Coal gangue-based catalyst activates peroxymonosulfate for efficient degradation of organic pollutants in wastewater

Coal gangue (CG), long treated as a low-cost support in peroxymonosulfate (PMS)-based advanced oxidation, deserves a more demanding reappraisal. The evidence assembled in this review suggests that, once properly reconstructed, CG is not merely a scaffold for externally introduced active species but can itself become part of the reactive interface that drives pollutant degradation. Starting from the mineralogical and environmental background of CG, this review follows a single mechanistic thread: how thermal, mechanical, chemical, and composite pretreatments reshape its mineral phases, defect structure, surface hydroxyls, and electronic microenvironment, and how these changes govern PMS activation and oxidation behavior. Particular attention is paid to the degradation of representative pollutants, where tetracycline and phenolic compounds serve not simply as model substrates but as functional probes for testing catalytic selectivity and pathway evolution. Across reported systems, CG/PMS catalysis is shown to involve a dynamic interplay among free-radical oxidation, non-radical processes, and interfacial electron transfer, with pollutant structure, water chemistry, and catalyst reconstruction jointly determining the dominant route. More importantly, the review argues for a conceptual shift in catalyst design: the key task is no longer just to load more active components onto CG, but to identify the conditions under which CG itself expresses the strongest intrinsic oxidative potential—especially its contribution to hydroxyl-radical generation—and then match it with the most compatible active phase. This perspective opens a more distinctive path for CG-based catalyst development and sets a sharper agenda for future work on mechanistic discrimination, catalyst matching, and performance validation in real wastewater. The revised framework further clarifies that the intrinsic role of reconstructed CG must be evaluated through controlled comparisons of active sites, kinetic parameters, water-matrix effects, catalyst durability, and real-wastewater validation, rather than simply by removal efficiency alone.