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决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。以前的研究表明，吸附的亚铁在矿物相的氧化可能导致矿水界面的重塑，从而影响缺氧含水层中的电子转移过程。在第一个资助期，我们详细研究了亚铁在矿物表面的氧化如何以及在什么条件下影响电子转移过程。以四氯化碳(CCl4)为模型氧化剂，我们可以进一步证明，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表面结合的Fe(II)物种在Fe(III)氢氧化物上的表面反应性和动力学。到目前为止，氧化还原活性溶质在铁矿物体系中的表面催化转化研究主要是在无天然有机物的模型体系中进行的。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可能会影响多相电子转移过程，因为它在水溶液中和矿物表面都与铁相互作用。一方面，DOM在氢氧化铁表面的吸附可能干扰了Fe(II)表面活性中心的形成。另一方面，DOM含有氧化还原活性的苯二酚部分，可能起到促进矿物表面电子转移的介体作用。在这个后续的项目中，我们建议研究各种有机山梨酸酯，如氧化还原惰性有机酸以及氧化还原活性的苯二酚、腐殖质和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-Iron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.