The Counterion Effect of Imidazolium-Type Poly(ionic liquid) Brushes on Carbon Dioxide Adsorption

Graphical Solitary confinement : The confined structure of poly(ionic liquid)s (PILs) attached to the surfaces of silica nanoparticles can facilitate carbon dioxide transport and thus enhance its adsorption. The carbon dioxide adsorption properties are strongly dependent on the type of counterion associated with the anchored molecules. Imidazolium-based poly(ionic liquid) brushes were attached to spherical silica nanoparticles bearing various functionalities by using a surface-initiated atom transfer radical polymerization (“grafting from” technique). A temperature-programmed desorption process was applied to evaluate and analyze the carbon dioxide adsorption performance of the synthesized polymer brushes. The confined structure of the surface-attached polymer chains facilitates gas transport and adsorption, leading to an enhanced adsorption capacity of carbon dioxide molecules compared with pure polymer powders. Temperature-programmed desorption profiles of the synthesized polymer brushes after carbon dioxide adsorption reveal that the substituent groups on the nitrogen atom at the 3-position of the imidazole ring, as well as the associated anions significantly affect the adsorption capacity of functionalized poly(ionic liquid) brushes. Of the tested samples, amine-functionalized poly(ionic liquid) brushes associated with hexafluorophosphate ions exhibit the highest carbon dioxide adsorption capacity of 2.56 mmol g −1 (112.64 mg g −1 ) at 25 °C under a carbon dioxide partial pressure of 0.2 bar.