Cerium-doped red-light antibacterial carbon dots derived from residual sisal hemp and preparation method and application of cerium-doped red-light antibacterial carbon dots

Abstract

The invention discloses cerium-doped red-light antibacterial carbon dots derived from residual sisal hemp and a preparation method and application of the cerium-doped red-light antibacterial carbon dots, and belongs to the technical field of crossing of biomass conversion and nanotechnology. According to the preparation method disclosed by the invention, the multifunctional carbon dots with red fluorescence emission and excellent antibacterial activity are successfully prepared by taking a large amount of waste excess materials generated in a sisal hemp processing process as raw materials through a cerium doping strategy. High-value resource utilization of agricultural waste is achieved, the technical bottleneck that traditional sisal-based carbon dots can only emit blue-green fluorescence and are single in function is broken through, and a new way is provided for developing low-cost and multifunctional biomass carbon dot materials.

Description

A cerium-doped red-light antibacterial carbon dot derived from sisal residue, its preparation method and application Technical Field

[0001] This invention belongs to the interdisciplinary field of biomass conversion and nanotechnology, specifically relating to a cerium-doped red-light antibacterial carbon dot derived from sisal waste, its preparation method, and its application. Background Technology

[0002] Fluorescent carbon dots, as an emerging nanomaterial, have shown great application potential in fields such as bioimaging, sensing, and optoelectronic devices due to their excellent biocompatibility, low toxicity, and wide availability of raw materials. Among these, fluorescent carbon dots prepared using biomass as a precursor are more in line with the requirements of green chemistry and sustainable development, and have become a current research hotspot. However, existing biomass-based fluorescent carbon dots still suffer from the following significant drawbacks, severely limiting their practical applications:

[0003] 1) Limitations in Fluorescence Emission Wavelength: Currently, most reported biomass carbon dots only emit blue or green light. When used for bioimaging, this short-wavelength fluorescence is easily interfered with by the autofluorescence of biological tissues, leading to low signal-to-background ratio and high background noise, thus affecting image clarity and accuracy. To achieve deep, high-resolution bioimaging, developing carbon dots with long-wavelength emission characteristics, especially red or near-infrared light emission, has become an urgent technological need in this field. However, biomass carbon dot systems capable of stably emitting red light are still rarely reported, and their preparation techniques are not yet mature.

[0004] 2) Functional limitation: Most fluorescent carbon dots are limited to optical properties and do not possess antibacterial activity. This functional limitation greatly restricts the application of carbon dots in fields requiring multifunctional synergy. For example, in the field of integrated diagnosis and treatment of infectious diseases in animals and plants, there is an urgent need for a multifunctional formulation that can perform both fluorescence imaging localization and simultaneous antibacterial treatment.

[0005] Sisal, a widely cultivated hard-leaved fiber crop worldwide, accounts for more than two-thirds of global hard fiber production, making it an important industrial raw material and strategic resource. During sisal fiber processing, the fiber portion accounts for only about 3% to 5% of the leaf's dry weight. This means that for every ton of sisal fiber extracted, 20 to 30 tons of sisal leaf residue (mainly including leaf pulp and sap) are generated. Due to the large-scale cultivation and processing of sisal globally, the amount of this residue is enormous, reaching millions of tons annually. However, most of this residue is currently considered agricultural waste, either discarded or simply treated, resulting in low resource utilization rates. This not only causes a serious waste of biomass resources but also poses certain environmental risks. Although existing studies have attempted to prepare fluorescent carbon dots using sisal fiber as a carbon source, these efforts have significant limitations: First, the selected raw material remains sisal fiber itself, failing to fully utilize the more inexpensive and readily available sisal processing waste, thus failing to achieve the goal of high-value utilization through "waste treatment"; second, the prepared carbon dots are mostly limited to the blue or green light emission range, and no reports have been found of them possessing effective antibacterial properties. Therefore, there is currently a lack of an effective method to transform the abundant but underutilized sisal processing waste into multifunctional carbon dot materials that possess both red fluorescence emission properties and inherent antibacterial functions, thereby establishing a feasible path between material construction and waste resource utilization. Summary of the Invention

[0006] The purpose of this invention is to provide a cerium-doped red-light antibacterial carbon dot derived from sisal residue, its preparation method, and its applications. By using sisal residue as raw material and combining specific processes with cerium doping technology, red fluorescent carbon dots with a fluorescence emission peak at 674 nm were successfully prepared. This overcomes the limitation of existing sisal-based carbon dots that can only emit blue-green light, and solves the technical problem of the scarcity of materials emitting red light in biomass carbon dots. The obtained red-light carbon dots can effectively avoid interference from the autofluorescence of biological tissues, laying the foundation for high-quality bioimaging applications. Furthermore, the introduction of cerium endows the carbon dots with excellent antibacterial activity. This makes the carbon dots prepared by this invention no longer a single-function fluorescent probe, but a novel "diagnostic" nanomaterial integrating fluorescence tracing and antibacterial functions, achieving functional fusion and synergy, and significantly expanding its application range.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One of the technical solutions of this invention is to provide a method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal residue, comprising the following steps:

[0009] Sisal residue was diluted with water and mixed with tetravalent cerium salt. The pH of the mixture was adjusted to 1-4, and after hydrothermal reaction, cerium-doped red light antibacterial carbon dots derived from the sisal residue were obtained.

[0010] The sisal residue is the material remaining after sisal fibers have been removed from sisal.

[0011] The mass of the sisal residue and the Ce content in the tetravalent cerium salt 4+ The molar ratio is not less than 2056g:1mol.

[0012] Preferably, the mass ratio of the sisal residue to the water is 1:60~240.

[0013] Preferably, the mass of the sisal residue is related to the Ce content in the tetravalent cerium salt. 4+ The molar ratio is 2056~8224g:1mol.

[0014] Preferably, the hydrothermal reaction is carried out at a temperature of 120-160°C for 3-6 hours.

[0015] The second technical solution of the present invention provides a method for preparing cerium-doped red light antibacterial carbon dots derived from sisal waste, which yields cerium-doped red light antibacterial carbon dots derived from sisal waste.

[0016] The third technical solution of the present invention provides an application of cerium-doped red light antibacterial carbon dots derived from the above-mentioned sisal residue in bioimaging.

[0017] The fourth technical solution of the present invention provides an application of cerium-doped red antibacterial carbon dots derived from the above-mentioned sisal residue in the preparation of materials with both fluorescent tracer and antibacterial functions.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] This invention utilizes a large amount of waste material generated during sisal processing as raw material and successfully prepares multifunctional carbon dots with both red fluorescence emission and excellent antibacterial activity through a cerium doping strategy. This not only realizes the high-value resource utilization of agricultural waste, but also breaks through the technical bottleneck of traditional sisal-based carbon dots that can only emit blue-green fluorescence and have a single function, providing a new approach for developing low-cost, multifunctional biomass carbon dot materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 is a schematic diagram of the method for obtaining sisal residue in this invention.

[0022] Figure 2 is a transmission electron microscope image of the cerium-doped red light antibacterial carbon dots prepared in Example 1.

[0023] Figure 3 shows the X-ray photoelectron spectrum of the cerium-doped red antibacterial carbon dots prepared in Example 1.

[0024] Figure 4 shows the Raman spectrum of the cerium-doped red antibacterial carbon dots prepared in Example 1.

[0025] Figure 5 shows the fluorescence spectrum of the cerium-doped red light antibacterial carbon dots prepared in Example 1 after excitation at a wavelength of 420 nm, as well as actual images under sunlight and ultraviolet light.

[0026] Figure 6 is a bar chart showing the cell viability of cerium-doped red light antibacterial carbon dots prepared in Example 1 after co-culturing with L929 cells and B16 cells at different concentrations for 24 hours.

[0027] Figure 7 shows a laser confocal microscope image of L929 cells and B16 cells after the cerium-doped red antibacterial carbon dots prepared in Example 1 were used as fluorescent probes.

[0028] Figure 8 shows the antibacterial effect of cerium-doped red light antibacterial carbon dots in Example 1 and undoped carbon dots in Comparative Example 1 on the soft rot pathogen of cabbage at the same concentration.

[0029] Figure 9 shows the staining results of live and dead bacteria before and after treatment of soft rot pathogens of cabbage with cerium-doped red light antibacterial carbon dots in Example 1.

[0030] Figure 10 shows the fluorescence spectra of cerium-doped red antibacterial carbon dots in Examples 1-5 under 420 nm excitation.

[0031] Figure 11 shows the fluorescence spectrum of the undoped carbon dots in Comparative Example 1 after excitation at a wavelength of 380 nm, as well as actual images of the objects under sunlight and ultraviolet light.

[0032] Figure 12 shows the X-ray photoelectron spectrum of the carbon dots obtained in Comparative Example 3.

[0033] Figure 13 shows the fluorescence spectrum of the cadmium-doped carbon dots prepared in Comparative Example 4 after excitation at a wavelength of 380 nm, as well as actual images under sunlight and ultraviolet light. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0035] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0036] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] In this invention, room temperature refers to a temperature of 20±10℃.

[0040] The cerium ammonium nitrate and cadmium chloride used in this invention are chemically pure reagents.

[0041] Example 1

[0042] (1) Collect the waste material generated during the production of sisal fiber in the factory (i.e. the remaining material after removing sisal fiber), crush it in a pulverizer, filter it with four layers of gauze, and obtain the sisal residue as a carbon source.

[0043] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water (mass ratio 1:240). Then add cerium ammonium nitrate (the ratio of the mass of the sisal residue to the molar mass of cerium ammonium nitrate is 4112 g:1 mol). Disperse the mixture ultrasonically at room temperature for 10 min to form a mixed solution and adjust the pH of the solution to 2. Transfer the mixed solution to a hydrothermal reactor and react at 140 °C for 3 h. After the reaction is completed, filter, dialyze (3500 Da), and dry the reaction product in sequence to obtain cerium-doped red light antibacterial carbon dots.

[0044] Figure 1 is a schematic diagram of the method for obtaining sisal residue in this invention.

[0045] Figure 2 is a transmission electron microscope image of the cerium-doped red-light antibacterial carbon dots prepared in Example 1. Figure 2 shows that the carbon dots are uniform spherical particles with a narrow particle size distribution, ranging from 2 to 6 nm.

[0046] Figure 3 shows the X-ray photoelectron spectrum of the cerium-doped red-light antibacterial carbon dots prepared in Example 1. Figure 3 shows that the characteristic peak of Ce element appears in the spectrum, confirming that cerium was successfully doped into the carbon dots.

[0047] Figure 4 shows the Raman spectrum of the cerium-doped red antibacterial carbon dots prepared in Example 1. Figure 4 shows distinct D and G peaks in the spectrum, indicating that the obtained product has a typical carbon dot structure.

[0048] Figure 5 shows the fluorescence spectrum of the cerium-doped red antibacterial carbon dots prepared in Example 1 after excitation at a wavelength of 420 nm, as well as actual images under sunlight and ultraviolet light. Figure 5 shows that at an excitation wavelength of 420 nm, the emission peak of the prepared cerium-doped red antibacterial carbon dots is located at 674 nm. The inset shows actual photographs of the aqueous dispersion of the carbon dots under sunlight (left) and 365 nm ultraviolet light (right), showing that it is uniformly dispersed in water and exhibits bright red fluorescence under ultraviolet excitation, indicating that it has good water dispersibility and red light emission performance.

[0049] Figure 6 shows a bar graph of cell viability after co-culturing L929 and B16 cells with cerium-doped red-light antibacterial carbon dots prepared in Example 1 at different concentrations for 24 h (culture conditions: 37℃, 5% CO2). Viability was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The experimental steps were as follows: Evaluation was performed on mouse fibroblast L-929 cells and mouse melanoma cells B16 cells. Cultured cells were transferred to 96-well plates and cultured at 37℃, 5% CO2 for 24 h. The culture medium was then changed, and different concentrations of B,N-CPDs solutions diluted with the culture medium were added, with a blank control group included. Cells were cultured for another 24 h at concentration gradients of 0, 25, 50, 100, and 200 μg / mL. After adding MTT solution for 4 h, the culture medium was replaced with DMSO solution, and cytotoxicity screening was performed using a microplate reader. Figure 6 shows that the carbon dot material exhibited low cytotoxicity and good biocompatibility.

[0050] Figure 7 shows laser confocal microscopy images of L929 and B16 cells labeled with cerium-doped red antibacterial carbon dots prepared in Example 1 as fluorescent probes. The experimental steps were as follows: Mouse fibroblast L-929 cells and mouse melanoma cells B16 cells were cultured at 37°C with 5% CO2 for 24 hours. After aspirating the cell suspension, the cells were washed three times with PBS solution. Three solutions of B,N-CPDs diluted with the same concentration in culture medium were added and cultured until approximately 50% confluence. The culture medium was aspirated again and the cells were washed twice with PBS solution. After adding PBS solution, cell imaging was performed using a confocal microscope. Figure 7 shows that the labeled cells exhibited clear red fluorescence, indicating that the carbon dots can be used for cell imaging.

[0051] Figure 8 shows the antibacterial effect of cerium-doped red-light antibacterial carbon dots (Ce-CDs) in Example 1 and undoped carbon dots (CDs) in Comparative Example 1 against *Brassica napus*, the pathogen causing soft rot of Chinese cabbage, at the same concentration (128 µg / mL). The experimental procedure is as follows: 1 mL of CDs and Ce-CDs at different concentrations were mixed with 1 mL of a solution containing 7 × 10⁻⁶ ppm of cerium-doped red-light antibacterial carbon dots (Ce-CDs) and ...cerium-doped red-light antibacterial carbon dots (CDs) in Comparative Example 1. 5 The CFU of *Bacillus subtilis*, the pathogen causing soft rot in Chinese cabbage, was mixed and incubated together at 30°C for 6 hours. After incubation, 100 μL of the mixture was spread onto the surface of NB-Agar solid medium and incubated at 30°C for another 18 hours. The results were then photographed and recorded. Figure 8 shows that, compared with the blank control group (0 µg / mL), CDs did not show significant antibacterial activity; while Ce-CDs almost completely inhibited colony growth at this concentration, indicating that they have excellent antibacterial properties and good potential for antibacterial applications.

[0052] Figure 9 shows the staining results of live and dead bacteria before and after treatment with cerium-doped red-light antibacterial carbon dots (final concentration 1 mg / mL) for the soft rot pathogen of Chinese cabbage in Example 1. Staining was performed using calcein (live bacteria, green fluorescence) and propidium iodide (dead bacteria, red fluorescence). The experimental procedure was as follows: 1 mL of different concentrations of CDs and Ce-CDs were mixed with 1 mL of 7 × 10⁻⁶ C₀C ... 5 The CFU (Cerium Fusarium oxysporum) culture of *Bacillus subtilis*, the pathogen causing soft rot in Chinese cabbage, was mixed and incubated together at 30°C for 6 hours. After incubation, the mixture was centrifuged at 4000 rpm for 5 minutes, the supernatant was removed, and 100 μL of calcein was added and incubated in the dark for 25 minutes, followed by 100 μL of propidium iodide and incubation for 10 minutes. After incubation, the staining solution was removed, and the mixture was rinsed twice with PBS buffer, then dropped onto a glass slide and observed using a confocal laser microscope. The results were photographed and recorded. Figure 9 shows that the untreated bacterial colony exhibited green fluorescence, indicating that all bacteria were viable. After treatment with cerium-doped carbon dots, the bacterial colony turned red fluorescence, confirming that the material could effectively induce bacterial death and exhibited significant antibacterial activity.

[0053] Example 2

[0054] (1) Same as step (1) in Example 1.

[0055] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water (mass ratio 1:240). Then add cerium ammonium nitrate (the ratio of the mass of the sisal residue to the molar mass of cerium ammonium nitrate is 8224 g:1 mol). The mixed solution is ultrasonically dispersed at room temperature for 10 min, the pH is adjusted to 1, and then transferred to a hydrothermal reactor and reacted at 120 °C for 6 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried in sequence to obtain cerium-doped red light antibacterial carbon dots.

[0056] Example 3

[0057] (1) Same as step (1) in Example 1.

[0058] (2) Weigh 300 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water (mass ratio 1:120). Then add cerium ammonium nitrate (mass ratio of sisal residue to cerium ammonium nitrate molar is 4112 g:1 mol). Place the mixed solution at room temperature and ultrasonically disperse for 10 min. After adjusting the pH to 3, transfer it to a hydrothermal reactor and react at 130 °C for 5 h. After the reaction is completed, filter, dialyze (3500 Da) and dry the product in sequence to obtain cerium-doped red light antibacterial carbon dots.

[0059] Example 4

[0060] (1) Same as step (1) in Example 1.

[0061] (2) Weigh 450 mg of the sisal residue obtained in step (1) and disperse it in 36 mL of ultrapure water (mass ratio 1:80). Then add cerium ammonium nitrate (the ratio of the mass of the sisal residue to the molar mass of cerium ammonium nitrate is 6168 g:1 mol). The mixed solution is ultrasonically dispersed at room temperature for 10 min, the pH is adjusted to 4, and then transferred to a hydrothermal reactor and reacted at 150 °C for 4 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried sequentially to obtain cerium-doped red light antibacterial carbon dots.

[0062] Example 5

[0063] (1) Same as step (1) in Example 1.

[0064] (2) Weigh 600 mg of the sisal residue obtained in step (1) and disperse it in 36 mL of ultrapure water (mass ratio 1:60). Then add cerium ammonium nitrate (the ratio of the mass of the sisal residue to the molar mass of cerium ammonium nitrate is 2056 g:1 mol). The mixed solution is ultrasonically dispersed at room temperature for 10 min, the pH is adjusted to 2, and then transferred to a hydrothermal reactor and reacted at 160 °C for 3 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried sequentially to obtain cerium-doped red light antibacterial carbon dots.

[0065] Figure 10 shows the fluorescence spectra of cerium-doped red antibacterial carbon dots in Examples 1-5 under 420 nm excitation. As can be seen from Figure 10, the blue and red emission peaks of the carbon dots exhibit different intensity ratios under different reaction conditions. In Example 1, the blue emission peak of the carbon dots completely disappears, leaving only the red emission peak. In Examples 2-5, the blue emission peak is retained to varying degrees, which affects the red emission.

[0066] Comparative Example 1

[0067] Compared to Example 1, no cerium ammonium nitrate was added in Comparative Example 1, while the remaining steps remained unchanged:

[0068] (1) Same as step (1) in Example 1.

[0069] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water (mass ratio 1:240); ultrasonically disperse the solution at room temperature for 10 min, adjust the pH to 2, and then transfer it to a hydrothermal reactor and react at 140 °C for 3 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried in sequence to obtain undoped cerium carbon dots.

[0070] Figure 11 shows the fluorescence spectrum of undoped carbon dots (CDs) in Comparative Example 1 after excitation at 380 nm, as well as photographs under sunlight and ultraviolet light. Figure 11 shows that the emission peak of the undoped carbon dots is located at 445 nm at the excitation wavelength of 380 nm. The inset shows photographs of the aqueous dispersion of the carbon dots under sunlight (left) and 365 nm ultraviolet light (right). The photographs show that the carbon dots are uniformly dispersed in the aqueous phase, but exhibit bright blue fluorescence under ultraviolet excitation instead of red fluorescence. This indicates that without the introduction of cerium, the prepared carbon dots only emit blue fluorescence and do not show antibacterial effect against the soft rot pathogen of cabbage (Figure 8). This demonstrates that cerium doping plays a key role in achieving red fluorescence emission of carbon and endowing the carbon dots with antibacterial function.

[0071] Comparative Example 2

[0072] Compared with Example 1, Comparative Example 2 only changed the mass ratio of sisal residue to ceric ammonium nitrate to 2:1 (which exceeds the range of 3.75~15:1 in the technical solution of this invention), while the other steps remained the same:

[0073] (1) Same as step (1) in Example 1.

[0074] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water (mass ratio 1:240). Then add cerium ammonium nitrate (the ratio of the mass of the sisal residue to the molar mass of cerium ammonium nitrate is 1097 g:1 mol). The mixed solution is ultrasonically dispersed at room temperature for 10 min, the pH is adjusted to 2, and then transferred to a hydrothermal reactor and reacted at 140 °C for 3 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried in sequence to obtain carbon dots.

[0075] The results showed that the synthesized carbon dots exhibited only weak red fluorescence. This is attributed to the fact that when the amount of cerium ions added exceeded the optimal range, the introduction of excess metal ions led to a significant decrease in energy transfer efficiency, and even caused fluorescence quenching. These synthesis conditions not only consumed the raw materials but also resulted in a severe decline in the fluorescence performance of the product, even causing it to lose its functional luminescent ability.

[0076] Comparative Example 3

[0077] Compared with Example 1, Comparative Example 3 only adjusted the pH of the reaction solution to 7 (which is outside the pH range of 1-4 in the technical solution of this invention), while the other steps remained unchanged:

[0078] (1) Same as step (1) in Example 1.

[0079] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water. Then add cerium ammonium nitrate (mass ratio of sisal residue to cerium ammonium nitrate is 7.5:1). The mixed solution is ultrasonically dispersed at room temperature for 10 min. After adjusting the pH to 7, it is transferred to a hydrothermal reactor and reacted at 140 °C for 3 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried to obtain carbon dots.

[0080] Figure 12 shows the X-ray photoelectron spectrum of the carbon dots obtained in Comparative Example 3. Figure 12 shows that the cerium content in the carbon dots is only 0.29 wt%, which is significantly lower than that of the carbon dots prepared in Example 1 under the preferred pH conditions.

[0081] The results showed that when the pH of the reaction system exceeded the preferred range, the doping amount of cerium in the carbon dots decreased significantly, which affected their performance (highlighting the necessity of limiting the reaction conditions compared to Example 1).

[0082] Comparative Example 4

[0083] Compared to Example 1, the added ion was cadmium ions, and the remaining steps were the same:

[0084] (1) Same as step (1) in Example 1.

[0085] (2) Weigh 150 mg of the sisal residue obtained in step (1) and disperse it in 36 g of ultrapure water. Then add cadmium chloride (the mass ratio of sisal residue to cadmium chloride is 7.5:1). The mixed solution is ultrasonically dispersed at room temperature for 10 min, the pH is adjusted to 2, and then transferred to a hydrothermal reactor and reacted at 140 °C for 3 h. After the reaction is completed, the product is filtered, dialyzed (3500 Da), and dried in sequence to obtain cadmium-doped carbon dots (Cd-CDs).

[0086] Figure 13 shows the fluorescence spectrum of the cadmium-doped carbon dots (Cd-CDs) prepared in Comparative Example 4 after excitation at a wavelength of 380 nm, as well as actual images under sunlight and ultraviolet light. Figure 13 shows that the strongest emission peak of Cd-CDs is located at 467 nm under an excitation wavelength of 380 nm. The inset shows actual images of the aqueous dispersion of the carbon dots under sunlight (left) and 365 nm ultraviolet light (right). The inset shows that the aqueous dispersion of the carbon dots exhibits obvious blue-green fluorescence under 365 nm ultraviolet light irradiation, which is significantly different from the red fluorescence obtained in Example 1. Under the same synthesis conditions, doping with cadmium did not achieve red light emission, and the fluorescence of the product was still limited to the blue-green light region. This indicates that the key to preparing the red antibacterial carbon dots in this invention lies in selecting a suitable dopant element, not just in the doping process itself. Cerium ions, as a dopant, have a unique role. Their introduction is the decisive factor in achieving red light emission and simultaneously endowing antibacterial activity, further highlighting the importance of dopant ion selection in regulating the optical properties and functions of carbon dots.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal scraps, characterized in that, Includes the following steps: Sisal residue was diluted with water and mixed with tetravalent cerium salt. The pH of the mixture was adjusted to 1-4, and after hydrothermal reaction, cerium-doped red-light antibacterial carbon dots derived from the sisal residue were obtained. The sisal residue is the material remaining after sisal fibers are removed. The mass of the sisal residue is related to the Ce content in the tetravalent cerium salt. 4+ The molar ratio is not less than 2056g:1mol.

2. The method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal residue according to claim 1, characterized in that, The mass ratio of the sisal residue to the water is 1:60~240.

3. The method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal residue according to claim 1, characterized in that, The mass of the sisal residue and the Ce content in the tetravalent cerium salt 4+ The molar ratio is 2056~8224g:1mol.

4. The method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal scraps according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 120~160℃ for 3~6 hours.

5. A method for preparing cerium-doped red-light antibacterial carbon dots derived from sisal scrap according to any one of claims 1 to 4.

6. The application of cerium-doped red-light antibacterial carbon dots derived from sisal residue as described in claim 5 in bioimaging.

7. The application of cerium-doped red antibacterial carbon dots derived from sisal residue as described in claim 5 in the preparation of materials with both fluorescent tracing and antibacterial functions.

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