Control synthesis of magnetic Fe3O4–chitosan nanoparticles under UV irradiation in aqueous system

Novel magnetic Fe3O4–chitosan nanoparticles were synthesized via photochemical method in an emulsifier-free aqueous system at room temperature for the first time. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the Fe3O4–chitosan nanoparticles were in regular shape with a mean diameter of 41 nm, whereas the average size in aqueous solution measured by photocorrelation spectroscopy (PCS) was 64 nm, which indicated that the nanoparticles had water-swelling properties. X-ray diffraction (XRD) patterns indicated that the Fe3O4 nanoparticles were pure Fe3O4 with a spinel structure, and the irradiation under UV light did not result in a phase change. The Fe3O4–chitosan nanoparticles were also characterized by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Magnetic measurement revealed that the saturated magnetization (Ms) of the Fe3O4–chitosan nanoparticles reached 48.6 emu/g and the nanoparticles showed the characteristics of superparamagnetism. The stability test showed these novel nanoparticles had high magnetic stability. The PCS and TGA results indicated that the size and chitosan content of Fe3O4–chitosan nanoparticles formed was pH- and chitosan/Fe3O4 ratio-dependent, which could be used to synthesize magnetic Fe3O4–chitosan nanoparticles with different size to meet the requirements of different applications.