Pivotal Role of Surface Sulfur Atoms in CdS Nanoparticles for the C–C Coupling of Benzyl Alcohol

Metal sulfides have been extensively explored as efficient semiconductors for the photocatalytic carbon–carbon (C–C) coupling of alcohols to diols under ambient conditions. However, the intrinsic mechanism of the unique performance for metal sulfides toward C–C coupling reactions has been ignored and lacks intensive study. Herein, we report a CdS nanosphere with abundant surface-attached sulfur synthesized by a common hydrothermal method for the selective photocatalytic C–C coupling of benzyl alcohol. Encouragingly, the desired coupling products (hydrobenzoin, benzoin, and deoxybenzoin) with 88.4% yield and a formation rate of 3.54 mmol·gcat–1·h–1 are achieved upon blue-light irradiation under ambient conditions. More importantly, based on the experimental results, it is supposed that the high performance for photocatalytic C–C coupling of benzyl alcohol is mainly due to the surface-attached sulfur of CdS, which acts as a trapping center for both holes and benzyl alcohol radicals (BA•) via suppressin of the recombination rate of photogenerated charge carriers and the overoxidation process.