Insight into metal-based catalysts for heterogeneous peroxymonosulfate activation: A critical review

Heterogeneous activation of peroxymonosulfate (PMS) for producing radicals and/or non-radicals to eliminate refractory organic contaminants has received increasing attention by utilizing metal-based catalysts recently. To design a "smart" metal-based catalyst for environmental application, one must comprehend the up-to-date advances in material classification, preparation methods and activation mechanisms. In this review, various kinds of metal-based catalysts, including mono-metallic catalysts, perovskite, spinel, metal–organic frameworks (MOFs), and their composite or loaded materials, were interpreted based on crystal structures and surface properties. The activation mechanisms and fundamental behaviors of these catalysts in PMS activation are emphatically elucidated, in which contaminants can be degradation through radical (•OH, SO4•- and O2•-) and/or non-radical reaction pathways. The non-radical oxidation includes 1O2, surface-activated complexes, electron transfer processes and high-valent metal species. Besides, the effects of surface-activated reaction sites of catalysts, oxygen vacancies (Vo) concentration and initial pH on the activation of PMS by metal-based catalysts are discussed. In order to design superior catalysts to achieve better PMS activation for pollutants removal, perspectives for future research are given. This review conducts a critical and thorough overview and analysis of the mechanisms by metal-based catalysts for heterogeneous PMS activation by sorting through numerous state-of-the-art research papers.