Vertically aligned ZnO@CdS nanorod heterostructures for visible light photoinactivation of bacteria

Vertically aligned ZnO@CdS nanorod heterostructure films with various loadings of CdS nanoparticle shell were synthesized and applied in photoinactivation of Escherichia coli bacteria under visible light irradiation. While neither the bare ZnO nanorods (with band-gap energy (E-g) of similar to 3.28 eV) under visible light irradiation nor the nanorod heterostructures in dark exhibited any significant antibacterial activity, the ZnO@CdS nanorod heterostructures (with E-g similar to 2.5-2.6 eV) could successfully inactivate the bacteria under visible light irradiation. Furthermore, it was found that an optimum loading of the CdS shell (corresponding to the effective thickness less than similar to 15 nm) is required to achieve a complete inactivation of the bacteria after 24 h visible light irradiation at room temperature. Using X-ray photoelectron spectroscopy, the lower photoinactivation efficiencies of the ZnO@CdS nanorod heterostructure at CdS thicknesses lower and higher than the optimum one were assigned to lower amounts of CdS nanoparticles and OH bonds (substantially existed on the hydrothermally synthesized ZnO nanorods) which are responsible for absorption of the visible light and production of hydroxyl radicals, respectively. Water contact angle measurements showed that the sample with more surface OH groups has a more hydrophilic surface and so more antibacterial activity. (C) 2013 Elsevier B.V. All rights reserved.