Engineering a poly(methyl methacrylate)–sodium mordenite hybrid composite for efficient adsorptive removal of indigo dye from aqueous media

Abstract A poly(methyl methacrylate)-modified sodium mordenite (PMMA–Na-MOR) composite was prepared by in situ polymerization and evaluated for indigo removal under controlled batch conditions. FTIR, SEM, XPS, XRD, zeta-potential, BET surface-area, and pore-size-distribution measurements were used to examine polymer-associated surface modification, framework retention, interfacial charge, and accessible porosity. Quantitative PMMA loading was not determined and is identified as a limitation. Dye uptake approached equilibrium within approximately 90 min and was favored under near-neutral to mildly alkaline conditions. Increasing temperature reduced adsorption, consistent with exothermic behavior. Among the tested equilibrium models, Sips provided the best fit in the original qₑ domain (R² = 0.999, RMSE = 0.128, χ² = 0.016), with a model-derived q max of 29.07 mg g⁻¹ and n S = 0.786; the Langmuir q max was 17.59 mg g⁻¹. Apparent thermodynamic analysis based on K d, app = qₑ/Cₑ yielded ΔH app = − 26.43 kJ mol⁻¹ and ΔS app = − 95.60 J mol⁻¹ K⁻¹. Because K d, app is conditional and dimensional, the positive ΔG app values are not interpreted as standard-state Gibbs energies. Removal remained above 80% in the presence of each tested salt, while removal efficiency declined from 92.4% in cycle 1 to 76.8% in cycle 5. In one real-effluent sample, PMMA–Na-MOR reduced the measured indigo concentration from 50 to 10 mg L⁻¹ under the stated batch conditions. These results support preliminary batch performance, while quantitative polymer loading, replicate-based inferential statistics, polymer-leaching assessment, extended regeneration, and fixed-bed validation remain necessary.