Urea-functionalized ionic polymeric materials with adjustable ion density for efficient CO2 fixation and iodine adsorption

Abstract

Ionic polymeric materials have unique physical and chemical properties that make them crucial in the fields of catalysis and adsorption. This study successfully synthesized a series of urea-functionalized ionic polymeric materials, designated as UP-x (x = 2, 3, 4). The synthesis employed a simple solvothermal method in conjunction with a three-component condensation and the Menshutkin reaction, facilitating the precise incorporation of highly active urea units and the intentional modulation of ion density by varying the connecting monomers. The functional groups, microstructure, thermal stability and pore structure of the materials were characterized using FT-IR, ¹³C NMR, SEM, TGA and BET. Subsequently, these materials were applied in CO₂ fixation and iodine adsorption. All synthesized materials demonstrated effective catalytic activity, with UP-4 achieving a yield of up to 91.3 %. Experimental investigations have demonstrated that UP-4 is recyclable and can accommodate a wide range of substrates. Kinetic analyses revealed a reduction in the activation energy of the reaction to 50.5 kJ/mol. UP-x (x = 2, 3, 4) exhibited exceptional performance in the adsorption of iodine vapors, achieving maximum adsorption capacities of 4.51 g/g, 4.30 g/g, and 4.40 g/g, respectively. Results from DFT calculation confirm that the urea groups in the polymer framework can effectively activate epoxides and CO₂ molecules, thereby enhancing the cycloaddition reaction. The urea units, bromine ions, and aromatic rings serve as iodine adsorption sites, enabling efficient iodine capture. The adsorption mechanism of iodine vapor on these materials involves both physisorption and chemisorption.