Carbon quantum dot, fire early warning film, and preparation method and application of carbon quantum dot and fire early warning film

Abstract

The invention relates to the technical field of fire early warning materials, and particularly discloses a carbon quantum dot, a fire early warning film, a preparation method and application. According to the carbon quantum dot provided by the invention, an imidazole heterocyclic compound is used as a hydrogen bond donor, amino acid is used as a hydrogen bond receptor, and aluminum oxide is used as a ligand, so that a precursor with good chemical stability is obtained; the precursor is used as a raw material, and the carbon quantum dots are prepared through solvothermal reaction. According to the carbon quantum dot provided by the invention, fluorescence is quenched due to energy transfer or structural change at a high temperature and is recovered after cooling, and the reversible response can realize continuous monitoring after a fire hazard and an efficient and stable fire hazard early warning function, and meanwhile, the carbon quantum dot has environmental friendliness. When the composite film obtained by compounding the carbon quantum dots and the chitosan is applied to a high-molecular polymer base material, the fire early warning of the high-molecular polymer material can be accurately realized, and the composite film has important significance in expanding the application of the high-molecular polymer material in occasions with higher fireproof requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of fire warning materials, and in particular to carbon quantum dots, a fire warning film, a preparation method and applications thereof. Background Art

[0002] Fire is one of the major disasters threatening industrial production. Its frequent occurrence results in massive casualties and irreparable property losses. Developing precise fire detection technology to minimize potential fire hazards has always been a major global challenge. Traditional fire or gas smoke alarms rely primarily on smoke generated by combustion to trigger. Fire detectors only activate when smoke or gas concentrations reach a critical value. This method generally suffers from a slow early warning response, typically exceeding 100 seconds. Furthermore, during the pre-combustion stage, when no open flames are visible, it is difficult to issue a timely alarm signal, and the equipment is easily damaged, making it impossible to provide timely and effective early warnings before a fire occurs. This makes it difficult to take effective measures to control a fire in its early stages, often causing the fire to spread and expand, resulting in more serious consequences.

[0003] Thermal fire sensors have significant advantages over smoke detectors. They can detect early behavioral changes caused by fire and issue early warnings by monitoring the temperature change characteristics of early combustion behavior, thereby creating conditions for controlling the fire and buying time for rescue, thereby avoiding or reducing losses. Chitosan, as a typical thermosensitive material, can form proton transmission channels when driven by high temperatures, causing specific properties of the material, such as conductivity, color, or shape, to change under temperature stimulation. Therefore, it can be used as a thermal warning material. However, chitosan has a long response time to temperature changes and its sensitivity still needs to be further improved. This has to some extent limited its application in the early and accurate warning of fires. Summary of the Invention

[0004] In view of the problems in the existing technology that chitosan has a long response time to temperature changes and its sensitivity still needs to be further improved, which limits its application in early and accurate fire warning. The present invention provides carbon quantum dots, a fire warning film and a preparation method.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A carbon quantum dot, wherein the preparation method of the carbon quantum dot comprises the following steps:

[0007] S1, hydrothermally reacting an amino acid, an imidazole heterocyclic compound, and aluminum oxide to obtain a precursor solution; wherein the amino acid comprises at least one of L-cysteine, glutathione, or methionine;

[0008] S2. Mix the precursor solution and glycerol evenly, conduct a solvothermal reaction, and perform solid-liquid separation to obtain a carbon quantum dot solution.

[0009] Compared with the prior art, for the carbon quantum dots provided by the present invention, imidazole heterocyclic compounds are used as hydrogen bond donors, amino acids are used as hydrogen bond acceptors, and alumina is used as a ligand to obtain a precursor with good chemical stability; using this precursor as a raw material, carbon quantum dots are prepared through a solvothermal reaction. The surface of the carbon quantum dots prepared by the above method is doped with atoms such as sulfur and nitrogen. Sulfur and nitrogen elements can form a hydrogen bond network with the amino group (-NH2) in the chitosan molecule through lone pairs of electrons, which not only enhances the interfacial binding force between the carbon quantum dots and chitosan, but also can trigger a proton transfer synergy effect when the temperature changes, improving the sensitivity of chitosan to temperature response; the introduction of heterocyclic imidazole can significantly improve the fluorescence efficiency and stability of the carbon quantum dots, enabling them to maintain a fluorescence signal even under high-temperature or flame conditions. When exposed to a fire source, the change in the fluorescence intensity or wavelength of the carbon quantum dots can be used as an optical signal for early fire warning. Introducing them into chitosan can endow chitosan with the ability to output fluorescence signals; as a ligand, alumina can improve the thermal stability of the carbon quantum dots through interfacial action or nanocomposite effects. The high-temperature-resistant carbon quantum dots can delay the decomposition of chitosan, and at the same time, the high thermal conductivity of alumina itself helps to disperse heat and inhibit the spread of flames, thereby extending the fire warning time.

[0010] For the carbon quantum dots provided by the present invention, the fluorescence quenches due to energy transfer or structural changes at high temperatures and recovers after cooling. This reversible response can achieve continuous monitoring after a fire, realizing an efficient and stable fire warning function, and at the same time being environmentally friendly, providing new ideas for chitosan-based fire warning materials.

[0011] Further, the imidazole heterocyclic compound includes at least one of imidazolidinyl urea, imidazole propionic acid, or 1-acetylimidazole.

[0012] Preferred imidazole heterocyclic compounds can significantly enhance the stability and sensitivity of the carbon quantum dot fluorescence signal, enabling them to still respond quickly at high temperatures; in addition, the imidazole heterocycle can also promote chitosan to form a denser carbon layer, delay combustion and improve the thermal stability of the material, inhibit the spread of flames, thereby extending the fire warning time.

[0013] Further, the molar ratio of the amino acid, imidazole heterocyclic compound, and alumina is (1-2):(5-8):(0.5-2).

[0014] Further, in S1, the temperature of the hydrothermal reaction is 50°C to 150°C, and the hydrothermal reaction is carried out until the system is uniformly transparent.

[0015] Further, in S2, the mass-volume ratio of the precursor solution to glycerol is 1 g:30 mL to 1 g:40 mL.

[0016] Further, in S2, the time of the solvothermal reaction is 180 °C to 230 °C, and the reaction time is 12 h to 18 h.

[0017] The method for preparing carbon quantum dots provided by the present invention is simple, suitable for large-scale production applications, and both amino acids and chitosan are biobased materials, meeting environmental protection requirements. It is applicable to fire warning applications in the indoor or biomedical fields and has broad application prospects.

[0018] In a second aspect, the present invention also provides a fire warning film, including the carbon quantum dots and chitosan described above.

[0019] The surface of the carbon quantum dots provided by the present invention is doped with heteroatoms such as sulfur, nitrogen, and aluminum. At the same time, it also has various functional groups such as carboxyl, amino, and hydroxyl groups. By using it to modify chitosan, the thermosensitive performance of chitosan can be significantly improved.

[0020] Further, the chitosan is one or both of chitin or carboxymethyl chitosan.

[0021] In a third aspect, the present invention also provides a method for preparing a fire warning film, including the following steps:

[0022] Dissolve chitosan in an acid solution, neutralize it to obtain a chitosan solution;

[0023] Mix the chitosan solution and the above-mentioned carbon quantum dots evenly to obtain a casting solution;

[0024] Dry the casting solution to obtain a fire warning film.

[0025] Further, the acid solution is an acetic acid solution with a mass concentration of 1% to 2%, and the mass ratio of chitosan to the acid solution is 1:(8 - 12).

[0026] Exemplarily, sodium hydroxide is used for neutralization.

[0027] Further, the mass ratio of the chitosan solution to the carbon quantum dots is (5 - 10):1.

[0028] In a fourth aspect, the present invention also provides the application of the above-mentioned fire warning film in the fire warning of polymer polymers.

[0029] In a fifth aspect, the present invention also provides a polymer-based composite material, including a polymer substrate and the above-mentioned fire warning film.

[0030] The thermosensitivity of chitosan modified by carbon quantum dots is significantly improved, and chitosan is in the form of a thin film, which can be combined more closely with polymer polymers to obtain a polymer-based composite material with a fire warning function. At the same time, dispersing carbon quantum dots in chitosan can also avoid aggregation quenching caused by the size effect, ensure the more sensitive optical properties of carbon quantum dots, and achieve an efficient thermosensitive color change response.

[0031] Sixthly, the present invention also provides a preparation method of a polymer-based composite material, which includes the following steps:

[0032] Coat the above-mentioned casting solution on a polymer substrate and dry it to obtain a polymer-based composite material.

[0033] In the present invention, various functional groups are introduced through amino acids, alumina, and imidazole heterocyclic compounds, and glycerol enhances hydrophilicity, synergistically improving the interaction and thermal responsiveness between carbon quantum dots and chitosan. Through the fluorescence labeling characteristics of carbon quantum dots, the physical process of the thermal decomposition of chitosan can be converted into detectable fluorescence signal changes (such as quenching or displacement), realizing the precise perception of the fire temperature threshold, thereby providing a solid material basis for the precise early fire warning of polymer-based materials and having high potential application value. Description of the Drawings

[0034] Figure 1 It is the transmission electron microscope image of the carbon quantum dots prepared in Example 2 of the present invention;

[0035] Figure 2 It is the ultraviolet spectrum of the carbon quantum dots prepared in Example 2 of the present invention;

[0036] Figure 3 It is the X-ray photoelectron spectroscopy of the carbon quantum dots prepared in Example 2 of the present invention;

[0037] Figure 4 It is the infrared spectrum of the carbon quantum dots prepared in Example 2 of the present invention;

[0038] Figure 5 It is the physical image of the carbon quantum dot / carboxymethyl chitosan composite film prepared in Example 2 of the present invention, where (a) is under natural light conditions and (b) is under ultraviolet light conditions;

[0039] Figure 6 It is the scanning electron microscope image of the carbon quantum dot / carboxymethyl chitosan composite film prepared in Comparative Example 2 of the present invention;

[0040] Figure 7 It is the fluorescence emission spectrum of the carbon quantum dot / carboxymethyl chitosan composite film prepared in Example 2 of the present invention measured under the conditions of 35-90 °C;

[0041] Figure 8 This is a physical picture of the carbon quantum dot / carboxymethyl chitosan composite film prepared in Example 2 of the present invention under ultraviolet light conditions at 35-90 °C. Detailed implementation manners

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] To better illustrate the present invention, further illustrative examples are given below through embodiments.

[0044] Example 1

[0045] The embodiment of the present invention provides a kind of carbon quantum dots, including methionine, imidazolidinyl urea and alumina with a molar ratio of 1:4:1, and its preparation specifically includes the following steps:

[0046] Mix 0.01 mol of methionine, 0.04 mol of imidazolidinyl urea and 0.01 mol of alumina evenly, heat to 90 °C, and stir at a constant temperature for 3 h to obtain a precursor solution;

[0047] Take 1 g of the above precursor solution, add it to 30 mL of glycerol, heat to 200 °C and react for 16 h, and filter through a 0.22 μm filter membrane to obtain a carbon quantum dot solution.

[0048] The method for preparing a carbon quantum dot / chitin composite film using the above carbon quantum dot solution includes the following steps:

[0049] Step a, add chitin to a 1% acetic acid solution according to a mass ratio of 1:8, stir at 70 °C for 1 h, after cooling, neutralize with sodium hydroxide to obtain a chitin solution;

[0050] Step b, mix the chitin solution and the carbon quantum dot solution prepared above evenly according to a mass ratio of 7:1 to obtain a casting solution;

[0051] Step c, pour the casting solution into a petri dish and dry it at 35 °C to obtain a carbon quantum dot / chitin composite film.

[0052] Use a fluorescence spectrophotometer to measure the fluorescence characteristics of the above carbon quantum dot / chitin composite film at different temperatures, which specifically includes the following steps:

[0053] The carbon quantum dot / chitin composite films prepared above were heated to 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C respectively, placed in a fluorescence spectrophotometer, and their fluorescence emission spectra were detected at an excitation wavelength of 435 nm. The emission spectra of the films at different temperatures were plotted, and the fluorescence intensities of the films at different temperatures were observed. The experimental results showed that the carbon quantum dot / chitin composite films exhibited different fluorescence intensities at different temperatures.

[0054] The carbon quantum dot / chitin composite film was applied to an epoxy resin substrate, which specifically included the following steps:

[0055] 40 g of epoxy resin was added into a mold of 100 mm * 100 mm * 3 mm, and then 50 mL of the casting solution prepared above was coated on the surface of the epoxy resin and dried to obtain ethylene oxide with a fire warning function.

[0056] The epoxy resin with a fire warning function was placed under an ultraviolet lamp and heated from 35 °C to 90 °C. It was observed that the film could cause a change in film color by changing the fluorescence intensity, thereby realizing low-temperature alarm below 100 °C, and the fire warning response time was 0.8 s. The fire warning continuous response time was 1470 s at 90 °C.

[0057] The above-mentioned epoxy resin with a warning function was heated and raised in temperature successively at 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C respectively, and kept at each temperature for 735 s, then cooled to room temperature. This was one cycle, and the alarm test was carried out 5 times in a cycle. The results showed that the film could achieve cyclic alarm.

[0058] Example 2

[0059] The embodiment of the present invention provides a kind of carbon quantum dots, which includes L-cysteine, 1-acetylimidazole and alumina with a molar ratio of 1:6:1, and its preparation specifically includes the following steps:

[0060] 0.01 mol of L-cysteine, 0.06 mol of 1-acetylimidazole and 0.01 mol of alumina were mixed evenly, heated to 105 °C, and stirred at a constant temperature for 2 h to obtain a precursor solution;

[0061] 1 g of the above-mentioned precursor solution was taken, added into 30 mL of glycerol, heated to 220 °C and reacted for 14 h, and filtered through a 0.22 μm filter membrane to obtain a carbon quantum dot solution.

[0062] Figure 1 This is the transmission electron microscope image of the carbon quantum dots prepared in this example. It can be seen from the figure that the carbon quantum dots are relatively evenly distributed, the average diameter is 3 nm, and the particle size distribution is between 1 and 10 nm. The ultraviolet spectrum of the carbon quantum dots is as Figure 2As shown, it can be seen from the figure that an obvious ultraviolet absorption peak can be observed between 300 and 500 nm. The absorption peak at 321 nm is caused by the π-π* bond transition, and the absorption peak at 434 nm belongs to the electronic transition of the n→π* bond. Figures 3 to 4 They are respectively the X-ray photoelectron spectroscopy and infrared spectroscopy of the carbon quantum dots, which confirm that the surface of the carbon quantum dots has abundant functional groups such as amino groups and carboxyl groups.

[0063] The method for preparing the carbon quantum dot / carboxymethyl chitosan composite film using the above carbon quantum dot solution includes the following steps:

[0064] Step a: Add carboxymethyl chitosan to a 1% acetic acid solution according to a mass ratio of 1:10, stir at 70 °C for 1 h, and after cooling, neutralize with sodium hydroxide to obtain a carboxymethyl chitosan solution.

[0065] Step b: Mix the carboxymethyl chitosan solution and the above-prepared carbon quantum dot solution evenly according to a mass ratio of 6:1 to obtain a casting solution.

[0066] Step c: Pour the casting solution into a petri dish and dry it at 35 °C to obtain the carbon quantum dot / carboxymethyl chitosan composite film.

[0067] Figure 5 It is a physical picture of the above-prepared carbon quantum dot / carboxymethyl chitosan composite film under natural light and ultraviolet light conditions. It can be seen that the film has high transparency. Figure 6 It is the scanning electron microscopy image of the film. It can be seen from the figure that the carbon quantum dots are successfully loaded onto the film and are relatively evenly distributed. The embedding of the carbon quantum dots into the film structure can reduce the accumulation of carbon quantum dots, increase the distance between carbon quantum dots, thereby effectively inhibiting the π-π interaction in the aggregated state of carbon quantum dots and reducing the loss of energy transfer.

[0068] Use a fluorescence spectrophotometer to measure the fluorescence properties of the above carbon quantum dot / carboxymethyl chitosan composite film at different temperatures, which specifically includes the following steps:

[0069] Respectively heat the above-prepared carbon quantum dot / carboxymethyl chitosan composite film to 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C, put it into a fluorescence spectrophotometer, detect its fluorescence emission spectrum at an excitation wavelength of 435 nm, draw the emission spectrum diagram of the film at different temperatures, and observe the fluorescence intensity of the film at different temperatures. Figure 7 It is the fluorescence emission spectrum diagram of the carbon quantum dot / carboxymethyl chitosan composite film measured under the condition of 35 - 90 °C. The experimental results show that the carbon quantum dot / chitin composite film exhibits different fluorescence intensities at different temperatures.

[0070] The carbon quantum dot / chitin composite film is applied to an epoxy resin substrate, which specifically includes the following steps:

[0071] Add 40 g of epoxy resin into a mold of 100 mm * 100 mm * 3 mm, and then coat 50 mL of the above-prepared casting solution on the surface of the epoxy resin, and dry it to obtain an epoxy resin with a fire warning function.

[0072] Place the epoxy resin with a fire warning function under an ultraviolet lamp, heat it from 35 °C to 90 °C. As a result, it can be observed that the film can cause a change in the film color by using the change in fluorescence intensity, so as to achieve low-temperature alarm below 100 °C, and the fire warning response time is 0.4 s. The fire warning continuous response time is 1680 s at 90 °C.

[0073] Heat and raise the temperature of the above epoxy resin with a warning function successively at 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C respectively, keep it at each temperature for 840 s, and then cool it to room temperature. This is one cycle, and conduct 5 cycles of alarm tests. The result shows that the film can achieve cyclic alarm.

[0074] Example 3

[0075] The embodiment of the present invention provides a kind of carbon quantum dots, which includes glutathione, imidazole propionic acid and alumina with a molar ratio of 2:5:0.5, and its preparation specifically includes the following steps:

[0076] Mix 0.02 mol of glutathione, 0.05 mol of imidazole propionic acid and 0.005 mol of alumina evenly, heat it to 110 °C, and stir it at a constant temperature for 2 h to obtain a precursor solution;

[0077] Take 1 g of the above precursor solution, add it into 35 mL of glycerol, heat it to 230 °C and react for 15 h, and filter it through a 0.22 μm filter membrane to obtain a carbon quantum dot solution.

[0078] The method for preparing a carbon quantum dot / chitin composite film by using the above carbon quantum dot solution includes the following steps:

[0079] Step a: Add chitin into a 1% acetic acid solution according to a mass ratio of 1:12, stir it at 70 °C for 1.5 h, and after cooling, neutralize it with sodium hydroxide to obtain a chitin solution;

[0080] Step b: Mix the chitin solution and the above-prepared carbon quantum dot solution evenly according to a mass ratio of 8:1 to obtain a casting solution;

[0081] Step c: Pour the casting solution into a petri dish and dry it at 35 °C to obtain a carbon quantum dot / chitin composite film.

[0082] The fluorescence properties of the above carbon quantum dot / chitin composite film at different temperatures were measured using a fluorescence spectrophotometer, and the specific steps are as follows:

[0083] The above-prepared carbon quantum dot / chitin composite films were respectively heated to 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C, placed in a fluorescence spectrophotometer, and their fluorescence emission spectra were detected at an excitation wavelength of 435 nm. The emission spectra of the films at different temperatures were plotted, and the fluorescence intensities of the films at different temperatures were observed. The experimental results showed that the carbon quantum dot / chitin composite film exhibited different fluorescence intensities at different temperatures.

[0084] The application of the carbon quantum dot / chitin composite film to an epoxy resin substrate specifically includes the following steps:

[0085] 40 g of epoxy resin was added into a mold of 100 mm * 100 mm * 3 mm, and then 50 mL of the above-prepared casting solution was coated on the surface of the epoxy resin and dried to obtain an epoxy resin with a fire warning function.

[0086] The epoxy resin with a fire warning function was placed under an ultraviolet lamp and heated from 35 °C to 90 °C. It was observed that the film could cause a change in film color by changing the fluorescence intensity, thereby realizing low-temperature alarm below 100 °C, and the fire warning response time was 0.6 s. The fire warning continuous response time was 1000 s at 90 °C.

[0087] The above epoxy resin with a warning function was heated and raised in temperature successively at 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C, and kept at each temperature for 500 s, and then cooled to room temperature. This was one cycle, and 5 cycles of alarm tests were carried out. The results showed that the film could achieve cyclic alarm.

[0088] Example 4

[0089] An embodiment of the present invention provides a carbon quantum dot, which includes methionine, 1-acetylimidazole, and alumina with a molar ratio of 1:6:2. The specific preparation steps are as follows:

[0090] 0.01 mol of methionine, 0.06 mol of 1-acetylimidazole, and 0.02 mol of alumina were mixed evenly, heated to 130 °C, and stirred at a constant temperature for 1 h to obtain a precursor solution;

[0091] 1 g of the above precursor solution was taken, added to 40 mL of glycerol, heated to 210 °C and reacted for 17 h, and filtered through a 0.22 μm filter membrane to obtain a carbon quantum dot solution.

[0092] The method for preparing a carbon quantum dot / chitin composite film using the above carbon quantum dot solution includes the following steps:

[0093] Step a: Chitin is added to a 1% acetic acid solution in a mass ratio of 1:11, stirred at 70 °C for 1 h, cooled, and neutralized with sodium hydroxide to obtain a chitin solution.

[0094] Step b: The chitin solution is mixed with the above-prepared carbon quantum dot solution in a mass ratio of 5:1 and stirred evenly to obtain a casting solution.

[0095] Step c: The casting solution is poured into a petri dish and dried at 35 °C to obtain a carbon quantum dot / chitin composite film.

[0096] The fluorescence properties of the above carbon quantum dot / chitin composite film at different temperatures are measured using a fluorescence spectrophotometer, and the specific steps are as follows:

[0097] The above-prepared carbon quantum dot / chitin composite film is heated to 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C respectively, placed in a fluorescence spectrophotometer, and its fluorescence emission spectrum is detected at an excitation wavelength of 435 nm. The emission spectrum diagram of the film at different temperatures is plotted, and the fluorescence intensity of the film at different temperatures is observed. The experimental results show that the carbon quantum dot / chitin composite film exhibits different fluorescence intensities at different temperatures.

[0098] The carbon quantum dot / chitin composite film is applied to an epoxy resin substrate, and the specific steps are as follows:

[0099] 40 g of epoxy resin is added to a mold of 100 mm * 100 mm * 3 mm, and then 50 mL of the above-prepared casting solution is coated on the surface of the epoxy resin and dried to obtain an epoxy resin with a fire warning function.

[0100] The epoxy resin with a fire warning function is placed under an ultraviolet lamp and heated from 35 °C to 90 °C. It can be observed that the film can cause a change in the film color by changing the fluorescence intensity, thereby realizing low-temperature alarm below 100 °C, and the fire warning response time is 0.9 s. The fire warning continuous response time is 890 s at 90 °C.

[0101] The above epoxy resin with a warning function is heated and raised in temperature successively at 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and 90 °C respectively, lasting for 445 s at each temperature, and then cooled to room temperature. This is one cycle, and 5 cycles of alarm tests are carried out. The results show that the film can achieve cyclic alarm.

[0102] Example 5

[0103] The embodiment of the present invention provides a kind of carbon quantum dots, which includes L-cysteine, imidazolidinyl urea and alumina with a molar ratio of 2:8:1, and its preparation specifically includes the following steps:

[0104] Mix 0.02 mol L - cysteine, 0.08 mol imidazolidinyl urea, and 0.01 mol alumina evenly, heat to 105 °C, and stir constantly for 2 h to obtain a precursor solution;

[0105] Take 1 g of the above - mentioned precursor solution, add it to 30 mL of glycerol, heat to 200 °C and react for 18 h, and filter through a 0.22 - μm filter membrane to obtain a carbon quantum dot solution.

[0106] The method for preparing a carbon quantum dot / chitin composite film using the above - mentioned carbon quantum dot solution includes the following steps:

[0107] Step a: Add chitin to a 1% acetic acid solution according to a mass ratio of 1:9, stir at 70 °C for 1 h, cool, and neutralize with sodium hydroxide to obtain a chitin solution;

[0108] Step b: Mix the chitin solution and the above - prepared carbon quantum dot solution evenly according to a mass ratio of 10:1 to obtain a casting solution;

[0109] Step c: Pour the casting solution into a petri dish and dry at 35 °C to obtain a carbon quantum dot / chitin composite film.

[0110] Use a fluorescence spectrophotometer to measure the fluorescence characteristics of the above - mentioned carbon quantum dot / chitin composite film at different temperatures, which specifically includes the following steps:

[0111] Respectively heat the above - prepared carbon quantum dot / chitin composite film to 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 90 °C, put it into a fluorescence spectrophotometer, detect its fluorescence emission spectrum at an excitation wavelength of 435 nm, draw the emission spectrum diagram of the film at different temperatures, and observe the fluorescence intensity of the film at different temperatures. The experimental results show that the carbon quantum dot / chitin composite film presents different fluorescence intensities at different temperatures.

[0112] Apply the carbon quantum dot / chitin composite film to an epoxy resin substrate, which specifically includes the following steps:

[0113] Add 40 g of epoxy resin into a mold of 100 mm * 100 mm * 3 mm, then coat 50 mL of the above - prepared casting solution on the surface of the epoxy resin, and dry to obtain an epoxy resin with a fire warning function.

[0114] Place the epoxy resin with a fire warning function under an ultraviolet lamp, heat it from 35 °C to 90 °C. As a result, it can be observed that the film can cause a change in film color by changing the fluorescence intensity, thereby realizing low - temperature alarm below 100 °C, and the fire warning response time is 1.3 s. The fire warning continuous response time at 90 °C is 1250 s.

[0115] The above epoxy resin with a warning function was heated and raised in temperature successively at 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, and 90°C, and maintained at each temperature for 625 s, then cooled to room temperature. This was taken as one cycle, and the alarm test was carried out for 5 cycles. It was found that the film could achieve cyclic alarm.

[0116] Comparative Example 1

[0117] This comparative example provides a carbon quantum dot solution / chitosan composite film. The only difference in its preparation method from Example 2 is that L-cysteine in Example 2 was replaced with an equal amount of alanine, and the rest is exactly the same, which will not be elaborated here.

[0118] It was applied to epoxy resin in exactly the same way as in Example 2, and a fire warning test was carried out. The results showed that the fire warning response time of the film was 1.6 s, the fire warning continuous response time at 90°C was 940 s, and cyclic alarm could not be achieved.

[0119] Comparative Example 2

[0120] This comparative example provides a carbon quantum dot solution / chitosan composite film. The only difference in its preparation method from Example 2 is that 1-acetylimidazole in Example 2 was replaced with an equal amount of imidazole, and the rest is exactly the same, which will not be elaborated here.

[0121] It was applied to epoxy resin in exactly the same way as in Example 2, and a fire warning test was carried out. The results showed that the fire warning response time of the film was 3.2 s, the fire warning continuous response time at 90°C was 800 s, and cyclic alarm could not be achieved.

[0122] Comparative Example 3

[0123] This comparative example provides a carbon quantum dot solution / chitosan composite film. The only difference in its preparation method from Example 2 is that alumina in Example 2 was replaced with an equal amount of ferric chloride, and the rest is exactly the same, which will not be elaborated here.

[0124] It was applied to epoxy resin in exactly the same way as in Example 2, and a fire warning test was carried out. The results showed that the fire warning response time of the film was 5 s, the fire warning continuous response time at 90°C was 740 s, and cyclic alarm could not be achieved.

[0125] To sum up, the carbon quantum dots provided by the present invention have a simple preparation method, wide sources of raw materials, and the composite film prepared by using the carbon quantum dots and chitosan has excellent fire warning function, which is beneficial to expanding the application of polymer materials in occasions with higher fire protection requirements and has high practical value.

[0126] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A carbon quantum dot, characterized in that, The preparation method of the carbon quantum dots comprises the following steps: S1. Hydrothermally react an amino acid, an imidazole heterocyclic compound and alumina to obtain a precursor solution; wherein, the amino acid comprises at least one of L-cysteine, glutathione or methionine; S2. Mix the precursor solution and glycerol uniformly, carry out a solvothermal reaction, and perform solid-liquid separation to obtain a carbon quantum dot solution.

2. The carbon quantum dots according to claim 1, characterized in that, The imidazole heterocyclic compound comprises at least one of imidazolidinyl urea, imidazole propionic acid or 1-acetyl imidazole.

3. The carbon quantum dots according to claim 1 or 2, characterized in that, The molar ratio of the amino acid, the imidazole heterocyclic compound and alumina is (1-2):(5-8):(0.5-2).

4. The carbon quantum dots according to claim 1, characterized in that, In S1, the temperature of the hydrothermal reaction is 50°C to 150°C, and the hydrothermal reaction is carried out until the system is uniformly transparent.

5. The carbon quantum dots according to claim 1, characterized in that, In S2, the mass-volume ratio of the precursor solution to glycerol is 1 g:30 mL to 1 g:40 mL; and / or In S2, the temperature of the solvothermal reaction is 180°C to 230°C, and the reaction time is 12 h to 18 h.

6. A fire warning film, characterized in that, Comprising the carbon quantum dots and chitosan according to any one of claims 1 to 5.

7. A preparation method of a fire warning film, characterized in that Comprises the following steps: Dissolve chitosan in an acid solution, and neutralize to obtain a chitosan solution; Mix the chitosan solution and the carbon quantum dots according to any one of claims 1 to 5 uniformly to obtain a casting solution; Dry the casting solution to obtain a fire warning film.

8. Application of the fire warning film according to claim 6 in fire warning of polymer.

9. A polymer matrix composite material, characterized in that, Comprising a polymer substrate and the fire warning film according to claim 6.

10. A method for preparing a polymer matrix composite material, characterized in that, Comprises the following steps: Coat the casting solution described in claim 7 onto the polymer substrate and dry to obtain a polymer-based composite material.

Images