Modification using additional NaOH for the preparation of γ-Fe2O3 nanoparticles by chemically induced transition

γ-Fe₂O₃ nanoparticles coated with a layer of FeCl₃·6H₂O were prepared by chemically induced transition in FeCl₂ solution. NaOH was added to the reaction solution, to investigate the effect of alkalinity on the resulting particles. Vibrating sample magnetometry, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were used to characterise the products. Additional NaOH stimulated the epitaxial growth of γ-Fe₂O₃ on the γ-Fe₂O₃ crystallites and more FeCl₃·6H₂O adsorbed on γ-Fe₂O₃. Under the experimental conditions, the increase in γ-Fe₂O₃ content was larger than that of FeCl₃·6H₂O, at ≤0.7 M NaOH. At >0.7 M NaOH, the increase in γ-Fe₂O₃ content was less than that of FeCl₃·6H₂O. The non-monotonic variation of the FeCl₃·6H₂O/γ-Fe₂O₃ ratio was consistent with this result, and was consistent with the variation in apparent specific magnetisation with increasing NaOH concentration.