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Understanding Mono- and Bivalent Ion Selectivities of Nanoporous Graphene Using Ionic and Bi-ionic Potentials
Mandakranta Ghosh1, Lukas Madauß2, Marika Schleberger2
1Soft Matter, Fluidics and Interfaces, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, Netherlands.
Langmuir : the ACS Journal of Surfaces and Colloids
|June 6, 2020
Summary
Nanoporous graphene shows different ion behavior based on charge. Bivalent cations adsorb onto graphene, affecting membrane potential differently than monovalent cations.
Area of Science:
- Materials Science
- Electrochemistry
- Nanotechnology
Background:
- Nanoporous graphene membranes exhibit selective ion transport.
- Donnan potentials are crucial for understanding ion behavior across membranes.
Purpose of the Study:
- Investigate differences in Donnan potentials between reservoirs separated by nanoporous graphene with varying cations.
- Compare monovalent and bivalent cation interactions with nanoporous graphene.
Main Methods:
- Donnan dialysis experiments using monovalent (KCl, NH4Cl) and bivalent (MgCl2, CaCl2, CuCl2) salts.
- Measurement of ionic potential (single cation) and bi-ionic potential (different cations).
Main Results:
- Clear Donnan and diffusion potential plateaus observed for most salts, except CuCl2.
- Bivalent cations showed lower scaled membrane potential (≈50%) than monovalent cations (≈72%) in the Donnan exclusion regime, attributed to adsorption.
- Diffusion regime reached at lower ionic strength for bivalent cations.
- Membrane potential independent of ion type for Mg2+, Ca2+, KCl, and NH4Cl.
- CuCl2 showed a shifted potential curve and no observed Donnan plateau at low ionic strength.
- Bi-ionic potential measurements provided insights into cation selectivity.
Conclusions:
- Ion adsorption on graphene significantly influences membrane potential, particularly for bivalent cations.
- Graphene's ion selectivity is dependent on cation charge and specific ion-graphene interactions.
- Ion exchange with monovalent salts can mitigate ion adsorption effects.
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