A two-dimensional sheet-shaped porphyrin metal organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization, a preparation method thereof and application thereof

Abstract

The application discloses a two-dimensional sheet porphyrin metal organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization, a preparation method thereof and application thereof. The two-dimensional sheet porphyrin metal organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization is prepared from two-dimensional sheet Zn-TCPP and hydroxyethyl cellulose under the action of a crosslinking agent; the two-dimensional sheet Zn-TCPP is prepared by ultrasonic crushing after reaction of Zn(NO3)2.6H2O and racemic-tetra(4-hydroxyphenyl porphyrin) in N-N-diethylformamide. The two-dimensional sheet porphyrin metal organic framework with extremely strong stability is used to modify hydroxyethyl cellulose, the water solubility of the hydroxyethyl cellulose is effectively improved, and the antibacterial effect is significantly enhanced; the prepared packaging film has strong antibacterial property, high biological safety and good mechanical property, has the dual effects of shielding ultraviolet rays and high visible light transmittance, and can significantly prolong the shelf life of food.

Description

Technical Field

[0001] This invention relates to a two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization, its preparation method and its application, belonging to the field of food packaging technology. Background Technology

[0002] The development of high-value-added chemicals and materials using biomass raw materials to replace petrochemical raw materials is progressing towards targeted conversion, functionalization, intelligentization, environmental friendliness, standardization, and comprehensive utilization. Hydroxyethyl cellulose (HEC) is a type of cellulose derivative containing abundant hydroxyl groups in its molecules. Through chemical modification, it readily reacts with metal ions. Hydroxyethyl cellulose membranes are a novel biomaterial with excellent biocompatibility, biodegradability, and bioabsorbability. It can be gradually absorbed by the human body without causing harm and can be used in food, medical, and cosmetic fields. While hydroxyethyl cellulose can effectively protect the quality and nutritional components of food in food packaging, pure hydroxyethyl cellulose as a food packaging film material lacks antibacterial properties and has poor UV shielding capabilities. Photodynamic sterilization, as a safe and effective antibacterial method, is an emerging means of ensuring food safety.

[0003] Photodynamic sterilization combines light of a specific wavelength, oxygen, and a photosensitizer to generate reactive oxygen species (ROS), especially singlet oxygen, through energy transfer or electron transfer. 1 O2 can oxidize lipids, proteins, and nucleic acids within microorganisms, leading to their death. Traditional thermal and chemical methods used for microbial control in the food industry can adversely affect food quality and bacterial resistance. Photodynamic sterilization, as a novel and innovative sterilization technology, has attracted widespread attention due to its advantages such as good sterilization effect, environmental friendliness, and safety.

[0004] Traditional photosensitizers, porphyrins, are large planar heterocyclic compounds formed by four pyrrole rings interconnected by methylene bridges (=CH-). The central atom of the porphyrin can coordinate with metal ions to form metalloporphyrins. Porphyrins are characterized by strong biocompatibility, few side effects, and effective clearance by organisms. However, most porphyrins and their derivatives are unstable and prone to self-quenching in aqueous solutions, which limits their applications.

[0005] To address the issue of poor antibacterial properties and limited application of biodegradable hydroxyethyl cellulose in food packaging, the inventors proposed a food composite packaging film with excellent photodynamic antibacterial properties, UV shielding, and biosafety. Summary of the Invention

[0006] This invention provides a two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization, its preparation method, and its application. The invention uses Zn(NO3)2·6H2O, racemic tetra(4-hydroxyphenylporphyrin), and N,N-diethylformamide (DEF) as raw materials to prepare a zinc-based porphyrin metal-organic framework. The two-dimensional sheet-like metal-porphyrin framework is synthesized by ultrasonication, which greatly improves the photodynamic antibacterial properties. Then, the two-dimensional sheet-like porphyrin metal-organic framework is added to hydroxyethyl cellulose to form a film solution, which is then prepared into a composite packaging film using a casting method. This addresses the problem of limited application of biomass hydroxyethyl cellulose in food packaging, enhances antibacterial effects and UV shielding, and extends the shelf life of packaged foods.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization is prepared by reacting two-dimensional sheet-like Zn-TCPP (two-dimensional layered porphyrin metal-organic framework) and hydroxyethyl cellulose under the action of a crosslinking agent;

[0009] Two-dimensional sheet-like Zn-TCPP is prepared by reacting Zn(NO3)2·6H2O and racemic tetra(4-hydroxyphenylporphyrin) in N-N-diethylformamide (DEF) followed by ultrasonic disruption.

[0010] This application describes a composite membrane prepared from a two-dimensional sheet-like porphyrin metal-organic framework Zn-TCPP and HEC, which can effectively solve the problem of poor antibacterial performance of HEC, has high biosafety, and has the dual effect of shielding ultraviolet rays and high transmittance of visible light, which can significantly extend the shelf life of food.

[0011] In porphyrin MOFs, porphyrins or metalloporphyrins act as organic ligands, binding to metal ions or ion clusters via coordination bonds to become building blocks in the MOF structure. The porphyrin units are periodically arranged within the MOF structure, maintaining a monodisperse state and effectively preventing self-aggregation and self-quenching of porphyrins, thus improving their physicochemical properties. Simultaneously, the high porphyrin loading and porous structure of MOFs facilitate the diffusion of singlet oxygen, enhancing the material's photodynamic properties.

[0012] Compared to two-dimensional layered Zn-TCPP, two-dimensional sheet-like Zn-TCPP has a larger effective specific surface area, more sufficient contact with oxygen, stronger singlet oxygen generation, and stronger photodynamic sterilization performance. When incorporated into hydroxyethyl cellulose, it enhances the antibacterial properties of the hydroxyethyl cellulose film, reduces bacterial adhesion and accumulation, and allows the film to better exert its antibacterial effect. Furthermore, it does not generate high temperatures or harmful substances during the photodynamic sterilization process.

[0013] To improve reaction efficiency and product purity, the preparation method of two-dimensional sheet-like Zn-TCPP includes the following steps:

[0014] 1) Zn-TCPP was synthesized by a one-pot solvothermal method: Zn(NO3)2·6H2O and meso-tetra(4-hydroxyphenylporphyrin) were dissolved in a mixed solvent of NN-diethylformamide (DEF) and H2O, placed in a glass bottle with a sealed polytetrafluoroethylene cap, and reacted at 80-85℃ for 24-48 h. The mixture was washed with NN-diethylformamide (DEF) and centrifuged. The resulting precipitate was dried to obtain two-dimensional layered purple crystals of Zn-TCPP.

[0015] 2) Two-dimensional layered Zn-TCPP was ultrasonically broken up in water and freeze-dried to obtain two-dimensional sheet-like Zn-TCPP.

[0016] The two-dimensional sheet-like porphyrin metal-organic framework prepared above generates strong reactive oxygen species and can be used to prepare hydroxyethyl cellulose composite membranes.

[0017] To further ensure the antibacterial effect, in step 1), the molar ratio of Zn(NO3)2·6H2O to meso-tetra(4-hydroxyphenylporphyrin) is 1:(0.1-0.3); in the mixed solvent, the volume ratio of NN-diethylformamide (DEF) to H2O is 3:(0.8-1.2); and drying is carried out at 50-60℃ for 5-12 hours.

[0018] To improve the photodynamic antibacterial properties, step 2) is as follows: two-dimensional layered Zn-TCPP is dispersed in ultrapure water by ice bath ultrasonication and then freeze-dried to obtain two-dimensional sheet-like porphyrin metal-organic framework Zn-TCPP; the ice bath ultrasonication time is 0.5-1h and the ultrasonic power is 300-600w; more preferably, the ice bath ultrasonication time is 1h and the ultrasonic power is 600w.

[0019] By comparing the two-dimensional layered Zn-TCPP before dispersion with the two-dimensional sheet-like Zn-TCPP obtained by dispersion with different ultrasonic powers and times, it was found that the two-dimensional sheet-like Zn-TCPP of the present invention has good stability in water. The two-dimensional sheet-like Zn-TCPP obtained by ultrasonication at 600W for 60 minutes has the most stable optical properties and a stronger ability to generate singlet oxygen under white LED light irradiation.

[0020] This application utilizes the indicator 9,10-anthratridiyl-bis(methylene)-dimalonic acid (ABDA) to detect the strength of singlet oxygen generated by two-dimensional layered Zn-TCPP.

[0021] The preparation method of the above-mentioned two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization is as follows: two-dimensional sheet-like Zn-TCPP (600W, 60min) is dispersed in deionized water, hydroxyethyl cellulose is added and stirred continuously. After the solution changes from turbid to clear, crosslinking agent citric acid monohydrate and plasticizer glycerol are added and stirred. The film is cast by casting and dried in a vacuum drying oven to obtain the composite film.

[0022] The aforementioned two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite material with photodynamic bactericidal properties is prepared by using two-dimensional sheet-like porphyrin metal-organic frameworks Zn-TCPP and HEC as the main raw materials, citric acid monohydrate as the crosslinking agent, and glycerol as the plasticizer to prepare the film-forming liquid, and then preparing the film by casting method. It has excellent UV shielding, antibacterial activity and biocompatibility.

[0023] The dosage of the above-mentioned hydroxyethyl cellulose is 3-5g / 100ml of water, that is, 3-5g of hydroxyethyl cellulose is added to every 100ml of water.

[0024] To improve the antibacterial and mechanical properties of the resulting membrane, the mass of two-dimensional sheet-like Zn-TCPP is 0.3% to 3% of the mass of hydroxyethyl cellulose (HEC); the mass of citric acid monohydrate is 20% to 25% of the mass of hydroxyethyl cellulose (HEC); and the mass of glycerol is 10% to 15% of the mass of hydroxyethyl cellulose (HEC).

[0025] To ensure the antibacterial properties of the resulting composite film, as one specific implementation method, two-dimensional sheet-like Zn-TCPP (600W, 60min) was ultrasonically dispersed in ultrapure water, hydroxyethyl cellulose was added and stirred at 400-600 rpm for 1-3 hours, citric acid monohydrate and glycerol were added and stirred at 400-600 rpm for 2-4 hours, the film was cast using a casting method, and dried in a vacuum drying oven at 40-60℃ for 5-12 hours to obtain a two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic bactericidal properties.

[0026] The aforementioned two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization is used for food packaging and food preservation, and can also be used directly to shield ultraviolet rays and / or for antibacterial purposes.

[0027] The above-mentioned hydroxyethyl cellulose-based porphyrin metal-organic framework composite membrane does not require a complex reaction process, and its preparation method is very simple.

[0028] The inventors discovered that two-dimensional sheet-like porphyrin metal-organic frameworks (Zn-TCPP) obtained by ultrasonically breaking down two-dimensional layered porphyrin metal-organic frameworks (Zn-TCPP) have stronger reactive oxygen species (ROS) generation capabilities, a larger effective specific surface area, more sufficient contact with oxygen, and stronger singlet oxygen generation. This results in stronger photodynamic bactericidal performance, enhancing the antibacterial properties of hydroxyethyl cellulose films. This allows the films to better exert their antibacterial effects, and the photodynamic sterilization process does not generate high temperatures or harmful substances, meeting the requirements of green chemistry development. Furthermore, the ability of two-dimensional sheet-like Zn-TCPP to generate reactive oxygen species (ROS) under light irradiation, such as singlet oxygen (…), is utilized. 1 O2 or hydroxyl radicals (·OH) can oxidize lipids, proteins, and nucleic acids within microorganisms, leading to microbial death. The prepared composite membrane is simple to synthesize and possesses excellent photodynamic antibacterial activity, UV shielding performance, and biocompatibility. With the increase of the content of two-dimensional sheet-like Zn-TCPP, the antibacterial performance and UV shielding ability of the composite membrane under light irradiation are enhanced.

[0029] Unless otherwise specified, all processes in this application were performed at room temperature, which includes the range of 20–40°C. For drying conditions not specifically specified, drying was carried out to constant weight.

[0030] Any techniques not mentioned in this invention are based on existing technologies.

[0031] The present invention achieves the following beneficial effects:

[0032] 1) The two-dimensional sheet-like Zn-TCPP of the present invention has a stronger ability to generate reactive oxygen species than the two-dimensional layered Zn-TCPP, and its photodynamic antibacterial activity is significantly improved. The raw material porphyrin has excellent biocompatibility and photophysical properties.

[0033] 2) The two-dimensional sheet-like Zn-TCPP of the present invention exhibits good stability in water;

[0034] 2) The hydroxyethyl cellulose composite membrane prepared by the present invention based on two-dimensional sheet-like Zn-TCPP is simple to prepare, uses bio-based HEC as the substrate, has a wide range of raw material sources, is low in cost, has high biocompatibility, and the prepared composite membrane has high photodynamic antibacterial activity.

[0035] 3) This invention alters the water solubility of hydroxyethyl cellulose, solves the application problems of hydroxyethyl cellulose in food packaging, and expands its application directions;

[0036] 4) The food packaging film prepared by this invention has high transparency, not only with extremely high transmittance in the visible light region, but also with a significant shielding effect against ultraviolet rays, which is beneficial for the preservation of the food inside.

[0037] 5) The food packaging film prepared by this invention has excellent mechanical properties and can well meet the needs of food packaging;

[0038] 6) The photodynamic sterilization technology used is a new and innovative sterilization technology with good sterilization effect, environmental protection and safety. Attached Figure Description

[0039] Figure 1 The images show the SEM (ab) of two-dimensional layered Zn-TCPP, the SEM (c) of two-dimensional sheet-like Zn-TCPP, and the FT-IR spectra (d) of two-dimensional layered Zn-TCPP and two-dimensional sheet-like Zn-TCPP obtained in this invention.

[0040] Figure 2 The UV absorption spectra of ABDA solutions of two-dimensional layered Zn-TCPP and two-dimensional sheet-like Zn-TCPP after 30 min of illumination.

[0041] Figure 3 The SEM (a), FT-IR (b), XRD (c), and UV spectra (d) of the thin films obtained in each example are shown.

[0042] Figure 4 Examples of tensile stress-strain spectra of thin films;

[0043] Figure 5 The obtained antibacterial images of the films;

[0044] Figure 6 The images shown are of strawberries preserved with film after seven days. Detailed Implementation

[0045] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0046] In all examples, the temperature operation was not specifically mentioned and was performed at room temperature, which was 20–30°C.

[0047] Example 1

[0048] 0.1 mmol Zn(NO3)2·6H2O and 0.02 mmol meso-tetra(4-hydroxyphenylporphyrin) were dissolved in a mixed solvent of N,N-diethylformamide (DEF) / H2O (V / V = 3:1, 4 ml), and placed in a 20 ml glass bottle with a sealed polytetrafluoroethylene cap. The mixture was reacted at 85 °C for 48 h, washed with DEF and centrifuged. The precipitate obtained by centrifugation was dried overnight (12 h) in a vacuum drying oven at 60 °C to obtain two-dimensional layered Zn-TCPP, which is a two-dimensional layered purple crystal.

[0049] Two-dimensional layered Zn-TCPP was ultrasonically dispersed in ultrapure water in an ice bath, followed by freeze-drying to obtain two-dimensional sheet-like Zn-TCPP. Two-dimensional sheet-like samples were obtained using different ultrasonic powers and durations: Zn-TCPP (300 W, 30 min), Zn-TCPP (300 W, 60 min), Zn-TCPP (600 W, 30 min), and Zn-TCPP (600 W, 60 min).

[0050] Figure 1 In the image, (a) is a SEM image of two-dimensional layered Zn-TCPP, (b) is an energy-dispersive X-ray spectroscopy (EDS) elemental mapping (Zn, C, N, O), and (c) is a SEM image of two-dimensional sheet-like Zn-TCPP. The scanning electron microscope (SEM) images of Zn-TCPP clearly show that Zn-TCPP has a large lateral dimension and an ordered stacked layered structure. Figure 1 In (a)), these layers are tightly packed on a very clean surface. Energy dispersive spectroscopy (EDS) elemental mapping shows that Zn, C, N, and O elements are uniformly distributed in 2DZn-TCPP. Figure 1 In (b), two-dimensional layered Zn-TCPP was broken up using ultrasonic treatment with different powers and times. Figure 1 The SEM image in (c) clearly shows that the layered structure of Zn-TCPP is dispersed into sheets by ultrasound and its size is reduced. The two-dimensional layered Zn-TCPP is dispersed into sheets more uniformly by ultrasound at a power of 600W for 60 minutes.

[0051] Infrared spectroscopy was performed on Zn-TCPP before and after ultrasonic dispersion: The sample was mixed with dry KBr powder and analyzed using an FTIR spectrometer in the range of 400-4000 cm⁻¹, with 32 scans and a resolution of 4 cm⁻¹. The analysis results are as follows:

[0052] Figure 1 Image (d) shows the FT-IR spectra of two-dimensional layered Zn-TCPP and two-dimensional sheet-like Zn-TCPP formed by ultrasound at different times and powers. Figure 1 As shown in (d), the FT-IR spectrum of TCPP is at 1694 cm⁻¹. -1 There is a distinct absorption peak at 3319 cm⁻¹, which is attributed to the stretching vibration of the C=O bond on the carboxyl group forming the dimer. -1 The absorption peaks at this point belong to the stretching vibrations of the NH bond. These peaks disappear in Zn-TCPP, indicating that TCPP and Zn... 2+ A coordination reaction occurred. Several characteristic infrared absorption peaks of Zn-TCPP are observed at 3425 cm⁻¹. -1 (-OH), 1625cm -1 (-COO -) and 1403cm -1 (-C=N-). Two-dimensional layered Zn-TCPP was broken up by ultrasonic treatment with different powers and times. The infrared spectrum showed that the structure of the two-dimensional sheet-like Zn-TCPP obtained by ultrasonic treatment was basically unchanged, indicating that the two-dimensional layered Zn-TCPP and the two-dimensional sheet-like Zn-TCPP have good stability in water. Figure 1 In the figure, Zn-TCPP(300W, 30min), Zn-TCPP(300W, 60min), Zn-TCPP(600W, 30min), and Zn-TCPP(600W, 60min) are two-dimensional sheet-like Zn-TCPPs obtained by ultrasonic dispersion under different ultrasonic powers and ultrasonic times, respectively. Figure 1 The Zn-TCPP at the bottom is a two-dimensional layered Zn-TCPP before ultrasonic dispersion.

[0053] Ultraviolet spectroscopy test: Two-dimensional layered Zn-TCPP and two-dimensional sheet-like t-Zn-TCPP dispersions were irradiated with a white LED lamp (100W) for different times, and their absorption spectra were scanned. It can be seen that the absorbance of the two-dimensional sheet-like Zn-TCPP (600W, 60min) decreased to 63.88% of the initial absorbance, which is better than the optical stability of the two-dimensional layered Zn-TCPP. Moreover, the two-dimensional sheet-like Zn-TCPP obtained by sonication at 600W for 60min has the most stable optical properties. After irradiation for 40min, the absorbance remained basically unchanged. Zn-TCPP (600W, 60min) was selected for subsequent photodynamic experiments.

[0054] Singlet oxygen assay: Weigh 10.3 mg of ABDA powder (9,10-anthracitediylbis(methylene)-dimalonic acid), dissolve in DMSO (dimethyl sulfoxide) and bring the volume to 5 mL to prepare a solution with a concentration of 5.0 × 10⁻⁶. -3 The ABDA stock solution was prepared at a concentration of mol / L and stored protected from light. Using ultrapure water as the solvent, stock solutions of Zn-TCPP (two-dimensional layered Zn-TCPP) and t-Zn-TCPP (two-dimensional sheet-like Zn-TCPP) with a concentration of 1 mg / mL were prepared. 15 μL of ABDA stock solution was mixed with 30 μL of Zn-TCPP and t-Zn-TCPP stock solutions, respectively, and ultrapure water was added to prepare a final solution volume of 1.5 mL. The final concentration of porphyrin MOF in this mixed solution was 0.02 mg / mL. 15 μL of ABDA stock solution was mixed with ultrapure water to prepare a final solution volume of 1.5 mL, serving as the blank control. The final concentration of ABDA in all groups was 5.0 × 10⁻⁶. -5 mol / L. Figure 2In the middle (a), the relative absorbance at 423 nm of two-dimensional layered Zn-TCPP and two-dimensional sheet-like Zn-TCPP formed by ultrasound for different times and powers is shown. Figure 2 Image (b) shows the UV absorption spectra of ABDA solutions containing two-dimensional layered Zn-TCPP and two-dimensional sheet-like Zn-TCPP formed by ultrasound for different times and powers after 30 min of illumination. Figure 2 The UV absorption spectrum shows the effect of Zn-TCPP (600W, 60min) on ABDA solution after 30min of illumination. 1 The intensity of the characteristic absorption peak corresponding to the O2-specific indicator 9,10-anthracene dimethylbis(methylene)-dimalonic acid (ABDA) is significantly reduced. ABDA is an anthracene derivative that can be oxidized by singlet oxygen to form peroxides, leading to a decrease in ABDA absorbance. Based on the attenuation trend of ABDA, Zn-TCPP (600W, 60min) has a stronger ability to generate singlet oxygen under white LED light irradiation.

[0055] Example 2

[0056] Preparation of hydroxyethyl cellulose composite membrane:

[0057] Add 4g of hydroxyethyl cellulose to 100ml of ultrapure water and stir at 500rpm for 1h. Once the solution is clear, add 1g of citric acid monohydrate crosslinking agent and 0.6g of plasticizer glycerol, and stir for 2h at a stirring speed of 600rpm. Pour 15mL of the membrane solution onto a 100mm×100mm square plastic petri dish and dry in a vacuum drying oven at 50℃ overnight (12h) to obtain a pure HEC membrane.

[0058] Example 3

[0059] 12 mg of two-dimensional Zn-TCPP flakes (600 W, 60 min) was ultrasonically dispersed in 100 ml of ultrapure water. 4 g of hydroxyethyl cellulose was added and stirred at 500 rpm for 1 h. The solution changed from turbid to clear. Then, 1 g of citric acid monohydrate crosslinking agent and 0.6 g of plasticizer glycerol were added and stirred for 2 h at a stirring speed of 600 rpm. 15 ml of the membrane solution was poured onto a 100 mm × 100 mm square plastic petri dish and dried overnight (12 h) in a vacuum drying oven at 50 °C.

[0060] Example 4

[0061] 20 mg of two-dimensional Zn-TCPP flakes (600 W, 60 min) was ultrasonically dispersed in 100 ml of ultrapure water. 4 g of hydroxyethyl cellulose was added and stirred at 500 rpm for 1 h. The solution changed from turbid to clear. Then, 1 g of citric acid monohydrate crosslinking agent and 0.6 g of plasticizer glycerol were added and stirred for 2 h at a stirring speed of 600 rpm. 15 ml of the membrane solution was poured onto a 100 mm × 100 mm square plastic petri dish and dried overnight (12 h) in a vacuum drying oven at 50 °C.

[0062] Example 5

[0063] 40 mg of two-dimensional Zn-TCPP flakes (600 W, 60 min) was ultrasonically dispersed in 100 ml of ultrapure water. 4 g of hydroxyethyl cellulose was added and stirred at 500 rpm for 1 h. The solution changed from turbid to clear. Then, 1 g of citric acid monohydrate crosslinking agent and 0.6 g of plasticizer glycerol were added and stirred for 2 h at a stirring speed of 600 rpm. 15 ml of the membrane solution was poured onto a 100 mm × 100 mm square plastic petri dish and dried overnight (12 h) in a vacuum drying oven at 50 °C.

[0064] Example 6

[0065] 120 mg of two-dimensional Zn-TCPP flakes (600 W, 60 min) was ultrasonically dispersed in 100 ml of ultrapure water. 4 g of hydroxyethyl cellulose was added and stirred at 500 rpm for 1 h. The solution changed from turbid to clear. Then, 1 g of citric acid monohydrate crosslinking agent and 0.6 g of plasticizer glycerol were added and stirred for 2 h at a stirring speed of 600 rpm. 15 ml of the membrane solution was poured onto a 100 mm × 100 mm square plastic petri dish and dried overnight (12 h) in a vacuum drying oven at 50 °C.

[0066] The membranes obtained in the above embodiments were subjected to performance tests.

[0067] Morphology testing of the thin films: The surface morphology of different composite films was observed by SEM. As shown in Figure 3(a), the HEC film surface is relatively smooth, without obvious cracks or wrinkles. After adding Zn-TCPP (600W, 60min), the film surface exhibits typical lamellar particles. With the increase of Zn-TCPP (600W, 60min) doping content, its distribution density on the film surface gradually increases, and the film surface becomes rougher, indicating that it has been successfully incorporated into the HEC matrix as a filler and is tightly bonded to the film components.

[0068] Infrared testing of the thin film: The thin film sample was measured using an attenuated total internal reflection (ATR) attachment, with 16 scans and a wavelength range of 4000-400 cm⁻¹. -1 The resolution is 4cm. -1 The analysis is as follows: Figure 3As shown in (b), the interaction between the HEC groups and Zn-TCPP (600 W, 60 min) resulted in subtle changes in the functional group peaks and intensities of the film. 3381 cm⁻¹ -1 The characteristic peak is -OH, at 2922 cm⁻¹. -1 The characteristic peak at 1720 cm⁻¹ is CH₄. -1 The characteristic peak at this location is C=O, 1033 cm⁻¹ -1 The characteristic peak at the position is CO. As the content of Zn-TCPP (600W, 60min) increases, the peak of the HEC / Zn-TCPP (600W, 60min) film shifts to a lower wavenumber, indicating that hydrogen bonds are formed between the carboxyl groups in Zn-TCPP (600W, 60min) and the oxygen-containing groups (such as hydroxyl and carboxyl groups) in the HEC matrix.

[0069] The XRD diffraction pattern of the thin film is shown in the figure ( Figure 3 The peak at 21.25° (c) indicates that HEC (hydroxyethyl cellulose) is an amorphous, non-crystalline mixture. Furthermore, a major diffraction peak appears at 17.61°, which gradually increases with increasing Zn-TCPP (600W, 60min), demonstrating that the two-dimensional porphyrin-sheet Zn-TCPP (600W, 60min) was successfully incorporated into the hydroxyethyl cellulose membrane. Moreover, its structure remains intact after embedding into the biological matrix, indicating that Zn-TCPP (600W, 60min) has good compatibility with hydroxyethyl cellulose.

[0070] Transparency testing of the film: The UV-Vis spectrophotometry (UV / vis) method was used to record the UV transmittance of the film samples in the range of 200–800 nm. For food packaging, high transparency facilitates observation of the contents; common commercially available food preservation films all have high UV transmittance. The porphyrin metal-organic framework / hydroxyethyl cellulose packaging film prepared in this application also exhibits high transparency. With increasing Zn-TCPP (600W, 60min) doping content, the film's appearance gradually deepens, changing from colorless to reddish-brown. UV blocking ability and transparency are crucial in food packaging. UV blocking ability helps protect food from UV damage, while a certain degree of transparency allows us to identify the specific condition of the food. After adding two-dimensional sheet-like Zn-TCPP (600W, 60min), the UV transmittance of the film at 600 nm, 560 nm, and 430 nm significantly decreased. Figure 3As shown in (d), with the increase of Zn-TCPP (600W, 60min) content, the ultraviolet transmittance at 405nm-450nm decreases to 0, and the wavenumber range of ultraviolet shielding expands. This indicates that the composite film has a strong ability to shield ultraviolet rays, which can reduce the loss and deterioration of food nutrients caused by ultraviolet radiation during transportation or storage. Overall, the transmittance of the visible light region of the film can also have a certain ultraviolet shielding effect, which is beneficial to the preservation of the food inside.

[0071] Mechanical property testing of the film: Compared with pure HEC film, the addition of Zn-TCPP (600W, 60min) increased the degree of internal hydrogen bond crosslinking and significantly increased the elongation at break of the composite film, indicating that the composite material improved the film's ductility. Figure 4 When the Zn-TCPP (600W, 60min) doping concentration is 0.3%, the tensile strength of the film decreases, and the two-dimensional sheet-like metal-organic framework partially agglomerates, leading to a decline in the mechanical properties of the material. When the added porphyrin MOF reaches a certain level, the mechanical properties of the material no longer improve. Due to weak interfacial adhesion, the tensile strength of the composite material decreases.

[0072] Antibacterial performance test of the film: The antibacterial activity of the film against Staphylococcus aureus and Escherichia coli was determined by the plate count method in GB / T 37206-2018 standard. Staphylococcus aureus and Escherichia coli suspensions were pre-cultured and then diluted to 10⁻⁶. 7 CFU / mL. During the test, equal masses (5 mg) of different films were added to EP tubes, and a certain amount of bacterial suspension (20 μL) was dropped onto different films. Then, the films were incubated with LED white light for 0 min, 5 min, 10 min, 15 min, 20 min, and 30 min at 37°C for 1 h. After incubation, the films were diluted with phosphate buffered saline (PBS; pH = 7.4), and 100 μL of the diluted bacterial suspension was then spread on LB plates and incubated at 37°C for 24 h. The antibacterial properties of the films were evaluated by colony counting.

[0073] Figure 5 Escherichia coli (a) and Staphylococcus aureus (b) on the membrane were examined under LED white light (light power density of 135 mW / cm²). -2 Photographs of bacterial colonies on plate after 0 min, 5 min, 10 min, 15 min, 20 min, and 30 min of illumination. Figure 5As shown, the HEC film exhibited no significant antibacterial effect under dark conditions. The film with added Zn-TCPP (600W, 60min) inhibited bacterial growth, and the bacterial survival rate decreased with increasing light intensity. Furthermore, within the same light exposure time, the inhibitory effect of the HEC / Zn-TCPP (600W, 60min) composite film increased with increasing Zn-TCPP (600W, 60min) content. In Example 6, the HEC / Zn-TCPP (600W, 60min) composite film showed inhibition rates of 99.9% and 99.7% against Staphylococcus aureus and Escherichia coli, respectively, after 15min of light exposure.

[0074] Fresh strawberries were selected for a packaging and preservation experiment. Prepared film was cut into 100mm x 100mm pieces and used to wrap the fresh strawberries. They were stored at 25℃ and 50% RH for 7 days. The strawberries were photographed and recorded daily. On the 7th day, samples were taken from the surface of the strawberries to detect the number of bacterial colonies. Figure 6 As shown, strawberries wrapped in pure HEC at room temperature exhibited the highest degree of spoilage. This is due to the airtight nature of HEC, which prevents strawberries from breathing and exchanging gases with the outside environment. The moisture accumulated inside the plastic wrap makes it easier for bacteria and mold to grow. In contrast, the control group exposed to air showed only 80% signs of mold and blackening. With increasing Zn-TCPP (600W, 60min) content, the degree of spoilage decreased. The films from Examples 5 and 6 showed excellent results, with no mold or rot observed after 7 days. In summary, the two-dimensional sheet-like porphyrin metal-organic framework-based hydroxyethyl cellulose composite antibacterial film prepared in this study possesses excellent UV shielding, antibacterial activity, and biocompatibility, effectively extending the shelf life of food.

Claims

1. A two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization, characterized in that: The two-dimensional sheet Zn-TCPP is prepared by reacting Zn(NO3)2.6H2O and meso-tetra(4-hydroxyphenyl porphyrin) in N-N-dimethylformamide, and then ultrasonic crushing. The two-dimensional sheet Zn-TCPP is prepared by reacting Zn(NO3)2.6H2O and meso-tetra(4-hydroxyphenyl porphyrin) in N-N-dimethylformamide, and then ultrasonic crushing. The crosslinking agent is monohydrate citric acid. The mass amount of the two-dimensional sheet Zn-TCPP is 1% to 3% of the mass of the hydroxyethyl cellulose.

2. The two-dimensional sheet-shaped porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to claim 1, characterized in that: The method for preparing the two-dimensional sheet Zn-TCPP comprises the following steps: 1) Zn-TCPP is synthesized by one-pot solvothermal method: Zn(NO3)2.6H2O and meso-tetra(4-hydroxyphenyl porphyrin) are dissolved in a mixed solvent of N-N-dimethylformamide and H2O, and are reacted at 80-85°C for 24-48 hours, and then washed with N-N-dimethylformamide and centrifuged, and the obtained precipitate is dried to obtain two-dimensional layered Zn-TCPP; 2) The two-dimensional layered Zn-TCPP is ultrasonic crushed in water, and freeze-dried to obtain the two-dimensional sheet Zn-TCPP.

3. The two-dimensional sheet-shaped porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to claim 2, characterized in that: In step 1), the molar ratio of Zn(NO3)2.6H2O to meso-tetra(4-hydroxyphenyl porphyrin) is 1:(0.1-0.3), the volume ratio of N-N-dimethylformamide to H2O in the mixed solvent is 3:(0.8-1.2), and the drying is performed at 50-60°C for 5-12 hours.

4. The two-dimensional sheet-shaped porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to claim 2 or 3, characterized in that: In step 2), the two-dimensional layered Zn-TCPP is ice-bath ultrasonic dispersed in ultrapure water, and freeze-dried to obtain the two-dimensional sheet Zn-TCPP; wherein the ice-bath ultrasonic dispersion time is 0.5-1 hour, and the power is 300-600w.

5. A method for preparing the two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to any one of claims 1-4, characterized in that: The two-dimensional sheet Zn-TCPP is ultrasonic dispersed in water, hydroxyethyl cellulose is added and continuously stirred, after the solution is stirred from turbidity to clarity, monohydrate citric acid and plasticizer glycerol are added and stirred, and the film is laid by casting method, dried to obtain a composite film.

6. The production method according to claim 5, characterized by: The amount of hydroxyethyl cellulose is 3-5g / 100ml water.

7. The production method according to claim 5 or 6, characterized by: The mass amount of monohydrate citric acid is 20-25% of the mass of the hydroxyethyl cellulose; and the mass amount of glycerol is 10-15% of the mass of the hydroxyethyl cellulose.

8. The production method according to claim 5 or 6, characterized by: The two-dimensional sheet Zn-TCPP is ultrasonic dispersed in ultrapure water, hydroxyethyl cellulose is added and stirred at 400-600rpm for 1-3 hours, then monohydrate citric acid and glycerol are added and stirred at 400-600rpm for 2-4 hours, the film is laid by casting method, and dried in a vacuum drying oven at a temperature of 40-60°C for 5-12 hours to obtain a two-dimensional sheet porphyrin metal organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization.

9. Use of the two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to any one of claims 1-4, characterized in that: Used for food packaging and food preservation.

10. Use of the two-dimensional sheet-like porphyrin metal-organic framework / hydroxyethyl cellulose-based composite packaging film with photodynamic sterilization according to any one of claims 1-4, characterized in that: Used for shielding ultraviolet rays, and / or for antibacterial purposes.

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