Preparation of mesoporous ZnAl2O4 nanoflakes by ion exchange from a Na-dawsonite parent material in the presence of an ionic liquid

Abstract

Herein, mesoporous ZnAl₂O₄ spinel nanoflakes were prepared by an ion-exchange method from a Na-dawsonite parent material in the presence of an ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride ([bdmim][Cl]), followed by calcination at 700 °C for 2 h. The as-obtained products were characterized by several techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The ZnAl₂O₄ nanoflakes with the thickness of ∼20 nm were composed of numerous nanoparticles, which resulted in a high specific surface area of 245 m² g⁻¹. The formation mechanism of the ZnAl₂O₄ nanoflakes was comprehensively investigated, and the results showed that a 2D growth process of the Zn₆Al₂(OH)₁₆(CO₃)·4H₂O crystallites with the assistance of [bdmim][Cl] was the key for the induction of ZnAl₂O₄ nanoflakes. Moreover, mesopores were formed between adjacent nanoparticles due to the release of CO₂ and H₂O molecules from Zn₆Al₂(OH)₁₆(CO₃)·4H₂O during the calcination process.