Constructing bio-inspired anion channels by dual-ligand MOF in membranes for efficient CO2 separation

Abstract

One of the biggest challenges of Pebax-based membranes is how to simultaneously achieve high CO2 permeability and selectivity. Hence, three-dimensional L-histidine@zeolitic imidazole framework-8 (His@ZIF-8 (X)) was synthesized as dual-ligand metal-organic framework (MOF), and it was incorporated into the Pebax 1657 matrix to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The three-dimensional His@ZIF-8 (X) with abundant His mimicked anion transport protein, and it constructed bio-inspired anion transport channels. His@ZIF-8 (X) played important functions when it was incorporated into the MMMs: the bio-inspired active sites of His@ZIF-8 with the Zn2+ bonded to three Hmim and one water molecule had similar function with the active sites in carbonic anhydrase (CA), which can catalyze CO2 into water-soluble bicarbonate (HCO3-). Subsequently, the bio-inspired anion transport channels allowed HCO3- to rapidly transport, because they had His residues that can form anion-dipole interactions with HCO3- in His@ZIF-8 (X). Therefore, Pebax 1657/His@ZIF-8 (X) MMMs were endowed with the excellent separation performance due to the bio-inspired anion transport channels constructed by His@ZIF-8 (X). In particularly, MMM contained 4 wt.% His@ZIF-8 (12.5) achieved the optimal separation performance with a CO2 permeability of 541 ± 9 Barrer and CO2/CH4 selectivity of 35 ± 0.6. The work implies that the construction of the bio-inspired anion transport channels within MMMs was a potential strategy for efficient CO2 separation.