A biomass carbon quantum dot modified fresh-keeping material and its preparation method and application

Abstract

The present invention discloses a method for preparing a preservative material modified with biomass carbon quantum dots, comprising the following steps: (1) preparing a biomass carbon quantum dot solution; (2) preparing titanium dioxide nanosheets; (3) ultrasonically dispersing the titanium dioxide nanosheets in deionized water and then ultrasonicating, then mixing the titanium dioxide nanosheets with the biomass carbon quantum dot solution and then ultrasonicating, and then performing a high-temperature treatment. The obtained product is subsequently treated to obtain carbon quantum dot-modified titanium dioxide nanosheets with antibacterial and ethylene decomposition functions, i.e., a preservative material modified with biomass carbon quantum dots. The present invention also discloses a preservative material modified with biomass carbon quantum dots prepared by the above method, and the use of the preservative material modified with biomass carbon quantum dots in the preparation of products with antibacterial and photocatalytic ethylene decomposition functions, as well as the use of the preservative material in the preservation of fruits and vegetables.

Description

Technical Field

[0001] The present invention belongs to the technical field of new titanium dioxide materials, and specifically relates to a fresh-keeping material modified with biomass carbon quantum dots, a preparation method and an application thereof, and in particular to a titanium dioxide nanosheet modified with biomass carbon quantum dots having antibacterial and ethylene decomposition functions, a preparation method and a fresh-keeping application thereof. Background Art

[0002] Functional fresh-keeping materials have a huge market in my country. Functional fresh-keeping packaging will have a good market prospect in my country in the future.

[0003] Nano-titanium dioxide (TiO2) boasts advantages such as high safety, stability, and catalytic activity. It is widely used in antibacterial coatings, antibacterial plastics, antibacterial water treatment devices, cosmetics, textiles, antibacterial tableware, air purification, and medical equipment. In many applications, TiO2 has been used to inactivate a variety of microorganisms. Based on the principle of photocatalysis, the reaction generates highly chemically active hydroxyl free radicals and superoxide anions. These free radicals and anions can attack bacterial and fungal organisms, causing the decomposition of organic matter within the bacterial and fungal cells, thereby quickly killing the bacteria and molds. This inhibits bacterial and mold reproduction, produces a deodorizing effect, and can also decompose ethylene, which causes spoilage. Nano-TiO2 composite films can theoretically effectively reduce the CO2 and ethylene produced during the metabolic process of fruits and vegetables, effectively inhibiting microorganisms, thereby stabilizing the quality of agricultural products and reducing labor costs.

[0004] However, traditional methods of producing nano-TiO2 have drawbacks such as difficulty controlling particle size, excessively coarse particles, unstable structure, and low catalytic efficiency. Most importantly, TiO2 has a wide bandgap, absorbs virtually no visible light, has low quantum efficiency, and a high recombination rate of photogenerated carriers. Consequently, research in the preservation field is limited, making its application in extending the shelf life of fruits and vegetables difficult to implement.

[0005] Carbon quantum dots (CQDs), also known as carbon dots or carbon nanodots, are a new type of zero-dimensional carbon nanomaterial. This material features ultrafine particles, good dispersion, a quasi-spherical shape, and a particle size less than 10 nm. They also exhibit remarkable fluorescence properties. Modification with carbon quantum dots, which possess excellent optical and fluorescence upconversion properties, can enhance TiO2's light absorption response and the separation of photogenerated carriers, thereby improving TiO2's photocatalytic performance under visible light, achieving antibacterial and harmful gas removal. This is key to its application in the preservation, storage, and transportation of fruits and vegetables. Summary of the Invention

[0006] The first object of the present invention is to provide a method for preparing a biomass carbon quantum dot-modified fresh-keeping material, in particular a method for preparing a biomass carbon quantum dot-modified titanium dioxide nanosheet having antibacterial and ethylene decomposition functions.

[0007] The present invention also aims to provide a biomass carbon quantum dot-modified fresh-keeping material prepared by the above method, in particular, a biomass carbon quantum dot-modified titanium dioxide nanosheet with antibacterial and ethylene decomposition functions prepared by the above method.

[0008] The last object of the present invention is to provide the application of the above-mentioned biomass carbon quantum dot modified preservative material, especially biomass carbon quantum dot modified titanium dioxide nanosheets, in the preparation of products with antibacterial and photocatalytic ethylene decomposition functions, as well as their application in fruit and vegetable preservation.

[0009] The first object of the present invention can be achieved by the following technical solution: a method for preparing a fresh-keeping material modified with biomass carbon quantum dots, comprising the following steps:

[0010] (1) The biomass material is ultrafinely ground and heated in a muffle furnace at 290-310° C. for 2-4 hours, and then dispersed in deionized water to obtain a dispersion, and organic small molecules are dissolved in water to obtain an organic small molecule aqueous solution, and the dispersion and the organic small molecule aqueous solution are hydrothermally reacted at 180-200° C. for 6 hours, cooled, and centrifuged to obtain a biomass carbon quantum dot solution;

[0011] (2) mixing a nano-titanium dioxide precursor and an acidic solution, subjecting the resulting mixture to a high-temperature treatment, naturally cooling the product after the high-temperature treatment, removing a layer of precipitate, washing, drying, and grinding to obtain titanium dioxide nanosheets;

[0012] (3) ultrasonically dispersing the titanium dioxide nanosheets obtained in step (2) in deionized water, then mixing with the biomass quantum dot solution obtained in step (1) and ultrasonically treating the mixture, and then high-temperature treating the mixture in an oil bath or oven at 120 to 150° C. The obtained product is centrifuged and washed, and the precipitate is collected and dried to obtain biomass carbon quantum dot-modified titanium dioxide nanosheets having antibacterial and ethylene decomposition functions, i.e., biomass carbon quantum dot-modified fresh-keeping materials.

[0013] In the preparation method of the above-mentioned biomass carbon quantum dot modified fresh-keeping material:

[0014] Preferably, the biomass material in step (1) is litchi peel, sugarcane bagasse or other straw-like materials.

[0015] Preferably, the organic small molecule in step (1) is citric acid, citrate, glucose or ascorbic acid.

[0016] In step (1) of the present invention, the carbon source is preferably a composite of biomass and organic small molecules. The biomass carbon source is litchi peel, sugarcane bagasse or other straw-like materials; the organic small molecule carbon source is citric acid, citrate, glucose or ascorbic acid.

[0017] The present invention uses natural biomass waste such as lychee peel and organic small molecules as composite raw materials, and prepares carbon quantum dots (CQDs) below 10nm through carbonization combined with hydrothermal reaction. CQDs prepared from natural biomass can simultaneously introduce rich heteroatom functional groups because they contain heteroatoms, providing active sites, optimizing energy level structure, and enhancing the ability to utilize visible light.

[0018] Preferably, the nano-titanium dioxide precursor in step (2) is one or more of butyl titanate, isopropyl titanate, titanyl sulfate, titanium tetrachloride, titanium trichloride and titanium dioxide P25.

[0019] More preferably, the nano-titanium dioxide precursor in step (2) is butyl titanate.

[0020] The present invention uses butyl titanate as a titanium source to prepare anatase TiO2 nanosheets (TNS) with a larger specific surface area than TiO2 nanotubes and nanoparticles. The anatase TiO2 nanosheets can adsorb many oxygen atoms on the surface, and photogenerated carriers are not easily recombined, so that the obtained TiO2 nanosheets have higher photocatalytic activity.

[0021] Preferably, the acidic solution in step (2) is a strong acid, and the strong acid is concentrated hydrochloric acid, concentrated sulfuric acid or hydrofluoric acid.

[0022] More preferably, the acidic solution in step (2) is hydrofluoric acid.

[0023] Preferably, in step (2), the obtained mixture is subjected to high-temperature treatment in a silicone oil bath at 175-200° C. for 23-25 ​​hours.

[0024] More preferably, in step (2), the obtained mixture is subjected to high-temperature treatment in a silicone oil bath at 180° C. for 24 hours.

[0025] Preferably, in step (3), the dosage of the titanium dioxide nanosheets TNS and the biomass quantum dot solution is 0.1 g: 1-6 mL.

[0026] More preferably, in step (3), high temperature treatment is performed in a 150° C. oil bath for 2 to 4 hours.

[0027] Optionally, in step (2) and step (3), washing is performed using ethanol and deionized water, and drying is performed in an oven at 60° C. for 12 h.

[0028] After the carbon quantum dots are compounded with titanium dioxide nanosheets, the modification of the carbon quantum dots is verified by a variety of characterization methods. Then, analysis after detection by ultraviolet-visible near-infrared spectrophotometer shows that after the carbon quantum dots are modified into the nanosheets, their energy band gap is significantly reduced, and the photocatalytic activity in the visible light region is significantly improved compared with titanium dioxide nanosheets.

[0029] The above-mentioned second object of the present invention can be achieved by the following technical solution: a fresh-keeping material modified with biomass carbon quantum dots is prepared by the above-mentioned method.

[0030] The present invention prepares a biomass carbon quantum dot-modified fresh-keeping material through the above method, in particular a biomass carbon quantum dot-modified titanium dioxide nanosheet with antibacterial and ethylene decomposition functions.

[0031] The last object of the present invention can be achieved by the following technical solution: the application of the above-mentioned biomass carbon quantum dot modified fresh-keeping material, especially the biomass carbon quantum dot modified titanium dioxide nanosheets, in the preparation of products with antibacterial and photocatalytic decomposition of ethylene functions.

[0032] Furthermore, the present invention also discloses the application of the above-mentioned biomass carbon quantum dot modified preservative material, especially biomass carbon quantum dot modified titanium dioxide nanosheets in the preservation of fruits and vegetables.

[0033] The present invention can prepare the carbon quantum dot-modified titanium dioxide nanosheets into products with antibacterial and photocatalytic ethylene decomposition functions, and further use them as food, especially fruit and vegetable preservation materials.

[0034] To verify the effectiveness of this method, the modified nanosheets were blended with polyolefins and cast using a tape-casting process to produce a 10nm thick polyethylene-based cling film. Strawberries and Chinese cabbage were used as fresh-keeping test subjects. At room temperature (28°C), strawberries were preserved for one day, while at 4°C, the fresh-keeping of Chinese cabbage was extended by nine days. The results are shown in the accompanying figure. The preservation effect varies depending on the film-making process, film thickness, and film-forming substrate, and is not limited to strawberries and Chinese cabbage.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) The present invention uses organic small molecules and natural biomass waste such as lychee peel as composite raw materials, and prepares carbon quantum dots (CQDs) below 10 nm through carbonization combined with hydrothermal reaction. CQDs prepared from natural biomass can simultaneously introduce rich heteroatom functional groups because they contain heteroatoms, providing active sites, optimizing energy level structure, and enhancing the ability to utilize visible light;

[0037] (2) The present invention uses butyl titanate as a titanium source to prepare anatase TiO2 nanosheets (TNS) having a larger specific surface area than TiO2 nanotubes and nanoparticles. The anatase TiO2 nanosheets can adsorb many oxygen atoms on the surface, making it difficult for photogenerated carriers to recombine, resulting in the obtained TiO2 nanosheets having higher photocatalytic activity.

[0038] (3) The present invention composites carbon quantum dots (CQDs) prepared from natural biomass waste such as lychee peel and organic small molecules with titanium dioxide nanosheets, and verifies the modification of carbon quantum dots by various characterization methods. The analysis after detection by UV-visible near-infrared spectrophotometer shows that after carbon quantum dots are modified into nanosheets, their energy band gap is significantly reduced, the photocatalytic activity in the visible light region is improved, and they have antibacterial properties.

[0039] (4) The present invention significantly improves the photocatalytic removal rate of ethylene under visible light and ultraviolet light conditions for CQDs@TiO2 composite materials with different composite concentrations, indicating that the composite of CQDs helps to improve the photocatalytic performance of TNS; when the addition amount of CQDs solution is 4mL, the photocatalytic removal rate of ethylene of CQDs@TiO2 composite material CT-4 under visible light conditions reaches 48.84%, and the photocatalytic removal rate of ethylene under ultraviolet light conditions reaches 53.93%, which is the best sample among all composite samples. When the composite amount of CQDs is further increased, when the added CQDs solution is 6mL, the photocatalytic performance of the composite material CT-6 decreases instead, indicating that excessive CQDs composite concentration will make CQDs act as the center of electron and hole recombination, thereby reducing the separation efficiency of photogenerated carriers;

[0040] (5) The CQDs@TiO2 composite material CT-4 of the present invention has a very significant antibacterial effect on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis under visible light. The larger the diameter of the inhibition zone, the better the antibacterial effect.

[0041] (6) To verify the effect, the modified nanosheet new material was blended with polyolefin and a 10 nm thick polyethylene-based cling film was prepared using a casting process. Strawberries and Chinese cabbage were used as the preservation test objects. At room temperature of 28°C, the preservation of strawberries was extended by 1 day; at 4°C, the preservation of Chinese cabbage was extended by 9 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1The UV-Vis DRS spectra of TNS and CQDs@TiO2 in Example 5 and the band gaps of TNS and CQDs@TiO2 calculated based on the UV-vis DRS data, wherein (a) is the UV-Vis DRS spectra of TNS and CQDs@TiO2, and (b) is the band gaps of TNS and CQDs@TiO2 calculated based on the UV-vis DRS data;

[0043] Figure 2 TEM images of titanium dioxide nanosheets in Example 5, wherein (a) and (c) are TEM images of titanium dioxide nanosheets prepared in an oil bath at 180°C, and (b) and (d) are TEM images of titanium dioxide nanosheets prepared in an oil bath at 200°C;

[0044] Figure 3 TEM images, carbon quantum dot lattice spacing images, and particle size statistical distribution images of carbon quantum dots in Example 5, wherein (a) is a TEM image of carbon quantum dots, (b) is a carbon quantum dot lattice spacing image, and (c) is a particle size statistical distribution image;

[0045] Figure 4 These are the EPR spectra of TNS and CT-4 in Example 5 in the dark, under illumination for 1 min, under illumination for 5 min, and under illumination for 10 min: (a) DMPO-·O2-; (b) DMPO-·OH;

[0046] Figure 5 The ethylene removal rates of TNS and CQDs@TiO2 under visible light and ultraviolet light in Example 5, wherein (a) shows the ethylene removal rates of TNS and CQDs@TiO2 under visible light, and (b) shows the ethylene removal rates of TNS and CQDs@TiO2 under ultraviolet light;

[0047] Figure 6 TEM images of Staphylococcus aureus before and after contact with CT-4 in Example 5, wherein (a) is a TEM image of Staphylococcus aureus before contact, and (b) is a TEM image of Staphylococcus aureus after contact;

[0048] Figure 7 The antibacterial effect of CT-4 in Example 5 on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis and Aspergillus niger under visible light in turn;

[0049] Figure 8 This is a diagram showing the preservation effect of strawberries in Example 5;

[0050] Figure 9 The changes in the physical and chemical indicators of chlorophyll, weight loss rate and solid content of the fresh-keeping packaged Chinese cabbage in Example 5, wherein (a) chlorophyll, (b) weight loss rate, and (c) solid content;

[0051] Figure 10 This is a diagram showing the fresh-keeping effect of Chinese cabbage in Example 5. DETAILED DESCRIPTION

[0052] Example 1

[0053] The preparation method of the biomass carbon quantum dot modified fresh-keeping material provided in this embodiment comprises the following steps:

[0054] (1) After ultrafine grinding of litchi peel, the peel was heated in a muffle furnace at 300°C for 3 hours, and then dispersed in deionized water to obtain a dispersion; anhydrous citric acid with small organic molecules was dissolved in water to obtain an aqueous solution of citric acid with small organic molecules; the dispersion and the aqueous solution of citric acid with small organic molecules were hydrothermally reacted at 200°C for 6 hours, cooled, and centrifuged to obtain a biomass carbon quantum dots (CQDs) solution;

[0055] (2) Preparation of TiO2 nanosheets by hydrothermal method: 10 mL of butyl titanate was absorbed into a polytetrafluoroethylene liner, 1.2 mL of HF was slowly added to 10 mL of butyl titanate and mechanically stirred, butyl titanate and HF were stirred and mixed to make them uniform, and then the mixed solution was poured into the white inner liner of a high-pressure reactor. The top of the reactor was tightened with a small stainless steel rod and placed in an oil bath of 180°C and 200°C silicone oil respectively. The hydrothermal reaction was carried out for 24 hours and then naturally cooled to room temperature. After the liner was removed, the upper layer of yellow oily liquid was poured out to leave the lower layer of light blue viscous solid, which was washed twice with ethanol and then washed twice with deionized water. The final product was placed in a 60°C oven and dried for 12 hours. It was ground into powder with an agate mortar to obtain TiO2 nanosheets (TNS);

[0056] (3) Weigh 0.1 g of TNS powder, add 9 mL of deionized water to a beaker, ultrasonicate, and then add 1 mL of CQDs solution to keep the total volume of the solution at 10 mL. Mechanically stir the mixed solution in the beaker for 30 min, then take it to an ultrasonic cleaner and ultrasonicate it for 30 min to obtain a uniform white suspension. Pour the suspension into the white inner liner of a high-pressure reactor, tighten the reactor tightly, and then place it in a 150 °C oil bath for hydrothermal reaction for 3 h. After the reaction is completed, wait for the reactor and its inner liner to cool to room temperature and then pour out the upper white transparent liquid. Rinse the white product at the bottom with deionized water and pour it into a centrifuge tube. Place it in a high-speed desktop centrifuge (10,000 rpm, 5 min) for centrifugal washing. Wash it 4 times in total. Finally, place the product in a 60 °C oven to dry for 12 h and grind it into powder to obtain a biomass carbon quantum dot-modified preservative material CQDs@TiO2 composite material, recorded as CT-1.

[0057] Example 2

[0058] The difference from Example 1 is that in step (3), 0.1 g of TNS powder was weighed, 8 mL of deionized water was added to a beaker, ultrasonically treated, and then 2 mL of CQDs solution was added to keep the total volume of the solution at 10 mL. The mixed solution in the beaker was mechanically stirred for 30 min, and then ultrasonicated in an ultrasonic cleaner for 30 min to obtain a uniform white suspension. The suspension was poured into the white inner liner of the high-pressure reactor, the reactor was tightened, and then placed in a 150 ° C oil bath for hydrothermal reaction for 3 h. After the reaction was completed, the reactor and its inner liner were cooled to room temperature and then the upper white transparent liquid was poured out. The white product at the bottom was rinsed with deionized water and poured into a centrifuge tube, placed in a high-speed desktop centrifuge (10000 rpm, 5 min) for centrifugal washing, washed 4 times in total, and finally the product was placed in a 60 ° C oven to dry for 12 h, ground into powder to obtain a biomass carbon quantum dot modified preservative material CQDs@TiO2 composite material, recorded as CT-2.

[0059] Example 3

[0060] The difference from Example 1 is that in step (3), 0.1 g of TNS powder was weighed, 6 mL of deionized water was added to a beaker, ultrasonically treated, and then 4 mL of CQDs solution was added to keep the total volume of the solution at 10 mL. The mixed solution in the beaker was mechanically stirred for 30 min, and then ultrasonicated in an ultrasonic cleaner for 30 min to obtain a uniform white suspension. The suspension was poured into the white inner liner of the high-pressure reactor, the reactor was tightened, and then placed in a 150 ° C oil bath for hydrothermal reaction for 3 h. After the reaction was completed, the reactor and its inner liner were cooled to room temperature and then the upper white transparent liquid was poured out. The white product at the bottom was rinsed with deionized water and poured into a centrifuge tube, placed in a high-speed desktop centrifuge (10000 rpm, 5 min) for centrifugal washing, washed 4 times in total, and finally the product was placed in a 60 ° C oven to dry for 12 h, ground into powder to obtain a biomass carbon quantum dot modified preservative material CQDs@TiO2 composite material, recorded as CT-3.

[0061] Example 4

[0062] The difference from Example 1 is that in step (3), 0.1 g of TNS powder was weighed, 4 mL of deionized water was added to a beaker, ultrasonically treated, and then 6 mL of CQDs solution was added to keep the total volume of the solution at 10 mL. The mixed solution in the beaker was mechanically stirred for 30 min, and then ultrasonicated in an ultrasonic cleaner for 30 min to obtain a uniform white suspension. The suspension was poured into the white inner liner of the high-pressure reactor, the reactor was tightened, and then placed in a 150 ° C oil bath for hydrothermal reaction for 3 h. After the reaction was completed, the reactor and its inner liner were cooled to room temperature and then the upper white transparent liquid was poured out. The white product at the bottom was rinsed with deionized water and poured into a centrifuge tube, placed in a high-speed desktop centrifuge (10000 rpm, 5 min) for centrifugal washing, washed 4 times in total, and finally the product was placed in a 60 ° C oven to dry for 12 h, ground into powder to obtain a biomass carbon quantum dot modified preservative material CQDs@TiO2 composite material, recorded as CT-4.

[0063] That is, in Examples 1-4, four portions of 0.1 g TNS powder were weighed, and different volumes of deionized water (9 mL, 8 mL, 6 mL, 4 mL) were added to four beakers respectively. Then, different volumes of CQDs solution (1 mL, 2 mL, 4 mL, 6 mL) were added respectively to keep the total volume of the solution at 10 mL. After subsequent treatment, four CQDs@TiO2 composite materials with different CQDs concentrations were obtained, which were recorded as CT-1, CT-2, CT-4, and CT-6 respectively.

[0064] Example 5

[0065] The characterization method of the biomass carbon quantum dot modified fresh-keeping material CQDs@TiO2 composite material prepared in Examples 1-4 is as follows:

[0066] 1. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS)

[0067] A UV-3600 ultraviolet-visible diffuse reflectometer was used to characterize the light absorption capacity of the prepared samples. The band gap of the samples was calculated based on the test results and the formula, and the light response range of the samples was determined based on this result.

[0068] Semiconductor bandgap calculation formula:

[0069] (αhv) n =K(hv-E g )

[0070] hv=1240 / λ

[0071] α is the absorption coefficient, h is Planck's constant, v is the frequency, K is a constant, E gis the semiconductor bandgap width, and λ is the test wavelength. Anatase TiO2 has an indirect bandgap, with n = 1 / 2. Since the UV-visible diffuse reflectance spectroscopy data is the absorption value Abs, which is proportional to α and will not affect α, the measured Abs data can be used instead of α in the calculation.

[0072] Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) was used to study the photoresponse wavelength and band gap of TNS, CQDs, and CQDs@TiO2 composites.

[0073] UV-Vis DRS spectra of TNS and CQDs@TiO2 and the band gaps of TNS and CQDs@TiO2 calculated based on UV-vis DRS data are shown in Figure 2. Figure 1 As shown, (a) is the UV-Vis DRS spectrum of TNS and CQDs@TiO2, and (b) is the band gap of TNS and CQDs@TiO2 calculated based on UV-vis DRS data.

[0074] Depend on Figure 1 As can be seen in Figure (a), after compounding with different concentrations of CQDs, the absorption intensity of the composite catalyst in the ultraviolet light region of 350-400nm has been significantly improved, indicating that the unique optical properties of CQDs enable it to act as a photosensitizer to enhance the absorption of TNS for ultraviolet light, thereby improving its photocatalytic activity under ultraviolet light conditions. The absorption intensity of CT-4 in the visible light region of 400-500nm is better than that of TNS, indicating that the compounding of CQDs can enhance the absorption intensity of TNS for ultraviolet and visible light. At the same time, Figure 1 As shown in Figure (b), based on the UV-Vis DRS data, the band gap of TNS is calculated to be 3.03eV, the band gap of CQDs is 2.42eV, and the band gap width of the composited CQDs@TiO2 is shortened due to the composite of CQDs.

[0075] 2. TEM analysis of titanium dioxide nanosheets

[0076] The TEM image of the titanium dioxide nanosheets prepared in step (2) of Example 1-4 is as follows: Figure 2 As shown, from Figure 2 The layered structure of the prepared titanium dioxide nanosheets is more pronounced in TEM examinations. The nanosheets are stacked together, with complex lattice spacings interlaced. Nanosheets heated in an oil bath at 180°C are relatively uniform in size, measuring 53.96 nm in length, 45.53 nm in width, and approximately 5 nm in thickness. The lattice spacing of 0.22 nm belongs to the {001} plane. However, nanosheets heated in an oil bath at 200°C exhibit damage, with large nanosheets reaching 75.64 nm in length, 57.51 nm in width, and 7 nm in thickness, showing significant size disparity.

[0077] Compared with the preparation conditions of 200°C, the oil bath conditions of 180°C can obtain nanosheets with relatively small size differences, uniform size, and complete rectangular layers. The smaller particle size of titanium dioxide nanosheet particles also provides ample illumination area and chemical reaction groups, so the oil bath conditions of 180°C are the most preferred.

[0078] 3. Characterization of carbon quantum dots - TEM analysis of carbon quantum dots

[0079] From transmission electron microscopy Figure 3 As can be seen from Figures (a), (b) and (c), the carbon quantum dots prepared by the hydrothermal method in step (3) of Example 1 are relatively uniform in size and are roughly spherical. During the sample preparation process, the carbon quantum dot solution was pretreated using a dispersion method such as ultrasound. As can be seen from the TEM image, there is no contact between the carbon quantum dots, and they maintain a distance and are dispersed without any aggregation. The carbon dot size can be clearly measured at 10nm. 60 carbon dots were extracted from the sample and their particle size statistics were performed. It was found that their particle size was mainly distributed between 1.5 and 5.5nm, with an average particle size of 2.9nm and a lattice spacing of 0.09nm.

[0080] 4. EPR analysis of samples

[0081] In order to verify the free radicals generated by TNS and CT-4 during the photocatalytic process, EPR technology was used to detect ·O2- free radicals and ·OH free radicals. The results are shown in the figure. Figure 4 As shown in Figures a) and b), the characteristic signal peaks of DMPO-·O2- and DMPO-·OH in CQDs are very weak and almost absent, both in the dark and under illumination. This indicates that the amount of ·O2- and ·OH radicals generated by CQDs under illumination is very small and has no negligible effect on the amount of ·O2- and ·OH radicals generated by the CT-4 composite material. In the dark, neither TNS without CQDs nor CT-4 after CQDs composite material exhibits the characteristic signal peaks of DMPO-·O2- and DMPO-·OH, indicating that free radicals must be generated in the presence of light. After 1 minute of illumination, it can be seen that samples TNS and CT-4 begin to have characteristic signal peaks of DMPO-·O2- and DMPO-·OH, and as the illumination time increases, the characteristic signal peaks of DMPO-·O2- and DMPO-·OH become stronger. It is worth noting that compared with TNS without composite CQDs, the characteristic peak signals of DMPO-·O2- and DMPO-·OH of CT-4 after CQDs composite modification are stronger, indicating that CT-4 after composite CQDs can produce more ·O2- free radicals and ·OH free radicals, which is undoubtedly more beneficial for photocatalytic degradation and antibacterial.

[0082] 5. Study on the photocatalytic ethylene removal performance of NS and CQDs@TiO2

[0083] Place an acrylic box and turn on a small visible light lamp or ultraviolet lamp for irradiation. Set up the ethylene detector and place it in it. Place TNS powder (0.2g) and the four prepared CQDs@TiO2 composite materials (0.2g) in the acrylic box in turn. Seal the acrylic box, then use a syringe to fill ethylene gas from the hole, and then plug the hole with vaseline. The ethylene detector records data every hour, recording the ethylene concentration in the acrylic box under visible light and ultraviolet light respectively. Record the data for four hours, and finally collect the data to calculate the ethylene removal rate of the sample.

[0084] The photocatalytic performance of different samples was evaluated by photocatalytic removal of ethylene under simulated visible light and ultraviolet light conditions. The results are as follows: Figure 5 As shown in Figures (a) and (b), the samples are TNS and CQDs@TiO2 composite materials modified with different concentrations of CQDs.

[0085] from Figure 5 It can be seen that after 240 minutes of photocatalytic removal, the final ethylene removal rates of the five samples under visible light conditions were 21.25%, 22.00%, 22.58%, 48.84%, 34.41%, Figure 5 In the middle (a) figure, the final ethylene removal rates under UV conditions were 30.90%, 32.09%, 32.81%, 53.93%, 39.87%, Figure 5 Figure (b). The order of photocatalytic performance of the five samples under visible and UV light is CT-4 > CT-6 > CT-2 > CT-1 > TNS. It can be seen that the CQDs@TiO2 composites with different composite concentrations significantly improve the photocatalytic removal rate of ethylene under visible and UV light conditions, indicating that the incorporation of CQDs helps improve the photocatalytic performance of TNS. When the amount of CQDs solution added is 4mL, the composite material CT-4 achieves an ethylene photocatalytic removal rate of 48.84% under visible light and 53.93% under UV light, ranking it the best among all composite samples. Further increasing the CQDs content to 6mL, the photocatalytic performance of the composite material CT-6 actually decreases, indicating that excessive CQDs concentration can actually cause the CQDs to degrade.

[0086] From the comparison of the photocatalytic removal rates of ethylene under visible light and ultraviolet light conditions, the photocatalytic removal rates of ethylene of all samples under ultraviolet light conditions are higher than those under visible light conditions, and the effect is better. This is because ultraviolet light has a short wavelength and high energy, so the samples absorb more energy under ultraviolet light conditions than visible light, and therefore the photocatalytic removal rate of ethylene is also better.

[0087] 6. Study on the photocatalytic antibacterial properties of TNS and CQDs@TiO2

[0088] (1) Activation of bacterial strains: Use a sterilized inoculation loop to streak the second-generation slant bacterial strains stored at low temperature onto a plate culture medium that has solidified into a white solid, and then place it in a 37°C bacterial incubator for 24 hours to allow it to multiply and grow.

[0089] (2) Preparation of bacterial liquid: Inoculate a single colony into 100 mL of liquid culture medium that has been sterilized by high pressure and cooled to about 40°C. Incubate the culture in a shaker at 37°C and 150 rpm for 8 h. Store the bacterial liquid at low temperature for later use.

[0090] (3) After sterilizing the culture medium, pour 15 mL of the culture medium into the conical flask at about 45°C on the plate. After the culture medium solidifies, draw 0.1 mL of the bacterial solution and pour it on the plate. Use a coating rod to evenly spread the culture medium, and then use a 4 mm punch to punch holes in the culture medium. After punching, pour 10 mg of the sample evenly into the holes of the solidified culture medium, and place it in a 37°C incubator with visible light and ultraviolet light on for 24 hours. The photocatalytic antibacterial activity of the obtained sample is determined by subtracting the size of the punch hole from the size of the inhibition zone.

[0091] The morphological changes of Staphylococcus aureus after contact with bacterial solution were detected by TEM. Figure 6 As shown in Figure 1, (a) shows the smooth and regular morphology of the bacteria before treatment. (b) shows that after treatment, the bacterial morphology has changed significantly, with the outer membrane partially disintegrating. The cytoplasmic matrix has leaked out, and the cell wall boundaries have become blurred and asymmetrical. It can be concluded that its mechanism of action is to induce bacterial cell death by disrupting the biofilm and causing intracellular fluid leakage, thereby exerting its antibacterial effect.

[0092] The antibacterial effect of CT-4 on Staphylococcus aureus, Escherichia coli and Bacillus subtilis under visible light is as follows: Figure 7 The larger the diameter of the inhibition zone, the better the antibacterial effect.

[0093] Table 1 Different materials and the size of the antibacterial diameter

[0094] Group Escherichia coli Staphylococcus aureus Bacillus subtilis a1 0 0 0 b1 6.1 7.0 5.6 c1 10.2 10.8 9.8

[0095] Note: a1 represents stock solution, b1 represents TNS, and c1 represents CT-4.

[0096] Therefore, the CQDs@TiO2 prepared in the present invention has both photocatalytic ethylene production and antibacterial effects, and can be used as a product with both antibacterial and photocatalytic ethylene decomposition functions, such as as a fresh-keeping packaging material for food, especially fruits and vegetables.

[0097] 7. Study on the preservation effect of CQDs@TiO2

[0098] To verify the effect, the present invention blended the modified CQDs nanosheets in Example 4 with polyolefins and used a casting process to prepare a polyethylene-based fresh-keeping film with a thickness of 10nm. Strawberries and Chinese cabbage were used as the preservation test objects. At room temperature of 28°C, the preservation of strawberries was extended by 1 day; at 4°C, the preservation of Chinese cabbage was extended by 9 days. At room temperature of 28°C, ordinary packaged strawberries without functional masterbatch can be stored for 3 days, and fresh-keeping packaged strawberries can be stored for 4 days. Figure 8 As shown in the figure, from the perspective of physical and chemical indicators, the chlorophyll, weight loss rate and solid content of fresh-packed choy sum are significantly better than those of ordinary packaged choy sum, as shown in the figure. Figure 9 As shown in Figures (a), (b) and (c), the overall shelf life can reach more than 15 days, while ordinary packaging begins to turn yellow on the 6th day. Figure 10 shown.

[0099] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, based on the principles of the present invention, optimization, improvement, combination, substitution, etc. of the present invention should be regarded as within the scope of protection of the present invention.

Claims

1. Application of biomass carbon quantum dot modified fresh-keeping materials in fruit and vegetable preservation, characterized in that: The preparation method of the biomass carbon quantum dot modified fresh-keeping material comprises the following steps: (1) The biomass material is ultrafinely ground and heated in a muffle furnace at 290-310° C. for 2-4 hours, and then dispersed in deionized water to obtain a dispersion, and organic small molecules are dissolved in water to obtain an organic small molecule aqueous solution, and the dispersion and the organic small molecule aqueous solution are hydrothermally reacted at 180-200° C. for 6 hours, cooled, and centrifuged to obtain a biomass carbon quantum dot solution; (2) mixing a nano-titanium dioxide precursor and an acidic solution, subjecting the resulting mixture to a high-temperature treatment, naturally cooling the product after the high-temperature treatment, removing a layer of precipitate, washing, drying, and grinding to obtain titanium dioxide nanosheets; (3) ultrasonically dispersing the titanium dioxide nanosheets obtained in step (2) in deionized water, then uniformly mixing with the biomass carbon quantum dot solution obtained in step (1) and ultrasonically treating the mixture, and then high-temperature treating the mixture in an oil bath at 120 to 150° C. The obtained product is centrifuged and washed, and the precipitate is collected and dried to obtain biomass carbon quantum dot-modified titanium dioxide nanosheets having antibacterial and ethylene decomposition functions, i.e., biomass carbon quantum dot-modified fresh-keeping materials; The biomass material in step (1) is litchi peel; The organic small molecule in step (1) is citric acid; The acidic solution in step (2) is a strong acid, and the strong acid is concentrated hydrochloric acid, concentrated sulfuric acid or hydrofluoric acid; The dosage of the titanium dioxide nanosheets and the biomass carbon quantum dot solution in step (3) is 0.1 g: 1 to 6 mL.

2. The use according to claim 1, characterized in that The nano-titanium dioxide precursor in step (2) is one or more of butyl titanate, isopropyl titanate, titanyl sulfate, titanium tetrachloride, titanium trichloride and titanium dioxide P25.

3. The use according to claim 1, characterized in that In step (2), the obtained mixture is subjected to high temperature treatment in a silicone oil bath at 175-185° C. for 23-25 ​​hours.

4. The use according to claim 1, characterized in that In step (3), high temperature treatment is performed in an oil bath at 150° C. for 3 h.

5. The use according to claim 1, characterized in that In step (2) and step (3), the washing was performed with ethanol and deionized water, and the product was dried in an oven at 60° C. for 12 h.

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