PEI-Induced Simultaneous Functionalization and Defect Engineering of RHO-Topology ZIF(Cu) for Enhanced CO2 Separation Performance in Mixed Matrix Membranes.

Defect engineering and the functionalization of metal-organic frameworks (MOFs) are acknowledged as an effective method to boost the separation capability of mixed-matrix membranes (MMMs). However, these processes are often carried out separately, making it difficult to achieve both objectives simultaneously. Herein, a polyethyleneimine (PEI)-induced simultaneous functionalization and defect engineering strategy is proposed, in which PEI is introduced during the synthesis of RHO-topology ZIF(Cu) to in situ generate structural defects through competitive coordination with Cu2+ centers. PEI enhanced the interfacial compatibility between the filler and the Pebax matrix through hydrogen-bonding interactions and introduced a facilitated transport effect. Meanwhile, defect engineering exposed additional Cu2+ Lewis acid sites capable of adsorbing CO2 and generated additional transport pathways. The synergy between amine functionalization and defect engineering resulted in a substantial enhancement in the separation performance of the MMMs. Under humid conditions, the MMM containing 5 wt % PEI-RHO ZIF(Cu) presented a CO2 permeability of 188.1 Barrer and a CO2/N2 separation factor of 73.0, representing increases of 95.10% and 78.14%, respectively, relative to Pebax, and surpassing the 2008 Robeson upper bound. This integrated strategy, combining defect engineering with amine functionalization, provides a promising avenue for the development of high-efficiency CO2 capture MMMs.