A MXene / quaternized chitosan-based photothermal antibacterial film and a preparation method and application thereof

Abstract

The application discloses a kind of photothermal antibacterial film based on MXene / quaternized chitosan and its preparation method and application.The photothermal antibacterial film includes: quaternized chitosan matrix, cinnamaldehyde grafted on the molecular chain of chitosan and MXene embedded in quaternized chitosan matrix.The photothermal antibacterial film has antibacterial ability, excellent photothermal conversion ability and photothermal stability.Under the irradiation of 808 nm wavelength NIR light, the temperature of the photothermal antibacterial film is about 70 DEG C, and the inhibition rate of E. coli And S. aureus is close to 100%.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, and more particularly to a photothermal antibacterial film based on MXene / quaternized chitosan, its preparation method, and its application. Background Technology

[0002] Food products are susceptible to microbial contamination, oxidative deterioration, and moisture loss during storage, transportation, and sales, leading to quality degradation and shortened shelf life. Chitosan, a natural biodegradable polysaccharide, possesses excellent film-forming properties, biocompatibility, and intrinsic antibacterial activity, making it a highly promising food packaging substrate. However, pure chitosan films suffer from inherent limitations such as limited mechanical strength, insufficient barrier properties, and single function, restricting their application in demanding preservation scenarios. Therefore, current technologies often employ chemical modification of chitosan (such as quaternization modification) to enhance its application performance.

[0003] Chinese patent CN119139930A discloses a method for preparing a quaternized chitosan-based composite membrane material. The method involves dissolving quaternized chitosan and a crosslinking agent in an organic solvent to obtain a mixed solution; pouring the mixed solution onto the surface of a substrate material and drying it to obtain a chitosan membrane; then pouring a suspension of a two-dimensional layered material (including MXene) onto the surface of the chitosan membrane and drying it to obtain the quaternized chitosan-based composite membrane material. Although this patented solution uses both quaternized chitosan and MXene materials, its technical focus is on solving the technical problem of large-scale fabrication of nanochannels in the field of permeable energy power generation due to their small size, difficult-to-control structural parameters, and complex preparation process. It does not address antibacterial and food packaging applications. Existing research on antibacterial properties of quaternized chitosan composite membranes is mostly limited to medical applications where the material has short-term contact with the human body.

[0004] In food packaging applications, quaternized chitosan's mechanical and barrier properties are insufficient to meet practical requirements. Its lack of toughness and susceptibility to tearing make it unsuitable for the bending and folding processes required in food packaging. Furthermore, its barrier properties have significant limitations. While MXene possesses some oxygen barrier capacity, structural defects easily form within the composite system, hindering its ability to effectively extend food shelf life. Moreover, existing photothermal treatment methods are prone to uneven heating, leading to localized overheating and consequently, nutrient loss or even spoilage, thus limiting its practical application value.

[0005] Therefore, in response to the aforementioned technological shortcomings in the food packaging field, there is an urgent need for a photothermal antibacterial film based on MXene / quaternized chitosan to solve problems such as substandard mechanical and barrier properties, poor photothermal stability, low cytotoxicity, and easy food spoilage caused by existing materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a photothermal antibacterial film based on MXene / quaternized chitosan.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned photothermal antibacterial film. This method involves quaternizing chitosan to introduce quaternary ammonium salt groups for long-lasting antibacterial action; then, cinnamaldehyde is grafted onto the amino groups on the quaternized chitosan molecular chain via a Schiff base reaction; finally, the photothermal material MXene is composited with the above-mentioned crosslinked network, utilizing its two-dimensional nano-effect to enhance barrier properties and endow the photothermal antibacterial film with excellent photothermal conversion capabilities.

[0008] Another object of the present invention is to provide the application of the above-mentioned photothermal antibacterial film in food packaging substrates.

[0009] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0010] A photothermal antibacterial film based on MXene / quaternized chitosan, the photothermal antibacterial film comprising: a quaternized chitosan matrix, cinnamaldehyde grafted onto the chitosan molecular chain, and MXene embedded in the quaternized chitosan matrix.

[0011] In the above technical solution, the thickness of the photothermal antibacterial film is 43.5~51.7μm.

[0012] In the above technical solution, the MXene nanoparticles are Ti3C2T. x T x These are represented as surface functional groups, including -OH, -O, and -F.

[0013] A method for preparing a photothermal antibacterial film includes the following steps:

[0014] Step 1: Place the purified chitosan in isopropanol, slowly heat to 70-80℃, and then add 2,3-epoxypropyltrimethylammonium chloride (GTMAC) solution dropwise. After the addition is complete, react at 70-80℃ for 8-10 h. After the reaction is complete, add acetone to precipitate a solid precipitate, filter, wash, and dry to obtain quaternized chitosan. The ratio of purified chitosan monomer to 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is (1-2):(3-6). In step 1, the method for obtaining purified chitosan includes: dissolving chitosan in an aqueous acetic acid solution, adding an aqueous sodium hydroxide solution until precipitation is complete, allowing it to stand at room temperature for 10-15 h, filtering, washing, and drying to obtain purified chitosan, wherein the ratio of the mass fraction of chitosan to the volume fraction of the aqueous acetic acid solution is (1-2):(100-200), where the mass fraction is in g and the volume fraction is in mL.

[0015] In the above technical solution, the acetic acid content in the acetic acid aqueous solution is 1~2% (v / v), and the sodium hydroxide content in the sodium hydroxide aqueous solution is 10~20% (w / w).

[0016] In the above technical solution, the precipitate is washed with deionized water until it becomes neutral.

[0017] In step 1, the ratio of the mass fraction of the purified chitosan to the volume fraction of isopropanol is (1~2):(40~80), where the mass fraction is in g and the volume fraction is in mL.

[0018] In step 1, the 2,3-epoxypropyltrimethylammonium chloride solution is a mixture of 2,3-epoxypropyltrimethylammonium chloride and isopropanol, and the content of 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is 20~40% (w / w).

[0019] In step 1, the 2,3-epoxypropyltrimethylammonium chloride solution is added dropwise over a time controlled to be 0.5 to 1 h.

[0020] In step 1, the solid precipitate is washed with ethanol.

[0021] Step 2: Dissolve quaternized chitosan in PBS buffer, add cinnamaldehyde to obtain a reaction solution, and stir the reaction solution at room temperature for 20-30 h under light-protected conditions. After stirring, place the reaction solution in a dialysis bag with a molecular weight cutoff of 1500-3500 D and dialyze for 70-85 h to obtain quaternized chitosan grafted with cinnamaldehyde. The ratio of quaternized chitosan to cinnamaldehyde by mass is (1-2):(0.5-1). In step 2, the pH of the PBS buffer is 7.2 to 7.4.

[0022] In step 2, the dialysis fluid is changed every 12-24 hours during dialysis.

[0023] Step 3: Dissolve the quaternized chitosan grafted with cinnamaldehyde in ultrapure water to obtain a QCS-S solution. Add a plasticizer and a monolayer MXene dispersion containing MXene to the QCS-S solution in sequence to obtain a mixed solution. Cast the mixed solution onto a glass plate and dry it at 40~55℃ for 48~72h using the EISA process to obtain a photothermal antibacterial film on the glass plate. The ratio of the quaternized chitosan grafted with cinnamaldehyde, plasticizer and MXene by mass is (1500~3000):(600~1200):(2.0~4.0).

[0024] In step 3, the method for obtaining a monolayer MXene dispersion includes: dissolving lithium fluoride in hydrochloric acid solution, stirring at 350-400 r / min at 40-50℃ for 15-30 min, adding Ti3AlC2 powder in portions, and continuing to stir at 350-400 r / min at 40-50℃ for 48-60 min to obtain a mixture, centrifuging and washing until the pH of the supernatant is 6-7 to obtain a precipitate; dispersing the precipitate in water, and sonicating it for 1-2 h under ice bath and protective gas conditions, then centrifuging at 4500-5000 r / min for 1-2 h, collecting the supernatant to obtain a monolayer MXene dispersion containing MXene, wherein the concentration of MXene in the monolayer MXene dispersion is 0.5-1 mg / mL.

[0025] In the above technical solution, the ratio of the mass fraction of lithium fluoride, the volume fraction of hydrochloric acid solution, and the mass fraction of Ti3AlC2 powder is (2.0~2.5):(40~50):(2.0~2.5), where the mass fraction is in g and the volume fraction is in mL.

[0026] In the above technical solution, the concentration of hydrochloric acid in the hydrochloric acid solution is 9~10 M.

[0027] In step 3, the ratio of the mass fraction of the quaternized chitosan grafted with cinnamaldehyde to the volume fraction of the ultrapure water is (1.5~3):(100~200), where the mass fraction is in g and the volume fraction is in mL.

[0028] In step 3, the plasticizer is glycerin.

[0029] The above-mentioned photothermal antibacterial film is used in food packaging substrates.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of this invention, through quaternization modification and crosslinking of chitosan, yields quaternized chitosan grafted with cinnamaldehyde possessing antibacterial properties. Further addition of MXene, which possesses photothermal antibacterial properties, enhances the antibacterial ability of the photothermal antibacterial film while endowing it with excellent photothermal conversion capability and photothermal stability. Under irradiation with NIR light at a wavelength of 808 nm, the temperature of the photothermal antibacterial film reaches approximately 70°C. E. coli and S. aureus The inhibition rates are all close to 100%, effectively delaying quality deterioration. Furthermore, the materials used in this invention are mostly renewable resources with good biocompatibility. Attached Figure Description

[0031] Figure 1The images show scanning electron microscope (SEM) images of the surface (first row) and cross-section (second row) of the photothermal antibacterial film or antibacterial film, where the first column is Comparative Example 1, the second column is Comparative Example 2, the third column is Comparative Example 3, and the fourth column is Example 1. Figure 2 Fourier transform infrared spectra of the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3; Figure 3 (a) shows the antibacterial test results of the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 against Gram-negative bacteria. Figure 3 (b) is the corresponding Figure 3 (a) Bar chart of antibacterial rate results from antibacterial experiments; Figure 4 (a) shows the antibacterial test results of the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 against Gram-positive bacteria. Figure 4 (b) is the corresponding Figure 4 (a) Bar chart of antibacterial rate results from antibacterial experiments; Figure 5 The temperature change curves of the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 under NIR light irradiation at a wavelength of 808 nm over time. Figure 6 The temperature change curve of the photothermal antibacterial film obtained in Example 1 under photothermal cycling under NIR light irradiation at a wavelength of 808 nm is shown as a function of time. Figure 7 The storage conditions of strawberries after being packaged with the photothermal antibacterial film obtained in Example 1, the antibacterial film prepared in Comparative Examples 1 to 3, and PE film are shown. (a) is under non-irradiation conditions, and (b) is under near-infrared light irradiation. Figure 8 The cell survival rate of NIH3T3 mouse embryonic fibroblasts was measured using photothermal antibacterial films obtained in Example 1 at different concentrations. Detailed Implementation

[0032] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0033] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0034] In the following examples and comparative examples, the method for obtaining purified chitosan includes: dissolving chitosan (1 g) in 1% (v / v) aqueous acetic acid solution (100 mL), then adding 10% (w / w) aqueous sodium hydroxide solution until precipitation is complete, allowing it to stand at room temperature for 12 h, filtering, washing the precipitate with deionized water until neutral, and drying to obtain purified chitosan.

[0035] In the following examples, the method for obtaining a monolayer MXene dispersion includes: dissolving lithium fluoride (2 g) in hydrochloric acid solution (40 mL), stirring at 350 r / min at 40 °C for 15 min, then adding Ti3AlC2 powder (2 g) in portions, and continuing to stir at 350 r / min at 40 °C for 48 min to obtain a mixture, transferring the mixture to a centrifuge tube for centrifugation, discarding the supernatant, washing with deionized water until the pH of the supernatant is about 6 to obtain a precipitate; dispersing the precipitate in water, sonicating it for 1 h in an ice bath at 0 °C and under nitrogen, then centrifuging at 5000 r / min for 1 h, collecting the supernatant to obtain a monolayer MXene dispersion containing MXene.

[0036] Example 1 A method for preparing a photothermal antibacterial film (No.: QCS-SM) includes the following steps: Step 1: Place the purified chitosan (1g) in a round-bottom flask containing isopropanol (40 mL), slowly heat to 75°C, and then add dropwise a 2,3-epoxypropyltrimethylammonium chloride (GTMAC) solution (GTMAC solution is a mixture of GTMAC and isopropanol, with a GTMAC content of 20% (w / w)) to the round-bottom flask. Control the dropwise addition time to 1 h, and after the addition is complete, react at 75°C for 8 h. After the reaction is complete, add acetone to precipitate a solid precipitate, filter, wash with ethanol, and dry at 40°C for 12 h to obtain white quaternized chitosan. The ratio of purified chitosan monomer to 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is 1:3 by molar amount.

[0037] Step 2: Dissolve 1 g of quaternized chitosan in 100 mL of PBS buffer at pH 7.4, add 0.5 g of cinnamaldehyde to obtain a reaction solution. Stir the reaction solution at room temperature for 24 h under light-protected conditions. After stirring, place the reaction solution in a dialysis bag with a molecular weight cutoff of 1500 D and dialyze it in deionized water for 72 h (no UV signal of free cinnamaldehyde can be detected in deionized water after 72 h). Replace the deionized water every 12 h to obtain quaternized chitosan grafted with cinnamaldehyde.

[0038] Step 3: Dissolve 1.5 g of quaternized chitosan grafted with cinnamaldehyde in ultrapure water (100 mL) to obtain QCS-S solution. Add glycerol and a solution containing MXene (MXene nanoparticles are Ti3C2T) sequentially to the QCS-S solution. x T x A monolayer MXene dispersion (represented by surface functional groups, including -OH, -O, and -F) was prepared to obtain a mixed solution. The mixed solution was cast onto a glass plate and dried at 55°C for 48 h using the EISA process to obtain a photothermal antibacterial film (number: QCS-SM) with a thickness of 47.6 μm on the glass plate. The ratio of quaternized chitosan grafted with cinnamaldehyde, glycerol, and MXene in the monolayer MXene dispersion was 1500:600:2.0 by mass, and the concentration of MXene in the monolayer MXene dispersion was 0.6 mg / mL.

[0039] Comparative Example 1 A method for preparing an antibacterial film (No.: CS) includes the following steps: The purified chitosan (1.5 g) was dissolved in 1% (v / v) aqueous acetic acid (100 mL) to obtain a CS solution. Glycerin (0.6 g) was added to the CS solution to obtain a mixed solution. The mixed solution was cast onto a glass plate and dried at 55 °C for 48 h using the EISA process to obtain an antibacterial film (number: CS).

[0040] Comparative Example 2 A method for preparing an antibacterial film (No.: QCS) includes the following steps: Step 1: Place the purified chitosan (1g) in a round-bottom flask containing isopropanol (40 mL), slowly heat to 75°C, and then add dropwise a 2,3-epoxypropyltrimethylammonium chloride (GTMAC) solution (GTMAC solution is a mixture of GTMAC and isopropanol, with a GTMAC content of 20% (w / w)) to the round-bottom flask. Control the dropwise addition time to 1 h, and after the addition is complete, react at 75°C for 8 h. After the reaction is complete, add acetone to precipitate a solid precipitate, filter, wash with ethanol, and dry at 40°C for 12 h to obtain white quaternized chitosan. The ratio of purified chitosan monomer to 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is 1:3 by molar amount.

[0041] Step 3: Dissolve quaternized chitosan (1.5 g) in 1% (v / v) aqueous acetic acid solution (100 mL) to obtain QCS solution. Add glycerol (0.6 g) to QCS solution to obtain mixed solution. Cast the mixed solution onto a glass plate and dry it at 55 °C for 48 h using EISA process to obtain antibacterial film (number: QCS).

[0042] Comparative Example 3 A method for preparing an antibacterial film (No.: QCS-S) includes the following steps: Step 1: Place the purified chitosan (1g) in a round-bottom flask containing isopropanol (40 mL), slowly heat to 75°C, and then add dropwise a 2,3-epoxypropyltrimethylammonium chloride (GTMAC) solution (GTMAC solution is a mixture of GTMAC and isopropanol, with a GTMAC content of 20% (w / w)) to the round-bottom flask. Control the dropwise addition time to 1 h, and after the addition is complete, react at 75°C for 8 h. After the reaction is complete, add acetone to precipitate a solid precipitate, filter, wash with ethanol, and dry at 40°C for 12 h to obtain white quaternized chitosan. The ratio of purified chitosan monomer to 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is 1:3 by molar amount.

[0043] Step 2: Dissolve 1 g of quaternized chitosan in 100 mL of PBS buffer at pH 7.4, add 0.5 g of cinnamaldehyde to obtain a reaction solution. Stir the reaction solution at room temperature for 24 h under light-protected conditions. After stirring, place the reaction solution in a dialysis bag with a molecular weight cutoff of 1500 D and dialyze it in deionized water for 72 h (no UV signal of cinnamaldehyde was detected in deionized water after 72 h). Replace the deionized water every 12 h to obtain quaternized chitosan grafted with cinnamaldehyde.

[0044] Step 3: Dissolve 1.5 g of quaternized chitosan grafted with cinnamaldehyde in 1% (v / v) aqueous acetic acid solution (100 mL) to obtain QCS-S solution. Add 0.6 g of glycerol to QCS-S solution to obtain mixed solution. Cast the mixed solution onto a glass plate and dry it at 55 °C for 48 h using EISA process to obtain antibacterial film (number: QCS-S).

[0045] Figure 1 The images show scanning electron microscope (SEM) images of the surface (first row) and cross-section (second row) of the photothermal antibacterial film or antibacterial film. The first column is Comparative Example 1, the second column is Comparative Example 2, the third column is Comparative Example 3, and the fourth column is Example 1. Figure 1It can be seen that the antibacterial film (No.: CS) obtained in Comparative Example 1 has a smooth surface and a dense and homogeneous cross-section; after quaternization modification, the surface of the antibacterial film (No.: QCS) becomes rough, and preliminary layer separation appears in the cross-section, indicating changes in intermolecular forces and hydrophilicity / hydrophobicity; after Schiff base crosslinking, the surface roughness and cross-sectional roughness of the antibacterial film (No.: QCS-S) obtained in Comparative Example 3 increase significantly, which is the result of the separation morphology of the fixed phase in the crosslinked network; after being compounded with MXene, the photothermal antibacterial film obtained in Example 1 transforms the cross-section into a highly ordered dense layered structure, which is due to the two-dimensional nanosheets being restricted and oriented by the polymer matrix during the film formation process.

[0046] The photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 were subjected to infrared spectroscopy tests, and the Fourier transform infrared (FTIR) spectra were obtained as follows: Figure 2 As shown, by Figure 2 It can be seen that the antibacterial film obtained in Comparative Example 1 has a viscosity of 3450 cm⁻¹. -1 It exhibits a broad and strong -OH / -NH stretching vibration peak at 1645 cm⁻¹. -1 and 1554 cm -1 The locations correspond to amide I and amide II bands, respectively. Comparative Example 2, using quaternized chitosan modified with quaternization, was analyzed at 3450 cm⁻¹. -1 The peak shifted at 1481 cm⁻¹. -1 Quaternary ammonium groups (–N) appear at the position + The characteristic absorption peak of (CH3)3) was observed. The antibacterial film obtained in Comparative Example 3, using Schiff base-grafted cinnamaldehyde quaternized chitosan, showed an absorption peak at 1639 cm⁻¹. -1 The presence of a characteristic peak indicating a C=N bond confirms the success of the Schiff base reaction. After incorporating MXene, the characteristic peak positions of the photothermal antibacterial film obtained in Example 1 are essentially consistent with those in Comparative Example 3, indicating that the introduction of MXene did not change the main chemical bond type.

[0047] The antibacterial effect of the film on *Escherichia coli* was evaluated using a combination of film contact and plating methods. E. coli ATCC 25922 (purchased from Beijing Chemical Glass Station Bioanalytical Technology Co., Ltd.) or Staphylococcus aureus ( S. aureus The antibacterial activity of ATCC 12600 (purchased from Shanghai Luwei Technology Co., Ltd.) was tested. The antibacterial test results are as follows: Irradiation group: with a concentration of 1×10 8 A bacterial suspension of CFU / mL (200 µL) was inoculated into a sterile 96-well plate. A film (0.03 g) sterilized by UV irradiation for 30 minutes was added, or no film was added (as a control). The film was one of the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3. The film was prepared at a wavelength of 808 nm and a wavelength of 2 W·cm⁻¹.-2 Irradiate the bacteria under near-infrared light at the specified intensity for 10 minutes (surface temperature monitored by infrared thermal imaging), then incubate at 37°C for 24 hours. After incubation, take 100 μL of bacterial culture and perform serial dilutions, with a dilution factor of 10⁻⁶. 3 The concentration was increased by 10 times to obtain a diluted solution. This diluted solution was then spread onto LB agar plates and incubated at 37°C for 12 hours. Colonies were counted to determine the viable count. The number of colonies with a membrane attached was labeled C1, and the number without a membrane was labeled C0. The antibacterial rate was calculated using the following formula:

[0048] Non-irradiated group: Basically the same as the illuminated group, except that it does not use the 808 nm wavelength and 2 W·cm⁻¹. -2 Irradiate with near-infrared light at the specified intensity for 10 minutes, then incubate directly at 37°C for 24 hours.

[0049] Test results are as follows Figure 3 and Figure 4 As shown, by Figure 3 and Figure 4 It can be seen that after irradiation with near-infrared (NIR) light at a wavelength of 808 nm, the antibacterial films obtained in Comparative Examples 1 and 2 showed weak antibacterial effects against *Escherichia coli* and *Staphylococcus aureus*. Comparative Example 3, which used quaternized chitosan grafted with cinnamaldehyde, exhibited better antibacterial effects under non-light irradiation, indicating that quaternized chitosan grafted with cinnamaldehyde possesses better antibacterial activity. Regardless of whether near-infrared light irradiation was performed, the photothermal antibacterial film (number: QCS-SM) obtained in Example 1 showed excellent antibacterial properties against *Escherichia coli* and *Staphylococcus aureus*. E. coli and S. aureus The inhibition rates were close to 100%, attributed to the synergistic effect of MXene's photothermal properties and its inherent chemical antibacterial activity. On one hand, MXene efficiently converts light energy into localized heat energy under near-infrared irradiation, leading to an increase in temperature around bacteria, disrupting cell membrane integrity, and enhancing membrane permeability. On the other hand, the photothermal heating may enhance the interaction between bacteria and chemical antibacterial components such as quaternary ammonium salts and Schiff base-grafted cinnamaldehyde, thereby improving bactericidal efficiency. Furthermore, MXene may induce the generation of reactive oxygen species (ROS) under NIR irradiation, further exacerbating oxidative damage.

[0050] The photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 were subjected to a photothermal experiment for 10 minutes under NIR light irradiation at a wavelength of 808 nm. The results are as follows. Figure 5 As shown, by Figure 5As can be seen from the heating curves, the antibacterial film obtained in Comparative Example 1 showed almost no significant temperature rise during irradiation, indicating a lack of photothermal conversion capability. The antibacterial films obtained in Comparative Examples 2 and 3 showed a slight increase in temperature, but the magnitude was limited. In contrast, the photothermal antibacterial film obtained in Example 1, which incorporated MXene, heated up the fastest and reached the highest steady-state temperature (approximately 70°C). This is attributed to the excellent photothermal conversion capability of MXene and the thermally conductive network it forms in the polymer matrix.

[0051] The photothermal antibacterial film obtained in Example 1 was subjected to the following cycle five times: first, the infrared lamp was turned on and irradiated with 808 nm wavelength NIR light for 60 seconds, then the infrared lamp was turned off and NIR light irradiation was stopped for 60 seconds. The photothermal cycle stability was as follows: Figure 6 As shown, by Figure 6 It can be seen that after 5 consecutive "on-off" cycles, the temperature of the photothermal antibacterial film obtained in Example 1 changes stably and rapidly in the range of high temperature (about 70°C) and low temperature (about 30°C), and the extreme points of each cycle highly overlap, indicating that the photothermal antibacterial film obtained in Example 1 has good photothermal response reversibility and cycle stability.

[0052] Strawberries were packaged using the photothermal antibacterial film obtained in Example 1, the antibacterial films obtained in Comparative Examples 1-3, and PE films, respectively. Their preservation performance was tested by storing them for 7 days under non-irradiation conditions or under NIR light irradiation at a wavelength of 808 nm. Storage conditions were recorded on days 0, 1, 3, 5, and 7. The results are as follows: Figure 7 As shown, by Figure 7 It was found that strawberries packaged in PE film showed skin damage on day 3 under both non-irradiation conditions and 808 nm NIR light irradiation, were covered with mold on day 5, and completely rotted on day 7 (unable to be photographed). In contrast, strawberries packaged with the photothermal antibacterial film obtained in Example 1 and the antibacterial films obtained in Comparative Examples 1-3 maintained their basic appearance after 7 days of storage, with less surface mold. Among them, the strawberries packaged with the photothermal antibacterial film obtained in Example 1 maintained the best appearance: under non-irradiation conditions, the strawberry surface was slightly dented; while under NIR light irradiation conditions, the strawberries remained plump, without obvious dents or mold. This phenomenon indicates that NIR light irradiation enhanced the preservation effect of the photothermal antibacterial film obtained in Example 1 to a certain extent.

[0053] The tensile strength of the photothermal antibacterial film obtained in Example 1 was tested, and the tensile strength of the photothermal antibacterial film obtained in Example 1 was measured to be 14.55 MPa.

[0054] The cytotoxicity of the photothermal antibacterial membrane obtained in Example 1 was evaluated using the Cell Counting Kit-8 (CCK-8) assay. The cytotoxicity results are as follows: NIH3T3 mouse embryonic fibroblast suspension (concentration 1×10⁻⁶)6 Cells / T25 flasks (purchased from Qisai Biotechnology) were placed in centrifuge tubes containing 5 mL of complete culture medium and centrifuged at 1000 rpm for 5 minutes at room temperature. The supernatant was discarded, and the cells were resuspended in 5 mL of DMEM medium containing 10% fetal bovine serum (FBS) and inoculated into culture dishes. The cells were then cultured in a humidified incubator at 37°C and 5% CO2 until the logarithmic growth phase. The density was then adjusted to 4 × 10⁶ cells per well. 3 Cells were seeded at a density of 1,000 μL in 96-well plates and incubated overnight to promote cell adhesion. To minimize edge effects, 100 μL of sterile phosphate-buffered saline (PBS) was added to each well around the perimeter of the 96-well plate.

[0055] The photothermal antibacterial membrane obtained in Example 1, sterilized by ultraviolet irradiation for 30 minutes, was immersed in DMEM medium for 24 hours to obtain membrane extracts with concentrations of 5 mg / mL, 10 mg / mL, and 15 mg / mL, respectively. The DMEM medium in the above 96-well plates was then replaced with the membrane extract or with new DMEM medium (replacing with new DMEM medium was used as...). Figure 8 The "control" in the text refers to a wavelength of 808 nm and a wavelength of 2 W·cm⁻¹. -2 Cells were cultured for 72 h at 37°C and 5% CO2 under near-infrared light irradiation or non-irradiation conditions. Cell viability was detected by the CCK-8 assay after culture, and absorbance at 450 nm was measured using a microplate reader to obtain cell viability.

[0056] Cell survival rate, such as Figure 8 As shown, by Figure 8 It can be seen that the photothermal antibacterial films obtained in Example 1 at different concentrations all exhibited cell activity greater than 70% against NIH3T3 mouse embryonic fibroblasts. According to GB 31604.1-2023 "National Food Safety Standard - General Rules for Migration Testing of Food Contact Materials and Articles", a 6 dm² concentration is typically used. 2 The food contact materials and articles were tested in contact with 1 kg of food, which means that the concentration of substances migrating into the food is usually in the µg / mL range (0.001~0.1 mg / mL). The photothermal antibacterial film obtained in Example 1 of the present invention still has a concentration greater than 70% at a concentration of 15 mg / mL, which meets the in vitro cytotoxicity safety requirements for food contact materials and packaging materials.

[0057] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A photothermal antibacterial film based on MXene / quaternized chitosan, characterized in that, The photothermal antibacterial film comprises: a quaternized chitosan matrix, cinnamaldehyde grafted onto the chitosan molecular chain, and MXene embedded in the quaternized chitosan matrix.

2. The photothermal antibacterial film according to claim 1, characterized in that, The thickness of the photothermal antibacterial film is 43.5~51.7μm.

3. The photothermal antibacterial film according to claim 1, characterized in that, The MXene is Ti3C2T x T x These are represented as surface functional groups, including -OH, -O, and -F.

4. A method for preparing the photothermal antibacterial film according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: Place the purified chitosan in isopropanol, slowly heat to 70-80℃, and then add 2,3-epoxypropyltrimethylammonium chloride solution dropwise. After the addition is complete, react at 70-80℃ for 8-10 h. Add acetone to precipitate a solid precipitate, filter, wash, and dry to obtain quaternized chitosan. The ratio of purified chitosan monomer to 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is (1-2):(3-6). Step 2: Dissolve quaternized chitosan in PBS buffer, add cinnamaldehyde to obtain a reaction solution, and stir the reaction solution at room temperature for 20-30 h under light-protected conditions. After stirring, place the reaction solution in a dialysis bag with a molecular weight cutoff of 1500-3500 D and dialyze for 70-85 h to obtain quaternized chitosan grafted with cinnamaldehyde. The ratio of quaternized chitosan to cinnamaldehyde by mass is (1-2):(0.5-1). Step 3: Dissolve the quaternized chitosan grafted with cinnamaldehyde in ultrapure water to obtain a QCS-S solution. Add a plasticizer and a monolayer MXene dispersion containing MXene to the QCS-S solution in sequence to obtain a mixed solution. Cast the mixed solution onto a glass plate and dry it at 40-55℃ for 48-72 h using the EISA process to obtain a photothermal antibacterial film on the glass plate. The ratio of the quaternized chitosan grafted with cinnamaldehyde, plasticizer and MXene by mass is (1500-3000):(600-1200):(2.0-4.0).

5. The preparation method according to claim 4, characterized in that, The method for obtaining purified chitosan includes: dissolving chitosan in an aqueous acetic acid solution, adding an aqueous sodium hydroxide solution until precipitation is complete, allowing it to stand at room temperature for 10-15 h, filtering, washing, and drying to obtain purified chitosan, wherein the ratio of the mass fraction of chitosan to the volume fraction of the aqueous acetic acid solution is (1-2):(100-200), where the mass fraction is in g and the volume fraction is in mL; The acetic acid aqueous solution contains 1-2% (v / v) acetic acid, and the sodium hydroxide aqueous solution contains 10-20% (w / w) sodium hydroxide. Wash the precipitate with deionized water until it is neutral.

6. The preparation method according to claim 4, characterized in that, The mass fraction of the purified chitosan to the volume fraction of isopropanol is (1~2):(40~80), the mass fraction of the quaternized chitosan grafted with cinnamaldehyde to the volume fraction of the ultrapure water is (1.5~3):(100~200), the mass fraction is in g, and the volume fraction is in mL.

7. The preparation method according to claim 4, characterized in that, The 2,3-epoxypropyltrimethylammonium chloride solution is a mixture of 2,3-epoxypropyltrimethylammonium chloride and isopropanol, and the content of 2,3-epoxypropyltrimethylammonium chloride in the 2,3-epoxypropyltrimethylammonium chloride solution is 20~40% (w / w).

8. The preparation method according to claim 4, characterized in that, The method for obtaining a monolayer MXene dispersion includes: dissolving lithium fluoride in hydrochloric acid solution, stirring at 350-400 r / min at 40-50℃ for 15-30 min, adding Ti3AlC2 powder in portions, and continuing to stir at 350-400 r / min at 40-50℃ for 48-60 min to obtain a mixture, centrifuging and washing until the pH of the supernatant is 6-7 to obtain a precipitate; dispersing the precipitate in water, sonicating under ice bath and protective gas for 1-2 h, centrifuging at 4500-5000 r / min for 1-2 h, collecting the supernatant to obtain a monolayer MXene dispersion containing MXene, wherein the concentration of MXene in the monolayer MXene dispersion is 0.5-1 mg / mL; The ratio of the mass fraction of lithium fluoride, the volume fraction of hydrochloric acid solution, and the mass fraction of Ti3AlC2 powder is (2.0~2.5):(40~50):(2.0~2.5), where the mass fraction is in g and the volume fraction is in mL.

9. The preparation method according to claim 4, characterized in that, The plasticizer is glycerin.

10. The application of the photothermal antibacterial film as described in any one of claims 1 to 3 in food packaging substrates.

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