Functional nano zinc oxide as well as preparation method and application thereof

Abstract

The invention discloses functional nano zinc oxide as well as a preparation method and application thereof, and belongs to the technical field of food packaging materials and functional nano composite materials. The preparation method comprises the following steps: dissolving dialdehyde cellulose in a hydrochloric acid solution, mixing with a procyanidine solution dissolved in DMSO (Dimethylsulfoxide), heating to react, dialyzing and drying to obtain a cellulose-polyphenol graft; and uniformly mixing the cellulose-polyphenol graft aqueous solution with a zinc nitrate aqueous solution, adjusting the pH value, carrying out a hydrothermal reaction, carrying out centrifugal separation, washing the precipitate, and drying to obtain the functional zinc oxide nanoparticles. Through an aldehyde cellulose-polyphenol grafting strategy, the particle size controllability and dispersity of ZnO nano particles are improved, the ZnO nano particles are endowed with higher specific surface area and functionality, and after the ZnO nano particles are loaded to a chitosan film, the oxidation resistance, antibacterial property and mechanical strength of the film are remarkably enhanced.

Description

Technical Field

[0001] This invention relates to a functional nano zinc oxide, its preparation method and application, belonging to the technical field of food packaging materials and functional nanocomposite materials. Background Technology

[0002] Chitosan, an abundant natural polysaccharide, has been widely used in food preservation and active packaging materials due to its film-forming properties, biocompatibility, and certain antibacterial activity. However, single chitosan films suffer from insufficient mechanical properties, poor barrier properties, and limited antioxidant and antibacterial activity, which restricts their widespread application in food packaging. To address this, researchers have attempted to introduce inorganic nanomaterials (such as zinc oxide and titanium dioxide) or plant-based active substances (such as polyphenols and essential oils) to enhance and functionalize them. Among these, zinc oxide nanoparticles have attracted significant attention due to their excellent antibacterial properties and UV shielding capabilities; however, traditional synthesis methods often result in uneven particle size, severe agglomeration, and poor dispersibility in polymer matrices.

[0003] On the other hand, polyphenols possess natural antioxidant properties and metal ion complexing capabilities, making them suitable as green inducers to aid in the synthesis of metal oxides. However, due to the easy oxidation of polyphenol monomers and their insufficient stability in aqueous phases, their effect on regulating crystal growth is limited. Current technologies lack an effective strategy that can both improve the dispersibility and controllability of nanoparticles and enhance their function in polymer films. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention proposes a functional nano zinc oxide, its preparation method, and its application.

[0005] A method for preparing functional nano zinc oxide includes the following steps: (1) Dissolve dialdehyde cellulose (DCF) in hydrochloric acid solution, mix with proanthocyanidin (PA) solution dissolved in DMSO, heat to react, and then dialyze and dry to obtain cellulose-polyphenol graft (DCP). (2) After mixing the aqueous solution of cellulose-polyphenol graft with the aqueous solution of zinc nitrate, the pH was adjusted, followed by hydrothermal reaction, centrifugation and washing of the precipitate, and drying to obtain functional zinc oxide nanoparticles (DCP@ZnO).

[0006] In a preferred embodiment of the present invention, the heating reaction temperature is 30-70°C and the reaction time is 12-48 h. More preferably, the reaction temperature is 40°C and the reaction time is 48 h.

[0007] In a preferred embodiment of the present invention, the hydrothermal reaction is carried out at a temperature of 120-160°C for a time of 4-10 hours. More preferably, the hydrothermal reaction is carried out at a temperature of 120°C for a time of 4 hours.

[0008] As a preferred embodiment of the present invention, in step (1), the mass ratio of dialdehyde cellulose to proanthocyanidins is 1:(0.5-1.5).

[0009] In a preferred embodiment of the present invention, the volume ratio of the cellulose-polyphenol graft aqueous solution to the zinc nitrate aqueous solution is 1:(0.5-2), the concentration of the cellulose-polyphenol graft aqueous solution is 0.7±0.01 mg / mL, and the concentration of the zinc nitrate aqueous solution is 10 mM. More preferably, the volume ratio of the cellulose-polyphenol graft aqueous solution to the zinc nitrate aqueous solution is 1:1.

[0010] In a preferred embodiment of the present invention, in step (2), the pH is adjusted to 9-11, preferably 10, using a 1 mol / L NaOH solution.

[0011] The present invention also claims protection for the functional nano zinc oxide prepared by the method described above.

[0012] The present invention also claims protection for the application of the functional nano zinc oxide in the preparation of chitosan membranes, comprising the following steps: adding functional nano zinc oxide to a chitosan solution containing 1% (v / v) glacial acetic acid, and obtaining a chitosan membrane (DCPZ) after film formation and drying.

[0013] In a preferred embodiment of the present invention, the mass ratio of the functional nano zinc oxide to the chitosan solution is (0.4-2):100.

[0014] The beneficial effects of this invention are as follows: This invention improves the controllability and dispersibility of ZnO nanoparticles through an aldehyde-based cellulose-polyphenol grafting strategy, endowing them with higher specific surface area and functionality. Furthermore, after being loaded onto a chitosan membrane, the membrane's antioxidant properties, antibacterial properties, and mechanical strength are significantly enhanced. The synthesis method of the functional nano-zinc oxide and chitosan membrane of this invention is green and environmentally friendly, requiring no strong reducing agents or organic solvents, and is suitable for food packaging materials. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the preparation method of functional zinc oxide nanoparticles and their application in chitosan membranes.

[0016] Figure 2Comparative graphs show the antioxidant capacity of zinc oxide nanoparticles prepared in Examples 1, 2, and 3. (a) Comparative graph of the DPPH free radical scavenging rate and macroscopic scavenging capacity of DCP@ZnO, PA@ZnO, and Control@ZnO concentrations; (b) Comparative graph of the ABTS free radical scavenging rate and macroscopic scavenging capacity of DCP@ZnO, PA@ZnO, and Control@ZnO concentrations; (c) Comparative graph of the Fe... 3+ Comparison charts of reducing power and their macroscopic representation.

[0017] Figure 3 The graph shows a comparison of the mechanical properties of the chitosan composite membranes in Examples 1-7 and Comparative Examples 1-5. TS represents the tensile strength of the composite membrane, and EAB represents the elongation at break of the composite membrane.

[0018] Figure 4 The antioxidant capacity of the chitosan composite membranes in Examples 1-5 and Comparative Example 1 is shown. (a) Comparison of DPPH free radical scavenging rates of the chitosan composite membrane solutions prepared in Examples 1-5 and Comparative Example 1; (b) Macroscopic diagram of DPPH free radical scavenging capacity of the chitosan composite membrane solutions prepared in Examples 1-5 and Comparative Example 1; (c) Comparison of ABTS free radical scavenging rates of the chitosan composite membrane solutions prepared in Examples 1-5 and Comparative Example 1; (d) Macroscopic diagram of ABTS free radical scavenging capacity of the chitosan composite membrane solutions prepared in Examples 1-5 and Comparative Example 1; (e) Reduced Fe2+ of the chitosan composite membrane solutions prepared in Examples 1-5 and Comparative Example 1. 3+ Comparison chart, (f) shows the reduced Fe content of the chitosan composite film solution prepared in Examples 1-5 and Comparative Example 1. 3+ Macro-level capability diagram.

[0019] Figure 5 The antibacterial activity of the chitosan composite membranes in Examples 1-5 and Comparative Example 1 is shown in the following graphs: (a) Plate count results of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Staphylococcus aureus; (b) Plate count results of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Escherichia coli; (c) Inhibition zone diagram of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Staphylococcus aureus; (d) Inhibition zone diagram of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Escherichia coli; (e) Comparison of cell reduction rates of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Staphylococcus aureus and Escherichia coli; (f) Statistical graph of inhibition zone diameter of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Staphylococcus aureus; (g) Statistical graph of inhibition zone diameter of the composite membrane solutions prepared in Examples 1-5 and Comparative Example 1 against Escherichia coli.

[0020] Figure 6 This is a cytotoxicity diagram of the chitosan composite membranes in Comparative Examples 1-5 and Examples 1-7. Detailed Implementation

[0021] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0022] Example 1 A method for preparing functional zinc oxide nanoparticles, specifically comprising: Preparation of S1 aldehyde-modified cellulose-proanthocyanidin graft (DCP): 0.1 g of dialdehyde-modified cellulose was dissolved in 4 ml of hydrochloric acid solution (1 mol / L), and 0.15 g of proanthocyanidin was dissolved in 2.68 ml of DMSO. The hydrochloric acid solution containing dialdehyde cellulose was mixed with the DMSO solution containing proanthocyanidin, and the mixture was heated in a constant temperature water bath at 40 ℃ for 48 h to obtain the reaction solution. The reaction solution was then dialyzed against 25% wt DMSO aqueous solution (12000-14000 Da) for 24 h, dialyzed against deionized water for 48 h, and freeze-dried to obtain the graft (DCP).

[0023] Preparation of S2 functional zinc oxide nanoparticles (DCP@ZnO): 0.0425 g of DCP obtained in step S1 was dissolved in 60 ml of water, and an equal volume of 10 mM zinc nitrate solution was added. The pH was adjusted to 10 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 120 °C for 4 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 °C for 12 h to obtain functional zinc oxide nanoparticles (DCP@ZnO).

[0024] The functional zinc oxide nanoparticles prepared in Example 1 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-1.

[0025] Example 2 The functional zinc oxide nanoparticles prepared in Example 1 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 0.8% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-2.

[0026] Example 3 The functional zinc oxide nanoparticles prepared in Example 1 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 1.2% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-3.

[0027] Example 4 The functional zinc oxide nanoparticles prepared in Example 1 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 1.6% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-4.

[0028] Example 5 The functional zinc oxide nanoparticles prepared in Example 1 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 2.0% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-5.

[0029] Example 6 A method for preparing functional zinc oxide nanoparticles, specifically comprising: Preparation of S1 aldehyde-modified cellulose-proanthocyanidin graft (DCP): 0.1 g of dialdehyde-modified cellulose was dissolved in 4 ml of hydrochloric acid solution (1 mol / L), and 0.05 g of proanthocyanidin was dissolved in 2.68 ml of DMSO solution. The hydrochloric acid solution containing dialdehyde cellulose was mixed with the DMSO solution containing proanthocyanidin, and the mixture was heated in a constant temperature water bath at 30 ℃ for 48 h to obtain the reaction solution. The reaction solution was then dialyzed against 25% wt DMSO aqueous solution (12000-14000 Da) for 24 h, dialyzed against deionized water for 48 h, and freeze-dried to obtain the graft (DCP).

[0030] Preparation of S2 functional zinc oxide nanoparticles (DCP@ZnO): 0.0425 g of DCP obtained in step S1 was dissolved in 60 ml of water, and 30 ml of zinc nitrate solution (10 mM) was added. The pH was adjusted to 9 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 160 ℃ for 10 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 60 ℃ for 24 h to obtain functional zinc oxide nanoparticles (DCP@ZnO).

[0031] The functional zinc oxide nanoparticles prepared in Example 6 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-6.

[0032] Example 7 A method for preparing functional zinc oxide nanoparticles, specifically comprising: Preparation of S1 aldehyde-modified cellulose-proanthocyanidin graft (DCP): 0.1 g of dialdehyde-modified cellulose was dissolved in 4 ml of hydrochloric acid solution (1 mol / L), and 0.1 g of proanthocyanidin was dissolved in 2.68 ml of DMSO. The hydrochloric acid solution containing dialdehyde cellulose was mixed with the DMSO solution containing proanthocyanidin, and the mixture was heated in a constant temperature water bath at 70 ℃ for 12 h to obtain the reaction solution. The reaction solution was then dialyzed against 25% wt DMSO aqueous solution (12000-14000 Da) for 12 h, dialyzed against deionized water for 48 h, and freeze-dried to obtain the graft (DCP).

[0033] Preparation of S2 functional zinc oxide nanoparticles (DCP@ZnO): 0.0425 g of DCP obtained in step S1 was dissolved in 60 ml of water, and 120 ml of zinc nitrate solution (10 mM) was added. The pH was adjusted to 11 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 140 ℃ for 8 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 ℃ for 12 h to obtain functional zinc oxide nanoparticles (DCP@ZnO).

[0034] The functional zinc oxide nanoparticles prepared in Example 7 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. DCP@ZnO nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-7.

[0035] Comparative Example 1 Chitosan was dissolved in 1 wt% acetic acid solution to prepare a 1 wt% chitosan solution, which was then poured into a dry petri dish and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain a chitosan membrane CS.

[0036] Comparative Example 2 A method for preparing functional zinc oxide nanoparticles, specifically comprising: 0.0425 g of proanthocyanidins was dissolved in 60 ml of water, and an equal volume of 10 mM zinc nitrate solution was added. The pH was adjusted to 10 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 120 °C for 4 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 °C for 12 h to obtain functional zinc oxide nanoparticles, denoted as PA@ZnO nanoparticles.

[0037] The functional zinc oxide nanoparticles prepared in Comparative Example 2 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. Functional zinc oxide nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-8.

[0038] Comparative Example 3 A method for preparing zinc oxide nanoparticles, specifically comprising: The pH of 60 ml of 10 mM zinc nitrate solution was adjusted to 10 with 1 mol / L NaOH solution. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 120 °C for 4 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 °C for 12 h to obtain zinc oxide nanoparticles, denoted as Control@ZnO nanoparticles.

[0039] The zinc oxide nanoparticles prepared in Comparative Example 3 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. Zinc oxide nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50%RH) for 24 h to obtain the chitosan composite membrane DCPZ-9.

[0040] Comparative Example 4 A method for preparing functional zinc oxide nanoparticles, specifically comprising: Preparation of functional zinc oxide nanoparticles: 0.0425 g of aldehyde-modified cellulose was dissolved in 60 ml of water, and an equal volume of zinc nitrate solution (10 mM) was added. The pH was adjusted to 10 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 120 °C for 4 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 °C for 12 h to obtain functional zinc oxide nanoparticles, denoted as DCF@ZnO nanoparticles.

[0041] The functional zinc oxide nanoparticles prepared in Comparative Example 4 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. Functional zinc oxide nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-10.

[0042] Comparative Example 5 A method for preparing functional zinc oxide nanoparticles, specifically comprising: 0.017 g of dialdehyde-modified cellulose and 0.0255 g of proanthocyanidins were dissolved in 60 ml of water, and an equal volume of zinc nitrate solution (10 mM) was added. The pH was adjusted to 10 with 1 mol / L NaOH solution. The mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed for reaction at 120 °C for 4 h. After the reaction was complete, the reaction solution was centrifuged, washed several times with ethanol and water, and dried in an oven at 40 °C for 12 h to obtain functional zinc oxide nanoparticles.

[0043] The functional zinc oxide nanoparticles prepared in Comparative Example 5 were applied to the preparation of chitosan composite membranes. Specifically, chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 1wt% chitosan solution. Functional zinc oxide nanoparticles with a chitosan solid content of 0.4% were added, stirred at room temperature for 6 h, sonicated for 15 min, poured into a dry petri dish, and dried in a constant temperature and humidity chamber (45 ℃, 50% RH) for 24 h to obtain the chitosan composite membrane DCPZ-11.

[0044] Example 1 Test samples: DCP@ZnO, PA@ZnO, and Control@ZnO aqueous solutions prepared in Examples 1, 2, and 3 with concentrations of 3.0, 2.5, 2, 1.5, 1, and 0.5 mg / ml, respectively.

[0045] DPPH free radical scavenging activity assay: Prepare 0.1 mmol DPPH (2,2-biphenyl-1-picrylhydrazyl) ethanol solution, measure 4 ml and add it to a transparent reagent bottle, simultaneously add 1 ml of the test sample and mix well. Incubate at room temperature in the dark for 30 min, and measure the absorbance at 517 nm as A. i A j The absorbance value is calculated as follows: A0 is the absorbance value after reacting 4 ml of anhydrous ethanol with 1 ml of the test sample. Alternatively, 4 ml of DPPH solution is added to anhydrous ethanol instead of the test sample, and the absorbance value A0 is measured at 517 nm. The DPPH scavenging activity is calculated using the following formula: .

[0046] Assay for ABTS free radical scavenging activity: Preparation of ABTS solution: 7.4 mmol of ABTS ethanol stock solution and 2.6 mmol of potassium persulfate ethanol solution were mixed at a volume ratio of 1:1. After incubation at room temperature in the dark for 12 h, the solution was diluted with anhydrous ethanol to obtain an absorbance of 0.7 ± 0.02 at 734 nm. 1 ml of the test sample was mixed with 4 ml of ABTS solution and reacted at room temperature in the dark for 20 min. The absorbance at 734 nm was then measured (A2). Simultaneously, 1 ml of ABTS solution was mixed with 4 ml of ethanol solution, and the absorbance at 734 nm was measured (A1). The ABTS scavenging activity was calculated using the following formula.

[0047] .

[0048] Reducing power determination: Take 2.5 ml of the sample to be tested and mix it with 2.5 ml of phosphate buffer (pH = 6.6) and 2.5 ml of 1% (w / v) potassium ferricyanide solution. Incubate the mixture in a constant temperature water bath at 50 ℃ for 20 min. Then add 2.5 ml of 10% (w / v) trichloroacetic acid to terminate the reaction. Centrifuge the mixture and take 2.5 ml of the supernatant. Incubate it with 0.5 ml of 0.1% (w / v) ferric chloride at 37 ℃ for 10 min. Measure the absorbance of the solution at 700 nm using a UV spectrophotometer.

[0049] according to Figure 2It can be seen that with the increase of zinc oxide concentration, the scavenging ability of each sample for DPPH and ABTS free radicals is enhanced, among which DCP@ZnO prepared in Example 1 shows the best scavenging effect. In the DPPH test, at a concentration of 2 mg / mL, the DPPH free radical scavenging rates of DCP@ZnO, PA@ZnO and Control@ZnO were 70.91%, 47.14% and 14.98%, respectively; among them, the solution of DCP@ZnO (2 mg / mL) almost completely faded from purple to only slightly brown after treatment, while the PA@ZnO solution remained light purple, and Control@ZnO remained basically unchanged. In the ABTS test, at a concentration of 0.5 mg / mL, the DCP@ZnO solution prepared in Example 1 was almost colorless, while the PA@ZnO prepared in Comparative Example 2 and the Control@ZnO prepared in Comparative Example 3 remained blue, indicating that DCP@ZnO has a significant free radical scavenging ability. At this point, the ABTS free radical scavenging rates of DCP@ZnO, PA@ZnO, and Control@ZnO were 87.26%, 56.61%, and 36.46%, respectively. Its excellent free radical scavenging performance is mainly attributed to the synergistic effect between the surface dialdehyde cellulose-polyphenol graft layer and the zinc oxide nanoparticles: the polyphenol groups can provide hydrogen atoms or electrons to neutralize free radicals, while the oxygen vacancies on the zinc oxide surface can promote electron transfer, thereby accelerating the free radical reduction reaction; the synergistic effect of both gives DCP@ZnO higher electronic activity and antioxidant capacity, significantly better than unmodified or single polyphenol-induced zinc oxide nanoparticles.

[0050] Similarly, as the concentration of the tested samples increased, the reducing ability of each sample gradually increased, with DCP@ZnO showing the most significant reducing effect. When the concentration of DCP@ZnO was 3 mg / mL, the solution after the reaction of DCP@ZnO was light green, while the solutions after the reaction of PA@ZnO prepared in Example 2 and Control@ZnO prepared in Example 3 were yellow-green and bright yellow, respectively, indicating that their reducing abilities were limited. At this concentration, the absorbance of the reaction solutions of DCP@ZnO, PA@ZnO, and Control@ZnO were 0.4120, 0.2429, and 0.2157, respectively. The excellent reducing performance of DCP@ZnO is mainly attributed to the inductive effect of the dialdehyde cellulose-proanthocyanidin graft during the synthesis process. This graft layer not only promotes the uniform generation of zinc oxide crystal nuclei and the enrichment of surface electrons, but also provides electrons and hydrogen atoms through surface polyphenol groups, achieving synergistic reduction with zinc oxide oxygen vacancies, thereby significantly improving the overall electron transfer efficiency and reducing activity of the material.

[0051] The present invention further explored the DPPH free radical scavenging activity (functional zinc oxide nanoparticle concentration of 2 mg / mL), ABTS free radical scavenging activity (functional zinc oxide nanoparticle concentration of 0.5 mg / mL), and reducing power (functional zinc oxide nanoparticle concentration of 3 mg / mL) of the functional zinc oxide nanoparticles prepared in Examples 6 and 7, and Comparative Examples 4 and 5 at corresponding concentrations, following the method of Example 1 above.

[0052] The DCP@ZnO solutions prepared in Examples 6 and 7 exhibited similar DPPH, ABTS, and reducing abilities to those in Example 1, with corresponding DPPH radical scavenging rates of 57.32% and 63.10%, ABTS radical scavenging rates of 68.89% and 76.2%, and absorbances of 0.2701 and 0.3429, respectively. This indicates that the antioxidant and reducing abilities exhibited by the particles are primarily driven by the polyphenols in the system. The DAC@ZnO solution prepared in Comparative Example 4 showed DPPH and ABTS radical scavenging abilities, as well as absorbance of 0.23, at 19.58%, 40.75%, and 40.75%, respectively, which were not significantly different from those of Control@ZnO. This is attributed to the fact that dialdehyde cellulose alone only provides physical confinement and complexation, lacking active electron-donating groups, resulting in limited improvement in the antioxidant performance of zinc oxide. In Comparative Example 5, the dialdehyde cellulose and polyphenol were in a physical mixture system (DAC+PA@ZnO). Under alkaline and high-temperature hydrothermal conditions, the polyphenols were easily oxidized and deactivated, resulting in uneven distribution on the zinc oxide surface, unstable antioxidant effect, low electron transfer efficiency, and poor system stability and repeatability. Therefore, it lacked representativeness or engineering application value. Its antioxidant and reducing abilities were between those of PA@ZnO and DCP@ZnO. The DPPH radical scavenging ability, APTS radical scavenging ability, and absorbance of the solution after the reaction were 53.07%, 60.99%, and 0.2573, respectively. In contrast, in the dialdehyde cellulose-polyphenol grafted zinc oxide (DCP@ZnO) prepared in the Example, the polyphenols were firmly fixed to the cellulose chains through chemical bonds between the aldehyde and hydroxyl groups, constructing a stable organic graft layer, thereby endowing the zinc oxide nanoparticles with significantly enhanced and stable antioxidant properties.

[0053] Example 2 Preparation of liquid culture medium (NB): Add 5 g of nutrient broth to 200 ml of distilled water, heat to dissolve, pour into an Erlenmeyer flask, and seal with sealing film.

[0054] Solid culture medium (MH): Dissolve 4.2 g of MH agar in 100 mL of distilled water, pour into an Erlenmeyer flask and seal. Sterilize the prepared liquid culture medium and agar at 120 °C for 20 min. Wrap appropriate amounts of pipette tips (10 mL, 1 mL, and 100 μL) in newspaper. Place the required spreading rods, centrifuge tubes, forceps, Oxford cups, test tubes, inoculation loops, etc., into a sterilization bag. After preparation, sterilize the required solid items at 120 °C for 40 min. Sterilize an appropriate amount of disposable culture dishes under UV light on a laminar flow hood.

[0055] Selected Gram-positive bacteria: Staphylococcus aureus ( S. aureus Gram-negative bacteria: Escherichia coli ( E. coli Take 100 μL of the lyophilized bacterial powder solution and add it to a petri dish containing solid culture medium. Spread the solution evenly with a spreader and then incubate in an incubator for 24 h. After the bacteria have grown completely, use an inoculation loop to transfer the bacteria to a test tube containing solid culture medium, streak the tube, seal it with a rubber stopper, and finally incubate all the test tubes in an incubator for 24 h.

[0056] Bacterial activation: After bacterial growth is complete, take one test tube containing Staphylococcus aureus and one containing Escherichia coli, respectively. Use a 1 mL pipette to draw an appropriate amount of liquid culture medium to rinse the bacteria off the agar surface, then transfer the solution to an Erlenmeyer flask containing an appropriate amount of liquid culture medium and incubate at 37°C in a shaker for 24 h. Take 1 mL of the activated bacterial solution and add it to a centrifuge tube, along with 9 mL of sterile water. Measure the absorbance (OD600) at 600 nm. Based on the relationship between OD600 and bacterial concentration, determine the bacterial concentration in the centrifuge tube.

[0057] Using the broth microdilution method, the minimum inhibitory concentrations (MICs) of different types of functional zinc oxide prepared in Examples 1-7 and Comparative Examples 2-5 against Gram-positive and Gram-negative bacteria were studied.

[0058] Taking the DCP@ZnO prepared in Example 1 as an example, its minimum inhibitory concentration (MIC) against Staphylococcus aureus or Escherichia coli was determined. A DCP@ZnO solution with a concentration of 0.5 mg / ml was prepared. Seven test tubes were used. A certain amount of liquid culture medium and zinc oxide solution were added to the first test tube, and the solution was diluted sequentially using the two-fold dilution method. An appropriate amount of distilled water was added to the seventh test tube as a control. A DCP@ZnO solution with a concentration of 10 mg / ml was added to all test tubes. 5After incubating CFU / mL bacterial suspension at 37°C for 24 h, turbidity was visually assessed and OD600 was measured. MIC was defined as the lowest sample concentration at which no visible growth was observed (or ΔOD600 ≤ 0.05) compared to the control group. Each group was tested at least three times independently, and the mean was reported. The same method was used to test the minimum inhibitory concentrations (MICs) of DCP@ZnO prepared in Examples 2-7 against Escherichia coli or Staphylococcus aureus, as well as the MICs of PA@ZnO, Control@ZnO, DAC@ZnO, and DAC+PA@ZnO.

[0059] As shown in Table 1, the minimum inhibitory concentrations (MICs) of the DCP@ZnO particles prepared in Examples 1-7, PA@ZnO prepared in Comparative Example 2, Control@ZnO prepared in Comparative Example 3, DAC@ZnO prepared in Comparative Example 4, and DAC+PA@ZnO prepared in Comparative Example 5 against Staphylococcus aureus were 0.0625 mg / mL, 0.0625 mg / mL, 0.125 mg / mL, 0.125 mg / mL, and 0.0625 mg / mL, respectively; and the MICs against Escherichia coli were 0.125 mg / mL, 0.125 mg / mL, 0.0625 mg / mL, 0.0625 mg / mL, and 0.125 mg / mL, respectively. The results indicate that there are significant differences in the inhibitory effects of zinc oxide particles on Gram-positive and Gram-negative bacteria in Examples 1-7 and Comparative Examples 2-5, which is closely related to the bacterial cell wall structure and the chemical properties of the particle surface.

[0060] Table 1 Zinc oxide particles prepared using different induction systems exhibit significant differences in surface chemical composition and interfacial reactivity, resulting in varying antibacterial properties. Control@ZnO relies solely on oxygen vacancies to induce a small amount of reactive oxygen species (ROS) for bacterial inhibition, thus exhibiting limited bactericidal ability. While DAC@ZnO prepared in Comparative Example 4 possesses some dispersibility and coordination properties, it lacks active electron-donating groups, leading to low ROS generation efficiency. PA@ZnO prepared in Comparative Example 2 complexes Zn with surface polyphenolic hydroxyl groups. 2+ This promotes ROS generation and disrupts cell membranes, significantly enhancing antibacterial properties. Comparative Example 5's DAC+PA@ZnO exhibits both confinement and polyphenol-inducing effects, further improving antibacterial activity. However, due to the physical mixing of polyphenols and cellulose, its chemical stability and sustained activity are insufficient. In contrast, the DCP@ZnO prepared in Examples 1-7, due to the chemical grafting structure of dialdehyde cellulose and polyphenols, firmly immobilizes polyphenols on the ZnO surface, improving polyphenol stability and forming a continuous electron transport pathway. This allows for the continuous generation of ROS and oxidation of polyunsaturated phospholipids in the cell membrane, leading to membrane structure damage and leakage of cell contents.

[0061] Example 3 Following the test methods in GB / T 1040.2-2006 "Determination of Tensile Properties of Plastics", the chitosan composite films prepared in Examples 1-7 and Comparative Examples 1-5 were cut into 25×2 mm strips using a dumbbell-shaped cutter. The tensile strength (TS) and elongation at break (EAB) of the specimens were determined using an electric universal testing machine. The initial gauge length was 18 mm, the tensile speed was set to 2 mm / min, and each sample was tested five times in parallel. The average value was recorded as the final result. (See attached table). Figure 3 .

[0062] according to Figure 3 In Comparative Example 1, the tensile strength of the pure chitosan membrane was 27.71 MPa, and the elongation at break was 5.07%. With the introduction of DCP@ZnO, the tensile strength (TS) of the composite membrane significantly increased, gradually increasing with the increase of DCP@ZnO content (Examples 1–5). When the amount of DCP@ZnO added was 1.2% (Example 3), the tensile strength of the composite membrane reached its maximum value of 42.92 MPa. This is because an appropriate amount of DCP@ZnO particles can be uniformly dispersed in the chitosan matrix, and the polyphenolic hydroxyl groups on their surface form a dense hydrogen bond network with the -OH and -NH2 groups on the chitosan molecular chain, thereby enhancing the interfacial bonding force and stress transfer efficiency, significantly improving the overall strength of the membrane. Furthermore, the good compatibility and interfacial matching between DCP@ZnO and chitosan allow the inorganic nanophase to effectively bear external forces without causing stress concentration. With further increases in the DCP@ZnO content, the elongation at break (EAB) of the composite membrane gradually decreased. This is because the high content of inorganic particles increases the rigidity of the membrane, restricting the migration and orientation of chitosan molecular chains. Simultaneously, localized aggregation between particles may form rigid regions or micro-defects in the matrix, reducing the membrane's extensibility. In other words, the addition of DCP@ZnO, on the one hand, improves tensile strength through interfacial strengthening; on the other hand, it increases the crosslinking density and chain segment constraint of the system, resulting in a membrane exhibiting higher modulus but lower extensibility.

[0063] Compared to DCP@ZnO, zinc oxide nanoparticles prepared by other induction systems showed significantly weaker mechanical strengthening effects in chitosan composite films. The differences mainly stemmed from variations in the surface chemical structure of the particles and their interaction with the matrix interface. Control@ZnO in Comparative Example 3 relied solely on physical dispersion, resulting in weak interactions with chitosan and a tendency to aggregate, leading to numerous interfacial defects and limited tensile strength improvement (only 26.33 MPa). While DAC@ZnO prepared in Comparative Example 4 possessed some hydroxyl and aldehyde coordination effects, it lacked active electron-donating groups, limiting its strengthening effect. The surface polyphenolic hydroxyl groups of PA@ZnO prepared in Comparative Example 2 could form hydrogen bonds with chitosan, improving interfacial bonding and increasing tensile strength. However, the polyphenols were easily oxidized and deactivated under alkaline conditions, resulting in insufficient interfacial stability. DAC+PA@ZnO prepared in Comparative Example 5 combined physical confinement with polyphenol induction, exhibiting superior dispersibility and stress transfer compared to the former. However, due to the weak chemical bonding caused by the physical mixing of the two components, the system exhibited poor stability and repeatability. In contrast, the DCP@ZnO prepared in Examples 6 and 7 exhibited similar reinforcing effects to that in Example 1, with the differences being related to the particle size. In summary, the DCP@ZnO prepared in these examples forms a stable organic shell through the chemical grafting of dialdehyde cellulose and polyphenols, establishing a high-density hydrogen bond and coordination network with the chitosan matrix. The particles are uniformly dispersed in the matrix, resulting in efficient stress transfer and thus exhibiting the highest tensile strength. Regarding the elongation at break of the composite film, the DCP@ZnO, due to the dense organic shell formed by the "dialdehyde cellulose-polyphenol" chemical grafting, opens the hydrogen bond network within the chitosan before establishing a hydrogen bond / coordination network between the particles and chitosan and achieving nanoscale uniform dispersion. This transforms the originally rigid, crystalline segments into amorphous flexible chains, resulting in a slight increase in elongation at break. Compared to Example 1, the DAC+PA@ZnO prepared in Comparative Example 5 exhibits confinement and polyphenol interfacial interaction, but it is only a physical mixture. Its crosslinking strength and continuity are inferior to the grafted system, and its elongation at break is slightly higher. PA@ZnO and DAC@ZnO rely on polyphenol hydrogen bonds or cellulose coordination / hydrogen bonds, respectively. Their interfacial networks are loose and lack continuity, allowing for greater chain segment mobility. Their elongation at break is close to and higher than that of DCP@ZnO and DAC+PA@ZnO. Control@ZnO, on the other hand, has the weakest interaction with the matrix and is relatively loosely dispersed, resulting in the lowest equivalent crosslinking density and therefore the highest elongation at break (7.67%). It should be noted that a slight increase in elongation at break occasionally occurs in each system at low dosages (due to particle microplasticization and defect filling). However, with increasing dosage, the interfacial crosslinking density, rigidity dominance, and stress concentration caused by microagglomeration lead to a monotonic decrease in elongation at break. In summary, DCP@ZnO possesses the best interfacial compatibility and stress transfer efficiency, making it the most effective inducing system for enhancing the mechanical properties of chitosan composite films.

[0064] Example of effect 4 The methods for testing the antioxidant and reducing abilities of the chitosan composite membranes prepared in Examples 1-5 and Comparative Example 1 were the same as those used in Effect Example 1.

[0065] according to Figure 4 It can be seen that the pure CS membrane (Comparative Example 1) exhibited certain antioxidant activity in both free radical scavenging tests. This is because DPPH or ABTS free radicals can react with the free –NH2 groups on the chitosan molecular chain, thereby achieving partial free radical neutralization. The pure CS membrane scavenged 21.32% of DPPH free radicals and 84.87% of ABTS free radicals. With the increase of the proportion of DCP@ZnO particles (Examples 1-5), the antioxidant performance of the composite membrane was significantly improved. The DPPH scavenging rate gradually increased from 22.63% to 27.36%, and the ABTS scavenging rate increased from 87.06% to 89.56%. The solution color gradually lightened after the reaction, which also directly demonstrated the enhanced free radical scavenging ability of the composite membrane. The introduction of DCP@ZnO particles significantly improved the antioxidant activity of the composite membrane. This is because its surface polyphenol groups have hydrogen and electron donation capabilities, and at the same time, they form a synergistic electron transfer pathway with the oxygen vacancies on the ZnO surface, thereby achieving efficient free radical scavenging.

[0066] The antioxidant capacity of the composite membrane mainly originates from the doped zinc oxide nanoparticles. When functional zinc oxide nanoparticles are dispersed in a chitosan matrix (Comparative Examples 2-5), their influence on the antioxidant activity of the composite membrane follows the same pattern as the antioxidant trend of the particles themselves.

[0067] With increasing DCP@ZnO content in the composite membrane, its reducing power gradually increases. The reducing power of the pure CS membrane is 0.125, while when the proportion of DCP@ZnO in the composite membrane increases to 2% (DCPZ-5), the reducing power increases to 0.198, indicating that the introduction of DCP@ZnO significantly enhances the electron donor capacity of the composite membrane. The strengthening effect of DCP@ZnO in this study is attributed to the chemical grafting structure of dialdehyde cellulose and proanthocyanidins. This structure effectively improves the thermal and chemical stability of proanthocyanidins, preventing their oxidation and deactivation during alkaline or heating processes; simultaneously, a synergistic electron transfer channel is formed between the polyphenol groups and oxygen vacancies on the ZnO surface, enhancing the electron migration efficiency and free radical reduction capacity of the material.

[0068] Example 5 The Oxford cup method was used to determine the antibacterial activity of the composite membrane: 100 μL of bacterial solution (10 7(CFU / mL) was transferred into a disposable culture dish containing solid culture medium and spread evenly with a spreader. An appropriate amount of Oxford cup was placed in the culture dish, and 200 uL of different composite membrane solutions was injected into each Oxford cup. All culture dishes were placed in a constant temperature incubator (37℃) for 24 h, and the diameter of their inhibition zone was measured.

[0069] The antibacterial activity of the composite membrane was further determined by plate counting: two bacteria (Staphylococcus aureus and Escherichia coli) were diluted to 10⁻⁶ with sterile water. 5 CFU / mL was prepared for use. An appropriate amount of composite membrane solution was mixed with bacterial culture. In the control group, the composite membrane solution was replaced with sterile water. The mixture was incubated in a constant temperature shaker (37℃) for 24 h. 100 μL of the mixed solution was then transferred to a solid culture medium and incubated in a constant temperature incubator (37℃) for 24 h. The number of colonies formed on the surface of the solid culture medium was observed.

[0070] according to Figure 5 The plate test results showed that the inhibitory effect of the composite membrane on bacterial growth gradually increased with the increase of DCP@ZnO particle content, and the number of colonies on the plate decreased significantly. When the DCP@ZnO content in the composite membrane reached 2% (DCPZ-5), no colonies appeared on the plate, indicating that the composite membrane has significant antibacterial activity. Combined with the results of the inhibition zone diameter, it can be seen that the addition of DCP@ZnO effectively improved the antibacterial performance of the composite membrane, and significantly increased the inhibition zone. The inhibition zone diameters of pure CS membranes against Staphylococcus aureus and Escherichia coli were 13.2 mm and 13.5 mm, respectively. With the increase of DCP@ZnO doping, the inhibition zone diameters of DCPZ-1 to DCPZ-5 membranes against Staphylococcus aureus were 14.7 mm, 15.5 mm, 16.5 mm, 17.8 mm and 18.2 mm, respectively, and the inhibition zone diameters against Escherichia coli were 14.0 mm, 14.2 mm, 14.5 mm, 15.2 mm and 16.5 mm, respectively.

[0071] The antibacterial properties of the composite membrane are mainly determined by the surface chemical composition and interfacial reactivity of the doped zinc oxide nanoparticles. Therefore, in this example, when these particles are dispersed in the chitosan matrix, their influence on the antibacterial ability of the composite membrane is consistent with the antibacterial activity trend of the particles themselves.

[0072] Example 6 The cytotoxicity of the composite membrane was determined using the MTT assay and L929 mouse fibroblasts (NCTC clone 929). Before use, cells in the cell flask were digested with trypsin to prepare a cell suspension. After trypan blue staining, 10 μL of the suspension was pipetteed into a hemocytometer. Cells were counted under an optical microscope and then diluted to 1000 cells / mL with DMEM high-glucose liquid medium containing a mixture of 10% fetal bovine serum, 100 U / mL penicillin, and 100 μg / mL streptomycin. 100 μL of the diluted cell suspension was added to each well of a 96-well plate and incubated at 37°C for 24 h in a 5% CO2 incubator. The original medium was discarded, and 100 μL of the chitosan composite membrane solution from Examples (1-7) and Control Examples (1-5) was added as drug-containing medium. The cells were then cultured for another 48 h, and finally, 10 μL of MTT was added, and the plates were incubated for 4 h. Remove the 96-well plate, discard the original culture medium, add 150 μL of DMSO to each well and shake until the purple color is uniform, indicating that the formazan is completely dissolved. Place the plate in a microplate reader, perform background calibration at 630 nm, and measure the absorbance at 570 nm. Set up three parallel wells for each sample, and take the average absorbance value as the absorbance value at this concentration. Calculate the cell viability using the following formula.

[0073] A1 represents the absorbance of the treatment group (chitosan composite membrane solution), and A0 represents the absorbance of the blank control group.

[0074] from Figure 6 As can be seen, the cytotoxicity of the composite membranes in each group was relatively small, and all maintained a high cell viability (>80%), indicating that the material has good biocompatibility. Specifically, Comparative Example 1 (pure CS membrane) had the highest cell viability, indicating that the chitosan matrix itself has no significant cytotoxicity. As the DCP@ZnO doping content increased from 0.4% (Example 1) to 2% (Example 5), cell activity gradually decreased (due to the increase in ion / ROS microdomains caused by local aggregation), but remained within a safe range. The cell activity of Examples 6 and 7 was slightly lower than that of Example 1, attributed to the increased ion / ROS microdomains caused by their larger particle size. This indicates that the polyphenol-cellulose grafted layer on the DCP@ZnO surface can effectively slow down the release of Zn. 2+ It also scavenges ROS, thereby significantly reducing cytotoxicity. The Control@ZnO prepared in Comparative Example 3, due to its exposed particles and Zn... 2+High dissolution rate and strong ROS generation resulted in the lowest cell viability. While the DAC@ZnO prepared in Comparative Example 4 improved dispersibility, it lacked antioxidant groups, limiting its cell protection effect. The polyphenol layer of PA@ZnO prepared in Comparative Example 2 could initially alleviate oxidative stress, but it was easily oxidized and inactivated, exhibiting poor long-term stability. The DAC+PA@ZnO prepared in Comparative Example 5 combined confinement and polyphenol protection, exhibiting lower toxicity, but not as high as the chemically grafted system. In summary, DCP@ZnO, through a synergistic mechanism of "grafting stabilization—ion slow release—ROS scavenging," endowed the composite membrane with optimal cell compatibility and lowest toxicity, maintaining good biosafety even at high doping levels.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing functional nano-zinc oxide, characterized in that: Includes the following steps: (1) Dissolve dialdehyde-modified cellulose in hydrochloric acid solution, mix with proanthocyanidin solution dissolved in DMSO, heat to react, dialyze and dry to obtain cellulose-polyphenol graft; (2) After mixing the aqueous solution of cellulose-polyphenol graft with the aqueous solution of zinc nitrate, the pH was adjusted, followed by hydrothermal reaction, centrifugation and washing of the precipitate, and drying to obtain functional zinc oxide nanoparticles.

2. The method for preparing functional nano-zinc oxide according to claim 1, characterized in that: The heating reaction is carried out at a temperature of 30-70℃ for a duration of 12-48 h.

3. The method for preparing functional nano-zinc oxide according to claim 1, characterized in that: The hydrothermal reaction is carried out at a temperature of 120-160℃ for 4-10 hours.

4. The method for preparing functional nano-zinc oxide according to claim 1, characterized in that: In step (1), the mass ratio of dialdehyde cellulose to proanthocyanidins is 1:(0.5-1.5).

5. The method for preparing functional nano-zinc oxide according to claim 1, characterized in that: The volume ratio of the cellulose-polyphenol graft aqueous solution to the zinc nitrate aqueous solution is 1:(0.5-2), the concentration of the cellulose-polyphenol graft aqueous solution is 0.7±0.01mg / mL, and the concentration of the zinc nitrate aqueous solution is 10 mM.

6. The method for preparing functional nano-zinc oxide according to claim 1, characterized in that: In step (2), the pH is adjusted to 9-11 using NaOH solution.

7. Functional nano zinc oxide prepared by the method of any one of claims 1-6.

8. The application of the functional nano zinc oxide according to claim 7 in the preparation of chitosan membranes, characterized in that: The process includes the following steps: adding functional nano zinc oxide to a chitosan solution in which glacial acetic acid is dissolved, and then drying the solution to obtain a chitosan membrane.

9. The application according to claim 8, characterized in that: The mass ratio of the functional nano zinc oxide to the chitosan solution is (0.4-2):100.

Images