Degradation of Organic Contaminants by Reactive Iron/Manganese Species: Progress and Challenges

Many iron(II, III, VI)-and manganese(II, IV, VII)-based oxidation processes can generate reactive iron/manga-nese species (RFeS/RMnS, i.e., Fe(IV)/Fe(V) and Mn(III)/Mn(V)/Mn(VI)), which have mild and selective reac-tivity toward a wide range of organic contaminants, and thus have drawn significant attention. The reaction mechanisms of these processes are rather complicated due to the simultaneous involvement of multiple radical and/or nonradical species. As a result, the ambiguity in the occurrence of RFeS/RMnS and divergence in the degradation mechanisms of trace organic contaminants in the presence of RFeS/RMnS exist in literature. In order to improve the critical understanding of the RFeS/RMnS-mediated oxidation processes, the detection methods of RFeS/RMnS and their roles in the destruction of trace organic contaminants are reviewed with special attention to some specific problems related to the scavenger and probe selection and experimental results analysis potentially resulting in some questionable conclusions. Moreover, the influence of background constituents, such as organic matter and halides, on oxidation efficiency of RFeS/RMnS-mediated oxidation processes and for-mation of byproducts are discussed through their comparison with those in free radicals-dominated oxidation processes. Finally, the prospects of the RFeS/RMnS-mediated oxidation processes and the challenges for future applications are presented.

Automated summary

Many iron and manganese-based oxidation processes can generate reactive iron/manganese species with selective reactivity towards organic contaminants. However, the reaction mechanisms and occurrence of these species are complicated due to the involvement of multiple radical and nonradical species. This review focuses on the detection methods and roles of these species in the degradation of organic contaminants, as well as the influence of background constituents on the efficiency and byproduct formation of these oxidation processes. The prospects and challenges for future applications are also discussed.