Effect of hydrothermal conditions on structural and textural properties of synthetic hydrotalcites of varying Mg/Al ratio

The synthetic hydrotalcites with Mg/Al molar ratios of 2.0-3.5 were synthesized by coprecipitation method at low supersaturation conditions followed by hydrothermal treatment under autogenous water vapor pressure at 70-140 degrees C. These synthesized samples were characterized by powder X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and surface area measurements. The hydrothermal treatment at increasing temperature and longer aging time increased the crystallinity and crystallite size of the hydrotalcite significantly. The crystallinity and crystallite size of the hydrotalcite were observed to decrease on increasing the Mg/Al ratio. The surface area of hydrotalcite was observed to increase on increasing the Mg/Al molar ratio from 2.0 to 3.5. From the kinetic data for crystallization of hydrotalcite at different temperatures, the values of rate constants and activation energy were calculated. The Avrami-Erofeev model (nucleation-growth model) was used for fitting the crystallization data.