Effect of calcination on the microstructures of titania nanoparticles prepared in W/O microemulsions

Monodispersed titania nanoparticles were prepared from reacting TiOCl₂ with NH₄OH in water/Triton X-100/n-hexanol/cyclohexane microemulsions. The effect of calcination on the microstructures of the particles was investigated. The particles synthesized were amorphous, transformed into the anatase phase at 300°C, and further into the rutile phase at 850°C. The crystallite size of the particles was 9.7 to 35.6 nm in the temperature range between 300 and 900°C. Secondary particles, agglomerates of finer primary particles, were about 20 nm in size at 200°C and increased markedly by a factor of 10 to 20 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, whereas the average pore radius increased considerably from 2.9 to 31.8 nm as the result of shrinkage of the agglomerates, destruction of the minute intercrystallite pores, and interagglomerate densification.