Improved Photocatalytic Degradation of Methyl Orange by Polyoxometalates Supported on Titanium Dioxide Doping with Rare Earth

摘要

Dye wastewater pollution has become a global issue with the development of textile industry. Polyoxometalates photocatalysis is an effective process in degradation of dye wastewater. This paper is to develop a novel supported polyoxometalates photocatalytic material. The H3PW12O40-Y2O3-TiO2 nano photocatalyst was prepared by impregnation method while the Y2O3-TiO2 support was synthesized via sol-gel technology for the first time. The compound was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nitrogen adsorption-desorption determination and scanning electron microscopy (SEM). The measurements results demonstrate that the original Keggin structure of the polyoxometalates remained intact and there exist anatase phase in the prepared material. The photocatalytic degradation of azo-dye, Methyl Orange (MO) under UV light (λ≥365 nm) in the presence of H3PW12O40-Y2O3-TiO2 photocatalyst in aqueous solution had been investigated and compared with the photodegradation by TiO2 and Y2O3-TiO2 suspensions. The supported polyoxometalates exhibited excellent photocatalytic activity due to the fact that MO was almost completely degraded in 20 min with initial pH=1.0. The photocatalytic activity of polyoxometalates was greatly enhanced, comparing with the staring polyoxometalates, by the synergistic effect between polyoxometalates and anatase Y2O3-TiO2 as well as the increased surface area. Leakage of H3PW12O40 from the compound was hardly observed during catalytic tests, which attributes to the strong chemical but not simply physical interaction between the Keggin units and the Y2O3-TiO2 support. The prepared material is insoluble and easily separated from reaction system for recovery. Any drop of the photocatalytic activity after 8 times’ cyclic operation was not found, revealing that the prepared catalysts are stable.