Preparation method of monodisperse and particle size controllable silica sol

Abstract

The invention discloses a preparation method of monodisperse and controllable particle size silica sol, belonging to the technical field of silica sol preparation. The preparation method comprises the following steps: performing an exchange reaction on an aqueous sodium silicate solution and a cation exchange resin to prepare an active silicic acid solution; adding a water-soluble polymer into the active silicic acid solution to prepare a polymer silicic acid solution with a water-soluble polymer concentration of 1-5 mg·mL-1; dropping the polymer silicic acid solution into an alkaline aqueous solution at 65-95 °C under stirring; aging and cooling after dropping to obtain silica sol; adjusting the particle size of the silica sol by adjusting the concentration of the water-soluble polymer. The preparation process of the silica sol of the invention is simple and convenient, the raw material price is low, the size of the silica sol can be conveniently controlled by adjusting the addition amount of the water-soluble polymer in the active silicic acid, and the particle size of the silica sol shows a monodisperse distribution, having very good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of silica sol preparation, and particularly relates to a method for preparing monodisperse silica sol with controllable particle size. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Silica sol is a colloidal solution formed by the uniform dispersion of amorphous silica particles in water, and is widely used in coatings, chemical industry, textiles, precision casting, refractory materials, electronic industry and other aspects as an important inorganic polymer material.

[0004] Currently, the main methods for preparing silica sol include ion exchange method, organosiloxane hydrolysis method, silicon powder dissolution method, electrolytic electrodialysis method, etc. The main preparation methods used in industry are ion exchange method and silicon powder dissolution method. The traditional ion exchange method includes two steps: the preparation and growth of seeds, which means a cumbersome process and low production efficiency. For example, Patent CN111732107 B (authorization publication date: 2021.03.30) discloses a method for preparing super-large particle size and high-concentration silica sol from water glass, which includes four steps: seed mother liquor preparation, colloid particle growth, colloid particle secondary growth, and colloid particle enlargement. Finally, silica sol with a particle size of 140-160 nm is prepared, and the preparation method is cumbersome.

[0005] Preparing silica sols with different sizes for specific scenarios can broaden the application scope of silica sol and better play the advantages of silica sol. Patent CN 114249330 B (authorization publication date: 2023.01.17) prepares large particle size and narrow distribution silica sol suitable for chemical mechanical polishing of silicon wafers, with a particle size of 65-90 nm. Patent CN112340740A (publication date: 2021.02.09) prepares double particle size distribution silica sol applied in the fields of chemical mechanical polishing and optical film coating solution, with the small particle size of 60 nm-120 nm and the large particle size of 130 nm-250 nm. Patent CN 103964448 A (publication date: 2014.08.06) prepares small-scale nano-silica organic sol and aqueous sol suitable for the coating field, with a particle size of 2-20 nm. Thus, preparing silica sol with controllable particle size is crucial for it to play a role in specific fields.

[0006] Some work has been carried out on the preparation of silicon sol with controllable particle size. Patent CN 112340740 A (Publication date: February 9, 2021) prepares high-purity silicon sol with controllable particle size by the ion exchange method. An ion exchange column loaded with a DC voltage is used, and silicon sol with the required particle size is obtained through two steps of seed preparation and growth. However, the equipment used is complex and the process is rather cumbersome. Patent CN 105731468 A (Publication date: July 6, 2016) uses silicon powder as the raw material to carry out two processes of seed preparation and growth to prepare silicon sol with controllable particle size. Silicon powder is added in batches under an alkaline catalyst, which also has the drawback of cumbersome operation. Although Patent CN 106744998 A (Publication date: May 31, 2017) uses the one-step Stober method to prepare amorphous monodisperse nano-silica powder with controllable particle size, the solvent environment is toxic methanol, which limits the further application of silica.

[0007] The above-mentioned patents all need to prepare seeds first, and then control the injection speed of the silicic acid solution / the addition amount of silicon powder to make the seeds grow uniformly to prepare silicon sol with controllable particle size. If the preparation and growth of seeds are carried out simultaneously, the size distribution of silicon sol is often relatively wide, and the requirements of monodispersity and controllable particle size cannot be met. Therefore, how to prepare silicon sol with a narrow particle size distribution, monodispersity and controllable particle size in a simple one-step method using water as the solvent is an urgent problem to be solved. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing monodisperse silicon sol with controllable particle size, which overcomes the cumbersome process in the preparation of existing silicon sol. By using the ion exchange method, the preparation and growth of seeds are carried out synchronously in the same container. By adding a polymer in the reactor to change the viscosity of the reaction system, thereby affecting the diffusion speed and collision probability of silicic acid molecules, and precisely controlling the reaction conditions, silicon sol with a narrow particle size distribution, monodispersity and controllable particle size is prepared.

[0009] The present invention provides a method for preparing monodisperse silicon sol with controllable particle size, comprising the following steps:

[0010] Carry out an exchange reaction between an aqueous sodium silicate solution and a cation exchange resin to prepare an active silicic acid solution;

[0011] Add a water-soluble polymer to the active silicic acid solution to prepare a polymer silicic acid solution with a water-soluble polymer concentration of 1 - 5 mg·mL -1 of;

[0012] Dropwise add the polymer silicic acid solution to an alkaline aqueous solution at 65 - 95 °C under stirring conditions; after the dropwise addition, age and cool to obtain silicon sol; adjust the particle size of the silicon sol by adjusting the concentration of the water-soluble polymer.

[0013] Preferably, the modulus of the sodium silicate is 1.5 - 3.5, and the mass fraction of the sodium silicate aqueous solution is 1 - 10 wt%.

[0014] Preferably, the type of the cation exchange resin includes macroporous type or gel type; the cation exchange resin is selected from strong acid type cation exchange resin or weak acid type cation exchange resin.

[0015] Preferably, the concentration of the active silicic acid solution is 1 - 10 wt%, and the pH of the active silicic acid is < 3.

[0016] Preferably, the water-soluble polymer is selected from one or more of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxymethyl cellulose (HMC), polyvinylpyrrolidone (PVP), and polyacrylamide (PAM).

[0017] Preferably, the rotation speed of the stirring is 400 - 800 rpm.

[0018] Preferably, the pH of the alkaline aqueous solution is 9 - 11.

[0019] Preferably, the base of the alkaline aqueous solution is selected from one or more of sodium hydroxide, ammonia water, triethanolamine, ethylenediamine, and sodium carbonate.

[0020] Preferably, the volume ratio of the alkaline aqueous solution to the polymer silicic acid solution is 1:0.5 - 2.

[0021] Preferably, the dropping rate of the polymer silicic acid solution is 4 - 8 mL·min -1 。

[0022] Preferably, the aging time is 100 - 200 min.

[0023] Preferably, the particle size of the silica sol shows a monodisperse distribution, and the average particle size is 20 - 250 nm.

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

[0025] In the preparation process of the present invention, the reaction process for preparing silica sol by the conventional ion exchange method is simplified. The preparation process is simple and convenient, the raw materials are inexpensive, the size of the silica sol can be conveniently controlled by adjusting the addition amount of the water-soluble polymer in the active silicic acid, and the particle size of the silica sol shows a monodisperse distribution. Therefore, it has a very good application prospect. Description of the Drawings

[0026] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments and descriptions thereof of the invention are used to explain the invention and do not unduly limit the invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 is the particle size distribution diagram of the silica sol prepared in Example 1 of the present invention with a PVP concentration of 1 mg·mL -1 ;

[0028] Figure 2 is the particle size distribution diagram of the silica sol prepared in Example 1 of the present invention with a PVP concentration of 3 mg·mL -1 ;

[0029] Figure 3 is the scanning electron microscope image of the silica sol prepared in Example 1 of the present invention with a PVP concentration of 2 mg·mL -1 ;

[0030] Figure 4 is the particle size distribution diagram of the silica sol prepared in Comparative Example 1 of the present invention;

[0031] Figure 5 is the scanning electron microscope image of the silica sol prepared in Comparative Example 1 of the present invention. Detailed Description of the Invention

[0032] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0033] The present invention provides a method for preparing a monodisperse and particle size controllable silica sol, comprising the following steps:

[0034] Performing an exchange reaction on an aqueous sodium silicate solution and a cation exchange resin to prepare an active silicic acid solution;

[0035] Adding a water-soluble polymer to the active silicic acid solution to prepare a polymer silicic acid solution with a water-soluble polymer concentration of 1-5 mg·mL -1 ;

[0036] Adding dropwise the polymer silicic acid solution to an alkaline aqueous solution at 65-95 °C under stirring conditions; after the addition is completed, aging and cooling are carried out to obtain the silica sol; the particle size of the silica sol is adjusted by adjusting the concentration of the water-soluble polymer.

[0037] In the prior art, the preparation of silica sol with adjustable particle size often focuses on the concentration of active silicic acid / silicon powder in the system, while ignoring that the diffusion rate of silicic acid also plays an important role in the particle formation process. In the present invention, by adjusting the amount of polymer, the viscosity of the system is changed, thereby affecting the diffusion rate of silicic acid and the collision probability of silicic acid molecules to prepare silica sol with different sizes and controllable particle size. In addition, in the prior art, during the preparation of silica sol, the preparation process of seeds and the growth process of colloidal particles are often carried out separately, which will result in cumbersome preparation steps and extended preparation cycles. The cumbersome preparation procedure leads to the introduction of impurities and an increase in preparation costs. If the preparation and growth of seeds are carried out simultaneously, the size of the silica sol often has a wide distribution and cannot meet the requirements of monodispersity and controllable particle size. The present invention discovers that by regulating the viscosity of the system, the diffusion rate of active silicic acid in the system can be effectively reduced, the collision probability of silicic acid molecules due to thermal motion can be reduced, and the generation of new crystal nuclei caused by the high-speed collision of silicic acid molecules after the formation of crystal grains can be avoided. The dropped active silicic acid is more adsorbed on the surface of the crystal grains to promote the uniform growth of particles, reduce the particle size non-uniformity during the nucleation process, and enable the crystal grains to grow uniformly under thermal equilibrium conditions, achieving the purpose of uniform particle size and controllable size. Reducing the diffusion rate of active silicic acid and avoiding the generation of new crystal nuclei due to the collision of rapidly diffusing active silicic acid during the crystal grain growth process is beneficial for the preparation of monodisperse silica sol. Therefore, the present invention can prepare monodisperse silica sol with controllable particle size. In the present invention, the main function of the water-soluble polymer is to change the viscosity of the water reaction system, affect the diffusion rate and collision probability of silicic acid molecules, and thus prepare monodisperse silica sol with controllable particle size.

[0038] In the present invention, the modulus of sodium silicate is 1.5 - 3.5, and the mass fraction of the sodium silicate aqueous solution is 3 - 7 wt%. When the concentration of the used sodium silicate solution is low, the production efficiency is low. When the concentration of sodium silicate used is relatively high, it is difficult to obtain active silicic acid through an ion exchange column. Therefore, a sodium silicate concentration of 3 - 7 wt% is preferred.

[0039] The present invention does not impose special restrictions on the type of cation exchange resin. The cation exchange resin commonly used in the art for preparing active silicic acid can be adopted. The type of cation exchange resin in the present invention preferably includes macroporous type or gel type, and can be selected from strong acid type cation exchange resin or weak acid type cation exchange resin.

[0040] In the present invention, the concentration of the active silicic acid solution is 3 - 7 wt%, and the pH of the active silicic acid < 3. The concentration of active silicic acid depends on the concentration of sodium silicate. The pH of silicic acid is generally 2 - 3, and active silicic acid is relatively stable in the above pH range.

[0041] In the present invention, the water-soluble polymer includes, but is not limited to, one or more of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxymethyl cellulose (HMC), polyvinylpyrrolidone (PVP), and polyacrylamide (PAM). Its main function is to regulate the viscosity of the reaction system, thereby controlling the particle size of the silica sol.

[0042] The present invention does not impose special restrictions on the stirring speed. The stirring speed is preferably 400 - 800 rpm.

[0043] In the present invention, under alkaline conditions, silicic acid molecules and silicate anions undergo an oxygen-bonding reaction, promoting the growth of orthosilicic acid from monomers to polymers. The pH of the alkaline aqueous solution is 9 - 11, preferably 10. A larger pH can promote the polymerization growth of orthosilicic acid, but when pH > 10, small particles will partially dissolve in the alkaline solution. Therefore, pH = 10 is preferred.

[0044] The present invention does not impose special restrictions on the base of the alkaline aqueous solution. Commonly used bases in the art can be used. For example, it can be selected from one or more of sodium hydroxide, ammonia water, triethanolamine, ethylenediamine, and sodium carbonate.

[0045] In the present invention, the volume ratio of the alkaline aqueous solution to the polymer silicic acid solution is 1:0.5 - 2, preferably 1:1.

[0046] In the present invention, in order to improve production efficiency while satisfying the uniform growth of particles, the dropping rate of the polymer silicic acid solution is 4 - 8 mL·min -1 。

[0047] The present invention does not impose special restrictions on the aging time and method. Common aging methods and times in the art can be used. The aging time in the present invention is 100 - 200 min.

[0048] The silica sol prepared by the present invention through the above method has a monodisperse particle size distribution, and the average particle size is 20 - 250 nm.

[0049] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0050] Example 1

[0051] This example provides a method for preparing silica sol using polyvinylpyrrolidone (PVP) as the polymer.

[0052] Prepare an aqueous sodium silicate solution with a mass fraction of 6% and obtain an active silicic acid solution with pH < 3 through a strong acid cation exchange resin. Add PVP to the active silicic acid to obtain solutions with concentrations of 1, 2, 3, 4, 5 mg·mL -1PVP-activated silicic acid solution. Add 100 mL of ammonia water solution with pH = 10 into a three-necked flask, keep the oil bath temperature constant at 95 °C, and the stirring speed is 600 rpm. Use a peristaltic pump to drip 100 mL of activated silicic acid solution with different PVP concentrations into the ammonia water solution at a dripping speed of 6 mL·min -1 During the reaction process, continuously drip ammonia water solution with pH = 10 to keep the system pH at 9 - 10. After the dripping is completed, age for 180 min, and perform tests after cooling for 24 h.

[0053] The particle size and Zeta potential of the silica sols prepared by adding different PVP concentrations were tested, and the test results are shown in Table 1. It can be seen from Table 1 that as the concentration of the polymer PVP increases, the average particle size of the silica sol gradually increases, indicating that the regulation of the particle size of the silica sol has been successfully achieved by adjusting the concentration of PVP.

[0054] Table 1 Test results of silica sols prepared in Example 1 with different PVP concentrations

[0055] <![CDATA[PVP concentration (mg·mL -1 )]]> Average particle size (nm) Zeta potential (mV) 1 40 -35.8 2 79 -38.7 3 92 -37.7 4 127 -37.8 5 230 -34.7

[0056] The particle size distribution diagram of the silica sol prepared with a PVP concentration of 1 mg·mL -1 is as shown in Figure 1 The particle size distribution diagram of the silica sol prepared with a PVP concentration of 3 mg·mL -1 is as shown in Figure 2 It can be seen that the particle size distribution of the silica sol is all single-peak. Figure 3 This is the scanning electron microscope image of the silica sol prepared with a PVP concentration of 2 mg·mL -1 It can be seen that the silica sol is spherical.

[0057] Example 2

[0058] This example provides a method for preparing silica sol using polyvinyl alcohol (PVA) as a polymer.

[0059] Prepare an aqueous sodium silicate solution with a mass fraction of 6% and obtain an activated silicic acid solution with pH < 3 through a strong-acid cation exchange resin. Add PVA to the activated silicic acid to obtain PVA-activated silicic acid solutions with concentrations of 1, 2, 3, 4, and 5 mg·mL -1 Add 100 mL of ammonia water solution with pH = 10 into a three-necked flask, keep the oil bath temperature constant at 95 °C, and the stirring speed is 600 rpm. Use a peristaltic pump to drip at a speed of 6 mL·min -1The active silica solution containing different PVA concentrations was added dropwise to the ammonia water solution at a dropping rate. During the reaction process, the ammonia water solution with pH = 10 was continuously added dropwise to keep the pH of the system at 9 - 10. After the dropping was completed, it was aged for 180 min, and after cooling for 24 h, the test was carried out.

[0060] The particle size and Zeta potential of the silica sols prepared by adding different PVA concentrations were tested, and the test results are shown in Table 2. It can be seen from Table 2 that the absolute value of the Zeta potential of the silica sols is all > 30 mV, indicating excellent stability of the silica sols. With the increase of the polymer PVA concentration, the average particle size of the silica sols gradually increases, indicating that the regulation of the particle size of the silica sols has been successfully achieved by controlling the PVA concentration.

[0061] Table 2 Test results of silica sols prepared with different PVA concentrations in Example 2

[0062] <![CDATA[PVA concentration (mg·mL -1 )]]> Average particle size (nm) Zeta potential (mV) 1 21 -37.6 2 34 -37.5 3 71 -36.5 4 106 -36.2 5 128 -38.4

[0063] Comparative Example 1

[0064] Compared with Example 1, no polymer was added in this comparative example. The specific method is as follows:

[0065] A sodium silicate aqueous solution with a mass fraction of 6% was prepared and passed through a strong acid cation exchange resin to obtain an active silica solution with pH < 3. 100 mL of ammonia water solution with pH = 10 was added to a three-necked flask, the oil bath temperature was kept constant at 95 °C, and the stirring speed was 600 rpm. The active silica solution was added dropwise to the alkali solution at a dropping rate of 6 mL·min -1 . During the reaction process, the ammonia water solution with pH = 10 was continuously added dropwise to keep the pH of the system at 9 - 10. After the dropping was completed, it was aged for 180 min, and after cooling for 24 h, the test was carried out. The data are shown in Table 3.

[0066] Table 3 Test data of silica sol in Comparative Example 1

[0067] Average particle size (nm) Zeta potential (mV) Silica sol of Comparative Example 1 8；70 -35.2

[0068] Figure 4 is the particle size distribution diagram of the silica sol prepared in Comparative Example 1, showing a bimodal peak; Figure 5 is the scanning electron microscope picture of the silica sol prepared in Comparative Example 1. It can be seen that the size distribution of the silica sol is uneven.

[0069] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of monodisperse and particle size controllable silica sol, characterized in that, It includes the following steps: Preparing an active silicic acid solution by performing an exchange reaction between an aqueous sodium silicate solution and a cation exchange resin; Add a water-soluble polymer to the active silicic acid solution to prepare a polymer silicic acid solution with a water-soluble polymer concentration of 1 to 5 mg·mL -1 ; the water-soluble polymer is selected from one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxymethyl cellulose, polyvinylpyrrolidone, and polyacrylamide; Dropping the polymerized silicic acid solution into an alkaline aqueous solution at 65 - 95 °C under stirring conditions; the pH of the alkaline aqueous solution is 9 - 11, and the pH of the system is maintained at 9 - 10 during the reaction process; after the dropping is completed, aging and cooling are carried out to obtain silica sol; the particle size of the silica sol is adjusted by adjusting the concentration of the water-soluble polymer; The particle size of the silica sol shows a monodisperse distribution, and the average particle size is 20 - 250 nm.

2. The preparation method according to claim 1, characterized in that, The modulus of the sodium silicate is 1.5 - 3.5, and the mass fraction of the aqueous sodium silicate solution is 1 - 10 wt%.

3. The preparation method according to claim 1, characterized in that The type of the cation exchange resin includes macroporous type or gel type; the cation exchange resin is selected from strong acid type cation exchange resins or weak acid type cation exchange resins.

4. The preparation method according to claim 1, characterized in that The concentration of the active silicic acid solution is 1 - 10 wt%, and the pH of the active silicic acid solution is < 3.

5. The preparation method according to claim 1, characterized in that, The rotation speed of the stirring is 400 - 800 rpm.

6. The preparation method according to claim 1, characterized in that, The base of the alkaline aqueous solution is selected from one or more of sodium hydroxide, ammonia water, triethanolamine, ethylenediamine, and sodium carbonate.

7. The preparation method according to claim 1, wherein The volume ratio of the alkaline aqueous solution to the polymerized silicic acid solution is 1:0.5 - 2.

8. The preparation method according to claim 1, characterized in that The dropping rate of the polymer silicate solution is 4-8 mL·min -1 ; The aging time is 100-200 min

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