The unique and fascinating properties of silica-based zeolites and mesoporous silicas have opened up new possibilities for many chemical and physical processes.Because they are transparent to UVvisible light,silica materials have often been functionalized with elements such as Ti,Cr,V,Mo,and W whose corresponding bulk oxides are known to be suitable photocatalysts.These well-defined active centers have shown to be highly dispersed at the atomic level in a tetrahedral-coordination geometry and have been named as “single-site photocatalysts”.The single-sites can be implanted into silica matrices by various techniques including hydrothermal synthesis,sol–gel method and chemical vapor deposition.