XPS determination of Mn oxidation states in Mn (hydr)oxides
XPS determination of Mn oxidation states in Mn (hydr)oxides
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DOI：
10.1016/j.apsusc.2015.12.159
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发表时间：
2016-03-15
影响因子：
6.7
通讯作者：
Kerisit, Sebastien N.
中科院分区：
文献类型：
--
作者：
Ilton, Eugene S.;Post, Jeffrey E.;Kerisit, Sebastien N.
含水锰氧化物是一类重要的矿物，有助于调节近地表环境中的地球化学氧化还原循环，也被认为是有前途的能源应用催化剂，如水的氧化。为了更好地了解它们的催化和氧化还原活性，需要对这些矿物进行完整的表征。在这篇文章中，使用x射线光电子能谱（XPS）开发了一种经验方法来量化含水多价锰氧化物的氧化状态，重点是铋矿，一种层状结构，通常存在于土壤中，但也是仿生水氧化催化剂的氧化端元。近单价Mn（II）、Mn（III）和Mn（IV）氧化物的Mn2p（3/2）、Mn3p和Mn3s谱线与组分峰相吻合；得到最佳拟合后，固定各组分的相对宽度、高度和结合能。对未知的多价样品进行拟合，使得由一组相关组分峰组成的每个氧化态的结合能、强度和峰宽允许变化。峰宽被限制以保持标准之间的差异。所有三个能级的平均氧化态和单个摩尔分数氧化态都是强相关的，Mn3s和Mn3p的分析结果非常一致，而基于Mn2p（3/2）光谱的计算给出了系统地更简化的结果。有限的化学计量分析与Mn3p和Mn3s一致。此外，有证据表明，Mn3p线的形状对成键环境的敏感性低于Mn2p线。因此，拟合Mn3p和Mn3s谱线产生了一系列Mn（氢）氧化物相的氧化态的可靠量化。相比之下，利用Mn3s线的多重分裂来确定氧化态的常用方法被发现不适用于birnessite。(C) 2016年Elsevier B.V.出版
Hydrous manganese oxides are an important class of minerals that help regulate the geochemical redox cycle in near-surface environments and are also considered to be promising catalysts for energy applications such as the oxidation of water. A complete characterization of these minerals is required to better understand their catalytic and redox activity. In this contribution an empirical methodology using X-ray photoelectron spectroscopy (XPS) is developed to quantify the oxidation state of hydrous multivalent manganese oxides with an emphasis on birnessite, a layered structure that occurs commonly in soils but is also the oxidized endmember in biomimetic water-oxidation catalysts. The Mn2p(3/2), Mn3p, and Mn3s lines of near monovalent Mn(II), Mn(III), and Mn(IV) oxides were fit with component peaks; after the best fit was obtained the relative widths, heights and binding energies of the components were fixed. Unknown multivalent samples were fit such that binding energies, intensities, and peak-widths of each oxidation state, composed of a packet of correlated component peaks, were allowed to vary. Peak-widths were constrained to maintain the difference between the standards. Both average and individual mole fraction oxidation states for all three energy levels were strongly correlated, with close agreement between Mn3s and Mn3p analyses, whereas calculations based on the Mn2p(3/2) spectra gave systematically more reduced results. Limited stoichiometric analyses were consistent with Mn3p and Mn3s. Further, evidence indicates the shape of the Mn3p line was less sensitive to the bonding environment than that for Mn2p. Consequently, fitting the Mn3p and Mn3s lines yielded robust quantification of oxidation states over a range of Mn (hydr)oxide phases. In contrast, a common method for determining oxidation states that utilizes the multiplet splitting of the Mn3s line was found to be not appropriate for birnessites. (C) 2016 Published by Elsevier B.V.