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

Abstract

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.