Mesoporous silica and preparation method thereof

Abstract

The invention provides mesoporous silica and a preparation method thereof. The preparation method of the mesoporous silica comprises the following steps: obtaining a mixed system containing a first silicon source precursor, a soft template reagent and a second silicon source precursor; carrying out a sol-gel reaction on the double-silicon-source mixed system, carrying out solid-liquid separation, and collecting a solid phase to obtain a mesoporous silica precursor; wherein the first silicon source precursor comprises sodium silicate; the second silicon source precursor comprises sodium fluosilicate and / or ammonium fluosilicate. According to the method for preparing the mesoporous silicon dioxide, a double-silicon-source synergistic hydrolysis method is creatively used, the mesoporous silicon dioxide with a high specific surface area is prepared under the condition that an additional acid reagent or alkali reagent is not needed, and a brand new method is provided for synthesis of the mesoporous silicon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of mesoporous silica synthesis technology, specifically relating to a mesoporous silica and its preparation method. Background Technology

[0002] Mesoporous silica, a type of silica-based material with a unique mesoporous structure (pore size typically between 2-50 nm), exhibits extremely broad application prospects in numerous fields such as medicine, catalysis, environmental remediation, and new energy development due to its high specific surface area, regular and tunable pore structure, and good chemical and thermal stability. In the pharmaceutical field, mesoporous silica can serve as a drug carrier, utilizing its large specific surface area and tunable pore size to achieve efficient drug loading and controlled release, improving drug bioavailability and targeting. In catalysis, its regular pore structure facilitates the diffusion of reactant molecules and the exposure of active sites, significantly enhancing the activity and selectivity of catalytic reactions. In environmental remediation, mesoporous silica can be used to adsorb pollutants in water and air, such as heavy metal ions and organic pollutants. In the new energy field, it can serve as a carrier for electrode materials or energy storage materials, improving the electrochemical performance of these materials.

[0003] Currently, the synthesis of mesoporous silica mainly relies on the acid- or base-catalyzed hydrolysis of silicon source precursors, combined with the use of soft template agents to regulate the mesoporous structure. Specifically, common synthesis methods include: using tetraethyl orthosilicate (TEOS) as a silicon source precursor, adding it to a hydrochloric acid solution or sodium hydroxide solution containing soft template agents such as hexadecyltrimethylammonium bromide (CTAB), and under the catalysis of acid or base, TEOS undergoes a hydrolysis reaction, subsequently forming mesoporous silica through a self-assembly process; or using sodium silicate as a silicon source precursor, carrying out a hydrolysis-condensation reaction in a hydrochloric acid solution containing CTAB, followed by a self-assembly process to obtain mesoporous silica.

[0004] However, the existing synthesis methods described above require the consumption of considerable amounts of acid or alkali to hydrolyze the silicon precursor. The use of large quantities of acid or alkali not only significantly increases synthesis costs, including the procurement costs of raw materials and subsequent wastewater treatment, but also poses potential environmental risks if these wastewaters are discharged directly without proper treatment, such as causing water pH imbalances and soil pollution, which does not meet the requirements of current green chemistry and sustainable development. Therefore, there is an urgent need for a mesoporous silica and its preparation method to alleviate or solve the above problems. Summary of the Invention

[0005] To address the technical problem that the preparation of mesoporous silica in the aforementioned commonly used techniques requires the consumption of a considerable amount of acid or alkali to achieve the hydrolysis reaction of the silicon source precursor, this invention provides a method for preparing mesoporous silica, comprising the following steps:

[0006] A mixed system comprising a first silicon source precursor, a soft template reagent, and a second silicon source precursor is obtained; the mixed system undergoes a sol-gel reaction, followed by solid-liquid separation, and the solid phase is collected to obtain a mesoporous silica precursor; the first silicon source precursor comprises sodium silicate; the second silicon source precursor comprises sodium fluorosilicate and / or ammonium fluorosilicate;

[0007] The mesoporous silica precursor is calcined to obtain mesoporous silica.

[0008] Furthermore, obtaining the mixed system comprising the first silicon source precursor, the soft template reagent, and the second silicon source precursor includes the following steps:

[0009] The first silicon source precursor and the soft template reagent are mixed in a first solvent and homogenized to obtain a silicon source-soft template composite solution.

[0010] The second silicon source precursor is then dissolved in the second solvent to obtain a silicon source suspension.

[0011] The silicon source suspension is added to the silicon source-soft template composite solution to obtain the mixed system.

[0012] Furthermore, the soft template reagent includes one or more cationic surfactants such as hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0013] Furthermore, in the silicon source-soft template composite solution, the concentration of the first silicon source precursor is 0.05-0.3 mol / L, and the concentration of the soft template reagent is 0.001-0.02 mol / L; in the silicon source suspension, the concentration of the second silicon source precursor is 0.1-0.5 mol / L.

[0014] Furthermore, the temperature of the sol-gel reaction is 25-60℃, and the reaction time is 30-120 min.

[0015] Furthermore, in the step of adding the silicon source suspension to the silicon source-soft template composite solution to obtain the mixed system, the volume ratio of the silicon source suspension to the silicon source-soft template composite solution is 1:4 to 30.

[0016] In the hybrid system, the molar ratio of the first silicon source precursor to the second silicon source precursor is 1.2 to 4:1.

[0017] Furthermore, the calcination treatment is carried out at a temperature of 450-650℃ for a time of 0.5-6h, and the flow rate of the calcination atmosphere during the calcination treatment is 5-25L / min.

[0018] This invention provides a mesoporous silica, prepared by any of the preparation methods described above.

[0019] Furthermore, the specific surface area of ​​the mesoporous silica is 150–950 m². 2 / g, wherein the pore size of the mesoporous silica surface is 3-5.5nm.

[0020] Compared with the prior art, the present invention has at least the following advantages:

[0021] This invention provides a method for preparing mesoporous silica that requires no additional acid or base catalysts. It utilizes only the alkaline environment provided by sodium silicate and the interaction between sodium fluorosilicate and sodium silicate to achieve the formation of mesoporous silica through its own hydrolysis-based acid-base properties, without the need for any acid or base catalysts. This feature effectively reduces raw material costs, eliminates the need for subsequent wastewater treatment, and lowers the potential environmental pollution risk.

[0022] Furthermore, this invention utilizes dual silicon sources (sodium silicate and sodium fluorosilicate / ammonium fluorosilicate) to synergistically self-assemble with a soft template agent during the conversion process to form a mesoporous structure. Specifically, the soft template agent forms a specific micelle structure in solution, while the dual silicon sources undergo hydrolysis and condensation reactions on the micelle surface. As the reaction proceeds, a mesoporous silica structure using micelles as templates is gradually formed. This synergistic self-assembly method facilitates the formation of regular and ordered mesoporous structures, increasing the specific surface area and pore volume of mesoporous silica, thereby enhancing its application performance in adsorption, catalysis, and other fields.

[0023] Finally, the preparation method provided by this invention is simple and easy to operate, requiring no complex equipment or cumbersome procedures. First, sodium silicate and a soft template agent are dissolved in deionized water to form an alkaline solution. Then, sodium fluorosilicate is introduced to react with the solution. Finally, the soft template is removed by calcination to obtain mesoporous silica. This simple preparation method facilitates large-scale industrial production, reduces production costs, improves production efficiency, and meets the large market demand for mesoporous silica. Attached Figure Description

[0024] 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 based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a TEM image of the calcined sample in Example 1 of this invention;

[0026] Figure 2This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 1 of this invention;

[0027] Figure 3 This is a pore size distribution diagram of the calcined sample in Example 1 of the present invention;

[0028] Figure 4 This is a TEM image of the calcined sample in Example 2 of this invention;

[0029] Figure 5 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 2 of this invention;

[0030] Figure 6 This is a pore size distribution diagram of the calcined sample in Example 2 of the present invention;

[0031] Figure 7 This is a TEM image of the calcined sample in Example 3 of this invention;

[0032] Figure 8 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 3 of this invention;

[0033] Figure 9 This is a pore size distribution diagram of the calcined sample in Example 3 of the present invention;

[0034] Figure 10 This is a TEM image of the calcined sample in Comparative Example 1 of this invention;

[0035] Figure 11 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Comparative Example 1 of this invention;

[0036] Figure 12 This is a pore size distribution diagram of the calcined sample in Comparative Example 1 of this invention;

[0037] Figure 13 This is a TEM image of the calcined sample in Example 4 of this invention;

[0038] Figure 14 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 4 of this invention;

[0039] Figure 15 This is a pore size distribution diagram of the calcined sample in Example 4 of the present invention;

[0040] Figure 16 This is a TEM image of the calcined sample in Example 5 of this invention;

[0041] Figure 17 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 5 of this invention;

[0042] Figure 18 This is a pore size distribution diagram of the calcined sample in Example 5 of the present invention;

[0043] Figure 19 This is a TEM image of the calcined sample in Example 6 of this invention;

[0044] Figure 20 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Example 6 of this invention;

[0045] Figure 21 This is a pore size distribution diagram of the calcined sample in Example 6 of the present invention;

[0046] Figure 22 This is a TEM image of the calcined sample in Comparative Example 2 of this invention;

[0047] Figure 23 This is a diagram showing the nitrogen adsorption-desorption process of the calcined sample in Comparative Example 2 of this invention;

[0048] Figure 24 This is a pore size distribution diagram of the calcined sample in Comparative Example 2 of this invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0050] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0051] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0052] This invention provides a method for preparing mesoporous silica, comprising the following steps:

[0053] S1. Obtain a mixed system containing a first silicon source precursor, a soft template reagent, and a second silicon source precursor; after the mixed system undergoes a sol-gel reaction, solid-liquid separation is performed, and the solid phase is collected to obtain a mesoporous silica precursor.

[0054] In this invention, the first silicon source precursor includes sodium silicate; the second silicon source precursor includes sodium fluorosilicate. It should be noted that the sodium silicate here includes hydrated sodium silicate, such as sodium silicate nonahydrate.

[0055] In this invention, the soft template reagent includes one or more of cationic surfactants such as hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and octadecyltrimethylammonium chloride.

[0056] In this invention, the temperature of the sol-gel reaction can be 25-60℃, and the reaction time can be 30-120 min. The sol-gel reaction can be carried out under stirring conditions, and the stirring speed can be 100-600 rpm.

[0057] In this invention, obtaining the mixed system comprising a first silicon source precursor, a soft template reagent, and a second silicon source precursor includes the following steps:

[0058] S11. The first silicon source precursor and the soft template reagent are mixed in a first solvent and homogenized to prepare a silicon source-soft template composite solution.

[0059] In some embodiments, the first solvent comprises deionized water.

[0060] In some embodiments, in the silicon source-soft template composite solution, the concentration of the first silicon source precursor can be 0.05-0.3 mol / L, and the concentration of the soft template reagent can be 0.001-0.02 mol / L.

[0061] In some specific embodiments, the concentration of the soft template reagent in the silicon source-soft template composite solution can be 0.008–0.02 mol / L; in some more specific embodiments, the concentration of the soft template reagent can be 0.01–0.02 mol / L.

[0062] The applicant discovered that as the concentration of the soft template reagent in the silicon source-soft template composite solution increases, the specific surface area of ​​the mesoporous silica significantly increases. For example, in the silicon source-soft template composite solution, when the concentration of the soft template reagent is 0.01–0.02 mol / L, the specific surface area of ​​the mesoporous silica can stably exceed 400 m² / L. 2 / g; For example, in the silicon source-soft template composite solution, the concentration of the soft template reagent is 0.018–0.02 mol / L, and the specific surface area of ​​the mesoporous silica can be stably greater than 800 m² / g. 2 / g, this is an unexpected technical effect.

[0063] In some embodiments, the homogenization process includes a stirring process, wherein the temperature during the stirring process is 25–60°C, the rotation speed is 100–600 rpm, and the stirring time is 30–180 min.

[0064] It should be noted that the homogenization process should meet the following requirements: heating and stirring until the sodium silicate-soft template solution is clear and transparent, with no suspended solids.

[0065] S12. Dissolve the second silicon source precursor in the second solvent to obtain a silicon source suspension.

[0066] In some embodiments, the concentration of the second silicon source precursor in the silicon source suspension is 0.1-0.5 mol / L.

[0067] It should be noted that in the method described in this invention, the execution order of steps S11 and S12 is not important and can be flexibly arranged according to actual process requirements.

[0068] S13. Add the silicon source suspension to the silicon source-soft template composite solution to obtain the mixed system.

[0069] In some embodiments, in the step of adding the silicon source suspension to the silicon source-soft template composite solution to obtain the mixed system, the volume ratio of the silicon source suspension to the silicon source-soft template composite solution is 1:4 to 30; and the molar ratio of the first silicon source precursor to the second silicon source precursor in the mixed system is 1.2 to 4:1.

[0070] In some embodiments, the addition rate of the silicon source suspension to the silicon source-soft template composite solution can be 0.3-3 ml / min.

[0071] Specifically, in step S1, sodium silicate in the aqueous solution undergoes hydrolysis, making the solution alkaline:

[0072]

[0073] Fluorosilicates, on the other hand, undergo hydrolysis in alkaline solutions (taking sodium fluorosilicate as an example):

[0074] Na₂SiF₆ + 4NaOH → H₄SiO₄ + 6NaF

[0075] Therefore, when sodium fluorosilicate is introduced into a sodium silicate solution, it continuously consumes the NaOH produced by the hydrolysis of sodium silicate, causing sodium silicate to continuously convert into orthosilicic acid (H4SiO4). Sodium fluorosilicate also continuously converts into orthosilicic acid, which further undergoes dehydration and condensation to form silicon dioxide. This allows for the formation of silicon dioxide from two silicon sources without the need for acid-base catalysis. The soft template agent, on the other hand, can achieve mesoporous structure formation through a synergistic self-assembly process with the generated orthosilicic acid.

[0076] It should be noted that the first silicon source precursor in step S1 includes sodium silicate, and the second silicon source precursor includes sodium fluorosilicate, ammonium fluorosilicate, etc. (taking sodium fluorosilicate as an example): Sodium silicate and sodium fluorosilicate form a mesoporous structure through synergistic self-assembly with the soft template agent during the conversion process. First, an alkaline sodium silicate solution is formed, and then sodium fluorosilicate is added, which allows the two silicon sources to gradually convert in a relatively stable environment and interact orderly with the soft template agent.

[0077] Specifically: First, the soft template agent has high compatibility with sodium silicate solution.

[0078] Initial alkaline environment requirement: Sodium silicate and the soft template agent are first dissolved in deionized water to form an alkaline sodium silicate solution. This alkaline environment is conducive to better dispersion and stable existence of the soft template agent. Taking common soft template agents such as hexadecyltrimethylammonium bromide (CTAB) as an example, their micellar structure is more easily formed and remains stable under alkaline conditions.

[0079] Synergistic effect basis: Sodium silicate has certain solubility and reactivity in alkaline solutions, which provides a basis for subsequent synergistic reactions with sodium fluorosilicate and synergistic self-assembly with soft template agents.

[0080] Secondly, sodium fluorosilicate possesses alkaline hydrolysis properties.

[0081] Alkaline hydrolysis reaction conditions: Sodium fluorosilicate needs an alkaline solution to be converted into silicon dioxide through the alkaline hydrolysis process. If sodium fluorosilicate is added first, without the prior formation of an alkaline sodium silicate solution, the sodium fluorosilicate cannot effectively undergo the alkaline hydrolysis reaction, and therefore cannot produce enough silicon dioxide to participate in the subsequent mesoporous structure formation process.

[0082] pH adjustment mechanism: Sodium silicate solution is alkaline. After adding sodium fluorosilicate, the alkaline hydrolysis reaction of sodium fluorosilicate consumes hydroxide ions in the solution, thereby gradually changing the pH of the solution from alkaline to neutral to weakly alkaline. This pH change is crucial for the hydrolysis reaction of sodium silicate and the formation of mesoporous structure.

[0083] S2. The mesoporous silica precursor is subjected to drying and calcination treatments in sequence to obtain mesoporous silica.

[0084] In some embodiments, the drying process includes freeze drying or oven drying at a constant temperature.

[0085] In some more specific embodiments, when the drying process is constant temperature drying, the drying temperature can be 60-100°C and the duration can be 10-14 hours.

[0086] In some embodiments, the calcination treatment is carried out at a temperature of 450-650°C for a time of 0.5-6 hours, and the flow rate of the calcination atmosphere during the calcination treatment is 5-25 L / min. Specifically, in this step, the soft template agent is usually an organic material. After the reaction, the template agent remains inside the mesopores of the silica precipitate. The soft template agent can be removed through an aerobic high-temperature calcination process, thereby forming a mesoporous structure in the silica.

[0087] In some more specific embodiments, the calcination atmosphere includes air, pure oxygen, or an inert atmosphere.

[0088] This invention provides a mesoporous silica, prepared by any of the preparation methods described above.

[0089] Furthermore, the specific surface area of ​​the mesoporous silica is 150–950 m². 2 / g, wherein the pore size of the mesoporous silica surface is 3-5.5nm.

[0090] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0091] Example 1

[0092] Dissolve 2.84 g of sodium silicate nonahydrate and 1.365 g of hexadecyltrimethylammonium bromide in 200 ml of deionized water, heat to 60 °C, and stir at 500 rpm for 30 min to prepare a silicon source-soft template composite solution (sodium silicate concentration is 0.05 mol / L, soft template agent concentration is 0.0187 mol / L).

[0093] Add 1.415g of sodium fluorosilicate to 50ml of deionized water to form a sodium fluorosilicate suspension (concentration of 0.15mol / L).

[0094] Sodium fluorosilicate suspension was added to silicon source-soft template composite solution at a rate of 1 ml / min. The reaction temperature was 60℃, and the mixture was stirred at 500 rpm for 120 min. After the reaction, the precipitate was filtered to obtain mesoporous silica precursor.

[0095] The mesoporous silica precursor was dried at 80°C for 12 hours and then placed in a muffle furnace and calcined at 550°C for 3 hours in air atmosphere to obtain mesoporous silica.

[0096] Figure 1 This is a TEM image of the mesoporous silica prepared in Example 1. Figure 2 The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 1. Figure 3 This is a pore size distribution diagram of the mesoporous silica prepared in Example 1.

[0097] from Figure 1 It can be observed that the silica obtained after the reaction using this method exhibits a distinct ordered mesoporous structure. Combined with... Figure 2 Nitrogen adsorption-desorption test and Figure 3 Pore ​​size analysis revealed that the formed mesoporous silica possesses a very large specific surface area of ​​950.11 m². 2 / g, the resulting mesoporous silica has a pore size of 3.24nm. The above results demonstrate that this method can yield mesoporous silica with a uniform mesoporous structure.

[0098] Example 2

[0099] Keep all other reaction conditions the same as in Example 1, except that the amount of added hexadecyltrimethylammonium bromide is changed to 0.91 g (soft template concentration is 0.0125 mol / L).

[0100] Figure 4 This is a TEM image of the mesoporous silica prepared in Example 2. Figure 5 The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 2. Figure 6 This is a pore size distribution diagram of the mesoporous silica prepared in Example 2.

[0101] from Figure 4 It can be observed that the silica obtained after the reaction using this method exhibits a distinct ordered mesoporous structure. Combined with... Figure 5 Nitrogen adsorption-desorption test and Figure 6 Pore ​​size analysis revealed that the formed mesoporous silica has a large specific surface area of ​​456.26 m². 2 / g, the resulting mesoporous silica has a pore size of 3.21nm. The above results demonstrate that this method can yield mesoporous silica with a uniform mesoporous structure.

[0102] Example 3

[0103] Keep all other reaction conditions the same as in Example 1, except that the amount of added hexadecyltrimethylammonium bromide is changed to 0.45 g (soft template concentration is 0.00625 mol / L).

[0104] Figure 7 This is a TEM image of the mesoporous silica prepared in Example 3. Figure 8The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 3. Figure 9 This is a pore size distribution diagram of the silica obtained in Example 3.

[0105] from Figure 7 It can be observed that the silica obtained after the reaction has a mesoporous structure. Combined with... Figure 8 Nitrogen adsorption-desorption test and Figure 9 Pore ​​size analysis revealed that the specific surface area of ​​the formed mesoporous silica was 152.43 m². 2 / g, the formed silica has a pore size of 3.12nm. The above results show that mesoporous silica can be formed under these reaction conditions, but the specific surface area is relatively lower than that of Examples 1 and 2.

[0106] Comparative Example 1

[0107] Dissolve 2.84g of sodium silicate nonahydrate in 200ml of deionized water, heat to 60℃, and stir at 500rpm for 30min to prepare a sodium silicate solution (sodium silicate concentration is 0.05mol / L).

[0108] Add 1.415g of sodium fluorosilicate to 50ml of deionized water to form a sodium fluorosilicate suspension (concentration of 0.15mol / L).

[0109] Sodium fluorosilicate suspension was added to sodium silicate solution at a rate of 1 ml / min. The reaction temperature was 60℃, and the mixture was stirred at 500 rpm for 120 min. After the reaction, the precipitate was filtered to obtain the silica precursor.

[0110] The silica precursor was dried at 80°C for 12 hours and then placed in a muffle furnace and calcined at 550°C for 3 hours in air atmosphere to obtain calcined silica.

[0111] Figure 10 This is a TEM image of the silica sample after calcination in Comparative Example 1. Figure 11 The attached diagram shows the nitrogen adsorption-desorption process of the silica sample after calcination in Comparative Example 1. Figure 12 This is a pore size distribution diagram of the silica sample after calcination in Comparative Example 1.

[0112] from Figure 10 It can be observed that the sample synthesized directly from sodium fluorosilicate and sodium silicate exhibits a non-porous, dense structure. Combined with... Figure 11 Nitrogen adsorption-desorption analysis revealed that the specific surface area of ​​silica synthesized directly from sodium fluorosilicate and sodium silicate is relatively small, at 26.47 m². 2 / g. From Figure 12It can be observed that the synthesized silica lacks a porous structure. These results combined indicate that silica can be directly synthesized from sodium fluorosilicate and sodium silicate, but a high specific surface area cannot be achieved.

[0113] Example 4

[0114] Dissolve 2.84 g of sodium silicate nonahydrate and 1.365 g of hexadecyltrimethylammonium bromide in 200 ml of deionized water, heat to 60 °C, and stir at 500 rpm for 30 min to prepare a silicon source-soft template composite solution (sodium silicate concentration is 0.05 mol / L, soft template agent concentration is 0.0187 mol / L).

[0115] Add 1.340g of ammonium fluorosilicate to 50ml of deionized water to form an ammonium fluorosilicate solution (concentration of 0.15mol / L).

[0116] Ammonium fluorosilicate solution was added to silicon source-soft template composite solution at a rate of 1 ml / min. The reaction temperature was 60℃, and the mixture was stirred at 500 rpm for 120 min. After the reaction, the precipitate was filtered to obtain mesoporous silica precursor.

[0117] The mesoporous silica precursor was dried at 80°C for 12 hours and then placed in a muffle furnace and calcined at 550°C for 3 hours in air atmosphere to obtain mesoporous silica.

[0118] Figure 13 This is a TEM image of the mesoporous silica prepared in Example 4. Figure 14 The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 4. Figure 15 This is a pore size distribution diagram of the mesoporous silica prepared in Example 4.

[0119] from Figure 13 It can be observed that the silica obtained after the reaction using this method exhibits a distinct mesoporous structure. From... Figure 14 The structure reveals that the formed mesoporous silica has a very large specific surface area of ​​899.86 m². 2 / g. From Figure 15 The formed mesoporous silica was found to have a pore size of 4.58 nm. These results demonstrate that mesoporous silica can also be obtained through a dual-silicon source synergistic reaction of ammonium fluorosilicate and sodium silicate.

[0120] Example 5

[0121] Keep all other reaction conditions the same as in Example 4, except that the amount of added hexadecyltrimethylammonium bromide is changed to 0.91 g (soft template concentration is 0.0125 mol / L).

[0122] Figure 16 This is a TEM image of the mesoporous silica prepared in Example 5. Figure 17 The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 5. Figure 18 This is a pore size distribution diagram of the mesoporous silica prepared in Example 5.

[0123] from Figure 16 It can be observed that the silica obtained after the reaction using this method exhibits a distinct mesoporous structure. Combined with... Figure 17 Nitrogen adsorption-desorption test and Figure 18 Pore ​​size analysis revealed that the formed mesoporous silica has a very large specific surface area of ​​512.98 m². 2 / g, the resulting mesoporous silica has a pore size of 5.28nm. The above results demonstrate that mesoporous silica can also be obtained under these conditions.

[0124] Example 6

[0125] Keep all other reaction conditions the same as in Example 5, except that the amount of added hexadecyltrimethylammonium bromide is changed to 0.45 g (soft template concentration is 0.00625 mol / L).

[0126] Figure 19 This is a TEM image of the mesoporous silica prepared in Example 6. Figure 20 The attached diagram shows the nitrogen adsorption-desorption process of the mesoporous silica prepared in Example 6. Figure 21 This is a pore size distribution diagram of the mesoporous silica prepared in Example 6.

[0127] from Figure 19 It can be observed that the silica obtained after the reaction has a mesoporous structure. Combined with... Figure 20 Nitrogen adsorption-desorption test and Figure 21 Pore ​​size analysis revealed that the specific surface area of ​​the formed mesoporous silica was 150.77 m². 2 / g, the formed silica has a pore size of 3.01nm. The above results show that mesoporous silica can be formed under these reaction conditions, but the specific surface area is relatively lower than that of Examples 4 and 5.

[0128] Comparative Example 2

[0129] Dissolve 2.84g of sodium silicate nonahydrate in 200ml of deionized water, heat to 60℃, and stir at 500rpm for 30min to prepare a sodium silicate solution (sodium silicate concentration is 0.05mol / L).

[0130] Add 1.340g of ammonium fluorosilicate to 50ml of deionized water to form an ammonium fluorosilicate solution (concentration of 0.15mol / L).

[0131] Ammonium fluorosilicate solution was added to sodium silicate solution at a rate of 1 ml / min. The reaction temperature was 60℃, and the mixture was stirred at 500 rpm for 120 min. After the reaction, the precipitate was filtered to obtain the silica precursor.

[0132] The silica precursor was dried at 80°C for 12 hours and then placed in a muffle furnace and calcined at 550°C for 3 hours in air atmosphere to obtain silica.

[0133] Figure 22 This is a TEM image of the mesoporous silica prepared in Comparative Example 2. Figure 23 The attached diagram shows the nitrogen adsorption-desorption process of silica prepared in Comparative Example 2. Figure 24 This is a pore size distribution diagram of the mesoporous silica prepared in Comparative Example 2.

[0134] from Figure 22 It can be observed that the sample synthesized directly from ammonium fluorosilicate and sodium silicate exhibits a non-porous, dense structure. Combined with... Figure 23 Nitrogen adsorption-desorption analysis revealed that the silica synthesized directly from ammonium fluorosilicate and sodium silicate has a relatively small specific surface area of ​​65.32 m². 2 / g. From Figure 24 It was observed that the synthesized silica lacked a porous structure. These results combined indicate that silica can be directly synthesized from ammonium fluorosilicate and sodium silicate, but a high specific surface area cannot be achieved.

[0135] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing mesoporous silica, characterized in that, Including the following steps: A mixed system comprising a first silicon source precursor, a soft template reagent, and a second silicon source precursor is obtained; the mixed system undergoes a sol-gel reaction, followed by solid-liquid separation, and the solid phase is collected to obtain a mesoporous silica precursor; the first silicon source precursor comprises sodium silicate; the second silicon source precursor comprises sodium fluorosilicate and / or ammonium fluorosilicate; The mesoporous silica precursor is calcined to obtain mesoporous silica.

2. The method for preparing mesoporous silica according to claim 1, characterized in that, The steps for obtaining the mixed system comprising the first silicon source precursor, the soft template reagent, and the second silicon source precursor include: The first silicon source precursor and the soft template reagent are mixed in a first solvent and homogenized to obtain a silicon source-soft template composite solution. The second silicon source precursor is then dissolved in the second solvent to obtain a silicon source suspension. The silicon source suspension is added to the silicon source-soft template composite solution to obtain the mixed system.

3. The method for preparing mesoporous silica according to claim 2, characterized in that, The soft template reagent includes one or more cationic surfactants such as hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

4. The method for preparing mesoporous silica according to claim 2, characterized in that, In the silicon source-soft template composite solution, the concentration of the first silicon source precursor is 0.05-0.3 mol / L, and the concentration of the soft template reagent is 0.001-0.02 mol / L; in the silicon source suspension, the concentration of the second silicon source precursor is 0.1-0.5 mol / L.

5. The method for preparing mesoporous silica according to claim 2, characterized in that, The sol-gel reaction is carried out at a temperature of 25-60℃ for a duration of 30-120 minutes.

6. The method for preparing mesoporous silica according to any one of claims 2 to 5, characterized in that, In the step of adding the silicon source suspension to the silicon source-soft template composite solution to obtain the mixed system, the volume ratio of the silicon source suspension to the silicon source-soft template composite solution is 1:4 to 30. In the hybrid system, the molar ratio of the first silicon source precursor to the second silicon source precursor is 1.2 to 4:

1.

7. The method for preparing mesoporous silica according to claim 1, characterized in that, The calcination treatment is carried out at a temperature of 450-650℃ for a time of 0.5-6 hours.

8. The method for preparing mesoporous silica according to claim 7, characterized in that, The flow rate of the calcination atmosphere during the calcination process is 5-25 L / min.

9. A mesoporous silica, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The mesoporous silica according to claim 9, characterized in that, The specific surface area of ​​the mesoporous silica is 150–950 m². 2 / g, wherein the pore size of the mesoporous silica surface is 3-5.5nm.

Images