NH₂-MIL-101(Fe) Nanocrystals Synthesized by the Ionic Liquid–Ethanol Interface for Efficient CO₂ Fixation at Mild Conditions

In this study, an ionic liquid-ethanol interface strategy is proposed to synthesize NH₂-MIL-101(Fe) nanocrystals at room temperature. The as-synthesized nanocrystals exhibit small crystal sizes, abundant ligand defects, and unsaturated metal sites. The NH₂-MIL-101(Fe) nanocrystals present superior catalytic activity for the cycloaddition reaction of CO₂ at mild conditions (room temperature and 1 bar CO₂ pressure), much higher than the NH₂-MIL-101 (Fe) microcrystals synthesized by the conventional solvothermal method. The conversion of propylene oxide catalyzed by NH₂-MIL-101(Fe) nanocrystals achieves a 99% yield within 2.5 h, accompanied by a generation rate of carbonate production per gram of catalyst (<i>R</i>_carbonate) of 52.8 mmol g^-1 h^-1. In contrast, the system employing NH₂-MIL-101(Fe) microcrystals shows a much lower yield of 19.28% and a generation rate (<i>R</i>_carbonate) of 10.28 mmol g^-1 h^-1. The NH₂-MIL-101(Fe) nanocrystals were further used for the treatment of simulated industrial flue gas conditions with a volume ratio of N₂/CO₂ = 85:15. The results show the efficient conversion of CO₂ at ambient temperature and pressure, even at relatively low CO₂ concentrations. This work not only offers a facile, low energy-consumed, and environmentally benign interface method for the fabrication of MOF nanostructures but also provides high-performance systems for CO₂ fixation and gas separation.