Distinguished Visitor Seminar - Unravelling Mechanisms of Redox Reactions Facilitated by Iron-Bearing Clay Minerals
The Fe(II)/Fe(III) redox couple plays a commanding role in geochemistry, biology, and environmental science. Under reducing conditions, aqueous-soluble Fe(II) is an important source of electrons that control the valence and speciation of other metals, the transformation of organics, the production of radical oxygen species (ROS), and the metabolism of iron oxidizing bacteria.Under oxic conditions, sparingly soluble Fe(III) minerals are important metals sorbents, catalytic substrates, and electron acceptors for dissimilatory iron reducing bacteria.Any biogeochemical or hydrological process that causes movement of a redox boundary is thus likely to profoundly affect the system chemistry and microbiology by driving changes in the concentration balance between Fe(II) and Fe(III).
Iron-bearing clay minerals are important buffers for this concentration balance, through their unique ability to reversibly accept and release electron density by manipulation of structural Fe valance without decomposition of the enclosing silicate framework.However, relating structural iron content to redox buffering capacity and its associated redox reactivity remains poorly predictable, due in part to key fundamental knowledge gaps in 1) electron transfer mobility within iron-rich components of clay structures, 2) edge versus basal surface access to these electrons for interfacial redox reactions, and 3) the role and impact of adsorbed Fe(II).
This presentation will overview more than a decade of research into these fundamental questions, drawing heavily upon computational molecular simulations, synchrotron X-ray absorption spectroscopies, and temperature-dependent Mössbauer spectroscopy of redox reactions within and at surfaces of iron-bearing clay mineral structures.In particular, this has required a marriage of modern ab initio simulations and the electron transfer theory pioneered by Marcus more than half a century ago, to accurately predict electron hopping mobilities at room temperature in clays. Modeling and measurements of interfacial electron transfer kinetics to/from adsorbed Fe at edges and basal surfaces will be presented, and key remaining questions will be discussed.In addition to its basic importance to geochemical and biogeochemical redox processes in natural systems, these advances may also aid understanding of the antibacterial properties of clays, because of their direct connection to heterogeneous Fenton reactions that sustain ROS generation at the clay/environment interface.
About Professor Kevin Rosso
Kevin Rossois a Laboratory Fellow and the Associate Director of the Physical Sciences Division for Geochemistry at Pacific Northwest National Laboratory (PNNL), in Washington State, U.S.A.He received his B.S. degree in Geological Sciences from Cal Poly at Pomona, California in 1992, and his M.S. and Ph.D. degrees in Geochemistry from Virginia Tech in 1994 and 1998.His career to date has been at PNNL where, after starting as an entry-level research scientist in 1998, he was promoted to its highest rank by 2010 and now leads a research group of approximately 35 Ph.D. students, post-doctoral fellows, and staff scientists.Professor Rosso has published over 300 papers and book chapters, a body of work with an H-index of 56 and over 12,000 citations. He is a regularly invited speaker, with over 100 distinguished lectures delivered at University colloquia, workshops and conferences internationally.
Professor Rosso is best known for his pioneering research on electron transfer reactions between aqueous ions, mineral surfaces, and bacterial enzymes. Beginning with topics such as metal sulfide oxidation, bacterial reduction of metal oxides, contaminant interactions with clay minerals, and mechanisms of crystal growth and dissolution, his research expanded into geologic carbon sequestration, stress corrosion cracking in alloys, performance optimization of lithium battery materials, and the design of semiconductor materials for solar photocatalysis. Professor Rosso is well recognized as being at the center of the field of molecular geochemistry, a field he helped create with the inception of advanced tools such as scanning probe microscopy, quantum mechanical molecular simulations, and massively parallel supercomputers.
Professor Rosso won the Mineralogical Society of America Award in 2004, where he serves as Life Fellow, PNNL’s Laboratory Director’s Award in 2004, Virginia Tech’s Outstanding Recent Alumnus Award in 2009, and the Mineralogical Society’s Hallimond Lectureship in 2016. He held a Visiting Professorship at the University of Manchester, U.K. in 2014-2016, and is currently an Adjunct Professor at the University of New South Wales, Australia and an Invited Professor at the University of Grenoble, France. Professor Rosso was an Associate Editor for American Mineralogist in 2004-2006, for Geochimica et Cosmochimica Acta in 2008-2011, and currently serves on the Editorial Boards of ACS Earth and Space Chemistry and PLOS One. He leads the U.S. Department of Energy’s major geochemistry program at PNNL.
The aim of IAS seminars is to develop new thinking on the big issues that are of current concern/interest for IAS visiting Fellows.Each Fellow is asked to present a core idea that informs their current work, or a problem that they are tackling, that could benefit from cross-disciplinary thinking. These seminars are informal and designed to encourage discussion.
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