Controlling Interlayer Spacing of Graphene Oxide Membranes by External Pressure Regulation

Graphene oxide (GO) membranes have been attracting numerous attention due to their impressive performance in various applications, especially in water purification. However, because the swelling in water and polar organic solvents causes the increase of interlayer channels, GO membranes usually possess inferior rejection for subnanometer-sized molecules. How to control the transport channels of GO membranes at angstrom level is a significantly scientific and practical issue. Herein, a concept of external pressure regulation (EPR) is reported for restraining GO swelling and controlling its interlayer spacing precisely. Since anisotropic GO films only swell at vertical direction, the interlayer channels can be manipulated by externally unidirectional reverse force. Based on this concept, an EPR system with GO membranes is designed for water desalination by adjusting the external pressure that has high resolution. In cross-flow filtration, the compressed GO membranes show high KCl, NaCl, and CaCl₂ rejections of 94%, 97%, and 98%, respectively, accompanied by large water permeance up to 25 L m^-2 h^-1 under low feed pressure of 2 bar, despite the fact that the semi-free spatial swelling of ultrathin GO layer above the substrate pores can deteriorate salt rejection. Our work provides a straightforward physical strategy to adjust the interlayer spacing of the membranes fabricated by two-dimensional nanosheets for achieving desired filtration capacity.