Article pubs.acs.org/IC
Cite This: Inorg. Chem. 2019, 58, 2183−2190
Layered Bismuth Oxyfluoride Nitrates Revealing Large SecondHarmonic Generation and Photocatalytic Properties Eun Jeong Cho,† Seung-Jin Oh,† Hongil Jo,† Junsu Lee,‡ Tae-Soo You,‡ and Kang Min Ok*,† †
Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
‡
Inorg. Chem. 2019.58:2183-2190. Downloaded from pubs.acs.org by STOCKHOLM UNIV on 04/28/19. For personal use only.
S Supporting Information *
ABSTRACT: Two novel bismuth oxyfluoride nitrates, Bi2OF3(NO3) and Bi6O6F5(NO3), have been synthesized via hydrothermal reactions. Whereas Bi2OF3(NO3) crystallizes in the centrosymmetric (CS) hexagonal space group, P63/m, Bi6O6F5(NO3) crystallizes in the polar noncentrosymmetric (NCS) trigonal space group, R3. The backbones of the title compounds reveal double layered structures composed of asymmetric BiF3(O/F)3 or BiO3F2 polyhedra and NO3 trigonal planar groups. The diffuse reflectance spectra indicate that Bi2OF3(NO3) and Bi6O6F5(NO3) contain wide band gaps of 3.5 and 4.0 eV, respectively. Powder second-harmonic generation (SHG) measurements suggest that NCS Bi6O6F5(NO3) is Type-I phase-matchable and has a large SHG response of ca. 3 times that of KH2PO4 (KDP). Electron localization function (ELF) analysis indicates that the large SHG efficiency of Bi6O6F5(NO3) is attributed to the synergistic effect of the alignment of NO3− trigonal planar groups and strong interactions between highly polarizable lone pair electrons on Bi3+ and π-delocalized electrons in NO3− groups. Bi2OF3(NO3) also exhibits a very good photocatalytic degradation efficiency of Rhodamine B (RhB) under the UV light irradiation.
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INTRODUCTION Functional materials with macroscopic noncentrosymmetric (NCS) crystal structures consisting of asymmetric building blocks have drawn huge attentions attributed to their various structure-driven interesting characteristics including piezoelectricity, (nonlinear) optical property, ferroelectricity, and pyroelectricity.1−10 Owing to their various applications such as chiral catalysts, motion sensors, memories, lithographic devices, lasers, and alarms, discovering superior performing crystalline materials with NCS structures is an ongoing challenge.11−14 Synthetically, novel compounds with overall NCS structures have been quite successfully prepared by combining several so-called NCS chromophores such as πdelocalized anionic groups,8,15−20 highly polarizable d10 cations,21−23 and two families of second-order Jahn−Teller (SOJT) distortive cations.24−30 In order to obtain novel compounds with NCS structures more systematically, however, a careful alignment of the aforementioned asymmetric groups should be very important. In fact, it is also critical to understand factors strongly affecting the framework structures that are controlling the centricity.31 In this work, we have combined an asymmetric lone pair cation, Bi3+ and a πdelocalized anionic group, NO3− along with F− anion in a single compound to produce novel NLO materials revealing wide band gap and strong second harmonic generation (SHG) efficiency. By doing so, we have successfully synthesized two bismuth oxyfluoride nitrates, Bi2OF3(NO3) and Bi6O6F5(NO3) with double layered structures. Specifically, our synthetic © 2019 American Chemical Society
strategy was to mimic the representative layered NLO material, KBe2BO3F2 (KBBF), yet to replace the toxic cation, Be2+ with a lone pair cation, Bi3+. Quite a few bismuth nitrate materials revealing various structural features and interesting optical and catalytic properties have been reported thus far.32−46 Herein, we present synthesis, structure determination, SHG properties, electronic structure calculations, and photocatalytic activity of the newly discovered bismuth oxyfluoride nitrates.
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EXPERIMENTAL SECTION
Bi(NO3)3·5H2O (Alfa Aesar, 98%), KF (Aldrich, 99+%), H3BO3 (Aldrich, 99.5+%), and HBF4 solution (Alfa Aesar, 48%) were used as reagents. Single crystals of the title compounds were synthesized under hydrothermal conditions. For Bi2OF3(NO3), a 0.970 g (2.00 mmol) portion of Bi(NO3)3·5H2O was mixed with 0.124 g (2.00 mmol) of H3BO3, and 2 mL of HBF4 solution. For Bi6O6F5(NO3), a 0.728 g (1.50 mmol) portion of Bi(NO3)3·5H2O was combined with 0.109 g (1.88 mmol) of KF and 14 mL of deionized water. Each reaction mixture was transferred to 23 mL Teflon-lined autoclaves. After sealing, the reactors were heated slowly to 200 °C, dwelled at the temperature for 72 h, and gradually cooled to room temperature at a rate of 6 °C h−1 for Bi2OF3(NO3) and 60 °C h−1 for Bi6O6F5(NO3). The products were isolated through vacuum filtration, washed with water, and dried in air for 1 d. Colorless hexagonal prism crystals of Bi2OF3(NO3) and colorless hexagonal plate crystals of Received: December 1, 2018 Published: January 16, 2019 2183
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
Article
Inorganic Chemistry
Powder X-ray diffraction (PXRD) measurements for the reported materials were taken by a Bruker New D8-Advance instrument at room temperature with 40 kV and 40 mA using Cu Kα radiation (λ = 1.5418 Å). The measured PXRD patterns matched well with those of the calculated obtained from the SCXRD analyses (Figures S1 and S2). Thermogravimetric analysis (TGA) was performed on a TGA-N 1000 (SCINCO) thermal analyzer. The samples were heated in platinum crucibles from room temperature to 900 °C at a rate of 10 °C min−1 under flowing argon. Infrared (IR) spectra were recorded using a Bruker TENSOR 27 ATR-FTIR spectrometer in the range from 400 to 4000 cm−1 at room temperature. UV−vis diffuse reflectance spectra were measured in the range of 200−2500 nm on a Varian Cary 500 scan UV−vis−near-IR spectrometer at room temperature. Powder second harmonic generation (SHG) measurements were performed with a modified Kurtz-NLO system using a DAWA Qswitched Nd:YAG solid-state laser (1064 nm radiation).48 The polycrystalline samples were grounded, sieved to specific particle size ranges, and packed into capillary tubes. To properly compare the SHG efficiency, polycrystalline KH2PO4 (KDP) was also sieved into the same particle size ranges and used as reference materials. The photocatalytic activity of Bi2OF3(NO3) was investigated by monitoring the photodegradation of Rhodamine B (RhB). A 50 mg portion of Bi2OF3(NO3) and 100 mL of an aqueous suspension of RhB (15 ppm) were put into a 100 mL glass beaker. The suspension was then magnetically stirred for 4 h in a dark condition to establish an adsorption−desorption equilibrium. After that, the reaction mixture was irradiated by a DXP300 Xe lamp (DY TECH, 300 W). The light intensity was over 200 mW/cm2 when the reactor was placed 10 cm away from the Xe lamp. About 3 mL of the reaction solution was taken at every 10 min and centrifuged to remove the photocatalyst at 6000 rpm for 15 min. The concentration of RhB in
Bi6O6F5(NO3) were obtained in 37.6% and 68.4% yields, respectively, based on Bi(NO3)3·5H2O. Single crystal X-ray diffraction (SCXRD) data for Bi2OF3(NO3) and Bi6O6F5(NO3) were collected on a Bruker SMART BREEZE diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature on a 1 K CCD area detector. A hexagonal prism crystal of Bi2OF3(NO3) (0.11 × 0.14 × 0.31 mm3) and a hexagonal plate crystal of Bi6O6F5(NO3) (0.03 × 0.06 × 0.18 mm3) were mounted on glass fibers for data collection. The diffraction data were collected through the narrow-frame method with an exposure time of 10 s frame−1 and scan widths of 0.30° in ω. The crystal structures of the title compounds were determined and refined using SHELXS-97 and SHELXL-97, respectively.47 Crystallographic information for Bi2OF3(NO3) and Bi6O6F5(NO3) is summarized in Table 1.
Table 1. Crystallographic data for Bi2OF3(NO3) and Bi6O6F5(NO3) formula
[Bi2OF3(NO3)]3
[Bi6O6F5(NO3)]3
fw space group a = b (Å) c (Å) V (Å3) Z T (K) λ (Å) ρcalcd (g cm−3) Flack parameter R(F)a Rw(Fo2)b
1658.91 P63/m (No. 176) 7.2066(2) 17.5313(3) 788.51(5) 2 298.0(2) 0.71073 6.987 N/A 0.0576 0.1126
4520.67 R3 (No. 146) 7.2615(10) 23.785(9) 1086.1(6) 1 298.0(2) 0.71073 6.912 0.46(9) 0.0446 0.1983
R(F) = ||Fo| − |Fc||/Σ|Fo|. bRw(Fo2) = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2.
a
Figure 1. Ball-and-stick models of Bi2OF3(NO3) (orange, Bi; blue, N; red, O; green, F; yellow, O/F). (a) Corner-sharing of BiF3(O/F)3 polyhedra produces Bi3(F/O)6F7 trimers. Further corner-sharing of Bi3(F/O)6F7 trimers results in an infinite layer in the ab-plane. (b) Each layer is then further linked via O/F(4) along the approximate c-direction and forms a double-layered structure. Note lone pairs on Bi3+ cations point toward approximate [001] and [00−1] directions. (c) The layered structure is completed by the introduction of NO3− groups into the interlayer space of Bi2OF3(NO3). Note the NO3− groups are almost perpendicularly residing to the layers. 2184
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
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Inorganic Chemistry
Figure 2. Ball-and-stick representations of Bi6O6F5(NO3) (orange, Bi; blue, N; red, O; green, F). (a) Corner-sharing of Bi(1)O3F2 polyhedron results in Bi3O6F4 trimers. Further corner-sharing of Bi3O6F4 trimers form a layer in the ab-plane. Note 3-MRs and 6-MRs exist within the layer. (b) Further connection of the layers through O(1) along the approximate c-direction results in a double-layered structure. (c) The integrated layered structure of Bi6O6F5(NO3) is completed by adding NO3− groups and F− anions to the interlayer area. Note that F(1) and F(2) effectively inhibit the direct interactions between Bi3+ cations and oxygen atoms in NO3− groups. The π-delocalized electrons located in the above and below of NO3− groups interact with lone pairs on Bi3+ cations. (d) All of the NO3− trigonal planar groups are aligned in parallel with the layers. obtained using 270 and 451 irreducible k-points in the Brillouin zone, respectively, for Bi2OF3(NO3)and Bi6O6F5(NO3).
solution was analyzed using a SCINCO S-3100 UV−vis spectrophotometer. To understand overall electronic structures and the interactions between paired-electrons densities of Bi3+ and NO3− moieties in two title compounds, Bi2OF3(NO3) and Bi6O6F5(NO3), we conducted a series of theoretical calculations by Stuttgart TB-LMTO47 program with the atomic sphere approximation (ASA) method.49−53 Due to the mixed occupation of O and F in Bi2OF3(NO3) and the partial occupation of two F sites in Bi6O6F5(NO3), we exploited two hypothetical structural models for these series of calculations. The local density approximation was applied for exchange and correlation.49−53 A scalar relativistic approximation was taken to treat all relativistic effects, except spin−orbit coupling. In the ASA method, space was filled with overlapping Wigner-Seitz (WS) atomic spheres.49−53 The symmetry of the potential inside each WS sphere was considered spherical, and a combined correction was used to take into account the overlapping part.54 The radii of WS sphere were obtained by requiring the overlapping potential be the best possible approximation to the full potential and were determined by an automatic procedure.54 This overlap should not be too large because the error in kinetic energy introduced by the combined correction was proportional to the fourth power of the relative sphere overlap. The used WS radii are listed as follows: Bi = 1.461−1.487 Å, F = 0.958− 1.315 Å, O = 0.656−0.683 Å, and N = 0.680 Å for Bi2OF3(NO3); and Bi = 1.392−1.410 Å, O = 0.698−0.952 Å, F = 1.257−1.948 Å and N = 0.711 Å for Bi6O6F5(NO3). The basis sets included 6s, 6p, 6d, and 5f orbitals for Bi; 2s, 3s, 2p, and 3d orbitals for O; 3s, 2p, and 3d orbitals for F; 2s, 2p, and 3d for N for the both models. The Bi 6d and 5f, O 3s and 3d, F 3s and 3d, and N 3d orbitals were treated by the Löwdin downfolding technique.55 The k-space integration was conducted by the tetrahedron method,56 and the self-consistent charge density was
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RESULTS AND DISCUSSION Structures. Bi2OF3(NO3). The new bismuth oxyfluoride nitrate, Bi2OF3(NO3) with the highly symmetric hexagonal space group, P63/m (No. 176), reveals a double layered structure composed of unsymmetrical BiF3(O/F)3 polyhedra and NO3 trigonal planar groups (Figure S3). Specifically, the unique cation, Bi(1)3+ in an asymmetric unit is in an 6coordinate environment with fluoride or oxide ligands. It should be pointed out that F(4) and O(4) are statistically disordered in the crystallographic 12i site with a 50:50 occupancy. The observed bond lengths for Bi−F and Bi−O/F range from 2.398(7)−2.555(3) Å and 2.229(10)−2.353(11) Å, respectively. As seen in Figure S3, the local coordination environment of BiF3(O/F)3 polyhedron is very distorted due to the lone pair. Each BiF3(O/F)3 polyhedron shares its corners via F(3) and O/F(4) and produces Bi3(F/O)6F7 trimers (Figure 1a). Here, F(3)− anion, in fact, caps three Bi(1)3+ cations along the c-direction. Each Bi3(F/O)6F7 trimer shares its corners through F(1) and F(2), which results in an infinite layer in the ab-plane. Each layer is then further linked via O/F(4) along the approximate c-direction, which forms an interesting double-layered structure (Figure 1b). As seen in the inset of Figure 1b, lone pairs on Bi3+ cations direct to approximate c- and−c-directions. Therefore, the overall polarization occurring from the asymmetric local BiF3(O/F)3 2185
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
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bending and stretching vibrations, respectively, for nitrates.59−62 The absorption data were calculated after obtaining the UV−vis diffuse reflectance spectra for both reported materials (Figure 3).63,64 The absorption spectra suggest that both
groups cancels attributable to their antiparallel alignment. Finally, the layered structure is completed by the introduction of NO3− groups into the interlayer space of Bi2OF3(NO3) (Figure 1c). The NO3− groups are almost perpendicularly residing to the layers, which should be attributed to the substantial interactions between Bi(1)3+ and O(1) in the nitrate groups, where the observed Bi(1)−O(1) contact distances are 2.867(11)−3.169(15) Å. Thus, the charge balance of {2[Bi(1)3+F3/3(O0.5/F0.5)3/3]0.5+}+ cationic layer is retained by the NO3− located in the interlayer space. Bond valence sum calculations57,58 for Bi3+ and N5+ result in values of 2.7 and 5.1, respectively. Bi6O6F5(NO3). Another new layered bismuth oxyfluoride nitrate, i.e., Bi6O6F5(NO3), is crystallizing in the polar group, R3. The backbone of the layer in Bi6O6F5(NO3) consists of asymmetric BiO3F2 polyhedra, NO3 trigonal planar groups, and isolated F− anions (Figure S4). Within an asymmetric unit, two unique heavy atom cations, namely, Bi(1)3+ and Bi(2)3+, reveal 5-coordinate moiety with oxide and fluoride ligands, and form BiO3F2 polyhedra. The observed Bi−F bond distances are 2.433(2)−2.53(2) Å, whereas those of Bi−O are 2.13(3)− 2.22(3) Å. Similar to those in Bi2OF3(NO3), both of BiO3F2 polyhedra containing lone pairs in Bi6O6F5(NO3) are highly unsymmetrical. The corner-sharing of Bi(1)O3F2 polyhedron through an oxide ligand results in Bi3O6F4 trimers (Figure 2a). Similar to that of Bi2OF3(NO3), fluoride anions cap the Bi3+ cations in Bi3O6F4 trimers along the c-direction. The Bi3O6F4 trimers share the vertices via fluorides and form a layer in the ab-plane (Figure 2a). Both three- and six-membered rings exist within the layer. Further connection of the layers through oxide ligand [O(1)] along the approximate c-direction results in a double-layered structure (Figure 2b). The integrated layered structure of Bi6O6F5(NO3) is obtained by adding NO3− groups and F− anions to the interlayer area (Figure 2c). Interestingly, the NO3− units are aligned in parallel with the layers (Figure 2d), which is responsible for the polar structure of Bi6O6F5(NO3). The parallel alignment of NO3− has been achieved by the incorporation of isolated F− anions [F(1) and F(2)] in the interlayer space. As seen in the inset of Figure 2c, F(1) and F(2) effectively inhibit the direct interactions between Bi3+ cations and oxygen atoms in NO3− groups. Instead, the π-delocalized electrons located in the above and below of NO3− groups rather reveal significant interactions with lone pairs on Bi3+ cations that are pointing toward approximate [001] and [00−1] directions (inset of Figure 2c). The framework structure of Bi6O6F5(NO3) may be represented as a cationic layer of {3[2(Bi3+O3/3F2/3)0.333+]0.666+}2+ with the charge balance maintained by the NO3− and F− anions located in the interlayer space. Bond valence sum calculation results57,58 for Bi3+ (2.8−2.9) and N5+ (4.6) are consistent with the respective oxidation states. TGA. The TGA diagrams indicate that the frameworks of Bi2OF3(NO3) and Bi6O6F5(NO3) are maintained to ca. 300 and 400 °C, respectively. Both materials decomposed to mixtures of BiOF and Bi2O3 by losing fluorides and nitrates upon further heating, which was verified by the PXRD patterns obtained at different temperatures (Figure S5). IR and UV−Vis Diffuse Reflectance Spectroscopy. IR spectra exhibited Bi−O or Bi−F, and N−O vibrations in the title materials. While the peaks occurring at 415−558 cm−1 can be assigned to Bi−O/F vibrations, those occurring at 812−874 cm−1 and 1311−1384 cm−1 are due to the peaks for N−O
Figure 3. UV−vis diffuse reflectance spectra for Bi2OF3(NO3) and Bi6O6F5(NO3). Bi2OF3(NO3) and Bi6O6F5(NO3) have broad transparency from the mid-IR to the near UV region and reveal wide band gaps of 3.5 and 4.0 eV, respectively. The abrupt changes of absorbance found at ca. 800 and 2000 nm are due to the replacement of appropriate lamps.
Bi2OF3(NO3) and Bi6O6F5(NO3) have broad transparency from the near UV to mid-IR region. In addition, the spectra (inset of Figure 3) show that Bi2OF3(NO3) and Bi6O6F5(NO3) contain wide band gaps of 3.5 and 4.0 eV, respectively. The observed larger gaps for the reported materials compared to those of normal oxides with lower gaps should be due to the introduction of fluoride anions possessing a very large electronegativity. SHG. Polycrystalline NCS Bi6O6F5(NO3) in the 45−63 μm shows a large SHG response of ca. 3 × KH2PO4 (KDP) as a nitrate NLO material. On the basis of the d36 coefficient for KDP, the derived deff coefficient for Bi6O6F5(NO3) should be ca. 1.2 pm/V.65 In addition, the SHG signal acquired from the sieved polycrystalline samples of Bi6O6F5(NO3) with distinct particle size indicates the material is phase-matchable (type-I, Figure 4). Local dipole moment calculations have been also carried out to understand the observed SHG properties of
Figure 4. Plots of SHG intensity as a function of particle size for Bi6O6F5(NO3) and KDP. Note that the curves are drawn to guide the eye. 2186
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
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interaction than Bi−O (Figure 5c). In addition, the bottom section of the conduction band just above EF is the antibonding state. ELF analysis for Bi6O6F5(NO3) is also carefully conducted to examine the interatomic interactions between Bi3+ and NO3− moieties, and the sliced-plane of ELF along the O(3)− Bi(2) bond direction is plotted in Figure 6. As we previously
Bi6O6F5(NO3) further. Dipole moments of BiO3F2 polyhedra are calculated to be ca. 8.6−10.2 D (Debyes). Although substantial local dipole moments are observed, net polarization from BiO3F2 polyhedra is dramatically reduced owing to the antiparallel alignment of the asymmetric units. However, the observed large SHG of Bi6O6F5(NO3) should be due to the parallel alignment of NO3− trigonal planes as well as the interactions between lone pairs on polarizable Bi3+ cations and π-delocalized electrons on NO3− groups. Electronic Structure Calculations. To study the pairedelectron density distributions around Bi3+ and NO3− moieties as well as the overall electronic structures, electron localization functions (ELF) and the density of states (DOS) were thoroughly analyzed. Due to the mixed occupation of O and F (Wyckof f 12i) in Bi2OF3(NO3), the hypothetical model structure with a subgroup Pm (No. 6) was exploited rather than the refined P63/m (No. 176) to allow alternating arrangements of O and F along all three axes directions. In Bi6O6F5(NO3), two F sites (both Wyckof f 3a) show only 50% of occupations. Thus, we used the model structure with the doubled a and b lattice parameters to arrange F and vacancy alternately in a unit cell. The total and partial DOS (TDOS and PDOS) curves for Bi2OF3(NO3) are shown in Figure 5. A
Figure 6. Sliced-plane of ELF for Bi6O6F5(NO3) along the O(3)− Bi(2) bond direction. Diagram is depicted as a filled contour map, and overall crystal structure is overlaid on top of the ELF diagram. Color scheme ranges from blue to red (0−0.8 e−/Å3), and values higher than 0.5 represent the area exceeding free-electron ELF value. Unit cell is outlined in white color, and labels for the selected atoms are also provided.
mentioned based upon the local coordination geometry around Bi3+ and NO3−, the slightly distorted lone pairs of electrons on Bi3+ are nicely observed, and the nearby O atoms on the NO3− moieties also show the large localized electron densities toward Bi3+ in this ELF diagram. This type of pairedelectrons distributions and interactions eventually represent a strong influence for the observed SHG values of Bi6O6F5(NO3). Photocatalytic Reactions. Since Bi2OF3(NO3) reveals a layered structure consisting of highly polarizable Bi3+ cations, the photocatalytic property was investigated using Rhodamine B (RhB). Photolysis reactions of RhB in the presence of TiO2 (P25) and in the absence of any photocatalyst (Blank) were also tested under the same conditions as references. As seen in the absorption spectra of RhB with Bi2OF3(NO3) as a photocatalyst, the absorption maximum of RhB gradually decrease as the catalytic reactions occur (Figure 7a). The plots of the RhB concentration (C/C0) versus the irradiation time for each photocatalyst indicate while no significant change is observed from the blank test in the absence of any catalyst, complete photocatalytic degradation of RhB occurs in 60 min (Figure 7b). The degradation efficiency (DE) measured at 40
Figure 5. (a) Total DOS and (b) two partial DOS curves of p-states of O(4) and O(1) and (c) O(2) of Bi2OF3(NO3) are displayed. EF (dashed vertical line) is the energy reference (0 eV). Color codes: TDOS, bold black outline; Bi PDOS, orange region; O PDOS, red region; F PDOS, green region; and N PDOS, blue region.).
strong overall orbital mixing is observed over the entire energy window. Interestingly, two different types of O atoms show distinctive p-orbital distributions below the Fermi level (EF). First, the O(4) atom bridging nearby Bi atoms shows its major contribution of p-orbitals just below EF forming the top section of the valence band (Figure 5b). On the other hand, two O atoms, i.e., O(1) and O(2), consisting of the NO3− moiety display their major contributions of p-orbitals between −6 and −2 eV, indicating the relatively stronger N−O interatomic 2187
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
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Article
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03343. Calculated and observed X-ray diffraction patterns, ORTEP drawings, TGA diagrams, and IR spectra for Bi2OF3(NO3) and Bi6O6F5(NO3) (PDF) Accession Codes
CCDC 1881057 and 1881058 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*Tel: +82-2-820-5197. Fax: +82-2-825-4736. E-mail: kmok@ cau.ac.kr. ORCID
Hongil Jo: 0000-0002-0627-4921 Tae-Soo You: 0000-0001-9710-2166 Kang Min Ok: 0000-0002-7195-9089 Notes
The authors declare no competing financial interest.
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Figure 7. (a) UV−vis spectral changes of RhB over Bi2OF3(NO3) as a function of illumination time and (b) photocatalytic degradation of RhB (15 ppm) over Bi2OF3(NO3) and TiO2 (P25) under UV light irradiations. Note the decomposition of RhB solution with the Bi2OF3(NO3) can be clearly confirmed by the color change of the solution in time.
ACKNOWLEDGMENTS This research was supported by the Chung-Ang University Graduate Research Scholarship in 2017. This research was also supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (Grants 2014M3A9B8023478 and 2018R1A5A1025208).
min for Bi2OF3(NO3) reaches to 90.5%, which is almost close to that of the representative photodegradation catalyst, TiO2 (P25, 98.3%). The decomposition of RhB solution with the Bi2OF3(NO3) can be clearly confirmed by the color change of the solution in time (inset of Figure 7b).
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REFERENCES
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CONCLUSIONS Crystals of two novel bismuth oxyfluoride nitrates, Bi2OF3(NO3) and Bi6O6F5(NO3), have been grown successfully in phase pure forms by hydrothermal reactions. Both of the title compounds revealed similar double layered structures consisting of unsymmetrical basic building units. While Bi2OF3(NO3) containing the perpendicularly aligned interlayer NO3− groups through the Bi−O long-range interactions showed a CS structure, Bi6O6F5(NO3) with the parallel alignment of NO 3 − trigonal planes achieved by the incorporation of isolated F− anions in the interlayer space exhibited a polar NCS structure. The title compounds were quite thermally stable and had broad transparency from the mid-IR to the near UV region. Powder SHG measurements on the NCS Bi6O6F5(NO3) indicated that the material was Type-I phase-matchable and had a large SHG response of ca. 3 times that of KDP. The strong SHG efficiency found from the nitrate material was attributable to the synergistic effect of the parallel alignment of π-delocalized NO3− anions as well as their interactions with the polarizable Bi3+ cations. Bi2OF3(NO3) with highly polarizable Bi3+ cations also revealed a very good photocatalytic activity on the degradation of Rhodamine B (RhB) under UV light. 2188
DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
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DOI: 10.1021/acs.inorgchem.8b03343 Inorg. Chem. 2019, 58, 2183−2190
