Valorization of coal gangue into molecular sieve assisting Co₃O₄ in promoting Co2+/Co3+ cycle and oxygen vacancy generation for efficient peroxymonosulfate activation in water purification.

Spinel cobalt oxide (Co3O4) has the ability to activate peroxymonosulfate (PMS) for pollutant degradation, but agglomeration and poor active sites of pure Co3O4 limit its efficiency, even its mechanism is ambiguous. Herein, coal gangue (CG)-derived molecular sieve (CGMS) was prepared via an alkali fusion-hydrothermal method and the Co3O4/CGMS composite was fabricated by a simple calcination process. Co3O4/CGMS was utilized to activate PMS for methylene blue (MB) degradation. Under optimized conditions, 95.29% of MB was removed within 21 min in the Co3O4/CGMS-PMS system, outperforming the pristine Co3O4-PMS and CGMS-PMS systems. the catalyst also delivered excellent stability and reusability with MB removal efficiency over 90% after five cycles. Quenching experiments and EPR analysis indicated that 1O₂ played the dominant role in MB degradation with the assistance of •OH, SO₄•- and O₂•- during the oxidation process. More importantly, Co3O4/CGMS can also degrade Acid Orange G, Rhodamine B, and Methyl Orange, confirming its ability to purify water. Electrochemical tests and X-ray photoelectron spectroscopy (XPS) analysis confirm that Co3O4/CGMS with the promoted Co2+/Co3+ redox, and oxygen-vacancy generation. These synergistic structural and catalytic effects collectively endowed Co3O4/CGMS with exceptional capabilities for PMS activation to remove organic dyes. This work not only provides a feasible strategy for converting coal gangue into functional catalytic materials, but also offers insight into PMS activation over supported cobalt-based catalysts.