Tunable Sieving of Ions Using Graphene Oxide: Swelling Peculiarities in Free-Standing and Confined States

Abstract

The paper describes a comparative study of swelling processes in free-standing graphene oxide (GO) membranes and GO laminates encapsulated with epoxy glue. For free-standing graphene oxide membranes, a huge variation in d-spacing in the range of 8–12 Å depending on the ambient humidity and from 12 to >30 Å depending on the electrolyte type and its concentration was revealed using direct in situ and in operando XRD studies. Limited swelling at various humidity levels as well as in electrolyte solution with low constriction/expansion of epoxy-encapsulated GO is counterposed to that of free-standing graphene oxides. The swelling suppression was explained by both physical constriction and the intercalation of amines into GO laminates, which was proved by local EDX studies. This results in ion diffusivity variation for over 2 orders of magnitude in free-standing and constrained graphene oxide membranes and provides factual evidence for tunable sieving of ions with confined graphene oxides.

Swelling of Thin Graphene Oxide Film in Water Vapor Studied by In Situ Spectroscopic Ellipsometry

“…The interlayer spacing plays an important role in the transport properties of GO. The unique interlayer expansion of GO opens up opportunities for accurate control of functional properties such as tunable ionic transport through GO membranes for water purification and desalination. , The rapid responses of ordered GO layer structures can be utilized in ultrafast humidity sensors. ,, However, the swelling can also have an adverse effect on certain applications. For example, it has been found that the water purification performance of a GO membrane is far below its ideal performance due to the swelling effect of GO in aqueous solutions …”

“…The swelling behavior of GO is typically studied by measuring the change in d -spacing by X-ray diffraction (XRD). ,,, However, the disruption of the interlayer periodicity by swelling results in substantial peak broadening in diffraction spectra . In addition, XRD scans typically take at least a few minutes and are not easily obtained in controlled environments.…”

“…The unique interlayer expansion of GO opens up opportunities for accurate control of functional properties such as tunable ionic transport through GO membranes for water purification and desalination. 28,29 The rapid responses of ordered GO layer structures can be utilized in ultrafast humidity sensors. 21,30,31 However, the swelling can also have an adverse effect on certain applications.…”