Improving the Sunscreen Properties of TiO₂ through an Understanding of Its Catalytic Properties

The use of particulate titanium dioxide (TiO₂) as an active sunscreen ingredient has raised concerns about potential risks from TiO₂-mediated free radical formation. To date, remediation attempts have concentrated on reducing the yield of free radical generation by TiO₂ upon sunlight exposure. The problem with this approach is that given the band gap in TiO₂, production of radical and the ensuing reactive oxygen species (ROS) is completely normal. Our strategy is based on a nontoxic, biocompatible shell that neutralizes the free radicals by scavenging them with natural antioxidants before they exit the particle. The new lignin@TiO₂ composites preserve the scattering and absorption properties of TiO₂ because the particles retain their nanoscale dimensions as preferred by the cosmetic industry. Although the target properties for photocatalysis and sun-protection applications are opposite, we argue that exactly the same knowledge is required to optimize either one.