An Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, its preparation method and application

Abstract

This invention discloses an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane, its preparation method, and its applications, relating to the field of fruit and vegetable preservation technology. Chitosan quaternary ammonium salt, starch, glycerol, lignocellulose nanoparticles, and Ag / TiO2 / Ag3PO4 photocatalyst are mixed in water, and the starch is gelatinized by heating to obtain a composite film-forming solution; this solution is then cast to obtain the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane. The chitosan quaternary ammonium salt in the composite membrane can modify the surface of the Ag / TiO2 / Ag3PO4 photocatalyst, and its polar groups can form a hydrogen bond network with the hydroxyl groups of cellulose and starch, improving the composite membrane's ability to enrich ethylene and the interfacial bonding force between the photocatalyst and the matrix, thereby enhancing the composite membrane's adsorption and degradation effect on ethylene. The chitosan quaternary ammonium salt and the photocatalyst form a dual long-lasting antibacterial effect—both photoresponsive and contact-type—synergistically improving the antibacterial performance of the composite membrane.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation technology, specifically to an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, its preparation method, and its application. Background Technology

[0002] my country is a major producer of fruits and vegetables, and suffers huge losses every year due to improper preservation. Microorganisms and ethylene are the two major obstacles to fruit and vegetable preservation. Developing new technologies to solve the problems of microbial infection and ethylene-induced ripening is of great significance for fruit and vegetable preservation. Semiconductor photocatalysis technology is a rapidly developing green technology in recent years. The active free radicals generated by photocatalysts after light excitation can effectively kill microorganisms and degrade ethylene. However, single semiconductor materials have problems such as low light utilization and high photogenerated electron-hole recombination rate. Powdered photocatalysts also have limitations in use and are difficult to recycle, which limits their application scope.

[0003] CN 116139933 A discloses a nanofiber membrane with visible light photocatalytic degradation of ethylene, which involves adding TiO2-Ag nanoparticles to a polyacrylonitrile spinning solution via electrospinning. However, this prior art has low light utilization, the TiO2-Ag nanoparticles are easily lost from the fiber membrane, resulting in low photocatalytic efficiency, and the fiber membrane has no adsorption effect on ethylene. Therefore, the mass transfer process needs to be enhanced through the rational design of the fan and air duct. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the primary objective of this invention is to provide a method for preparing an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane.

[0005] Another object of the present invention is to provide an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane.

[0006] Another object of the present invention is to provide the application of the above-mentioned Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite film in fruit and vegetable preservation.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane includes the following steps: Chitosan quaternary ammonium salt, starch, glycerol, lignocellulose nanoparticles, and Ag / TiO2 / Ag3PO4 photocatalyst are mixed in water and heated to gelatinize the starch to obtain a composite film-forming solution; the solution is then cast to obtain the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite film. The Ag / TiO2 / Ag3PO4 photocatalyst is a ternary heterojunction complex formed by Ag, TiO2 and Ag3PO4; the chitosan quaternary ammonium salt accounts for 2 to 15 wt% of the starch mass.

[0008] This invention introduces chitosan quaternary ammonium salt into a composite membrane. During the mixing process, the chitosan quaternary ammonium salt modifies the surface of the Ag / TiO2 / Ag3PO4 photocatalyst, effectively preventing photocatalyst aggregation in the composite membrane through electrostatic interactions and steric hindrance, thus ensuring uniform distribution of the photocatalyst within the membrane. The polar groups in the chitosan quaternary ammonium salt can form a hydrogen bond network with the hydroxyl groups of cellulose and starch, improving the composite membrane's ability to enrich ethylene and the interfacial bonding between the photocatalyst and the matrix, thereby enhancing the composite membrane's adsorption and degradation effect on ethylene. Furthermore, the chitosan quaternary ammonium salt and the photocatalyst form a dual long-lasting antibacterial effect, combining photoresponsiveness and contact-type action, synergistically improving the antibacterial performance of the composite membrane.

[0009] Preferably, the chitosan quaternary ammonium salt accounts for 2 to 10 wt% of the starch mass.

[0010] More preferably, the chitosan quaternary ammonium salt accounts for 5 to 8 wt% of the starch mass.

[0011] Preferably, the chitosan quaternary ammonium salt is hydroxypropyltrimethylammonium chloride chitosan.

[0012] Preferably, the mixing process involves first dissolving chitosan quaternary ammonium salt in water, then sequentially adding starch, glycerol, lignocellulose nanoparticles, and Ag / TiO2 / Ag3PO4 photocatalyst, followed by stirring and ultrasonication.

[0013] Preferably, the heating temperature is 80~100℃.

[0014] Preferably, the thickness of the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite film is 0.1~0.15mm.

[0015] Preferably, the casting process involves adding 20-40g of the composite film-forming liquid to a petri dish with a diameter of 110-115mm, drying it, and obtaining the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite film.

[0016] Preferably, the preparation method of the Ag / TiO2 / Ag3PO4 photocatalyst includes: firstly, mixing and reacting TiO2, phosphorus source and soluble silver source to prepare TiO2 / Ag3PO4, and then loading nano Ag sol onto TiO2 / Ag3PO4 to obtain the Ag / TiO2 / Ag3PO4 photocatalyst.

[0017] The Ag / TiO2 / Ag3PO4 photocatalyst of this invention possesses a ternary heterojunction, which not only enables electron transfer between different semiconductors through Ag particles but also benefits from enhanced localized surface plasmon resonance, resulting in high carrier separation efficiency and surface electron utilization under visible light conditions. In this process, electrons are more readily enriched on the side favorable to the reduction reaction, promoting O2... - The continuous generation of O2 - It has strong redox capabilities, and can damage microbial cell membranes and degrade ethylene.

[0018] The TiO2 / Ag3PO4 refers to a binary heterojunction catalyst formed by combining Ag3PO4 and TiO2 through in-situ precipitation (i.e., Ag3PO4 precipitate generated by the reaction of phosphorus source and soluble silver source).

[0019] More preferably, the molar ratio of TiO2 to soluble silver source is 1:(0.5~2).

[0020] More preferably, the mass of the nano-Ag sol is 2.5~25wt% of the mass of TiO2 / Ag3PO4.

[0021] More preferably, the preparation method of the Ag / TiO2 / Ag3PO4 photocatalyst includes the following steps: S1. Mix TiO2, Na2HPO4, and PVP-K30, then add a soluble silver source and react under light-protected conditions to obtain TiO2 / Ag3PO4; S2. Mix the soluble silver source, PVP-K30, and free radical scavenger, and... 60 Nano-Ag sol was obtained by irradiation under Co-γ rays; S3. Under light-protected conditions, TiO2 / Ag3PO4 is mixed with nano-Ag sol to obtain the Ag / TiO2 / Ag3PO4 photocatalyst.

[0022] More preferably, in S1, the mass of PVP-K30 is 10 to 20 wt% of the mass of the soluble silver source.

[0023] More preferably, in S1, the pH value needs to be adjusted after mixing TiO2, Na2HPO4, and PVP-K30.

[0024] More preferably, the pH value is 4 to 10.

[0025] More preferably, in S1, the mixing includes stirring and ultrasonic dispersion.

[0026] More preferably, the stirring time is 20-40 minutes.

[0027] More preferably, in S1, the reaction includes stirring and sonication under light-protected conditions.

[0028] More preferably, the stirring time is 60-180 min.

[0029] More preferably, the power of the ultrasonic dispersion is 200~300W.

[0030] More preferably, the soluble silver source is silver nitrate.

[0031] More preferably, in S2, the free radical scavenger is isopropanol and / or tert-butanol.

[0032] More preferably, in S2, the irradiation dose is 15~25kGy.

[0033] Preferably, the mass of the Ag / TiO2 / Ag3PO4 photocatalyst accounts for 1 to 9 wt% of the starch mass.

[0034] More preferably, the mass of the Ag / TiO2 / Ag3PO4 photocatalyst accounts for 1 to 5 wt% of the starch mass.

[0035] Preferably, the glycerol accounts for 8-18 wt% of the starch mass.

[0036] Preferably, the mass of the lignocellulose nanoparticles accounts for 1.3 to 3.2 wt% of the starch mass.

[0037] Preferably, the heating process, after gelatinizing the starch, further includes defoaming.

[0038] More preferably, the defoaming includes vacuum defoaming and ultrasonic defoaming.

[0039] More preferably, the vacuum treatment time is 5 to 16 minutes.

[0040] More preferably, the power of the ultrasound is 200~600W.

[0041] More preferably, the duration of the ultrasound is 15-25 minutes.

[0042] This invention also protects the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane prepared by the above preparation method.

[0043] This invention also protects the application of the above-mentioned Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite film in fruit and vegetable preservation.

[0044] Preferably, the application is the use of Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane in the adsorption and / or photocatalytic degradation of ethylene.

[0045] Preferably, the application is the use of Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane in antibacterial applications.

[0046] The Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane of the present invention extends the shelf life of fruits and vegetables by adsorbing and degrading ethylene produced by fruits and vegetables and its antibacterial effect.

[0047] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane. The chitosan quaternary ammonium salt in the composite membrane modifies the surface of the Ag / TiO2 / Ag3PO4 photocatalyst, improving the dispersibility and interfacial bonding of the photocatalyst in the membrane matrix. Its polar groups can form a hydrogen bond network with the hydroxyl groups of cellulose and starch, enhancing the composite membrane's ethylene enrichment capacity and the interfacial bonding between the photocatalyst and the matrix, thereby improving the composite membrane's adsorption and degradation effect on ethylene. Furthermore, the chitosan quaternary ammonium salt and the photocatalyst form a dual long-lasting antibacterial mechanism of photoresponsiveness and contact, synergistically improving the antibacterial performance of the composite membrane. Attached Figure Description

[0048] Figure 1 The graph shows the trend of ethylene adsorption amount in Examples 1-5 and Comparative Example 1.

[0049] Figure 2 The images show the antibacterial effects of Examples 1-5 and Comparative Examples 1-4.

[0050] Figure 3 This is a schematic diagram of a self-made adsorption and degradation platform for ethylene.

[0051] Figure 4 This is a schematic diagram of the antimicrobial zone method. Detailed Implementation

[0052] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0053] The chitosan quaternary ammonium salt used in this invention is from Shanghai Maclean Biochemical Technology Co., Ltd., item number: 850124, with a degree of substitution of 92%.

[0054] Example 1 This embodiment provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane, including the following steps: Chitosan quaternary ammonium salt (i.e., hydroxypropyltrimethylammonium chloride chitosan) was added to distilled water at 50℃, with the mass of chitosan quaternary ammonium salt being 8wt% of the starch mass. After stirring and dissolving for 1 hour, 10 g of starch acetate, 14wt% glycerol (based on starch weight, in g), 1.95wt% lignocellulose nanoparticle dispersion (based on starch weight, in g), and 3wt% (based on starch weight, in g) Ag / TiO2 / Ag3PO4 photocatalyst were added to 200 mL of deionized water. The mixture was stirred with a glass rod until the lumps disappeared. The mixture was then vigorously magnetically stirred for 30 min to fully mix, followed by sonication at 400W for 30 min. Subsequently, it was placed in a 90℃ water bath and stirred for 30 min. The paste was transferred to a vacuum filtration flask, vacuumed at 0.1 MPa for 10 min, and then sonicated at 400W for 20 min to remove bubbles, resulting in a transparent gel-like starch / cellulose nanoparticle composite film-forming solution. 30g of the composite film-forming solution was slowly added to a 113mm diameter petri dish coated with a non-stick coating. The mixture was then cast and dried in an electric heating oven at 50℃ for 3 hours to form a film; the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / wood nanocellulose / starch composite film was obtained. The thickness of the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / wood nanocellulose / starch composite film was 0.13±0.02mm.

[0055] The preparation method of the Ag / TiO2 / Ag3PO4 photocatalyst includes the following steps: S1. Dissolve TiO2 and Na2HPO4·12H2O in 60 mL of deionized water at a molar ratio of 1:1. Add 10% PVP-K30 (based on AgNO3 mass) and stir for 30 min. Sonicate at 400 W for 30 min to form a homogeneous suspension. Adjust the pH to 4 and set aside as solution A. Weigh 0.5 g AgNO3 (TiO2 to AgNO3 molar ratio of 1:1) into a mixture of 20 mL of deionized water and 20 mL of methanol solution. Sonicate at 400 W for 30 min and set aside as solution B. Slowly add solution B to solution A while magnetically stirring. Continue stirring for 120 min in the dark, then sonicate at 200 W for 30 min. Centrifuge at 12000 r / min for 5 min at 25 °C. Wash three times each with deionized water and anhydrous ethanol. Dry at 60 °C overnight to obtain TiO2 / Ag3PO4 powder.

[0056] S2. Preparation of nano-Ag sol: Weigh 0.5 wt% silver nitrate and dissolve it in deionized water to obtain a silver nitrate solution. Add 0.6% surfactant polyvinylpyrrolidone (PVP-K30) (by solution mass) and 2% (by deionized water volume) free radical scavenger (isopropanol) to the silver nitrate solution. Stir well with a glass rod, inject the mixed solution into an irradiation bottle, and degas using ultrasound for 60 min (400W). Then place the treated solution in... 60 Nano-Ag sol was prepared by irradiation with Co-γ rays (20 kGy).

[0057] S3. Weigh 1.0 g of TiO2 / Ag3PO4 powder into a beaker, add 20 mL of anhydrous ethanol, stir for 10 min, sonicate at 400 W for 30 min to completely disperse it, then add 10 wt% (based on the mass of TiO2 / Ag3PO4) of nano Ag sol, stir magnetically in the dark for 60 min, dry at 70℃ for 12 h, and then grind with an agate mortar to obtain Ag / TiO2 / Ag3PO4 powder.

[0058] Example 2 This embodiment provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, which differs from Example 1 in that the mass of chitosan quaternary ammonium salt is 2 wt% of the mass of starch. The rest is the same as in Example 1.

[0059] Example 3 This embodiment provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, which differs from Example 1 in that the mass of chitosan quaternary ammonium salt is 5 wt% of the mass of starch. The rest is the same as in Example 1.

[0060] Example 4 This embodiment provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, which differs from Example 1 in that the mass of chitosan quaternary ammonium salt is 10 wt% of the mass of starch. The rest is the same as in Example 1.

[0061] Example 5 This embodiment provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, which differs from Example 1 in that the mass of chitosan quaternary ammonium salt is 15 wt% of the mass of starch. The rest is the same as in Example 1.

[0062] Comparative Example 1 This comparative example provides an Ag / TiO2 / Ag3PO4 / lignocellulose / starch composite membrane, which differs from Example 1 in that chitosan quaternary ammonium salt is not added. The rest is the same as Example 1.

[0063] Comparative Example 2 This comparative example provides an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, which differs from Example 1 in that the mass of chitosan quaternary ammonium salt is 20 wt% of the mass of starch. The rest is the same as in Example 1.

[0064] Comparative Example 3 This comparative example provides an Ag / TiO2 / Ag3PO4 / wood-based nanocellulose / starch composite membrane, which differs from Example 2 in that, in S1, chitosan quaternary ammonium salt is not added, but 5 wt% (based on starch weight, g) of Ag / TiO2 / Ag3PO4 photocatalyst is added. The rest is the same as in Example 2.

[0065] Comparative Example 4 This comparative example provides a chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite membrane, which differs from Example 2 in that, in S1, the Ag / TiO2 / Ag3PO4 photocatalyst is not added, but 5 wt% (based on starch weight, g) of chitosan quaternary ammonium salt is added. The rest is the same as in Example 2.

[0066] Performance testing Evaluation of the antibacterial effect of composite membrane The antibacterial effect of the membrane was determined using the inhibition zone method, with the diameter of the inhibition zone used as the evaluation index. Before the experiment, the membrane was cut into small circular slices with a diameter of 6 mm using a punch, paying attention to the position of the external mixing surface, and the slices were placed in disposable petri dishes for later use.

[0067] In a clean bench, take a petri dish containing solidified Bengal red culture medium and use a pipette to transfer 1 mL of a medium with a concentration of approximately 1×10⁻⁶.6 A CFU / mL spore dispersion was placed in a petri dish and evenly distributed using a sterile spreader. The mixture was allowed to stand for 10 minutes to allow the bacterial solution to penetrate the culture medium and stabilize. Then, the film was carefully lifted with sterile forceps and placed onto the surface of the culture medium. Two placement methods were used in the experiment as follows: Figure 4 As shown. The petri dishes were placed in a 28℃ constant temperature incubator with an incubator temperature of 1 mw / cm². 2 Irradiate with light intensity for 30 minutes, then incubate for 5 days.

[0068] Adsorption Degradation Test of Ethylene A schematic diagram of the self-made adsorption degradation ethylene platform is shown below. Figure 3 As shown. A 113 mm diameter film was placed in a closed glass reactor with a volume of approximately 5 L. The reactor opening was sealed to the transparent quartz glass with Vaseline. A visible light filter with wavelengths greater than 400 nm was placed on the glass slide. The reactor was completely covered with a photographic reflective cloth to ensure that the light in the reactor came primarily from the experimental light source. Before the experiment, 2.4 mL of high-purity ethylene (approximately 0.15 mg / L) was injected into the reactor through the sampling port using a medical syringe. One ethylene degradation experiment lasted 8 h, with the first 4 h being the dark adsorption time and the last 4 h being the illumination time (the light intensity at the center of the glass slide was 100 mW / cm²). 2 The edge illumination intensity is 40 mw / cm 2 During the photocatalytic reaction, circulating cooling water was used to maintain the temperature at around 20°C. Timing began after the injection of high-concentration ethylene. Every 30 minutes, 2.2 mL of mixed gas was extracted from the reactor using a medical syringe and injected into a gas chromatograph equipped with a flame ionization detector to detect the instantaneous concentration of ethylene. A total of 16 measurements were taken, and the ethylene adsorption rate (the rate of change of ethylene during dark adsorption) and the adsorption degradation rate (the rate of change of ethylene during both dark adsorption and photodegradation processes) were calculated.

[0069] Figure 1 The graph shows the ethylene adsorption rate trends for Examples 1-5 and Comparative Example 1.

[0070] Table 1. Ethylene adsorption rate and adsorption degradation rate of Examples 1-5 and Comparative Example 1

[0071] Depend on Figure 1 As shown in Table 1, the ethylene adsorption and degradation rate of the composite membrane first increases and then decreases with the increase of chitosan quaternary ammonium salt addition. This is because the chitosan quaternary ammonium salt molecule contains abundant hydroxyl (–OH), amino (–NH2), and quaternary ammonium (–N) groups. +(CH3)3) and other polar groups. When chitosan quaternary ammonium salt is gradually introduced into the system, these functional groups can form hydrogen bonds with the hydroxyl groups of cellulose and starch, increasing the adsorption of ethylene by the composite membrane. Chitosan quaternary ammonium salt can modify the Ag / TiO2 / Ag3PO4 photocatalyst, improve the dispersibility of the photocatalyst in the composite membrane, and enhance the adsorption and degradation rate of ethylene by the composite membrane by enriching ethylene in the gaseous environment. When the addition amount is 8wt%, the density of active sites reaches the "monolayer saturated coverage" state—providing the maximum number of adsorption sites without causing steric hindrance due to excessive stacking. At this time, the composite membrane has the best adsorption performance. Therefore, the composite membrane of Example 1 has the best ethylene adsorption and degradation rate.

[0072] As shown in Examples 1 and 5 and Comparative Example 2, when the amount of chitosan quaternary ammonium salt added is too large, the adsorption and degradation rate of ethylene by the composite membrane actually decreases. This is because an excessive amount of chitosan quaternary ammonium salt will cover or shield the adsorption sites of the composite membrane and the active sites of the catalyst, thereby leading to a decrease in the adsorption and degradation rate of the composite.

[0073] Figure 2 The diagrams show the antibacterial effects of Examples 1-5 and Comparative Example 1. As the chitosan quaternary ammonium salt content increases, the diameter of the inhibition zone also increases. This is because the chitosan quaternary ammonium salt molecular chain contains a large number of quaternary ammonium salt cationic groups (–N). + (CH3)3). These positively charged functional groups can electrostatically interact with the negatively charged phospholipids, proteins, and polysaccharide structures on the surface of microbial cells, thereby disrupting the cell membrane or spore structure, ultimately leading to spore rupture and inhibiting microbial growth. As shown in Examples 2, 3, and 4, in Example 2, the sum of the mass of chitosan quaternary ammonium salt and the photocatalyst was 5 wt% of the starch mass, resulting in an inhibition zone diameter of 11.1 mm. In Comparative Examples 3 and 4, equal masses of Ag / TiO2 / Ag3PO4 photocatalyst and chitosan quaternary ammonium salt were added separately, resulting in inhibition zone diameters of 9.6 mm and 8.6 mm, respectively. The comparison shows that, under the premise of equal mass, the inhibition zone of Example 2 is significantly larger than that of Comparative Examples 3 and 4. This indicates that the chitosan quaternary ammonium salt and the photocatalyst form a dual long-lasting antibacterial mechanism of photoresponsiveness and contact, synergistically improving the antibacterial performance of the composite membrane.

[0074] Obviously, the above embodiments of the present invention 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 neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane, characterized in that, Includes the following steps: Chitosan quaternary ammonium salt, starch, glycerol, lignocellulose nanoparticles, and Ag / TiO2 / Ag3PO4 photocatalyst are mixed in water and heated to gelatinize the starch to obtain a composite film-forming solution; the solution is then cast to obtain the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanoparticles / starch composite film. The Ag / TiO2 / Ag3PO4 photocatalyst is a ternary heterojunction complex formed by Ag, TiO2 and Ag3PO4; the chitosan quaternary ammonium salt accounts for 2 to 15 wt% of the starch mass.

2. The preparation method according to claim 1, characterized in that, The chitosan quaternary ammonium salt accounts for 2 to 10 wt% of the starch mass.

3. The preparation method according to claim 1, characterized in that, The chitosan quaternary ammonium salt is hydroxypropyltrimethylammonium chloride chitosan.

4. The preparation method according to claim 1, characterized in that, The heating temperature is 80~100℃.

5. The preparation method according to claim 1, characterized in that, The preparation method of the Ag / TiO2 / Ag3PO4 photocatalyst includes: firstly, mixing and reacting TiO2, phosphorus source and soluble silver source to prepare TiO2 / Ag3PO4, and then loading nano Ag sol onto TiO2 / Ag3PO4 to obtain the Ag / TiO2 / Ag3PO4 photocatalyst.

6. The preparation method according to claim 5, characterized in that, The molar ratio of TiO2 to soluble silver source is 1:(0.5~2).

7. The preparation method according to claim 5, characterized in that, The mass of the nano-Ag sol is 10-15 wt% of the mass of TiO2 / Ag3PO4.

8. The preparation method according to claim 1, characterized in that, The mass of the Ag / TiO2 / Ag3PO4 photocatalyst is 1~9 wt% of the starch mass.

9. The Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane prepared by any of the preparation methods described in claims 1 to 8.

10. The application of the Ag / TiO2 / Ag3PO4 / chitosan quaternary ammonium salt / lignocellulose nanofiber / starch composite membrane according to claim 9 in the preservation of fruits and vegetables.

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