Synthesis, structure refinement and chromate sorption characteristics of an Al-rich bayerite-based layered double hydroxide

Abstract

a b s t r a c t "Imbibition" of Zn 2 þ ions into the cation vacancies of bayerite-Al(OH) 3 and NO 3 À ions into the interlayer gallery yields an Al-rich layered double hydroxide with Al/Zn ratio $3. NO 3 À ions are intercalated with their molecular planes inclined at an angle to the plane of the metal hydroxide slab and bonded to it by hydrogen bonds. Rietveld refinement of the structure shows that the monoclinic symmetry of the precursor bayerite is preserved in the product, showing that the imbibition is topochemical in nature. The nitrate ion is labile and is quantitatively replaced by CrO 4 2 À ions from solution. The uptake of CrO 4 2 À ions follows a Langmuir adsorption isotherm, thus showing that the hydroxide is a candidate material for green chemistry applications for the removal of CrO 4 2 À ions from waste water. Rietveld refinement of the structure of the hydroxide after CrO 4 2 À inclusion reveals that the CrO 4 2 À ion is intercalated with one of its 2-fold axes parallel to the b-crystallographic axis of the crystal, also the principal 2 axis of the monoclinic cell.

M(II)Al4 Type Layered Double Hydroxides—Preparation Using Mechanochemical Route, Structural Characterization and Catalytic Application

“…The increase of the initial Cu:Al molar ratio facilitated the formation of thicker LDHs; the intensity of the reflections increased and split at around 20 and 22 • 2θ for the CuAl 4 -ClO 4 − -LDH, which is a common phenomenon. This effect was already observed for LiAl 2 - [26], ZnAl 4 -LDHs [27] and, in our recent work, for NiAl 4 -ClO 4 − -LDH and for NiAl 4 -NH 2 SO 3 − -LDH [24]. The FT-IR of the solids also verified the formation of phase-pure CuAl 4 -X n− -LDHs.…”

Synthesis and Structural Characterization of a Pure ZnAl4(OH)12(SO4)·2.6H2O Layered Double Hydroxide

“…However, their sample contained excess Zn (Al:Zn ≈ 3:1), which was modeled as Zn substitution on one of the four crystallographic Al sites and with substantial Zn/Al vacancies . Williams et al reported the structure of ZnAl 4 -LDH with nitrate, but the sample was heated at 175 °C to remove interlayer water, and a number of structural ambiguities remain. , Recently, Pushparaj et al reported a Rietveld refined structure of a ZnAl 4 -LDH sample that contained no crystalline impurities according to PXRD. Several structural models were validated using input from 27 Al solid-state NMR spectroscopy (SSNMR) and transmission electron microscopy (TEM).…”

“…, and Eqs. 1-317 ) corresponds to 2.62(5) H2O, 5.99(5) OH, and 0.99(5) SO4 , respectively based on a composition of ZnO + 2 Al2O3 for the end product. Thus, a formula of ZnAl4(OH)5.99(5)(SO4)⋅2.62(5) H2O is derived, i.e., a stoichiometric sample within the 3-3.3 interlayer water molecules and positional disorder for one of the interlayer O site from single crystal XRD,15 i.e., a variable interlayer water content.…”

Calcined ZnAl- and Fe3O4/ZnAl–layered double hydroxides for efficient removal of Cr(vi) from aqueous solution

“…20 Due to their high charge density of the sheets and the exchangeability of the interlayer anions, LDHs have been employed for removing different anions by both surface adsorption and anion exchange. [21][22][23][24] Some studies of hexavalent chromium adsorption by MgAl-LDH, 23,25 Mg 3Àx Ca x Fe-LDH, 24 MgAlFe-LDH, 26 ZnAl 4 -LDH, 27 CoBi-LDH 28 and MgAl-, NiAl-, ZnAl-LDHs 29 were investigated in detail.…”