Preparation of N-methylimidazolium-based strongly basic macroporous resins and their adsorption performance towards aromatic acids

Abstract

Herein, N-methylimidazolium-based strongly basic macroporous resins were synthesized according to bimolecular nucleophilic substitution (SN2), and they were applied to adsorb aromatic acids of different molecular weights in aqueous and isopropanol. Using chloromethylated polystyrene (PS) as the matrix and N-methylimidazole as the functional monomer, a bimolecular nucleophilic substitution reaction at 383 K produced the functionalized resin PS-R-X. Subsequently, ion exchange with NaOH, HCl, and HNO₃ was performed respectively to obtain the resin in three distinct ionic forms (PS-R-OH, PS-R-Cl, and PS-R-NO₃). Consistent with the Type I strongly basic anion exchange resin selectivity order for anions (that is the binding affinity order NO₃⁻ > Cl⁻ > OH⁻), PS-R-OH exhibited higher adsorption capacities for naphthol, binaphthol, and benzoic acid than PS-R-Cl and PS-R-NO₃, and hydrophobic interactions also influenced the adsorption process. Adsorption experiments were conducted on benzoic acid, naphthol and binaphthol, and the adsorption capacity reached 405.90, 511.55, and 453.28 mg/g at 298 K, respectively. PS-R-OH also showed superior adsorption selectivity, good reproducibility, and effective reusability, highlighting its strong potential for aromatic acid adsorption. Mechanistic analysis revealed that the adsorption process was dominated by hydrophobic interactions and desolvation effects, operating in conjunction with π-π interactions and hydrogen bonding. A novel N-methylimidazolium-based macroporous resin (PS-R-OH) was synthesized via SN2 reaction. PS-R-OH showed high adsorption capacities for benzoic acid, naphthol, and binaphthol at 298 K. The resin achieved rapid equilibrium, complete removal at 100 mg/L, and 90% performance after 8 cycles. Hydrophobic interactions, desolvation, π-π interactions, and hydrogen bonding governed the adsorption process.