Synthesis of TiO₂/SiO₂ nanoparticles in a water-in-carbon-dioxide microemulsion and their photocatalytic activity

TiO₂ and TiO₂/SiO₂ nanoparticles were prepared by controlled hydrolysis of titanium tetraisopropoxide and tetraethylorhtosilicate in water-in-carbon-dioxide microemulsion using ammonium carboxylate perfluoro-polyether (PFPE-NH4) as a surfactant. These particles were characterized by HRTEM, XRD, FT-IR, TGA and DTA. The particles calcined at 500°C were identified as a nanocrystalline anatase phase, regardless of the titanium tetraisopropoxide/teraethylorthosilicate (TTIP/TEOS) molar ratio. The crystallite size decreased with an increase of the silica content. From FT-IR analysis, the band for Ti-O-Si vibration was observed and the band intensity for Si-O-Si vibration increased with an increase of the silica content. The micrographs of HRTEM showed that the TiO₂/SiO₂ nanoparticles had a spherical morphology with a narrow size distribution and the lattice fringe was 0.35 nm, which corresponds to the lattice spacing of (101) plane in the anatase phase. In addition, TiO₂/SiO₂ particles showed higher photocatalytic activity than pure TiO₂ and the TiO₂/SiO₂ (80:20) particles showed the highest activity on the photocatalytic decomposition of p-nitrophenol.