自识别疏水性分子筛负载纳米Fe/Pd催化剂对环境水体中三氯生的同步吸附与催化还原降解机理研究

Triclosan [5-chloro-2-(2,4-dichlorophenoxy)-phenol](TCS), along with its widely used in human activities, is among one of the most frequently detected pharmaceuticals and personal care products (PPCPs) in waters and sediments, which is found to accumulate in environment and have potential ecological risk continuously. Owing to the hydrophobic character of TCS and the electronegative chlorines in its structure, it may provide a potential application of simultaneous adsorption and catalytic reduction method for TCS removal, however, the relative study is still missing. Therefore, we want to take the advantage of both adsorption method and catalytic reductive dechlorination approach, by using the TCS-identified hydrophobic mesoporous material which is modified with nano-sized zero valent Fe or Fe/Pd, to realize the simultaneous adsorption and catalytic reductive degradation of TCS. In this project, the influence factors on the adsorption and catalytic reduction processes will be carefully discussed and identified, the interface behaviors of TCS adsorption onto the new synthesized catalytic materials are going to be demonstrated, and the dechlorination route of TCS over the catalytic materials is to be indicated, so as to fully understand the mechanisms of simultaneous adsorption and catalytic reductive dechlorination of TCS over the new prepared composites. In conclusion, we hope it not only provide a potential application method for the TCS pollution control, and provide theoretical and technical supports for the simultaneous adsorption and catalytic reduction of TCS method, but also it can provide a guide for other compounds of pharmaceuticals and personal care products through this research.

三氯生（TCS）是一种在人类生产生活中大量使用、在环境中持续积累并具有潜在生态风险、在各类水体及沉积物中极易监测到的典型药品和个人护理品（PCPPs）类物质。针对TCS具有疏水性和带有电负性氯原子的特点，当前研究中还缺少对该类污染物的吸附与催化还原去除的协同机制研究。本研究拟耦合吸附与催化还原技术，采用基于TCS识别的疏水性介孔材料作为吸附剂，在其上负载纳米零价铁或铁/钯催化剂，以期实现对TCS的同步吸附与还原降解。拟通过探讨各影响因素对TCS吸附去除、还原降解过程的影响规律，阐明TCS在新型材料表面的界面吸附行为，揭示其在催化剂表面的还原脱氯机理，从而全面揭示TCS在新型复合材料表面的同步吸附与催化还原降解机制。总之，希望通过本研究不但能够为TCS的污染控制提供可应用的新方法，为TCS的同步吸附和还原降解提供理论依据和技术支撑，还能够为环境中其它PCPPs类物质的污染控制提供借鉴和指导。

三氯生，氯硝基苯、对氯苯酚等有机氯化物是环境中最常见、毒性最高、受关注度最多的一类持久性有机污染物，广泛存在于各类环境介质中。吸附、还原脱氯是对这类物质最常用的处理方法。采用常温一步法合成了疏水性介孔相MCM-41-dry。通过XRD、FT-IR、TG、N2吸附-脱附以及疏水性分析，结果表明MCM-41-dry具有稳定的介孔相结构且表面疏水。静态吸附实验表明，MCM-41-dry对TCS能实现快速吸附，吸附容量高达241.55 mg/g。溶液pH升高和共存阴离子都会降低TCS吸附容量。吸附过程符合准二级动力学模型。等温吸附曲线符合Freundlich方程。热力学计算表明吸附为自发放热过程且使体系的混乱度减小。MCM-41-dry对TCS的吸附机理主要为分配作用，且同时存在疏水作用和静电作用。采用液相还原法分别制备了纳米零价铁、纳米Fe/Ni和纳米Pd/Fe双金属复合颗粒。通过材料表征发现，纳米颗粒呈球形，粒径分布在40~100 nm间，Ni/Pd催化剂经还原后均匀的沉积在纳米零价铁颗粒表面。催化还原实验表明，催化剂的最佳投加量为1.0 g/L，Ni/Pd负载率最佳为1.0 wt%，2 h内可实现完全脱氯反应，反应过程符合一级反应动力学；氯代甲烷类物质还原脱氯活性为：四氯化碳 > 氯仿 > 二氯甲烷，这与三种物质C-Cl键断裂能的顺序刚好相反；脱氯机理遵循顺序还原脱氯加氢过程。研究还考察了纳米零价铁及纳米双金属颗粒对邻、间、对三种氯代硝基苯的还原加氢过程，结果显示：纳米零价铁可实现氯硝基苯向氯苯胺的迅速转化（选择率达100%），但不能发生脱氯反应；负载Pd或Ni催化剂后，可实现对氯硝基苯的完全脱氯反应，且Pd的催化活性大于Ni；氯代硝基苯的反应活性遵循：p-CNB > o-CNB > m-CNB，且与有机氯化物分子结构相关的量子化学参数，如HOMO、LUMO、BDE、E2等可作为指示剂揭示并预测有机氯化物的还原脱氯活性及机理。本项目所取得的成果可为环境中三氯生等有机氯化物的有效去除提供理论及技术支撑，并且可为其他有机氯化物的还原脱氯活性及机理研究提供新的参考。