Lewis-Acid-Catalyzed Interfacial Polymerization of Covalent Organic Framework Films

Covalent organic frameworks (COFs) are crystalline polymers with covalent bonds in two or three dimensions, providing pores 1–5 nm in diameter. COFs are typically isolated as microcrystalline powders, which are unsuitable for many applications that would leverage their tunable structures, such as optoelectronic devices and nanofiltration membranes. Here, we report the interfacial polymerization of polyfunctional amine and aldehyde monomers with a Lewis acid catalyst, Sc(OTf)3. Immiscible solutions segregate the catalyst from the monomers, confining polymerization to the solution interface. This method provides large-area, continuous COF films (several cm2) with a thickness tuned from 100 μm to 2.5 nm. Relatively thick films were crystalline, whereas the films that are a few nanometers thick were presumably amorphous. The COF films were transferred onto polyethersulfone supports, and the resulting membranes showed enhanced rejection of Rhodamine WT, a model water contaminant. The large area, tunable pore size, and tailored molecular composition show promise for nanofiltration applications.