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首页> 外文期刊>Environmental Science & Technology >Understanding Reduction of Carbon Tetrachloride at Nickel Surfaces
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Understanding Reduction of Carbon Tetrachloride at Nickel Surfaces

机译：了解镍表面四氯化碳的还原

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Nickel has been found to be an effective cathode material and catalyst for reductive destruction of chlorinated solvents in contaminated water. This study investigated reductive dechlorination of carbon tetrachloride (CT) at a nickel rotating disk electrode using chronoamperometry and electrochemical impedance spectroscopy. Chronoamperometry experiments were performed to determine rates of CT reduction as a function of the electrode potential, pH, CT concentration, and temperature. The reaction products of CT dechlorination were 95±4% methane and 4.1±2.5% chloroform. Only trace levels of methylene chloride and chloromethane were produced, indicating that sequential hydrogenolysis was not the predominant pathway for methane production. Electrochemical impedance spectroscopy showed that the rate-limiting step for methane production was the transfer of the first electron to a physically adsorbed CT molecule. The temperature independence of the electron transfer coefficient and the decreasing activation energy with decreasing electrode potential indicated that the rate-limiting step involved an outer-sphere electron transfer. At neutral pH values, oxides inactivated much of the electrode surface for both CT reduction and hydrogen evolution. At lower pH values, oxide dissolution served to increase the electroactive surface area of the disk electrode. Anson analysis and kinetic modeling showed that CT adsorption to electroactive sites was a nonlinear function of the CT concentration and was in equilibrium with the bulk solution. CT dechlorination rates on nickel electrodes were 16 times slower than those on iron electrodes under similar conditions. However, CT reactions at nickel surfaces produced predominantly methane as the first detectable product, while reduction at iron surfaces produced chloroform. These results suggest that, although nickel is not a catalyst for the rate-limiting step for CT dechlorination, it may serve a catalytic role in subsequent reaction steps.
机译：镍已被发现是一种有效的阴极材料和催化剂，用于还原性销毁被污染水中的氯化溶剂。这项研究使用计时安培法和电化学阻抗光谱法研究了镍旋转盘电极上四氯化碳（CT）的还原脱氯。进行了计时安培法实验，以确定CT降低率与电极电位，pH，CT浓度和温度的关系。 CT脱氯反应产物为95±4％甲烷和4.1±2.5％氯仿。仅产生痕量的二氯甲烷和氯甲烷，表明顺序的氢解不是甲烷产生的主要途径。电化学阻抗谱表明，甲烷生产的限速步骤是将第一个电子转移到物理吸附的CT分子上。电子转移系数的温度独立性以及随着电极电位的降低而降低的活化能表明限速步骤涉及外层电子转移。在中性pH值下，氧化物会钝化大部分电极表面，从而减少CT还原和析氢。在较低的pH值下，氧化物溶解有助于增加圆盘电极的电活性表面积。 Anson分析和动力学建模表明，CT吸附到电活性部位是CT浓度的非线性函数，并且与本体溶液处于平衡状态。在类似条件下，镍电极上的CT脱氯速率比铁电极上的CT脱氯速率慢16倍。但是，镍表面的CT反应主要产生甲烷，这是第一种可检测的产物，而铁表面的还原反应则产生氯仿。这些结果表明，尽管镍不是CT脱氯限速步骤的催化剂，但它可能在随后的反应步骤中起催化作用。

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