Preparation method of hollow SiO2 microspheres with uniform size

Abstract

The invention belongs to the field of microsphere material synthesis, and particularly relates to a preparation method of hollow SiO2 microspheres with uniform size. The method comprises the following steps: by taking polyacrylic acid and ammonia water as raw materials, carrying out ultrasonic treatment, stirring, standing and the like, dripping a mixed solution into absolute ethyl alcohol A, stirring, and adding absolute ethyl alcohol B to form sol; uniformly mixing tetraethyl orthosilicate and absolute ethyl alcohol, then dropwise adding the sol, and after the reaction is completed, performing centrifugation, deionized water ultrasonic treatment and centrifugation again to obtain the hollow SiO2 microspheres. By accurately controlling the addition amount of polyacrylic acid, ammonia water, absolute ethyl alcohol and tetraethyl orthosilicate, setting ultrasonic time and stirring speed, adding absolute ethyl alcohol in batches and controlling parameters such as the dripping rate of a tetraethyl orthosilicate mixed solution, the problem that the particle size uniformity is difficult to regulate and control in the process of preparing the hollow SiO2 microspheres by an existing soft template method is effectively solved; good application prospects are realized in the field of materials.

Description

Technical Field

[0001] The invention belongs to the field of microsphere material synthesis, and in particular relates to a method for preparing hollow SiO2 microspheres with uniform size. Background Art

[0002] In the field of materials research, hollow silica (SiO2) microspheres with uniform particle size have significant application value in biomedicine, catalysis science, optical devices, and other fields due to their unique structural properties. For example, in targeted drug delivery systems, the hollow structure can achieve high drug molecule loading and controlled release performance; in the field of heterogeneous catalysis, their regular cavities and large specific surface area can provide optimized mass transfer pathways and active sites for catalytic reactions; and in the construction of photonic crystals, the uniform size of hollow microspheres can help form ordered optical structures to control light scattering behavior.

[0003] Currently, the template method is the mainstream technology for preparing hollow SiO2 microspheres, which is mainly divided into two categories: hard template method and soft template method. Although the hard template method can achieve structural controllability, it generally has problems such as complex template removal process and residual impurities affecting performance.

[0004] The soft template method, based on dynamic template systems such as surfactant micelles and polymer self-assemblies, offers advantages such as simplicity and environmental friendliness. However, due to the variability of soft templates in existing technologies, the resulting hollow microspheres generally exhibit poor size uniformity. For example, hollow SiO2 particles synthesized using the soft template method, as reported in Chinese patent CN202411158316.3, the papers "Preparation of low-density organosilica monoliths containing hollow silica nanospheres as thermal insulation materials," and "Influence of the PAA concentration on PAA / NH3 emulsion template method for synthesizing hollow silica nanoparticles," all exhibit poor size uniformity. Summary of the Invention

[0005] Based on the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing hollow SiO2 microspheres with uniform size, which can be synthesized using a soft template.

[0006] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing hollow SiO2 microspheres of uniform size, comprising the following steps: S1. Dissolve polyacrylic acid in ammonia water, then sonicate for 10-15 min, stir for 2 h, and let stand for 24 h to obtain a mixed solution; S2, adding the mixed solution in step S1 dropwise into anhydrous ethanol A, and then stirring for 4 h, and then adding anhydrous ethanol B, and stirring for another 10-30 min to form a sol; S3, adding tetraethyl orthosilicate to anhydrous ethanol and stirring evenly, then adding dropwise to the sol in step S2 while stirring. After the addition is complete, react for 8 to 12 hours to obtain a sol that has completed the reaction; S4. Centrifuge the sol after the reaction in step S3, then add deionized water, sonicate, and centrifuge again to obtain hollow SiO2 microspheres.

[0007] As an improved technical solution of the present application, the amounts of polyacrylic acid and ammonia water added in step S1 are 3 parts by mass and 33 parts by mass, respectively; In step S2, the added amounts of anhydrous ethanol A and anhydrous ethanol B are 300-400 parts by mass and 300 parts by mass, respectively; In step S3, the added amounts of tetraethyl orthosilicate and anhydrous ethanol are 3 to 6 parts by mass and 100 parts by mass, respectively; The amount of deionized water added in step S4 is 50 parts by mass.

[0008] As an improved technical solution of the present application, the stirring speed in step S2 is 800~1000 r / min; the stirring speed of the simultaneous stirring in step S3 is 300~400 r / min.

[0009] As an improved technical solution of the present application, the mixed solution of tetraethyl orthosilicate and anhydrous ethanol in step S3 is continuously added dropwise for 3 to 4 hours.

[0010] As an improved technical solution of this application, the average size of the hollow SiO2 microspheres is 286.4~308.2nm, and the coefficient of variation of the particles is 1.39%~2.08%. The beneficial effects of the present invention compared to the prior art are: In response to the key problem of difficulty in controlling the uniformity of particle size when preparing hollow SiO2 microspheres using the existing soft template method, the present invention effectively controls the dispersion and polymerization process of substances in the reaction system by precisely adjusting the ultrasound and stirring speeds and adopting unique process parameter settings such as adding anhydrous ethanol in batches. Hollow SiO2 microspheres with uniform size can be stably prepared, and the coefficient of variation (CV) of the particles of the hollow SiO2 microspheres is 1.39%~2.08%. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1: is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Example 1; Figure 2 This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 1; Figure 3 This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 2; Figure 4 This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 3; Figure 5 This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 4. DETAILED DESCRIPTION

[0012] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0013] In this article: anhydrous ethanol A, anhydrous ethanol B and anhydrous ethanol are all commercially available ethanol with a purity greater than 99.7%, and the concentration of ammonia water is 25.0-28.0%.

[0014] A method for preparing hollow SiO2 microspheres of uniform size comprises the following steps: S1. Dissolve polyacrylic acid in ammonia water (NH3·H2O), then sonicate for 10-15 minutes, stir for 2 hours, and let stand for 24 hours to obtain a mixed solution; the added amounts of polyacrylic acid and ammonia water are 3 parts by mass and 33 parts by mass, respectively; the sonication in step S1 can make the polyacrylic acid and ammonia water mix more uniformly, thereby forming a more uniform micelle template.

[0015] S2. The mixed solution from step S1 is added dropwise to anhydrous ethanol A, followed by stirring for 4 hours. Anhydrous ethanol B is then added and stirred for an additional 10-30 minutes to form a sol; the amounts of anhydrous ethanol A and anhydrous ethanol B added are 300-400 parts by mass and 300 parts by mass, respectively. Experiments have shown that when an excessive amount of anhydrous ethanol is added, the resulting particle size uniformity is poor, indicating that the micelle template formed with a large amount of anhydrous ethanol is less uniform. Adding a small amount of anhydrous ethanol, on the other hand, results in an excessively high ammonia concentration in the system, accelerating the reaction and making it difficult to form hollow particles. Therefore, a portion of anhydrous ethanol is added during the micelle template formation reaction. After the micelle template is formed, additional anhydrous ethanol is added to reduce the ammonia concentration in the system.

[0016] S3. Add tetraethyl orthosilicate to anhydrous ethanol and stir evenly, then add dropwise to the sol in step S2 while stirring. After the addition is complete, react for another 8-12 hours; the added amounts of tetraethyl orthosilicate and anhydrous ethanol are 3-6 parts by mass and 100 parts by mass, respectively.

[0017] S4. Centrifuging the sol after the reaction in step S3, then adding deionized water, sonicating, and centrifuging again to obtain hollow SiO2 microspheres; the amount of deionized water added is 50 parts by mass. The hollow SiO2 grows on a soft template. To obtain the hollow SiO2, the template needs to be removed. The template is soluble in water. Adding water for washing can dissolve the internal template, thereby forming a hollow structure.

[0018] Preferably, the stirring speed in step S2 is 800-1000 r / min; the stirring speed during the simultaneous stirring in step S3 is 300-400 r / min. Step S2 is the process of forming the micelle template, and the reaction time is short, so rapid stirring is required to ensure a more uniform formation of the stirring template. However, in the subsequent growth of SiO2, the reaction time is longer, and prolonged rapid stirring will increase the number of particle collisions. Small particles have higher surface energy, and this increased number of collisions can lead to aggregation.

[0019] Preferably, the mixed solution of tetraethyl orthosilicate and anhydrous ethanol in step S3 is continuously added dropwise for 3 to 4 hours.

[0020] The present invention also provides hollow SiO2 microspheres with uniform size, wherein the average size of the hollow SiO2 microspheres is 286.4-308.2 nm, and the coefficient of variation (CV) of the particles is 1.39%-2.08%.

[0021] The present invention is described below by means of specific examples and comparative examples.

[0022] In the following examples, polyacrylic acid was obtained from Sinopharm Chemical Reagent Co., Ltd. (model: Wokai, Mw ~5000), aqueous ammonia was obtained from Sinopharm Chemical Reagent Co., Ltd. (model: GR (Shanghai trial), 25.0%-28.0%), and tetraethyl orthosilicate was obtained from Sinopharm Chemical Reagent Co., Ltd. (model: AR (Shanghai trial)). Example 1

[0023] This embodiment provides a method for preparing hollow SiO2 microspheres of uniform size, and the preparation steps are as follows: S1. Dissolve 3 parts by mass of polyacrylic acid in 33 parts by mass of aqueous ammonia, then sonicate for 10 minutes, stir for 2 hours, and allow to stand for 24 hours to obtain a mixed solution; S2, dropping the mixed solution in step S1 into 300 parts by mass of anhydrous ethanol (anhydrous ethanol A), stirring at a stirring speed of 800 r / min for 4 hours, then adding 300 parts by mass of anhydrous ethanol (anhydrous ethanol B), and stirring for another 10 minutes to form a sol; S3, adding 3 parts by mass of tetraethyl orthosilicate to 100 parts by mass of anhydrous ethanol and stirring uniformly, then adding the mixture dropwise to the sol in step S2, while stirring the sol in step S2 at a stirring speed of 300 r / min; the mixed solution of tetraethyl orthosilicate and anhydrous ethanol was continuously added dropwise for 3 h, and after the addition was completed, the mixture was reacted for another 8 h; S4. Centrifuge the sol after the reaction in step S3, then add 50 parts by mass of deionized water, sonicate, and centrifuge again to obtain hollow SiO2 microspheres. Example 2

[0024] This embodiment provides a method for preparing hollow SiO2 microspheres of uniform size, and the preparation steps are as follows: S1. Dissolve 3 parts by mass of polyacrylic acid in 33 parts by mass of aqueous ammonia, then sonicate for 12 minutes, stir for 2 hours, and allow to stand for 24 hours to obtain a mixed solution; S2, dropping the mixed solution in step S1 into 350 parts by mass of anhydrous ethanol (anhydrous ethanol A), stirring at a stirring speed of 900 r / min for 4 hours, then adding 300 parts by mass of anhydrous ethanol (anhydrous ethanol B), and stirring for another 20 minutes to form a sol; S3, adding 4 parts by mass of tetraethyl orthosilicate to 100 parts by mass of anhydrous ethanol and stirring uniformly, then adding the mixture dropwise to the sol in step S2, while stirring the sol in step S2 at a stirring speed of 350 r / min, and continuously adding the mixed solution of tetraethyl orthosilicate and anhydrous ethanol dropwise for 3.5 hours. After the addition is completed, the mixture is reacted for another 10 hours; S4. Centrifuge the sol after the reaction in step S3, then add 50 parts by mass of deionized water, sonicate, and centrifuge again to obtain hollow SiO2 microspheres. Example 3

[0025] This embodiment provides a method for preparing hollow SiO2 microspheres of uniform size, and the preparation steps are as follows: S1. Dissolve 3 parts by mass of polyacrylic acid in 33 parts by mass of aqueous ammonia, then sonicate for 15 min, stir for 2 h, and let stand for 24 h. S2, dropping the mixed solution in step S1 into 400 parts by mass of anhydrous ethanol (anhydrous ethanol A), stirring at a stirring speed of 1000 r / min for 4 hours, then adding 300 parts by mass of anhydrous ethanol (anhydrous ethanol B), and stirring for another 30 minutes to form a sol; S3, adding 6 parts by mass of tetraethyl orthosilicate to 100 parts by mass of anhydrous ethanol and stirring uniformly, then adding the mixture dropwise to the sol in step S2, while stirring the sol in step S2 at a stirring speed of 400 r / min, and continuously adding the mixed solution of tetraethyl orthosilicate and anhydrous ethanol dropwise for 4 h. After the addition is completed, the mixture is reacted for another 12 h; S4. Centrifuge the sol after the reaction in step S3, then add 50 parts by mass of deionized water, sonicate, and centrifuge again to obtain hollow SiO2 microspheres. Comparative Example 1

[0026] Refer to Example 1, except that there is no ultrasonic treatment in step S1. Comparative Example 2

[0027] Refer to Example 1, except that: in step S2, the mixed solution in step S1 is directly dropped into 600 parts by mass of anhydrous ethanol A, and no anhydrous ethanol B is added subsequently. Comparative Example 3

[0028] Refer to Example 1, except that: in step S2, the mixed solution in step S1 is directly dropped into 300 parts by mass of anhydrous ethanol A, and no anhydrous ethanol B is added subsequently. Comparative Example 4

[0029] Refer to Example 1, except that: in step S2, the stirring speed is 500 r / min.

[0030] Analyze the experimental data of the embodiment and the comparative example. Figure 1 1 is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Example 1. As can be seen from the figure, the present invention synthesized hollow SiO2 microspheres of uniform size by the soft template method.

[0031] Figure 2 This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 1. It can be seen that the size uniformity of the prepared microspheres is poor. This indicates that the ultrasound in step S1 has an impact on the size uniformity.

[0032] Figure 3 This is a transmission electron micrograph of the hollow SiO2 microspheres prepared in Comparative Example 2. It can be seen that the size uniformity of the prepared microspheres is poor. This indicates that the hollow SiO2 microspheres synthesized by directly adding the mixed solution of polyacrylic acid and ammonia to 600 mL of anhydrous ethanol have poor size.

[0033] Figure 4This is a transmission electron microscope photograph of the hollow SiO2 microspheres prepared in Comparative Example 3. It can be seen that many SiO2 particles with open pore structures are formed, which indicates that adding only 300 mL of anhydrous ethanol in step S2 can easily form particles with open pore structures.

[0034] from Figure 1 、 Figure 3 and Figure 4 This comparison shows that in step S2, when adding the mixed solution of polyacrylic acid and ammonia to anhydrous ethanol, it is necessary to first add a portion of anhydrous ethanol, then a portion. Directly adding all of the anhydrous ethanol results in poorly uniform hollow SiO2 particles, while adding only the first portion of anhydrous ethanol results in open-pore SiO2 particles. This is because the micelle template formed with the first portion of anhydrous ethanol is more uniform, but the ammonia content is too high. After the addition of tetraethyl orthosilicate, the catalytic rate is too fast, resulting in the formation of open-pore SiO2 particles. Therefore, it is necessary to wait until the micelles are stable before adding anhydrous ethanol.

[0035] Figure 5 This is a transmission electron micrograph of the hollow SiO2 microspheres prepared in Comparative Example 4. It can be seen that the size uniformity of the prepared microspheres is poor. This indicates that the stirring speed of the polyacrylic acid and ammonia solution added to anhydrous ethanol also affects the uniformity of the final synthesized microspheres.

[0036] In the comparative examples, the particle uniformity is relatively poor, so the average size is not very meaningful.

[0037] Table 1 Average particle size and coefficient of variation of hollow SiO2 particles prepared in Examples 1 to 3 and Comparative Examples 1 to 4

[0038] It can be seen from the table that the average size of the hollow SiO2 particles prepared by the present invention is 286.4~308.2nm, and the variation coefficients of Examples 1~3 and Comparative Examples 1~3 can be compared. The variation coefficients of Examples 1~3 are smaller, with a maximum of 2.08%, which indicates that the uniformity of the synthesized hollow SiO2 particles is better, while the variation coefficient of the particles in the comparative example is larger and the size uniformity is poor. Figures 1 to 4 It can also be seen intuitively.

[0039] The coefficient of variation (CV) is a relative indicator to measure the degree of data dispersion. The calculation formula is: coefficient of variation (CV) = (standard deviation ÷ mean) × 100%.

[0040] In summary, the present invention synthesized hollow SiO2 microspheres of uniform size by adjusting parameters such as ultrasound, stirring speed, and adding anhydrous ethanol in batches during the operation process.

[0041] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing hollow SiO2 microspheres of uniform size, characterized in that: The following steps are involved: S1. Dissolve polyacrylic acid in ammonia water, then sonicate for 10-15 min, stir for 2 h, and let stand for 24 h to obtain a mixed solution; S2, adding the mixed solution in step S1 dropwise into anhydrous ethanol A, and then stirring for 4 h, and then adding anhydrous ethanol B, and stirring for another 10-30 min to form a sol; S3, adding tetraethyl orthosilicate to anhydrous ethanol and stirring evenly, then adding dropwise to the sol in step S2 while stirring. After the addition is complete, react for 8 to 12 hours to obtain a sol that has completed the reaction; S4. Centrifuge the sol after the reaction in step S3, then add deionized water, sonicate, and centrifuge again to obtain hollow SiO2 microspheres.

2. The method for preparing hollow SiO2 microspheres of uniform size according to claim 1, wherein: The amounts of polyacrylic acid and ammonia added in step S1 are 3 parts by mass and 33 parts by mass, respectively; In step S2, the added amounts of anhydrous ethanol A and anhydrous ethanol B are 300-400 parts by mass and 300 parts by mass, respectively; In step S3, the added amounts of tetraethyl orthosilicate and anhydrous ethanol are 3 to 6 parts by mass and 100 parts by mass, respectively; The amount of deionized water added in step S4 is 50 parts by mass.

3. The method for preparing hollow SiO2 microspheres of uniform size according to claim 1, wherein: The stirring speed in step S2 is 800-1000 r / min; the stirring speed of the simultaneous stirring in step S3 is 300-400 r / min.

4. The method for preparing hollow SiO2 microspheres of uniform size according to claim 1, wherein: The mixed solution of tetraethyl orthosilicate and anhydrous ethanol in step S3 is continuously added dropwise for 3 to 4 hours.

5. The method for preparing hollow SiO2 microspheres of uniform size according to any one of claims 1 to 4, characterized in that: The average size of the obtained hollow SiO2 microspheres was 286.4~308.2nm, and the coefficient of variation of the particles was 1.39%~2.08%.

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