Teschke Omar, Roberto de Castro Jose, Soares David Mendez
UNICAMP, IFGW, DFA, Laboratório de Nanoestruturas e Interfaces, 13083-859 Campinas, São Paulo, Brazil.
ACS Omega. 2019 Sep 10;4(13):15684-15693. doi: 10.1021/acsomega.9b02299. eCollection 2019 Sep 24.
A technique to image ion pairs in solution is reported. We investigated structural and dynamic properties of ion-pair distributions deposited on highly oriented pyrolytic graphite (HOPG) surfaces in electrolyte solutions. Atomic force microscopy images of HOPG immersed in NaCl and KCl solutions display regular arrangements on top of the hexagonal carbon rings forming the HOPG atomic structure. These arrangements are the result of the low value of the aqueous interfacial dielectric constant (ε ≈ 3-11). The measured ion-pair radius is a function of the salt present in the solution; for KCl, the ion-pair radius is equal or smaller than 0.42 nm; for NaCl, the ion-pair radius is 0.36 nm. A comparison of these values with their crystalline lattice dimensions indicates that both KCl and NaCl ion pairs in solution at the HOPG/solution interfacial region exist as tight contact ion pairs in quasistationary distributions. The NaCl ion-pair distribution forms an aligned arrangement, and the KCl distribution is formed by intercalated pairs.
报道了一种对溶液中的离子对进行成像的技术。我们研究了沉积在电解质溶液中高度取向热解石墨（HOPG）表面的离子对分布的结构和动力学性质。浸入NaCl和KCl溶液中的HOPG的原子力显微镜图像显示，在构成HOPG原子结构的六边形碳环顶部有规则排列。这些排列是水相界面介电常数较低（ε≈3 - 11）的结果。测得的离子对半径是溶液中存在的盐的函数；对于KCl，离子对半径等于或小于0.42 nm；对于NaCl，离子对半径为0.36 nm。将这些值与其晶格尺寸进行比较表明，在HOPG/溶液界面区域的溶液中，KCl和NaCl离子对均以紧密接触离子对的形式存在于准静态分布中。NaCl离子对分布形成排列整齐的结构，而KCl分布由插入对形成。
