The Effect of Cu(II) Nanoparticle Decoration on the Electron Relaxations and Gaseous Photocatalytic Oxidations of Nanocrystalline TiO2

Abstract

A photocatalytic effect arises from the electron relaxation of semiconductors. Directing the electron relaxation toward photocatalytic reactions is the focus of photocatalytic studies. Co-catalyst decoration is a main way to modulate the electron relaxation, and the Cu(II) nanoparticles have been widely studied as an important co-catalyst. However, the detailed mechanism is still not well known. The current study is devoted to investigating the effect of the Cu(II) nanoparticle decoration on the electron relaxations for TiO2 through in situ photochromism and photoconductances, based on which the relation to the photocatalytic properties was discussed. The result shows that the Cu(II)/Cu(0) redox couple assists the double electron transfer from TiO2 to O2, while the Cu(I)/Cu(0) redox couple assists the single electron transfer to O2. Although the Cu(II) decoration changes the mechanism and increases the rate of the electron relaxations, the electron relaxation does not occur via the Cu redox couple assistance. It was found that the electron relaxation kinetics depends on the reduced Cu species, which can be greatly increased when the Cu(II) was reduced to Cu(0). It is also revealed that the electron relaxation corresponds to the electron transfer from TiO2 to O2, but it does not occur through the Cu redox couple assistance. The result also shows that the increase in the electron relaxation is mainly directed toward the recombination rather than photocatalytic reactions. The present research gains some insights on the role of the co-catalysts in the electron relaxations and its relation to photocatalysis; this should be meaningful for designing novel photocatalytic materials.