Inactivation of bacterial endospores by photocatalytic nanocomposites

A novel biocidal photocatalytic nanocomposite, composed of TiO2 and multi-walled carbon nanotubes (MWNTs), was synthesized via wet chemistry followed by a heat treatment. Uniform anatase coatings on MWNTs were successfully obtained with a thickness of a few nanometers. The nanostructure of the composite was determined by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The needle-like shape of the nanocomposite provided more than three times higher photocatalytic specific surface area than commercial TiO2 nanoparticles (Degussa P25) when dispersed in water. Moreover, under ultraviolet (UV) radiation the excited electrons can be trapped at the interface between the TiO2 layer and MWNTs and they can also be scavenged through the conductive graphitic layers. Thus, an intense photochemical reaction yielding a powerful biocide can be expected. Irradiating bacterial endospores (Bacillus cereus) with solar UV lamps in presence of the novel photocatalyst successfully inactivated the spores while solar UV lamps only or solar UV Lamps with Degussa P25 showed no significant inactivating behavior. Performance of photocatalytic nanocomposites was assessed based on time to achieve 90% inactivation of spores (LD90) and also in terms of time required to achieve a 1.0 log10 reduction of spores in the tail region of the inactivation curve.