Abstract: The particle size is a very important factors for photocatalytic activity of TiO 2 , and the smaller TiO2 has a higher photocatalytic property .A slurry explosive mixed by Ti-contained precursor , ammonium nitrate, hexogen and some polystyrene beads was exploded in a pressure-tight reaction kettle to prepare ultra small TiO2 nanoparticle.The influence of explosive formulation on morphology , dispersivity and particle size was studied .Furthermore, the photocatalytic property of ultra small TiO 2 was tested by degradation of methyl orange solution .It is found that the TiO2 nanoparticles are consisted of rutile and anatase;most of them are spherical or irregular quadrangular; the particle size is about 10 nm; a small amount of particles'size is greater than 20 nm.The crystallinity of TiO2 is good.The explosive formulation has great influence on crystallinity , particle size and dispersivity of TiO 2 .The band gap of TiO2 is about 2.8 eV, which is less than that of anatase and rutile , and it indicates that the ultra small TiO2 can increase the utilization of sunlight .The degradation rate of methyl orange is 30;when the ultra small TiO2 was used to degrade methyl orange solution for 50 min, which is much higher than the TiO 2 and Cu-doped nano TiO 2 prepared by detonation method with larger particle size .The photocatalytic property is improved obviously .

Key words: The particle size is a very important factors for photocatalytic activity of TiO 2 , and the smaller TiO2 has a higher photocatalytic property .A slurry explosive mixed by Ti-contained precursor , ammonium nitrate, hexogen and some polystyrene beads was exploded in a pressure-tight reaction kettle to prepare ultra small TiO2 nanoparticle.The influence of explosive formulation on morphology , dispersivity and particle size was studied .Furthermore, the photocatalytic property of ultra small TiO 2 was tested by degradation of methyl orange solution .It is found that the TiO2 nanoparticles are consisted of rutile and anatase;most of them are spherical or irregular quadrangular; the particle size is about 10 nm; a small amount of particles'size is greater than 20 nm.The crystallinity of TiO2 is good.The explosive formulation has great influence on crystallinity , particle size and dispersivity of TiO 2 .The band gap of TiO2 is about 2.8 eV, which is less than that of anatase and rutile , and it indicates that the ultra small TiO2 can increase the utilization of sunlight .The degradation rate of methyl orange is 30;when the ultra small TiO2 was used to degrade methyl orange solution for 50 min, which is much higher than the TiO 2 and Cu-doped nano TiO 2 prepared by detonation method with larger particle size .The photocatalytic property is improved obviously .