The Stability and Surface Chemistry of Allophane and Imogolite

本研究的目的是建立表面特征与合成allophane和imogolite的结构特征的依赖关系，确定allophane和imogolite的热力学稳定性（亚稳性），并开始研究比较合成和天然allophane和imogolite的表面和结构特征和稳定性。Al的配位和Si的配位环境将通过MAS-NMR、溶解体组成和能量色散x射线分析来确定。表面酸度和电荷特性将通过电位滴定、离子保留和电泳来确定。碱和卤化物系列的单价离子将用于测试离子选择性模型，大型有机阳离子将用于测试提出的表面和内部位置之间阳离子和离子不均匀分布的假设。我们将开始比较合成材料与从土壤和浮石沉积物中分离出来的相应材料之间的表面和体积特征。所有材料的稳定性测定将基于溶解度实验。Allophane和imogoite是存在于各种土壤中的非晶体铝硅酸盐。从理论的角度来看，它们很有趣，因为它们展示了广泛的组成，同时保持了一些一致和独特的结构特征。从实际的角度来看，它们非常高的比表面积对土壤性质的影响超出了它们的质量所能预期的范围。已知它们会影响土壤中的持水能力、肥力、有机化合物的降解或聚合以及铝的运输。这项研究的潜在应用也可能扩展到解决废物处理、雨水和污染等问题。

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.