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

Abstract

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.