Porous TiO2 microspheres with tunable properties for photocatalytic air purification

The synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa).