Heteronanostructured Photocatalysts with Epitaxial Junctions between the Components

Abstract

Heteronanostructured (HNS) photocatalysts are the key material for various important solar-to-chemical transformations. In the semiconductor photoelectrodes, efficient charge separation can be achieved by the Schottky barrier. However, in the particulate HNS photocatalysts, the dimension of semiconductor is usually too small to accommodate the space charge layer. Even if the space charge layer can be formed at the initial stage, the band bending would become weak at the photostationary state due to the accumulation of the electrons in the conduction band. Thus, the major subject in the HNS photocatalysts is the enhancement of charge separation through the efficient interfacial charge transfer between the components for which the construction of the high-quality interface is crucial [1]. On the other hand, Au NP possesses strong and broad absorption in the visible region due to the localized surface plasmon resonance, and loading Au NPs on wide gap semiconductor photocatalysts such as TiO2, SnO2, and ZnO (Au/semiconductor) can induce the visible-light responsiveness and/or work as a catalyst for various reactions [1]. Importantly, the optical property and catalytic activity of Au NPs strongly depend on the size and shape.This talk focusses on our recent works on the interfacial control in the HNSs at an atomic level, and the effects on the photocatalytic activity. Firstly, a novel nanoscale charge separation mechanism is presented in a HNS consisting of SnO2 nanorods and rutile TiO2 with a heteroepitaxial (HEPI) junction (SnO2-NR#TiO2, # denotes HEPI junction). SnO2-NR#TiO2 shows photocatalytic activity for selective oxidation of ethanol to acetaldehyde much higher than the physical mixture of SnO2 and TiO2 [2]. Secondly, the SnO2-NR#TiO2 charge separator was further modified with Au NPs (Au/SnO2-NR#TiO2) to impart visible-light activity. The Au/SnO2-NR#TiO2 plasmonic photocatalyst exhibits a high level of visible-light activity for the synthesis of H2O2 by two-electron oxygen reduction reaction (ORR) with the assistance of the catalytic activity of Au NP [3]. Thirdly, the HEPI junction-induced shape change of Au NPs is shown to occur on the surface of ZnO in the Au#ZnO system. The extremely high UV-light activity of Au#ZnO for two-electron ORR far exceeding that of Au/TiO2 is discussed in terms of the catalytic activity of Au NPs and the adsorption ability of ZnO for H2O2 [4].[1] H. Tada, Dalton Trans. 2019, 48, 6308, and the references therein.[2] K. Awa, R. Akashi, A. Akita, S. Naya, H. Kobayashi, H. Tada, ChemPhysChem 2019, 20, 2155.[3] K. Awa, S. Naya, M. Fujishima, H. Tada, J. Phys. Chem. C 2020, 124, 7599.[4] M. Teranishi, S. Naya, H. Tada, J. Am. Chem. Soc. 2010, 132, 7850.