Monodisperse spherical micro / nano silica, their preparation methods, and applications

Abstract

This invention relates to a monodisperse spherical micro / nano silica, its preparation method, and its applications. First, an aqueous sodium silicate solution is added to a crown ether aqueous solution, followed by the dropwise addition of sulfuric acid solution and stirring to initiate the reaction. Then, an organic extractant is added to extract the aqueous and organic phases. The aqueous phase is then mixed with an aqueous sulfuric acid solution and an alcohol solvent, respectively, to obtain two different solutions. These two solutions are then mixed and stirred, followed by centrifugation, washing, and drying to obtain the target product. The organic phase is subjected to vacuum distillation, water dissolution, and adsorption with an ion exchange resin to obtain a regenerated crown ether aqueous solution, which is then recycled. This invention adjusts the ionic strength of the reaction system by adding an organic complexing agent, precisely controlling the particle size of SiO2 particles to 20-1300 nm. This results in particles with uniform size, high sphericity, and good dispersibility. The entire preparation process has advantages such as simple technology, low cost, high yield, and ease of large-scale industrial production, showing promising application prospects in aerospace, biomedicine, and electronic packaging fields.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials and nanomaterials, specifically to a monodisperse spherical micro / nano silica, its preparation method, and its applications. Background Technology

[0002] Silicon dioxide (SiO2) is a non-toxic, odorless, and pollution-free inorganic non-metallic material. Due to its low coefficient of thermal expansion and superior properties such as high heat resistance, high moisture resistance, high filling capacity, low dielectric constant, and low coefficient of friction, it has broad application prospects in many fields such as aerospace, biomedicine, electronics, and electrical appliances.

[0003] Currently, common methods for preparing micro / nano SiO2 include gas-phase methods, sol-gel methods, microemulsion methods, and chemical precipitation methods. The gas-phase method mainly uses silicon tetrachloride as a raw material to prepare SiO2. This method has disadvantages such as high reaction temperature, demanding equipment, expensive raw materials, and harsh operating conditions. The sol-gel method uses silicate esters as raw materials and synthesizes well-dispersed SiO2 particles (particle size 50-1000 nm) in an ethanol-water binary solvent system using ammonia as a catalyst. This method also has some drawbacks, such as expensive raw materials, large amounts of organic solvents, long preparation time, and unsuitability for large-scale production. The microemulsion method uses two immiscible solvents to form a microemulsion under the action of a surfactant. Nano SiO2 is prepared in the oil phase of the microemulsion by controlling the reaction conditions. This method requires a large amount of organic solvents and the preparation process is relatively complex. The chemical precipitation method mainly uses sodium silicate and inorganic acids as raw materials. The pH of the solution is adjusted to precipitate silicate ions, and nano SiO2 is obtained through filtration, washing, and drying. The advantages of this method are that the process is simple, the raw materials are cheap and widely available, but it also has disadvantages such as difficulty in controlling the product morphology and particle size, wide pore size distribution, and easy formation of aggregated particles. In addition, the low concentration of nanoparticles in a single batch leads to high energy consumption for subsequent concentration.

[0004] In recent years, significant progress has been made in the research of preparing micro / nano SiO2 materials using sodium silicate as a raw material. Various compounds have been applied to the preparation of micro / nano SiO2, with research focusing primarily on morphology / form control, modification, selection of low-cost template agents, and simplification of synthesis methods. For example, Chinese patent CN113880098A describes a method where sodium silicate is passed through a strong acid cation exchange resin and a weak base anion exchange resin to remove sodium ions. Then, hydrophobic trifluoromethanesulfonic acid anions are introduced to disrupt the double-layer structure and improve the crystallization activity of the particle surface. Secondary growth is then performed to increase the silicic acid polymerization rate of large-diameter particles, ultimately producing silica powder. Another example is Chinese patent CN104058415A, which discloses a method for preparing highly dispersed nano-SiO2. By using sodium carboxymethyl cellulose surfactant and a microporous membrane, the drawbacks of high surface energy and easy polymerization of silanol groups in SiO2 are overcome, improving the product's dispersibility. Although the specific surface area of ​​SiO2 prepared by this method is 80~300 m², the method still yields a different product. 2 While the particle size is 10-35 nm, the dispersibility is poor, failing to achieve satisfactory application results. Chinese patent CN111196606A uses oxidized polyethylene wax and polyethylene glycol as modifiers to sequentially modify SiO2, reducing the degree of polymerization between silica particles and resulting in more uniform dispersion. Chinese patent CN1715183A uses cationic and nonionic surfactants as dual templates, producing SiO2 particles with a size of 1-5 μm and a specific surface area of ​​800-1400 m². 2 / g, with a pore size of 2~5nm.

[0005] In summary, while numerous methods exist for preparing micro / nano silica, they all suffer from various problems, including poor product dispersibility, suboptimal performance, and inability to meet the demands of high-end applications. Furthermore, the template agents, dispersants, modifiers, and other additives used or introduced in current preparation methods are not only expensive, difficult to remove, and non-reusable, but also lead to resource waste and environmental pollution. Summary of the Invention

[0006] The main objective of this invention is to address the aforementioned problems in existing technologies and provide a novel method for preparing monodisperse spherical micro / nano silica. This method uses high-concentration, inexpensive sodium silicate as the silicon source and employs a chemical precipitation method to prepare micro / nano-sized SiO2 with uniform particle size, high sphericity, good dispersibility, and controllable size. This completely solves the common problem of balancing manufacturing cost and product quality in micro / nano SiO2, ensuring its broad application prospects in high-end fields such as aerospace, biomedicine, and electronic packaging.

[0007] To achieve the above objectives and effects, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for preparing monodisperse spherical micro / nano silica, comprising: mixing crown ether with sodium silicate solution and reacting the mixture; extracting the resulting mixture with an organic extractant to obtain an aqueous phase and an organic phase; taking a portion of the aqueous phase and adjusting its pH to 8.5-10.5 as a base solution; taking another portion of the aqueous phase and mixing it with an organic solvent to obtain a composite solution; mixing the base solution and the composite solution to carry out a precipitation reaction, and finally obtaining monodisperse spherical micro / nano silica.

[0009] Specifically, the crown ether is selected from at least one of 21-crown-7, 18-crown-6, 15-crown-5, or derivatives thereof, wherein the derivatives include benzo-15-crown-5 and R-benzo-15-crown-5, wherein R = CH3, NH2, NO2, etc., as shown in the example below. Figure 1 As shown.

[0010] Specifically, the modulus of the sodium silicate is 1.5-3.5. The higher the modulus of sodium silicate, the more silica it contains, the weaker its alkalinity, and the less inorganic acid it consumes; conversely, the lower the modulus of sodium silicate, the stronger its alkalinity, and the more inorganic acid it consumes.

[0011] Specifically, the molar ratio of crown ether to sodium silicate during mixing is 0.05 to 1:1.

[0012] More specifically, the specific process of the reaction between crown ether and sodium silicate solution is as follows: Prepare sodium silicate aqueous solution and crown ether aqueous solution separately, and then add crown ether aqueous solution to sodium silicate aqueous solution under stirring. The resulting mixture is reacted at 20-80℃ for 0.1-2h. Then, the pH of the mixture is adjusted to 10.5-11.5 by adding sulfuric acid solution dropwise, and the reaction is continued to be stirred for 1-2h.

[0013] More specifically, the mass fraction of the prepared sodium silicate aqueous solution is 3%-20%, and the concentration of the prepared crown ether aqueous solution is 1-32 mol / L.

[0014] Specifically, the organic extractant is selected from at least one of solvents such as dichloromethane, chloroform, ethyl acetate, diethyl ether, toluene, and xylene.

[0015] Specifically, the bottom liquid is obtained by adding sulfuric acid solution dropwise to the aqueous phase obtained from extraction and adjusting the pH of the mixture to 8.5-10.5.

[0016] More specifically, the sulfuric acid solution has a mass fraction of 0.5%-39%.

[0017] Specifically, the organic solvent is an alcohol solvent, selected from at least one of methanol, ethanol, propanol, and isopropanol.

[0018] Specifically, the volume ratio of the aqueous phase to the organic solvent in the preparation of the composite solution is 1-10:1.

[0019] Specifically, the volume ratio of the base liquid to the composite liquid when mixed is 1:8-16.

[0020] Specifically, the reaction temperature after mixing the base liquid and the composite liquid is 20-80℃, and the reaction time is 1-3h. After the reaction is completed, the supernatant is removed by centrifugation. The obtained solid precipitate is washed with water until the supernatant is neutral. After drying, monodisperse spherical micro / nano SiO2 is obtained.

[0021] Specifically, the crown ether in the extracted organic phase is recovered and reused. The specific process is as follows: the organic phase is placed in a sealed container and heated to 35-100℃. The organic extractant is removed by vacuum distillation (and recovered and reused after cooling). The resulting solid is dissolved in water and then adsorbed using a cation exchange resin. The resulting crown ether aqueous solution is then mixed and reacted with sodium silicate solution again.

[0022] This invention also provides a monodisperse spherical micro / nano silica prepared according to the above method, with a size of 20nm-1300nm and a specific surface area of ​​50-600m². 2 / g.

[0023] In addition, this invention also provides applications of the aforementioned monodisperse spherical micro / nano silica in aerospace, biomedicine, and electronic packaging. Compared with traditional braking materials, silica has higher heat resistance, wear resistance, and processing performance, and is widely used in aircraft braking systems in the aerospace field, significantly improving the reliability and lifespan of brakes. In the biomedical field, silica microspheres can be used for drug delivery, diagnosis, biomarking, imaging agents, and nanocarriers, providing more assistance in the diagnosis and treatment of diseases. In the electronic packaging field, high-purity spherical micro / nano SiO2 has superior properties such as high dielectric constant, low expansion, and low coefficient of friction, making it a necessary raw material for large-scale and ultra-large-scale integrated circuit packaging. Currently, most electronic packaging materials at home and abroad are polymers, among which epoxy resin is the most widely used. However, the high water absorption rate and viscosity of epoxy resin limit its application in ultra-large-scale integrated circuits. Studies have shown that adding 70% to 90% high-purity silica micropowder to epoxy resin can effectively reduce the thermal expansion coefficient, water absorption rate, internal stress, shrinkage rate, and improve the thermal conductivity of the molding compound.

[0024] The principle of this invention is as follows: Using sodium silicate as a raw material, the pH value of the system is adjusted by inorganic acid. After adding a macrocyclic crown ether compound, it selectively forms a complex with sodium ions in the solution. A simple solvent extraction process transfers the sodium ions from the aqueous phase to the organic phase. The crown ether in the organic phase can be recovered and reused through subsequent processes. The resulting aqueous phase is divided into two parts. One part of the aqueous solution is further treated with an appropriate amount of inorganic acid. The resulting silicic acid solution (this is the seed solution) can polymerize and grow into primary nanoparticles, which are used as the base solution for the subsequent preparation of larger nanoparticles. A suitable organic solvent is added to the other part of the aqueous phase to prepare a composite solution. This composite solution is added to the base solution. By controlling the volume ratio of the composite solution to the base solution, the concentration of silicic acid in the system is regulated to avoid secondary / multiple nucleation in the system, ultimately producing monodisperse spherical micro / nano silica with good particle size uniformity. The reactions involved in this process are as follows:

[0025]

[0026] This invention fully leverages the inherent advantages of chemical precipitation methods, such as the low cost of raw materials. By using organic macrocyclic crown ethers as complexing agents, the ionic strength of the solution is controlled, and the nanomicelles are stabilized. This solves the common problems of chemical precipitation methods, such as difficulty in controlling product morphology and particle size, easy formation of aggregated particles, and high energy consumption for subsequent concentration due to low concentration. It achieves the preparation of low-cost, high-quality silica micro / nanoparticles. The SiO2 micro / nanoparticles prepared according to this invention have many advantages, including high production intensity, high sphericity, uniform particle size, and good dispersibility, and have high economic and practical value in many fields such as aerospace, biomedicine, and electronic packaging.

[0027] This invention comprehensively considers the influence of sodium silicate solution nucleation, growth mechanism, solution ionic strength, and other factors on the growth of spherical particles, as well as the dispersibility of SiO2 in different solvents. It proposes a novel method for preparing monodisperse spherical SiO2 micro / nanoparticles using an organic macrocyclic compound as a complexing agent and high-concentration, inexpensive sodium silicate as a raw material. The resulting particles have a diameter between 20-1300 nm and are adjustable and controllable. This invention utilizes the complexation effect of the organic macrocyclic compound with sodium ions to avoid the damage to the electrical double layer of the silicon microspheres caused by excessive free sodium ions, reducing particle collision and adhesion, thereby promoting the growth of spherical particles. It also significantly increases the concentration of sodium silicate in a single feed.

[0028] Compared with the prior art, the present invention achieves the following beneficial technical effects:

[0029] (1) The present invention can prepare micro / nano-scale SiO2 using high-concentration and inexpensive sodium silicate (single feeding concentration up to 20%) as silicon source, and the product has uniform particle size, high sphericity, good dispersibility, and the particle size can be flexibly adjusted in the range of 20~1300nm;

[0030] (2) This invention proposes for the first time to adjust the ionic strength of the reaction system by adding an organic complexing agent, thereby precisely controlling the growth of spherical SiO2 particles, and the added complexing agent can be recycled and reused after simple chemical treatment;

[0031] (3) The process conditions of the present invention are stable, and it does not involve high temperature, high pressure and expensive equipment. It has many advantages such as simple production process, easy operation, low cost, high yield and easy large-scale industrial production. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the chemical structure of each crown ether in this invention.

[0033] Figure 2 This is a transmission electron microscope (TEM) image of the spherical silica nanoparticles prepared in Example 11.

[0034] Figure 3 This is a dynamic light scattering (DLS) image of the spherical silica nanoparticles prepared in Example 12.

[0035] Figure 4 This is a DLS image of the spherical silica nanoparticles prepared in Example 14.

[0036] Figure 5 This is a scanning electron microscope (SEM) image of the spherical silica nanoparticles prepared in Example 15.

[0037] Figure 6 This is a SEM image of the spherical silica nanoparticles prepared in Example 16. Detailed Implementation

[0038] To enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description is provided below in conjunction with specific embodiments and accompanying drawings. It should be noted that the following embodiments are only some implementations of the present invention, and other implementations derived without departing from the spirit of the present invention should fall within the protection scope of the present invention.

[0039] Example 1

[0040] (1) Dissolve a certain amount of sodium silicate in 100 mL of deionized water to obtain a sodium silicate solution with a mass fraction of 15%. Dissolve 0.04 mol of 15-crown ether-5 in 5 mL of water to obtain a crown ether aqueous solution with a concentration of 8 mol / L. Add the prepared crown ether aqueous solution to the sodium silicate solution while stirring (110-120 r / min), and react at 20 °C for 1 h to obtain the first solution.

[0041] (2) Transfer the first solution to a round-bottom flask, keep the stirring speed (110-120 r / min) and reaction temperature (20℃) constant, add an appropriate amount of sulfuric acid solution (mass fraction of 25%) to the flask, and control the pH value of the system to be maintained in the range of 10.5-11.5. After reacting for 2 hours, the second solution is obtained. Add 25 mL of dichloromethane to the second solution and stir evenly. After standing and separating the layers, the aqueous phase solution and the organic phase solution are obtained respectively.

[0042] (3) Measure 10 mL of the aqueous phase solution and add it to a round-bottom flask. While stirring (290~300 r / min), add sulfuric acid solution (mass fraction 6.5%) dropwise to the flask, controlling the pH of the system to be maintained in the range of 9.5-10.5. React at 20℃ for 30 min to obtain the bottom liquid. Measure 80 mL of the aqueous phase solution and 10 mL of anhydrous methanol and mix them evenly to obtain the composite solution. Add all of the composite solution to the bottom liquid and stir at 20℃ for 1 h to obtain the nano-SiO2 dispersion.

[0043] (4) The nano-SiO2 dispersion was centrifuged and the supernatant was removed. The supernatant was washed repeatedly with water until it was neutral. Then the solid precipitate was dried by step heating and baking. Monodisperse spherical nano-SiO2 was obtained. The test results showed that its average particle size was 212 nm.

[0044] (5) Place the organic phase solution obtained by extraction and separation in step (2) in a sealed container, heat to 45°C and remove dichloromethane by vacuum distillation, disperse the obtained product in water and pass it through a cation exchange resin to obtain a regenerated crown ether aqueous solution, adjust the solution concentration and reuse it in step (1), thereby realizing recycling.

[0045] Examples 2-9

[0046] Referring to the preparation method of Example 1, Examples 2-9 were carried out by changing key conditions such as the type of crown ether and the feeding ratio of crown ether to sodium silicate. The specific details are shown in Table 1 below.

[0047] Table 1 Comparison of Process Conditions for Examples 2-9

[0048]

[0049] Examples 1-9 show that different types of crown ethers can be introduced to prepare nano-silica of different sizes. By adjusting the feeding ratio of crown ether to sodium silicate and temperature-related parameters, the particle size of nano-silica can be controlled, with a particle size range of 100-600 nm.

[0050] Example 10

[0051] (1) Dissolve a certain amount of sodium silicate in 100 mL of deionized water to obtain a sodium silicate solution with a mass fraction of 3%. Dissolve 0.012 mol of 21-crown ether-7 in 5 mL of water to obtain a crown ether aqueous solution with a concentration of 2.4 mol / L. Add the prepared crown ether aqueous solution to the sodium silicate solution while stirring (110-120 r / min), and react at 80 °C for 30 min to obtain the first solution.

[0052] (2) Transfer the first solution to a round-bottom flask, keep the stirring speed (110-120 r / min) and reaction temperature (80℃) constant, add an appropriate amount of sulfuric acid solution (mass fraction of 25%) to the flask, and control the pH value of the system to be maintained in the range of 10.5-11.5. After reacting for 2 hours, the second solution is obtained. Add 25 mL of dichloromethane to the second solution and stir evenly. After standing and separating the layers, the aqueous phase solution and the organic phase solution are obtained respectively.

[0053] (3) Measure 10 mL of the aqueous phase solution and add it to a round-bottom flask. While stirring (290~300 r / min), add sulfuric acid solution (mass fraction 6.5%) dropwise to the flask, controlling the pH of the system to be maintained in the range of 9.5-10.5. React at 80℃ for 1 h to obtain the bottom liquid. Measure 80 mL of the aqueous phase solution and 10 mL of anhydrous methanol and mix them evenly to obtain the composite solution. Add all of the composite solution to the bottom liquid and stir at 80℃ for 2 h to obtain the nano-SiO2 dispersion.

[0054] (4) The nano-SiO2 dispersion was centrifuged and the supernatant was removed. The supernatant was washed repeatedly with water until it was neutral. Then the solid precipitate was dried by step heating and baking. Monodisperse spherical nano-SiO2 was obtained. The test results showed that its average particle size was 30 nm.

[0055] (5) Place the organic phase solution obtained by extraction and separation in step (2) into a sealed container, heat it to 45°C and remove dichloromethane under reduced pressure. Dissolve the obtained product in water and pass it through a cation exchange resin to obtain a regenerated crown ether aqueous solution. Adjust the solution concentration and reuse it in step (1) to achieve recycling.

[0056] Examples 11-14

[0057] Referring to the preparation method of Example 10, Examples 11-14 were carried out by changing key conditions such as the type of crown ether and the concentration of sodium silicate. The specific details are shown in Table 2 below.

[0058] Table 2 Comparison of Process Conditions for Examples 11-14

[0059]

[0060] Examples 10-14 show that, under the same conditions, by adjusting parameters such as the type of crown ether, the mass fraction of sodium silicate (1-5%), and the reaction time, small-particle-size SiO2 with good dispersibility and high particle size uniformity can be prepared. These particles have a particle size between 20-200 nm. Specifically, as shown in the examples... Figure 2-4 As shown.

[0061] Example 15

[0062] (1) Dissolve a certain amount of sodium silicate in 100 mL of deionized water to obtain a sodium silicate solution with a mass fraction of 20%. Dissolve 0.12 mol of 15-crown-5 in 5 mL of water to obtain a crown ether aqueous solution with a concentration of 24 mol / L. Add the prepared crown ether aqueous solution to the sodium silicate solution while stirring (110-120 r / min), and react at 50 °C for 30 min to obtain the first solution.

[0063] (2) Transfer the first solution to a round-bottom flask, keep the stirring speed (110-120 r / min) and reaction temperature (50℃) constant, add an appropriate amount of sulfuric acid solution (mass fraction of 25%) dropwise to the flask, and control the pH value of the system to be maintained in the range of 10.5-11.5. After reacting for 2 hours, the second solution is obtained. Add 25 mL of ethyl acetate to the second solution and stir evenly. After standing and separating the layers, the aqueous phase solution and the organic phase solution are obtained respectively.

[0064] (3) Measure 10 mL of the aqueous phase solution and add it to a round-bottom flask. While stirring (290~300 r / min), add sulfuric acid solution (mass fraction 39%) dropwise to the flask, controlling the pH of the system to be maintained in the range of 9.5-10.5. React at 50℃ for 1 h to obtain the bottom liquid. Measure 80 mL of the aqueous phase solution and 30 mL of isopropanol and mix them evenly to obtain the composite solution. Add all of the composite solution to the bottom liquid and stir at 50℃ for 3 h to obtain the nano-SiO2 dispersion.

[0065] (4) The nano-SiO2 dispersion was centrifuged and the supernatant was removed. The supernatant was washed repeatedly with water until it was neutral. Then the solid precipitate was dried by step heating and baking to obtain monodisperse spherical nano-SiO2.

[0066] (5) Place the organic phase solution obtained by extraction and separation in step (2) into a sealed container, heat it to 45°C and remove dichloromethane under reduced pressure. Dissolve the obtained product in water and pass it through a cation exchange resin to obtain a regenerated crown ether aqueous solution. Adjust the solution concentration and reuse it in step (1) to achieve recycling.

[0067] The SEM image of the nano-SiO2 obtained in this embodiment is as follows: Figure 5As shown in the figure, the SiO2 particles are regular spherical shapes with no obvious agglomeration, and the average particle size is 620 nm.

[0068] Example 16

[0069] (1) Dissolve a certain amount of sodium silicate in 100 mL of deionized water to obtain a sodium silicate solution with a mass fraction of 15%. Dissolve 0.12 mol of 18-crown-6 in 5 mL of water to obtain a crown ether aqueous solution with a concentration of 24 mol / L. Add the prepared crown ether aqueous solution to the sodium silicate solution while stirring (110-120 r / min), and react at 50 °C for 30 min to obtain the first solution.

[0070] (2) Transfer the first solution to a round-bottom flask, keep the stirring speed (110-120 r / min) and reaction temperature (50℃) constant, add an appropriate amount of sulfuric acid solution (mass fraction of 25%) dropwise to the flask, and control the pH value of the system to be maintained in the range of 10.5-11.5. After reacting for 2 hours, the second solution is obtained. Add 25 mL of ethyl acetate to the second solution and stir evenly. After standing and separating the layers, the aqueous phase solution and the organic phase solution are obtained respectively.

[0071] (3) Measure 10 mL of the aqueous phase solution and add it to a round-bottom flask. While stirring (290~300 r / min), add sulfuric acid solution (mass fraction 39%) dropwise to the flask, controlling the pH of the system to be maintained in the range of 8.5-9.5. React at 50℃ for 1 h to obtain the bottom liquid. Measure 80 mL of the aqueous phase solution and 30 mL of isopropanol and mix them evenly to obtain the composite solution. Add all of the composite solution to the bottom liquid and stir at 50℃ for 3 h to obtain the nano-SiO2 dispersion.

[0072] (4) The nano-SiO2 dispersion was centrifuged and the supernatant was removed. The supernatant was washed repeatedly with water until it was neutral. Then the solid precipitate was dried by step heating and baking to obtain monodisperse spherical nano-SiO2.

[0073] (5) Place the organic phase solution obtained by extraction and separation in step (2) into a sealed container, heat it to 45°C and remove dichloromethane under reduced pressure. Dissolve the obtained product in water and pass it through a cation exchange resin to obtain a regenerated crown ether aqueous solution. Adjust the solution concentration and reuse it in step (1) to achieve recycling.

[0074] The SEM image of the monodisperse spherical SiO2 nanoparticles obtained in this embodiment is as follows: Figure 6 As shown in the figure, the SiO2 particles are regular spherical shapes with no obvious agglomeration, and the average particle size is 1134 nm.

Claims

1. A method for preparing monodisperse spherical micro / nano silica, characterized in that... The method is as follows: Crown ether and sodium silicate solution were mixed and reacted. The resulting mixture was extracted with an organic extractant to obtain an aqueous phase and an organic phase. A portion of the aqueous phase was taken and its pH was adjusted to 8.5-10.5 to obtain a base liquid. Another portion of the aqueous phase was taken and mixed with an organic solvent to obtain a composite liquid. The base liquid and the composite liquid were mixed and subjected to a precipitation reaction. Solid-liquid separation was performed to obtain monodisperse spherical micro / nano silica. The crown ether is selected from at least one of 21-crown-7, 18-crown-6, 15-crown-5 or their derivatives; the organic extractant is selected from at least one of dichloromethane, chloroform, ethyl acetate, diethyl ether, toluene, and xylene; the organic solvent is specifically an alcohol solvent; the molar ratio of crown ether to sodium silicate is 0.05-1:1, the mixing reaction temperature is 20-80℃; the volume ratio of aqueous phase to organic solvent is 1-10:1, the volume ratio of base liquid to composite liquid is 1:8-16, and the precipitation reaction temperature is 20-80℃.

2. The preparation method according to claim 1, characterized in that: The derivatives include benzo-15-crown-5 and R-benzo-15-crown-5, wherein R = CH3, NH2, or NO2, and the organic solvent is selected from at least one of methanol, ethanol, propanol, and isopropanol.

3. The preparation method according to claim 1, characterized in that: The modulus of the sodium silicate is 1.5-3.

5.

4. The preparation method according to claim 1, characterized in that... The specific process of the reaction between crown ether and sodium silicate solution is as follows: Prepare sodium silicate aqueous solution and crown ether aqueous solution separately, then add crown ether aqueous solution to sodium silicate aqueous solution under stirring to allow the reaction to proceed fully, then add sulfuric acid solution dropwise to adjust the pH of the mixture to 10.5-11.5, and continue stirring the reaction.

5. The preparation method according to claim 4, characterized in that: The mass fraction of the prepared sodium silicate aqueous solution is 3%-20%, and the concentration of the prepared crown ether aqueous solution is 1-2.4 mol / L.

6. The preparation method according to claim 1, characterized in that: The bottom liquid is obtained by adjusting the pH of the mixture by adding sulfuric acid solution dropwise to the aqueous phase obtained from extraction.

7. The preparation method according to claim 1, characterized in that: After the precipitation reaction was completed, the solid obtained by centrifugation was washed with water until neutral and dried to obtain monodisperse spherical micro / nano SiO2.

8. The preparation method according to claim 1, characterized in that: The extracted organic phase was placed in a sealed container and heated to 35-100℃. The organic extractant was recovered by vacuum distillation. The resulting solid was dissolved in water and adsorbed by a cation exchange resin. The resulting crown ether aqueous solution was then mixed and reacted with sodium silicate solution again.

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