Metal–Organic Framework Nanosheets for Thin-Film Composite Membranes with Enhanced Permeability and Selectivity

Widespread applications of reverse osmosis (RO)-based processes call for high-performance thin-film composite (TFC) membranes. In this study, a TFC membrane by incorporating an ultrathin 2D metal–organic framework (MOF) (ZnTCPP) interlayer was developed for water purification, and the mechanisms in enhancing membrane permeability and selectivity were revealed. The introduction of the 2D MOF nanosheet interlayer nearly tripled the membrane water permeance (4.82 ± 0.55 L m–2 h–1 bar–1) with a simultaneous increase of NaCl rejection (97.4 ± 0.6%) compared to the control, successfully overcoming the permeability–selectivity trade-off. The combined use of quartz crystal microbalance and transmission electron microscopy revealed that the MOF interlayer induced the significant changes in the polyamide membrane structure that favors water permeation, i.e., decreased intrinsic thickness, increased void volume fraction, and enhanced effective filtration surface area. Such improvements in the polyamide structure can be attributed to the synergistic effects of enhanced confinement to interfacially degassed nanobubbles and reduced diffusivity of m-phenylenediamine monomers due to the MOF interlayer. This interlayer also increased the cross-linking degree of the polyamide layer (contributing to the increase of membrane selectivity) and served as a gutter layer (to further enhance membrane permeance by reducing the geometric restriction of the support layer). Our study highlights the potential of using ultrathin MOF nanosheets to fabricate high-performance TFC membranes for desalination and water purification.