Photocatalytic depolymerization of organosolv lignin into valuable chemicals

Catalytic conversion of lignin to certain aromatic compounds has been extensively studied but still has great challenges. Photocatalytic depolymerizing lignin is a very promising method to obtain valuable chemicals. Herein, Zn₄In₂S₇ (ZIS)-based photocatalyst was successfully synthesized by simply combining ZIS and graphene oxide (GO). Photocatalyst ZIS-100 can efficiently depolymerize organosolv lignin into phenols and ketones. The relative content of valuable compounds in the depolymerized product was increased by 2.5 times as compared that without photocatalyst. The photocatalyst can effectively break C_β-O bonds in 2-phenoxy-1-phenylethanol (PP-ol, a model compound) and the conversion of PP-ol is 93.27%. Mechanism studies show that the thiol groups on the surface of ZIS-100 play an important role in the formation of C_α radical intermediates. Photocatalytic cleavage of C_β-O bond mainly follows a one-step reaction mechanism through a self‑hydrogen transfer process. This study provides a new strategy for selectively breaking C_β-O bond in lignin to form valuable chemicals.