Preparation of infrared stealth MXene film and emissivity regulation method

Abstract

This invention discloses a method for preparing and controlling the emissivity of infrared stealth MXene thin films, belonging to the field of infrared stealth technology. The method uses Ti3C2T... X Using MXene as a raw material, it is coated onto a graphite plate as the anode and a platinum mesh as the cathode. Electrolysis is performed for 5 minutes in a tannic acid-sodium chloride aqueous electrolyte at 5V. After ultrasonication, centrifugation, and washing, e-MXene is obtained. The e-MXene film is then obtained by filtration, or it can be composited with BC nanocellulose to obtain an e-BC-MXene film. This invention achieves efficient MXene modification through anodic electrochemical exfoliation. The synergistic effect of tannic acid and sodium chloride enhances its antioxidant properties and structural integrity. The resulting film can be water-controlled by humidity and electrothermally controlled by current. Compared with the traditional cathode exfoliation method, the yield, sheet size, and control responsiveness are significantly improved. The preparation process is green and low-consumption. The film is suitable for adaptive infrared stealth requirements in complex scenarios and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of infrared stealth technology, and in particular to a method for preparing and controlling the emissivity of an infrared stealth MXene thin film. Background Technology

[0002] In modern warfare, the application of infrared thermal imaging technology is becoming increasingly widespread, and infrared stealth materials have become an indispensable part of future electronic warfare. At the same time, the constantly fluctuating external environment and the demands of cross-regional operations create an urgent need for stealth materials capable of adaptive camouflage that can adapt to environmental changes.

[0003] Two-dimensional material MXene (Ti3C2T) X As a novel two-dimensional material composed of transition metals, nitrides, or carbonitrides, it has become a research hotspot in electromagnetic shielding materials due to its advantages such as low infrared emissivity, abundant mid-terminal groups, efficient photothermal conversion capability, and excellent mechanical properties. Using it as a thin film material can achieve broad-spectrum stealth against targets.

[0004] In the prior art, patent CN 120774420 A discloses a method for preparing antioxidant MXene through electrochemical exfoliation. This method uses an aqueous solution containing chitosan, lithium chloride, nickel chloride, and tetramethylammonium hydroxide as the electrolyte, and electrochemically exfoliates a copper foil coated with wet MXene solid at the cathode. However, the MXene obtained through this cathode exfoliation still needs improvement in terms of structural integrity, exfoliation efficiency, system compatibility, film performance, and green controllability. Summary of the Invention

[0005] Technical issues Existing cathodic electrochemical stripping methods for MXene have shortcomings in structural integrity, stripping efficiency, system compatibility, film performance, and green controllability. Furthermore, traditional electrolyte systems have low ionic strength and poor stripping effect, MXene is prone to oxidation and collapse, and the preparation of composite films is also affected by acidic electrolytes, making it difficult to meet the application requirements of adaptive infrared stealth.

[0006] Technical content To address the aforementioned technical problems, this invention provides a method for preparing MXene using an anode via electrochemical stripping, which can improve the antioxidant properties, preparation efficiency, and application performance of MXene.

[0007] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0008] This invention provides a method for preparing MXene by anodic stripping, comprising the following steps: (1) Ti3C2T XThe MXene dispersion was centrifuged to obtain wet MXene solid, which was then coated onto one side of a graphite plate electrode. (2) The graphite plate coated with MXene is used as the anode and placed in the electrolyte together with the cathode; (3) Adjust the voltage for electrolysis, stop electrolysis after a certain time, collect MXene on the graphite plate by ultrasonication, and obtain MXene film by ultrasonication, centrifugation, washing and filtration.

[0009] In one embodiment of the present invention, in step (1), the Ti3C2T X The preparation method of MXene dispersion is as follows: First, Ti3AlC2MAX phase powder is added to a mixed acid solution prepared with LiF and HCl, and in-situ etching is performed by stirring. After reacting for a period of time, the solid is centrifuged and washed with water until the pH value is neutral. Then, the resulting multilayer Ti3C2T x The precipitate was redispersed in water, and interlayer exfoliation was achieved by ultrasonic treatment to obtain Ti3C2T. x MXene dispersion.

[0010] In one embodiment of the present invention, in step (1), the coating method can be either scraping or spraying.

[0011] In one embodiment of the present invention, in step (2), a platinum mesh is selected as the cathode.

[0012] In one embodiment of the present invention, in step (2), the electrolyte is an aqueous solution containing tannic acid and sodium chloride; the mass ratio of tannic acid to sodium chloride in the aqueous solution is 1:0.5~1.5.

[0013] In one embodiment of the present invention, in step (2), the electrolyte is an aqueous solution containing 1~5 g / L tannic acid and 1~5 g / L sodium chloride.

[0014] In one embodiment of the present invention, in step (2), the electrolyte is an aqueous solution containing 1~3 g / L tannic acid and 1~3 g / L sodium chloride.

[0015] In one embodiment of the present invention, in step (3), the electrolysis voltage is 5~10V.

[0016] In one embodiment of the present invention, in step (3), the electrolysis time is 5 to 20 minutes.

[0017] The present invention provides an MXene composite film, which is composed of nanocellulose and MXene; the mass ratio of nanocellulose to MXene is 1~3:3~1.

[0018] Furthermore, the nanocellulose is: cellulose prepared from natural cellulose through physical, chemical, biological or composite modification methods, with a one-dimensional size at the nanoscale (1~100 nm) and retaining the basic molecular structure of cellulose; the nanocellulose includes nanocrystalline cellulose (NCC / NFC), cellulose nanofibers (CNF) or bacterial cellulose (BC).

[0019] Preferably, the mass ratio of the nanocellulose to MXene is 2~3:1.

[0020] Most preferably, the mass ratio of the nanocellulose to MXene is 3:1.

[0021] The MXene composite film provided by this invention has the properties of dual water / electricity regulation of infrared emissivity, high oxidation resistance, and infrared stealth.

[0022] Furthermore, the infrared emissivity of the MXene composite film increases with increasing humidity and / or current.

[0023] This invention provides a method for preparing the MXene composite film, comprising the following steps: The MXene obtained by the above exfoliation process is mixed with nanocellulose, water is added and stirred, and the mixture is sonicated. Finally, it is spread in a mold and dried to obtain the MXene composite film.

[0024] Furthermore, the concentration of MXene was 1~10 mg / mL when water was added and stirred.

[0025] Furthermore, drying includes natural air drying, heat drying, or freeze drying.

[0026] This invention provides an application of MXene composite film in the fields of national defense, aerospace, and high-precision instruments.

[0027] The principle of this invention is as follows: anions are moved toward the anode (multilayer MXene) by an electric field and inserted into the interlayer gaps of MXene, thereby increasing the interlayer spacing and obtaining a single layer of MXene, which is then collected by short-term ultrasound.

[0028] In this invention, sodium chloride in the electrolyte provides strong ionic conductivity and the physical driving force for interlayer intercalation / expansion; tannic acid provides interlayer lubrication and MXene surface modification to achieve chemical protection against oxidation and corrosion. The two work synergistically to achieve intercalation expansion, interlayer dissociation, and in-situ stabilization. This is because the resistance at the interface between the MXene coating and the graphite plate is high, and the ionic strength in a single pure water / pure tannic acid system is extremely low, making effective electrochemical stripping impossible. The essence of anodic electrochemical stripping is ion insertion + interlayer expansion + electrostatic repulsion. Under anodic polarization, the MXene surface is positively charged, and the Na in the solution... + As a highly hydrating ion, Cl is embedded in the interlayer of MXene, where the accumulation of interlayer cations generates strong electrostatic repulsion, widening the interlayer spacing. Simultaneously, Cl... - Under anodic potential, residual metallic phases on MXene can be weakly etched, loosening the interlayer structure and reducing the voltage and energy consumption required for stripping. Tannic acid contains a large amount of catechol and gallic acid polyhydroxyl groups, which can be inserted into the interlayer spacing of MXene through hydrogen bonding, π-π interactions, and weak coordination. Under electric field and Na... + The combined effect of these factors reduces interlayer van der Waals forces, making it easier for the layers to slip and dissociate. At the same time, tannic acid is a highly efficient free radical scavenger and antioxidant, which can quickly form a passivation layer on the MXene surface, isolating oxygen and water, inhibiting Ti oxidation and structural collapse, and macroscopically improving the structural integrity and antioxidant properties of the exfoliated MXene. In addition, tannic acid molecules adsorb on the surface of MXene sheets, introducing negatively charged surface groups, generating strong electrostatic repulsion and steric hindrance, which makes the exfoliated MXene nanosheets uniformly dispersed in solution and stable for a long time without settling.

[0029] Beneficial effects 1. The preparation efficiency and quality are greatly improved. The anodic electrochemical stripping is completed in a short time of 5 min with a low voltage of 5V. The MXene yield reaches 91% and the single sheet size is 2.2 μm, which is far superior to the traditional cathode stripping process. The larger sheet is conducive to the construction of a continuous conductive network.

[0030] 2. The material's stability and antioxidant properties are significantly enhanced. Tannic acid forms a passivation layer on the MXene surface, making its antioxidant stability period reach 80 days, which is 4 times that of the existing technology. The dispersion can remain uniform and free of precipitation for a long time, and there are no significant fluctuations in zeta potential and particle size.

[0031] 3. Achieve dual water / electricity control of infrared emissivity. The e-MXene film can control the emissivity through humidity, and the e-BC-MXene composite film can achieve linear adjustment of emissivity through current. The control response value is much higher than that of traditional materials, making it suitable for complex infrared stealth scenarios. Attached Figure Description

[0032] Figure 1This is a diagram of the electrochemical stripping apparatus used in Example 1.

[0033] Figure 2 This is a scanning electron microscope image of the peeling process in Example 2.

[0034] Figure 3 The image shows the XRD pattern of e-MXene prepared in Example 1.

[0035] Figure 4 The images show the FTIR test results of e-MXene prepared in Example 1 under different humidity conditions.

[0036] Figure 5 The images show infrared thermal images of e-MXene prepared in Example 1 under different ambient humidity conditions.

[0037] Figure 6 The emissivity of the e-BC-MXene thin film prepared in Example 1 under different currents is shown.

[0038] Figure 7 FTIR test plots for e-BC-MXene at different ratios.

[0039] Figure 8 XRD test images of e-BC-MXene at different scales.

[0040] Figure 9 The image shows a thermal infrared image of an e-BC-MXene film with a BC nanocellulose to e-MXene solid content ratio of 3:1 under energized conditions.

[0041] Figure 10 Radar comparison chart of yield, size, antioxidant days, water-controlled emissivity range, and electrothermal-controlled emissivity range for e-MXene obtained by anodic electrochemical exfoliation, s-MXene obtained by conventional liquid-phase exfoliation, and n-MXene obtained by cathodic electrochemical exfoliation. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to specific examples.

[0043] Test methods 1. The surface cross-sectional morphology of MXene powder was observed using a scanning electron microscope (SEM) at an accelerating voltage of 5 kV, with a magnification of 10 kx.

[0044] 2. The crystal structure was analyzed using an X-ray diffractometer (XRD). The wide-angle test range was 5-90° with a 2θ range and a scan rate of 5° / min. The XRD patterns were analyzed using MDIJade6 software.

[0045] 3. Qualitative analysis was performed using Fourier Transmission Infrared Spectroscopy (FTIR). A small amount of sample was mixed with KBr, ground, and then pressed into a pellet for testing at a wavelength of 400-4000 cm⁻¹. -1 .

[0046] 4. Use a thermal infrared imager to observe the camouflage effect of e-MXene and e-BC-MXene films under different humidity conditions.

[0047] Example 1 A method for preparing MXene thin films by electrochemical measurement includes the following steps: Ti3C2T prepared by acid etching method X Centrifugation of the MXene dispersion yielded multilayered MXene wet solids, which were then coated onto one side of a graphite plate. The graphite plate coated with the MXene wet solids served as the anode, and a platinum mesh as the cathode. An electrolysis apparatus was constructed, using an electrolyte of 2 g / mL tannic acid and 2 g / mL sodium chloride. A 5V voltage was applied, and electrolysis was performed for 5 minutes. The product was collected by brief sonication, followed by repeated centrifugation and washing to obtain e-MXene wet solids. The e-MXene wet solids were then formulated into a 2 mg / mL dispersion and filtered to obtain an e-MXene film. The e-MXene wet solids were mixed with BC nanocellulose and mechanically stirred for 3 minutes, followed by sonication for 3 minutes to prepare an e-BC-MXene composite membrane. The mass ratios of e-MXene to BC nanocellulose were 3:1, 2:1, 1:1, 1:2, and 1:3, respectively.

[0048] Figure 1 This is a diagram of the electrolytic device used in the stripping process of this embodiment. Figure 2 The images shown are scanning electron microscope (SEM) images of the exfoliation process in this embodiment, namely, Ti3AlC2 synthesized powder, etched multilayer MXene, electrochemically intercalated MXene, and ultrasonically treated MXene. It can be seen that the interlayer spacing of MXene is increased due to the intercalation of the electrolyte during electrolysis. The e-MXene film was fully hygroscopic under different ambient humidity conditions and then subjected to FTIR testing. The results are as follows... Figure 4 As shown, the emissivity of e-MXene increases with increasing ambient humidity. Further thermal camouflage performance testing yielded the following results. Figure 5 As shown, the camouflage effect of the e-MXene film varies under different humidity levels. Simultaneously, the e-MXene film also exhibits good camouflage effects at different temperatures. For e-BC-MXene films with different proportions, Figure 6 The emissivity curves of an e-BC-MXene film with a BC nanocellulose to e-MXene solid content ratio of 3:1 are shown under different currents. The emissivity increases linearly with increasing current. Simultaneously, its thermal camouflage performance was tested. Figure 10As shown, the e-BC-MXene composite film can also achieve excellent camouflage effects by controlling the magnitude of the current.

[0049] Comparative Example 1 The preparation of MXene using a conventional liquid-phase exfoliation method includes the following steps: The multilayer Ti3C2MXene etched with LiF / HCl was prepared into a dispersion, and then the MXene was exfoliated by sonication for 1 hour. After centrifugation, washing and drying, MXene was obtained, denoted as s-MXene.

[0050] Comparative Example 2 The preparation of MXene is carried out according to CN 120774420 A, including the following steps: Ti3C2T prepared by acid etching method X Centrifugation of the MXene dispersion yielded multilayered wet MXene solids, which were then coated onto both sides of a copper foil. The copper foil coated with the wet MXene solids served as the cathode, and a platinum foil served as the anode. An electrolysis apparatus was constructed, and an electrolyte containing 0.3 wt% chitosan and 2 wt% acetic acid was prepared. A voltage of 25 V was applied, and electrolysis was performed for 25 min. The deposits were collected, repeatedly centrifuged and washed, filtered, and dried to obtain an MXene film, denoted as n-MXene.

[0051] The performance of e-MXene, s-MXene, and n-MXene was compared, and the results are shown below. Figure 10 .from Figure 10 The radar multi-dimensional performance characterization diagrams clearly show that e-MXene prepared by anodic electrochemical exfoliation outperforms traditional liquid-phase exfoliated s-MXene and cathodic electrochemical exfoliated n-MXene in all key indicators, including yield, sheet size, antioxidant stability period, water-controlled emissivity range, and electrothermal-controlled emissivity range. Specifically, the e-MXene yield reaches 91%, far exceeding that of s-MXene and n-MXene; the single-sheet size reaches 2.2 μm, which is more than 6 times that of s-MXene and significantly larger than that of n-MXene. The larger sheet size facilitates the construction of a continuous conductive network, laying the structural foundation for the infrared modulation performance of the thin film. In terms of antioxidant properties, e-MXene has a stability period of 80 days, which is 4 times that of s-MXene and more than 2 times that of n-MXene, demonstrating extremely strong environmental stability. In terms of regulatory responsiveness, e-MXene has a water-regulated emissivity response value of 0.34 and an electrothermal regulation response value of 0.56, which are much higher than s-MXene and also better than n-MXene. Its sensitive response characteristics make it better suited for complex infrared stealth scenarios.

[0052] The anode stripping, tannic acid + sodium chloride electrolyte, and graphite plate system used in this invention have significant and irreplaceable advantages over the cathode stripping, chitosan-acetic acid electrolyte, and copper foil substrate used in Comparative Example 2 in terms of MXene structural integrity, stripping efficiency, system compatibility, film performance, and green controllability. It is particularly suitable for the preparation of high-quality e-MXene films and e-BC-MXene composite films. Regarding the compatibility between the substrate and the electrolyte, in Comparative Example 2, where copper foil is used as the cathode substrate, it is corroded by the acidic acetic acid electrolyte, introducing Cu... 2+ Metallic impurities contaminate MXene, and 25V high-voltage cathode polarization causes copper foil swelling and detachment, resulting in uneven MXene coating peeling. However, the graphite plate used in this invention as the anode substrate is chemically inert, and the tannic acid-sodium chloride electrolyte system is mild and environmentally friendly, free from metal ion contamination, ensuring the high purity of e-MXene from the source. From the perspective of peeling principles, anodic peeling is more suitable for the intercalation characteristics of cations between multilayer MXene layers, and the Na+ dissociation from sodium chloride... + As ions with strong hydration capacity, they can quickly embed into the MXene interlayer to form cation enrichment, generating strong electrostatic repulsion to make the interlayer expansion more uniform and rapid, achieving efficient stripping without high voltage; while cathode stripping has low intercalation efficiency, requires high voltage to achieve interlayer dissociation, and is also prone to causing damage to the MXene sheets.

[0053] Meanwhile, the sodium chloride-tannic acid electrolyte system of the present invention has the unique advantage of synergistic effect, Na + The electrostatic repulsion generated by rapid intercalation provides the physical driving force for peeling, Cl - It can also subtly etch away residual metallic phases on MXene, loosening the interlayer structure and further reducing stripping energy consumption. The abundant catechols and gallic acid polyhydroxys in tannic acid can both weaken van der Waals forces by inserting into the MXene interlayer spacing through hydrogen bonds and π-π interactions, reducing stripping resistance to obtain larger-sized e-MXenes, and form a passivation layer on the MXene surface, providing in-situ antioxidant protection and inhibiting Ti oxidation and structural collapse. Furthermore, this electrolyte system is a neutral / weakly acidic environment, perfectly suited for the composite process of BC nanocellulose, without damaging the nanocellulose structure, thus ensuring the mechanical and controllable properties of the composite film. In contrast, the chitosan-acetic acid electrolyte in Comparative Example 2 shows that the strong acid environment will erode the Ti atoms on the MXene surface during long-term electrolysis, resulting in weak antioxidant properties. Chitosan also cannot replace the interlayer lubrication and in-situ antioxidant effect of tannic acid. At the same time, the strong acid environment will destroy the subsequent composite with BC nanocellulose, resulting in a double decline in the mechanical and controllability properties of the composite membrane. Furthermore, the use of ultra-high voltage of 25V also makes the preparation process energy-intensive and unsafe, which does not meet the requirements of green and controllable preparation.

[0054] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing MXene by anodic exfoliation, characterized in that, Includes the following steps: (1) Ti3C2T X The MXene dispersion was centrifuged to obtain wet MXene solid, which was then coated onto one side of a graphite plate electrode. (2) The graphite plate coated with MXene is used as the anode and placed in the electrolyte together with the cathode; The electrolyte is an aqueous solution containing tannic acid and sodium chloride; the mass ratio of tannic acid to sodium chloride in the aqueous solution is 1:0.5~1.

5. (3) Adjust the voltage for electrolysis, stop electrolysis after a certain time, collect MXene on the graphite plate by ultrasonication, and obtain MXene film by ultrasonication, centrifugation, washing and filtration; the electrolysis voltage is 5~10V; the electrolysis time is 5~20min.

2. The method according to claim 1, characterized in that, In step (1), the Ti3C2T X The preparation method of MXene dispersion is as follows: First, Ti3AlC2 MAX phase powder is added to a mixed acid solution prepared with LiF and HCl, and in-situ etching is performed by stirring. After reacting for a period of time, the solid is centrifuged and washed with water until the pH value is neutral. Then, the resulting multilayer Ti3C2T x The precipitate was redispersed in water, and interlayer exfoliation was achieved by ultrasonic treatment to obtain Ti3C2T. x MXene dispersion.

3. The method according to claim 1, characterized in that, In step (2), a platinum mesh is selected as the cathode.

4. The method according to claim 1, characterized in that, In step (2), the electrolyte is an aqueous solution containing 1~5 g / L tannic acid and 1~5 g / L sodium chloride.

5. An MXene composite film, characterized in that, The MXene composite film is composed of nanocellulose and MXene prepared by the method according to any one of claims 1 to 4; the mass ratio of nanocellulose to MXene is 1 to 3: 3 to 1.

6. The MXene composite film according to claim 5, characterized in that, The nanocellulose includes nanocrystalline cellulose, cellulose nanofibers, or bacterial cellulose.

7. The MXene composite film according to claim 5, characterized in that, The mass ratio of nanocellulose to MXene is 2~3:

1.

8. The application of the MXene composite film according to any one of claims 5 to 7 in the fields of national defense, aerospace, and high-precision instruments.

9. The method for preparing the MXene composite film according to any one of claims 5 to 7, characterized in that, Includes the following steps: The MXene obtained by the above exfoliation process is mixed with nanocellulose, water is added and stirred, ultrasonicated, and finally spread flat in a mold to dry, thus obtaining the MXene composite film.

10. The preparation method according to claim 9, characterized in that, When adding water and stirring, the concentration of MXene is 1~10 mg / mL; drying includes natural air drying, heat drying or freeze drying.

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