(Invited) Semiconductor Facet Effects Toward Photocatalysis

Photo-induced charge transfer has been found to strongly depend on the exposed semiconductor surfaces. For instance, {110}-bound Cu 2 O rhombic dodecahedra exhibit a high photocatalytic activity toward dye degradation, but {100}-terminated Cu 2 O cubes are inert. Photocatalytic behaviors of Cu 2 O-based semiconductor heterostructures, such as Cu 2 O-ZnS and Cu 2 O-ZnO composites, can both enhance and suppress photocatalytic activity depending on the contacting planes at the heterojunction. Significantly, Cu 2 O photocatalytic activity can be greatly enhanced by functionalizing with conjugated molecules such as 4-nitrophenylacetylene (4-NA) to tune the surface band structure. This can turn the inactive cubes to possess a superior photocatalytic activity. Recently, Cu 2 O rhombic dodecahedra with and without 4-NA modification have been employed in photocatalytic hydroxylation of boronic acids, aryl sulfide oxidation, and amine coupling. SrTiO 3 truncated rhombic dodecahedra were also found to be effective in amine coupling. Oxidative cyclization of thioamides is the latest example of surface control to photocatalytic organic transformations.