Controllable Preparation Method of Hierarchical Porous ZSM-5 Molecular Sieve Microspheres and Its Application in Loudspeakers

Abstract

A controllable preparation method of hierarchical pore ZSM-5 zeolite microspheres and its application in loudspeakers, belonging to the technical field of acoustic material preparation. Using surfactant silica composite nanoparticles and fumed silica as the mixed silicon source, sodium aluminate as the aluminum source, and sodium hydroxide as the base source, adding pre-prepared ZSM-5 zeolite seeds, ZSM-5 zeolites with tertiary and quaternary pore structures were synthesized. ZSM-5 zeolite microspheres were prepared by spray drying, and finally ZSM-5 zeolite microspheres with quaternary and even quinary pores were obtained after calcination. The ZSM-5 zeolite microspheres prepared by this method have the characteristics of adjustable structure, pore size and high crystallinity, and have important application prospects in the fields of catalytic loading, chemical industry, acoustic enhancement materials, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of acoustic materials, and particularly relates to a controllable preparation method of hierarchical pore ZSM-5 type molecular sieve microspheres. Background Art

[0002] With the development of social economy and the rapid progress of technology, people's requirements for the quality of electronic products are getting higher and higher, especially for the sound quality of speakers. However, nowadays, electronic products pay more and more attention to function integration and miniaturization, which greatly limits the design space of speakers. High-quality large speakers are difficult to be used to improve the sound of small speakers. To correct the sound quality in the low-frequency range of small speakers, a common practice is to create a space in the rear cavity of the mobile phone to enhance the intensity of the sound emitted by the speaker. In the 1970s, scientists found that at specific sound wave frequencies, the pores in solid materials would deform. To further improve the sound quality in the low-frequency range of small speakers, a common practice is to add gas-adsorbing porous material particles to the rear cavity of the speaker, and use the structure and physical properties of these particles to absorb high-frequency noise, thereby improving the sound quality.

[0003] ZSM-5 type molecular sieve is a crystalline aluminosilicate material with a double ten-membered ring intersecting pore structure. It is a microporous material with special pore sizes and shapes. Filling the molecular sieve into the rear cavity of a small speaker, the vibration of sound waves causes air to rapidly adsorb and desorb on the active sites of the molecular sieve. The sound waves are conducted in the pore structure of the molecular sieve. Reasonably controlling the pore size will absorb high-frequency noise and improve the sound quality. Since the initial particle size of the molecular sieve powder is small, directly filling it into the rear cavity of the speaker will cause the powder to leak into the speaker interior and damage the circuit. Therefore, it is necessary to prepare the molecular sieve into a certain shape. Therefore, the initial powder of the molecular sieve with a larger particle size and a hierarchical pore structure is beneficial to the rapid conduction of sound.

[0004] Patent CN 115259177 A discloses a hierarchical pore ZSM-5 molecular sieve for VOCs adsorption and its preparation method. This method uses the repeated hydrothermal method, the steps are cumbersome, and only microporous and mesoporous structures are obtained. The specific surface area of the sample is 364.2 m 2 ·g -1 , the micropore volume is 0.10 cm 3 ·g -1 , the mesopore volume is 0.17 cm 3 ·g -1Patent CN104511296 A discloses a porous molecular sieve composite material and its preparation method. Although a tertiary pore structure including micropores, mesopores, and macropores is obtained by this method, the crystallinity of the molecular sieve composite material is relatively low, and only 20 - 70% of it is NaY type molecular sieve, which seriously affects the catalytic activity of the molecular sieve. Patent CN 108479858 A discloses a binderless spray forming process for improving the strength of molecular sieve catalysts. By using the binderless spray forming process to improve the strength of molecular sieve catalysts, after spray forming, through drying and calcination, the internal and external parts of the catalyst particles shrink uniformly, increasing the compactness of the catalyst particles, and ultimately improving the abrasion resistance strength of the catalyst. However, this patent does not mention increasing the hierarchical pore structure and particle size control of molecular sieve microspheres through spray forming. Summary of the Invention

[0005] The purpose of the present invention is to solve the deficiencies of the prior art and provide a controllable preparation method for hierarchical pore ZSM-5 type molecular sieve microspheres. The hierarchical pore ZSM-5 type molecular sieve microspheres prepared by the present invention have the advantages of adjustable pore size and structure, and have important application prospects in fields such as the chemical industry and functional materials.

[0006] A controllable preparation method for hierarchical pore ZSM-5 type molecular sieve microspheres includes the following steps:

[0007] (1) Preparation of seed crystals: Dissolve the structure-directing agent in a solvent and stir evenly, add tetraethyl orthosilicate and mix evenly, and load the completely mixed mixture into an autoclave for hydrothermal crystallization to obtain a seed crystal suspension;

[0008] (2) Synthesis of surfactant-silica composite nanoparticles: Dissolve the base source and surfactant in water and stir evenly, add the silicon source to the above solution and stir. After the reaction, recover, wash, and dry to obtain surfactant-silica composite nanoparticles, which serve as silicon source 1 for the next reaction;

[0009] (3) Preparation of hierarchical pore molecular sieve: Dissolve the base source and aluminum source in water and stir evenly, sequentially add the seed crystal suspension, silicon source 1, and silicon source 2. After the reactants are subjected to low-temperature reaction, transfer them to an autoclave for hydrothermal crystallization, recover the precipitate and wash it thoroughly with water; Add deionized water to the above precipitate to prepare a suspension with a certain solid content, and obtain microspheres with different particle sizes through spray drying; The spray microspheres are calcined to obtain the final hierarchical pore ZSM-5 type molecular sieve microspheres.

[0010] The above-mentioned controllable preparation method for hierarchical pore ZSM-5 type molecular sieve microspheres, wherein:

[0011] In the step (1), the structure-directing agent is one or a combination of more than one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; preferably, the structure-directing agent is tetrapropylammonium hydroxide. The solvent is a mixed solution of water and ethanol.

[0012] In the step (1), during the hydrothermal crystallization process, the hydrothermal temperature is 80 - 130 °C, and the hydrothermal time is 24 - 120 h; preferably, the hydrothermal temperature is 100 °C and the hydrothermal time is 96 h.

[0013] In the step (2), the surfactant is one or a combination of two of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride; preferably, the surfactant is cetyltrimethylammonium bromide (CTAB). The silicon source is tetraethyl orthosilicate (TEOS).

[0014] In the step (2), the reaction temperature is 50 - 100 °C, and the time is 1 - 4 h.

[0015] In the steps (2) - (3), the base source is one or a combination of more than one of ammonia water, sodium hydroxide, and potassium hydroxide; preferably, the base source is sodium hydroxide.

[0016] In the step (3), the silicon source 2 is one or a combination of more than one of silica sol, water glass, tetraethyl orthosilicate, and silicon dioxide; preferably, the silicon source 2 is fumed silica. The aluminum source is one or a combination of more than one of sodium aluminate, pseudoboehmite, aluminum sulfate, aluminum isopropoxide, aluminum chloride, and aluminum nitrate; preferably, the aluminum source is sodium aluminate.

[0017] In the step (3), the hydrothermal crystallization conditions are 100 - 180 °C, and the time is 12 - 48 h.

[0018] In the step (3), the solid content of the prepared suspension is 5% - 40%.

[0019] In the step (3), the spray drying conditions are: pressure spray drying is carried out at an inlet temperature of 110 - 200 °C, an outlet temperature of 70 - 140 °C, and a feed rate of 400 - 800 ml / h. The particle size of the microspheres obtained by spray drying is 1 - 500 μm. The calcination temperature is 400 - 600 °C, and the calcination time is 3 - 6 h.

[0020] The hierarchical pore ZSM-5 type molecular sieve microspheres prepared by the preparation method contain four-level or five-level pores, including micropores, hierarchical mesopores and macropores; the micropore pore diameter ranges from 0.5 to 1.5 nm, the hierarchical mesopore pore diameter ranges from 2 to 50 nm, and the macropore pore diameter ranges from 50 to 300 nm. Taking the five-level pore ZSM-5 type molecular sieve microspheres as an example, its five-level pores ( Figure 3 ) are as follows: The first-level pores are the characteristic micropores of ZSM-5 molecular sieve, and the pore diameter range is about 0.5 nm; the second-level pores are the mesopores of the molecular sieve, and the pore diameter range is 1.5 - 2.0 nm; the third-level pores are the mesopores of the molecular sieve, and the pore diameter range is 2.5 - 4.0 nm; the fourth-level pores are the mesopores of the molecular sieve, and the pore diameter range is 15 - 35 nm; the fifth-level pores are the inter-particle macropores formed during spray drying, and the pore diameter range is 40 - 300 nm, and the micropore pore volume is 0.10 cm 3 ·g -1 , the mesopore pore volume is 0.18 cm 3 ·g -1 .

[0021] Another object of the present invention is to fill the prepared hierarchical pore ZSM-5 type molecular sieve microspheres into the rear cavity of a small speaker as an acoustic enhancement material to improve the sound quality of the speaker in the low-frequency range.

[0022] Beneficial effects of the present invention:

[0023] The present invention increases the hierarchical pore structure ( Figure 1 ) of the molecular sieve microspheres through spray forming, and the particle size of the molecular sieve microspheres can be controllably prepared in the range of 1 - 500 μm.

[0024] The hierarchical pore ZSM-5 type molecular sieve microspheres prepared by the method of the present invention have a four-level or five-level pore structure: micropores, three-level mesopores, and macropores, with a relatively developed pore structure and a relatively high crystallinity ( Figure 2 ), and its crystallinity reaches 99% (Table 1, with the crystallinity of the ZSM-5 type molecular sieve produced by the Catalysis Factory of Nankai University as 100% as a reference). Description of the drawings

[0025] Figure 1 It is the scanning electron microscope image of the molecular sieve microspheres after spray drying in Example 2;

[0026] Figure 2 It is the X-ray diffraction pattern of the sample in Example 2;

[0027] Figure 3 It is the nitrogen adsorption-desorption curve and pore size distribution curve of the sample in Example 2;

[0028] Figure 4Graph of the acoustic performance test results for Example 2; (a) Graph of the sound pressure level (SPL) test of the speaker filled and unfilled with the sample of Example 2; (b) Difference (ΔSPL) in the sound pressure level of the filled and unfilled samples of Example 2.

[0029] Figure 5 Graph of the acoustic performance test results for Example 4; (a) Graph of the sound pressure level (SPL) test of the speaker filled and unfilled with the sample of Example 4; (b) Difference (ΔSPL) in the sound pressure level of the filled and unfilled samples of Example 4.

[0030] Figure 6 Graph of the acoustic performance test results for Example 6; (a) Graph of the sound pressure level (SPL) test of the speaker filled and unfilled with the sample of Example 6; (b) Difference (ΔSPL) in the sound pressure level of the filled and unfilled samples of Example 6. Detailed implementation mode

[0031] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will be described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0032] Example 1

[0033] A controllable preparation method for penta - pore ZSM - 5 type molecular sieve microspheres, and the specific operation steps are as follows:

[0034] (1) Preparation of seed crystals

[0035] First, add 15 g of deionized water, 9.7 g of ethanol, and 10.4 g of tetrapropylammonium hydroxide into a beaker, place it in a constant temperature water bath at 30 °C and stir for 30 min until the solution is uniformly mixed. Then add 10.9 g of tetraethyl orthosilicate and continue to stir at room temperature for 2 h. Put the mixture into a polytetrafluoroethylene bottle and place it in an autoclave, and carry out hydrothermal treatment at 100 °C for 96 h to obtain a seed crystal suspension.

[0036] (2) Synthesis of surfactant - silica composite nanoparticles

[0037] First, add 1.4 g of 2M NaOH solution and 0.4 g of CTAB into 192 g of deionized water, place it in a constant temperature water bath at 80 °C and stir for 40 min. After the above - mentioned mixed solution is uniform, slowly add 1.89 g of TEOS dropwise to the mixed solution and continuously stir for 2 h. Then take it out from the constant temperature water bath and cool it to room temperature. Carry out centrifugation treatment, wash until neutral, and place it in an oven at 80 °C to dry for 12 h to obtain surfactant - silica composite nanoparticles, which are used as silicon source 1 for the next reaction.

[0038] (3) Preparation of penta - pore molecular sieve

[0039] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, slowly add 0.4 g of the seed suspension, 1.0 g of surfactant silica composite nanoparticles (silica source 1), and 1.99 g of fumed silica (silica source 2) to the above mixed solution in sequence, and continue to stir at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After hydrothermal treatment, centrifuge, wash with deionized water until neutral, and prepare the precipitate into a suspension with a solid content of 15% for spray drying. The feed rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain the hierarchical pore ZSM-5 zeolite microspheres. Compared with Example 2, the mesopore volume of the second stage is smaller, and the total mesopore volume is also small.

[0040] Example 2

[0041] A controllable preparation method of hierarchical pore ZSM-5 zeolite microspheres, and the specific operation steps are as follows:

[0042] (1) Preparation of seeds

[0043] First, add 15 g of deionized water, 9.7 g of ethanol, and 10.4 g of tetrapropylammonium hydroxide to a beaker, place it in a constant temperature water bath at 30 °C and stir for 30 min until the solution is evenly mixed, then add 10.9 g of tetraethyl orthosilicate, and continue to stir at room temperature for 2 h. Load the mixture into a polytetrafluoroethylene bottle and place it in an autoclave. Perform hydrothermal treatment at 100 °C for 96 h to obtain the seed suspension.

[0044] (2) Synthesis of surfactant silica composite nanoparticles

[0045] First, add 1.4 g of 2 M NaOH solution and 0.4 g of CTAB to 192 g of deionized water, place it in a constant temperature water bath at 80 °C and stir for 40 min. After the above mixed solution is uniform, slowly drop 1.89 g of TEOS into the mixed solution, and continuously stir for 2 h. Then take it out of the constant temperature water bath and cool to room temperature. Perform centrifugation, wash until neutral, and place it in an oven at 80 °C to dry for 12 h to obtain the surfactant silica composite nanoparticles, which are used as silica source 1 for the next reaction.

[0046] (3) Preparation of hierarchical pore zeolite

[0047] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, slowly add 0.8 g of the seed suspension, 1.0 g of surfactant silica composite nanoparticles (silica source 1), and 1.99 g of fumed silica (silica source 2) to the above mixed solution in sequence, and continue to stir at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After hydrothermal treatment, centrifuge and wash with deionized water until neutral. Prepare the precipitate into a suspension with a solid content of 15% for spray drying. The molecular sieve microsphere structure after spray drying is as Figure 1 shown. The feeding rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain a hierarchical pore ZSM-5 type molecular sieve microsphere. The X-ray diffraction pattern of the sample is as Figure 2 shown. The nitrogen adsorption-desorption curve and pore size distribution curve are as Figure 3 shown. It can be seen from Figure 3 that the product prepared in Example 2 is a five-level pore ZSM-5 type molecular sieve microsphere. Its first-level pore channels are the characteristic micropores of ZSM-5 molecular sieve, with a pore size range of about 0.5 nm; the second-level pore channels are the mesopores of the molecular sieve, with a pore size range of 1.5 - 2.0 nm; the third-level pore channels are the mesopores of the molecular sieve, with a pore size range of 2.5 - 4.0 nm; the fourth-level pore channels are the mesopores of the molecular sieve, with a pore size range of 15 - 35 nm; the fifth-level pores are the macropores between particles formed during spray drying, with a pore size range of 40 - 300 nm. The micropore pore volume is 0.10 cm 3 ·g -1 , and the mesopore pore volume is 0.18 cm 3 ·g -1 .

[0048] Apply the five-level pore ZSM-5 type molecular sieve microsphere prepared in this example to a speaker. The results of its acoustic performance diagram are as Figure 4 shown. At low frequencies, the frequency range with enhanced performance is relatively wide. The overall performance improvement intensity is 2.6 - 2.7 dB, and the performance can be maintained above 2.5 dB at 500 Hz.

[0049] Example 3

[0050] Same as Example 2. The difference from Example 2 is that during the preparation of the five-level pore molecular sieve in step (3), the addition amount of the seed suspension is increased. Step (3) is specifically as follows:

[0051] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, slowly add 1.6 g of seed suspension, 1.0 g of surfactant silica composite nanoparticles (silica source 1), and 1.99 g of fumed silica (silica source 2) to the above mixed solution in sequence, and continue to stir at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After hydrothermal treatment, centrifuge and wash with deionized water until neutral. Prepare the precipitate into a suspension with a solid content of 15% for spray drying. The feed rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain pentaporous ZSM-5 molecular sieve microspheres. Compared with Example 2, the pore volume of the first-order mesopores decreases, and the total mesopore volume also decreases.

[0052] Example 4

[0053] Same as Example 2, the difference from Example 2 is that 1.0 g of surfactant silica composite nanoparticles (silica source 1) is not added during the preparation of the hierarchical pore molecular sieve in step (3). Step (3) is specifically as follows:

[0054] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, slowly add 0.8 g of seed suspension and 1.99 g of fumed silica (silica source 2) to the above mixed solution in sequence, and continue to stir at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After hydrothermal treatment, centrifuge and wash with deionized water until neutral. Prepare the precipitate into a suspension with a solid content of 15% for spray drying. The feed rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain tritoporous ZSM-5 molecular sieve microspheres. Compared with Example 2, only the 1st-order mesoporous structure remains.

[0055] Apply the tritoporous ZSM-5 molecular sieve microspheres prepared in Example 4 to a speaker, and the results of its acoustic performance graph are as Figure 5 shown. At low frequencies, the frequency range with enhanced performance is relatively narrow, and the overall performance improvement intensity is 2.2 - 2.3 dB. The enhanced performance significantly decreases at 400 Hz, and the performance drops below 2.0 dB at 500 Hz. This shows that in the technical solution of the present invention, the acoustic performance can be significantly improved only under the condition of a dual silica source.

[0056] Example 5

[0057] Same as Example 2. The difference from Example 2 is that during the preparation of the hierarchical zeolite in step (3), the addition amount of the surfactant-silica composite nanoparticles (silica source 1) is increased. Step (3) is specifically as follows:

[0058] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, sequentially and slowly add 0.8 g of the seed suspension, 2.0 g of the surfactant-silica composite nanoparticles (silica source 1), and 1.99 g of fumed silica (silica source 2) to the above mixed solution, and continue stirring at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After the hydrothermal treatment, centrifuge, wash with deionized water until neutral, prepare the precipitate into a suspension with a solid content of 15% for spray drying. The feed rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain the hierarchical pore ZSM-5 zeolite microspheres. Compared with Example 2, the third-level mesopores disappear.

[0059] Increasing the addition amount of silica source 1 is beneficial to increasing the pore volume of the second-level mesopores of the sample, but the pore volume of the first-level mesopores decreases, and the total mesopore volume decreases relatively, and the improvement of the acoustic enhancement performance is not obvious.

[0060] Example 6

[0061] Same as Example 2. The difference from Example 2 is that during the preparation of the hierarchical zeolite in step (3), the solid content of the suspension is increased to 30%. Step (3) is specifically as follows:

[0062] Dissolve 0.34 g of sodium hydroxide and 0.04 g of sodium aluminate in 32 g of deionized water. After stirring at room temperature for 30 min, sequentially and slowly add 0.8 g of the seed suspension, 1.0 g of the surfactant-silica composite nanoparticles (silica source 1), and 1.99 g of fumed silica (silica source 2) to the above mixed solution, and continue stirring at room temperature for 2 h. Load the well-stirred mixture into a polytetrafluoroethylene bottle and place it in an autoclave. First, perform hydrothermal treatment at a low temperature of 120 °C for 12 h, and then perform hydrothermal treatment at a high temperature of 170 °C for 24 h. After the hydrothermal treatment, centrifuge, wash with deionized water until neutral, prepare the precipitate into a suspension with a solid content of 30% for spray drying. The feed rate of the spray dryer is 600 ml / h, the inlet temperature is 130 °C, and the outlet temperature is 90 °C. The sample obtained by spray drying is calcined at a calcination temperature of 500 °C for 4 h to obtain the hierarchical pore ZSM-5 zeolite microspheres.

[0063] Compared with Example 2, the macropore volume decreases and the particle size of the microspheres after spraying becomes larger.

[0064] The microspheres of five-level pore ZSM-5 zeolite prepared in this example are applied to the speaker, and the results of its acoustic performance diagram are as Figure 6 shown. At low frequencies, the frequency range with enhanced performance is relatively wide, and the overall performance improvement intensity is 2.4 - 2.5 dB. However, the performance drops to about 2.0 dB at 500 Hz.

[0065] Table 1 Pore structure parameters of the hierarchically porous ZSM-5 zeolite microspheres prepared in the examples (nitrogen adsorption test results)

[0066]

[0067] Note: S BET : Total specific surface area, unit is m 2 ·g -1 ; S micro : Micropore surface area, unit is m 2 ·g -1 ; S meso : Mesopore surface area, unit is m 2 ·g -1 ; V total : Total pore volume, unit is cm 3 ·g -1 ; V micro : Micropore volume, unit is cm 3 ·g -1 ; V meso : Mesopore volume, unit is cm 3 ·g -1 ; R.C.: Relative crystallinity, unit is %.

Claims

1. A controllable preparation method of hierarchical pore ZSM-5 molecular sieve microspheres, characterized in that, It includes the following steps: (1) Preparation of seeds: Dissolve the structure-directing agent in a solvent and stir evenly, add tetraethyl orthosilicate and mix evenly, load the completely mixed mixture into an autoclave for hydrothermal crystallization to obtain a seed suspension; (2) Synthesis of surfactant-silica composite nanoparticles: Dissolve the base source and surfactant in a solution and stir evenly, add the silicon source to the above solution and stir. After the reaction, it is recovered, washed and dried to obtain surfactant-silica composite nanoparticles, which are used as silicon source 1 for the next reaction; The surfactant is one or a combination of two of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride; The silicon source is tetraethyl orthosilicate; The reaction temperature is 50-100 °C and the time is 1-4 h; (3) Preparation of hierarchical zeolite molecular sieve: Dissolve the base source and aluminum source in a solution and stir evenly, sequentially add the seed suspension, silicon source 1 and silicon source 2. After the reactants are subjected to a low-temperature reaction, they are transferred to an autoclave for hydrothermal crystallization, and the precipitate is recovered and washed thoroughly with water; Add deionized water to the above precipitate to prepare a suspension with a certain solid content, and obtain microspheres with different particle sizes by spray drying; The spray microspheres are calcined to obtain the final hierarchical ZSM-5 zeolite molecular sieve microspheres.

2. The controllable preparation method of a hierarchical pore ZSM-5 molecular sieve microsphere according to claim 1, wherein, The hierarchical ZSM-5 zeolite molecular sieve microspheres contain four-level or five-level pores, including micropores, hierarchical mesopores and macropores; The micropore pore size range is 0.5-1.5 nm, the hierarchical mesopore pore size range is 2-50 nm, and the macropore pore size range is 50-300 nm.

3. The controllable preparation method of a hierarchical pore ZSM-5 molecular sieve microsphere according to claim 1, characterized in that, In the step (1), the structure-directing agent is one or a combination of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetramethylammonium hydroxide and tetraethylammonium hydroxide; The solvent is a mixed solution of water and ethanol; In the hydrothermal crystallization process, the hydrothermal temperature is 80-130 °C and the hydrothermal time is 24-120 h.

4. The controllable preparation method of a hierarchical pore ZSM-5 type molecular sieve microsphere according to claim 1, characterized in that, In the steps (2) and (3), the base source is one or a combination of ammonia water, sodium hydroxide and potassium hydroxide.

5. The controllable preparation method of a hierarchical pore ZSM-5 type molecular sieve microsphere according to claim 1, wherein, In the step (3), the silicon source 2 is one or a combination of silica sol, water glass, tetraethyl orthosilicate, and silica; The aluminum source is one or a combination of sodium aluminate, pseudo-boehmite, aluminum sulfate, aluminum isopropoxide, aluminum chloride and aluminum nitrate.

6. The controllable preparation method of a hierarchical pore ZSM-5 molecular sieve microsphere according to claim 1, wherein, In the step (3), the hydrothermal crystallization conditions are 100-180 °C and the time is 12-48 h; The solid content of the prepared suspension is 5%-40%.

7. The controllable preparation method of a hierarchical pore ZSM-5 type molecular sieve microsphere according to claim 1, characterized in that, In the step (3), the spray drying conditions are: carry out pressure spray drying at an inlet temperature of 110-200 °C, an outlet temperature of 70-140 °C, and a feed rate of 400-800 ml / h; The particle size of the microspheres obtained by spray drying is 1-500 μm.

8. The controllable preparation method of a hierarchical pore ZSM-5 molecular sieve microsphere according to claim 1, characterized in that, In the step (3), the calcination temperature is 400-600 °C and the calcination time is 3-6 h.

9. Application of the hierarchical ZSM-5 zeolite molecular sieve microspheres prepared by the preparation method according to any one of claims 1-8 as an acoustic enhancement material in a loudspeaker.

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