Crystals with nanometer-scale dimensions formed by chemical weathering and biomineralization reactions are found in rivers, lakes, oceans, soils, sediments, and atmospheric dust. Because of their novel size-dependent properties, nanoparticles may play disprotionately large roles in environmental processes. However, the variation of reactivity of geologically important nanomaterials with particle size has received little attention. The tendency of ions to adsorb onto nanocrystalline metal oxide surfaces is predicted to be size-dependent. Adsorption will be studied experimentally over the temperature range of 0 - 150 degrees C in gases and environmentally-relevant aqueous solutions. Models will be developed to quantitatively explain differences between results for nanoparticles and those obtained on macroscopic equivalents. If nanocrystals grow via oriented aggregations, as has been shown previously, adsorbed ions (e.g. phosphate, arsenate, and zinc adsorbed from solution onto iron oxyhydroxide surfaces), may be incorporated into point defects. This may represent an important environmental ion sequestration pathway, with direct relevance to the long-term fate of nutrients and contaminants. Coupling of aggregation and adsorption under controlled conditions may also provide a new approach for creation of synthetic materials with technologically interesting properties. Ion sequestration during nanocystal growth will be tested experimentally and explored via molecular modeling and simulation. Calorimetric studies designed to measure surface and adsorption energies will provide date to be used in models that will explore size-dependent reactivity. This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 00-119).
