The sprayed TiO2 spheres on the aluminum target were carefully collected and dried in air overnight in order to let the Ti precursors completely hydrolyzed. The dried spheres were put in a Teflon-sealed steel autoclave with a mixture of ethanol–water solution (20 ml:10 ml) containing 1.0 ml ammonia or not inside. The hydrothermal reaction was performed at 160◦C for 24 h.