Optical, structural and semiconducting properties of Mn doped TiO2 nanoparticles for cosmetic applications

Titanium dioxide (TiO2) nanoparticles, have been routinely used in cosmetic and sunscreen applications,
due to their ability to absorb in the UV spectrum. Nevertheless, one of the main disadvantages has been
the generation of reactive oxygen species (ROS), especially the hydroxyl radical, upon photoexcitation of
titania. In this work, we investigate TiO2 nanoparticles doped with 0.6–0.7% manganese (Mn), based in
the more stable rutile polymorph of titania. In particular, while the anatase crystal form has the ability
to destroy almost any organic matter under UV illumination, rutile is less photoreactive, and with Mn
doping its photoactivity is reduced further. In particular, we study its optical, structural and semiconducting properties via the Seebeck effect and show that the material displays p-type characteristics.
This is very significant because it shifts the energy levels with respect to formation of hydroxyl free radicals. This ensures that for Mn doped p-type titania it is not energetically possible for the hole created in
the valence band by photoexcitation to create an OH. free radical and this may explain its low photoreactivity. It also means that this material can act as a very effective scavenger for hydroxyl free radicals