Structural Stability of Iron Oxide Nanotubes and an Enhancement of Photo Induced Current Detected in the Complex with Fullerenols

Abstract

ABSTRACTIron oxide nanotubes (Fe-ox-NTs) were prepared by a sol-gel technique using a mixture of an Fe(NO3)3·9H2O and a Pluronic F-127 nonionic surfactant in 1-propanol, gelatinizing at 35 °C for 5 days. Crude nanotubes thus obtained were well rinsed by deionized water in order to remove the surfactant. Transmission electron microscopy showed that the products have tubule structure with the outer (inner) diameter ∼10-15 (∼5-10) nm and the length ∼100 nm. X-ray diffraction profile of the crude nanotubes indicated a broadened feature characteristic for a defective or amorphous-like material, and whose profile may associate with the structure of ɣ-Fe2O3 (maghemite). By heating the crude nanotubes in open air, a phase transition occurs in a defective ɣ-Fe2O3 and its structure changes to a relaxed α-Fe2O3 (hematite) without morphological transformation. A further increase of the temperature results a destruction of the tube structure to the spherical nanoparticles without changing the crystallographic structure. A structurally relaxed Fe-ox-NT complex with fullerenols (C60(OH)n, n∼20) has larger photosensitive response under visible light irradiation, but the crude and defective Fe-ox-NTs and their complexes with fullerenols do not indicate noticeable response.