Hollow-cage CoZn / C-coated Ti3C2Tx / TiO2 composite material, preparation method and application

Abstract

The invention discloses a hollow-cage CoZn / C-coated Ti3C2Tx / TiO2 composite material, a preparation method and application, and relates to the technical field of wave-absorbing materials, and the preparation method of the hollow-cage CoZn / C-coated Ti3C2Tx / TiO2 composite material comprises the following steps: preparing few layers of Ti3C2Tx nanosheets; the preparation method comprises the following steps: preparing a precursor CoZn-MOF; the preparation method comprises the following steps: dispersing a precursor CoZn-MOF and a Ti3C2Tx nanosheet in a first solvent, then adding epoxy chloropropane for reaction, then adding a second solvent for rotary evaporation, and performing high-temperature annealing on a product after the reaction to prepare the hollow-cage CoZn / C-coated Ti3C2Tx / TiO2 composite material. The wave absorbing range of the prepared composite material can cover the whole C wave band, X wave band and 57% of Ku wave band.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and more particularly to hollow-cage CoZn / C@Ti3C2T x / TiO2 composite materials, preparation methods and applications. Background Technology

[0002] With the rapid development of 5G communication technology and the widespread use of smart devices such as mobile phones, computers, and electric vehicles, people's lives have become more convenient and efficient. However, excessive electromagnetic radiation (EMA) not only damages instruments but also has negative effects on human health. Currently, electromagnetic absorbing materials (EMAs) play a crucial role in eliminating harmful radiation pollution; however, traditional EMAs have some specific drawbacks in practical applications, such as narrow effective absorption bandwidth (EAB), high filler content, and high density. Therefore, how to design and fabricate EMAs with a wide EAB, strong attenuation capability, and low filler content has attracted the attention of many scientists. Overcoming these shortcomings is key by rationally adjusting the chemical composition and microstructure of EMAs and fully utilizing the synergistic effect of impedance matching and high attenuation capability.

[0003] Metal-organic frameworks (MOFs), with their tunable composition and controllable microstructure, have become precursors for the synthesis of advanced carbon-based EMAs. Furthermore, MOFs and their derived composites possess synergistic magnetoelectric dissipation mechanisms, providing a practical approach for designing highly efficient EMAs. However, most MOFs and their derivatives have solid structures, resulting in low pore volumes and relatively high filler ratios. Hollow structures can expand pore volumes, reduce material density, and are an effective strategy for achieving better impedance matching and lightweight properties. Moreover, this structure promotes multiple reflections of EMA within the material, contributing to effective EMA absorption over a wider frequency range. However, realizing a simple and effective hollow MOF fabrication strategy remains a challenge. Recently, Ban et al. successfully prepared hollow Co@NCMs derived from ZIF-67@PPy microcages using a polymerization-induced assembly etching strategy and applied them to EMA absorption. The results showed that Co@NCM-900, with a thickness (d) of 2.7 mm, exhibited high resistance to irradiation (RL). min The impedance is -50.4 dB, and the EAB is 3.8 GHz. Huang et al. designed and fabricated a core-shell ZIF-8@HZIF-CoMo polyhedron, which, after appropriate calcination, yields a hollow Co and Mo bimetallic carbon polyhedron (CoMo@HNCP). In the N-doped carbon shell, the heterostructure formed by Mo2C and Co nanoparticles excites more dipole polarization, interfacial polarization, and multiple reflections, enhancing the matched impedance and attenuation capability. At d = 2.5 mm, the RL... min=-44.8dB, EAB is 6.6GHz. Du et al. reported a core-shell iron-cobalt alloy nanomaterial (FeCo@C) with good impedance matching, strong magnetism, and RL. min =-67.8dB (d=2mm), EAB is 5.3GHz.

[0004] In traditional preparation methods, MOF and Ti3C2T x The composite formed through electrostatic self-assembly suffers from insufficient bonding due to the limited contact interface area. Furthermore, this two-dimensional planar composite structure struggles to form a conductive pathway throughout the entire material and is prone to inducing Ti3C2T... x The re-stacking of layers reduces the conductivity of the material and weakens the interfacial polarization effect. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, this invention proposes a hollow-cage CoZn / C@Ti3C2T x / TiO2 composite materials, preparation methods and applications: the absorption range of the composite material can cover the entire C-band, X-band and 57% of the Ku-band.

[0006] This invention proposes a "hollow-cage" CoZn / C@Ti3C2T x The preparation method of the / TiO2 composite material is as follows:

[0007] Step (1): Few-layer Ti3C2T x Preparation of nanosheets;

[0008] Step (2): Preparation of the precursor CoZn-MOF;

[0009] Step (3): Combine the precursor CoZn-MOF and few-layer Ti3C2T x Nanosheets were dispersed in a first solvent, and epichlorohydrin was added to initiate the reaction. Subsequently, a second solvent was added for rotary evaporation. The product was then annealed at high temperature to obtain hollow-cage CoZn / C@Ti3C2T. x / TiO2 composite material.

[0010] Preferably, few-layer Ti3C2T x The preparation method of the nanosheets is as follows: LiF is dissolved in hydrochloric acid, then Ti3AlC2 powder is added, stirred and etched, and then washed and ultrasonically exfoliated to obtain few-layer Ti3C2T nanosheets. x Nanosheets.

[0011] Preferably, the mass ratio of LiF to Ti3AlC2 is 1-3:1;

[0012] And / or, the temperature for stirring etching is 40-60℃, and the time is 12-36h.

[0013] Preferably, the preparation method of the precursor CoZn-MOF is as follows:

[0014] Step (2.1): Dissolve the zinc source in methanol, add 2-methylimidazole and allow the reaction to stand at room temperature. After the reaction, the product is dried to obtain ZIF-8.

[0015] Step (2.2): Disperse ZIF-8 in methanol, then add cobalt source and 2-methylimidazole in sequence and stir at room temperature to react. After the reaction, dry to obtain the precursor CoZn-MOF.

[0016] Preferably, the zinc source in step (2.1) is one or more of zinc nitrate and its hydrate, zinc chloride and its hydrate, and zinc acetate and its hydrate;

[0017] And / or, in step (2.1), the molar ratio of zinc source to 2-methylimidazole is 1:2-5;

[0018] And / or, the conditions for the static reaction in step (2.1) are a temperature of 20-30℃ and a time of 12-36h.

[0019] Preferably, the cobalt source in step (2.2) is one or more of cobalt nitrate and its hydrate, cobalt chloride and its hydrate, and cobalt acetate and its hydrate;

[0020] And / or, the molar ratio of the cobalt source and 2-methylimidazole in step (2.2) to the zinc source in step (2.1) is 1-8:20-30:1;

[0021] And / or, the stirring reaction conditions in step (2.2) are a temperature of 20-30℃ and a time of 12-36h.

[0022] Preferably, in step (3), the precursor CoZn-MOF and the few-layer Ti3C2T x The mass-to-volume ratio of nanosheets to epichlorohydrin is 400-800 mg: 100-500 mg: 1 ml;

[0023] And / or, the reaction temperature in step (3) is 40-60℃, and the time is 30-90 min;

[0024] And / or, the first solvent is an aqueous solution of an alcohol;

[0025] And / or, the second solvent is acetone.

[0026] Preferably, the conditions for high-temperature annealing in step (3) are a temperature of 600-700℃ and a time of 1-3h.

[0027] This invention proposes a hollow-cage CoZn / C@Ti3C2T x The / TiO2 composite material was prepared using the method described above.

[0028] The hollow-cage CoZn / C@Ti3C2T proposed in this invention, as described above, x Application of TiO2 composite materials in electromagnetic wave absorption.

[0029] Beneficial technical effects of the present invention:

[0030] The CoZn / C@Ti3C2T prepared in this invention x / TiO2 composite material is a multi-component heterogeneous EMA with both hollow and cage-like structures, which can effectively enhance multiple reflections of EMA and improve impedance matching characteristics. Furthermore, the construction of multi-heterogeneous interface and Ti3C2T x TiO2 can improve the conductivity, interfacial polarization, and dipole polarization of the absorber, ultimately enhancing its EMA absorption performance. Meanwhile, CST simulation results verify that this composite material can effectively attenuate electromagnetic energy under practical application conditions. With a diameter (d) of 3.0 mm and a frequency of 12.02 GHz, RL... min The value is -72.51dB, and its EAB is 5.53GHz. The S2 has both high electromagnetic wave absorption performance and a wide EAB, and its absorption range can cover the entire C-band, X-band and 57% of the Ku-band, fully meeting the requirements of practical applications. Attached Figure Description

[0031] Figure 1 The CoZn / C and CoZn / C@Ti3C2T proposed in this invention x A schematic diagram of the TiO2 preparation process;

[0032] Figure 2 The diagram shows the structural characterization of S2 proposed in this invention; where (a) is an XRD pattern, (b) is an IR pattern, (c) is a Raman pattern, (d) is a VSM pattern, and the inner diagram in (d) is a magnified view of a portion of the VSM pattern.

[0033] Figure 3 The XPS spectrum of S2 proposed in this invention is shown below; where (a) is the full spectrum, (b) is the Ti 2p narrow spectrum, (c) is the N 1s narrow spectrum, (d) is the C 1s narrow spectrum, (e) is the O 1s narrow spectrum, and (f) is the Co 2p narrow spectrum.

[0034] Figure 4The SEM image, secondary electron image, elemental superposition distribution map, and elemental image map proposed in this invention are shown below; where (ab) is the SEM image of S0, (cd) is the SEM image of S1, (ef) is the SEM image of S2, (gh) is the SEM image of S3, (i) is the secondary electron image of S2, (j) is the elemental superposition distribution map of C, N, O, Ca, Zn and Ti of S2, and (kp) are the elemental image maps of C, N, O, Ca, Zn and Ti of S2 in sequence.

[0035] Figure 5 The images are TEM and HRTEM images of S2 proposed in this invention; where (a) is the TEM image at 500 nm, (b) is the TEM image at 200 nm, (c) is the TEM image at 100 nm, (d) is the HRTEM image of CoO at 5 nm, (e) is the HRTEM image of Co at 5 nm, and (f) is the HRTEM image of TiO2 at 5 nm.

[0036] Figure 6 The diagram shows the electromagnetic parameters proposed in this invention; where (a) is the real part of the dielectric constant, (b) is the imaginary part of the dielectric constant, (c) is the real part of the permeability, (d) is the imaginary part of the permeability, (e) is the dielectric loss tangent, and (f) is the magnetic loss tangent.

[0037] Figure 7 The Cole-Cole curves proposed in this invention are shown below; where (a) is S0, (b) is S1, (c) is S2, and (d) is S3.

[0038] Figure 8 The diagram shows the electromagnetic wave absorption performance proposed in this invention; where (a) is the C0-f curve, (b) is the attenuation constant curve, and (c) is the impedance matching curve.

[0039] Figure 9 This is the reflection loss map proposed in this invention; where (ac) represents the RL value, 2D contour map, and 3D RL value color map of S0, respectively; (df) represents the RL value, 2D contour map, and 3D RL value color map of S1, respectively; (gi) represents the RL value, 2D contour map, and 3D RL value color map of S2, respectively; and (jl) represents the RL value, 2D contour map, and 3D RL value color map of S3, respectively.

[0040] Figure 10 This is a curve of the 1 / 4 wavelength matching model of S2 proposed in this invention;

[0041] Figure 11 The simulation diagram of CST proposed in this invention is shown; where (a) is the RCS simulation curve, and (bf) are the 3D radar wave scattering signals of perfect electrical conductor (PEC), S0, S1, S2 and S3, respectively.

[0042] Figure 12 The CoZn / C@Ti3C2T proposed in this invention x Schematic diagram of the electromagnetic wave absorption mechanism of TiO2 composite material;

[0043] Figure 13 SEM images of composite materials prepared by electrostatic self-assembly at different sizes proposed in this invention; where (a) is 1 μm and (b) is 200 nm.

[0044] Figure 14 The diagram shows the electromagnetic parameters proposed in this invention; where (a) is the real part of the dielectric constant, (b) is the imaginary part of the dielectric constant, (c) is the real part of the permeability, (d) is the imaginary part of the permeability, (e) is the dielectric loss tangent, and (f) is the magnetic loss tangent.

[0045] Figure 15 The diagram shows the electromagnetic wave absorption performance proposed in this invention; where (a) is the C0-f curve, (b) is the attenuation constant curve, (c) is the impedance matching curve, and (d) is the Cole-Cole curve.

[0046] Figure 16 The diagram shows the reflection loss proposed in this invention; where (a) is the RL value, (b) is a 2D contour map, and (c) is a 3D RL value color map. Detailed Implementation

[0047] The present invention will be further explained below with reference to specific embodiments.

[0048] Example 1

[0049] Reference Figure 1 The hollow-cage CoZn / C@Ti3C2T proposed in this invention x The preparation steps of the / TiO2 composite material are as follows:

[0050] Ti3AlC2 nanosheets were prepared using an in-situ acid etching method, with improvements made to the exfoliation process. 1.6 g of LiF was dissolved in 20 mL of 12 M hydrochloric acid and stirred for 10 min to ensure complete dissolution. Subsequently, 1.0 g of Ti3AlC2 powder was added to the solution in small, repeated additions, and the mixture was stirred continuously at 50 °C for 24 h to etch the Al layer. After etching, the nanosheets were washed 2-3 times with 1 M hydrochloric acid solution, followed by washing with deionized water until neutral. Under N2 protection, the black, mud-like solid was dispersed sequentially in ice water and 95% ethanol for ultrasonic exfoliation for 1 h. Finally, the resulting suspension was centrifuged to obtain few-layer Ti3C2T nanosheets. x Nanosheets.

[0051] Weigh 1.7851 g of Zn(NO3)2·6H2O (6 mmol) and add it to 60 mL of methanol. Stir for 20 min until completely dissolved. Simultaneously, weigh 1.9705 g (24 mmol) of 2-methylimidazole and add it to 10 mL of methanol. Stir for 20 min until completely dissolved, then pour the dissolved Zn(NO3)2·6H2O methanol solution into the solution and continue stirring for 30 min. After stopping stirring, let it stand at room temperature for 24 h. Centrifuge the reaction mixture, wash the solid twice with methanol, and dry it under vacuum at 60 °C to obtain ZIF-8. Add 0.5 g of ZIF-8 to 150 mL of methanol and sonicate for 20 min for later use. Then, dissolve 5.82 g (20 mmol) of Co(NO3)2·6H2O and 6.16 g (75 mmol) of 2-methylimidazole in 100 mL of methanol to obtain solutions A and B, respectively. Solution A was first added to the methanol dispersion of ZIF-8, and the mixture was stirred for 10 min before adding solution B. The reaction mixture was stirred at room temperature for 24 h. The purple precipitate was separated by centrifugation, washed twice with methanol, and dried under vacuum at 60 °C for 12 h to obtain the precursor CoZn-MOF.

[0052] Ti3C2T is achieved through the synergistic effect of solvent evaporation induction and chemical crosslinking. x CoZn-MOF encapsulation was followed by the preparation of CoZn / C@Ti3C2T via pyrolysis. x / TiO2 nanocomposite material. The specific preparation steps are as follows: CoZn-MOF (400 mg) is dispersed in a mixed solution of 150 mL of ethanol and water (V 乙醇 V 水 =2:1), add 10 mL of Ti3C2T x The dispersion (50 mg) was stirred at room temperature for 30 min, and then the pH was adjusted to 8-9 with NaOH (1 M). Epichlorohydrin (ECH) (0.30 mL) was added dropwise. This is because ECH reacts with CoZn-MOF and Ti3C2T... x Surface hydroxyl reactions to achieve CoZn-MOF and Ti3C2T x Micro-crosslinking of Ti3C2T was observed. After stirring the reaction mixture at 50°C for 1 h, 50 mL of acetone was added. Finally, the solvent was slowly evaporated in a rotary evaporator at a water bath temperature of 45°C. Acetone, as a poor solvent and a fast evaporator, reduces the dielectric constant of the system, compresses the electric double layer, and enhances the attraction between particles. The capillary force generated by the evaporation of acetone and ethanol further contributes to the micro-crosslinking of Ti3C2T. x The product was coated on a CoZn-MOF surface. After centrifugation, washing, and vacuum drying, a few-layer Ti3C2T was obtained. xNanosheet-coated CoZn-MOF (CoZn-MOF@Ti3C2T) x Finally, CoZn-MOF@Ti3C2T x The mixture was heated to 650 °C at a heating rate of 5 °C / min in a N2 atmosphere and annealed at this temperature for 2 h to obtain a heterobimetallic CoZn / C derived CoZn / C@Ti3C2T. x / TiO2 nanocomposite material, denoted as S1.

[0053] Example 2

[0054] The Ti3C2T in this embodiment x The addition amount was 75 mg, the epichlorohydrin addition amount was 0.45 mL, and all other conditions were the same as in Example 1. The prepared CoZn / C@Ti3C2T x / TiO2 nanocomposite material, denoted as S2.

[0055] Example 3

[0056] The Ti3C2T in this embodiment x The addition amount was 100 mg, the epichlorohydrin addition amount was 0.6 mL, and all other conditions were the same as in Example 1. The prepared CoZn / C@Ti3C2T x / TiO2 nanocomposite material, denoted as S3.

[0057] Comparative Example 1

[0058] The precursor CoZn-MOF powder sample prepared in Example 1 was placed in a ceramic container and placed in a tube furnace. Under a N2 atmosphere, it was heated to 650°C at a heating rate of 5°C / min and calcined at 650°C for h. After cooling to room temperature, the CoZn / C composite material was obtained, denoted as S0.

[0059] Comparative Example 2

[0060] The composite material was prepared using an electrostatic self-assembly method, and the specific steps are as follows:

[0061] First, the CoZn-MOF (400 mg) prepared in Example 1 was dispersed in 100 mL of a 40% aqueous solution of polydiallyl dimethylammonium chloride. After stirring for 40 min, the mixture was centrifuged and washed to obtain PDDA-treated CoZn-MOF. Then, it was dispersed in 200 mL of pure water, and 10 mL of the few-layer Ti3C2T prepared in Example 1 was added. x The nanosheet dispersion (75 mg) was added to the above solution, and the mixture was stirred at room temperature for 24 h. The product was then centrifuged, washed, and vacuum dried to obtain a few-layer Ti3C2T. xNanosheet composite CoZn-MOF (CoZn-MOF / Ti3C2T) x Finally, CoZn-MOF / Ti3C2T x The temperature was increased to 650°C in a N2 atmosphere at a heating rate of 5°C / min, and then annealed at this temperature for 2 h to obtain a heterobimetallic CoZn / C-derived composite material, denoted as ESA.

[0062] Figure 2 For the structural characterization of S0-S3, from Figure 2 As can be seen from part (a), before etching, the diffraction peaks of Ti3AlC2 are concentrated at 9.6° (002), 36.8° (103), 39.0° (104), 41.8° (105), and 60.1° (110), corresponding one-to-one with JCPDS#52-0875. The few-layer Ti3C2T obtained after acid etching and ultrasonic ablation... x The diffraction peaks of the Ti3C2 showed significant changes compared to the raw material Ti3AlC2. Specifically, the diffraction peak between 20-80° disappeared, and the diffraction peak at 9.60° shifted to a smaller angle at 6.80° with a wider peak shape. This indicates that the aluminum atomic layer in Ti3AlC2 was successfully etched, resulting in the formation of Ti3C2T. X The increased interlayer spacing indicates that the two-dimensional layered Ti3C2T x It was successfully prepared.

[0063] Furthermore, strong peaks appear at 44.2°, 51.4°, and 75.7° in the XRD patterns of S0, S1, S2, and S3. Analysis and comparison with the JCPDS#04-2681 card show that these peaks correspond one-to-one with the characteristic peaks of the (111), (200), and (220) crystal planes of Co. Additionally, the diffraction peaks at 36.5°, 42.4°, 61.5°, 73.7°, and 77.6° correspond to the (111), (200), (220), (311), and (222) crystal plane diffraction peaks of CoO (JCPDS#04-8626), respectively. Since Ti3C2T x The Ti source readily transforms into the TiO2 phase at high temperatures, resulting in five distinct diffraction peaks (27.4°, 36.1°, 41.2°, and 54.3°) in the XRD patterns of S1, S2, and S3, corresponding to the (110), (101), (200), (111), (210), and (211) crystal planes of rutile TiO2 (JCPDS#71-0650). Furthermore, due to the amorphous state or low-crystallinity compounds resulting from high-temperature pyrolysis, the Zn element did not meet the crystal order requirements for XRD detection, and therefore no related diffraction peaks were observed in the XRD patterns.

[0064] Depend on Figure 2 As can be seen from part (b), Ti3AlC2 and Ti3C2T x At 3442cm -1 1654cm -1 1620cm -1 1340cm -1 and 1068cm -1 The absorption peaks at these locations correspond to the stretching vibrations of -OH, C=O, C=C, CF, and COC, respectively. Compared to Ti3AlC2, Ti3C2T x The stretching vibration peaks of -OH, C=O, and CO are significantly broadened and strengthened, which may be due to the exposure of more oxygen-containing functional groups on the material surface after etching and exfoliation of Ti3AlC2. x The abundant oxygen-containing functional groups on the surface are highly hydrophilic, serving as both anchoring sites for metals and reaction sites for cross-linking reactions, thus facilitating the immobilization of CoZn-MOF on Ti3C2T. x Surface. From the IR spectra of S1~S3, it can be observed that the -OH vibration peak narrows while the COC vibration peak becomes stronger. This may be due to the change in Ti3C2T. x With increased content, more -OH groups participate in the cross-linking reaction to transform into COC. In the IR spectra of S0~S3, 544 cm⁻¹... -1 The absorption peaks at these locations correspond to the absorption vibration peaks of CM (metal), indicating that CoZn-MOF has been successfully immobilized with Ti3C2T. x Surface. Furthermore, with Ti3C2T x The increased content is evident in the infrared spectra of S2 and S3 at 610 cm⁻¹. -1 The presence of a Ti-O stretching vibration peak at this location indicates that during self-assembly and pyrolysis, some Ti3C2T... x Oxidation occurred, which is consistent with the XRD results.

[0065] The defects and graphite structure of the composite materials S0-S3 were analyzed using Raman spectroscopy, such as... Figure 2 As shown in section (c). D band (1340cm) -1 ) represents internal structural defects or disordered parts of the material, G-band (1580cm) -1 This is related to the ordered carbon graphitization characteristics in the material. Therefore, the ratio of the D band to the G band (I) is used. D / I G This is used to determine the degree of lattice disorder / defects in a material. With the development of Ti3C2T... x With the increase of content, the I content of composite material S0-S3 increases. D / I G The value increased from 0.879 to 1.011.D / I G The increase in value is mainly attributed to Ti3C2T x Increase. With Ti3C2T x Increase, the metal in the composite material and Ti3C2T x The enhanced interactions between these elements ultimately lead to the formation of local defects and lattice distortions, thus hindering the graphitization process of carbon atoms. On the other hand, the presence of defects in the composite material will facilitate its absorption of electromagnetic waves.

[0066] Depend on Figure 2 As shown in section (d), the magnetic properties of composite materials S0-S3 were characterized using VSM at room temperature, and S-shaped hysteresis loops typical of four soft magnetic materials were observed. The saturation magnetization (Ms) of S0~S3 are 97.25, 75.37, 60.41, and 47.52 emu·g, respectively. -1 The coercivity (Hc) values ​​were 81.4, 147.6, 162.7, and 178.8 Oe, respectively. With the development of Ti3C2T... x With increasing addition, the Ms of the composite material S0-S3 shows a decreasing trend while Hc shows an increasing trend. This phenomenon may be due to the following factors: firstly, the CoZn / C size decreases; secondly, the non-magnetic component Ti3C2T... x The incorporation of TiO2, and the combination of CoZn / C and Ti3C2T x Enhanced interfacial interactions, along with these factors, ultimately lead to a decrease in the total magnetic moment of the material and an increase in the resistance to magnetic moment reversal.

[0067] To further determine CoZn / C@Ti3C2T x The elemental valence states and chemical composition of TiO2 were analyzed using XPS for the composite material S2, and the results are as follows: Figure 3 As shown. XPS full spectrum ( Figure 3 Part (a) indicates the presence of C, N, O, Ti, Co, and Zn elements in S2. The narrow spectrum of Ti2p ( Figure 3 Part (b) can be divided into two parts, with binding energies of 464.3 eV (2p). 1 / 2 ) and 458.5eV (2p 3 / 2 455.4 eV and 461.2 eV correspond to Ti 2+ 456.6 eV and 462.4 eV correspond to Ti 3+ 458.8 eV and 464.9 eV correspond to Ti-O; 458.4 eV and 464.0 eV correspond to Ti-C. Figure 3Part (c) is the narrow spectrum of N1s, where 398.0 eV, 398.6 eV, 400.3 eV, and 401.1 eV are attributed to pyridine nitrogen, Co-N, pyrrole nitrogen, and graphitic nitrogen, respectively. For example... Figure 3 As shown in section (d), the narrow spectrum of C1s can be fitted with five peaks with binding energies of 281.0 eV, 284.0 eV, 285.2 eV, 286.7 eV and 288.2 eV, respectively, which correspond to C-Ti, CC (C=C), CO, CN and C=O. Figure 3 Part (e) is the fitted spectrum of O1s, with the values ​​at 529.9 eV, 530.5 eV, 531.8 eV, 532.5 eV, and 533.5 eV belonging to Ti-O / Co-O, C=O, Ti-OH, COC, and COH, respectively. Figure 3 Part (f) is a narrow spectrum of Co 2p, obtained by fitting six different peaks with binding energies of 792.9 eV (Co 2p). 0 2p 1 / 2 ), 795.8 eV (Co 2+ 2p 1 / 2 ), 797.8 eV (Co 3+ 2p 1 / 2 ), 778.1eV (Co 0 2p 3 / 2 ), 780.4 eV (Co 2+ 2p 3 / 2 ) and 781.8 eV (Co 3+ 2p 3 / 2 Additionally, the satellite peaks at 786.6 eV and 802.1 eV correspond to Co 2p, respectively. 3 / 2 and Co 2p 1 / 2 .

[0068] The microstructure of the composite material S0-S3 was investigated using scanning electron microscopy (SEM). S0 was obtained by pyrolysis of the precursor CoZn-MOF in a nitrogen atmosphere at 650℃. Figure 4 As shown in parts (a) and (b), although S0 retains the rhombic dodecahedral structure of the precursor CoZn-MOF with a size of approximately 7–9 μm, each surface exhibits bowling ball-shaped depressions. This is likely due to the decomposition and gas release of the organic ligand (2-methylimidazole) in the MOF during pyrolysis, which creates cavities within the material, resulting in surface depressions. On the other hand, the decomposition of 2-methylimidazole leads to the deposition of a carbon layer on the surface of the CoZn / C nanoparticles, increasing the surface roughness of S0. Figure 4 As can be seen from the (ch) part, Ti3C2T xNanosheets are coated on the CoZn / C surface, and Ti3C2T x The surface exhibits a wrinkled appearance. Ti3C2T x After crosslinking with CoZn-MOF, the capillary force generated during the subsequent solvent evaporation induction phase will cause Ti3C2T to crosslink. x The material bends, thus encapsulating the CoZn-MOF and forming a cage-like structure on the outer layer of the material. This wrinkled cage-like structure can be achieved in CoZn / C and Ti3C2T. x The gaps between these gaps allow electromagnetic waves to be reflected and refracted multiple times within the material, thus dissipating energy. Furthermore, while S1-S3 retain the rhombic dodecahedral structure, their size shrinks to 1-4 μm. This result may have two reasons: firstly, Ti3C2T... x Encapsulating CoZn-MOF restricts the contact and fusion of adjacent CoZn-MOF particles during subsequent pyrolysis, preventing the formation of large aggregates; on the other hand, Ti3C2T x The high specific surface area and mechanical support of MOF stabilize the intermediate products during pyrolysis, thereby preventing grain growth. Figure 4 Parts (i) and (j) are local secondary electron images and elemental superposition distribution maps of S2. The wrinkled Ti3C2T structure can be seen more clearly from the figures. x Nanosheets encapsulate CoZn / C to form a cage-like structure. From Figure 4 The (kp) part clearly shows that S2 contains Ti, Co, Zn, N, C, and O elements, and their distribution is relatively uniform. This also verifies the CoZn / C@Ti3C2T x Successful preparation of / TiO2 composite materials.

[0069] Figure 5 These are the TEM and HRTEM images for S2. From Figure 5 As can be seen from the (ac) part, Ti3C2T x The CoZn / C nanoparticles are encapsulated within the Ti3C2T matrix. Through pyrolysis at 650°C, the initial rhombic dodecahedrons of the CoZn-MOF are transformed into cavities with hollow interiors and perforated edges (indicated by blue ellipses), with a cavity size of approximately 1.4 μm. Furthermore, the figure also shows a large number of reduced cobalt nanoparticles embedded within the Ti3C2T matrix. x In the middle, irregularly curled Ti3C2T can be seen at the edge of the composite material. x (Indicated by the blue arrow). Figure 5The lattice spacing in the (df) portion is 0.213 nm, 0.205 nm, and 0.325 nm, corresponding to the (200) crystal plane of CoO, the (111) crystal plane of Co, and the (110) crystal plane of TiO2 in the composite nanoparticles, respectively, which is consistent with the XRD analysis results. Due to the decomposition of organic ligands in the MOF structure, the pyrolysis-derived CoZn / C nanoparticles are more uniformly dispersed in graphitic carbon, so the surface of the CoZn / C particles is wrapped with a layer of amorphous graphitic carbon, marked by the yellow dashed line, forming a core-shell structure. The carbon layer on the surface of the magnetic CoZn / C, and the outermost Ti3C2T x The interconnected nanosheets and TiO2 nanoparticles form a cross-linked network, which significantly promotes the surface transport speed of electrons between the two-dimensional layers and improves the stability of the material. In addition, the heterogeneous interfaces and potential defects formed between the above components also provide favorable structural conditions for dielectric losses involved in the electromagnetic wave dissipation mechanism, thereby improving the material's ability to absorb electromagnetic waves.

[0070] The electromagnetic parameters of the composite materials S0-S3 were tested using the coaxial method. According to Maxwell's equations, the absorption performance of electromagnetic waves by EMAs is mainly affected by the relative complex permittivity (ε). r =ε′-jε′′) and relative complex permeability (μ r The influence of electromagnetic parameters such as ε′ - jμ′′ is considered, where the real part of the permittivity (ε′) and the real part of the permeability (μ′) represent the material's ability to store electrical and magnetic energy, while the imaginary part of the permittivity (ε") and the imaginary part of the permeability (μ") represent the corresponding electrical and magnetic losses. Figure 6 As can be seen from parts (a) and (b), ε′ and ε′′ show a significant decreasing trend with increasing frequency (f). Specifically, the ε′ values ​​of S0~S3 decrease from 4.79, 6.78, 7.82, and 9.59 GHz to 3.38, 4.38, 4.70, and 5.98, respectively; the ε″ values ​​of S0~S3 decrease from 0.85, 1.94, 2.98, and 3.54 GHz to 0.73, 1.27, 1.38, and 1.98 GHz, respectively. This is due to the dispersion phenomenon caused by the dipole's inability to respond promptly to frequency changes and its reorientation when the applied electromagnetic field frequency increases. Furthermore, in Figure 6 In part (b), S0-S3 all exhibit significant relaxation peaks in the high-frequency region. This may be because the polarization process inside the material lags behind the change in the applied magnetic field, resulting in the loss of polarization energy as heat at specific frequencies. On the other hand, in the frequency range of 2-18 GHz, the ε' and ε" values ​​of S0-S3 all increase with the change in Ti3C2T x The content increases with increasing Ti3C2T content. xThe addition of [a specific substance] not only enhances the electrical conductivity of the composite material but also introduces numerous heterogeneous interfaces, thereby increasing dielectric loss against electromagnetic waves. The variations of µ' and µ'' of S0-S3 with frequency are shown below. Figure 6 Parts (c) and (d) show the results. Compared to S3, the µ' and µ'' values ​​of S0-S2 exhibit significant fluctuations in the frequency range of 3.11~10.98 GHz, which may be due to the higher proportion of magnetic components in S0-S2. Furthermore, the µ'~ƒ images of S0, S1, and S2 all show a significant decrease, which may be caused by the scattering of local electromagnetic waves due to the hollow or porous structure of the material. Figure 6 In part (d), µ'' of S0-S3 fluctuates greatly with ƒ and multiple resonance peaks appear, indicating that its magnetic loss is composed of natural resonance and exchange resonance.

[0071] To more intuitively compare the dielectric loss capabilities of each sample, the dielectric loss tangent (tanδ) was calculated using electromagnetic parameters. e =ε" / ε') and magnetic loss tangent (tanδ) μ =μ′′ / μ′), and plot their relationship with f ( Figure 6 (e) and (f) parts). tanδ of S0-S3 e ~ƒ curve and tanδ μ The ~ƒ curves show trends roughly similar to those of the ε"~ƒ and μ′′~ƒ curves, respectively. Furthermore, comparative analysis reveals that the tanδ values ​​of S0 and S1... ε Value lower than tanδ µ , while the tanδ of S2 and S3 ε The values ​​are generally higher than tanδ µ This indicates that magnetic loss is the main mechanism for electromagnetic wave absorption in S0 and S1, while dielectric loss is the main mechanism in S2 and S3.

[0072] The Debye relaxation polarization theory is typically used to analyze the impact of conductivity and dielectric loss on microwave absorption performance. When the ε′~ε″ curve exhibits a semi-circular relationship, dielectric loss is the dominant loss mechanism; when the ε′~ε″ curve exhibits a linear relationship, conductivity loss is the dominant loss mechanism. (The Cole-Cole plot of S0 is also mentioned.) Figure 7 Part (a) consists of multiple semicircles, each corresponding to a Debye relaxation process. The Cole-Cole diagram of S1-S3 ( Figure 7 The (bd) portion consists of multiple semicircles and a straight line, indicating the simultaneous presence of dielectric loss and conductive loss. Dielectric loss is the result of multiple polarization relaxations, including dipole polarization and interfacial polarization. Dipole polarization originates from Ti3C2T xThe surface of TiO2 is rich in oxygen-containing functional groups, and the interfacial polarization mainly originates from the interaction between CoZn / C and Ti3C2T. x / TiO2 defects and numerous multi-component heterogeneous interfaces. It is worth noting that with the development of Ti3C2T x As the proportion increases, the conductivity of the composite material is enhanced, and the straight line range at the end of the Cole-Cole curve shows an expanding trend, indicating that conductivity loss plays a decisive role.

[0073] Magnetic loss is generally caused by hysteresis loss, eddy current loss, and magnetic resonance (natural resonance and exchange resonance). In the 2–18 GHz range, the main causes of magnetic loss are eddy current loss and magnetic resonance loss. Typically, natural resonance is significant in the low-frequency range, while exchange resonance exists in the high-frequency range. Eddy current loss refers to the phenomenon where eddy currents are generated in a conductor due to electromagnetic induction in an alternating magnetic field, leading to heat loss of electromagnetic energy.

[0074] If the magnetic loss is caused by eddy current loss, then the eddy current coefficient C0 does not change with frequency. The C0~ƒ curve from S0 to S3 ( Figure 8 As can be seen from part (a), the C0 value of S3 remains basically unchanged in the range of 7~18 GHz, indicating that the main mechanism of magnetic loss in S3 is eddy current loss. The C0 values ​​of S0~S2 show obvious fluctuations at both low and high frequencies, remaining unchanged only in the frequency range of 13~18 GHz. This indicates that the magnetic loss in S0~S2 is the result of the combined effect of magnetic resonance and eddy current loss.

[0075] Promising impedance matching (EMAs) typically require a balance between impedance matching (Z) and attenuation constant (α). EMAs exhibit excellent impedance matching characteristics when the Z value is close to 1. (The last sentence appears to be incomplete and possibly refers to a specific type of Ti3C2T.) x The Z values ​​of S0, S1, S2, and S3 under the added amount are as follows: Figure 8 As shown in section (c), the Z values ​​of S0 and S1 are 1.59 and 2.42, respectively, indicating poor impedance matching, which is attributed to a single dielectric loss mechanism. With Ti3C2T x With the increase of the amount added, the electrical conductivity of the composite material increases, and the impedance matching of S2 and S3 is improved, with the Z value of S2 being closer to 1 than that of S3.

[0076] The attenuation constant (α) reflects a material's ability to convert EMA into other forms of energy. For example... Figure 8 As shown in section (b), the α values ​​of all samples exhibit a continuous upward trend. The α value of S2 is higher than that of S0 and S1 in the range of 2–11 GHz, indicating that Ti3C2T xThe combination with CoZn / C nanoparticles can significantly enhance the attenuation capability of the composite material. Compared with S3, S2 has better impedance matching, and therefore exhibits a better α value.

[0077] Reflection loss (RL) can directly reflect a material's ability to absorb electromagnetic waves. Figure 9 The diagram displays the RL, 2D contour plots, and 3D color maps of S0-S3 with variable absorption thickness (different colored curves represent different thicknesses) within the 2~18GHz frequency band. Figure 9 As can be seen from the (ac) part, due to the poor impedance matching caused by high magnetism, S0 at 10.48 GHz RL min =-22.83dB (d=3.0mm), EAB is 2.8GHz (9.28-11.84GHz). When CoZn / C and Ti3C2T x After recombination with TiO2, the absorption capabilities of S1, S2, and S3 for electromagnetic waves are all improved due to the coupling effect of dielectric and magnetic losses. Among them, S1 shows improved absorption at f=12.43GHz. min =-41.81dB (d=3.1mm), EAB=3.11GHz (10.57~13.68GHz) ( Figure 9 (df ​​portion). S2 in the case of d=3.0mm, f=12.02GHz, RL min Reaching -72.51dB, its EAB is 5.53GHz (8.92~14.45GHz) ( Figure 9 (gi part). S3 at f=5.12GHz, RL min -38.61dB (d=3.1mm) Figure 9 (jl part). When d is 2.5mm, EAB is 3.55GHz (11.4GHz~14.96GHz). It is worth noting that S2 has RL at f=6.08GHz and f=10.48GHz. min The values ​​are -54.43dB (d=5.0mm) and -46.53dB (d=3.4mm), respectively, with EAB values ​​of 2.71GHz and 5.06GHz. This indicates that S2 possesses both high electromagnetic wave absorption performance and a wide EAB, with an absorption range covering the entire C-band, X-band, and 57% of the Ku-band, fully meeting the requirements of practical applications.

[0078] As the thickness (different colored curves represent different thicknesses) increases, the absorption peaks of the sample shift towards lower frequencies. Figure 10 The results show that the theoretically calculated thickness of S2 (purple) matches the actual matching thickness (orange pentagram) very well, confirming the consistency of the quarter-wavelength matching model.

[0079] To evaluate the absorption characteristics of the sample to EMA under real-world conditions, radar cross section (RCS) distribution data were obtained by modeling S0–S3 using CSTMicrowaveStudio. The simulation model consists of two layers: the sample film and a perfect electrical conductor (PEC). Figure 11 Part (a) shows the two-dimensional RCS spectra of PEC, S0, S1, S2, and S3 from -90° to 90°. Figure 11 As can be seen from part (a), with Ti3C2T x With increasing content, the RCS value first decreases and then increases, with the RCS value of S2 reaching a minimum of -43.15 dB·m at 25°. 2 It is lower than -42.42 dB·m of S1. 2 (19°), S3 -39.54dB·m 2 (28°) and S0 -37.41 dB·m 2 (42°). Furthermore, the RCS values ​​of S0 to S3 at 0° are 1.26, -18.37, -22.12, and -15.05 dB·m, respectively. 2 Compared to the RCS value of PEC (13.72 dB·m), 2 These values ​​reduced by 12.46, 32.09, 35.84, and 28.77 dB·m, respectively. 2 The simulation results of the RCS above are consistent with the analysis results of RL for S0~S3. Furthermore, from the three-dimensional plot of the RCS (part (bf) of 11), it can be seen that PEC ( Figure 11 In part (b), there are obvious "strong scattering directions" (red / yellow areas) and the scattering distribution has a strong "three-dimensional effect," indicating that PEC strongly reflects radar waves and is easily detected by radar from multiple angles. From the three-dimensional RCS spectra of S0~S3, it can be clearly seen that the scattering "cloud" is significantly more "converged," and the high scattering area is greatly reduced, demonstrating the radar stealth advantage of the absorbing material. Furthermore, the overall scattering intensity decreases (the blue area accounts for a large proportion), indicating that S0~S3 significantly reduces reflected energy by absorbing radar waves. The above analysis results further confirm the effectiveness of CoZn / C@Ti3C2T. x / TiO2 composite materials exhibit excellent electromagnetic wave attenuation capabilities and application potential.

[0080] CoZn / C@Ti3C2T x / TiO2 electromagnetic wave attenuation mechanism as follows Figure 12 As shown. Overall, CoZn / C@Ti3C2T xThe high microwave absorption performance of the CoZn / C@TiO2 composite material mainly stems from the synergistic effect of its dielectric and magnetic losses, as well as the optimization of impedance matching. Firstly, the partial volatilization of zinc in the CoZn-MOF structure at 650℃ leads to its amorphous state. The resulting defects and vacancies increase the number of dipoles, thereby enhancing dipole polarization relaxation. Simultaneously, numerous heterojunctions and polarization centers significantly enhance the interfacial polarization effect through the accumulation of free electrons at these interfaces. The porosity and hollow structure in CoZn / C enhance the multiple reflection and scattering of electromagnetic waves, thus significantly improving energy dissipation efficiency. Secondly, the CoZn / C@Ti3C2T... x The abundant heterogeneous interfaces in the / TiO2 composite material effectively enhance interfacial polarization. Furthermore, the magnetic CoZn / C nanoparticles endow the composite material with strong magnetic loss capacity, primarily due to eddy current loss, natural resonance, and exchange resonance. Overall, CoZn / C@Ti3C2T x The high-performance microwave absorption properties of the / TiO2 composite material are due to the synergistic effect of good impedance matching, significant magnetic loss, and electrical loss.

[0081] SEM images of composite material ESA are shown below. Figure 13 As shown. By Figure 13 Part (a) shows that CoZn / C particles in ESA adhere to Ti3C2T x On the surface, a large number of CoZn / C@Ti3C2T particles were formed. x Heterogeneous structure. Meanwhile, Ti3C2T x The layered structure exhibits significant stacking. This tight stacking significantly reduces the contact area between the layers, thus hindering electron transport between them. Furthermore, the surface-loaded CoZn / C particles may further obstruct electron transport paths. Figure 13 In part (b), the visible CoZn / C edges become blurred, and the size shrinks to approximately 200 nm. This is attributed to the CoZn-MOF in the ESA within Ti3C2T. x The surface is highly dispersed, lacking the coating and protection of a template, thus directly melting and collapsing during pyrolysis to form smaller particles. These smaller particles are more easily sintered into dense, rounded, and even smaller spheres, or adhere to Ti3C2T due to collapse. x The surface layer causes the CoZn / C profile to be unclear and the size to appear smaller.

[0082] To compare the absorption performance differences between ESA and S2, the electromagnetic parameters of ESA were tested using the coaxial method. Figure 14 As shown in part (a), within the frequency range of 2–18 GHz, the ε′ value of S2 is significantly higher than that of ESA, and shows a gradual decreasing trend with increasing f. The capillary force induced by solvent evaporation will affect Ti3C2T.x The material is "kneaded" into a coiled shape, thus encapsulating CoZn / C. This "hollow-cage" structure significantly increases the specific surface area and the number of heterogeneous interfaces. Simultaneously, the chemical cross-linking of ECH forms rigid connections at the interfaces, effectively restricting the free movement of charges and inducing stronger space charge polarization (interfacial polarization). In contrast, ESA mainly relies on Ti3C2T. x Electrostatic adsorption with the CoZn / C surface. Although this bonding method is uniformly distributed, the interfacial contact is mainly based on physical adsorption, resulting in relatively weak interfacial bonding forces. Therefore, Ti3C2T x The layers are mostly planar stacks or simple coatings, making it difficult to form complex three-dimensional conductive networks, which is the reason for the low ε′.

[0083] exist Figure 14 In part (b), the ε″ value of S2 is higher than that of ESA in the low-to-mid frequency range (2-10 GHz), but lower in the high-frequency range (10-12 GHz). This may be due to the presence of numerous defects and dipoles in S2, providing sufficient time for field reversal in the low-frequency range, resulting in strong dipole polarization relaxation loss. However, in the high-frequency range, the tortuous electron transport path caused by the binding and curling of the cross-linked network leads to a decrease in the contribution of conductivity loss. The continuous Ti3C2T in ESA... x Although the conductive network is not as rich in interfaces as S2, its Ti3C2T x The lattice structure integrity of ESA may be superior to that of S2. Therefore, when the electromagnetic field changes extremely rapidly, ESA can provide a smoother electron transport path and exhibits higher ε″ at high frequencies.

[0084] In addition, by Figure 14 As shown in section (c), the μ′~f curves of S2 and ESA exhibit roughly the same trend within the 2–18 GHz frequency range. During the coiling process, CoZn / C in Ti3C2T x A certain degree of aggregation occurred within the cage, resulting in a localized magnetic field enhancement effect, triggering natural or exchange resonance. Therefore, S2 exhibits a higher μ′ value than ESA. Figure 14 In part (d), multiple resonance peaks appear in the μ″~ƒ spectrum of ESA, indicating that its magnetic loss is composed of both natural and exchange resonances. However, the amplitudes of these resonance peaks are less than those in S2, which may be because the magnetic loss of ESA mainly originates from CoZn / C and lacks Ti3C2T. x Magnetoelectric coupling with CoZn / C. tanδ of S2 and ESA. ε ~ƒ curve (14e) and tanδ μ The ~ƒ curve (14f) shows a similar trend to the ε″~ƒ and μ″~ƒ curves, respectively. The tanδ values ​​of S2 and ESA... εAll are higher than tanδ μ This indicates that the loss of electromagnetic waves by both is mainly due to dielectric loss.

[0085] from Figure 15 As can be seen from the C0~ƒ curves of the ESA in part (a), the C0 value of the ESA, like that of S2, exhibits vibrational characteristics in both the low-frequency and mid-to-high-frequency regions, while remaining basically stable in the 11~18GHz frequency range. This indicates that the magnetic loss of the ESA is the result of the combined effects of magnetic resonance and eddy current loss. From... Figure 15 As can be seen from part (b), the trends of α with frequency variation for ESA and S2 are basically the same. The α value of S2 rises rapidly in the 2–8 GHz range, then reaches a peak in the 8–11 GHz range. Compared to the "multi-peak" fluctuations of S2, the curve of ESA is relatively smooth, and its peak corresponds to a narrower bandwidth, making it difficult to form an effective broadband absorption band. From... Figure 15 As can be seen from part (c), |Z of S2 in The / Z0|~f curve is closer to the dashed line than the ESA curve (|Z in / Z0|=1), especially in the 10.67~13.12GHz range, where it is almost a perfect match. In contrast, ESA's |Z in The / Z0|~f curve is far from the dashed line, and in most frequency bands |Z in A / Z0| value greater than 1 or less than 1 causes the EMA to be reflected back into free space. This result may be due to the Ti3C2T in the ESA. x The interaction with CoZn-MOF mainly relies on electrostatic adsorption, and this binding force is relatively weak. Therefore, Ti3C2T x The nanosheets stack in the ESA, leading to weakened interfacial polarization and difficulty in forming a complex three-dimensional conductive network, ultimately resulting in reduced conductivity. Furthermore, Ti3C2T x The magnetoelectric coupling between CoZn and CoZn-MOF is not significant; the magnetic loss in the ESA mainly originates from the CoZn-MOF. The cage structure of S2 causes the incident electromagnetic wave to undergo multiple reflections and refractions within the gap, thus lengthening the propagation path and allowing for sufficient energy dissipation. Chemical crosslinking optimizes the interfacial polarization response, achieving a balance between dielectric and magnetic losses while maintaining loss capacity. The CoZn / C magnetic phase and Ti3C2T... x The conductive phase forms spatial recombination within the coiled structure, enhancing the synergistic effect of magnetic and dielectric losses. Similar to S2, Figure 15 In part (d), the Cole-Cole diagram of ESA also consists of multiple semicircles and a straight line, indicating that both dielectric loss and conductive loss mechanisms exist simultaneously.

[0086] Depend on Figure 16It can be seen that ESA has RL at f=6.16GHz min The absorption band is -60.6 dB (d=5.5 mm), and the EAB is 2.66 GHz. At other thicknesses (different colored curves represent different thicknesses), its maximum absorption intensity is generally below -50 dB. In contrast, S2 not only exhibits stronger absorption intensity at specific thicknesses but also achieves a wider effective absorption bandwidth across multiple thickness ranges. Figure 9 (gi) part). Specifically, when d=3.0mm, the RL of S2 min Reaching -72.51dB (f=12.02GHz), EAB=5.53GHz; when d=5.0mm, RL min The voltage is -54.43 dB (f = 6.08 GHz), and the energy level EAB is 2.71 GHz; when d = 3.4 mm, the RL... min It also achieved -46.53 dB (f=10.48 GHz) and EAB=5.06 GHz. Furthermore, S2 exhibits excellent absorption capacity and a wide effective absorption bandwidth at thinner thicknesses (e.g., d=3.0 mm), while ESA requires a larger thickness (d=5.5 mm) to achieve good absorption performance, and its performance is relatively poor at thinner thicknesses. This result is attributed to the synergistic effect of its optimized impedance matching and multiple loss mechanisms. The above analysis results indicate that by precisely controlling the solvent evaporation-induced curling process and the degree of chemical crosslinking, the absorption peak frequency can be effectively tuned at different thicknesses. This flexibility makes it more suitable for frequency band customization requirements in practical applications. Moreover, this method can significantly reduce material thickness while maintaining high performance, which is crucial for lightweight and compact EMAs. In contrast, the ESA method relies on a larger thickness to compensate for performance losses caused by structural defects.

[0087] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application. The scope of this application is defined by the appended claims and their equivalents, all of which should be included within the protection scope of this application.

Claims

1. A hollow-cage CoZn / C@Ti3C2T x The method for preparing the / TiO2 composite material is characterized by, The steps are as follows: Step (1): Few-layer Ti3C2T x Preparation of nanosheets; Step (2): Preparation of the precursor CoZn-MOF; Step (3): Combine the precursor CoZn-MOF and few-layer Ti3C2T x Nanosheets were dispersed in a first solvent, and epichlorohydrin was added to initiate the reaction. Subsequently, a second solvent was added for rotary evaporation. The product was then annealed at high temperature to obtain hollow-cage CoZn / C@Ti3C2T. x / TiO2 composite material.

2. The hollow-cage CoZn / C@Ti3C2T according to claim 1 x The method for preparing the / TiO2 composite material is characterized by, Few-layer Ti3C2T x The preparation method of the nanosheets is as follows: LiF is dissolved in hydrochloric acid, then Ti3AlC2 powder is added, stirred and etched, and then washed and ultrasonically exfoliated to obtain few-layer Ti3C2T nanosheets. x Nanosheets.

3. The hollow-cage CoZn / C@Ti3C2T according to claim 2 x The method for preparing the / TiO2 composite material is characterized by, The mass ratio of LiF to Ti3AlC2 is 1-3:1; And / or, the temperature for stirring etching is 40-60℃, and the time is 12-36h.

4. The hollow-cage CoZn / C@Ti3C2T according to claim 1 x The method for preparing the / TiO2 composite material is characterized by, The preparation method of the precursor CoZn-MOF is as follows: Step (2.1): Dissolve the zinc source in methanol, add 2-methylimidazole and allow the reaction to stand at room temperature. After the reaction, the product is dried to obtain ZIF-8. Step (2.2): Disperse ZIF-8 in methanol, then add cobalt source and 2-methylimidazole in sequence and stir at room temperature to react. After the reaction, dry to obtain the precursor CoZn-MOF.

5. The hollow-cage CoZn / C@Ti3C2T according to claim 4 x The method for preparing the / TiO2 composite material is characterized by, In step (2.1), the zinc source is one or more of zinc nitrate and its hydrate, zinc chloride and its hydrate, and zinc acetate and its hydrate; And / or, in step (2.1), the molar ratio of zinc source to 2-methylimidazole is 1:2-5; And / or, the conditions for the static reaction in step (2.1) are a temperature of 20-30℃ and a time of 12-36h.

6. The hollow-cage CoZn / C@Ti3C2T according to claim 4 x The method for preparing the / TiO2 composite material is characterized by, In step (2.2), the cobalt source is one or more of cobalt nitrate and its hydrate, cobalt chloride and its hydrate, and cobalt acetate and its hydrate; And / or, the molar ratio of the cobalt source and 2-methylimidazole in step (2.2) to the zinc source in step (2.1) is 1-8:20-30:1; And / or, the stirring reaction conditions in step (2.2) are a temperature of 20-30℃ and a time of 12-36h.

7. The hollow-cage CoZn / C@Ti3C2T according to claim 1 x The method for preparing the / TiO2 composite material is characterized by, In step (3), the precursor CoZn-MOF and few-layer Ti3C2T x The mass-to-volume ratio of nanosheets to epichlorohydrin is 400-800 mg: 100-500 mg: 1 ml; And / or, the reaction temperature in step (3) is 40-60℃, and the time is 30-90 min; And / or, the first solvent is an aqueous solution of an alcohol; And / or, the second solvent is acetone.

8. The hollow-cage CoZn / C@Ti3C2T according to claim 1 x The method for preparing the / TiO2 composite material is characterized by, In step (3), the conditions for high-temperature annealing are a temperature of 600-700℃ and a time of 1-3h.

9. A hollow-cage CoZn / C@Ti3C2T x / TiO2 composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A hollow-cage CoZn / C@Ti3C2T as described in claim 9 x Application of TiO2 composite materials in electromagnetic wave absorption.

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