Hydrophobic carbon dots as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of food and environment detection, and relates to a hydrophobic carbon dot as well as a preparation method and application thereof, in particular to preparation of the hydrophobic carbon dot and a method for detecting micro-plastics in food and environment. A carbon source and a nitrogen source are used as reactants, the carbon source is citral, the nitrogen source is ethylenediamine and / or urea, ethanol is used as a reaction medium, and the hydrophobic carbon dots are prepared through solvothermal reaction, insoluble substance removal, dialysis and drying. The hydrophobic carbon dots are fast in dyeing, low in quenching rate, free of heating, capable of distinguishing common interferents, not affected by pH and polarity of a sample and capable of achieving efficient and fast detection in food and environmental micro-plastic detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of food and environmental detection, and more specifically relates to a kind of hydrophobic carbon dots and its preparation method and application. Background Art

[0002] Microplastics are a kind of plastic particles with a diameter less than 5mm, which widely exist in various foods and the environment. Microplastics may accumulate in the food chain, and long-term exposure may pose risks to health. For example, it may trigger an immune response and lead to immune system disorders. Therefore, microplastics are considered an emerging pollutant, seriously endangering life safety.

[0003] Microplastics in food and the environment mainly come from food packaging, processing processes and physical abrasion. Limited by instruments, methods, etc., the detection of microplastics is still a major challenge globally. The conventional detection of microplastics often relies on sophisticated and complex instruments, and the analysis of microplastics by visual recognition methods with the aid of microscopes usually has problems such as large errors. For example, small particles of sediment mixed in microplastic particles are usually misidentified as microplastics, resulting in an increase in counting. Therefore, dyes (including fluorescent dyes) are usually used to stain microplastics for judgment and counting. However, these dyes are usually not environmentally friendly and have serious photobleaching properties, and it is very difficult to achieve consistent staining effects due to the different properties of different types of plastics. Therefore, the efficient and rapid detection of common microplastics in life has become a difficult problem that needs to be overcome by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide a kind of hydrophobic carbon dots and its preparation method and application, and more specifically provide a preparation of hydrophobic carbon dots and a method for detecting microplastics in food and the environment to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: Provide a preparation method of hydrophobic carbon dots, and the steps include:

[0007] Using a carbon source and a nitrogen source as reactants, using ethanol as a reaction medium, through solvothermal reaction, removal of insoluble substances, dialysis, and drying, the hydrophobic carbon dots are obtained.

[0008] Further, the molar concentration ratio of the carbon source to the nitrogen source is 1.6 - 16.4:4.2 - 74.8.

[0009] Further, the volume ratio of the sum of the volumes of the carbon source and the nitrogen source to the volume of ethanol is 1 - 8:1 - 4.

[0010] Further, the carbon source is citral.

[0011] Further, the nitrogen source is ethylenediamine and / or urea.

[0012] Further, the temperature of the solvothermal reaction is 140 - 220 °C, and the time is 0.5 - 10 h.

[0013] Further, the removal of the insoluble matter is carried out by filtration or centrifugation.

[0014] Optionally, the filtration is carried out using a 0.22 μm filter membrane.

[0015] Optionally, the centrifugation is carried out at a centrifugal force of 2000 - 8000 g for 5 - 20 min.

[0016] Preferably, the centrifugation is carried out at a centrifugal force of 6800 g for 10 min.

[0017] Further, the dialysis is carried out using absolute ethanol as the dialysis solution and dialyzing through a 500 - 2000 Da dialysis membrane for 24 - 48 h.

[0018] For the carbon dots obtained in the present invention, by measuring the contact angle and the oil - water partition coefficient, it is determined that the carbon dots are hydrophobic (where the contact angle of the carbon dots prepared by reacting 5 mL of citral, 3 mL of ethylenediamine and 10 mL of ethanol at 180 °C for 6 hours is 107˚, and the oil - water partition coefficient LogP = 2.22). In this reaction, citral serves as the main framework of the hydrophobic structure of the carbon dots, endowing the carbon dots with high hydrophobicity, showing insolubility in water and high affinity for microplastics.

[0019] The second technical solution of the present invention: Provide a kind of hydrophobic carbon dots, and the hydrophobic carbon dots are prepared by the above - mentioned preparation method.

[0020] The third technical solution of the present invention: Provide an application of the above - mentioned hydrophobic carbon dots in the detection of microplastics in food or environment.

[0021] The fourth technical solution of the present invention: Provide a method for detecting microplastics, and the steps include:

[0022] Mix the above - mentioned hydrophobic carbon dots with ethanol to prepare a carbon dot solution;

[0023] Add the carbon dot solution to the sample to be detected and mix well to obtain a mixed solution;

[0024] Observe the mixed solution through a fluorescence microscope to complete the detection of microplastics.

[0025] Further, the final concentration of the hydrophobic carbon dots in the mixed solution is 0.05 - 20 mg / L.

[0026] Further, the fluorescence microscope observation step includes: placing the mixed solution on a glass slide, drying it, and then placing it under a fluorescence microscope for detection.

[0027] By mixing the carbon dot solution and the sample to be detected, the microplastics and the carbon dots are brought into full contact, and the hydrophobic interaction, electrostatic interaction, etc. between the microplastics and the carbon dots are utilized for adsorption.

[0028] The present invention discloses the following technical effects:

[0029] The hydrophobic carbon dots prepared by the present invention are used in the detection of microplastics in food and the environment, with rapid staining, consistency, low quenching rate, no need for heating, can distinguish common interfering substances (such as sediment, etc.), and can achieve efficient and rapid detection.

[0030] The hydrophobic carbon dots prepared by the present invention have good anti-photobleaching performance and excellent fluorescence properties. Description of the Drawings

[0031] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0032] Figure 1 It is the 3D fluorescence spectrum image of the hydrophobic carbon dots prepared in Example 1.

[0033] Figure 2 It is the transmission electron microscope (TEM) image of the hydrophobic carbon dots prepared in Example 1.

[0034] Figure 3 It is the hydrophilic and hydrophobic properties of the carbon dots prepared in Example 1.

[0035] Figure 4 It is the adsorption kinetic curve of 9 kinds of microplastics on the hydrophobic carbon dots.

[0036] Figure 5 It is the staining effect diagram of the hydrophobic carbon dots prepared in Example 1 on 9 kinds of microplastics.

[0037] Figure 6 It is the identification image of the hydrophobic carbon dots prepared in Example 1 on the microplastics containing sand. Among them, a is dark field ultraviolet excitation, b is dark field blue light excitation, c is dark field green light excitation, and d is bright field.

[0038] Figure 7 It is the staining effect diagram of the hydrophobic carbon dots prepared in Example 1 on the microplastics in different media. Among them, (a) is in honey, (b) is in honey water, and (c) is in milk.

[0039] Figure 8Quenching rate of the hydrophobic carbon dots prepared in Example 1 under different pH conditions.

[0040] Figure 9 Imaging effect of the hydrophobic carbon dots prepared in Example 1 on microplastics under different polarity conditions.

[0041] Figure 10 Quenching rate of the carbon dots prepared in Example 1 under ultraviolet light irradiation. Detailed implementation manners

[0042] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation manners of the present invention.

[0043] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0045] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0046] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0047] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0048] The raw materials and reagents used in the specific implementation manners of the present invention are commercially available products, and the purchase channels do not affect the realization of the technical effects.

[0049] Example 1

[0050] The preparation steps of the hydrophobic carbon dots are as follows:

[0051] Add 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, and then transfer them to a 50 mL polytetrafluoroethylene-lined autoclave and seal it tightly. Place the autoclave in an oven and heat it at 180 °C for 6 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0052] Example 2

[0053] The preparation steps of the hydrophobic carbon dots are as follows:

[0054] Add 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, and then transfer them to a polytetrafluoroethylene reaction kettle and tighten the seal to ensure no air leakage. Connect the reaction kettle to a microwave-assisted synthesizer and heat it at 200 °C for 0.5 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0055] Example 3

[0056] The preparation steps of the hydrophobic carbon dots are as follows:

[0057] Add 4 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, and then transfer them to a 50 mL polytetrafluoroethylene-lined autoclave and seal it tightly. Place the autoclave in an oven and heat it at 180 °C for 6 h. After cooling to room temperature, centrifuge at a centrifugal force of 6800 g for 10 min to remove insoluble particles. Dialyze the supernatant with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0058] Example 4

[0059] The preparation steps of the hydrophobic carbon dots are as follows:

[0060] Add 3 mL of citral, 5 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, and then transfer them to a 50 mL polytetrafluoroethylene-lined autoclave and seal it tightly. Place the autoclave in an oven and heat it at 180 °C for 6 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0061] Example 5

[0062] The preparation steps of the hydrophobic carbon dots are as follows:

[0063] Add 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, then transfer them to a 50 mL high-pressure reaction kettle with a polytetrafluoroethylene liner and seal it tightly. Place the reaction kettle in an oven and heat it at 190 °C for 6 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0064] Example 6

[0065] The preparation steps of the hydrophobic carbon dots are as follows:

[0066] Add 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, then transfer them to a 50 mL high-pressure reaction kettle with a polytetrafluoroethylene liner and seal it tightly. Place the reaction kettle in an oven and heat it at 180 °C for 10 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0067] Example 7

[0068] The preparation steps of the hydrophobic carbon dots are as follows:

[0069] Add 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, then transfer them to a 50 mL high-pressure reaction kettle with a polytetrafluoroethylene liner and seal it tightly. Place the reaction kettle in an oven and heat it at 140 °C for 6 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0070] Example 8

[0071] The preparation steps of the hydrophobic carbon dots are as follows:

[0072] Add 5 mL of citral, 3 mL of urea (882 mg / L), and 10 mL of absolute ethanol into a beaker, stir evenly to make them fully mixed, then transfer them to a 50 mL high-pressure reaction kettle with a polytetrafluoroethylene liner and seal it tightly. Place the reaction kettle in an oven and heat it at 180 °C for 6 h. After cooling to room temperature, filter it with a 0.22 μm filter membrane, dialyze the filtrate with absolute ethanol (500 Da) for 48 h, and dry it to obtain the hydrophobic carbon dots.

[0073] Test Example

[0074] The hydrophobic carbon dots prepared in Example 1 are used for exemplary illustration below. The technical effects of the hydrophobic carbon dots prepared in other examples are similar, and will not be elaborated one by one here.

[0075] Figure 1 is the 3D fluorescence spectral image of the hydrophobic carbon dots prepared in Example 1. It can be found from the figure that the hydrophobic carbon dots have a single fluorescence center.

[0076] Figure 2 is the transmission electron microscope (TEM) image of the hydrophobic carbon dots prepared in Example 1. It can be seen from the figure that the hydrophobic carbon dots prepared in Example 1 have a relatively small particle size.

[0077] Figure 3 is the hydrophilic and hydrophobic property of the carbon dots prepared in Example 1. It can be seen from the figure that the carbon dots prepared in the present invention are hydrophobic carbon dots.

[0078] Microplastic detection method:

[0079] Take the hydrophobic carbon dots and place them in a centrifuge tube, add ethanol solution to dissolve, and prepare a 10 mg / L carbon dot solution for standby;

[0080] Add the carbon dot solution to the sample to be tested. Specifically:

[0081] Add 1 mL of the carbon dot solution (10 mg / L) to 10 mL of the sample to be tested, mix, and make the carbon dots fully contact with the microplastics;

[0082] Take an appropriate amount of the mixed sample to be tested, place it on a glass slide, dry it and then place it under a fluorescence microscope for detection.

[0083] Figure 4 is the adsorption kinetic curve of 9 kinds of microplastics on the hydrophobic carbon dots. It can be known from the adsorption kinetic curve that after the microplastics are mixed with the hydrophobic carbon dots, they can immediately adsorb the carbon dots, and the adsorption equilibrium is reached in 10 minutes.

[0084] Figure 5 is the staining effect diagram of the hydrophobic carbon dots prepared in Example 1 on 9 kinds of microplastics. It can be found from the figure that the staining effects of the hydrophobic carbon dots prepared in Example 1 on 9 kinds of microplastics are the same. And it can be observed through experiments that the carbon dots can be immediately imaged after being blended with the microplastics, corresponding to the Figure 4 adsorption kinetic curve of the microplastics on the hydrophobic carbon dots.

[0085] Using sand as an interfering substance, the microplastics are detected by the above method, and the anti-interference performance is tested. The results are as Figure 6 shown. Specifically:

[0086] Add 10 mL of the microplastic sample to be tested with sand as the interfering substance, add 1 mL (10 mg / L) of the carbon dot solution, and then place it under a fluorescence microscope for bright-field and dark-field (blue light, green light, and ultraviolet excitation) observation.

[0087] Figure 6 Identification image of hydrophobic carbon dots prepared in Example 1 for microplastics containing sand. Among them, a is dark-field ultraviolet excitation, b is dark-field blue light excitation, c is dark-field green light excitation, and d is bright-field. As can be seen from the figure, the hydrophobic carbon dots prepared in the present invention do not stain the interfering substance (sand), the interfering substance and microplastics can be seen under bright-field, the interfering substance does not show fluorescence under dark-field, and the microplastics show fluorescence under different excitation lights.

[0088] In order to further verify the anti-interference performance of the hydrophobic carbon dots prepared in the present invention when detecting microplastics, the staining of microplastics by the hydrophobic carbon dots in honey, honey water, and milk was detected, and the results are as Figure 6 shown.

[0089] Figure 7 Staining effect diagram of hydrophobic carbon dots prepared in Example 1 for microplastics in different media. Among them, (a) is in honey, (b) is in honey water, and (c) is in milk. As can be seen from the figure, the hydrophobic carbon dots prepared in the present invention have excellent anti-interference performance when detecting microplastics.

[0090] Adjust the pH value of the sample to be tested to 2, 4, 6, 8, and 10, and test the quenching rate under different pH conditions. The results are as Figure 8 shown.

[0091] Quenching rate = (I 0 - I) / I 0 * 100%;

[0092] Among them, I 0 is the fluorescence value before adjusting the pH; I is the fluorescence value after adjustment.

[0093] Figure 8 Quenching rate of hydrophobic carbon dots prepared in Example 1 under different pH conditions. As can be seen from the figure, the hydrophobic carbon dots prepared in the present invention have strong pH stability.

[0094] Add the carbon dot solution to the microplastics dispersed in different solvents, and then observe the imaging effect, as Figure 9 shown.

[0095] The above different solvents are dimethylformamide (DMF), methanol (MeOH), ethanol (EtOH), dichloromethane (DCM), ethyl acetate (EA), and petroleum ether (PE).

[0096] Figure 9 Imaging effect of the hydrophobic carbon dots prepared in Example 1 on microplastics under different polarity conditions.

[0097] As can be seen from the figure, the hydrophobic carbon dots prepared in the present invention are not interfered by the solvent polarity.

[0098] Figure 10 Quenching rate of the carbon dots prepared in Example 1 under ultraviolet light irradiation. As can be seen from the figure, under continuous ultraviolet light irradiation, the quenching rate of the carbon dots is very low, and they have excellent anti-photobleaching performance.

[0099] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0100] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing hydrophobic carbon dots, characterized in that the steps include: The hydrophobic carbon dots are obtained by using a carbon source and a nitrogen source as reactants and ethanol as a reaction medium through solvent thermal reaction, removal of insoluble matter, dialysis and drying.

2. The preparation method according to claim 1, characterized in that The molar ratio of the carbon source to the nitrogen source is 1.6-16.4:4.2-74.8; and / or, the volume ratio of the sum of the volumes of the carbon source and the nitrogen source to ethanol is 1-8:1-4; and / or, the carbon source is citral; and / or, the nitrogen source is ethylenediamine and / or urea.

3. The preparation method according to claim 1, characterized in that: The temperature of the solvent thermal reaction is 140-220°C and the time is 0.5-10 h.

4. The preparation method according to claim 1, characterized in that: The insoluble matter is removed by filtration or centrifugation; and / or, the dialysis is performed by using anhydrous ethanol as a dialysis fluid through a 500-2000 Da dialysis membrane for 24-48 hours.

5. A hydrophobic carbon dot, characterized in that: The hydrophobic carbon dots are prepared by the preparation method according to any one of claims 1 to 4.

6. An application of the hydrophobic carbon dots described in claim 5 in the detection of microplastics in food or the environment.

7. A method for detecting microplastics, characterized in that the steps include: Mixing the hydrophobic carbon dots according to claim 5 with ethanol to prepare a carbon dot solution; Adding the carbon dot solution to the sample to be tested and mixing to obtain a mixed solution; The mixed solution is observed under a fluorescence microscope to complete the detection of microplastics.

8. The detection method according to claim 7, characterized in that The final concentration of the hydrophobic carbon dots in the mixed solution is 0.05-20 mg / L.

9. The detection method according to claim 7, characterized in that: The fluorescence microscope observation step comprises: placing the mixed solution on a glass slide, and placing it under a fluorescence microscope for detection after drying.

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