Regulating Cutoff Size of Metal-Organic Frameworks by In Situ Anchoring of Poly(ethylene glycol) to Boost CO2 Capture

Pore engineering of metal-organic frameworks is essential to achieve selective sieving of gas molecules for mixed matrix membranes (MMMs). In this work, poly(ethylene glycol) diglycidyl ether (PEGDGE) small molecules were proposed to be immobilized into the cage of NH2-MIL-101(Cr) (NMIL-101) by a covalent bond. A precise adjustment in pore size of NMIL-101 was achieved through controlling PEGDGE content. The ring-opening reaction is confirmed to happen between epoxy and amino groups by Fourier transform infrared spectroscopy. CO2/N-2 selectivity increases gradually with increasing PEGDGE content, demonstrating the effective screening of the pores regulated by PEGDGE. When PEGDGE content is 20.8 wt %, the MMMs have the best gas separation performance, with a CO2 permeability of 111.6 Barrer and a CO2/N-2 selectivity of 72.8, which are increased by 31.2% and 30.8%, respectively. Specifically, compared with PEGDGE(13)(.0)/NMIL-101-based MMM without a ring-opening reaction, PEGDGE(11)(.1)@NMIL-101 presents an improvement in both CO2 permeability and selectivity, indicating the necessity of in situ anchoring of PEGDGE.