Osman MA, Suter UW
Department of Materials, Institute of Polymers, ETH Zentrum, CH-8092, Zürich, Switzerland
J Colloid Interface Sci. 1999 Jun 15;214(2):400-406. doi: 10.1006/jcis.1999.6195.
Model muscovite with high cation exchange capacity was prepared, the surface of which was saturated with a single species of alkali metal ions. The kinetics and thermodynamics of the exchange reaction of the 1-dodecylpyridinium ion (NDP+) with alkali metal ions onto that substrate were studied. The exchange rate depended on the type of alkali metal ions present on the surface because of their different affinities to mica. However, in all cases the reaction was fast at the beginning and about 50% of the ions were exchanged within one hour; then the reaction rate decreased and equilibrium was only reached after several hours. This was attributed to a rate-determining rearrangement step in which the alkyl chains rearrange to adopt a dense packing. The reactivity of the alkali metal ions was in the order Li+ > Na+ > K+ > Rb+, Cs+, and in the case of K+, Rb+, and Cs+, equilibrium was only reached after 72 h. The lithium and sodium ions were exchanged almost quantitatively until a saturation value was nearly reached, while the K+, Rb+, and Cs+ exchange isotherms were less steep. The equilibrium constants (K) as well as the ion exchange capacity (S) were calculated by least-squares fits. Since K is infinite for quantitative exchange and decreases asymptotically upon deviation from this ideal behavior, the high K values (>10) of the NDP+/Li+ and Na+ exchange cannot be accurately determined. K ranges between 1 and 3 for the NDP+/K+, Rb+, and Cs+ exchange. The affinity of NDP+ to muscovite was similar or slightly higher than that of K+, Rb+, and Cs+, but was much higher than that of Li+ and Na+. The presence of oxonium ions in water did not strongly influence the exchange reaction on delaminated mica, as in the case of mica sheets, due to its high CEC. Copyright 1999 Academic Press.
制备了具有高阳离子交换容量的模型白云母，其表面被单一碱金属离子饱和。研究了1-十二烷基吡啶鎓离子（NDP +）与碱金属离子在该底物上的交换反应动力学和热力学。由于碱金属离子对云母的亲和力不同，交换速率取决于表面存在的碱金属离子类型。然而，在所有情况下，反应开始时都很快，约50%的离子在一小时内被交换；然后反应速率下降，数小时后才达到平衡。这归因于一个速率决定的重排步骤，其中烷基链重排以形成紧密堆积。碱金属离子的反应活性顺序为Li + > Na + > K + > Rb +，Cs +，对于K +、Rb +和Cs +，仅在72小时后才达到平衡。锂和钠离子几乎定量地被交换，直到接近饱和值，而K +、Rb +和Cs +的交换等温线较平缓。通过最小二乘法拟合计算了平衡常数（K）以及离子交换容量（S）。由于定量交换时K是无限的，并且偏离这种理想行为时会渐近减小，因此NDP + /Li +和Na +交换的高K值（>10）无法准确确定。NDP + /K +、Rb +和Cs +交换的K值在1到3之间。NDP +对白云母的亲和力与K +、Rb +和Cs +相似或略高，但远高于Li +和Na +。由于其高阳离子交换容量，水中氧鎓离子的存在对分层云母上的交换反应没有强烈影响，就像云母片的情况一样。版权所有1999年学术出版社。
