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 O, generating •O 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.