Effect of low Fe3+ doping on characteristics, sonocatalytic activity and reusability of TiO2 nanotubes catalysts for removal of Rhodamine B from water

Highlights: ► Preparation of Fe-TiO2 nanotubes using sol–gel and hydrothermal methods. ► Activity in the oxidation of Rhodamine B in water under ultrasonic irradiation. ► Band gap energies, surface areas and active surface oxygen vacancies. ► Fe-doped TiO2 nanotubes can be reused for up to 4 cycles. ► Fe:Ti of 0.005 showed the highest sonocatalytic activity. - Abstract: Fe-doped titanium dioxide (TiO2) nanotubes were prepared using sol–gel followed by hydrothermal methods and characterized using various methods. The sonocatalytic activity was evaluated based on oxidation of Rhodamine B under ultrasonic irradiation. Iron ions (Fe3+) might incorporate into the lattice and intercalated in the interlayer spaces of TiO2 nanotubes. The catalysts showed narrower band gap energies, higher specific surface areas, more active surface oxygen vacancies and significantly improved sonocatalytic activity. The optimum Fe doping at Fe:Ti = 0.005 showed the highest sonocatalytic activity and exceeded that of un-doped TiO2 nanotubes by a factor of 2.3 times. It was believed that Fe3+ doping induced the formation of new states close to the valence band and conduction bands and accelerated the separation of charge carriers. Leached Fe3+ could catalyze Fenton-like reaction and led to an increase in the hydroxyl radical (·OH) generation. Fe-doped TiO2 nanotubes could retain high degradation efficiency even after being reused for 4 cycles with minimal loss of Fe from the surface of the catalyst.