Electrochemical Characterization of Redox Processes Mediated by Natural Organic Matter: Effects of Molecular Size/Shape on Electron Transfer at Environmental Interfaces

With support from the Environmental Chemical Sciences program in the Division of Chemistry, Professor Paul Tratnyek at Oregon Health & Science University and his students will study how the molecular size and shape of natural organic matter (NOM) influences its redox reactions with mineral surfaces. NOM plays significant roles in many biogeochemical/environmental processes and in almost all cases, these processes involve redox (oxidation-reduction) reactions that occur on the surfaces of particulate materials such as minerals and microbes.

To characterize these reactions, the project will use a suite of electrochemical methods to measure electron transfer to and from samples of NOM with varying size and shape. The results will have a wide range of potential applications, including modeling of air pollution, management of agricultural soils, and optimization of drinking water disinfection.

As well as graduate students, the project team will include interns from several nearby colleges that have strong programs for including undergraduate students in research.

Reactions of NOM with the surfaces of minerals (and microbes) require sufficient proximity between the redox-active moieties in NOM and redox-active sites on the surface. This proximity is strongly dependent on the size and shape of the NOM, which can vary from discrete monomers to unfolded polymers to aggregates and other supramolecular structures like micelles.

These effects can be studied electrochemically, since electrode response to NOM also is an interfacial process that is strongly dependent on NOM size/shape. The overarching technical objective of the proposed project will be to determine qualitative and quantitative relationships between the size and structure of NOM and its redox potentials, kinetics, and capacities using a complementary suite of electrochemical methods that allows for resolution of the many complex interactions involved.

In the process, we expect to address several fundamental, cross-cutting issues regarding NOM redox chemistry, including that its bulk redox properties are the net effect of multiple redox active moieties that are linked by intra-molecular transfer, and that its capacity for electron exchange/storage reflects both labile and kinetically-limited components to varying degrees depending on operational factors.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.