Matrix assisted synergistic enhancement fluorescence solid-state dual-mode emitting carbon dots and preparation method thereof

Abstract

The application discloses a kind of matrix-assisted synergistic enhancement fluorescence solid-state dual-mode emission type carbon dots and preparation method thereof.The preparation method comprises the following steps: the precursor of carbon source, doped nitrogen source and auxiliary matrix are mixed and dissolved into water to obtain a mixed solution;the mixed solution is heated under semi-closed condition to carry out reaction, and after reaction is completed, it is cooled to room temperature, then the reaction product is ground into powder to obtain matrix-assisted synergistic enhancement fluorescence solid-state dual-mode emission type carbon dots;wherein, the auxiliary matrix is boric acid and organosilane.The application realizes synergistic enhancement of carbon dots solid-state dual-mode emission fluorescence and phosphorescence;The application is simple in operation, low in cost, does not need harsh reaction conditions and complicated experimental process, does not need subsequent separation process, and does not need expensive and complex equipment, and is suitable for large-scale preparation;The fluorescent powder prepared by the application has high yield, high fluorescence and phosphorescence quantum yield, high fluorescence brightness, long phosphorescence life, good water dispersibility and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial preparation, and in particular to a matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dot and a preparation method thereof. Background Art

[0002] Phosphors are substances that emit a specific fluorescent color when exposed to light. They are ubiquitous in our daily lives, playing a particularly important role in lighting. Currently, commercial phosphors are primarily based on rare earth phosphors, which present significant challenges such as high cost, environmental pollution, and uncontrollable emission wavelengths. As people's needs for quality of life continue to increase, there is an urgent need for green, low-cost alternatives to rare earth phosphors.

[0003] Carbon dots (Cdots), a novel class of carbon-based fluorescent nanomaterials, are widely used in bioimaging, drug delivery, sensing, optoelectronic devices, and photocatalysis due to their numerous unique properties, including low toxicity, environmental friendliness, low cost, high luminescence quantum efficiency, photoluminescence tunability, good biocompatibility, and stability. They are expected to become a viable alternative to conventional commercial fluorescent materials. However, when Cdots are prepared in a solid state, their luminescence intensity is significantly reduced or even completely quenched due to the π-electron stacking effect between carbon nuclei. This aggregation-induced fluorescence quenching significantly limits their application in solid-state luminescence applications, such as white light LEDs, anti-counterfeiting, and fingerprint imaging. Solid-state luminescence from CDs typically requires the use of auxiliary matrices, such as polymers (PMMA, PVA, PVP, etc.) or inorganic salt matrices (Ba2SO4, NaSiO3, NaCl, NaOH, etc.). However, this method has many problems: 1) It requires a multi-step experimental operation, which is tedious, complex, time-consuming and labor-intensive; 2) The carbon dots in the matrix are unevenly distributed; 3) The synthesized solid-state CDs have low fluorescence quantum yield, poor reproducibility, poor stability and low loading rate; 4) The synthesized carbon dots only have single-mode emission, such as only fluorescence or phosphorescence emission.

[0004] Patent number CN 112745838 A discloses a method for preparing large-scale solid-state green fluorescent carbon nanodots. By introducing inorganic crystals such as potassium hydroxide or potassium citrate, the problem of fluorescence quenching of the carbon dots in the solid state is successfully suppressed, achieving in situ confined growth of solid-state luminescent carbon nanodots. The carbon dots exhibit green fluorescence in the solid state with a fluorescence efficiency of up to 75.9%. Patent number CN 114015441A discloses green solid-state fluorescent carbon dots and their preparation method. Using biuret and trisodium citrate as raw materials, a direct microwave reaction produces solid-state green carbon dots with a quantum efficiency of 45-75%. These patents all achieve solid-state fluorescence and large-scale preparation of carbon dots, as well as high fluorescence quantum yields. However, these patents only address single-mode emission—fluorescence—of the carbon dot fluorescence.

[0005] In addition, studies have shown that the fluorescent and phosphorescent dual-mode emission type solid-state carbon dots are beneficial to manufacture more efficient white light LEDs. Therefore, efficient, rapid and high-quality preparation of the fluorescent and phosphorescent dual-mode emission type solid-state carbon dots is one of the urgent breakthroughs in the field of carbon dot luminescent materials at present. SUMMARY

[0006] The purpose of the present application is to overcome the above technical deficiencies, and to provide a matrix-assisted synergistically enhanced fluorescent solid-state dual-mode emission type carbon dots and a preparation method thereof, which solves the technical problems of complicated preparation steps, low quantum yield and only single-mode emission of carbon dots in the prior art.

[0007] In a first aspect, the present application provides a preparation method of a matrix-assisted synergistically enhanced fluorescent solid-state dual-mode emission type carbon dot, comprising the following steps:

[0008] The precursor of the carbon source, the doped nitrogen source and the auxiliary matrix are mixed and dissolved into water to obtain a mixed solution;

[0009] The mixed solution is subjected to a heating reaction under semi-closed conditions, and after the reaction is completed, it is cooled to room temperature, and then the reaction product is ground into a powder to obtain the matrix-assisted synergistically enhanced fluorescent solid-state dual-mode emission type carbon dot;

[0010] The auxiliary matrix is boric acid and organosilane.

[0011] In a second aspect, the present application provides a matrix-assisted synergistically enhanced fluorescent solid-state dual-mode emission type carbon dot, which is obtained by the preparation method of the matrix-assisted synergistically enhanced fluorescent solid-state dual-mode emission type carbon dot provided in the first aspect of the present application.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] The present application adopts the co-assistance of two matrices, proposes a new synergistic effect of matrix-assisted enhancement, and realizes the synergistic enhancement of the solid-state dual-mode emission fluorescence and phosphorescence of the carbon dots. The present application is simple to operate and low in cost, does not require harsh reaction conditions and complicated experimental processes, nor does it require a subsequent separation process, nor does it require expensive and complex equipment, is suitable for large-scale preparation, and also has the characteristics of being fast and simple, and can provide a realistic possibility for the application and promotion of carbon dot fluorescent powder. The carbon dots prepared by the present application have dual-mode emission of fluorescence and phosphorescence, high yield of fluorescent powder (more than 90%), high quantum yield of fluorescence and phosphorescence, high brightness of fluorescence, long phosphorescence lifetime, good water dispersibility and stability. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1The fluorescence and phosphorescence spectra (a) and fluorescence quantum yield (b) of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention at an excitation wavelength of 365 nm;

[0015] Figure 2 SEM (a-b) and TEM (c) images of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention;

[0016] Figure 3 This is an optical image of the phosphorescence afterglow discernible to the naked eye of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention;

[0017] Figure 4 The fluorescence spectra (a1-a2), phosphorescence spectra (b1-b2) and phosphorescence lifetime diagram (b3) of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Examples 1-5 of the present invention at an excitation wavelength of 365 nm;

[0018] Figure 5 The phosphorescence spectra (a) and phosphorescence lifetime diagrams (b) of the carbon dots prepared in Example 1 of the present invention and Comparative Examples 1-2;

[0019] Figure 6 Fluorescence spectra (a) and fluorescence quantum yields (bc) of the carbon dots prepared in Example 1 of the present invention and Comparative Examples 1-2 at an excitation wavelength of 365 nm. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] As mentioned above, the preparation of carbon dots in the prior art has the following disadvantages: 1) The preparation methods used are too cumbersome and complicated, usually requiring high-temperature hydrothermal reaction, product centrifugation and dialysis purification, and freeze-drying of the final product to achieve solid-state processes; 2) The yield of the final product is low, and large-scale preparation cannot be achieved; 3) Most solid-state emissions exhibit single-mode emission, i.e., fluorescence emission; 4) The realization of carbon dot phosphorescence is also limited to a single-state mode of a rigid structure, and enhancement phenomenon cannot be achieved; 5) The experimental operations are too dangerous and costly, such as hydrothermal or solvent thermal reactions under high temperature and pressure, which are too time-consuming, and each reaction takes too long (including reaction, natural cooling, washing, purification, and drying, etc.). Based on this, the present invention is proposed.

[0022] In a first aspect, the present invention provides a method for preparing matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots, comprising the following steps:

[0023] S1. Mix and dissolve a carbon source precursor, a doped nitrogen source, and an auxiliary matrix in water to obtain a mixed solution; wherein the auxiliary matrix is ​​boric acid and organosilane; the present invention can fully exert its synergistic enhancement effect by using boric acid and organosilane as auxiliary matrices, thereby enhancing both phosphorescence and fluorescence.

[0024] S2. The mixed solution is heated to react under semi-sealed conditions, cooled to room temperature after the reaction is completed, and then the reaction product is ground into powder to obtain matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots.

[0025] In this embodiment, the precursor of the carbon source is citric acid, and the doped nitrogen source is o-phenylenediamine.

[0026] In this embodiment, the organosilane is at least one of 3-aminopropyltriethoxysilane (APTES), 3-aminopropyl-trimethoxysilane (APTMS) and N-β-(aminoethyl)-γaminopropyltrimethoxysilane (KH792), preferably KH792.

[0027] In this embodiment, the molar ratio of the carbon source precursor to the doped nitrogen source is 1:(0.1-10), further 1:(0.5-2), and further 1:1.

[0028] In this embodiment, the molar ratio of the carbon source precursor to boric acid is 1:(10-60), and further 1:(45-50).

[0029] In this embodiment, the molar ratio of the carbon source precursor to the organosilane is 1:(1-8), and further 1:(4-5).

[0030] In this embodiment, the concentration of the carbon source precursor in the mixed solution is 0.001 to 1 mol / L, further 0.01 to 0.1 mol / L, and further 0.02 to 0.07 mol / L.

[0031] In this embodiment, during the dissolution process, the water bath temperature is 50-100° C., preferably 80° C.; and the stirring time is 5-30 min, preferably 15 min.

[0032] In this embodiment, the heating reaction temperature is 140-220° C., further 160-200° C., further 160-180° C.; the heating reaction time is 4-10 h, further 6 h.

[0033] In some specific embodiments of the present invention, during the heating reaction of the mixed solution under semi-closed conditions, the water evaporation time is 0.5 to 2 hours, further 0.8 to 1.2 hours; the reaction time after the water is evaporated is 2 to 9 hours, further 4 to 5.5 hours.

[0034] In some more specific embodiments of the present invention, the step of subjecting the mixed solution to a semi-enclosed heating reaction comprises: sealing the container containing the mixed solution with tin foil, puncturing a plurality of small holes in the tin foil with pointed tweezers, and then subjecting the mixture to the heating reaction. The present invention does not limit the number of small holes; for example, the number can be 5 to 10. The present invention can directly utilize an open container (such as a beaker) for semi-sealing, which is simple, convenient, and low-cost. It eliminates the need for a complex purification process and enables large-scale production of carbon dots.

[0035] In the second aspect, the present invention provides a matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission type carbon dot, which is obtained by the preparation method of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission type carbon dot provided by the first aspect of the present invention.

[0036] Example 1

[0037] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0038] Example 2

[0039] Dissolve 1 mmol of citric acid, 0.5 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0040] Example 3

[0041] Dissolve 1 mmol of citric acid, 2 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0042] Example 4

[0043] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 160°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0044] Example 5

[0045] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 200°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0046] Comparative Example 1

[0047] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, and 3 g of boric acid in 30 mL of water. Stir in a water bath at 80°C for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0048] Comparative Example 2

[0049] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, and 1 mL of KH792 in 30 mL of water. Stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder.

[0050] Comparative Example 3

[0051] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 3 g of boric acid, and 1 mL of KH792 in 30 mL of water. Stir in a water bath at 80°C for 15 min. Once completely dissolved, place the beaker, unsealed, in an electric heated air drying oven at 180°C for 6 h. After the reaction is complete, cool the beaker to room temperature. No residue should remain.

[0052] Comparative Example 4

[0053] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 5 g of boric acid, and 1 mL of KH792 in 30 mL of water and stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder. The final product is bluish-white with a cyan-green fluorescence and exhibits phosphorescence, but the lifetime is short.

[0054] Comparative Example 5

[0055] Dissolve 1 mmol of citric acid, 1 mmol of o-phenylenediamine, 3 g of boric acid, and 2 mL of KH792 in 30 mL of water and stir in an 80°C waterbath for 15 minutes. Once completely dissolved, seal the beaker with tin foil and poke eight small holes in the foil with pointed tweezers. Place the beaker in an electric forced-air drying oven at 180°C for 6 hours. After the reaction is complete, cool the beaker to room temperature and grind the reaction product into a powder. The final product exhibits a bluish-white fluorescence and exhibits phosphorescence, but the lifetime is short.

[0056] See also Figure 1 , Figure 1 The fluorescence and phosphorescence spectra (a) and fluorescence quantum yield (b) of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention at an excitation wavelength of 365 nm. Figure 1 It can be observed that the solid-state dual-mode emission carbon dot phosphor achieved by matrix-assisted synergistic enhancement effect has obvious fluorescence and phosphorescence signal peaks, and the solid-state fluorescence quantum yield is as high as 70.7%, which is expected to become a substitute for commercial phosphors.

[0057] See also Figure 2 , Figure 2 The SEM (a-b) and TEM (c) images of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention. Figure 2It can be observed in Figures a-2b) that the matrix silica nanoparticles are embedded in the boric acid matrix. Figure 2 c), it can be observed that the SiO2 nanoparticles obviously wrapped the Cdots, which proves the auxiliary synergistic enhancement effect of the two matrices.

[0058] See also Figure 3 , Figure 3 This is an optical image of the phosphorescence afterglow of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Example 1 of the present invention that can be distinguished by naked eyes. Figure 3 It can be clearly observed that the prepared matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots have a visible phosphorescence afterglow of up to 15 seconds.

[0059] See also Figure 4 , Figure 4 The fluorescence spectra (a1-a2), phosphorescence spectra (b1-b2) and phosphorescence lifetime diagram (b3) of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots prepared in Examples 1-5 of the present invention at an excitation wavelength of 365 nm are shown. Figure 4 It can be observed in (a1) that the amount of nitrogen source used has a significant effect on fluorescence. As the amount of nitrogen source increases, the fluorescence shows a significant red shift, but when the amount of nitrogen source reaches a certain level, the effect on fluorescence is not significant. Figure 4 As shown in (b1), the corresponding phosphorescence also has similar changes, but the excess nitrogen source causes the phosphorescence spectrum to shift blue. In addition, the reaction temperature is also a key influencing factor in the experiment, such as Figure 4 As shown in (a2), the reaction temperature significantly enhances the red shift of fluorescence; at the same time, a similar trend also occurs for phosphorescence. Excessively high temperature has little effect on the phosphorescence spectrum, but it will seriously shorten the phosphorescence lifetime, as shown in Figure 4 (b3) is shown.

[0060] See also Figures 5-6 And Table 1, Figure 5 The phosphorescence spectra (a) and phosphorescence lifetime diagrams (b) of the carbon dots prepared in Example 1 of the present invention and Comparative Examples 1-2; Figure 6 The fluorescence spectra (a) and fluorescence quantum yields (bc) of the carbon dots prepared in Example 1 and Comparative Examples 1-2 at an excitation wavelength of 365 nm are shown. Figures 5-6As can be clearly observed in Table 1, the fluorescence intensity is significantly enhanced in the presence of both organosilane and boronic acid matrices. Furthermore, when the auxiliary matrix is ​​solely organosilane, phosphorescence is not achieved. When the auxiliary matrix is ​​solely boric acid, both fluorescence and phosphorescence can be achieved simultaneously, but the fluorescence quantum yield and phosphorescence quantum yield are both extremely low, and the phosphorescence lifetime is extremely short. This indicates that the combination of organosilane and boronic acid matrices can synergistically enhance the solid-state dual-mode fluorescence and phosphorescence emission of carbon dots, demonstrating the key role of both matrices in achieving both fluorescence and phosphorescence.

[0061] Table 1 Statistics of phosphorescence, phosphorescence emission and quantum yield of different carbon dots

[0062]

[0063] In summary, the beneficial effects of the present invention include: the present invention directly prepares solid-state fluorescent powder by heating reaction under semi-closed conditions, which is completely different from the products obtained by traditional hydrothermal synthesis or solvent thermal synthesis methods; the method of the present invention is simple to operate, low-cost, does not require harsh reaction conditions and tedious separation processes, and is safe and environmentally friendly. The reaction product is directly a solid-state fluorescent and phosphorescent dual-emission phosphor, which can be widely promoted and applied. The carbon dots obtained by the present invention have a synergistic enhancement effect in both fluorescence and phosphorescence properties, and have a high fluorescence quantum yield and strong water dispersibility.

[0064] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots, characterized in that: The following steps are involved: mixing and dissolving a carbon source precursor, a doped nitrogen source, and an auxiliary matrix into water to obtain a mixed solution; The mixed solution is heated to react under semi-sealed conditions, cooled to room temperature after the reaction, and then the reaction product is ground into powder to obtain matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots; wherein, The precursor of the carbon source is citric acid; the doped nitrogen source is o-phenylenediamine; the auxiliary matrix is ​​boric acid and an organosilane, and the organosilane is at least one of 3-aminopropyltriethoxysilane, 3-aminopropyl-trimethoxysilane and N-β-(aminoethyl)-γaminopropyltrimethoxysilane; The molar ratio of the carbon source precursor to the doped nitrogen source is 1:(0.5-2); the molar ratio of the carbon source precursor to boric acid is 1:(45-50); the molar ratio of the carbon source precursor to organosilane is 1:(4-5); The temperature of the heating reaction is 140~220 o C, the heating reaction time is 4 to 10 hours; During the heating reaction of the mixed solution under semi-closed conditions, the evaporation time of the water is 0.5 to 2 hours, and the reaction time after the water is evaporated is 2 to 9 hours; The step of allowing the mixed solution to undergo a heating reaction under semi-sealed conditions comprises: sealing a container containing the mixed solution with tin foil, poking a number of small holes in the tin foil with pointed tweezers, and then conducting a heating reaction.

2. The method for preparing matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots according to claim 1, characterized in that: In the mixed solution, the concentration of the carbon source precursor is 0.001-1 mol / L.

3. The method for preparing matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots according to claim 1, characterized in that: The temperature of the heating reaction is 160~180 o C, and the heating reaction time is 6 h.

4. A matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dot, characterized in that: The matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots are obtained by the preparation method of the matrix-assisted synergistically enhanced fluorescence solid-state dual-mode emission carbon dots according to any one of claims 1 to 3.

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