Ultrafast Photosynthetic Reduction of Elemental Sulfur by Au Nanoparticle-Loaded TiO₂

Abstract

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S8) led to the energetically uphill reduction of S8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters (substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.

Photocatalytic Activity of Vis-Responsive Ag-Nanoparticles/TiO2 Composite Thin Films Fabricated by Molecular Precursor Method (MPM)

“…The increase of Ag NP on the surface of titania may result in a lower electron density of the Ti atoms in the Ag/TiO 2 samples. However, it is widely accepted that the Ag NPs in TiO 2 will benefit the separation of photogenerated electron-hole pairs due to electrical conductivity, thus enhancing the photocatalytic activity [44]. The electrical resistivity of the high-Ag-level thin films increases again from 10 −5 Ω cm-10 −2 Ω cm [32] with an increase in the amount of Ag in titania from 70 mol%-80 mol%, respectively.…”

“…This reveals that the electrical conductivity of Ag-NP/TiO 2 composite thin film is important for the higher photocatalytic decoloration rate observed under both UV and vis-light irradiation. Thus, the electrical conductivity property of the thin film facilitates the transportation of extra electrons to the conduction band, which in turn are able to produce more reactive species at the titania surface [45], blocking electron-hole recombination which stops the production of radicals at the surface [44].…”

The solid–solid interface: Explaining the high and unique photocatalytic reactivity of TiO2-based nanocomposite materials

“…For example, interfacial electron transfer was found to proceed to a much greater extent in mixed-phase TiO 2 with smaller aggregate sizes [68]. When Ag/TiO 2 nanocomposites were used in dye degradation, photoexcited electrons were found to readily transfer from TiO 2 to the metal nanoparticles, but their subsequent release to the dye molecules occurred only via the smaller metal nanoparticles [76,172]. For coupled semiconductor nanocomposites, size quantization alters the relative energy levels of the conduction band and valance band edges [173].…”

Enhanced photocatalytic H2 evolution over CdS/Au/g-C3N4 composite photocatalyst under visible-light irradiation

“…Owing to the great affinity between Au and S atoms, S 8 is preferred to adsorb on the Au surface of the Au/g-C 3 N 4 composite. 39 Under light irradiation, the photogenerated electrons in g-C 3 N 4 are effectively transferred to Au with large work function. As a result, the adsorbed S 8 molecules would be reduced into S 2− ions by the electrons accumulated on Au nanoparticles.…”