A g-C3N4 / BiOBrS type heterojunction composite photocatalyst, its preparation method and application

Abstract

This invention discloses a BiOBr S-type heterojunction composite photocatalyst, its preparation method, and its application, relating to the field of photocatalytic materials technology. It comprises layers and BiOBr nanosheets, with the layers and BiOBr nanosheets tightly composited to form an S-type heterojunction composite structure, the mass ratio of the layers to BiOBr being 85:15. S1. Preparation: Melamine is placed in a muffle furnace, heated and calcined, then cooled, ground, washed, and dried to obtain a layered structure. S2. In-situ growth of BiOBr: The BiOBr obtained in step S1 is dispersed in a mixed solvent... In step S2, ultrasonic treatment forms a suspension. Bismuth and bromine sources are added to the suspension, and after stirring evenly, it is transferred to a high-pressure reactor for hydrothermal reaction. Step S3. Drying: The product obtained in step S2 is the / BiOBrS type heterojunction composite photocatalyst. The / BiOBrS type heterojunction composite photocatalyst is prepared by in-situ growth method. The process is simple and does not require secondary calcination. It can enable BiOBr to form a heterojunction composite structure with a tight interface, effectively suppressing the recombination of photogenerated electron-hole pairs and improving carrier separation and migration efficiency.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, and particularly to a... / BiOBrS type heterojunction composite photocatalyst, its preparation method and application. Background Technology

[0002] Hydrogen energy, as a clean and high-energy-density secondary energy source, is considered an important alternative to fossil fuels. Photocatalytic water splitting technology driven by solar energy can directly convert light energy into chemical energy, which has the advantages of high energy conversion efficiency, mild conditions, and no secondary pollution. It is an important way to achieve green hydrogen production and carbon neutrality.

[0003] Among numerous photocatalytic materials, graphitic carbon nitride (… Because of its suitable band gap, excellent visible light response capability, high chemical stability, and cheap and readily available synthetic raw materials, it is considered to be the most promising visible light responsive semiconductor material.

[0004] In the existing technology, Photocatalytic hydrogen production suffers from drawbacks such as low efficiency, rapid recombination rate of photogenerated electron-hole pairs, small specific surface area, and few interfacial active sites. While BiOBr possesses excellent visible light absorption capabilities, its catalytic activity remains limited when used alone. Furthermore, operating parameters significantly impact hydrogen yield during photocatalytic hydrogen production, ultimately hindering the achievement of efficient, stable, and controllable visible light-based hydrogen production. Therefore, a new method is needed. / BiOBrS type heterojunction composite photocatalyst, its preparation method and application. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and to propose a solution. / BiOBrS type heterojunction composite photocatalyst, its preparation method and application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A sort of / BiOBrS type heterojunction composite photocatalyst, made of The layers and BiOBr nanosheets are tightly composited to form an S-shaped heterojunction composite structure. The mass ratio of BiOBr is 85:15; The preparation method of the composite photocatalyst includes the following steps: S1. Preparation Melamine was placed in a muffle furnace, heated and calcined, then cooled, ground, washed and dried to obtain a sheet-like structure. ; S2. In-situ growth of BiOBr: The BiOBr obtained in step S1 The mixture is dispersed in a mixed solvent, ultrasonically treated to form a suspension, and bismuth source and bromine source are added to the suspension. After stirring evenly, the mixture is transferred to a high-pressure reactor for hydrothermal reaction. S3. Drying: The product obtained in step S2 is centrifuged, washed, and then dried to obtain the product described above. / BiOBrS type heterojunction composite photocatalyst.

[0007] The above technical solution further includes: Specifically, in step S1, the heating rate of calcination is 15℃ / min, the calcination temperature is 550℃, and the calcination time is 4 hours.

[0008] Specifically, the drying in step S1 is vacuum drying at a temperature of 50°C until constant weight is achieved.

[0009] Specifically, the mixed solvent in step S2 is a mixture of ethanol and deionized water, with a volume ratio of 1:1–1:2; the ultrasonic treatment time is 30–60 minutes.

[0010] Specifically, in step S2, the bismuth source is bismuth nitrate pentahydrate (Bi(NO3)3・5H2O), and the bromine source is ammonium bromide (NH4Br), with a molar ratio of 1:1.

[0011] Specifically, the hydrothermal reaction temperature in step S2 is 160°C, the reaction time is 8 hours, and the lining of the high-pressure reactor is made of polytetrafluoroethylene.

[0012] Specifically, the washing in steps S2 and S3 involves alternating between deionized water and ethanol at least three times.

[0013] Specifically, the drying temperature in step S3 is 70°C and the drying time is 8 hours.

[0014] Specifically, the aforementioned The application of the / BiOBrS type heterojunction composite photocatalyst in photocatalytic hydrogen production: the reaction system for photocatalytic hydrogen production is a pure water system, without the need to add sacrificial agents, and the reaction is carried out under visible light irradiation with an irradiation wavelength λ>420nm and a light intensity of 400–600mW / cm².

[0015] The present invention has the following beneficial effects: In this invention, an in-situ growth method is used to prepare... / BiOBrS-type heterojunction composite photocatalyst, with simple process and no need for secondary calcination, enables BiOBr to combine with... The formation of a tightly bonded heterojunction structure effectively suppresses the recombination of photogenerated electron-hole pairs, improves carrier separation and migration efficiency, and retains the material's strong redox capability. This catalyst can achieve photocatalytic hydrogen production in a pure water system under visible light irradiation without the need for sacrificial agents. It also has cycle stability and can maintain good photocatalytic performance after multiple uses. Attached Figure Description

[0016] Figure 1 For the present invention / Flowchart of the preparation process of BiOBrS-type heterojunction composite photocatalyst; Figure 2 The diagram shows a schematic of a photocatalyst, including: (a) XRD pattern, (b) FT-IR spectrum, (c) N2 adsorption-desorption isotherm and (d) pore size distribution curve. Figure 3 Here are SEM images of the photocatalyst, where: (a) (b) BiOBr and (c) CB-15 composite materials; Figure 4 The samples were irradiated with visible light, including: (a) the photocatalytic hydrogen production rate, (b) a comparison of the average hydrogen production rates of all tested samples, (c) the stability of the photocatalyst in four consecutive cycles, and (d) the apparent quantum yield of the photocatalyst at different monochromatic light wavelengths. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example

[0019] like Figures 1-4 As shown, the present invention proposes a method / BiOBrS type heterojunction composite photocatalyst, made of The layers are tightly bonded with BiOBr nanosheets to form an S-shaped heterojunction composite structure. The mass ratio of BiOBr is 85:15; The preparation method of composite photocatalysts includes the following steps: S1. Preparation Melamine was placed in a muffle furnace, heated and calcined, then cooled, ground, washed and dried to obtain a sheet-like structure. ; S2. In-situ growth of BiOBr: The BiOBr obtained in step S1 The mixture is dispersed in a mixed solvent, ultrasonically treated to form a suspension, bismuth source and bromine source are added to the suspension, stirred evenly, and then transferred to a high-pressure reactor for hydrothermal reaction. S3. Drying: Centrifuge, wash, and dry the product obtained in step S2 to obtain... / BiOBrS type heterojunction composite photocatalyst.

[0020] Furthermore, melamine was first placed in a muffle furnace and calcined at 550°C for 4 hours at a heating rate of 15°C / min. After cooling, it was ground, washed with deionized water and ethanol, and vacuum dried at 50°C to constant weight to obtain a sheet-like structure. Subsequently, the g-C3N4 was dispersed in ethylene glycol and sonicated for 30 minutes to form a uniform suspension. Bismuth nitrate pentahydrate and ammonium bromide (molar ratio 1:1) were added and stirred until homogeneous. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene (PTFE) and subjected to a hydrothermal reaction at 160°C for 8 hours, allowing the BiOBr nanosheets to... The surface is tightly anchored to form an S-shaped heterojunction; finally, the reaction product is centrifuged, washed three times alternately with deionized water and ethanol, and dried to obtain the final product. A composite photocatalyst with a mass ratio of 85:15 to BiOBr.

[0021] In step S1, the heating rate of calcination is 15℃ / min, the calcination temperature is 550℃, and the calcination time is 4 hours.

[0022] Furthermore, 10.0g of melamine was weighed and placed in a covered alumina crucible. The crucible was then placed in a muffle furnace and heated to 550℃ at a rate of 15℃ / min. The mixture was then calcined at this temperature for 4 hours.

[0023] In step S1, the drying is performed under vacuum at a temperature of 50°C until constant weight is achieved.

[0024] In step S2, the mixed solvent is a mixture of ethanol and deionized water in a volume ratio of 1:1–1:2; the ultrasonic treatment time is 30–60 minutes.

[0025] Furthermore, accurately weigh 0.3g of the product obtained in step S1. The powder is dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1–1:2 (total volume 30 mL) and subjected to ultrasonic treatment for 30–60 minutes to form a uniform suspension.

[0026] In step S2, the bismuth source is bismuth nitrate pentahydrate (Bi(NO3)3・5H2O), and the bromine source is ammonium bromide (NH4Br), with a molar ratio of 1:1.

[0027] Furthermore, after obtaining 0.3g in step S1 After dispersing the powder in 30 mL of ethylene glycol and sonicating for 30 minutes to form a homogeneous suspension, bismuth nitrate pentahydrate (Bi(NO3)3・5H2O) and ammonium bromide (NH4Br) were added sequentially to the suspension. The feed masses of the two were 0.192 g and 0.0268 g, respectively, with a molar ratio strictly controlled at 1:1. The mixed solution was then sonicated for another 30 minutes to ensure that the two precursors were fully dissolved and reacted with the solution. The suspension is mixed evenly.

[0028] In step S2, the hydrothermal reaction temperature is 160℃, the reaction time is 8 hours, and the lining of the high-pressure reactor is made of polytetrafluoroethylene.

[0029] Furthermore, the already dispersed A suspension of bismuth nitrate pentahydrate and ammonium bromide (molar ratio 1:1) was added and ultrasonically mixed. This mixture was then transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and sealed. The reactor was then placed in a drying oven and reacted at 160°C for 8 hours to allow the BiOBr nanosheets to... The surface is tightly anchored to form an S-shaped heterojunction. After the reaction is completed, the reactor is allowed to cool naturally to room temperature in preparation for subsequent centrifugal separation.

[0030] In steps S2 and S3, the washing process involves alternating between deionized water and ethanol at least three times.

[0031] In step S3, the drying temperature is 70℃ and the drying time is 8 hours.

[0032] Further, after the hydrothermal reaction in step S2 is completed, the reactor is naturally cooled to room temperature, the product is removed and separated into precipitates by centrifugation, and then the precipitates are washed at least three times with alternating deionized water and ethanol to remove impurities; after proceeding to step S3, the washed solid product is dried at 70°C for 8 hours, and after drying, it is ground to obtain the final product. The mass ratio of BiOBr is 85:15. / BiOBrS type heterojunction composite photocatalyst.

[0033] The application of BiOBrS-type heterojunction composite photocatalyst in photocatalytic hydrogen production: The reaction system for photocatalytic hydrogen production is a pure water system, without the need to add sacrificial agents. The reaction is carried out under visible light irradiation with an irradiation wavelength λ>420nm and a light intensity of 400–600mW / cm².

[0034] Furthermore, weigh out an appropriate amount The / BiOBrS type heterojunction composite photocatalyst was dispersed in a pure water system (without the addition of sacrificial agents). The suspension was then injected into a closed quartz reactor. Before the reaction started, high-purity nitrogen gas was continuously introduced into the system to completely remove dissolved oxygen. Then, under visible light irradiation with a wavelength λ>420nm and a light intensity of 400–600mW / cm², the reactor was kept at room temperature by magnetic stirring and a circulating water system. The hydrogen produced during the reaction was analyzed in a timely and quantitative manner using an all-glass automatic online system and a gas chromatograph equipped with a thermal conductivity detector, thus achieving efficient photocatalytic hydrogen production.

[0035] In this embodiment, the specific implementation method is as follows: Reagents and instruments; All reagents used in this embodiment are analytical grade and can be used directly. The main instruments include: a box-type muffle furnace, a 100mL stainless steel high-pressure reactor with a polytetrafluoroethylene liner, a CNC ultrasonic cleaner, a high-speed centrifuge, and a vacuum drying oven.

[0036] Constructed using in-situ growth method / BiOBrS-type heterojunction, in-situ growth method refers to... The layered substrate surface directly provides the reaction environment for BiOBr growth, allowing BiOBr to crystallize in situ from the precursor and tightly anchor to the substrate surface without subsequent mechanical mixing or secondary calcination. This fundamentally solves the defects of insufficient interfacial contact and particle agglomeration in traditional composite methods. The layered substrate is first prepared through the thermal polymerization reaction of melamine. A substrate (providing stable support for in-situ growth); subsequently, an in-situ hydrothermal growth method is used to grow a certain mass of... The substrate was dispersed in ethylene glycol solvent and ultrasonically formed into a uniform suspension (ensuring sufficient dispersion of the substrate and providing ample active sites for in-situ growth of BiOBr). Bismuth nitrate pentahydrate and ammonium bromide were then added sequentially as bismuth and bromine sources (precisely controlling the concentration of growth raw materials). By controlling the precursor feed ratio, BiOBr was grown at a mass percentage of 10% to 25%. In-situ crystallization growth on the surface (avoiding the formation and recombination of independent particles); the mixed solution is ultrasonically dispersed and then transferred to a high-pressure reactor for hydrothermal reaction at 160℃ for 8 hours (hydrothermal conditions provide a mild and uniform reaction environment for in-situ growth, promoting the crystallization of BiOBr nanosheets). (The substrate forms chemical bonds or strong physical adsorption) During the reaction, the BiOBr nanosheets are tightly anchored to the substrate. On top, a heterojunction structure with a closely contacted interface is formed; after the reaction, the product is centrifuged, washed, and dried to obtain a series of products with different mass ratios. / BiOBr composite photocatalyst, specifically exhibiting the following characteristics: (1) Preparation 10.0 g of melamine was weighed and placed in a covered alumina crucible. The crucible was then placed in a muffle furnace, and the temperature was raised to 550 °C at a heating rate of 15 °C / min. The mixture was then calcined at this temperature for 4 hours. After the calcination process, the mixture was allowed to cool naturally to room temperature. The resulting pale yellow lumpy product was ground into powder and washed three times with deionized water and ethanol to remove residual impurities. Finally, it was dried to constant weight in a vacuum drying oven at 50 °C to obtain a layered product. Powder, sealed and stored for later use.

[0037] (2) In-situ hydrothermal synthesis of / BiOBrS composite photocatalyst This embodiment takes the preparation of a composite catalyst with a BiOBr mass fraction of 15% (denoted as CB-15) as an example; First, accurately weigh 0.3g of the solution prepared in the above steps. The powder was dispersed in 30 mL of ethylene glycol and sonicated for 30 minutes to form a uniform suspension.

[0038] Subsequently, 0.192 g Bi(NO3)3·5H2O and 0.0268 g NH4Br (molar ratio of 1:1) were added to the suspension in sequence, and the mixed solution was sonicated for another 30 minutes to ensure that the precursor was fully dissolved and mixed.

[0039] Next, the well-mixed suspension was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), sealed, and placed in a forced-air drying oven for reaction at 160°C for 8 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature.

[0040] The resulting precipitate was separated using a centrifuge and washed three times alternately with deionized water and ethanol.

[0041] Finally, the washed solid product was dried in a vacuum drying oven at 50°C for 12 hours, and then ground to obtain the final product. / BiOBrS type heterojunction composite photocatalyst CB-15.

[0042] By adjusting the amount of Bi(NO3)3·5H2O and NH4Br, composite materials with BiOBr mass fractions of 10%, 20% and 25% can be obtained, and are labeled as CB-10, CB-20 and CB-25 respectively. Specifically, by adjusting the feed amounts of bismuth nitrate pentahydrate (Bi(NO3)3・5H2O) and ammonium bromide (NH4Br), three composite materials—CB-10 (BiOBr mass fraction 10%), CB-20 (BiOBr mass fraction 20%), and CB-25 (BiOBr mass fraction 25%)—all showed superior performance compared to pure water in photocatalytic hydrogen production tests under the same visible light irradiation (λ>420nm) and pure water system. The activity of pure BiOBr, of which; The hydrogen production rate of CB-10 is 938.1 μmol・g⁻¹・h⁻¹, which are respectively pure (50.55 μmol・g⁻¹・h⁻¹) and pure BiOBr (21.10 μmol・g⁻¹・h⁻¹) were 18.56 times and 44.46 times, respectively; The hydrogen production rate of CB-20 is 492.2 μmol・g⁻¹・h⁻¹, which are respectively pure It is 9.74 times and 23.33 times that of pure BiOBr; The hydrogen production rate of CB-25 is 241.96 μmol・g⁻¹・h⁻¹, which are respectively pure It is 4.79 times and 11.47 times that of pure BiOBr; In the cycle stability test, after four consecutive cycles of 6 hours each, the hydrogen production of the three catalysts remained above 95%, 92%, and 88% of their initial values, respectively, demonstrating good recyclability. However, when the BiOBr mass fraction deviated by 15%, the bonding tightness of the heterojunction interface or the separation efficiency of photogenerated carriers decreased, resulting in lower hydrogen production activity and stability compared to the CB-15 sample, further confirming the previous findings. A mass ratio of 85:15 to BiOBr is the optimal ratio for constructing an efficient S-shaped heterojunction.

[0043] Photocatalytic hydrogen production performance of catalysts (1) Photocatalytic hydrogen production test The photocatalytic hydrogen production experiment was carried out in a closed quartz reactor, using a 300W xenon lamp (Newport, USA) as the light source, and equipped with a 420nm cutoff filter to provide visible light illumination. The specific steps are as follows: accurately weigh 10.0 mg of the catalyst prepared in Example 1, disperse it in a 30 mL reaction solution consisting of 27 mL of deionized water and 3 mL of triethanolamine (TEOA) (TEOA is used as a hole sacrificial agent), inject the suspension into the reactor, and before the reaction starts, continuously introduce high-purity nitrogen into the system for 30 minutes to completely remove dissolved oxygen from the system.

[0044] The reaction was carried out under magnetic stirring. The reactor was kept at room temperature by a circulating water system. After the light was introduced, the system automatically sampled online. Every hour, the generated hydrogen was quantitatively analyzed by a gas chromatograph (Shimadzu GC-2014, Japan) equipped with a thermal conductivity detector (TCD).

[0045] (2) Experimental Results and Data Analysis After 6 hours of visible light irradiation, the hydrogen production performance of each catalyst was analyzed. The results showed that the pure hydrogen production performance of the catalyst was better than that of the pure hydrogen production performance ... The hydrogen production yields of pure BiOBr and pure BiOBr were only 308.70 μmol and 143.92 μmol, respectively, exhibiting limited photocatalytic activity, while all The / BiOBrS composite materials all showed significantly improved hydrogen production performance, with the CB-15 sample (15wt%BiOBr) exhibiting the best performance, achieving a cumulative hydrogen production of 11,670.63 μmol in 6 hours.

[0046] Calculations showed that the hydrogen production rate of the CB-15 sample reached 1925.9 μmol·g⁻¹·h⁻¹, which is respectively... The S-type heterojunction's performance is 38 times that of (50.55 μmol·g⁻¹·h⁻¹) and 91 times that of pure BiOBr (21.10 μmol·g⁻¹·h⁻¹), which fully demonstrates the advantages of the S-type heterojunction in improving photocatalytic performance.

[0047] Cyclic stability tests were conducted on the CB-15 sample. After four consecutive cycles of six hours each, the hydrogen production of the catalyst decreased only slightly. The hydrogen production in the fourth cycle still reached 10,980 μmol, indicating that it has excellent cyclic stability and can meet the basic requirements for material life in practical applications.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A kind / BiOBrS type heterojunction composite photocatalyst, characterized in that... include Sheets and BiOBr nanosheets, the The layers and BiOBr nanosheets are tightly composited to form an S-shaped heterojunction composite structure. The mass ratio of BiOBr is 85:15; The preparation method of the composite photocatalyst includes the following steps: S1. Preparation Melamine was placed in a muffle furnace, heated and calcined, then cooled, ground, washed and dried to obtain a sheet-like structure. ; S2. In-situ growth of BiOBr: The BiOBr obtained in step S1 The mixture is dispersed in a mixed solvent, ultrasonically treated to form a suspension, and bismuth source and bromine source are added to the suspension. After stirring evenly, the mixture is transferred to a high-pressure reactor for hydrothermal reaction. S3. Drying: The product obtained in step S2 is centrifuged, washed, and then dried to obtain the product described above. / BiOBrS type heterojunction composite photocatalyst.

2. As described in claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The calcination heating rate in step S1 is 15℃ / min, the calcination temperature is 550℃, and the calcination time is 4 hours.

3. As described in claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The drying process described in step S1 is vacuum drying at a temperature of 50°C until constant weight is achieved.

4. As described in claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The mixed solvent in step S2 is a mixture of ethanol and deionized water in a volume ratio of 1:1–1:2; the ultrasonic treatment time is 30–60 minutes.

5. The method according to claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The bismuth source in step S2 is bismuth nitrate pentahydrate (Bi(NO3)3・5H2O), and the bromine source is ammonium bromide (NH4Br), with a molar ratio of 1:

1.

6. The method according to claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The hydrothermal reaction in step S2 is carried out at a temperature of 160°C for 8 hours, and the lining of the high-pressure reactor is made of polytetrafluoroethylene.

7. The method according to claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The washing described in steps S2 and S3 shall be performed by alternating between deionized water and ethanol at least three times.

8. The method according to claim 1 / BiOBrS type heterojunction composite photocatalyst, characterized in that... The drying temperature in step S3 is 70°C and the drying time is 8 hours.

9. The claim 1–8 Application of / BiOBrS type heterojunction composite photocatalyst in photocatalytic hydrogen production.

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