Carboxyl‐Rich PMAA‐ co ‐DVB Microspheres for High‐Capacity Cationic Dye Adsorption and Charge‐Based Discrimination

ABSTRACT

Poly(methacrylic acid‐co‐divinylbenzene) (PMAA‐ co ‐DVB) microspheres were prepared by one‐pot precipitation polymerization as carboxyl‐rich adsorbents for cationic dye removal. Despite a low BET surface area of 4.96 m ² ·g ⁻¹ , the microspheres exhibited a high carboxyl‐group density of 7.85 ± 0.17 mmol·g ⁻¹ . Decreasing the MAA content reduced the carboxyl‐group density, negative surface charge, and adsorption capacities toward methylene blue (MB) and methyl violet (MV), establishing a composition, functional site, surface charge, and adsorption relationship. Adsorption approached equilibrium within approximately 20 min, and the Langmuir model provided the best empirical description among the tested models, with model‐derived maximum capacities of 911.04 and 749.78 mg g ⁻¹ for MB and MV, respectively. In binary‐dye systems, PMAA‐ co ‐DVB preferentially adsorbed the tested cationic dyes over anionic dyes, with apparent selectivity coefficients of 1133.98–2594.76. XPS and zeta‐potential analyses supported an important contribution of ionized carboxyl sites and electrostatic interactions. The microspheres also retained appreciable adsorption capacity over 10 regeneration cycles and showed preliminary applicability in actual textile wastewater.