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.