CN108017061B

CN108017061B - Method for preparing large-specific-surface-area nano SiO by using water glass2Method (2)

Info

Publication number: CN108017061B
Application number: CN201711273344.XA
Authority: CN
Inventors: 杨宇翔; 康诗钊; 黄艳; 秦利霞; 李向清; 王磊
Original assignee: East China University of Science and Technology; Shanghai Institute of Technology
Current assignee: East China University of Science and Technology; Shanghai Institute of Technology
Priority date: 2017-12-06
Filing date: 2017-12-06
Publication date: 2020-12-08
Anticipated expiration: 2037-12-06
Also published as: CN108017061A

Abstract

The invention belongs to the technical field of nano materials, and particularly relates to a method for preparing large-specific-surface-area nano SiO by using water glass₂The method of (1). The method adopts a micelle method or a mixed micelle method, and water glass SiO is uniformly mixed with a surfactant in a pool enclosed by micelles₃ ^2‑H hydrolyzed by anion and precipitant ethyl acetate⁺Reaction to produce nano SiO₂Aging, washing and drying by adopting an alcohol solvent displacement method, and roasting at a certain temperature to prepare the nano SiO₂And (3) powder. Multiple conditions are adopted in the preparation process to improve the dispersion performance of the nano-powder, and the nano-SiO prepared by the method₂Good dispersibility, uniform particle size distribution, large specific surface area, good chemical stability and high purity, can be widely applied to the fields of machinery, petrochemical industry, plastics, coatings and the like, and has the advantages of low price, suitability for industrial production and the like.

Description

Method for preparing large-specific-surface-area nano SiO by using water glass2Method (2)

Technical Field

The invention relates to the technical field of chemical industry, in particular to a method for preparing large-specific-surface-area nano SiO by using water glass₂The method of (1).

Background

SiO₂White carbon black is a very important industrial raw material, is a white powdery substance, is light and loose, is insoluble in water, is soluble in sodium hydroxide and sodium hydroxideHydrofluoric acid. The macrostructure of the carbon black is similar to that of carbon black, and the particles are spherical. The single particles are in surface contact with each other and form a chain-shaped connection structure (secondary structure). The linking structures interact with hydrogen bonds to form aggregates. The primary particles are extremely fine and light, and become aggregated fine particles after absorbing moisture in the air. SiO 2₂And also has high activity, and thus exhibits many characteristics such as optical shielding, nonlinear resistance, etc., thereby having wide applications.

With the development of science and technology, SiO₂The performance and purity of the product have higher requirements. Nano SiO₂Is one of the most important high-tech superfine inorganic new materials, and not only can be applied to the high-tech fields of the electronic industry, the aerospace technology, novel catalyst carriers and the like, but also has wide application value in the industries of high-grade transparent toothpaste, high-grade rubber, synthetic resin, plastics, printing ink, high-grade paint and the like.

At present, the preparation of nano SiO₂The raw materials mainly adopt organic silicon such as Tetraethoxysilane (TEOS), 3-aminopropyl triethoxysilane (APTES), methyl orthosilicate (TMOS) and the like as silicon sources, and inorganic silicon sources are applied to prepare the nano SiO₂There are few reports. The organic silicon source can be adopted to prepare the nano SiO with good dispersibility₂However, it is expensive, requires high conditions, and is not suitable for mass production.

In addition, as for the precipitant used for decomposing the silicon source, inorganic strong acid such as hydrochloric acid, sulfuric acid and the like is widely reported in the literature, although the inorganic acid is cheap, the inorganic acid is added into the water glass, and the acidity is too strong, so that the inorganic acid is not easy to be controlled in the aqueous solution, the local acidity in the solution is too high, agglomeration is easily generated, and stirring is difficult, and the prepared SiO is difficult₂Not easy to be filtered and has poor uniformity of particle size.

Superfine SiO₂The following properties are also provided: small particle size, large specific surface area, strong surface adsorption force, high adhesion to SiO₂The catalyst has special performances of hygroscopicity, extinction, heat insulation, insulativity and the like due to the fact that silanol and active silane bond can form hydrogen bond with different strengths, and the catalyst is used as a novel catalyst carrier and selectedThe selective adsorbent is widely applied to the high-tech fields such as selective adsorbents, insulating materials for aviation and the like, has special properties different from bulk phase materials and single molecules due to the special structural hierarchy, has very important application prospects in the aspects of light, electricity, catalysis and the like, and is more and more attracted by people.

Due to the nanometer SiO₂The powder material has great application value, so the research and exploration on preparing the superfine SiO₂The method of the material is particularly important. Preparation of nano SiO₂The methods mainly include precipitation method, gas phase method, sol-gel method and microemulsion method.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a method for preparing large-specific-surface-area nano SiO by using water glass₂The method of (1). The invention adopts micelle method or mixed micelle method to prepare nano SiO₂The method is simple, and the BET specific surface area of the obtained nano silicon dioxide is larger than the national standard. Especially when the micelle method is adopted, the BET specific surface area is basically 480m²More than g, even up to 590m²/g。

The technical scheme of the invention is specifically introduced as follows.

Method for preparing large-specific-surface-area nano SiO by using water glass₂The method takes water glass as a silicon source and ethyl acetate as a precipitator for decomposing the silicon source, and prepares the nano SiO with large specific surface area by a micelle method or a mixed micelle method₂(ii) a Wherein: in the micelle method, CTAB is adopted as a surfactant; the mixed micelle method adopts a compound surfactant formed by CTAB and PEG-4000.

In the invention, the silicon source is water glass, and the modulus of the silicon source is between 2.4 and 3.8.

In the invention, the nano SiO with large specific surface area is prepared₂The method comprises the following specific steps: firstly stirring and mixing a water glass solution and a surfactant CTAB or a compound surfactant formed by CTAB and PEG-4000 in a mixed solvent consisting of water and glycerol, then adding a precipitator of ethyl acetate, fully stirring and aging, washing with warm water containing CTAB after aging is finished,then using alcohol compounds to replace solvents and age, finally drying, putting the dried sample into a muffle furnace for roasting, and naturally cooling to room temperature after roasting is finished to obtain the nano SiO with large specific surface area₂。

In the present invention, SiO in the water glass solution₂The mass concentration of (a) is 12-16 mol/L; the volume ratio of water to glycerol in the mixed solvent is 4: 1-2: 1.

In the invention, SiO in the water glass₂And CTAB in a molar ratio of 15: 1-30: 1, SiO in water glass₂The molar ratio of the ethyl acetate to the water glass is 9: 10-12: 5, and the volume ratio of the water glass to the water is 2: 1-1: 8.

In the invention, in the mixed micelle method, the mass ratio of CTAB to PEG-4000 is 1: 1-1: 10, and the preferable mass ratio is 1: 5-1: 10; SiO 2₂The ratio of mass to sum of mass of CTAB and PEG-4000 was 9: 20-27: 20; SiO in water glass₂The molar ratio of the ethyl acetate to the water glass is 9: 10-21: 10, and the volume ratio of the water glass to the water is 1: 1-3: 2.

In the invention, after adding a precipitator of ethyl acetate, the aging temperature is 20-50 ℃, and the aging reaction is carried out for 20-30 h; after the solvent is replaced, the aging temperature is 20-40 ℃, and the aging time is 4-8 h; the drying temperature is 60-80 ℃, and the drying time is 4-7 h; the roasting temperature is 550-600 ℃, and the roasting time is 4-7 h.

In the invention, the nano SiO obtained by the micelle method₂Has a particle diameter of 10 to 50nm and a BET specific surface area of 480 to 590m²Between/g; nano SiO obtained by mixed micelle method₂Has a particle diameter of 100 to 300nm and a BET specific surface area of 235 to 445m²Between/g.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention adopts a micelle method and a mixed micelle method, which is a new method for improving and innovating a chemical precipitation method by micelle based on a surfactant. In solution, when the concentration of the surfactant exceeds a certain value, aggregates in a colloidal state, i.e., micelles, are polymerized from individual molecules or ions. This concentration is called the critical micelle concentration of the surfactant, expressed as CMC. When the concentration of the surfactant is greater than CMC, the surface of the micelle adsorbs counter ions in the solution due to a hydrophobic effect and an electrostatic effect. When the precipitant is added to the reaction solution, a large amount of high-concentration ions around the micelle provide an instantaneous supersaturation for the formation of crystal nuclei, and precipitation crystal nuclei are generated in large amounts, but cannot grow large due to the low overall concentration of the solution. On the other hand, after the micelle absorbs a certain amount of ions in the aqueous solution, the particles are wrapped by the micelle to form a protective layer, so that the reaggregation among the particles is hindered, the particle size distribution is uniform, and the fine and uniform nano particles are prepared. Moreover, the method has the advantages of simple process, convenient operation, easily obtained raw materials and low cost, and is suitable for industrial production.

2. The invention adopts inorganic silicon source, greatly saves cost, and prepares the nano SiO₂The dispersibility is good, and the particle size distribution is uniform. Large specific surface area, and when the micelle method is adopted, the BET specific surface area is basically 480m²More than g, even up to 590m²/g。

3. The invention adopts a CTAB micelle method and a CTAB/PEG-4000 mixed micelle method, takes ethyl acetate as a latent acid reagent, and hydrolyzes the ethyl acetate in the middle of a water pool formed by the CTAB micelle (or the CTAB/PEG-4000 mixed micelle) and cosurfactant glycerol to generate H⁺The pH value of the reaction system in the ' water pool ' can be uniformly reduced, and the silicate anions in the water glass are reacted with H in the ' water pool⁺Gel reaction is carried out to generate nano SiO₂. Thus avoiding the phenomena of over-high local acidity and over-quick alkalinity reduction caused by directly adding acid. Compared with the method of directly adding inorganic strong acid into the system, the micelle can be nano SiO₂The formation provides a uniform microenvironment and the ethyl acetate latent acid provides more moderate reaction conditions. Only by combining the two, the nano SiO with excellent dispersibility and large specific surface area can be prepared₂。

4. The nano silicon dioxide prepared by the method has good dispersibility, uniform particle size distribution, high chemical stability, high purity and yield, and the yield is over 80 percent; can be widely applied to the fields of machinery, plastics, coatings and the like, and has the advantages of low price, suitability for industrial production and the like.

Drawings

FIG. 1: micelle method for synthesizing nano SiO₂A process flow diagram.

FIG. 2: mixed micelle method for synthesizing nano SiO₂A process flow diagram.

FIG. 3: micelle method based nano SiO₂Forming a mechanism diagram.

FIG. 4: based on mixed micelle method nanometer SiO₂Forming a mechanism diagram.

FIG. 5: (a) is nano SiO under the condition of example 1₂A TEM image of (B); (b) is nano SiO under the condition of example 2₂A TEM image of (B); (c) is nano SiO under the condition of example 3₂A TEM image of (a).

FIG. 6: example 1 conditions of Nano SiO₂Particle size analysis of (2).

FIG. 7: EXAMPLE 2 Nano SiO₂Particle size analysis of (2).

FIG. 8: example 3 conditions of Nano SiO₂Particle size analysis of (2).

FIG. 9: example 1 conditions of Nano SiO₂N of (A)₂Adsorption-desorption curve chart.

FIG. 10: EXAMPLE 2 Nano SiO₂N of (A)₂Adsorption-desorption curve chart.

FIG. 11: example 3 conditions of Nano SiO₂N of (A)₂Adsorption-desorption curve chart.

FIG. 12: (a) is nano SiO under the condition of example 4₂A TEM image of (B); (b) is nano SiO under the condition of example 5₂A TEM image of (a).

FIG. 13: example 4 Nano SiO₂Particle size analysis of (2).

FIG. 14: example 5 conditions of Nano SiO₂Particle size analysis of (2).

FIG. 15: example 4 Nano SiO₂N of (A)₂Adsorption-desorption curve chart.

FIG. 16: example 5 conditions of Nano SiO₂N of (A)₂Adsorption-desorption curve chart.

FIG. 17: nanometer SiO based on CTAB micelle method₂XRD pattern of (a).

FIG. 18: nano SiO based on mixed micelle method₂XRD pattern of (a).

FIG. 19: nanometer SiO based on CTAB micelle method₂IR spectrum of (a).

FIG. 20: nano SiO based on mixed micelle method₂IR spectrum of (a).

FIG. 21: nano SiO₂Differential heat-thermogravimetric curve of (c).

Detailed Description

FIG. 1 is the micellar synthesis of nano-SiO in the present invention₂A process flow diagram.

FIG. 2 is the synthesis of nano SiO by mixed micelle method in the present invention₂A process flow diagram.

In the present invention, as shown in FIG. 3, the micelle method is used to synthesize nano SiO₂The reaction mechanism of (a) is as follows: in a pool surrounded by micelles formed by CTAB, OH^‐Because of the negative charge, the silicate anion is closely adsorbed on the CTAB cation polar head group surface, so that the acidity in the microenvironment of the water tank is close to neutral and weak alkaline, and the silicate anion is also adsorbed on the CTAB cation polar head group surface, because of SiO₃ ^2‐Si in the anion has electronegativity smaller than O, so SiO₃ ^2‐The combination of anionic and polar head group surfaces is free of OH^‐The bonding with the polar head group surface is firm, and H hydrolyzed when encountering ethyl acetate latent acid agent⁺When is SiO₃ ^2‐And H⁺Gel reaction is carried out to generate nano SiO₂。

In the present invention, as shown in FIG. 4, the mixed micelle method is used to synthesize nano SiO₂The reaction mechanism of (a) is as follows: in a water pool surrounded by a mixed micelle formed by PEG-4000 and CTAB, OH^‐Because of the negative charge, the water-soluble silicate anion-exchange resin is tightly adsorbed on the surface of a CTAB cation polar head group, so that the acidity in a microenvironment of a water tank is close to neutral and is weak and alkaline, and O in silicate anions^2‐The ions form weak hydrogen bonds with OH in the PEG-4000 surfactant, but the weak hydrogen bonds are not the same as OH in the CTAB micelle method^‐With polar head base surfaceThe electrostatic bonding is firm, and H hydrolyzed when encountering ethyl acetate latent acid agent⁺When is SiO₃ ^2‐And H⁺The gel reaction is relatively fast to generate the nano SiO₂. Due to silicic acid anion SiO₃ ^2‐Middle O^2‐Ion and PEG-4000 surfactant OH group weak hydrogen bonding ratio SiO₃ ^2‐The anions have weak interaction with the CTAB polar head group surface, so that SiO is based on mixed micelle₃ ^2‐And H⁺Gel reaction to produce nano SiO₂The speed is higher, so that the nano SiO prepared based on the mixed micelle method₂The particle size may be larger.

The invention is further described with reference to the following figures and specific examples, which are intended to be illustrative only and not limiting, and which are included to illustrate the advantages and details of the invention.

Example 1

n_(SiO2)/n_(CTAB)＝26.49～29.80，n_(SiO2)/n_{(Ethyl acetate)}＝1.53，V_{Water glass}V_{Water (W)}＝1.5

That is, under laboratory conditions, 10mL of water, 4mL of glycerol, and 15mL of water glass (in water glass, modulus is 3.3, SiO)₂The concentration of the sodium hydroxide is 15.4 percent), 0.61g CTAB, stirring for 30min at 50 ℃ to uniformly mix the sodium hydroxide and the ethyl acetate, slowly dropwise adding 2.64g of ethyl acetate, keeping the solution in a gel state, continuously stirring for reacting for 4h, aging for 24h, washing for 3 times by warm water containing 0.1 percent CTAB, adding 20mL of absolute ethyl alcohol for solvent replacement, aging for 5h at 40 ℃, filtering, drying, calcining for 5h at 600 ℃, and finally obtaining the nano SiO with the particle size of about 10-20 nm and good dispersibility₂The product, its TEM is shown in fig. 5 (a).

FIG. 6 shows the nano SiO₂The particle size analysis and test result shows that the nano SiO₂Not only has smaller grain diameter and more uniform distribution, but also has the average grain diameter of the secondary grain diameter of about 20.83 nm. FIG. 9 shows the nano SiO under the condition₂N of (A)₂Adsorption-desorption diagram, from which it can be seen that the IUPAC exhibits a class IV adsorption isotherm pattern, illustrating the oxidationThe silicon material is a mesoporous material, the adsorption capacity of the silicon material in the latter half period of relative pressure continuously rises, a certain macroporous channel still exists, and the average data of the specific surface area obtained by a BET test is 589.67m²The volume per gram is far higher than the national standard (70-220 m) of precipitation method²/g)。

Example 2

n_(SiO2)/n_(CTAB)＝24.91，n_(SiO2)/n_{(Ethyl acetate)}＝1.43，V_{Water glass}V_{Water (W)}＝1.5

That is, under laboratory conditions, 10mL of water, 4mL of glycerol, and 15mL of water glass (in water glass, modulus of 3.3, SiO) were sequentially added to a three-necked flask₂The concentration of the mixed solution is 15.4 percent), then 0.67g of CTAB is added, the mixed solution is stirred for 30min at 50 ℃ and uniformly mixed, 2.64-3.17 g of ethyl acetate is slowly dripped, the solution is in a gel shape, the stirring is continued for 4h and is aged for 24h, warm water containing 0.1 percent of CTAB is used for washing for 3 times, 20mL of absolute ethyl alcohol is added for solvent replacement, the mixed solution is aged for 5h at 40 ℃, the filtration and the drying are carried out, the mixed solution is calcined for 5h at 600 ℃, and finally the nano SiO with the particle size of about 40nm and good dispersibility is obtained₂The product, its TEM is shown in FIG. 5 (b).

FIG. 7 shows the nano SiO₂The particle size analysis and test result shows that the nano SiO₂The particle size is small, the distribution is uniform, and the average particle size of the secondary particle size is about 49.56 nm. FIG. 10 shows the nano SiO under this condition₂N of (A)₂The adsorption-desorption curve chart shows that the nano SiO is₂The same type of IUPAC IV adsorption isotherm is presented, which indicates that the obtained product is also mesoporous, and the average data of the BET specific surface area is 480.88m²The volume per gram is far higher than the national standard (70-220 m) of precipitation method²/g)。

Example 3

n_(SiO2)/n_(CTAB)＝27.65，n_(SiO2)/n_{(Ethyl acetate)}＝1.76，V_{Water glass}V_{Water (W)}＝1.7

Namely, under the laboratory conditions, 10mL of water, 4mL of glycerol and 15-18 mL of water glass (in the water glass, the modulus is 3.3, SiO) are sequentially added into a three-neck flask₂The concentration of the sodium hydroxide is 15.4 percent), then 0.67g of CTAB is added, the mixture is stirred for 30min at 50 ℃ to be uniformly mixed, 2.64g of ethyl acetate is slowly dripped, the solution is in a gel shape, the stirring is continued for 4h and is aged for 24h, warm water containing 0.1 percent of CTAB is used for washing for 3 times, 20mL of absolute ethyl alcohol is added for solvent replacement, the mixture is aged for 5h at 40 ℃, the filtration and drying are carried out, the mixture is calcined for 5h at 600 ℃, and finally the nano SiO with the particle size of about 20-30 nm and good dispersibility is obtained₂The product, its TEM is shown in FIG. 5 (c).

FIG. 8 shows the nano SiO₂The particle size analysis and test result shows that the nano SiO₂Not only has smaller grain diameter and more uniform distribution, but also has the average grain diameter of the secondary grain diameter of about 27.56 nm. FIG. 11 shows the nano SiO under this condition₂N of (A)₂The adsorption-desorption diagram shows that the adsorption curve shows the IUPAC type IV adsorption isotherm, which indicates that the obtained product is mesoporous, and the average data of the BET specific surface area is 493.64m²The volume per gram is far higher than the national standard (70-220 m) of precipitation method²/g)。

Example 4

W_(SiO2)/W_{(PEG‐4000/CTAB)}＝0.90，n_(SiO2)/n_{(Ethyl acetate)}＝1.12，V_{Water glass}V_{Water (W)}1.0; (CTAB and PEG-4000 are compounded according to the mass ratio of 1: 10)

That is, under laboratory conditions, 10mL of water, 5mL of glycerol, and 10mL of water glass (in water glass, modulus of 3.3, SiO) were sequentially added to a three-necked flask₂The concentration of the compound is 15.4 percent), then adding a composite surfactant (1.852g of PEG-4000, 0.1852g of CTAB), stirring for 30min at 25 ℃, uniformly mixing, slowly dropwise adding 2.4g of ethyl acetate, enabling the solution to be in a gel state, continuously stirring for reaction for 4h, aging for 24h, filtering the product, washing the product with warm water containing 0.1 percent of CTAB for 3 times, washing with ethanol for 2 times, adding 20mL of absolute ethyl alcohol for solvent replacement, aging for 5h at 40 ℃, filtering, drying, calcining for 5h at 600 ℃, and finally obtaining the nano SiO with the particle size of 100-300 nm, the particle size of most of particles being about 156.7nm and good dispersibility₂A TEM of the sample is shown in FIG. 12 (a).

FIG. 13 is the nanoSiO rice₂The particle size analysis and test result shows that the nano SiO₂The particle size distribution is relatively concentrated, 83.2% of the particles having a size of 156.7nm, and the secondary particles having an average size of about 217.1 nm. FIG. 15 shows the nano SiO under this condition₂N of (A)₂The adsorption-desorption curve chart shows that the adsorption curve presents IUPAC type I adsorption isotherm, in most cases, the type I isotherm usually reflects the micropore filling phenomenon on the micropore adsorbent, and the saturated adsorption value is equal to the filling volume of the micropore. The average data of the specific surface area of the BET test is 441.75m²The volume per gram is far higher than the national standard (70-220 m) of precipitation method²/g)。

Example 5

W_(SiO2)/W_{(PEG‐4000/CTAB)}＝1.19，n_(SiO2)/n_{(Ethyl acetate)}＝1.68，V_{Water glass}V_{Water (W)}1.5; (CTAB and PEG-4000 are compounded according to the mass ratio of 1: 10)

Namely, under the laboratory conditions, 10mL of water, 5mL of glycerol and 10-15 mL of water glass (in the water glass, the modulus is 3.3, SiO) are sequentially added into a three-neck flask₂The concentration of the compound is 15.4 percent), then adding a composite surfactant (1.937 g of PEG-4000, 0.1937g of CTAB), stirring for 30min at 25 ℃, uniformly mixing, slowly dropwise adding 2.4g of ethyl acetate, enabling the solution to be in a gel state, continuously stirring for reacting for 4h, aging for 24h, carrying out suction filtration on the product, washing for 3 times with warm water containing 0.1 percent of CTAB, washing for 2 times with ethanol, adding 20mL of absolute ethyl alcohol for solvent replacement, aging for 5h at 40 ℃, carrying out suction filtration, drying, calcining for 5h at 600 ℃, and finally obtaining the nano SiO with the particle size of 200-300 nm, the test particle size of 211.3nm and good dispersibility₂A TEM of the sample is shown in FIG. 12 (b).

FIG. 14 shows the nano SiO₂The particle size analysis and test result shows that the nano SiO₂The particle size distribution is relatively uniform, and the average particle size of the secondary particle size is 245.5 nm. FIG. 16 shows the nano SiO under the above conditions₂N of (A)₂The adsorption-desorption diagram, from which it can be seen that the adsorption curve also exhibits the IUPAC class I adsorption isotherm type, indicates that the silica material is predominantly microporous in structure. BET measurementThe average data of the specific surface area of the test is 264.74m²(g) exceeds the national standard of precipitation (70-220 m)²/g)。

Example 6

W_(SiO2)/W_{(PEG‐4000/CTAB)}＝0.90，n_(SiO2)/n_{(Ethyl acetate)}＝1.12，V_{Water glass}V_{Water (W)}1.0; (CTAB and PEG-4000 are compounded according to the mass ratio of 1: 5)

That is, under laboratory conditions, 10mL of water, 5mL of glycerol, and 10mL of water glass (in water glass, modulus of 3.3, SiO) were sequentially added to a three-necked flask₂The concentration of the sodium thiosulfate is 15.4 percent), then adding a composite surfactant (0.9260g of PEG-4000, 0.1852g of CTAB), stirring for 30min at 25 ℃, uniformly mixing, slowly dropwise adding 2.4g of ethyl acetate, enabling the solution to be in a gel state, continuously stirring for reaction for 4h, aging for 24h, carrying out suction filtration on the product, washing the product with warm water containing 0.1 percent of CTAB for 3 times, washing the product with ethanol for 2 times, adding 20mL of absolute ethyl alcohol for solvent replacement, aging for 5h at 40 ℃, carrying out suction filtration, drying, calcining for 5h at 600 ℃, and finally obtaining uniform particle size distribution, wherein 83.3 percent is 232.9nm, and the test average particle size is 251.8 nm. The average data of the specific surface area of the BET test is 238.26m²(g) exceeding the national standard of precipitation (70-220 m)²/g)。

Example 7

W_(SiO2)/W_{(PEG‐4000/CTAB)}＝0.90，n_(SiO2)/n_{(Ethyl acetate)}＝1.12，V_{Water glass}V_{Water (W)}1.0; (CTAB and PEG-4000 are compounded according to the mass ratio of 1: 1)

That is, under laboratory conditions, 10mL of water, 5mL of glycerol, and 10mL of water glass (in water glass, modulus of 3.3, SiO) were sequentially added to a three-necked flask₂The concentration of the sodium hydroxide is 15.4 percent), then adding a composite surfactant (0.1852g PEG-4000, 0.1852g CTAB), stirring for 30min at 25 ℃ to mix uniformly, slowly dropwise adding 2.4g ethyl acetate to obtain a solution in a gel state, continuously stirring for reaction for 4h, aging for 24h, filtering the product, washing the product with warm water containing 0.1 percent CTAB for 3 times, washing with ethanol for 2 times, adding 20mL absolute ethyl alcohol for solvent replacement, aging for 5h at 40 ℃, filtering, drying, calcining for 5h at 600 ℃, and finally obtaining the sodium hydroxideThe resulting particle size distribution was not uniform and the average particle size was found to be 858.7 nm. The average data of the specific surface area of the BET test is 203.75m²(g) approaching the national standard of precipitation (70-220 m)²/g)。

FIG. 17 shows the nano SiO obtained in example 2 based on CTAB micelle method₂The XRD pattern of the sample after being calcined at 600 ℃ for 5h shows that the peak shape appearing at about 22.5 degrees 2 theta is not sharp and is in a peak bag shape, which indicates that the nano-silica prepared by the micelle method has less crystalline components and is in an amorphous state.

FIG. 18 is a nano SiO obtained in example 4 based on the mixed micelle method₂The XRD pattern of the sample after being calcined at 600 ℃ for 5h shows that the sample has a broad peak around 2 θ ═ 22 °, and the sample has more amorphous components on the X-ray diffraction spectrum, which indicates that the sample prepared by the mixed micelle method has an amorphous structure.

FIG. 19 is an infrared spectrum of the nano-silica obtained in example 2 based on CTAB micelle method. The figure is consistent with the infrared spectrum of the nano-silica standard. As shown, at 3447.3cm^‐1Is caused by stretching vibration of-OH, 1636.5cm^‐1The absorption peak H-O-H is shifted to a high wave number direction and weakened in strength by high-temperature calcination due to bending vibration, but the tendency is not clear. 1096.8cm^‐1The absorption peak at (A) is caused by the antisymmetric stretching vibration of Si-O-Si, 810.3cm^‐1The absorption peak at (a) is related to bending vibration or rocking vibration of the Si-O bond.

FIG. 20 shows the nano SiO obtained in example 4 based on the mixed micelle method₂The IR spectrum of (A) shows that these peaks are consistent with the standard spectrum of silica. Wherein 3435.2cm^‐1Is the stretching vibration absorption peak of surface silicon hydroxyl-OH on silicon dioxide, 1633.9cm^‐1Is a bending vibration absorption peak of H-O-H physically adsorbed with water of 1091.7cm^‐1Is the antisymmetric stretching vibration absorption peak of Si-O, 804.8cm^‐1Is the symmetrical vibration absorption peak of Si-O, 478.9cm^‐1Is the bending vibration absorption peak of Si-O-Si. This shows the preparationThe silica of (2) has a high purity and is almost free of other impurities.

FIG. 21 is a differential thermal-thermogravimetric analysis curve of the nano-silica obtained in example 2 based on the CTAB micelle method, a is a TG curve, and b is a DTA curve, i.e., sample particles dried by air blowing at 80 ℃ for 5 hours were taken and measured by a thermal analyzer. Analysis conditions were as follows: nitrogen atmosphere, rate of temperature rise: 10 ℃/min, temperature rise range: 50-900 ℃. As can be seen, the first absorption peak is around 100 ℃ and is caused by the loss of crystal water from the precursor. All significant endothermic and exothermic processes are shown to be completed by the DTA curve before 650 ℃, and the TG curve shows that all the thermal weight loss of the precursor is completed at 600 ℃. Therefore, 600 ℃ was chosen as the temperature for thermal decomposition of the precursor.

Number of hydroxyl groups on silica surface:

example 2 obtaining of nano SiO based on CTAB micelle method₂Calculating the surface hydroxyl number: the hydroxyl content of the nano silicon dioxide prepared by a titration calcination method is 20.0mL of NaOH, and the nano SiO₂Surface area S_BET＝(589.67+480.88+ 493.64)/3＝521.4m²(ii) in terms of/g. Thus, the number of hydroxyl groups per square nanosilica surface area is:

example 4 preparation of nano SiO based on Mixed micelle method₂Calculating the surface hydroxyl number: the hydroxyl content of the nano silicon dioxide prepared by the titration calcination method is 6.2mL of NaOH, and the nano SiO₂Surface area S_BET＝254m²(ii) in terms of/g. Thus, the number of hydroxyl groups per square nanosilica surface area is:

nano SiO prepared only based on CTAB micelle method₂64% of the number of hydroxyl groups.

The invention is achieved byIn the reaction process, different proportions of the added reactants are changed, and the product is analyzed by particle size analysis, infrared spectrum analysis, transmission electron microscope and scanning electron microscope, so that the SiO with the secondary particle size of 20-50 nm, the surface hydroxyl number of 1.155/square nanometer, good dispersibility, high purity and almost no other impurities is synthesized by the CTAB micelle method₂(ii) a Based on the mixed micelle method, the SiO with the secondary particle size of 100 nm-300 nm, the surface hydroxyl number of 0.735/square nanometer, good dispersibility, high purity and almost no other impurities is synthesized₂. Despite the nano SiO prepared based on the mixed micelle method₂Particle diameter ratio nanometer SiO prepared based on CTAB micelle method₂The particle size was large and the number of surface hydroxyl groups was small, but the amount of CTAB consumed in the preparation process was 0.2301g, whereas the amount of CTAB consumed by the CTAB micelle method was 0.670g, and therefore, the amount of CTAB consumed by the mixed micelle method was 34.34% of the amount of CTAB consumed by the CTAB micelle method. Because the market price of CTAB is 4.5 ten thousand yuan/ton, the market price of PEG-4000 is only 1.23 ten thousand yuan/ton, and the price is relatively low, the mixed micelle method is adopted, and the formula of the patent is used for preparing the nano SiO₂The cost price of the product is only 7.4 ten thousand yuan/ton; in contrast, the micelle method is adopted, and the formula of the patent is used for preparing the nano SiO₂The cost price of (2) is 13.5 ten thousand yuan/ton. Thus, the preparation of nano SiO based on mixed micelles₂And the cost is low, and the method is worthy of popularization.

The preferred embodiments of the present invention shown in fig. 1 to 21 show the substantial features and the significant advantages of the present invention, and the equivalent modifications in shape, structure and the like can be made according to the actual use requirements and under the technical teaching of the present invention, but all are within the protection scope of the present invention.

Claims

1. Method for preparing large-specific-surface-area nano SiO by using water glass₂The method is characterized in that water glass is used as a silicon source, ethyl acetate is used as a precipitator for decomposing the silicon source, and the micelle method or the mixed micelle method is used for preparing the nano SiO with large specific surface area₂(ii) a Wherein: in the micelle method, CTAB is adopted as a surfactant; using C in the mixed micelle methodA compound surfactant formed by TAB and PEG-4000; the method comprises the following specific steps: firstly stirring and mixing a water glass solution and a surfactant CTAB or a compound surfactant formed by CTAB and PEG-4000 in a mixed solvent formed by water and glycerol, then adding a precipitator ethyl acetate, fully stirring and aging, washing with warm water containing CTAB after aging is finished, replacing and aging with an alcohol compound, finally drying, putting a dried sample into a muffle furnace for roasting, and naturally cooling to room temperature after roasting is finished to obtain the nano SiO with large specific surface area₂(ii) a The volume ratio of water to glycerol in the mixed solvent is 4: 1-2: 1.

2. The method of claim 1, wherein the water glass has a modulus of between 2.4 and 3.8.

3. The method of claim 1, wherein the SiO in the water glass solution₂The concentration of (A) is 12-16 wt%.

4. The method of claim 1, wherein the SiO in the water glass is in the micelle method₂And CTAB in a molar ratio of 15: 1-30: 1, SiO in water glass₂The molar ratio of the ethyl acetate to the water glass is 9: 10-12: 5, and the volume ratio of the water glass to the water is 2: 1-1: 8.

5. The method according to claim 1, wherein in the mixed micelle method, the mass ratio of CTAB to PEG-4000 is 1:1 to 1: 10; SiO 2₂The ratio of mass to sum of mass of CTAB and PEG-4000 was 9: 20-27: 20; SiO in water glass₂The molar ratio of the ethyl acetate to the water glass is 9: 10-21: 10, and the volume ratio of the water glass to the water is 1: 1-3: 2.

6. The method according to claim 5, wherein the mass ratio of CTAB to PEG-4000 in the mixed micelle method is 1:5 to 1: 10.

7. The method as claimed in claim 1, wherein the aging reaction is carried out at 20-50 ℃ for 20-30 h after adding the precipitant ethyl acetate; after the solvent is replaced, the aging temperature is 20-40 ℃, and the aging time is 4-8 h; the drying temperature is 60-80 ℃, and the drying time is 4-7 h; the roasting temperature is 550-600 ℃, and the roasting time is 4-7 h.

8. The method of claim 1, wherein the nano SiO is obtained by micelle method₂Has a particle diameter of 10 to 50nm and a BET specific surface area of 480 to 590m²Between/g; nano SiO obtained by mixed micelle method₂Has a particle diameter of 100 to 300nm and a BET specific surface area of 235 to 445m²Between/g.