Radical-mediated Cα-Cβ cleavage by ZnIn2S4-based heterojunction materials in photo-electro-catalysis

Abstract

The selective cleavage of lignin specific linkages for production of high-value chemicals remains a significant challenge due to inherent inertness and complex structure. In this study, we developed a Photo-Electro-Catalysis (PEC) strategy utilizing radicals, which achieved high catalytic efficiency for lignin depolymerization at room temperature (from 10 °C to 35 °C). A heterojunction material composed of 2D ZnIn₂S₄ nanosheets and carbon nanoparticles was synthesized to facilitate efficient electron transfer and radical generation. The quantum yield (2.1858) exceeding 1 suggested a radical chain mechanism in the PEC process. Mechanistic studies revealed that oxygen radical combine with C-centered radicals to form a C_β-OOH peroxide intermediate, leading to CC bond cleavage. Notably, chlorine radicals (•Cl) were introduced for the first time in lignin PEC depolymerization, initiating C_β-H functionalization, cyclization and ring-opening reactions. This approach achieved 100 % C_α-C_β cleavage and over 90 % mass conversion of native G-units lignin. The highest product yields were 233.34 mg g⁻¹ (benzaldehyde), 66.03 mg g⁻¹ (acetophenone), and 54.98 mg g⁻¹ (phenol) from the β-O-4 dimer. This study provides novel insights into radical mechanisms and catalytic strategies for lignin depolymerization into high-value chemicals.