Moo 3 / fe 2(moo 4) 3 composite material, preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of chemical catalytic materials. Disclosed are an MoO3 / Fe2(MoO4)3 composite material, a preparation method therefor, and a use thereof. The preparation method comprises the following steps: firstly, separately dissolving (NH4)6Mo7O24·4H2O and Fe(NO3)3·9H2O in a solvent to obtain a solution A and a solution B, then mixing and stirring the solutions for a reaction, and finally, separating a solid from a reactant, and drying, grinding, and calcining the solid to prepare Fe2(MoO4)3; uniformly mixing Fe2(MoO4)3, PVP, and water, adding a NaBH4 solution, stirring the mixture, and separating a solid product; and mixing the solid product with (NH4)6Mo7O24·4H2O in a solvent, continuously stirring and then evaporating and drying the mixture to obtain a solid, and calcining the solid to obtain the composite material. The composite material prepared in the present invention has high photoelectrocatalytic performance and relatively high ammonia synthesis yield, Faradaic efficiency, and chemical stability.

Description

MoO3 / Fe2(MoO4)3 composite material and preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical catalytic materials, in particular to a MoO3 / Fe2(MoO4)3 composite material and a preparation method and application thereof. BACKGROUND

[0002] Ammonia (NH3), as an indispensable chemical raw material for human society, plays an important role in industry and agriculture. However, commercial NH3 synthesis is mainly achieved by the Haber-Bosch (HB) process under harsh reaction conditions (650-750 K, 150-350 bar). The preparation and compression of precursors (H2 and N2) consume about 2% of global fossil fuels, which leads to a large amount of greenhouse gas emissions. Therefore, developing an efficient and sustainable NH3 synthesis route is one of the key topics of concern in today's society. So far, various advanced methods have been proposed to promote the conversion of N2 to NH3, such as biochemical, electrochemical, photocatalytic and photoelectrochemical (PEC); these technologies do not produce a large amount of CO2, especially photoelectrocatalytic N2 reduction reaction (PEC NRR), due to the synergistic effect of photocatalysis and electrochemistry in NH3 synthesis, which usually exhibits significant catalytic performance.

[0003] Since N2 is an extremely stable molecule, it is crucial to design photoelectric materials with excellent N2 adsorption / activation capacity. In recent years, the emergence of abundant reaction sites in photoelectrode materials has provided new opportunities and challenges for the PEC NRR field. So far, Fe2O3 has certain effect as a N2 reduction catalyst for synthesizing ammonia, and the solar energy conversion ideal efficiency is about 15.5% in a tandem PEC cell under AM 1.5G solar irradiation, however, the photoelectrocatalytic performance of α-Fe2O3 is limited by some factors, such as high recombination rate of electrons and holes, low diffusion length of holes (2-4 nm) and poor electrical conductivity, which leads to large photo-assisted nitrogen reduction overpotential and low ammonia synthesis efficiency. How to prepare a composite material with multiple composite sites, high photocatalytic performance and electrical conductivity, high selectivity and photoelectrocatalytic efficiency is one of the key problems to be solved in the field of photoelectrocatalytic synthesis of ammonia at present.

[0004] SUMMARY

[0005] In order to solve the above technical problems, the purpose of the present application is to provide a MoO3 / Fe2(MoO4)3 composite material and a preparation method and application thereof, in order to solve the problems of poor catalytic performance, poor electrical conductivity and low ammonia synthesis efficiency of existing photoelectrocatalysts.

[0006] The technical solution of the present application to solve the above technical problems is as follows:

[0007] A preparation method of a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0008] (1) First, (NH4)6Mo7O 24 ·4H2O and Fe(NO3)·9H2O are dissolved in a solvent to obtain solution A and solution B, then solution A and solution B are mixed and continuously stirred to react; finally, the solid in the reaction product is separated, dried, ground, calcined, and Fe2(MoO4)3 is prepared;

[0009] (2) The Fe2(MoO4)3 obtained in step (1), PVP and water are uniformly mixed, and a NaBH4 solution is added, and the solid product is obtained by stirring and separating;

[0010] (3) The solid product obtained in step (2) and (NH4)6Mo7O 24 ·4H2O are mixed in a solvent, continuously stirred and dried by evaporation to obtain a solid, which is calcined to obtain.

[0011] The beneficial effects of the present application are: the present application successfully composites MoO3 and Fe2(MoO4)3, and according to the molar ratio of Mo atoms, a MoO3 / Fe2(MoO4)3-x composite catalyst with high photoelectric catalytic nitrogen reduction and ammonia synthesis performance is prepared. Studies have shown that the construction of defects reduces the valence band position of Fe2(MoO4)3-x, reduces the free energy of the electron transition from MoO3 to Fe2(MoO4)3-x, and is beneficial to accelerate the transfer of electrons, thereby further promoting the N2 reduction reaction. Fe2(MoO4)3-x has a strong N2 adsorption effect due to the construction of oxygen vacancies, which provides a good basis for the subsequent rupture of N≡N triple bond and hydrogenation reduction step; at the same time, the construction of heterojunction reduces the recombination of photo-generated electrons and holes, accelerates the charge transfer, and significantly improves the photoelectric catalytic synthesis of ammonia.

[0012] Further, the volume ratio of solution A to solution B in step (1) is 0.8-1.2:0.8-1.2.

[0013] Preferably, the volume ratio of solution A to solution B in step (1) is 1:1.

[0014] Further, the mass-volume ratio of (NH4)6Mo7O 24 ·4H2O and the solvent in solution A is 1g:4-8mL, and the solvent is ethylene glycol; the mass-volume ratio of Fe(NO3)·9H2O and the solvent in solution B is 1g:5-10mL, and the solvent is ethylene glycol.

[0015] Further, the time for continuous stirring in step (1) is 5-10h; the temperature for reaction is 150-200℃, the time is 10-15h; the temperature for drying is 50-70℃, the time is 5-10h; the temperature for calcination is 500-600℃, the time is 8-12h.

[0016] Preferably, the time for continuous stirring in step (1) is 8h; the temperature for reaction is 170℃, the time is 12h; the temperature for drying is 60℃, the time is 8h; the temperature for calcination is 550℃, the time is 10h.

[0017] Further, the mass ratio of Fe2(MoO4)3 and PVP in step (2) is 1:1.5-2; the volume ratio of NaBH4 solution to the mixed solution of Fe2(MoO4)3, PVP and water is 1:4-6, and the concentration of NaBH4 solution is 5-100μmol·L -1 .

[0018] Preferably, the mass ratio of Fe2(MoO4)3 and PVP in step (2) is 1:1.7; the volume ratio of NaBH4 solution to the mixed solution of Fe2(MoO4)3, PVP and water is 1:5.

[0019] Further, the adding mode of NaBH4 solution in step (2) is dropwise, and the time for stirring is 30-90min.

[0020] Further, the mass-volume ratio of solid product, (NH4)6Mo7O 24 ·4H2O and solvent in step (3) is 8-9g:1g:100-200mL, and the solvent is ethanol.

[0021] Further, the time for continuous stirring in step (3) is 20-30h; the calcination condition is: heating to 500-600℃ at a heating rate of 4-6℃, and calcining for 8-12h.

[0022] Preferably, the time for continuous stirring in step (3) is 24h; the calcination condition is: heating to 550℃ at a heating rate of 5℃, and calcining for 10h.

[0023] A MoO3 / Fe2(MoO4)3 composite material is prepared by the above preparation method.

[0024] The application of the above MoO3 / Fe2(MoO4)3 composite material in photoelectrocatalytic synthesis of ammonia.

[0025] The application has the following beneficial effects:

[0026] (1) The MoO3 / Fe2(MoO4)3 composite material prepared by the application has oxygen vacancies, which makes there be defect energy levels in the band gap of Fe2(MoO4)3, reduces the valence band energy, reduces the band gap width, and improves the light absorption performance; the construction of MoO3 / Fe2(MoO4)3 heterojunction reduces the recombination of photo-generated electrons and holes, accelerates electron transfer, and promotes the participation of high reduction potential electrons in the N2 reduction reaction.

[0027] (2) The MoO3 / Fe2(MoO4)3 composite material provided by the application can make the synthesis of ammonia reach 2.04 mmol·h -1 ·g cat -1 and 40% Faraday efficiency, and the ammonia production efficiency has little decline after 6 cycles of testing, and has good chemical stability. BRIEF DESCRIPTION OF DRAWINGS

[0028] Fig. 1 is an XRD spectrum in test example 1;

[0029] Fig. 2 is an ultraviolet-visible diffuse reflectance spectrum and a band gap diagram in test example 2, wherein (a) and (c) are spectrum diagrams, and (b) and (d) are band gap diagrams;

[0030] Fig. 3 is a nitrogen adsorption-desorption isotherm and a pore size distribution diagram in test example 3, wherein (a) is a nitrogen adsorption-desorption isotherm, and (b) is a pore size distribution diagram;

[0031] Fig. 4 is a linear sweep voltammetry curve diagram in test example 4;

[0032] Fig. 5 is a transient photocurrent diagram in test example 5;

[0033] Fig. 6 is an electrochemical impedance diagram in test example 6;

[0034] Fig. 7 is an electrochemical synthesis of ammonia efficiency and Faraday efficiency diagram in test example 7;

[0035] Fig. 8 is a cycle stability test result diagram of-0.6V vs.RHE bias voltage in test example 8. DETAILED DESCRIPTION

[0036] The principles and characteristics of the application are described below in conjunction with the drawings, and the examples are only used to explain the application and are not used to limit the scope of the application. If no specific conditions are specified in the examples, conventional conditions or manufacturer recommended conditions are used. If no manufacturer of the reagents or instruments is specified, it is a conventional product that can be purchased on the market.

[0037] Example 1:

[0038] A method for preparing a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0039] (1) Preparation of Fe2(MoO4)3

[0040] First, 2.47 g of (NH4)6Mo7O 24 ·4H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution A. 3.77 g of Fe(NO3)·9H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution B.

[0041] Then, after mixing solution A and solution B, the solution turned orange red, and after continuous stirring for 8 h, orange red precipitate appeared in the solution. The stirred mixed solution was transferred to a 100 mL polytetrafluoroethylene liner, the liner was placed in a stainless steel reaction kettle and sealed, and the reaction kettle was placed in a 170°C air drying oven for reaction for 12 h.

[0042] Finally, after cooling to room temperature, the reaction product was taken out and centrifuged with pure water and ethanol respectively, the obtained solid was dried in a 60°C oven for 8 h, then ground thoroughly with a mortar, and the ground powder was placed in a magnetic boat and calcined at 550°C for 10 h, and then cooled to room temperature to obtain brick red Fe2(MoO4)3 powder.

[0043] (2) Preparation of Fe2(MoO4)3-x

[0044] 0.592 g of Fe2(MoO4)3 powder obtained in step (1) and 1 g of PVP were added to 100 mL of pure water and ultrasonicated for 30 min until uniformly dispersed. 20 mL of 10 μmol·L -1 of NaBH4 solution was slowly added dropwise into the mixed solution under vigorous stirring, and after continuous stirring for 1 h, the solid was separated to obtain Fe2(MoO4)3-10.

[0045] (3) Preparation of MoO3 / Fe2(MoO4)3 composite material

[0046] 1.478 g of Fe2(MoO4)3-10 prepared in step (2) was added to 20 mL of ethanol, and after uniform stirring, 0.17 g of (NH4)6Mo7O 24 ·4H2O was added, and after continuous stirring for 24 h, evaporation was carried out at 80°C to obtain dry solid, which was calcined in a muffle furnace for 6 h at a heating rate of 5°C / min to obtain the composite material MoO3 / Fe2(MoO4)3-10.

[0047] Example 2:

[0048] A method for preparing a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0049] (1) Preparation of Fe2(MoO4)3

[0050] First, 2.47 g of (NH4)6Mo7O 24 ·4H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution A. 3.77 g of Fe(NO3)·9H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution B.

[0051] Then, solution A and solution B were mixed, and the solution turned orange red. After continuous stirring for 8 h, orange red precipitate appeared in the solution. The stirred mixed solution was transferred to a 100 mL polytetrafluoroethylene liner, the liner was placed in a stainless steel reaction kettle and sealed, and the reaction kettle was placed in a 170°C air drying oven for reaction for 12 h.

[0052] Finally, after cooling to room temperature, the reaction product was taken out and centrifuged with pure water and ethanol respectively. The obtained solid was dried in a 60°C oven for 8 h, then ground with a mortar, and the ground powder was placed in a magnetic boat and calcined at 550°C for 10 h. After cooling to room temperature, a brick red Fe2(MoO4)3 powder was prepared.

[0053] (2) Preparation of Fe2(MoO4)3-x

[0054] 0.592 g of Fe2(MoO4)3 powder obtained in step (1) and 1 g of PVP were added to 100 mL of pure water and ultrasonicated for 30 min until uniformly dispersed. A 20 mL solution of 30 μmol·L -1 of NaBH4 was slowly added dropwise into the mixed solution under vigorous stirring, and the stirring was continued for 1 h. The solid was separated to obtain Fe2(MoO4)3-30.

[0055] (3) Preparation of MoO3 / Fe2(MoO4)3 composite material

[0056] 1.478 g of Fe2(MoO4)3-30 prepared in step (2) was added to 20 mL of ethanol, and 0.17 g of (NH4)6Mo7O 24 ·4H2O was added after uniform stirring. After continuous stirring for 24 h, evaporation was carried out at 80°C to obtain dry solid. The solid was calcined in a muffle furnace for 6 h at a heating rate of 5°C / min to obtain the composite material MoO3 / Fe2(MoO4)3-30.

[0057] Example 3:

[0058] A method for preparing a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0059] (1) Preparation of Fe2(MoO4)3

[0060] First, 2.47 g of (NH4)6Mo7O 24 ·4H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution A. 3.77 g of Fe(NO3)·9H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution B.

[0061] Then, after mixing solution A and solution B, the solution turned orange red, and after continuous stirring for 8 h, orange red precipitate appeared in the solution. The stirred mixed solution was transferred to a 100 mL polytetrafluoroethylene liner, the liner was placed in a stainless steel reaction kettle and sealed, and the reaction kettle was placed in a 170°C air drying oven for reaction for 12 h.

[0062] Finally, after cooling to room temperature, the reaction product was taken out and centrifuged with pure water and ethanol respectively, the obtained solid was dried in a 60°C oven for 8 h, then ground with a mortar, and the ground powder was placed in a magnetic boat and calcined at 550°C for 10 h, and then cooled to room temperature to obtain brick red Fe2(MoO4)3 powder.

[0063] (2) Preparation of Fe2(MoO4)3-x

[0064] 0.592 g of Fe2(MoO4)3 powder obtained in step (1) and 1 g of PVP were added to 100 mL of pure water and ultrasonicated for 30 min until uniformly dispersed. 20 mL of 50 μmol·L -1 of NaBH4 solution was slowly added dropwise into the mixed solution under vigorous stirring, and after continuous stirring for 1 h, the solid was separated to obtain Fe2(MoO4)3-50.

[0065] (3) Preparation of MoO3 / Fe2(MoO4)3 composite material

[0066] 1.478 g of Fe2(MoO4)3-50 prepared in step (2) was added to 20 mL of ethanol, and after uniform stirring, 0.17 g of (NH4)6Mo7O 24 ·4H2O was added, and after continuous stirring for 24 h, evaporation was carried out at 80°C to obtain dry solid, which was calcined in a muffle furnace for 6 h at a heating rate of 5°C / min to obtain the composite material MoO3 / Fe2(MoO4)3-50.

[0067] Example 4:

[0068] A method for preparing a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0069] (1) Preparation of Fe2(MoO4)3

[0070] First, 2.47 g of (NH4)6Mo7O 24 ·4H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution A. 3.77 g of Fe(NO3)·9H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution B;

[0071] Then, solution A and solution B were mixed, and the solution turned orange red. After continuous stirring for 8 h, orange red precipitate appeared in the solution. The stirred mixed solution was transferred to a 100 mL polytetrafluoroethylene liner, the liner was placed in a stainless steel reaction kettle and sealed, and the reaction kettle was placed in a 170°C air drying oven for reaction for 12 h;

[0072] Finally, after cooling to room temperature, the reaction product was taken out and centrifuged with pure water and ethanol respectively. The obtained solid was dried in a 60°C oven for 8 h, then ground with a mortar, and the ground powder was placed in a magnetic boat and calcined at 550°C for 10 h. After cooling to room temperature, a brick red Fe2(MoO4)3 powder was prepared.

[0073] (2) Preparation of Fe2(MoO4)3-x

[0074] 0.592 g of Fe2(MoO4)3 powder obtained in step (1) and 1 g of PVP were added to 100 mL of pure water and ultrasonicated for 30 min until uniformly dispersed. A 20 mL solution of 70 μmol·L -1 of NaBH4 was slowly added dropwise into the mixed solution under vigorous stirring, and the stirring was continued for 1 h. The solid was separated to obtain Fe2(MoO4)3-70.

[0075] (3) Preparation of MoO3 / Fe2(MoO4)3 composite material

[0076] 1.478 g of Fe2(MoO4)3-70 prepared in step (2) was added to 20 mL of ethanol, and 0.17 g of (NH4)6Mo7O 24 ·4H2O was added after uniform stirring. After continuous stirring for 24 h, evaporation was carried out at 80°C to obtain dry solid. The solid was calcined in a muffle furnace for 6 h at a heating rate of 5°C / min to obtain the composite material MoO3 / Fe2(MoO4)3-70.

[0077] Comparative Example 1:

[0078] A method for preparing a MoO3 / Fe2(MoO4)3 composite material, comprising the following steps:

[0079] (1) Preparation of Fe2(MoO4)3

[0080] First, 2.47 g of (NH4)6Mo7O 24 ·4H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution A. 3.77 g of Fe(NO3)·9H2O was added to 20 mL of ethylene glycol and ultrasonicated for 30 min until completely dissolved to obtain solution B.

[0081] Then, solution A and solution B were mixed, and the solution turned orange red. After continuous stirring for 8 h, orange red precipitate appeared in the solution. The stirred mixed solution was transferred to a 100 mL polytetrafluoroethylene liner, and the liner was placed in a stainless steel reaction kettle and sealed. The reaction kettle was placed in a 170℃ air drying oven for reaction for 12 h.

[0082] Finally, after cooling to room temperature, the reaction product was taken out and centrifuged with pure water and ethanol, respectively. The obtained solid was dried in a 60℃ oven for 8 h, then ground with a mortar, and the ground powder was placed in a magnetic boat and calcined at 550℃ for 10 h. After cooling to room temperature, brick red Fe2(MoO4)3 powder was obtained.

[0083] (2) Preparation of MoO3 / Fe2(MoO4)3 composite material

[0084] 1.478 g of Fe2(MoO4)3 prepared in step (1) was added to 20 mL of ethanol, and 0.17 g of (NH4)6Mo7O 24 ·4H2O was added respectively after uniform stirring. After continuous stirring for 24 h, evaporation was carried out at 80℃ to obtain dry solid. The solid was calcined in a muffle furnace for 6 h at a heating rate of 5℃ / min to obtain the composite material MoO3 / Fe2(MoO4)3.

[0085] Test Example 1: XRD analysis

[0086] Fe2(MoO4)3, MoO3 / Fe2(MoO4)3-30 and pure MoO3 prepared in Example 2 were subjected to X-ray diffraction analysis. The above samples were detected by a Panalytical X'Pert PRO type X-ray diffractometer at a scanning speed of 10° / min and a scanning angle of 10-80°.

[0087] The experimental results are shown in Figure 1. As can be seen from Figure 1, the peaks of Fe2(MoO4)3at 13.79°, 15.32°, 20.43°, 21.76°, 22.66°, 22.99°, 24.90°, 25.71°, 27.50° completely correspond to the (200), (012), (120), (214), (022), (202), (212), (122), (224) crystal planes of the standard card PDF #83-1701, indicating the successful preparation of the material. The diffraction peaks of MoO3at 23.33°, 25.698°, 25.88°, 27.32°, 33.76°, 38.9° completely correspond to the (110), (040), (120), (021), (111), (060) crystal planes of the standard card PDF #76-1003. The Fe2(MoO4)3 / MoO3-30 composite material has all the peaks corresponding to the two substances, indicating the successful preparation of the material.

[0088] Test Example 2: UV-Vis Diffuse Reflectance Analysis

[0089] Pure MoO3, Fe2(MoO4)3prepared in Example 1, Fe2(MoO4)3-10, Fe2(MoO4)3-30, Fe2(MoO4)3-50, Fe2(MoO4)3-70 prepared in Examples 1-4, MoO3 / Fe2(MoO4)3-30 prepared in Example 2, and MoO3 / Fe2(MoO4)3prepared in Comparative Example 1 were characterized. The UV-Vis diffuse reflectance spectra of the samples were obtained using an Agilent Cary 100 UV spectrophotometer with barium sulfate as a reference under the condition of a spectral range of 200-800 nm.

[0090] The experimental results are shown in Figure 2. As can be seen from Figure 2, MoO3has light absorption in the wavelength range of 300-450 nm, Fe2(MoO4)3has light absorption in the range of 300-630 nm, MoO3 / Fe2(MoO4)3and MoO3 / Fe2(MoO4)3-30 both have light absorption in the range of 300-800 nm, and the light absorption intensity in the range of 300-800 nm is greatly improved compared with MoO3and Fe2(MoO4)3. Notably, the light absorption of MoO3 / Fe2(MoO4)3-30 is higher than that of MoO3 / Fe2(MoO4)3in the range of 480-800 nm. Fe2(MoO4)3-x containing different amounts of oxygen vacancies has different responses to light. In the range of 300-800 nm, Fe2(MoO4)3-30 has the largest light absorption range and the highest light absorption intensity.

[0091] As shown in (b) and (d) of FIG. 2, the band gaps of MoO3 and Fe2(MoO4)3 are 2.80 eV and 2.87 eV, respectively. When different amounts of oxygen vacancies are introduced, the band gaps are narrowed to different degrees, and the band gap of Fe2(MoO4)3-30 changes the most, to 2.30 eV. Therefore, Fe2(MoO4)3-30 exhibits strong light absorption performance and a wide light absorption range, and is likely to generate more photo-generated carriers under irradiation, which is conducive to the photoexcitation of valence band electrons to the conduction band, so as to participate in the subsequent nitrogen reduction reaction.

[0092] Test Example 3: Adsorption isotherm and specific surface area and pore size distribution analysis

[0093] The adsorption isotherm, specific surface area and pore size distribution of Fe2(MoO4)3, Fe2(MoO4)3-30 and MoO3 / Fe2(MoO4)3-30 prepared in Example 2 were analyzed using an instrument with a model of Micromeritics ASAP 2460.

[0094] The experimental results are shown in FIG. 3. As can be seen from FIG. 3, all the samples exhibit H3 type hysteresis curves, proving that the three electrode materials have mesoporous structures. The average pore sizes of Fe2(MoO4)3, Fe2(MoO4)3-30 and MoO3 / Fe2(MoO4)3-30 are 17.63, 12.2 and 16.04 nm, respectively. According to the Brunauer-Emmett-Teller (BET) method, the specific surface areas of Fe2(MoO4)3, Fe2(MoO4)3-30 and MoO3 / Fe2(MoO4)3-30 electrode materials are 7.29, 13.35 and 35.12 m2 / g, respectively. 2 g -1 The manufacture of oxygen vacancies and the compounding of materials increase the specific surface area of Fe2(MoO4)3. The larger specific surface area increases the reaction active sites, which is conducive to the adsorption and reaction of N2. The pore size distribution graph (FIG. 3(b)) analyzed by the Barrett-Joyner-Halenda (BJH) method shows that the channels of Fe2(MoO4)3, Fe2(MoO4)3-30 and MoO3 / Fe2(MoO4)3-30 electrode materials are mainly mesoporous.

[0095] Test Example 4: Measurement of photoresponse performance

[0096] LSV curve determination of Fe2(MoO4)3, Fe2(MoO4)3-30, MoO3 / Fe2(MoO4)3-30 prepared in Example 2, MoO3 / Fe2(MoO4)3 prepared in Comparative Example 1 and pure MoO3 was carried out by using an electrochemical workstation with model CHI6503, using a three-electrode system, Ag / AgCl electrode as reference electrode, platinum electrode as counter electrode, and the sample to be detected as working electrode.

[0097] The experimental results are shown in Figure 4. It can be seen from Figure 4 that the photocurrents of Fe2(MoO4)3, MoO3, MoO3 / Fe2(MoO4)3, Fe2(MoO4)3-30 and MoO3 / Fe2(MoO4)3-30 at the voltage of -1.2 V vs. RHE are -0.15, -1.04, -3.02, -4.98 and -6.22 mA·cm-2, respectively. -2 The photocurrent of MoO3 / Fe2(MoO4)3-30 is 41.5 and 5.98 times that of pure Fe2(MoO4)3 and pure MoO3, respectively.

[0098] Test Example 5: Photosensitivity determination

[0099] Photosensitivity determination of Fe2(MoO4)3, Fe2(MoO4)3-30, MoO3 / Fe2(MoO4)3-30 prepared in Example 2, MoO3 / Fe2(MoO4)3 prepared in Comparative Example 1 and pure MoO3 was carried out by using an electrochemical workstation with model CHI6503, and I-t curve was determined.

[0100] The experimental results are shown in Figure 5. It can be seen from Figure 5 that the TPR value of MoO3 / Fe2(MoO4)3-30 photocatalytic material is 5 μA·cm-2 at the moment of turning on and turning off the light, and the photocurrent is stable in the operation of turning on and turning off the light for 10 times. The TPR value of Fe2(MoO4)3-30 is smaller, which is 4.03 μA·cm-2, and the TPR values of Fe2(MoO4)3, MoO3 and MoO3 / Fe2(MoO4)3 are very low, which are 2.32 μA·cm-2, 1.05 μA·cm-2 and 0.98 μA·cm-2, respectively. -2 -2 -2 -2 -2

[0101] Test Example 6: Electrochemical impedance spectrogram determination

[0102] ​​​​​Electrochemical impedance spectroscopy was performed on Fe2(MoO4)3, Fe2(MoO4)3-30, MoO3 / Fe2(MoO4)3-30 prepared in Example 2, MoO3 / Fe2(MoO4)3 prepared in Comparative Example 1 and pure MoO3 to test the carrier migration and separation kinetics of the test electrode. Generally, the smaller the electrochemical impedance spectroscopy radius, the greater the photoelectron-hole transfer rate.

[0103] The experimental results are shown in FIG. 6. As can be seen from FIG. 6, the radius of Fe2(MoO4)3 is the largest, and the electrochemical impedance spectroscopy radius of MoO3 / Fe2(MoO4)3 becomes smaller after MoO3 is compounded, indicating that the construction of the MoO3 heterojunction increases the reaction kinetics and improves the carrier transport efficiency. The radius of Fe2(MoO4)3-30 is smaller than that of Fe2(MoO4)3, and even smaller than that of MoO3 / Fe2(MoO4)3, indicating that the construction of oxygen vacancies improves the electron capture ability of Fe2(MoO4)3, to a certain extent, reduces the recombination of electrons and holes, and is conducive to the participation of holes in subsequent reactions. The radius of MoO3 / Fe2(MoO4)3-30 is the smallest, indicating that the synergistic effect of the heterojunction and the defect oxygen vacancies improves the reaction kinetics.

[0104] Test Example 7: Measurement of photocatalytic activity

[0105] The photocatalytic synthesis of ammonia was studied using nitrogen as the nitrogen source, a xenon lamp to simulate sunlight, and 1 mol / L KOH as the electrolyte. The test samples were Fe2(MoO4)3, Fe2(MoO4)3-30, MoO3 / Fe2(MoO4)3-30 prepared in Example 2, MoO3 / Fe2(MoO4)3 prepared in Comparative Example 1 and pure MoO3. Before the reaction, nitrogen was introduced into the cathode tank for 0.5-1 h to form a nitrogen-saturated KOH solution, and then constant potential electrolysis was performed (nitrogen reduction reaction and hydrogen evolution reaction occurred at the cathode, and oxygen evolution reaction occurred at the anode). The reaction time was 2 h, the stirring speed was set to 400 rpm, and the sample was taken after 2 h of reaction for testing, and the yield was obtained.

[0106] The experimental results are shown in FIG. 7. At a bias voltage of -0.6 V vs. RHE, the ammonia synthesis efficiency of Fe2(MoO4)3, MoO3, MoO3 / Fe2(MoO4)3, Fe2(MoO4)3-30, MoO3 / Fe2(MoO4)3-30 was 0.30, 0.85, 1.08, 1.36, 2.04 mmol·h -1 ·g cat -1, Faraday efficiency: 19.02%, 3.40%, 1.28%, 8.86%, 43.00%. The synthesis ammonia efficiency and Faraday efficiency of MoO3 / Fe2(MoO4)3-30 are 6.8 times and 2.26 times of Fe2(MoO4)3 respectively. The synthesis ammonia efficiency and Faraday efficiency of MoO3 / Fe2(MoO4)3-30 are 2.4 times and 12.65 times of MoO3 respectively. The heterojunction composed of MoO3 and Fe2(MoO4)3-30 regulates the carrier transmission channel, which is conducive to the separation of electrons and holes, and improves the synthesis ammonia efficiency.

[0107] Test Example 8: Stability test

[0108] The MoO3 / Fe2(MoO4)3-30 composite material prepared in Example 2 was subjected to a stability test, and 6 cycles of ammonia synthesis experiments were carried out under the same conditions as in Test Example 7.

[0109] As shown in Figure 8, after 6 cycles of 2h nitrogen reduction to synthesize ammonia at a bias voltage of -0.6V vs.RHE using MoO3 / Fe2(MoO4)3-30 as a photoelectrocatalyst, the ammonia yield of the catalyst remained stable at about 98%.

[0110] In summary, the MoO3 and Fe2(MoO4)3 are successfully compounded in the present application, and MoO3 / Fe2(MoO4)3-x composite catalysts with high photoelectrocatalytic nitrogen reduction to synthesize ammonia performance are prepared according to the Mo atomic molar ratio. Studies have shown that the construction of defects reduces the valence band position of Fe2(MoO4)3-x, reduces the free energy of the transition of electrons from MoO3 to Fe2(MoO4)3-x, and is conducive to accelerating the transfer of electrons, thereby further promoting the N2 reduction reaction. Fe2(MoO4)3-x has a strong N2 adsorption effect due to the construction of oxygen vacancies, which provides a good basis for the subsequent breaking of N≡N triple bond and hydrogenation reduction step; at the same time, the construction of heterojunction reduces the recombination of photo-generated electrons and holes, and accelerates the charge transfer, so that the photoelectrocatalytic synthesis of ammonia of MoO3 / Fe2(MoO4)3-x is obviously improved.

[0111] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a MoO3 / Fe2(MoO4)3 composite material, characterized in that, The method comprises the following steps: (1) First, (NH4)6Mo7O 24 • 4H2O and Fe(NO3)·9H2O are dissolved in a solvent to obtain solution A and solution B, respectively, then solution A and solution B are mixed and continuously stirred to carry out the reaction; finally, the solid in the reaction mixture is separated, dried, ground, calcined, and Fe2(MoO4)3is prepared; (2) mixing Fe2(MoO4)3, PVP and water obtained in step (1) uniformly, adding NaBH4 solution, stirring and separating to obtain solid product; (3) mixing the solid product from step (2) and (NH4)6Mo7O 24 • 4H2O in a solvent, continuously stirring and evaporating to dryness to obtain a solid, which is calcined to obtain 2. The method for preparing MoO3 / Fe2(MoO4)3 composite according to claim 1, characterized in that, The volume ratio of solution A to solution B in step (1) is 0.8-1.2:0.8-1.

2.

3. The method for producing a MoO3 / Fe2(MoO4)3 composite material according to claim 1 or 2, characterized by, The mass-volume ratio of (NH4)6Mo7O 24 4H2O and solvent in solution A is 1g:4-8mL, and the solvent is ethylene glycol; the mass-volume ratio of Fe(NO3)·9H2O and solvent in solution B is 1g:5-10mL, and the solvent is ethylene glycol.

4. The method for preparing the MoO3 / Fe2(MoO4)3 composite material according to claim 1, characterized in that, The continuous stirring time in step (1) is 5-10 h; the reaction temperature is 150-200 ℃, the reaction time is 10-15 h; the drying temperature is 50-70 ℃, the drying time is 5-10 h; the calcination temperature is 500-600 ℃, and the calcination time is 8-12 h.

5. The method for preparing the MoO3 / Fe2(MoO4)3 composite material according to claim 1, characterized in that, The mass ratio of Fe2(MoO4)3 and PVP in the step (2) is 1:1.5-2; the volume ratio of the NaBH4 solution to the mixed solution of Fe2(MoO4)3, PVP and water is 1:4-6, and the concentration of the NaBH4 solution is 5-100 μmol·L -1 .

6. The method for preparing the MoO3 / Fe2(MoO4)3 composite material according to claim 1, characterized in that, The adding mode of NaBH4 solution in step (2) is dropwise, and the stirring time is 30-90 min.

7. The method for preparing the MoO3 / Fe2(MoO4)3 composite material according to claim 1, characterized in that, The mass volume ratio of the solid product in step (3), (NH4)6Mo7O 24 • 8-9 g: 1 g: 100-200 mL, and the solvent is ethanol.

8. The method for preparing the MoO3 / Fe2(MoO4)3 composite material according to claim 1, characterized in that, The continuous stirring time in step (3) is 20-30 h; the calcination conditions are as follows: the temperature is increased to 500-600 ℃ at a temperature increasing rate of 4-6 ℃, and the calcination time is 8-12 h.

9. A MoO3 / Fe2(MoO4)3 composite material, characterized in that, The method is prepared by any one of claims 1-7.

10. The application of MoO3 / Fe2(MoO4)3 composite material in photoelectrocatalytic synthesis of ammonia according to claim 9.

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