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 opto-electronic 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 cm(2)) with a thickness tuned from 100 mu m 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.