Preparation method and application of monodisperse hollow silica microspheres

Abstract

The application provides a preparation method and application of monodisperse hollow silica. The preparation method of the monodisperse hollow silica comprises the following steps: S1, adding a silane containing a hydrophobic group into an acidic aqueous solution, adjusting the system to neutral after heating reaction, and obtaining a microdroplet solution containing the hydrophobic group; S2, adding a tetraalkoxysilane into the microdroplet solution obtained in the step S1, adjusting the system to alkaline after uniformly mixing, hydrolyzing under heating, taking the precipitate after centrifugation, and washing and drying, so as to obtain the monodisperse hollow silica. The method provided by the application can obtain complete hollow silica microspheres by using the tetraalkoxysilane to perform hydrolysis and polycondensation reaction on the surface of the microdroplets obtained by hydrolysis of the silane compound with the hydrophobic group. The method can obtain the hollow silica microspheres without using any template and surfactant. The by-product of the method is single, easy to separate, low in cost, and simple in method, and is conducive to industrialized production of the hollow silica microspheres.

Description

Technical Field

[0001] This invention relates to the field of silica microsphere technology, and more specifically, to a method for preparing monodisperse hollow silica microspheres and their application. Background Technology

[0002] Hollow silica nanomaterials possess excellent advantages such as large specific surface area, low density, high chemical and thermal stability, and biocompatibility, making their preparation and performance research a hot topic in materials science. Based on this, hollow silica microspheres have broad application prospects in many fields, including thermal insulation materials, catalyst supports, dielectric materials, auxiliary materials, and controlled drug release.

[0003] Currently, there are various methods for preparing hollow silica microspheres, but they are basically all based on soft template methods and hard template methods. The template is the main factor determining the morphology and size of hollow mesoporous silica microspheres. Specifically, the hard template method uses polymer microspheres as templates to deposit and grow silica precursors on the polymer surface, ultimately obtaining silica composite core-shell microspheres. After the reaction, high-temperature calcination or solvent etching is required to achieve hollow silica microspheres. The soft template method typically uses microemulsion droplets as templates, requiring the introduction of a large amount of surfactant. The silicon source undergoes hydrolysis, polymerization, sol-gel reactions, and other chemical reactions at the two-phase interface to form a film, which is then separated and dried to obtain porous silica microspheres. However, both methods ultimately require the removal of the soft template and all surfactant molecules from the system. Both methods suffer from complex preparation processes, poor dispersibility and structural integrity, which not only increase production costs but also affect their applications to some extent.

[0004] Furthermore, template-free methods, such as emulsion polymerization, are now used to prepare hollow porous silica microspheres. For example, patent CN109289719A discloses a method for preparing hollow mesoporous silica microspheres. While this method avoids energy-intensive and cumbersome processes such as high-temperature calcination and solvent etching, it still uses organic reagents such as emulsifiers, alkanes, and surfactants, resulting in complex post-processing and limiting its large-scale production. Other existing technologies also use organic solvents such as polyethylene glycol and ethanol, increasing recycling and processing costs, and resulting in hollow microspheres with a wider particle size distribution. Summary of the Invention

[0005] To solve or at least partially solve the above problems, the present invention provides a method for preparing monodisperse hollow silica microspheres. The preparation method provided by the present invention does not require cumbersome and energy-consuming processes such as high-temperature calcination or solvent etching to remove the internal template or the use of organic reagents such as emulsifiers, alkanes, and surfactants. At the same time, the obtained microspheres have a complete hollow spherical structure and good monodispersity.

[0006] The method for preparing monodisperse hollow silica microspheres provided by the present invention includes the following steps:

[0007] S1, add silane containing hydrophobic groups to acidic aqueous medium, heat the reaction, and then adjust the system to neutral to obtain a microdroplet solution containing hydrophobic groups;

[0008] S2, add tetraalkoxysilane to the microdroplet solution obtained in step S1, mix well, adjust the system to alkaline, heat to hydrolyze, centrifuge, take the precipitate, wash and dry to obtain the final product.

[0009] The preparation method provided by this invention solves the problems of the cumbersome and energy-consuming process of high-temperature calcination or solvent etching to remove the internal template in the preparation of hollow silica microspheres in the prior art, as well as the insufficient integrity of the hollow spherical structure and the insufficient monodispersity of the spheres. It successfully synthesizes complete and monodisperse hollow silica microspheres.

[0010] In a preferred embodiment of the present invention, in step S1, the silane containing the hydrophobic group is at least one of vinylsilane, alkane, piperazine, acryloyloxysilane, and mercaptosilane, preferably vinylsilane, and more preferably vinyltriethoxysilane.

[0011] In a preferred embodiment of the present invention, in step S1, the hydrogen ion concentration of the acidic aqueous solution is 0.001-0.1 mol / L. Within this concentration range, the formation of hollow silica microspheres is beneficial. One of the core inventive points of the present invention is that, in order to better obtain microspheres with a hollow morphology, the mass ratio of the acidic aqueous solution to the tetraalkoxysilane is preferably (10-100):1. In a preferred embodiment of the present invention, the acidic aqueous solution can be an aqueous solution of HCl, acetic acid, oxalic acid, or nitric acid.

[0012] In a preferred embodiment of the present invention, in step S1, the heating reaction temperature is 30-60°C, and the heating reaction time is 10-60 min. Within this temperature and time range, microspheres with a moderate hollow particle size distribution and a complete hollow structure can be obtained. If the heating temperature is too low or the heating time is too short, microspheres with a complete hollow structure cannot be obtained. In a specific embodiment of the present invention, step S1 involves heating and stirring simultaneously.

[0013] In a specific embodiment of the present invention, the system in step S1 can be adjusted to neutral (i.e., pH around 7) using a commonly used alkaline solvent in the art. The alkaline solvent can be ammonia or other commonly used alkaline solvents.

[0014] In a preferred embodiment of the present invention, in step S2, the tetraalkoxysilane is tetraethoxysilane. The mass ratio of the silane containing the hydrophobic group to the tetraalkoxysilane is preferably (0.2-1):1, more preferably (0.2-0.3):1.

[0015] In a preferred embodiment of the present invention, the mass ratio of the silane containing the hydrophobic group to the tetraalkoxysilane is (0.2-1):1, and the mass ratio of the acidic aqueous medium to the tetraalkoxysilane is (10-100):1. In a specific embodiment of the present invention, the tetraalkoxysilane can be added slowly dropwise. That is, step S2 may include: "Adding tetraalkoxysilane to the microdroplet solution obtained in step S1, stirring while adding, and adjusting the system to alkaline after mixing evenly." To obtain more effective intact hollow silica microspheres, the stirring speed is preferably 50-1000 rpm.

[0016] In a preferred embodiment of the present invention, the system is adjusted to alkalinity in step S2, preferably with a pH value of 8-10. Within this pH range, the resulting hollow silica microspheres exhibit a more suitable particle size distribution and better monodispersity. In a specific embodiment of the present invention, step S2 can be achieved by adding an alkaline solvent to the system to adjust its pH value to alkalinity. This alkaline solvent can be at least one of ammonia, sodium hydroxide aqueous solution, and triethylamine.

[0017] In a preferred embodiment of the present invention, in order to obtain hollow silica microspheres with better monodispersity, in step S2, the temperature of heating and hydrolysis is 30-60°C, and the reaction time of heating and hydrolysis is 1-4 hours.

[0018] In a specific embodiment of the present invention, in step S2, the washing solvent can be ethanol and / or water, the drying is performed by a heating drying method, the heating temperature can be 60-90°C, and the drying time is controlled within 1-5 hours.

[0019] Another objective of this invention is to provide monodisperse hollow silica microspheres obtained by the above-described preparation method. The hollow silica microspheres obtained by this invention have a complete hollow spherical structure and good monodispersity.

[0020] The preparation method and the hollow silica microspheres prepared by the present invention have better applications in the field of thermal insulation materials. Another object of the present invention is to provide the above-mentioned preparation method or the monodisperse hollow silica microspheres prepared by the above-mentioned preparation method for the preparation of thermal insulation materials.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention utilizes microdroplets obtained by hydrolysis of hydrophobic silane compounds as templates, on which tetraalkoxysilanes undergo hydrolysis and condensation to obtain hollow silica microspheres with uniform particle size and intact spherical structure. This method yields hollow silica microspheres without the use of any templates or surfactants, and the microspheres do not exhibit structural damage or collapse after drying. This process is low-cost, simple, and yields high-quality hollow microspheres. It eliminates the need for complex and energy-intensive template removal steps. Furthermore, the process operates under mild conditions, produces a single, easily separated byproduct, and is conducive to the industrial production of hollow silica microspheres.

[0023] (2) The present invention can obtain silica microspheres with controllable particle size and shape by changing the hydrophobic silane compound and adjusting the mass ratio of hydrophobic silane to tetraalkoxysilane, thus meeting the industrial application requirements for silica microspheres.

[0024] (3) The hollow silica microspheres prepared by this invention have a large hollow cavity volume, controllable size and shape, and good monodispersity, which is superior to the microsphere morphology in the prior art (for example, the particle size distribution of the hollow microspheres obtained by this invention is narrower than that of the microspheres given in CN201910431905.7, etc.). The hollow cavity structure inside the microspheres can serve as a carrier, and the internal cavity can suppress the internal air movement, making convective heat transfer less likely to occur. It has broad application prospects in the fields of heat insulation, coating and slow release, adsorption and separation. Attached Figure Description

[0025] Figure 1 This is a SEM image of the monodisperse hollow silica microspheres obtained in Example 1.

[0026] Figure 2 The image shows a TEM image of the monodisperse hollow silica microspheres obtained in Example 1. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, "%" in this invention refers to a percentage by mass.

[0029] Example 1

[0030] This embodiment provides a monodisperse hollow silica microsphere, the preparation method of which includes the following steps:

[0031] (1) A silane with hydrophobic groups, vinyltriethoxysilane, was added to a hydrochloric acid aqueous solution with a hydrogen ion concentration of 0.01 mol / L. The mixture was heated at 40 °C for 60 min with stirring. After the reaction was complete, ammonia was added to neutralize the system, resulting in a microdroplet solution with hydrophobic groups. The mass ratio of vinyltriethoxysilane to tetraethoxysilane was 0.2:1. The mass ratio of the acidic aqueous solution to tetraethoxysilane was 50:1.

[0032] (2) Add tetraethoxysilane dropwise to the microdroplet solution obtained in step (1) while stirring continuously (stirring speed is 500 rpm). After the mixture is evenly dispersed, add ammonia water to adjust the pH value of the system to 8. Heat the reaction at 40°C for 2 hours to allow the silane to undergo hydrolysis and condensation reaction. Then centrifuge the solution after the reaction to obtain the precipitate.

[0033] (3) The precipitate was washed with ethanol and then heated and dried for 2 hours at 60°C to obtain hollow silica microspheres.

[0034] The SEM image of the hollow silica microspheres obtained in this embodiment is as follows: Figure 1 As shown, the polydispersity index of the microspheres was calculated to be 1.0. The TEM image of the hollow silica microspheres obtained in this embodiment is shown below. Figure 2 As shown.

[0035] Example 2

[0036] This invention provides a monodisperse hollow silica microsphere, the preparation method of which includes the following steps:

[0037] (1) A silane with hydrophobic groups, vinyltriethoxysilane, was added to an acidic aqueous solution with a hydrogen ion concentration of 0.001 mol / L. The mixture was heated at 30 °C for 60 min with stirring. After the reaction was complete, ammonia was added to neutralize the system, resulting in a microdroplet solution with hydrophobic groups. The mass ratio of vinyltriethoxysilane to tetraalkoxysilane was 0.2:1. The mass ratio of the acidic aqueous solution to tetraalkoxysilane was 10:1.

[0038] (2) Add tetraethoxysilane dropwise to the microdroplet solution obtained in step (1) while stirring continuously (stirring speed is 200 rpm). After the mixture is evenly dispersed, add ammonia water to adjust the pH value of the system to 8. Heat the reaction at 30°C for 4 hours to allow the silane to undergo hydrolysis and condensation reaction. Then centrifuge the solution after the reaction to obtain the precipitate.

[0039] (3) The precipitate was washed with ethanol and then heated and dried for 2 hours at 60°C to obtain hollow silica microspheres.

[0040] The polydispersity index of the hollow silica microspheres obtained in this embodiment is 1.2.

[0041] Example 3

[0042] This invention provides a monodisperse hollow silica microsphere, the preparation method of which includes the following steps:

[0043] (1) A silane with hydrophobic groups, vinyltriethoxysilane, was added to an acidic aqueous solution with a hydrogen ion concentration of 0.1 mol / L. The mixture was heated at 60 °C for 10 min with stirring. After the reaction was complete, ammonia was added to neutralize the system, resulting in a solution of microdroplets with hydrophobic groups. The mass ratio of vinyltriethoxysilane to tetraethoxysilane was 0.2:1. The mass ratio of the acidic aqueous solution to tetraethoxysilane was 100:1.

[0044] (2) Add tetraethoxysilane dropwise to the microdroplet solution obtained in step (1) while stirring continuously (stirring speed is 1000 rpm). After the mixture is evenly dispersed, add ammonia water to adjust the pH value of the system to 10. Heat the system at 60°C for 1 hour to allow the silane to undergo hydrolysis and condensation reaction. Then centrifuge the solution after the reaction to obtain the precipitate.

[0045] (3) The precipitate was washed with ethanol and then heated and dried for 2 hours at 60°C to obtain hollow silica microspheres.

[0046] The polydispersity index of the hollow silica microspheres obtained in this embodiment is 1.8.

[0047] Finally, the method of this invention is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing monodisperse hollow silica microspheres, characterized in that, Includes the following steps: S1, a silane containing a hydrophobic group is added to an acidic aqueous solution, heated to react, and then the system is adjusted to neutral to obtain a microdroplet solution containing a hydrophobic group; the silane containing the hydrophobic group is vinyltriethoxysilane; the hydrogen ion concentration of the acidic aqueous solution is 0.001-0.1 mol / L; S2, add tetraalkoxysilane to the microdroplet solution obtained in step S1 while stirring. After mixing evenly, adjust the system to alkaline, heat to hydrolyze, centrifuge, collect the precipitate, wash and dry to obtain the product; the mass ratio of the silane containing the hydrophobic group to the tetraalkoxysilane is (0.2-1):1; the mass ratio of the acidic aqueous solution to the tetraalkoxysilane is (10-100):

1.

2. The preparation method according to claim 1, characterized in that, In step S2, the tetraalkoxysilane is tetraethoxysilane.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the silane containing the hydrophobic group to the tetraalkoxysilane is (0.2-0.3):

1.

4. The preparation method according to claim 1 or 2, characterized in that, In step S1, the temperature of the heating reaction is 30-60℃, and the heating reaction time is 10-60 min.

5. The preparation method according to claim 1 or 2, characterized in that, In step S2, the pH value of the system is 8-10.

6. The preparation method according to claim 1 or 2, characterized in that, In step S2, the hydrolysis temperature is 30-60℃ and the reaction time is 1-4h.

7. The preparation method according to claim 1 or 2, characterized in that, In step S2, the stirring speed is 50-1000 rpm.

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