Hierarchical Cobalt Selenides as Highly Efficient Microwave Absorbers with Tunable Frequency Response

Multilevel Heterogeneous Interfaces Enhanced Polarization Loss of 3D-Printed Graphene/NiCoO2/Selenides Aerogels for Boosting Electromagnetic Energy Dissipation

Heterointerface engineering is an attractive approach to modulating electromagnetic (EM) parameters and EM wave absorption performance. However, the weak interfacial interactions and poor impedance matching would lead to unsatisfactory EM absorption performance due to the limitation of the construction materials and design strategies. Herein, multilevel heterointerface engineering is proposed by in situ growing nanosheet-like NiCoO2 and selenides with abundant interface structures on 3D-printed graphene aerogel (GA) skeletons, which strengthens the interfacial effect and improves the dielectric polarization loss. Benefiting from the features of substantially enhanced polarization loss and optimized impedance matching, the graphene/S-NiCoO2/selenides (G/S-NCO/Se) have achieved brilliant EM wave absorption performance with a strong reflection loss (RL) value of -60.7 dB and a broad effective absorption bandwidth (EAB) of 8 GHz, which is about six times greater than that of the graphene aerogel (-9.8 dB). Moreover, it is further confirmed by charge density differences and off-axis electron holography that a large amount of polarized charge accumulates at the interface, leading to significant polarization relaxation behaviors. This work provides a deep understanding of the effect of a multilevel heterogeneous interface on dielectric polarization loss, which injects a fresh and infinite vitality for designing high-efficiency EM wave absorbers.

Combinatorial Structural Engineering of Multichannel Hierarchical Hollow Microspheres Assembled from Centripetal Fe/C Nanosheets to Achieve Effective Integration of Sound Absorption and Microwave Absorption

Electromagnetic radiation and noise pollution are two of the four major environmental pollution sources. Although various materials with excellent microwave absorption performances or sound absorption properties have been manufactured, it is still a great challenge to design materials with both microwave absorption and sound absorption abilities due to different energy consumption mechanisms. Herein, a combination strategy based on structural engineering was proposed to develop bi-functional hierarchical Fe/C hollow microspheres composed of centripetal Fe/C nanosheets. Both of the interconnected channels created by multiple gaps among the adjacent Fe/C nanosheets and the hollow structure have positive effects on the absorbing performances by promoting the penetration of microwaves and acoustic waves and prolonging action time between microwave energy and acoustic energy with materials. In addition, a polymer-protection strategy and a high-temperature reduction process were applied to keep this unique morphology and further improve the performances of the composite. As a result, the optimized hierarchical Fe/C-500 hollow composite exhibits a wide effective absorption bandwidth of 7.52 GHz (10.48-18.00 GHz) at only 1.75 mm. Furthermore, the Fe/C-500 composite can effectively absorb sound wave in the frequency of 1209-3307 Hz, basically including part of the low frequency range (<2000 Hz) and most of the medium frequency range (2000-3500 Hz), and has 90% absorption of sound at 1721-1962 Hz. This work puts new insight into the engineering and development of microwave absorption-sound absorption-integrated functional materials with promising applications.

Constructing MoSe2/MoS2 and MoS2/MoSe2 inner and outer-interchangeable flower-like heterojunctions: A combined strategy of interface polarization and morphology configuration to optimize microwave absorption performance

Interfacial polarization and geometrical morphology play a significant role in the attenuation of electromagnetic (EM) wave. Herein, the two-dimensional (2D)/2D heterojunction with flower-like geometrical morphology is proposed and produced, which may simultaneously provide a large contact area for achieving strong interfacial polarization and activates more sites for the possible multiple EM wave reflection and scattering. By adopting a simple two-step hydrothermal method, MoSe₂/MoS₂and MoS₂/MoSe₂ inner and outer-interchangeable heterojunctions consisting of 2D MoSe₂ and MoS₂ nanosheets with flower-like geometrical morphology were successfully synthesized. The results revealed that the hydrothermal temperatures significantly impacted the flower-like geometrical morphology and MoS₂ content. By optimizing the microstructures, the designed MoSe₂/MoS₂ and MoS₂/MoSe₂ heterojunctions presented enhanced comprehensive EM wave absorption properties (EMWAPs), possessing strong absorption capability, wide absorption bandwidth and thin matching thicknesses. Generally, this work demonstrates that the optimized EMWAPs of designed heterojunctions mainly originate from the special interfaces and morphology configuration, which also paves a new way for the designing and synthesis of transition metal dichalcogenides-based heterojunction as a novel and desirable candidate for high-performance microwave absorbers.

Ferromagnetic Ti3CNCl2-decorated RGO aerogel: From 3D interconnecting conductive network construction to ultra-broadband microwave absorber with thermal insulation property

It remains urgent challenges to adopt suitable strategies to consume unwanted microwave pollution emitted by high-tech electronic devices satisfactorily. Confronted with narrow effective absorption bandwidth (EAB) and high filler loading bottlenecks of MXene-Based microwave absorber, herein, we employ Lewis molten salt etching approach to both exfoliate Ti₃AlCN powders into Ti₃CNCl₂ suspension and intercalate ferromagnetic composition into interlamination simultaneously. By utilizing the crosslinking effect of dopamine, the Ti₃CNCl₂ are anchored on the surfaces of graphene oxide (GO) nanosheets, constructing interconnecting microstructure. Both the 3D conductive network and the modification of MXene manifest crucial impacts on enhancing microwave absorption performance of the resulting ultra-lightweight reduced GO (RGO)-based aerogel. The minimum intensity of reflection loss achieves -62.62 dB with the absorber mass loading of 0.7 wt%. Remarkably, more than 90% of the incident microwave is qualified to be absorbed over the whole Ku band. The EAB is broadened while tailoring the thickness to 3 mm, ranging from 10.2 to 18 GHz. Besides, the aerogel presents valuable thermal insulation properties. Our methodology of synthesizing MXene/RGO aerogel not only provides promising insights into microstructural construction but also endows the possibility for integrating thermal insulation property towards next-generation high-performance microwave absorption devices.

Synergistically Assembled Cobalt-Telluride/Graphene Foam with High-Performance Electromagnetic Wave Absorption in Both Gigahertz and Terahertz Band Ranges

Electromagnetic wave (EMW)-absorbing materials have a great impact on civil use and national defense. In this paper, a novel composite, RGO@6CoTe₂-300 (the mass ratio of reduced graphene oxide to CoTe₂ is 1:6, annealed at 300 °C), has been obtained through a facile melt-diffusion method and solvothermal method. The as-prepared samples have shown excellent reflection losses (RL) and effective adsorption bandwidth (EAB) by controlling the loading of CoTe₂ and the annealing temperature. The sample has exhibited a RL of -62.2 dB at 13.04 GHz with the matching thickness of 3.53 mm, and the EAB reaches 8.2 GHz at 2-18 GHz. Moreover, excellent terahertz (THz) absorption property is also obtained at 0.2-2.0 THz. A RL of 54.07 dB is acquired, and the EAB covers 100% of the entire measured bandwidth. Thus, RGO@6CoTe₂-300 can be considered as a promising EMW absorption material in both gigahertz and terahertz band ranges.

A Review on Metal-Organic Framework-Derived Porous Carbon-Based Novel Microwave Absorption Materials

The development of microwave absorption materials (MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human's health. And MAMs are also used in radar stealth for protecting the weapons from being detected. Many nanomaterials were studied as MAMs, but not all of them have the satisfactory performance. Recently, metal-organic frameworks (MOFs) have attracted tremendous attention owing to their tunable chemical structures, diverse properties, large specific surface area and uniform pore distribution. MOF can transform to porous carbon (PC) which is decorated with metal species at appropriate pyrolysis temperature. However, the loss mechanism of pure MOF-derived PC is often relatively simple. In order to further improve the MA performance, the MOFs coupled with other loss materials are a widely studied method. In this review, we summarize the theories of MA, the progress of different MOF-derived PC‑based MAMs, tunable chemical structures incorporated with dielectric loss or magnetic loss materials. The different MA performance and mechanisms are discussed in detail. Finally, the shortcomings, challenges and perspectives of MOF-derived PC‑based MAMs are also presented. We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.

Advances of 3D graphene and its composites in the field of microwave absorption

The intensive progress of information technology increases the demand for urgent development of practical materials for microwave absorption (MA), meeting the general requirement "thin, wide, light and strong". In the past 6 years, graphene is of great interest for MA performance due to its unique properties such as high specific surface area, high electrical conductivity, strong dielectric loss, and low density. Taking in account that the structure of absorber plays a key role in MA performance, the attempts to produce an efficient microwave absorbing materials (MAMs) have led to 3D graphene - aerogels and foams - due to their extremely high porosity, large specific surface area, excellent mechanical properties with ability of compression and further maintaining the original shape, lightweight, reduced agglomeration of graphene sheets. All listed parameters enhance the impedance matching of MAMs, generate the synergistic loss effects, thereby improving the MA properties. The review describes the bases of MA theory and summarizes the recent achievements in the fabrication of pure 3D graphene networks and their composites with magnetic, ceramic nanoparticles and nanowires, polymers, MXenes, and multicomponent systems, directed to improve the impedance matching and generate loss mechanisms for the overall improvement of their performance as MAMs.

Tailored design of p-phenylenediamine functionalized graphene decorated with cobalt ferrite for microwave absorption

Structural design and componential optimization are two primary directions in the study of microwave absorbers. In this study, a novel cobalt ferrite (CoFe2O4) decorated with p-phenylenediamine (PPD) functionalized graphene (PG/CoFe2O4) binary hybrid with unique hierarchical porous structure was synthesized by a two-step route. The chemical composition, morphology and electromagnetic parameters of the as-prepared sample were investigated successively. The porous CoFe2O4 microspheres with an average diameter of about 160 nm were uniformly anchored on rGO nanosheets. Owing to the uniquely hierarchical porous structure, synergistic effects of dielectric loss (conductive loss, interface and dipole polarization) and magnetic loss (eddy current loss, natural and exchange resonance), the as-prepared sample exhibited excellent microwave absorption (MA) performance. The maximum reflection loss (RLmax) could attain up to -53.3 dB, and the effective absorption bandwidth (EAB) reached 6.6 GHz (11.4-18.0 GHz) at 2.40 mm, which completely covered the K u band. These results showed that this functional material can be applied in the MA field.