Constructing the electrostatic potential microenvironment in MMMs by poly(ionic liquid)s functionalized metal–organic frameworks for efficient CO2/CH4 separation

The construction of electrostatic potential microenvironment in MOF is an effective strategy to improve the separation performance of mixed matrix membranes (MMMs). Different functional groups of poly(ionic liquid)s (PIL-F, F=OH, COOH, NH2) are used to modify MOF to synthesize the PIL-F@MIL-101, which were incorporated into Pebax MH 1657 (Pebax) to prepare MMMs for CO2/CH4 separation. PIL-F@MIL-101 possess positive charge, and their order of positive charge is PIL-OH@MIL-101 > PIL-COOH@MIL-101 > PIL-NH2@MIL-101. The MMMs doped with 7.0 wt% PIL-OH@MIL-101 represented the optimal CO2 permeability of 1480.7 Barrer and CO2/CH4 selectivity of 35.2. The performance of Pebax/PIL-OH@MIL-101 approached the 2019 upper bound. It mainly considered to the following reasons: on one hand, the positively charged filler constructed the positively electrostatic potential microenvironment in MMMs, enhancing the electrostatic attraction with the negatively charged O atoms of CO2 and promoting the preferential transport of CO2. On the other hand, the positively electrostatic potential microenvironment in MMMs obstructs the transport of positively charged H atoms of CH4, improving the CO2/CH4 selectivity. The design on constructing electrostatic potential microenvironments in MMMs provides a promising strategy for efficient CO2 separation.