Here, we report CdS QD gels as a new type of d-HAT photocatalyst for activating C-H bonds of a broad range of substrates, including cyclic thio/ethers, amides, aldehydes, and benzylic compounds. The proposed mechanism is that upon photoexcitation, the valence band electrons that predominantly reside on the S sites of CdS QDs in the ground state would shift to the Cd sites (Figures and). As a result, the excited QDs exhibit the characteristics of thiyl radicals, which are highly reactive toward hydrogen abstractions from C-H bonds (Figure ).