Synthesis of ZIF-7, ZIF-8, ZIF-67 and ZIF-L from recycled mother liquors

ZIF-8, ZIF-L, ZIF-7 and ZIF-67 were synthesized from fresh and recycled synthesis solutions. ZIF-8, ZIF-L and ZIF-7 includes Zn2+, while ZIF-67 includes Co2+. ZIF-7 was synthesized in dimethyl formamide, while the others in water. The organic linker was 2-methyl imidazole for ZIF-8, ZIF-L and ZIF-67, and benzimidazole for ZIF-7. The recycling was proceeded two steps for each type of ZIF. For the synthesis in the recycled solutions, the pH and the metal ion content of the mother liquor should be adjusted for a successful synthesis. All synthesis using fresh and recycled solutions resulted in highly crystalline ZIFs. The crystal morphology, N2 adsorption capacity and thermal behavior of ZIFs from recycled solutions were similar to those obtained from the fresh solution. The recycling procedures improved the efficiency of crystallization such that 0.36 g ZIF-7/g organic linker was obtained after two recycling steps, although only 0.16 g ZIF-7/g organic linker can be obtained after single step synthesis using fresh solution. From an environmental perspective, the developed procedures allowed to consume a great extent of organic linker used for synthesis, therefore the amount of waste organic linker was reduced.