A hydrophobic carbon dot, a preparation method thereof and an application thereof

Abstract

The present invention belongs to the field of food and environmental testing technology, and relates to a hydrophobic carbon dot and its preparation method and application, and more specifically to a method for preparing a hydrophobic carbon dot and for detecting microplastics in food and the environment. The present invention uses a carbon source and a nitrogen source as reactants, wherein the carbon source is citral and the nitrogen source is ethylenediamine and / or urea, and ethanol as the reaction medium. Hydrophobic carbon dots are prepared through solvent thermal reaction, insoluble matter removal, dialysis, and drying. In the detection of microplastics in food and the environment, the hydrophobic carbon dots have fast dyeing, low quenching rate, and no heating is required. They can distinguish common interferences and are not affected by sample pH and polarity, enabling efficient and rapid detection.

Description

Technical Field

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

[0002] Microplastics are plastic particles smaller than 5mm in diameter that are widely found in various foods and the environment. Microplastics can accumulate in the food chain, and long-term exposure can pose health risks, such as triggering immune responses and disrupting the immune system. Therefore, microplastics are considered an emerging pollutant that poses a serious threat to life.

[0003] Microplastics in food and the environment primarily originate from food packaging, processing, and physical wear. Due to limitations in instrumentation and methods, the detection of microplastics remains a major global challenge. Conventional microplastic detection often relies on sophisticated instruments, while visual identification methods using microscopes often suffer from significant errors. For example, small particles of sediment mixed with microplastic particles can be mistakenly identified as microplastics, inflating the count. Therefore, dyes (including fluorescent dyes) are commonly used to stain microplastics for identification and counting. However, these dyes are often environmentally unfriendly and exhibit significant photobleaching properties. Furthermore, achieving consistent staining results is difficult due to the varying properties of different plastic types. Therefore, efficient and rapid detection of common microplastics in our daily lives has become a pressing challenge for those skilled in the art. Summary of the Invention

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

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

[0006] One of the technical solutions of the present invention is to provide a method for preparing hydrophobic carbon dots, comprising the following steps:

[0007] 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.

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

[0009] Furthermore, 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] Furthermore, the carbon source is citral.

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

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

[0013] Furthermore, the insoluble matter is removed by filtration or centrifugation.

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

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

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

[0017] Furthermore, the dialysis is performed using anhydrous ethanol as a dialysis fluid through a 500-2000 Da dialysis membrane for 24-48 hours.

[0018] The carbon dots obtained in this study were determined to be hydrophobic by measuring their contact angle and oil-water partition coefficient (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 was 107°C, and the oil-water partition coefficient (LogP) was 2.22). In this reaction, citral serves as the main framework of the carbon dots' hydrophobic structure, endowing them with high hydrophobicity, demonstrating their insolubility in water and high affinity for microplastics.

[0019] The second technical solution of the present invention: provides a hydrophobic carbon dot, which is prepared by the above preparation method.

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

[0021] The fourth technical solution of the present invention is to provide a method for detecting microplastics, comprising the following steps:

[0022] The hydrophobic carbon dots are mixed with ethanol to prepare a carbon dot solution;

[0023] Adding the carbon dot solution to the sample to be tested and mixing to obtain a mixed solution;

[0024] The mixed solution is observed under a fluorescence microscope to complete the detection of microplastics.

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

[0026] Furthermore, 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 tested, the microplastics and carbon dots are fully in contact, and adsorption is carried out by utilizing the hydrophobic interaction and electrostatic interaction between the microplastics and carbon dots.

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

[0029] The hydrophobic carbon dots prepared by the present invention have fast and consistent staining, low quenching rate, and no need for heating in the detection of microplastics in food and the environment. They can distinguish common interferences (such as mud and sand), and can achieve efficient and rapid detection.

[0030] The hydrophobic carbon dots prepared by the invention have good photobleaching resistance and excellent fluorescence performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

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

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

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

[0035] Figure 4 The adsorption kinetic curves of 9 types of microplastics on hydrophobic carbon dots.

[0036] Figure 5 This is a diagram showing the dyeing effect of the hydrophobic carbon dots prepared in Example 1 on 9 types of microplastics.

[0037] Figure 6 This is the identification image of the hydrophobic carbon dots prepared in Example 1 on microplastics containing sand, where 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 These are diagrams showing the dyeing effects of the hydrophobic carbon dots prepared in Example 1 on microplastics in different media, where (a) is in honey, (b) is in honey water, and (c) is in milk.

[0039] Figure 8The quenching rates of the hydrophobic carbon dots prepared in Example 1 under different pH conditions.

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

[0041] Figure 10 The quenching rate of the carbon dots prepared in Example 1 under ultraviolet light irradiation. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice 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 associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0048] The raw materials and reagents used in the specific embodiments 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 hydrophobic carbon dots are as follows:

[0051] 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 180°C in an oven for 6 h. After cooling to room temperature, the autoclave was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0052] Example 2

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

[0054] 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a polytetrafluoroethylene reactor and sealed tightly to ensure airtightness. The reactor was connected to a microwave-assisted synthesizer and heated at 200 °C for 0.5 h. After cooling to room temperature, the reactor was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0055] Example 3

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

[0057] 4 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 180°C in an oven for 6 hours. After cooling to room temperature, the insoluble particles were removed by centrifugation at 6800 g for 10 minutes. The supernatant was dialyzed against anhydrous ethanol (500 Da) for 48 hours and then dried to obtain hydrophobic carbon dots.

[0058] Example 4

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

[0060] 3 mL of citral, 5 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 180°C in an oven for 6 h. After cooling to room temperature, the autoclave was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0061] Example 5

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

[0063] 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 190°C in an oven for 6 h. After cooling to room temperature, the autoclave was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0064] Example 6

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

[0066] 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 180°C in an oven for 10 h. After cooling to room temperature, the autoclave was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0067] Example 7

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

[0069] 5 mL of citral, 3 mL of ethylenediamine, and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 140°C in an oven for 6 h. After cooling to room temperature, the reaction mixture was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0070] Example 8

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

[0072] 5 mL of citral, 3 mL of urea (882 mg / L), and 10 mL of anhydrous ethanol were added to a beaker and stirred evenly to mix thoroughly. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined autoclave and tightly sealed. The autoclave was heated at 180 °C in an oven for 6 h. After cooling to room temperature, the mixture was filtered using a 0.22 μm filter membrane. The filtrate was dialyzed against anhydrous ethanol (500 Da) for 48 h and dried to obtain hydrophobic carbon dots.

[0073] Test example

[0074] The hydrophobic carbon dots prepared in Example 1 are used as an example below. The technical effects of the hydrophobic carbon dots prepared in other examples are similar and will not be elaborated on here one by one.

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

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

[0077] Figure 3 The hydrophilic and hydrophobic properties of the carbon dots prepared in Example 1. As can be seen from the figure, the carbon dots prepared in the present invention are hydrophobic carbon dots.

[0078] Microplastic detection methods:

[0079] Place the hydrophobic carbon dots in a centrifuge tube and dissolve them in ethanol to prepare a 10 mg / L carbon dot solution for later use.

[0080] Add the carbon dot solution to the sample to be tested, specifically:

[0081] Add 1 mL of carbon dot solution (10 mg / L) to 10 mL of the sample to be tested and mix to allow the carbon dots to fully contact 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 The adsorption kinetics curves of nine microplastics on hydrophobic carbon dots show that microplastics are immediately adsorbed after mixing with hydrophobic carbon dots, and adsorption equilibrium is reached after 10 minutes.

[0084] Figure 5 The figure shows the dyeing effect of the hydrophobic carbon dots prepared in Example 1 on 9 kinds of microplastics. It can be seen from the figure that the dyeing effect of the hydrophobic carbon dots prepared in Example 1 on 9 kinds of microplastics is consistent. And through the experiment, it can be observed that the carbon dots can be immediately imaged after being blended with microplastics, which is consistent with the Figure 4 The adsorption kinetic curves of microplastics on hydrophobic carbon dots correspond to each other.

[0085] Using sand as an interfering substance, the above method was used to detect microplastics and test their anti-interference performance. The results are as follows: Figure 6 As shown, specifically:

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

[0087] Figure 6 These images show the hydrophobic carbon dots prepared in Example 1 identifying microplastics containing sand. (a) shows dark-field UV excitation, (b) dark-field blue light excitation, (c) dark-field green light excitation, and (d) bright-field excitation. As can be seen, the hydrophobic carbon dots prepared in this invention do not stain the interfering substance (sand). Both the interfering substance and the microplastics are visible under bright-field conditions, while the interfering substance exhibits no fluorescence under dark-field conditions. The microplastics fluoresce under different excitation conditions.

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

[0089] Figure 7 Figures show the staining effects of the hydrophobic carbon dots prepared in Example 1 on microplastics in different media: (a) in honey, (b) in honey water, and (c) in milk. As shown, the hydrophobic carbon dots prepared in this invention exhibit excellent anti-interference properties when detecting microplastics.

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

[0091] Quenching rate = (I0-I) / I0*100%;

[0092] Where I0 is the fluorescence value before pH adjustment; I is the fluorescence value after adjustment.

[0093] Figure 8 The quenching rates of the hydrophobic carbon dots prepared in Example 1 under different pH conditions are shown in FIG. As can be seen from the figure, the hydrophobic carbon dots prepared in the present invention have strong pH stability.

[0094] The carbon dot solution was added to microplastics dispersed in different solvents, and then the imaging effect was observed, such as Figure 9 shown.

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

[0096] Figure 9This is the 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 by the present invention are not affected by the polarity of the solvent.

[0098] Figure 10 The quenching rate of the carbon dots prepared in Example 1 under ultraviolet light irradiation is shown in the figure. 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, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0100] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform 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, and performing solvent thermal reaction, removing insoluble matter, dialysis, and drying. The carbon source is citral; the nitrogen source is ethylenediamine and / or urea.

2. The preparation method according to claim 1, wherein 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 the volume of ethanol is 1-8:1-4.

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

4. The preparation method according to claim 1, wherein 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. Use of the hydrophobic carbon dots according to 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, wherein 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, wherein The fluorescence microscope observation step comprises: placing the mixed solution on a glass slide, drying it, and then placing it under a fluorescence microscope for detection.

Images