Silica prepared based on a pH shock strategy and method thereof

Abstract

The application discloses silica prepared based on a pH shock strategy and a method thereof, and comprises the following steps: S1: preparing a sodium silicate aqueous solution and an acid hydrolyzed starch solution; S2: controlling gel self-assembly through a pH shock strategy; the acid hydrolyzed starch solution is added into the sodium silicate solution, and is fully stirred and mixed to form a uniform mixed solution; acid liquid is slowly added into the mixed solution, and pH is adjusted to 2-4; then, high-concentration sodium silicate aqueous solution is added to adjust pH to 8-10; acid liquid is added again, and pH is adjusted to 2-4; S3: the gel formed in the step S2 is aged and washed; S4: the washed gel is dried and calcined to obtain high-pore-volume silica. Through accurate control of the ratio of a silicon source and a biomass template, control of pH-induced self-assembly of silicon species on a starch template and effective control of the assembly kinetics of the two in a solution through a pH shock strategy, a new way is provided for low-cost and environment-friendly manufacturing of high-performance porous silica materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic porous material preparation, and particularly relates to a low-cost high-pore-volume silicon dioxide prepared based on a pH shock strategy and a method thereof. BACKGROUND

[0002] Porous silica materials have a wide range of applications in adsorption, catalysis, drug delivery and separation science due to their high specific surface area, tunable pore size, easy functionalization of the surface and good biocompatibility. Traditional mesoporous silica is mainly prepared by using expensive silane salts such as tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS) as the silicon source, and organic surfactants such as cetyltrimethylammonium bromide (CTAB) and block copolymers as the template agent, which is costly and may cause environmental pollution.

[0003] In recent years, in order to reduce production costs, researchers have begun to explore the use of cheap silicon sources such as water glass (sodium silicate) to replace traditional silane salts. For example, patent CN107010632A discloses a method for extracting biomass-based nanosilica from straw, heating with NaOH solution to obtain a biomass-based water glass solution, and further preparing a silica aerogel. This method realizes waste recycling, but the process is complex and requires multiple processes such as high-temperature pyrolysis, high-speed vibration ball milling and ultrasonic dispersion.

[0004] In terms of template agents, biomass templates have attracted attention due to their low cost, wide availability and environmental friendliness. Starch, as a renewable and biodegradable natural polysaccharide, has a large number of hydroxyl groups on its molecular chain, which can interact with silicon species through hydrogen bonds, serving as a pore-forming agent to induce the formation of porous structures. Therefore, developing a method for preparing high-pore-volume silica using inexpensive water glass as a silicon source and biomass starch as a template agent through a simple process has important scientific value and application prospects. SUMMARY

[0005] In view of the above deficiencies in the prior art, the present application provides a method for preparing silica based on a pH shock strategy, which is simple, low-cost and environmentally friendly.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a method for preparing silica based on a pH shock strategy, comprising the following steps:

[0008] S1: preparing a sodium silicate aqueous solution and an acid-treated starch solution;

[0009] S2: pH shock strategy for controlling gel self-assembly;

[0010] S21: adding the acid hydrolyzed starch solution into the sodium silicate solution, mixing thoroughly to form a homogeneous mixture; slowly adding acid solution into the mixture to adjust the pH to 2-4;

[0011] S22: subsequently, adding high concentration sodium silicate solution to adjust the pH to 8-10;

[0012] S23: again adding acid solution to adjust the pH to 2-4;

[0013] S3: aging and washing the gel formed in step S2;

[0014] S4: drying and calcining the washed gel to obtain silica.

[0015] Further, in step S1, the concentration of the sodium silicate solution is 0.05-0.2 M, and the modulus of sodium silicate is 2-3.5.

[0016] Further, the preparation step of the acid hydrolyzed starch solution is as follows:

[0017] First, preparing a starch water dispersion solution with a concentration of 5-60 wt%, then adjusting the pH to 3 by adding acid, heating to reflux at 65-95°C for 5-60 min, and finally transferring it to an ice water bath for rapid cooling and regeneration, thereby obtaining a clear and transparent acid hydrolyzed starch solution; the acid is sulfuric acid, hydrochloric acid or nitric acid.

[0018] Further, in step S21, the mass ratio of sodium silicate to acid hydrolyzed starch is 1:12-12:1; the addition rate of the acid hydrolyzed starch solution and acid solution is controlled at 0.1-2 mL / min; the acid solution is dilute sulfuric acid, dilute hydrochloric acid or acetic acid with a concentration of 0.1-3 M; after adjusting the pH by adding acid, standing at 40-60°C for 20-60 min to ensure sufficient self-assembly of silicon species and starch molecules.

[0019] Further, in step S22, the concentration of the sodium silicate solution is 0.5-2 M; the addition rate of the sodium silicate solution is controlled at 0.1-2 mL / min.

[0020] Further, in step S23, the addition rate of the acid solution is controlled at 0.1-2 mL / min; the acid solution is dilute sulfuric acid, dilute hydrochloric acid or acetic acid.

[0021] Further, the specific process of step S3 is as follows: aging the gel at 40-80°C for 5 min-6 h; washing the aged gel with deionized water until the washing liquid is neutral; then, replacing the residual water in the gel with ethanol.

[0022] Further, the specific process of step S4 is: drying the washed gel at 75-120 DEG C for 12-24 hours; calcining the dried product at 400-600 DEG C for 2-6 hours to remove the starch template, to obtain the silicon dioxide.

[0023] In a second aspect, the present application provides the silicon dioxide prepared by the above preparation method.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The present application proposes a green synthesis route using cheap and readily available water glass (sodium silicate) as a silicon source and biomass starch as a dual-functional template / pore-forming agent to prepare high-porosity silicon dioxide materials. By precisely controlling the ratio of silicon source to biomass template, the self-assembly of silicon species on the starch template is induced by pH, and the assembly kinetics of the two in solution is effectively controlled by a pH shock strategy. This method not only significantly reduces the dependence on expensive organic silicon sources (such as tetraethyl orthosilicate) and organic template agents (such as surfactants) in traditional silicon dioxide preparation processes, thereby greatly reducing production costs; it also effectively avoids the use and residue of harmful organic reagents, providing a new approach with high economic efficiency and sustainability for the low-cost, environmentally friendly manufacturing of high-performance porous silicon dioxide materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a preparation flowchart of the high-porosity silicon dioxide of the present application.

[0027] Figure 2 is a regulation diagram for regulating the self-assembly kinetics of the gel by the pH shock strategy.

[0028] Figure 3 is the X-ray diffraction pattern of the silicon dioxide prepared in Example 1.

[0029] Figure 4 is the electron microscope image of the silicon dioxide prepared in Example 1. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0031] Reference Figure 1 and Figure 2 The method for preparing silicon dioxide based on the pH shock strategy of the present application comprises the following steps:

[0032] S1: preparing a sodium silicate aqueous solution and an acid hydrolyzed starch solution;

[0033] S2: pH shock strategy for regulating gel self-assembly;

[0034] S21: adding the acid hydrolyzed starch solution into the sodium silicate solution, fully stirring to form a uniform mixture; slowly adding acid into the mixture to adjust the pH to 2-4;

[0035] S22: subsequently, adding a high-concentration sodium silicate aqueous solution to adjust the pH to 8-10;

[0036] S23: again adding acid to adjust the pH to 2-4;

[0037] S3: aging and washing the gel formed in step S2;

[0038] S4: drying and calcining the washed gel to obtain silicon dioxide.

[0039] Example 1

[0040] First, a 20 mL sodium silicate aqueous solution with a concentration of 0.1 M (sodium silicate modulus of 3.3) was prepared, and the pH thereof was 10.97. A 20% by mass starch aqueous solution was also prepared, and sulfuric acid was added to adjust the pH to 3, and the solution was heated to reflux at 90°C for 30 min; subsequently, the solution was transferred to an ice water bath for rapid cooling and regeneration to obtain a clear and transparent 20wt% acid hydrolyzed starch solution.

[0041] 1 mL of the above 20wt% acid hydrolyzed starch solution was added to 20 mL of the 0.1 M sodium silicate aqueous solution at a rate of 2 mL / min, and fully mixed under stirring at a speed of 800 rpm to form a uniform mixture. Subsequently, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min to adjust the pH of the mixture to 2.88, and the mixture was left to stand at 50°C for 30 min to form a gel. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the pH of the system was adjusted to 9.82 by vigorous stirring (800 rpm). Next, 2 mL of 1 M sulfuric acid was immediately added again to adjust the pH to 3.02, and the gel was aged at 75°C for 10 min.

[0042] After aging, the obtained gel was washed with deionized water until neutral, and the solvent was replaced with anhydrous ethanol for 3 times. Then, the sample was transferred to an oven at 80°C for drying for 18 h. Finally, the dried powder was transferred to a muffle furnace, and the temperature was increased to 600°C at a rate of 1°C / min for calcination for 3 h, and then cooled to room temperature to obtain the high-pore-volume silicon dioxide. Figure 3 and Figure 4X-ray diffraction pattern and electron microscope image of the obtained silica, respectively.

[0043] Example 2

[0044] First, 20 mL of 0.2 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH thereof was 11.25. In addition, a 20% by mass starch aqueous solution was prepared, and sulfuric acid was added to adjust the pH to 3, and the solution was heated to reflux at 90°C for 30 min; then, the solution was transferred to an ice water bath to rapidly cool and regenerate, to obtain a clear and transparent 20 wt% acid hydrolyzed starch solution.

[0045] The 0.2 mL of the above 20 wt% acid hydrolyzed starch solution was added to 20 mL of 0.2 M sodium silicate aqueous solution at a rate of 2 mL / min, and the mixture was mixed at a stirring speed of 800 rpm to form a uniform mixture. Then, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min, the pH of the mixture was adjusted to 2.86, and the mixture was left to stand to assemble at 50°C for 30 min to form a gel. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the pH of the system was adjusted to 9.88 by vigorous stirring (800 rpm). Next, sulfuric acid was immediately added again to adjust the pH to 2.97, and the mixture was aged at 75°C for 10 min.

[0046] After the aging was completed, the obtained gel was washed with deionized water until neutral, and the solvent was replaced with anhydrous ethanol for 3 times. Then, the sample was transferred to an oven at 80°C to dry for 18 h. Finally, the dried powder was transferred to a muffle furnace, and the temperature was increased to 600°C at a rate of 1°C / min, and the powder was calcined for 3 h, and then cooled to room temperature, to obtain the high pore volume silica.

[0047] Example 3

[0048] First, 20 mL of 0.2 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH thereof was 11.25. In addition, a 20% by mass starch aqueous solution was prepared, and sulfuric acid was added to adjust the pH to 3, and the solution was heated to reflux at 90°C for 30 min; then, the solution was transferred to an ice water bath to rapidly cool and regenerate, to obtain a clear and transparent 20 wt% acid hydrolyzed starch solution.

[0049] 2.5 mL of the 20 wt% acid-hydrolyzed starch solution was added to 20 mL of 0.05 M sodium silicate aqueous solution at a rate of 2 mL / min, and the mixture was stirred thoroughly at 800 rpm to form a homogeneous solution. Then, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min to adjust the pH to 2.91, and the mixture was allowed to stand at 50 °C for 30 min to form a gel. Next, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the mixture was stirred vigorously (800 rpm) to adjust the pH to 9.85. Immediately afterwards, sulfuric acid was added again to adjust the pH to 3.06, and the mixture was aged at 75 °C for 10 min.

[0050] After aging, the resulting gel was washed with deionized water until neutral, and then the solvent was replaced three times with anhydrous ethanol. Next, the sample was transferred to an 80°C oven and dried for 18 hours. Finally, the dried powder was transferred to a muffle furnace and calcined at 600°C for 3 hours at a rate of 1°C / min, then cooled to room temperature to obtain high-porosity silica.

[0051] Example 4

[0052] First, prepare 20 mL of a 0.1 M sodium silicate aqueous solution (sodium silicate modulus 3.3) with a pH of 10.97. Separately, prepare a 20% starch aqueous solution, adjust the pH to 3 with sulfuric acid, and heat under reflux at 90°C for 30 min. Then, transfer the solution to an ice-water bath for rapid cooling and regeneration, yielding a clear and transparent 20 wt% acid-hydrolyzed starch solution.

[0053] 0.5 mL of the above 20 wt% acid-hydrolyzed starch solution was added to 20 mL of 0.1 M sodium silicate aqueous solution at a rate of 2 mL / min, and the mixture was stirred thoroughly at 800 rpm to form a homogeneous solution. Then, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min to adjust the pH to 2.95, and the mixture was allowed to stand at 50 °C for 30 min to form a gel. Next, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the mixture was stirred vigorously (800 rpm) to adjust the pH to 9.83. Immediately afterwards, sulfuric acid was added again to adjust the pH to 2.99, and the mixture was aged at 75 °C for 10 min.

[0054] After aging, the resulting gel was washed with deionized water until neutral, and then the solvent was replaced three times with anhydrous ethanol. Next, the sample was transferred to an 80°C oven and dried for 18 hours. Finally, the dried powder was transferred to a muffle furnace and calcined at 600°C for 3 hours at a rate of 1°C / min, then cooled to room temperature to obtain high-porosity silica.

[0055] Example 5

[0056] First, 20 mL of 0.1 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH of which was 10.97. A 60wt% starch solution was prepared by adding sulfuric acid to adjust the pH to 3, and then heated to reflux at 90°C for 30 min; then the solution was transferred to an ice water bath for rapid cooling and regeneration, and a clear and transparent 60wt% acid hydrolysis starch solution was obtained.

[0057] 5 mL of the above 60wt% acid hydrolysis starch solution was added to 20 mL of 0.1 M sodium silicate aqueous solution at a rate of 2 mL / min, and mixed well at a stirring speed of 800 rpm to form a uniform mixture. Then, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min to adjust the pH of the mixture to 3.01, and the mixture was left to stand at 50°C for 30 min to form a gel. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the pH of the system was adjusted to 9.88 by vigorous stirring (800 rpm). Next, sulfuric acid was immediately added again to adjust the pH to 3.04, and the gel was aged at 75°C for 10 min.

[0058] After aging, the obtained gel was washed with deionized water until neutral, and then the solvent was replaced with anhydrous ethanol for 3 times. Then, the sample was transferred to an oven at 80°C for drying for 18 h. Finally, the dried powder was transferred to a muffle furnace, and then the temperature was increased to 600°C at a rate of 1°C / min, and calcined for 3 h, and then cooled to room temperature to obtain high pore volume silica.

[0059] Comparative Example 1 : No template used

[0060] First, 20 mL of 0.1 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH of which was 10.97.

[0061] To 20 mL of 0.1 M sodium silicate aqueous solution, 2 mL of 1 M sulfuric acid was added at a rate of 2 mL / min to adjust the pH to 2.98, and the mixture was left to stand at 50°C for 30 min. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the pH of the system was adjusted to 8.91 by vigorous stirring (800 rpm). Next, sulfuric acid was immediately added again to adjust the pH to 3.90, and the gel was aged at 75°C for 10 min.

[0062] After aging, the obtained gel was washed with deionized water until neutral, and then the solvent was replaced with anhydrous ethanol for 3 times. Finally, the sample was transferred to an oven at 80°C for drying for 18 h, and then cooled to room temperature.

[0063] Comparative Example 2: Starch not acid treated

[0064] First, 20 mL of 0.1 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH of the solution was 10.97. A 20% by mass starch aqueous solution was also prepared.

[0065] 1 mL of the above 20% by mass starch aqueous solution was added to 20 mL of 0.1 M sodium silicate aqueous solution at a rate of 2 mL / min, and the mixture was mixed well at a stirring speed of 800 rpm to form a uniform mixture. Subsequently, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min, the pH of the mixture was adjusted to 3.02, and the mixture was left to stand for assembly at 50°C for 30 min. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the mixture was stirred vigorously (800 rpm) to adjust the pH of the system to 9.91. Next, the pH was immediately adjusted to 2.94 again by adding sulfuric acid, and the mixture was left to age at 75°C for 10 min.

[0066] After the aging was completed, the obtained gel was washed with deionized water until neutral, and the solvent was replaced with anhydrous ethanol three times. Next, the sample was transferred to an oven at 80°C and dried for 18 h. Finally, the dried powder was transferred to a muffle furnace, and the temperature was increased to 600°C at a rate of 1 °C / min and calcined for 3 h, and then cooled to room temperature to obtain high pore volume silica.

[0067] Comparative Example 3: No staged pH adjustment

[0068] First, 20 mL of 0.1 M sodium silicate aqueous solution (modulus of sodium silicate is 3.3) was prepared, and the pH of the solution was 10.83. A 10% by mass starch aqueous solution was also prepared, and the pH was adjusted to 3 by adding sulfuric acid, and the solution was heated to reflux at 90°C for 30 min; then the solution was transferred to an ice water bath to rapidly cool and regenerate to obtain a clear and transparent 10% by mass acid hydrolyzed starch solution.

[0069] 2 mL of the above 10% by mass acid hydrolyzed starch solution was added to 20 mL of 0.1 M sodium silicate aqueous solution at a rate of 2 mL / min, and the mixture was mixed well at a stirring speed of 800 rpm to form a uniform mixture. Subsequently, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min, the pH of the mixture was adjusted to 3.12, and the mixture was left to stand for assembly at 50°C for 30 min, and then left to age at 75°C for 10 min.

[0070] After aging was completed, the resulting gel was washed with deionized water by syneresis until neutral (5000 rpm, 5 min, 5 times) and the solvent was replaced with anhydrous ethanol 3 times. Next, the sample was transferred to an oven at 80 °C for drying for 18 h. Finally, the dried powder was transferred to a muffle furnace and calcined at 600 °C for 3 h with a ramp of 1 °C / min, and then cooled to room temperature to obtain the high pore volume silica.

[0071] Comparative Example 4

[0072] First, 20 mL of aqueous sodium silicate solution (modulus of sodium silicate 3.3) with a concentration of 0.1 M was prepared, and the pH was 10.97. A 20% by mass aqueous starch solution was prepared, and the pH was adjusted to 3 by adding sulfuric acid, and heated to reflux at 90 °C for 30 min; then it was transferred to an ice water bath for rapid cooling and regeneration to obtain a clear and transparent 20% acid hydrolyzed starch solution.

[0073] 1 mL of the above 20% acid hydrolyzed starch solution was added to 20 mL of 0.1 M aqueous sodium silicate solution at a rate of 2 mL / min, and mixed well at a stirring speed of 800 rpm to form a uniform mixture. Then, 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 2 mL / min to adjust the pH of the mixture to 1.57, and the mixture was left to stand for assembly at 50 °C for 30 min to form a gel. Then, 2 mL of 0.5 M sodium silicate solution was added at a rate of 2 mL / min, and the pH of the system was adjusted to 10.85 by vigorous stirring (800 rpm). Then, 2 mL of 1 M sulfuric acid was immediately added again to adjust the pH to 1.32, and the aging was carried out at 75 °C for 10 min.

[0074] After aging was completed, the resulting gel was washed with deionized water by syneresis until neutral (5000 rpm, 5 min, 5 times) and the solvent was replaced with anhydrous ethanol 3 times. Next, the sample was transferred to an oven at 80 °C for drying for 18 h. Finally, the dried powder was transferred to a muffle furnace and calcined at 600 °C for 3 h with a ramp of 1 °C / min, and then cooled to room temperature to obtain the high pore volume silica.

[0075] Comparative Example 5

[0076] First, 20 mL of aqueous sodium silicate solution (modulus of sodium silicate 3.3) with a concentration of 0.1 M was prepared, and the pH was 10.97. A 20% by mass aqueous starch solution was prepared, and the pH was adjusted to 3 by adding sulfuric acid, and heated to reflux at 90 °C for 30 min; then it was transferred to an ice water bath for rapid cooling and regeneration to obtain a clear and transparent 20% acid hydrolyzed starch solution.

[0077] A 1 mL of the above 20 wt% acid hydrolyzed starch solution was added to 20 mL of 0.4 M sodium silicate aqueous solution and mixed thoroughly at 800 rpm to form a homogeneous mixture. 2 mL of 1 M sulfuric acid was added to the mixture at a rate of 5 mL / min (the mixture gelled instantly upon addition of the sulfuric acid), the pH of the mixture was adjusted to 2.96, and the mixture was allowed to stand at 50 °C for 30 min. Then, 2 mL of 0.5 M sodium silicate aqueous solution was added to the mixture at a rate of 2 mL / min, the mixture was mixed thoroughly at 800 rpm, and the pH of the mixture was adjusted to 9.89. Next, sulfuric acid was added again to adjust the pH to 3.11, and the mixture was allowed to age at 75 °C for 10 min.

[0078] After aging, the resulting gel was washed with deionized water until neutral, and the solvent was replaced with anhydrous ethanol three times. Next, the sample was transferred to an 80 °C oven and dried for 18 h. Finally, the dried powder was transferred to a muffle furnace and calcined at 600 °C at a rate of 1 °C / min for 3 h, and then cooled to room temperature.

[0079] Comparative Example 6

[0080] First, a 20 mL of 2 M sodium silicate aqueous solution (the modulus of the sodium silicate was 3.3) was prepared, and the pH of the solution was 12.95. A 20 wt% starch aqueous solution was also prepared, and the pH of the solution was adjusted to 3 by adding sulfuric acid. The solution was heated to reflux at 90 °C for 30 min, and then transferred to an ice water bath to rapidly cool and regenerate, thereby obtaining a 20 wt% acid hydrolyzed starch solution.

[0081] A 15 mL of the above 20 wt% acid hydrolyzed starch solution was added to 20 mL of 2 M sodium silicate aqueous solution at a rate of 5 mL / min, and the mixture was mixed thoroughly at a stirring speed of 500 rpm to form a homogeneous mixture. Next, 2 mL of 1 M sulfuric acid was added (the mixture gelled instantly upon addition of the sulfuric acid, and it was difficult to stir. The addition of the sulfuric acid was continued, but the pH of the mixture did not change, which reflected the pH of the sulfuric acid. Therefore, the pH of the mixture could not be adjusted any further). Then, the mixture was allowed to stand at 50 °C for 30 min, and then aged at 75 °C for 10 min.

[0082] After aging, the resulting gel was washed with deionized water until neutral, and the solvent was replaced with anhydrous ethanol three times. Next, the sample was transferred to an 80 °C oven and dried for 18 h. Finally, the dried powder was transferred to a muffle furnace and calcined at 600 °C at a rate of 1 °C / min for 3 h, and then cooled to room temperature.

[0083] The preparation of the raw materials and the process of kinetic adjustment of gel assembly of Examples 1-5 and Comparative Examples 1-6 above are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] Pore structure characterisation

[0087] The pore structure of the silica prepared in Example 1-Example 5 and Comparative Example 1-Comparative Example 6 above was tested by a volumetric adsorption instrument under N2-77K conditions, including specific surface area, pore volume and pore size, and the test results are summarized in Table 2 below.

[0088] Table 2. Pore size properties

[0089]

[0090] From the comparison of Example 1-Example 5 in Table 2, it is found that the hierarchical porous silica prepared in Example 1 exhibits the optimal specific surface area and pore volume, which is beneficial for subsequent modification applications. That is, the optimal ratio of silicon source to acid hydrolyzed starch is 1.2:1.

[0091] By comparing Example 1 and Comparative Example 1-Comparative Example 6, the influence mechanism of the key process parameters in the method for preparing high-pore-volume silica based on the pH shock strategy of the present application is further revealed:

[0092] Effect of silicon source concentration: In Comparative Example 5-6, due to the excessively high initial concentration of sodium silicate, the gel assembly rate is too fast, which causes the silicon species to fail to achieve uniform and orderly assembly with the starch template, resulting in a significant decrease in the specific surface area and pore volume of the prepared silica.

[0093] Role of starch template pretreatment: The comparison of Example 1 and Comparative Example 2 shows that acid hydrolysis treatment of the starch template under acidic conditions can effectively increase the density of surface hydroxyl functional groups and reduce the molecular weight. This process enhances the hydrophilicity and reactivity of the template, thereby more effectively inducing the uniform deposition and assembly of silicon species on its surface and in its pores during the subsequent gel self-assembly process.

[0094] Necessity of pH shock strategy: Comparative Example 3 and Comparative Example 6 fail to adopt the pH shock strategy, and their assembly process is out of control, resulting in poor product structure and performance. The results of Comparative Example 4 further clarify that the pH value of the system during the acidic self-assembly stage should not be lower than 2. An excessively low pH environment will excessively accelerate the gelation process due to the excessively high concentration of hydrogen ions, which is not conducive to the formation of uniform structure. The pH shock strategy of the present application precisely controls the condensation reaction rate by timely and controllable switching between acidic and alkaline environments, effectively avoiding the assembly defects caused by the excessive gelation under acidic conditions.

[0095] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing silica based on a pH oscillation strategy, characterized in that, Includes the following steps: S1: Prepare an aqueous solution of sodium silicate and an acid-hydrolyzed starch solution; the concentration of the aqueous solution of sodium silicate is 0.05-0.2 M, and the modulus of sodium silicate is 2-3.5; S2: pH oscillation strategy regulates gel self-assembly; S21: Add the acid-hydrolyzed starch solution to the sodium silicate solution and stir thoroughly to form a homogeneous mixture; slowly add acid to the mixture to adjust the pH to 2-4; the mass ratio of sodium silicate to acid-hydrolyzed starch is 1:12-12:1; the addition rate of the acid-hydrolyzed starch solution and acid is controlled at 0.1-2 mL / min; the acid is dilute sulfuric acid, dilute hydrochloric acid, or acetic acid, with a concentration of 0.1-3M. S22: Subsequently, add a high-concentration sodium silicate aqueous solution to adjust the pH to 8-10; S23: Add acid again and adjust the pH to 2-4; S3: Aging and washing the gel formed in step S2; S4: Dry the washed gel, and calcine the dried product at 400-600 ℃ for 2-6 hours to remove the starch template and obtain silica.

2. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, The preparation steps of the acid-hydrolyzed starch solution are as follows: First, prepare a starch aqueous dispersion with a concentration of 5-60 wt%. Then, add acid to adjust the pH to 3, heat and reflux at 65-95 ℃ for 5-60 min, and finally transfer it to an ice-water bath for rapid cooling and regeneration to obtain a clear and transparent acid-hydrolyzed starch solution. The acid is sulfuric acid, hydrochloric acid, or nitric acid.

3. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, After adjusting the pH with acid in step S21, let it stand at 40-60 ℃ for 20-60 min.

4. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, In step S22, the concentration of the sodium silicate aqueous solution is 0.5-2 M; the addition rate of the sodium silicate aqueous solution is controlled at 0.1-2 mL / min.

5. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, In step S23, the acid addition rate is controlled at 0.1-2 mL / min; the acid is dilute sulfuric acid, dilute hydrochloric acid, or acetic acid.

6. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, The specific process of step S3 is as follows: age the gel at 40-80 ℃ for 5 min-6 h; wash the aged gel with deionized water until the washing solution is neutral; then replace the residual water in the gel with ethanol.

7. The method for preparing silica based on a pH oscillation strategy according to claim 1, characterized in that, In step S4, the washed gel is dried at 75-120 °C for 12-24 h.

8. A silicon dioxide prepared by the method according to any one of claims 1-7.

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