Preparation of a multi-active site germanotungstate-based crystal material and its application in photocatalytic hydrogen production

Abstract

The purpose of this invention is to develop a multi-active-site germanium tungstate-based crystal material, effectively overcoming the shortcomings of traditional polyoxometalates, such as easy water solubility and the need for noble metals as co-catalysts. This is achieved by introducing transition metal elements to form mixed or hybridized atomic orbitals, thereby increasing the lowest unoccupied orbital (LUMO) energy level of the polyoxometalate and improving its catalytic activity. The chemical formula of the multi-active-site germanium tungstate-based crystal material is [Cd]. II 2(bipy)4(H2O)4](GeW 12 O 40 Method: 0.27g of germanic tungstate K4 (GeW) was added. 12 O 40 0.135g cadmium chloride (CdCl2·4H2O), 0.45g 2,2-bipyridine (CdCl2·4H2O) 10 H8N2 was dissolved in 36 mL of deionized water, and then... ‑1 hydrochloric acid and 1 mol L ‑1 The pH of the solution was adjusted to 2.4 with sodium hydroxide solution, and the mixture was stirred at room temperature for 3.5 h. The solution was then divided into three equal portions and transferred to 20 mL reaction vessels, and kept at 160 °C for 72 h to obtain pale yellow blocky crystals. This invention provides a germanate-tungstate-based crystal material with excellent photocatalytic hydrogen production activity and multiple active sites.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation of a multi-active site germanium tungstate-based crystal material and its photocatalytic hydrogen production application BACKGROUND

[0002] Solar water splitting is considered as one of the most attractive methods for hydrogen fuel development, and in this process, photocatalysts are the key factor to determine the photocatalytic hydrogen production efficiency and cost.

[0003] The band gap structure of polyoxometalate is similar to that of metal oxide, has a suitable band gap, and can be reduced to heteropoly blue species under light conditions. Compared with the ground state heteropoly acid, heteropoly blue can absorb visible light. Therefore, polyoxometalate is an ideal photocatalyst. However, polyoxometalate still faces many challenges in the photocatalytic process, such as the conduction band position does not meet the thermodynamic requirements of photocatalytic water splitting, is usually a homogeneous catalyst, and needs a noble metal as a cocatalyst to increase the rate of photocatalytic hydrogen production. By introducing transition metal elements to form a mixture or hybrid of atomic orbitals, the lowest unoccupied orbital (LUMO) level of polyoxometalate is improved, which is one of the ways to solve the above problems.

[0004] At present, Cd-based materials are widely used in the field of photocatalysis due to their suitable band gap structure, which can play a role in rapid transfer of electrons in the photocatalytic process, such as CdS, CdSe and Cd-based MOF, etc. Therefore, in order to improve the catalytic activity of polyoxometalate, introducing transition metal Cd is a feasible means. In addition, Cd metal has a suitable coordination mode, and by introducing organic ligands, a variety of dimensional polyoxometalate-based Cd metal organic complexes can be formed, thereby forming a hybrid material with multiple catalytic active sites for photocatalytic water splitting to produce hydrogen, which can promote the rapid transfer of photo-generated electrons and thus increase the rate of photocatalytic hydrogen production. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of traditional polyoxometalate, which is easily soluble in water and needs a noble metal as a cocatalyst, and to provide a preparation of a multi-active site germanium tungstate-based crystal material and its photocatalytic hydrogen production application.

[0006] A multi-active site germanium tungstate-based crystal material has a chemical formula of [Cd II 2(bipy)4(H2O)4](GeW 12 O 40 ), wherein bipy is 2,2-bipyridine C 10 H8N2; the crystal system of a multi-active site germanium tungstate-based crystal material is monoclinic; the space group is P21 / n; the unit cell parameters are α = 90°, β = 92.2600(10)°, γ = 90°, z = 4.

[0007] A method for preparing a multi-active-site germanium tungstate-based crystal material is carried out according to the following steps:

[0008] I. Synthesis of germanate standby solution: Add 10.5g cadmium powder to 60mL of 6.25mol / L solution. -1 Stir the NaOH solution, slowly add 50 mL of H2O2 until the cadmium powder is completely dissolved, heat to 80°C until no more oxygen is generated, and cool to obtain germanate solution for later use.

[0009] II. Germanium tungstate K4 (GeW 12 O 40 Synthesis of 7H₂O: Add 35 mL of germanate solution to 125 mL of 1.25 mol / L solution. -1 In a sodium tungstate solution, heat to 80°C, and add 22.5 mL of 13 mol / L solution dropwise. -1 Concentrated nitric acid was added, and after 1 hour the solution was cooled to room temperature. Then 5 mL of 1.25 mol / L nitric acid was added. -1 After adding concentrated nitric acid, the mixture was extracted with diethyl ether to separate the layers. The ether layer was diluted with water, and the organic layer was placed in a vacuum desiccator containing concentrated sulfuric acid and allowed to stand until colorless crystals precipitated, which is H4 (GeW). 12 O 40 )·14H2O, then add 1 mol L -1 K2CO3 solution was added to H4 (GeW) 12 O 40 In a saturated solution of 14H2O, white microcrystals precipitate out, which is germanotungstate K4 (GeW). 12 O 40 )·7H2O, abbreviated as GeW 12 ;

[0010] III. Preparation of a multi-active-site germanium-tungstate-based crystal material: 0.27 g of K4 (GeW 12 O 40 0.135g cadmium chloride (CdCl2·4H2O), 0.45g 2,2-bipyridine (CdCl2·4H2O) 10 H8N2 was dissolved in 36 mL of deionized water, and then... -1 hydrochloric acid and 1 mol L -1 The pH of the solution was adjusted to 2.4 with sodium hydroxide solution, and the mixture was stirred at room temperature for 3.5 h to obtain a reaction solution with a pH of 2.4. The reaction solution with a pH of 2.4 was divided into three equal portions and transferred to a 20 mL reaction vessel. The mixture was kept at 160 °C for 72 h to obtain light yellow blocky crystals, which is a multi-active site germanium tungstate-based crystal material.

[0011] The molar ratio of the germanotungstate described in step three to the metal cadmium salt is: 1:6;

[0012] The molar ratio of the germanotungstate described in step three to 2,2-bipyridine C 10 H8N2 is: 1:34;

[0013] The volume ratio of the amount of substance of the germanotungstate described in step three to deionized water is: 0.08 mmol: 36 mL;

[0014] The chemical formula of the multi-active site germanotungstate-based crystal material described in step three is [Cd II 2(bipy)4(H2O)4] (GeW 12 O 40 ), wherein bipy is 2,2-bipyridine C 10 H8N2; the crystal system of the multi-active site germanotungstate-based crystal material is monoclinic; the space group is P21 / n; the unit cell parameters are alpha = 90 degrees, beta = 92.2600(10) degrees, gamma = 90 degrees, z = 4.

[0015] The multi-active site germanotungstate-based crystal material is applied to a photocatalytic hydrogen production material as an electrode material.

[0016] Compared with the prior art, the present application has the following characteristics:

[0017] The present application combines GeW 12 O and Cd metal organic complexes through one-pot hydrothermal method, realizes the rapid transfer of photo-generated electrons by connecting the polyacid and transition metal Cd coordination, thereby promoting the efficient photocatalytic hydrogen production. The relationship between the molecular structure of the compound and the photocatalytic hydrogen production performance is studied. This compound is a 2,2-bipyridine constructed polyacid-based metal organic complex. A large number of exposed polyacid anions can combine with the sacrificial agent to form HPB state, and then transfer electrons to four Cd metal active sites through the end oxygen, thereby enhancing the proton reduction reaction of photo-generated electrons, and thus has more excellent photocatalytic hydrogen production activity.

[0018] The application adopts an offline photocatalysis test system and a gas phase spectrometer to test the photocatalyst. The light source is a 500W xenon lamp, the hydrogen content is measured by a GC9800 type gas phase spectrometer, a TCD thermal conductivity detector is used as a detector, high-purity nitrogen is used as a carrier gas, and the photocatalysis reaction container is a 30mL quartz reaction container. The photocatalytic hydrogen production performance test process is as follows: 5mg of the photocatalyst is weighed and placed in the quartz reaction kettle, a sacrificial agent is added, the reaction system is irradiated by the 500W xenon lamp, the stirrer is turned on, 200ul of gas is extracted from the reaction system every 1h and injected into the GC-9800, the hydrogen content is tested and recorded. The photocatalytic hydrogen production cycle stability test is as follows: after the optimal photocatalytic solution system is determined, 5 cycles of tests are carried out.

[0019] The application can obtain a germanium tungstate-based crystal material with multiple active sites. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A structure schematic diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0021] Figure 2 An infrared spectrum diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0022] Figure 3 An X-ray powder diffraction spectrum diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0023] Figure 4 An X-ray photoelectron spectroscopy diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0024] Figure 5 A photocatalytic hydrogen production activity comparison diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0025] Figure 6 A photocatalytic hydrogen production stability diagram of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application

[0026] Figure 7 A preparation flowchart of the germanium tungstate-based crystal material with multiple active sites prepared in embodiment 1 of the application DETAILED DESCRIPTION

[0027] The process parameters and process routes of the present application are not limited to the following specific embodiments. The following specific embodiments are only used to illustrate the present application and are not limited to the process parameters and process routes described in the embodiments. Those skilled in the art should understand that the present application can be modified or replaced equivalently in practical application to achieve the same technical effects. As long as the application requirements are met, it is within the protection scope of the present application.

[0028] Specific embodiment one: the chemical formula of the germanium tungstate-based crystal material with multiple active sites is [Cd II 2(bipy)4(H2O)4](GeW 12 O 40 ), wherein bipy is 2,2-bipyridine C 10 H8N2; the crystal system of the germanium tungstate-based crystal material with multiple active sites is monoclinic; the space group is P21 / n; the unit cell parameters are α=90°, β=92.2600(10)°, γ=90°, z=4.

[0029] Compared with the prior art, the present embodiment has the following characteristics:

[0030] The present application combines GeW 12 polyacid and Cd metal organic complex by one-pot hydrothermal method, realizes the rapid transfer of photo-generated electrons by the coordination connection of polyacid and transition metal Cd, thereby promoting the efficient progress of photocatalytic hydrogen production. The relationship between the molecular structure of the compound and the photocatalytic hydrogen production performance is studied. The compound is a 2,2-bipyridine constructed polyacid-based metal organic complex. A large number of exposed polyacid anions can combine with the sacrificial agent to form HPB state, and then transfer electrons to four Cd metal active sites through the end oxygen, thereby enhancing the proton reduction reaction of photo-generated electrons, and thus having more excellent photocatalytic hydrogen production activity.

[0031] The present application uses an offline photocatalytic test system and a gas phase spectrometer to test the photocatalyst. The light source is a 500W xenon lamp, the hydrogen content is measured by a GC9800 type gas phase spectrometer, a TCD thermal conductivity detector is used as a detector, high-purity nitrogen is used as a carrier gas, and the photocatalytic reaction container is a 30mL quartz reaction container. The photocatalytic hydrogen production performance test process is as follows: 5mg of photocatalyst is weighed and placed in a quartz reaction kettle, a sacrificial agent is added, a 500W xenon lamp is used to irradiate the reaction system, a stirrer is opened, 200μL of gas is extracted from the reaction system every 1h and injected into the GC-9800, the hydrogen content is tested and recorded. The photocatalytic hydrogen production cycle stability test: after determining the optimal photocatalytic solution system, 5 cycles of tests are carried out.

[0032] DETAILED DESCRIPTION TWO: A multi-active site germanotungstate-based crystalline material is prepared according to the following steps:

[0033] I. Synthesis of germanate stock solution: 10.5 g of cadmium powder was added to 60 mL of 6.25 mol L -1 NaOH solution with stirring, 50 mL of H2O2 was added slowly until the cadmium powder was completely dissolved, heated to 80 °C until no more oxygen was generated, and cooled to obtain the germanate stock solution;

[0034] II. Synthesis of K4(GeW 12 O 40 )·7H2O: 35 mL of the germanate stock solution was added to 125 mL of 1.25 mol L -1 Na2WO4 solution, heated to 80 °C, 22.5 mL of 13 mol L -1 concentrated nitric acid was added dropwise, the solution was cooled to room temperature after 1 h, 5 mL of 1.25 mol L -1 K2CO3 solution was added, and the organic layer was placed in a vacuum dryer with concentrated sulfuric acid, and left to stand until colorless crystals were precipitated, which were H4(GeW 12 O 40 )·14H2O, 1 mol L -1 K2CO3 solution was added to the saturated solution of H4(GeW 12 O 40 )·14H2O, and white microcrystals were precipitated, which were K4(GeW 12 O 40 )·7H2O, abbreviated as GeW 12 ;

[0035] III. Preparation of a multi-active site germanotungstate-based crystalline material: 0.27 g of K4(GeW 12 O 40 )·7H2O, 0.135 g of cadmium chloride CdCl2·4H2O, and 0.45 g of 2,2-bipyridine C 10 H8N2 were dissolved in 36 mL of deionized water, the solution pH was adjusted to 2.4 using 1 mol L -1 hydrochloric acid and 1 mol L -1 sodium hydroxide solution, and stirred at room temperature for 3.5 h to obtain a reaction solution with a pH of 2.4; the reaction solution with a pH of 2.4 was divided into three equal parts and transferred to 20 mL reaction kettles, and kept at 160 °C for 72 h to obtain light yellow block-shaped crystals, which were a multi-active site germanotungstate-based crystalline material.

[0036] The molar ratio of germanotungstate to metal cadmium salt in step III was 1:6;

[0037] The molar ratio of germanium tungstate described in step three to 2,2-bipyridine C 10 The molar ratio of H8N2 is 1:34.

[0038] The volume ratio of the amount of substance of germanium tungstate described in step three to deionized water is 0.08 mmol:36 mL.

[0039] Compared with the prior art, the embodiment has the following characteristics:

[0040] The present application realizes the rapid transfer of photo-generated electrons by one-pot hydrothermal method of GeW 12 The compound is a 2,2-bipyridine constructed polyacid based metal organic complex. A large number of exposed polyacid anions can combine with the sacrificial agent to form HPB state, and then rapidly transfer electrons to four Cd metal active sites through the end oxygen, thereby enhancing the proton reduction reaction of photo-generated electrons, and thus having more excellent photocatalytic hydrogen production activity.

[0041] The present application adopts an offline photocatalytic test system and a gas phase spectrometer to test the photocatalyst. The light source is a 500W xenon lamp, the hydrogen content is measured by a GC9800 type gas phase spectrometer, a TCD thermal conductivity detector is used as a detector, high-purity nitrogen is used as a carrier gas, and the photocatalytic reaction container is a 30mL quartz reaction container. The photocatalytic hydrogen production performance test process is as follows: 5mg of photocatalyst is weighed and placed in a quartz reaction kettle, a sacrificial agent is added, a 500W xenon lamp is used to irradiate the reaction system, a stirrer is opened, 200ul of gas is extracted from the reaction system every 1h and injected into the GC-9800, the hydrogen content is tested and recorded. The photocatalytic hydrogen production cycle stability test: after determining the optimal photocatalytic solution system, 5 cycles of tests are carried out.

[0042] Specific implementation method three: the difference between the present embodiment and the specific implementation method two is that the metal cadmium salt described in step three is chromium chloride. The others are the same as the specific implementation method two.

[0043] Specific implementation method four: the difference between the present embodiment and the specific implementation methods two to three is that the molar ratio of germanium tungstate to metal cadmium salt described in step three is 1:6. The others are the same as the specific implementation methods two or three.

[0044] Specific implementation method five: the difference between the present embodiment and the specific implementation methods two to four is that the molar ratio of germanium tungstate to 2,2-bipyridine C 10 The molar ratio of H8N2 is 1:34. The others are the same as the specific implementation methods two to four.

[0045] Specific implementation six: the difference between this embodiment and specific implementation two to five is that the mass of the germanium tungstate and the volume of the deionized water in step three is 0.08 mmol:36 mL. The others are the same as specific implementation two to five.

[0046] Specific implementation seven: the difference between this embodiment and specific implementation two to six is that the pH value of the reaction solution in step three is adjusted to 2.4 by using 1 mol L -1 hydrochloric acid and 1 mol L -1 sodium hydroxide solution. The others are the same as specific implementation two to six.

[0047] Specific implementation eight: this embodiment is a cadmium-vanadium bimetallic modified germanium tungstate-based crystal material for photocatalytic decomposition of water to produce hydrogen, and has a high photocatalytic hydrogen production rate, Cd2-GeW 12 The catalytic rate reaches 4522 μmol g -1 h -1 , which is 75.36 times that of the parent germanium tungstate.

[0048] The beneficial effects of the present application are verified by the following examples:

[0049] Example one: a preparation method of a germanium tungstate-based crystal material with multiple active sites is completed by the following steps:

[0050] I. Synthesis of germanate stock solution: 10.5 g of cadmium powder is added to 60 mL of 6.25 mol L -1 NaOH solution and stirred, 50 mL of H2O2 is slowly added until the cadmium powder is completely dissolved, heated to 80°C until no oxygen is generated, and cooled to obtain a germanate stock solution;

[0051] II. Synthesis of germanium tungstate K4(GeW 12 O 40 )·7H2O: 35 mL of germanate stock solution is added to 125 mL of 1.25 mol L -1 sodium tungstate solution, heated to 80°C, 22.5 mL of 13 mol L -1 concentrated nitric acid is added dropwise, the solution is cooled to room temperature after 1 h, 5 mL of 1.25 mol L -1 concentrated nitric acid is added, and then extracted with ether, the ether layer is diluted with water, and then the organic layer is placed in a vacuum dryer with concentrated sulfuric acid, and left to stand until colorless crystals are precipitated, which is H4(GeW 12 O 40 )·14H2O, and then 1 mol L -1 K2CO3 solution is added to H4(GeW 12 O40 In a saturated solution of 14H2O, white microcrystals precipitate out, which is germanotungstate K4 (GeW). 12 O 40 )·7H2O, abbreviated as GeW 12 ;

[0052] III. Preparation of a multi-active-site germanium-tungstate-based crystal material: 0.27 g of K4 (GeW 12 O 40 0.135g cadmium chloride (CdCl2·4H2O), 0.45g 2,2-bipyridine (CdCl2·4H2O) 10 H8N2 was dissolved in 36 mL of deionized water, and then... -1 hydrochloric acid and 1 mol L -1 The pH of the solution was adjusted to 2.4 with sodium hydroxide solution, and the mixture was stirred at room temperature for 3.5 h to obtain a reaction solution with a pH of 2.4. The reaction solution with a pH of 2.4 was divided into three equal portions and transferred to a 20 mL reaction vessel. The mixture was kept at 160 °C for 72 h to obtain light yellow blocky crystals, which is a multi-active site germanium tungstate-based crystal material.

[0053] The molar ratio of germanotungstic acid to cadmium salt in step three is 1:6;

[0054] The germanotungstic acid and 2,2-bipyridine C mentioned in step three 10 The molar ratio of H8N2 is 1:34;

[0055] The molar ratio of germanic tungstic acid to deionized water in step three is 0.08 mmol: 36 mL.

[0056] The X-ray single-crystal diffraction structure analysis data of the multi-active-site germanium tungstate-based crystal material prepared in Example 1 are shown in Table 1. The instrument used was the Bruker Apex II single-crystal diffractometer. Table 1 shows the X-ray single-crystal diffraction structure analysis data of the multi-active-site germanium tungstate-based crystal material prepared in Example 1.

[0057] Table 1

[0058]

[0059]

[0060] a R1=∑║F o │─│F c ║ / ∑│F o │, b wR2={∑[w(F o 2 —F c 2) 2 ] / ∑[w(F o 2 ) 2 ]} 1 / 2

[0061] Single-crystal X-ray diffraction showed that Cd2-GeW 12 Belongs to the monoclinic crystal system, space group P 21 / n, crystallographic data are shown in the table. This demonstrates Cd2-GeW 12 Two-dimensional structures (such as) Figure 1 (As shown in the table). Crystallographic data are shown in the table. It is worth noting that one polyacid anion in the structure can transfer electrons to four Cd metal ions, while each Cd ion acts as an electron acceptor, simultaneously accepting electrons from two polyacid anions, thus increasing the electron transfer efficiency.

[0062] Figure 1 This is a schematic diagram of the two-dimensional layered structure of a multi-active-site germanium tungstate-based crystal material prepared in Example 1;

[0063] from Figure 1 It can be seen that the germanium tungstate-based crystal material with multiple active sites prepared in Example 1 contains polyacid anions [GeW 12 O 40 ] 4- It forms a two-dimensional layered structure of inorganic polyoxometalates with metal Cd ions. 2,2-Bipyridine C 10 The H8N2 organic ligand acts as the terminal ligand and chelates with metal Cd ions to form an organic-inorganic hybrid 2D-POMOC layered structure.

[0064] Figure 2 The infrared spectrum of a germanate-tungstate-based crystal material with multiple active sites prepared in Example 1 is shown below.

[0065] from Figure 2 It can be seen that the infrared spectrum of a multi-active-site germanate-tungstate-based crystal material is in the range of 620-1020 cm⁻¹. -1 The strong characteristic peaks appearing at this location belong to GeW 12 Anion clusters, of which 10¹⁸ cm -1 961cm -1 876cm -1 and 767cm -1 The corresponding characteristic peaks are ν(Ge-O), ν(W=Ot), ν(W-Ob-W), and ν(W-Oc-W). These peaks are located in the range of 1050-1820 cm⁻¹. -1 The characteristic peak appearing at this location is attributed to 2,2-bipyridine C. 10 The stretching vibration peak of H8N2 indicates the presence of germanotungstic acid and 2,2-bipyridine C in the crystal. 10H8N2;

[0066] Figure 3 X-ray powder diffraction spectrum of a multi-active site germanotungstate-based crystal material prepared in Example 1;

[0067] From Figure 3 It can be seen that, in order to verify the purity of the crystalline material, the crystalline material was subjected to X-ray powder diffraction experiment, and the test results (as shown in Figure 3 Due to the influence of anisotropy of the crystal, the intensity of the diffraction peak is slightly different, but the peak position obtained by the experiment has good matching with the peak position obtained by single crystal simulation, which shows that the two kinds of crystals have good purity.

[0068] Figure 4 X-ray photoelectron spectrogram of a multi-active site germanotungstate-based crystal material prepared in Example 1;

[0069] Cd2-GeW 12 The XPS spectrum of the material is shown in the figure, the XPS spectrum of Cd 3d shows two characteristic peaks, the characteristic peaks of Cd 3d 3 / 2 and Cd 3d 5 / 2 are respectively located at 410.68eV and 403.98eV, indicating that Cd exists in the form of +2 valence in the crystalline material. The peaks at 36.58 and 34.48eV respectively belong to W 4f 5 / 2 and W 4f 7 / 2 , which are typical W(VI) characteristic peaks.

[0070] In summary, in this embodiment, a one-step hydrothermal synthesis method is used, and a multi-active site germanotungstate-based crystal material is successfully synthesized by using germanotungstate, cadmium chloride, 2,2-bipyridine C 10 H8N2;

[0071] Example 2: The effect of different conditions on the photocatalytic hydrogen evolution reaction. 5mg photocatalyst was added into the reaction system, water / acetone (1 / 2) was used as the photocatalytic reaction solution, and the photocatalytic hydrogen evolution reaction was carried out under 500W xenon lamp irradiation. First, no hydrogen was released when any one of the light source, the sacrificial agent or the catalyst was absent. Then, the effect of three different sacrificial agents, lactic acid, methanol and triethylamine, on the photocatalytic hydrogen evolution reaction was investigated. When 2mL lactic acid or 2mL methanol was used as the sacrificial agent, only trace amounts of hydrogen were detected after 6h of irradiation, which indicated that the reduction ability of lactic acid and methanol was not enough to effectively prevent the recombination of photo-generated electrons and holes. Under irradiation, the organic amine solution could reduce the tungsten heteropoly acid to heteropoly blue (HPB) species, which could absorb visible light. After the W center absorbed ultraviolet light, the excited electrons jumped to the 5d orbital of W. The reducing organic amine solution could provide electrons to the f orbital of W, thereby reducing the W(VI) center to W(V). In addition, triethylamine was often used as a reducing agent during the preparation of polyacid-based crystalline hybrid materials, which could reduce metals such as Cu to a lower valence. Considering the above two points, triethylamine was chosen as the electron sacrificial agent.

[0072] Figure 5 The photocatalytic hydrogen evolution activity of a multi-active site germanium tungstate-based crystalline material prepared in Example 1 under irradiation of a light source with λ > 350 nm after 6h of photocatalytic hydrogen evolution reaction is compared.

[0073] As Figure 5 can be seen, under 500W xenon lamp irradiation, 2mL triethylamine was used as the sacrificial agent, and the photocatalytic hydrogen evolution rate of Cd2-GeW 12 was 4522μmol g -1 h -1 , which was 75.36 times that of the parent germanium tungstate.

[0074] Figure 6 The photocatalytic water decomposition stability test of a multi-active site germanium tungstate-based crystalline material prepared in Example 1 is shown in the figure.

[0075] As Figure 6 can be seen, under the optimal photocatalytic hydrogen evolution test conditions, there was little difference in the photocatalytic hydrogen evolution activity of Cd2-GeW 12 after 30h of irradiation, i.e. 5 cycles of testing, which indicated that the Cd2-GeW 12 crystalline material had good photocatalytic stability. The Cd2-GeW 12 crystalline material after the photocatalytic reaction was collected by centrifugation, and X-ray powder diffraction was used to verify the stability of the structure. As shown in the figure, the X-ray powder diffraction characteristic peaks of Cd2-GeW 12 did not change significantly, which indicated that the structure of Cd2-GeW12 The structural stability of the material does not change. The high stability of the crystalline material is mainly attributed to the preparation under high temperature and high pressure conditions, in addition, the polyacid is connected with metal Cd ions through end oxygen coordination, which increases the stability of the two-dimensional layered structure, and the two-dimensional surfaces are stacked with each other through hydrogen bond interaction, thereby enhancing the stability of the overall structure.

[0076] Figure 7 A preparation flow chart of a multi-active site germanotungstate-based crystal material prepared in Example 1.

[0077] It can be seen from Figure 7 that the preparation flow chart of the germanotungstate-based crystal material, 0.27 g of K4(GeW 12 O 40 )·7H2O, 0.135 g of cadmium chloride CdCl2·4H2O, and 0.45 g of 2,2-bipyridine C 10 H8N2 are dissolved in 36 mL of deionized water, and the solution pH is adjusted to 2.4 with 1 mol L -1 hydrochloric acid and 1 mol L -1 sodium hydroxide solution, and the solution is stirred at room temperature for 3.5 h to obtain a reaction solution with a pH value of 2.4; the reaction solution with a pH value of 2.4 is divided into three parts and transferred to a 20 mL reaction kettle, and kept at 160°C for 72 h to obtain light yellow block crystals, which are a multi-active site germanotungstate-based crystal material.

[0078] In summary, the multi-active site germanotungstate-based crystal material prepared in Example 1 has the following advantages: first, germanotungstate, transition metal elements, and 2,2-bipyridine are used as raw materials, a multi-acid metal-organic complex that has not been reported is prepared by one-pot hydrothermal synthesis, the shortcomings of traditional polyacids, such as easy dissolution in water and the need for noble metals as a cocatalyst, are overcome, and the material has more excellent photocatalytic hydrogen production activity, with a hydrogen production rate of 4522 μmol g -1 h -1 , which is 75.36 times that of the parent germanotungstate.

Claims

1. A multi-active-site germanium-tungstate-based crystal material, with the chemical formula [Cd] II 2(bipy)4(H2O)4](GeW 12 O 40 ), abbreviated as Cd2-GeW 12 ,in, Bipy is 2,2-bipyridine, with the molecular formula C2. 10 H8N2; a multi-active-site germanotungstate-based crystal material with a monoclinic crystal system; space group P21 / n; unit cell parameters α=90°, β=92.2600(10)°, γ=90°, z = 4.

2. The preparation method of the multi-active-site germanium tungstate-based crystal material as described in claim 1 is carried out according to the following steps: I. Synthesis of germanate standby solution: Add 10.5g of germanium powder to 60mL of 6.25mol / L solution. -1 Stir the NaOH solution and slowly add 50 mL of H2O2 until the germanium powder is completely dissolved. Heat to 80°C until no more oxygen is generated. Cool to obtain a germanate solution for later use. II. Germanium tungstate K4 (GeW 12 O 40 Synthesis of 7H₂O: Add 35 mL of germanate solution to 125 mL of 1.25 mol / L solution. -1 In a sodium tungstate solution, heat to 80°C, and add 22.5 mL of 13 mol / L solution dropwise. -1 Concentrated nitric acid was added, and after 1 hour the solution was cooled to room temperature. Then 5 mL of 1.25 mol / L nitric acid was added. -1 After adding concentrated nitric acid, the mixture was extracted with diethyl ether to separate the layers. The ether layer was diluted with water, and the organic layer was placed in a vacuum desiccator containing concentrated sulfuric acid and allowed to stand until colorless crystals precipitated, which is H4 (GeW). 12 O 40 )·14H2O, then add 1 mol L - 1 K2CO3 solution was added to H4 (GeW) 12 O 40 In a saturated solution of 14H2O, white microcrystals precipitate out, which is germanotungstate K4 (GeW). 12 O 40 )·7H2O, abbreviated as GeW 12 ; III. A multi-active-site germanium-tungstate-based crystal material, Cd2-GeW 12 Preparation: 0.27g of K4 (GeW) was added. 12 O 40 0.135g cadmium chloride (CdCl2·4H2O), 0.45g 2,2-bipyridine (CdCl2·4H2O) 10 H8N2 was dissolved in 36 mL of deionized water, and then... -1 hydrochloric acid and 1 mol L -1 The pH of the solution was adjusted to 2.4 with sodium hydroxide solution, and the mixture was stirred at room temperature for 3.5 h to obtain a reaction solution with a pH of 2.

4. The reaction solution with a pH of 2.4 was divided into three equal portions and transferred to a 20 mL reaction vessel. The mixture was kept at 160 °C for 72 h to obtain light yellow blocky crystals, which is a multi-active site germanium tungstate-based crystal material. The chemical formula of the multi-active-site germanium tungstate-based crystal material described in step three is [Cd]. II 2(bipy)4(H2O)4](GeW 12 O 40 A multi-active-site germanotungstate-based crystal material has a monoclinic crystal system; space group P21 / n; unit cell parameters are α=90°, β=92.2600(10)°, γ=90°, z = 4.

3. The application of the multi-active-site germanium-tungstate-based crystal material as described in claim 1, characterized in that... A multi-active-site germanium-tungstate-based crystal material exhibits excellent photocatalytic hydrogen production performance, with a photocatalytic hydrogen production rate of 4522 μmol / g. -1 h -1 It is 75.36 times the photocatalytic hydrogen production rate of the parent material germanium tungstate.

Images