Abstract
The adsorption complexes which consist of imogolite and humified clover extract were characterized by x-ray analysis, measurement for adsorption of water vapor, infrared absorption spectroscopy and thermogravimetry. The x-ray and water retention data indicated that considerable portions of humified material in the complexes, particularly that adsorbed from dilute solutions, were accommodated between the structure units of imogolite, resulting in displacement of water from the surfaces of the clay and humus molecules. This indication was also supported from very remarkable reduction of adsorption by preheating of imogolites in which the pores between the structure units were collapsed. About 30 to 70 % of the adsorbed humified material was estimated to come into contact with 10 to 35 % of the imogolite surface. The difference infrared spectrum of the adsorbed humified material indicated removal of adsorbed water from the complex, but failed to show any sign of specific interactions between inorganic and organic functional groups. The complex formation resulted in changes on the DTG curve of the humified material similar to those observed for the Al-fulvic acid complex by Schnitzer et al.(1967).
From the foregoing observations (Part I and II), the adsorbed humified material was divided into two fractions accommodated and unaccommodated into the imogolite thread. Two different bonding mechanisms were assumed to operate in this accommodation reaction; the first is the co-ordination of the carboxyl groups of the humus molecules to the Al atoms on the surfaces of imogolite. The second is multiple surface-segment interactions primarily associated with hydrogen bonding and/or van der Waals forces. The difference in the energetics of interactions was interpreted in terms of different orientations of the humus molecules with respect to the thread axis of imogolite.
