Chapter 11.1.5 - Supercritical Hydrothermal Synthesis

Abstract

This chapter describes specific features of a supercritical hydrothermal synthesis method. First, the some characteristic properties of supercritical water are summarized, and then the mechanism of supercritical hydrothermal synthesis is explained. Higher reaction rate and lower solubility are the key factors to synthesize nanosize crystals in a short reaction time. The flow reaction system to achieve rapid heating is explained. Some commercialized process is introduced. This method is useful to synthesize organic molecule modified nanoparticles (NPs). Since the organic molecules and metal–salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic–inorganic conjugate NPs can be synthesized under the condition. The mechanism of the conjugate forming reaction is explained. NPs’ superlattice structure and bioconjugate materials are also formed under the condition. The hybrid NPs show high affinity for the organic solvent or the polymer matrix, which leads to fabricate the organic–inorganic hybrid nanomaterials with the trade-off function (superhybrid nanomaterials). One of the applications is to fabricate a heat-conductive flexible hybrid-polymer sheet. By the surface modification of BN particles by supercritical method, affinity of BN and polymers could be improved so that high BN content of hybrid materials, thus high thermal conductivity materials, could be synthesized.