Site Partition: Turning One Site into Two for Adsorbing CO2

We propose the concept of site partition to explain the role of guest molecules in increasing CO2 uptake in metal-organic frameworks and to design new covalent porous materials for CO2 capture. From grand canonical Monte Carlo simulations of CO2 sorption in the recently synthesized CPM-33 MOFs, we show that guest insertion divides one open metal site into two relatively strong binding sites, hence dramatically increasing CO2 uptake. Further, we extend the site partition concept to covalent organic frameworks with large free volume. After insertion of a designed geometry-matching guest, we show that the volumetric uptake of CO2 doubles. Therefore, the concept of site partition can be used to engineer the pore space of nanoporous materials for higher gas uptake.