INFLUENCE OF CALCINATION ON MICROSTRUCTURES AND PHOTOACTIVITIES OF ALKOXIDE-DERIVED TiO2 NANOPARTICLES PREPARED IN W/O MICROEMULSIONS

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Abstract
Ultrafine titania particles were synthesized by hydrolysis of titanium tetraisoproxide (TTIP) in the nanodroplets of water/NP-5/cyclohexane microemulsions. The as-prepared particles were amorphous, transformed into the anatase phase at 450°C, and completely into the rutile phase at 700°C. The amorphous-to-anatase phase transition temperature decreased with increasing water/surfactant molar ratio. With increasing temperature from 500 to 900°C, the crystallite size increased about twice from 11.7 to 24.4 nm, while the size of the secondary particles, agglomerates of the primary panicles, increased by a factor of about 10. The particles grew largely by intra-agglomerate densification below 700°C, whereas they grew by interagglomerate densification above 700°C. The anatase phase formed at 500-600°C showed considerable photoactivity for the degradation of phenol, whereas both the amorphous phase at 300°C and the rutile phase at 700°C were almost inactive for this reaction.