Synthesis and Characterization of Methanesulfonate and Ethanesulfonate Intercalated Lithium Aluminum LDHs

Abstract

LDH-phases become increasingly interesting due to their broad ability to be able to incorporate many different cat ions 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 P6 3 /m [LiAl 2 (OH) 6 ][Cl?1 . 5H 2 O] (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 (CH 3 O 3 S ? ) and ethanesulfonate (C 2 H 5 O 3 S ? ) 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 ' (d 001 ) 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 [LiAl 2 (OH) 6 ]CH 3 SO 3 ?nH 2 O (n = 2.24 - 3.72 (Li-Al-MS) and [LiAl 2 (OH) 6 ]C 2 H 5 SO 3 }?nH 2 O (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.