Abstract:

Organic pesticides such as triazolone (TDF) have environmental risks in the production and application processes, which are difficult to effectively remove by the conventional water treatment methods. The electrochemical oxidation processes have great potential to organic pesticides removal from water and wastewater, the performances of which is greatly dependent on the activity and stability of the anode materials. This study investigated the electrochemical oxidation of TDF in water over the Ti/RuO₂-IrO₂, Pt, and Ti₄O₇ anodes. The degradation and mineralization efficiencies of TDF were compared and evaluated in the electro-oxidation processes within these anodes. The effects of various reaction, including the current density, the TDF initial concentration and the initial solution pH, on the degradation kinetics of TDF were investigated. The degradation pathway of TDF electro-oxidation and the toxicities of TDF degradation intermediates were also explored. The Ti/Ti₄O₇ flat anode presented relatively high removal efficiencies of TDF and total organic carbon (TOC) in water compared with the Ti/RuO₂-IrO₂ and Pt anodes. The Ti₄O₇ flat and membrane anodes both showed relatively high electrochemical activity for TDF degradation and mineralization, the TDF and TOC removal efficiencies of which reached 94.5%-95.7% and 72.5%-75.5%, respectively. Achieving similar TOC removal efficiencies, the energy consumption of the Ti₄O₇ membrane anode was about 50% lower than that of the Ti₄O₇ plate anode. The TDF removal efficiencies was related to the reaction parameters including the current density, the initial TDF concentration, and the initial solution pH, which increased with the current density increasing, and decreased with the increase of the initial solution pH and the initial TDF concentration. The TDF (m/z=294.5) was gradually degraded into intermediates A (m/z=224.5) and B (m/z=103), and intermediate A (m/z=224.5) was further degraded into intermediates C (m/z=173.5) and D (m/z=86). These intermediates might be finally oxidized to inorganic compounds such as carbon dioxide and water. The TDF, A, B, C, and D were classified as toxic, harmless, harmless, harmful, and harmless compounds to aquatic organisms, respectively. The toxic TDF gradually degraded into non-toxic intermediates, which might lead to the decrease of solution toxicity. Based on the study, TDF could be efficiently degraded and mineralized by the electrochemical oxidation technology over the Ti₄O₇ anodes, providing reference ideas for the researches and practices on the electrochemical oxidation of organic pesticides in water and wastewater.

Key words: triazolone electro-oxidation, Ti/RuO₂-IrO₂ flat anode, Pt flat anode, Ti₄O₇ anode, membrane anode, energy consumption, degradation pathway, toxicity

摘要：

三唑酮（TDF）等有机农药在生产和使用中存在环境风险，其难以被常规水处理工艺有效去除。电化学氧化技术应用于水中有机农药去除极具潜力，有机农药降解效率与电化学阳极材料性能有关。以Ti/RuO₂-IrO₂、Pt、Ti₄O₇电极为电化学阳极，开展电化学氧化技术降解和矿化水中TDF研究，比较和评估了不同类型阳极电化学降解TDF和溶液中TOC的效率；考察了电流密度、TDF初始浓度、溶液初始pH等反应参数对TDF电化学降解效率的影响；探究了TDF电化学降解路径及其降解产物毒性对溶液毒性的影响。结果表明：与Ti/RuO₂-IrO₂和Pt平板阳极相比，Ti/Ti₄O₇平板阳极对水中TDF和溶液总有机碳（TOC）去除效果较好；Ti₄O₇平板和膜阳极均对水中TDF的降解和矿化具有较高活性，TDF电化学降解效率和溶液TOC去除率可达94.5%－95.7%和72.5%－75.5%，达到相同TOC去除率时Ti₄O₇膜阳极较其平板阳极反应能耗低低50%左右；水中TDF电化学降解效率与电流密度、TDF初始浓度、溶液初始pH值等反应参数有关，TDF电化学降解效率随电流密度增大而增大、随TDF初始浓度和溶液初始pH的增大而减少；水中TDF（m/z=294.5）电化学降解生成A（m/z=224.5）和B（m/z=103），A（m/z=224.5）继续氧化生成了C（m/z=173.5）和D（m/z=86），这些中间产物可进一步氧化为二氧化碳、水等无机物；TDF、A、B、C和D对水生生物分别呈有毒性、无害性、无害性、有害性和无害性，有毒性的TDF逐渐降解为无毒性的降解副产物，可能是造成TDF溶液毒性随着反应时间逐渐下降的原因。该研究表明TDF可被Ti₄O₇阳极电化学氧化技术高效降解和矿化，为电化学氧化技术去除水中TDF等有机农药的研究与实践提供思路借鉴。

关键词: 三唑酮电化学氧化, Ti/RuO₂-IrO₂平板阳极, Pt平板阳极, Ti₄O₇阳极, 膜阳极, 反应能耗, 降解路径, 毒性