混合淋洗结合石墨烯-TiO2复合催化剂光催化修复憎水性芳香族有机物污染土壤研究

Based on the advantage of mild reaction condition, high mineralization efficiency and the need of no extra oxidant, the soil washing - photocatalysis technology for soil remediation of persistant organic pollution has become a technic of global concern. However, the competitive effect of surfactant for active catalytic sites as well as the recombination of photo generated electron and hole of TiO2 had been the bottleneck for the application of this technology. In this study, we developed the combined soil washing and graphene-TiO2 photocatalysis technology for soil remediation, where the stable mixed micelle with lower critical micellization concentration and higher washing efficiency for pollutants can be formed through mixed surfactant washing process. Taking advantage of the formation of bilayer mixed admicelle structure and the specific adsorption effect of graphene toward aromatic organic compounds, the adsorption of pollutants on catalyst surface can be greatly enhanced, so as to improve the degradation of pollutants, hence, the synergistic effect of surfactant soil washing and photocatalysis can be acquired. With the high electric conductivity of graphene, the seperation of photo generated electron-hole can be significantly enhanced on the surface of the well-distributed graphene-TiO2 catalyst, and the coating of such catalyst on porous glass-ceramic plate should highly improve catalytic efficiency. With the research into affecting mechanism of the complex components in soil washing eluent on photocatalysis and its optimization, the application of washing combined photocatalysis technic on real polluted sites can be proposed. This study gives more light to the effective remediation of organic polluted soil under mild condition.

淋洗结合光催化是绿色土壤修复方法，因其反应条件温和、矿化率高、无需氧化助剂而成为持久性有机污染土壤修复的前沿。淋洗液中表面活性剂竞争催化剂活性位点和TiO2光催化剂光生电子与空穴易复合致使其活性低是该方法的瓶颈。本研究提出混合淋洗协同石墨烯-TiO2光催化土壤修复技术，通过混合离子型表面活性剂淋洗控制，形成低临界胶束浓度的稳定混合胶束，有效洗脱污染物；利用其形成的双层混合胶束结构和石墨烯对芳香族有机物的专性吸附特性，捕集污染物附着于催化剂表面，提高催化剂对污染物的降解性，实现淋洗与光催化的协同增效。通过均匀负载石墨烯-TiO2复合光催化剂制备和在多孔玻璃-陶瓷板的负载固定，利用石墨烯的高导电性高效分离空穴-电子对，大幅提高其催化活性；通过揭示土壤淋洗液复杂成分的光催化效应并实施优化控制，推动淋洗-光催化土壤修复向实用化迈进。本研究将为温和条件下高效修复憎水性有机污染土壤开辟新途径。

针对土壤淋洗技术与光催化反应技术结合过程目标污染物光降解速率下降的问题，对多种有机溶剂和表面活性剂分子化学键键能进行研究，发现酮类溶剂或TX-100等分子化学键能较高的稳定型淋洗液体系适合光催化处理，而对分子化学键能较低的醇类溶剂或生物表面活性剂淋洗液光催化处理会造成目标污染物降解速率的下降。pH值、温度和光照强度与光降解反应效率正相关，氯代芳香族有机物在光降解时脱氯和裂环速率高于矿化速率。另外对于不适合使用光催化剂进行处理的淋洗液体系提出了二氧化钛配合过氧化氢的应急光催化处理方案，其反应机理为光催化分解过氧化氢产生大量羟基自由基从而对目标污染物进行降解。.以氧化石墨烯和粉末二氧化钛为前驱物，使用水热法合成了均匀分布G-TNT光催化剂，纳米管外径10 nm，内径3 nm左右，比表面积达到128.8 m2 g–1，有效入射波长由387 nm红移至430 nm。石墨烯与二氧化钛纳米管结合，石墨烯碳元素进入二氧化钛晶格使其带隙降低，光生电子可以快速转移至石墨烯表面与空穴分离，同时石墨烯与氯代芳香族有机物产生π–π键专性吸附。使用G-TNT对淋洗液体系五氯酚、多氯联苯和八氯萘等典型氯代芳香族有机污染物进行光催化降解，利用紫外光或太阳光作为光源时，光催化剂催化活性分别为单纯二氧化钛的2.0倍和2.6倍，同时淋洗液降解速率只有目标污染物的1/15，可回用淋洗剂达75%。.本文利用类溶胶凝胶涂布法成功制备了可重复使用的G-TNT复合板，并使用于实际淋洗液光催化处理。以太阳光为光源，G-TNT复合板将淋洗液体系氯代芳香族有机物光催化降解速率提高了5倍以上，连续使用时复合板光催化活性无明显降低，为纳米级光催化剂的实用提供了新的方法。