The structure of an intercalated ordered kaolinite — a Raman microscopy study

Abstract

A B S T R A C T: Changes in the molecular structure of a highly ordered kaolinite, intercalated with urea and potassium acetate, have been studied using Raman microscopy. A new Raman band, attributed to the inner surface hydroxyl groups strongly hydrogen bound to the acetate, is observed at 3605 cm -1 for the potassium acetate intercalate with the consequential loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm -l. Remarkable changes in intensity of the Raman spectral bands of the low-frequency region of the kaolinite occurred upon intercalation. In particular, the 144 and 935 cm -1 bands increased by an order of magnitude and were found to be polarized. These spectroscopic changes provide evidence for the inner surface hydroxyl group-acetate bond being at an angle approaching 90 ~ to the 001 face. Decreases in intensity of the bands at 243, 271 and 336 cm -1 were observed. The urea intercalate shows additional Raman bands at 3387, 3408 and 3500 cm -~ which are attributed to N-H vibrations after formation of the urea-kaolinite complex. Changes in the spectra of the inserting molecules were also observed.Clay minerals can interact with both organic and inorganic chemicals through a number of mechanisms such as adsorption, intercalation and cation exchange. The basic principles of intercalation reactions have been elucidated for kaolinite by Lagaly (1984). The reactive guest molecules enter the interlayer spaces and expand the kaolinite layers, essentially making the kaolinite into a single layered mineral. Reactive molecules have been classified into groups according to the point of clay interaction. Group A consists of those compounds which can form strong hydrogen bonds to the silicate layers, e.g. hydrazine, urea, formamide and acetamide. Group B consists of molecules with strong dipole interactions which can interact with the silicate layers and includes molecules such as dimethyl sulphoxide. Group C consists of the alkali salts of short chain fatty acids, in particular acetic and propionic acids (Weiss et al., 1966). In this paper one example from group A and one example from C have been selected for an intercalation study with a very highly ordered kaolinite.

Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K

“…Raman spectra of urea-intercalated kaolinite at room temperature have been reported recently [3][4][5]. The present paper reports the Raman spectra of urea-intercalated kaolinite (ordered and disordered) at 77K.…”

“…In recent Raman studies at room temperature [4,5], evidence was found for hydrogen bonding involving the NH 2 groups, rather than the C=O group of urea. Large shifts in the NH stretching bands of urea were observed, but there was little change in the intensity of the bands attributed to vibrations of the inner surface hydroxyl groups.…”

The performance of urea-intercalated and delaminated kaolinites-adsorption kinetics involving copper and lead

“…Depending on pH, different cationic species may be held to the clay surface at appropriate ion-exchange sites. 27 …”

“…The adsorption using the Lagergren model can also be explored, [26][27][28][29][30][31][32][33][34][35][36][37][38] as proposed in equation 12.…”

“…When the rate of reaction of an adsorption reaction is controlled by chemical exchange, then a pseudo-second order model can be better adjusted to the experimental kinetic data, [26][27][28][29][30][31][32][33][34][35][36][37][38][39] as expressed by equation 14. (14) After integration and applying the boundary conditions, N t = 0 for t = 0 and N t = N t at t = t, the integrated form of equation 14 becomes: (15) where k 2 is the pseudo-second order rate (mmol -1 min -1 ).…”