Self‐Standing Covalent Organic Framework Membranes for H2/CO2 Separation

Covalent organic frameworks (COFs) are proposed as promising candidates for engineering advanced molecular sieving membranes due to their precise pore sizes, modifiable pore environment, and superior stability. However, COFs are insoluble in common solvents and do not melt at high temperatures, which presents a great challenge for the fabrication of COF‐based membranes (COFMs). Herein, for the first time, a new synthetic strategy is reported to prepare continuous and intact self‐standing COFMs, including 2D N‐COF membrane and 3D COF‐300 membrane. Both COFMs show excellent selectivity of H2/CO2 mixed gas (13.8 for N‐COF membrane and 11 for COF‐300 membrane), and especially ultrahigh H2 permeance (4319 GPU for N‐COF membrane and 5160 GPU for COF‐300 membrane), which is superior to those of COFMs reported so far. It should be noted that the overall separation performance of self‐standing COFMs exceeds the Robeson upper bound. Furthermore, a theoretical study based on Grand Canonical Monte Carlo (GCMC) simulation is performed to explain the excellent separation of H2/CO2 through COFMs. Thus, this facile preparation method will provide a broad prospect for the development of self‐standing COFMs with highly efficient H2 purification. Herein, two self‐standing covalent organic framework (COF) membranes are successfully prepared by using steam‐assisted methods to overcome the difficult processing characteristics of COFs. Due to the abundant mass transfer channels and CO2 adsorption sites, these self‐standing membranes have excellent selectivity and ultra‐high H2 permeance in the separation of H2/CO2.