Porous Carbonaceous Aerogels Composed of Multiscale Carbon-Based Units for High-Performance Microwave Absorption

3D Porous Graphene with Atomic Fe Coordinated by Pyrrole-N Dopants for Efficient Electromagnetic Wave Absorption with Low Filler Loading and Thin Thickness

Achieving effective electromagnetic wave (EMW) absorption performance with less than 2 mm remains a significant challenge in developing EMW absorption materials. Herein, Fe atoms embedded into NH3-treated 3D porous graphene (3DPG-NH3-Fe) are synthesized via a simple method of Fe ion impregnation for efficient EMW absorption. The NH3-treated process enables the formation of specific pyrrole-N dopants in 3DPG, which provide the anchoring sites for complexing Fe atoms to construct FeNx moieties. Compared to pristine 3DPG, 3DPG-NH3-Fe exhibits remarkable EMW absorption characteristics, achieving a minimum reflection loss (RL) of -56.35 dB and an effective absorption bandwidth (EAB) of 4.45 GHz at a low filler loading of 3 wt.% and a thin thickness of 1.4 mm, exceeding the most of reported graphene-based EMW absorption materials. The outstanding performance is critically attributed to the incorporation of the specific Fe coordinated by pyrrole-N dopants with a strong orbital hybridization of N-py and Fe-3dx2-y2 into graphene, which not only produces additional dipoles but also generates high spin Fe atomic magnetic moment, thus enhancing both dielectric loss and magnetic loss for EMW. This work demonstrates a new route for modulating the electromagnetic characteristics of graphene to achieve low filler loading and thin thickness of EMW absorption.

Tunable 1D-2D Carbon Nanomaterials for Broadband and High-Performance Microwave Absorption via Ultrasonic Spray Ice Template

Polymer-based one- and two-dimensional (1D-2D) carbon nanomaterials are considered promising microwave-absorbing materials (MAMs) due to their high atomic utilization efficiency and tunable microscopic/macroscopic morphology. The tunable design of 1D-2D carbon nanomaterials through a facile method to meet the requirements of advanced MAMs remains a challenge. In this work, the environmentally friendly processing method of ultrasonic spray ice template (USIT) is employed to fabricate porous carbon nanomaterials based on Kapton-type polyimide, which exhibit the intriguing morphology of both 1D nanowires and 2D nanosheets. Under subsequent carbonization at 700 and 800 °C, the obtained carbon nanomaterials inherit the original morphology. Furthermore, the 1D or 2D nanomorphology can be readily controlled by adjusting the concentration of the precursor solution. For samples fabricated with lower precursor concentrations (0.1%), 1D nanowire structures are predominant. Interconnected conductive networks and heterogeneous interfaces are formed by intertwining and stacking nanowires, thereby enhancing the conductivity loss. Additionally, the abundant porous structure provides an effective channel for electromagnetic wave entrance, significantly improving the impedance matching ability. The results show that the 1D nanowire-dominated samples (700 °C carbonization) show excellent electromagnetic microwave absorption performance. The reflection loss minimum (RLmin) is -67.2 dB at 8.1 GHz and 4.65 mm, and the maximum effective absorption bandwidth (<-10 dB) is 7.7 GHz at 3.03 mm. Exemplified by MAMs, the USIT strategy has broad prospects, providing enormous potential for various practical applications and bridging the gap between polymer precursors and 1D/2D tunable carbon nanomaterials.

Multifunctional Carbon Foam with Nanoscale Chiral Magnetic Heterostructures for Broadband Microwave Absorption in Low Frequency

The construction of carbon nanocoil (CNC)-based chiral-dielectric-magnetic trinity composites is considered as a promising approach to achieve excellent low-frequency microwave absorption. However, it is still challenging to further enhance the low frequency microwave absorption and elucidate the related loss mechanisms. Herein, the chiral CNCs are first synthesized on a three-dimensional (3D) carbon foam and then combined with the FeNi/NiFe2O4 nanoparticles to form a novel chiral-dielectric-magnetic trinity foam. The 3D porous CNC-carbon foam network provides excellent impedance matching and strong conduction loss. The formation of the FeNi-carbon interfaces induces interfacial polarization loss, which is confirmed by the density functional theory calculations. Further permeability analysis and the micromagnetic simulation indicate that the nanoscale chiral magnetic heterostructures achieve magnetic pinning and coupling effects, which enhance the magnetic anisotropy and magnetic loss capability. Owing to the synergistic effect between dielectricity, chirality, and magnetism, the trinity composite foam exhibits excellent microwave absorption performance with an ultrabroad effective absorption bandwidth (EAB) of 14 GHz and a minimum reflection of loss less than - 50 dB. More importantly, the C-band EAB of the foam is extended to 4 GHz, achieving the full C-band coverage. This study provides further guidelines for the microstructure design of the chiral-dielectric-magnetic trinity composites to achieve broadband microwave absorption.

Enhanced electromagnetic wave absorption of bacterial cellulose/ reduced graphene oxide aerogel by eco-friendly in-situ construction

Electromagnetic wave absorption materials (EWAMs) have become an effective means to address electromagnetic (EM) radiation and enhance stealth technology, among which aerogels are valued for their lightweight nature and excellent designability. This study utilized environmentally friendly preparation and in-situ reduction techniques to fabricate bacterial cellulose (BC) / reduced graphene oxide (RGO) aerogels, achieving tailored EM wave loss capabilities by controlling the reduction time of ascorbic acid. Benefitting from the effects of freeze-casting, BC winding, hydrogen bond, and RGO layers coupling, the aerogel maintains their original structure after reduction and exhibits satisfactory EM wave absorption. The minimum reflection loss (RLmin) is -38.52 dB, with an effective absorption bandwidth (EAB) of 6.68 GHz and a maximum radar cross section (RCS) reduction of 44.69 dBsm. Additionally, the aerogel's lightweight (a low density of 9.03 mg/cm3) and outstanding thermal insulation properties enable it to adapt to complex conditions. Thus, the study provides a novel approach for the construction of industrialized and sustainable RGO-based EWAMs.

A Developed Approach for Synthesizing Novel Fe3O4/FeO/BaCl2 Composites with Broadband and High-Efficiency Microwave Absorption Performance

Designing high-performance microwave absorbing materials that are thin and exhibit strong absorption capabilities across a wide frequency range is critical for mitigating electromagnetic pollution through a simple, highly adaptable, and cost-effective approach. However, achieving these three targets remains a significant challenge. In this research a simple approach suitable for large-scale production of microwave absorbing materials, namely, Fe3O4/FeO/BaCl2 composites, is proposed, which includes the processes of chemical coprecipitation and calcination. The above approach can adjust the mass ratio of Fe3O4/FeO while prompt the formation of BaCl2 with mesoporous structure on the surface of Fe3O4/FeO, meeting the need for desirable microwave absorbing performance. Subsequently, the impacts of varying mass ratios of the Fe3O4/FeO/BaCl2 composites on microstructures, magnetic properties, and microwave absorption properties were examined. Based on this investigation, a mass ratio close to 3.5:5.5:1 was determined to be optimal. At this ratio, the Fe3O4/FeO/BaCl2 composites realize an effective absorption bandwidth of 6.70 GHz at only 1.16 mm thickness, covering the whole Ku-band, and the maximum reflection loss can be close to -46.8 dB at 1.4 mm. The robust microwave absorption performance of Fe3O4/FeO/BaCl2 composites can be attributed to heterostructured multi-interface structural design, the comprehensive effects of multiple reflections and dielectric/magnetic losses induced by BaCl2 with mesoporous structure as well as the aggregated Fe3O4/FeO particles. This work may offer insights into designing and preparing effective microwave absorption materials.

Two-phase magnetic nanospheres with magnetic coupling effect encapsulated in porous carbon to achieve lightweight and efficient microwave absorbers

Component selection is crucial for microwave absorbents. Multi-component absorbers are increasingly useful and can be prepared through the rational design and control of various electrical, magnetic, and other auxiliary components. In this paper, Ni3Fe/NiFe2O4 nanospheres with two-phase magnetism were designed for use as a multi-component absorber. Specifically, a Ni3Fe/ NiFe2O4@SPC composite with 3D networks was successfully fabricated by hydrothermal method, high-temperature carbonization for activation, and electrostatic self-assembly. The contact interface and coupling effect between the two magnetic components can promote the attenuation of electromagnetic waves. Moreover, the introduction of porous carbon successfully inhibits the easy aggregation of the magnetic particles. Impressively, with a filling load of 10 wt%, the optimal RL of the prepared Ni3Fe/NiFe2O4@SPC composite reaches -60.6 dB, and the effective absorption bandwidth is 5.2 GHz at 2 mm. The combination of two magnetic components and porous carbon in this multiphase microwave-absorbing composite demonstrates a feasible strategy for designing efficient microwave absorbers in the future.

Designing a Microstructure of NiCo-LDH@CNTs@Carbon Foam for Efficient Electromagnetic Wave Absorption and Excellent Environmental Tolerance

The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

N-doped carbon layer cladded carbon sphere for broadband and boosted microwave attenuation capacity

Structural construction and heteroatom doping are deemed effective strategies for designing a high-performance microwave absorbing composite to eliminate electromagnetic hazards. Herein, a series of core-shell structural carbon@N-doped carbon (C@NC) nanospheres were successfully fabricated without employing additional modifying agents and sophisticated operation. After incorporating them into a polyvinylidene fluoride (PVDF) matrix, the C@NC/PVDF composites possess tunable wave attenuation capacity obtained by regulating the coating layer thickness and filler loading. Benefitting from the design strategy of the core-shell structure and N-doped C, the C@NC-2/PVDF composites displayed the broadest effective absorption bandwidth of 6.29 GHz (11.71-18 GHz) under a filler content of only 10 wt% at 2.01 mm. Additionally, the minimum reflection loss value of C@NC-3/PVDF composites achieves -62.87 dB within the same mass ratio at a thickness of 2.35 mm. The excellent wave dissipation ability is attributed to the combination of optimized impedance matching and synergistically enhanced multiple loss mechanisms including conduction loss, interfacial polarization as well as dipolar polarization. This work offers a ponderable paradigm for the deeper exploitation of high-efficiency carbon absorbers.

Electrostatically fabricated heterostructure of interfacial-polarization-enhanced Fe3O4/C/MXene for ultra-wideband electromagnetic wave absorption

Electromagnetic (EM) pollution can disrupt the functioning of advanced electronic devices, hence it's necessary to design EM wave absorbers with high-level absorption capabilities. The Ti3C2Tx (MXene) is classified as a potential EM absorbing material; nevertheless, the lack of magnetic loss mechanism leads to its inadequate EM absorbing performance. On this basis, a novel composite design with promising EM absorption properties is hypothesized to be the integration of few-layer MXene and heterogeneous magnetic MOF derivatives (Fe3O4/C) with complementary advantages. Herein, we synthesized two-dimensional (2D) interfacial-polarization-enhanced MXene hybrid (Fe3O4/C/MXene) by electrostatic assembly. It is notable that the interfacial polarization is realized by adding a small amount of magnetic Fe3O4/C. Furthermore, the Fe3O4/C/ MXene demonstrates an astonishing effective absorption bandwidth (EAB) of 10.7 GHz and an excellent EM wave absorption performance (RLmin) of -66.9 dB. Moreover, the radar cross section (RCS) of Fe3O4/C/MXene is lower than -15.1 dB m2 from -90° to 90° with a minimum RCS value of -52.6 dB m2 at 32°. In addition, the significant attenuation of the EM wave is due to the synergistic effect of improved impedance matching, dielectric loss, and magnetic loss. Thus, the magnetized Fe3O4/C/MXene hybrid is expected to emerge as a strong contender for high-performance EM wave absorbers.