Ultrathin Subnanoporous Covalent Organic Framework Membranes with Triangular Topologies for Efficient Pharmaceutical Separation

Abstract Covalent organic frameworks (COFs) with customizable pore structures have aroused immense interest in pharmaceutical separation relying on organic solvent nanofiltration (OSN). Nevertheless, devising durable COF membranes with fine nanochannels for high‐efficiency separation remains challenging. Here, a triangular‐topology COF membrane is reported with subnanometer pores through designing a six‐fold symmetric hexa(4‐formylphenyl)benzene as a building block. A dense COF membrane is interfacially synthesized through the sustained diffusion and reaction of hydrazine from porous substrates under catalysis. Thus‐synthesized membrane features an ultrathin thickness of 54 nm, high‐density nanochannels, and high solvent affinity. The membrane yielded exceptional solvent permeances (24.9 L m ⁻¹ h ⁻¹ bar ⁻¹ for methanol) and sharp molecular rejection curves with low molecular weight cut‐offs of 380 Da, outperforming congeneric OSN membranes. This further translated into an excellent separation capability toward mixed antitumor pharmaceuticals within organic solvents, despite under high concentration and prolonged operation. This skillful design drives COF membranes as a promising candidate for reforming separation processes of high‐value pharmaceuticals in industries.