Microwave absorbers with layered structures that can provide abundant interfaces are highly desirable for enhancing electromagnetic absorbing capability and decreasing the thickness. The atomically ...thin layers of two-dimensional (2D) transition-metal carbides (MXenes) make them a convenient precursor for synthesis of other 2D and layered structures. Here, laminated carbon/TiO2 hybrid materials composed of well-aligned 2D carbon sheets with embedded TiO2 nanoparticles were synthesized and showed excellent microwave absorption. Disordered 2D carbon layers with an unusual structure were obtained by annealing multilayer Ti3C2 MXene in a CO2 atmosphere. The minimum reflection coefficient of laminated carbon/TiO2 composites reaches −36 dB, and the effective absorption bandwidth ranges from 3.6 to 18 GHz with the tunable thickness from 1.7 to 5 mm. The effective absorption bandwidth covers the whole Ku band (12.4–18 GHz) when the thickness of carbon/TiO2/paraffin composite is 1.7 mm. This study is expected to pave the way to the synthesis of carbon-supported absorbing materials using a large family of 2D carbides.
Alloying is a long-established strategy to tailor properties of metals for specific applications, thus retaining or enhancing the principal elemental characteristics while offering additional ...functionality from the added elements. We propose a similar approach to the control of properties of two-dimensional transition metal carbides known as MXenes. MXenes (M n+1X n ) have two sites for compositional variation: elemental substitution on both the metal (M) and carbon/nitrogen (X) sites presents promising routes for tailoring the chemical, optical, electronic, or mechanical properties of MXenes. Herein, we systematically investigated three interrelated binary solid-solution MXene systems based on Ti, Nb, and/or V at the M-site in a M2XT x structure (Ti2‑yNb y CT x , Ti2‑yV y CT x , and V2‑yNb y CT x , where T x stands for surface terminations) showing the evolution of electronic and optical properties as a function of composition. All three MXene systems show unlimited solubility and random distribution of metal elements in the metal sublattice. Optically, the MXene systems are tailorable in a nonlinear fashion, with absorption peaks from ultraviolet to near-infrared wavelength. The macroscopic electrical conductivity of solid solution MXenes can be controllably varied over 3 orders of magnitude at room temperature and 6 orders of magnitude from 10 to 300 K. This work greatly increases the number of nonstoichiometric MXenes reported to date and opens avenues for controlling physical properties of different MXenes with a limitless number of compositions possible through M-site solid solutions.
MXene is a large family of two-dimensional transition metal carbides, nitrides or carbonitrides. Its characteristics（various compositions, two-dimensional atomic layer structures, metallic electrical ...conduction, active surfaces, etc.） render MXene unique interactions with electromagnetic waves at different frequencies（visible light,infrared, terahertz, microwave, etc.）, deriving a variety of electromagnetic functional applications. In the infrared range,MXene has a wide range of infrared radiation properties, and its active surface endows tunable infrared absorption.These features have attracted researchers' interest in exploring infrared properties of MXene and the corresponding applications in recent years. In this perspective, the intrinsic infrared characteristics and manipulation strategies of different MXenes are systematically summarized, and the research progress of representative infrared applications are briefly introduced, including infrared identification/camouflage, surface plasmon, photothermal conversion, and infrared photodetection. Particularly, the contribution and mechanism of MXene in these applications are discussed.Finally, the outlook for infrared functional applications with MXenes is proposed.
The rapid development of communication and electronic technologies has brought forward new and compelling demands for electromagnetic radiation protection. Two-dimensional transition metal carbides ...and nitrides known as MXenes entered the field in 2016 and have been quickly reshaping it. Here, we provide a perspective on recent progress and challenges of the MXene family for protection against electromagnetic jamming, including electromagnetic interference (EMI) shielding and microwave absorption. We examine the intrinsic electronic and dielectric properties of MXenes, which are of critical importance for fundamental understanding of electromagnetic response. By tracing the state-of-the-art design strategies, we explore how to optimize MXene-based EMI shielding and microwave absorption materials. Particularly, we highlight the metrics and fundamental mechanisms of electromagnetic protection, aimed to clarifying common misconceptions, and objectively assess the performance of the reported materials. Finally, we discuss challenges to be addressed and give an outlook to future opportunities in the development of MXenes for electromagnetic radiation protection.
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A broadband microwave absorbing composite with a multi-scale layered structure is proposed, in which a reduced graphene oxide (RGO) film sandwiched between two layers of epoxy glass fiber laminates ...serves as the frequency selective surface (FSS). RGO films with the desired electrical properties were synthesized directly by hydrothermal reaction, vacuum filtration, and heat treatment without subsequent processing. With the novel layer-by-layer structure ranging from micro to macro scale, the optimized composite exhibits excellent microwave absorption performance with a total thickness of 3.2 mm. Its reflection coefficient (RC) is less than -10 dB in the entire X and Ku band, reaching a minimum value of -32 dB at 10.2 GHz and an average RC of -22.8 dB from 8 to 18 GHz. Enhanced microwave absorption of the composites is achieved through the optimization of layer thickness in the sandwich structure to promote destructive interference. Improved impedance matching by the introduction of FSS along with the polarization and conduction loss of layered graphene films also contribute to the increased absorption.
Constructing three-dimensional (3D) porous structures is an effective method to improve microwave absorbing performance due to the multiple reflections. However, in traditional 3D porous structures, ...multiple reflections only occur within the pores. Promoting multiple reflections beyond the pores should further improve the absorbing performance. Herein, a 3D porous composite foam with sandwiched cell walls was developed to boost multiple reflections in both the submillimeter-scale pores and the submicron-scale cell walls, achieving multiscale microwave absorption. Polydopamine (PDA)-modified polyimide foam (PIF) was used as the 3D porous skeleton. The cell walls of the PDA@PIF were sandwiched by Ti
3
C
2
T
x
MXene. The resulting Ti
3
C
2
T
x
@PDA@PIF can absorb over 90% of the incident microwave over the whole X band, which is contributed by multiscale multiple reflections, conduction loss, and interfacial polarization. Meanwhile, the composite foam exhibits excellent flexibility and a low density of ∼30 mg cm
−3
. This work offers a realistic approach for lightweight, flexible, and broadband microwave absorbers, enriching the structures for effective electromagnetic protection.
Camouflage is a common technique in nature, enabling organisms to protect themselves from predators. The development of novel camouflage technologies, not only in fundamental science, but also in the ...fields of military and civilian applications, is of great significance. In this study, we propose a new type of deep-subwavelength four-layered meta-coating consisting of Si, Bi, Si, and Cr from top to bottom with total thickness of only ∼355 nm for visible-infrared compatible camouflage. The visible color and the infrared emission properties of the meta-coating can be independently adjusted. Colorful meta-coating for visible camouflage can be obtained by changing the thickness of top Si layer, while the selective high emissivity in non-atmospheric window for infrared camouflage remains. Due to the deep-subwavelength properties, the meta-coating shows high angle tolerance in both visible and infrared regions. The compatible camouflage capability of our proposed meta-coating in the visible-infrared region is validated under different environments. The deep-subwavelength, angular insensitivity, visible-infrared compatibility and large-area fabrication feasibility promise the meta-coating an effective solution for camouflage in various applications such as military weapons and anti-counterfeiting.
MAX/MAB phases are a series of non-van der Waals ternary layered ceramic materials with a hexagonal structure, rich in elemental composition and crystal structure, and embody physical properties of ...both ceramics and metals. They exhibit great potential for applications in extreme environments such as high temperature, strong corrosion, and irradiation. In recent years, two-dimensional（2D） materials derived from the MAX/MAB phase（MXene and MBene） have attracted enormous interest in the fields of materials physics and materials chemistry and become a new 2D van der Waals material after graphene and transition metal dichalcogenides. Therefore, structural modulation of MAX/MAB phase materials is essential for understanding the intrinsic properties of this broad class of layered ceramics and for investigating the functional properties of their derived structures. In this paper, we summarize new developments in MAX/MAB phases in recent years in terms of structural modulation, theoretical calculation, and fundamental application research and provide an outlook on the key challenges and prospects for the future development of these layered materials.
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