Electron transfer reactions at iron mineral surfaces in the presence of organic sorbates

铁矿物表面的氧化还原反应在确定缺氧地下水系统的整体生物地球化学环境中起着重要作用。先前的研究表明，在矿物相中吸附的亚铁氧化可能导致矿物质-水界面的重塑，从而可能影响缺氧含水层中的电子传递过程。在第一个资助期内，我们详细研究了矿物表面亚铁氧化如何以及在何种条件下影响电子转移过程。以四氯化碳（CCl4）为模型氧化剂，我们进一步证明，基于模型氧化剂稳定同位素组成变化的反应示踪方法可以成功地用于表征铁（III）氢氧化物表面结合铁（II）的表面反应活性和动力学。迄今为止，基于过程的铁矿物系统中氧化还原活性溶质表面介导转化的研究主要是在缺乏天然有机质的模型系统中进行的。然而，在自然系统中，矿物表面不可避免地与OM接触。吸附的DOM在水溶液和矿物表面与铁相互作用，可能影响非均相电子转移过程。一方面，DOM在铁氢氧化物上的吸附可能会干扰活性Fe（II）表面位点的形成。另一方面，DOM含有氧化还原活性醌基团，可能作为介质增强电子在矿物表面的转移。在这个后续项目中，我们计划研究各种有机山梨酸，如氧化还原惰性有机酸、氧化还原活性醌、腐殖质物质和DOM对铁矿物表面电子转移反应的影响。此外，我们将研究硫化物作为额外的氧化还原活性天然成分对dom -铁界面氧化还原过程的影响。

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 mineralwater interphase and thus may affect electron transfer processes in anoxic aquifers. In the first funding period, we studied in detail how and at which conditions oxidation of ferrous iron at mineral surfaces affects electron transfer processes. Using carbon tetrachloride (CCl4) as model oxidant, we could further demonstrate, that the proposed reactive tracer approach, which is based on changes of the stable isotopic composition of model oxidants, could be successfully applied to characterize the surface reactivity and dynamics of surface bound Fe(II) species at iron(III)hydroxides. 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 contain redox active quinone moieties and may act as a mediator enhancing the electron-transfer across the mineral surface. In this follow-up project we propose to investigate the effects of various organic sorbates such as redox-inert organic acids as well as redox-active quinones, humic substances and DOM on electron transfer reactions at iron mineral surfaces. Furthermore, we will investigate the effects of sulfide as additional redox active natural component on DOM-iron interfacial redox processes.