Electrochemical reduction of acetone on mercury electrode in aqueous sulphuric acid solution

Electrochemical reduction of acetone in aqueous H₂SO₄ solution was studied on Hg electrode by galvanostatic, potentiodynamic and polarographic methods. Electrocapillary curves show that acetone molecule adsorbs to a monolayer at concentrations larger than 0·5 M in a potential range of 0 > V > ? 1·0 V (nhe). It orients with the positive end of the dipole toward electrode surface and extends an attractive interaction to its neighbours.Kinetics oberved by galvanostatic pulse method and polarography leads the following conclusions; (1) adsorbed acetone molecule undergoes elecrochemical reduction at potentials more negative than ?1·0 V (nhe), (2) reaction rate is the first and second order with respect to the amount of adsorbed acetone and proton activity, and (3) one electron transfer step determines the reaction rate (Tafel slope is 0·12 V). Reaction intermediate is concluded from the potentiodynamic study to be isopropanol radical, (CH₃)₂??OH, whose amount is proportional to that of adsorbed acetone and to a_H+. From the above results, the rate of the electrochemical reduction of acetone is H₂SO₄ solution is concluded as determined by the step, (CH₃)₂?OH(a) + H⁺ + e^? → (CH₃)₂CHOH.     

Electrochemical reduction off 4-aminopyrimidine in aqueous media

The redox and associated chemical behavior of 4-aminopyrimidine (4-AP) and its reduction products in buffered aqueous media have been examined by a variety of electrochemical techniques. In acidic medium (pH 0–2), 4-AP undergoes a two-step reduction: pH-dependent wave I corresponds to a three-electron (3e) process; wave II, which corresponds to a 1e transfer, is accompanied by catalytic hydrogen discharge. Between pH 2 and 7.5, only wave I is visible; its height diminishes above pH 4, becoming zero by pH 8. Macroscale electroreduction at potentials on the crests of waves I and II has been followed electrochemically and by ultraviolet spectrophotometry with isolation and identification of the wave I reduction products. The photochemical transformation of the reduction products on ultraviolet irradiation has been examined. The reduction of 4-AP is accompanied by isomerization, ring opening and/or deamination of the primary reduction products and of the resulting secondary chemical products.     

脱除浓NaCl水溶液中硫酸钠的工艺

介绍了几种脱除浓盐水系统中富集硫酸钠工艺的原理，比较了各种工艺方法的特点。     

超声作用对NaCl和MgSO4溶液在纳滤膜内传质的影响

将超声波用于强化电解质溶液在纳滤膜内的传质过程,研究超声作用下NaCl和MgSO₄溶液在聚酰胺纳滤膜内的传质机理,考察超声作用对膜通量、截留率和跨膜电位随跨膜压差变化规律的影响。实验结果表明,与无超声作用相比,施加在膜表面的超声作用增大了膜通量,降低了截留率,提高了跨膜电位。     

Adsorption of Cd(II) from aqueous solution onto pyrite

The physicochemical factors such as equilibrium time, solution pH, initial concentration of Cd(II), particle size and temperature that control the adsorption of Cd(II) from aqueous solutions onto pyrite has been investigated through batch experiments. Prior to this study, pyrite was characterized through chemical and XRD-analysis. The point of zero charge, pH_pzc was determined using the batch equilibrium technique and was found to be 6.4. The equilibrium time was 30 min at the solution pH of 6.0. The pH influence of Cd(II) adsorption was remarkable and maximum metal uptake was observed at 6.0 which is closer to pH_pzc. Under this weakly acidic condition Cd(II) ions are responsible for adsorption. Concentration dependence of metal uptake indicates that saturation of pyrite surface by adsorbate occurs at an initial Cd(II) concentration of 350 mg/L and the corresponding metal uptake was 576.5 mg/L of −150 mesh size pyrite at pH 6.0 and 30 °C. Particle size affects the adsorption capacity to a great extent and a decrease in particle diameter enhances metal uptake. The effect of temperature on adsorption performance reveals that the effective temperature for Cd(II) adsorption is 30 °C. The empirical Freundlich isotherm was applied to represent the adsorption process, which fits the experimental data quite well. The work reveals that natural pyrite is a very good choice as an adsorbent for the removal of toxic metals from industrial wastewater and bears significant industrial implications.     

Electrochemical behavior of vanadium-substituted Keggin-type polyoxometalates in aqueous solution

Cyclic voltammetry was carried out on selected vanadium-substituted Keggin polyoxometalates in aqueous solution with a focus on K₃H₂[α-SiVW₁₁O₄₀] · 6H₂O (SiVW₁₁O₄₀) and K₄H₂[γ(1, 2)-SiV₂W₁₀O₄₀] · 4H₂O (SiV₂W₁₀O₄₀). The redox waves of the V-O and W-O framework for both polyanions are pH- and scan rate-dependent. The first vanadium-centered wave (V-wave) for SiVW₁₁O₄₀ shows a classical potential shift as a function of acidity at pH < 3.5, and then becomes pH-independent above this value. Above pH 3.5, the W-centers in SiVW₁₁O₄₀ and SiV₂W₁₀O₄₀ exhibit efficient electrocatalytic activity towards the reduction of nitrite and hydrogen peroxide while the V-waves also exhibit an electrocatalytic response in nitrite-containing solutions.     

Electrochemical behaviour of phenylethanolamine at gold in aqueous solution

The electrooxidation of phenylethanolamine (2-amino-1-phenylethanol) at a gold electrode in alkaline electrolyte has been studied. Measurement of the differential capacitance of the electric double layer versus the electrode potential has shown that the adsorption of phenylethanolamine at the gold-solution interface plays a significant role in the oxidation mechanism. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation is analysed.     

NaCl溶液静态闪蒸的蒸发特性

对不同初始条件下NaCl溶液静态闪蒸过程中蒸发质量的变化规律进行了实验研究,实验过程中溶液初始质量分数为5%～26%,初温为74～104℃,初始液位高度为0.1～0.3 m,过热度为0.79～42 K。结果表明:在以ΔT_s为过程参量时,溶液闪蒸蒸发质量随NaCl初始质量分数的增加明显下降;以ΔT为过程参量时,相同初始液位高度,不同初始质量分数NaCl溶液闪蒸蒸发质量相差较小;增加初始液位高度虽可增加总蒸发质量,但使单位质量溶液闪蒸蒸发质量下降;闪蒸蒸发质量随过热度增大而呈近似线性增加。综合分析静态闪蒸过程中主要过程参量对蒸发质量的影响,在实验基础上,提出蒸发质量的量纲1关联式。     

Electrochemical reduction of 2,3′-dinitrobenzidine in buffered aqueous methanol

2,2-dinitrobenzidine (2,3-DNB) gives a single diffusion-limited irreversible polarographic wave in buffered aqueous methanol. Microcoulometric experiments indicate a transfer of ten electrons in the reduction and cyclic voltammetric studies show direct proof for the existence of a nitroso intermediate. Based on the results obtained, a suitable mechanism is proposed for the reduction of 2,3-DNB in buffered methanolic solutions.     

Electrochemical behaviour of copper in aqueous solution containing potassium ethylxanthate

The electrochemical behaviour of copper in aqueous potassium ethylxanthate (KEX) is studied by using potentiodynamic techniques at different sweep rates, complemented with SEM and EDAX. In NaCl solutions a cuprous xanthate film is formed at low potentials, the initial stage of this reaction being the electroadsorption of KEX on copper competing with the adsorption of chloride ions and water. At low surface coverages for electroadsorbed KEX the electrodissolution of copper is partially inhibited as compared to plain NaCl solutions. As the KEX monolayer is completed, a tri-dimensional cuprous xanthate film grows in the electrode surface. On subsequent increase of the applied potential a complex anodic layer is formed leading to copper passivity. Passivity breakdown promoted by either chloride ions or electro-oxidation of the organic film can be observed when the potential exceeds a certain critical value.Facultad de Ciencias Exactas, Universidad Nacional de La Plata.     

盐水体系中环戊烷-甲烷水合物的相平衡及分解热

利用可视化水合物相平衡实验装置,采用恒温压力搜索法,测定了284～303K内环戊烷(CP)-甲烷在NaCl溶液中的水合物相平衡数据,并采用Clausius-Clapeyron方程计算了其生成/分解热数据。实验结果表明,CP-甲烷水合物生成条件远低于纯甲烷水合物;采用甲烷辅助气体可使CP在高于其纯水合物四相点的更高温度范围内生成CP-甲烷水合物;CP-甲烷水合物相平衡压力随温度增大而升高;随着NaCl浓度的增大,相平衡压力线性升高,且温度越高,温度和NaCl浓度对相平衡压力的影响越大。CP-甲烷水合物的生成/分解热随着温度的升高而逐渐减小,随NaCl浓度的增加而减小。     

Electrochemical studies of pyrite oxidation and reduction using freshly-fractured electrodes and rotating ring-disc electrodes

Oxidation and reduction processes on coal- and mineral-pyrite surfaces have been investigated to better understand the reactions that control the hydrophobicity and flotation behavior of pyrite. The incipient oxidation and reduction reactions were studied using fresh surfaces of pyrite that were created by in situ fracturing electrodes potentiostated at a predetermined potential. Chronoamperometry immediately after fracture and subsequent cyclic voltammetry have established that fresh fracture surfaces of pyrite instantaneously assume a unique potential (referred to as the “stable” potential) at which neither oxidation nor reduction takes place. For Peruvian and Chinese pyrites, the stable potential is −0.28 V (standard hydrogen electrode, SHE) at pH 9.2 and 0 V at pH 4.6. The initial oxidation of pyrite begins at potentials slightly positive of the stable potential and is believed to produce a hydrophobic sulfur-rich species, most likely a polysulfide or metal-deficient sulfide. A rotating ring-disc electrode (RRDE) was employed to study the kinetics and mechanisms of surface reactions on pyrite over moderate potential ranges. Two distinct soluble reduction products (ferrous hydroxide and HS⁻) and one distinct soluble oxidation product (ferrous hydroxide) were observed on pyrite in alkaline solutions. It is concluded that the initial oxidation of pyrite and the oxidation of ferrous to ferric hydroxide occur in a similar potential range. When the electrode is oxidized, e.g. by polishing, prior to experiments, the initial oxidation of pyrite is masked by the oxidation of ferrous hydroxide, making it difficult to study the oxidation of pyrite itself.     

Electrochemical impedance studies of sol-gel based ceramic coatings systems in 3.5% NaCl solution

Ceramic coatings based on salts like vanadia, ceria, silica and molybdate prepared by sol-gel route are proposed as alternatives to the process involving toxic hexavalent chromate. The surface of the specimens were modified under different conditions and then dipped in a corresponding salt solution prepared via sol-gel method. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which such treatments can provide good corrosion protection to the aluminum substrate were determined. The surface morphologies of the treated samples were investigated using SEM and EDS. Optical microscope was also used to investigate the occurrence of pitting corrosion. The surface preparation prior to sol-gel treatment was found to have a marked effect on the corrosion protection of AA6061 T6.     

活性炭纤维电极法降解水中有机物的研究

电化学氧化作为处理废水中的有机物 ,尤其是生物难降解有机物的方法之一 ,具有广泛的应用前景。采用一种新型电极———活性炭纤维电极 ,在低的电流密度 (<10mA/cm2 )和低的电解质浓度 (0 .0 7mol/LNa2 SO4)下 ,实现了对水杨酸水溶液的在线降解。同时还研究了电流密度、传质、电解质种类和浓度等因素对电解过程的影响 ,并对氧化机理进行了初步的讨论     

Electrochemical polymerization of aniline on carbon fibers in aqueous toluene sulfonate solution

Polyaniline has been successfully formed by aqueous electrochemical polymerization on carbon fibers. The coatings were formed under potentiostatic conditions with toluene‐4‐sulphonic acid sodium salt as the electrolyte. The effect of monomer concentration, electrolyte concentration, and the applied potential on the rate of polymerization were studied. The amount of polyaniline coatings formed on carbon fibers increased with increased aniline and electrolyte concentration. Increasing the applied potential also increased the weight of coatings formed on the fibers. The presence of positive y‐intercept in the weight gain plots are attributed to the adsorption of the electrolyte on the fibers before electropolymerization. The effect of the electrochemical parameters on the degradation of the polymer has been analyzed using infrared spectroscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1503–1509, 2000     

催化还原技术处理水溶液中氯代有机物的实验研究

以四氯化碳和四氯乙烷为代表物,研究了水溶液中氯代烷烃的催化还原脱氯技术,使用的还原剂为废铁刨花并添加催化剂和极化材料．结果表明该方法能使氯代有机物在零价铁体系中有效地发生还原反应,能迅速脱氯为氯离子,降低氯代有机物的毒性。探讨了有机物浓度对反应速率的影响,并分析了还原脱氯速率和反应中间产物,四氯化碳的反应产物主要是二氯甲烷,而1,1,2,2-四氯乙烷的主要反应产物是二氯乙烯。氯代有机物直接得到电子而发生还原脱氯是其主要反应机理。     

Electrochemical reforming of an acidic aqueous glycerol solution on Pt electrodes

The feasibility of the electrochemical conversion of glycerol to alternative, more valuable compounds was evaluated with platinum electrode under galvanostatic conditions. The results indicated a potentially good feasibility of reforming glycerol by electrolysis, particularly under strong acidic conditions (pH 1). Indeed, under controlled conditions at pH 1, various commercially valuable compounds, such as propanediol, glycidol, and 2-propenol, amongst others, were produced. The mechanism for the generation of the key compounds is proposed.     

Production of pyrrhotites by pyrite reduction

Research in coal conversion, aimed at gaining an understanding of the catalytic and magnetic properties of iron sulphides found in coal, could benefit from studying well-defined materials. A method is given for the production of pyrrhotites of known stoichiometry by the reduction of pyrite. Theoretical calculations are provided for this reduction by H₂ and CO. Experimental results, confirmed by X-ray analysis, are given for the H₂ reduction of pyrite to form three different pyrrhotites in the temperature range 400–500 °C.