In situ preparation of magnetic Fe3O4/chitosan nanoparticles via a novel reduction–precipitation method and their application in adsorption of reactive azo dye

Magnetic Fe3O4/chitosan nanoparticles (MFe3O4/CS NPs) were in situ prepared successfully by a simple reduction–precipitation method through partial reduction of Fe3 + with sodium sulfite, precipitation with ammonia at room temperature, and then cross-linking with epoxy chloropropane. The nanoparticles were characterized by HRTEM, BET, XRD, FT-IR, TGA and VSM. MFe3O4/CS NPs were quasi-spherical or ellipsoidal in shape and about 7 nm in average diameter, exhibiting superparamagnetic properties with a saturation magnetization value of 17.1 emu/g. The adsorption behaviors of MFe3O4/CS NPs towards reactive brilliant red X-3B (X-3B) were investigated, including pH effect, adsorbent dosage, adsorption equilibrium and adsorption kinetics. It was found that the adsorption performances of X-3B on MFe3O4/CS NPs were strongly dependent on both initial pH and the adsorbent dosage. The adsorption equilibrium data fitted well with the Langmuir isotherm model and the adsorption process followed the pseudo-second-order kinetic model. Thermodynamic parameters such as free energy (ΔGo), enthalpy (ΔHo), and entropy (ΔSo) indicated that the adsorption was spontaneous and endothermic. Besides, the recycling experiments showed good reusability of MFe3O4/CS NPs as adsorbents.