Effect of Structure and Morphology of Kaolin Minerals on the Intercalation of Urea.

Abstract

The effect of the structural properties of kaolin minerals on the intercalation process of urea was investigated using kaolinite and two kinds of halloysite. The results are summarized as follow.(1) The urea intercalated gradually and regularly into the interlayer site of kaolinite with plate morphology, but intercalated immediately and irregularly into that of halloysite with tubular and spherical morphologies.(2) The decomposition temperature of the urea intercalated into kaolin minerals were lower than that of pure urea. The difference between the decomposition of the urea intercalated and that of pure urea was examined by IR spectrum analysis. The asymmetric and symmetric ν(NH2) stretching frequencies at 3, 504cm-1 and 3, 389cm-1 correspond to NH2 groups interacting with the oxygens located on the basal tetrahedral layer. Intercalation of urea within the kaolin minerals structure increased the ν(CN) stretching frequency from 1, 468cm-1 for the urea to 1, 477cm-1 for intercalated molecules. These results indicate that the hydrogen bonding of urea molecules intercalated into the interlayer site of kaolin minerals are weak as compared with the hydrogen bonding of pure urea molecules.(3) The ν(CN) stretching frequency of two kinds of halloysite showed broader pattern compared with that of kaolinite, but the ν(NH2) bending frequency of halloysites shifted to higher frequency than that of kaolinite. These results show that the hydrogen bonding of urea intercalated into the interlayer site of halloysite is different from the that of kaolinite.