North Konami can provide MXene (can be customized)

The popularization of high-frequency communication such as 5G technology not only makes it convenient to manufacture, but also produces a large amount of electromagnetic radiation pollution, which not only endangers human life and health, but also seriously interferes with the normal operation of various electronic instruments. The wave absorbing material absorbs electromagnetic waves through electromagnetic energy-thermal energy conversion, which can effectively solve the above radiation problems. Transition metal carbides or carbonitrides (MXenes) have important potential applications in the field of electromagnetic functions. However, the high dielectric constant of MXene makes it difficult for electromagnetic waves to enter the material, resulting in poor wave-absorbing properties. In this work, a flexible MXene-rGO/CoNi composite absorbing film was prepared by using electrostatic interaction, and excellent absorbing performance was achieved through the modulation of the dielectric properties and magnetization of MXene.

Self-Assembly MXene-rGO/CoNi Film with Massive Continuous Heterointerfaces and Enhanced Magnetic Coupling for Superior Microwave Absorber

Xiao Li, Zhengchen Wu, Wenbin You, Liting Yang, Renchao Che*

Nano-Micro Letters (2022)14: 73

https://doi.org/10.1007/s40820-022-00811-x

Highlights of this article

1. The flexible composite film exhibits strong absorption and wide-spectrum absorbing properties, the lowest reflection loss value reaches −54.1 dB, and the effective absorption bandwidth is 5.1 GHz;

2. Two strategies of interface design and magnetization are proposed to control the permittivity and permeability of MXene respectively, which can effectively optimize its impedance matching properties;

3. The multi-interface polarization mechanism and the magnetic coupling interaction mechanism between CoNi nanoparticles were demonstrated by TEM electron holography, explaining the physical relationship between microstructure and macroscopic properties.

brief introduction

Absorbing materials can effectively shield electromagnetic wave detection and eliminate radiation pollution, and have important applications in electromagnetic protection and military stealth. In addition, the absorbing material also integrates the advantages of high sensitivity, long distance and high electromagnetic energy conversion efficiency, and has broad application prospects in the fields of motion detection, biomedicine, and energy conversion. Che Renchaos research group from Fudan University took advantage of the high conductivity and rich surface functional groups of MXene, through the interface design of rGO intercalation and CoNi alloy modification magnetization, to prepare a flexible MXene wave-absorbing film with excellent wave-absorbing properties. In this material, the interface design modulates the dielectric properties of the composite material, and the magnetization strategy enhances the magnetic loss performance, thereby optimizing the impedance matching properties of the film and realizing the wave-absorbing performance of broadband strong absorption. In addition, the load distribution at the interface and the stray magnetic field distribution of the magnetic nanoparticles were observed in situ by TEM electron holography, which proved the interface polarization and magnetic coupling interaction. The structural design provides the theoretical basis.

Graphical guide

Preparation of I MXene-rGO/CoNi Composite Thin Films

The surfaces of MXene and rGO are both rich in functional groups, with Zeta potentials of −20.1 mV and −5.57 mV, respectively. To achieve electrostatic assembly, the rGO/CoNi composite was first modified by diallyldimethylammonium chloride to make its surface positively charged. Then, MXene and rGO/CoNi were uniformly assembled by suction filtration method to prepare flexible composite films.

Figure 1. The flow chart of the preparation of the MXene-rGO/CoNi composite film, the Zeta potential change during the assembly process, and the actual photo.

II Microstructural Characterization

The thin films assembled by electrostatic interactions have uniform composition distribution. CoNi nanoparticles were uniformly distributed on the surface of rGO without spontaneous aggregation. CoNi nanoparticles-modified rGO intercalation in MXene films effectively suppressed the self-aggregation of MXene. As the content of rGO/CoNi in the films was gradually increased, the peak representing the (002) plane in the XRD spectrum shifted from 6.6° to 5.8°, proving the interplanar spacing expansion due to intercalation. In addition, obvious stress distributions appear in both CoNi nanoparticles and MXene, indicating a large number of defects. These defects can contribute to electromagnetic energy loss as dipole polarization sites.

Figure 2. Morphological characterization and XRD pattern of the MXene-rGO/CoNi composite film.

Figure 3. Structural characterization and stress distribution of the MXene-rGO/CoNi composite film. III Absorbing properties

The MXene-rGO/CoNi composite films have excellent wave-absorbing properties. At a thickness of 2.01 mm, the lowest reflection loss value reaches −54.1 dB; at a thickness of 2.00 mm, the effective absorption bandwidth is 5.1 GHz. In addition, in the thickness range of 2.00–5.00 mm, the composites have a wide absorption band. Compared with MXene and rGO/CoNi, the composite film not only has stronger absorption intensity, but also has a wider absorption bandwidth at low frequencies. The above results demonstrate that the interface design and magnetization strategy in the film can effectively enhance the wave absorbing performance.

Figure 4. Comparison of the absorbing properties of MXene-rGO/CoNi composite films with MXene and rGO/CoNi. IV Electron Holographic Characterization

The interfacial polarization at various interfaces in the composite material and the interaction mechanism of magnetic coupling between magnetic units are demonstrated by TEM electron holography. First, the blue and red colors in the hologram represent the gathering areas of positive and negative electrons, respectively. Significant load separation and aggregation were observed at the rGO/rGO, rGO/CoNi, and MXene/MXene interfaces, proving that various interfaces in the composite films induce interfacial polarization and contribute to the dielectric loss performance. Second, the dispersed magnetic nanoparticles are connected by stray magnetic lines of force, proving that a magnetic coupling interaction mechanism occurs between the magnetic nanoparticles, which significantly contributes to the magnetic loss performance.

Figure 5. Load distribution plots at various interfaces as characterized by electron holography in TEM.

Figure 6. Stray magnetic field distribution and magnetic coupling interaction of CoNi nanoparticles characterized by TEM electron holography.

V Absorption Mechanism

Through the above structure, properties and electron holographic analysis, the absorbing mechanism of MXene-rGO/CoNi composite film includes the following three points. First, the interface between the three components in the composite induces interface polarization relaxation and enhances the dielectric loss capability. Second, the magnetized MXene enhances the magnetic loss performance through natural resonance and magnetic coupling interactions. Finally, the macroscopic conductive network constructed by the two 2D materials significantly enhances the conduction loss.

Figure 7. Schematic diagram of the absorbing mechanism of the MXene-rGO/CoNi composite film.

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