Formation of poorly crystalline iron monosulfides: Surface redox reactions on high purity iron, spectroelectrochemical studies
Formation of poorly crystalline iron monosulfides: Surface redox reactions on high purity iron, spectroelectrochemical studies
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DOI：
10.1016/j.corsci.2006.03.010
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发表时间：
2006-11
影响因子：
8.3
通讯作者：
E. Hansson;M. Odziemkowski;R. Gillham
中科院分区：
文献类型：
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作者：
E. Hansson;M. Odziemkowski;R. Gillham
在使用铁对地下水中的氯化溶剂进行还原性脱卤时，由于硫酸盐还原菌的存在，预计会形成硫化氢。为了模拟这些过程，研究了99.99%纯铁与0.1M NaHCO 3脱氧溶液（添加3.1×10−5-7.8×10− 3 M Na 2S·9 H2O）之间的界面。通过原位正常拉曼光谱（NRS）和非原位技术、X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）、能量色散X射线（EDX）表征表面过程。在原位NRS测量过程中监测开路电位（OCP），并进行动电位阳极极化测量以揭示铁电极的电化学行为。开路电位-时间瞬变表明，天然氧化物在脱气碳酸氢盐溶液中不稳定，并发生还原溶解（即自还原），使金属Fe被Fe（OH）2覆盖，吸附OH−和“磁铁矿样”氧化物斑块。在注射Na 2S溶液后，铁界面立即经历复杂的氧化还原表面过程，并形成结晶不良的FeS膜。动电位阳极极化测量表明FeS膜的机械击穿。这个击穿过程的起源和起始尚不清楚，但可能是薄膜生长过程中产生的内应力的结果。基于电化学测量支持的表面研究，提出了在铁界面发生的复杂氧化还原过程的概念模型。该模型描述了结晶不良的FeS的结构发展，其分解，允许Fe的进一步溶解和在界面处形成FeOOH。同时，尽管存在厚的FeS层，但氢的进入是明显的，因为在铁材料的本体中典型的氢裂纹。这项工作揭示了铁/硫化物溶液界面的复杂性，这方面的知识是重要的，以了解有机地下水污染物的还原动力学。
In the use of iron for reductive dehalogenation of chlorinated solvents in ground water, due to presence of sulfate-reducing bacteria the formation of hydrogen sulfide is expected. To simulate those processes the interface between 99.99% pure iron and 0.1M NaHCO3deoxygenated solution with 3.1×10−5–7.8×10−3M Na2S·9H2O added was studied. The surface processes were characterised by the in situ normal Raman spectroscopy (NRS) and ex situ techniques; X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX). The open circuit potential (OCP) was monitored during in situ NRS measurements, and potentiodynamic anodic polarization measurements were carried out to reveal electrochemical behaviour of iron electrode. Open circuit potential–time transients indicated that the native oxide is unstable in deaerated bicarbonate solution and undergoes reductive dissolution (i.e. autoreduction) leaving the metallic Fe covered by Fe(OH)2, adsorbed OH−, and patches of ‘magnetite-like’ oxide. Immediately upon injection of the Na2S-solution the iron interface undergoes complex redox surface processes and a poorly crystalline FeS film forms. Potentiodynamic anodic polarization measurements indicated a mechanical breakdown of the FeS film. The origin and initiation of this breakdown process is not clear but is probably a result of internal stress developed during film growth. Based on surface studies supported by electrochemical measurements, a conceptual model for the complex redox processes occurring at the iron interface is proposed. This model describes the structural development of a poorly crystalline FeS, which breaks down, allowing further dissolution of the Fe and formation of FeOOH at the interface. Simultaneously and despite the existence of thick layer of FeS the entrance of hydrogen was evident as the typical hydrogen cracks in bulk of the iron material. This work shed the light on the complexity of the iron/sulfide solution interface, this knowledge is important to understand the kinetic of reduction of organic groundwater contaminants.