Preparation method and application of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots

Abstract

The present invention belongs to the field of inorganic flame retardant material preparation, specifically, a method for preparing a nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dot and its application. The present invention prepares nitrogen-silicon co-doped carbon quantum dots by adding a carbon source compound, a nitrogen source compound and a silanizing agent in a hydrothermal synthesis process. Meanwhile, the carbon quantum dot surface contains abundant amino groups, wherein one hydrogen atom in the amino group is replaced by a phosphorus source compound spirocyclic phosphate dichloride to obtain nitrogen-phosphorus-silicon co-doped carbon quantum dots, and nitrogen, phosphorus and silicon elements can improve the fluorescence yield and flame retardant properties of carbon quantum dots. Moreover, the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dot surface prepared by the present invention has a spirocyclic structure, which is sprayed on the fabric surface in the form of subsequent finishing, and is open-loop cross-linked under the action of a photoinitiator and UV light, and can be effectively combined with a fiber substrate, solving the problem of subsequent washing and falling off during use.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic flame retardant material preparation, in particular to a preparation method of nitrogen-phosphorus-silicon co-doped flame retardant fluorescent carbon quantum dots and application thereof. Background Art

[0002] In recent years, with the increasing incidence of fire accidents and the increasing awareness of fire prevention, the development of flame-retardant polymer materials and fiber products has become a hot research area. However, traditional flame retardants containing halogens (bromide and chloride), phosphorus, and nitrogen often have problems such as toxicity, environmental pollution, and bioaccumulation. Therefore, there is an urgent need to develop more environmentally friendly and efficient flame-retardant materials.

[0003] Among various flame retardant systems, nanocarbon materials (such as fullerenes, carbon nanotubes, and graphene) have gradually become a research hotspot as a halogen-free, heat-resistant, green and environmentally friendly flame retardant material. Among them, carbon quantum dots, as an emerging nanocarbon material with an average diameter of less than 10 nm, have shown potential application prospects in the field of flame retardants due to their good biocompatibility and physicochemical properties. So far, some work has reported the application of carbon quantum dots in the field of flame retardancy: (1) Professor Niu Mei's team reported in "Cellulose" 2022, 29, 9469–9486 that biomass carbon dots (CDs) particles were interspersed in an ammonium polyphosphate (APP) layer, and a new type of high-efficiency CDs-based APP (CDs-APP) composite flame retardant was realized through integrated technology, and it was coated on cotton fibers to improve the flame retardant properties. (2) Professor Wang Rui's team reported in the journal Polymer Degradation and Stability 2021, 109766 that gelatin-based carbon dots were prepared using a simple one-step hydrothermal method using biomaterial gelatin as raw material, and were integrated into the PET molecular chain through copolymerization. The limiting oxygen index reached 29%, the peak heat release was reduced by 42.66%, and the total smoke content was reduced by 62.64%, showing good flame retardant effect. (3) Professor Chen Su's team reported in the Journal of Materials Science & Technology 2021, 06, 056 that carbon quantum dots were prepared using polypropylene carbonate (PPC) and ethylenediamine as raw materials, and demonstrated their application as "ink" for printing highly fluorescent patterns and as a green flame retardant for highly flammable materials.

[0004] While the research reports listed above demonstrate the ability to produce carbon quantum dots with certain flame retardancy, achieving greater flame retardancy often requires the creation of a synergistic flame retardant system with conventional flame retardants. Furthermore, carbon quantum dots, when applied to various fiber substrates in a post-processing manner, exhibit poor adhesion to the substrates. Therefore, there is an urgent need to develop carbon quantum dots that exhibit flame retardancy and excellent fiber substrate bonding. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a preparation method and application of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots. While maintaining the good fluorescence properties of carbon quantum dots, a nitrogen-phosphorus-silicon co-doping synthesis method is provided to prepare new nitrogen-phosphorus-silicon co-doped carbon quantum dots with excellent fluorescence and flame retardant properties, and they are well bonded with fiber substrates, providing new possibilities for the application of carbon quantum dots in the flame retardant and fiber fields.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] One of the purposes of the present invention is to provide a nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, the characteristics of the carbon quantum dots are: good monodispersity, a particle size range of 2-8 nm, and a fluorescence yield of 11-18%.

[0008] A second object of the present invention is to provide a method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, the preparation method comprising the following steps:

[0009] S1. Preparation of phosphorus source compound

[0010] Pentaerythritol is added to an appropriate amount of tetrahydrofuran, stirred evenly, and heated to 40-50°C. Catalyst triethylamine is added, phosphorus oxychloride is continuously added dropwise, and the reaction is carried out for 90-120 minutes. The temperature is then raised to 60-80°C and the reaction is carried out for 2-3 hours. The temperature is then raised to 100-110°C over 60-90 minutes to complete the reaction. The spirocyclic phosphate dichloride is obtained by suction filtration and drying.

[0011] Preferably, the molar ratio of pentaerythritol to phosphorus oxychloride is 1:2.5-4.

[0012] Preferably, the amount of the catalyst triethylamine added is 1 to 2% of the mass of pentaerythritol.

[0013] Preferably, the phosphorus oxychloride is added at a rate of 8 to 15 ml / min.

[0014] S2. Preparation of nitrogen-silicon co-doped carbon quantum dots

[0015] S21: dissolving the carbon source compound and the nitrogen source compound in deionized water, and uniformly dispersing them by ultrasonication to obtain a mixed solution A;

[0016] S22: adding the silanization reagent dropwise into the mixed solution A, and mixing uniformly with ultrasound to obtain a mixed solution B;

[0017] S23: The mixed solution B is transferred to a reactor, and subjected to a hydrothermal reaction at 160-220° C. for 4-10 hours. The mixture is filtered, purified, and washed with deionized water to obtain nitrogen-silicon co-doped carbon quantum dots.

[0018] Preferably, the mass ratio of the carbon source compound to the nitrogen source compound in the mixed solution A is 1:0.2-2; the mass ratio of the carbon source compound to deionized water is 1:10-100.

[0019] Preferably, the carbon source compound is one or more organic acids such as citric acid, tartaric acid, and oxalic acid.

[0020] Preferably, the nitrogen source compound is one or more organic amines such as melamine, dicyandiamide, aromatic amine and polyethyleneimine.

[0021] Preferably, the mass ratio of the carbon source compound to the silanization agent in the mixed solution B is 1:0.5-4.

[0022] Preferably, the silanization agent is one or more aminosilanes such as 3-aminopropyltrimethoxysilane and γ-aminopropyltrimethoxysilane.

[0023] S3. Preparation of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots

[0024] The spirocyclic phosphate dichloride was dissolved in DMF, and nitrogen-silicon co-doped carbon quantum dots and stabilizer were added. After mixing evenly, the temperature was raised to 40-50°C for reaction for 3-5 hours. After the reaction, the temperature was lowered to room temperature. After filtration, ether washing and drying, nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots were obtained.

[0025] Preferably, the mass ratio of the nitrogen-silicon co-doped carbon quantum dots to the spirocyclic phosphate dichloride is 6 to 9:1.

[0026] Preferably, the stabilizer is N,N-dimethylaniline, and the added amount is 25-35% of the mass of the spirocyclic phosphate dichloride.

[0027] The working principle of this preparation method is mainly to add carbon source compounds, nitrogen source compounds and silanization agents during the hydrothermal synthesis process, and add nitrogen and silicon elements during the carbon quantum dot formation process to prepare nitrogen-silicon co-doped carbon quantum dots. At the same time, the surface of the carbon quantum dots contains rich amino groups, in which one hydrogen atom in the amino group is replaced by a phosphorus source compound spirocyclic phosphate dichloride to obtain nitrogen-phosphorus-silicon co-doped carbon quantum dots. Nitrogen, phosphorus and silicon elements can improve the fluorescence yield and flame retardant properties of the carbon quantum dots. At the same time, the surface of the carbon quantum dots contains a spirocyclic structure with good rigidity and strong thermal stability, which can be further applied to fiber substrates to improve their thermal stability and mechanical properties. Moreover, by doping these three elements into the carbon quantum dots at the same time, their flame retardant properties can be significantly improved through the multi-element synergistic effect.

[0028] The third object of the present invention is to provide an application of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, wherein the application comprises adding nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots and a photoinitiator to anhydrous ethanol, stirring evenly, spraying the mixture onto the surface of a fabric, and irradiating the fabric with UV light to obtain a modified fabric with flame retardant properties.

[0029] Preferably, the mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, the photoinitiator and anhydrous ethanol is 12-16:0.5-1:60-70.

[0030] Preferably, the photoinitiator is one or more of a diaryliodonium salt and a triarylsulfonium salt.

[0031] Due to the adoption of the above technical solution, the technical effects achieved by the present invention are:

[0032] 1. The nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared by the present invention have good monodispersity and uniform particle size. At the same time, the carbon quantum dots contain nitrogen, phosphorus and silicon elements and have excellent fluorescence and flame retardant properties.

[0033] 2. The preparation method of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots provided by the present invention is simple and easy, does not require complicated experimental conditions, and has the characteristics of being non-toxic, easy to synthesize, and environmentally friendly.

[0034] 3. The nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared by the present invention have a spirocyclic structure on their surface. After being sprayed on the fabric surface in a finishing form, they undergo ring-opening and cross-linking under the action of photoinitiator and UV light, and can be effectively combined with the fiber substrate, thus solving the problem of falling off during subsequent washing and use.

[0035] 4. The nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared by the present invention, as an emerging carbon material, maintain the good fluorescence properties of carbon quantum dots and also have excellent flame retardant properties. Therefore, they have broad application prospects in the fields of green and environmentally friendly flame retardancy and fluorescence detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a TEM characterization image of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots synthesized in Example 4. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1: A preparation method and application of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, the method comprising the following steps:

[0039] S1. Preparation of phosphorus source compound

[0040] Pentaerythritol was added to an appropriate amount of tetrahydrofuran, stirred evenly, and heated to 45°C. Catalyst triethylamine was added, and phosphorus oxychloride was continued to be added dropwise and reacted for 110 minutes. Then, the temperature was raised to 70°C and reacted for 2.5 hours. The temperature was then raised to 105°C after 80 minutes to complete the reaction. The spirocyclic phosphate dichloride was obtained by filtration and drying.

[0041] The molar ratio of pentaerythritol to phosphorus oxychloride is 1:3.2.

[0042] The added amount of the catalyst triethylamine is 1.5% of the mass of pentaerythritol.

[0043] The phosphorus oxychloride was added at a rate of 12 ml / min.

[0044] S2. Preparation of nitrogen-silicon co-doped carbon quantum dots

[0045] S21: dissolving citric acid and dicyandiamide in deionized water, and uniformly dispersing them by ultrasonication to obtain a mixed solution A;

[0046] S22: adding 3-aminopropyltrimethoxysilane dropwise to the mixed solution A, and mixing by ultrasonication to obtain a mixed solution B;

[0047] S23: The mixed solution B was transferred to a reactor and subjected to hydrothermal reaction at 200° C. for 6 h. The nitrogen-silicon co-doped carbon quantum dots were obtained by filtration, purification, and washing with deionized water.

[0048] The mass ratio of citric acid to dicyandiamide in the mixed solution A is 1:0.5; the mass ratio of citric acid to deionized water is 1:20.

[0049] The mass ratio of citric acid to 3-aminopropyltrimethoxysilane in the mixed solution B is 1:1.5.

[0050] S3. Preparation of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots

[0051] Spirocyclic phosphate dichloride was dissolved in DMF, and nitrogen-silicon co-doped carbon quantum dots and stabilizer were added. After mixing evenly, the temperature was raised to 45°C for reaction for 4 hours. After the reaction was completed, the temperature was lowered to room temperature. After filtration, ether washing and drying, nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots were obtained.

[0052] The mass ratio of the nitrogen-silicon co-doped carbon quantum dots to the spirocyclic phosphate dichloride is 7:1.

[0053] The stabilizer is N,N-dimethylaniline, and the added amount is 29% of the mass of the spirocyclic phosphate dichloride.

[0054] S4. Application

[0055] Flame-retardant fluorescent carbon quantum dots co-doped with nitrogen, phosphorus and silicon and diaryl iodonium salt are added into anhydrous ethanol and stirred evenly, and then sprayed onto the surface of cotton fabric and irradiated with UV light to obtain a modified fabric with flame-retardant properties.

[0056] The mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, diaryliodonium salt and anhydrous ethanol is 14:0.8:65.

[0057] The spraying amount is 400g / m 2 , the UV light wavelength is 365nm.

[0058] The particle size range of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared in Example 1 is 4 to 7 nm, and the fluorescence yield is 16%. They are sprayed onto the surface of cotton fabric and the flame retardant properties of the modified cotton fabric are tested. The LOI value is measured to be 30.6%, and the flame retardant performance loss rate after 50 washings is 1.2%.

[0059] Example 2: A method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots and its application, the method comprising the following steps:

[0060] S1. Preparation of phosphorus source compound

[0061] Pentaerythritol was added to an appropriate amount of tetrahydrofuran, stirred evenly, and heated to 40°C. Catalyst triethylamine was added, and phosphorus oxychloride was continued to be added dropwise and reacted for 90 minutes. Then, the temperature was raised to 60°C and reacted for 3 hours. The temperature was then raised to 100°C after 60 minutes to complete the reaction. The spirocyclic phosphate dichloride was obtained by filtration and drying.

[0062] The molar ratio of pentaerythritol to phosphorus oxychloride is 1:2.5.

[0063] The added amount of the catalyst triethylamine is 1% of the mass of pentaerythritol.

[0064] The phosphorus oxychloride was added at a rate of 8 ml / min.

[0065] S2. Preparation of nitrogen-silicon co-doped carbon quantum dots

[0066] S21: dissolving citric acid and dicyandiamide in deionized water, and uniformly dispersing them by ultrasonication to obtain a mixed solution A;

[0067] S22: adding 3-aminopropyltrimethoxysilane dropwise to the mixed solution A, and mixing by ultrasonication to obtain a mixed solution B;

[0068] S23: The mixed solution B was transferred to a reactor and subjected to a hydrothermal reaction at 160° C. for 10 h. The mixture was filtered, purified, and washed with deionized water to obtain nitrogen-silicon co-doped carbon quantum dots.

[0069] The mass ratio of citric acid to dicyandiamide in the mixed solution A is 1:0.2; the mass ratio of citric acid to deionized water is 1:10.

[0070] The mass ratio of citric acid to 3-aminopropyltrimethoxysilane in the mixed solution B is 1:0.5.

[0071] S3. Preparation of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots

[0072] The spirocyclic phosphate dichloride was dissolved in DMF, and nitrogen-silicon co-doped carbon quantum dots and stabilizer were added. After mixing evenly, the temperature was raised to 40°C for reaction for 3 hours. After the reaction was completed, the temperature was lowered to room temperature. After filtration, ether washing and drying, nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots were obtained.

[0073] The mass ratio of the nitrogen-silicon co-doped carbon quantum dots to the spirocyclic phosphate dichloride is 9:1.

[0074] The stabilizer is N,N-dimethylaniline, and the added amount is 25% of the mass of the spirocyclic phosphate dichloride.

[0075] S4. Application

[0076] Flame-retardant fluorescent carbon quantum dots co-doped with nitrogen, phosphorus and silicon and diaryl iodonium salt are added into anhydrous ethanol and stirred evenly, sprayed onto the surface of fabric, and irradiated with UV light to obtain a modified fabric with flame-retardant properties.

[0077] The mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, diaryliodonium salt and anhydrous ethanol is 12-16:0.5-1:60-70.

[0078] The spraying amount is 400g / m 2 , the UV light wavelength is 365nm.

[0079] The particle size range of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared in Example 2 is 4 to 7 nm, and the fluorescence yield is 11%. They are sprayed onto the surface of cotton fabric and the flame retardant properties of the modified cotton fabric are tested. The LOI value is measured to be 28.8%, and the flame retardant performance loss rate after 50 washings is 3.5%.

[0080] Example 3: A method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots and its application, the method comprising the following steps:

[0081] S1. Preparation of phosphorus source compound

[0082] Pentaerythritol was added to an appropriate amount of tetrahydrofuran, stirred evenly, and heated to 50°C. Catalyst triethylamine was added, and phosphorus oxychloride was continued to be added dropwise and reacted for 120 minutes. Then, the temperature was raised to 80°C and reacted for 2 hours. The temperature was then raised to 110°C after 90 minutes to complete the reaction. The spirocyclic phosphate dichloride was obtained by filtration and drying.

[0083] The molar ratio of pentaerythritol to phosphorus oxychloride is 1:4.

[0084] The added amount of the catalyst triethylamine is 2% of the mass of pentaerythritol.

[0085] The phosphorus oxychloride was added at a rate of 15 ml / min.

[0086] S2. Preparation of nitrogen-silicon co-doped carbon quantum dots

[0087] S21: Dissolve citric acid and polyethyleneimine in deionized water and disperse them uniformly by ultrasonication to obtain a mixed solution A;

[0088] S22: adding 3-aminopropyltrimethoxysilane dropwise to the mixed solution A, and mixing by ultrasonication to obtain a mixed solution B;

[0089] S23: The mixed solution B was transferred to a reactor and subjected to hydrothermal reaction at 220° C. for 4 h. The mixture was filtered, purified, and washed with deionized water to obtain nitrogen-silicon co-doped carbon quantum dots.

[0090] The mass ratio of citric acid to polyethyleneimine in the mixed solution A is 1:2; the mass ratio of citric acid to deionized water is 1:100.

[0091] The mass ratio of citric acid to 3-aminopropyltrimethoxysilane in the mixed solution B is 1:4.

[0092] S3. Preparation of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots

[0093] Spirocyclic phosphate dichloride was dissolved in DMF, and nitrogen-silicon co-doped carbon quantum dots and stabilizer were added. After mixing evenly, the temperature was raised to 50°C for reaction for 5 hours. After the reaction was completed, the temperature was lowered to room temperature. After filtration, ether washing and drying, nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots were obtained.

[0094] The mass ratio of the nitrogen-silicon co-doped carbon quantum dots to the spirocyclic phosphate dichloride is 6:1.

[0095] The stabilizer is N,N-dimethylaniline, and the added amount is 35% of the mass of the spirocyclic phosphate dichloride.

[0096] S4. Application

[0097] Flame-retardant fluorescent carbon quantum dots co-doped with nitrogen, phosphorus and silicon and diaryl iodonium salt are added into anhydrous ethanol and stirred evenly, sprayed onto the surface of fabric, and irradiated with UV light to obtain a modified fabric with flame-retardant properties.

[0098] The mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, diaryliodonium salt and anhydrous ethanol is 16:1:70.

[0099] The spraying amount is 400g / m 2 , the UV light wavelength is 365nm.

[0100] The particle size range of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared in Example 3 is 4 to 8 nm, and the fluorescence yield is 18%; they are sprayed onto the surface of cotton fabric and the flame retardant properties of the modified cotton fabric are tested. The LOI value is measured to be 31.2%, and the flame retardant performance loss rate after washing 50 times is 1.6%.

[0101] Example 4: The difference between this example and Example 2 is that citric acid is replaced by tartaric acid, and the rest is consistent with Example 4. The particle size range of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared in Example 4 is 2 to 6 nm, and the fluorescence yield is 12%; it is sprayed onto the surface of cotton fabric and the flame retardant properties of the modified cotton fabric are tested. The measured LOI value is 28.5%, and the flame retardant performance loss rate after washing 50 times is 3.1%.

[0102] Comparative Example 1: The flame retardant properties of the cotton fabric were directly tested without flame retardant treatment. The results were as follows: the LOI value was 18.2%.

[0103] Comparative Example 2: Citric acid was dissolved in 20 times the volume of deionized water and ultrasonically dispersed to obtain a mixed solution A. The mixed solution A was transferred to a reactor and subjected to a hydrothermal reaction at 180°C for 6 hours. After filtration, purification, and washing, carbon quantum dots without doping with other elements were obtained. The prepared carbon quantum dots had a particle size of 2 to 8 nm and a fluorescence yield of 8%.

[0104] Comparative Example 3: S1, citric acid, dicyandiamide and phytic acid were mixed and dissolved in deionized water, and ultrasonically dispersed to obtain a mixed solution A;

[0105] S2. Add 3-aminopropyltrimethoxysilane dropwise into the mixed solution A, and mix thoroughly with ultrasonic waves to obtain a mixed solution B;

[0106] S3, transferring the mixed solution B to a reactor, performing a hydrothermal reaction at 200°C for 6 hours, and filtering, purifying, and washing to obtain nitrogen-phosphorus-silicon co-doped carbon quantum dots;

[0107] The mass ratio of citric acid, dicyandiamide and phytic acid in the mixed solution A is 1:0.5:0.5; the mass ratio of citric acid to deionized water is 1:20.

[0108] The mass ratio of citric acid to 3-aminopropyltrimethoxysilane in the mixed solution B is 1:1.5;

[0109] S4, adding nitrogen-phosphorus-silicon co-doped carbon quantum dots and diaryliodonium salt to anhydrous ethanol, stirring evenly, spraying the mixture onto the surface of cotton fabric, and irradiating the fabric with UV light to obtain a modified fabric with flame retardant properties;

[0110] The mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, diaryliodonium salt and anhydrous ethanol is 14:0.8:65;

[0111] The spraying amount is 400g / m 2 , the UV light wavelength is 365nm.

[0112] The particle size of the nitrogen-phosphorus-silicon co-doped carbon quantum dots prepared in Comparative Example 3 is 3 to 6 nm, and the fluorescence yield is 10%. They are sprayed onto the surface of cotton fabric and the flame retardant properties of the modified cotton fabric are tested. The LOI value is 24.3%, and the flame retardant performance loss rate after 50 washings is 18.7%; the flame retardant loss rate after washing is large. This is because the nitrogen-phosphorus-silicon co-doped carbon quantum dots in Comparative Example 3 do not have a spirocyclic structure and cannot be open-ring cross-linked. Therefore, the bonding strength with the fabric is poor, which is manifested as a significant decrease in the flame retardant effect after washing.

[0113] Figure 1This is a TEM characterization image of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots synthesized in Example 4 (the inset is a TEM image at a high magnification). The particle size of the carbon quantum dots is between 2 and 6 nm, and a clear lattice can be observed, which is consistent with the structural characteristics of graphitic carbon.

[0114] Unless otherwise specified, the ratios and percentages described in the present invention are all by mass; all raw materials are commercially available.

[0115] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, characterized in that: The preparation method includes the preparation of a phosphorus source compound, the preparation of nitrogen-silicon co-doped carbon quantum dots, and the preparation of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots; The phosphorus source compound is prepared by adding pentaerythritol to an appropriate amount of tetrahydrofuran, stirring evenly, heating to 40-50° C., adding catalyst triethylamine, continuously adding phosphorus oxychloride dropwise and reacting for 90-120 minutes, then heating to 60-80° C. and reacting for 2-3 hours, then heating to 100-110° C. over 60-90 minutes to complete the reaction, and filtering and drying to obtain spirocyclic phosphate dichloride; The preparation of nitrogen-silicon co-doped carbon quantum dots comprises the following steps: S21: dissolving the carbon source compound and the nitrogen source compound in deionized water, and uniformly dispersing them by ultrasonication to obtain a mixed solution A; S22: adding the silanization reagent dropwise into the mixed solution A, and mixing uniformly with ultrasound to obtain a mixed solution B; S23: transferring the mixed solution B to a reactor, subjecting it to a hydrothermal reaction at 160-220° C. for 4-10 h, filtering, purifying, and washing with deionized water to obtain nitrogen-silicon co-doped carbon quantum dots; The method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots comprises dissolving spirocyclic phosphate dichloride in DMF, adding nitrogen-silicon co-doped carbon quantum dots and a stabilizer, mixing evenly, heating to 40-50° C. for reaction for 3-5 hours, cooling to room temperature after the reaction, filtering, washing with ether, and drying to obtain nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots.

2. The method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to claim 1, characterized in that: The molar ratio of pentaerythritol to phosphorus oxychloride is 1:2.5-4; The amount of the catalyst triethylamine added is 1-2% of the mass of pentaerythritol; The phosphorus oxychloride is added at a rate of 8-15 ml / min.

3. The method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to claim 1, characterized in that: The mass ratio of the carbon source compound to the nitrogen source compound in the mixed solution A is 1:0.2-2; the mass ratio of the carbon source compound to deionized water is 1:10-100.

4. The method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to claim 1, characterized in that: The carbon source compound is one or more of citric acid, tartaric acid, and oxalic acid; The nitrogen source compound is one or more of melamine, dicyandiamide, aromatic amine and polyethyleneimine; The mass ratio of the carbon source compound to the silanization agent in the mixed solution B is 1: 0.5-4; The silanization agent is one or more of 3-aminopropyltrimethoxysilane and γ-aminopropyltrimethoxysilane.

5. The method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to claim 1, characterized in that: The mass ratio of the nitrogen-silicon co-doped carbon quantum dots to the spirocyclic phosphate diacyl chloride is 6 to 9:1; The stabilizer is N,N-dimethylaniline, and the added amount is 25-35% of the mass of the spirocyclic phosphate diacyl chloride.

6. Use of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots prepared by the method for preparing nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to any one of claims 1 to 5, characterized in that: The application is to add nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots and a photoinitiator into anhydrous ethanol, stir evenly, spray them onto the surface of the fabric, and irradiate them with UV light to obtain a modified fabric with flame retardant properties.

7. The use of nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots according to claim 6, characterized in that: The mass ratio of the nitrogen-phosphorus-silicon co-doped flame-retardant fluorescent carbon quantum dots, the photoinitiator and the anhydrous ethanol is 12-16:0.5-1:60-70; The photoinitiator is one or more of diaryliodonium salt and triarylsulfonium salt.

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