Novel Phosphotungstate-titania Nanocomposites from Aqueous Media

摘要

We report a novel method to synthesize nanocomposites composed of titania nanoparticles and phosphotungstate ions with various composition ratios ranging from W/Ti = 12/10 to 12/500 by inducing the electrostatic interaction between the positively charged protonated titania sol-particles and the negatively charged phosphotungstate anions to flocculate and precipitate.The precipitates showed varied features depending on the composition.The precipitate from the tungsten-richest W/Ti = 12/10 reaction is amorphous in its powder X-ray diffraction(XRD),transmission electron microscopy(TEM),and Raman spectroscopy data.This material shows the Type II adsorption characteristics in its N2-adsorption isotherm,but with quite low surface area of 34 m~2/g.To the contrary,the precipitates from the titanium-richer reactions(W/Ti = 12/50-12/500)are composed of anatase nanoparticles of 2-6 nm by XRD,TEM and Raman and show the Type I adsorption characteristics.The surface area linearly increases with the titanium content from 131 m~2/g for W/ Ti = 12/50 to 228 m~2/g for 12/500.The precipitate from the reaction with the intermediate composition W/Ti = 12/20 is composed of anatase nanoparticles and does not have any pore accessible to N2.With the wide variety of the physical properties of the precipitates,the present method can be a novel,viable means to tailor synthesis of nanocomposite materials.A formation mechanism of the precipitates is based on the electrostatic interactions between the titania nanoparticles and phosphotungstate ions.