A preparation method of hollow silica

Abstract

The present invention discloses a method for preparing hollow silica, which belongs to the technical field of inorganic non-metallic materials. The preparation method comprises weighing a silicon source and dissolving it in an acidic solution, stirring at a temperature of 20 to 50°C until a uniformly mixed solution A is obtained; weighing a soluble substance and dissolving it in an alcohol-water solution to obtain a solution B, adding solution A to solution B, and at a certain temperature, the inorganic salts and / or organic salts in the system form crystal nuclei, adding an appropriate amount of alkali, and under stirring conditions, the silicon source is deposited and grown on the surface of the crystal nuclei. After a period of reaction, the crystal nuclei inside the solution dissolve to form a hollow silica solution, which is then filtered, washed, and dried to obtain the hollow silica. The hollow silica prepared by the present invention has uniform particle size, good dispersibility, and controllable shell thickness. The preparation process does not require calcination or chemical etching, is green and environmentally friendly, and is convenient for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic non-metallic materials, and in particular to a method for preparing hollow silica. Background Art

[0002] As a new lightweight material, hollow silica has attracted the attention of many scholars due to its excellent characteristics such as large specific surface area, good chemical stability, low dielectric constant and low thermal expansion coefficient. It has a promising future in application fields such as chemical catalysis, biomedicine, integrated circuit packaging and copper clad laminates.

[0003] Currently, hollow silica is prepared by three methods: template method, hydrothermal method, and emulsion method. The template method is the most prevalent, and is further divided into soft template method and hard template method according to the properties of the template. The former mainly uses emulsions, bubbles, surfactants, liquid crystals and other substances to create hollow structures. The reaction process is a dynamic equilibrium, and generally, problems such as interconnection, agglomeration, poor dispersion, and wide particle size distribution will occur during the preparation process. The latter mainly uses polymer particles, metals, metal oxides, and carbon nanoparticles as templates, deposits them on the template surface, and finally removes the template by calcination or chemical etching. In this process, calcination easily produces small organic molecules, and etching easily destroys the surface density.

[0004] For example, in the patent with publication number CN 112194140A, entitled "A Method for Preparing Small-Sized Hollow Silica," an emulsifier and metal oxide particles are used in an organic solvent under acid / base catalysis to prepare small-sized hollow silica with a particle size between 10-30 nm and a shell thickness of 5-7 nm. This method inevitably uses organic solvents such as n-hexane and dichloromethane, which are difficult to completely remove during the subsequent washing process.

[0005] In the patent with publication number CN 116282052A, entitled "A method for rapidly preparing nano hollow silica," calcium carbonate was used as a template using ultra-gravity technology to prepare hollow silica with a shell thickness of 1-20 nm. However, the particle size distribution was wide, the shell was thin, and the compressive resistance was low.

[0006] In the patent publication number CN 113816388 A, entitled "Method for preparing low-dielectric hollow silica microspheres," a silica layer is formed by reactive deposition of methyltrimethoxysilane on the surface of synthesized spherical polystyrene as a template. During this process, the template requires long-term segmented calcination, which consumes a lot of energy and is not environmentally friendly.

[0007] In the patent publication number CN 114620737 A, entitled "Hollow Silica and Its Preparation Method and Application," hollow silica is prepared using elemental silicon powder as a raw material and utilizing the Kirkendall effect at the interface. Although the process is simple, the prepared silica particles are sticky and have poor dispersion. Summary of the Invention

[0008] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for preparing hollow silica based on crystal nuclei in a solution as a template, so as to provide a green, environmentally friendly, well-dispersed, and controllable particle size distribution hollow silica preparation method.

[0009] To achieve the above-mentioned purpose, the present invention proposes the following technical solution: a method for preparing hollow silica, comprising the following steps:

[0010] A method for preparing hollow silica, characterized by comprising the following steps:

[0011] S1. Weigh a silicon source and dissolve it in an acidic solution, stir at a temperature of 20 to 50 ° C until no stratification occurs to obtain a uniform mixed solution A to form a precursor, wherein the silicon source is selected from one or more of tetraethyl silicate, tetramethyl silicate, methyltrimethoxysilane, ethyltriethoxysilane, and sodium silicate;

[0012] S2. Weigh the soluble substance and dissolve it in a certain proportion of alcohol-water solution, place it in a reactor to react to obtain a solution B, wherein the soluble substance is selected from one or more of ammonium chloride, sodium chloride, urea, sucrose, and glucose;

[0013] S3. Under stirring conditions, solution A is added to solution B, mixed evenly, at a temperature of -30 to 20 ° C, the inorganic salt and / or organic salt in the system forms a crystal nucleus, an appropriate amount of base is added dropwise, under stirring conditions, the silicon source is deposited and grown on the surface of the crystal nucleus, and the reaction is carried out for a period of time to obtain a solution C, wherein the base is selected from one or more of ammonia, ethylenediamine, triethylamine, and triethanolamine;

[0014] S4. When the reactor temperature is adjusted to 30-90°C, the crystal nuclei inside the solution dissolve to form a hollow silica solution D;

[0015] S5. Filter solution D, wash with pure water, and finally obtain hollow silica.

[0016] Preferably, in S1, the acidic solution is one or more of hydrochloric acid, acetic acid, and nitric acid, and the pH of the acidic solution is controlled at 1-5.

[0017] Preferably, in S1, the mass ratio of the silicon source to the acid solution is 1:5 to 1:30.

[0018] Preferably, in S2, the alcohol substance is one or more of methanol, ethanol, and ethylene glycol; wherein the mass ratio of soluble matter to alcohol and water is 1:0.2-10:5-100.

[0019] Preferably, the reactor is a double-layer stainless steel reactor, and the temperature of the reactor is controlled by an external circulation machine.

[0020] Preferably, the amount of alkali in S3 is 10% to 60% of the amount of silicon source.

[0021] Preferably, in S3, the reaction time is 1 to 6 hours.

[0022] Preferably, the reaction time in S4 is 1-3 hours, and the drying temperature in S5 is 60-100°C.

[0023] In the preparation method of the present invention, since the soluble substance is selected from one or more of ammonium chloride, sodium chloride, urea, sucrose, and glucose, after solution A is added to solution B, different types of inorganic salts and / or organic salts will be produced, and the specific production of inorganic salts and / or organic salts is determined by the specific soluble substance selected. Due to the different types of inorganic salts and / or organic salts, the solubility in the solution and the temperature at which the crystal nucleus appears will also be different, so the size of the crystal nucleus will also be different. In the range of -30-20°C, in the existing system, the solubility changes greatly with the decrease in temperature, and when the temperature drops to a certain value, the crystal nucleus appears. The present invention can prepare crystal nuclei of different sizes by controlling the type selection, dosage, system solvent ratio and temperature of the inorganic and / or organic salts.

[0024] The particle size of the hollow silica is mainly controlled by the size of the crystal nucleus formed by the inorganic salt and / or organic salt in the appropriate temperature range, and secondly by the thickness of the coating layer (the coating layer is smaller than the core particle); and because the system is composed of water and alcohol, the surface of the generated silica is easily wetted by the water and alcohol in this ratio, so the dispersion is better.

[0025] Upon forming a fixed-size crystal nucleus, the silicon source precursor forms a coating on the nucleus due to hydrogen bonding and intermolecular forces. Under alkali catalysis, the coated silicon source precursor deposits a silica shell on the nucleus, which is then fixed in place by the action of inorganic and / or organic salts. The thickness of the silica shell is primarily controlled by the amount of silicon source and alkali used. At the appropriate ratio, a higher amount of silicon source results in a thicker shell and a smoother surface. The amount of alkali increases the accumulation rate of the deposited particles. Exceeding a certain range results in a rough surface with holes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The hollow silica prepared by the present invention has uniform particle size, good dispersibility, low dielectric constant and controllable shell thickness;

[0028] 2. The present invention prepares hollow silica by adopting a preparation method of surface deposition of silica using inorganic salts and / or organic salts as cores within a certain temperature range. The process steps are simple, no calcination or chemical etching is required, it is green and environmentally friendly, and is convenient for large-scale industrial production.

[0029] 3. The preparation method of the present invention effectively controls the particle size and wall thickness of the product by controlling the size of the crystal nucleus, the amount of silicon source and the alkali. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the SEM image of the hollow silica prepared in Example 1;

[0031] Figure 2 This is a TEM image of hollow silica prepared in Example 1;

[0032] Figure 3 This is the SEM image of the hollow silica prepared in Example 2;

[0033] Figure 4 This is the SEM image of the hollow silica prepared in Example 3;

[0034] Figure 5 This is the SEM image of the hollow silica prepared in Example 4;

[0035] Figure 6 This is the SEM image of the hollow silica prepared in Example 5;

[0036] Figure 7 This is the SEM image of hollow silica prepared in Comparative Example 1-1;

[0037] Figure 8 This is the SEM image of the hollow silica prepared in Comparative Example 2-1;

[0038] Figure 9 This is the SEM image of the hollow silica prepared in Comparative Example 3-1;

[0039] Figure 10 This is the SEM image of the hollow silica prepared in Comparative Example 4-1. DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0041] Unless expressly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising", etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0042] The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0043] Example 1

[0044] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 20°C until the mixture becomes a homogeneous solution A.

[0045] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0046] After continuing to stir for 10 minutes, the temperature was set to -5°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0047] The slurry was filtered and washed, and then dried at 80°C.

[0048] like Figure 1 The figure shows a scanning electron microscope image of hollow silica prepared under the process conditions of this embodiment. Figure 2 The figure shows a transmission electron microscope image of the hollow silica prepared under the process conditions of this embodiment. It can be seen from the figure that the prepared hollow silica has a spherical morphology, the particles are evenly dispersed, the median diameter is about 2.2μm, the shell thickness is 100-200nm, the surface is dense and undamaged, and the tested dielectric constant is 2.1.

[0049] Example 2

[0050] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 30°C until the mixture becomes a homogeneous solution A.

[0051] Weigh 20g of urea and dissolve it in a mixture of 10g of ethanol and 200g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20min. Then, slowly add the prepared mixed solution A dropwise into the reactor.

[0052] After continuing to stir for 10 minutes, the temperature was set to -10°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0053] The slurry was filtered and washed, and then dried at 80°C.

[0054] This Example 2 repeats the preparation process of Example 1, except that the salt type and reaction temperature are changed. Figure 3 The figure shows a scanning electron microscope image of the product under the process conditions of Example 2; it can be seen from the figure that the prepared product is spherical hollow silica with uniform particle size dispersion, a median diameter of about 4 μm, a shell thickness of 150-260 nm, and a tested dielectric constant of 1.9.

[0055] Example 3

[0056] Weigh 6g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 45°C until the mixture becomes a homogeneous solution A.

[0057] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0058] After continuing to stir for 10 minutes, the temperature was set to -5°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0059] The slurry was filtered and washed, and then dried at 80°C.

[0060] This Example 3 repeats the preparation process of Example 1, except that the amount of silicon source used is reduced. Figure 4 The figure shows a scanning electron microscope image of the product under the process conditions of Example 3. It can be seen from the figure that the prepared product is spherical hollow silica with uniformly dispersed particle size, a median diameter of about 2.0 μm, a shell thickness of 80-100 nm, and a tested dielectric constant of 2.5.

[0061] Example 4

[0062] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 30°C until the mixture becomes a homogeneous solution A.

[0063] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0064] After continuing to stir for 10 minutes, the temperature was set to -5°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 4 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0065] The slurry was filtered and washed, and then dried at 80°C.

[0066] This Example 4 repeats the preparation process of Example 1, except that the amount of ammonia water is increased. Figure 5 The figure shows a scanning electron microscope image of the product under the process conditions of Example 4. It can be seen from the figure that the prepared product is spherical hollow silica with uniform particle size dispersion, smooth and dense surface, median diameter of about 2.3 μm, shell thickness of 150-200 nm, and a tested dielectric constant of 2.4.

[0067] Example 5

[0068] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 30°C until the mixture becomes a homogeneous solution A.

[0069] Weigh 20g of urea and dissolve it in a mixture of 10g of ethanol and 200g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20min. Then, slowly add the prepared mixed solution A dropwise into the reactor.

[0070] After continuing to stir for 10 minutes, the temperature was set to -15°C. As the temperature dropped, crystal nuclei gradually formed and grew. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0071] The slurry was filtered and washed, and then dried at 80°C.

[0072] This Example 5 repeats the preparation process of Example 1, except that the external circulation temperature is changed. Figure 6 The figure shows a scanning electron microscope image of the product under the process conditions of Example 5. It can be seen from the figure that the prepared product is spherical hollow silica with uniform particle size dispersion, a median diameter of about 2.4 μm, a shell thickness of 80-100 nm, and a tested dielectric constant of 2.2.

[0073] Comparative Example 1-1

[0074] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 20°C until the mixture becomes a homogeneous solution A.

[0075] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0076] After continuing to stir for 10 minutes, the temperature was set to 25°C. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0077] The slurry was filtered and washed, and then dried at 80°C.

[0078] This comparative example 1-1 repeated the preparation steps of Example 1, except that the temperature of the reactor was adjusted to 25°C after the addition of the silicon source. Figure 7 The SEM image of the product produced under the process conditions of Comparative Example 1-1 is shown. The image shows that the resulting product is nanoscale irregular agglomerates. This indicates that due to the different types of inorganic and organic salts used in the preparation process, their solubility in solution and the crystal nucleation temperatures vary, resulting in different crystal nuclei sizes. When the temperature is adjusted to 25°C, the added inorganic and organic salts do not undergo crystal nucleation at this temperature, resulting in the product being nanoscale irregular agglomerates.

[0079] Comparative Example 2-1

[0080] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 30°C until the mixture becomes a homogeneous solution A.

[0081] 50 g of urea was weighed and dissolved in a mixture of 10 g of ethanol and 200 g of pure water. The mixture was placed in a double-layer stainless steel reactor and stirred for 20 min. Then, the prepared mixed solution A was slowly added dropwise to the reactor.

[0082] After continuing to stir for 10 minutes, the temperature was set to -10°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0083] The slurry was filtered and washed, and then dried at 80°C.

[0084] The preparation steps of Example 1 were repeated in Comparative Example 2-1, except that the amount of urea was increased to 50 g. Figure 8 The SEM image of the product produced under the process conditions of Comparative Example 2-1 shows severe adhesion and the presence of irregular, non-spherical particles. This indicates that during the preparation process, the solute content of inorganic and organic salts in the solution increases. As the temperature decreases, the number of crystal nuclei in the system gradually increases. When the temperature exceeds a certain range, the crystals adhere to each other, the silicon source per unit volume remains unchanged, and the coated product eventually exhibits connected particles and irregular, non-spherical particles.

[0085] Comparative Example 3-1

[0086] Weigh 1.5g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 45°C until the mixture becomes a homogeneous solution A.

[0087] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0088] After continuing to stir for 10 minutes, the temperature was set to -5°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 2 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0089] The slurry was filtered and washed, and then dried at 80°C.

[0090] This comparative example 3-1 repeated the preparation steps of Example 3, except that the amount of silicon source was reduced to 1.5 g. Figure 9 The following is a scanning electron micrograph of the product produced under the process conditions of Comparative Example 3-1. The image shows a thin shell layer and severe fragmentation. The dielectric constant is 3.6. This indicates that the crystal core is fixed within the unit volume, but the silicon source is reduced, the surface coating is thinner, the shell layer is thinner, and localized fragmentation occurs.

[0091] Comparative Example 4-1

[0092] Weigh 10g of tetraethyl silicate and add it to 60g of hydrochloric acid solution with a pH of 3. Stir at 30°C until the mixture becomes a homogeneous solution A.

[0093] Weigh 20 g of sucrose and dissolve it in a mixture of 10 g of ethanol and 200 g of pure water. Place the mixture in a double-layer stainless steel reactor and stir for 20 min. Then slowly add the prepared mixed solution A dropwise to the reactor.

[0094] After continuing to stir for 10 minutes, the temperature was set to -5°C. As the temperature dropped, crystal nuclei gradually formed. At this time, 8 g of triethylamine was added dropwise to the reactor. After stirring and reacting for 4 hours, the temperature was set to 40°C. After reacting for 1 hour, the crystal nuclei dissolved to form hollow silica.

[0095] The slurry was filtered and washed, and then dried at 80°C.

[0096] This comparative example 4-1 repeats the preparation steps of Example 4, except that the amount of base is increased to 8g, such as Figure 10 The following is a scanning electron micrograph of the product produced under the process conditions of Comparative Example 4-1. The image shows a rough, uneven surface, with some broken, connected packages. The dielectric constant is 3.3. This indicates that increasing the alkali dosage increases the size of the nano-sized silica particles generated by the surface silicon source and accelerates the reaction. The surface accumulation is less dense, rough, and easily broken.

[0097] The description of specific exemplary embodiments of the present invention is for the purpose of illustration and description. These descriptions are not intended to limit the invention to the precise form disclosed, and it is apparent that many changes and variations are possible in light of the above teachings. The exemplary embodiments are selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to make and utilize the various exemplary embodiments of the invention and various options and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing hollow silica, characterized in that: The following steps are involved: S1. Weigh a silicon source and dissolve it in an acidic solution. Stir at a temperature of 20 to 50°C until a uniform mixture is obtained. Solution A is prepared. The silicon source is selected from one or more of tetraethyl silicate, tetramethyl silicate, methyltrimethoxysilane, ethyltriethoxysilane, and sodium silicate. The acidic solution is selected from one or more of hydrochloric acid, acetic acid, and nitric acid. The pH of the acidic solution is controlled between 1 and 5. S2 weighed a soluble substance dissolved in a certain proportion of an alcohol aqueous solution, placed in a reactor to react to obtain a solution B, the soluble substance is selected from urea, sucrose, glucose, one or more; S3. Under stirring conditions, solution A is added to solution B, mixed evenly, and crystal nuclei are formed at a temperature of -30 to 20°C. An appropriate amount of base is added dropwise, and under stirring conditions, the silicon source is deposited and grown on the surface of the crystal nuclei. The reaction is carried out for a period of time to obtain solution C, wherein the base is selected from one or more of ammonia, ethylenediamine, triethylamine, and triethanolamine; S4. When the reactor temperature is adjusted to 30-90°C, the crystal nuclei inside the solution dissolve to form a hollow silica solution D; S5. Solution D is filtered, washed, and dried to obtain hollow silica.

2. The method for preparing hollow silica according to claim 1, wherein: In S1, the mass ratio of the silicon source to the acidic solution is 1:5 to 1:

30.

3. The method for preparing hollow silica according to claim 1, wherein: In S2, the alcohol is selected from one or more of methanol, ethanol, and ethylene glycol.

4. The method for preparing hollow silica according to claim 1, wherein: In the S2, the mass ratio of the soluble substance to the alcohol and water is 1:0.2-10:5-100.

5. The method for preparing hollow silica according to claim 1, wherein: The reactor is a double-layer stainless steel reactor, and the temperature of the reactor is controlled by an external circulation machine.

6. The method for preparing hollow silica according to claim 1, wherein: The amount of alkali in the S3 is 10% to 60% of the amount of the silicon source.

7. The method for preparing hollow silica according to claim 1, wherein: The reaction time in S3 is 1 to 6 hours.

8. The method for preparing hollow silica according to claim 1, wherein: The reaction time in S4 is 1-3 h.

9. The method for preparing hollow silica according to claim 1, wherein: The drying temperature in S5 is 60-100°C.

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