A method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions

Abstract

This invention relates to a method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions, overcoming the technical problems of existing technologies requiring strong acidic conditions and being environmentally unfriendly. It uses a nonionic block copolymer as a template agent, polyacrylic acid as a co-templating agent, and aminosilane as a co-structure directing agent to synthesize SBA-15 mesoporous silica material under near-neutral pH conditions. In particular, it raises the pH value of the liquid environment required for SBA-15 synthesis from the commonly used pH < 1 to near-neutral pH, significantly reducing the amount of acid required for synthesis. The product obtained by this invention has uniform pore size and high order, and uses environmentally friendly and inexpensive polyacrylic acid as a co-templating agent, avoiding the use of strong acids or ammonium fluoride and other polluting raw materials, making it easy to promote.

Description

Technical Field

[0001] This invention relates to a method for preparing mesoporous silica molecular sieves, specifically a method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions. Background Technology

[0002] SBA-15 mesoporous silica is one of a series of mesoporous silica materials developed by the Stucky research group at the University of California, possessing a highly ordered hexagonal structure and a regular pore distribution. Compared to MCM-41, SBA-15 has thicker pore walls, larger pore sizes, and significantly improved thermal and hydrothermal stability. Therefore, SBA-15 mesoporous materials have promising applications in catalysis, adsorption, separation, and biomedicine. However, the synthesis of SBA-15 requires a strongly acidic medium. The use of large amounts of acid not only corrodes industrial reactors but also causes serious environmental pollution, thus severely limiting the industrial application of SBA-15.

[0003] Currently, the most common method for synthesizing SBA-15 is the hydrothermal method proposed by Stucky et al., which uses an amphiphilic triblock copolymer as a template agent. This method can produce SBA-15 with a highly ordered pore structure and adjustable pore size. However, it requires a strongly acidic solution environment (pH < 1), making it unsuitable for large-scale industrial production. Stucky et al. introduced a method for synthesizing SBA-15 under near-neutral conditions using fluoride as a catalyst (Chem. Commun., 2000, 24, 2437-2438). However, this method uses ammonium fluoride, and the large amount of fluoride ions poses a threat to the environment and organisms, making it unsuitable for industrial production. Finding an environmentally friendly method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions is a direction being explored by materials scientists.

[0004] Chinese patent CN 108483453 A discloses a method for preparing SBA-15 type mesoporous silica microspheres, using polyvinyl alcohol as an additive and a classic P123 / silicon source / dilute hydrochloric acid system, with sodium silicate, tetraethyl orthosilicate, or methyl orthosilicate as the silica precursor. To date, no method for synthesizing the mesoporous silica material SBA-15 under near-neutral pH conditions has been reported. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions, overcoming the technical problems of existing technologies that require strongly acidic conditions and are environmentally unfriendly. It uses a nonionic block copolymer as a template agent, polyacrylic acid as a co-templating agent, and aminosilane as a co-structure directing agent to synthesize SBA-15 mesoporous silica material under near-neutral pH conditions. In particular, it raises the pH value of the liquid environment required for SBA-15 synthesis from the commonly used pH < 1 to near-neutral pH, significantly reducing the amount of acid required for synthesis. The product obtained by this invention has uniform pore size and high order, and uses environmentally friendly and inexpensive polyacrylic acid as a co-templating agent, avoiding the use of catalysts such as ammonium fluoride that cause environmental pollution, making it easy to promote.

[0006] The present invention provides a method for synthesizing mesoporous silica material SBA-15 under near-neutral pH conditions, which specifically includes the following steps:

[0007] 1) At room temperature, mix the aqueous solution of P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer) template agent with polyacrylic acid template agent, stir for 0.5-1h to obtain a mixed solution, then slowly add acid solution dropwise to make pH=4-5, stir thoroughly for 0.5-1h to obtain an emulsion;

[0008] 2) Add aminosilane dropwise to the emulsion while stirring, and add silicon source dropwise at the same time. Heat in a water bath and keep at 30-35℃, stirring thoroughly for 4-6 hours.

[0009] 3) The emulsion from step 2) is allowed to stand at 80°C for 24-48 hours to crystallize, preferably 24 hours; after the crystallization is completed, the reaction mixture is separated by centrifugation, the product is washed with water 1-3 times, and dried at 50-60°C to obtain a white solid product.

[0010] 4) Calcine the white solid product at 400-600℃ for 3-6 h; preferably 6 h; to obtain SBA-15 mesoporous silica.

[0011] Step 1) The mass ratio of P123 to polyacrylic acid is 1:2; the molecular weight of the polyacrylic acid is 3000-240000; the amount of HCl used is 0.7-1 ml, preferably 0.9 ml. The molecular weight of P123 is 5800.

[0012] In step 2), the mass ratio of P123 to silicon source is 1:1.5-2.1.

[0013] The molar ratio of aminosilane to silicon source in step 2) is 1:15-20.

[0014] The silicon source mentioned in step 2) is either tetraethyl orthosilicate or methyl orthosilicate.

[0015] The aminosilane mentioned in step 2) is 3-aminopropyltrimethoxysilane.

[0016] The SBA-15 prepared by this invention has uniform pore size, high degree of order, and regular morphology, and can be widely used in adsorption separation, drug loading, and catalysis.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This invention provides a method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions. The pH value of the liquid environment required for SBA-15 synthesis is increased from the commonly used pH < 1 to near-neutral pH, and the amount of acid required for synthesis is significantly reduced.

[0019] This invention uses environmentally friendly and inexpensive polyacrylic acid as a template agent, avoiding the use of catalysts such as ammonium fluoride that pollute the environment, and is easy to promote. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0021] Figure 1 The small-angle X-ray diffraction (XRD) pattern of the product in Example 1 is shown.

[0022] Figure 2 This is a scanning electron microscope (SEM) image of the product from Example 1.

[0023] Figure 3 This is a transmission electron microscope (TEM) image of the product from Example 1.

[0024] Figure 4 The nitrogen adsorption-desorption isotherms curves for the product of Example 1 are shown.

[0025] It should be noted that the product obtained in Example 2 is similar to the result in Example 1. To avoid redundancy, the accompanying drawings only show the various test results of the product in Example 1. Detailed Implementation

[0026] To further illustrate the technical means and effects of this invention, specific embodiments are provided to further explain the technical solution. However, this invention is not limited to the scope of these embodiments, meaning that it does not necessarily require the detailed methods described below for implementation. Those skilled in the art can make various modifications or variations within the scope of the claims, and can make equivalent substitutions for the raw materials and add auxiliary components, without affecting the substantive content of this invention. Example

[0027] A method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions includes the following steps:

[0028] 1) First, accurately weigh 1.00 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer into a beaker, dissolve it with 30.00 mL of H2O to obtain a solution;

[0029] 2) Add 2.00 g of 25wt% polyacrylic acid (molecular weight 240,000) dropwise to the above solution and stir at room temperature for 0.5 h to obtain a mixed solution;

[0030] 3) Under stirring conditions, slowly add 0.9 ml of 0.1 mol / L HCl solution dropwise to the mixed solution. The pH is 4.5. Stir continuously at room temperature for 0.5 h to obtain an emulsion.

[0031] 4) Add 89.60 mg of 3-aminopropyltrimethoxysilane dropwise to the emulsion under stirring conditions, followed by 2.08 g of tetraethyl orthosilicate. The molar ratio of 3-aminopropyltrimethoxysilane to tetraethyl orthosilicate is 1:20. Heat the emulsion in a water bath and keep it at 35°C. Stir thoroughly for 4 h.

[0032] 5) Allow the emulsion to stand at 80°C for 24 hours to react;

[0033] 6) After the reaction is allowed to stand, the reaction mixture is separated by centrifugation. The white solid obtained is washed three times with deionized water or ethanol and dried at 60 °C to obtain the white solid product.

[0034] 7) The white solid product was calcined at 550 °C for 6 h to remove the organic template agent, yielding SBA-15 mesoporous silica. Example

[0035] A method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions includes the following steps:

[0036] 1) First, accurately weigh 1.00 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer into a beaker, dissolve it with 30.00 mL of H2O to obtain a solution;

[0037] 2) Add 2.00 g of 25wt% polyacrylic acid (molecular weight 240,000) dropwise to the solution and stir at room temperature for 0.5 h to obtain a mixed solution;

[0038] 3) Slowly add 0.9 ml of 0.1 mol / L HCl solution dropwise to the mixed solution under stirring conditions, and continue stirring at room temperature for 0.5 h to obtain an emulsion;

[0039] 4) Add 89.60 mg of 3-aminopropyltrimethoxysilane dropwise to the emulsion under stirring conditions, then add 1.52 g of methyl orthosilicate dropwise, heat in a water bath and keep at 35°C, and stir for 4 h;

[0040] 5) Allow the emulsion to stand at 80°C for 24 hours to react;

[0041] 6) After the reaction is allowed to stand, the reaction mixture is separated by centrifugation. The white solid obtained is washed three times with deionized water and dried at 60 °C to obtain the white solid product.

[0042] 7) The white solid product was calcined at 550 °C for 6 h to remove the organic template agent, yielding SBA-15 mesoporous silica. Example

[0043] A method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions includes the following steps:

[0044] 1) First, accurately weigh 1.00 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer into a beaker, dissolve it with 30.00 mL of H2O to obtain a solution;

[0045] 2) Add 2.00 g of 25wt% polyacrylic acid (molecular weight 240,000) dropwise to the solution and stir at room temperature for 0.5 h to obtain a mixed solution;

[0046] 3) Slowly add 2 ml of 0.1 mol / L tartaric acid solution dropwise to the mixed solution under stirring conditions, and continue stirring at room temperature for 0.5 h to obtain an emulsion;

[0047] 4) Add 89.60 mg of 3-aminopropyltrimethoxysilane dropwise to the emulsion under stirring conditions, then add 1.52 g of methyl orthosilicate dropwise, heat in a water bath and keep at 35°C, and stir for 4 h;

[0048] 5) Allow the emulsion to stand at 80°C for 24 hours to react;

[0049] 6) After the reaction is allowed to stand, the reaction mixture is separated by centrifugation. The white solid obtained is washed three times with deionized water and dried at 60 °C to obtain the white solid product.

[0050] 7) The white solid product was calcined at 550 °C for 6 h to remove the organic template agent, yielding SBA-15 mesoporous silica.

Claims

1. A method for synthesizing SBA-15 mesoporous silica under near-neutral pH conditions, characterized in that... Includes the following steps: 1) Mix the P123 template agent aqueous solution with the polyacrylic acid template agent at room temperature and stir for 0.5-1h to obtain a mixed solution. Then slowly add an acid solution dropwise to make the pH 4-5 and stir thoroughly for 0.5-1h to obtain an emulsion. 2) Add aminosilane dropwise to the emulsion while stirring, and add silicon source dropwise at the same time. Heat in a water bath and keep at 30-35℃, stirring thoroughly for 4-6 hours. 3) The emulsion from step 2) was allowed to stand at 80°C for 24-48 hours to crystallize. After the crystallization was completed, the reaction mixture was separated by centrifugation, the product was washed with water 1-3 times, and dried at 50-60°C to obtain a white solid product. 4) Calcine the white solid product at 400-600℃ for 3-6 h to obtain SBA-15 mesoporous silica; Step 1) The mass ratio of P123 template agent to polyacrylic acid is 1:2; the molecular weight of the polyacrylic acid is 3000-240000; In step 2), the molar ratio of aminosilane to silicon source is 1:15-20; the mass ratio of P123 template agent to silicon source is 1:1.5-2.1; and the silicon source is tetraethyl orthosilicate or methyl orthosilicate.

2. The method according to claim 1, characterized in that... The acid mentioned in step 1) is 0.1 M HCl or 0.1 M tartaric acid.

3. The method according to claim 1, characterized in that... The aminosilane mentioned in step 2) is 3-aminopropyltrimethoxysilane.

4. The method according to claim 1, characterized in that... The emulsion described in step 3) is allowed to stand at 80°C for 24 hours to crystallize.

5. The method according to claim 1, characterized in that... The white solid product described in step 4) is calcined at 400-600℃ for 6 h.

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