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

This scheme shows the adsorption mechanism of polyethylenimine-grafted Fe3O4@chitosan core-shell magnetic particle (Fe3O4/CS/PEI) toward phosphate and the recovery of the used particles under an applied magnetic field. The largest adsorption of phosphate was achieved at an equilibrium pH of 3.0–4.0, where more than 92% of phosphate exists in the H2PO4− form. This is because the free amino and hydroxyl groups on the Fe3O4/CS/PEI surface are protonated to NH3+ (major) and OH2+ (minor) groups under such low pH conditions. In this regard, the Fe3O4/CS/PEI surface has a strong affinity to H2PO4− anions. Moreover, the prepared Fe3O4/CS/PEI nanoparticles could be rapidly separated from the solution environment, which again demonstrated their promising application potential. [Display omitted] •Polyethylenimine-grafted Fe3O4@chitosan core-shell magnetic nanoparticles were prepared.•SQUID analysis determined the saturation magnetization of the nanoparticles to be 52emug−1.•The Langmuir maximum amount of phosphate adsorbed at 25°C equaled 50.8mgg−1 at pH 4.0.•One protonated amino cation on particle surface was mainly bound with one H2PO4− ion in water.•The polyaminated magnetic particles showed preferential adsorption of phosphate over other anions. 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 48.2mgg−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 part