Self-supporting hollow SiO2 nanospheres and a method for preparing the same

Abstract

The application belongs to the field of nanometer materials, and relates to a self-supporting hollow SiO2 nanosphere and a preparation method thereof. The application uses ZnS nanospheres with pore structures as templates, performs SiO2 coating on surfaces of the templates, obtains ZnS-SiO2 core-shell structure nanospheres, and then removes ZnS cores through an acid etching method to obtain the self-supporting hollow SiO2 nanospheres, the preparation method has low cost and simple operation, and the template does not need to be removed through high-temperature annealing, so that the problems of particle aggregation and dispersion difficulty after annealing are solved, the prepared hollow SiO2 nanospheres are uniform in size, the self-supporting structure can avoid the situation of shell breakage in a centrifugal process, and the structure is more stable than that of common hollow SiO2 spheres.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and relates to a self-supporting hollow SiO2 nanosphere and its preparation method. Background Technology

[0002] SiO2, a transparent material with a low dielectric constant and a refractive index of 1.46, possesses excellent optical properties, superior mechanical properties, and chemical stability. It is also abundant and inexpensive, making it widely applicable in semiconductor processing, high-temperature ceramics, optical materials, coatings, and silicone rubber. In recent years, hollow materials with specific structures and different morphologies have attracted considerable attention. Among them, hollow SiO2 nanospheres, as a novel inorganic material, exhibit good stability, high melting point, large specific surface area, and excellent optical properties, demonstrating significant application value in thermal insulation coatings, optical nanodevices, drug delivery, and bioimaging. However, the preparation of hollow SiO2 nanospheres faces several challenges, such as high synthesis costs, complex operations, uneven particle size and wall thickness, and poor particle dispersion.

[0003] There are many methods for preparing hollow SiO2 nanospheres, with the template method being the most commonly used. The template method uses organic polymers or inorganic materials as templates, coating the surface with a SiO2 shell, and then removing the template through chemical solvent treatment or high-temperature calcination to obtain a hollow structure. The choice of template has the most direct and profound impact on the morphology and structure of the final product. For example, existing technology (Ceramics International 49(2023)6805–6810) uses polyacrylic acid (PAA) as a template, forming a PAA / SiO2 core-shell structure via a sol-gel method; subsequently, high-temperature calcination removes the PAA, yielding hollow SiO2 nanospheres with an average particle size of 50 nm and a shell thickness of approximately 20 nm. Although this method can successfully prepare hollow SiO2 nanospheres with good structure and morphology, the organic polymer templates used are expensive, and the synthesized particles have a low degree of hollowness. Furthermore, for hollow SiO2 materials, the greater the degree of hollowness and the thinner the shell, the easier the structure is to collapse, which will greatly limit its application scenarios and service life. Therefore, it is of great significance to prepare hollow SiO2 materials with highly stable structures. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing hollow SiO2 nanospheres with a highly stable structure. These hollow SiO2 nanospheres have uniform size, stable structure, and are not easily collapsed, and are expected to be applied in fields such as optical films, biochemistry, and construction.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing hollow SiO2 nanospheres with a highly stable structure, comprising the following steps:

[0006] S1. Add thiourea and zinc acetate to deionized water and stir until completely dissolved. Then add polyvinylpyrrolidone (PVP) and stir thoroughly to obtain a mixed solution. Transfer the mixed solution to a reaction vessel and seal it. React at 120℃~150℃ for 4~6h and then cool naturally to room temperature. Wash the reaction product to obtain monodisperse ZnS nanospheres with internal pore structures and a diameter of 30~300nm.

[0007] S2. Weigh the ZnS nanospheres obtained in step S1 and add them to anhydrous ethanol for ultrasonic dispersion. While stirring at room temperature, add PVP, 13-15 mol / L ammonia and deionized water in sequence. After stirring thoroughly, obtain solution A.

[0008] Separately, add tetraethyl orthosilicate (TEOS) to anhydrous ethanol and stir at room temperature; this solution is denoted as solution B.

[0009] Solution B was slowly added dropwise to solution A, wherein the mass ratio of ZnS nanospheres in solution A to TEOS in solution B was 1:(1.9–4.6). After reacting at room temperature and aging, the reaction product was washed to obtain core-shell structured nanospheres with ZnS nanospheres as the core and SiO2 as the outer shell, with a shell thickness of 10–50 nm and an outer diameter of 40–350 nm.

[0010] S3. Disperse the core-shell structured nanospheres obtained in step S2 in anhydrous ethanol, then add acid etching solution, stir and react at a constant temperature of 20℃~30℃ for 2~3 days, wash the reaction product to obtain hollow SiO2 nanospheres with a self-supporting internal structure and an outer diameter of 40~350nm.

[0011] Further improvements to the preparation method of hollow SiO2 nanospheres with highly stable structures:

[0012] Preferably, in step S1, the mass ratio of deionized water, thiourea, zinc acetate, and PVP is 25:(2.85~5.70):0.22:0.75.

[0013] Preferably, in step S2, the mass ratio of ZnS nanospheres, anhydrous ethanol, PVP, ammonia, and deionized water constituting solution A is 0.5:30:0.5:1.8:2.

[0014] Preferably, in step S2, after slowly adding solution B to solution A, the mixture is reacted at room temperature for 7-9 hours and then aged for 3-7 days.

[0015] Preferably, the room temperature is 20℃~30℃.

[0016] Preferably, the reaction products in steps S1, S2 and S3 are washed sequentially by centrifugation with deionized water and anhydrous ethanol to remove residual reaction solution.

[0017] Preferably, in step S3, the mass ratio of the core-shell structured nanospheres dispersed in anhydrous ethanol is 1:5.

[0018] Preferably, in step S2, the preparation of solution A and the reaction between solution A and solution B are carried out under water bath conditions of 20℃~30℃, and the stirring speed is set to 750~1000r / min.

[0019] The acid etching solution in step S3 is a 0.5-1 mol / L hydrochloric acid solution.

[0020] The second objective of this invention is to provide a method for preparing hollow SiO2 nanospheres with a highly stable structure as described in any one of the above-mentioned methods, resulting in hollow SiO2 nanospheres with a highly stable structure.

[0021] The advantages of this invention compared to the prior art are as follows:

[0022] 1) This invention uses porous ZnS nanospheres as templates, coating their surfaces with SiO2 to obtain ZnS-SiO2 core-shell nanospheres. The ZnS core is then removed by acid etching to obtain hollow SiO2 nanospheres with an internal self-supporting structure. This design is based on the fact that the surface of nano-ZnS is rich in amino groups and carries a positive charge, while the surface of nano-SiO2 is rich in hydroxyl groups and carries a negative charge. Therefore, under the electrostatic attraction of the positive and negative charges, the stable ZnS nanoparticles dispersed in the solution will adsorb a large number of in-situ generated SiO2 nanoparticles, forming composite microspheres of ZnS and SiO2. Furthermore, this invention uses polyvinylpyrrolidone (PVP) as a modifier. On the one hand, PVP coating the surface of the ZnS nanospheres reduces the surface energy of the nanoparticles, reduces particle aggregation, and ensures that ZnS is uniformly and stably dispersed in the solvent. On the other hand, the PVP molecular structure contains a large number of carbonyl groups, which easily combine with the hydroxyl groups in SiO2, which also facilitates the formation of the ZnS-SiO2 core-shell structure. Furthermore, this invention uses ZnS nanospheres prepared by a hydrothermal method. These nanospheres have internal pores, which are used as templates. When coating the surface with SiO2 using the sol-gel method, the SiO2 sol can penetrate into the interior of the ZnS nanospheres. Therefore, after acid etching, the small amount of SiO2 filling the pores inside the ZnS nanospheres is retained, resulting in hollow SiO2 nanospheres with a self-supporting structure. The method is simple and reproducible. Using ZnS nanospheres as an inorganic template is more cost-effective and has better shape retention than organic templates, resulting in more uniform size of the synthesized hollow SiO2 nanoparticles. The ZnS nanosphere template can be removed by acid etching, and subsequent template removal does not require high-temperature annealing, solving the problem of particle aggregation and poor dispersion caused by high-temperature annealing.

[0023] 2) In this invention, the ZnS nanospheres and ZnS-SiO2 core-shell structures were prepared using a hydrothermal method and a sol-gel method, respectively. These processes are mature, simple to operate, and low in cost. By adjusting the size of the ZnS nanosphere template and the proportions of other reagents, hollow SiO2 nanospheres of different sizes can be obtained. These nanospheres possess a self-supporting internal structure, making the shell less prone to breakage and preventing shell fragmentation during centrifugation. The structure is more stable and the size is more uniform than ordinary hollow SiO2. These hollow SiO2 nanospheres hold promise for applications in optical films, biochemistry, and construction. Attached Figure Description

[0024] Figure 1 (a) is a SEM image of the ZnS nanospheres prepared in Example 1, and (b) is a SEM image of the ZnS-SiO2 core-shell structured nanospheres prepared in Example 1.

[0025] Figure 2(a)-(b) are TEM images of the ZnS-SiO2 core-shell structured nanospheres prepared in Example 1, and (c)-(d) are TEM images of the self-supporting hollow SiO2 nanospheres prepared in Example 1.

[0026] Figure 3 (a) is a TEM image of the ZnS-SiO2 core-shell nanospheres prepared in Example 2, and (b) is a TEM image of the ZnS-SiO2 core-shell nanospheres prepared in Example 3. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing self-supporting hollow SiO2 nanospheres, which specifically includes the following steps:

[0030] (1) Preparation of ZnS nanospheres by hydrothermal method.

[0031] Add 2.85g of thiourea and 0.22g of zinc acetate to 25ml of deionized water and stir until completely dissolved. Then add 0.75g of polyvinylpyrrolidone (PVP) and stir thoroughly. Transfer the solution to a polytetrafluoroethylene liner and seal the reaction vessel. React at 140℃ for 5h and then cool naturally to room temperature. Wash the reaction product with deionized water and anhydrous ethanol by centrifugation to remove residual reaction liquid and obtain monodisperse ZnS nanospheres with a diameter of 90nm and an internal porous structure.

[0032] (2) Preparation of ZnS-SiO2 core-shell structured nanospheres by sol-gel method.

[0033] Weigh 0.5g of the above ZnS spheres and add them to 40ml of anhydrous ethanol. After ultrasonic dispersion for 5min, transfer them to an Erlenmeyer flask and then place it in a water bath set at 25℃ and 750r / min for stirring. Then add 0.5g of PVP and continue stirring. After 30min, add 2ml of ammonia and 2ml of deionized water and continue stirring. This is denoted as solution A.

[0034] Separately, measure 2.3g of tetraethyl orthosilicate (TEOS) and add it to 10ml of anhydrous ethanol. Stir at room temperature and label this solution as solution B.

[0035] Solution B was slowly added dropwise to solution A. The mass ratio of ZnS nanospheres in solution A to TEOS in solution B was 1:4.6. After reacting for 8 hours, the solution was removed from the water bath and aged at room temperature for 3 days. The reaction product was washed by centrifugation with deionized water and anhydrous ethanol to remove residual reaction solution, yielding ZnS-SiO2 core-shell structured nanospheres with a shell thickness of 15 nm and an outer diameter of 120 nm.

[0036] (3) Preparation of hollow SiO2 nanospheres by acid etching method.

[0037] 1.6 g of the ZnS-SiO2 core-shell structured nanospheres prepared above were dispersed in 10 ml of anhydrous ethanol to a dispersion concentration of 0.16 g / ml. Then, 100 ml of 1 mol / L hydrochloric acid solution was added, and the mixture was placed in a water bath at 25°C and 750 r / min with stirring. After reacting for 2 days, the product was washed by centrifugation with deionized water and anhydrous ethanol to remove residual reaction liquid, yielding hollow SiO2 nanospheres 1 with a self-supporting internal structure, an outer diameter of 120 nm, and a shell thickness of 15 nm.

[0038] Figure 1 Image (a) shows a SEM image of ZnS nanospheres, and image (b) shows a SEM image of ZnS-SiO2 core-shell structured nanospheres. Figure 1 (a) It can be seen that the ZnS nanospheres synthesized by the hydrothermal method have uniform size and high dispersibility; after coating with SiO2 using the sol-gel method, the surface of the nanospheres is smoother and the size increases, such as... Figure 1 As shown in (b), it is demonstrated that SiO2 was successfully coated on the surface of ZnS nanospheres, resulting in a stable ZnS-SiO2 core-shell structure.

[0039] Figure 2 Images (a)-(b) are TEM images of the ZnS-SiO2 core-shell structured nanospheres prepared in Example 1, and images (c)-(d) are TEM images of the self-supporting hollow SiO2 nanospheres prepared in Example 1. Figure 2 As shown in (a)-(b), the synthesized ZnS-SiO2 core-shell nanospheres have uniform size and high dispersibility, with SiO2 uniformly coating the ZnS surface; after sufficient etching with hydrochloric acid solution, the ZnS core can be completely removed, such as... Figure 2 As shown in (c)-(d), hollow SiO2 nanospheres with internal support structures are obtained, with uniform particle dispersion and stable structure.

[0040] Example 2

[0041] This embodiment provides a method for preparing self-supporting hollow SiO2 nanospheres. The specific steps are the same as in Example 1, except that: the amount of thiourea used in step S1 is 3.80 g, the amount of TEOS used in step S2 is 1.8 ml, and the mass ratio of ZnS nanospheres in solution A to TEOS in solution B is 1:3.4. Hollow SiO2 nanospheres 2 are finally obtained, with a nanosphere diameter of 100 nm and a shell thickness of 12 nm.

[0042] Example 3

[0043] This embodiment provides a method for preparing self-supporting hollow SiO2 nanospheres. The specific steps are the same as in Example 1, except that: the amount of thiourea used in step S1 is 4.75 g, the amount of TEOS used in step S2 is 1.5 ml, and the mass ratio of ZnS nanospheres in solution A to TEOS in solution B is 1:2.8. Hollow SiO2 nanospheres 3 are finally obtained, with a nanosphere diameter of 80 nm and a shell thickness of 10 nm.

[0044] Figure 3 (a) is a TEM image of the ZnS-SiO2 core-shell nanospheres prepared in Example 2, and (b) is a TEM image of the ZnS-SiO2 core-shell nanospheres prepared in Example 3. Figure 3 It can be seen that the product is a hollow SiO2 nanosphere with an internal support structure, the particles are uniformly dispersed and the structure is stable.

[0045] Example 4

[0046] This embodiment provides a method for preparing self-supporting hollow SiO2 nanospheres. The specific steps are the same as in Example 1, except that: the amount of thiourea used in step S1 is 5.70 g, the amount of TEOS used in step S2 is 1.0 ml, and the mass ratio of ZnS nanospheres in solution A to TEOS in solution B is 1:1.9. Hollow SiO2 nanospheres 4 are finally obtained.

[0047] Testing revealed that the product is a hollow SiO2 nanosphere with an internal support structure, with a diameter of 50 nm and a shell thickness of 10 nm.

[0048] The experimental results of Examples 1-4 show that hollow SiO2 nanospheres of different sizes can be obtained by adjusting the size of the ZnS nanosphere template and the proportion of other reagents.

[0049] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting hollow Si02 nanosphere, characterized by, It comprises the following steps: S1, adding thiourea and zinc acetate into deionized water, stirring until completely dissolved, then adding polyvinylpyrrolidone PVP, fully stirring to obtain a mixed solution; transferring the mixed solution into a reaction kettle, sealing, reacting at 120-150℃ for 4-6h, then naturally cooling to room temperature, washing the reaction product to obtain monodisperse ZnS nanospheres with internal pore structure, with a diameter of 30-300nm; S2, weighing the ZnS nanospheres prepared in step S1, adding into anhydrous ethanol, ultrasonic dispersion, stirring at room temperature, then adding PVP, 13-15mol / L ammonia water and deionized water in sequence, fully stirring to obtain solution A; Separately, adding tetraethyl orthosilicate TEOS into anhydrous ethanol, stirring at room temperature, denoted as solution B; Slowly adding solution B into solution A, with a mass ratio of ZnS nanospheres in solution A to TEOS in solution B being 1:(1.9-4.6), reacting at room temperature, then aging, washing the reaction product to obtain core-shell structure nanospheres with ZnS nanospheres as the core and SiO2 as the shell, with a shell thickness of 10-50nm and an outer diameter of 40-350nm; S3, dispersing the core-shell structure nanospheres prepared in step S2 into anhydrous ethanol, then adding acid etching solution, stirring at a constant temperature of 20-30℃ for 2-3 days, washing the reaction product to obtain hollow SiO2 nanospheres with self-supporting structure, with an outer diameter of 40-350nm.

2. The method of claim 1, wherein the self-supporting hollow Si02 nanospheres are prepared by the steps of: In step S1, the mass ratio of deionized water, thiourea, zinc acetate and PVP is 25:(2.85-5.70):0.22:0.

75.

3. The method for preparing self-supporting hollow SiO2 nanospheres according to claim 1, characterized in that, In step S2, the mass ratio of ZnS nanospheres, anhydrous ethanol, PVP, ammonia water and deionized water for preparing solution A is 0.5:30:0.5:1.8:

2.

4. The method of claim 1, wherein the self-supporting hollow Si02 nanospheres are prepared by the steps of: In step S2, after slowly adding solution B into solution A, reacting at room temperature for 7-9h, then aging for 3-7 days.

5. The method for preparing self-supporting hollow SiO2 nanospheres according to claim 1, characterized in that, The temperature at room temperature is 20-30℃.

6. The method of claim 1, wherein the self-supporting hollow Si02 nanospheres are prepared by the steps of: The reaction products in steps S1, S2 and S3 are washed by centrifugation with deionized water and anhydrous ethanol in sequence to remove residual reaction liquid.

7. The method for preparing self-supporting hollow SiO2 nanospheres according to claim 1, characterized in that, In step S3, the dispersion mass ratio of core-shell structure nanospheres in anhydrous ethanol is 1:

5.

8. The method for preparing self-supporting hollow SiO2 nanospheres according to claim 1, characterized in that, In step S2, the preparation of solution A and the reaction of solution A and solution B are carried out at 20-30℃ water bath, with the stirring speed being set at 750-1000r / min.

9. The method for preparing self-supporting hollow SiO2 nanospheres according to claim 1, characterized in that, In step S3, the acid etching solution is 0.5-1mol / L hydrochloric acid solution.

10. Self-supporting hollow SiO2 nanospheres prepared by the method of any one of claims 1-9.

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