Ghosh Mandakranta, Madauß Lukas, Schleberger Marika, Lebius Henning, Benyagoub Abdenacer, Wood Jeffery A, Lammertink Rob G H
Soft Matter, Fluidics and Interfaces, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, Netherlands.
Fakultät für Physik und CENIDE, Universität Duisburg-Essen, 47048 Duisburg, Germany.
Langmuir. 2020 Jul 7;36(26):7400-7407. doi: 10.1021/acs.langmuir.0c00924. Epub 2020 Jun 19.
Nanoporous graphene displays salt-dependent ion permeation. In this work, we investigate the differences in Donnan potentials arising between reservoirs, separated by a perforated graphene membrane, containing different cations. We compare the case of monovalent cations interacting with nanoporous graphene with the case of bivalent cations. This is accomplished through both measurements of membrane potential arising between two salt reservoirs at different concentrations involving a single cation (ionic potential) and between two reservoirs containing different cations at the same concentration (bi-ionic potential). In our present study, Donnan dialysis experiments involve bivalent MgCl, CaCl, and CuCl as well as monovalent KCl and NHCl salts. For all salts, except CuCl, clear Donnan and diffusion potential plateaus were observed at low and high salt concentrations, respectively. Our observations show that the membrane potential scaled to the Nernst potential for bivalent cations has a lower value (≈50%) than for monovalent cations (≈72%) in the Donnan exclusion regime. This is likely due to the adsorption of these bivalent cations on monolayer graphene. For bivalent cations, the diffusion regime is reached at a lower ionic strength compared to the monovalent cations. For Mg and Ca, the membrane potential does not seem to depend upon the type of ions in the entire ionic strength range. A similar behavior is observed for the KCl and NHCl membrane potential curves. For CuCl, the membrane potential curve is shifted toward lower ionic strength compared to the other two bivalent salts and the Donnan plateau is not observed at the lowest ionic strength. Bi-ionic potential measurements give further insight into the strength of specific interactions, allowing for the estimation of the relative ionic selectivities of different cations based on comparing their bi-ionic potentials. This effect of possible ion adsorption on graphene can be removed through ion exchange with monovalent salts.
纳米多孔石墨烯表现出盐依赖性离子渗透。在这项工作中，我们研究了由穿孔石墨烯膜隔开的含有不同阳离子的储液器之间产生的唐南电位差异。我们将单价阳离子与纳米多孔石墨烯相互作用的情况与二价阳离子的情况进行了比较。这是通过测量在涉及单一阳离子的不同浓度的两个盐储液器之间产生的膜电位（离子电位）以及在相同浓度下含有不同阳离子的两个储液器之间产生的膜电位（双离子电位）来实现的。在我们目前的研究中，唐南透析实验涉及二价的MgCl₂、CaCl₂和CuCl₂以及单价的KCl和NH₄Cl盐。对于所有盐，除了CuCl₂，在低盐浓度和高盐浓度下分别观察到了清晰的唐南电位和扩散电位平台。我们的观察结果表明，在唐南排斥区，与单价阳离子相比，二价阳离子的膜电位按能斯特电位缩放后的值较低（约50%），而单价阳离子的膜电位按能斯特电位缩放后的值较高（约72%）。这可能是由于这些二价阳离子在单层石墨烯上的吸附。对于二价阳离子，与单价阳离子相比，在较低的离子强度下就达到了扩散区。对于Mg²⁺和Ca²⁺，在整个离子强度范围内，膜电位似乎不依赖于离子类型。对于KCl和NH₄Cl的膜电位曲线也观察到了类似的行为。对于CuCl₂，与其他两种二价盐相比，膜电位曲线向较低的离子强度偏移，并且在最低离子强度下未观察到唐南平台。双离子电位测量进一步深入了解了特定相互作用的强度，通过比较不同阳离子的双离子电位，可以估算它们的相对离子选择性。通过与单价盐进行离子交换，可以消除石墨烯上可能的离子吸附效应。
