Fine tuning of Cd_xZn_1-xS for photo-depolymerization of alkaline lignin into vanillin

Lignin is abundant and contains a large number of aromatic groups. Herein, Cd_xZn_1-xS photocatalyst with tunable band gap energy was successfully synthesized by using 3-mercaptopropionic acid as a structure tuning additive. Cd_xZn_1-xS can depolymerize alkaline lignin to vanillin by the photocatalytic process. Each gram of alkaline lignin can produce 46.5 mg of vanillin. 2-Phenoxy-1-phenylethanol (PP-ol) and other model compounds were used to understand the depolymerizing process of lignin. Fine tuned Cd_xZn_1-xS can effectively cleave the C_β-O-4 bond existed in PP-ol under simulated sunlight. The highest conversion of PP-ol was 89.5% with phenol and acetophenone yields of 66.2% and 33.5%, respectively. The mechanism studies confirm that the C_α-H in PP-ol and lignin is firstly dehydrogenated to form C_α radical intermediates, and then the photogenerated electrons break the adjacent C_β-O bond. This research provides a new strategy to prepare valuable chemicals by virtue of renewable biomass and simulated sunlight.