A Comparative Study of Cerium Phosphates for Sunscreens

Crystalline cerium(III) phosphate (CePO[sub.4]), cerium(IV) phosphates, and nanocrystalline ceria are considered to be promising components of sunscreen cosmetics. This paper reports on a study in which, for the first time, a quantitative comparative analysis was performed of the UV-shielding properties of CePO[sub.4], Ce(PO[sub.4])(HPO[sub.4])[sub.0.5](H[sub.2]O)[sub.0.5], and CePO[sub.4]/CeO[sub.2] composites. Both the sun protection factor and protection factor against UV-A radiation of the materials were determined. Ce(PO[sub.4])(HPO[sub.4])[sub.0.5](H[sub.2]O)[sub.0.5] was shown to have a sun protection factor of 2.9, which is comparable with that of nanocrystalline ceria and three times higher than the sun protection factor of CePO[sub.4]. Composites containing both cerium dioxide and CePO[sub.4] demonstrated higher sun protection factors (up to 1.8) than individual CePO[sub.4]. When compared with the TiO[sub.2] Aeroxide P25 reference sample, cerium(III) and cerium(IV) phosphates demonstrated negligible photocatalytic activity. A cytotoxicity analysis performed using two mammalian cell lines, hMSc and NCTC L929, showed that CePO[sub.4], Ce(PO[sub.4])(HPO[sub.4])[sub.0.5](H[sub.2]O)[sub.0.5], and nanocrystalline ceria were all non-toxic. The results of this comparative study indicate that cerium(IV) phosphate Ce(PO[sub.4])(HPO[sub.4])[sub.0.5](H[sub.2]O)[sub.0.5] is more advantageous for use in sunscreens than either cerium(III) phosphate or CePO[sub.4]/CeO[sub.2] composites, due to its improved UV-shielding properties and low photocatalytic activity.