Polytypism, Disorder, and Anion Exchange Properties of Divalent Ion (Zn, Co) Containing Bayerite-Derived Layered Double Hydroxides
journal contributionposted on 20.12.2010, 00:00 by Sylvia Britto, P. Vishnu Kamath
Incorporation of Zn2+ into bayerite results in the formation of a cation-ordered layered double hydroxide (LDH) of monoclinic symmetry in which about half the vacancies of Al(OH)3 are occupied by Zn2+ giving rise to positively charged layers. Charge compensation takes place by the incorporation of sulfate ions in the interlayer region. Structure refinement reveals that the adjacent layers in the crystal are related by a 21 axis (we call it 2M1 polytype) with sulfate coordinating in the D2d symmetry in the interlayer region. Another polytype in which adjacent layers are related by a 2-fold axis (2M2 polytype) can also be envisaged. Faulted crystals arising from intergrowths of the 2M2 polytype within the 2M1 structure were also obtained. These bayerite-based LDHs have a distinctly different interlayer chemistry when compared to the better known brucite-based LDHs, in that they have a strong affinity for tetrahedral ions such as SO42−, CrO42−, and MoO42− and a poor affinity for CO32− ions. These observations have implications for the use of LDHs in applications related to chromate sorption.