Promoting charge migration of Co(OH)2/g-C3N4 by hydroxylation for improved PMS activation: Catalyst design, DFT calculation and mechanism analysis

Cobalt-based materials were considered as promising catalysts for peroxymonosulfate (PMS) activation, while few reactive sites and ion leaching limit its environmental application. Herein, Co(OH)2 nanosheets in-situ anchored hydroxylated hollow tubular g-C3N4 (Co/CNH) was successfully fabricated by a facile impregnation method, and used to activate PMS for enrofloxacin hydrochloride (ERF) degradation. Compared with neat Co(OH)2 and CNH, the optimum catalyst (10 %Co/CNH) exhibited higher ERF degradation efficiency for 95.6 % within 30 min. The enhanced performance was attributed to the synergistic effect between Co(OH)2 and CNH. CNH can not only provide numerous nucleation sites for Co(OH)2 to inhibit its agglomeration, but also provide abundant OH− for formation of the key PMS activation species CoOH+. Furthermore, DFT-based electron density difference elucidated that the sp3 hybridization introduced by OH− greatly facilitated charge transfer from 10 %Co/CNH to PMS. A series of characterization verified that 1O2 dominated the degradation of ERF (nonradical pathway), SO4•− and •OH (radical pathway) as well as electron transfer also contributed to this process. Fukui index (f−) and bond degree (BD) indicated that reactive oxygen species tend to attack atoms with higher f− and scavenge covalent bonds with larger BD in the process of ERF degradation.