Modification of Kaolinite Surfaces through Intercalation with Deuterated Dimethylsulfoxide

Abstract

The surfaces of kaolinite have been modified through intercalation with deuterated dimethylsulfoxide (d-DMSO). X-ray diffraction shows the kaolinite to be expanded from 7.2 to 11.19 Å. Modification of the surface has been explored through (a) changes to the hydroxyl surfaces of the kaolinite and (b) through changes to the d-dimethylsulfoxide inserting molecule. Upon intercalation of the kaolinite with d-DMSO, additional infrared bands at 3660, 3538, and 3502 cm-1 and additional Raman bands at 3660, 3537, 3507, and 3480 cm-1 are observed. The first band at 3660 cm-1 is attributed to the inner-surface hydroxyls hydrogen bonded to the d-DMSO and the other bands to water hydroxyl-stretching modes. Both infrared and Raman spectroscopy shows that significant changes in the molecular structure of the d-DMSO occur upon intercalation. First, the CD stretching modes observed for d-DMSO at 2125 and 2249 cm-1 in the DRIFT spectrum lose the degeneracy and split into 2140 and 2127 cm-1 and 2267, 2250, and 2238 cm-1. The Raman spectrum shows this loss of degeneracy through the bands observed at 2272, 2267, 2263, and 2251 cm-1 for the antisymmetric CD stretching vibration and at 2129 and 2141 cm-1 for the symmetric stretching vibrations. Upon intercalation with d-DMSO, the SO stretching region shows bands at 1066, 1023, and 1010 cm-1. The 1066 cm-1 band is assigned to the free monomeric SO group and the 1023 and 1010 cm-1 bands to two different polymeric SO groups. Bands attributed to the CS stretching vibrations, the in-plane and out-of-plane SO bending and the CSC symmetric bends all move to higher frequencies upon intercalation with d-DMSO. It is proposed that intercalation depends on the presence of water and that the additional bands at 3536 and 3501 cm-1 are due to the presence of water. The precise positions of the hydroxyl stretching modes of water at these positions suggest that water is in a well-defined position within the intercalation structure.