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

EAR-0544246 SPARKS研究是研究在土壤氧化还原化学中起核心作用的对环境重要的锰氧化物的化学和物理性质。地球科学界普遍认为，锰氧化物在土壤中以涂层和离散颗粒的形式存在，部分以纳米尺度存在。其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。研究将主要集中在氧化锰的块状水钠锰矿(MnO2)相和纳米MnOOH相在各种环境相关条件下的表面结构和化学反应活性。特别是，将使用一系列先进的表面光谱技术，包括衰减全反射红外光谱(ATR-FTIR)和基于同步加速器的光电子能谱(PES)，来绘制氧化锰反应表面的图像，例如在一系列既定的土壤pH值范围内确定不同锰氧化态的相对表面浓度。这些氧化锰表面将通过与水中砷氧阴离子的反应来探测，以建立锰氧化物结构和反应性的差异对环境中氧化还原反应的控制。虽然在广泛的土壤环境中发现的水钠锰矿是拟议研究的主要目标，但纳米氧化锰也存在于环境中，并对当前的研究感兴趣。为了加深对纳米锰氧化物在低温地球化学中可能发挥的作用的理解，研究人员将研究纳米MnOOH颗粒的反应性和电子结构随尺寸的变化。将制备粒径分布均匀的纳米MnOOH，范围从20到80A，并在不同pH的溶液中进行研究，AS氧化反应将再次用作反应活性的探针。该研究项目的这一特定阶段不仅将发展对氧化锰的尺寸-反应关系的了解，而且总体上将有助于地球化学界评估纳米化学在环境中的重要性的更广泛的努力。拟议的研究具有重要的教育和宣传部分。首先，NSF资金将用于支持和培训特拉华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，特拉华大学的一名本科生优等生将进行有关该项目的研究。研究小组成员将参加在每个参与机构轮流举行的两年一次的会议，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，参与该项目的研究人员的科学广度将受益于在不同土壤和表面化学领域拥有专业知识的小组之间不断交流思想和概念。这一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对在受AS工业和农业投入影响的土壤上建造住房开发非常关注，将与特拉华州资源和环境控制部的人员合作举行市政厅会议，向公民通报我们的研究。这种形式的外联，以及在特拉华大学农业和自然资源学院年度开放日(农业日)上与感兴趣的公民的直接接触，对于向特拉华州人介绍环境科学的类型和意义以及学术机构正在处理的问题至关重要。

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.