Double-heterojunction structure of SbxSn1-xO2/TiO2/CdSe for efficient decomposition of gaseous 2-propanol under visible-light irradiation

Abstract

Highly crystallized antimony-doped tin oxide (ATO; Sb_xSn_1-xO₂, x = 0.1) of ∼50 nm size was prepared by co-precipitation of SnCl₄·5H₂O and SbCl₃, followed by heat-treatment at 1000 °C. The prepared ATO nanoparticles of deep blue color revealed a profound light-absorption in the visible range. ATO/TiO₂ composites were prepared by covering the surface of ATO nanoparticles with TiO₂ using the sol–gel method. Under visible-light irradiation (λ ≥ 420 nm), the prepared ATO/TiO₂ showed a notable photocatalytic efficiency in decomposing gaseous 2-propanol (IP), which seemed to be caused by the hole-transfer mechanism between the valence bands (VB) of ATO and TiO₂, since the ATO's VB level is located lower than that of TiO₂. Subsequently, a double-heterojunction ATO/TiO₂/CdSe structure was prepared by loading CdSe quantum dots (QDs) onto the surface of the ATO/TiO₂, which dramatically enhanced the visible-light photocatalytic efficiency. In fact, the catalytic activity of ATO/TiO₂/CdSe in evolving CO₂ from IP, was ∼3 times that of ATO/TiO₂ and twice that of typical N-doped TiO₂. The unexpectedly high efficiency of ATO/TiO₂/CdSe seemingly is due to the unique band matching among these semiconductors. With sensitization of ATO and CdSe, not only the holes but also the electrons are generated in the VB and CB, respectively, of TiO₂ under visible-light irradiation.