Crystallization Pathways of Cerium(IV) Phosphates Under Hydrothermal Conditions: A Search for New Phases with a Tunnel Structure

Amorphous and crystalline cerium(IV) phosphates: biocompatible ROS-scavenging sunscreens

This paper reports on a comprehensive study of the UV-shielding properties (namely, the sun protection factor and the factor of protection against UV-A radiation) and cytotoxicity (including photocytotoxicity) of amorphous and crystalline cerium(IV) phosphates. It has been shown that cerium(IV) phosphate NH₄Ce₂(PO₄)₃ is characterised by UV-shielding properties that are comparable to those of nanocrystalline TiO₂ and CeO₂. Moreover, cerium(IV) phosphates did not show toxicity towards cell cultures of NCTC L929 line mouse fibroblasts and human mesenchymal stem cells, in a wide range of concentrations, and even enhanced the proliferative activity of the latter. In a model study of the photoprotective properties of cerium(IV) phosphates on human mesenchymal stem cells, the pronounced protective effect of NH₄Ce₂(PO₄)₃ was observed, which was comparable to the shielding action of nanocrystalline CeO₂. The results have shown that tetravalent cerium phosphates can be considered as promising UV-filters for sunscreen applications.

Meet the Cerium(IV) Phosphate Sisters: CeIV (OH)PO4 and CeIV 2 O(PO4 )2

Two new cerium(IV) phosphates were obtained: cerium(IV) hydroxidophosphate, Ce(OH)PO₄ , and cerium(IV) oxidophosphate, Ce₂ O(PO₄ )₂ , which were shown to complement the classes of isostructural compounds M(OH)PO₄ and R₂ O(PO₄ )₂ , where M=Th, U and R=Th, U, Np, Zr. Ce₂ O(PO₄ )₂ oxidophosphate is formed by elimination of H₂ O from the crystal structure of Ce(OH)PO₄ during its thermal decomposition. The structures of Ce(OH)PO₄ and Ce₂ O(PO₄ )₂ are related to each other with the same Cmce space group and similar unit cell parameters (a=6.9691(3) Å, b=9.0655(4) Å, c=12.2214(4) Å, V=772.13(8) ų , Z=8; a=7.0220(4) Å, b=8.9894(5) Å, c=12.544(1) Å, V=791.8(1) ų , Z=4, respectively).

Synthesis of Micro- and Nanoparticles in Sub- and Supercritical Water: From the Laboratory to Larger Scales

The use of micro- and nanoparticles is gaining more and more importance because of their wide range of uses and benefits based on their unique mechanical, physical, electrical, optical, electronic, and magnetic properties. In recent decades, supercritical fluid technologies have strongly emerged as an effective alternative to other numerous particle generation processes, mainly thanks to the peculiar properties exhibited by supercritical fluids. Carbon dioxide and water have so far been two of the most commonly used fluids for particle generation, the former being the fluid par excellence in this field, mainly, because it offers the possibility of precipitating thermolabile particles. Nevertheless, the use of high-pressure and -temperature water opens an innovative and very interesting field of study, especially with regards to the precipitation of particles that could hardly be precipitated when CO2 is used, such as metal particles with a considerable value in the market. This review describes an innovative method to obtain micro- and nanoparticles: hydrothermal synthesis by means of near and supercritical water. It also describes the differences between this method and other conventional procedures, the most currently active research centers, the types of particles synthesized, the techniques to evaluate the products obtained, the main operating parameters, the types of reactors, and amongst them, the most significant and the most frequently used, the scaling-up studies under progress, and the milestones to be reached in the coming years.