A graphite / iron oxide nanoparticle with near-infrared photodynamic sterilization, its preparation method and application

Abstract

This invention discloses a graphite / ferric oxide nanoparticle with near-infrared photodynamic sterilization, its preparation method, and its application. The method includes: preparing and purifying graphite nanospheres using hexane as a carbon source via an arc method; reacting the graphite nanospheres with FeCl3·6H2O to form a gel; and then heat-treating the gel under an Ar / H2 mixed atmosphere to obtain graphite-ferric oxide nanoparticles. This invention couples graphite and ferric oxide together, which can suppress the recombination of graphite charge-hole pairs and improve the ability of the nanoparticles to generate reactive oxygen species using photogenerated electrons and holes. Sterilization using reactive oxygen species avoids damage to the flavor and texture of food, and the strong self-decomposition ability of reactive oxygen species avoids toxicity and pollution. Photodynamic antibacterial properties, achieved by controlling the space, time, and power of light irradiation, allow for controllable antibacterial function, making it more suitable for process control in the preservation of different types of food and possessing strong application value.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, and in particular to a method for preparing graphite / ferric oxide nanoparticles with near-infrared photodynamic sterilization, the graphite / ferric oxide nanoparticles, and their applications. Background Technology

[0002] Food is highly susceptible to microbial contamination during harvesting, processing, transportation, and storage. The growth of microorganisms such as bacteria, molds, and yeasts is not only a major cause of food spoilage and shortened shelf life, but can also lead to foodborne illnesses by producing toxins or pathogens, posing a serious threat to public health and causing enormous food waste and economic burden.

[0003] Currently, commercial food packaging mainly relies on inert polymer materials (such as polyethylene, polypropylene, and polyester), whose core function is a physical barrier—isolating oxygen, moisture, and external contaminants. This type of packaging cannot actively inhibit microorganisms already present inside or on the surface of the packaging; once the packaging is opened or the surface is contaminated, microorganisms can multiply rapidly. Therefore, developing food packaging materials with active antimicrobial functions has become a research hotspot in the field of food preservation.

[0004] Introducing antibacterial active ingredients directly into packaging materials is the most direct way to achieve active antibacterial activity. Among these, inorganic nano-antibacterial agents (such as nano-silver, nano-copper, and nano-zinc oxide) have attracted much attention due to their broad-spectrum and highly efficient bactericidal properties, and have been widely used in medical devices, textiles, and water treatment. However, using such nanoparticles in food packaging faces serious safety challenges: First, copper and silver ions are prone to leaching in humid or acidic food environments, and if the amount migrating into the food exceeds safety limits, it may cause cumulative toxicity to organs such as the liver and kidneys; second, nanoparticles tend to aggregate in the packaging matrix, leading to a decrease in antibacterial activity; third, some metal nanoparticles have poor long-term stability and may oxidize and discolor under light or high-temperature conditions, affecting the appearance and function of the packaging. Therefore, despite their excellent antibacterial effects, safety and stability bottlenecks severely restrict their practical application in the food industry.

[0005] Photodynamic sterilization, as an emerging non-thermal sterilization technology, has demonstrated unique advantages in the field of food science in recent years. Its principle involves using light of a specific wavelength to excite a photosensitizer, transferring energy to surrounding oxygen molecules to generate reactive oxygen species such as singlet oxygen, superoxide anions, and hydroxyl radicals. These reactive oxygen species can irreversibly damage the cell membranes, proteins, and nucleic acids of microorganisms, thereby achieving highly efficient sterilization. Compared with traditional sterilization technologies, photodynamic sterilization has significant advantages in food applications: Highly efficient and controllable: By adjusting the range, time and intensity of light, specific areas of food (such as damaged areas of fruit peels or cut surfaces of meat) can be precisely treated, avoiding unnecessary heat damage or chemical residues to the whole food.

[0006] Safety and environmental friendliness: Reactive oxygen species have an extremely short lifespan, only functioning during periods of light exposure and in localized areas. Once light exposure ceases, they rapidly decompose into water or oxygen, producing no persistent toxic byproducts. Therefore, they do not pose a risk to the food itself or the health of end consumers.

[0007] Less likely to induce drug resistance: Because reactive oxygen species kill microorganisms through a multi-target mechanism, unlike the single-target inhibition of traditional antibiotics, microorganisms are less likely to develop drug resistance.

[0008] However, the performance of existing photosensitizers in food packaging applications still has significant shortcomings. Current research mostly uses natural photosensitizers (such as curcumin, riboflavin, chlorophyll derivatives, and porphyrin), which, although their natural origin grants them a certain degree of safety, generally suffer from the following drawbacks: Poor photostability: Natural photosensitizers are prone to photobleaching under continuous light, leading to rapid decline in activity and making it difficult to maintain long-lasting antibacterial effects.

[0009] Low photodynamic yield: Most natural photosensitizers have low singlet oxygen quantum yield (usually <0.5), requiring high concentrations or extremely long light exposure times to achieve effective sterilization, which is difficult to achieve in rapid processing or large packaging scenarios.

[0010] It is difficult to maintain activity in the packaging matrix: natural photosensitizers have poor compatibility with hydrophobic polymer substrates and are prone to aggregation or migration, resulting in photodynamic efficiency in actual packaging environments that is far lower than that in solution tests.

[0011] Strong dependence on specific wavelengths: The optimal excitation wavelengths of many natural photosensitizers are located in the ultraviolet region or the short-wavelength band of visible light. These bands have limited penetration depth under actual light conditions on food, and ultraviolet light may have adverse effects on food components.

[0012] Therefore, there is an urgent need to provide a solution for graphite / iron oxide nanoparticles with near-infrared photodynamic sterilization, their preparation method, and their applications. Summary of the Invention

[0013] To address the above problems, the present invention provides a graphite / iron oxide nanoparticle with near-infrared photodynamic sterilization, its preparation method, and its application, which can preserve food and avoid damaging its flavor and texture.

[0014] According to a first aspect of the present invention, a method for preparing graphite / ferric oxide nanoparticles with near-infrared photodynamic sterilization is provided, comprising: S1. Using a graphite rod as the cathode, after the electric arc furnace reaches a vacuum state, n-hexane is injected into the vacuum chamber as a carbon source to react and generate nano-graphite spheres. After the reaction, the nano-graphite spheres are purified in argon gas to obtain black nano-graphite sphere powder. S2. Prepare an anhydrous ethanol suspension of nano-graphite using the black nano-graphite ball powder from step S1, and mix it with ultrasound. Then add FeCl3·6H2O aqueous solution to the suspension and stir to obtain a black gel. Wash and dry the black gel. S3. The dried gel was heat-treated under an Ar / H2 mixed atmosphere to obtain graphite / iron tetroxide nanoparticles.

[0015] In the above scheme, in step S1, nanographite spheres are prepared using the plasma arc method.

[0016] In the above scheme, in step S1, the vacuum state is when the vacuum degree of the electric arc furnace reaches 10. -4 Pa or above.

[0017] In the above scheme, in step S1, the purification time of the nanographite spheres in argon gas is 20-25 hours.

[0018] In the above scheme, in step S2, a nano-graphite anhydrous ethanol suspension with a concentration of 10 mg / mL is prepared using the black nano-graphite sphere powder from step S1 and ultrasonically mixed for 30-60 min.

[0019] In the above scheme, in step S2, the volume fraction of FeCl3·6H2O aqueous solution is 5%, the volume ratio of nano-graphite ethanol suspension to FeCl3·6H2O aqueous solution is 2:1 to 1:1, the mixing temperature range of nano-graphite ethanol suspension and FeCl3·6H2O aqueous solution is between 80℃ and 90℃, and the mixing time is 5 hours to 8 hours.

[0020] In the above scheme, in step S3, the furnace heating rate is 2~4℃ / min, the furnace temperature is raised to 430~470℃, held for 4 hours, and then cooled down to room temperature at a rate of 2~4℃ / min.

[0021] According to a second aspect of the present invention, graphite / ferric oxide nanoparticles with near-infrared photodynamic sterilization are provided, which are prepared by the method described in any one of the above schemes, wherein the graphite / ferric oxide nanoparticles use graphite spheres as carriers and the surface of the graphite spheres is loaded with nano-ferric oxide.

[0022] The graphite / ferric oxide nanoparticles described in the above scheme can kill bacteria under near-infrared light irradiation. The near-infrared light irradiation conditions include: a near-infrared wavelength of 800–1100 nm and a laser power density of 0.5–1.0 W / cm². 2 The irradiation time is 5 to 10 minutes.

[0023] The graphite / iron oxide nanoparticles described in the above scheme are used in food preservation.

[0024] The beneficial effects of this invention are: Graphite and magnetite (Fe3O4) are coupled together. Magnesium tetroxide is a narrow bandgap semiconductor (~0.1 eV) exhibiting both n / p-type semiconductor characteristics; while graphite is a highly conductive carbon material. The interface between the two forms a built-in electric field, leading to the generation of photoelectrons (electrons). - The rapid transfer of cells from graphite to iron oxide (Fe3O4) creates holes (h). + The electrons remain on the graphite surface. Therefore, the presence of iron(III) oxide can inhibit the recombination of graphite charge-hole pairs, thereby improving the ability of nanoparticles to generate reactive oxygen species using photogenerated electrons and holes, resulting in a nanocomposite with high photodynamic bactericidal properties. Furthermore, iron(III) oxide itself has good biocompatibility, reducing the risk of metal ion toxicity.

[0025] Sterilization using active oxygen avoids damage to the flavor and texture of food, and active oxygen itself has a strong decomposition ability, avoiding toxicity and pollution.

[0026] Photodynamic antibacterial technology allows for controllability of antibacterial function by controlling the space, time, and power of light. It is more suitable for process control of preservation of different types of food, is simple to operate, and has strong application value. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the method of the present invention; Figure 2 The images show the scanning electron microscope morphology and energy dispersive spectroscopy (EDS) spectrum of the graphite / iron oxide nanoparticles synthesized in this invention.

[0029] Figure 3 This invention evaluates the performance of the graphite / iron tetroxide nanoparticles synthesized in this invention in generating singlet oxygen.

[0030] Figure 4 This image shows the preservation effect of the graphite / iron oxide nanoparticles synthesized in this invention on strawberries under near-infrared long-wavelength light.

[0031] Figure 5 This image shows the preservation effect of the graphite / iron oxide nanoparticles synthesized in this invention on bananas under near-infrared long-wavelength light irradiation.

[0032] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0034] The terms "first," "second," etc., used in this disclosure are for distinguishing similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0035] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0036] Multiple, including two or more.

[0037] And / or, it should be understood that, for the purposes of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0038] like Figure 1 As shown, one embodiment of the technical solution of the present invention provides a method for preparing graphite / iron oxide nanoparticles with near-infrared photodynamic sterilization, comprising: S1. Using a graphite rod as the cathode, after the electric arc furnace reaches a vacuum state, n-hexane is injected into the vacuum chamber as the carbon source to react and generate nano-graphite spheres. After the reaction, the nano-graphite spheres are purified in argon gas to obtain black nano-graphite sphere powder. S2. Prepare an anhydrous ethanol suspension of nano-graphite using the black nano-graphite ball powder from step S1, and mix it with ultrasound. Then add FeCl3·6H2O aqueous solution to the suspension and stir to obtain a black gel. Wash and dry the black gel. S3. The dried gel was heat-treated under an Ar / H2 mixed atmosphere to obtain graphite / iron tetroxide (C@Fe3O4) nanoparticles.

[0039] In step S1, nanographite spheres are prepared using the plasma arc method. The vacuum state is such that the vacuum degree of the arc furnace reaches 10. -4 The pressure is above 10 Pa. The purification time for the nanographite spheres in argon is 20-25 hours. Step S1 ensures that the graphite spheres have uniform particle size and clean surface.

[0040] In step S2, a 10 mg / mL anhydrous ethanol suspension of nano-graphite was prepared using the black nano-graphite sphere powder from step S1 and ultrasonically mixed for 30-60 min. The volume fraction of the FeCl3·6H2O aqueous solution was 5%, and the volume ratio of the nano-graphite ethanol suspension to the FeCl3·6H2O aqueous solution was 2:1 to 1:1. The mixing temperature of the nano-graphite ethanol suspension and the FeCl3·6H2O aqueous solution was between 80℃ and 90℃, and the mixing time was between 5 and 8 hours. In step S2, the coordinated control of temperature and time ensured that the iron(III) oxide precursor was uniformly loaded onto the graphite surface.

[0041] In step S3, the furnace heating rate is 2~4℃ / min, the furnace temperature rises to 430~470℃, and after holding at that temperature for 4 hours, it is cooled down to room temperature at a rate of 2~4℃ / min. This mild and slow heat treatment process in step S3 ensures the integrity of the iron oxide crystal structure while avoiding excessive ablation of graphite, thereby obtaining graphite / iron oxide nanoparticles with stable structure and excellent activity.

[0042] Existing photodynamic sterilization technologies mostly employ natural organic photosensitizers such as curcumin or riboflavin. While these substances possess certain photosensitizing activity, they suffer from poor stability and insufficient photodynamic efficiency, making it difficult to meet practical food preservation needs. This invention combines graphite nanospheres with iron oxide (Fe3O4) to construct a fully inorganic photodynamic nanosystem, fundamentally improving the material's stability and photoresponsiveness. Compared to existing technologies, traditional graphite-based composite materials are primarily used in electrochemical energy storage or adsorption separation, without being combined with iron oxide for near-infrared photodynamic sterilization. Furthermore, conventional iron oxide nanoparticles are typically used in magnetothermal therapy or magnetic resonance imaging, lacking application in photodynamic antibacterial applications. This solution, for the first time, explicitly achieves an effective heterojunction interface between graphite and iron oxide through precise control of process parameters, laying a material foundation for subsequent synergistic enhancement of photodynamic performance.

[0043] This invention also discloses a graphite / iron oxide nanoparticle with near-infrared photodynamic sterilization, prepared using the above method as follows: Figure 2 The image shows the scanning electron microscope (SEM) morphology and energy dispersive spectroscopy (EDS) spectrum of the nanoparticles synthesized in this embodiment. The nanoparticles exhibit a uniform spherical distribution and are composed of C, O, and Fe elements. Specifically, the core structure of the nanoparticles in this invention uses highly conductive graphite spheres as a carrier, with nanoscale iron oxide (Fe3O4) particles uniformly loaded on the surface. Graphite itself has good light absorption and charge transport characteristics, enabling it to generate photogenerated electrons and holes under near-infrared light excitation. However, photogenerated charge carriers in pure graphite are prone to recombination, resulting in low reactive oxygen species (ROS) yield. Iron oxide (Fe3O4), as a narrow bandgap semiconductor with a bandgap width of approximately 0.1 eV, possesses both n-type and p-type semiconductor characteristics. When graphite and iron oxide are in close contact, a built-in electric field is formed at their interface, driving photogenerated electrons to rapidly transfer from graphite to iron oxide, while holes remain on the graphite surface. This spatial separation of electrons and holes effectively suppresses their recombination process and significantly extends the lifetime of photogenerated charge carriers. Subsequently, the vacancies remaining on the graphite surface can react with water molecules or hydroxide ions to generate hydroxyl radicals, while electrons migrating to iron(III) oxide can reduce oxygen to superoxide anions, and further generate singlet oxygen through an energy transfer process. These three reactive oxygen species work together to cause extensive oxidative damage to bacterial cell membranes, proteins, and nucleic acids, thereby achieving highly efficient sterilization.

[0044] The graphite / ferric oxide nanoparticles prepared by this invention can be used for food preservation. These nanoparticles can kill bacteria under near-infrared light irradiation, wherein the near-infrared light irradiation conditions include: a near-infrared wavelength of 800–1100 nm and a laser power density of 0.5–1.0 W / cm². 2The irradiation time is 5–10 minutes. Near-infrared light irradiation offers deeper tissue penetration and a lower risk of photothermal damage. Furthermore, graphite exhibits surface plasmon resonance in this wavelength range, further enhancing light absorption efficiency. This allows the nanoparticles of this invention to possess highly efficient photodynamic bactericidal properties while ensuring safety.

[0045] Compared with existing food preservation technologies, the graphite / ferric oxide nanoparticles in this solution exhibit several irreplaceable advantages in the field of food preservation. Firstly, they possess highly efficient and broad-spectrum antibacterial capabilities, far exceeding the antibacterial levels achieved by using nanoparticles alone or by light irradiation alone. This photodynamic synergistic enhancement effect enables the invention to effectively inhibit common spoilage bacteria and foodborne pathogens in food, significantly extending the shelf life of food. Secondly, they offer safety. Ferric oxide, as a safe food contact material, has excellent biocompatibility. Unlike traditional antibacterial nanoparticles such as silver and copper, ferric oxide does not release toxic metal ions, avoiding the potential threat to food safety posed by heavy metal residues. Simultaneously, the reactive oxygen species generated during the photodynamic process have an extremely short lifespan, decomposing into water and oxygen within microseconds to milliseconds, leaving no harmful byproducts on the food surface. The nanoparticles themselves can also be removed through a simple washing process, preventing them from penetrating the food interior, further ensuring food safety. Thirdly, they offer controllability. The effect of photodynamic sterilization can be precisely controlled by adjusting the wavelength, power density, and irradiation time of the light. For example, the irradiation time can be appropriately extended for fruits with thicker skins, while a lower power density can be used for berries with delicate textures. This controllability allows the present invention to adapt to the preservation needs of different types of food, avoiding the drawbacks of traditional chemical preservatives such as difficulty in accurately controlling the dosage and easy residue.

[0046] In summary, this invention overcomes the limitations of traditional photosensitizers in its preparation method, achieving efficient composite of graphite and iron(III) oxide through precisely controlled processes. In terms of its mechanism of action, it utilizes the built-in electric field of the heterojunction to suppress charge-hole pair recombination, significantly improving the yield of reactive oxygen species excited by near-infrared light. In food preservation applications, it combines highly efficient antibacterial properties, high safety, strong controllability, and significant practical preservation effects. Example 1

[0047] This embodiment studies the photodynamic generation performance of C@Fe3O4 nanoparticles prepared in this invention to generate singlet oxygen. Using 1,3-diphenylisobenzofuran (DPBF) as a probe, it can be generated by singlet oxygen (… 1 O2 (a type of ROS) oxidizes and significantly reduces absorbance at 410 nm. Therefore, 50 μg / mL C@Fe3O4 nanoparticles were mixed with DPBF dissolved in diformamide (DMF) (1 mg / mL). 1The mixture was then placed in a near-infrared environment with a wavelength of 1064 nm and a laser power density of 1.0 W / cm². 2 Irradiate for 5 minutes. After irradiation, incubate for a total of 10 minutes, and detect the absorption spectrum in the 300 nm–600 nm range using a UV-Vis absorption spectrophotometer. Figure 3 As shown, after near-infrared II illumination treatment, the DPBF characteristic peak decreased significantly, indicating that C@Fe3O4 nanoparticles have a significant ability to generate singlet oxygen excited by photodynamics. Example 2

[0048] This embodiment studies the C@Fe3O4 nanoparticles prepared according to the present invention and their photodynamic bactericidal properties. The specific process is as follows: (1) Pathogens tested: Escherichia coli (ATCC 8739), Staphylococcus aureus (ATCC 6538), Salmonella enterica subsp. enterica (ATCC 14028).

[0049] (2) Test culture medium: The above bacterial cultures all use general nutrient broth culture medium.

[0050] (3) Inoculate the bacteria into nutrient broth medium and incubate at 37 ℃ for 8-10 hours. Measure the optical density (OD) at 600 nm using a UV spectrophotometer. 600 When the concentration is 1.0, the bacteria grow to 10 per milliliter. 8 10 colony-forming units (10 8 (CFU / mL).

[0051] (4) C@Fe3O4 nanoparticles were prepared into a suspension (100 μg / mL) using PBS buffer. Then, different bacterial suspensions were mixed with the nanoparticle suspension of the same concentration in equal volumes, resulting in a final nanoparticle concentration of 50 μg / mL. Two sets of each mixture were prepared. One set was incubated in a shaker at 37°C for 24 hours. The other set was incubated in a shaker at 37°C for 4 hours and then subjected to near-infrared laser light at a wavelength of 1064 nm and a power density of 1.0 W / cm². 2 Irradiate for 5 min, then continue culturing for 24 h. In addition, the different bacterial cultures were mixed in equal volumes with PBS buffer without nanoparticles and placed in a near-infrared laser at a wavelength of 1064 nm and a power density of 1.0 W / cm². 2Irradiation for 5 min followed by 24 h of culture served as the photodynamic control group. Bacteria cultured naturally for 24 h without any treatment served as the blank control group. After all groups were cultured, 100 μL of the mixture was transferred and evenly spread onto solid culture medium, and incubated at 37℃ for 24 hours. Bacterial colonies on the plates were observed and recorded, with bacterial colonies not treated with nanoparticles serving as the control group.

[0052] (5) The antibacterial rate is calculated using the following formula: Antibacterial rate = (Average colony count in blank control group - Average colony count in experimental group) × 100% / Average colony count in blank control group Test results: The test results are shown in Table 1 below.

[0053] Table 1 Testing revealed that PBS buffer itself lacks photodynamic response capabilities, therefore photodynamic treatment alone did not exhibit antibacterial properties. However, when C@Fe3O4 nanoparticles were applied alone at a final concentration of 50 μg / mL, they demonstrated antibacterial activity due to the nano-effect. Combined with photodynamic therapy, they produced 95% antibacterial activity against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus), and foodborne pathogens (Salmonella enterica subsp. enterica). Example 3

[0054] This embodiment describes a photodynamic sterilization and preservation method for strawberries using C@Fe3O4 nanoparticles prepared according to the present invention. The specific steps are as follows: Prepare a 50 μg / mL C@Fe3O4 aqueous suspension and fill it into a light-proof spray bottle; The prepared C@Fe3O4 aqueous suspension was evenly sprayed onto the bottom of a stainless steel food storage container and left to stand in the dark for 30 minutes. Strawberries with bright color, intact and uniform size were selected and placed in the stainless steel food storage box in (2). Strawberries placed in the food storage box that was not treated in (2) were used as the control group. Both the experimental group and the control group were stored at room temperature. The strawberries in (3) were placed in a near-infrared laser with a wavelength of 1064 nm and a power density of 1.0 W / cm². 2 Irradiate for 5 minutes to complete the photodynamic sterilization and preservation process.

[0055] The preservation process in (3) was monitored, and the process of strawberry spoilage was recorded by taking pictures. Strawberry samples were taken at the initial placement (D0), 2 days after placement (D2), and 5 days after placement (D5) for total bacterial count detection. The specific method was as follows: 25 g of sample was weighed and placed in a sterile homogenizing bag containing 225 mL of diluent. The sample was homogenized by tapping for 1 min to 2 min to prepare a 1:10 sample homogenate. Then, the sample homogenate was serially diluted 10 times. Three gradient dilutions of each sample homogenate were evenly spread on a solid culture medium and incubated at 37℃ for 24 hours. The bacterial colonies on the plates were recorded and the total bacterial count was calculated.

[0056] like Figure 4 As shown, strawberries in the control group without photodynamic sterilization and preservation showed blackening after 1 day (D1), and significant spoilage and mold growth after 2 days (D2). In contrast, strawberries in the experimental group did not show slight black mold spots until the 4th day (D4). Accordingly, Table 2 records the changes in total bacterial count during the photodynamic sterilization and preservation process of strawberries. Compared with the control group, the experimental group effectively reduced the rate of bacterial reproduction in strawberries. Therefore, the nanoparticles prepared in this invention can delay strawberry spoilage and possess near-infrared photodynamic sterilization and preservation functions.

[0057] Table 2 Example 4

[0058] To further verify that the C@Fe3O4 nanoparticles prepared in this invention possess near-infrared photodynamic sterilization and preservation functions, we applied this photodynamic sterilization and preservation method to banana preservation. For example... Figure 5 As shown, after 2 days (D2), the bananas in the control group had significant black mold spots all over their surface, while the bananas in the experimental group only showed slight mold spots after 4 days (D4). Correspondingly, Table 3 records the changes in the total bacterial count of the bananas during the photodynamic sterilization and preservation process. After photodynamic sterilization and preservation treatment, bacterial proliferation in the bananas was significantly slowed down. These results fully demonstrate that the nanoparticles prepared in this invention possess near-infrared photodynamic sterilization and preservation functions.

[0059] Table 3 It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0060] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0061] Through the above description of the embodiments, those skilled in the art can clearly understand that the above implementation methods can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0062] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing graphite ferroferric oxide nanoparticles with near-infrared photodynamic sterilization, characterized in that, include: Graphite nanospheres were prepared and purified by an electric arc method using hexane as the carbon source. The graphite nanospheres were then reacted with FeCl3·6H2O to form a gel, which was then heat-treated in an Ar / H2 mixed atmosphere to obtain graphite iron tetroxide nanoparticles.

2. The method of claim 1, wherein the method is characterized by: Specifically, the steps include the following: S1. Using a graphite rod as the cathode, after the electric arc furnace reaches a vacuum state, n-hexane is injected into the vacuum chamber as a carbon source to react and generate nano-graphite spheres. After the reaction, the nano-graphite spheres are purified in argon gas to obtain black nano-graphite sphere powder. S2. Prepare a nano-graphite anhydrous ethanol suspension using the black nano-graphite ball powder from step S1, and ultrasonically mix it. Then add FeCl3·6H2O aqueous solution to the suspension and stir to obtain a black gel. Wash and dry the black gel. S3. The dried gel was heat-treated under an Ar / H2 mixed atmosphere to obtain graphite iron oxide nanoparticles.

3. The method for preparing graphite iron tetroxide nanoparticles with near-infrared photodynamic sterilization according to claim 2, characterized in that, In step S1, the vacuum state is that the vacuum degree of the electric arc furnace reaches 10 -4 Pa or more.

4. The method of claim 2, wherein the method is characterized by: In step S1, the purification time of the nanographite spheres in argon gas is 20-25 hours.

5. The method for preparing graphite iron tetroxide nanoparticles with near-infrared photodynamic sterilization according to claim 2, characterized in that, In step S2, a nano-graphite anhydrous ethanol suspension with a concentration of 10 mg / mL is prepared using the black nano-graphite sphere powder from step S1 and ultrasonically mixed for 30-60 min.

6. The method for preparing graphite iron tetroxide nanoparticles with near-infrared photodynamic sterilization according to claim 2, characterized in that, In step S2, the volume fraction of FeCl3·6H2O aqueous solution is 5%, the volume ratio of nano-graphite ethanol suspension to FeCl3·6H2O aqueous solution is 2:1 to 1:1, the mixing temperature range of nano-graphite ethanol suspension and FeCl3·6H2O aqueous solution is between 80℃ and 90℃, and the mixing time is 5 hours to 8 hours.

7. The method for preparing graphite iron tetroxide nanoparticles with near-infrared photodynamic sterilization according to claim 2, characterized in that, In step S3, the furnace heating rate is 2~4℃ / min, the furnace temperature is raised to 430~470℃, held for 4 hours, and then cooled to room temperature at a rate of 2~4℃ / min.

8. Graphite ferroferric oxide nanoparticles having near-infrared photodynamic sterilization, characterized by, The graphite / ferric oxide nanoparticles are prepared by the method described in any one of claims 1-7, wherein graphite spheres are used as carriers and the surface of the graphite spheres is loaded with nano-ferric oxide.

9. The graphitic ferroferric oxide nanoparticle for killing bacteria under near-infrared light irradiation according to claim 8, wherein, The near-infrared light irradiation conditions include: near-infrared wavelength of 800-1100 nm, laser power density of 0.5-1.0 W / cm 2 , and irradiation time of 5-10 min.

10. The application of the graphite / iron oxide nanoparticles as described in claim 8 in food preservation.

Images