Microporous Decatungstates: Synthesis and Photochemical Behavior

Photoreactive decatungstates Na 4 W 10 O 32 and (nBu 4 N) 4 W 10 O 32 were heterogenized inside the silica network via a sol−gel technique, resulting in the Na 4 W 10 O 32 /SiO 2 (Na 1 ) and (nBu 4 N) 4 W 10 O 32 /SiO 2 (Q 1 ) composites. The physicochemical properties of as-synthesized composites were measured by UV diffuse reflectance spectrum, Fourier transform infrared, thermogravimetric analysis and differential thermal analysis, inductively coupled plasma-atomic emission spectroscopy, and scanning electron microgragh, suggesting that the structural integrity of the decatungstates has been preserved after incorporation into the silica network. The microporous structures of the Na 1 and Q 1 were confirmed by the nitrogen adsorption measurements. The photocatalytic behaviors of the composites were studied via degradation and mineralization of organophosphorus pesticide, trichorofon (TCF), under near-UV irradiation and in media where they are insoluble. The photocatalytic behaviors of the Na 1 and Q 1 were also compared with two silica-supported decatungstates, Na 4 W 10 O 32 −SiO 2 (Na 2 ) and (nBu 4 N) 4 W 10 O 32 −SiO 2 (Q 2 ). It indicated that the Na 1 had the highest photocatalytic efficiency among four insoluble decatungstates, and the leakage of the catalyst from the support was hardly observed for Na 1 . Studies on the reaction mechanism indicate that OH • radical attack may be responsible for the degradation and final mineralization of TCF.