Highly Selective Photocatalytic Valorization of Lignin Model Compounds Using Ultrathin Metal/CdS

Depolymerization of recalcitrant lignin is a crucial step in realizing the full potential of transforming biomass to value-added small organic molecules. Herein, we report a photocatalytic system consisting of ultrathin CdS nanosheets decorated with first-row transition metals (M/CdS) for the direct photocleavage of lignin model compounds to small aromatic products. In the meantime, the reducing power of M/CdS is utilized to simultaneously generate another valuable product, H-2, hence eliminating the necessity of sacrificial reagents and maximizing the energy conversion efficiency. We further demonstrate that, by judiciously modulating the photocatalytic conditions, it is feasible to yield different products with very high selectivity using the same catalyst of Ni/CdS. A series of control experiments were performed to investigate the mechanistic steps of each reaction and highlight the important roles played by both solvent and base in the photocleavage of the beta-O-4 bond in lignin valorization.