Polynitro bistriazole energetic co-crystal compounds and methods of making same

Abstract

The application relates to the technical field of energetic materials, and specifically discloses a polynitro-bistrizole energetic co-crystal compound and a preparation method thereof, which comprises a triimidazotriazine and a polynitro-bistrizole energetic co-crystal ligand; the polynitro-bistrizole energetic co-crystal ligand comprises 3,3'-dinitro-5,5'-azo-1,2,4-triazole or 3,3'-dinitro-5,5'-bistriazol-1,2,4-triazole. The method comprises the following steps: placing selected polynitro-bistrizole compounds and triimidazotriazine in a mortar and wet grinding for several minutes, placing the grinding product in a solvent and heating and dissolving, and finally successfully preparing two kinds of energetic co-crystal compounds through constant-temperature standing and volatilization; the method is simple in operation and obvious in effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energetic materials, in particular to a multi-nitro double-triazole energetic co-crystal compound and a preparation method thereof. BACKGROUND

[0002] Co-crystal is a single homogeneous material formed by self-assembly of two or more components through non-covalent interactions, including hydrogen bonding, pi-pi stacking and van der Waals interactions; compared with traditional chemical synthesis methods, co-crystal synthesis method is simple, safe and efficient, and only one step reaction is needed for synthesis and crystallization, avoiding complex organic synthesis steps, and the formation conditions of co-crystal are generally mild, which will not destroy the chemical structure of raw materials, and basically no other by-products are generated. More importantly, co-crystal technology has strong designability in structure and performance adjustment, and the co-crystal product may have all the characteristics of the raw material components, or may obtain some novel properties that the raw material components do not have. Especially for energetic compounds, co-crystal technology can effectively overcome the defects of existing energetic materials at the molecular level, and endow the new energetic co-crystal product with more excellent physical and chemical properties (such as density, mechanical sensitivity, hygroscopicity and detonation performance), so that the co-crystal technology has become an important way to regulate the physical and chemical properties of existing energetic materials and construct new energetic materials, and has great research prospect in the field of energetic materials.

[0003] However, a large number of literature researches show that the currently reported energetic co-crystal materials are mainly single-ring azole compounds (including pyrazole, imidazole, triazole and tetrazole with nitro or amine groups), and there are few reports on energetic co-crystals with multi-nitro double-triazole compounds as ligands, which have high density, high stability and high detonation performance, so the preparation of multi-nitro double-triazole energetic co-crystal compounds is of great significance in the field of energetic materials. SUMMARY

[0004] In view of the above problems, the first object of the present application is to provide a multi-nitro double-triazole energetic co-crystal compound, which has application value as heat-resistant and insensitive explosive.

[0005] The second object of the present application is to provide a preparation method of a multi-nitro double-triazole energetic co-crystal compound, which comprises the following steps: placing selected multi-nitro double-triazole compounds and tri-imidazole-triazine in a mortar and wet grinding for several minutes, then placing the grinding product in a solvent and heating to dissolve, and finally successfully preparing two kinds of energetic co-crystal compounds by constant temperature standing and volatilization method; the method is simple in operation and obvious in effect.

[0006] The first technical solution adopted by the present application is a multi-nitro double-triazole energetic co-crystal compound, comprising tri-imidazole-triazine and a multi-nitro double-triazole energetic co-crystal ligand; the multi-nitro double-triazole energetic co-crystal ligand comprises 3,3'-dinitro-5,5'-azo-1,2,4-triazole or 3,3'-dinitro-5,5'-linked-1,2,4-triazole.

[0007] The second technical solution adopted by the present application is a preparation method of a multi-nitro double-triazole energetic co-crystal compound, comprising the following steps:

[0008] S1: weigh tri-imidazole-triazine and multi-nitro double-triazole energetic co-crystal ligand and place them in a reaction device, drop a first solvent into the reaction device, and grind until the tri-imidazole-triazine and multi-nitro double-triazole energetic co-crystal ligand are both in powder form and uniformly mixed, to obtain a mixed powder;

[0009] S2: place the mixed powder in a second solvent, heat in a water bath and stir until completely dissolved, and continue constant temperature stirring,

[0010] filter to obtain a mixed solution;

[0011] S3: place the mixed solution in a constant temperature oven and stand still, and precipitate transparent crystals, to obtain the multi-nitro double-triazole energetic co-crystal compound.

[0012] Preferably, the multi-nitro double-triazole energetic co-crystal ligand in the step S1 comprises 3,3'-dinitro-5,5'-azo-1,2,4-triazole or 3,3'-dinitro-5,5'-linked-1,2,4-triazole.

[0013] Preferably, the molar ratio of tri-imidazole-triazine to multi-nitro double-triazole energetic co-crystal ligand in the step S1 is 1:1-3:1.

[0014] Preferably, the dropwise amount of the first solvent in the step S1 is 100-500 μL, and the grinding time is 10-25 min.

[0015] Preferably, the first solvent is one or more of deionized water, methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

[0016] Preferably, the use amount of the second solvent in the step S2 is 10-30 mL, the water bath heating and stirring are performed at 30-65°C until complete dissolution, and the constant temperature stirring is continued for 20-50 min.

[0017] Preferably, the second solvent is deionized water and an organic solvent, and the volume ratio of the deionized water to the organic solvent is 1:4-1:7; the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

[0018] Preferably, the step S3 of placing the mixed solution in a constant temperature oven for standing includes: placing the mixed solution in a small glass bottle, covering with a hole sealing film, and then placing the glass bottle in a constant temperature oven at 20-50 DEG C for standing.

[0019] Preferably, the step S3 of placing the mixed solution in a constant temperature oven at 20-50 DEG C for standing is for 7-14 days.

[0020] The beneficial effects of the above technical solution are:

[0021] (1) The preparation method of the multi-nitro double-triazole energetic co-crystal compound disclosed in the present application places the selected multi-nitro double-triazole compound and tri-imidazole-triazine in a mortar for wet grinding for several minutes, then places the grinding product in a solvent for heating and dissolving, and finally successfully prepares two kinds of energetic co-crystal compounds through constant temperature standing and volatilization method. The method is simple in operation, mild in conditions, safe and efficient, and obvious in effect. Not only can the preparation of high-quality multi-nitro double-triazole energetic co-crystal compounds be realized, but also the prepared energetic co-crystal compounds have application potential as heat-resistant insensitive explosives.

[0022] (2) The preparation method of the multi-nitro double-triazole energetic co-crystal compound disclosed in the present application can realize the preparation of multi-nitro double-triazole energetic co-crystal compounds through simple grinding, heating and dissolving, and constant temperature standing and crystallization operations. When the TT and DNAT reaction system and the TT and DNBT system are used respectively, two different multi-nitro double-triazole energetic co-crystal compounds of TT / DNAT and TT / DNBT can be obtained.

[0023] (3) The two multi-nitro double-triazole energetic co-crystal compounds of TT / DNAT and TT / DNBT prepared by the method disclosed in the present application both have application value as heat-resistant insensitive explosives. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The chemical structural formula of the solid raw material TT, DNAT and DNBT provided for an embodiment of the present application;

[0025] Figure 2 The flowchart of the preparation method of the multi-nitro double-triazole energetic co-crystal compound provided for an embodiment of the present application;

[0026] Figure 3 The optical microscope picture of the TT / DNAT energetic co-crystal provided for an embodiment of the present application;

[0027] Figure 4 The optical microscope picture of the TT / DNBT energetic co-crystal provided for an embodiment of the present application;

[0028] Figure 5 TT, DNAT and TT / DNAT energetic co-crystal FT-IR spectra provided for one embodiment of the present application;

[0029] Figure 6 TT, DNBT and TT / DNBT energetic co-crystal FT-IR spectra provided for one embodiment of the present application;

[0030] Figure 7 TT, DNAT and TT / DNAT energetic co-crystal PXRD spectra provided for one embodiment of the present application;

[0031] Figure 8 TT, DNBT and TT / DNBT energetic co-crystal PXRD spectra provided for one embodiment of the present application;

[0032] Figure 9 TT / DNAT energetic co-crystal SXRD spectra provided for one embodiment of the present application;

[0033] Figure 10 TT / DNBT energetic co-crystal SXRD spectra provided for one embodiment of the present application;

[0034] Figure 11 TT / DNAT energetic co-crystal DSC spectra provided for one embodiment of the present application;

[0035] Figure 12 TT / DNBT energetic co-crystal DSC and TG spectra provided for one embodiment of the present application. DETAILED DESCRIPTION

[0036] The present application is further described by the following specific examples. It should be pointed out that for those skilled in the art, without departing from the principles of the present application, a number of variations and improvements can be made, which should be considered as falling within the scope of the present application.

[0037] The contents not described in detail in the present application are known to those skilled in the art. If not specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art.

[0038] The synthesis method of the triimidazotriazine (TT) used in the application refers to the literature "Schubert D M, Natan DT, Wilson D C, et al. Facile synthesis and structures of cyclic triimidazole and its boric acid adduct [J]. Cryst. Growth. Des, 2011, 11 (3): 843-850.", and the chemical structural formula of the TT is as shown in Figure 1 . .

[0039] The synthesis method of the 3,3'-dinitro-5,5'-azo-1,2,4-triazole (DNAT) used in the application refers to the literature "Synthesis and Crystal Structure of 3,3'-Dinitro-5,5'-azo-1H-1,2,4-triazole [J]. Chinese Journal of Explosives and Propellants, 2009, 32 (1): 25-28.", and the chemical structural formula of the DNAT is as shown in Figure 1 . .

[0040] The synthesis method of the 3,3'-dinitro-5,5'-bis-1,2,4-triazole (DNBT) used in the application refers to the literature "Dippold A, A, Klapötke T M. Nitrogen-Rich Bis-1,2,4-triazoles—A Comparative Study of Structural and Energetic Properties [J]. Chem. Eur. J, 2012, 18, 16742-16753.", and the chemical structural formula of the DNBT is as shown in . Figure 1 . .

[0041] The application discloses a multi-nitro bis-triazole energetic co-crystal compound, which comprises triimidazotriazine and a multi-nitro bis-triazole energetic co-crystal ligand; the multi-nitro bis-triazole energetic co-crystal ligand comprises 3,3'-dinitro-5,5'-azo-1,2,4-triazole or 3,3'-dinitro-5,5'-bis-1,2,4-triazole. .

[0042] As shown in Figure 2 , the application discloses a preparation method of a multi-nitro bis-triazole energetic co-crystal compound, which comprises the following steps: .

[0043] S1: take the tri-imidazotriazine (TT) and the multi-nitro-bis-triazole energetic co-crystal ligand into a reaction device (for example, a mortar), drop 100-500 μL (preferably 100-200 μL) of the first solvent into the reaction device, grind thoroughly for 10-25 min (preferably 10-20 min), until the tri-imidazotriazine and the multi-nitro-bis-triazole energetic co-crystal ligand are both in powder form (i.e. the solvent in the mortar is substantially volatilized or there are no obvious drops of condensed solvent in the mortar) and are uniformly mixed, to obtain a mixed powder;

[0044] The multi-nitro-bis-triazole energetic co-crystal ligand includes 3,3'-dinitro-5,5'-azo-1,2,4-triazole (DNAT) or 3,3'-dinitro-5,5'-bi-1,2,4-triazole (DNBT); the molar ratio of the tri-imidazotriazine and the multi-nitro-bis-triazole energetic co-crystal ligand is 1:1-3:1 (preferably 1:1-2:1), and the total mass of the tri-imidazotriazine and the multi-nitro-bis-triazole energetic co-crystal ligand is 0.5-1.5 g (preferably 0.5-1.0 g).

[0045] The first solvent is one or more of deionized water, methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

[0046] S2: place the mixed powder in 10-30 mL (preferably 10-20 mL) of the second solvent, heat in a 30-65°C (preferably 40-50°C) water bath and stir until completely dissolved, continue to stir at constant temperature for 20-50 min (preferably 20-30 min), and filter to obtain a clear and transparent mixed solution;

[0047] The second solvent is deionized water and an organic solvent, and the volume ratio of the deionized water to the organic solvent is 1:4-1:7; the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

[0048] The filtering operation is performed using a polytetrafluoroethylene organic filter head with a pore size of 0.22 μm.

[0049] S3: place the mixed solution in a constant-temperature oven at 20-50°C (preferably 25-35°C) and stand for 7-14 days (preferably 7-10 days), to precipitate transparent crystals, i.e. to obtain the multi-nitro-bis-triazole energetic co-crystal compound.

[0050] Placing the mixed solution in a constant-temperature oven at 20-50°C includes: placing the mixed solution in a small glass bottle, covering the bottle with a sealing film having holes; and then placing the glass bottle in a constant-temperature oven at 20-50°C; for example, the small glass bottle has a specification of 20 mL, the bottle opening is covered with a sealing film after being filled with liquid, and 5-10 small holes are punched on the sealing film using a syringe needle.

[0051] Example 1

[0052] TT (396 mg, 2 mmol) and DNAT (254 mg, 1 mmol) were placed in a mortar, and then 150 μL of methanol solution was added. The mixture was ground repeatedly for 15 min until the solvent in the mortar was basically evaporated. The mixed solid powder sample in the mortar was then collected. The obtained mixed solid powder sample was placed in a single-necked flask, and then 3 mL of water / 15 mL of acetonitrile mixed solvent was added to the flask. The solid sample was dissolved in a water bath at 50 °C and stirred at a constant temperature for 25 min. The mixture was filtered using a polytetrafluoroethylene organic filter with a pore size of 0.22 μm, and the filtered clear and transparent solution was transferred to a 20 mL glass bottle. The bottle mouth was covered with a sealing film with 10 pinholes. The glass bottle was placed in a constant temperature oven at 30 °C and left to stand for 10 days, during which yellow crystals precipitated.

[0053] The yellow crystals obtained above were subjected to optical microscopy (using an OLYMPUS-BX43 microscope manufactured by Olympus Corporation of Japan), and the resulting microscopic images are shown below. Figure 3 As shown; FT-IR testing was performed on the yellow crystal (using a Nicolet Magna IR 560 infrared spectrometer manufactured by Bruker), and the test spectrum results are as follows. Figure 5 As shown, the infrared spectrum of the yellow crystalline product not only contains the infrared absorption peaks of both raw materials, but also exhibits red-shift and blue-shift phenomena in some peaks and the formation of new peaks. This result preliminarily indicates the formation of an energetic TT / DNAT eutectic. Further PXRD testing of the above yellow crystalline product (using a Bruker D2 Advance diffractometer) yielded the following spectral results: Figure 7 As shown, new diffraction peaks appear in the spectrum, representing the formation of new crystal forms and crystal planes. At the same time, the test results are consistent with the theoretical results of eutectic, proving the formation of the eutectic compound.

[0054] The above-mentioned yellow crystalline product was subjected to SXRD testing (using a Bruker Rigaku RAXIS IP diffractometer), and the test results are as follows. Figure 9 As shown, the single-crystal diffraction results indicate that the yellow product is a eutectic compound formed by TT and DNAT. Combined with the unit cell parameters in Table 1, it can be seen that TT and DNAT form a new crystal form in the single-crystal unit cell at a molar ratio of 2:1.

[0055] Table 1. Single-crystal unit cell parameters of energetic eutectic crystals of TT / DNAT and TT / DNBT.

[0056]

[0057] The yellow crystal product was subjected to DSC test (using DSC-209 differential scanning calorimeter produced by Netzsch Company), and the DSC test spectrum is shown in Figure 11 The results show that the peak thermal decomposition temperature of the TT / DNAT eutectic is 309.24°C. The impact sensitivity and friction sensitivity of the eutectic were tested by using BAM impact sensitivity tester of BFH-10 type and BAM friction sensitivity tester of FSKM-10 type, and the results show that the impact sensitivity is 38 J and 180 N. Further, the parameters such as detonation velocity and detonation pressure were calculated by using Gussian 09 and EXPLO5 software, and the results show that the detonation velocity and detonation pressure of the TT / DNAT eutectic with a molar ratio of 2:1 are 6486 m·s -1 and 17.1 GPa, respectively. The calculation results show that the TT / DNAT eutectic compound has application value as heat-resistant insensitive explosive.

[0058] Example 2

[0059] TT (594 mg, 3 mmol) and DNAT (254 mg, 1 mmol) were placed in a mortar, and then 500 μL of methanol solution was added. The mortar was repeatedly ground for 25 min until the solvent in the mortar was basically volatilized. The mixed solid powder sample in the mortar was collected. The obtained mixed solid powder sample was placed in a single-neck flask. Then 3 mL of water / 21 mL of acetone mixed solvent was added to the flask. The solid sample was dissolved at a water bath temperature of 65°C. The constant temperature stirring was continued for 50 min. The polytetrafluoroethylene organic filter head with a pore size of 0.22 μm was used for filtration. The filtered clear transparent solution was transferred to a 20 mL small glass bottle, and the bottle opening was covered with a sealing film with 10 needle holes. The above-mentioned small glass bottle was placed in a constant temperature oven at 50°C, and was left to stand for 14 days. Yellow crystals were precipitated, and the TT / DNAT eutectic compound was prepared.

[0060] Example 3

[0061] TT (396 mg, 2 mmol) and DNAT (508 mg, 2 mmol) were placed in a mortar, and then 100 μL of methanol solution was added. The mortar was repeatedly ground for 10 min until the solvent in the mortar was basically volatilized. The mixed solid powder sample in the mortar was collected. The obtained mixed solid powder sample was placed in a single-neck flask. Then 2 mL of water / 8 mL of acetone mixed solvent was added to the flask. The solid sample was dissolved at a water bath temperature of 30°C. The constant temperature stirring was continued for 20 min. The polytetrafluoroethylene organic filter head with a pore size of 0.22 μm was used for filtration. The filtered clear transparent solution was transferred to a 20 mL small glass bottle, and the bottle opening was covered with a sealing film with 10 needle holes. The above-mentioned small glass bottle was placed in a constant temperature oven at 20°C, and was left to stand for 7 days. Yellow crystals were precipitated, and the TT / DNAT eutectic compound was prepared.

[0062] Example 4

[0063] TT (396 mg, 2 mmol) and DNBT (226 mg, 1 mmol) were placed in a mortar, and then 150 μL of acetone solution was added. The mixture was ground repeatedly for 15 min until the solvent in the mortar was basically evaporated. The mixed solid powder sample in the mortar was then collected. The obtained mixed solid powder sample was placed in a single-necked flask, and then 3 mL of water / 15 mL of methanol mixed solvent was added to the flask. The solid sample was dissolved in a water bath at 50 °C and stirred at a constant temperature for 25 min. The mixture was filtered using a polytetrafluoroethylene organic filter with a pore size of 0.22 μm, and the filtered clear and transparent solution was transferred to a 20 mL glass bottle. The bottle mouth was covered with a sealing film with 10 pinholes. The glass bottle was placed in a constant temperature oven at 25 °C and left to stand for 7 days, during which colorless and transparent crystals precipitated.

[0064] The colorless and transparent crystal prepared above was subjected to optical microscopy, and the resulting microscopic images are shown below. Figure 4 As shown; FT-IR testing was performed on the colorless and transparent crystal, and the test spectrum results are as follows. Figure 6 As shown, the infrared spectrum of the colorless and transparent crystalline product not only contains the infrared absorption peaks of both raw materials, but also exhibits red-shift and blue-shift phenomena in some peaks and the formation of new peaks. This result preliminarily indicates the formation of an energetic TT / DNBT eutectic. Further PXRD testing of the above-mentioned colorless and transparent crystalline product yielded the following spectral results: Figure 8 As shown, new diffraction peaks appear in the spectrum, representing the formation of new crystal forms and crystal planes. At the same time, the test results are consistent with the theoretical results of eutectic, proving the formation of the eutectic compound.

[0065] The above-mentioned colorless and transparent crystalline product was subjected to SXRD testing, and the test results are as follows: Figure 10 As shown, the single-crystal diffraction results indicate that the colorless and transparent crystal is a eutectic compound formed by TT and DNBT. Combined with the unit cell parameters in Table 1, it can be seen that TT and DNBT form a new crystal form in the single crystal cell at a molar ratio of 2:1.

[0066] The above colorless and transparent crystalline product was subjected to DSC and TG tests (using a Netzsch STA-449C thermogravimetric analyzer), and the test spectra are shown below. Figure 12 As shown, the results indicate that the peak thermal decomposition temperature of the TT / DNBT eutectic is 301.6℃. Sensitivity tests were conducted on the eutectic using a BFH-10 BAM impact sensitivity meter and an FSKM-10 BAM friction sensitivity meter, revealing impact sensitivities of 38J and 192N, respectively. Further calculations using Gussian 09 and EXPLO5 software for detonation velocity and detonation pressure showed that the detonation velocity and detonation pressure of the TT / DNBT eutectic with a molar ratio of 2:1 were 6325 m / s².-1 and 15.9 GPa, which indicates that the TT / DNBT eutectic compound has application value as a heat-resistant insensitive explosive.

[0067] The two different energetic eutectic compounds of TT / DNAT and TT / DNBT disclosed in the application are disclosed for the first time, the preparation method is simple in operation, mild in condition, safe and efficient, the two eutectic compounds of TT / DNAT and TT / DNBT synthesized by the method have application value as heat-resistant insensitive explosives; the synthesis method of the energetic eutectic compound provides a new research idea for the technical field of energetic materials, and has wide application prospect.

[0068] The application is described in detail above in combination with the specific embodiments and exemplary examples, and the above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as a limitation of the application. It is understood by those skilled in the art that various equivalent replacements, modifications or improvements can be made to the technical solutions and embodiments of the application without departing from the spirit and scope of the application, which all fall within the scope of the application; the protection scope of the application is subject to the appended claims.

Claims

1. A polynitrobistriazole energetic eutectic compound, characterized in that, Including triimidazole triazine and polynitrobistriazole energetic co-crystal ligands; the polynitrobistriazole energetic co-crystal ligands are 3,3′-dinitro-5,5′-azo-1,2,4-triazole or 3,3′-dinitro-5,5′-bi-1,2,4-triazole; The molar ratio of the triimidazole triazine and the polynitrobistriazole energetic eutectic ligand is 1:1 to 3:

1.

2. A method for preparing a polynitrobistriazole energetic eutectic compound, characterized in that, Includes the following steps: S1: Weigh out triimidazole triazine and polynitrobistriazole energetic cocrystalline ligands and place them in a reaction apparatus. Add the first solvent dropwise to the reaction apparatus and grind until both triimidazole triazine and polynitrobistriazole energetic cocrystalline ligands are in powder form and uniformly mixed to obtain a mixed powder. The polynitrobistriazole energetic cocrystalline ligand is 3,3′-dinitro-5,5′-azo-1,2,4-triazole or 3,3′-dinitro-5,5′-bi-1,2,4-triazole, and the molar ratio of triimidazole triazine to polynitrobistriazole energetic cocrystalline ligands is 1:1 to 3:

1. S2: Place the mixed powder in a second solvent, heat in a water bath and stir until completely dissolved, continue stirring at a constant temperature, filter, and obtain a mixed solution; S3: Place the mixed solution in a constant temperature oven and let it stand until transparent crystals precipitate, thus obtaining a polynitrobistriazole energetic eutectic compound.

3. The preparation method according to claim 2, characterized in that, In step S1, the amount of the first solvent added is 100~500 μL, and the grinding is carried out for 10~25 min.

4. The preparation method according to claim 3, characterized in that, The first solvent is one or more of deionized water, methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

5. The preparation method according to claim 2, characterized in that, In step S2, the amount of the second solvent used is 10-30 mL. The solvent is heated in a water bath at 30-65°C and stirred until completely dissolved. Then, the solvent is stirred at a constant temperature for 20-50 min.

6. The preparation method according to claim 5, characterized in that, The second solvent is deionized water and an organic solvent, wherein the volume ratio of the deionized water to the organic solvent is 1:4 to 1:7; the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, ethyl acetate and chloroform.

7. The preparation method according to claim 2, characterized in that, The step S3 of placing the mixed solution in a constant temperature oven to stand includes: placing the mixed solution in a small glass bottle and covering it with a perforated sealing film; then placing the glass bottle in a constant temperature oven at 20~50℃.

8. The preparation method according to claim 2, characterized in that, In step S3, the mixed solution is placed in a constant temperature oven at 20~50℃ and left to stand for 7~14 days.

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