Mesoporous H₆P₂W₁₈O₆₂-TiO₂ Composite Photocatalyst: Preparation And Photocatalytic Activity

Since Fujishima found out that the hydrogen can be generated from water by TiO2 electrode in 1972, many efforts have been done to improve photocatalytic performance of TiO2. Comparing to other semiconductor photocatalysts, TiO2 shows many advantages, such as steady chemical property, nontoxicity and low-cost. However, it is still not applied in practice due to its low light quantum yield, narrow light-response range and difficult separation. Some attractive researching progresses about solid polyoxometalate (POM) as heterogeneous photocatalyst have developed in recent years. Although POM exhibit UV-light photocatalytic activity in homogeneous system, the main disadvantages of them as photocatalysts lie in their low surface area and difficulty of separation from reaction mixture. Therefore, development of novel solid catalysts with advanced characteristics has been a challenge for a long time. There are some similarities in chemical position and electron property between the POM and TiO2. The POM molecure has also transition metal (W atom) with d0 electron structure and oxygen atom. The energy difference of HOMO and LUMO corresponds to band gap of TiO2. Therefor, there is the sense to prepare photocatalytic active catalysts,Dawson heterpolyacid coupled with anatase TiO2.The nanosized H6P2W18O62-TiO2 composite was prepared by sol–gel method followed by hydrothermal treatment in the presence of triblock copolymer surfactant (P123). UV-vis diffuse reflectance spectroscopy (UV/DRS), infrared spectroscopy (IR), Raman spectroscopy and powder X-ray diffraction (XRD) were used to characterize the composition, phase structure and the integrity of the starting H6P2W18O62 after formation of the composite. The results indicated that the primary Dawson structure of as-prepared composites remain intact after formation of the composites, and the strong chemical interactions between POM molecules and titania network existed. The morphology and surface physicochemical properties of as-prepared solid photocatalytic materials was analyzed by transmission electron microscopy (TEM) and N2 absorption-desorption. The results indicated that as-prepared material exhibited nanosized (< 10 nm), mesoporous structures (pore diameter with 4.3 nm), and large BET surface area (204.58 m2 g-1).Photocatalytic property and selectivity of the composite were tested by the degradation of dyes like Rhodamoine B (RB), Comassie Brilliant Blue (CBB), Xylidne Ponceau (XP) and organic contaminations such as 4-nitrophenol (4-NP), 2,4-dichlorophenoxyacetic acid (2,4-D), Dimethyl Phthalate (DMP) under ultravilet-light irradiation. The high photoactivities of as-prepared nanocomposites could be attributed to the synergistic effect existed between the H6P2W18O62 and the TiO2 matrix, stronger optical absorption ability, wormhole-like porous structure and stronger absorption ability. The above composite catalysts also had the advantages of easily being separated and taken on a wide application prospect.