Synthesis and Physico-chemical Properties of Crystalline Cerium(IV) Orthophosphates

Currently, the class of crystalline cerium(IV) orthophosphates has only 14 reliably characterized structures, which is significantly less than the number of representatives of classes of their chemical analogues, for example, thorium or uranium phosphates. Nevertheless, the list of their beneficial properties, such as high sorption capacity, ion exchange properties, chemical and thermal stability, biocompatibility and significant photoprotective activity determine their potential application in the fields of radiation safety and sunscreen cosmetics. The aim of this work was to study the patterns of formation of crystalline cerium(IV) orthophosphates from amorphous cerium phosphate gels under hydrothermal treatment and to analyze the practical potential of this class of compounds. As a result of the work, new crystalline cerium(IV) orthophosphates of the composition Na2Ce(PO4)2·0.55H2O, KCe2(PO4)3, RbCe2(PO4)3, Rb2Ce(PO4)2·H2O were synthesized and characterized. In addition, a number of new double cerium(IV) orthophosphates containing divalent metal cations (Ca, Zn, Sr and Cd) were obtained and characterized by different structures. In terms of strontium nitrate, a method for immobilizing radioactive waste has been developed based on the hydrothermal treatment of cerium phosphate gels in the appropriate medium gels. For the first time, the comparative analysis of UV-protective properties of cerium orthophosphates (III and IV) and composites CePO4/CeO2 was conducted. It is concluded that cerium(IV) orthophosphate CeIV(PO4)(HPO4)0.5(H2O)0.5 is more preferable for applications in sunscreen cosmetics. It is demonstrated that the new compounds with the composition KCe2(PO4)3 and Na2Ce(PO4)2·0.55H2O have close photoprotective properties with CeO2 and the compound NH4Ce2(PO4)3 along with a pronounced photoprotective effect and no toxicity to the human stem cells exhibits cytotoxicity to B16/F10 line mouse melanoma cells.