Preparation method and application of boron nitride black phosphorus heterojunction photocatalyst and purification method of dye wastewater

Abstract

This patent application discloses a preparation method, application and purification method of a boron nitride black phosphorus heterojunction type photocatalyst, the preparation method comprises: (1) weighing red phosphorus, grinding and passing through a 150-250 mesh sieve, washing and drying the portion under the sieve; (2) weighing the red phosphorus treated in step (1) and mixing it with hexagonal boron nitride in a container, wherein the mass ratio of red phosphorus to hexagonal boron nitride is 1:1-4; (3) adding ethylenediamine and dispersing it by ultrasonication for 20-60 minutes; (4) reacting the mixture in an autoclave at 150-170°C for 18-36 hours to obtain a crude product; (5) washing the obtained crude product with anhydrous ethanol and deionized water, and vacuum drying it at 35-45°C for 20-30 hours to obtain a boron nitride black phosphorus heterojunction type photocatalyst. The photocatalytic preparation method of this scheme can improve the problem of generally low catalytic efficiency of traditional photocatalysts; at the same time, h-BN / BP has excellent acid and alkali resistance; in addition, the cost is low and the preparation process is simple.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a preparation method and application of a boron nitride-black phosphorus heterojunction photocatalyst and a method for purifying dye wastewater. Background Art

[0002] Organic dyes are widely used in industries such as textiles, papermaking, and food, and as much as 100,000 tons of them are discharged into the environment annually. Dye wastewater is characterized by high organic content, dark color, significant water quality variability, high biotoxicity, and resistance to degradation. Direct discharge into external water bodies without treatment can cause serious environmental pollution, waste resources, and harm human health. Therefore, dye wastewater treatment is crucial for environmental protection, resource recovery, and human health and safety.

[0003] The unique organic pollutants in dye wastewater are not only extremely complex in composition but also highly toxic. Efficiently, rapidly, and cost-effectively converting these organic compounds into non-toxic products is a key concern for researchers. Photocatalysis, an emerging advanced chemical oxidation technology, utilizes light energy to generate highly oxidizing active species (such as hydroxyl radicals and superoxide radicals). These active species combine with dyes to initiate redox reactions, disrupting the dye structure and effectively degrading many difficult-to-degrade organic compounds in dye wastewater into non-toxic or low-toxic small molecules. This method offers low energy consumption, fast reaction times, and zero secondary pollution, demonstrating excellent degradation efficiency for a wide range of difficult-to-degrade organic dye wastewaters. However, the catalytic efficiency of current photocatalytic technologies remains to be improved. Methods for enhancing photocatalytic efficiency include: 1) enhancing efficiency by absorbing the entire solar spectrum, such as ultraviolet, visible light, and near-infrared light; and 2) improving catalyst efficiency by reducing the recombination of photoinduced charge pairs, such as through band gap design.

[0004] To develop efficient photocatalysts, researchers have prepared various 2D photocatalytic materials, such as transition metal oxides, transition metal sulfides, perovskites, and graphitic carbon nitride. However, many metal photocatalysts contain heavy metals and toxic elements, which can cause secondary pollution. Oxide catalysts also suffer from limitations such as difficulty in modification and poor acid and alkali resistance, which severely limit their industrial application. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a preparation method, application and purification method of dye wastewater of a boron nitride black phosphorus heterojunction photocatalyst. The preparation method of this scheme forms a heterojunction composite structure by uniformly loading h-BN on BP, effectively regulating the band gap width, enhancing the light response ability, and improving the photocatalytic removal rate of organic dyes, thereby improving the problem of generally low catalytic efficiency of traditional photocatalysts. At the same time, h-BN / BP has excellent acid and alkali resistance and can be used in a wide pH range to meet the application needs of different conditions. In addition, the preparation method of this scheme is low in cost and simple in preparation process.

[0006] The technical solutions adopted in the present invention are as follows:

[0007] A method for preparing a boron nitride-black phosphorus heterojunction photocatalyst comprises the following steps:

[0008] (1) Weigh red phosphorus, grind it, and pass it through a 150-250 mesh sieve. Wash and dry the portion below the sieve.

[0009] (2) Weighing the red phosphorus treated in step (1) and hexagonal boron nitride and mixing them in a container, wherein the mass ratio of red phosphorus to hexagonal boron nitride is 1:1 to 4;

[0010] (3) Add ethylenediamine and disperse using ultrasound for 20 to 60 minutes;

[0011] (4) reacting the mixture in an autoclave at 150-170° C. for 18-36 hours to obtain a crude product;

[0012] (5) The obtained crude product is washed with anhydrous ethanol and deionized water, and vacuum dried at 35-45°C for 20-30h to obtain a boron nitride-black phosphorus heterojunction photocatalyst.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. Hexagonal boron nitride (h-BN) and black phosphorus (BP) are new non-metallic semiconductor materials, among which h-BN has a wide band gap, good optical properties, chemical inertness and stability. In particular, the sheet-like h-BN has the characteristics of large specific surface area, strong adsorption capacity, and adjustable band gap. The BP nanostructure has unique band gap tunability (i.e., the band gap is adjusted by controlling the number of layers) and excellent carrier mobility. The method of this invention can be used to prepare h-BN / BP heterojunction photocatalysts. By uniformly loading h-BN on BP to form a heterojunction composite structure, the band gap width can be effectively regulated, the light response ability is enhanced, and the photocatalytic removal rate of organic dyes is improved, thereby improving the generally low catalytic efficiency of traditional photocatalysts. At the same time, h-BN / BP has excellent acid and alkali resistance and can be used in a wide pH range to meet the application needs of different conditions.

[0015] 2. This scheme prepares hexagonal boron nitride-black phosphorus composite photocatalysts, and uses red phosphorus as the raw material for preparation. Compared with using black phosphorus as the raw material, the cost is greatly reduced. The traditional idea is usually to carry out the compounding in steps. The first step is to prepare monomers such as black phosphorus, and the second step is to compound the monomers. The step-by-step method is cumbersome, and the black phosphorus product obtained in the first step is prone to loss of yield and oxidation and deterioration during step switching. Although BP has unique physicochemical properties, its water-oxygen instability seriously affects its application potential in photocatalysis and other aspects. It is urgent to find a method to reduce the surface oxidation of BP. Through a one-step solvothermal method, red phosphorus generates black phosphorus in situ and spontaneously composites with h-BN, which not only shortens the preparation process and makes the synthesis process simpler, but also effectively avoids the oxidation of BP. The h-BN / BP prepared by this scheme has excellent photocatalytic degradation performance and excellent stability. It solves the shortcomings of insufficient inherent band gap of h-BN and poor water-oxygen stability of BP, thereby enhancing its application potential in the field of sewage treatment.

[0016] 3. In this scheme, when the red phosphorus (RP) content is 20% or 30%, the rate of dark adsorption equilibrium to photocatalytic reaction is relatively slow. This is because the composite catalyst provides fewer effective active sites, and the dye cannot adhere well to the catalyst surface. The degradation efficiency of methylene blue (MB) solution is less than 60%. When the RP content is 40%, the degradation efficiency of the composite material for MB solution increases to 70%. When the RP content is 50% to 80%, the degradation efficiency of MB solution is further improved to 80%+. The increase in RP content provides more reactive sites and increases the specific surface area, which facilitates MB adsorption on the photocatalyst surface and promotes MB degradation.

[0017] As a preferred embodiment of the present invention, the mass ratio of red phosphorus to hexagonal boron nitride is 1: 1. With this ratio of red phosphorus to hexagonal boron nitride, the prepared catalyst has a better degradation rate of MB in organic dye wastewater.

[0018] As a preferred embodiment of the present invention, the reaction temperature in step (4) is 160°C, and the reaction time is 20-25 hours. This scheme employs the above reaction temperature and reaction time ranges to effectively improve the catalytic efficiency of the final catalyst prepared. Regarding the reaction temperature, temperature has a significant impact on the formation of the composite material. The catalyst's MB removal rate first increases and then decreases with increasing temperature. Both lower and higher temperatures are not conducive to the formation of BP. The reduced BP generated affects the photocatalyst's ability to absorb light, thereby affecting the removal efficiency. Regarding the reaction time, as the reaction time increases, RP continues to activate and convert into BP, increasing the generated h-BN / BP ratio and gradually improving the material's MB degradation efficiency. As the reaction time continues to increase, the composite catalyst's MB degradation efficiency gradually decreases. This is because, if the reaction time is too long, BP agglomerates, reducing the specific surface area and the number of exposed active sites, resulting in a decrease in photocatalytic efficiency.

[0019] As a preferred embodiment of the present invention, prior to step (2), the method further includes the step of fluorinating the hexagonal boron nitride. After the hexagonal boron nitride is fluorinated, F-BN / BP can be finally prepared. The surface roughness of the fluorinated catalyst is significantly increased. The successful doping of fluorine creates more defect sites on the surface of the composite catalyst, thereby exposing more active sites, effectively promoting the improvement of the degradation rate of MB in organic dye wastewater by the photocatalyst.

[0020] As a preferred embodiment of the present invention, the fluorination modification comprises the following steps:

[0021] (1) NH4F and hexagonal boron nitride were dissolved in distilled water at a ratio of 2:1, and hexagonal boron nitride was dispersed in the NH4F solution under the assistance of ultrasound;

[0022] (2) Transfer the mixture into a reactor and heat at 185-195°C for 10-12 hours.

[0023] (3) After natural cooling, the product boron nitride fluoride is collected, cleaned and dried.

[0024] The above-mentioned fluorination modification method is simple, and hexagonal boron nitride can be modified into fluorinated boron nitride (F-BN), and finally an F-BN / BP composite material is prepared. The fluorinated catalyst still has good stability, and the surface roughness is increased. The successful doping of fluorine causes more defect sites on the surface of the composite catalyst, exposing more active sites, and its efficiency in photodegrading methylene blue dye is also significantly improved.

[0025] The application of the boron nitride black phosphorus heterojunction photocatalyst as described in the above scheme is used for the purification of dye wastewater.

[0026] Using the above-mentioned boron nitride black phosphorus heterojunction photocatalyst for the purification of dye wastewater can improve the photocatalytic efficiency of organic dyes. Compared with single h-BN and BP materials, the removal rate of MB wastewater is significantly enhanced by more than 80%. The removal rate of MB wastewater by single h-BN and BP materials is less than 40%.

[0027] The present invention also provides a method for purifying dye wastewater, comprising the following steps:

[0028] (1) The MB concentration in the dye wastewater was adjusted to 30 mg / L, and the dye wastewater was placed in a photocatalytic degradation reaction device in the dark. By mass, 30-40 mg of boron nitride black phosphorus heterojunction photocatalyst was added per 100 ml of dye wastewater, and dark adsorption was carried out for 50-70 minutes;

[0029] (2) Turn on the light source and react for 1 to 3 hours. The degradation reaction uses an ultraviolet lamp as the light source and is ventilated and stirred with an oxygen pump;

[0030] (4) Take samples every 25 to 35 minutes and measure the absorbance.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The purification method described above, based on a boron nitride-black phosphorus heterojunction photocatalyst, significantly enhances the MB wastewater removal rate to over 80% compared to single h-BN and BP materials. Furthermore, the composite material's MB degradation efficiency is unaffected by pH, allowing for application across a wide range of pH conditions, demonstrating its universal applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a scanning electron microscope image of the catalyst prepared in Example 1 of the preparation method of a boron nitride black phosphorus heterojunction photocatalyst of the present invention ( Figure 1 a) and element distribution diagram ( Figure 1 bd);

[0034] Figure 2 is the degradation efficiency of h-BN, BP and Example 1 (h-BN / BP) heterojunction photocatalyst for dye wastewater;

[0035] Figure 3 The effect of different pH on MB removal rate. DETAILED DESCRIPTION

[0036] Typical embodiments that embody the features and advantages of the present invention are described in detail in the following description. It should be understood that the present invention is capable of various variations in different embodiments without departing from the scope of the present invention, and that the descriptions and illustrations are intended to be illustrative rather than limiting.

[0037] Example 1

[0038] A method for preparing a boron nitride-black phosphorus heterojunction photocatalyst comprises the following steps:

[0039] (1) Weigh 4 g of red phosphorus, grind it, and pass it through a 200-mesh sieve. Wash the sieve portion three times with deionized water and dry it in a vacuum drying oven at 35°C for 24 h.

[0040] (2) weighing the red phosphorus pretreated in step (1) and mixing it with hexagonal boron nitride, wherein the mass ratio of red phosphorus to hexagonal boron nitride is 1:1;

[0041] (3) Add 60 ml of ethylenediamine and disperse evenly using ultrasound for 20-30 min;

[0042] (4) The mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 160°C for 24 h to obtain a crude product;

[0043] (5) The obtained crude product was washed with anhydrous ethanol and deionized water, and vacuum dried at 40°C for 24 h to obtain a boron nitride-black phosphorus heterojunction photocatalyst.

[0044] The boron nitride black phosphorus heterojunction photocatalyst prepared in Example 1 was subjected to electron microscopy scanning detection and elemental analysis, and the scanning electron microscopy image ( Figure 1 a) and element distribution diagram ( Figure 1 bd).

[0045] like Figure 1 As shown in a, BP is used as the matrix material, and h-BN is loaded on the surface more evenly. The successful composite of h-BN and BP significantly increases the specific surface area of ​​BP, providing more reaction active sites for photocatalytic organic dyes.

[0046] Depend on Figure 1 (bd) It can be seen that the P, N, and B elements are evenly distributed, and the composite strategy improves the dispersibility of h-BN, which is beneficial to the exposure of active sites and promotes the degradation of MB in organic dye wastewater by photocatalysis.

[0047] Example 2

[0048] The difference between this embodiment and embodiment 1 is that the mass ratio of red phosphorus to hexagonal boron nitride in step (2) is 1:1.5.

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the mass ratio of red phosphorus to hexagonal boron nitride in step (2) is 1:2.3.

[0051] Example 4

[0052] The difference between this embodiment and embodiment 1 is that the mass ratio of red phosphorus to hexagonal boron nitride in step (2) is 1:4.

[0053] Example 5

[0054] The difference between this embodiment and embodiment 1 is that the reaction temperature of step (4) is 150° C. and the reaction time is 24 h.

[0055] Example 6

[0056] The difference between this embodiment and embodiment 1 is that the reaction temperature of step (4) is 170° C. and the reaction time is 24 h.

[0057] Example 7

[0058] The difference between this embodiment and embodiment 1 is that the reaction temperature of step (4) is 160° C. and the reaction time is 18 h.

[0059] Example 8

[0060] The difference between this embodiment and embodiment 1 is that the reaction temperature of step (4) is 160° C. and the reaction time is 36 h.

[0061] Example 9

[0062] A method for preparing a boron nitride-black phosphorus heterojunction photocatalyst comprises the following steps:

[0063] (1) Weigh 4 g of red phosphorus, grind it, and pass it through a 200-mesh sieve. Wash the sieve portion three times with deionized water and dry it in a vacuum drying oven at 35°C for 24 h.

[0064] (2) NH4F and h-BN were dissolved in 50 mL of distilled water at a mass ratio of 2:1. h-BN was dispersed in the NH4F solution with the aid of ultrasound for 30 min.

[0065] (3) The mixture was transferred into a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 200 °C for 12 h.

[0066] (4) After natural cooling, the product fluorinated boron nitride (F-BN) was collected and washed with ultrapure water, and dried in a constant temperature drying oven at 40°C;

[0067] (5) Weighing the red phosphorus pretreated in step (2) and mixing it with boron nitride fluoride, wherein the mass ratio of red phosphorus to boron nitride fluoride is 1:1;

[0068] (6) Add ethylenediamine and disperse it evenly using ultrasound for 20-30 minutes;

[0069] (7) The mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 160°C for 24 h to obtain a crude product;

[0070] (8) The obtained crude product was washed with anhydrous ethanol and deionized water, and vacuum dried at 40 °C for 24 h to obtain a fluorinated boron nitride-black phosphorus heterojunction photocatalyst.

[0071] The present invention also provides a method for purifying dye wastewater, comprising the following steps:

[0072] (1) 100 mL of MB dye wastewater was placed in a photocatalytic degradation reaction device in the dark. The MB content in the MB dye wastewater was adjusted to 30 mg / L. 30 mg of boron nitride black phosphorus heterojunction photocatalyst was added by mass. The pH value was about 7, and dark adsorption was performed for 60 minutes.

[0073] (2) Turn on the light source and react for 3 h. The degradation reaction uses a 254 nm, 20 W ultraviolet lamp as the light source, 5 cm away from the reaction tube, and is ventilated and stirred with an aerator. The power of the aerator pump is 3 W and the exhaust flow rate is 4 L / min.

[0074] (3) After turning on the light source, take a sample every 30 minutes and measure the absorbance.

[0075] According to the above purification method, the catalysts h-BN / BP prepared in Examples 1 to 8, the catalyst F-BN / BP prepared in Example 9, and single BP and h-BN were used to degrade MB dye wastewater.

[0076] The removal capacity of MB wastewater by BP, h-BN, h-BN / BP (Examples 1 to 8), and F-BN / BP (Example 9) with a dosage of 30 mg was studied. The degradation efficiency results are shown in Table 1 and Figure 2 shown.

[0077] Step (1) After dark adsorption is completed and adsorption equilibrium is reached, 5 mL of the sample is taken and diluted to 25 mL, the sample is filtered with a 0.22 μm water filter, and the absorbance at a wavelength of 664 nm is measured using a UV-visible spectrophotometer, which is recorded as C0;

[0078] The absorbance measured in step (4) is recorded as C t .

[0079] Table 1 Degradation efficiency of BP, h-BN and h-BN / BP (Examples 1 to 4)

[0080]

[0081]

[0082] As shown in Table 1 and Figure 2 As shown, the boron nitride-black phosphorus heterojunction photocatalyst of this embodiment significantly enhances the removal efficiency of MB wastewater to over 80%, while the removal efficiency of h-BN and BP materials alone is less than 40%. The photocatalyst prepared by this solution significantly improves the photocatalytic removal efficiency of organic dyes, effectively improving the generally low catalytic efficiency of traditional photocatalysts.

[0083] As shown in Table 1, compared with Examples 1-4, when the mass ratio of red phosphorus to hexagonal boron nitride is 1:1, the degradation rate of the prepared catalyst is the highest, reaching 92.35%. The preferred mass ratio of red phosphorus to hexagonal boron nitride in the present invention is 1:1.

[0084] As shown in Table 1, compared with Example 1, Examples 5-8, the degradation rate of the catalyst prepared using the reaction temperature (160°C) and reaction time (24h) of Example 1 is the highest. The preferred reaction temperature of the present invention is 160°C and the reaction time is 20-25h.

[0085] The boron nitride black phosphorus heterojunction photocatalyst prepared in Example 1 was used to purify MB dye wastewater under different pH environments. The purification method was the same as described in the example. The effects of different pH on MB removal rates were shown in Tables 2 and 3. Figure 3 shown.

[0086] Table 2 Effect of different pH on MB removal rate

[0087]

[0088] From Table 2 and Figure 3 It can be seen that the boron nitride black phosphorus heterojunction photocatalyst prepared by the present invention has excellent acid and alkali resistance. When the pH is in the range of 4 to 10, the photocatalytic removal rate of the photocatalyst for organic dyes fluctuates little. The photocatalyst prepared by the present invention can be used in a wide pH range to meet the application needs under different conditions.

[0089] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a boron nitride-black phosphorus heterojunction photocatalyst, characterized in that: The following steps are involved: (1) Weigh red phosphorus, grind it and pass it through a 150-250 mesh sieve. Wash and dry the part below the sieve. (2) Weigh the red phosphorus treated in step (1) and the fluorinated hexagonal boron nitride and mix them in a container, with the mass ratio of red phosphorus to hexagonal boron nitride being 1:(1-4); (3) Add ethylenediamine and disperse using ultrasound for 20 to 60 minutes; (4) reacting the mixture in an autoclave at 150-170°C for 18-36 hours to obtain a crude product; (5) The obtained crude product is washed with anhydrous ethanol and deionized water, and vacuum dried at 35-45°C for 20-30h to obtain a boron nitride-black phosphorus heterojunction photocatalyst; Before step (2), the method further includes a step of fluorinating the hexagonal boron nitride, wherein the fluorinating modification includes the following steps: (1) NH4F and hexagonal boron nitride are dissolved in distilled water, and hexagonal boron nitride is dispersed in the NH4F solution with the assistance of ultrasound; (2) Transfer the mixture to a reactor and heat at 185-195°C for 10-12 hours; (3) After natural cooling, collect the product boron nitride fluoride, clean and dry it.

2. The method for preparing a boron nitride-black phosphorus heterojunction photocatalyst according to claim 1, wherein: The mass ratio of the red phosphorus to the hexagonal boron nitride is 1:

1.

3. The method for preparing a boron nitride-black phosphorus heterojunction photocatalyst according to claim 1, wherein: The reaction temperature of step (4) is 160° C., and the reaction time is 20 to 25 h.

4. The method for preparing a boron nitride-black phosphorus heterojunction photocatalyst according to claim 1, wherein: In the fluorination modification, the mass ratio of NH4F to hexagonal boron nitride is 2:

1.

5. Use of the boron nitride black phosphorus heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 4 for purification of dye wastewater.

6. A method for purifying dye wastewater, characterized in that: The steps include: (1) The MB concentration in the dye wastewater is adjusted to 30 mg / L, and the dye wastewater is placed in a photocatalytic degradation reaction device in the dark. By mass, 30 to 40 mg of the boron nitride black phosphorus heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 4 is added to every 100 ml of the dye wastewater, and dark adsorption is carried out for 50 to 70 minutes; (2) Turn on the light source and react for 1 to 3 hours. The degradation reaction uses an ultraviolet lamp as the light source and uses an oxygen pump for ventilation and stirring; (3) Take samples every 25 to 35 minutes and measure the absorbance.

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