Stable cation-controlled reduced graphene oxide membranes for improved NaCl rejection

Abstract

Reduced graphene oxide (rGO) membranes have drawn intensive attention in applications of desalination and molecular sieving, owing to their stable and selective two-dimensional (2D) channels. However, their performance, particularly the selectivity for water and ions separation, is still under the theoretical limit. In this research, we incorporated potassium cations (K+) into the laminar channels of rGO membranes to form stable and selective K-controlled rGO (K-rGO) membranes for water and NaCl separation. These K-rGO membranes can be prepared by either thermally reducing K-controlled GO (K-GO) membranes in air or by soaking rGO membranes thermal-reduced in air (Air-rGO) in KCl solutions. Compared with reported K-GO and Air-rGO membranes, as-prepared K-rGO membranes exhibit narrower interlayer spacing in NaCl solutions due to the strong K+-π interaction between K+ and π-electron cloud on rGO nanosheets. This strong K+-π interaction can stabilize and confine 2D nanochannels and prevent the permeation of other cations, such as Na+, into rGO laminates, contributing to the enhanced NaCl rejection (91%) of K-rGO membranes. This work advances the understanding of the mass transport in rGO membranes and provides new insights into the design of selective 2D membranes for desalination, ionic sieving and other environmental applications.