TiO2 nanoparticles doped SiO2 films with ordered mesopore channels: a catalytic nanoreactor

Abstract

Titanium dioxide (TiO₂) incorporated ordered 2D hexagonal mesoporous silica (SiO₂) films on a glass substrate were fabricated for use as a catalytic nanoreactor. Films were prepared using a tetraethyl orthosilicate (TEOS) derived SiO₂ sol and a commercially available dispersion of TiO₂ nanoparticles (NPs) in the presence of pluronic P123 as the structure directing agent. The effect of TiO₂ doping (4–10 mol% with respect to the equivalent SiO₂) into the ordered mesoporous SiO₂ matrix was thoroughly investigated. The undoped SiO₂ film showed a mesostructural transformation after heat-treatment at 350 °C whereas incorporation of TiO₂ restricted such a transformation. Among all the TiO₂ incorporated films, TEM showed that the 7 equivalent mol% TiO₂ doped SiO₂ film (ST-7) had an optimal composition which could retain the more organized 2D hexagonal (space group p6mm)-like mesostructures after heat-treatment. The catalytic activities of the TiO₂ doped (4–10 mol%) films were investigated for the reduction of toxic KMnO₄ in an aqueous medium. ST-7 film showed the maximum catalytic activity, as well as reusability. A TEM study on the resultant solution after KMnO₄ reduction revealed the formation of MnO₂ nanowires. It was understood that the embedded TiO₂ NPs bonded SiO₂ matrix increased the surface hydroxyl groups of the composite films resulting in the generation of acidic sites. The catalytic process can be explained by this enhanced surface acidity. The mesoporous channel of the ST-7 films with TiO₂ doping can be used as a nanoreactor to form extremely thin MnO₂ nanowires.