Carbon dioxide capture using diaminoalkane-grafted MIL-101(Cr)s: Critical role of geometric configuration of loaded amines

[Display omitted] •Isostructural Cr-based MOFs, MIL-101 and MIL-100, were grafted with diaminoalkanes.•Only MIL-101 with butanediamine or propanediamine was very effective in CO2 capture.•First study to demonstrate the importance of geometric configuration in amine-loaded MOFs.•MIL-101-butanediamine showed 4.0 times CO2 capacity (at 15 kPa) that of MIL-101.•The MOF showed 20.6 CO2/N2 times IAST selectivity (at 100 kPa) that of pristine MIL-101. Preventing the increase of CO2 content in the atmosphere is crucial to mitigating climate change. In this study, we investigated the adsorption of CO2 using isostructural Cr-based MOFs, MIL-101 and MIL-100, after grafting diaminoalkanes with various chain lengths to determine the effect of the geometric configuration of the amines and to develop a competitive adsorbent. The performance of CO2 adsorption (e.g., adsorption capacity, selectivity, and adsorption heat) over MIL-101 increased as the size of diaminoalkanes increased, topped with 1,4-butanediamine, and declined with longer diaminoalkanes. The favorable contribution of grafted 1,4-butanediamine in increasing the performances in CO2 adsorption could be explained by the adequate size of the amines for the optimized configuration in the pore window of the MIL-101. However, interestingly, none of the MIL-100s grafted with diaminoalkanes showed a similar positive effect probably because of the smaller pore window of MIL-100 than that of MIL-101. To the best of our knowledge, this is the first study to demonstrate the importance of geometric configuration (or, the chain length of amines) in amine-grafted MOFs for the CO2 adsorption that follows the general mechanism that requires interactions between two uncoordinated amines for the formation of ammonium carbamates. Moreover, one of the modified MIL-101 grafted with 1,4-butanediamine exhibited remarkable performance in CO2 adsorption with 4.0 times the adsorption capacity of CO2 at 15 kPa and 20.6 times CO2/N2 selectivity (based on ideal adsorbed solution theory, at 100 kPa) compared to the virgin MIL-101.