Abstract:

TiO₂ nanocrystals were synthesized by the method of volatilization and decomposition of TiC_l4 in the existence of NH4Cl. The influence of NH4Cl on the structure of crystalline phase and the properties of the sample was discussed. The samples were characterized by XRD, TEM, IR, specific surface areas and thermal analysis. The samples completely changed to anatase phase and are nanocrystals with a diameter less than 7 nm by calcination at 150 ℃ for 5 h; the samples calcined at 300-600 ℃ with the particle diameter about 9-23 nm are composed of pure anatase TiO₂; the samples calcined at 700 ℃ with the particle diameter of about 33 nm are composed of a large quantity of anatase phase and a little amount of rutile phase. By dynamics analysis of crystal growth, calcination below 700 ℃, there are two kinds of driving power to crystal growth, and 400 ℃ is the turning point: calcination below 400 ℃ the required energy of crystal growth is 8.23 kJ/mol; calcination at above 400 ℃ the required energy of crystal growth is 45.71 kJ/mol. The catalytic activity of the samples calcined at 200 ℃, which had the largest specific surface area and the particle diameter is about 7 nm, are the highest in the reaction of methyl orange decomposition.

Key words: TiO₂; NH₄Cl; Nanomaterials; Kinetics of particle growth