Time-Resolved Structural Analysis of Heavy Metal Cation Exchange Reactions in Anionic Clay and Manganese Oxide Nanoparticles

阴离子粘土和锰氧化物大量存在于表层环境中的土壤和沉积物颗粒上作为纳米晶涂层。 它们表现出显着的设施，交换离子溶解在水溶液中，并作为主要的陷阱阴离子和阳离子。 该提案的研究人员将采用一种新的晶体学方法来解决层状双氢氧化物和锰氧化物材料中的阳离子交换机制。 在阳离子交换过程中，粉末样品将通过同步加速器X射线衍射进行监测。 这些实验将产生第一个时间分辨分析的结构扭曲发生，以适应过渡金属在低温矿物中的替代。 此外，与高温红外光谱相结合，同步加速器XRD分析将在样品加热时进行，使热分解的结构表现与阳离子交换容量相关联。这些研究将使研究人员能够捕获中间过渡步骤，这些步骤被更传统的最终产品静态分析所忽略。由于与化学取代相关的结构扰动倾向于稳定交换相，这些研究将表明哪些因素限制了所选阳离子的交换程度。 因此，这些实验将建议新的修复材料与放大交换特性的设计方法。

HeaneyEAR-0125908Anionic clays and manganese oxides occur abundantly as nanocrystalline coatings on soil and sediment particles in surficial environments. They exhibit a remarkable facility for exchanging ions dissolved in aqueous fluids and act as major traps for anions and cations. The investigators of this proposal will apply a novel crystallographic approach to resolve mechanisms of cation exchange in layered double hydroxide and Mn oxide materials. Powdered samples will be monitored by synchrotron X-ray diffraction during the process of cation exchange. These experiments will yield the first time-resolved analyses of the structural distortions that occur to accommodate substitutions by transition metals in low-temperature minerals. Additionally, in concert with high-temperature infrared spectroscopy, synchrotron XRD analyses will be performed as samples are heated, allowing the structural manifestations of thermal decomposition to be correlated with cation exchange capacity.These studies will allow the investigators to capture intermediate transition steps that are overlooked by a more conventional static analysis of final run products. As the structural perturbations that are associated with chemical substitutions tend to stabilize the exchanged phases, these studies will indicate which factors limit the degree of exchange for selected cations. Consequently, these experiments will suggest approaches to the design of new remediation materials with amplified exchange characteristics.