TiO2-based Photocatalysis: Surface Defects, Oxygen and Charge Transfer

Abstract

A detailed discussion of the photochemistry of TiO 2 surfaces is presented, covering important work from the literature as well as more recent studies. The production and characterization of surface defects is discussed, and studies of the adsorption of molecular oxygen on these defects is presented. In addition, both chemical and physical methods for detection and measurement of defect sites on TiO 2 are reviewed. The role of nitrogen doping on shifting the photothreshold energy of TiO 2 is discussed and the active chemical state of the nitrogen is described, based on XPS N(1s) binding energies. Observations of charge transfer between excited TiO 2 and adsorbates are presented, and it is shown that the electronegativity of the attachment atom which forms the surface bond is important in governing charge transfer.

Evidence for photogenerated intermediate hole polarons in ZnO

“…After the dissociation of the photoinduced exciton, the charge carriers-free electrons and free holes-may be trapped in polaronic states, which in turn can diffuse through the crystal. When the carriers reach the surface, they can trigger reactions in the adsorbed chemical species 1,[10][11][12] . Compared with the ultrafast formation dynamics of excitons in ZnO(10-10) single crystals 7 , polaron formation involves the motion of nuclei and thus occurs on a much longer timescale.…”

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO2

“…In recent years, the role of oxygen vacancies and Ti 3+ in the photocatalytic activity of TiO2 has been of great interest [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] . While characterisation of TiO2-based photocatalysts uses standard techniques such as UV-vis spectroscopy, valence band XPS, dye degradation insights into the dynamics of electrons and holes and defects can be obtained from Transient Absorption Spectroscopy (TAS) [51][52][53][54][55] and photoluminescence (PL) [56][57][58] .…”

Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling

“…This shift is related to the excitation of long-lived IR absorbing states below the conduction band of TiO 2 , which become populated upon UV irradiation [27].…”