Polyvinylamine/ZIF-8-decorated metakaolin composite membranes for CO2/N2 separation

Mixed-matrix composite membranes (MMCMs) have great potential in chemical separation process due to high performance, but the dispersibility of the filler is an enormous challenge we face. In this study, a ZIF-8-decorated metakaolin (ZIF-8-d-MK) hybrid was prepared by the AlO4 tetrahedron oxygens in amorphous MK coordinating with the zinc ions of ZIF-8. MMCMs by coating polysulfone (PSf) ultrafiltration membranes with a mixture of hybrid and polyvinylamine (PVAm) were obtained, which can efficiently separate CO2 from N-2. SEM and TEM results indicated that ZIF-8 particles were present between the amorphous MK sheets, and the coordination between the two phases was validated by FTIR. ZIF-8-d-MK, with a partially amorphous structure, exhibited homogeneous distribution in the PVAm matrix, as verified by SEM and XRD, and ZIF-8-d-MK had a strong interaction with the polymer matrix as certified by attenuated total reflectance-FTIR. A highest CO2 permeance of 169 GPU with CO2/N-2 selectivity of 86.7 were acquired for MMCMs, loaded with 3 wt% ZIF-8-d-MK under pure gas conditions, which were much higher than those of MMCMs loaded with MK, ZIF-8, or a mixture of MK and ZIF-8. The improved values were primarily ascribed to the well-dispersed ZIF-8-d-MK serving as CO2 transport pathways because of its molecular sieving effect for CO2/N-2. Importantly, under mixed gas feed conditions, the stability measurement demonstrated that the MMCMs adding 3 wt% ZIF-8-d-MK did long-term operation for over 360 h, and maintained great CO2 separation performance.

Automated summary

In this study, a ZIF-8-decorated metakaolin (ZIF-8-d-MK) hybrid was successfully prepared and coated on polysulfone ultrafiltration membranes to efficiently separate CO2 from N-2. The well-dispersed ZIF-8-d-MK in the PVAm matrix showed strong interaction with the polymer matrix, leading to improved CO2 permeance and selectivity. The molecular sieving effect of ZIF-8-d-MK contributed to the enhanced separation performance of MMCMs under both pure gas and mixed gas feed conditions.