Preparation and photocatalytic activity of TiO2 powders from titanium citrate complex using two-step hydrothermal treatments

White, almost carbon-free TiO2 powders were prepared from a titanium citrate complex ((NH4)4[Ti2(C6H4O7)2(O2)2]·4H2O) using a two-step hydrothermal treatment. The product yield, carbon contamination, and crystalline phase of TiO2 depended on both the temperature and pH value for each treatment. Titanium was precipitated as a solid phase (H2Ti2O5·H2O) using the first hydrothermal treatment in the basic condition (pH = 12) at temperatures less than 150 °C. Then white rutile or anatase powder was crystallized using the second hydrothermal treatment at 200 °C. By changing the pH condition of the second hydrothermal treatment, rutile and anatase were synthesized selectively. The photocatalytic decomposition activity of obtained rutile powder for gaseous 2-propanol under visible light was increased by Cu-grafting.