MXene/COFs membrane with sandwich structure for rapid salt/dye separation by layer-by-layer electrophoretic deposition
Covalent organic frameworks (COFs) have evolved into a transformative category of nanofiltration materials due to their intrinsic pore channels and high porosity, sparking a burgeoning interest in fully harnessing the potential of COFs for applications in nanofiltration . Herein, a sandwich structured MXene/COFs membrane was fabricated by the technique of layer-by-layer electrophoretic deposition (LBL EPD), with COFs nanospheres (COFs NPs) serving as the intermediate layer. During the EPD process , controlling the deposition time allows for convenient regulation of each layer's thickness, enabling rapid production of defect-free MXene/COFs membranes. The ultra-thin MXene layer offers excellent film-forming properties for COFs NPs, whereas the intermediate layer of COFs NPs plays a primary sieving function. Moreover, the pore-rich COFs NPs, the ultra-thin MXene layer, and the COFs NPs layer with abundant slits guarantee short and successive mass transport pathways. Under optimal conditions, the MXene/COFs membrane provided a permeance as high as 200.2 L‧m −2 ‧h −1 ‧bar −1 and a rejection rate of Congo red (CR) as high as 98.9 %. This exceptional performance holds steadfast even within pH ranges of 7–11 and during long-term operation. Meanwhile, MXene/COFs membranes exhibit commendable salt/dye separation performance, achieving an excellent separation factor of 121.1 for NaCl/CR. Moreover, the membrane's exceptional robustness and mechanical strength further facilitate its stable utilization under high transmembrane pressure (1–5 bar). To summarize, MXene/COFs membranes, characterized by their excellent nanofiltration and salt/dye separation performance, highlight the advantages of COFs within the nanofiltration field. This study introduces an innovative alternative approach to designing COFs membranes for highly efficient and high-precision molecular separations.
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