Crystalline cerium(III) phosphate (CePO₄), 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 CePO₄, Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5, and CePO₄/CeO₂ composites. Both the sun protection factor and protection factor against UV-A radiation of the materials were determined. Ce(PO₄)(HPO₄)_0.5(H₂O)_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 CePO₄. Composites containing both cerium dioxide and CePO₄ demonstrated higher sun protection factors (up to 1.8) than individual CePO₄. When compared with the TiO₂ 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 CePO₄, Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5, and nanocrystalline ceria were all non-toxic. The results of this comparative study indicate that cerium(IV) phosphate Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5 is more advantageous for use in sunscreens than either cerium(III) phosphate or CePO₄/CeO₂ composites, due to its improved UV-shielding properties and low photocatalytic activity.

In this study, organo-inorganic nanohybrids LHGd-MTSPP with enzyme-like activity were prepared by in situ intercalation of anionic 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin and its complexes with Zn(II) and Pd(II) (MTSPP, M = 2H, Zn(II) and Pd(II)) into gadolinium layered hydroxide (LHGd). The combination of powder XRD, CHNS analysis, FT-IR, EDX, and TG confirmed the layered structure of the reaction products. The basal interplanar distances in LHGd-MTSPP samples were 22.3–22.6 Å, corresponding to the size of an intercalated tetrapyrrole molecule. According to SEM data, LHGd-MTSPP hybrids consisted of individual lamellar nanoparticles 20–50 nm in thickness. The enzyme-like activity of individual constituents, LHGd-Cl and sulfoporphyrins TSPP, ZnTSPP and PdTSPP, and hybrid LHGd-MTSPP materials, was studied by chemiluminescence analysis using the ABAP/luminol system in phosphate buffer solution. All the individual porphyrins exhibited dose-dependent antioxidant properties with respect to alkylperoxyl radicals at pH 7.4. The intercalation of free base TSPP porphyrin into the LHGd preserved the radical scavenging properties of the product. Conversely, in LHGd-MTSPP samples containing Zn(II) and Pd(II) complexes, the antioxidant properties of the porphyrins changed to dose-dependent prooxidant activity. Thus, an efficient approach to the design and synthesis of advanced LHGd-MTSPP materials with switchable enzyme-like activity was developed.

A comparative study of the redox behaviour of nanocrystalline isostructural ACe ₂ (PO ₄ ) ₃ (A = NH ⁺ ₄ , K ⁺ , Rb ⁺ ) double ceric phosphates was performed. It has been established that with respect to alkylperoxyl radicals or hydrogen peroxide as reactive oxygen species, all the double ceric phosphates acted as antioxidants or prooxidants, respectively. The antioxidant activity towards alkylperoxyl radicals was found to be the higher for the phosphates containing potassium or rubidium. Notably, for KCe ₂ (PO ₄ ) ₃ and RbCe ₂ (PO ₄ ) ₃ an inverse dependence of catalytic activity on concentration in the reaction with H ₂ O ₂ was found, in contrast to NH ₄ Ce ₂ (PO ₄ ) ₃ . The redox behaviour of nanoscale cerium dioxide used for comparison was similar to that of ammonium ceric phosphate, but significantly lower in absolute values. This was explained by the suppressive effect of phosphate anions presented in the buffer solutions.