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Synthesis of Three-Layer Perovskite Oxynitride K2Ca2Ta3O9N·2H2O and Photocatalytic Activity for H2 Evolution under Visible Light
journal contribution
posted on 2020-07-19, 12:44 authored by Ya Tang, Kosaku Kato, Takayoshi Oshima, Hiroto Mogi, Akinobu Miyoshi, Kotaro Fujii, Kei-ichi Yanagisawa, Koji Kimoto, Akira Yamakata, Masatomo Yashima, Kazuhiko MaedaSubstitution of oxide
anions (O2–) in a metal oxide for nitrogen (N3–) results in reduction of the band gap, which is attractive
in heterogeneous photocatalysis; however, only a handful of two-dimensional
layered perovskite oxynitrides have been reported, and thus, the structural
effects of layered oxynitrides on photocatalytic activity have not
been sufficiently examined. This study reports the synthesis of a
Ruddlesden–Popper phase three-layer oxynitride perovskite of
K2Ca2Ta3O9N·2H2O, and the photocatalytic activity is compared with an analogous
two-layer perovskite, K2LaTa2O6N·1.6H2O. Topochemical ammonolysis reaction of a Dion–Jacobson
phase oxide KCa2Ta3O10 at 1173 K
in the presence of K2CO3 resulted in a single-phase
layered perovskite, K2Ca2Ta3O9N·2H2O, which belongs to the tetragonal P4/mmm space group, as demonstrated by
synchrotron X-ray diffraction, scanning transmission electron microscopy
measurements, and elemental analysis. The synthesized K2Ca2Ta3O9N·2H2O has
an absorption edge at around 460 nm, with an estimated band gap of
ca. 2.7 eV. K2Ca2Ta3O9N·2H2O modified with a Pt cocatalyst generated H2 from an aqueous solution containing a dissolved NaI as a
reversible electron donor under visible light (λ > 400 nm)
with no noticeable change in the crystal structure and light absorption
properties. However, the H2 evolution activity of K2Ca2Ta3O9N·2H2O was an order of magnitude lower than that of K2LaTa2O6N·1.6H2O. Femtosecond transient
absorption spectroscopy revealed that the lifetime of photogenerated
mobile electrons in K2Ca2Ta3O9N·2H2O was shorter than that in K2LaTa2O6N·1.6H2O, which could
explain the low photocatalytic activity of K2Ca2Ta3O9N·2H2O.