Recent trends on the catalytic activation of peroxymonosulfate for the abatement of organic dyes in waters

Peroxymonosulfate (HSO5−, PMS) is a well-known oxidant for water treatment. It needs to be activated to form strong oxidizing agents of organic pollutants like sulfate radical (SO4●−), hydroxyl radical (●OH), superoxide ion radical (O2•−), and the non-radical singlet oxygen (1O2). Recently, the removal of synthetic organic dyes from waters by PMS upon homogeneous and heterogeneous catalysts has received a great research attention due to their high effectiveness and oxidation rate determined by simple treatments centered at bench scale in the laboratory. The present review summarizes and analyzes the recent trends of this topic over the period 2020-2023. Homogeneous catalysts with transition metal ions like iron ions and Cu2+, and heterogeneous catalysts with single or mixed transition metals such as Co, Cu, Fe, and Mn, MOFs, and carbonaceous and other materials, have been examined. The action of these catalysts has been detailed for the generation of oxidizing agents from PMS activation. Selected examples describe the discoloration rate of synthetic waters contaminated with organic dyes and the influence of the operating variables on process performance. The production of oxidants via radical and non-radical mechanisms of PMS reduction has been confirmed by specific scavengers and EPR analysis. In some cases, the effect of the aqueous matrix on the dye discoloration has been analyzed and the detection of its by-products has been described with proposal of pathways for the degradation/mineralization of dyes to better know their oxidation process. A final section proposes the future development of dyes remediation with catalytic activators of PMS.