Electroregulation of graphene-nanofluid interactions to coenhance water permeation and ion rejection in vertical graphene membranes

Graphene oxide (GO) membranes with nanoconfined interlayer channels theoretically enable anomalous nanofluid transport for ultrahigh filtration performance. However, it is still a significant challenge for current GO laminar membranes to achieve ultrafast water permeation and high ion rejection simultaneously, because of the contradictory effect that exists between the water-membrane hydrogen-bond interaction and the ion-membrane electrostatic interaction. Here, we report a vertically aligned reduced GO (VARGO) membrane and propose an electropolarization strategy for regulating the interfacial hydrogen-bond and electrostatic interactions to concurrently enhance water permeation and ion rejection. The membrane with an electro-assistance of 2.5 V exhibited an ultrahigh water permeance of 684.9 L m-2 h-1 bar-1, which is 1-2 orders of magnitude higher than those of reported GO-based laminar membranes. Meanwhile, the rejection rate of the membrane for NaCl was as high as 88.7%, outperforming most reported graphene-based membranes (typically 10 to 50%). Molecular dynamics simulations and density-function theory calculations revealed that the electropolarized VARGO nanochannels induced the well-ordered arrangement of nanoconfined water molecules, increasing the water transport efficiency, and thereby resulting in improved water permeation. Moreover, the electropolarization effect enhanced the surface electron density of the VARGO nanochannels and reinforced the interfacial attractive interactions between the cations in water and the oxygen groups and & pi;-electrons on the VARGO surface, strengthening the ion-partitioning and Donnan effect for the electrostatic exclusion of ions. This finding offers an electroregulation strategy for membranes to achieve both high water permeability and high ion rejection performance.SignificanceThe accurate regulation of membrane-nanofluid interfacial interactions in nanoscale channels is of fundamental importance for achieving high membrane filtration performance. However, concurrently attaining ultrafast water permeation and high ion rejection is challenging for current graphene oxide (GO) membranes, owing to the contradictory effect of water- membrane hydrogen-bond and ion-membrane electrostatic interactions. This study demonstrates a methodology of electropolarization to coregulate water-membrane and ion- membrane interactions through a vertical graphene membrane, resulting in a 1-2 orders of magnitude improvement in the water permeation and superior ion rejection over most reported GO membranes, breaking the permeability/rejection trade-off. This study proposes a powerful interfacial electroregulation strategy that can guide the design of nanofluidic membranes and multifunctional membrane based devices.

Automated summary

Researchers propose an electropolarization strategy using vertically aligned reduced graphene oxide (VARGO) membrane to regulate interfacial hydrogen-bond and electrostatic interactions, achieving high water permeation and ion rejection performance.