Mechanistic Study of Methyl Orange Removal by Fe3O4@MIL-53(Fe Cu) Composite Material

A novel magnetic composite, Fe3O4@MIL-53(Fe Cu), was successfully synthesized and applied for the efficient removal of methyl orange (MO) from aqueous solutions. The ad sorption performance was systematically evaluated under various conditions, including adsorbent dosage, solution pH, coexisting anions, and regeneration cycles. The results demonstrated that an optimal dosage of 20 mg achieved a removal efficiency exceeding 85%, with maximum adsorption observed at pH 3. The presence of common anions (Cl−, SO42−, CO32−, and PO43−) showed negligible effects on MO removal. Kinetic studies revealed that the adsorption process followed the pseudo-second-order model. Although minor chemisorption contributions were observed, the Dubinin–Radushkevich (D–R) model confirmed the predominance of physical adsorption. The Freundlich isotherm provided the best fit to the equilibrium data, indicating a maximum adsorption capacity of 193.65 mg/g and suggesting multilayer adsorption on a heterogeneous surface. Thermodynamic analysis confirmed the spontaneous and endothermic nature of the adsorption process. The primary mechanisms governing MO adsorption were identified as electrostatic attraction, π–π interactions, and hydrogen bonding. The composite exhibited excellent reusability over multiple cycles, demonstrating its potential for practical wastewater treatment applications.