Effects of the Exchange Capacity and Cross-Linking Degree on the Hydration States of Anions in Quantitative Loading onto Strongly Basic Anion-Exchange Resins
Effects of the Exchange Capacity and Cross-Linking Degree on the Hydration States of Anions in Quantitative Loading onto Strongly Basic Anion-Exchange Resins
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DOI：
10.1021/ac101707j
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发表时间：
2010-10-15
影响因子：
7.4
通讯作者：
Nakao, Satoshi
中科院分区：
文献类型：
--
作者：
Yuchi, Akio;Kuroda, Shigeo;Nakao, Satoshi
测定了在25 ℃和50%相对湿度下干燥的确定阴离子形式（10种单电荷、3种双电荷、1种三电荷和1种四电荷）的5种强碱性阴离子交换树脂（具有不同交换容量和二乙烯基苯交联度的三甲基铵型）的含水量。采用X射线吸收精细结构和衍射方法对传统树脂进行了研究，结果表明，本方法给出了与阴离子强烈相互作用的固有水分子的数量。弱水合阴离子（Cl（-）、Br（-）和ClO（4）（-））和小阴离子（F（-））的水合数与交换容量无关，并随交联度的增加而略有下降，特别是在8%时。小的强水合离子F（-）保持在水中的水合结构，在树脂中形成水分离离子对，而其他弱水合离子略微脱水，形成接触离子对。强水化离子H（2）PO（4）（-）的水化数随交换容量和交联度的增加而明显降低，并伴有阴离子间的氢键作用。这可能与H（2）PO（4）（-）型树脂的其它特性有关，如定量交换所需的较高浓度、交换程度的红外光谱的系统性变化以及易于热脱水而得到H（2）P（2）O（7）（2-）。相比之下，多价阴离子在不脱水的情况下进行交换，因为与一价阴离子相比，树脂中允许的空间更大，并且与水的相互作用更强。
The water content was determined for five strongly basic anion-exchange resins (trimethyammonium type having different exchange capacities and cross-linking degrees by divinylbenzene) in definite anionic forms (ten singly, three doubly, one triply, and one quadruply charged) dried at 25 degrees C and at a relative humidity of 50%. Incorporation of the results of the previous research on the conventional resins by X-ray absorption fine structure and diffraction methods indicated that the present method gave the number of intrinsic water molecules strongly interacting with an anion. The hydration numbers of weakly hydrating anions (Cl(-), Br(-), and ClO(4)(-)) and a small anion (F(-)) were independent of the exchange capacity and slightly decreased with an increase in cross-linking, especially at 8%. The small and strongly hydrating ion F(-) kept the in-water hydration structure to form a water-separated ion pair in the resins, while the other weakly hydrating ions were appreciably dehydrated to form a contact ion pair. The hydration number of a strongly hydrating ion, H(2)PO(4)(-), appreciably decreased with increases in both the exchange capacity and cross-linking degree accompanied by intermolecular hydrogen bonding between the anions. This may be related to other characteristics of the H(2)PO(4)(-) form resin, such as a higher concentration required for quantitative exchange, a systematic change in infrared spectra on the degree of exchange, and facile thermal dehydration, giving H(2)P(2)O(7)(2-). In contrast, multivalent anions were exchanged without dehydration, due to the larger space allowed for in the resins and the stronger interaction with water compared to those of monovalent anions.