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.