Chemical and Valence Electron Structure of the Core and Shell of Sn(II)-Perovskite Oxide Nanoshells

Photocatalytic reactions occur at surfaces; therefore, understanding the valence electronic structure of a photocatalyst is an important aspect in the selection of suitable materials. A new class of kinetically stable metastable Sn(II)-perovskite oxide nanoshell was synthesized previously, which has a core–shell (BZT-SZT) ((Ba(Zr1–yTiy)O3–Sn(Zr1–yTiy)O3)) structure, but the electronic structure was not fully resolved. This work reports a detailed electron spectroscopic study of BZT-SZT (or BSZT) to determine the valence electronic structure and the chemical nature of the surface near region with a focus on Sn as the element added to the outer shell via a molten-salt reaction. Near edge X-ray absorption fine structure was used to understand the chemical state of Sn in the BSZT. X-ray photoelectron spectroscopy reveals that the flux reaction of Sn into the BZT does not significantly change the oxidation state of Sn, but the chemical environment of Sn changes from the surface to the bulk, and the chemical state of Sn corresponds to the Sn(II)-based oxide based on NEXAFS and 119Sn Mössbauer spectroscopy. The increase in Sn content decreases the valence band (VB) cutoff. The change in the VB occurs in the 2p O electron density region and is caused by the change in the Sn concentration. The change in the VB occurs to a stronger degree in the inner part of the BSZT and aligns with the change in the overall band gap from UV–vis measurements. Accordingly, it is likely that the condution band position at the surface does not depend on the amount of Sn content. The material developed is suitable for the oxidation half reaction of the overall water splitting reaction.