Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

Abstract

A novel dopant-free TiO(2) photocatalyst (V(o)(.)-TiO(2)), which is self-modified by a large number of paramagnetic (single-electron-trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO(2) precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO(2) precursor, imidazole, and hydrochloric acid are all necessary for the formation of V(o)(.)-TiO(2). Although the synthesis of V(o)(.)-TiO(2) originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X-ray diffraction, XPS, and EPR spectroscopy reveal that the V(o)(.)-TiO(2) material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse-reflectance spectroscopy and photoelectrochemical measurement demonstrate that V(o)(.)-TiO(2) is a stable visible-light-responsive material with photogenerated charge separation efficiency higher than N-TiO(2) and P25 under visible-light irradiation. The V(o)(.)-TiO(2) material exhibits not only satisfactory thermal- and photostability, but also superior photocatalytic activity for H(2) evolution (115 μmol h(-1) g(-1)) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO(2) precursor) and calcination time on the photocatalytic activity and the microstructure of V(o)(.)-TiO(2) were elucidated.

Photocatalytic Reduction of CO2 from Simulated Flue Gas with Colored Anatase

“…Raman spectroscopy (Figure 5c) reveals that the strongest vibration mode area (Eg) at 144 The EPR technique was further employed to analyze the Ti 3+ -related vacancy defects. From Figure 5b, there is an obvious signal at g = 2.058 for the g-anatase sample, which can be attributed to oxygen vacancy [30]; therefore, the defects probed from slow negative annihilation spectroscopy may be considered to be oxygen-related vacancy, which is consistent with the XPS results. Oxygen-related vacancy defects mainly exist in the bulk (or surface) lattice of the TiO 2 samples after reduction treatment.…”

“…Raman spectroscopy (Figure 5c) reveals that the strongest vibration mode area (Eg) at 144 cm −1 had a significant peak broadening and blue shifting after reduction treatment, compared with commercial anatase. The peak broadening effect and shift have been observed in several recent studies on hydrogenated TiO 2 [22,[30][31][32], which are attributed to the presence of lattice disorder resulting from phonon confinement or nonstoichiometry as the result of oxygen vacancy (VO) doping.…”

Facile synthesis and enhanced visible-light photocatalytic activity of Ti3+-doped TiO2 sheets with tunable phase composition

“…2(b). The absorption of visible light may be attributed to the existence of Ti 3+ and oxygen vacancy [11][12][13][14][15][16][17]31]. Zuo et al found that Ti 3 + generated from the reduction of Ti 4+ by H 2 produced from the reaction between Ti powder and HCl solution could induce a vacancy band of electronic states right below the conduction band, which narrows the band gap [11].…”

“…Rapid recombination of charge carriers (i.e., electron and hole) drastically reduces the solar energy conversion efficiency. Recently, self-modification of the atomic structures by removing or reconstructing atoms has been demonstrated as an effective method to extend the absorption spectra of photocatalysts, while significantly alleviating electron-hole recombination [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. For example, self-modified TiO 2 displayed satisfactory performance for visible light photocatalytic H 2 O reduction to hydrogen [9,[11][12][13][14][15].…”

Heterojunction Ag–TiO2 Nanopillars for Visible‐Light‐Driven Photocatalytic H2 Production

“…), which is consistent with the reported result. [30] Sample Ag-P25 with the same Ag and Ti molar ratio as AT-20 was investigated and shows an H 2 production activity of 36.8 mmol h the samples are stable that produce H 2 during the time evolution. These results illustrate the clear promotion of heterojunction Ag-TiO 2 nanopillars for the following reasons: 1) the junctions between Ag and TiO 2 are propitious to charge separation, which promotes the photocatalytic activity; 2) the surface plasmon resonance effect of Ag can utilize much visible light; and 3) the one-dimensional structure favors charge transport.…”