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

Abstract

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.

Keywords: CO2 adsorption; nanoparticles; poly(ionic liquid)s; polymer brushes; surfaces.