Abstract
• ZIF-8-d-MK hybrid with the interlayer spaces was developed by coordinating ZIF-8 particles to amorphous MK sheets. • PVAm/ZIF-8-d-MK MMCMs for CO 2 /N 2 separation were successfully fabricated. • The interlayer spaces of ZIF-8-d-MK in the MMCMs function as CO 2 transport pathways. • The ZIF-8-d-MK hybrid was homogenously dispersed in PVAm matrix due to amorphous structure of MK sheets. 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 AlO 4 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 CO 2 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 CO 2 permeance of 169 GPU with CO 2 /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 CO 2 transport pathways because of its molecular sieving effect for CO 2 /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 CO 2 separation performance.
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