Visible light photo-induced antibacterial activity of CNT–doped TiO2 thin films with various CNT contents

Carbon nanotube (CNT)-doped TiO2 thin films with various CNT contents were synthesized by sol–gel method for visible light photoinactivation of Escherichia coli bacteria. Post annealing of the CNT–doped TiO2 thin films at 450 °C resulted in anatase TiO2 and formation of Ti–C and Ti–O–C carbonaceous bonds in the film. By increasing the CNT content, the thin films could further inactivate the bacteria in the dark. Meanwhile, as the CNT content increased from zero to 40 wt% the effective optical band gap energy of the CNT–doped TiO2 thin films annealed at 450 °C decreased from 3.2–3.3 to less than ∼2.8 eV providing light absorption in the visible region. Concerning this, visible light photoinactivation of the bacteria on the surface of the films was found to be optimum for 20 wt% CNT content. The CNT–doped TiO2 thin films annealed at 450 °C showed a further improved photoinactivation of bacteria than the films annealed at 100 °C. The improvement in the visible light photocatalytic performance was assigned to the charge transfer through the carbonaceous bonds formed between the TiO2 and the CNT content of the films annealed at 450 °C, in contrast to the thin films annealed at 100 °C which contained no such effective bonds.