Generation and engineering applications of sulfate radicals in environmental remediation.

Sulfate radical (SO ₄ ^•- )-based advanced oxidation processes (AOPs) have become promising alternatives in environmental remediation due to the higher redox potential (2.6-3.1 V) and longer half-life period (30-40 μs) of sulfate radicals compared with many other radicals such as hydroxyl radicals (•OH). The generation and mechanisms of SO ₄ ^•- and the applications of SO ₄ ^•- -AOPs have been examined extensively, while those using sulfite as activation precursor and their comparisons among various activation precursors have rarely reviewed comprehensively. In this article, the latest progresses in SO ₄ ^•- -AOPs were comprehensively reviewed and commented on. First of all, the generation of SO ₄ ^•- was summarized via the two activation methods using various oxidant precursors, and the generation mechanisms were also presented, which provides a reference for guiding researchers to better select two precursors. Secondly, the reaction mechanisms of SO ₄ ^•- were reviewed for organic pollutant degradation, and the reactivity was systematically compared between SO ₄ ^•- and •OH. Thirdly, methods for SO ₄ ^•- detection were reviewed which include quantitative and qualitative ones, over which current controversies were discussed. Fourthly, the applications of SO ₄ ^•- -AOPs in various environmental remediation were summarized, and the advantages, challenges, and prospects were also commented. At last, future research needs for SO ₄ ^•- -AOPs were also proposed consequently. This review could lead to better understanding and applications of SO ₄ ^•- -AOPs in environmental remediations.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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