Preparation method of calcium carbonate-polyvinyl alcohol composite aerogel material

Abstract

The invention discloses a preparation method of a calcium carbonate-polyvinyl alcohol composite aerogel material, and belongs to the technical field of thermal insulation materials. The invention aims to solve the problems that the crystallization behavior of calcium carbonate is difficult to effectively regulate and control and the porous structure and the heat insulation function of aerogel are easily damaged in the prior art. The method comprises the following steps: reacting a mixed solution of calcium chloride and magnesium chloride with carbon dioxide to prepare micro-nano amorphous calcium carbonate and a small amount of nano calcite; co-doping the chitosan and aspartic acid into polyvinyl alcohol hydrogel, uniformly mixing, and carrying out directional freezing and freeze-drying treatment; finally, high-concentration carbon dioxide atmosphere treatment is adopted in a humid and hot environment, amorphous calcium carbonate is induced to be dissolved on the polyvinyl alcohol framework and recrystallized into calcite and vaterite shell layers, and therefore the composite aerogel material is obtained. While good heat insulation performance and flexibility are maintained, the mechanical strength and damp and heat resistance stability of the material are remarkably improved, efficient curing and utilization of carbon dioxide are achieved, and the material is suitable for the field of green energy-saving buildings.

Description

Technical Field

[0001] This invention belongs to the field of thermal insulation materials, specifically, it relates to a method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material. Background Technology

[0002] With the increasing urgency of building energy conservation and green low-carbon development, the development of high-performance thermal insulation materials to reduce energy loss and carbon emissions has become an important research direction in the field of materials science. Aerogels, with their unique three-dimensional nanoporous structure, can effectively suppress gas convection and solid-state heat conduction, exhibiting excellent thermal insulation performance and showing broad application potential in building insulation, industrial equipment insulation, and other fields. Among them, polyvinyl alcohol (PVA) aerogel has attracted widespread attention due to its wide availability of raw materials, biodegradability, and ease of forming an elastic porous framework through physical or chemical crosslinking. However, PVA aerogel still suffers from insufficient mechanical strength, poor water resistance, and susceptibility to structural relaxation or creep under humid and hot conditions, severely limiting its application in long-term practical engineering. To improve the mechanical properties of PVA aerogel, existing research typically employs strategies such as introducing other polymer chains for blending or strengthening chemical crosslinking. However, these methods still have significant limitations: compatibility issues between different polymer chains may lead to microphase separation, affecting material uniformity; while excessive chemical crosslinking often sacrifices the material's flexibility and porosity, and may even introduce toxic chemical residues, which is detrimental to the development of green and sustainable materials.

[0003] Calcium carbonate—especially its thermodynamically stable aragonite and calcite crystal forms—is a key structural component in widely found biogenic minerals (such as shells and nacre) and possesses excellent mechanical strength, making it an ideal natural reinforcing phase. However, current traditional methods for introducing calcium carbonate into aerogels mostly employ direct blending. In this method, the interfacial bonding between calcite particles and the aerogel crosslinker is weak, resulting in limited reinforcing effects. More importantly, it cannot effectively control the crystallization behavior of calcium carbonate; calcite crystals often grow disorderly in the pores, causing structural damage and pore collapse, making it difficult to achieve stable improvements in mechanical properties and instead damaging the core porous structure and thermal insulation function of the aerogel. Summary of the Invention

[0004] This invention addresses the technical problems of existing methods, such as weak interfacial bonding between calcite particles and aerogel crosslinkers, resulting in limited enhancement effects; inability to effectively control the crystallization behavior of calcium carbonate, leading to disordered growth of calcite crystals in pores, causing structural damage and pore collapse, making it difficult to achieve stable improvement in mechanical properties, and instead damaging the core porous structure and thermal insulation function of the aerogel. Therefore, this invention provides a method for preparing calcium carbonate-polyvinyl alcohol composite aerogel materials.

[0005] This invention develops a simple method that can precisely guide calcium carbonate (especially aragonite and calcite phases) to nucleate, grow, and form strong interfacial bonds within a three-dimensional PVA network while preserving the porous structure of the aerogel. This addresses the key challenge of synergistically improving the mechanical and thermal insulation properties of this type of material and has significant scientific and engineering application value.

[0006] To address the aforementioned technical problems, the present invention adopts the following technical solution: This invention first prepares a hydrogel by dissolving polyvinyl alcohol (PVA); then prepares micro-nano amorphous calcium carbonate (ACC) and a small amount of nano-calcite by introducing CO2 gas into a mixed solution of calcium chloride and magnesium chloride; subsequently, ACC, calcite and a small amount of aspartic acid are added to the PVA hydrogel and mixed uniformly, and then ACC-PVA composite aerogel is obtained by directional freezing and freeze-drying; finally, the ACC is induced to dissolve and recrystallize on the PVA framework to form a calcite shell by treating with a high concentration of CO2 atmosphere under humid heat conditions, thereby obtaining a calcium carbonate-polyvinyl alcohol composite aerogel material.

[0007] The purpose of this invention is to provide a method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material, comprising the following steps: Step 1: Add calcium chloride and magnesium chloride to deionized water and stir until dissolved. While sonicating, introduce CO2 gas. Stop the gas flow after a white suspension is completely formed. After filtration, obtain a mixture of amorphous calcium carbonate and nano-calcite. Step 2: Add polyvinyl alcohol to water, let it stand to absorb water and swell, heat to 60℃-90℃, stir while keeping warm until completely transparent, cool and let stand to remove bubbles, and obtain PVA solution; Step 3: Add aspartic acid, amorphous calcium carbonate and nano-calcite to the PVA solution in sequence, and stir until homogeneous to form a homogeneous calcium carbonate-PVA hydrogel. Step 4: Place the mold on a pre-cooled copper plate, pour the calcium carbonate-PVA hydrogel into the mold, freeze it in a directional manner, and freeze-dry it after demolding to obtain ACC-PVA aerogel. Step 5: Then, place the material in a humid and hot atmosphere with a high concentration of CO2, and then dry it; thus, calcium carbonate-polyvinyl alcohol composite aerogel material is obtained.

[0008] To facilitate those skilled in the art in fully implementing and scaling up this invention, detailed limitations are now provided on the process parameters, preferred ranges, typical implementation conditions, criteria, and control strategies for each step of the invention. The parameters are optional ranges: 1. Polyvinyl alcohol (PVA) Molecular weight (Mw): 10,000-205,000 g·mol -1(Example 1: 205,000 g·mol) -1 ).

[0009] PVA solution mass fraction: 3-10wt% (Example 1: 5wt% corresponds to 5g PVA / 95g water).

[0010] Dissolution conditions: Heat to 60-90℃, stir at 50-300 r / min (low speed to reduce gas introduction), for 30-90 min, and let stand for more than 8 hours after defoaming.

[0011] 2. Calcium and magnesium sources CaCl2 and MgCl2 (anhydrous or hydrated): The mass concentration depends on the final Ca... 2+ and Mg 2+ Concentration. Different Ca 2+ / Mg 2+ The concentration ratio affects the ratio of ACC to calcite in the calcium carbonate formation. When the Ca / Mg molar ratio is 9:1-4:1, stable ACC that can be transformed under subsequent induction can be obtained. Example 1 selected Ca... 2+ / Mg 2+ =8.5:1.5.

[0012] 3. Aspartic acid (L-Asp) The molar ratio was selected as 0.5%–3%; Example 1 used 1%.

[0013] Addition method: It can be added after dissolving in a small amount of deionized water or added directly as a solid and stirred evenly.

[0014] II. Preparation of ACC and a small amount of calcite Ventilation parameters (CO2) CO2 purity: Industrial CO2 (99%).

[0015] Flow rate: 0.05-1.0 L·min -1 (For a 100g solution, Example 1 selected 0.2L·min) -1 ).

[0016] Ventilation time: Determined by the appearance of calcium carbonate precipitation. Example 1: Stop venting CO2 after a white turbidity appears for 300 seconds.

[0017] Ultrasound is performed simultaneously during ventilation to ensure a full and uniform response.

[0018] Temperature and pH Reaction temperature: 5-40℃, low temperature is conducive to ACC formation; Example 1: room temperature 20-25℃.

[0019] pH monitoring: Before aeration, the pH is approximately 6-7. After aeration, the pH will decrease. Maintaining the pH in the range of 6-5 is beneficial for the formation of calcium bicarbonate intermediates and promotes ACC formation. Avoid pH < 4 (as this will make the system too acidic and dissolve CaCO3).

[0020] solid-liquid separation Filtration (vacuum filtration) or centrifugation: Centrifuge at 300-10,000g for 3-5 minutes or filter using a Buchner funnel; then wash briefly 2-3 times with deionized water or alcohol to remove residual salts (wash volume is 0.5-2 times that of the mother liquor).

[0021] The product is a moist precipitate; avoid prolonged exposure to air to prevent further transformation. It can be stored at low temperature for a short time or in alcohol for a long time until the next use.

[0022] Product Quality Criteria (ACC) The XRD pattern shows no or weak crystallization peaks, with broad arcs or no significant diffraction peaks; if obvious calcite or aragonite peaks are observed, it indicates that partial crystallization has occurred, and semi-quantitative analysis can be performed using GSAS or Rietveld.

[0023] III. Preparation of PVA-CaCO3 hydrogel Taking 100g of total water as an example: PVA 5g (5wt%), CaCl2 original solution to an equal amount of ACC (the precipitate is all about 1mol), aspartic acid to calcium carbonate mass ratio of 0.5%-2%, Example 1: 0.11g of aspartic acid was selected, which is 1% of the mass of calcium carbonate.

[0024] Mixed conditions Stirring rate: 200-400 r / min, temperature: 20-30℃, time: 10-30 min.

[0025] To ensure uniform dispersion, the ACC can be suspended and sonicated for 1-10 minutes (the time depends on the instrument power to prevent overheating).

[0026] The mixture is viscous suspension / gel. If necessary, the PVA content can be adjusted or the temperature can be maintained to achieve a suitable rheological state for casting. If too much gas is introduced by stirring before casting, vacuum treatment at 100 Pa for 10 min should be performed first.

[0027] IV. Directional Freezing and Freeze-Drying (Forming Section) directional freezing conditions Freezing temperature: -40 to -80°C; Example 1: -50°C.

[0028] Directional freezing time: 20-60 min (the higher the PVA and calcium carbonate content, the longer the freezing time should be; Example 1: 30 min).

[0029] Freeze-drying Freeze-drying temperature: -50℃ to -20℃, Example 1: -50℃.

[0030] Vacuum degree: 1-10 Pa; Example 1: 1 Pa.

[0031] Drying time: 24-72h (the higher the PVA and calcium carbonate content, the longer the drying time should be; Example 1: 48h).

[0032] V. Induction Treatment with Humid Heat and High Concentration CO2 Atmosphere (Key Step) Humid and hot conditions Relative humidity (RH): 70-95%, Example 1: 90%.

[0033] Temperature: 20-80℃, Example 1: 60℃.

[0034] Processing time: 0-10 days, relative humidity 97%, temperature 20℃ (the following data).

[0035] Humidity and temperature work together to significantly improve ACC solubility and promote ion migration.

[0036] CO2 partial pressure (local / circulating system): 0.1-1.0 atm (preferably 0.2-0.8 atm); a pure CO2 atmosphere will induce conversion more strongly.

[0037] CO2 flow rate: 0.1-1 L·min⁻¹ for static filling or circulation (depending on the size of the tank).

[0038] pH / Chemical Environment: CO2 and humid heat form a weakly acidic medium. A local pH of 5-6 favors the formation of the HCO3⁻ / Ca(HCO3)2 intermediate and promotes the redeposition of ACC into calcite. Avoid excessive acidity (pH < 4) to prevent over-dissolution.

[0039] Handling method It is recommended to place the aerogel sample block in a temperature and humidity controlled chamber and introduce CO2 to make the CO2 concentration in the chamber controllable; or place the sample in a reactor with CO2 circulation to create a humid and hot environment with saturated water vapor.

[0040] After processing, remove the product and place it in a desiccator for slight drying (at room temperature or 40°C, relative humidity above 50% for 1-4 hours) to stabilize the structure.

[0041] Compared with the prior art, the present invention has the following beneficial effects: In this invention, PVA forms a three-dimensional porous framework through physical cross-linking, and ACC adsorption and directional recrystallization generate a calcite layer on the framework surface, achieving a biomimetic structure of "organic framework – inorganic shell". The resulting material, while maintaining excellent thermal insulation performance and flexibility, significantly improves mechanical strength and resistance to humid heat, and simultaneously achieves efficient CO2 curing and utilization, making it suitable for the field of green and energy-saving buildings.

[0042] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0043] Figure 1 These are curves showing the change in calcium carbonate content of different crystal forms over time. Figure 2 These are XRD patterns of samples after different high-humidity curing times; Figure 3 This is a SEM image of aerogel that has not undergone high humidity curing (without crystal form transformation); Figure 4 This is a SEM image of aerogel after 6 days of high humidity maintenance (after crystal transformation); Figure 5 This is a SEM image of aerogel after 10 days of high humidity maintenance (after crystal transformation); Figure 6 This is a TEM image of calcium carbonate without high humidity conditioning (no crystal form transformation); Figure 7 This is a TEM image of calcium carbonate after 6 days of high humidity conditioning (after crystal transformation); Figure 8 This is a TEM image of calcium carbonate after 10 days of high humidity conditioning (after crystal transformation); Figure 9 These are the thermogravimetric (TG) curves of uncured, 6-day-cured, and 10-day-cured samples. Figure 10 These are the derivative thermogravimetric (DTG) curves of uncured, 6-day-cured, and 10-day-cured samples. Figure 11 It is a computed tomography (XCT) image; Figure 12 The stress-strain curve of an aerogel prepared with 5% PVA and 7.5% calcium carbonate is shown. Figure 13 These are Fourier transform infrared (FTIR) spectra of uncured, 6-day-cured, and 10-day-cured spectra. Figure 14 These are uncured, 6d-cured, and 10d-cured X-ray photoelectron spectroscopy (XPS) images. Figure 15This is an infrared thermogram of an aerogel prepared with 5% PVA and 7.5% calcium carbonate, used in a thermal conductivity experiment. Figure 16 This is a physical image of the calcium carbonate-polyvinyl alcohol composite aerogel material prepared according to the present invention. Detailed Implementation

[0044] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0045] Example 1: Combination Figures 1 to 16 This embodiment describes the preparation method of the calcium carbonate-polyvinyl alcohol composite aerogel material, which is carried out according to the following steps: Step 1: Add 9.4g of calcium chloride and 1.4g of magnesium chloride to 100g of deionized water and stir at 300r / min until dissolved, which takes 30min. While sonicating, CO2 gas is introduced until a stable white suspension is formed (the white turbidity lasts for 300s). Then stop the gas introduction and filter to obtain a mixture of amorphous calcium carbonate and nano-calcite. Step 2: Add 5g of polyvinyl alcohol to 95g of water, let it stand to absorb water and swell for 4 hours, heat to 90℃, stir under heat until completely transparent, which takes 1 hour, cool and let stand for 12 hours to defoam, and obtain PVA solution; Step 3: Add 0.11g of aspartic acid, the amorphous calcium carbonate obtained in Step 1 and nano-calcite to the PVA solution in sequence, and stir at 300r / min until homogeneous to form a homogeneous calcium carbonate-PVA hydrogel. Step 4: Place the mold on a pre-cooled copper plate, pour the calcium carbonate-PVA hydrogel into the mold, transfer it to a -50℃ low temperature bath for directional freezing for 30 min, demold it and place it in a freeze dryer, dry it at -50℃ and 1 Pa for 48 h to obtain ACC-PVA aerogel. Step 5: Then, place it in a high-concentration CO2 atmosphere with a relative humidity (RH) of 90%, a temperature of 60℃, and a CO2 partial pressure of 0.8 atm for 10 days, and then place it in a desiccator to dry for 4 hours at 0℃ and a relative humidity of 50%; thus, calcium carbonate-polyvinyl alcohol composite aerogel material is obtained.

[0046] The organic framework-inorganic shell biomimetic structure constructed in this invention effectively combines the flexibility of the PVA three-dimensional porous framework with the rigidity of the calcite inorganic shell, achieving a synergistic performance of "flexible yet not brittle, tough yet solid" in the material, and providing a standardized and reasonable approach for the structural design of high-performance composite aerogels.

[0047] This invention, while retaining the inherent excellent thermal insulation and flexibility of PVA aerogel, strengthens the mechanical strength and resistance to damp heat by forming a calcite shell layer through ACC directional recrystallization, breaking through the technical bottleneck of traditional aerogels that "difficult to balance thermal insulation and mechanical properties".

[0048] The preparation process of this invention achieves efficient solidification and utilization of CO2, transforming greenhouse gas into functional inorganic components that enhance material performance. It has the dual value of environmental benefits and material performance improvement, providing a stable and advantageous complete processing method for green and low-carbon material research and development.

[0049] Depend on Figure 2 It can be seen that characteristic peaks of calcite and aragonite appear and their peak intensities increase (calcite 2θ positions: 29.4°, 39.4°, 43.1°, etc.; aragonite 2θ positions: 24.7°, 26.9°, 32.7°, etc.).

[0050] Depend on Figure 3 , 4 Figures 5 and 6 show that the PVA framework surface forms a thin layer / shell composed of continuous or semi-continuous amorphous calcium carbonate, aragonite, and calcite, with the particle size changing from amorphous small particles to aragonite and calcite grains.

[0051] Figure 6 , 7 The transmission electron microscopy (TEM) images in Figure 8 also show the transformation of small amorphous calcium carbonate particles into aragonite and calcite grains.

[0052] TG / TGA evidence shows that the calcium carbonate crystal form has changed; pore structure (XCT): after high humidity curing, the porosity remains almost unchanged and the porousness is still preserved.

[0053] FTIR and XPS showed that no new bonds were formed between PVA and calcium carbonate, and no chemical changes occurred during high-humidity curing.

[0054] Figure 15 In the hot plate experiment, the hot plate temperature was 200 degrees Celsius. After 30 minutes, the temperature of the upper surface of the aerogel stabilized at 45.7 degrees Celsius. The thermal conductivity of the 5% PVA + 7.5% calcium carbonate aerogel in the experiment was calculated to be 0.0226 W / (m·K).

[0055] Figure 11The image shows an X-ray computed tomography (XCT) scan of the aerogel, and the porosity was calculated to be 90.374% through modeling. Physical properties: Compressive strength reaches over 2 mPa at low strain of 5%, thermal conductivity ≤0.021–0.030 W·m -1 ·K -1 (Apparent density).

[0056] Mg 2+ The presence of Ca can partially replace Ca during the formation stage of ACC. 2+ Mg enters the crystal lattice or adsorbs on the surface, forming local structural defects, thereby delaying the spontaneous transformation of calcium carbonate into calcite. 2+ The increase in Mg content was positively correlated with ACC stabilization time, but excessively high Mg content... 2+ This leads to a decrease in solution alkalinity and a reduction in ACC formation. Experiments have determined that a Ca / Mg molar ratio of 9:1–4:1 yields stable ACC that can be converted under subsequent induction. This regularity indicates that Mg in this system… 2+ Not only does it act as a phase-regulating ion, but it also provides a potential energy window for CO2-induced conversion.

[0057] Aspartic acid (Asp) contains two carboxyl groups, which can react with Ca... 2+ Weakly coordinated complexes are formed. Low doses (0.5–3%) of Asp can competitively adsorb onto the surface of ACC particles, locally weakening the stability of the Mg-Ca-CO3 bond in ACC, making it more soluble under humid and hot conditions. Simultaneously, the carboxyl groups of Asp provide directional sites, inducing the recrystallization of CaCO3 into aragonite and calcite on the PVA framework. This creates a two-way regulatory pattern of "weakening followed by recrystallization."

[0058] By adjusting the Asp content, the relationship between the ACC conversion rate and the shell thickness can be controlled. Asp < 0.5% → Incomplete conversion, discontinuous shell; Asp=0.5-3% → The recrystallization rate matches the adsorption rate of the PVA framework, forming a dense and continuous shell; Asp > 5% → Excessive complexation of Ca 2+ This leads to delayed crystallization or even the formation of disordered deposits.

[0059] This pattern indicates that the Asp content directly affects the density and uniformity of the shell, and is the core control parameter that determines the mechanical enhancement effect of aerogel.

[0060] Under humid and hot conditions with high CO2 concentration, CO2 dissolves to form H2CO3, which then reacts with the ACC surface. CaCO3 + CO2 + H2O ⇋ Ca 2+ +2HCO3 - When the local CO2 partial pressure increases or the pH decreases, the equilibrium shifts to the right, promoting ACC dissolution; as the Ca in the solution increases... 2+ With the increase of HCO3⁻ concentration, calcite redeposited on the PVA framework surface after local supersaturation, realizing a dynamic dissolution-recrystallization process.

[0061] There exists a quantifiable optimal condition window for this stage: temperature 40-70℃, CO2 partial pressure 0.2-0.8 atm, and relative humidity 85%-95%. When the CO2 concentration is too low, the system struggles to form sufficient calcium bicarbonate ions; while too high a concentration leads to an excessively low pH, causing partial hydrolysis or swelling of the PVA framework. This establishes the synergistic window law of the three factors—CO2 partial pressure, humidity, and temperature—in this induced process.

[0062] Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that no new bonds were formed between PVA and ACC nanoparticles. However, scanning electron microscopy (SEM) results showed that ACC was uniformly attached to the PVA surface, indicating that the stability of the aerogel mainly depends on physical adsorption and network structure. SEM observation of aerogels with different amounts of PVA and calcium carbonate revealed that controlling the PVA concentration could alter the framework pore size, thereby adjusting the calcite shell thickness. A general trend emerged: increased PVA content → decreased pore size → denser shell; excessively low PVA content → large pore size → discontinuous shell.

[0063] The preparation method of calcium carbonate-polyvinyl alcohol composite aerogel material in this invention At the level of interfacial interaction mechanism, it is explained that in the PVA / ACC aerogel system, non-chemically bonded physical adsorption and three-dimensional network entanglement can serve as the core driving force for material stability. Uniform loading of ACC nanoparticles on the PVA matrix surface can be achieved without relying on chemical bonding, thus expanding the application boundaries of weak interactions in the preparation of composite materials.

[0064] This invention identifies PVA concentration as the key regulatory factor for the microstructure of the aerogel at the structural control strategy level. By adjusting the gradient of a single variable, a precise match between the pore size of the framework and the compactness of the calcite shell can be achieved, providing a simple and efficient control path for the structural customization of aerogel materials.

[0065] Furthermore, by determining the control rules, this invention enhances the performance of aerogels by using high porosity for adsorption and dense shells for mechanical processes, thereby enabling targeted treatment of aerogels to meet the performance requirements of different application scenarios and improving the practical application flexibility and adaptability of calcium carbonate-polyvinyl alcohol composite aerogel materials.

[0066] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material, characterized by, The method comprises the following steps: Step 1, calcium chloride and magnesium chloride are added to deionized water, stirred to dissolve, CO2 gas is introduced while ultrasonic agitation, and the gas is stopped after the complete formation of white suspension, and then the mixture of amorphous calcium carbonate and nanometer calcite is obtained by filtration; Step 2, polyvinyl alcohol is added to water, and the water is absorbed and swelled by standing, heated to 60-90 DEG C, and stirred under heat preservation until completely transparent, and then the bubbles are removed by standing after cooling to obtain a PVA solution; Step 3, aspartic acid, amorphous calcium carbonate and nanometer calcite are sequentially added to the PVA solution, and stirred until uniform to form a uniform calcium carbonate-PVA hydrogel; Step 4, the mold is placed on a pre-cooled copper plate, the calcium carbonate-PVA hydrogel is poured into the mold, and directional freezing is carried out, and then the mold is removed after freezing and drying to obtain an ACC-PVA aerogel; Step 5, then placed in a humid heat and high concentration CO2 atmosphere, and then dried; that is, a calcium carbonate-polyvinyl alcohol composite aerogel material is obtained.

2. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 1, Ca 2+ and Mg 2+ are present in a molar ratio of (9-4):

1.

3. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 1, the volume purity of CO2 was 99%, and the flow rate was 0.05-1.0 L·min -1 .

4. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, Molecular weight (Mw) of polyvinyl alcohol in Step 2: 10,000-205,000 g·mol -1 .

5. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, The molar ratio of aspartic acid to calcium carbonate in step 3 is 0.5%-2%.

6. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 4, directional freezing is carried out at-40 to-80 DEG C.

7. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 4, freeze-drying is carried out at-50 DEG C to-20 DEG C.

8. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 5, CO2 is filled statically or circulated, and the CO2 partial pressure is 0.1 atm-1.0 atm.

9. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 5, the relative humidity is 70%-95%, and the temperature is 20 DEG C-80 DEG C.

10. The method for preparing a calcium carbonate-polyvinyl alcohol composite aerogel material according to claim 1, characterized in that, In step 5, freeze-drying is carried out at-50 DEG C to-20 DEG C.

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