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Density of the states (DOS) calculated for S-doped surfaces: (a) Ti24O47S(A-STO), (b) Ti23SO48(C-STO), and (c) Ti23SO47S(AC-STO). Fermi level is at 0 eV and U is 8.50 eV for Ti 3d electrons. The 3p states of S dopant at O 2 C site and that of S dopant at Ti 5 C site are represented by dark grey and black area, respectively.
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The electronic structures of sulfur (S) or carbon (C)-doped TiO2 anatase (101) surfaces have been investigated by density functional theory (DFT) plane-wave pseudopotential method. The general gradient approximation (GGA) + U (Hubbard coefficient) method has been adopted to describe the exchange-correlation effects. All the possible doping situatio...
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Citations
... 3A, are consistent with previous calculations using the PBE functional and underestimate the bandgap, as expected.184,[352][353]356 For the anatase surface decorated with a tridentate sulfatelike structure(Figure 4-3B), the sulfur derived bands at -6 eV are below the titania valence band and there are no mid-gap states. ...
Heterogeneous catalysis, including thermal- and photocatalysis, is a key technology toward developing industrial processes for a sustainable future. Therefore, the study of surface reactions and catalyst properties includes most studies in this area. There has been extensive work put into developing experimental and computational tools to understand surface and interface phenomena, describe mechanistic chemical transformations, and simulate the behavior of surface reactions to develop better catalysts and more efficient processes. This thesis describes experimental and theoretical investigations to explain the reaction mechanism of ethanol conversion to value-added products over an MgO/SiO2 catalyst, a kinetic model describing the surface changes during pretreatment of WO3 as hydrogenation and hydrodeoxygenation catalyst, and a fundamental study of the electronic structure of sulfur-doped TiO2 to explain the enhanced photocatalytic activity of this material. The main goal of all the chapters of this thesis is to generate knowledge of these heterogeneous catalysis systems and add a small step in the bridge toward a sustainable future.
... Moreover, the structure of sulphur atom surrounding in cationically doped TiO 2 with isomorphic substitution of Ti 4þ is often reported as weakly distorted from the structure of the initial TiO 2 [28,32]. This cannot be taken seriously because the structure of oxygen compounds of S(IV) and S(VI) is very different from the structure of TiO 6 octahedrons in TiO 2 [33,34]. Indeed, Fig. 1 shows that sulphur has tetrahedral oxygen surrounding in both sulphuric acid and sulphate anion, whereas sulphur takes the position in the vertice of trigonal pyramid for H 2 SO 3 and SO 3 ...
Cationic doping of TiO2 anatase with sulphur represents a facile method to improve catalytic and photocatalytic activity for hydrogen production and extend the action spectrum of TiO2 into the visible light region. However, there is a lot of misunderstanding when trying to explain the experimental findings and suggest theoretical models. In the present computational research work, novel theoretical models are put forward representing fully hydroxylated small anatase nanoparticles with S(IV) and S(VI) doping in various surface positions and in the bulk. It was found that sulfur in the doped anatase nanoparticles preserves its typical coordination geometries of trigonal pyramid for S(IV) and tetrahedron for S(VI). Doping in the anatase surface is much more energetically favorable compared to doping in the bulk. Doping with S(IV) causes decrease of the band gap from 3.22 to 2.65 eV while S(VI) doping could decrease Eg only to 2.96 eV. Location of photogenerated electrons and holes depends strongly on the position of dopant atoms and their valent state. Contrary to some experimental works, no strong and extended visible light absorption bands could be found with cationic doped hydroxylated anatase nanoparticles. However, improved charges separation is observed indeed and causes improved photocatalytic hydrogen production.
... The geometry of the clean surface and adsorption complexes was optimized until the residual forces were below 0.001 Ry/au. The geometrical parameters of the relaxed top layer of the (101) and (001) slabs are given in Table 1 with atom labels in Fig. 1, and are in complete agreement with previous studies [33][34][35]. ...
... Numbering of the atoms in the top layers of (a) the anatase (101) and (b) the anatase (001) surfaces. Red and gray spheres represent oxygen and titanium atoms, respectively.D. Geldof et al.Surface Science 655 (2017)[31][32][33][34][35][36][37][38] larger variation. The O-Ti bonds of (001-T) are elongated in order to accommodate the bonding with three of the Ti atoms of the surface. ...
