A method for preparing fluorescent carbon dots based on coffee grounds and its application in the detection of imidacloprid.

Abstract

This invention relates to novel carbon nanomaterials, specifically carbon quantum dots, and a method for preparing fluorescent carbon dots based on coffee grounds and their application in the detection of imidacloprid. The preparation method is as follows: dried coffee grounds are transferred to a muffle furnace for calcination. The resulting solid powder is thoroughly mixed with hydrogen peroxide. The mixed solution is then transferred to a household microwave oven for heating. The target fluorescent carbon dots are obtained after centrifugation, dialysis, and vacuum drying. The fluorescent carbon dots prepared by this invention are synthesized using a microwave-assisted method, possess stable fluorescent properties, and are non-toxic. They can be used as fluorescent probes for the quantitative measurement of imidacloprid.

Description

Technical Field

[0001] This invention belongs to the field of novel carbon nanomaterials technology, specifically relating to a method for preparing fluorescent carbon dots based on coffee grounds and its application in the detection of imidacloprid. Background Technology

[0002] Coffee is one of the most popular beverages, and global coffee consumption continues to grow. Coffee grounds are produced during the roasting and extraction process of coffee beans, with a recovery rate as high as 99.5%. The main component of coffee grounds is caffeine, which can produce toxic gases and accumulate salts. Considering the coffee roasting and extraction process, carbon quantum dots synthesized from waste coffee grounds can easily synthesize carbon or graphene components. Pesticides are widely used to control various pests in vegetable cultivation, but this can lead to pesticide residues in harvested products. Among all types of vegetables, leafy vegetables are the most frequently exposed to pesticides. Imidacloprid, a common carbamate pesticide, is widely used for pest control. Excessive use of imidacloprid residues in vegetables can cause kidney damage, metabolic encephalopathy, ventricular fibrillation, and multiple organ failure, and in severe cases, even death. This invention uses coffee grounds as a carbon source and employs a microwave-assisted method to synthesize blue-light carbon dots, which exhibit excellent selectivity and sensitivity to imidacloprid. Summary of the Invention

[0003] To achieve the above objectives, this invention utilizes a microwave-assisted method to prepare high-purity carbon quantum dots with high fluorescence properties, and verifies that they can be widely used as fluorescent detectors for detecting imidacloprid.

[0004] The technical solution adopted in this invention is:

[0005] A method for preparing fluorescent carbon dots based on coffee grounds includes the following steps:

[0006] 1) Place the dried coffee grounds into a muffle furnace and calcine them. Then, add the calcined coffee grounds powder into hydrogen peroxide.

[0007] 2) Transfer the mixed solution obtained in step 1) to a household microwave oven and heat it;

[0008] 3) Cool the reaction system obtained in step 2) to room temperature naturally, remove impurities by filtration, centrifugation and dialysis, and then dry under vacuum to obtain the target fluorescent carbon dots.

[0009] Furthermore, in the above preparation method, step 1), the calcination conditions are: calcination at 300°C for 120 min.

[0010] Furthermore, in the above preparation method, in step 1), the ratio of calcined coffee grounds powder to hydrogen peroxide is 0.5g:30mL.

[0011] Furthermore, in the above preparation method, step 2), the microwave oven has a power of 900W and a heating time of 2min.

[0012] Furthermore, in the above preparation method, step 3), the centrifugation conditions are: centrifugation at 10000 rpm for 10 min.

[0013] Furthermore, in the above preparation method, step 3), the dialysis bag used for dialysis is 500 Da.

[0014] Furthermore, in the above preparation method, step 3), the vacuum drying is performed at -49°C for 24 hours.

[0015] The application of coffee grounds-based fluorescent carbon dots prepared by any of the above methods as fluorescent probes in the detection of imidacloprid.

[0016] Furthermore, the above applications are implemented as follows:

[0017] 1) Measure 200 μL of the test solution, add 600 μL of ultrapure water and 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe, and after mixing evenly, react for 10 min.

[0018] 2) Place the mixed solution obtained in step 1) into a fluorescence spectrometer, select 332nm as the excitation wavelength, and set the spectral range to 332nm~600nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454nm.

[0019] 3) Measure 800 μL of ultrapure water and add 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe. After mixing evenly, react for 10 min.

[0020] 4) Place the mixed solution obtained in step 3) into a fluorescence spectrometer, select 332nm as the excitation wavelength, set the spectral range to 332nm~600nm, and after obtaining the complete fluorescence spectrum, read the fluorescence intensity value I0 at 454nm.

[0021] 5) Calculate the value of (I-I0) / I0, and calculate the concentration of imidacloprid in the test solution using the standard curve of imidacloprid.

[0022] Furthermore, in the above application, the method for plotting the standard curve of imidacloprid is as follows: Take different volumes of imidacloprid standard solution with a concentration of 0.01 mol / L, and add 200 μL of a coffee grounds-based fluorescent carbon dot solution with a concentration of 0.2 mg / mL to each solution. After mixing thoroughly, react for 10 min to obtain a gradient concentration of imidacloprid fluorescent carbon dot mixed solution. Place the mixed solution in a fluorescence spectrometer, select 332 nm as the excitation wavelength, and set the spectral range to 332 nm-600 nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454 nm. x Plotting the concentration of imidacloprid as the x-axis and (I) as the y-axis, the concentration of im x The value of -I0) / I0 is used as the ordinate to plot the standard curve of imidacloprid.

[0023] The beneficial effects of this invention are:

[0024] 1. The fluorescent carbon dots prepared by the present invention using the microwave method have high fluorescence intensity, good stability, simple synthesis method, and the carbon source is coffee grounds, which are inexpensive and readily available, resulting in low cost.

[0025] 2. Fluorescence testing experiments show that the coffee grounds-based fluorescent carbon dots prepared in this invention can be used as fluorescent probes for the quantitative detection of imidacloprid, and are expected to become a simple, rapid, convenient, sensitive and selective fluorescent probe for the detection of imidacloprid. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the synthesis of the fluorescent carbon dots prepared in this invention.

[0027] Figure 2 This is a transmission electron microscope image of the fluorescent carbon dots prepared in this invention.

[0028] Figure 3 The optimal excitation and emission spectra of the fluorescent carbon dots prepared in this invention are shown.

[0029] Figure 4 The fluorescence spectra of the fluorescent carbon dots prepared in this invention at different excitation wavelengths are shown.

[0030] Figure 5 The fluorescence spectrum of the fluorescent carbon dots prepared in this invention is a photostrace of their photostraceability.

[0031] Figure 6 The fluorescence spectra of the fluorescent carbon dots prepared in this invention at different imidacloprid concentrations are shown.

[0032] Figure 7 The standard curve for detecting imidacloprid using fluorescent carbon dots prepared in this invention as probes is shown in the inset, where the linear relationship is shown in the range of 0.30-0.42 g / L.

[0033] Specific implementation methods

[0034] The present invention will be further illustrated below with specific embodiments. The present invention is not limited to these embodiments; minor variations may be made without departing from the scope described.

[0035] Example 1: A method for preparing fluorescent carbon dots based on coffee grounds (I) The preparation method includes the following steps:

[0036] 1) Place the dried coffee grounds into a muffle furnace and calcine at 300℃ for 120 minutes to obtain coffee ground powder;

[0037] 2) Take 0.5g of the coffee grounds powder obtained in step 1) and mix it with 30mL of hydrogen peroxide;

[0038] 3) Place the mixed solution obtained in step 2) into a 900W household microwave oven and heat for 2 minutes, then let it cool naturally to room temperature;

[0039] 4) Filter the brownish-yellow liquid obtained in step 3), then centrifuge at 10,000 rpm for 10 min, and take the supernatant;

[0040] 5) The supernatant obtained in step 4) is placed into a 500 Da dialysis bag and poured into ultrapure water for dialysis to remove impurities, resulting in a brownish-yellow solution.

[0041] 6) Place the brownish-yellow solution obtained in step 5) in a vacuum dryer and dry it under vacuum at -49°C for 24 hours to obtain the target fluorescent carbon dots.

[0042] (II) The fluorescent carbon dots prepared in Example 1 were characterized, and the specific characterization results are as follows:

[0043] (1) Transmission electron microscopy (TEM) image: The fluorescent carbon dots prepared in Example 1 above were characterized by transmission electron microscopy (TEM) images, and it can be seen that their size is approximately 2.1 nm. Figure 2 ).

[0044] (2) The optimal excitation and emission wavelengths of the fluorescent carbon dot solution are 332 nm and 454 nm, respectively (e.g., ...). Figure 3 It exhibits blue fluorescence under a 365nm ultraviolet lamp. Studies of its fluorescence spectra at different excitation wavelengths revealed (…). Figure 4 The emission peak of the carbon dots redshifts, which is related to the non-uniform size distribution and surface defects of the synthesized carbon quantum dots.

[0045] (3) The fluorescence stability of the coffee grounds-based fluorescent carbon dots was tested. After continuous irradiation with a UV lamp at 365 nm for 60 min, the fluorescence intensity of the carbon dots remained stable. Figure 5 This indicates that it has strong resistance to photobleaching.

[0046] Example 2: The fluorescent carbon dots prepared in Example 1 were used as fluorescent probes for the detection of imidacloprid.

[0047] The specific testing method includes the following steps:

[0048] 1) Measure 200 μL of the test solution, add 600 μL of ultrapure water and 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe, and after mixing evenly, react for 10 min.

[0049] 2) Place the mixed solution obtained in step 1) into a fluorescence spectrometer, select 332nm as the excitation wavelength, and set the spectral range to 332nm~600nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454nm.

[0050] 3) Measure 800 μL of ultrapure water and add 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe. After mixing evenly, react for 10 min.

[0051] 4) Place the mixed solution obtained in step 3) into a fluorescence spectrometer, select 332nm as the excitation wavelength, set the spectral range to 332nm~600nm, and after obtaining the complete fluorescence spectrum, read the fluorescence intensity value I0 at 454nm.

[0052] 5) Take different volumes of 0.01 mol / L imidacloprid standard solution, and add 200 μL of 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution to each. After mixing thoroughly, react for 10 min to obtain imidacloprid fluorescent carbon dot mixed solutions with gradient concentrations. Place each mixed solution in a fluorescence spectrometer, select 332 nm as the excitation wavelength, and set the spectral range to 332 nm-600 nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454 nm. x Plotting the concentration of imidacloprid as the x-axis and (I) as the y-axis, the concentration of im x The value of -I0) / I0 is used to plot the standard curve of imidacloprid on the ordinate. Figure 6 and Figure 7 ).

[0053] 6) Calculate the value of (I-I0) / I0, and calculate the concentration of imidacloprid in the test solution using the standard curve of imidacloprid.

[0054] Within the imidacloprid concentration range of 0.3 g / L–0.42 g / L, the imidacloprid concentration showed a good linear relationship with the quenching efficiency of fluorescent carbon dots. Figure 7 Its linear equation is y = 0.0715 + 1.0306x (R 2 =0.996).

[0055] In summary, the fluorescent carbon quantum dots prepared by the microwave-assisted method of this invention possess high purity, stable fluorescence properties, and are non-toxic. Detection experiments show that the prepared fluorescent carbon dots can be used as fluorescent probes for the quantitative detection of imidacloprid.

Claims

1. A method for preparing fluorescent carbon dots based on coffee grounds, characterized in that, Includes the following steps: 1) Place the dried coffee grounds into a muffle furnace and calcine them. Then, add the calcined coffee grounds powder into hydrogen peroxide. 2) Transfer the mixed solution obtained in step 1) to a household microwave oven and heat it; 3) Cool the reaction system obtained in step 2) to room temperature naturally, remove impurities by filtration, centrifugation and dialysis, and then dry under vacuum to obtain the target fluorescent carbon dots.

2. The preparation method according to claim 1, characterized in that, In step 1), the calcination conditions are: calcination at 300°C for 120 minutes.

3. The preparation method according to claim 1, characterized in that, In step 1), the ratio of calcined coffee grounds powder to hydrogen peroxide is 0.5g:30mL.

4. The preparation method according to claim 1, characterized in that, In step 2), the microwave oven has a power of 900W and a heating time of 2 minutes.

5. The preparation method according to claim 1, characterized in that, In step 3), the centrifugation conditions are: centrifugation at 10,000 rpm for 10 min.

6. The preparation method according to claim 1, characterized in that, In step 3), the dialysis bag used for the dialysis is 500 Da.

7. The preparation method according to claim 1, characterized in that, In step 3), the vacuum drying is performed at -49°C for 24 hours.

8. The application of coffee grounds-based fluorescent carbon dots prepared by the preparation method according to any one of claims 1-7 as fluorescent probes in the detection of imidacloprid.

9. The application according to claim 8, characterized in that, The method is as follows: 1) Measure 200 μL of the test solution, add 600 μL of ultrapure water and 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe, and after mixing evenly, react for 10 min. 2) Place the mixed solution obtained in step 1) into a fluorescence spectrometer, select 332nm as the excitation wavelength, and set the spectral range to 332nm~600nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454nm. 3) Measure 800 μL of ultrapure water and add 200 μL of a 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution as a fluorescent probe. After mixing evenly, react for 10 min. 4) Place the mixed solution obtained in step 3) into a fluorescence spectrometer, select 332nm as the excitation wavelength, set the spectral range to 332nm~600nm, and after obtaining the complete fluorescence spectrum, read the fluorescence intensity value I0 at 454nm. 5) Calculate the value of (I-I0) / I0, and calculate the concentration of imidacloprid in the test solution using the standard curve of imidacloprid.

10. The application according to claim 9, characterized in that, The method for plotting the standard curve of imidacloprid is as follows: Take different volumes of 0.01 mol / L imidacloprid standard solution, and add 200 μL of 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution to each. After mixing thoroughly, react for 10 min to obtain a gradient concentration of imidacloprid fluorescent carbon dot mixed solution. Place the mixed solution in a fluorescence spectrometer, select 332 nm as the excitation wavelength, and set the spectral range to 332 nm-600 nm. After obtaining the complete fluorescence spectrum, read the fluorescence intensity value I at 454 nm. x Plotting the concentration of imidacloprid as the x-axis and (I) as the y-axis, the concentration of im x The value of -I0) / I0 is used as the ordinate to plot the standard curve of imidacloprid.

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