Preparation method of nacre-like titanium carbide reinforced aragonite flake block composite material

Abstract

The present application relates to a kind of preparation methods of imitating shell titanium carbide reinforced aragonite sheet bulk composite materials.First, aragonite sheet is obtained from shell waste by peeling, aragonite sheet is bridged by titanium carbide MXene nanosheet, and is combined with cellulose nanofiber and polyvinyl alcohol by hydrogen bond, finally, imitating shell titanium carbide reinforced aragonite sheet bulk composite materials are prepared by the technology of blade coating and hot pressing.The obtained imitating shell titanium carbide reinforced aragonite sheet bulk composite materials have excellent mechanical properties and conductivity, and are called conductive shell.The bending strength and fracture toughness of conductive shell are 282 MPa and 6.3 MPa m 1 / 2 , respectively, which are better than natural shell.In addition, the conductivity of conductive shell is about 0.01 S m ‑1 , which can realize the self-monitoring function of structural integrity, and has electromagnetic shielding performance of 37 dB in the frequency range of 8.2-12.4 GHz.

Description

Technical Field

[0001] This invention relates to a method for preparing a shell-like titanium carbide reinforced aragonite flake bulk composite material, belonging to the field of nanocomposite material preparation. Background Technology

[0002] Shell waste is an abundant and inexpensive natural renewable resource, attracting significant research attention due to its bioactivity, corrosion resistance, excellent strength and toughness, high hardness, and adsorption properties. However, limited by recycling technology, over 10 million tons of shells are dumped in landfills globally each year, causing severe environmental pollution and leading to the loss of natural resources. Therefore, increasing the added value of shell waste is beneficial for mitigating organic pollution and enhancing sustainable development. Specifically, the nacreous layer of shells, composed of 95 vol% aragonite flakes (calcium carbonate) and a thin layer of organic matter, exhibits three orders of magnitude greater toughness than aragonite flakes. Inspired by this, high-performance shell-like bulk composite materials were prepared using various two-dimensional materials as assembly units, including alumina (Al2O3) (Science 2008, 322, 1516-1520), montmorillonite (MMT) (Adv. Funct. Mater. 2017, 27, 1605378), mica (Nat. Commun. 2020, 11, 5401), layered double hydroxide (LDH) (Adv. Funct. Mater. 2018, 28, 1801614), graphene oxide (GO) (Nat. Mater. 2022, 21, 1121-1129), and transition metal carbides / nitrides (MXene) (Angew. Chem. Int. Edit. 2023, 62, e202216874). While high-performance shell-like bulk composites have been prepared using these two-dimensional materials, these composites involve costly and complex chemical synthesis or mineral resource extraction. Aragonite flakes, as natural "bricks" from shells, are ideal assembly building blocks, but are often overlooked and discarded, causing environmental pollution and resource waste. Therefore, utilizing aragonite flakes peeled from natural shells as assembly building blocks, and introducing functional components to reassemble high-performance bulk composites, is a very promising strategy that will effectively utilize shell waste and alleviate resource shortages.

[0003] Currently, relevant patents concerning shell-like bulk composite materials include: a bulk biomimetic material and its preparation method and application (CN105079887A), a composite material with a shell-like nacre layered structure and its preparation method and application (CN105774182A), a three-dimensional shell-like structural material and its preparation method (CN108912602B), a preparation method of a biomimetic shell-like ceramic and metal composite material (CN110004347B), a nanocellulose-mica sheet composite board and its preparation method (CN112094439A), a wood fiber-based composite material with a shell-like nacre structure and its preparation method (CN110978679B), and a lightweight, high-strength shell-like composite material and its preparation method (CN112266497B), etc. However, these patents only discuss the development of novel two-dimensional nanomaterials and their use as assembly units to prepare bulk composite materials, with few reports on the interfacial interactions and mechanisms related to aragonite sheet bulk composite materials. Summary of the Invention

[0004] The technical problem solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material, which can successfully prepare a shell-like titanium carbide reinforced aragonite flaky block composite material with high flexural strength, high fracture toughness and electrical conductivity.

[0005] This invention provides a simple and scalable bottom-up assembly method that combines coating and hot-pressing processes to bridge aragonite flakes peeled from shell waste with MXene nanosheets, preparing a strong and tough shell-inspired titanium carbide-reinforced aragonite flake bulk composite material. The synergistic effect of MXene nanosheet bridging and hydrogen bonding effectively inhibits crack propagation, thereby improving the fracture toughness and flexural strength of the composite material. Simultaneously, the conductive network formed by the MXene nanosheet bridging gives the shell-inspired titanium carbide-reinforced aragonite flake bulk composite material a self-monitoring function for structural integrity and electromagnetic shielding properties.

[0006] The present invention is achieved through the following technical solution: First, aragonite flakes are stripped off on a large scale from shell waste; second, aragonite flakes are functionalized with MXene to obtain MXene-functionalized aragonite flakes; then, a composite film of MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol is obtained by a scraping coating method; finally, the composite film is stacked, soaked and hot-pressed to obtain a shell-inspired titanium carbide reinforced aragonite flake block composite material.

[0007] The specific implementation steps of this invention are as follows:

[0008] A method for preparing a shell-inspired titanium carbide reinforced aragonite flaky bulk composite material includes the following steps:

[0009] (1) Disperse the nacreous layer of the shell into a sodium hydroxide / urea / deionized water system, and obtain aragonite flakes by stirring, filtration and drying; then disperse the aragonite flakes into deionized water by ultrasonic treatment to form an aragonite flake dispersion.

[0010] (2) Titanium carbide (Ti3C2T) was obtained by in-situ chemical etching. x MXene nanosheet solution;

[0011] (3) Disperse the aragonite flakes described in step (1) into a mixed solution of deionized water and ethanol, and then add MXene nanosheet solution for stirring reaction; obtain MXene functionalized aragonite flake (MXene / aragonite flake) dispersion by washing and centrifugation;

[0012] (4) Dissolve cellulose nanofibers in deionized water to prepare a cellulose nanofiber solution;

[0013] (5) Weigh out polyvinyl alcohol and dissolve it in deionized water to prepare a polyvinyl alcohol solution;

[0014] (6) Mix the MXene-functionalized aragonite flake dispersion, cellulose nanofiber solution and polyvinyl alcohol solution evenly to obtain a uniform dispersion of MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol.

[0015] (7) After degassing the MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol uniform dispersion obtained in step (6), a composite film is obtained by a scraping method.

[0016] (8) Cut the composite film obtained in step (7) into films of the same size, stack them, soak them and hot press them to obtain a shell-like titanium carbide reinforced aragonite sheet block composite material.

[0017] Furthermore, in step (1), the particle size of the cellulose nanofibers is 2–10 nm. For example, the particle size of the cellulose nanofibers is 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm.

[0018] Furthermore, in step (4), the weight-average molecular weight of polyvinyl alcohol is 25,000 to 300,000, and the degree of alcoholysis is 98 to 99%.

[0019] Further, in step (7), the thickness of the film is 5 to 20 μm. For example, the thickness of the film is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 17 μm, 19 μm or 20 μm.

[0020] Further, in step (1), the preparation process of aragonite flakes is as follows: the nacreous shell layer is added to a mixed solution containing urea, sodium hydroxide and deionized water and stirred. The mass ratio of sodium hydroxide to urea is 1:9 to 5:5 (for example, the mass ratio of sodium hydroxide to urea is 1:9, 1:8.5, 1:8, 1:7.5, 1:7, 1:6.5, 1:6, 1:5.5, 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5 or 5:5). Then the supernatant is removed, the precipitate is washed, filtered, and aragonite flakes are obtained and prepared into an aragonite flake aqueous dispersion. Preferably, in step (1), the mass ratio of sodium hydroxide to urea is 1:2.

[0021] Further, in step (2), the preparation process of the MXene solution is as follows: the raw material Ti3AlC2MAX phase is added to a solution containing hydrochloric acid (HCl) and lithium fluoride (LiF), and the mixture is stirred under heating conditions; the reaction mixture is centrifuged, washed with deionized water, and the supernatant is discarded; the precipitate is then dispersed in deionized water, and Ti3C2T is obtained by shaking and gradient centrifugation. x MXene nanosheet dispersion.

[0022] Further, in step (3), the mass ratio of deionized water to ethanol is 1:9 to 5:5 (for example, the mass ratio of deionized water to ethanol is 1:9, 1:8.5, 1:8, 1:7.5, 1:7, 1:6.5, 1:6, 1:5.5, 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5 or 5:5), and the mass ratio of MXene to aragonite flakes is 1:9 to 9:1 (the mass ratio of MXene to aragonite flakes is 1:9, 1:8.5, 1:8, 1:7.5, 1:1.5 or 5:5). :7, 1:6.5, 1:6, 1:5.5, 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1 or 9:1); Preferably, in step (3), the mass ratio of deionized water to ethanol is 2:8, and the mass ratio of MXene to aragonite flakes is 2:8.

[0023] Further, in step (4), the concentration of cellulose nanofibers in the cellulose nanofiber solution is 20 mg / mL to 60 mg / mL (for example, the concentration of cellulose nanofibers is 20 mg / mL, 25 mg / mL, 30 mg / mL, 35 mg / mL, 40 mg / mL, 45 mg / mL, 50 mg / mL, 55 mg / mL or 60 mg / mL); preferably, in step (4), the concentration of cellulose nanofibers in the cellulose nanofiber solution is 40 mg / mL.

[0024] Further, in step (5), the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 60 mg / mL to 120 mg / mL (for example, the concentration of polyvinyl alcohol is 60 mg / mL, 65 mg / mL, 70 mg / mL, 75 mg / mL, 80 mg / mL, 85 mg / mL, 90 mg / mL, 95 mg / mL, 100 mg / mL, 105 mg / mL, 110 mg / mL, 115 mg / mL or 120 mg / mL); preferably, in step (5), the concentration of cellulose nanofibers in the cellulose nanofiber solution is 100 mg / mL.

[0025] Further, in step (6), the concentration of the MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol uniform dispersion is 20 mg / mL to 120 mg / mL (for example, the concentration of the MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol uniform dispersion is 20 mg / mL, 25 mg / mL, 30 mg / mL, 35 mg / mL, 40 mg / mL, 45 mg / mL, 50 mg / mL, 55 mg / mL, 60 mg / mL, 65 mg / mL, 70 mg / mL, 75 mg / mL, 80 mg / mL, 85 mg / mL, 90 mg / mL, 95 mg / mL, 100 mg / mL, 110 mg / mL, 115 mg / mL or 120 mg / mL). The mass ratio of MXene functionalized aragonite flakes, cellulose nanofibers and polyvinyl alcohol is 8-4:1-3:1-3 (for example, the mass ratio of MXene functionalized aragonite flakes, cellulose nanofibers and polyvinyl alcohol is 8:1-3:1-3, 7.5:1-3:1-3, 7:1-3:1-3, 6.5:1-3:1-3, 6:1-3:1-3, 5.5:1-3:1-3, 5:1-3:1-3, 4.5:1-3:1-3 or 4:1-3:1-3); preferably, in step (6), the concentration of the uniform dispersion of MXene functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol is 70 mg / mL, and the mass ratio of MXene functionalized aragonite flakes, cellulose nanofibers and polyvinyl alcohol is 6:3:1.

[0026] Further, in step (7), the degassing process involves placing the uniformly dispersed liquid into a sealed dryer and evacuating it to a vacuum level of 800–2000 Pa (e.g., 800 Pa, 850 Pa, 900 Pa, 1000 Pa, 1500 Pa, or 2000 Pa); then dropping the degassed uniformly dispersed liquid onto the substrate surface of the coating machine, adjusting the height of the scraper to the substrate to 200–1000 μm (e.g., adjusting the height of the scraper to the substrate to 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 700 μm). The coating process involves applying a coating at a speed of 10–200 mm / s (e.g., 10 mm / s, 20 mm / s, 30 mm / s, 40 mm / s, 50 mm / s, 60 mm / s, 70 mm / s, 80 mm / s, 90 mm / s, 100 mm / s, 120 mm / s, 140 mm / s, 160 mm / s, 180 mm / s, or 200 mm / s) and drying at a temperature of 3–60 °C (e.g., 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, or 60 °C). The coating machine is then started for coating, and the composite film is obtained after the moisture is removed.

[0027] Further, in step (8), the multilayer composite film is soaked in deionized water, and the hot pressing temperature is 60-100℃ (for example, the hot pressing temperature is 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃), the hot pressing pressure is 5-100MPa (for example, the hot pressing pressure is 5MPa, 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, 60MPa, 70MPa, 80MPa, 90MPa or 100MPa), and the hot pressing time is 12-48 hours (for example, the hot pressing time is 12 hours, 14 hours, 16 hours, 18 hours, 24 hours, 30 hours, 46 hours, 42 hours or 48 hours), so as to obtain the imitation seashell titanium carbide reinforced aragonite sheet block composite material.

[0028] Further, in step (8), the flexural strength and fracture toughness of the shell-like titanium carbide reinforced aragonite flaky block composite material are tested using a mechanical testing machine. The flexural strength of the shell-like titanium carbide reinforced aragonite flaky block composite material is ~282 MPa, and the fracture toughness is ~6.3 MPa m. 1 / 2 .

[0029] The principle of this invention: Inspired by the structure and performance structure-property relationship of natural seashells, this invention first extracts aragonite flakes from seashell waste. Then, using a coating and hot-pressing technique, MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol are used to construct a seashell-inspired titanium carbide-reinforced aragonite flake bulk composite material. The synergistic effect of hydrogen bonding and MXene nanosheet bridging effectively induces densification and high orientation of the seashell-inspired titanium carbide-reinforced aragonite flake bulk composite material. The flexural strength of the seashell-inspired titanium carbide-reinforced aragonite flake bulk composite material reaches ~282 MPa, and the fracture toughness reaches ~6.3 MPa m. 1 / 2 Meanwhile, the electrical conductivity of the shell-like titanium carbide-reinforced aragonite flaky block composite material is ~0.01 S / m. -1 It can be used for in-situ monitoring of the structural integrity of composite materials and electromagnetic shielding protection.

[0030] The advantages of this invention compared to the prior art are:

[0031] Currently, most shell-inspired bulk composite materials use two-dimensional nanomaterials such as alumina, graphene oxide, or montmorillonite as assembly units. These materials suffer from high costs, complex synthesis processes, or the extraction of mineral resources. Aragonite flakes, as natural "bricks" from shells, are an ideal assembly unit, but are often overlooked and discarded, causing environmental pollution and resource waste. Therefore, this invention proposes using aragonite flakes derived from shell waste as assembly units to prepare high-performance shell-inspired titanium carbide-reinforced aragonite flake bulk composite materials. This construction strategy helps solve the environmental pollution problems caused by shells while simultaneously achieving the resource utilization of shells. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating a method for preparing a shell-like titanium carbide-reinforced aragonite flake block composite material according to the present invention. First, a large-area composite film is prepared by a blade coating method; then, the film is cut into films of uniform size, stacked, soaked, and hot-pressed to obtain the shell-like titanium carbide-reinforced aragonite flake block composite material.

[0033] Figure 2 This invention relates to a method for preparing a biomimetic titanium carbide-reinforced aragonite flake composite material, specifically focusing on the microstructure and mechanical properties of the biomimetic titanium carbide-reinforced aragonite flake composite material. a) Digital photograph of a large biomimetic titanium carbide-reinforced aragonite flake composite material (conductive shell); b) Scanning electron microscope image of a cross-section of the conductive shell; c) Bending stress-strain curves of natural shell, biomimetic aragonite flake-cellulose nanofiber-polyvinyl alcohol composite material (artificial shell), and conductive shell; d) R-curves of fracture toughness versus crack propagation for natural shell, artificial shell, and conductive shell.

[0034] Figure 3This invention relates to the self-monitoring function and electromagnetic shielding performance of a conductive shell in a method for preparing a biomimetic titanium carbide-reinforced aragonite flake bulk composite material. a) During the first loading process, when cracks begin to initiate and propagate, the resistance increases rapidly instead of slowly increasing; the load is removed before the conductive shell is destroyed. b) During the second loading process, since cracks have already formed in the conductive shell during the first loading, the resistance of the conductive shell increases sharply as the cracks further propagate. c) Shielding performance of the artificial shell, the blended MXene-functionalized aragonite flake-cellulose nanofiber-polyvinyl alcohol composite bulk material (blended bulk), and the conductive shell in the frequency range of 8.2-12.4 GHz. d) Comparison of the electromagnetic shielding performance of the artificial shell, the blended bulk, and the conductive shell. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0036] Figure 1 This is a schematic diagram illustrating a method for preparing a shell-inspired titanium carbide-reinforced aragonite flake composite material according to the present invention. Specifically, MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol are uniformly dispersed on a coating machine substrate using a blade coating method, and a composite film is obtained after drying. The film is cut into films of uniform size and stacked together, then immersed in deionized water, and finally hot-pressed to obtain the shell-inspired titanium carbide-reinforced aragonite flake composite material.

[0037] The preparation methods of some of the raw materials used in the following embodiments of the present invention are as follows:

[0038] The method for removing aragonite flakes includes the following steps: First, 80g of nacreous shell is added to a mixed solution containing 80g of sodium hydroxide, 160g of urea, and 1000mL of deionized water, and stirred continuously for 2 days. After standing, the supernatant is discarded, and the solution is washed, filtered 6 times, and then vacuum dried to obtain aragonite flakes.

[0039] Ti3C2T xThe preparation method of MXene nanosheets includes the following steps: 3.2 g of lithium fluoride (LiF) is added to a polytetrafluoroethylene bottle containing a mixed solution of 10 mL deionized water and 30 mL hydrochloric acid (HCl) (12M). After stirring evenly, 2 g of Ti3AlC2MAX powder is added, and the mixture is stirred at a constant temperature of 50°C for 30 hours. The reaction solution is uniformly dispersed into 6 centrifuge tubes, deionized water is added, and the mixture is centrifuged at 3500 rpm for 5 minutes. The supernatant is discarded, and this process is repeated 10 times. Then, deionized water is added and shaken for 3 minutes, followed by centrifugation at 1500 rpm for 30 minutes, and the supernatant is collected. The collected supernatant is further centrifuged at 4500 rpm for 20 minutes, and the precipitate is collected. The precipitate is dispersed in deionized water to obtain an MXene nanosheet solution.

[0040] Three-point bending tests were performed on the bulk material using a universal testing machine (EM6.103-T, Shenzhen Tesmet Instrument Equipment Co., Ltd.). The bending strength of the bulk material was calculated using ASTM standard D790-03, and the fracture toughness was calculated using ASTM standard E1820-06.

[0041] Some of the raw materials used in the following examples are:

[0042] Cellulose nanofibers (NanoFC, average particle size ~6nm);

[0043] Polyvinyl alcohol (Greagent, weight-average molecular weight ~130,000, degree of alcoholysis 98-99%).

[0044] Example 1

[0045] First, a solution of cellulose nanofibers (NanoFC, average particle size ~6 nm) with a concentration of 40 mg / mL and a solution of polyvinyl alcohol (Greagent, weight average molecular weight ~130,000, degree of alcoholysis 98-99%) with a concentration of 100 mg / mL were prepared. To prepare the conductive shell, MXene-functionalized aragonite flakes were obtained through hydrogen bonding. Specifically: 2 g of aragonite flakes were dispersed in a mixture of 110 mL of deionized water and 640 mL of ethanol and sonicated for 30 minutes; then 50 mL of MXene nanosheet solution (10 mg / mL) was added, and the mixture was stirred for 4 hours. After stirring, the supernatant was removed by allowing it to stand; then deionized water was added, and the mixture was centrifuged at 3000 rpm for 5 minutes. The supernatant was discarded, and this process was repeated 9 times to obtain MXene-functionalized aragonite flakes. A 70 mg / mL homogeneous dispersion of MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol was prepared by adding cellulose nanofiber solution and polyvinyl alcohol solution. The mass ratio of MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol was 6:3:1. The homogeneous dispersion was placed in a sealed desiccator and evacuated to a vacuum degree of 900 Pa to remove air bubbles. The homogeneous dispersion was then dropped onto a substrate, and the doctor blade was set to a height of 500 μm and coated at a speed of 50 mm / s. The coating was dried at 50 °C to obtain a composite film. The film was cut into films of uniform size and stacked together. Then, it was immersed in deionized water and hot-pressed at a pressure of 100 MPa and a temperature of 80 °C for 24 hours to obtain a conductive shell (thickness ~2 mm). Figure 2 'a' represents a large conductive seashell (10cm × 10cm × 0.2cm). For example... Figure 2 As shown in b, the fracture morphology of the conductive shell exhibits a typical "brick-and-mortar" layered structure. Further mechanical properties of the conductive shell were tested using a three-point bending test. The bending strength of the conductive shell was ~282 MPa, and the fracture toughness was ~6.3 MPa m. 1 / 2 Both are far superior to the bending strength (~179 MPa) and fracture toughness (~4.0 MPa m) of natural seashells. 1 / 2 ).

[0046] Example 2

[0047] First, a cellulose nanofiber solution with a concentration of 40 mg / mL and a polyvinyl alcohol solution with a concentration of 100 mg / mL were prepared. Aragonite flakes were ultrasonically dispersed in deionized water to obtain an aragonite flake dispersion. Then, the cellulose nanofiber solution and the polyvinyl alcohol solution were added to prepare a uniform dispersion of aragonite flakes-cellulose nanofibers-polyvinyl alcohol with a concentration of 70 mg / mL, and the mass ratio of aragonite flakes, cellulose nanofibers, and polyvinyl alcohol was 6:3:1. The uniform dispersion was placed in a sealed desiccator and evacuated to a vacuum degree of 900 Pa to remove air bubbles. The uniform dispersion was then dropped onto a substrate, and a doctor blade with a height of 500 μm was used for coating at a speed of 50 mm / s. The coating was dried at 50 °C to obtain a composite film. The film was cut into films of uniform size and stacked together, then immersed in deionized water and hot-pressed at a pressure of 100 MPa and a temperature of 80 °C for 24 hours to obtain an artificial seashell (thickness ~2 mm). Figure 2 As shown in c and d, the flexural strength of the artificial shell is ~239 MPa, which is superior to that of the natural shell. The fracture toughness of the artificial shell is ~3.9 MPa m. 1 / 2 Its fracture toughness is comparable to that of natural seashells.

[0048] Example 3

[0049] First, a cellulose nanofiber solution with a concentration of 40 mg / mL and a polyvinyl alcohol solution with a concentration of 100 mg / mL were prepared. To prepare the conductive shell, MXene-functionalized aragonite flakes were obtained through hydrogen bonding. Specifically: 2 g of aragonite flakes were dispersed in a mixture of 110 mL of deionized water and 640 mL of ethanol and sonicated for 30 minutes; then 50 mL of MXene nanosheet solution (10 mg / mL) was added, and the mixture was stirred for 4 hours. After stirring, the supernatant was removed by allowing it to stand; then deionized water was added, and the mixture was centrifuged at 3000 rpm for 5 minutes. The supernatant was discarded, and this process was repeated 9 times to obtain MXene-functionalized aragonite flakes. The cellulose nanofiber solution and polyvinyl alcohol solution were then added to prepare a 70 mg / mL homogeneous dispersion of MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol, with a mass ratio of 6:3:1. The homogeneous dispersion was placed in a sealed desiccator and evacuated to a vacuum of 900 Pa to remove air bubbles. The uniformly dispersed liquid was then dropped onto the substrate, with the doctor blade height set to 500 μm and the coating applied at a speed of 50 mm / s. The coating was then dried at 50°C to obtain a composite film. The film was cut into uniform sizes and stacked together, then immersed in deionized water and hot-pressed at 100 MPa and 80°C for 24 hours to obtain a conductive seashell (thickness ~2 mm). Figure 2As shown in b, due to the effective bridging of aragonite sheets by MXene nanosheets and the formation of a conductive network within the conductive shell, the conductivity of the conductive shell reaches 0.01 S / m. -1 Therefore, the conductive shell possesses a self-monitoring function for structural integrity. The self-monitoring performance of the bulk material was tested using a combination of a universal testing machine and a digital source meter (Keithley 2400), such as... Figure 3 As shown in a and b, during the first loading process, the resistance slowly increases before cracks initiation when a load is applied to the conductive shell. When the load reaches its maximum value, the load gradually decreases because cracks have already formed, while the resistance increases rapidly, with a resistance change rate of ~7%. During the second loading process, since cracks already exist inside the conductive shell, the cracks further expand when the load increases, with a resistance change rate of ~21%. Therefore, monitoring the change in resistance can effectively monitor the structural integrity of the conductive shell.

[0050] Example 4

[0051] First, a cellulose nanofiber solution with a concentration of 40 mg / mL and a polyvinyl alcohol solution with a concentration of 100 mg / mL were prepared. To prepare the conductive shell, MXene-functionalized aragonite flakes were obtained through hydrogen bonding. Specifically: 2 g of aragonite flakes were dispersed in a mixture of 110 mL of deionized water and 640 mL of ethanol and sonicated for 30 minutes; then 50 mL of MXene nanosheet solution (10 mg / mL) was added, and the mixture was stirred for 4 hours. After stirring, the supernatant was removed by allowing it to stand; then deionized water was added, and the mixture was centrifuged at 3000 rpm for 5 minutes. The supernatant was discarded, and this process was repeated 9 times to obtain MXene-functionalized aragonite flakes. The cellulose nanofiber solution and polyvinyl alcohol solution were then added to prepare a 70 mg / mL homogeneous dispersion of MXene-functionalized aragonite flakes, cellulose nanofibers, and polyvinyl alcohol, with a mass ratio of 6:3:1. The homogeneous dispersion was placed in a sealed desiccator and evacuated to a vacuum of 900 Pa to remove air bubbles. The uniformly dispersed solution was then dropped onto the substrate, and the doctor blade height was set to 500 μm. The coating was applied at a speed of 50 mm / s and dried at 50 °C to obtain a composite film. The film was cut into uniform sizes and stacked together, then immersed in deionized water and hot-pressed at 100 MPa and 80 °C for 24 hours to obtain a conductive shell (thickness ~2 mm). Aragonite flakes were ultrasonically dispersed in deionized water to obtain an aragonite flake dispersion. Then, cellulose nanofiber solution and polyvinyl alcohol solution were added to prepare a uniformly dispersed aragonite-cellulose nanofiber-polyvinyl alcohol solution with a concentration of 70 mg / mL, and the mass ratio of aragonite flakes, cellulose nanofibers, and polyvinyl alcohol was 6:3:1. The uniformly dispersed solution was placed in a sealed desiccator and evacuated to a vacuum degree of 900 Pa to remove air bubbles. The uniformly dispersed solution was then dropped onto the substrate, and the doctor blade height was set to 500 μm. The coating was applied at a speed of 50 mm / s and dried at 50 °C to obtain a composite film. The films were cut to uniform dimensions and stacked together, then immersed in deionized water and hot-pressed at 100 MPa and 80°C for 24 hours to obtain an artificial seashell (thickness ~2 mm). Furthermore, to create a conductive seashell, a uniformly dispersed MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol mixture was freeze-dried, moistened, and then hot-pressed at 100 MPa and 80°C for 24 hours to obtain a blended bulk material (thickness ~2 mm). The electromagnetic shielding performance of the bulk material was tested using a DR-WX rectangular waveguide instrument and an N9917A network analyzer. Figure 3 As shown in c and d, the electromagnetic shielding performance of the conductive shell is ~37dB, which is better than that of the artificial shell (~5dB) and the blended bulk (~19dB). This is attributed to the MXene nanosheet bridging and the replication of the "brick-and-mortar" layered structure.

[0052] It should be noted that, according to the above embodiments of the present invention, those skilled in the art can fully realize the scope of claim 1 and its dependent rights, and the implementation process and method are the same as those in the above embodiments; and the parts of the present invention not described in detail belong to the well-known technology in the art.

[0053] The above description is only a part of the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material, characterized in that, Includes the following steps: (1) Disperse the nacreous layer of the shell into a sodium hydroxide / urea / deionized water system, and obtain aragonite flakes by stirring, filtration and drying; (2) Titanium carbide Ti3C2T was obtained by in-situ chemical etching. x MXene nanosheet solution; (3) Disperse the aragonite flakes described in step (1) into a mixed solution of deionized water and ethanol, and then add titanium carbide (Ti3C2T). x The MXene nanosheet solution was stirred and reacted; MXene-functionalized aragonite flakes were obtained by washing and centrifugation; among which, titanium carbide Ti3C2T x The mass ratio of MXene nanosheets to aragonite sheets is 1:9 to 9:1; (4) Dissolve cellulose nanofibers in deionized water to prepare a cellulose nanofiber solution; (5) Weigh out polyvinyl alcohol and dissolve it in deionized water to prepare a polyvinyl alcohol solution; (6) Mix MXene-functionalized aragonite flakes, cellulose nanofiber solution and polyvinyl alcohol solution evenly to obtain a uniform dispersion of MXene-functionalized aragonite flakes-cellulose nanofiber-polyvinyl alcohol; wherein the concentration of the uniform dispersion of MXene-functionalized aragonite flakes-cellulose nanofiber-polyvinyl alcohol is 20 mg / mL~115 mg / mL, and the mass ratio of MXene-functionalized aragonite flakes, cellulose nanofibers and polyvinyl alcohol is 4~8:1~3:1~3; (7) After degassing the MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol uniform dispersion obtained in step (6), a composite film is obtained by a scraping method. (8) Cut the composite film obtained in step (7) into films of the same size, stack them, soak them and hot press them to obtain a shell-like titanium carbide reinforced aragonite sheet block composite material.

2. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (1), the preparation process of aragonite flakes is as follows: the nacreous shell is added to a mixed solution containing urea, sodium hydroxide and deionized water and stirred. The mass ratio of sodium hydroxide to urea is 1:9 to 5:

5. Then the supernatant is removed, the precipitate is washed and filtered to obtain aragonite flakes.

3. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (2), titanium carbide Ti3C2T x The preparation process of MXene nanosheet solution is as follows: The raw material Ti3AlC2 MAX phase is added to a solution containing hydrochloric acid and lithium fluoride, and the mixture is stirred under heating conditions. The resulting mixture is centrifuged, washed with deionized water, and the supernatant is discarded. The precipitate is then dispersed in deionized water, and titanium carbide Ti3C2T is obtained by shaking and gradient centrifugation. x MXene nanosheet dispersion.

4. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (3), the mass ratio of deionized water to ethanol is 1:9 to 5:

5.

5. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (4), the concentration of cellulose nanofibers in the cellulose nanofiber solution is 20 mg / mL to 60 mg / mL.

6. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (5), the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 60 mg / mL to 120 mg / mL.

7. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (6), the concentration of the uniform dispersion of MXene-functionalized aragonite flakes-cellulose nanofibers-polyvinyl alcohol is 70 mg / mL, and the mass ratio of MXene-functionalized aragonite flakes, cellulose nanofibers and polyvinyl alcohol is 6:3:

1.

8. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (7), the degassing process involves placing the uniformly dispersed liquid into a sealed dryer and evacuating it to a vacuum level of 800-2000 Pa; dropping the degassed uniformly dispersed liquid onto the substrate surface of the coating machine, adjusting the height of the scraper to the substrate to 200-1000 micrometers, the scraping speed to 10-200 mm / s, the drying temperature to 35-60 ℃, and then starting the coating machine to perform scraping. After the moisture is removed, a composite film is obtained.

9. The method for preparing a shell-like titanium carbide reinforced aragonite flaky block composite material according to claim 1, characterized in that: In step (8), the multilayer composite film is soaked in deionized water, the hot pressing temperature is 60~100 ℃, the hot pressing pressure is 5~100 MPa, and the hot pressing time is 12~48 hours, so as to obtain the imitation seashell titanium carbide reinforced aragonite sheet block composite material.

10. The shell-like titanium carbide reinforced aragonite flaky bulk composite material prepared by the preparation method according to any one of claims 1-8, characterized in that: In step (8), the obtained imitation seashell titanium carbide reinforced aragonite flaky block composite material has a flexural strength of 282 MPa and a fracture toughness of 6.3 MPa⋅m. 1 / 2 .

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