A photocatalytic nitrogen-fixing material with built-in electric field to regulate carrier separation, as well as its preparation method and application

Abstract

The present invention provides a photocatalytic nitrogen fixation material with built-in electric field to regulate carrier separation, a preparation method and an application thereof, H5PMo 10 V2O 40 Uniformly deposited on the surface of NH2-MIL-125(Ti), the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulating carrier separation 10 V2O 40 At the two-phase interface of / NH2-MIL-125(Ti), a strong built-in electric field is spontaneously generated due to the equilibrium trend of the Fermi level, which accelerates the electron migration rate. At the same time, the electrons and holes with strong redox ability in the catalyst are retained, and the photocatalytic nitrogen fixation activity is improved. The ammonia generation rate can reach 81.5μmol·g ‑1 ·h ‑1 After multiple cycles of use, the catalyst can still maintain a high ammonia production rate. The experimental process is convenient and the 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 (NH3) is one of the world's most abundant inorganic compounds and plays a vital role in promoting the development of human society. In agriculture, ammonia is used to produce nitrogen fertilizer, which increases crop yields and ensures global food supply. In industrial applications, ammonia can be used as a heat-absorbing refrigerant. Ammonia synthesis primarily relies on the high-temperature, high-pressure Haber-Bosch process. Due to the harsh reaction conditions, the production equipment requirements are very high. Furthermore, this ammonia synthesis process consumes 2% of global energy. Photocatalytic nitrogen fixation technology uses light energy to trigger the reaction between N2 and H2O, achieving nitrogen fixation under mild conditions, which 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 photocatalytic research. Metal organic frameworks (MOFs) are a new type of porous three-dimensional material composed of metal clusters and organic ligands. Among them, NH2-MIL-125 (Ti) has multiple advantages in photocatalytic nitrogen fixation: large specific surface area, which can provide more active sites for photocatalytic reactions; high-valent metal cations Ti 4+The abundant unoccupied d orbitals in the porous NH2-MIL-125(Ti) serve as active sites for nitrogen. Light energy is reflected and scattered multiple times within the porous NH2-MIL-125(Ti), increasing the catalyst's efficiency in utilizing light energy. Researchers have further enhanced the photocatalytic activity of NH2-MIL-125(Ti) by slightly modifying it. For example, patent CN110548545A discloses four titanium-based metal-organic framework materials. The study found that -NH2-modified MIL-125(Ti) can expand the light absorption range of the catalyst and has better catalytic performance than the other three catalysts, but the ammonia generation rate is still at a low level. For example, patent CN118388778A discloses a Ni-doped NH2-MIL-125(Ti). By introducing Ni, the electronic structure around the titanium cluster is changed, but the rate of N2 reduction to NH3 by NH2-MIL-125-Ni is not significantly increased. In patent CN118325103A, NH2-MIL-125(Ti) is heated at a certain rate in an N2 atmosphere to form oxygen defects in the material, thereby promoting the separation of photogenerated carriers. However, the preparation process has strict requirements on the flow rate and heating rate of the gas flow. It is often difficult to ensure the accuracy of the nitrogen flow rate in actual operation. In repeated experiments, the amount of oxygen defects contained in NH2-MIL-125(Ti) is difficult to achieve complete consistency. However, in the existing technology, the photocatalyst using NH2-MIL-125(Ti) as the main nitrogen fixation body still cannot achieve rapid migration of carriers within the NH2-MIL-125(Ti) system, resulting in a low ammonia production rate; in the analysis of the electron migration process, the influence of the built-in electric field on the catalytic activity is not considered.

[0004] Therefore, how to improve the migration rate of photogenerated carriers in NH2-MIL-125(Ti) through a simple modification method to provide 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 acknowledgment 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 ammonia generation rate of the single-phase catalyst NH2-MIL-125 (Ti) is low. 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, thereby significantly accelerating electron migration. At the same time, 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 (abbreviated as polyoxometalates, POMs) is a very promising method to improve photocatalytic performance. Keggin-type polyoxometalates H5PMo 10 V2O 40 It is the most widely used POMs, with an anion diameter of about 1nm, and has the characteristics of simple composition, convenient preparation method, and high stability, especially H5PMo 10 V2O 40 Its reversible multi-electron redox conversion characteristics make it a hot topic in photocatalytic research. 10 V2O 40 The specific surface area is small (<10m 2 / g), which is not conducive to fully exerting its catalytic performance. H5PMo was loaded on the NH2-MIL-125(Ti) carrier. 10 V2O 40 It can prevent the problem of catalytic performance degradation caused by polyacid aggregation.

[0007] Therefore, the present invention provides a photocatalytic nitrogen-fixing material with built-in electric field-regulated carrier separation, as well as its preparation method and application, to address the problem of unsatisfactory ammonia synthesis rate using NH2-MIL-125(Ti) photocatalytic methods. This photocatalytic nitrogen-fixing material with built-in electric field-regulated carrier separation has a simple synthesis process and high nitrogen-fixing activity.

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

[0009] A photocatalytic nitrogen fixation material with built-in electric field to regulate carrier separation and a preparation method thereof, wherein the photocatalyst comprises NH2-MIL-125 (Ti) and Keggin-type polyacid H5PMo 10 V2O 40 Under the action of electrostatic force, NH2-MIL-125(Ti) and H5PMo 10 V2O 40 Self-assembly occurs, and H5PMo 10 V2O 40 Uniformly deposited on the surface of NH2-MIL-125(Ti).

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

[0011] (1) Preparation of H5PMo by mixing sodium metavanadate, disodium hydrogen phosphate and sodium molybdate solutions 10 V2O 40 ;

[0012] (2) NH2-MIL-125(Ti) was synthesized by a solvothermal method. 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 NH2-MIL-125(Ti);

[0013] (3)H5PMo 10 V2O 40 Stirring with NH2-MIL-125(Ti) in HCl solution, it self-assembles into H5PMo under the action of electrostatic force. 10 V2O 40 / NH2-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 added dropwise to the solution. Finally, the obtained solution is mixed with 50 mL of ether, and after layering, the middle layer of orange solution is collected, and after the ether is evaporated, H5PMo can be obtained. 10 V2O 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 minutes, and then tetrabutyl titanate (0.52 mL) is added and stirred for 30 minutes. The resulting solution is transferred to an autoclave and heated. After cooling to room temperature, the solid product is collected by centrifugation at 10,000 rpm for 5 minutes.

[0016] In some embodiments, 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.

[0017] In some embodiments, 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 of Ti to NH2-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 the previous and the next stirring are 1000-1200 rpm.

[0022] In some embodiments, washing H5PMo 10 V2O 40 / NH2-MIL-125(Ti) catalyst, characterized in that H5PMo is washed 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.

[0023] In some embodiments, the step (3) may also be performed by adding H5PMo 10 V2O 40 The photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation was obtained by ball milling the mixture with NH2-MIL-125(Ti). 10 V2O 40 / NH2-MIL-125(Ti).

[0024] The third aspect of the present invention provides a photocatalytic material H5PMo with built-in electric field to regulate carrier separation. 10 V2O 40 / NH2-MIL-125(Ti) in nitrogen fixation performance.

[0025] In some embodiments, the application of a photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation is 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.

[0026] In some embodiments, the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation 10 V2O 40 The mass ratio of / NH2-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 with built-in electric field regulated carrier separation provided by the present invention, H5PMo 10 V2O 40 The photocatalytic nitrogen fixation material is uniformly deposited on the surface of NH2-MIL-125(Ti). At the two-phase interface of the photocatalytic nitrogen fixation material, a strong built-in electric field is spontaneously generated due to the equilibrium trend of the Fermi level, which accelerates the electron migration rate. At the same time, 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 regulated carrier separation, and the synthesized H5PMo 10 V2O 40 By stirring NH2-MIL-125(Ti) in HCl solution, the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation can be obtained. 10 V2O 40 / NH2-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 H5PMo with built-in electric field to regulate carrier separation in Example 1 10 V2O 40 / NH2-MIL-125(Ti) scanning electron microscope image;

[0033] Figure 2 Example 1H5PMo 10 V2O 40 / NH2-MIL-125(Ti), Comparative Example 1H5PMo 10 V2O 40 and X-ray diffraction pattern of comparative example 2NH2-MIL-125(Ti);

[0034] Figure 3 It is H5PMo of Example 1-3 10 V2O 40 / NH2-MIL-125(Ti) and the photocurrent spectra of NH2-MIL-125(Ti) of Comparative Example 2;

[0035] Figure 4 Example 1H5PMo 10 V2O 40 / NH2-MIL-125(Ti) and comparative example 2NH2-MIL-125(Ti) photoluminescence spectra;

[0036] Figure 5 Comparative Example 1H5PMo 10 V2O 40 and the UV photoelectron spectrum of comparative example 2NH2-MIL-125(Ti);

[0037] Figure 6 Comparative Example 1H5PMo 10 V2O 40 The built-in electric field generated between NH2-MIL-125(Ti) and the directional transfer of electrons under light irradiation;

[0038] Figure 7 The photocatalytic nitrogen fixation material H5PMo with built-in electric field to regulate carrier separation in Example 1 10 V2O 40 Photocatalytic cycling test of / NH2-MIL-125(Ti). DETAILED DESCRIPTION

[0039] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

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

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

[0042] The structure and morphology of the prepared samples were observed using a scanning electron microscope (SEM) using a Hitachi SU-8000FE-SEM. The composition of the synthesized samples was studied using an X-ray diffractometer (XRD) using a Siemens D5005. The photocurrent performance of the samples was tested using a three-electrode CHI661D electrochemical workstation. The photoluminescence (PL) spectra of the prepared samples were measured using an F-7000 fluorescence spectrophotometer, the UV photoelectron spectra were measured using a Thermo Scientific K-Alpha photoelectron spectrometer, and the UV-visible diffuse reflectance spectra of the samples were measured using 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 is 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 separation, the orange solution in the middle layer was collected. After the ether evaporated, H5PMo was obtained. 10 V2O 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 NH2-MIL-125(Ti) was collected by centrifugation at 10,000 rpm for 5 min.

[0048] (3) 0.01 mol H5PMo 10 V2O 40 Dissolve in 10mL HCl (0.1mol / L) solution, add 1mol NH2-MIL-125(Ti), stir at 1100rpm for 10h at room temperature, and wash H5PMo with pure water. 10 V2O 40 / NH2-MIL-125(Ti) catalyst 3 times and heated at 70°C for 12h.

[0049] Example 2

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

[0051] Same as Example 1, except that in step (3), H5PMo 10 V2O 40 The amount added is 0.005 mol.

[0052] Example 3

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

[0054] Same as Example 1, except that in step (3), H5PMo 10 V2O 40 The amount added is 0.015 mol.

[0055] Example 4

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

[0057] Same as Example 1, except that the solution obtained in step (2) was transferred to an autoclave and heated in an electric blast drying oven for 18 h.

[0058] Example 5

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

[0060] Same as Example 1, except that the solution obtained in step (2) was transferred to an autoclave and heated in an electric blast drying oven for 22 h.

[0061] Example 6

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

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

[0064] Example 7

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

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

[0067] Example 8

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

[0069] Same as Example 1, except that in step (3), 0.01 mol H5PMo 10 V2O 40 The photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation was obtained by grinding 1 mol NH2-MIL-125(Ti) in a ball mill for 10 h. 10 V2O 40 / NH2-MIL-125(Ti).

[0070] Comparative Example 1 Single-phase catalyst H5PMo 10 V2O 40 Preparation

[0071] According to the preparation method of step (1) of Example 1, the single-phase catalyst H5PMo was prepared 10 V2O 40 .

[0072] Comparative Example 2 Preparation of single-phase catalyst NH2-MIL-125(Ti)

[0073] According to the preparation method of step (2) of Example 1, a single-phase catalyst NH2-MIL-125(Ti) was prepared.

[0074] Verification Example

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

[0076] The photocatalytic nitrogen fixation material H5PMo with built-in electric field regulating carrier separation prepared in Example 1 10 V2O 40 / NH2-MIL-125(Ti) was tested by scanning electron microscopy. Figure 1 The photocatalytic nitrogen fixation material H5PMo with built-in electric field to regulate carrier separation in Example 1 10 V2O 40 / NH2-MIL-125 (Ti) scanning electron microscope image, from which it can be observed that many tiny particles H5PMo are evenly deposited on the surface of NH2-MIL-125 (Ti) 10 V2O 40 , H5PMo 10 V2O 40 A close interface connection is formed between NH2-MIL-125(Ti).

[0077] 2. X-ray diffraction test

[0078] The photocatalytic nitrogen fixation material H5PMo with built-in electric field regulating carrier separation prepared in Example 1 10 V2O 40 / NH2-MIL-125(Ti), Comparative Example 1H5PMo 10 V2O 40 The X-ray diffraction test of NH2-MIL-125 (Ti) was carried out on the comparative example 2. Figure 2 As shown in the figure, it can be observed that H5PMo 10 V2O 40 The signal peak of / NH2-MIL-125(Ti) is almost the same as that of comparative example 2NH2-MIL-125(Ti), which may be due to the 10 V2O 40 Due to the low content.

[0079] 3. Photocurrent test

[0080] Figure 3 It is H5PMo of Example 1-3 10 V2O 40 / NH2-MIL-125(Ti) and the photocurrent spectra of comparative example 2NH2-MIL-125(Ti). Compared with the comparative example 2NH2-MIL-125(Ti), the H5PMo of Examples 1-3 10 V2O 40 / NH2-MIL-125(Ti) has a stronger photocurrent signal. As can be seen from the figure, Example 1H5PMo 10 V2O 40 The photocurrent intensity of / NH2-MIL-125(Ti) is about 5 times that of NH2-MIL-125(Ti) in comparative example 2, indicating that Example 1 has better photocatalytic activity.

[0081] 4. Photoluminescence test

[0082] Figure 4 Example 1H5PMo 10 V2O 40 / NH2-MIL-125(Ti) and comparative example 2NH2-MIL-125(Ti) photoluminescence spectra. The signal peak intensity of comparative example 2NH2-MIL-125(Ti) is significantly higher than that of example 1H5PMo 10 V2O 40 / NH2-MIL-125(Ti), suggesting that Example 1H5PMo 10 V2O 40 The photogenerated carriers in / NH2-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 1H5PMo 10 V2O 40 The UV photoelectron spectroscopy test was carried out on the comparative example 2NH2-MIL-125(Ti). 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 results. Therefore, NH2-MIL-125 and H5PMo 10 V2O 40 The Φ of the materials are 7.77 and 9.70 eV respectively. The Fermi level (E f ) is calculated by the following formula: E f =E vac -Φ, where Evac is the vacuum energy level (assumed to be 0eV), the calculated values ​​for NH2-MIL-125 and H5PMo 10 V2O 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 1H5PMo 10 V2O 40 The built-in electric field generated between NH2-MIL-125(Ti) and the directional transfer of electrons under light irradiation, such as Figure 6 As shown, comparative example 1H5PMo 10 V2O 40 E f Significantly lower than the comparative example 2NH2-MIL-125(Ti), NH2-MIL-125(Ti) and H5PMo 10 V2O 40 After the interface is in close contact, due to E f The balance trend in H5PMo 10 V2O 40 / NH2-MIL-125(Ti) heterojunction forms a strong built-in electric field (IEF), and the presence of IEF promotes the spontaneous electron 10 V2O 40 Migrate to NH2-MIL-125(Ti), due to electron loss, NH2-MIL-125(Ti) presents a positively charged interface, H5PMo 10 V2O 40 The interface region of NH2-MIL-125(Ti) exhibits electronegativity due to the electron acceptance. Since the electrons in NH2-MIL-125(Ti) are subjected to the IEF repulsive force, the potential energy increases and the energy band bends upward. 10 V2O 40 The band bends downward. Under the dual effects of IEF and band bending, H5PMo 10 V2O 40 The photoelectrons generated in the conduction band (CB) of NH2-MIL-125(Ti) will migrate to the valence band (VB) of H5PMo 10 V2O 40 / NH2-MIL-125(Ti) heterojunction retains holes and electrons with strong redox ability, compared with the example 1H5PMo 10 V2O 40 The built-in electric field formed between the NH2-MIL-125(Ti) and the comparative example 2 is an effective way to accelerate the migration of photogenerated carriers and improve the electron utilization, thereby promoting photocatalytic nitrogen fixation.

[0087] 7. Photocatalytic cycle test

[0088] Figure 7 The photocatalytic nitrogen fixation material H5PMo with built-in electric field to regulate carrier separation in Example 1 10 V2O40 / NH2-MIL-125(Ti) photocatalytic cycle test, 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 H5PMo with built-in electric field to regulate carrier separation 10 V2O 40 / NH2-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 were as follows:

[0091] 0.05 g of photocatalyst was added to the photocatalytic reactor, and then 100 mL of pure water was added and stirred evenly. High-purity nitrogen was introduced into the reactor in the dark to remove the air in the reaction vessel. The bubbling was continued for 30 min. The photocatalytic reaction was carried out using a 300 W xenon lamp (200 mW·cm -2 ) simulated full spectrum irradiation, removed the catalyst from 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 examples / comparative examples in nitrogen fixation reaction

[0094]

[0095]

[0096] As can be seen from Table 1, the comparative example 1H5PMo prepared by the present invention 10 V2O 40 The ammonia generation rates of NH2-MIL-125(Ti) and comparative example 2 were 3.1 μmol·g -1 ·h -1 and 10.7 μmol·g -1 ·h -1 , photocatalytic nitrogen fixation material H5PMo with built-in electric field to regulate carrier separation 10 V2O 40The nitrogen fixation performance of / NH2-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. At the same time, electrons and holes with strong redox ability in the catalyst are retained.

[0097] From the ammonia generation rate of the synthesized photocatalyst Examples 1-3, it can be seen that the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation 10 V2O 40 / NH2-MIL-125(Ti) in H5PMo 10 V2O 40 The ratio of H5PMo to NH2-MIL-125(Ti) has an important influence on the nitrogen fixation performance. 10 V2O 40 When the molar ratio of Ti to NH2-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 rate of the synthesized photocatalyst Examples 1, 4, and 5, it can be seen that the synthesis of NH2-MIL-125(Ti) in step (2) and the different heating times make the photocatalyst H5PMo 10 V2O 40 The nitrogen fixation performance of / NH2-MIL-125(Ti) was affected.

[0099] From the ammonia generation rates of the synthesized photocatalysts Examples 1, 6, and 7, it can be seen that the H5PMo 10 V2O 40 Effect of stirring time of NH2-MIL-125(Ti) in HCl solution on the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation 10 V2O 40 Nitrogen fixation performance of / NH2-MIL-125(Ti).

[0100] From the ammonia generation rates of the synthesized photocatalysts Example 1 and Example 8, it can be seen that the photocatalytic nitrogen fixation material H5PMo with built-in electric field regulated carrier separation is constructed in step (3). 10 V2O 40 / NH2-MIL-125(Ti),H5PMo 10 V2O 40The method of combining with NH2-MIL-125(Ti) affects the nitrogen fixation activity.

Claims

1. A method for preparing a photocatalytic nitrogen fixation material with built-in electric field regulated 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, 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, it self-assembles into H5PMo under the action of electrostatic force. 10 V2O 40 / NH2-MIL-125(Ti); In the step 2, the autoclave is kept in an electric heated forced air drying oven at 150° C. for 18-22 hours; In the step 3, H5PMo 10 V2O 40 Dissolve in HCl solution, continue to add NH2-MIL-125(Ti) and stir at room temperature for 10-14h, then wash H5PMo 10 V2O 40 / NH2-MIL-125(Ti) catalyst and heated at 70 °C for 12 h; In the step 3, H5PMo 10 V2O 40 The molar ratio to NH2-MIL-125(Ti) is 1.0-1.5:

100.

2. 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 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 10 mL of water, and the mixture was stirred with the above solution for 0.5-2 h. 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 separation, the orange solution in the middle layer was collected. After evaporation of the ether, H5PMo was obtained. 10 V2O 40 .

3. 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 2, 1.086 g of 2-aminoterephthalic acid was dissolved in 1-3 mL of methanol and 17-19 mL of N,N-dimethylformamide. The mixed solution was stirred for 20 minutes, and then 0.52 mL of tetrabutyl titanate was added and stirring continued for 30 minutes. The resulting solution was transferred to an autoclave, heated, cooled to room temperature, and centrifuged at 10,000 rpm for 5 minutes to collect the solid product.

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

100.

5. 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 3, the concentration of the HCl solution is 0.1 mol / L, and the volume of the HCl solution is 8-12 mL.

6. The method for preparing a photocatalytic nitrogen-fixing material with built-in electric field-regulated carrier separation according to claim 1, characterized in that: Wash H5PMo with deionized water 10 V2O 40 / NH2-MIL-125(Ti) 2-4 times to remove H5PMo that is not bound to 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.

7. A photocatalytic nitrogen fixation material with built-in electric field regulated carrier separation, characterized in that: Prepared by any one of the preparation methods of claims 1-6.

8. Use of the photocatalytic nitrogen-fixing material with built-in electric field regulated carrier separation according to claim 7 in nitrogen fixation, characterized in that: 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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