Facile synthesis of morphology and size-controlled α -Fe 2 O 3 and Fe 3 O 4 nano-and microstructures by hydrothermal/solvothermal process: The roles of reaction medium and urea dose

This paper reports a systematic study of the influences on the synthesis of α-Fe2O3 and Fe3O4 via a hydro/solvothermal process at 200 °C. Both the reaction medium and urea dose have been investigated. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). Results showed that the reaction mediums, such as water and ethylene glycol, played important roles in forming different types of iron oxides. Pure crystalline α-Fe2O3 was formed via the hydrothermal process, and Fe3O4 was obtained through a solvothermal route with ethylene glycol as reaction medium. Increasing urea dose tuned the particle sizes of α-Fe2O3 and Fe3O4 from a few hundreds to several tens of nanometers. With addition of urea, the morphology of α-Fe2O3 evolved from olive-like to rhomb-like, and Fe3O4 evolved from hollow sphere, to pinecone-like, and finally into cracked nanostructures. The variations of the surface area of products were mainly dependent on the microstructure and intrinsic features of the iron oxide particles. Results of the mechanistic studies indicated that the generation of CO2 and NH3 via in situ thermal decomposition of urea was crucial for the formation of α-Fe2O3 and Fe3O4 nano-and microstructures. The as-synthesized α-Fe2O3 and Fe3O4 were used as catalysts for methylene blue degradation in the presence of H2O2, and α-Fe2O3 showed a higher degradation efficiency. Our findings demonstrated a promising strategy for the developments of rationally designed iron oxides.