Supercritical hydrothermal synthesis of nano-zinc oxide: Process and mechanism

Abstract

Nano-zinc oxide is a type of multifunctional inorganic material, which had been extensively used due to the excellent properties such as piezoelectricity, sterilization, and UV shielding. The methods used for preparing nano-zinc oxides include precipitation, low-temperature hydrothermal, sol-gel, spray pyrolysis, and gas-phase synthesis. All of the current methods share the same problems of long reaction time, large particle sizes, and uneven distribution of particle sizes. The supercritical hydrothermal synthesis is a promising method for nano-ZnO preparation, which has the advantages of fast reaction rates and uniform particle size distribution. In this paper, the mechanism of supercritical hydrothermal synthesis of ZnO (including reaction, crystallization, and growth mechanism) is introduced. Then the effects of key parameters (materials and process parameters) are summarized. Moreover, the effects of surface modification and doping on ZnO are analyzed. Some suggestions for improving the particle quality by supercritical hydrothermal synthesis are also presented, as well as the future research directions.