Polyoxometalate (POM) is an eco-friendly solid acid. It a polyatomic anion containing transition metal (group Ⅴ or group Ⅵ) oxyanions, which are connected by common oxygen atoms. In addition to the advantages of other photocatalysts, such as non-toxic, no secondary pollution, convenient, fast and efficient, it also has characteristics high rich surface, because there large number centers in its...