(searched for: doi:10.1016/j.carbon.2021.03.042)
Journal of Materials Science & Technology; https://doi.org/10.1016/j.jmst.2021.06.052
The electromagnetic wave absorption (EMWA) performance of materials is affected by their dielectric and magnetic properties. Here, ferroferric [email protected] residual carbon (Fe3O4@NRC) composites were successfully fabricated by decorating NRC with Fe3O4 nanoparticles via a facile chemical co-precipitation method. The RC was obtained through acid treatment to remove the inorganic minerals in coal gasification fine slag. The structure, composition, thermal stability, morphology, and related EM parameters of the as-fabricated Fe3O4@NRC composites were thoroughly tested via analytical techniques. Notably, both the Fe3O4@NRC-2 and Fe3O4@NRC-3 composites exhibited superior EMWA capacity. When 40% mass was added, the value of minimal reflection loss (RLmin) for Fe3O4@NRC-2 was −37.4 dB, and the effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 4.16 GHz (13.84–18.00 GHz) at a thickness of 1.5 mm. Besides, the value of impedance matching was 1.00 as the RLmin was achieved. The results demonstrated that the EMWA performance of the composites could be adjusted by controlling the content of Fe3O4 nanoparticles. The magnetic/carbon composites exhibited superior EMWA performance, thus promoting the resource utilization of residual carbon in coal gasification fine slag from coal gasification.
Chemical Engineering Journal, Volume 429; https://doi.org/10.1016/j.cej.2021.132238
Rational construction of heterogeneous interfaces is an effective strategy to explore high-performance electromagnetic waves (EMWs) absorption materials. Herein, we adopt a facile solvothermal and pyrolysis process to fabricate the multicomponent and multidimensional composites containing the bimetallic FeNi or [email protected] graphene layer core-shell heterojunctions/N-doped carbon nanorods/reduced graphene oxide ([email protected]/NCR/rGO or [email protected]/NCR/rGO) derived from NH2-bimetallic (FeNi or FeCo)-metal organic frameworks (MOFs)/GO precursors. The excellent EMWs absorption performances are effectively achieved and regulated via the content of rGO and the filler loading. Compared with the case without rGO, the [email protected]/NCR/rGO composite (25 wt% filler loading) displays a strong reflection loss (RL) of −52.61 dB at 14.44 GHz with a thin thickness of 1.65 mm, and effective absorption bandwidth (EAB) is 4.64 GHz. And the [email protected]/NCR/rGO composite (20 wt% filler loading) displays a strong RL of −59.42 dB at 17.8 GHz with a thinner thickness of 1.42 mm, and EAB is 5.28 GHz at 1.66 mm. Their excellent absorption properties result from the synergistic effect between the increased dielectric loss (interfacial polarization, dipole polarization and conduction loss), impedance matching and attenuation constant. These results provide a pathway to prepare the multicomponent and multidimensional composites with superior EMWs absorption.
Journal of Colloid and Interface Science, Volume 607, pp 192-202; https://doi.org/10.1016/j.jcis.2021.08.203
Strong absorption and large bandwidth are two contributors to materials’ absorbing performance. In this work, a series of multi-element core-shell magnetic nano-particle composite layered graphene absorbing materials CoFe2O4@C/rGO (CCr) were prepared by adjusting carbon shell thickness. The CCr at a low thickness achieved strong microwave absorption and a wide effective absorption bandwidth. Not only the core-shell structure of the magnetic nanoparticle CoFe2O4@C ([email protected]) increases the interface loss, but both the coating carbon shell and the core CoFe2O4 (CFO) are beneficial to improve impedance matching. Due to the synergistic effect of the dielectric and magnetic properties of graphene and ferrite, CCr possessed high absorption performance, and its minimum reflection loss reached (RLmin) -52.5 dB when the thickness was only 2 mm. At the same time, the effective absorption bandwidth (EAB) was 5.68 GHz when the thickness was only 1.7 mm. The chemically stable core-shell dielectric nanocomposite provided a new solution for preparing materials with excellent chemical structure and high absorbing properties.
Carbon, Volume 184, pp 223-231; https://doi.org/10.1016/j.carbon.2021.08.009
Constructing magnetic/dielectric composites with core-shell structure is an effective strategy for the development of high-efficiency microwave absorbers owing to the synergistic effect of multiple attenuation mechanisms. In this work, FeCo2O4 nanoparticles of 8 nm prepared by the nitrate decomposition method were used as the precursor, and the core-shell structured [email protected] nanocapsules with an average particle size of only 30 nm were fabricated through subsequent carbonization-reduction process. The [email protected] nanocapsules exhibit high-efficient microwave absorption performance. At an ultra-thin thickness of 1.6 mm, the minimum reflection loss (RL) value reaches up to −117.4 dB at 11.9 GHz. Notably, at the same thickness, the effective absorption bandwidth (RL ≤ −10 dB) is as wide as 9.2 GHz (8.8–18 GHz), covering almost the whole X and Ku bands. Moreover, the microwave absorption mechanism is revealed in detail through in-depth analysis of electromagnetic parameters. The outstanding microwave absorption capability is ascribed to the synergetic effect of strong magnetic loss of Co7Fe3 alloy cores and strong dielectric loss of amorphous carbon shells, as well as the superior impedance matching. It is believed that the core-shell structured [email protected] nanocapsules should be promising as high-efficiency microwave absorbers with thin thickness, strong absorption strength and broad absorption bandwidth.
Carbon, Volume 183, pp 100-107; https://doi.org/10.1016/j.carbon.2021.07.015
Graphene-based metal-free aerogel is desirable for lightweight electromagnetic wave (EMW) absorbing materials. However, the weak van-der-Waals combination between graphene sheets, accompanied by the repulsion from surface oxygen-related polar groups, significantly hinder the transfer of electrons between the sheets, and lead to poor mechanical strength. These become bottlenecks for the further improvement of EMW absorption and have a huge impact on achieving multi-functions. Here, we used an iodine modification strategy to fabricate reduced graphene oxide (RGO) aerogel, in which graphene sheets are bridged by iodine cations (I+). Meanwhile, iodine promotes the conversion of epoxy groups to hydroxyl groups on graphene, thereby facilitating the adhension of I+ on the surface. These iodine cations rather than iodine anions are essential to strengthen the interconnection between graphene sheets, which enables the RGO aerogel to exhibit higher electrical conductivity, larger mechanical strength, higher thermal stability, and significantly improved EMW absorbing capability. With the improvement in conduction loss and impedance matching, the iodine-bridged RGO aerogel exhibits a maximium reflection loss of −52.8 dB and an effective absorption bandwidth of 7.2 GHz at 2 wt% filler loading, which are 3.8 and 1.5 times of pure RGO, respectively. Besides, the improved mechanical strength and resistance to temperature change benefit expanding the application fields of this aerogel.
Materials Chemistry Frontiers, Volume 5, pp 5063-5070; https://doi.org/10.1039/d1qm00364j
MoS2/rGO nanocomposites are successfully prepared as enhanced electromagnetic wave absorbers, and the maximum reflection loss of −26.7 dB and effective absorption bandwidth of 5.05 GHz were obtained through regulating the filler loadings.