The role of nitrogen and sulfur doping in the peroxymonosulfate activation of cobalt-immobilized Polygonatum kingianum dregs biochar

Abstract

Biomass wastes from agriculture are very important sources to fabricate high-value materials for water purification. Herein, we encapsulated cobalt inside Polygonatum kingianum (PK) dregs biochar with no doping and the doping of N, S, and N-S to investigate the roles of Co/N/S in promoting the catalytic activity on activating peroxymonosulfate (PMS) to degrade emerging pollutant. Cobalt nanoparticles were evenly wrapped in the carbon matrix by N doping, leading to no apparent cobalt nanoparticles in Co@BC-N and presenting a poorer activity. Additionally, Co was converted to Co₉S₈ (Co@BC-S) and Co₄S₃ (Co@BC-N,S) by S doping and N-S co-doping, respectively. Particularly, both the experiments and DFT calculations revealed an outstanding synergistic effect between Co₄S₃ and the N-S co-modified carbon matrix, which significantly raised the adsorption of PMS and activated it into non-radical (¹O₂ and electron transfer) and radical pathways (SO₄^•−, •OH, and O₂^•−). The Co@BC-N,S/PMS system completely degraded carbamazepine (CBZ) within 20 min, with an apparent rate constant (k_app) of 2.7, 16.0, and 19.6 times higher than that of Co@BC-S, Co@BC, and Co@BC-N, respectively. Furthermore, this system exhibited good tolerance to environmental matrix, great effectiveness in actual water body, and high degradation efficiency of CBZ in five cycles. Overall, this work not only bridged the knowledge gap of the connections between structural properties of the modified Co@BC hybrid and catalytic performance, but also introduced a new view for utilization of PK dregs in catalytic decontamination.