A F-19 NMR Probe of Mineral Surface Reactivity

矿物表面反应性的 F-19 NMR 探针

• 批准号: 0310200
• 负责人: Brian Phillips
• 金额: $ 25.98万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-08-01 至 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310200&HistoricalAwards=false
• 关键词: 19; NMR; Probe; Mineral; Surface

EAR-0310200PhillipsThis research project will study the molecular-level structure of aluminum oxyhydroxide mineral surfaces and their fundamental reactivity with water. A primary goal of this work is to develop a spectroscopic technique for characterizing the mineral surface in terms of the types of reactive surface sites and their concentrations. Aluminum oxyhydroxides are common in soils and acid-rock drainage areas and provide a simplified model system for the reactive sites in clay minerals. The experimental approach is to react mineral surfaces with dissolved fluoride under carefully controlled conditions, and then determine the resulting fluoride distribution on the surface using F-19 NMR spectroscopy. Previous work on large dissolved molecules with similar structure show that fluoride ions substitute for oxygen in both terminal- and bridging-type surface sites, and that F?19 NMR spectroscopy can resolve these distinct coordination environments. If successful, this technique can be applied to study the surfaces of other heterogeneous disordered solids. Further time-resolved experiments will test the hypothesis that initial fluoride substitution occurs at terminal sites, followed by migration to bridging sites on crystal edges and basal surfaces at longer reaction times. The timescale for fluoride migration among these sites will provide estimates for the fundamental reactivity of the surface oxygens. Additional experiments on dissolved Al-oxyhydroxide nanoclusters, using NMR kinetic techniques, will attempt to determine detailed mechanistic pathways for the fluoride substitution reactions. The results of this study will contribute a deeper understanding of fundamental processes governing bulk geochemical behavior of mineral/fluid systems. Reactions at mineral surfaces control the ability of soil minerals to adsorb and sequester contaminants in near-surface geochemical environments. Significant changes in the mineral surface structure and reactivity toward contaminants can occur through surface rearrangement during reaction with water and dissolved constituents. Techniques developed in this study can allow these changes to be quantified at the molecular level.

本研究项目将研究氢氧化铝矿物表面的分子级结构及其与水的基本反应活性。这项工作的一个主要目标是开发一种光谱技术，根据活性表面位置的类型及其浓度来表征矿物表面。氢氧化铝普遍存在于土壤和酸岩排水地区，为粘土矿物中的反应部位提供了一个简化的模型体系。实验方法是在严格控制的条件下，使矿物表面与溶解的氟化物反应，然后使用F-19核磁共振光谱确定氟化物在表面上的分布。前人对结构相似的大分子的研究表明，氟离子取代了末端和桥式表面上的氧，而F？19核磁共振谱可以分辨出这些不同的配位环境。如果成功，这项技术可以应用于研究其他非均质无序固体的表面。进一步的时间分辨实验将检验这一假设，即最初的氟替代发生在末端位置，随后在更长的反应时间内迁移到晶体边缘和基面上的桥位。这些地点之间氟迁移的时间表将提供对表面氧的基本反应性的估计。使用核磁共振动力学技术对溶解的氢氧化铝纳米团簇进行的其他实验将试图确定氟化物取代反应的详细机理路径。这项研究的结果将有助于更深入地理解控制矿物/流体系统整体地球化学行为的基本过程。矿物表面的反应控制着土壤矿物在近地表地球化学环境中吸附和隔离污染物的能力。矿物表面结构和对污染物的反应性可通过与水和溶解成分反应过程中的表面重排发生显著变化。这项研究中开发的技术可以在分子水平上量化这些变化。