Explaining the Enhanced Photoelectrochemical Behavior of Highly Ordered TiO₂ Nanotube Arrays: Anatase/Rutile Phase Junction

Abstract

The effect of calcination temperature on the photoelectrochemical properties of TiO 2 nanotube arrays (TNTAs) has been investigated in many studies. Most work focused on improving the photoelectrochemical properties through optimization of the microstructure. In this paper, however, an anatase/rutile phase junction formed in TiO 2 nanotubes has been demonstrated to account for the enhancement of the photoelectrochemical performance. Observations by the UV−visible diffuse reflectance spectra, glancing incidence angle X-ray diffraction (GIA-XRD), and electrochemical impedance spectroscopy indicate that the rutile fraction is at the bottom of the nanotubes while the anatase fraction is at the body of the nanotubes. The TNTAs with a coexistence of about 60% anatase and 40% rutile exhibit optimal performance and show a 1.4-times improved photocurrent density compared with the pure anatase TNTAs. Detailed synchrotron radiation photoemission spectroscopy further confirms the existence and effect of the phase junction. The results suggest photogenerated electrons transfer from the rutile phase to the anatase phase in the nanotubes due to the band edge alignment, which facilitates the photogenerated carriers separation and transport along the nanotubes and leads to apparent enhancement of the photoelectrochemical behavior.

Engineering the Morphology and Crystal Phase of 3 D Hierarchical TiO2 with Excellent Photochemical and Photoelectrochemical Solar Water Splitting

“…[23] To improvet he applicability of anatase TiO 2 by utilizing the full solar spectrum,t he design and engineering of anataseT iO 2 have been done by doping [24] and phase control. [25] Enhanced photocatalytic activity of TiO 2 can thus be achieved by forming mixed-phase TiO 2 with an optimum ratio of anatase to rutile, Owing to their unique characteristics, hierarchical TiO 2 nanostructures have several advantages in solar-fuel production. In this work, as ingle-step approach has been developedt oc ontrol both the crystal phasea nd morphology of TiO 2 with 3D urchin-like structure via as urfactant-free solvothermalr oute.…”

Transforming Photocatalytic g‐C3N4/MoSe2 into a Direct Z‐Scheme System via Boron‐Doping: A Hybrid DFT Study

“…In addition, the optical absorption coefficient of MoSe 2 , g-C 3 N 4 , g-C 3 N 4 /MoSe 2 and B-doped-g C 3 N 4 /MoSe 2 were also investigated according to the complex dielectric function. [67] The absorption coefficient I(ω) was obtained by Equation 9 (9) where e 1 w ð Þ is the real part of the frequency dependent complex dielectric constant e w ð Þ and e 2 w ð Þ is the imaginary part of e w ð Þ. e 1 w ð Þ and e 2 w ð Þ are average values of three directions (x, y and z) of the frequency-dependent real and imaginary dielectric constants, respectively.…”

“…[3][4][5][6][7] Nevertheless, photocatalytic technique requires highly efficient, stable, low-cost and pollution-free photocatalysts. Many semiconductor photocatalysts, such as TiO 2 , [8,9] g-C 3 N 4 , [10] BiVO 4 , [11] ZnO [12] and MoSe 2 , [13] have been widely investigated by researchers. However, poor visible-light absorption, low separation efficiency of photo-induced carriers or weak electron conductivity greatly limits large-scale applications of these single-component photocatalysts.…”

Portable wastewater treatment system based on synergistic photocatalytic and persulphate degradation under visible light

“…However, pristine TiO 2 photocatalysts can only be stimulated by UV irradiation because the bandgap of pristine TiO 2 is higher than 3.0 eV, which seriously impedes its utilization in low-cost and environmentally friendly solar energy applications [8]. According to previous studies, building heterojunctions between anatase and rutile TiO 2 effectively enhances solar energy utilization and PC efficiency [9][10][11][12]. Though the energy level position of the anatase/rutile heterophase junction is unclear, markedly improved separation rates of photogenerated electrons and holes have been experimentally verified [13][14][15].…”