Synergy between Ionic Capacity and Intrinsic Porosity in Imidazolium-Based Cationic Organic Polymers and Its Effect on Anionic Dye Adsorption

Abstract

A series of novel imidazolium-based cationic organic polymers (COPs) with various ionic capacities (ICs) and porosities were synthesized by adjusting the structure of the building units and applied to the adsorption of organic dyes from aqueous solutions. The charge-incorporated polymer without pores was almost incapable of adsorbing dyes. Among polymers with similar porosities, COPs with higher IC values exhibited higher adsorption capacities, and the polymer with the largest IC but only a surface area of 74.2 m2 g–1 exhibited the best adsorption performance toward Acid Orange 7 (559.4 mg g–1, 21 times that of the uncharged polymer). The results demonstrated the synergistic effect between IC and intrinsic porosity: high porosity was necessary for adsorption, whereas electrostatic interactions between charges and dyes dominate removal efficiency; increasing the charge content is more effective than increasing the surface area in this polymer system. This work provides in-depth insight into the organic-dye adsorption process and a path toward the rational molecular design of high-performance COPs.