Structure and Electronic States of Zinc-Doped Iron Oxide Nanotubes Prepared by a Surfactant-Assisted Sol–Gel Method

Abstract

We report the doping of iron oxide nanotubes with zinc, and the characterization of the resulting zinc ferrite nanotubes. Gels were prepared by polycondensing iron nitrate nonahydrate and zinc nitrate hexahydrate on the surface of a self-assembled non-ionic surfactant in 1-propanol at 45 °C. Evaporation of the solvent within the gels at 120 °C led to the formation of tubular structures, as evidenced by transmission electron microscopy. The nanotubes had internal and external diameters of ~2–6 and 4–10 nm, respectively, and were ~50 nm long. X-ray diffraction and X-ray photoelectron spectroscopy indicated that the nanotubes possessed a spinel structure, and had a composition of ZnxFe3−xO4, with x ranging from 0 to 0.66. Direct band gaps were evaluated from optical absorption spectra, using the Tauc plot method. The band gaps ranged from 2.4 (x = 0) to 2.0 eV (x = 0.27), thus narrowing upon doping with Zn. This was tentatively attributed to a widening of the band width, and the formation of sub-levels at octahedral B sites of the spinel structure.