零价铁双金属催化剂活化过氧单硫酸盐降解水中污染物的机理研究

Some persistent micro-pollutants are hardly removed by conventional water-treatment process. And oxidation by-product bromate might be produced in bromide-containing water when oxidants with high redox potential are used as pre- or post- oxidants, such as ozone，persulfate, and peroxymonosulfate (PMS). Hence, zero-valent iron based bimetallic catalyst (MFe0) is introduced to activate PMS in order to enhance the removal of organics and eliminate the production of bromate. First, several MFe0 will be screened based on the low content of additive metal and high efficiency to activate PMS. And active species, responsible for organics degradation in the MFe0/PMS system, will be identified by different efficiencies of various probes, different decontamination efficiencies under changed gas conditions, as well as the scavenging effect of different alcohols. Second, parameters of water quality and operation will be varied to investigate their influences on the decontamination efficiency. Then, the mechanisms of the interaction between MFe0 and PMS will be analyzed based on the changes of crystalline nature and valence of catalyst during the experiments with former experimental results. Finally, the production and elimination of bromate will be discussed when MFe0/PMS is used to treat bromide-containing water. This project aims to provide theoretical basis for the synthesis of MFe0 with low toxicity, high catalytic efficiency, and convenience to be separated from water, and further to guide the application of MFe0/PMS.

水体中的难降解微污染物很难通过常规水处理工艺去除，而采用基于强氧化剂如臭氧、过硫酸盐、过氧单硫酸盐(PMS)的相关工艺进行深度处理时，有可能导致氧化副产物溴酸盐的生成。本研究拟采用强还原性的零价铁双金属催化剂 (MFe0)活化PMS，去除水中难降解有机物，同时控制溴酸盐的生成。首先，筛选出高效、添加金属投量低的MFe0。结合目标物竞争实验、醇类抑制实验及不同气体条件的对比实验，鉴定MFe0/PMS降解污染物的主要活性物种。其次，研究不同水质参数和操作条件对MFe0/PMS除污染效果的影响，分析不同水质条件下活性物种的转化机制。再者，结合MFe0反应前后的晶体结构和元素价态的变化，探讨MFe0/PMS产生活性物种的机制。最后，研究MFe0/PMS体系处理含溴离子水体时，溴酸盐的产生/控制机理。本研究旨在为合成低毒、高效、易于分离的催化剂提供理论基础，并为MFe0/PMS的应用提供理论依据。

本项目研究了负载不同金属的零价铁双金属催化剂活化过氧单硫酸盐的效果。选取零价铜铁双金属催化剂作为研究对象，研究了过氧单硫酸盐和催化剂投量及水质参数对污染物去除效率的影响，探讨了零价铜铁双金属催化剂活化过氧单硫酸盐降解污染物的机理。研究结果表明，在催化剂投量为0-0.1g/L，过氧单硫酸盐投量为0-2.5mM时，污染物的去除效率随着过氧单硫酸盐和催化剂投量的增加而增加。水质参数对均相过氧单硫酸盐的影响结果表明，磷酸盐和硝酸盐由于对羟基自由基和硫酸根自由基的捕获作用而导致的对污染物的去除的影响可以忽略。氯离子的存在可以使得体系中的硫酸根自由基转化为羟基自由基、氯自由基和二氯自由基而影响污染物的去除。天然有机物与硫酸根自由基和羟基自由基的反应速率常数计算为(2.31±0.06)×103(mg C·L-1)-1·s-1和(1.14±0.1)×104(mg C·L-1)-1·s-1，其对两种自由基的捕获作用明显。水质参数对非均相体系的影响结果表明，氯离子和硝酸盐对污染物的去除有一定的抑制作用，而天然有机物和磷酸盐能够明显的抑制污染物的去除，pH值的增加会降低污染物的去除效率。当有溴离子或氯离子存在时，体系中没有检测到溴酸盐或氯酸盐的生成。推测零价铁双金属催化剂活化过氧单硫酸盐的机理为双金属中的零价铁在H+和PMS的作用下，发生腐蚀，释放Fe2+。Fe2+与PMS反应产生羟基自由基和硫酸根自由基。双金属中的铜起到原电池的阳极作用，加速了零价铁的腐蚀。产生的Fe3+在零价铁和PMS的作用下，又可以生成Fe2+，使得部分铁离子可以循环使用。