Structural and Photoprotective Characteristics of Zn-Ti, Zn-Al, and Mg-Al Layered Double Hydroxides—A Comparative Study

Abstract

Organic UV filters have been known to generate harmful by-products and undergo photoreactive degradation, which ultimately poses a great threat to consumers using sunscreen products. Inorganic UV filters such as TiO2 and ZnO, although considered safer options, are not without threat considering their photocatalytic nature and ability to generate reactive oxygen species. A study was conducted to identify the influence of different metal ions on the photochemical properties of layered double hydroxides (LDH), Zinc-Titanium LDH (Zn-Ti LDH), Zinc-Aluminium LDH (Zn-Al LDH), and Magnesium- Aluminium LDH (Mg-Al LDH) and their prospects in photoprotection. The photocatalytic properties of the LDH were analyzed and compared to TiO2 and ZnO. The intermediate band gaps of Zn-Ti (3.72 eV) and Zn-Al LDH (3.3 eV) proved favorable and safer for the use of these LDH in cosmetic formulations as they offer lower photo-reactivity when compared to cosmetic grade ZnO and TiO2. The in vitro SPF values obtained for formulations containing 2 wt% Zn-Ti and 2 wt% Zn-Al LDH showed promise, with both samples claiming “broad spectrum” protection and valid claims of UVA protection.