Temperature dependence on bandgap of semiconductor photocatalysts

Abstract

Light irradiation onto a semiconductor generates heat; however, its electronic structure under high temperature has not yet been well investigated. In this study, we have carefully examined the temperature dependence on the bandgap of simple metal oxides, which are well-known photocatalysts, i.e., TiO2, CeO2, Nb2O5, SnO2 Ta2O5, WO3, ZnO, and ZrO2, using operando UV–visible spectroscopy under controlled temperature (from room temperature to 500 °C). Consequently, a linear decrease in bandgap was seen as a function of temperature with a different slope for each semiconductor. We found that the slope was dependent on the bonding distance between metal and oxygen. This finding is essential to develop a photocatalyst used under the condition involving photo-thermal effect.

Photocatalytic Methane Reforming: Recent Advances

“…Pan et al [46] and Han et al [51] also found that photocatalytic activity increased as they induced heat energy (Figure 56). Very recently, we found that the absorption spectra of semiconductors are largely changed under heat treatment, which was analyzed by operando UV-vis spectroscopy [73]. This bandgap shift phenomenon should be considered since the surface temperature of most of the photocatalysts increases, especially for gas-phase reactions, such as methane conversion.…”

“…Therefore, an evaluation of the absorption spectra under heat input (operando UV-vis absorption spectra) is very important for determining the photocatalytic performance factors, such as internal quantum efficiency. Very recently, we found that the absorption spectra of semiconductors are largely changed under heat treatment, which was analyzed by operando UV-vis spectroscopy [73]. This bandgap shift phenomenon should be considered since the surface temperature of most of the photocatalysts increases, especially for gas-phase reactions, such as methane conversion.…”

“…It was also discovere that the effect of bandgap narrowing is more remarkable when the metal-oxygen ion dis tance in a crystal lattice is large (Figure 58b). Reprinted from [73] with permission of AIP Publishing.…”

“…Figure 57. Temperature dependence of the UV-vis absorption spectra for various semiconductors.Reprinted from[73] with permission of AIP Publishing.…”

Gas‐Phase Photoelectrocatalysis Mediated by Oxygen Ions for Uphill Conversion of Greenhouse Gases

“…We speculate this slight response under the cutoff filter would depend on the intrinsic electric structural change in the YSZ at high temperatures. Thus, we measured the optical absorption spectrum of the YSZ powder at the controlled temperature conditions using an Operando UV‐Vis spectroscope [45] equipped with a heat chamber as shown in Supporting Information (Figure S10). As a result, bandgap narrowing of the YSZ was seen under high temperatures.…”