Professors Yingwei Li and Kui Shen of the School of Chemistry and Chemical Engineering at the South China University of Technology are the study’s principal authors.
In this study, they describe how N-doped carbon was enclosed in metal-organic frameworks (MOFs) with controlled nanoarchitectures and porosities as multifunctional catalysts for extremely effective CO2 fixation.
They created BmimBr@MIL, or MIL-101 embedded ionic liquids, which are then employed as a precursor to create composite materials with mesopore holes that range in size from 3.5 to 20 nm.
The crystallinity of MIL-101 can be kept intact during pyrolysis, and the N-doped nanocarbon (CN) that was generated in the framework of MIL-101 allowed for a dense-to-porous transition of the material’s structure.
With high catalytic performance in the synthesis of cyclic carbonates from epoxides and CO2 under moderate and co-catalyst-free conditions (90 °C and ambient pressure of CO2), the resulting CN@MIL can effectively promote the mass diffusion of substrates.
The study authors persisted in creating effective heterogeneous catalysts without co-catalysts for CO2 cycloaddition under benign circumstances. For in-situ encapsulation of N-doped nanocarbons into the pores of MOFs and the creation of multi-functional catalytic sites in the resulting MOF-based composites, their team presented a simple one-step pyrolysis technique.
They have discovered that the key to keeping MIL-101’s porous structure from collapsing is its improved thermal stability, which is caused by the space-occupying action of BmimBr.
Therefore, during pyrolysis, MIL-101’s crystallinity can be substantially maintained while also undergoing a dense-to-porous structural change with the creation of N-doped nanocarbon (CN) in the framework.
The mechanism of dense-to-porous transition by TG-MS was also studied by the researchers. The data obtained clearly shows that the ligands of BmimBr@MIL(0.67) can be broken down through a different method than those of its parent MIL-101, which further supports the idea that BmimBr@MIL(0.67improved)’s stability can effectively stop the porous structure of MIL-101 from collapsing.
They assessed the catalytic performances of the as-synthesized materials for the CO2 cycloaddition with large-size epoxides to concurrently study the benefits of hierarchical pores and multi-active sites of CN@MIL (400, 0.67, 30).
In the absence of co-catalysts, they discovered that the optimized CN@MIL (400, 0.67, 30) has good catalytic activity and can reach 96% yield in the cycloaddition of 4-(2,3-epoxypropoxy) carbazole (4-EPC) to 4-(((9H-carbazol-4-yl) oxy) methyl)-1,3-dioxolan-2-one (4-CDO).
This method of controlled pyrolysis offers a different and effective technique to combine MOFs with a variety of other functional big molecules for cutting-edge applications, as well as fresh insight into the pyrolysis of ILs contained inside MOF frameworks.
Chen, F., et al. (2022) N-doped nanocarbon embedded in hierarchically porous metal-organic frameworks for highly efficient CO2 fixation. Science China Chemistry. doi:10.1007/s11426-022-1298-9.