电流密度对BDD电极电化学矿化吲哚的影响与机制

掺硼金刚石膜(BDD)电极电化学氧化法是去除难降解有机污染物的有效手段.与总有机碳(TOC)等的测定相比,气态中间产物的逸出量能够更直观有效地反映有机物的矿化程度与去除效果.本研究以吲哚为代表性污染物,通过对比不同电流密度(10、20和30 m A·cm-2)下BDD电极对吲哚的去除率与矿化率,结合降解过程中碳和氮形态的变化与守恒情况,分析吲哚的降解机制.结果表明,BDD电极对吲哚有良好的去除效果,电流密度为10、20、30 m A·cm-2时,吲哚达到100%去除的时间分别为8、5和4 h;TOC去除率、CO_2产生量均随电流密度的增加而增大,证明矿化率与电流密度成正相关;电解产生的CO_2气体与TOC、无机碳(TIC)构成了碳守恒体系.4~5 h时,体系TOC、TON和CO_2产生量均没有变化,表明电解产生的靛红具有较高的稳定性,此时为中间产物积累阶段;XPS表征进一步证实了中间产物靛红、苯醌等在电极表面的吸附,随着电解时间的延长,这些吸附的中间产物可进一步被降解.本研究从气态产物检测及碳氮形态分析与守恒的角度阐释吲哚矿化过程,对于辅助揭示有机物的电解过程有重要意义.

Influence of Current Densities on Mineralization of Indole by BDD Electrode

Electrochemical oxidation by boron-doped diamond (BDD) electrode is an effective method of degrading refractory organics. Compared with TOC detection, the amount of gas escape can more effectively and intuitively reflect the mineralization and the removal extent. In this study, indole is chosen as a typical pollutant and the detection of its removal rate was compared at current densities of 10, 20, and 30 mA·cm^-2. Meanwhile, the degradation mechanism was analyzed based on the changes in the carbon and nitrogen forms and conservation status. As a result, BDD electrodes displayed a higher removal efficiency to indole, which can completely be removed after 8 h, 5 h, and 4 h with current densities of 10, 20 and 30 mA·cm^-2, respectively. Changes in TOC removal and CO₂ generation were both increased with increasing the current densities, suggesting that the mineralization extent was in accordance with current densities. Furthermore, the escaped CO₂, combined with TOC and TIC constituted a conservative carbon system. The byproduct isatin was stable and accumulated at 4-5 h, as TOC, TON, and CO₂ generation was unchanged at this stage. Finally, the XPS analysis suggested the adsorption by-products such as isatin and benzoquinone on the BDD surface, which can further be removed by increasing the electrolysis time. This study demonstrated the mineralization process of indole based on the escaped gas detection and the changes in the carbon and nitrogen forms, which will increase the understanding of the electrolysis process.