Nanosize and bimodal porous polyoxotungstate-anatase TiO2 composites: Preparation and photocatalytic degradation of organophosphorus pesticide using visible-light excitation

New and efficient heterogeneous photocatalytic materials, H3PW12O40/TiO2 and H6P2W18O62/TiO2, with anatase crystalline phase, dual-pore structures (micro- and meso-porosity), and nanometer sizes (average particle size of 6 nm) were prepared by combination of the methods of sol-gel and hydrothermal treatment at a lower temperature (200 °C, 2 °C/min). Compositions, structures, physicochemical properties, and surface morphology of the composites were characterized by inductively coupled plasma atomic emission spectrum (ICP-AES), X-ray diffraction (XRD) patterns, UV diffuse reflectance spectroscopy (UV/DRS), 31P magic-angle spinning (MAS) NMR, Raman scattering spectra, nitrogen adsorption/desorption determination, and transmission electron microscopy (TEM), respectively. It indicated that the primary Keggin or Dawson structure remained intact after immobilization of the unit into TiO2 network, and hydrogen bonding and chemical interactions between the unit and the anatase network existed in the composites. Both of the composites exhibited visible-light photocatalytic activity to degradation of an aqueous organophosphorus pesticide, parathion-methyl, and the deactivation of the catalysts was hardly observed after five times catalytic cycling.