Preparation of cellulose derived carbon/reduced graphene oxide composite aerogels for broadband and efficient microwave dissipation.

The development of cellulose derived carbon-based composite aerogels with light weight, broad bandwidth and strong absorption remains a challenging task. In this work, the cellulose derived carbon/reduced graphene oxide composite aerogels were prepared by a two-stage process of chemical crosslinking and high-temperature carbonization. The results revealed that the as-fabricated binary composite aerogels had a unique lightweight characteristic and three-dimensional porous network structure, which was chemically crosslinked by epichlorohydrin. Furthermore, the weight concentration of graphene oxide (GO) had a notable influence on the electromagnetic parameters and microwave absorption properties of the composite aerogels. The obtained binary composite aerogel possessed the optimal microwave dissipation capability when the concentration of GO was 1.5 mg/mL. Remarkably, the minimum reflection loss reached -50.42 dB at a thickness of 2.47 mm and a filling ratio of 17.5 wt%. Concurrently, the composite aerogel with a comparable thickness of 2.73 mm showed a wide effective absorption bandwidth of 7.28 GHz, spanning the total Ku-band and extending into a portion of the X-band. The radar cross section contribution of binary composite aerogels in the far-field was also simulated by computer simulation technique. In addition, the potential microwave attenuation mechanism was proposed. It was believed that the results of this paper would offer a reference for the preparation of cellulose derived carbon-based composite aerogels as efficient and broadband microwave absorbers.

Lightweight and efficient luffa sponge carbon/Co composites with adjustable electromagnetic wave absorption properties.

Biomass material has gained significant popularity due to its potential to meet the requirements of green and sustainable development in modern times. It is widely used in various fields, especially for absorbing electromagnetic waves (EMW). In this study, we used luffa sponge carbon (CLS) as a lightweight and porous carbon source. Through a static reaction and heat treatment process, we successfully loaded coral sheet cobalt onto the surface of CLS to create lightweight and efficient luffa sponge carbon/cobalt (CLS/Co) composites for EMW absorption. We controlled the microstructure and electromagnetic properties of the CLS/Co composites by adjusting the pyrolysis temperature. At 700 °C, the CLS/Co composites showed a minimum reflection loss (RLmin) of -60.81 dB and an effective absorption bandwidth (EAB) of 5.56 GHz at a very thin thickness of 1.68 mm. Moreover, at a pyrolysis temperature of 800 °C, the absorption strength of the CLS/Co composites reached -50 dB at various thicknesses.

Existence of Radial Global Smooth Solutions to the Pressureless Euler-Poisson Equations with Quadratic Confinement.

We consider the pressureless Euler-Poisson equations with quadratic confinement. For spatial dimension d≥2,d≠4, we give a necessary and sufficient condition for the existence of radial global smooth solutions, which is formulated explicitly in terms of the initial data. This condition appears to be much more restrictive than the critical-threshold conditions commonly seen in the study of Euler-type equations. To obtain our results, the key observation is that every characteristic satisfies a periodic ODE system, and the existence of a global smooth solution requires the period of every characteristic to be identical.

Synthesis of hollow CuFe2O4 microspheres decorated nitrogen-doped graphene hybrid composites for broadband and efficient electromagnetic absorption.

The development of graphene-based electromagnetic wave (EMW) absorbers with broad bandwidth, strong absorption and low filling ratio remains a big challenge. In this work, hollow copper ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/hollow CuFe2O4) hybrid composites were prepared by a two-step route of solvothermal reaction and hydrothermal synthesis. Results of microscopic morphology analysis showed that the NRGO/hollow CuFe2O4 hybrid composites had a special entanglement structure between hollow CuFe2O4 microspheres and wrinkled NRGO. Moreover, the EMW absorption properties of as-prepared hybrid composites could be regulated by changing the additive amounts of hollow CuFe2O4. It was worth noting that when the additive amount of hollow CuFe2O4 was 15.0 mg, the attained hybrid composites showed the optimal EMW absorption performance. The minimum reflection loss reached up to -34.18 dB at a thin matching thickness of 1.98 mm and a low filling ratio of 20.0 wt%, and the corresponding effective absorption bandwidth was as large as 5.92 GHz, covering almost the whole Ku band. Furthermore, when the matching thickness was increased to 3.02 mm, the EMW absorption capacity was significantly enhanced, and the optimal reflection loss value of -58.45 dB was achieved. In addition, the possible EMW absorption mechanisms were proposed. Therefore, the structural design and composition regulation strategy presented in this work would provide a great reference value for the preparation of broadband and efficient graphene-based EMW absorbing materials.

Carbon cloth based flexible electromagnetic wave absorbing materials loaded with Co3O4 array and tunable electromagnetic wave absorption performance.

The demand for flexible electromagnetic wave (EMW) absorbing materials has increased, highlighting the importance of designing efficient and adaptable EMW absorbing materials. In this study, flexible Co3O4/carbon cloth (Co3O4/CC) composites with high EMW absorption properties were prepared via a static growth method and annealing process. The composites exhibited remarkable properties, with the minimum reflection loss (RLmin) and maximum effective absorption bandwidth (EAB, RL ≤ -10 dB) of -54.43 dB and 4.54 GHz, respectively. The flexible carbon cloth (CC) substrates exhibited outstanding dielectric loss due to their conductive networks. Moreover, the uniformly and tightly organized Co3O4 arrays on the flexible CC substrate played a crucial role in fine-tuning the impedance matching and facilitating abundant multiple scattering and interface polarization. This study proposes a promising approach to preparing flexible Co3O4/CC composites with a significant reference value for the field of flexible EMW.

Construction of porous carbon-based magnetic composites derived from iron zinc bimetallic metal-organic framework as broadband and high-efficiency electromagnetic wave absorbers.

The fabrication of broadband and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge. Metal-organic framework (MOF) with large porosity and high specific surface area has been considered as a promising precursor for the preparation of novel EM wave absorbers. In this work, porous carbon-based magnetic composites derived from iron zinc bimetallic MOF were prepared by the two-step method of solvothermal reaction and high-temperature pyrolysis. Results of micromorphology analysis demonstrated that the morphology of carbon frameworks evolved from octahedron, polyhedron, sphere to porous sphere-like shape with the increase of pyrolysis temperature. Furthermore, the EM parameters and absorbing properties of obtained composites were regulated through simply changing the pyrolysis temperature. It was noteworthy that the as-prepared Fe3O4/C composite pyrolyzed at 700 °C exhibited the best EM absorption performance. The minimum reflection loss was as large as -60 dB and broad absorption bandwidth reached up to 4 GHz (8-12 GHz, covering the whole X band) at a matching thickness of 2.5 mm and a filler loading ratio of 40 wt%. Furthermore, the maximum absorption bandwidth could be enlarged to 5.4 GHz via reducing the matching thickness to 1.85 mm. Additionally, the probable EM attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of porous carbon-based composites as broadband and high-efficiency EM wave absorbers.

Synthesis of FeCoNi/C decorated graphene composites derived from trimetallic metal-organic framework as ultrathin and high-performance electromagnetic wave absorbers.

High-temperature pyrolysis of metal-organic framework (MOF) is an effective way to prepare lightweight and high-performance electromagnetic wave absorbers. In this work, iron cobalt nickel/carbon (FeCoNi/C) decorated graphene composites were fabricated by the two-step method of solvothermal reaction and pyrolysis treatment. Results of micromorphology analysis demonstrated that numerous octahedral FeCoNi/C carbon frameworks were almost uniformly distributed on the wrinkled surfaces of flaky graphene. Moreover, the electromagnetic parameters and wave absorbing properties of obtained composites were regulated through simply changing the addition amounts of graphene oxide. Significantly, the as-prepared FeCoNi/C decorated graphene composite with the addition amount of graphene oxide of 67.2 mg exhibited the best electromagnetic absorption performance. The minimum reflection loss was as large as -66 dB at 15.6 GHz and broad absorption bandwidth reached up to 4.8 GHz with an ultrathin thickness of 1.53 mm and a filler loading ratio of 30 wt%. Furthermore, the maximum absorption bandwidth was enlarged to 5.2 GHz via slightly adjusting the matching thickness to 1.56 mm. Additionally, the probable electromagnetic attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of MOF derived carbon-based magnetic composites as ultrathin and high-performance electromagnetic absorbers.

Fabrication of nitrogen-doped reduced graphene oxide/hollow copper ferrite composite aerogels as lightweight, thin and high-efficiency electromagnetic wave absorbers in the X band.

The development of lightweight, thin and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge in the field of EM absorption. Graphene aerogels with three-dimensional (3D) network structure and low bulk density have been considered as potential EM absorbing materials. In this work, nitrogen-doped reduced graphene oxide/hollow copper ferrite (NRGO/hollow CuFe2O4) composite aerogels were fabricated by the three-step method of solvothermal reaction, hydrothermal self-assembly and calcination treatment. The as-prepared composite aerogels had a unique 3D hierarchical porous network structure. Furthermore, results demonstrated that the EM absorption performance of attained composite aerogels could be improved by adjusting the calcination temperature. Notably, the obtained composite aerogel calcined at 400.0 ℃ exhibited the best EM absorption performance. When the loading ratio was as low as 15.0 wt%, the minimum reflection loss reached up to -54.5 dB with a matching thickness of 2.0 mm, and the maximum effective absorption bandwidth of 5.0 GHz could be achieved under an extremely thin thickness of 1.6 mm. Additionally, the probable EM attenuation mechanisms of attained composite aerogels were proposed. The results of this work could be helpful for developing graphene-based 3D composites as lightweight, thin and high-efficiency EM wave absorbers.

In-situ synthesis of graphite carbon nitride nanotubes/Cobalt@Carbon with castor-fruit-like structure as high-efficiency electromagnetic wave absorbers.

The increasingly electromagnetic wave (EMW) pollution has rendered the study and development of new, high-efficiency EMW absorbers a sought-after topic. In this study, graphite carbon nitride nanotubes/cobalt@carbon (GCNNs/Co@C) composites were fabricated using an in-situ synthesis method, which included facile grinding and carbonization pyrolysis. The synthesized GCNNs/Co@C composites exhibited a unique castor-fruit-like structure, that is, GCNNs formed an entwined three-dimensional (3D) network structure on the surface of cobalt@carbon (Co@C), which improved the EMW absorption properties of composites. The obtained GCNNs/Co@C composites exhibited excellent EMW absorption performance. For the fabricated GCNNs/Co@C composites, the minimum reflection loss (RLmin) value reached -63.90 dB at a thickness of 1.96 mm, and the effective absorption bandwidth (EAB, RL ≤  -10 dB) achieved 4.44 GHz at an ultra-thin thickness of 1.51 mm. The EAB covered the entire X and Ku bands (6.96-18.00 GHz) through thickness adjustment from 1.51 to 2.50 mm. Underlying EMW absorption mechanisms were briefly discussed. This study presents a novel design method to prepare light-weight and highly-efficient EMW absorbing absorbers.

In-situ hydrothermal synthesis of NiCo alloy particles@hydrophilic carbon cloth to construct corncob-like heterostructure for high-performance electromagnetic wave absorbers.

NiCo alloy particles (NiCo-APs)@hydrophilic carbon cloth (HCC) composites were successfully prepared by uniformly decorating magnetic NiCo-APs on the surface of three-dimensional HCC by employing an in-situ hydrothermal method. The NiCo-APs@HCC composites exhibited a unique corncob-like network structure that helped improve the electromagnetic wave (EMW) absorption performance of composites. The EMW absorption properties of the composites could be controlled by altering the Ni/Co molar ratio. The optimal minimum reflection loss (RLmin) of -41.80 dB was achieved with the NiCo-APs@HCC composite thickness of 2.29 mm. The effective absorption bandwidth (EAB) reached the maximum of 5.8 GHz, spanning nearly the entire Ku band. In addition, the improved EMW absorption performance was further promoted by favorable impedance matching, strong conduction loss, magnetic loss, dipole polarization, interface polarization, multiple reflections, and scattering. A novel strategy for designing magnetic metal/carbon matrix composites with excellent EMW absorption performance is reported in this study.

Constructing interpenetrating structured NiCo2O4/HCNT composites with heterogeneous interfaces as low-thickness microwave absorber.

Low matching thickness, broad effective absorption bandwidth (EAB, RL < -10 dB) and excellent reflection loss (RL) are desirable properties for the advanced microwave absorption materials (MAMs). We synthesized novel interpenetrating structured rod-like nickel cobaltite (NiCo2O4)/helical carbon nanotubes (HCNT) composites using the facile hydrothermal technique and heat-treatment process. Owing to the optimum structural design and electromagnetic parameter regulation, the NiCo2O4/HCNT composites displayed outstanding microwave absorption (MA) across regions of low thickness. When the thickness was only 1.35 mm, the optimized RL and EAB reached -55.9 dB and 4.8 GHz (13.2-18.0 GHz), respectively. Furthermore, the EAB was 10 GHz as the corresponding thickness was regulated with 1.35-2.10 mm, covering both X and the Ku bands. Multiple reflection and scattering, natural resonance, eddy current loss, strong conduction loss, interface polarization, cross-poalarization, and dipolar polarization can be considered to improve MA. Our study proposes a simple approach of synthesizing low-thickness MAMs based on NiCo2O4 and HCNT.

Fabrication of bimetallic metal-organic frameworks derived cobalt iron alloy@carbon-carbon nanotubes composites as ultrathin and high-efficiency microwave absorbers.

Developing lightweight and high-efficiency microwave absorbents derived from metal-organic frameworks (MOFs) was proven to be a promising strategy to solve the increasingly serious problem of electromagnetic radiation pollution. In this work, nitrogen-doped cobalt iron alloy@carbon-carbon nanotubes (CoFe alloy@C-CNTs) composites were fabricated through an aging and pyrolysis two-step method. Results revealed that the attained composites presented a unique four-pointed star morphology and lots of CoFe alloy nanoparticles were uniformly embedded into the porous carbon matrix. Moreover, it was found that the pyrolysis temperature had a notable effect on the microwave absorption properties of CoFe alloy@C-CNTs composites. Remarkably, the obtained composite under 700.0 °C pyrolysis treatment showed the optimal minimum reflection loss of -54.5 dB with an ultrathin thickness of 1.4 mm and maximum effective absorption bandwidth of 5.0 GHz at a low thickness of 1.6 mm. Additionally, the possible electromagnetic attenuation loss mechanisms of attained composites were illuminated. It was believed that our results could be helpful for fabricating ultrathin and high-performance microwave absorbing materials derived from MOFs.

Fabrication of ultralight nitrogen-doped reduced graphene oxide/nickel ferrite composite foams with three-dimensional porous network structure as ultrathin and high-performance microwave absorbers.

The development of lightweight and high-performance microwave absorbers is still a challenge in the field of electromagnetic absorption. Graphene foam with three-dimensional (3D) network structure and low bulk density has been considered as an ideal candidate for microwave absorption. In this work, nitrogen-doped reduced graphene oxide/nickel ferrite composite foams were prepared by the solvothermal and hydrothermal two-step method. The as-prepared composite foams had very low bulk density (7.8 âˆ¼ 10.0 mg·cm-3) and a unique 3D porous network structure. Furthermore, results revealed that the microwave absorption performance of attained composite foams could be improved by adjusting the calcination temperature. Significantly, the obtained composite foam exhibited the best microwave absorption performance when calcined at 650.0 °C for 2.0 h. The minimum reflection loss was as large as -60.6 dB at an ultrathin matching thickness of only 1.55 mm, and the effective absorption bandwidth could reach 5.5 GHz with a thin thickness of 1.62 mm. In addition, the possible microwave attenuation mechanisms of attained composite foams were proposed. It was believed that our results could be helpful for developing graphene-based 3D magnetic composites as lightweight and high-performance microwave absorbers.

Preparation of FeNi/C composite derived from metal-organic frameworks as high-efficiency microwave absorbers at ultrathin thickness.

Developing metal-organic frameworks (MOFs) derived microwave absorbers with the merits of thin matching thickness, broad bandwidth and strong absorption still remains a big challenge in the electromagnetic absorption field. Herein, FeNi-MOFs derived magnetic-carbon composites were fabricated via a solvothermal and pyrolytic two-step strategy. It was found that the micromorphology of carbon frameworks could be regulated from the regular octahedron to spherical shape through facilely adjusting the molar ratios of Fe3+ to Ni2+ in the precursors. Furthermore, results revealed that the molar ratios of Fe3+ to Ni2+ had notable effects on the electromagnetic parameters and microwave attenuation capacity of attained composites. Significantly, the obtained FeNi/C composite with the molar ratio of Fe3+ to Ni2+ of 1:0.5 showed the comprehensively optimal electromagnetic attenuation performance, i.e. the reflection loss achieved -40.2 dB (larger than 99.99% absorption) and absorption frequency band was as high as 5.8 GHz (from 11.9 to 17.7 GHz, covering 96.7% of Ku-band) under an ultrathin thickness of 1.65 mm. Besides, the probable microwave dissipation mechanisms were clarified, which mainly derived from the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, enhanced conduction loss and natural resonance effect. Therefore, our results would be helpful for designing and developing high-performance microwave absorbing composites derived from MOFs.

Synthesis of three-dimensional porous netlike nitrogen-doped reduced graphene oxide/cerium oxide composite aerogels towards high-efficiency microwave absorption.

Three-dimensional (3D) graphene aerogels with porous structure and lightweight feature have been regarded as promising candidates for microwave attenuation. Herein, nitrogen-doped reduced graphene oxide/cerium oxide (NRGO/CeO2) composite aerogels were fabricated via a hydrothermal route. The obtained composite aerogels possessed low bulk density and unique 3D porous netlike structure constructed by the stacking of lamellar NRGO. Moreover, it was found that the microwave dissipation performance of NRGO aerogel could be notably improved through complexing with CeO2 nanoparticles and carefully regulating the contents of CeO2 in the composite aerogels. Remarkably, the attained NRGO/CeO2 composite aerogel with the content of CeO2 of 44.11 wt% presented the comprehensively excellent microwave attenuation capacity, i.e. the optimal reflection loss reached -50.0 dB (larger than 99.999% absorption) at a thickness of 4.0 mm and wide bandwidth achieved 5.7 GHz (from 12.3 GHz to 18.0 GHz, covering 95.0% of Ku-band) under an ultrathin thickness of only 1.9 mm. Furthermore, the probable microwave dissipation mechanisms of as-synthesized composite aerogels were clarified, which included the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, notable oxygen vacancy effect and enhanced conduction loss. This work could shed light on developing graphene-based 3D broadband microwave absorption composites.

Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers.

Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe2O4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9-13.5 mg·cm-3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached -40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites.

Fabrication of three-dimensional nitrogen-doped reduced graphene oxide/tin oxide composite aerogels as high-performance electromagnetic wave absorbers.

Developing light-weight and high-efficiency electromagnetic wave (EMW) absorbers has been considered as an effective strategy to resolve the electromagnetic radiation pollution problem. Herein, nitrogen-doped reduced graphene oxide/tin oxide (NRGO/SnO2) composite aerogels were facilely prepared through the hydrothermal process and subsequent lyophilization treatment. Morphological characterization results manifested that the attained NRGO/SnO2 composite aerogels possessed unique three-dimensional (3D) porous network structure constituted by the tiny SnO2 nanoparticles decorated wrinkled surfaces of flake-like NRGO. Moreover, excellent EMW absorption performance could be achieved through facilely regulating the additive volumes of ethylenediamine and filler contents. Impressively, the composite aerogel with a doped nitrogen concentration of 6.5 wt% displayed the optimal minimum reflection loss of -62.3 dB at a matching thickness of 3.5 mm and the broadest effective absorption bandwidth of 5.1 GHz under an ultrathin thickness of merely 1.6 mm. Furthermore, the as-synthesized composite aerogels showed a light-weight characteristic with the low bulk density of 19.9-25.7 mg·cm-3. Additionally, the potential EMW absorption mechanisms of obtained composite aerogels were revealed, which were mainly ascribed to the unique 3D porous network structure, synergistic effects between conduction loss and polarization loss, as well as the balanced attenuation loss and impedance matching. This work could be valuable for the structural design and fabrication of 3D graphene-based dielectric composites as light-weight and high-efficiency EMW absorbers.

Synthesis of ultralight three-dimensional nitrogen-doped reduced graphene oxide/multi-walled carbon nanotubes/zinc ferrite composite aerogel for highly efficient electromagnetic wave absorption.

Developing light-weight, thin thickness and high-efficiency electromagnetic wave (EMW) absorbers was regarded as an effective strategy for dealing with the increasingly serious problem of electromagnetic radiation pollution. Herein, nitrogen-doped reduced graphene oxide/multi-walled carbon nanotubes/zinc ferrite (NRGO/MWCNTs/ZnFe2O4) composite aerogel was synthesized via solvothermal followed by hydrothermal and lyophilization processes. Morphological characterization results manifested that the attained ternary composite aerogel displayed unique three-dimensional porous netlike structure, which was composed of partial stack of adjacent NRGO sheets entangled by MWCNTs and decorated with ZnFe2O4 microspheres. Moreover, the influences of complexing with conductive MWCNTs and magnetic ZnFe2O4, and filler contents on the EMW attenuation performance of ternary composite aerogel were examined. Significantly, the ternary composite aerogel exhibited notably strengthened EMW absorption capacity in comparison with NRGO/MWCNTs composite aerogel, NRGO aerogel and ZnFe2O4 microspheres. The minimum reflection loss (RLmin) was up to -52.6 dB at a thin matching thickness of 1.7 mm and effective absorption bandwidth (EAB) was 5.1 GHz (12.7-17.8 GHz) under an ultrathin thickness of 1.65 mm with a low filler content of 10 wt%. Remarkably, the |SRLmin| (|specific RLmin value per thickness|) could achieve 30.9 dB/mm, which overwhelmed almost all the reported RGO-based composite aerogels. Besides, the possible EMW absorption mechanisms of as-synthesized ternary composite aerogel were proposed. It was believed that our results provided a valuable guidance for fabricating graphene-based composites with three-dimensional netlike structure as light-weight, thin thickness and high-performance EMW absorbers.

Synthesis of nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite composite aerogels with superior compression recovery and electromagnetic wave absorption performance.

Graphene aerogels possessing a three-dimensional (3D) porous netlike structure, good electrical conductivity and ultralow density have been widely regarded as a promising candidate for high-efficiency electromagnetic wave (EMW) absorption. Herein, nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite (NRGO/Co0.5Zn0.5Fe2O4) composite aerogels were synthesized through a solvothermal and subsequent hydrothermal self-assembly two-step method. The results of micromorphology analysis showed that the 3D networks were well constructed through the partial stacking of adjacent NRGO sheets, which were decorated with numerous Co0.5Zn0.5Fe2O4 microspheres. The as-synthesized NRGO/Co0.5Zn0.5Fe2O4 composite aerogels have a very low density (12.1-14.6 mg cm-3) and good compression recovery. Moreover, excellent EMW absorption performance could be achieved through facilely regulating the additive volume of ethylenediamine (i.e. nitrogen doping contents) and filler contents. Impressively, the composite aerogel with a doped nitrogen content of 2.5 wt% displayed the optimal minimum reflection loss (RLmin) of -66.8 dB in the X-band at a thickness of 2.6 mm and the broadest effective absorption bandwidth of 5.0 GHz under an ultrathin thickness of merely 1.6 mm. Meanwhile, the RLmin of NRGO/Co0.5Zn0.5Fe2O4 composite aerogels below -20 dB could be reached in almost the whole tested thickness range (1.4-5.0 mm). Additionally, the potential EMW absorption mechanisms were revealed, which was mainly due to the unique 3D porous netlike structure, synergistic effects among conduction loss, magnetic resonance loss and polarization loss, as well as the balanced attenuation capacity and impedance matching. It was believed that this work provided an alternative way for fabricating strong mechanical graphene-based 3D magnetic/dielectric composites as light-weight and high-efficiency EMW absorbers.

Facile synthesis of nitrogen-doped reduced graphene oxide/nickel ferrite hybrid nanocomposites with superior electromagnetic wave absorption performance in the X-band.

In this work, nitrogen-doped reduced graphene oxide/nickel ferrite (NRGO/NiFe2O4) hybrid nanocomposites were synthesized by a one-pot hydrothermal method. Results manifested that the as-synthesized NiFe2O4 nanoparticles displayed hexagonal morphology with a mean size of 40 nm. Moreover, it was found that the entangled structure consisting of crumpled RGO and hexagonal NiFe2O4 nanoparticles was well constructed in the as-fabricated hybrid nanocomposites. Furthermore, the additive volumes of hydrazine hydrate and filler loadings had significant influences on the electromagnetic wave (EMW) absorption properties of obtained nanocomposites. Remarkably, the NRGO/NiFe2O4 hybrid nanocomposite with 15 mL additive volume of hydrazine hydrate showed the optimal reflection loss of -54.4 dB at 9.2 GHz (X band) under a matching thickness of 2.2 mm and maximum absorption bandwidth of 4.5 GHz (13.5-18 GHz) at a very thin thickness of only 1.5 mm. The dual absorption peaks located at the low and high frequency regions could be achieved by facilely modulating the matching thicknesses. In addition, the underlying EMW absorption mechanisms were uncovered. Therefore, our results could shed light on the design and fabrication of graphene-based dielectric/magnetic hybrid composites as light-weight and high-efficiency EMW absorbers.