A BP / Bi5O7I heterojunction and a preparation method and application thereof

Abstract

The application provides a BP / Bi5O7I heterojunction preparation method and application thereof in photocatalytic preparation of H2O2. Bulk black phosphorus is prepared by using red phosphorus as a reaction precursor through a chemical vapor transfer method, and the bulk black phosphorus is subjected to a ball milling method to obtain black phosphorus nanosheets (BPNSs). The BPNSs are stirred and dissolved in a mixed solvent of ethylene glycol and ultrapure water, Bi(NO3)3.5H2O is added and stirred and dissolved, then KI is added and stirred to form a uniform mixed solution, then the pH of the solution is adjusted to 11 by using a NaOH solution, the stirring reaction is continued, centrifugal separation is performed, the precipitate is washed with water and ethanol, and vacuum drying is performed to obtain the BP / Bi5O7I heterojunction. The BP / Bi5O7I heterojunction has the advantages of good stability, high carrier separation efficiency, and super strong visible light response capability. Under the condition that isopropanol is used as a sacrificial agent, the BP / Bi5O7I heterojunction can generate H2O2 under xenon lamp irradiation, and has the advantages of economy, energy saving, environmental protection and the like.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology and relates to a method for preparing BP / Bi5O7I heterojunctions and their applications. Specifically, it relates to a method for photocatalytically producing H2O2 using BP / Bi5O7I heterojunctions. Background Technology

[0002] Hydrogen peroxide is one of the most green and efficient oxidants, widely used in fine synthesis, biopharmaceuticals, environmental remediation, and many other fields. Traditional industrial production methods for H2O2 face problems such as high production costs, difficult storage and transportation, and high risks. Therefore, exploring more efficient, economical, and safe H2O2 production methods is urgent. Photocatalytic production of H2O2, using light as the driving force, has become a research hotspot due to its economic, energy-saving, and environmentally friendly advantages. BP has a two-dimensional layered structure similar to graphene. BP nanosheets possess high carrier mobility, tunable band gaps, and strong light absorption characteristics. Since the first successful exfoliation of 2D ultrathin BP nanosheets in 2014, it has attracted widespread attention worldwide. Few-layer BP is sensitive to air and water, and is easily oxidized and decomposed, leading to a significant reduction in its photocatalytic activity, seriously affecting its practical applications. Bi5O7I is a novel semiconductor with highly efficient photocatalytic performance, rich in surface defects, possessing suitable band positions, and a unique layered structure. We constructed a BP / Bi5O7I heterojunction based on Bi5O7I, which significantly improved its stability, broadened its visible light response range, and enhanced the separation efficiency of photogenerated electron-hole pairs. It exhibited excellent photocatalytic performance in the field of photocatalysis technology, with advantages that single photocatalysts could not match. It has important practical significance for the photocatalytic water splitting to produce H2O2. Summary of the Invention

[0003] The technical problem this invention aims to solve is to overcome the shortcomings of existing materials in terms of stability and catalytic performance. It provides a BP / Bi5O7I heterojunction material with strong visible light absorption, high photogenerated electron-hole separation efficiency, good stability, and efficient photocatalytic water splitting to produce H2O2. Furthermore, it provides a method for preparing the BP / Bi5O7I heterojunction, which is simple, requires low equipment standards, and allows for easy control of experimental conditions. This addresses the problems of existing photocatalyst preparation methods being complex, demanding in terms of equipment, and exhibiting relatively poor stability and catalytic activity.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A BP / Bi5O7I heterojunction material, wherein the BP / Bi5O7I heterojunction uses nanoscale Bi5O7I as a carrier and BP nanosheets are modified on the surface.

[0006] The mass ratio of Bi5O7I to BP nanosheets in the BP / Bi5O7I heterojunction is 100:1 to 100:20.

[0007] As a general technical concept, the present invention also provides a method for preparing a BP / Bi5O7I heterojunction, comprising the following steps:

[0008] Step 1: Take red phosphorus, Sn powder, and SnI4 into a quartz tube, seal it under vacuum, place it horizontally in a tube furnace, heat it at high temperature, and then let it cool naturally to room temperature to obtain blocky BP. Remove the by-products to obtain pure black phosphorus crystals.

[0009] Step 2: Take pure black phosphorus crystals and grind them in a mortar, then disperse them in anhydrous ethanol, and then transfer them to a sealed stainless steel ball mill jar for grinding. Centrifuge to obtain black phosphorus nanosheets.

[0010] Step 3: Take a mixture of ultrapure water and ethylene glycol, add black phosphorus nanosheets and stir to dissolve. Add bismuth nitrate pentahydrate to dissolve, then add KI. Next, adjust the pH of the solution with NaOH solution and continue the reaction. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water respectively, and vacuum dry overnight to obtain the BP / Bi5O7I heterojunction.

[0011] In step one above, the mass ratio of red phosphorus, Sn powder, and SnI4 is 50:2:1; the quartz tube has an inner diameter of 0.5–2 cm, a length of 5–10 cm, and a thickness of 1–5 mm; the heating program is as follows: heating to 650 °C at a rate of 0.5–5 °C / min, heating for 1–5 h, then cooling to 450 °C at a rate of 0.1–2 °C / min, maintaining for 2–6 h, and then naturally cooling to room temperature; the byproduct removal method is to repeatedly sonicate in a toluene solution and reflux for 20–120 min.

[0012] In step two above, 0.05g to 0.5g of pure black phosphorus crystals are ground in a mortar; the grinding time in the mortar is 15 to 30 minutes; the volume of anhydrous ethanol is 5 to 30 mL; the volume of the stainless steel ball mill jar is 50 mL; and 50 to 500g of stainless steel balls with diameters of 10 mm and 5 mm are used for ball milling; the ball milling rate is 300 to 1000 rpm; and the ball milling time is 2 to 10 hours. The centrifugation is performed as follows: first, centrifuge at 5000 to 8000 rpm to remove large particles of black phosphorus, and then centrifuge at 10000 to 20000 rpm to separate the precipitate, which is black phosphorus nanosheets.

[0013] In step three above, the volume ratio of ultrapure water to ethylene glycol is 1:1; the mass of bismuth nitrate pentahydrate is 0.1–3 g; the mass of KI is 0.01–0.5 g; and the mass of black phosphorus nanosheets is 0.1–500 mg. The concentration of the NaOH solution is 0.5–5 M; the pH value is 10–12; the reaction is a stirred reaction at room temperature; the reaction time is 2–10 h; the centrifugation rate is 5000–8000 rpm; and the vacuum drying temperature is 50–80 °C for 5–20 h.

[0014] This invention also provides an application of BP / Bi5O7I heterojunction, which is used to produce H2O2. The specific method is as follows: weigh the BP / Bi5O7I heterojunction in a double-layered beaker, dissolve it in ultrapure water and then disperse it ultrasonically. Add isopropanol as a sacrificial agent, introduce oxygen under dark conditions to reach adsorption equilibrium, and react under 300W xenon lamp irradiation to produce H2O2.

[0015] In the above applications, the mass of the BP / Bi5O7I heterojunction is 10-500 mg, the ultrapure water is 18-900 mL, the isopropanol is 2-100 mL, the ultrasonic dispersion time is 2-20 min, the oxygen equilibration time is 10-300 min, and the reaction temperature is controlled at room temperature.

[0016] In the above applications, the analysis method for the H2O2 content is as follows: the reaction liquid is aspirated in segments during the reaction time, centrifuged, the supernatant is aspirated, and the H2O2 content is calculated by potassium permanganate titration under acidic conditions.

[0017] The specific analytical method described above is as follows: the reaction time was set at 20 h, and the sampling times were segmented at 0–2 h, 2–6 h, 6–10 h, and 10–20 h of the reaction. The sample volume for each sampling was 25 mL, the centrifugation rate was 6000 rpm, and 20 mL of the supernatant was collected each time. The acidic environment was achieved by adding 5 mL of 0.5–5 mol / L... -1 The H2SO4, wherein the concentration of potassium permanganate used in the titration is 0.1–2 mmol / L. -1 .

[0018] The basis for the above analysis and calculation of H2O2 content is: The H2O2 content can be calculated using the stoichiometric relationship between 8H2O and 8H2O. The formula is as follows: The unit is mmol / L·g.

[0019] Compared with existing technologies, this invention combines black phosphorus nanosheets with Bi5O7I to form a heterojunction. The resulting BP / Bi5O7I heterojunction exhibits strong light absorption, high photogenerated electron-hole separation efficiency, strong redox ability, and good stability, showing great application prospects. Its preparation method is simple, requires low equipment, and the experimental conditions are easy to control, making it suitable for large-scale industrial preparation. Furthermore, this invention utilizes the BP / Bi5O7I heterojunction to efficiently generate H2O2 under xenon lamp irradiation with isopropanol as a sacrificial agent, offering advantages such as economy, energy saving, environmental protection, and simple operation, thus demonstrating excellent application prospects. Attached Figure Description

[0020] Figure 1 The image shows the effect of generating H2O2 under 300W xenon lamp irradiation on the BP / Bi5O7I heterojunction material prepared in Example 1 of this invention.

[0021] Figure 2 The images show the H2O2 generation effect of BP / Bi5O7I heterojunction materials with different mass ratios prepared in this invention under 300W xenon lamp irradiation. The mass ratio is the mass ratio of black phosphorus nanosheets to Bi5O7I. Detailed Implementation

[0022] To further illustrate the present invention and make its objectives, technical solutions, and advantages clearer, the following detailed description, in conjunction with embodiments, describes the preparation of a BP / Bi5O7I heterojunction provided by the present invention and its application in photocatalytic production of H2O2, but this does not limit the scope of protection of the present invention.

[0023] Example 1:

[0024] This embodiment provides a BP / Bi5O7I heterojunction material, which uses nanoscale Bi5O7I as a carrier and then modifies the surface of Bi5O7I with BP nanosheets.

[0025] In this embodiment, the BP / Bi5O7I heterojunction material has a Bi5O7I mass percentage content of 95%, a black phosphorus nanosheet mass percentage content of 5%, and a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 5:1.

[0026] Simultaneously, a method for preparing the BP / Bi5O7I heterojunction material of the above embodiment is provided, including the following steps:

[0027] 1. 500 mg of red phosphorus, 20 mg of Sn powder, and 10 mg of SnI4 were vacuum-sealed in a quartz tube with an inner diameter of 1 cm (10 cm long and 2.5 mm thick). The tube was placed horizontally in a tube furnace and heated to 650 °C at a rate of 2 °C / min for 6 hours. Then, the temperature was lowered to 450 °C at a rate of 0.33 °C / min and heated for 2 hours. The mixture was then allowed to cool naturally to room temperature. Byproducts were obtained by repeatedly sonicating the sample in toluene and refluxing for 30 minutes until pure black phosphorus crystals were obtained.

[0028] 2. Grind 0.1g of crystalline agate in a mortar (15-30 min) into black phosphorus powder, then disperse it in 20mL of anhydrous ethanol, and pour it into a 50mL sealed stainless steel ball mill jar. Use approximately 100g of stainless steel balls (50% of the total weight) with diameters of 10mm and 5mm, and grind at 600rpm for 6 hours. Centrifuge at 5000rpm to remove large black phosphorus particles, then centrifuge at 12000rpm to separate the precipitate, which is the black phosphorus nanosheet.

[0029] 3. Mix 20 mL of ethylene glycol with 20 mL of ultrapure water, add 5 mg of black phosphorus nanosheets, and stir for 30 minutes to form a mixture. Add 0.378 g of bismuth nitrate pentahydrate and stir to dissolve, then add 0.0267 g of KI to dissolve. Adjust the pH of the solution to 11 with 2 M NaOH solution and stir at room temperature for 4 hours. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water, and dry it overnight at 60 °C to obtain the BP / Bi5O7I heterojunction.

[0030] Example 2:

[0031] This embodiment provides a BP / Bi5O7I heterojunction material, which uses nanoscale Bi5O7I as a carrier and then modifies the surface of Bi5O7I with BP nanosheets.

[0032] In this embodiment, the BP / Bi5O7I heterojunction material has a Bi5O7I mass percentage content of 99%, a black phosphorus nanosheet mass percentage content of 1%, and a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 5:1.

[0033] Simultaneously, a method for preparing the BP / Bi5O7I heterojunction material of the above embodiment is provided, including the following steps:

[0034] 1. 500 mg of red phosphorus, 20 mg of Sn powder, and 10 mg of SnI4 were vacuum-sealed in a quartz tube with an inner diameter of 1 cm (10 cm long and 2.5 mm thick). The tube was placed horizontally in a tube furnace and heated to 650 °C at a rate of 2 °C / min for 6 hours. Then, the temperature was lowered to 450 °C at a rate of 0.33 °C / min and heated for 2 hours. The mixture was then allowed to cool naturally to room temperature. Byproducts were obtained by repeatedly sonicating the sample in toluene and refluxing for 30 minutes until pure black phosphorus crystals were obtained.

[0035] 2. Grind 0.1g of crystalline agate in a mortar (15-30 min) into black phosphorus powder, then disperse it in 20mL of anhydrous ethanol, and pour it into a 50mL sealed stainless steel ball mill jar. Use approximately 100g of stainless steel balls (50% of the total weight) with diameters of 10mm and 5mm, and grind at 600rpm for 6 hours. Centrifuge at 5000rpm to remove large black phosphorus particles, then centrifuge at 12000rpm to separate the precipitate, which is the black phosphorus nanosheet.

[0036] 3. Mix 20 mL of ethylene glycol with 20 mL of ultrapure water, add 1 mg of black phosphorus nanosheets, and stir for 30 minutes to form a mixture. Add 0.378 g of bismuth nitrate pentahydrate and stir to dissolve, then add 0.0267 g of KI to dissolve. Adjust the pH of the solution to 11 with 2 M NaOH solution, and stir at room temperature for 4 hours. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water, and dry it overnight at 60 °C to obtain the BP / Bi5O7I heterojunction.

[0037] Example 3:

[0038] This embodiment provides a BP / Bi5O7I heterojunction material, which uses nanoscale Bi5O7I as a carrier and then modifies the surface of Bi5O7I with BP nanosheets.

[0039] In this embodiment, the BP / Bi5O7I heterojunction material has a Bi5O7I mass percentage content of 99%, a black phosphorus nanosheet mass percentage content of 1%, and a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 5:1.

[0040] Simultaneously, a method for preparing the BP / Bi5O7I heterojunction material of the above embodiment is provided, including the following steps:

[0041] 1. 500 mg of red phosphorus, 20 mg of Sn powder, and 10 mg of SnI4 were vacuum-sealed in a quartz tube with an inner diameter of 1 cm (10 cm long and 2.5 mm thick). The tube was placed horizontally in a tube furnace and heated to 650 °C at a rate of 2 °C / min for 6 hours. Then, the temperature was lowered to 450 °C at a rate of 0.33 °C / min and heated for 2 hours. The mixture was then allowed to cool naturally to room temperature. Byproducts were obtained by repeatedly sonicating the sample in toluene and refluxing for 30 minutes until pure black phosphorus crystals were obtained.

[0042] 2. Grind 0.1g of crystalline agate in a mortar (15-30 min) into black phosphorus powder, then disperse it in 20mL of anhydrous ethanol, and pour it into a 50mL sealed stainless steel ball mill jar. Use approximately 100g of stainless steel balls (50% of the total weight) with diameters of 10mm and 5mm, and grind at 600rpm for 6 hours. Centrifuge at 5000rpm to remove large black phosphorus particles, then centrifuge at 12000rpm to separate the precipitate, which is the black phosphorus nanosheet.

[0043] 3. Mix 20 mL of ethylene glycol with 20 mL of ultrapure water, add 2 mg of black phosphorus nanosheets, and stir for 30 minutes to form a mixture. Add 0.378 g of bismuth nitrate pentahydrate and stir to dissolve, then add 0.0267 g of KI to dissolve. Adjust the pH of the solution to 11 with 2 M NaOH solution, and stir at room temperature for 4 hours. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water, and dry it overnight at 60 °C to obtain the BP / Bi5O7I heterojunction.

[0044] Example 4:

[0045] This embodiment provides a BP / Bi5O7I heterojunction material, which uses nanoscale Bi5O7I as a carrier and then modifies the surface of Bi5O7I with BP nanosheets.

[0046] In this embodiment, the BP / Bi5O7I heterojunction material has a Bi5O7I mass percentage content of 99%, a black phosphorus nanosheet mass percentage content of 1%, and a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 5:1.

[0047] Simultaneously, a method for preparing the BP / Bi5O7I heterojunction material of the above embodiment is provided, including the following steps:

[0048] 1. 500 mg of red phosphorus, 20 mg of Sn powder, and 10 mg of SnI4 were vacuum-sealed in a quartz tube with an inner diameter of 1 cm (10 cm long and 2.5 mm thick). The tube was placed horizontally in a tube furnace and heated to 650 °C at a rate of 2 °C / min for 6 hours. Then, the temperature was lowered to 450 °C at a rate of 0.33 °C / min and heated for 2 hours. The mixture was then allowed to cool naturally to room temperature. Byproducts were obtained by repeatedly sonicating the sample in toluene and refluxing for 30 minutes until pure black phosphorus crystals were obtained.

[0049] 2. Grind 0.1g of crystalline agate in a mortar (15-30 min) into black phosphorus powder, then disperse it in 20mL of anhydrous ethanol, and pour it into a 50mL sealed stainless steel ball mill jar. Use approximately 100g of stainless steel balls (50% of the total weight) with diameters of 10mm and 5mm, and grind at 600rpm for 6 hours. Centrifuge at 5000rpm to remove large black phosphorus particles, then centrifuge at 12000rpm to separate the precipitate, which is the black phosphorus nanosheet.

[0050] 3. Mix 20 mL of ethylene glycol with 20 mL of ultrapure water, add 10 mg of black phosphorus nanosheets, and stir for 30 minutes to form a mixture. Add 0.378 g of bismuth nitrate pentahydrate and stir to dissolve, then add 0.0267 g of KI to dissolve. Adjust the pH of the solution to 11 with 2 M NaOH solution and stir at room temperature for 4 hours. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water, and dry it overnight at 60 °C to obtain the BP / Bi5O7I heterojunction.

[0051] Example 5:

[0052] This embodiment provides a BP / Bi5O7I heterojunction material, which uses nanoscale Bi5O7I as a carrier and then modifies the surface of Bi5O7I with BP nanosheets.

[0053] In this embodiment, the BP / Bi5O7I heterojunction material has a Bi5O7I mass percentage content of 99%, a black phosphorus nanosheet mass percentage content of 1%, and a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 5:1.

[0054] Simultaneously, a method for preparing the BP / Bi5O7I heterojunction material of the above embodiment is provided, including the following steps:

[0055] 1. 500 mg of red phosphorus, 20 mg of Sn powder, and 10 mg of SnI4 were vacuum-sealed in a quartz tube with an inner diameter of 1 cm (10 cm long and 2.5 mm thick). The tube was placed horizontally in a tube furnace and heated to 650 °C at a rate of 2 °C / min for 6 hours. Then, the temperature was lowered to 450 °C at a rate of 0.33 °C / min and heated for 2 hours. The mixture was then allowed to cool naturally to room temperature. Byproducts were obtained by repeatedly sonicating the sample in toluene and refluxing for 30 minutes until pure black phosphorus crystals were obtained.

[0056] 2. Grind 0.1g of crystalline agate in a mortar (15-30 min) into black phosphorus powder, then disperse it in 20mL of anhydrous ethanol, and pour it into a 50mL sealed stainless steel ball mill jar. Use approximately 100g of stainless steel balls (50% of the total weight) with diameters of 10mm and 5mm, and grind at 600rpm for 6 hours. Centrifuge at 5000rpm to remove large black phosphorus particles, then centrifuge at 12000rpm to separate the precipitate, which is the black phosphorus nanosheet.

[0057] 3. Mix 20 mL of ethylene glycol with 20 mL of ultrapure water, add 20 mg of black phosphorus nanosheets, and stir for 30 minutes to form a mixture. Add 0.378 g of bismuth nitrate pentahydrate and stir to dissolve, then add 0.0267 g of KI to dissolve. Adjust the pH of the solution to 11 with 2 M NaOH solution and stir at room temperature for 4 hours. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water, and dry it overnight at 60 °C to obtain the BP / Bi5O7I heterojunction.

[0058] Example 6:

[0059] This embodiment provides a method for efficiently generating H2O2 using BP / Bi5O7I heterojunction material under xenon lamp irradiation with isopropanol as a sacrificial agent. The method includes the following steps:

[0060] 1. Take 100 mg of BP / Bi5O7I heterojunction in a double-layered beaker, add 180 mL of ultrapure water and 20 mL of isopropanol, and sonicate for 5 min.

[0061] 2. In the dark, oxygen was introduced for 30 minutes to reach adsorption equilibrium. Oxygen was continuously introduced, and the temperature was controlled at 298K. The reaction was irradiated with a 300W xenon lamp.

[0062] 3. Take 25 mL samples at 1, 4, 8, and 12 hours respectively, and centrifuge. Take 20 mL of the supernatant and add 1 mol L... -1 5 mL of H₂SO₄ was dissolved using potassium permanganate (0.2 mmol / L). -1 The H2O2 content was calculated by titration analysis.

[0063] Figure 1The figure shows the H2O2 generation effect of the BP / Bi5O7I heterojunction material prepared in Example 1 of this invention under 300W xenon lamp irradiation. As can be seen from the figure, under the condition of isopropanol as a sacrificial agent, xenon lamp irradiation can efficiently generate H2O2, and the H2O2 concentration of 1g catalyst reaches 1.57mmol / L within 12h.

[0064] Figure 2 The figures show the H2O2 generation efficiency of BP / Bi5O7I heterojunction materials with different mass ratios prepared in this invention under 300W xenon lamp irradiation. The mass ratio refers to the ratio of black phosphorus nanosheets to Bi5O7I. As can be seen from the figures, the BP / Bi5O7I heterojunction material with a mass fraction of 5% exhibits the highest H2O2 generation efficiency under light irradiation with isopropanol as a sacrificial agent.

Claims

1. A BP / Bi5O7I heterojunction, characterized in that... The BP / Bi5O7I heterojunction uses nanoscale Bi5O7I as a carrier and is surface-modified with black phosphorus nanosheets (BPNSs). The mass ratio of Bi5O7I to black phosphorus nanosheets in the BP / Bi5O7I heterojunction is 100:1 to 100:

20. The preparation method of the BP / Bi5O7I heterojunction includes the following steps: Step 1: Take red phosphorus, Sn powder, and SnI4 into a quartz tube, seal it under vacuum, place it horizontally in a tube furnace, heat it at high temperature, and then let it cool naturally to room temperature to obtain blocky BP. Remove the by-products to obtain pure black phosphorus crystals. Step 2: Take pure black phosphorus crystals and grind them in a mortar, then disperse them in anhydrous ethanol, and then transfer them to a sealed stainless steel ball mill jar for grinding. Centrifuge to obtain black phosphorus nanosheets. Step 3: Take a mixture of ultrapure water and ethylene glycol, add black phosphorus nanosheets and stir to dissolve. Add bismuth nitrate pentahydrate to dissolve, then add KI. Next, adjust the pH of the solution with NaOH solution and continue the reaction. Centrifuge to collect the white precipitate, wash it several times with ethanol and ultrapure water respectively, and vacuum dry overnight to obtain the BP / Bi5O7I heterojunction.

2. The preparation method according to claim 1, characterized in that, In step one, the mass ratio of red phosphorus, Sn powder, and SnI4 is 50:2:1; the quartz tube has an inner diameter of 0.5–2 cm, a length of 5–10 cm, and a thickness of 1–5 mm; the heating program is as follows: heating to 650 °C at a rate of 0.5–5 °C / min for 1–5 h, then cooling to 450 °C at a rate of 0.1–2 °C / min for 2–6 h, followed by natural cooling to room temperature; the byproduct removal method is to repeatedly sonicate in a toluene solution and reflux for 20–120 min.

3. The preparation method according to claim 1, characterized in that, In step two, 0.05 g to 0.5 g of pure black phosphorus crystals are ground in a mortar; the grinding time in the mortar is 15 to 30 min; the volume of anhydrous ethanol is 5 to 30 mL; the volume of the stainless steel ball mill jar is 50 mL, and 50 to 500 g of stainless steel balls with diameters of 10 mm and 5 mm are used for ball milling; the ball milling rate is 300 to 1000 rpm, and the ball milling time is 2 to 10 h; the centrifugation is as follows: first, centrifuge at 5000 to 8000 rpm to remove large particles of black phosphorus, and then centrifuge at 10000 to 20000 rpm to separate the precipitate, which is black phosphorus nanosheets.

4. The preparation method according to claim 1, characterized in that, In step three, the volume ratio of ultrapure water to ethylene glycol is 1:1; the mass of bismuth nitrate pentahydrate is 0.1–3 g; the mass of KI is 0.01–0.5 g; and the mass of black phosphorus nanosheets is 0.1–500 mg. The concentration of the NaOH solution is 0.5–5 M; the pH value is 10–12; the reaction is a stirred reaction at room temperature; the reaction time is 2–10 h; the centrifugation rate is 5000–8000 rpm; and the vacuum drying temperature is 50–80°C for 5–20 h.

5. The application of the BP / Bi5O7I heterojunction as described in claim 1, characterized in that, The BP / Bi5O7I heterojunction is used to produce H2O2. The specific method is as follows: Weigh the BP / Bi5O7I heterojunction into a double-layered beaker, dissolve it in ultrapure water and disperse it by ultrasonication, add isopropanol as a sacrificial agent, introduce oxygen under dark conditions to reach adsorption equilibrium, and react under 300 W xenon lamp irradiation to produce H2O2.

6. The application according to claim 5, characterized in that: The mass of the BP / Bi5O7I heterojunction is 10-500 mg, the amount of ultrapure water is 18-900 mL, the amount of isopropanol is 2-100 mL, the ultrasonic dispersion time is 2-20 min, the oxygen equilibration time is 10-300 min, and the reaction temperature is controlled at room temperature.

7. The analytical method for the content of H2O2 obtained according to claim 5, characterized in that: The reaction solution was sampled in segments during the reaction time, centrifuged, and the supernatant was collected. The H2O2 content was calculated by potassium permanganate titration under acidic conditions.

8. The analytical method according to claim 7, characterized in that, The specific method is as follows: the reaction time is set at 20 h, and the sampling times are segmented at 0–2 h, 2–6 h, 6–10 h, and 10–20 h of the reaction. The sample volume for each sampling is 25 mL, the centrifugation rate is 6000 rpm, and 20 mL of the supernatant is taken each time. The acidic environment is achieved by adding 5 mL of 0.5–5 mol / L... -1 The H2SO4, wherein the concentration of potassium permanganate used in the titration is 0.1–2 mmol / L. -1 .

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