Kinetics study for photodegradation of methylene blue dye by titanium dioxide powder prepared by selective leaching method

The kinetics of photodegradation of methylene blue (MB) dye by titanium dioxide (TiO 2 ) powder were investigated using elementary reactions. TiO 2 powders were prepared by a selective leaching method consisted of processes of CaHPO 4 precipitation, heat treatment, and acid leaching to obtain high crystalline anatase. The obtained TiO 2 samples had wide ranges of specific surface areas (5–23 m 2 /g) and densities of Ti 3+ defects (90–480×10 12 spin/g) without a significant change in the anatase phase ratio ranging 0.86–0.91 in mass ratio. The MB photodegradation rate was expressed as functions of specific surface area and density of Ti 3+ defects under the experimental condition that the photodegradation rate was proportional to UV irradiation intensity and the adsorbed MB amount was proportional to specific surface area. A proposed equation for calculation of photodegradation ate demonstrated greater effect of specific surface area than density of Ti 3+ defects for MB photodegradation.