Preparation and application of a double-lsp effect nitrogen fixation material for improving the concentration of active sites of hot electrons

Abstract

This invention provides the preparation and application of a dual LSPR effect nitrogen-fixing material with increased hot electron concentration at active sites. PMoV and Ag are attached to W via electrostatic self-assembly and photodeposition. 18 O 49 On the surface, Ag / W with dual LSPR effect was successfully prepared. 18 O 49 / PMoV heterojunction, experimental data show that W 18 O 49 It can absorb photogenerated electrons produced by PMoV and Ag, and the injected photogenerated electrons are in W 18 O 49 Enrichment at OVs on the surface, thus preserving W 18 O 49 Plasma effect, Ag / W 18 O 49 The fluorescence lifetime of photogenerated carriers in PMoV is prolonged, and the loading of Ag and PMoV is Ag / W. 18 O 49 / PMoV provides a new pathway for the migration of photogenerated electrons and holes, Ag / W 18 O 49 The nitrogen fixation activity of the / PMoV heterojunction was enhanced, and the ammonia generation rate reached 118.4 µmol g. −1 h −1 , is W 18 O 49 The yield is 3.6 times higher, and the experimental parameters are easy to control in this synthetic route.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to the preparation and application of a dual LSPR effect nitrogen fixation material that improves the hot electron concentration of active sites. Background Technology

[0002] Ammonia (NH3) is an important chemical widely used in industrial production for manufacturing fertilizers, pesticides, dyes, rubber, and other high-value products. Approximately 150 million tons of ammonia are synthesized annually primarily through the Haber-Bosch process. In this process, N2 and H2 are used as raw materials to generate NH3 under high temperature (400–450°C) and high pressure (15–25 MPa). Ammonia production consumes 3% of global energy annually, while also generating and emitting significant amounts of carbon dioxide and other pollutants. Photocatalytic nitrogen fixation driven by renewable energy has attracted widespread attention; this catalyst converts N2 into ammonia under the influence of light energy. However, the photocatalytic nitrogen fixation process involves multiple steps of proton-coupled electron transfer. Limited light energy utilization of the catalyst and low carrier separation efficiency remain the main reasons why it cannot meet minimum industrial requirements.

[0003] The construction of composite catalysts can overcome the above-mentioned problems, especially by introducing precious metals such as gold, platinum, and silver. Given the price and scarcity of precious metals, silver nanoparticles are the most widely used in catalyst construction. Silver possesses a unique electron configuration (4d²). 10 5S 1 The free electrons on the silver surface undergo collective oscillations under light irradiation, generating a localized surface plasmon resonance (LSPR) effect. Enhanced light absorption facilitates the formation of high-energy hot electrons, thereby improving catalytic activity. For example, patent CN118513068A provides Ag-BiOBr / Bi2O2(CO3). 1-x N x The catalyst preparation method utilizes the LSPR effect of metallic Ag, which significantly extends the BiOBr / Bi2O2(CO3) ratio. 1-x N x The light response range is limited. Designing and fabricating composite catalysts with the LSPR effect can effectively improve light absorption performance, but compared with composite materials with dual localized surface plasmon resonance, the light absorption performance is still limited, thus affecting the separation efficiency of photoexcited carriers. Tungsten oxide (WO3) is a strong candidate for constructing nonmetallic plasmonic materials; its structural characteristics facilitate oxygen loss and structural deformation, thereby forming non-stoichiometric W... 18 O 49 In W 18 O 49 In the middle, W 5+ -W 5+The periodic arrangement of ion pairs provides the structural basis for the localization of electrons. W 18 O 49 The oxygen vacancies (OVs) formed in the catalytic reaction contain abundant free electrons, which can serve as adsorption and activation sites in the catalytic reaction. Ensuring the concentration of OVs is crucial for promoting the catalytic reaction. Patent CN111495355A discloses a WO3 with visible light LSPR absorption. 3-x Nanosheet photocatalysts and their preparation methods have enabled the realization of WO 3-x The LSPR absorption and modulation in the visible light region exhibited good catalytic degradation performance for methyl orange. It is worth noting that W... 18 O 49 The LSPR effect is closely related to the oxygen vacancies (OVs) on its surface. Studies have found that after a long catalytic reaction, W 18 O 49 Oxidation of oxygen vacancies on the surface leads to the loss of the LSPR effect and severely affects light absorption performance and catalytic activity.

[0004] W containing stable OVs 18 O 49 High-energy hot electrons can be generated through the LSPR effect, thereby rapidly reducing coupled product intermediates. However, in existing technologies, W... 18 O 49 Photocatalysts with a dominant electron matrix are easily oxidized by photogenerated holes during the catalytic process, resulting in a shortened hot electron lifetime on the surface and limiting the photocatalytic reaction activity; W 18 O 49 The generated localized surface plasmon resonances still affect the light absorption performance of the catalyst.

[0005] Therefore, how can we prevent W from being modified using simple methods? 18 O 49 The OVs in the process are oxidized, maintaining their LSPR effect and providing abundant high-energy hot electrons for the photocatalytic nitrogen fixation process.

[0006] The information disclosed in this background section is intended to enhance understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] As mentioned above, W 18 O 49 The LSPR effect of W can produce strong absorption in the visible or near-infrared region. This effect is caused by oxygen oxidants (OVs) on its surface. However, after long-term use and exposure to air, these OVs will be oxidized and lose their LSPR ability, which greatly limits the potential of W. 18 O49 The light absorption capacity and catalytic activity of W. 18 O 49 The surface OV concentration and free electron density can be maintained or enhanced through continuous electron injection to ensure the surface LSPR strength. Constructing heterojunctions is a promising solution that enables continuous photoelectron injection into W. 18 O 49 In addition, it enhances interfacial charge separation. This dual-functional strategy not only solves the W 18 O 49 This study addresses the inherent limitations of polyoxometalates (POMs) and provides solutions for optimizing photocatalytic activity. PMoVs can store multiple electrons or protons while maintaining structural stability. Among them, PMoVs, with their excellent light absorption range, reversible redox properties, and rapid migration of photogenerated carriers, have secured their leading position in photocatalysis research. However, PMoVs still face several bottlenecks, such as small specific surface area, limited recyclability, and easy aggregation. Combining PMoVs with other support materials can effectively improve their dispersibility, stability, and photocatalytic activity. Attaching small-sized PMoVs and Ag to W... 18 O 49 On the surface, a heterostructure with a dual LSPR effect is prepared to enhance the light absorption performance of the material, while simultaneously implanted into W 18 O 49 Photogenerated electrons on the surface increase its electron density, thereby maintaining W 18 O 49 Plasma effect.

[0008] Therefore, this invention provides a method for preparing and applying a dual LSPR effect nitrogen-fixing material that increases the hot electron concentration at active sites, in order to solve the W 18 O 49 The oxidation of surface oxygen vapors (OVs) during long-term use and exposure to air presents a problem. This dual LSPR effect nitrogen-fixing material exhibits a high concentration of hot electrons at its active sites, resulting in excellent photocatalytic nitrogen fixation activity.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] Preparation of a dual LSPR effect nitrogen-fixing material with increased hot electron concentration at active sites, wherein the nitrogen-fixing material comprises Ag and W 18 O 49 The PMoV three-phase system, with PMoV and Ag uniformly attached to W via electrostatic self-assembly and photodeposition, respectively. 18 O 49 The surface.

[0011] In another aspect, this invention provides a method for synthesizing a dual LSPR effect nitrogen-fixing material with increased hot electron concentration at active sites, the detailed experimental steps of which are as follows:

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

[0013] (2) Add AgNO3 solution to the solution in step 1, stir the mixture under ultraviolet light for 60 min, collect the solid and wash it several times with water, and dry it to obtain Ag / W 18 O 49 / PMoV.

[0014] In some implementations, as described in step (1), W 18 O 49 / PMoV was prepared according to the following process, W 18 O 49 The solid product was dispersed in an aqueous solution of PMoV, stirred overnight, washed three times with deionized water, and dried at 60 °C for 10 h. The resulting solid powder was labeled as W. 18 O 49 / PMoV.

[0015] In some implementations, as described in step (1), W 18 O 49 / PMoV was synthesized as follows, by stirring 0.5 g of W 18 O 49 It was dispersed in 250 mL of a 0.2 mM / L PMoV aqueous solution and stirred at 1000 rpm.

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

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

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

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

[0020] In some implementations, step (2) is described in W 18 O 49 Add 25 mL of 0.5-1.5 mM AgNO3 solution to the / PMoV solution.

[0021] In some implementations, as described in step (1), W 18 O 49 Prepared as follows: 0.1 g of WCl6 was dissolved in 70 mL of ethanol and stirred thoroughly (1000 rpm) for 30 min until the powder was completely dissolved. The solution was transferred to an autoclave reactor and heated in an electrically heated drying oven at 200 °C for 20 h. The product was washed several times with ethanol and dried to obtain WCl6. 18 O 49 .

[0022] In some implementations, as described in step (1), W 18 O 49 In the preparation method, the heating rate of the electric heating drying oven is 2 ℃ / min.

[0023] In some implementations, as described in step (1), W 18 O 49 In the preparation method, the product is washed with ethanol 6 times and dried at 60 °C for 10 h.

[0024] In some embodiments, as described in step (1), PMoV is synthesized via the following route: sodium metavanadate (2.44 g) is dissolved in 10 mL of boiling water, 0.71 g of disodium hydrogen phosphate is added to 10 mL of water, the solution is then stirred thoroughly and mixed with the sodium metavanadate solution, cooled, and 0.5 mL of concentrated sulfuric acid is added to the mixed solution, 20 mL of sodium molybdate (12.1 g) solution is added to the solution, the resulting mixed solution is mixed with 8.5 mL of concentrated sulfuric acid, 50 mL of diethyl ether is added to the resulting solution, after extraction, the sample dissolves in the middle orange solution layer, and the target product PMoV is obtained after solvent evaporation.

[0025] In some implementations, step (1), W 18 O 49 The synthesis of PMoV can also be achieved by combining equal masses of PMoV with W. 18 O 49 The mixture was obtained by ball milling and compounding.

[0026] In a third aspect, the present invention provides a photocatalytic material Ag / W with a dual LSPR effect that enhances the hot electron concentration at active sites. 18 O 49Application of / PMoV in nitrogen fixation performance.

[0027] In some embodiments, the application of dual LSPR effect nitrogen-fixing materials with increased hot electron concentration at active sites is characterized by the preparation of a composite photocatalyst Ag / W. 18 O 49 / PMoV was dispersed in pure water, and high-purity nitrogen gas was introduced in the dark. The nitrogen fixation performance was studied under stirring and light radiation.

[0028] In some implementations, the dual LSPR effect nitrogen fixation material with increased hot electron concentration at active sites is used in pure water with Ag / W 18 O 49 The mass ratio of / PMoV is 10000:(1-10).

[0029] In some implementations, high-purity nitrogen is introduced into the reactor at a rate of 50 mL / min;

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

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention provides a dual LSPR effect nitrogen-fixing material that increases the hot electron concentration at active sites. PMoV and Ag are attached to W via electrostatic self-assembly and photodeposition. 18 O 49 On the surface, Ag / W with dual LSPR effect was prepared. 18 O 49 / PMoV heterojunction catalyst, W 18 O 49 It can absorb photogenerated electrons generated by PMoV and Ag, and the injected photogenerated electrons enrich W 18 O 49 The electron density at surface OV, thus maintaining W 18 O 49 Plasma effect. Ag / W 18 O 49 The fluorescence lifetime of photogenerated carriers in PMoV is prolonged, and the loading of Ag and PMoV is Ag / W. 18 O 49 The migration of photogenerated electrons and holes in / PMoV provides new channels, thereby promoting catalytic reactions. W 18 O 49 The photocatalytic ammonia synthesis rate can reach 32.9 µmol g. −1 h −1 Ag / W 18 O 49The nitrogen fixation activity of / PMoV was enhanced, and the ammonia formation rate reached 118.4 µmol g. −1 h −1 , is W 18 O 49 The yield was 3.6 times higher, and after multiple cycles, the Ag / W 18 O 49 / PMoV still maintains a high ammonia generation rate.

[0033] 2. The dual LSPR effect nitrogen-fixing material synthesized in this invention, which increases the hot electron concentration of active sites, has Ag attached to W 18 O 49 / PMoV surface, which broadens W 18 O 49 The light absorption range of / PMoV is extended to 600 nm, and the experimental parameters are easy to control in this synthesis route. Attached Figure Description

[0034] Figure 1 Example 1 shows the Ag / W nitrogen-fixing material with a dual LSPR effect that increases the hot electron concentration at active sites. 18 O 49 Scanning electron microscope image of / PMoV;

[0035] Figure 2 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 X-ray diffraction pattern of / PMoV;

[0036] Figure 3 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 photocurrent spectrum;

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

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

[0039] Figure 6 Comparative Example 1 W 18 O 49 Comparative Example 2: UV photoelectron spectrum of PMoV;

[0040] Figure 7 Comparative Example 1 W 18 O 49 Comparative Example 2: Directed carrier transfer between PMoV;

[0041] Figure 8 Example 1 Ag / W 18 O 49 / PMoV and ratio 1 W 18 O 49 Mid-electron spin resonance test spectrum;

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

[0043] Figure 10 Example 1 shows the Ag / W nitrogen-fixing material with a dual LSPR effect that increases the hot electron concentration at active sites. 18 O 49 / PMoV photocatalytic cycling test. Detailed Implementation

[0044] 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 scope of protection of the present invention is not limited to the specific embodiments.

[0045] The embodiments of the present invention are described below through specific examples. Those skilled in the art can understand in detail the other advantages and effects of the present invention from the content set forth 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 based on different viewpoints and applications without departing from the spirit of the present invention.

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

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

[0048] Sodium metavanadate, tungsten chloride, disodium hydrogen phosphate, silver nitrate, and sodium molybdate were all purchased from Aladdin Reagent Co., Ltd., while concentrated sulfuric acid, ethanol, diethyl ether, and isopropanol were all purchased from Sinopharm Chemical Reagent Co., Ltd. None of the chemical reagents were treated before use.

[0049] Example 1

[0050] The detailed steps of the synthesis method for nitrogen-fixing materials with enhanced hot electron concentration at active sites using the dual LSPR effect are as follows:

[0051] (1) W 18 O 49 Prepared as follows: 0.1 g of WCl6 was dissolved in 70 mL of ethanol and stirred thoroughly (1000 rpm) for 30 min to completely dissolve the powder. The solution was then transferred to an autoclave reactor and heated in an electric heating oven at 200 °C for 20 h at a heating rate of 2 °C / min. The product was washed with ethanol 6 times and dried at 60 °C for 10 h.

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

[0053] W 18 O 49 / PMoV was synthesized as follows, by stirring 0.5 g of W 18 O49 The solid product was dispersed in 250 mL of a 0.2 mM / L PMoV aqueous solution and stirred at 1000 rpm overnight. After washing three times with deionized water, the product was dried at 60 °C for 10 h. The resulting solid powder was labeled 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 being treated in an ultrasonic cleaner for 30 min.

[0055] (2) Add 25 mL of 1 mM AgNO3 solution to the solution in step 1, stir the mixture under ultraviolet light for 60 min at a stirring speed of 1100 rpm, collect the solid and wash it several times with water, and dry it to obtain Ag / W 18 O 49 / PMoV.

[0056] Example 2

[0057] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0058] Same as Example 1, except that in step (2), the mixture is stirred under ultraviolet light for 30 min.

[0059] Example 3

[0060] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0061] Same as Example 1, except that in step (2), the mixture is stirred under ultraviolet light for 90 min.

[0062] Example 4

[0063] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0064] Same as Example 1, except that 25 mL of 0.5 mM AgNO3 solution is added in step (2).

[0065] Example 5

[0066] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0067] Same as Example 1, except that 25 mL of 1.5 mM AgNO3 solution is added in step (2).

[0068] Example 6

[0069] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0070] Similar to Example 1, except that the stirring speed of the solution in step (2) is 1000 rpm.

[0071] Example 7

[0072] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0073] Similar to Example 1, except that the stirring speed of the solution in step (2) is 1200 rpm.

[0074] Example 8

[0075] A method for synthesizing nitrogen-fixing materials with enhanced hot electron concentration at active sites using a dual LSPR effect includes the following steps:

[0076] Same as Example 1, except that in step (1) 0.5 g W 18 O 49 W was obtained by grinding 0.087 g of PMoV in a ball mill for 12 h. 18 O 49 / PMoV complex.

[0077] Comparative Example 1: Single-phase catalyst W 18 O 49 Preparation

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

[0079] Comparative Example 2: Preparation of Single-Phase Catalyst PMoV

[0080] The single-phase catalyst PMoV was prepared according to the preparation method in step (2) of Example 1.

[0081] Comparative Example 3 Composite Catalyst W 18 O 49 Preparation of / PMoV

[0082] The composite catalyst W was prepared according to the preparation method in step (2) of Example 1. 18 O 49 / PMoV.

[0083] Verification of Examples

[0084] 1. Characterization by scanning electron microscopy and transmission electron microscopy

[0085] The double LSPR effect nitrogen-fixing material Ag / W with increased hot electron concentration at active sites in Example 1 was prepared. 18 O 49 The / PMoV was subjected to scanning electron microscopy and transmission electron microscopy tests. Figure 1 (a) and (b) are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Example 1, respectively. Ag / W can be observed in the images. 18 O 49 / PMoV has a nanosheet structure, with silver loaded on W 18 O 49 The surface, in addition W 18 O 49 The surface contains a large number of small particles, which are PMoV.

[0086] 2. X-ray diffraction test

[0087] The double LSPR effect nitrogen-fixing material Ag / W with increased hot electron concentration at active sites in Example 1 was prepared. 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 Comparative Example 2 PMoV and Comparative Example 3 W 18 O 49 / PMoV underwent X-ray diffraction testing, such as Figure 2 As shown, the signal peak position in the spectrum of Comparative Example 3 is the same as that of Example 1, while the low content of Comparative Example 2 resulted in its characteristic peak not appearing in the spectrum of Example 1. No new peaks related to Ag also appeared in the spectrum of Example 1, indicating that Ag nanoparticles did not aggregate.

[0088] 3. Photocurrent test

[0089] Figure 3 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 The photocurrent spectrum of / PMoV shows that, 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 photogenerated carriers are better excited and migrated in Example 1.

[0090] 4. Photoluminescence test

[0091] Figure 4 Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 Comparative Example 3 W 18 O 49 The photoluminescence spectrum of / PMoV shows a negative correlation between the degree of carrier recombination and the intensity of the photoluminescence signal peak. Comparative Example 1 exhibits the highest peak intensity, while the peak intensity decreases after the formation of the binary complex in Example 3. The W modified with silver nanoparticles... 18 O 49 The peak intensity of / PMoV further decreased, indicating that there is carrier migration between the components of the heterojunction. In Example 1, new channels were provided for the migration of photogenerated electrons and holes.

[0092] 5. Transient photoluminescence test

[0093] Figure 5 Example 1 Ag / W 18 O 49 / PMoV, Comparative Example 1 W 18 O 49 Comparative Example 3 W 18 O 49 The transient photoluminescence spectrum of / PMoV shows that the PL decay lifetime of each catalyst is in the order of Example 1 > Comparative Example 3 > Comparative Example 1. This phenomenon is due to the silver-induced LSPR effect, which leads to the enhancement of the local electric field, thereby promoting the transfer of photogenerated carriers, reducing the carrier recombination rate, and prolonging the fluorescence lifetime.

[0094] 6. Ultraviolet photoelectron spectroscopy test

[0095] Figure 6 Comparative Example 1 W 18 O 49 Comparative Example 2 shows the ultraviolet photoelectron spectrum of PMoV. The work function (Φ) is calculated as follows: Φ = φ + ΔV (φ is the work function of the photoelectron spectroscopy analyzer, φ = 4.42 eV, ΔV is the contact potential difference). The Φ values ​​for Comparative Example 1 and Comparative Example 2 are determined to be 8.09 and 9.93 eV, respectively. The Fermi levels (E) of Comparative Example 1 and Comparative Example 2 are... f Further calculations yielded -8.09 and -9.93 eV.

[0096] 7. Carrier directional transfer

[0097] Figure 7 Comparative Example 1 W 18 O 49 Comparative Example 2: Directed carrier transfer between PMoV. After Comparative Example 1 and Comparative Example 2 come into contact, the high E of Comparative Example 1...f The potential causes its own electrons to spontaneously migrate to the surface of Comparative Example 2. Ultimately, the potential difference between Example 1 and Example 2 is... f An equilibrium state was reached, and a built-in electric field was generated at the semiconductor interface from Comparative Example 1 to Comparative Example 2. Light radiation generated photogenerated carriers in the semiconductor, and the built-in electric field caused photogenerated electrons in the conduction band of Comparative Example 2 to migrate to Comparative Example 1. If photogenerated electrons in Comparative Example 2 migrated to the conduction band of Comparative Example 1, Coulomb repulsion would occur between the two materials, thus inhibiting the migration of photogenerated electrons. Therefore, under the combined effect of the built-in electric field and kinetic factors, photogenerated electrons in the conduction band of Comparative Example 2 were more inclined to combine with holes in the valence band of Comparative Example 1. Photogenerated electrons in Comparative Example 2 were injected into Comparative Example 1. Furthermore, the standard work function of Ag is 4.26 eV, and the hot electrons generated by silver can overcome W... 18 O 49 The Schottky barrier at the / PMoV interface, and was blocked by W 18 O 49 Absorption, E f The generated built-in electric field promotes the migration of charge carriers in the heterojunction, which helps the catalytic reaction to occur.

[0098] 8. Electron Spin Resonance Test

[0099] Figure 8 a is Example 1 Ag / W 18 O 49 / PMoV and comparative example 1 W 18 O 49 In the dark-state electron spin resonance (ESR) spectra, both Example 1 and Comparative Example 1 exhibited a Lorentz-shaped symmetric signal (g = 2.003), which is caused by single electrons surrounding the oxygen vacancies (OVs). Oxygen atoms detach from the lattice, forming positively charged holes. These holes attract surrounding electrons, leading to an increase in the number of free electrons near the oxygen vacancies. The signal peak intensity of Example 1 was slightly higher than that of Comparative Example 1. The OVs in Comparative Example 1 were preserved during sample synthesis. The ESR spectra of Example 1 and Comparative Example 1 were detected under illumination. Figure 8 As shown in b, the signal peak intensity of Example 1 increased significantly, with Ag and PMoV shifting towards W. 18 O 49 Electrons are injected into the middle, which increases W 18 O 49 The concentration of free electrons in the oxygen vacancy promotes the formation of oxygen vacancies.

[0100] 9. X-ray photoelectron spectroscopy test

[0101] For Example 1 Ag / W 18 O 49XPS tests were performed using / PMoV to observe the electron transfer process after light irradiation. Figure 9 After illumination, W in Example 1 5+ The proportions of OVs increased from 25.2% to 32.3% and from 18.1% to 22.8%, respectively. Meanwhile, compared to the XPS spectra in the dark state, the peak positions of P 2p, Mo 3d, V 2p, and Ag 3d shifted slightly towards higher binding energies. This indicates that Ag and PMoVs are bounding towards W... 18 O 49 The injection of photogenerated electrons provides strong evidence.

[0102] 10. Photocatalytic cycle test

[0103] Figure 10 Example 1 shows the Ag / W nitrogen-fixing material with a dual LSPR effect that increases the hot electron concentration at active sites. 18 O 49 The photocatalytic cycling test of / PMoV showed that after five cycles, the photocatalytic nitrogen fixation capacity of Example 1 remained stable, and the ammonia generation rate did not change significantly. Example 1 has excellent stability and can be repeatedly used for photocatalytic reactions.

[0104] 11. Photocatalytic nitrogen fixation reaction

[0105] The nitrogen fixation performance of the photocatalysts prepared in Examples 1-8 and Comparative Examples 1-3 was studied. 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 used 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 gas was introduced into the suspension in the reactor under no-light conditions. After 30 min, the nitrogen fixation performance was tested under light conditions.

[0107] To test the photocatalytic nitrogen fixation performance of Examples 1-8 and Comparative Examples 1-3, the catalytic solution was taken, the catalyst was removed by high-speed centrifugation, and the supernatant was injected into a quartz cuvette. The amount of ammonia was detected using a Varian Cary 700 UV-Vis spectrophotometer. The ammonia synthesis rate of different samples is shown in Table 1.

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

[0109]

[0110] As can be seen from Table 1, the comparative example 1 W prepared in this invention... 18 O 49 Comparative Example 2 PMoV and Comparative Example 3 W18 O 49 The ammonia formation rate of / PMoV was 32.9 μmol·g. -1 ·h -1 5.37 μmol·g -1 ·h -1 and 82.5 μmol·g -1 ·h -1 The OVs contained in Comparative Example 1 can act as adsorption and activation centers for nitrogen, in W 18 O 49 After PMoV was attached to the surface to form Comparative Example 3, PMoV and W 18 O 49 The tight interfacial contact formed between them is beneficial for the transformation from PMoV to W 18 O 49 Surface-transferred photogenerated electrons, and W 18 O 49 The concentration of oxides 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 formation rate in Example 1 reached 118.4 μmol·g. -1 ·h -1 This yields 3.6 times that of the control group 1; the high-energy hot electrons produced by Ag are injected into W. 18 O 49 In the middle, W 18 O 49 The increase in surface electron density promotes product formation.

[0111] From the ammonia generation rates of the synthesized photocatalysts in Examples 1-3, it can be seen that during the photodeposition method for loading Ag, the duration of light irradiation affects the catalyst activity. With shorter irradiation times, some Ag... + If the catalyst is not completely reduced, prolonged exposure to light may cause the attached Ag to detach under magnetic stirring, resulting in differences in the catalyst's catalytic performance.

[0112] It is not difficult to see from the ammonia generation rates of the synthesized photocatalysts in Examples 1, 4, and 5 that W 18 O 49 The amount of Ag loaded on the PMoV surface leads to different catalytic performance of the catalyst. Insufficient Ag may result in limited light absorption of the sample, but excessive Ag loading may cause aggregation and inhibit the transport capacity of charge carriers.

[0113] From the ammonia generation rates of the synthesized photocatalysts in Examples 1, 6, and 7, it can be seen that in step (2), Ag is attached to W 18 O 49On the / PMoV surface, the magnitude of the magnetic force exerted by the reaction of reactants in solution affects the double LSPR effect of nitrogen-fixing materials Ag / W that increase the hot electron concentration at active sites. 18 O 49 Nitrogen fixation activity of / PMoV.

[0114] From the ammonia generation rates of the synthesized photocatalysts in Examples 1 and 8, it can be seen that in the preparation of Ag / W, a nitrogen-fixing material with a dual LSPR effect that increases the hot electron concentration at active sites... 18 O 49 / PMoV, W 18 O 49 The combination of PMoV and other methods affects the nitrogen fixation activity of the catalyst.

Claims

1. A dual LSPR effect nitrogen-fixing material that increases the hot electron concentration at active sites, characterized in that, The dual LSPR effect nitrogen-fixing material is Ag / W. 18 O 49 / PMoV, where PMoV is H5PMo 10 V2O 40 The preparation method of the dual LSPR effect nitrogen-fixing material includes the following steps: Step 1: Add 0.1 g W 18 O 49 / PMoV was dispersed in a mixture of 25 mL deionized water and 10 mL isopropanol; Step 2: Add AgNO3 solution to the solution from Step 1, stir the mixture under ultraviolet light for 60 min, collect the solid, wash it several times with water, and dry it to obtain Ag / W. 18 O 49 / PMoV; In step 1, the W 18 O 49 / PMoV was prepared according to the following process, W 18 O 49 The solid product was dispersed in an aqueous solution of PMoV, stirred overnight, washed with deionized water, and dried at 60 °C. The resulting solid powder was labeled as W. 18 O 49 / PMoV; In step 2, in W 18 O 49 Add 25 mL of 1 mM AgNO3 solution to the / PMoV solution.

2. The dual LSPR effect nitrogen-fixing material for increasing the hot electron concentration at active sites according to claim 1, characterized in that, In step 1, 0.5 g of W 18 O 49 It was dispersed in 250 mL of a 0.2 mM PMoV aqueous solution.

3. The dual LSPR effect nitrogen-fixing material for increasing the hot electron concentration at active sites according to claim 1, characterized in that, In step 1, W 18 O 49 Prepared as follows: 0.1 g of WCl6 was dissolved in 70 mL of ethanol, and the powder was stirred thoroughly until completely dissolved. The solution was transferred to an autoclave reactor and heated in an electrically heated drying oven at 200 °C for 20 h. The product was washed several times with ethanol and dried to obtain WCl6. 18 O 49 .

4. The dual LSPR effect nitrogen-fixing material for increasing the hot electron concentration at active sites according to claim 1, characterized in that, In step 1, PMoV was synthesized via the following route: 2.44 g of sodium metavanadate was dissolved in 10 mL of boiling water, and 0.71 g of disodium hydrogen phosphate was added to 10 mL of water. The solution was then stirred thoroughly and mixed with the sodium metavanadate solution. After cooling, 0.5 mL of concentrated sulfuric acid and 20 mL of sodium molybdate solution were added to the mixed solution. The resulting mixed solution was then mixed with 8.5 mL of concentrated sulfuric acid. 50 mL of diethyl ether was added to the resulting solution. After extraction, the sample dissolved in the middle orange solution layer. After solvent evaporation, the target product PMoV was obtained.

5. The application of the dual LSPR effect nitrogen-fixing material with increased hot electron concentration at active sites as described in claim 1, characterized in that, The prepared dual LSPR effect nitrogen fixation material Ag / W 18 O 49 / PMoV is dispersed in pure water, and high-purity nitrogen gas is introduced in the dark for nitrogen fixation under stirring and light radiation.

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