CO2 discharge into the atmosphere has risen with the increasing consumption of fossil fuels, adversely affecting the fight against global warming. CO2 scrubbing by ethanolic aqueous amines is yet to be challenged as a practical solution. Porous solids offer reversible capture/release and safe operations at high temperatures, while retaining their structural integrity, and thermal and chemical stability, in addition to their gas selectivity. Most existing porous materials, however, suffer from water instability, not to mention the difficulty to tune their structures or the lack of sustainable synthesis, owing to the use of rare earth catalysts. We have recently discovered water stable, azo-bridged, nitrogen-rich, aromatic, nanoporous covalent organic polymers (azo-COPs) which can be synthesized by catalyst-free direct coupling of aromatic nitro and amine moieties under basic conditions. Unlike other porous materials, azo-COPs exhibit an unprecedented  increase in CO2/N2 selectivity with rise in temperature, while reaching to the highest value (288 at 323 K) reported to date. We observed that azo groups reject N2, in other words making the framework �N2-phobic�. In addition, we have also established structural design principles for azo-COPs and demonstrated that increasing the p-surface area of the polymer further enhances its CO2 selectivity. Our simulations suggest that the origin of N2-phobicity of the azo-group is the entropic loss of N2gas molecules upon binding. Azo-COPs' unique ability to retain high CO2/N2 selectivity at elevated temperatures combined with their chemical stability makes them ideal candidates for post-combustion CO2 capture. We believe that the tailoring of structural features in azo-COPs with control over both the functionality and surface area will further contribute to the development of superior CO2 sorbents and also to the fight against global warming and ocean acidification.

Porous covalent amorphous polymers for efficient CO<sub>2</sub> capture and separation

247th National Meeting (2014)

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Porous covalent amorphous polymers for efficient CO2 capture and separation

Porous covalent amorphous polymers for efficient CO₂ capture and separation