Hydrothermal Synthesis of Metal Oxide Nanoparticles in Supercritical Water

Abstract

This paper summarizes specific features of supercritical hydrothermal synthesis of metal oxide particles. Supercritical water allows control of the crystal phase, morphology, and particle size since the solvent's properties, such as density of water, can be varied with temperature and pressure, both of which can affect the supersaturation and nucleation. In this review, we describe the advantages of fine particle formation using supercritical water and describe which future tasks need to be solved.

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…Performing the reactions in such aqueous solutions at high temperature and pressure conditions produces high crystalline MNPs with uniform small size. A review on hydrothermal synthesis of metal oxide nanoparticles has been published, [80] which gives detailed information on what exactly happens within hydrothermal process. Herein we briefly explain the basic mechanism behind this method.…”

Synthesis of Polyhedral Magnetite Particles by Hydrothermal Process under High Pressure Condition

“…Figure 1 shows the general work of magnetite particle synthesis by hydrothermal process. Next, the solution was transferred into a reactor (8.8 ml of volume, SUS 316, AKICO, Japan), sealed and heated at 250 °C and 290 °C [15][16][17]. The reactor was allowed to work at a temperature of 300 °C and a pressure of 30 MPa.…”

“…As mentioned above, the hydrothermal process is simple and can easily produce highly crystalline metal oxides, including magnetite particles, where the size and morphology of the metal oxides particles are prone to be restrained by changing the conditions of synthesis [8,16]. Hayashi and Hakuta [16] explain that the size of metal oxide particles can be controlled by nucleation and grain growth processes during hydrothermal treatment.…”

“…Hayashi and Hakuta [16] explain that the size of metal oxide particles can be controlled by nucleation and grain growth processes during hydrothermal treatment. They state that the temperature and pressure in hydrothermal conditions can be modified in subcritical water to accomplish control of the solvent media during nucleation and crystallization of metal oxide particles.…”

“…These figures show that the hydrothermal process in which the chemical reactions can take place in aqueous media under high temperature and pressure allows to generate iron oxide particles due to the change in dielectric constant. Hayashi and Hakuta [16] explain that synthesis by hydrothermal method respects the heterogeneous particle synthesis or particle growth in the presence of solvent liquids or mineralizers under high temperature and high pressure from materials that are insoluble at temperatures and pressures lower than 100 °C and 1 atm, respectively. At these conditions, the water acts as a reactant for inorganic nanoparticle synthesis.…”