Photocatalytic nitrogen fixation material with built-in electric field for adjusting carrier separation as well as preparation method and application of photocatalytic nitrogen fixation material

Abstract

The invention provides a photocatalytic nitrogen fixation material with a built-in electric field for adjusting carrier separation as well as a preparation method and application of the photocatalytic nitrogen fixation material, H5PMo10V2O40 is uniformly deposited on the surface of NH2-MIL-125 (Ti), and on a two-phase interface of the constructed photocatalytic nitrogen fixation material H5PMo10V2O40 / NH2-MIL-125 (Ti) with the built-in electric field for adjusting carrier separation, the surface of the photocatalytic nitrogen fixation material is uniformly deposited on the surface of the NH2-MIL-125 (Ti). A strong built-in electric field is spontaneously generated due to the balance trend of Fermi level, the electron migration rate is increased, electrons and holes with strong oxidation-reduction capacity in the catalyst are reserved, the photocatalytic nitrogen fixation activity is improved, the generation rate of ammonia can reach 81.5 mu mol.g <-1 >. H <-1 >, and after the catalyst is recycled for multiple times, the generation rate of ammonia can reach 81.5 mu mol.g <-1 >. H <-1 >. The experimental process is convenient and fast, and experimental parameters are easy to control.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and in particular relates to a photocatalytic nitrogen-fixing material with a built-in electric field to regulate carrier separation, and a preparation method and application thereof. Background Art

[0002] Ammonia (NH 3 ) is one of the most highly produced inorganic compounds in the world and plays an important role in promoting the development of human society. In agriculture, ammonia is used to produce nitrogen fertilizers, which can increase crop yields and ensure global food supply. In industrial applications, ammonia can be used as a refrigerant to absorb heat. The synthesis of ammonia mainly relies on the high temperature and high pressure Haber-Bosch method. Due to the harsh reaction conditions, the requirements for production equipment are very high. In addition, the energy consumed by this ammonia synthesis process accounts for 2% of the world's energy. Photocatalytic nitrogen fixation technology uses light energy to trigger N 2 and H 2 O reaction, achieving nitrogen fixation under mild conditions, can reduce energy consumption and pollutant emissions.

[0003] With the continuous deepening of research on photocatalytic nitrogen fixation technology, three-dimensional porous structures with unique physical and chemical properties have become a hot topic in photocatalyst research. Metal organic frameworks (MOFs) are a new type of porous three-dimensional material composed of metal clusters and organic ligands. 2 -MIL-125(Ti) has multiple advantages in photocatalytic nitrogen fixation: large specific surface area, which can provide more active sites for photocatalytic reaction; high-valent metal cation Ti 4+ There are abundant unoccupied d orbitals in the 2 active sites; light energy 2 -MIL-125(Ti) can be reflected and scattered multiple times inside, which improves the utilization rate of light energy by the catalyst. 2 -MIL-125(Ti) is slightly modified to further enhance its photocatalytic activity. For example, patent CN110548545A discloses four titanium-based metal organic framework materials. 2 The modified MIL-125(Ti) can expand the light absorption range of the catalyst, and its catalytic performance is better than the other three catalysts, but the ammonia generation rate is still at a low level. For example, patent CN118388778A discloses a Ni-doped NH 2 -MIL-125(Ti), the electronic structure around the titanium clusters is changed by introducing Ni, but NH 2 -MIL-125-NiN 2 Reduction to NH 3The rate increase is not obvious; in patent CN118325103A, NH 2 -MIL-125(Ti) in N 2 The material is heated at a certain rate in the atmosphere to form oxygen defects, thereby promoting the separation of photogenerated carriers. However, the flow rate and heating rate of the gas flow are strictly required during the preparation process. It is often difficult to ensure the accuracy of the nitrogen flow rate in actual operation. In repeated experiments, NH 2 -MIL-125(Ti) contains oxygen defects that are difficult to achieve complete consistency. 2 -MIL-125(Ti) as a photocatalyst for nitrogen fixation still cannot achieve NH 2 -The rapid migration of carriers in the MIL-125(Ti) system results in a low rate of ammonia generation; the effect of the built-in electric field on the catalytic activity is not considered in the analysis of the electron migration process.

[0004] Therefore, how to improve NH 2 -The migration rate of photogenerated carriers in MIL-125(Ti) provides a rich source of reducing electrons for the photocatalytic nitrogen fixation process.

[0005] The information disclosed in this background section is intended to enhance understanding of the overall background of the invention and should not be taken as an acknowledgement or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0006] As mentioned above, the single-phase catalyst NH 2 -MIL-125 (Ti) has a low ammonia generation rate. It is an effective strategy to construct a photocatalytic nitrogen fixation material with built-in electric field to regulate carrier separation. At the two-phase interface of the heterojunction, a strong built-in electric field is spontaneously generated due to the equilibrium trend of the Fermi level, which significantly accelerates electron migration. At the same time, the electrons and holes with strong redox ability in the catalyst are retained. Studies have shown that the catalyst with built-in electric field to regulate carrier separation constructed by MOFs and polyoxometalates (POMs) is a promising method to improve photocatalytic performance. Keggin-type polyoxometalates H 5 PMo 10 V 2 O 40 It is the most widely used POMs. Its anion diameter is about 1 nm. It has the characteristics of simple composition, convenient preparation method and high stability, especially H 5 PMo 10 V 2 O 40 The reversible multi-electron redox conversion characteristics make it a hot topic in photocatalytic research.5 PMo 10 V 2 O 40 The specific surface area is small (<10m 2 / g), which is not conducive to fully exerting its catalytic performance. 2 -H loaded on MIL-125(Ti) carrier 5 PMo 10 V 2 O 40 The problem of degradation of catalytic performance caused by polyacid aggregation can be prevented.

[0007] Therefore, the present invention provides a photocatalytic nitrogen fixation material with built-in electric field to regulate carrier separation and a preparation method and application thereof to solve the problem of NH 2 -The photocatalytic ammonia synthesis rate of MIL-125 (Ti) is not ideal. The photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation has a simple synthesis process and high nitrogen fixation activity.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0009] A photocatalytic nitrogen-fixing material with built-in electric field to regulate carrier separation and a preparation method thereof, wherein the photocatalyst comprises NH 2 -MIL-125(Ti) and Keggin type polyacid H 5 PMo 10 V 2 O 40 , under the action of electrostatic force, NH 2 -MIL-125(Ti) and H 5 PMo 10 V 2 O 40 Self-assembly occurs, and H 5 PMo 10 V 2 O 40 Uniform deposition in NH 2 -MIL-125(Ti) surface.

[0010] In another aspect, the present invention provides a method for synthesizing the photocatalytic nitrogen-fixing material with built-in electric field regulating carrier separation. The detailed experimental steps are as follows:

[0011] (1) Prepare H by mixing sodium metavanadate, disodium hydrogen phosphate and sodium molybdate solutions 5 PMo 10 V 2 O 40 ;

[0012] (2) Solvothermal synthesis of NH 2-MIL-125(Ti), 2-aminoterephthalic acid and tetrabutyl titanate were dissolved in a mixed solution of methanol and N,N-dimethylformamide (DMF), and the resulting mixture was heated in an autoclave to obtain NH 2 -MIL-125(Ti);

[0013] (3)H 5 PMo 10 V 2 O 40 With NH 2 -MIL-125(Ti) was stirred in HCl solution and self-assembled into H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti).

[0014] In some embodiments, as described in step (1), 2.44 g of sodium metavanadate is added to 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate is dissolved in water (10 mL) and mixed with the above solution and stirred for 0.5-2 h, and after cooling to room temperature, 0.5 mL of concentrated sulfuric acid is added to obtain a red mixed solution, and then 20 mL of an aqueous solution containing 12.1 g of sodium molybdate is mixed with the red solution, and then 8.5 mL of concentrated sulfuric acid is continued to be dropped into the solution, and finally the obtained solution is mixed with 50 mL of ether, and after stratification, the intermediate orange solution is collected, and after ether is evaporated, H 5 PMo 10 V 2 O 40 .

[0015] In some embodiments, as described in step (2), 2-aminoterephthalic acid (1.086 g) is dissolved in 1-3 mL of methanol and 17-19 mL of DMF, the mixed solution is stirred for 20 min, tetrabutyl titanate (0.52 mL) is added and stirring is continued for 30 min, the resulting solution is transferred to an autoclave and heated, cooled to room temperature, and then centrifuged at 10,000 rpm for 5 min to collect the solid product.

[0016] In some embodiments, in step (3), H 5 PMo 10 V 2 O 40 Dissolve in HCl solution and continue to add NH 2 -MIL-125(Ti) was stirred at room temperature for 6-14h and then washed with H 5 PMo 10 V 2 O 40 / NH 2-MIL-125(Ti) catalyst and heated at 70°C for 12h.

[0017] In some embodiments, in step (3), H 5 PMo 10 V 2 O 40 With NH 2 -MIL-125(Ti) molar ratio is (0.5-1.5):100; preferably, H 5 PMo 10 V 2 O 40 With NH 2 -The molar ratio of MIL-125(Ti) is 1.0:100.

[0018] In some embodiments, in step (2), the autoclave is kept in an electric blast drying oven at 150° C. for 18-22 hours, and the heating rate of the electric blast drying oven is 2-3° C. / min.

[0019] In some embodiments, in step (2), the stirring speed is 1000-1200 rpm.

[0020] In some embodiments, in step (3), the concentration of the HCl solution is 0.1 mol / L, and the volume of the HCl solution is 8-12 mL.

[0021] In some embodiments, in step (3), the stirring speeds for both times are 1000-1200 rpm.

[0022] In some embodiments, washing H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) catalyst, characterized in that H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) 2-4 times to remove the uncontaminated 2 -MIL-125(Ti) combined with H 5 PMo 10 V 2 O 40 and HCl in the solution, so that the obtained H 5 PMo 10 V 2 O 40 / NH 2-MIL-125(Ti) does not contain other impurity ions.

[0023] In some embodiments, step (3) may also be performed by adding H 5 PMo 10 V 2 O 40 With NH 2 -MIL-125(Ti) mixture was ball milled to obtain the photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation. 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti).

[0024] In a third aspect, the present invention provides a photocatalytic material H having a built-in electric field to regulate carrier separation. 5 PMo 10 V 2 O 40 / NH 2 -Application of MIL-125(Ti) in nitrogen fixation performance.

[0025] In some embodiments, the use of a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation is characterized in that the composite photocatalyst H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) is dissolved in pure water, high-purity nitrogen is introduced, and nitrogen fixation reaction is carried out under the combined action of stirring and full light irradiation.

[0026] In some embodiments, the photocatalytic nitrogen fixation material H with built-in electric field regulated carrier separation 5 PMo 10 V 2 O 40 / NH 2 -The mass ratio of MIL-125(Ti) to pure water is (1-10): 10000;

[0027] In some embodiments, the flow rate of high purity nitrogen is 50 mL / min;

[0028] In some embodiments, full light illumination is provided by a 300W xenon lamp.

[0029] The beneficial effects of the present invention are:

[0030] 1. The photocatalytic nitrogen fixation material provided by the present invention has a built-in electric field to regulate carrier separation, H 5 PMo 10 V2 O 40 Uniform deposition in NH 2 -MIL-125(Ti) surface; at the two-phase interface of the photocatalytic nitrogen fixation material constructed with built-in electric field regulating carrier separation, a strong built-in electric field is spontaneously generated due to the equilibrium trend of the Fermi level, which accelerates the electron migration rate, while the electrons and holes with strong redox ability in the catalyst are retained; the photocatalytic nitrogen fixation activity is improved, and the ammonia generation rate can reach 81.5μmol·g -1 ·h -1 , the catalyst can still maintain a high ammonia production rate after multiple cycles of use.

[0031] 2. The present invention uses solvent thermal and electrostatic self-assembly methods to prepare a photocatalytic nitrogen fixation material with built-in electric field to regulate carrier separation. 5 PMo 10 V 2 O 40 and NH 2 -MIL-125(Ti) is stirred in HCl solution to obtain a photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation. 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti), the experimental process is convenient and the experimental parameters are easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The photocatalytic nitrogen fixation material H with built-in electric field regulating carrier separation in Example 1 5 PMo 10 V 2 O 40 / NH 2 -SEM image of MIL-125(Ti);

[0033] Figure 2 Example 1H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti), Comparative Example 1H 5 PMo 10 V 2 O 40 And comparative example 2NH 2 - X-ray diffraction pattern of MIL-125(Ti);

[0034] Figure 3 is H of Example 1-35 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) and NH of Comparative Example 2 2 -Photocurrent spectrum of MIL-125(Ti);

[0035] Figure 4 Example 1H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) and Comparative Example 2NH 2 -Photoluminescence spectrum of MIL-125(Ti);

[0036] Figure 5 Comparative Example 1H 5 PMo 10 V 2 O 40 And comparative example 2NH 2 -Ultraviolet photoelectron spectrum of MIL-125(Ti);

[0037] Figure 6 Comparative Example 1H 5 PMo 10 V 2 O 40 And comparative example 2NH 2 -The built-in electric field generated between MIL-125(Ti) and the directional transfer of electrons under light irradiation;

[0038] Figure 7 The photocatalytic nitrogen fixation material H with built-in electric field regulating carrier separation in Example 1 5 PMo 10 V 2 O 40 / NH 2 -Photocatalytic cycle test of MIL-125(Ti). DETAILED DESCRIPTION

[0039] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0040] The embodiments of the present invention are described by the following specific examples, and those skilled in the art can understand other advantages and effects of the present invention in detail from the contents described in this specification. The present invention can also be implemented or applied using other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] The reagents and instruments used in the embodiments are as follows:

[0042] The structure and morphology of the prepared samples were observed by scanning electron microscope (SEM) with model Hitachi SU-8000FE-SEM, the composition of the synthesized samples was studied by X-ray diffractometer (XRD) with model Siemens D5005, the photocurrent performance of the samples was tested by a three-electrode CHI661D electrochemical workstation, the photoluminescence (PL) spectra of the prepared samples were detected by F-7000 fluorescence spectrophotometer, the UV photoelectron spectrum was measured by a Thermo Scientific K-Alpha photoelectron spectrometer, and the UV-visible diffuse reflectance spectrum of the samples was detected by a Varian cary 700 spectrophotometer.

[0043] Sodium metavanadate, disodium hydrogen phosphate, sodium molybdate, and 2-aminoterephthalic acid were purchased from Aladdin Reagent Co., Ltd., and concentrated sulfuric acid, ether, methanol, DMF, tetrabutyl titanate, and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemical reagents were not treated before use.

[0044] Example 1

[0045] The synthesis method of photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation, the detailed steps are as follows:

[0046] (1) 2.44 g of sodium metavanadate was added to 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate was dissolved in water (10 mL) and mixed with the above solution and stirred for 1 h at a stirring speed of 1100 rpm. After cooling to room temperature, 0.5 mL of concentrated sulfuric acid was added to obtain a red mixed solution. Then 20 mL of an aqueous solution containing 12.1 g of sodium molybdate was mixed with the red solution. Subsequently, 8.5 mL of concentrated sulfuric acid was added dropwise to the solution. Finally, the obtained solution was mixed with 50 mL of ether. After stratification, the orange solution in the middle layer was collected. After ether evaporated, H 5 PMo 10 V 2 O 40 .

[0047] (2) 2-Aminoterephthalic acid (1.086 g) was dissolved in 2 mL of methanol and 18 mL of DMF. The mixed solution was stirred for 20 min, and then tetrabutyl titanate (0.52 mL) was added and stirred for 30 min. The stirring speed was 1100 rpm. The obtained solution was transferred to an autoclave and heated in an electric blast drying oven for 20 h at a heating rate of 2°C / min. After cooling to room temperature, the solid product NH 2 -MIL-125(Ti).

[0048] (3) 0.01 mol H 5 PMo 10 V 2 O 40 Dissolve in 10mL HCl (0.1mol / L) solution and add 1mol NH 2 -MIL-125(Ti), stirred at 1100 rpm for 10 h at room temperature, and then washed with pure water. 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) catalyst 3 times and heated at 70°C for 12h.

[0049] Example 2

[0050] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0051] Same as Example 1, except that in step (3), H 5 PMo 10 V 2 O 40 The amount added is 0.005 mol.

[0052] Example 3

[0053] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0054] Same as Example 1, except that in step (3), H 5 PMo 10 V 2 O 40 The amount added is 0.015 mol.

[0055] Example 4

[0056] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0057] The same as Example 1, except that the solution obtained in step (2) is transferred to an autoclave and heated in an electric heated forced air drying oven for 18 hours.

[0058] Example 5

[0059] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0060] The same as Example 1, except that the solution obtained in step (2) is transferred to an autoclave and heated in an electric heated forced air drying oven for 22 hours.

[0061] Example 6

[0062] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0063] Same as Example 1, except that in step (3), the mixture was stirred at 1100 rpm for 6 h at room temperature.

[0064] Example 7

[0065] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0066] Same as Example 1, except that in step (3), the mixture was stirred at 1100 rpm for 14 h at room temperature.

[0067] Example 8

[0068] The synthesis method of the photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation specifically comprises the following steps:

[0069] Same as Example 1, except that in step (3), 0.01 mol H 5 PMo 10 V 2 O 40 and 1 mol NH 2 -MIL-125(Ti) was ground in a ball mill for 10 h to obtain the photocatalytic nitrogen fixation material H with built-in electric field regulated carrier separation. 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti).

[0070] Comparative Example 1 Single-phase Catalyst H 5 PMo 10 V 2 O 40 Preparation

[0071] According to the preparation method of step (1) of Example 1, a single-phase catalyst H was prepared. 5 PMo 10 V 2 O 40 .

[0072] Comparative Example 2 Single-phase catalyst NH 2 -Preparation of MIL-125(Ti)

[0073] According to the preparation method of step (2) of Example 1, a single-phase catalyst NH 2 -MIL-125(Ti).

[0074] Verification Example

[0075] 1. Scanning electron microscopy and transmission electron microscopy characterization

[0076] The photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation prepared in Example 1 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) was tested by SEM, Figure 1 The photocatalytic nitrogen fixation material H with built-in electric field regulating carrier separation in Example 1 5 PMo 10 V 2 O 40 / NH 2 -SEM image of MIL-125(Ti), from which we can observe NH 2 -Many tiny particles H are uniformly deposited on the surface of MIL-125(Ti) 5 PMo 10 V 2 O 40 , H 5 PMo 10 V 2 O 40 With NH 2 -MIL-125(Ti) formed a close interface connection.

[0077] 2. X-ray diffraction test

[0078] The photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation prepared in Example 1 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti), Comparative Example 1H 5 PMo 10V 2 O 40 And comparative example 2NH 2 -MIL-125(Ti) was tested by X-ray diffraction. The test results are as follows Figure 2 As shown in the figure, it can be observed that H 5 PMo 10 V 2 O 40 / NH 2 -Signal peak of MIL-125(Ti) and comparative example 2NH 2 -MIL-125(Ti) is almost the same, which may be due to the comparative example 1H 5 PMo 10 V 2 O 40 due to low content.

[0079] 3. Photocurrent test

[0080] Figure 3 is H of Example 1-3 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) and Comparative Example 2NH 2 -Photocurrent spectrum of MIL-125(Ti), compared with comparative example 2NH 2 -MIL-125(Ti), the H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) has a stronger photocurrent signal. As can be seen from the figure, Example 1H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125 (Ti) photocurrent intensity is about the same as that of NH in Example 2 2 -5 times that of MIL-125(Ti), indicating that Example 1 has better photocatalytic activity.

[0081] 4. Photoluminescence test

[0082] Figure 4 Example 1H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) and Comparative Example 2NH 2- Photoluminescence spectrum of MIL-125(Ti), comparative example 2NH 2 -The signal peak intensity of MIL-125(Ti) is significantly higher than that of Example 1H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti), implying Example 1H 5 PMo 10 V 2 O 40 / NH 2 -The photogenerated carriers in MIL-125(Ti) are more easily separated, which is conducive to the occurrence of photocatalytic nitrogen fixation reaction.

[0083] 5. Ultraviolet photoelectron spectroscopy test

[0084] Comparative Example 1H 5 PMo 10 V 2 O 40 And comparative example 2NH 2 -MIL-125(Ti) was tested for UV photoelectron spectroscopy. The test results Figure 5 As shown, the work function (Φ) is calculated as follows: ( is the work function of the photoelectron spectrometer, ΔV is the contact potential difference), from Figure 5 The ΔV values ​​of Comparative Examples 1 and 2 can be obtained from the table. Therefore, NH 2 -MIL-125 and H 5 PMo 10 V 2 O 40 The Φ of the materials are 7.77 and 9.70 eV respectively. f ) is calculated by the following formula: f =E vac -Φ, where Evac is the vacuum energy level (assumed to be 0 eV), and the calculated NH 2 -MIL-125 and H 5 PMo 10 V 2 O 40 E f The values ​​are 7.77 and 9.70 eV eV respectively.

[0085] 6. Built-in electric field and directional electron transfer

[0086] Figure 6 Comparative Example 1H 5 PMo 10 V2 O 40 And comparative example 2NH 2 -MIL-125(Ti) generated between the built-in electric field and the directional transfer of electrons under light irradiation, such as Figure 6 As shown, Comparative Example 1H 5 PMo 10 V 2 O 40 E f Significantly lower than comparative example 2NH 2 -MIL-125(Ti), NH 2 -MIL-125(Ti) and H 5 PMo 10 V 2 O 40 After the interface is in close contact, due to E f The equilibrium trend of H 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) heterojunction forms a strong built-in electric field (IEF), and the existence of IEF promotes the spontaneous electrons from H 5 PMo 10 V 2 O 40 To NH 2 -MIL-125(Ti) migration, due to electron loss, NH 2 -MIL-125(Ti) presents a positively charged interface, H 5 PMo 10 V 2 O 40 The interface region of NH 2 -The electrons in MIL-125(Ti) are repelled by the IEF, which increases the potential energy and bends the energy band upward. 5 PMo 10 V 2 O 40 The energy band bends downward. Under the dual effects of IEF and energy band bending, H 5 PMo 10 V 2 O 40 The photoelectrons generated in the conduction band (CB) of the 2 -In the valence band (VB) of MIL-125(Ti), H 5 PMo 10 V 2 O 40 / NH 2-MIL-125(Ti) heterojunction retains holes and electrons with strong redox ability, comparative example 1H 5 PMo 10 V 2 O 40 And comparative example 2NH 2 The built-in electric field formed between the Ti and MIL-125(Ti) is an effective way to accelerate the migration of photogenerated carriers and improve the utilization of electrons, thereby promoting photocatalytic nitrogen fixation.

[0087] 7. Photocatalytic cycle test

[0088] Figure 7 The photocatalytic nitrogen fixation material H with built-in electric field regulating carrier separation in Example 1 5 PMo 10 V 2 O 40 / NH 2 -Photocatalytic cycle test of MIL-125(Ti), Figure 7 It can be observed that after five cycles, the ammonia generation rate can still reach 70.8 μmol g -1 h -1 , photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti) has good stability.

[0089] 8. Photocatalytic nitrogen fixation reaction

[0090] The photocatalytic performance of the synthesized photocatalyst Examples 1-7 and Comparative Examples 1-2 was tested to explore their nitrogen fixation activity. The specific steps are as follows:

[0091] Add 0.05 g of photocatalyst to the photocatalytic reactor, add 100 mL of pure water, stir evenly, and introduce high-purity N into the reactor in the dark. 2 To remove the air in the reaction vessel, bubbling was continued for 30 min, and a 300 W xenon lamp (200 mW cm -2 ) simulated full spectrum irradiation, removed the catalyst in the catalytic solution by centrifugation, and detected the amount of ammonia generated in the supernatant. The detailed photocatalytic nitrogen fixation results are shown in Table 1.

[0092] The photocatalytic nitrogen fixation performance of the synthesized photocatalyst Examples 1-7 and Comparative Examples 1-2 was tested. The supernatant obtained by centrifugation was injected into a quartz cuvette, and the amount of ammonia was detected using a Varian Cary 700 UV-visible spectrophotometer. The test results of the ammonia generation rate are shown in Table 1.

[0093] Table 1 Ammonia generation rate of photocatalysts prepared in different embodiments / comparative examples in nitrogen fixation reaction

[0094]

[0095]

[0096] As can be seen from Table 1, the comparative example 1H prepared by the present invention 5 PMo 10 V 2 O 40 And comparative example 2NH 2 -MIL-125(Ti) had ammonia generation rate of 3.1 μmol·g -1 ·h -1 and 10.7 μmol·g -1 ·h -1 , photocatalytic nitrogen fixation material H with built-in electric field to regulate carrier separation 5 PMo 10 V 2 O 40 / NH 2 -The nitrogen fixation performance of MIL-125(Ti) is much higher than that of the two comparative examples, and the ammonia generation rate is 81.5 μmol·g -1 ·h -1 The built-in electric field constructed in the present invention to regulate carrier separation is an effective method to improve nitrogen fixation activity. At the two-phase interface of the heterojunction, a strong built-in electric field is spontaneously generated due to the equilibrium trend of the Fermi level, thereby significantly accelerating electron migration, while electrons and holes with strong redox ability in the catalyst are retained.

[0097] From the ammonia generation rates of the synthesized photocatalyst Examples 1-3, it can be seen that the photocatalytic nitrogen fixation material H with built-in electric field regulated carrier separation 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti)H 5 PMo 10 V 2 O 40 and NH 2 -MIL-125(Ti) ratio has an important influence on nitrogen fixation performance. 5 PMo 10 V 2 O 40 and NH 2When the molar ratio of -MIL-125(Ti) is 1:100, the catalytic performance of the synthesized heterojunction photocatalyst is significantly higher than that of heterojunction catalysts with other ratios.

[0098] From the ammonia generation rates of the synthesized photocatalysts in Examples 1, 4, and 5, it can be seen that the synthesis of NH 2 -MIL-125(Ti), different heating time makes the photocatalyst H 5 PMo 10 V 2 O 40 / NH 2 -The nitrogen fixation performance of MIL-125(Ti) is affected.

[0099] From the ammonia generation rates of the synthesized photocatalysts Examples 1, 6, and 7, it can be seen that H 5 PMo 10 V 2 O 40 and NH 2 -The effect of stirring time in HCl solution on the photocatalytic nitrogen fixation material H with built-in electric field regulating charge carrier separation 5 PMo 10 V 2 O 40 / NH 2 -Nitrogen fixing properties of MIL-125(Ti).

[0100] From the ammonia generation rates of the synthesized photocatalysts in Examples 1 and 8, it can be seen that the photocatalytic nitrogen fixation material H with built-in electric field regulated carrier separation is constructed in step (3). 5 PMo 10 V 2 O 40 / NH 2 -MIL-125(Ti),H 5 PMo 10 V 2 O 40 and NH 2 -MIL-125(Ti) composite method affects the nitrogen fixation activity.

Claims

1. A method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation, characterized in that: The synthesis steps include: Step 1: Prepare H5PMo by mixing sodium metavanadate, disodium hydrogen phosphate and sodium molybdate solutions 10 V2O 40 ; Step 2: NH2-MIL-125(Ti) is synthesized by a solvothermal method, wherein 2-aminoterephthalic acid and tetrabutyl titanate are dissolved in a mixed solution of methanol and N,N-dimethylformamide (DMF), and the resulting mixture is heated in an autoclave to obtain NH2-MIL-125(Ti); Step 3: H5PMo 10 V2O 40 Stirring with NH2-MIL-125(Ti) in HCl solution, the self-assembled into H5PMo under the action of electrostatic force 10 V2O 40 / NH2-MIL-125(Ti).

2. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 1, characterized in that: In step 1, 2.44 g of sodium metavanadate was added to 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate was dissolved in water (10 mL) and mixed with the above solution and stirred for 0.5-2 h, and 0.5 mL of concentrated sulfuric acid was added after cooling to room temperature to obtain a red mixed solution, and then 20 mL of an aqueous solution containing 12.1 g of sodium molybdate was mixed with the red solution, and then 8.5 mL of concentrated sulfuric acid was continued to be dropped into the solution, and finally the obtained solution was mixed with 50 mL of ether, and the intermediate orange solution was collected after stratification, and H5PMo was obtained after the ether was evaporated. 10 V2O 40 .

3. The method for preparing a photocatalytic nitrogen-fixing material with built-in electric field regulated carrier separation according to claim 1, characterized in that: In step 2, 2-aminoterephthalic acid (1.086 g) was dissolved in 1-3 mL of methanol and 17-19 mL of DMF. After the mixed solution was stirred for 20 min, tetrabutyl titanate (0.52 mL) was added and stirred for 30 min. The obtained solution was transferred to an autoclave and heated. After cooling to room temperature, the solid product was collected by centrifugation at 10,000 rpm for 5 min.

4. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 1, characterized in that: In step 3, H5PMo 10 V2O 40 Dissolve in HCl solution, continue to add NH2-MIL-125(Ti) and stir at room temperature for 6-14h, then wash H5PMo 10 V2O 40 / NH2-MIL-125(Ti) catalyst and heated at 70°C for 12h.

5. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 1, characterized in that: In step 3, H5PMo 10 V2O 40 The molar ratio of H5PMo to NH2-MIL-125(Ti) is (0.5-1.5):100; preferably, 10 V2O 40 The molar ratio to NH2-MIL-125(Ti) is 1.0:

100.

6. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 3, characterized in that: In step 2, the autoclave is kept in an electric heated forced air drying oven at 150° C. for 18-22 hours.

7. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 4, characterized in that: In step 3, the concentration of the HCl solution is 0.1 mol / L, and the volume of the HCl solution is 8-12 mL.

8. The method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation according to claim 4, characterized in that: Wash H5PMo with deionized water 10 V2O 40 / NH2-MIL-125(Ti) 2-4 times to remove H5PMo that is not combined with NH2-MIL-125(Ti) 10 V2O 40 and HCl in the solution to obtain H5PMo 10 V2O 40 / NH2-MIL-125(Ti) does not contain other impurity ions.

9. A photocatalytic nitrogen fixation material with built-in electric field regulating carrier separation, characterized in that: Prepared by any one of the preparation methods of claims 1-8.

10. The use of a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation in nitrogen fixation according to claim 9, characterized in that: The composite photocatalyst H5PMo 10 V2O 40 / NH2-MIL-125(Ti) is dissolved in pure water, high-purity nitrogen is introduced, and nitrogen fixation reaction is carried out under the combined action of stirring and full light irradiation.

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