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

Photocatalytic\nreactions occur at surfaces; therefore,\nunderstanding\nthe valence electronic structure of a photocatalyst is an important\naspect in the selection of suitable materials. A new class of kinetically\nstable metastable Sn(II)-perovskite oxide nanoshell was synthesized\npreviously, which has a core–shell (BZT-SZT) ((Ba(Zr<sub>1–<i>y</i></sub>Ti<i><sub>y</sub></i>)O<sub>3</sub>–Sn(Zr<sub>1–<i>y</i></sub>Ti<i><sub>y</sub></i>)O<sub>3</sub>)) structure, but the electronic structure was not fully resolved.\nThis work reports a detailed electron spectroscopic study of BZT-SZT\n(or BSZT) to determine the valence electronic structure and the chemical\nnature of the surface near region with a focus on Sn as the element\nadded to the outer shell via a molten-salt reaction. Near edge X-ray\nabsorption fine structure was used to understand the chemical state\nof Sn in the BSZT. X-ray photoelectron spectroscopy reveals that the\nflux reaction of Sn into the BZT does not significantly change the\noxidation state of Sn, but the chemical environment of Sn changes\nfrom the surface to the bulk, and the chemical state of Sn corresponds\nto the Sn(II)-based oxide based on NEXAFS and <sup>119</sup>Sn Mössbauer\nspectroscopy. The increase in Sn content decreases the valence band\n(VB) cutoff. The change in the VB occurs in the 2p O electron density\nregion and is caused by the change in the Sn concentration. The change\nin the VB occurs to a stronger degree in the inner part of the BSZT\nand aligns with the change in the overall band gap from UV–vis\nmeasurements. Accordingly, it is likely that the condution band position\nat the surface does not depend on the amount of Sn content. The material\ndeveloped is suitable for the oxidation half reaction of the overall\nwater splitting reaction.