Physisorption and chemisorption of CO2 on Fe-MIL-88B derivatives: Impact of the functional groups on the electronic properties and adsorption tendency - A theoretical investigation.

ABSTRACT

The carbon dioxide adsorption process on Fe-MIL-88B-X (X = -H, -OH, -CH3, -CN, -F, -NH2) derivatives was investigated using a combination of the density functional theory approach, taking into account van der Waals (vdW) interactions (DFT-D2) method, conformer search algorithm (CREST) combined with the partially polarizable generic force-field (GFN-FF) and the Climbing Images - Nudge Elastic Band (CI-NEB) method. The results demonstrate that CO2 may be adsorbed on different active sites via chemisorption or physisorption. The contribution of the vdW interactions to chemisorption and physisorption nodes has been determined. The presence of functional groups has been shown to have a substantial effect on the electronic characteristics of the Fe-MIL-88B, such as ionization energy (IP), electron affinity (EA), and the global electrophilic index (GEI), and therefore on CO2 selective adsorption in a certain direction. The correlation between adsorption energy and the parameters IP, EA, and GEI was analyzed through a multivariable linear regression method.