Ligand-Controlled Photocatalysis of CdS Quantum Dots for Lignin Valorization under Visible Light

Manipulating surface organic ligands has emerged as a useful strategy to enhance the efficiency of heterogeneous catalysts. However, ligand-controlled catalysis for biomass valorization remains unexplored because of the limited knowledge of the ligand functions in heterogeneous catalytic systems involving macromolecules. Here, we report a strong dependence of photocatalytic conversion of native lignin into high-value functionalized aromatics on the ligand attached on cadmium sulfide quantum dots (QDs). The formation of a QD colloidal solution by tuning the hydrophilicity/hydrophobicity of ligands is essential to enable intimate contact between QDs and lignin, leading to high catalytic activity. The surface engineering by manipulating the anchor group and the length of ligands demonstrates that the ligand participates in the electron-transfer process, a crucial step of photocatalysis. The electron decay kinetic study reveals a ligand-mediated electron-tunneling mechanism. These insights offer useful guidance for the design of efficient QD photocatalysts for biomass valorization through ligand modification.