English

• 0.   Introduction

  Hydrogen energy is considered one of the most attractive clean energy sources due to its high energy capacity and environmental friendliness^[1-3], but the development of stable hydrolysis catalysts for visible - light reactions is currently a huge technical challenge for the scientific community^[4-5]. To make better use of the solar spectrum, mixed anionic compounds, such as oxynitrides^[6], oxysulphides^[7], and oxyhalides^[8], are promising candidates because their band gaps are narrower than those of typical oxides. Recently, a series of Aurivillius - like layered bismuth oxyhalides with [Bi₂O₂]²⁺ layers have been found to have a high potential for visible - light water splitting. They usually have a high valence band maximum due to their highly dispersed O2p orbitals, which results in a very narrow band gap and also is structurally stable for photocatalytic water separation^{[5, 9-10]}. The structure of the Aurivillius compound is composed of the fluorite - like layers [Bi₂O₂]²⁺ interspersed between perovskite - like layers [A_n-1B_nO_3n+1]^2- (A=Na⁺, K⁺, Sr²⁺, Bi³⁺, Ba²⁺, etc. and B=Ti⁴⁺, Fe³⁺, Nb⁵⁺, W⁶⁺, etc.), where n is the layer number of the perovskite-like layers^[11-12]. In this structure, the [A_n-1B_nO_3n+1]^2- layer is sandwiched between the [Bi₂O₂]²⁺ layers, which will allow rapid separation of photoinduced electrons from holes, resulting in highly quantum -efficient photocatalysis^[13-14]. And that layered metal oxide semiconductor particles produce hydrogen more readily than other compounds, due to the efficient movement of light - generated electron - hole pairs to the surface^[15]. Moreover, the Aurivillius compounds have potential applications in photocatalysis and optical properties due to their unique layered crystal structure and ideal visible-light sensitivity^[16-19].

  In 1997, Mentre and Abraham reported the structure of Bi₉V₂O₁₈Cl for the first time^[20]. In Bi₉V ₂O₁₈Cl, the [Bi₂O₂]²⁺ layers, similar to those of Aurivillius compound, also can be found. In 2020, Ji et al. synthesized the phosphate-analogous compounds Bi₉P₂O₁₈Cl via sol - gel - assisted solid - state reaction (SSR) and found that Bi₉ P ₂O₁₈ Cl has a band gap of 2.58 eV and its potentials of the conduction and valence bands cover the reduction and oxidation potentials of the water. Additionally, Rietveld's refinement from powder X - ray diffraction (PXRD) data showed that Bi₉P₂O₁₈Cl is isostructural with Bi₉V₂O₁₈Cl and also contains [Bi₂O ₂]²⁺ layers, which will lead to a huge polarization to enhance the separation of the photoinduced charges^[19]. These indicate that Bi₉P₂O₁₈Cl is a suitable semiconductor for the visible-light-driven photocatalytic splitting of water. Therefore, the performance of hydrogen production of Bi₉P₂O₁₈Cl from water-splitting raises concerns for us. However, the crystal structure of Bi₉P₂O₁₈Cl remains dubious because there are several disordered O and Bi atoms. To figure out the structure, we grew the crystals and then revisited the structure

  through the single - crystal diffraction method. Interestingly, the structural results showed that Bi₉P₂ O₁₈Cl experiences a crystal - to - crystal phase transition from room temperature to 100 K. Hereafter, the room - and low - temperature phases can be denoted as“α”and “β”, respectively. In addition, results from photocatalytic water - splitting also showed that Bi₉P ₂O₁₈Cl was indeed active to produce H₂.

  1.   Experimental

  1.1   Syntheses

  NH₄H₂PO₄ (98%, Aladdin), BiCl₃ (99%, Aladdin), Bi₂O₃ (99%, Aladdin) were purchased from a commercial provider and used without further purification. The powder sample of the title compound was synthesized by the conventional SSR method. In the reaction, Bi₂O ₃, BiCl₃, and NH ₄H₂PO₄ were mixed in a molar ratio of 13∶1∶6 and packed into a Platinum crucible. After that, the mixture was heated in a muffle furnace at 300 ℃ for 6 h, 500 ℃ for 6 h, and 700 ℃ for 10 h with several mid - grinding. Finally, a pale-yellow powder sample was obtained.

  Single crystals were obtained by the hightemperature molten salt method. 0.3 g Bi₉P₂O₁₈ Cl and 1.0 g CsCl were ground sufficiently in the Ar - filled glovebox and then encapsulated into a quartz tube using a vacuum sealing device. After that, the mixture was melted at 850 ℃, held for 5 h, and then slowly cooled down at a rate of 3 ℃·h^-1 to 550 ℃. Finally, the colorless transparent crystals were successfully obtained.

  1.2   PXRD

  The PXRD data were collected by a Bruker D8 advance diffractometer (tube voltage was 40 kV; tube current was 40 mA) using Cu Kα radiation (λ=0.154 18 nm) with a step size of 0.02° at room temperature. The PXRD data were collected for phase purity checking and Rietveld refinement (5°≤2θ≤95°, 1.0 s·step^-1).

  1.3   Single-crystal X-ray diffraction

  Single crystals were selected under an optical microscope and mounted on glass fibers for X-ray diffraction studies. The diffraction data of single-crystal samples were respectively collected at room temperature and low temperature on a Bruker Smart diffractometer equipped with a CCD area detector and Mo Kα (λ= 0.071 073 nm) radiation source. Intensities were corrected for Lorenz and polarization effects. The structure was solved directly using the SHELEX - 97 program^[21] and refined on F2 by least-squares, full - matrix techniques. The final results were tested using PLATON^[22] and no additional symmetry elements were found. The main related crystallographic data are listed in Table 1 (The residual peaks show a little big because there are nine heavy-atoms Bi in one-unit cell and the quality of single crystals is not so good). The atomic coordinates and equivalent isotropic displacement parameters of the α - and β - phases are summarized in Table S1 and Table S2, and the selected bond lengths are given in Table 2 and Table 3.

  表 1

  

  表 1  Crystal data and structure refinement for Bi₉P₂O₁₈Cl

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  Parameter	β-phases Bi9P2O18Cl	α-phases Bi9P2O18Cl
  Formula weight	2 266.21	2 266.21
  Temperature / K	100	300
  Space group	P21/n (14)	P21/m (11)
  a / nm	1.790 56(4)	1.149 10(7)
  b / nm	0.538870(10)	0.54064(4)
  c / nm	1.915 57(4)	1.463 69(9)
  β/(°)	103.693(2)	93.741(6)
  V / nm3	1.795 76(6)	0.907 38(10)
  Z	4	2
  Dc / (g·cm-3)	8.382	8.295
  Absorption coefficient / mm-1	88.271	87.347
  F(000)	3 752	1 876
  θ range for data collection / (°)	1.78-29.31	1.78-29.20
  Reflection collected, unique	21 094, 4 928	7 128, 2 240
  Rint	0.042 8	0.056 7
  Goodness-of-fit on F 2	1.141	1.044
  Final R indices [I > 2σ(I)]	R1=0.036 6, wR1=0.095 6	R1=0.049 0, wR1=0.121 9
  R indices (all data)	R2=0.042 6, wR2=0.097 3	R2=0.056 5, wR2=0.134 0
  Largest diff. peak and hole / (e·nm-3)	5 107 and -4 977	7 132 and -9 686

  表 2

  

  表 2  Selected bond lengths (nm) and bond angles (°) of α-phase Bi₉P₂O₁₈Cl

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  Bi1—O2i	0.222 2(10)	Bi4—O12ii	0.241(2)	Bi9—O1ii	0.250 4(11)
  Bi1—O2	0.222 2(10)	Bi5—O1	0.220 5(11)	Bi9—O5	0.254 2(6)
  Bi1—O5	0.222 6(16)	Bi5—O1i	0.220 5(11)	Bi9—O2ii	0.269 3(10)
  Bi1—O3	0.251 7(11)	Bi5—O2i	0.233 2(10)	Bi9—O1vii	0.273 3(11)
  Bi1—O3i	0.251 7(11)	Bi5—O2	0.233 2(10)	P1—O10	0.152 2(19)
  Bi2—O2ii	0.220 3(10)	Bi6—O3i	0.222 4(11)	P1—O9	0.154(2)
  Bi2—O2	0.220 3(10)	Bi6—O3	0.222 4(11)	P1—O7ii	0.155 6(12)
  Bi2—O3iii	0.232 4(10)	Bi6—O4i	0.223 6(10)	P1—O7	0.155 6(12)
  Bi2—O3i	0.232 4(10)	Bi6—O4	0.223 6(10)	P2—O11ii	0.148(2)
  Bi2—O10	0.262 5(18)	Bi7—O5vii	0.209 2(17)	P2—O11	0.148(2)
  Bi3—O3i	0.224 4(11)	Bi7—O1ii	0.216 7(11)	P2—O13	0.152(2)
  Bi3—O3iii	0.224 4(10)	Bi7—O1	0.216 7(11)	P2—O13ii	0.152(2)
  Bi3—O4i	0.228 7(10)	Bi7—O13vii	0.253 6(19)	P2—O6	0.154(2)
  Bi3—O4iii	0.228 7(10)	Bi7—O13viii	0.253 6(19)	P2—O12	0.162(2)
  Bi3—O6	0.264 4(18)	Bi8—O4iii	0.219 1(10)	P2—O12ii	0.162(2)
  Bi4—O8	0.207 7(16)	Bi8—O4ii	0.219 1(10)	Cl—Bi2	0.326 05(39)
  Bi4—O11	0.234(2)	Bi8—O8iii	0.226 9(16)	Cl—Bi2iii	0.326 05(39)
  Bi4—O11i	0.234(2)	Bi8—O4ix	0.256 1(10)	Cl—Bi2xi	0.326 65(74)
  Bi4—O7v	0.236 7(12)	Bi8—O4x	0.256 1(10)	Cl—Bi5iii	0.339 55(74)
  Bi4—O7vi	0.236 7(12)	Bi9—O1	0.213 4(11)	Cl—Bi6xi	0.345 89(43)
  Bi4—O12iv	0.241(2)	Bi9—O2	0.235 0(10)	Cl—Bi6xii	0.345 89(43)
  O10—P1—O9	113.6(11)	O11—P2—O13ii	132.0(13)	O13—P2—O12	107.2(11)
  O10—P1—O7ii	108.3(6)	O11ii—P2—O13ii	116.8(12)	O13ii—P2—O12	75.0(10)
  O9—P1—O7ii	109.1(6)	O13—P2—O13ii	32.5(14)	O6—P2—O12	97.4(8)
  O10—P1—O7	108.3(6)	O11ii—P2—O6	113.8(12)	O11ii—P2—O12ii	105.5(13)
  O9—P1—O7	109.1(6)	O11—P2—O6	113.8(12)	O11—P2—O12ii	59.8(11)
  O7ii—P1—O7	108.3(9)	O13—P2—O6	113.7(11)	O13—P2—O12ii	75.0(10)
  O11ii—P2—O11	45.9(18)	O13ii—P2—O6	113.7(11)	O13ii—P2—O12ii	107.2(11)
  O11ii—P2—O13	132.0(13)	O11ii—P2—O12	59.8(11)	O6—P2—O12ii	97.4(8)
  O11—P2—O13	116.8(12)	O11—P2—O12	105.5(13)	O12—P2—O12ii	162.6(16)
  Symmetry codes: i x, -y+5/2, z; ii x, -y+3/2, z; iii x, y-1, z; iv x, y+1, z; v x-1, y, z; vi x-1, -y+5/2, z; vii -x+1, -y+2, -z; viii -x+1, y-1/2, -z; ix -x, -y+2, -z+1; x -x, y-3/2, -z+1; xi -x+1, -1/2+y, 1-z; xii -x+1, -3/2+y, 1-z.

  表 3

  

  表 3  Selected bond lengths (nm) and bond angles (°) of β-phase Bi₉P₂O₁₈Cl

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  Bi1—O10	0.215 2(8)	Bi4—O14	0.267 0(9)	Bi8—O13	0.221 7(9)
  Bi1—O5i	0.232 7(8)	Bi4—O15iii	0.274 4(9)	Bi8—O7	0.224 6(8)
  Bi1—O9	0.237 9(8)	Bi5—O8	0.219 8(9)	Bi9—O9	0.209 2(9)
  Bi1—O12i	0.242 9(8)	Bi5—O5	0.221 2(8)	Bi9—O12ii	0.212 1(8)
  Bi1—O8i	0.267 7(9)	Bi5—O11i	0.228 7(8)	Bi9—O10ix	0.222 0(8)
  Bi2—O12	0.215 8(8)	Bi5—O13	0.235 5(9)	Bi9—O17i	0.254 2(9)
  Bi2—O10	0.225 9(9)	Bi5—O4	0.263 0(10)	P1—O2viii	0.153 8(9)
  Bi2—O8	0.227 3(8)	Bi6—O7	0.217 4(8)	P1—O4	0.153 0(11)
  Bi2—O5i	0.241 1(8)	Bi6—O6	0.222 3(8)	P1—O3	0.154 4(10)
  Bi2—O1	0.267 2(8)	Bi6—O15iii	0.227 2(9)	P1—O1	0.158 1(9)
  Bi3—O8	0.217 6(8)	Bi6—O6iv	0.252 3(8)	P2—O17	0.153 3(9)
  Bi3—O5i	0.221 6(8)	Bi6—O7v	0.258 6(8)	P2—O16	0.155 6(9)
  Bi3—O9	0.222 8(9)	Bi6—O3iii	0.263 4(9)	P2—O14	0.153 9(10)
  Bi3—O13i	0.247 9(9)	Bi7—O15	0.207 3(10)	P2—O18	0.153 6(9)
  Bi3—O11i	0.255 2(9)	Bi7—O18vi	0.227 0(9)	Cl—Bi2x	0.338 89(39)
  Bi3—O14i	0.271 4(9)	Bi7—O1	0.228 8(8)	Cl—Bi5	0.324 10(39)
  Bi4—O13	0.223 4(9)	Bi7—O16vii	0.243 5(8)	Cl—Bi5x	0.327 91(30)
  Bi4—O7	0.223 8(8)	Bi7—O2	0.244 0(9)	Cl—Bi5xi	0.320 44(30)
  Bi4—O11i	0.226 2(8)	Bi8—O11	0.219 1(8)	Cl—Bi8	0.352 02(30)
  Bi4—O6i	0.229 6(8)	Bi8—O6	0.222 2(8)	Cl—Bi8i	0.337 50(31)
  O4—P1—O2viii	110.9(5)	O2viii—P1—O1	109.4(5)	O18—P2—O14	109.5(5)
  O4—P1—O3	113.3(6)	O3—P1—O1	108.3(5)	O17—P2—O16	109.3(5)
  O2viii—P1—O3	109.0(5)	O17—P2—O18	112.6(5)	O18—P2—O16	108.4(5)
  O4—P1—O1	105.8(5)	O17—P2—O14	109.3(5)	O14—P2—O16	107.6(5)
  Symmetry codes: i x, y+1, z; ii -x+3/2, y+1/2, -z+1/2; iii x+1/2, -y+1/2, z+1/2; iv -x+3/2, y+1/2, -z+3/2; v -x+3/2, y-1/2, -z+3/2; vi x-1/2, -y+1/2, z-1/2; vii x-1/2, -y+3/2, z-1/2; viii x, y-1, z; ix -x+3/2, y-1/2, -z+1/2; x -x+1, -y+1, -z+1; xi -x+1, -y, -z+1.

  CCDC: 2128785, α - phase Bi₉P₂O₁₈Cl; 2145491, β-phase Bi₉P₂O₁₈Cl.

  1.4   UV-Vis-NIR diffuse reflectance

  A PerkinElmer Lambda 950 UV-Vis-NIR spectrophotometer was performed to collect the optical diffuse reflectance data in the range of 200-1 200 nm.

  1.5   Calculations of electronic structures

  The DFT (density functional theory) calculation was given by using the Vienna ab initio Simulation Package (VASP) ^[23] with the projector-augmented wave (PAW) pseudopotentials^[24]. The Perdew - Burke - Ernzerhof (PBE) of the generalized gradient approximation (GGA)^[25] was applied in the exchange and correlation potentials. Gamma grids of 2×5×2 and 5×1×1 were applied for the room-temperature and low-temperature bulk cell, respectively.

  1.6   Photocatalytic H₂ production

  To investigate the photocatalytic hydrogen production performance of Bi₉P₂O₁₈ Cl, a 300 W xenon lamp was used as a light source to imitate sunlight, and photocatalytic hydrogen production experiments were carried out at ambient temperature and pressure. The production of H₂ was achieved by dispersing 20 mg of catalyst into an aqueous solution containing Na₂S/ Na₂SO₃ (Na₂S 0.1 mol·L^-1, Na₂SO₃ 0.1 mol·L^-1). The reaction vessel was evacuated and purged by Ar for about 20 min to completely remove air before irradiation. The photocatalytic reaction was typically performed for 4 h. To detect the amount of H₂, 1 mL gas component was extracted from the vessel and then injected into a gas chromatograph (GC 7900, Tianmei, TCD, detector, Shanghai, nitrogen carrier gas) equipped with a TCD (thermal conductivity detector) detector.

  2.   Results and discussion

  2.1   Syntheses

  The title compound can be synthesized using the SSR method. And its single crystals can be obtained in the CsCl molten media. To refine the structure and check the phase purity of Bi₉P₂O ₁₈Cl, the Rietveld method was performed to the PXRD data by using the TOPAS software. The starting structural model was constructed using the crystallographic data obtained from our single - crystal diffraction. The final refinement converged to small reliability factors (R_wp=15.55%, R_p=9.61%, GOF=6.58). As shown in Fig. 1, the experimental PXRD pattern is in good agreement with the pattern calculated on the base of single-crystal diffraction data of Bi₉P₂O₁₈Cl, indicating that the high pure samples were synthesized.

  图 1

  

  图 1.  Rietveld refinement XRD pattern of Bi₉P₂O₁₈Cl

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  2.2   Crystal structure description

  2.2.1   Room-temperature structure (α-phase)

  Bi₉P₂O ₁₈Cl at room temperature crystallizes in the monoclinic space group P2₁/m (11) with unit cell parameters a=1.149 10(7) nm, b=0.540 64(4) nm, c= 1.463 69(9) nm, β=93.741(6)°, and V=0.907 38(10) nm³. The α - phase structure from our single-crystal diffraction data is almost the same as that of Bi₉V₂O₁₈Cl^[20] and Bi₉P₂O₁₈Cl from PXRD data^[19]. Therefore, herein we don't discuss the detailed α - phase structure anymore, but the atomic coordinates, selected bond lengths, and bond angles are still given in Table S1 (Supporting information) and Table 2. It is worth mentioning that in the process of solving the α - phase structure from our single-crystal diffraction data, many attempts to remove the disordered O and Bi atoms were made, but failed, indicating the disordered O and Bi atoms exist indeed in the α-phase structure of Bi₉P₂O₁₈Cl.

  2.2.2   Low-temperature structure (β-phase)

  When the temperature decreases, the singlecrystal X-ray diffraction analyses reveal that Bi₉P₂O₁₈Cl undergoes a crystal- to- crystal phase transition. At 100 K, Bi₉P₂O ₁₈Cl crystallizes in the monoclinic space group P2₁/n (14) with unit cell parameters a=1.790 56(4) nm, b=0.538 870(10) nm, c=1.915 57(4) nm, β =103.693(2)°, and V=1.795 76(6) nm³. The asymmetric unit includes nine independent Bi atoms, two P atoms, eighteen O atoms, and one Cl atom, which all occupy fully at 4e positions and no disorder appears (Table S2). As listed in Table 3, the bond length of Bi— O ranges from 0.207 3(10) to 0.274 4(9) nm, and the bond length of Bi—Cl ranges from 0.320 44(30) to 0.352 02(30) nm, which don't show a big difference from the Bi—O and B—Cl bond lengths of the α - phase structure and Bi₉V ₂O ₁₈Cl. But the P —O bond lengths and coordination environment of P are different between α - and β - phase structures. In the α-phase, P1 is four-coordinated to O atoms with reasonable P—O band distances (Fig. 2a). While P2 atom is linked with the disordered O11, O12, and O13 to form a configuration as shown in Fig. 2b. Because the site occupancy of O11, O12, and O13 is 0.5, the configuration is still considered as a PO₄ tetrahedron. A long (0.162(2) nm) and short (0.148(2) nm) P—O bond lengths appear in the PO₄ tetrahedron. By contrast, in the β - phase, P1 and P2 atoms are respectively coordinated with four oxygen atoms to form normal PO ₄ tetrahedra with reasonable P—O bond lengths and angles (Fig. 2c, 2d). Fig. 3 shows the projected views of α - and β - phases along b - direction. As can be seen, the two frameworks, constructed by [Bi₂O₂]²⁺ layers stacking along [101] direction, look very similar. The main difference lies in the change of unit cells. The unit cell of the β -phase is almost twice that of the α - phase. The reason may be that when the temperature decrease, the atom vibrations become not drastic so that the disorder of O and Bi atoms disappear and the symmetry reduces, which makes the unit cell of α-phase enlarge.

  图 2

  

  图 2.  P—O bond lengths (nm) and coordination environment of P in α- and β-phase structures

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  图 3

  

  图 3.  Projection view of the crystal structures of α- and β-phase Bi₉P₂O₁₈Cl along the b-direction

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  2.3   Experimental band gap

  The Kubelka- Munk equation was applied to calculate the energy of band gap from the following equation: αhνⁿ= A(hν -E_g), where n=2 for direct transitions and 1/2 for indirect transitions, and α, h, ν, A, and E_g are the optical absorption coefficient, Planck constant, light frequency, constant, and band gap respectively. According to the band structure calculated through the first-principle theory, an indirect optical gap was determined. So, the value of 1/2 is adopted to n. As shown in Fig. 4, the extrapolation of the linear part intercept at 2.62 eV in the axis of photon energy. This is in general agreement with the experimental results obtained by Ji (2.58 eV)^[19].

  图 4

  

  图 4.  UV-Vis-NIR absorption spectrum of Bi₉P₂O₁₈Cl

  Inset: Tauc plot from indirect transitions

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  2.4   Band structures and density of states

  The DFT calculation was applied to further understand the band structure of Bi₉P₂O₁₈Cl. As shown in Fig. 5, the band gaps of α - and β- phases are 2.64 and 2.62 eV, respectively, which are accordant with the experimental results of 2.62 eV. It can be seen that the electronic structure of α- and β-phases are almost identical. The valance band mostly originates from O2p orbital. The Bi6s, Bi6p, Cl3p, and P3p also make some contribution to the formation of the top of the valance band. The conduction band mostly consists of O2p and Bi6p orbitals.

  图 5

  

  图 5.  PDOS (partial density of state) of α- and β-phases Bi₉P₂O₁₈Cl

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  2.5   Photocatalytic performance

  The photocatalytic hydrogen production activity of Bi₉P₂O₁₈Cl was investigated under simulated sunlight conditions. As shown in Fig.S1, the results demonstrated that Bi₉P₂O₁₈Cl had a good photocatalytic performance with a hydrogen production rate of 33.69 μmol· g^-1·h^-1. It is well known that heterojunction engineering usually will enhance the photocatalytic performance, so the junctions of Bi₉P₂O₁₈Cl with metals or other semiconductors may show amazing photocatalytic performance.

  3.   Conclusions

  In summary, we have prepared Bi₉P₂O₁₈Cl using SSR and its single crystals were grown through the molten salt method. Single - crystal X - ray diffraction data analyses demonstrated that Bi₉P₂O ₁₈Cl undergoes a crystal-to-crystal phase transition from room temperature to 100 K. The room -temperature phase (α -phase) and low - temperature phase (β - phase) have a similar configuration of atom arrangement. The big difference is that in the α-phase there exist the disorders of O and Bi atoms, but in the β-phase, the disordered O and Bi atoms disappear due to the reduction of symmetry with the decrease of temperature. The DFT calculations reveal that the valance band and conduction band of α- and β-phase Bi₉P₂O₁₈Cl mostly originates from O2p and Bi2p orbitals, respectively. The calculated band gaps are in good agreement with the experimental value of 2.62 eV. In photocatalytic hydrogen production experiments, Bi₉P₂O₁₈Cl showed excellent photocatalytic performance with an H₂ production rate of 33.69 μmol· g^-1·h^-1.

  Supporting information is available at http://www.wjhxxb.cn

  
  
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• 

  图 1  Rietveld refinement XRD pattern of Bi₉P₂O₁₈Cl

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  图 2  P—O bond lengths (nm) and coordination environment of P in α- and β-phase structures

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  图 3  Projection view of the crystal structures of α- and β-phase Bi₉P₂O₁₈Cl along the b-direction

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  图 4  UV-Vis-NIR absorption spectrum of Bi₉P₂O₁₈Cl

  Inset: Tauc plot from indirect transitions

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  图 5  PDOS (partial density of state) of α- and β-phases Bi₉P₂O₁₈Cl

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  表 1  Crystal data and structure refinement for Bi₉P₂O₁₈Cl

  Parameter	β-phases Bi9P2O18Cl	α-phases Bi9P2O18Cl
  Formula weight	2 266.21	2 266.21
  Temperature / K	100	300
  Space group	P21/n (14)	P21/m (11)
  a / nm	1.790 56(4)	1.149 10(7)
  b / nm	0.538870(10)	0.54064(4)
  c / nm	1.915 57(4)	1.463 69(9)
  β/(°)	103.693(2)	93.741(6)
  V / nm3	1.795 76(6)	0.907 38(10)
  Z	4	2
  Dc / (g·cm-3)	8.382	8.295
  Absorption coefficient / mm-1	88.271	87.347
  F(000)	3 752	1 876
  θ range for data collection / (°)	1.78-29.31	1.78-29.20
  Reflection collected, unique	21 094, 4 928	7 128, 2 240
  Rint	0.042 8	0.056 7
  Goodness-of-fit on F 2	1.141	1.044
  Final R indices [I > 2σ(I)]	R1=0.036 6, wR1=0.095 6	R1=0.049 0, wR1=0.121 9
  R indices (all data)	R2=0.042 6, wR2=0.097 3	R2=0.056 5, wR2=0.134 0
  Largest diff. peak and hole / (e·nm-3)	5 107 and -4 977	7 132 and -9 686

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  表 2  Selected bond lengths (nm) and bond angles (°) of α-phase Bi₉P₂O₁₈Cl

  Bi1—O2i	0.222 2(10)	Bi4—O12ii	0.241(2)	Bi9—O1ii	0.250 4(11)
  Bi1—O2	0.222 2(10)	Bi5—O1	0.220 5(11)	Bi9—O5	0.254 2(6)
  Bi1—O5	0.222 6(16)	Bi5—O1i	0.220 5(11)	Bi9—O2ii	0.269 3(10)
  Bi1—O3	0.251 7(11)	Bi5—O2i	0.233 2(10)	Bi9—O1vii	0.273 3(11)
  Bi1—O3i	0.251 7(11)	Bi5—O2	0.233 2(10)	P1—O10	0.152 2(19)
  Bi2—O2ii	0.220 3(10)	Bi6—O3i	0.222 4(11)	P1—O9	0.154(2)
  Bi2—O2	0.220 3(10)	Bi6—O3	0.222 4(11)	P1—O7ii	0.155 6(12)
  Bi2—O3iii	0.232 4(10)	Bi6—O4i	0.223 6(10)	P1—O7	0.155 6(12)
  Bi2—O3i	0.232 4(10)	Bi6—O4	0.223 6(10)	P2—O11ii	0.148(2)
  Bi2—O10	0.262 5(18)	Bi7—O5vii	0.209 2(17)	P2—O11	0.148(2)
  Bi3—O3i	0.224 4(11)	Bi7—O1ii	0.216 7(11)	P2—O13	0.152(2)
  Bi3—O3iii	0.224 4(10)	Bi7—O1	0.216 7(11)	P2—O13ii	0.152(2)
  Bi3—O4i	0.228 7(10)	Bi7—O13vii	0.253 6(19)	P2—O6	0.154(2)
  Bi3—O4iii	0.228 7(10)	Bi7—O13viii	0.253 6(19)	P2—O12	0.162(2)
  Bi3—O6	0.264 4(18)	Bi8—O4iii	0.219 1(10)	P2—O12ii	0.162(2)
  Bi4—O8	0.207 7(16)	Bi8—O4ii	0.219 1(10)	Cl—Bi2	0.326 05(39)
  Bi4—O11	0.234(2)	Bi8—O8iii	0.226 9(16)	Cl—Bi2iii	0.326 05(39)
  Bi4—O11i	0.234(2)	Bi8—O4ix	0.256 1(10)	Cl—Bi2xi	0.326 65(74)
  Bi4—O7v	0.236 7(12)	Bi8—O4x	0.256 1(10)	Cl—Bi5iii	0.339 55(74)
  Bi4—O7vi	0.236 7(12)	Bi9—O1	0.213 4(11)	Cl—Bi6xi	0.345 89(43)
  Bi4—O12iv	0.241(2)	Bi9—O2	0.235 0(10)	Cl—Bi6xii	0.345 89(43)
  O10—P1—O9	113.6(11)	O11—P2—O13ii	132.0(13)	O13—P2—O12	107.2(11)
  O10—P1—O7ii	108.3(6)	O11ii—P2—O13ii	116.8(12)	O13ii—P2—O12	75.0(10)
  O9—P1—O7ii	109.1(6)	O13—P2—O13ii	32.5(14)	O6—P2—O12	97.4(8)
  O10—P1—O7	108.3(6)	O11ii—P2—O6	113.8(12)	O11ii—P2—O12ii	105.5(13)
  O9—P1—O7	109.1(6)	O11—P2—O6	113.8(12)	O11—P2—O12ii	59.8(11)
  O7ii—P1—O7	108.3(9)	O13—P2—O6	113.7(11)	O13—P2—O12ii	75.0(10)
  O11ii—P2—O11	45.9(18)	O13ii—P2—O6	113.7(11)	O13ii—P2—O12ii	107.2(11)
  O11ii—P2—O13	132.0(13)	O11ii—P2—O12	59.8(11)	O6—P2—O12ii	97.4(8)
  O11—P2—O13	116.8(12)	O11—P2—O12	105.5(13)	O12—P2—O12ii	162.6(16)
  Symmetry codes: i x, -y+5/2, z; ii x, -y+3/2, z; iii x, y-1, z; iv x, y+1, z; v x-1, y, z; vi x-1, -y+5/2, z; vii -x+1, -y+2, -z; viii -x+1, y-1/2, -z; ix -x, -y+2, -z+1; x -x, y-3/2, -z+1; xi -x+1, -1/2+y, 1-z; xii -x+1, -3/2+y, 1-z.

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  表 3  Selected bond lengths (nm) and bond angles (°) of β-phase Bi₉P₂O₁₈Cl

  Bi1—O10	0.215 2(8)	Bi4—O14	0.267 0(9)	Bi8—O13	0.221 7(9)
  Bi1—O5i	0.232 7(8)	Bi4—O15iii	0.274 4(9)	Bi8—O7	0.224 6(8)
  Bi1—O9	0.237 9(8)	Bi5—O8	0.219 8(9)	Bi9—O9	0.209 2(9)
  Bi1—O12i	0.242 9(8)	Bi5—O5	0.221 2(8)	Bi9—O12ii	0.212 1(8)
  Bi1—O8i	0.267 7(9)	Bi5—O11i	0.228 7(8)	Bi9—O10ix	0.222 0(8)
  Bi2—O12	0.215 8(8)	Bi5—O13	0.235 5(9)	Bi9—O17i	0.254 2(9)
  Bi2—O10	0.225 9(9)	Bi5—O4	0.263 0(10)	P1—O2viii	0.153 8(9)
  Bi2—O8	0.227 3(8)	Bi6—O7	0.217 4(8)	P1—O4	0.153 0(11)
  Bi2—O5i	0.241 1(8)	Bi6—O6	0.222 3(8)	P1—O3	0.154 4(10)
  Bi2—O1	0.267 2(8)	Bi6—O15iii	0.227 2(9)	P1—O1	0.158 1(9)
  Bi3—O8	0.217 6(8)	Bi6—O6iv	0.252 3(8)	P2—O17	0.153 3(9)
  Bi3—O5i	0.221 6(8)	Bi6—O7v	0.258 6(8)	P2—O16	0.155 6(9)
  Bi3—O9	0.222 8(9)	Bi6—O3iii	0.263 4(9)	P2—O14	0.153 9(10)
  Bi3—O13i	0.247 9(9)	Bi7—O15	0.207 3(10)	P2—O18	0.153 6(9)
  Bi3—O11i	0.255 2(9)	Bi7—O18vi	0.227 0(9)	Cl—Bi2x	0.338 89(39)
  Bi3—O14i	0.271 4(9)	Bi7—O1	0.228 8(8)	Cl—Bi5	0.324 10(39)
  Bi4—O13	0.223 4(9)	Bi7—O16vii	0.243 5(8)	Cl—Bi5x	0.327 91(30)
  Bi4—O7	0.223 8(8)	Bi7—O2	0.244 0(9)	Cl—Bi5xi	0.320 44(30)
  Bi4—O11i	0.226 2(8)	Bi8—O11	0.219 1(8)	Cl—Bi8	0.352 02(30)
  Bi4—O6i	0.229 6(8)	Bi8—O6	0.222 2(8)	Cl—Bi8i	0.337 50(31)
  O4—P1—O2viii	110.9(5)	O2viii—P1—O1	109.4(5)	O18—P2—O14	109.5(5)
  O4—P1—O3	113.3(6)	O3—P1—O1	108.3(5)	O17—P2—O16	109.3(5)
  O2viii—P1—O3	109.0(5)	O17—P2—O18	112.6(5)	O18—P2—O16	108.4(5)
  O4—P1—O1	105.8(5)	O17—P2—O14	109.3(5)	O14—P2—O16	107.6(5)
  Symmetry codes: i x, y+1, z; ii -x+3/2, y+1/2, -z+1/2; iii x+1/2, -y+1/2, z+1/2; iv -x+3/2, y+1/2, -z+3/2; v -x+3/2, y-1/2, -z+3/2; vi x-1/2, -y+1/2, z-1/2; vii x-1/2, -y+3/2, z-1/2; viii x, y-1, z; ix -x+3/2, y-1/2, -z+1/2; x -x+1, -y+1, -z+1; xi -x+1, -y, -z+1.

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•