Abstract
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.
Highlights
Layered double hydroxides (LDHs) consist of alternate positively charged mixed metal hydroxide layers and negatively charged interlayer anions and can be normally described by the formula: ( ) ( ) M1z−+x M 3+ x OH p+ An−p n ⋅ mH2O with z = 2, M = bi- and trivalent metallic elements, A = organic or inorganic anions and m = amount of interlayer H2O depending on the relative humidity, hydration level and temperature [1] [2]
10 mg of the respective LDH were dissolved in 0.5 ml suprapure 65% HNO3, diluted with 10 ml deionized H2O and measured with inductively coupled plasma optical emission spectroscopy (ICP-OES)
The amount of interlayer water and the amount of the absorbed organic molecule was determined by thermogravimetric analysis (TGA)/DTA-mass spectrometer (MS) with approximately 10 mg of the respective LDH
Summary
Layered double hydroxides (LDHs) consist of alternate positively charged mixed metal hydroxide layers and negatively charged interlayer anions and can be normally described by the formula: ( ) ( ) M1z−+x M 3+ x OH p+ An−. P n ⋅ mH2O with z = 2, M = bi- and trivalent metallic elements, A = organic or inorganic anions and m = amount of interlayer H2O depending on the relative humidity, hydration level and temperature [1] [2]. The Al(OH) structure is built up of double-layered sheets of hexagonally packed O atoms. Two-thirds of the octahedral holes are occupied by Al Atoms. During a LDH synthesis with LiX (X = Cl−, OH−, NO3− , etc.), the remaining third will be occupied by Li Atoms which will lead to the 1:2 ratio [1] [4] [5] [6] [7]
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