Transient IR absorption study of charge carriers photogenerated in sulfur-doped TiO2

Abstract

Sulfur-doped TiO 2 was prepared by two methods; one was simple oxidation annealing of TiS 2 , the other was mixing of titanium isopropoxide and thiourea. These two sulfur-doped TiO 2 preparations showed fairly different photocatalytic activity under visible light. The dynamics of photogenerated charge carriers were studied by the transient absorption measurement in the region of mid-IR. In both samples, excitation by 532 nm pulse led to photocarrier generation to the same extent. Nevertheless, the reactivity of the photocarriers was totally different. Photogenerated electrons and holes transferred to reactant gas in the latter sample, whereas they did not in the former sample. We attributed the different carrier behavior to the difference in the distribution of S atoms or particle size. These observations can explain the difference in capability of photocatalysis under visible light.

Photocatalytical Properties of TiO₂ Nanotubes

“…In such doping, the p states (from N dopants) mix with O 2p states (from TiO 2 ) to narrow the bandgap and then transfer the photogenerated charge carriers to the reactive sites of TiO 2 surface. Although doping by S shows a similar bandgap narrowing, its ionic radius is too big to enable it to be substituted into the TiO 2 lattice [116]. The states introduced by C and P are energetically too deep in the bandgap of TiO 2 to promptly transfer the charge carriers to the surface reactive sites.…”

Tungsten trioxide and titanium dioxide photocatalytic degradations of quinoline

“…Takeshita and coworkers contrasted the behavior of S-TiO 2 made by oxidative annealing of TiS 2 and by the Ohno method with thiourea 57 . Essential to their analysis was the observation that the sulfur remaining in the TiS 2 -based catalyst was largely in the center of the particle, with very little remaining in the exterior.…”

“…Essential to their analysis was the observation that the sulfur remaining in the TiS 2 -based catalyst was largely in the center of the particle, with very little remaining in the exterior. This is in contrast to the sol-gel method, assumed to produce approximately homogeneously dispersed S. They argue, on the basis of flash photolysis experiments, that the sol-gel materials produce near-surface holes that are not capable of oxidizing water to produce HO•, but are able to oxidize methanol 57 . (This occurs whatever the excitation wavelength.)…”

“…13,47,55,57 Others have recently noted wavelength-dependent chemistry for N-TiO 2 remediation of ethylene glycol in acetonitrile, 55 as well as C-TiO 2 -mediated degradation of molecules with different binding abilities and oxidation potentials. 13 To probe the photocatalytic activity of doped titania, many other studies have used dyes as chemical probes, some of which are prone to both oxidative and reductive degradation pathways and are often unrepresentatively easy to oxidize or reduce, compared to more common relevant pollutants.…”

Synthesis, morpho-structural characterization and environmental application of titania photocatalysts obtained by rapid crystallization

“…) and the high number of doping possibilities (metals: nickel [15][16], iron [17][18], chromium [19], vanadium [20], tungsten [21], copper [22], cerium [23], europium [24][25]) and nonmetals (nitrogen [21,[26][27], sulfur [28][29], phosphorus [30], carbon [31][32], iodine [33], boron [34][35]), fine tuning of the crystallinity [10]/ shape [6], crystal phase composition [10] and nevertheless synthesis of composite materials [36]. Because of the numerous synthesis ways and process complexity, a detailed study could be done for each step.…”