Polymer-functionalized metal-organic framework nanosheet membranes for efficient CO₂ capture

Two-dimensional metal-organic frameworks (2DMOFs) have emerged as highly appealing candidates as advanced separation membrane materials. However, constructing 2DMOF membranes with appropriate channel sizes to separate CO₂ from N₂ remains a great challenge. Here, we propose an in-situ crystallization approach to synthesize CO₂-philic-polymer functionalized Zr-based MOF nanosheets, enabling the fabrication of efficient CO₂ capture membranes. The in-situ MOF crystallization with polyethylenimine (PEI) polymers leads to a uniform distribution of amines, resulting in the formation of PEI-NUS hybrid nanosheet characterized by both high porosity and strong affinity to CO₂. These nanosheets are assembled into ultrathin lamellar membranes with thicknesses ranging from 40 to 120 nm. The amines of PEI polymers significantly facilitate the CO₂ transfer as reaction carriers, resulting in a substantially improved CO₂/N₂ separation performance with a CO₂ permeance of 410 GPU and a CO₂/N₂ selectivity of 90, which are among the best for MOF membranes in CO₂ separation. This in-situ functionalization strategy paves the way for the fabrication of ultrathin 2D membranes for various separations.