KR102042321B1 - Method for preparing silica particle having improved surface area - Google Patents

Abstract

According to one embodiment of the invention, (a) preparing a silicic acid (silicic acid) solution from the silica precursor solution; (b) mixing and diluting water in the silicic acid solution; (c) emulsifying the diluted silicic acid solution to prepare an emulsion; (d) gelling the emulsion to form an outer film; And (e) heating the gel to shrink the outer membrane. A method of preparing silica particles is provided.

Description

Method for producing silica particles with increased surface area {METHOD FOR PREPARING SILICA PARTICLE HAVING IMPROVED SURFACE AREA}

The present invention relates to a method for producing silica particles having an increased surface area.

Porous microstructures can be applied to a variety of applications, such as catalyst supports, membrane filters, adsorbents, reflective pigments, energy materials. Currently, porous structures can be classified into three types depending on their components such as porous polymers, ceramics and metals.

For example, the porous polymeric film can be applied to separation media such as the separation of various gas components or dialysis membranes. Porous ceramics can be applied as components of filters or membranes, and their applications have recently been extended to electrodes for energy devices or structures for tissue engineering. In the case of porous metals, they are mainly applied to applications such as sound absorbers, heat insulating materials and catalysts.

As such, numerous studies on the development of porous materials having a large surface area and high porosity have been made, and among them, research on a method for producing a porous material through a relatively economical and simple method has been mainstream.

Conventionally, a method of forming a porous structure by inserting polymer beads or surfactant templates into a micrometer-sized emulsion and then removing them to produce a porous material has been used.

However, these methods require the use of expensive raw materials because additional steps are required to remove the mold to form a porous structure and severe conditions such as hydrofluoric acid or high temperature calcination are involved during the removal of the mold. There are limitations in economic terms, such as the need to manufacture porous materials.

The present invention is to solve the above-mentioned problems of the prior art, an object of the present invention is to provide a manufacturing method capable of synthesizing silica particles having a large surface area in a simple and economical manner through a simple process using a relatively low cost raw material. .

However, the problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

According to one embodiment of the invention, (a) preparing a silicic acid (silicic acid) solution from the silica precursor solution; (b) mixing and diluting water in the silicic acid solution; (c) emulsifying the diluted silicic acid solution to prepare an emulsion; (d) gelling the emulsion to form an outer film; And (e) heating the gel to shrink the outer membrane. A method of preparing silica particles is provided.

According to one side, the silica precursor may be sodium silicate (sodium silicate).

According to one side, in the step (b), the silicic acid solution and the water may be mixed in a volume ratio of 1: 1 to 10, respectively.

According to one side, the silica particles may have a spherical shape of the wrinkled surface.

According to one side, the method for producing the silica particles may further include (f) evaporating the outer film.

The silica particle manufacturing method of the present invention uses a relatively inexpensive raw material as a silica precursor without using a separate template for forming a porous structure to produce silica particles having a large surface area through a simple economic method. can do.

Since the silica particles having an increased surface area exhibit superhydrophobicity, they can be effectively applied to superhydrophobic films and the like.

It is to be understood that the effects of the present invention are not limited to the above effects, and include all effects deduced from the configuration of the invention described in the detailed description or claims of the present invention.

(A) of FIG. 1 is a schematic diagram of a method for producing porous silica particles using polymer beads as a template, and (b) is a schematic diagram of a moldless production method of silica particles.
Figure 2 (a) shows a scanning electron microscope (SEM) image of the polystyrene (PS) nanospheres used as a template in the production of porous silica particles, (b) is a zeta potential (zeta) showing the average particle diameter of the polystyrene nanospheres potential).
(A) of FIG. 3 shows a scanning electron microscope (SEM) observation result of porous silica particles prepared using a polystyrene nanosphere having a diameter of 700 nm as a template, and (b) shows particle size distribution of the silica particles. . (c) shows a scanning electron microscope (SEM) observation result of the porous silica particles prepared by using polystyrene nanospheres having a diameter of 650 nm as a template, and (d) shows the particle size distribution of the silica particles. (e) shows a scanning electron microscope (SEM) observation result of the porous silica particles prepared by using polystyrene nanospheres having a diameter of 450 nm as a template.
4 shows FT-IR spectra before and after calcination of porous silica particles having spherical air cavities.
Figure 5 (a) shows a scanning electron microscope (SEM) image of the silica particles prepared according to the templateless synthesis method, (b) shows the particle size distribution of the silica particles.
Figure 6 (a) shows the nitrogen adsorption / desorption results of the silica particles prepared according to the casting-free synthesis method, (b) shows the pore size distribution of the silica particles.
Figure 7 (a) shows the FT-IR spectrum of the silica particles prepared through the calcination process before and after the casting-free synthesis method, (b) shows the TGA analysis results of the silica particles.
Figure 8 (a) shows a scanning electron microscope (SEM) image of the silica particles prepared according to the templateless synthesis method, (b) shows the particle size distribution of the silica particles.
Figure 9 (a) schematically shows the process of forming a super water-repellent coating film surface-treated with silica particles. (b) is an image showing the results of measuring the contact angle of the droplets added on the silica particle coating film prepared using a polystyrene nanosphere mold, (c) is a dropwise addition on the silica particle coating film prepared by a casting-free synthesis method It is an image showing the result of measuring the contact angle of the droplets.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

Various modifications may be made to the embodiments described below. The examples described below are not intended to be limited to the embodiments and should be understood to include all modifications, equivalents, and substitutes for them.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of examples. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

In addition, in the description with reference to the accompanying drawings, the same components regardless of reference numerals will be given the same reference numerals and redundant description thereof will be omitted. In the following description of the embodiment, when it is determined that the detailed description of the related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

FIG. 1 (a) is a schematic diagram illustrating a method for preparing self-assembled porous silica particles via an emulsion using polystyrene nanospheres as a template according to a conventional method.

According to the conventional method, the polystyrene nanospheres synthesized through dispersion polymerization are encapsulated in an aqueous droplet together with silicic acid purified from sodium silicate, and the droplets are evaporated at high temperature to induce internal capillary pressure, thereby causing the magnetism of the organic / inorganic microparticle material. Can lead to organization. The dried particles can then be converted to porous silica particles by removing organic components such as polymer beads through high temperature heat treatment such as calcination.

However, this conventional method uses a costly material such as TEOS (Tetraethyl orthosilicate) as the silica precursor, and there is a limit in terms of economics because it involves an additional process for removing the template. Accordingly, the present inventors have developed a method for producing silica particles having an increased surface area without using a mold as shown in FIG. 1 (b).

Referring to Figure 1 (b), after heating the aqueous emulsion droplets of silicic acid, by further heating the thin silica gel outer membrane formed on the interface of the droplets it can be induced by the inner capillary pressure and the shrinkage of the emulsion shrinkage.

Specifically, according to one embodiment of the invention, (a) preparing a silicic acid (silicic acid) solution from the silica precursor solution; (b) mixing and diluting water in the silicic acid solution; (c) emulsifying the diluted silicic acid solution to prepare an emulsion; (d) gelling the emulsion to form an outer film; And (e) heating the gel to shrink the outer membrane. A method of preparing silica particles is provided.

In the step (a), the silica precursor solution may be passed through an ion exchange resin to prepare a silicic acid solution. Specifically, the silica precursor may be sodium silicate, and passing the sodium silicate through an ion exchange resin may remove sodium ions and finally obtain a silicic acid solution.

In step (b), water may be added to the silicic acid solution to dilute the concentration of silicic acid. The degree of concentration dilution can control the surface morphology and specific surface area of the final product, silica particles.

Specifically, in the step (b), the silicic acid solution and the water may each be mixed in a volume ratio of 1: 1 to 10, preferably 1: 1 to 6. When the volume ratio of the water is less than 1 based on the volume ratio of the silicic acid solution, the surface area may not be increased due to the degree of wrinkles of the surface during particle manufacturing. You may not.

In step (c), the silicic acid solution may be converted into an emulsion using an emulsifier. The emulsifier may be used as a tetradecane (tetradecane) containing an Abil EM 90 emulsifier, but is not limited thereto.

In the step (d) it is possible to form a thin outer film made of silica gel (silica gel) on the outside of the emulsion by heating the prepared emulsion. The specific heating temperature may be 85 ° C. to 95 ° C., preferably 90 ° C., but is not limited thereto.

In the step (e) it is possible to shrink the outer film by maintaining the heating of the step (d) continuously, thereby inducing wrinkles and folding of the emulsion present therein. Specifically, the heating time may be 1 hour to 2 hours, preferably 1.5 hours, but is not limited thereto.

Silica particles prepared by the above method may have a spherical shape having wrinkled surfaces. Therefore, since the silica particles exhibit superhydrophobicity due to the pores present therein, the silica particles may be applied to a superhydrophobic film or the like. For example, the silica particles may be deposited on a substrate such as glass to prepare a super water repellent film, and the super water repellency may be further improved by further treating a silane coupling agent containing fluorine. The super water-repellent film prepared as described above exhibits excellent water repellency with respect to water, and may exhibit a contact angle of 140 ° or more when water is dropped onto the film.

In addition, the method for producing the silica particles may further include (f) evaporating the outer film. As the method of evaporating the outer film, heating, that is, calcining (calcinations) may be used, thereby reducing the content of impurities contained in the silica particles. Specifically, the calcination may be performed at a temperature of about 500 ℃, but is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are described for the purpose of illustrating the present invention, but the scope of the present invention is not limited thereto.

Comparative example : Polystyrene Bead  Silica Particle Preparation by Using Mold

(1) polystyrene Nanospheres (PS nanosphere ) Produce

After adding styrene monomer (99%, Daejeong Chemical) to a batch reactor containing a ethanol (HPLC grade) solution in which stabilizer PVP k30 (MW = 40,000 g / mol, Sigma-Aldrich) was dissolved, 200 rpm While stirring, comonomer MTC (2- (methacryloyloxy) ethyltrimethylammonium chloride,%, Sigma-Aldrich) was added.

Thereafter, air was removed by injecting nitrogen into the reactor for 1 hour to remove air, and then AIBN (azobisisobutyronitrile, 98%, Sigma-Aldrich) initiator dissolved in a small amount of styrene was added to the reaction mixture and dispersion polymerization was performed while raising the temperature. The polystyrene (PS) nanospheres were prepared by centrifuging the resulting polymer latex beads by sonication for 19 hours, sonicating and redispersing in distilled water.

(2) polystyrene Nanospheres  Shape and Average Particle Size Analysis

The size and distribution in the dispersion of the polystyrene particles were measured using a particle size analyzer (ZETA PLUS, Marlvern Instruments). The morphology of the polystyrene particles was observed using a field emission scanning electron microscope (FE-SEM, Hitachi-S4700).

Observation results of the polystyrene nanospheres are shown in Figure 2 (a), it was confirmed that the synthesized spherical polymer particles can be used as a template for the production of porous silica particles.

On the other hand, since the nanostructure of the porous particles may be affected by the surface charge of the polymer template, the zeta potential value of the polystyrene nanospheres was measured as a function of the average particle diameter, and the result is shown in FIG. Shown in

The zeta potential in all cases was determined as a positive value due to the amine groups on the polystyrene nanosphere surface derived from the chemical structure of the comonomer MTC. Thus, it was confirmed that electrostatic attraction between precursor, silicic acid and polymer template can be induced during the self-organization process as the emulsion droplets shrink due to evaporation.

(3) the preparation of porous silica particles

Deionized water (18.2 MΩcm ⁻¹ ) was produced using a distilled water system (Millipore) and used as the reaction medium for silica dilution. Sodium silicate (water glass, Na ₂ O (SiO ₂ ) _x xH ₂ O%), a silica precursor, was purchased from Sigma-Aldrich.

Sodium silicate and distilled water were mixed at a volume ratio of 1: 2 and stirred under vigorous conditions for 30 minutes. The resulting mixture was passed through an ion exchange resin (amberlite IR 120, hydrogen form) purchased from Sigma-Aldrich to obtain an aqueous silicic acid solution.

Subsequently, 6 ml of an aqueous dispersion of polystyrene nanospheres was mixed with 1 ml of an aqueous silicic acid solution. The resulting mixture was used as a dispersed phase by emulsification with tetradecane (Beyond Industries Limited) containing as much as 3% by weight of Abil EM 90 emulsifier (Cosnet) in the continuous phase. For this, mechanical homogenization was performed for 1 minute using a homogenizer (hg-15a-set-a, witeg Labortechnik).

The self-assembly of polystyrene (PS) nanospheres and silicic acid was induced by heating a multistage fluid system at 90 ° C. for 1.5 hours. The particles synthesized using hexane were washed several times, dried at room temperature for at least one day to remove the oil phase, and then calcined using a box furnace (M13P, Hantech) at 500 ° C. for 5 hours to obtain porous silica particles. Prepared.

(4) Analysis of morphology, particle size distribution and molecular structure of silica particles

Figure 3 (a) shows the results of scanning electron microscopy (FE-SEM, Hitachi-S4700) of the macroporous silica particles prepared using a polystyrene nanospheres of 700nm diameter as a template. As can be seen in Figure 3 (a), macroporous particles having a high porosity can be prepared by calcination at high temperature.

The particle size distribution of the porous silica particles was calculated by measuring the diameters of some particles from the SEM image of FIG. 3 (a), and the results are shown in FIG. 3 (b). The average particle diameter of the calculated porous particles was found to be 2.87 μm. As can be seen from the SEM image of FIG. 3 (a), the isotropic arrangement of the pores in the porous particles after calcination can be expected depending on the mixing of precursors and polymer beads in the droplets.

Similarly, FIGS. 3 (c) and 3 (d) observed the scanning electron microscope (SEM) observation results and particle size distribution of macroporous silica particles prepared using polystyrene nanospheres having a diameter of 650 nm as a template. (e) observed a scanning electron microscope (SEM) image of the macroporous silica particles prepared using a 450nm diameter polystyrene nanosphere as a template.

Meanwhile, FT-IR spectra were analyzed using a Nicolet FT-IR spectrometer (Thermo Fisher Scientific co. Ltd.) before and after calcination of the porous silica particles, that is, before and after mold removal, and the results are shown in FIG. 4. Comparing the FT-IR spectrum before and after calcination at 500 ℃ was confirmed the change of composition of the fine particles according to the heat treatment.

Referring to FIG. 4, the characteristic peak of the polystyrene nanospheres before calcination was found at 1600.8 cm ⁻¹ due to the stretching vibration of the polystyrene benzene ring. The stabilizer PVP showed a peak near 1670 cm ^-1 , indicating that the PVP molecules remained on the particle surface after dispersion polymerization. However, most of the peaks disappeared after calcination, and the resulting porous silica particles showed characteristic peaks at about 800, 1110, 1630 and 3440 cm ⁻¹ , confirming that the porous silica particles could be prepared from the starting sodium silicate. It was.

Example  One: No casting  Preparation of Silica Particles by Synthesis

(1) silica particle production

Deionized water (18.2 MΩcm ⁻¹ ) was produced using a distilled water system (Millipore) and used as the reaction medium for silica dilution. Sodium silicate (water glass, Na ₂ O (SiO ₂ ) _x xH ₂ O%), a silica precursor, was purchased from Sigma-Aldrich.

A mixture of sodium silicate and distilled water in a 1: 2 volume ratio was passed through an ion exchange resin (amberlite IR 120, hydrogen form) purchased from Sigma-Aldrich to obtain an aqueous silicic acid solution. The silicic acid aqueous solution was diluted by mixing the silicic acid aqueous solution and distilled water in a volume ratio of 3: 4.

Emulsion droplets containing a silica raw material were prepared by emulsifying an aqueous silicic acid solution with tetratradecane (Beyond Industries Limited) containing Abil EM 90 emulsifier (Cosnet) using a mechanical homogenizer.

The silica particles were then prepared by evaporating an aqueous medium and volatile solvents such as ethanol by heating at 90 ° C. for 1.5 hours in a multistage fluid system without the use of a polymer template. The resulting silica particles were washed with hexane and dried at room temperature.

(2) Analysis of Morphology and Particle Size Distribution of Silica Particles

Figure 5 (a) shows a scanning electron microscope (FE-SEM, Hitachi-S4700) image of the silica particles. Referring to FIG. 5 (a), it can be seen that the silica particles have a spherical spherical surface, and the particle size distribution of the final silica particles also varies because the emulsion droplets vary in particle size.

The particle size distribution of the silica particles was calculated by measuring the diameters of some particles from the image of FIG. 5 (a), and the results are shown in FIG. 5 (b). The calculated average particle diameter of the porous particles was found to be 7.56㎛.

(3) of silica particles Specific surface area  analysis

The characteristics of the silica particles prepared through the nitrogen adsorption / desorption method using the specific surface area analyzer (ASAP-2010) were confirmed, and the results are shown in FIG. 6 (a). Referring to FIG. 6 (a), the BET surface area of the silica particles was measured to be 157.5 m 2 / g, which is similar to the measurement result of the porous silica particles prepared according to the comparative example.

In addition, the binary pore size distribution was measured by BJH desorption measurement, the results are shown in Figure 6 (b). The average pore size of the silica particles was measured at 3.3 nm, but macropores were observed together, indicating that the macropores can be successfully formed according to the method for preparing a template.

(4) molecular structure analysis of silica particles

The composition of silica particles prepared using a Nicolet FT-IR spectrometer (Thermo Fisher Scientific co. Ltd) was confirmed, and the analysis results before and after calcination are shown in FIG. Particles after calcination resulted in characteristic peaks at 470 and 800 cm ⁻¹ due to stretching and bending vibrations of Si—O bonds, suggesting that silica particles could be prepared from sodium silicate precursors.

In addition, the weight loss of the porous particles with temperature was measured using a thermal analysis system (TGA, TG-8120), the results are shown in Figure 7 (b). After preparing the emulsion diesel self-assembled silica particles, the resulting particles were heated under nitrogen atmosphere to confirm the change in weight of the sample, and thus the final weight was about 70% of the initial value. Since the hydroxyl group of the silica particles could be removed with water in the heating step, the weight loss of the particles was observed up to about 600 ° C. as shown in FIG.

Example  2: No casting  Preparation of Silica Particles by Synthesis

The present inventors observed that changes in the morphology and particle size distribution of the silica particles produced according to the templateless synthesis method were changed by decreasing the silicic acid concentration inside the emulsion droplets. A mixture of sodium silicate and distilled water in a 1: 2 volume ratio was passed through an ion exchange resin (amberlite IR 120, hydrogen form) purchased from Sigma-Aldrich to obtain an aqueous silicic acid solution. The silicic acid aqueous solution was diluted by mixing the silicic acid aqueous solution and distilled water in a volume ratio of 1: 6.

FIG. 8 (a) shows a scanning electron microscope (SEM) image of silica particles synthesized using a mixture of silicic acid and distilled water mixed at a volume ratio of 1: 6. As shown in Figure 8 (a), by reducing the concentration of the precursor material it was possible to observe the microstructure of the porous particles of the corrugated form. This suggests that after the formation of the thin silica gel envelope having a mechanically foldable strength, a corrugated surface was formed according to the capillary pressure.

In addition, the particle size distribution of the resulting porous particles was measured and shown in FIG. 8 (b). According to this, the average diameter of the particles is 3.41 μm, which means that the particle size can be adjusted according to the concentration change of the precursor silicic acid in the droplets.

The present inventors have identified a mechanism in which spherical silica particles having corrugated surfaces are formed by wrinkles and folds of thin silica gel formed inside droplets contracted by internal capillary pressure during heating. After the silicic acid dissolved in the aqueous droplets is converted to a solid silica outer membrane upon heating of the multistage fluid system, the shrunk droplets can cause wrinkles and folds of the amorphous silica outer membrane to form porous silica particles without the use of a polymer bead template. have.

Experimental Example : Super water-repellent  Coating film production

The silica powders prepared according to Comparative Examples and Example 1 were washed, and then dried at room temperature to evaporate hexane. Each particle was then sonicated for 30 seconds and redispersed in water at 1% solids concentration. The resulting aqueous dispersion was added dropwise onto a glass substrate and dried at room temperature to produce a coating film.

Thereafter, the coating film was immersed in a methanol solution containing 1% by volume of HDFTHDTES ((heptadecafluoro-1, 1, 2, 2-tetrahydrodecyl) triethoxysilane) as a silane coupling agent, as schematically shown in FIG. 9 (a). A super water repellent coating film was produced.

After dropping water droplets on each superhydrophobic coating film, the contact angle for the droplets on each film was measured using a contact angle measuring system (Phoenix-Mini, Surface & Electro-Optics Co. Ltd).

FIG. 9 (b) is an image of droplets on a film coated with porous silica particles prepared using polystyrene nanospheres having a diameter of 700 nm. The measured contact angle was found to be 141 °, which is a relatively large value.

Similarly, the results of FIG. 9 (c) also showed similar results for coating samples of silica particles prepared through a templateless synthesis method. Due to the corrugated form of the surface of the silica particles prepared according to Example 1, the contact angle for water droplets on the coating film was measured to be relatively high, about 140 °.

Although the embodiments have been described by the limited embodiments and the drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the techniques described may be performed in a different order than the described method, and / or the described components may be combined or combined in a different form than the described method, or replaced or substituted by other components or equivalents. Appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the following claims.

Claims (5)

(a) preparing a silicic acid solution from a silica precursor solution;
(b) mixing and diluting water in the silicic acid solution;
(c) emulsifying the diluted silicic acid solution to prepare an emulsion;
(d) gelling the emulsion to form an outer film; And
(e) heating the gel to shrink the outer membrane;
Gelatinizing the emulsion to form an outer film, by heating the prepared emulsion to form a thin outer film made of silica gel on the outside of the emulsion,
The heating temperature of the emulsion is 85 ℃ to 95 ℃, to prepare a porous silica in a moldless,
Method for producing silica particles.
The method of claim 1,
The silica precursor is sodium silicate (sodium silicate), the method for producing silica particles.
The method of claim 1,
In the step (b), the silicic acid solution and the water are mixed in a volume ratio of 1: 1 to 10, respectively.
The method of claim 1,
The silica particles have a surface of wrinkled spherical form, the method for producing silica particles.
The method of claim 1,
(f) evaporating the envelope; further comprising, silica particles.

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