Ultrathin Covalent Organic Framework Membranes with Tailorable Porous Channels for High-Permeance Helium Separation.

Covalent organic frameworks (COFs) are a unique class of porous crystalline materials featuring precisely ordered structures and well-tunable porous channels as well as abundant active functional groups, which enable them as promising membranes for high-performance gas separation. However, construction of thin COF membranes to simultaneously realize high-permeability and high-selectivity He separation has remained a challenge. Here, we report the synthesis of ultrathin (<5 nm thick) porphyrinyl two-dimensional polyimine (Por-2DPI) COF membranes, which comprise single-crystalline domains and highly ordered, vertically aligned one-dimensional (1D) porous channels. We further develop an inner-pore coordination (IPC) strategy to graft bulky phenyl (Ph) and naphthyl (Np) groups on the inner walls of the porous channels. This strategy effectively narrows the intrinsic pore size from ∼2.0 to ∼1.4 nm, which leads to the efficient tailoring of the transmembrane transport toward the high-permeance He separation with high selectivity. Notably, the resultant Por-2DPI-Np COF membrane simultaneously delivers a record-high He permeance of 4323 GPU and a high selectivity of 77.4 (He/CH