molecules might play a key role.As a result,an obvious decrease of overpotential was achieved at such a PVP-graphene electrode through a possible adsorption/enrichment process,which will probably trigger potential applications for the electroanalysis of some aromatic and heterocyclic compounds.     

Oxidation of toluene on Bi-doped PbO<Subscript>2</Subscript> studied by electrochemical impedance spectroscopy and UV spectrophotometry

Oxidation of organics in the potential region of O₂ evolution is supposed to proceed through the oxidation of water to hydroxyl radicals, which then may either be further oxidized to give molecular oxygen or interact with organic molecules in an oxygen transfer reaction. Therefore, the electrode material must ensure (1) the preferential adsorption of the organic compound, (2) the production of adsorbed hydroxyl radicals able to react with this compound in a selective oxidation reaction (with as little as possible oxygen evolution), and (3) a long-term stability. In the present paper, the oxidative decomposition of toluene in sulfuric acid solution on PbO₂ coatings deposited on Ti substrate from acidic nitrate + fluoride baths containing Pb²⁺ and Bi³⁺ is investigated by voltammetry, electrochemical impedance spectroscopy, and UV spectrophotometry. The chemical composition and structure of the catalytic coatings is characterized with X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic activity is estimated both from current density vs potential and polarization resistance vs potential plots using measurements on the same electrodes in sulfuric acid without toluene to eliminate the oxygen evolution reaction that proceeds in parallel to the oxidation of toluene. A skeletal reaction mechanism of the process is proposed to account for the steady-state and transient response of the catalytic electrodes during oxidation of toluene.     

The influence of organic adsorbates on the UPD process. Oxidation of formic acid at UPD lead-modified platinum electrodes

The oxidation of formic acid at Pt electrodes in the presence of underpotentially deposited (UPD) Pb has been studied using an electrochemical quartz crystal microbalance (EQCM). Although the current associated with the UPD process is largely obscured by current from the oxidation of formic acid, the mass response is dominated by the changes in UPD coverage. Thus examination of mass responses accompanying cyclic voltammetric and constant-potential experiments reveals both variations in UPD coverage and the manner in which the underpotential deposits are affected by adsorbates derived from formic acid. At low concentrations of formic acid there is some suppression of the underpotential deposit and data suggest that strongly adsorbing intermediates form most rapidly in the hydrogen adsorption region of potential. Mass responses also indicate slight increases in UPD coverage upon removal of strongly adsorbed species by oxidation. Oxidation of high concentrations (0.1 M) of formic acid induces a significant positive shift in the potential for removal of the UPD deposit on the positive scan, and on the subsequent negative scan the rapid reaction between the oxidized Pt surface and formic acid removes the oxide at a higher potential than normal and consequently allows the UPD process to begin at a more positive potential. Adsorption of Pb²⁺ at oxidized Pt surfaces is also inhibited by the presence of formic acid.     

Preparation of PVA-GA-CS/PVA-Fe-SA bipolar membrane and its application in electro-generation of 2,2-dimethyl-3-hydroxypropionic acid

PVA-GA-CS/PVA-Fe-SA bipolar membrane was prepared by a paste method. PVA-sodium alginate (SA) and PVA-chitosan (CS) were cross-linked by FeCl₃ and glutaraldehyde (GA), respectively. The charge densities of PVA-CS and PVA-SA solutions were determined by the colloid titration. The swelling level of bipolar membrane was in the range of 25–85%, meanwhile the permeability and the ion-exchange capacity as well as co-ion transport properties was investigated. FTIR was applied to analyze the functional groups of the bipolar membrane. Furthermore, SEM photographs of the BPM cross-section illustrated a structure that consists of an anion layer (PVA-GA-CS) and a cation layer (PVA-Fe-SA). TG analysis of PVA-GA-CS/PVA-Fe-SA bipolar membranes exhibited a good thermal stability. PVA-GA-CS/PVA-Fe-SA bipolar membranes were used as the separator in the electrolysis cell for electro-generation of 2,2-dimethyl-3-hydroxypropionic acid. The average current efficiency was 52.2%, and the highest current efficiency reached 68.9%.     

碱性介质中W,Ni和Sn掺杂的Pt-Ru/C电催化氧化甲醇的性能

直接以Pt, Ru, W, Ni和Sn的金属盐为前驱体, 通过溶胶法制备了不同原子比的Pt-Ru-M/C(M=W, Ni, Sn)碳载纳米合金催化剂, 用X射线衍射(XRD)和X光电子能谱(XPS)表征催化剂的晶相结构、表面组成及价态形式, 采用循环伏安法测试催化剂电催化氧化甲醇活性. 结果表明, 掺杂Ni和W可明显提高Pt-Ru/C催化活性, 掺杂Sn则降低了Pt-Ru/C催化活性. 其中Pt5-Ru4-Ni0.7/C的活性最高, 在1.0 mol/L NaOH＋1.0 mol/L CH3OH溶液中峰电流达835.2 mA/mg, 甲醇起始氧化电位比Pt5-Ru5/C低约0.11 V.     

负载型离子液体在C-H键电氧化活化中的应用研究

本文将1-乙基-3-甲基咪唑醋酸盐离子液体修饰在多壁碳纳米管上,制备出离子液体/碳纳米管复合材料,并研究了对甲氧基甲苯（p-MT）在该复合离子液体水溶液体系中的电氧化性能. 同时,通过循环伏安法和计时电流法考查了扫描速率、温度、反应底物浓度等因素对电氧化性能的影响,研究了p-MT在该体系中的动力学过程. 实验结果表明,p-MT在复合离子液体水溶液体系中发生不可逆的电氧化反应,且该过程受扩散控制,扩散系数为7.69×10^-10 cm²·s^-1. 适当地升高温度和增大反应底物浓度都有利于促进p-MT中C-H键选择性电氧化为相应醛基,选择性可达到95%. 通过在不同结构电解槽中进行恒电位电解研究,发现离子液体/MWCNTs复合电解质在一室型电解槽中进行p-MT电氧化的电解效率更高、对目标产物对甲氧基苯甲醛（p-MBA）的选择性也更好.     

Graphene Oxide as a Platform for Copper Pentacyanonitrosylferrate Nanoparticles and their Behavior in the Electro‐oxidation of N‐Acetylcysteine

This work describes the preparation of graphene oxide by the Modified Hummers Method and the chemical modification of its surface with nanoparticles of copper pentacyanonitrosylferrate(III) (GOCuNP). The materials obtained were characterized by Raman spectroscopy, x‐ray photoelectron spectroscopy and transmission electron microscopy. The GOCuNP was characterized by cyclic voltammetry using a graphite paste electrode that presented electrocatalytic response for N‐acetylcysteine with detection limit of 2.97×10^?5 mol L^?1 at concentration range of 3.00×10^?5 to 6.00×10^?3 mol L^?1 of N‐acetylcysteine. By this way, the bimetallic complex formed is included in the list of materials obtained as potential candidates for the construction of electrochemical sensors for N‐acetylcysteine detection.     

Electroanalysis of Carbendazim using MWCNT/Ca‐ZnO Modified Electrode

The present research involves the report on electrochemical deportment of Carbendazim (MBC) at multiwalled carbon nanotubes and calcium‐doped zinc oxide nanoparticles altered nanocomposite based carbon paste electrode (MWCNTs/Ca‐ZnO‐CPE). The modified carbon paste evidenced manifest electrocatalytic behavior for MBC in 0.2 M phosphate buffer (PB) solutions. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV) techniques were used for the analysis. The working electrode assembly exhibits faster electron transfer of MBC with increase in the peak current. At bare CPE, MBC showed maximum peak current of 1.098 μA at potential 0.7568 V whereas at MWCNT/Ca‐ZnO/CPE peak current of 5.203 μA was observed at potential 0.7541 V in 0.2 M PBS of pH 7.0 at the sweep rate of 50 mV s^?1. The synthesized 5 % Ca‐ZnO nanoparticles (NPs) were characterized by X‐ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X‐ray analysis (EDX), and Transmission electron microscopy (TEM) analysis. Various factors influencing the voltammetry of MBC such as pre‐concentration time, pH, sweep rate, and amount of MBC were studied and from the studies we observed that the response was found to be diffusion‐controlled. The concentration variation studies for MBC was watched in the linear working range of 0.01 μM to 0.45 μM and the detection limit was found by SWV technique.     

Thiol oxidation at 2-mercaptopyrimidine-appended cobalt phthalocyanine modified glassy carbon electrodes

The electrocatalytic activity of cobalt tetra-2-mercaptopyrimidylphthalocyanine-modified glassy carbon electrode (CoTMPyrPc-GCE) toward gluthathione, l-cysteine and 2-mercaptoethanol has been investigated. CoTMPyrPc-GCE provides a significant improvement on the reported oxidation potential of l-cysteine in pH 4.0 phosphate buffered solution. The oxidation peak potential (E_p), for l-cysteine, was 0.15 V – a relatively lowered oxidation potential compared to reported phthalocyanine complexes. The electrode prepared by drop-dry/thermal annealing method was very stable and sensitive over a long period of time. The stability has been attributed to the thermal annealing and the structure of the mercaptopyrimidine on the periphery of the CoPc.     

Parametric study for the treatment of tannery dye wastewater by electro-oxidation

Degradation of tannery effluents is a difficult operation because of their intricate chemical structures. Most of the conventional approaches are becoming ineffective because of the wide variation in the composition of tannery effluent. Dyes from the wastewater is also dangerous, as the wastewater has negative impact on the health of human being, plants and aquatic animals. For the first time once through continuous approach was employed for the removal of Acid yellow 110 tannery dye in electro-oxidation process on Mix Metal Oxide of ruthenium and iridium on titanium sheet electrode. The effects of pH, time (t) and current (i) on % color removal and energy consumed were investigated in a batch setup and found the optimum condition with the help of RSM design. The values of the responses Y₁ and Y₂ were found to be 93.08% and 1.07 kWh/m³ respectively at the optimum condition. Toxicity Bioassay analysis, GC-MS analysis and the kinetic study were performed at optimum condition. At the flow rates of 10–40 ml/min once through continuous experiments was conducted to found the feasibility of the process at pilot scale or industrial scale application.