Preparation and characterization of a novel chitosan/Al₂O₃/magnetite nanoparticles composite adsorbent for kinetic, thermodynamic and isotherm studies of Methyl Orange adsorption

In this study we developed a novel chitosan/Al₂O₃/magnetic iron oxide nanoparticle composite acting as an adsorbent for removing Methyl Orange (MO), a model anionic dye, from aqueous solution. The new adsorbent was characterized by Scanning Electron Microscope (SEM), Thermo Gravimetric Analysis (TGA), Brunauer-Emmett-Teller (BET) specific surface area, Energy Dispersive spectrometer (EDAX), powder X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) methods. The MO removal by the developed adsorbent was investigated using batch adsorption technique and all parameters influencing the removal efficiency such as: dose of adsorbent, pH and initial MO concentration were considered. The optimum adsorbent amount was determined to be 0.4gL^-1 and adsorption process was found to be optimal in the wide pH range of 4-10.Also, the adsorption activity of synthesized adsorbent including kinetics, thermodynamics, isotherm and desorption were comprehensibly studied. The adsorption isotherm was well described by the Langmuir model and showed high MO adsorption capacity (1.27mmolg^-1, i.e., 417mgg^-1 at 25°C). MO adsorption kinetics followed a pseudo-second-order kinetic model, indicating that adsorption was the rate-limiting step. At 10mgL^-1, only 14min was required to reach 93% adsorption and about 50% of the MO was adsorbed in 2min. The fitting of experimental data with Weber and Morris model indicates that the adsorption kinetic was controlled simultaneously by film diffusion and intra-particle diffusion. Furthermore, the desorption studies of MO using 0.1M HCl showed the reusability of the adsorbent.