Alumina hollow microsphere and preparation method thereof

Abstract

The application relates to an alumina hollow microsphere and a preparation method thereof, and belongs to the technical field of alumina microspheres. The method comprises the following steps: obtaining a biodegradable template; performing ultrasonic treatment on a mixed solution of the biodegradable template and an aluminum precursor solution to obtain a sol precursor; adjusting the pH value of the sol precursor to 3.9-4.7; aging the sol precursor with the adjusted pH value to obtain a gel; and performing calcination on the gel to decompose the biodegradable template, so as to obtain the alumina hollow microsphere. The method adopts the biodegradable template, and the decomposition temperature is lower than that of a traditional template; meanwhile, the template is decomposed into carbon dioxide and water after decomposition, harmful gas is avoided, the method is more friendly to the environment, and therefore, the alumina hollow microsphere can be efficiently and lowly prepared.

Description

Technical Field

[0001] This application relates to the field of alumina microsphere preparation technology, and in particular to a hollow alumina microsphere and its preparation method. Background Technology

[0002] Hollow alumina microspheres are widely used in various fields due to their advantages such as large specific surface area and low density. In existing technologies, polystyrene or silica is typically used as a template to prepare hollow alumina microspheres. The removal of these templates requires high-temperature conditions exceeding 600℃, which is not only energy-intensive but also causes environmental pollution. Furthermore, traditional polystyrene or silica template preparation processes are cumbersome, demanding on equipment, and inefficient, all of which hinder the widespread application of this technology in large-scale production. Therefore, developing a low-energy-consumption, low-pollution, and high-efficiency method for preparing hollow alumina microspheres is of significant practical importance. Summary of the Invention

[0003] This application provides alumina hollow microspheres and a method for preparing the same, in order to solve the following technical problem: how to prepare alumina hollow microspheres in an environmentally friendly and low-consumption manner.

[0004] In a first aspect, embodiments of this application provide a method for preparing hollow alumina microspheres, comprising the following steps:

[0005] Obtain a biodegradable template;

[0006] The mixture of the biodegradable template and the aluminum precursor solution was subjected to ultrasonic treatment to obtain a sol precursor.

[0007] The pH of the sol precursor was adjusted to 3.9 to 4.7, and the pH-adjusted sol precursor was aged to obtain a gel.

[0008] The gel was calcined to decompose the biodegradable template, yielding hollow alumina microspheres.

[0009] Optionally, the volume ratio of the biodegradable template to the aluminum precursor solution is 1:3 to 1:6; and the molar concentration of the aluminum precursor solution is 0.8 mol / L to 1.2 mol / L.

[0010] Optionally, the ultrasonic treatment time is 15 min to 30 min, and the ultrasonic treatment power is 200 W to 500 W.

[0011] Optionally, the aging time is 6 to 10 hours.

[0012] Optionally, the calcination temperature range is 300°C to 450°C.

[0013] Optionally, obtaining the biodegradable template specifically includes:

[0014] A starch solution and a chitosan acetate solution were obtained, respectively.

[0015] The starch solution and the chitosan acetate solution are mixed to obtain a starch-chitosan mixed solution;

[0016] Glycerol was added to the starch-chitosan mixed solution to obtain a membrane solution;

[0017] The membrane solution is dried, shaped, and strengthened to obtain a biodegradable template.

[0018] Optionally, the mass concentration of the starch solution is from 0.5% to 2.0%.

[0019] Optionally, the mass concentration of the chitosan acetate solution is from 0.5% to 2.0%.

[0020] Optionally, the mass ratio of starch to chitosan in the starch-chitosan mixed solution is 2:1 to 4:1.

[0021] Optionally, the volumetric amount of glycerol added is 0.2% to 5% of the volume of the starch-chitosan mixed solution.

[0022] Optionally, the step of drying, shaping, and strengthening the membrane solution to obtain a biodegradable template specifically includes:

[0023] The membrane solution is poured into a mold, and the membrane solution poured into the mold is dried to obtain a dried membrane;

[0024] The dried membrane is subjected to alkali treatment, and the alkali-treated dried membrane is neutralized and cleaned to obtain an alkali-treated membrane.

[0025] The alkali-treated membrane is soaked and dried to obtain a biodegradable template.

[0026] Optionally, the ambient humidity during the alkali treatment is 40% to 60%.

[0027] Optionally, the drying process shall meet at least one of the following conditions: the drying temperature is 25°C to 75°C; the drying time is 15h to 72h; and the drying humidity is 35% to 75%.

[0028] Optionally, the drying process includes a first drying process and a second drying process, wherein:

[0029] The first drying process satisfies at least one of the following conditions: the temperature of the first drying process is 30°C to 60°C; the time of the first drying process is 24h to 48h; and the humidity of the first drying process is 50% to 65%.

[0030] The second drying process satisfies at least one of the following conditions: the temperature of the second drying process is 35°C to 45°C; the time of the second drying process is 25h to 48h; and the humidity of the second drying process is 35% to 45%.

[0031] Optionally, the step of subjecting the dried membrane to alkali treatment, followed by neutralization and washing of the alkali-treated dried membrane to obtain an alkali-treated membrane solution, specifically includes:

[0032] The dried membrane was soaked in sodium hydroxide solution, then neutralized with an acidic solution, and then washed multiple times to obtain an alkaline-treated membrane solution.

[0033] The sodium hydroxide solution has a mass concentration of 5% to 10%; the soaking time is 0.5 h to 1 h; the acidic solution can be hydrochloric acid solution, nitric acid solution, etc., and the concentration of the acidic solution is 0.1 mol / L to 0.5 mol / L.

[0034] Optionally, the step of soaking and drying the alkali-treated membrane to obtain a biodegradable template specifically includes:

[0035] The membrane was treated with alkali by soaking it in deionized water, and then vacuum dried to obtain a biodegradable template.

[0036] The soaking time in deionized water is 6 to 12 hours, and the vacuum drying temperature is 35°C to 45°C.

[0037] Secondly, embodiments of this application provide alumina hollow microspheres, which are prepared using the alumina hollow microsphere preparation method described in any embodiment of the first aspect.

[0038] Optionally, the particle size of the hollow alumina microspheres ranges from 180 nm to 10 μm, the wall thickness of the hollow alumina microspheres ranges from 15 nm to 500 nm, and the specific surface area of ​​the hollow alumina microspheres is 150 m². 2 / g to 350m 2 / g.

[0039] The technical solutions provided in this application have the following advantages compared with the prior art:

[0040] This application provides an embodiment of hollow alumina microspheres and a method for preparing the same. The method includes: obtaining a biodegradable template to provide a biodegradable template for preparing hollow alumina microspheres; ultrasonically treating a mixture of the biodegradable template and an aluminum precursor solution to ensure thorough mixing and obtain a sol precursor; adjusting the pH of the sol precursor to 3.9 to 4.7 to allow aluminum salts to hydrolyze under acidic conditions to form aluminum ion monomers, thereby condensing at an appropriate rate to form a sol, while also preventing template aggregation or decomposition under this acidic environment; aging the pH-adjusted sol precursor to allow the gel precursor to solidify into a shell on the surface of the biodegradable template, thereby obtaining a gel; and calcining the gel to decompose the biodegradable template, ultimately obtaining hollow alumina microspheres. This method, through four steps of "template-sol-gel-calcination," transforms the high-energy-consuming and high-emission traditional melt-blowing route into a low-temperature chemical replication route. Its essence lies in replacing "1800℃ high-temperature melting + inert gas spheroidization" with "biodegradable template + low-temperature sol-gel", thereby achieving the goals of environmental protection and low energy consumption at the same time.

[0041] The biodegradable template used in this application selects renewable microparticles such as starch, chitosan, and cellulose as "temporary cores," with adjustable particle size (5µm to 200µm), and is widely available and non-toxic. The cycle is neutral; during subsequent template removal, calcination at 600℃ to 800℃ completely decomposes the material into carbon dioxide and water, producing no nitrogen oxides or sulfur oxides. The exhaust gas can be directly discharged, eliminating the need for acid and alkali washing and solving the secondary pollution caused by the use of urea and carbon black for pore-forming in traditional melting methods.

[0042] Sol-gel low-temperature fixation: aluminum precursor ( or It hydrolyzes into [a substance] in the pH range of 3.9 to 4.7. The polycations are positively charged; the biodegradable template surface becomes negatively charged after ultrasonic oxidation. A dense layer of hydrated alumina sol is uniformly coated at room temperature via electrostatic self-assembly, with a coating thickness of only 10 nm to 50 nm. The aluminum source utilization rate is >95%, and there is no dust emission. Subsequent aging forms a three-dimensional... The network (boehmite / bibium silicate gel) "locks" a biodegradable template inside, enabling shape replication.

[0043] Low-temperature calcination for pore formation: The gel is calcined at 150℃ to 350℃, causing the biodegradable template to undergo pyrolysis. The resulting water vapor and carbon dioxide escape from the nanopores, forming internal cavities; at 350℃ to 450℃, boehmite transforms into... At this point, the gel volume shrinks by 8%, which perfectly matches the template shrinkage, and the shell does not crack. The highest temperature throughout the process is only 450℃, which is 1350℃ lower than the traditional melting method. The overall energy consumption can be reduced by more than 70%. The equipment requirements are low, and ordinary resistance furnaces can be used, without the need for high-purity argon or plasma.

[0044] Environmental protection and low consumption synergy: raw materials are renewable, the process has no acid or alkali waste liquid, and the tail gas has no harmful components; low temperature and high aluminum yield reduce carbon dioxide emissions per unit product from the traditional 2.8 t to 0.6 t, further saving energy and materials. Attached Figure Description

[0045] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0046] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic flowchart of a method for preparing hollow alumina microspheres according to some embodiments of this application;

[0048] Figure 2 This is a schematic flowchart of a method for preparing a biodegradable template according to some embodiments of this application. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0051] like Figure 1 As shown in the embodiments of this application, a method for preparing hollow alumina microspheres is provided, comprising:

[0052] S1. Obtain a biodegradable template;

[0053] Step S1 provides a biodegradable template for the subsequent preparation of hollow microspheres.

[0054] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0055] In step S2, since the biodegradable template is essentially a dry solid film, the biodegradable template and precursor solution are thoroughly mixed. Due to rapid swelling stress and interfacial tension differences, the biodegradable template will spontaneously fragment. With the aid of ultrasonic treatment, cavitation further pulverizes the template fragments to the target size, while simultaneously promoting the entry of the aluminum precursor solution into the pores of the template fragments, resulting in a uniform coverage of the aluminum precursor solution around the biodegradable template. Electrostatic adsorption and hydrolytic condensation reactions can occur between the biodegradable template and the aluminum precursor solution. Electrostatic adsorption enables the initial anchoring of the aluminum precursor solution on the template surface; the hydrolytic condensation reaction completes the gel shell construction, laying the structural foundation for the hollow microspheres in the subsequent aging and calcination processes.

[0056] S3. Adjust the pH of the sol precursor to 3.9 to 4.7, and age the pH-adjusted sol precursor to obtain a gel;

[0057] In step S3, adjusting the pH of the sol precursor to 3.9 to 4.7 serves the following purposes: 1) At this pH, the aluminum salt in the aluminum precursor can hydrolyze to form aluminum ion monomers, which then form a stable linear oligomer sol through a condensation reaction at an appropriate rate, ensuring sol homogeneity; 2) At this pH, the solubility of the biodegradable template can be maintained, preventing the biodegradable template from agglomerating or decomposing, thus ensuring the stability of the biodegradable template; 3) In a weakly acidic environment, the electrostatic repulsion between the aluminum precursor solution and the biodegradable template is minimized, which is beneficial for promoting adsorption.

[0058] S4. The gel is calcined to decompose the biodegradable template, resulting in hollow alumina microspheres.

[0059] In the above embodiments, a biodegradable template is first used as the template for preparing "hollow microspheres". Compared with the templates commonly used in the prior art, the demolding requirements are lower, and only calcination is required, and the calcination temperature is lower. In addition, the biodegradable template can be directly decomposed into carbon dioxide and water after calcination, avoiding the emission of harmful gases generated by the calcination of traditional templates, which is more environmentally friendly.

[0060] Furthermore, the preparation method in this application is simple, requiring only the mixing of a biodegradable template and an aluminum precursor solution, followed by aging in an appropriate pH environment to obtain a gel with the target size. Finally, calcination and demolding yield alumina hollow microspheres. Therefore, this method can efficiently and with low consumption prepare alumina hollow microspheres.

[0061] As an optional implementation, the volume ratio of the biodegradable template to the aluminum precursor solution is 1:3 to 1:6.

[0062] In the above embodiments, the volume ratio of the biodegradable template to the aluminum precursor solution is controlled between 1:3 and 1:6 to optimize the structure and performance of the hollow microspheres. This controlled ratio ensures sufficient reaction between the biodegradable template and the aluminum precursor solution during microsphere formation, resulting in a uniform hollow microsphere structure with high porosity. This structure not only increases the specific surface area of ​​the microspheres but also enhances their adsorption capacity and catalytic activity. Furthermore, an appropriate volume ratio contributes to the mechanical strength and thermal stability of the microspheres. During subsequent heat treatment, the hollow microspheres maintain good structural integrity, avoiding cracking or deformation due to thermal stress. This is crucial for the performance of the hollow microspheres in practical applications.

[0063] As an optional implementation, the molar concentration of the aluminum precursor solution is from 0.8 mol / L to 1.2 mol / L.

[0064] In the above embodiments, the molar concentration of the aluminum precursor solution is controlled within the range of 0.8 mol / L to 1.2 mol / L. This is done to balance the sol penetration depth and gel formation rate, achieving a balance between shell densification and structural integrity, ensuring efficient reaction and excellent product quality. If the molar concentration is less than 0.8 mol / L, insufficient hydrolysis products of aluminum ions will result. If the molar concentration of the aluminum precursor solution is greater than 1.2 mol / L, the excessively high concentration will lead to a significant increase in solution viscosity, making it difficult to effectively penetrate the pores of the biodegradable template. This results in localized accumulation rather than uniform coverage on the template surface, ultimately failing to obtain a gel shell with a complete structure and uniform thickness. For example, the molar concentration of the aluminum precursor solution can be 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, or 1.2 mol / L.

[0065] As an optional implementation, when the molar concentration of the aluminum precursor solution is 0.8 mol / L to 1.0 mol / L, the pH value of the sol precursor is adjusted to 4.0 to 4.7;

[0066] When the molar concentration of the aluminum precursor solution is 1.0 mol / L to 1.2 mol / L, the pH value of the sol precursor is adjusted to 3.9 to 4.3.

[0067] As an optional implementation, the ultrasonic treatment time is 15 min to 30 min, and the ultrasonic treatment power is 200 W to 500 W.

[0068] In the above embodiments, controlling the time and power of ultrasonic treatment can effectively control the fragment size of the biodegradable template, obtaining fragments of the target size. For example, the ultrasonic treatment time can be 15 min, 20 min, 25 min, or 30 min; the ultrasonic treatment power can be 200 W, 250 W, 300 W, 350 W, 400 W, 450 W, or 500 W.

[0069] As an optional implementation, the aluminum precursor solution may be an aluminum nitrate solution, an aluminum isopropoxide solution, or an aluminum chloride solution.

[0070] In the above embodiments, the aluminum precursor solution needs to meet the following three conditions:

[0071] It is water-soluble, ensuring uniform mixing with biodegradable templates;

[0072] 2. The anions are decomposable and can be completely volatilized at a calcination temperature of 300℃ to 450℃, avoiding residue contamination of the microbeads;

[0073] 3. It exhibits controllable hydrolysis; ions can be generated when the pH of the sol precursor solution is between 3.9 and 4.7. To ensure targeted aggregation.

[0074] Choosing aluminum nitrate solution or aluminum isopropoxide solution as the aluminum precursor solution can fully meet the above conditions and avoid the introduction of pollutants such as chlorine and sulfur, which is in line with environmental protection trends. If aluminum chloride is chosen, 1 wt% urea needs to be added during calcination, and the temperature should be gradually increased to 150℃ and held for 1 hour to ensure… by It volatilizes but requires nitrogen protection; roasting produces It neutralizes excess hydrochloric acid and other acidic substances.

[0075] As an optional implementation, the aging time is 6 to 10 hours.

[0076] In the above embodiments, the reason for controlling the aging time to be 6 to 10 hours is that, in a specific weakly acidic pH environment, aluminum ions are generated. It requires more than 5 hours, and will It takes another hour to form a continuous network, and the sol precursor needs time to penetrate the surface of the biodegradable template for directional polycondensation. However, if the aging time exceeds 10 hours, excessive polycondensation stress may cause surface cracking of the microspheres; the water absorption and swelling of the bio-template will damage the bonding force at the coating layer interface.

[0077] It should be noted that the essence of this preparation method is to precisely regulate the generation of precursors by controlling the pH environment. Ions, and also because the surface of the biodegradable template is rich in ions. (Starch) and Functional groups such as chitosan, under acidic conditions of pH 3.9–4.7, interact through electrostatic attraction. Ions can be directionally adsorbed onto the template surface, achieving bio-template interface catalysis; at the same time, combined with ultrasound-enhanced mass transfer, the gelation process is transformed from random bulk polymerization to directional polymerization on the template surface, which greatly improves efficiency while ensuring the integrity of the microbead structure, thus effectively shortening the aging time.

[0078] As an optional implementation, the method for obtaining a biodegradable template specifically includes:

[0079] S11. Obtain starch solution and chitosan acetate solution respectively;

[0080] S12. Mix the starch solution and the chitosan acetate solution to obtain a starch-chitosan mixed solution;

[0081] S13. Add glycerol to the starch-chitosan mixed solution to obtain a membrane solution;

[0082] S14. The membrane solution is dried, shaped, and strengthened to obtain a biodegradable template.

[0083] As an optional implementation, obtaining the starch solution and chitosan acetate solution respectively specifically includes:

[0084] To obtain a starch solution: Add starch to deionized water, heat and stir for a certain time to gelatinize the starch, and obtain a starch solution with a gelatinization degree ≥95%. Cool to 50℃ for later use.

[0085] To obtain a chitosan acetic acid solution: a certain amount of high-deacetylation chitosan (≥85%) is weighed and dissolved in acetic acid solution. The mixture is thoroughly mixed by magnetic stirring to ensure that the amino groups in the chitosan molecules form salts with the hydrogen ions in the acid and undergo solvation, thereby destroying the original hydrogen bond structure of chitosan and achieving complete dissolution, thus preparing a chitosan acetic acid solution.

[0086] The concentration of the acetic acid solution is from 0.5% to 2.0%.

[0087] As an optional implementation, the mass concentration of the starch solution is between 0.5% and 2.0%. This is to balance film-forming properties and solution permeability. If the mass concentration of the starch solution is below 0.5%, the film-forming properties are poor, and a continuous film cannot be formed. If the mass concentration of the starch solution is above 2.0%, the viscosity is too high, and the permeability is poor, which may hinder the molecular-level interpenetration between the starch solution and the chitosan solution. For example, the mass concentration of the starch solution can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0088] As an optional implementation, the mass concentration of the chitosan acetate solution is 0.5% to 2.0%. This concentration allows for control of the deacetylation chain extension while preventing acetate ion residue. If the mass concentration of the chitosan acetate solution is below 0.5%, the concentration is too low, potentially causing the deacetylation chains to not fully extend due to hydrogen bonding, resulting in low template porosity. If the mass concentration is above 2.0%, a large amount of acetic acid is used to dissolve the chitosan, making it difficult to completely remove acetate ions, leading to excessive acetic acid residue. For example, the mass concentration of the chitosan acetate solution can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0089] As an optional implementation, the mass ratio of starch to chitosan in the starch-chitosan mixed solution is 2:1 to 4:1. This is because when the mass ratio of starch to chitosan in the mixed solution is less than 2:1, it indicates that there is an excess of chitosan in the mixed solution, resulting in an excess of chitosan in the obtained biodegradable template. Subsequently, mixing with the aluminum precursor solution will trigger aluminum sol flocculation; when the mass ratio of starch to chitosan is higher than 4:1, it indicates that there is an excess of starch in the mixed solution, resulting in insufficient chitosan encapsulation. For example, the mass ratio of starch to chitosan in the starch-chitosan mixed solution can be 2:1, 2.5:1, 3:1, 3.5:1, or 4:1.

[0090] As an optional implementation, the volumetric amount of glycerol added is 0.2% to 5% of the total volume of the starch-chitosan mixed solution. This is because adding 0.2% to 5% glycerol by volume of the starch-chitosan mixed solution can effectively regulate the plasticity and dehydration stress of the biodegradable template. For example, the volumetric amount of glycerol added can be 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0% of the volume of the starch-chitosan mixed solution.

[0091] In a more preferred embodiment, the volume of glycerol added is 0.5% to 2% of the volume of the starch-chitosan mixed solution. This is because it optimizes the pore structure and thermal decomposition characteristics of the biodegradable template, and avoids micro-explosion of the biodegradable template during calcination, which would damage the structure of the hollow microspheres.

[0092] As an optional implementation, the step of drying, shaping, and strengthening the membrane solution to obtain a biodegradable template specifically includes:

[0093] S141. Pour the membrane solution into a mold and dry the membrane solution in the mold to obtain a dried membrane;

[0094] Step S141 first uses a mold to shape the membrane, and then removes free water and accelerates structural shaping through drying.

[0095] S142. The dried membrane is subjected to alkali treatment, and the alkali-treated dried membrane is neutralized and cleaned to obtain an alkali-treated membrane.

[0096] In step S142, the dried film is first treated with alkali to neutralize the excess acetic acid during the preparation process and induce the chitosan to achieve physical cross-linking, for example, through the enhancement of hydrogen bonds or crystallization process, thereby significantly improving the thermal stability and anti-swelling ability of the film and enhancing the mechanical strength of the template. Then, after the alkali treatment is completed, the excess alkali solution is removed by neutralization and cleaning to prevent residual alkali from damaging the stability of the aluminum sol and the corrosion of aluminum oxide by alkali at high temperature during subsequent preparation processes.

[0097] S143. The alkali-treated membrane is soaked and dried to remove excess impurity ions and moisture, thereby obtaining a starch-chitosan biodegradable template with high mechanical strength and good water resistance.

[0098] As an optional implementation, the drying process satisfies at least one of the following conditions: the drying temperature is 25°C to 75°C; the drying time is 15h to 72h; and the drying humidity is 30% to 75%.

[0099] In the above embodiments, the drying process serves to first remove free water from the biodegradable template, then accelerate the structural stabilization of the biodegradable template, and simultaneously prevent cracking. For example, the drying temperature can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C. The drying humidity can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%. The drying time can be 15h, 20h, 24h, 30h, 35h, 36h, 40h, 45h, 48h, 50h, 55h, 60h, 65h, 70h, or 72h. The humidity during the drying process can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%.

[0100] As an optional implementation, the drying process includes a first drying process and a second drying process, wherein:

[0101] The first drying process satisfies at least one of the following conditions: the temperature of the first drying process is 30°C to 60°C; the time of the first drying process is 24h to 48h; and the humidity of the first drying process is 50% to 65%.

[0102] In the above embodiments, the reason for controlling the temperature of the first drying process to be between 30°C and 60°C is that this temperature range is below the critical temperature for starch gelatinization. Drying within this temperature range can prevent starch gelatinization due to excessively high temperatures, while simultaneously achieving efficient dehydration. For example, the temperature of the first drying process can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0103] The reason for controlling the first drying treatment time to be between 24h and 48h is that only within this range can the free water be completely removed. The final time needs to be determined according to the actual dehydration situation. For example, the first drying treatment time can be 24h, 25h, 30h, 36h, 40h, 45h or 48h.

[0104] The reason for controlling the humidity of the first drying process to be between 50% and 65% is that this humidity range is intended to keep the evaporation stress within the membrane rupture threshold. The starch-chitosan composite membrane can achieve linear shrinkage rather than abrupt change, thus ensuring the geometric integrity of the template. For example, the humidity of the first drying process can be 50%, 55%, 60%, or 65%.

[0105] The second drying process satisfies at least one of the following conditions: the temperature of the second drying process is 35°C to 45°C; the time of the second drying process is 25h to 48h; and the humidity of the second drying process is 30% to 40%.

[0106] In the above embodiments, the reason for controlling the temperature of the second drying treatment to be 30°C to 40°C is that this temperature range falls within the glycerol plasticization window temperature, within which deep dehydration can be achieved; the reason for controlling the time of the second drying treatment to be 25h to 48h is that the removal of strongly bound water can be achieved; the reason for controlling the humidity of the second drying treatment to be 30% to 40% is that, referring to the relationship between the glass transition temperature Tg of the chitosan film and its hygroscopicity, the optimal vapor pressure difference is constructed to quickly remove bound water, which can suppress stress defects in the biodegradable template, achieve structural fixation, and avoid the template strength reduction caused by moisture regain.

[0107] As an optional implementation, the dried membrane undergoes an alkaline treatment step, followed by neutralization and washing to obtain an alkaline-treated membrane solution. The specific process is as follows: first, the dried membrane is soaked in a sodium hydroxide solution to induce a deacetylation reaction; then, an acidic solution is used to neutralize and remove excess sodium hydroxide; and after multiple washings, the alkaline-treated membrane solution is finally obtained. The sodium hydroxide solution has a mass concentration of 5% to 10%; the soaking time is 0.5 h to 1 h; and the acidic solution can be hydrochloric acid, nitric acid, etc., with a concentration of 0.1 mol / L to 0.5 mol / L.

[0108] In the above embodiments, the reason for controlling the mass concentration of sodium hydroxide solution to 5% to 10% is that sodium hydroxide within this concentration range can precisely control the degree of deacetylation and integrity of the biodegradable template, ensuring the surface activity of the template and preventing structural collapse. The reason for controlling the soaking time to 0.5 to 1 hour is to ensure the completion of the deacetylation reaction while inhibiting the occurrence of side reactions. The purpose of using an acidic solution for cleaning is to neutralize excess sodium hydroxide and balance the residual amount of sodium ions. The reason for choosing hydrochloric acid solution is that chloride ions can also catalyze… The phase transition; nitric acid solution was chosen because nitrate ions can decompose to create micropores. The concentration of the acidic solution was controlled to be between 0.1 mol / L and 0.5 mol / L because this concentration range can control residual sodium ions to <10 ppm, while also avoiding the corrosion risk of the biodegradable template.

[0109] As an optional implementation, the step of soaking and drying the alkali-treated membrane to obtain a biodegradable template specifically includes:

[0110] A biodegradable template was obtained by soaking the membrane in deionized water with alkali treatment and then vacuum drying.

[0111] The soaking time in deionized water is 6 to 12 hours, and the vacuum drying temperature is 35°C to 45°C.

[0112] In the above embodiments, the purpose of soaking in deionized water is to balance the swelling degree of the membrane and prevent excessive swelling. It also allows for the removal of ionic impurities, such as chloride and sodium ions, through dialysis. The reason for controlling the soaking time to 6 to 12 hours is that if the soaking time is less than 6 hours, ionic impurities may not be completely removed, leaving residues; if the time exceeds 12 hours, excessive swelling may lead to membrane collapse. For example, the soaking time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0113] In the above embodiments, the vacuum drying conditions of 35°C to 45°C are selected because this temperature range can both gently dehydrate and effectively maintain the porous structure, thereby preventing the thermal decomposition of chitosan or the reversal of starch gelatinization caused by high temperature, and thus avoiding the thermal degradation of the template.

[0114] As an optional implementation, the humidity during the alkali treatment is 40% to 60%. The purpose of controlling the humidity during alkali treatment is to control the chemical reaction process and ensure template activity. For example, the humidity during alkali treatment can be 40%, 45%, 50%, 55%, or 60%.

[0115] Secondly, based on a general inventive concept, embodiments of this application provide alumina hollow microspheres, which are prepared using the alumina hollow microsphere preparation method described in any embodiment of the first aspect.

[0116] As an optional implementation, the alumina hollow microspheres have a particle size ranging from 180 nm to 10 μm; a wall thickness ranging from 15 nm to 500 nm; and a specific surface area of ​​150 m². 2 / g to 350m 2 / g.

[0117] The alumina hollow microspheres are prepared based on the above-described method for preparing alumina hollow microspheres. The specific steps of this method can be referred to the above embodiments. Since the alumina hollow microspheres adopt some or all of the technical solutions of the above embodiments, they have at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0118] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0119] Examples 1 to 4 provide alumina hollow microspheres with different parameters and their preparation methods, as detailed in the following specific parameters and properties.

[0120] Example 1

[0121] This embodiment provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0122] S1. Obtain a biodegradable template;

[0123] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0124] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0125] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:4. During the mixing process, a magnetic stirrer was first used for preliminary mixing, followed by ultrasonic treatment to ensure that the template could be uniformly and fully dispersed in the aluminum nitrate solution, and finally a uniformly mixed sol precursor was obtained.

[0126] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0127] The pH of the sol precursor was adjusted to 4.2 with citric acid, and after aging for 8 hours, a gel was obtained.

[0128] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0129] Testing revealed that the prepared hollow alumina microspheres had a particle size of 200 nm to 220 nm, a wall thickness of 20 nm to 30 nm, and a specific surface area of ​​280 m². 2 / g to 290m 2 / g, compressive strength of 120Mpa to 125Mpa, impurity content Na≤10ppm.

[0130] Example 2

[0131] This embodiment provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0132] S1. Obtain a biodegradable template;

[0133] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0134] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0135] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:5. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0136] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0137] The pH of the sol precursor was adjusted to 4.0 with citric acid, and after aging for 8 hours, a gel was obtained.

[0138] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0139] Testing revealed that the prepared hollow alumina microspheres had a particle size ranging from 197 nm to 280 nm, a wall thickness ranging from 18 nm to 25 nm, and a specific surface area of ​​300 m². 2 / g to 380m 2 / g, compressive strength 140Mpa to 180Mpa, impurity content Na≤10 ppm.

[0140] Example 3

[0141] This embodiment provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0142] S1. Obtain a biodegradable template;

[0143] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0144] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0145] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:5. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0146] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0147] The pH of the sol precursor was adjusted to 4.0 with citric acid, and after aging for 6 hours, a gel was obtained.

[0148] S4. The gel is calcined at 450°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0149] Testing revealed that the prepared hollow alumina microspheres had a particle size of 200 nm to 250 nm, a wall thickness of 15 nm to 17 nm, and a specific surface area as high as 165 m². 2 With a compressive strength of 85 MPa and extremely low impurity content (Na ≤ 3 ppm), this material exhibits excellent physical and chemical properties.

[0150] Example 4

[0151] This embodiment provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0152] S1. Obtain a biodegradable template;

[0153] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0154] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0155] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:4. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0156] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0157] The pH of the sol precursor was adjusted to 4.0 with citric acid, and after aging for 8 hours, a gel was obtained.

[0158] S4. The gel is calcined at 450°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0159] Testing revealed that the prepared hollow alumina microspheres had a particle size of 180 nm to 260 nm, a wall thickness of 15 nm to 20 nm, and a specific surface area of ​​165 m². 2 / g to 185 m 2 / g, compressive strength 130 Mpa to 150 Mpa, impurity content Na≤10ppm.

[0160] Comparative Examples 1 to 3 were modified from Example 1, using different templates, different volume ratios, or different aging times. Their performance decreased compared to the Example 1. See the specific data below for details.

[0161] Comparative Example 1

[0162] This comparative example provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0163] S1. Obtain a biodegradable template;

[0164] A biodegradable template with a particle size of 10 μm was prepared using starch and chitosan as raw materials.

[0165] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0166] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:4. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0167] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0168] The pH of the sol precursor was adjusted to 4.0 with citric acid, and after aging for 8 hours, a gel was obtained.

[0169] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0170] Testing revealed that the prepared hollow alumina microspheres had a particle size of 8 μm to 12 μm, a wall thickness of 50 nm to 200 nm, and a specific surface area of ​​30 m². 2 / g to 50m 2 / g, compressive strength 20Mpa to 40Mpa, impurity Na content 80ppm.

[0171] Comparative Example 2

[0172] This comparative example provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0173] S1. Obtain a biodegradable template;

[0174] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0175] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0176] The prepared biodegradable template was added to a 1.0 mol / L aluminum chloride solution and mixed at a volume ratio of 1:2. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a uniformly mixed sol precursor.

[0177] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0178] The pH of the sol precursor was adjusted to 4.2 with citric acid, and after aging for 8 hours, a gel was obtained.

[0179] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0180] Testing revealed that the prepared hollow alumina microspheres had a particle size of 220 nm to 350 nm, a wall thickness of 40 nm to 60 nm, and a specific surface area of ​​90 m². 2 / g to 120 m 2 / g, compressive strength 50Mpa to 80Mpa, impurity chloride ion content 500ppm to 1000ppm.

[0181] Comparative Example 3

[0182] This comparative example provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0183] S1. Obtain a biodegradable template;

[0184] A biodegradable template with a particle size of 150 nm was prepared using starch and chitosan as raw materials.

[0185] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0186] The prepared biodegradable template was added to a 1.0 mol / L aluminum nitrate solution and mixed at a volume ratio of 1:4. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0187] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0188] The pH of the sol precursor was adjusted to 4.1 with citric acid, and after aging for 4 hours, a gel was obtained.

[0189] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0190] Testing revealed that the prepared hollow alumina microspheres had a particle size of 210 nm to 260 nm, a wall thickness of 12 nm to 17 nm, and a specific surface area of ​​132 m². 2 / g to 155m 2 / g, compressive strength 42Mpa to 49Mpa, impurity Na content 300ppm, impurity Cl- content 500ppm to 1000ppm.

[0191] Comparative Example 4

[0192] This comparative example provides alumina hollow microspheres, the preparation method of which includes the following steps:

[0193] S1. Obtain a biodegradable template;

[0194] A biodegradable template with a particle size of 10 μm was prepared using starch and chitosan as raw materials.

[0195] S2. The mixture of the biodegradable template and the aluminum precursor solution is subjected to ultrasonic treatment to obtain a sol precursor;

[0196] The prepared biodegradable template was added to a 1.0 mol / L aluminum chloride solution and mixed at a volume ratio of 1:3. During mixing, magnetic stirring was used for initial mixing, followed by ultrasonic treatment to ensure that the template was completely and uniformly dispersed in the aluminum nitrate solution, resulting in a homogeneous sol precursor.

[0197] S3. Adjust the pH of the sol precursor to a set pH value, and age the pH-adjusted sol precursor to obtain a gel;

[0198] The pH of the sol precursor was adjusted to 4.0 with citric acid, and after aging for 6 hours, a gel was obtained.

[0199] S4. The gel is calcined at 400°C for 3 hours to decompose the biodegradable template, thereby obtaining alumina hollow microspheres.

[0200] Testing revealed that the prepared hollow alumina microspheres had a particle size of 9 μm to 13 μm, a wall thickness of 100 nm to 500 nm, and a specific surface area of ​​15 m². 2 / g to 30m 2 / g, compressive strength 5Mpa to 15Mpa; impurity Na content ≤200ppm, impurity chloride ion content 1200ppm to 2000ppm.

[0201] The following conclusions can be drawn from the data in the examples and comparative examples:

[0202] 1. As the calcination temperature increases, the sintering and crystallinity of the hollow microspheres increase, resulting in a reduction in porosity, thus the final specific surface area decreases.

[0203] 2. The compressive strength of the obtained hollow microspheres is directly related to the aging time. The compressive strength of the hollow microspheres in Example 3 is lower than that in Example 1, which can be attributed to its shorter aging time (6h vs 8h), resulting in a less robust gel network. Comparative Example 3 provides strong evidence to support this (4h aging, strength only 42MPa to 49MPa). In Example 4, although the higher calcination temperature led to increased brittleness of the hollow microspheres, the sufficient 8h aging and the densification advantage brought by the higher calcination temperature not only compensated for the shortcomings of Example 3 but also exceeded the level of Example 1. This reflects the final result of the synergistic effect of the two parameters: calcination temperature and aging time. Temperature contributes to densification, while aging time contributes to structural stability. By appropriately increasing the calcination temperature (550℃) to improve the product's density and compressive strength, and by restoring sufficient 8-hour aging to ensure the stability of the gel skeleton, the combined effect resulted in a strength of 130MPa to 150MPa. At the same time, the increase in temperature will inevitably lead to a further decrease in specific surface area, dropping to 165 m². 2 / g to 185 m 2 / g level.

[0204] 3. Comparative Example 2 differs from Example 1 only in the ratio of the biodegradable template to the aluminum precursor solution, changing the volume ratio from 1:4 in Example 1 to 1:2. This means that in the same volume of aluminum precursor solution, the number of biodegradable template particles doubles, i.e., the amount of precursor that each template particle can adsorb and load is halved, resulting in a thinner and potentially uneven alumina gel wall layer. A thinner, more uneven wall layer will have inconsistent shrinkage and stress distribution during subsequent drying and high-temperature calcination, making it more prone to deformation, cracking, or partial collapse. This leads to a wider particle size distribution and wall thickness range in the final product, but the baseline particle size remains fundamentally unchanged.

[0205] In summary, the alumina hollow microspheres prepared by the method described in this application have smaller and more uniform particle size, uniform wall thickness, and higher specific surface area, resulting in stronger adsorption capacity. They also have higher compressive strength and lower impurity content, making them widely applicable in fields such as catalyst supports and adsorption materials.

[0206] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for producing alumina hollow microspheres, characterized by, The method comprises the following steps: obtaining a starch solution and a chitosan acetic acid solution respectively; mixing the starch solution and the chitosan acetic acid solution to obtain a starch-chitosan mixed solution; adding glycerol to the starch-chitosan mixed solution to obtain a film solution; pouring the film solution into a mold, and performing drying treatment on the film solution poured into the mold to obtain a dry film; performing alkali treatment on the dry film, and performing neutralization cleaning on the dry film subjected to the alkali treatment to obtain an alkali-treated film; immersing and drying the alkali-treated film to obtain a biodegradable template; performing ultrasonic treatment on a mixed solution of the biodegradable template and an aluminum precursor solution to obtain a sol precursor; adjusting the pH value of the sol precursor to 3.9-4.7, and performing aging on the sol precursor subjected to the pH value adjustment to obtain a gel; performing calcination on the gel to decompose the biodegradable template, thereby obtaining aluminum oxide hollow microspheres; the volume ratio of the biodegradable template to the aluminum precursor solution is 1:3-1:6; the temperature range of the calcination is 300-450 DEG C; the aging time is 6-10 h; the aluminum precursor solution is an aluminum nitrate solution, an aluminum isopropyl alcohol solution, or an aluminum chloride solution.

2. The production method according to claim 1, characterized by, The molar concentration of the aluminum precursor solution is 0.8-1.2 mol / L.

3. The preparation method according to claim 1, characterized in that, The ultrasonic treatment time is 15-30 min, and the ultrasonic treatment power is 200-500 W.

4. The preparation method according to claim 1, characterized in that, The mass concentration of the starch solution is 0.5-2.0%, and the mass concentration of the chitosan acetic acid solution is 0.5-2.0%.

5. The preparation method according to claim 1, characterized in that, The mass ratio of starch to chitosan in the starch-chitosan mixed solution is 2:1-4:1, and the volume addition amount of glycerol is 0.2-5% of the total volume of the starch-chitosan mixed solution.

6. The alumina hollow microsphere produced by the method according to any one of claims 1 to 5, characterized in that, The aluminum oxide hollow microspheres at least meet one of the following requirements: The particle size of the aluminum oxide hollow microspheres ranges from 180 nm to 10 μm. The wall thickness of the aluminum oxide hollow microspheres is 15-500 nm. The specific surface area of the alumina hollow microspheres is 150 m 2 / g to 350 m 2 / g.

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