Bismuth ferrite-graphite phase carbon nitride photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a bismuth ferrite-graphite phase carbon nitride photocatalyst and a preparation method and application thereof, and relates to the technical field of photocatalysis, the preparation method comprises the following steps: dissolving a bismuth source and an iron source in a solvent, mixing with a mineralizing agent, and carrying out a hydrothermal synthesis reaction to obtain bismuth ferrite; performing first roasting treatment on the nitrogen-containing organic matter precursor to obtain graphite-phase carbon nitride; and mixing bismuth ferrite and graphite phase carbon nitride, and carrying out grinding treatment and second roasting treatment to obtain the bismuth ferrite-graphite phase carbon nitride photocatalyst. According to the preparation method, bismuth ferrite and graphite-phase carbon nitride which are prepared respectively are compounded, a Z-type heterojunction can be constructed at an interface of the bismuth ferrite and the graphite-phase carbon nitride, an internal electric field is formed, so that photo-induced electrons and holes are efficiently separated, compounding of the photo-induced electrons and the holes is effectively inhibited, and finally the oxidation-reduction capacity of the material is remarkably enhanced; therefore, the photocatalyst shows excellent photocatalytic performance, high selectivity and good cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocatalysis, in particular to a BiFeO3-g-C3N4 photocatalyst and a preparation method and application thereof. BACKGROUND

[0002] With the rapid advancement of global industrialization, the environmental pollution and energy shortage problems caused by a large amount of carbon dioxide (CO2) generated by the combustion of fossil fuels have become a serious challenge. Carbon dioxide, as the main greenhouse gas, is a key factor leading to global climate change. Therefore, effectively capturing carbon dioxide in the atmosphere and converting it into high-value-added chemicals or fuels not only can alleviate the greenhouse effect, but also can realize the recycling of carbon resources, which is an important way to cope with the dual crisis of energy and environment. Under this background, photocatalytic technology emerged as the times require, which uses abundant and clean solar energy as the driving force to convert low-energy carbon dioxide molecules into high-energy hydrocarbons through semiconductor photocatalysts, showing great application potential and becoming the frontier and hotspot of current scientific research.

[0003] Among the many photocatalytic materials, titanium dioxide (TiO2) is one of the most widely and deeply studied photocatalysts due to its high catalytic activity, excellent chemical stability, non-toxicity, and low cost. However, as a wide-bandgap semiconductor material, the application of titanium dioxide is severely restricted by its intrinsic properties. In addition, in order to overcome the problem of low utilization rate of sunlight of traditional photocatalytic materials, researchers have developed a variety of new narrow-bandgap semiconductor photocatalysts. For example, bismuth-based photocatalytic materials are widely concerned in the field of photocatalytic reduction of carbon dioxide due to their unique electronic band structure, good chemical and thermal stability, and wide visible light response range. Among them, bismuth ferrite (BiFeO3) is a typical perovskite oxide with a narrow band gap of about 2.2 eV, which enables it to effectively absorb visible light. At the same time, its inherent ferroelectric properties are also conducive to promoting the separation of photo-generated charges.

[0004] Although the existing photocatalytic technology has made some progress, there are still many technical bottlenecks. For titanium dioxide, its wide band gap leads to its ability to only absorb the ultraviolet light part of the solar spectrum with high energy, which accounts for only about 5%, and has almost no response to the dominant visible light, which greatly limits its overall utilization efficiency of solar energy. More importantly, the photo-generated electrons and holes generated under light are extremely prone to rapid recombination in the material interior or surface before migrating to the catalyst surface to participate in the reaction, resulting in low quantum efficiency, which seriously affects its catalytic performance. In addition, the bismuth ferrite material prepared by the conventional method usually has a small specific surface area, which leads to a limited number of exposed catalytically active sites, further restricting its photocatalytic efficiency.

[0005] In summary, the current semiconductor materials for photocatalytic reduction of carbon dioxide, whether traditional wide-bandgap catalysts or emerging narrow-bandgap catalysts, generally face two major technical problems: one is the insufficient utilization rate of solar energy, and the other is the low separation efficiency of photo-generated charges. These two problems together lead to low overall photocatalytic quantum yield. At the same time, the small specific surface area of the catalyst itself also limits the number of reaction active sites. These defects together make the carbon dioxide conversion efficiency and product selectivity of the existing photocatalytic system far from meeting the requirements of practical applications, and a breakthrough in technology is urgently needed.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The purpose of the present application is to provide a bismuth ferrite-graphitic carbon nitride photocatalyst and its preparation method and use. The preparation method effectively separates the photo-generated charges by building a Z-type heterojunction between bismuth ferrite and graphitic carbon nitride, thereby significantly improving the photocatalytic performance, selectivity and stability of the composite material.

[0008] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: In a first aspect, the present application provides a preparation method of a bismuth ferrite-graphitic carbon nitride photocatalyst, comprising: dissolving a bismuth source and an iron source in a solvent and mixing with a mineralizer to perform a hydrothermal synthesis reaction to obtain bismuth ferrite; performing first calcination treatment on a nitrogen-containing organic precursor to obtain graphitic carbon nitride; mixing the bismuth ferrite and the graphitic carbon nitride, and then performing grinding treatment and second calcination treatment to obtain a bismuth ferrite-graphitic carbon nitride photocatalyst.

[0009] In an optional embodiment, the iron source comprises at least one of ferric nitrate, ferric chloride and ferric sulfate; and / or, the bismuth source comprises at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride and bismuth chloride; and / or, the solvent comprises at least one of deionized water, methanol, ethanol, ethylene glycol and dilute nitric acid solution; and / or, the mineralizer comprises at least one of sodium hydroxide and potassium hydroxide; and / or, the nitrogen-containing organic matter precursor comprises at least one of melamine, thiourea, urea and dicyanediamine.

[0010] In an optional embodiment, the molar ratio of the iron source to the bismuth source is (0.1-3):1.

[0011] In an optional embodiment, the concentration of the iron source is 0.01-0.5 mol / L; and / or, the concentration of the bismuth source is 0.01-0.5 mol / L; the concentration of the mineralizer is 2-8 mol / L.

[0012] In an optional embodiment, the reaction temperature of the hydrothermal synthesis reaction is 140-200°C; and / or, the reaction time of the hydrothermal synthesis reaction is 4-20 hours.

[0013] In an optional embodiment, the temperature of the first calcination treatment is 400-650°C; and / or, the time of the first calcination treatment is 0.5-4 hours; and / or, the heating rate of the first calcination treatment is 2.5-10°C / min.

[0014] In an optional embodiment, the mixing ratio of the bismuth ferrite to the graphite-phase carbon nitride is (0.1-10):1.

[0015] In an optional embodiment, the temperature of the second calcination treatment is 200-500°C; and / or, the time of the second calcination treatment is 0.5-8 hours; and / or, the heating rate of the second calcination treatment is 2.5-10°C / min.

[0016] In a second aspect, the present application provides a bismuth ferrite-graphite-phase carbon nitride photocatalyst, which is prepared by the preparation method of the bismuth ferrite-graphite-phase carbon nitride photocatalyst according to any one of the preceding embodiments.

[0017] In a third aspect, the present application provides a use of the BiFeO3-g-C3N4 photocatalyst as described in the foregoing embodiments for photocatalytic reduction of carbon dioxide.

[0018] The present application provides a BiFeO3-g-C3N4 photocatalyst, a preparation method and a use thereof. Compared with the prior art, the composite photocatalytic material with excellent performance can be obtained. Firstly, the three-step preparation process is simple and universal. The hydrothermal synthesis reaction in the first step helps to controllably prepare the BiFeO3 with a target morphology and a high degree of crystallinity. The first calcination treatment in the second step can convert the common nitrogen-containing organic precursor into the g-C3N4 with a target structure. The final step of compounding the two materials through mechanical grinding and the second calcination treatment can prepare the final product with uniform particles and stable morphology.

[0019] Secondly, the prepared BiFeO3 and g-C3N4 are compounded. Due to the matched energy band structures of the two, a Z-type heterojunction can be constructed at the interface thereof. The formation of the heterojunction can construct an electric field in the material, which plays a key role in efficiently separating the photo-generated electrons and holes and inhibiting the recombination of the photo-generated electrons and holes.

[0020] Finally, due to the effective separation of the photo-generated electrons and holes, the overall redox capacity of the composite material is significantly enhanced. This directly improves the performance and selectivity of the final product in the photocatalytic application, and enables the final product to maintain a high catalytic activity after multiple cycles and exhibit good stability. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 It is a flowchart of the preparation method of the BiFeO3-g-C3N4 photocatalyst in the embodiments of the present application; Figure 2 It is an XRD pattern of the precursors BiFeO3, g-C3N4 and BiFeO3 / g-C3N4 in the embodiment 2 of the present application; Figure 3 It is a SEM image of the BiFeO3 / g-C3N4 composite catalyst in the embodiment 2 of the present application; Figure 4 It is an EDS area scanning result of the BiFeO3 / g-C3N4 composite catalyst in the embodiment 2 of the present application; Figure 5 TEM image of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of the present application; Figure 6 CO production rate graph of the photocatalytic reduction of CO2 to CO by the catalyst in the examples and comparative examples of the present application; Figure 7 CO2 selectivity graph of the photocatalytic reduction of CO2 by the catalyst in the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0023] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not noted by the manufacturer are all conventional products that can be obtained by purchase.

[0024] REFERENCE Figure 1 In the examples of the present application, a preparation method of a bismuth ferrite-graphitic carbon nitride photocatalyst is provided, comprising: Step S1, dissolving a bismuth source and an iron source in a solvent and mixing with a mineralizer to carry out a hydrothermal synthesis reaction to obtain bismuth ferrite.

[0025] This step aims to synthesize the first component of the composite photocatalyst, bismuth ferrite. The process first dissolves the chemical raw materials containing bismuth and iron elements (i.e. bismuth source and iron source) in one or more liquids (i.e. solvent) to form a uniform solution. Subsequently, a "mineralizer" is added to the solution, which functions to regulate the reaction environment (such as pH value) and promote the subsequent crystallization process. Finally, the obtained mixture is placed in a sealed container (such as a hydrothermal reactor) and heated at a temperature higher than the normal pressure boiling point of the solvent and the corresponding autogenous pressure, which is the "hydrothermal synthesis reaction".

[0026] After the reaction is completed, the solid bismuth ferrite powder product can be obtained by cooling, washing and drying.

[0027] By using the hydrothermal synthesis method, the morphology of the product can be controlled by adjusting the reaction conditions. The material prepared by this method has the characteristics of high crystallinity.

[0028] For example, bismuth nitrate pentahydrate (as a bismuth source) and ferric nitrate nonahydrate (as an iron source) can be dissolved in deionized water (as a solvent) at a molar ratio of 1:1. Then, potassium hydroxide (KOH) solution (as a mineralizer) is added dropwise to the solution until the concentration of KOH in the mixed solution reaches a certain value (e.g., 4 mol / L). This mixed precipitation solution is transferred to a 50 mL hydrothermal synthesis reactor, and reacted in an oven at 200°C for 6 hours. After the reaction is completed, the obtained precipitate is cooled in the oven, and the obtained precipitate is bismuth ferrite.

[0029] Step S2, the nitrogen-containing organic precursor is subjected to first calcination treatment to obtain graphite phase carbon nitride.

[0030] This step aims to synthesize the second component of the composite photocatalyst, graphite phase carbon nitride. The process selects a nitrogen-rich organic compound (i.e., a nitrogen-containing organic precursor) and places it in a high-temperature device (such as a muffle furnace) for heating treatment, which is called "first calcination treatment" or thermal polycondensation. At high temperatures, the organic precursor decomposes and undergoes a polymerization reaction.

[0031] After calcination, the precursor is converted into a new, structurally stable non-metallic semiconductor material, graphite phase carbon nitride. By selecting different precursors and controlling the temperature and time of calcination, graphite phase carbon nitride with the target structure can be synthesized.

[0032] For example, melamine (as a nitrogen-containing organic precursor) is placed in a crucible and calcined at a temperature of 550°C for 4 hours, with a controlled heating rate of 10°C / min. After grinding the calcination product, graphite phase carbon nitride is obtained.

[0033] Step S3, after mixing the bismuth ferrite and the graphite phase carbon nitride, the mixture is subjected to grinding treatment and second calcination treatment to obtain a bismuth ferrite-graphite phase carbon nitride photocatalyst.

[0034] This step is the key step for the final formation of the composite material, which physically mixes the bismuth ferrite powder and the graphite phase carbon nitride powder prepared in the previous two steps in a certain proportion. In order to make the two powders closely contact, the mixture needs to be subjected to "grinding treatment". Subsequently, the ground mixture is subjected to high-temperature heating again, i.e., "second calcination treatment", to promote the combination of the two materials at the interface.

[0035] After this series of treatments, the final product is a bismuth ferrite-graphite phase carbon nitride photocatalyst composed of two components. In this composite material, graphite phase carbon nitride particles are dispersed and combined on the surface of bismuth ferrite.

[0036] The method is simple to operate, and the prepared composite particles are uniform and stable in morphology. The interface combination (heterojunction) of the two materials constructed by this step can effectively separate photo-generated electrons and holes, thereby significantly improving the photocatalytic performance and selectivity of the material.

[0037] For example, the bismuth ferrite obtained in the first step and the graphite phase carbon nitride obtained in the second step can be mixed uniformly at a ratio of 2:1. Then, the mixed product is calcined at 400°C for 4 hours, and the temperature rising speed is controlled at 5°C / min. Finally, after grinding the calcined product, the bismuth ferrite-graphite phase carbon nitride composite photocatalytic material is obtained.

[0038] In some embodiments, the iron source includes at least one of ferric nitrate, ferric chloride, and ferric sulfate.

[0039] In some embodiments, the bismuth source includes at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride, and bismuth chloride.

[0040] In some embodiments, the solvent includes at least one of deionized water, methanol, ethanol, ethylene glycol, and dilute nitric acid solution.

[0041] In some embodiments, the mineralizer includes at least one of sodium hydroxide and potassium hydroxide.

[0042] In some embodiments, the nitrogen-containing organic precursor includes at least one of melamine, thiourea, urea, and dicyanediamine.

[0043] In some embodiments, the molar ratio of the iron source to the bismuth source is (0.1-3):1. For example, it can be 0.1:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, etc.

[0044] In some embodiments, the concentration of the iron source is 0.01 mol / L-0.5 mol / L. For example, it can be 0.01 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.

[0045] In some embodiments, the concentration of the bismuth source is 0.01 mol / L-0.5 mol / L. For example, it can be 0.01 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.

[0046] In some embodiments, the concentration of the mineralizer is 2 mol / L to 8 mol / L. For example, it can be 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, and the like.

[0047] In some embodiments, the reaction temperature of the hydrothermal synthesis reaction is 140°C to 200°C. For example, it can be 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, and the like.

[0048] In some embodiments, the reaction time of the hydrothermal synthesis reaction is 4 hours to 20 hours. For example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, and the like.

[0049] In some embodiments, the temperature of the first calcination treatment is 400°C to 650°C. For example, it can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, and the like.

[0050] In some embodiments, the time of the first calcination treatment is 0.5 hours to 4 hours. For example, it can be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, and the like.

[0051] In some embodiments, the heating rate of the first calcination treatment is 2.5°C / min to 10°C / min. For example, it can be 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, and the like.

[0052] In some embodiments, the mixing ratio of the bismuth ferrite and the graphite phase carbon nitride is (0.1 to 10):1. For example, it can be 0.1:1, 0.2:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 2:1, 5:1, 8:1, 10:1, and the like.

[0053] In some embodiments, the temperature of the second calcination treatment is 200°C to 500°C. For example, it can be 200°C, 250°C, 300°C, 400°C, 450°C, 500°C, and the like.

[0054] In some embodiments, the time of the second calcination treatment is 0.5 hours to 8 hours. For example, it can be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, and the like.

[0055] In some embodiments, the second calcination process has a heating rate of 2.5℃ / min ~ 10℃ / min. For example, it can be 2.5℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, and the like.

[0056] In the embodiments of the present application, a BiFeO3-graphitic carbon nitride photocatalyst is provided, which is prepared by the preparation method of the BiFeO3-graphitic carbon nitride photocatalyst according to any one of the preceding embodiments.

[0057] The BiFeO3-graphitic carbon nitride photocatalyst provided in the embodiments can be a composite material, in which the graphitic carbon nitride particles are dispersed and distributed on the surface of the BiFeO3microspheres. This structure enables the two materials to form a Z-type heterojunction with a band match. The composite material has the characteristics of high crystallinity, uniform particles, regular morphology, and stability.

[0058] The core advantage of the catalyst lies in the formation of a Z-type heterojunction, which can effectively separate photo-generated electrons and holes, thereby enhancing the redox capacity of the catalyst. This enables the catalyst to exhibit a wide visible light absorption range, a high photo-generated charge interface migration rate, and excellent photocatalytic activity and selectivity. In applications, the catalyst exhibits good photocatalytic performance and stability, for example, when used to catalyze the reduction of CO2 under visible light, the effect does not substantially decrease after 5 cycles. In addition, since the BiFeO3component has a certain magnetic property, the catalyst can be recovered by magnetism, and the recovery method is simple and the catalyst loss is small.

[0059] In the embodiments of the present application, a use of the BiFeO3-graphitic carbon nitride photocatalyst according to the preceding embodiments for photocatalytic reduction of carbon dioxide is provided.

[0060] The use of the BiFeO3-graphitic carbon nitride photocatalyst described above is for photocatalytic reduction of carbon dioxide. In this application, the catalyst can be used to react under room temperature and visible light irradiation.

[0061] One of the remarkable effects is that carbon dioxide (CO2) is effectively converted into carbon monoxide (CO), and the amount of product generated increases with the extension of light time. The catalyst exhibits good performance and high stability in this application, and the effect of catalyzing the reduction of CO2 does not substantially decrease after 5 cycles under visible light. In addition, an important feature of this use is the recyclability of the catalyst; since the material has a magnetic property, it can be separated and recycled by a simple magnetic recovery method after the reaction, thereby reducing the loss of the catalyst.

[0062] The application will be further described below by means of specific examples, but it should be understood that these examples are only used for a more detailed description and should not be understood as limiting the application in any form.

[0063] Example 1 A photocatalyst is provided in this example.

[0064] Experimental method: (1) Bismuth nitrate pentahydrate and ferric nitrate nonahydrate were weighed according to a molar ratio of 1:1 and dissolved in 10 mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source could reach 0.24 mol / L. After stirring for 30 min to completely uniform, 10 mol / L of KOH solution was added dropwise to the above solution, and the concentration of KOH in the solution was controlled to reach 4 mol / L. After stirring to completely uniform, a uniformly dispersed mixed precipitate solution was obtained. The above precipitate solution was transferred to a 50 mL hydrothermal synthesis reaction kettle, and reacted in a 200℃ oven for 6 h. The furnace was cooled to room temperature, and the precipitate was washed with deionized water and ethanol alternately for 3 times, and then vacuum dried at 80℃ for 10 h to obtain the product BiFeO3; (2) Melamine was placed in a crucible and calcined at 550℃ for 4 h, with a heating rate of 10℃ / min. The calcined product was ground to obtain g-C3N4; (3) The above obtained BiFeO3 and g-C3N4 were mixed uniformly in a ratio of 2:1, and the mixed product was calcined at 400℃ for 4 h, with a heating rate of 5℃ / min. After grinding, the BiFeO3 / g-C3N4 composite photocatalytic material was obtained.

[0065] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in Example 1 is denoted as BFO / CN-1, and the CO yield is 43.83 μmol·g -1 ·h -1 .

[0066] Example 2 A photocatalyst is provided in this example.

[0067] Experimental method: (1) Bismuth nitrate pentahydrate and ferric nitrate nonahydrate are weighed according to a molar ratio of 1:1, and dissolved in 10 mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source can reach 0.12 mol / L, and after stirring for 30 min to completely uniform, 10 mol / L of KOH solution is added dropwise into the above solution, the concentration of KOH in the solution is controlled to reach 4 mol / L, and after stirring to completely uniform, a uniformly dispersed mixed precipitate solution is obtained, the above precipitate solution is transferred into a 50 mL hydrothermal synthesis reaction kettle, and reaction is carried out at 200℃ in an oven for 6 h, and the kettle is cooled to room temperature with the furnace, and the precipitate is washed with deionized water and ethanol alternately for 3 times, and vacuum drying is carried out at 80℃ for 10 h, and the product BiFeO3 is obtained; (2) Melamine is placed in a crucible and calcined at 550℃ for 4 h, and the heating rate is controlled to be 10℃ / min, and after the calcined product is ground, g-C3N4 is obtained; (3) The above obtained BiFeO3 and g-C3N4 are mixed uniformly at a ratio of 2:1, and the mixed product is calcined at 400℃ for 4 h, and the heating rate is controlled to be 5℃ / min, and after grinding, the BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0068] The difference between the embodiment and example 1 is that the concentration of the iron source and the bismuth source is changed to 0.12 mol / L.

[0069] Reference Figure 2 It is the XRD pattern of the precursor BiFeO3, g-C3N4 and BiFeO3 / g-C3N4 composite catalyst in example 2 of the application; Figure 3 It is the SEM image of the BiFeO3 / g-C3N4 composite catalyst in example 2 of the application; Figure 4 It is the EDS surface scanning result of the BiFeO3 / g-C3N4 composite catalyst in example 2 of the application; Figure 5 It is the TEM image of the BiFeO3 / g-C3N4 composite catalyst in example 2 of the application.

[0070] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in example 2 is recorded as BFO / CN-2, and the CO yield is 59.20 μmol·g -1 ·h -1 .

[0071] Example 3 The embodiment provides a photocatalyst.

[0072] Experimental method: (1) Weigh bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a molar ratio of 1:1 and dissolve them completely in 10 mL of deionized water so that the concentration of iron source and bismuth source can reach 0.06 mol / L. Stir for 30 min until completely homogeneous, then add 10 mol / L KOH solution dropwise to the above solution to control the KOH concentration in the solution to reach 4 mol / L. Stir until completely homogeneous to obtain a uniformly dispersed mixed precipitate solution. Transfer the above precipitate solution to a 50 mL hydrothermal synthesis reactor and react in an oven at 200 °C for 6 h. Cool the furnace to room temperature and wash the precipitate three times with deionized water and ethanol alternately. Then dry it under vacuum at 80 °C for 10 h to obtain the product BiFeO3. (2) Melamine was placed in a crucible and calcined at 550°C for 4 hours, with the heating rate controlled at 10°C / min. The calcined product was then ground to obtain g-C3N4. (3) The BiFeO3 and g-C3N4 obtained above are mixed evenly in a ratio of 2:1. The mixed product is calcined at 400℃ for 4h, and the heating rate is controlled at 5℃ / min. After grinding, BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0073] The only difference between this embodiment and Example 1 is that the concentrations of the iron source and bismuth source are changed to 0.06 mol / L.

[0074] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 3 is designated BFO / CN-3, with a CO yield of 34.09 μmol·g. -1 ·h -1 .

[0075] Example 4 This embodiment provides a photocatalyst.

[0076] Experimental methods: (1) Weigh bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a molar ratio of 1:1 and dissolve them completely in 10 mL of deionized water so that the concentration of iron source and bismuth source can reach 0.24 mol / L. Stir for 30 min until completely homogeneous, then add 10 mol / L KOH solution dropwise to the above solution to control the KOH concentration in the solution to reach 4 mol / L. Stir until completely homogeneous to obtain a uniformly dispersed mixed precipitate solution. Transfer the above precipitate solution to a 50 mL hydrothermal synthesis reactor and react in an oven at 200 °C for 6 h. Cool the furnace to room temperature and wash the precipitate three times with deionized water and ethanol alternately. Then dry it under vacuum at 80 °C for 10 h to obtain the product BiFeO3. (2) Place urea in a crucible and calcine at 400℃ for 4 hours, controlling the heating rate to be 10℃ / min. Grind the calcined product to obtain g-C3N4. (3) The BiFeO3 and g-C3N4 obtained above are mixed uniformly at a ratio of 2:1, the mixed product is calcined at 400℃ for 4h, the temperature rising speed is controlled at 5℃ / min, and after grinding, a BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0077] The difference between this embodiment and embodiment 1 is that the precursor used for preparing the graphite phase carbon nitride is urea.

[0078] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in embodiment 4 is recorded as BFO / CN-4, and the CO yield is 55.49μmol·g -1 ·h -1 .

[0079] Embodiment 5 A photocatalyst is provided in this embodiment.

[0080] Experimental method: (1) Bismuth nitrate pentahydrate and iron nitrate nonahydrate are weighed according to a molar ratio of 1:1, and dissolved in 10mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source can reach 0.24mol / L, after stirring for 30min to completely uniform, 10mol / L of KOH solution is added dropwise to the above solution, and the concentration of KOH in the solution is controlled to reach 4mol / L, and after stirring to completely uniform, a uniformly dispersed mixed precipitate solution is obtained, the above precipitate solution is transferred to a 50mL hydrothermal synthesis reaction kettle, and reacted in a 200℃ oven for 6h, and cooled to room temperature with the furnace, and the precipitate is washed with deionized water and ethanol alternately for 3 times, and vacuum dried at 80℃ for 10h, and the product BiFeO3 is obtained; (2) Urea is placed in a crucible and calcined at 400℃ for 4h, the temperature rising speed is controlled at 5℃ / min, and after grinding, g-C3N4 is obtained; (3) The BiFeO3 and g-C3N4 obtained above are mixed uniformly at a ratio of 2:1, the mixed product is calcined at 400℃ for 4h, the temperature rising speed is controlled at 5℃ / min, and after grinding, a BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0081] The difference between this embodiment and embodiment 1 is that the temperature rising speed for preparing the graphite phase carbon nitride is 5℃ / min.

[0082] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in embodiment 5 is recorded as BFO / CN-5, and the CO yield is 48.12μmol·g -1 ·h -1 .

[0083] Embodiment 6 A photocatalyst is provided in this embodiment.

[0084] Experimental method: (1) Bismuth nitrate pentahydrate and iron nitrate nonahydrate were weighed according to a molar ratio of 1:1, and dissolved in 10 mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source could reach 0.24 mol / L. After stirring for 30 min until completely uniform, 10 mol / L of KOH solution was added dropwise to the above solution, and the KOH concentration in the solution was controlled to reach 4 mol / L. After stirring until completely uniform, a uniformly dispersed mixed precipitate solution was obtained. The above precipitate solution was transferred to a 50 mL hydrothermal synthesis reaction kettle, and reacted in a 200℃ oven for 6 h. The furnace was cooled to room temperature, and the precipitate was washed with deionized water and ethanol alternately for 3 times, and then vacuum dried at 80℃ for 10 h to obtain the product BiFeO3; (2) Melamine was placed in a crucible and calcined at 500℃ for 4 h, with a heating rate of 5℃ / min. The calcined product was ground to obtain g-C3N4; (3) The above obtained BiFeO3 and g-C3N4 were mixed uniformly in a ratio of 2:1, and the mixed product was calcined at 500℃ for 4 h, with a heating rate of 5℃ / min. After grinding, the BiFeO3 / g-C3N4 composite photocatalytic material was obtained.

[0085] The difference between this embodiment and Example 1 is only that the calcination temperature for preparing the composite photocatalytic material is 500℃.

[0086] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in Example 6 is denoted as BFO / CN-6, and the CO yield is 31.76 μmol·g -1 ·h -1 .

[0087] Example 7 A photocatalyst is provided in this embodiment.

[0088] Experimental method: (1) Bismuth nitrate pentahydrate and iron nitrate nonahydrate were weighed according to a molar ratio of 1:1, and dissolved in 10 mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source could reach 0.24 mol / L. After stirring for 30 min until completely uniform, 10 mol / L of KOH solution was added dropwise to the above solution, and the KOH concentration in the solution was controlled to reach 4 mol / L. After stirring until completely uniform, a uniformly dispersed mixed precipitate solution was obtained. The above precipitate solution was transferred to a 50 mL hydrothermal synthesis reaction kettle, and reacted in a 200℃ oven for 6 h. The furnace was cooled to room temperature, and the precipitate was washed with deionized water and ethanol alternately for 3 times, and then vacuum dried at 80℃ for 10 h to obtain the product BiFeO3; (2) Melamine was placed in a crucible and calcined at 500°C for 4h, with a heating rate of 5°C / min. The calcined product was ground to obtain g-C3N4; (3) The BiFeO3 and g-C3N4 obtained above were mixed at a ratio of 1:1 and calcined at 500°C for 4h, with a heating rate of 5°C / min. After grinding, the BiFeO3 / g-C3N4 composite photocatalytic material was obtained.

[0089] The difference between this example and Example 1 is only that the ratio of BiFeO3 and g-C3N4 for preparing the composite photocatalytic material is 1:1.

[0090] The BiFeO3 / g-C3N4 composite photocatalytic material prepared in Example 7 is denoted as BFO / CN-7, and the CO yield is 39.74 μmol·g -1 ·h -1 .

[0091] Comparative Example 1 A photocatalyst is provided in this comparative example.

[0092] Bismuth nitrate pentahydrate and iron nitrate nonahydrate were weighed according to a molar ratio of 1:1 and dissolved in 10 mL of deionized water to completely dissolve, so that the concentration of the iron source and the bismuth source could reach 0.12 mol / L. After stirring for 30 min until completely uniform, 10 mol / L of KOH solution was added dropwise to the above solution, and the concentration of KOH in the solution was controlled to reach 4 mol / L. After stirring until completely uniform, a uniformly dispersed mixed precipitate solution was obtained. The above precipitate solution was transferred to a 50 mL hydrothermal synthesis reaction kettle, and reacted in an oven at 200°C for 6h. The kettle was cooled to room temperature with the oven, and the precipitate was washed with deionized water and ethanol alternately for 3 times, and then vacuum dried at 80°C for 10h to obtain the product BiFeO 3。

[0093] The BiFeO3 photocatalytic material prepared in Comparative Example 1 is denoted as BFO-1, and the CO yield is 21.78 μmol·g -1 ·h -1 .

[0094] Comparative Example 2 A photocatalyst is provided in this comparative example.

[0095] Melamine was placed in a crucible and calcined at 550°C for 4h, with a heating rate of 10°C / min. The calcined product was ground to obtain g-C3N4.

[0096] The g-C3N4 photocatalytic material prepared in Comparative Example 2 is denoted as CN-1, and the CO yield is 17.80 μmol·g -1 ·h -1 .

[0097] Comparative Example 3 A photocatalyst is provided in this comparative example.

[0098] The experiment uses 5 mL of tetrabutyl titanate and 0.6 mL of hydrofluoric acid mixed in a 25 ml reactor, heated to 180°C in an oven and kept for 24 h, and then naturally cooled to room temperature. Washed with ethanol and water three times respectively, white precipitate was collected by filtration, and dried in an oven.

[0099] The TiO2 photocatalytic material prepared in Comparative Example 3 is denoted as TO-1, and the CO yield is 9.62 μmol·g -1 ·h -1 .

[0100] Test experiment 1. Test method: The product yield and selectivity of the BiFeO3 / graphitic carbon nitride heterojunction catalyst, BiFeO3 monomer material, graphitic carbon nitride monomer material, and titanium dioxide material prepared in Examples 1-7 and Comparative Examples 1-3 of the present application in the process of photocatalytic reduction of CO2 are investigated.

[0101] Photocatalytic reduction of carbon dioxide activity test: 20 mg of prepared photocatalyst was added to 0.1 mL of deionized water and ultrasonically dispersed into a uniform solution, which was dropped on a quartz fiber filter membrane. Then the filter membrane was placed in a quartz reactor and sealed for vacuum treatment. Then high-purity CO2 was filled into the reactor until the pressure was 80 kPa. Finally, a 300W xenon lamp was used to irradiate the reactor, and a 420nm filter was used to make the reaction a photocatalytic reaction under visible light. The whole reaction was carried out at room temperature and Ar was used as the carrier gas. The experiment lasted for 5h, and the sampling interval was 1h. The products were analyzed by gas chromatography.

[0102] 2. Test results: Table 1, CO yield and selectivity of catalysts in examples and comparative examples

[0103] Analysis: The test results of the above examples and comparative examples are analyzed (see Table 1 and the attached Figure 6 , attached Figure 7 ), the following conclusions can be drawn: (1) The superiority of the heterojunction structure: the CO yield and CO selectivity of all Examples 1-7 (BFO / CN composite catalysts) are at a high level. In contrast, Comparative Example 1 (BFO-1, CO yield 21.78 μmol·g -1 ·h -1Comparative Example 2 (CN-1, CO yield 17.80 μmol·g) and Comparative Example 3 (CN-1, CO yield 17.80 μmol·g) -1 ·h -1 The catalytic activity of ) is significantly lower.

[0104] Meanwhile, the composite material in the examples is also far superior to the common TiO2 photocatalyst (TO-1, CO yield 9.62 μmol·g) in Comparative Example 3. -1 ·h -1 ).

[0105] This fully demonstrates that constructing a Z-shaped heterojunction by combining bismuth ferrite (BFO) and graphitic carbon nitride (g-C3N4) can efficiently separate photogenerated electrons and holes and suppress their recombination, thereby significantly enhancing the redox capability of the material and ultimately greatly improving photocatalytic performance and product selectivity. (Appendix) Figure 6 The CO yield-time curves also visually demonstrate that the yields of all BFO / CN composites are higher than those of the three comparative materials.

[0106] (2) Optimization analysis of preparation parameters: 1) Effect of precursor concentration (comparative examples 1, 2, and 3): The only variable in these three sets of experiments was the concentration of iron and bismuth sources during BFO preparation. Example 2 (0.12 mol / L) CO yield (59.20 μmol·g⁻¹) -1 ·h -1 Both selectivity (97%) and selectivity reached their highest levels.

[0107] refer to Figure 6 It is evident that the concentration was too high (Example 1, 0.24 mol / L, yield 43.83 μmol·g). -1 ·h -1 ) and too low (Example 3, 0.06 mol / L, yield 34.09 μmol·g) -1 ·h -1 All of these will lead to a decrease in performance.

[0108] 2) Effect of g-C3N4 precursor (comparative examples 1 and 4): Example 1 used melamine (calcined at 550℃), with a yield of 43.83 μmol·g. -1 ·h -1 The selectivity was 89%. Example 4 used urea (calcined at 400°C), increasing the yield to 55.49 μmol·g. -1 ·h -1 The selectivity is as high as 99%. This indicates that using urea as a precursor (BFO / CN-4) can produce a composite catalyst with excellent performance and selectivity.

[0109] 3) Effect of heating rate on g-C3N4 preparation (Comparative Examples 4, 5): Both of these groups use urea as precursor. The yield (55.49) and selectivity (99%) of Example 4 (10°C / min) are superior to those of Example 5 (5°C / min) (48.12 and 87%, respectively). This shows that a faster heating rate (10°C / min) is more conducive to the synthesis of high-performance g-C3N4 components.

[0110] 4) Effect of calcination temperature of composite (Comparative Examples 1, 6): Example 1 calcines the composite at 400°C, with a yield of 43.83 μmol·g -1 ·h -1 . Example 6 increases the calcination temperature to 500°C, with a significant decrease in yield to 31.76 μmol·g -1 ·h -1 . This shows that 400°C is a more suitable calcination temperature for the composite, and that a too high temperature can be detrimental to the effective formation of the heterojunction or destroy the material structure.

[0111] 5) Effect of composite ratio (Comparative Examples 1, 7): Example 1 has a BFO:g-C3N4 ratio of 2:1, with a yield of 43.83 μmol·g -1 ·h -1 . Example 7 has a ratio of 1:1, with a yield of 39.74. This shows that a mass ratio of 2:1 (BFO / CN-1) is superior to a ratio of 1:1 (BFO / CN-7).

[0112] In summary, the experimental results consistently show that the performance of the BFO / g-C3N4 composite heterojunction photocatalyst far exceeds that of its monomer components (BFO and g-C3N4) and traditional TiO2. At the same time, the performance of the catalyst is highly dependent on the preparation parameters, with Example 2 (BFO / CN-2) and Example 4 (BFO / CN-4) showing the most optimal CO yield and selectivity in their respective comparative groups.

[0113] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limiting. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art will understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a bismuth ferrite-graphite phase carbon nitride photocatalyst, characterized in that, include: Bismuth and iron sources are dissolved in a solvent and mixed with a mineralizing agent to carry out a hydrothermal synthesis reaction to obtain bismuth ferrite. A nitrogen-containing organic precursor was subjected to a first calcination treatment to obtain graphitic carbon nitride. The bismuth ferrite and the graphitic carbon nitride were mixed and then subjected to grinding and second calcination to obtain a bismuth ferrite-graphitic carbon nitride photocatalyst.

2. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The iron source includes at least one of ferric nitrate, ferric chloride, and ferric sulfate; and / or, The bismuth source includes at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride, and bismuth chloride; and / or, The solvent includes at least one selected from deionized water, methanol, ethanol, ethylene glycol, and dilute nitric acid solution; and / or, The mineralizing agent includes at least one of sodium hydroxide and potassium hydroxide; and / or, The nitrogen-containing organic precursor includes at least one of melamine, thiourea, urea, and dicyandiamine.

3. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The molar ratio of the iron source to the bismuth source is (0.1~3):

1.

4. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The concentration of the iron source is 0.01 mol / L to 0.5 mol / L; and / or, The concentration of the bismuth source is 0.01 mol / L to 0.5 mol / L; and / or, The concentration of the mineralizing agent is 2 mol / L to 8 mol / L.

5. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The hydrothermal synthesis reaction is carried out at a temperature of 140℃~200℃; and / or, The reaction time for the hydrothermal synthesis reaction is 4 to 20 hours.

6. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The temperature of the first calcination treatment is 400℃~650℃; and / or, The first calcination treatment lasts for 0.5 hours to 4 hours; and / or, The heating rate of the first calcination treatment is 2.5℃ / min to 10℃ / min.

7. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The mixing ratio of bismuth ferrite and graphitic carbon nitride is (0.1~10):

1.

8. The preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 1, characterized in that, The temperature of the second calcination treatment is 200℃~500℃; and / or, The second calcination treatment lasts for 0.5 hours to 8 hours; and / or, The heating rate of the second calcination treatment is 2.5℃ / min to 10℃ / min.

9. A bismuth ferrite-graphite phase carbon nitride photocatalyst, characterized in that, It was prepared by the method for preparing bismuth ferrite-graphite phase carbon nitride photocatalyst as described in any one of claims 1-8.

10. The use of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in claim 9 in the photocatalytic reduction of carbon dioxide.

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