Direct Observation of Interfacial Charge Transfer between Rutile TiO₂ and Ultrathin CuO_x Film by Visible‐Light Illumination and Its Application for Efficient Photocatalysis

Abstract

A well‐defined interface between CuOx film and TiO2 is constructed as a model for elucidating the interfacial charge transfer (IFCT) process that occurs during photocatalysis. Spectroscopic analysis revealed strong blue light absorption at 2.7 eV in this film system. Based on photoemission spectroscopy and the UV‐visible absorption analysis, the band offset of CuOx and TiO2 was investigated, and the observed blue absorption at 2.7 eV could be explained by an IFCT process, in which electrons in the valence band of TiO2 were excited into the conduction band of the ultrathin CuOx film. Furthermore, the IFCT transition was found to strongly depend on the crystal face of TiO2, as the IFCT absorption was significantly increased in the ultrathin CuOx film coated over the rutile TiO2 (110) substrate. Probe reduction and oxidation reactions were also used to investigate the charge transport process and determine photocatalytic reaction sites, which were located around a few nanometers‐scale region from the edge of the ultrathin CuOx and TiO2. The present findings provide a powerful method for the development of efficient visible‐light sensitive photocatalysts based on the IFCT concept.

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

“…The photocatalytic activity of TiO 2 materials is dependent on the kinetics of charge carriers (the holes and the electrons) and the reactant diffusion to their surfaces [31][32][33][34][35]. Under conventional conditions, the diffusion of reactants (O 2 , organics molecule, and others) is usually fast [36][37][38], so often the charge carrier kinetics determine the photocatalytic efficiency.…”

Antiviral Effect of Visible Light-Sensitive CuxO/TiO2 Photocatalyst

“…Using an atomic force microscope (AFM), the authors observed the formation of metal Ag particles on the film resulting from the photoreduction of Ag + ions, and Ag particles were selectively deposited on the edge of a CuO film under visible-light irradiation [74]. These results also suggest that the IFCT transition occurs by visible light and that the Cu(II) species acts as reduction sites.…”

“…Furthermore, Osako et al visualized the reduction and oxidation sites in a Cu(II)/TiO 2 system by using an ultrathin CuO film with a well-defined pattern coated onto a TiO 2 single crystal prepared by pulsed laser deposition and photolithography [73]. Using an atomic force microscope (AFM), the authors observed the formation of metal Ag particles on the film resulting from the photoreduction of Ag + ions, and Ag particles were selectively deposited on the edge of a CuO film under visible-light irradiation [74]. These results also suggest that the IFCT transition occurs by visible light and that the Cu(II) species acts as reduction sites.…”

Sequential ionic layer adsorption reaction formation of LaVO4–TiO2 nanocomposites for photocatalytic water treatment

“…Many different oxides and sulfides have been shown to form a type-II junction with TiO 2 , 12,13 and these often demonstrate improvements in a variety of different photocatalytic reactions due to improved charge separation. [14][15][16][17][18][19][20][21] A potential candidate material for formation of a type-II junction with TiO 2 is lanthanum vanadate (LaVO 4 ). Thoroughly explored as a phosphor matrix material, 22 it has been somewhat overlooked in the field of photocatalysis.…”