水环境中ZVI/氧化剂体系及其电子迁移作用机制

ZVI/Oxidant Systems Applied in Water Environment and Their Electron Transfer Mechanisms

利用零价铁(Zero-Valent Iron,ZVI)去除水环境中的污染物成为近年来的研究热点。当O_2、H_2O_2等氧化剂存在时,ZVI、氧化剂与污染物之间的电子迁移机制非常复杂,ZVI和氧化剂之间的相互影响机制尚无定论。传统观点认为,O_2会促进ZVI钝化膜的形成并阻断电子传递从而降低ZVI的还原性能。然而O_2可在ZVI作用下通过双电子传输转化为H_2O_2,构成ZVI/O2类Fenton体系;在此基础上,利用额外加入H_2O_2、HSO_5^-、S_2O_8^(2-)等氧化剂,发展出了基于·OH或SO_4^(·-)的ZVI/氧化剂高级氧化体系(ZVI-AOPs),从而氧化降解有机污染物。有学者认为H_2O_2、KMnO_4、S_2O_8^(2-)等强氧化剂的加入反而可以加快ZVI腐蚀和失电子的速率,从而提高ZVI去除重金属等污染物的还原性能,该研究结论对钝化膜机制提出了挑战。ZVI与氧化剂的联合作用还可以实现同时还原去除重金属和氧化降解有机物,也可以对卤代有机物等抗氧化污染物实现先还原后氧化去除。本文综述了基于ZVI/氧化剂的高级氧化或还原体系及其电子迁移机制,同时对ZVI与氧化剂的联合作用体系作一总结,并就值得深入研究的问题进行了展望。

In recent years,the use of zero-valent iron（ZVI） for treatment of toxic contaminants in w ater system has been w idely investigated. In the presence of oxidant,such as oxygen（O2） or hydrogen peroxide（H2O2）,the electron transfer processes among ZVI,oxidants and contaminants are extremely complex,and the interaction mechanisms betw een ZVI and oxidants are still inconclusive. Generally speaking,O2 can promote the formation of iron oxide layer via corrosion of ZVI by w ater and oxygen,w hich may block the outw ard electron transfer and then decrease the reductive ability of ZVI. How ever,O2 could be activated via tw o-electron reduction pathw ay to produce H2O2,thereby forming ZVI/O2Fenton-like system. Based on this,the extra addition of H2O2,peroxymonosulfate（HSO-5） or persulfate（S2O82-） can react with ZVI and the generated Fe2＋and then producestrong oxidizing hydroxyl radicals（·OH） and sulfate radicals（SO4·-,which can efficiently degrade organic contaminants through advanced oxidation processes（ZVI-AOPs）. Otherw ise,some researchers recently propose another critical role of common oxidants in accelerating ZVI corrosion and then hence in facilitating the electron transfer rate and promoting the reductive performance of ZVI. The combination of ZVI and oxidants can not only show significant synergistic degradation betw een heavy metals and organic contaminants,but also achieve the degradation and mineralization of refractory pollutants through reduction through ZVI firstly and then oxidation through AOPs. This review summarizes the ZVI-AOPs system and ZVI-reduction system based on the interaction betw een ZVI and oxidants and their electron transfer processes,as w ell as makes a summary of the associative effect of ZVI and oxidants. At last,the prospects of the research areas meriting further investigation are pointed out.