This paper aimed at enhancing the photoactivity of nano-TiO_2, disclosing the nature of effects of doping on nano-TiO_2. According to the current problems such as low quantum efficiency, limited available wavelength rang, resulted from the practical using of photocatalysis, nano-particles of TiO_2 doped with various transition metal ions and rare earth metal ions were prepared through wet impregnation method. Doped and pure TiO_2 samples were characterized by X-ray diffraction (XRD), BET surface are...