Direct bottom-up synthesis of ZnAl2O4 nanoparticle via organic ligand dissolution method

This study improves the hydrothermal synthesis of ZnAl2O4 to realize direct bottom-up chemical synthesis from a liquid precursor solution. The liquid solution was prepared by the organic ligand dissolution (OLD) method. Synthesized ZnAl2O4 was identified as a single phase comprising ZnAl2O4 with organic components speculated to work as surfactants that aid in size stabilization. The synthesized ZnAl2O4 product was observed to be in nanoparticle form, exhibiting a wide-band gap attribute to the quantum size effect. The growth rate of ZnAl2O4 nanoparticles in the proposed method is low, and a series of results revealed the phase formation process of synthesized ZnAl2O4. This formation process seems common for chemically synthesized ZnAl2O4 and indicates the importance of compositional analysis in the study for chemical synthesis of this material. The application of the OLD method enables us to synthesize ZnAl2O4 across a wide pH range (3–11), and it is applicable to the continuous synthesis using a flow-type reaction system of hydrothermal reaction. Moreover, our technique is basically applicable to the synthesis of other spinel oxide. These characteristics of the OLD method are expected to extensively improve the investigation of chemical processing of spinel oxides.