Maruti Vibhuti Ravikumar, Balagopalan Gayathri, Vellanki Lakshmi
Conjugated porous polymers (CPPs) have attracted significant interest for environmental remediation, particularly in removing organic dyes from water, due to their permanent porosity, chemical robustness, and extended π-conjugated frameworks. In this work, we demonstrate that cationic CPPs can be highly effective adsorbents for a wide range of organic dyes in aqueous solution. The pyrylium-based CPPs (TMPA-O and TMPB-O) and thio-pyrylium-based CPPs (TMPA-S and TMPB-S) were synthesized and systematically evaluated for the adsorption of both cationic dyes, malachite green (MG), methylene blue (MB), and crystal violet (CV), and an anionic dye, methyl red (MR). Detailed kinetic and adsorption isotherm analyses revealed fast uptake behaviour and substantial adsorption capacities across the dye set. The adsorption of cationic dyes was screened by polarizable counterions (BF4 - and CF3SO3 -), which formed counterion-mediated bridges with the polymer and dye, thereby reducing electrostatic repulsion between the cationic dye and the polymer. The highest adsorption capacity was observed for MG with TMPB-S, reaching 667 mg g-1, and TMPB-S also showed notable uptake of MB (92 mg g-1) and MR (485 mg g-1). The superior performance of TMPB-S is attributed to the combination of its relatively higher surface area and pore volume among the investigated materials, alongside the counterion mediation in cationic dye adsorption. These findings bypass the limitations of charge-based adsorption and highlight cationic CPPs with polarizable counterions as effective and versatile options for removing dyes from water.