Anaerobic environment-induced efficient degradation of chloroquine phosphate: Insights into the role of metal-free C₃N₄ nanotube in visible light-driven peroxymonosulfate activation

Catalytic efficiency is the main bottleneck in metal-free photocatalyst-mediated visible light-driven peroxymonosulfate (PMS) activation processes (PMS-Vis). In this study, a nanotubular carbon nitride (C₃N₄ NT) photocatalyst was prepared and applied to a PMS-Vis system to degrade chloroquine phosphate (CQP). The special structure and excellent photoelectrochemical properties of C₃N₄ NT optimized its active site exposure and charge transport performance, which in turn enabled its use as a photocatalyst for PMS activation and CQP degradation. Importantly, the anaerobic environment enhanced the degradation performance, and the degradation kinetic constant for the C₃N₄ NT/PMS-Vis-N₂ system reached 0.0898 min⁻¹ at a 0.2 g·L⁻¹ catalyst dosage and 0.8 mM PMS concentration. Mechanistic studies and theoretical calculations clarified that the anaerobic environment prevented the competitive adsorption and consumption behavior of dissolved O₂ and PMS on the photocatalyst surface, thus maximizing the transfer of surface photogenerated charges to PMS for PMS activation and active species generation. Thus, CQP was efficiently degraded, and its toxicity was reduced. The developed process demonstrated high catalyst utilization efficiency and overcame interference from real water matrices. This study provides a reference for improving the environmental applicability of metal-free photocatalysts and developing water treatment technologies for anaerobic environments.