Highly stable membrane comprising MOF nanosheets and graphene oxide for ultra-permeable nanofiltration

Abstract

The separation application of two-dimensional (2D) material membrane, e.g., graphene oxide (GO) membrane, has long been limited by the low stability and uncontrollable permeability originated from their severe swelling in water and uneven interlayer spacing caused by the loose and imperfect stacking of GO laminates. Herein, we conceive a composite membrane by integrating a highly porous 2D Al-MOF nanosheets into a graphene oxide membrane that simultaneously improves membrane stability and solvent permeability. On one hand, strong interactions, including Al–O coordination and π−π stacking between Al-MOF and GO nanosheets help tightening the GO stacking, which improves the structural stability of the composite membrane. On the other hand, the high porosity of Al-MOF greatly enhances the mass transfer efficiency by affording more pathways in the membrane. When used for nanofiltration, the GO@Al-MOF composite membrane exhibits 99.9% rejection of Congo red and ultrahigh water permeance of 51.6 L m−2 h−1 bar−1, which is more than 17-fold higher than that of the pure GO membrane. This high separation performance can be maintained for up to 140 h, suggesting the superior chemical and structural stability of the composite membrane. This work provides a useful co-stacking strategy to construct 2D material membranes with high chemical and structural stability as well as outstanding selectivity and permeability.