JP2009184839A - Silica nanosheet, method for producing the same and dispersion of silica nanosheet in organic solvent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a silica nanosheet by which a silica nanosheet dispersible in an organic solvent can be obtained. <P>SOLUTION: The method for producing a silica nanosheet includes a step of mixing monocalcium disilicide and concentrated hydrochloric acid to form layered siloxene, and a step of mixing and stirring the layered siloxene and an organic solvent to form a silica nanosheet in the organic solvent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silica nanosheet and a method for producing the same, and further relates to an organic solvent dispersion of silica nanosheet.

  In a narrow sense, the silica nanosheet is formed by oxidizing a single layer of siloxane and spreading Si-O-Si bonds two-dimensionally. It is considered that a hydroxyl group or a hydrogen atom is bonded to each Si atom. Yes. Theoretically, the thickness of the silica nanosheet is about 0.6 nm, and there is no restriction on the spread in the plane direction, but the length usually has a spread of 100 times or more of the thickness.

As a method for preparing such silica nanosheet, Japanese 2006-49729 (Patent Document 1), a layered silicon compound _(e.g., CaSi _2, YbSi 2) is reacted by adding concentrated hydrochloric acid, by-products ( For example, CaCl ₂ , YbCl ₂ ) is removed by washing to take out a hydrogen-type layered compound (for example, Weiss-type siloxane: Si ₆ H ₃ (OH) ₃ .HCl), and this hydrogen-type layered compound is used as a surfactant ( For example, a method is disclosed in which an aqueous solution containing sodium dodecyl sulfate or tetrabutylammonium) is added to an aqueous solution whose pH is adjusted to 5 or less, and the aqueous solution is shaken for a predetermined time (for example, 10 days). The silica nanosheet obtained by this method is dispersed in water. In Patent Document 1, this silica nanosheet aqueous dispersion is used as it is as a coating liquid containing silica.

  On the other hand, silica fine particles conventionally used as inorganic fillers are often dispersed in an organic solvent when mixed with an organic polymer, and when added to an aqueous solution such as when mixed with a hydrophilic polymer. In some cases, the surface of silica fine particles may be coated with an organic polymer, and in this case as well, it is often dispersed in an organic solvent. For this reason, what was disperse | distributed to the organic solvent also about the silica nanosheet was calculated | required.

However, when preparing an organic solvent dispersion from an aqueous dispersion of silica nanosheets, if water is removed from the aqueous dispersion of silica nanosheets by drying or the like, the silica nanosheets aggregate and this aggregate is redispersed in the organic solvent. Therefore, it was practically difficult to convert an aqueous dispersion of silica nanosheets into an organic solvent dispersion.
JP 2006-49729 A

  This invention is made | formed in view of the subject which the said prior art has, and aims at providing the manufacturing method of the silica nanosheet which can obtain the silica nanosheet which can be disperse | distributed in an organic solvent.

  As a result of intensive studies to achieve the above object, the present inventors have mixed and stirred a layered siloxene obtained by reacting monocalcium disilicide and concentrated hydrochloric acid with an organic solvent, The inventors have found that silica nanosheets that can be dispersed in an organic solvent can be formed, and have completed the present invention.

  That is, in the method for producing a silica nanosheet of the present invention, the step of reacting monocalcium disilicide and concentrated hydrochloric acid to form a layered siloxene, the layered siloxene and an organic solvent are mixed and stirred, and the organic Forming a silica nanosheet in a solvent. Moreover, the silica nanosheet of this invention is obtained by such a manufacturing method, and can be disperse | distributed in an organic solvent.

  The organic solvent preferably contains dimethyl sulfoxide and / or N, N-dimethylformamide, more preferably contains dimethyl sulfoxide and / or N, N-dimethylformamide as the main component, and dimethyl sulfoxide and / or N N-dimethylformamide is particularly preferred.

  Further, the organic solvent dispersion of the silica nanosheet of the present invention is prepared by mixing and stirring a layered siloxene formed by reacting monocalcium disilicide and concentrated hydrochloric acid, and stirring the silica nanosheet in the organic solvent. It is obtained by forming a sheet.

  The reason why the silica nanosheet can be dispersed in the organic solvent by the method for producing a silica nanosheet of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, since the organic solvent has higher affinity with siloxene than water, it is presumed that the organic solvent easily enters the layer of the layered siloxene and acts advantageously on delamination. And it is guessed that the single layer siloxene peeled in this way is oxidized by oxygen, organic solvent molecules and moisture in the air to form a silica nanosheet. Furthermore, as shown in FIG. 1, the silica nanosheet in the organic solvent is mainly covered with organic solvent molecules, and the organic solvent molecules have a lower affinity with silanol groups than the water molecules, so that the dispersion medium can be easily replaced. It is presumed that a desired substance can be allowed to act.

  On the other hand, when forming a silica nanosheet using water, large-sized ions are inserted between layers of layered siloxene, swelled, and then mechanically vibrated to cause delamination. At the same time, siloxene is oxidized to form a silica nanosheet. However, as shown in FIG. 4, the silica nanosheet in the aqueous solution is mainly covered with water molecules, and this water molecule is presumed to be coordinated to the silanol group. In order to convert such an aqueous dispersion of silica nanosheets into an organic solvent dispersion, a step of removing water from the aqueous dispersion by drying or the like is required. At this time, silanols are formed via coordinated water molecules. It is presumed that it becomes difficult to convert the aqueous dispersion of silica nanosheets into an organic solvent dispersion because a dehydration condensation reaction occurs between the groups to form silica gel. In addition, such a dehydration condensation reaction is considered to occur during the production of the silica nanosheet, and it is presumed that the silica nanosheet is formed during the production of the silica nanosheet and the yield of the silica nanosheet is lowered.

  According to the present invention, a silica nanosheet that can be dispersed in an organic solvent can be obtained. In addition, it is possible to produce silica nanosheets with a significantly higher yield than when prepared in an aqueous solution.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof. In the method for producing a silica nanosheet of the present invention, a step of reacting monocalcium disilicide and concentrated hydrochloric acid to form a layered siloxene, the layered siloxene and an organic solvent are mixed and stirred, and the organic solvent And a step of forming a silica nanosheet. In the present invention, concentrated hydrochloric acid means a concentration of 30% by mass or more, and a higher concentration is preferable.

  The silica nanosheet obtained by the production method of the present invention is preferably a single layer, but a single layer of silica nanosheets overlapped by two layers or several layers (preferably 2 to 5 layers), and mixtures thereof are also included. It shall be contained in the silica nanosheet of this invention. Single-layer silica nanosheets with two or several layers, and mixtures thereof can also form transparent organic solvent dispersions and can be handled in substantially the same manner as single-layer silica nanosheets. is there.

(Layered siloxene formation process)
In the method for producing a silica nanosheet of the present invention, first, monocalcium disilicide and concentrated hydrochloric acid are mixed and stirred to form a layered siloxene (Weiss-type siloxene). The obtained layered siloxane is preferably washed several times with an organic solvent such as acetone as necessary to remove by-products (CaCl ₂ ) and the like. Further, if necessary, the organic solvent between the layered siloxene particles remaining after the washing may be removed by drying or the like.

The monocalcium disilicide (hereinafter referred to as “CaSi ₂ ”) is preferably pulverized as necessary. The particle size of the pulverized CaSi ₂ is not particularly limited, but is preferably 2 mm or less from the viewpoint of shortening the reaction time.

The mixing ratio of CaSi ₂ and concentrated hydrochloric acid is preferably such that the mass of concentrated hydrochloric acid is 20 times or more the mass of CaSi ₂ . When the mixing ratio is less than the above lower limit, the yield of layered siloxene tends to decrease. Moreover, it is preferable that the temperature at the time of mixing and stirring in this process is 0-50 degreeC, and it is more preferable that it is 10-30 degreeC. When the mixing / stirring temperature is less than the above lower limit, the reaction rate tends to decrease. On the other hand, when the upper limit is exceeded, a large number of interlayer Si-O-Si bonds of layered siloxene are formed, and delamination becomes difficult. The yield of the sheet tends to decrease. In addition, since the reaction rate tends to increase in the above temperature range, the temperature during mixing and stirring is preferably higher. Further, the stirring speed and stirring time are not particularly limited, and can be appropriately set according to the amount of CaSi ₂ and concentrated hydrochloric acid.

(Silica nanosheet formation process)
The layered siloxene obtained in the layered siloxene forming step is mixed with an organic solvent and stirred to delaminate the layered siloxene. Thereafter, the peeled siloxane is thought to be oxidized by oxygen in the air, organic solvent molecules, and water contained in the organic solvent to form silica nanosheets.

  Examples of the organic solvent used in this step include dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, acetonitrile, methyl Isobutyl ketone (MIBK), toluene, chloroform, 1,3-dimethyl-2-imidazolidinone and the like are preferable. These organic solvents may be used alone or in combination of two or more. Among these organic solvents, those containing DMSO and / or DMF are more preferable from the viewpoint of higher yield of silica nanosheets, those containing DMSO and / or DMF as the main component are more preferable, and DMSO and / or DMF is particularly preferred. Moreover, in the method for producing a silica nanosheet of the present invention, the organic solvent may contain water, but the water content in that case is 40% by mass or less from the viewpoint of increasing the yield of the silica nanosheet. It is preferable that it is, and it is more preferable that it is 20 mass% or less.

  The mixing ratio of the layered siloxene and the organic solvent is preferably such that the mass of the organic solvent is at least 5 times the mass of the layered siloxene. When the mixing ratio is less than the above lower limit, the yield of silica nanosheets tends to decrease.

As a stirring method, a general stirring method in which the shear rate is 1 second ⁻¹ or more can be used at any position in the mixture of the layered siloxene and the organic solvent. A method of adding inorganic beads made of alumina or alumina (preferably having a diameter of about 2 mm) and stirring using a roller type pot mill or a stirring blade made of a fluororesin is preferable. When using inorganic beads having a diameter of 2 mm, the amount of inorganic beads added is preferably an amount that is 5 to 100 times the mass of layered siloxene in the case of zirconia beads, for example, an amount that is 15 to 20 times It is more preferable that The stirring speed is preferably in the range of 3 to 150 rpm, and more preferably in the range of 80 to 120 rpm. In the method for producing silica nanosheets of the present invention, the yield of silica nanosheets is improved by stirring, but when the stirring speed is less than the above lower limit, the effect of improving the yield of silica nanosheets by stirring tends to decrease, on the other hand, When the upper limit is exceeded, control of the reaction temperature tends to be difficult due to frictional heat. In the production method of the present invention, a continuous mixing apparatus having a shear rate of 1 second- ¹ or more can also be used.

  The temperature during mixing and stirring in this step is preferably 10 to 70 ° C, more preferably 10 to 25 ° C. However, the temperature needs to be equal to or higher than the melting point of the organic solvent to be used (for example, 19 ° C. or higher in the case of DMSO). When the mixing / stirring temperature is less than the above lower limit, the delamination rate tends to decrease. On the other hand, when the above upper limit is exceeded, a condensation reaction of the generated silica nanosheet occurs, so that a precipitate such as silica gel is generated, and the silica nano The substantial yield of the sheet tends to decrease.

  The stirring time in this step is preferably 4 to 100 hours, more preferably 8 to 20 hours. When the stirring time is shorter than the above lower limit, the production amount of silica nanosheets is small, and the yield of silica nanosheets tends to be reduced. On the other hand, when the stirring time is longer than the upper limit, the production efficiency of silica nanosheets (production amount per unit time) is reduced. At the same time, a condensation reaction of the generated silica nanosheet occurs, so that a precipitate such as silica gel is generated, and the substantial yield of the silica nanosheet tends to be reduced.

(Purification process)
The solution (silica nanosheet organic solvent dispersion) containing the silica nanosheet obtained in the silica nanosheet forming step may contain solid impurities such as unreacted layered siloxane and by-products. In this step, it is preferable to remove these solid impurities by a known separation / purification method such as centrifugation or suction filtration, if necessary. For example, the solution containing the silica nanosheet obtained in the silica nanosheet forming step is subjected to centrifugation (3500 rpm × 20 minutes) to collect the supernatant, or suction filtration (using a 5 μm membrane filter) to obtain the filtrate. By collecting, a transparent silica nanosheet organic solvent dispersion can be obtained. The centrifugation conditions and suction filtration conditions are not limited to the above conditions, and can be set as appropriate.

(Coupling process)
In the method for producing a silica nanosheet of the present invention, a coupling agent is added to the organic solvent dispersion (preferably purified) of the obtained silica nanosheet and subjected to a heat treatment to react the silica nanosheet with the coupling agent. It is preferable to make it. This makes it possible to stably disperse the silica nanosheet in the organic solvent for a longer period without aggregating the silica nanosheet. The coupling agent is not particularly limited, but a silane coupling agent having an alkoxysilyl group in the molecule is preferable.

  The silica nanosheet obtained by the production method of the present invention is mainly composed of silicon and oxygen, and is a flake having a length of 100 nm or more in the surface direction and a thickness of 1 nm or less. The silica nanosheet can be usually obtained in a state of being dispersed in an organic solvent, and the organic solvent dispersion of the silica nanosheet can be easily replaced with a solvent depending on the purpose and application. Examples of the organic solvent used for solvent substitution include those exemplified in the silica nanosheet forming step. Further, the solvent replacement is not limited to organic solvents, and can be replaced with water.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Example 1)
24.4 g of CaSi ₂ (reagent manufactured by Soekawa Rikagaku Co., Ltd.) was pulverized so as to pass through a sieve having an aperture of 1.4 mm. Half of the CaSi ₂ pulverized product (12.2 g) and 500 ml of concentrated hydrochloric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a 1000 ml conical beaker and magnetically stirred in a water bath maintained at 10-15 ° C. For 40 minutes. As a result, a solution containing a yellowish green bulky solid (Weiss-type siloxene) was obtained. This solution was immediately filtered by suction using a membrane filter having a pore size of 5 μm, and then washed by mixing a filter cake (Weiss siloxane) with acetone and filtering. This acetone washing was repeated three times. The remaining CaSi ₂ pulverized product (12.2 g) was similarly treated with concentrated hydrochloric acid, washed three times with acetone, and then mixed with the previous filter cake.

  85.4 g of the filter cake (Weiss-type siloxene) containing acetone was placed in a separable flask having a capacity of 1000 ml, and 365 g of dimethyl sulfoxide (a reagent manufactured by Wako Pure Chemical Industries, Ltd., hereinafter abbreviated as “DMSO”) and a diameter of 2 mm. Zirconia beads (500 g) were added, and the mixture was stirred at room temperature (20-23 ° C.) for 15 hours using a fluororesin stirring blade (rotation speed: 120 rpm). The mixture after stirring was a cloudy brown liquid. The mixture is centrifuged (3500 rpm × 20 minutes) to remove mud, and the supernatant is suction filtered using a membrane filter with a pore size of 5 μm to collect the filtrate. A pale yellow transparent solution containing silica nanosheets (DMSO dispersion of silica nanosheets) 163 g was obtained.

  As a result of performing thermogravimetric analysis (heating from 25 ° C. to 1000 ° C. at a heating rate of 10 ° C./min in the air) for this pale yellow transparent solution, the content of silica nanosheets calculated from the ash content was 0.00. It was 50 mass% (Table 1). Moreover, the yield with respect to the theoretical value of the production amount of the silica nanosheet calculated from the amount of the raw material (hereinafter referred to as “silica nanosheet yield”) was 12% (Table 1).

  Next, to 20 g of an ethanol solution containing 0.2% by mass of acetic acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) and 20% by mass of water, a silane coupling agent (manufactured by Chisso Corporation, trade name “Syra Ace S510”). ) 3.2g was mixed and allowed to stand for 5 minutes. To this solution, 163 g of the DMSO dispersion of silica nanosheets was mixed and placed in a beaker having a capacity of 500 ml. The mixed solution after the heat treatment was light yellow and transparent, and its mass was 132 g. When this mixed solution was allowed to stand for 1 month, no precipitate was formed, and it was confirmed that the silica nanosheet was stably dispersed in the organic solvent over a long period of time.

  A part of this mixed solution was collected, dried under vacuum, and observed with a transmission electron microscope (TEM) and subjected to fluorescent X-ray elemental analysis (EDX). 2A and 2B show TEM photographs of the obtained silica nanosheet. FIG. 3 shows a fluorescent X-ray spectrum of the obtained silica nanosheet. As apparent from the TEM photograph shown in FIG. 2A, the obtained silica nanosheet was a thin piece having a spread of 100 nm or more in the surface direction. Moreover, it was guessed that the light-colored part in the silica nanosheet part in FIG. 2B is a single layer (theoretical value 0.65 nm). Further, as is clear from the results of EDX shown in FIG. 3, it was confirmed that the main components of the obtained silica nanosheet were silicon and oxygen.

(Example 2)
A CaSi ₂ pulverized product (12.0 g) obtained in the same manner as in Example 1 was treated with 500 ml of concentrated hydrochloric acid in the same manner as in Example 1, and washed with acetone three times to recover a filter cake. This filter cake was dried at room temperature using a vacuum dryer to obtain Weiss-type siloxene. In a glass container with a capacity of 50 ml, 0.5 g of the above-mentioned Wyls type siloxene and an organic solvent (N, N-dimethylformamide (DMF), N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, acetonitrile , 10 g of methyl isobutyl ketone (MIBK), toluene, chloroform, or 1,3-dimethyl-2-imidazolidinone) and 60 g of zirconia beads having a diameter of 2 mm were sealed. This mixture was stirred at room temperature (20-23 ° C.) for 20 hours using a roller mill (rotation speed: 15 rpm). The mixture after completion of stirring was subjected to suction filtration using a membrane filter having a pore size of 5 μm, and the filtrate was collected. As a result, a pale yellow transparent solution containing silica nanosheets (various organic solvent dispersions of silica nanosheets) was obtained. The pale yellow transparent solution was subjected to thermogravimetric analysis in the same manner as in Example 1 to determine the content and yield of silica nanosheets. The results are shown in Table 1.

(Example 3)
The CaSi ₂ pulverized product (4.0 g) obtained in the same manner as in Example 1 was treated with 400 ml of concentrated hydrochloric acid in the same manner as in Example 1 and washed three times with acetone to obtain a filter cake (Weiss siloxane). It was collected. In a glass container with a capacity of 50 ml, 1.0 g of the above-mentioned Wyeth-type siloxene containing acetone, 10 g of DMSO (having a water content of 0% by mass, 10% by mass, 20% by mass or 40% by mass) and 60 g of zirconia beads having a diameter of 2 mm. And the mixture was stirred as in Example 1 for 16 hours. The mixture after completion of stirring was subjected to suction filtration using a membrane filter having a pore size of 5 μm, and the filtrate was collected. As a result, a pale yellow transparent solution containing silica nanosheets (DMSO dispersion of silica nanosheets) was obtained. The pale yellow transparent solution was subjected to thermogravimetric analysis in the same manner as in Example 1 to determine the content of silica nanosheets. The results are shown in Table 2.

(Comparative Example 1)
A CaSi ₂ pulverized product (2.0 g) obtained in the same manner as in Example 1 was treated with 200 ml of concentrated hydrochloric acid in the same manner as in Example 1, and washed with acetone three times to recover a filter cake. This filter cake was dried at room temperature using a vacuum dryer to obtain Weiss-type siloxene.

  This Weiss-type siloxene was mixed with an aqueous solution (pH 3.2) obtained by dissolving 2.71 g of sodium dodecyl sulfate (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) in 800 ml of water, and the mixture was stirred using a magnetic stirrer. The color of the suspension at the start of stirring was orange, but when it was stirred for about 6 days, it turned pale yellow. Stirring was further continued, and the color became light gray 10 days after the start of stirring.

  Centrifugation (3500 rpm × 20 minutes) was performed on the suspension stirred for 10 days, and the supernatant was collected. As a result, the supernatant was turbid. The supernatant was suction filtered using a membrane filter having a pore size of 5 μm, and the filtrate was collected to obtain a colorless and transparent aqueous solution (silica nanosheet aqueous dispersion) containing silica nanosheets. The colorless and transparent aqueous solution was removed with a rotary evaporator to remove water-soluble components and concentrated 10 times. The content of the silica nanosheet in the concentrated liquid calculated from the mass of ash was 0.02% by mass, and the yield was 0.6% (Table 1).

(Comparative Example 2)
In a glass container having a capacity of 50 ml, 20 ml of the concentrate containing the silica nanosheet obtained in Comparative Example 1 and 5 ml of an organic solvent (hexane, toluene or chloroform) are placed and shaken vigorously, and then the aqueous phase and the oil phase are separated. Left to stand. The obtained oil phase was dried, but nothing was precipitated when any organic solvent was used.

(Comparative Example 3)
An ethanol solution (concentration) of 20 ml of the concentrated solution containing the silica nanosheet obtained in Comparative Example 1 and a silane coupling agent (Silaace S310, S320, S330 or S510 (trade name, manufactured by Chisso Corporation)) in a glass container having a capacity of 50 ml. (1% by mass) 0.2 g was added and stirred. As a result, cotton-like precipitation occurred in any silane coupling agent. The flocculent precipitate was collected by centrifugation, mixed with ethanol, and centrifuged again to dry the flocculent precipitate. To this flocculent precipitate, 20 ml of methyl isobutyl ketone (MIBK) was added and stirred and sonicated, but the flocculent precipitate was not dissolved when any silane coupling agent was used.

  As is apparent from the results shown in FIGS. 2A, 2B, and 3, silica nanosheets mainly composed of silicon and oxygen are formed even when weiss siloxane is treated with an organic solvent (Example 1). It was confirmed. Moreover, in the manufacturing method (Examples 1-3) of the silica nanosheet of this invention which uses an organic solvent as evident from the result shown to Tables 1-2, when manufacturing in aqueous solution (Comparative Example 1). In comparison, it was confirmed that the yield of silica nanosheets was significantly improved. Further, as is clear from the results shown in Table 2, it was confirmed that the organic solvent having a lower water content has a higher content of silica nanosheets, that is, a higher yield of silica nanosheets.

  Further, as is clear from the results shown in Comparative Example 2, it was difficult to extract the silica nanosheet in the aqueous solution with an organic solvent. Furthermore, as is clear from the results shown in Comparative Example 3, even if the silica nanosheet in the aqueous solution was treated with a silane coupling agent, it aggregated and precipitated, and it was difficult to disperse it in an organic solvent. It was. That is, it was confirmed that it was difficult to disperse the silica nanosheet prepared in an aqueous solution in an organic solvent.

  As described above, according to the present invention, it is possible to produce silica nanosheets dispersed in an organic solvent. In addition, it is possible to produce silica nanosheets with a significantly higher yield than when prepared in an aqueous solution.

  Therefore, the method for producing silica nanosheets of the present invention makes it possible to obtain silica nanosheets dispersed in an organic solvent in a high yield, so that organic polymers such as paints, adhesives, rubbers, and plastic products are used as a continuous phase. It is useful as silica fine particles used for materials.

It is a schematic diagram which shows the state of the silica nanosheet disperse | distributed in DMSO. 2 is an electron micrograph showing the silica nanosheet obtained in Example 1. FIG. 2 is an electron micrograph showing the silica nanosheet obtained in Example 1. FIG. 2 is a graph showing a fluorescent X-ray spectrum of the silica nanosheet obtained in Example 1. FIG. It is a schematic diagram which shows the state change from the silica nanosheet aqueous dispersion to a silica gel at the time of performing a drying process on the silica nanosheet dispersed in water.

Claims (4)

Reacting monocalcium disilicide and concentrated hydrochloric acid to form layered siloxene;
Mixing the layered siloxane and the organic solvent and stirring to form a silica nanosheet in the organic solvent;
The manufacturing method of the silica nanosheet characterized by including.   The method for producing a silica nanosheet according to claim 1, wherein the organic solvent contains dimethyl sulfoxide and / or N, N-dimethylformamide.   A silica nanosheet obtained by the production method according to claim 1 or 2.   It is obtained by mixing and stirring a layered siloxene formed by reacting monocalcium disilicide and concentrated hydrochloric acid and an organic solvent, and forming a silica nanosheet in the organic solvent. An organic solvent dispersion of silica nanosheets.