Removal of Methylene Blue Dye from Aqueous Solutions Using Carboxymethyl-β-Cyclodextrin-Fe₃O₄ Nanocomposite: Thermodynamics and Kinetics of Adsorption Process

Abstract—The applicability of the synthesized carboxymethyl-β-cyclodextrin-Fe₃O₄ nanocomposite (CM‑β-CD-Fe₃O₄NPs) as a novel adsorbent for eliminating Methylene blue dye (MB) from aqueous media was investigated. Various techniques including Brunauer Emmett Teller analysis (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to characterize this novel adsorbent. The effect of initial concentration (C₀), pH, adsorbent dosage (dose), contact time (t_c), and temperature (T, K) on the removal percentage (Ad%) of MB dye onto CM-β-CD-Fe₃O₄NPs was studied, and the optimum value of each factor was determined (pH 6.0, dose = 0.20 g, t_c = 45.0 min, and T = 298.0 K). Several isotherm models, such as Langmuir, Freundlich and Redlich–Peterson models were used to represent the adsorption experimental results, but the Freundlich model represents better the results than others. The pseudo-second-order kinetics coincided quite with the kinetic results. Based on the obtained thermodynamic values such as standard Gibbs free energy change ($\Delta G_{{{\text{ad}}}}^{^\circ }$ < 0), standard enthalpy change ($\Delta H_{{{\text{ad}}}}^{^\circ }$ < 0) and standard entropy change ($\Delta S_{{{\text{ad}}}}^{^\circ }$ < 0), the nature of the adsorption process was spontaneous, exothermic and mainly physisorption.