Silver-loaded graphitic carbon nitride nanosheets and their preparation method and application

Abstract

The present invention discloses a silver-loaded graphitic carbon nitride nanosheet and its preparation method and application. The preparation method includes: firstly mixing an ammonium salt and a carbon source, drying and then performing high-temperature calcination to generate graphitic carbon nitride nanosheets, and then secondarily mixing the graphitic carbon nitride nanosheets with a reducing agent and a silver source in a solvent, and obtaining the silver-loaded graphitic carbon nitride nanosheets through a hydrothermal reaction. The preparation method is simple, low in cost and environmentally friendly, and the silver-loaded graphitic carbon nitride nanosheets prepared by this method have a high specific surface area, a low photo-generated electron-hole recombination rate and a wide visible light absorption range.

Description

Technical Field

[0001] The present invention relates to the field of research on carbon-based semiconductor photocatalysts. Specifically, it relates to a silver-loaded graphitic carbon nitride nanosheet and its preparation method and application. Background Art

[0002] Microbial infection is the main cause of human diseases and seriously endangers human health. However, with the increasing frequency of use of traditional antibacterial drugs, the expansion of clinical application scope, and the increase in the variety of drugs, the problem of bacterial drug resistance has become increasingly serious. Therefore, it is of great significance to develop new antibacterial agents with high efficiency, broad spectrum, low toxicity, stable properties, long-lasting effects, environmental friendliness, and not easily causing bacterial drug resistance. Photocatalysts have been favored by researchers due to their economic, environmental, and high efficiency. Photocatalytic antibacterial agents can absorb light energy to produce a bactericidal effect and are not easily prone to causing bacterial drug resistance, which is one of the important directions in the research and development of antibacterial agents. Among them, graphitic carbon nitride (g-C3N4), as a non-metallic semiconductor composed of C and N elements with a band gap of about 2.7 eV, responds to visible light, has a controllable structure, good stability, and good photocatalytic performance, thus becoming a research hotspot in the field of photocatalysis. However, g-C3N4 also shows some deficiencies during application, such as a large particle size, a low specific surface area, a high photogenerated electron-hole recombination rate, a low carrier migration ability, and a limited visible light absorption range.

[0003] Therefore, it is necessary to develop a photocatalyst with a high specific surface area, a low photogenerated electron-hole recombination rate, a high carrier migration ability, and a broad visible light absorption range. Summary of the Invention

[0004] The purpose of the present invention is to provide a silver-loaded graphitic carbon nitride nanosheet and its preparation method and application. The preparation method is simple, low-cost, and environmentally friendly. Moreover, the silver-loaded graphitic carbon nitride nanosheet prepared by this method has a high specific surface area, a low photogenerated electron-hole recombination rate, and a broad visible light absorption range, shows a good visible light response, and thus has excellent antibacterial and bactericidal properties.

[0005] To achieve the above purpose, the present invention provides a preparation method of a silver-loaded graphitic carbon nitride nanosheet, which includes: first mixing an ammonium salt and a carbon source, drying and then performing high-temperature calcination to generate graphitic carbon nitride nanosheets, and then second mixing the graphitic carbon nitride nanosheets with a reducing agent and a silver source in a solvent, and obtaining the silver-loaded graphitic carbon nitride nanosheet through a hydrothermal reaction.

[0006] The present invention also provides a silver-loaded graphitic carbon nitride nanosheet.

[0007] The present invention further provides an application of silver-loaded graphitic carbon nitride nanosheets as a photocatalyst in bacterial inhibition and inactivation.

[0008] In the above technical solution, the present invention has the following advantages:

[0009] The preparation method of the silver-loaded graphitic carbon nitride nanosheets provided by the present invention uses an ammonium salt as a gas template, and then silver nanoparticles are loaded on the graphitic carbon nitride nanosheets by a hydrothermal reduction method. After that, centrifugation is carried out at 2000 - 4000 rpm for 5 - 15 min, and the product is washed 2 - 4 times with deionized water and dried at 40 - 80 °C to obtain the silver-loaded graphitic carbon nitride nanosheets. The silver nanoparticles can be evenly distributed, and during the process of regulating the ratio of the ammonium salt to the carbon source, the thickness of the nanosheets gradually becomes thinner, and the specific surface area also increases to a certain extent. The prepared silver-loaded graphitic carbon nitride nanosheets have strong light absorption ability, good visible light response, and thus excellent antibacterial and bactericidal properties. The preparation method is simple in operation and avoids a complex exfoliation process. It provides a reliable solution for improving the photocatalytic antibacterial efficiency and the development and application of graphitic carbon nitride. The silver-loaded graphitic carbon nitride nanosheets prepared by the present invention are simple to prepare, controllable, low in production cost, and less harmful to the human body.

[0010] Furthermore, the inventors of the present invention found through research that the silver-loaded ultrathin graphitic carbon nitride photocatalyst has excellent Escherichia coli inactivation effect. The minimum inhibitory concentration (MIC) of graphitic carbon nitride nanosheets (CNS) is 200 ppm, while the MIC of silver-loaded graphitic carbon nitride nanosheets (AgCNS-5) reaches 40 ppm, and the antibacterial efficiency is greatly improved. We speculate that it may be because the SPR effect of silver nanoparticles can broaden the visible light absorption range, effectively transfer and separate carriers, and slow down the recombination rate of electron-hole pairs. Thus, more reactive oxygen species can be generated in the reaction, inhibiting and killing bacteria. The inventors of the present invention further found that an excessive silver loading amount does not promote the photocatalytic efficiency, but instead occupies the reaction active sites and affects the photocatalytic reaction process.

[0011] In summary, when the silver-loaded graphitic carbon nitride nanosheets provided by the present invention through thermal polymerization and hydrothermal method are applied to Escherichia coli inactivation, they have good bactericidal and antibacterial effects, and their performance is greatly improved compared with the original graphitic carbon nitride.

[0012] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Description of the Drawings

[0013] The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the accompanying drawings:

[0014] Figure 1 Scanning electron microscope photos (SEM) of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0015] Figure 2 Transmission electron microscope images (TEM) of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0016] Figure 3 X-ray energy spectrum elemental mapping diagram of AgCNS-5 prepared in Example 1;

[0017] Figure 4 Schematic diagram of the specific surface area of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0018] Figure 5 UV-Vis diffuse reflectance diagrams of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0019] Figure 6 Schematic diagram of photocurrent of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0020] Figure 7 Electrochemical impedance diagrams of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2;

[0021] Figure 8 Active oxygen species capture diagram of AgCNS-5 prepared in Example 1;

[0022] Figure 9 Fluorescence intensity diagrams of AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2 at 525 nm.

[0023] Figure 10 Growth curve diagram of Escherichia coli for exploring the minimum inhibitory concentration (MIC) of AgCNS-5 prepared in Example 1;

[0024] Figure 11 Morphology diagram of Escherichia coli photocatalytically treated with AgCNS-5 prepared in Example 1;

[0025] Figure 12 Schematic diagram of the morphology of normal Escherichia coli;

[0026] Figure 13 Growth curve of Escherichia coli for exploring the minimum inhibitory concentration (MIC) of BCN prepared in Comparative Example 1 and CNS prepared in Comparative Example 2;

[0027] Figure 14 Growth curve of Escherichia coli for exploring the minimum inhibitory concentration (MIC) of AgCNS-1, AgCNS-3, and AgCNS-7 prepared with different silver contents in Examples 2-4;

[0028] Figure 15 Bacterial colony maps after photocatalytic treatment with AgCNS-5 prepared in Example 1, BCN prepared in Comparative Example 1, and CNS prepared in Comparative Example 2, respectively. Detailed Description of the Invention

[0029] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0030] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0031] The present invention provides a method for preparing silver-loaded graphitic carbon nitride nanosheets. The preparation method includes: first mixing an ammonium salt and a carbon source, drying and then performing high-temperature calcination to generate graphitic carbon nitride nanosheets, and then second mixing the graphitic carbon nitride nanosheets with a reducing agent and a silver source in a solvent, and obtaining silver-loaded graphitic carbon nitride nanosheets through a hydrothermal reaction.

[0032] In the above preparation method, the type of ammonium salt can be selected within a relatively wide range. To avoid a complex exfoliation process, preferably, the ammonium salt is at least one of ammonium chloride, ammonium bicarbonate, and ammonium iodide; more preferably ammonium chloride.

[0033] In the above preparation method, the type of carbon source can be selected within a relatively wide range. To increase the specific surface area of the prepared silver-loaded graphitic carbon nitride nanosheets, preferably, the carbon source is at least one of melamine, urea, cyanamide, and dicyandiamide; more preferably melamine.

[0034] In the above preparation method, the type of reducing agent can be selected within a relatively wide range. To ensure that silver can be completely reduced, preferably, the reducing agent is at least one of ascorbic acid, sodium bisulfite, and sodium borohydride; more preferably ascorbic acid.

[0035] In the above preparation method, the type of silver source can be selected within a relatively wide range. To enable better attachment of silver nanoparticles to the carbon nitride nanosheets, preferably, the silver source is at least one of silver nitrate, silver oxide, and silver chloride; more preferably silver nitrate.

[0036] In the above preparation method, the reaction conditions can be selected within a relatively wide range. To ensure the specific surface area and optical properties of the prepared silver-loaded graphitic carbon nitride nanosheets, preferably, the conditions for high-temperature calcination include: a heating rate of 5 - 15 °C / min, a temperature of 500 - 600 °C, and a time of 1 - 3 h; more preferably, the conditions for the hydrothermal reaction include: a temperature of 160 °C - 200 °C and a time of 1 - 3 h.

[0037] In the above preparation method, the mass ratio of the ammonium salt to the carbon source can be selected within a relatively wide range. To ensure the synthesis rate of the silver-loaded graphitic carbon nitride nanosheets, preferably, the mass ratio of the ammonium salt to the carbon source is 1 - 3:1;

[0038] More preferably, the mass ratio of the graphitic carbon nitride nanosheets to the reducing agent and the silver source is 20:1 - 7:1 - 7.

[0039] The present invention also provides silver-loaded graphitic carbon nitride nanosheets prepared by the above preparation method.

[0040] The present invention further provides an application of the silver-loaded graphitic carbon nitride nanosheets as described above as a photocatalyst in bacteria inhibition and inactivation.

[0041] In the above method, preferably, the bacteria are Escherichia coli and / or Staphylococcus; more preferably Escherichia coli.

[0042] The present invention will be described in detail below by way of examples. In the following examples, the drugs and reagents are all conventional commercially available products.

[0043] Example 1

[0044] (1) Dissolve 3.0 g of melamine and 6.0 g of ammonium chloride in 30 mL of deionized water, mix well, dry, transfer to a crucible, and heat to 550 °C in a muffle furnace at a heating rate of 10 °C·min -1 and calcine for 2 h to obtain light yellow graphitic carbon nitride nanosheets, which are ground into powder for later use.

[0045] (2) Disperse 0.2 g of the above powder in 10 mL of deionized water and 10 mL of ethanol, then add 0.05 g of ascorbic acid and 0.05 g of AgNO3, stir for 2 h, transfer to a 50 mL polytetrafluoroethylene reactor, calcine at 180 °C for 2 h, take out the reactor and let it cool naturally to room temperature. Then, centrifuge at 3000 rpm for 10 min, wash the purified product with deionized water 3 times, and dry at 60 °C for 24 h to obtain silver-loaded ultrathin graphitic carbon nitride nanosheets, denoted as AgCNS-5.

[0046] Example 2

[0047] Carry out in the same manner as in Example 1, except that in step (2), 0.01 g of AgNO3 is added, and other conditions remain unchanged. The obtained silver-loaded ultrathin graphitic carbon nitride nanosheets are denoted as AgCNS-1.

[0048] The silver-loaded ultrathin graphitic carbon nitride nanosheets obtained in this example are consistent with the characteristics in Example 1.

[0049] Example 3

[0050] Carry out in the same manner as in Example 1, except that in step (2), 0.03 g of AgNO3 is added, and other conditions remain unchanged. The obtained silver-loaded ultrathin graphitic carbon nitride nanosheets are denoted as AgCNS-3.

[0051] The silver-loaded ultrathin graphitic carbon nitride nanosheets obtained in this example are consistent with the characteristics in Example 1.

[0052] Example 4

[0053] Carry out in the same manner as in Example 1, except that in step (2), 0.07 g of AgNO3 is added, and other conditions remain unchanged. The obtained silver-loaded ultrathin graphitic carbon nitride nanosheets are denoted as AgCNS-7.

[0054] The silver-loaded ultrathin graphitic carbon nitride nanosheets obtained in this example are consistent with the characteristics in Example 1.

[0055] Example 5

[0056] (1) Dissolve 3.0 g of urea and 6.0 g of ammonium bicarbonate in 30 mL of deionized water, mix well, dry and transfer to a crucible, and heat in a muffle furnace at a heating rate of 5 °C·min -1 to 500 °C and calcine for 3 h to obtain light yellow graphitic carbon nitride nanosheets, and grind them into powder for standby.

[0057] (2) Disperse 0.2 g of the above powder in 10 mL of deionized water and 10 mL of ethanol, then add 0.05 g of sodium borohydride and 0.05 g of AgO, stir for 2 h, transfer to a 50 mL polytetrafluoroethylene reactor, calcine at 160 °C for 1 h, take out the reactor and cool it naturally to room temperature. Then, centrifuge at 3000 rpm for 10 min, wash the purified product with deionized water 3 times, and dry at 60 °C for 24 h to obtain silver-loaded ultrathin graphitic carbon nitride nanosheets, denoted as AgCNS-5-3.

[0058] The silver-loaded ultrathin graphitic carbon nitride nanosheets obtained in this example are consistent with the characteristics in Example 1.

[0059] Example 6

[0060] (1) Dissolve 3.0 g and 6.0 g of ammonium bicarbonate in 30 mL of deionized water, mix evenly, dry and transfer to a crucible, and heat it in a muffle furnace at a heating rate of 15 °C·min -1 to 600 °C and calcine for 3 h to obtain light yellow graphitic carbon nitride nanosheets, grind them into powder for standby.

[0061] (2) Disperse 0.2 g of the above powder in 10 mL of deionized water and 10 mL of ethanol, then add 0.05 g of sodium borohydride and 0.05 g of AgO, stir for 2 h, transfer to a 50 mL polytetrafluoroethylene reactor, calcine at 200 °C for 3 h, take out the reactor and cool it naturally to room temperature. Then, centrifuge at 3000 rpm for 10 min, wash the purified product with deionized water 3 times, and dry at 60 °C for 24 h to obtain silver-loaded ultrathin graphitic carbon nitride nanosheets, denoted as AgCNS-5-3.

[0062] The silver-loaded ultrathin graphitic carbon nitride nanosheets obtained in this example are consistent with the characteristics in Example 1.

[0063] Comparative Example 1

[0064] Put 3.0 g of melamine into a covered alumina crucible, and heat it in a muffle furnace at a heating rate of 10 °C·min -1 to 550 °C and calcine for 2 h. After natural cooling, collect the dark yellow product, grind it into powder to obtain bulk graphitic carbon nitride, denoted as BCN.

[0065] Comparative Example 2

[0066] Carry out according to the method of Example 1, the difference is that the treatment in step (2) is not carried out, and graphitic carbon nitride nanosheets are obtained, denoted as CNS.

[0067] Figure 1 , Figure 2The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the photocatalytic materials prepared in Example 1 and Comparative Examples 1-2 are shown, respectively, where a is BCN, b is CNS, and c is AgCNS-5. Figure 1-2 As shown: the original BCN showed a block-like structure, while the treated CNS showed a layered structure like a stack of slices, which indicated that the BCN was successfully exfoliated. SEM combined with TEM images confirmed the lamellar structure of AgCNS-5.

[0068] like Figure 3 As shown, the X-ray energy spectrum elemental image analysis diagram of AgCNS-5 prepared in Example 1 shows that the silver nanoparticles are evenly distributed on the nanosheets.

[0069] Test Example 1

[0070] The specific surface areas of the product AgCNS-5 of Example 1, the product BCN of Comparative Example 1, and the product CNS of Comparative Example 2 were tested by nitrogen desorption and adsorption experiments. The specific results are shown in Figure 4 .

[0071] Depend on Figure 4 It can be seen that compared with BCN and CNS, the specific surface area of ​​AgCNS-5 is increased to a certain extent.

[0072] The products of Examples 2-8 were tested in the same manner, and the test results were substantially consistent with the SEM images of AgCNS-5 obtained in Example 1.

[0073] Test Example 2

[0074] The optical properties of the product AgCNS-5 of Example 1, the product BCN of Comparative Example 1, and the product CNS of Comparative Example 2 were characterized respectively. The fluorescence intensity was measured using a fluorescence meter, and the visible light absorption intensity of the ultraviolet visible diffuse reflectance test material was measured. The band gap value was calculated using the formula (αhv)1 / 2=A(hv-Eg).

[0075] like Figure 5 Compared with BCN and CNS, the absorption edge of AgCNS-5 undergoes an obvious red shift, and the band gap value is also decreasing, indicating that the absorption of visible light is gradually increasing.

[0076] The products of Examples 2-8 were tested in the same manner, and the test results were substantially consistent with the SEM images of AgCNS-5 obtained in Example 1.

[0077] Test Example 3

[0078] Electrochemical testing

[0079] The photoelectrochemical properties of the materials were tested using a typical three - electrode system consisting of a working electrode (sample electrode), a counter electrode (platinum wire), and a reference electrode (Ag / AgCl).

[0080] The products AgCNS - 5 of Example 1, BCN of Comparative Example 1, and CNS of Comparative Example 2 were respectively dip - coated on ITO glass. After drying, measurements were carried out. PBS (pH 7.0) was selected as the supporting electrolyte, and a 300 - w xenon lamp was used as the visible - light source for photocurrent and impedance measurements. The photoresponse measurement was carried out at a bias of 0.0 V. The EIS spectrum recorded at an AC voltage of 10 mV ranged from 0.01 Hz to 100000 Hz.

[0081] As Figure 6 shown, compared with BCN and CNS, AgCNS - 5 has the strongest photocurrent intensity; further, according to Figure 7 the electrochemical impedance diagram, AgCNS - 5 has the smallest radius. The above data indicate that the transfer and transportation of carriers in AgCNS - 5 are the best, so the recombination rate of electron - hole pairs is the slowest, which is more conducive to the generation of reactive oxygen species.

[0082] The products of Examples 2 - 8 were detected by the same method, and the detection results were basically consistent with the SEM images of AgCNS - 5 obtained in Example 1.

[0083] Detection Example 4

[0084] Reactive species capture

[0085] The ESR technique was used to conduct an experiment on the capture of reactive oxygen species for the product AgCNS - 5 material of Example 1.

[0086] As Figure 8 , no signal could be detected under dark conditions. After 10 min of visible - light illumination, ·OH and ·O 2- could be captured. And the signal of ·O 2- was stronger, indicating that ·O 2- plays a decisive role in the photocatalytic process.

[0087] Detection Example 5

[0088] The generation of reactive oxygen free radicals was monitored by the degradation of 2′,7′ - dichlorofluorescein diacetate (DCFH - DA). The specific method is as follows:

[0089] E. coli was separately mixed and cultured with the product AgCNS-5 of Example 1 at 100 μg / mL, the product BCN of Comparative Example 1, and the product CNS of Comparative Example 2 at 37 °C for 3 h. Then, the bacterial suspension was centrifuged at 7000 rpm for 10 min. The supernatant DCFH-DA (100 mM) was treated under visible light for 30 min. Finally, the fluorescence intensity was monitored on a fluorescence spectrometer (F-7000) with an excitation wavelength of 485 nm and an emission wavelength of 525 nm.

[0090] As Figure 9 shown, the fluorescence intensity of AgCNS-5 was significantly higher than that of BCN and CNS, being the strongest among the three, and also indicating the largest amount of reactive oxygen species generated.

[0091] Application Example

[0092] The photocatalysts prepared in Examples 1-4 and the photocatalysts prepared in Comparative Examples 1-2 were verified for their bactericidal effects by the following method. The specific method is as follows:

[0093] (1) Preparation of culture medium

[0094] Liquid culture medium: 2 g of tryptone, 2 g of sodium chloride, 1 g of yeast extract powder, 200 mL of deionized water;

[0095] Solid culture medium: 2 g of tryptone, 2 g of sodium chloride, 1 g of yeast extract powder, 1.8 g of agar, 200 mL of deionized water.

[0096] (2) Cultivation of bacteria

[0097] 20 μL of E. coli was transferred from an -80 °C refrigerator to 20 mL of liquid culture medium, and then cultured in an incubator at 37 °C with an oscillation speed of 180 rpm until the optical density absorption value at 600 nm was 0.5 (OD600 = 0.5).

[0098] (3) Determination of the minimum inhibitory concentration (MIC) by monitoring the bacterial growth curve

[0099] Different volumes of the photocatalytic materials prepared in Examples 1-4 and Comparative Examples 1-2 were separately and uniformly mixed with 20 mL of bacteria. A xenon lamp (300 W) and a UV cut-off filter (λ < 420 nm) were used as the visible light source. After 60 min of illumination, the mixture was placed in an incubator at 37 °C for 24 h, and the change in OD600 was measured every 2 h using an ultraviolet-visible (UV-vis) spectrophotometer.

[0100] (4) Evaluation of the bactericidal performance of the material by the plate counting method

[0101] First, Escherichia coli was cultured to the exponential growth phase, and bacterial cells were obtained by low-speed centrifugation. Equal volumes of deionized water (control group) and the photocatalysts prepared in Examples 1-4 and Comparative Examples 1-2 were diluted with phosphate buffer (PBS) and then mixed with the diluted bacterial solution. After irradiation with visible light for 60 min, the mixture was incubated in a water bath shaker at 37 °C for 3 h. Then, 100 μL of the diluted solution was evenly spread on a nutrient agar plate and incubated in an incubator at 37 °C for 24 h. The bacterial suspension was centrifuged at 8000 rpm / min for 5 min, and after removing the supernatant, the bacterial cells were fixed with glutaraldehyde (2.5%) at 4 °C overnight and washed 3 times with PBS (pH 7.4). Subsequently, the samples were dehydrated successively with 30, 50, 70, 80, 90, and 100% ethanol solutions. Then, 10 μL of the suspension was dropped on a clean silicon wafer and air-dried at room temperature. Finally, the morphology of Escherichia coli was observed by scanning electron microscopy.

[0102] As Figure 10 , AgCNS-5 can completely inhibit the growth of bacteria at the lowest concentration of 40 ppm.

[0103] As Figure 11 After treatment with the AgCNS-5 bactericidal photocatalyst, the cell membrane of Escherichia coli ruptured or curled, and the cell contents leaked out; as Figure 12 shown, Escherichia coli without photocatalyst treatment presented a typical rod-shaped structure with a smooth and intact surface.

[0104] As Figure 13 , the minimum inhibitory concentration (MIC) of bulk graphitic carbon nitride (BCN) was 400 ppm, the minimum inhibitory concentration (MIC) of graphitic carbon nitride nanosheets (CNS) was 200 ppm, while the minimum inhibitory concentration (MIC) of silver-loaded graphitic carbon nitride nanosheets reached 40 ppm, far superior to BCN and CNS, and the antibacterial efficiency was greatly improved.

[0105] As Figure 14 , the MICs of AgCNS-1, AgCNS-3, and AgCNS-7 were 70 ppm, 50 ppm, and 70 ppm, respectively, all greater than the MIC of AgCNS-5, which was 40 ppm. It can be seen that AgCNS-5 has the best antibacterial effect.

[0106] As Figure 15 , the culture medium of the control group (without photocatalyst) was covered with bacterial colonies. The number of colonies in the culture medium treated with BCN and CNS decreased to a certain extent, while all the bacteria in the culture medium treated with AgCNS-5 were killed.

[0107] In summary, through the characterization of optical properties and electrochemical properties, it is verified that the separation rate of electron-hole pairs plays an important role in the photocatalysis process. Further, it can be seen that the optical performance of the silver-loaded graphitic carbon nitride nanosheets prepared by the present invention has been effectively improved. The surface plasmon of silver effectively changes the intrinsic electronic structure and energy band structure of g-C3N4, enabling it to have sufficient biological optical absorption, low internal resistance, high separation of photo-generated charges, and a large specific surface area, providing more active sites, thereby generating more reactive oxygen species. These reactive oxygen species can attack the cell wall of Escherichia coli, oxidize and tear the semi-permeable membrane, resulting in the leakage of cell contents and ultimately cell death.

[0108] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0109] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0110] In addition, any combination can be made between different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of silver-loaded graphitic carbon nitride nanosheets, characterized in that, The preparation method includes: firstly mixing an ammonium salt and a carbon source, drying and then performing high-temperature calcination to generate graphitic carbon nitride nanosheets, and then mixing the graphitic carbon nitride nanosheets with a reducing agent and a silver source in a solvent for a second mixing, and obtaining silver-loaded graphitic carbon nitride nanosheets through a hydrothermal reaction; the mass ratio of the graphitic carbon nitride nanosheets, the reducing agent and the silver source is 20:1-7:1-7; The conditions of the hydrothermal reaction include: temperature 160°C - 200°C, time 1 - 3 h; The ammonium salt is at least one of ammonium chloride, ammonium bicarbonate and ammonium iodide, the carbon source is at least one of melamine, urea, cyanamide and dicyandiamide, the reducing agent is at least one of ascorbic acid, sodium bisulfite and sodium borohydride, and the silver source is at least one of silver nitrate, silver oxide and silver chloride; The mass ratio of the ammonium salt and the carbon source is 1-3∶1.

2. The preparation method according to claim 1, wherein, The ammonium salt is ammonium chloride.

3. The preparation method according to claim 1 or 2, wherein The carbon source is melamine.

4. The preparation method according to claim 1 or 2, wherein The reducing agent is ascorbic acid.

5. The preparation method according to claim 1 or 2, wherein The silver source is silver nitrate.

6. The preparation method according to claim 1 or 2, wherein The conditions of the high-temperature calcination include: heating rate 5 - 15°C / min, temperature 500 - 600°C, time 1 - 3 h.

7. The silver-loaded graphitic carbon nitride nanosheets prepared by the preparation method according to any one of claims 1-6.

8. Use of the silver-loaded graphitic carbon nitride nanosheets according to claim 7 as a photocatalyst in the preparation of a drug for inhibiting and inactivating bacteria by rupturing or curling cell membranes; the bacteria is Escherichia coli.

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