Hydration of halide anions in ion-exchange resin and their dissociation from cationic groups
Hydration of halide anions in ion-exchange resin and their dissociation from cationic groups
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DOI：
10.1021/ac049602h
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发表时间：
2004-08-01
影响因子：
7.4
通讯作者：
Harada, M
中科院分区：
文献类型：
--
作者：
Okada, T;Harada, M
用X射线吸收精细结构（XAFS）研究了阴离子交换树脂中Cl-和Br-的局域结构。的树脂，已被平衡在各种水蒸气分压下，以允许阴离子具有各种水合数，提供XAFS测量。XAFS光谱表明，存在两个散射基团周围的抗衡阴离子，即水分子和离子交换基团。回归分析允许分离来自这两个散射基团的贡献;因此，确定平均水合数（N）。水化数随离子交换对（离子交换基团和抗衡阴离子）吸附的水分子数（n）的增加而线性增加，直到离子交换对吸附ca. 3个水分子，表明所有吸附的水分子与抗衡阴离子配位。然而，当n超过3时，随着n的增加，N的增加变得很小;对于Cl-和Ca，N最终达到3.9（+/-0.4）。3.4（+/-0.5）。对水吸附等温线的详细研究表明，当这些阴离子被离子交换基团束缚时，它们的最大水合数为3，并且随着更多的水分子被供应，它们从离子交换基团解离;约。总抗衡阴离子的40%从离子交换基团解离。
The local structures of Cl- and Br- in an anion-exchange resin have been investigated by X-ray absorption fine structure (XAFS). The resins, which have been equilibrated under various partial water vapor pressures to allow the anions to have various hydration numbers, are provided for XAFS measurements. The XAFS spectra indicate that two scattering groups around the counter-anion are present, that is, water molecules and an ion-exchange group. Regression analyses allow the separation of the contributions from these two scattering groups; thus, the average hydration number (N) is determined. The hydration number linearly increases with increasing the number of water molecules (n) adsorbed by an ion-exchange pair (an ion-exchange group and a counteranion) until the ion-exchange pair adsorbs ca. 3 water molecules, indicating that all of the adsorbed water molecules coordinate the counteranion. However, an increase in N with increasing n becomes small as n exceeds 3; N finally reaches 3.9 (+/-0.4) for Cl- and ca. 3.4 (+/-0.5) for Br-. Detailed studies of the water adsorption isotherms imply that the maximum hydration number of these anions is three when they are bound by the ion-exchange groups, and as more water molecules are supplied, they are dissociated from the ion-exchange groups; ca. 40% of total counteranions are dissociated from the ion-exchange groups.