Microscopic and Molecular Characterization of Fe and Mn Hydrous Oxides

9815090 Gaillard这项建议的总体目标是确定在水生系统的缺氧/缺氧转变中形成的铁和锰氧化物的元素组成、氧化还原形态和分子性质。特别是，我们主要感兴趣的是获得关于环境颗粒的形态、结构和反应性的纳米级信息，以及关于组成这些颗粒的矿物相/组合的分子信息。我们的中心假设是，铁和锰的混合价态的存在控制了这些自生铁和锰相的反应活性。这项研究将集中在一个以生物混合为特征的小湖泊--保罗湖(MI)中，在半永久性缺氧/缺氧转变过程中形成的颗粒。为了达到这些目标，我们将使用显微和光谱方法相结合的方法。将收集保罗湖的颗粒，并准备用扫描电子显微镜和透射电子显微镜进行显微观察。单个粒子的元素组成将在纳米尺度上使用EDS或EELS来确定。同时，还将利用原位X射线吸收精细结构XAFS技术来探索颗粒中部分金属的局部分子环境的变化。本研究的预期结果是更好地表征了水生体系中在氧/缺氧转变时形成的颗粒。这些颗粒的化学成分、氧化还原形态和分子结构将为预测选择性地与这些颗粒相结合的金属和外来化学物质的命运提供有价值的信息。

9815090GaillardThe overall objective of this proposal is to determine the elemental composition,redox speciation, and the molecular nature of iron and manganese oxides that are formed at oxic/anoxic transitions in aquatic systems. In particular, we are primarily interested in obtaining nanoscale information on the morphology, structure, and reactivity of environmental particles as well as molecular information on the mineral phases/assemblages that comprise these particles. Our central hypothesis is that the existence of mixed valence states of Fe and Mn governs the reactivity of these authigenic iron and managanese phases. This investigation will focus on particles formed at the semi-permanent oxic/anoxic transition present in a small lake characterized by a biogenic meromixis: Paul Lake (MI).To reach these objectives we shall use a combination of microscopic and spectroscopic methods. Paul Lake particles will be collected and prepared for microscopic observations using SEM and TEM. The elemental composition of individual particles will be determined, at the nano-scale, using either EDS or EELS. Concurrently, the changes of the local molecular environment of selected metals in the particles will be probed using in situ X-Ray Absorption Fine Structure XAFS techniques.The expected result of this research is a better characterization of the particlesthat are formed at oxic/anoxic transitions in aquatic systems. The chemical composition, redox speciation, and molecular structure of these particles will provide valuable information for predicting the fate of metals and exotic chemicals that bind selectively to these particulate phases.