Electron transfer reactions at iron mineral surfaces in the presence of organic sorbates
Dr. Lic Chem Silvia Orsetti
(Funding: DFG Research Group FOR 580 "Electron Transfer Processes in Anoxic Aquifers)
Redox reactions at iron mineral surfaces play an important role in determining the overall biogeochemical milieu in anoxic groundwater systems. Previous studies have shown that oxidation of sorbed ferrous iron at mineral phases may cause remodelling of the mineral- water interphase and thus may affect electron transfer processes in anoxic aquifers.
Up to date, process based studies on surface mediated transformation of redox active solutes in iron mineral systems have been conducted primarily in model systems devoid of natural organic matter. In natural systems, however, mineral surfaces are inevitably in contact with OM. Sorbed DOM is likely to affect heterogeneous electron transfer processes due to its interactions with iron both in aqueous solution and at the mineral surface. On one hand, DOM sorption at iron hydroxides may interfere with the formation of reactive Fe(II) surface sites. On the other hand, DOM contains redox active quinone moieties and may act as a mediator enhancing the electron-transfer across the mineral surface. In this project we propose to investigate the effects of various organic sorbates such as redox-active quinones, humic substances and DOM on electron transfer reactions at iron mineral surfaces. In order to achieve this aim, fluorescence properties of quinones and natural organic matter in different redox states will be analyzed, since it is known that fluorescence behavior of these substances depend on redox speciation. In particular, multivariate chemiometric tools will be applied, such as Parallel Factor Analysis (PARAFAC), to analyze the emission-excitation maps of the different species. Regarding the redox modification of the samples, a well-controlled electrochemical process will be applied, which allows following up both the electron and proton transfer.