γ-Fe2O3 and Fe3O4 magnetic hierarchically nanostructured hollow microspheres: Preparation, formation mechanism, magnetic property, and application in water treatment

In this paper, we report the preparation of γ-Fe2O3 and Fe3O4 magnetic hierarchically nanostructured hollow microspheres by a solvothermal combined with precursor thermal conversion method. These γ-Fe2O3 and Fe3O4 magnetic hierarchically nanostructured hollow microspheres were constructed by three-dimensional self-assembly of nanosheets, forming porous nanostructures. The effects of experimental parameters including molar ratio of reactants and reaction temperature on the precursors were studied. The time-dependent experiments indicated that the Ostwald ripening was responsible for the formation of the hierarchically nanostructured hollow microspheres of the precursors. γ-Fe2O3 and Fe3O4 magnetic hierarchically nanostructured hollow microspheres were obtained by the thermal transformation of the precursor hollow microspheres. Both γ-Fe2O3 and Fe3O4 hierarchically nanostructured hollow microspheres exhibited a superparamagnetic property at room temperature and had the saturation magnetization of 44.2 and 55.4 emu/g, respectively, in the applied magnetic field of 20 KOe. Several kinds of organic pollutants including salicylic acid (SA), methylene blue (MB), and basic fuchsin (BF) were chosen as the model water pollutants to evaluate the removal abilities of γ-Fe2O3 and Fe3O4 magnetic hierarchically nanostructured hollow microspheres. It was found that γ-Fe2O3 hierarchically nanostructured hollow microspheres showed a better adsorption ability over SA than MB and BF. However, Fe3O4 hierarchically nanostructured hollow microspheres had the best performance for adsorbing MB.

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► A solvothermal combined with precursor thermal conversion method is demonstrated.
► γ-Fe2O3 and Fe3O4 hierarchically nanostructured hollow microspheres are obtained.
► The effects of experimental parameters on the precursors are investigated.
► The removal abilities for organic pollutants of the products are evaluated.