ZnO/TiO₂ composites for photocatalytic inactivation of Escherichia coli

ZnO/TiO₂ composite was synthesized from zinc nitrate and anatase TiO₂ by using the incipient wet impregnation method followed by calcination at 350°C for 3h. These samples were characterized through several characterization techniques. XRD peaks confirms the presence of single anatase phase of titania in the 3 and 6wt% ZnO/TiO₂ composite, whereas in all other composites both anatase titania and zinc oxide phases were found. UV-visible (diffuse) reflectance spectra show titania and ZnO absorbs in the ultraviolet (UV) region whereas ZnO/TiO₂ absorbs both UV and visible light. The shift in absorbance facilitates ZnO/TiO₂ composites to exhibit photocatalytic activity under UV-visible light irradiation. FE-SEM and TEM analysis reveals that the particle size of ZnO is around 0.2μm and its size significantly reduced to 25nm when it is deposited on TiO₂ support. The E. coli inactivation study shows that ZnO/TiO₂ composites exhibit high inactivation compared to ZnO and titania under UV alone and the combination of both UV-visible. With the increasing loading concentration of ZnO, the photocatalytic inactivation potential of ZnO/TiO₂ composites also increases. The E. coli inactivation of ZnO/TiO₂ is explained based on the photocatalytically generated ROS, ZnO dissolution and charge carrier separation due to hybrid structures.