Solid nanotubes comprising alpha-Fe2O3 nanoparticles prepared from ferritin protein.

Solid nanotubes comprising alpha-Fe2O3 nanoparticles were prepared from iron-storage protein ferritin. Their structure, magnetic properties, and photocatalytic activities were characterized. The initial ferritin nanotube precursors were fabricated using alternating layer-by-layer depositions of poly-L-arginine (PLA) and ferritin into a track-etched polycarbonate membrane (pore diameter, 400 nm) with subsequent dissolution of the template. The obtained uniform cylinders of (PLA/ferritin)3 (outer diameter, 410 +/- 14 nm) were calcinated at 500 degrees C under air, yielding reddish-brown iron oxide nanotubes. The one-dimensional hollow structure remained perfect, but its diameter, wall thickness, and maximum length were markedly diminished. Disappearance of the protein shell and the PLA layers were confirmed using IR and EDX spectroscopy. Subsequent SEM, TEM, and XPS measurements showed that the tubular walls comprise fine alpha-Fe2O3 nanoparticles with a 5 nm diameter. These alpha-Fe2O3 nanotubes demonstrated superparamagnetic properties with a blocking temperature of 37 K and efficient photocatalytic activity for degradation of 4-chlorophenol.