A cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, a preparation method thereof and antibacterial use

Abstract

The present application relates to the field of bacteriostatic material, and discloses a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, a preparation method thereof and antibacterial application. When the composite material is prepared, a rare earth metal salt containing cerium and an organic ligand are dissolved in a polar organic solvent, an equal volume of ethylene glycol solvent is added, and then the mixture is uniformly mixed and transferred to a reaction kettle for reaction. After centrifugal separation and drying, Ce-OFDC powder is obtained. Then, PCN powder is prepared by using melamine. Finally, the Ce-OFDC powder and the PCN powder are mixed and dissolved in a DMA solution, and then ethylene glycol solution is added after stirring. After reaction, the precipitate is collected by centrifugation, washed and vacuum dried to obtain a yellow Ce-OFDC / PCN composite material. The material has good bacteriostatic effect. The material can be widely applied to food packaging, water treatment, air purification, textile cleaning and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of photocatalytic composite material, its preparation and its use, especially it relates to a kind of cerium-based organic framework material (Ce-OFDC) and polymeric carbon nitride (PCN) photocatalytic composite material, its preparation and its use in antibacterial field. BACKGROUND

[0002] In recent years, photocatalytic materials are widely used, covering energy, environmental management, organic synthesis, self-cleaning materials, nitrogen fixation, plastic degradation and other aspects. In the field of antibacterial, photocatalytic materials gradually become a powerful tool to replace antibiotics to treat bacterial pollution and water pollution due to their green, efficient, economical and environmentally friendly characteristics. Traditional antibacterial methods such as ultraviolet sterilization can damage the nucleic acid structure of biological molecules, high-temperature sterilization can damage the protein structure, and antibiotics can damage the specific physiological processes of microorganisms, but long-term use has problems such as high energy consumption, low efficiency, and bacterial resistance, limiting their practical application and easily causing 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 and controllable crystal structure, rich unsaturated metal sites of ligands, and interchangeable components, which have been widely studied and applied in gas storage, adsorption and separation, sensing, organic catalysis, photocatalysis, and removal of pollutants in water or gas. The application of MOFs materials in the field of antibacterial is also increasing. Compared with traditional antibacterial agents, the easily doped metal components and replaceable organic ligands of MOFs give them the highest occupied molecular orbital and the lowest unoccupied molecular orbital vacancy, so they can form various reactive oxygen species (ROS) and have high 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 kill bacteria.

[0004] In the prior art, polymeric carbon nitride (PCN) is a semiconductor photocatalyst with a narrow band gap, which has good visible light absorption capacity and stability. At the same time, as a photosensitizer, it efficiently generates photo-generated electrons and holes, and then generates a large amount of reactive oxygen (ROS), such as superoxide radical (·O2 - ), hydroxyl radical (·OH), etc., causing oxidative damage to bacterial cell membranes, proteins and DNA, achieving efficient sterilization.

[0005] However, MOFs materials and PCN materials have their own shortcomings:

[0006] For MOFs materials

[0007] 1. In the aspect of photocatalysis:

[0008] 1.1, Weak conductivity: The charge transfer efficiency between the organic ligand and the metal node in MOFs materials is low, which leads to low separation efficiency of photo-generated electrons and holes, affecting the photocatalytic activity. The electron-hole pairs generated under light are prone to recombination, which can reduce the photocatalytic efficiency.

[0009] 1.2, Insufficient stability: Easily degraded in water, acid, base or humid environment, structure collapse at high temperature, possible photo-corrosion under long-term light, leading to decreased activity.

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

[0011] 2, In terms of antibacterial:

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

[0013] 2.2, Limited penetration ability to biofilm: MOFs materials are usually difficult to effectively penetrate the biofilm formed by bacteria, resulting in poor killing effect on bacteria in the biofilm.

[0014] 2.3, Insufficient antibacterial durability: The antibacterial activity of MOFs materials may gradually weaken after releasing metal ions or generating reactive oxygen species (ROS), making it difficult to achieve long-term antibacterial effect.

[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 low utilization rate of sunlight, limiting its efficiency in photocatalysis.

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

[0019] 1.3, Limited catalytic active sites: The catalytic active sites of PCN materials are usually limited and difficult to accurately control, limiting its application in complex photocatalytic reactions.

[0020] 2, In terms of antibacterial:

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

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

[0023] 2.3 Environmental dependence: The antibacterial performance of PCN materials usually depends on light conditions (such as ultraviolet light or visible light), and its antibacterial effect is significantly reduced in the absence of light or weak light. SUMMARY

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

[0025] To this end, the technical solution of the present application 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 cerium-containing rare earth metal salt and organic ligand in the polar organic solvent DMF, add an equal volume of ethylene glycol solvent, mix uniformly, then transfer the obtained mixed solution to a reaction kettle, heat at 100-150℃ 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 and place it in a program-controlled temperature furnace, heat to 550℃ and keep for a period of time to obtain PCN powder;

[0030] S3, preparation of Ce-OFDC / PCN composite material:

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

[0032] Further, 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 the 9-fluorenone-2,7-dicarboxylic acid is (0.68-5):1.

[0033] Further, in step S2, the PCN powder is obtained by heating to 550 DEG C at a heating rate of 5 DEG C / min in a program-controlled furnace and keeping for 4 hours.

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

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

[0036] The application synthesizes a new type of Ce-based organic framework material (Ce-OFDC) by a hydrothermal method, and the Ce-OFDC is compounded with a polymer carbon nitride (PCN) to form a Ce-OFDC / PCN heterojunction composite material. Under visible light irradiation, the material can form an internal boundary electric field at the interface of the Ce-OFDC and the PCN, so that the PCN conduction band electrons can be transferred to the Ce-OFDC conduction band through the internal boundary electric field. At the same time, the holes on the Ce-OFDC valence band can be transferred to the PCN valence band through the internal boundary electric field, so as to effectively separate the photo-generated electrons and holes, and generate a large amount of active oxygen species (ROS) such as superoxide anion (·O2-) and hydroxyl radical (·OH) at the end of the Ce-OFDC valence band. The high-energy active oxygen species can destroy the cell membrane of bacteria and cause the death of bacteria.

[0037] Compared with the prior art, the application has the beneficial effects that:

[0038] 1. The antibacterial efficiency is significantly improved. The antibacterial efficiency of the existing photocatalytic material is low, especially the antibacterial effect under visible light is not ideal. The inhibition rate of single PCN on E. coli is 47.5%, and the inhibition rate of Ce-OFDC is 78.6%. However, the inhibition rates of the Ce-OFDC / PCN composite material on E. coli and S. aureus are 99.5% and 94.3%, respectively.

[0039] 2. The problem of high recombination rate of photo-generated carriers is solved.

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

[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 capacity of visible light by forming a heterojunction, thereby improving the photocatalytic efficiency.

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

[0044] The amount of reactive oxygen species (such as ·OH and ·O2 - ) generated during the photocatalytic process of existing photocatalytic materials is insufficient, affecting its antibacterial effect. The Ce-OFDC / PCN composite material significantly increases the generation 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] The stability of existing photocatalytic materials under long-term light or complex environment is poor, and they are prone to photo-corrosion or structural damage. The Ce-OFDC / PCN composite material exhibits good stability in photocatalytic experiments and can be used repeatedly without significantly reducing performance.

[0047] 6. Solve the problem 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 is synthesized by hydrothermal method, which simplifies the preparation process and demonstrates its potential for large-scale application.

[0049] The photocatalytic composite material obtained by the present application can be applied in the field of material science, such as surface modification, such as coating photocatalytic antibacterial coating on the surface of medical devices, building materials, etc. Metal organic framework (MOFs) materials can be effectively applied to the design of porous structure materials due to their high porosity and adsorption capacity, which can effectively improve the photocatalytic antibacterial performance. In the field of photocatalytic antibacterial, it can be widely used in food packaging, water treatment, air purification, textile cleaning, etc. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1: Ce-OFDC / PCN composite material antibacterial principle diagram.

[0051] Figure 2 : Schematic diagram of photoelectron-hole recombination.

[0052] Figure 3 : Ce-OFDC / PCN composite material synthesis and characterization technical roadmap.

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

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

[0055] Figure 6 : Ce-OFDC, PCN and Ce-OFDC / PCN XPS spectra show the surface elemental composition and chemical state of the material.

[0056] Figure 7 : Ce-OFDC, PCN and Ce-OFDC / PCN photocurrent response, electrochemical impedance spectroscopy, UV-Vis absorption spectrum and photoluminescence spectrum show the photoelectrochemical properties of the material.

[0057] Figure 8 : Ce-OFDC / PCN composite material antibacterial effect on Escherichia coli and Staphylococcus aureus.

[0058] Figure 9 : Ce-OFDC / PCN composite material antibacterial rate under different light conditions.

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

[0060] Figure 11 : Ce-OFDC / PCN composite material reactive oxygen species scavenging experiment results. DETAILED DESCRIPTION

[0061] Example 1

[0062] A preparation method of a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material is carried out as follows:

[0063] S1, preparation of Ce-OFDC powder:

[0064] Ce-OFDC / PCN composite material was prepared by the following steps: 2 grams of Ce-OFDC and PCN powders were weighed and dissolved in 24 mL of DMA solution, stirred for 1 hour, then 24 mL of ethylene glycol solution was added, and stirring was continued for 1 hour. The mixture was then poured into a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 110°C for 72 hours. After the reaction was completed, it was naturally cooled, the precipitate was collected by centrifugation, and it was washed with deionized water and acetone alternately for 3 times, and then dried in vacuum for 12 hours to obtain the Ce-OFDC / PCN composite material.

[0065] S2, Preparation of PCN powder:

[0066] 10 grams of melamine powder was evenly spread in an alumina crucible, and was heated to 550°C at a heating rate of 5°C / min in a program-controlled furnace, and was kept for 4 hours to obtain PCN powder.

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

[0068] 2 grams of Ce-OFDC and PCN powders were weighed and dissolved in 24 mL of DMA solution, stirred for 1 hour, then 24 mL of ethylene glycol solution was added, and stirring was continued for 1 hour. The mixture was then poured into a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 110°C for 72 hours. After the reaction was completed, it was naturally cooled, the precipitate was collected by centrifugation, and it was washed with deionized water and acetone alternately for 3 times, and then dried in vacuum for 12 hours to obtain the Ce-OFDC / PCN composite material.

[0069] Antibacterial experiment:

[0070] E. coli and S. aureus were inoculated into conical flasks containing 30 mL of liquid medium, respectively, and cultured in a constant temperature shaker at 37°C and 170 r / min for 12 hours. The bacterial solution was diluted 100 times, 0.01 g of photocatalytic material was dispersed in 1 mL of water to prepare a water dispersion of 10 mg / mL. 10 μL of photocatalytic material water dispersion and 990 μL of bacterial solution were added to a 24-well plate to obtain a suspension of 100 μg / mL. The experiment was divided into blank group, dark control group and light group. Xenon lamp was used as light source (light intensity 150 mW / cm 2 ), after the experiment, the bacterial suspension was diluted 10 4 times, evenly coated on the surface of solid medium, and cultured at 37°C for 36 hours, and the survival rate of bacteria was calculated. The results are shown in Table 1:

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

[0072] Serial number Sample Antibacterial rate (%) 1 Ce-OFDC + E. coli 78.6 2 PCN + E. coli 47.5 3 Ce-OFDC / PCN + E. coli 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 of the above table show that the Ce-OFDC / PCN composite material has high-efficiency antibacterial performance, and when the weight ratio of Ce-OFDC and PCN is 1:1, the inhibition rates of 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 material.

[0074] Figure 1-11 In the middle, the following results can be seen:

[0075] Figure 1 , 2 : Under visible light irradiation, the material can form an internal boundary electric field 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 the internal boundary electric field. At the same time, the holes on the valence band of Ce-OFDC can be transferred to the valence band of PCN through the internal boundary electric field, thereby effectively separating the photo-generated electrons and holes, and generating a large number of active oxygen species (ROS) such as superoxide anion (·O2 - ) and hydroxyl radical (·OH) at the valence band end of Ce-OFDC. These high-energy active oxygen species can destroy the cell membrane of bacteria, leading to the death of bacteria.

[0076] Figure 3 : The technical roadmap of the patent is studied. First, Ce-OFDC / PCN composite material is synthesized, then the composite material is characterized, and the proportion of material synthesis is adjusted according to the characterization results, and then antibacterial experiment is carried out. Finally, according to the results of all the above experiments, the antibacterial mechanism of the material is speculated.

[0077] Figure 4 : (a) Ce-OFDC, (b) PCN, (c) SEM images of Ce-OFDC / PCN; (d) Ce-OFDC, (e) PCN, (f) TEM images of Ce-OFDC / PCN and (g-k) Element mapping images of Ce-OFDC / PCN. (a) and (d) show that Ce-OFDC has a typical MOF structure, which is composed of a layer of sheet and forms a layered framework. (b) and (e) show that the surface of PCN is a smooth multi-layer block structure. (c) and (f) show that the layered Ce-OFDC and the layered PCN are stacked with each other to form a Ce-OFDC / PCN composite material. The mapping image results in (e) further show that the elements of Ce, O and N are uniformly distributed on the surface and body area of Ce-OFDC / PCN. It can be inferred that the Ce-OFDC / PCN photocatalyst is successfully prepared by simple in-situ hydrothermal synthesis.

[0078] Figure 5: (a) XRD patterns of Ce-OFDC, PCN, Ce-OFDC / PCN; (b) FT-IR patterns of Ce-OFDC, PCN, Ce-OFDC / PCN. The characteristic peaks of Ce-OFDC appeared at 6.12° and 12.2° in the composite. No other impurity peaks were found in the diffraction pattern of the composite, indicating that these samples are pure Ce-OFDC / PCN composite, without the presence of other phases. The intensity of the PCN characteristic peak in all composite samples is significantly higher than that of the Ce-OFDC characteristic peak. In these diffraction patterns, the PCN signal is always dominant, but as the Ce-OFDC content increases, the intensity of the Ce-OFDC characteristic peak also increases. In order to further determine the internal structure and chemical bonding of the semiconductor photocatalyst, the samples were also tested by Fourier transform infrared spectroscopy (FT-IR). Figure 5 b shows the FT-IR spectra of Ce-OFDC, PCN and Ce-OFDC / PCN. With the increase of PCN loading, the intensity of all peaks increases slightly, indicating that interactions are formed between PCN nanosheets and Ce-OFDC nanoparticles, and these nanosheets and nanoparticles are successfully composited.

[0079] Figure 6 : XPS elemental analysis of Ce-OFDC, PCN, Ce-OFDC / PCN. Figure 6 a shows the high-resolution spectrum of C 1s. Ce-OFDC has 3 peaks at 288.43, 285.63 and 284.83 eV, corresponding to O-C=O, O-C-O and C-C bonds, respectively. PCN has 2 peaks at 288.33 and 284.80 eV, representing C-N and C-C bonds, respectively. Ce-OFDC / PCN has 4 peaks at 288.38, 286.33 and 284.78 eV, and each peak has different degrees of shift, indicating that the introduction of PCN has a great impact on the Ce-OFDC framework. Figure 6 b shows the high-resolution spectrum of Ce, which is fitted into 10 peaks after peak separation. From Figure 6 b, it can be seen that the 6 peaks marked as V1, V4, V5, U, U2 and U3 correspond to Ce 4+ ions, and the 4 peaks marked as V, V2, V3 and U1 are related to trivalent cerium ions. By reference formula calculation, the concentration of [Ce 3+ ] in Ce-OFDC / PCN is 35.8%, while that in Ce-OFDC is 41.5%. The difference in [Ce 3+ ] content proves that Ce-OFDC and PCN have strong interactions in Ce-OFDC / PCN. Figure 6c shows the high-resolution XPS spectra of O 1s. The binding energy values of O 1s 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 H2OFDC ligands and the existence of -COO-Ce functional framework. In addition, the peaks of Ce-OFDC / PCN shift to lower binding energy direction after deconvolution and peak processing. Figure 6 d shows the N 1s spectrum, which can be divided into 3 peaks. The main peak is at 398.7 eV, corresponding to sp 2 N in heterocycle (C-N=C). The peak at 400.2 eV is attributed to pyrrole N, and the peak at 401.4 eV is attributed to graphitic N [29-30]. The above 3 peaks of Ce-OFDC / PCN are at 398.28, 399.78 and 401.03 eV, respectively. The XPS test results show 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, PCN and Ce-OFDC / PCN, (e) PL spectrum, (f) TRPL spectrum of Ce-OFDC, PCN and Ce-OFDC / PCN. As shown in a, the photocurrent of Ce-OFDC / PCN reaches 1.2 μA / cm Figure 7 2 , which is 1.5 times and 12 times of PCN (0.8 μA / cm 2 ) and Ce-OFDC (0.1 μA / cm 2 ), respectively. This indicates that the composite has enhanced light absorption capacity, leading to an increase in the generation of photo-generated electron-hole pairs and higher separation and transport efficiency. Figure 7 b shows the Nyquist plot of Ce-OFDC, PCN and Ce-OFDC / PCN, and the Nyquist radius of Ce-OFDC / PCN is smaller than that of Ce-OFDC and PCN, which indicates that the resistance of electron-hole migration in the composite is lower, so that the separation speed of photo-generated electrons and holes is faster. The electron-hole separation and photocurrent response of the heterojunction material are superior to Ce-OFDC and PCN. This enhanced electron transfer efficiency helps to increase the generation of free radicals, which may improve the photocatalytic antibacterial efficiency. Figure 7 ​cThe UV-Visible diffuse reflectance spectra for the analysis of optical response and band gap of the studied materials are presented. This red shift indicates that the light absorption capacity of the composite is enhanced due to the formation of heterojunction, while the introduction of Ce-OFDC expands the visible light absorption range. Based on the absorption spectra, the band gap of PCN and Ce-OFDC is determined to be 2.65 eV and 2.49 eV, respectively. Both PCN and Ce-OFDC show a negative slope, indicating that they have n-type semiconductor behavior. According to experience, the conduction band edge of n-type semiconductors is about 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. These results, combined with the band gaps obtained from the UV-Visible analysis (2.65 eV for PCN and 2.49 eV for Ce-OFDC), construct the energy band diagram Figure 7 d) Photogenerated electrons (e - ) and holes (h + ) recombine with high efficiency, which plays a key role in photocatalytic activity. The recombination rate of e - and h + was evaluated using photoluminescence (PL) spectra. Figure 7 f) Pure PCN shows the highest emission peak at about 514 nm, indicating a high rate of photogenerated carrier recombination, which leads to lower photocatalytic activity. When PCN is formed into a composite with Ce-OFDC, the intensity of the emission peak is significantly reduced, which is attributed to the formation of Ce-OFDC / PCN heterojunction, which improves carrier migration and reduces the electron-hole recombination rate.

[0081] Figure 8 、 9 : (a), (e) represent the number of E. coli and S. aureus in the control group medium, (b), (f) represent the number of E. coli and S. aureus in the medium added with Ce-OFDC, (c), (g) represent the number of E. coli and S. aureus in the medium added with PCN, (d), (h) represent the number of E. coli and S. aureus in the medium added with Ce-OFDC / PCN heterojunction. It is observed that after PCN is compounded with Ce-OFDC to form a heterojunction, the inhibition rate on E. coli is significantly improved (up to 99.5%), and the inhibition rate on S. 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) Superoxide radical detection by Ce-OFDC, PCN, Ce-OFDC / PCN EPR spectra, (b) Hydroxyl radical detection by Ce-OFDC, PCN, Ce-OFDC / PCN EPR spectra. The signal peak of Ce-OFDC / PCN is stronger than that of Ce-OFDC and PCN, indicating that Ce-OFDC / PCN produces a higher concentration of ·O2 and ·OH in the antibacterial process. - and ·OH. This is attributed to the heterojunction structure of the composite, which improves the separation efficiency of photo-generated carriers, thereby producing 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 E. coli under light conditions was studied by gradient experiments Figure 11 ). The experiment showed the results of ROS inhibition by introducing different types of ROS scavengers. In the absence of test samples, the addition of active oxygen 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 Ce-OFDC / PCN composite, 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 does indeed produce ROS and plays an important role in its antibacterial mechanism. After introducing D-mannitol to the Ce-OFDC / PCN suspension to scavenge ·OH, the inhibition rate decreased to 54.7% Figure 11 c). Similarly, after adding SOD to remove ·O2 - , the inhibition rate decreased to 65.4% Figure 11 d). This indicates that ·OH and ·O2 - are the key active species in the antibacterial mechanism, and their relatively long lifetimes allow them to diffuse from the active site to the target cell surface. On the other hand, when CAT was added to eliminate H2O2, the inhibition rate decreased to 85.4% Figure 11 e), indicating that H2O2 has a weaker effect on inhibiting bacteria. Hydrogen peroxide is a relatively stable intermediate species of ROS transformation and needs to penetrate the cell membrane to hinder cell activity. Therefore, H2O2 is less efficient than ·OH and ·O2 - . Although H2O2 can be converted to ·OH, its low production and extremely short lifetime limit its antibacterial effect. In summary, the experiment with scavengers shows that ·OH and ·O2 -Ce-OFDC is the main factor affecting the antibacterial property of the composite material, and H2O2 plays a secondary role in the bacterial inhibition mechanism of Ce-OFDC / PCN.

[0084] Example 2

[0085] On the basis of Example 1, only the weight ratio of cerium acetate and 9-fluorenone-2,7-dicarboxylic acid in step S1 was changed, and the experiment was performed again, and the results are shown in Table 2:

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

[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, good antibacterial effect is obtained, and when the weight ratio of cerium acetate and 9-fluorenone-2,7-dicarboxylic acid is 2.5:1, the inhibition rate of Escherichia coli and Staphylococcus aureus is the best.

[0090] Example 3

[0091] On the basis of Example 1, only the weight ratio of Ce-OFDC powder and PCN powder in step S3 was changed, and the experiment was performed again, and the results are shown in Table 2:

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

[0093]

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

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

Claims

1. A preparation method of a cerium-based organic framework and polymeric carbon nitride photocatalytic composite material, characterized in that, It comprises the following steps: S1, preparation of Ce-OFDC powder: Dissolve cerium-containing rare earth metal salt and organic ligand in polar organic solvent DMF, add an equal volume of ethylene glycol solvent, mix uniformly, then transfer the obtained mixed solution to a reaction kettle, heat 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; S2, preparation of PCN: Spread melamine powder in an alumina crucible, put it into a program-controlled temperature furnace, heat to 550°C, keep for a period of time, and obtain PCN powder; S3, preparation of Ce-OFDC / PCN composite material: Dissolve the Ce-OFDC powder obtained in step S1 and the PCN powder obtained in step S2 in DMA solution, stir, then add ethylene glycol solution, continue to stir uniformly, then pour the mixture into a stainless steel autoclave with a polytetrafluoroethylene liner, react at 100-150°C for 50-80 hours, after the reaction is completed, naturally cool, centrifuge to collect the precipitate, wash with deionized water and acetone alternately for 2-5 times, and vacuum dry to obtain yellow Ce-OFDC / PCN composite material.

2. The preparation method of the 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 cerium acetate to 9-fluorenone-2,7-dicarboxylic acid is (0.68-5):

1.

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

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

7. Use of cerium-based organic framework and polymeric carbon nitride photocatalytic composite material according to claim 6, characterized in that, Antibacterial for E. coli or Staphylococcus aureus.

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