Layered Double Hydroxides as Cation Exchange Materials
Paul Braterman, Nandika A. D'Souza, Jeffrey W. Gilman, Mickey C. Richardson, Laxmi K. Sahu, Mauro Zammarano
Layered double hydroxides (LDH) are a class of materials formally related to brucite-like hydroxides by the incorporation of higher valent cations, such as Al(III). The layer charge is neutralized by the insertion of any of a large range of exchangeable anions, and this anion exchange behavior has been the subject of intense investigation for many years. We now report that the most common type of LDH (based on a magnesium aluminum hydroxide layer) can, under certain conditions, undergo facile cation exchange by either of two distinct mechanisms. This result has implications for the removal of cationic contaminants, the preparation of LDH-based catalysts, and the geochemical evolution of LDH-type minerals. We showed some years ago that the solubility of freshly prepared LDH of type M(II)2Al(OH)6Cl.xH2O was dependent on the nature of M(II), and that those metals giving the most insoluble hydroxides also gave rise to the most insoluble LDH. This led us to wonder whether simply suspending Mg2Al(OH)6Cl.xH2O in a solution of a transition metal salt, such as nickel(II) chloride in water, would lead to complete or partial replacement of Mg by Ni, and what the mechanism of such replacement, and its effect on the individual layer structure, might be. The question is of particular interest in the case of catalytically active metals, such as nickel, where it is highly desirable to achieve maximum dispersion, and to discourage aggregation and sintering, in LDH derived bifunctional metal-acid/base catalysts. We therefore decided to expose samples of the magnesium aluminum LDH to nickel chloride solution at room temperature and to investigate the effect of starting material crystallinity on the nature of the final product.
, D'Souza, N.
, Gilman, J.
, Richardson, M.
, Sahu, L.
and Zammarano, M.
Layered Double Hydroxides as Cation Exchange Materials, Journal of Materials Chemistry
(Accessed December 8, 2023)