BiFeO3 / MoO3 composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, in particular to a BiFeO3 / MoO3 composite material as well as a preparation method and application thereof. The preparation method of the BiFeO3 / MoO3 composite material comprises the following steps: S1, preparation of Mo154: adding Na2S2O4 into a Na2MoO4. 2H2O aqueous solution, adding an HCl solution in a stirring state, fully and uniformly mixing, sealing and standing for 5 days, filtering, removing blue crystal precipitate, washing, and drying to obtain Mo154; s2, preparation of MoO3: after grinding Mo154, calcining the ground Mo154 at 400 DEG C for 2 hours to obtain MoO3; s3, preparation of BiFeO3: adding citric acid into an ethylene glycol aqueous solution, uniformly mixing, adding Bi (NO3). 5H2O and Fe (NO3) 3.9 H2O, continuously stirring for 120 minutes, heating in a water bath at 80 DEG C in a stirring state to form sol, drying, fully grinding, calcining at 300 DEG C for 4 hours, and calcining at 600 DEG C for 2 hours to obtain BiFeO3; and S4, preparation of BiFeO3 / MoO3: dispersing BiFeO3 and MoO3 in water, carrying out ultrasonic treatment for 1 hour, drying, fully grinding, and reacting at 200 DEG C for 2 hours to obtain the BiFeO3 / MoO3. The composite material prepared by the invention can be used as a photocatalytic hydrogen production catalyst, and the hydrogen production performance can reach 306.45 [mu] mol.g <-1 > under the action of a magnetic field.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and more particularly to a BiFeO3 / MoO3 composite material and a preparation method and application thereof. Background Art

[0002] The continuous growth of energy consumption and the resulting climate change and environmental problems have made it urgent to find renewable and environmentally friendly alternative energy sources to replace fossil fuels. H2 is considered to be the most promising candidate for future energy supply due to its high gravimetric energy density and calorific value, as well as clean combustion products (H2O). Currently, the main industrial methods are to produce hydrogen from fossil resources, including coal gasification, natural gas steam reforming and partial oxidation of hydrocarbons. Although large amounts of hydrogen can be produced at a low cost in these processes, the consumption of fossil resources will lead to greenhouse gas emissions. Therefore, it is crucial to develop a green, sustainable and efficient hydrogen production strategy.

[0003] Photocatalytic hydrogen production, with its advantages of low cost, high efficiency, high stability, and environmental friendliness, has been widely applied in energy conversion and environmental governance, attracting widespread attention from researchers both domestically and internationally. Converting unstable solar energy into clean and convenient hydrogen through photocatalytic reactions is a key research direction in green energy technology. Suitable photocatalysts are essential for efficient and stable conversion. There are three main types of photocatalysts: metal-organic framework photocatalysts, nanomaterial photocatalysts, and semiconductor photocatalysts. Semiconductor photocatalysts are a representative example of photocatalytic hydrogen production technology, with attempts to enhance the photocatalytic activity of semiconductor materials through methods such as composite noble metal particles, composite heterogeneous semiconductors, anion / cation doping, and surface modification. Semiconductor photocatalysts can effectively improve the efficiency of photogenerated electron-hole separation, but their low visible light utilization and poor stability limit their large-scale application in practical production. The development of efficient, low-cost, stable, and environmentally friendly semiconductor photocatalyst materials is urgently needed. Molybdenum-based materials, as semiconductor catalysts, are widely used in photocatalysis due to their wide availability, diverse morphologies, simple preparation, and excellent photocatalytic performance, and have become a hot topic of research. For example, molybdenum-based metal oxides and molybdenum-based polyoxometalates semiconductors. However, due to the wide band gap energy of most molybdenum-based materials, it is easy to photo-induce electrons / holes (e - / h + ) are easy to recombine, resulting in low conversion efficiency of incident light, and the disadvantage of molybdenum-based polyacids being easily soluble in water means that a single material often cannot meet the needs of practical applications. Therefore, improving the photocatalytic performance of molybdenum-based materials has become a research problem that needs to be urgently solved.

[0004] Introducing external fields into photocatalytic reaction systems is a common method for improving photocatalytic performance because it does not alter the composition or geometry of the photocatalyst and avoids complex preparation processes. To date, multiple external fields have been successfully applied to some photocatalytic systems. These include microwaves, mechanical stress, temperature gradients, electric fields, magnetic fields, and coupled fields. Electric fields, mechanical stress, and temperature fluctuations have been reported to be driving forces for the separation of photoinduced electrons and holes. However, charge separation under these fields typically requires a continuous energy supply, which often results in complex photocatalytic devices and higher costs. Using magnetic fields generated by permanent magnets, on the other hand, is a relatively simple, convenient, contactless, and environmentally friendly method for improving photocatalytic performance. Furthermore, magnetic fields can not only induce the Lorentz force to separate photoexcited electrons and holes but can also modulate the electronic configuration of the photocatalyst's ground state, namely, the electron spin orientation. Most strategies primarily focus on the charge properties of electrons. It is well known that electrons possess two intrinsic properties: charge and spin. Spin directions are categorized as up and down, with opposite spin directions generating opposite magnetic fields. The electron spin state in a catalyst determines its ground-state electronic configuration, which significantly regulates light absorption, the recombination and separation of photogenerated carriers, and the reaction barrier of the intermediate medium. As an inherent property of electrons, regulating electron spin polarization is an important factor affecting the performance of photocatalysts. However, most semiconductor photocatalysts do not possess electron spin polarization, and for most photocatalysts, magnetic field regulation of spin polarization is unattainable. Semiconductors are combined with magnetic materials to form magnetically responsive composite materials to achieve electron spin polarization.

[0005] MoO3 is an excellent n-type semiconductor material that has attracted much attention due to its advanced optoelectronic properties, large specific surface area, and high active sites. It has been applied in various fields, including sensors, environmental remediation, batteries, supercapacitors, transistors, and catalysts. However, MoO3's limited visible light absorption capacity has seriously hindered its practical application. Fortunately, coupling MoO3 with other semiconductors as heterojunction photocatalysts can enhance the spatial separation of electrons and photogenerated holes through a synergistic effect and enhance its visible light absorption. Compared with traditional type I and type II heterojunctions, the Z-type scheme can effectively separate electrons and holes in different semiconductors while maintaining a high hole oxidation potential and a high electron reduction potential.

[0006] Perovskite-type ABO3 ferroelectric semiconductors, represented by BiFeO3, have attracted increasing attention in recent years in photocatalysis, not only due to their strong photon absorption but also due to their tunable spontaneous polarization, which influences charge behavior, compared to traditional metal compound photocatalysts. However, the photocatalytic performance of pure BiFeO3 is poor due to its high recombination rate of photogenerated electron-hole pairs and the easy formation of impurity phases during the preparation process, which limits its practical application in photocatalysis. Currently, efforts to modify BiFeO3 focus primarily on preparation methods, such as precious metal deposition and heterojunction construction.

[0007] In summary, molybdenum-based materials and the photocatalyst materials that have been studied have outstanding performance in the field of photocatalysis, but they themselves have certain shortcomings. Summary of the Invention

[0008] This invention overcomes the wide bandgap of MoO3 and creates a magnetic molybdenum-based material. MoO3 is loaded onto magnetic BiFeO3, resulting in a spin-polarized Z-type heterojunction BiFeO3 / MoO3. This approach aims to fully utilize light energy, maximize its utilization rate, and improve the separation efficiency of photogenerated carriers, thereby enhancing photocatalytic activity.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0010] In a first aspect of the present invention, a BiFeO3 / MoO3 composite material is provided, wherein BiFeO3 / MoO3 is obtained by loading MoO3 on the surface of BiFeO3, and the mass ratio of MoO3 to BiFeO3 is (1-5):20.

[0011] Furthermore, the BiFeO3 / MoO3 composite material is Z-type.

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned BiFeO3 / MoO3 composite material, comprising the following steps:

[0013] S1.Mo 154 Preparation: Na2S2O4 was added to Na2MoO4·2H2O aqueous solution to obtain a first solution. HCl solution was added to the first solution under stirring, and the mixture was fully mixed. The mixture was sealed and allowed to stand for 5 days. The blue crystal precipitate was removed by filtration, washed, and dried at 60℃ for 6 hours to obtain Mo 154 ;

[0014] Preparation of S2.MoO3: Mo 154 After grinding, calcination at 400℃ for 2h gave MoO3;

[0015] Preparation of BiFeO3: Citric acid was added to an ethylene glycol aqueous solution and mixed thoroughly. Bi(NO3)·5H2O and Fe(NO3)3·9H2O were then added. Stirring was continued for 120 minutes. The mixture was then heated in an 80°C water bath with stirring to form a sol. After drying, the mixture was thoroughly ground and calcined at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3.

[0016] S4. Preparation of BiFeO3 / MoO3: BiFeO3 and MoO3 were dispersed in water, ultrasonically treated for 1 h, dried, fully ground, and reacted at 200°C for 2 h to obtain BiFeO3 / MoO3.

[0017] In a preferred embodiment, in step S1, the first solution contains 0.2 g Na2S2O4 and 3 g Na2MoO4·2H2O per 10 mL of water; the concentration of the HCl solution is 1.25 mol / L, and the volume ratio of the first solution to the HCl solution is 1:3.

[0018] Under the preferred embodiment, in the ethylene glycol aqueous solution, the volume ratio of ethylene glycol and water is 1:2; the mass volume ratio (g / L) of citric acid and ethylene glycol aqueous solution is 1:60; the molar ratio of Bi(NO3)·5H2O and Fe(NO3)3·9H2O is 15:16; and the molar volume ratio (mol / mL) of Fe(NO3)3·9H2O and ethylene glycol aqueous solution is 1:15.

[0019] In the preferred embodiment, in step S4, the mass ratio of MoO3 to BiFeO3 is (1-5):20.

[0020] The third aspect of the present invention provides an application of a BiFeO3 / MoO3 composite material prepared by any of the above methods in photocatalytic hydrogen production.

[0021] In the preferred embodiment, under the action of a magnetic field with a magnetic field strength of 300 Gs and a light intensity of 15,000 to 18,000 lx, a hydrogen production reaction is carried out using a BiFeO3 / MoO3 composite material as a catalyst.

[0022] In the preferred embodiment, 100 mg / mL BiFeO3 / MoO3 composite material is added to an aqueous solution containing 0.25M Na2S and 0.35M Na2SO3. After degassing for 0.5 h, a magnetic field with a field strength of 300 Gs is applied, and a dehydrogenation reaction is carried out under constant temperature conditions of a light intensity of 15000-18000 lx and a temperature of 25-40°C.

[0023] The beneficial effects of the present invention are:

[0024] The BiFeO3 / MoO3 composite material prepared by loading MoO3 on the surface of BiFeO3 is used as a catalyst to participate in the photocatalytic hydrogen production reaction under the condition of applying a magnetic field, and the hydrogen production performance is as high as 306.45μmol·g -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the calcination method for synthesizing MoO3;

[0026] Figure 2 This is a flow chart of the sol-gel method for synthesizing BiFeO3 of the present invention;

[0027] Figure 3 is the XRD pattern of BiFeO3 synthesized at different calcination temperatures;

[0028] Figure 4 (a) FT-IR and (b) XRD test results of MoO3, BiFeO3 and BiFeO3 / MoO3;

[0029] Figure 5 These are the SEM images of (a): MoO3, (b): BiFeO3 and (c): BiFeO3 / MoO3-15%, (d): EDS image of BiFeO3 / MoO3-15% and its (e)-(h): Bi, Fe, Mo, O element mappings;

[0030] Figure 6 (a) The XPS overall spectrum of BiFeO3 / MoO3-15% and (b)-(e) the high-resolution XPS spectra of Bi 4f, Fe 2p, Mo 3d and O1s peaks;

[0031] Figure 7 is the ultraviolet absorption graph of MoO3, BiFeO3 and BiFeO3 / MoO3 obtained in Examples 1 to 5;

[0032] Figure 8 (a) Photoluminescence spectra of MoO3 and BiFeO3 / MoO3 obtained in Examples 1 to 5 and (b) photoluminescence spectra after applying a magnetic field;

[0033] Figure 9 The photocurrent and impedance diagrams of MoO3, BiFeO3 and BiFeO3 / MoO3 under (a)-(b): no magnetic field conditions and (c)-(d): applied magnetic field conditions;

[0034] Figure 10 Graphs showing the hydrogen production of the BiFeO3 / MoO3 composite materials obtained in Examples 1 to 5 under (a) no magnetic field conditions and (b) an applied magnetic field conditions;

[0035] Figure 11 (a)-(b): UV band gap diagrams and (c)-(d): Mott-Schottky diagrams of MoO3 and BiFeO3, and (e)-(f): EPR test results of BiFeO3 / MoO3-15%;

[0036] Figure 12 This is a diagram of the photocatalytic mechanism of the BiFeO3 / MoO3 composite material of the present invention. DETAILED DESCRIPTION

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0038] In the present invention, unless otherwise specified, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. The experimental methods in the examples are conventional methods unless otherwise specified. Where specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, for which the manufacturer is not specified, are all commercially available conventional products.

[0039] Example 1: BiFeO3 / MoO3-5%

[0040] A method for preparing a BiFeO3 / MoO3 composite material comprises the following steps:

[0041] S1.Mo 154 Preparation: 0.2g Na2S2O4 was added to a 3.0g Na2MoO4·2H2O aqueous solution in 10mL of water. Subsequently, 30mL of 1.25mol / L HCl solution was added while stirring continuously. The mixed solution was stirred in a conical flask for 10min. After that, the solution was stored in a closed conical flask and allowed to stand for 5d. Finally, the precipitated blue crystals were removed by filtration, washed with a small amount of cold water, and dried at room temperature for 6h to obtain Mo 154 ,spare.

[0042] Preparation of S2.MoO3: Prepared Mo 154 Grind in a mortar and then calcine in a muffle furnace at 400℃ for 2h to obtain MoO3. Figure 1 shown.

[0043] Preparation of S3.BiFeO3: Add 40mL of ethylene glycol and 80mL of water into a conical flask and stir for 20min. Add 2g of citric acid as a complexing agent and continue stirring for 20min. Then add 7.5mmol Bi(NO3)·5H2O and 8mmol Fe(NO3)3·9H2O and continue stirring for 120min. Subsequently, stir in an 80℃ water bath for 100min to obtain a sol, which is then placed in a drying oven at 100℃ and dried for 3 hours to obtain a dry gel. Finally, the obtained dry gel is fully ground and placed in a muffle furnace. It is first calcined at 300℃ for 4h and then calcined at 600℃ for 2h to obtain BiFeO3. The preparation process is as follows: Figure 2 shown.

[0044] S4. Preparation of BiFeO3 / MoO3 Composite Material: A BiFeO3 / MoO3 composite material was prepared by ultrasonic calcination. Weigh 0.6 g of the prepared BiFeO3, add 0.03 g of MoO3, and add 20 mL of H2O. Ultrasonicate for 1 hour, dry in a drying oven at 60°C for 6 hours, grind thoroughly, and react in a muffle furnace at 200°C for 2 hours to obtain the BiFeO3 / MoO3 composite material, labeled BiFeO3 / MoO3-5%.

[0045] Example 2: BiFeO3 / MoO3-10%

[0046] A method for preparing a BiFeO3 / MoO3 composite material comprises the following steps:

[0047] S1.Mo 154 Preparation: 0.2g Na2S2O4 was added to a 3.0g Na2MoO4·2H2O aqueous solution in 10mL of water. Subsequently, 30mL of 1.25mol / L HCl solution was added while stirring continuously. The mixed solution was stirred in a conical flask for 10min. After that, the solution was stored in a sealed conical flask and allowed to stand for 5 days. Finally, the precipitated blue crystals were removed by filtration, washed with a small amount of cold water, and dried at room temperature to obtain Mo. 154 ,spare.

[0048] Preparation of S2.MoO3: Prepared Mo 154 The product was ground in a mortar and then calcined in a muffle furnace at 400 °C for 2 h to obtain MoO3.

[0049] Preparation of S3. BiFeO3: 40 mL of ethylene glycol and 80 mL of water were added to a conical flask and stirred for 20 minutes. 2 g of citric acid was added as a complexing agent and stirring continued for 20 minutes. Subsequently, 7.5 mmol of Bi(NO3)·5H2O and 8 mmol of Fe(NO3)3·9H2O were added and stirring continued for 120 minutes. Subsequently, the mixture was stirred in an 80°C water bath for 100 minutes to obtain a sol, which was then dried in a drying oven at 100°C to obtain a xerogel. Finally, the xerogel was thoroughly ground and calcined in a muffle furnace at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3.

[0050] S4. Preparation of BiFeO3 / MoO3 Composite Material: A BiFeO3 / MoO3 composite material was prepared by ultrasonic calcination. Weigh 0.6 g of the prepared BiFeO3, add 0.06 g of MoO3, and add 20 mL of H2O. Ultrasonicate for 1 hour, dry in a drying oven, thoroughly grind, and react in a muffle furnace at 200°C for 2 hours to obtain the BiFeO3 / MoO3 composite material, labeled BiFeO3 / MoO3-10%.

[0051] Example 3: BiFeO3 / MoO3-15%

[0052] A method for preparing a BiFeO3 / MoO3 composite material comprises the following steps:

[0053] S1.Mo 154 Preparation: 0.2g Na2S2O4 was added to a 3.0g Na2MoO4·2H2O aqueous solution in 10mL of water. Subsequently, 30mL of 1.25mol / L HCl solution was added while stirring continuously. The mixed solution was stirred in a conical flask for 10min. After that, the solution was stored in a sealed conical flask and allowed to stand for 5 days. Finally, the precipitated blue crystals were removed by filtration, washed with a small amount of cold water, and dried at room temperature to obtain Mo. 154 ,spare.

[0054] Preparation of S2.MoO3: Prepared Mo 154 The product was ground in a mortar and then calcined in a muffle furnace at 400 °C for 2 h to obtain MoO3.

[0055] Preparation of S3. BiFeO3: 40 mL of ethylene glycol and 80 mL of water were added to a conical flask and stirred for 20 minutes. 2 g of citric acid was added as a complexing agent and stirring continued for 20 minutes. Subsequently, 7.5 mmol of Bi(NO3)·5H2O and 8 mmol of Fe(NO3)3·9H2O were added and stirring continued for 120 minutes. Subsequently, the mixture was stirred in an 80°C water bath for 100 minutes to obtain a sol, which was then dried in a drying oven at 100°C to obtain a xerogel. Finally, the xerogel was thoroughly ground and calcined in a muffle furnace at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3.

[0056] S4. Preparation of BiFeO3 / MoO3 Composite Material: A BiFeO3 / MoO3 composite material was prepared by ultrasonic calcination. Weigh 0.6 g of the prepared BiFeO3, add 0.09 g of MoO3, and add 20 mL of H2O. Ultrasonicate for 1 hour, dry in a drying oven, thoroughly grind, and react in a muffle furnace at 200°C for 2 hours to obtain the BiFeO3 / MoO3 composite material, labeled BiFeO3 / MoO3-15%.

[0057] Example 4: BiFeO3 / MoO3-20%

[0058] A method for preparing a BiFeO3 / MoO3 composite material comprises the following steps:

[0059] S1.Mo 154 Preparation: 0.2g Na2S2O4 was added to a 3.0g Na2MoO4·2H2O aqueous solution in 10mL of water. Subsequently, 30mL of 1.25mol / L HCl solution was added while stirring continuously. The mixed solution was stirred in a conical flask for 10min. After that, the solution was stored in a sealed conical flask and allowed to stand for 5 days. Finally, the precipitated blue crystals were removed by filtration, washed with a small amount of cold water, and dried at room temperature to obtain Mo. 154 ,spare.

[0060] Preparation of S2.MoO3: Prepared Mo 154 The product was ground in a mortar and then calcined in a muffle furnace at 400 °C for 2 h to obtain MoO3.

[0061] Preparation of S3. BiFeO3: 40 mL of ethylene glycol and 80 mL of water were added to a conical flask and stirred for 20 minutes. 2 g of citric acid was added as a complexing agent and stirring continued for 20 minutes. Subsequently, 7.5 mmol of Bi(NO3)·5H2O and 8 mmol of Fe(NO3)3·9H2O were added and stirring continued for 120 minutes. Subsequently, the mixture was stirred in an 80°C water bath for 100 minutes to obtain a sol, which was then dried in a drying oven at 100°C to obtain a xerogel. Finally, the xerogel was thoroughly ground and calcined in a muffle furnace at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3.

[0062] S4. Preparation of BiFeO3 / MoO3 Composite Material: A BiFeO3 / MoO3 composite material was prepared by ultrasonic calcination. Weigh 0.6 g of the prepared BiFeO3, add 0.12 g of MoO3, and add 20 mL of H2O. Ultrasonicate for 1 hour, dry in a desiccator, thoroughly grind, and react in a muffle furnace at 200°C for 2 hours to obtain the BiFeO3 / MoO3 composite material, labeled BiFeO3 / MoO3-20%.

[0063] Example 5: BiFeO3 / MoO3-25%

[0064] A method for preparing a BiFeO3 / MoO3 composite material comprises the following steps:

[0065] S1.Mo 154 Preparation: 0.2g Na2S2O4 was added to a 3.0g Na2MoO4·2H2O aqueous solution in 10mL of water. Subsequently, 30mL of 1.25mol / L HCl solution was added while stirring continuously. The mixed solution was stirred in a conical flask for 10min. After that, the solution was stored in a sealed conical flask and allowed to stand for 5 days. Finally, the precipitated blue crystals were removed by filtration, washed with a small amount of cold water, and dried at room temperature to obtain Mo. 154 ,spare.

[0066] Preparation of S2.MoO3: Prepared Mo 154 The product was ground in a mortar and then calcined in a muffle furnace at 400 °C for 2 h to obtain MoO3.

[0067] Preparation of S3. BiFeO3: 40 mL of ethylene glycol and 80 mL of water were added to a conical flask and stirred for 20 minutes. 2 g of citric acid was added as a complexing agent and stirring continued for 20 minutes. Subsequently, 7.5 mmol of Bi(NO3)·5H2O and 8 mmol of Fe(NO3)3·9H2O were added and stirring continued for 120 minutes. Subsequently, the mixture was stirred in an 80°C water bath for 100 minutes to obtain a sol, which was then dried in a drying oven at 100°C to obtain a xerogel. Finally, the xerogel was thoroughly ground and calcined in a muffle furnace at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3.

[0068] S4. Preparation of BiFeO3 / MoO3 Composite Material: A BiFeO3 / MoO3 composite material was prepared by ultrasonic calcination. Weigh 0.6 g of the prepared BiFeO3, add 0.15 g of MoO3, and add 20 mL of H2O. Ultrasonicate for 1 hour, dry in a drying oven, thoroughly grind, and react in a muffle furnace at 200°C for 2 hours to obtain the BiFeO3 / MoO3 composite material, labeled BiFeO3 / MoO3-25%.

[0069] Experimental Example 1: FT-IR and XRD tests of BiFeO3 / MoO3

[0070] Impurity phases are easily generated during the BiFeO3 synthesis process. Different calcination temperatures were used to remove these impurities and synthesize pure BiFeO3. Two control experiments were conducted for the BiFeO3 preparation process. The preparation process in step S3 of Example 1 was followed, with the difference being that control group 1 was calcined at 550°C for 2 hours, while control group 2 was calcined at 400°C for 1 hour and then at 650°C for 2 hours. Figure 3 The XRD patterns of BiFeO3 synthesized at different calcination temperatures show that the impurity phase Bi 25 FeO 40 Coexist with BiFeO3. The characteristic diffraction peaks at 2θ=21.365°, 24.718°, 27.691°, 30.394°, 32.896°, 37.454°, 41.580°, 43.521°, 54.007°, and 55.613° correspond to the impurity phase Bi 25 FeO 40The (211), (220), (310), (222), (321), (330), (332), (422), (600), and (611) crystal planes (JCPDF#78-1543). Attempts were made to remove the impurity phases by increasing the calcination temperature and time in steps. Ultimately, pure BiFeO3 was successfully synthesized by calcining at 300°C for 4 hours and then at 600°C for 2 hours.

[0071] The functional groups and structures of MoO3 and BiFeO3 / MoO3 were analyzed by Fourier transform infrared spectroscopy. Figure 4 As shown in a, at 1629cm -1 and 3443cm -1 The sharp and broad absorption at 880 cm is the bending vibration and OH stretching vibration of adsorbed water. -1 The vibration peak of 992 cm-1 is attributed to the bending vibration of the bidentate oxygen atom (Mo-O-Mo). -1 and 568cm -1 The characteristic vibration peaks of MoO3 correspond to the stretching bonds of Mo=O. In addition, compared with MoO3, the functional groups of all composite samples MoO3 / BiFeO3 have not changed.

[0072] The chemical composition and crystal structure of the samples were analyzed by X-ray diffractometer (XRD). Figure 4 As shown in (b), the characteristic peaks at 2θ = 22.417°, 31.753°, 32.068°, 39.480°, 45.754°, 51.312°, 51.737°, 56.366°, 56.965°, 57.163°, and 67.067° correspond to the (012), (104), (110), (202), (024), (116), (122), (018), (214), (300), and (220) crystal planes of BiFeO3, respectively. The obvious diffraction peaks of the pure BiFeO3 curve are consistent with the standard card of rhombic R3c-type BiFeO3 (JCPDF#86-1518), and there are no other impurity phases. The obvious diffraction peaks of the synthesized pure MoO3 are consistent with the standard card (JCPDF#76-1003). Furthermore, the XRD patterns of the BiFeO3 / MoO3-X samples obtained in Examples 1 to 5 are similar to those of pure BiFeO3 and MoO3, confirming that the crystal structure remains unchanged after the BiFeO3 and MoO3 are combined. As the MoO3 percentage increases, BiFeO3 / MoO3-15% exhibits distinct MoO3 diffraction peaks (2θ = 23.328°, 27.324°). The XRD patterns further demonstrate the successful preparation of the composite samples, and the XRD analysis results are consistent with the Fourier transform infrared spectroscopy results.

[0073] Experimental Example 2: SEM test of BiFeO3 / MoO3

[0074] The morphology and elemental composition of BiFeO3 and MoO3 were observed by SEM, EDS and elemental mapping. Figure 5 As shown in a, MoO3 consists of a prismatic rod-like structure. Figure 5 b is the SEM image of BiFeO3, from which it can be observed that BiFeO3 is composed of irregular nanoparticles with a highly crystalline and smooth surface. Figure 5 c is the SEM image of the BiFeO3 / MoO3 composite sample, from which it can be clearly seen that irregular BiFeO3 nanoparticles are attached to the rod-shaped MoO3. Figure 5 As shown in d~5h, it can be seen that Bi, Fe, Mo, and O elements are uniformly distributed in the composite sample, proving the successful preparation of BiFeO3 / MoO3 composite sample.

[0075] Experimental Example 3: XPS Test of BiFeO3 / MoO3

[0076] The composition and chemical state of the prepared BiFeO3 / MoO3 were further analyzed by X-ray photoelectron spectroscopy (XPS). Figure 6 As shown in a, the XPS survey spectrum shows that all peaks are composed of Bi, Fe, Mo, and O, and there are no other impurity peaks. Figure 6 b~6e are high-resolution scans of Bi 4f, Fe 2p, Mo 3d and O1s, respectively. The high-resolution XPS spectrum of Bi 4f shows two characteristic peaks at approximately 158.73eV and 164.00eV, respectively, which belong to Bi 3+ Bi 4f 7 / 2 and Bi 4f 5 / 2 orbital. The Fe 2p spectrum contains two peaks centered at 709.48 and 723.01 eV, which belong to the Fe 2p 3 / 2 and Fe 2p 1 / 2 In addition, the satellite peak (719.12 eV) is larger than the Fe 2p 3 / 2 The binding energy of Fe is about 9 eV higher, indicating that the oxidation state of Fe ions is Fe 3+ The Mo 3d spectrum shows two sets of heavy states, one of which is Mo 6+ , the binding energies are 232.25 and 235.39 eV corresponding to Mo 6+ 3d 5 / 2 and Mo 6+ 3d 3 / 2 ; The other group is Mo 5+ , corresponding to Mo 5+ 3d 5 / 2and Mo 5+ 3d 3 / 2 The O 1s spectrum peak has an asymmetric nature and is therefore decomposed into two peaks, namely O L : lattice oxygen and O D : Defective oxygen. Lattice oxygen O L The corresponding peak (~529.7 eV) can be attributed to the O in the metal-oxygen bond. 2- .O V The peak (~531.1eV) is caused by the O near the oxygen-deficient site. 2- ions. The binding energies are 529.53 and 531.33 eV, respectively, corresponding to O V and O D The above results confirm the coexistence of MoO3 and BiFeO3 without any impurities.

[0077] Experimental Example 4: UV-Vis Test of BiFeO3 / MoO3

[0078] The light absorption capacity of the constructed catalyst was estimated by UV-Vis DRS. Figure 7 As shown, the MoO3 sample has strong absorption in the wavelength range below 450nm, but weak absorption in the visible light range. BiFeO3 shows a broader light absorption capacity in the visible light range. Compared with single-component MoO3 and BiFeO3, the combination of MoO3 and BiFeO3 broadens and enhances its light absorption capacity in the visible light region.

[0079] Experimental Example 5: Characterization of the catalytic performance of BiFeO3 / MoO3 before and after magnetization

[0080] The recombination ability of photogenerated electrons and holes was determined using photoluminescence spectroscopy (PL). The intensity of PL is related to the separation rate of photogenerated electrons and holes. The lower the PL intensity, the higher the carrier separation rate. Figure 8 As shown in a, all samples have similar fluorescence peaks around 621nm. In contrast, MoO3 has a stronger fluorescence peak intensity, that is, e - and h + The recombination rate of charge carriers is high. Compared with MoO3, the BiFeO3 / MoO3 composites all exhibit weaker fluorescence intensity, which is due to the heterogeneous structure formed between MoO3 and BiFeO3, which hinders the recombination of charge carriers. Among them, the PL peak intensity of BiFeO3 / MoO3-15% is the lowest, indicating the lowest carrier recombination rate and potentially higher photocatalytic activity.

[0081] In order to investigate the separation efficiency of carriers under magnetic field conditions, the MoO3 and BiFeO3 / MoO3 composite powder samples prepared in Examples 1 to 5 were placed in a permanent magnet environment and magnetized for 12 hours, and then PL tests were performed under magnetic field conditions. The experimental results are shown in Figure 2. Figure 8 As shown in Figure b, due to the magnetic properties of BiFeO3, spin polarization can occur under magnetic field conditions. After applying a magnetic field, BiFeO3 / MoO3 undergoes spin polarization. Spin-polarized electrons can reduce the recombination of photoinduced electrons and holes during the charge transfer process. When a spin-down electron is excited (to CB), the remaining hole (in VB) also exhibits the same spin-down characteristic and maintains this spin direction unchanged. During the electron transfer process, due to spin-orbit coupling, hyperfine interactions, etc., the electron will lose its original spin direction (becoming spin-up). Therefore, in a spin-polarized environment, due to the lack of spin-up holes, recombination will be suppressed. Therefore, it can be observed that after applying a magnetic field, the fluorescence peak intensity of all composite materials decreases, among which the peak intensity of BiFeO3 / MoO3-15% is the lowest. Figure 8 The illustration in b shows the comparison of the fluorescence peak intensity of BiFeO3 / MoO3-15% with and without magnetic field conditions.

[0082] Electrochemical experiments provided a deeper understanding of the charge transfer efficiency of the BiFeO3 / MoO3 composite. First, transient photocurrent measurements were performed on the samples. The photocurrent response can be used to determine the separation and transfer kinetics of photogenerated carriers during photocatalysis. Figure 9 Figure a shows the transient photocurrent responses of MoO3, BiFeO3, and the BiFeO3 / MoO3 composite under visible light irradiation. It is clearly observed that all catalysts produce a photocurrent response. A higher photocurrent response indicates faster photogenerated carrier separation and transfer. Clearly, BiFeO3 / MoO3-15% exhibits the highest photocurrent response, reflecting the enhanced separation and transfer efficiency of photogenerated carriers achieved by the BiFeO3 / MoO3 heterojunction.

[0083] Electrochemical impedance spectroscopy (EIS) is another effective method to test the electron transfer efficiency. Figure 9As shown in b. It is generally believed that the Nyquist diagram is divided into two parts: the high-frequency region and the low-frequency region. The high-frequency region usually appears as a semicircle, and the low-frequency region appears as a linear change curve. The arc radius of the high-frequency region of the Nyquist diagram is positively correlated with the charge transfer impedance (Rct) of the sample. The smaller the arc radius, the smaller the charge transfer impedance and the faster the charge carrier separation efficiency. The low-frequency region of the Nyquist diagram is positively correlated with the slope of the curve. The larger the slope, the faster the electron diffusion rate. It can be seen from the figure that BiFeO3 / MoO3-15% has the smallest radius, indicating that its interface charge transfer rate is fast and the photosensitive electron-hole pair separation efficiency is the highest. This is consistent with the results of photoluminescence spectroscopy and transient photocurrent analysis.

[0084] In order to study the effect of magnetic field on the carrier separation activity at the interface, the powder samples of MoO3, BiFeO3 and BiFeO3 / MoO3 composite materials prepared in Examples 1 to 5 were ground into electrodes and magnetized in a permanent magnet environment for 12 hours. Then, electrochemical tests were carried out under the action of magnetic field. Figure 9 As shown in Figures c-9d, the photocurrent intensity of all composite samples increased after applying a magnetic field compared to the absence of a magnetic field. The application of a magnetic field facilitates carrier separation and transfer. Similarly, the EIS analysis is consistent with the photocurrent analysis. The magnetic field enhances carrier transport. The BiFeO3 / MoO3-15% composite exhibits lower EIS values ​​and a significantly stronger photocurrent response.

[0085] Experimental Example 6: Photocatalytic Performance Test of BiFeO3 / MoO3 Composite Material

[0086] Photocatalytic water splitting experiments were conducted using a CEL-SPH2N / PAEM series photocatalytic activity evaluation system. Specifically, 100 mg of photocatalyst was added to 100 mL of an aqueous solution containing 0.25 M Na₂S and 0.35 M Na₂SO₃. Prior to irradiation with 15,000 to 18,000 lux of light, the system was degassed for half an hour, and the solution temperature was maintained constant by circulating cold water. The amount of hydrogen generated was measured by gas chromatography. Photocatalytic hydrogen production was also tested under an applied magnetic field of 300 gs.

[0087] The standard curve of hydrogen production performance was obtained by initial debugging and calibration of the testing instrument of Zhongjiao Jinyuan, and the hydrogen production of the BiFeO3 / MoO3 composite materials with different composite ratios obtained in Examples 1 to 5 was calculated based on the standard curve. Figure 10Figure a compares the hydrogen production performance of samples with different composite ratios. As can be seen from the figure, the composite photocatalysts of BiFeO3 / MoO3-25% and BiFeO3 / MoO3-5% have very low hydrogen production activity, which may be attributed to the loading of MoO3. Excessive loading covers the active sites on BiFeO3, resulting in weaker hydrogen production performance. However, in the same time, the composite photocatalyst of BiFeO3 / MoO3-15% produced 296μmol·g of hydrogen. -1 , which is 3.33 times that of BiFeO3 / MoO3-25%. The appropriate composite ratio and valence band position between BiFeO3 and MoO3 samples make a large number of photogenerated electrons concentrated in the conduction band of BiFeO3, which is conducive to the reaction with H + A reduction reaction occurs to generate H2.

[0088] Figure 10 b shows the hydrogen production performance of the BiFeO3 / MoO3-15% composite photocatalyst before and after applying a magnetic field. It can be seen that under the conditions of applying a magnetic field, the hydrogen production performance reached 306.45 μmol·g -1 Compared to the absence of a magnetic field, hydrogen production performance improved. The application of a magnetic field facilitated carrier separation due to the spin polarization of the composite catalyst. However, the hydrogen production performance did not improve significantly under high magnetic field strength. This may be due to the low strength of the applied magnetic field, resulting in only a slight improvement.

[0089] Based on the experimental results and analysis, the photocatalytic mechanism of BiFeO3 / MoO3 was revealed. 2 vs hv data chart (UV band gap see Figure 11 a~11b), the calculated band gap energy (Eg) of BiFeO3 and MoO3 are 2.15eV and 2.96eV respectively. Figure 11 c~11d) show the flat band potential (E fb vs SCE) are 1.52 eV and -0.22 eV respectively. In contrast, the flat band potential of the hydrogen electrode is given by formula (1):

[0090] E NHE =E SCE +0.2415V (1)

[0091] The flat band potentials (E fbvs NHE) are 1.76eV and 0.02eV, respectively. It can be observed that BiFeO3 exhibits a negative slope, indicating that BiFeO3 is a p-type semiconductor; in contrast, MoO3 exhibits a positive slope, indicating that it is an n-type semiconductor. It is generally believed that the Mott-Schottky band of a p-type semiconductor is associated with its valence band (VB), while conversely, the Mott-Schottky band of an n-type semiconductor is associated with its conduction band (CB). The valence band and conduction band are calculated using formula (2):

[0092] ECB=Efb vs NHE-0.2V (2)

[0093] The final calculation shows that the valence band of BiFeO3 is 1.56eV and the conduction band of MoO3 is -0.18eV. According to the formula Eg=E VB -E CB The calculated conduction band and valence band of BiFeO3 and MoO3 are -0.59eV and 2.78eV respectively. To further explore the photocatalytic mechanism, electron paramagnetic resonance (EPR) analysis was used to explore the superoxide radical (·O2 - ) and hydroxyl radicals (·OH), 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used as a scavenger. Figure 11 As shown in e to 11f, no free radical signal was observed in the BiFeO3 / MoO3-15% catalyst under dark conditions. However, after light irradiation, O2 - and ·OH signal peaks. This indicates that the catalyst has good photoresponse and produces active groups under light conditions, which is a necessary condition for photocatalysis.

[0094] Based on the above analysis, two possible interface charge separation and migration models are proposed: type II and type Z schemes. Both schemes can generate photogenerated electrons (e - ) and holes (h + If BiFeO3 is coupled with MoO3 to form a conventional type II heterojunction, the e on the BiFeO3 CB will - will migrate toward the CB direction of MoO3, and at the same time, h + will migrate to the VB of BiFeO3. However, the photogenerated electrons accumulated on the MoO3 CB (-0.18eV) are not enough to reduce O2 to ·O2 - (-0.33V vs NHE), the photogenerated holes accumulated on BiFeO3 VB (1.56eV) cannot react with OH - The reaction generates ·OH (2.40V vs NHE). This is inconsistent with the EPR test results. Therefore, we have successfully formed a Z-type heterojunction. Under light excitation, the e in the MoO3 CB -With the h in BiFeO3 VB + This is due to the e in the CB of MoO3 - With the h in BiFeO3 + There is a strong electrostatic attraction between them, which preserves the e in the more negative CB of BiFeO3. - , h is retained in the more positive VB of MoO3 + In this way, the holes in MoO3 (2.78eV) VB can oxidize OH- to produce ·OH, and the electrons in BiFeO3 (-0.59eV) CB can be captured by dissolved O2 to form ·O2 - The photocatalytic mechanism diagram is shown in the figure below. Figure 12 shown.

[0095] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A BiFeO3 / MoO3 composite material, characterized in that Bi The FeO3 / MoO3 composite material is obtained by loading MoO3 on the surface of BiFeO3, and the mass ratio of MoO3 to BiFeO3 is (1-5):

20.

2. The BiFeO3 / MoO3 composite material according to claim 1, wherein Bi The FeO3 / MoO3 composite material is Z-type.

3. A method for preparing the BiFeO3 / MoO3 composite material according to any one of claims 1 to 2, characterized in that: The steps include: S1.Mo 154 Preparation: Na2S2O4 was added to Na2MoO4·2H2O aqueous solution to obtain a first solution. HCl solution was added to the first solution under stirring, and the mixture was fully mixed. The mixture was sealed and allowed to stand for 5 days. The blue crystal precipitate was removed by filtration, washed, and dried at 60℃ for 6 hours to obtain Mo 154 ; Preparation of S2.MoO3: Mo 154 After grinding, calcination at 400℃ for 2h gave MoO3; Preparation of BiFeO3: Citric acid was added to an ethylene glycol aqueous solution and mixed thoroughly. Bi(NO3)·5H2O and Fe(NO3)3·9H2O were then added. Stirring was continued for 120 minutes. The mixture was then heated in an 80°C water bath with stirring to form a sol. After drying, the mixture was thoroughly ground and calcined at 300°C for 4 hours and then at 600°C for 2 hours to obtain BiFeO3. S4. Preparation of BiFeO3 / MoO3: BiFeO3 and MoO3 were dispersed in water, ultrasonically treated for 1 h, dried, fully ground, and reacted at 200°C for 2 h to obtain BiFeO3 / MoO3.

4. The method for preparing the BiFeO3 / MoO3 composite material according to claim 3, characterized in that: In step S1, the first solution contains 0.2 g of Na2S2O4 and 3 g of Na2MoO4·2H2O per 10 mL of water; the concentration of the HCl solution is 1.25 mol / L, and the volume ratio of the first solution to the HCl solution is 1:

3.

5. The method for preparing the BiFeO3 / MoO3 composite material according to claim 3, characterized in that: In the ethylene glycol aqueous solution, the volume ratio of ethylene glycol and water is 1:2; the mass volume ratio (g / L) of citric acid and ethylene glycol aqueous solution is 1:60; the molar ratio of Bi(NO3)·5H2O and Fe(NO3)3·9H2O is 15:16; the molar volume ratio of Fe(NO3)3·9H2O and ethylene glycol aqueous solution is (mol / mL) 1:

15.

6. The method for preparing the BiFeO3 / MoO3 composite material according to claim 3, characterized in that: In step S4, the mass ratio of MoO3 to BiFeO3 is (1-5):

20.

7. Use of the BiFeO3 / MoO3 composite material prepared by the method according to any one of claims 3 to 6 in photocatalytic hydrogen production.

8. The use according to claim 7, characterized in that Under the action of a magnetic field with a strength of 300 Gs and a light intensity of 15,000 to 18,000 lx, a hydrogen production reaction is carried out using a BiFeO3 / MoO3 composite material as a catalyst.

9. The use according to claim 8, characterized in that 100 mg / mL BiFeO3 / MoO3 composite material was added to an aqueous solution containing 0.25MNa2S and 0.35MNa2SO3. After degassing for 0.5 h, a magnetic field with a field strength of 300 Gs was applied, and hydrogen production reaction was carried out under constant temperature conditions of light intensity of 15,000-18,000 lx and temperature of 25-40°C.

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