All-organic heterojunction photocatalyst and preparation method thereof

Abstract

The application provides a kind of all-organic heterojunction photocatalyst and preparation method, the all-organic heterojunction photocatalyst is porphyrin-based metal organic framework and phenolic resin heterojunction photocatalyst, wherein, the mass ratio of porphyrin-based metal organic framework and phenolic resin is (0.05-4):1.The preparation method comprises: carboxylic acid ligand, metal salt, porphyrin ligand and organic solvent are added into hydrothermal reactor, ultrasonic dispersion is carried out, and mixture is obtained;The mixture is transferred to electric oven, heated, cooled to room temperature, and washed repeatedly, then dried and activated to obtain porphyrin-based metal organic framework;A certain amount of phenol ligand and the porphyrin-based metal organic framework are added to a certain volume of solution, and a mixed solution is obtained after dispersion;Formaldehyde solution and ammonia solution are added to the mixed solution, and the obtained precipitate is washed several times after reaction for a period of time, and dried, to obtain all-organic heterojunction photocatalyst.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and energy materials, and more specifically, relates to an all-organic heterojunction photocatalyst and its preparation method. Background Technology

[0002] Hydrogen peroxide is an essential oxidant and disinfectant, widely used in environmental protection, healthcare, and food processing. Traditionally, hydrogen peroxide production has heavily relied on industrial chemical methods, which face challenges such as high energy consumption, high cost, and environmental pollution. In recent years, photocatalytic hydrogen peroxide production has attracted increasing attention, utilizing photocatalysts to directly convert water and oxygen into hydrogen peroxide upon exposure to light. This innovative method not only demonstrates superior efficiency and minimal energy requirements but also offers broad prospects for environmental sustainability.

[0003] Photocatalytic hydrogen peroxide production revolves around the generation of electron-hole pairs on the surface of the photocatalyst, thereby promoting water oxidation and oxygen reduction reactions to ultimately produce hydrogen peroxide. Sacrificial agents in the photocatalytic reaction are mainly used to consume photogenerated electrons or holes; however, these sacrificial agents reduce the yield of hydrogen peroxide. Furthermore, the introduction of sacrificial agents complicates the photocatalytic system, leading to competition between multiple reaction pathways. Therefore, selecting a suitable photocatalyst is crucial for the efficient and selective production of hydrogen peroxide. Summary of the Invention

[0004] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes an all-organic heterojunction photocatalyst and its preparation method. The all-organic heterojunction photocatalyst prepared by the method of the present invention can improve the efficiency of photocatalytic hydrogen peroxide production in pure water. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production applications.

[0005] Therefore, in a first aspect, embodiments of the present invention provide an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and a phenolic resin heterojunction photocatalyst, wherein the mass ratio of the porphyrin-based metal-organic framework to the phenolic resin is (0.05-4):1.

[0006] Secondly, embodiments of the present invention provide a method for preparing the all-organic heterojunction photocatalyst provided in the first aspect above. The preparation method includes: Step S1: adding a certain amount of carboxylic acid ligand, metal salt, porphyrin ligand and a certain volume of organic solvent into a hydrothermal reactor and ultrasonically dispersing them to obtain a mixture; Step S2: transferring the mixture into an electric oven, heating it for a certain time, cooling it to room temperature, washing it multiple times, and then drying and activating it to obtain a porphyrin-based metal-organic framework; Step S3: adding a certain amount of phenol ligand and the porphyrin-based metal-organic framework into a certain volume of solution and dispersing it to obtain a mixed solution; Step S4: adding formaldehyde solution and ammonia solution to the mixed solution, keeping it at a certain temperature for a period of time, and after the reaction is completed, washing the obtained precipitate several times and drying it to obtain the all-organic heterojunction photocatalyst.

[0007] Preferably, the carboxylic acid ligand is one or a combination of several selected from terephthalic acid, 2-aminoterephthalic acid, benzoic acid, and phthalic acid; the metal salt is one or a combination of several selected from hafnium chloride, hafnium chloride oxychloride, zirconium chloride, zirconium oxychloride, zinc chloride, nickel chloride, nickel nitrate, copper nitrate, cobalt acetate, and ferric chloride; the porphyrin ligand is one or a combination of several selected from MESO-tetra(4-carboxyphenyl)porphyrin, 5,15-bis(4-carboxyphenyl)porphyrin, Ni-TCPP (tetracarboxyphenylporphyrin nickel), Cu-TCPP (tetracarboxyphenylporphyrin copper), Zn-TCPP (tetracarboxyphenylporphyrin zinc), and Co-TCPP (tetracarboxyphenylporphyrin cobalt); and the organic solvent is one or a combination of several selected from N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, and dimethyl sulfoxide.

[0008] Preferably, in step S1, the molar ratio of the carboxylic acid ligand, metal salt, porphyrin ligand, and organic solvent is (100-600):1:1:(1000-80000).

[0009] Preferably, in step S2, the heating temperature is 100-140℃ and the heating time is 12-72h; the washing liquid used during washing is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, dimethyl sulfoxide or acetone.

[0010] Preferably, in step S2, the drying method is vacuum drying, the drying temperature is 60-250℃, and the drying time is 12-72h.

[0011] Preferably, in step S3, the phenol ligand is one or more of resorcinol, m-aminophenol, 3,3'-biphenol, and 2,2'-binaphthol, and the solution is water.

[0012] Preferably, in step S4, the volume ratio of the formaldehyde solution to the ammonia solution is (1-5):1; the heat preservation temperature is 30-250℃, and the heat preservation time is 0.5-24h.

[0013] Preferably, in step S4, the washing method is one or a combination of centrifugal washing and vacuum filtration washing, and the washing agent is one or a combination of methanol, anhydrous ethanol, or water.

[0014] Preferably, in step S4, the drying method is one or more of the following: forced air drying, vacuum drying, freeze drying, and spray drying, and the drying time is 24 hours.

[0015] The all-organic heterojunction photocatalyst and its preparation method provided in this invention couple a phenolic resin with a donor-acceptor structure to a porphyrin-based metal-organic framework with a high specific surface area to form an all-organic heterojunction. This optimizes charge separation efficiency while maximizing the system's redox capacity. The all-organic heterojunction photocatalyst prepared by this invention significantly accelerates the oxygen reduction reaction kinetically through excellent adsorption of oxygen intermediates. Simultaneously, the generation of a built-in electric field at the interface provides an effective driving force for charge separation. This heterojunction electron transfer mechanism effectively suppresses rapid electron-hole recombination and significantly improves photocatalytic activity, exhibiting excellent photocatalytic hydrogen peroxide production activity in pure water, tap water, surface water, and saline systems. Furthermore, the all-organic heterojunction photocatalyst provided by this invention has many advantages, including a simple preparation process, environmentally friendly and inexpensive raw materials, and strong photocatalytic hydrogen peroxide production activity, showing broad application and industrialization prospects in the energy and environmental fields. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the preparation method of the all-organic heterojunction photocatalyst provided in this embodiment of the invention;

[0017] Figure 2 Transmission electron microscope image of the all-organic heterojunction photocatalyst prepared in Example 1 of the present invention. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided, but those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0020] The purpose of this invention is to provide an all-organic heterojunction photocatalyst and its preparation method. By coupling a phenolic resin with a donor-acceptor structure with a porphyrin-based metal-organic framework with a high specific surface area, a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst is prepared. This preparation method maximizes the redox capability of the system while optimizing the charge separation efficiency, thereby improving the stability and production efficiency of the photocatalytic system.

[0021] A first aspect of this invention provides an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and a phenolic resin heterojunction photocatalyst. The mass ratio of the porphyrin-based metal-organic framework to the phenolic resin is (0.05-4):1. Under visible light irradiation, the porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst continuously generates hydrogen peroxide from water and oxygen, and the resulting high-purity hydrogen peroxide solution is used in situ for pollutant degradation.

[0022] The all-organic heterojunction photocatalyst provided in this embodiment greatly accelerates the oxygen reduction reaction kinetically through the good adsorption of oxygen intermediates. At the same time, the generation of the built-in electric field at the interface provides an effective driving force for charge separation. This heterojunction electron transfer mechanism effectively inhibits the rapid recombination of electrons and holes and significantly improves photocatalytic activity. It has excellent photocatalytic hydrogen peroxide production activity in pure water, tap water, surface water and salt water systems.

[0023] A second aspect of this invention provides a method for preparing an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst. For example... Figure 1 As shown, the preparation method includes the following steps:

[0024] Step S1: A certain amount of carboxylic acid ligand, metal salt, porphyrin ligand and a certain volume of organic solvent are added to a hydrothermal reactor and ultrasonically dispersed to obtain a mixture;

[0025] Wherein, the carboxylic acid ligand can be one or a combination of several of terephthalic acid, 2-aminoterephthalic acid, benzoic acid, and phthalic acid; the metal salt can be one or a combination of several of hafnium chloride, hafnium chloride oxychloride, zirconium chloride, zirconium chloride oxychloride, zinc chloride, nickel chloride, nickel nitrate, copper nitrate, cobalt acetate, and ferric chloride; the porphyrin ligand can be one or a combination of several of MESO-tetra(4-carboxyphenyl)porphyrin, 5,15-bis(4-carboxyphenyl)porphyrin, Ni-TCPP (tetracarboxyphenylporphyrin nickel), Cu-TCPP (tetracarboxyphenylporphyrin copper), Zn-TCPP (tetracarboxyphenylporphyrin zinc), and Co-TCPP (tetracarboxyphenylporphyrin cobalt); and the organic solvent can be one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, and dimethyl sulfoxide. In this embodiment of the invention, the molar ratio of the carboxylic acid ligand, metal salt, porphyrin ligand, and organic solvent is (100-600):1:1:(1000-80000).

[0026] Step S2: The mixture is transferred to an electric oven, heated for a certain time, cooled to room temperature, washed multiple times, and then dried and activated to obtain a porphyrin-based metal-organic framework.

[0027] The heating temperature can be 100-140℃, and the heating time can be 12-72h; the washing solution used during washing can be one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, dimethyl sulfoxide, or acetone, and the number of washing cycles can be 6-10; the drying method is vacuum drying, the drying temperature can be 60-250℃, and the drying time can be 12-72h.

[0028] Step S3: Add a certain amount of phenol ligand and the porphyrin-based metal-organic framework to a certain volume of solution, and disperse to obtain a mixed solution;

[0029] The phenol ligand may be one or more of resorcinol, m-aminophenol, 3,3'-biphenol, and 2,2'-binaphthol; the solution is water.

[0030] Step S4: Add formaldehyde solution and ammonia solution to the mixed solution, keep warm for a period of time, and after the reaction is complete, wash the resulting precipitate several times and dry it to obtain the all-organic heterojunction photocatalyst.

[0031] The volume ratio of formaldehyde solution to ammonia solution is (1-5):1; the heat preservation temperature can be 30-250℃, and the heat preservation time can be 0.5-24h; the washing method can be one or a combination of centrifugal washing and vacuum filtration washing, the washing agent can be one or a combination of methanol, anhydrous ethanol, or water, and the number of washing times can be 6-10; the drying method can be one or more of forced air drying, vacuum drying, freeze drying, and spray drying, and the drying time can be 24h. In this embodiment of the invention, the mass ratio of porphyrin-based metal-organic framework to phenolic resin in the all-organic heterojunction photocatalyst is 0.05-4:1.

[0032] The method for preparing an all-organic heterojunction photocatalyst provided in this invention couples a phenolic resin with a donor-acceptor structure to a porphyrin-based metal-organic framework with a high specific surface area to form an all-organic heterojunction. This optimizes charge separation efficiency while maximizing the system's redox capability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

[0033] The all-organic heterojunction photocatalyst prepared by the method of this invention significantly accelerates the oxygen reduction reaction kinetically through good adsorption of oxygen intermediates and effectively inhibits the photocorrosion of porphyrin-based metal-organic frameworks, thereby improving the stability of the photocatalytic system. Furthermore, the all-organic heterojunction photocatalyst can directly and continuously produce high-purity hydrogen peroxide solution in situ from oxygen and water in a sacrificial agent-free system, thereby improving the efficiency of photocatalytic hydrogen peroxide production.

[0034] The following detailed description, in conjunction with some specific embodiments, further illustrates the specific process and effects of the preparation method of the all-organic heterojunction photocatalyst of the present invention, but does not limit the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment provides a method for preparing an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst, and the preparation method includes the following steps:

[0037] Step S1: Add 500g of benzoic acid, 40mg of hafnium chloride, 30mg of MESO-tetra(4-carboxyphenyl)porphyrin and 8mL of N,N-dimethylformamide to a hydrothermal reactor and disperse by ultrasonication to obtain a mixture;

[0038] Step S2: The obtained mixture was transferred to an electric oven and heated at 120°C for 72 hours. After cooling to room temperature, it was washed 5 times each with N,N-dimethylformamide and acetone, and then dried and activated at 60°C for 24 hours to obtain porphyrin-based metal-organic frameworks.

[0039] Step S3: Add 20 mg of m-aminophenol ligand and 20 mg of porphyrin-based metal-organic framework to 30 mL of aqueous solution, disperse to obtain a mixed solution;

[0040] Step S4: Transfer the obtained mixed solution to an oil bath, add 300 μL of formaldehyde solution and 100 μL of ammonia solution, keep warm at 30 °C and stir for 30 min. After the reaction is complete, wash the obtained precipitate three times each with water and anhydrous ethanol, and dry to obtain the porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst.

[0041] Figure 2 The image shown is a transmission electron microscope image of the heterojunction photocatalyst of porphyrin-based metal-organic framework and phenolic resin prepared in this embodiment.

[0042] Example 2

[0043] This embodiment provides a method for preparing an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst, and the preparation method includes the following steps:

[0044] Step S1: Add 500g of benzoic acid, 40mg of zirconium chloride, 30mg of MESO-tetra(4-carboxyphenyl)porphyrin and 10mL of N,N-dimethylformamide to a hydrothermal reactor and disperse by ultrasonication to obtain a mixture;

[0045] Step S2: The obtained mixture was transferred to an electric oven and heated at 120°C for 72 hours. After cooling to room temperature, it was washed 5 times each with N,N-dimethylformamide and acetone, and then dried and activated at 60°C for 24 hours to obtain porphyrin-based metal-organic frameworks.

[0046] Step S3: Add 30 mg of m-aminophenol ligand and 20 mg of porphyrin-based metal-organic framework to 30 mL of aqueous solution, disperse to obtain a mixed solution;

[0047] Step S4: Transfer the obtained mixed solution to an oil bath, add 300 μL of formaldehyde solution and 100 μL of ammonia solution, keep warm at 30°C and stir for 24 h. After the reaction is complete, wash the obtained precipitate three times each with water and anhydrous ethanol, and dry to obtain the porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst.

[0048] Example 3

[0049] This embodiment provides a method for preparing an all-organic heterojunction photocatalyst, wherein the all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst, and the preparation method includes the following steps:

[0050] Step S1: Add 2700g of benzoic acid, 70mg of zirconium tetrachloride, 50mg of Ni-TCPP (tetracarboxyphenylporphyrin nickel) and 8mL of N,N-diethylformamide to a hydrothermal reactor and disperse by ultrasonication to obtain a mixture;

[0051] Step S2: The obtained mixture was transferred to an electric oven, heated at 130°C for 24 hours and then cooled to room temperature. It was washed 5 times each with N,N-diethylformamide and acetone, and then dried and activated at 60°C for 24 hours to obtain porphyrin-based metal-organic frameworks.

[0052] Step S3: Add 50 mg of m-aminophenol ligand and 20 mg of porphyrin-based metal-organic framework to 30 mL of aqueous solution, disperse to obtain a mixed solution;

[0053] Step S4: Transfer the obtained mixed solution to an oil bath, add 80 μL of formaldehyde solution and 20 μL of ammonia solution, keep warm at 30°C and stir for 30 min. After the reaction is complete, wash the obtained precipitate three times each with water and anhydrous ethanol, and dry to obtain the porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst.

[0054] To verify the quality of the all-organic heterojunction photocatalyst prepared by the preparation method of the all-organic heterojunction photocatalyst provided in the embodiments of the present invention, the all-organic heterojunction photocatalysts prepared in Examples 1-3 above were tested using the PerfectLight multichannel photocatalytic reaction system, and the test results are shown in Table 1.

[0055] Table 1. Test items and test results for Examples 1-3

[0056] Example sequence number water quality <![CDATA[Hydrogen peroxide yield (μmol.g -1 .h -1 )]]> Example 1 pure water 2977.5 Example 2 River water 2550.73 Example 3 brine 2092.935

[0057] In summary, the method for preparing the all-organic heterojunction photocatalyst provided in this invention couples a phenolic resin with a donor-acceptor structure to a porphyrin-based metal-organic framework with a high specific surface area to form an all-organic heterojunction, maximizing the system's redox capability while optimizing charge separation efficiency. Furthermore, this preparation method has a simple process flow and is suitable for large-scale industrial production applications.

[0058] The all-organic heterojunction photocatalyst prepared by the method of this invention significantly accelerates the oxygen reduction reaction kinetically through excellent adsorption of oxygen intermediates. Simultaneously, the built-in electric field at the interface provides an effective driving force for charge separation. This heterojunction electron transfer mechanism effectively suppresses rapid electron-hole recombination and significantly improves photocatalytic activity. It exhibits excellent photocatalytic hydrogen peroxide production activity in pure water, tap water, surface water, and saline systems. The all-organic heterojunction photocatalyst provided by this invention has many advantages, including a simple preparation process, environmentally friendly and inexpensive raw materials, and strong photocatalytic hydrogen peroxide production activity, showing broad application and industrialization prospects in the energy and environmental fields.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An all-organic heterojunction photocatalyst, characterized in that, The all-organic heterojunction photocatalyst is a porphyrin-based metal-organic framework and phenolic resin heterojunction photocatalyst, wherein the mass ratio of the porphyrin-based metal-organic framework to the phenolic resin is (0.05-4):

1.

2. A method for preparing an all-organic heterojunction photocatalyst as described in claim 1, characterized in that, The preparation method includes: Step S1: A certain amount of carboxylic acid ligand, metal salt, porphyrin ligand and a certain volume of organic solvent are added to a hydrothermal reactor and ultrasonically dispersed to obtain a mixture; Step S2: The mixture is transferred to an electric oven, heated for a certain time, cooled to room temperature, washed multiple times, and then dried and activated to obtain a porphyrin-based metal-organic framework. Step S3: Add a certain amount of phenol ligand and the porphyrin-based metal-organic framework to a certain volume of solution, and disperse to obtain a mixed solution; Step S4: Add formaldehyde solution and ammonia solution to the mixed solution, keep warm for a period of time, and after the reaction is complete, wash the resulting precipitate several times and dry it to obtain the all-organic heterojunction photocatalyst.

3. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S1, the carboxylic acid ligand is one or a combination of several of terephthalic acid, 2-aminoterephthalic acid, benzoic acid, and phthalic acid; the metal salt is one or a combination of several of hafnium chloride, hafnium oxychloride, zirconium chloride, and zirconium oxychloride; the porphyrin ligand is one or a combination of several of MESO-tetra(4-carboxyphenyl)porphyrin, 5,15-bis(4-carboxyphenyl)porphyrin, nickel tetracarboxyphenylporphyrin Ni-TCPP, copper tetracarboxyphenylporphyrin Cu-TCPP, zinc tetracarboxyphenylporphyrin Zn-TCPP, and cobalt tetracarboxyphenylporphyrin Co-TCPP; and the organic solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, and dimethyl sulfoxide.

4. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S1, the molar ratio of the carboxylic acid ligand, metal salt, porphyrin ligand, and organic solvent is (100-600):1:1:(1000-80000).

5. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S2, the heating temperature is 100-140℃ and the heating time is 12-72h; the washing liquid used during washing is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, dimethyl sulfoxide or acetone.

6. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S2, the drying method is vacuum drying, the drying temperature is 60-250℃, and the drying time is 12-72h.

7. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S3, the phenol ligand is one or more of resorcinol and m-aminophenol, and the solution is water.

8. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S4, the volume ratio of formaldehyde solution to ammonia solution is (1-5):1; the heat preservation temperature is 30-250℃, and the heat preservation time is 0.5-24h.

9. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S4, the washing method is one or a combination of centrifugal washing and vacuum filtration washing, and the washing agent is methanol, anhydrous ethanol or water.

10. The method for preparing the all-organic heterojunction photocatalyst according to claim 2, characterized in that, In step S4, the drying method is one or more of the following: forced air drying, vacuum drying, freeze drying, and spray drying, and the drying time is 24 hours.

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