An AgFeO2 / BiOCl nanoheterojunction photocatalyst, its preparation method and application

Abstract

The application discloses an AgFeO2 / BiOCl nano-heterojunction photocatalyst and a preparation method and application thereof, and belongs to the field of nano-photocatalysts. The photocatalyst comprises nano-sheet AgFeO2 and nano-sheet BiOCl, AgFeO2 is uniformly loaded on the surface of BiOCl and forms a closely contacted heterojunction interface, and the mass fraction of AgFeO2 is 10% to 20%. The preparation method comprises the following steps: firstly, preparing nano-sheet BiOCl rich in oxygen vacancies; then dispersing the nano-sheet BiOCl in water, adding silver salt and iron salt, and performing hydrothermal reaction to generate AgFeO2 on the surface of BiOCl in situ. The heterojunction structure is used for promoting the separation of photo-generated carriers, the narrow-band-gap characteristic of AgFeO2 is used for enhancing the visible light response, and excellent photocatalytic degradation performance of Ranna red 5B under visible light is exhibited. The method is simple, the conditions are mild, and the method has a good application prospect in the field of organic pollutant degradation.

Description

Technical Field

[0001] This invention relates to the field of nanophotocatalysts, specifically to an AgFeO2 / BiOCl nanoheterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] Dye wastewater primarily originates from industries such as colored paper, textiles, printing, and leather products. Most of this wastewater is toxic and chemically stable, making it difficult to biodegrade in natural water bodies and posing a sustained threat to the ecological environment. The complex, non-biodegradable substances in dye wastewater persist in water bodies for extended periods, reducing light transmittance, inhibiting algal growth, increasing algal mortality, and affecting photosynthesis in aquatic plants, thus impacting the life activities of aquatic organisms. Some dyes also contain radioactive elements (such as uranium-238 and radium-226), and long-term exposure can seriously harm human health. Furthermore, dye substances and degradation intermediates may pose carcinogenic and mutagenic risks.

[0003] Currently, traditional methods for treating dye wastewater mainly include physical, chemical, and biological methods. Physical methods, such as adsorption and membrane separation, while relatively simple to operate, suffer from problems such as difficult adsorbent regeneration and membrane fouling, resulting in high treatment costs. Furthermore, adsorption only transfers pollutants from the aqueous phase to the solid phase, without achieving complete degradation. Chemical methods, such as coagulation sedimentation and chemical oxidation, require the addition of large amounts of chemical reagents, leading to high operating costs and the generation of large amounts of chemical sludge, causing secondary pollution. Biological methods, while having lower operating costs, have long treatment cycles, poor removal efficiency for recalcitrant organic matter, and are ill-suited to the complex composition and poor biodegradability of dye wastewater. All of these traditional methods have limitations in treating dye wastewater and cannot meet increasingly stringent environmental protection requirements. Therefore, finding a highly efficient, economical dye wastewater treatment technology capable of completely mineralizing organic pollutants is of great significance for reducing ecological risks, protecting water quality, and safeguarding public health.

[0004] Photocatalytic oxidation, as an emerging advanced oxidation technology, can directly utilize sunlight to excite semiconductor catalysts to produce highly oxidizing active species, mineralizing organic pollutants into carbon dioxide and water. It boasts advantages such as mild reaction conditions, no secondary pollution, simple operation, and low operating costs, and is hailed as one of the world's most ideal environmental purification technologies. Since Fujishima and Honda discovered the decomposition of water by TiO2 electrodes under ultraviolet light in 1972, photocatalysis technology has been extensively studied and has demonstrated enormous application potential in the degradation of water pollutants.

[0005] However, traditional photocatalysts generally suffer from the following technical drawbacks: First, they have large band gaps (e.g., TiO2 has a band gap of approximately 3.2 eV, and BiOCl has a band gap of approximately 3.54 eV), enabling them to respond only to short-wavelength ultraviolet light, which accounts for only about 5% of the solar spectrum, resulting in extremely low solar energy utilization. Second, photogenerated electron-hole pairs recombine readily in the bulk phase, leading to short carrier lifetimes and low quantum efficiency. A large number of photogenerated carriers recombine and annihilate before reaching the surface to participate in the reaction, severely limiting the improvement of photocatalytic efficiency. To address these issues, researchers have conducted extensive modification studies, including elemental doping, noble metal deposition, co-catalyst modification, and semiconductor composites. Among these, constructing heterojunction structures is considered one of the most effective modification methods. By compositing two semiconductor materials with matched band structures, a built-in electric field can be formed at the interface, promoting the effective separation of photogenerated electrons and holes, thereby significantly improving photocatalytic activity.

[0006] BiOCl, as a novel photocatalytic material, possesses a unique layered structure. This layered structure generates a built-in electric field, which facilitates the rapid separation of photogenerated carriers, thus attracting widespread attention in the field of photocatalysis. However, BiOCl has a large bandgap (approximately 3.54 eV), meaning it can only be excited by ultraviolet light and cannot effectively utilize visible light, severely limiting its practical application under sunlight conditions. AgFeO2, a narrow bandgap semiconductor material with a bandgap of approximately 1.5-2.0 eV, exhibits stronger visible light response. However, due to its high cost and poor photogenerated carrier transfer efficiency, its economic efficiency and photocatalytic efficiency are not ideal when used alone.

[0007] Therefore, overcoming the technical shortcomings of low visible light utilization of single BiOCl and poor carrier separation efficiency of single AgFeO2, and providing a photocatalytic material with both broad spectral response and high carrier separation capability, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the technical challenges of low visible light utilization, easy recombination of photogenerated electron-hole pairs, and limited photocatalytic activity of single materials in existing photocatalytic materials, this invention proposes a technique of constructing heterojunction photocatalysts by combining AgFeO2 and BiOCl. It provides an AgFeO2 / BiOCl nano-heterojunction photocatalyst, its preparation method, and its applications. This invention prepares the AgFeO2 / BiOCl heterojunction via a hydrothermal method, utilizing the layered structure of BiOCl to promote carrier separation, while leveraging the strong visible light response of AgFeO2 to extend the photoresponse range. This achieves efficient separation of photogenerated carriers and effective utilization of visible light, thereby significantly improving the efficiency of photocatalytic degradation of organic pollutants.

[0009] To achieve the above objectives, the specific solution adopted by the present invention is as follows: In a first aspect, the present invention provides an AgFeO2 / BiOCl nanoheterojunction photocatalyst, comprising nanosheet AgFeO2 and nanosheet BiOCl, wherein a plurality of nanosheet AgFeO2 are uniformly loaded on the surface of the nanosheet BiOCl, and a heterojunction interface is formed between the nanosheet AgFeO2 and the nanosheet BiOCl in close contact; the nanosheet AgFeO2 has a hexagonal crystal structure; and the mass fraction of the nanosheet AgFeO2 in the photocatalyst is 10%~20%.

[0010] Furthermore, the diameter of the nanosheet-like BiOCl is 100~300nm, and the diameter of the nanosheet-like AgFeO2 is 50~200nm.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned AgFeO2 / BiOCl nanoheterojunction photocatalyst, comprising the following steps: Step (1): Dissolve bismuth salt in diethylene glycol to prepare a first solution; dissolve chloride in deionized water to prepare a second solution; add the second solution dropwise to the first solution, stir and react under water bath conditions, and after washing and drying, obtain oxygen-vacancy-rich nanosheet BiOCl. Step (2): Disperse the nanosheet BiOCl obtained in step (1) in deionized water, add silver salt and iron salt, stir and mix, then add NaOH solution, transfer the resulting suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction, so that the silver salt and iron salt react on the surface of the nanosheet BiOCl to generate nanosheet AgFeO2, and form a heterostructure with the nanosheet BiOCl. After washing and drying, the AgFeO2 / BiOCl nanoheterojunction photocatalyst is obtained.

[0012] Further, in step (1), the bismuth salt is Bi(NO3)3·5H2O, and the chloride is NaCl; The water bath heating temperature is 100℃, and the stirring reaction time is 5 hours; The drying temperature is 60℃ and the drying time is 24 hours.

[0013] Further, in step (2), the silver salt is AgNO3 and the iron salt is Fe(NO3)3·9H2O; The concentration of the NaOH solution is 1.6 mol / L; The hydrothermal reaction temperature was 160℃, and the reaction time was 8 hours. The drying temperature is 60℃ and the drying time is 24 hours.

[0014] Furthermore, in step (2), the mass fraction of the nanosheet AgFeO2 in the AgFeO2 / BiOCl nanoheterojunction photocatalyst is 10%~20%.

[0015] Furthermore, in step (2), the mass fraction of the nanosheet AgFeO2 is achieved by controlling the amount of silver salt and iron salt added; When the mass fraction of nanosheet AgFeO2 is 10%, the dosage of AgNO3 is 0.019g and the dosage of Fe(NO3)3·9H2O is 0.046g. When the mass fraction of nanosheet AgFeO2 is 15%, the dosage of AgNO3 is 0.031g and the dosage of Fe(NO3)3·9H2O is 0.073g. When the mass fraction of nanosheet AgFeO2 is 20%, the dosage of AgNO3 is 0.043g and the dosage of Fe(NO3)3·9H2O is 0.103g.

[0016] Thirdly, the present invention provides the application of the above-mentioned AgFeO2 / BiOCl nanoheterojunction photocatalyst in the degradation of organic pollutants.

[0017] Furthermore, the organic pollutant is an azo dye.

[0018] Furthermore, the azo dye is Lannerisal Red 5B.

[0019] The photocatalytic degradation mechanism of the AgFeO2 / BiOCl heterojunction photocatalyst in this invention is as follows: Under visible light irradiation, AgFeO2 has a narrow band gap (approximately 1.5-2.0 eV), which is first effectively excited by visible light, generating photogenerated electrons and holes. Simultaneously, the large number of oxygen vacancies introduced in step (1) form defect energy levels in the band gap of BiOCl, effectively reducing the energy required for its excitation. This allows BiOCl with a wide band gap (approximately 3.54 eV) to also be partially excited by visible light, thereby broadening the photoresponse range of the composite system. When AgFeO2 and BiOCl are combined to form a heterojunction, due to the difference in band structure between the two materials, a built-in electric field is formed at the heterojunction interface. Photogenerated electrons migrate from the conduction band of AgFeO2 to the conduction band of BiOCl, while photogenerated holes migrate from the valence band of BiOCl to the valence band of AgFeO2, thus achieving effective separation of photogenerated electrons and holes and suppressing carrier recombination. The separated photogenerated electrons migrate to the catalyst surface and react with dissolved oxygen to generate superoxide radicals (·O2). - ); Photogenerated holes (h + These active species migrate to the catalyst surface, directly oxidizing organic pollutants, or react with water molecules / hydroxyl radicals to generate hydroxyl radicals (·OH).- h + ·OH (·O2) possesses strong oxidizing properties and can oxidize and decompose organic pollutants such as Lanazol Red 5B, ultimately mineralizing them into carbon dioxide and water. Free radical capture experiments show that ·O2... - and h + ·OH is the main active species in the degradation process, while its contribution to the degradation reaction is relatively small. In summary, this invention constructs an AgFeO2 / BiOCl heterojunction, which on the one hand utilizes the unique layered structure of BiOCl to promote the rapid separation of photogenerated carriers, and on the other hand utilizes the narrow bandgap of AgFeO2 to enhance the material's response to visible light. The synergistic effect of these two factors significantly improves the separation efficiency of photogenerated carriers and the efficiency of photocatalytic reaction, thereby achieving highly efficient photocatalytic degradation of organic pollutants.

[0020] The main raw materials involved in the preparation method of this invention and their functions are as follows: Bi(NO3)3·5H2O: serves as a bismuth source, providing Bi 3+ Ions, with Cl - The reaction produces BiOCl. BiOCl is the main matrix material of the heterojunction photocatalyst of this invention, and its unique layered structure is beneficial to the rapid separation of photogenerated carriers.

[0021] Diethylene glycol (DEDG) acts as a solvent and reaction medium to dissolve bismuth salts. It also functions as a morphology guide during the reaction, facilitating the formation of nanosheet-like BiOCl structures. Furthermore, DEDG helps introduce oxygen vacancies into the BiOCl lattice, resulting in oxygen-vacancy-rich BiOCl nanosheets. The presence of oxygen vacancies can modulate the electronic structure of the semiconductor, improve carrier separation efficiency, and thus enhance photocatalytic activity.

[0022] NaCl (sodium chloride): serves as a chlorine source, providing Cl. - Ions, with Bi 3+ The reaction produces BiOCl. NaCl is dissolved in deionized water and added dropwise to ensure sufficient contact and uniform reaction of the reactants.

[0023] AgNO3 (silver nitrate): serves as a silver source, providing Ag. + Ions, under hydrothermal conditions, react with Fe 3+ and OH - The reaction produces AgFeO2. AgFeO2 is the narrow bandgap component of the heterojunction photocatalyst of this invention, responsible for enhancing the material's response to visible light.

[0024] Fe(NO3)3·9H2O (ferric nitrate nonahydrate): serves as an iron source, providing Fe 3+ Ions, reacting with Ag under hydrothermal conditions + and OH- The reaction produces AgFeO2. Fe 3+ and Ag + The dosage ratio is adjusted according to the mass fraction of AgFeO2 in the target product to ensure the accuracy of the stoichiometry of AgFeO2 in the product.

[0025] NaOH (sodium hydroxide): Used as a precipitant and alkali source, providing OH- - The NaOH solution is added to adjust the pH of the reaction system to alkaline, providing the necessary alkaline environment for the formation of AgFeO2. Magnetic stirring is required during the addition of the NaOH solution to ensure the precipitation reaction proceeds uniformly.

[0026] Deionized water and anhydrous ethanol: used as detergents for centrifugal washing of reaction products to remove unreacted raw material ions and impurities, ensuring product purity.

[0027] Beneficial effects Compared with the prior art, the present invention has the following advantages: (1) The AgFeO2 / BiOCl heterojunction photocatalyst prepared by the hydrothermal method of the present invention has a large number of uniformly dispersed nanosheets of AgFeO2 loaded on nanosheet BiOCl, forming a closely contacted heterojunction interface. This heterojunction structure is conducive to the rapid separation of photogenerated electron-hole pairs, thereby significantly improving the photocatalytic performance of the material.

[0028] (2) By constructing an AgFeO2 / BiOCl heterostructure, this invention utilizes the unique layered structure of BiOCl to promote the rapid separation of photogenerated carriers, and utilizes the narrow bandgap (approximately 1.5-2.0 eV) of AgFeO2 to enhance the material's response to visible light. The synergistic effect of the two significantly improves the transport efficiency of photogenerated carriers and the photocatalytic response of the material, thereby greatly enhancing the photocatalytic efficiency.

[0029] (3) The heterojunction photocatalyst prepared in this invention exhibits excellent photocatalytic degradation performance of Lanazon Red 5B (LR5B) under visible light irradiation. Within 120 minutes of visible light irradiation, the degradation rate of AB-10 with an AgFeO2 mass fraction of 10% was 57.52%, approximately 1.86 times that of pure BiOCl; the degradation rate of AB-15 with an AgFeO2 mass fraction of 15% was 64.48%, 2.09 times that of pure BiOCl; and the degradation rate of AB-20 with an AgFeO2 mass fraction of 20% was 86.60%, 2.81 times that of pure BiOCl. When the LR5B concentration was 30 mg / L, the degradation rate of AB-20 reached 98.72%.

[0030] (4) The AgFeO2 / BiOCl heterojunction photocatalyst prepared in this invention still maintains good photocatalytic performance in complex water environments where multiple ions coexist, and has good prospects for practical application.

[0031] (5) The preparation method of the present invention is simple, easy to operate, mild reaction conditions, and high product purity. It uses common chemical reagents and hydrothermal synthesis process, which is suitable for large-scale production and has good industrial application prospects. Attached Figure Description

[0032] Figure 1 The XRD patterns are those of the products obtained in Examples 1-3 and Comparative Examples 1-2.

[0033] Figure 2 The images are SEM images of the products obtained in Comparative Example 1, Comparative Example 2, and Example 2.

[0034] Figure 3 The TEM image and elemental distribution diagram of the product obtained in Example 3 are shown.

[0035] Figure 4 XPS spectra of the products obtained in Comparative Example 1, Comparative Example 2, and Example 3.

[0036] Figure 5 The graph shows the degradation rate of Lanazol Red 5B for each product.

[0037] Figure 6 The degradation patterns of LR5B at different concentrations and under different ion interferences are shown for the product obtained in Example 3.

[0038] Figure 7 The image shows the free radical capture experiment spectrum of the product obtained in Example 3. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to specific 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 skilled in the art without creative effort are within the protection scope of the present invention.

[0040] This invention provides an AgFeO2 / BiOCl nanoheterojunction photocatalyst, which is composed of nanosheet-like AgFeO2 and nanosheet-like BiOCl. The nanosheet-like BiOCl serves as the matrix material, and its unique layered structure facilitates the rapid separation of photogenerated carriers. The nanosheet-like AgFeO2, as a narrow bandgap semiconductor material, possesses strong visible light response and is uniformly loaded on the surface of the nanosheet-like BiOCl, forming a tightly contacted heterojunction interface between the two. Under illumination, this heterojunction interface generates a built-in electric field, driving photogenerated electrons and holes to migrate in different directions, thereby effectively suppressing the recombination of photogenerated carriers and significantly improving photocatalytic efficiency. The mass fraction of nanosheet-like AgFeO2 in this photocatalyst is 10%~20%.

[0041] The preparation method of this photocatalyst includes two steps: Step (1), Preparation of oxygen-vacancy-rich nanosheet BiOCl: The purpose of this step is to prepare oxygen-vacancy-rich nanosheet BiOCl as a substrate material for subsequent heterojunction growth. Specifically, bismuth salt is dissolved in diethylene glycol to prepare a first solution; chloride is dissolved in deionized water to prepare a second solution; the second solution is added dropwise to the first solution, and the reaction is carried out under water bath conditions with stirring. After washing and drying, oxygen-vacancy-rich nanosheet BiOCl is obtained. Diethylene glycol acts as both a solvent and a morphology guide in this step, which is beneficial for forming nanosheet-like BiOCl structures and helps introduce oxygen vacancies into the BiOCl lattice. The presence of oxygen vacancies can regulate the electronic structure of the semiconductor, improve carrier separation efficiency, and thus enhance photocatalytic activity. The dropwise addition method facilitates uniform mixing and sufficient contact of the reactants, avoiding excessively high local concentrations that lead to uneven product particle size; water bath heating provides a uniform and stable thermal environment, which is beneficial for the orderly growth of crystals. In this step, the water bath temperature is preferably 100℃, and the stirring reaction time is preferably 5 hours. Under these conditions, BiOCl crystals can grow fully into complete nanosheet structures. The molar ratio of bismuth salt to chloride is preferably 1:2 to ensure that Bi 3+ With Cl - The reaction proceeds at the stoichiometric ratio to produce pure-phase BiOCl. After the reaction is complete, unreacted starting material ions and impurities are removed by washing, and the product is dried to obtain oxygen-vacancy-rich nanosheet-like BiOCl. Step (2), Preparation of AgFeO2 / BiOCl heterojunction: The purpose of this step is to generate AgFeO2 on the surface of nanosheet BiOCl and form a heterostructure with BiOCl. Specifically, the nanosheet BiOCl obtained in step (1) is dispersed in deionized water, silver salt and iron salt are added, and magnetic stirring is used to uniformly disperse and adsorb silver and iron ions onto the surface of the nanosheet BiOCl; NaOH solution is added to adjust the system to alkalinity, providing the necessary alkaline environment for the generation of AgFeO2; the resulting suspension is transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction, allowing silver and iron salts to react on the surface of the nanosheet BiOCl to generate nanosheet AgFeO2, forming a closely contacted heterostructure with the nanosheet BiOCl; after the reaction, unreacted ions and byproducts are removed by washing, and the AgFeO2 / BiOCl nanoheterojunction photocatalyst is obtained after drying. Silver salt provides Ag... + Iron salts provide Fe 3+ Under alkaline conditions, a reaction occurs to generate AgFeO2. Magnetic stirring ensures thorough mixing of the reactants, guaranteeing a uniform distribution of silver and iron ions on the BiOCl surface. The high temperature and pressure conditions of the hydrothermal reaction are conducive to the full formation and crystallization of AgFeO2 on the BiOCl nanosheet surface, resulting in a hexagonal crystal structure and uniform loading. In this step, the hydrothermal reaction temperature is preferably 160℃, and the reaction time is preferably 8 hours. Under these conditions, AgFeO2 can fully crystallize and be uniformly loaded on the BiOCl surface. The mass fraction of nanosheet AgFeO2 in the photocatalyst is adjusted by controlling the amount of silver and iron salts added, preferably within the range of 10%~20%.

[0042] The AgFeO2 / BiOCl nano-heterojunction photocatalyst prepared in this invention can be used for the photocatalytic degradation of organic pollutants, especially suitable for the treatment of wastewater containing azo dyes (such as Lanazon Red 5B). The specific application method is as follows: the AgFeO2 / BiOCl nano-heterojunction photocatalyst prepared in this invention is added to wastewater containing organic pollutants, and the reaction is carried out under visible light irradiation with stirring to ensure that the photocatalyst is fully dispersed and in contact with the pollutants, thereby achieving efficient degradation of organic pollutants. The amount of catalyst can be adjusted according to the concentration of organic pollutants in the wastewater, generally 0.5~2 g / L; the reaction time can be adjusted according to the type and concentration of pollutants, generally 60~180 minutes. After the reaction, the photocatalyst can be recovered by centrifugation or filtration, achieving catalyst reuse.

[0043] Example 1: Preparation of AB-10 heterojunction photocatalyst An AgFeO2 / BiOCl nanoheterojunction photocatalyst includes the following steps: Step (1): Dissolve 0.728g of Bi(NO3)3·5H2O in 30mL of diethylene glycol to prepare the first solution; dissolve 0.175g of NaCl in 20mL of deionized water to prepare the second solution; add the second solution dropwise to the first solution, and react with magnetic stirring in a water bath at 100℃ for 5 hours. After natural cooling, wash the solution three times each with deionized water and anhydrous ethanol by centrifugation, and dry it at 60℃ for 24 hours to obtain nanosheet BiOCl rich in oxygen vacancies. Step (2): Disperse 0.2g of the nanosheet BiOCl obtained in step (1) in 40mL of deionized water, add 0.019g AgNO3 and 0.046g Fe(NO3)3·9H2O, and stir magnetically for 10min to ensure full contact between the substances. Then add 20mL of 1.6mol / L NaOH solution and stir magnetically for 30min. Transfer the resulting suspension to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160℃ for 8 hours. After natural cooling, wash the mixture three times each with deionized water and anhydrous ethanol by centrifugation, and dry it at 60℃ for 24 hours to obtain the AgFeO2 / BiOCl nanoheterojunction photocatalyst with a mass fraction of 10% of nanosheet AgFeO2, denoted as AB-10.

[0044] Example 2: Preparation of AB-15 heterojunction nanomaterials The difference between this embodiment and embodiment 1 is that in step (2), the amount of AgNO3 is 0.031g and the amount of Fe(NO3)3·9H2O is 0.073g; in the prepared AgFeO2 / BiOCl nano heterojunction photocatalyst, the mass fraction of nanosheet AgFeO2 is 15%, denoted as AB-15.

[0045] Example 3: Preparation of AB-20 heterojunction nanomaterials The difference between this embodiment and embodiment 1 is that in step (2), the amount of AgNO3 is 0.043g and the amount of Fe(NO3)3·9H2O is 0.103g; in the prepared AgFeO2 / BiOCl nano heterojunction photocatalyst, the mass fraction of nanosheet AgFeO2 is 20%, denoted as AB-20.

[0046] Comparative Example 1: Preparation of BiOCl The difference between this comparative example and Example 1 is that step (2) is omitted, and oxygen-vacancy-rich nanosheet BiOCl is prepared only according to step (1) of Example 1.

[0047] Comparative Example 2: Preparation of AgFeO2 The difference between this comparative example and Example 1 is that: in step (2), no nanosheet BiOCl is added, but only 0.019g AgNO3 and 0.046g Fe(NO3)3·9H2O are dissolved in 40mL of deionized water, and 20mL of 1.6mol / L NaOH solution is added. The mixture is then subjected to hydrothermal reaction at 160℃ for 8 hours. After washing and drying, pure AgFeO2 nanomaterials are obtained.

[0048] The products obtained in Examples 1-3 and Comparative Examples 1-2 are characterized structurally and tested for performance.

[0049] (1) XRD phase structure analysis The phase structure of the products prepared in the above embodiments and comparative examples was characterized by X-ray diffraction (XRD) analysis. Detailed test results can be found in [link to relevant documentation]. Figure 1 . Figure 1 The XRD patterns of the photocatalytic materials in Examples 1-3 and Comparative Examples 1-2 are shown. As shown in the figure, the pure BiOCl obtained in Comparative Example 1 has diffraction peaks at 2θ = 12.0352°, 24.1266°, 26.0022°, 32.6265°, 33.5443°, 36.6171°, 41.0067°, 49.7860°, 54.2155°, 55.2131°, 58.7647°, 60.5605°, 68.2224°, 75.0861°, and 77.8396, corresponding to the crystal planes (001), (002), (101), (110), (102), (003), (112), (200), (113), (211), (104), (212), (114), (220), and (214), respectively. These peaks correspond to the crystal planes of the standard card (JCPDS). The results (06-0249) are consistent, indicating that the synthesized BiOCl is a pure phase.

[0050] The pure AgFeO2 obtained in Comparative Example 2 has diffraction peaks at 2θ = 14.2300°, 28.8754°, 34.9011°, 43.4809°, 50.5043°, 61.2389°, and 68.9008° corresponding to the (002), (004), (101), (006), (105), (110), and (114) crystal planes, respectively. These peaks are consistent with the standard card (JCPDS 25-0765), which proves that the synthesized AgFeO2 has a hexagonal crystal structure.

[0051] The XRD patterns of AB-10 obtained in Example 1, AB-15 obtained in Example 2, and AB-20 obtained in Example 3 show that the main characteristic diffraction peaks are similar to those of BiOCl. Furthermore, with the increase of AgFeO2 loading, the intensity of the diffraction peaks on the AgFeO2 (004) crystal plane gradually increases, further demonstrating the successful synthesis of the AgFeO2 / BiOCl heterojunction. Moreover, the synthesized AgFeO2 / BiOCl heterojunction is free of impurity peaks, indicating that the prepared material has high purity.

[0052] (2) SEM morphology analysis The surface morphology of the catalyst was observed using field emission scanning electron microscopy (SEM). Detailed test results can be found in [link to relevant documentation]. Figure 2 . Figure 2 The images show the SEM images of the products obtained in Comparative Examples 1, 2, and 2. (a) is the SEM image of pure BiOCl obtained in Comparative Example 1, (b) is the SEM image of pure AgFeO2 obtained in Comparative Example 2, and (c) is the SEM image of the AB-15 heterojunction obtained in Example 2. Figure 2 As shown in Figure (a), pure BiOCl has a nanosheet structure with a relatively smooth surface and a sheet diameter of approximately 100-300 nm. Figure 2 Figure (b) shows the outline of pure AgFeO2 through red hexagons, indicating that pure AgFeO2 has a hexagonal nanosheet structure with a sheet diameter of approximately 50-200 nm. Figure 2 Figure (c) shows a SEM image of the AgFeO2 / BiOCl heterostructure. The presence of numerous and uniformly dispersed nanosheets of AgFeO2 loaded onto the nanosheet-like BiOCl confirms the formation of the AgFeO2 / BiOCl heterostructure.

[0053] (3) TEM and elemental distribution analysis Figure 3 The images show the TEM image and elemental distribution of the AB-20 product obtained in Example 3. Figure (a) is the TEM image of AB-20, figure (b) is the HRTEM image of AB-20, figure (c) is the overall elemental distribution of AB-20, and figures (d)-(h) are the EDS-mapping distributions of O, Cl, Fe, Bi, and Ag elements in AB-20, respectively. Specifically, as shown... Figure 3 As shown in Figure (a), a significant amount of AgFeO2 is loaded onto the surface of the nanosheet-like BiOCl, forming an effective interface through close contact between the two. In HRTEM, as... Figure 3As shown in Figure (b), both materials exhibit clear lattice fringes, indicating good crystallinity. The observed lattice spacings of 0.242 nm and 0.303 nm correspond to the (101) crystal plane of AgFeO2 and the (110) crystal plane of BiOCl, respectively, confirming the successful fabrication of the AB-20 heterojunction. The formation of this heterojunction facilitates the rapid separation of photogenerated electron-hole pairs, thereby significantly improving the photocatalytic performance of the material.

[0054] In the overall elemental distribution map and EDS-mapping spectrum of the AB-20 heterojunction, such as Figure 3 As shown in Figures (c)-(h), O, Cl, Fe, Bi, and Ag elements are uniformly dispersed on the surface of the AB-20 heterojunction, further verifying the successful preparation of the AB-20 heterojunction.

[0055] (4) XPS surface elemental analysis To investigate the surface elemental composition and valence state of the samples, X-ray photoelectron spectroscopy (XPS) analysis was performed, such as... Figure 4 As shown. Figure 4 The XPS spectra of pure BiOCl obtained in Comparative Example 1, pure AgFeO2 obtained in Comparative Example 2, and AB-20 obtained in Example 3 are shown. Among them, (a) is the full spectrum of AB-20, pure BiOCl, and pure AgFeO2; (b) is the high-resolution spectrum of Bi 4f; (c) is the high-resolution spectrum of Cl 2p; (d) is the high-resolution spectrum of O 1s; (e) is the high-resolution spectrum of Ag 3d; and (f) is the high-resolution spectrum of Fe 2p.

[0056] like Figure 4 As shown in Figure (a), strong Bi 4f, O 1s, and Cl 2p element peaks were detected in the full spectrum of pure BiOCl; strong Ag 3d, Fe 2p, and O 1s element peaks were detected in the full spectrum of pure AgFeO2; and Bi 4f, O 1s, Cl 2p, Ag 3d, and Fe 2p were detected simultaneously in AB-20, proving the successful synthesis of the AB-20 heterojunction.

[0057] The high-resolution spectrum of the element was fitted, and the fitting was calibrated using the binding energy of the C 1s peak at 284.8 eV. For example... Figure 4 As shown in Figure (b), the Bi4f binding energy exhibits two characteristic peaks at 158.61 eV and 163.94 eV, corresponding to Bi4f, respectively. 7 / 2 and Bi 4f 5 / 2 This indicates that the Bi element is in Bi... 3+ It exists in BiOCl. For example... Figure 4As shown in Figure (c), two characteristic peaks of Cl 2p exist at 198.21 eV and 200.05 eV, corresponding to Cl 2p, respectively. 3 / 2 Cl 2p 1 / 2 .like Figure 4 As shown in Figure (d), two characteristic peaks of O 1s appear at 529.57 eV and 531.07 eV, corresponding to lattice oxygen and surface hydroxyl groups in the sample, respectively. Figure 4 As shown in Figure (e), two characteristic peaks of Ag 3d exist at 368.03 eV and 374.02 eV, corresponding to Ag 3d , respectively. 3 / 2 Ag3d 5 / 2 This indicates that Ag element in the material is in the form of Ag + It exists in the form of... (e.g.) Figure 4 As shown in Figure (f), Fe 2p exhibits spin-orbit splitting peaks, with peaks at 718.51 eV and 732.73 eV corresponding to Fe 2p, respectively. 3 / 2 Fe 2p 1 / 2 .

[0058] (5) Performance test of photocatalytic degradation of LR5B Lanneriscor Red 5B (LR5B), a typical azo dye, is a representative organic pollutant in textile industrial wastewater and is widely used in the dyeing and printing of cotton, silk, wool, and other fiber fabrics. The photocatalytic performance of the samples was evaluated by simulating visible light degradation of LR5B.

[0059] The photocatalytic degradation experiment was conducted under visible light irradiation. 40 mg of photocatalyst was dispersed in 40 mL of an LR5B solution of a specific concentration (catalyst concentration 1 g / L), and stirred for 30 minutes under dark conditions to reach adsorption-desorption equilibrium. Subsequently, the visible light source was turned on, and a certain amount of reaction solution was taken at regular intervals. After centrifugation, the absorbance of the supernatant was measured, and the degradation rate of LR5B was calculated.

[0060] Figure 5The degradation rates of Lanazol Red 5B by each product are shown in Figure (a). Figure (a) shows the degradation rate curves of AB-20 on LR5B in four systems: blank control (LR5B dye solution only, without any photocatalyst, only visible light irradiation to verify the photostability of the dye itself), dark reaction (AB-20 catalyst added, the entire process is conducted in the dark without turning on visible light, only the adsorption and removal effect of the catalyst on the dye is examined), mechanically ground sample (BiOCl obtained from Comparative Example 1 and AgFeO2 obtained from Comparative Example 2 are simply physically mixed and ground without hydrothermal in-situ composite, to compare the effect of heterojunction on catalytic performance), and normal reaction (AB-20 heterojunction photocatalyst prepared in-situ by the hydrothermal method of this invention, and the complete dark adsorption + visible light photocatalytic degradation process is performed); Figure (b) shows the degradation rate curves of LR5B on AB-10, AB-15, AB-20 and pure BiOCl.

[0061] like Figure 5 As shown in Figure (a), the horizontal axis represents reaction time. The period from -30 min to 0 min is the dark adsorption stage in the absence of light, and the period from 0 min to 120 min is the visible light irradiation stage. This figure contains four curves. For the blank control curve, the dark adsorption stage curve shows almost no decrease, and the degradation rate remains near 0 throughout the entire light irradiation process, indicating that the dye can hardly self-degrade without a catalyst under visible light irradiation alone. For the dark reaction curve, visible light is not turned on throughout the process, and the degradation rate only increases slightly in the early dark adsorption stage, then quickly stabilizes, indicating no photocatalytic degradation process. For the mechanical grinding curve, after dark adsorption reaches equilibrium, the degradation rate increases slowly during the light irradiation stage, with limited overall degradation effect, indicating that the composite sample prepared by simple mechanical mixing is difficult to form an effective heterojunction and has poor photocatalytic activity. For the normal reaction curve, after the dark adsorption stage reaches adsorption equilibrium, the degradation rate increases significantly under light irradiation, reaching its maximum value at 120 min. The degradation performance is far superior to the other three systems, proving that the AB-20 heterojunction prepared by the in-situ synthesis process has excellent visible light photocatalytic degradation capability.

[0062] like Figure 5 As shown in Figure (b), the degradation rate of LR5B by pure BiOCl obtained in Comparative Example 1 after 120 min of visible light irradiation was approximately 30.80%; the degradation rate of AB-10 obtained in Example 1 was 57.52%, which was 1.86 times that of pure BiOCl; the degradation rate of AB-15 obtained in Example 2 was 64.48%, which was 2.09 times that of pure BiOCl; and the degradation rate of AB-20 obtained in Example 3 was 86.60%, which was 2.81 times that of pure BiOCl. The results indicate that the AgFeO2 / BiOCl heterojunction photocatalyst prepared in this invention exhibits excellent photocatalytic degradation performance of LR5B under visible light irradiation, and the photocatalytic degradation rate significantly increases with increasing AgFeO2 loading.

[0063] (6) Degradation experiments of LR5B at different concentrations and under different ion interferences To investigate the effects of initial dye concentration and different anions on the photocatalytic degradation performance of AB-20, a degradation experiment with interference conditions was conducted, such as... Figure 6 As shown. Figure (a) shows the degradation concentration changes of AB-20 at four initial LR5B concentrations of 30 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L. The reaction system consisted of 40 mL of LR5B solution, with a fixed catalyst dosage of 40 mg and a catalyst concentration of 1 g / L. Figure (b) shows the degradation concentration changes of AB-20 at ion-free and Cl-free concentrations. - NO3 - SO4 2- PO4 3- HPO4 2- H2PO4 - The degradation concentration change curves of AB-20 under seven anion systems, with each ion added at a concentration of 1 mmol / L.

[0064] like Figure 6 As shown in Figure (a), the horizontal axis represents reaction time, with -30 min to 0 min representing the dark adsorption stage and 0 min to 120 min representing the visible light irradiation stage. The vertical axis represents C / C0, comprising four curves corresponding to LR5B concentrations of 30 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L, respectively. Dye adsorption and removal are present in all four curves during the dark adsorption stage, and all curves show a continuous decreasing trend during the light irradiation stage. As the LR5B concentration increases, the degradation rate decreases at 120 min; the degradation rate is highest at 30 mg / L (98.72%), decreasing to 62.09% when the LR5B concentration increases to 80 mg / L. This variation is attributed to the high light transmittance of the low-concentration dye solution, allowing the catalyst to fully absorb light energy and generate active species. As the dye concentration increases, the light transmittance of the solution decreases, preventing the catalyst from fully absorbing light energy to generate sufficient active species, ultimately reducing the dye degradation rate.

[0065] like Figure 6 As shown in Figure (b), the seven curves correspond to no ion interference, Cl, and so on. - NO3 - SO4 2- PO4 3- HPO4 2- H2PO4 - The system. The addition of various ions will affect the 120-minute degradation rate of LR5B to varying degrees: PO4 3- It has the greatest inhibitory effect on the photocatalytic process, corresponding to a degradation rate of 12.34%; HPO42- It has a significant inhibitory effect on the photocatalytic process, with a corresponding degradation rate of 43.07%; H2PO4 - It has a certain inhibitory effect on the photocatalytic process, with a corresponding degradation rate of 49.79%; NO3 - It has little impact on the photocatalytic process, resulting in a corresponding degradation rate decrease to 80.56%; SO4 2- and Cl - It has almost no effect on the degradation rate. PO4 3- The reason for the strongest inhibitory effect is PO4. 3- Capable of capturing photogenerated holes h + And transform into HPO4 2- HPO4 2- It can then be further converted into H2PO4. - And PO4 3- Converted to HPO4 2- The reaction is more likely to occur, therefore PO4 3- Its inhibitory effect on photocatalytic systems is far stronger than that of other phosphorus-containing anions.

[0066] (7) Free radical capture experiment To identify the main active species in the photocatalytic degradation of LR5B by AB-20, a free radical capture control experiment was conducted, such as... Figure 7 As shown. Figure 7 The graph shows the free radical capture experiment of the AB-20 product obtained in Example 3. The horizontal axis represents the four experimental groups: no capture agent, IPA, EDTA-2Na, and BQ. The vertical axis represents the dye degradation rate at 120 min. Isopropanol (IPA) was used to capture hydroxyl radicals ·OH, and disodium ethylenediaminetetraacetate (EDTA-2Na) was used to capture photogenerated holes h. + p-Benzoquinone (BQ) is used to capture superoxide radicals ·O2. - The dosage of all three capture agents was 2 mmol.

[0067] like Figure 7 It can be seen that the degradation rate of the blank control group without any capture agent was 86.60%; the degradation rate of h was 86.60% with the addition of EDTA-2Na. + Subsequently, the degradation rate of LR5B decreased significantly from 86.60% to 19.79%, indicating that the photocatalytic degradation process was significantly inhibited; the addition of BQ to capture O2... - Subsequently, the degradation rate decreased to 39.98%, significantly impacting the catalyst's degradation performance. After adding IPA to capture ·OH, the degradation rate decreased by only 0.96%, having virtually no impact on the overall degradation effect. Based on the combined degradation rate data from each group, it can be determined that ·O2... - and h +It is the main active species in the visible light catalytic degradation of LR5B by AB-20, while ·OH contributes almost nothing to the degradation of the dye.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. An AgFeO2 / BiOCl nanoheterojunction photocatalyst, characterized in that, The catalyst comprises nanosheet-like AgFeO2 and nanosheet-like BiOCl, wherein a plurality of nanosheet-like AgFeO2 are uniformly loaded on the surface of the nanosheet-like BiOCl, and a heterogeneous interface with close contact is formed between the nanosheet-like AgFeO2 and the nanosheet-like BiOCl; the nanosheet-like AgFeO2 has a hexagonal crystal structure; the mass fraction of nanosheet-like AgFeO2 in the photocatalyst is 10%~20%; The preparation method of this catalyst includes the following steps: Step (1): Dissolve bismuth salt in diethylene glycol to prepare a first solution; dissolve chloride in deionized water to prepare a second solution; add the second solution dropwise to the first solution, stir and react under water bath conditions, and after washing and drying, obtain oxygen-vacancy-rich nanosheet BiOCl. Step (2): Disperse the nanosheet BiOCl obtained in step (1) in deionized water, add silver salt and iron salt, stir and mix, then add NaOH solution, transfer the resulting suspension to a high-pressure reactor with polytetrafluoroethylene lining for hydrothermal reaction, so that the silver salt and iron salt react on the surface of the nanosheet BiOCl to generate nanosheet AgFeO2, and form a heterostructure with the nanosheet BiOCl. After washing and drying, the AgFeO2 / BiOCl nanoheterojunction photocatalyst is obtained. In step (2), the silver salt is AgNO3 and the iron salt is Fe(NO3)3·9H2O; The concentration of the NaOH solution is 1.6 mol / L; The hydrothermal reaction temperature was 160℃, and the reaction time was 8 hours. The drying temperature is 60℃ and the drying time is 24 hours.

2. The AgFeO2 / BiOCl nanoheterojunction photocatalyst according to claim 1, characterized in that, The diameter of the nanosheet-like BiOCl is 100~300nm, and the diameter of the nanosheet-like AgFeO2 is 50~200nm.

3. The AgFeO2 / BiOCl nanoheterojunction photocatalyst according to claim 1, characterized in that, In step (1), the bismuth salt is Bi(NO3)3·5H2O, and the chloride is NaCl; The water bath heating temperature is 100℃, and the stirring reaction time is 5 hours; The drying temperature is 60℃ and the drying time is 24 hours.

4. The AgFeO2 / BiOCl nanoheterojunction photocatalyst according to claim 1, characterized in that, In step (2), the mass fraction of the nanosheet AgFeO2 is achieved by controlling the amount of silver salt and iron salt added; When the mass fraction of nanosheet AgFeO2 is 10%, the dosage of AgNO3 is 0.019g and the dosage of Fe(NO3)3·9H2O is 0.022g. When the mass fraction of nanosheet AgFeO2 is 15%, the dosage of AgNO3 is 0.031g and the dosage of Fe(NO3)3·9H2O is 0.035g. When the mass fraction of nanosheet AgFeO2 is 20%, the dosage of AgNO3 is 0.043g and the dosage of Fe(NO3)3·9H2O is 0.103g.

5. The application of the AgFeO2 / BiOCl nanoheterojunction photocatalyst as described in claim 1 in the degradation of organic pollutants.

6. The application according to claim 5, characterized in that, The organic pollutant is an azo dye.

7. The application according to claim 6, characterized in that, The azo dye is Lannerisal Red 5B.

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