SPARKS Research 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.
