Adjustable\nFunctionalization of Hyper-Cross-Linked\nPolymers of Intrinsic Microporosity for Enhanced CO₂ Adsorption\nand Selectivity over N₂ and CH₄

Abstract

In this paper, we\nreport the design, synthesis, and characterization\nof a series of hyper-cross-linked polymers of intrinsic microporosity\n(PIMs), with high CO₂ uptake and good CO₂/N₂ and CO₂/CH₄ selectivity, which makes\nthem competitive for carbon capture and biogas upgrading. The starting\nhydrocarbon polymers’ backbones were functionalized with groups\nsuch as −NO₂, −NH₂, and −HSO₃, with the aim of tuning their adsorption selectivity toward\nCO₂ over nitrogen and methane. This led to a significant\nimprovement in the performance in the potential separation of these\ngases. All polymers were characterized via Fourier transform infrared\n(FTIR) spectroscopy and ¹³C solid-state NMR to confirm\ntheir molecular structures and isothermal gas adsorption to assess\ntheir porosity, pore size distribution, and selectivity. The insertion\nof the functional groups resulted in an overall decrease in the porosity\nof the starting polymers, which was compensated with an improvement\nin the final CO₂ uptake and selectivity over the chosen\ngases. The best uptakes were achieved with the sulfonated polymers,\nwhich reached up to 298 mg g^–1 (6.77 mmol g^–1), whereas the best CO₂/N₂ selectivities\nwere recorded by the aminated polymers, which reached 26.5. Regarding\nCH₄, the most interesting selectivities over CO₂ were also obtained with the aminated PIMs, with values up to 8.6.\nThe reason for the improvements was ascribed to a synergetic contribution\nof porosity, choice of the functional group, and optimal isosteric\nheat of adsorption of the materials.