Synthesis and adsorption performance of a novel pyridinium-functionalized hypercrosslinked resin for the removal of chromium(vi) ions

This study presents the synthesis and characterization of a novel anion exchange hypercrosslinked resin (HPR1) designed for the removal of high-concentration hexavalent chromium Cr(VI) from aqueous solutions. The resin was synthesized via a one-step Friedel–Crafts alkylation reaction using a low-crosslinking copolymer of divinylbenzene and vinylbenzyl chloride (DVB-co-VBC), prepared by suspension polymerization with toluene as a porogen. The successful incorporation of pyridinium groups into the resin network was confirmed using elemental analysis, FTIR spectroscopy, and solid-state ¹³C NMR spectroscopy. The adsorption performance of HPR1 was evaluated at various pH (2, 4, and 6.5) and initial Cr(VI) concentrations. The nonlinear Langmuir isotherm model provided the best fit for the experimental data compared with tc Freundlich and Redlich–Peterson isotherms. Notably, the adsorption equilibrium was achieved within 4 min, with a maximum capacity of 207 mg g⁻¹ at pH 2. Kinetic studies indicated that the adsorption process was best described by a pseudo-second-order model, with higher rates observed at pH 4 than at pH 2. Additionally, intraparticle diffusion has been identified as the mechanism that controls the adsorption process. The high adsorption capacity of HPR1 at acidic pH values suggests its potential for treating industrial wastewater containing elevated concentrations of Cr(VI).