Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Synthesis of a Layered Niobium Oxynitride, Rb2NdNb2O6N·H2O, Showing Visible-Light Photocatalytic Activity for H2 Evolution Haruki Wakayama,† Keisuke Hibino,† Kotaro Fujii,† Takayoshi Oshima,†,‡ Keiichi Yanagisawa,§ Yuuga Kobayashi,§ Koji Kimoto,§ Masatomo Yashima,† and Kazuhiko Maeda*,†
Downloaded via KEAN UNIV on April 16, 2019 at 12:49:42 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
†
Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1-NE-2 Ookayama, Meguro-ku, Tokyo 152-8550, Japan ‡ Japan Society for the Promotion of Science, Kojimachi Business Center Building, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan § Electronic Functional Materials Group, Polymer Materials Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan S Supporting Information *
ABSTRACT: Two-dimensional (2D) layered oxynitrides are promising candidates as visible-light-driven photocatalysts, but the actual examples are rare because of the difficulty in synthesizing the 2D oxynitrides. Here a phase-pure layered perovskite, Rb2NdNb2O6N·H2O, that belongs to a tetragonal P4/mmm space group was successfully synthesized by thermal ammonolysis of a mixture of layered RbNdNb2O7 and Rb2CO3, as revealed by synchrotron X-ray diffraction, elemental analyses, and atomicscale electron microscopy observation. The synthesized Rb2NdNb2O6N· H2O had an absorption edge at around 500 nm and a sufficiently high conduction-band potential to allow for proton reduction. With modification by a platinum cocatalyst, Rb2NdNb2O6N·H2O became photocatalytically active for H2 evolution in the presence of triethanolamine as an electron donor under visible light (λ > 400 nm).
■
INTRODUCTION
In contrast to the nitrogen-doped metal oxides, undoped oxynitrides contain a stoichiometric amount of nitrogen in their phase, which guarantees strong visible-light absorption through band-to-band electron transitions. Oxynitrides have thus been studied as visible-light-responsive photocatalysts.1,4,7,8 Among oxynitride photocatalysts, niobium-based ones are attractive in terms of their wider absorption band in the visible-light region compared to tantalum counterparts.9 This is primarily due to the relatively shallow conduction-band minimum of niobium oxynitrides, which mainly consist of Nb 4d orbitals. However, this, in turn, restricts their use as photocatalysts for reductive conversion (e.g., H2 evolution and CO2 reduction) because the reactivity of photogenerated electrons is determined by the conduction-band potential of a semiconductor.9,10 Furthermore, the Nb5+ cations in niobiumbased oxynitrides are more susceptible to reduction than Ta5+ in tantalum-based analogues during the thermal nitridation process from an oxide precursor.9 As a result, niobium oxynitrides usually contain relatively large amounts of anionic defects that arise from such reduced niobium species. It has been reported that oxynitrides containing a larger amount of reduced metal species show lower photocatalytic activity for
Recently, water splitting and CO2 reduction using photocatalysts have been intensive research targets, aimed at addressing energy and environmental problems.1 Among semiconductor photocatalysts, two-dimensional (2D) layered metal oxides have attracted attention because they have unique reactivity,2 which is unattainable using bulk-type (threedimensional, 3D) metal oxides. For example, the layered space may be utilized as reaction sites, showing high watersplitting activity under UV irradiation.3 Because metal oxides in general absorb only UV light (98%, Wako Pure Chemicals). The solution was stirred at 353 K for 1 h in order to allow Nb species to form a CA complex. Then, 8.03 mmol of Rb2CO3 (>97%, Wako Pure Chemicals), 10.7 mmol of Nd(NO3)3· 6H2O (>99.5%, Wako Pure Chemicals), and 1.1 mol of ethylene glycol (EG; >99.5%, Kanto) were added to the solution. A 50% excess amount of Rb was added to compensate for the volatilization loss of Rb during calcination. The reaction mixture was heated at ∼353 K to promote complete dissolution on a hot-plate stirrer. The as-obtained transparent orange solution was heated to 473 K to promote esterification between EG and CA, yielding a glassy resin. The resin was heated in a mantle heater with a gradual elevation of temperatures at 523, 623, and 723 K, yielding a white-gray powder, which was then subjected to further calcination on an Al2O3 plate at 823 K for 5 h in air to remove the residual carbon-containing species. Finally, the resulting powder was collected and heated in air at 1073 K for 2 h in an Al2O3 crucible (ramp rate: 10 K min−1). Rb 2 NdNb 2 O 6 N was prepared by a conventional thermal ammonolysis procedure, similar to a method reported by Mallouk et al.14 First, a stoichiometric mixture of RbNdNb2O7 and Rb2CO3 was put on an Al2O3 boat inside a tubular furnace under a N2 stream. After purging of the residual air, NH3 was flowed at a rate of 50 mL min−1. Then, the temperature was elevated to 973 K at a ramp rate of 10 K min−1, maintaining the temperature for 10 h and finally cooling naturally. When the temperature became lower than 373 K, the NH3 flow was stopped and changed to N2 to remove NH3 gas from the tubular furnace. Characterization of Materials. The synthesized materials were characterized by X-ray diffraction (XRD; Rigaku MiniFlex600), UV− visible diffuse-reflectance spectroscopy (DRS; JASCO V-565), scanning electron microscopy combined with energy-dispersive Xray spectroscopy (SEM/EDS; JEOL JSM-IT100LA), and thermogravimetry−differential thermal analysis (TG/DTA; Shimadzu DTG60). The concentrations of hydrogen and nitrogen in the prepared materials were determined using a J-SCIENCE JM10 elemental analyzer. The Brunauer−Emmett−Teller surface area was measured
■
RESULTS AND DISCUSSION Structural Characterization of Rb2NdNb2O6N. The XRD pattern of the as-obtained material is shown in Figure 1, along with the data for the oxide precursor of RbNdNb2O7. The nitrided product does not contain the precursor oxide phase, let alone rubidium oxide or carbonate. The appearance B
DOI: 10.1021/acs.inorgchem.9b00414 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
and nitrogen in this model and did not consider the surfaceadsorbed nitrogen species because the contribution of the surface to the bulk of Rb2NdNb2O6N·H2O is negligible because of the low specific surface area (∼1 m2 g−1), as mentioned later. The final Rietveld analysis gave the following lattice parameters: a (=b) = 3.891607(4) Å and c = 14.62922(6) Å, with reasonable reliability factors Rwp = 0.028, RB = 0.055, and RF = 0.060, indicating that the nitrided product was obtained as a single phase (Figure 2 and Table Figure 1. XRD patterns of RbNdNb2O7 and the nitrided product.
of a strong peak at 2θ = 6.0° suggests that the product possesses a layered structure. Compared to the 200 reflections of RbNdNb2O7 at 2θ = 8.0°, the peak position in the nitrided product was shifted to lower 2θ angles. This strongly suggests that the layered space was expanded, most likely because of the larger amount of rubidium content in the targeted composition (Rb2NdNb2O6N) and/or more hydration of the interlayer space, which has been reported in several layered materials.14,20 The amount of hydrated H2O in the nitrided product was quantified by TG/DTA measurement. As shown in Figure S1, the decrease of the sample mass at temperatures lower than ∼700 K was assigned to the desorption of H2O from the sample.14 Elemental analysis also revealed that the nitrided product contained 0.42 wt % hydrogen, which corresponded to n ≈ 1.3, assuming that the composition of the sample was Rb2NdNb2O6N·nH2O. It was also found that the amount of hydrogen in Rb2NdNb2O6N·nH2O was greater than that in RbNdNb2O7 (0.17 wt %), which does not undergo interlayer hydration. Thus, more hydration occurs in Rb2NdNb2O6N· nH2O than in RbNdNb2O7. However, we cannot distinguish hydrated water in the interlayer from physisorbed water in both elemental analysis and TG/DTA measurements. Therefore, we deduced that the hydration number of n in Rb2NdNb2O6N·nH2O is approximately 1. The nitrogen content of the material was determined to be 2.4 wt % by elemental analysis, which was in good agreement with the ideal value of 2.2 wt % (nitrogen content in Rb2NdNb2O6N·H2O). EDS analyses showed that the atomic ratios of Rb/Nd and Nb/Nd were 2.1 and 1.7, respectively, which were close to the theoretical values of Rb/Nd = 2 and Nb/Nd = 2 in Rb2NdNb2O6N·H2O. On the basis of these results, we deduced that phase-pure Rb2NdNb2O6N·H2O was obtained. The valence state of Rb2NdNb2O6N·H2O was examined by means of XPS. Figure S2 shows Rb 3d, Nd 3d, Nb 3d, O 1s, and N 1s XPS spectra for Rb 2 NdNb 2 O 6 N·H 2 O and RbNdNb2O7. Compared to the oxide precursor, the valence states of Rb and Nd in Rb2NdNb2O6N·H2O remained largely unchanged, while that of Nb was less cationic. This result is reasonable considering coordination of the less electronegative N to the octahedral Nb center in Rb2NdNb2O6N·H2O.21 The O 1s spectrum of Rb2NdNb2O6N·H2O was very similar to that of RbNdNb2O7, but the N 1s spectrum was more complicated, giving at least two peaks at 398.2 and 395.3 eV, respectively. The former may arise from surface-adsorbed nitrogen species, while the latter is assignable to lattice N.22,23 Rietveld analysis of the SXRD data of Rb2NdNb2O6N·H2O was performed using the crystal structure of Rb1+xLaNb2O7−xNx·yH2O (x = 0.7−0.8 and y = 0.5−1.0; tetragonal, P4/mmm) reported by Mallouk et al.14 as an initial structure model. Here we assumed mixed occupancy of oxygen
Figure 2. Rietveld pattern for the SXRD data of Rb2NdNb2O6N·H2O showing observed (red line) and calculated (green line) intensities and difference (blue marks). Black line and red triangle marks indicate the background and Bragg reflection positions, respectively.
S1). Rb2NdNb2O6N·H2O is composed of double-layer [NdNb2O6N]2− perovskite slabs that are separated by two Rb cations and one H2O molecule. The refined lattice parameters of Rb2NdNb2O6N·H2O are smaller than those of Rb1+xLaNb2O7−xNx·yH2O: a (=b) = 3.934 Å and c = 14.697 Å. This is reasonable considering that the ionic radius of Nd3+ is smaller than that of La3+. Namely, the smaller Nd3+ contributes to the smaller lattice parameters of Rb2NdNb2O6N·H2O compared to Rb1+xLaNb2O7−xNx·yH2O. As listed in Table S1, the Nb−O/N bond lengths of Rb2NdNb2O6N·H2O are very similar to those of Rb1+xLaNb2O7−xNx·yH2O,14 although the Nb1−O/N3 bond [1.864(3) Å] of the former is longer than that of the latter [1.601(23) Å]. Both Rb2NdNb2O6N· H2O and Rb1+xLaNb2O7−xNx·yH2O perovskites consist of corner-sharing NbO6−xNx octahedral units, which are distorted in the axial direction. This is more obvious compared to the 3D niobium oxynitride of LaNbON2, which possesses nearly ideal NbO6−xNx octahedra.24 The as-synthesized Rb2NdNb2O6N·H2O consisted of aggregated platelike particles, reflecting the layered structure (Figure 3A). The specific surface area was determined by nitrogen adsorption measurement at 77 K to be ∼1 m2 g−1. Further electron microscopy observation was conducted by means of STEM in order to obtain atomic-resolution images.25,26 Parts B and C of Figure 3 show high-angle annular dark-field (HAADF) and annular bright-field STEM (ABF-STEM) images along the [100] direction, respectively. Because the signal intensity in HAADF imaging is approximately proportional to Z2 (where Z represents the atomic number),27 60Nd atomic columns in the HAADF images can be seen as the brightest dots. 41Nb atoms in the perovskite blocks and the interlayer 37Rb are observable as brighter dots. It is clear that the arrangement of these bright dots is in good agreement with the atomic positions of Nd, Nb, and Rb, as expected from the crystal structure of Rb2NdNb2O6N·H2O. The observed c-axis length (14.6 Å) is consistent with the lattice constant obtained by SXRD analysis. The arrangement C
DOI: 10.1021/acs.inorgchem.9b00414 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 3. Electron microscopy data for Rb2NdNb2O6N·H2O. (A) Low-resolution SEM image and (B) HAADF and (C) ABF-STEM images taken along the [100] direction. The crystal structure of Rb2NdNb2O6N·H2O is added. Color code: Rb+, pink; Nd3+, purple; Nb5+, green; O2−/N3−, orange.
of anions was visualized in the ABF images and is again consistent with that in the layered perovskite structure. The STEM observations thus confirmed generation of the layered perovskite-type structure, which is consistent with the result of SXRD analysis (Figure 2). It is thus reasonable to conclude that the nitrided product is a new layered oxynitride of Rb2NdNb2O6N·H2O. For simplicity, Rb2NdNb2O6N·H2O will be represented hereafter as Rb2NdNb2O6N. Light Absorption Properties of Rb2NdNb2O6N. The DRS spectra of RbNdNb2O7 and Rb2NdNb2O6N are shown in Figure 4. RbNdNb2O7 essentially absorbs UV light with a steep
Schottky plot. Considering that the potential of the conduction-band minimum is 0.1−0.3 V more negative than the flat-band potential in an n-type semiconductor,29 the conduction-band minima are located at −1.9 ± 0.1 V for RbNdNb2O7 and −1.7 ± 0.1 V for Rb2NdNb2O6N (vs Ag/ AgNO3). The flat-band potential (or conduction-band minimum) of Rb2NdNb2O6N is more negative than those of bulk-type 3D perovskite oxynitrides such as SrNbO2N and BaTaO2N.30,31 The proposed band structures of RbNdNb 2O 7 and Rb2NdNb2O6N are schematically illustrated in Figure 5.
Figure 4. DRS spectra of RbNdNb2O7 and Rb2NdNb2O6N. Photographs of RbNdNb2O7 and Rb2NdNb2O6N are also shown.
Figure 5. Proposed band-gap structures of RbNdNb2O7 and Rb2NdNb2O6N.
absorption edge at around 330 nm. Several absorption peaks appearing in the visible region are attributed to f−f transitions derived from Nd3+.28 On the other hand, Rb2NdNb2O6N has an absorption edge at around 500 nm, approximately 150 nm red-shifted from that of RbNdNb2O7. The band gaps of RbNdNb2O7 and Rb2NdNb2O6N were estimated to be 3.7 and 2.5 eV, respectively, from the onset wavelength of DRS. This red shift in the absorption edge should result from the N 2p state in Rb2NdNb2O6N, as observed in many oxynitride materials.4,7,9,12 It also strongly suggests that compared to RbNdNb2O7 the valence-band maximum of Rb2NdNb2O6N was elevated because of nitrogen introduction. We therefore measured the band-edge potentials of the two materials by means of Mott−Schottky analysis. This methodology has a certain reliability for estimation of the band-edge potentials of a semiconductor material.21 Figure S3 shows the Mott−Schottky plots of RbNdNb2O7 and Rb2NdNb2O6N, which indicate that both are n-type semiconductors judging from the positive slopes. Here one can determine a flat-band potential of a semiconductor by extrapolating the Mott−
Here it is clear that the valence-band maximum of Rb 2 NdNb 2 O 6 N is much more negative than that of RbNdNb2O7 because of the existence of N 2p orbitals in the valence-band formation. On the other hand, the conductionband minimum, which is likely to consist mainly of Nb 4d orbitals, remains largely unchanged even upon nitrogen introduction. We also note that, except for peaks attributed to f−f transitions, Rb2NdNb2O6N showed almost the same background level at wavelengths longer than the absorption edge (i.e., >500 nm) as the oxide precursor RbNdNb2O7. This indicates that the Nb cations in Rb 2NdNb 2 O 6 N are dominantly in the pentavalent state, as are those in RbNdNb2O7; if reduction of Nb5+ in Rb2NdNb2O6N occurs a certain extent, a rise in the background level of the DRS spectrum would be observable.9 Therefore, it is considered that although quantitative analysis remains a challenge because of the lack of a suitable technique, Rb2NdNb2O6N has a relatively low density of anionic defects, different from the already known 3D niobium oxynitrides. Nevertheless, the n-type D
DOI: 10.1021/acs.inorgchem.9b00414 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
Article
■
CONCLUSIONS Phase-pure Rb2NdNb2O6N·H2O was successfully synthesized by nitriding a physical mixture of Rb2CO3 and RbNdNb2O7 under a flow of dry NH3 at 973 K for 10 h. Structure characterization by means of SXRD, STEM, TG/DTA, and elemental analyses revealed that Rb2NdNb2O6N·H2O has a layered perovskite structure with a space group of P4/mmm. The present Rb2NdNb2O6N·H2O served as a visible-lightdriven photocatalyst for H2 evolution with the aid of a platinum cocatalyst in the presence of TEOA as an electron donor. Although the activity of Rb2NdNb2 O6 N·H2 O for H2 evolution was lower than that of the 3D niobium oxynitride CaNbO2N,9 this study presents the first example of a 2D niobium oxynitride photocatalyst showing H2 evolution activity. Besides, several unique features of Rb2NdNb2O6N· H2O have been highlighted, including the relatively low density of anionic defects and high conduction-band potential, which had not been seen in the known 3D niobium oxynitrides. The result of the present study therefore reinvigorates the further search for a new layered oxynitride material as a heterogeneous photocatalyst.
semiconducting character of Rb2NdNb2O6N, as observed in the Mott−Schottky plot, indicates that there are certain densities of anionic defects in the material. Photocatalytic Activity. On the basis of the physicochemical characterization, Rb2NdNb2O6N seems to be promising as a visible-light-driven photocatalyst. In this work, we conducted H2 evolution as a test reaction in the presence of a TEOA electron donor under visible light (λ > 400 nm).4 Platinum was deposited onto Rb2NdNb2O6N as a cocatalyst for H2 evolution by an impregnation method, followed by H2 reduction at 473 K.11 A typical time course of H2 evolution is shown in Figure 6. Stable H2 evolution was observed for 20 h.
■
ASSOCIATED CONTENT
* Supporting Information
Figure 6. Time course of H2 evolution over Pt/Rb2NdNb2O6N in a DMSO/TEOA solution containing 1 mL of water. Reaction conditions: catalyst, 100 mg; light source, 300 W xenon lamp with a L42 cutoff filter (λ > 400 nm).
S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00414.
■
Upon irradiation of light with longer wavelengths (λ > 500 nm), however, no H2 evolution was observed. The oxide precursor RbNdNb2O7 did not produce H2 under the same reaction conditions as well because of the lack of a visible-light absorption band. These results indicate that H2 evolution was driven by the light absorption of Rb2NdNb2O6N, but the f−f transitions derived from Nd3+ ions, as seen in 500−700 nm region, did not contribute to H2 evolution. Unfortunately, however, the photocatalytic performance of Rb2NdNb2O6N was lower than that of the 3D niobium oxynitride CaNbO2N.9 We deduce that the low activity arises at least, in part, from the existence of Nd 4f orbitals in the forbidden band of Rb2NdNb2O6N, as suggested by the DRS spectrum (Figure 4). Machida et al. have examined the photocatalytic activities of LnTaO4 (Ln = La, Ce, Pr, Nd, and Sm) for H2 evolution from an aqueous methanol solution under UV irradiation (λ > 300 nm).32 According to that study, it is claimed that CeTaO4 and SmTaO4 showed much lower activity compared to others because unoccupied 4f levels of Ce and Sm lying below the conduction band would act as effective traps of photogenerated electrons. Here, one may expect a similar situation in Rb2NdNb2O6N; that is, the lower photocatalytic activity would be due to Nd 4f states formed in the forbidden band of the material. Another possible reason for the low activity is the low specific surface area of Rb2NdNb2O6N (∼1 m2 g−1), which is an order of magnitude lower than those of reported 3D niobium oxynitride photocatalysts such as CaTaO2N.9 A lower specific surface area, in principle, reflects a smaller number of reaction sites, which leads to a lower photocatalytic activity.1
Additional characterization and spectroscopic data (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Keisuke Hibino: 0000-0002-0587-3287 Kotaro Fujii: 0000-0003-3309-9118 Masatomo Yashima: 0000-0001-5406-9183 Kazuhiko Maeda: 0000-0001-7245-8318 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Area “Mixed Anion” (Projects JP16H06440 and JP16H06441; JSPS). T.O. acknowledges support by a JSPS Fellowship for Young Scientists (Project JP16J10084). SXRD measurements were conducted at the BL02B2 beamline of SPring-8, Japan (Proposal 2017B1265).
■
REFERENCES
(1) Kudo, A.; Miseki, Y. Heterogeneous Photocatalyst Materials for Water Splitting. Chem. Soc. Rev. 2009, 38, 253−278. (2) Zhang, G.; Liu, G.; Wang, L.; Irvine, J. T. Inorganic Perovskite Photocatalysts for Solar Energy Utilization. Chem. Soc. Rev. 2016, 45, 5951−5984. (3) Kudo, A.; Tanaka, A.; Domen, K.; Maruya, K.; Aika, K.; Onishi, T. Photocatalytic Decomposition of Water over Nickel OxidePotassium Niobate (NiO-K4Nb6O17) Catalyst. J. Catal. 1988, 111, 67−76. E
DOI: 10.1021/acs.inorgchem.9b00414 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
(21) Chun, W.-J.; Ishikawa, A.; Fujisawa, H.; Takata, T.; Kondo, J. N.; Hara, M.; Kawai, M.; Matsumoto, Y.; Domen, K. Conduction and Valence Band Positions of Ta2O5, TaON, and Ta3N5 by UPS and Electrochemical Methods. J. Phys. Chem. B 2003, 107, 1798−1803. (22) Diwald, O.; Thompson, T. L.; Zubkov, D.; Walck, S. D.; Yates, J. T. Photochemical Activity of Nitrogen-Doped Rutile TiO2(110) in Visible Light. J. Phys. Chem. B 2004, 108, 6004−6008. (23) Hojamberdiev, M.; Bekheet, M. F.; Zahedi, E.; Wagata, H.; Vequizo, J. J. M.; Yamakata, A.; Yubuta, K.; Gurlo, A.; Domen, K.; Teshima, K. The Contrasting Effect of the Ta/Nb Ratio in (111)Layered B-Site Deficient Hexagonal Perovskite Ba5Nb4−xTaxO15Crystals on Visible-Light-Induced Photocatalytic Water Oxidation Activity of their Oxynitride Derivatives. Dalton Trans. 2016, 45, 12559−12568. (24) Logvinovich, D.; Ebbinghaus, S. G.; Reller, A.; Marozau, I.; Ferri, D.; Weidenkaff, A. Synthesis, Crystal Structure and Optical Properties of LaNbON2. Z. Anorg. Allg. Chem. 2010, 636, 905−912. (25) Kimoto, K.; Asaka, T.; Yu, X.; Nagai, T.; Matsui, Y.; Ishizuka, K. Local Crystal Structure Analysis with Several Picometer Precision Using Scanning Transmission Electron Microscopy. Ultramicroscopy 2010, 110, 778−782. (26) Findlay, S. D.; Shibata, N.; Sawada, H.; Okunishi, E.; Kondo, Y.; Ikuhara, Y. Dynamics of Annular Bright Field Imaging in Scanning Transmission Electron Microscopy. Ultramicroscopy 2010, 110, 903− 923. (27) Pennycook, S. J.; Jesson, D. E. High-Resolution Z-contrast Imaging of Crystals. Ultramicroscopy 1991, 37, 14−38. (28) Machida, M.; Yabunaka, J.; Kijima, T. Synthesis and Photocatalytic Property of Layered Perovskite Tantalates, RbLnTa2O7 (Ln = La, Pr, Nd, and Sm). Chem. Mater. 2000, 12, 812−817. (29) Matsumoto, Y. Energy Positions of Oxide Semiconductors and Photocatalysis with Iron Complex Oxides. J. Solid State Chem. 1996, 126, 227−234. (30) Maeda, K.; Higashi, M.; Siritanaratkul, B.; Abe, R.; Domen, K. SrNbO2N as a Water-Splitting Photoanode with a Wide Visible-Light Absorption Band. J. Am. Chem. Soc. 2011, 133, 12334−12337. (31) Seo, J.; Nishiyama, H.; Yamada, T.; Domen, K. Visible-LightResponsive Photoanodes for Highly Active, Stable Water Oxidation. Angew. Chem., Int. Ed. 2018, 57, 8396−8415. (32) Machida, M.; Murakami, S.; Kijima, T.; Matsushima, S.; Arai, M. Photocatalytic Property and Electronic Structure of Lanthanide Tantalates, LnTaO4 (Ln = La, Ce, Pr, Nd, and Sm). J. Phys. Chem. B 2001, 105, 3289−3294.
(4) Maeda, K.; Domen, K. New Non-Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem. C 2007, 111, 7851−7861. (5) Nakada, A.; Nishioka, S.; Vequizo, J. J.M.; Muraoka, K.; Kanazawa, T.; Yamakata, A.; Nozawa, S.; Kumagai, H.; Adachi, S.; Ishitani, O.; Maeda, K. Solar-Driven Z-scheme Water Splitting Using Tantalum/Nitrogen Co-doped Rutile Titania Nanorod as an Oxygen Evolution Photocatalyst. J. Mater. Chem. A 2017, 5, 11710−11719. (6) Miyoshi, A.; Vequizo, J. J. M.; Nishioka, S.; Kato, Y.; Yamamoto, A.; Yamashita, S.; Yokoi, T.; Iwase, A.; Nozawa, S.; Yamakata, A.; Yoshida, T.; Kimoto, K.; Kudo, A.; Maeda, K. Nitrogen/FluorineCodoped Rutile Titania as a Stable Oxygen-Evolution Photocatalyst for Solar-Driven Z-Scheme Water Splitting. Sustainable Energy Fuels. 2018, 2, 2025−2035. (7) Oshima, T.; Ichibha, T.; Qin, K. S.; Muraoka, K.; Vequizo, J. J. M.; Hibino, K.; Kuriki, R.; Yamashita, S.; Hongo, K.; Uchiyama, T.; Fujii, K.; Lu, D.; Maezono, R.; Yamakata, A.; Kato, H.; Kimoto, K.; Yashima, M.; Uchimoto, Y.; Kakihana, M.; Ishitani, O.; Kageyama, H.; Maeda, K. Undoped Layered Perovskite Oxynitride Li2LaTa2O6N for Photocatalytic CO2 Reduction with Visible Light. Angew. Chem., Int. Ed. 2018, 57, 8154−8158. (8) Seo, J.; Moriya, Y.; Kodera, M.; Hisatomi, T.; Minegishi, T.; Katayama, M.; Domen, K. Photoelectrochemical Water Splitting on Particulate ANbO2N (A = Ba, Sr) Photoanodes Prepared from Perovskite-Type ANbO3. Chem. Mater. 2016, 28, 6869−6876. (9) Siritanaratkul, B.; Maeda, K.; Hisatomi, T.; Domen, K. Synthesis and Photocatalytic Activity of Perovskite Niobium Oxynitrides with Wide Visible-Light Absorption Bands. ChemSusChem 2011, 4, 74−78. (10) Hisatomi, T.; Katayama, C.; Moriya, Y.; Minegishi, T.; Katayama, M.; Nishiyama, H.; Yamada, T.; Domen, K. Photocatalytic Oxygen Evolution Using BaNbO2N Modified with Cobalt Oxide under Photoexcitation up to 740 nm. Energy Environ. Sci. 2013, 6, 3595−3599. (11) Maeda, K.; Higashi, M.; Lu, D.; Abe, R.; Domen, K. Efficient Nonsacrificial Water Splitting through Two-Step Photoexcitation by Visible Light Using a Modified Oxynitride as a Hydrogen Evolution Photocatalyst. J. Am. Chem. Soc. 2010, 132, 5858−5868. (12) Sasaki, R.; Maeda, K.; Kako, Y.; Domen, K. Preparation of Calcium Tantalum Oxynitride from Layered Oxide Precursors to Improve Photocatalytic Activity for Hydrogen Evolution under Visible Light. Appl. Catal., B 2012, 128, 72−76. (13) Kaga, M.; Kurachi, H.; Asaka, T.; Yue, B.; Ye, J.; Fukuda, K. Crystal Structure of Layered Perovskite Compound, Li2LaTa2O6N. Powder Diffr. 2011, 26, 4−8. (14) Schottenfeld, J. A.; Benesi, A. J.; Stephens, P. W.; Chen, G.; Eklund, P. C.; Mallouk, T. E. Structural Analysis and Characterization of Layer Perovskite Oxynitrides Made from Dion−Jacobson Oxide Precursors. J. Solid State Chem. 2005, 178, 2313−2321. (15) Kakihana, M.; Domen, K. The Synthesis of Photocatalysts Using the Polymerizable-Complex Method. MRS Bull. 2000, 25, 27− 31. (16) Kawaguchi, S.; Takemoto, M.; Osaka, K.; Nishibori, E.; Moriyoshi, C.; Kubota, Y.; Kuroiwa, Y.; Sugimoto, K. HighThroughput Powder Diffraction Measurement System Consisting of Multiple MYTHEN Detectors at Beamline BL02B2 of SPring-8. Rev. Sci. Instrum. 2017, 88, 085111. (17) Rodríguez-Carvajal, J. Recent Advances in Magnetic Structure Determination by Neutron Powder Diffraction. Phys. B 1993, 192, 55−69. (18) Rodríguez-Carvajal, J. Recent Developments of the Program FULLPROF. Comm. Powder Diffr. Newsl. 2001, 26, 12−19. (19) Oishi, R.; Yonemura, M.; Nishimaki, Y.; Torii, S.; Hoshikawa, A.; Ishigaki, T.; Morishima, K.; Mori, K.; Kamiyama, T. Rietveld Analysis Software for J-PARC. Nucl. Instrum. Methods Phys. Res., Sect. A 2009, 600, 94−96. (20) Schaak, R. E.; Mallouk, T. E. KLnTiO4 (Ln=La, Nd, Sm, Eu, Gd, Dy): A New Series of Ruddlesden−Popper Pases Synthesized by Ion-Exchange of HLnTiO4. J. Solid State Chem. 2001, 161, 225−232. F
DOI: 10.1021/acs.inorgchem.9b00414 Inorg. Chem. XXXX, XXX, XXX−XXX
