TiO2:Mn nanoparticles as enhanced UVA absorption, photostable sunscreen components

Titanium oxide (TiO2) nanoparticles are added to sunscreens as they have broad absorbance across the whole UV spectrum. Although photostable, TiO2 nanoparticles can de-excite via surface states giving rise to reactive oxygen species (ROS) formation within the sunscreen formulation. An increased ROS load can degrade organic components within the sunscreen, such as UV absorbers or anti-oxidants, decreasing efficacy during topical use. Modifying the TiO2 host lattice with manganese ions has three principal beneficial effects for application as a sunscreen component. Firstly, Mn-O states act as deexcitation centres for photoexcited charges. This almost completely eliminates production of free radicals via the particle surface. Secondly, manganese oxide associated with the particle surface acts to scavenge ROS generated in other formulation components, thus decreasing component degradation. Thirdly, Mn-O anti-bonding states increase the intrinsic UVA absorbance of TiO2:Mn nanoparticles. The net result of these benefits is that sunscreens formulated with TiO2:Mn nanoparticles show enhanced UVA absorption and extended photostability during topical use.