A preparation method of monodisperse nanoscale calcium fluoride

Abstract

The present invention relates to a method for preparing monodisperse nanoscale calcium fluoride, comprising the following steps: (S1) calcium long-chain alkylbenzenesulfonate 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, C1-C4 alkyl (meth)acrylate; (S2) a fluorine salt is dissolved in water, and polyvinyl alcohol is added and mixed evenly to obtain a solution B; (S3) under stirring and ultrasonic conditions, the solution B is slowly added dropwise to the emulsion A, allowed to stand and age, centrifuged, washed and dried to obtain monodisperse nanoscale calcium fluoride. The present invention uses calcium long-chain alkylbenzenesulfonate with surface activity as a calcium source, and cooperates with a self-made acrylate as a dispersant to form an emulsion under a solvent with a specific combination. The aqueous solution of the fluorine salt is added dropwise to the above emulsion under ultrasonic conditions. Under the action of the microemulsion, nanoscale calcium fluoride with uniform and controllable particle size can be prepared.

Description

Technical Field

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

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

[0003] CN104229853A discloses a method for preparing nano calcium fluoride, which uses calcium nitrate and ammonium fluoride, in a mixed solvent of distilled water and ethanol, with PEG6000 as a dispersant. After the reaction, it is left to age, centrifuged, washed, and ground to obtain nano calcium fluoride with a particle size of 13 - 22 nm. CN111514843A discloses a nano calcium fluoride, which uses disodium salt of EDTA as a complexing agent, calcium acetate as a calcium source, and boron tetrafluoride as a fluorine source, and is prepared by a hydrothermal method. CN113527910A discloses a monodisperse nano calcium fluoride transparent liquid-phase dispersion, which is obtained by mixing and precipitating solutions of calcium salt and fluorine salt, adding a solvent and a modifier, centrifuging and washing, and ultrasonic dispersing. The modifier is some surfactants. 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, which is to add xylene to a solution of calcium nitrate and ammonium fluoride, and then add an ethanol solution of polyvinylpyrrolidone, and mix the two solutions under ultrasonic conditions, and the product is left to age. The above prior arts record some methods for preparing nano calcium fluoride, and obtain nano-scale calcium fluoride with relatively small particle size, but the degree of particle size uniformity is still not satisfactory. Summary of the Invention

[0004] To solve the defect of insufficient uniformity in particle size in the preparation of nano-calcium fluoride in the prior art, the present invention provides a method for preparing monodisperse nano-calcium fluoride. By using calcium dodecylbenzenesulfonate as a calcium source, an acrylate copolymer prepared with a specific monomer, and a solvent with a specific combination, a microemulsion system is formed. At this time, when a fluoride salt is added under ultrasonic conditions, nano-calcium fluoride with a particle size of 20-50 nm and a uniform and stable particle size can be prepared. To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing monodisperse nano-calcium fluoride, comprising the following steps:

[0006] (S1) Calcium dodecylbenzenesulfonate 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.

[0007] (S2) A fluoride salt is dissolved in water, and polyvinyl alcohol is added and mixed evenly to obtain a solution B;

[0008] (S3) Under stirring and ultrasonic conditions, solution B is slowly added dropwise to emulsion A, allowed to stand and age, centrifuged, washed, and dried to obtain monodisperse nano-calcium fluoride.

[0009] The inventors unexpectedly found that when calcium dodecylbenzenesulfonate is used as a calcium source and combined with a specific dispersion system, that is, an emulsion formed by dispersing an acrylate copolymer in a mixed solution of water, n-hexane, and alcohol, the calcium fluoride produced after mixing with the fluoride salt solution has a small particle size. The particle size can be regulated by the stirring speed and the dropping speed, and the particle size is uniform, stable, and has good particle size dispersibility, being monodisperse nanoparticles. The possible reason is that the calcium source of the present invention uses calcium dodecylbenzenesulfonate, which is itself a surfactant. Combined with other components of the emulsion, the calcium source in the formed emulsion exists in the form of micelles with a specific size. When it contacts the fluoride salt to generate precipitation, the generated calcium fluoride does not have enough time to continue growing and accumulating. Moreover, in the microemulsion system, the probability of each micelle contacting the fluoride salt is equal, and finally, calcium fluoride nanoparticles with a nano-scale and very good particle size uniformity are obtained.

[0010] Furthermore, in step (S1), the mass ratio of water, n-hexane, and alcohol is 100:50-70:30-40, and the alcohol is selected from at least one of ethanol, ethylene glycol, and isopropanol. The mass ratio of calcium dodecylbenzenesulfonate, the acrylate copolymer, and the mixed solution is 10-15:5-8:100.

[0011] Further, in step (S1), the calcium long-chain alkylbenzenesulfonate is selected from at least one of calcium dodecylbenzenesulfonate, calcium tetradecylbenzenesulfonate, and calcium hexadecylbenzenesulfonate; the polyether macromonomer is selected from at least one of methoxypolyethylene glycol methacrylate, isopentenyl polyoxyethylene ether, and vinyl polyoxyethylene ether, and the number-average molecular weight of the polyether macromonomer is 1500 - 3000.

[0012] Further, 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.

[0013] Further, the acrylate copolymer is obtained by a preparation method including the following steps: (meth)acrylic acid, polyether macromonomer, C1-4 alkyl acrylate, and water are mixed to obtain a monomer mixed solution, and a water-soluble initiator is slowly added under an inert atmosphere, stirring, and heating conditions, the temperature is raised to 70 - 90 °C for heat preservation reaction, after the reaction ends, it is cooled, neutralized with an alkali, and dried to obtain the acrylate copolymer.

[0014] Furthermore, the total mass concentration of the monomers in the monomer mixed solution is 30 - 40%, 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%, and the addition amount of the water-soluble initiator is 1 - 5% of the total mass of the monomers. The inert atmosphere is a nitrogen and / or argon atmosphere, and the heat preservation reaction is carried out for 3 - 5 h; the alkali neutralization is to neutralize with NaOH and / or KOH to near neutral, and there is no special limitation on the drying method to obtain a powder, such as spray drying, vacuum drying, and freeze drying.

[0015] Further, 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.

[0016] Further, in step (S3), the addition amounts of solution B and emulsion A make the molar ratio of Ca:F in the system 1:2.1 - 2.3.

[0017] Further, in step (S3), the stirring speed is 300 - 600 rpm. The particle size of the product nano-calcium fluoride can be regulated by adjusting the rotation speed. The faster the rotation speed, the smaller the particle size. However, the rotation speed cannot be too fast or too slow, otherwise, a product with uniform particle size cannot be obtained. The inventor found that when the rotation speed is controlled within the range of 300 - 600 rpm, the particle size of the obtained nano-calcium fluoride meets the requirements of monodispersity. The frequency of the ultrasonic wave is 60 - 100 kHz, and ultrasonic wave is also beneficial to obtain a calcium fluoride product with uniform and stable particle size. The dropping time for slowly dropping solution B into emulsion A is 20 - 100 min. The faster the dropping speed, the larger the particle size of the obtained calcium fluoride product. However, the dropping time cannot be shorter than 20 min, otherwise, the particle size uniformity is poor. Preferably, the dropping time is controlled within 30 - 60 min. The static aging time is 24 - 72 h, the centrifugal separation is carried out at 5000 - 15000 rpm for 3 - 5 min, the washing is with absolute ethanol and can be washed multiple times, such as 3 - 5 times, and the drying is under vacuum drying.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention uses calcium dodecylbenzenesulfonate with surface activity as the calcium source, cooperates with a self-made acrylate as the dispersant, forms an emulsion under a solvent with a specific combination, and drops an aqueous fluoride solution into the above emulsion under ultrasonic conditions. Under the action of the microemulsion, nano-calcium fluoride with uniform and controllable particle size can be prepared. Description of the Drawings

[0020] Figure 1 It is the XRD pattern of the nano-calcium fluoride prepared in Example 1.

[0021] Figure 2 It is the SEM photograph of the nano-calcium fluoride prepared in Example 1.

[0022] Figure 3 It is the SEM photograph of the nano-calcium fluoride prepared in Comparative Example 1. Detailed Embodiments

[0023] The following further illustrates the present invention with specific embodiments, but it is not limited to the content in the specification. Unless otherwise specified, the "parts" in the embodiments of the present invention are all parts by weight. The reagents used are all commercially available reagents in the art.

[0024] Preparation Example 1

[0025] 70 parts of acrylic acid, 30 parts of methoxypolyethylene glycol methacrylate (M n3000), 50 parts of butyl acrylate and 300 parts of water were mixed to obtain a monomer mixed solution. Under nitrogen protection, with stirring, and at 80 °C, 40 parts of a 5 wt% aqueous solution of ammonium persulfate was added dropwise. The reaction was carried out at 80 °C for 3 h. After the reaction, it was cooled to room temperature and neutralized with an aqueous sodium hydroxide solution to pH 7.2, and then dried under vacuum to obtain an acrylate copolymer. The weight-average molecular weight of the acrylate copolymer prepared in Preparation Example 1 was 51,000 measured by gel permeation chromatography.

[0026] Preparation Example 2

[0027] Other conditions were the same as those in Preparation Example 1, except that the monomers were 100 parts of acrylic acid, 20 parts of isopentenyl polyethylene glycol ether (M n = 2000), and 35 parts of methyl methacrylate. The weight-average molecular weight of the acrylate copolymer prepared in Preparation Example 2 was 54,000.

[0028] Comparative Preparation Example 1

[0029] 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, methoxypolyethylene glycol methacrylate was not added; the weight-average molecular weight of the acrylate copolymer was 44,000.

[0030] Example 1

[0031] (S1) 10 parts of calcium dodecylbenzenesulfonate and 5 parts of the acrylate copolymer prepared in Preparation Example 1 were dispersed in 100 parts of a mixed solution (the mixed solution is a mixed solution of water, n-hexane and ethanol in a mass ratio of 100:50:40) to form a stable emulsion A;

[0032] (S2) 5 parts of ammonium fluoride was dissolved in 100 parts of water, and 3 parts of polyvinyl alcohol (M n was about 10,000) was added and mixed evenly to obtain solution B;

[0033] (S3) Under the ultrasonic condition with a stirring speed of 300 rpm and an ultrasonic frequency of 60 kHz, solution B was slowly added dropwise to emulsion A, and the dropping time was 30 min. The amounts of solution B and emulsion A were such that the molar ratio of calcium dodecylbenzenesulfonate to ammonium fluoride was 1:2.1. It was allowed to stand and age for 48 h, centrifuged, washed 3 times with absolute ethanol, and dried under vacuum to obtain monodisperse nano-calcium fluoride.

[0034] Figure 1 is the XRD pattern of the nano-calcium fluoride prepared in Example 1, which is consistent with the PDF#35-0816 standard card.

[0035] Figure 2 is the 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.

[0036] Example 2

[0037] Other conditions and operations are the same as those in Example 1. The difference is that in step (S1), the acrylate copolymer prepared in Preparation Example 1 is replaced with an equal mass of the acrylate copolymer prepared in Preparation Example 2.

[0038] Example 3

[0039] Other conditions and operations are the same as those in Example 1. The difference is that steps (S1) and (S2) are replaced as follows:

[0040] (S1) 15 parts of calcium dodecylbenzenesulfonate and 8 parts of the acrylate copolymer prepared in Preparation Example 1 are dispersed in 100 parts of a mixed solution (the mixed solution is a mixed solution of water, n - hexane, and ethanol in a mass ratio of 100:70:30) to form a stable emulsion A;

[0041] (S2) 10 parts of ammonium fluoride are dissolved in 100 parts of water, and 5 parts of polyvinyl alcohol (M n is about 10,000) are added and mixed evenly to obtain solution B.

[0042] Example 4

[0043] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), the stirring speed is 600 rpm.

[0044] Example 5

[0045] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), the stirring speed is 200 rpm.

[0046] Example 6

[0047] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), the stirring speed is 1000 rpm.

[0048] Example 7

[0049] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), solution B is slowly added dropwise to emulsion A, and the dropping time is 60 min.

[0050] Example 8

[0051] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), solution B is slowly added dropwise to emulsion A, and the dropping time is 20 min.

[0052] Example 9

[0053] Other conditions and operations are the same as those in Example 1. The difference is that in step (S3), solution B is slowly added dropwise to emulsion A, and the dropping time is 100 min.

[0054] Comparative Example 1

[0055] Other conditions and operations are the same as those in Example 1. The difference is that in step (S1), the acrylate copolymer of Preparation Example 1 is replaced with an acrylate copolymer of equal mass prepared in Comparative Preparation Example 1.

[0056] Comparative Example 2

[0057] Other conditions and operations are the same as those in Example 1. The difference is that in step (S1), the acrylate copolymer of Preparation Example 1 is replaced with PEG6000.

[0058] Figure 3 This is the SEM photograph of the nano calcium fluoride prepared in Comparative Example 1, and it can be seen that the particle size dispersion is poor.

[0059] The particle sizes D50, D10 and D90 are measured by using Nano Measure software, and the particle sizes and particle size dispersions of the nano calcium fluoride prepared in the above Examples and Comparative Examples are listed in Table 1 below. The particle size dispersion is calculated by the span (D90 - D10) / D50. The smaller the span, the better the dispersion. A span ≤ 1.6 can be considered as monodisperse.

[0060] Table 1 Particle Sizes and Particle Size Dispersions of Nano Calcium Fluoride

[0061]

[0062]

Claims

1. A preparation method of monodisperse nanoscale calcium fluoride, characterized in that, It includes the following steps: (S1) Calcium long-chain alkyl benzene sulfonate 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, C1-4 alkyl (meth)acrylate; the weight-average molecular weight of the acrylate copolymer is 40,000 to 60,000; (S2) The fluoride salt is dissolved in water, and polyvinyl alcohol is added and mixed evenly to obtain solution B; (S3) Under stirring and ultrasonic conditions, solution B is slowly added dropwise to emulsion A, allowed to stand and age, centrifuged, washed and dried to obtain monodisperse 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 selected from at least one of ethanol, ethylene glycol and isopropanol; the mass ratio of calcium long-chain alkyl benzene sulfonate, acrylate copolymer and the mixed solution is 10-15:5-8:

100.

3. The preparation method according to claim 1, characterized in that, In step (S1), the calcium long-chain alkyl benzene sulfonate is selected from at least one of calcium dodecyl benzene sulfonate, calcium tetradecyl benzene sulfonate and calcium hexadecyl benzene sulfonate; the polyether macromonomer is selected from at least one of methoxypolyethylene 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, C1-4 alkyl (meth)acrylate is 70-100:20-30:35-50, and the C1-4 alkyl (meth)acrylate is selected from at least one of (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester and (meth)acrylic acid butyl ester.

5. The preparation method according to claim 1, characterized in that, The acrylate copolymer is obtained by a preparation method including the following steps: (meth)acrylic acid, polyether macromonomer, C1-4 alkyl (meth)acrylate and water are mixed to obtain a monomer mixed solution, and a water-soluble initiator is slowly added under an inert atmosphere, stirring and heating conditions, and the temperature is raised to 70-90 °C for heat preservation reaction. After the reaction is completed, it 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 the monomers in the monomer mixed solution is 30-40%, 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, the mass concentration is 5-10%, and the addition amount of the water-soluble initiator is 1-5% of the total mass of the monomers; the inert atmosphere is a nitrogen and / or argon atmosphere, and the heat preservation reaction is 3-5 h; the alkali neutralization is to neutralize with NaOH and / or KOH to near neutral.

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.

8. The preparation method according to claim 7, characterized in that, In step (S2), the number-average molecular weight of the polyvinyl alcohol is 5000-10000.

9. The preparation method according to claim 1, characterized in that, In step (S3), the addition amounts of solution B and emulsion A make the molar ratio of Ca:F in the system 1:2.1-2.

3.

10. 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 dropping time for slowly dropping solution B into emulsion A is 20 - 100 min.

11. The preparation method according to claim 10, characterized in that, In step (S3), the dropping time for slowly dropping solution B into emulsion A is controlled within 30 - 60 min.

12. The preparation method according to claim 1, characterized in that, In step (S3), the static aging time is 24 - 72 h, the centrifugal separation is carried out at 5000 - 15000 rpm for 3 - 5 min, the washing is carried out with absolute ethanol, and the drying is carried out by vacuum drying.

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