Hole Scavenging and Photo-Stimulated Recombination of Electron−Hole Pairs in Aqueous TiO₂ Nanoparticles

Abstract

It is shown that 532 nm and 1064 nm laser photoexcitation of trapped electrons generated by 355 nm photolysis of aqueous titania (TiO 2 ) nanoparticles causes rapid photobleaching of their absorbance band in the visible and near IR. This photobleaching occurs within the duration of the laser pulse (3 ns FWHM); it is caused by photoinduced electron detrapping followed by rapid recombination of the resulting free electron and a trapped hole. The quantum yield for the electron photobleaching is ca. 0.28 for 532 nm and ca. 0.024 for 1064 nm photoexcitation. Complete separation of the spectral contributions from trapped electron and hole is demonstrated using glycerol as a selective hole scavenger. When glycerol is added to the solution, some light-absorbing holes are scavenged promptly within the duration of the 355 nm photoexcitation pulse, some are scavenged at a slower rate over the first 200 ns after the 355 nm pulse, and the rest are not scavenged, even at high concentration of the scavenger (> 10 vol %). A reaction with chemi-and physi-sorbed glycerol would account for the prompt and the slow hole decay, respectively. The implications of these results are discussed.

Multicycle photocatalytic reduction of Cr(VI) over transparent PVA/TiO2 nanocomposite films under visible light

“…The well dispersion of TiO2 nanoparticles was attributed to the strong interaction between PVA and TiO2. The large amount of hydroxyl groups on PVA chains acted as anchoring sites for TiO2 nanoparticles via the formation of octahedral complex or other chelating ligands with under-coordinated Ti atoms on TiO2 surfaces [31]. Attenuated total reflectance FTIR (ATR-FTIR) spectroscopic measurement was used to investigate the formation of surface complex.…”

“…Therefore, addition of holes scavengers can greatly improve the photocatalytic reduction rate of Cr(VI) [25]. It has been reported that polyhydroxylated compounds, such as glycerol, sugar, and PVA, are highly efficient hole scavengers for TiO2 nanoparticles [31]. 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin-trapping EPR technique was employed to determine the species generated during photocatalytic reduction process.…”

Hydrogen Production by Photoreforming of Renewable Substrates

“…They also serve as active sites for the adsorption of reactants and intermediates [201]. It was concluded by time-resolved transient absorption spectroscopy [202,203] that C2-C6 polyols and carbohydrates could scavenge 50-60% of the photogenerated holes of TiO 2 in the time lapse of 6 ns. The scavenging efficiency was higher for increasing the number of OH groups.…”

Template-assisted synthesis of core–shell α-Fe2O3@TiO2 nanorods and their photocatalytic property

“…From the viewpoint of utilizing solar light, visible light responsive TiO 2 -based photocatalysts are highly desired [9][10][11][12]. Moreover, TiO 2 has a relatively high electron-hole recombination rate, which will decrease its photoactivity [13][14][15].…”