Red fluorescent carbon nanodot as well as preparation method and application thereof

Abstract

The invention provides a red fluorescent carbon nanodot as well as a preparation method and application thereof. The preparation method of the red fluorescent carbon nanodot provided by the invention comprises the following steps: weighing 0.1-2.8 g of 1, 8-diaminonaphthalene solid, dissolving the 1, 8-diaminonaphthalene solid in 20mL of phosphoric acid, and magnetically stirring to dissolve the 1, 8-diaminonaphthalene solid; transferring the solution into a hydrothermal kettle, carrying out hydrothermal reaction for 6-26 hours under the condition of 120-300 DEG C, and cooling the reaction kettle to room temperature in a natural environment after heating is finished; purifying by using a column chromatography, and taking absolute ethyl alcohol as a washing solvent to obtain a pure carbon dot solution; and finally, evaporating the ethanol solvent by adopting a rotary evaporator, and drying to obtain pure carbon nanodot solid powder. The carbon dot solution can emit bright red fluorescence under the excitation of xenon lamp light with the wavelength of 380-550 nm. The method has a wide application prospect in the fields of time-resolved imaging, advanced information encryption, anti-counterfeiting and the like.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nano material preparation, in particular to a red fluorescent carbon nano dot and a preparation method and application thereof. Background Art

[0002] Carbon dots are quasi-spherical nanoparticles with a particle size in the range of 10nm and have photoluminescent properties. Researchers have divided carbon dots into four categories based on the formation mechanism, structure and surface groups, namely graphene quantum dots, carbon quantum dots, carbon nanodots and carbonized polymer dots. Among them, although carbon nanodots have a high degree of carbonization, the carbon core structure generally has no obvious lattice and does not have a quantum confinement effect. Its structural characteristics are that highly carbonized amorphous carbon is the carbon core, with simple functional groups as surface states. The photoluminescence of carbon nanodots mainly comes from defects and subdomains.

[0003] Carbon dots have the advantages of chemical inertness, thermal stability, high quantum yield and good biocompatibility, so they have attracted much attention from researchers. Currently, carbon dots have been widely used in catalysis, energy storage and optoelectronic devices, diagnosis and treatment. Red fluorescent carbon dots have great advantages in biological imaging because they can penetrate deeply into tissues and avoid the interference of the body's own fluorescence. At the same time, as red is one of the three primary colors, red fluorescent carbon dots have become an indispensable component for constructing carbon dot-based white light-emitting diodes. Based on this, red carbon dots have been considered to be one of the key factors to promote the practical application of carbon dots in most fields. Summary of the invention

[0004] The purpose of the present invention is to provide a red fluorescent carbon nanodot and a preparation method and application thereof. The present invention prepares the red fluorescent carbon nanodots by using 1,8-diaminonaphthalene and phosphoric acid. The red fluorescent carbon nanodots have strong fluorescence emission and nanosecond fluorescence lifetime, and can therefore be used in time-resolved imaging, advanced information encryption, anti-counterfeiting and other fields.

[0005] The present invention is achieved in that:

[0006] The invention utilizes a mixed solution of 1,8-diaminonaphthalene and phosphoric acid to undergo a hydrothermal reaction in a reactor to obtain a precursor product of red fluorescent carbon nanodots, which is then purified by column chromatography to obtain a pure red fluorescent carbon nanodot solution, and finally thermally dried to obtain a carbon nanodot solid powder.

[0007] The specific steps are:

[0008] (1) Weigh 0.1-2.8 g of 1,8-diaminonaphthalene solid and dissolve it in 20 mL of phosphoric acid. Stir magnetically to dissolve it.

[0009] (2) The above solution is transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120-300° C. for 6-26 hours. After the heating is completed, the reactor is cooled to room temperature in a natural environment to obtain a precursor of red fluorescent carbon nanodots.

[0010] (3) Column chromatography is used for purification. Deionized water is first used as a washing solvent to remove the green fluorescent carbon dots in the precursor. Then, dichloromethane is used as a solvent to remove impurities (some organic ligands, unknown organic products generated, etc.) and other colored (other than red, such as blue, green, yellow, etc.) carbon dots in the precursor again until the discharged dichloromethane has no obvious fluorescence. Finally, anhydrous ethanol is added to the silica gel column, and the target product red fluorescent carbon nanodots are discharged along with the anhydrous ethanol.

[0011] (4) The red fluorescent carbon nanodot solution is subjected to rotary evaporation to obtain carbon nanodot solid powder.

[0012] In the above scheme, the purification in step (3) is to remove impurities and fluorescent carbon dots of other colors except red in the precursor by column chromatography. In the purification process using column chromatography, the washing solvent used to remove the phosphorus element introduced by the raw materials is deionized water, that is, in the first step of using deionized water as the washing solvent to remove the green fluorescent carbon dots in the precursor, the phosphorus element introduced by the raw materials is removed, so the red fluorescent carbon nanodots finally prepared do not contain phosphorus.

[0013] The carbon nanodot solid powder prepared by the present invention has no fluorescence emission, but has strong red fluorescence emission after being dissolved in anhydrous ethanol, and has good solubility in anhydrous ethanol.

[0014] The method of the present invention overcomes the drawbacks of the existing method, such as cumbersome preparation, high cost, limited types of red fluorescent carbon dots and weak fluorescence intensity. The red fluorescent carbon nanodots are prepared by a one-step hydrothermal method, and a pure red fluorescent carbon nanodot solution is obtained after purification by column chromatography. Finally, a carbon nanodot solid powder can be obtained by heat drying. It has broad application prospects in the fields of time-resolved imaging, advanced information encryption and anti-counterfeiting. The method described in the present invention is simple, easy to operate, low in cost, high in output, and can achieve batch synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a flow chart of preparing red fluorescent carbon nanodots.

[0016] Figure 2 This is a transmission electron microscope image of the red fluorescent carbon nanodots prepared in Example 1 of the present invention.

[0017] Figure 3 This is the total X-ray photoelectric spectrum of the red fluorescent carbon nanodots prepared in Example 1 of the present invention.

[0018] Figure 4 This is the high-resolution P 2p spectrum of the red fluorescent carbon nanodots prepared in Example 1 of the present invention.

[0019] Figure 5 It is the fluorescence emission spectrum of the red fluorescent carbon nanodot solution prepared in Example 1 of the present invention under the excitation of the wavelength of 380nm to 460nm.

[0020] Figure 6 It is the fluorescence emission spectrum of the red fluorescent carbon nanodot solution prepared in Example 1 of the present invention under the excitation of the wavelength of 480nm to 540nm.

[0021] Figure 7 This is the fluorescence attenuation curve of the red fluorescent carbon nanodots prepared in Example 1 of the present invention.

[0022] Figure 8 This is the total X-ray photoelectric spectrum of the red fluorescent carbon nanodots prepared in Example 2 of the present invention.

[0023] Fig. 9 This is the fluorescence emission spectrum of the red fluorescent carbon nanodots prepared in Example 2 of the present invention under excitation at a wavelength of 365nm to 455nm.

[0024] Fig.10 Time-resolved imaging of two different carbon dots in Example 3 of the present invention. DETAILED DESCRIPTION

[0025] Example 1

[0026] Combination Figure 1 The preparation method of the red fluorescent carbon nanodots provided in this embodiment is as follows:

[0027] (1) Weigh 1.6 g of 1,8-diaminonaphthalene and dissolve it in 20 mL of 85% phosphoric acid. Stir magnetically to dissolve it.

[0028] (2) The dissolved solution in step (1) is transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 240° C. for 16 hours. After the heating is completed, the reactor is cooled to room temperature in a natural environment to obtain a precursor of red fluorescent carbon nanodots.

[0029] (3) Column chromatography is used for purification. Deionized water is first used as a washing solvent to remove the green fluorescent carbon dots in the precursor (green fluorescent carbon dots have fluorescent properties in both liquid and solid states); then dichloromethane is used as a solvent to remove impurities and other colored carbon dots in the precursor again until the discharged dichloromethane has no obvious fluorescence under ultraviolet light; finally, anhydrous ethanol is added to the silica gel column, and the target product, red fluorescent carbon nanodots, is discharged along with the anhydrous ethanol.

[0030] (4) The red fluorescent carbon nanodot solution is subjected to rotary evaporation to obtain carbon nanodot solid powder.

[0031] In order to evaluate the purity of the sample and grasp its morphological characteristics, the distribution and structure of the prepared carbon nanodots were observed at different magnifications. Figure 2 As shown in (a) and (b), the carbon nanodots are distributed throughout the plane, the sample quantity is abundant in the field of view, and there are no obvious impurities, which confirms the feasibility of the purification method and the purity of the sample. Figure 2 As shown in (c) and (d), the carbon nanodots have a particle size between 10 nm and 15 nm and have an amorphous structure similar to amorphous carbon. Based on the morphology and structural information, it is confirmed that the synthesized carbon dots are carbon nanodots.

[0032] Figure 3 This is the X-ray photoelectric spectrum (XPS) of the red fluorescent carbon nanodots prepared in this example. In the XPS spectrum, characteristic peaks belonging to C 1s, N 1s, and O 1s are monitored at 284.8 eV, 399.5 eV, and 531 eV, respectively. Figure 4 This is the high-resolution P 2p spectrum of the red fluorescent carbon nanodots prepared in this example. Although phosphoric acid exists in the raw material, no characteristic peak of P is observed in the XPS total spectrum and the high-resolution P 2p spectrum. By integrating the peak areas, it is calculated that the proportions of C, O, N, and P are 88.2%, 9.6%, 2.2%, and 0%, respectively.

[0033] Therefore, the red fluorescent carbon nanodots prepared in this embodiment are composed of three elements: C, O, and N, and the main component is C. There is no characteristic peak of P in the XPS spectrum, which, on the one hand, indicates that the fluorescence emission of the red fluorescent carbon nanodots is not related to the P element; on the other hand, it indicates that the residual P in the product has been removed, which once again confirms the feasibility of the purification method of the present invention.

[0034] The carbon nanodot solid powder prepared in the embodiment of the present invention does not have fluorescent properties, but after the carbon nanodot solid powder is dissolved in anhydrous ethanol, the solution thereof emits bright red fluorescence under 380nm-540nm xenon light irradiation. Figure 5 and Figure 6 shown. Figure 5 and Figure 6 The fluorescence emission spectrum shows that the main peak of the fluorescence emission of the carbon nanodot solution is located at 628nm, and the shoulder peak is located at 660nm. As the excitation wavelength changes, the position of the double peaks remains unchanged, only the fluorescence intensity changes with the excitation wavelength, and the double peaks maintain a trend of increasing and decreasing at the same time, and the emission peak intensity at 660nm is always lower than the fluorescence peak intensity at 628nm.

[0035] The fluorescence decay curve records the change of fluorescence intensity over time, which is important for evaluating the optical properties of a substance. In this example, a 450nm laser was used as the excitation source, and the decay process of fluorescence at 628nm and 660nm was monitored. The results are shown in Figure 2. Figure 7 The double exponential function was used to fit the decay curve, and the calculation results showed that the red fluorescent carbon nanodots had a nanosecond fluorescence lifetime, and the double peak fluorescence lifetimes were 5.36ns and 5.39ns respectively.

[0036] Example 2

[0037] The preparation method of the red fluorescent carbon nanodots provided in this embodiment is as follows:

[0038] (1) Weigh 1.6 g of 1,8-diaminonaphthalene and dissolve it in 20 mL of 85% phosphoric acid. Stir magnetically to dissolve it.

[0039] (2) The dissolved solution in step (1) is transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 240° C. for 16 hours. After the heating is completed, the reactor is cooled to room temperature in a natural environment to obtain a precursor of red fluorescent carbon nanodots.

[0040] (3) Column chromatography is used for purification, and dichloromethane, a mixture of dichloromethane and ethyl acetate in a volume ratio of 1:1, and ethyl acetate are used as washing solvents in order to remove impurities in the precursor and fluorescent carbon dots of other colors except red fluorescent carbon nanodots. Finally, anhydrous ethanol is added to the silica gel column, and the target product red fluorescent carbon nanodots are discharged along with the anhydrous ethanol.

[0041] (4) The red fluorescent carbon nanodot solution is subjected to rotary evaporation to obtain colloidal carbon nanodots.

[0042] In this embodiment, the carbon nanodot solution cannot be completely dried into powder after rotary evaporation, and the obtained colloidal carbon nanodots also do not have fluorescent properties. Figure 8 As shown, the X-ray photoelectron spectrum of carbon nanodots was measured, and the characteristic peaks belonging to P 2p, C 1s, N1s, and O1s were monitored at 134.7eV, 284.8eV, 399.5eV, and 531eV, respectively. The appearance of the P 2p characteristic peak and the inability of the colloidal carbon nanodots to be completely dried into powders indicate that the purification method using dichloromethane, a mixture of dichloromethane and ethyl acetate with a volume ratio of 1:1, ethyl acetate, and anhydrous ethanol as washing solvents in turn cannot effectively remove the P element and the generated organic byproducts, and cannot obtain pure red fluorescent carbon nanodots.

[0043] After the colloidal carbon nanodots were dissolved in anhydrous ethanol, their emission spectra under excitation at 365nm to 455nm were measured as follows: Fig. 9 As shown by Fig. 9It can be seen that the double peaks of fluorescence emission are located at 610nm and 658nm, indicating that the impurities present in the red fluorescent carbon nanodots will affect their fluorescence emission.

[0044] Example 3, application of red fluorescent carbon nanodots in the field of advanced information encryption and anti-counterfeiting.

[0045] The preparation process of red fluorescent carbon nanodots is as in Example 1. The prepared carbon nanodot solid powder is dissolved in anhydrous ethanol to a concentration of 5 mg / mL. A 532 nm pulse laser is used as an excitation source. Under the excitation of a high-level pulse signal, the carbon nanodot solution emits bright red fluorescence. A "river" pattern is set in advance on the propagation light path (combined with Fig.10 ), when the red fluorescent beam passes through the pattern, the pattern information is cleverly hidden in the beam. After conversion by the photon receiving device and the imaging device, the time-resolved image can be presented on the display. Under the low-level pulse signal, the intensity of the light excitation signal is zero, which is equivalent to removing the excitation light source. Before the next high-level pulse signal arrives, the fluorescence intensity of the carbon nanodots will decay rapidly, and the pattern based on the fluorescence intensity imaging will gradually blur. When the next high-level pulse signal arrives, the carbon nanodots will be excited again, and the decayed fluorescence intensity will return to the strongest.

[0046] At the same time, another type of carbon dots with a shorter fluorescence lifetime (shorter than the fluorescence lifetime of the above-mentioned carbon nanodots, 5.3ns) is used to image the word "North". During the low-level pulse signal, the fluorescence intensity of the carbon nanodots and the carbon dots with a short fluorescence lifetime begins to decay. Since the fluorescence of the two carbon dots is relatively strong in the early stage of decay, the images of the words "River" and "North" are clear. As the decay time increases, the fluorescence intensity continues to decay and weaken, but due to the different fluorescence lifetimes of the carbon nanodots and the carbon dots with a short fluorescence lifetime, the fluorescence decay rate of the short-lived carbon dots is faster, and the "North" pattern gradually becomes blurred from clear as its fluorescence rapidly decays, until the fluorescence intensity is insufficient to support the imaging of the text pattern, and the "North" pattern disappears. The fluorescence decay of long-lived carbon nanodots is relatively slow, so the "River" pattern can still be clearly presented after the "North" pattern disappears (see Fig.10 ).

[0047] Since the fluorescence lifetime of carbon nanodots is in the nanosecond range, the imaging pattern needs to be captured within a nanosecond period of time, which is difficult for ordinary human eyes to detect and requires special equipment to observe. If the time-resolved imaging technology based on carbon dots is used for information encryption and anti-counterfeiting, it is difficult for ordinary people to detect it. Even if it can be detected by outsiders, the real useful information can be hidden in it by writing information with carbon dots with different fluorescence lifetimes. Except for those who know the correct way to read the information, it is difficult for others to extract the real useful information from the cumbersome data. If the information pattern is drawn into a QR code, etc., further encryption of the information can be achieved.

Claims

1. A method for preparing red fluorescent carbon nanodots, characterized in that: The steps include: (1) Weigh 0.1-2.8 g of 1,8-diaminonaphthalene solid and dissolve it in 20 mL of phosphoric acid, stirring it magnetically to dissolve it; (2) transferring the dissolved solution in step (1) to a hydrothermal reactor, performing a hydrothermal reaction at 120 to 300° C. for 6 to 26 hours, and then naturally cooling to room temperature to obtain a precursor of red fluorescent carbon nanodots; (3) Purification by column chromatography: first, deionized water is used as a washing solvent to remove the green fluorescent carbon dots in the precursor; then, dichloromethane is used as a solvent to remove impurities and other colored carbon dots in the precursor; finally, anhydrous ethanol is added, and the target product red fluorescent carbon nanodots are discharged along with the anhydrous ethanol; (4) The red fluorescent carbon nanodot solution is subjected to rotary evaporation to obtain carbon nanodot solid powder.

2. The method for preparing red fluorescent carbon nanodots according to claim 1, characterized in that: In step (3), dichloromethane is used to remove impurities and other colored carbon dots in the precursor until the outflowing dichloromethane has no obvious fluorescence under ultraviolet light.

3. The method for preparing red fluorescent carbon nanodots according to claim 1, characterized in that: The hydrothermal reaction temperature in step (2) is 180-300°C.

4. The method for preparing red fluorescent carbon nanodots according to claim 1, characterized in that: The phosphoric acid concentration in step (1) is 85%.

5. Red fluorescent carbon nanodots prepared by the method according to any one of claims 1 to 4.

6. Application of the red fluorescent carbon nanodots described in claim 5 in the fields of time-resolved imaging, advanced information encryption and anti-counterfeiting.

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