A green method for efficiently killing toxin-producing aflatoxin

Abstract

The present invention relates to the field of fungal control in agricultural products, specifically disclosing a green method for efficiently killing toxin-producing aflatoxin. This method uses a Ag-AgCl / α-Fe2O3 nanocomposite material, comprising micron-sized quadrangular pyramidal α-Fe2O3 particles and Ag-AgCl particles attached to the pyramidal α-Fe2O3, to effectively kill aflatoxin under visible light. This highly effective fungal killing method can effectively control aflatoxin contamination at the source, is low-cost, and has broad application prospects in agricultural product storage and transportation.

Description

Technical Field

[0001] The invention belongs to the field of fungus control of agricultural products, and specifically discloses a green method for efficiently killing toxigenic aflatoxin. Background Art

[0002] Aspergillus flavus ( Aspergillus flavus ) is a common saprophytic fungus that spreads rapidly through conidia and is widely distributed in the natural environment (air, soil and water). According to the Food and Agriculture Organization of the United Nations, approximately 25% of crops worldwide are contaminated by aflatoxin and its toxins each year, causing hundreds of billions of dollars in economic losses. Aflatoxin can easily contaminate crops such as peanuts, and the highly toxic and carcinogenic secondary metabolites it produces, namely aflatoxins, seriously threaten the life and health of humans and animals. Therefore, the prevention and control of aflatoxin is of great significance. In recent decades, a large number of chemical pesticides and other fungicides have been widely used to prevent and control pathogenic fungi. Although the prevention and control effect is good, it also brings about problems such as secondary environmental pollution and fungal resistance. Therefore, it is of great significance to explore green and efficient methods for the control of aflatoxin.

[0003] In 1985, photocatalytic technology was first reported to be used for bacterial control. Due to its advantages such as environmental friendliness and low probability of drug resistance, it is considered a method for pathogen control with broad application prospects. Currently, researchers have done a lot of research on enhancing the killing efficiency of pathogenic bacteria and viruses, but little research on fungal control. In addition, the photocatalytic bactericidal effect mainly depends on the superoxide free radical (•O2 − ) and hydroxyl radicals (•OH). These free radicals can enter the bacterial cell and interact with pathogenic microorganisms. However, compared to bacteria, fungi have thicker cell walls and membranes, and more complex structural components. To kill fungi, improving the catalytic activity of materials and generating more reactive free radicals are key issues. Photocatalytic performance primarily depends on factors such as light energy utilization efficiency and the separation and transfer efficiency of photogenerated charge carriers. Plasmon resonance visible light photocatalytic systems can both extend the charge separation lifetime and enhance optical absorption within the visible spectrum, providing an excellent opportunity for efficient fungal killing. Plasmon resonance photocatalytic systems typically consist of precious metal nanoparticles dispersed on a semiconductor, promoting light absorption at the surface plasmon resonance frequency. The Schottky junction between the precious metal nanoparticles and the semiconductor promotes the diffusion of electrons and holes in different directions and charge separation, generating a large number of reactive free radicals, which is more conducive to controlling toxin-producing fungi. Therefore, exploring efficient, stable, and green methods for killing toxin-producing Aspergillus flavus using visible light catalysis using the surface plasmon resonance effect is of great significance for ensuring food safety and promoting high-quality development of the industry. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention proposes a green method for efficiently killing toxin-producing Aspergillus flavus and a visible light catalytic composite material for efficiently killing toxin-producing Aspergillus flavus, which can reduce the pollution of toxin-producing Aspergillus flavus and its toxins, and ensure the quality safety of agricultural products and industrial development.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] Provided is a green method for efficiently killing toxigenic aflatoxin. The method uses an Ag-AgCl / α-Fe2O3 nanocomposite material to efficiently kill aflatoxin under visible light irradiation. The Ag-AgCl / α-Fe2O3 nanocomposite material comprises micron-sized quadrangular pyramidal α-Fe2O3 and Ag-AgCl particles attached to the quadrangular pyramidal α-Fe2O3.

[0007] According to the above scheme, in the Ag-AgCl / α-Fe2O3 composite material, the mass ratio of Ag, AgCl and α-Fe2O3 is 4~10:5~20:100, more preferably 6~10:10~20:100.

[0008] According to the above scheme, the particle size of α-Fe2O3 is 0.8~1.2 μm, the particle size of Ag is 3~5 nm, and the particle size of AgCl is 100~150 nm.

[0009] According to the above scheme, the Ag-AgCl / α-Fe2O3 nanocomposite material is used in the form of powder, suspension or film dispersed on a carrier such as SiO2 non-metallic carrier.

[0010] According to the above scheme, the light source is natural light or a xenon lamp; the irradiation time is 10 to 25 minutes. When using a xenon lamp, the xenon lamp power is 150 to 300 W, the light wavelength range is 420 to 700 nm, and the distance between the sample and the xenon lamp is 20 to 25 cm.

[0011] Provided is an Ag-AgCl / α-Fe2O3 nanocomposite material that can effectively kill aflatoxin under visible light irradiation. The Ag-AgCl / α-Fe2O3 nanocomposite material comprises micron-sized quadrangular pyramidal α-Fe2O3 and Ag-AgCl particles attached to the quadrangular pyramidal α-Fe2O3.

[0012] According to the above scheme, in the Ag-AgCl / α-Fe2O3 composite material, the mass ratio of Ag, AgCl and α-Fe2O3 is 4~10:5~20:100, more preferably 6~10:10~20:100.

[0013] Provide a preparation method of the above-mentioned Ag-AgCl / α-Fe2O3 nanocomposite material:

[0014] (1) Ferric chloride hexahydrate and terephthalic acid are dissolved in an organic solution, and then dried after solvent thermal reaction to prepare α-Fe2O 3；

[0015] (2) A uniform suspension of α-Fe2O3 is provided, and then chlorine and silver precursors are slowly added to the α-Fe2O3 suspension and stirred. After reacting for a period of time under dark conditions, AgCl / α-Fe2O3 material is obtained, and then the Ag-AgCl / α-Fe2O3 nanocomposite material is obtained by treating the mixture under visible light for 30 to 90 minutes.

[0016] According to the above scheme, the solvent thermal reaction conditions of step (1) are: at 80~120 o C for 12-15 h.

[0017] The post-treatment of step (1) is to cool the reaction to room temperature after the reaction is completed, centrifuge the obtained product, wash it, and dry it overnight to obtain α-Fe2O3.

[0018] According to the above scheme, the organic solvent in step (1) is N,N-dimethylformamide; the molar ratio of ferric chloride hexahydrate to terephthalic acid is 1.3-1.5:1, measured as iron.

[0019] According to the above scheme, step (2) is as follows: weigh a certain mass of α-Fe2O3 and disperse it in deionized water, stir to obtain a uniform suspension, then dissolve chlorine and silver precursors in deionized water, slowly add them to the α-Fe2O3 suspension, stir, and after the reaction is completed, centrifuge, wash, and dry overnight the obtained solid; take a certain mass of the above obtained product and uniformly disperse it in deionized water, treat it under visible light for 30 to 90 minutes, centrifuge, wash, and dry overnight the obtained solid to obtain a composite material.

[0020] According to the above scheme, the chlorine and silver precursors are sodium chloride and silver nitrate respectively.

[0021] Provided is a method for efficiently killing toxin-producing aflatoxin Aspergillus flavus. The method comprises adding an Ag-AgCl / α-Fe2O3 nanocomposite material to a biological sample system to be processed, and performing visible light irradiation treatment to efficiently kill the mold and reduce the risk of aflatoxin contamination.

[0022] According to the above scheme, the biological samples are agricultural products, and the agricultural products are peanuts and corn.

[0023] The composite material provided by the present invention exhibits a strong synergistic effect, demonstrating a stronger surface plasmon resonance effect and expanding the visible light absorption range. Furthermore, the electron transfer effect of Ag promotes electron transport and the transfer of excess electrons to the conduction band of silver chloride, reducing the recombination efficiency of photoinduced carriers during the photocatalytic process and promoting the effective separation of photogenerated electrons and holes, thereby improving photocatalytic efficiency. During photocatalytic redox, holes in the forbidden band of α-Fe₂O₃ oxidize water or hydroxyl groups into hydroxyl radicals (•OH). This generates a large number of active free radicals, which in turn destroy the cell structure of Aspergillus flavus, causing cell death. Ultimately, the bactericidal efficiency of the Ag-AgCl / α-Fe₂O₃ composite material of the present invention is far superior to that of single α-Fe₂O₃ or Ag-AgCl.

[0024] Advantages of the present invention:

[0025] 1. The method of the present invention has excellent performance in killing aflatoxin.

[0026] 2. The present invention first uses a solvothermal method to prepare α-Fe2O3, which is then mixed with chlorine and silver precursors to undergo a deposition-photoreduction reaction to prepare the composite material Ag-AgCl / α-Fe2O3. The preparation method is simple and easy, low in cost, has high performance and structural stability, and is reusable.

[0027] 3. The Ag-AgCl / α-Fe2O3 nanocomposite material provided by the present invention, which is highly effective in killing toxigenic aflatoxin, is in the shape of a quadrangular pyramid and has a large specific surface area, providing more active sites for photocatalytic reactions. The Ag in the composite material has plasma surface and electron transport effects, which are beneficial for increasing the light absorption range, improving the utilization rate of visible light, promoting carrier separation and transfer, reducing recombination, and improving photocatalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the X-ray diffraction pattern of the nanocomposite material prepared by the present invention.

[0029] Figure 2 It is an X-ray photoelectron spectrum of the nanocomposite material prepared by the present invention.

[0030] Figure 3 Schematic diagram of the charge transfer mechanism of the nanocomposite material prepared by the present invention.

[0031] Figure 4 This is a diagram showing the effect of the nanomaterial prepared by the present invention in killing toxin-producing aflatoxin.

[0032] Figure 5 The invention discloses a five-round recycling of nanocomposite materials for killing toxigenic aflatoxin and its XRD patterns before and after use.

[0033] Figure 6This is a diagram showing the effect of the composite material bactericidal film prepared by the present invention on toxin-producing aflatoxin.

[0034] Figure 7 This figure shows the damaging effect of the nanocomposite material prepared by the present invention on the cell structure of Aspergillus flavus.

[0035] Figure 8 The invention discloses a nano composite material having a sterilizing effect on peanuts. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to specific examples, but the methods and technical parameters involved in the scheme should not be understood as limiting the present invention.

[0037] Example 1

[0038] Preparation of visible light catalytic composite materials with surface plasmon resonance effect:

[0039] 1) Preparation of α-Fe2O3:

[0040] Weigh 1.67 mg of ferric chloride hexahydrate and 0.75 mg of terephthalic acid and dissolve them in 40 mL of N,N-dimethylformamide solution. Stir evenly. Transfer the mixed solution to a 50 mL polytetrafluoroethylene reactor and heat at 100 o C for 15 h. After cooling to room temperature, the product was centrifuged, washed, dried overnight, and ground to obtain α-Fe2O3;

[0041] 2) Preparation of AgCl / α-Fe2O3: Weigh a certain amount of the above α-Fe2O3 and disperse it in 60 mL of deionized water. Stir for 30 minutes to obtain a uniform suspension. Add sodium chloride to the suspension and stir for 20 minutes. Then add a certain concentration of silver nitrate solution. Stir in the dark for 60 minutes. Wash the resulting product with ethanol and deionized water three times. Then, sieve the mixture in a 60-minute oven. o C was dried and ground to obtain AgCl / α-Fe2O3 composite materials with different proportions of AgCl and α-Fe2O3.

[0042] 3) Preparation of Ag-AgCl / α-Fe2O3 composite material: Weigh a certain amount of AgCl / α-Fe2O3 composite material and disperse it in 30 mL of deionized water. After treating it under a visible light source such as a xenon lamp for 30-60 min, the product was collected and washed with ethanol and deionized water three times, and then heated at 60 o C drying and grinding to obtain Ag-AgCl / α-Fe2O3 composite materials with different composition ratios. The ratios of Ag:AgCl:α-Fe2O3 in the samples were characterized by electron energy spectrum and elemental analysis, see Table 1.

[0043] AgCl and Ag-AgCl were prepared using the aforementioned method without the addition of α-Fe2O3. The composites exhibited uniform morphology, with 3-5 nm Ag and 100-150 nm AgCl uniformly supported on the surface of tetrahedral α-Fe2O3 with an average length of approximately 0.8-1.2 microns. Figure 1 The X-ray diffraction pattern of the visible light catalytic composite material with plasma resonance effect prepared by the present invention shows that the diffraction peak of the prepared α-Fe2O3 is consistent with the standard card JCPDS No. 79-1741, and is a hexagonal crystal form, and has no other diffraction peaks. The prepared Ag-AgCl is consistent with the standard cards JCPDS No. 06-0480 and JCPDS No. 65-2871. The prepared AgCl / α-Fe2O3 and Ag-AgCl / α-Fe2O3 composite materials have a peak at 24.1 o , 33.2 o , 35.9 o , 40.9 o , 49.6 o , 54.2 o , 62.5 o and 64.1 o The characteristic peaks at 27.8 correspond to the (012), (104), (110), (113), (024), (116), (214) and (300) planes of α-Fe2O3; o , 32.3 o , 46.2 o , 54.9 o , 57.5 o , 67.4 o , 74.5 o , 76.8 o and 85.8 o The characteristic peaks at 37.9 correspond to the (111), (200), (220), (311), (222), (400), (331), (420) and (422) crystal planes of AgCl; o and 44.4 o The characteristic peaks at correspond to the (111) and (200) crystal planes of Ag. The above results show that the composite material was successfully prepared and is composed only of α-Fe2O3 and Ag-AgCl. Figure 2 This is an X-ray photoelectron spectrum of the visible light catalytic composite material with plasma resonance effect prepared by the present invention. As can be seen from the figure, the prepared nanomaterial is mainly composed of four elements: iron, oxygen, chlorine, and silver. Figure 3 This is a charge transfer mechanism diagram of the Ag-AgCl / α-Fe2O3 composite material with a visible light catalytic composite material having a plasma resonance effect prepared by the present invention. Figure 3(a) It can be seen that after visible light excites α-Fe2O3, the photogenerated electrons transfer from the forbidden band to the conduction band (the band gap of silver chloride is wide (3.25 eV) and cannot be excited by visible light). Due to the metallic silver plasmon resonance effect, the visible light absorption range can be expanded ( Figure 3 (b) The electron transfer effect of metallic silver promotes electron transport and transfers excess electrons to the conduction band of silver chloride, thereby reducing the recombination efficiency of photoinduced carriers during the photocatalytic process, promoting the effective separation of photogenerated charges, and improving photocatalytic efficiency. During photocatalytic redox, holes in the band gap of α-Fe₂O₃ oxidize water or hydroxyl groups into hydroxyl radicals (•OH). These reactive radicals attack and damage cells, causing oxidation of cellular components and perforation of the microbial cell wall, leading to membrane leakage, structural damage, and ultimately death.

[0044] Example 2

[0045] Evaluation of the effectiveness of composite materials in killing toxigenic aflatoxin:

[0046] Preparation of Aspergillus flavus suspension:

[0047] Toxigenic Aspergillus flavus ( Aspergillus flavus 3.4408, purchased from China General Microbiological Culture Collection Center) was inoculated into sterile aspergillus agar-based medium and incubated in a mold incubator (28 o Cultivate for about 3 days until the bottom of the Aspergillus flavus turns orange. Use a sterile toothpick to pick the Aspergillus flavus hyphae and inoculate it on sterile chloranilamine glycerol agar medium. o Cultivate the Aspergillus flavus with sterile Tween-80 (0.1%) and count the Aspergillus flavus with a hemocytometer under an optical microscope. o C Store in refrigerator for future use.

[0048] 100 μL of the bacterial suspension and 0.02 g of the prepared catalyst powder were dispersed in 9.9 mL of sterile water, the mixture was stirred evenly and placed under visible light for photocatalytic treatment. 1.0 mL of the suspension was diluted with sterile water at regular intervals and evenly spread on malt extract agar medium. o After culturing for 24-28 hours, observe and record the number of colonies. The sterilization rate R% = (N0-N t ) / N0*100%, where N0 is the number of surviving Aspergillus flavus colonies at treatment time 0 min, and Nt is the number of surviving colonies at treatment time tmin.

[0049] Figure 4 (a) is a graph showing the effect of the nanomaterial prepared by the present invention in killing toxin-producing aflatoxin under dark conditions; Figure 4(b) is a diagram showing the effect of the nanomaterial prepared by the present invention in killing toxin-producing aflatoxin under visible light irradiation; Figure 4 (c) is a picture of the surviving colonies of Aspergillus flavus after Ag-AgCl / α-Fe2O3 photocatalytic treatment for 25 min; Table 1 shows the killing efficiency of the nanocomposites with different mass ratios prepared by the present invention against toxin-producing Aspergillus flavus under visible light irradiation. Figure 4 Under dark conditions, the bactericidal efficiencies of Ag-AgCl and Ag-AgCl / α-Fe2O3 were 28% and 30%, respectively, attributable to the inherent bactericidal properties of Ag. Furthermore, no significant bactericidal effect was observed under visible light irradiation alone without a catalyst, indicating that the cytotoxicity of visible light against Aspergillus flavus is negligible. Under visible light irradiation, the bactericidal efficiencies of catalysts with different compositions varied. Specifically, when the mass ratio of Ag:AgCl:α-Fe2O3 was 8:15:100, the bactericidal efficiency of Ag-AgCl / α-Fe2O3 against Aspergillus flavus reached over 99% after 25 minutes of photocatalytic treatment, significantly exceeding the bactericidal efficiencies of α-Fe2O3, AgCl / α-Fe2O3, and Ag-AgCl.

[0050] Table 1. Killing efficiency of nanocomposites with different mass ratios against toxigenic Aspergillus flavus under visible light irradiation (25 min).

[0051]

[0052] Repeatability and stability experiments:

[0053] In order to prove the bactericidal stability and structural stability of the photocatalytic nanomaterials, this study conducted five cycle experiments. After the photocatalytic bactericidal experiment, Ag-AgCl / α-Fe2O3 was recovered and washed with deionized water and ethanol. o After drying at 3 °C for 3 h, it was used again in the photocatalytic sterilization experiment and repeated 5 times. The results are as follows Figure 5 (a). After five cycles of use, the bactericidal rate of Ag-AgCl / α-Fe2O3 remained at around 95%, indicating that the bactericidal performance of the composite material was stable. In addition, the XRD spectra of Ag-AgCl / α-Fe2O3 did not change significantly before and after the cycles, proving the structural stability of the composite material ( Figure 5 (b)).

[0054] Example 3

[0055] Preparation and effect evaluation of photocatalytic composite bactericidal film

[0056] Preparation of photocatalytic composite material sterilization film:

[0057] Weigh 1.0-2.0 g of the Ag-AgCl / α-Fe2O3 composite material prepared in Example 1 (with a mass ratio of 8:15:100 for Ag, AgCl, and α-Fe2O3) and evenly disperse it in 20-30 mL of deionized water. Ultrasonicate for 30 minutes, then slowly add 3-5 mL of dimethylformamide or methanol. Grind the mixture thoroughly until it becomes a uniform, viscous suspension. The suspension is then dripped onto a substrate and naturally cast into a film. Under inert gas, calcination at 300-350°C is performed to strengthen the composite film, thereby forming a photocatalytic composite film.

[0058] Evaluation of the bactericidal effect of photocatalytic composite film:

[0059] Take 100 μL of the bacterial suspension and the prepared photocatalytic composite bactericidal film respectively to 9.9 mL of sterile water and perform photocatalytic treatment under visible light. Take 1.0 mL of the suspension at regular intervals and dilute it with sterile water, then evenly spread it on malt extract agar medium and place it at 28 o After culturing for 24-28 hours, observe and record the number of colonies. The sterilization rate R% = (N0-N t ) / N0*100%, where N0 is the number of surviving Aspergillus flavus colonies at 0 min of treatment, and Nt is the number of surviving colonies at t min of treatment.

[0060] Figure 6 is the bactericidal efficiency of the prepared photocatalytic composite film. It can be seen from the figure that after 25 minutes of photocatalytic treatment, the bactericidal rate of the prepared composite film against Aspergillus flavus is greater than 95%, which has good application potential.

[0061] Example 4

[0062] Scanning electron microscope observation of Aspergillus flavus cells:

[0063] The bacterial suspensions from Example 2 were collected after different photocatalytic treatment times, washed three times by centrifugation, and fixed with 2.5% glutaraldehyde. The samples were dehydrated and fixed with different concentrations of ethanol (30%, 50%, 70%, 90%, and 100%) for 15 minutes, freeze-dried, and then sprayed with gold for observation using a scanning electron microscope.

[0064] like Figure 7 As shown in (a), before photocatalytic treatment, the Aspergillus flavus cells were complete and regular spherical structures. After 5 minutes of photocatalytic treatment, the cells were obviously shrunken and deformed ( Figure 7 (b). After 10 minutes of photocatalytic treatment, obvious holes appeared on the surface of Aspergillus flavus cells ( Figure 7 (c)). As the photocatalytic treatment time increases, larger cracks appear on the cells, causing the cell contents to leak and causing the intracellular components to be degraded by active free radicals ( Figure 7(d) and Figure 7 (e)). Finally, the protrusions on the surface of the Aspergillus flavus were completely destroyed and disappeared, and the cells became flat due to the leakage of their contents ( Figure 7 (f)). The above results show that photocatalytic treatment can destroy the structure of Aspergillus flavus, causing the leakage of intracellular components and eventually death.

[0065] Example 5

[0066] Evaluation of the performance of visible light catalytic composite materials with surface plasmon resonance effect in killing aflatoxin-producing peanuts:

[0067] Collect uniform and complete peanut samples for sterilization, then inoculate the surface of peanuts with a suspension of Aspergillus flavus. After natural drying, take 100 mg of Ag-AgCl / α-Fe2O3 (the mass ratio of Ag, AgCl and α-Fe2O3 is 8:15:100) powder and evenly sprinkle it on the surface of peanuts. After light treatment for a certain period of time, separate the peanuts from the material. o After culturing for 7 days, the peanuts were collected and sterilized (121 o C, 30 min), and dried in an oven (80 o C, 60 min). The dried peanut samples were crushed, 1.00 g of the peanut powder was weighed and extracted with methanol, and then enriched with an immunoaffinity column. The aflatoxins (AFTs, AFB1+AFB2+AFG1+AFG2) and aflatoxin B1 (AFB1) in the peanut samples were determined by high performance liquid chromatography (HPLC). Figure 8 As shown in Figure 2, the aflatoxin content increased from 405.21 μg kg -1 decreased to 27.15 μg kg -1 , and the content of AFB1 increased from 310.53 μg kg -1 decreased to 16.35 μg kg -1 The above results show that under visible light irradiation, the prepared Ag-AgCl / α-Fe2O3 can not only effectively kill Aspergillus flavus, but also effectively reduce aflatoxin contamination, which helps to ensure the quality safety of agricultural products such as peanuts.

Claims

1. A method for killing toxigenic Aspergillus flavus, characterized in that: Ag-AgCl / α-Fe2O3 nanocomposite material is used to kill aflatoxin under visible light irradiation. The Ag-AgCl / α-Fe2O3 nanocomposite material is prepared by the following preparation method: ferric chloride hexahydrate and terephthalic acid are dissolved in N,N-dimethylformamide, and dried after solvent thermal reaction. After the reaction is completed and cooled to room temperature, the obtained product is centrifuged, washed, dried overnight, and ground to obtain α-Fe2O3. The solvent thermal reaction conditions for preparing α-Fe2O3 are: at 80-120 o The reaction was carried out under conditions of C for 12 to 15 h, and the molar ratio of ferric chloride hexahydrate to terephthalic acid was 1.3 to 1.5:

1. ； A uniform suspension of α-Fe2O3 is provided, and then chlorine and silver precursors are slowly added to the α-Fe2O3 suspension, stirred, and reacted in the dark for a period of time to obtain an AgCl / α-Fe2O3 material. The Ag-AgCl / α-Fe2O3 nanocomposite material is then treated under visible light for 30 to 90 minutes to obtain an Ag-AgCl / α-Fe2O3 nanocomposite material. The Ag-AgCl / α-Fe2O3 nanocomposite material comprises micron-sized quadrangular pyramid-shaped α-Fe2O3 and Ag-AgCl particles attached to the micron-sized quadrangular pyramid-shaped α-Fe2O3. The particle size of the micron-sized quadrangular pyramid-shaped α-Fe2O3 is 0.8 to 1.2 μm, the particle size of the Ag is 3 to 5 nm, and the particle size of the AgCl is 100 to 150 nm. In the Ag-AgCl / α-Fe2O3 composite material, the mass ratio of Ag, AgCl, and α-Fe2O3 is 6 to 10:10 to 20:

100.

2. The method according to claim 1, wherein: The Ag-AgCl / α-Fe2O3 nanocomposite material is used in the form of powder, suspension or film dispersed on a carrier.

3. The method according to claim 1, wherein: The light source is natural light or a xenon lamp; the irradiation time is 10-25 min; when a xenon lamp is used as the light source, the power of the xenon lamp is 150-300 W, the wavelength range of the light is 420-700 nm; the distance between the sample and the xenon lamp is 20-25 cm.

4. A method for killing toxigenic Aspergillus flavus, characterized in that: The Ag-AgCl / α-Fe2O3 nanocomposite material is added to the biological sample system to be processed and subjected to visible light irradiation treatment to effectively kill mold and reduce the risk of aflatoxin contamination. The Ag-AgCl / α-Fe2O3 nanocomposite material is prepared by the following preparation method: ferric chloride hexahydrate and terephthalic acid are dissolved in N,N-dimethylformamide, and dried after solvent thermal reaction. After the reaction is completed and cooled to room temperature, the obtained product is centrifuged, washed, dried overnight, and ground to obtain α-Fe2O3. The solvent thermal reaction conditions for preparing α-Fe2O3 are: at 80-120 o The reaction was carried out under conditions of C for 12 to 15 h, and the molar ratio of ferric chloride hexahydrate to terephthalic acid was 1.3 to 1.5:

1. ； A uniform suspension of α-Fe2O3 is provided, and then chlorine and silver precursors are slowly added to the α-Fe2O3 suspension, stirred, and reacted in the dark for a period of time to obtain an AgCl / α-Fe2O3 material. The Ag-AgCl / α-Fe2O3 nanocomposite material is then treated under visible light for 30 to 90 minutes to obtain an Ag-AgCl / α-Fe2O3 nanocomposite material. The Ag-AgCl / α-Fe2O3 nanocomposite material comprises micron-sized quadrangular pyramid-shaped α-Fe2O3 and Ag-AgCl particles attached to the micron-sized quadrangular pyramid-shaped α-Fe2O3. The particle size of the micron-sized quadrangular pyramid-shaped α-Fe2O3 is 0.8 to 1.2 μm, the particle size of the Ag is 3 to 5 nm, and the particle size of the AgCl is 100 to 150 nm. In the Ag-AgCl / α-Fe2O3 composite material, the mass ratio of Ag, AgCl, and α-Fe2O3 is 6 to 10:10 to 20:

100.

5. The method according to claim 4, characterized in that: The biological sample is an agricultural product, and the agricultural product is peanuts or corn.

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