Lignocellulosic herbal waste-derived hydrochar composites for activating peroxodisulfate in visible light photocatalytic degradation of minocycline

The photocatalytic system was developed through the self-assembly of lignocellulosic-based waste Panax notoginseng residue converted into hydrochar (PHC) with the organic semiconductor perylene diimide (PDI) to facilitate the visible-light photocatalytic degradation of minocycline hydrochloride (Mino-HCl) with the assistance of peroxodisulfate (PDS). The optimal PHC/PDI ratio of 1:4 was selected for further experiments, achieving 90.8 % minocycline removal under visible light after 2 h. At the optimal ratio, the visible light photocatalytic performance of PHC/PDI composites under PDS activation was 5.18 and 8.61 times higher than that of PDI and PHC, respectively. The system also exhibited excellent mineralization of minocycline, with a mineralization rate of 73.7 %. The PHC/PDI/PDS (P-P-P) system demonstrated good stability under visible light and showed general adaptability to different environmental conditions, including pH, coexisting anions and cations, and real water matrix. Theoretical calculations identified the O5, O7, N9, C20 and C29 sites of Mino-HCl as key targets for free radical attack. Toxicity assessments indicated significant reductions in both acute and chronic toxicity, particularly for fish and algae, indicating the transformation of Mino-HCl into less harmful products. This work provided a theoretical basis and reference for the research on waste management and wastewater treatment by employing lignocellulosic-based waste residues converted into biochar and an organic semiconductor PDI composite under PDS activation for visible light photocatalysis.