Figure 4. Cross sectional SEM images of the (a,b) MOF-NP/PSF and (c,d) pMOF-MS/PSF MMMs.
Gas separation performance
To evaluate the separation performance, the gas permeation properties of the prepared membranes was tested and presented in Figure 5a. The pristine PSF membrane exhibited normal CO2 permeability of 5.1 Barrer, in comparison with the membranes reported in previous studies.59,60 The CO2 permeability of the MOF-NP/PSF MMM increased by 78%. The enhancement of permeability was attributed to that the large permanent pores, high internal surface area, and invalid defects from filler incorporation of the MOF NPs led to faster transport of CO2 molecules. Since the larger porous MSs provided straighter and longer channels for gas permeation, the pMOF-MS/PSF MMM had even higher permeability of 220% as the PSF membrane. Analogously, the pUiO-66-MS/PSF MMM displayed large CO2 permeability of 190% as the PSF membrane. Owing to the aggregation of MOF NPs and the existence of invalid defects, the MOF-NP/PSF MMM exhibited degraded CO2/CH4 selectivity of 18.0, relative to the pristine PSF membrane with typical selectivity of 20.0. Attractively, the CO2/CH4 selectivity of the pMOF-MS/PSF MMM reached at 26.1 due to the outstanding compatibility. The pUiO-66-MS/PSF MMM also displayed larger CO2/CH4 selectivity of 23.6. For CO2/N2 separation, the incorporation of the pMOF MSs could improve the CO2/N2selectivity from 10.9 (PSF membrane) to 16.2 (pMOF-MS/PSF MMM). Compared with the reported MMMs, although the separation performance of the pMOF-MS/PSF MMM was moderate (Table S2), the permeability (2.2) and selectivity (1.3) ratios of MMMs to pristine membranes caused by incorporation of pMOF MSs were impressive (Figure S7 and Table S3). These results strongly demonstrated that the presence of pMOF MSs could not only remarkably accelerate the passport of CO2molecules through the membranes but also improve the CO2separation ability due to the reduced interfacial voids and filler aggregations.