Electrostatic-induced ion-confined partitioning in graphene nanolaminate membrane for breaking anion–cation co-transport to enhance desalination

Constructing nanolaminate membranes made of two-dimensional graphene oxide nanosheets has gained enormous interest in recent decades. However, a key challenge facing current graphene-based membranes is their poor rejection for monovalent salts due to the swelling-induced weak nanoconfinement and the transmembrane co-transport of anions and cations. Herein, we propose a strategy of electrostatic-induced ion-confined partitioning in a reduced graphene oxide membrane for breaking the correlation of anions and cations to suppress anion-cation co-transport, substantially improving the desalination performance. The membrane demonstrates a rejection of 95.5% for NaCl with a water permeance of 48.6 L m⁻² h⁻¹ bar⁻¹ in pressure-driven process, and it also exhibits a salt rejection of 99.7% and a water flux of 47.0 L m⁻² h⁻¹ under osmosis-driven condition, outperforming the performance of reported graphene-based membranes. The simulation and calculation results unveil that the strong electrostatic attraction of membrane forces the hydrated Na⁺ to undergo dehydration and be exclusively confined in the nanochannels, strengthening the intra-nanochannel anion/cation partitioning, which refrains from the dynamical anion-cation correlations and thereby prevents anions and cations from co-transporting through the membrane. This study provides guidance for designing advanced desalination membranes and inspires the future development of membrane-based separation technologies.