3D polyphenol-intercalated covalent organic framework membranes: Toward interlayer manipulation for high-permeability nanofiltration

Controllable assembly of covalent organic framework (COF) nanosheets into two-dimensional (2D) layered membranes is crucial to prepare advanced membranes. However, the prevalence of disordered stacking of COF nanosheets often leads to tortuous or overlapped pores and sacrifices membrane permeability. Further, membrane stability is often questioned due to weak interlayer interactions. Herein, a three-dimensional (3D) polyphenol-mediated interlayer engineering strategy was proposed for manipulating the interlayer channels and interactions of COF membranes for simultaneous enhancement of membrane permeability and stability. The COF membranes (TTSBI/TFTA-TG (Cl) ) were prepared via vacuum-assisted self-assembly method with TFTA-TG (Cl) COF nanosheets as the building host and 3D polyphenols 5,5′,6,6′-Tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane (TTSBI) as intercalating guests. The stereoscopic spirocyclic architecture of TTSBI provides rigid interlayer support to expand the 2D nanochannels within the COF membranes, which optimizes the water molecule transport pathway to enhance water permeance. The multiple interactions (e.g., electrostatic and cation-π interactions) between TTSBI and COF nanosheets strengthen the interlayer combination, thereby enhancing the structural stability of the COF membrane. The as-prepared TTSBI/TFTA-TG (Cl) membrane exhibited water permeance of 77.3 L m −2  h −1 ·bar −1 (approximately 2.5 times that of the pristine TFTA-TG (Cl) membrane) with methylene blue rejection above 91 %. Furthermore, the TTSBI/TFTA-TG (Cl) membrane can effectively reject dye molecules with molecular weight of ≥800 Da, and simultaneously demonstrate superior stability. This polyphenol-mediated interlayer engineering strategy may provide new insights into the construction and manipulation of the channels in COF membranes for high-permeability separation application.