Tailoring metal-organic frameworks for CO₂ capture: The amino effect

Carbon dioxide capture from processes is one of the strategies adopted to decrease anthropogenic greenhouse gas emissions. To lower the cost associated with the regeneration of amine-based scrubber systems, one of the envisaged strategies is the grafting of amines onto high-surface-area supports and, in particular, onto metal-organic frameworks (MOFs). In this study, the interaction between CO₂ and aliphatic and aromatic amines has been characterized by quantum mechanical methods (MP2), focusing attention both on species already reported in MOFs and on new amine-based linkers, to inspire the rational synthesis of new high-capacity MOFs. The calculations highlight binding-site requisites and indicate that CO₂ vibrations are independent of the adsorption energy and monitoring them in probe-molecule experiments is not a suitable marker of efficient adsorption. Scrubbed away: Quantum mechanics is used as a screening tool to investigate the affinity of different functional groups towards CO₂. The calculations explain the large CO₂ affinity observed experimentally for 2-amino-1,4-benzenedicarboxylate-based materials by the presence of pairs of -NH₂ groups and not by the direct interaction with isolated -NH₂ groups (see picture).