A novel water-stable two-dimensional zeolitic imidazolate frameworks thin-film composite membrane for enhancements in water permeability and nanofiltration performance
Polymer membranes for water treatment are constrained by the permeability-separation trade-off. Herein, two-dimensional (2D) zeolitic imidazolate frameworks (ZIFs) made of benzimidazole interconnected with Zn ions are used to create 2D Zn 2 (Bim) 4 molecular sieve nanosheets, which is explored as an asymmetric, thin-film composite (TFC) nanofiltration (NF) membrane for removing organic dyes and salts from water with a high water permeability under a low operating pressure (1 bar). The 2D Zn 2 (Bim) 4 TFC NF membrane is synthesized via ionic bonds between polycations and the peripheral hydroxy groups of 2D Zn 2 (Bim) 4 nanosheets, regulating the assembly of 2D Zn 2 (Bim) 4 to create a novel crack-free functional layer on top of a polyvinylidene fluoride (PVDF) ultrafiltration membrane. FESEM and XPS confirmed the presence of a polycations-regulated ultrathin functional layer with a thickness of ∼37 nm on the PVDF support. Benefiting from its structural feature, our 2D Zn 2 (Bim) 4 TFC NF membrane could achieve an ultra-high flux of ∼290 L/(m 2 ·h·bar) (5–10-fold higher than that of graphene-based membranes), good anti-fouling properties and high rejection rates (above 98%) for organic dyes. Moreover, the desalinization rate is 50–75%. That is, our membrane is endowed with NF capability, and its intrinsic ultrafiltration features (high water permeance, ultrafast, and energy-saving) are also well maintained.
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