ZIF-8@NENP-NH2 embedded mixed matrix composite membranes utilized as CO2 capture

Abstract

Mixed matrix composite membranes (MMCMs) for CO2 capture have great potential in carbon neutral goal. However, simultaneous enhancement in permeance and selectivity is very difficult, since mismatching pore and chemical structures of filler with polymer matrix are the stumbling block. Herein, novel core–shell MOFs@COFs hybrids were prepared by growing hierarchical pore covalent organic frameworks (COFs, nitrogen-enriched nanoporous polytriazine (NENP)) on the surface of metal organic framework (MOFs, zeolite imidazolate framework-8 (ZIF-8)), where ethylenediamine were impregnated into NENP pore to adjust the chemistry environment of the shell. Subsequently, a porous polysulfone (PSf) membrane-supported MMCMs were developed by a coating method using a mixed dispersion of ZIF-8@NENP-NH2 and polyvinylamine (PVAm), which was used to efficiently separate CO2 from N2. The rough COFs layer (NENP-NH2) was closely wrapped on the smooth surface of ZIF-8 as identified by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and N2 adsorption. Even-distributed ZIF-8@NENP-NH2 had well miscibility with the PVAm matrix from hydrogen bonding as evidenced by SEM, attenuated total reflectance-FTIR and differential scanning calorimetry. The CO2 permeance as high as 301 GPU accompanied with a selectivity of 91 was obtained for MMCMs loaded with 7 wt% ZIF-8@NENP-NH2, which were enhanced by 296.1% and 89.6%, respectively, when compared with the pristine PVAm membrane, transcending 2019 upper bound. We assume that the surface chemistry environment in hierarchical pore of the shell and molecular sieving pore in the core in the short-range order facilitate CO2 permeation. Furthermore, this membrane maintained an average CO2 permeance of 369 GPU and a CO2/N2 selectivity of 97.3 for over 360 h using CO2/N2 mixed gas as feed gas.