Origin Of Visible Light Absorption Research Articles

Fabrication and characterization of black TiO2 with different Ti3+ concentrations under atmospheric conditions

Black TiO2 samples with different concentrations of Ti3+ on the surface were fabricated by heat treatment in air. After heat treatment, the concentrations of Ti3+ on the surface of black TiO2 samples decreased and a layered structure was not observed. Oxygen vacancies were demonstrated to be the origin of visible light absorption. Ti3+ oxidation on the surface of black TiO2 samples caused the decrease of oxygen vacancies. In addition, black TiO2 samples with different Ti3+ concentrations showed differences in visible light absorbance, band gap, fate of photogenerated electrons, and photocatalytic activity. The optimum concentration of Ti3+ for achieving is shown to be the highest photocatalytic activity under the irradiation of visible light.

Electronic structure-sunlight driven water splitting activity correlation of (Zn1-yGay)(O1-zNz).

(Zn1-yGay)(O1-zNz) (y≤ 0.10; z≤ 0.15) solid solutions have been investigated for their electronic structure and visible light photocatalytic activity, and a correlation was found between them. (Zn1-yGay)(O1-zNz) with ZnO as the major component have been synthesized by a solution combustion method in 10 minutes using simple raw materials. The local structures of Zn K edge and Ga K edge, and changes in the chemical environment with the incorporation of Ga and N in ZnO were determined by EXAFS study. EXAFS and XRD results suggested the dissolution of GaN in the ZnO lattice. The homogeneity of the solid solution was demonstrated from HRTEM studies. Photoluminescence studies revealed the creation of a new band at the top of the ZnO valence band (VB), and thus the broadening of the VB of (Zn1-yGay)(O1-zNz) or a decrease in the band gap was attributed to the origin of visible light absorption. UV-Vis spectral studies showed light absorption up to 550 nm, which directly supports the VB broadening. Predominant oxygen vacancies and high photocorrosion observed for ZnO were fully suppressed for (Zn1-yGay)(O1-zNz), indicating the minimization of defects, and thus more sustainability under irradiation conditions. The bare solid solution exhibited reasonable and promising activity for solar hydrogen evolution and photoelectrochemical current generation at 0 V. The present work explained factors such as the preparation method, single phase structure with the stabilization of integral parts, homogeneity in the structure, compensation of oxygen vacancies, and suppression of the density of recombination centres that play a pivotal role in realizing solar energy harvesting.

Band-Gap Engineering of NaNbO3for Photocatalytic H2Evolution with Visible Light

A new visible light response photocatalyst has been developed for H2evolution from methanol solution by elemental doping. With lanthanum and cobalt dopants, the photoabsorption edge of NaNbO3was effectively shifted to the visible light region. It is also found that the photoabsorption edge is effectively controlled by the dopant concentration. Under visible light irradiation, H2was successfully generated over the doped NaNbO3samples and a rate of 12 μmol·h−1was achieved over (LaCo)0.03(NaNb)0.97O3. Densityfunctional theory calculations show that Co-induced impurity states are formed in the band gap of NaNbO3and this is considered to be the origin of visible-light absorption upon doping with La and Co.

Effect of Electronegativity and Charge Balance on the Visible-Light-Responsive Photocatalytic Activity of Nonmetal Doped Anatase TiO2

The origin of visible light absorption and photocatalytic activity of nonmetal doped anatase TiO2were investigated in details in this work based on density functional theory calculations. Our results indicate that the electronegativity is of great significance in the band structures, which determines the relative positions of impurity states induced by the doping species, and further influences the optical absorption and photocatalytic activities of doped TiO2. The effect of charge balance on the electronic structure was also discussed, and it was found that the charge-balance structures may be more efficient for visible light photocatalytic activities. In addition, the edge positions of conduction band and valence band, which determine the ability of a semiconductor to transfer photoexcited electrons to species adsorbed on its surface, were predicted as well. The results may provide a reference to further experimental studies.

The Origin of Visible Light Absorption in Chalcogen Element (S, Se, and Te)-Doped Anatase TiO2 Photocatalysts

We use first-principles calculations to clarify the origin of the visible light absorption in chalcogen element-doped TiO2. Our results show that interstitial doping is not the origin of visible light absorption under any equilibrium growth conditions, but rather, sensitization is achievable via substitutional doping of O (or Ti) at Ti-rich (or O-rich) conditions, respectively. With increasing atomic number (from S to Te), it is harder to form anion-doped TiO2 but easier to achieve cationic doping. Both anionic and cationic doping can confer visible light absorption, but the former is more effective. The effect increases with increasing atomic number of the chalcogen element. Dopant pairing is found in anionic S-, Se-, and Te- and cationic S-doped TiO2. We further identified that anion pairing induces a bathochromic shift in the absorption, whereas cationic pairing causes the opposite, that is, a hypsochromic (blue) shift, predictions that agree well with the experimental findings.