A Comparative Study of Cerium(III) and Cerium(IV) Phosphates for Sunscreens.

Crystalline cerium(III) phosphate (CePO 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 4 , Ce(PO 4 )(HPO 4 ) 0.5 (H 2 O) 0.5 , and CePO 4 /CeO 2 composites. Both the sun protection factor and protection factor against UV-A radiation of the materials were determined. Ce(PO 4 )(HPO 4 ) 0.5 (H 2 O) 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 4 . Composites containing both cerium dioxide and CePO 4 demonstrated higher sun protection factors (up to 1.8) than individual CePO 4 . When compared with the TiO 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 4 , Ce(PO 4 )(HPO 4 ) 0.5 (H 2 O) 0.5 , and nanocrystalline ceria were all non-toxic. The results of this comparative study indicate that cerium(IV) phosphate Ce(PO 4 )(HPO 4 ) 0.5 (H 2 O) 0.5 is more advantageous for use in sunscreens than either cerium(III) phosphate or CePO 4 /CeO 2 composites, due to its improved UV-shielding properties and low photocatalytic activity.