Pillar[5]arene cross-linked chitosan polymer with enhanced selective removal of toxic anionic dyes: Preparation, characterization, adsorption mechanism, and cytotoxicity assessment.

Polymer networks constructed from chitosan possess abundant active adsorption sites and exhibit efficient adsorption and separation capabilities, highlighting their considerable potential for water pollution treatment. Herein, we report the synthesis of a novel macrocyclic cross-linked network (CS-DBEP5) via a one-pot nucleophilic substitution reaction between CS and per-(2-bromoethyl) pillar[5]arene (DBEP5). Importantly, substitution reactions yielded distinct cross-linking motifs containing secondary/tertiary amines and quaternary ammonium groups within the polysaccharide backbone. This well-defined chemical modification generated multidimensional interaction interfaces, including hydrogen bonding, electrostatic attraction, host-guest complexation, and π-π stacking, that synergistically drive ultrafast anionic dye capture (>95 % removal within 30 s). A systematic investigation revealed that the adsorption of various anionic dyes onto CS-DBEP5 conformed to the Freundlich isotherm model, suggesting a multilayer heterogeneous adsorption mechanism. Furthermore, efficient removal of multiple dye pollutants was achieved even in complex water environments. For the model dye orange G, a high removal efficiency of 91 % was maintained after ten adsorption-desorption cycles. Finally, molecular modeling and toxicity assessments validated the dye adsorption mechanism of CS-DBEP5 and confirmed its non-toxic nature. This work innovatively merged pillararene's supramolecular traits with chitosan's functional benefits to create an efficient adsorbent, offering theoretical and technical insights for macrocyclic polysaccharide composites in wastewater treatment.