Adsorption of fluoride on a chitosan-based magnetic nanocomposite: equilibrium and kinetics studies

A new derivative of chitosan functionalized with chloroacyl chloride and 2-(2-aminoethylamino) ethanol was synthesized for the preparation of the magnetic nanocomposite containing Fe 3 O 4 @TiO 2 nanoparticles. Characterizations were done by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Nanocomposite was examined for the defluoridation of water, and the effect of contact time, pH, initial fluoride ion concentration, contact time and adsorbent dosage were investigated. Langmuir model showed the best agreement with the experimental data. The maximum adsorption capacity for the fluoride removal from aqueous solutions was 15.385 mg/g at 318 K and pH = 5.0. The adsorption mechanism matches the pseudo-second-order kinetic model with a rate constant ( k 2 ) of 0.68 g/mg·min. Thermodynamics study of the nature of adsorption showed that ΔH and ΔS was 13.767 kJ/mol and 0.066 kJ/mol·K respectively. A mechanism for the fluoride sorption was proposed by considering the electrostatic and hydrogen bonding interactions.