Mechanistic understanding of cellulose β-1,4-glycosidic cleavage via photocatalysis

Photoreforming of lignocellulosic biomass is an emerging and sustainable strategy for coproduction of high-value chemicals and fuels. Challenges remain to selectively convert biomass macromolecular via sunlight-driven photocatalysis due to limited mass diffusion, insufficient charge separation and lack of mechanistic understanding. Herein, inspired by natural photosynthesis, we demonstrate a hierarchically threedimensionally ordered macroporous (3DOM) TiO2-Au-CdS Z-scheme heterojunction photocatalyst to improve mass diffusion, charge separation and light absorption efficiency. We show the photocatalytic cleavage pathway of cellulose β-1,4-glycosidic linkage (the most abundant linkage within biomass) over 3DOM TiO2-Au-CdS heterojunction by using cellobiose as a model component. Similar to the oxidative enzymes in nature, the all-solid-state Z-scheme photocatalyst demonstrates oxygen insertion at C1 position followed by the elimination reaction, which oxidatively cleaves the β-1,4-glycosidic bond and results in gluconic acid and glucose generation. In presence of oxygen, glucose is further oxidized into gluconic acid which is subsequently oxidized or decarboxylated into glucaric acid or arabinose. The present study may serve as a framework to rationally design photocatalyst to reveal mechanistic understanding of biomass photoreforming towards high-value fuels and chemical feedstocks.