Preparation of polyaminated Fe₃O₄@chitosan core-shell magnetic nanoparticles for efficient adsorption of phosphate in aqueous solutions

In this study, novel polyethylenimine (PEI)-grafted chitosan (CS) core-shell (called as Fe₃O₄/CS/PEI) magnetic nanoparticles were synthesized and applied for adsorbing phosphate in water. The magnetic and physicochemical properties of as-synthesized nanoparticles were first analyzed by means of a superconducting quantum interference device, X-ray diffractometer, X-ray photoelectron spectroscope, Fourier-transform infrared spectroscope, transmission electron microscope, zeta potential analyzer, and nitrogen sorptiometer. The followed experiments indicated that the amount of phosphate adsorbed increased with increasing equilibrium pH to near 4.0 and then decreased when the pH was further increased. The adsorption isotherms of phosphate on Fe₃O₄/CS/PEI particles were well fit by the Langmuir equation, and its maximum adsorption was 48.2 mg g⁻¹ at an equilibrium pH of 3.0 and 25 °C. The primary mechanism for phosphate adsorption on Fe₃O₄/CS/PEI particles was electrostatic attraction. The preferential adsorption of phosphate in the presence of other excess anions including chloride, nitrate, carbonate, and sulfate was presented. Under the conditions studied, more than 90% of phosphate was desorbed from the laden Fe₃O₄/CS/PEI particles by 0.05 mol L⁻¹ of NaOH solution. The remained adsorption efficiency obtained in the five-cycle reusability tests has demonstrated the promising application potential of Fe₃O₄/CS/PEI particles.