A dual-functional fruit and vegetable preservation film with the functions of adsorbing and degrading pesticide residues, its preparation method and application

Abstract

This invention discloses a dual-functional fruit and vegetable preservation film with adsorption and degradation capabilities for pesticide residues, its preparation method, and its applications, belonging to the field of food preservation materials technology. The invention first prepares a nickel-doped zinc oxide / carbon nitride S-type heterojunction composite photocatalyst, then loads it onto a carboxymethyl chitosan membrane to form a dual-functional preservation film with both adsorption and photocatalytic degradation capabilities for pesticide residues. The composite photocatalyst prepared by this invention exhibits excellent visible light performance and high photoelectric conversion efficiency, converting more light energy into chemical energy and significantly improving the reaction rate of the photocatalyst. By loading it onto the preservation film, the film possesses excellent adsorption and degradation performance for pesticides, while also exhibiting good moisturizing, antibacterial, and preservation properties. The preparation process of this invention is simple and low-cost, suitable for pesticide residue removal and quality maintenance throughout the entire process of post-harvest storage, transportation, and sales of fruits and vegetables, and has promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of food preservation materials technology, specifically relating to a dual-function fruit and vegetable preservation film that adsorbs and degrades pesticide residues, its preparation method, and its application. Background Technology

[0002] With consumers' increasing demands for food safety and quality, pesticide residues in post-harvest processing of fruits and vegetables and preservation technologies have become core concerns in the industry. Currently, preservation technologies on the market mainly focus on inhibiting microbial growth, regulating respiration, and preventing moisture loss. Commonly used solutions include: 1. Traditional functional food preservation film technology: Existing food preservation films mainly achieve preservation through physical barriers (such as PE and PP films) or the addition of a single active ingredient (such as antibacterial agents, ethylene absorbers, and antioxidants). For example, Chinese patent CN121045608A discloses an antibacterial food preservation film containing chrysanthemum essential oil, which mainly targets microbial spoilage and is ineffective against organic pesticide residues that have migrated from the surface or interior of fruits and vegetables. This type of technology has a single function and cannot address the critical food safety hazard of pesticide residues.

[0003] 2. Current Status of Pesticide Residue Removal Technology: Currently, pesticide residue removal in harvested fruits and vegetables mainly relies on methods such as rational pre-harvest pesticide application, post-harvest washing with clean water or chemical cleaning agents, ultrasonic treatment, and ozone treatment. However, these methods have significant drawbacks: (1) Post-harvest washing is a one-time treatment and cannot continue to function during subsequent storage, transportation, and sales; (2) Chemical cleaning may lead to secondary pollution; (3) Strong oxidizing treatments such as ozone may damage the epidermal cells of fruits and vegetables, accelerating quality deterioration. Therefore, there is an urgent need for a technology that can continuously and safely reduce pesticide residues throughout the entire shelf life of fruits and vegetables.

[0004] 3. Research on Static Adsorption or Degradation Materials: In recent years, some studies have attempted to combine adsorption materials (such as activated carbon and cyclodextrin) with photo / chemical catalytic degradation materials (such as metal oxides and metal sulfides) to remove pesticide residues. For example, Chinese patent CN121016682A discloses a bifunctional material of a heterojunction of baijiu lees biochar / cerium oxide / cadmium zinc sulfur solid solution, which can degrade imidacloprid, thiamethoxam, chlorpyrifos, and glyphosate under 300W xenon lamp irradiation. However, its application in the actual removal of pesticide residues from fruits and vegetables has significant shortcomings: First, these materials are usually in powder form and cannot be directly applied to the surface of fruits and vegetables to remove pesticide residues; second, some photocatalysts can only degrade pesticides under ultraviolet light, which requires harsh reaction conditions and may pose a carcinogenic risk; third, strong oxidizing catalysts may indiscriminately oxidize the nutrients on the surface of fruits and vegetables, affecting their flavor and color.

[0005] In summary, existing technologies suffer from a disconnect between preservation and pesticide residue removal functions, as well as the significant drawbacks of passive, static, and conditionally dependent methods. Currently, the market lacks an integrated intelligent packaging solution that can proactively respond, operate continuously, and simultaneously achieve preservation and dynamic removal of pesticide residues seeping from the surface of fruits and vegetables throughout the entire logistics process. Summary of the Invention

[0006] To address the limitations of pesticide residue removal technology for harvested fruits and vegetables and the inability of photocatalysts to be practically applied to pesticide residue removal, this invention provides a dual-functional fruit and vegetable preservation film that adsorbs and degrades pesticide residues, along with its preparation method and application.

[0007] This invention prepares a nickel-doped zinc oxide / carbon nitride composite photocatalyst and loads it onto a carboxymethyl chitosan membrane to form a preservation film with dual functions of adsorption and photocatalytic degradation.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention is a method for preparing a dual-functional fruit and vegetable preservation film that adsorbs and degrades pesticide residues, comprising the following steps: (1) Preparation of nickel-doped zinc oxide ((Ni)ZnO): Dissolve nickel salt and zinc salt in water to obtain a mixed solution, adjust the pH of the solution to alkaline, centrifuge after precipitation, take the lower layer of precipitate and wash, repeat three times, put it in a muffle furnace for calcination, and cool to obtain nickel-doped zinc oxide; preferably, nickel chloride and zinc chloride are selected as nickel salt and zinc chloride respectively, and the mass ratio of nickel chloride to zinc chloride is (1-9):100. If there is too little nickel, it will not play the role of hole trap, and if there is too much, nickel oxide clusters will be formed, and nickel doping will not be formed, which will also lead to the inability to form hole traps. Therefore, in the preparation process, the relative amount of nickel salt and zinc must be strictly controlled to form a good nickel doping effect; (2) Preparation of nickel-doped zinc oxide / carbon nitride ((Ni)ZnO-g-C3N4) composite photocatalyst: nickel-doped zinc oxide and melamine were thoroughly ground and mixed in a mortar at a mass ratio of (0.5-3.0):10, calcined in a muffle furnace, and cooled to obtain nickel-doped zinc oxide / carbon nitride composite photocatalyst; during the mixing process of nickel-doped zinc oxide and melamine, if there is too little Ni-ZnO powder, carbon nitride will completely cover Ni-ZnO, and a heterojunction cannot be formed, only showing the properties of carbon nitride, and the degradation effect is not good; if there is too much Ni-ZnO powder, during the in-situ generation of carbon nitride, Ni-ZnO powder will prevent melamine from condensing, resulting in carbon nitride not being generated; (3) Preparation of a dual-function fruit and vegetable preservation film with adsorption and degradation of pesticide residues: The composite photocatalyst described in step (2) is dispersed in water as solution A, and carboxymethyl chitosan and glycerol are dissolved in water as solution B. Solution A and solution B are mixed evenly, poured into a mold, and dried to obtain a dual-function fruit and vegetable preservation film with adsorption and degradation of pesticide residues. The mass ratio of photocatalyst, carboxymethyl chitosan, and glycerol is (0.05-0.5):3:1.2. If there is too much Ni-ZnO / g-C3N4 heterojunction catalyst, it will cause powder agglomeration, poor dispersibility, and decreased mechanical properties of the film, resulting in poor performance.

[0009] Specifically, in step (1), nickel chloride and zinc chloride are dissolved in deionized water and 37% hydrochloric acid is added to aid dissolution; the pH of the mixture is adjusted to be alkaline by adding alkaline substances such as sodium hydroxide or potassium hydroxide, and the specific pH value can be designed to be 9; the centrifugation speed is 10000 rpm and the centrifugation time is 5 min.

[0010] Specifically, in step (1), the calcination conditions in the muffle furnace are a reaction at 150~600℃ for 120 min.

[0011] Specifically, in step (2), the calcination conditions in the muffle furnace are a reaction at 150~550℃ for 240 min.

[0012] Specifically, in step (3), the drying conditions are 50°C for 12 hours.

[0013] The second aspect of the present invention is to provide a dual-function fruit and vegetable preservation film that adsorbs and degrades pesticide residues, which is prepared by the preparation method described in the first aspect above.

[0014] A third aspect of the present invention is to provide a dual-function fruit and vegetable preservation film as described in the second aspect, which has the functions of adsorbing and degrading pesticide residues, for use in the degradation of pesticide residues in fruits and vegetables under visible light and for preservation.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The nickel-doped zinc oxide / carbon nitride photocatalyst prepared in this invention has excellent visible light performance and high photoelectric conversion efficiency, converting more light energy into chemical energy and significantly improving the reaction rate of the photocatalyst. Its working principle is as follows: carbon nitride and zinc oxide can generate superoxide radicals and photogenerated holes through photoexcitation, which can be used to degrade pesticides; zinc oxide can also release zinc ions, which can be used to preserve fruits and vegetables; the 3d orbital of Ni preferentially captures holes from g-C3N4, thereby inhibiting the recombination of electrons and holes at the interface, while reducing the effective oxidation potential of the captured holes, and directionally generating mild superoxide radicals to achieve mild oxidative degradation of pesticides without affecting the nutrients and firmness of fruits and vegetables.

[0016] (2) The adsorption-degradation pesticide residue preservation film for fruits and vegetables prepared by the method of this invention has the ability to adsorb pesticides. The principle is as follows: carboxymethyl chitosan can efficiently adsorb neonicotinoid pesticides through electrostatic interaction and hydrogen bonding; carbon nitride can adsorb neonicotinoid pesticides through π-π conjugation; and the porous system composed of photocatalyst powder and carboxymethyl chitosan is also conducive to the adsorption of neonicotinoid pesticides. This adsorption effect localizes the oxidative degradation of neonicotinoid pesticides on the preservation film, reducing the loss of nutrients in fruits and vegetables. At the same time, the adsorption of neonicotinoid pesticides achieves the enrichment of degradation substances and improves the degradation efficiency. Attached Figure Description

[0017] Figure 1 The images show the structural characterization of the ZnO-g-C3N4 and (Ni)ZnO-g-C3N4 photocatalysts prepared in Example 1. (a) is the N 1s XPS image of ZnO-g-C3N4 before and after irradiation; (b) is the N 1s XPS image of (Ni)ZnO-g-C3N4 before and after irradiation; (c) are the XRD patterns of ZnO-g-C3N4 and (Ni)ZnO-g-C3N4; (d) is the Zn 2p XPS image of ZnO-g-C3N4 before and after irradiation; (e) is the Zn 2p XPS image of (Ni)ZnO-g-C3N4 before and after irradiation; and (f) to (j) are the SEM images and elemental mapping diagrams of (Ni)ZnO-g-C3N4. Figure 2 The photocatalytic mechanism diagrams and fipronil degradation efficiency diagrams of the photocatalysts prepared in Example 2 (g-C3N4), Example 3 (ZnO-g-C3N4), Comparative Example 3 (g-C3N4-(Ni)ZnO), and Example 1 ((Ni)ZnO-g-C3N4) are shown. (a) shows the AC impedance diagrams of g-C3N4, ZnO-g-C3N4, g-C3N4-(Ni)ZnO, and (Ni)ZnO-g-C3N4. (b) shows the AC impedance diagrams of g-C3N4, ZnO-g-C3N4, and g-C3N4. Photoluminescence spectra of N4-(Ni)ZnO and (Ni)ZnO-g-C3N4, (c) photocurrent response of g-C3N4, ZnO-g-C3N4, g-C3N4-(Ni)ZnO and (Ni)ZnO-g-C3N4, (d) surface photovoltage spectra of ZnO and (Ni)ZnO, (e) EPR spectra of g-C3N4, ZnO-g-C3N4, g-C3N4-(Ni)ZnO and (Ni)ZnO-g-C3N4, and (f) degradation efficiency of fipronil; Figure 3 The image shows the in-situ infrared spectrum of a nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film that has adsorbed fipronil under sunlight exposure for a period of time.

[0018] Figure 4 The images show the preservation performance of blueberries without plastic wrap. (a) is a photo of the blueberry preservation effect, and (bf) is a trend chart of the blueberry preservation quality during the 12-day storage period, which shows the blueberry's firmness, weight loss rate, vitamin C content, anthocyanin content, and total flavonoid content, respectively. Detailed Implementation

[0019] This application will now be described in detail through specific embodiments.

[0020] Example 1: Preparation of nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film 1. Preparation of nickel-doped zinc oxide Weigh 175 mg of nickel chloride hexahydrate (NiCl2·6H2O) and 3.348 g of anhydrous zinc chloride (ZnCl2), and dissolve them together in 50 mL of deionized water. Add 5 drops of 37% hydrochloric acid to the solution to aid dissolution, and stir magnetically for 30 minutes at room temperature to form a homogeneous mixed salt solution.

[0021] While continuously stirring, a 1 mol / L sodium hydroxide (NaOH) aqueous solution was slowly added dropwise to the above mixed salt solution to adjust the pH of the solution to 9. The reaction was then continued for 60 minutes with stirring to obtain a suspension containing the precipitate.

[0022] Centrifuge the above suspension at 10,000 rpm for 5 minutes and carefully discard the supernatant. Add an appropriate amount of deionized water to the collected precipitate, disperse by sonication, and centrifuge again. Repeat this washing process three times to thoroughly remove impurity ions.

[0023] The washed precipitate was transferred to an alumina crucible and calcined in a muffle furnace. The calcination program was set as follows: the temperature was increased to 150°C at a rate of 5°C / min and held at that temperature for 60 minutes; then the temperature was increased to 600°C at a rate of 5°C / min and held at 600°C for 120 minutes. After calcination, the muffle furnace was allowed to cool naturally to room temperature, and the precipitate was removed and ground. The resulting light green powder was nickel-doped zinc oxide nanomaterial, abbreviated as (Ni)ZnO.

[0024] 2. Preparation of nickel-doped zinc oxide-carbon nitride S-type heterojunction Weigh 1.0 g of the Ni-ZnO powder prepared in the above steps and grind it thoroughly with 10.0 g of melamine (C3H6N6) in a mortar until homogeneous. Transfer the mixture to a covered alumina crucible and place it in a muffle furnace.

[0025] The muffle furnace calcination program was set as follows: the temperature was increased from room temperature to 150°C at a rate of 5°C / min, and held at 150°C for 60 minutes to remove moisture; then the temperature was increased to 550°C at the same rate, and held at 550°C for 240 minutes. After calcination, the muffle furnace was turned off and allowed to cool naturally to room temperature before being removed. The resulting loose, blocky product was ground into a fine powder, which is the nickel-doped zinc oxide-carbon nitride S-type heterojunction composite photocatalyst, abbreviated as (Ni)ZnO / g-C3N4.

[0026] 3. Preparation of nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film (1) Preparation of solution A (photocatalyst dispersion): Accurately weigh 100 mg of Ni-ZnO / g-C3N4 heterojunction powder prepared in step 2, and disperse it in 100 mL of deionized water. Stir magnetically at room temperature for 1 hour to fully disperse it and form a uniform suspension for later use.

[0027] (2) Preparation of solution B (carboxymethyl chitosan-based solution): In a 250 mL beaker, add 100 mL of deionized water, 3.0 g of carboxymethyl chitosan powder, and 1.2 g of glycerol in sequence. Place the beaker in an 80°C water bath and stir magnetically for 2 hours until the carboxymethyl chitosan is completely dissolved and the system becomes uniform and transparent. Then, place the solution in an ultrasonic cleaner and sonicate for 15-20 minutes to remove air bubbles from the solution, obtaining a clear, viscous solution B.

[0028] (3) Film formation: Pour all of the prepared solution A into solution B, and continue magnetic stirring at room temperature for 30 minutes to ensure that the photocatalyst is evenly dispersed in the carboxymethyl chitosan solution, thus obtaining a mixed casting solution. Apply a thin layer of Tween 20 evenly to the inner surface of a smooth stainless steel mold as a release agent. Slowly pour the mixed casting solution into the mold and gently shake to level the surface. Then transfer the mold to a 50°C drying oven and dry for 12 hours.

[0029] (4) Demolding: After the film is completely dried and formed, carefully peel it off from the mold to obtain a carboxymethyl chitosan-based adsorption-degradation fruit and vegetable preservation film loaded with (Ni)ZnO / g-C3N4 type heterostructure.

[0030] Example 2: Preparation of carbon nitride / carboxymethyl chitosan food preservation film 1. Preparation of carbon nitride (g-C3N4) Weigh 10.0 g of melamine (C3H6N6) and grind it thoroughly in a mortar until homogeneous. Transfer the mixture to a covered alumina crucible and place it in a muffle furnace. Set the muffle furnace calcination program as follows: raise the temperature from room temperature to 150°C at a rate of 5°C / min and hold at 150°C for 60 minutes to remove moisture; then continue heating at the same rate to 550°C and hold at 550°C for 240 minutes. After calcination, turn off the muffle furnace and allow it to cool naturally to room temperature before removing it. Grind the resulting loose, blocky product into a fine powder, which is the carbon nitride (g-C3N4) photocatalytic material.

[0031] 2. Preparation of carbon nitride / carboxymethyl chitosan preservation film Accurately weigh 100 mg of the g-C3N4 powder prepared in step 1 and disperse it in 100 mL of deionized water. Stir magnetically at room temperature for 1 hour to ensure thorough dispersion and form a uniform suspension, which will be used as solution A. The preparation, film formation, and demolding processes of solution B are the same as in step 3 of Example 1 above, to prepare carbon nitride / carboxymethyl chitosan preservation film.

[0032] Example 3: Preparation of Zinc Oxide-Carbon Nitride / Carboxymethyl Chitosan Food Preservative Film 1. Preparation of Zinc Oxide (ZnO) Weigh 3.348 g of anhydrous zinc chloride (ZnCl2) and dissolve it in 50 mL of deionized water. Add 5 drops of 37% hydrochloric acid to the solution to aid dissolution, and stir magnetically for 30 minutes at room temperature to form a homogeneous salt solution. The remaining steps are the same as step 1 in Example 1. The resulting white powder is zinc oxide.

[0033] 2. Preparation of zinc oxide-carbon nitride heterojunction (ZnO / g-C3N4) Weigh 1.0 g of the ZnO powder prepared in the above steps and grind it thoroughly with 10.0 g of melamine (C3H6N6) in a mortar until homogeneous. Transfer the mixture to a covered alumina crucible and calcine it in a muffle furnace. The remaining steps are the same as step 2 in Example 1. The resulting powder is a zinc oxide-carbon nitride heterojunction.

[0034] 3. Preparation of Zinc Oxide-Carbon Nitride / Carboxymethyl Chitosan Preservative Film Accurately weigh 100 mg of the zinc oxide-carbon nitride powder prepared in step 1 and disperse it in 100 mL of deionized water. Stir magnetically at room temperature for 1 hour to ensure thorough dispersion and form a uniform suspension, which will be used as solution A. The preparation, film formation, and demolding processes of solution B are the same as in step 3 of Example 1 above, to prepare carbon nitride / carboxymethyl chitosan preservation film.

[0035] Comparative Example 1: Preparation of Carboxymethyl Chitosan Membranes In a 250 mL beaker, add 200 mL of deionized water, 3.0 g of carboxymethyl chitosan powder, and 1.2 g of glycerol sequentially. Place the beaker in an 80°C water bath and stir magnetically for 2 hours until the carboxymethyl chitosan is completely dissolved and the system becomes homogeneous and transparent. Then, sonicate the solution in an ultrasonic cleaner for 15-20 minutes to remove air bubbles, obtaining a clear, viscous solution. Slowly pour the solution into a mold, gently shaking to level the surface. Transfer the mold to a 50°C drying oven and dry for 12 hours. After the membrane is completely dry and set, carefully peel it off the mold to obtain the carboxymethyl chitosan membrane.

[0036] Comparative Example 2: Nickel-doped zinc oxide-carbon nitride S-type heterojunction 1. Preparation of Nickel-Doped Zinc Oxide (Ni-ZnO) Weigh 175 mg of nickel chloride hexahydrate (NiCl2·6H2O) and 3.348 g of anhydrous zinc chloride (ZnCl2), and dissolve them together in 50 mL of deionized water. Add 5 drops of 37% hydrochloric acid to the solution to aid dissolution, and stir magnetically for 30 minutes at room temperature to form a homogeneous mixed salt solution.

[0037] While continuously stirring, a 1 mol / L sodium hydroxide (NaOH) aqueous solution was slowly added dropwise to the above mixed salt solution to adjust the pH of the solution to 9. The reaction was then continued for 60 minutes with stirring to obtain a suspension containing the precipitate.

[0038] Centrifuge the above suspension at 10,000 rpm for 5 minutes and carefully discard the supernatant. Add an appropriate amount of deionized water to the collected precipitate, disperse by sonication, and centrifuge again. Repeat this washing process three times to thoroughly remove impurity ions.

[0039] The washed precipitate was transferred to an alumina crucible and calcined in a muffle furnace. The calcination program was set as follows: the temperature was increased to 150°C at a rate of 5°C / min and held at that temperature for 60 minutes; then the temperature was increased to 600°C at a rate of 5°C / min and held at 600°C for 120 minutes. After calcination, the muffle furnace was allowed to cool naturally to room temperature, and the precipitate was removed and ground. The resulting light green powder was nickel-doped zinc oxide (Ni-ZnO) nanomaterial, abbreviated as (Ni)ZnO.

[0040] 2. Preparation of nickel-doped zinc oxide-carbon nitride S-type heterojunction Weigh 1.0 g of the (Ni)ZnO powder prepared in the above steps and grind it thoroughly with 10.0 g of melamine (C3H6N6) in a mortar until homogeneous. Transfer the mixture to a covered alumina crucible and place it in a muffle furnace.

[0041] The muffle furnace calcination program was set as follows: the temperature was increased from room temperature to 150°C at a rate of 5°C / min, and held at 150°C for 60 minutes for pre-decomposition; then the temperature was increased to 550°C at the same rate, and held at 550°C for calcination for 240 minutes. After calcination, the muffle furnace was turned off and allowed to cool naturally to room temperature before being removed. The resulting loose, blocky product was ground into a fine powder, which is the nickel-doped zinc oxide-carbon nitride S-type heterojunction photocatalytic material, abbreviated as (Ni)ZnO / g-C3N4.

[0042] 3. Preparation of nickel-doped zinc oxide-carbon nitride S-type heterojunction food preservation film The process is the same as step 3 in Example 1 above, except that the catalyst used is changed to (Ni)ZnO / g-C3N4.

[0043] Comparative Example 3: Carbon nitride-nickel-doped zinc oxide heterojunction 1. Preparation of carbon nitride (g-C3N4) g-C3N4 powder was obtained by thermal polycondensation of melamine. 15 g of melamine was placed in a muffle furnace and calcined at 520°C for 5 h. The resulting yellow product, obtained by pulverizing with a mortar, was g-C3N4.

[0044] 2. Preparation of carbon nitride-nickel doped zinc oxide heterojunction (g-C3N4 / Ni-ZnO) Carbon nitride-nickel-doped zinc oxide heterojunctions were prepared via a hydrothermal method. 1 g g-C3N4 was dispersed in 30 mL of deionized water and simultaneously exposed to ultrasonic dispersion for 30 min. 0.5 mmol nickel nitrate was dissolved in 50 mL of deionized water, and then 1 mmol zinc nitrate was added to another 50 mL of distilled water. The zinc nitrate solution, g-C3N4 solution, and nickel nitrate solution were mixed, and the pH of the mixture was adjusted to 9 with NaOH solution, followed by continuous stirring for 2 h. The resulting mixture was transferred to an autoclave and heated at 160°C for 12 h, then cooled to room temperature. The product was washed repeatedly with ethanol and deionized water, and dried in an air oven at 100°C for 12 h. The resulting fine powder was the carbon nitride-nickel-doped zinc oxide heterojunction.

[0045] Performance characterization results The structures of Ni-ZnO / g-C3N4 and ZnO-g-C3N4 prepared in the above examples were characterized, and the results are shown in the figure. Figure 1Among them, (a) is the N 1s image of XPS before and after illumination of ZnO-g-C3N4, (b) is the N 1s image of XPS before and after illumination of (Ni)ZnO-g-C3N4, (c) is the XRD pattern of ZnO-g-C3N4 and (Ni)ZnO-g-C3N4, (d) is the Zn 2p image of XPS before and after illumination of ZnO-g-C3N4, (e) is the Zn 2p image of XPS before and after illumination of (Ni)ZnO-g-C3N4, and (f) to (j) are the SEM and elemental mapping diagrams of (Ni)ZnO-g-C3N4. Figure 1 Figures a through e show that ZnO-g-C3N4 and (Ni)ZnO-g-C3N4 have characteristic peaks of carbon nitride and zinc oxide, indicating the successful preparation of ZnO-g-C3N4 and (Ni)ZnO-g-C3N4; Figure 1 The presence of nickel in (Ni)ZnO-g-C3N4 was detected in Figures f to j, which also proves that nickel enters zinc oxide in the form of doping.

[0046] The photocatalyst performance and pesticide (fipronil) degradation of the g-C3N4 prepared in Example 2, the ZnO-g-C3N4 prepared in Example 3, the g-C3N4-(Ni)ZnO prepared in Comparative Example 3, and the (Ni)ZnO-g-C3N4 prepared in Example 1 were tested. The pesticide used was fipronil. The degradation test method was as follows: blueberries were soaked in a 0.2% concentration of fipronil aqueous solution for 5 minutes, then the blueberries were dried. The prepared membrane or photocatalyst was then applied to the blueberries, and after irradiation under fluorescent light for 48 hours, the remaining fipronil content in the blueberries was measured using liquid chromatography-mass spectrometry according to the national standard GB23200.121-2026, thereby calculating the degradation effect of fipronil. The results are as follows: Figure 2 As shown. From Figure 2 Figures a to c show that, compared with the catalyst g-C3N4-(Ni)ZnO prepared by the conventional method in Comparative Example 3, the catalyst prepared by the method provided in Example 1 of this invention through in-situ generation of carbon nitride on nickel-doped zinc oxide has a smaller carrier transfer resistance. Although the electron-hole pair recombination degree is slightly larger, the photoelectric conversion efficiency is higher. Figure 2 The middle d figure shows that nickel in the (Ni)ZnO-g-C3N4 prepared in Example 1 can act as a hole trap to capture photogenerated holes. Figure 2 e and 2f indicate that the nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan preservation film has excellent free radical generation and pesticide degradation efficiency.

[0047] The reason why the (Ni)ZnO-g-C3N4 prepared by this invention has the above-mentioned performance advantages is that this invention utilizes the co-thermal polycondensation of pre-synthesized nickel-doped zinc oxide and melamine to grow carbon nitride in situ on the surface of nickel-doped zinc oxide, achieving a tight bond between nickel-doped zinc oxide and carbon nitride. Compared with Comparative Example 3, the nickel-doped zinc oxide-carbon nitride S-type heterojunction in Example 1 has a smaller carrier transfer resistance and a stronger photoelectric conversion efficiency, as well as a higher free radical generation and fipronil degradation efficiency. Compared with the zinc oxide-carbon nitride heterojunction in Example 3, the nickel element in the nickel-doped zinc oxide-carbon nitride S-type heterojunction acts as a hole trapping agent, realizing the adsorption of photogenerated holes in carbon nitride, reducing the recombination of photogenerated electron-hole pairs at the heterojunction interface, and improving its photoelectric conversion efficiency. Compared to Comparative Example 2, the nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan preservation film has adsorption function, enriching more pesticides on blueberries into the film, thus achieving efficient degradation of pesticides by photocatalyst.

[0048] Figure 3 The in-situ infrared spectrum of the nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film adsorbed with fipronil after sunlight exposure is shown. This food preservation film was obtained by spraying a 1% aqueous solution of fipronil onto the nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film from Example 1, followed by air drying at room temperature. Figure 3 It was demonstrated that after the nickel-doped zinc oxide-carbon nitride S-type heterojunction / carboxymethyl chitosan food preservation film adsorbed fipronil, the photo-excited nickel-doped zinc oxide-carbon nitride S-type heterojunction could effectively and directionally degrade fipronil.

[0049] Results and Analysis of the Application of Plastic Wrap in Blueberry Preservation Take a number of fresh blueberries of similar size and ripeness and randomly group them. Cover the surface of the blueberries with the (Ni)ZnO-g-C3N4-loaded preservative film prepared in Example 1, the g-C3N4-loaded preservative film prepared in Example 2, the ZnO-g-C3N4-loaded preservative film prepared in Example 3, and the carboxymethyl chitosan film prepared in Comparative Example 1, or place them in a storage box containing blueberries. All samples were stored under simulated shelf conditions (room temperature, natural light / dark cycle). The skin color and wrinkling of the blueberries were observed periodically, and their firmness, weight loss rate, and vitamin C content were measured.

[0050] See results Figure 4Figure (a) shows a photograph of the blueberry preservation effect, and Figures (b) to (f) show the trend of blueberry preservation quality during the 12-day storage period, representing the blueberry's firmness, weight loss rate, vitamin C content, anthocyanin content, and total flavonoid content, respectively. The results indicate that, compared with the control group blueberries covered with pure carboxymethyl chitosan film and those without film, blueberries covered with the Ni-ZnO / g-C3N4 / carboxymethyl chitosan composite film prepared in this invention can more effectively inhibit moisture loss, maintain higher firmness and vitamin C content during storage, showing superior preservation effects. This is attributed to the efficient generation of mildly oxidizing superoxide radicals by the Ni-ZnO / g-C3N4 heterojunctions in the carboxymethyl chitosan composite film under light irradiation. This reduces the generation of strong oxidizing species (photogenerated vacancies and hydroxyl radicals) while adsorbing and degrading pesticide residues on the fruit surface.

[0051] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a dual-functional fruit and vegetable preservation film that adsorbs and degrades pesticide residues, characterized in that: Includes the following steps: (1) Dissolve nickel salt and zinc salt in water to obtain a mixed solution, adjust the pH of the mixed solution to be alkaline, precipitate out, separate the precipitate and wash it before calcining to obtain nickel-doped zinc oxide; (2) Nickel-doped zinc oxide and melamine were ground and mixed and then calcined to obtain nickel-doped zinc oxide / carbon nitride composite photocatalyst; (3) Prepare a membrane solution of carboxymethyl chitosan, glycerol and water, add nickel-doped zinc oxide / carbon nitride composite photocatalyst, mix evenly and then prepare it into a membrane to obtain the target product.

2. The preparation method according to claim 1, characterized in that: In step (1), the nickel salt is nickel chloride and the zinc salt is zinc chloride; the mass ratio of nickel chloride to zinc chloride is (1-9):

100.

3. The preparation method according to claim 1, characterized in that: In step (1), the method to adjust the pH of the mixture to be alkaline is to add sodium hydroxide or potassium hydroxide solution to the mixture.

4. The preparation method according to claim 1, characterized in that: In step (1), the calcination temperature is 150~600℃.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of nickel-doped zinc oxide to melamine is (0.5-3.0):

10.

6. The preparation method according to claim 1, characterized in that: In step (2), the calcination temperature is 150~550℃.

7. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of the nickel-doped zinc oxide / carbon nitride composite photocatalyst, carboxymethyl chitosan, and glycerol is (0.05-0.5):3:1.

2.

8. A dual-functional fruit and vegetable preservation film with the functions of adsorbing and degrading pesticide residues, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 7.

9. The application of the dual-function fruit and vegetable preservation film with adsorption and degradation of pesticide residues as described in claim 8 in the preservation of fruits and vegetables.

10. The application according to claim 9, characterized in that: The pesticide in question is a neonicotinoid pesticide.

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