Kaolinite hydroxyls in dimethylsulphoxide-intercalated kaolinites at 77 K — a Raman spectroscopic study
Kaolinite hydroxyls in dimethylsulphoxide-intercalated (DMSO-intercalated) kaolinites have been determined using Raman spectroscopy at 298 and 77 K. The inner surface hydroxyl frequencies at 3650, 3670, 3684 and 3693 cm-1 move to higher wavenumbers upon cooling to 77 K and are observed at 3659, 3676, 3692 and 3702 cm-1. The inner hydroxyl frequency is at 3620 cm-1 at 298 K and is at 3615 cm-1 at 77 K. Upon intercalation with DMSO, additional bands are found at 3660, 3536 and 3501 cm-1 for the low-defect kaolinite and at 3664, 3543 and 3509 cm-1 for the high-defect kaolinite at 298 K. The 3660 cm-1 band at 298 K is resolved into two bands at 3658 and 3663 cm-1 at 77 K for the low-defect kaolinite and these bands are assigned to the inner surface hydroxyl groups, hydrogen-bonded to the DMSO molecule. It is proposed that the DMSO molecule exists with two different orientations in the intercalate and these two molecular forms are differentiated by the OH-stretching bands of the inner surface hydroxyl groups. This band for the high-defect kaolinite is found at 3664 cm-1 at 298 K and resolves into two bands at 3664 and 3673 cm-1 at 77 K.
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