Photoinduced Dynamics of TiO₂ Doped with Cr and Sb

Abstract

Rutile particles doped by Cr and Sb with Sb/Cr ratios greater than unity were active for photocatalytic O 2 evolution from an aqueous silver nitrate solution under visible light irradiation. Two vibrational bands appeared in Raman scattering resonant to the electronic absorption and were assigned to symmetric breathing modes of the CrO 6 octahedron and neighboring TiO 6 octahedra, on the assumption that Cr dopant atoms exactly replaced Ti cations in rutile. Electrons excited with 355-nm and 532-nm light pulses showed absorption of mid-IR light, which was traced as a function of the time delay in a microsecond domain. By optimizing the Sb/Cr ratio, electron-hole recombination was retarded compared with that in non-doped rutile. Chromium dopants when accompanied with antimony dopants are proposed to trap the charge carriers without much enhancement of the recombination. The optimized Sb/Cr ratios were common for both the visible lightinduced O 2 production and the retarded recombination, suggesting that the charge carriers of the retarded recombination are used to produce O 2 .

Density Functional Characterization of the Electronic Structure and Visible‐Light Absorption of Cr‐Doped Anatase TiO2

“…As will be discussed later, the obtained electronic structure is in agreement with the proposed photoexcitation scheme based on the experimental optical absorption spectra (see Figure 1 in ref. [15]), [18] and hence, the effective U value U eff = 3.0 eV for Cr 3d electrons was used in the following calculations. [14,16,19,40] In addition, the d-d transition, i.e., the electron transition between the occupied t 2g states and unoccupied t 2g and e g states will cause a further optical gap decrease (about 0.8 and 2.0 eV), and this electron transition process may account for the experimental weak optical absorption band from about 620 to 800 nm.…”

“…[15]). [18] To examine the splitting behavior of Cr 3d states in detail, its projected DOS plot is shown in Figure 2 b. With respect to the local Cartesian coordinates defined in Figure 1 a, [16,19,41,42] in fact, Cimino et al has pointed out that XPS cannot distinguish between Cr 4 + and Cr 3 + because they have nearly the same binding energy of Cr 2p.…”

Evaluation of surface energy state distribution and bulk defect concentration in DSSC photoanodes based on Sn, Fe, and Cu doped TiO2

“…Controlled doping with specific n-type and p-type elements can be employed to adjust the electronic and the crystal A c c e p t e d M a n u s c r i p t structure towards smaller band gaps for more light absorption and enhanced charge transfer [1,6,9,13]. Doping different metals into the TiO 2 and the influence this has on photocatalysis [2,13,14] and photoelectric conversion [15][16][17][18] has been widely studied. Doping TiO 2 with selected metal ions may create grain boundaries, generate oxygen vacancies, introduce surface and bulk defects for efficient charge trapping and reduced recombination rates [16,19,20], cause flat band gap (E fb ) shifts resulting in a higher V oc , [16,21] increase dye adsorption leading to greater charge carrier injection [20], cause particle size reduction, [22] induce phase transitions, [23,24] reduce band gaps for absorption in the visible or near Infrared [15] and facilitate the formation of radicals to improve oxide -dye attachment for better charge injection (in the case of photovoltaics).…”

Serendipity following attempts to prepare C-doped rutile TiO2

“…One approach which has received a large amount of attention to alter the band gap of TiO 2 and shift towards visible light absorbance is via selective doping of metallic and/or non-metallic elements (such as carbon) into the TiO 2 lattice [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. In general anionic carbide dopants are considered more beneficial than cationic dopants for photocatalytic performance [28].…”