New hydrotalcite-like anionic clays containing Zr⁴⁺ in the layers: synthesis and physicochemical properties

Abstract

A new series of hydrotalcite (HT)-like anionic clays containing Zr⁴⁺ in the brucite-like layer has been synthesized by a simple coprecipitation method at constant pH. The incorporation of Zr in the layer has been investigated by various analytical methods, such as powder X-ray diffraction (PXRD), chemical analysis, FT-IR, ultraviolet-visible diffuse reflectance (UV-vis DR) spectra, and thermogravimetric analysis (TGA). The PXRD of as-synthesized samples showed that the crystallinity of the material decreased with increasing Zr content due to the distortions introduced by the incorporation of the larger cation, Zr. Thermal calcination at 723 K results in the formation of a poorly crystalline MgO phase in which some of the Zr⁴⁺ cations are dissolved. The crystallinity of the resulting MgO phase decreases with increasing Zr content and forms a ZrO₂ phase, in addition to the MgO phase, at higher Zr content. Calcination at higher temperatures (>1000 K) yields a mixture of MgO, MgAl₂O₄ spinel, and ZrO₂ phases. The UV-vis DR spectra showed that the Zr⁴⁺ cations are well-dispersed in both uncalcined as well as in calcined samples, similar to that in Zr-silicalites.