Synthesis, characterization, thermal behavior and exchange reactions of new phases of layered double hydroxides with the chemical composition [M6+2Al3(OH)18(SO4)2]•(A(H2O)6)•6H2O (M+2 = Co, Ni; A= Li+, Na+, K+)

Layered double hydroxides (LDH) with the composition [M6+2Al3(OH)(18)(SO4)(2)]center dot(A(H2O)(6))center dot 6H(2)O (M+2 = Co, Ni; A= Li+, Na+, K+) were synthesized and characterized by several instrumental techniques. All the compounds presented X-ray diffraction (XRD) patterns with a sequence of basal reflections, typical of layered materials. Cobalt derivatives presented bigger and better organized crystals than the nickel counterparts. Fourier-transform infrared (FTIR) spectra indicated the presence of sulfate in a distorted tetrahedral environment, while scanning electron microscopic (SEM) images indicated the presence of micrometric platelet-like particles. Quantitative analysis by inductively coupled plasma-optical emission spectrometry (ICP/OES) and thermogravimetric analysis (TGA) corroborated the suggested formulas, but with a small reduction of sulfate content, substituted by carbonate, especially in the samples after exchange reactions which were performed under air. Only alkali metal cations, sulfate anions or both cations and sulfate can be simultaneously replaced when the right solution is used in the exchange process, indicating new characteristics for this class of compounds.