Microstructure and photoactivity of titania nanoparticles prepared in nonionic W/O microemulsions

Ultrafine titania particles were prepared from reacting TiOCl2 with NH4OH in the nanodroplets of water/Triton X-100/n-hexanol/cyclohexane microemulsions. The as-prepared particles were amorphous, transformed into the anatase phase at 460°C, and further into the rutile phase at 850°C. The crystallite size of the particles was in the range of 10–36 nm at temperatures between 500 and 900°C. Secondary particles were 40–50 nm in size at 500°C and increased markedly by a factor of 10 at 900°C due to a significant interagglomerate densification. With increasing calcination temperature from 300 to 900°C, the specific surface area of the particles decreased rapidly from 317.5 to 8.4 m2 g−1, while the average pore radius increased considerably from 2.9 to 31.8 nm as the result of shrinkage and densification of the agglomerates and destruction of the minute intercrystallite pores. The anatase phase formed at 500–700°C showed considerable photoactivity for the degradation of phenol, whereas both the amorphous phase at 300°C and the rutile phase at 900°C were inactive for this reaction.