Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Environ Sci Technol. 2010 Jan 1;44(1):61-7. doi: 10.1021/es901882a.
Electron exchange between aqueous Fe(II) and structural Fe(III) in iron oxides and oxyhydroxides is important for understanding degradation of environmental pollutants through its apparent constitutive role underlying highly reactive "sorbed Fe(II)" and by catalyzing phase interconversion among these minerals. Although a mechanistic understanding of relationships between interfacial Fe(II)(ads)-Fe(III)(oxide) electron transfer, bulk electron conduction, Fe(II) release, and phase transformation behavior is emerging, much remains unclear, in part due to poorly interconnected investigations. The focus of this study is on reconciling two mutually similar observations of Fe(II)-catalyzed hematite growth documented spectroscopically and microscopically under substantially different chemical conditions. Here, we employ iron isotopic labeling to demonstrate that hematite grown on the (001) surface in Fe(II)-oxalate solution at pH 2.10 and 348 K has magnetic properties that closely correspond to those of hematite grown in Fe(II) solution at pH 7.4 and room temperature. The temperature evolution and extent of the Morin transition displayed in these two materials strongly suggest a mechanistic link involving trace structural Fe(II) incorporation into the growing hematite. Our findings indicate that Fe(II) catalyzed growth of hematite on hematite can occur under environmentally relevant conditions and may be due to bulk electron conduction previously demonstrated for hematite single crystals.
水溶液中 Fe(II) 和铁氧化物及氢氧化物中结构 Fe(III) 之间的电子交换对于理解环境污染物的降解非常重要，因为它在高反应性“吸附态 Fe(II)”的形成中起着明显的组成作用，并通过催化这些矿物之间的相转化来实现。尽管人们对界面 Fe(II)(ads)-Fe(III)(氧化物)电子转移、体相电子传导、Fe(II)释放和相转变行为之间的关系有了一定的机制理解，但仍有许多问题尚不清楚，部分原因是研究之间缺乏相互关联。本研究的重点是调和在化学条件明显不同的情况下，通过光谱和显微镜记录到的两个相互类似的赤铁矿生长的 Fe(II)催化观察结果。在这里，我们采用铁同位素标记来证明在 pH 2.10 和 348 K 的 Fe(II)-草酸盐溶液中在(001)表面生长的赤铁矿具有与在 pH 7.4 和室温下的 Fe(II)溶液中生长的赤铁矿非常相似的磁性。这两种材料中显示的温度演变和 Morin 转变程度强烈表明存在涉及痕量结构 Fe(II)掺入生长赤铁矿的机制联系。我们的发现表明，在环境相关条件下，赤铁矿可以在赤铁矿上发生 Fe(II)催化生长，这可能是由于之前在赤铁矿单晶中证明的体相电子传导所致。
