Study on Methyl Orange Adsorption by Fe3O4@SiO2 Decorated Chitosan Schiff Base: Insights from Kinetics, Thermodynamics and Response Surface Methodology for Optimization

Water pollution caused by anionic dyes such as methyl orange poses a serious environmental problem due to their high stability and resistance to degradation. In this study, the Fe 3 O 4 @SiO 2 @Cs-SA magnetic adsorbent was synthesized by coating Fe₃O₄—used as the magnetic core—with SiO₂ derived from sugarcane bagasse, followed by a coating of chitosan derived from mussel shell waste and modified with salicylaldehyde via a Schiff base reaction to enhance adsorption performance. The resulting material was characterized using FTIR, XRD, SEM-EDX, VSM, BET, DLS, zeta potential, and pHpzc. The effects of the main adsorption parameters, i.e., adsorbent dose (0.03–0.12 g/L), contact time (5–75 minutes), initial concentration (40–120 mg/L), pH (1–9), and temperature (25–45°C) were optimized using a Box–Behnken design (BBD) within response surface methodology (RSM). The results indicated that the adsorption process followed pseudo-second-order kinetics and the Elovich isotherm model. Thermodynamic analysis revealed that the adsorption process occurred spontaneously and was exothermic. The adsorption mechanism was dominated by electrostatic interactions, hydrogen bonding, and π–π and n–π interactions between the adsorbent’s aromatic groups and methyl orange, consistent with the results of pHpzc analysis and functional group characterization. These findings indicate that Fe₃O₄@SiO₂@Cs-SA derived from waste biomass was an effective and promising adsorbent for sustainable dye wastewater treatment applications.