Kilogram-level full-color high-efficiency solid-state fluorescent carbon dots and preparation method thereof

Abstract

The present invention belongs to the field of nanomaterials, and relates to kilogram-level full-color high-efficiency solid-state fluorescent carbon dots and their preparation methods. The method for synthesizing full-color solid-state fluorescent carbon dots comprises the following steps: o-phenylenediamine and 1,2,4,5-pyromellitic anhydride are dissolved in an ethanol aqueous solution according to a molar ratio of 1: (1-11); the resulting solution is then subjected to microwave heating treatment, the microwave heating power is 500-1000W, and the microwave heating time is 5-25min to obtain a carbon dot crude liquid; after the obtained carbon dot crude liquid is naturally volatilized, dimethyl sulfoxide is added thereto to fully dissolve, and centrifuge; the supernatant is taken, water is added, and filtered; the precipitate is taken, dried, and solid-state fluorescent carbon dot powder is obtained; by adjusting the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride, and the microwave heating time, blue solid-state fluorescent carbon dot powder, green solid-state fluorescent carbon dot powder, yellow solid-state fluorescent carbon dot powder, and red solid-state fluorescent carbon dot powder are obtained respectively. The method of the present invention obtains kilogram-level full-color solid-state fluorescent carbon dots with a quantum yield of up to 55.3-27.9% for the first time.

Description

Technical Field

[0001] The invention belongs to the field of nano materials, and specifically relates to a kilogram-level full-color high-efficiency solid-state fluorescent carbon dot and a preparation method thereof. Background Art

[0002] In the past decade, carbon dots (CDs) have been actively studied in the fields of imaging, sensing, light-emitting devices, and security systems due to their outstanding advantages such as simple preparation, excellent optical properties, good biocompatibility, and low cost. However, similar to organic fluorescent molecules, most CDs are quenched in the solid state due to π-π direct stacking interactions or excessive fluorescence resonance energy transfer between them, which limits their direct application in lighting and display devices. In order to overcome this severe aggregation-induced quenching effect, the existing technologies usually disperse CDs into suitable solid matrices (polymers, inorganic salts, silica, etc.) or modify the surface of CDs with functional ligands (alkylamines, chlorosalicylaldehyde, dithiosalicylic acid, etc.). The former strategy produces very large particles or even bulk materials, and the photoluminescence output is insufficient because the quenching effect still exists. The latter requires complicated procedures such as time-consuming reactions, tedious post-treatments, and tedious purification processes (such as dialysis, gel column chromatography, etc.) that result in extremely low production efficiency of CDs (less than 1 g / h). Neither of the above two methods can synthesize a large number of carbon dots with efficient solid-state fluorescence in a short time. In addition, the photoluminescence emission mechanism of the full-color solid-state fluorescence characteristics of carbon dots is still unclear. Therefore, it is difficult to achieve large-scale production of carbon dots with full-color solid-state fluorescence by simple experimental conditions.

[0003] Aggregation-induced emission effect (AIE) is considered to be an effective strategy for large-scale preparation of solid-state luminescent carbon dots. This is because such carbon dots have efficient solid-state luminescence without post-modification, and only a certain amount of poor solvent needs to be added during the purification process to achieve rapid precipitation of carbon dots. These two advantages lay the foundation for the large-scale preparation of efficient solid-state luminescent carbon dots. However, in the existing technology, most AIE-CDs only emit blue or yellow fluorescence, and it is difficult to adjust their emission wavelengths. So far, only a few studies have reported the successful preparation of tunable multicolor emission AIE-CDs by changing the carbon source. In 2021, Hu et al. synthesized AIE-CDs from green to red by solvothermal treatment of dithiosalicylic acid and amines with different numbers of nitrogen atoms. Recently, Lu's group prepared a series of full-color luminescent AIE-CDs by modifying previously prepared carbon dots with different salicylaldehyde-type ligands. Despite these efforts, existing AIE-CDs still have the following shortcomings: (1) these carbon dots are either not full-color or require time-consuming (more than 20 days) post-processing; (2) the highest quantum yield of these carbon dot powders is only 11.7%; (3) different carbon sources change the photoluminescence emission, which is not conducive to the analysis of the luminescence mechanism. Therefore, it is a real challenge to develop a simple one-step synthesis of efficient full-color solid-state fluorescent AIE-CDs from the same precursor, which is also important for the large-scale production and practical application of full-color solid-state fluorescent carbon dots and the understanding of their intrinsic emission mechanism. Summary of the invention

[0004] Technical problem: Based on the same precursor, develop a simple preparation method to synthesize high quantum yield, kilogram-scale full-color solid-state fluorescent AIE-CDs.

[0005] Technical solution:

[0006] On the one hand, a method for synthesizing full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy is provided, which comprises the following steps:

[0007] (1) Synthesis of carbon dots: o-phenylenediamine and 1,2,4,5-pyromellitic anhydride are dissolved in an ethanol aqueous solution at a molar ratio of 1:(1-11); the resulting solution is then subjected to microwave heating at a microwave heating power of 500-1000 W for a microwave heating time of 5-25 min to obtain a crude carbon dot solution;

[0008] (2) Separation and purification of carbon dots: After the obtained carbon dot crude liquid is naturally volatilized, dimethyl sulfoxide is added thereto to fully dissolve it, and centrifuge it; the supernatant is taken, water is added, and filtered; the precipitate is taken and dried to obtain a solid fluorescent carbon dot powder;

[0009] Based on step (1) and step (2), by adjusting the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride and the microwave heating time, blue solid fluorescent carbon dot powder, green solid fluorescent carbon dot powder, yellow solid fluorescent carbon dot powder and red solid fluorescent carbon dot powder are obtained respectively.

[0010] In some embodiments, in the ethanol aqueous solution, the volume ratio of ethanol to water is (10-20):1.

[0011] In some embodiments, in the ethanol-water solution, the volume ratio of ethanol to water is 20:1.

[0012] In some embodiments, the microwave heating power is 750 W, and the microwave heating time is 10 to 20 min.

[0013] In some embodiments, the step of synthesizing carbon dots is performed under normal pressure.

[0014] In some embodiments, the key parameters corresponding to obtaining the blue solid fluorescent carbon dot powder are as follows: in the synthesis step of the carbon dots, the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride is 1:10.4, the microwave heating power is 750 W, the microwave heating time is 10 min, and the volume ratio of ethanol to water in the ethanol aqueous solution is 20:1.

[0015] In some embodiments, the key parameters corresponding to obtaining the green solid-state fluorescent carbon dot powder are as follows: in the synthesis step of the carbon dots, the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride is 1:8.6, the microwave heating power is 750 W, the microwave heating time is 12 min, and the volume ratio of ethanol to water in the ethanol-water solution is 20:1.

[0016] In some embodiments, the key parameters corresponding to the yellow solid fluorescent carbon dot powder are as follows: in the synthesis step of the carbon dots, the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride is 1:5.3, the microwave heating power is 750 W, the microwave heating time is 16 min, and the volume ratio of ethanol to water in the ethanol aqueous solution is 20:1.

[0017] In some embodiments, the key parameters corresponding to obtaining the red solid fluorescent carbon dot powder are as follows: in the synthesis step of the carbon dots, the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride is 1:1.1, the microwave heating power is 750 W, the microwave heating time is 20 min, and the volume ratio of ethanol to water in the ethanol aqueous solution is 20:1.

[0018] In some embodiments, the microwave heating treatment is performed in a microwave digestion instrument.

[0019] On the other hand, the present invention provides an application of the aforementioned method in the rapid synthesis of kilogram-level full-color solid-state fluorescent carbon dots.

[0020] In another aspect, a full-color solid-state fluorescent carbon dot prepared by the aforementioned method is provided. Beneficial effects:

[0021] 1. The present invention uses carefully selected 1,2,4,5-pyromellitic anhydride and o-phenylenediamine as cheap precursors (carbon sources), and performs microwave heating treatment for a short time (5 to 25 minutes) at normal pressure (open system), synthesizes aggregation-induced emission carbon dots (AIE-CDs) with solid-state fluorescence in one step, and dissolves and centrifuges in dimethyl sulfoxide to remove unreacted raw materials, and finally quickly precipitates it into solid-state fluorescent carbon dot powder by poor solvent water, thereby achieving the separation and purification of solid-state fluorescent carbon dots. Based on the aggregation-induced emission effect (AIE), the present invention successfully obtains solid-state fluorescent carbon dots close to kilograms in a short time at normal pressure for the first time, which is a breakthrough in the large-scale production of carbon dots. Compared with the prior art, the method of the present invention has simple steps and low cost. Based on the selection of 1,2,4,5-pyromellitic anhydride and o-phenylenediamine, the synergistic effect of aggregation-induced emission effect (AIE) and microwave-assisted heating is utilized to greatly shorten the synthesis of carbon dots and the time required for the separation and purification of carbon dots, improve the production efficiency of solid-state fluorescent carbon dots, and provide a new method for the large-scale production of solid-state fluorescent carbon dots.

[0022] 2. Different from the existing preparation method of full-color fluorescent carbon dots, which is prepared by changing the carbon source or by modifying the previously prepared carbon dots with different salicylaldehyde-type ligands, the method of the present invention is based on the same precursors o-phenylenediamine and 1,2,4,5-pyromellitic anhydride. Only by adjusting the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride and the microwave heating time, the emission wavelength of the carbon dots can be adjusted, and blue solid fluorescent carbon dot powder, green solid fluorescent carbon dot powder, yellow solid fluorescent carbon dot powder and red solid fluorescent carbon dot powder can be successfully prepared, that is, full-color solid fluorescent carbon dots are obtained; it provides a new idea for the successful synthesis of full-color solid fluorescent carbon dots. At the same time, since the method of the present invention is based on the same precursors o-phenylenediamine and 1,2,4,5-pyromellitic anhydride, it is more conducive to the mechanism analysis and research of full-color solid fluorescent carbon dots.

[0023] 3. The full-color solid-state fluorescent carbon dots prepared by the method of the present invention have a high quantum yield, which can reach up to 55% or more.

[0024] 4. The full-color solid-state fluorescent carbon dots prepared by the present invention can be used in the fields of pattern encryption, anti-counterfeiting, fingerprint detection, multi-color display, luminous fiber, luminous device or lighting, and have good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1are four types of carbon dot powders: (a) B-CDs prepared in Example 1, (b) G-CDs prepared in Example 2, (c) Y-CDs prepared in Example 3, and (d) R-CDs prepared in Example 4;

[0026] Figure 2 The fluorescence normalized absorption spectra of four carbon dot powders, namely, B-CDs prepared in Example 1, G-CDs prepared in Example 2, Y-CDs prepared in Example 3, and R-CDs prepared in Example 4;

[0027] Figure 3 These are the fluorescence emission spectra of four carbon dot powders: (a) is B-CDs prepared in Example 1, (b) is G-CDs prepared in Example 2, (c) is Y-CDs prepared in Example 3, and (d) is R-CDs prepared in Example 4. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific examples.

[0029] Example 1

[0030] A method for synthesizing kilogram-level blue solid-state fluorescent carbon dots (B-CDs) based on an aggregation-induced emission strategy comprises the following steps:

[0031] Dissolve 5.72 mol of 1,2,4,5-pyromellitic anhydride (PMDA) and 0.55 mol of o-phenylenediamine (o-PDA) in 3000 mL of ethanol-water solution (volume ratio of ethanol to water is 20:1) and stir for 10 min. The obtained solution was heated in a microwave digester at 750 W for 10 min under normal pressure (open system). After the reaction, the solution evaporated naturally, and 1000 mL of dimethyl sulfoxide was added to form a carbon dot solution, which was centrifuged at a speed of 3000 r / min for 10 min to remove large particles. Take the supernatant, add 9000 mL of water, filter, take the precipitate, and dry it to obtain a blue solid fluorescent carbon dot (B-CDs) powder (such as Figure 1 (as shown in (a)).

[0032] After testing, by Figure 2 and Figure 3 It can be seen that the maximum emission wavelength of the blue solid-state fluorescent carbon dots (B-CDs) prepared in Example 1 in the fluorescence emission spectrum is 443 nm, and the optimal excitation wavelength is 370 nm; the quantum yield of the blue solid-state fluorescent carbon dots (B-CDs) prepared in Example 1 is calculated to be 55.3% by integrating sphere at the optimal excitation wavelength of 370 nm and the acceptance range of 385-750 nm.

[0033] Example 2

[0034] A method for synthesizing kilogram-level green solid-state fluorescent carbon dots (G-CDs) based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level blue solid-state fluorescent carbon dots (B-CDs) based on an aggregation-induced emission strategy in Example 1, the only difference being that the raw material ratio and the microwave heating time are changed, that is, the molar ratio of o-phenylenediamine (o-PDA): 1,2,4,5-pyromellitic anhydride (PMDA) is 1:8.6, and the heating time is 12 min, to obtain green solid-state fluorescent carbon dots (G-CDs) powder (such as Figure 1 (as shown in (b)).

[0035] After testing, by Figure 2 and Figure 3 It can be seen that the maximum emission wavelength of the green solid-state fluorescent carbon dots (G-CDs) prepared in Example 2 in the fluorescence emission spectrum is 509 nm, and the optimal excitation wavelength is 385 nm; the quantum yield of the green solid-state fluorescent carbon dots (G-CDs) prepared in Example 2 is calculated to be 48.8% by integrating sphere at the optimal excitation wavelength of 385 nm and the acceptance range of 400-800 nm.

[0036] Example 3

[0037] A method for synthesizing kilogram-level yellow solid fluorescent carbon dots (Y-CDs) based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level blue solid fluorescent carbon dots (B-CDs) based on an aggregation-induced emission strategy in Example 1, the only difference being that the raw material ratio and the microwave heating time are changed, that is, the molar ratio of o-phenylenediamine (o-PDA): 1,2,4,5-pyromellitic anhydride (PMDA) is 1:5.3, and the heating time is 16 min, to obtain yellow solid fluorescent carbon dots (Y-CDs) powder (such as Figure 1 (c)).

[0038] After testing, by Figure 2 and Figure 3 It can be seen that the maximum emission wavelength of the yellow solid-state fluorescent carbon dots (Y-CDs) prepared in Example 3 in the fluorescence emission spectrum is 563 nm, and the optimal excitation wavelength is 443 nm; the quantum yield of the yellow solid-state fluorescent carbon dots (Y-CDs) prepared in Example 3 is calculated to be 36.7% by integrating sphere at the optimal excitation wavelength of 443 nm and the acceptance range of 468-850 nm.

[0039] Example 4

[0040] A method for synthesizing kilogram-level red solid-state fluorescent carbon dots (R-CDs) based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level blue solid-state fluorescent carbon dots (B-CDs) based on an aggregation-induced emission strategy in Example 1, the only difference being that the raw material ratio and the microwave heating time are changed, that is, the molar ratio of o-phenylenediamine (o-PDA): 1,2,4,5-pyromellitic anhydride (PMDA) is 1:1.1, and the heating time is 20 min, to obtain red solid-state fluorescent carbon dots (R-CDs) powder (such as Figure 1 (d)).

[0041] After testing, by Figure 2 and Figure 3 It can be seen that the maximum emission wavelength of the red solid-state fluorescent carbon dots (R-CDs) prepared in Example 4 in the fluorescence emission spectrum is 613 nm, and the optimal excitation wavelength is 520 nm; the quantum yield of the red solid-state fluorescent carbon dots (R-CDs) prepared in Example 4 is calculated to be 27.9% by integrating sphere at the optimal excitation wavelength of 520 nm and the acceptance range of 535-950 nm.

[0042] Example 5

[0043] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: the microwave heating power is changed, the microwave heating power is 500 W, and blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots are respectively prepared, thereby obtaining full-color solid-state fluorescent carbon dots.

[0044] After testing, the maximum emission wavelengths of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 5 in the fluorescence emission spectrum are 421nm, 503nm, 559nm and 604nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 5 were calculated to be 10.4%, 22.3%, 14.8% and 5.9%, respectively.

[0045] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 5 all underwent a certain degree of blue shift, and the quantum yields all showed a significant decrease. It can be seen that based on the method of the present invention, reducing the microwave heating power will have a significant effect on the optical properties of the solid fluorescent carbon dots.

[0046] Example 6

[0047] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: the microwave heating power is changed, the microwave heating power is 1000W, and blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots are respectively prepared, thereby obtaining full-color solid-state fluorescent carbon dots.

[0048] After testing, the maximum emission wavelengths of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 6 in the fluorescence emission spectrum are 454nm, 523nm, 574nm and 626nm, respectively; through an integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 6 were calculated to be 22.3%, 36.6%, 27.6% and 6.9%, respectively.

[0049] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 6 all underwent a certain degree of red shift, and the quantum yields all showed a significant decrease. It can be seen that based on the method of the present invention, increasing the microwave heating power will have a significant effect on the optical properties of the solid fluorescent carbon dots.

[0050] Example 7

[0051] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: changing the microwave heating time, the microwave heating time is 8 minutes, and blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots are respectively prepared, thereby obtaining full-color solid-state fluorescent carbon dots.

[0052] After testing, the maximum emission wavelengths of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 7 in the fluorescence emission spectrum are 433nm, 505nm, 549nm and 601nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 7 were calculated to be 45.3%, 11.3%, 19.7% and 2.6%, respectively.

[0053] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 7 all underwent a certain degree of blue shift; the quantum yields all showed a certain decrease; in particular, the green solid fluorescent carbon dots, yellow solid fluorescent carbon dots and red solid fluorescent carbon dots showed obvious fluorescence blue shift and a decrease in luminous efficiency. It can be seen that based on the method of the present invention, shortening the microwave heating time will have a significant effect on the optical properties of the solid fluorescent carbon dots.

[0054] Example 8

[0055] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: changing the microwave heating time, the microwave heating time is 25 minutes, and blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots are respectively prepared, thereby obtaining full-color solid-state fluorescent carbon dots.

[0056] After testing, the maximum emission wavelengths in the fluorescence emission spectra of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots of Example 8 under the same conditions are 486nm, 535nm, 579nm and 632nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots of Example 8 were calculated to be 24.3%, 35.3%, 20.7% and 21.4%, respectively.

[0057] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 8 all underwent obvious red shifts; the quantum yields all showed a certain decrease; in particular, the green solid fluorescent carbon dots, yellow solid fluorescent carbon dots and red solid fluorescent carbon dots showed obvious fluorescence blue shifts and decreased luminous efficiency. It can be seen that based on the method of the present invention, extending the microwave heating time will have a significant effect on the optical properties of the solid fluorescent carbon dots.

[0058] Example 9

[0059] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: the reaction pressure is increased, i.e., the open system is replaced with a closed system for microwave heating, to respectively produce blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots, thereby obtaining full-color solid-state fluorescent carbon dots.

[0060] After testing, the maximum emission wavelengths in the fluorescence emission spectra of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots of Example 9 under the same conditions are 451nm, 487nm, 570nm and 618nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots of Example 9 were calculated to be 64.3%, 35.9%, 25.3% and 7.6%, respectively.

[0061] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 9 all undergo a certain degree of red shift; except that the quantum yield of the blue solid fluorescent carbon dots has been improved to a certain extent, the quantum yields of the other solid fluorescent carbon dots have all shown a certain decrease. It can be seen that based on the method of the present invention, the reaction pressure has an important influence on the emission wavelength and quantum yield of the solid fluorescent carbon dots.

[0062] Example 10

[0063] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that: changing the reaction solvent ratio, that is, the volume ratio of ethanol and water is 10:1, and respectively preparing blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots, thereby obtaining full-color solid-state fluorescent carbon dots.

[0064] After testing, the maximum emission wavelengths in the fluorescence emission spectra of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 10 under the same conditions are 429nm, 499nm, 561nm and 595nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 10 were calculated to be 61.3%, 42.5%, 34.2% and 7.6%, respectively.

[0065] As can be seen from Examples 1 to 4, the fluorescence emission spectra of the solid fluorescent carbon dots of various colors in Example 10 all underwent a certain degree of blue shift; except that the quantum yield of the blue solid fluorescent carbon dots was improved to a certain extent, the quantum yields of the solid fluorescent carbon dots of other colors all showed a certain decrease. It can be seen that based on the method of the present invention, the reaction solvent ratio has an important influence on the emission wavelength and quantum yield of the solid fluorescent carbon dots.

[0066] Embodiment 11

[0067] A method for synthesizing kilogram-level full-color solid-state fluorescent carbon dots based on an aggregation-induced emission strategy, referring to the method for synthesizing kilogram-level solid-state fluorescent carbon dots based on an aggregation-induced emission strategy of Examples 1 to 4, with the only difference being that the type of reaction solvent is changed, i.e., ethanol is replaced with ethyl acetate, and the volume ratio of ethyl acetate to water is 20:1, and blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots are respectively prepared, thereby obtaining full-color solid-state fluorescent carbon dots.

[0068] After testing, the maximum emission wavelengths in the fluorescence emission spectra of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 11 under the same conditions are 429nm, 471nm, 503nm and 525nm, respectively; through integrating sphere, the quantum yields of the blue solid-state fluorescent carbon dots, green solid-state fluorescent carbon dots, yellow solid-state fluorescent carbon dots and red solid-state fluorescent carbon dots in Example 11 were calculated to be 33.1%, 14.6%, 24.1% and 6.4%, respectively.

[0069] Compared with Examples 1 to 4, it can be seen that based on the method of the present invention, the selection of the reaction solvent ethanol has an important influence on the emission wavelength and quantum yield of the solid-state fluorescent carbon dots.

[0070] Comparative Example 1

[0071] The method for synthesizing kilogram-level solid fluorescent carbon dots based on the aggregation-induced emission strategy is referred to in Example 1, except that 1,2,4,5-pyromellitic anhydride is replaced with other acidic organic substances (for example, biphenyl-4-carboxylic acid).

[0072] After testing, the solid carbon dots prepared by using other acid organic compounds (such as biphenyl-4-carboxylic acid) in Comparative Example 1 do not have the aggregation-induced emission effect under the same conditions, and do not have solid-state fluorescence characteristics. It can be seen that based on the method of the present invention, the selection of 1,2,4,5-pyromellitic anhydride is one of the keys to the successful synthesis of aggregation-induced emission carbon dots.

[0073] Comparative Example 2

[0074] Referring to the method of synthesizing kilogram-level solid fluorescent carbon dots based on the aggregation-induced emission strategy of Examples 1 to 4, the only difference is that o-phenylenediamine is replaced with other amine organic substances (taking m-phenylenediamine as an example).

[0075] After testing, the solid carbon dots prepared by using other amine organic compounds (such as m-phenylenediamine) in Comparative Example 2 have the aggregation-induced emission effect under the same conditions, but can only obtain blue fluorescence and blue-green fluorescence, and cannot obtain red and yellow fluorescence. It can be seen that based on the method of the present invention, the synergistic effect of 1,2,4,5-pyromellitic anhydride and o-phenylenediamine can successfully achieve full-color solid-state fluorescence.

[0076] The various embodiments and comparative examples are summarized to obtain Table 1.

[0077] Table 1 Performance comparison of each embodiment and each comparative example

[0078]

[0079]

Claims

1. A method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy, characterized in that: The steps include: (1) Synthesis of carbon dots: o-phenylenediamine and 1,2,4,5-pyromellitic anhydride are dissolved in an ethanol aqueous solution at a molar ratio of 1:(1-11); the resulting solution is then subjected to microwave heating at a microwave heating power of 500-1000 W for a microwave heating time of 5-25 min to obtain a crude carbon dot solution; (2) Separation and purification of carbon dots: After the obtained carbon dot crude liquid is naturally volatilized, dimethyl sulfoxide is added thereto to fully dissolve it, and centrifuge it; the supernatant is taken, water is added, and filtered; the precipitate is taken and dried to obtain a solid fluorescent carbon dot powder; Based on step (1) and step (2), by adjusting the molar ratio of o-phenylenediamine and 1,2,4,5-pyromellitic anhydride and the microwave heating time, blue solid fluorescent carbon dot powder, green solid fluorescent carbon dot powder, yellow solid fluorescent carbon dot powder and red solid fluorescent carbon dot powder are obtained respectively.

2. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 1, characterized in that: In ethanol aqueous solution, the volume ratio of ethanol to water is (10-20):

1.

3. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 1, characterized in that: The microwave heating power is 750 W, and the microwave heating time is 10 to 20 minutes.

4. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 1, characterized in that: The synthesis steps of carbon dots were carried out under normal pressure; in an ethanol-water solution, the volume ratio of ethanol to water was 20:1; and the microwave heating power was 750W.

5. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 4, characterized in that: The key parameters corresponding to the blue solid fluorescent carbon dot powder are obtained: In the synthesis step of carbon dots, the molar ratio of o-phenylenediamine to 1,2,4,5-pyromellitic anhydride is 1:10.4, and the microwave heating time is 10 min.

6. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 4, characterized in that: The key parameters corresponding to the green solid fluorescent carbon dot powder are obtained: In the synthesis step of carbon dots, the molar ratio of o-phenylenediamine to 1,2,4,5-pyromellitic anhydride is 1:8.6, and the microwave heating time is 12 min.

7. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 4, characterized in that: The key parameters corresponding to the yellow solid fluorescent carbon dot powder are: In the synthesis step of carbon dots, the molar ratio of o-phenylenediamine to 1,2,4,5-pyromellitic anhydride is 1:5.3, and the microwave heating time is 16 min.

8. The method for synthesizing full-color solid-state fluorescent carbon dots based on aggregation-induced emission strategy according to claim 4, characterized in that: The key parameters corresponding to the red solid fluorescent carbon dot powder are obtained: In the synthesis step of carbon dots, the molar ratio of o-phenylenediamine to 1,2,4,5-pyromellitic anhydride is 1:1.1, and the microwave heating time is 20 min.

9. Use of the method according to any one of claims 1 to 8 in the rapid synthesis of kilogram-level full-color solid-state fluorescent carbon dots.

10. Full-color solid-state fluorescent carbon dots prepared by the method according to any one of claims 1 to 8.

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