Abstract
In this article, recent researches on ionic hydration in subcritical and supercritical water with neutron diffraction (ND) and X-ray absorption spectroscopy (XAS) were introduced. ND with an isotopic substitution technique is one of the powerful methods to reveal the hydration structure of ions in electrolyte solutions. XAS can also observe the hydration structure of ions and ion-pair formation at a lower concentration of the ions. The fundamental information on ionic hydration is important to understand the underlying mechanism of formation of metal oxide nanoparticles from electrolyte solutions in subcritical and supercritical water, which is expected as a new fabrication technique of nanoparticles in the engineering field.
