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

Coating anatase TiO₂ onto three different particle supports, activated carbon (AC), γ-alumina (Al₂O₃) and silica gel (SiO₂), by chemical vapor deposition (CVD) was studied. The effect of the CVD synthesis conditions on the loading rate of anatase TiO₂ was investigated. It was found that introducing water vapor during CVD or adsorbing water before CVD was crucial to obtain 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 parameters to obtain more uniform and repeatable TiO₂ coating. High inflow precursor concentration, high CVD reactor temperature and long coating time tended to cause block problem. Coating TiO₂ onto small particles by CVD involved both chemical vapor deposition and particle deposition. It was believed that the latter was the reason for the block problem. In addition, the mechanism 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 efficient support in terms of both anatase TiO₂ coating and photocatalytic reaction.