To test the photocatalytic C-H bond activation ability of CdS QD gels, we used the alkylation of C-H bonds via radical addition to an electron-deficient alkene (e.g., 2-benzylidene malononitrile, 1) as a model reaction. Initially, we added the C-H partners as the solvent and 2 x 10 -3 mol% QD gel catalysts (Method A in Figure ). The catalyst loading was defined as the molar ratio between QD building units in the added gel catalyst and the limiting reagent (in this case, 1). The reactions were conducted at room temperature under 440 nm blue light irradiation and Ar atmosphere in the same homebuilt photocatalytic reaction apparatus as our previous work. Various five-member-ring cyclic ethers, including tetrahydrofuran (THF), 2-methyl-1,3-dioxolane, 1,3-dioxolane, and 2-methyl-tetrahydrofuran afforded their corresponding alkylation products (3a-3d) in good to excellent yields of 60 -96% in less than 3 hours. However, sixmember ring 1,3-dioxane and 1,4-dioxane only gave a product yield of ~10%, and the reaction did not complete even after up to 80 hours (Figure ). In the absence of light or QD gel catalyst, no reaction product was observed (Figure ), confirming the C-H activation was catalyzed by CdS QD gels. As a heterogeneous catalyst, CdS QD gel can be easily recycled by centrifugation. The recycled CdS QD gel preserved its photocatalytic reactivity without appreciable loss in the product yield (Figure ).