Functionalized metal–organic framework MIL-101 for CO2 capture: multi-scale modeling from ab initio calculation and molecular simulation to breakthrough prediction

Abstract

By synergizing ab initio calculation, molecular simulation and breakthrough prediction, we investigate CO₂ capture in metal–organic framework MIL-101 functionalized by a series of groups (–NH₂, –CH₃, –Cl, –NO₂ and –CN). CO₂ uptake and isosteric heat in a low-pressure regime increase in the order of MIL-101 < MIL-101-CN < MIL-101-NO₂ < MIL-101-Cl < MIL-101-CH₃ < MIL-101-NH₂. This order follows the strength of the binding energies between CO₂ and the functional groups. However, the effect of the functional groups is marginal for N₂ adsorption. In terms of the separation of a CO₂/N₂ mixture, CO₂/N₂ selectivity is enhanced by functionalization following the order of MIL-101 < MIL-101-CN < MIL-101-CH₃ < MIL-101-NO₂ < MIL-101-Cl < MIL-101-NH₂. At an infinite dilution, the enhancement of CO₂/N₂ selectivity is 2.5 times. The predicted breakthrough time is extended by functionalization, and the longest breakthrough time in MIL-101-NH₂ is 2 times that in MIL-101. Furthermore, the working capacity of CO₂ increases by approximately 40%. This multi-scale modeling study suggests that CO₂ capture in MIL-101 can be considerably improved by functionalization, in terms of CO₂ capacity, CO₂/N₂ selectivity, breakthrough time and working capacity.