Photocatalytic property of Fe2O3 nanograin chains coated by TiO2 nanolayer in visible light irradiation

The visible light photocatalytic activity of alpha-Fe2O3 nanograin chains coated by anatase TiO2 nanolayer, as a photocatalyst thin film for inactivation of Escherichia coli bacteria, was investigated for the solutions containing 106 colony forming units per milliliter of the bacteria, without and with H2O2 (60 mu M). Thin films of the alpha-Fe2O3 nanograins with the grain size of 40-280 nm were grown on glass substrates by post-annealing of the thermal evaporated Fe3O4 thin films at 400 degrees C in air. The TiO2 layer with thickness of about 20 nm was coated on the nanograins by dipping the Fe2O3 thin films in a prepared TiO2 sol and re-annealing them at 400 degrees C in air. The antibacterial activity of the alpha-Fe2O3 nanograins with the optical band-gap of 2.1 eV (so better activity than the TiO2 in the visible light) was doubled in presence of the low-concentration H2O2. Deposition of the TiO2 nanolayer on the alpha-Fe2O3 nanograins resulted in 24 and 54% (59 and 276%) improvement in the photocatalytic activity of the TiO2/alpha-Fe2O3 thin film than the bare alpha-Fe2O3 nanograin (TiO2) thin film, for the solution without and with H2O2, respectively. In addition, for the TiO2/alpha-Fe2O3 thin film, the bactericidal activity was improved by a factor of 2.5 in presence of the low-concentration H2O2 as compared to the case without H2O2. A mechanism was proposed based on which the electrons excited in the photocatalytic process were directly or indirectly absorbed by H2O2 to produce active OH-center dot radicals for promoting inactivation of the bacteria. (C) 2009 Elsevier B.V. All rights reserved.