Synthesis and Characterization of Methanesulfonate and Ethanesulfonate Intercalated Lithium Aluminum LDHs

LDH-phases become increasingly interesting due to their broad ability to be able to incorporate many different cations and anions. The intercalation of methanesulfonate and ethanesulfonate into a Li-LDH as well as the behavior of the interlayer structure as a function of the temperature is presented. A hexagonal P63/m [LiAl2(OH)6][Cl?1.5H2O] (Li-Al-Cl) precursor LDH was synthesized by hydrothermal treating of a LiCl solution with γ-Al(OH)3. This precursor was used to intercalate methanesulfonate (CH3O3S?) and ethanesulfonate (C2H5O3S?) through anion exchange by stirring Li-Al-Cl in a solution of the respective organic Li-salt (90?C, 12 h). X-ray diffraction pattern showed an increase of the interlayer space c' (d001) of Li-Al-methanesulfonate (Li-Al-MS) with 1.2886 nm and Li-Al-ethanesulfonate (Li-Al-ES) with 1.3816 nm compared to the precursor with 0.7630 nm. Further investigations with Fourier-transform infrared spectroscopy and scanning electron microscopy confirmed a complete anion exchange of the organic molecules with the precursor Cl?. Both synthesized LDH compounds [LiAl2(OH)6]CH3SO3?nH2O (n = 2.24-3.72 (Li-Al-MS) and [LiAl2(OH)6]C2H5SO3}?nH2O (n = 1.5) (Li-Al-ES) showed a monomolecular interlayer structure with additional interlayer water at room temperature. By increasing the temperature, the interlayer water was removed and the interlayer space c' of Li-Al-MS decreased to 0.87735 nm (at 55?C). Calculations showed that a slight displacement of the organic molecules is necessary to achieve this interlayer space. Different behavior of Li-Al-ES could be observed during thermal treatment. Two phases coexisted at 75?C - 85?C, one with a reduced c' (0.9015 nm, 75?C) and one with increased c' (1.5643 nm, 85?C) compared to the LDH compound at room temperature. The increase of c' is due to the formation of a bimolecular interlayer structure.