Influence of Adsorbed Water on Phonon and UV-Induced IR Absorptions of TiO₂ Photocatalytic Particle Films

Abstract

The role of adsorbed water in photocatalytic processes on TiO 2 surfaces has been addressed using ATR-IR spectroscopy. Changes in the IR spectra of thin films of Degussa P25 TiO 2 photocatalyst have been observed in the presence of adsorbed water and under near-UV light. Removal of adsorbed water results in the appearance of absorption peaks at 828, 745, and 685 cm -1 attributed to TiO 2 surface phonon modes. UV irradiation of the dry TiO 2 results in a broad IR absorption which toward lower wavenumbers increases in absorbance, reaches a peak at 880 cm -1 , and then drops sharply to a minimum absorption at about 750 cm -1 . From observations of the behavior of P25 thin films under a drying regime and comparisons with transient IR studies, the broad absorption generated by the UV light has been assigned to excitation of shallow trap electrons to the conduction band with an excitation energy of ∼0.1 eV.

Surface-Modified Photocatalysts

“…A good examination of electron trapping is reported by the recent review of Henderson [16]. The electron trapping energy could range between 0.1 and 1 eV [14,17], in agreement with photoemission results for electronic defects on the surface of TiO 2 single crystal surfaces [18].…”

Photoinduced electron transfer and photodegradation of malonic acid at Au/TiO2 investigated by in situ ATR-IR spectroscopy

“…Overall this leads to an increased photodegradation rate of adsorbed organic compounds. In this case, the broad IR absorption due to trapped electrons [14] can be regarded as an indicator of electron-hole pair separation and organic pollutant photodegradation efficiency.…”

“…As most important finding it was shown that under certain reaction conditions cyanide is formed, which can adsorb on the gold and even lead to leaching the latter. ATR-IR has also been used to study the band gap irradiation of TiO 2 particle films in contact with water [14]. Vibrational bands below 1000 cm −1 that appeared upon UV illumination were first assigned to surface peroxo or hydroperoxo species [15].…”

Rate of Ag Photodeposition on Sr-doped NaTaO₃Photocatalysts as Controlled by Doping Sites

“…Infrared absorption induced by band-gap excitation provides a quantitative measure of the excited electrons that are still separated in semiconductor photocatalysts such as NaTaO 3 [6][7][8] and TiO 2 [9][10][11][12][13]. In our earlier study [4], the four photocatalysts were excited in vacuum by using a Hg-Xe lamp, and the steady-state electron population was quantified by electron-induced infrared light absorption.…”