The Role of Colloidal Quantum Dots Capping Ligands in Photocatalytic Lignin Valorization

The efficient transformation of biomass into high-value chemicals remains a significant challenge, with surface ligand manipulation offering a promising approach to enhance catalytic performance. In this study, we investigate the role of organic ligands in the photocatalytic conversion of lignin into functionalized aromatics using cadmium sulfide (CdS) quantum dots (QDs). By tuning the hydrophilicity/hydrophobicity of ligands, we successfully form stable QD colloidal solutions, ensuring effective contact between the QDs and lignin. We determined that thiyl ligands triggered the photocatalytic conversion of lignin models. These ligand modifications, including the anchor group and alkyl chain length, are shown to play a critical role in facilitating electron transfer during photocatalysis. Furthermore, it was discovered that the mechanism of C-C and C-O bond cleavage at the β-O-4 linkages can be influenced by the substituents on the aromatic rings of lignin, a finding that has not been previously reported. Our findings not only advance the understanding of ligand-controlled catalysis but also present a new pathway for efficient lignin biomass valorization and organic transformation processes using QD-based photocatalysts.