The pristine-TiO2 array was grown on a Ti mesh (TM) substrate through a hydrothermal method. Firstly, a piece of clean TM (3 cm × 3 cm) was steeped into a 40 mL aqueous solution including 5 M NaOH for 1 hour. And then it is transferred into a 50 mL Teflon-lined stainless steel autoclave, and reacted for 20 h at 200℃ in the oven.