Preparation method of fluorescent carbon dots based on coffee grounds and application of fluorescent carbon dots in detection of imidacloprid

Abstract

The invention relates to a novel carbon nanomaterial carbon quantum dot, in particular to a preparation method of a fluorescent carbon dot based on coffee grounds and application of the fluorescent carbon dot in detection of imidacloprid. The preparation method comprises the following steps: transferring dried coffee grounds into a muffle furnace for calcining, fully mixing the obtained solid powder with hydrogen peroxide, transferring the mixed solution into a household microwave oven for heating, and carrying out centrifugation, dialysis and vacuum drying to obtain the target fluorescent carbon dots. The fluorescent carbon dots prepared by the invention are synthesized by adopting a microwave-assisted method, have stable fluorescent properties and no toxicity, and can be used as a fluorescent probe for quantitative measurement of imidacloprid.

Description

Technical Field

[0001] The invention belongs to the technical field of novel carbon nanomaterials, and particularly relates to a method for preparing fluorescent carbon dots based on coffee grounds and an application of the same in detecting imidacloprid. Background Art

[0002] Coffee is one of the most popular beverages, and the world's coffee consumption is growing. Coffee beans produce coffee grounds during roasting and extraction, and the recovery rate is as high as 99.5%. The main component of coffee grounds is caffeine, which produces toxic gases and accumulates salt. Considering the roasting and extraction process of coffee, carbon quantum dots synthesized using waste coffee grounds can easily synthesize carbon or graphene components. Pesticides are widely used to control various pests in vegetable cultivation, but they will cause pesticide residues in the harvested products. Among all types of vegetables, leafy vegetables are most often exposed to pesticides. Imidacloprid is a common carbamate pesticide that is widely used in pest control. Vegetables with excessive imidacloprid residues may cause kidney damage, metabolic encephalopathy, ventricular fibrillation and multiple organ failure, and even lead to death in severe cases. The present invention uses coffee grounds as a carbon source and synthesizes blue light carbon dots using a microwave-assisted method, which shows excellent selectivity and sensitivity to imidacloprid. Summary of the invention

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

[0004] The technical solution adopted by the present invention is:

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

[0006] 1) taking the dried coffee grounds and placing them in a muffle furnace for calcination, and taking the calcined coffee grounds powder and adding it into hydrogen peroxide;

[0007] 2) transferring the mixed solution obtained in step 1) to a household microwave oven for heating;

[0008] 3) The reaction system obtained in step 2) is naturally cooled to room temperature, and the solution after the reaction is filtered, centrifuged, and dialyzed to remove impurities, and vacuum dried to obtain the target fluorescent carbon dots.

[0009] Furthermore, in the above preparation method, in 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 the calcined coffee grounds powder to hydrogen peroxide is 0.5 g:30 mL.

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

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

[0013] Furthermore, in the above-mentioned preparation method, in step 3), the dialysis bag used for dialysis has a specification of 500Da.

[0014] Furthermore, in the above preparation method, in 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 preparation methods described above as fluorescent probes in the detection of imidacloprid.

[0016] Further, the above application method is 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, mix well, and react for 10 minutes;

[0018] 2) placing the mixed solution obtained in step 1) into a fluorescence spectrometer, selecting 332 nm as the excitation light wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I at 454 nm;

[0019] 3) 800 μL of ultrapure water was measured, and 200 μL of a 0.2 mg / mL fluorescent carbon dot solution based on coffee grounds was added thereto as a fluorescent probe. After mixing evenly, the mixture was reacted for 10 minutes;

[0020] 4) placing the mixed solution obtained in step 3) into a fluorescence spectrometer, selecting 332 nm as the excitation wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I0 at 454 nm;

[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 drawing the standard curve of imidacloprid is as follows: different volumes of imidacloprid standard solution with a concentration of 0.01 mol / L are taken respectively, and 200 μL of a fluorescent carbon dot solution based on coffee grounds with a concentration of 0.2 mg / mL is added thereto respectively, and after being mixed evenly, the mixture is reacted for 10 minutes to obtain a mixed solution of imidacloprid fluorescent carbon dots with a gradient concentration, and the mixed solution is placed in a fluorescence spectrometer respectively, 332 nm is selected as the excitation light wavelength, and the spectral range is set to 332 nm-600 nm. After obtaining a complete fluorescence spectrum, the fluorescence intensity value I at 454 nm is read. x , with the concentration of imidacloprid as the horizontal axis and (I x The standard curve of imidacloprid was drawn with the value of -I0) / I0 as the ordinate.

[0023] The beneficial effects of the present invention are:

[0024] 1. The fluorescent carbon dots prepared by the microwave method of the present invention have high fluorescence intensity, good stability, simple synthesis method, and the carbon source is coffee grounds, which is cheap and easy to obtain, and has low cost.

[0025] 2. Fluorescence test experiments show that the fluorescent carbon dots based on coffee grounds prepared in the present invention can be used as a fluorescent probe for quantitative detection of imidacloprid, and are expected to become a fluorescent probe for simple, rapid, convenient, sensitive and selective detection of imidacloprid. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the synthesis of fluorescent carbon dots prepared in the present invention.

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

[0028] Figure 3 The best excitation and emission spectra of the fluorescent carbon dots prepared by the present invention are shown in FIG.

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

[0030] Figure 5 This is a fluorescence spectrum diagram of the photostability of the fluorescent carbon dots prepared in the present invention.

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

[0032] Figure 7 This is a standard curve diagram of the fluorescent carbon dots prepared in the present invention used as a probe to detect imidacloprid, wherein the inset is a linear relationship diagram within the range of 0.30-0.42 g / L.

[0033] Specific implementation method

[0034] The present invention is further described below by way of specific examples. The present invention is not limited to the examples, and slight variations are possible without departing from the scope described.

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

[0036] 1) placing the dried coffee grounds in a muffle furnace and calcining at 300° C. for 120 min to obtain coffee grounds powder;

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

[0038] 3) placing the mixed solution obtained in step 2) in a 900W household microwave oven and heating it for 2 minutes, and then cooling it naturally to room temperature;

[0039] 4) filtering the brown-yellow liquid obtained in step 3), and then centrifuging at 10,000 rpm for 10 min to obtain the supernatant;

[0040] 5) The supernatant obtained in step 4) was placed in a 500Da dialysis bag and dialyzed in ultrapure water to remove impurities to obtain a brown-yellow solution;

[0041] 6) The brown-yellow solution obtained in step 5) was placed in a vacuum dryer and vacuum dried at -49°C for 24 hours to obtain the target fluorescent carbon dots.

[0042] (II) Characterization of the fluorescent carbon dots prepared in Example 1, the specific characterization results are as follows:

[0043] (1) Transmission electron microscopy: The fluorescent carbon dots prepared in Example 1 were characterized by transmission electron microscopy, and it was found that their size was about 2.1 nm ( Figure 2 ).

[0044] (2) The optimal excitation wavelength and emission wavelength of the fluorescent carbon dot solution are 332 nm and 454 nm, respectively (e.g. Figure 3 ), and it exhibits blue fluorescence under 365nm ultraviolet light. The study of its fluorescence spectrum under different excitation wavelengths found that ( Figure 4 ), the emission peak of carbon dots red-shifts, which is related to the uneven size distribution and surface defects of the synthesized carbon quantum dots.

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

[0046] Example 2 The fluorescent carbon dots prepared in Example 1 were used as fluorescent probes to detect imidacloprid

[0047] The specific detection 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, mix well, and react for 10 minutes;

[0049] 2) placing the mixed solution obtained in step 1) into a fluorescence spectrometer, selecting 332 nm as the excitation light wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I at 454 nm;

[0050] 3) 800 μL of ultrapure water was measured, and 200 μL of a 0.2 mg / mL fluorescent carbon dot solution based on coffee grounds was added thereto as a fluorescent probe. After mixing evenly, the mixture was reacted for 10 minutes;

[0051] 4) placing the mixed solution obtained in step 3) into a fluorescence spectrometer, selecting 332 nm as the excitation wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I0 at 454 nm;

[0052] 5) Different volumes of 0.01 mol / L imidacloprid standard solution were taken respectively, and 200 μL of 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution was added thereto respectively. After being mixed evenly, the mixture was reacted for 10 min to obtain gradient concentrations of imidacloprid fluorescent carbon dot mixed solutions. The mixed solutions were placed in a fluorescence spectrometer respectively, 332 nm was selected as the excitation light wavelength, the spectral range was set to 332 nm-600 nm, and after a complete fluorescence spectrum was obtained, the fluorescence intensity value I at 454 nm was read. x , with the concentration of imidacloprid as the horizontal axis and (I x -I0) / I0 is used as the vertical axis to draw the standard curve of imidacloprid ( 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] In the range of imidacloprid concentration from 0.3 g / L to 0.42 g / L, there is a good linear relationship between the concentration of imidacloprid and 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 microwave-assisted method in the present invention have 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 quantitative detection of imidacloprid.

Claims

1. A method for preparing fluorescent carbon dots based on coffee grounds, characterized in that: The steps include: 1) taking the dried coffee grounds and placing them in a muffle furnace for calcination, and taking the calcined coffee grounds powder and adding it into hydrogen peroxide; 2) transferring the mixed solution obtained in step 1) to a household microwave oven for heating; 3) The reaction system obtained in step 2) is naturally cooled to room temperature, and the solution after the reaction is filtered, centrifuged, and dialyzed to remove impurities, and vacuum dried to obtain the target fluorescent carbon dots.

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

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

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

5. The preparation method according to claim 1, characterized in that: In step 3), the centrifugation condition is: centrifugation at 10000 rpm for 10 min.

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

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. Use of fluorescent carbon dots based on coffee grounds prepared by the preparation method according to any one of claims 1 to 7 as fluorescent probes in detecting imidacloprid.

9. The use according to claim 8, characterized in that: Here’s how: 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, mix well, and react for 10 minutes; 2) placing the mixed solution obtained in step 1) into a fluorescence spectrometer, selecting 332 nm as the excitation light wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I at 454 nm; 3) 800 μL of ultrapure water was measured, and 200 μL of a 0.2 mg / mL fluorescent carbon dot solution based on coffee grounds was added thereto as a fluorescent probe. After mixing evenly, the mixture was reacted for 10 minutes; 4) placing the mixed solution obtained in step 3) into a fluorescence spectrometer, selecting 332 nm as the excitation wavelength, setting the spectral range to 332 nm to 600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I0 at 454 nm; 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 use according to claim 9, characterized in that: The method for drawing the standard curve of imidacloprid is as follows: taking different volumes of 0.01 mol / L imidacloprid standard solution, respectively, adding 200 μL of 0.2 mg / mL coffee grounds-based fluorescent carbon dot solution thereto, after being evenly mixed, reacting for 10 minutes to obtain gradient concentrations of imidacloprid fluorescent carbon dot mixed solutions, respectively putting the mixed solutions into a fluorescence spectrometer, selecting 332 nm as the excitation light wavelength, setting the spectral range to 332 nm-600 nm, and after obtaining a complete fluorescence spectrum, reading the fluorescence intensity value I at 454 nm. x , with the concentration of imidacloprid as the horizontal axis and (I x The standard curve of imidacloprid was drawn with the value of -I0) / I0 as the ordinate.

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