Method for preparing monodisperse nanoscale calcium fluoride

Abstract

A method for preparing monodisperse nanoscale calcium fluoride, comprising the following steps: (S1) dispersing calcium long-chain alkylbenzenesulfonate and an acrylate copolymer in a mixed solution of water, n-hexane, and an alcohol to form a stable emulsion A, wherein monomers of the acrylate copolymer comprise (meth)acrylic acid, a polyether macromonomer, and a C1-4 alkyl (meth)acrylate; (S2) dissolving a fluoride salt in water, adding polyvinyl alcohol, and uniformly mixing these materials to obtain a solution B; and (S3) slowly dropwise adding the solution B to the emulsion A under stirring and ultrasonic conditions, and carrying out standing for aging, centrifugal separation, washing, and drying to obtain monodisperse nanoscale calcium fluoride. By using the calcium long-chain alkylbenzenesulfonate with surface activity as a calcium source in combination with homemade acrylate as a dispersing agent, an emulsion is formed in a specific combined solvent, and by dropwise adding a fluorine salt aqueous solution to the emulsion under an ultrasonic condition, nanoscale calcium fluoride with a uniform and controllable particle size can be prepared under the action of a microemulsion.

Description

A method for preparing monodisperse nanoscale calcium fluoride Technical Field

[0001] The invention belongs to the technical field of calcium fluoride production, and particularly relates to a method for preparing monodisperse nanoscale calcium fluoride. Background Art

[0002] Calcium fluoride has excellent chemical stability, biocompatibility, weather resistance, and a wide bandgap, and has been widely used in fluorescent materials, optical glass, crystals, anti-reflective coatings, and other fields. Nanoscale materials, due to their size, exhibit special spatial and confinement effects, exhibiting some unique properties. For example, nanoscale calcium fluoride exhibits significantly improved conductivity and lubricity, which are characteristics not possessed by micron-scale calcium fluoride. In addition, nanoscale calcium fluoride exhibits high optical transmittance over a wide wavelength range from vacuum ultraviolet to mid-infrared. The preparation of dispersed nanoscale calcium fluoride can be applied in multiple technical fields. However, the preparation of nanoscale calcium fluoride has the disadvantages of large particle size and poor particle size dispersion. Currently, the main methods for producing nanoscale calcium fluoride are precipitation, solvothermal, microemulsion, and vapor deposition. Precipitation is the earliest developed method, with a simple process, readily available raw materials, and no need for large and expensive equipment. However, the precipitation method makes it difficult to obtain nanoscale calcium fluoride with small particle size and uniform dispersion.

[0003] CN104229853A discloses a method for preparing nano-calcium fluoride, which is prepared by reacting calcium nitrate and ammonium fluoride in a mixed solvent of distilled water and ethanol with PEG6000 as a dispersant. After the reaction, the mixture is allowed to age, centrifuged, washed, and ground to obtain nano-calcium fluoride of 13-22 nm. CN111514843A discloses a method for preparing nano-calcium fluoride, which is prepared by a hydrothermal method using the disodium salt of EDTA as a complexing agent, calcium acetate as a calcium source, and boron tetrafluoride as a fluorine source. CN113527910A discloses a monodisperse nano-calcium fluoride transparent liquid phase dispersion, which is obtained by mixing and precipitating a solution of a calcium salt and a fluoride salt, adding a solvent and a modifier, centrifuging and washing, and ultrasonically dispersing. The modifier is a surfactant. CN110835533A discloses a method for preparing calcium fluoride nanoparticles, which is obtained by reacting calcium hydroxide and ammonium fluoride, and the solvent is a mixture of oleic acid and octadecene. CN107697941A discloses a method for preparing nano-calcium fluoride particles. The method comprises adding xylene to a solution of calcium nitrate and ammonium fluoride, followed by adding an ethanol solution of polyvinyl pyrrolidone, mixing the two solutions under ultrasonic conditions, and allowing the product to age. The above-mentioned prior art describes several methods for preparing nano-calcium fluoride, which yield nano-scale calcium fluoride with relatively small particle sizes. However, the particle size uniformity remains unsatisfactory.

[0004] Summary of the Invention

[0005] To address the existing problem of insufficient particle size uniformity in the preparation of nano-calcium fluoride, the present invention provides a method for preparing monodisperse nano-calcium fluoride. This method uses long-chain alkylbenzene sulfonate calcium as a calcium source, an acrylate copolymer prepared from specific monomers, and a specific combination of solvents to form a microemulsion system. Fluoride salts are then added under ultrasonic conditions to produce nano-scale calcium fluoride with a particle size of 20-50 nm and uniform and stable particle size. To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A method for preparing monodisperse nano-calcium fluoride comprises the following steps:

[0007] (S1) Long-chain alkylbenzene sulfonate calcium and acrylate copolymer are dispersed in a mixed solution of water, n-hexane and alcohol to form a stable emulsion A; the monomers of the acrylate copolymer include (meth)acrylic acid, polyether macromonomer, and (meth)acrylate C1-4 alkyl ester; the weight-average molecular weight of the acrylate copolymer is 40,000 to 60,000.

[0008] (S2) dissolving a fluoride salt in water, adding polyvinyl alcohol, and mixing well to obtain solution B;

[0009] (S3) Under stirring and ultrasonic conditions, solution B is slowly added dropwise to emulsion A, and the mixture is allowed to stand for aging, centrifuged, washed, and dried to obtain monodispersed nano-calcium fluoride.

[0010] The inventors unexpectedly discovered that using calcium fluoride as a calcium source, in conjunction with a specific dispersion system, namely, an emulsion formed by dispersing it with an acrylate copolymer in a mixed solution of water, n-hexane, and alcohol, and then mixing it with a fluoride salt solution, produces calcium fluoride with a small particle size. The particle size can be controlled by stirring speed and addition rate, and the particle size is uniform and stable, with good particle size dispersibility, resulting in monodisperse nanoparticles. This may be due to the fact that the calcium source of the present invention is calcium fluoride, which is itself a surfactant. When combined with the other components of the emulsion, the calcium source exists in the form of micelles of a specific size in the emulsion. When the calcium fluoride then contacts the fluoride salt to produce precipitation, the produced calcium fluoride does not have sufficient time to continue to grow and accumulate. Furthermore, in the microemulsion system, each micelle has an equal probability of contacting the fluoride salt, ultimately resulting in nanoscale calcium fluoride nanoparticles with excellent particle size uniformity.

[0011] Furthermore, in step (S1), the mass ratio of water, n-hexane, and alcohol is 100:50-70:30-40, and the alcohol is at least one selected from ethanol, ethylene glycol, and isopropyl alcohol. The mass ratio of long-chain alkylbenzene sulfonate calcium, acrylate copolymer, and mixed solution is 10-15:5-8:100.

[0012] Furthermore, in step (S1), the long-chain alkylbenzene sulfonate calcium is selected from at least one of dodecylbenzene sulfonate, tetradecylbenzene sulfonate, and hexadecylbenzene sulfonate; the polyether macromonomer is selected from at least one of methoxy polyethylene glycol methacrylate, isopentenyl polyoxyethylene ether, and vinyl polyoxyethylene ether, and the number average molecular weight of the polyether macromonomer is 1500-3000.

[0013] Furthermore, in step (S1), the mass ratio of (meth)acrylic acid, polyether macromonomer, and C1-4 alkyl acrylate is 70-100:20-30:35-50, and the C1-4 alkyl (meth)acrylate is selected from at least one of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate.

[0014] Furthermore, the acrylate copolymer is obtained by a preparation method comprising the following steps: (meth)acrylic acid, a polyether macromonomer, a C1-4 alkyl acrylate and water are mixed to obtain a monomer mixed solution; a water-soluble initiator is slowly added under inert atmosphere, stirring and heating conditions; the temperature is raised to 70-90° C. and the mixture is kept warm for reaction; after the reaction is completed, the mixture is cooled, neutralized with alkali, and dried to obtain the acrylate copolymer.

[0015] Furthermore, the total weight concentration of the monomers in the monomer mixture solution is 30-40%. The water-soluble initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate, and is added dropwise as an aqueous solution at a weight concentration of 5-10%. The amount of the water-soluble initiator added is 1-5% of the total weight of the monomers. The inert atmosphere is nitrogen and / or argon, and the reaction is incubated for 3-5 hours. Alkaline neutralization is performed using NaOH and / or KOH to near neutrality. The powder is dried to form a powder by any method, such as spray drying, vacuum drying, or freeze drying.

[0016] Furthermore, in step (S2), the fluoride salt is selected from at least one of ammonium fluoride, sodium fluoride, and potassium fluoride, and the mass ratio of the fluoride salt, polyvinyl alcohol, and water is 5-10:3-5:100; furthermore, the number average molecular weight of the polyvinyl alcohol is 5000-10000.

[0017] Furthermore, in step (S3), the amount of solution B and emulsion A added is such that the molar ratio of Ca:F in the system is 1:2.1-2.3.

[0018] Furthermore, in step (S3), the stirring speed is 300-600rpm, and the particle size of the product nano calcium fluoride can be controlled by adjusting the rotation speed. The faster the rotation speed, the smaller the particle size; but the rotation speed cannot be too fast or too slow, otherwise it is impossible to obtain a product with uniform particle size. The inventors found that by controlling the rotation speed within the range of 300-600rpm, the particle size of the obtained nano calcium fluoride meets the requirements of monodispersity. The frequency of the ultrasound is 60-100kHz, and ultrasound is also conducive to obtaining a calcium fluoride product with uniform and stable particle size. The solution B is slowly added dropwise to the emulsion A for a time of 20-100min. The faster the addition speed, the larger the particle size of the obtained calcium fluoride product. However, the addition time cannot be shorter than 20min, otherwise the particle size uniformity is poor. Preferably, the addition time is controlled at 30-60min. The standing aging time is 24-72 hours, the centrifugal separation is performed at 5000-15000 rpm for 3-5 minutes, the washing is performed with anhydrous ethanol, and the washing can be performed multiple times, such as 3-5 times, and the drying is performed under vacuum.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The invention adopts surface-active long-chain alkylbenzene sulfonate calcium as a calcium source and homemade acrylate as a dispersant to form an emulsion in a specific combination of solvents. Fluoride salt aqueous solution is added dropwise to the emulsion under ultrasonic conditions. Under the action of microemulsion, nano calcium fluoride with uniform and controllable particle size can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is an XRD pattern of nano-calcium fluoride obtained in Example 1.

[0022] FIG2 is a SEM photograph of nano-calcium fluoride prepared in Example 1.

[0023] FIG3 is a SEM photograph of nano-calcium fluoride prepared in Comparative Example 1. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0025] Preparation Example 1

[0026] 70 parts of acrylic acid, 30 parts of methoxy polyethylene glycol methacrylate (M n=3000), 50 parts of butyl acrylate and 300 parts of water were mixed to obtain a monomer mixed solution. Under nitrogen protection, 40 parts of a 5 wt% aqueous solution of ammonium persulfate was added dropwise at 80°C with stirring. The mixture was kept at 80°C for 3 hours. After the reaction, the mixture was cooled to room temperature, neutralized with sodium hydroxide to a pH of 7.2, and dried in vacuo to obtain an acrylate copolymer. The weight-average molecular weight of the acrylate copolymer prepared in Preparation Example 1 was 51,000 as determined by gel chromatography.

[0027] Preparation Example 2

[0028] Other conditions were the same as those in Preparation Example 1, except that the monomers were 100 parts of acrylic acid and 20 parts of isopentenyl polyoxyethylene ether (M n =2000), 35 parts of methyl methacrylate. The acrylic acid ester copolymer prepared in Preparation Example 2 has a weight average molecular weight of 54,000.

[0029] Comparative Preparation Example 1

[0030] Other conditions were the same as those in Preparation Example 1, except that the monomers were 80 parts of acrylic acid and 57 parts of butyl acrylate, that is, methoxy polyethylene glycol methacrylate was not added; and the weight-average molecular weight of the acrylate copolymer was 44,000.

[0031] Example 1

[0032] (S1) 10 parts of calcium dodecylbenzenesulfonate and 5 parts of the acrylic acid ester copolymer prepared in Preparation Example 1 were dispersed in 100 parts of a mixed solution (the mixed solution was a mixed solution of water, n-hexane, and ethanol in a mass ratio of 100:50:40) to form a stable emulsion A;

[0033] (S2) 5 parts of ammonium fluoride are dissolved in 100 parts of water, and 3 parts of polyvinyl alcohol (M n about 10,000), and mixed evenly to obtain solution B;

[0034] (S3) Under ultrasonic conditions of a stirring speed of 300 rpm and an ultrasonic frequency of 60 kHz, solution B is slowly added dropwise to emulsion A for 30 min. The amounts of solution B and emulsion A are such that the molar ratio of calcium dodecylbenzenesulfonate to ammonium fluoride is 1:2.1. The mixture is allowed to stand for 48 h, centrifuged, washed three times with anhydrous ethanol, and vacuum dried to obtain monodisperse nano-calcium fluoride.

[0035] FIG1 is an XRD pattern of nano-calcium fluoride prepared in Example 1, which is consistent with the standard card PDF#35-0816.

[0036] FIG2 is a SEM image of the nano-calcium fluoride prepared in Example 1. It can be seen that the D50 of the nano-calcium fluoride is 37 nm and the particle size is monodisperse.

[0037] Example 2

[0038] Other conditions and operations are the same as those in Example 1, except that in step (S1), the acrylic acid ester copolymer of Preparation Example 1 is replaced by an acrylic acid ester copolymer of equal mass obtained in Preparation Example 2.

[0039] Example 3

[0040] Other conditions and operations are the same as those in Example 1, except that steps (S1) and (S2) are replaced as follows:

[0041] (S1) 15 parts of calcium dodecylbenzenesulfonate and 8 parts of the acrylic acid ester copolymer of Preparation Example 1 were dispersed in 100 parts of a mixed solution (the mixed solution was a mixed solution of water, n-hexane, and ethanol in a mass ratio of 100:70:30) to form a stable emulsion A;

[0042] (S2) 10 parts of ammonium fluoride are dissolved in 100 parts of water, and 5 parts of polyvinyl alcohol (M n about 10,000), and mixed evenly to obtain solution B.

[0043] Example 4

[0044] Other conditions and operations were the same as those in Example 1, except that in step (S3), the stirring speed was 600 rpm.

[0045] Example 5

[0046] Other conditions and operations were the same as those in Example 1, except that in step (S3), the stirring speed was 200 rpm.

[0047] Example 6

[0048] Other conditions and operations were the same as those in Example 1, except that in step (S3), the stirring speed was 1000 rpm.

[0049] Example 7

[0050] Other conditions and operations were the same as those in Example 1, except that in step (S3), solution B was slowly added dropwise to emulsion A for 60 min.

[0051] Example 8

[0052] Other conditions and operations were the same as those in Example 1, except that in step (S3), solution B was slowly added dropwise to emulsion A for 20 min.

[0053] Example 9

[0054] Other conditions and operations were the same as those in Example 1, except that in step (S3), solution B was slowly added dropwise to emulsion A for 100 min.

[0055] Comparative Example 1

[0056] Other conditions and operations are the same as those in Example 1, except that in step (S1), the acrylic acid ester copolymer in Preparation Example 1 is replaced by an acrylic acid ester copolymer of equal mass obtained in Comparative Preparation Example 1.

[0057] Comparative Example 2

[0058] Other conditions and operations were the same as those in Example 1, except that in step (S1), the acrylic acid ester copolymer in Preparation Example 1 was replaced with PEG6000.

[0059] FIG3 is a SEM photograph of nano-calcium fluoride prepared in Comparative Example 1, from which it can be seen that the particle size dispersion is poor.

[0060] NanoMeasure software was used to measure particle sizes D50, D10, and D90. The particle sizes and particle size dispersities of the nano-calcium fluoride prepared in the above examples and comparative examples are listed in Table 1. Particle size dispersity is calculated as span D90-D10 / D50. The smaller the span, the better the dispersibility. A span ≤1.6 is considered monodisperse.

[0061] Table 1 Nano calcium fluoride particle size and particle size dispersity

Claims

1. A method for preparing monodisperse nanoscale calcium fluoride, characterized in that: The following steps are involved: (S1) long-chain alkylbenzene sulfonate calcium and an acrylate copolymer are dispersed in a mixed solution of water, n-hexane, and alcohol to form a stable emulsion A; the monomers of the acrylate copolymer include (meth)acrylic acid, a polyether macromonomer, and a C1-4 alkyl (meth)acrylate; the weight-average molecular weight of the acrylate copolymer is 40,000 to 60,000; (S2) dissolving a fluoride salt in water, adding polyvinyl alcohol, and mixing well to obtain solution B; (S3) Under stirring and ultrasonic conditions, solution B is slowly added dropwise to emulsion A, and the mixture is allowed to stand for aging, centrifuged, washed, and dried to obtain monodispersed nano-calcium fluoride.

2. The preparation method according to claim 1, characterized in that In step (S1), the mass ratio of water, n-hexane, and alcohol is 100:50-70:30-40, and the alcohol is at least one selected from ethanol, ethylene glycol, and isopropyl alcohol. The mass ratio of long-chain alkylbenzene sulfonate calcium, acrylate copolymer, and mixed solution is 10-15:5-8:

100.

3. The preparation method according to claim 1, characterized in that In step (S1), the long-chain alkylbenzene sulfonate calcium is selected from at least one of dodecylbenzene sulfonate, tetradecylbenzene sulfonate, and hexadecylbenzene sulfonate; the polyether macromonomer is selected from at least one of methoxy polyethylene glycol methacrylate, isopentenyl polyoxyethylene ether, and vinyl polyoxyethylene ether, and the number average molecular weight of the polyether macromonomer is 1500-3000.

4. The preparation method according to claim 1, characterized in that In step (S1), the mass ratio of (meth)acrylic acid, polyether macromonomer, and C1-4 alkyl acrylate is 70-100:20-30:35-50, and the C1-4 alkyl (meth)acrylate is selected from at least one of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate.

5. The preparation method according to claim 1, characterized in that The acrylate copolymer is obtained by a preparation method comprising the following steps: (meth)acrylic acid, a polyether macromonomer, a C1-4 alkyl acrylate and water are mixed to obtain a monomer mixed solution; a water-soluble initiator is slowly added under inert atmosphere, stirring and heating conditions; the temperature is raised to 70-90° C. and kept for reaction; after the reaction is completed, the solution is cooled, neutralized with alkali and dried to obtain the acrylate copolymer.

6. The preparation method according to claim 5, characterized in that The total mass concentration of monomers in the monomer mixed solution is 30-40%, and the water-soluble initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate. The water-soluble initiator is added dropwise in the form of an aqueous solution with a mass concentration of 5-10%. The amount of the water-soluble initiator added is 1-5% of the total mass of the monomers. The inert atmosphere is nitrogen and / or argon atmosphere, and the reaction is kept warm for 3-5 hours. Alkaline neutralization is performed using NaOH and / or KOH to near neutrality.

7. The preparation method according to claim 1, characterized in that In step (S2), the fluoride salt is selected from at least one of ammonium fluoride, sodium fluoride, and potassium fluoride, and the mass ratio of the fluoride salt, polyvinyl alcohol, and water is 5-10:3-5:100; further, the number average molecular weight of the polyvinyl alcohol is 5000-10000.

8. The preparation method according to claim 1, characterized in that In step (S3), the amount of solution B and emulsion A added is such that the molar ratio of Ca:F in the system is 1:2.1-2.

3.

9. The preparation method according to claim 1, characterized in that In step (S3), the stirring speed is 300-600 rpm, the frequency of the ultrasound is 60-100 kHz, and the solution B is slowly added dropwise to the emulsion A for 20-100 min; preferably, the addition time is controlled at 30-60 min.

10. The preparation method according to claim 1, characterized in that In step (S3), the standing aging time is 24-72 hours, the centrifugal separation is centrifuged at 5000-15000 rpm for 3-5 minutes, the washing is done by washing with anhydrous ethanol, and the drying is done by vacuum drying.

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