Photoelectroactivity and Raman spectroscopy of anodized titania (TiO2) photoactive water-splitting catalysts as a function of oxygen-annealing temperature

Abstract

The photoelectrochemical (PEC) activity of untreated (not anodized) and anodized nanotubular TiO 2 films (synthesized by the electrochemical anodization of Ti foil) was correlated with the phase composition of the film as a function of O 2 -annealing temperature at 400, 500 and 600 C. TiO 2 nanotubes have been shown to be more efficient than polycrystalline TiO 2 for the photocatalytic splitting of water. Raman spectroscopy was used to identify the amorphous and crystalline TiO 2 phases as well as the carbon species. The amorphous TiO 2 nanotubular array (unheated) exhibits a Raman spectrum consistent with TiO 6 8À octahedra having the same average structure as those present in the anatase and rutile phases of TiO 2 . Ratios of integrated Raman peaks were used as a semi-quantitative measure of the degree of crystallinity for rutile and the rutile/anatase weight ratio in the films. Results show that the anatase-to-rutile transformation on Ti metal initiates at much lower temperatures compared to polycrystalline TiO 2 and this is attributed to oxygen vacancies located at the metal/oxide interface. For untreated films, the amorphous TiO 2 crystallizes directly to rutile, and the photocurrent density increases almost linearly with rutile crystallinity as the O 2 -annealing temperature is increased; anatase does not form on untreated O 2 -annealed Ti foil. By comparison, amorphous TiO 2 nanotubular arrays are converted to about three times as much anatase as rutile at 400 C, where the photocurrent density is only slightly greater than the corresponding untreated film. At 500 C, however, the photocurrent density increases to 2.3Â that of the untreated-oxidized film, where $83% of the TiO 2 nanotubular film is rutile and $17% is anatase; this enhancement is attributed to the increase in surface area and photoactive sites of the rutile provided by the TiO 2 nanotubular array architecture acting as a support. At 600 C the rutile transformation continues ($92% rutile), but this is countered by the significant loss of surface area and surface photoactive sites due to degradation and collapse of the nanotubular structure as seen by SEM.

Carbon-incorporated TiO2 photoelectrodes prepared via rapid-anodic oxidation for efficient visible-light hydrogen generation

“…Rutile TiO 2 has two TiO 6 octahedra in its unit cell and is in the D 4h space group (P 42 /mmm). Thus, it has four Raman active modes, A 1g þ B 1g þ B 2g þ E g , appearing at 143 cm À1 (B 1g ), 447 cm À1 (E g ), 612 cm À1 (A 1g ), and 826 cm À1 (B 2g ) [6, 25,26]. The Raman spectrum of the sample prepared at 10 V shows a mixture of anatase and rutile phases with poor crystallinity (inset I in Fig.…”

Photocatalytic activity of titania layer prepared by oxidizing titanium compounds on titanium plate surface

“…For the Ti and TiN-a plates, broad peaks were observed at around 200-400 and 600 cm −1 , which can be assigned to the amorphous titania formed on the plate surface [24][25][26]. The rutile peaks clearly appeared in the spectra of these plates after heating and their relative intensity increased with an increase in the temperature.…”

“…The amorphous titania formed on the titanium surface should contain a large number of oxygen vacancies. The oxygen vacancies promote cleavage of the TiO bonds in the anatase structure which reduces the lattice volume and forms the denser rutile structure [26,27].…”

Characterisation of Porphyrin-TiO2Complex Using Raman Spectroscopy and Electron Paramagnetic Resonance

“…Results and discussion Figure 1 presents the Raman scattering spectrum of TiO 2 nanoparticles and that of a complex of TiO 2 with TSPP porphyrin. The spectra of TiO 2 and its complex with TSPP porphyrin in the range 2501000 cm −1 are characterized by strong bands and show active modes of B 1g , E g , A 1g and B 2g symmetry at 143, 448, 609, and 836 cm −1 assigned to TiO 2 [6]. The frequencies of the Raman bands assigned to TiO 2 are of the same intensity and at the same positions in the spectra of both TiO 2 and its complex with TSPP, which suggests the lack of possible oscillation changes caused by complex formation.…”