Synthesis of melted ZIF-62 and Ag-ZIF-62 mixed matrix
membranes
In the formation of the 6FDA-DAM-based membrane, the polymer percentage
in the solvent-polymer mixture was retained at 7.7 wt%. The melted
ZIF-62 or Ag-ZIF-62 filler was first dispersed in chloroform for at
least 12 hours before the addition of 6FDA-DAM. Occasional
ultrasonication was also performed using an ultrasonic bath during the
12-hour filler dispersion period. This step is essential to ensure
better dispersion of fillers and reduced chances of agglomeration before
the addition of the polymer of choice. After filler dispersion, 3 wt%
of the full amount of 6FDA-DAM (7.7 wt%) was added to the dispersed
filler chloroform solution and left to stir for 24 hours. This step is
important as a priming step to ensure full dissolution and dispersion of
6FDA-DAM polymer while having good contact with the fillers. Occasional
ultrasonication was also performed using an ultrasonic bath during these
24 hours to ensure efficient dispersion and reduced agglomeration. After
this period, the remaining amount of 6FDA-DAM was added slowly to reduce
the formation of agglomerates and then left to be stirred overnight. The
highly viscous 6FDA-DAM-filler solution was then sonicated for 20-30
minutes to remove any remaining trapped air in the solution. The
solution was then cast on a glass slide using a casting blade at the
height of 500 µm. The glass slide was then immediately covered in a
solvent-saturated enclosed container and left to evaporate overnight
slowly. The resulting membrane was then slowly peeled off and activated
in a vacuum oven at 30 oC for 24 hours before use. A
lower activation temperature of 30 oC was used for
Ag-doped fillers to minimise the possibility of Ag nanoparticle
formation during activation. All the drying/activation processes for
Ag-doped fillers were also performed in a light-enclosed environment to
minimise possible changes in the filler structure, such as further Ag
nanoparticle formation.