FTIR investigation of CTAB–Al–montmorillonite complexes

In this study, CTAB–Al–montmorillonite complexes were synthesized by pre-modifying montmorillonite using different concentrations of surfactant (resulting in different surfactant loadings and basal spacings), then pillaring the organoclays with hydroxy-Al cations. The resultant inorganic–organic montmorillonite complexes were characterized using FTIR, with a combination of XRD, TG and chemical analysis. This study indicates that the basal spacings of the CTAB–Al–montmorillonite complexes and the amounts of Al-contained pillars strongly depend on the surfactant loadings in the clay interlayer space, resulted from the mobility variation of the intercalated surfactants. During pillaring hydroxy-Al cations into clay interlayer space, part of the intercalated surfactants were removed, resulting in a decrease of the ordering of alkyl chains and the frequency shifts of Si(Al)–O, Si–O–Al and (M–O)Td stretching vibrations. The hydrophobicity of the CTAB–Al–montmorillonite complex also strongly depends on the surfactant loading whereas that of the CTAB–Al–montmorillonite complex is relative lower than that of the corresponding organoclay, indicated by the frequency shift of the vibrations corresponding to the sorbed water and their contents estimated by TG curves. With the decrease of the sorbed water content, the frequency of the band of H–O–H bending (ν2) shifts to higher frequency while the O–H stretching vibration (ν1 and ν3) shifts to lower frequency, indicating that H2O is less hydrogen bonded. Meanwhile, the ordered conformations of the alkyl chains in CTAB–Al–montmorillonite complex decrease when compared with that of the corresponding organoclay.