Thin film nanocomposite membrane incorporated with 2D-MOF nanosheets for highly efficient reverse osmosis desalination

Metal-organic frameworks (MOFs) have drawn significant attention in the fabrication of thin film nanocomposite (TFN) membranes. In particular, two-dimensional MOFs (2D-MOFs) are advantageous in improving compatibility and molecular sieving performance depending on the sub-atomic surface thickness, high exposure of surface functional groups and controllable pore structure properties. In this study, a robust high performance TFN membrane for reverse osmosis (RO) desalination was fabricated using an interfacial polymerization strategy on the surface of polysulfone (PSF) substrate with embedded ultrasonically exfoliated nickel-based 2D-MOF nanosheet in the selective layer. The TFN membrane modified by adding 0.015 wt% 2D-MOF nanosheet to the aqueous phase exhibits a 2.5 times higher water permeability with a well-maintained salt rejection (water permeance up to 50.0 L m−2 h−1·MPa−1, NaCl rejection of 99.2%) compared to pristine thin film composite (TFC) membrane (water permeance 20.6 L m−2 h−1·MPa−1, NaCl rejection 99.3%). Meanwhile, the modified TFN membrane features outstanding anti-fouling properties against 500 ppm humic acid with a high water permeance recovery ratio of 96.9%. In addition, the diffusions of water molecules both in pristine TFC membrane and modified TFN membrane were investigated by the molecular dynamics (MD) simulation, showing good agreement with the experimental results. The simulation results reveal that the incorporation of 2D-MOF nanosheets can reduce transfer resistance and increase water diffusion because of the extra pores of 2D-MOF and H bonds between free water molecules and the coordination water of 2D-MOF. This study presents a new strategy to fabricate high-performance RO membranes, and also provides further insights into the great potential of 2D-MOFs in the water-treatment field.