Photocatalytic degradation of an organophosphorus compound by porous Au- and WO3- modified TiO2

Organophosphorus (OP) compounds are highly toxic substances that are often used as chemical warfare agents and pesticides. OP pesticides are the most widely used class of pesticide in the world, and due to their ubiquity, the contamination of agricultural runoff by OP pesticides has become a problem of global concern. One of the more attractive solutions that has been proposed is the use of photocatalytic degradation to decontaminate affected water supplies. In the present work, the visible-light photocatalytic activity of a series of porous Au-WO3-TiO2 photocatalysts with variable concentrations of Au (0, 1, 3, and 5 weight percent) synthesized using mesoporous SiO2 as a template was evaluated in the aqueous degradation reaction of an OP agent, dimethyl methylphosphonate (DMMP). The Au and WO3 were added to the catalysts using sonochemical deposition and incipient wetness impregnation, respectively. The photocatalytic activity of the ternary Au-WO3-TiO2 series was compared to that of a WO3-free series of Au-TiO2 catalysts with comparable Au loadings. The catalysts were characterized by scanning electron microscopy (SEM), powder x-ray diffractometry (PXRD), and N2-physisorption. The SEM and N2-physisorption analyses indicated the Au-TiO2 and Au-WO3-TiO2 particles had high surface areas of 135 m2 g-1 and 100 m2 g-1, respectively, with particle diameters of 1-3 μm. No crystalline WO3 was detected on the WO3-containing species, indicating the formation of a monolayer of WO3 on the surface of the TiO2. The sonochemically deposited gold nanoparticles (NPs) were found to be 3-10 nm in diameter. The photocatalytic degradation of DMMP was monitored by quantitative GCMS analysis. The independent addition of Au NPs or WO3 to the surface of the TiO2 did not significantly affect the total degradation of DMMP after 30 hours of irradiation relative to unmodified TiO2, however the presence of both Au and WO3 on the surface of the TiO2 significantly increased the total degradation of DMMP after 30 hours, reaching the detection limit for the 1 and 3 weight percent catalysts. It was found that the photocatalytic activity of the Au-WO3-TiO2 catalysts was not significantly influenced by the weight percent Au for the concentrations studied