A method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating and its application.

Abstract

This invention relates to the field of coatings, and discloses a method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating and its application. The preparation method includes: S1 preparing carbon black@silica nanospheres; S2 dissolving citric acid and urea in water and reacting them, followed by dialysis purification to obtain a carbon quantum dot mother liquor; S3 dispersing the carbon black@silica nanospheres and the carbon quantum dot mother liquor in an alcohol solvent, adding PVP, and stirring until homogeneous to obtain a photoresponsive fluorescent photonic crystal anti-counterfeiting material. The coating of this invention contains both carbon quantum dots and photonic crystals. Utilizing the structural color of the photonic crystals and the ultraviolet-excited fluorescence characteristics of carbon quantum dots, the coating can be endowed with excellent photoresponsive fluorescent anti-counterfeiting functionality. Therefore, this coating can be used to construct various anti-counterfeiting patterns.

Description

Technical Field

[0001] This invention relates to the field of coatings, and in particular to a method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating and its application. Background Technology

[0002] Throughout human history, chemical pigments have been widely used in various industries such as textiles, pharmaceuticals, and cosmetics. However, chemical dyes not only cause serious environmental pollution, but the colors also fade over time. In recent years, photonic crystals, due to their pollution-free and colorfast structural colors, have been widely used in high-end products such as ornaments, cosmetics, and textiles. However, counterfeiting and substandard products are becoming increasingly prevalent in the high-end market, severely damaging national and corporate reputation and consumer rights. Therefore, developing new anti-counterfeiting technologies is crucial for enhancing national image, improving corporate reputation, and protecting consumer rights. However, traditional anti-counterfeiting technologies such as barcodes, watermarks, and laser holography are easily cracked and counterfeited because their images and colors are fixed and visible, and their decryption methods are simple and singular. Therefore, there is an urgent need to develop new color-variable anti-counterfeiting technologies.

[0003] Quantum dot fluorescent anti-counterfeiting technology has significant application value in the field of optical anti-counterfeiting technology due to its optical properties such as instantaneous color generation, high fluorescence brightness, and tunable fluorescence color. Carbon quantum dots, as a novel fluorescent nanomaterial, possess characteristics such as high fluorescence yield, good chemical stability, low cost, and low toxicity, making them a hot topic in the field of luminescent materials research. Combining carbon quantum dots with photonic crystals to prepare fluorescent structural color anti-counterfeiting patterns, and applying them to products such as home decorations and textiles, will greatly enhance the functionality and anti-counterfeiting complexity of the products.

[0004] However, in the applicant's preliminary experiments, it was found that: on the one hand, after adding carbon quantum dots to the photonic crystal system, the carbon quantum dots are difficult to disperse sufficiently, which can easily lead to fluorescence quenching due to excessively high local concentration of carbon quantum dots, resulting in a significant reduction in fluorescence intensity; on the other hand, the doping of carbon quantum dots can also affect the structural color rendering of the photonic crystal. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating and its application. The coating of this invention simultaneously contains carbon quantum dots and photonic crystals. Utilizing the structural color of the photonic crystals and the ultraviolet-excited fluorescence properties of the carbon quantum dots, the coating can be endowed with excellent photoresponsive fluorescent anti-counterfeiting functionality. Therefore, this coating can be used to construct various anti-counterfeiting patterns.

[0006] The specific technical solution of this invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating, comprising:

[0008] S1: Preparation of carbon black@silica nanospheres;

[0009] S2: Citric acid and urea are dissolved in water and reacted. After dialysis purification, carbon quantum dot mother liquor is obtained; the particle size of the carbon quantum dots is ≤10nm;

[0010] S3: Disperse the carbon black@silica nanospheres obtained in S1 and the carbon quantum dot mother liquor obtained in S2 in an alcohol solvent, add PVP (polyvinylpyrrolidone), stir evenly, and obtain a photoresponsive fluorescent photonic crystal anti-counterfeiting material.

[0011] In the aforementioned photoresponsive fluorescent photonic crystal anti-counterfeiting material, the concentration range of carbon black@silica nanospheres is 3–10 wt%, the concentration of carbon quantum dots is 0.5–5 wt%, and the concentration of PVP is 0.1–0.7 wt%.

[0012] In the above steps, in S1, the present invention first prepares carbon black@silica nanospheres; the obtained carbon black@silica nanospheres can self-assemble into an ordered photonic crystal structure after coating, and the periodic microstructure of the regularly arranged photonic crystal modulates light to produce structural color. In S2, using citric acid as a carbon source and urea as a passivating agent, carbon quantum dots with high fluorescence yield are prepared after the reaction. In S3, the present invention disperses carbon black@silica nanospheres and carbon quantum dots in the same system. The present invention combines carbon quantum dots with photonic crystals, and utilizes the structural color of photonic crystals and the ultraviolet excitation fluorescence characteristics of carbon quantum dots to endow the coating with excellent photoresponsive fluorescent anti-counterfeiting function.

[0013] As described in the background section of this application, when carbon quantum dots are added to a system containing photonic crystals, the carbon quantum dots are difficult to disperse sufficiently, which can easily lead to fluorescence quenching due to excessively high local concentration of carbon quantum dots, resulting in a significant reduction in fluorescence intensity. At the same time, the doping of carbon quantum dots also affects the structural color rendering of the photonic crystal (the presence of carbon quantum dots affects the ordered arrangement of the photonic crystal (carbon black@silica nanospheres)).

[0014] Therefore, the present invention provides the following solution:

[0015] (1) This invention discovers that by utilizing the high transparency, high compatibility, and viscosity characteristics of PVP, if the coating contains an appropriate amount of PVP, the compatibility and dispersion of carbon quantum dots and carbon black@silica nanospheres in the system can be improved without affecting the color development of the photonic crystal and the fluorescence intensity of carbon quantum dots, thereby reducing the risk of local aggregation of carbon quantum dots. In addition, PVP can also enhance the adhesion of the coating, thus enabling the preparation of a photoresponsive photonic crystal anti-counterfeiting coating with uniform color and strong adhesion after the coating is cured.

[0016] (2) This invention has discovered that the particle size of carbon quantum dots has a certain influence on the structural color rendering of photonic crystals. Through experiments, this invention has found that controlling the particle size of carbon quantum dots to ≤10nm will not excessively affect the structural color rendering of photonic crystals.

[0017] (3) This invention has found that controlling the concentration of carbon quantum dots in the coating within a reasonable range can not only avoid excessively high local carbon quantum dot concentrations, but also reduce the impact on the ordered arrangement of photonic crystals. Therefore, this invention controls the concentration of carbon quantum dots in the coating to within 2.5 wt%.

[0018] Preferably, in S1, the particle size of the carbon black@silica nanospheres is 350-400 nm.

[0019] Preferably, in S1, the preparation method of the carbon black@silica nanospheres is as follows: carbon black is dispersed in 3-mercaptopropyltrimethoxysilane and xylene ketone to obtain carbon black suspension A. After irradiation with ultraviolet light and complete reaction, alkoxysilane-modified carbon black is obtained; alkoxysilane-modified carbon black is mixed evenly with anhydrous ethanol to obtain carbon black suspension B. Ammonia and water are added, and the mixture is heated and stirred to obtain reaction mixture A; tetraethyl silicate is mixed evenly with anhydrous ethanol and added to reaction mixture A. The mixture is stirred and reacted. After centrifugation, washing, drying, and grinding, carbon black@silica nanospheres are obtained.

[0020] The preparation principle of carbon black@silica nanospheres in this invention is as follows: First, sulfur / silicon functional groups are grafted onto the surface of carbon black using a photochemical method for modification. Alkoxysilane-modified carbon black is added to tetraethyl orthosilicate. The silicon-oxygen bonds on the carbon black surface undergo hydrolysis with water molecules in the system, generating silanol bonds on the carbon black surface. Under heating conditions, the silanols generated by the hydrolysis of tetraethyl orthosilicate not only undergo self-condensation but also condense with the silanols on the carbon black surface to form Si-O-Si bonds, creating a rivet structure that firmly coats the carbon black surface with silica, forming a silica coating layer, thus obtaining carbon black@silica nanospheres.

[0021] Preferably, in S2, the particle size of the carbon quantum dots is ≤5nm.

[0022] This invention has found that, with such small particle sizes, carbon quantum dots have virtually no impact on the structural color rendering of photonic crystals.

[0023] As a preferred embodiment, in S2, the ratio of citric acid, urea and water is 0.3-0.5g: 0.2-0.4g: 8-12ml; the reaction temperature is 150-200℃; and the reaction time is 8-12h.

[0024] This invention prepares carbon quantum dots using citric acid as a carbon source and urea as a passivating agent. The invention reveals that the selection of the carbon source, the material ratio, and the reaction temperature directly affect the particle size of the carbon quantum dots during the preparation process. Under the process conditions described above, a higher proportion of carbon quantum dots with a particle size ≤5nm can be successfully obtained.

[0025] Preferably, in S2, the molecular weight cutoff of the dialysis bag used for dialysis is 500–1000 Da; the dialysis solution used is deionized water; and the dialysis time is 12–24 h.

[0026] Preferably, in S3, the concentration of carbon black@silica nanospheres in the photoresponsive fluorescent photonic crystal anti-counterfeiting material is 3-6 wt%, the concentration of carbon quantum dots is 1-2.5 wt%, and the concentration of PVP is 0.2-0.4 wt%.

[0027] Within the material dosage range described above in this invention, not only will carbon quantum dots not affect the presentation of pigment structural color, but it will also ensure that they have appropriate fluorescence intensity.

[0028] As a preferred embodiment, in S3, carbon black@silica nanospheres and carbon quantum dot mother liquor are dispersed in an alcohol solvent by ultrasonication for 1-2 hours.

[0029] Preferably, in S3, the stirring rate is 200–500 rpm and the time is 30–90 min.

[0030] Preferably, in S3, the alcohol solvent is ethanol.

[0031] Secondly, the present invention provides the application of the photoresponsive fluorescent photonic crystal anti-counterfeiting coating obtained by the above preparation method in the preparation of fluorescent anti-counterfeiting patterns.

[0032] This invention combines carbon quantum dots with photonic crystals, utilizing the structural color of photonic crystals and the ultraviolet-excited fluorescence properties of carbon quantum dots to endow the coating with excellent photoresponsive fluorescence anti-counterfeiting functions. Therefore, various anti-counterfeiting patterns can be constructed using this coating.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] (1) This invention first prepares carbon black@silica nanospheres with structural color; then, using citric acid as a carbon source and urea as a passivating agent, carbon quantum dots with high fluorescence yield are prepared by reaction. Finally, this invention combines carbon quantum dots with photonic crystals, utilizing the structural color of photonic crystals and the ultraviolet excitation fluorescence characteristics of carbon quantum dots, thereby endowing the coating with excellent photoresponsive fluorescent anti-counterfeiting function.

[0035] (2) By adding PVP and controlling the particle size / content of carbon quantum dots, this invention can not only avoid fluorescence quenching caused by the aggregation of carbon quantum dots in the coating, but also significantly reduce the adverse effects of carbon quantum dots on the color presentation of photonic crystal structures.

[0036] (3) The present invention uses PVP, which has excellent transparency, compatibility and viscosity, as an additive, which can not only improve the compatibility and dispersion of carbon quantum dots and photonic crystals in the system, but also enhance the adhesion of the coating. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating the preparation mechanism of the photoresponsive fluorescent photonic crystal anti-counterfeiting coating of the present invention.

[0038] Figure 2 The image shown is a SEM image of Comparative Example 1, along with its particle size distribution histogram.

[0039] Figure 3 Digital photographs of a mixture of carbon quantum dots and anhydrous ethanol under ultraviolet light, and digital photographs of an LED lamp made of carbon quantum dots encapsulated in a 365nm wavelength ultraviolet chip when it is excited.

[0040] Figure 4 Digital photographs of Comparative Example 1, Comparative Example 2, and Example 2 under natural light and ultraviolet light, respectively.

[0041] Figure 5 Digital photographs and optical micrographs of Comparative Example 2, Example 1, Example 2, and Example 3;

[0042] Figure 6 The reflectance spectra of Comparative Example 1, Example 1, Example 2, and Example 3 are compared with the 1931 color chart of the International Commission on Illumination (CIE).

[0043] Figure 7 Digital photographs and optical micrographs of Comparative Examples 1, 4, 2 and 5 under natural light, and digital photographs under ultraviolet light.

[0044] Figure 8 The reflectance spectra and CIE color charts of Comparative Examples 1, 4, 2 and 5 are shown. Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments.

[0046] General Implementation Examples

[0047] A method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating, the preparation schematic diagram of which is shown below. Figure 1 As shown, the specific steps include:

[0048] (1) Carbon black with a particle size of 20-30 nm, after ball milling for 1-3 h, is dispersed in 3-mercaptopropyltrimethoxysilane and xylene ketone to obtain carbon black suspension A. After irradiation with ultraviolet light for 1-30 min and complete reaction, alkoxysilane-modified carbon black is obtained. The ratio of carbon black, 3-mercaptopropyltrimethoxysilane, and xylene ketone is 50-100 mg: 80-220 mg: 0.5-20 mg.

[0049] (2) The alkoxysilane-modified carbon black obtained in step (1) is ultrasonically dispersed and mixed with anhydrous ethanol for 30-60 min to obtain carbon black suspension B. Ammonia and water are added separately, and the mixture is heated to 55-65℃ under stirring at 200-500 rpm and kept at this temperature for 5-15 min to obtain reaction mixture A. The ratio of alkoxysilane-modified carbon black, anhydrous ethanol, ammonia (concentration of 25-28 wt%) and water is 0.01-0.05 g : 30-40 ml : 6-10 ml : 2-5 ml.

[0050] (3) Tetraethyl silicate and anhydrous ethanol are ultrasonically dispersed and mixed evenly for 30-60 min, and then added to reaction mixture A. The mixture is stirred and reacted for 1-3 h. After centrifugation (5000-6000 rpm, 5-10 min), washing (washing with deionized water 2-4 times, washing with ethanol 2-4 times), drying (45-55℃, 10-15 h), and grinding, carbon black@silica nanospheres (particle size 375±25 nm) are obtained. The ratio of tetraethyl silicate, anhydrous ethanol and reaction mixture A is 4-10 ml: 10-15 ml: 30-35 ml.

[0051] (4) Dissolve citric acid and urea in deionized water and pour the solution into a high-pressure reactor. React the mixture in an oven at 150–200°C for 8–12 hours. Then, purify the product by dialysis for 12–24 hours (dialysis bag molecular weight 500–1000 Da) to obtain carbon quantum dot mother liquor (carbon quantum dot particle size ≤10 nm, more preferably ≤5 nm). The ratio of citric acid, urea, and deionized water is 0.3–0.5 g : 0.2–0.4 g : 8–12 ml.

[0052] (5) The carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) are added to ethanol and ultrasonically dispersed for 1-2 hours. Then PVP is added and magnetically stirred for 30-90 minutes (200-500 rpm) to obtain a photoresponsive fluorescent photonic crystal anti-counterfeiting coating. The concentration of carbon black@silica nanospheres is 3-10 wt% (preferably 3-6 wt%), the concentration of carbon quantum dots is 0.5-5 wt% (preferably 1-2.5 wt%), and the concentration of PVP is 0.1-0.7 wt% (preferably 0.2-0.4 wt%).

[0053] Comparative Example 1

[0054] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0055] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0056] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres (average particle size of 375 nm).

[0057] (4) The carbon black@silica nanospheres obtained in step (3) are added to ethanol and ultrasonically dispersed for 1 hour to prepare a nanosphere suspension with a concentration of 4wt%. A structural color coating without carbon quantum dots and PVP is prepared and applied to the substrate. After the ethanol evaporates, a structural color coating is obtained.

[0058] Comparative Example 2

[0059] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0060] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0061] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0062] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0063] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm) so that the concentration of carbon black@silica nanospheres in the system is 4 wt% and the concentration of carbon quantum dots is 2 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent structural color coating without PVP is obtained. Apply it to the substrate and obtain a fluorescent anti-counterfeiting structural color coating after the ethanol evaporates.

[0064] Example 1

[0065] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0066] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0067] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0068] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0069] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm). Then add PVP to make the concentration of carbon black@silica nanospheres in the system 4 wt%, the concentration of carbon quantum dots 2 wt%, and the concentration of PVP 0.2 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent structural color coating is obtained. Apply it to the substrate and wait for the ethanol to evaporate to obtain a fluorescent anti-counterfeiting structural color coating.

[0070] Example 2

[0071] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0072] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0073] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0074] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0075] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm). Then add PVP to make the concentration of carbon black@silica nanospheres in the system 4 wt%, the concentration of carbon quantum dots 2 wt%, and the concentration of PVP 0.3 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent anti-counterfeiting structural color coating is obtained. Apply it to the substrate and wait for the ethanol to evaporate to obtain the fluorescent anti-counterfeiting structural color coating.

[0076] Example 3

[0077] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0078] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0079] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0080] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0081] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dots obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm). Then add PVP to make the concentration of carbon black@silica nanospheres in the system 4 wt%, the concentration of carbon quantum dots 2 wt%, and the concentration of PVP 0.4 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent anti-counterfeiting structural color coating is obtained. Apply it to the substrate and wait for the ethanol to evaporate to obtain the fluorescent anti-counterfeiting structural color coating.

[0082] Example 4

[0083] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0084] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0085] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0086] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0087] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm). Then add PVP to make the concentration of carbon black@silica nanospheres in the system 4 wt%, the concentration of carbon quantum dots 1 wt%, and the concentration of PVP 0.3 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent anti-counterfeiting structural color coating is obtained. Apply it to the substrate and wait for the ethanol to evaporate to obtain the fluorescent anti-counterfeiting structural color coating.

[0088] Example 5

[0089] (1) Add 50g of carbon black to a ball mill and ball mill for 2 hours. The average particle size after ball milling is 24nm. Then add it to a mixed solution of 3-mercaptopropyltrimethoxysilane (100mg) and xylene ketone (5mg), and ultrasonically disperse to obtain a carbon black suspension. Then irradiate with a UV lamp for 5 minutes. After the reaction is complete, alkoxysilane modified carbon black is obtained.

[0090] (2) Mix 3.7 mg of alkoxysilane modified carbon black obtained in step (1) with 32 ml of anhydrous ethanol and ultrasonically disperse to obtain a carbon black suspension. Add 8 ml of ammonia water (concentration of 25 wt%) and 3 ml of deionized water to the suspension respectively. Then place the suspension in a three-necked flask and stir (300 rpm). During stirring, heat to 60°C and keep warm for 10 min to obtain the reaction mixture.

[0091] (3) Mix 8 ml of tetraethyl silicate with 32 ml of anhydrous ethanol, sonicate for 30 min, and then add the mixture to the reaction mixture in step (2). Continue stirring at the same speed for 2 h. Centrifuge the resulting reaction solution at 5000 rpm for 10 min, wash (wash 3 times with deionized water and 3 times with alcohol), dry at 50 °C for 12 h, and finally grind to obtain carbon black@silica nanospheres.

[0092] (4) Dissolve 0.425g citric acid and 0.4g urea in 10ml of deionized water and pour into a high-pressure reactor. React at 180℃ in an oven for 10h. Then, purify the product by dialysis for 20h (dialysis bag molecular weight is 500Da) to obtain carbon quantum dot mother liquor.

[0093] (5) Add the carbon black@silica nanospheres obtained in step (3) and the carbon quantum dot mother liquor obtained in step (4) to ethanol and ultrasonically disperse for 1 h (carbon quantum dot particle size ≤ 5 nm). Then add PVP to make the concentration of carbon black@silica nanospheres in the system 4 wt%, the concentration of carbon quantum dots 2.5 wt%, and the concentration of PVP 0.3 wt%. After magnetic stirring for 60 min (300 rpm), a fluorescent anti-counterfeiting structural color coating is obtained. Apply it to the substrate and wait for the ethanol to evaporate to obtain the fluorescent anti-counterfeiting structural color coating.

[0094] The main differences between the various embodiments and comparative examples are shown below:

[0095]

[0096]

[0097] Performance testing and characterization

[0098] Figure 2 The SEM image of Example 1 shows an ordered photonic crystal structure obtained by the self-assembly of carbon black@silica nanospheres. The periodic microstructure of the regularly arranged photonic crystal modulates light, thereby producing structural color. We used Nano Measurer 1.2 software to perform particle size analysis on 100 randomly selected particles in the SEM image and calculated the particle size of the carbon black@silica nanospheres. Figure 2 The particle size distribution histogram shows that the average particle size of carbon black@silica nanospheres is 375 nm.

[0099] Figure 3 A digital photograph shows the fluorescence of carbon quantum dots prepared in Example 1 in ethanol under ultraviolet light excitation. As shown in the figure, the carbon quantum dot solution emits strong fluorescence under ultraviolet light irradiation at a wavelength of 365 nm. Further, carbon quantum dots were encapsulated in a 365 nm ultraviolet chip to prepare LED beads. Specifically, trimethylolpropane triacrylate (TMPTA) was used as a curing monomer and mixed with carbon quantum dots. After the water in the mixture evaporated, dihydroxydimethylacetone (DMA) was added as a photoinitiator to obtain a pre-curing solution containing carbon quantum dots. 3 μl of the pre-curing solution was titrated into the ultraviolet chip, and cured under ultraviolet light for 5 min to obtain LED beads. As shown in the figure, after connecting a 3W test power supply, the LED beads emitted strong blue light. The ratio of TMPTA:carbon quantum dot mother liquor:dihydroxydimethylacetone was 0.25 g:0.1 g:2 mg.

[0100] Figure 4Digital photographs of Comparative Example 1, Comparative Example 2, and Example 2 under natural and ultraviolet light are shown. As shown in the figures, Comparative Example 1, without PVP and carbon quantum dots, exhibits a bright structural color and does not show fluorescence under ultraviolet light. Comparative Example 2, with 2 wt% carbon quantum dots added, shows obvious fluorescence under ultraviolet light. Compared to Comparative Example 2 without PVP, Example 2, with 0.3 wt% PVP added, shows higher fluorescence intensity and more uniform fluorescence distribution under ultraviolet light at the same carbon quantum dot concentration. This is because in Comparative Example 2, the aggregation of carbon quantum dots in the solid state after solvent evaporation leads to fluorescence quenching, while in Example 2, after solvent evaporation, the PVP, as an additive, forms a polymer film, effectively dispersing the carbon quantum dots and maintaining high fluorescence intensity in the solid state. The results indicate that the addition of PVP contributes to uniform fluorescence distribution and improves the fluorescence intensity of the coating. Based on this, under the condition of ensuring the same amount of carbon quantum dots added, the effect of PVP on structural color was investigated through Example 1, Example 2, and Example 3.

[0101] Figure 5 Digital photographs and optical micrographs of Comparative Example 2, Example 1, Example 2, and Example 3 are shown. As the PVP content increases, the structural color of the coating gradually becomes darker. The optical micrographs clearly show that the color changes of Comparative Example 2 (PVP concentration 0 wt%), Example 1 (PVP concentration 0.2 wt%), and Example 2 (PVP concentration 0.3 wt%) are relatively small, while the structural color of Example 3 is relatively dark. Figure 6 Showing Figure 5The reflection spectra and CIE spectra of the comparative examples and embodiments are shown in the figure. Compared with Comparative Example 2 without PVP, the reflection peak intensities of Examples 1 and 2 with added PVP are slightly decreased, but the changes in reflection peak width are small. This indicates that the structural color brightness of Examples 1 and 2 is slightly decreased, but the degree of color change is small. However, Example 3 has low reflection intensity and a wide reflection peak, indicating that the saturation and brightness of the structural color of Example 3 are significantly reduced. This is attributed to the addition of PVP. After ethanol evaporates, PVP forms a thin film. In the photonic crystal structure that was originally filled with air, a small portion of the space is occupied by the PVP film. The difference in refractive index between the PVP film and the air medium leads to the change in structural color. The CIE coordinates of Comparative Example 2, Example 1, Example 2, and Example 3 are (0.2733, 0.2994), (0.2747, 0.3072), (0.2784, 0.3120), and (0.2889, 0.3210), respectively. As the PVP content increases, the CIE coordinates move closer to the center region, indicating a trend of decreasing saturation. Examples 1 and 2 are closer to the CIE coordinates of Comparative Example 2, while Example 3 is farther from Comparative Example 2, already very close to the center region, indicating low structural color saturation. Therefore, the PVP content in Examples 1 and 2 has a relatively small impact on the structural color, and their colors are also similar. Without affecting the structural color, a higher PVP content results in stronger coating adhesion; therefore, the PVP content should not exceed 0.4 wt%. Example 2, with its higher PVP content, is selected as the optimal PVP ratio. Based on this, and under the condition of determining the amount of PVP added, the effects of the amount of carbon quantum dots added on the structural color and fluorescence intensity of the coating were investigated through Examples 2, 4 and 5.

[0102] Figure 7 Digital photographs of Comparative Example 1, Example 4, Example 2, and Example 5 under ultraviolet light are shown. As expected, Comparative Example 1 did not exhibit fluorescence. After introducing 1 wt% carbon quantum dots, Example 4 exhibited blue fluorescence under ultraviolet light. The fluorescence intensity increased with increasing carbon quantum dot content. Example 2 (2 wt% carbon quantum dot concentration) showed strong fluorescence; however, when the carbon quantum dot content was further increased, the fluorescence intensity decreased, as shown in Example 5 (2.5 wt% carbon quantum dot concentration). This is due to fluorescence quenching caused by excessively high carbon quantum dot concentration; therefore, the carbon quantum dot concentration should not exceed 2.5 wt%.

[0103] Figure 8 Showing Figure 7The reflectance spectra and CIE chromaticity diagrams of each embodiment are shown in the figure. The reflectance peaks of the embodiments with added carbon quantum dots are similar, and the impact on structural color is small. The CIE coordinates of Comparative Example 1, Example 4, Example 2, and Example 5 are (0.2681, 0.2998), (0.2765, 0.3098), (0.2795, 0.3128), and (0.2815, 0.3154), respectively. Among them, the CIE coordinates of Example 2, Example 4, and Example 5 are close in position, indicating that the color saturation of the three is relatively similar. In summary, Example 2 is the optimal formulation.

[0104] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a photoresponsive fluorescent photonic crystal anti-counterfeiting coating, characterized in that: S1: Prepare carbon black@silica nanospheres with a particle size of 350~400nm; S2: Citric acid and urea are dissolved in water and reacted. After dialysis purification, carbon quantum dot mother liquor is obtained; the particle size of the carbon quantum dots is ≤10nm; S3: Disperse the carbon black@silica nanospheres obtained in S1 and the carbon quantum dot mother liquor obtained in S2 in an alcohol solvent, add PVP, stir evenly, and prepare a photoresponsive fluorescent photonic crystal anti-counterfeiting coating. In the photoresponsive fluorescent photonic crystal anti-counterfeiting coating, the concentration of carbon black@silica nanospheres is 3~10wt%, the concentration of carbon quantum dots is 1~2.5wt%, and the concentration of PVP is 0.2~0.4wt%.

2. The preparation method according to claim 1, characterized in that: In S2, the particle size of the carbon quantum dots is ≤5nm.

3. The preparation method according to claim 2, characterized in that: In S2, the ratio of citric acid, urea, and water is 0.3~0.5g: 0.2~0.4g: 8~12ml.

4. The preparation method according to claim 2, characterized in that: In S2, the reaction temperature is 150~200℃ and the reaction time is 8~12h.

5. The preparation method according to claim 2, characterized in that: In S2, the molecular weight cutoff of the dialysis bag used for dialysis is 500~1000 Da; the dialysis solution used is deionized water; and the dialysis time is 12~24 h.

6. The preparation method according to claim 1, characterized in that: In S3, the concentration of carbon black@silica nanospheres in the photoresponsive fluorescent photonic crystal anti-counterfeiting coating is 3~6wt%.

7. The preparation method according to claim 1, characterized in that: In S3, carbon black@silica nanospheres and carbon quantum dot mother liquor are dispersed in alcohol solvent by ultrasonication for 1-2 hours.

8. The preparation method according to claim 1, characterized in that: In S3, the stirring speed is 200~500 rpm and the time is 30~90 min.

9. The preparation method according to claim 1, characterized in that: In S3, the alcohol solvent is ethanol.

10. The application of the photoresponsive fluorescent photonic crystal anti-counterfeiting coating obtained by the preparation method according to any one of claims 1 to 9 in the preparation of fluorescent anti-counterfeiting patterns.

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