Effects of process parameters on preparation of Ti@SiO2 particles during fluidized bed chemical vapor deposition via design of experiments

Abstract

Fluidized bed chemical vapor deposition (FBCVD) is a promising technology for preparing photocatalysts. However, the photocatalyst performance depends on numerous parameters, and the effects of process parameters on photocatalyst performance are not well understood. In this work, the effects of deposition time, fluidization number, reactant molar ratio and deposition temperature on photocatalysts prepared by FBCVD are investigated via a full factor factorial design approach, which is a kind of Design of Experiments. The results show that the deposition time, reactant molar ratio and deposition temperature are the main factors affecting the photocatalytic performance, while the fluidization number and the interactions between different parameters are insignificant factors. The characterization of the elemental content, elemental distribution and crystalline structure of Ti-deposited SiO2, Ti@SiO2, particles reveals that the formation of Ti-O-Si bonds and Ti-based nanoparticles on the Ti@SiO2 surface enhances the photocatalytic performance of the particles. Finally, the formation mechanisms of Ti@SiO2 particles are summarized which can be distinguished into two stages. At around 120 °C, intermediates such as Ti(OH)4 are generated and reactions consist of homogeneous and heterogeneous reactions. At around 400–600 ℃, the Ti@SiO2 particles are formed, which is dominated by heterogeneous reactions. The results of this study can improve understanding and control of photocatalyst preparation.