Excellent Electromagnetic Absorption Capability of Ni/Carbon Based Conductive and Magnetic Foams Synthesized via a Green One Pot Route

Plasma-assisted doping of pyrolyzed corn husk strengthened by MoS2/polyethersulfone for fascinating microwave absorbing/shielding and energy saving properties

To address the ever-increasing electromagnetic pollution, numerous efforts have been made. In this case, biomass-derived materials as green, affordable, lightweight, capable, and sustainable microwave-absorbing materials have become a research hotspot; meanwhile, transition metal-based microwave absorbers and sulfide structures as polarizable electromagnetic absorbers have intrigued researchers. Alternatively, plasma treatment as a novel strategy has been applied in different fields, and doping strategies are in the spotlight to modify the microwave-absorbing features of materials. Thus, herein, corn husk biomass was pyrolyzed and doped with N via plasma treatment, followed by coating with MoS2 nanoflowers to promote its microwave-absorbing characteristics. More interestingly, the influence of absorbing media was carefully evaluated using polyethersulfone (PES) and polyethylene (PE) as polymeric matrices. The as-developed MoS2/N-doped pyrolyzed corn husk (PCH) demonstrated outstanding electromagnetic interference shielding effectiveness (EMISE) based on its absorption covering the entire K-band frequency with ≈100% shielding, a fascinating reflection loss (RL) of -95.32 dB at 21.28 GHz, and outstanding efficient bandwidth (EBW) of 7.61 GHz (RL ≤ -10) with a thickness of only 0.45 mm. It is noteworthy that the energy-saving features of the final composites were precisely investigated using an infrared (IR) absorption approach.

Large Microsphere Structure of a Co/C Composite Derived from Co-MOF with Excellent Wideband Electromagnetic Microwave Absorption Performance

In the field of electromagnetic wave (EMW) absorption, carbon matrix materials based on metal-organic frameworks (MOFs) have drawn more interest as a result of their outstanding advantages, such as porous structure, lightweight, controlled morphology, etc. However, how to broaden the effective absorption bandwidth [EAB; reflection loss (RL) ≤ -10 dB] is still a challenge. In this paper, large microsphere structures of a Co/C composite composed of small particle clusters were successfully prepared by the solvothermal method and annealing treatment. At a filling ratio of 40 wt %, the Co/C composite shows attractive microwave absorption (MA) performance after being annealed at 600 °C in an atmosphere of argon. With an EAB of 6.32 GHz (9.92-16.24 GHz) and a thickness of just 2.57 mm, the minimum RL can be attained at -54.55 dB. Most importantly, the EAB can attain 7.12 GHz (10.88-18.0 GHz) when the thickness is 2.38 mm, which is larger than that of the majority of MOF-derived composites. The superior MA performance is strongly related to excellent impedance matching and a higher attenuation constant. This study provides a simple strategy for synthesizing a MOF-derived Co/C composite with a wide EAB.

High-Temperature, Lightweight Ceramics with Nano-Sized Ferrites for EMI Shielding: Synthesis, Characterisation, and Potential Applications

The present study focuses on the synthesis and characterisation of a lightweight ceramic material with electromagnetic interference (EMI) shielding properties, achieved using mullite containing micrometre-sized hollow spheres (cenospheres) and CoFe2O4 nanoparticles. This research explores compositions with varying CoFe2O4 contents ranging from 0 up to 20 wt.%. Conventional sintering in an air atmosphere is carried out at a temperature between 1100 and 1300 °C. The addition of ferrite nanoparticles was found to enhance the process of sintering cenospheres, resulting in improved material density and mechanical properties. Furthermore, this study reveals a direct correlation between the concentration of ferrite nanoparticles and the electromagnetic properties of the material. By increasing the concentration of ferrite nanoparticles, the electromagnetic shielding effect of the material (saturation magnetisation (Ms) and remanent magnetisation (Mr)) was observed to strengthen. These findings provide valuable insights into designing and developing lightweight ceramic materials with enhanced electromagnetic shielding capabilities. The synthesized ceramic material holds promise for various applications that require effective electromagnetic shielding, such as in the electronics, telecommunications, and aerospace industries.

Preparation of MXene/BN Composites with Adjustable Microwave Absorption Performance

The challenge of developing a high-efficiency microwave absorbent remains, because of the compatibility between microwave absorption and high-temperature-resistant performance in practical application. Herein, a facile method is used to obtain serial MXene/BN-zxy composites, where zx:y indicates the weight ratio of MXene and boron nitride (BN) in the composites, with adjustable microwave absorption performance (MAP) which can be regulated by the ratio of MXene and the BN nanosheet. In particular, the as-prepared absorbents with supercapacitance-like structure significantly enhanced the MAP and could be served more than 900 °C. The results of MAP reveal that the minimum reflection loss (RL) can reach -20.94 dB with a MXene/BN-101 composite coating thickness of 4.0 mm; the effective attenuation bandwidth (RL< -10 dB, i.e., 90% microwave energy is attenuated) is up to 9.71 GHz (7.94-17.65 GHz). From a detailed analysis, it is observed that attenuation is the critical limiting factor for MAPs rather than impedance mismatch, which can be assigned to the poor MAP of BN nanosheets. In any case, as-prepared absorbents have potential applications in the field of heating components.

Modulation of electromagnetic wave absorption via porosity in Pechini-derived carbon guided by a random network model

It is well established that porosity in carbon materials can benefit electromagnetic wave absorption by providing stronger interfacial polarization, better impedance matching, multiple reflections, and lower density, but an in-depth assessment is still lacking on this issue. The random network model describes the dielectric behavior of a conduction-loss absorber-matrix mixture with two parameters related to the volume fraction and conductivity, respectively. In this work, the porosity in carbon materials was tuned by a simple, green, and low-cost Pechini method, and the mechanism of how porosity affects EM wave absorption was investigated quantitatively based on the model. It was discovered that porosity was crucial for the formation of a random network, and a higher specific pore volume led to a larger volume fraction parameter and a lower conductivity parameter. Guided by the high throughput parameter sweeping based on the model, the Pechini-derived porous carbon could achieve an effective absorption bandwidth of 6.2 GHz at 2.2 mm. This study further verifies the random network model, unveiling the implication and influencing factors of the parameters, and opens a new path to optimize the electromagnetic wave absorption performance of conduction-loss materials.

Study on Electromagnetic Performance of La0.5Sr0.5CoO3/Al2O3 Ceramic with Metal Periodic Structure at X-Band

A radar absorbing material (RAM) is designed by combining the La0.5Sr0.5CoO3/Al2O3 ceramic and the metal periodic structure. The phase constitution and the microscopic morphology of the La0.5Sr0.5CoO3/Al2O3 ceramic are examined, respectively. The electrical properties and magnetic properties of the La0.5Sr0.5CoO3/Al2O3 ceramic are also measured at the temperature range of 25~500 °C. Based on the experimental and simulation results, the changes in the reflection loss along with the structure parameters of RAM are analyzed at 500 °C. The analytical results show that the absorption property of the RAM increases with the increase in the temperature. When the thickness of the La0.5Sr0.5CoO3/Al2O3 ceramic is 1.5 mm, a reflection loss <−10 dB can be obtained in the frequency range from approximately 8.2 to 16 GHz. More than 90% microwave energy can be consumed in the RAM, which may be applied in the high temperature environment.

Achieving Ultra-Wideband and Elevated Temperature Electromagnetic Wave Absorption via Constructing Lightweight Porous Rigid Structure

Realizing ultra-wideband absorption, desirable attenuation capability at high temperature and mechanical requirements for real-life applications remains a great challenge for microwave absorbing materials. Herein, we have constructed a porous carbon fiber/polymethacrylimide (CP) structure for acquiring promising microwave absorption performance and withstanding both elevated temperature and high strength in a low density. Given the ability of porous structure to induce desirable impedance matching and multiple reflection, the absorption bandwidth of CP composite can reach ultra-wideband absorption of 14 GHz at room temperature and even cover the whole X-band at 473 K. Additionally, the presence of imide ring group in polymethacrylimide and hard bubble wall endows the composite with excellent heat and compressive behaviors. Besides, the lightweight of the CP composite with a density of only 110 mg cm^-3 coupled with high compressive strength of 1.05 MPa even at 453 K also satisfies the requirements in engineering applications. Compared with soft and compressible aerogel materials, we envision that the rigid porous foam absorbing material is particularly suitable for environmental extremes.

Flower-like bimetal-organic framework derived composites with tunable structures for high-efficiency electromagnetic wave absorption

Recently, high-performance functional composites for electromagnetic wave absorption (EWA) with tunable nano/micro-structures have attracted extensive attention. Herein, the flower-like electrically conductive and magnetic cobalt-nickel@carbon (CoNi@C) composites derived from bimetallic metal-organic frameworks (MOFs) were fabricated via solvothermal method and pyrolysis. By adjusting the ratios of different precursors, different morphological features of composites were formed. When the molar ratio of Co and Ni was 1:2, the CoNi@C composites exhibited the optimal minimum reflection loss (RL_min) of -56.89 dB at 6.7 GHz with an effective absorption bandwidth of 4.7 GHz, due to the coordinated dielectric and magnetic loss caused by the electromagnetic properties of each component as well as the interactions between the unique three-dimensional (3D) interfaces of flower-like structures that promoted the absorption and dissipation of composites for microwaves. The composites are expected to become promising candidates as high-efficiency absorbers in the electromagnetic protection field.

Radio-Absorbing Materials Based on Polymer Composites and Their Application to Solving the Problems of Electromagnetic Compatibility

Recently, designers of electronic equipment have paid special attention to the issue of electromagnetic compatibility (EMC) of devices with their own components and assemblies. This is due to the high sensitivity of semiconductor microcircuits to electromagnetic interference. This interference can be caused either by natural phenomena, such as lightning strikes, or by technical processes, such as transients in circuits during fast periodic or random switching. Either way, interference implies a sudden change in voltage or current in a circuit, which is undesirable, whether it propagates along a cable or is transmitted as an electromagnetic wave. The purpose of this article is to review the works devoted to the development, creation, and investigation of modern polymeric nanocomposite materials used for shielding electromagnetic radiation and their effective application for solving problems of electromagnetic compatibility. Additionally, the approach to design EMI shielding complex media with predetermined parameters based on investigation of various properties of possible components is shown. In the review, all polymer composites are classified according to the type of filler. The issues of the interaction of a polymer with conductive fillers, the influence of the concentration of fillers and their location inside the matrix, and the structure of the nanocomposite on the mechanisms of electromagnetic interaction are considered. Particular attention is paid to a new generation of nanocomposite materials with widely adjustable electrical and magnetic properties. A wide class of modern filled polymeric materials with dielectric and magneto-dielectric losses is considered. These materials make it possible to create effective absorbers of electromagnetic waves that provide a low level of reflection coefficient in the microwave range. The model mechanisms for shielding electromagnetic radiation are considered in the paper. A detailed review of the electro-physical properties of polymer nanocomposites is provided. Multilayer electrodynamic media containing combinations of layers of filled polymer composite materials with nanoparticles of different compositions and manufactured using a single technology will make it possible to create electrodynamic media and coatings with the required electro-physical characteristics of absorption, transmission, and reflection. Within the framework of the two-layer coating model, the difference in the effects of the interaction of electromagnetic radiation with conductive layers located on a dielectric and metal substrate is demonstrated. It is shown that in order to achieve optimal (maximum) values of reflection and absorption of electromagnetic radiation in the appropriate frequency range, it is necessary to fit the appropriate layer thicknesses, specific conductivity, and permittivity. Such approach allows designers to create new shielding materials that can effectively vary the shielding, absorbing, and matching characteristics of coatings over a wide frequency band. In general, it can be said that the development of innovative polymer composite materials for shielding electronic devices from electromagnetic interference and excessive electromagnetic background is still an important task. Its solution will ensure the safe and uninterrupted operation of modern digital electronics and can be used for other applications.

Macroscopic Electromagnetic Cooperative Network-Enhanced MXene/Ni Chains Aerogel-Based Microwave Absorber with Ultra-Low Matching Thickness

Electromagnetic cooperative strategy has been presented as a mainstream approach that can effectively optimize the matching thickness of dielectric loss dominant system. However, it is still challenging for dielectric-magnetic loss coexisting-type absorber to develop electromagnetic wave (EMW) performance with ultra-low matching thickness (≤ 1 mm). Breaking the limitation of traditional electromagnetic response at microscopic/mesoscopic scale, a ficus microcarpa-like magnetic aerogel with macroscopical electromagnetic cooperative effect was fabricated through highly oriented self-assembly engineering. The highly oriented Ni chains with unique macroscopic morphology (~ 1 cm in length) were achieved via a special magnetic field-induced growth. Strong magnetic coupling was observed in the Ni chains confirmed by the micromagnetic simulation. The deductive calculation validates that maintaining high value of electromagnetic parameters at high frequencies is the prerequisites of ultrathin absorber. The electromagnetic cooperative networks with uninterrupted and dual pathways spread through the entire aerogel skeleton, resulting in the impressive permittivity even at high frequencies. Consequently, the aerogel exhibits a remarkable EMW performance at an ultrathin thickness of 1 mm. Thus, based on the modulation of electromagnetic parameters, this work proposed a macroscopic ordered structure with the electromagnetic cooperative effect useful to develop a suitable strategy for achieving ultrathin EMW absorbers.

Corrosion-Resistant Graphene-Based Magnetic Composite Foams for Efficient Electromagnetic Absorption

Designing and fabricating high-performance microwave absorption materials with efficient electromagnetic absorption and corrosion resistance becomes a serious and urgent concern. Herein, novel corrosion-resistant graphene-based carbon-coated iron (Fe@C) magnetic composite foam is fabricated via self-assembly of iron phthalocyanine/Fe₃O₄ (FePc hybrid) on the graphene skeletons under solvothermal conditions and then annealing at high temperature. As a result, the rational construction of a hierarchical impedance gradient between graphene skeletons and Fe@C particles can facilitate the optimization in impedance matching and attenuation characteristic of the foam, realizing the efficient dissipation for incident electromagnetic waves. Additionally, the performance of electromagnetic absorption can be controllably regulated by optimizing annealing temperature and/or time. More importantly, the formation of a carbon-coated iron structure substantially improves the corrosion resistance of magnetic particles, endowing the composite foam with excellent stability and durability in microwave absorption performance.

Polydopamine-treated hierarchical cellulosic fibers as versatile reinforcement of polybutylene succinate biocomposites for electromagnetic shielding

There is a need for scalable technologies to reduce electromagnetic pollution with materials of low density and low carbon footprint. Unfortunately, environmental adaptability, economic feasibility and lightweight are factors that are still far from optimal in most electromagnetic shielding materials. Herein, we address these challenges with polybutylene succinate (PBS) reinforced with bamboo fibers functionalized with Fe₃O₄ nanoparticles (Fe₃O₄-NPs) and polypyrrole (PPy). Such hybrid system was compatibilized via polydopamine (PDA) coupling, demonstrating magnetic, dielectric and interfacial polarization losses as well as distributed reflection, yielding a shielding effectiveness of ~36.9 dB. Simultaneously, the composite displayed gains in tensile strength and modulus (by 18 and 38%, respectively) combined with improved flexural strength and modulus (by 33% and 15%, respectively). Overall, this work demonstrates a new pathway toward low cost and lightweight bio-based materials for high-performance electromagnetic shielding.

Regulating Percolation Threshold via Dual Conductive Phases for High-Efficiency Microwave Absorption Performance in C and X Bands

The development of high-efficiency microwave absorbers for C and X bands still remains a challenge, limiting the settlement of corresponding electromagnetic pollution and radar stealth. In this work, a reduced graphene oxide (RGO)/Cu/Fe₃O₄ composite is successfully proposed by a one-step solvothermal method with a GO dispersion content of 5 mL, where Fe₃O₄ exhibits high magnetic loss from natural resonance at the C band, and Cu nanorods and RGO are introduced as dual conductive phases to produce suitable dielectric properties by regulating the percolation threshold. The results show that the existence of Cu nanorods significantly reduces the conductivity and dielectric loss of the composites, optimizing the coordination of attenuation capacity and impedance matching in the C and X bands. Consequently, the obtained RGO/Cu/Fe₃O₄ composite shows outstanding microwave absorption performance with the maximum effective absorption bandwidth (EAB) value of 5.2 GHz at a thin thickness of 3.1 mm, which covers 84% of the C band and 46% of the X band (4.64-9.84 GHz). The performance is superior to the vast majority of previous absorbers in the corresponding bands.

A generalizable strategy for constructing ultralight three-dimensional hierarchical network heterostructure as high-efficient microwave absorber

Using previous models and theories to construct and develop high-efficient microwave absorbers (MAs) should be a strategic and effective ways to optimize the electromagnetic wave attenuation. Herein, the ultralow density and flexible graphene oxide foam (GOF) and reduced graphene oxide foam (RGOF)/MoS₂ nanosheets were designed and fabricated by the method of chemical vapor deposition and hydrothermal reaction. The obtained GOF and RGOF/MoS₂ samples exhibited very excellent microwave absorption properties while their densities were merely 0.0082 and 0.0084 g•cm^-3, respectively. More importantly, benefiting from the excellent synergistic effect between RGOF and MoS₂, the designed RGOF/MoS₂ well inherited the combined advantages of GOF and MoS₂ in terms of strong absorption abilities, broad absorption bandwidth and thin matching thicknesses. The values of minimum reflection loss and effective frequency bandwidth for RGOF/MoS₂ sample could reach up to -62.92 dB with the matching thickness of 2.27 mm and 4.48 GHz with the matching thickness of 2.12 mm, which were very desirable for high-performance MAs. Moreover, the obtained results indicated that the microwave absorption properties of RGOF/MoS₂ sample could be further optimized by regulating the MoS₂ content. Therefore, a new and effective strategy was proposed to develop high efficiency MAs with ultra-lightweight, wide-band, thin thickness and strong absorption capabilities.

Flexible and Waterproof 2D/1D/0D Construction of MXene-Based Nanocomposites for Electromagnetic Wave Absorption, EMI Shielding, and Photothermal Conversion

ABSTRACT

High-performance electromagnetic wave absorption and electromagnetic interference (EMI) shielding materials with multifunctional characters have attracted extensive scientific and technological interest, but they remain a huge challenge. Here, we reported an electrostatic assembly approach for fabricating 2D/1D/0D construction of Ti₃C₂T_x/carbon nanotubes/Co nanoparticles (Ti₃C₂T_x/CNTs/Co) nanocomposites with an excellent electromagnetic wave absorption, EMI shielding efficiency, flexibility, hydrophobicity, and photothermal conversion performance. As expected, a strong reflection loss of -85.8 dB and an ultrathin thickness of 1.4 mm were achieved. Meanwhile, the high EMI shielding efficiency reached 110.1 dB. The excellent electromagnetic wave absorption and shielding performances were originated from the charge carriers, electric/magnetic dipole polarization, interfacial polarization, natural resonance, and multiple internal reflections. Moreover, a thin layer of polydimethylsiloxane rendered the hydrophilic hierarchical Ti₃C₂T_x/CNTs/Co hydrophobic, which can prevent the degradation/oxidation of the MXene in high humidity condition. Interestingly, the Ti₃C₂T_x/CNTs/Co film exhibited a remarkable photothermal conversion performance with high thermal cycle stability and tenability. Thus, the multifunctional Ti₃C₂T_x/CNTs/Co nanocomposites possessing a unique blend of outstanding electromagnetic wave absorption and EMI shielding, light-driven heating performance, and flexible water-resistant features were highly promising for the next-generation intelligent electromagnetic attenuation system. [Image: see text]

HIGHLIGHTS

The 2D/1D/0D Ti₃C₂T_x/carbon nanotubes/Co nanocomposite is successfully synthesized via an electrostatic assembly. Nanocomposites exhibit an excellent electromagnetic wave absorption and a remarkable electromagnetic interference shielding efficiency. The flexible, waterproof, and photothermal conversion performances are achieved.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00673-9.

Antidegradation Property of Alginate Materials by Riveting Functionalized Carbon Nanotubes on the Sugar Chain

Alginate materials with the advantages of being renewable, inexpensive, and environment-friendly have been considered promising fiber materials. However, they are prone to degrade under UV light, limiting their large-scale application in the textile field. Herein, the fracture of glycosidic bonds during the degradation process is revealed clearly by Fourier transform infrared (FT-IR) and ¹H NMR. To effectively inhibit this process, functionalized multiwalled carbon nanotubes (MWCNTs) are chosen as dopants and used to interact with the sugar chain via hydrogen bonds. The results demonstrate that alginate materials with functionalized MWCNTs exhibit slower degradation rates. The intermolecular energy transfer between functionalized MWCNTs and sodium alginate (SA) is proposed for the antidegradation effect of functionalized MWCNTs, which is supported by the experiments. Moreover, SA/MWCNT fibers also show enhanced mechanical properties compared with pure alginate fibers. The appealing effect of the degradation inhibition feature makes the composite alginate materials very promising candidates for their future use in textile material development.

1D Electromagnetic-Gradient Hierarchical Carbon Microtube via Coaxial Electrospinning Design for Enhanced Microwave Absorption

1D structures have been gaining traction in the microwave absorption (MA) field benefiting from their electromagnetic (EM) anisotropy. However, there remain considerable challenges in adjusting EM properties by structural design. Herein, using the coaxial electrospinning and solvothermal method, the EM gradient has been achieved in TiO₂@Co/C@Co/Ni multilayered microtubes. From the outer layer to the inner one, the impedance matching is gradually worsened, while the EM loss capacity is continuously enhanced, facilitating both the incidence and attenuation of microwave. Besides, 1D structural anisotropy simultaneously realizes multilevel magnetic interaction and 3D conductive double network. Therefore, the 1D EM-gradient hierarchical TiO₂@Co/C@Co/Ni carbon microtube composite exhibits excellent MA performance. Its maximum reflection loss (RL) value reaches -53.99 dB at 2.0 mm and effective absorption bandwidth (EAB, RL ≤ -10 dB) is as wide as 6.0 GHz, covering most of the Ku band with only 15% filling. The unique design of 1D EM-gradient hierarchical composites promises great potential in the construction of advanced MA materials.

Magnetic aerogel: an advanced material of high importance

Magnetic materials have brought innovations in the field of advanced materials. Their incorporation in aerogels has certainly broadened their application area. Magnetic aerogels can be used for various purposes from adsorbents to developing electromagnetic interference shielding and microwave absorbing materials, high-level diagnostic tools, therapeutic systems, and so on. Considering the final use and cost, these can be fabricated from a variety of materials using different approaches. To date, several studies have been published reporting the fabrication and uses of magnetic aerogels. However, to our knowledge, there is no review that specifically focuses only on magnetic aerogels, so we attempted to overview the main developments in this field and ended our study with the conclusion that magnetic aerogels are one of the emerging and futuristic advanced materials with the potential to offer multiple applications of high value.

Methods of Protecting Buildings against HPM Radiation-A Review of Materials Absorbing the Energy of Electromagnetic Waves

The pulsed high power microwave (HPM) technology has been developed worldwide for over 20 years. The sources of HPM pulses are a weapon of mass destruction. They pose danger especially to computer and telecommunications equipment and systems, both the military and civilian ones. This paper presents a survey of literature on electromagnetic wave radiation absorbing and shielding materials to be used in construction. Relevant protective measures should include the shielding of buildings or their parts and the absorption of radiation by building envelopes and their elements. The main focus is on the possibilities of improving the shielding and absorptive properties of common construction materials, such as concrete, mortars and synthetic resins. The survey covers the following groups of materials: carbon-based admixtures, nickel powder, iron powders, ferrites, magnetite and polymers. The final part of the survey is devoted to hybrid foam microwave absorbers in which the shape of the material’s inner structure and that of its surface play a special role.

Effects of Carbonyl Iron Powder (CIP) Content on the Electromagnetic Wave Absorption and Mechanical Properties of CIP/ABS Composites

Three-dimensional (3D) printing technology has proven to be a convenient and effective method to fabricate structural electromagnetic wave (EMW) absorbers with tunable EMW absorption properties. To obtain a functional material with strong EMW absorbing performance and excellent mechanical properties for fused deposition modeling (FDM) 3D printing technology, in this work, carbonyl iron powder (CIP)/acrylonitrile-butadiene-styrene copolymer (ABS) composites with different CIP contents were prepared by the melt-mixing process. The effects of the CIP content on the EMW absorption and mechanical properties of CIP/ABS composites were investigated. The CIP/ABS composite with a CIP content of 40 wt.% presented the lowest reflection loss (RL) of -48.71 dB for the optimal impedance matching. In addition, this composite exhibited optimal mechanical properties due to the good dispersion of the CIPs in the matrix ABS. Not only were the tensile and flexural strength similar to pure ABS, but the tensile and flexural modulus were 32% and 37% higher than those of pure ABS, respectively. With a CIP content of 40 wt.%, the CIP/ABS composite proved to be a novel functional material with excellent EMW absorbing and mechanical properties, providing great potential for the development of structural absorbers via FDM 3D printing technology.

Banana Leaflike C-Doped MoS2 Aerogels toward Excellent Microwave Absorption Performance

We describe the design and manufacturing method of a lightweight C-doped MoS₂ aerogel with a special regular banana leaflike microstructure used for high-performance microwave absorbers. The aerogel precursor was first fabricated by a self-assembly process between alginate (Alg) and ammonium thiomolybdate (ATM), where Alg as a template was assembled with ATM into regular banana leaflike architectures along the ice growth direction during oriented freezing. After pyrolysis at 900 °C, the C-doped MoS₂ aerogels maintained low densities and porous hierarchal banana leaflike structures, where the banana leaves ranged in diameter from about 2 to 5 μm with the growth of small branches. Benefitting from these features, the C-doped MoS₂ aerogel possessed excellent microwave absorption performance in the frequency range of 2-18 GHz. The minimum reflection loss (RL) reached -43 dB at 5.4 GHz with a matching thickness of 4 mm, and the effective microwave absorption band (RL < -10 dB) reached 4 GHz (14-18 GHz) at a thickness of 1.5 mm. Our findings also provide strategies for designing MoS₂ aerogel nanostructures for electronic devices, catalysis, and other potential applications.

Facile fabrication of sepiolite functionalized composites with tunable dielectric properties and their superior microwave absorption performance

Although various materials have been studied for the purpose of microwave absorption (MA), natural sepiolite (SEP) has never been reported as MA absorber. Herein, the series of sepiolite@polyaniline composites (SEP@PANI-x) with "skeleton/skin" structure were fabricated through a facile in-situ polymerization technique and firstly developed as MA materials. The electrical conductivity and dielectric properties can be well controlled via modulating the PANI content in the composites. With a lower mass ratio of 30 wt%, it is worth noting that the optimized SEP@PANI-50 could simultaneously display the optimal minimum reflection loss (RL_min) of -50.23 dB and effective absorption bandwidth (EAB, RL < -10 dB) of 5.01 GHz with thicknesses of 2.5 and 1.8 mm, respectively. Moreover, when changing absorber thickness (1.5-5.0 mm), the RL_min values lower than -20 dB (99% absorption) are all achieved and the EAB ranges the entire Ku, X, and C bands. Such excellent MA performance comes from rich conductive network and polarization relaxation, which ultimately balance the impedance matching and attenuation ability. In view of its facile synthesis route, low-cost, lightweight and excellent MA performance, SEP@PANI-50 would be a very promising MA candidate in many practical applications. More importantly, we also think that our findings will expand the application of SEP-based composites in the electromagnetic field.

A Convenient and Versatile Strategy for the Functionalization of Silica Foams Using High Internal Phase Emulsion Templates as Microreactors

Functional porous materials show extensive applications in the environment, biology, aerospace, and so on. In this work, the generation of silica foams and functionalization of pore surface were simultaneously realized through an interfacial sol-gel reaction within high internal phase emulsion (HIPE) microreactors, where a hyperbranched polyethoxysiloxane (PEOS) was used as the sole stabilizer for the HIPEs. With various functional substances containing amino, epoxy, and carboxyl groups initially dissolved in the aqueous phase of HIPEs, these functional groups could be grafted onto the pore surface in the process of forming silica foams. Amino-functionalized silica foam showed fast adsorption of sunset yellow, and the adsorption capacity could reach as high as 1213.13 mg/g. Sodium polyacrylate-modified silica foam exhibited good adsorption capacity of cationic dyes and metal ions, e.g., 280.11 mg/g to methylene and 226.24 mg/g to Cu(II). Epoxy-functionalized silica foam particles were confirmed with a pronounced activity at the oil/water interface due to their Janus-like surface, which could be used as Pickering stabilizer. This HIPE-based synthesis strategy for silica foams shows promising future in adsorption, emulsion stabilization, and compatibilization.

Enhanced Electromagnetic Absorption Properties of Commercial Ni/MWCNTs Composites by Adjusting Dielectric Properties

In this manuscript, we constructed a Ni/MWCNTs absorber and properly adjusted the permittivity resulted from absorber content in the PVDF to optimize impedance matching properties. Both ε' and ε″ increase obviously with the increasing content of Ni/MWCNTs in PVDF, demonstrating that dielectric properties are dependent on the conductivity. Moderate dielectric properties and excellent impedance matching can be obtained for the filler content of 20 wt% Ni/MWCNTs. Reasonable impedance matching allows electromagnetic waves to propagate into the materials and finally realize energy dissipation through dielectric loss and interfacial polarization. As expected, the minimum reflection loss (RL) of -46.85 dB at 6.56 GHz with a low filler loading (20 wt%) and wide effective bandwidth (RL<-10 dB) of 14.0 GHz in the thickness range of 1.5-5.0 mm was obtained for the commercial Ni/MWCNTs composites, which is promising for mass production in industrial applications. Our findings offer an effective and industrialized way to design high-performance material to facilitate the research in microwave absorption.

A new flexible and ultralight carbon foam/Ti3C2T X MXene hybrid for high-performance electromagnetic wave absorption

A new ultralight carbon foam/Ti3C2T X (CF/MXene) electromagnetic (EM) absorbing hybrid with three-dimensional network structure was fabricated by vacuum impregnation and freeze-drying process. These hybrids display excellent flexibility and steady compression-resilience properties and also the special three-dimensional structure with ultralow density of only 5-7 mg cm-3 shows higher EM absorption than most foam-based EM absorbers. Studies have shown that the minimum reflection loss of CF/MXene-N2 reaches -45 dB at 8.8 GHz with the Ti3C2T X nanosheets content of 9.8%. In the meanwhile, the effective absorption bandwidth of CF/MXene-N2 can also reach up to 5 GHz (from 6.9 GHz to 11.9 GHz) with the thickness of 4.5 mm. Moreover, the fundamental EM absorption mechanism of CF/MXene hybrids involved to impedance matching, conductive loss and polarization loss is carefully analyzed. Thus, it is expected that the new ultralight carbon foam/Ti3C2T X hybrids with three-dimensional network structure will have great application prospects in the fields of EM absorption.

Ultralight Three-Dimensional Hierarchical Cobalt Nanocrystals/N-Doped CNTs/Carbon Sponge Composites with a Hollow Skeleton toward Superior Microwave Absorption

It is extremely desirable but remains greatly challenging to obtain high-performance microwave absorption (MA) materials with thin thickness, lightweight, wide frequency bandwidth, and strong absorption by facile and low-cost preparing methods. In this work, by utilizing an inexpensively commercial melamine-formaldehyde sponge (MFS) as a template for growth of a Co-based metal-organic framework (ZIF-67) and subsequently carbonizing this ZIF-67-decorated MFS in a nitrogen atmosphere, an ultralight (8 mg cm^-3), three-dimensional hybrid carbon sponge composite with a hierarchical micro/nanostructure and hollow skeleton is successfully prepared to acquire excellent MA performances for the first time. The as-obtained composite consisted of interconnected carbon microtubes as a skeleton, intertwined N-doped carbon nanotubes (CNTs) grew on the outer surface of the carbon microtubes, and metallic Co nanocrystals encapsulated at the tips of the CNTs. Benefiting from the unique architecture and hierarchical composite which contribute to a good conductive network, moderate magnetic loss, strong matched impedance, and multiple polarization, the composite (Co/CNTs/CS) exhibited a minimum reflection loss (RL) of -51.2 dB and an effective absorption bandwidth (EAB, RL < -10 dB) of 4.1 GHz with a matching thickness of 2.2 mm at a filler loading of as low as 10 wt % in paraffin wax. Even with the thickness of 1.6 mm or at the filler loading of 5 wt %, the composites can also gain the low minimum RL value of -30.9 or -17.9 dB, respectively. In addition, the largest EAB was 5.4 GHz at the thickness of 2.0 mm, and the tunable EAB can be achieved in the range of 3.6-18 GHz, covering 90% of the measured frequency range via adjusting the absorber thickness between 1 and 5.5 mm. The results offer new insights for designing advanced microwave absorbers with lightweight, thin thickness, strong RL, and wide absorption frequency range.

Retracted Article: The influence of gradient and porous configurations on the microwave absorbing performance of multilayered graphene/thermoplastic polyurethane composite foams

Single-layer graphene/TPU composite foams with different graphene content were prepared through a thermally induced phase separation (TIPS) process. Multilayer graphene/TPU composite foams were fabricated by bonding single-layer foams together. The arrangement of single-layer graphene/TPU composite foams in different orders could realize a gradient distribution of the graphene to endow the multilayer foams with good impedance matching characteristics. Facile regulation of the effective absorption bandwidth (EB) value and minimum reflection loss (RLmin) have been realized by adjusting the thickness and layer number or altering the combinatorial mode of single-layer foams with different graphene contents to endow these multilayered composite foams with optimal microwave-absorbing (MA) properties. In addition, the mechanism of microwave dissipation by gradient multilayers and porous structures has been elucidated. The EB values of the multilayer foams were all wider than those of their corresponding single-layer foams with the same graphene content and multilayer foams displayed much lower RLmin than single-layer foams. Among all the multilayer foams, 2L graphene/TPU composite foams with a thickness of 5 mm exhibit the widest EB value of 9.9 GHz and the lower RLmin (-36.7 dB) while 5L graphene/TPU composite foams with a thickness of only 2.5 mm show the lowest RLmin of -43.7 dB and wider EB values (5.3 GHz).

Fabrication of Three-Dimensional Flower-like Heterogeneous Fe3O4/Fe Particles with Tunable Chemical Composition and Microwave Absorption Performance

Heterogeneous Fe₃O₄ and Fe composites are highly desirable for microwave absorption application because of their complementary electromagnetic (EM) properties. With three-dimensional (3D) Fe₂O₃ as a sacrificing template, we realize the construction of Fe₃O₄/Fe composites with tunable chemical composition, and more importantly, these composites inherit the unique 3D microstructure from their precursor. The change in chemical composition produces significant impacts on the EM functions of these composites. On the one hand, dielectric loss can be improved greatly through positive interfacial polarization and reach the peak when the mass contents of Fe₃O₄ and Fe are 72.1 and 27.9 wt %, respectively. On the other hand, high Fe content slightly pulls down magnetic loss in the low-frequency range but favors strong magnetic loss in the high-frequency range because of the breakthrough of Snoek's limitation. The attenuation constant reveals that dielectric loss dominates overall consumption of incident EM waves. As a result, the optimized composite, F-350 (the reduction of Fe₂O₃ is conducted at 350 °C), shows the best microwave absorption performance, whose strongest reflection loss is -56.0 dB at 17.5 GHz and the effective bandwidth can cover the frequency range of 12.0-15.5 GHz with the thickness of 1.5 mm. Furthermore, an ultrawide effective bandwidth of 15.3 GHz can be achieved with the integrated thickness of 1.0-5.0 mm. Such a performance is superior to those of many reported Fe₃O₄/Fe composites, and a comparative analysis manifests that good microwave absorption of F-350 is also benefited from its unique 3D architecture.

Light-weight Gadolinium Hydroxide@polypyrrole Rare-Earth Nanocomposites with Tunable and Broadband Electromagnetic Wave Absorption

Light-weight and highly efficient nanocomposite absorbing materials are gaining tremendous interest in recent years. Because of the unique electronic structure characteristics, nanoscale rare-earth materials are of great significance in the development of advanced functional materials. Herein, gadolinium hydroxide/polypyrrole (Gd(OH)₃@PPy) nanocomposites were synthesized by a facial chemical solution route. The composites could achieve an absorbing performance of -51.4 dB at 16.2 GHz with a bandwidth of 4.8 GHz, covering the entire Ku band at a thickness of only 2.2 mm. Furthermore, the absorption intensity and bandwidth can be effectively tuned by adjusting the concentration of Gd(OH)₃ in the composite. Because of the improvement of impedance matching, dual-loss mechanism, and the synergistic effect of rare-earth hydroxides and conductive polymers, light-weight gadolinium hydroxide@polypyrrole composites are considered as promising candidates for strong and broadband electromagnetic wave absorption.

Biomass-Derived Porous Carbon-Based Nanostructures for Microwave Absorption

Currently, electromagnetic (EM) pollution poses severe complication toward the operation of electronic devices and biological systems. To this end, it is pertinent to develop novel microwave absorbers through compositional and structural design. Porous carbon (PC) materials demonstrate great potential in EM wave absorption due to their ultralow density, large surface area, and excellent dielectric loss ability. However, the large-scale production of PC materials through low-cost and simple synthetic route is a challenge. Deriving PC materials through biomass sources is a sustainable, ubiquitous, and low-cost method, which comes with many desired features, such as hierarchical texture, periodic pattern, and some unique nanoarchitecture. Using the bio-inspired microstructure to manufacture PC materials in mild condition is desirable. In this review, we summarize the EM wave absorption application of biomass-derived PC materials from optimizing structure and designing composition. The corresponding synthetic mechanisms and development prospects are discussed as well. The perspective in this field is given at the end of the article.

Enhanced Photothermal Effect in Ultralow-Density Carbon Aerogels with Microporous Structures for Facile Optical Ignition Applications

The exact mechanism responsible for the phenomenon known as photoignition with an enhanced photothermal effect in high-surface-area carbon with the addition of a metal catalyst is an open issue. Here, we report the first successful flash ignition of a pure carbon material in ambient air microporous carbon aerogels (CAs) with ultralow density and high surface area. Under flash exposure, the CAs show a strong local heat confinement effect near microporous structures (0.6-2 nm), and the graphite crystallite structures existing in single carbon nanoparticles (∼15 nm) are damaged. The local heat confinement effects are mainly derived from the low gaseous thermal conductivity in micropores and low solid thermal conductivity in low-density CAs. In addition, the limiting effects of the microporous structure on the vibration amplitude of free-state electrons in low-density CAs result in a dramatic increase in optical absorption. Numerical simulations of unsteady temperature fields of CAs with different densities and thicknesses are also performed, and the calculated maximum temperature of a 17 μm-thick 20 mg/cm³ CA bed is 1782 °C. CAs with higher density can also give rise to enhanced photothermal response and ignition with the addition of metal Fe nanoparticles. The metal catalyst increases both the light absorption capacity in the visible-light range and the heat accumulation capacity. These results are important for understanding the mechanism of flash ignition, especially the local high temperature and effects of metal catalyst in carbon materials during the photothermal process.

NiFe2O4 nanoparticles supported on cotton-based carbon fibers and their application as a novel broadband microwave absorbent

In this work, NiFe₂O₄ nanoparticles were successfully supported on cotton-based carbon fibers through a flexible two-step approach consisting of calcination of cotton in a N₂ atmosphere and subsequent hydrothermal reaction. The incorporation of the NiFe₂O₄ nanoparticles into cotton-based carbon fibers resulted in better impedance matching, leading to better microwave absorption performance than cotton-based carbon fibers and NiFe₂O₄ nanoparticles. For NiFe₂O₄/carbon fibers, reflection loss (RL) values less than −10 dB were obtained in the frequency range of 11.5–18 GHz with 2.4 mm thickness, which covered the entire Ku-band (from 12 to 18 GHz). Meanwhile, when the matching thickness was 3.2 mm, the RL values less than −10 dB were in the range of 8.0–12.7 GHz, which covered the entire X-band (from 8 to 12 GHz). This excellent and interesting microwave absorption performance can satisfy multiple applications. Owing to the characteristics of a cost-effective synthetic route, low density and excellent microwave absorption, the NiFe₂O₄/carbon fibers have a promising future in X-band and Ku-band absorption.

NiFe₂O₄ nanoparticles supported on cotton-based carbon fibers exhibited excellent microwave absorption performance in the X-band and Ku-band.

Bimetallic MOF-derived porous CoNi/C nanocomposites with ultra-wide band microwave absorption properties

The CoNi bimetallic MOF-derived composites were synthesized in this work. The target product is composed of fine particles with uniformly distributed elements of Ni, Co, C. The CoNi/C-650 sample displays good microwave absorbing properties.

rGO/Fe3O4 hybrid induced ultra-efficient EMI shielding performance of phenolic-based carbon foam

Phenolic-based carbon foam with ultra-efficient EMI shielding performance was achieved by incorporating rGO/Fe₃O₄ hybrid.

Retracted Article: A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption

A broadband electromagnetic wave (EW) absorbing material should possess both wider effective absorption bandwidth and lower minimum reflection loss, depending on good impedance matching between the absorber and air and strong attenuation of EW.

Performance enhanced electromagnetic wave absorber from controllable modification of natural plant fiber

Short, surface rough carbon rods, which were derived from natural sisal fiber and went through two different modifications, with excellent electromagnetic wave absorption performance, were studied in this work for the first time. The structure–property relationship was clearly established here. It was shown that these green, cheap and easily obtained carbon rods with mass preparation possibility presented eye-catching absorbing behaviors towards electromagnetic wave. Based on the natural structure of sisal fiber, the minimum reflection loss of KOH activated product reached −51.1 dB and the maximum effective absorbing bandwidth achieved 7.88 GHz. The magnetically modified sample presented −48.6 dB of minimum reflection loss and 4.32 GHz of optimal absorbing bandwidth. Its pioneering application in this field not only opens a new road for this traditional textile sisal fiber but also would possibly make a referable contribution to the design and synthesis of superior carbonaceous electromagnetic wave absorption materials based on bioresource.

Novel carbon rods derived from plant fiber with excellent electromagnetic wave absorption performance have been facilely accomplished via two different modifications.

Ultrathin Flexible Carbon Fiber Reinforced Hierarchical Metastructure for Broadband Microwave Absorption with Nano Lossy Composite and Multiscale Optimization

The implementation of thin structure for broadband microwave absorption is challenging due to the requirement of impedance match across several frequency bands and poor mechanical properties. Herein, we demonstrate a carbon fiber (CF) reinforced flexible thin hierarchical metastructure (HM) composed of lossy materials including carbonyl iron (CI), multiwall carbon nanotube (MWCNT), and silicone rubber (SR) with thickness of 5 mm and optimal concentration selected from 12 formulas. Optimization for the periodical unit size is applied, and impacts of structural sizes on absorption performance are also investigated. An effective process combining the vacuum bag method and the hand lay-up technique is used to fabricate the HM. Experimental reflectivity of the absorber achieves broadband absorption below -10 dB in 2-4 GHz and 8-40 GHz. The full band in 2-40 GHz is covered below -8 dB. Yielding stress of the HM is increased to 24 MPa with attachment of CF, while the fracture strain of the composite reaches 550%. The soft HM is suitable to adhere to the curved surface of objects needed to be protected from microwave radiation detection and electromagnetic interference. Enhanced mechanical properties make it possible for further practical applications under harsh service environments such as the ocean and machines with constant vibration.

Self-cross-linked melamine-formaldehyde-pectin aerogel with excellent water resistance and flame retardancy

Self-cross-linked aerogel based on pectin and melamine-formaldehyde resin (MF) was fabricated via freeze-drying method using water as solvent, where pectin is structural material meanwhile acting as acid to catalyse the cross-linking of MF. The cross-linking reaction easily occurs without additional additives, which can be significantly accelerated at elevated temperatures, with a critical value of about 55 °C. The obtained aerogel shows network microstructures as observed with SEM. With increasing pectin content, the aerogel shows significantly increased compressive modulus. The compressive modulus of M10Pe5 arrives 23.2 MPa, the specific modulus of which arrives 188 MPa cm³/g, while pure MF aerogel are too fragile to keep intact after freeze-dried. The resulting aerogel has good thermal stability, excellent water resistance (can be second dried with limited strength loss) and low flammability. This partially bio-based novel aerogel with impressive properties is promising in many applications.

Synthesis and Microwave Absorbing Properties of Porous One-Dimensional Nickel Sulfide Nanostructures

One-dimensional (1D) porous NixSy nanostructures have been successfully fabricated by two-step method consisting of solvothermal and subsequent annealing process. The suitable heat treatment temperature and reaction time play crucial roles in the final structure, morphology, as well as performance. The uniform and perfect porous NixSy nanostructures obtained at 310°C exhibit outstanding microwave absorption performances. A minimum reflection loss of -35.6 dB is achieved at 8.5 GHz, and the effective absorption bandwidth almost covers 14.5 GHz with the absorber thickness range of 2.0-5.0 mm. It can be supposed that this porous structure with rough surface which is favor for increasing the microwave multiple reflection and scattering, contributes a high-performance electromagnetic absorption.

Solvent-regulated preparation of well-intercalated Ti3C2Tx MXene nanosheets and application for highly effective electromagnetic wave absorption

MXene-derived nanostructures provide the possibility of meeting the requirements of strong absorption, thin thickness and flexible layer for electromagnetic (EM) wave absorption. However, exploration of pure and well-intercalated MXene nanosheets for efficient EM wave absorption is still in the nascent stages. Herein, Ti₃C₂T_x nanosheets with solvent-manipulated properties were achieved via ultrasonication-solvothermal treatment of bulk Ti₃C₂T_x in different solvents including dimethylformamide (DMF), ethanol, and dimethyl sulfoxide (DMSO), respectively, because of their combined influences of molecular size, oxidation capability, and boiling point. Especially, it was found that a larger layer space and less oxidation effects on the Ti₃C₂T_x nanosheets were observed upon solvothermal treatment in DMF than those in ethanol or DMSO treatment. As a result, the DMF-treated Ti₃C₂T_x nanosheets can be used as highly effective dielectric materials for EM wave absorption. The reflection loss value reached -41.9 dB (more than 99.99%) at 13.4 GHz with the sample thickness of only 1.1 mm. Characterization techniques including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and density functional theory calculation were used to elaborate the possible mechanisms.

In Situ Preparation of Cobalt Nanoparticles Decorated in N-Doped Carbon Nanofibers as Excellent Electromagnetic Wave Absorbers

Electrospinning and annealing methods are applied to prepare cobalt nanoparticles decorated in N-doped carbon nanofibers (Co/N-C NFs) with solid and macroporous structures. In detail, the nanocomposites are synthesized by carbonization of as-electrospun polyacrylonitrile/cobalt acetylacetonate nanofibers in an argon atmosphere. The solid Co/N-C NFs have lengths up to dozens of microns with an average diameter of ca. 500 nm and possess abundant cobalt nanoparticles on both the surface and within the fibers, and the cobalt nanoparticle size is about 20 nm. The macroporous Co/N-C NFs possess a hierarchical pore structure, and there are macropores (500 nm) and mesopores (2-50 nm) existing in this material. The saturation magnetization ( M_s) and coercivity ( H_c) of the solid Co/N-C NFs are 28.4 emu g^-1 and 661 Oe, respectively, and those of the macroporous Co/N-C NFs are 23.3 emu g^-1 and 580 Oe, respectively. The solid Co/N-C NFs exhibit excellent electromagnetic wave absorbability, and a minimum reflection loss (RL) value of -25.7 dB is achieved with a matching thickness of 2 mm for solid Co/N-C NFs when the filler loading is 5 wt %, and the effective bandwidth (RL ≤ -10 dB) is 4.3 GHz. Moreover, the effective microwave absorption can be achieved in the whole range of 1-18 GHz by adjusting the thickness of the sample layer and content of the dopant sample.

Microwave absorption properties of reduced graphene oxide strontium hexaferrite/poly(methyl methacrylate) composites

The key factors to consider when designing microwave absorber materials for eradication of electromagnetic (EM) pollution are absorption of incident EM waves and good impedance matching. By keeping these things in mind, flexible microwave absorber composite films can be fabricated by simple gel casting techniques using reduced graphene oxide (RGO) and strontium ferrite (SF) in a poly(methyl methacrylate) (PMMA) matrix. SF nanoparticles are synthesized by the well known sol-gel method. Subsequently, reduced graphene oxide (RGO) and SF nanocomposite (RGOSF) are prepared through a chemical reduction method using hydrazine. The structure, morphology, chemical composition, thermal stability and magnetic properties of the nanocomposite are characterized in detail by various techniques. The SF particles are found to be nearly 500 nm and decorated on RGO sheets as revealed by field emission scanning electron microscopy and transmission electron microscopy analysis. Fourier transform infrared and and Raman spectroscopy clearly show the presence of SF in the graphene sheet by the lower peak positions. Finally, ternary polymer composites of RGO/SF/PMMA are prepared by an in situ polymerization method. Magnetic and dielectric studies of the composite reveal that the presence of RGO/SF/PMMA lead to polarization effects contributing to dielectric loss. Also, RGO surrounding SF provides a conductive network in the polymer matrix which is in turn responsible for the magnetic loss in the composite. Thus, the permittivity as well as the permeability of the composite can be controlled by an appropriate combination of RGO and SF in PMMA. More than 99% absorption efficiency is achieved by a suitable combination of magneto-dielectric coupling in the X-band frequency range by incorporating 9 wt% of RGO and 1 wt% of SF in the polymer matrix.

Hybrid nanowires and nanoparticles of WO3 in a carbon aerogel for supercapacitor applications

In the field of electrochemical energy storage, incorporation of metal oxides into porous carbon has attracted significant attention. Since each advantage of nanoparticles and nanowires of metal oxide has been distinguished for supercapacitor applications, a combination of the advantages of both structures together can meet a capacitive synergy. In this study, WO₃ nanowires and nanoparticles were first incorporated into a carbon aerogel (CA) simultaneously via a facile and one-pot route. A comparative study on the capacitive properties of this novel hybrid structure and single nanoparticles in CA was conducted. The introduction of WO₃ nanowires with diameter <40 nm provided an additional pair of redox peaks and improved the specific capacitance by 50% and the rate capacity by 61%. The composite within the hybrid nanowires and nanoparticles exhibits an excellent cycling stability of only 2% decay in specific capacitance detected at 50 mV s^-1 for 1000 cycles. The individual contribution of nanowires and nanoparticles to the enhanced capacitance has been discussed, and the enhanced capacitive properties can be ascribed to the hybrid structure better for charge transport during the electrochemical process. More importantly, this route can be extended to incorporate nanowires of other metal oxides into mesoporous carbon, and enhanced capacitive properties can be expected.

Green Approach to Improving the Strength and Flame Retardancy of Poly(vinyl alcohol)/Clay Aerogels: Incorporating Biobased Gelatin

Biobased gelatins were used to improve the compressive properties and flammability of poly(vinyl alcohol)/montmorillonite (PVA/MMT) aerogels, fabricated using a simple and environmentally friendly freeze-drying method. Because of the excellent compatibility and strong interfacial adhesion between PVA and gelatin, the compressive moduli of aerogels were enhanced dramatically with the incorporation of gelatin. PVA/MMT/porcine-gelatin aerogels exhibit compressive modulus values as much as 12.4 MPa, nearly 300% that of the control PVA/MMT aerogel. The microstructure of the PVA/MMT/gelatin aerogels shows a three-dimensional co-continuous network. Combustion testing demonstrated that with the addition of gelatin, the self-extinguishing time of the aerogel was cut by half and the limiting-oxygen-index values increased to 28.5%. The peak heat-release rate, obtained from cone calorimetry, also decreased with the incorporation of gelatin. Thermogravimetric analysis demonstrated that the gelatins slowed the sharp decomposition of the PVA matrix polymer and increased the thermal stability of the aerogels at the major decomposition stage of the composite aerogels. These results indicate that as a green, biobased material, gelatin could simultaneously improve the mechanical properties and the properties of flame retardancy.