Cerium-based organic framework and polymerized carbon nitride photocatalytic composite material as well as preparation method and antibacterial application thereof

Abstract

The invention relates to a cerium-based organic framework and polymerized carbon nitride photocatalytic composite material in the field of antibacterial materials, and a preparation method and antibacterial application thereof. During preparation of the composite material, cerium-containing rare earth metal salt and an organic ligand are dissolved in a polar organic solvent, an isometric ethylene glycol solvent is added, uniform mixing is performed, and the cerium-based organic framework and polymerized carbon nitride photocatalytic composite material is prepared. The yellow Ce-OFDC / PCN composite material is prepared by the following steps: firstly preparing Ce-OFDC powder, then transferring the Ce-OFDC powder into a reaction kettle for reaction, carrying out centrifugal separation and drying to obtain Ce-OFDC powder, then preparing PCN powder from melamine, finally mixing and dissolving the Ce-OFDC powder and the PCN powder in a DMA solution, stirring, then adding an ethylene glycol solution, carrying out reaction again, centrifugally collecting precipitates, washing, and carrying out vacuum drying to obtain the yellow Ce-OFDC / PCN composite material. The material has a good bacteriostatic effect. The method can be widely applied to food packaging, water treatment, air purification, textile cleaning and the like.

Description

Technical Field

[0001] The present invention relates to a photocatalytic composite material, its preparation and its uses, and particularly to a cerium-based organic framework material (Ce-OFDC) and a polymeric carbon nitride (PCN) photocatalytic composite material, its preparation and its uses in the antibacterial field. Background Art

[0002] In recent years, photocatalytic materials have been widely applied in many aspects, including energy, environmental governance, organic synthesis, self-cleaning materials, nitrogen fixation, plastic degradation, etc. In the antibacterial field, due to their green, efficient, economical and environmentally friendly characteristics, photocatalytic materials have gradually become a powerful tool to replace antibiotics for treating bacterial contamination and water pollution. Traditional antibacterial methods such as ultraviolet sterilization will damage the nucleic acid structure of biomolecules, high-temperature sterilization will damage the protein structure, and antibiotics will damage specific physiological processes of microorganisms. However, long-term use has problems such as high energy consumption, low efficiency, and bacteria developing drug resistance, which limit their practical applications and are prone to cause secondary pollution.

[0003] Metal-organic frameworks (MOFs) are low-density porous crystalline materials composed of metal nodes and organic ligands, with high specific surface area, adjustable crystal structure, abundant ligand-unsaturated metal sites, and interchangeable components. They have been widely studied and applied in the fields of gas storage, adsorption and separation, sensing, organic catalysis, photocatalysis, and removal of pollutants in water or gas. The application of MOFs materials in the antibacterial field is also increasing. Compared with traditional antibacterial agents, their easily doped metal components and replaceable organic ligands endow MOFs with the highest occupied molecular orbital and the lowest unoccupied molecular orbital vacancy. Therefore, they can form a variety of photoactive oxygen species (ROS), thus possessing efficient photocatalytic antibacterial performance. In addition, the chelation effect of MOFs reduces the polarity of metal ions and enhances their lipophilicity, which helps to penetrate the bacterial cell membrane and then kill bacteria.

[0004] In the prior art, polymeric carbon nitride (PCN) is a semiconductor photocatalyst with a narrow bandgap, possessing good visible light absorption ability and stability. At the same time, as a photosensitizer, it efficiently generates photogenerated electrons and holes, and then generates a large amount of reactive oxygen species (ROS), such as superoxide radical (·O 2 - ) and hydroxyl radical (·OH), etc., causing oxidative damage to the bacterial cell membrane, proteins and DNA, and achieving efficient sterilization.

[0005] However, for MOFs materials and PCN materials, they both have their deficiencies:

[0006] For MOFs materials

[0007] 1. In terms of photocatalysis:

[0008] 1.1. Weak conductivity: The charge transfer efficiency between organic ligands and metal nodes in MOF materials is relatively low, resulting in inefficient separation of photo-generated electrons and holes, which affects the photocatalytic activity. The electron-hole pairs generated under light are prone to recombination, leading to a decrease in photocatalytic efficiency.

[0009] 1.2. Insufficient stability: It is prone to degradation in water, acid, base or humid environments, structural collapse at high temperatures, and possible photocorrosion under long-term light irradiation, resulting in a decrease in activity.

[0010] 1.3. High synthesis cost: The synthesis of MOFs usually requires expensive organic ligands and metal precursors, and the synthesis process may involve complex processes and long reaction times, resulting in a high synthesis cost.

[0011] 2. In terms of antibacterial properties:

[0012] 2.1. Uncontrollable release rate of metal ions: The antibacterial performance of MOF materials mainly depends on the release of metal ions, but the release rate is difficult to precisely control. Too fast release may cause local toxicity, while too slow release may not be able to effectively kill bacteria.

[0013] 2.2. Limited ability to penetrate biofilms: MOF materials usually have difficulty effectively penetrating the biofilms formed by bacteria, resulting in poor killing effects on bacteria inside the biofilms.

[0014] 2.3. Insufficient antibacterial persistence: After MOF materials release metal ions or generate reactive oxygen species (ROS), their antibacterial activity may gradually weaken, making it difficult to achieve long-term antibacterial effects.

[0015] For PCN materials

[0016] 1. In terms of photocatalysis:

[0017] 1.1. Limited light absorption range: The light absorption of PCN materials is usually concentrated in a narrow range of ultraviolet or visible light, with a low utilization rate of sunlight, which limits its efficiency in photocatalysis.

[0018] 1.2. High recombination rate of photo-generated carriers: The electron-hole pairs generated in PCN materials under light excitation are prone to rapid recombination, resulting in a decrease in photocatalytic activity and affecting its performance in degrading pollutants or producing hydrogen.

[0019] 1.3. Limited catalytic active sites: PCN materials usually have fewer catalytic active sites and are difficult to precisely regulate, which limits their application in complex photocatalytic reactions.

[0020] 2. In terms of antibacterial properties:

[0021] 2.1. Insufficient antibacterial activity: The antibacterial mechanism of the PCN material mainly relies on the reactive oxygen species (ROS) generated by photocatalysis. However, its photocatalytic efficiency is limited, resulting in insufficient generation of ROS and weak antibacterial effect.

[0022] 2.2. Poor selectivity for bacteria: The antibacterial effect of the PCN material may vary significantly for different types of bacteria (such as Gram-positive bacteria and Gram-negative bacteria), lacking broad-spectrum antibacterial properties.

[0023] 2.3. Environmental dependence: The antibacterial performance of the PCN material usually depends on the light conditions (such as ultraviolet light or visible light). In the absence or weak light environment, its antibacterial effect is significantly reduced. Summary of the Invention

[0024] The object of the present invention is to provide a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, its preparation method and antibacterial use, with high photocatalytic antibacterial efficiency, good material stability, simple preparation process and low cost.

[0025] To this end, the technical solution of the present invention is: A preparation method of a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, comprising the following steps:

[0026] S1. Preparation of Ce-OFDC powder:

[0027] Dissolve the rare earth metal salt containing cerium and the organic ligand in the polar organic solvent DMF, add an equal volume of ethylene glycol solvent, mix evenly, transfer the obtained mixed solution to a reaction kettle, heat and react at 100-150 °C for 50-80 hours, cool to room temperature, centrifuge to collect the precipitate, wash and vacuum dry to obtain yellow Ce-OFDC powder;

[0028] S2. Preparation of PCN:

[0029] Spread the melamine powder in an alumina crucible, put it into a programmable temperature furnace, heat up to 550 °C and keep warm for a period of time to obtain PCN powder;

[0030] S3. Preparation of Ce-OFDC / PCN composite material:

[0031] Mix and dissolve the Ce-OFDC powder obtained in step S1 and the PCN powder obtained in step S2 in the DMA solution, stir and then add the ethylene glycol solution, continue to stir evenly, then pour the mixture into a stainless steel autoclave with a polytetrafluoroethylene lining, react at 100-150 °C for 50-80 hours, after the reaction is completed, naturally cool, centrifuge to collect the precipitate, wash it 2-5 times alternately with deionized water and acetone, and vacuum dry to obtain yellow Ce-OFDC / PCN composite material.

[0032] Further, in step S1, the rare earth metal salt containing cerium is cerium acetate, and the organic ligand is 9-fluorenone-2,7-dicarboxylic acid; the weight ratio of cerium acetate to 9-fluorenone-2,7-dicarboxylic acid is (0.68 - 5):1.

[0033] Further, in step S2, in a programmable temperature-controlled furnace, it is heated to 550 °C at a heating rate of 5 °C / min and held for 4 hours to obtain PCN powder.

[0034] Further, in step S3, the weight ratio of Ce-OFDC powder to PCN powder is (0.8 - 1.2):1. Preferably, the weight ratio of Ce-OFDC powder to PCN powder is 1:1.

[0035] The cerium-based organic framework and polymeric carbon nitride photocatalytic composite material prepared according to the above method can be used for antibacterial of Escherichia coli or Staphylococcus aureus. Its antibacterial effect is better than the antibacterial rate of single PCN or Ce-OFDC material.

[0036] In the present invention, a novel cerium-based organic framework material (Ce-OFDC) is synthesized by a hydrothermal method and compounded with polymeric carbon nitride (PCN) to form a Ce-OFDC / PCN heterojunction composite material. Under visible light irradiation, an internal electric field can be formed at the interface of Ce-OFDC and PCN, so that the conduction band electrons of PCN can be transferred to the conduction band of Ce-OFDC through this internal electric field. At the same time, the holes in the valence band of Ce-OFDC can be transferred to the valence band of PCN through this internal electric field, thereby effectively separating photogenerated electrons and holes, and generating a large number of reactive oxygen species (ROS) at the valence band end of Ce-OFDC, such as superoxide anion (·O2-) and hydroxyl radical (·OH). These high-energy reactive oxygen species can damage the cell membrane of bacteria, resulting in the death of bacteria.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. Significantly improve the antibacterial efficiency. The antibacterial efficiency of existing photocatalytic materials is relatively low, especially the antibacterial effect under visible light conditions is not ideal. The inhibition rate of single PCN against Escherichia coli is 47.5%, and that of Ce-OFDC is 78.6%. While the inhibition rates of the Ce-OFDC / PCN composite material against Escherichia coli and Staphylococcus aureus reach 99.5% and 94.3% respectively.

[0039] 2. Solve the problem of high recombination rate of photogenerated carriers:

[0040] The recombination rate of photo-generated electrons and holes in photocatalytic materials is relatively high, resulting in low photocatalytic efficiency. The recombination rate of photo-generated carriers in single PCN and Ce-OFDC materials is relatively high, while the Ce-OFDC / PCN composite material significantly reduces the recombination rate of photo-generated electrons and holes and improves the photocatalytic activity by forming a heterojunction structure.

[0041] 3. Solve the problem of narrow light absorption range:

[0042] The light absorption range of existing photocatalytic materials is relatively narrow, mainly limited to the ultraviolet region, and the utilization rate of visible light is low. The Ce-OFDC / PCN composite material expands the light absorption range and enhances the absorption ability of visible light by forming a heterojunction, thereby improving the photocatalytic efficiency.

[0043] 4. Solve the problem of insufficient generation amount of reactive oxygen species (ROS):

[0044] The amount of reactive oxygen species (such as ·OH and ·O 2 - ) generated by existing photocatalytic materials during the photocatalytic process is insufficient, which affects their antibacterial effect. The Ce-OFDC / PCN composite material significantly increases the generation amount of reactive oxygen species by improving the separation efficiency of photo-generated carriers, thereby enhancing the antibacterial performance.

[0045] 5. Solve the problem of poor material stability:

[0046] Existing photocatalytic materials have poor stability under long-term light irradiation or in complex environments, and are prone to photocorrosion or structural damage. The Ce-OFDC / PCN composite material shows good stability in photocatalytic experiments and can be recycled multiple times without significantly reducing its performance.

[0047] 6. Solve the problems of complex material preparation and high cost:

[0048] The preparation process of existing photocatalytic materials is complex and the cost is high, making it difficult to achieve large-scale application. The Ce-OFDC / PCN composite material was synthesized by a hydrothermal method in this invention, which simplifies the preparation process and demonstrates its potential for large-scale application.

[0049] The photocatalytic composite material obtained in this invention can be applied to surface modification in the field of materials science, such as coating photocatalytic antibacterial coatings on the surfaces of medical devices, building materials, etc. Metal-organic framework (MOFs) materials are applied to the design of porous structural materials because of their high porosity and adsorption ability, which can effectively improve the photocatalytic antibacterial performance. In the field of photocatalytic antibacterial, it can be widely applied to food packaging, water treatment, air purification, textile cleaning, etc. Brief Description of the Drawings

[0050] Figure 1: Schematic diagram of the antibacterial principle of Ce-OFDC / PCN composite materials.

[0051] Figure 2 : Schematic diagram of the photo-generated electron-hole recombination.

[0052] Figure 3 : Technical roadmap for the synthesis and characterization of Ce-OFDC / PCN composite materials.

[0053] Figure 4 : SEM and TEM images of Ce-OFDC, PCN, and Ce-OFDC / PCN, showing the morphology and element distribution of the materials.

[0054] Figure 5 : XRD and FT-IR spectra of Ce-OFDC, PCN, and Ce-OFDC / PCN, showing the crystal structure and chemical bonds of the materials.

[0055] Figure 6 : XPS spectra of Ce-OFDC, PCN, and Ce-OFDC / PCN, showing the surface element composition and chemical state of the materials.

[0056] Figure 7 : Photocurrent response, electrochemical impedance spectroscopy, UV-visible absorption spectroscopy, and photoluminescence spectroscopy of Ce-OFDC, PCN, and Ce-OFDC / PCN, showing the photoelectrochemical properties of the materials.

[0057] Figure 8 : Antibacterial effects of Ce-OFDC / PCN composite materials against Escherichia coli and Staphylococcus aureus.

[0058] Figure 9 : Antibacterial rates of Ce-OFDC / PCN composite materials under different light conditions.

[0059] Figure 10 : EPR spectra of Ce-OFDC, PCN, and Ce-OFDC / PCN under visible light, showing the generation of reactive oxygen species.

[0060] Figure 11 : Experimental results of the scavenging of reactive oxygen species by Ce-OFDC / PCN composite materials. Specific implementation manners

[0061] Example 1

[0062] A preparation method of a cerium-based metal-organic framework and polymeric carbon nitride photocatalytic composite material is carried out according to the following steps:

[0063] S1. Preparation of Ce-OFDC powder:

[0064] Dissolve 0.276 g of cerium acetate and 0.108 g of 9-fluorenone-2,7-dicarboxylic acid in 24 mL of DMF solution and stir for 1 hour. Then add 24 mL of ethylene glycol solution and continue stirring for 1 hour. Transfer the mixture solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 110 °C for 72 hours. After the reaction is completed, the system is naturally cooled to room temperature, the precipitate is collected by centrifugation, washed 3 times with deionized water and acetone, and then dried under vacuum for 12 hours to obtain the target yellow Ce-OFDC powder.

[0065] S2. Preparation of PCN powder:

[0066] Evenly spread 10 g of melamine powder in an alumina crucible, place it in a programmable temperature-controlled furnace, heat it to 550 °C at a heating rate of 5 °C / min, and hold for 4 hours to obtain PCN powder.

[0067] S3. Preparation of Ce-OFDC / PCN composite:

[0068] Weigh 2 g each of Ce-OFDC and PCN powders and dissolve them in 24 mL of DMA solution, stir for 1 hour, then add 24 mL of ethylene glycol solution, continue stirring for 1 hour, and then pour the mixture into a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 110 °C for 72 hours. After the reaction is completed, it is naturally cooled, the precipitate is collected by centrifugation, washed 3 times alternately with deionized water and acetone, and dried under vacuum for 12 hours to obtain the Ce-OFDC / PCN composite.

[0069] Antibacterial experiment:

[0070] Inoculate Escherichia coli and Staphylococcus aureus into conical flasks containing 30 mL of liquid medium respectively and culture them in a constant temperature shaker at 37 °C and 170 r / min for 12 hours. Dilute the bacterial solution 100 times, take 0.01 g of the photocatalytic material and disperse it in 1 mL of water to make a 10 mg / mL aqueous dispersion. Add 10 μL of the photocatalytic material aqueous dispersion and 990 μL of the bacterial solution to a 24-well plate to obtain a 100 μg / mL suspension. The experiment is divided into a blank group, a dark control group and a light irradiation group. The light irradiation group uses a xenon lamp as the light source (light intensity 150 mW / cm 2 ), after the experiment is completed, dilute the bacterial suspension 10 4 times, evenly coat it on the surface of the solid medium, culture it at 37 °C for 36 hours, and calculate the bacterial survival rate. The results are shown in Table 1:

[0071] Table 1: Comparison table of antibacterial rates of Ce-OFDC, PCN and Ce-OFDC / PCN

[0072] Serial number Sample Antibacterial rate (%) 1 Ce-OFDC + E.coil 78.6 2 PCN + E.coil 47.5 3 Ce-OFDC / PCN + E.coil 99.5 4 Ce-OFDC + S.aureus 85.5 5 PCN + S.aureus 76.5 6 Ce-OFDC / PCN + S.aureus 94.3

[0073] The results in the above table show that the Ce-OFDC / PCN composite material has high antibacterial performance. When the weight ratio of Ce-OFDC to PCN is 1:1, the inhibition rates against Escherichia coli and Staphylococcus aureus are the best, reaching 98.6% and 94.3% respectively, which are significantly better than those of single Ce-OFDC or PCN materials.

[0074] Figures 1 - 11 In it, the following results can be seen:

[0075] Figure 1 、 2 : Under visible light irradiation, an internal electric field can be formed at the interface of Ce-OFDC and PCN in this material, which promotes the transfer of electrons in the conduction band of PCN to the conduction band of Ce-OFDC through this internal electric field. At the same time, the holes in the valence band of Ce-OFDC can be transferred to the valence band of PCN through this internal electric field, effectively separating photo-generated electrons and holes, and generating a large number of reactive oxygen species (ROS) at the valence band end of Ce-OFDC, such as superoxide anion (·O 2 - ₂) and hydroxyl radical (·OH). These high-energy reactive oxygen species can damage the cell membrane of bacteria, leading to the death of bacteria.

[0076] Figure 3 : The technical roadmap of the research in this patent. First, the Ce–OFDC / PCN composite material is synthesized, then the composite material is characterized, the synthesis ratio of the material is adjusted according to the characterization results, and then the antibacterial experiment is carried out. Finally, based on the results of all the above experiments, the speculation on the antibacterial mechanism of the research material is carried out.

[0077] Figure 4 : (a) SEM images of Ce–OFDC, (b) PCN, (c) Ce–OFDC / PCN; (d) TEM images of Ce–OFDC, (e) PCN, (f) Ce–OFDC / PCN and (g–k) elemental mapping images of Ce–OFDC / PCN. (a) and (d) show that Ce–OFDC has a typical MOF structure, consisting of a layer of flakes, forming a layered framework. (b) and (e) show that the surface of PCN is a smooth multi-layered block structure. (c) and (f) show that the layered Ce–OFDC and layered PCN are stacked on each other to form the Ce–OFDC and PCN composite material. The results of the mapping images in (e) further show that Ce, O, and N elements are evenly distributed on the surface and bulk region of Ce–OFDC / PCN. It can be inferred that the Ce–OFDC / PCN photocatalyst was successfully prepared by a simple in-situ hydrothermal synthesis.

[0078] Figure 5: (a) XRD patterns of Ce–OFDC, PCN, and Ce-OFDC / PCN; (b) FT-IR spectra of Ce–OFDC, PCN, and Ce-OFDC / PCN. Characteristic peaks of Ce–OFDC appeared at 6.12° and 12.2°. No other impurity peaks were found in the diffraction patterns of the composites, indicating that these samples are pure Ce–OFDC / PCN composites without the presence of other phases. The intensity of the PCN characteristic peaks in all composite samples was significantly higher than that of the Ce–OFDC characteristic peaks. In these diffraction patterns, the PCN signal always dominated, but as the content of Ce–OFDC increased, the intensity of the Ce–OFDC characteristic peaks also increased. To further determine the internal structure and chemical bonding of the semiconductor photocatalyst, Fourier transform infrared spectroscopy (FT-IR) tests were also conducted on the samples. Figure 5 b shows the FT-IR spectra of Ce–OFDC, PCN, and Ce–OFDC / PCN. As the PCN loading increased, the intensity of all peaks increased slightly, indicating that interactions were formed between the PCN nanosheets and Ce–OFDC nanoparticles, and these nanosheets and nanoparticles were successfully compounded.

[0079] Figure 6 : XPS elemental analysis of Ce–OFDC, PCN, and Ce-OFDC / PCN. Figure 6 a shows the high-resolution spectrum of C1s. Ce–OFDC had three peaks at 288.43, 285.63, and 284.83 eV, corresponding to O–C=O, O–C–O, and C–C bonds, respectively. PCN had two peaks at 288.33 and 284.80 eV, representing C–N and C–C bonds, respectively. Ce–OFDC / PCN had four peaks at 288.38, 286.33, and 284.78 eV, and each peak had different degrees of shift, indicating that the introduction of PCN had a significant impact on the Ce–OFDC framework. Figure 6 b shows the high-resolution spectrum of Ce, which was fitted into 10 peaks after peak deconvolution. Figure 6 As can be seen from 1 b, the six peaks labeled as V 4 , V 5 , U, U 2 and U 3 corresponded to Ce 4+ ions, while the four peaks labeled as V, V 2 , V 3 and U 1 were related to trivalent cerium ions. Through calculation using the reference formula, the concentration of [Ce 3+ in Ce–OFDC / PCN was 35.8%, while in Ce–OFDC it was 41.5%. [Ce3+ The difference in content proves the strong interaction between Ce–OFDC and PCN in Ce–OFDC / PCN. Figure 6 c shows the high-resolution XPS spectrum of O1s. The binding energy values of O1s in Ce–OFDC are 533.12, 531.41, and 529.39 eV, corresponding to C–O, C=O, and Ce–O bonds respectively. The appearance of Ce–O reveals the effective coordination between Ce ions and H 2 OFDC ligands and the existence of the –COO–Ce functional framework. In addition, each peak of Ce–OFDC / PCN shifts towards a lower binding energy direction after deconvolution and peak processing. Figure 6 d shows the N1s spectrum, which can be divided into 3 peaks. The main peak is located at 398.7 eV, corresponding to sp 2 –N (pyridine N) in the heterocycle (C–N=C). The peak at 400.2 eV is attributed to pyrrole N, while the peak at 401.4 eV is attributed to graphitic N [29 - 30]. The above 3 peaks of Ce–OFDC / PCN are located at 398.28, 399.78, and 401.03 eV respectively. The XPS test results indicate that there is a strong interaction between Ce–OFDC and PCN, which is highly consistent with the above TEM, XRD, and FT-IR results.

[0080] Figure 7 : (a) Transient photocurrent response, (b) EIS Nyquist plot, (c) UV–vis spectrum, (d) Band gap structure diagram of Ce–OFDC and PCN, (e) PL spectrum, (f) TRPL spectrum of Ce–OFDC, PCN, and Ce–OFDC / PCN. As Figure 7 shown in a, the photocurrent of Ce–OFDC / PCN reaches 1.2 μA / cm 2 , which are 1.5 times and 12 times that of PCN (0.8 μA / cm 2 ) and Ce–OFDC (0.1 μA / cm 2 ) respectively. This indicates that the composite material has enhanced light absorption ability, resulting in an increase in the generation of photoexcited electron-hole pairs and higher separation and transport efficiency. Figure 7 b shows the Nyquist plots of Ce–OFDC, PCN, and Ce–OFDC / PCN. The Nyquist radius of Ce–OFDC / PCN is smaller than that of Ce–OFDC and PCN, indicating that the resistance of electron-hole migration in the composite material is lower, thus enabling faster separation of photoexcited electrons and holes. The electron-hole separation and photocurrent response of the heterojunction material are superior to those of Ce–OFDC and PCN. This enhanced electron transfer efficiency helps increase the generation of free radicals, thereby potentially improving the photocatalytic antibacterial efficiency. Figure 7c shows the ultraviolet-visible diffuse reflectance spectra used to analyze the optical response and bandgap of the research materials. This redshift indicates an enhanced light absorption ability of the composite due to the formation of the heterojunction, and the introduction of Ce–OFDC extends the visible light absorption range. Based on the absorption spectra, the bandgaps of PCN and Ce–OFDC are determined to be 2.65 eV and 2.49 eV, respectively. Both PCN and Ce–OFDC show a negative slope, indicating n-type semiconductor behavior. Empirically, the conduction band edge of an n-type semiconductor is approximately 0.2 to 0.3 V more negative than the flat-band potential. Using the formula described in the literature, the conduction band edge values of PCN and Ce–OFDC relative to the standard hydrogen electrode are estimated to be –0.89 V and –0.34 V, respectively. The valence band potentials of PCN and Ce–OFDC are calculated to be 1.76 eV and 2.15 eV, respectively. Combining these results with the bandgaps obtained from the ultraviolet-visible analysis (2.65 eV for PCN and 2.49 eV for Ce–OFDC), a band energy diagram ( Figure 7 d) is constructed. The efficiency of the recombination of photo-generated electrons (e - ) and holes (h + ) plays a key role in photocatalytic activity. The recombination rate of e - and h + is evaluated using photoluminescence (PL) spectroscopy ( Figure 7 f). Pure PCN shows the highest emission peak at approximately 514 nm, indicating a relatively high recombination rate of photo-excited carriers, resulting in lower photocatalytic activity. When PCN forms a complex with Ce–OFDC, the intensity of the emission peak decreases significantly, which is attributed to the formation of the Ce–OFDC / PCN heterojunction, improving carrier migration and reducing the electron-hole recombination rate.

[0081] Figure 8 9 : (a), (e) represent the numbers of Escherichia coli and Staphylococcus aureus in the control group medium, (b), (f) represent the numbers of Escherichia coli and Staphylococcus aureus in the medium added with Ce–OFDC, (c), (g) represent the numbers of Escherichia coli and Staphylococcus aureus in the medium added with PCN, and (d), (h) represent the numbers of Escherichia coli and Staphylococcus aureus in the medium added with the Ce–OFDC / PCN heterojunction. It is experimentally observed that after the heterojunction is formed by the combination of PCN and Ce–OFDC, the inhibition rate against Escherichia coli is significantly improved (up to 99.5%), and the inhibition rate against Staphylococcus aureus is also significantly improved (up to 94.3%). Overall, the Ce–OFDC / PCN composite material exhibits the best antibacterial performance.

[0082] Figure 10 ​:(a) Detection of superoxide radicals in the EPR spectra of Ce–OFDC, PCN, and Ce-OFDC / PCN, (b) Detection of hydroxyl radicals in the EPR spectra of Ce–OFDC, PCN, and Ce-OFDC / PCN. The signal peaks of Ce–OFDC / PCN are stronger than those of Ce–OFDC and PCN, indicating that Ce–OFDC / PCN generates a higher concentration of ·O 2 - and ·OH during the antibacterial process. This is attributed to the heterojunction structure of the composite material, which improves the separation efficiency of photo-generated carriers, thereby generating more reactive oxygen species (ROS).

[0083] Figure 11 : Since the generation of ROS is the main antibacterial mechanism of the photocatalyst in this study, the antibacterial mechanism of Ce–OFDC / PCN against Escherichia coli (E. coli) under light illumination was investigated through gradient experiments ( Figure 11 ). The results of ROS inhibition were demonstrated by introducing different types of ROS scavengers in the experiment. In the absence of the test sample, the addition of reactive oxygen species scavengers such as glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and D-mannitol had little effect on bacterial activity. However, when these reagents were added to the bacterial solution containing the Ce–OFDC / PCN complex, the bacterial activity was affected to varying degrees. Obviously, the antibacterial rate of Ce–OFDC / PCN without the addition of scavengers was 97.3% ( Figure 11 f). After adding GSH to remove all ROS, the antibacterial rate of Ce–OFDC / PCN decreased significantly by 40% ( Figure 11 b). These results indicate that the composite material does generate ROS and plays an important role in its antibacterial mechanism. After introducing D-mannitol into the Ce–OFDC / PCN suspension to scavenge ·OH, the inhibition rate decreased to 54.7% ( Figure 11 c). Similarly, after adding SOD to remove ·O 2 - , the inhibition rate decreased to 65.4% ( Figure 11 d). This indicates that ·OH and ·O 2 - are the key reactive species in the antibacterial mechanism, and their relatively long lifetimes enable them to diffuse from the active sites to the surface of target cells. On the other hand, when CAT was added to eliminate H 2 O 2 , the inhibition rate decreased to 85.4% ( Figure 11 e), indicating that H 2 O 2 has a weaker effect on inhibiting bacteria. Hydrogen peroxide is relatively stable and is an intermediate species in the transformation of ROS. It needs to penetrate the cell membrane to hinder cell activity. Therefore, H 2O 2 is less efficient than ·OH and ·O 2 - Although H 2 O 2 can be converted to ·OH, its low yield and extremely short lifespan limit its antibacterial effect. In summary, the experiments with scavengers added show that ·OH and ·O 2 - are the main factors affecting the antibacterial properties of the composite material, while H 2 O 2 plays a secondary role in the antibacterial mechanism of Ce–OFDC / PCN.

[0084] Example 2

[0085] On the basis of Example 1, only change the weight ratio of cerium acetate and 9-fluorenone-2,7-dicarboxylic acid in step S1, and conduct the experiment again. The results are shown in Table 2 as follows:

[0086] Table 2: Comparison table of antibacterial rates of Ce-OFDC, PCN and Ce-OFDC / PCN Table 2

[0087]

[0088]

[0089] The results in the above table show that when the weight ratio of cerium acetate and 9-fluorenone-2,7-dicarboxylic acid is (0.68 - 5):1, it has good antibacterial effect. When the weight ratio of cerium acetate and 9-fluorenone-2,7-dicarboxylic acid is 2.5:1, the inhibition rates against Escherichia coli and Staphylococcus aureus are the best.

[0090] Example 3

[0091] On the basis of Example 1, only change the weight ratio of Ce-OFDC powder and PCN powder in step S3, and conduct the experiment again. The results are shown in Table 3 as follows:

[0092] Table 3: Comparison table of antibacterial rates of Ce-OFDC, PCN and Ce-OFDC / PCN Table 3

[0093]

[0094] The results in the above table show that when the weight ratio of Ce-OFDC to PCN is (0.8 - 1.2):1, it has good antibacterial effect. When the weight ratio of Ce-OFDC to PCN is 1:1, the inhibition rates against Escherichia coli and Staphylococcus aureus are the best.

[0095] The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative labor according to the disclosed technical content, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A method for preparing a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, characterized in that: The steps include: S1. Preparation of Ce-OFDC powder: The cerium-containing rare earth metal salt and the organic ligand are dissolved in a polar organic solvent DMF, an equal volume of ethylene glycol solvent is added, and after being mixed evenly, the resulting mixed solution is transferred to a reactor, heated at 100-150° C. for reaction for 50-80 hours, cooled to room temperature, and the precipitate is collected by centrifugation, washed, and vacuum dried to obtain a yellow Ce-OFDC powder; S2. Preparation of PCN: The melamine powder was spread in an alumina crucible, placed in a programmable temperature-controlled furnace, heated to 550°C, and kept warm for a period of time to obtain PCN powder; Preparation of S3, Ce-OFDC / PCN composite materials: The Ce-OFDC powder obtained in step S1 and the PCN powder obtained in step S2 are mixed and dissolved in a DMA solution, and ethylene glycol solution is added after stirring, and the stirring is continued to be uniform. Then, the mixture is poured into a stainless steel autoclave with a polytetrafluoroethylene liner, and reacted at 100-150° C. for 50-80 hours. After the reaction is completed, it is naturally cooled, and the precipitate is collected by centrifugation, washed alternately with deionized water and acetone for 2-5 times, and vacuum dried to obtain a yellow Ce-OFDC / PCN composite material.

2. The method for preparing a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 1, characterized in that: In step S1, the cerium-containing rare earth metal salt is cerium acetate, and the organic ligand is 9-fluorenone-2,7-dicarboxylic acid; the weight ratio of the cerium acetate to 9-fluorenone-2,7-dicarboxylic acid is (0.68-5):

1.

3. The method for preparing a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 1, characterized in that: In step S2, in a programmable temperature-controlled furnace, the temperature is heated to 550°C at a heating rate of 5°C / min and maintained for 4 hours to obtain PCN powder.

4. The method for preparing a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 1, characterized in that: In step S3, the weight ratio of Ce-OFDC powder to PCN powder is (0.8-1.2):

1.

5. The method for preparing a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 4, characterized in that: In step S3, the weight ratio of Ce-OFDC powder to PCN powder is 1:

1.

6. A cerium-based organic framework and polymeric carbon nitride photocatalytic composite material prepared according to the method of any one of claims 1 to 5.

7. The use of the cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 6, characterized in that: Used for antibacterial treatment of Escherichia coli or Staphylococcus aureus.

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