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 ₂O₃ (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-Fe₂O₃ phase was confirmed, although some residues of amorphous and/or γ-Fe₂O₃ phases were also present. With a further increase in the calcination time (up to 7 h), the α-Fe₂O₃ phase was predominantly formed. The obtained sample exhibited high surface area, which will be useful for photocatalytic applications. Hollow Prussian blue nanoparticles are calcined under various reaction conditions to prepare nanoporous Fe oxides with a crystallized α-Fe₂O₃ (hematite) phase. The morphologies, surface areas, and degrees of crystallinity of the samples are varied by changing the number of hours of calcination. After calcination at 400 °C for 4 h, formation of a crystallized α-Fe₂O₃ phase is confirmed.