scholarly journals Theoretical insights of codoping to modulate electronic structure of $$\hbox {TiO}_2$$ and $$\hbox {SrTiO}_3$$ for enhanced photocatalytic efficiency

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Manish Kumar ◽  
Pooja Basera ◽  
Shikha Saini ◽  
Saswata Bhattacharya
Keyword(s):  
Electronic Structure ◽  
Visible Light ◽  
Band Gap ◽  
Density Functional ◽  
Low Cost ◽  
Visible Region ◽  
Photocatalytic Efficiency ◽  
Large Shift ◽  
Realistic Condition ◽  
Charged Defects

Abstract $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it’s necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase $$\hbox {TiO}_2$$ TiO 2 and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in $$\hbox {SrTiO}_3$$ SrTiO 3 mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O (i.e. Mn is substituted at Ti site and S is substituted at O site), $$\hbox {S}_\text {O}$$ S O in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O , $$\hbox {Mn}_\text {Sr}\hbox {N}_\text {O}$$ Mn Sr N O in $$\hbox {SrTiO}_3$$ SrTiO 3 are the most potent candidates to enhance the photocatalytic efficiency of anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 under visible light irradiation.

scholarly journals DFT Study of Se and Te Doped SrTiO 3 for Enhanced Visible-Light Driven Phtocatalytic Hydrogen Production

2021 ◽  
Author(s):  
Hakim BENTOUR ◽  
Mourad Boujnah ◽  
Mohamed Houmad ◽  
Mourad El Yadari ◽  
Abdelilah BENYOUSSEF ◽  
...  
Keyword(s):  
Visible Light ◽  
Band Gap ◽  
Water Splitting ◽  
Density Functional ◽  
Hydrogen Generation ◽  
Visible Region ◽  
Solar Spectrum ◽  
Photogenerated Electron ◽  
Generalized Gradient ◽  
Light Activity

Abstract The pure STiO3 has been experimentally demonstrated to catalyze H2 production using water splitting, but the reaction can only be driven by Ultraviolet (UV) radiation due to the large band gap of SrTiO3. This motivated us to search efficient strategy to tune its band gap, so that it can function in the visible region of the solar spectrum. In this study, the electronic, optical and photocatalytic properties of Se-doped, and Te-doped SrTiO3 has been investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). Our results reveal that the effect of doping can lead to band gap narrowing without introducing any isolated mid-gap states. This improves greatly the visible light activity of SrTiO3 and depresses the recombination of photogenerated electron-hole pairs. Furthermore, the locations of calculated band edges relative to the water reduction and oxidation levels for doped systems meet the water-splitting requirements. Consequently, our results show that the performance of SrTiO3 for hydrogen generation by photocatalytic water splitting is significantly enhanced with Se and Te doping. In particular, Te doping can enhance greatly the visible light photocatalytic activity of SrTiO3. We expect this study can provide a theoretical basis for a prospective experimental works.

scholarly journals DFT Study of the Electronic Structure of Cubic-SiC Nanopores with a C-Terminated Surface

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
M. Calvino ◽  
A. Trejo ◽  
M. I. Iturrios ◽  
M. C. Crisóstomo ◽  
Eliel Carvajal ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Density Functional ◽  
Surface Passivation ◽  
Phase Changes ◽  
Surface Relaxation ◽  
Oh Radicals ◽  
Functional Theory ◽  
Band Gap Engineering ◽  
Chemical Surface

A study of the dependence of the electronic structure and energetic stability on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using density functional theory (DFT) and the supercell technique. The pores were modeled by removing atoms in the [001] direction to produce a surface chemistry composed of only carbon atoms (C-phase). Changes in the electronic states of the porous structures were studied by using different passivation schemes: one with hydrogen (H) atoms and the others gradually replacing pairs of H atoms with oxygen (O) atoms, fluorine (F) atoms, and hydroxide (OH) radicals. The results indicate that the band gap behavior of the C-phase pSiC depends on the number of passivation agents (other than H) per supercell. The band gap decreased with an increasing number of F, O, or OH radical groups. Furthermore, the influence of the passivation of the pSiC on its surface relaxation and the differences in such parameters as bond lengths, bond angles, and cell volume are compared between all surfaces. The results indicate the possibility of nanostructure band gap engineering based on SiC via surface passivation agents.

Electronic Structure and Optical Properties of Non-Metals (N, F, P, Cl, S)-Doped Cubic NaTaO3 by Density Functional Theory

2009 ◽  
Vol 79-82 ◽  
pp. 1245-1248 ◽  
Author(s):  
Pei Lin Han ◽  
Xiao Jing Wang ◽  
Yan Hong Zhao ◽  
Chang He Tang
Keyword(s):  
Density Functional Theory ◽  
Optical Properties ◽  
Electronic Structure ◽  
Visible Light ◽  
Absorption Edge ◽  
Density Functional ◽  
Red Shift ◽  
Functional Theory ◽  
Photoactive Materials ◽  
Metal Doped

Electronic structure and optical properties of non-metals (N, S, F, P, Cl) -doped cubic NaTaO3 were investigated systematically by density functional theory (DFT). The results showed that the substitution of (N, S, P, Cl) for O in NaTaO3 was effective in narrowing the band-gap relative to the F-doped NaTaO3. The larger red shift of the absorption edge and the higher visible light absorption at about 520 nm were found for the (N and P)-doped NaTaO3. The excitation from the impurity states to the conduction band may account for the red shift of the absorption edge in an electron-deficiency non-metal doped NaTaO3. The obvious absorption in the visible light region for (N and P)-doped NaTaO3 provides an important guidance for the design and preparation of the visible light photoactive materials.

scholarly journals Properties of Novel Non-Silicon Materials for Photovoltaic Applications: A First-Principle Insight

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2006 ◽  
Author(s):  
Murugesan Rasukkannu ◽  
Dhayalan Velauthapillai ◽  
Federico Bianchini ◽  
Ponniah Vajeeston
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Crystalline Silicon ◽  
Visible Region ◽  
Initial Population ◽  
First Principle ◽  
Direct Band Gap ◽  
Depth Analysis ◽  
Photovoltaic Applications ◽  
Direct Band

Due to the low absorption coefficients of crystalline silicon-based solar cells, researchers have focused on non-silicon semiconductors with direct band gaps for the development of novel photovoltaic devices. In this study, we use density functional theory to model the electronic structure of a large database of candidates to identify materials with ideal properties for photovoltaic applications. The first screening is operated at the GGA level to select only materials with a sufficiently small direct band gap. We extracted twenty-seven candidates from an initial population of thousands, exhibiting GGA band gap in the range 0.5–1 eV. More accurate calculations using a hybrid functional were performed on this subset. Based on this, we present a detailed first-principle investigation of the four optimal compounds, namely, TlBiS2, Ba3BiN, Ag2BaS2, and ZrSO. The direct band gap of these materials is between 1.1 and 2.26 eV. In the visible region, the absorption peaks that appear in the optical spectra for these compounds indicate high absorption intensity. Furthermore, we have investigated the structural and mechanical stability of these compounds and calculated electron effective masses. Based on in-depth analysis, we have identified TlBiS2, Ba3BiN, Ag2BaS2, and ZrSO as very promising candidates for photovoltaic applications.

scholarly journals Electronic structure, elasticity, Debye temperature and anisotropy of cubic WO 3 from first-principles calculation

2018 ◽  
Vol 5 (6) ◽  
pp. 171921 ◽  
Author(s):  
Xing Liu ◽  
Hui-Qing Fan
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Debye Temperature ◽  
Density Functional ◽  
Elastic Wave Velocity ◽  
Point Of View ◽  
First Principles Calculation ◽  
Shear Moduli ◽  
Charge Densities ◽  
Indirect Band Gap

The electron structure, elastic constant, Debye temperature and anisotropy of elastic wave velocity for cubic WO 3 are studied using CASTEP based on density functional theory. The optimized structure is consistent with previous work and the band gap is obtained by computing the electronic structure; the top of the valence band is not at the same point as the bottom of the conduction band, which is an indirect band-gap oxide. Electronic properties are studied from the calculation of band structure, densities of states and charge densities. The bulk and shear moduli, Young's modulus, hardness and Poisson's ratio for WO 3 are studied by the elastic constants. We calculated acoustic wave velocities in different directions and estimated the Debye temperature from the acoustic velocity. The anisotropy of WO 3 was analysed from the point of view of a pure wave and quasi wave.

A hybrid density functional study on the visible light photocatalytic activity of (Mo,Cr)–N codoped KNbO3

2015 ◽  
Vol 17 (43) ◽  
pp. 28743-28753 ◽  
Author(s):  
Guangzhao Wang ◽  
Hong Chen ◽  
Yang Li ◽  
Anlong Kuang ◽  
Hongkuan Yuan ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photocatalytic Activity ◽  
Visible Light ◽  
Density Functional ◽  
Photocatalytic Performance ◽  
Functional Study ◽  
Redox Level ◽  
Hybrid Density Functional ◽  
Decomposition Of Water ◽  
Visible Light Photocatalytic

To improve the photocatalytic performance of KNbO3 for the decomposition of water into hydrogen and oxygen, the electronic structure of KNbO3 should be modified to have a suitable bandgap with band edge positions straddling the water redox level so as to sufficiently absorb visible light.

Study on Design and Mechanism of a New Invisible Cloak for Visible Light

2014 ◽  
Vol 1035 ◽  
pp. 514-519
Author(s):  
Jing Bo Zhao ◽  
Hong Yao ◽  
Juan Na Jiang
Keyword(s):  
Visible Light ◽  
Total Internal Reflection ◽  
Low Cost ◽  
Visible Region ◽  
Transformation Method ◽  
Macroscopic Object ◽  
Propagation Of Light ◽  
Invisible Cloak ◽  
New Type ◽  
Macroscopic Objects

In order to realize the macroscopic objects invisible in the visible region, according to the law of refraction, total internal reflection law and symmetry reduction transformation method, a new type of visible light stealth cloak was designed. The cloak was prepared using the ordinary homogeneous and isotropic glass materials, which can guide the light around the hidden region, and the direction of propagation of light has not changed. Thus the macroscopic object achieve the perfect stealth. The invisible cloak in air environment for arbitrary polarized visible light have stealth features, easy processing, low cost, has potential application value.

Atomic and Electronic Structure of LaAlO3 and LaAlO3:Mg from First-Principles Calculations

2009 ◽  
Vol 79-82 ◽  
pp. 1257-1260
Author(s):  
Li Guan ◽  
Li Tao Jin ◽  
Wei Zhang ◽  
Qiang Li ◽  
Jian Xin Guo ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Band Gap ◽  
Density Functional ◽  
Lattice Structure ◽  
Cell Structure ◽  
Functional Theory ◽  
Super Cell ◽  
Direct Band ◽  
Experimental Values

In the present paper, the lattice structure, band structure and density of state of LaAlO3 and LaAlO3:Mg are calculated by first-principle method based on density functional theory. Firstly, we select the different cutoff energy and k-point grid in the calculations, and obtain the most stable geometry structure of single crystal LaAlO3. The calculated lattice parameters are a=b=5.441 Å, c=13.266 Å, which matches with experimental values. To deeply understand the electronic structure of LaAlO3, a 2×1×1 super-cell structure is established and the doping concentration of Mg at Al sites is 25%. From the band structure and density of states, it can be seen that LaAlO3 has a direct band gap Eg=3.6 eV. However, LaAlO3:Mg has a larger band gap Eg=3.89 eV and the Fermi level enters into the valence band, which indicates the holes are introduced. The calculated results show that the conductivity of LaAlO3:Mg is better than pure LaAlO3, which is in good agreement with experimental results.

scholarly journals Phase transition-induced band edge engineering of BiVO4 to split pure water under visible light

2015 ◽  
Vol 112 (45) ◽  
pp. 13774-13778 ◽  
Author(s):  
Won Jun Jo ◽  
Hyun Joon Kang ◽  
Ki-Jeong Kong ◽  
Yun Seog Lee ◽  
Hunmin Park ◽  
...  
Keyword(s):  
Phase Transition ◽  
Visible Light ◽  
Band Gap ◽  
Conduction Band ◽  
Density Functional ◽  
Density Functional Theory Calculation ◽  
Pure Water ◽  
Volume Growth ◽  
Band Edge ◽  
Conduction Band Edge

Through phase transition-induced band edge engineering by dual doping with In and Mo, a new greenish BiVO4 (Bi1-XInXV1-XMoXO4) is developed that has a larger band gap energy than the usual yellow scheelite monoclinic BiVO4 as well as a higher (more negative) conduction band than H+/H2 potential [0 VRHE (reversible hydrogen electrode) at pH 7]. Hence, it can extract H2 from pure water by visible light-driven overall water splitting without using any sacrificial reagents. The density functional theory calculation indicates that In3+/Mo6+ dual doping triggers partial phase transformation from pure monoclinic BiVO4 to a mixture of monoclinic BiVO4 and tetragonal BiVO4, which sequentially leads to unit cell volume growth, compressive lattice strain increase, conduction band edge uplift, and band gap widening.

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