TiO 2 coating on silica particles by deposition of sol-gel-derived nanoparticles

Abstract

TiO 2 was coated on nonporous transparent silica particles of 3.2 μm diameter by deposition of sol-gel-derived TiO 2 nanoparticles. Effects of water concentration, feed rate of titanium tetraisopropoxide (TTIP) solution and amount of supplied TTIP solution on the amount of TiO 2 coated on the silica particles were examined. Scanning electron microscopy observation confirmed that TiO 2 was coated on the silica particles in the form of ‘nanoparticles’ by using this method. Because of that, even though the TiO 2 surface area decreased due to sintering after calcination at high temperature to change the crystalline phase of TiO 2 to the anatase phase, the final surface area was still much larger than that of the original silica particles. The results also showed that as the water concentration increased, the amount of coated TiO 2 decreased. On the other hand, when the amount of supplied TTIP solution increased, the amount of coated TiO 2 increased. It was also confirmed that the feed rate of TTIP solution had little effect on the amount of coated TiO 2. The photocatalytic activities of the resulting TiO 2-coated silica particles were also evaluated by the photocatalytic decomposition of 2,4-dinitrophenol as a model substance. The results showed that the photocatalytic activity of the particles is not a function of the total surface area, but of the surface area in which anatase phase TiO 2 is exposed to the reaction space. The sedimentation velocity of the TiO 2-coated silica particles becomes about 5 orders of magnitude faster than that of the primary particles of the TiO 2. This indicates that the handling of the TiO 2 was also improved considerably by coating on the silica particles.