A new post-synthetic route to graft amino groups in porous organic polymers for CO₂ capture

Herein, we report the development of a post-synthetic modification approach to introduce a high loading of formyl groups onto porous aromatic framework (PAF)-5 <i>via</i> Friedel-Crafts alkylation followed by hydrolysis. Rigorous characterization by NMR, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy authenticated the successful integration of aldehyde moieties into PAF-5, affording PAF-5-CHO. Subsequent functionalization of PAF-5-CHO with various amines produced three amine-functionalized PAF derivatives. Notably, PAF-5-C[double bond, length as m-dash]N-EDA exhibited a 78% enhancement in carbon dioxide (CO₂) adsorption capacity, reaching 3.78 mmol g^-1 at 1 bar and 298 K relative to PAF-5-CHO. Breakthrough experiments demonstrated that PAF-5-C[double bond, length as m-dash]N-EDA could effectively separate CO₂ from simulated flue gas (CO₂/N₂ = 15 : 85, v/v; 10 mL min^-1). <i>In situ</i> infrared spectroscopy, density functional theory calculations and temperature-programmed desorption studies provided insights into the CO₂ adsorption mechanism.