Facile Synthesis of Substantially Magnetic Hollow Nanospheres of Maghemite (γ-Fe2O3) Originated from Magnetite (Fe3O4) via Solvothermal Method

In the present study, we report on the successful synthesis of hollow nanospheres of maghemite (γ-Fe2O3). The γ-Fe2O3 hollow nanospheres were synthesized by annealing magnetite (Fe3O4) hexagonal nanoparticles produced by solvothermal method. Structural analysis by slow-scan X-ray diffraction (XRD) marks a small peak shift towards high angle confirming the change in the iron oxide phase from Fe3O4 to γ-Fe2O3. Further, FT-IR spectroscopy reveals for Fe3O4 a band at 571 cm−1, which shows the Fe-O stretching mode of tetrahedral and octahedral sites. Formation of γ-Fe2O3 upon annealing was again confirmed from the broadening and splitting of band 571 cm−1 into two bands, viz. 556 cm−1 and 637 cm−1. Magnetic properties of the synthesized samples were studied using a vibrating sample magnetometer (VSM) at 300 K. The value of saturation magnetization (MS) of Fe3O4 nanoparticles and γ-Fe2O3 hollow nanospheres was 56 emu/g and 43 emu/g, respectively. For Fe3O4, infrequent Verwey transition appeared when variation in magnetization with temperature was studied. Morphological analysis confirms the hexagonal shape of Fe3O4 nanoparticles with an average particle size of 57 nm. The same study interestingly epitomizes a hollow nanospherical shape with an average particle size of 12 nm for γ-Fe2O3. The emergence of the Verwey transition in Fe3O4 hexagonal nanoparticles and the existence of significant magnetization of 43 emu/g in hollow nanospheres of γ-Fe2O3 in this study are contentious and fascinating for possible applications.