We also ruled out the possibility of an i-HAT pathway via thiyl radicals from the oxidation of thiol ligands that were possibly not fully removed during QD gel synthesis. The reasons are two-fold. First, adding thiols suppressed the C-H activation; and second, commercial CdS powder without any thiol ligands exhibited similar C-H activation capability, albeit less efficient than CdS QD gel (Figure ). These findings indicate that CdS material has an inherent ability to photocatalytically activate C-H bonds, regardless of their form. Inspired by the similarity between metal oxides and metal sulfides, we hypothesized that the CdS QD gels activate the C-H bonds through a d-HAT mechanism. This mechanism involves excited QD gels exhibiting the characteristics of thiyl radicals, which allows them to abstract hydrogen from C-H bonds.