PAN electrospun nanofiber skeleton induced MOFs continuous distribution in MMMs to boost CO2 capture

Metal organic frameworks (MOFs) based mixed matrix membrane (MMM) for CO2 capture shows insufficient CO2 permeability due to random disperse of MOFs in form of individual particle. Therefore, in this work, a continuous MOFs transport pathway for CO2 with low resistance was constructed in the MMM by assistance of electrospun nanofiber. Specifically, PAN electrospun nanofiber mat (NFM) was utilized as skeleton to obtain continuous ZIF-8 nanofibers. Then flexible polyethylene glycol (PEG) molecules were photo-polymerized in situ into the inner-voids within ZIF-8@PAN NFM to form dense membrane. As a result, ZIF-8 particles are distributed in PEO matrix continuously, leading to a low-resistance transport pathway for gas molecules in MMM, which is proved by the cross-sectional SEM images. Furthermore, the higher Tg of ZIF-8@PAN-x/PEO MMM by DSC also indicates the good interfacial compatibility between ZIF-8 and PEO. Compared with pure PEO membrane, all the ZIF-8@PAN-x/PEO MMMs present both enhanced CO2 permeability and CO2/N-2 selectivity. The enhanced CO2 permeability is attributed to the continuous ZIF-8 transport pathway, and the improved selectivity is ascribed to the size screening from nanofibers overlapping and stacking and the tortuous transport pathway. Importantly, compared with ZIF-8/PEO MMM, in which ZIF-8 particles are randomly dispersed into PEO matrix, the ZIF8@PAN-4/PEO MMM with the same ZIF-8 loading of about 16.6 wt% presents enhanced CO2 permeability and CO2/N-2 selectivity, which are increased by 52.4% and 44.3%, respectively. This is due to the continuous ZIF-8 transport pathway and good interfacial compatibility, which is also confirmed by the result of gas diffusivity and solubility coefficients. Together with the outstanding mechanical strength and stability, the proposed MMM with continuous ZIF-8 transport pathway paves a new way to improve CO2 permeability.

Automated summary

This study constructed a continuous metal organic frameworks (MOFs) transport pathway in a mixed matrix membrane (MMM) for CO2 capture using electrospun nanofibers. The continuous transport pathway enhanced the CO2 permeability and CO2/N-2 selectivity of the MMM by improving size screening and interfacial compatibility.