Metal chalcogenide quantum dots (QDs), such as CdS and CdSe, are semiconductor nanocrystals with tunable electronic and optical characteristics by their sizes. Recently, QDs have emerged as powerful photocatalysts in organic synthesis. For example, CdS QDs were found to be a potent photoreductant with a reduction potential < -3.4 V vs SCE due to the Auger process of excited QDs. Moreover, the van der Waals interactions between the CdS surface and carboxylate-bearing substrates enable selective intermolecular [2+2] photocycloadditions. In addition, Wu et al. recently reported that the QD surface could also stabilize allylic and thiyl radicals, enabling direct radical cross-coupling for allylic C(sp 3 )-H or vinylic C-H thiolation. CdS QD gels are a 3-D connected pore-matter architecture of interconnected CdS QD networks, prepared by electrochemical or chemical oxidation of QDs. Compared with colloidal QDs, QD gels lose most surface ligands during gelation but retain the quantum confinement characteristics of the QDs. Previously, we found that CdS QD gel exhibited higher photocatalytic activity than its ligand-capped CdS QDs with the same bandgap because its surface sites are highly accessible to the substrates. Due to the surface interactions, CdS QD gel also catalyzed a unique ring-opening reaction during α-amine arylation of tetrahydroisoquinoline.