Nanometer calcium hydroxide and preparation method thereof

Abstract

This invention relates to a method for obtaining nano-calcium hydroxide by mixing commercially available calcium hydroxide (micron-sized large particles) with ethyl acetate, allowing it to stand, and then washing, sonicating, rinsing, and centrifuging. The method involves a slow reaction of large-particle calcium hydroxide with ethyl acetate, generating calcium acetate within the large-particle calcium hydroxide. The calcium acetate is then washed away, exposing numerous tiny cracks in the calcium hydroxide particles. Ultrasonic sonication causes the calcium hydroxide particles to split at these cracks, and centrifugation separates them to obtain nano-calcium hydroxide. The nano-calcium hydroxide prepared by this method has a size of ~10 nm and relatively uniform particle size. More importantly, the method is extremely simple, requiring no heating or other complex operations, and has good prospects for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and relates to a nano-calcium hydroxide and its preparation method. Background Technology

[0002] Calcium hydroxide is an important inorganic alkaline material. In the plastics and rubber industries, it is used as a filler, modifier, and heat stabilizer; in cement manufacturing, it accelerates the hydration reaction; in the environmental field, it is used for flue gas desulfurization, sewage treatment, and heavy metal precipitation; in agriculture, it can neutralize acidic soil, supplement calcium, and inhibit pathogens.

[0003] Nano-calcium hydroxide, due to its small particle size and strong permeability, has received widespread attention in the field of cultural relic preservation since its initial application in 2001 for the restoration of efflorescence and flaking defects in murals (Langmuir 2001, 17, 4251-4255). This material has been successfully applied to the deacidification of paper artifacts, the reinforcement of bone artifacts, and the reinforcement of stone artifacts (Langmuir 2014, 30, 660-668; Journal of Cultural Heritage 2006, 7, 264-272; Langmuir 2013, 29, 11457). 11470).

[0004] The preparation strategies for nano-calcium hydroxide are mainly divided into two categories: physical grinding and chemical synthesis. Physical methods employ grinding technology from top to bottom, but the resulting products have a wide particle size distribution, and achieving nanoscale uniformity is often difficult (Journal of Colloid and Interface Science 2013, 392, 42-49). Chemical methods utilize a bottom-up approach, including precipitation, homogeneous synthesis, and calcium metal precursor methods. However, these methods generally suffer from limitations such as uneven particle size (50-500 nm), the need for surfactants, and stringent process conditions: precipitation requires high temperatures, resulting in high energy consumption and long cycles; homogeneous synthesis produces products with poor stability and still requires high-temperature calcination; and calcium metal precursor methods are costly due to complex synthesis steps and the use of metallic calcium (Journal of Colloid and Interface Science 473: 1-8; Chinese Patent 201410705481.6). In summary, existing methods for synthesizing nano-calcium hydroxide generally suffer from problems such as uneven particle size, complex processes, and high costs.

[0005] Furthermore, patent application number 201510994803.8, entitled "A Method for Preparing Highly Dispersible Nanoscale Calcium Hydroxide," requires polyvinylpyrrolidone and polyethylene glycol dispersants, SDBS, and a constant temperature environment of 35–45°C to prepare nanoscale calcium hydroxide. The nanoscale calcium hydroxide prepared in the prior art has a size of 95–120 nm. The nanoscale calcium hydroxide prepared by this invention has a particle size of approximately 10 nm, and the preparation does not require dispersants or heating. Currently, there are no reports on the preparation of 10 nm nanoscale calcium hydroxide. Different particle sizes and nanoparticles result in significant performance differences; therefore, the nanoscale calcium hydroxide particle size prepared by this invention is approximately one-tenth that of the one in the prior art. Summary of the Invention

[0006] Technical problems to be solved To avoid the shortcomings of the prior art, this invention proposes a nano-calcium hydroxide and its preparation method. The method involves mixing commercially available calcium hydroxide (micron-sized large particles) with ethyl acetate and allowing it to stand. Then, the nano-calcium hydroxide can be obtained by washing, sonicating, rinsing, and centrifuging.

[0007] Technical solution A method for preparing nano-calcium hydroxide, characterized by the following steps: Micron-sized large-particle calcium hydroxide was mixed with ethyl acetate and allowed to stand, and calcium acetate was generated in the micron-sized large-particle calcium hydroxide. The mixture was then ultrasonically cleaned, and then filtered and cleaned with a mixed solution of saturated limestone and ethanol to obtain a precipitate. Calcium acetate was washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The precipitate was ultrasonically dispersed in ethanol to obtain a dispersion, and the calcium hydroxide particles were broken at the cracks by ultrasonication. The dispersion was centrifuged, and the resulting supernatant was granular nano-calcium hydroxide.

[0008] The mass ratio of the micron-sized calcium hydroxide to ethyl acetate is 2:1-5:1.

[0009] The micron-sized calcium hydroxide was mixed with ethyl acetate and allowed to stand for 12-24 hours.

[0010] The ultrasonic cleaning process uses an ultrasonic power of 3000W and lasts for 10-30 minutes.

[0011] The volume ratio of the saturated limestone and ethanol mixture is 1:1 to 1:3.

[0012] The dispersion is centrifuged at a speed of 5000 r / min to 8000 r / min.

[0013] The micron-sized large-particle calcium hydroxide is commercially available.

[0014] A nano-calcium hydroxide obtained by the aforementioned method is characterized in that: the particle size of the granular nano-calcium hydroxide is 5~16nm, and the central distribution is 8nm~10nm.

[0015] The granular nano-calcium hydroxide particles are irregularly spherical with an average diameter of 10 nm.

[0016] Beneficial effects This invention proposes a method for preparing nano-calcium hydroxide. The method involves the slow reaction of large-particle calcium hydroxide with ethyl acetate to generate calcium acetate in the large-particle calcium hydroxide. The calcium acetate is then washed away, exposing numerous tiny cracks in the calcium hydroxide particles. Ultrasonic treatment is then used to cause the calcium hydroxide particles to split at the cracks, and centrifugation is used to separate them into nano-calcium hydroxide. The nano-calcium hydroxide prepared by this method has a size of ~10 nm and relatively uniform particle size. More importantly, the method is extremely simple, requiring no heating or other complex operations, and has good prospects for widespread application.

[0017] Compared with existing technologies, the preparation method of nano-calcium hydroxide provided by this invention is extremely simple and effective. It only requires mixing and reacting large-particle calcium hydroxide with ethyl acetate, followed by washing and sonication to obtain uniformly sized nano-calcium hydroxide (~10 nm). This method is significantly simpler than traditional methods that require heating and surfactants. Furthermore, the nano-calcium hydroxide particles prepared by this method are smaller and more uniformly distributed, while the calcium hydroxide particles prepared by traditional precipitation methods are 50-500 nm in size and have extremely uneven distribution. The nano-calcium hydroxide prepared by this invention has great application potential. Attached Figure Description

[0018] Figure 1 This is a transmission electron microscope (TEM) image of the nano-calcium hydroxide prepared according to an example of the present invention. The numbers in the image are scale bars. As can be seen from the image, the size of the nano-calcium hydroxide particles is 5-12 nm. Detailed Implementation The present invention will now be further described in conjunction with the embodiments and accompanying drawings: Example 1: This invention involves mixing commercially available micron-sized calcium hydroxide with ethyl acetate at a mass ratio of 2:1 and shaking well, then allowing it to stand at room temperature for 12 hours. The large-particle calcium hydroxide reacts slowly with ethyl acetate, generating calcium acetate within the large-particle calcium hydroxide. The mixture is then ultrasonically cleaned for 10 minutes using a high-power ultrasonic cleaner (3000W). Afterward, it is filtered and cleaned with a mixed solution of saturated limestone and ethanol (volume ratio 1:1). The resulting precipitate is ultrasonically dispersed in ethanol, and the dispersion is then centrifuged (5000 r / min). The supernatant contains nano-sized calcium hydroxide particles. In this process, calcium acetate is washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The calcium hydroxide particles are then split at the cracks by ultrasound, and nano-calcium hydroxide can be obtained by centrifugation.

[0019] Existing technology: Heat the prepared calcium chloride solution (1.1 g dissolved in 50 mL of water) to 90 degrees Celsius and stir continuously. Then, slowly add the prepared sodium hydroxide solution (0.6 g dissolved in 50 mL of water) dropwise into the calcium chloride solution and continue stirring for 10 minutes. After cooling to room temperature, centrifuge with saturated limestone and wash to obtain nano calcium hydroxide.

[0020] Dynamic light scattering test results show that the nano-calcium hydroxide particles prepared by the present invention have a size of 5-16 nm and a central distribution of 8.8 nm, while the nano-calcium hydroxide particles prepared by the traditional method have a size of 60-450 nm and a central distribution of 261 nm.

[0021] Example 2: Commercially available micron-sized calcium hydroxide and ethyl acetate were mixed at a mass ratio of 3:1 and shaken well. The mixture was then left at room temperature for 18 hours. Calcium acetate was generated from the large-particle calcium hydroxide through a slow reaction between the large-particle calcium hydroxide and ethyl acetate. The mixture was then ultrasonically cleaned for 15 minutes using a high-power ultrasonic cleaner (3000W). After cleaning, the mixture was filtered with a mixed solution of saturated limestone and ethanol (volume ratio 1:2). The precipitate obtained after cleaning was ultrasonically dispersed in ethanol. The resulting dispersion was then centrifuged (6000 r / min), and the supernatant contained nano-sized calcium hydroxide particles.

[0022] In this process, calcium acetate is washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The calcium hydroxide particles are then split at the cracks by ultrasound, and nano-calcium hydroxide can be obtained by centrifugation.

[0023] Existing technology: Heat the prepared calcium chloride solution (2.2g dissolved in 80mL water) to 92 degrees Celsius and stir continuously. Then, slowly add the prepared sodium hydroxide solution (1.2g dissolved in 80mL water) dropwise into the calcium chloride solution and continue stirring for 15 minutes. After cooling to room temperature, centrifuge with saturated limestone and wash to obtain nano calcium hydroxide.

[0024] Dynamic light scattering test results show that the nano-calcium hydroxide particles prepared by the present invention have a size of 8-14 nm and a central distribution of 9.2 nm, while the nano-calcium hydroxide particles prepared by the traditional method have a size of 50-550 nm and a central distribution of 273 nm.

[0025] Example 3: Commercially available micron-sized calcium hydroxide and ethyl acetate were mixed at a mass ratio of 4:1 and shaken well. The mixture was then left at room temperature for 20 hours. Calcium acetate was generated from the large-particle calcium hydroxide through a slow reaction with ethyl acetate. The mixture was then ultrasonically cleaned for 20 minutes using a high-power ultrasonic cleaner (3000W). After cleaning, the mixture was filtered with a mixed solution of saturated limestone and ethanol (volume ratio 1:3). The precipitate obtained after cleaning was ultrasonically dispersed in ethanol. The resulting dispersion was then centrifuged (7000 r / min), and the supernatant contained nano-sized calcium hydroxide particles.

[0026] In this process, calcium acetate is washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The calcium hydroxide particles are then split at the cracks by ultrasound, and nano-calcium hydroxide can be obtained by centrifugation.

[0027] Existing technology: Heat the prepared calcium chloride solution (3.3 g dissolved in 100 mL of water) to 95 degrees Celsius and stir continuously. Then, slowly add the prepared sodium hydroxide solution (2.4 g dissolved in 100 mL of water) dropwise into the calcium chloride solution and continue stirring for 20 minutes. After cooling to room temperature, centrifuge with saturated limestone and wash to obtain nano calcium hydroxide.

[0028] Dynamic light scattering test results show that the nano-calcium hydroxide particles prepared by the present invention have a size of 7-15 nm and a central distribution of 10 nm, while the nano-calcium hydroxide particles prepared by the traditional method have a size of 55-460 nm and a central distribution of 253 nm.

[0029] Example 4: Commercially available micron-sized calcium hydroxide and ethyl acetate were mixed at a mass ratio of 5:1 and shaken well. The mixture was then left at room temperature for 24 hours. Calcium acetate was generated from the large-particle calcium hydroxide through a slow reaction between the large-particle calcium hydroxide and ethyl acetate. The mixture was then ultrasonically cleaned for 30 minutes using a high-power ultrasonic cleaner (3000W). After cleaning, the mixture was filtered with a mixed solution of saturated limestone and ethanol (volume ratio 1:3). The precipitate obtained after cleaning was ultrasonically dispersed in ethanol. The resulting dispersion was then centrifuged (8000 r / min), and the supernatant contained nano-sized calcium hydroxide particles.

[0030] In this process, calcium acetate is washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The calcium hydroxide particles are then split at the cracks by ultrasound, and nano-calcium hydroxide can be obtained by centrifugation.

[0031] Existing technology: Heat the prepared calcium chloride solution (3.3g dissolved in 100mL water) to 95 degrees Celsius and stir continuously. Then, slowly add the prepared sodium hydroxide solution (1.8g dissolved in 100mL water) dropwise into the calcium chloride solution and continue stirring for 30 minutes. After cooling to room temperature, centrifuge with saturated limestone and wash to obtain nano calcium hydroxide.

[0032] Dynamic light scattering test results show that the nano-calcium hydroxide particles prepared by the present invention have a size of 6-13 nm and a central distribution of 8 nm, while the nano-calcium hydroxide particles prepared by the traditional method have a size of 51-425 nm and a central distribution of 286 nm.

[0033] Furthermore, compared to the patent application with application number 201510994803.8, entitled "A Method for Preparing Highly Dispersible Nanoscale Calcium Hydroxide," this invention has a simpler process, and the size of the prepared nanoscale calcium hydroxide particles is approximately one-tenth that of the document. The preparation of nanoscale calcium hydroxide in prior art document 2 requires polyvinylpyrrolidone and polyethylene glycol dispersants, SDBS, and a constant temperature environment of 35–45°C. The nanoscale calcium hydroxide prepared in the prior art document has a size of 95–120 nm. The nanoscale calcium hydroxide particles prepared by this invention are around 10 nm in size, and the preparation does not require dispersants or heating. Currently, there are no reports on the preparation of 10 nm nanoscale calcium hydroxide. Different particle sizes and nanoparticles result in significant performance differences. Therefore, the nanoscale calcium hydroxide particles prepared by this invention are approximately one-tenth the size of those in the prior art document. Therefore, from the perspective of the invention's purpose and the comparison of the final product, this invention is fundamentally different from the prior art document.

Claims

1. A method for preparing nano-calcium hydroxide, characterized in that... The steps are as follows: Micron-sized large-particle calcium hydroxide was mixed with ethyl acetate and allowed to stand, and calcium acetate was generated in the micron-sized large-particle calcium hydroxide. The mixture was then ultrasonically cleaned, and then filtered and cleaned with a mixed solution of saturated limestone and ethanol to obtain a precipitate. Calcium acetate was washed away, exposing a large number of tiny cracks in the calcium hydroxide particles. The precipitate was ultrasonically dispersed in ethanol to obtain a dispersion, and the calcium hydroxide particles were broken at the cracks by ultrasonication. The dispersion was centrifuged, and the resulting supernatant was granular nano-calcium hydroxide.

2. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The mass ratio of the micron-sized calcium hydroxide to ethyl acetate is 2:1-5:

1.

3. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The micron-sized calcium hydroxide was mixed with ethyl acetate and allowed to stand for 12-24 hours.

4. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The ultrasonic cleaning process uses an ultrasonic power of 3000W and lasts for 10-30 minutes.

5. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The volume ratio of the saturated limestone and ethanol mixture is 1:1 to 1:

3.

6. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The dispersion is centrifuged at a speed of 5000 r / min to 8000 r / min.

7. The method for preparing nano-calcium hydroxide according to claim 1, characterized in that: The micron-sized large-particle calcium hydroxide is commercially available.

8. A nano-calcium hydroxide obtained by the preparation method of nano-calcium hydroxide according to any one of claims 1 to 7, characterized in that: The particle size of granular nano-calcium hydroxide is 5~16nm, with a central distribution of 8nm~10nm.

9. The nano-calcium hydroxide according to claim 8, characterized in that: The granular nano-calcium hydroxide particles are irregularly spherical with an average diameter of 10 nm.

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