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Aurivillius layered perovskites are one of the most promising starting materials of a monolayer nanosheet for opening up unique applications of two-dimensional nanomaterials because of a large variety of applicable elements in the perovskite layer. In particular, the wide range of chemical compositions is convenient to explore an effective combination of A- and B-site elements for photoluminescent perovskite nanosheets. In the present study, tungsten- and lanthanide-containing aurivillius layered perovskites, Bi2Na0.63Ln0.37Ta1.75W0.25O9 (Ln = La, Ce, Pr, Nd, Eu, Gd, Tb, Sm, Dy, Ho, Er, Tm, and Yb), were prepared in order to investigate the photoluminescence (PL) associated with Bi3+/Ln3+-based layered perovskites and monolayer perovskite nanosheets. The comparison of PL spectra for the perovskite nanosheets derived from W-containing (Bi2Na0.63Ln0.37Ta1.75W0.25O9) and non-W-containing aurivillius phase layered perovskite (Bi2Na0.5La0.13Ln0.37Ta2O9) under UV-light illumination (λex. = 280–300 nm) indicated that introducing W into B sites in the perovskite layers resulted in selective energy transfer toward Eu3+. Several types of aurivillius layered perovskites were prepared to investigate the degree of inversion symmetry around Eu3+ ions. [ABSTRACT FROM AUTHOR]

Pt/ZrP2O7 catalysts exhibiting high activity for catalytic NOx reduction by H2 in the presence of excess O2 were developed in this study. At a low temperature of 125 °C and a high space velocity of approximately 5 × 104 h–1, 0.4 wt % Pt/ZrP2O7 facilitated a higher NO conversion to N2 (51%) than 0.4 wt % Pt/ZrO2 (<5%) for a reaction mixture of 200 ppm NO, 5000 ppm H2, 10% O2, and He balance. However, N2O and NO2 production increased at temperatures lower than 100 °C and higher than 200 °C, thereby decreasing the N2 yield. High-resolution electron microscopy and X-ray photoelectron spectroscopy analyses of 0.4 wt % Pt/ZrP2O7 revealed the coexistence of large metallic Pt crystallites with sizes of ∼20 nm and highly dispersed Pt oxide nanoclusters. When Pt loading was decreased to 0.05 wt %, the large metallic Pt crystallites disappeared, and only the Pt oxide nanoclusters remained on ZrP2O7. Owing to this structural change, N2O/NO2 formation was significantly suppressed, enabling highly selective NO reduction to N2. Moreover, catalyst preparation by equilibrium adsorption instead of wet impregnation further improved the reaction, achieving >90% selective NO conversion to N2, which was nearly free of undesired byproducts (NH3, N2O, and NO2) at 175 °C. The Pt oxide nanocluster supported on ZrP2O7 was more tolerant to the presence of 10% water vapor in the exhaust gas than the metallic Pt particles. Therefore, the developed catalyst is suitable for applications in practical exhaust gas purification for H2-fueled internal combustion engines. [ABSTRACT FROM AUTHOR]

Multicolor photoluminescent Bi0.4Ln0.1Na0.5Ta2O72− nanosheets (Ln = Eu, Tb, Dy, Sm, La) are prepared by delaminating an Aurivillius‐phase layered perovskite, Bi2.4Ln0.1Na0.5Ta2O9. Both Bi3+ and Ln3+ (except La3+) successfully function as luminescent centers under UV‐light illumination (λex. = 240–340 nm), which result in a photoluminescence color that can be tuned by changing the lanthanide doping. The emission spectra are influenced by pH because the energy distribution to Ln3+ or to Bi3+ is different in acidic or in basic solutions. Freestanding Bi0.4Ln0.1Na0.5Ta2O72− nanosheet membranes are prepared by vacuum filtration, and the relationship between the photoluminescence and structural properties of the nanosheet membranes is investigated. The results indicate that differences in the electron orbitals involved in the photoluminescence of Bi3+ (6s2–6s6p) and Ln3+ (4fn–4fn) influence the responsiveness to changes in the environment surrounding those luminescent centers. [ABSTRACT FROM AUTHOR]

Two‐dimensional semiconducting materials have attracted attention as photocatalysts, electrode catalysts and electronic materials. However, preparation of metal nitride nanosheet is still a significant challenge. Here, we show a tantalum nitride (Ta3N5) nanosheet with a thickness of 1.5 nm prepared via tantalum oxide [TaO3]− nanosheet derived from layered rubisium tantalum oxide (RbTaO3). The monolayer tantalum oxide nanosheet was converted to Ta3N5 nanosheet with a [110] preferred orientation in the in‐plane direction during annealing under NH3 gas flow, and showed a photocatalytic activity for H2 evolution under visible light illumination (550 nm). The H2 evolution ratio of the ultrathin Ta3N5 nanosheet was much higher than that of bulk Ta3N5 prepared from Ta2O5 powder, indicating that nanosheet structure suppresses the recombination in the photocatalytic reaction. [ABSTRACT FROM AUTHOR]

Pulsed cathodic arc-plasma deposition was employed to create a few nanometre-thick Pt overlayer on a 50 μm-thick Fe-Cr-Al metal (SUS) foil, resulting in an effective NH 3 oxidation catalyst fabrication. This catalyst exhibited a turnover frequency (TOF) exceeding 100 times that of Pt nanoparticles. In this study, Pt overlayer catalysts with varying degrees of surface roughness were fabricated using different metal foil substrates: mirror-polished (Pt/p-SUS), unpolished (Pt/SUS) and roughened by the formation of a surface oxide layer (Pt/Al 2 O 3 /SUS). The nanoscale roughness was comprehensively analysed using electron microscopy, laser scanning confocal microscopy and chemisorption techniques. NH 3 oxidation activity, measured at 200 °C, followed an increasing trend in the order of Pt/Al 2 O 3 /SUS < Pt/SUS < Pt/p-SUS, despite a decrease in the apparent Pt surface area in the same order. Consequently, the calculated TOF was markedly higher for Pt/p-SUS (267 min -1 ) compared to Pt/SUS (107 min -1 ) and Pt/Al 2 O 3 /SUS (≤22 min -1 ). The smooth Pt overlayer surface also favoured N 2 yield over N 2 O at this temperature. This discovery enhances our fundamental understanding of high-TOF NH 3 oxidation over Pt overlayer catalysts, which holds significance for the advancement and industrial implementation of selective NH 3 oxidation processes.

Bandgap tunable lanthanum niobium oxynitride [LaNb 2 O 7-x N x ] (1+x)- nanosheet is prepared by the delamination of a Ruddlesden-Popper phase perovskite oxynitride via ion-exchange and two-step intercalation processes. The lanthanum niobium oxynitride nanosheets have a homogeneous thickness of 1.6 nm and exhibit a variety of chromatic colors depending on the nitridation temperature of the parent-layered oxynitride. The bandgap energy of the nanosheets is determined by ultraviolet photoemission spectroscopy, Mott-Schottky, and photoelectrochemical measurements and is found to be tunable in the range of 2.03-2.63 eV. Furthermore, the oxide/oxynitride superlattice structures are fabricated by face-to-face stacking of 2D crystals using oxynitride [LaNb 2 O 7-x N x ] (1+x)- and oxide [Ca 2 Nb 3 O 10 ] - nanosheets as building blocks. Moreover, the superlattices-like restacked oxynitride/oxide nanosheets hybrid exhibits unique proton conductivity and dielectric properties strongly influenced by the oxynitride nanosheets and enhanced photocatalytic activity under visible light irradiation., (© 2023 Wiley-VCH GmbH.)

Layered nanosheet materials showing a drastic luminescence change in response to changes in proton concentration (pH) were prepared by sandwiching Eu 3+ and Tb 3+ cations with anionic TiNbO 5 - nanosheets using electrostatic interaction. Each trivalent lanthanide ion showed a different response to pH change: a strong red emission from Eu 3+ was observed at low proton concentrations (pH: 13) and a green emission from Tb 3+ was dominant at high proton concentrations (pH: 1). The photoluminescence intensity was determined by the balance between the photocatalytic activity of TiNbO 5 - nanosheets and energy transfer from the host layer to the guest lanthanide ions. Moreover, the trivalent lanthanide/TiNbO 5 - nanosheet hybrid formed a gel-like solid in aqueous solution, which functioned as an inorganic gel electrolyte when mixed with Na 2 SO 4 . The multicolor luminescence (red-yellow-green) of the lanthanide/TiNbO 5 - nanosheet hybrid enabled direct visualization of the diffusion of protons in an inorganic gel electrolyte during water electrolysis.