A graphene-calcium carbonate composite material, its preparation method and application

Abstract

This application relates to the field of reinforcing materials, specifically disclosing a graphene-calcium carbonate composite material, its preparation method, and its application. The preparation method includes the following steps: S1, adding natural graphite to an aqueous solution of sodium carboxymethyl cellulose and ball milling it under supercritical carbon dioxide conditions to obtain a graphene nanosheet dispersion; S2, adding calcium chloride solution to the graphene nanosheet dispersion, adjusting the pH to 8-11, stirring, and obtaining a mixed solution; S3, adding sodium carbonate solution dropwise to the mixed solution, reacting, then centrifuging, washing with water, and drying to obtain the graphene-calcium carbonate composite material. This application also discloses the application of the graphene-calcium carbonate composite material prepared by the above method in cement-based composite materials. This application has the characteristic of achieving an organic combination of graphene and calcium carbonate, which can better enhance the function of cement-based materials.

Description

Technical Field

[0001] This application relates to the field of composite materials, and more specifically, to a graphene-calcium carbonate composite material, its preparation method, and its application. Background Technology

[0002] With the increasing demands for material performance in modern construction engineering, nanomaterials, due to their unique size effect, surface effect, and quantum effect, have shown great potential in improving the performance of cement-based materials. Graphene nanosheets (GNPs) and calcium carbonate (CaCO3), as two important nanomaterials, have received widespread attention in the field of cement-based material reinforcement.

[0003] Graphene nanosheets, as a two-dimensional material composed of a single layer of carbon atoms, possess excellent intrinsic properties, including an extremely high theoretical elastic modulus (approximately 1 TPa) and a high specific surface area (up to 2630 m²). 2 The graphene nanosheets possess unique two-dimensional sheet structure and other properties that give them a significant advantage in reinforcing cement-based materials. They can enhance the mechanical properties of cement-based materials through mechanisms such as filling pores, bridging microcracks, and providing heterogeneous nucleation sites.

[0004] Calcium carbonate, as an important inorganic nanomaterial, plays a dual role in the cement hydration process: physically, it provides heterogeneous nucleation sites for CSH gel and has a nanofilling effect; chemically, it reacts with aluminates to generate carboaluminate hydration products.

[0005] Based on the above characteristics, research on graphene, calcium carbonate and their composite nanomaterials has gradually emerged in recent years. However, current research mainly adopts the physical mixing method of graphene and calcium carbonate. The above method has a key problem: there is a lack of effective chemical bonding between graphene and calcium carbonate, and their dispersion behavior in cement paste is significantly different, making it difficult to ensure uniform distribution. As a result, when the above two nanomaterials are physically mixed to reinforce cement-based materials, the reinforcement effect is insufficient.

[0006] To address the aforementioned issues and further improve the reinforcing effect on cement-based materials, new solutions are needed for graphene-calcium carbonate composite materials. Summary of the Invention

[0007] In order to provide a new method for graphene-calcium carbonate composite materials to achieve organic combination of the two and better enhance their reinforcing effect, this application provides a graphene-calcium carbonate composite material, its preparation method and application.

[0008] In a first aspect, this application provides a method for preparing a graphene-calcium carbonate composite material, employing the following technical solution:

[0009] A method for preparing a graphene-calcium carbonate composite material includes the following steps:

[0010] S1. Natural graphite was added to an aqueous solution of sodium carboxymethyl cellulose (CMC) and ball-milled under supercritical carbon dioxide conditions to obtain a graphene nanosheet dispersion.

[0011] S2. Add calcium chloride solution to the graphene nanosheet dispersion, adjust the pH value to 8-11, stir and process to obtain a mixed solution;

[0012] S3. Add sodium carbonate solution dropwise to the mixture to induce a chemical reaction. Then, after centrifugation, wash with water and dry to obtain the graphene-calcium carbonate composite material.

[0013] By employing the above-mentioned technical solution, sodium carboxymethyl cellulose (CMC) is added as a dispersant during the supercritical carbon dioxide exfoliation process to prepare graphene nanosheets. CMC contains hydrophilic groups, and during supercritical carbon dioxide-assisted ball milling, CMC molecules adsorb onto the graphene surface, forming a protective adsorption layer that prevents the exfoliated sheets from re-aggregating. Furthermore, CMC forms a stable anchorage at the graphene edges, providing additional stabilization and reducing defects. The supercritical carbon dioxide environment promotes the uniform distribution of CMC molecules, reducing structural defects in the graphene during exfoliation and resulting in a graphene dispersion with good stability.

[0014] Calcium chloride solution was then added to the prepared graphene nanosheet dispersion. Under alkaline conditions, calcium ions were adsorbed onto the graphene surface. Simultaneously, sodium carboxymethyl cellulose on the graphene surface coordinated with the calcium ions, forming a calcium ion-rich layer. This controlled distribution of calcium ions on the graphene surface created conditions for subsequent calcium carbonate nucleation. The calcium ion-rich layer also provided active sites for calcium carbonate nucleation. Finally, sodium carbonate solution was added, and after a chemical reaction, the resulting calcium carbonate selectively precipitated and directionally grew on the graphene nanosheet surface, leading to chemical bonding between the calcium carbonate and graphene.

[0015] In the aforementioned nucleation process, the two-dimensional planar structure of graphene provides low-energy nucleation sites for calcium carbonate, especially at edges and defect sites, thus lowering the nucleation energy barrier. Sodium carboxymethyl cellulose molecules promote the formation of stable chemical bonds between calcium carbonate and graphene by regulating crystal growth and interfacial interactions. As a bridge, sodium carboxymethyl cellulose molecules form stable coordination between graphene and calcium carbonate, enhancing the interfacial bonding force and addressing the problem of missing chemical bonds in physical mixing. Supercritical fluid graphite exfoliation combined with sodium carboxymethyl cellulose molecules can regulate the calcium enrichment layer, enabling in-situ synthesis of calcium carbonate. This achieves uniform distribution of calcium carbonate on the graphene surface, forming a supported composite structure that can better enhance its reinforcing effect in cementitious matrices.

[0016] Optionally, after adding sodium carbonate solution to the mixture in step S3, the reaction conditions are controlled as follows: pH value of 9-11, temperature of 20-30℃, stirring speed of 200-400 rpm, and reaction time of 5-10 min.

[0017] By employing the above technical solutions and adjusting the conditions as described above, different types of calcium carbonate crystals can be formed. Under weakly alkaline conditions with a pH of 9-10, the two-dimensional structure of graphene can act as a template, and the calcium ions pre-adsorbed on its surface combine with carbonate ions, forming thermodynamically stable calcite-type calcium carbonate nanoparticles in situ under conditions of low stirring speed and short reaction time. Under strongly alkaline conditions with a pH of 10.5-11, and with the addition of sodium carboxymethyl cellulose during the preparation of graphene nanosheet dispersion by graphite exfoliation, its long-chain structure influences crystal growth during the formation of carbonic acid, leading to the formation of spherical aggregate structures, and finally obtaining spheroidal aragonite-type calcium carbonate nanoparticles in situ.

[0018] More specifically: Under strongly alkaline conditions with a pH of 10.5-11, sodium carboxymethyl cellulose (CMC) and graphene nanosheets synergistically regulate the crystal form and morphology of calcium carbonate: (1) The carboxyl group (-COO) in the CMC molecule - ) and Ca 2+ (1) Ions coordinate with each other, promoting multi-center nucleation; (2) The long-chain molecular structure of CMC selectively inhibits the growth of {104} crystal planes through steric hindrance, which is conducive to the formation of the kinetic product aragonite; (3) Graphene nanosheets provide a nucleation substrate with a large specific surface area, which together with CMC molecules constructs a three-dimensional network structure, guiding the uniform distribution of aragonite nanoparticles on the graphene surface; (4) Under high pH conditions, CMC molecules are fully ionized, enhancing their interaction with Ca. 2+ Its complexing ability, while promoting CO3 2- Increased concentration provides a driving force for the rapid formation of aragonite. This multi-layered synergistic effect ultimately enables the controllable in-situ synthesis of aragonite-type calcium carbonate nanoparticles.

[0019] In this application, by controlling the above reaction conditions, different types of calcium carbonate crystals can be formed. Specifically, under pH conditions of 10.5-11, a higher stirring speed is conducive to the formation of aragonite; while under pH conditions of 9-10, a lower stirring speed is conducive to the formation of calcite.

[0020] The formation of the two crystal forms mentioned above can create a graphene-calcium carbonate (calcite or aragonite) supported composite structure, achieving an effective combination of the two types of nanomaterials. When applied to cement-based materials, this structure can significantly improve their mechanical properties.

[0021] Optionally, in step S1, the mass concentration of the sodium carboxymethyl cellulose aqueous solution is 1.5-2.0%, and the concentration of graphene nanosheets in the graphene nanosheet dispersion is 50-100 mg / mL.

[0022] The conditions for supercritical carbon dioxide ball milling are: a processing temperature of 45-55℃ and a processing pressure of 12-18MPa.

[0023] By adopting the above technical solution, this application first obtains highly exfoliated graphene nanosheets through ball milling under supercritical CO2 conditions. Then, a calcium ion solution is added to the graphene dispersion to form a calcium ion enrichment layer on the graphene surface. Next, by adding sodium carbonate solution dropwise, calcium carbonate nanoparticles of a specific crystal form are synthesized in situ on the graphene surface, forming a composite structure of graphene nanosheets loaded with calcium carbonate.

[0024] By controlling the above conditions, a stable graphene nanosheet dispersion was obtained, with a graphene dispersion viscosity <3000 mPa·s, a graphene nanosheet thickness of 1-5 nm, a layer count of 1-10, a lateral dimension (sheet diameter) of 2-7 μm, and an electrical conductivity of 2.48-6.02 × 10⁻⁶. 4 S / m.

[0025] Optionally, in step S2, the molar concentration of the calcium chloride solution is 5-10 mM, and the volume ratio of the calcium chloride solution to the sodium carboxymethyl cellulose solution is 1:(1.8-2.2). After adjusting the pH value to 8-11, the solution is stirred at 25-40℃ for 3-5 min.

[0026] Optionally, in step S3, the molar concentration of the sodium carbonate solution is 5-10 mM, and the volume ratio of the sodium carbonate solution to the calcium chloride solution is 1:(0.8-1.2).

[0027] Optionally, the mass ratio of graphene nanosheets to calcium carbonate in the graphene-calcium carbonate composite material is 1:(20-50).

[0028] By adopting the above technical solution, the composite material with the above proportion can better exert a synergistic reinforcing effect in cement paste. When the graphene content is too low, it cannot provide enough nucleation sites; when the graphene content is too high, it will lead to agglomeration and consume too much sodium carboxymethyl cellulose dispersant. At the above proportion, both the dispersion stability of graphene and the effective loading of calcium carbonate particles can be ensured, achieving good bonding.

[0029] Optionally, the specific operation of washing with water after centrifugation in step S3 is as follows: after the reaction is completed, centrifuge at 5000-8000 rpm for 5-10 min, then wash the precipitate with water 3-5 times and dry it at 50-55℃ for 12-24 h. The amount of water added during washing is 2-3 times the mass of the precipitate, and graphene-calcium carbonate composite material is obtained.

[0030] By adopting the above technical solution, the control of the above purification steps, especially the reasonable control of the number of water washes and the amount of water added, can achieve the degree of CMC removal, retain an appropriate amount of functional CMC as a dispersant and interfacial compatibilizer. By controlling the above parameters, the interfacial structure of the composite material can be optimized, and the retention of an appropriate amount of CMC can help the composite material disperse in cement paste.

[0031] Secondly, this application provides a graphene-calcium carbonate composite material, which adopts the following technical solution:

[0032] A graphene-calcium carbonate composite material is prepared by the aforementioned preparation method.

[0033] By adopting the above technical solution, this application constructs a graphene-calcium carbonate composite control material with a gradient interface structure by in-situ loading calcium carbonate phase on the surface of graphene nanosheets based on liquid phase coprecipitation-interface control technology.

[0034] Thirdly, this application provides an application of a graphene-calcium carbonate composite material, employing the following technical solution:

[0035] Application of a graphene-calcium carbonate composite material in cement-based composite materials.

[0036] By adopting the above technical solution, the graphene-calcium carbonate composite material prepared by the method of this application is applied to cement-based materials. During the cement hydration process, it achieves a multi-effect synergistic enhancement effect of "nucleation site effect - chemical effect - template effect". More specifically, in the initial stage, the calcium carbonate phase provides heterogeneous nucleation sites, while the graphene nanosheets exert a template effect to guide the formation of CSH gel; in the middle stage, calcium carbonate participates in chemical reactions to generate carbon aluminate hydration products, and graphene continues to guide the directional growth of hydration products; in the later stage, a dense two-dimensional network structure is formed.

[0037] This composite material achieves coordinated temporal and spatial control during cement hydration. Temporally, it achieves full-process control of hydration through mechanisms at different stages. Spatially, it achieves directional growth and structural optimization of hydration products through a two-dimensional template effect. Ultimately, the composite material obtained in this application increases the compressive strength of cement-based materials by 25-35% and significantly improves the density of the microstructure, making it widely applicable to high-performance concrete and special engineering materials.

[0038] Optionally, the amount of graphene-calcium carbonate composite material added is 0.01-0.1 wt% of cement.

[0039] Optionally, the specific method for adding the composite material to the cement-based composite material is as follows:

[0040] The graphene-calcium carbonate composite material was ultrasonically pre-dispersed in water for 5 minutes to form a uniform dispersion.

[0041] Add the dispersion liquid during cement mixing.

[0042] In summary, this application has the following beneficial effects:

[0043] 1. In this application, highly exfoliated graphene nanosheets are first obtained through ball milling under supercritical CO2 conditions. Then, a calcium ion solution is added to the graphene dispersion to form a calcium ion enrichment layer on the graphene surface. Next, a sodium carbonate solution is added dropwise to synthesize calcium carbonate nanoparticles of a specific crystal form in situ on the graphene surface, forming a composite structure of graphene nanosheets loaded with calcium carbonate. Compared with the traditional method of simply mixing the two materials and adding them to cement-based materials, which results in insufficient reinforcement effect, the method provided in this application is based on liquid-phase co-precipitation-interface control technology to load calcium carbonate in situ on the surface of graphene nanosheets, constructing a graphene-calcium carbonate composite control material with a gradient interface structure.

[0044] 2. The graphene-calcium carbonate composite material in this application has significant technical advantages and application value in cement-based materials. Specifically: In terms of performance improvement, after adding the composite material, the 28-day compressive strength of cement-based materials increases by 15-30%, and the flexural strength increases by 10-30%. Moreover, the reinforcing effect of the composite material significantly exceeds the simple superposition of graphene nanosheets and calcium carbonate used alone, demonstrating a clear synergistic reinforcing effect. In terms of microstructure optimization, the composite material reduces the porosity of cement-based materials by 20-35% and the average pore size by 30-40%, forming a more dense and uniform microstructure. In terms of economic benefits, the composite material dosage is only 0.01-0.10% of the cement mass, the preparation process is simple and easy to control, and the equipment investment is small. It has good prospects for industrial application and cost-effectiveness, providing a new technical path for the development of high-performance cement-based materials. Attached Figure Description

[0045] Figure 1 This is a SEM scan of the graphene-calcium carbonate composite material prepared in Example 1 of this application;

[0046] Figure 2 This is a SEM scan of the graphene-calcium carbonate composite material prepared in Example 2 of this application;

[0047] Figure 3This is a SEM scan of the graphene "templating effect" in the cement paste prepared in Comparative Example 2 of this application;

[0048] Figure 4 This is a SEM scan of the graphene-calcium carbonate composite material in the cement paste prepared in Application Example 2 of this application, showing the "templating effect".

[0049] Figure 5 The activation energy of calcium carbonate in Example 2 of this application is calculated by thermogravimetric analysis combined with kinetic equations.

[0050] Figure 6 The activation energy is calculated by thermogravimetric analysis combined with kinetic equations for the graphene-calcium carbonate composite material prepared in Example 2 of this application. Detailed Implementation

[0051] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0052] This application, based on the multi-scale mechanism of cement hydration product formation, utilizes the two-dimensional structural characteristics and surface tunability of graphene nanosheets. Active groups are introduced through surface functionalization, and calcium carbonate is in-situ loaded onto the surface using liquid-phase co-precipitation technology to form a composite material with a gradient interface structure. This composite material organically combines the template-directing effect of graphene nanosheets with the nucleation-promoting effect of calcium carbonate, constructing a multifunctional composite material structure system with synergistic reinforcement. It possesses novel functional properties such as directional growth induction and multi-scale structural regulation, providing a new technical path for developing next-generation high-performance cement-based materials.

[0053] Example 1

[0054] A method for preparing a graphene-calcium carbonate composite material includes the following steps:

[0055] S1. Preparation and functionalization of graphene nanosheets:

[0056] 8.0 g of natural graphite (thickness 3 nm, transverse dimension 2-5 μm) was weighed and added to 100 mL of sodium carboxymethyl cellulose aqueous solution with a mass fraction of 1.8%. The solution was ball-milled for 4 h under supercritical carbon dioxide conditions at a temperature of 50 °C, a pressure of 15 MPa, and a flow rate of 8 L / min to obtain a highly exfoliated graphene nanosheet dispersion with a graphene nanosheet concentration of 80 mg / mL.

[0057] S2, calcium ion pre-adsorption:

[0058] In step S1, 50 mL of calcium chloride solution with a molar concentration of 8 mM was added to the graphene dispersion, sodium hydroxide was added to adjust the pH value to 9.0, and the mixture was stirred at 35°C for 4 min to obtain a mixed solution, so that a calcium ion enrichment layer was formed on the graphene surface.

[0059] S3, In-situ synthesis of calcite-type calcium carbonate:

[0060] 50 mL of sodium carbonate solution with a molar concentration of 8 mM was added dropwise to the mixture at a flow rate of 100 mL / min. The mixture was then reacted for 10 min at a pH of 10, a temperature of 25 °C, and a stirring speed of 300 rpm to generate calcite-type calcium carbonate nanoparticles with a particle size of 600-800 nm in situ.

[0061] Then, the graphene-calcium carbonate composite material was obtained by centrifugation at 6000 rpm for 8 min, followed by washing with deionized water 4 times and drying at 50℃ for 18 h. The mass ratio of graphene nanosheets to calcium carbonate in the graphene-calcium carbonate composite material was 1:30.

[0062] The obtained graphene-calcium carbonate was observed by SEM as follows: Figure 1 As shown, the microstructure of calcium carbonate particles uniformly distributed on the surface of graphene nanosheets is revealed. Calcite-type calcium carbonate nanoparticles (approximately 600-800 nm in diameter) are successfully loaded onto the graphene nanosheets, forming a composite material with a gradient interface structure. This demonstrates that the in-situ composite of graphene and calcium carbonate achieved in this application through liquid-phase co-precipitation-interface control technology provides a foundation for the subsequent directional growth of cement hydration products. Furthermore, XRD analysis shows that the composite material contains approximately 85% calcite-type calcium carbonate.

[0063] Example 2

[0064] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 1, except that in step S2, the molar concentration of calcium chloride is 6 mM, and sodium hydroxide is added to adjust the pH value to 11. The mixture is stirred at 30°C for 3 min to obtain a mixed solution.

[0065] Step S3: In-situ synthesis of spheroidal calcium carbonate:

[0066] 50 mL of a 6 mM sodium carbonate solution was added dropwise to the mixture at a flow rate of 80 mL / min. The mixture was then reacted for 10 min at a pH of 11, a temperature of 25 °C, and a stirring speed of 400 rpm to generate spheroidal calcium carbonate nanoparticles with a particle size of 400-600 nm in situ.

[0067] The remaining operations are the same as in Example 1. The SEM image of the resulting graphene-calcium carbonate composite material, which is predominantly of the spheroidal aragonite type, is shown below. Figure 2 As shown, the uniform distribution of aragonite-type calcium carbonate nanoparticles on the surface of graphene nanosheets proves that graphene composite materials with different crystalline calcium carbonate loadings can be prepared by adjusting the reaction conditions.

[0068] Example 3

[0069] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 1, with the difference being:

[0070] S1. Preparation and functionalization of graphene nanosheets:

[0071] Weigh 5.0g of natural graphite (thickness 3nm, transverse dimension 2-5μm) and add it to 100mL of sodium carboxymethyl cellulose aqueous solution with a mass fraction of 1.5%. Ball mill the solution for 3h under supercritical carbon dioxide conditions at a temperature of 45℃, a pressure of 12MPa, and a flow rate of 5L / min to obtain a highly exfoliated graphene nanosheet dispersion with a graphene nanosheet concentration of 50mg / mL.

[0072] S2, calcium ion pre-adsorption:

[0073] In step S1, 50 mL of calcium chloride solution with a molar concentration of 5 mM was added to the graphene dispersion, sodium hydroxide was added to adjust the pH value to 8.0, and the mixture was stirred at 25°C for 5 min to obtain a mixed solution, so that a calcium ion enrichment layer was formed on the graphene surface.

[0074] S3, In-situ synthesis of calcite-type calcium carbonate:

[0075] 50 mL of a 5 mM sodium carbonate solution was added dropwise to the mixture at a flow rate of 100 mL / min. The mixture was then reacted for 5 min at a pH of 9, a temperature of 20 °C, and a stirring speed of 200 rpm to generate calcite-type calcium carbonate nanoparticles in situ.

[0076] Then, the graphene-calcium carbonate composite material was obtained by centrifugation at 5000 rpm for 10 min, followed by washing with deionized water three times and drying at 50℃ for 24 h.

[0077] Example 4

[0078] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 1, with the difference being:

[0079] S1. Preparation and functionalization of graphene nanosheets:

[0080] 10.0 g of natural graphite (thickness 3 nm, transverse dimension 2-5 μm) was weighed and added to 100 mL of sodium carboxymethyl cellulose aqueous solution with a mass fraction of 2.0%. The solution was ball-milled for 5 h under supercritical carbon dioxide conditions at a temperature of 55 °C, a pressure of 18 MPa, and a flow rate of 10 L / min to obtain a highly exfoliated graphene nanosheet dispersion with a graphene nanosheet concentration of 100 mg / mL.

[0081] S2, calcium ion pre-adsorption:

[0082] In step S1, 50 mL of calcium chloride solution with a molar concentration of 10 mM was added to the graphene dispersion, sodium hydroxide was added to adjust the pH value to 10.5, and the mixture was stirred at 40°C for 3 min to obtain a mixed solution, so that a calcium ion enrichment layer was formed on the graphene surface.

[0083] S3, in-situ synthesis of aragonite-type calcium carbonate:

[0084] 50 mL of a 10 mM sodium carbonate solution was added dropwise to the mixture at a flow rate of 100 mL / min. The mixture was then reacted for 10 min at a pH of 11, a temperature of 30 °C, and a stirring speed of 400 rpm to generate spheroidal calcium carbonate nanoparticles in situ.

[0085] Then, the graphene-calcium carbonate composite material was obtained by centrifugation at 8000 rpm for 5 min, followed by washing with deionized water 5 times and drying at 55℃ for 12 h.

[0086] Comparative Example 1

[0087] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 1, except that in step S1, the sodium carboxymethyl cellulose solution is replaced by an equal amount of sodium dodecyl sulfate solution with the same mass concentration.

[0088] In the following application examples, PO 52.5 ordinary Portland cement is used.

[0089] Application Example 1

[0090] A method for applying a graphene-calcium carbonate composite material involves adding the graphene-calcium carbonate composite material obtained in Example 1 to a cement-based material with a water-cement ratio of 0.5 (mass ratio of water to cement), wherein the amount of graphene-calcium carbonate composite material added is 0.03% of the cement mass, thereby obtaining a cement paste containing the graphene-calcium carbonate composite material. The specific method of adding the graphene-calcium carbonate composite material is as follows:

[0091] The graphene-calcium carbonate composite material was added to 3 times its mass of water and ultrasonically pre-dispersed for 5 minutes to form a uniform dispersion.

[0092] When mixing cement and water, the dispersion obtained after ultrasonic pre-dispersion is added and mixed evenly to ensure uniform distribution of the graphene-calcium carbonate composite material in the cement paste, thus obtaining the cement paste.

[0093] Application Example 2-4

[0094] A method for applying a graphene-calcium carbonate composite material is carried out according to the method in Application Example 1, except that the graphene-calcium carbonate composite material obtained in Examples 2-4 is added to a cement-based material with a water-cement ratio of 0.5 to obtain a cement paste.

[0095] Application Example 5-7

[0096] An application method of a graphene-calcium carbonate composite material is carried out according to the method in Application Example 2, except that the amount of graphene-calcium carbonate composite material added is 0.01%, 0.05% and 0.1% of the cement mass, respectively.

[0097] Performance testing

[0098] A cement-based material with a water-cement ratio of 0.5 was prepared as a baseline control group;

[0099] Cement slurry was prepared by replacing the graphene-calcium carbonate composite material with graphene nanosheets in equal amounts as Application Example 1.

[0100] Cement paste was prepared according to the method in Application Example 1, with an equal amount of graphene-calcium carbonate composite material replaced by calcite-type calcium carbonate, as Application Comparative Example 2.

[0101] The cement paste prepared according to the method in Application Example 1, but with the graphene-calcium carbonate composite material replaced by calcite-type calcium carbonate and the addition amount being 1% of the cement mass, is used as Application Comparative Example 3.

[0102] Following the method in Application Example 1, the graphene-calcium carbonate composite material was replaced with a mixture of graphene nanosheets and calcite-type calcium carbonate. The graphene nanosheets and calcium carbonate were added to the cement material by physical mixing. The mass ratio of graphene nanosheets to calcite-type calcium carbonate was 1:30. The resulting cement paste was used as Application Comparative Example 4.

[0103] The cement paste prepared by adding the graphene-calcium carbonate composite material obtained in Comparative Example 1 to the cement material according to the method in Application Example 1 is used as Application Comparative Example 5.

[0104] The cement pastes prepared from the above application examples, application comparison examples, and benchmark control groups were tested for 3d compressive strength, 3d flexural strength, 28d compressive strength, and 28d flexural strength according to GB / T 17671-2021. The test results are shown in Table 1 below.

[0105] Table 1:

[0106]

[0107] Referring to the test results in Table 1 above, and comparing them with those of Application Example 1 and the baseline control group, it can be seen that the addition of graphene-calcium carbonate composite material to cement-based materials can have a significant reinforcing effect. Combining the test results of Application Example 1 and Application Example 2, the composite material formed by the spheroidal calcium carbonate crystal form has a better reinforcing effect on cement. Furthermore, combining the test results of Application Example 2 and Application Examples 5-7, it can be seen that the reinforcing effect is better when the graphene-calcium carbonate composite material content is 0.03% of the cement mass, especially with a significant increase in 3-day compressive strength. Excessive addition can lead to the aggregation of graphene in the matrix, affecting its interfacial interaction with calcium carbonate and thus limiting its reinforcing effect.

[0108] Referring to the test results of the baseline control group and Comparative Examples 2 and 4, when graphene-calcium carbonate was replaced with graphene or calcium carbonate nanoparticles in equal amounts for reinforcement, the reinforcement effect was effective, but weaker than that of the composite material in Application Example 1. Combining this with the test results of Comparative Example 3, using calcium carbonate alone for reinforcement, even with increased dosage, was effective. Combining this with the test results of Comparative Example 4, when graphene and calcium carbonate nanomaterials were simply physically mixed and directly added, the reinforcement effect was weak, which is related to the interface bonding and distribution of the two materials. The graphene-calcium carbonate composite material prepared by the in-situ composite method in this application showed a significantly better reinforcement effect than the physical mixing method. The composite significantly reduced the activation energy of calcium carbonate, demonstrating the effectiveness of the multi-scale synergistic reinforcement mechanism of "nucleation effect-chemical effect-template effect".

[0109] Additionally, refer to Figure 3 In Comparative Example 2, when only graphene nanosheets were added to the cement, the microstructure of the cement slurry was observed. Although the graphene nanosheets themselves have a certain template effect, guiding the growth of hydration products, the lack of synergistic effect from calcium carbonate limits their reinforcing effect. Furthermore, combined with... Figure 4 Microscopic images show the template effect of graphene-calcium carbonate composite materials in cement during the cement hydration process. The composite material guides the cement products to grow directionally along a two-dimensional axis, forming a high-density gel network. This directional growth structure improves the microstructure density of the cement paste and enhances the mechanical properties of cement-based materials. Combined with... Figure 5 and Figure 6The activation energy curve of the composite material reflects the promoting effect of the composite material on the cement hydration reaction.

[0110] This application utilizes an in-situ composite preparation technology of graphene nanosheets loaded with calcium carbonate (especially aragonite type) to achieve synergistic regulation of the cement hydration process, significantly improving the overall performance of cement-based materials. This technology is simple, cost-effective, and has broad application prospects in high-performance concrete, precast components, and special engineering materials.

[0111] To further address the issue of reduced reinforcing effect due to graphene agglomeration in the matrix affecting the effective bonding of calcium carbonate when the amount of graphene added to the composite material increases, this application incorporates polyvinylpyrrolidone (PVP) into the sodium carboxymethyl cellulose aqueous solution during the preparation of the graphene-calcium carbonate composite material. The hydrophobic segments of PPVD adsorb onto the graphene surface, while the hydrophilic segments bind with sodium carboxymethyl cellulose through hydrogen bonding, enhancing the steric hindrance effect and further improving the dispersion uniformity of graphene. A stable dispersion system is formed between PPVD and sodium carboxymethyl cellulose. The resulting composite material exhibits even higher reinforcing effects when its addition to the cement matrix increases, as detailed below:

[0112] Example 5

[0113] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 2, except that when natural graphite is added to the sodium carboxymethyl cellulose aqueous solution in step S1, polyvinylpyrrolidone is also added at the same time, and the amount of polyvinylpyrrolidone added is 0.2 wt% of natural graphite.

[0114] Example 6

[0115] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 2, except that when natural graphite is added to the sodium carboxymethyl cellulose aqueous solution in step S1, polyvinylpyrrolidone is also added at the same time, and the amount of polyvinylpyrrolidone added is 0.1 wt% of natural graphite.

[0116] Example 7

[0117] A method for preparing a graphene-calcium carbonate composite material is carried out according to the method in Example 2, except that when natural graphite is added to the sodium carboxymethyl cellulose aqueous solution in step S1, polyvinylpyrrolidone is also added at the same time, and the amount of polyvinylpyrrolidone added is 0.3 wt% of natural graphite.

[0118] Application Example 8-10

[0119] A method for applying a graphene-calcium carbonate composite material is carried out according to the method in Application Example 2, except that the graphene-calcium carbonate composite material obtained in Examples 5-7 is added to the cement-based material at 0.03% of the cement mass to obtain cement paste.

[0120] Application Example 11-13

[0121] A method for applying a graphene-calcium carbonate composite material is carried out according to the method in Application Example 8, except that the graphene-calcium carbonate composite material obtained in Example 5 is added to the cement-based material at addition amounts of 0.05, 0.07 and 0.1% of the cement mass, respectively, to obtain cement paste.

[0122] The cement pastes prepared in Application Examples 8-13 were also tested for 3d compressive strength, 7d flexural strength, 28d compressive strength, and 28d flexural strength. The test results are shown in Table 2 below.

[0123] Table 2:

[0124]

[0125] Referring to the test results in Table 2 above, when adding the same mass of graphene-calcium carbonate composite material, the composite material prepared in Example 5, which uses a mixture of polyvinylpyrrolidone and sodium carboxymethyl cellulose to form a dispersion system, has a better reinforcing effect. Combined with the test results of Application Examples 11-13, the graphene-calcium carbonate composite material prepared in Example 5 has a better reinforcing effect when the amount added to cement material is increased to 0.05%. It has a better reinforcing effect on cement material, and the problem of agglomeration caused by its large addition is improved, further enhancing the reinforcing effect.

[0126] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a graphene-calcium carbonate composite material, characterized in that, Includes the following steps: S1. Natural graphite was added to an aqueous solution of sodium carboxymethyl cellulose and ball-milled under supercritical carbon dioxide conditions to obtain a graphene nanosheet dispersion. S2. Add calcium chloride solution to the graphene nanosheet dispersion, adjust the pH value to 8-11, stir and process to obtain a mixed solution; S3. Add sodium carbonate solution dropwise to the mixture, react, then centrifuge, wash with water, and dry to obtain graphene-calcium carbonate composite material; In step S3, after adding sodium carbonate solution to the mixture, the reaction conditions are controlled as follows: pH value is 9-11, temperature is 20-30℃, stirring speed is 200-400rpm, and reaction time is 5-10 minutes. The conditions for ball milling under supercritical carbon dioxide in step S1 are: processing temperature of 45-55℃ and processing pressure of 12-18MPa. In step S1, the mass concentration of sodium carboxymethyl cellulose aqueous solution is 1.5-2.0%, and the concentration of graphene nanosheets in the graphene nanosheet dispersion is 50-100 mg / mL. In step S2, the molar concentration of the calcium chloride solution is 5-10 mM, and the volume ratio of the calcium chloride solution to the sodium carboxymethyl cellulose solution is 1:(1.8-2.2).

2. The method for preparing a graphene-calcium carbonate composite material according to claim 1, characterized in that: In step S3, the molar concentration of the sodium carbonate solution is 5-10 mM, and the volume ratio of the sodium carbonate solution to the calcium chloride solution is 1:(0.8-1.2).

3. The method for preparing a graphene-calcium carbonate composite material according to claim 1, characterized in that: In the graphene-calcium carbonate composite material, the mass ratio of graphene nanosheets to calcium carbonate is 1:(20-50).

4. The method for preparing a graphene-calcium carbonate composite material according to claim 1, characterized in that: The specific operation of washing with water after centrifugation in step S3 is as follows: after the reaction is completed, centrifuge at 5000-8000 rpm for 5-10 min, then wash with water 3-5 times, and then dry at 50-55℃ for 12-24 h to obtain graphene-calcium carbonate composite material.

5. A graphene-calcium carbonate composite material, characterized in that: It is prepared by the preparation method described in any one of claims 1-4.

6. The application of the graphene-calcium carbonate composite material as described in claim 5, characterized in that: Application of graphene-calcium carbonate composites in cement-based composites.

7. The application of the graphene-calcium carbonate composite material according to claim 6, characterized in that, The amount of graphene-calcium carbonate composite material added is 0.01-0.1 wt% of cement.

Images