Clarifying the roles of hydrothermal treatment and silica addition to synthesize TiO2-based nanocomposites with high photocatalytic performance

Abstract

In this work we investigated the effect of hydrothermal treatment and silica addition on the structure and photocatalytic performance of synthesized TiO2-based nanocomposites. These materials were prepared by combining sol–gel process and hydrothermal treatment, and no templates or surfactants were used in these syntheses. The optimal synthesis conditions were investigated based on the variation of the preparation parameters. Anatase TiO2 crystals were synthesized without the need of a hydrothermal treatment, but this process appeared necessary to form an anatase phase with better structural quality and high photoactivity. The heat treatment step induced competitive phenomena toward the TiO2 structural properties and its photodegradation activity, but it proved to be advantageous as long as the pore structure, anatase phase, and high specific surface area were maintained. The addition of silica was then justified, aiming to stabilize the crystalline structure of TiO2 upon heat treatment. The ideal molar ratio of Si/(Si + Ti) was 0.2 for samples heat-treated at either 500 or 700 °C. The high photocatalytic efficiency of the synthesized nanocomposites is due to the combined effect of the photoactivity of TiO2 and adsorption capacity of SiO2. When compared with a commercial TiO2 sample (Degussa Evonik P25), increasing the catalyst loading proved to greatly enhance the performance of the synthesized nanocomposite, whereas the commercial one did not follow the same trend.