Synthesis of anatase TiO2 supported on porous solids by chemical vapor deposition

Coating anatase TiO2 onto three different particle supports, activated carb on (AC), gamma -alumina (Al2O3) and silica gel (SiO2), by chemical vapor de position (CVD) was studied. The effect of the CVD synthesis conditions on t he loading rate of anatase TiO2 was investigated. It was found that introdu cing water vapor during CVD or adsorbing water before CVD was crucial to ob tain anatase TiO2 on the surface of the particle supports. The evaporation temperature of precursor, deposition temperature in the reactor, flow rate of carrier gas, and the length of coating time were also important paramete rs to obtain more uniform and repeatable TiO2 coating. High inflow precurso r concentration, high CVD reactor temperature and long coating time tended to cause block problem. Coating TiO2 onto small particles by CVD involved b oth chemical vapor deposition and particle deposition. It was believed that the latter was the reason for the block problem. In addition, the mechanis m of CVD process in this study included two parts, pyrolysis and hydrolysis , and one of them was dominant in the CVD process under different synthesis route. Among the three types of materials, silica gel, with higher surface hydroxyl groups and macropore surface area, was found to be the most effic ient support in terms of both anatase TiO2 coating and photocatalytic react ion. (C) 2001 Elsevier Science B.V. All rights reserved.