Glutaraldehyde cross-linked chitosan-coated Fe 3 O 4 nanocomposites (MCNPs) were successfully synthesized for the removal of methyl orange (MO) from wastewater. Experimental conditions such as the pH, cation surfactant dosage, nanoadsorbent dosage, and ionic strength were also investigated. Kinetics date was better fit by a pseudosecond-order model, indicating that adsorption was the ratelimiting step. The Freundlich models (R 2 = 0.9794) fit the experimental data better than the Langmuir models, and the theoretical maximum adsorption capacity was 758 mg g −1 . The values of the Gibbs free energy (ΔG°= −7.27 kJ mol −1 ), enthalpy (ΔH°= 0.001 kJ mol −1 ), and entropy (ΔS°= 23.58 J mol −1 ) indicated the spontaneous and endothermic process of MO adsorption. The prepared MCNPs showed 96−98% adsorption of MO by adding 0.2 mg of cationic surfactant cetyltrimethylammonium bromide (CTAB) to form mixed hemimicelles and can be easily regenerated with a 0.1 mol L −1 HCl solution.

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