Synthesis of titania/carbon nanotube heterojunction arrays for photoinactivation of E. coli in visible light irradiation

TiO₂/multi-wall carbon nanotube (MWNT) heterojunction arrays were synthesized and immobilized on Si(0 0 1) substrate as photocatalysts for inactivation of Escherichia coli bacteria. The vertically aligned MWNT arrays were grown on ∼5 nm Ni thin film deposited on the Si by using plasma enhanced chemical vapor deposition at 650 °C. Then, the MWNTs were coated by TiO₂ using dip-coating sol-gel method. Post annealing of the TiO₂/MWNTs at 400 °C resulted in crystallization of the TiO₂ coating and formation of Ti-C and Ti-O-C carbonaceous bonds at the heterojunction. The visible light-induced photoinactivation of the bacteria increased from MWNTs to TiO₂ to TiO₂/MWNTs, in which the bacteria could even slightly breed on the MWNTs. In addition, the TiO₂/MWNTs annealed at 400 °C showed a highly improved antibacterial activity than the TiO₂/MWNTs annealed at 100 °C. The excellent visible light-induced photocatalytic efficiency of the TiO₂/MWNTs/Si film annealed at 400 °C was attributed to formation of the carbonaceous bonds at the heterojunction, in contrast to the 100 °C annealed TiO₂/MWNTs/Si sample which had no such effective bonds.