| AVS 60th International Symposium and Exhibition | |
| Nanometer-scale Science and Technology | Monday Sessions |
| Session NS+AS+EM-MoA |
| Session: | Nanowires and Nanotubes |
| Presenter: | P.M. Hosseinpour, Northeastern University |
| Authors: | P.M. Hosseinpour, Northeastern University J. Liu, Northeastern University and Brookhaven National Laboratory I. McDonald, Northeastern University D. Arena, Brookhaven National Laboratory D. Heiman, Northeastern University L. Menon, Northeastern University L.H. Lewis, Northeastern University |
| Correspondent: | Click to Email |
Ordered arrays of Fe-doped TiO2 nanotubes are semiconductors with potential enhanced catalytic properties and have prospective applications in photocatalytic devices, sensors and dye-sensitized solar cells. Unified understanding of the interrelations between the band structure, crystal structure and response in presence of dopants is fundamental for tailoring functionality. In this study, Fe (1.8 at%)-doped TiO2 nanotubes are synthesized via electrochemical anodization followed by annealing in an oxygen-rich environment at 450 °C to induce crystallization. The morphology, crystal structure and electronic structure of nominally-pure and Fe-doped titania nanotubes are investigated in the as-anodized and annealed states. Regardless of precise composition, scanning electron micrographs show that the nanotubes are 50 microns in length with 100-nm pore size, arranged in a closed-packed architecture. In the as-anodized state the nanostructures are amorphous; upon annealing in oxygen the anatase structure forms, with a slight expansion (~0.3% increase) in the unit cell volume and larger calculated crystallite size in presence of iron. Near-edge x-ray absorption fine structure spectroscopy (NEXAFS) carried out at the U7A beamline of the National Synchrotron Light Source at Brookhaven National Laboratory clarifies the electronic structure and chemical environment in pure and Fe-doped titania nanotubes. Preliminary results obtained from the oxygen K-edge and the Ti and Fe L-edge data of the nanotube surface confirm formation of the anatase structure upon annealing, with a lower oxidation state of titanium (lower than Ti4+) noted in presence of iron. Furthermore, the surface anatase formation was more significant (higher surface crystallinity) in the pure nanotubes versus the iron-doped nanotubes. Annealing the nanotubes in an oxygen-rich environment changes the oxidation state of iron. Correlations between the surface and bulk characteristics of the pure and Fe-doped titania nanotubes confirm incorporation of the iron into the lattice structure which modifies the electronic structure by changing the bonding and oxidation state of titanium. These results highlight potential pathways towards further optimization of these nanostructures in order to enhance catalytic functionality.
Funding: National Science Foundation (Grants No. DMR-0906608 and DMR-0908767), U.S. Department of Energy, Division of Materials Science, Office of Basic Energy Sciences (Contract No. DE-SC0005250). Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Basic Energy Sciences (Contract No. DE-AC02-98CH10886).