Method for preparing HgS crystal by controlling crystal form through wet recrystallization

Abstract

The invention provides a method for preparing HgS crystals by controlling a crystal form through wet recrystallization, and belongs to the technical field of preparation of mercury compounds. The preparation method comprises the following steps: dissolving mercuric sulfide powder in an alkali metal sulfide solution, then carrying out a hydrothermal reaction, cooling to room temperature after the reaction is finished, and preparing different crystal forms of HgS crystals by controlling the speed and dosage of adding deionized water into a reaction solution. The reaction condition for preparing the HgS crystal is mild, the cost is low, the size of the obtained crystal reaches the millimeter level, the size of the crystal is easy to control, and the growth period of the crystal is short.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of mercury compounds, and particularly relates to a method for preparing HgS crystals by wet recrystallization to control crystal form. Background Art

[0002] Mercury sulfide (HgS) is an important semiconductor material and has wide applications in the fields of infrared detection, optoelectronic devices, sensors, etc. Two common crystal forms of mercury sulfide are α-HgS (red hexagonal crystal form) and β-HgS (black cubic crystal form), and these two crystal forms are applied to different fields due to their respective different physical properties. For example, the optoelectronic properties of α-HgS are suitable for infrared detection; while β-HgS has good electrical conductivity and is suitable for use in sensing and optoelectronic conversion devices. Therefore, the preparation of high-quality mercury sulfide crystals has a crucial impact on their performance and application effects.

[0003] In the prior art, the synthesis and growth of mercury sulfide crystals mostly adopt methods such as solid-phase reaction method, chemical vapor deposition (CVD), etc. However, these methods have many limitations: in the solid-phase reaction method, there are often problems such as particle agglomeration and uneven crystal grains; although the CVD method can obtain relatively pure mercury sulfide, it has high costs, complex equipment, and is not conducive to large-scale production. Therefore, it is necessary to develop a method that can prepare mercury sulfide crystals with high purity, large size, and uniform crystal grains under mild conditions. Summary of the Invention

[0004] Based on the above problems, the present invention provides a method for preparing HgS crystals by wet recrystallization to control crystal form. This method dissolves HgS powder in an alkali metal sulfide solution, conducts a hydrothermal reaction, and then controls the crystal form of the generated HgS crystals by controlling the dropping speed of deionized water.

[0005] Specifically, the present invention adopts the following technical solutions to achieve the above purpose:

[0006] A method for preparing HgS crystals by wet recrystallization to control crystal form, comprising the following steps:

[0007] S1. Prepare an alkali metal sulfide solution, add HgS powder to the alkali metal sulfide solution, stir and heat until HgS is completely dissolved to obtain a saturated HgS solution;

[0008] S2. Place the saturated HgS solution in a sealed container, heat it to conduct a hydrothermal reaction; after the reaction is completed, cool it to room temperature, dropwise add deionized water in batches or add deionized water at one time to the reaction solution, avoid light, and let it stand for crystal precipitation; centrifuge, wash the crystals, and dry; the α-HgS crystals are obtained by dropwise adding deionized water in batches, and the β-HgS crystals are obtained by adding deionized water at one time.

[0009] In a preferred embodiment, the alkali metal sulfide in step S1 is sodium sulfide or / and potassium sulfide.

[0010] In a preferred embodiment, the molar ratio of the alkali metal sulfide to the HgS powder in step S1 is 10:3.

[0011] In a preferred embodiment, when preparing the alkali metal sulfide solution in step S1, stir at a speed of 400 - 500 rpm at 160 - 180 °C.

[0012] In a preferred embodiment, the conditions for the hydrothermal reaction in step S2 are: heat from room temperature to 200 - 225 °C at a rate of 5.5 - 6.5 °C / min, and keep warm for 1200 - 1440 min; then cool down to 120 - 180 °C and keep warm for 2000 - 2580 min.

[0013] In a preferred embodiment, step S2 includes the step of adding HgS seeds to the saturated HgS solution.

[0014] In a preferred embodiment, the time required to cool to room temperature in step S2 is 6 - 8 h.

[0015] In a preferred embodiment, when adding deionized water in batches in step S2, the ratio of the total volume of the finally added deionized water to the volume of the reaction solution is 1:12 - 1:2.

[0016] In a preferred embodiment, when adding deionized water in batches in step S2, the operation is as follows: add 1 - 2 drops of deionized water every 30 min.

[0017] In a preferred embodiment, when adding deionized water at one time in step S2, the ratio of the volume of the added deionized water to the volume of the reaction solution > 1:1.

[0018] In a preferred embodiment, the centrifugation speed in step S2 is 5000 - 10000 rpm, and the centrifugation time is 1 - 5 min.

[0019] In a preferred embodiment, the drying temperature in step S2 is 60 - 90 °C, and the drying time is 10 - 15 h.

[0020] In a preferred embodiment, when washing the crystals in step S2, the operation is as follows: wash the crystals 2 - 4 times each with absolute ethanol and deionized water.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] (1) In the present invention, HgS crystals with different crystal forms are prepared by the method of wet recrystallization. The reaction conditions are mild, the preparation cost is low, the obtained crystals are larger in size (millimeter level), higher in purity, shorter in crystal growth period, and easier to control the crystal size.

[0023] (2) Due to the large size of the millimeter-level HgS crystals prepared in the present invention, the crystal defects can be significantly reduced, the performance and stability of the crystals can be improved, and at the same time, they are convenient for processing and utilization. They can be used in technical fields such as electronics, optics, medicine, and handicraft preparation. For example, they are used to prepare infrared detectors in the electronic field; they are used to make optical lenses in some optical instruments with special requirements for optical materials in the optical field (such as optical systems with high transmittance or high absorption rate in a specific wavelength range, or lasers for generating specific wavelengths and characteristics); α-HgS, also known as cinnabar, can be used to make ornaments or as traditional Chinese medicine.

[0024] (3) In the present invention, the conditions for the mutual conversion between different crystal forms of HgS are studied, and the controllable mutual conversion between the two crystal forms is successfully achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the macroscopic appearance diagram of the α-HgS crystal prepared in Example 1 of the present invention;

[0026] Figure 2 It is the XRD diagram of the α-HgS crystal prepared in Example 1 of the present invention;

[0027] Figure 3 It is the appearance diagram of the α-HgS crystal prepared in Example 1 of the present invention magnified 50 times under an optical microscope;

[0028] Figure 4 It is the appearance diagram of the α-HgS crystal prepared in Example 1 of the present invention magnified 100 times under an optical microscope;

[0029] Figure 5 It is the HAADF-STEM diagram and EDS diagram of the α-HgS crystal prepared in Example 1 of the present invention;

[0030] Figure 6 It is the appearance diagram of the HgS crystal prepared in Comparative Example 1 magnified 100 times under an optical microscope;

[0031] Figure 7 It is the appearance diagram ((a) figure) and XRD diagram ((b) figure) of the β-HgS crystal prepared in Example 6 of the present invention;

[0032] Figure 8 It is the appearance diagram of the massive α-HgS crystal prepared in Example 5 of the present invention;

[0033] Figure 9 Appearance diagrams of α-HgS ((a) figure) and β-HgS ((b) figure) prepared in Example 7 of the present invention. Detailed implementation manners

[0034] The following content describes the technical solutions of the present application clearly and completely in combination with embodiments, so that those skilled in the art can fully understand the present application. Obviously, the described embodiments are only some preferred embodiments of the present application, rather than all embodiments. Any equivalent transformation or substitution made to the following implementation manners by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0035] The purity of sodium sulfide nonahydrate used in the following examples is ≥98%.

[0036] Example 1

[0037] A method for preparing α-HgS crystals by wet recrystallization, comprising the following steps:

[0038] S1. Clean the beaker, weigh 12 g (0.05 mol) of sodium sulfide nonahydrate (Na2S·9H2O), add it to 50 mL of deionized water to prepare a Na2S solution, stir evenly on a magnetic stirrer at 180 °C and 400 r / min until completely dissolved to obtain a clear solution. Subsequently, add 3.6 g (0.015 mol) of HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a HgS saturated solution.

[0039] S2. Transfer the obtained HgS saturated solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first raise the temperature from room temperature to 200 °C within 30 min (the heating rate is 5.5 - 5.7 °C / min), keep it at 200 °C for 1440 min. Then cool it to 150 °C and keep it for 2000 min, and finally cool it to room temperature within 7 h. Transfer the reaction solution to a sealed bottle, slowly add 1 - 2 drops of deionized water every 30 min, let it stand, and the volume ratio of the finally added deionized water to the reaction solution is 1:4. Place it in a dark place to allow the solution to slowly crystallize. After the crystallization is completed, centrifuge at 7000 rpm for 3 min, wash the solid with anhydrous ethanol and deionized water 3 times each, and then dry it at 75 °C for 12 h to obtain the red HgS crystals as shown in Figure 1 、 Figure 3 、 Figure 4 Shown. After grinding the HgS crystals, perform XRD (X-ray diffraction) tests, and the results are as shown in Figure 2 Shown, from Figure 2As can be seen above, the obtained product is an α-HgS crystal. The α-HgS crystal was analyzed by HAADF-STEM (High Angle Annular Dark Field Scanning Transmission Electron Microscopy) and EDS (Energy Dispersive X-ray Spectroscopy), and the analysis result diagrams as shown in Figure 5 were obtained. Figure 5 In the upper left figure in the middle, it is the total element distribution diagram of EDS of the α-HgS crystal obtained in this embodiment. The HAADF figure in the upper right corner is the HAADF-STEM image of the α-HgS crystal. The lower left figure is the EDS distribution diagram of a single Hg (mercury) element, and the lower right figure is the EDS distribution diagram of a single S (sulfur) element. From Figure 5 it can be seen that the Hg element and the S element are evenly distributed in each part of the crystal, and no other impurity elements were significantly detected in the test results; at the same time, combined with Figure 2 the XRD test results, it can be concluded that the prepared crystal exhibits excellent crystallinity and uniform element distribution, thus proving that the purity of the α-HgS crystal is relatively high.

[0040] Example 2

[0041] The method for preparing the α-HgS crystal in this embodiment is basically the same as that in Example 1, except that:

[0042] S2. The obtained saturated HgS solution was transferred to the inner lining of a hydrothermal autoclave and sealed, and then placed in an oven for heating reaction. During the heating process, the temperature was first raised from room temperature to 225 °C within 30 min (the heating rate was about 6.5 °C / min), and kept at 225 °C for 1200 min. Then the temperature was lowered to 120 °C and kept for 2200 min, and finally cooled to room temperature within 6 h. The reaction solution was transferred to a closed bottle, and 1 - 2 drops of deionized water were slowly added every 30 min and allowed to stand. The final volume ratio of the added deionized water to the reaction solution was 1:2. It was placed in a dark place to allow the solution to slowly crystallize. After the crystallization ended, it was centrifuged at 5000 rpm for 5 min, and the solid was washed 4 times each with absolute ethanol and deionized water, and then dried at 60 °C for 15 h to obtain a red HgS crystal. This HgS crystal was confirmed to be an α-HgS crystal and showed no significant difference from the α-HgS crystal in Example 1.

[0043] Example 3

[0044] The method for preparing the α-HgS crystal in this embodiment is basically the same as that in Example 1, except that:

[0045] S1. Clean the beaker, weigh 10 g (0.05 mol) of potassium sulfide pentahydrate (K₂S·5H₂O), add it to 50 mL of deionized water to prepare a K₂S solution, stir evenly on a magnetic stirrer at 160 °C and 500 r / min until completely dissolved to obtain a clear solution. Subsequently, add 3.6 g (0.015 mol) of HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0046] Step S2 yields red HgS crystals. These HgS crystals are confirmed to be α-HgS crystals and show no significant difference from the α-HgS crystals in Example 1.

[0047] Example 4

[0048] A method for preparing α-HgS crystals by wet recrystallization, comprising the following steps:

[0049] S1. Clean the beaker, weigh 12 g (0.05 mol) of sodium sulfide nonahydrate (Na₂S·9H₂O), add it to 50 mL of deionized water to prepare a Na₂S solution, stir evenly on a magnetic stirrer at 170 °C and 450 r / min until completely dissolved to obtain a clear solution. Subsequently, add 3.6 g (0.015 mol) of HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0050] S2. Transfer the obtained saturated HgS solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first raise the temperature from room temperature to 210 °C within 30 min (the heating rate is about 6.0 °C / min), and keep it at 210 °C for 1300 min. Then cool it to 180 °C and keep it for 2580 min, and finally cool it to room temperature within 8 h. Transfer the reaction solution to a closed bottle, slowly add 1 - 2 drops of deionized water every 30 min, let it stand, and the volume ratio of the finally added deionized water to the reaction solution is 1:12. Place it in a dark place to allow the solution to slowly crystallize. After the crystallization is completed, centrifuge at 10000 rpm for 1 min, wash the solid with anhydrous ethanol and deionized water twice each, and then dry it at 90 °C for 10 h to obtain red HgS crystals. These HgS crystals are confirmed to be α-HgS crystals and show no significant difference from the α-HgS crystals in Example 1.

[0051] Example 5

[0052] A method for preparing bulk α-HgS crystals by wet recrystallization, comprising the following steps:

[0053] S1. Clean the beaker, weigh 12g (0.05mol) sodium sulfide nine hydrate (Na2S·9H2O), add 50mL of deionized water to prepare Na2S solution, stir evenly on a magnetic stirrer at 180℃ and 400r / min until completely dissolved to obtain a clear solution. Then add 3.6g (0.015mol) HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0054] S2. Move the obtained HgS saturated solution into a hydrothermal kettle, add 0.0558g HgS seed crystals to the solution and seal the hydrothermal kettle. Place the hydrothermal kettle in an oven for heating reaction. During the heating process, first raise the temperature from room temperature to 200°C within 30 minutes (heating rate is 5.5~5.7°C / min), and keep it at 200°C for 1440 minutes. Then cool to 150°C and keep it for 2000 minutes, and finally cool to room temperature within 7 hours. Transfer the reaction solution to a sealed bottle, slowly add 1 to 2 drops of deionized water every 30 minutes, let it stand, and the final volume ratio of deionized water added to the reaction solution is 1:4. Place it in a dark place to allow the solution to slowly crystallize. After the crystallization is completed, centrifuge it at 7000rpm for 3 minutes. Wash the solid with anhydrous ethanol and deionized water 3 times each, and then dry it at 75°C for 12 hours to obtain the following: Figure 8 The red block α-HgS crystal weighs 0.102 g. The size of the α-HgS crystal is 0.8-2.3 mm. It can be seen that adding HgS seed crystals (seed crystals purchased from commercial channels or prepared according to the methods of Examples 1-4) to the HgS saturated solution in step S2 can greatly increase the size of the α-HgS crystals.

[0055] Example 6

[0056] A method for preparing β-HgS crystals by wet recrystallization comprises the following steps:

[0057] S1. Clean the beaker, weigh 12g (0.05mol) sodium sulfide nine hydrate (Na2S·9H2O), add 50mL of deionized water to prepare Na2S solution, stir evenly on a magnetic stirrer at 180℃ and 400r / min until completely dissolved to obtain a clear solution. Then add 3.6g (0.015mol) HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0058] S2. Transfer the obtained saturated HgS solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first raise the temperature from room temperature to 200 °C within 30 min (heating rate: 5.5 - 5.7 °C / min), and keep it at 200 °C for 1440 min. Then cool it down to 150 °C and keep it for 2000 min. Finally, cool it to room temperature within 7 h. Transfer the reaction solution to a closed bottle, add a large amount of deionized water at one time, let it stand, and finally the volume ratio of the added deionized water to the reaction solution exceeding 1:1 is sufficient. Place it in a dark place to allow the solution to slowly crystallize. After crystallization, centrifuge at 7000 rpm for 3 min, wash the solid with anhydrous ethanol and deionized water three times each, and then dry it at 75 °C for 12 h to obtain the black HgS crystals as shown in Figure 7 Figure (a) in the following. Grind the HgS crystals and then perform XRD testing. The results are as shown in Figure 7 Figure (b) in the following. It can be seen from Figure 7 Figure (b) in the following that the obtained product is β-HgS crystals.

[0059] Example 7

[0060] In this example, the feasibility of using ultrasonic-assisted energy supply to regulate the formation of α-HgS and β-HgS was studied. The specific steps are as follows:

[0061] S1. Clean a beaker, weigh 12 g (0.05 mol) of sodium sulfide nonahydrate (Na2S·9H2O), add it to 50 mL of deionized water to prepare a Na2S solution, and stir it evenly until completely dissolved at 180 °C and 400 r / min on a magnetic stirrer to obtain a clear solution. Subsequently, add 3.6 g (0.015 mol) of HgS powder, continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0062] S2. Transfer the obtained saturated HgS solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first raise the temperature from room temperature to 200 °C within 30 min (heating rate: 5.5 - 5.7 °C / min), and keep it at 200 °C for 1440 min. Then cool it down to 150 °C and keep it for 2000 min. Finally, cool it to room temperature within 7 h. Transfer the reaction solution to a beaker, heat it to 60 °C, and take two 1-mL reaction solutions as sample A and sample B respectively. Add 2 - 3 drops of deionized water to sample A, and then ultrasonicate sample A at 180 W and 40000 Hz for 3 min. It can be found that a small amount of red crystals precipitate (as shown in Figure 9 Figure (a) in the following). Add 0.5 mL of deionized water directly to sample B, and the interface of the solution quickly turns black (as shown in Figure 9(as shown in Figure (b)). Centrifuge sample B at a speed of 4000 rpm for 5 minutes, and centrifuge it repeatedly 3 to 6 times (for example, centrifuge 4 times). Dry the obtained crystals at 60 °C to obtain black β-HgS crystals.

[0063] From the experiments in this example, it can be seen that due to the relatively high symmetry of the crystal structure of the cubic phase, it has a lower nucleation energy barrier. The energy required to form the cubic structure of β-HgS is less than that required to form the trigonal structure of α-HgS. Therefore, it is easier to form. When it is necessary for HgS crystals to precipitate in the α-phase, a certain amount of energy needs to be provided during the crystallization process to help overcome the kinetic phase transition barrier for the transformation of β-HgS to α-HgS. Therefore, the control of the crystallization rate during the crystallization process and the provision of additional energy for the crystallization process can be used to achieve the regulation of the HgS crystal phase.

[0064] Example 8

[0065] In this example, the feasibility of heating α-HgS to transform into β-HgS and the feasibility of β-HgS transforming into α-HgS were studied under light-shielded conditions and in an air-free environment.

[0066] 8.1 Feasibility of α-HgS Transforming into β-HgS

[0067] Load the α-HgS crystal powder prepared in Example 1 into a small crucible, place the small crucible in a quartz tube, and then place the quartz tube in a tube furnace. First, evacuate the tube furnace, and the vacuum degree is 5×10 -5 Pa. Then, introduce argon to fill the quartz tube and then heat it. Heating temperature control settings: the temperature is set to 350 °C, and the heating duration is 2 h. After the heating and heat preservation are completed, it is observed that the red crystal powder in the crucible changes from red to black. This shows that α-HgS can be transformed into β-HgS by heating, and the phase transition temperature is between 300 and 400 °C.

[0068] 8.2 Feasibility of β-HgS Transforming into α-HgS

[0069] Prepare a saturated HgS solution according to the method of step S1 in Example 6. Transfer the obtained saturated HgS solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first increase the temperature from room temperature to 200 °C within 30 min (the heating rate is 5.5 - 5.7 °C / min), and keep it at 200 °C for 1440 min. Then cool it down to 150 °C and keep it for 2000 min, and finally cool it to room temperature within 7 h. Take out 5 mL of the reaction solution and transfer it to a sealed bottle, directly add 3 mL of deionized water, and black β-HgS crystals will rapidly precipitate from the solution. Seal the bottle and place it in a light-shielded condition. After a period of time (36 h), it can be observed that the black precipitate crystals gradually turn into red crystals. This indicates that β-HgS can spontaneously transform into α-HgS.

[0070] Comparative Example 1

[0071] A method for preparing HgS crystals by wet recrystallization, comprising the following steps:

[0072] P1. Clean the beaker, weigh 12 g (0.05 mol) of sodium sulfide nonahydrate (Na2S·9H2O), add it to 50 mL of deionized water to prepare a Na2S solution, stir evenly until completely dissolved at 180 °C and 400 r / min on a magnetic stirrer to obtain a clear solution. Subsequently, add 3.6 g (0.015 mol) of HgS powder and 0.36 g of polyvinylpyrrolidone (PVP, molecular weight 40,000 Da), and continue heating and stirring until HgS is completely dissolved to obtain a saturated HgS solution.

[0073] P2. Transfer the obtained saturated HgS solution to the inner lining of a hydrothermal autoclave, seal it, and place it in an oven for heating reaction. During the heating process, first increase the temperature from room temperature to 200 °C within 30 min (the heating rate is 5.5 - 5.7 °C / min), and keep it at 200 °C for 1440 min. Then cool it down to 150 °C and keep it for 2000 min, and finally cool it to room temperature within 7 h. Transfer the reaction solution to a sealed bottle, slowly add 1 - 2 drops of deionized water every 30 min, let it stand, and finally the volume ratio of the added deionized water to the reaction solution is 1:4. Place it in a light-shielded place to allow the solution to slowly crystallize. After the crystallization is completed, centrifuge at 7000 rpm for 3 min, wash the solid with anhydrous ethanol and deionized water 3 times each, and then dry it at 75 °C for 12 h to obtain the Figure 6 HgS crystals as shown. The crystals appear as black powder. Observed under an optical microscope, their size is significantly reduced compared to the size of the α-HgS crystals in Example 1, and the crystals show a connection of red and black.

[0074] The embodiments described above are only preferred embodiments of the present application and are not intended to limit the protection scope of the present application. For any person skilled in the art, various changes and modifications can be made to the present application. Any simple equivalent changes and modifications made based on the protection scope of the present application and the content of the specification shall be included within the protection scope of the present application.

Claims

1. A method for preparing HgS crystals by wet recrystallization to control crystal form, characterized in that, It includes the following steps: S1. Prepare an alkali metal sulfide solution, add HgS powder to the alkali metal sulfide solution, stir and heat until HgS is completely dissolved to obtain a saturated HgS solution; S2. Place the saturated HgS solution in a sealed container, heat it for hydrothermal reaction; after the reaction ends, cool it to room temperature, add deionized water dropwise in batches or add deionized water at one time to the reaction solution, avoid light, and let it stand for crystallization; centrifuge, wash the crystals, and dry them. α-HgS crystals are obtained by adding deionized water dropwise in batches, and β-HgS crystals are obtained by adding deionized water at one time.

2. The method according to claim 1, wherein In step S1, the alkali metal sulfide is sodium sulfide or / and potassium sulfide.

3. The method according to claim 1, wherein In step S1, the molar ratio of the alkali metal sulfide to the HgS powder is 10:

3.

4. The method according to claim 1, characterized in that When preparing the alkali metal sulfide solution in step S1, stir at a speed of 400-500 rpm at 160-180 °C; or / and, the conditions for the hydrothermal reaction in step S2 are: heat from room temperature to 200-225 °C at a rate of 5.5-6.5 °C / min, keep warm for 1200-1440 min; then cool to 120-180 °C and keep warm for 2000-2580 min.

5. The method according to claim 1, characterized in that, Step S2 includes the step of adding HgS seeds to the saturated HgS solution.

6. The method according to claim 1, characterized in that, When adding deionized water dropwise in batches in step S2, the total volume of the finally added deionized water and the volume of the reaction solution are in a ratio of 1:12-1:

2.

7. The method according to claim 6, characterized in that, When adding deionized water dropwise in batches in step S2, the operation is carried out as follows: add 1-2 drops of deionized water every 30 min.

8. The method according to claim 1, characterized in that When adding deionized water at one time in step S2, the volume of the added deionized water and the volume of the reaction solution are in a ratio >1:

1.

9. The method according to claim 1, wherein In step S2, the centrifugation speed is 5000-10000 rpm and the centrifugation time is 1-5 min; or / and in step S2, the drying temperature is 60-90 °C and the drying time is 10-15 h.

10. The method according to claim 1, characterized in that, When washing the crystals in step S2, the operation is carried out as follows: wash the crystals 2-4 times with anhydrous ethanol and deionized water respectively.

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