Time-resolved Infrared Absorption Study of Photochemical Reactions Over Metal Oxides

Abstract

The present account describes how photochemical reactions over metal oxides are traced by time-resolved infrared (IR) absorption spectroscopy. The ac-coupled amplification of the IR signal allows detection of transient absorbance changes as small as 10 )6 with a time resolution of 50 ns. Band-gap excited electrons in TiO 2 and NaTaO 3 present a structureless absorption of IR light from 3000 to 1000 cm )1 . Reaction-perturbed decay of this absorption evidences the assignment to photoexcited electrons, not to holes. The efficiency of the water splitting reaction on NaTaO 3 -based catalysts correlates with the quantity of electrons detected by the IR absorption. A short-lived intermediate state of 2-propanol oxidation on TiO 2 is identified by its vibrational band at 1640 cm )1 superposed on the structureless absorption of electrons. Ru dye (N3) on a TiO 2 film is irradiated with a 532-nm light pulse to simulate dye-sensitized solar cells. The neutralization rate of dye cations and the decay rate of electrons injected in the film are quantified, leading to a three-state model which describes the relaxation of injected electrons. These results demonstrate the ability of this method in tracing photochemical kinetics over metal oxides.

Mesoporous Titanium Dioxide Nanofibers with a Significantly Enhanced Photocatalytic Activity

“…The IR absorbance difference spectra collected after the adsorption of ethanol on P25 TiO 2 and T600 nanofibers in O 2 atmosphere and after 0, 1, 5, 10, and 60 min of UV irradiation are presented in Figure a and e. The difference spectra were obtained by subtracting the absorbance spectra before UV irradiation ( A τ =0 min ) from the absorbance spectra after τ min of a UV irradiation ( A τ min ). UV irradiation on TiO 2 caused a decrease in the intensity of the C−H stretching bands at =2971, 2931, and 2870 cm −1 (Figure a and e) and the evolution of new bands at =1718 cm −1 (acetaldehyde, CH 3 CHO), 1442 cm −1 (acetate, CH 3 COO − ), 1581 cm −1 (formate, HCOO − ), and 2360 cm −1 (CO 2 ) …”

“…In addition, the fibrous morphology plays a significant role in photogenerated charge accumulation during photocatalytic oxidation of ethanol as evident from the result of the background shift. The variation of the IR intensity at =2000 cm −1 ( I 2000 , background shift) during 60 min of ethanol photocatalytic oxidation on P25‐TiO 2 powder and T600 nanofibers is shown in Figure c and g. The variation of I 2000 is a manifestation of the accumulation or depletion of the photogenerated electrons within the conduction band of TiO 2 . The accumulation of photogenerated electrons proceeds if the rate of the electron‐generating reaction in Equation (2) is greater than the rate of electron‐consuming reactions in Equations (5) and (6) and the rate of e‐h recombination in Equation (4).…”

Photoelectrochemical Property of Tungsten Oxide Films of Vertically Aligned Flakes for Visible-Light-Induced Water Oxidation

“…[21][22][23] Although the lifetime of positive holes is elongated with an increase in the anodic polarization, the time constant is not sufficient to induce water oxidation at the upper limit of photocurrent density. As shown in Fig.…”

Time-Resolved Infrared Absorption Study of SrTiO3 Photocatalysts Codoped with Rhodium and Antimony

“…This pump and probe method is appropriate for quantifying the relative amount of electrons excited in photocatalyst particles of submicrometer sizes, as it is free from the scattering problems of probe light. 18,19 2. EXPERIMENTAL SECTION Rhodium and antimony were doped into SrTiO 3 by hydrothermal synthesis; details of this method appear in a separate paper.…”