Synthesis of ZIF-8 from recycled mother liquors

• A procedure was developed for the synthesis of ZIF-8 from recycled mother liquors.
• Recycling procedure can be repeated as 5 times as with the addition of zinc.
• Effect of zinc/organic linker molar ratio on the particle size of ZIF-8 was investigated.
• Crystallization was monitored in situ by a turbidimeter.

The effect of the methanol/Zn(NO3)2 molar ratio on the particle size, BET surface area and on the rate of the crystallization have been studied. The use of excess methanol leads to a decrease in particle size and rate of crystallization. Crystals grown from solutions with methanol/Zn(NO3)2 molar ratios of 1043 and 87 are 60 and 600 nm based on SEM images, respectively.A systematic study was also conducted in which mother liquor recovered from the synthesis of ZIF-8 was used to produce second, third and even fourth generations of ZIF-8 crystals. Crystals produced from recycled solutions have similar morphology, BET surface area and thermal stability from the population crystallized by the fresh solution. The incorporation of NaOH and Zn(NO3)2 to the recycled mother liquor initiated the nucleation and stimulated the crystal growth. This approach enabled a substantial rise in the yield of nanosize ZIF-8. The ZIF-8 yield was about 38% during the synthesis from fresh solution, whereas the total yield rose to about 80% by recycling. From an environmental perspective, this process is very favorable since the recycle of the mother liquor minimizes the amount of waste produced during the synthesis of ZIF-8.

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