Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

Abstract

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 (TiO ₂) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO ₂ 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 TiO ₂ NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO ₂ NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO ₂ NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO ₂ 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 TiO ₂ NPs and Cu-doped TiO ₂ 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 TiO ₂ nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.