Liquid-liquid interface-assisted solvothermal synthesis of durian-like α-Fe ₂O ₃ hollow spheres constructed by nano-polyhedrons

Novel durian-like α-Fe ₂O ₃ hollow spheres have been successfully synthesized via a simple benzene/water two-phase interface-assisted solvothermal approach and sequential calcinations. The prepared samples were characterized using XRD, FESEM, TEM, HRTEM, SAED, FT-IR, VSM and N ₂ adsorption-desorption isotherms. The results revealed that the as-obtained hierarchical hollow spheres were assembled by numerous single-crystalline polyhedral particles and had an average diameter of 480-600 nm. It was found that both the interfacial reaction and PVP molecules in the reaction system played key roles in the formation of the hierarchical hollow spheres. In the absence of a benzene/water interface, only a large number of microrods were obtained. The presence of the benzene/water interface could also accelerate the phase transformation from α-FeOOH to α-Fe ₂O ₃. When no PVP was introduced into the reaction system, solid spherical particles were synthesized. On the basis of a series of time-dependent experiments, the mechanism for the formation of the novel hierarchical hollow spheres was proposed. Furthermore, the as-obtained hierarchical structured hematite hollow spheres have been used as an absorbent in wastewater treatment to remove the heavy metal ion Cr(vi).