A method for producing mesoporous silica

Abstract

The present invention discloses a method for producing mesoporous silica. By introducing PPA, CTAB has pH-responsive characteristics, and using this as a template for the synthesis of mesoporous silica, and removing the template by adjusting the pH, which is not only simple and environmentally friendly, but also avoids the destruction of the mesoporous structure, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the field of chemical synthesis, and particularly to a production method of mesoporous silica. Background Art

[0002] Since the mesoporous material MCM-41 was discovered in 1992, its unique physical and chemical properties, such as large specific surface area and pore volume, ordered pore channels, and easily modified inner and outer surfaces, have made it widely used in many fields such as catalysts, biomedicine, and optics.

[0003] The preparation methods of mesoporous materials include soft template method and hard template method. Because the soft template method does not require complex equipment, is easy to operate, and can synthesize mesoporous materials with different morphologies and mesoporous structures, it has been widely used. The traditional soft template method for synthesizing mesoporous materials needs to go through a template removal process to obtain the mesoporous structure. Currently, the main template removal methods include high-temperature calcination method, oxidation method, supercritical CO2 extraction method, solvent extraction method, etc. However, the above methods all have certain defects. For example, the high-temperature calcination method is prone to cause the collapse of the mesoporous structure, cannot retain silanol groups, and cannot recycle the template agent, which is easy to cause environmental pollution; the solvent extraction method takes a long time and consumes a large amount of solvents; the oxidation method has complex operations and harsh conditions; the supercritical CO2 extraction method requires different extraction conditions for different mesoporous materials, with low efficiency. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a production method of mesoporous silica. By using the method of the present invention to prepare mesoporous silica, the template can be removed without consuming too much energy or extra steps, which is simple and environmentally friendly.

[0005] The technical solution of the present invention is realized as follows:

[0006] The present invention provides a production method of mesoporous silica, which specifically includes the following steps:

[0007] S1: Modification of surfactant: Dissolve the surfactant and the modifier in deionized water, stir and heat to obtain a modified surfactant;

[0008] S2: Preparation of mesoporous silica; Add a silicon source and a chelating agent to the modified surfactant, and dropwise add hydrochloric acid to adjust the pH, stir and react. After the reaction is completed, dropwise add sodium hydroxide to adjust the pH and purify to obtain the mesoporous silica.

[0009] Further, in step S1, the surfactant is cetyltrimethylammonium bromide.

[0010] Hexadecyltrimethylammonium Bromide (CTAB for short) is a common cationic surfactant, consisting of a hydrophilic head group and a hydrophobic tail chain. It has a wide range of applications in industrial production and daily life, with functions such as emulsification, softening, decontamination, solubilization, antistatic, and biodegradation. Therefore, it is widely used in fields such as emulsion foaming agents, analytical reagents, leather fatliquors, and soldering fluxes.

[0011] CTAB can spontaneously aggregate to form various micelle morphologies in aqueous solutions, such as spherical and rod-like shapes. Since CTAB molecules themselves do not have environmental-responsive groups such as -COOH and -NH2, CTAB does not have environmental-responsive functions, which to a certain extent limits the application of CTAB. However, because CTAB molecules themselves have good coordination properties and can be compounded with anions, cations, amphoteric surfactants, alcohols, etc., such structural characteristics provide a good structural basis for the realization of CTAB intelligence.

[0012] Furthermore, the modifier in step S1 is potassium hydrogen phthalate.

[0013] Potassium hydrogen phthalate (PPA) has a protonatable group -COOH. The essence of its pH response is that when the pH condition changes, the protonatable group can accept or provide protons, thereby causing changes in the hydrophilicity and hydrophobicity of the molecule.

[0014] Furthermore, the molar ratio of the surfactant to the modifier is 6:3 - 6:5.

[0015] Furthermore, the heating temperature in step S1 is 70 - 80 °C.

[0016] During the pH-responsive demulsification process, the electrostatic repulsion between emulsions and the steric hindrance caused by the interfacial film are two crucial factors affecting the stability of emulsions. When the pH is less than 2.9, that is, in the low pH region, since the introduced PPA molecules are not charged themselves at this time and the positive charges carried by CTAB itself are not neutralized, the electrostatic repulsion between the two emulsions is very strong. At the same time, the PPA molecules are closer to the centroid of the oil droplets and the density of the film is also greater. This results in the stability of the emulsion at low pH. This is not the case at medium and high pH. The emulsion is unstable at this time, mainly for the following two reasons: First, since the PPA molecules carry negative charges opposite to the CTAB head groups at this time, which can neutralize the positive charges of CTAB on the emulsion surface, this will lead to a weakening of the electrostatic repulsion between the two emulsions; Second, due to the charged PPA head groups, there is an electrostatic attraction between the CTAB head group Q0 and the PPA head group Qa, making the distance between CTAB and PPA closer, which will cause the interfacial film to become looser, the molecular density to decrease, and the steric hindrance between the two emulsions to decrease, resulting in demulsification. Based on the above two reasons, when the pH is adjusted from low to medium or high, pH-induced emulsification demulsification will occur. This leads to the separation of the hydrophilic surfactant template and water-insoluble silica.

[0017] Further, the silicon source described in step S2 is tetraethyl orthosilicate.

[0018] Further, the chelating agent described in step S2 is disodium ethylenediaminetetraacetate.

[0019] Disodium ethylenediaminetetraacetate (Na2EDTA) is a commonly used chelating agent. It forms aggregates with the modified surfactant in the solution and covers the outer layer of the micelles after forming micelles, thereby reducing the probability of connection with the pore wall. In theory, it can improve the removal rate of the template agent. At the same time, it can also catalyze the hydrolysis process of the silicon source TEOS, resulting in more nucleation and easily obtaining particles with smaller particle sizes.

[0020] Further, the molar ratio of the chelating agent to the silicon source is 1:2 - 1:3.

[0021] Further, the pH value after adding hydrochloric acid in step S2 is less than 2.9.

[0022] Further, the pH value after adding sodium hydroxide in step S2 is greater than 5.4.

[0023] Compared with the prior art: The beneficial effects of the present invention are:

[0024] By introducing PPA, CTAB has pH-responsive characteristics, and using this as a template for the synthesis of mesoporous silica, and removing the template by adjusting the pH, which is not only simple and environmentally friendly, but also avoids the destruction of the mesoporous structure. Detailed implementation manners

[0025] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Reagent description:

[0027] Cetyltrimethylammonium bromide, potassium hydrogen phthalate, tetraethyl orthosilicate, disodium ethylenediaminetetraacetate, hydrochloric acid, sodium hydroxide, analytical pure, Sinopharm Chemical Reagent Co., Ltd. Example 1

[0028] S1: Modification of surfactant: Dissolve 0.06 mol of cetyltrimethylammonium bromide and 0.04 mol of potassium hydrogen phthalate in 2000 mL of deionized water, and stir at 75 °C to obtain a modified surfactant;

[0029] S2: Preparation of mesoporous silica; Add 0.06 mol of tetraethyl orthosilicate and 0.024 mol of disodium ethylenediaminetetraacetate to the modified surfactant, and dropwise add hydrochloric acid to adjust the pH to 2.5, stir and react. After the reaction is completed, dropwise add sodium hydroxide to adjust the pH to 6.0, and perform centrifugal separation and wash with water and acetone to obtain the mesoporous silica. Example 2

[0030] The difference between this example and Example 1 is that the addition amount of potassium hydrogen phthalate in step S1 is 0.03 mol.

[0031] Other parts are exactly the same as those in Example 1. Example 3

[0032] The difference between this example and Example 1 is that the addition amount of potassium hydrogen phthalate in step S1 is 0.05 mol.

[0033] Other parts are exactly the same as those in Example 1. Example 4

[0034] The difference between this example and Example 1 is that the addition amount of disodium ethylenediaminetetraacetate in step S2 is 0.02 mol.

[0035] Other parts are exactly the same as those in Example 1. Example 5

[0036] The difference between this example and Example 1 is that the addition amount of disodium ethylenediaminetetraacetate in step S2 is 0.03 mol.

[0037] The other parts are exactly the same as those in Example 1.

[0038] Detection and Results

[0039] The results are shown in Table 1.

[0040] Table 1

[0041] Project Template removal rate (%) Example 1 60 Example 2 57 Example 3 58 Example 4 49 Example 5 55

[0042] As can be seen from Table 1, the EDTA anions are electrostatically adsorbed on the outer layer of the micelles, making it difficult for DDAB to be adsorbed on the mesoporous wall through hydrogen bonding, thereby increasing the template removal rate. In addition, the electrostatic attraction between the EDTA anions and the CTAB cationic head groups reduces the hydrophilicity of the surfactant, resulting in a decrease in the hydrophilicity of the small particles of the inorganic-organic composite formed by self-assembly and making it difficult to disperse and grow into monodisperse spheres in an aqueous solution, which affects the template removal.

[0043] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A method for producing mesoporous silica, characterized in that: The following steps are involved: S1: Modification of surfactant: dissolving the surfactant and the modifier in deionized water, stirring and heating to obtain a modified surfactant; S2: Preparation of mesoporous silica: adding a silicon source and a chelating agent to the modified surfactant, dripping hydrochloric acid to adjust the pH, stirring to react, dripping sodium hydroxide to adjust the pH after the reaction, and purifying to obtain the mesoporous silica; The surfactant in step S1 is hexadecyltrimethylammonium bromide; The modifier in step S1 is potassium hydrogen phthalate; The molar ratio of the surfactant to the modifier is 6:3-6:5; The heating temperature in step S1 is 70-80°C; The silicon source in step S2 is ethyl silicate; The chelating agent in step S2 is disodium ethylenediaminetetraacetate; The molar ratio of the chelating agent to the silicon source is 1:2-1:3; The pH value after adding hydrochloric acid in step S2 is less than 2.9; The pH value after adding sodium hydroxide in step S2 is greater than 5.4.