Zinc oxide loaded with monatomic silver, preparation method of zinc oxide and application of zinc oxide in food preservation

Abstract

The invention belongs to the technical field of synthesis of nano materials, and particularly relates to zinc oxide loaded with monatomic silver, a preparation method of the zinc oxide and application of the zinc oxide in food preservation. The preparation method of the zinc oxide loaded with monatomic silver comprises the following steps: S1, dispersing a zinc-containing compound and a polyamine compound in a solvent, adjusting the pH value of the system to 8-10, and carrying out hydrothermal synthesis to obtain zinc oxide nanoflowers; s2, ultrasonically mixing the zinc oxide nanoflower with a silver-containing compound in a dissolved state, filtering to obtain a precipitate, and calcining the precipitate to obtain zinc oxide loaded with monatomic silver; the polyamine compound is one or two of hexamethylenetetramine and urea. According to the preparation method disclosed by the invention, loading (AgSA / ZnO) of atomic-scale Ag single atoms in the three-dimensional flower-shaped ZnO nanostructure is realized through a silver nanoparticle thermal conversion and surface reconstruction strategy for the first time, so that the atom utilization rate and the catalytic activity are remarkably improved, and the integration of dual functions of synergistic antibacterial and ethylene removal is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial synthesis, and particularly relates to a single-atom silver-loaded zinc oxide, a preparation method thereof and application of the single-atom silver-loaded zinc oxide in food preservation. BACKGROUND

[0002] The loss caused by physiological loss of freshness and microbial spoilage has become a bottleneck restricting the transportation and preservation of fruits. Some metal oxide nanomaterials (such as zinc oxide and titanium dioxide), as food additives, exhibit dual preservation functions through antibacterial activity and ethylene degradation, but face major challenges in practical applications. Generally, they need to be combined with noble metal nanoparticles to establish a diatomic catalytic structure, and need external energy input (such as ultraviolet / thermal energy activation) to achieve sufficient catalytic performance for practical preservation applications. However, this traditional method has three fundamental limitations: (1) low utilization rate of noble metal atoms, which raises economic concerns and also poses potential cytotoxicity risks; (2) energy-dependent activation mechanism weakens practical applicability and scalability; (3) excessive energy exposure or prolonged treatment time can lead to a decline in the sensory quality and loss of nutritional ingredients of fresh agricultural products.

[0003] Single-atom nanomaterials have emerged in cross-disciplinary fields including precision medicine, food safety and environmental remediation due to their excellent atomic utilization efficiency and outstanding catalytic activity. Single-atom nanomaterials can also endow enhanced antibacterial and ethylene scavenging performance, thereby improving the utilization rate of noble metals and avoiding additional energy assistance. However, the single-atom Fe and Pt studied in general research are controversial in terms of safety and are not suitable for the food field.

[0004] The prior art CN 118929733 A discloses a large-size zinc oxide nanoflower, a preparation method and application thereof. The preparation method comprises the following steps: 1) dispersing zinc oxide nanoparticles in an alkaline aqueous solution to obtain a mixed solution; 2) performing a hydrothermal reaction on the mixed solution, and obtaining a sodium zincate nanoflower after solid-liquid separation, the sodium zincate nanoflower comprising a plurality of sodium zincate nanosheets, and the particle size of the sodium zincate nanoflower being 2-20 μm; and 3) calcining the sodium zincate nanoflower to obtain the zinc oxide nanoflower, the zinc oxide nanoflower comprising a plurality of zinc oxide nanosheets, and the particle size of the zinc oxide nanoflower being 2-20 μm. The method can obtain large-size zinc oxide nanoflowers, and the structure of the zinc oxide nanoflowers is easy to control. However, the zinc oxide nanoflowers alone have poor effects when applied to food packaging materials.

[0005] The prior art CN 110404533 A discloses a preparation method of noble metal silver loaded nano zinc oxide powder. The method uses water-soluble polymer and zinc nitrate hexahydrate and silver nitrate as raw materials, and through simple mixing reaction, a gel solution with a certain concentration is configured. A brown foam-shaped intermediate is obtained through freeze-drying, and finally calcination is performed to obtain the silver-zinc oxide target product. Through the entropy effect of the chain conformation of the water-soluble polymer and the strong hydrogen bond association between the hydrophilic groups on the chain and the hydroxyl groups on the particle surface, the dispersion of zinc oxide and silver nanoparticles in the polymer aqueous solution is promoted, and high-dispersity nano silver particle loaded zinc oxide is obtained. However, the performance of noble metal silver loaded nano zinc oxide is poor, especially when used for ethylene removal, an external light source is needed to catalyze the reaction. SUMMARY

[0006] The purpose of the present application is to provide a single-atom silver loaded zinc oxide with synergistic antibacterial and ethylene removal performance, and a preparation method thereof and its application in food preservation.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0008] A preparation method of single-atom silver loaded zinc oxide, comprising the following steps:

[0009] S1, dispersing a zinc-containing compound and a polyamine compound in a solvent, adjusting the pH of the system to 8-10, and performing hydrothermal synthesis to obtain zinc oxide nanoflower;

[0010] S2, ultrasonically mixing the zinc oxide nanoflower in a dissolved state with a silver-containing compound, then filtering to obtain a precipitate, and calcining the precipitate to obtain single-atom silver loaded zinc oxide;

[0011] The polyamine compound is one or both of hexamethylene tetramine and urea.

[0012] The present application successfully constructs zinc oxide nanoflower by pH regulation of zinc oxide precursor morphology, and loads silver nanoparticles, and then successfully prepares single-atom silver loaded zinc oxide nanoflower through thermal conversion of silver nanoparticles and surface reconstruction of zinc oxide.

[0013] The application creatively synthesizes silver single atom supported zinc oxide (AgSA / ZnO) through silver nanoparticles (AgNPs) thermal conversion and ZnO surface reconstruction. The preparation process is simple, easy and green, and can be popularized to the preparation of other metal oxide supported single atom materials. The application uses zinc oxide nanoflowers (ZnO NFs) with good biological safety as a substrate, and prepares AgSA / ZnO nanocomposites with antibacterial and ethylene scavenging properties through trace loading of silver single atom (AgSA).

[0014] According to the embodiments of the application, the application can be further optimized, and the following is a technical solution formed after optimization:

[0015] In one preferred embodiment, the zinc-containing compound includes one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate.

[0016] In one preferred embodiment, the silver-containing compound includes one or more of silver nitrate, silver acetate or silver sulfate.

[0017] In one preferred embodiment, the solvent in step S1 is water.

[0018] In one preferred embodiment, in step S1, ammonia or an organic strong base is used to adjust the pH of the system to 8-10.

[0019] In one preferred embodiment, the organic strong base is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide or choline hydroxide.

[0020] In this step, if an inorganic strong base such as NaOH or KOH is used, it will affect the control of the morphology, leading to agglomeration and failure to obtain nanoflowers.

[0021] In one preferred embodiment, in step S1, the hydrothermal synthesis time is 8-10h, the pressure is 0.1-0.3MPa, and the temperature is 80-100℃.

[0022] In one preferred embodiment, in step S2, the ultrasonic mixing time is 0.5-2.0h, and the frequency is 20-40kHz.

[0023] In one preferred embodiment, the calcination process in step S2 is performed at a heating rate of 0.5-10℃ / min, a calcination temperature of 300-450℃, and a calcination time of 1-3h.

[0024] A too fast heating rate (>15℃ / min) would cause the silver atoms to migrate too fast and sinter into particles, collapsing the nanoflower structure of the support zinc oxide; a too slow heating rate (<5℃ / min) would reduce the efficiency and possibly leave impurities.

[0025] A too high calcination temperature (>450℃) would cause severe agglomeration of silver and coarsening of the support; a too low calcination temperature (<350℃) would cause insufficient decomposition of silver nitrate and uneven loading of silver.

[0026] A too long calcination time (>3h) would cause the silver particles to mature and grow and the support to sinter; a too short calcination time (<1h) would cause incomplete reaction and insufficient formation of anchoring sites.

[0027] Based on the same inventive concept, the present application also claims the single-atom silver supported zinc oxide prepared by the preparation method.

[0028] Based on the same inventive concept, the present application also claims the use of the single-atom silver supported zinc oxide in fruit and vegetable preservation and / or antibacterial applications.

[0029] Based on the same inventive concept, the present application also claims a preservative bag containing the single-atom silver supported zinc oxide.

[0030] Other components of the preservative bag are conventional preservative bag components, and any available preservative bag disclosed in the prior art can be used in the present application.

[0031] Based on the same inventive concept, the present application also claims a preservative film containing the single-atom silver supported zinc oxide.

[0032] In one preferred embodiment, the preservative film further comprises one or more of chitosan, gelatin, polyethylene, polyvinyl chloride, polyvinylidene dichloride, and polylactic acid.

[0033] Other components of the preservative film are conventional preservative film components, and any available preservative film disclosed in the prior art can be used in the present application.

[0034] Based on the same inventive concept, the present application also claims the use of the preservative film and / or the preservative film in fruit and vegetable preservation and / or antibacterial applications.

[0035] In one preferred embodiment, the fruit and vegetable is a climacteric fruit and vegetable or a non-climacteric fruit and vegetable.

[0036] In one preferred embodiment, the respiratory climacteric fruit or vegetable is any one of banana, apple, pear, kiwi, apricot, plum, peach, persimmon, avocado, lychee, papaya, fig, mango, etc.

[0037] In one preferred embodiment, the non-respiratory climacteric fruit or vegetable is any one of cherry, loquat, grape, citrus, strawberry, lychee, longan, pineapple, lemon, lime, carambola, loquat, olive, pomegranate, raspberry, blackberry, cocoa, cashew apple, cucumber, eggplant, jujube, okra, cucumber, sweet pepper, tomato, zucchini.

[0038] In one preferred embodiment, the bacteria are gram-negative bacteria and gram-positive bacteria.

[0039] In one preferred embodiment, the bacteria are one or more of Escherichia coli, Staphylococcus aureus, Listeria, Salmonella, etc.

[0040] Compared with the prior art, the present application has the following advantages:

[0041] (1) The present application first realizes the loading of atomic Ag single atoms in three-dimensional flower-like ZnO nanostructures (AgSA / ZnO) through a silver nanoparticle thermal conversion and surface reconstruction strategy. This system breaks through the limitations of insufficient exposure of active sites in traditional nanomaterials through oxygen vacancy defect engineering and Ag-ZnO interface synergistic effect, realizes a significant improvement in atomic utilization and catalytic activity, and provides a new material basis for the integration of synergistic antibacterial-ethylene scavenging dual functions.

[0042] (2) The present application proposes a dual antibacterial mechanism based on the mechanical perforation effect of three-dimensional nanoflower structures and oxygen vacancy-mediated reactive oxygen species (ROS), realizing broad-spectrum inhibition of gram-negative / positive bacteria. The three-dimensional nanotaper structure of AgSA / ZnO destroys the integrity of the bacterial cell wall / membrane through a mechanical perforation effect; electron transfer induced by surface oxygen vacancies (Oxygen vacancy, OVs) promotes the activation of oxygen molecules at the Ag-ZnO interface, triggering an intracellular ROS explosion and leading to an imbalance in the antioxidant system; ultimately, excess ROS causes irreversible oxidative damage to biological macromolecules such as nucleic acids, leading to bacterial death. In addition, through the defect synergistic effect of AgSA-ZnO, the reaction energy barrier is reduced, realizing ethylene scavenging without external energy input, breaking through the functional single bottleneck of traditional preservation technology.

[0043] (3) Based on the material properties, the present application innovatively develops two types of products, pouches and composite films (reusability), realizing the preservation of respiratory climacteric / non-climacteric fruits through synergistic antibacterial and ethylene scavenging. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 This is a schematic diagram illustrating the synthesis of zinc oxide nanoflowers loaded with single-atom silver.

[0045] Figure 2 This is an experimental characteristic diagram of the morphology of single-atom silver-supported zinc oxide nanoflowers synthesized by the method of this invention.

[0046] in, Figure 2 A is a scanning electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2 B is a transmission electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2 C Figure 2 D is a spherical aberration electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2 E, Figure 2 G, Figure 2 G, Figure 2 EDS elemental mapping of a spherical aberration electron microscope image of zinc oxide nanoflowers supported by single-atom silver (H).

[0047] Figure 3 The antibacterial activity diagrams are for ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO.

[0048] in, Figure 3 A is a plate graph showing the antibacterial effects of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO on Gram-negative and Gram-positive bacteria. Figure 3 B is a bar chart showing the inhibition rates of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO against Escherichia coli; Figure 3 C is a bar chart showing the inhibition rates of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO against Salmonella; Figure 3 D is a bar chart showing the inhibition rates of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO against Staphylococcus aureus. Figure 3 E is a bar graph showing the inhibition rates of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO against Listeria.

[0049] Figure 4 The antibacterial effects of different forms of AgSA / ZnO (100 μg / mL) on Escherichia coli and Staphylococcus aureus were investigated.

[0050] Figure 5 The inhibition rates of AgSA / TiO2 and AgSA / ZnO against Escherichia coli are given.

[0051] Figure 6Ethylene removal performance of zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO), and zinc oxide nanoflowers loaded with single-atom silver (AgSA / ZnO).

[0052] in, Figure 6 A represents the ethylene degradation efficiency graph; Figure 6 B is the corresponding pseudo-first-order dynamic diagram.

[0053] Figure 7 Photographs showing the changes over time of banana samples preserved in "lucky bags" prepared from zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO), and zinc oxide nanoflowers loaded with single-atom silver (AgSA / ZnO).

[0054] Figure 8 Photographs showing the changes over time of strawberry samples preserved by composite films prepared from zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO), and zinc oxide nanoflowers loaded with single-atom silver (AgSA / ZnO). Detailed Implementation

[0055] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0056] Evaluation of the antibacterial properties of the present invention: Typical Gram-negative bacteria Escherichia coli (CMCC 44102) and Salmonella (ATCC 14028), and Gram-positive bacteria Staphylococcus aureus (CMCC 26003) and Listeria monocytogenes (ATCC 19115) were selected as research subjects. The antibacterial activity of single-atom silver-loaded zinc oxide nanoflowers against Gram-negative and Gram-positive bacteria was evaluated by standard colony counting method.

[0057] Evaluation of the ethylene removal performance of the present invention: Zinc oxide nanoflowers supported on single-atom silver were placed in a sealed container and high-purity ethylene gas (99.95%) was injected for ethylene removal analysis. The ethylene concentration in the headspace of the container was measured hourly using an F-950 three-gas analyzer (Felix Instruments, USA) to evaluate the ethylene removal capability of the single-atom silver-supported zinc oxide nanoflowers.

[0058] To preserve the banana samples, the banana samples and the lucky bags were placed together in a polyethylene container without contact between them for a preservation experiment. To preserve the strawberry samples, the strawberry samples were placed separately in an open, transparent plastic bowl and sealed with a composite film.

[0059] Example 1

[0060] Synthesis of single-atom silver-supported zinc oxide nanoflowers

[0061] according to Figure 1 The schematic diagram shown illustrates the synthesis of single-atom silver-supported zinc oxide nanoflowers. The process is as follows:

[0062] (1) Mix 4 mmol of Zn(NO3)2·6H2O and 0.561 g of hexamethylenetetramine (C6H 12 N4) was dissolved in 40 mL of distilled water. Then, 25% ammonia (NH3·H2O) was added to adjust the pH of the solution to 9, and the mixture was magnetically stirred for 30 min at room temperature. The resulting solution was then transferred to a Teflon-lined high-pressure reactor and reacted at 90 °C and 0.3 MPa for 10 h, followed by natural cooling to room temperature. The resulting precipitate was washed repeatedly with distilled water and anhydrous ethanol, and then vacuum dried at 60 °C for 6 h to obtain zinc oxide nanoflowers (ZnO). When the pH values ​​during the synthesis process were 6, 7, 8, and 9, prismatic, columnar, semi-flower-like, and flower-like ZnO nanomaterials were obtained, respectively.

[0063] (2) 0.1079 g of zinc oxide nanoparticles were dissolved in 5 mL of ethanol, followed by the addition of 5 mL of 1 mM silver nitrate solution, and ultrasonic treatment was performed for 1 h at a frequency of 40 kHz. The resulting solution was filtered to remove the supernatant, and the precipitate was washed multiple times and vacuum dried at 60 °C for 6 h to obtain silver nanoparticle-supported zinc oxide nanoflowers (AgNPs / ZnO). Subsequently, the silver nanoparticle-supported zinc oxide nanoflowers were directly heated at 400 °C (heating rate of 10 °C / min). -1 The zinc oxide nanoflowers (AgSA / ZnO) were calcined in air for 2 hours. After cooling to 25°C, single-atom silver-supported zinc oxide nanoflowers were obtained. To further compare the structural differences of the materials before and after morphology regulation, the ZnO precursor was directly calcined under the same conditions (400°C, air atmosphere, heating rate of 10°C min⁻¹, holding time of 2 hours) to obtain calcined zinc oxide nanoflowers (ZnOΔ).

[0064] Analysis of single-atom silver-supported zinc oxide nanoflowers yielded the following results: Figure 2 As shown, where, Figure 2 A is a scanning electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2 B is a transmission electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2C Figure 2 D is a spherical aberration electron microscope image of zinc oxide nanoflowers supported by single-atom silver. Figure 2 E, Figure 2 G, Figure 2 G, Figure 2 EDS elemental mapping of a spherical aberration electron microscope image of zinc oxide nanoflowers supported by single-atom silver (H).

[0065] from Figure 2 As can be seen in Figure A, the zinc oxide nanoflowers supported by single-atom silver exhibit a three-dimensional flower-like structure. Figure 2 B shows that the surface of the zinc oxide nanoflowers supported by single-atom silver exhibits nanoscale porous features. This phenomenon can be attributed to the escape of gases such as NO2 and O2 generated during the thermal decomposition of the Zn(NO3)2 precursor into the crystal lattice during calcination, which, along with the dehydroxylation reaction, introduces localized stress, thereby forming defects. Additionally, HAADF images of AgSA / ZnO (…) Figure 2 In C), lattice fringes with spacings of 0.285 nm and 0.248 nm can be observed, corresponding to the (100) and (101) crystal planes of ZnO, respectively. Figure 2 The formation of Ag superstructures can be observed in D, leading to stacking defects in the ZnO crystal structure (marked by the red box). EDS mapping results for AgSA / ZnO ( Figure 2 EH also verified the uniform distribution of Ag atoms in the sample. Therefore, single-atom silver-supported zinc oxide nanoflowers (AgSA / ZnO) were successfully prepared by simple heat treatment of Ag NPs on the ZnO surface.

[0066] Example 2

[0067] Study on the antibacterial properties of synthesized single-atom silver-supported zinc oxide nanoflowers

[0068] Zinc oxide nanomaterials of different shapes supported by 100 μg / mL single-atom silver, zinc oxide nanoflowers (ZnO), zinc oxide nanoflowers supported by silver nanoparticles (AgNPs / ZnO), calcined zinc oxide nanoflowers (ZnOΔ), and AgSA / TiO2 (prepared according to Example 1 of CN 108499561 B) were added to bacterial suspensions (1 mL, 10 6 Incubate with CFU / mL for 2 h. Then, spread 100 μL of the mixture onto Luria-Bertani (LB) agar plates. A bacterial solution without added material serves as the control group. After 12 h of incubation, count and calculate the visible colony units. The antibacterial efficiency is calculated using the formula: Antibacterial Rate (%) = (N0 - Ni) / N0 × 100, where N0 is the colony count in the control group, and Ni is the colony count after different treatments. Results are as follows: Figure 3-5 As shown. Among them, Figure 3A is a plate graph showing the antibacterial effects of ZnO, ZnOΔ, AgNPs / ZnO, and AgSA / ZnO on Gram-negative and Gram-positive bacteria. Figure 3 BE are bar graphs showing the inhibition rates of ZnO NFs, ZnO NFsΔ, AgNPs / ZnO NFs, and AgSA / ZnO against Escherichia coli (3B), Salmonella (3C), Staphylococcus aureus (3D), and Listeria (3E), respectively. Figure 4 The antibacterial effects of different forms of AgSA / ZnO (100 μg / mL) on Escherichia coli and Staphylococcus aureus were investigated. Figure 5 The inhibition rates of AgSA / TiO2 and AgSA / ZnO against Escherichia coli are given.

[0069] from Figure 3 It can be seen that the inhibition rate of zinc oxide nanoflowers supported by single-atom silver was 99.99% against Gram-negative bacteria Escherichia coli and Salmonella, and the inhibition rates against Gram-positive bacteria Staphylococcus aureus and Listeria monocytogenes were 95.29% and 93.60%, respectively, all showing significant inhibitory effects. Moreover, except for Salmonella, the antibacterial rate of zinc oxide nanoflowers supported by single-atom silver (AgSA / ZnO) was significantly better than that of zinc oxide nanoflowers (ZnO), zinc oxide nanoflowers supported by silver nanoparticles (AgNPs / ZnO), and calcined zinc oxide nanoflowers (ZnOΔ).

[0070] from Figure 4 It is evident that the antibacterial rate of AgSA / ZnO is significantly influenced by its morphology. The inhibition rates of prismatic, columnar, semi-floral, and floral AgSA / ZnO against *Escherichia coli* were 97.62%, 97.75%, 99.47%, and 99.99%, respectively. Among these, the antibacterial rate of floral AgSA / ZnO against *Staphylococcus aureus* was 1.82 times that of prismatic AgSA / ZnO. The antibacterial rate of AgSA / ZnO is clearly affected by its morphology; the floral structure is more efficient at penetrating and disrupting bacterial cell membranes compared to other morphologies, thus enhancing its antibacterial activity.

[0071] from Figure 5 It can be seen that the antibacterial effect of AgSA / ZnO is significantly better than that of AgSA / TiO2.

[0072] Example 3

[0073] Study on the ethylene scavenging performance of synthesized single-atom silver-supported zinc oxide nanoflowers

[0074] 50 mg of zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO), and zinc oxide nanoflowers loaded with single-atom silver (AgSA / ZnO) were placed in a 100 mL sealed container. Then, 100 μL of high-purity ethylene gas (99.95%) was injected into the container through a rubber stopper using a syringe and stored at 25 °C for ethylene scavenging analysis. The ethylene concentration in the headspace of the container was measured hourly using an F-950 three-gas analyzer (Felix Instruments, USA), with a detection range of 0-200 ppm. The ethylene scavenging capacity (%) was calculated using the formula: Ethylene scavenging capacity (%) = (C0 – Ct) / C0 × 100, where C0 is the initial ethylene concentration and Ct is the remaining concentration. The results are as follows: Figure 6 As shown, where, Figure 6 A represents the ethylene degradation efficiency graph; Figure 6 B is the corresponding pseudo-first-order dynamic diagram.

[0075] from Figure 6 It can be seen that the zinc oxide nanoflowers supported by single-atom silver exhibit an ethylene scavenging rate as high as 39.83% without the need for external energy assistance, with a rate constant of K' = 0.09374 h⁻¹. -1 It exhibits highly efficient ethylene catalytic activity. In comparison, this rate constant is significantly lower than that of ZnO (0.00872h). -1 ), ZnOΔ(0.01460h -1 ),AgNPs / ZnO(0.01439h -1 The results were 11 times, 6 times, and 7 times higher, respectively, which fully verified the key role of single-atom silver interface modification in improving the dark catalytic activity of ZnO.

[0076] Example 4

[0077] Multifunctional Preservation Applications of Synthesized Single-Atom Silver-Supported Zinc Oxide Nanoflowers

[0078] (1) Zinc oxide nanoflowers loaded with single-atom silver (AgSA / ZnO), zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), and zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO) were respectively packed into nylon bags to make single-atom silver loaded zinc oxide nanoflower lucky bags, which were used for the preservation of respiratory climacteric fruits and vegetables (such as bananas).

[0079] (2) Dissolve 1.08 g of chitosan in 72 mL of 1% acetic acid solution and heat at 40 °C until the starch polymer is completely dissolved. Then, dissolve 0.6 g of gelatin in 48 mL of deionized water and mix it with the chitosan solution at a ratio of 2:3 (v / v). Add glycerol (2%, calculated based on the volume of the chitosan / gelatin solution) as a plasticizer to form a chitosan / gelatin film-forming solution. Subsequently, while stirring continuously at 40 °C, add 0.24 mg of single-atom silver-loaded zinc oxide nanoflowers (AgSA / ZnO), zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), and zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO). Finally, pour 20 mL of the film-forming solution evenly into a petri dish (90 mm in diameter) and dry at 50 °C for 12 h to obtain a composite film for preservation of non-climacteric fruits and vegetables (such as strawberries).

[0080] (3) Climax-type fruits (bananas) and non-climax-type fruits (strawberries) were selected as research subjects. Samples of uniform size, color, and weight, without obvious defects or mechanical damage, were chosen for the preservation experiment. To preserve the banana samples, the banana samples and the fruit bags were placed simultaneously in a polyethylene container without contact between them and stored for 18 days. The results are as follows: Figure 7 As shown.

[0081] To preserve the strawberry samples, they were placed individually in an uncovered, transparent plastic bowl and sealed with a composite film for 12 days. Results were as follows: Figure 8 As shown.

[0082] from Figure 7 and Figure 8 It can be seen that the preservation device based on single-atom silver-loaded zinc oxide nanoflowers (AgSA / ZnO) extended the shelf life of bananas and strawberries by 4 days and 5 days, respectively. However, zinc oxide nanoflowers (ZnO), calcined zinc oxide nanoflowers (ZnOΔ), and zinc oxide nanoflowers loaded with silver nanoparticles (AgNPs / ZnO) could not extend the shelf life of bananas. These three methods slightly extended the shelf life of strawberries, but the effect was significantly worse than that of single-atom silver-loaded zinc oxide nanoflowers (AgSA / ZnO). This indicates that single-atom silver-loaded zinc oxide nanoflowers (AgSA / ZnO) can meet the post-harvest preservation requirements of both climacteric and non-climacteric fruits and vegetables.

[0083] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing a silver monolayer supported on zinc oxide, characterized by, The method comprises the following steps: S1, dispersing a zinc-containing compound and a polyamine compound in a solvent, adjusting the pH of the system to 8-10, and performing hydrothermal synthesis to obtain zinc oxide nanoflowers; S2, mixing the zinc oxide nanoflowers in a dissolved state with a silver-containing compound under ultrasonic, then filtering to obtain a precipitate, and calcining the precipitate to obtain silver monatomic atom-loaded zinc oxide; The polyamine compound is one or both of hexamethylenetetramine or urea.

2. The production method according to claim 1, characterized by, The zinc-containing compound includes one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate.

3. The production method according to claim 1, characterized by, The silver-containing compound includes one or more of silver nitrate, silver acetate or silver sulfate.

4. The method of claim 1, wherein, The solvent in step S1 is water; ammonia or an organic strong base is used to adjust the pH of the system to 8-10; the organic strong base is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide or choline hydroxide.

5. The preparation method according to claim 1, characterized in that, In step S1, the hydrothermal synthesis is performed for 8-10 hours, the pressure is 0.1-0.3 Mpa, and the temperature is 80-100℃.

6. The method of claim 1, wherein, In step S2, the calcination process is as follows: The heating rate is 0.5-10℃ / min, the calcination temperature is 300-450℃, and the calcination time is 1-3h.

7. The silver monatomic atom-loaded zinc oxide obtained by the preparation method according to any one of claims 1-6.

8. The application of the silver monatomic atom-loaded zinc oxide according to claim 7 in fruit and vegetable preservation and / or antibiosis.

9. A fresh-keeping bag, characterized in that, The preservative bag contains the silver monatomic atom-loaded zinc oxide according to claim 7.

10. A preservative film characterized by, The preservative film contains the silver monatomic atom-loaded zinc oxide according to claim 7.

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