Method and application for preparing sodium alginate-silica core-shell microspheres by a template method

Abstract

The present invention discloses a method for preparing sodium alginate / silica core-shell microspheres by a template method, and the method comprises the following steps: (1) Preparation of sodium alginate microspheres: By using a microsphere preparation instrument, sodium alginate microspheres of different sizes are prepared according to the required dimensions as the template cores for subsequent silica layer coating; (2) Coating of the silica shell layer: The sodium alginate microspheres in step (1) are placed in an aqueous solution containing tetraethoxysilane (TEOS), and a silica layer is in-situ polymerized on the surface of the sodium alginate microspheres through hydrolysis and self-condensation of TEOS to obtain sodium alginate / silica core-shell structure microspheres of different sizes. In the preparation process of this method, ethanol catalysis is not relied on, thereby weakening the condensation reaction between silanol groups and hydroxyl groups in sodium alginate. Through the hydrolysis of TEOS in the aqueous phase system and the self-condensation between silanol groups, a silica coating is formed and coated on the surface of the sodium alginate microspheres, and the controllable preparation of sodium alginate / silica core-shell microspheres of different sizes can be realized. In addition, the present invention also studies the influence of the size of the core-shell structure microspheres on their adsorption performance.

Description

Technical Field

[0001] The present invention relates to a method for preparing sodium alginate / silica core-shell microspheres by a template method, belonging to the fields of material chemistry and nanotechnology. Background Art

[0002] Sodium alginate / silica composite microspheres (SA@SiO2) have become important materials in the fields of environmental governance, gas purification, and water treatment due to their excellent adsorption properties and broad application prospects. However, there are some limitations in the traditional preparation methods of SA@SiO2 microspheres. The traditional preparation method involves mixing a sodium alginate solution with TEOS, ethanol, and an ammonia water solution, and then extruding it into a calcium chloride solution for solidification to form composite microspheres. This method is simple and easy to implement, but it has some obvious disadvantages. First, it cannot precisely control the particle size of the microspheres, resulting in uneven size distribution of the obtained microspheres. Second, due to the lack of precise control over the microsphere size, it is difficult to study the specific influence of size on the adsorption properties of SA@SiO2, limiting its application.

[0003] Furthermore, in the preparation of SA / SiO2 core-shell structure microspheres, the condensation reaction between tetramethoxysilane and the hydroxyl groups of sodium alginate in an ethanol solution was utilized to prepare a composite microsphere structure with silica embedded sporadically on the surface of sodium alginate microspheres (Roosen, J., et al. Industrial&Engineering Chemistry Research, 54(51), 12836-12846.), which improved the strength of sodium alginate microspheres, but the preparation of multi-sized SA / SiO2 core-shell structures could not be achieved.

[0004] Therefore, developing a new preparation method to prepare core-shell composite microspheres by a template method to achieve precise control of the size of SA / SiO2 microspheres, and at the same time combining the hydrogel properties of sodium alginate to achieve rapid swelling of the microspheres and enhance their adsorption properties is of great significance for improving their application in environmental governance. Summary of the Invention

[0005] The purpose of the present invention is to provide a new method for preparing sodium alginate / silica core-shell microspheres (SA / SiO2) by a template method, which overcomes the limitation of the traditional method that cannot precisely control the size of the composite microspheres by the condensation of silicon hydroxyl groups and hydroxyl groups of sodium alginate catalyzed by ethanol.

[0006] In the present invention, a silica shell layer is formed on the surface of alginate microspheres through the hydrolysis of TEOS and the polycondensation reaction between silanol groups, thereby obtaining alginate / silica core-shell structured microspheres of different sizes. The preparation of the core-shell microspheres is achieved in two steps: (1) First, alginate microspheres of different sizes are prepared as templates by a microsphere preparation instrument; (2) The alginate microspheres of different sizes are placed in TEOS, water, and ammonia water, and a silica shell layer is polymerized on the surface of the alginate microsphere template through the hydrolysis of TEOS and the polycondensation between silanol groups. During the preparation process, the size of the composite microspheres is further controlled by the reaction time between alginate and the TEOS aqueous solution and the concentration of TEOS. The prepared alginate / silica core-shell microspheres can achieve efficient adsorption of tetracycline pollutants.

[0007] In the present invention, an alginate solution with a certain concentration is used as the raw material, and alginate microspheres of different sizes (120 μm, 150 μm, 200 μm, 450 μm, 300 μm, 750 μm) are rapidly prepared by a microsphere preparation instrument. Through its cross-linking reaction with Ca 2+ , it is cured and stabilized. Further, using TEOS as the silicon source, a silica shell layer (30 min) is rapidly formed on the surface of the alginate microspheres through hydrolysis and polycondensation, realizing the preparation of SA / SiO2 core-shell structured microspheres with controllable sizes. The specific steps are as follows:

[0008] (1) Prepare an aqueous alginate solution with a mass fraction of 0.5 - 1.5%, and ultrasonically remove the bubbles;

[0009] (2) Place the prepared alginate solution in a solution bottle, connect the solution bottle to the microsphere preparation instrument, and prepare different-sized alginate microspheres as the inner core as templates; the particle size of the alginate microsphere templates is 120 - 750 μm;

[0010] The parameters of the microsphere preparation instrument are: nozzle particle size: 120 - 750 μm, Frequency: 170 - 1500, Electrode: 250V, Pressure: 270 - 600 mbar, Heating: 60 °C;

[0011] (3) Add the prepared alginate microspheres to a 2 - 4% CaCl2 solution and continue to stir at room temperature for 10 - 50 min to obtain cured and stabilized alginate microspheres;

[0012] (4) Add tetraethoxysilane (TEOS), water, and ammonia water to the alginate microspheres in (3), react at room temperature for 10 - 50 min, collect the microspheres, and freeze-dry to obtain alginate / silica core-shell microspheres;

[0013] The mass ratio of sodium alginate microspheres to TEOS is 5:1 to 268:1; the mass ratio of sodium alginate microspheres to water is 2.5:1 to 2.5:1.5; the mass ratio of sodium alginate microspheres to ammonia water is 14:1 to 9:1. Freeze-drying is carried out at -45 to -25 °C for 24 to 48 h. The schematic diagram of the preparation process is as Figure 1 shown.

[0014] In the present invention, by controlling the size of sodium alginate microspheres and the coating thickness of silica, microspheres with a SA / SiO2 core-shell structure having good biocompatibility and mechanical stability are prepared. The method includes the following steps: (1) Preparation of sodium alginate microspheres: Using a microsphere preparation instrument, sodium alginate microspheres of different sizes are prepared according to the required size as templates for subsequent silica layer coating. (2) Coating of the silica layer: The sodium alginate microspheres in step (1) are placed in a reaction solution containing tetraethoxysilane (TEOS), and silica layers are polymerized on the surface of the sodium alginate microspheres through TEOS hydrolysis and self-condensation to obtain sodium alginate / silica core-shell structure microspheres of different sizes. Compared with other methods for preparing sodium alginate / silica microspheres, this method does not rely on ethanol catalysis during the preparation process, thereby weakening the condensation reaction between silanol groups and hydroxyl groups in sodium alginate. A silica coating is formed by TEOS hydrolysis and self-condensation between silanol groups and coated on the surface of sodium alginate microspheres, enabling the controllable preparation of SA / SiO2 core-shell microspheres of different sizes. In addition, the present invention also studies the influence of size on the adsorption performance, further broadening its application prospects in the fields of sewage treatment, air purification, and drug delivery.

[0015] In summary, the novel method for preparing SA / SiO2 core-shell microspheres provided by the present invention not only prepares SA / SiO2 core-shell structure microspheres of different sizes, but also has excellent adsorption performance, especially suitable for fields such as water treatment and gas purification. By adjusting the dosage of TEOS, reaction time, etc., the size and adsorption performance of SA / SiO2 microspheres can be further optimized to achieve efficient adsorption of different pollutants. Description of the Drawings

[0016] Figure 1 It is a schematic diagram for the preparation of sodium alginate / silica (SA / SiO2) core-shell microspheres of different sizes in the present invention.

[0017] Figure 2 It is the physical map and SEM characterization results of SA / SiO2 core-shell microspheres of different sizes prepared in Example 1.

[0018] Figure 3 It is the physical map and SEM characterization results of SA / SiO2 core-shell microspheres of different sizes prepared in Example 2.

[0019] Figure 4 Photographs of SA / SiO2 core-shell microspheres with different sizes prepared in Example 3.

[0020] Figure 5 Photographs of SA / SiO2 core-shell microspheres prepared in Example 4.

[0021] Figure 6 Photographs of SA / SiO2 core-shell microspheres prepared in Example 5 and SEM characterization results.

[0022] Figure 7 Experimental result graphs of different-sized SA / SiO2 core-shell microspheres adsorbing tetracycline (TC). Detailed implementation manners

[0023] Below, taking tetracycline as the adsorption marker, the preparation by the template method and the adsorption capacity of SA / SiO2 core-shell microspheres will be further described in conjunction with the accompanying drawings.

[0024] Example 1

[0025] This example provides a new method for preparing SA / SiO2 core-shell microspheres by the template method, specifically as follows:

[0026] (1) Prepare a 1% sodium alginate solution and ultrasonically remove bubbles;

[0027] (2) Place the prepared sodium alginate solution in a solution bottle, connect the solution bottle to a microsphere preparation instrument, and the instrument parameters are: nozzle diameter: 750 μm, Frequency: 220, Electrode: 250 V, Pressure: 170 mbar, Heating: 60 °C; prepare a sodium alginate microsphere template;

[0028] (3) Stir the sodium alginate microspheres prepared under the parameters set in (2) in a 3% CaCl2 solution for 30 min;

[0029] (4) Place 2.5 g (wet weight) of the sodium alginate microspheres prepared in (3) into a round-bottom flask, add 30 μL TEOS, 1 mL of water, and 200 μL of ammonia water to the flask, react at room temperature for 30 min, and freeze-dry at -40 °C for 48 h to obtain SA / SiO2-750;

[0030] Figure 2 (A, B) are respectively the photograph and SEM image of SA / SiO2-750. The prepared SA / SiO2-750 has a particle size of about 1.2 mm; the SEM results show that on the basis of the original SA inner core template, silica has successfully formed a shell structure on its surface, increasing the size of the original inner core, and at the same time having a certain roughness on the surface.

[0031] Example 2

[0032] This example provides a method for preparing sodium alginate / silica core-shell microspheres by the template method. The difference in the preparation process from Example 1 is as follows: The parameters of the microsphere preparation instrument are: nozzle diameter: 450 μm, Frequency: 270, Electrode: 250 V, Pressure: 270 mbar, Heating: 60°C; other steps are the same as those in Example 1, and SA@SiO2-450 is obtained.

[0033] Figure 3 The physical map and SEM map of SA / SiO2-450 prepared in Example 2 are shown. The prepared SA@SiO2-450 has a particle size of about 1 mm. The SEM results show that on the basis of the original SA inner core template, silica has successfully formed a shell structure on its surface, increasing the size of the original inner core and having a certain roughness at the same time.

[0034] Example 3

[0035] This example provides a method for preparing SA / SiO2 core-shell microspheres by the template method. The difference in the preparation process from Example 1 is as follows: The nozzle diameters of the microsphere preparation instrument are 300 μm, 200 μm, 150 μm, and 120 μm respectively, Frequency: 470, Pressure: 300 mbar, Heating: 60°C; other steps are the same as those in Example 1, and SA@SiO2-300, SA@SiO2-200, SA@SiO2-150, and SA@SiO2-120 are obtained.

[0036] Figure 4 The physical maps of SA / SiO2-300, SA / SiO2-200, SA / SiO2-150, and SA / SiO2-120 prepared in Example 3 are shown.

[0037] Example 4

[0038] This example provides a method for preparing sodium alginate / silica core-shell microspheres by the template method. The difference in the preparation process from Example 1 is as follows: The dosages of TEOS are 100 μL and 500 μL respectively, and other steps are the same as those in Example 1.

[0039] Figure 5 The physical maps of SA / SiO2-750-100 and SA / SiO2-750-500 prepared in Example 4 are shown. It can be seen from the figure that SA / SiO2 core-shell microspheres with different sizes can be prepared by changing the dosage of TEOS.

[0040] Example 5

[0041] This example provides a method for obtaining a silica hollow shell structure by calcining sodium alginate to further prove that TEOS is coated on the surface of sodium alginate by forming a silica shell layer. The preparation process is as follows: Place the prepared SA / SiO2-750 in a tube furnace and heat it to 600 °C for calcination for 30 min.

[0042] Figure 6 The physical map and SEM characterization result map of the SiO2 prepared in Example 5 are shown. The results show that after calcining to remove the sodium alginate core, the outer layer is indeed a silica shell layer structure with a spherical morphology, verifying the effectiveness of the template method.

[0043] Taking tetracycline (TC) as the target pollutant, the relationship between the size of the core-shell structure SA / SiO2 and the adsorption performance was studied as follows:

[0044] (1) Take 2 mg of each SA / SiO2 core-shell microsphere sample in Examples 1-3;

[0045] (2) Prepare a 100 mg / L tetracycline (TC) solution;

[0046] (3) Add the SA / SiO2 sample to TC and use a magnetic stirrer at a rotation speed of 200 rpm to conduct an adsorption experiment. Then calculate the adsorption amount of SA / SiO2 for TC and record the adsorption capacity.

[0047] Figure 7 The adsorption effect diagram of SA@SiO2 with different sizes for 100 mg / L TC. Figure 7 The adsorption experiment results show that the adsorption capacity of SA / SiO2-750 in Example 1 for TC is: 486.47 mg / g; the adsorption capacity of SA / SiO2-450 in Example 2 for TC is: 413.66 mg / g; the adsorption capacity of SA / SiO2-300 in Example 3 for TC is: 301.73 mg / g, the adsorption capacity of SA / SiO2-200 for TC is: 293.58 mg / g, the adsorption capacity of SA / SiO2-150 for TC is: 190.89 mg / g, the adsorption capacity of SA@SiO2-120 for TC is: 133.84 mg / g; as the size decreases, the adsorption performance decreases.

Claims

1. A method for preparing sodium alginate / silica core-shell microspheres by a template method, characterized in that, It is prepared by the following steps: (1) Prepare an aqueous sodium alginate solution with a mass fraction of 0.5 - 1.5%, and remove air bubbles by ultrasonic treatment; (2) Place the prepared aqueous sodium alginate solution in a solution bottle, connect the solution bottle to a microsphere preparation instrument, and drop it into calcium chloride solution to prepare sodium alginate microspheres; the particle size of the sodium alginate microspheres is 300 - 750 μm; (3) Add the sodium alginate microspheres to a 2 - 4% CaCl₂ solution and stir at room temperature for 10 - 50 min to obtain solidified and stable sodium alginate microspheres; (4) Add tetraethoxysilane, water, and ammonia water to the solidified and stable sodium alginate microspheres, react at room temperature for 10 - 50 min to obtain sodium alginate / silica core - shell microspheres, and perform freeze - drying on them to obtain dry microspheres.

2. The method for preparing sodium alginate / silica core-shell microspheres by the template method according to claim 1, characterized in that: The mass ratio of sodium alginate microspheres to TEOS is 5:1 - 268:1; the mass ratio of sodium alginate microspheres to water is 2.5:1 - 2.5:1.5; the mass ratio of sodium alginate microspheres to ammonia water is 14:1 - 9:

1.

3. The method for preparing sodium alginate / silica core-shell microspheres by the template method according to claim 1, characterized in that, The freeze - drying is carried out at - 45 - - 25 °C for 24 - 48 h.

4. Application of the sodium alginate / silica core - shell microspheres prepared by the method according to claim 1 as an adsorbent in the adsorption of tetracycline.

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