Silicon dioxide with novel core-shell structure and preparation method thereof

Abstract

The invention discloses silicon dioxide with a novel core-shell structure and a preparation method thereof, and relates to the technical field of silicon dioxide preparation. The preparation method of the silicon dioxide comprises the following steps: uniformly mixing absolute ethyl alcohol, deionized water and a surfactant, adding ammonia water, dropwise adding an absolute ethyl alcohol solution of a silicon source, heating for reaction, and filtering to obtain a silicon dioxide solid; the preparation method comprises the following steps: uniformly mixing deionized water and silicon dioxide solid, heating and reacting to obtain a silicon dioxide precursor; and calcining the silicon dioxide precursor in a muffle furnace to obtain the silicon dioxide with the core-shell structure. The silicon dioxide with the core-shell structure prepared by the preparation method disclosed by the invention is uniform in shell thickness, controllable in particle size, good in dispersity and relatively large in specific surface area.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silica preparation, in particular to a novel core-shell structure silica and a preparation method thereof. BACKGROUND

[0002] Silica is widely concerned in the fields of catalysis, drug controlled release, optical encryption and energy storage due to its high chemical stability, mechanical strength and biocompatibility. Core-shell structure has the advantages of large specific surface area, regular shape and stable performance, and is widely used in the fields of electronics, biology, catalysis, optical devices, medicine, coatings, plastics, composite materials and the like. With the continuous deepening of research, different applications have put forward specific requirements for core-shell structure, which has promoted the diversification of its structure design. Although the silica material with core-shell structure has made significant progress, it still faces problems such as difficulty in controlling the thickness of the shell layer and small specific surface area.

[0003] The Chinese patent application with the publication number CN116783143A discloses a method for manufacturing core-shell porous silica particles and core-shell porous silica particles. The manufacturing method comprises: a shell precursor forming process, by adding a liquid containing a silica source to an aqueous suspension containing non-porous silica particles, a cationic surfactant, an alkaline catalyst, and an alcohol, a shell precursor is formed on the surface of the non-porous silica particles; the cationic surfactant is removed to form a porous shell, but the thickness of the shell layer is large. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a novel core-shell structure silica and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the present application realizes the technical scheme as follows: A preparation method of a novel core-shell structure silica, comprising the following steps: (1) uniformly mixing anhydrous ethanol, deionized water and a surfactant, adding ammonia water, and dropwise adding a silicon source anhydrous ethanol solution, and then performing a warming reaction to obtain a silica solid; (2) uniformly mixing deionized water and the silica solid, and then performing a warming reaction to obtain a silica precursor; (3) placing the silica precursor into a muffle furnace to calcine to obtain a core-shell structure silica.

[0006] The surfactant is prepared by the following method: S1: glycidyl ether reacts with oleic acid to generate an intermediate 1, and the reaction equation is as follows:

[0007] S2: intermediate 1 generates intermediate 2 under the action of hydrogen peroxide and formic acid, and the reaction equation is shown as follows:

[0008] S3: intermediate 2 reacts with hexadecyl dimethyl tertiary amine to generate a surfactant, and the reaction equation is shown as follows:

[0009] In step S1, the molar ratio of the glycidyl ether to oleic acid is 1:(3.1-3.2).

[0010] In step S2, the molar ratio of intermediate 1, hydrogen peroxide and formic acid is 1:(3.5-4):(3.3-3.8).

[0011] In step S3, the molar ratio of intermediate 2 to hexadecyl dimethyl tertiary amine is 1:(3.1-3.3).

[0012] In step (1), the mass ratio of the silicon source to the surfactant, ammonia and the silicon source is (0.05-0.3):(1.5-2):4.

[0013] In step (1), the mass ratio of the silicon source to the surfactant, ammonia and the silicon source is (0.05-0.3):(1.5-2):4.

[0014] In step (1), the temperature of the temperature rising reaction is 60-70℃, and the time is 8-12h.

[0015] In step (2), the temperature of the temperature rising reaction is 70-90℃, and the time is 12-15h.

[0016] In step (3), the temperature of the calcination is 500-600℃, and the time is 4-6h.

[0017] A novel core-shell structure silica is prepared by the above method.

[0018] By adopting the above technical scheme, the present application has the following beneficial effects: The core-shell structure silica prepared by the present application has a uniform shell thickness, controllable particle size, good dispersibility and large specific surface area. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A scanning electron microscope image of the core-shell structure silica prepared in Example 4; Figure 2 A scanning electron microscope image of the core-shell structure silica prepared in Example 4; Figure 3Scanning electron microscope image of the core-shell structured silica prepared in Example 4; Figure 4 Graph of different surfactant addition amount and most probable particle size, specific surface area; Figure 5 Graph of different surfactant addition amount and shell thickness. DETAILED DESCRIPTION

[0020] The application will be further described in connection with the following examples, but the application is not limited to these examples.

[0021] Example 1 Preparation of surfactant: S1: 500 ml of toluene, 0.1 mol of glycidyl ether, 0.31 mol of oleic acid were added into a reaction kettle under nitrogen protection, stirred and mixed uniformly, 5 mmol of chromium acetate was added, the temperature was raised to 90°C, and reacted for 10 h, then cooled to room temperature, filtered, washed with 200 ml of saturated sodium bicarbonate solution and 200 ml of deionized water in sequence, dried with 20 g of anhydrous sodium sulfate for 2 h, filtered, distilled at 70°C under reduced pressure for 2 h, purified by silica gel column chromatography (petroleum ether and ethyl acetate in a volume ratio of 5:1), and distilled at 50°C under reduced pressure for 3 h to obtain intermediate 1; the proton nuclear magnetic resonance spectrum data of intermediate 1 is as follows: 1 H NMR (300 MHz, DMSO-d6) δ 5.39 - 5.28 (m, 6H), 4.25 (d, J =5.7 Hz, 3H), 4.02 (dd, J = 11.8, 5.7 Hz, 3H), 3.98 - 3.82 (m, 7H), 3.77 -3.36 (m, 10H), 2.29 (d, J = 17.0 Hz, 6H), 2.08 - 1.94 (m, 12H), 1.55 (qd, J =8.1, 7.0 Hz, 6H), 1.39 - 1.19 (m, 60H), 0.96 - 0.82 (m, 9H); S2: 800 ml of DMF, 10 g of strong acid cation exchange resin, and 0.1 mol of intermediate 1 were added into a reaction kettle, stirred and mixed uniformly, the temperature was raised to 50°C, a mixed solution of 40 g of 30 wt% hydrogen peroxide solution and 15.2 g of formic acid was added dropwise, the dropping was completed in 30 min, and the reaction was carried out for 8 h, then cooled to room temperature, adjusted to the starch iodide paper not to change color with saturated sodium sulfite solution, filtered, extracted with dichloromethane (3×200 ml), washed with deionized water (3×100 ml), dried with 20 g of anhydrous sodium sulfate for 1 h, filtered, distilled at 30°C under reduced pressure for 2 h to obtain intermediate 2, and the proton nuclear magnetic resonance spectrum data of intermediate 2 is as follows: 1H NMR (300 MHz, DMSO-d6) δ 4.32 - 4.23 (m, 3H), 4.02 (dd, J = 11.8, 5.8 Hz, 3H), 3.98 - 3.82(m, 7H), 3.77 - 3.37 (m, 10H), 3.08 (d, J = 8.5 Hz, 6H), 2.29 (d, J = 16.9Hz, 6H), 1.83 - 1.19 (m, 78H), 0.96 - 0.80 (m, 9H); S3: Under ice bath conditions, 1200 ml of anhydrous ethanol, 0.31 mol of hexadecyl dimethyl tertiary amine, and 0.1 mol of intermediate 2 were added to a reaction vessel and stirred until homogeneous. 35 g of 36 wt% HCl solution was added dropwise over 30 min. The mixture was then refluxed for 12 h, cooled to room temperature, and the pH was adjusted to 9 using 10 wt% NaOH solution. The mixture was then distilled under reduced pressure at 50 °C for 3 h. Recrystallization was performed by adding 600 ml of a mixture of ethyl acetate and anhydrous ethanol (ethyl acetate to anhydrous ethanol volume ratio of 8:2), filtered, and dried under vacuum at 60 °C for 12 h to obtain the surfactant. Its 1H NMR data are as follows: 1 H NMR (300 MHz, DMSO-d6) δ 4.41 (d, J = 6.1 Hz, 3H), 4.31 (dd, J = 11.8, 6.0 Hz, 3H), 4.08 (d, J = 6.0 Hz, 6H), 4.01 - 3.81 (m,4H), 3.80 - 3.68 (m, 5H), 3.60 - 3.28 (m, 17H), 3.20 (dd, J = 15.0, 1.5 Hz,18H), 2.30 (t, J = 8.5 Hz, 6H), 2.01 - 1.18 (m, 162H), 0.96 - 0.80 (m, 18H).

[0022] Example 2: Preparation of surfactants: S1: Under nitrogen protection, 500 ml toluene, 0.1 mol glycidyl ether, and 0.315 mol oleic acid were added to a reaction vessel and stirred until homogeneous. 5 mmol of chromium acetate was added, the temperature was raised to 95 °C, and the reaction was carried out for 9 h. After cooling to room temperature, the mixture was filtered and washed successively with 200 ml of saturated sodium bicarbonate solution and 200 ml of deionized water. The mixture was dried with 20 g of anhydrous sodium sulfate for 2 h, filtered, and distilled under reduced pressure at 70 °C for 2 h. The mixture was then purified by silica gel column chromatography (petroleum ether and ethyl acetate in a volume ratio of 5:1) and distilled under reduced pressure at 50 °C for 3 h to obtain intermediate 1. S2: Add 800ml DMF, 10g strong acid cation exchange resin, and 0.1mol intermediate 1 to a reaction vessel, stir and mix well, heat to 55℃, add 42g of a mixed solution of 30wt% hydrogen peroxide and 16.1g of formic acid dropwise over 30min, react for 7h, cool to room temperature, adjust to the desired color on starch-potassium iodide paper using saturated sodium sulfite solution, filter, extract with dichloromethane (3×200ml), combine organic phases and wash with deionized water (3×100ml), dry with 20g anhydrous sodium sulfate for 1h, filter, and distill under reduced pressure at 30℃ for 2h to obtain intermediate 2; S3: Under ice bath conditions, 1200 ml of anhydrous ethanol, 0.32 mol of hexadecyl dimethyl tertiary amine, and 0.1 mol of intermediate 2 were added to the reaction vessel and stirred until well mixed. 35 g of 36 wt% HCl solution was added dropwise over 30 min. The mixture was then refluxed for 14 h and cooled to room temperature. The pH was adjusted to 9 using 10 wt% NaOH solution. The mixture was distilled under reduced pressure at 50 °C for 3 h. 600 ml of a mixture of ethyl acetate and anhydrous ethanol (volume ratio of ethyl acetate to anhydrous ethanol was 8:2) was added for recrystallization. The mixture was filtered and dried under vacuum at 60 °C for 12 h to obtain the surfactant.

[0023] Example 3: Preparation of surfactants: S1: Under nitrogen protection, 500 ml toluene, 0.1 mol glycidyl ether, and 0.32 mol oleic acid were added to a reaction vessel and stirred until homogeneous. 5 mmol of chromium acetate was added, and the mixture was heated to 100 °C and reacted for 8 h. After cooling to room temperature, the mixture was filtered and washed successively with 200 ml of saturated sodium bicarbonate solution and 200 ml of deionized water. The mixture was dried with 20 g of anhydrous sodium sulfate for 2 h, filtered, and distilled under reduced pressure at 70 °C for 2 h. The mixture was then purified by silica gel column chromatography (petroleum ether and ethyl acetate in a volume ratio of 5:1) and distilled under reduced pressure at 50 °C for 3 h to obtain intermediate 1. S2: Add 800ml DMF, 10g strong acid cation exchange resin, and 0.1mol intermediate 1 to a reaction vessel, stir and mix well, heat to 60℃, add 45g of a mixed solution of 30wt% hydrogen peroxide and 17.5g of formic acid dropwise over 30min, react for 6h, cool to room temperature, adjust to the desired color on starch-potassium iodide paper using saturated sodium sulfite solution, filter, extract with dichloromethane (3×200ml), combine organic phases and wash with deionized water (3×100ml), dry with 20g anhydrous sodium sulfate for 1h, filter, and distill under reduced pressure at 30℃ for 2h to obtain intermediate 2; S3: Under ice bath conditions, 1200 ml of anhydrous ethanol, 0.33 mol of hexadecyl dimethyl tertiary amine, and 0.1 mol of intermediate 2 were added to the reaction vessel and stirred until well mixed. 35 g of 36 wt% HCl solution was added dropwise over 30 min. The mixture was then refluxed for 15 h and cooled to room temperature. The pH was adjusted to 9 using 10 wt% NaOH solution. The mixture was distilled under reduced pressure at 50 °C for 3 h. 600 ml of a mixture of ethyl acetate and anhydrous ethanol (volume ratio of ethyl acetate to anhydrous ethanol was 8:2) was added for recrystallization. The mixture was filtered and dried under vacuum at 60 °C for 12 h to obtain the surfactant.

[0024] Example 4: Preparation of core-shell structured silicon dioxide: (1) Add 300ml of anhydrous ethanol, 200ml of deionized water and 1g of surfactant (prepared in Example 1) to the reaction vessel and stir for 2h. Add 15g of 25wt% ammonia solution and dropwise add 200ml of anhydrous ethanol solution containing 22.9g of tetraethyl orthosilicate and 17.1g of bis[3-(triethoxysilyl)propyl]amine at a dropping rate of 0.5ml / min. After the dropping is completed, heat to 60℃ and react for 12h. Cool to room temperature, filter, wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence, and vacuum dry at 60℃ for 10h to obtain solid silica. (2) Disperse 200ml of deionized water and the above-mentioned silica solid by ultrasonication (50Hz) for 30min, stir, heat to 70℃ and react for 15h, cool to room temperature, filter, wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence, and vacuum dry at 60℃ for 10h to obtain silica precursor. (3) The above-mentioned silica precursor was placed in a muffle furnace and heated to 500°C at a rate of 3°C / min. The temperature was held for 6 hours and then naturally cooled to room temperature to obtain silica with a core-shell structure.

[0025] Figure 1 , Figure 2 and Figure 3 The image shown is a scanning electron microscope (SEM) image of the core-shell structured silica prepared in Example 4. Figure 1 and Figure 2 It can be seen that silica exists in the form of monodisperse nanospheres with uniform size; Figure 3 It is silica with a broken core-shell structure, and you can see its walnut-like kernel structure.

[0026] Example 5: Preparation of core-shell structured silicon dioxide: (1) Add 300ml of anhydrous ethanol, 200ml of deionized water and 1g of surfactant (prepared in Example 2) to the reaction vessel and stir for 2h. Add 18g of 25wt% ammonia solution and dropwise add 200ml of anhydrous ethanol solution containing 21g of tetraethyl orthosilicate and 19g of bis[3-(triethoxysilyl)propyl]amine at a rate of 0.5ml / min. After the addition is complete, heat to 65℃ and react for 10h. Cool to room temperature, filter, and wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence. Dry under vacuum at 60℃ for 10h to obtain the silica core. (2) Disperse 200ml of deionized water and the above-mentioned silica solid by ultrasonication (50Hz) for 30min, stir, heat to 80℃ and react for 14h, cool to room temperature, filter, wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence, and vacuum dry at 60℃ for 10h to obtain silica precursor. (3) The above-mentioned silica precursor was placed in a muffle furnace and heated to 550°C at a rate of 3°C / min. The temperature was held for 5 hours and then naturally cooled to room temperature to obtain silica with a core-shell structure.

[0027] Example 6: Preparation of core-shell structured silicon dioxide: (1) Add 300ml of anhydrous ethanol, 200ml of deionized water and 1g of surfactant (prepared in Example 3) to the reaction vessel and stir for 2h. Add 20g of 25wt% ammonia solution and dropwise add 200ml of anhydrous ethanol solution containing 20g of tetraethyl orthosilicate and 20g of bis[3-(triethoxysilyl)propyl]amine at a rate of 0.5ml / min. After the addition is complete, heat to 70℃ and react for 12h. Cool to room temperature, filter, and wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence. Dry under vacuum at 60℃ for 10h to obtain the silica core. (2) Disperse 200ml of deionized water and the above-mentioned silica solid by ultrasonication (50Hz) for 30min, stir, heat to 90℃ and react for 12h, cool to room temperature, filter, wash with 50ml of deionized water and 50ml of anhydrous ethanol in sequence, and vacuum dry at 60℃ for 10h to obtain silica precursor. (3) The above-mentioned silica precursor was placed in a muffle furnace and heated to 600°C at a rate of 3°C / min. The temperature was held for 4 hours and then naturally cooled to room temperature to obtain silica with a core-shell structure.

[0028] Figure 4 and Figure 5 The figures show line graphs illustrating the relationship between different surfactant dosages and the most probable particle size, specific surface area, and shell thickness of core-shell structured silica. The preparation method of the core-shell structured silica is basically the same as that in Example 5, except that the amount of surfactant added in step (1) is different.

[0029] Depend on Figure 4 It can be seen that as the amount of surfactant added increases, the most probable particle size of the resulting core-shell structured silica gradually decreases, while its specific surface area increases accordingly. Figure 5 It can be seen that the amount of surfactant added has little effect on the shell thickness. By changing the amount of surfactant, core-shell silica structures with similar shell thickness but different particle sizes can be prepared.

[0030] Comparative Example 1 The preparation method of silica is basically the same as that in Example 5, except that the surfactant used in step (1) is replaced with an equal weight of the surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 2, except that the glycidyl ether in step S1 is replaced with 0.157 mol of ethylene glycol diglycidyl ether; the hydrogen peroxide in step S2 is replaced with 2.8 mol and the formic acid is replaced with 2.33 mol; and the hexadecyl dimethyl tertiary amine in step S3 is replaced with 0.21 mol.

[0031] Comparative Example 2 The preparation method of silica is basically the same as that in Example 5, except that the surfactant used in step (1) is replaced with an equal weight of the surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 2, except that the glycidyl ether in step S1 is replaced with 0.078 mol of pentaerythritol tetraglycidyl ether, the hydrogen peroxide in step S2 is replaced with 4.8 mol, the formic acid is replaced with 4.667 mol, and the hexadecyl dimethyl tertiary amine in step S3 is replaced with 0.41 mol.

[0032] Comparative Example 3 The preparation method of silica is basically the same as that in Example 5, except that the surfactant used in step (1) is replaced with an equal weight of the surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 2, except that the oleic acid in step S1 is replaced with an equimolar amount of 9-decenoic acid.

[0033] Comparative Example 4 The preparation method of silica is basically the same as that of comparative example 3, except that the surfactant used in step (1) is replaced with 2g.

[0034] Comparative Example 5 The preparation method of silica is basically the same as that in Example 5, except that the surfactant used in step (1) is replaced with an equal weight of CTAB.

[0035] The silica prepared in Examples 4-6 and Comparative Examples 1-5 of this application was tested for silica morphology and shell thickness by scanning electron microscopy, particle size distribution by LT3600 Plus laser particle size analyzer, and specific surface area by physical adsorption experiment. The test results are shown in Table 1.

[0036] Table 1 Data on Silica

[0037] Note: The particle size distribution values ​​in the table above are rounded.

[0038] pass Figures 1-5 As can be seen from the data in Table 1, the silica prepared by the present invention has a core-shell structure with uniform shell thickness, controllable particle size, good dispersibility, and a large specific surface area.

[0039] The surfactant used in the preparation of the core-shell structured silica in this application contains quaternary ammonium salts, hydroxyl groups, and hydrophobic alkyl chains. The positively charged quaternary ammonium salts adsorb onto the negatively charged silica core, suppressing uneven nucleation through electrostatic repulsion. The hydroxyl groups form a hydrogen bond network with the silanol groups (Si-OH) on the silica surface, guiding the directional deposition of tetraethyl orthosilicate hydrolysis products on the core surface. The hydrophobic alkyl chains self-assemble in solution to form micelle structures, which act as "soft templates" embedded in the shell matrix, inhibiting excessive particle growth.

[0040] The surfactant used in Comparative Example 1 contained only two quaternary ammonium salt groups, resulting in numerous nucleation sites and a thin shell, leading to poor mechanical stability. The surfactant used in Comparative Example 2 contained four quaternary ammonium salt groups, resulting in fewer nucleation sites and a thicker shell, which increased the diffusion path of the loaded material and reduced mass transfer efficiency during catalysis and drug release. The surfactant used in Comparative Example 3 lacked a hydrophobic alkyl chain, reducing micellar interaction and resulting in a wider particle size distribution.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a novel core-shell structured silicon dioxide, characterized in that, Includes the following steps: (1) Mix anhydrous ethanol, deionized water and surfactant evenly, add ammonia water, add anhydrous ethanol solution of silicon source dropwise, heat the reaction, and filter to obtain solid silicon dioxide. (2) Mix deionized water and solid silica evenly, and heat to react to obtain silica precursor; (3) The silica precursor was calcined in a muffle furnace to obtain core-shell silica; The surfactant is prepared by the following method: S1: Glycidyl ether reacts with oleic acid to form intermediate 1. S2: Intermediate 1 is reacted with hydrogen peroxide and formic acid to form intermediate 2. S3: Intermediate 2 reacts with hexadecyl dimethyl tertiary amine to generate a surfactant.

2. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step S1, the molar ratio of glycidyl ether to oleic acid is 1:(3.1-3.2).

3. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step S2, the molar ratio of intermediate 1, hydrogen peroxide and formic acid is 1:(3.5-4):(3.3-3.8).

4. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step S3, the molar ratio of intermediate 2 to hexadecyl dimethyl tertiary amine is 1:(3.1-3.3).

5. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step (1), the silicon source is tetraethyl orthosilicate and bis[3-(triethoxysilane)propyl]amine, and the mass ratio of the two materials is 2:(1.5-2).

6. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step (1), the mass ratio of the surfactant, ammonia and silicon source is (0.05-0.3):(1.5-2):

4.

7. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step (1), the temperature of the heating reaction is 60-70℃ and the time is 8-12h.

8. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step (2), the temperature of the heating reaction is 70-90℃ and the time is 12-15h.

9. The method for preparing a novel core-shell structured silicon dioxide according to claim 1, characterized in that, In step (3), the calcination temperature is 500-600℃ and the time is 4-6h.

10. A novel core-shell structured silicon dioxide, characterized in that, It is prepared by the method according to any one of claims 1 to 9.

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