Multifunctional amine mediated synthesis of COF nanosheets for desalination membranes

Abstract

Synthesis of high-aspect-ratio covalent organic framework (COF) nanosheets with well-defined nanopores is essential for diverse applications, yet balancing in-plane bond formation and out-of-plane π–π stacking disruption remains a challenge. Here, we design a multifunctional mediator, triethylenetetramine (TETA), yielding COF nanosheets with aspect ratios surpassing 2500 and enhanced functionality. TETA is chosen as the optimal candidate considering the key factors of pH/pK_a balance, amine site distribution, and molecular length, achieving a “one-stone-three-birds” effect. Specifically, as a catalyst, its moderate alkalinity facilitates controlled in-plane polymerization; as an intercalator, its protonated secondary amines effectively suppress the π–π stacking; and as a defect remediator, its symmetrical primary amines and compatible molecular length facilitate defect-healing to preserve structural integrity. The resulting nanosheets are self-assembled into crystalline, defect-free COF membranes, achieving an ultrahigh water flux of 230.10 kg m⁻² h⁻¹ and a salt rejection of 99.99% in seawater desalination, attributed to vertically aligned nanochannels and TETA-induced hydrophilicity. This work presents a facile approach to designing efficient mediators for the synthesis of COFs and many other crystalline framework nanosheets.