Silica-coated nanocrystalline TiO2 with improved thermal stability

Abstract Deposition of a SiO 2 coating on anatase TiO 2 nanocrystals is shown to improve their thermal stability. As low as 0.5% Si was shown to preserve the small anatase crystallite size after calcination at 600 °C. Such treatment led to considerable sintering of TiO 2 nanocrystals without the silica with the average particle size growth from 9 to 50 nm, surface area decrease from 135 to 22 m 2 /g and partial anatase conversion to rutile. The phase composition, crystallite size, and surface area of 5%Si-TiO 2 samples were largely preserved till the temperatures as high as 800 °C whereas the anatase phase was mostly stably even after calcination at 1000 °C. The phase transformation from anatase to rutile in xerogel TiO 2 and TiO 2 @SiO 2 samples apparently did not occur until the crystallites grew larger than the critical size about 50 nm. Electron-acceptor sites capable of ionizing perylene to its radical cations were observed on all samples with anatase crystalline structure. So, the silica shell deposition improves the TiO 2 thermal stability without limiting access to the surface active sites.