Adsorption of reactive red dye (RR-120) on nanoadsorbent O-carboxymethylchitosan/γ-Fe2O3: kinetic, equilibrium and factorial design studies

Abstract

In this study, a novel magnetically separable nanoadsorbent, consisting of a γ-Fe₂O₃ and O-carboxymethylchitosan (O-CM), was synthesized in a three-step procedure. The structure of O-CM was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), vibrating-sample magnetometer (VSM), and transmission electron microscope (SEM). Adsorption features of the magnetic nanoadsorbent were evaluated using the dye reactive red 120 (RR120). The isotherms, kinetics, and thermodynamics of the dye adsorption were studied in various experimental conditions, i.e., initial dye concentration, contact time, solution pH and temperature. The effects of pH, initial dye concentration and temperature were investigated by the 3³ Box–Behnken factorial experimental design method, and the statistical approach analysis of variance was used to optimize the operating conditions. The results obtained fitted well to the Langmuir–Freundlich model, and the kinetics of the adsorption process were found to follow the pseudo-second-order kinetics. The thermodynamic study was conducted by calculating a number of thermodynamic parameters, such as the standard changes in ΔG°, ΔH° and ΔS°. The high sensitivity of the magnetic nanoadsorbent to the external magnetic field culminates in its efficient and easy separation and good adsorption ability, demonstrating great potential in the application of water treatment.