Carbon nanodot synthesized by using naturally withered leaves, and preparation method therefor and application thereof

Abstract

The present invention belongs to the technical field of new materials and the technical field of energy conservation and environmental protection. Disclosed are a carbon nanodot synthesized by using naturally withered leaves, and a preparation method therefor and an application thereof. In the method of the present invention, naturally withered leaves of camphor trees are used as a carbon source, and a carbon nanodot is obtained by means of drying, high-temperature calcination, ultrasonic oscillation, and centrifugal separation and purification. The method of the present invention is low-cost and environmentally friendly and involves a simple preparation process; and the prepared carbon nanodot can be used in the aspects of biological imaging, anti-counterfeiting, metal ion detection, etc., and has a good economic value and practicability.

Description

Carbon nanodots synthesized from naturally dried leaves, preparation method and application Technical Field

[0001] The present invention relates to carbon nanodots synthesized from naturally dried leaves, a preparation method and applications, and belongs to the technical fields of new materials and energy conservation and environmental protection. Background Art

[0002] With the rapid advancement of technology, materials previously studied were primarily micron-scale. In recent decades, however, research has shifted towards the nanoscale, becoming a key area of ​​current technological development. Nanoscale materials have broad applications in medicine, biosensor development, energy research, and reaction catalysis. Fluorescent nanomaterials, due to their inherent fluorescence, hold considerable potential for use in biomarker technologies and optoelectronic materials. Semiconductor quantum dots such as cadmium sulfide (CdS) and cadmium selenide (CdSe) have been extensively studied due to their highly stable fluorescence.

[0003] Currently, most high-quantum-yield (QY) materials on the market contain heavy metals, which increases the risk of biotoxicity and cytotoxicity. Not only are they prone to contamination during the synthesis process, but without proper post-use recycling, they pose significant environmental risks. These drawbacks limit the application of semiconductor quantum dots. In recent years, luminescent carbon nanodots have emerged as a novel material, offering advantages such as ease of preparation, low cost, low cytotoxicity, photostability, and quantum size effects (Zhang et al., 2010). Recent research has also reported the presence of carbon nanodots in the three-in-one coffee powder consumed daily (Jiang et al., 2014), suggesting that carbon nanodots should have high biocompatibility and low toxicity. Numerous techniques have been developed to synthesize carbon nanodots, including laser ablation, arc discharge, electrochemical, thermal decomposition, ultrasonic, and microwave methods. Among them, the thermal decomposition method is simple, safe, fast and effective. In the study of Wang, Liu, Zhang, and Lv (2012), it was found that this method has good optical properties, stability and biocompatibility.

[0004] There are some reports on the use of biomass materials to prepare luminescent carbon nanodots. For example, CN 114044511 A discloses a preparation method and application of beer-based nitrogen and phosphorus co-doped biomass carbon dots, which can be used for Fe 3+ A new method for detecting ascorbic acid; CN109734073A uses wormwood leaves as a carbon source to prepare carbon quantum dots. The prepared carbon quantum dot solution is yellow and transparent under natural light, and bright blue fluorescence can be seen under 365nm ultraviolet light excitation; CN 110373185 A uses paper mulberry leaves as a carbon source to synthesize fluorescent carbon dots, which can selectively detect Bi3+ , with a detection limit of 2.0 μmol / L; CN 110308126 A used neem leaves to synthesize fluorescent nanocarbon dots through a hydrothermal method, which can be used for cell imaging; CN 113023708 A dissolved the smoke from the combustion of sugarcane bagasse in a sugarcane sugar factory into pure water, and separated and extracted nanocarbon dots from the particulate matter contained in the smoke through multi-stage membrane filtration, centrifugation and dialysis.

[0005] The current preparation of luminescent carbon nanodots has problems such as complicated operation, high raw material cost, the need to use chemicals such as organic solvents, which is not environmentally friendly, the need to dope metals and other components, or high requirements for preparation equipment. The prepared luminescent carbon nanodots also have problems such as low fluorescence intensity, metal doping, or limited functions, resulting in limited application scenarios.

[0006] Summary of the Invention

[0007] To solve at least one of the above problems, the inventors used naturally dried camphor tree fallen leaves as materials, dried them, calcined them at high temperature, and then subjected them to ultrasonic vibration and centrifugal separation and purification to obtain carbon nanodots. This method has the advantages of simple and safe operation and widely available materials. At the same time, the production process does not require the use of any chemicals and the requirements for preparation equipment are simple. The fluorescent nanomaterials prepared by the method of the present invention are low in cost, low in toxicity and environmentally friendly, with a fluorescence intensity of more than 1300, and can be used for anti-counterfeiting, cell imaging, Co 2+ Detection and other fields.

[0008] The first object of the present invention is to provide a method for synthesizing carbon nanodots using naturally dried fallen leaves, comprising the following steps:

[0009] (1) Pre-treating naturally dried camphor tree leaves and grinding them into powder;

[0010] (2) placing the powder obtained in step (1) into a high-temperature furnace for calcining to obtain carbonized leaf powder, and then uniformly grinding it into fine powder;

[0011] (3) adding the fine powder obtained in step (2) into water and performing ultrasonic treatment to obtain a solution;

[0012] (4) Centrifuging the solution in step (3) and taking out the supernatant to obtain a carbon nanodot solution.

[0013] In one embodiment, the pretreatment in step (1) refers to oven drying of the naturally dried leaves.

[0014] In one embodiment, the oven drying is drying in an oven at 80-85°C for 20-28 hours;

[0015] Optionally, the oven drying is drying at 82° C. for 24 hours.

[0016] In one embodiment, the temperature of the high-temperature furnace calcination in step (2) is controlled at 230-260°C.

[0017] Optionally, the temperature of the high-temperature furnace calcination in step (2) is controlled at 280°C.

[0018] In one embodiment, the calcination time in step (2) is 3-6 hours.

[0019] Optionally, the calcination time in step (2) is 3.5-4h

[0020] Optionally, the calcination time in step (2) is 4 hours.

[0021] In one embodiment, the uniform grinding time in step (2) can be determined according to actual conditions; optionally, it is 30-60 minutes; further, it is 30 minutes.

[0022] In one embodiment, the ratio of fine powder to water in step (3) is 5-30 mL of water per gram of fine powder.

[0023] In one embodiment, the ratio of fine powder to water in step (3) is 10 mL of water per gram of fine powder.

[0024] In one embodiment, the water in step (3) refers to distilled water or ultrapure water.

[0025] In one embodiment, the ultrasonic treatment shaking time in step (3) can be determined according to actual conditions; ultrasonic shaking can effectively break up agglomerated or large particles of carbon blocks, allowing the fluorescent substance to be effectively dissolved in water. Optionally, it is 2 hours.

[0026] In one embodiment, the number of revolutions of the centrifugation in step (4) is 5000 rpm.

[0027] In one embodiment, the centrifugation time in step (4) is 10 minutes.

[0028] The second object of the present invention is to provide a carbon nanodot solution prepared according to the above method.

[0029] In one embodiment, the carbon nanodot solution can be further dried to obtain solid or semi-solid carbon nanodots.

[0030] The third object of the present invention is to provide fluorescent ink containing the carbon nanodots.

[0031] A fourth object of the present invention is to provide an anti-counterfeiting material, which uses the carbon nanodots of the present invention or fluorescent ink containing the carbon nanodots of the present invention.

[0032] In one embodiment, the anti-counterfeiting material is an anti-counterfeiting film material, and the carbon nanodots of the present invention are added during the preparation process of the film.

[0033] The fifth object of the present invention is to provide applications of the carbon nanodots.

[0034] In one embodiment, the application includes use in the field of detection of cobalt ions.

[0035] In one embodiment, the detection of the cobalt ions is qualitative detection or quantitative detection.

[0036] In one embodiment, the application is for detecting cobalt ions in soil systems, water systems, and organisms.

[0037] In one embodiment, the application includes use in the field of cell imaging.

[0038] In one embodiment, the application is for preparing fluorescent ink for printing anti-counterfeiting marks.

[0039] Advantages and effects of the present invention:

[0040] (1) The method for preparing synthetic carbon nanodots of the present invention uses naturally dried camphor tree fallen leaves as raw materials and does not require the use of any chemicals. The materials are widely available, low in cost, can achieve waste recycling, are environmentally friendly and safe, and have good economic value and practicality.

[0041] (2) The method for preparing the synthetic carbon nanodots of the present invention is simple to operate, has simple requirements on preparation equipment, has a fast synthesis speed, and is easy to realize industrial application.

[0042] (3) The synthetic carbon nanodots prepared by the present invention have no cytotoxicity, a fluorescence intensity of more than 1300, good water solubility, fluorescence properties, and stability, and can achieve Co 2+ Selective detection.

[0043] (4) The carbon nanodots synthesized by the present invention can be used for anti-counterfeiting, cell imaging, Co 2+ In areas such as detection, for example, invisible ink or test paper can be developed. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart of the drying, grinding, calcining, and crushing of naturally dried leaves in Example 1 of the present invention; wherein 1 is a drying oven uamato DX-400, 2 is a mortar, 3 is a high-temperature furnace A-550, 4 is powder, 5 is fine powder, and 6 is a solution;

[0045] FIG2 is a diagram of the experimental steps of ultrasound and centrifugation in Example 1 of the present invention; wherein 7 is an ultrasonic oscillator DC-200H, 8 is a centrifuge E-centrifuge, and 9 is a sample bottle;

[0046] FIG3 is a UV-visible spectrum of plant-synthesized carbon nanodots diluted 400 times in Example 1 of the present invention;

[0047] FIG4 is a fluorescence spectrum of carbon nanodots synthesized from plants at different excitation wavelengths in Example 1 of the present invention;

[0048] FIG5 is a fluorescence spectrum of carbon nanodots synthesized from plants at different dilution ratios in Example 1 of the present invention;

[0049] FIG6 is a comparison diagram of carbon nanodots synthesized using plants in Example 1 of the present invention under (1) sunlight and (2) UV light;

[0050] FIG7 is a comparison diagram of the Tyndall effect phenomenon observed under sunlight using carbon nanodots synthesized from plants and pure water in Example 1 of the present invention;

[0051] FIG8 is a comparison chart of writing NttU using ink made of plant-synthesized carbon nanodots under UV light and under sunlight in Example 1 of the present invention;

[0052] Figure 9 shows the relationship between log(F0 / F) and Co 2+ Linear relationship graph of concentration;

[0053] Figure 10 is a test graph of the selectivity of fluorescent carbon dots to common metal ions. DETAILED DESCRIPTION

[0054] 1. Instruments used in the present invention

[0055] 1. Oven uamato DX-400

[0056] 2. High temperature furnace A-550

[0057] 3. Ultrasonic Oscillator DC-200H

[0058] 4. Centrifuge

[0059] 5. Ultraviolet lamp UVGL-25

[0060] 6. Fluorescence Detector F-4500

[0061] 7. Lambda EZ-201 UV / Visible Light Detector

[0062] 2. Experimental Materials Used in the Present Invention

[0063] 1. Centrifuge tube

[0064] 2. Sample bottle

[0065] 3. Plastic nipple dropper

[0066] 4. Quartz glass bottle

[0067] 5. Mortar

[0068] 6. Naturally dried camphor leaves

[0069] 7. Distilled water

[0070] Example 1: A method for preparing synthetic carbon nanodots

[0071] A method for preparing carbon nanodots, comprising the following steps:

[0072] (1) As shown in Figure 1, fallen leaves of camphor trees were collected, dried naturally, and then placed in an oven 1 at approximately 82°C for 24 hours. 2 g of the dried leaves were ground into powder 4 using a mortar 2, and then calcined in a high-temperature furnace 3 at 280°C for 4 hours. After burning, the carbonized leaf powder was taken and evenly ground into a fine powder using a mortar for 30 minutes.

[0073] (2) As shown in FIG2 , the carbonized leaf powder 5 ground into a fine powder in the previous step was placed in a sample bottle 9 , 20 mL of distilled water was added, and the sample was placed in an ultrasonic oscillator 7 . After oscillation for 2 hours, the solution was poured into a centrifuge tube and placed in a centrifuge 8 . The tube was centrifuged at 5000 rpm for 10 minutes. The supernatant was collected after centrifugation to obtain a carbon nanodot solution. The carbon nanodot solution was placed in a sample bottle and stored in aluminum foil to protect from light.

[0074] The obtained carbon nanodot solution is analyzed, specifically including:

[0075] (1) UV-visible spectroscopy and fluorescence spectroscopy analysis

[0076] The carbon nanodot solution was diluted with distilled water to the required concentration for the experiment, and after uniform mixing, UV-visible light spectrum and fluorescence spectrum tests were performed. The optical properties of the synthesized fluorescent substance were analyzed using absorption spectrum and fluorescence spectrum.

[0077] Figure 3 shows the absorption spectrum of the carbon nanodot solution after dilution 400 times. As can be seen from Figure 3, within the wavelength range of 265nm-290nm, the absorbance is linearly related to the wavelength.

[0078] Figure 4 shows the fluorescence emission spectra at different excitation wavelengths. As can be seen from Figure 4, when the incident light is 320nm, the strongest fluorescence emission is obtained at 455nm. Furthermore, as the incident light increases from 300nm to 340nm, the position of the strongest emission spectrum shifts toward longer wavelengths. The different emission wavelengths at different excitation wavelengths also confirm the presence of carbon nanodots.

[0079] Figure 5 shows fluorescence spectra at different dilution ratios. The fluorescence intensity of the carbon nanodot solution obtained in the experiment was measured at different dilution ratios using an excitation wavelength of 320 nm. As shown in Figure 5, when the sample solution was diluted with distilled water, the fluorescence intensity increased with the dilution ratio, reaching a peak of 1325 at a 100-fold dilution. The fluorescence intensity then gradually decreased with further dilution. This is likely due to the high sample concentration being prone to self-absorption, which is reduced by dilution.

[0080] (2) Analysis of fluorescence characteristics of UV lamps

[0081] By taking advantage of the fact that fluorescent substances can be affected by short wavelengths (such as UV light) and produce fluorescence, the carbon nanodot solution obtained in the experiment was observed to see whether it has fluorescent properties.

[0082] The left and right figures in Figure 6 show the fluorescence of the carbon nanodot solution obtained in this example, diluted 100-fold, under a standard fluorescent lamp and an ultraviolet lamp (i.e., UV lamp). The results show that the diluted sample is transparent and colorless under standard fluorescent lamps, but emits blue fluorescence under UV lamps. This indicates that the carbon nanomaterial obtained in this example does not fluoresce under sunlight.

[0083] (3) Analysis of the Tyndall effect

[0084] When a laser beam is transmitted through a colloid, a beam of light can be observed scattered perpendicularly from the colloid. This phenomenon is called the Tyndall effect. The Tyndall effect distinguishes true solutions from colloidal solutions. When the particle size of a sol is between 1 and 100 nm, a light path can be observed due to light scattering, whereas no light path can be observed in a true solution.

[0085] Figure 7 shows the laser irradiation of a 100-fold diluted carbon nanodot solution and pure water. Figure 7 clearly shows the generation of a beam of light in the diluted carbon nanodot solution, confirming that the synthesized carbon nanodot solution is a colloidal solution. However, this phenomenon is absent in the pure water sample on the right. These results indicate that the carbon nanodots synthesized in this example contain fluorescent material, including particles ranging from 1 to 100 nm.

[0086] (4) Fluorescence stability analysis

[0087] A. Storage stability

[0088] The carbon nanodot solution was placed in a sample vial, protected from light by aluminum foil, and stored at room temperature for various periods of time. The solution was then diluted 100-fold and its fluorescence intensity was measured at an excitation wavelength of 320 nm to analyze its change over time. The results, shown in Table 1, show that after two months of storage at room temperature, the solution retained over 97% of its fluorescence intensity.

[0089] Table 1

[0090] B Ionic Strength Stability

[0091] The obtained carbon nanodot solution was diluted 100 times with NaCl solution of different concentrations, and the fluorescence intensity at an excitation wavelength of 320 nm was measured to analyze the change of the fluorescence intensity with the ionic strength.

[0092] The results are shown in Table 2, which are basically unaffected by the concentration of NaCl solution.

[0093] Table 2

[0094] Example 2: A method for preparing synthetic carbon nanodots

[0095] A method for preparing carbon nanodots, comprising the following steps:

[0096] (1) Collect fallen leaves from camphor trees, dry them naturally in an oven at approximately 85°C for 20 hours, grind 2 g of the dried leaves into powder using a mortar and pestle, and calcine them in a high-temperature furnace at 260°C for 3.6 hours. After burning, take the carbonized leaf powder and grind it evenly in a mortar and pestle for 50 minutes to form a fine powder.

[0097] (2) The carbonized leaf powder ground into a fine powder in the previous step was placed in a sample bottle. 20 mL of distilled water was added and the sample was placed in an ultrasonic oscillator. After oscillation for 3 hours, the solution was poured into a centrifuge tube and centrifuged at 6000 rpm for 12 minutes. The supernatant was collected after centrifugation to obtain the carbon nanodot solution. The carbon nanodot solution was placed in a sample bottle and stored in aluminum foil to protect from light.

[0098] The obtained carbon nanodot solution has a fluorescence intensity of 1321 at an excitation wavelength of 320 nm after being diluted 100 times, and can maintain more than 97% of the fluorescence intensity after being stored at room temperature for 2 months, and can also maintain a fluorescence intensity of 1319 in 6M NaCl solution.

[0099] Example 3: A method for preparing synthetic carbon nanodots

[0100] A method for preparing carbon nanodots, comprising the following steps:

[0101] (1) Collect fallen leaves from camphor trees, dry them naturally in an oven at approximately 80°C for 28 hours, grind 2 g of the dried leaves into powder using a mortar and pestle, and calcine them in a high-temperature furnace at 230°C for 3.8 hours. After burning, take the carbonized leaf powder and grind it evenly in a mortar and pestle for 40 minutes to form a fine powder.

[0102] (2) The carbonized leaf powder ground into a fine powder in the previous step was placed in a sample bottle. 20 mL of distilled water was added and the sample was placed in an ultrasonic oscillator. After oscillation for 4 hours, the solution was poured into a centrifuge tube and centrifuged at 8000 rpm for 16 minutes. The supernatant was collected after centrifugation to obtain the carbon nanodot solution. The carbon nanodot solution was placed in a sample bottle and stored in aluminum foil to protect from light.

[0103] The obtained carbon nanodot solution has a fluorescence intensity of 1319 at an excitation wavelength of 320 nm after being diluted 100 times, and can maintain 98% of the fluorescence intensity after being stored at room temperature for 2 months. It has a fluorescence intensity of 1320 in a 6M NaCl solution. Optimization Example 4: Effect of Calcination Time on Carbon Nanodots

[0104] The calcination time of Example 1 was adjusted, and the other steps and parameters were consistent with Example 1. The fluorescence intensity of the carbon nanodots obtained with different calcination times at an excitation wavelength of 320 nm after being diluted 100 times was compared.

[0105] The results are shown in Table 3. The fluorescence intensity is higher within 3.5-4 hours.

[0106] Table 3

[0107] Application Example 1: Preparation of fluorescent ink using carbon nanodot solution

[0108] The results in FIG5 show that the carbon nanodot solution obtained in Example 1 has the strongest fluorescence when diluted 100 times.

[0109] The synthesized fluorescent material (i.e., a 100-fold diluted carbon nanodot solution) was used to write on a black desktop, as shown in FIG8 .

[0110] The written words are clearly visible under UV light (the upper picture of Figure 8), but there is no fluorescence under fluorescent light (the lower picture of Figure 8).

[0111] Therefore, the carbon nanodot solution prepared in Example 1 can be further made into invisible ink and developed into a special anti-counterfeiting mark.

[0112] Application Example 2: Application of Carbon Nanodots in Bioimaging

[0113] (1) Analysis of the cytotoxicity of fluorescent carbon nanodot solution

[0114] In order to determine the cytotoxic effect of the fluorescent carbon nanodots prepared in Example 1 on cells, a cytotoxicity test was performed using mouse mononuclear macrophage RAW264.7 cells using the MTT method.

[0115] Specifically:

[0116] Mouse mononuclear macrophage RAW264.7 cells were cultured at 8×10 3 / well were seeded in a 96-well plate. After the cells adhered, phosphate buffered saline (PBS) containing the fluorescent carbon nanodot solution prepared in Example 1 was added (the concentrations of the fluorescent carbon nanodot solution were 0, 50, 100, 200, 400, and 800 μL / mL, respectively). After incubation in a 37°C, 5% (volume fraction) CO2 incubator for 24 hours, 20 μL of thiazolyl blue solution (MTT, 5 mg / mL) was added to each well. After incubation in the incubator for 4 hours, the original culture medium was discarded, 150 μL of DMSO solution was added to each well, and the absorbance of each well at 490 nm was measured using a microplate reader. The parallel experiment was repeated 3 times.

[0117] The MTT results in Table 4 below show that the fluorescent carbon nanodots prepared in Example 1 have almost no cytotoxicity and have no effect on cell proliferation when the concentration reaches 800 μL / mL, indicating that the carbon nanodot solution prepared in Example 1 has almost no toxicity to cells, has good biocompatibility, and can be used for cell imaging.

[0118] Table 4

[0119] (2) Application of fluorescent carbon nanodots in cell imaging

[0120] The fluorescent carbon nanodot solution prepared in Example 1 was used to perform imaging analysis on cells.

[0121] Specifically:

[0122] RAW264.7 cells were seeded at 150,000 cells / well in a multiwell plate and incubated in a 37°C, 8% (volume fraction) CO2 incubator for 24 hours. The culture medium was then discarded and a PBS solution containing the fluorescent carbon nanodot solution prepared in Example 1 (100 μL / mL) was added. After overnight incubation, the culture medium was discarded and the cells were washed three times with PBS buffer to remove any residual fluorescent carbon nanodots on the cell surface.

[0123] The excitation wavelength was set to 320nm and the cells were imaged. The results showed that green fluorescence was emitted from inside the cells and the cell structure could be clearly seen, indicating that the fluorescent carbon nanodots were able to enter the cells and effectively mark the cells.

[0124] Application Example 3: Carbon nanodots in metal ion Co 2+ Application in detection

[0125] Cobalt is a key industrial metal material in the production of heat-resistant alloys, cemented carbides, corrosion-resistant alloys, and magnetic alloys. Cobalt-based compounds (such as cobalt oxide, cobalt hydroxide, and lithium cobaltate) are increasingly used in lithium-ion batteries, supercapacitors, and electrocatalytic oxidation. However, long-term exposure to high cobalt concentrations can lead to toxic effects, including pneumonia, asthma, cardiomyopathy, contact dermatitis, goiter, and gastrointestinal disorders. Furthermore, cobalt and cobalt compounds are classified as Group 2A probable human carcinogens by the International Agency for Cancer.

[0126] Cobalt ions share the common characteristics of heavy metal ions: they are non-biodegradable and can accumulate hundreds or even thousands of times through the food chain, ultimately entering the human body. Consequently, environmental and biological monitoring of cobalt ions has increasingly attracted attention and become a research priority, particularly the effective detection of cobalt ions in water.

[0127] This example analyzes the carbon nanodots in Example 1. 2+ Application effect in detection.

[0128] (1) Qualitative and quantitative test analysis

[0129] With different concentrations of Co 2+ Solution (cobalt chloride) dilute the carbon nanodot solution obtained in Example 1 by 100 times to make the Co 2+ The final concentrations were 0, 0.02, 0.04, 0.08, 0.2, 0.4, 0.80, 2, 4, 8, 10, 20, 40, 60, 80, 100, 120, 150, and 200 μM. After 5 min, the fluorescence intensity at 455 nm was measured under an excitation wavelength of 320 nm. 2+ The concentration is taken as the horizontal axis, and the value without Co 2+ Concentration (i.e. adding Co 2+ Before joining Co 2+ The ratio of the fluorescence intensity of the solution after adding Co is taken as the logarithm log (F0 / F) as the ordinate, where F0 is the fluorescence intensity of the solution after adding Co 2+ The fluorescence intensity before adding Co 2+ The fluorescence intensity was then logarithmically calculated with a base of 10 to plot a standard curve, as shown in FIG9 .

[0130] The results show that the fluorescence intensity of the system increases with the 2+ The solubility of Co 2+ The concentration was 2×10 -8 ~2×10 -4 In the range of M, the logarithm of relative fluorescence intensity log(F0 / F) and Co 2+The concentration has a good linear relationship, and the linear regression equation is log(F0 / F)=0.0046C(Co 2+ )+0.0137, R 2 Greater than 0.99, the minimum detection limit is 2×10 -8 M.

[0131] (2) Anti-interference capability test analysis

[0132] The carbon nanodots obtained in Example 1 were used to detect various metal ions in water;

[0133] The specific method is:

[0134] The solutions containing different metal ions were diluted 100 times respectively with the carbon nanodot solution of Example 1 to make the final concentration of metal ions in each solution 2×10 -4 M; 5 min later, the samples containing different metal ions (Mg 2+ 、Ni 2+ , Ca 2+ 、Al 3+ 、Na + 、Li + , K + 、Sr 2+ 、Ba 2+ 、Mn 2+ , Pb 2+ 、Ag + 、Fe 2+ 、Cd 2+ 、Zn 2+ Cr 3+ 、Cu 2+ 、Fe 3+ 、Hg 2+ 、Bi 3+ Cr 6+ 、Co 2+ ) at 455nm, and then compared with F0 in Example 1 to calculate the F / F0 value of the solution containing different metal ions. F0 is the fluorescence intensity of the solution containing Co 2+ F is the fluorescence intensity before addition of metal ions; the results are shown in FIG10 .

[0135] It can be seen from Figure 10 that only when Co 2+ When the carbon nanoparticles in Example 1 are present, the fluorescence intensity of the system is significantly weakened, and its F / F0 value is significantly reduced, indicating that the carbon nanoparticles in Example 1 have a significant effect on the fluorescence of Co. 2+ There is good selectivity.

[0136] (3) Co 2+ Analysis of spike recovery

[0137] Co 2+ The spike recovery was analyzed and the results showed that the spike recovery was 105%.

[0138] Application Example 4: Carbon nanodots in metal ion Co 2+ Application in detection

[0139] On the basis of Example 1, some preparation processes were changed to obtain carbon nanodots (other processes or parameters remained the same), and then the obtained carbon nanodot solution was subjected to the method in Example 3. 2+ The detection effect was analyzed, including the logarithm of the relative fluorescence intensity log (F0 / F) and Co 2+ concentration, and through the common metal ions (Pb 2+ 、Fe 2+ 、Cd 2+ Cr 3+ 、Cu 2+ 、Hg 2+ 、Bi 3+ ) to determine whether the anti-interference test is effective for Co 2+ Be selective.

[0140] Table 5 Carbon nanodots obtained from different raw materials

[0141] Table 6 Carbon nanodots obtained by different processes

[0142] Wherein, the process of comparative example 1 is:

[0143] (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them in an oven at about 82℃ for 24 hours. Take 2g of dried leaves, grind them into powder with a mortar, add 20mL of distilled water, and then put them into a high-temperature furnace for calcination at 280℃ for 4 hours.

[0144] (2) Place the solution in an ultrasonic oscillator and shake for 2 hours. Pour the solution into a centrifuge tube and centrifuge it at 5000 rpm for 10 minutes. After centrifugation, collect the supernatant to obtain the carbon nanodot solution.

[0145] Application Example 5: Carbon nanodots in soil Co 2+ Application in detection

[0146] Distilled water was added to the soil sample to be tested, ultrasonicated for a period of time, and the supernatant was collected by centrifugation. The carbon nanodot solution obtained in Example 1 was diluted 100 times with the supernatant as solvent. The fluorescence intensity at 455 nm was measured under an excitation wavelength of 320 nm. The logarithm of the relative fluorescence intensity was calculated as log(F0 / F), where F0 is the concentration of Co added. 2+ The fluorescence intensity before adding Co2+ The fluorescence intensity is then logarithmically based on 10 and substituted into the linear regression equation to calculate the Co content in the soil sample. 2+ Qualitative and quantitative detection.

[0147] Application Example 6: Fluorescent Anti-Counterfeiting Film

[0148] A fluorescent anti-counterfeiting film comprises a base layer, a visible / hidden layer and a surface coating layer which are sequentially stacked, wherein the base layer is made of polyvinyl pyrrolidone, the visible / hidden layer is drawn with fluorescent nano-carbon dots prepared in Example 1, and the surface coating layer is made of acrylic resin and epoxy acrylic resin.

[0149] Optionally, the preparation steps include the following steps:

[0150] S1. Add polyvinyl pyrrolidone to dichloromethane to prepare a solution, then spread the solution on a glass slide and air-dry to obtain a base layer;

[0151] S2. Draw a pattern on the base layer using the fluorescent nano-carbon dot solution prepared in Example 1, and air-dry to form a visible / hidden layer;

[0152] S3. Apply a mixture of acrylic resin and epoxy acrylic resin on the visible and invisible layer so that it covers the visible and invisible layer, and air-dry to form a surface coating layer to obtain an anti-counterfeiting film.

Claims

1. A method for preparing carbon nanodots by using naturally dried fallen leaves, characterized in that: The preparation method comprises the following steps: (1) Pre-treating naturally dried camphor tree leaves and grinding them into powder; (2) placing the powder obtained in step (1) into a high-temperature furnace for calcining to obtain carbonized leaf powder, and then grinding the powder into fine powder; (3) adding the fine powder obtained in step (2) into water and subjecting it to ultrasonic treatment to obtain a solution; (4) Centrifuge the solution in step (3) and take out the supernatant to obtain carbon nanodots.

2. The method according to claim 1, characterized in that: The method for preparing carbon nanodots by using naturally dried fallen leaves comprises the following steps: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

3. A carbon nanodot, characterized in that: The product is prepared by the preparation method according to claim 1 or 2.

4. The carbon nanodots according to claim 3, characterized in that: The carbon nanodots are in solid, semi-solid or liquid form.

5. A fluorescent ink, characterized in that: Containing the carbon nanodots according to claim 3.

6. The fluorescent ink according to claim 5, characterized in that: The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

7. An anti-counterfeiting material, characterized in that: The anti-counterfeiting material uses the carbon nanodots described in claim 3, or uses the fluorescent ink described in claim 5.

8. The anti-counterfeiting material according to claim 5, characterized in that: The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

9. The anti-counterfeiting material according to claim 7, characterized in that: The anti-counterfeiting material is an anti-counterfeiting film, and the carbon nanodots described in claim 3 are added during the preparation process of the film.

10. A cell imaging method, characterized in that: The cell imaging method uses the carbon nanodots described in claim 3 as fluorescent markers.

11. The cell imaging method according to claim 10, characterized in that: The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

12. A method for detecting cobalt ions, characterized in that: The method uses the carbon nanodots according to claim 3.

13. The method according to claim 12, characterized in that The detection is used for detecting cobalt ions in soil systems, water systems or organisms.

14. The method according to claim 12, characterized in that The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

15. A method for preparing an anti-counterfeiting material, characterized in that: The method uses the carbon nanodots according to claim 3.

16. The method according to claim 15, characterized in that The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

17. A method for specific detection of cobalt ions, characterized in that: The method uses the carbon nanodots described in claim 3; the detection is used for the detection of cobalt ions in a water system; The preparation of carbon nanodots is as follows: (1) Pick up fallen leaves of camphor trees, dry them naturally, and then put them into an oven at 82°C for 24 hours; (2) Take 2 g of dry leaves, grind them into powder with a mortar, and then calcine them in a high-temperature furnace at 280°C for 4 h. After burning, take the carbonized leaf powder and grind it evenly with a mortar for 30 min into a fine powder. (3) The carbonized leaf powder ground into fine powder in the previous step was placed in a sample bottle, 20 mL of distilled water was added, and then placed in an ultrasonic oscillator. After oscillation for 2 hours, the solution was poured into a centrifuge tube, placed in a centrifuge, and centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was taken to obtain a carbon nanodot solution.

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