Sol–gel synthesis of Al-doped TiO2 nanoparticles as UV filters with diminished photocatalytic activity for the application in sunscreen products.

Al-doped TiO₂ nanoparticles with different Al contents were prepared by a simple sol–gel method and were applied as UV filters for sunscreen products. These materials were characterized by XRD, Raman, FESEM, N₂ adsorption-desorption, WDXRF, FTIR, and UV–visible diffuse reflectance spectroscopy. Their color and photocatalytic activity were evaluated through CIE L*a*b* colorimetric method and the degradation of methylene blue under UV light, respectively. According to the results, the insertion of Al³⁺ ions into TiO₂ successfully reduced the photocatalytic performance via the decrease in the mass fraction of rutile phase, the decrease in surface hydroxyl groups, and the increase in dislocation density. These Al-doped powders display better UV absorption than the undoped TiO₂, which can be attributed to the increase in anatase content and the decrease in particle size due to Al-doping. Consequently, the sunscreen using 4 mol% Al-doped TiO₂ reveals the enhanced SPF value and improved color stability, which are suitable for UV protection cosmetics. Highlights: Preparation of Al-doped TiO₂ nanoparticles by sol-gel method. Al-doping successfully reduces the photocatalytic activity of TiO₂. Al-doped TiO₂ nanoparticles show high UV absorption and bright ivory-white color. Sunscreen using Al-doped TiO₂ display high SPF values and high color stability. Al-doped TiO₂ nanoparticles can be safety used as UV filters in sunscreens. [ABSTRACT FROM AUTHOR]