The Stability and Surface Chemistry of Allophane and Imogolite

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The objectives of this research are to establish the dependence of surface characteristics on structural characteristics of synthetic allophane and imogolite, determine the thermodynamic stability (metastability) of allophane and imogolite and to initiate investigations comparing the surface and structural characteristics and stability of synthetic and naturally-occurring allophane and imogolite. The coordination of Al and the coordination environment of Si will be determined by MAS-NMR and bulk composition by dissolution and by energy-dispersive X-ray analysis. Surface acidity and charge characteristics will be determined by potentiometric titration, ion retention, and electrophoresis. Monovalent ions of the alkali and halide series will be used to test models of ion selectivity and large organic cations will be used to test a hypothesis that proposed unequal distribution of cations and ions between surface and interior sites. We will initiate a comparison of surface and bulk characteristics between the synthetic materials and their counterparts isolated from soils and pumice deposits. Stability determinations on all materials will be based on solubility experiments. Allophane and imogolite are noncrystalline aluminosilicates which occur in a variety of soils. They are interesting from a theoretical standpoint because they exhibit a wide range of composition while maintaining some consistent and unique structural characteristics. From a practical standpoint, their very high specific surface areas impart an influence on soil properties in excess to what is expected from their mass. They are known to influence water holding capacity, fertility, degradation or polymerization of organic compounds, and transport of Al in soils. Potential applications of this research may also extend to addressing problems in waste disposal, and rain and pollution.