Method for preparing silicon dioxide nanosheet hydrosol from clay minerals and application of silicon dioxide nanosheet hydrosol

Abstract

The invention provides a method for preparing silicon dioxide nanosheet hydrosol from clay minerals and application, and the method for preparing the silicon dioxide nanosheet hydrosol from the clay minerals comprises the following steps: mixing and melting the clay minerals and an intercalator to obtain intercalated clay minerals; wherein the mass ratio of the clay mineral to the intercalator is 1: 1-1: 20; carrying out dispersion treatment on the intercalated clay minerals to obtain clay mineral nanosheet dispersion liquid; the clay mineral nanosheet dispersion liquid is sequentially subjected to acid soaking water heat treatment and centrifugation, and the silicon dioxide nanosheet hydrosol is obtained. The silicon dioxide nanosheet prepared by the method exists in the form of uniform hydrosol, the content of silicon dioxide is not lower than 95%, and the preparation method is simple and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of silica synthesis technology, specifically relating to a method and application for preparing silica nanosheet hydrosols from clay minerals. Background Technology

[0002] Nanoscale silica materials have found wide application in cutting-edge fields such as separation, adsorption, catalysis, optics, electronics, drug delivery, and chemical sensing due to their relatively simple synthesis process, easily controllable morphology, and convenient functionalization. Among them, SiO2 nanosheets, with their large specific surface area and high surface energy, have shown great development potential. Currently, the main synthesis methods for SiO2 nanosheets include acid leaching, chemical vapor deposition (CVD), and template methods. However, CVD and template methods suffer from problems such as harsh conditions, high template costs, and complex separation techniques, and suitable mass production routes have not yet been found. In contrast, acid leaching can utilize widely distributed and inexpensive clay minerals to prepare silica nanosheets through a simple leaching process, and is considered a promising synthesis method.

[0003] However, with current commonly used technologies, nanosheets obtained by acid leaching have poor dispersibility and are difficult to form a uniform sol system, thus limiting their further utilization. Summary of the Invention

[0004] To address the technical problem that acid leaching in commonly used techniques fails to form a uniform sol system, this invention provides a method for preparing silica nanosheet hydrosols from clay minerals, comprising:

[0005] Clay minerals and intercalating agents are reacted at high temperature to obtain intercalated clay minerals; wherein the mass ratio of the clay minerals to the intercalating agent is 1:1 to 1:20.

[0006] The intercalated clay minerals were dispersed to obtain a clay mineral nanosheet dispersion.

[0007] The clay mineral nanosheet dispersion was subjected to acid immersion and heat treatment to separate silica nanosheet hydrosol.

[0008] Furthermore, the temperature of the high-temperature reaction is 250–850°C, and the duration of the high-temperature reaction is 1–24 hours.

[0009] Furthermore, the dispersion treatment includes: dispersing the intercalated clay mineral in a solvent, homogenizing, sonicating, and centrifuging to obtain the clay mineral nanosheet dispersion; wherein the homogenization speed is 10000-20000 rpm, the homogenization time is 10-720 min, the sonication power is 100-3000 W, and the sonication time is 10-720 min.

[0010] Furthermore, during the homogenization process, the mass ratio of the intercalated clay mineral to the solvent is 1:2 to 50.

[0011] Furthermore, the temperature of the acid leaching heat treatment is 40–200°C, and the duration of the acid leaching heat treatment is 0.5–24 h.

[0012] Furthermore, during the acid leaching hydrothermal treatment process, the concentration of the leaching acid in the mixed system formed by the leaching acid and the clay mineral nanosheet dispersion is 1-18 mol / L, and the leaching acid includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0013] Furthermore, the clay minerals include one or more of talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite, and the intercalating agent includes one or more of sodium chloride, sodium nitrate, lithium chloride, lithium nitrate, magnesium chloride, zinc chloride, zinc nitrate, copper chloride, and copper nitrate.

[0014] Furthermore, the process involves dispersing the intercalated clay mineral in a solvent, homogenizing, sonicating, and centrifuging to obtain a clay mineral nanosheet dispersion, wherein the clay mineral nanosheet dispersion is the upper suspension of the centrifuged product; the concentration of clay mineral nanosheets in the clay mineral nanosheet dispersion is greater than 1 g / L, the exfoliation rate is 10% to 90%, and the number of silica nanosheet layers in the clay mineral nanosheet dispersion is less than 5.

[0015] Furthermore, the silica content in the silica nanosheet hydrosol is not less than 95%, and the silica in the silica nanosheet hydrosol has a porous nanosheet morphology.

[0016] This invention provides a silica nanosheet hydrosol, which is prepared by any of the preparation methods described above.

[0017] Compared with the prior art, the present invention has at least the following advantages:

[0018] This invention provides an innovative method for preparing highly uniform, low-impurity silica nanosheet hydrosols using clay minerals as raw materials. This method comprehensively utilizes three synergistic steps—melting treatment, dispersion treatment, and acid leaching hydrothermal treatment—to effectively improve the quality and purity of the silica nanosheet hydrosols.

[0019] Specifically, in the melting stage, this invention innovatively mixes clay minerals with a specific intercalating agent and melts them under high temperature conditions. During this process, the intercalating agent molecules undergo ion exchange reactions with the cations between the clay mineral layers under heating. This reaction mechanism effectively expands the interlayer spacing of the clay minerals, significantly enhancing their exfoliability, thereby obtaining intercalated clay minerals. This step lays a solid foundation for subsequent exfoliation and dispersion.

[0020] Subsequently, in the dispersion stage, this invention employs advanced dispersion technology to further process the intercalated clay minerals. Through physical or chemical means, the intercalated clay minerals are exfoliated layer by layer, forming a highly stable clay mineral nanosheet dispersion. In this dispersion, the nanosheets exist in monolayer or few-layer form, possessing extremely high specific surface area and activity, providing favorable conditions for subsequent chemical reactions.

[0021] Building upon this foundation, the present invention proceeds to the crucial acid leaching hydrothermal treatment stage. In this stage, by introducing an acidic solution and reacting in a hydrothermal environment, hydrogen ions undergo a rapid and efficient mass transfer process with metal ions on the surface of the clay minerals. From a kinetic perspective, this process significantly enhances the leaching efficiency of impurities, enabling the efficient removal of impurities such as metal ions. Simultaneously, after the leaching of metal ions, a large number of silanol groups are formed on the surface of the clay minerals. These silanol groups not only further stabilize the dispersion of the silica nanosheets, preventing the weakening of the nanostructure advantages due to re-combination, but also provide abundant reactive sites for the nanosheets, facilitating their functional modification in subsequent applications. In contrast, commonly used acid leaching techniques are limited by incomplete leaching leading to high impurity content in the synthesized silica, and by incomplete exfoliation of the layered structure of the clay minerals resulting in poor nanosheet dispersion, making it impossible to form a uniform hydrosol.

[0022] In summary, this invention successfully prepared highly uniform, low-impurity silica nanosheet hydrosols through the synergistic effects of melt treatment, dispersion treatment, and acid leaching hydrothermal treatment. This method is not only simple and low-cost, but the resulting silica nanosheet hydrosols also have broad application prospects in separation, adsorption, and catalysis. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1This is a flowchart illustrating the technology roadmap for producing silica sol from clay minerals in one embodiment of the present invention.

[0025] Figure 2 This is a SEM image of the silica nanosheets in the silica nanosheet hydrosol prepared in Example 4 of the present invention;

[0026] Figure 3 This is an EDS spot scan image of the silica nanosheets in the silica nanosheet hydrosol prepared in Example 4 of the present invention;

[0027] Figure 4 This is a statistical table of the elemental content of silica nanosheets in the silica nanosheet hydrosol prepared in Example 4 of the present invention, obtained by EDS spot scan.

[0028] Figure 5 The image shows the XRD pattern of silica nanosheets in the silica nanosheet hydrosol prepared in Example 4 of this invention.

[0029] Figure 6 The image shows the FTIR spectrum of silica nanosheets in the silica nanosheet hydrosol prepared in Example 4 of this invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0033] like Figure 1 As shown, this invention provides a method for preparing silica nanosheet hydrosols from clay minerals, comprising the following steps:

[0034] S1. Clay minerals and intercalating agents are mixed and reacted at high temperature to obtain intercalated clay minerals; wherein the mass ratio of the clay minerals to the intercalating agent is 1:1 to 1:20. In some embodiments of the present invention, the mass ratio of the clay minerals to the intercalating agent can be 1:1 to 10.

[0035] In this invention, the temperature of the high-temperature reaction can be 250℃ to 850℃, and the duration of the high-temperature reaction can be 1 to 24 hours. In some embodiments of this invention, the temperature of the high-temperature reaction can be 350℃ to 850℃; in some more specific embodiments of this invention, the temperature of the high-temperature reaction can be 350℃ to 700℃.

[0036] In some embodiments of the present invention, the high-temperature reaction can be carried out under molten conditions, that is, the clay minerals and the intercalating agent can be mixed and melted in a solid state, and the molten product is cooled to room temperature to obtain the intercalated clay minerals. Under heating conditions, the intercalating agent can undergo ion exchange with the clay minerals, thereby increasing the interlayer spacing between the clay mineral layers.

[0037] In this invention, the duration of the high-temperature reaction can be 1 to 24 hours; in some embodiments of this invention, the duration of the high-temperature reaction can be 5 to 24 hours; in some more specific embodiments of this invention, the duration of the high-temperature reaction can be 10 to 24 hours.

[0038] In some embodiments of the present invention, clay minerals may exist in the form of clay mineral powder, wherein the particle size of the clay mineral powder is not greater than 100 mesh.

[0039] In some specific embodiments of the present invention, before melting, the clay mineral powder and intercalating agent can be vibrated and mixed for 1 to 10 minutes; then loaded into a corundum crucible and melted in a muffle furnace under an air atmosphere.

[0040] In some specific embodiments of the present invention, the method for preparing clay mineral powder includes: crushing clay mineral blocks or particles with a mineral crusher and then sieving them to obtain clay mineral powder; wherein the crushing time is 0.5 to 10 min and the rotation speed is 5000 to 30000 rpm.

[0041] In this invention, the clay minerals include one or more of the following: talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite.

[0042] In some embodiments of the present invention, the silica content in the clay mineral is 30wt% to 70wt%.

[0043] In this invention, the intercalating agent includes one or more of sodium chloride, sodium nitrate, lithium chloride, lithium nitrate, magnesium chloride, zinc chloride, zinc nitrate, copper chloride, and copper nitrate.

[0044] S2. The intercalated clay minerals are dispersed to obtain a clay mineral nanosheet dispersion.

[0045] In this invention, the dispersion process includes: dispersing intercalated clay minerals in a solvent, homogenizing, sonicating, and centrifuging to obtain the clay mineral nanosheet dispersion; wherein the homogenization speed is 10000-20000 rpm, the homogenization time is 10-720 min, the sonication power is 100-3000 W, and the sonication time is 10-720 min.

[0046] In some embodiments of the present invention, during the homogenization process, the mass ratio of the intercalated clay mineral to the solvent can be 1:2 to 50. In some specific embodiments of the present invention, the mass ratio of the intercalated clay mineral to the solvent can be 1:2 to 30.

[0047] In some embodiments of the present invention, the solvent includes water.

[0048] The separation in this invention can be centrifugal separation; in some embodiments of this invention, the centrifugal speed can be 500-4000 rpm, and the centrifugal separation time is 5-20 min. The centrifugal separation can separate monolayer or few-layer nanosheets from the unseparated clay mineral powder, and the unprecipitated suspension at the top of the centrifuged product containing monolayer or few-layer nanosheets can be collected to obtain a clay mineral nanosheet dispersion.

[0049] In some embodiments of the present invention, the concentration of the clay mineral nanosheet dispersion is greater than 1 g / L, the peeling rate is 10% to 90%, and the number of nanosheet layers in the clay mineral nanosheet dispersion is less than 5.

[0050] In some specific embodiments of the present invention, the concentration of the clay mineral nanosheet dispersion is 1-20 g / L, the peeling rate is 70%-90%, and the number of nanosheet layers in the clay mineral nanosheet dispersion is less than 5 layers.

[0051] S3. The clay mineral nanosheet dispersion is subjected to acid immersion and heat treatment in sequence to separate silica nanosheet hydrosol.

[0052] In this invention, the temperature of the acid leaching hydrothermal treatment can be 40–200°C, and the duration of the acid leaching hydrothermal treatment can be 0.5–24 hours. In some embodiments of this invention, the temperature of the acid leaching hydrothermal treatment can be 80–200°C; exemplaryly, the temperature of the acid leaching hydrothermal treatment can be 100–200°C; and even more exemplaryly, the temperature of the acid leaching hydrothermal treatment can be 150–200°C. In some embodiments of this invention, the duration of the acid leaching hydrothermal treatment can be 5–24 hours.

[0053] In some embodiments of the present invention, during the acid leaching hydrothermal treatment, the concentration of the leaching acid in the mixed system formed by the leaching acid and the clay mineral nanosheet dispersion is 1–18 mol / L, and the leaching acid includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. In some specific embodiments of the present invention, the concentration of the leaching acid in the mixed system formed by the leaching acid and the clay mineral nanosheet dispersion can be 5–18 mol / L; in some more specific embodiments of the present invention, the concentration of the leaching acid in the mixed system formed by the leaching acid and the clay mineral nanosheet dispersion can be 10–18 mol / L.

[0054] In some embodiments of the present invention, the solid-liquid ratio of the clay mineral nanosheet dispersion to the leaching acid can be 3:1 to 1:10.

[0055] In some embodiments of the present invention, the acid leaching hydrothermal treatment can be carried out in a hydrothermal reactor, and the lining of the hydrothermal reactor can be a polytetrafluoroethylene lining.

[0056] The separation in this invention can be centrifugal separation; in some embodiments of this invention, the centrifugal speed can be 2000-10000 rpm and the centrifugation time can be 5-20 min.

[0057] In this invention, the silica content in the prepared silica nanosheet hydrosol is not less than 95%. In some preferred embodiments, the silica content in the prepared silica nanosheet hydrosol is higher than 98%.

[0058] In the above-mentioned method for preparing silica nanosheet hydrosol, intercalating clay mineral powder with an intercalating agent expands the interlayer spacing of the clay minerals and enhances their exfoliability. Homogenization and ultrasonication further enhance the layer-by-layer exfoliation and dispersion of the intercalated clay mineral powder, while physical shear force and vibrational cavitation further strengthen the exfoliation between clay mineral layers. Acid leaching of the dispersed clay mineral nanosheets significantly improves the mass transfer process between hydrogen ions and metal ions on the clay mineral surface compared to bulk clay minerals. This kinetically enhances the leaching of impurities, and the formation of numerous silanol groups after metal ion leaching further stabilizes the dispersion of the silica nanosheets, preventing further recombination and weakening of the nanostructure advantages. Stable silica nanosheet hydrosols can be easily obtained through centrifugation.

[0059] The present invention also provides a silica nanosheet hydrosol, which is prepared by any of the preparation methods described above.

[0060] The silica nanosheet hydrosol prepared by this invention is redispersed in deionized water to obtain a stable silica sol dispersion, wherein the silica component has the morphology of porous nanosheets and the silica concentration is 0.5% to 20%.

[0061] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0062] The clay minerals used in the embodiments of the present invention were purchased from expanded vermiculite particles from China Maclean Company. The main component of the particles is vermiculite (AlFeMgO3Si), and it also contains silicon dioxide, etc. Specifically, the content of quartz impurities is less than 5 wt%.

[0063] The clay minerals used in the embodiments of this invention also include dried mica sand separated from pegmatite, whose main component is mica (KAl2(AlSi3O)). 10 It contains )(OH)2), and also contains silicon dioxide, etc. Specifically, the content of quartz impurities is less than 5 wt%.

[0064] The intercalating agent used in the embodiments of the present invention is lithium nitrate, which was purchased from China Maclean Company.

[0065] The leaching acid used in the embodiments of this invention is sulfuric acid, which was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0066] In this embodiment of the invention, the method for analyzing the silica content of raw materials and products is to determine the elemental content using an energy-dispersive X-ray spectrometer.

[0067] Example 1

[0068] S1. Vermiculite powder sieved through 100 mesh and lithium nitrate were mixed in a mass ratio of 1:1 in a corundum crucible and placed in a muffle furnace. The mixture was reacted at 350°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0069] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1000 rpm for 10 min, and collect the unprecipitated suspension at the top to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 4.5 mg / ml, the exfoliation rate is 75.4%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0070] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with a sulfuric acid concentration of 5 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 100°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content as high as 97.1%.

[0071] Example 2

[0072] S1. Vermiculite powder sieved through 100 mesh and lithium nitrate were mixed in a mass ratio of 1:10 in a corundum crucible and placed in a muffle furnace. The mixture was reacted at 350°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0073] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1000 rpm for 10 min, and collect the unprecipitated suspension at the top to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 7.5 mg / ml, the exfoliation rate is 84.3%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0074] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 5 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 100°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content as high as 93.4%.

[0075] Example 3

[0076] S1. Vermiculite powder sieved through 100 mesh and lithium nitrate were mixed in a mass ratio of 1:20 in a corundum crucible and placed in a muffle furnace. The mixture was reacted at 350°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0077] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1,000 rpm for 10 min, and collect the suspension to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 12.6 mg / ml, the exfoliation rate is 97.1%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0078] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 5 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 100°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content as high as 90.3%.

[0079] Example 4

[0080] S1. Vermiculite powder sieved through 100 mesh and lithium nitrate were mixed in a mass ratio of 1:10 in a corundum crucible and placed in a muffle furnace. The mixture was reacted at 350°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0081] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1000 rpm for 10 min, and collect the suspension to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 7.5 mg / ml, the exfoliation rate is 84.3%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0082] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 10 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 200°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content as high as 98.82%.

[0083] Example 5

[0084] S1. Vermiculite powder sieved through 100 mesh is mixed with lithium nitrate at a mass ratio of 1:10 in a corundum crucible and placed in a muffle furnace. The mixture is reacted at 250°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0085] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1000 rpm for 10 min, and collect the suspension to obtain a clay mineral nanosheet dispersion. The concentration of clay mineral nanosheets in the dispersion is 10.4 mg / ml, the exfoliation rate is 24.4%, and the number of silica nanosheets in the dispersion is less than 5 layers.

[0086] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 10 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 200°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content as high as 97.6%.

[0087] Example 6

[0088] S1. Vermiculite powder sieved through 100 mesh is mixed with lithium nitrate at a mass ratio of 1:10 in a corundum crucible and placed in a muffle furnace. The mixture is reacted at 550°C for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0089] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1000 rpm for 10 min, and collect the suspension to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 10.4 mg / ml, the exfoliation rate is 81.4%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0090] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 10 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 200°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content of 99.12%.

[0091] Example 7

[0092] S1. Mica powder sieved through 100 mesh and lithium nitrate were mixed in a mass ratio of 1:20 in a corundum crucible and placed in a muffle furnace. The mixture was reacted at 350 degrees Celsius for 12 hours in air atmosphere to obtain intercalated clay minerals.

[0093] S2. Disperse the intercalated clay minerals with deionized water of twice the amount of intercalated clay minerals, homogenize at 10,000 rpm for 30 min, sonicate at 400 W for 30 min, centrifuge at 1,000 rpm for 10 min, and collect the suspension to obtain a clay mineral nanosheet dispersion. The concentration of the clay mineral nanosheet dispersion is 12.6 mg / ml, the exfoliation rate is 97.1%, and the number of silica nanosheets in the clay mineral nanosheet dispersion is less than 5 layers.

[0094] S3. The clay mineral nanosheet dispersion and sulfuric acid were mixed to prepare a mixed suspension with an acid concentration of 10 mol / L. The suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor and heated to 200°C under sealed conditions for 12 h. The resulting reactant was centrifuged at 8000 rpm for 10 min, and the supernatant was discarded to obtain a silica nanosheet hydrosol with a silica content of 98.9%.

[0095] Comparative Example 1

[0096] This comparative example is the same as Example 4 in all other conditions, except that steps S1 and S2 are omitted, and the clay mineral nanosheet dispersion in step S3 is adjusted to vermiculite powder that has passed through a 100-mesh sieve.

[0097] Vermiculite powder was prepared into a suspension with the same concentration as in the above example, and then mixed with sulfuric acid to prepare a mixed suspension with an acid concentration of 10 mol / L. This suspension was added to the polytetrafluoroethylene liner in a hydrothermal reactor, and heated to 200°C under sealed conditions for 12 hours. The resulting reactant was centrifuged at 8000 rpm for 10 minutes, and the supernatant was discarded. Only silica flake precipitates with more than 50 silica nanosheets were obtained, which could not form a hydrosol, and the silica content was only 76.3%.

[0098] Analysis example 1

[0099] The results of measuring the silica content in the vermiculite raw material powder, the exfoliation rate in the above embodiments, and the silica content in the silica nanosheet hydrosol obtained, as well as the results of measuring the silica content in the silica flake precipitate obtained in the comparative example, are shown in Table 1. It can be seen that silica sol can be prepared by intercalation exfoliation followed by acid leaching, while silica sol cannot be obtained without intercalation exfoliation. Furthermore, intercalation exfoliation can significantly increase the silica yield. Increasing the intercalation treatment temperature, the hydrothermal acid leaching temperature, and increasing the acid concentration in the mixture of clay mineral nanosheet dispersion and sulfuric acid can further improve the exfoliation rate of clay minerals and the silica yield in the silica hydrosol.

[0100] Table 1. Peeling rate and silica content

[0101] Sample name or source Peeling rate Silica content vermiculite raw material powder 0％ 57.1％ Example 1 75.4％ 97.1％ Example 2 84.3％ 93.4％ Example 3 97.1％ 90.3％ Example 4 84.3％ 98.82％ Example 5 24.4％ 97.6％ Example 6 81.4％ 99.12％ Example 7 97.1％ 98.9％ Comparative Example 1 \ 76.3％

[0102] SEM was performed on the silica nanosheet hydrosol obtained in Example 4, as follows: Figure 2 As shown, the results yielded nanosheets with a thickness of less than 10 nm and a lateral dimension of more than 1 micrometer. The basic structure of the nanosheets was preserved after the acid leaching process, and there were traces of partial dissolution and reconstruction on the surface.

[0103] EDS was measured on the silica nanosheet hydrosol obtained in Example 4, as follows: Figure 3 As shown, the elemental distribution is mainly silicon and oxygen, which can be basically identified as silicon dioxide. Statistical analysis of the above EDS elemental content results yielded... Figure 4 Calculations show that the average silica content reaches 98.82%.

[0104] XRD was measured on the silica nanosheet hydrosol obtained in Example 4, as follows: Figure 5 As shown, the material is amorphous silicon dioxide, which suggests that the acid leaching process destroyed the original vermiculite structure, while basically preserving the macroscopic structure of the original silicon-oxygen tetrahedral layers, thus exhibiting a broad peak.

[0105] FTIR was measured on the silica nanosheet hydrosol obtained in Example 4, as follows: Figure 6 As shown, there is a large peak in the wavelength range of 3000-3600 nm, which reflects the presence of a large number of hydroxyl groups in the silica nanosheets, further confirming the good dispersion stability of the silica nanosheets.

[0106] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing silica nanosheet hydrosol from clay minerals, characterized in that, include: Clay minerals and intercalating agents are reacted at high temperature to obtain intercalated clay minerals; wherein the mass ratio of the clay minerals to the intercalating agent is 1:1 to 1:

20. The intercalated clay minerals were dispersed to obtain a clay mineral nanosheet dispersion. The clay mineral nanosheet dispersion was subjected to acid immersion and heat treatment to obtain silica nanosheet hydrosol.

2. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 1, characterized in that, The high-temperature reaction is carried out at a temperature of 250–850°C for 1–24 hours.

3. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 1, characterized in that, The dispersion process includes: dispersing the intercalated clay mineral in a solvent, homogenizing, sonicating, and centrifuging to obtain the clay mineral nanosheet dispersion; wherein the homogenization speed is 10000-20000 rpm, the homogenization time is 10-720 min, the sonication power is 100-3000 W, and the sonication time is 10-720 min.

4. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 3, characterized in that, During the homogenization process, the mass ratio of the intercalated clay mineral to the solvent is 1:2 to 50.

5. The method for preparing silica nanosheet hydrosols from clay minerals according to any one of claims 1 to 4, characterized in that, The temperature of the acid leaching heat treatment is 40–200°C, and the duration of the acid leaching heat treatment is 0.5–24 h.

6. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 1, characterized in that, During the acid leaching hydrothermal treatment, the concentration of the leaching acid in the mixed system formed by the leaching acid and the clay mineral nanosheet dispersion is 1-18 mol / L, and the leaching acid includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

7. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 1, characterized in that, The clay minerals include one or more of talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite, and the intercalating agent includes one or more of sodium chloride, sodium nitrate, lithium chloride, lithium nitrate, magnesium chloride, zinc chloride, zinc nitrate, copper chloride, and copper nitrate.

8. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 3, characterized in that, The process involves dispersing the intercalated clay mineral in a solvent, homogenizing, sonicating, and centrifuging to obtain a clay mineral nanosheet dispersion, wherein the clay mineral nanosheet dispersion is the upper suspension of the centrifuged product; the concentration of clay mineral nanosheets in the clay mineral nanosheet dispersion is greater than 1 g / L, the exfoliation rate is 10%-90%, and the number of silica nanosheet layers in the clay mineral nanosheet dispersion is less than 5.

9. The method for preparing silica nanosheet hydrosol from clay minerals according to claim 1, characterized in that, The silica nanosheet hydrosol contains no less than 95% silica, and the silica in the silica nanosheet hydrosol has a porous nanosheet morphology.

10. A silica nanosheet hydrosol, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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