Sn-doped Fe2O3 was synthesized by hydrothermal method on cleaned FTO substrate. Briefly, precursor solution containing 0.15 M FeCl3•6H2O and 1.0 M NaNO3 was transferred to Teflonlined stainless-steel autoclave. FTO was placed at the bottom of the autoclave with conductive side facing up, and heat-treatment was conducted at 95 °C for 4 h to form β-FeOOH nanowires on the FTO substrate. After heating process, β-FeOOH was sintered in ambient air condition at 550 °C for 2 h (ramping rate of 4 K min -1 ) and then annealed at 800 °C for 20 min.