A multi-level porous submicron silica microsphere and its preparation method

Abstract

This invention proposes a hierarchical porous submicron silica microsphere and its preparation method. The preparation includes: (1) preparing a W / O type microemulsion; (2) adding a template agent to the oil phase mixture, heating and stirring until the template agent is completely dissolved; then slowly adding deionized water to form a reverse microemulsion; adding an alkaline catalyst; (3) slowly adding a mixture of pure silicon source reagent and functionalized silane reagent to the reverse microemulsion; (4) adding acetone to the microemulsion after further reaction and stirring; centrifuging to collect the white precipitate; washing; (5) drying and then calcining in an air atmosphere to obtain hierarchical porous submicron silica microsphere material. This invention adopts a one-pot method. In terms of preparation method, the reaction system simply involves adding different types of raw materials sequentially, followed by solid-liquid separation and post-processing. Therefore, the operation is simple, the reproducibility is high, and it can be applied to large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of silica microsphere technology, and in particular to a multi-level porous submicron silica microsphere and its preparation method. Background Technology

[0002] Silica microspheres, due to their excellent chemical stability, high specific surface area, and controllable particle size and pore structure, have shown broad application prospects in catalysis, adsorption separation, biomedicine, semiconductors, and optoelectronic devices. Among them, silica microspheres with multi-level pore structures can effectively shorten molecular diffusion paths and increase diffusion space through the synergistic effect of pores of different sizes, thereby further improving the performance of materials in adsorption and catalysis scenarios. Compared with single-pore silica microspheres, they have significant advantages and have therefore become a research hotspot in recent years.

[0003] Currently, existing methods for preparing hierarchical porous silica microspheres are mainly divided into two categories: soft template methods and hard template methods. Among them, the soft template method is the closest to the present invention and is the most widely used due to its relatively simple operation and strong controllability of pore structure. The soft template method mainly involves selecting soft templates of different sizes, utilizing the spatial confinement effect of the template to guide the polymerization and shaping of silica precursors, and then removing the template in a specific way to form channels of corresponding sizes inside the silica microspheres. The hard template method generally uses hard templates (such as polystyrene microspheres) as sacrificial templates to form macropores (usually several hundred nanometers) and soft templates (such as nonionic and cationic surfactants) as structure directing agents to form mesopores.

[0004] However, in existing technologies, most hierarchical porous silica microspheres only contain two pore sizes (e.g., mesopore-macropore, micropore-mesopore, and macro-mesopore-small mesopore). Even those few studies that have attempted to prepare three pore sizes mainly focus on macropore-macro-mesopore, failing to extend this to the micropore range. Consequently, they struggle to meet the stringent requirements for pore size and distribution in high-end catalysis and precise adsorption applications. Therefore, it is essential to develop a simple synthetic method to prepare silica microspheres with three pore structures. Summary of the Invention

[0005] This invention proposes a multi-level porous submicron silica microsphere and its preparation method, which solves the technical problem that silica microspheres with a three-level pore structure cannot be expanded into micropores in the prior art.

[0006] This invention also solves the technical problem that the current technology cannot accurately control the size and distribution of the three types of channels.

[0007] The technical solution of this invention is implemented as follows: A method for preparing hierarchical porous submicron silica microspheres, comprising: (1) Preparation of W / O type microemulsion: Add oil-soluble emulsifier and n-butanol to an organic solvent and stir until a homogeneous and transparent oil phase mixture is formed. (2) Add the template agent to the oil phase mixture, heat to 30-50℃, stir until the template agent is completely dissolved; then slowly add deionized water, the mixture changes from clear to milky white, forming a reverse microemulsion; at this time, slowly add an alkaline catalyst. (3) Under the condition of maintaining a temperature of 30-50℃ and continuous stirring, the mixture of pure silicon source reagent and silane reagent containing functional groups is slowly added dropwise to the reverse microemulsion; After the addition is complete, heat the system by 10-15°C and continue the reaction; (4) Add acetone to the microemulsion after the reaction continues, stir to destroy the microemulsion structure and cause the product to precipitate; collect the white precipitate by centrifugation; wash to remove residual oil phase, surfactant and solvent; (5) The washed precipitate is dried and then calcined in air to obtain multi-level porous submicron silica microspheres.

[0008] In some embodiments, the oil-soluble emulsifier is sorbitan monooleate.

[0009] In some embodiments, the organic solvent is selected from one or more of cyclohexane, n-hexane, decahydronaphthalene, and olefins.

[0010] In some embodiments, the stirring speed in step (1) is 300-500 rpm, and the selectable speed range is 300 rpm, 400 rpm, or 500 rpm.

[0011] In some embodiments, the ratio of the oil-soluble emulsifier, n-butanol, and organic solvent is 1g:1.5-3.5ml:20-70ml. The ratio of the oil-soluble emulsifier, n-butanol, and organic solvent is selected from any of the following ranges: 1g:1.5-2ml:20-30ml, 1g:2-3ml:30-50ml, 1g:3-3.5ml:50-70ml.

[0012] In some embodiments, the ratio of the template agent to the organic solvent is 0.5-1g:30-80ml. The ratio of the template agent to the organic solvent is selected from any of the following ranges: 0.5g:30-40ml, 1g:30-40ml, 1g:40-60ml, 1g:60-70ml.

[0013] In some embodiments, the volume ratio of the pure silicon source reagent to the functionalized silane reagent is 2-6:1. The volume ratio of the pure silicon source reagent to the functionalized silane reagent is selected from any of the following ranges: 2-3:1, 3-4:1, 4-5:1, 5-6:1.

[0014] In some embodiments, the volume ratio of the mixture of pure silicon source reagent and functionalized silane reagent to the reverse microemulsion is 1:20-70. The volume ratio of the mixture of pure silicon source reagent and functionalized silane reagent to the reverse microemulsion is selected from any of the following ranges: 1:20-30, 1:30-40, 1:40-50, 1:50-60, 1:60-70.

[0015] In some embodiments, the volume ratio of acetone to reverse microemulsion is 1:2.5-8. The volume ratio of acetone to reverse microemulsion is selected from any of the following ranges: 1:2.5-4, 1:4-6, 1:6-8.

[0016] In some embodiments, the template agent is selected from one or more quaternary ammonium cationic surfactants.

[0017] In some embodiments, the pure silicon source reagent is selected from one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

[0018] In some embodiments, the functional group-containing silane reagent is selected from one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, and epoxytrimethoxysilane.

[0019] In some embodiments, the alkaline catalyst is selected from one or more of ammonia and alcohol amines.

[0020] In some embodiments, the drying conditions are 50-70°C for more than 6 hours.

[0021] In some embodiments, the calcination conditions are as follows: the temperature is increased from room temperature to 400-800°C at a rate of 0.5-5°C / min, and maintained for more than 1 hour.

[0022] The present invention also provides multi-level porous submicron silica microspheres obtained by the above preparation method.

[0023] In some embodiments, the hierarchical submicron silica microspheres have a three-tiered pore structure consisting of micropores (≤ 2 nm), mesopores (2-50 nm), and macropores (≥ 50 nm).

[0024] The multi-level porous submicron silica microspheres prepared by this invention have the characteristics of high sphericity and mechanical stability.

[0025] Compared with the prior art, the present invention has the following advantages: (1) This invention uses a one-pot method to synthesize low-cost hierarchical porous silica microspheres. In terms of preparation method, the reaction system simply involves adding different types of raw materials one after another, followed by solid-liquid separation and post-processing. Therefore, the operation is simple, the reproducibility is high, and it can be applied to large-scale industrial production.

[0026] (2) This invention employs a W / O microemulsion system, in which the water core is encapsulated by a surfactant to form nanoscale droplets. Silica polymerizes on the surface of the droplets, and the droplets themselves act as "sacrificial templates," ultimately leaving macropores ≥ 50 nm inside the microspheres.

[0027] (3) This invention employs a W / O microemulsion system, in which quaternary ammonium cationic surfactants and some oil phase molecules self-assemble into micelles within the water core. Silica precursors assemble around these micelles, leaving a mesoporous structure after removal.

[0028] (4) The present invention introduces silane containing functional groups. When the functional groups are hydrolyzed and polycondensed, they will generate steric hindrance, resulting in insufficient density of the silica framework network, thus naturally forming micropores inside the framework.

[0029] (5) The microspheres prepared by this invention have regular morphology and mechanical stability, and can precisely control the three pore sizes and distributions. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a transmission electron microscope (TEM) image of the characteristics of the hierarchical porous silica microspheres in Example 1.

[0032] Figure 2 This is a pore size distribution diagram of the hierarchical porous silica microspheres in Example 1.

[0033] Figure 3 This is a transmission electron microscope (TEM) image of the characteristics of the hierarchical porous silica microspheres in Example 2.

[0034] Figure 4 This is a pore size distribution diagram of the hierarchical porous silica microspheres in Example 2. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Currently, there are not many preparations of hierarchical porous silica. The few reports in the literature mainly use soft-hard template methods, but their practicality is insufficient. The main reasons are: a) Insufficient adaptability of template systems: The size of existing template agents does not match the target pore size, and the compatibility of template agents of different sizes (templates corresponding to micropores, mesopores, and macropores) is poor. When mixed, they are prone to agglomeration and cannot be uniformly dispersed in the reaction system. As a result, the spatial confinement effect of the template agents cannot be accurately exerted, making it difficult to form pores of the three target sizes. For example, microporous templates are mostly small molecules, mesoporous templates are mostly surfactant micelles, and macroporous templates are mostly polymer microspheres. The size difference between the three is too large, and they are prone to stratification and agglomeration during dispersion, which cannot synergistically guide the formation of pores. b) Limitations in the reaction mechanism: The hydrolysis and polymerization rate of the silica precursor is difficult to synergistically match with the spatial confinement effect of the template agent. The guiding effect of the microporous template is easily affected by the steric hindrance of the mesoporous and macroporous templates, resulting in the inability of micropores to form uniformly within the microsphere framework. At the same time, the formation processes of mesopores and macropores interfere with each other, making it impossible to achieve precise control of the three pore sizes. c) Difficulty in maintaining the structure: During the template removal stage, high-temperature calcination or acid-base etching to remove hard templates (such as polymer microspheres and inorganic microspheres) can easily lead to stress differences within the silica microspheres, causing microsphere cracking and breakage, and reducing their mechanical stability. d) Complex preparation process and high cost: It often requires the use of multiple expensive template agents (such as special block copolymers and polymer microspheres), and the amount of template agent used is large. The subsequent template removal process requires high temperature, strong acid, organic solvents, etc., which not only increases the preparation cost but also has problems of high energy consumption and environmental pollution. At the same time, the process steps are cumbersome, the reaction parameters are difficult to control, and the repeatability is poor, making it difficult to achieve large-scale industrial production.

[0037] Example 1 A method for preparing hierarchical porous submicron silica microspheres includes the following steps: (1) Preparation of W / O type microemulsion: Add 30 mL of n-hexane to a round-bottom flask, then add 1 g of sorbitan monooleate (Span-80, an oil-soluble emulsifier) ​​and 2 mL of n-butanol to the emulsion system. Stir at 300 rpm for 30 minutes at room temperature until a homogeneous and transparent oil phase mixture is formed.

[0038] (2) Introducing mesoporous templates and catalysts Introduce a mesoporous template: Weigh 0.5 g of dodecyltrimethylammonium chloride and add it to the above oil phase mixture. Heat to 40°C and continue stirring for 1 hour to ensure complete dissolution.

[0039] Introduce the water core: Slowly add 2.5 mL of deionized water. The system will then undergo a transformation from clear to milky white, forming a reverse microemulsion.

[0040] Introduce a catalyst: Slowly add 0.4 mL of ammonia water.

[0041] (3) Silicon source hydrolysis and cocondensation While maintaining a constant temperature of 40°C and stirring continuously, a mixture of 1 mL tetraethyl orthosilicate and 0.5 mL ethyltrimethoxysilane was slowly added dropwise to the above microemulsion. After the addition was complete, the system was heated to 60°C and reacted for 24 hours.

[0042] (4) Solid-liquid separation Add 5 mL of acetone to the system and stir for 30 minutes to disrupt the microemulsion structure and precipitate the product. Collect the white precipitate by centrifugation (8000 rpm). Wash the precipitate three times with ethanol to remove residual oil phase, surfactant, and solvent.

[0043] (5) Post-processing The silica microspheres were dried in a vacuum oven at 60℃ for 12 hours. Then, under an air atmosphere, the temperature was increased from room temperature to 500℃ at a rate of 1℃ / min and maintained for 3 hours to obtain hierarchical porous silica microspheres. Nitrogen adsorption-desorption tests showed that the pore sizes were 0.9 nm, 23.1 nm, and 64.4 nm. The microspheres exhibited regular morphology and mechanical stability.

[0044] Example 2 A method for preparing hierarchical porous submicron silica microspheres includes the following steps: (1) Add 70 mL of cyclohexane to a round-bottom flask, then add 1 g of sorbitan monooleate (Span-80, an oil-soluble emulsifier) ​​and 3.5 mL of n-butanol to the emulsion system. Stir at 300 rpm for 30 minutes at room temperature until a homogeneous and transparent oil phase mixture is formed.

[0045] (2) Weigh 1g of hexadecyltrimethylammonium bromide and add it to the above oil phase mixture. Heat the mixture to 40°C and continue stirring for 1 hour to ensure complete dissolution.

[0046] (3) Slowly add 5 mL of deionized water. At this time, the system will undergo a transformation from clear to milky white, forming a reverse microemulsion. Then slowly add 0.8 mL of triethanolamine.

[0047] (4) While maintaining a constant temperature of 40°C with continuous stirring, slowly add a mixture of 1 mL methyl orthosilicate and 0.2 mL phenyltrimethoxysilane to the above microemulsion. After the addition is complete, heat the system to 60°C and react for 24 hours.

[0048] (5) Add 20 mL of acetone to the system and stir for 30 minutes to disrupt the microemulsion structure and precipitate the product. Collect the white precipitate by centrifugation (8000 rpm). Wash the precipitate three times with ethanol to remove residual oil phase, surfactant and solvent.

[0049] (5) Dry in a vacuum drying oven at 60℃ for 12 hours. Then place in an air atmosphere and raise the temperature from room temperature to 800℃ at a rate of 5℃ / min and hold for 1 hour to obtain hierarchical porous silica microspheres. The nitrogen adsorption-desorption test results show that the pore sizes are 1.4nm, 30.6nm and 82.2nm, respectively.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 hierarchically porous submicron silica microspheres, characterized in that, include: (1) Preparation of W / O type microemulsion: Add oil-soluble emulsifier and n-butanol to an organic solvent and stir until a homogeneous and transparent oil phase mixture is formed. (2) Add the template agent to the oil phase mixture, heat to 30-50℃, stir until the template agent is completely dissolved; then slowly add deionized water, the mixture changes from clear to milky white, forming a reverse microemulsion; at this time, slowly add an alkaline catalyst. (3) Under the condition of maintaining a temperature of 30-50℃ and continuous stirring, the mixture of pure silicon source reagent and silane reagent containing functional groups is slowly added dropwise to the reverse microemulsion; After the addition is complete, heat the system by 10-15°C and continue the reaction for at least 6 hours. (4) Add acetone to the microemulsion after the reaction continues, stir to destroy the microemulsion structure and cause the product to precipitate; collect the white precipitate by centrifugation; wash to remove residual oil phase, surfactant and solvent; (5) The washed precipitate is dried and then calcined in air to obtain multi-level porous submicron silica microspheres.

2. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The oil-soluble emulsifier is sorbitan monooleate.

3. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The organic solvent is selected from one or more of cyclohexane, n-hexane, decahydronaphthalene, and olefins.

4. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The template agent is selected from one or more of the quaternary ammonium salt cationic surfactants.

5. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The pure silicon source reagent is selected from one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

6. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The functional group-containing silane reagent is selected from one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, and epoxytrimethoxysilane.

7. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The alkaline catalyst is selected from one or more of ammonia and alcohol amines.

8. The method for preparing multi-level porous submicron silica microspheres according to claim 1, characterized in that, The calcination conditions are as follows: the temperature is raised from room temperature to 400-800℃ at a rate of 0.5-5℃ / min, and maintained for more than 1 hour.

9. A hierarchical porous submicron silica microsphere, characterized in that, The multi-level porous submicron silica microspheres are prepared by the preparation method according to any one of claims 1-8.

10. The hierarchical porous submicron silica microsphere according to claim 9, characterized in that, The multi-level porous submicron silica microspheres have a three-tiered pore structure: micropores ≤ 2 nm, mesopores 2-50 nm, and macropores ≥ 50 nm.

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