title: The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives.
abstract: The effect of the Ta/Nb ratio in the (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 (0 ≤ x ≤ 4) crystals grown by a KCl flux method on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives BaNb1-xTaxO2N (0 ≤ x ≤ 1) was investigated. The Rietveld refinement of X-ray data revealed that all Ba5Nb4-xTaxO15 samples were well crystallized in the space group P3[combining macron]m1 (no. 164). Phase-pure BaNb1-xTaxO2N (0 ≤ x ≤ 1) porous structures were obtained by nitridation of the flux-grown oxide crystals at 950 °C for 20, 25, 30, 35, and 40 h, respectively. The absorption edge of BaNb1-xTaxO2N (0 ≤ x ≤ 1) was slightly shifted from 720 to 690 nm with the increasing Ta/Nb ratio. The O2 evolution rate gradually progressed and reached the highest value (127.24 μmol in the first 2 h) with the Ta content up to 50 mol% but decreased at 75 and 100 mol% presumably due to the reduced specific surface area and high density of structural defects, such as grain boundaries acting as recombination centers, originated from high-temperature nitridation for prolonged periods. Transient absorption spectroscopy provided evidence for the effect of the Ta/Nb ratio on the behavior and energy states of photogenerated charge carriers, indicating a direct correlation with photocatalytic water oxidation activity of BaNb1-xTaxO2N.
authors.affiliation: Department of Environmental Science and Technology, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan. teshima@shinshu-u.ac.jp.
authors.forename: Mirabbos
authors.initials: M
authors.lastname: Hojamberdiev
authors.affiliation: Fachgebiet Keramische Werkstoffe, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin, Germany.
authors.forename: Maged F
authors.initials: MF
authors.lastname: Bekheet
authors.affiliation: Department of Physical Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Zahedi
authors.affiliation: Department of Environmental Science and Technology, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan. teshima@shinshu-u.ac.jp.
authors.forename: Hajime
authors.initials: H
authors.lastname: Wagata
authors.affiliation: Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan.
authors.forename: Junie Jhon M
authors.initials: JJ
authors.lastname: Vequizo
authors.affiliation: Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yamakata
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Yubuta
authors.affiliation: Fachgebiet Keramische Werkstoffe, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin, Germany.
authors.forename: Aleksander
authors.initials: A
authors.lastname: Gurlo
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Domen
authors.affiliation: Department of Environmental Science and Technology, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan. teshima@shinshu-u.ac.jp and Center for Energy and Environmental Science, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Teshima