Lightweight TiO2@C/Carbon Fiber Aerogels Prepared from Ti3C2Tx/Cotton for High-Efficiency Microwave Absorption

Progress, Challenges and Prospects of Biomass-Derived Lightweight Carbon-Based Microwave-Absorbing Materials

The widespread use of electronic devices in daily life, industry and military has led to a large amount of electromagnetic pollution, which has become an increasingly serious security issue. To eliminate or mitigate such risks and hazards, various advanced microwave absorption technologies and materials have been reported. As a new type of microwave absorber, biomass-derived carbon-based materials have received extensive attention. They have the characteristics of low cost, easy preparation, high porosity and environmental friendliness while retaining the advantageous adjustable dielectric properties, high conductivity and good stability of traditional carbon materials. The development of biomass microwave-absorbing materials not only provides a new idea for solving electromagnetic radiation but also helps to create an environmentally friendly and harmonious environment. Herein, various biomass-derived carbon-based microwave-absorbing materials (MAMs) including plant shells, plant fibers and other potential biomass materials are generalized and discussed including their preparation technology, microstructure design and so on. The two critical factors affecting microwave absorption properties, impedance matching and attenuation characteristics, are analyzed in detail. Finally, the confronting challenges and future development prospects of biomass-based microwave-absorbing materials are pointed out.

Structural, Magnetic, and Electrical Investigations of PVA/Ni Ferrite/(MoS2)x Nanocomposites

Transition metal sulfides (TMDs) possess exceptional dielectric properties and a narrow band gap, rendering them highly efficient as electromagnetic absorbing materials. Among these TMDs, the two-dimensional MoS2 nanosheet has received significant attention in research. However, the quest for new absorbers no longer finds satisfaction in solitary absorption mechanisms. This article introduces a successful method for creating PVA/NiFe2O4/(MoS2)x nanocomposites via a straightforward sol-gel technique, wherein porous amorphous NiFe2O4 microspheres are integrated into MoS2 nanosheets. The investigation uncovers that the incorporation of MoS2 results in an enhanced complex permittivity, facilitating the attainment of a desirable permittivity level. The PVA/NiFe2O4/(MoS2)x nanocomposite absorber exhibits an incredibly low reflection loss (RL) of -16.75 dB at a mere thickness of 1 mm, achieved through the cooperative interaction of dielectric and magnetic loss, along with the advantages of the structure and composition. Consequently, the PVA/NiFe2O4/(MoS2)x nanocomposites effectively absorb electromagnetic waves. Therefore, it is posited that MoS2-based composites hold great promise as highly effective microwave absorbers, boasting strong absorption intensity and a wide absorption frequency range, given the exceptional performance of the as-fabricated PVA/NiFe2O4/(MoS2)x nanocomposites.

Construction of Self-Assembly Based Tunable Absorber: Lightweight, Hydrophobic and Self-Cleaning Properties

Although multifunctional aerogels are expected to be used in applications such as portable electronic devices, it is still a great challenge to confer multifunctionality to aerogels while maintaining their inherent microstructure. Herein, a simple method is proposed to prepare multifunctional NiCo/C aerogels with excellent electromagnetic wave absorption properties, superhydrophobicity, and self-cleaning by water-induced NiCo-MOF self-assembly. Specifically, the impedance matching of the three-dimensional (3D) structure and the interfacial polarization provided by CoNi/C as well as the defect-induced dipole polarization are the primary contributors to the broadband absorption. As a result, the prepared NiCo/C aerogels have a broadband width of 6.22 GHz at 1.9 mm. Due to the presence of hydrophobic functional groups, CoNi/C aerogels improve the stability in humid environments and obtain hydrophobicity with large contact angles > 140°. This multifunctional aerogel has promising applications in electromagnetic wave absorption, resistance to water or humid environments.

Controllable preparation of 2D carbon paper modified with flower-like WS2 for efficient microwave absorption

In the practical application of microwave absorbing materials, traditional powder materials need to be mixed with the matrix to fabricate composite coatings. However, the complex preparation process of composite coatings and the uneven dispersion of powders in the matrix limit their application. To solve these problems, two-dimensional (2D) F-WS₂/CP composite films were prepared by using carbon paper (CP) as a dispersion matrix and loading flower-like WS₂ on its surface through a simple hydrothermal method. The morphology and microwave absorption (MA) performance of the composite films are easily regulated by adjusting the amount of reaction precursors. The combination of WS₂ and CP facilitates impedance matching and improves the electromagnetic wave attenuation performance based on the synergistic effect of different loss mechanisms including multiple reflections and scattering, interfacial polarization, dipolar polarization, and conduction loss. At a low filler content (5 wt%), the maximum reflection loss (RL) of the composite film is up to -50 dB (99.999% energy absorption) at 12.5 GHz with 2.8 mm thickness. Moreover, at a relatively thin 1.8 mm thickness, its maximum RL remains -35 dB (>99.9% energy absorption). The as-prepared composite film shows excellent MA properties at a thinner thickness and lower filling content, providing inspiration for the preparation of light weight and efficient 2D thin-film microwave absorbers in the future.

Porous Molybdenum Compound Design for Strong Microwave Absorption

Exploring highly efficient microwave absorption (MA) materials with a facile preparation method is of great significance for tackling electromagnetic pollution and remains a challenge. Herein, ternary MoO₂/Mo₂C/Mo₂N composites with porous structures are fabricated by a simple precursor pyrolysis process. The unique structure and multiple components, which could generate sufficient heterogeneous interfaces, are conducive to improve impedance matching, trigger polarization loss, and strengthen conduction loss. Profiting from the synergistic effect of multiple dissipation mechanisms, the composites exhibit exceedingly good MA performance. The minimum reflection loss value reaches -38.0 dB at 10.4 GHz when the thickness is 2.0 mm, and the maximum effective absorbing bandwidth is 4.11 GHz ranged from 12.41 to 16.52 GHz when the thickness is 1.5 mm. These strategies pave opportunities for rational design of Mo-related composites for high-efficiency electromagnetic-wave absorption performance.

Enhancement of microwave absorption performance of porous carbon induced by Ce (CO3) OH

In recent years, electromagnetic pollution has become more and more serious, resulting in a very negative impact on people's health. Therefore, it is important to develop efficient microwave absorbers to reduce electromagnetic pollution. Here, we construct a novel absorbing material of the polymer gel-derived porous carbon decorated by rare earth compounds (Ce (CO₃) OH). When the thickness is 2.2 mm, the composite exhibits excellent microwave absorption performance with the optimal RL_min value and EAB reached up to -47.67 dB and 5.52 GHz, respectively, covering the Ku band. The high-efficiency microwave absorption is mainly attributed to the synergistic effect of dipole polarization, defect polarization and interfacial polarization. This work not only provides a new view for designing superior absorber materials, but also lay a foundation for their real applications.

Ultralight Hierarchically Structured RGO Composite Aerogels Embedded with MnO2/Ti3C2Tx for Efficient Microwave Absorption

Although intensive efforts have been devoted to fabricating Ti₃C₂T_x MXene composites for microwave absorption, it remains a great challenge to achieve excellent MA performance at low loading and thin thickness. Herein, a three-dimensional (3D) lightweight hierarchically structured MnO₂/Ti₃C₂T_x/RGO composite aerogel with abundant heterointerfaces was fabricated via a hydrothermal and chemical reduction self-assembly method. The RGO aerogel embedded with laminated MnO₂/Ti₃C₂T_x provides a lot of heterogeneous interfaces, 3D porous interconnected conductive networks, and reasonable combination of various loss materials for rich interfacial polarization, conductivity loss, multiple reflections and scattering, and good impedance matching. Benefiting from the synergy of different loss mechanisms, the maximum reflection loss (RL) is up to -66.5 dB (>99.9999% energy absorption) at only 10 wt % loading and 2.0 mm thickness, and even at only 1.5 mm thickness, the maximum RL value remains at -36 dB (>99.9% energy absorption). The work provides a promising route to construct 3D hierarchically heterogeneous composite aerogels for efficient MA at thin thickness and low loading.

Tunable Ti3C2Tx MXene-Derived TiO2 Nanocrystals at Controlled pH and Temperature

While two-dimensional (2D) Ti₃C₂T_x MXene in aqueous dispersions spontaneously oxidizes into titanium dioxide (TiO₂) nanocrystals, the crystallization mechanism has not been comprehensively understood and the resultant crystal structures are not controlled among three representative polymorphs: anatase, rutile, and brookite. In this study, such control on the lattice structures and domain sizes of the MXene-derived TiO₂ crystallites is demonstrated by means of the oxidation conditions, pH, and temperature (3.0-11.0 and 20-100 °C, respectively). It is observed that the formation of anatase phase is preferred against rutile phase in more basic and hotter oxidizing solutions, and even 100% anatase can be obtained at pH 11.0 and 100 °C. At lower pH and temperature, the portion of rutile phase increases such that it reaches ∼70% at pH 3 and 20 °C. Under certain circumstances, small portion of brookite phase is also observed. Smaller domain sizes of both anatase and rutile phases are observed in more basic oxidizing solutions and at lower temperatures. Based on these experimental results, we propose the crystallization mechanism in which the oxidative dissociation of Ti₃C₂T_x first produces Ti ions as the intermediate state, and they bind to abundant oxygen in the aqueous dispersions, and nucleate and crystallize into TiO₂.