Abstract:To comprehend the photocatalytic mechanisms of anatase Ti 1−x Fe x O 2 with various concentrations of Fe, this study performed first principles calculations based on density functional theory with Hubbard U on-site correction to evaluate the crystal structure, impurity formation energy, and electronic structure. We adopted the effective Hubbard U values of 8.47 eV for Ti 3d and 6.4 eV for Fe 3d. The calculations show that higher concentrations of Fe are easily formed in anatase TiO 2 due to a reduction in the … Show more
“…Here we took into consideration the strong Coulomb interactions for the localized d electrons of Fe and Cr as well, therefore introducing the U term parameter for the 3d states of Cr and the 3d states of Fe. The choice for the Hubbard term in this work was 4 eV for Cr and 6.4 for Fe, in accordance with previous work 38 , 39 . Figure 4 DOS of Cr-doped TiO 2 with Cr as interstitial dopant (Cr i ) under biaxial tensile stress of ( a ) 0 GPa ( b ) 4 GPa ( c ) 8 GPa and DOS of TiO 2 with Cr as substitutional dopant (Cr Ti ) under biaxial tensile stress of ( d ) 0 GPa ( e ) 4 GPa and ( f ) 8 GPa .…”
Section: Resultssupporting
confidence: 63%
“…In our calculations the generalized-gradient approximation along with the Hubbard U correction was applied. The parameter U set to 8.2 eV for the Ti 3d orbitals, 4 eV for Cr 3d orbitals and 6.4 eV for Fe 3d orbitals 14 , 38 , 39 .…”
Anatase titanium oxide is important for its high chemical stability and photocatalytic properties, however, the latter are plagued by its large band gap that limits its activity to only a small percentage of the solar spectrum. In that respect, straining the material can reduce its band gap increasing the photocatalytic activity of titanium oxide. We apply density functional theory with the introduction of the Hubbard + U model, to investigate the impact of stress on the electronic structure of anatase in conjunction with defect engineering by intrinsic defects (oxygen/titanium vacancies and interstitials), metallic dopants (iron, chromium) and non-metallic dopants (carbon, nitrogen). Here we show that both biaxial and uniaxial strain can reduce the band gap of undoped anatase with the use of biaxial strain being marginally more beneficial reducing the band gap up to 2.96 eV at a tensile stress of 8 GPa. Biaxial tensile stress in parallel with doping results in reduction of the band gap but also in the introduction of states deep inside the band gap mainly for interstitially doped anatase. Dopants in substitutional positions show reduced deep level traps. Chromium-doped anatase at a tensile stress of 8 GPa shows the most significant reduction of the band gap as the band gap reaches 2.4 eV.
“…Here we took into consideration the strong Coulomb interactions for the localized d electrons of Fe and Cr as well, therefore introducing the U term parameter for the 3d states of Cr and the 3d states of Fe. The choice for the Hubbard term in this work was 4 eV for Cr and 6.4 for Fe, in accordance with previous work 38 , 39 . Figure 4 DOS of Cr-doped TiO 2 with Cr as interstitial dopant (Cr i ) under biaxial tensile stress of ( a ) 0 GPa ( b ) 4 GPa ( c ) 8 GPa and DOS of TiO 2 with Cr as substitutional dopant (Cr Ti ) under biaxial tensile stress of ( d ) 0 GPa ( e ) 4 GPa and ( f ) 8 GPa .…”
Section: Resultssupporting
confidence: 63%
“…In our calculations the generalized-gradient approximation along with the Hubbard U correction was applied. The parameter U set to 8.2 eV for the Ti 3d orbitals, 4 eV for Cr 3d orbitals and 6.4 eV for Fe 3d orbitals 14 , 38 , 39 .…”
Anatase titanium oxide is important for its high chemical stability and photocatalytic properties, however, the latter are plagued by its large band gap that limits its activity to only a small percentage of the solar spectrum. In that respect, straining the material can reduce its band gap increasing the photocatalytic activity of titanium oxide. We apply density functional theory with the introduction of the Hubbard + U model, to investigate the impact of stress on the electronic structure of anatase in conjunction with defect engineering by intrinsic defects (oxygen/titanium vacancies and interstitials), metallic dopants (iron, chromium) and non-metallic dopants (carbon, nitrogen). Here we show that both biaxial and uniaxial strain can reduce the band gap of undoped anatase with the use of biaxial strain being marginally more beneficial reducing the band gap up to 2.96 eV at a tensile stress of 8 GPa. Biaxial tensile stress in parallel with doping results in reduction of the band gap but also in the introduction of states deep inside the band gap mainly for interstitially doped anatase. Dopants in substitutional positions show reduced deep level traps. Chromium-doped anatase at a tensile stress of 8 GPa shows the most significant reduction of the band gap as the band gap reaches 2.4 eV.
“…Namely, an optimal introduced Fe concentration needed to be determined for the optimal band gap energy, which corresponded to the There was a disparity that existed between the result of the DFT calculation and that of the experiment. However, this difference was also observed by other researchers [62][63][64][65][66]. The disparity can be explained by not considering the discontinuity in the exchange-correlation potential in the DFT calculation [63,67].…”
Section: Catalysts 2019 9 X For Peer Review 7 Of 17mentioning
A mild in situ method was developed to construct an iron doped rutile TiO2 photocatalyst like cauliflower for degradation synthetic textile dye-methyl orange. The synthesized photocatalysts presented distinguished photocatalytic activity. At the optimal Fe concentration (0.5%), the decomposition rate of methyl orange (MO) was about 90% under 40 min of ultraviolet (UV) light irradiation. Whereas, to our knowledge, only 70% of the decomposition rate of MO was achieved by commercial photocatalyst P25 under the similar reaction condition. Additionally, the rutile preparation temperature did not exceed 100 °C, which was much lower than the traditional preparation calcination temperature (e.g., 600 °C). The specific surface area of Fe doped catalysts was bigger than that of the control sample and the catalyst characterization indicated that the doped iron was incorporated into the rutile TiO2 lattice and resulted in the lattice disorder. The lattice disorder would have generated surface defects in the crystal structure, which was in favor of the photocatalytic reaction. The UV-Vis diffuse refection characterization and Density Functional Theory (DFT) calculation suggested that doping a small amount of Fe into the lattice of rutile would lead to a narrower band gap and the formation of a doping energy level between conduction and valence bands of TiO2. This further increased the degradation efficiency of synthetic textile dyes in wastewaters. Our study has provided a relatively easy operation for synthesis Fe doped rutile TiO2, which is a benefit to decrease the cost in wastewater treatment process.
Oxygen vacancies and Ti-related defects (OTDs) are the main lattice defects ofTiO2, which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i) influence the energy structure of the pristineTiO2as the isolate acceptor/donor level or hybrid with the original orbital, (ii) provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii) act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites forO2,H2O, and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
