Electronic properties of free-standing TiO₂ nanotube arrays fabricated by electrochemical anodization

Abstract

Nanotubular TiO2 has attracted considerable attention owing to its unique functional properties, including high surface area and vectorial charge transport along the nanotube, making it a good photocatalytic material. Anodic TiO2-nanotube (TiNT) arrays on a Ti foil substrate were prepared by electrochemical anodic oxidation and SEM/HRTEM/XRD analyses have suggested that the walls of TiO2 tubes are formed from stacked [101] planes (anatase). Both HRTEM and XRD indicate an interplanar spacing of d101 = 0.36 nm in the wall structure. Despite the large amount of work done on nanotube synthesis, a thorough investigation of the electronic and atomic structures of free-standing TiNT arrays has not yet been carried out. X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and scanning photoelectron microscopy (SPEM) are employed herein to examine the electronic and atomic structures at the top and bottom of TiNT arrays. These analyses demonstrate the presence of mixed valence states of the Ti ions (Ti(3+) and Ti(4+)) and a structural distortion at the bottom cap region of the TiNT. Additionally, the results obtained herein suggest the formation of a defective anatase phase at the bottom cap barrier layer between the Ti foil substrate and TiNT during the growth of electrochemically anodized nanotubes.

Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment

“… 35 The lesser resolved peaks B and C, the reduction of the A/B intensity ratio ( Figure 3 c), and the shift of peak A to lower energy confirm the presence of Ti 3+ in Blue and Black NTA as well. 35 , 36 The O K-edge XAS is shown in Figure 3 b. Peaks a and b can be assigned to the electronic transition from O 1s to O 2p hybridized with the Ti 3d t 2g and 3d e g states, respectively.…”

“…Peaks A–C correspond to the electronic transition from 2p 3/2 to 3d, while peaks D and E can be assigned to the transition from 2p 1/2 to 3d. 35 The single crystal of TiO 2 has octahedral ( O h ) symmetry. The O h crystal field splits the Ti 3d band into t 2g and e g degenerate orbitals.…”

Directional ionic transport across the oxide interface enables low-temperature epitaxy of rutile TiO2

“…Furthermore, the contribution of Ti 3+ L-edge signals slightly increased the dips at 458 eV and 461 eV in the H24mT relative to those in H6mT (inset of Fig. 5a, yellow arrow); 36 these results reveal that rutile TiO 2 films toward the stoichiometry with low oxygen deficiency can be formed more easily by the TiO 2 growth with low pO 2 than with high pO 2 . Moreover, EELS data from the top TiO 2 layers in H6mT show that the t 2g peaks of Ti-L edge from TiO 2 layers is exactly same as those from stoichiometric bulk TiO 2 substrates (reference) ( Supplementary Fig.…”

“…5a), which is consistent with our results in HRXRD and STEM. The Ti L 2,3 -edge signals from H6mT were more intense and sharper than from H24mT 36,37 . Furthermore, the contribution of Ti 3+ L-edge signals slightly increased the dips at 458 eV and 461 eV in the H24mT relative to those in H6mT (inset of Fig.…”

Enhancing Solar‐Driven Water Splitting with Surface‐Engineered Nanostructures

“…However, electron enrichment in Ti 3d states results from the electronic reconstruction of the α‐Fe 2 O 3 /TiO 2 interface. This effect is indicated by the absorption intensity of the Fe L ‐edge and Ti L ‐edge before and after overlayer addition (Figure F); the intensity of Fe L ‐edge of α‐Fe 2 O 3 /TiO 2 compared with that of α‐Fe 2 O 3 is enhanced and the intensity of Ti L ‐edge of α‐Fe 2 O 3 /TiO 2 compared with that of TiO 2 is decreased. These results reveal that TiO 2 gains some charges while α‐Fe 2 O 3 loses them at the α‐Fe 2 O 3 /TiO 2 interface.…”