Preparation and application of double-LSPR-effect nitrogen fixation material for improving active site hot electron concentration

Abstract

The invention provides preparation and application of a double-LSPR-effect nitrogen fixation material capable of improving active site hot electron concentration, PMoV and Ag are attached to the surface of W18O49 through electrostatic self-assembly and photodeposition, an Ag / W18O49 / PMoV heterojunction with the double LSPR effect is successfully prepared, experimental data shows that W18O49 can absorb photo-induced electrons generated by PMoV and Ag, and therefore the nitrogen fixation material with the double LSPR effect can be used for improving the active site hot electron concentration. The injected photo-induced electrons are enriched at OVs on the energy surface of the W18O49, so that the plasma effect of the W18O49 is maintained, the fluorescence lifetime of a photo-induced carrier in the Ag / W18O49 / PMoV is prolonged, the load of Ag and PMoV provides a new channel for migration of the photo-induced electrons and holes in the Ag / W18O49 / PMoV, the nitrogen immobilization activity of the Ag / W18O49 / PMoV heterojunction is enhanced, the ammonia generation rate reaches 118.4 mol g1h1 and is 3.6 times of the yield of the W18O49, and in the synthesis route, the nitrogen immobilization activity of the Ag / W18O49 / PMoV heterojunction is greatly improved. And experimental parameters are easy to control.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysis, and particularly relates to preparation and application of a double-LSPR-effect nitrogen-fixing material for improving the concentration of hot electrons at active sites. BACKGROUND

[0002] Ammonia (NH3) is an important chemical that is widely used in the production industry for the manufacture of fertilizers, pesticides, dyes, rubber, and other high-value products. About 150 million tons of ammonia are synthesized annually, mainly relying on the Haber-Bosch method. In the synthesis process, N2 and H2 are used as raw materials to generate NH3 under high temperature (400 ~ 450℃) and high pressure (15 ~ 25 MPa). The production of ammonia consumes 3% of the world's energy each year, while a large amount of carbon dioxide and other pollutants are generated and discharged. Photocatalytic nitrogen fixation driven by renewable energy has attracted widespread attention, which converts N2 into ammonia under the action of light energy. The photocatalytic nitrogen fixation process involves multiple steps of proton-coupled electron transfer, and the catalyst has limited light energy utilization rate and low carrier separation efficiency, which are still the main reasons why it cannot meet the minimum industrial requirements.

[0003] The construction of composite catalysts can overcome the above problems, especially the introduction of noble metals such as gold, platinum, and silver. Due to the price and scarcity of noble metals, silver nanoparticles are most widely used in the construction of catalysts. Silver has a unique electronic arrangement (4d 10 5S 1 ) and electron density. Under the irradiation of light energy, the free electrons on the surface of silver will undergo collective oscillation to produce a localized surface plasmon resonance (LSPR) effect. The enhanced light absorption capacity helps to form high-energy hot electrons, thereby improving the catalytic activity. For example, patent CN118513068A provides a preparation method of Ag-BiOBr / Bi2O2(CO3) 1-x N x catalyst, the metal Ag has an LSPR effect, which significantly expands the light response range of BiOBr / Bi2O2(CO3) 1-x N x ). The design and manufacture of composite catalysts with LSPR effect can effectively improve the light absorption performance, but compared with double-localized surface plasmon resonance composite materials, the light absorption performance is still limited, which affects the separation efficiency of photo-excited carriers. Tungsten oxide (WO3) is a strong candidate for constructing non-metallic plasmonic materials, and its structural characteristics are conducive to the loss of oxygen and structural deformation, thereby forming a non-stoichiometric W 18 O 49 . In W 18 O 49 , W 5+ -W 5+The periodic arrangement of ion pairs provides a structural basis for the localization of electrons. 18 O 49 The oxygen vacancies (OVs) formed in the middle contain a large number of free electrons, which can act as adsorption and activation sites in catalytic reactions, and the concentration of OVs therein is crucial to promote the occurrence of catalytic reactions. Patent CN111495355A discloses a WO 3-x nanosheet photocatalyst and a preparation method, which realizes the LSPR absorption of WO 3-x in the visible light region and good catalytic degradation performance of methyl orange. It is worth noting that the LSPR effect of WO 18 O 49 is closely related to the oxygen vacancies (OVs) on its surface, and research has found that after a long time of catalytic reaction, the OVs on the surface of WO 18 O 49 oxidation will cause the loss of LSPR effect, and the light absorption performance and catalytic activity are severely affected.

[0004] WO 18 O 49 containing stable OVs can produce high-energy hot electrons through LSPR effect, thereby quickly reducing the coupled product intermediates. However, in the prior art, the photocatalyst mainly using WO 18 O 49 as the main body is easily oxidized by photo-generated holes in the catalytic process, the lifetime of hot electrons on the surface is shortened, and the photocatalytic reaction activity is limited; the single-localized surface plasmon resonance generated by WO 18 O 49 still affects the light absorption performance of the photocatalyst.

[0005] Therefore, how to prevent the OVs in WO 18 O 49 from being oxidized through a simple modification method, and maintain its LSPR effect to provide abundant high-energy hot electrons for the photocatalytic nitrogen fixation process.

[0006] The information disclosed in this background section is intended to increase an understanding of the general context of the application and is not to be taken in any way as an acknowledgment or any form of suggestion that this information forms the prior art commonly owned by those skilled in the art. SUMMARY

[0007] As described above, the LSPR effect of WO 18 O 49 can produce strong absorption in the visible light or near-infrared region, and this effect is caused by the OVs on its surface, but after long-term use and exposure to air, these oxygen OVs will be oxidized and lose the LSPR ability, which greatly limits the use of WO 18 O49 light absorption ability and catalytic activity. 18 O 49 The surface OV concentration and free electron density can be maintained or enhanced by continuous electron injection to ensure the surface LSPR intensity. Building a heterojunction is a promising solution that can achieve continuous photoelectron injection into W 18 O 49 , while enhancing the interface charge separation. This dual-function strategy not only solves the inherent limitations of W 18 O 49 , but also provides a solution for optimizing photocatalytic activity. Polyoxometalates (POMs) can store multiple electrons or protons while maintaining structural stability. Among them, PMoV has a good light absorption range, reversible redox properties, and fast migration of photo-generated carriers, making POMs occupy a leading position in photocatalytic research. However, PMoV still faces many bottleneck problems, such as small specific surface area, limited recyclability, and easy aggregation. Combining POMs with other support materials can effectively improve their dispersibility, stability, and photocatalytic activity. Attaching small-sized PMoV and Ag to the surface of W 18 O 49 , a heterojunction with dual LSPR effect is prepared to improve the light absorption performance of the material, while the photo-generated electrons injected into the surface of W 18 O 49 increase its electron density, thereby maintaining the plasmonic effect of W 18 O 49 .

[0008] Therefore, the present application provides a preparation and application of a dual LSPR effect nitrogen fixation material for improving the thermal electron concentration of active sites to solve the problem that the OVs on the surface of W 18 O 49 are oxidized in long-term use and exposure to air. The dual LSPR effect nitrogen fixation material has a rich thermal electron concentration at the active site and excellent photocatalytic nitrogen fixation activity.

[0009] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0010] A preparation of a dual LSPR effect nitrogen fixation material for improving the thermal electron concentration of active sites, the nitrogen fixation material comprising Ag, W 18 O 49 , PMoV three phases, PMoV and Ag are uniformly attached to the surface of W 18 O 49 by electrostatic self-assembly and photodeposition, respectively.

[0011] In another aspect of the present application, a method for synthesizing a dual LSPR effect nitrogen fixation material with improved active site hot electron concentration is provided, and the detailed experimental steps are as follows:

[0012] (1) W 18 O 49 / PMoV is dispersed in a mixture of deionized water and isopropanol;

[0013] (2) AgNO3 solution is added to the solution in step 1, and the mixture is stirred under ultraviolet light for 60 min. The solid is collected and washed with water several times, and then dried to obtain Ag / W 18 O 49 / PMoV.

[0014] In some embodiments, as described in step (1), W 18 O 49 / PMoV is prepared by the following process: W 18 O 49 is dispersed in a PMoV aqueous solution, and after stirring overnight, the solid product is washed with deionized water three times and dried at 60°C for 10 h. The obtained solid powder is marked as W 18 O 49 / PMoV.

[0015] In some embodiments, as described in step (1), W 18 O 49 / PMoV is synthesized by the following method: 0.5 g of W 18 O 49 is dispersed in 250 mL of PMoV aqueous solution with a concentration of 0.2 mM / L by stirring, and the stirring speed is 1000 rpm.

[0016] In some embodiments, as described in step (1), W 18 O 49 / PMoV is added to a mixture of deionized water and isopropanol, and is completely dispersed after being treated in an ultrasonic cleaner for 30 min.

[0017] In some embodiments, as described in step (2), the stirring time under ultraviolet light irradiation is 30-90 min.

[0018] In some embodiments, as described in step (2), the stirring speed of the solution under ultraviolet light is 1000-1200 rpm.

[0019] In some embodiments, as described in step (1), 0.1 g of W 18 O 49 / PMoV is dispersed in a mixture of 25 mL of deionized water and 10 mL of isopropanol.

[0020] In some embodiments, as described in step (2), W 18 O 49 A solution of 25 mL of AgNO3 with a concentration of 0.5-1.5 mM was added to the solution of W

[0021] In some embodiments, as described in step (1), W 18 O 49 was prepared as follows: 0.1 g of WCl6 was dissolved in 70 mL of ethanol, and the powder was completely dissolved by stirring (1000 rpm) for 30 min, and the solution was transferred to a high-pressure autoclave reactor and heated in an electric heating drying oven at 200 ℃ for 20 h, and the product was washed with ethanol for several times, and dried to obtain W 18 O 49 .

[0022] In some embodiments, as described in step (1), W 18 O 49 was prepared by heating the electric heating drying oven at a rate of 2 ℃ / min.

[0023] In some embodiments, as described in step (1), W 18 O 49 was prepared by washing the product with ethanol for 6 times, and drying at 60 ℃ for 10 h.

[0024] In some embodiments, as described in step (1), PMoV was synthesized as follows: sodium metavanadate (2.44 g) was dissolved in 10 mL of boiling water, 0.71 g of sodium phosphate dibasic was added to 10 mL of water, and then the solution was stirred well and mixed with the sodium metavanadate solution, and after cooling, 0.5 mL of concentrated sulfuric acid was continuously added to the mixed solution, and 20 mL of sodium molybdate (12.1 g) solution was continuously added to the solution, and the obtained mixed solution was mixed with 8.5 mL of concentrated sulfuric acid, and 50 mL of diethyl ether was added to the obtained solution, and after extraction, the sample was dissolved in the middle orange solution layer, and after evaporation of the solvent, the target product PMoV was obtained.

[0025] In some embodiments, as described in step (1), W 18 O 49 / PMoV can also be obtained by ball-milling a mixture of PMoV and W 18 O 49 with the same mass.

[0026] In a third aspect, the application provides a photocatalytic material Ag / W 18 O 49Application of / PMoV in nitrogen fixation performance.

[0027] In some embodiments, the application of the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at active sites is characterized in that the prepared composite photocatalyst Ag / W 18 O 49 / PMoV is dispersed in pure water, high-purity nitrogen is introduced under dark state, and nitrogen fixation performance is studied under stirring and light energy radiation.

[0028] In some embodiments, the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at active sites is characterized in that the mass ratio of pure water to Ag / W 18 O 49 / PMoV is 10000: (1-10).

[0029] In some embodiments, the speed of high-purity nitrogen introduced into the reactor is 50 mL / min.

[0030] In some embodiments, the light energy in the catalytic experiment is provided by a 300 W xenon lamp.

[0031] The beneficial effects of the present application are:

[0032] 1. The double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at active sites provided by the present application, PMoV and Ag are attached to the W 18 O 49 surface through electrostatic self-assembly and photodeposition, and an Ag / W 18 O 49 / PMoV heterojunction catalyst with double LSPR effect is prepared. 18 O 49 The Ag / W 18 O 49 / PMoV can absorb the photoelectrons generated by PMoV and Ag, and the injected photoelectrons enrich the electron density at the OV on the W 18 O 49 surface, thereby maintaining the plasmonic effect of W 18 O 49 The fluorescence lifetime of photo-generated carriers in Ag / W 18 O 49 / PMoV is prolonged, and the loading of Ag and PMoV provides new channels for the migration of photo-generated electrons and holes in Ag / W 18 O 49 / PMoV, thereby promoting the catalytic reaction. The photocatalytic ammonia synthesis rate of W −1 h −1 can reach 32.9 µmol g 18 O 49The nitrogen fixation activity of / PMoV was enhanced, and the ammonia production rate reached 118.4 µmol g −1 h −1 , which is 3.6 times the yield of W 18 O 49 / PMoV, and after multiple cycles of use, Ag / W 18 O 49 / PMoV still maintains a high ammonia production rate.

[0033] 2. The dual LSPR effect nitrogen fixation material synthesized in the application to increase the concentration of hot electrons at the active site, Ag is attached to the surface of W 18 O 49 / PMoV, which widens the light absorption range of W 18 O 49 / PMoV, and its absorption boundary is expanded to 600 nm. In this synthesis route, the experimental parameters are easy to control. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a scanning electron microscope image of the dual LSPR effect nitrogen fixation material Ag / W 18 O 49 / PMoV of Example 1 to increase the concentration of hot electrons at the active site;

[0035] Figure 2 is an X-ray diffraction pattern of Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 , Comparative Example 2 PMoV, and Comparative Example 3 W 18 O 49 / PMoV;

[0036] Figure 3 is a photocurrent spectrum of Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 , Comparative Example 2 PMoV, and Comparative Example 3 W 18 O 49 / PMoV;

[0037] Figure 4 is a photoluminescence spectrum of Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 , and Comparative Example 3 W 18 O 49 / PMoV;

[0038] Figure 5 is Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 and Comparative Example 3 W 18 O 49 Transient photoluminescence spectra of / PMoV;

[0039] Figure 6 is Comparative Example 1 W 18 O 49 UV photoelectron spectra of / PMoV, Comparative Example 2 PMoV;

[0040] Figure 7 is Comparative Example 1 W 18 O 49 Carrier directional transfer between / PMoV, Comparative Example 2 PMoV;

[0041] Figure 8 is Example 1 Ag / W 18 O 49 / PMoV and Comparative Example 1 W 18 O 49 Electron spin resonance test spectra of / PMoV;

[0042] Figure 9 is Example 1 Ag / W 18 O 49 X-ray photoelectron spectra test spectra of / PMoV under dark state and light radiation;

[0043] Figure 10 is Example 1 Ag / W 18 O 49 / PMoV with double LSPR effect of increasing active site thermal electron concentration for nitrogen fixation material. DETAILED DESCRIPTION

[0044] The specific embodiments of the present application will be described in conjunction with the drawings, which are by way of illustration, not by way of limitation. It should be noted that the scope of the present application is not limited to the specific embodiments described in this detailed description.

[0045] The embodiments of the present application will be described in detail with specific examples below, and those skilled in the art related to the present application can understand the other advantages and effects of the present application in detail from the content set forth in the present specification. The present application can also be implemented or applied using other different embodiments, and the details in the present specification can also be modified or changed based on different views and applications without departing from the spirit of the present application.

[0046] The reagents and instruments applied in the examples are as follows:

[0047] The microstructure of the catalyst and the distribution of PMoV and Ag were observed by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the catalyst was measured by X-ray diffractometer (XRD) with model Dmax2200PC, the crystallinity and lattice parameters of the sample were analyzed by spectral test, the elemental composition and chemical state of the catalyst surface were studied by X-ray photoelectron spectroscopy (XPS) (model: USWHA150), the photoluminescence (PL) spectrum of the sample was detected by transient fluorescence spectrometer, the light absorption range of the catalyst was analyzed by ultraviolet-visible diffuse reflectance spectrometer (DRS) with model Cary 500, the oxygen vacancy content was detected by electron spin resonance spectrometer (ESR), and the photoelectrochemical behavior of the prepared sample was studied by three-electrode electrochemical workstation (CHI661D).

[0048] Sodium metavanadate, tungsten chloride, disodium hydrogen phosphate, silver nitrate and sodium molybdate were purchased from Aladdin Reagent Co., Ltd., and concentrated sulfuric acid, ethanol, diethyl ether and isopropanol were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., and all the chemical reagents were not treated before use.

[0049] Example 1

[0050] The synthesis method of the double-LSPR effect nitrogen fixation material for improving the thermal electron concentration of active sites is as follows:

[0051] (1) W 18 O 49 Prepared as follows: 0.1 g of WCl6 was dissolved in 70 mL of ethanol, and the powder was completely dissolved by stirring (1000 rpm) for 30 min, the solution was transferred to a high-pressure autoclave reactor, and heated in a 200 ℃ electric heating air drying oven for 20 h, the heating rate was 2 ℃ / min, the product was washed with ethanol for 6 times, and dried at 60 ℃ for 10 h.

[0052] PMoV was synthesized as follows: sodium metavanadate (2.44 g) was dissolved in 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate was added to 10 mL of water, then the solution was stirred and mixed with the sodium metavanadate solution, 0.5 mL of concentrated sulfuric acid was continuously added to the mixed solution after cooling, 20 mL of sodium molybdate (12.1 g) solution was continuously added to the solution, the obtained mixed solution was mixed with 8.5 mL of concentrated sulfuric acid, 50 mL of diethyl ether was added to the obtained solution, after extraction, the sample was dissolved in the middle orange solution layer, and the target product PMoV was obtained after solvent evaporation.

[0053] W 18 O 49 / PMoV was synthesized as follows: 0.5 g of W 18 O49 Dispersed in 250 mL aqueous solution of PMoV with a concentration of 0.2 mM / L, the stirring speed was 1000 rpm, after stirring overnight, the solid product was washed with deionized water for three times, and dried at 60 ℃ for 10 h, the obtained solid powder was marked as W 18 O 49 / PMoV.

[0054] 0.1 g of W 18 O 49 / PMoV was dispersed in a mixture of 25 mL deionized water and 10 mL isopropanol after treated in an ultrasonic cleaner for 30 min.

[0055] (2) 25 mL of AgNO3 solution with a concentration of 1 mM was added to the solution of step 1, the mixture was placed under ultraviolet light and stirred for 60 min, the stirring speed of the solution was 1100 rpm, the solid was collected and washed with water for several times, and dried to obtain Ag / W 18 O 49 / PMoV.

[0056] Example 2

[0057] The synthesis method of the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons of active sites, specifically includes the following steps:

[0058] The same as example 1, except that in step (2), the mixture was placed under ultraviolet light and stirred for 30 min.

[0059] Example 3

[0060] The synthesis method of the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons of active sites, specifically includes the following steps:

[0061] The same as example 1, except that in step (2), the mixture was placed under ultraviolet light and stirred for 90 min.

[0062] Example 4

[0063] The synthesis method of the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons of active sites, specifically includes the following steps:

[0064] The same as example 1, except that in step (2), 25 mL of AgNO3 solution with a concentration of 0.5 mM was added.

[0065] Example 5

[0066] The synthesis method of the double LSPR effect nitrogen fixation material for increasing the concentration of hot electrons of active sites, specifically includes the following steps:

[0067] The same as example 1, except that in step (2), 25 mL of AgNO3 solution with a concentration of 1.5 mM was added.

[0068] Example 6

[0069] The synthesis method of the dual LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at the active site specifically includes the following steps:

[0070] The same as example 1, except that in step (2), the stirring speed of the solution was 1000 rpm.

[0071] Example 7

[0072] The synthesis method of the dual LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at the active site specifically includes the following steps:

[0073] The same as example 1, except that in step (2), the stirring speed of the solution was 1200 rpm.

[0074] Example 8

[0075] The synthesis method of the dual LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at the active site specifically includes the following steps:

[0076] The same as example 1, except that in step (1), 0.5 g of W 18 O 49 and 0.087 g of PMoV were ground in a ball mill for 12 h to obtain a W 18 O 49 / PMoV composite.

[0077] Preparation of single-phase catalyst W 18 O 49

[0078] According to the preparation method of step (1) of example 1, a single-phase catalyst W 18 O 49 was prepared.

[0079] Preparation of single-phase catalyst PMoV

[0080] According to the preparation method of step (2) of example 1, a single-phase catalyst PMoV was prepared.

[0081] Preparation of composite catalyst W 18 O 49 / PMoV

[0082] According to the preparation method of step (2) of example 1, a composite catalyst W 18 O 49 / PMoV was prepared. ​

[0083] Verification Example

[0084] 1. Scanning Electron Microscope and Transmission Electron Microscope Characterization

[0085] The prepared example 1 Ag / W 18 O 49 / PMoV was tested by scanning electron microscope and transmission electron microscope, Figure 1 (a) and (b) are the scanning electron microscope and transmission electron microscope images of example 1, respectively, from which it can be observed that Ag / W 18 O 49 / PMoV is a nanosheet structure, silver is loaded on the surface of W 18 O 49 , in addition, there are a large number of small particles on the surface of W 18 O 49 , these small particles are PMoV.

[0086] 2. X-ray Diffraction Test

[0087] The prepared example 1 Ag / W 18 O 49 / PMoV, comparative example 1 W 18 O 49 , comparative example 2 PMoV and comparative example 3 W 18 O 49 / PMoV were tested by X-ray diffraction, as shown in Figure 2 , the signal peak position in the spectrum of comparative example 3 is the same as that of comparative example 1, and the low content of comparative example 2 causes its characteristic peak not to appear in the spectrum of example 1, and there is no new peak related to Ag in the spectrum of example 1, which indicates that the Ag nanoparticles are not aggregated.

[0088] 3. Photocurrent Test

[0089] Figure 3 is the photocurrent spectrum of example 1 Ag / W 18 O 49 / PMoV, comparative example 1 W 18 O 49 , comparative example 2 PMoV and comparative example 3 W 18 O 49 / PMoV, compared with comparative examples 1-3, the photocurrent signal of example 1 is more obvious, the recombination of electrons and holes affects the photocurrent density, and the photo-generated carriers are better excited and migrated in example 1.

[0090] 4. Photoluminescence Test

[0091] Figure 4 is Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 and Comparative Example 3 W 18 O 49 Photoluminescence spectra of Ag / W / PMoV, the degree of carrier recombination is negatively correlated with the intensity of the photoluminescence signal peak, the signal peak intensity of Comparative Example 1 is the highest, and the peak intensity is reduced after the formation of the binary complex of Comparative Example 3, the silver nanoparticle modified W 18 O 49 / PMoV is further reduced, which indicates that there is carrier migration between the components of the heterojunction, and in Example 1, the migration of photo-generated electrons and holes is provided with a new channel.

[0092] 5. Transient photoluminescence test

[0093] Figure 5 is Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 and Comparative Example 3 W 18 O 49 Transient photoluminescence spectra of Ag / W / PMoV, the PL decay lifetime of each catalyst is in the order of Example 1 > Comparative Example 3 > Comparative Example 1, and this phenomenon is due to the local electric field enhancement caused by the LSPR effect of silver, which promotes the transfer of photo-generated carriers, reduces the carrier recombination rate, and prolongs the fluorescence lifetime.

[0094] 6. Ultraviolet photoelectron spectroscopy test

[0095] Figure 6 is Comparative Example 1 W 18 O 49 , Comparative Example 2 PMoV, the formula for calculating the work function (Φ) is as follows: Φ = φ + ΔV (φ is the work function of the photoelectron spectrometer, φ = 4.42 eV, ΔV is the contact potential difference), and the Φ values of Comparative Example 1 and Comparative Example 2 are determined to be 8.09 and 9.93 eV, respectively, and the Fermi energy levels (E f ) of Comparative Example 1 and Comparative Example 2 are further calculated to be -8.09 and -9.93 eV, respectively.

[0096] 7. Carrier directional transfer

[0097] Figure 7 is Comparative Example 1 W 18 O 49 , Comparative Example 2 PMoV, after the contact between Comparative Example 1 and Comparative Example 2, the high Ef The potential causes the electrons to spontaneously migrate to the surface of Comparative Example 2. Eventually, the E f A balance is reached, a built-in electric field is generated at the semiconductor interface from Comparative Example 1 to Comparative Example 2, the light energy radiation forms photo-generated carriers in the semiconductor, and the built-in electric field causes the photo-generated electrons on the conduction band of Comparative Example 2 to migrate to Comparative Example 1. If the photo-generated electrons on Comparative Example 2 migrate to the conduction band of Comparative Example 1, then a Coulomb repulsion will be generated between the two materials, thereby inhibiting the migration of the photo-generated electrons, and thus under the combined action of the built-in electric field and the kinetic factor, the photo-generated electrons on the conduction band of Comparative Example 2 are more inclined to combine with the holes on the valence band of Comparative Example 1, and the photo-generated electrons in Comparative Example 2 are injected into Comparative Example 1, and the standard work function value of Ag is 4.26 eV, and the hot electrons generated by silver can overcome the W 18 O 49 Schottky barrier at the Ag / W 18 O 49 interface and are absorbed, and the built-in electric field generated by E f promotes the migration of carriers in the heterojunction, which helps the occurrence of the catalytic reaction.

[0098] 8. Electron spin resonance test

[0099] Figure 8 a is the electron spin resonance test spectrum of Example 1 Ag / W 18 O 49 PMoV and Comparative Example 1 W 18 O 49 The electron spin resonance test spectrum in the dark state shows that both Example 1 and Comparative Example 1 exhibit a symmetrical signal with a Lorentz shape (g = 2.003), which is caused by a single electron around the OVs, and the oxygen atoms are separated from the lattice to form positively charged holes, which attract the surrounding electrons, resulting in an increase in the number of free electrons near the oxygen vacancies. The signal peak intensity of Example 1 is slightly higher than that of Comparative Example 1, and the OVs in Comparative Example 1 are maintained during the synthesis of the sample. The ESR spectra of Example 1 and Comparative Example 1 were detected under light conditions, as shown in Figure 8 b, the signal peak intensity of Example 1 is significantly increased, and Ag and PMoV inject electrons into W 18 O 49 , which increases the concentration of free electrons in W 18 O 49 , thereby promoting the formation of oxygen vacancies.

[0100] 9. X-ray photoelectron spectroscopy test

[0101] The X-ray photoelectron spectroscopy test spectrum of Example 1 Ag / W 18 O 49XPS test was performed on the PMoV to observe the electron transfer process after light irradiation Figure 9 ), after light irradiation, the W 5+ , the ratio of OVs increased from 25.2% to 32.3%, 18.1% to 22.8%, respectively, and compared with the XPS spectrum under dark state, the peak positions of P 2p, Mo 3d, V 2p and Ag 3d slightly shifted to the high binding energy direction, which provided strong evidence for the injection of photo-generated electrons 18 49 The injection of photo-generated electrons provides strong evidence.

[0102] 10. Photocatalytic cycle test

[0103] Figure 10 is a double LSPR effect nitrogen fixation material Ag / W 18 49 of the application 1, after five cycles, the photocatalytic nitrogen fixation ability of the application 1 remains stable, and the generation rate of ammonia does not change significantly, the application 1 has excellent stability and can be repeatedly used for photocatalytic reaction.

[0104] 11. Photocatalytic nitrogen fixation reaction

[0105] The prepared photocatalysts of examples 1-8 and comparative examples 1-3 were subjected to nitrogen fixation performance research, and the specific steps were as follows:

[0106] The photocatalytic nitrogen fixation experiment was carried out in a quartz glass reactor, a 300W xenon lamp with an AM 1.5 cutoff filter was selected as the light source, 0.05 g of catalyst was placed in the reactor, and 100 mL of ultrapure water was added, high-purity nitrogen was introduced into the suspension in the reactor under dark conditions, and after 30 min, the nitrogen fixation performance was tested under light irradiation.

[0107] The photocatalytic nitrogen fixation performance of examples 1-8 and comparative examples 1-3 was detected, the catalyzed solution was taken, the catalyst was removed by high-speed centrifugation, and the supernatant was injected into a quartz cuvette, and the amount of ammonia was detected by using a UV-visible spectrophotometer with a model of varian cary 700, and the ammonia generation rate of different samples was as shown in Table 1.

[0108] Table 1: Ammonia generation rate of photocatalysts prepared by different examples / comparative examples in nitrogen fixation reaction

[0109]

[0110] As can be seen from Table 1, the comparative example 1 W 18 49 , the comparative example 2 PMoV and the comparative example 3 W​​​18 O 49 The ammonia generation rates of PMoV were 32.9 μmol·g -1 ·h -1 , 5.37 μmol·g -1 ·h -1 and 82.5 μmol·g -1 ·h -1 , respectively. The OVs contained in Comparative Example 1 could serve as adsorption and activation centers for nitrogen, and the W 18 O 49 surface attached PMoV formed after Comparative Example 3 formed a close interface contact between PMoV and W 18 O 49 , which was conducive to the transfer of photo-generated electrons from PMoV to the W 18 O 49 surface, and the concentration of oxides in W 18 O 49 did not decrease, which ensured the smooth progress of the catalytic reaction. The nitrogen fixation activity of the catalyst was further enhanced, and the ammonia generation rate of Example 1 reached 118.4 μmol·g -1 ·h -1 , which was 3.6 times that of Comparative Example 1. The high-energy hot electrons generated by Ag were injected into W 18 O 49 , and the increase in the electron density on the W 18 O 49 surface promoted the formation of products.

[0111] From the ammonia generation rates of the synthesized photocatalysts Example 1-3, it can be seen that the length of the light irradiation time affected the activity of the catalyst during the process of loading Ag by photodeposition. When the light irradiation time was short, part of the Ag + was not completely reduced, and when the light irradiation time was too long, the attached Ag might fall off under the action of magnetic stirring, resulting in differences in the catalytic performance of the catalyst.

[0112] From the ammonia generation rates of the synthesized photocatalysts Example 1, 4 and 5, it can be seen that the amount of Ag loaded on the W 18 O 49 / PMoV surface led to differences in the catalytic performance of the catalyst. An insufficient amount of Ag might limit the light absorption of the sample, but an excessive amount of Ag might cause aggregation, and the transport ability of the carriers was inhibited.

[0113] From the ammonia generation rates of the synthesized photocatalysts Example 1, 6 and 7, it can be seen that the attachment of Ag to the W 18 O 49The magnetic stirring strength of the reactants in solution affects the double LSPR effect of Ag / W for increasing the concentration of hot electrons at active sites on the surface of / PMoV for nitrogen fixation 18 O 49 The nitrogen fixation activity of / PMoV.

[0114] From the ammonia generation rates of the synthesized photocatalysts of Example 1 and Example 8, it can be known that the double LSPR effect of Ag / W for increasing the concentration of hot electrons at active sites 18 O 49 W 18 O 49 The composite method of W and PMoV affects the nitrogen fixation activity of the catalyst.

Claims

1. A dual LSPR effect nitrogen fixation material for increasing the concentration of hot electrons at active sites, characterized in that, Composition comprising Ag, W 18 O 49 , H5PMo 10 V2O 40 (PMoV) triphase.

2. The method for preparing a dual LSPR effect nitrogen fixation material for increasing the concentration of hot electrons in active sites according to claim 1, characterized in that, The following synthesis steps are included: Step 1 : W 18 O 49 / PMoV was dispersed in a mixture of deionized water and isopropyl alcohol; Step 2: AgNO3 solution was added to the solution of step 1, the mixture was stirred under UV light for 60 min, the solid was collected and washed with water several times, and dried to obtain Ag / W 18 O 49 / PMoV.

3. The method of claim 2, wherein the method further comprises the step of: In step 1, the W 18 O 49 / PMoV was prepared as follows, W 18 O 49 dispersed in a PMoV aqueous solution, the solid product was washed with deionized water and dried at 60 °C, the obtained solid powder was labeled as W 18 O 49 / PMoV. ​ 4. The method of claim 3, wherein the method further comprises the step of: 4-1) adding a metal salt to the solution of step 3-1) to form a metal salt solution; and 4-2) adding the metal salt solution to the solution of step 3-2) to form the solution of step 4-1). In step 1, W 18 O 49 / PMoV was synthesized as follows, 0.5 g of W 18 O 49 was dispersed in 250 mL of PMoV aqueous solution with a concentration of 0.2 mM / L.

5. The method for preparing a dual LSPR effect nitrogen-fixing material with increased hot electron concentration at active sites according to claim 2, characterized in that, In step 2, the time for stirring under UV irradiation is 30-90 min.

6. The method of claim 2, wherein the method further comprises the step of: 6-1) applying a voltage to the material to increase the concentration of hot electrons in the active sites. In Step 1, 0.1 g of W 18 O 49 / PMoV was dispersed in a mixture of 25 mL of deionized water and 10 mL of isopropanol.

7. The method of claim 2, wherein the method further comprises the step of: 7-1) applying a voltage to the material to increase the concentration of hot electrons at the active sites. In step 2, in the solution of W 18 O 49 To the solution of / PMoV was added 25 mL of AgNO3solution at a concentration of 0.5-1.5 mM.

8. The method of claim 2, wherein the method further comprises the step of: 8.

1. applying a magnetic field to the material of claim 2 to increase the concentration of hot electrons at the active sites of the material. In step 1, W 18 O 49 was prepared as follows, 0.1 g of WCl6was dissolved in 70 mL of ethanol, the powder was completely dissolved by stirring, the solution was transferred to an autoclave reactor, heated in an electric heating drying oven at 200 °C for 20 h, the product was washed with ethanol for several times, and dried to obtain W 18 O 49 .

9. The method of claim 2, wherein the method further comprises the step of: 9-1) applying a voltage to the material to increase the concentration of hot electrons at the active sites. In step 1, PMoV is synthesized as follows, 2.44 g of sodium metavanadate is dissolved in 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate is added to 10 mL of water, then the solution is stirred well and mixed with the sodium metavanadate solution, after cooling, 0.5 mL of concentrated sulfuric acid is continuously added to the mixed solution, 20 mL of sodium molybdate solution is continuously added to the solution, the obtained mixed solution is mixed with 8.5 mL of concentrated sulfuric acid, 50 mL of diethyl ether is added to the obtained solution, after extraction, the sample is dissolved in the middle orange solution layer, and after evaporation of the solvent, the target product PMoV is obtained.

10. The use of a dual LSPR effect nitrogen fixation material of claim 1 or a dual LSPR effect nitrogen fixation material prepared by any one of the preparation methods of claims 2-9 to increase the concentration of hot electrons at active sites, characterized in that, The prepared composite photocatalyst Ag / W 18 O 49 / PMoV is dispersed in pure water, high-purity nitrogen is introduced in a dark state, and nitrogen fixation is performed under stirring and light energy radiation.

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