Collaborative Research: NIRT: Surface Reactivity of Nanocrystalline Oxides and Oxyhydroxides: Implications for Processes in the Environment

由化学风化和生物矿化反应形成的纳米级晶体存在于河流、湖泊、海洋、土壤、沉积物和大气尘埃中。由于其新颖的尺寸依赖特性，纳米颗粒可能在环境过程中发挥不成比例的重要作用。然而，地质上重要的纳米材料的反应性随粒径的变化却很少受到关注。离子吸附到纳米晶金属氧化物表面的趋势预测与尺寸有关。吸附将在0 - 150摄氏度的温度范围内的气体和环境相关的水溶液中进行实验研究。将开发模型来定量地解释纳米颗粒的结果与宏观等效结果之间的差异。如果纳米晶体通过定向聚集生长，如前所述，吸附的离子（如磷酸盐、砷酸盐和锌从溶液中吸附到氧化铁表面）可能被纳入点缺陷中。这可能是一种重要的环境离子封存途径，与营养物和污染物的长期命运直接相关。在受控条件下，聚合和吸附的耦合也可能为创造具有技术上有趣性质的合成材料提供新的途径。纳米晶体生长过程中的离子隔离将通过实验测试和分子建模和模拟来探索。设计用于测量表面和吸附能的量热研究将为探索尺寸依赖性反应性的模型提供数据。该提案是响应“纳米尺度科学与工程”（NSF 00-119）的征求而提交的。

EAR-0123967EAR-123998EAR-0124036EAR-0124001Crystals 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).