Preparation method of double-s heterojunction photocatalyst and application of degrading antibiotic

Abstract

The application provides a preparation method of a double-S heterojunction photocatalyst, comprising the following steps: dispersing nitrogen-defect-containing carbon nitride and beta-Bi2O3 in a solvent according to a certain proportion, and then removing the solvent to obtain a mixed powder; and performing calcination treatment on the mixed powder to obtain an alpha-Bi2O3 / beta-Bi2O3 / DCN double-S heterojunction photocatalyst. In the prepared catalyst, Bi2O3 exists in alpha and beta two crystal phases, and is compounded with DCN to form a double-S heterojunction structure. The heterojunction photocatalytic material combined with defect engineering and phase transition synthesis has good light absorption characteristics and excellent free radical production capacity, and has low preparation cost and simple method. The alpha-Bi2O3 / beta-Bi2O3 / DCN double-S heterojunction photocatalyst is mixed with water containing antibiotics, and a photocatalytic reaction is performed under visible light, so that efficient degradation of the antibiotics in the water can be realized.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis technology, specifically relating to a method for preparing a double S-type heterojunction α-Bi2O3 / β-Bi2O3 / DCN catalyst, and the application of this catalyst in the efficient degradation of antibiotics under visible light. Background Technology

[0002] Antibiotics are widely used to treat and prevent human and animal diseases, but their large-scale emissions and accumulation have led to severe water and soil pollution. Currently, various methods for remediating antibiotic pollution have been reported, including adsorption, electrocatalysis, bioremediation, and photocatalytic oxidation-reduction. Among these, photocatalysis technology has received widespread attention due to its environmental friendliness, low cost, and lack of secondary pollution.

[0003] Graphitic carbon nitride (g-C3N4) is considered one of the most promising non-metallic photocatalysts due to its controllable synthesis, high stability, and non-toxicity, and has been used for solar energy collection and pollutant degradation. However, g-C3N4 suffers from problems such as low specific surface area, high photogenerated charge recombination rate, and insufficient visible light absorption, which limit its photocatalytic efficiency. To address these issues, researchers have developed various modification strategies, including elemental doping, defect engineering, semiconductor recombination, and morphology manipulation. Among these, defect engineering can effectively tune the electronic band structure of g-C3N4, making it a direct and effective modification method.

[0004] On the other hand, Bi₂O₃, as an excellent metal semiconductor photocatalyst, typically exists in various crystal phases, including monoclinic (α), tetragonal (β), hexagonal (γ), and face-centered cubic (δ). Studies have shown that phase transformations in Bi₂O₃ can be induced by controlling reaction conditions. The heterogeneous interfaces formed between different crystal phases, due to their band structure matching, are beneficial for the separation of photogenerated carriers, thereby improving photocatalytic performance.

[0005] Although defect-modified g-C3N4 and mixed-phase Bi2O3 have been studied separately, effective composite synthesis remains a technical challenge. This challenge involves simultaneously addressing the controllable introduction of nitrogen defects from g-C3N4, the in-situ conversion of β-Bi2O3 to α-Bi2O3 to form a mixed phase, and the formation of a double-S-type heterojunction interface between α-Bi2O3, β-Bi2O3, and DCN. Existing methods are often complex in steps and lack tight interfacial bonding, making it difficult to simultaneously meet these requirements within the same system.

[0006] Based on this, a photocatalyst capable of simultaneously introducing nitrogen defects, generating biphase Bi2O3 in situ, and constructing a double S-type heterostructure, along with its simple and efficient preparation method, is needed to achieve efficient and rapid degradation of antibiotics in water. This is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for preparing an α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst. This method involves mixing nitrogen-defective carbon nitride with β-Bi2O3 and then calcining the mixture to generate α / β biphase Bi2O3 in situ and construct a double S-type heterojunction. This method is characterized by its simple operation and tight interfacial bonding.

[0008] The second objective of this invention is to provide an α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst prepared by the above preparation method. This catalyst simultaneously contains α-Bi2O3, β-Bi2O3, and nitrogen-defective carbon nitride, which form a double S-type heterojunction structure, resulting in high photogenerated carrier separation efficiency.

[0009] The third objective of this invention is to provide an application of the above-mentioned α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst in the degradation of antibiotics. This catalyst can efficiently and rapidly degrade antibiotics in water under visible light irradiation and has good stability.

[0010] One of the technical solutions adopted by this invention to achieve its objective is to provide a method for preparing a double S-type heterojunction photocatalyst, characterized by comprising the following steps: Nitrogen-defective carbon nitride and β-Bi2O3 are dispersed in a solvent at a mass ratio of 1-6:1, and then the solvent is removed to obtain a mixed powder. The mixed powder is calcined at 300-400℃ for 0.5-1.5h to obtain an α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst.

[0011] The overall concept and inventive principle of this invention are as follows: This invention disperses nitrogen-deficient carbon nitride (DCN) and β-Bi₂O₃ in a solvent in a suitable ratio, and then evaporates the solvent to obtain a uniform mixed powder. The mixed powder is then calcined at a suitable temperature for a certain time. During this heat treatment, the β-Bi₂O₃ in the mixed powder undergoes a partial phase transformation, generating α-Bi₂O₃ in situ, forming an α / β-Bi₂O₃ mixed phase, which then forms a double-S-type α-Bi₂O₃ / β-Bi₂O₃ / DCN photocatalyst with DCN. In the resulting catalyst, nitrogen-deficient carbon nitride (DCN) contains nitrogen ions. V The introduction of αβ-Bi2O3 modulates the band structure, and the mixed phase with αβ-Bi2O3 dual interface contact promotes the formation of double S-type heterojunction. The three work together to construct a double S-type heterojunction photocatalyst.

[0012] The principle behind the enhanced photocatalytic performance resulting from this structure is as follows: Ultraviolet photoelectron spectroscopy (UPS) analysis reveals that the work function of the nitrogen-defective carbon nitride DCN5-DCN20 (graphitic carbon nitride to sodium borohydride mass ratio of 5-20:1) prepared in this invention is 1.83-2.24 eV, while the work function values ​​of β-Bi2O3 and α-Bi2O3 are 2.49 and 2.74 eV, respectively. Due to the difference in Fermi levels, electrons spontaneously migrate from the nitrogen-defective carbon nitride to β-Bi2O3, and further from β-Bi2O3 to α-Bi2O3, until the interface reaches equilibrium. This process establishes internal electric fields (IEFs) at the DCN / β-Bi2O3 and β-Bi2O3 / α-Bi2O3 interfaces, pointing from the nitrogen-defective carbon nitride towards β-Bi2O3 and from β-Bi2O3 towards α-Bi2O3, respectively. Under visible light irradiation, the tandem built-in electric field promotes the recombination of photogenerated electrons in the conduction band of α-Bi₂O₃ with holes in the valence band of β-Bi₂O₃, while electrons in the conduction band of β-Bi₂O₃ recombine with holes in the valence band of nitrogen-defective carbon nitride. Ultimately, electrons with strong reducing power are retained in the conduction band of nitrogen-defective carbon nitride, while holes with high oxidizing power accumulate in the valence band of α-Bi₂O₃, forming a typical double-S-type charge transfer pathway. This double-S-type heterojunction significantly suppresses the recombination of photogenerated carriers and retains a high redox potential, thereby endowing the catalyst with excellent photocatalytic degradation performance of antibiotics.

[0013] In this invention, the mass ratio of nitrogen-defective carbon nitride (DCN) to β-Bi₂O₃ is 1-6:1. Studies have shown that when the proportion of αβ-Bi₂O₃ in the heterojunction is too high, some effective active sites may be shielded by Bi₂O₃, leading to a decrease in photocatalytic performance. Conversely, excessive loading of DCN also weakens the dominant role of αβ-Bi₂O₃ as the host of the heterojunction, which is also detrimental to photocatalytic activity.

[0014] Furthermore, the calcination temperature of the mixed powder is controlled between 300-400℃, and the calcination time is controlled between 0.5-1.5h. Excessive temperature or prolonged calcination time will lead to the complete conversion of β-Bi₂O₃ to α-Bi₂O₃. According to UV-Vis diffuse reflectance spectroscopy, α-Bi₂O₃ has weaker absorption of visible light than β-Bi₂O₃, resulting in lower photocatalytic performance of α-Bi₂O₃ compared to β-Bi₂O₃. Simultaneously, based on the Fermi electrode formation mechanism of this invention, only a suitable ratio of α-Bi₂O₃ and β-Bi₂O₃ mixed phases can facilitate interfacial contact, forming a heterojunction material and improving the photocatalytic performance of the material.

[0015] Furthermore, the nitrogen-defect-containing carbon nitride is obtained by mixing graphitic carbon nitride and sodium borohydride at a mass ratio of 5-20:1 and then calcining. The calcination temperature is 300-400℃, the time is 20-40 min, and the calcination is carried out under an inert atmosphere. Sodium borohydride (NaBH4) is a strong reducing agent, which is beneficial for the generation of nitrogen defects at low temperatures. Simultaneously, the mass ratio of graphitic carbon nitride to sodium borohydride also determines the photocatalytic performance of the catalyst; for example, the excessive introduction of nitrogen-defect-containing carbon nitride... V This can lead to the destruction of the BCN structure, thereby reducing photocatalytic activity. Preferably, the mass ratio of graphitic carbon nitride to sodium borohydride is 10:1, and studies have found that this ratio provides the optimal photocatalytic performance.

[0016] Furthermore, the graphitic carbon nitride is prepared by calcining dicyandiamide at 500-600℃ for 4-6 hours.

[0017] Further, the preparation method of β-Bi₂O₃ includes: dissolving bismuth nitrate pentahydrate (Bi(NO₃)₃·5H₂O) in dilute nitric acid solution, adding citric acid, adjusting the pH of the solution to 3-5, and carrying out a hydrothermal reaction; the product is washed, dried, ground, and calcined to obtain β-Bi₂O₃. Bi(NO₃)₃·5H₂O, as a raw material, can dissolve well in dilute nitric acid solution, balancing cost and efficiency to obtain suitable β-Bi₂O₃. Citric acid forms a complex with Bi, controlling the formation of the precursor and facilitating the subsequent formation of the β-Bi₂O₃ crystal phase. Preferably, the mass ratio of bismuth nitrate pentahydrate to citric acid is 1-2:1. This step of adjusting the solution pH to 3-5 is beneficial to the formation of the Bi-citric acid complex and does not affect the synthesis of subsequent materials.

[0018] Furthermore, the hydrothermal reaction is carried out at a temperature of 150-200℃ for a time of 12-36 hours, and suitable temperature and time are conducive to the full reaction of the materials.

[0019] Furthermore, the calcination temperature is 300-400℃ and the time is 1.5-2.5h.

[0020] Furthermore, the concentration of the dilute nitric acid solution is 0.05-0.2 mol / L, and the pH is adjusted using a sodium hydroxide solution with a concentration of 1-3 mol / L.

[0021] Further, the mass ratio of the nitrogen-defective carbon nitride to β-Bi₂O₃ is 3-5:1, and the solvent is ethanol. Ethanol has low surface tension, which allows it to better wet the surface of the raw material powder, reduce particle agglomeration, and promote full contact between the two phases during mixing. Simultaneously, the volatility of ethanol ensures that the mixed powder retains a uniform dispersion during drying, which is more conducive to forming a denser heterojunction interface. Furthermore, ethanol has relatively mild chemical properties and will not damage the original crystalline phase and surface structure of the material. Preferably, the ratio of raw material to ethanol is 5-20 mg / mL.

[0022] Furthermore, during the calcination of a mixture of nitrogen-deficient carbon nitride and β-Bi2O3, the heating rate was controlled at 4-6 °C / min.

[0023] The second objective of this invention is to provide a double S-type heterojunction photocatalyst, which is prepared by the preparation method described in the first objective of this invention. The catalyst contains α-Bi2O3, β-Bi2O3 and nitrogen-defective graphitic carbon nitride, and forms a double S-type heterojunction structure.

[0024] The third objective of this invention is to provide the application of the double S-type heterojunction photocatalyst described in the second objective of this invention in the degradation of antibiotics. The double S-type heterojunction photocatalyst is mixed with water containing antibiotics and a photocatalytic reaction is carried out under visible light irradiation to achieve the degradation of antibiotics.

[0025] Furthermore, the wavelength range of the visible light irradiation is 380-780 nm.

[0026] Furthermore, the mass ratio of the double S-type heterojunction photocatalyst to the antibiotic is 5-20:1.

[0027] Furthermore, before irradiation with visible light, the catalyst is pre-adsorbed by stirring and mixing with the antibiotic water for 10-120 min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention provides a method for preparing α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunctions. The method involves a hydrothermal combined with calcination process. First, dicyandiamide is calcined at 500-600℃ to obtain BCN. Then, NaBH4 is used to etch the BCN to introduce nitrogen vacancies (N). VThe process involves obtaining nitrogen-deficient carbon nitride (DCN), then mixing DCN with β-Bi₂O₃ in a suitable ratio and calcining at 300-400℃ for 0.5-1.5 h to obtain the final product. In the catalyst prepared by this invention, Bi₂O₃ exists in both α and β crystal phases, forming a double-S-type heterostructure with DCN. The heterojunction photocatalyst material synthesized by this invention, combining defect engineering and phase transformation, possesses excellent light absorption characteristics and superior free radical production capability. Furthermore, it is low-cost and simple to prepare. By mixing the α-Bi₂O₃ / β-Bi₂O₃ / DCN double-S-type heterojunction photocatalyst with water containing antibiotics and carrying out a photocatalytic reaction under visible light, the efficient degradation of antibiotics in water can be achieved.

[0029] (2) The α-Bi₂O₃ / β-Bi₂O₃ / DCN double S-type heterojunction catalyst prepared in this invention for efficient photodegradation of antibiotics successfully introduces nitrogen defects into the BCN material through high-temperature calcination, solving the problems of high charge recombination rate and insufficient light absorption in BCN. Combined with in-situ phase transition, two crystal phases of Bi₂O₃ material are introduced to form a tight interfacial contact. Among them, the three semiconductors α-Bi₂O₃, β-Bi₂O₃ and DCN have matched band structures, forming a double S-type heterostructure, providing a novel electron-hole separation pathway and optimizing photocatalytic performance. This discovery not only provides direction for optimizing catalyst design, but also provides new inspiration for developing effective methods to remove antibiotic pollutants. More importantly, the application of this catalyst to the visible light photocatalytic degradation of antibiotics in actual water bodies can significantly improve the degradation efficiency, and has the advantages of simple operation, environmental friendliness, and reusability, providing an efficient and feasible technical solution for solving the problem of antibiotic pollution. Attached Figure Description

[0030] Figure 1 The reaction mechanism diagram of the double S-type heterojunction photocatalyst provided by the present invention; Figure 2 The image shows a scanning electron microscope (SEM) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1. Figure 3 High-resolution transmission electron microscopy (HRTEM) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1. Figure 4 Energy dispersive X-ray spectroscopy (EDS) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1. Figure 5 The XRD pattern of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1; Figure 6The electron paramagnetic resonance (EPR) spectra of the α-Bi2O3 / β-Bi2O3, BCN, DCN10, and αβBODN-4 catalysts prepared in Example 1 are shown below. Figure 7 XPS image of the αβBODN-4 catalyst prepared in Example 1; wherein, Figure 7 a is the C 1s spectrum of the catalyst; Figure 7 b is the N 1s spectrum of the catalyst; Figure 7 c represents the Bi 4f spectrum of the catalyst; Figure 7 d represents the O 1s spectrum of the catalyst; Figure 8 The UV-Vis diffuse reflectance spectra (UV-vis-DRS) of the β-Bi2O3, α-Bi2O3, and DCN10 catalysts prepared in Example 1 are shown in the figure. Figure 8 a) and related Tauc diagrams ( Figure 8 b) Figure 9 VB-XPS images of the DCN10, β-Bi2O3 and α-Bi2O3 catalysts prepared in Example 1; Figure 10 Ultraviolet photoelectron spectroscopy (UPS) of DCN10, β-Bi2O3 and α-Bi2O3 prepared in Example 1; Figure 11 The graph shows the photodegradation performance of the αβBODN-4 catalyst prepared in Example 1 on tetracycline hydrochloride. Figure 12 The graph shows the stability and recyclability test results of the αβBODN-4 catalyst prepared in Example 1. Figure 13 The image shows the experimental test results of active species quenching in the photocatalytic reaction of the αβBODN-4 catalyst prepared in Example 1. Figure 14 The image shows the electron paramagnetic resonance (EPR) test results of the active compound bismuth in the photocatalytic reaction of the αβBODN-4 catalyst prepared in Example 1. Figure 15 The image shows the photodegradation performance of the αβBODN-4 catalyst prepared in Example 1 on the pollutant ofofloxacin. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing a double S-type heterojunction photocatalyst, comprising the following steps: Step 1: Place dicyandiamide in a box furnace and calcine it at 500-600℃ for 4-6 hours to prepare graphitic carbon nitride (BCN); Step 2: Mix graphitic carbon nitride (BCN) and sodium borohydride (NaBH4) at a mass ratio of 5-20:1, place in a tube furnace, and calcine at 300-400℃ for 20-40 minutes under an inert atmosphere to obtain carbon nitride (DCN) containing nitrogen defects. Step 3: Dissolve bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) in a dilute nitric acid solution with a concentration of 0.05-0.2 mol / L. Add citric acid to the solution at a mass ratio of bismuth nitrate pentahydrate to citric acid of 1-2:1. Adjust the pH of the reaction system to 3-5 using a sodium hydroxide solution with a concentration of 1-3 mol / L. Carry out a hydrothermal reaction at 150-200℃ for 12-36 h. After washing, drying, and grinding, place the product in a box furnace and calcine it at 300-400℃ for 1.5-2.5 h to obtain β-Bi2O3.

[0033] Step 4: Disperse nitrogen-deficient carbon nitride and β-Bi2O3 in ethanol at a mass ratio of 1-6:1, and then remove the solvent to obtain a mixed powder; place the mixed powder in a box furnace and calcine it at 300-400℃ for 0.5-1.5h, controlling the heating rate at 4-6℃ / min, to obtain an α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst.

[0034] The reaction mechanism of the α-Bi₂O₃ / β-Bi₂O₃ / DCN double S-type heterojunction photocatalyst provided by this invention is as follows: Figure 1 As shown, semiconductor catalysts with different crystal phases can form interfacial contacts. The two crystal phases of the same semiconductor have well-matched band structures and similar properties, which is conducive to the formation of heterojunctions. After α-Bi2O3 / β-Bi2O3 forms a double S-type heterojunction with DCN, it provides a novel electron-hole separation pathway, retaining electrons and holes with strong redox capabilities, thereby enhancing photocatalytic performance.

[0035] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0036] The main parameters and variables of the various embodiments and comparative examples of the present invention are shown in Table 1 below.

[0037] Table 1

[0038] Example 1 This embodiment provides a method for preparing an α-Bi₂O₃ / β-Bi₂O₃ / DCN double S-type heterojunction catalyst for efficient photodegradation of antibiotics, comprising the following steps: Step 1: Place 8 grams of dicyandiamide in a covered crucible and place it in a box furnace. Calcination temperature is 350 ℃, holding time is 30 min, and heating rate is 5 ℃ / min to obtain BCN.

[0039] Step 2: Then, 1 gram of synthesized BCN was uniformly mixed with 100 mg of NaBH4 and ground. Subsequently, it was placed in a tube furnace and calcined at a high temperature of 350 °C for 30 min with a heating rate of 5 °C / min. The resulting material was named DCN10.

[0040] Step 3: Dissolve 0.97 g of Bi(NO3)3·5H2O in 10 mL of 1 M HNO3 solution and stir continuously for 40 minutes. Then, add 0.64 g of citric acid to the mixture. While stirring, adjust the pH of the solution to 4 using 2 M NaOH solution. Transfer the resulting solution to a 50 mL PTFE-sealed autoclave and heat at 180 °C for 24 hours. After cooling, wash the product several times with deionized water and ethanol, and then dry at 60 °C for 12 hours. Subsequently, calcine it in a box furnace at 350 °C for 2 hours at a heating rate of 5 °C / min to obtain β-Bi2O3.

[0041] Step 4: The products obtained in Steps 2 and 3, along with 50 mg of β-Bi₂O₃ and 200 mg of DCN₁₀, were dispersed in 20 mL of ethanol at room temperature by stirring. The mixture was then dried in a 60 °C oven to remove the solvent. The resulting solid powder was placed in a box furnace and calcined at 350 °C for 1 hour at a heating rate of 5 °C / min to obtain the final product, named αβBODN-4.

[0042] Example 2 The only difference between this embodiment and Embodiment 1 is the mass ratio of DCN to β-Bi2O3 in step 4.

[0043] Step 2: Same as in Example 1, obtain DCN (denoted as DCN10).

[0044] Step 4: Take 150 mg of DCN10 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 3:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 350 °C at a heating rate of 5 °C / min, and calcine it at that temperature for 1 hour. The final product obtained is named αβBODN-3.

[0045] The remaining steps are the same as in Example 1.

[0046] Example 3 The only difference between this embodiment and Embodiment 1 is the mass ratio of DCN to β-Bi2O3 in step 4.

[0047] Step 2: Same as in Example 1, obtain DCN (denoted as DCN10).

[0048] Step 4: Take 250 mg of DCN10 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 5:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 350 °C at a heating rate of 5 °C / min, and calcine it at that temperature for 1 hour. The final product obtained is named αβBODN-5.

[0049] The remaining steps are the same as in Example 1.

[0050] Example 4 The difference between this embodiment and Embodiment 1 lies in the mass ratio of BCN to NaBH4 in step 2, the mass ratio of DCN to β-Bi2O3 in step 4, the calcination temperature, the calcination time, and the heating rate.

[0051] Step 2: Mix 1 gram of BCN obtained in Step 1 with 200 mg of NaBH4 (the mass ratio of BCN to NaBH4 is 5:1) and grind them evenly. Then, put the mixture into a tube furnace and heat it to 350 °C at a heating rate of 5 °C / min. Hold the temperature for 30 min to obtain DCN (denoted as DCN5).

[0052] Step 4: Take 50 mg of DCN5 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 1:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 400 °C at a heating rate of 4 °C / min, and calcine it at that temperature for 0.5 hours. The final product is named αβBODN-1.

[0053] The remaining steps are the same as in Example 1.

[0054] Example 5 The difference between this embodiment and Embodiment 1 lies in the mass ratio of BCN to NaBH4 in step 2, the mass ratio of DCN to β-Bi2O3 in step 4, the calcination temperature, the calcination time, and the heating rate.

[0055] Step 2: Mix 1 gram of BCN obtained in Step 1 with 50 mg of NaBH4 (the mass ratio of BCN to NaBH4 is 20:1) and grind them evenly. Then, put the mixture into a tube furnace and heat it to 350 °C at a heating rate of 5 °C / min. Hold the temperature for 30 min to obtain DCN (denoted as DCN20).

[0056] Step 4: Take 300 mg of DCN20 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 6:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 300 °C at a heating rate of 6 °C / min, and calcine it at that temperature for 1.5 hours. The final product is named αβBODN-6.

[0057] The remaining steps are the same as in Example 1.

[0058] Comparative Example 1 The difference between this comparative example and Example 1 is that calcination is not performed in step 4.

[0059] Step 2: Same as in Example 1, obtain DCN (denoted as DCN10).

[0060] Step 4: Take 200 mg of DCN10 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 4:1), stir and disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent, to obtain a directly physically mixed powder without subsequent calcination treatment, which is recorded as Comparative Example 1 sample.

[0061] The remaining steps are the same as in Example 1.

[0062] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass ratio of DCN to β-Bi2O3 in step 4 is adjusted to make Bi2O3 in excess.

[0063] Step 2: Same as in Example 1, obtain DCN (denoted as DCN10).

[0064] Step 4: Take 25 mg of DCN10 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 0.5:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 350 °C at a heating rate of 5 °C / min, and calcine it at that temperature for 1 hour. The product obtained is recorded as Comparative Example 2 sample.

[0065] The remaining steps are the same as in Example 1.

[0066] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass ratio of DCN to β-Bi2O3 in step 4 is adjusted to make DCN in excess.

[0067] Step 2: Same as in Example 1, obtain DCN (denoted as DCN10).

[0068] Step 4: Take 500 mg of DCN10 obtained in Step 2 and 50 mg of β-Bi2O3 obtained in Step 3 (mass ratio 10:1), disperse them in 20 mL of ethanol at room temperature, and then dry them in an oven at 60 °C to remove the solvent. Place the resulting solid powder in a box furnace, heat it to 350 °C at a heating rate of 5 °C / min, and calcine it at that temperature for 1 hour. The product obtained is recorded as Comparative Example 3 sample.

[0069] The remaining steps are the same as in Example 1.

[0070] Catalyst structure and morphology characterization Figure 2 The image shows a scanning electron microscope (SEM) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1. It can be observed that the granular structure of the material shown in the SEM image is α-Bi2O3 / β-Bi2O3, in which the dispersed plate-like structure is derived from DCN10.

[0071] Figure 3 The high-resolution transmission electron microscope (HRTEM) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1 reveals the tight interfacial contact between the phases, where the lattice spacings of 0.331 nm and 0.273 nm are clearly visible, corresponding to the (111) facet of α-Bi2O3 and the (222) facet of β-Bi2O3, respectively.

[0072] Figure 4 The energy dispersive X-ray spectroscopy (EDS) image of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1 shows the uniform distribution of the four elements Bi, C, N and O, confirming the successful synthesis of the heterojunction.

[0073] Figure 5 The image shows the XRD pattern of the αβBODN-4 double S-type heterojunction catalyst prepared in Example 1. The figure shows the characteristic diffraction peaks of α-Bi2O3, β-Bi2O3 and DCN10, confirming the coexistence of the three phases and verifying the formation of the ternary αβBODN-4 heterojunction.

[0074] Figure 6The electron paramagnetic resonance (EPR) spectra of the α-Bi2O3 / β-Bi2O3, BCN, DCN10, and αβBODN-4 catalysts prepared in Example 1 not only demonstrate the existence of nitrogen defects but also confirm that nitrogen defects are retained in the αβBODN-4 catalyst.

[0075] Figure 7 XPS image of the αβBODN-4 catalyst prepared in Example 1. Figure 7 a represents the C 1s spectrum of the catalyst. Peak splitting confirmed the presence of CC and C-NH in the sample. x Characteristic peaks of NC=N. Figure 7 b is the N 1s spectrum of the catalyst. Peak splitting confirmed that the sample contained characteristic peaks of C–N=C, N-(C)3 and N–H. Figure 7 c represents the Bi 4f spectrum of the catalyst. Peak splitting confirmed that the dominant valence state of Bi in the catalyst is Bi. Ⅲ . Figure 7 d represents the O 1s spectrum of the catalyst. Peak splitting confirmed that the catalyst mainly contains lattice oxygen (O). lat ) and chemically adsorbed oxygen (O) that binds to the catalyst surface after exposure to air. ads ).

[0076] Figure 8 The UV-Vis diffuse reflectance spectra (UV-vis-DRS) and related Tauc plots of the β-Bi₂O₃, α-Bi₂O₃, and DCN₁₀ catalysts prepared in Example 1 are shown. The band gaps of DCN₁₀, β-Bi₂O₃, and α-Bi₂O₃ are 2.82 eV, 2.40 eV, and 2.73 eV, respectively. Figure 7 b).

[0077] Figure 9 The VB-XPS diagrams of the DCN10, β-Bi2O3, and α-Bi2O3 catalysts prepared in Example 1 are shown. The valence bands of DCN10, β-Bi2O3, and α-Bi2O3 are 1.65 eV, 1.70 eV, and 3.19 eV, respectively.

[0078] Figure 10Ultraviolet photoelectron spectroscopy (UPS) of DCN10, β-Bi2O3, and α-Bi2O3 prepared for Example 1 is shown. The work functions of DCN10, β-Bi2O3, and α-Bi2O3 are 1.95, 2.49, and 2.74 eV, respectively. Analysis of the work function values ​​leads to the conclusion that, due to the Fermi level difference, electrons spontaneously migrate from DCN10 to β-Bi2O3, and then from β-Bi2O3 to α-Bi2O3, until interfacial equilibrium is established. Therefore, an internal electric field (IEF) is established at their interface from DCN10 to β-Bi2O3 and from β-Bi2O3 to α-Bi2O3. Under light irradiation, the cascaded IEF promotes recombination between photogenerated electrons in the conduction band of α-Bi2O3 and holes in the valence band of β-Bi2O3, and between electrons in the conduction band of β-Bi2O3 and holes in the valence band of DCN10. Therefore, electrons with strong reducing power are retained in the conduction band of DCN10, while holes with high oxidizing power accumulate in the valence band of α-Bi2O3, corresponding to the double S-type charge transfer path.

[0079] Application performance testing (I) Evaluation of the performance of visible light in degrading tetracycline hydrochloride The catalyst prepared in Example 1 was used for the photodegradation of a typical antibiotic pollutant—tetracycline hydrochloride (a tetracycline). Specifically, a multi-channel photochemical reaction system equipped with a magnetic stirrer and a circulating cooling water circuit was used to simulate sunlight (wavelength = 380-780 nm), with a lamp rated power of 10 W. 20 mg of catalyst was weighed and dispersed in 50 mL of a tetracycline hydrochloride solution containing 30 mg / L. After stirring and adsorption for 60 minutes to reach adsorption equilibrium, the lamp was turned on. At regular intervals, a suitable amount of solution was taken using a disposable syringe and filtered through a 0.45 μm filter. The peak area change was measured using high-performance liquid chromatography (HPLC) to calculate the removal rate of tetracycline hydrochloride.

[0080] like Figure 11 As shown, the αβBODN-4 heterojunction exhibits excellent photodegradation performance of tetracycline hydrochloride, achieving complete degradation of tetracycline hydrochloride within 15 minutes. Calculations revealed that the apparent reaction rate constant of αβBODN-4 reaches 0.373 min. -1 .

[0081] The stability and recyclability of the αβBODN-4 heterojunction were evaluated through continuous cycling tests of TCH degradation under visible light. Figure 12As shown, the removal efficiency decreased from 100% in the first cycle to 90.7% after three cycles within 15 minutes, reflecting a moderate decrease in activity. Nevertheless, complete removal of TCH could still be achieved in the third cycle by extending the irradiation time to 30 minutes, indicating that the catalyst retained considerable photocatalytic performance.

[0082] Free radical quenching experiments were then performed to determine the major reactive species. Ascorbic acid (AA), potassium iodide (KI), and isopropanol (IPA) were used as ·O2. - h + A scavenger of ·OH radicals. For example... Figure 13 As shown, the photocatalytic degradation efficiency of tetracycline hydrochloride was significantly inhibited in the presence of AA, indicating that ·O2 - It plays a dominant role in the reaction. Simultaneously, the addition of KI also led to a significant decrease in degradation efficiency, indicating that photogenerated h... + It participated in the oxidation process. In contrast, the addition of IPA caused almost no change in degradation efficiency, indicating that the role of ·OH in this system is negligible. In summary, these results suggest that ·O2... - It is the main reactive species, while h + It plays an auxiliary role in the photocatalytic degradation process.

[0083] Electron paramagnetic resonance (EPR) tests were performed on the prepared αβBODN-4 catalyst using DMPO as a trapping agent, such as... Figure 14 As shown, αβBODN-4 exhibits a clear DMPO-·O2 - Characteristic signals. These data indicate that the main active species of αβBODN-4 in the degradation of tetracycline hydrochloride is ·O2. - The secondary active species is h + .

[0084] (II) Evaluation of the performance of ofloxacin degrading under visible light The catalyst prepared in Example 1 was used for the photodegradation of another typical antibiotic contaminant—ofloxacin (a fluoroquinolone), such as... Figure 15 As shown, the αβBODN-4 heterojunction exhibits excellent photodegradation performance of ofloxacin, achieving complete degradation of ofloxacin within 15 minutes. Calculations revealed that the apparent reaction rate constant of αβBODN-4 reaches 0.357 min⁻¹. -1 .

[0085] Furthermore, under the same test conditions, the catalytic degradation performance (in terms of reaction rate constant) of the other examples and comparative examples for the two pollutants was tested. Test conditions: catalyst dosage 20 mg, antibiotic solution concentration 30 mg / L, volume 50 mL, visible light irradiation time 15 min. The test results are shown in Table 2 below.

[0086] Table 2

[0087] As can be seen from the above table, Example 1 (DCN to β-Bi₂O₃ mass ratio 4:1) showed a rate constant of 0.373 min for the degradation of tetracycline hydrochloride and ofloxacin. - ¹ and 0.357 min - ¹, all are superior to Examples 2-5. Although the degradation performance of Examples 2 (mass ratio 3:1) and 3 (mass ratio 5:1) is slightly lower than that of Example 1, it still remains at a high level, indicating that 3-5:1 is the preferred mass ratio range. Examples 4 (mass ratio 1:1, calcination temperature 400℃) and 5 (mass ratio 6:1, calcination temperature 300℃) are at the edge of the parameter window, yet catalysts with good catalytic activity can still be obtained, verifying the rationality of the parameter range protected by this invention.

[0088] The degradation rate of Comparative Example 1 (direct mixing without calcination) was significantly reduced, demonstrating that calcination is a key step in the formation of double S-type heterojunctions. The performance of Comparative Example 2 (excess Bi2O3) and Comparative Example 3 (excess DCN) both decreased significantly, indicating that the mass ratio of DCN to β-Bi2O3 needs to be controlled within the range of 1-6:1 to effectively construct double S-type heterojunctions.

[0089] In summary, the α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst prepared in this invention exhibits rapid and efficient photocatalytic degradation performance of tetracycline hydrochloride and ofloxacin under visible light, and also has good stability and recyclability, showing broad application prospects in the field of antibiotic wastewater treatment.

[0090] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a double S-type heterojunction photocatalyst, characterized in that, Includes the following steps: Carbon nitride containing nitrogen defects and β-Bi2O3 are dispersed in a solvent at a mass ratio of 1-6:1, and then the solvent is removed to obtain a mixed powder. The mixed powder was calcined at 300-400℃ for 0.5-1.5h to obtain an α-Bi2O3 / β-Bi2O3 / DCN double S-type heterojunction photocatalyst.

2. The preparation method according to claim 1, characterized in that, The nitrogen-defect-containing carbon nitride is prepared by mixing graphitic carbon nitride and sodium borohydride at a mass ratio of 5-20:1 and calcining at 300-400℃ for 20-40 minutes under an inert atmosphere.

3. The preparation method according to claim 2, characterized in that, The graphitic carbon nitride was prepared by calcining dicyandiamide at 500-600℃ for 4-6 hours.

4. The preparation method according to claim 1, characterized in that, The preparation method of β-Bi2O3 includes: dissolving bismuth nitrate pentahydrate in dilute nitric acid solution, adding citric acid, adjusting the pH of the solution to 3-5, and carrying out a hydrothermal reaction; the product is washed, dried, ground and calcined to obtain β-Bi2O3.

5. The preparation method according to claim 4, characterized in that, The hydrothermal reaction is carried out at a temperature of 150-200℃ for a duration of 12-36 hours.

6. The preparation method according to claim 4, characterized in that, The calcination temperature is 300-400℃ and the time is 1.5-2.5h.

7. The preparation method according to claim 4, characterized in that, The concentration of the dilute nitric acid solution is 0.05-0.2 mol / L, and the pH is adjusted using a sodium hydroxide solution with a concentration of 1-3 mol / L.

8. The preparation method according to claim 1, characterized in that, The mass ratio of the nitrogen-defective carbon nitride to β-Bi2O3 is 3-5:1; the solvent is ethanol; and the heating rate during calcination is 4-6 °C / min.

9. A double S-type heterojunction photocatalyst, prepared by the method according to any one of claims 1-8, characterized in that, The catalyst contains α-Bi2O3, β-Bi2O3 and nitrogen-defective graphitic carbon nitride, forming a double S-type heterojunction structure.

10. The application of the double S-type heterojunction photocatalyst according to claim 9 in the degradation of antibiotics, characterized in that, The double S-type heterojunction photocatalyst is mixed with water containing antibiotics, and a photocatalytic reaction is carried out under visible light irradiation to achieve the degradation of antibiotics.

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