High-Gravity-Assisted Synthesis of Surfactant-Free Transparent Dispersions of Monodispersed MgAl-LDH Nanoparticles

As a family of important inorganic layered materials,layered double hydroxides (LDHs) have attracted considerable attention owing to their potential applications in wide areas. Generally, the size, shape, uniformity, and dispersity of LDHs have great effects on their application properties. Herein, we report an efficient approach to prepare surfactant-free transparent dispersions of monodispersed CO32--intercalated MgAl-LDH nanoparticles using a high-gravity-assisted intensified coprecipitation method in a rotating packed-bed (RPB) reactor, followed by hydrothermal treatment. After a rapid coprecipitation in the RPB reactor, monodispersed MgAl-LDH nanoparticles with an average particle size of about 31 nm can be obtained. As compared to that in a stirred tank reactor (STR), the product from the RPB has a much smaller particle size, narrower size distribution, and higher optical transparency. More importantly, the reaction time can be significantly reduced from 20 min to 20 s, realizing an efficient continuous preparation. Subsequent hydrothermal treatment will facilitate the particles to change from irregular shapes to hexagonal nanoflakes. Simultaneously, the average particle size of MgAlLDH nanoparticles rises to 65-72 nm on increasing the hydrothermal temperature from 90 to 130 degrees C. Furthermore, highly transparent and flexible nanocomposite films consisting of poly(vinyl alcohol) (PVA) and MgAl-LDH nanoparticles are readily fabricated with the spin-coating method and the layer-by-layer technique. It could be envisioned that such LDH dispersions may have a wide range of potential applications in the fields of optical devices, catalysis, gas separation, sensing, and antiflaming materials.