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

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 N-2 adsorption. In terms of the separation of a CO2/N-2 mixture, CO2/N-2 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/N-2 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/N-2 selectivity, breakthrough time and working capacity.