A method for preparing mesoporous silica hollow spheres with ultra-high specific surface area

Abstract

The present invention relates to a method for preparing hollow mesoporous silica spheres with ultra-high specific surface area, comprising the following steps: (1) using ethylenediamine as a catalyst to prepare monodisperse silica spheres; (2) ultrasonically dispersing the obtained monodisperse silica spheres in a mixed solution of water and alcohol, adding concentrated ammonia water, resorcinol and formaldehyde solution in sequence, stirring at room temperature, and washing to obtain silica spheres with a surface coated with an RF layer; (3) dispersing the obtained silica spheres with a surface coated with an RF layer in water, placing them in a reactor for hydrothermal reaction; (4) drying and baking the product obtained in step (3) to obtain hollow mesoporous silica spheres with ultra-high specific surface area. The hollow mesoporous silica spheres of the present invention have an ultra-high specific surface area and a low breakage rate, and the preparation process thereof is highly controllable, simple, easy to operate, and low in cost, and has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of hollow sphere materials, and particularly relates to a preparation method of mesoporous silica hollow spheres with a super high specific surface area. Background Art

[0002] Mesoporous silica hollow spheres, as the most novel branch of hollow sphere materials, not only have an obvious hollow structure, but also have the unique high specific surface area, large pore volume, and uniform pore channels of mesoporous materials. Since both the hollow structure and the mesoporous structure can endow the material with the ability to accommodate guest molecules, and the unique mesoporous channels endow the material with the ability of molecular-scale transportation and mass transfer, mesoporous silica hollow spheres are widely used in systems such as biomedicine, pollutant molecule adsorption, and oil-water separation. Therefore, scientific researchers have great interest in the preparation field of mesoporous silica hollow spheres.

[0003] At present, there are various preparation methods for mesoporous silica hollow spheres, such as: the sacrificial template method and the soft template method. The soft template method is limited by the aggregation of template molecules and their assembly with silica precursors, so the synthesized mesoporous silica hollow spheres have uneven particle sizes. The sacrificial template method is to first purchase or prepare a sacrificial template with uniform particle size (such as polymer spheres), then grow a layer of mesoporous silica on its surface, and finally selectively remove the sacrificial template. This method has a simple process and uniform particle size, but due to the relatively harsh or fast process of selectively removing the sacrificial template, the breakage rate of the obtained mesoporous silica hollow spheres is too high. Therefore, only by continuously increasing the thickness of the mesoporous silica layer can the breakage rate be reduced, but this method increases the wall thickness of the hollow spheres, thereby reducing the specific surface area of the material. Therefore, it is of great significance to develop a simple synthesis method to prepare mesoporous silica hollow spheres with a super high specific surface area and a low breakage rate. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of mesoporous silica hollow spheres with a super high specific surface area, which has a super high specific surface area and a low breakage rate, and the preparation process has strong controllability, a simple process, convenient operation, low cost, and good application prospects.

[0005] The present invention provides a preparation method of mesoporous silica hollow spheres with a super high specific surface area, comprising the following steps:

[0006] (1) Dissolve the catalyst in a mixed solution of water and alcohol, and stir until a clear solution is obtained; add the organosilicon source to the clear solution and stir to obtain monodisperse silica spheres;

[0007] (2) The obtained monodisperse silica spheres are ultrasonically dispersed in a mixed solution of water and alcohol. Concentrated ammonia water, resorcinol, and formaldehyde solution are added in sequence, and the mixture is stirred at room temperature and washed to obtain silica spheres with an RF layer coated on the surface;

[0008] (3) The obtained silica spheres with an RF layer coated on the surface are dispersed in water and hydrothermally reacted in a reaction kettle;

[0009] (4) The product obtained in step (3) is dried and baked to obtain mesoporous silica hollow spheres with a super high specific surface area.

[0010] Preferably, the catalyst in step (1) is ethylenediamine, and the mass ratio of the catalyst to the organosilicon source is 0.25 - 2.0:1.

[0011] Preferably, the concentration of the catalyst in the clarified solution in step (1) is 0.5 - 5 wt%.

[0012] Preferably, the organosilicon source in step (1) is selected from one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

[0013] Preferably, the alcohol in the mixed solution of water and alcohol in steps (1) and (2) is selected from one or more of methanol, ethanol, propanol, and isopropanol, and the concentration of the alcohol in the mixed solution is 50 - 80 wt%.

[0014] Preferably, the mass ratio of the monodisperse silica spheres, concentrated ammonia water, resorcinol, and formaldehyde in step (2) is 0.1 - 0.25:0.25 - 0.5:0.05 - 0.1:0.05 - 0.1.

[0015] Preferably, the concentration of the concentrated ammonia water in step (2) is 25 - 30 wt%; the concentration of the formaldehyde solution is 35 - 40 wt%.

[0016] Preferably, the hydrothermal reaction temperature in step (3) is 90 - 180 °C, and the time is 0.5 - 48 h.

[0017] Preferably, the drying temperature in step (4) is 80 - 90 °C, and the drying time is 6 - 10 hours.

[0018] Preferably, the baking process parameters in step (4) are: rising from room temperature to 400 - 800 °C under air conditions and maintaining for 1 - 6 h.

[0019] The characteristic transmission electron microscope (TEM) images of the silica spheres (a) synthesized in the present invention and the silica spheres with an RF layer (b) coated are as Figure 1 shown, and are composed of Figure 1It can be seen that the particle size of the silica spheres is relatively uniform, and the RF layer coated on the surface is very thin, only about 30 nm, and relatively uniform.

[0020] Advantages

[0021] (1) In the present invention, a resorcinol-formaldehyde resin (RF) layer is coated on the surface of the silica spheres, and its functions are as follows: The RF layer acts as a protective layer to reduce the speed of water molecules entering the interior, effectively reducing the hydrolysis rate of the internal silica spheres and preventing the collapse of the surface shell layer due to the rapid disappearance of the spheres; The surface of the RF layer has a large number of oxygen-containing groups. When the oligomers generated by the hydrolysis of silica re-polymerize, the abundant oxygen-containing groups provide sufficient nucleation sites. Therefore, a new silica layer is re-formed on the surface of the RF particles; In the high-temperature calcination stage, the RF small particles are removed, but the silica formed on their surface continues to be preserved, and the places where the RF small particles are located become mesoporous channels.

[0022] (2) In the present invention, extremely strong alkaline ethylenediamine is used as a catalyst to synthesize silica spheres. Therefore, during the hydrothermal treatment, the internal silica components can be etched to obtain a hollow structure.

[0023] (3) The present invention adopts a hydrothermal etching method protected by an RF layer, without the addition of a template agent. Therefore, the operation is simple and the repetition rate is high, and it can be applied to large-scale industrial production. Description of the Drawings

[0024] Figure 1 are the characteristic transmission electron microscope (TEM) images of the silica spheres (a) synthesized by the present invention and the RF layer-coated (b).

[0025] Figure 2 are the characteristic transmission electron microscope (TEM) images of the mesoporous silica hollow spheres prepared in Example 1.

[0026] Figure 3 are the characteristic transmission electron microscope (TEM) images of the mesoporous silica hollow spheres prepared in Example 1.

[0027] Figure 4 are the characteristic transmission electron microscope (TEM) images of the mesoporous silica hollow spheres prepared in Comparative Example 1. Detailed Embodiments

[0028] The following combines specific embodiments to further illustrate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0029] Example 1

[0030] (1) Dissolve 6.0 g of ethylenediamine in a mixed solution of 20 mL of deionized water and 80 mL of ethanol, and stir evenly to form a colorless and transparent solution. The stirring speed of the above stirring can be selected from 250 - 1200 revolutions per minute, and the time can be controlled within 0.1 - 10 h; in this example, the selected stirring speed is 300 revolutions per minute and the time is 10 h. Slowly add 3 mL of propyl orthosilicate to the clarified solution.

[0031] (2) React the system in step (1) at room temperature for 12 h; after the reaction is completed, centrifuge to collect the precipitate and wash it 3 times with water to obtain monodisperse silica spheres.

[0032] (3) Take 100 mg of the monodisperse silica spheres produced in step (2), and ultrasonically disperse them in a mixed solution of 20 mL of ethanol and 10 mL of water. Sequentially add 0.25 g of concentrated ammonia water (28 wt%), 0.05 g of resorcinol, and 0.05 g of formaldehyde solution (37 wt%). Mechanically stir the mixture at room temperature for 1 h, and wash it three times with water to obtain silica spheres coated with an RF layer on the surface.

[0033] (4) Ultrasonically disperse the silica sphere material coated with the RF layer produced in step (3) in 20 mL of water, then place it in a hydrothermal reaction kettle at 100 °C for 12 h, and wash it 3 times with water to obtain a hollow sphere material.

[0034] (5) Place the hollow spheres produced in step (4) in an oven and dry them at 80 °C for 6 hours, then place them in an air atmosphere, raise the temperature from room temperature to 800 °C at a heating rate of 2 °C / min, and hold for 1 h to obtain a silica hollow sphere material, and its TEM image is as Figure 2 shown. The specific surface area of the hollow spheres exceeds 1500 m 2 / g, and the pore diameter is 2 - 6 nm.

[0035] Example 2

[0036] (1) Dissolve 2.0 g of ethylenediamine in a mixed solution of 50 mL of deionized water and 50 mL of ethanol, and stir evenly to form a colorless and transparent solution. The stirring speed of the above stirring can be selected from 250 - 1200 revolutions per minute, and the time can be controlled within 0.1 - 10 h; in this example, the selected stirring speed is 300 revolutions per minute and the time is 0.5 h. Slowly add 8 mL of tetraethyl orthosilicate to the clarified solution.

[0037] (2) React the system in step (1) at room temperature for 24 h; after the reaction is completed, centrifuge to collect the precipitate and wash it 3 times with water to obtain a monodisperse silica sphere material.

[0038] (3) Take 250 mg of the monodisperse silica sphere material produced in step (2), and ultrasonically disperse it in a mixed solution of 20 mL of ethanol and 10 mL of water. Sequentially add 0.5 g of concentrated ammonia water (28 wt%), 0.1 g of resorcinol, and 0.1 g of formaldehyde solution (37 wt%). The mixture is mechanically stirred at room temperature for 1 h and washed three times with water to obtain silica spheres coated with an RF layer on the surface.

[0039] (4) Ultrasonically disperse the silica sphere material coated with the RF layer produced in step (3) in 5 mL of water, then place it in a hydrothermal reactor at 180 °C for 12 h, and wash it three times with water to obtain a hollow sphere material.

[0040] (5) Place the hollow spheres produced in step (4) in an oven and dry them at 80 °C for 6 hours, then place them in an air atmosphere, raise the temperature from room temperature to 400 °C at a heating rate of 0.5 °C / min, and hold for 3 h to obtain a silica hollow sphere material, and its TEM image is as Figure 3 shown. The specific surface area of the hollow spheres exceeds 1500 m 2 / g, and the pore size is 2 - 6 nm.

[0041] Comparative Example 1

[0042] (1) Dissolve 6.0 g of ethylenediamine in a mixed solution of 20 mL of deionized water and 80 mL of ethanol, and stir evenly to form a colorless and transparent solution. The stirring speed of the above stirring can be selected from 250 - 1200 revolutions per minute, and the time can be controlled within 0.1 - 10 h; in this example, the selected stirring speed is 300 revolutions per minute and the time is 10 h. Slowly add 3 mL of propyl orthosilicate to the clarified solution.

[0043] (2) React the system in step (1) at room temperature for 12 h; after the reaction is completed, centrifuge to collect the precipitate and wash it three times with water to obtain a monodisperse silica sphere material.

[0044] (3) Ultrasonically disperse the silica sphere material produced in step (2) in 20 mL of water, then place it in a hydrothermal reactor at 100 °C for 12 h, and only a small amount of solid powder appears, and wash it three times with water.

[0045] (4) Place the powder produced in step (3) in an oven and dry it at 80 °C for 6 hours, then place it in an air atmosphere, raise the temperature from room temperature to 800 °C at a heating rate of 2 °C / min, and hold for 1 h to obtain ultra-small irregular small particles, and its TEM image is as Figure 4 shown, indicating that the RF layer is crucial for the generation of hollow spheres.

Claims

1. A method for preparing hollow mesoporous silica spheres with ultra-high specific surface area, characterized in that: The steps include: (1) dissolving a catalyst in a mixed solution of water and alcohol, and stirring to obtain a clear solution; adding an organosilicon source to the clear solution, and stirring to obtain monodisperse silica spheres; the catalyst is ethylenediamine; (2) ultrasonically dispersing the obtained monodisperse silica spheres in a mixed solution of water and alcohol, adding concentrated ammonia water, resorcinol and formaldehyde solution in sequence, stirring at room temperature, and washing to obtain silica spheres with a surface coated with an RF layer; (3) dispersing the obtained silica spheres coated with the RF layer in water and placing them in a reactor for hydrothermal reaction; (4) Drying and baking the product obtained in step (3) to obtain mesoporous silica hollow spheres with ultra-high specific surface area.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the catalyst to the organosilicon source in step (1) is 0.25-2.0:

1.

3. The preparation method according to claim 1, characterized in that: The concentration of the catalyst in the clarified solution in step (1) is 0.5-5wt%.

4. The preparation method according to claim 1, characterized in that: The organic silicon source in step (1) is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate.

5. The preparation method according to claim 1, characterized in that: The alcohol in the mixed solution of water and alcohol in steps (1) and (2) is selected from one or more of methanol, ethanol, propanol, and isopropanol, and the concentration of the alcohol in the mixed solution is 50-80 wt %.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the monodisperse silica spheres, concentrated ammonia water, resorcinol and formaldehyde in step (2) is 0.1-0.25:0.25-0.5:0.05-0.1:0.05-0.

1.

7. The preparation method according to claim 1, characterized in that: The concentration of the concentrated ammonia solution in step (2) is 25-30wt%; the concentration of the formaldehyde solution is 35-40wt%.

8. The preparation method according to claim 1, characterized in that: The hydrothermal reaction temperature in step (3) is 90-180° C. and the reaction time is 0.5-48 hours.

9. The preparation method according to claim 1, characterized in that: The drying temperature in step (4) is 80-90° C. and the drying time is 6-10 hours.

10. The preparation method according to claim 1, characterized in that: The baking process parameters in step (4) are: raising the temperature from room temperature to 400-800° C. under air conditions and maintaining it for 1-6 hours.

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