Preparation of Transparent Suspension of Lamellar Magnesium Hydroxide Nanocrystals Using a High-Gravity Reactive Precipitation Combined with Surface Modification

Abstract

Transparent nanocrystal suspension exhibits many unique properties, and are thus attractive materials for numerous applications. However, the synthesis of transparent nanocrystal suspension of magnesium hydroxide (MH) with wide applications is yet to be realized. This paper presents a novel route of synthesizing transparent suspension of lamellar MH nanocrystals by using high-gravity reactive precipitation combined with successive surface modification. Reactive precipitation in ethanol phase instead of aqueous phase is conducted by introducing MgCl2·6H2O and NaOH ethanol solutions into a rotating packed bed (RPB) reactor with a rotating speed of 2500 rpm at 30 °C to form MH nanocrystal suspension, which is subsequently modified with KH570 (KH570/MH = 10 wt %) for an optimum time of 3 h and temperature of 70 °C to yield transparent suspension of lamellar MH nanocrystals with about 1 nm in thickness. The as-prepared transparent MH nanocrystal suspension is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), UV–vis, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) and compared with those synthesized by conventional stirred tank reactor (STR). The results indicated that the product prepared in RPB had a better transparency, and a smaller average particle size of 32 nm. As compared to STR, RPB had a greatly shortened reaction time from 20 min to 1 s. It is proven that this route has obvious advantages over STR. It could be envisioned that high-gravity reactive precipitation combined with surface modification would be promising in the large-scale preparation of transparent suspension of MH nanocrystals.