Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst

The decolorization of commercial dyes is still a pertinent issue since these azo dyes are relatively resistant to conventional biological treatment methods. It is well known that polyoxometalates can absorb light in UV-Vis range that delivers electrons to the reducible species resulting in the decomposition of organic compounds. In this paper, we present the third heteropolyoxotantalate under conventional synthetic conditions in the presence of hydrogen peroxide. The compound has been thoroughly characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction. The polyanion incorporates two 3-peroxotantalo-2-phosphate clusters that are linked together by four oxygen bridges. In addition, the photocatalytic activities of the title compound 1a were investigated. After 270 min irradiation, about 90% of Rhodamine B (RhB) was removed in the presence of 1a while the degradation of RhB could be negligible in the absence of 1a, indicating it can be a promising catalyst candidate for decolorization of organic dyes. Also, photocatalytic experiment for hydrogen generation was studied, and the results show that the H₂ evolution rate is 3383 µmol h^-1 g^-1 for compound 1a (100 mg) over 6 h with the corresponding turnover number of 432.