Large‐Area Soluble Covalent Organic Framework Oligomer Coating for Organic Solution Nanofiltration Membranes

Abstract Covalent organic frameworks (COFs) are a family of engaging membrane materials for molecular separation, which remain challenging to fabricate in the form of thin‐film composite membranes due to slow crystal growth and insoluble powder. Here, an additive approach is presented to construct COF‐based thin‐film composite membranes in 10 min via COF oligomer coating onto poly(ether ether ketone) (PEEK）ultrafiltration membranes. By the virtue of ultra‐thin liquid phase and liquid‐solid interface‐confined assembly, the COF oligomers are fast stacked up and grow along the interface with the solvent evaporation. Benefiting from the low out‐plane resistance of COFs, COF@PEEK composite membranes exhibit high solvent permeances in a negative correlation with solvent viscosity. The well‐defined pore structures enable high molecular sieving ability (Mw = 300 g mol −1 ). Besides, the COF@PEEK composite membranes possess excellent mechanical integrities and steadily operate for over 150 h in the condition of high‐pressure cross flow. This work not only exemplifies the high‐efficiency and scale‐up preparation of COF‐based thin‐film composite membranes but also provides a new strategy for COF membrane processing.