A critical review on the mechanisms of persulfate activation by iron-based materials: Clarifying some ambiguity and controversies

[Display omitted] •The mechanisms of PS activation by common iron-based materials are discussed.•The electron transport pathways and activator evolution during PS activation are analyzed.•Some ambiguity and controversies remain in PS activation mechanisms.•Current knowledge gaps and future research prospects are identified. Iron-based materials, as a series of effective persulfate (PS) activators, have been utilized extensively in PS-based advanced oxidation processes. However, there are some ambiguity cognitions and controversies surrounding the PS activation mechanisms by iron-based materials. For instance, does Fe(III) act as an electron donor or an electron receptor in an Fe(III) activating PS system? Is PS activation by nanoscale zero-valent iron and microscale zero-valent iron dominated by heterogeneous or homogeneous activation? To clarify these theories and resolve controversies, this review firstly summarizes the mechanisms of PS activation by conventional iron-based materials, and then thoroughly analyses the pathways of electron transport and the evolution of the activator constituent in the PS activation process. Finally, current knowledge gaps and future research prospects are identified. This review significantly improves our understanding of the PS activation by iron-based materials and provides useful insights to researchers in this field.