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 Zr 4+ 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 assynthesized 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 Zr 4+ cations are dissolved. The crystallinity of the resulting MgO phase decreases with increasing Zr content and forms a ZrO 2 phase, in addition to the MgO phase, at higher Zr content. Calcination at higher temperatures (>1000 K) yields a mixture of MgO, MgAl 2 O 4 spinel, and ZrO 2 phases. The UV-vis DR spectra showed that the Zr 4+ cations are well-dispersed in both uncalcined as well as in calcined samples, similar to that in Zrsilicalites.

Phosphate Adsorption Site on Zirconium Ion Modified MgAl-layered Double Hydroxides

“…The incorporation of tetravalent cations such as zirconium ions into the LDH layers have been also reported by Velu et al [38,39], Tichit et al [22], and Das et al [40]. Otherwise, Intissar et al analyzed the ill-crystalline Zr-MgAl-LDH prepared by the coprecipitation method according to Velu et al [38,39] using XAS spectroscopy [41]. They concluded that the incorporation of zirconium ions into LDH layers did not occur in the case of the ill-crystalline Zr-MgAl-LDH, and suggested that amorphous ZrO 2 -like oxides might be formed.…”

“…The superior phosphate adsorption property of the novel Zr-MgAl-LDH was explained by the incorporation of the zirconium ions into the LDH layers. The incorporation of tetravalent cations such as zirconium ions into the LDH layers have been also reported by Velu et al [38,39], Tichit et al [22], and Das et al [40]. Otherwise, Intissar et al analyzed the ill-crystalline Zr-MgAl-LDH prepared by the coprecipitation method according to Velu et al [38,39] using XAS spectroscopy [41].…”

Preparation, characterization and thermodynamic properties of Zr-containing Cl-bearing layered double hydroxides (LDHs)

“…To investigate the incorporation of tetravalent cations into the LDH structure is interesting task because there is no clarity concerning incorporation of tetravalent metals in LDHs. Some of studies reported the possibility of synthesizing LDHs containing M(IV) ions [5,[19][20][21][22][23][24]. Another authors based on results of X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy [25] concluded that the M(IV) cations are segregated from LDH structure and may form amorphous M(IV) oxide-like particles.…”

Reduction of heterocyclic carboxaldehydes via Meerwein–Ponndorf–Verley reaction

“…It has been reported by several authors [28,34,35] that in the case of Mg/Al LDHs, thermal decomposition at 400-500 8C yields an ill-crystallized MgO phase whose lattice constant a is less than that of pure MgO and has been attributed to the dissolution of a small amount of Al 3+ in the MgO lattice to form solid solutions. This lattice parameter a of the resulting MgO-like cubic phase (MgO solid solution) was evaluated from both d(2 0 0) and d(2 2 0) peaks, using the relation a = d  (h 2 + k 2 + l 2 ) 1/2 and the values for the catalysts are shown in Table 1.…”