Visible-light active titanium dioxide nanomaterials with bactericidal properties

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO₂) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO₂ NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO₂ NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO₂ NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO₂ NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO₂ NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO₂ NPs and Cu-doped TiO₂ NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO₂ nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.