Enhanced Visible Light Response of TiO₂ Codoped with Cr and Ta Photocatalysts by Electron Doping

Abstract

The importance of electron concentration in rutile TiO2 photocatalysts motivated us to apply H2 reduction treatment to visible-light-responsive TiO2 photocatalysts sensitized by chromium ion doping. We found that H2 reduction treatment of rutile TiO2 particles codoped with Ta and Cr (TiO2:Ta/Cr) enhanced photocatalytic activity for O2 evolution by water oxidation under visible irradiation (>2.2 eV). The enhanced visible light activity of H2-treated TiO2:Ta/Cr was attributed to the increase of electron concentration, which was confirmed by UV–vis diffuse reflectance and electron spin resonance (ESR) spectroscopy. The H2-treated TiO2:Ta/Cr photocatalyst was repeatedly used in aqueous media in spite of the presence of doped electrons. Photoluminescence and transient absorption spectroscopies revealed that electron doping with H2 treatment decreased the midgap states working as deep traps of photoexcited electrons and increased the accumulation of the photoexcited electrons in the conduction band. The optimized H2 reduction temperature was decreased with an increase in the amount of higher valence Ta5+ used as a donor-type dopant. This study shows that the precise control of the bulk electronic structure of rutile TiO2 by a combination of codoping and H2 reduction treatment improves the visible-light-driven photocatalytic activity because of the decrease of the trapping sites at deep energy levels and the recombination between deeply trapped electrons and valence band holes.

Unfolding the Impact of H2-Reduction Treatment in Enhancing the Photocatalytic Activity of Rutile TiO2 Based on Photocarriers Dynamics

“…It is noteworthy to mention that it is not only the reduction reaction that can benefit from the effect of H 2 -reduction but also the oxidation reaction as demonstrated in several works that achieve enhanced photocatalytic O 2 generation on reduced titania particles. 12,47 Aside from this, based on our findings, it is expected that the losses of reductive driving force of electrons as a result of trapping are significantly lowered due to disappearance of deep traps upon H 2 -reduction treatment, and hence the H 2 reduction treatment employed for TiO 2 is a strategic way to provide more active carriers for photocatalytic H 2 evolution by water splitting.…”

Phase Modulation of Ti3O/R-TiO2 Nanocomposites for the Self-Powered Photoelectrochemical Sensing of Tetracycline

“…The ultraviolet–visible diffuse reflectance spectroscopy was used to characterize the light response ability of the as-prepared samples (Figure S2). The absorption edge at around 400 nm for the R -TiO 2 -600 sample is assigned to the characteristic absorption of the rutile TiO 2 phase . Notably, the absorption band edge of Ti 3 O/ R -TiO 2 -700 and Ti 3 O/ R -TiO 2 -800 exhibited a distinct red-shift after introducing Ti 3 O and the increasing crystallinity and content of R -TiO 2 , indicating that the Ti 3 O/ R -TiO 2 formation of heterophase junction can enhance solar absorption and hence improve the PEC performance.…”

“…The absorption edge at around 400 nm for the R-TiO 2 -600 sample is assigned to the characteristic absorption of the rutile TiO 2 phase. 35 In order to identify the coupled biphase structure of Ti 3 O/ R-TiO 2 , an active species trapping experiment was carried out under illumination. The photocurrent changes in PBS solution with the respective addition of p-benzoquinone (BQ), (NH 4 ) 2 C 2 O 4 , and isopropyl alcohol (IPA) are depicted in Figure S3a.…”

Design and synthesis of an S-scheme TiO2homojunction with an adjusted, well-defined phase for directional carrier transfer in solar water splitting

“…60 By contrast, all TiO 2 -TELM samples show a strong PL band in the region of 483-513 nm, and the main peaks are located at about 504 nm (2.46 eV) because of the recombination of shallowly trapped electrons. 61 With the increasing ratio of the rutile phase, the intensity of the SSPL represents a valley-type change rather than a continuous increase or decrease. This result suggests that the recombination rate of the photogenerated e À and h + is strongly inhibited by the nanoarchitecture change in TiO 2 -TELM.…”