Valorization of industrial lignin waste: Synergistic mechanism of lignin-derived biochar for efficient dye removal

Lignin, an underutilized byproduct of the paper industry, was transformed into highly efficient biochar for malachite green (MG) removal (∼2900 mg/g), achieving dual goals of waste valorization and pollution control. Mechanistic studies reveal that the outstanding performance arises from the contributions of biochar skeleton (23.3 %-25.8 %), biochar dissolved matter (BDM) (43.3 %-46.0 %), and their synergistic interaction (28.2 %-33.4 %). Low-temperature biochar showed superior synergistic effects. This synergy enables a coupled process of electron transfer-driven degradation and adsorption. The graphitized biochar skeleton acts as an electron donor, while BDM components facilitate electron transfer to O₂, generating •O₂^- for MG degradation. Furthermore, functional groups on biochar skeleton provide adsorption sites via multiple interactions. This study presents a cost-effective MG removal strategy and, for the first time, elucidates BDM's role as an electron shuttle, advancing biochar application and lignin valorization in wastewater treatment.