Iron oxide hollow spheres: Microwave–hydrothermal ionic liquid preparation, formation mechanism, crystal phase and morphology control and properties

This paper reports on the microwave–hydrothermal ionic liquid method for the synthesis of a variety of iron oxide nanostructures such as α-FeOOH hollow spheres, β-FeOOH architectures and α-Fe2O3 nanoparticles. The formation mechanism for α-FeOOH hollow spheres is discussed. The effects of the reaction parameters on the morphology and crystal phase of the final product are studied. The relationship between the morphology and crystal phase of the product is discussed. A general thermal transformation strategy is designed to prepare α-Fe2O3 hollow spheres using α-FeOOH hollow spheres as the precursor and template. By thermal treatment of the as-prepared α-FeOOH hollow spheres, α-Fe2O3 hollow spheres showing good photocatalytic activity are obtained. And by autocatalysis of the adsorbed available Fe(II) on the α-FeOOH surfaces, Fe3O4 hollow spheres are also obtained.