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Due to the limitations of impedance matching and attenuation matching, carbon nanotubes (CNTs) employed alone have a weak capacity to attenuate electromagnetic wave (EMW) energy. In this work, B and N co-doped CNTs with embedded Ni nanoparticles (Ni@BNCNTs) are fabricated via an in situ doping method. Compared with a sample without B doping, Ni@BNCNTs demonstrate a superior EMW absorption performance, with all minimum reflection loss values below −20 dB, even at a matching thickness of 1.5 mm. The experimental and theoretical calculation results demonstrate that B doping increases conduction and polarization relaxation losses, as well as the impedance matching characteristic, which is responsible for the enhanced EMW absorption performance of Ni@BNCNTs. [ABSTRACT FROM AUTHOR]

Three−dimensional (3D) hierarchical nano−microstructures have shown unprecedented physicochemical properties. However, it still remains great challenge to construct well−defined architectures with 3D hierarchical feature. Herein, we develop an electrospinning technique followed by a high−temperature carbonization process to fabricate N−doped carbon fibers (NCF) with N−doped carbon nanotubes (NCNTs) vertically grown on the surface of NCF using the Fe species as catalysts. In the 3D hierarchical structures, the Fe 3 C nanoparticles (NPs) are embedded within NCF matrix, while the Fe NPs are encapsulated within NCNT. Due to the unique structural feature, the as−prepared hierarchical structure exhibits excellent electromagnetic wave absorption performance with an absorption bandwidth of 4.0 GHz and a minimum reflection loss of −49.56 dB with a thickness as low as 1.50 mm. Experimental and theoretical studies indicate that the enhanced electromagnetic wave absorption performance of the hierarchical structure can be explained by the increased conduction loss induced by the introduction of metallic NPs and formation of 3D conductive networks, and the enhanced polarization loss caused by the additional interfaces and defects in the hierarchical structure. This work provides an efficient way to fabricate 3D architecture for high−efficiency electromagnetic wave absorption. [Display omitted] • The 3D hierarchical structure (Fe 3 C@NCF/Fe@NCNT) is synthesized. • In the structure, Fe 3 C NPs are embedded within NCF, while the Fe NPs are in NCNT. • Fe 3 C@NCF/Fe@NCNT exhibits good microwave absorption property with a low thickness. • The metals, interfaces and 3D networks are responsible for the absorption property. [ABSTRACT FROM AUTHOR]

It is highly desirable for electromagnetic wave (EMW) absorbers to have a low high filler ratio in matrix and low matching thickness. Herein, atomically dispersed Mn sites are introduced into N-doped carbon nanotubes (Mn−N x /NCNT) to this aim. Structural characterizations indicate that the as-fabricated Mn−N x /NCNT exhibits tubular morphology with a large surface area of 295.56 m2 g−1 and the Mn sites are atomically dispersed in the NCNT with a loading of 1.56 wt%. Benefiting from the unique structural advantages, Mn−N x /NCNT has excellent EMW absorption property, showing an effective absorption bandwidth of 4.15 GHz at a filler ratio of only 7% and a matching thickness of only 1.7 mm. The experimental measurements of electromagnetic parameters and density functional theory calculation results indicate that electronic structure and polarizability of the NCNTs are adjusted by the atomically dispersed Mn sites, leading to the increase in conduction and polarization losses of Mn−N x /NCNT, and thus in the EMW property. Our results demonstrate that hollow nanotubes containing metal single-atoms are potential EMW absorbers with a lightweight feature. [Display omitted] [ABSTRACT FROM AUTHOR]

Rational design of the morphology and structure is important for the functional materials to improve their physicochemical properties. Herein, we design hierarchically three-dimensional (3D) structures assembled with yolk-shelled spheres-supported nitrogen-doped CNTs (NCNTs) using Ni(OH) 2 @SiO 2 core-shelled spheres as precursors for electromagnetic wave absorption. In the 3D structures, the yolk materials are SiO 2 spheres, while the shell materials are N-doped carbon layers containing Ni, Si and O elements. Importantly, The NCNT arrays with encapsulated Ni NPs are branched out from the yolk-shelled spheres. The hierarchical structures feature the merits of both yolk-shelled and 3D structures. Furthermore, the SiO 2 sphere in the 3D structure can tune the electrical conductivity, affording our hierarchically 3D structure better impedance matching characteristic for electromagnetic wave absorption. As a result, the reflection loss and effective absorption bandwidth of our optimal 3D structure can reach −59.90 dB and 4.24 GHz, respectively, while the thickness of the absorbing film is only 1.4 mm, superior to most of reported carbon-based absorbers. The present method for the regulation of the structure and morphology provides an efficient way to construction of high-performance electromagnetic wave absorbers. [Display omitted] • Yolk-shelled sphere-supported nitrogen-doped carbon nanotubes were fabricated. • The hierarchical structures have the merits of both yolk-shelled and 3D structures. • SiO 2 sphere in the 3D structure can optimize impedance matching characteristic. • The absorption bandwidth of the sample is 4.24 GHz with a thickness of 1.4 mm. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have important application in electromagnetic wave absorption due to their unique tubular structure, lightweight feature and high electrical conductivity. However, sole CNTs suffer from bad impedance matching characteristic, leading to unsatisfactory absorption performance. Herein we propose a universal SiO 2 -assisted strategy to fabricate Ni nanoparticle-encapsulated nitrogen-doped CNTs on the SiO 2 spheres (Ni@NCNT@SiO 2). Due to the spatial separating effect, the formation of large metal aggregates and large-sized NCNTs in the products are avoided effectively. In the meanwhile, the ideal impedance matching characteristic is also achieved due to the introduction of the non-conductive SiO 2 spheres. As a result, even with a low matching thickness (1.3–2.0 mm), the reflection loss values of Ni@NCNT@SiO 2 reaches −30 dB. Furthermore, the proposed method can be also used to fabricate Fe 3 C/Fe@NCNT@SiO 2 and Co@NCNT@SiO 2 with satisfactory absorption properties, demonstrating its universality for synthesis of high-performance absorbers based on CNTs. Image 1 • A universal SiO 2 -assisted method is proposed to fabricate magnetic NP-embedded NCNTs. • The size and impedance matching characteristic of the NCNTs are tailored effectively. • The absorption bandwidth of the NCNTs is 4.14 GHz with a thickness of merely 1.5 mm. • The proposed method can be extended to design other high-performance absorbers. [ABSTRACT FROM AUTHOR]

Lightweight and low filler loading of electromagnetic wave absorption materials remain a huge challenge under the premise of strong absorption and broad absorption band. Here, we offer a facile strategy to prepare the ultralight self-supported N-doped reduced graphene oxide aerogels containing pod-like N-doped carbon nanotubes and FeNi@N-doped graphene layer core-shell nanoparticles for high-performance electromagnetic wave absorbing materials. The mass density of the ultralight aerogels is 0.0131 g cm−3, greatly lower than those of activated carbons. With a filling loading of only 10 wt% and the matching thickness of 2.0 mm, the minimal reflection loss of aerogels reaches −39.39 dB at 13.28 GHz. When the matching thickness is smaller than 2.0 mm (1.6–2.0 mm), the minimal reflection loss values of the optimized aerogels can still exceed −20 dB superior to most of reported electromagnetic wave absorption counterparts. Moreover, its maximum effective absorption bandwidth is up to 4.7 GHz at the matching thickness of merely 1.8 mm. The excellent performance of the ultralight bimetal-based aerogels mainly derives from increased dielectric loss, better matching impedance and larger specific surface area. It could be believed our designed ultralight self-supported aerogels can be promising candidates for lightweight absorbers with strong attenuation abilities. Image 1 [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) graphene-based structures have attracted much attention due to their unique physicochemical properties and potential applications in various fields. In this work, we develop a facile strategy for growing Co and Zn-contained nitrogen-doped carbon nanotubes on the graphene sheets for the absorption of electromagnetic wave (EMW). The as-fabricated 3D structures with a larger surface area have high electrical conductivities, abundant defects, numerous interfaces and porous feature, endowing them to excellent EMW absorption performance. The minimal reflection loss and efficient absorption bandwidth of the optimized 3D structure can reach to −47.31 dB and 4.01 GHz at a low thickness of merely 1.5 mm, respectively. Even at the thickness of 1.2–1.5 mm, the minimal reflection losses are less than −10 dB. Furthermore, the filler mass loading of the 3D structures is only 6 wt%, lower than those of most of the reported absorbers. Our results highlight the importance of 3D structures composed of graphene and nitrogen-doped carbon nanotubes to high-efficiency EMW absorption. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Nitrogen-doped carbon sheets containing Fe 3 C nanoparticles encapsulated in nitrogen-doped graphene shells are fabricated through heating the mixture of urea and ferric acetylacetonate and the subsequent treatment in hot acid solution. The nitrogen-doped carbon sheets have a lateral length ranging from hundred nanometers to several micrometers, while the Fe 3 C nanoparticles encapsulated in nitrogen-doped graphene have a diameter of approximately 60 nm. The nitrogen-doped carbon sheets exhibit excellent electromagnetic wave absorption property. Typically, the optimal sample has the effective absorption bandwidth of 6.0 GHz at the absorber thicknesses of only 2.0 mm, favorably comparable to those of the magnetic absorbers reported previously. The excellent electromagnetic wave absorption property of nitrogen-doped carbon sheets containing Fe 3 C nanocapsules encapsulated in the nitrogen-doped graphene shells can be explained by their better impedance matching character and enhanced dielectric loss. Graphical abstract The optimal sample has the effective absorption bandwidth of 6.0 GHz at the absorber thicknesses of only 2.0 mm. Image 1 [ABSTRACT FROM AUTHOR]

Hierarchical and hollow heteronanostructures had attached wide attention in electromagnetic wave (EMW) absorption fields due to their adjustable impedance matching and loss property. However, fabrication of well-defined heteronanomaterials with hierarchical and hollow features is challenging. Here, we develop a simple method to prepare N-doped carbon hollow spheres supported by N-doped carbon nanotubes (Ni@NCNT/NCHSs). Due to the hierarchical and hollow features, the Ni@NCNT/NCHSs exhibit high-efficiency EMW absorption performance. With a thickness only 1.6 mm, the optimized heteronanostructure has an RL min of −64.75 dB and an EAB of 4.17 GHz. The experimental results demonstrate that the hierarchical and hollow heteronanostructures have significantly enhanced dielectric loss and conductive loss of the Ni@NCNT/NCHSs as well as the impedance matching characteristics, which are responsible for their enhanced EMW absorption performances. This work presents an effective method to synthesize hierarchical and hollow heteronanostructures for high-performance EMW absorption. [Display omitted] • N-doped CNTs were prepared and supported by N-doped hollow carbon sphere for electromagnetic wave absorption. • The hierarchical and heteronanostructures are beneficial to enhance the interfacial loss. • The hollow carbon sphere reduces the material density and improves the impedance matching characteristics. • The NCNT/NCHS shows good absorption performance with a filling load of only 15 wt%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unique nanostructure microwave absorber with ultrasmall magnetic particles was prepared. • A reflection loss of –41.08 dB at a matching thickness of 2.0 mm was achieved. • The effective absorption bandwidth of the designed absorbers reached 4.26 GHz. • The origin of increased microwave absorption performance has been explored. • The microwave absorption ability under actual conditions of absorbents has been considered. It is desirable but challenging to integrate 0D, 1D and 2D materials into 3D nanostructures for the microwave absorption. Herein, short and thin N-doped carbon nanotubes (NCNTs) encapsulated with sub-2-nm magnetic Co particles grafted on hollow nanoplates (HCNP) are fabricated after ZIF-67 nanoplates were annealed at a lower temperature relative to conventional chemical vapor deposition methods. The as-fabricated HCNP/NCNT assembled with 0D, 1D and 2D nanostructures features 3D interconnected open structure, endowing them with abundant interfaces and defects that facilitate its microwave absorption. The minimum reflection loss (RL min) of −41.08 dB with a thickness of 2 mm and effective absorption bandwidth (EAB) of 4.26 GHz with a thickness of 1.8 mm were achieved by the HCNP/NCNT, superior to the counterparts without NCNTs. Besides its unique structural feature, density functional theory (DFT) calculations demonstrate that the increased microwave absorbability of the HCNP/NCNT is also relevant to the additional dipole polarization and interfacial polarization caused by the NCNTs. Based on the computer simulation technology (CST) results, the HCNP/NCNT can attenuate microwave energy under the actual conditions. The proposed controllable synthesis method may open a new avenue for the reasonable design of high-performance microwave absorbers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexible and waterproof NCNT arrays on carbon fiber (NCNT@CF) were fabricated. • NCNT@CF exhibited excellent EMW absorption performances. • The R L,min value and EAB 10 of NCNT@CF are − 57.8 dB and 4.5 GHz, respectively. • RCS values of the materials were simulated under real far field conditions. • NCNT@CF had flexible, waterproof, and electric-thermal conversion functions. It is highly desirable, but challenging to develop multi-functional electromagnetic wave (EMW) absorbing material for practical applications in some special environments. Herein, we successfully fabricated cobalt-nanoparticle-embedded N-doped carbon nanotube arrays on the carbonized cotton fiber cloth as multifunctional material with an excellent EMW absorption, flexibility, hydrophobicity, and electric-thermal performance. The excellent multifunction benefits from high conductivity, large specific surface area, abundant N dopants, and three-dimensional open porous features. Minimal reflection loss and efficient absorption bandwidth of the optimized material as EMW absorbers can reach − 57.8 dB and 4.5 GHz, respectively, which are better than most reported carbon-based absorbers. Meanwhile, theoretical simulations of the radar cross-sectional (RCS) further confirm that the multifunctional material has excellent EMW attenuation performance and potential in practical application. Moreover, the materials possess strong hydrophobicity and high electrical conductivity, endowing them with other attractive functions of self-cleaning and good electric thermal performance, which expand the potential applications range of EMW absorption materials. Our present method can be extended to design next-generation EMW absorbing materials with multifunctionalities for practical applications in harsh environments. [ABSTRACT FROM AUTHOR]

Micro-nanospheres assembled with helically coiled nitrogen-doped carbon nanotube (HNCNT) are successfully fabricated using CoZn double hydroxide nanosheets as substrates and catalytic precursors and dicyandiamide as carbon and nitrogen sources. The micro-nanospheres have diameters of 3–5 μm, composed of helically coiled NCNTs with diameters of 40–100 nm. The metallic Co NPs covered with graphene shell were encapsulated in HNCNTs. Experimental results demonstrate that both Co and Zn are important to the formation of the specially coiled NCNTs. The optimized micro-nanostructures exhibit excellent microwave absorption property with a minimal reflection loss of −44.2 dB at the thickness of absorber film (d) of only 1.7 mm, and efficient absorption bandwidth (reflection loss less than −10 dB) of 4.8 GHz at d of 2.0 mm. Furthermore, even at a thin thickness (1.5–2.0 mm) the minimal reflection losses of the optimized micro-nanostructures can reach −10 dB. The enhanced microwave absorption property can be explained by increased dielectric loss caused by defects and N dopants, better impedance matching characteristic, and the unique helically coiled structure. Image 1 • Micro-nanospheres assembled with helically coiled carbon nanotube are designed. • Both cobalt and zinc are important to produce the coiled carbon nanotubes. • Nitrogen-doping, single atom sites and defects are formed in carbon nanotubes. • The micro-nanospheres have excellent microwave absorption property. [ABSTRACT FROM AUTHOR]