A pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x MXene thin films and their preparation methods

Abstract

This invention discloses a pre-oxidation-high-temperature expansion synergistic construction method for multi-scale porous Ti3C2T structures. x The method for preparing MXene thin films is as follows: 1. Preparation of Ti3C2T x The process involves: 1. MXene dispersion; 2. Pre-oxidation treatment and vacuum filtration; 3. High-temperature expansion of the film at 300℃~350℃; 4. Natural cooling to room temperature in air. This invention utilizes the synergistic effect of pre-oxidation and high-temperature expansion to construct a multi-scale pore structure within the film, where nanoscale in-plane mesopores and micron-scale interlayer expansion pores coexist. This process requires no external template or foaming agent, resulting in a Ti3C2T film. x MXene films have a complete structure, high specific surface area, good flexibility, and good conductivity. Furthermore, their electromagnetic shielding mechanism has shifted from reflection-dominant to absorption-dominant, effectively avoiding secondary electromagnetic pollution. They have broad application prospects in fields such as high-efficiency electromagnetic shielding, electrochemical energy storage, and flexible electronics.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterials and MXene thin film preparation technology, specifically relating to a pre-oxidation-high-temperature expansion synergistic construction of a multi-scale porous structure Ti3C2T. x MXene thin films and their preparation methods. Background Technology

[0002] Two-dimensional material Ti3C2T x MXenes have attracted significant attention in electromagnetic shielding, electrochemical energy storage, catalysis, and sensing due to their superior conductivity, abundant surface chemical groups, and tunable interlayer structure. Particularly in electromagnetic shielding, while traditional densely stacked MXene films exhibit high reflection loss, their inherent "reflection-dominated" shielding mechanism easily leads to secondary electromagnetic pollution, and their weight and flexibility fail to meet the demands of modern electronic devices for thinness, lightness, flexibility, and strength. Constructing multi-scale porous structures is widely recognized as a key strategy to overcome these challenges and achieve highly efficient absorption-based electromagnetic shielding. The introduction of pores not only significantly reduces material weight but also effectively promotes multiple reflections and scattering of electromagnetic waves by introducing numerous gas-solid interfaces, thereby shifting the shielding mechanism from reflection-dominated to absorption-dominated. In particular, nanoscale pores are crucial for improving the impedance matching of materials in electromagnetic fields, allowing electromagnetic waves to more easily penetrate the material's interior rather than be directly reflected; simultaneously, these nanopores can serve as additional interfacial polarization centers, further enhancing the conversion and dissipation of electromagnetic energy.

[0003] However, currently in Ti3C2T x Precisely constructing such hierarchical porous structures with both micron and nanoscale dimensions within MXene films remains a significant challenge. Existing technologies have explored various strategies for preparing porous MXene materials, but each has its own significant limitations. For example, patent CN109573989A discloses a method for preparing porous MXene powder by inducing localized oxidation and etching through mechanical oscillation. This method is time-consuming (1-6 hours), and the final product is in powder form, making it difficult to directly prepare continuous films. Patent CN111755685B uses a hydrothermal reaction of fluoride salts and boric acid to etch the MAX phase and expand the MXene interlayer spacing. This involves a long-term, high-temperature, and high-pressure reaction, resulting in high energy consumption. Furthermore, the hydrothermal process inevitably leads to excessive oxidation of MXene, impairing its intrinsic conductivity. Template methods (such as the nanocellulose used in patent CN117160251A) require complex template introduction and removal steps, easily resulting in template residue. All of the above methods generally face a common bottleneck: the difficulty in efficiently and environmentally constructing a large number of nanoscale pores on the MXene framework.

[0004] Foaming expansion using water vapor generated by the instantaneous vaporization of interlayer water molecules at high temperatures is a rapid, residue-free, and green process. However, when MXene films are directly expanded at high temperatures without proper pretreatment, the lack of control over the foaming process can easily lead to over-expansion. Although high electromagnetic shielding effectiveness (around 60-70 dB) can still be achieved, the following drawbacks exist: Firstly, due to the lack of nanoscale pore control during the foaming process, the resulting film has a low specific surface area (typically <5 μm²). 2 The film is predominantly composed of micron-sized macropores with a lack of nano-sized mesopores, resulting in a limited absorption efficiency in the shielding mechanism. Secondly, excessive interlayer expansion leads to a significant decrease in the mechanical properties of the film (tensile strength of about 10 MPa) and reduced flexibility, limiting its practical application in flexible devices.

[0005] Therefore, there is an urgent need in this field to develop a new method for pre-treating and controlling MXene sheets before high-temperature expansion, so as to simultaneously achieve the introduction of nanoscale pores and the controllable regulation of the foaming process, thereby improving the electromagnetic shielding performance of the material while maintaining the integrity of the film structure. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a pre-oxidation-high temperature expansion synergistic construction method for multi-scale porous Ti3C2T. x A method for preparing MXene thin films. This invention introduces a pre-oxidation treatment step before high-temperature expansion to introduce oxygen-containing functional groups and nanoscale defect sites on the surface and between layers of MXene sheets. This effectively controls the subsequent high-temperature expansion process, thereby constructing a multi-scale pore structure within the film where nanoscale in-plane mesopores and micron-scale interlayer expansion pores coexist. This increases the specific surface area of ​​the film while maintaining good conductivity and mechanical flexibility, solving the problems of existing Ti3C2T... x When MXene films are directly expanded at high temperatures to prepare porous structures, there are challenges such as missing nanopores, low specific surface area, and decreased mechanical properties.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x A method for preparing MXene thin films, characterized in that the method includes the following steps: Step 1: Preparation of Ti3C2T x MXene dispersion: Ti3AlC2MAX phase precursor material was selectively etched with a fluorine-containing etchant, and Ti3C2T was obtained after centrifugal washing and ultrasonic exfoliation. x MXene dispersion; the Ti3C2T xThe concentration of MXene dispersion is 5 mg / mL to 10 mg / mL; Step 2, Pre-oxidation treatment: Apply the Ti3C2T obtained in Step 1 to... x Hydrogen peroxide solution was added to the MXene dispersion for a room temperature pre-oxidation reaction. Then, dilute hydrochloric acid was added and stirred to remove some oxidation products. Subsequently, the mixture was centrifuged, washed, and redispersed. Finally, a pre-oxidized Ti3C2T with a thickness of 4μm~6μm was prepared by vacuum filtration. x MXene thin films; Step 3, High-Temperature Expansion: Under atmospheric conditions or an inert gas protective atmosphere, the pre-oxidized Ti3C2T prepared in Step 2 is expanded. x The MXene film was placed on a high-temperature heating stage of 300℃~350℃ and held for 5s~10s, and the high-temperature expansion of the film was achieved by the instantaneous vaporization of interlayer water. Step 4, Post-processing: The pre-oxidized Ti3C2T after high-temperature expansion in Step 3... x The MXene film was removed from the high-temperature heating stage and allowed to cool naturally to room temperature in air, resulting in a multi-scale porous Ti3C2T film. x MXene thin film.

[0008] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene thin films is characterized in that the fluorinated etchant in step one is a mixed solution of lithium fluoride and hydrochloric acid, and the concentration of the raw material hydrochloric acid is 6 mol / L to 12 mol / L, and the mass ratio of lithium fluoride to Ti3AlC2MAX phase precursor raw material is 1.6:1.

[0009] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene films is characterized in that the mass fraction of the hydrogen peroxide solution in step two is 30%, the room temperature pre-oxidation reaction time is 30 min to 60 min, the concentration of dilute hydrochloric acid is 1 mol / L, and the number of centrifugal washing cycles is 3 to 5.

[0010] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene thin films is characterized in that the amount of hydrogen peroxide solution added in step two is: 5 mg / mL Ti3C2T per 30 mL of solution. x 150 μL of 30% hydrogen peroxide solution was added to the MXene dispersion, and the room temperature pre-oxidation reaction time was 60 min.

[0011] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2Tx The method for preparing MXene films is characterized in that the vacuum filtration in step two uses a mixed cellulose filter membrane with a pore size of 0.22 μm.

[0012] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene thin films is characterized in that the inert gas in step three is argon or nitrogen.

[0013] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene thin films is characterized in that, in step three, pre-oxidized Ti3C2T... x The MXene film was placed on a high-temperature heating table at 350°C and held for 5 seconds.

[0014] The above-mentioned pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T x The method for preparing MXene thin films is characterized in that the multi-scale porous structure in step four includes in-plane nanopores at the 2nm~50nm level and interlayer expansion pores at the 10μm~100μm level. Furthermore, this invention also discloses a multi-scale porous Ti3C2T structure prepared by the method described above. x MXene thin film, characterized in that the multi-scale porous structure Ti3C2T x The specific surface area of ​​the MXene film is 10 m². 2 / g~30m 2 It has an in-plane electrical conductivity of 1000 S / cm to 3000 S / cm and is flexible.

[0015] The above-mentioned multi-scale porous structure Ti3C2T x MXene thin film, characterized in that the multi-scale porous structure Ti3C2T x The total electromagnetic shielding effectiveness of MXene films in the X-band (8.2GHz~12.4GHz) is 50dB~70dB, of which the absorption effectiveness accounts for more than 60%.

[0016] Compared with the prior art, the present invention has the following advantages: 1. Construction of a multi-scale porous structure: This invention employs a synergistic process of "pre-oxidation-high-temperature expansion," which involves introducing a pre-oxidation treatment step before high-temperature expansion. This introduces oxygen-containing functional groups and nanoscale defect sites on the surface and between layers of MXene sheets. After acid washing, in-plane nanopores are formed. During the subsequent high-temperature expansion process, the vapor pressure generated by the vaporization of water molecules between layers forms interlayer expansion pores, thereby synergistically constructing a multi-scale porous structure and significantly improving the efficiency of Ti3C2T. xMXene films have a specific surface area up to 10 m². 2 / g~30m 2 / g, significantly higher than the specific surface area of ​​approximately 3.2m² of films prepared by direct high-temperature expansion without pre-oxidation. 2 / g.

[0017] 2. The electromagnetic shielding mechanism shifts from reflection-dominant to absorption-dominant: The multi-scale porous structure Ti3C2T of this invention x MXene films possess a multi-scale pore structure with both nanoscale in-plane mesopores and micron-scale interlayer expansion pores. The nanoscale in-plane mesopores optimize the impedance matching between the material and air, facilitating the penetration of electromagnetic waves into the material. The micron-scale interlayer expansion pores and their tortuous pore wall structure induce multiple reflections and scatterings of electromagnetic waves, extending the propagation path and preserving the Ti3C2T... x The MXene conductive network and high specific surface area provide a large number of interfacial polarization centers, which together achieve efficient absorption and dissipation of electromagnetic wave energy, thus enabling Ti3C2T x The total electromagnetic shielding effectiveness of MXene films in the X-band (8.2GHz~12.4GHz) is 50dB~70dB, of which the absorption effectiveness accounts for more than 60%.

[0018] 3. Improved mechanical properties and structural integrity: The pre-oxidation treatment in this invention introduces oxygen-containing functional groups and trace amounts of TiO2 between MXene layers, which act as structural anchors, constraining the degree of high-temperature expansion and avoiding excessive interlayer separation. This ensures the structural integrity of the film, maintaining good conductivity (1000 S / cm~3000 S / cm) and improving the film's mechanical properties. Compared to films that expand directly without pre-oxidation, which have a tensile strength of only 10 MPa and significantly insufficient flexibility, the Ti3C2T film prepared by this invention... x MXene film has a tensile strength of up to 30 MPa and good flexibility, and can withstand repeated bending.

[0019] 4. Simple process, suitable for scale-up: The entire process of this invention does not require complex equipment or harsh conditions, nor does it require external templates or foaming agents, which greatly shortens the film preparation cycle. It is also green and residue-free, and has good prospects for large-scale production.

[0020] 5. Synergistic effect of pre-oxidation and high-temperature expansion: This invention achieves an effective combination of interlayer chemical regulation and physical expansion through the synergistic effect of pre-oxidation and high-temperature expansion, thus constructing a multi-scale porous film with complete structure and excellent performance. This overcomes the problems that pre-oxidation alone cannot form micron-level interlayer expansion pores and high-temperature expansion alone lacks nanoscale pore regulation, resulting in a decline in mechanical properties.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This invention relates to Example 1, which describes the pre-oxidation-high-temperature expansion synergistic construction of a multi-scale porous Ti3C2T structure. x Flowchart of MXene film fabrication process and preparation of multi-scale porous Ti3C2T x A photograph of an MXene thin film.

[0023] Figure 2 The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention x MXene thin films and Ti3C2T prepared by Comparative Examples 1 and 3 x Cross-sectional SEM and TEM images of the MXene thin film.

[0024] Figure 3 The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention x MXene thin film and Ti3C2T prepared in Comparative Example 1 x XRD pattern of MXene film and multi-scale porous Ti3C2T prepared in Example 1 x XPS plot of MXene thin film.

[0025] Figure 4 The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention x Frequency curves of electromagnetic shielding effectiveness of MXene films in the X-band (8.2GHz~12.4GHz) and comparative bar charts of total shielding effectiveness (SET), reflection effectiveness (SER), and absorption effectiveness (SEA).

[0026] Figure 5 The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention x Nitrogen adsorption-desorption isotherms and BJH pore size distribution of MXene thin films.

[0027] Figure 6 The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention x MXene thin film and Ti3C2T prepared in Comparative Example 1 x Comparison of X-band electromagnetic shielding effectiveness (SET) of MXene thin films.

[0028] Figure 7 Ti3C2T was prepared under different H2O2 dosages (0, 150, 250, 350 μL) in Examples 1-3 and Comparative Example 2 of this invention. x Graph showing the specific shielding effectiveness (SSE / t) of MXene thin films as a function of frequency. Detailed Implementation

[0029] Example 1 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Preparation of Ti3C2T x MXene dispersion: Under stirring conditions, 2.0 g of Ti3AlC2 powder was added in small batches to a fluorine-containing etchant consisting of 3.2 g of LiF and 55 mL of 9 mol / L HCl. Selective etching was performed by reacting in a 55°C water bath for 24 h. After the reaction, the supernatant was repeatedly centrifuged and washed with deionized water (3500 rpm, 5 min) until the pH > 6. The resulting precipitate was redispersed in 200 mL of deionized water and sonicated for 30 min under argon protection. Then, it was centrifuged at 3500 rpm for 30 min, and the supernatant was collected to obtain a monolayer Ti3C2T with a concentration of approximately 5 mg / mL. x MXene dispersion; Step 2, Pre-oxidation treatment: Add 30 mL of the Ti3C2T obtained in Step 1 to... x 150 μL of 30% hydrogen peroxide solution was added to the MXene dispersion for a pre-oxidation reaction at room temperature for 60 min. Then, 20 mL of 1 mol / L dilute hydrochloric acid was added and stirred for 10 min to remove some oxidation products. The mixture was then centrifuged at 10,000 rpm for 60 min and washed. This process was repeated 5 times. The washed precipitate was redispersed in deionized water to form a homogeneous dispersion. Vacuum filtration was then performed using a mixed cellulose membrane with a pore size of 0.22 μm to prepare a pre-oxidized Ti3C2T with a thickness of 4 μm to 6 μm. x MXene thin films; Step 3, High-Temperature Expansion: Under atmospheric conditions, the pre-oxidized Ti3C2T prepared in Step 2 is expanded... x The MXene film was rapidly transferred and placed on a high-temperature heating stage at 350°C for 5 seconds, and the high-temperature expansion of the film was achieved by the instantaneous vaporization of interlayer water. Step 4, Post-processing: Turn off the power to the high-temperature heating stage, and remove the pre-oxidized Ti3C2T after high-temperature expansion in Step 3. x The MXene film was removed from the high-temperature heating stage and allowed to cool naturally to room temperature in air, resulting in a multi-scale porous Ti3C2T film. x MXene thin films, such as Figure 1 As shown.

[0030] The multi-scale porous Ti3C2T prepared in this embodiment x The performance of the MXene film was tested, and the results are shown in Table 1 below.

[0031] Table 1

[0032] Based on the data in Table 1, such as Figure 2 As shown, the left images in the figure are all SEM images, and the right images are all TEM images. This embodiment shows the Ti3C2T prepared in this case. x MXene films have a complete structure, uniform thickness, and good flexibility; such as Figure 3 As shown, the Ti3C2T prepared in this embodiment x The XRD pattern of the MXene film shows a shift of the (002) characteristic peak to a lower angle, confirming the effective widening of the interlayer spacing. The XPS pattern shows a distinct TiO2 peak in the Ti2p region and TiO2 and C-Ti-O peaks in the O1s region. x The presence of CO and OC=O peaks in the C1s region demonstrates that pre-oxidation successfully introduced oxygen-containing functional groups and localized TiO2 into the sheets. These structures serve as the physical anchoring points for subsequent controllable foaming. Figure 4 As shown, the Ti3C2T prepared in this embodiment x MXene films achieve a total shielding effectiveness of 65dB~70dB in the X-band, with absorption accounting for approximately 70%, realizing an absorption-dominated shielding mechanism; such as Figure 5 As shown in the figure, the upper part is the nitrogen adsorption-desorption isotherm, and the lower part is the BJH pore size distribution diagram. This embodiment prepares Ti3C2T... x The BJH pore size distribution of the MXene film shows that the pore size is mainly concentrated between 2 nm and 50 nm, and the BET specific surface area is 20.4 m². 2 / g, with mesopores accounting for 97.18% of the total pore area, confirms that pre-oxidation successfully constructed abundant nanoscale mesopores on MXene sheets.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the Ti3C2T in step one is changed. x The MXene dispersion was not pre-oxidized at room temperature and was directly subjected to vacuum filtration in step two, without undergoing high-temperature expansion in step three, resulting in a Ti3C2T dispersion with a thickness of 4μm~6μm. x MXene thin film.

[0034] The Ti3C2T prepared in this comparative example x The performance of the MXene film was tested, and the results are shown in Table 2 below.

[0035] Table 2

[0036] Based on the data in Table 2, Comparative Example 1 uses Ti3C2T prepared by traditional vacuum filtration. xMXene films possess high electrical conductivity, but due to the lack of porous structure, impedance matching is poor, making it difficult for electromagnetic waves to penetrate the material's interior. The shielding mechanism is primarily reflection (with absorption accounting for approximately 40%). Meanwhile, ... Figure 2 As shown, the left images in the figure are all SEM images, and the right images are all TEM images. This Ti3C2T x MXene films are dense and non-porous, but prone to cracking when bent, making them unsuitable for lightweight and absorbent shielding materials; for example... Figure 6 As shown, the multi-scale porous structure Ti3C2T prepared in Example 1 x The overall shielding effectiveness of the MXene film (65dB~70dB) is higher than that of the conventional dense film (55dB~60dB) in Comparative Example 1 across the entire X-ray band, indicating that the present invention, through the synergistic construction of a multi-scale channel structure, not only achieves Ti3C2T x The electromagnetic shielding mechanism of MXene films has shifted from reflection-dominated to absorption-dominated (the absorption ratio has increased from about 40% to about 70%), and the overall shielding effectiveness has also been improved. This overcomes the drawbacks of traditional dense films, which have high shielding effectiveness but are mainly based on reflection and are prone to secondary electromagnetic pollution.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that the Ti3C2T in step one is changed. x The MXene dispersion was not pre-oxidized at room temperature and was directly subjected to vacuum filtration in step two to prepare a 5μm~6μm thick Ti3C2T filter. x The MXene film is then subjected to high-temperature expansion in step three and post-processing in step four to obtain Ti3C2T. x MXene thin film.

[0038] The Ti3C2T prepared in this comparative example x The performance of the MXene film was tested, and the results are shown in Table 3 below.

[0039] Table 3

[0040] Based on the data in Table 3, the Ti3C2T prepared by direct high-temperature expansion without pre-oxidation treatment in Comparative Example 2... x MXene films achieve high overall shielding effectiveness (60dB~70dB) due to the significantly increased interlayer spacing, but they have the following problems: (1) The specific surface area is only 3.2m². 2 / g, far lower than 20.4m in Example 1. 2 / g indicates that direct expansion cannot form nanoscale mesopores on the sheets, and the interior is mainly composed of micron-sized interlayer macropores. (2) Excessive expansion leads to a significant lack of flexibility. Comparing Example 1 of the present invention with Comparative Example 2, it can be seen that the pre-oxidation treatment in the construction of nanopores (BET specific surface area increased from 3.2m²) 2 / g increased to 20.4m 2 It plays an irreplaceable role in terms of increasing absorption efficiency by approximately 6.4 times (per g) and improving the proportion of absorption efficiency (from 50%~55% to approximately 70%), achieving the optimal balance of comprehensive performance.

[0041] Comparative Example 3 The difference between this comparative example and Example 1 is that the pre-oxidized Ti3C2T in step two is removed. x The MXene film is not subjected to the high-temperature expansion in step three, but directly proceeds to the post-processing in step four to obtain Ti3C2T. x MXene thin film.

[0042] The Ti3C2T prepared in this comparative example x The performance of the MXene film was tested, and the results are shown in Table 4 below.

[0043] Table 4

[0044] Based on the data in Table 4, such as Figure 2 As shown, the left images in the figure are all SEM images, and the right images are all TEM images. Comparative Example 3 shows Ti3C2T prepared after pre-oxidation treatment but without high-temperature expansion. x No micron-scale interlayer expansion pores were formed within the MXene film, resulting in a low specific surface area (6.9 μm). 2 / g), the scattering path of electromagnetic waves within the material is limited; at the same time, as Figure 3 As shown, although pre-oxidation introduces a certain amount of nanodefects, it alone cannot form micron-scale interlayer expansion pores. Furthermore, the electromagnetic wave multiple scattering paths are limited. Therefore, the Ti3C2T in Comparative Example 3... x The overall shielding performance of the MXene film is inferior to that of Example 1. This comparative example further demonstrates that the synergistic effect of "pre-oxidation" and "high-temperature expansion" is required to achieve the technical effect of this invention.

[0045] Example 2 The difference between this embodiment and Embodiment 1 is that the amount of hydrogen peroxide solution added in step two is 250 μL.

[0046] The multi-scale porous Ti3C2T prepared in this embodiment x The performance of the MXene film was tested, and the results are shown in Table 5 below.

[0047] Table 5

[0048] According to the data in Table 5, when the amount of hydrogen peroxide solution used in the pre-oxidation treatment increased from 150 μL in Example 1 to 250 μL in Example 2, the degree of pre-oxidation deepened, and more of the TiO2 generated in the reaction was dissolved and removed by acid washing, resulting in a further increase in the number of nanopores and a slight increase in the specific surface area (~23 μm). 2 / g vs 20.4m of Example 1 2 / g), but excessive pre-oxidation caused some damage to the conductive network of MXene, reducing the conductivity to 2000S / cm~2500S / cm, resulting in a decrease in the overall shielding effectiveness to 55dB~60dB; despite this, the multi-scale porous Ti3C2T prepared in Example 2 x The SSE / t of the MXene film still reaches approximately 23,000 dB·cm. 2 ·g -1 It is still higher than that of Comparative Example 2, which expanded directly without pre-oxidation (approximately 22,000 dB·cm). 2 ·g -1 This indicates that a pre-oxidation dose of 250 μL of hydrogen peroxide solution can still have a positive effect, but compared to Example 1 (approximately 25,000 dB·cm⁻¹), the effect is less. 2 ·g -1 Compared to the previous figure, SSE / t has shown a downward trend, indicating that 150μL is a better pre-oxidation dosage, with an absorption efficiency of about 65%. This suggests that increasing the pre-oxidation dosage helps to further improve impedance matching, but the overall shielding efficiency is reduced due to the decrease in conductivity loss.

[0049] Example 3 The difference between this embodiment and Embodiment 1 is that the amount of hydrogen peroxide solution added in step two is 350 μL.

[0050] The multi-scale porous Ti3C2T prepared in this embodiment x The performance of the MXene film was tested, and the results are shown in Table 6 below.

[0051] Table 6

[0052] According to the data in Table 6, when the hydrogen peroxide solution used in the pre-oxidation treatment was increased from 150 μL in Example 1 to 350 μL in Example 3, the MXene framework was excessively oxidized and destroyed, although the multi-scale porous structure Ti3C2T x The number of nanopores in the MXene film increased, and the specific surface area was further increased to approximately 27 m². 2 / g, but its conductive network is severely damaged, the conductivity drops to 1000S / cm~2000S / cm, and the overall shielding effectiveness decreases to 50dB~55dB. For example Figure 7 As shown, the multi-scale porous structure Ti3C2T in Example 3 x The SSE / t of MXene films decreased to approximately 21,500 dB·cm. 2 ·g -1 Compared with the Ti3C2T in Comparative Example 2, which expanded directly without pre-oxidation, x SSE / t of MXene film (approximately 22,000 dB·cm) 2 ·g -1 The values ​​are basically equivalent, with obvious overlap, indicating that the 350 μL pre-oxidation dosage is excessive. The SSE / t gain brought about by the introduction of nanopores and reduction of density by pre-oxidation has been offset by the severe loss of conductivity. This example further confirms that there is a clear optimal process window for the amount of pre-oxidation.

[0053] like Figure 7 As shown, the Ti3C2T prepared in Example 1 of this invention x The MXene film achieves a specific shielding effectiveness (SSE / t) of approximately 25,000 dB·cm. 2 ·g -1 The value is the highest among all films, indicating that the pre-oxidation amount of 150 μL of hydrogen peroxide solution achieves the best balance between film shielding effectiveness and lightweighting.

[0054] Example 4 The difference between this embodiment and Embodiment 1 is that the Ti3C2T obtained in step one... x The concentration of MXene dispersion was 10 mg / mL; in step two, the room temperature pre-oxidation reaction time was 30 min, and the centrifugation and washing were repeated 3 times; in step three, the pre-oxidized film was placed on a 300℃ high-temperature heating table for 10 s under an argon protective atmosphere.

[0055] The multi-scale porous Ti3C2T prepared in this embodiment x The performance of the MXene film was tested, and the results are shown in Table 7 below.

[0056] Table 7

[0057] Based on the data in Table 7, this embodiment adjusted the dispersion concentration, pre-oxidation reaction time, number of washing cycles, and high-temperature expansion temperature, time, and atmosphere. It can still effectively construct a multi-scale porous structure in which nanopores and micron-level interlayer expansion pores coexist, thus meeting the technical requirements of the present invention. However, the overall performance is slightly lower than the preferred scheme of Example 1, further verifying the optimal process conditions of Example 1 and demonstrating that the present invention can be effectively implemented in the dispersion concentration range of 5 mg / mL to 10 mg / mL, under atmospheric environment and inert gas protective atmosphere, and in the temperature range of 300℃ to 350℃.

[0058] The performance results of the thin films prepared according to Examples 1-4 and Comparative Examples 1-3 of the present invention show that: (1) The synergistic effect of pre-oxidation and high-temperature expansion is the key to constructing multi-scale porous structures. In Comparative Example 3, pre-oxidation alone failed to form micron-scale interlayer expansion pores. In Comparative Example 2, although high-temperature expansion alone achieved high shielding efficiency, the nanopore control was insufficient and the flexibility decreased. Only the synergistic effect of pre-oxidation and high-temperature expansion in Example 1 could simultaneously construct nano-mesopores and micron-scale interlayer pores in the film, thereby obtaining a multi-scale porous structure Ti3C2T with complete structure, good flexibility, high absorption efficiency, and optimal SSE / t. x MXene thin film.

[0059] (2) Pre-oxidation can effectively increase the specific surface area of ​​MXene films and regulate their structure. The multi-scale porous Ti3C2T structure prepared in Example 1 of this invention (150 μL of hydrogen peroxide solution) x The specific surface area of ​​the MXene thin film reaches 20.4 m². 2 / g, approximately the direct high-temperature expansion of Comparative Example 2 without pre-oxidation (3.2m) 2 The 6.4 times increase of / g) confirms the key role of pre-oxidation in the construction of nanoporous structures. The introduction of nanoporous structures effectively improves impedance matching, making it easier for electromagnetic waves to enter the material and be dissipated, thereby increasing the absorption efficiency ratio.

[0060] (3) An optimal pre-oxidation process window exists. As the amount of hydrogen peroxide solution increased from 150 μL in Example 1 to 250 μL in Example 2 and 350 μL in Example 3, although the multi-scale porous structure Ti3C2T x The specific surface area of ​​the MXene film was further increased, but its conductive network was gradually damaged, resulting in a gradual decrease in overall shielding effectiveness and SSE / t. The highest SSE / t value (approximately 25,000 dB·cm⁻¹) was obtained under the 150 μL condition in Example 1. 2 ·g -1This indicates that the degree of pre-oxidation needs to be controlled within a certain range in order to achieve a balance between pore structure construction and the maintenance of conductive network.

[0061] In summary, this invention successfully constructed a high specific surface area film with multi-scale channels, complete structure, and excellent flexibility while maintaining the good conductivity of MXene through a synergistic process of "pre-oxidation-high temperature expansion". It also successfully transformed the electromagnetic shielding mechanism into one that is mainly based on efficient absorption, resulting in the best overall performance and verifying the significant technical effect of this invention.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A Ti3C2T x Method for preparing a MXene film, characterized in that, The method includes the following steps: ​ Step 1: Preparation of Ti3C2T x MXene dispersion: Ti3AlC2 MAX phase precursor raw material was selectively etched with a fluorine-containing etchant, and Ti3C2T was obtained after centrifugation, washing, and ultrasonic exfoliation. x MXene dispersion; the Ti3C2T x The concentration of MXene dispersion is 5 mg / mL to 10 mg / mL; Step 2, Pre-oxidation treatment: Apply the Ti3C2T obtained in Step 1 to... x Hydrogen peroxide solution was added to the MXene dispersion for a room temperature pre-oxidation reaction. Then, dilute hydrochloric acid was added and stirred to remove some oxidation products. Subsequently, the mixture was centrifuged, washed, and redispersed. Finally, a pre-oxidized Ti3C2T with a thickness of 4μm~6μm was prepared by vacuum filtration. x MXene thin films; Step 3, High-Temperature Expansion: Under atmospheric conditions or an inert gas protective atmosphere, the pre-oxidized Ti3C2T prepared in Step 2 is expanded. x The MXene film was placed on a high-temperature heating stage of 300℃~350℃ and held for 5s~10s, and the high-temperature expansion of the film was achieved by the instantaneous vaporization of interlayer water. Step 4, Post-processing: The pre-oxidized Ti3C2T after high-temperature expansion in Step 3... x The MXene film was removed from the high-temperature heating stage and allowed to cool naturally to room temperature in air, resulting in a multi-scale porous Ti3C2T film. x MXene thin film.

2. The pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T according to claim 1 x The method for preparing MXene thin films is characterized by, The fluorinated etching agent mentioned in step one is a mixed solution of lithium fluoride and hydrochloric acid, and the concentration of the raw material hydrochloric acid is 6 mol / L to 12 mol / L. The mass ratio of lithium fluoride to Ti3AlC2 MAX phase precursor raw material is 1.6:

1.

3. The pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T according to claim 1 x The method for preparing MXene thin films is characterized by, In step two, the hydrogen peroxide solution has a mass fraction of 30%, the pre-oxidation reaction time at room temperature is 30-60 minutes, the concentration of dilute hydrochloric acid is 1 mol / L, and the centrifugal washing is performed 3-5 times.

4. The pre-oxidation-high-temperature-expansion synergistically constructed Ti3C2T x The method for preparing a MXene film is characterized by comprising the steps of: The amount of hydrogen peroxide solution added in step two is: 5 mg / mL Ti3C2T per 30 mL of solution. x 150 μL of 30% hydrogen peroxide solution was added to the MXene dispersion, and the room temperature pre-oxidation reaction time was 60 min.

5. The pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T according to claim 1 x The method for preparing MXene thin films is characterized by, The vacuum filtration in step two uses a mixed cellulose filter membrane with a pore size of 0.22 μm.

6. The pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T according to claim 1 x The method for preparing MXene thin films is characterized by, The inert gas mentioned in step three is argon or nitrogen.

7. The pre-oxidation-high temperature expansion synergistic construction of multi-scale porous Ti3C2T according to claim 1 x The method for preparing MXene thin films is characterized by, In step three, the pre-oxidized Ti3C2T x The MXene film was placed on a high-temperature heating table at 350°C and held for 5 seconds.

8. The Ti3C2Tx with synergistically constructed multi-scale pore structure by pre-oxidation-high temperature expansion according to claim 1. x The method for preparing a MXene film is characterized by comprising the steps of: The multi-scale porous structure described in step four includes in-plane nanopores at the 2nm~50nm level and interlayer expansion pores at the 10μm~100μm level.

9. A multi-scale porous structure Ti3C2T prepared by the method of any one of claims 1-8 x MXene film characterized in that, The multi-scale pore structure Ti3C2T x The specific surface area of the MXene film is 10 m 2 / g~30 m 2 / g, the in-plane conductivity is 1000 S / cm~3000 S / cm, and has flexibility.

10. The multiscale pore structured Ti3C2T of claim 9 x MXene thin film characterized in that, The multi-scale pore structure Ti3C2T x The total electromagnetic shielding efficiency of the MXene film in the X-band (8.2GHz~12.4GHz) is 50dB~70dB, and the absorption efficiency accounts for more than 60%.

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