Straightforward fabrication of lignin-derived carbon-bridged graphitic carbon nitride for improved visible photocatalysis of tetracycline hydrochloride assisted by peroxymonosulfate activation

Peroxymonosulfate (PMS)-assisted visible photocatalytic degradation of organic pollutants via graphitic carbon nitride (g-C₃N₄) is a promising and environmentally friendly technology. But pristine g-C₃N₄ still suffers from limited visible light utilization and low charge carrier mobility. Herein, g-C₃N₄ doped by C derived from lignin (LCN) was synthesized via a straightforward calcination process involving a physical blend of lignin and melamine, and its photocatalysis and PMS-assisted photocatalysis under visible light for typical organic pollutant tetracycline hydrochloride (TC) were studied. The experimental results show that due to the incorporation of C atoms by replacing bridging N atoms in g-C₃N₄, LCN has improved visible light utilization and enhanced charge transfer. Under the assistance of PMS, LCN-1 (1 wt% lignin in g-C₃N₄) exhibits a markedly high TC degradation efficiency, with a degradation rate 6.74 times that of pristine g-C₃N₄. In addition, the main radicals and reaction mechanisms in both systems were proposed through free radical quenching experiments and electron paramagnetic resonance signal. This work offers insights into the development of low-cost C-doped g-C₃N₄, using sustainably sourced lignin, and further demonstrates its superior efficiency in photocatalytic degradation of TC coupled with PMS activation.