# Tuneable Sieving of Ions Using Graphene Oxide Membranes

## TL;DR

This paper presents a method to precisely control the interlayer spacing of graphene oxide membranes, enabling tunable ion sieving with high salt rejection and minimal impact on water permeability, advancing desalination technology.

## Contribution

It introduces a scalable technique to achieve adjustable interlayer spacing in graphene oxide membranes for effective ion sieving in water.

## Key findings

- Interlayer spacing d can be tuned from ~9.8 to 6.4 Angstroms.
- Ion permeation is thermally activated with energy barriers of 10-100 kJ/mol.
- Membranes achieve 97% NaCl rejection with minimal water transport reduction.

## Abstract

Graphene oxide membranes show exceptional molecular permeation properties, with a promise for many applications. However, their use in ion sieving and desalination technologies is limited by a permeation cutoff of ~9 Angstrom, which is larger than hydrated ion diameters for common salts. The cutoff is determined by the interlayer spacing d ~13.5 Angstrom, typical for graphene oxide laminates that swell in water. Achieving smaller d for the laminates immersed in water has proved to be a challenge.Here we describe how to control d by physical confinement and achieve accurate and tuneable ion sieving. Membranes with d from ~ 9.8 Angstrom to 6.4 Angstrom are demonstrated, providing the sieve size smaller than typical ions' hydrated diameters.In this regime, ion permeation is found to be thermally activated with energy barriers of ~10-100 kJ/mol depending on d. Importantly, permeation rates decrease exponentially with decreasing the sieve size but water transport is weakly affected (by a factor of <2). The latter is attributed to a low barrier for water molecules entry and large slip lengths inside graphene capillaries. Building on these findings, we demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.

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Source: https://tomesphere.com/paper/1701.05519