High performance non-transition metal oxide based nano UVB filters for sunscreen applications

There are concerns regarding the safety of transition metal oxide nanoparticles, such as TiO 2 and ZnO, in health and cosmetic products, including sunscreens, due to their potential cytotoxic and genotoxic effects under ultraviolet (UV) exposure (320–400 nm). This challenge highlights the need for research and development of alternative UV filters that are both non-photocatalytic and biocompatible. In this study, the in vitro sun protection factor (SPF), cytotoxicity, phototoxicity, and photoluminescence properties of cerium(III) phosphate–based nanomaterials were systematically evaluated, including pristine CePO 4 , surface-functionalized CePO 4 and CePO 4 -CeO 2 composite nanoparticles. A silane coupling agent was employed for the first time to functionalize CePO 4 , facilitating the attachment of additional compounds to enhance its optical properties. Among the investigated materials, the CePO 4 -CeO 2 composite exhibited an SPF value of 3.92 ± 0.3, comparable to commercial TiO 2 (rutile) and nearly twice that of pure CePO 4 . Unlike TiO 2 , cerium (III) phosphate-based compounds demonstrated minimal photocatalytic activity, indicating superior photostability. Cytotoxicity assessment using human HaCaT skin cells confirmed their biocompatibility across a broad concentration range. Additionally, phototoxicity analysis—reported here for the first time for Ce III PO 4 -based compounds— demonstrated enhanced cell proliferation post-UV exposure, indicating photoprotective behaviour. Surface functionalization improved UV absorbance without compromising low photocatalytic nature of CePO 4 significantly, suggesting further optimization potential through the attachment of organic or inorganic molecules.