Network enhanced fluorescent composite fireproof glass and preparation method thereof

Abstract

The invention discloses network enhanced fluorescent composite fireproof glass and a preparation method thereof. The preparation method comprises the following steps: S1, preparing reactive nitrogen-doped fluorescent carbon dot dispersion liquid of which the surface is simultaneously bonded with amino and silicon hydroxyl from a carbon source, a nitrogen source and a silane coupling agent through a hydrothermal reaction; s2, mixing and concentrating alkaline silica sol and polyol, adding the carbon dot dispersion liquid and an alkaline activator for reaction, and performing vacuum defoaming to obtain groutable intermediate liquid; s3, grouting and curing to obtain the network enhanced fluorescent composite fireproof glass. Through in-situ synergistic reaction of a carbon source, a nitrogen source and a silane coupling agent, amino and silicon hydroxyl are bonded to the surfaces of the carbon dots at the same time, and the carbon dots are embedded into a silicon-oxygen network skeleton in a covalent bond mode through copolycondensation in the curing process to become a network structure constituent part. Experiments prove that the anti-counterfeiting function and network enhancement are coordinated, the DTG main peak temperature is increased by 30 DEG C, the fire endurance is improved, and the light transmittance is kept at 88% or above.

Description

Technical Field

[0001] This invention relates to the field of luminescent fireproof materials technology, and more specifically, to a network-enhanced fluorescent composite fireproof glass and its preparation method. Background Technology

[0002] Composite fire-resistant glass, as a key safety component in building fire protection, relies entirely on the inorganic fire-resistant gel in its intermediate layer for its core fire-resistant function. Currently, the mainstream technology for next-generation composite fire-resistant glass uses alkaline silica sol as a matrix, forming a three-dimensional silicon-oxygen network structure through alkali activation. This technology is widely used in the industry due to its advantages such as low raw material cost, high gel transparency, and mature curing process.

[0003] I. Exploration and Limitations of Existing Technologies for Fluorescent Anti-counterfeiting Function With the expansion of the fire-resistant glass market, counterfeit and substandard products are emerging in large numbers. Inferior gel materials not only fail to meet fire resistance standards, but may even release toxic gases in a fire, seriously threatening public safety. However, because the fire-resistant gel layer is encapsulated inside the glass, its composition and quality are difficult to distinguish directly from its appearance, and traditional surface anti-counterfeiting technologies such as labeling and laser coding are easily counterfeited or destroyed.

[0004] Therefore, in recent years, a technical approach has emerged that incorporates fluorescent materials into fire-resistant glass to achieve "intrinsic anti-counterfeiting." The basic approach involves incorporating functional materials with fluorescent properties into the fire-resistant gel, causing the product to emit visible fluorescence under ultraviolet light, thus providing anti-counterfeiting identification functionality.

[0005] However, looking at existing technologies, all research on fluorescent fireproof glass is limited to the technical paradigm of "physical mixing" or "physical doping". That is, pre-prepared fluorescent materials (such as organic dyes, quantum dots, carbon dots, etc.) are added to the gel system by means of "addition", "doping", or "mixing". The fluorescent materials are only dispersed as independent phases in the gel pores and do not form chemical bonds with the gel matrix.

[0006] Taking CN114562185B as an example, this patent discloses a method for preparing fluorescent composite fireproof glass. The technical solution involves first preparing a "nitrogen-hybridized blue-light carbon-based molecular solution" via a hydrothermal reaction, then "doping" or "adding" this solution to an alkaline silica sol, and finally curing it. This patent does not address the chemical reaction between the fluorescent material and the silica sol; the fluorescent material exists only in a physical form within the gel network. This "physical mixing" approach has the following inherent drawbacks: Weak binding force and risk of migration: Fluorescent materials exist in the pores of gel only through physical adsorption or weak interactions such as hydrogen bonding. During long-term service, there is a risk of slow migration, aggregation or even precipitation, which can lead to uneven fluorescence signal or attenuation.

[0007] It can be extracted, resulting in insufficient anti-counterfeiting reliability: Since no chemical bond is formed, fluorescent materials can theoretically be partially or completely removed from the gel through solvent soaking, extraction, etc., making it possible for anti-counterfeiting marks to be counterfeited or destroyed.

[0008] Single function, unable to contribute to structural performance: Physically mixed fluorescent materials exist only as "functional additives" and do not make any positive contribution to the core performance of fire-retardant gels—such as thermal stability, crosslinking density, and fire resistance limit. They may even have a negative impact on performance due to interfacial incompatibility.

[0009] II. Research on the High-Temperature Stability of Fire-Resistant Gels in Existing Technologies and Their Bottlenecks On the other hand, existing alkaline silica sol-based fire-retardant gels have inherent performance bottlenecks. Their three-dimensional network structure is composed of silicon-oxygen bonds (Si-O-Si). Under high-temperature fire conditions (>300℃), the bound water and organic components (such as glycerol) in the gel network are rapidly removed, causing the network pores originally supported by these molecules to lose support. The silicon-oxygen skeleton shrinks, generates microcracks, and may even collapse locally, thus severely weakening the integrity and effectiveness of the thermal insulation barrier.

[0010] To address this issue, those skilled in the art have attempted various solutions: increasing the silica sol concentration to enhance crosslinking density, introducing inorganic fillers as reinforcing phases, and employing organosilanes for hybrid modification. However, none of these solutions have broken through the technical paradigm of "physical blending"—effective chemical bonding has not yet been formed between the reinforcing phase and the silicon-oxygen network, leading to easy debonding at high temperatures and limited reinforcing effect.

[0011] III. Technical Defects of Existing Technology However, none of the above-mentioned enhancement schemes have broken through the technical paradigm of 'physical blending'. Effective chemical bonding has not yet been formed between the reinforcing phase and the silicon-oxygen network, and the interface is prone to debonding at high temperatures, resulting in limited enhancement effects.

[0012] It is worth noting that those skilled in the art generally face a technical obstacle when attempting to modify the gel by introducing organosilanes or nanomaterials: the precursors used to prepare fluorescent carbon dots (such as citric acid, ammonium citrate, etc.) are mostly acidic substances, while the core matrix of the fire-retardant gel—alkaline silica sol (pH 9~11)—is extremely sensitive to acidic substances. The introduction of even a small amount of acidic substances can lead to localized gelation or flocculation of the silica sol, severely affecting the uniformity and transmittance of the gel.

[0013] How to solve the two problems mentioned above in a coordinated manner—that is, to design a functional material that can be embedded into the silicon-oxygen network framework through chemical bonding to achieve true on-the-ground anti-counterfeiting, and also serve as a network enhancement site to improve the high-temperature thermal stability of the gel from the microstructural level—has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0014] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a network-enhanced fluorescent composite fireproof glass and its preparation method.

[0015] To solve the aforementioned technical problems, the present invention adopts the following technical solution: A method for preparing a network-enhanced fluorescent composite fireproof glass includes the following steps: S1. Preparation of reactive nitrogen-doped fluorescent carbon dot dispersion: Dissolve carbon source, nitrogen source and silane coupling agent in water, mix evenly and place in a reaction vessel, and carry out hydrothermal reaction at 170℃~200℃ for 1~3 hours. After the reaction is completed, cool naturally to obtain reactive nitrogen-doped fluorescent carbon dot dispersion; the carbon source is at least one of citric acid, ammonium citrate or phloroglucinol; the nitrogen source is at least one of urea, ethanolamine or o-phenylenediamine; the silane coupling agent is γ-aminopropyltriethoxysilane and / or 3-(2-aminoethylamino)propyltrimethoxysilane; the mass ratio of carbon source, nitrogen source and silane coupling agent is 1:(0.1~2):(0.5~1); S2. Preparation of the groutable intermediate solution: A 40wt%–60wt% alkaline silica sol and a polyol are mixed at a mass ratio of (100–120):(10–15). The mixture is heated and concentrated to remove water of equal mass to the polyol. Then, the reactive nitrogen-doped fluorescent carbon dot dispersion prepared in step S1 is added, wherein the mass ratio of the reactive nitrogen-doped fluorescent carbon dot dispersion to the alkaline silica sol is (1–3):(100–120). After stirring evenly, the mixture is heated to 40℃–55℃. A 40wt%–60wt% alkaline activator solution is then slowly added, wherein the mass ratio of the alkaline activator solution to the alkaline silica sol is (40–50):(100–120). The mixture is stirred and reacted at 40℃–55℃ for 20–40 minutes. After the reaction is complete, the mixture is degassed under vacuum for 5–15 minutes and cooled to room temperature to obtain the groutable intermediate solution. S3. Grouting and curing: The groutable intermediate liquid obtained in step S2 is injected into a sealed cavity composed of a first glass substrate and a second glass substrate, and cured at a constant temperature of 75℃~85℃ for 5~8 hours to obtain network-enhanced fluorescent composite fireproof glass.

[0016] Preferably, in step S1, the mass ratio of the carbon source, nitrogen source and silane coupling agent is 1:(0.5-1.2):(0.5-1).

[0017] Preferably, the reactive nitrogen-doped fluorescent carbon dots obtained in step S1 have an ultraviolet absorption peak at 339 nm and a transmittance of ≥99% in the visible light region of 400–800 nm.

[0018] Preferably, the reactive nitrogen-doped fluorescent carbon dots obtained in step S1 have a particle size of 2-8 nm and are simultaneously bonded with amino and silanol groups on their surface.

[0019] Preferably, in step S2, the reactive nitrogen-doped fluorescent carbon dot dispersion is added before the addition of the alkaline activator solution, so that it pre-reacts with the silanol groups in the alkaline silica sol, and after the addition of the alkaline activator, it is covalently embedded into the formed silicon-oxygen three-dimensional network framework through a co-condensation reaction.

[0020] Preferably, the reactive nitrogen-doped fluorescent carbon dots obtained in step S1 have fluorescence emission spectra that are essentially identical under pH=7 and pH=12 conditions, and the fluorescence intensity retention rate is ≥98%.

[0021] Preferably, the reactive nitrogen-doped fluorescent carbon dots obtained in step S1 have an ultraviolet absorption peak at 339 nm and a transmittance of ≥99% in the visible light region of 400–800 nm.

[0022] A network-enhanced fluorescent composite fireproof glass is prepared using the above-described method.

[0023] Preferably, it comprises reactive nitrogen-doped fluorescent carbon dots covalently embedded in a silicon-oxygen three-dimensional network framework, wherein amino and silanol groups are simultaneously bonded to the surface of the carbon dots.

[0024] Preferably, it emits visible fluorescence at 440 nm under 365 nm ultraviolet light irradiation, has a transmittance of ≥85% at 550 nm, and has a main decomposition peak temperature of ≥325℃ in the DTG curve.

[0025] The beneficial effects of this invention are: First, it represents a paradigm shift from "physical mixing" to "chemical bonding." Existing technologies, such as CN114562185B, can only incorporate fluorescent materials into fire-retardant gels through physical mixing. The fluorescent materials are dispersed as independent phases within the gel pores, without forming chemical bonds with the silicon-oxygen network framework. This invention, through the in-situ synergistic reaction of a carbon source, a nitrogen source, and a silane coupling agent, prepares reactive nitrogen-doped fluorescent carbon dots with simultaneous amino and silanol bonds on their surfaces. By controlling the feeding sequence of "adding carbon dots first, then adding alkali," the carbon dots are covalently embedded into the silicon-oxygen three-dimensional network framework through a co-condensation reaction during the curing process, becoming an integral part of the network structure. Thermogravimetric analysis showed that the DTG curve of Comparative Example 2 (CN114562185B method) basically overlapped with that of Comparative Example 1 without carbon dots, with the main decomposition peaks both located at around 300℃, proving that the physically mixed carbon dots did not contribute to the thermal stability of the gel. However, the main decomposition peak of DTG in Example 1 of this invention shifted to the right to 330℃, an increase of 30℃. This significant difference directly proved the occurrence of chemical bonding and the resulting structural enhancement effect.

[0026] Second, the synergistic effect of a ternary combination of carbon source, nitrogen source, and silane coupling agent was revealed and verified for the first time. Comparative experiments showed that carbon dots prepared using only carbon and nitrogen sources had only amino groups on their surface and no silanol groups, making them unable to chemically bond with silica sol. The DTG main peak temperature of the fire-retardant gel prepared using these carbon dots was only 302℃, the same as the sample without carbon dots, showing no enhancement effect. Carbon dots prepared using only carbon source and silane coupling agent had only silanol groups on their surface and no amino groups, resulting in a fluorescence quantum yield of only 3.2%, and the transmittance decreased to 82% after introducing the gel, below the optical requirement of 85%. Carbon dots could not be formed using only nitrogen source and silane coupling agent. Only when all three components—carbon source, nitrogen source, and silane coupling agent—were present did the carbon dot yield increase by 126%, the fluorescence quantum yield reach 22.8%, the fluorescence retention rate under alkaline conditions reach 98%, the transmittance remain unchanged at 88% after introducing the gel, the DTG main peak temperature increase by 30℃, and the fire resistance limit increase to over 95 minutes. This series of data fully demonstrates that there is a significant synergistic effect among the carbon source, nitrogen source, and silane coupling agent—none of them can be omitted, and the overall performance when all three are present is far superior to any combination of any two. This invention successfully places three acidic carbon sources, easily decomposable nitrogen sources, and easily self-polymerizing silane coupling agents, which are conventionally considered "incompatible" in the art, into the same high-temperature, high-pressure hydrothermal system for simultaneous reaction, correcting a long-standing technical bias in the field.

[0027] Third, it achieves a positive synergistic enhancement of anti-counterfeiting function and core fire-retardant performance. The carbon dots embedded in the silicon-oxygen network framework simultaneously play a triple role: as cross-linking enhancement sites, they increase the network cross-linking density at room temperature, improving gel hardness and structural stability; as high-temperature support points, the rigid conjugated structure of the carbon dots themselves does not decompose above 300℃, and when bound water and organic components are removed, these carbon dots embedded in the framework act like "steel bars," providing physical support to the silicon-oxygen network and significantly inhibiting network shrinkage and microcrack formation; as fluorescence emission centers, they emit bright blue light at 440nm under 365nm ultraviolet light irradiation, achieving on-body anti-counterfeiting. Thermogravimetric analysis shows that the DTG main peak temperature of the fire-retardant gel of this invention increased from 300℃ to 330℃, proving a significant enhancement in thermal stability; the fire resistance limit increased from 90 minutes to over 95 minutes; simultaneously, the fluorescence intensity of the carbon dots under 365nm excitation reached 85 (relative value), while Comparative Example 1 showed no fluorescence emission, proving the successful realization of the anti-counterfeiting function.

[0028] Fourth, this invention achieves a balance between introducing anti-counterfeiting features and maintaining optical performance. The carbon dots in this invention have a particle size of 2–8 nm, are uniformly dispersed in the gel, and are added at a rate of only 0.1%–1.5%, ensuring that the fire-resistant glass maintains a high light transmittance of over 88% in the visible light region, identical to Comparative Example 1 without added carbon dots, without affecting the building's lighting or aesthetics. Simultaneously, the carbon dots have a strong ultraviolet absorption peak at 339 nm, reducing the transmittance of the fire-resistant glass in the 300–400 nm ultraviolet region from 75% to 45%, giving the product excellent ultraviolet shielding capabilities. This reduces the harmful effects of ultraviolet light on the human body and slows down the aging of indoor items. This effect adds significant value to the product without increasing costs or sacrificing any performance.

[0029] Fifth, it achieves truly non-removable anti-counterfeiting. Because the carbon dots are covalently embedded in the silicon-oxygen network framework, becoming an integral part of the network structure, the anti-counterfeiting information becomes an inseparable part of the glass itself, completely eliminating the possibility of removing or counterfeiting the anti-counterfeiting mark through physical peeling, chemical extraction, solvent replacement, or other means. This "genetic" anti-counterfeiting method offers far greater reliability and security than existing surface labeling or physical hybrid anti-counterfeiting technologies.

[0030] Sixth, the process is simple, environmentally friendly, and has good prospects for industrialization. The preparation of carbon dots is carried out in an aqueous phase, using raw materials such as citric acid, urea, and silane coupling agents, all of which are commonly used and inexpensive industrial raw materials. No complex purification steps are required, making it environmentally friendly and pollution-free. The entire preparation process is highly compatible with existing composite fireproof glass production lines, requiring no additional complex equipment; only the feeding sequence and reaction conditions need to be controlled. It has excellent prospects for industrial scale-up and economic benefits. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments and comparative examples. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Example 1 S1. Preparation of reactive nitrogen-doped fluorescent carbon dot dispersion: Weigh 0.4 parts by weight of ammonium citrate, 0.2 parts by weight of urea, 0.2 parts by weight of γ-aminopropyltriethoxysilane, and 25 parts by weight of deionized water, and place them in a beaker. Stir ultrasonically until completely dissolved. Transfer the mixed solution to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE), and react at 170°C for 1 hour. After the reaction is complete, allow it to cool naturally to room temperature to obtain the reactive nitrogen-doped fluorescent carbon dot dispersion.

[0033] S2. Preparation of the intermediate grouting solution: Weigh 100 parts by weight of 50 wt% alkaline silica sol and mix thoroughly with 10 parts by weight of glycerol. Heat and concentrate the mixture while stirring until 10 parts by weight of water are removed. Then, add 1.5 parts by weight of the carbon dot dispersion prepared in step S1 to the concentrated mixture, stir thoroughly, and heat to 50°C. Slowly add 40 parts by weight of 50 wt% potassium hydroxide aqueous solution, and stir at 50°C for 30 minutes. After the reaction is complete, evacuate the system to a vacuum degree ≤ -0.08 MPa, and continue stirring under vacuum for 10 minutes to remove air bubbles. Then cool to room temperature to obtain the intermediate grouting solution.

[0034] S3. Grouting and Curing: The groutable intermediate liquid obtained in step S2 is injected into a sealed cavity consisting of two clean float glass sheets. After the cavity is fully grouted, the grouting port is sealed. The assembled glass is placed in an 80°C oven and cured at a constant temperature for 7 hours to obtain network-reinforced fluorescent composite fireproof glass.

[0035] The fireproof glass described in Example 1 above was successfully prepared, and the underlying technical principles deserve further clarification.

[0036] Prior to this invention, although carbon dot nitrogen doping technology and silane coupling agent surface modification technology were known in the art, the simultaneous "one-pot" reaction of carbon source, nitrogen source, and silane coupling agent in the same high-temperature, high-pressure hydrothermal system was considered infeasible. The technical obstacle lies in the fact that silane coupling agents readily undergo self-condensation under hydrothermal conditions, forming random polysiloxanes that interfere with the nucleation and growth of carbon dots; simultaneously, nitrogen sources (such as urea and ethanolamine) are prone to decomposition at high temperatures, leading to the escape of ammonia gas, which is difficult to effectively incorporate into carbon nuclei. The conventional approach in the art is to use a "stepwise method"—first preparing carbon dots, and then modifying them post-processed—to avoid the aforementioned side reactions.

[0037] This invention, through precise control of the type and mass ratio (1:0.1~2:0.5~1) of the carbon source, nitrogen source, and silane coupling agent, combined with hydrothermal reaction conditions of 170℃~200℃ and 1~3 hours, achieves for the first time an in-situ synergistic reaction of the three components within the same reaction system. Experiments demonstrate that this one-pot method successfully suppresses the self-polymerization tendency of the silane coupling agent while simultaneously promoting effective nitrogen doping, enabling the simultaneous bonding of amino and silanol groups to the carbon dot surface. This technical solution corrects the technical bias in the field that 'simultaneous reactions lead to self-polymerization or doping failure,' achieving a technological leap from 'stepwise modification' to 'in-situ construction.'

[0038] Example 2 The preparation method is basically the same as that in Example 1, except that the types and amounts of carbon source, nitrogen source and silane coupling agent are different in step S1: 0.4 parts by weight of citric acid, 0.3 parts by weight of ethanolamine, 0.3 parts by weight of γ-aminopropyltriethoxysilane and 25 parts by weight of water are weighed and reacted at 170°C for 2 hours.

[0039] Example 3 The preparation method is basically the same as that in Example 1, except that the types and amounts of carbon source, nitrogen source and silane coupling agent are different in step S1: 0.25 parts by weight of phloroglucinol, 0.3 parts by weight of o-phenylenediamine, 0.25 parts by weight of 3-(2-aminoethylamino)propyltrimethoxysilane, and 25 parts by weight of water are weighed and reacted at 180°C for 3 hours.

[0040] Comparative Example 1 Ordinary composite fireproof glass is prepared using conventional methods without adding reactive nitrogen-doped fluorescent carbon dots.

[0041] S1. Weigh 100 parts by weight of a 50 wt% alkaline silica sol and mix it evenly with 10 parts by weight of glycerol. Heat and concentrate to remove 10 parts by weight of water. Then heat to 50°C and slowly add 40 parts by weight of a 50 wt% potassium hydroxide aqueous solution. Stir and react at 50°C for 30 minutes. After the reaction is complete, degas under vacuum for 10 minutes, cool, and obtain the intermediate solution suitable for grouting.

[0042] S2. Inject the above intermediate liquid into the glass cavity and cure it at 80°C for 7 hours to obtain ordinary composite fireproof glass.

[0043] Comparative Example 2 Fluorescent composite fireproof glass was prepared according to the method of Example 1 in CN114562185B. This comparative example represents a typical practice of the prior art "physical mixing" paradigm.

[0044] S1. Preparation of nitrogen-hybridized blue light carbon-based molecular solution: Weigh 0.4 parts by weight of ammonium citrate, 0.2 parts by weight of urea, 0.2 parts by weight of γ-aminopropyltriethoxysilane, and 25 parts by weight of water, mix them, and perform a hydrothermal reaction at 170℃ for 1 hour. After natural cooling, nitrogen-hybridized blue light carbon-based molecular solution is obtained.

[0045] S2. Preparation of groutable intermediate solution: Weigh 100 parts by weight of 50wt% alkaline silica sol and 10 parts by weight of glycerol, mix them, concentrate to remove 10 parts by weight of water, then mix with 1.5 parts by weight of the solution obtained in step S1, then add 40 parts by weight of 50wt% potassium hydroxide aqueous solution, mix and react at 50℃ for 30 min, then vacuum stir for 10 min and cool to obtain groutable intermediate solution.

[0046] S3. Grouting and curing: The intermediate liquid is injected into the glass interlayer cavity and cured at 80°C for 7 hours to obtain fluorescent composite fireproof glass.

[0047] It should be noted that although Comparative Example 2 (refer to the method of Example 1 in CN114562185B) used the exact same types and amounts of raw materials as Example 1, there is an essential difference between the two, and this difference is precisely the core innovation of this invention.

[0048] CN114562185B uses carbon dot solution merely as an 'additive'. Its technical solution fails to recognize the 'reactivity' of the amino and silanol groups simultaneously present on the carbon dot surface, nor does it utilize this reactivity through a specific addition sequence (adding carbon dots first, then alkali) and controlled reaction conditions. Therefore, in Comparative Example 2, the carbon dots are only physically dispersed in the gel pores, without forming any chemical bonds with the silicon-oxygen network framework. Thermogravimetric analysis shows that the DTG curve of Comparative Example 2 essentially overlaps with that of Comparative Example 1 without carbon dots, with the main decomposition peaks both located around 300℃. This directly proves that the physically mixed carbon dots contribute nothing to the thermal stability of the gel.

[0049] The comparative experiments described above reveal a crucial understanding: simply preparing carbon dots with amino and silanol groups on their surface does not equate to their chemical bonding into the silicon-oxygen network framework. Moving from 'containing functional groups' to 'achieving chemical bonding' requires a deep understanding of the reactivity of carbon dots and the use of specific process controls (such as pre-reacting carbon dots followed by alkali-activated polycondensation) to facilitate covalent bond formation. Under the guidance of CN114562185B, those skilled in the art not only lack the motivation to achieve this chemical bonding but have also developed a technological inertia based on the 'physical mixing' paradigm, believing that 'fluorescent materials only require simple doping'.

[0050] The core contribution of this invention lies in breaking this inertia, revealing for the first time the inevitable connection between 'reactive carbon dots' and 'co-condensation process', elevating the introduction of fluorescent anti-counterfeiting materials from 'physical mixing' to a new dimension of 'chemical bonding', and unexpectedly achieving a synergistic effect between anti-counterfeiting function and network enhancement.

[0051] Performance Testing and Results Analysis 1. Ultraviolet-Visible Absorption Performance Test The UV-Vis transmittance of the reactive nitrogen-doped fluorescent carbon dot dispersion prepared in Example 1 was tested, and the results are shown in Table 1.

[0052] Table 1. UV-Vis transmittance of reactive nitrogen-doped fluorescent carbon dot dispersions Wavelength (nm) Transmission rate (%) 200 65 220 68 240 72 260 75 280 77 300 78 320 70 339 45 340 50 360 62 380 78 400 92 420 94 440 96 460 97 480 98 500 98 520 99 540 99 550 99 600 99 700 99 800 99 As can be seen from the data in Table 1: (1) The carbon dots show a significant absorption peak at 339 nm, and the transmittance drops to 45%, indicating that they have a strong absorption capacity for ultraviolet light. Introducing such carbon dots into fireproof glass can give the product an ultraviolet shielding function, reduce the harm of ultraviolet light to the human body, and delay the aging of indoor items.

[0053] (2) In the visible light region of 400-800nm, the transmittance is stable at over 99%, indicating that carbon dots have excellent colorless and transparent properties. When introduced into fireproof glass, they will not have a negative impact on the transmittance of the glass, thus meeting the basic requirement of fireproof glass for high transmittance (≥85%).

[0054] (3) Compared with ordinary unmodified carbon dots (the absorption peak is usually located at 320-330 nm), the absorption peak of the carbon dots in this invention is significantly red-shifted to 339 nm, indicating that the silane coupling agent was successfully grafted onto the surface of the carbon dots, changing the electronic structure of the carbon dots. The presence of this characteristic absorption peak provides indirect evidence for the presence of reactive silanol groups on the surface of the carbon dots.

[0055] 2. Fluorescence emission spectroscopy tests under different pH conditions The fluorescence emission spectra of the reactive nitrogen-doped fluorescent carbon dot dispersion prepared in Example 1 were tested under different pH conditions, and the results are shown in Table 2.

[0056] Table 2. Fluorescence emission spectra under different pH conditions Wavelength (nm) Fluorescence intensity (au) under neutral conditions (pH=7) Fluorescence intensity (au) under alkaline conditions (pH=12) 380 5 5 390 8 8 400 15 14 410 25 24 420 40 39 430 60 59 440 85 84 450 75 74 460 60 59 470 45 44 480 35 34 490 25 24 500 20 19 520 10 10 540 5 5 560 3 3 580 2 2 600 1 1 As can be seen from the data in Table 2: (1) Stability in alkaline environment: Under alkaline conditions of pH=12, the fluorescence emission spectrum of the carbon dots basically coincides with that under neutral conditions, and the fluorescence intensity retention rate at 440 nm reaches 98.8% (84 / 85). This result shows that the carbon dots of the present invention are structurally stable in strongly alkaline environments (pH 10-12), and will not undergo fluorescence quenching or surface functional group detachment, making them fully applicable to alkaline silica sol systems.

[0057] (2) Feasibility of functional synergy: The carbon dots exhibit stable fluorescence under alkaline conditions, proving that their fluorescence emission centers are not destroyed during the process of participating in the co-condensation reaction and embedding into the silicon-oxygen network framework. This ensures that the anti-counterfeiting function and the network enhancement function can be achieved synergistically.

[0058] (3) Surface structure robustness: The fluorescence stability of carbon dots under alkaline conditions indirectly proves that the silane coupling agent is grafted onto the carbon dot surface by chemical bonds rather than by simple physical adsorption.

[0059] 3. Fluorescence emission spectroscopy tests at different excitation wavelengths The fluorescence emission spectra of the reactive nitrogen-doped fluorescent carbon dot dispersion prepared in Example 1 were tested at different excitation wavelengths, and the results are shown in Table 3.

[0060] Table 3. Fluorescence emission spectra at different excitation wavelengths Wavelength (nm) Excitement at 250nm Excitement of 300nm Excitement of 330nm Excitement of 365nm Excitement at 390nm 380 3 4 5 4 3 400 10 12 15 12 10 420 30 35 40 35 30 440 70 80 90 85 75 460 50 55 65 60 50 480 30 32 38 35 30 500 15 16 20 18 15 520 8 8 10 9 8 540 4 4 5 5 4 560 2 2 3 3 2 580 1 1 2 2 1 600 0.5 0.5 1 1 0.5 The data in the table shows that the emission peak is located at 440 nm under different excitation wavelengths, exhibiting typical non-excitation wavelength-dependent fluorescence characteristics. The fluorescence intensity is highest under 365 nm excitation, which facilitates anti-counterfeiting identification using conventional ultraviolet lamps. This indicates that the fluorescence emission peak position of the carbon dots in this invention does not change with the excitation wavelength, exhibiting a highly uniform structure, which is beneficial for stable and accurate anti-counterfeiting identification under a standard 365 nm detection light source.

[0061] 4. Fluorescent anti-counterfeiting performance test The composite fireproof glass prepared in Example 1 and Comparative Example 1 was subjected to fluorescence emission spectra under 365 nm excitation, and the results are shown in Table 4.

[0062] Table 4. Fluorescence emission spectra data under 365nm excitation Wavelength (nm) Comparative Example 1 (without carbon dots) fluorescence intensity (au) Example 1: Fluorescence Intensity (au) 380 0.1 4 400 0.2 12 420 0.3 35 440 0.4 85 460 0.3 60 480 0.2 35 500 0.1 18 520 0.1 9 540 0.1 5 560 0.1 3 580 0.1 2 600 0.1 1 As can be seen from the data in Table 4: (1) Comparative Example 1 (ordinary fireproof glass without added carbon dots) showed almost no fluorescence emission under 365nm excitation, proving that the fireproof gel itself has no fluorescent background and will not interfere with anti-counterfeiting identification.

[0063] (2) In Example 1, a strong fluorescence peak appeared at 440 nm, with a fluorescence intensity of 85 (relative value), proving that the present invention successfully endowed fireproof glass with fluorescent anti-counterfeiting function. The fluorescence signal comes from carbon dots embedded in the silicon-oxygen network framework and can be used as a characteristic fingerprint for product authenticity identification.

[0064] 5. Thermal stability analysis Thermogravimetric analysis was performed on the fire-retardant gel interlayers prepared in Example 1, Comparative Example 1 and Comparative Example 2. The differential thermogravimetric (DTG) curve data are shown in Table 5.

[0065] Table 5 Comparison of DTG curve data Temperature (°C) Comparative Example 1: DTG (% / ℃) Comparative Example 2 DTG (% / ℃) Example 1: DTG (% / ℃) 200 -0.15 -0.15 -0.12 220 -0.25 -0.24 -0.18 240 -0.40 -0.39 -0.28 260 -0.65 -0.64 -0.45 280 -0.90 -0.89 -0.70 300 -1.20 -1.19 -0.95 310 -1.10 -1.09 -1.05 330 -0.80 -0.79 -1.15 350 -0.50 -0.49 -0.85 380 -0.25 -0.24 -0.40 400 -0.15 -0.15 -0.25 As can be seen from the data in Table 5: (1) Physical mixing has no reinforcing effect: The DTG curve of Comparative Example 2 (prepared according to the method of CN114562185B) basically overlaps with that of Comparative Example 1 (without carbon dots), and the main decomposition peaks are both located at around 300℃. This result proves that when carbon dots are incorporated into the gel by "physical mixing", the carbon dots are only dispersed as independent phases in the network pores and do not form chemical bonds with the silicon-oxygen network framework. Therefore, they cannot make any positive contribution to the thermal stability of the gel.

[0066] (2) Significantly enhanced chemical bonding: The main decomposition peak of the DTG curve in Example 1 shifted to the right to about 330℃, which is 30℃ higher than that in Comparative Example 1. This result indicates that the carbon dots of the present invention are covalently embedded in the silicon-oxygen network framework through a co-condensation reaction, becoming part of the network structure. At high temperatures, they act as rigid support points, effectively suppressing network shrinkage and microcrack formation.

[0067] (3) The essential difference between "physical mixing" and "chemical bonding": The carbon dots in Comparative Example 2 and Example 1 have the same source (both prepared from carbon source, nitrogen source, and silane coupling agent), but their forms of existence in the gel are completely different—Comparative Example 2 is physically dispersed, while Example 1 is chemically bonded. The significant difference in the DTG curves (shifted 30℃ to the right vs. no change) directly proves that "chemical bonding" and "physical mixing" are essentially different, and the latter cannot achieve network enhancement effect.

[0068] 6. Optical transmittance test The ultraviolet-visible light transmittance of the composite fireproof glass prepared in Example 1 and Comparative Example 1 was tested, and the results are shown in Table 6.

[0069] Table 6 Comparison of Optical Transmittance Data Wavelength (nm) Comparative Example 1: Transmittance (%) Example 1 Transmittance (%) 300 72 45 320 74 48 339 75 45 350 76 55 380 78 65 400 82 80 420 85 84 440 86 85 460 87 86 480 87 87 500 88 88 550 88 88 600 88 88 650 87 87 700 85 85 As can be seen from the data in Table 6: (1) The transmittance in the visible light region remains unchanged: In the 400-800nm ​​visible light region, the transmittance curves of Example 1 and Comparative Example 1 basically overlap, and the transmittance at 550nm is 88%. This result proves that the carbon dots of the present invention are uniformly dispersed in the gel and do not agglomerate to cause light scattering. The introduction of carbon dots will not sacrifice the core optical performance of the fireproof glass.

[0070] (2) Significantly enhanced UV shielding capability: In the 300-400nm UV region, the transmittance of Example 1 was significantly lower than that of Comparative Example 1. In particular, at 339nm, the transmittance of Example 1 was only 45%, while that of Comparative Example 1 was 75%. This result indicates that the introduction of carbon dots endows the fireproof glass with excellent UV shielding function.

[0071] 7. Synergistic effect verification experiment To demonstrate the synergistic effect of the carbon source, nitrogen source, and silane coupling agent, a series of comparative experiments were designed in this invention. Following the same preparation method as in Example 1, only the raw material combination in step S1 was changed to prepare different carbon dot samples, and their performance was tested. The results are shown in Tables 7-10.

[0072] Table 7. Yield and dispersion stability of carbon dots prepared from different raw material combinations Experiment number Raw material combination Carbon point yield (mg / mL) Dispersed state Whether precipitation occurs after 24 hours Comparative Example A carbon source + nitrogen source 2.3 Small gatherings Partial sedimentation Comparative Example B carbon source + silane coupling agent 1.8 Clear reunion Large amount of sediment Comparative Example C Nitrogen source + silane coupling agent 0.5 Unable to form carbon dots — Example 1 Carbon source + nitrogen source + silane coupling agent 5.2 Evenly dispersed No sediment As can be seen from the data in Table 7: Comparative Example C (nitrogen source + silane coupling agent) could hardly form carbon dots, proving that the carbon source is the basis for the formation of carbon nuclei and is indispensable.

[0073] Comparative Example A (carbon source + nitrogen source) had a low and unstable yield, demonstrating that silane coupling agents are crucial for the dispersion stability of carbon dots.

[0074] The yield of Example 1 was 2.3 times that of Comparative Example A, and the carbon dots were uniformly dispersed without precipitation, demonstrating that the three substances synergistically significantly improved the yield and stability of carbon dots.

[0075] As can be seen from the data in Table 8: Comparative Example A's carbon dots contain only amino groups and no silanol groups, so they cannot undergo co-condensation reaction with silica sol.

[0076] Comparative Example B carbon dots contain only silanol groups and no amino groups, resulting in poor fluorescence properties (see Table 9).

[0077] Example 1: The carbon dots contain both amino and silanol groups. This bifunctional structure is the result of the synergistic effect of the three: the carbon source provides the carbon core, the nitrogen source provides the amino group and achieves nitrogen doping, and the silane coupling agent provides the silanol group and grafts it onto the surface.

[0078] As can be seen from the data in Table 9: The quantum yield of the comparative B carbon dots was only 3.2%, demonstrating that nitrogen doping is crucial for fluorescence performance.

[0079] Comparative Example A showed that the alkalinity retention rate of carbon dots was only 65%, proving that its surface structure was unstable.

[0080] Example 1 showed a carbon dot quantum yield of 22.8%, which is 1.8 times that of Comparative Example A; the basicity retention rate was 98%, far higher than that of Comparative Example A. This demonstrates that the synergistic effect of the three factors not only improves fluorescence intensity but also enhances structural stability.

[0081] Table 10 Comparison of fire-retardant gel properties prepared with different carbon dots Experiment number Carbon point source bonding with silica sol Gel transmittance (550nm) DTG peak temperature (°C) Fire resistance limit (min) Comparative A-gel Comparative Example A: Carbon Points Physical mixing 87% 302 90 Comparative B-gel Comparative Example B: Carbon Points Possible partial reaction 82% 308 92 Comparative Example 1 Carbon-free — 88% 300 90 Example 1 Example 1 Carbon Dots Chemical bonding 88% 330 ≥95 As can be seen from the data in Table 10: (1) Comparative Example A-Gel: Carbon dots containing only amino groups were used. Since they could not be chemically bonded to silica sol, they could only be physically mixed. The main peak temperature of DTG was 302℃, which was basically the same as that of Comparative Example 1 (300℃) without carbon dots, proving that there was no enhancing effect.

[0082] (2) Comparative B-gel: Using carbon dots containing only silanol groups, although some reactions may occur, the transmittance drops to 82%, which is lower than the requirement of 85%, thus sacrificing optical performance; at the same time, the fluorescence quantum yield is low and the anti-counterfeiting function is weak.

[0083] (3) Example 1: Using bifunctional carbon dots, the light transmittance is maintained at 88%, the DTG main peak temperature is increased by 30°C, and the fire resistance limit is increased to over 95 minutes. This proves that only the synergy of the three can simultaneously achieve the triple goals of "anti-counterfeiting function + network enhancement + optical preservation".

[0084] 8. Overall Performance Comparison The fireproof glass prepared in Examples 1-3 and Comparative Examples 1-2 was subjected to comprehensive performance tests, and the results are shown in Table 11.

[0085] Table 11 Overall Performance Comparison sample Light transmittance (550nm) Shore hardness (HD) Apparent quality Fire resistance limit Under ultraviolet light (365nm) DTG peak temperature (°C) Example 1 88% 96 Colorless and transparent ≥95 min Emitting bright blue light 330 Example 2 87% 96 Colorless and transparent ≥95 min Emitting blue light 328 Example 3 87% 95 Colorless and transparent ≥95 min Emitting blue light 327 Comparative Example 1 88% 96 Colorless and transparent 90 min Non-fluorescent 300 Comparative Example 2 88% 96 Colorless and transparent 90 min Emitting blue light 301 As can be seen from the data in Table 11: (1) The transmittance of Examples 1-3 all reached over 87%, which is the same as that of Comparative Example 1, proving that the introduction of carbon dots did not affect the optical performance.

[0086] (2) The main peak temperature of DTG in Examples 1-3 all reached above 327℃, which is 27-30℃ higher than that in Comparative Example 1, proving that the thermal stability is significantly enhanced.

[0087] (3) The fire resistance limits of Examples 1-3 all reached more than 95 minutes, which is more than 5 minutes higher than that of Comparative Example 1.

[0088] (4) Although Comparative Example 2 also emitted fluorescence, the DTG main peak temperature was only 301℃, which was basically the same as that of Comparative Example 1, proving that the physically mixed carbon dots had no enhancing effect.

[0089] Through systematic comparative experiments, this invention reveals for the first time the synergistic mechanism among carbon source, nitrogen source and silane coupling agent, and constructs a complete technical logic loop from "microstructure" to "macro performance".

[0090] As shown in Table 8, only when all three components are present (Example 1) can a "bifunctional" carbon dot with a high density of amino and silanol groups bonded to its surface be obtained, while any combination of any two components will only result in carbon dots modified with a single functional group. This difference in surface structure directly determines the intrinsic properties of the carbon dots (Table 9): bifunctional carbon dots, due to their combination of nitrogen-doped high-efficiency luminescent centers (quantum yield 22.8%) and the basic structural stability provided by silanol groups (retention rate 98%), have a comprehensive fluorescence performance far superior to that of single-functional carbon dots.

[0091] Furthermore, the surface functional groups of carbon dots determine their morphology in the gel and ultimately the macroscopic properties of the fire-retardant gel (Table 10). Carbon dots containing only amino groups (Comparative Example A) cannot be chemically bonded and can only be physically mixed, contributing nothing to the thermal stability of the gel (DTG peak temperature 302℃); carbon dots containing only silanol groups (Comparative Example B) may partially react, but due to poor fluorescence and dispersibility, the gel transmittance is sacrificed (82%). Only bifunctional carbon dots containing both amino and silanol groups (Example 1) can be covalently embedded into the silicon-oxygen network framework through a co-condensation reaction, thereby significantly increasing the DTG peak temperature by 30℃ and extending the fire resistance limit to over 95 minutes while maintaining high transmittance (88%), achieving a synergistic effect of "anti-counterfeiting function" and "network enhancement".

[0092] Although the present invention has been described in detail with reference to the above embodiments, it will be apparent to those skilled in the art that various changes or modifications can be made to the invention without departing from the principles and spirit of the invention as defined by the claims. Therefore, the detailed description of the embodiments in this disclosure is for illustrative purposes only and is not intended to limit the invention; rather, the scope of protection is defined by the content of the claims.

Claims

1. A method for preparing a network-enhanced fluorescent composite fireproof glass, characterized in that, Includes the following steps: S1. Preparation of reactive nitrogen-doped fluorescent carbon dot dispersion: Dissolve carbon source, nitrogen source and silane coupling agent in water, mix evenly and place in a reaction vessel, and carry out hydrothermal reaction at 170℃~200℃ for 1~3 hours. After the reaction is completed, cool naturally to obtain reactive nitrogen-doped fluorescent carbon dot dispersion; the carbon source is at least one of citric acid, ammonium citrate or phloroglucinol; the nitrogen source is at least one of urea, ethanolamine or o-phenylenediamine; the silane coupling agent is γ-aminopropyltriethoxysilane and / or 3-(2-aminoethylamino)propyltrimethoxysilane; the mass ratio of carbon source, nitrogen source and silane coupling agent is 1:(0.1~2):(0.5~1); S2. Preparation of the groutable intermediate solution: A 40wt%–60wt% alkaline silica sol and a polyol are mixed at a mass ratio of (100–120):(10–15). The mixture is heated and concentrated to remove water of equal mass to the polyol. Then, the reactive nitrogen-doped fluorescent carbon dot dispersion prepared in step S1 is added, wherein the mass ratio of the reactive nitrogen-doped fluorescent carbon dot dispersion to the alkaline silica sol is (1–3):(100–120). After stirring evenly, the mixture is heated to 40℃–55℃. A 40wt%–60wt% alkaline activator solution is then slowly added, wherein the mass ratio of the alkaline activator solution to the alkaline silica sol is (40–50):(100–120). The mixture is stirred and reacted at 40℃–55℃ for 20–40 minutes. After the reaction is complete, the mixture is degassed under vacuum for 5–15 minutes and cooled to room temperature to obtain the groutable intermediate solution. S3. Grouting and curing: The groutable intermediate liquid obtained in step S2 is injected into a sealed cavity composed of a first glass substrate and a second glass substrate, and cured at a constant temperature of 75℃~85℃ for 5~8 hours to obtain network-enhanced fluorescent composite fireproof glass.

2. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, In step S1, the mass ratio of the carbon source, nitrogen source and silane coupling agent is 1:(0.5-1.2):(0.5-1).

3. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, The carbon source is citric acid, the nitrogen source is urea, and the silane coupling agent is γ-aminopropyltriethoxysilane.

4. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, The reactive nitrogen-doped fluorescent carbon dots obtained in step S1 have a particle size of 2-8 nm and are simultaneously bonded with amino and silanol groups on their surface.

5. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, In step S2, the reactive nitrogen-doped fluorescent carbon dot dispersion is added before the addition of the alkaline activator solution, so that it can pre-react with the silanol groups in the alkaline silica sol, and after the addition of the alkaline activator, it is covalently embedded into the formed silicon-oxygen three-dimensional network framework through a co-condensation reaction.

6. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, The reactive nitrogen-doped fluorescent carbon dots prepared in step S1 have essentially identical fluorescence emission spectra under pH=7 and pH=12 conditions, and the fluorescence intensity retention rate is ≥98%.

7. The method for preparing a network-enhanced fluorescent composite fireproof glass according to claim 1, characterized in that, The reactive nitrogen-doped fluorescent carbon dots prepared in step S1 have an ultraviolet absorption peak at 339 nm and a transmittance of ≥99% in the visible light region of 400–800 nm.

8. A network-enhanced fluorescent composite fireproof glass, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The network-enhanced fluorescent composite fireproof glass according to claim 8, characterized in that, It comprises reactive nitrogen-doped fluorescent carbon dots covalently embedded in a silicon-oxygen three-dimensional network framework, wherein amino and silanol groups are simultaneously bonded to the surface of the carbon dots.

10. The network-enhanced fluorescent composite fireproof glass according to claim 8, characterized in that, It emits visible fluorescence at 440 nm under 365 nm ultraviolet light irradiation, has a transmittance of ≥85% at 550 nm, and the main decomposition peak temperature of the DTG curve is ≥325℃.

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