A method for preparing polysilazane nanoparticles using the Stöber method

Abstract

The invention discloses a method for preparing polysilazane nanospheres using the imgabs0 method, comprising: (1) mixing deionized water, anhydrous ethanol, and ammonia to obtain solution A; (2) using anhydrous ethanol as a solvent, dissolving silazane oligomers in anhydrous ethanol to form a solution B having a concentration of 0.01-0.04 mol / L; (3) rapidly adding solution B to solution A, and performing a sealing reaction; (4) adjusting the stirring speed to 500-550 rpm after reacting for 1-2 min, and reacting for 20-24 h; (5) stopping the reaction, filtering the reaction solution and centrifuging it, and then placing the resulting solid in a vacuum drying oven and drying it for 10-12 h to obtain polysilazane nanospheres. The present invention uses the imgabs1 method to prepare nanospheres without using any template during the preparation process, and the operating steps are simple, reducing costs, and preparing polysilazane nanospheres with good dispersion.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic nanomaterials and specifically relates to a method of utilizing A method for preparing polysilazane nanoparticles. Background Art

[0002] Polysilazanes are polymers composed of alternating silicon and nitrogen atoms forming a main chain with Si-N bonds forming the basic skeleton. They are polymer-based ceramic precursors. In practical applications, they exhibit the following advantages: 1. Excellent physical and mechanical properties with high hardness; 2. Good adhesion to a variety of surfaces; 3. Excellent film-forming properties with high-temperature resistance, chemical stability, and environmental adaptability. They are currently commonly used in high-tech fields such as aerospace. In civilian applications, polysilazanes are often used as resins for surface protection of substrates. For example, Rossi et al. used polysilazane Durazane 1500 as a resin to cure the film on AA1050 aluminum sheets, imparting hydrophobicity to the substrate, making it suitable for anti-graffiti surface protection. Gardelle et al. studied the thermal degradation and fire resistance of polysilazane-based coatings using torch tests. The coatings exhibited excellent thermal stability and, in combination with flame retardants, could be used for applications such as heat resistance and corrosion resistance.

[0003] Although the application of organopolysilazanes has a certain research foundation, the controllable preparation of nano-polysilazanes remains difficult. W. Yang et al. produced ultralong single-crystalline silicon nitride nanoribbons through catalytically assisted pyrolysis of polysilazanes. These nanoribbons have smooth surfaces and uniform diameters, but the polycrystalline structure is prone to dislocation and stacking. J. Wan et al. used different methods to process silicon nitride and silicon carbide nanocomposites based on the pyrolysis of polymer precursors. Electric field-assisted sintering (EFAS) can produce micron-nano or nano-nano composites, but high-pressure sintering can easily lead to microstructural diversification. Y. Yu et al. used polysilazanes to prepare spherical, oxygen-free silicon carbonitride particles through a polymerization precipitation process followed by high-temperature pyrolysis and conversion. The synthesized ceramic spherical particles exhibited a near-perfect spherical shape and a narrow particle size distribution, but the prepared spherical particles were large in size, and the equipment was relatively expensive and complex to operate. Therefore, the development of a method for preparing polysilazane nanomaterials that is simple to develop, easy to operate, and economical and readily available has important practical application value.

[0004] The method is a physical and chemical method for synthesizing monodisperse silicon nanoparticles, which was first proposed by Werner In 1956, Kolbe first used ammonia as a catalyst to catalyze tetraethyl orthosilicate (TEOS) to obtain spherical silica particles. In 1968, Fink and others systematically studied the growth conditions of micron-sized SiO2 microspheres prepared by hydrolysis and condensation of tetraethyl orthosilicate in alcohol-ester mixed solvents. A variety of well-dispersed silica spherical films were synthesized using ammonia-catalyzed TEOS method, and their sizes could be controlled and their surfaces could be easily functionalized.

[0005] Tradition The method reacts rapidly in the initial stage and the nucleation process is very short, so it is difficult to control the nanostructure in the initial stage of the reaction. The polysilazane nanospheres were prepared by the method of Based on the method, the invention improves the preparation of polysilazane nanospheres with uniform particle size using only two steps. Furthermore, the invention adjusts the particle size of the nanoparticles by controlling the concentration of the reactants, resulting in a simple process, uniform particle size, and good dispersibility. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing polysilazane nanospheres, specifically in the classical Based on the method, the particle size of nanoparticles was regulated by controlling the concentration of reactants, and nanospheres with good dispersion were prepared.

[0007] In a first aspect, the present invention provides a method for preparing polysilazane nanospheres, characterized in that the method comprises the following steps:

[0008] (1) Mix deionized water, anhydrous ethanol, and ammonia to obtain solution A; wherein the volume ratio of water, anhydrous ethanol, and ammonia is 8-15:3-8:2-4;

[0009] (2) using anhydrous ethanol as a solvent, dissolving the silazane oligomer in anhydrous ethanol to form a solution B with a concentration of 0.01-0.04 mol / L;

[0010] (3) Quickly add solution B to solution A and seal the reaction;

[0011] (4) After reacting for 1-2 minutes, adjust the stirring speed to 500-550 rpm and react for 20-24 hours;

[0012] (5) Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0013] Preferably, the concentration of aqueous ammonia in step (1) is 25-50 wt %, and the volume ratio of water, anhydrous ethanol, and ammonia is 8-10:3-8:2-4.

[0014] Preferably, the concentration of the silazane oligomer in step (2) is preferably 0.01-0.03 mol / L.

[0015] Preferably, the structure of the silazane oligomer of the present invention is as shown in Formula I:

[0016]

[0017] Wherein, R1 and R2 are the same or different, R1 and R2 are independently selected from one of -H, -CH=CH2, C1-C4 alkyl, phenyl or -NH2, m and n represent the percentage of monomer composition, with a value between 0-1, and m+n=1.

[0018] The C1-C4 alkyl group described in the present invention is selected from methyl, ethyl, propyl, n-butyl, isobutyl and tert-butyl.

[0019] More preferably, the silazane oligomer of the present invention is prepared by the following method:

[0020] (a) adding an organic solvent and a silane compound to a reaction apparatus, introducing ammonia gas, and lowering the temperature to react;

[0021] (b) collecting the filtrate by vacuum filtration and removing the solvent from the filtrate by rotary evaporation;

[0022] (c) At room temperature, 3-aminopropyltriethoxysilane and the product of step (2) are mixed, allowed to stand for 10-20 hours, heated to 70-80° C. in an ammonia atmosphere, stirred for reaction for 1-2 hours, and cooled to room temperature to obtain a silazane oligomer.

[0023] The silane compound described in step (a) is selected from one or a combination of two or more of methyldichlorosilane, dimethyldichlorosilane, and methylphenyldichlorosilane.

[0024] In a specific embodiment of the present invention, the silazane oligomer is as shown in Formula II and III:

[0025]

[0026] Wherein, p+q+r=1, p, q, and r represent the percentage of monomer composition, and the value is between 0 and 1, and R2 is selected from one of methyl and hydrogen.

[0027]

[0028] Wherein, p+q+r=1, p, q, and r represent the percentage of monomer composition, and the value is between 0 and 1, and R2 is selected from one of phenyl and hydrogen.

[0029] The polysilazane nanospheres provided by the present invention are prepared by condensation polymerization of silazane oligomers as raw materials and alcohols as solvents under the catalytic action of ammonia water. The method for preparing nano-microspheres does not use surfactants and dispersants, is simple to operate, and provides convenient production conditions for the application of polysilazane nanomaterials. The method for preparing nanospheres does not require any template during the preparation process, has simple operation steps, and does not require further template removal by calcination or chemical etching, significantly reducing preparation costs. It also does not require the addition of an emulsifier, eliminating the problem of emulsifier residue during use. The present invention produces well-dispersed polysilazane nanospheres solely through a catalyst-catalyzed polycondensation reaction and subsequent processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Preparation route of polysilazane nanospheres;

[0031] Figure 2 Particle size distribution of polysilazane nanospheres prepared in Example 1;

[0032] Figure 3 Scanning electron microscopy image of polysilazane nanospheres prepared in Example 1;

[0033] Figure 4 Particle size distribution of polysilazane nanospheres prepared in Example 2;

[0034] Figure 5 Scanning electron microscopy image of polysilazane nanospheres prepared in Example 2;

[0035] Figure 6 Particle size distribution of polysilazane nanospheres prepared in Example 3;

[0036] Figure 7 Scanning electron microscopy image of polysilazane nanospheres prepared in Example 3;

[0037] Figure 8 Particle size distribution of polysilazane nanospheres at different concentrations of silazane oligomers;

[0038] Figure 9 Particle size distribution of polysilazane nanospheres at different water contents;

[0039] Figure 10 Particle size distribution of polysilazane nanospheres at different ammonia concentrations. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0041] The water (H2O) used in the embodiment of the present invention is deionized water, and the silazane oligomer is prepared by the method provided in the embodiment of the present invention.

[0042] Example 1

[0043] 1. Preparation of Silazane Oligomer PSZ1

[0044]

[0045] To a 1000mL three-necked flask equipped with a mechanical stirrer, a high and low temperature hot and cold cycle device (-20℃-100℃) and an ammonia inlet tube, n-hexane (550mL), dimethyldichlorosilane (61.92g, 0.48mol) and methyldichlorosilane (13.8g, 0.12mol) were added. After cooling to 0℃, ammonia was slowly introduced into the resulting mixture. After the solution in the tail gas absorption bottle became alkaline, ammonia was continued to be introduced for 2h before stopping the reaction. The ammonium chloride salt obtained by the reaction was removed by vacuum filtration, and the resulting filtrate was freed of the solvent by a rotary evaporator and dried in vacuo to obtain 29.5g of polysilazane oligomer. 3-Aminopropyltriethoxysilane (19.13 g, 0.085 mol) was added to the above polysilazane oligomer at room temperature, stirred evenly, and allowed to stand for 12 h. The temperature was slowly raised to 78 ° C. in a nitrogen atmosphere. After stirring for 2 h, the temperature was gradually lowered to room temperature to finally obtain polysilazane PSZ1.

[0046] 2. Preparation of polysilazane nanospheres

[0047] S1: Prepare solution A

[0048] 10 mL of deionized water, 8 mL of anhydrous ethanol, and 2 mL of aqueous ammonia were added to the round-bottom flask in sequence, and stirred at a constant temperature for 30 min at a speed of 1100 rpm to mix evenly;

[0049] S2: Prepare solution B

[0050] Silazane oligomer PSZ1 was dissolved in 19 mL of anhydrous ethanol and mixed evenly to form a solution with a concentration of 0.02 mol / L;

[0051] S3: Quickly add solution B to solution A, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0052] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0053] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0054] Before curing, 5 mL of the reaction solution was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size distribution of the obtained polysilazane nanospheres was tested by dynamic light scattering (DLS, Malvern laser particle size analyzer). The results are as follows: Figure 2 shown.

[0055] The particle size and particle size distribution of polysilazane nanospheres were determined by DLS. Figure 2 As shown, The average particle size of the polysilazane nanospheres prepared by the method is about 338nm, the particle size distribution is narrow, PDI = 0.263, Figure 2 The particle size distribution curve is shown in the following table:

[0056] Particle size (d.nm) strength(%) Peak 1 425 97.6 Peak 2 4682 2.4

[0057] The solidified sample was taken out and ground, and the powder was used to prepare the scanning electron microscopy sample. The electron microscopy results were as follows: Figure 3 shown. Figure 3 This is a scanning electron microscope (SEM) photo of polysilazane nanospheres. From the figure, it can be observed that the diameter of the polysilazane nanospheres is 300-500nm. The results are roughly the same as the DLS test results, indicating that the use of improved Polysilazane nanospheres can be obtained by a two-step method.

[0058] Example 2

[0059] S1: Prepare solution A

[0060] 14.416 mL of H2O, 3.584 mL of anhydrous ethanol, and 2 mL of aqueous ammonia were added to the round-bottom flask in sequence and stirred at a constant temperature for 30 min at a speed of 1100 rpm to mix them evenly.

[0061] S2: Prepare solution B

[0062] The silazane oligomer PSZ1 described in Example 1 was dissolved in 19 mL of anhydrous ethanol and mixed uniformly to form a solution with a concentration of 0.02 mol / L;

[0063] S3: Quickly add solution B to solution A, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0064] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0065] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0066] Before solidification, 5 mL of the reaction solution was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size distribution of the obtained polysilazane nanospheres was tested by DLS. The results were as follows: Figure 4 shown.

[0067] The particle size and size distribution of polysilazane nanospheres were determined by DLS. Figure 4 As shown, the average particle size of polysilazane measured by DLS is 401 nm, the particle size distribution is narrow, PDI = 0.265, Figure 4 The particle size distribution curve is shown in the following table:

[0068]

[0069]

[0070] The solidified sample was taken out and ground, and the powder was used to prepare the scanning electron microscopy sample. The electron microscopy results were as follows: Figure 5 shown. Figure 5 This is an SEM image of polysilazane nanospheres. It can be observed from the image that the diameter of the polysilazane nanospheres is approximately 500 nm, which is similar to the DLS test results, indicating that the particle size of the polysilazane nanospheres can be changed by increasing the amount of H2O.

[0071] Example 3

[0072] 1. Preparation of Silazane Oligomer PSZ2

[0073]

[0074] To a 1000mL three-necked flask equipped with a mechanical stirrer, a high and low temperature hot and cold cycle device (-20℃-100℃) and an ammonia inlet tube, n-hexane (550mL), methyldichlorosilane (55.25g, 0.48mol) and methylphenyldichlorosilane (22.94g, 0.12mol) were added. After cooling to 0℃, ammonia was slowly introduced into the resulting mixture. After the solution in the tail gas absorption bottle became alkaline, ammonia was continued to be introduced for 2h before stopping the reaction. The ammonium chloride salt obtained by the reaction was removed by vacuum filtration, and the resulting filtrate was freed of the solvent by a rotary evaporator and dried in vacuo to obtain 30.4g of polysilazane oligomer. 3-Aminopropyltriethoxysilane (20.71 g, 0.092 mol) was added to the above polysilazane oligomer at room temperature, stirred evenly, and allowed to stand for 12 h. The temperature was slowly raised to 78 ° C. in a nitrogen atmosphere. After stirring for 2 h, the temperature was gradually lowered to room temperature to finally obtain polysilazane PSZ2.

[0075] 2. Preparation of polysilazane nanospheres

[0076] S1: Prepare solution A

[0077] 10 mL of H2O, 8 mL of anhydrous ethanol, and 2 mL of aqueous ammonia were added to the round-bottom flask in sequence, and stirred at a constant temperature for 30 min at a speed of 1100 rpm to mix evenly;

[0078] S2: Prepare solution B

[0079] Silazane oligomer PSZ2 was dissolved in 19 mL of anhydrous ethanol and mixed evenly to form a solution with a concentration of 0.02 mol / L;

[0080] S3: Quickly add solution B to solution A, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0081] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0082] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0083] Before solidification, 5 mL of the reaction solution was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size distribution of the obtained polysilazane nanospheres was tested by DLS. The results were as follows: Figure 6 shown.

[0084] The particle size and particle size distribution of polysilazane nanospheres were determined by DLS. Figure 6 As shown, The average particle size of the polysilazane nanospheres prepared by the method is about 128nm, the particle size distribution is narrow, PDI = 0.193, Figure 2 The particle size distribution curve is shown in the following table:

[0085] Particle size (d.nm) strength(%) Peak 1 156 98.9 Peak 2 4231 1.1

[0086] The solidified sample was taken out and ground, and the powder was used to prepare the scanning electron microscopy sample. The electron microscopy results were as follows: Figure 7 shown. Figure 7 This is a scanning electron micrograph of polysilazane nanospheres. The diameter of the polysilazane nanospheres is observed to be between 100 and 300 nm, which is roughly consistent with the DLS results. This indicates that polysilazane nanospheres can be obtained using a silazane oligomer without double bonds via the modified two-step method.

[0087] Optimization of conditions for polysilazane nanoparticles

[0088] 1. Effect of Silazane Oligomer Concentration on Nanoparticle Size and Size Distribution

[0089] S1: 10 mL of H2O, 8 mL of anhydrous ethanol, and 2 mL of aqueous ammonia were added to a round-bottom flask in sequence and magnetically stirred at 1100 rpm for 5 min to obtain solution A.

[0090] S2: Using anhydrous ethanol as the solvent, silazane oligomer PSZ1 solutions with concentrations of 0.010 mol / L, 0.015 mol / L, 0.020 mol / L, 0.025 mol / L, 0.030 mol / L, 0.035 mol / L, and 0.040 mol / L were prepared as solution B;

[0091] S3: Quickly add solution B to solution A separately, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0092] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0093] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0094] Before curing, 5 mL of the reaction solution from each of the seven groups of tests was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size and particle size distribution of the obtained polysilazane nanospheres were tested by DLS. The results are as follows: Figure 8 shown.

[0095] like Figure 8 As shown in the figure, when the concentration of silazane oligomer increases from 0.01mol / L to 0.04mol / L, the particle size of polysilazane nanospheres increases significantly. PDI first shows a significant decreasing trend, and then increases slightly. The increase in the concentration of silazane monomer can promote the condensation rate to form larger particles, and the particle size distribution in the system is more uniform. When the concentration of silazane monomer increases further, it will promote hydrolysis to produce more nuclei, resulting in the generation of more and smaller particles. The size of the particles is not uniform, so it is easier to agglomerate. As can be seen from the figure, the concentration of silazane oligomer is preferably 0.01-0.03mol / L.

[0096] 2. Effect of H2O content on the particle size and particle size distribution of nanoparticles

[0097] S1: H2O, 8 mL of anhydrous ethanol, and 2 mL of ammonia were added to a round-bottom flask in sequence and magnetically stirred at 1100 rpm for 5 min to obtain solution A. The amount of H2O added was 5 mL, 8 mL, 10 mL, 14 mL, 15 mL, 18 mL, and 20 mL, respectively.

[0098] S2: Using anhydrous ethanol as solvent, prepare a 0.020 mol / L silazane oligomer PSZ1 solution as solution B;

[0099] S3: Quickly add solution B to solution A separately, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0100] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0101] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0102] Before curing, 5 mL of the reaction solution from each of the seven groups of tests was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size and particle size distribution of the obtained polysilazane nanospheres were tested by DLS. The results are as follows: Figure 9 shown.

[0103] like Figure 9As shown, the size of polysilazane nanoparticles increases with increasing water content. Furthermore, increasing water content leads to a decrease in the PDI of polysilazane nanoparticles, followed by a slight increase. Increased water content accelerates hydrolysis and improves the nucleation rate, resulting in smaller particles formed in a shorter time. However, at higher water concentrations, hydrogen bonding between polysilazane nanoparticles is stronger than at lower concentrations, making them more likely to agglomerate, resulting in larger particles. As can be seen from the figure, the preferred amount of water added to the reaction system is 8-10 mL.

[0104] 3. Effect of ammonia concentration on the particle size and particle size distribution of nanoparticles

[0105] S1: 10 mL of H2O, 8 mL of anhydrous ethanol, and 2 mL of ammonia (concentrations of 0.125 mol / L, 0.2 mol / L, 0.25 mol / L, 0.325 mol / L, 0.375 mol / L, 0.45 mol / L, and 0.5 mol / L, respectively) were sequentially added into a round-bottom flask and magnetically stirred at 1100 rpm for 5 min to obtain solution A.

[0106] S2: Using anhydrous ethanol as solvent, prepare a 0.020 mol / L silazane oligomer PSZ1 solution as solution B;

[0107] S3: Quickly add solution B to solution A separately, and try not to let solution B contact the wall of the flask containing solution A. Plug the flask mouth with a rubber stopper and seal the flask mouth with sealing film;

[0108] S4: After reacting for 1 min, adjust the stirring speed to 500 rpm and react for 24 h;

[0109] S5: Stop the reaction, filter and centrifuge the reaction solution, and then place the obtained solid in a vacuum drying oven and dry it for 10-12 hours to obtain polysilazane nanospheres.

[0110] Before curing, 5 mL of the reaction solution from each of the seven groups of tests was taken and filtered using a syringe filter with a pore size of 0.45 μm. The particle size and particle size distribution of the obtained polysilazane nanospheres were tested by DLS. The results are as follows: Figure 10 shown.

[0111] Figure 10 The effect of ammonia concentration on the particle size and distribution of prepared polysilazane nanospheres is shown. As the ammonia concentration increases, the particle size gradually increases, and the particle size distribution narrows. While increasing ammonia concentration can accelerate the hydrolysis rate, it also significantly increases the condensation rate. Therefore, a decrease in the nucleation rate ultimately leads to larger particle size and a narrower particle size distribution.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polysilazane nanospheres, characterized in that: The method comprises the following steps: (1) Mix deionized water, anhydrous ethanol, and ammonia to obtain solution A; wherein the volume ratio of water, anhydrous ethanol, and ammonia is 8-15:3-8:2-4; (2) using anhydrous ethanol as a solvent, dissolving the silazane oligomer in anhydrous ethanol to form a solution B with a concentration of 0.01-0.04 mol / L; (3) Quickly add solution B to solution A and seal the reaction; (4) After reacting for 1-2 minutes, adjust the stirring speed to 500-550 rpm and react for 20-24 hours; (5) stopping the reaction, filtering and centrifuging the reaction solution, and then drying the obtained solid in a vacuum drying oven for 10-12 hours to obtain polysilazane nanospheres; The structure of the silazane oligomer is shown in Formula I: Wherein, R1 and R2 are the same or different, R1 and R2 are independently selected from one of -H, -CH=CH2, C1-C4 alkyl, phenyl or -NH2, m and n represent the percentage of monomer composition, with a value between 0 and 1, m+n=1, and the C1-C4 alkyl is selected from methyl, ethyl, propyl, n-butyl, isobutyl, and tert-butyl.

2. The preparation method according to claim 1, characterized in that The concentration of aqueous ammonia in step (1) is 25-50 wt%.

3. The preparation method according to claim 1, characterized in that In step (1), the volume ratio of water, anhydrous ethanol and ammonia is 8-10:3-8:2-4.

4. The preparation method according to claim 1, characterized in that The concentration of the silazane oligomer in step (2) is 0.01-0.03 mol / L.

5. The preparation method according to claim 4, characterized in that The silazane oligomer is prepared by the following method: (a) adding an organic solvent and a silane compound to a reaction apparatus, introducing ammonia gas, and lowering the temperature to react; (b) collecting the filtrate by vacuum filtration and removing the solvent from the filtrate by rotary evaporation; (c) At room temperature, 3-aminopropyltriethoxysilane and the product of step (2) are mixed, allowed to stand for 10-20 hours, heated to 70-80° C. in an ammonia atmosphere, stirred for reaction for 1-2 hours, and cooled to room temperature to obtain a silazane oligomer.

6. The preparation method according to claim 5, characterized in that The silane compound described in step (a) is selected from one or a combination of two or more of methyldichlorosilane, dimethyldichlorosilane, and methylphenyldichlorosilane.

7. The preparation method according to claim 6, characterized in that The silane compound in step (a) is selected from a combination of methyldichlorosilane and dimethyldichlorosilane, or a combination of methyldichlorosilane and methylphenyldichlorosilane.

8. The preparation method according to claim 7, characterized in that The silazane oligomer is shown in Formula II: Wherein, p+q+r=1, p, q, and r represent the percentage of monomer composition, and the value is between 0 and 1, and R2 is selected from one of methyl and hydrogen.

9. The preparation method according to claim 7, characterized in that The silazane oligomer structural formula III is as follows: Wherein, p+q+r=1, p, q, and r represent the percentage of monomer composition, and the value is between 0 and 1, and R2 is selected from one of phenyl and hydrogen.

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