A novel gas-liquid contacting route for the synthesis of layered double hydroxides by decomposition of ammonium carbonate

Layered double hydroxides (LDHs) carbonate with the M^2+/Al^3+ (M=Mg or Zn) molar ratio of 2/1 has been synthesized by a gasliquid contacting route with the decomposition of ammonium carbonate. The key feature of this method is a pH gradient germinated by the diffusion of NH3 and CO2 vapors in the metal salts solutions from solid (NH4)2CO3 in a closed environment. The physicochemical properties of these two particles were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, simultaneous thermogravimetric and differential thermal analysis (TG-DTA), scanning electron micrograph (SEM) or transmission electron micrograph (TEM), laser particle size analysis and low-temperature N2 adsorption-desorption analysis. The results manifested that these two particles obtained by the method present well-crystalline, uniform crystallite size and relatively high surface area. The particle sizes of MgAl-LDH and ZnAl-LDH are around 0.55 and 0.069 (mu)m, respectively. Both the BET surface areas of them are about 100m^2/g.