Photoactivation of peroxymonosulfate by wood pulp cellulose biochar/g-C₃N₄ composite for diclofenac degradation: the radical and nonradical pathways

Highlights

•	Wood pulp cellulose biochar (WPBC) improved the catalytic performance of g-C3N4 via both radical and nonradical mechanisms.
•	The photoelectrical properties and PMS activation capability were improved by WPBC.
•	WPBC/g-C3N4 presented high stability for multiple runs.

Abstract

Metal-free photocatalysts have attracted growing concern recently. Herein, the composites combining g-C₃N₄ with wood pulp cellulose biochar (WPBC/g-C₃N₄) were synthesized to effectively activate peroxymonosulfate (PMS) under visible light for the degradation of diclofenac (DCF). The incorporation of WPBC endowed g-C₃N₄ with enhanced visible light absorption, improved charge separation capability, reduced electrical conductivity, and increased photocatalytic and PMS activation capability. Based on quenching tests, electron paramagnetic resonance (EPR), electrochemical analysis and solvent exchange experiments, both radical and nonradical mechanisms were proposed. Radical species including ·OH, h⁺, ·O₂^– were identified to contribute to DCF degradation. The ¹O₂ and electron transfer were the dominant nonradical pathways for DCF degradation. Moreover, the common influencing factors were examined, and DCF concentration was the most influential factor based on principal component analysis. Generally, the composites exhibited good reusability during consecutive runs. Based on HPLC/MS analysis, four intermediates were detected and the possible DCF degradation pathway was proposed. This work provided a potential strategy based on metal-free WPBC/g-C₃N₄ for the photocatalytic activation of PMS to effectively degrade emerging contaminants in wastewater.

Funding

China Postdoctoral Science Foundation(2019 M661856); Qing Lan Project of Jiangsu Province(2020); Natural Science Foundation of Jiangsu Province(BK20201385); National Key Research and Development Project(2017YFC0505803); National Natural Science Foundation of China(41977354)