Microwave assisted rapid crystallization of Mg-M(III) hydrotalcite where M(III) = Al, Fe or Cr

MgM(III)-carbonate hydrotalcites where M(III) = Al, Fe and Cr were rapidly synthesized through an instantaneous addition method coupled with microwave irradiation. The materials were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis, Al-27 MAS-NMR spectroscopy, transmission electron microscopy (TEM) and BET specific surface area measurements. Microwave irradiation resulted in a well crystallized material after a short synthesis time (12 min) compared to conventional coprecipitation and aging of the gel (25.5 h). However, the extent of enhancement in crystallinity upon irradiation depended on the nature of the trivalent metal ion. For the Mg-Cr system, microwave irradiation enhanced the crystallinity of the desired hydrotalcite-like phase at the expense of the impurity brucite phase, while the opposite effect was observed with conventional aging. The charged nature of the hydrotalcite network and water molecules present in the interlayer space enables uniform and effective absorption of microwaves, favoring long range ordering.