Thermal Conversion of Hollow Prussian Blue Nanoparticles into Nanoporous Iron Oxides with Crystallized Hematite Phase

We recently demonstrated that Prussian blue (PB) coordination polymers can be successfully etched by acidic solution for the preparation of hollow PB nanoparticles ( Angew. Chem. Int. Ed. 2012 , 51 , 984). In this paper, by using hollow PB nanoparticles as starting materials, we calcined them under various conditions to prepare nanoporous Fe oxides with a crystallized α‐Fe 2 O 3 (hematite) phase. The obtained particles were carefully characterized by scanning electron microscopy, wide‐angle X‐ray diffraction, nitrogen gas adsorption–desorption isotherms, transmission electron microscopy, and Mössbauer spectroscopy. The morphologies, surface areas, and degrees of crystallinity of the samples were varied by changing the number of hours of calcination. After calcination at 400 °C for 4 h, formation of a crystallized α‐Fe 2 O 3 phase was confirmed, although some residues of amorphous and/or γ‐Fe 2 O 3 phases were also present. With a further increase in the calcination time (up to 7 h), the α‐Fe 2 O 3 phase was predominantly formed. The obtained sample exhibited high surface area, which will be useful for photocatalytic applications.