Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Tetravalent cerium (Ce(IV)) is known to be one of the most commonly-used oxidizing agents in various chemical studies, such as organic synthesis. Furthermore, it recently draws considerable attention to its catalytic applications to water oxidation or biotechnology. As a versatile catalytic oxidant, Ce(IV) is often employed in the form of aqueous solution. Therefore, fundamental knowledge of Ce(IV) species in aqueous solution is essential not only for discussing its functionality in the applied systems, but also for further developing its applications; nevertheless, the nature of Ce(IV) species in aqueous solution is far less well understood. In this context, the present study aims to elucidate the chemical speciation and complex structure of soluble Ce(IV) species formed on hydrolysis, which is the most fundamental reaction of metal cations in the aqueous solution system, by employing X-ray absorption spectroscopy (XAS), high energy solution X-ray scattering (HEXS), and dynamic light scattering (DLS).
The obtained XAS data have clearly showed the systematic growing of Ce–Ce bonding in the soluble Ce(IV) hydrolytic species, as an increase in pH. This indicates that some soluble polymeric or cluster complexes are formed on the hydrolysis of Ce(IV). The diffraction patterns of Ce(IV) hydrolytic species have further revealed that the observed polymeric or cluster complex has a crystalline structure, not the amorphous one. The results of the detailed analysis on XAS and HEXS data will be presented on site, along with the DLS data for discussing the size of Ce(IV) hydrolytic polymers/clusters and its aging effect.