电化学还原-氧化工艺去除氯代有机污染物的Pd-Fe/石墨烯催化阴极制备及降解机制研究

It is well known that chlorinated organic pollutants are toxic due to the chlorine atom contained in their structure. However, advanced oxidation processes usually open aromatic rings of chlorinated compounds and then form some chlorinated aliphatic intermediates. The accumulation of chlorinated intermediates may be even more toxic than their parent compounds. In this research, the Pd-Fe/graphene gas-diffusion cathodes are prepared for chlorinated compounds wastewater treatment, which can not only reductively dechlorinate chlorinated compounds in aqueous medium by feeding hydrogen gas, but also accelerate the two-electron reduction of oxygen to hydrogen peroxide by feeding air. Furthermore, an effective and friendly method will be developed to treat contaminants of chloride compounds by using a combination process of reduction and oxidation. In the cathodic compartment, the chlorine atoms of chlorinated compounds are removed from the aromatic structure and chlorinated compounds are reduced to the non-chloride intermediates. Then, the degradation of the non-chloride intermediates could be attributed to the cooperatively oxidization processes including direct and/or indirect electrochemical oxidations at the anode and by hydrogen peroxide and free radicals produced by the reduction of oxygen at the cathode. It may be more worthwhile to degrade chlorinated organic pollutants to the biodegradable stage-aliphatic carboxylic acids which could then be economical treated by the biological process. In addition, the mechanism of Pd-Fe/graphene gas-diffusion cathodes is studied in the electrochemical reduction and oxidation processes. Electrochemical degradation behaviors of chlorinated compounds are systematically investigated by employing analytical techniques of LC-ESI-MS/MS, ESR and time-resolved Raman spectroscopy, to explore the mechanism of the simultaneous oxidation of anode and cathode.

针对在高级氧化工艺处理氯代有机污染物过程产生有高毒性含氯中间产物的问题，本研究将电化学还原-氧化耦合技术应用到难降解氯代有机污染物处理领域，以石墨烯作为载体可控合成Pd-Fe/石墨烯多功能催化剂，开发研制出在水溶液介质中既能高效产生H2O2又具有强还原脱氯作用的新型Pd-Fe/石墨烯气体扩散阴极，使氯代有机污染物在阴极还原作用下脱氯去毒，脱氯后的有机物通过阳极氧化和强氧化性阴极还原产物的共同作用下降解到有机酸阶段，有利于后续生物处理。这一结合充分发挥了还原、氧化的优势，既避免了脱氯去毒不完全的问题，又实现了氯代有机污染物完全矿化的最终目标。借助于LC-ESI-MS/MS、ESR、时间分辨拉曼光谱等现代分析技术，考察氯代有机物的电化学阴极还原脱氯及其脱氯后的氧化降解行为，从微观和宏观角度探索电化学还原-氧化工艺降解氯代有机物机理和动力学，为电化学处理技术的工业应用提供理论指导和技术支持。

为解决在高级氧化工艺处理氯代有机污染物过程中有高毒性含氯中间产物存在的问题，本研究将电化学还原-氧化耦合技术应用到难降解氯代有机污染物处理领域，以石墨烯作为载体来可控合成Pd-Fe/石墨烯多功能催化剂，开发研制出新型在水溶液介质中既能高效产生H2O2又具有强还原脱氯作用的Pd-Fe/石墨烯气体扩散阴极，使氯代有机污染物在阴极还原作用下脱氯去毒，脱氯后的有机物通过阳极氧化和阴极还原产物的氧化共同作用下处理有机酸阶段，有利于后续生物处理。这一结合充分发挥了还原、氧化的优势，既避免了脱氯去毒不完全的问题，又实现了氯代有机污染物完全矿化的最终目标。.采用改进的Hummer法制备的氧化石墨为载体，光还原法制备不同含量比例的金属/石墨烯催化剂，利用X射线衍射、扫描电镜、透射电镜、X光电子能谱和原子力显微镜进行分析表征，并采用电化学性能测试（循环伏安曲线、差分脉冲伏安曲线、电流-时间曲线）进行性能测试，优选出Pd0.5Fe0.5/石墨烯催化剂并制备出Pd-Fe/石墨烯多功能催化阴极。.在设计的双阴极单阳极的三电极体系下对4-氯酚进行降解。采用单因素法及响应面法中心组合设计，研究电解质浓度、电流密度、初始pH、反应时间等因素对降解效率的影响，得出在初始pH为7，电解质浓度为0.03 mol/L，电流密度为25 mA/cm2，通气方式采用前60 min通氢气后60 min通空气的条件下，降解效果最好。对降解反应进行一级反应动力学研究，得出总的电催化动力学方程。.在最佳降解条件下降解4-氯酚（100 mg/L），利用TOC测定仪、高效液相色谱和离子色谱对4-氯酚降解效果及中间产物进行测定。三电极体系阳极室、阴极室1和阴极室2中4-氯酚的降解率分别为94.0%，95.9%和95.4%。根据阴阳极室产生的中间产物推导动力学模型，实验数据点与模型达到较好的拟合。利用发光细菌法测定中间产物的毒性值，根据毒性值和浓度计算得到理论计算毒性，利用SPSS软件对2种毒性值进行相关性分析，相关性系数为1，表明2种毒性值显著相关。阳极室降解过程中毒性先升高后降低，阴极室毒性呈下降的趋势。.在最佳降解条件下利用三电极体系降解模拟造纸废水，对降解过程中4-氯酚的降解率、废水COD及毒性进行测定。三电极体系对模拟造纸废水中氯酚具有较强的降解作用和较好的脱毒效果。