Underestimated Properties of Nanosized Amorphous Titanium Dioxide

Abstract

Titanium dioxide is one of the best described photosensitive materials used in photocatalysis, solar cells, self-cleaning coatings, and sunscreens. The scientific and industrial attention has been focused on the highly photoactive crystalline phase of titanium dioxide (TiO2). It is commonly accepted that the smaller TiO2 particles, the higher photoactivity they present. Therefore, titanium dioxide nanoparticles are massively produced and widely used in everyday products. The amorphous phase of titanium dioxide has been treated with neglect, as the lack of its photocatalytic properties is assumed in advance. In this work, the complex experimental proof of the UV-protective properties of the nano-sized amorphous TiO2 phase is reported. Amorphous n-TiO2 is characterized by photocatalytic inactivity and, as a consequence, low cytotoxicity to fibroblast cells. When exposed to UV radiation, cells with amorphous TiO2 better survive under stress conditions. Thus, we postulate that amorphous n-TiO2 will be more beneficial and completely safe for cosmetic applications. Moreover, the results from in situ FTIR studies let us correlate the low toxicity of amorphous samples with low ability to form hydroperoxo surface species.