Strong hybridization between Bi-6s and O-2p orbitals in Sillén–Aurivillius perovskite Bi4MO8X (M = Nb, Ta; X = Cl, Br), visible light photocatalysts enabling stable water oxidation

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 6; no. 7; pp. 3100 - 3107
• Main Authors: Kunioku, Hironobu, Higashi, Masanobu, Tomita, Osamu, Yabuuchi, Masayoshi, Kato, Daichi, Fujito, Hironori, Kageyama, Hiroshi, Ryu, Abe
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Catalytic activity; Deactivation; Electrons; Hybridization; Niobium; Orbitals; Oxidation; Oxides; Oxyhalides; Perovskite structure; Photocatalysis; Photocatalysts; Tantalum; Valence band
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c7ta08619a

Bi4NbO8Cl with a Sillén–Aurivillius type perovskite structure has recently been demonstrated to stably and efficiently oxidize water under visible light, possibly related to its unique valence band with O-2p orbitals located at unusually high potentials compared with conventional oxides. Here we study a series of isostructural oxyhalides, Bi4MO8X (M = Nb, Ta; X = Cl, Br), to examine how the cation and anion substitution affects the band structure and the resultant photocatalytic activity. We found experimentally and theoretically that both M and X substitutions have little influence on the electronic structures, providing similar valence band maximums (VBMs) and band gaps to those of Bi4NbO8Cl. They all functioned as stable O2-evolving photocatalysts under visible light without suffering from self-oxidative deactivation, as opposed to BiOBr. DFT calculations further revealed a fairly strong hybridization between the Bi-6s orbitals and the O-2p orbitals, which is interpreted using a revised lone pair (RLP) model, thus explaining at least partly why the O-2p orbitals are elevated in energy.