Carbon quantum dot (CQD)-decorated CdS nanocomposites were successfully fabricated via the self-assembly of CdS in the presence of preformed CQDs and were found to be efficient photocatalysts for the hydrogenation of nitrobenzene under visible light. Due to the presence of the frustrated Lewis acid–base pairs (FLPs) in their structure, CQDs act as an efficient catalyst to promote the proton-coupled hydrogenation of nitrobenzene over CQDs/CdS nanocomposites. Controllable and chemoselective hydrogenation of nitrobenzene to produce aniline, azoxybenzene, azobenzene and hydrazobenzene can be realized over CQDs/CdS via simply regulating the reaction medium including the hydrogen source, the solvent and the alkalinity. This study provides a highly efficient and economical photocatalytic system for the controllable and chemoselective hydrogenation of nitrobenzene under visible light. This work also highlights the great potential of semiconductor-based photocatalysis in light-initiated organic syntheses.