Probing the site occupancies of Co-, Ni-, and Mn-substituted biogenic magnetite using XAS and XMCD
Probing the site occupancies of Co-, Ni-, and Mn-substituted biogenic magnetite using XAS and XMCD
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DOI：
10.2138/am.2008.2681
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发表时间：
2008-07-01
影响因子：
3.1
通讯作者：
Lloyd, Jonathan R.
中科院分区：
文献类型：
--
作者：
Coker, Victoria S.;Pearce, Carolyn I.;Lloyd, Jonathan R.
亚铁磁性纳米颗粒在工业中有许多用途，包括磁记录介质和变压器，然而这些颗粒的合成通常很昂贵。在这项研究中，Fe（3+）还原菌Geculum sulfurreducens和Shewanella oneidensis被用于合成尖晶石铁氧体纳米颗粒，其化学通式为M（x）Fe（3-x）O（4），其中M是Co、Ni、Mn、Zn或Mn和Zn的组合。这是在环境温度下，通过异化还原的Fe（3+）-羟基氧化物含有适当的取代阳离子。结合L-边和K-边X射线吸收光谱（XAS）和L-边X射线磁性圆二色性（XMCD）被用来确定的网站占位，价态，和本地结构的铁和取代阳离子内的尖晶石。使用每种细菌产生的Ni和Co铁氧体非常相似，因此本研究得出结论，尽管所用细菌的还原机制不同，但最终产物明显不变。镍铁氧体只含有Ni（2+），其中至少80%为O（h）配位。钴铁氧体只含有Co（2+），但在T（d）配位中占很大比例（高达45%），显示出对T（d）位置的轻微偏好。当Mn含量超过3%（相对于Fe的量）或还存在一些Zn时，Mn铁氧体仅在O（h）位上含有Mn（2+），而在T（d）位上含有Mn（2+）和Mn（3+）的混合物。这项研究成功地生产了一系列纳米颗粒铁氧体，这些铁氧体可以使用相对环境友好的方法在工业上生产。
Ferrimagnetic nanoparticles have many uses in industry including in magnetic recording media and transformers, however these particles are often expensive to synthesize. In this study, the Fe(3+)-reducing bacteria Geobacter sulfurreducens and Shewanella oneidensis were used to synthesize spinel ferrite nanoparticles of the general chemical formula M(x)Fe(3-x)O(4), where M is either Co, Ni, Mn, Zn, or a combination of Mn and Zn. This was done at ambient temperatures through the dissimilatory reduction of Fe(3+)-oxybydroxides containing the appropriate substitutional cations. A combination of L-edge and K-edge X-ray absorption spectroscopy (XAS) and L-edge X-ray magnetic circular dichroism (XMCD) was used to determine the site occupancies, valence, and local structure of the Fe and substitutional cations within the spinels. The Ni and Co ferrites produced using each bacterium were very similar and therefore this study concludes that, despite the difference in reduction mechanism of the bacteria used, the end-product is remarkably unaltered. Nickel ferrites contained only Ni(2+), with at least 80% in O(h) coordination. Cobalt ferrites contained only Co(2+) but with a significant proportion (up to 45%) in T(d) coordination, showing a slight preference for T(d) sites. The Mn-ferrites contained Mn(2+) only on the O(h) sites but a mixture of Mn(2+) and Mn(3+) on T(d) sites when the amount of Mn exceeded 3% (compared to the amount of Fe) or some Zn was also present. This study successfully produced a range of nanoparticulate ferrites that could be produced industrially using relatively environmentally benign methodologies.