An efficient lignin-biochar/ZnAl2O4/Bi2MoO6 composite photocatalyst for degradation of organic chlorine pollutants

Lignin, with its intrinsic polyphenolic structure, high carbon content, and diverse functional groups, has emerged as promising precursor for carbon-based materials in pollutant elimination. In this work, lignin-biochar (LC) was fabricated and integrated into LC/ZnAl₂O₄/Bi₂MoO₆ composites with adsorption-photocatalysis synergy, employed within an intimate coupling of photocatalysis and biodegradation (ICPB) system for AOX degradation. The formation of Bi-O-C bonds between lignin-biochar and Bi₂MoO₆ provides atomic-level channel for accelerating electron transfer. Notably, the 1 wt%LC/0.5 wt%ZnAl₂O₄/Bi₂MoO₆ (LM3) sample showed superior degradation efficiency, with the apparent rate constants of 13.82-fold (methylene blue, MB) and 5.56-fold (p-chlorophenol, 4-CP) higher than those of the pristine Bi₂MoO₆, respectively. DFT analyses demonstrated strong chemical adsorption interactions between 4-CP and lignin-biochar, with the highest adsorption energy of −46.3152 eV observed for LC/ZnAl₂O₄/Bi₂MoO₆. The synergistic adsorption-photocatalysis mechanism of the LC/ZnAl₂O₄/Bi₂MoO₆ composite was systematically explored, highlighting the critical role of lignin-biochar in enhancing adsorption, charge separation, and reactive oxygen species generation. The ICPB system demonstrated effective degradation of refractory 4-CP and bamboo ECF bleaching effluent. The visible-light driven ICPB system (VCPB) achieved 78.30 % TOC removal for 4-CP effluent within 24 h. Furthermore, the VCPB process achieved 80.03 % COD and 71.03 % AOX removals for an industrial bamboo ECF bleaching effluent sample, with long-term operational stability, while fostering robust microbial activity and enhanced biofilm diversity. The synergistic mechanism of the system between adsorption, photocatalysis, and biodegradation was discussed. This work provides a novel approach for designing bio-based photocatalysts for the degradation of refractory industrial effluents.