Wave-absorbing composite material MXene / MnO2 and preparation method thereof

Abstract

The invention belongs to the technical field of electromagnetic wave absorbing materials, and relates to a wave-absorbing composite material MXene / MnO2 and a preparation method thereof, and few layers of MXene and columnar MnO2 are compounded through an electrostatic self-assembly method; the minimum value of the reflection loss of the composite material is-53.57 dB, and the maximum value of the effective absorption bandwidth is 4.8 GHz; the preparation method comprises the following steps: preparing few-layer MXene, preparing columnar MnO2, modifying the columnar MnO2 to enable the surface of the columnar MnO2 to be positively charged, titrating a positively charged MnO2 solution into a negatively charged few-layer MXene solution, and combining the MnO2 solution and the negatively charged few-layer MXene solution by utilizing electrostatic interaction; according to the method, the hydrothermal reaction time is accurately controlled, so that the morphological characteristics of MnO2 can be effectively regulated and controlled, and the microstructure and performance of the composite material are remarkably influenced.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a wave-absorbing composite material MXene / MnO2 and its preparation method. Background Technology

[0002] With the rapid development of electronic information technology, electromagnetic radiation pollution has become an increasingly serious problem. MXene materials (such as Ti3C2T) x Due to its high metallic conductivity, abundant surface functional groups, and two-dimensional layered structure, it has shown great potential in the field of microwave absorption.

[0003] However, pure MXene materials suffer from impedance mismatch and a single loss mechanism. Specifically: Impedance mismatch: Strong surface reflection leads to inefficient absorption: MXene has extremely high electrical conductivity, resulting in a large difference between its impedance and that of free space. Incident electromagnetic waves are strongly reflected at the material surface, making it difficult for them to penetrate and dissipate, resulting in a "high reflection, low absorption" phenomenon. For example, the electromagnetic wave reflectivity of some pure MXene films can exceed 80%, significantly reducing the effective absorption ratio.

[0004] Interlayer stacking exacerbates impedance mismatch: MXene nanosheets tend to stack themselves into a dense layered structure due to van der Waals forces, reducing porosity and increasing overall conductivity, which further worsens impedance matching. Studies have shown that the equivalent characteristic impedance (Z) of MXene films with unoptimized interlayer spacing is often much lower than the ideal matching value, resulting in limited electromagnetic wave penetration depth.

[0005] The loss mechanism is simple: Over-reliance on dielectric loss: The electromagnetic energy dissipation of pure MXene mainly relies on conductivity loss (heat generated by the migration of free electrons under an alternating electric field) and limited interfacial polarization loss. Lacking magnetic components, it cannot generate magnetic loss mechanisms such as hysteresis loss or natural resonance, resulting in weak electromagnetic wave absorption in low-frequency bands and specific polarization directions.

[0006] Limited polarization forms: Although surface functional groups (–OH, –F, etc.) can induce dipole polarization, heterojunctions are scarce in pure MXene, making it difficult to form effective Maxwell-Wagner interfacial polarization (requiring charge accumulation at the interface of materials with different electrical conductivity). For example, compared to MXene / Fe3O4 composites, the polarization loss factor (ε″) of pure MXene is typically more than 30% lower.

[0007] Poor bandwidth adaptability: The single dielectric loss mechanism results in a narrow absorption bandwidth, making it difficult to meet the absorption requirements of wide bandwidths (such as 8–18 GHz covering C, X, and Ku bands). Experiments show that pure Ti3C2T... XThe effective absorption bandwidth (EAB) is typically less than 3 GHz, but can reach more than 5 GHz after composite modification.

[0008] Therefore, absorbing materials that can improve impedance matching and introduce interfacial polarization loss are needed to solve the above-mentioned technical problems. Summary of the Invention

[0009] This invention aims to improve the overall microwave absorption performance of materials by introducing transition metal oxides (such as MnO2) with different morphologies and constructing heterostructures using electrostatic self-assembly technology. This can effectively improve impedance matching and introduce interfacial polarization loss.

[0010] This invention provides the following technical solution: a microwave absorbing composite material MXene / MnO2, wherein the composite material is a powder material prepared by electrostatic self-assembly of columnar MnO2 and few-layer MXene.

[0011] Preferably, the composite material has a minimum reflection loss of -53.57 dB and a maximum effective absorption bandwidth of 4.8 GHz.

[0012] This invention also discloses a method for preparing the microwave absorbing composite material MXene / MnO2. This method is used to prepare the aforementioned composite material and includes the following steps: Step S1: Add MAX and LiF to hydrochloric acid solution for in-situ etching to generate few-layer MXene.

[0013] Step S2: After mixing KMnO4 with HCl solution evenly, add it to a hydrothermal reactor and react at 140-160℃ for 5-7 hours to obtain columnar MnO2.

[0014] Step S3: Disperse the columnar MnO2 powder obtained in step S2 in water, and add 10-30 μL of polydiallyldimethylammonium chloride for modification, so that the surface of the columnar MnO2 is positively charged.

[0015] Step S4: A positively charged MnO2 solution is titrated into a negatively charged few-layer MXene solution, and the two are combined by electrostatic interaction. Finally, the MXene / MnO2 composite powder is obtained by freeze-drying.

[0016] Preferably, in step S1, MAX, LiF and hydrochloric acid solution are used as raw materials. The generated hydrofluoric acid strips the Al atoms in the MAX phase to form Ti3C2. The exposed Ti atoms have good reactivity and readily react with H2O and HF acid to form compounds with -OH and -F, thereby obtaining few-layer MXene.

[0017] Preferably, in step S1, the concentration of the hydrochloric acid solution is 7–11 mol / L; the mass ratio of MAX to LiF is 0.4–0.6:0.7–0.9.

[0018] More preferably, in step S2, the amount of KMnO4 used is 1-3 mmol, and the amount of HCl used is 5-15 mmol.

[0019] More preferably, in step S3, the amount of polydiallyldimethylammonium chloride used is 18–22 μL.

[0020] Preferably, in step S2, the hydrothermal reaction temperature is 145–155 °C and the reaction time is 5.5–6.5 h.

[0021] The beneficial effects of this invention are: The invented method for preparing MXene / MnO2 composite materials utilizes widely available, environmentally friendly, and sustainable raw materials, enabling large-scale production. By adjusting the hydrothermal reaction time, the morphology of MnO2 can be precisely controlled, thereby optimizing the microstructure of the composite material. The electrostatic self-assembly technology induced by polydiallyldimethylammonium chloride ensures close contact between MnO2 and MXene sheets, facilitating the formation of more heterogeneous interfaces and enhancing interfacial polarization. The composite material combines the high conductivity loss of MXene with the dielectric loss of MnO2, significantly improving electromagnetic wave absorption capacity through improved impedance matching. Attached Figure Description

[0022] Figure 1 XRD patterns of MnO2 and MXene / MnO2 composite materials prepared in an embodiment of the microwave absorbing composite material MXene / MnO2 and its preparation method of the present invention; Figure 2 This is a SEM image of the columnar MnO2 material prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the MXene / MnO2 composite material prepared in Example 1 of the present invention; Figure 4 This is a SEM image of the MXene / MnO2 composite material prepared in Comparative Example 1 of this invention; Figure 5 The comparison diagram shows the reflection loss of the MXene / MnO2 composite material prepared in the embodiment (left figure) and the comparative example (right figure) of the present invention. Figure 6 The electromagnetic parameters of the MXene / MnO2 composite materials prepared in the embodiments (left figure) and the comparative examples (right figure) of the present invention are compared. Figure 7The image shows a comparison of the RCS values ​​of the MXene / MnO2 composite material and the perfect conductor PEC prepared in the embodiments (left) and comparative examples (right) of the present invention. Detailed Implementation

[0023] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figures 1-7 As shown, the specific solution of this embodiment is described as follows: The microwave absorbing composite material MXene / MnO2 of the present invention is obtained by electrostatic self-assembly of columnar MnO2 and MXene. The columnar MnO2 is prepared by hydrothermal processing. The composite material is formed by electrostatic self-assembly of columnar MnO2 and few layers of MXene.

[0025] The preparation method of MXene / MnO2 composite material includes the following steps: Step S1: Add MAX and LiF to hydrochloric acid solution for in-situ etching to generate few-layer MXene; using MAX, LiF and hydrochloric acid solution as raw materials, the generated hydrofluoric acid strips Al atoms from the MAX phase to form Ti3C2. The exposed Ti atoms have good reactivity and readily react with H2O and HF acid to form compounds with -OH and -F, thus successfully obtaining few-layer MXene.

[0026] Step S2: After mixing KMnO4 with HCl solution evenly, add it to a hydrothermal reactor and react at 150 °C for 6 h to obtain columnar MnO2.

[0027] Step S3: Disperse the MnO2 powder obtained in step S2 in water, and add 10-30 μL of polydiallyldimethylammonium chloride for modification, so that its surface is positively charged.

[0028] Step S4: A positively charged MnO2 solution is titrated into a negatively charged few-layer MXene solution, and the two are combined by electrostatic interaction. Finally, the MXene / MnO2 composite powder is obtained by freeze-drying.

[0029] Furthermore, in step S1, the concentration of the hydrochloric acid solution is 7–11 mol / L.

[0030] Furthermore, the concentration of the hydrochloric acid solution is 8–10 mol / L.

[0031] Furthermore, in step S1, the ratio of MAX to LiF is 0.4–0.6 g: 0.7–0.9 g.

[0032] Furthermore, in step S2, the amount of KMnO4 used is 1–3 mmol.

[0033] Furthermore, the amount of KMnO4 used is 1.5–2.5 mmol.

[0034] Furthermore, in step S2, the amount of HCl used is 5–15 mmol.

[0035] Furthermore, in step S2, the hydrothermal reaction temperature is 140–160 °C, and the time is 5–7 h.

[0036] Furthermore, the temperature of the hydrothermal reaction is 145–155 °C. o C, time is 5.5 to 6.5 hours.

[0037] Furthermore, in step S3, the amount of PDDA used is 18–22 μL.

[0038] Example The MAX used in this embodiment was purchased from Jilin Yiyi Technology Co., Ltd.; potassium permanganate, hydrochloric acid and polydiallyl dimethyl ammonium chloride were purchased from Sinopharm Corporation.

[0039] 0.8 g LiF and 0.5 g MAX were added sequentially to 10 mL of 9 mol / mL hydrochloric acid solution, and stirred at 500 rpm for 48 h in a 40℃ water bath. The product was then washed 3-5 times with deionized water at 3500 rpm for 5 minutes each time, until the pH of the supernatant reached approximately 6-7. The precipitate was then shaken well and sonicated for 1 h under nitrogen protection. The resulting solution was then centrifuged at 3000 rpm for 1 h, and the supernatant was collected. The obtained solution was a few-layer MXene solution.

[0040] 2 mmol KMnO4 and 10 mL of 1 M hydrochloric acid solution were added to 20 mL of deionized water. After stirring for 30 minutes, the homogeneous solution was transferred to a 50 mL hydrothermal reactor, which was heated to 150°C for 6 h. The product was collected by repeatedly washing with deionized water and ethanol, and then dried in a vacuum oven at 80°C for 6 h to obtain columnar MnO2.

[0041] First, 40 mg of MnO2 was dispersed in 10 mL of deionized water by ultrasonication, and then 20 μL of PDDA was added dropwise to modify it and impart a positive charge. Subsequently, the MnO2 solution was added dropwise to 10 mL of MXene solution with a concentration of 1 mg / mL, stirred evenly, and then freeze-dried to form a powder, thus obtaining the MXene / MnO2 composite material.

[0042] Comparative Example Following the method described in the embodiment, the brine thermal reaction time was adjusted to 0.5 h, while other experimental conditions remained the same.

[0043] Scanning electron microscope (SEM) images of the products prepared in the comparative example are as follows: Figure 4 As shown, by Figure 4 It can be seen that after changing the hydrothermal time, the MnO2 grown from the product exhibits a plate-like structure.

[0044] In summary, this invention effectively modulates the morphology of MnO2 by precisely controlling the hydrothermal reaction time, thereby significantly influencing the microstructure and performance of the composite material. Experimental results show that when the hydrothermal reaction time is set to 6 hours, uniform columnar MnO2 is obtained, with a tighter bond between it and the MXene sheets, resulting in a significantly increased number of heterojunctions and greatly enhancing the interfacial polarization effect. Furthermore, comparative experiments reveal that shortening the hydrothermal reaction time to 0.5 hours causes the MnO2 morphology to transform into a plate-like structure. This structure exhibits poor interfacial contact when composited with MXene, thus weakening the electromagnetic wave absorption performance. Further analysis of reflection loss data shows that the composite material prepared using columnar MnO2 exhibits lower reflection loss values ​​in the 2–18 GHz frequency band, demonstrating the superiority of the method of this invention in optimizing microwave absorption performance.

[0045] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A microwave absorbing composite material MXene / MnO2, characterized in that, The composite material is a powder material prepared by electrostatic self-assembly of columnar MnO2 and few-layer MXene.

2. The microwave absorbing composite material MXene / MnO2 according to claim 1, characterized in that, The composite material has a minimum reflection loss of -53.57 dB and a maximum effective absorption bandwidth of 4.8 GHz.

3. A method for preparing a microwave absorbing composite material MXene / MnO2, characterized in that, The preparation method is used to prepare the composite material according to claim 1 or 2, and the preparation method includes the following steps: Step S1: Add MAX and LiF to hydrochloric acid solution for in-situ etching to generate few-layer MXene; Step S2: After mixing KMnO4 with HCl solution evenly, add it to a hydrothermal reactor and react at 140-160℃ for 5-7 hours to obtain columnar MnO2; Step S3: Disperse the columnar MnO2 powder obtained in step S2 in water, and add 10-30 μL of polydiallyldimethylammonium chloride for modification, so that the surface of the columnar MnO2 is positively charged. Step S4: A positively charged MnO2 solution is titrated into a negatively charged few-layer MXene solution, and the two are combined by electrostatic interaction. Finally, the MXene / MnO2 composite powder is obtained by freeze-drying.

4. The method for preparing the microwave absorbing composite material MXene / MnO2 according to claim 3, characterized in that, In step S1, MAX, LiF and hydrochloric acid solution are used as raw materials. The Al atoms in the MAX phase are etched by hydrofluoric acid generated in situ, and then the few-layer MXene is peeled off by centrifugation.

5. The method for preparing the microwave absorbing composite material MXene / MnO2 according to claim 3, characterized in that, In step S1, the concentration of the hydrochloric acid solution is 7–11 mol / L; the mass ratio of MAX to LiF is 0.4–0.6:0.7–0.

9.

6. The method for preparing the microwave absorbing composite material MXene / MnO2 according to claim 5, characterized in that, In step S2, the amount of KMnO4 used is 1-3 mmol, and the amount of HCl used is 5-15 mmol.

7. The method for preparing the microwave absorbing composite material MXene / MnO2 according to claim 5, characterized in that, In step S3, the amount of polydiallyldimethylammonium chloride used is 18–22 μL.

8. The method for preparing the microwave absorbing composite material MXene / MnO2 according to claim 3, characterized in that, In step S2, the hydrothermal reaction temperature is 145–155 °C, and the reaction time is 5.5–6.5 h.

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