MMMs preparation
The membrane was prepared by the solution casting method. First of all, ZIFs nanoparticles were added in n-heptane and stirred it for 30 minutes and then sonicated for the next 30 minutes. The same steps were repeated three times simultaneously. Then the 10% PDMS of its total weight was added for “priming” in the ZIFs/n-heptane solution (wPDMS:wn-heptane = 0.1:9) and let it further stirred for next 3 hrs. Subsequently, more PDMS was added after each 3 h with different amounts of PDMS (20, 30 and 40%) and then remained it stirred for next 12 h. TEOS (crosslinker) was added with definite ratio (wPDMS:wn-heptane:wTEOS:wdibutyltin dilaurate = 1:9:0.1:0.01). After 2 h, the catalyst (DD) was added and stirred the solution for the next 20 minutes. Moreover, the casting solution was placed in the sonicator for 20 minutes before casting the membrane, as this method is helpful for the good dispersion of fillers within the polymer matrix. Then the slightly viscous solution was cast over PVDF support following the solution casting method. The membranes were dried in the open air for 3 h and kept in an oven at 120°C for the next 4 h for the sake of crosslinking and the complete removal of solvents from it. By following the same method, we have synthesized the pure PDMS/PVDF membrane without any loading of ZIFs. The ZIFs loading was defined by using the following equation,
\(w_{\text{ZIF}}=\frac{m_{\text{ZIF}}}{m_{\text{PDMS}}}\times 100\)(1)
here, w ZIF represents the loading of ZIFs nanoparticles in the MMMs, m ZIF, andm PDMS represents the mass of ZIFs and mass of PDMS added in the casting solution, respectively.
The Ni-ZIF-8 loading in these MMMs were 0, 5, 10, 15 and 20 % respectively and resultant membranes were labeled as, X-Ni-ZIF-8 MMM (X= 0, 5, 10, 15, 20). For the sake of comparison with ZIF-8 based MMMs, we made the same loading MMMs of ZIF-8 by following the same method.