Alumina microspheres having a hollow multilayer structure and a method for preparing the same

Abstract

A hollow multilayered alumina microsphere and its preparation method are disclosed, belonging to the field of nanomaterials technology. This method uses anionic surfactants with sulfonic acid or carboxyl groups as template agents, aluminum salts as aluminum sources, and molecules containing carboxyl or phenolic hydroxyl groups as metal ligands to slow the release of aluminum ions. Amide precipitants are added to control the aluminum ion hydrolysis rate, resulting in hollow multilayered microspheres. This method can also be used to synthesize alumina microspheres with various structures such as onion-shaped concentric multilayers, hollow microspheres, multi-chambered microspheres, and radially cavitary microspheres. This method employs a kinetic approach combined with a soft template method to achieve controllable construction of the microsphere structure, solving the problem of uncontrollable microsphere morphology and structure due to excessively rapid aluminum source hydrolysis during alumina microsphere preparation. The synthesis process is simple and convenient, requires minimal equipment, uses inexpensive and readily available raw materials, and the resulting alumina microspheres have excellent application prospects.

Description

Technical Field

[0001] This invention relates to an alumina microsphere with a hollow multilayer structure and its preparation method, belonging to the field of nanomaterials technology. Background Technology

[0002] Fine alumina refers to alumina products other than those used in the electrolytic aluminum industry, including aluminum hydroxide, specialty alumina, and aluminum-containing compounds, which are widely used in pharmaceuticals, catalysis, and new materials. Developing high-quality fine alumina is of great significance for the transformation of my country's alumina production capacity and the efficient and high-value utilization of related industrial resources. Alumina microspheres with hollow or multi-layered structures are a type of high-quality, high-value-added fine alumina material.

[0003] In terms of morphology, spherical particles offer advantages such as good fluidity, controllable particle size, high packing density, and resistance to agglomeration. Structurally, hollow and multilayered structures possess characteristics such as large specific surface area, high porosity, and spatial confinement. From a chemical and physical perspective, alumina exhibits high surface acidity and good thermal stability. Considering these advantages, alumina microspheres with hollow, multilayered, and radially channeled micro / nanostructures hold great promise for applications in catalyst supports, adsorption and separation, drug delivery, and electrochemistry. However, achieving controllable synthesis of alumina microspheres and precisely constructing micro / nano structures within them remains a pressing problem to be solved.

[0004] Currently, the template method is the main approach for synthesizing hollow, multilayered, and other structural alumina microspheres. The template method is mainly divided into hard template methods and soft template methods. Commonly used hard templates include molecular sieves, mesoporous silica, carbon materials, and nanoparticles. The preparation process involves hydrolyzing an aluminum source and coating it onto a template microsphere, followed by calcination to remove the template and obtain the alumina microspheres. The soft template method uses surfactants as structure-directing agents, utilizing micelles, vesicles, and other assemblies formed by the aluminum source and surfactant in the system as structural precursors. These precursors are then hydrolyzed to form aluminum hydroxide microspheres with the corresponding structures, and finally washed and calcined to obtain the alumina microspheres. Compared with the hard template method, the soft template method has the advantages of easy template removal, more complete microsphere structures, a relatively simple preparation process, and ease of large-scale production. However, the stability of the system has a significant impact on the morphology and structure during the preparation process. This requires precise control of the template type, solution pH, and hydrolysis reaction rate.

[0005] In the soft-template method for synthesizing alumina microsphere precursors, the rapid nucleation rate of Al(OH)3 precipitation, a product of aluminum salt hydrolysis, makes it easy for the precursor to detach from the template, ultimately hindering the construction of the microsphere's internal structure. The fundamental reason for this rapid Al(OH)3 precipitation nucleation rate is the high solubility product (K0.05) of Al(OH)3. sp Only 1.3*10 -33(293.15K). When Al(OH)3 is prepared by the hydrolysis reaction of aluminum salts or aluminum alkoxides, the aluminum ions in the system will rapidly react with OH-. - The reaction produces Al(OH)3 monomer. If the concentration of Al(OH)3 monomer in the system is too high, it easily forms nuclei, thus preventing the controllable synthesis of microspheres. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing alumina microspheres with multilayered, hollow, or other structures, thereby solving the problem that the aluminum source is easily hydrolyzed and the precipitate easily detaches from the template during the microsphere preparation process, making it difficult to controllably construct the internal structure of the microspheres. The preparation method provided by this invention uses a kinetic approach to control the hydrolysis rate of the aluminum source during the reaction process and uses a template agent with strong binding capacity as a soft template to achieve controllable construction of alumina microspheres.

[0007] To achieve the above objectives, the preparation method provided by the present invention is as follows: using an anionic surfactant with sulfonic acid or carboxyl groups as a template agent and aluminum salt as an aluminum source; adding an organic molecule containing multiple carboxyl groups, one carboxyl group and one phenolic hydroxyl group as a metal ligand to slowly release aluminum ions; adding an amide precipitant to control the slow hydrolysis of aluminum ions to obtain aluminum hydroxide microspheres with multilayer, hollow and other structures; and obtaining alumina microspheres with the corresponding structure after calcination.

[0008] The preparation method specifically includes the following steps:

[0009] (1) An aluminum source solution is added to a template agent solution and stirred to form a vesicle system; the aluminum source solution contains aluminum salt and metal ligand, and the molar ratio of metal ligand to aluminum ions is greater than 0 and less than or equal to 2; the concentration of aluminum salt in the vesicle system is 0.1–2 g·L⁻¹. -1 The template agent concentration is 0.1–2 g·L⁻¹ -1 The molar ratio of template agent to aluminum salt is 1:1 to 1:2;

[0010] (2) Add an amide precipitant to obtain a mixed reaction system, react for 3-5 hours, centrifuge, wash and dry after the reaction to obtain aluminum hydroxide microspheres; the concentration of the amide precipitant in the mixed reaction system is 5-15 wt%.

[0011] (3) Calcining aluminum hydroxide microspheres into aluminum oxide microspheres.

[0012] Furthermore, the specific steps are as follows:

[0013] (1) Prepare a template aqueous solution using the soft template;

[0014] (2) The aluminum source and ligand are mixed to prepare an aqueous precursor solution;

[0015] (3) Mix the template aqueous solution with the precursor aqueous solution and stir to form a homogeneous colloidal system;

[0016] (4) Heat the system in step (3) to 30-90°C, introduce the precipitant, and start the reaction;

[0017] (5) After the solution in step (4) reacts for 1 to 6 hours, the product is separated by filtration or centrifugation, the product is washed with solvents such as water, isopropanol, methanol, and ethanol, and dried by methods such as atmospheric pressure drying, vacuum drying, and freeze drying; calcination is used to obtain alumina microspheres.

[0018] In step (1), the template agent is one or more of the following: sodium diisooctyl succinate sulfonate (bis(2-ethylhexyl)sulfosuccinate, AOT), sodium di-n-octyl succinate sulfonate (di-n-octylsulfosuccinate), sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium palmitate, sodium oleate, sodium myristate, sodium stearate, and sodium palmitate.

[0019] In step (2), the aluminum salt is one or more of the following: anhydrous aluminum nitrate, aluminum nitrate nonahydrate, anhydrous aluminum sulfate, aluminum sulfate octahydrate, anhydrous aluminum chloride, aluminum chloride hexahydrate, and potassium aluminum sulfate dodecahydrate (alum). The ratio between different aluminum salts is arbitrary.

[0020] In step (2), the metal ligand is one of citric acid, sodium citrate, salicylic acid, sodium salicylate, phthalic acid, D,L-malic acid, tartaric acid, sodium tartrate, and catechol, preferably sodium salicylate. The molar ratio of the metal ligand to the metal ion is 0 to 2.

[0021] In step (4), the preferred reaction temperature is 80°C.

[0022] In step (4), the precipitant includes, but is not limited to, formamide, N-methylformamide, N,N-dimethylformamide, etc., and is preferably formamide.

[0023] In step (5), the preferred reaction time is 4 hours.

[0024] In step (5), the washing solvent is preferably ethanol and water.

[0025] In step (5), the ambient pressure drying temperature is 40-90℃.

[0026] In step (5), the roasting temperature is 500-900℃, and the maximum temperature is maintained for 1-3 hours.

[0027] Furthermore, the specific steps of this preparation method are as follows:

[0028] (1) Weigh out AOT and dissolve it in water to form a template solution. The concentration of AOT in the template solution is 1.67 g·L⁻¹. -1 ;

[0029] (2) Aluminum sulfate octadechydrate, aluminum chloride hexahydrate, and sodium salicylate are added to water to form an aluminum source solution. The concentration of aluminum salts in the aluminum source solution is 2 g·L⁻¹. -1 The concentration of sodium salicylate is 1 g·L⁻¹. -1 The molar ratio of aluminum sulfate octahydrate to aluminum chloride hexahydrate is 1:2; the volume ratio of template solution to aluminum source solution is 3:2.

[0030] (3) Place the template solution in a flask and stir at room temperature for 0.5 h. Then add the aluminum source solution to the template solution and stir for 0.5 h to form a vesicle system. Heat the system to 80 °C, add 3 mL of formamide, and react for 4 h.

[0031] (4) The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80℃ for 10 h to obtain aluminum hydroxide microspheres, and then calcined at 700℃ for 3 h at a heating rate of 1℃·min. -1 Alumina microspheres were obtained.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The method of the present invention addresses the problem of easy hydrolysis of aluminum source during the synthesis of alumina microspheres by using a kinetic regulation method to control the hydrolysis rate of aluminum source. By coordinating ligands with aluminum ions, the release of aluminum ions is controlled; by adding a suitable precipitant, the release of hydroxide ions is controlled; the combination of the two achieves the purpose of controlling the hydrolysis rate of aluminum ions, thereby realizing the controllable synthesis of alumina precursor microspheres and the controllable construction of internal micro-nano structures.

[0034] (2) The method described in this invention employs a soft template method, using anionic surfactants with sulfonic acid or carboxyl groups as template agents. Compared with the hard template method for preparing hollow alumina microspheres, the soft template method is simpler to operate, easier to process, and has higher atom economy. Anionic surfactants such as AOT are non-toxic and belong to environmentally friendly template agents.

[0035] (3) The method described in this invention uses aluminum salt as the aluminum source. Aluminum salt is inexpensive and has low cost; it is stable and water can be used as a solvent.

[0036] (4) The method described in this invention is an atmospheric pressure reaction, which can realize the construction of the internal structure of microspheres without the need for a hydrothermal synthesis process. The synthesis process is simple and convenient, and has low requirements for instruments and equipment.

[0037] (5) The method described in this invention can synthesize microspheres with various structures, such as hollow multilayer, onion-shaped concentric multilayer, hollow, multi-chambered, and radially cavitary, by changing factors such as the type of template agent, the compounding ratio, and the aluminum source. This demonstrates that the synthesis method of aluminum hydroxide microspheres and alumina microspheres described in this invention has certain universality and scalability. Attached Figure Description

[0038] Figure 1 TEM image of hollow multilayer aluminum hydroxide microspheres prepared by the AOT method of this invention.

[0039] Figure 2 TEM images and XRD patterns of hollow multilayer alumina microspheres obtained by calcining the aluminum hydroxide microspheres prepared in Example 1 of this invention at 700℃.

[0040] Figure 3 TEM image of alumina microspheres prepared by aluminum sulfate and aluminum chloride according to the present invention.

[0041] Figure 4 TEM images of alumina microspheres prepared with different aluminum source concentrations according to the present invention.

[0042] Figure 5 TEM images of alumina microspheres with different amounts of sodium salicylate added according to this invention.

[0043] Figure 6 TEM images of alumina microspheres prepared at different reaction times according to the present invention.

[0044] Figure 7 The pH change curve of the reaction system of this invention as a function of reaction time.

[0045] Figure 8 TEM image of divergent hollow alumina microspheres prepared by sodium dodecyl sulfonate according to the present invention.

[0046] Figure 9 TEM image of hollow alumina microspheres prepared by sodium oleate according to the present invention.

[0047] Figure 10 TEM image of hollow alumina microspheres prepared by sodium palmitate according to the present invention.

[0048] Figure 11 TEM image of hollow alumina microspheres prepared by combining AOT and sodium dodecyl sulfate according to the present invention.

[0049] Figure 12 TEM image of core-shell alumina microspheres prepared by combining AOT and sodium dodecyl sulfonate according to the present invention.

[0050] Figure 13TEM image of onion-shaped multilayer alumina microspheres prepared by combining AOT and sodium dodecylbenzenesulfonate according to the present invention.

[0051] Figure 14 TEM image of onion-shaped multilayer alumina microspheres prepared by combining a high concentration of AOT and sodium dodecylbenzenesulfonate according to the present invention. Detailed Implementation

[0052] Example 1

[0053] 0.10 g of AOT was dissolved in 120 mL of water to form a template solution. 0.094 g of aluminum sulfate octahydrate, 0.068 g of aluminum chloride hexahydrate, and 0.080 g of sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain hollow aluminum hydroxide microspheres, which were characterized by transmission electron microscopy. Figure 1 The microspheres have a hollow, multi-layered structure.

[0054] Example 2

[0055] The hollow multilayer aluminum hydroxide microspheres prepared in Example 1 were calcined at 700°C for 3 hours, with a heating rate of 1°C·min. -1 . Figure 2 Image a shows a transmission electron microscope (TEM) image of alumina microspheres calcined at 700℃, revealing that the microspheres retain a hollow, multi-layered structure. The characteristic peaks in the X-ray diffraction pattern, after comparison, belong to γ-Al₂O₃ (…). Figure 2 (b)

[0056] Example 3

[0057] 0.20 g of AOT was dissolved in 120 mL of water to form a template solution. 0.094 g of aluminum sulfate octahydrate, 0.068 g of aluminum chloride hexahydrate, and 0.080 g of sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres, which were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 3 Transmission electron microscopy images show that the microspheres have a solid structure.

[0058] Example 4

[0059] 0.10 g AOT was dissolved in 120 mL of water to form a template solution. 0.047 g aluminum sulfate octahydrate, 0.034 g aluminum chloride hexahydrate, and 0.040 g sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. The prepared alumina microspheres are as follows: Figure 4 As shown, the microspheres have a particle size of about 300 nm, and the sphere walls have multiple chambers. The interior of the microspheres has a multi-layered hollow structure.

[0060] Example 5

[0061] 0.10 g AOT was dissolved in 120 mL of water to form a template solution. 0.047 g aluminum sulfate octahydrate and 0.034 g aluminum chloride hexahydrate were added to 80 mL of water to form an aluminum source solution. 0 g, 0.040 g, 0.080 g, and 0.12 g sodium salicylate were weighed and added to the aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy (TEM). TEM images of the alumina microspheres are shown below. Figure 5 As shown in Figures a through d, the amounts of sodium salicylate added were 0 g, 0.040 g, 0.080 g, and 0.12 g, respectively. With increasing sodium salicylate addition, the microsphere particle size gradually decreased from 500 nm to 200 nm. The double-layered hollow structure inside the microspheres was most clearly visible when 0.08 g of sodium salicylate was added.

[0062] Example 6

[0063] 0.10 g AOT was dissolved in 120 mL of water to form a template solution. 0.094 g aluminum sulfate octahydrate, 0.068 g aluminum chloride hexahydrate, and 0.080 g sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was carried out for 1 h, 2 h, 3 h, and 4 h, respectively. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. Aluminum hydroxide microspheres were obtained by reacting for 1–4 h as shown below. Figure 6 As shown in Figures a through d.

[0064] Example 7

[0065] 0.10 g AOT was dissolved in 120 mL of water to form a template solution. 0.094 g aluminum sulfate octahydrate, 0.068 g aluminum chloride hexahydrate, and 0.080 g sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h, with real-time pH monitoring. The aluminum source solution was added to the template solution and stirred for 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The pH change of the system over reaction time is shown below. Figure 7 As shown.

[0066] Example 8

[0067] 0.061 g and 0.12 g of sodium dodecyl sulfate were dissolved in 120 mL of water to form a template solution. 0.094 g of aluminum sulfate octahydrate, 0.068 g of aluminum chloride hexahydrate, and 0.080 g of sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 8 When the amount of sodium dodecyl sulfonate added is 0.061g, the microspheres are solid microspheres with a diameter of about 400nm. When the amount added is 0.12g, the diameter of the microspheres is about 400nm, and the interior has a radial cavity structure.

[0068] Example 9

[0069] 0.13 g of sodium oleate was dissolved in 120 mL of water to form a template solution. 0.094 g of aluminum sulfate octahydrate, 0.068 g of aluminum chloride hexahydrate, and 0.080 g of sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained hollow alumina microspheres were characterized by transmission electron microscopy. Figure 9 The microspheres have a particle size of about 400 nm, a large internal cavity, and a wall thickness of about 50 nm.

[0070] Example 10

[0071] 0.12 g and 0.060 g of sodium palmitate were dissolved in 120 mL of water to form a template solution. 0.094 g of aluminum sulfate octahydrate, 0.068 g of aluminum chloride hexahydrate, and 0.080 g (0.20 mmol) of sodium salicylate were added to 80 mL of water to form an aluminum source solution. The template solution was placed in a flask and stirred at room temperature for 0.5 h. Then, the aluminum source solution was added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 10 When the amount of sodium palmitate added is 0.12g ( Figure 10 In sections a and b), the microspheres are interconnected to form large cavities with a wall thickness of approximately 10 nm. When the addition amount is 0.062 g ( Figure 10 In (c) and (d), the microspheres are more dispersed, their shape is closer to that of a sphere, they have cavities inside, and the sphere walls are about 20 nm thick.

[0072] Example 11

[0073] A template solution was prepared by dissolving 0.070 g AOT and 0.038 g sodium dodecyl sulfate in 120 mL of water. An aluminum source solution was prepared by adding 0.094 g aluminum sulfate octahydrate, 0.068 g aluminum chloride hexahydrate, and 0.080 g (0.20 mmol) sodium salicylate to 80 mL of water. The template solution was placed in a flask and stirred at room temperature for 0.5 h. The aluminum source solution was then added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 11 The microspheres are approximately 400 nm in diameter and have an internal cavity structure. The sphere walls are 100 nm thick, and the outer walls are uneven.

[0074] Example 12

[0075] A template solution was prepared by dissolving 0.070 g AOT and 0.036 g sodium dodecyl sulfate in 120 mL of water. An aluminum source solution was prepared by adding 0.094 g aluminum sulfate octahydrate, 0.068 g aluminum chloride hexahydrate, and 0.080 g sodium salicylate to 80 mL of water. The template solution was placed in a flask and stirred at room temperature for 0.5 h. The aluminum source solution was then added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 12 The microspheres are approximately 400 nm in diameter and have a core-shell structure with a small internal cavity. The sphere walls are 150 nm thick and contain a multi-layered structure with an interlayer spacing of 2 nm.

[0076] Example 13

[0077] A template solution was prepared by dissolving 0.07 g AOT and 0.047 g sodium dodecylbenzenesulfonate in 120 mL of water. An aluminum source solution was prepared by adding 0.094 g aluminum sulfate octahydrate, 0.068 g aluminum chloride hexahydrate, and 0.080 g sodium salicylate to 80 mL of water. The template solution was placed in a flask and stirred at room temperature for 0.5 h. The aluminum source solution was then added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 3 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min.-1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 13 The microspheres have a diameter of about 400 nm and an internal onion-like multilayer structure with an interlayer spacing of 2 nm.

[0078] Example 14

[0079] A template solution was prepared by dissolving 0.14 g AOT and 0.094 g sodium dodecylbenzenesulfonate in 120 mL of water. An aluminum source solution was prepared by adding 0.018 g aluminum sulfate octahydrate, 0.013 g aluminum chloride hexahydrate, and 0.15 g sodium salicylate to 80 mL of water. The template solution was placed in a flask and stirred at room temperature for 0.5 h. The aluminum source solution was then added to the template solution and stirred for another 0.5 h to form a vesicle system. The system was heated to 80 °C, and 5 mL of formamide was added. The reaction was allowed to proceed for 4 h. The product was centrifuged and washed three times with a mixture of water and ethanol. The product was dried at 80 °C for 10 h to obtain aluminum hydroxide microspheres. These microspheres were then calcined at 700 °C for 3 h at a heating rate of 1 °C·min. -1 The obtained alumina microspheres were characterized by transmission electron microscopy. Figure 14 The microspheres have a diameter of about 400 nm and an internal onion-like multilayer structure with an interlayer spacing of 2 nm.

[0080] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for preparing alumina microspheres with a hollow multilayer structure, characterized in that: Using anionic surfactants with sulfonic acid or carboxyl groups as template agents and aluminum salts as aluminum sources, molecules containing multiple carboxyl groups or containing one carboxyl group and one phenolic hydroxyl group are added as metal ligands to slow-release aluminum ions; amide precipitants are added to control the hydrolysis rate of aluminum ions to obtain aluminum hydroxide microspheres; after calcination, alumina microspheres with the corresponding structure are obtained. The preparation method specifically includes the following steps: (1) Add the aluminum source solution to the template agent solution and stir to form a vesicle system; dissolve 0.10g sodium diisooctyl succinate sulfonate in 120mL of water to form a template solution, and add 0.094g aluminum sulfate octahydrate, 0.068g aluminum chloride hexahydrate and 0.080g sodium salicylate to 80mL of water to form an aluminum source solution; place the template solution in a flask and stir at room temperature for 0.5h, then add the aluminum source solution to the template solution and stir for 0.5h to form a vesicle system; (2) Add an amide precipitant to obtain a mixed reaction system, react for 3-5 hours, centrifuge, wash and dry after the reaction to obtain aluminum hydroxide microspheres; the concentration of the amide precipitant in the mixed reaction system is 5-15 wt%; the amide precipitant is formamide; (3) Aluminum hydroxide microspheres were calcined to obtain aluminum oxide microspheres.

2. The method for preparing alumina microspheres with a hollow multilayer structure according to claim 1, characterized in that: The reaction temperature in step (2) is 30~90℃.

3. The method for preparing alumina microspheres with a hollow multilayer structure according to claim 1, characterized in that: In step (3), the roasting temperature is 500~900℃ and the time is 1~3h.

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