Thermodynamic analysis of hydrothermal synthesis of nanoparticles

Abstract

The hydrothermal method is one of the most commonly employed techniques for synthesis of metal oxides, metals, and metal composites with different crystalline structures and morphologies, that are in the form of fine particles. The hydrothermal synthesis of nanoparticles involves hydrolysis of metal salt and condensation of metal hydroxide to produce ultrafine metal or metal oxide particles. We propose a Thermodynamic Modeling Framework for predicting the stability of the chemical species under the hydrothermal conditions. This can help in identifying the feasible regions for the hydrothermal synthesis of materials. The method is based on the integration of the Gibbs free energy equation, modified Bromley model for predicting activity coefficients, and the revised Helgeson-Kirkham-Flowers (HKF) model for estimating the standard-state thermodynamic properties of the species. The framework is tested with published experimental data for the synthesis of boehmite under subcritical temperature and supercritical conditions. The stability diagrams are generated for ceria and boehmite. The effect of pressure on the stability of the ceria species is studied. The proposed thermodynamic framework is useful for determining and identifying the process conditions under which the metal complex of interest is thermodynamically stable.