Abstract: TiO₂ nanopowders were prepared by hydrothermal synthesis in distilled water, three small organic compounds (n-butyl alcohol, propane diacid and ethylenediamine) and three inorganic acids (HNO₃, H₂SO₄ and HCl) using the titanium n-buoxide as raw material. The product was characterized by powder X-ray diffraction (XRD) and transmission electron microscope (TEM). The effect of different solvent medium on the crystal phase composition, particles size and morphology of the product was investigated. The result shows that anatase TiO₂ with non-uniform grain size is obtained in distilled water. The ability to retard the anisotropic growth of anatase is as follows: n-butyl alcohol>propane diacid>ethylenediamine. Under the same experiment condition, rutile, anatase and mixed crystallite of anatase and rutile TiO₂ powders are obtained in HCl, H₂SO₄ and HNO₃ medium, respectively. The result of photocatalytic degradation methyl orange shows that the photocatalytic activity of mixed crystallite of anatase and rutile TiO₂ powders is higher than that of the pure anatase TiO₂ powders. The photocatalytic
activity of pure rutile TiO₂ powders is worst.

Key words: hydrothermal synthesis, TiO₂ nanopowders, medium, photocatalytic