Investigating the Surface Structure and Reactivity of Bulk and Nanosized Manganese Oxides

SPARKSResearch旨在研究在土壤氧化还原化学中起核心作用的环境重要锰氧化物（Mn）的化学和物理性质。在地球科学界，锰氧化物以涂层和离散颗粒的形式存在于土壤中，部分具有纳米尺寸。它们丰富的氧化还原化学影响环境毒素的流动性和生物利用度，包括许多金属和类金属。研究将主要集中在表面结构和化学反应性的两个散装水钠锰矿（二氧化锰）相的锰氧化物和纳米MnOOH相在各种环境相关的条件下。特别是，选择先进的表面光谱技术，包括衰减全反射红外（ATR-FTIR）光谱和同步加速器为基础的光电子能谱（PES）将被用来开发一个图片的反应锰氧化物表面，如确定不同的锰氧化态的相对表面浓度，在一个范围内建立土壤pH值。这些锰氧化物的表面，然后将通过与水砷含氧阴离子的反应，建立控制锰氧化物的结构和反应性的差异施加在环境中的氧化还原反应。虽然水钠锰矿，发现在广泛的土壤环境，是一个主要目标的拟议研究，纳米尺寸的锰氧化物也存在于环境中，是目前的研究兴趣。为了了解纳米锰氧化物在低温地球化学中可能发挥的作用，研究将调查MnOOH纳米颗粒的反应性和电子结构随尺寸的变化。纳米MnOOH与均匀的尺寸分布从20到80 A将制备和研究在溶液中具有不同的pH值和作为氧化反应将再次被用作探针的反应性。该研究项目的这一特定阶段不仅将发展对锰氧化物的尺寸-反应性关系的理解，而且将在总体上有助于地球化学界更广泛的努力，以评估纳米化学在环境中的重要性。首先，NSF的资金将用于支持和培训特拉华州大学的一名博士后研究员和坦普尔大学的一名研究生。此外，特拉华州大学的一名本科生将对该项目进行研究。研究小组的成员将参加一年两次的会议，轮流在每个参与机构举行，以评估研究计划的进展情况，并传播新的想法和信息。由于这项研究具有很强的跨学科性质，该项目研究人员的科学广度将受益于在土壤和表面化学不同领域具有专业知识的团体之间不断交流的想法和概念。这种合作符合跨学科研究的更广泛需求，以了解复杂的环境化学。由于特拉华州和其他地方的公民和政策制定者非常关注在受工业和农业投入影响的土壤上建造住房，市政厅会议将与特拉华州资源和环境控制部的人员合作举行，让市民了解我们的研究这种形式的推广，沿着与感兴趣的公民在农业和自然资源的特拉华州学院每年的开放日（银日）的大学直接接触，将是至关重要的介绍特拉华州的类型，意义，环境科学和正在解决的问题在学术机构。

EAR-0544246SPARKSResearch is proposed that investigates the chemical and physical properties of the environmentally important oxides of manganese (Mn) that play a central role in soil redox chemistry. It is well accepted in the geoscience community that Mn-oxides exist as coatings and as discrete particles in soils, in part with nano-dimensions. Their rich redox chemistry affects the mobility and bioavailability of environmental toxins including many metals and metalloids. Research will be focused primarily on the surface structure and chemical reactivity of both the bulk birnessite (MnO2) phase of Mn-oxide and also a nano-MnOOH phase under a variety of environmentally relevant conditions. In particular, a selection of advanced surface spectroscopic techniques, including attenuated total reflection infrared (ATR-FTIR) spectroscopy and synchrotron-based photoelectron spectroscopy (PES) will be used to develop a picture of the reacting Mn-oxide surface, such as determining the relative surface concentration of different Mn oxidation states, over a range of established soil pH values. These Mn-oxide surfaces will then be probed via reaction with aqueous arsenic oxyanions to establish the control that differences in Mn-oxide structure and reactivity exert on redox reactions in the environment.While birnessite, found in a wide range of soil environments, is a primary target of the proposed research, nano-sized Mn-oxides also exist in the environment and are of interest in the current research. Toward developing an understanding of the role that nano-Mn-oxides might play in low temperature geochemistry, research will investigate the reactivity and electronic structure of MnOOH nano-particles as a function of size. Nano-MnOOH with homogeneous size distributions from 20 to 80 A will be prepared and studied in solutions with varying pH and the As oxidation reaction will again be used as a probe for reactivity. This particular phase of the research project will not only develop an understanding of the size-reactivity relationship for Mn-oxide, but will in general contribute to the broader effort in the geochemical community to evaluate the importance of nano-chemistry in the environment.The proposed study has a significant educational and outreach component. First, NSF funds will be used to support and train a postdoctoral researcher at the University of Delaware and a graduate student at Temple University. Additionally, an undergraduate honors student at the University of Delaware will conduct research dealing with the project. The members of the research team will participate in a bi-annual meeting held alternatively at each participating institution in order to evaluate the progress of the research program and to disseminate new ideas and information. By virtue of this study being strongly interdisciplinary in nature, the scientific breadth of researchers in this project will benefit from the constant exchange of ideas and concepts between groups having expertise in diverse areas of soil and surface chemistry. This collaboration fits into the broader need for interdisciplinary studies to understand complex environmental chemistry.Since there is great concern on the part of citizens and policymakers in the State of Delaware and elsewhere on building housing developments on soils impacted by industrial and agricultural inputs of As, town hall meetings will be held in collaboration with personnel from the Delaware Department of Resources and Environmental Control, to inform the citizenry of our research. This form of outreach, along with direct contact with interested citizens at the University of Delaware College of Agriculture and Natural Resources yearly open-house (Ag Day), will be crucial to introducing Delawareans to the type, and significance, of environmental science and issues that are being addressed at academic institutions.