Figure 1. PXRD, N2 adsorption and desorption,
and SEM image of Ni-ZIF-8 (a), (b), and (c), while (d), (e), and (f)
showing the WXRD, FTIR, and TGA analysis of Ni-ZIF-8 MMMs.
The DSC test will observe the effect of ZIFs on polymer melting and
glass transition temperatures, as well as help us to estimate the
polymer-MOF interfacial interaction46. Table S3
representing the T g (glass transition
temperature), T m (melting temperature), andT c (crystallization temperature) of pure PDMS and
MMMs. With the increase in Ni-ZIF-8 loading, the DSC results showed the
increasing trends in the crystallization and melting temperatures of
MMMs as compared with the pure PDMS. The changes in melting and
crystallization temperatures were attributed to the reduction of chain
mobility of PDMS due to the addition of Ni-ZIF-8
nanoparticles47. The PDMS chain mobility reduction may
cause the rigid packings of polymer chains, which has shown excellent
interfacial interaction between Ni-ZIF-8 and PDMS phases.
SEM images were used at low and higher magnification to check the
surface morphologies of the synthesized membranes, as shown in Figure 2.
The PDMS control membrane surface was defect-free, dense, and
homogeneous (Figure 2 a and b). In comparison, Ni-ZIF-8 nanoparticles
observed on the membrane surface, which were well dispersed within the
PDMS matrix, implying their good compatibility. The incorporation of
Ni-ZIF-8 nanoparticles has resulted in some surface roughness of the
MMMs and has increased with respect to the loadings of Ni-ZIF-8. The
membrane showed good homogeneity even at high loading up to 15 wt% of
Ni-ZIF-8 (Figure 2 (c) and (d)). It was observed that the nanoparticles
of Ni-ZIF-8 started to agglomerate marginally at a loading of 20 wt%
(Figure S6 and S7), which may be due to the stronger surface tension of
ZIF particles than to the polymer affinity. The overall well scattered
ZIFs in the polymer is 15 wt% loadings. At lower magnification, the
nanoparticles of Ni-ZIF-8 tend to be aggregated, but at a higher
magnification, they are very well dispersed from each other, and no
defects were observed in the MMMs. Cross-sectional morphologies of the
15% Ni-ZIF-8 MMM have been shown in Figure 2 (e and f) with low and
high magnifications, respectively. There was no sign of voids observed
between the membrane active layer and the PVDF support. The average
thickness of the 15% Ni-ZIF-8 MMM active layer was 13 µm. At higher
magnification, Ni-ZIF-8 nanoparticles can be seen in the active layer of
the membrane within the PDMS.