CO2 capture using functionalized MIL-101(Cr) metal–organic frameworks: Functionality nanoarchitectonics of nanospace for CO2 adsorption

[Display omitted] •MIL-101 s with 6 functional groups (FGs: like alkyl and aryl –NH2) were prepared.•MIL-101 s with 6 FGs (in similar molar conc.) were compared in CO2 adsorption.•The performance of FGs is in the order: alkyl –NH2 > -SO3H>-aryl –NH2 > –NO2.•This hierarchy can be supported by different adsorption mechanisms because of FGs.•In CO2 adsorption, aryl amines should be differentiated from alkyl amines. In this study, we investigated the effect of functional groups of metal–organic frameworks (MOFs) on CO2 adsorption at low pressure through experimental and computational approaches. We compared the performance of −SO3H, –NO2, aryl –NH2, and alkyl –NH2 groups (in similar molar quantities) in CO2 adsorption under the same conditions. The adsorption efficiency followed in the order: alkyl –NH2 > -SO3H>aryl –NH2 > –NO2 because of the different adsorption mechanisms over the groups. The main mechanism over alkyl –NH2 was the formation of ammonium carbamate via the carbamic acid formation. The adsorption mechanism over −SO3H and aryl –NH2 groups was Lewis acid-base and H-bonding interactions, while that over –NO2 group was solely Lewis acid-base interaction. The alkyl amine exhibited the best performance (in adsorption capacity, selectivity, and adsorption heat) due to its ability to form carbamate readily. On the contrary, aryl amine demonstrated lower performance than −SO3H groups, attributed to their low capability to form carbamate. These findings underscore the importance of amine type in CO2 adsorption, highlighting that aryl amines, different from alkyl amines, perform worse than other functional groups, such as −SO3H.