Vacancy-strengthened Cu/Co composite oxides for efficient removal of methylene blue via peroxymonosulfate activation: Synergism of multiple Lewis acid sites

The development of suitable catalysts poses a challenge for the peroxymonosulfate (PMS) activation system used in decontamination process. Here we constructed a series of vacancy-strengthened Cu/Co composite oxides (CuCoO) composed of CuCo 2 O 4 and CuO containing multiple Lewis acid sites. The results demonstrate that the as-prepared CuCoO-2 exhibited exceptional activation performance, broad-ranging degradation capacity, remarkable reusability and stability. The optimized CuCoO-2+PMS system achieved complete removal of methylene blue (MB) in 40 min, while maintaining a degradation efficiency of above 86 % even after 5 cycles. A comprehensive survey revealed that hydroxyl radical (·OH), sulfate radical (SO 4 .- ) and singlet oxygen ( 1 O 2 ) collectively contribute to the degradation of MB in the CuCoO-2+PMS system. Especially, 1 O 2 was the dominant active species. The synergism of various Lewis acid sites (Cu +/2+ , Co 2+/3+ and V O/N ) as unsaturated surface-bound centers played a pivotal role in promoting non-radical-driven activation of PMS. Meanwhile, the generated V O/N facilitated enhanced metallic valence circulation in CuCoO-2, strengthening electron mediation between PMS and MB. Additionally, possible degradation pathways and toxicity evaluations of MB and its intermediates were proposed. In conclusion, this work offers valuable insights into PMS activation by vacancy-strengthened CuCoO and is of great significance for water purification.