Method for regulating and controlling multi-color luminescence of carbon dots through chemical oxidation, prepared multi-color carbon dots and application of prepared multi-color carbon dots

Abstract

The invention discloses a method for regulating and controlling multicolor luminescence of carbon dots through chemical oxidation, the prepared multicolor carbon dots and application of the multicolor carbon dots, and belongs to the technical field of nanometers.The method comprises the steps that hydrophobic fluorescent carbon dots prepared from melamine and dithiosalicylic acid and an oxidizing agent are dispersed in an organic solvent, and a pre-reaction solution is obtained; transferring the pre-reaction liquid into a container, stirring until the pre-reaction liquid is uniformly dispersed, condensing and refluxing at 40-100 DEG C for 10 minutes to 10 hours, and naturally cooling to room temperature to obtain a product; further centrifuging the product, collecting the precipitate, cleaning, centrifuging and drying to obtain the multicolor carbon dots; the method is simple in process and convenient to operate, does not need expensive preparation instruments, is mild in reaction condition, does not need the action of a catalyst, and realizes preparation of the multicolor luminescent carbon dots by regulating and controlling the surface oxidation degree of the hydrophobic fluorescent carbon dots.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a method for regulating the multicolor luminescence of carbon dots through chemical oxidation, the prepared multicolor carbon dots and applications thereof. Background Art

[0002] Fluorescent carbon dots are a type of zero-dimensional carbon nanomaterial with significant fluorescent properties. Compared with traditional fluorescent materials such as rare earth phosphors, fluorescent proteins and quantum dots, they have the advantages of diverse synthesis methods, good stability, low toxicity and good biocompatibility. Their uniqueness lies in their coordinated light absorption / emission properties, making them excellent light conversion materials. These properties give fluorescent carbon dots a wide range of application prospects, covering multiple fields such as sensing detection, display lighting, catalytic energy and biomedicine.

[0003] In recent years, multi-color tunable fluorescent carbon dots have attracted much attention in the fields of bioimaging, optoelectronics and sensors. Researchers have tried to achieve precise control of carbon dot particle size, surface modification, solvent environment and excitation light source by adjusting reaction conditions, optimizing raw material ratios, and introducing external stimuli to achieve multi-color luminescence.

[0004] A Chinese patent document with publication number CN110885680A discloses a method for preparing multicolor fluorescent carbon dots by a solvent-free method. The invention mixes different types of aniline derivatives with inorganic metal salts in proportion and grinds them into powder. The mixed powder is then transferred to the lining of a reactor and kept warm for reaction at 140 to 200°C for 5 to 10 hours. After the reaction is completed, it is naturally cooled to room temperature and washed and dried to obtain blue, green, and red fluorescent carbon dots.

[0005] A Chinese patent document with publication number CN111662713A discloses a method for preparing dual-carbon source and dual-nitrogen source multicolor fluorescent carbon dots. In the invention, the experimental raw materials are sunflower stem pith and urea, and the experimental solvents are deionized water, anhydrous ethanol and N,N-dimethylformamide, respectively. By adjusting the mass percentage of the raw materials, the type of solvent, the reaction time and the reaction temperature, multicolor fluorescent carbon dots are synthesized by a one-step hydrothermal method. The synthesized carbon dots have bright green, yellow and red fluorescence, respectively.

[0006] The Chinese patent document with publication number CN114591737A discloses a multicolor fluorescent carbon dot, its preparation method and application. The invention mixes a nitrogen-containing precursor, a hydroxyl-containing carbon precursor and a catalyst in a solvent for reaction, and obtains a multicolor fluorescent carbon dot after separation and purification; wherein the nitrogen-containing precursor is selected from one or more of o-phenylenediamine, m-phenylenediamine and p-phenylenediamine; the hydroxyl-containing carbon precursor is selected from one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, catechol, resorcinol, hydroquinone and 4-dimethylaminophenol; the mass ratio of the nitrogen-containing precursor to the hydroxyl-containing carbon precursor is (1-3): (1-3). Different organic solutions of the multicolor fluorescent carbon dots can produce red fluorescence, orange fluorescence, yellow fluorescence and green fluorescence under ultraviolet light excitation.

[0007] The Chinese patent document with publication number CN118406488A discloses a xylan-based carbon dot with multicolor fluorescence and its preparation method. The invention uses xylan and p-phenylenediamine as precursors, which are dissolved in different solvents in a certain proportion, mixed evenly, reacted in a hydrothermal reactor, cooled to room temperature, separated and purified by extraction, and dried to obtain four powdered carbon dots. These four fluorescent carbon dots are dispersed in an ethanol solution, and under a 365nm ultraviolet lamp, the carbon dots can emit blue, green, yellow, and red fluorescence respectively.

[0008] Although a variety of preparation methods for multicolor fluorescent carbon dots have been reported, the realization of controllable multicolor fluorescent carbon dot preparation still faces challenges. Research in this field is of great significance for deepening the understanding of the luminescence mechanism of carbon dots and expanding their potential in applications. Summary of the invention

[0009] The present invention provides a method for regulating the multicolor luminescence of carbon dots by chemical oxidation. The present invention regulates the surface oxidation degree of hydrophobic fluorescent carbon dots by chemical oxidation, thereby preparing multicolor carbon dots with a peak wavelength of emission spectrum between 420 and 620 nm and colors ranging from blue to red under an excitation wavelength of 365 nm.

[0010] The specific technical solutions adopted are as follows:

[0011] A method for chemical oxidation regulation of carbon dot multicolor luminescence, comprising the following steps:

[0012] (1) dispersing hydrophobic fluorescent carbon dots prepared by melamine and dithiosalicylic acid and an oxidant in an organic solvent to obtain a pre-reaction solution; the oxidant is at least one of ammonium persulfate, sodium hypochlorite, sulfuric acid, sodium ferrate or azobisisobutyronitrile;

[0013] (2) transferring the pre-reaction solution in step (1) into a container, stirring until uniformly dispersed, condensing and reflux at 40 to 100° C. for 10 min to 10 h, and naturally cooling to room temperature to obtain a product;

[0014] (3) After centrifuging the product obtained in step (2), collecting the precipitate, washing, centrifuging, and drying, to obtain multi-color carbon dots.

[0015] The present invention performs oxidation etching on the surface of hydrophobic fluorescent carbon dots prepared by melamine and dithiosalicylic acid, and can prepare carbon dots that can emit blue, red, and green fluorescence at 365nm by adjusting the type and amount of the oxidant, the oxidation time, etc.

[0016] The organic solvent is at least one of ethanol, acetic acid, dimethyl sulfoxide and formamide.

[0017] Preferably, the particle size of the hydrophobic fluorescent carbon dots is 1 to 100 nm.

[0018] In the pre-reaction solution, the mass concentration of the hydrophobic fluorescent carbon dots is 0.01-1 g / mL, and the mass concentration of the oxidant is 0.1-100 mg / mL.

[0019] The oxidant is preferably ammonium persulfate, which has high oxidation efficiency, wide sources, and is economical and practical.

[0020] Preferably, the product obtained in step (2) is centrifuged at 3000-50000 rpm for 1-100 min and then the precipitate is collected.

[0021] Specifically, when the excitation wavelength is 365 nm, the peak wavelength of the emission spectrum of the multicolor carbon dots is between 420 and 620 nm.

[0022] The yield of the multicolor carbon dots is 10% to 80%, and the quantum efficiency is 1% to 20%.

[0023] The present invention also provides multicolor carbon dots obtained by the method of regulating the multicolor luminescence of carbon dots by chemical oxidation.

[0024] The present invention also provides the application of the multi-color carbon dots in the field of fluorescent anti-counterfeiting and / or LED lighting.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a method for regulating the multicolor luminescence of carbon dots by chemical oxidation. The hydrophobic fluorescent carbon dots prepared by melamine and dithiosalicylic acid are used as raw materials. The degree of surface oxidation is regulated to achieve the preparation of multicolor luminescent carbon dots (the peak wavelength of the emission spectrum is between 420 and 620 nm under an excitation wavelength of 365 nm, and the colors range from blue to red). The method of the present invention has simple process, convenient operation, no need for expensive preparation instruments, mild reaction conditions, no need for a catalyst, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the process of oxidation etching of hydrophobic fluorescent carbon dots in the embodiment.

[0028] Figure 2 These are optical images of the carbon dots prepared in Example 1 under sunlight and 365 nm ultraviolet light.

[0029] Figure 3 1 is the fluorescence spectrum of the carbon dots prepared in Example 1.

[0030] Figure 4 These are optical images of the carbon dots prepared in Example 3 under sunlight and 365 nm ultraviolet light.

[0031] Figure 5 3 is the fluorescence spectrum of the carbon dots prepared in Example 3. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the examples and drawings. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer. Contents not described in detail in this specification belong to prior art known to professionals and technicians in the field.

[0033] In the following examples, hydrophobic fluorescent carbon dots are prepared using melamine and dithiosalicylic acid as raw materials according to the description in Chinese patent document CN109825288A. The particle size of the hydrophobic fluorescent carbon dots is 1 to 100 nm. The sources of the remaining raw materials are not particularly limited and can be commercially available.

[0034] Example 1

[0035] This embodiment illustrates a method for chemical oxidation to control the multi-color luminescence of carbon dots. The schematic diagram of the oxidation etching process is shown in FIG. Figure 1 The specific control method is as follows:

[0036] 0.01 g of hydrophobic fluorescent carbon dots prepared from melamine and dithiosalicylic acid was added to 1 mL of dimethyl sulfoxide and dispersed evenly, and 0.1 mg of ammonium persulfate was added and mixed evenly to obtain a pre-reaction solution. The pre-reaction solution was transferred to a three-necked flask, stirred until evenly dispersed, heated to 40°C and condensed under reflux for 20 min for oxidation reaction, and naturally cooled to room temperature to obtain a product; the product was centrifuged and the precipitate was collected, the centrifugal speed was 3000 rpm, the time was 30 min, washed with water several times, centrifuged, and finally the precipitate was collected and dried to obtain carbon dots, the yield of the carbon dots was 51%, and the quantum efficiency was 3%.

[0037] The optical images of the carbon dots prepared in this example under sunlight and 365nm ultraviolet light are as follows: Figure 2 As shown, after further testing, the fluorescence spectrum of the carbon dots is shown in Figure 3 As shown, when the excitation wavelength is 365 nm, the peak wavelengths of its emission spectrum are located at 450 nm and 611 nm, appearing blue in ethanol and red in water.

[0038] Example 2

[0039] This example illustrates a method for chemical oxidation to regulate the multicolor luminescence of carbon dots, focusing on the effect of the fluorescent carbon dot content on the fluorescence properties of the carbon dots, as shown below:

[0040] 1g of hydrophobic fluorescent carbon dots prepared by melamine and dithiosalicylic acid was added to 1mL of dimethyl sulfoxide, dispersed evenly, and 0.1mg of ammonium persulfate was added and mixed evenly to obtain a pre-reaction solution. The pre-reaction solution was transferred to a three-necked flask, stirred until dispersed evenly, heated to 40°C and condensed under reflux for 20min for oxidation reaction, and naturally cooled to room temperature to obtain a product; the product was centrifuged and the precipitate was collected, the centrifugal speed was 3000rpm, the time was 30min, washed with water several times, centrifuged, and finally the precipitate was collected and dried to obtain carbon dots, the yield of the carbon dots was 65%, and the quantum efficiency was 4.2%.

[0041] The results of the test showed that when the excitation wavelength of the carbon dots was 365 nm, the peak wavelengths of its emission spectrum were located at 460 nm and 618 nm, and it appeared blue in ethanol and red in water.

[0042] Example 3

[0043] This example illustrates a method for chemical oxidation to regulate the multicolor luminescence of carbon dots, focusing on the effect of the oxidant content on the fluorescence properties of carbon dots, as shown below:

[0044] 0.01 g of hydrophobic fluorescent carbon dots prepared from melamine and dithiosalicylic acid was added to 1 mL of dimethyl sulfoxide and dispersed evenly, and 100 mg of ammonium persulfate was added and mixed evenly to obtain a pre-reaction solution. The pre-reaction solution was transferred to a three-necked flask, stirred until evenly dispersed, heated to 40°C and refluxed for 20 min for oxidation reaction, and naturally cooled to room temperature to obtain a product; the product was centrifuged and the precipitate was collected, the centrifugal speed was 3000 rpm, the time was 30 min, washed with water several times, centrifuged, and finally the precipitate was collected and dried to obtain carbon dots, the yield of the carbon dots was 25%, and the quantum efficiency was 2.3%.

[0045] The optical images of the carbon dots prepared in this example under sunlight and 365nm ultraviolet light are as follows: Figure 4 As shown, after further testing, the fluorescence spectrum of the carbon dots is shown in Figure 5As shown, it was tested that when the excitation wavelength of the carbon dots was 365 nm, the peak wavelengths of its emission spectrum were located at 480 nm and 580 nm, and it appeared blue in ethanol and green in water.

[0046] Example 4

[0047] This embodiment illustrates a method for chemical oxidation to regulate the multi-color luminescence of carbon dots, focusing on the effect of oxidation temperature on the fluorescence properties of carbon dots, as shown below:

[0048] 0.01 g of hydrophobic fluorescent carbon dots prepared from melamine and dithiosalicylic acid was added to 1 mL of dimethyl sulfoxide and dispersed evenly, and 0.1 mg of ammonium persulfate was added and mixed evenly to obtain a pre-reaction solution. The pre-reaction solution was transferred to a three-necked flask, stirred until evenly dispersed, heated to 100°C and condensed under reflux for 20 min for oxidation reaction, and naturally cooled to room temperature to obtain a product; the product was centrifuged and the precipitate was collected, the centrifugal speed was 3000 rpm, the time was 60 min, washed with water several times, centrifuged, and finally the precipitate was collected and dried to obtain carbon dots, the yield of the carbon dots was 37%, and the quantum efficiency was 3.8%.

[0049] The results of the test showed that when the excitation wavelength of the carbon dots was 365 nm, the peak wavelengths of its emission spectrum were located at 470 nm and 598 nm, and it appeared blue in ethanol and red in water.

[0050] Example 5

[0051] This example illustrates a method for chemical oxidation to regulate the multicolor luminescence of carbon dots, focusing on the effect of oxidation time on the fluorescence properties of carbon dots, as shown below:

[0052] 0.01 g of hydrophobic fluorescent carbon dots prepared from melamine and dithiosalicylic acid was added to 1 mL of dimethyl sulfoxide and dispersed evenly, and 0.1 mg of ammonium persulfate was added and mixed evenly to obtain a pre-reaction solution. The pre-reaction solution was transferred to a three-necked flask, stirred until evenly dispersed, heated to 40°C and refluxed for 10 h for oxidation reaction, and naturally cooled to room temperature to obtain a product; the product was centrifuged and the precipitate was collected, the centrifugal speed was 3000 rpm, the time was 60 min, washed with water and centrifuged several times, and finally the precipitate was collected and dried to obtain carbon dots, the yield of the carbon dots was 41%, and the quantum efficiency was 3.5%.

[0053] The results of the test showed that when the excitation wavelength of the carbon dots was 365 nm, the peak wavelengths of its emission spectrum were located at 460 nm and 605 nm, and it appeared blue in ethanol and red in water.

[0054] Sample analysis

[0055] The stronger the oxidizing ability of the oxidant, the more it is used, and the longer the oxidation time, the shorter the emission spectrum of the obtained carbon dots. Therefore, the emission spectrum of the carbon dots can be changed from red light to blue light by regulating the oxidation conditions.

[0056] Based on the above results, it can be clearly seen that the method provided by the present invention, which is a method for regulating the multicolor luminescence of carbon dots by chemical oxidation, achieves the preparation of multicolor luminescent carbon dots by regulating the surface oxidation degree of hydrophobic fluorescent carbon dots by chemical oxidation; and the preparation method provided by the present invention is simple and easy to operate, and does not require expensive preparation instruments, high temperature and catalysts.

[0057] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating the multicolor luminescence of carbon dots by chemical oxidation, characterized in that: The following steps are involved: (1) dispersing hydrophobic fluorescent carbon dots prepared by melamine and dithiosalicylic acid and an oxidant in an organic solvent to obtain a pre-reaction solution; the oxidant is at least one of ammonium persulfate, sodium hypochlorite, sulfuric acid, sodium ferrate or azobisisobutyronitrile; (2) transferring the pre-reaction solution in step (1) into a container, stirring until uniformly dispersed, condensing and reflux at 40 to 100° C. for 10 min to 10 h, and naturally cooling to room temperature to obtain a product; (3) After centrifuging the product obtained in step (2), collecting the precipitate, washing, centrifuging, and drying, to obtain multi-color carbon dots.

2. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: The organic solvent is at least one of ethanol, acetic acid, dimethyl sulfoxide and formamide.

3. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: The particle size of the hydrophobic fluorescent carbon dots is 1-100 nm, and the oxidant is ammonium persulfate.

4. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: In the pre-reaction solution, the mass concentration of the hydrophobic fluorescent carbon dots is 0.01-1 g / mL, and the mass concentration of the oxidant is 0.1-100 mg / mL.

5. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: The product obtained in step (2) is centrifuged at 3000-50000 rpm for 1-100 min and the precipitate is collected.

6. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: When the excitation wavelength is 365 nm, the peak wavelength of the emission spectrum of the multicolor carbon dots is between 420 and 620 nm.

7. The method for chemical oxidation regulation of carbon dot multicolor luminescence according to claim 1, characterized in that: The yield of the multicolor carbon dots is 10% to 80%, and the quantum efficiency is 1% to 20%.

8. Multicolor carbon dots prepared according to the method for regulating multicolor luminescence of carbon dots by chemical oxidation according to any one of claims 1 to 7.

9. Use of the multicolor carbon dots according to claim 8 in the field of fluorescent anti-counterfeiting and / or LED lighting.

Images