Infrared Studies of the Hydroxyl Groups in Intercalated Kaolinite Complexes*

Robert L. Ledoux and Joe L. White
Université Laval, Québec, P.Qué., Canada
Purdue University, Lafayette, Indiana
* Journal paper No. 2423 of the Purdue University Agricultural Experiment Station, Lafayette, Indiana.

Abstract: Expansion of kaolinite with potassium acetate reduces the intensity of the 3695 cm−1 absorption band and causes the appearance of an additional one at 3600 cm−1. Subsequent deuteration with D2O vapor shifts the 3695 cm−1 and 3600 cm−1 absorption bands to 2725 cm−1 and 2650 cm−1 respectively. The hydroxyls absorbing at 3620 cm−1 do not interact with the acetate anion and do not readily exchange with D2O vapor.

Deuteration of expanded hydrazine-kaolinite complex at room temperature shifts the infrared stretching frequencies 3695, 3670, 3650 and 3620 cm−1 to 2725, 2710, 2698 and 2675 cm−1 respectively. The OH-OD exchanges for the hydroxyls absorbing at 3695, 3670 and 3650 cm−1 are 67, 60 and 62 per cent respectively, and for the 3620 cm−1 only 22 per cent. The 3695, 3670 and 3650 cm−1 absorption bands are correlated predominantly to inner-surface hydroxyls and the 3620 cm−1 to inner hydroxyls located below the holes in the silica tetrahedral layer.

The ν(OH) absorption bands at 3695, 3670 and 3650 cm−1, and the ν(OD) at 2725, 2698, and 2675 cm−1 are pleochroic, whereas the 3620 cm−1 absorption band is non-pleochroic. The direction of the dipole moment change of OH groups absorbing at 3695 cm−1 and 3670 cm−1, and of OD groups absorbing at 2725 cm−1 and 2698 cm−1, is nearly at right angles to the basal plane (001); for the 3650 cm−1 and 2675 cm−1 bands, the angle is large, but less than 90°. The inner hydroxyls absorbing at 3620 cm−1 have their dipole moment change inclined at about 15° to the “ab” cleavage plane.

A comparison of the ν(OH) and ν(OD) absorption intensities for the film rotated 45° and normal to the infrared incident radiation shows that the pleochroism is more intense in the ν(OD) region than in the ν(OH) region. This indicates that partial deuteration perturbs the direction of dipole moment change of the “hydrogen bond” with respect to the initial orientation prior to deuteration; the net result is the formation of larger angles between the direction of the OD dipole moment changes and the basal plane (001) than existed for OH prior to deuteration.

Clays and Clay Minerals; 1964 v. 13; no. 1; p. 289-315; DOI: 10.1346/CCMN.1964.0130128
© 1964, The Clay Minerals Society
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