A bismuth ferrite-graphite phase carbon nitride photocatalyst, and a preparation method and use thereof

Abstract

The application provides a BiFeO3-graphitic carbon nitride photocatalyst and a preparation method and application thereof, relates to the field of photocatalysis technology, and the preparation method comprises the following steps: dissolving a bismuth source and an iron source in a solvent, mixing with a mineralizer, and performing a hydrothermal synthesis reaction to obtain BiFeO3; performing first calcination treatment on a nitrogen-containing organic precursor to obtain graphitic carbon nitride; and performing grinding treatment and second calcination treatment on the mixture of BiFeO3 and graphitic carbon nitride to obtain the BiFeO3-graphitic carbon nitride photocatalyst. The preparation method can construct a Z-type heterojunction at the interface of the separately prepared BiFeO3 and graphitic carbon nitride, form an internal electric field, efficiently separate photo-generated electrons and holes, effectively inhibit the recombination of the photo-generated electrons and holes, finally significantly enhance the redox capacity of the material, and make the material exhibit excellent photocatalytic performance, high selectivity and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, and more specifically, to a bismuth ferrite-graphite phase carbon nitride photocatalyst, its preparation method, and its uses. Background Technology

[0002] With the rapid advancement of global industrialization, the environmental pollution and energy shortages caused by the massive amounts of carbon dioxide (CO2) produced from the combustion of fossil fuels have become a severe challenge. As a major greenhouse gas, carbon dioxide is a key factor contributing to global climate change. Therefore, effectively capturing atmospheric carbon dioxide and converting it into high-value-added chemicals or fuels can not only mitigate the greenhouse effect but also achieve the recycling of carbon resources, making it an important approach to addressing the dual crises of energy and the environment. Against this backdrop, photocatalysis technology has emerged. Utilizing abundant and clean solar energy as a driving force, it uses semiconductor photocatalysts to convert low-energy carbon dioxide molecules into high-energy hydrocarbons, demonstrating enormous application potential and becoming a frontier and hot topic in current scientific research.

[0003] Among numerous photocatalytic materials, titanium dioxide (TiO2) is one of the most widely and extensively 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 limited by its intrinsic properties. Furthermore, to overcome the problem of low solar energy utilization by traditional photocatalytic materials, researchers have developed various novel narrow-bandgap semiconductor photocatalysts. For example, bismuth-based photocatalytic materials have attracted much attention in the field of photocatalytic carbon dioxide reduction due to their unique electronic band structure, good chemical and thermal stability, and broad visible light response range. Among them, bismuth ferrite (BiFeO3), as a typical perovskite oxide, has a narrow bandgap of approximately 2.2 eV, enabling it to effectively absorb visible light, while its inherent ferroelectric properties also facilitate the separation of photogenerated charges.

[0004] Despite the progress made in photocatalysis technology, several technical bottlenecks remain. For titanium dioxide, its wide band gap means it can only absorb the high-energy, but relatively small (about 5%) ultraviolet light portion of the solar spectrum, while showing almost no response to the dominant visible light, significantly limiting its overall solar energy utilization efficiency. More critically, photogenerated electrons and holes under illumination readily recombine rapidly within or on the surface of the material before migrating to the catalyst surface to participate in the reaction, leading to low quantum efficiency and severely impacting its catalytic performance. For visible-light-responsive catalysts like bismuth ferrite, although they expand the spectral absorption range, the recombination problem of photogenerated electrons and holes is equally prominent, and in some cases even more severe. Furthermore, bismuth ferrite materials prepared by conventional methods typically have a small specific surface area, resulting in a limited number of exposed catalytic active sites, further restricting their photocatalytic efficiency.

[0005] In summary, current semiconductor materials used for photocatalytic carbon dioxide reduction, whether traditional wide-bandgap catalysts or emerging narrow-bandgap catalysts, generally face two major technical challenges: insufficient utilization of solar energy and low separation efficiency of photogenerated charges. These two issues together lead to low overall photocatalytic quantum yield. Simultaneously, the relatively small specific surface area of ​​the catalyst itself limits the number of reactive sites. These combined defects mean that the carbon dioxide conversion efficiency and product selectivity of existing photocatalytic systems fall far short of the requirements for practical applications, necessitating urgent technological breakthroughs.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a bismuth ferrite-graphite phase carbon nitride photocatalyst, its preparation method and uses. The preparation method constructs a Z-shaped heterojunction between bismuth ferrite and graphite phase carbon nitride, which effectively separates the photogenerated charge, thereby significantly improving the photocatalytic performance, selectivity and stability of the composite material.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a method for preparing a bismuth ferrite-graphite phase carbon nitride photocatalyst, comprising:

[0010] 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.

[0011] A nitrogen-containing organic precursor was subjected to a first calcination treatment to obtain graphitic carbon nitride.

[0012] 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.

[0013] In an optional embodiment, the iron source includes at least one of ferric nitrate, ferric chloride, and ferric sulfate; and / or,

[0014] The bismuth source includes at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride, and bismuth chloride; and / or,

[0015] The solvent includes at least one selected from deionized water, methanol, ethanol, ethylene glycol, and dilute nitric acid solution; and / or,

[0016] The mineralizing agent includes at least one of sodium hydroxide and potassium hydroxide; and / or,

[0017] The nitrogen-containing organic precursor includes at least one of melamine, thiourea, urea, and dicyandiamine.

[0018] In an optional embodiment, the molar ratio of the iron source to the bismuth source is (0.1~3):1.

[0019] In an optional embodiment, the concentration of the iron source is 0.01 mol / L to 0.5 mol / L; and / or,

[0020] The concentration of the bismuth source is 0.01 mol / L to 0.5 mol / L;

[0021] The concentration of the mineralizing agent is 2 mol / L to 8 mol / L.

[0022] In an optional embodiment, the hydrothermal synthesis reaction is carried out at a temperature of 140°C to 200°C; and / or,

[0023] The reaction time for the hydrothermal synthesis reaction is 4 to 20 hours.

[0024] In an optional embodiment, the temperature of the first calcination treatment is 400℃~650℃; and / or,

[0025] The first calcination treatment lasts for 0.5 hours to 4 hours; and / or,

[0026] The heating rate of the first calcination treatment is 2.5℃ / min to 10℃ / min.

[0027] In an optional embodiment, the mixing ratio of the bismuth ferrite and the graphitic carbon nitride is (0.1~10):1.

[0028] In an optional embodiment, the temperature of the second calcination treatment is 200°C to 500°C; and / or,

[0029] The second calcination treatment lasts for 0.5 hours to 8 hours; and / or,

[0030] The heating rate of the second calcination treatment is 2.5℃ / min to 10℃ / min.

[0031] Secondly, the present invention provides a bismuth ferrite-graphite phase carbon nitride photocatalyst, which is prepared by the preparation method of bismuth ferrite-graphite phase carbon nitride photocatalyst as described in any of the foregoing embodiments.

[0032] Thirdly, the present invention provides the use of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in the foregoing embodiments in the photocatalytic reduction of carbon dioxide.

[0033] This invention provides a bismuth ferrite-graphite-carbon nitride photocatalyst, its preparation method, and its applications. Compared with existing technologies, it can obtain composite photocatalytic materials with superior performance. Firstly, the three-step preparation process is simple and universally applicable. The first step, a hydrothermal synthesis reaction, facilitates the controllable preparation of bismuth ferrite with the target morphology and high crystallinity. The second step, a first calcination treatment, converts common nitrogen-containing organic precursors into graphite-phase carbon nitride with the target structure. The final step combines the two materials through mechanical grinding and a second calcination treatment. This method can prepare a final product with uniform particles and stable morphology.

[0034] Secondly, bismuth ferrite and graphitic carbon nitride, prepared separately, are combined. Due to their matched band structures, a Z-shaped heterojunction can be constructed at their interface. The formation of this heterojunction creates an electric field within the material, which plays a crucial role in efficiently separating electrons and holes generated under illumination and suppressing their recombination.

[0035] Finally, due to the effective separation of photogenerated 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 photocatalytic applications, and enables it to maintain high catalytic activity after multiple cycles, exhibiting good stability. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1This is a schematic flowchart illustrating the preparation method of the bismuth ferrite-graphite phase carbon nitride photocatalyst in the embodiments of this application;

[0038] Figure 2 The XRD patterns of the precursors BiFeO3, g-C3N4, and BiFeO3 / g-C3N4 composite catalyst in Example 2 of this invention are shown below.

[0039] Figure 3 This is a SEM image of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of the present invention;

[0040] Figure 4 The above are the EDS surface scan results of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of this invention;

[0041] Figure 5 This is a TEM image of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of the present invention;

[0042] Figure 6 The graph shows the photocatalytic reduction of CO2 to CO yield of the catalyst in the embodiments and comparative examples of the present invention;

[0043] Figure 7 This is a photocatalytic reduction CO2 selectivity diagram of the catalyst in the embodiments and comparative examples of the present invention. Detailed Implementation

[0044] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0045] refer to Figure 1 In this application embodiment, a method for preparing a bismuth ferrite-graphite phase carbon nitride photocatalyst is provided, comprising:

[0046] Step S1: Dissolve the bismuth source and iron source in a solvent and mix with a mineralizing agent to carry out a hydrothermal synthesis reaction to obtain bismuth ferrite.

[0047] This step aims to synthesize the first component of the composite photocatalyst: bismuth ferrite. The process begins by dissolving chemical raw materials containing bismuth and iron (i.e., bismuth and iron sources) in one or more liquids (i.e., solvents) to form a homogeneous solution. Subsequently, a "mineralizing agent" is added to this solution to regulate the reaction environment (e.g., pH value) and promote the subsequent crystallization process. Finally, the resulting mixture is placed in a sealed container (e.g., a hydrothermal reactor) and heated at a temperature higher than the solvent's boiling point at atmospheric pressure and under corresponding autogenous pressure; this process is known as the "hydrothermal synthesis reaction."

[0048] After the reaction is complete, solid bismuth ferrite powder can be obtained by cooling, washing and drying.

[0049] The morphology of the product can be controlled by adjusting the reaction conditions using a hydrothermal synthesis method. The material prepared by this method is characterized by a high degree of crystallinity.

[0050] For example, bismuth nitrate pentahydrate (as the bismuth source) and ferric nitrate nonahydrate (as the iron source) can be dissolved in deionized water (as the solvent) at a molar ratio of 1:1. Then, potassium hydroxide (KOH) solution (as a mineralizing agent) is added dropwise to the solution until the concentration of KOH in the mixed solution reaches a specific value (e.g., 4 mol / L). This mixed precipitate 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 complete, the reactor is cooled, and the resulting precipitate is bismuth ferrite.

[0051] Step S2 involves subjecting the nitrogen-containing organic precursor to a first calcination treatment to obtain graphitic carbon nitride.

[0052] This step aims to synthesize the second component of the composite photocatalyst: graphitic carbon nitride. The process involves using a nitrogen-rich organic compound (i.e., a nitrogen-containing organic precursor), which is then subjected to high-temperature treatment (such as a muffle furnace) in a process known as "first calcination" or thermal polycondensation. At high temperatures, the organic precursor decomposes and undergoes a polymerization reaction.

[0053] After calcination, the precursor transforms into a new, structurally stable non-metallic semiconductor material, namely graphitic carbon nitride. By selecting different precursors and controlling the calcination temperature and time, graphitic carbon nitride with the target structure can be synthesized.

[0054] For example, melamine (as a nitrogen-containing organic precursor) is placed in a crucible and calcined at 550°C for 4 hours, with the heating rate controlled at 10°C / min. After grinding, the calcined product yields graphitic carbon nitride.

[0055] Step S3: After mixing the bismuth ferrite and the graphite phase carbon nitride, the mixture is ground and then subjected to a second calcination treatment to obtain the bismuth ferrite-graphite phase carbon nitride photocatalyst.

[0056] This step is crucial for the final formation of the composite material. It involves physically mixing the bismuth ferrite powder and graphitic carbon nitride powder prepared in the first two steps in a specific ratio. To ensure close contact between the two powders, the mixture needs to undergo a "grinding process." Subsequently, the ground mixture is subjected to another high-temperature heating process, known as a "second calcination process," to promote bonding between the two materials at the interface.

[0057] After this series of processes, 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 bonded to the surface of bismuth ferrite.

[0058] This method is simple to operate and produces composite material particles with uniformity and stable morphology. The interfacial bonding (heterojunction) between the two materials constructed through this step can effectively separate photogenerated electrons and holes, thereby significantly improving the photocatalytic performance and selectivity of the material.

[0059] For example, the bismuth ferrite obtained in the first step and the graphitic carbon nitride obtained in the second step can be mixed uniformly in a 2:1 ratio. The mixed product is then calcined at 400°C for 4 hours, with the heating rate controlled at 5°C / min. Finally, the calcined product is ground to obtain the bismuth ferrite-graphitic carbon nitride composite photocatalyst material.

[0060] In some embodiments, the iron source includes at least one of ferric nitrate, ferric chloride, and ferric sulfate.

[0061] In some embodiments, the bismuth source includes at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride, and bismuth chloride.

[0062] In some embodiments, the solvent includes at least one of deionized water, methanol, ethanol, ethylene glycol, and dilute nitric acid solution.

[0063] In some embodiments, the mineralizing agent includes at least one of sodium hydroxide and potassium hydroxide.

[0064] In some embodiments, the nitrogen-containing organic precursor includes at least one of melamine, thiourea, urea, and dicyandiamine.

[0065] 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.

[0066] In some embodiments, the concentration of the iron source is 0.01 mol / L to 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.

[0067] In some embodiments, the concentration of the bismuth source is 0.01 mol / L to 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.

[0068] In some embodiments, the concentration of the mineralizing agent 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, etc.

[0069] 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, etc.

[0070] In some embodiments, the reaction time of the hydrothermal synthesis reaction is 4 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, etc.

[0071] 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, etc.

[0072] In some embodiments, the first calcination treatment time is 0.5 hours to 4 hours. For example, it can be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, etc.

[0073] In some embodiments, the heating rate of the first calcination treatment is 2.5℃ / min to 10℃ / min. For example, it can be 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.

[0074] In some embodiments, the mixing ratio of bismuth ferrite and graphitic carbon nitride is (0.1~10):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, etc.

[0075] 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, etc.

[0076] In some embodiments, the second calcination treatment time 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, etc.

[0077] In some embodiments, the heating rate of the second calcination treatment is 2.5℃ / min to 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, etc.

[0078] In this application embodiment, a bismuth ferrite-graphite phase carbon nitride photocatalyst is provided, which is prepared by the preparation method of bismuth ferrite-graphite phase carbon nitride photocatalyst as described in any of the foregoing embodiments.

[0079] The bismuth ferrite-graphite carbon nitride photocatalyst provided in this embodiment can be a composite material, in which graphite carbon nitride particles are dispersed and distributed on the surface of bismuth ferrite microspheres. This structure enables the two materials to form a band-matched Z-shaped heterojunction. This composite material has the characteristics of high crystallinity, uniform particle size, regular morphology, and stability.

[0080] The core advantage of this catalyst stems from the formation of a Z-shaped heterojunction, which effectively separates photogenerated electrons and holes, thereby enhancing the catalyst's redox capability. This results in a wide visible light absorption range, a high photogenerated charge interface migration rate, and excellent photocatalytic activity and selectivity. In applications, the catalyst exhibits good photocatalytic performance and stability; for example, in the catalytic reduction of CO2 under visible light, the effect shows virtually no degradation after five cycles. Furthermore, due to the magnetic properties of the bismuth ferrite component, the catalyst can be recovered magnetically, a simple recovery method with minimal catalyst loss.

[0081] In this application embodiment, the use of the bismuth ferrite-graphite phase carbon nitride photocatalyst as described in the foregoing embodiments in the photocatalytic reduction of carbon dioxide is provided.

[0082] The aforementioned bismuth ferrite-graphite phase carbon nitride photocatalyst is used for the photocatalytic reduction of carbon dioxide. In this application, the catalyst can react under conditions of room temperature and visible light irradiation.

[0083] One significant effect is the efficient conversion of carbon dioxide (CO2) into carbon monoxide (CO), with the amount of product increasing with prolonged light exposure. This catalyst exhibits excellent performance and high stability in this application; after five cycles under visible light, its catalytic reduction efficiency for CO2 shows virtually no degradation. Furthermore, an important feature of this application is the catalyst's recyclability; due to the material's magnetic properties, it can be separated and recycled using a simple magnetic recovery method after the reaction, reducing catalyst loss.

[0084] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0085] Example 1

[0086] This embodiment provides a photocatalyst.

[0087] Experimental methods:

[0088] (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.

[0089] (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.

[0090] (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.

[0091] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 1 is designated BFO / CN-1, with a CO yield of 43.83 μmol·g.-1 ·h -1 .

[0092] Example 2

[0093] This embodiment provides a photocatalyst.

[0094] Experimental methods:

[0095] (1) Weigh bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a 1:1 molar ratio and dissolve them in 10 mL of deionized water until they are completely dissolved, so that the concentration of iron source and bismuth source can reach 0.12 mol / L. Stir for 30 min until completely homogeneous, then add 10 mol / L KOH solution dropwise to the above solution, control the KOH concentration in the solution to reach 4 mol / L, stir until completely homogeneous, and 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 obtain the precipitate. Wash the precipitate three times alternately with deionized water and ethanol, and then dry it under vacuum at 80 °C for 10 h to obtain the product BiFeO3.

[0096] (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.

[0097] (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.

[0098] The only difference between this embodiment and Example 1 is that the concentrations of the iron source and bismuth source are changed to 0.12 mol / L.

[0099] refer to Figure 2 The XRD patterns of the precursors BiFeO3, g-C3N4, and BiFeO3 / g-C3N4 composite catalyst in Example 2 of this invention are shown below. Figure 3 This is a SEM image of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of the present invention; Figure 4 The above are the EDS surface scan results of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of this invention; Figure 5 This is a TEM image of the BiFeO3 / g-C3N4 composite catalyst in Example 2 of the present invention.

[0100] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 2 is designated BFO / CN-2, with a CO yield of 59.20 μmol·g. -1 ·h -1 .

[0101] Example 3

[0102] This embodiment provides a photocatalyst.

[0103] Experimental methods:

[0104] (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.

[0105] (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.

[0106] (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.

[0107] 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.

[0108] 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 .

[0109] Example 4

[0110] This embodiment provides a photocatalyst.

[0111] Experimental methods:

[0112] (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.

[0113] (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.

[0114] (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.

[0115] The only difference between this embodiment and Example 1 is that the precursor used to prepare graphitic carbon nitride is urea.

[0116] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 4 is designated BFO / CN-4, with a CO yield of 55.49 μmol·g. -1 ·h -1 .

[0117] Example 5

[0118] This embodiment provides a photocatalyst.

[0119] Experimental methods:

[0120] (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.

[0121] (2) Place urea in a crucible and calcine at 400℃ for 4 hours, controlling the heating rate to be 5℃ / min. Grind the calcined product to obtain g-C3N4.

[0122] (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.

[0123] The only difference between this embodiment and Example 1 is that the heating rate for preparing graphitic carbon nitride is 5°C / min.

[0124] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 5 is designated BFO / CN-5, with a CO yield of 48.12 μmol·g. -1 ·h -1 .

[0125] Example 6

[0126] This embodiment provides a photocatalyst.

[0127] Experimental methods:

[0128] (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.

[0129] (2) Melamine was placed in a crucible and calcined at 500°C for 4 hours, with the heating rate controlled at 5°C / min. The calcined product was ground to obtain g-C3N4.

[0130] (3) The BiFeO3 and g-C3N4 obtained above are mixed evenly in a ratio of 2:1. The mixed product is calcined at 500℃ for 4h with the heating rate controlled at 5℃ / min. After grinding, BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0131] The only difference between this embodiment and Example 1 is that the calcination temperature for preparing the composite photocatalytic material is 500℃.

[0132] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 6 is designated BFO / CN-6, with a CO yield of 31.76 μmol·g. -1 ·h -1 .

[0133] Example 7

[0134] This embodiment provides a photocatalyst.

[0135] Experimental methods:

[0136] (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.

[0137] (2) Melamine was placed in a crucible and calcined at 500°C for 4 hours, with the heating rate controlled at 5°C / min. The calcined product was ground to obtain g-C3N4.

[0138] (3) The BiFeO3 and g-C3N4 obtained above are mixed evenly in a 1:1 ratio. The mixed product is calcined at 500℃ for 4h with the heating rate controlled at 5℃ / min. After grinding, BiFeO3 / g-C3N4 composite photocatalytic material is obtained.

[0139] The only difference between this embodiment and Example 1 is that the ratio of BiFeO3 to g-C3N4 in the preparation of the composite photocatalytic material is 1:1.

[0140] The BiFeO3 / g-C3N4 composite photocatalyst prepared in Example 7 is designated BFO / CN-7, with a CO yield of 39.74 μmol·g. -1 ·h -1 .

[0141] Comparative Example 1

[0142] This comparative example provides a photocatalyst.

[0143] Bismuth nitrate pentahydrate and ferric nitrate nonahydrate were weighed at a 1:1 molar ratio and dissolved completely in 10 mL of deionized water to achieve a total iron and bismuth source concentration of 0.12 mol / L. The mixture was stirred for 30 min until completely homogeneous. Then, 10 mol / L KOH solution was added dropwise to the solution, maintaining a KOH concentration of 4 mol / L. After stirring until completely homogeneous, a uniformly dispersed mixed precipitate solution was obtained. This precipitate solution was transferred to a 50 mL hydrothermal synthesis reactor and reacted in an oven at 200 °C for 6 h. The reactor was then cooled to room temperature, and the precipitate was washed three times alternately with deionized water and ethanol, followed by vacuum drying at 80 °C for 10 h to obtain the product BiFeO. 3。

[0144] The BiFeO3 photocatalyst prepared in Comparative Example 1 is designated as BFO-1, with a CO yield of 21.78 μmol·g. -1 ·h -1 .

[0145] Comparative Example 2

[0146] This comparative example provides a photocatalyst.

[0147] Melamine was placed in a crucible and calcined at 550℃ for 4 hours, with the heating rate controlled at 10℃ / min. The calcined product was then ground to obtain g-C3N4.

[0148] The g-C3N4 photocatalyst prepared in Comparative Example 2 is designated CN-1, with a CO yield of 17.80 μmol·g. -1 ·h -1 .

[0149] Comparative Example 3

[0150] This comparative example provides a photocatalyst.

[0151] In the experiment, 5 mL of tetrabutyl titanate and 0.6 mL of hydrofluoric acid were mixed in a 25 mL reaction vessel, heated to 180 °C in an oven and kept at that temperature for 24 h, and then naturally cooled to room temperature. The mixture was washed three times with ethanol and water, respectively. The white precipitate was filtered, collected, and dried in an oven.

[0152] The TiO2 photocatalyst prepared in Comparative Example 3 is designated as TO-1, with a CO yield of 9.62 μmol·g. -1 ·h -1 .

[0153] Test Experiment

[0154] 1. Testing method:

[0155] The product yields and selectivity of the bismuth ferrite / graphite phase carbon nitride heterojunction catalysts, bismuth ferrite monomer materials, graphite phase carbon nitride monomer materials, and titanium dioxide materials prepared in Examples 1-7 and Comparative Examples 1-3 of this invention were investigated in the photocatalytic reduction of CO2 process.

[0156] Photocatalytic reduction of carbon dioxide activity test: 20 mg of the prepared photocatalyst was weighed and added to 0.1 mL of deionized water and ultrasonically dispersed into a uniform solution. This solution was then dropped onto a quartz fiber filter membrane. The filter membrane was then placed in a quartz reactor and sealed under vacuum. High-purity CO2 was then introduced into the reactor until the pressure reached 80 kPa. Finally, the reactor was irradiated with a 300 W xenon lamp using a 420 nm filter to allow the photocatalytic reaction to occur under visible light. The entire reaction was carried out at room temperature with Ar as the carrier gas. The experiment lasted for 5 hours, with sampling intervals of 1 hour. The products were analyzed by gas chromatography.

[0157] 2. Test Results:

[0158] Table 1. CO yield and selectivity of catalysts in examples and comparative examples

[0159]

[0160] analyze:

[0161] The test results of the above embodiments and comparative examples were analyzed (see Table 1 above and appendix). Figure 6 Appendix Figure 7 From this, we can draw the following conclusions:

[0162] (1) Advantages of heterostructure construction: All Examples 1-7 (BFO / CN composite catalysts) exhibited high CO yields and CO selectivity. In contrast, Comparative Example 1 (BFO-1, CO yield 21.78 μmol·g) without heterostructure construction showed significantly lower CO yields. -1 ·h -1 Comparative 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.

[0163] 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 ).

[0164] 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.

[0165] (2) Optimization analysis of preparation parameters:

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 3) Effect of heating rate on g-C3N4 preparation (comparative examples 4 and 5): Both groups used urea as a precursor. Example 4 (10 °C / min) showed better yield (55.49%) and selectivity (99%) than Example 5 (5 °C / min) (48.12%) and selectivity (87%). This indicates that a faster heating rate (10 °C / min) is more favorable for synthesizing high-performance g-C3N4 components.

[0170] 4) Effect of calcination temperature on composite materials (comparative examples 1 and 6): In Example 1, the composite material was calcined at 400℃, with a yield of 43.83 μmol·g. -1 ·h -1 In Example 6, increasing the calcination temperature to 500°C significantly reduced the yield to 31.76 μmol·g. -1 ·h -1This indicates that 400℃ is a more suitable composite calcination temperature; excessively high temperatures may hinder the effective formation of heterojunctions or damage the material structure.

[0171] 5) Effect of composite material ratio (comparative examples 1 and 7): In Example 1, the BFO:g-C3N4 ratio was 2:1, and the yield was 43.83 μmol·g. -1 ·h -1 In Example 7, the ratio was 1:1, and the yield decreased to 39.74%. This indicates that a 2:1 mass ratio (BFO / CN-1) is superior to a 1:1 ratio (BFO / CN-7).

[0172] In summary, the experimental results consistently demonstrate that the performance of the BFO / g-C3N4 composite heterojunction photocatalyst far surpasses that of its monomeric components (BFO and g-C3N4) and traditional TiO2. Furthermore, the catalyst performance is highly dependent on the preparation parameters, with Examples 2 (BFO / CN-2) and 4 (BFO / CN-4) exhibiting the best CO yield and selectivity in their respective comparative groups.

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a bismuth ferrite-graphite phase carbon nitride photocatalyst in the photocatalytic reduction of carbon dioxide, characterized in that, The preparation method of the photocatalyst includes: Bismuth and iron sources are dissolved in a solvent and mixed with a mineralizing agent to undergo a hydrothermal synthesis reaction to obtain bismuth ferrite; the concentration of the iron source is 0.1 mol / L to 0.2 mol / L; the concentration of the bismuth source is 0.1 mol / L to 0.2 mol / L; and the concentration of the mineralizing agent is 3 mol / L to 5 mol / L. A nitrogen-containing organic precursor was subjected to a first calcination treatment to obtain graphitic carbon nitride. The bismuth ferrite and the graphite phase carbon nitride were mixed and then subjected to grinding and second calcination to obtain a bismuth ferrite-graphite phase carbon nitride photocatalyst. The method for testing the photocatalytic reduction of carbon dioxide includes: weighing 20 mg of the prepared photocatalyst, adding it to 0.1 mL of deionized water, and ultrasonically dispersing it into a uniform solution, then dropping it onto a quartz fiber filter membrane; placing the filter membrane into a quartz reactor and sealing it under vacuum; filling the reactor with high-purity CO2 until the pressure reaches 80 kPa; irradiating the reactor with a 300 W xenon lamp and using a 420 nm filter to allow the photocatalytic reaction to occur under visible light.

2. The application as described in claim 1, characterized in that, The iron source includes at least one of ferric nitrate, ferric chloride, and ferric sulfate.

3. The application as described in claim 1, characterized in that, The bismuth source includes at least one of bismuth nitrate, bismuth oxide, bismuth oxychloride, and bismuth chloride.

4. The application as described in claim 1, characterized in that, The solvent includes at least one of deionized water, methanol, ethanol, ethylene glycol, and dilute nitric acid solution.

5. The application as described in claim 1, characterized in that, The mineralizing agent includes at least one of sodium hydroxide and potassium hydroxide.

6. The application as described in claim 1, characterized in that, The nitrogen-containing organic precursor includes at least one of melamine, thiourea, urea, and dicyandiamine.

7. The application as described in claim 1, characterized in that, The molar ratio of the iron source to the bismuth source is (0.1~3):

1.

8. The application as described in claim 1, characterized in that, The reaction temperature of the hydrothermal synthesis reaction is 140℃~200℃.

9. The application as described in claim 1, characterized in that, The reaction time for the hydrothermal synthesis reaction is 4 to 20 hours.

10. The application as described in claim 1, characterized in that, The temperature of the first calcination treatment is 400℃~650℃.

11. The application as described in claim 1, characterized in that, The first roasting process takes 0.5 to 4 hours.

12. The application as described in claim 1, characterized in that, The heating rate of the first calcination treatment is 2.5℃ / min to 10℃ / min.

13. The application as described in claim 1, characterized in that, The mixing ratio of bismuth ferrite and graphitic carbon nitride is (0.1~10):

1.

14. The application as described in claim 1, characterized in that, The temperature of the second roasting treatment is 200℃~500℃.

15. The application as described in claim 1, characterized in that, The second roasting process takes 0.5 to 8 hours.

16. The application as described in claim 1, characterized in that, The heating rate of the second calcination treatment is 2.5℃ / min to 10℃ / min.

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