Facile synthesis behavior and CO2 adsorption capacities of Zn-based metal organic framework prepared via a microchannel reactor

Abstract

MOFs are traditionally synthesized via intermittent synthesis, but its synthesis process is time consuming. Furthermore, many organic solvents used in the synthesis of MOF materials severely pollute the environment. Therefore, in this work, different types of Zn-MOFs were synthesized using a microchannel reactor with various proportions of MeOH and H2O as solvents. Unlike the direct mixing method, the microchannel reactor could synthesize Zn-MOF structures under any solvent proportion, and different solvents had a great influence on Zn-MOF morphology. Density functional theory (DFT) calculations were conducted to explain why Zn-MOFs with varied morphologies could be synthesized in different solvents. The calculation results showed that 2-methylimidazole was easier to coordinate with the zinc ions in the MeOH solvent due to its low free energy; thus, it was easier to form three-dimensional structures. However, in the H2O solvent, growth stopped due to a sudden increase in free energy in the coordination process, so a two-dimensional structure appeared in the aqueous solution. Finally, Zn-MOFs with more mesoporous structures had better adsorption performance. At 1 atm and 298 K, MOF-FNP-MeOH and MOF-FNP-H2O performed the maximum CO2 adsorption capacity of 3.28 mmol·g−1 and 4.09 mmol·g−1, respectively.