Electronic Structures of S/C-Doped TiO₂Anatase (101) Surface: First-Principles Calculations

Abstract

The electronic structures of sulfur (S) or carbon (C)-doped TiO2anatase (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 situations, including S/C dopants at lattice oxygen (O) sites (anion doping), S/C dopants at titanium (Ti) sites (cation doping), and the coexisting of anion and cation doping, were studied. By comparing the formation energies, it was found that the complex of anion and cation doping configuration forms easily in the most range of O chemical potential for both S and C doping. The calculated density of states for various S/C doping systems shows that the synergistic effects of S impurities at lattice O and Ti sites lead a sharp band gap narrowing of 1.35 eV for S-doped system comparing with the pure TiO2system.

Binding modes of phosphonic acid derivatives adsorbed on TiO2 surfaces: Assignments of experimental IR and NMR spectra based on DFT/PBC calculations

“…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 Figure 1, and are in complete agreement with previous studies [33][34][35].…”

Direct Evidence for Sulfur-Induced Deep Electron and Hole Traps in Titania and Implications for Photochemistry

“…77,78 Our calculations for sulfur substituted on a surface bridging oxygen (S O ) show occupied states located about 0.2 eV above the pure TiO 2 VBM derived from S 3p orbitals, as shown in the PDOS of Figure 4c. These results are consistent with previous calculations by Tian and Liu, 39 and Chen et al 43 in which S has a formal oxidation state of −2; the position is similar in the HSE06 calculations of Harb et al, 44 which is a more reliable (but computationally expensive) method for calculating band gaps. The substitution of sulfur on titanium sites (S Ti ) also leads to fully occupied states about 0.15 eV above the VBM (Figure 4d) with a formal oxidation state of S 4+ , consistent with work by Ohno et al, 78 Long and English, 45 and Harb et al 44 Both isolated and dimerized interstitial sulfurs have been predicted to create fully occupied states higher in the gap.…”

“…The total density of states (DOS), shown in Figure 4a, is consistent with previous calculations using the PBE functional and underestimates the band gap, as expected. 39,40,43,75 For the anatase surface decorated with a tridentate sulfate-like structure (Figure 3b), the sulfur-derived bands at −6 eV are below the titania VB, and there are no mid-gap states. The S 3p (green), Ti 3d (blue), and O 2p (red) partial DOS (PDOS) of the adatoms are shown in the right side of panels b−f.…”

“…Absorption in the visible region could, in principle, be explained by either new filled states above the valence band maximum (VBM) or new empty states below the CB minimum (CBM). The creation of new states above the VBM was clearly demonstrated in X-ray photoelectron spectroscopy (XPS) VB measurements, and theoretical electronic structure calculations generally predict sulfur-induced states above the VB. − …”

Multi-objective global optimization approach predicted quasi-layered ternary TiOS crystals with promising photocatalytic properties

“…The relevant research also considered the different oxidation states of sulfur in TiO 2 and found that different doping configurations have different effects on electronic structure and optical absorption characteristics, which optimizes the photocatalytic efficiency of TiO 2 . [42,43] Recently, Jovanović et al [44] studied TiO 1−x S x (x = 0, 0.25, 0.5, 0.75, and 1) crystal structures adopting anatase, rutile, and CdI 2 structure types, and found very interesting pressure-induced phase transitions in the TiOS compounds. However, doping, especially in a very high concentration, could possibly alter the crystal structure and atomic transmutation while keeping the parent lattice unchanged may not be enough.…”