POM-based photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalytic nitrogen fixation, and particularly relates to a POM-based photocatalyst as well as a preparation method and application thereof. The POM-based photocatalyst provided by the invention comprises TiO2 and Keplerate type POM, TiO2 is dispersed in water to prepare a suspension, then Keplerate type POM is added into the suspension, and stirring, washing and centrifugation are performed to prepare the POM-based photocatalyst. The POM-based photocatalyst provided by the invention is simple in preparation step and short in time consumption, water is mostly used as a solvent in the preparation process, the pollution is small, the requirement on equipment is not high, and the preparation can be realized at room temperature. The POM-based photocatalyst provided by the invention has a high-efficiency catalytic effect in a nitrogen fixation reaction taking N2 and ultrapure water as raw materials, can solve the problems of low light energy utilization rate of the catalyst, serious recombination of photon-generated carriers and the like, and realizes a high-efficiency photocatalytic nitrogen fixation effect.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic nitrogen fixation, and more specifically relates to a POM-based photocatalyst and a preparation method and application thereof. Background Art

[0002] Nitrogen is one of the essential mineral nutrients for the growth of organisms on Earth. Although nitrogen molecules account for 78% of the total volume of the atmosphere, due to their stable N≡N triple bonds, they are difficult for organisms to directly utilize and must be fixed or converted into ammonia, nitrates, etc. before they can be absorbed by organisms.

[0003] The nitrogenase produced by some organisms can fix nitrogen molecules, but it is difficult to meet all the needs of production and life by relying solely on biological nitrogen fixation. At present, the mature industrial nitrogen fixation technology is the Haber-Bosch process, which uses the iron-based catalyst surface to fix N under high temperature (573K~773K) and high pressure (100atm~200atm) conditions. 2 and H 2 The molecules are activated together to synthesize ammonia, and the harsh synthesis conditions cause additional energy consumption, and a large amount of greenhouse gases are emitted to cause environmental pollution. This process is an energy-intensive process with huge energy consumption and high greenhouse gas emissions (accounting for 1.2% of global carbon dioxide emissions).

[0004] It can be seen that the current mature industrial nitrogen fixation technology has two problems: energy crisis and environmental pollution. How to solve the energy and environmental problems in the process of synthetic ammonia has become a difficult problem that technicians in this field need to overcome urgently. Therefore, it is necessary to explore and develop or seek a clean way to achieve nitrogen fixation.

[0005] Inspired by photosynthesis in nature, the clean and inexhaustible solar energy is used to convert nitrogen 2 Reduction into ammonia (NH 3 ) or other high-value nitrogen-containing compounds. 2 Design strategies such as defect engineering, construction of single metal atoms, local surface plasmon resonance fields and formation of heterojunctions are used. Among them, the compatible energy gap between the two semiconductor materials can form a heterojunction structure. The formation of a heterojunction effectively enhances carrier separation by generating an internal electric field, thereby promoting more efficient charge separation and transport, and ultimately significantly improving the photocatalytic efficiency. However, the above methods have problems such as insufficient energy band matching and charge transfer efficiency, low ammonia production efficiency, and insufficient active sites. How to obtain a multi-metal synergistic nitrogen activation catalyst that can achieve energy band matching and efficient charge transfer has become the key to solving the problem. Summary of the invention

[0006] The purpose of the present invention is to provide a POM-based photocatalyst and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention is to provide a POM-based photocatalyst, wherein the POM-based photocatalyst comprises TiO 2 and Keplerate type POM.

[0009] Furthermore, the Keplerate type POM and TiO 2 The mass ratio is 1-4:10.

[0010] Furthermore, the TiO 2 P25 TiO 2 .

[0011] Further, the Keplerate type POM includes [Mo 72 Fe 30 O 252 (CH 3 COO 12 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 O and / or [Mo 72 Fe 30 O 252 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 O.

[0012] Optionally, the [Mo 72 Fe 30 O 252 (CH 3 COO 12 {Mo 2 O 7 (H 2O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 The preparation steps of O include: dissolving sodium molybdate and ferric chloride in a glacial acetic acid aqueous solution with a volume concentration of -60-65%, stirring, and obtaining a precipitate product, which is the [Mo 72 Fe 30 O 252 (CH 3 COO 12 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 O; wherein the dosage ratio of the sodium molybdate, ferric chloride and glacial acetic acid aqueous solution is 12-12.5mmol:7-8mmol:35-40mL.

[0013] Optionally, the [Mo 72 Fe 30 O 252 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 The preparation steps of O include: dissolving sodium molybdate and ferric chloride in a glacial acetic acid aqueous solution with a volume concentration of 60-65%, stirring, and obtaining a precipitate product, which is the [Mo 72 Fe 30 O 252 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H2 O; wherein the dosage ratio of the sodium molybdate, ferric chloride and glacial acetic acid aqueous solution is 12-12.5mmol:7-8mmol:20-25mL.

[0014] The second technical solution of the present invention is to provide a method for preparing the above-mentioned POM-based photocatalyst, comprising the following steps:

[0015] TiO 2 The photocatalyst is dispersed in water to prepare a suspension, and then Keplerate-type POM is added to the suspension, stirred, washed, and centrifuged to obtain the POM-based photocatalyst.

[0016] Furthermore, the TiO 2 The dosage ratio of 450-500mg to water is 20-25mL.

[0017] Furthermore, the Keplerate type POM and TiO 2 The mass ratio is 1-4:10.

[0018] The third technical solution of the present invention is to provide an application of the above-mentioned POM-based photocatalyst in photocatalytic nitrogen fixation.

[0019] The present invention discloses the following technical effects:

[0020] The catalyst prepared by the present invention can utilize N in the air 2 It uses water as raw materials to fix nitrogen under mild conditions. The overall reaction process is green, sustainable and pollution-free, and is expected to become a new generation of synthetic ammonia catalytic application technology.

[0021] The preparation steps of the POM-based photocatalyst provided by the present invention are simple and time-saving. Water is mostly used as a solvent in the preparation process, which has little pollution and low requirements on equipment. The preparation can be achieved at room temperature.

[0022] POM-based photocatalysts have a great potential in catalyzing the conversion of N 2 In the nitrogen fixation reaction with ultrapure water as raw materials, it has a highly efficient catalytic effect, which can solve the problems of low light energy utilization rate of catalysts and serious recombination of photogenerated carriers, and achieve efficient photocatalytic nitrogen fixation effect. Among them, POM plays a key role. POM has a wide spectrum in the range of 250-800nm, which improves the utilization rate of solar energy; POM, as an electron sponge, can store and transfer electrons, providing abundant electron-activated inert N 2 , thereby increasing the yield of the target product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 for Mo 72 Fe 30 -A and Mo 72 Fe 30 Characterization diagram of the product, where (a) is the XRD spectrum and (b) is the infrared spectrum.

[0025] Figure 2 P25, 100-Mo 72 Fe 30 @P25-A and Mo 72 Fe 30 -A characterization diagram, where (a) is P25 and 100-Mo 72 Fe 30 @XRD of P25-A, (b) P25, 100-Mo 72 Fe 30 @P25-A and Mo 72 Fe 30 -FT-IR of A.

[0026] Figure 3 P25, Mo 72 Fe 30 Characterization diagram of the POM-based photocatalysts prepared in Example 2-5, wherein (a) is the XRD of P25 and the POM-based photocatalysts prepared in Example 2-5, and (b) is the XRD of P25, Mo 72 Fe 30 FT-IR of the POM-based photocatalysts prepared in Examples 2-5.

[0027] Figure 4 for 100-Mo 72 Fe 30 @P25-A and 100-Mo 72 Fe 30 Photocatalytic performance diagram of @P25.

[0028] Figure 5 P25, Mo 72 Fe 30 And the photocatalytic performance diagram of the catalysts prepared in Examples 2-5.

[0029] Figure 6 for 100-Mo 72 Fe 30 @P25 photocatalytic performance cycle diagram.

[0030] Figure 7 for 100-Mo 72 Fe 30 @P25 produces NH 4 + of 1 HNMR spectrum.

[0031] Figure 8 for 100-Mo 72 Fe 30 @P25 photocatalytic oxygen production performance diagram. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0034] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0035] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0036] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0037] The raw materials and reagents involved in the specific implementation scheme of the present invention are all commercially available products; the "room temperature" and "normal temperature" involved all refer to 20-30°C.

[0038] Example 1

[0039] Preparation of POM-based photocatalysts:

[0040] S1. At room temperature, Na 2 MoO 4 ·2H 2 O (3 g, 12.3 mmol) was dissolved in 40 mL of 62.5% acetic acid aqueous solution (25 mL acetic acid + 15 mL deionized water) and ultrasonicated for 5 min until completely dissolved. 3 6H 2 O (2.09 g, 7.7 mmol) was added to the mixed solution and stirred vigorously for 30 min. The yellow precipitate was then collected, washed with deionized water, centrifuged (the washing and centrifugation steps were repeated 3 times), and dried at 80 °C to obtain [Mo 72 Fe 30 O 252 (CH 3 COO 12 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 O, recorded as Mo 72 Fe 30 -A; Grind for later use;

[0041] S2, take 500 mg of P25 type TiO 2 The powder was placed in 20 mL of deionized water to form a suspension, and then 100 mg of Mo was added to the suspension. 72 Fe 30 -A, stirred for 30 min, washed and centrifuged to obtain a POM-based photocatalyst, denoted as 100-Mo 72 Fe 30 @P25-A.

[0042] Example 2

[0043] Preparation of POM-based photocatalysts:

[0044] S1. At room temperature, Na 2 MoO 4 ·2H 2O (3 g, 12.3 mmol) was dissolved in 25 mL of 60.0% acetic acid aqueous solution (15 mL acetic acid + 10 mL deionized water) and ultrasonicated for 5 min until completely dissolved. 3 6H 2 O (2.09 g, 7.7 mmol) was added to the mixed solution and stirred vigorously for 30 min. The yellow precipitate was then collected, washed with deionized water, centrifuged (the washing and centrifugation steps were repeated 3 times), and dried at 80 °C to obtain [Mo 72 Fe 30 O 252 {Mo 2 O 7 (H 2 O)} 2 {H 2 Mo 2 O 8 (H 2 O)}(H 2 O) 91 ]·150H 2 O, recorded as Mo 72 Fe 30 ; Grind and set aside;

[0045] S2, take 500 mg of P25 type TiO 2 The powder was placed in 20 mL of deionized water to form a suspension, and then 50 mg of Mo was added to the suspension. 72 Fe 30 , stirred for 30 min, washed and centrifuged to obtain a POM-based photocatalyst, denoted as 50-Mo 72 Fe 30 @P25.

[0046] Example 3

[0047] Compared with Example 2, the only difference is that Mo 72 Fe 30 The dosage is 100 mg, and the product is recorded as 100-Mo 72 Fe 30 @P25.

[0048] Example 4

[0049] Compared with Example 2, the only difference is that Mo 72 Fe 30 The dosage is 150 mg, and the product is recorded as 150-Mo 72 Fe 30 @P25.

[0050] Example 5

[0051] Compared with Example 2, the only difference is that Mo 72 Fe 30 The dosage is 200 mg, and the product is recorded as 200-Mo 72 Fe 30 @P25.

[0052] Test Example 1

[0053] The Mo prepared in Example 1 72 Fe 30 -A and Mo prepared in Example 2 72 Fe 30 The results of X-ray diffraction and Fourier transform infrared spectroscopy tests are as follows: Figure 1 shown.

[0054] Figure 1 for Mo 72 Fe 30 -A and Mo 72 Fe 30 Characterization diagram, where (a) is the XRD spectrum and (b) is the infrared spectrum. 72 Fe 30 -A and Mo 72 Fe 30 All Bragg diffraction peaks are distributed only at 28°, indicating that the catalyst has non-qualitative characteristics. 72 Fe 30 -A diffraction peak intensity is higher than Mo 72 Fe 30 The intensity of the diffraction peak is stronger, which may be related to the amount of acetic acid added, making CH 3 The different coordination environments of COO- lead to different diffraction peak intensities. The structures of the two different POMs were verified by Fourier transform infrared spectroscopy (FT-IR). -1 、947cm -1 、863cm -1 、768cm -1 、625cm -1 and 571cm -1 Department, Mo 72 Fe 30 and Mo 72 Fe 30 -A all show characteristic absorption peaks, among which 1619cm -1 The characteristic peaks of OH groups are at 1000-500cm -1 The characteristic peaks in the range are attributed to 12{(Mo)Mo 5} pentagonal units, forming an icosahedral arrangement. Mo 72 Fe 30-A at 1537cm -1 and 1413cm -1 There is a characteristic absorption peak at , indicating the presence of the absorption peak of acetate ligand. 72 Fe 30 No absorption peaks were observed at these two wavenumber positions, further verifying the XRD results. The coordination environment was changed by adjusting the amount of acetic acid, resulting in differences in the material structure.

[0055] Test Example 2

[0056] The P25 (P25-type TiO 2 powder), Mo 72 Fe 30 、Mo 72 Fe 30 The chemical structures of the catalysts prepared in Example 1-5 were characterized. Figure 2-Figure 3 shown.

[0057] Figure 2 P25, 100-Mo 72 Fe 30 @P25-A and Mo 72 Fe 30 -A characterization diagram, where (a) is P25 and 100-Mo 72 Fe 30 @XRD of P25-A, (b) P25, 100-Mo 72 Fe 30 @P25-A and Mo 72 Fe 30 -FT-IR of A.

[0058] Figure 3 P25, Mo 72 Fe 30 Characterization diagram of the POM-based photocatalysts prepared in Example 2-5, wherein (a) is the XRD of P25 and the POM-based photocatalysts prepared in Example 2-5, and (b) is the XRD of P25, Mo 72 Fe 30 FT-IR of the POM-based photocatalysts prepared in Examples 2-5.

[0059] like Figure 2-Figure 3 As shown, P25 includes anatase TiO 2 (JCPDS 711-1166) and rutile TiO 2(JCPDS 75-7156). For the catalyst prepared in Example 2-5, after adding POM, the diffraction peak of the catalyst is consistent with the diffraction peak of P25, indicating that the introduction of POM will not affect the crystal shape of P25. From the infrared spectrum results, the characteristic absorption peak of POM in the composite material can be observed, which shows that the loaded POM maintains its original structural integrity. However, at 1000cm -1 Up to 500cm -1 In this range, the characteristic absorption peak of POM is relatively weak, which is attributed to the fact that the characteristic absorption peak of the Ti-O bond in P25 shows extremely high intensity in this range.

[0060] Test Example 3

[0061] A 300 W xenon lamp (PLS-SXE 300, Beijing Perfect Light Co., Ltd.) was used as the light source, and the reaction temperature of the photocatalytic reaction was maintained at 25°C.

[0062] Weigh 30 mg of the catalyst, place it in a quartz reactor, add 100 mL of ultrapure water, and apply ultrasound for 3 min to evenly disperse the photocatalyst to obtain a suspension. The nitrogen source is provided by air. Before irradiation, bubble the suspension in the dark with N 2 Stir for 30 min to allow N 2 The adsorption and desorption reached equilibrium; then the xenon lamp was turned on to irradiate the reactor at a rate of 80 mL min -1 The gas flow rate continuously passes through N 2 , 5 mL of the reaction solution was taken at regular intervals and centrifuged to remove the photocatalyst.

[0063] Figure 4 for 100-Mo 72 Fe 30 @P25-A and 100-Mo 72 Fe 30 Photocatalytic performance diagram of @P25.

[0064] Figure 5 P25, Mo 72 Fe 30 And the photocatalytic performance diagram of the catalysts prepared in Examples 2-5.

[0065] Depend on Figure 4-Figure 5 It can be seen that Figure 4 Medium 100-Mo 72 Fe 30 @P25 and 100-Mo 72 Fe 30 @P25-A's NH 4 + The yields were 48.83 μmol h-1 g -1 cat and 24.91 μmol h -1 g -1 cat ; Furthermore, Mo 72 Fe 30 The catalyst obtained by combining with P25 was further studied and it was found that the quality of doped POM was related to NH 4 + The yield shows a volcanic trend ( Figure 5 ).

[0066] Will 100-Mo 72 Fe 30 @P25 The above experiment was repeated 7 times, with an interval of 1 hour between each test cycle. The test results are as follows: Figure 6 shown.

[0067] Figure 6 for 100-Mo 72 Fe 30 @P25 photocatalytic performance cycle diagram, as shown in the figure, 100-Mo 72 Fe 30 @P25 has excellent cycle performance.

[0068] Test Example 4

[0069] To further explore NH 4 + The source of N is 15 N 2 Ultrapure water was used as feed gas. 15 N 2 Isotope experiments. Before irradiation, the solution was stirred in the dark with bubbling argon for 30 minutes to remove air from the quartz reactor. Then 200 mL 15 N 2 After the reaction, filter 100 mL of the reaction solution, add concentrated sulfuric acid to acidify to pH ~ 2, concentrate to 5 mL, take 0.6 mL of the solution, and mix with 0.1 mL D 2 O (Sigma-Aldrich, 99.99%). The mixed solution was 1 H NMR measurements ( 1 HNMR, Bruker Avance III 500MHz), the results are as follows Figure 7 shown.

[0070] Figure 7 for 100-Mo 72 Fe 30 @P25 produces NH 4+ of 1 HNMR spectrum, as can be seen from the figure, 1 The typical double peak at J=73Hz in the HNMR spectrum proves 15 NH 4 + existence.

[0071] Test Example 5

[0072] The photocatalytic nitrogen fixation process is often accompanied by O 2 To produce, disperse 30 mg of powder in 100 mL of ultrapure water, put it into the photocatalytic reaction device, pass the carrier gas to wash, and start irradiating with 300W xenon lamp; the generated gas is monitored online by gas chromatograph, the detector is TCD thermal conductivity detector, and the carrier gas is high-purity nitrogen. After irradiation for 3 hours, the oxygen production of the catalyst is detected by gas chromatography. The spectrum is collected once an hour, and the results are as follows Figure 8 shown.

[0073] Figure 8 for 100-Mo 72 Fe 30 @P25 photocatalytic oxygen production performance diagram, the figure shows that 100-Mo 72 Fe 30 @P25's O 2 The generation rate is 32.53 μmol h -1 g -1 cat .

[0074] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0075] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A POM-based photocatalyst, characterized in that: The POM-based photocatalyst includes TiO2 and Keplerate-type POM; The mass ratio of the Keplerate type POM to TiO2 is 1-4:

10.

2. The POM-based photocatalyst according to claim 1, characterized in that The TiO2 is P25 type TiO2.

3. The POM-based photocatalyst according to claim 1, characterized in that Keplerate type POM comprehensive [Mo 72 Fe 30 O 252 (CH3COO) 12 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 ]·150H2O sum / or[Mo 72 Fe 30 O 252 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 ]·150H2O.

4. The POM-based photocatalyst according to claim 3, characterized in that Said [Mo 72 Fe 30 O 252 (CH3COO) 12 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 The preparation steps of ]·150H2O include: dissolving sodium molybdate and ferric chloride in a glacial acetic acid aqueous solution with a volume concentration of 60-65%, stirring, and obtaining a precipitate product, which is the [Mo 72 Fe 30 O 252 (CH3COO) 12 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 ]·150H2O.

5. The POM-based photocatalyst according to claim 4, characterized in that The dosage ratio of the sodium molybdate, ferric chloride and glacial acetic acid aqueous solution is 12-12.5mmol:7-8mmol:35-40mL.

6. The POM-based photocatalyst according to claim 3, characterized in that Said [Mo 72 Fe 30 O 252 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 The preparation steps of ]·150H2O include: dissolving sodium molybdate and ferric chloride in a glacial acetic acid aqueous solution with a volume concentration of 60-65%, stirring, and obtaining a precipitate product, which is the [Mo 72 Fe 30 O 252 {Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O) 91 ]·150H2O.

7. The POM-based photocatalyst according to claim 6, characterized in that The dosage ratio of the sodium molybdate, ferric chloride and glacial acetic acid aqueous solution is 12-12.5mmol:7-8mmol:20-25mL.

8. A method for preparing a POM-based photocatalyst according to any one of claims 1 to 7, characterized in that the steps include: TiO2 is dispersed in water to prepare a suspension, and then Keplerate-type POM is added to the suspension, stirred, washed, and centrifuged to obtain the POM-based photocatalyst.

9. The preparation method according to claim 8, characterized in that: The dosage ratio of TiO2 and water is 400-500 mg:20-25 mL; and / or, the mass ratio of Keplerate-type POM to TiO2 is 1-4:

10.

10. Use of the POM-based photocatalyst according to any one of claims 1 to 7 in photocatalytic nitrogen fixation.

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