Synthesis of Amorphous Silica Nanoflakes

Abstract

To newly provide a synthetic technique of an amorphous silica nano-sheet, according to the present invention.SOLUTION: There is provided a synthetic technique of an amorphous silica nano-sheet.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to the synthesis of amorphous silica nanosheets.

Background Art

[0002] Non-Patent Document 1 discloses a method for synthesizing silica nanosheets (SNS) by using tetraethyl orthosilicate (TEOS) as a silica precursor and cetyltrimethylammonium bromide (CTAB) as a surfactant. However, the silica nanosheets obtained in Non-Patent Document 1 are thick and the acquisition of single layers has not been successful.

[0003] Non-Patent Document 2 discloses a method for synthesizing silica nanosheets (SiONS) by exfoliating and oxidizing layered polysilane (SiH)n. However, the synthesis method of silica nanosheets (SiONS) in Non-Patent Document 2 is complicated and not applicable.

[0004] The nanosheets of amorphous silica in the prior art have a thickness of 2 nm or more, and it has been very difficult to synthesize amorphous silica nanosheets with a thickness worthy of nanosheets. The manufacturing process of the nanosheets of amorphous silica in the prior art is very complicated and not suitable for practical use.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

[12] 3522-3524 (2005), Synthesis of Amorphous Silica Nanosheets and Their Photoluminescence Hideyuki Nakano, Osamu Ohtani, Takuya Mitsuoka, Yousuke Akimoto, and Hiroshi Nakamura.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The object of the present invention is to newly provide a synthesis technique for amorphous silica nanosheets.

Means for Solving the Problems

[0007] The present inventors have conducted intensive research to achieve the above object.

[0008] That is, the present invention relates to the following synthesis techniques for amorphous silica nanosheets, etc.

[0009] Item 1. A silica sheet, composed of amorphous silica, with a thickness of approximately 1 nm or less, silica sheet.

[0010] Item 2. The silica sheet according to Item 1, which is a nanosheet.

[0011] Item 3. The silica sheet according to Item 1 or 2, which is composed of a single layer of layered amorphous silica.

[0012] Item 4. The silica sheet according to any one of Items 1 to 3, having a diameter of approximately several tens of μm.

[0013] Item 5. The silica sheet has a theoretical specific surface area of approximately 1,100 m 2 / g, and is the silica sheet according to any one of Items 1 to 4 above.

[0014] Item 6. A colloidal solution containing the silica sheet according to any one of Items 1 to 5 above.

[0015] Item 7. A method for producing the silica sheet according to any one of Items 1 to 5 above, (1) A step of mixing an alkoxysilane and a surfactant in a solvent to produce layered amorphous silica, and (2) A step of exfoliating nanosheets from the layered amorphous silica, which comprises a method for producing a silica sheet.

[0016] Item 8. In the step (1), the solvent is an acidic aqueous solution, the alkoxysilane is tetraethoxysilane, and the surfactant is a nonionic surfactant, which is the method for producing a silica sheet according to Item 7 above.

[0017] Item 9. In the step (1), it is a step of mixing an alkoxysilane and a surfactant in a solvent, heating, and producing layered amorphous silica, which is the method for producing a silica sheet according to Item 7 or 8 above.

[0018] Item 10. In the step (2), the layered amorphous silica is collected by filtration, and the layered amorphous silica is subjected to ultrasonic treatment in at least one solvent selected from the group consisting of water, ethanol, and a mixed solution of ethanol and water to exfoliate the layered amorphous silica. which is the method for producing a silica sheet according to any one of Items 7 to 9 above.

[0019] Item 11. The method for manufacturing the silica sheet is to obtain a colloidal solution of the silica sheet, the method for manufacturing the silica sheet according to any one of Items 7 to 10 above.

[0020] According to the present invention, it is possible to simply synthesize an amorphous silica nanosheet.

[0021] The present invention enables the bottom-up creation of amorphous silica nanosheets by using a nonionic surfactant as a template.

Effects of the Invention

[0022] The present invention can newly provide a synthesis technique for amorphous silica nanosheets.

Brief Description of the Drawings

[0023]

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Mode for Carrying Out the Invention

[0024] Hereinafter, the present invention will be described in detail.

[0025] In this specification, "containing" is a concept that encompasses any of "comprise", "consist essentially of", and "consist of". Also, in this specification, when a numerical range is indicated as "A to B", it means A or more and B or less.

[0026] (1) Amorphous silica nanosheet (Figure 1) The silica sheet of the present invention is an amorphous silica nanosheet made of amorphous silica and having a thickness of approximately 1 nm or less.

[0027] Amorphous silica nanosheets (colloidal silica nanosheets) can, as a seed material, enhance their applications in plastics, rubbers, etc. Since amorphous silica nanosheets have many SiOH groups, the number of bonding points with various functional groups is large, and a material with high mechanical strength can be obtained. Therefore, by using amorphous silica nanosheets in, for example, a polymer composition for tire applications, they function as a high-performance filler.

[0028] Amorphous silica nanosheets are useful for the development of new applications of colloidal silica. Amorphous silica nanosheets do not require a vapor phase process (de-vapor phase process), and by relying on a solution process and coating at room temperature, an extremely thin film of several nanometers can be formed (Figure 1).

[0029] (1-1) Thickness of the silica sheet The silica sheet of the present invention is composed of amorphous silica and has a thickness of approximately 1 nm or less.

[0030] The silica sheet is preferably a nanosheet. The silica sheet is preferably composed of a single layer of amorphous silica (amorphous silica nanosheet). The silica sheet preferably has a thickness of approximately 1 nm or less and a diameter of approximately several tens of μm.

[0031] (1-2) Specific surface area of the silica sheet The silica sheet of the present invention preferably has a specific surface area of 500 m 2 / g to 1,200 m 2 / g, and more preferably approximately 1,100 m 2 / g. The specific surface area was theoretically calculated assuming that the thickness of the silica nanosheet is 0.9 nm and the density of silica is 2.0 g / cm 3

[0032] (1-3) Colloidal solution containing the silica sheet The present invention is preferably a colloidal solution containing a silica sheet.

[0033] Silica sheets (amorphous silica nanosheets) are important in that they have a large number of Si-OH groups. Amorphous silica nanosheets (colloidal silica nanosheets) can be used as seed materials to enhance their applications in plastics, rubbers, etc. Amorphous silica nanosheets have a large number of bonding points and high mechanical strength. By using amorphous silica nanosheets in, for example, polymer compositions for tire applications, they function as high-performance fillers (Figure 1).

[0034] (2) Synthesis technology of amorphous silica nanosheet (Figures 2 and 3) The method for producing the silica sheet of the present invention is as follows (1) A step of mixing an alkoxysilane and a surfactant in a solvent to produce layered amorphous silica, and (2) A step of peeling off the surfactant from the layered amorphous silica. It includes these steps.

[0035] The method for producing the silica sheet of the present invention is an efficient and highly selective synthesis method for amorphous silica nanosheets. In amorphous silica nanosheets, most of the amorphous silica is exposed on the surface (Figure 2).

[0036] (2-1) Step (1): Mix alkoxysilane and surfactant (Figure 3) The method for producing the silica sheet of the present invention (synthesis step of amorphous silica nanosheets) first includes (1) a step of mixing an alkoxysilane and a surfactant in a solvent to produce layered amorphous silica.

[0037] Step (1) is a step of mixing an alkoxysilane and a surfactant.

[0038] The alkoxysilane is the part that forms amorphous silica nanosheets. After the alkoxysilane becomes silicic acid by hydrolysis and then undergoes polycondensation, it is the part that forms amorphous silica nanosheets.

[0039] The surfactant is the part that serves as the template for the layered amorphous silica. The hydrophilic part of the surfactant is located on the side of the amorphous silica nanosheet of the layered amorphous silica. The hydrophobic part of the surfactant is located inside the template of the layered amorphous silica.

[0040] In step (1), preferably, the solvent is an acidic aqueous solution, the alkoxysilane is tetraethoxysilane or tetramethoxysilane, and the surfactant is a nonionic surfactant.

[0041] The surfactant of the present invention preferably does not contain a cationic surfactant.

[0042] Step (1) is preferably a step of mixing an alkoxysilane and a surfactant in a solvent, heating them, and producing layered amorphous silica (layered silica-surfactant composite).

[0043] The surfactant is preferably a nonionic surfactant, and more preferably polyoxyethylene-2-cetyl ether (polyethylene glycol hexadecyl ether) (Brij(R) 52, manufactured by Merck) is used.

[0044] The solvent for mixing the alkoxysilane and the surfactant to produce layered amorphous silica is preferably an aqueous solution, and more preferably an acidic aqueous solution containing hydrochloric acid.

[0045] The heating is preferably heating with stirring.

[0046] The method for manufacturing the silica sheet of the present invention specifically involves adding hydrochloric acid and tetraethoxysilane to an aqueous solution of a surfactant (e.g., (Brij(R)52, manufactured by Merck)) (acidic aqueous solution), preferably heating it to about 30°C and stirring to synthesize a surfactant-silica composite. More preferably, a solution with a molar ratio of surfactant:tetraethoxysilane:water:hydrochloric acid of 0.033:1:131:3.8 is heated to about 30°C and stirred to synthesize a surfactant-silica composite.

[0047] (2-2) Step (2): Exfoliate layered amorphous silica (Figure 3) The method for manufacturing the silica sheet of the present invention (the step of synthesizing amorphous silica nanosheets) includes, after step (1), (2) a step of peeling from the layered amorphous silica.

[0048] Step (2) is a step of peeling the layered amorphous silica. By peeling the layered amorphous silica, a dispersion of amorphous silica nanosheets (hydrophilic silica film) can be prepared.

[0049] Step (2) preferably involves recovering the layered amorphous silica by filtration and subjecting the layered amorphous silica to ultrasonic treatment in at least one solvent selected from the group consisting of water, ethanol, and a mixed solution of ethanol and water to peel the layered amorphous silica.

[0050] In step (2), the solvent is more preferably ethanol.

[0051] In step (2), the ultrasonic treatment is more preferably performed at three frequencies of 28 kHz, 45 kHz, and 100 kHz for about 30 minutes.

[0052] The manufacturing method of the silica sheet of the present invention is a synthesis technique capable of obtaining an amorphous silica nanosheet with a thickness of 1 nm by ultrasonic exfoliation in a solvent (preferably ethanol). An amorphous silica nanosheet (hydrophilic silica film) can be exfoliated from the layered amorphous silica to prepare a dispersion.

[0053] The manufacturing method of the silica sheet of the present invention may also exfoliate an amorphous silica nanosheet (hydrophilic silica film) and prepare a dispersion by removing the mold from the layered amorphous silica.

[0054] (2-3) Method for obtaining a colloidal solution (dispersion) of the silica sheet The manufacturing method of the silica sheet of the present invention preferably obtains a colloidal solution of the silica sheet.

[0055] After step (2), the obtained surfactant-silica composite is dispersed in, for example, ethanol and subjected to ultrasonic treatment for about 30 minutes, whereby a dispersion in which one silica layer (amorphous silica nanosheet) is exfoliated can be obtained. The obtained dispersion contains each (one) amorphous silica nanosheet, and the thickness of the amorphous silica nanosheet is about 0.9 nm, which is a thickness that can be called a nanosheet.

[0056] The silica sheet of the present invention can be applied to the technology of conventional spherical silica colloids. The amorphous silica nanosheet can be applied to the technology of conventional colloidal silica such as fillers of polymer composites and exhibits excellent performance. The silica sheet of the present invention is a material of a two-dimensional nanostructure, and since it strongly interacts with a polymer using the surface of the silica sheet, it can exhibit excellent functions as an additive. In the silica sheet of the present invention, silanol groups are exposed at a high density and form an amorphous silica nanosheet.

Example

[0057] Hereinafter, based on the examples, the embodiments of the present invention will be described more specifically.

[0058] However, the present invention is not limited to the scope of the examples.

[0059] (1) Amorphous silica nanosheet (Figures 4 to 8) Synthesis of amorphous silica nanosheet Step (1) Hydrochloric acid and tetraethoxysilane were added to an aqueous solution of a nonionic surfactant (polyoxyethylene-2-cetyl ether (polyethylene glycol hexadecyl ether), Brij(R)52, manufactured by Merck) (acidic aqueous solution), and by heating and stirring, the molar ratio of surfactant, tetraethoxysilane, water, and hydrochloric acid (surfactant:tetraethoxysilane:water:hydrochloric acid) was adjusted to 0.033:1:131:3.8 to prepare a solution, and by stirring, a surfactant-silica complex (layered complex) was synthesized.

[0060] Step (2) Next, the obtained surfactant-silica complex was dispersed in ethanol, and by subjecting it to ultrasonic treatment for about 30 minutes, a dispersion in which one layer of silica layer was peeled off was obtained. Each (single) amorphous silica nanosheet was included in this dispersion. By centrifugation, unpeeled substances were removed to produce amorphous silica nanosheets having a thickness of about 1 nm (about 0.9 nm).

[0061] The thickness of the amorphous silica nanosheet represents the thickness of the nanosheet.

[0062] Figure 4 represents the amorphous silica nanosheet of the present invention.

[0063] (1) From the fact that peaks are obtained at 1.4°, 2.8°, and 4.2° in the XRD pattern, the formation of a layered substance is confirmed.

[0064] (2) From the fact that peaks due to C-H stretching vibration and Si-O stretching vibration are seen in the IR spectrum, it was also confirmed that a complex of silica and a surfactant was obtained.

[0065] (3)29 In the Si MAS NMR spectrum, signals attributed to silicon of Q 4 , Q 3 , and Q 2 were obtained at -110 ppm, -100 ppm, and -90 ppm, respectively (Q n : Si(OSi) n (OH) 4-n ).

[0066] From the above, the synthesis of the layered amorphous silica surfactant composite was confirmed.

[0067] Figure 5 represents the amorphous silica nanosheet of the present invention. The amorphous silica nanosheet forms a silica nanosheet with a thickness of only 0.9 nm (AFM image).

[0068] Figure 6 represents the amorphous silica nanosheet of the present invention. From the TEM image, the formation of the amorphous nanosheet was confirmed, and from the EDS spectrum, it was found to contain Si.

[0069] Figures 7 and 8 represent the characteristics of the amorphous silica nanosheet of the present invention.

[0070] The synthesis step of the amorphous silica nanosheet is based on the sol-gel method and can be synthesized at low cost.

[0071] The amorphous silica nanosheet is a single-layer nanosheet, and its dispersibility can be obtained as a beautiful colloid. The amorphous silica nanosheet can be handled in the same way as spherical silica colloids.

[0072] The colloidal solution of the amorphous silica nanosheet can maintain wide dispersion stability in the acidic to basic range and can maintain its structure even when subjected to ultrasonic treatment or the like. The colloidal solution of the amorphous silica nanosheet can be adjusted in terms of concentration, solvent type, exfoliation rate, etc.

[0073] (2) Usefulness of amorphous silica nanosheet The amorphous silica nanosheet of the present invention can be used as a filler for polymer composites and the like. In the amorphous silica nanosheet of the present invention, a high density of silanol groups is exposed. Since the two-dimensional material of the amorphous silica nanosheet of the present invention strongly interacts with a polymer using the surface, it can exhibit excellent functions as an additive.

Claims

**Claim 1** A method for manufacturing a silica sheet, comprising: (1) a step of mixing an alkoxysilane and a surfactant in a solvent to produce layered amorphous silica; and (2) a step of exfoliating the layered amorphous silica, wherein the silica sheet is composed of amorphous silica and has a thickness of 1 nm or less. A method for manufacturing a silica sheet. **Claim 2** In the step (1), the solvent is an acidic aqueous solution, the alkoxysilane is tetraethoxysilane, and the surfactant is a nonionic surfactant. The method for manufacturing a silica sheet according to Claim 1. **Claim 3** The step (1) is a step of mixing an alkoxysilane and a surfactant in a solvent, heating the mixture, and producing layered amorphous silica. The method for manufacturing a silica sheet according to Claim 1 or 2. **Claim 4** In the step (2), the layered amorphous silica is collected by filtration, and the layered amorphous silica is subjected to ultrasonic treatment in at least one solvent selected from the group consisting of water, ethanol, and a mixed solution of ethanol and water to exfoliate the layered amorphous silica. The method for manufacturing a silica sheet according to any one of Claims 1 to 3. **Claim 5** The method for manufacturing a silica sheet is to obtain a colloidal solution of the silica sheet. The method for manufacturing a silica sheet according to any one of Claims 1 to 4. **Claim 6** The silica sheet is a nanosheet. The method for manufacturing a silica sheet according to any one of Claims 1 to 5. **Claim 7** The silica sheet is composed of a single layer of layered amorphous silica. The method for manufacturing a silica sheet according to any one of Claims 1 to 6. **Claim 8** The silica sheet has a diameter of several tens of μm. The method for manufacturing a silica sheet according to any one of Claims 1 to 7. **Claim 9** The silica sheet has a theoretical specific surface area of 1,100 m 2 / g. The method for manufacturing a silica sheet according to any one of Claims 1 to 8.

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