Hybridization-Induced Polarization of Graphene Sheets by Intercalation-Polymerized Polyaniline toward High Performance of Microwave Absorption

Freestanding Nanofiber-Assembled Aptasensor for Precisely and Ultrafast Electrochemical Detection of Alzheimer's Disease Biomarkers

Amyloid beta-protein (AβAβ) is a main hallmark of Alzheimer's disease (AD), and a low amount of Aβ protein accumulation appears to be a potential marker for AD. Here, an electrochemical DNA biosensor based on polyamide/polyaniline carbon nanotubes (PA/PANI-CNTs) is developed with the aim of diagnosing AD early using a simple, low-cost, and accessible method to rapidly detect Aβ42 in human blood. Electrospun PA nanofibers served as the skeleton for the successive in situ deposition of PANI and CNTs, which contribute both high conductivity and abundant binding sites for the Aβ42 aptamers. After the aptamers are immobilized, this aptasensor exhibits precise and specific detection of Aβ42 in human blood within only 4 min with an extremely fast response rate, lower detection limit, and excellent linear detection range. These findings make a significant contribution to advancing the development of serum-based detection techniques for Aβ42, thereby paving the way for improved diagnostic capabilities in the field of AD.

Construction and application of carbon aerogels in microwave absorption

Electromagnetic pollution that threatens human health, the ecological environment and electronic equipment has been recognized as a serious environmental issue. In view of this, microwave absorbing materials (MAMs) are urgently required in modern society. Compared with traditional MAMs, carbon aerogels have inherent advantages in microwave absorption because of their high porosity and controllable conductive networks. Moreover, they are self-supporting 3D architectures with tailorable shapes, which satisfy most application scenarios. Therefore, carbon aerogels have aroused great interest in recent years and are being developed as promising absorption materials. In this review, we emphasize recent developments in carbon-aerogel-based MAMs constructed with some typical carbon nanomaterials, including graphene, carbon nanotubes and pyrolytic carbon. Their preparation methods, especially some newly developed strategies, are introduced as well as their influence on the structures and properties of aerogels. With a brief analysis of classic microwave absorption processes, we propose the requirements and strategies for modifying carbon aerogels to achieve ideal microwave absorption performance. Finally, we provide comprehensive comparisons of the MA performances of various carbon aerogels that show application potential and set forth the challenges and prospects of this kind of MAM.

Intercalation of p-Aminopyridine and p-Ethylenediamine Molecules into Orthorhombic In1.2Ga0.8S3 Single Crystals

A single crystalline layered semiconductor In_1.2Ga_0.8S₃ phase was grown, and by intercalating p-aminopyridine (NH₂-C₅H₄N or p-AP) molecules into this crystal, a new intercalation compound, In_1.2Ga_0.8S₃·0.5(NH₂-C₅H₄N), was synthesized. Further, by substituting p-AP molecules with p-ethylenediamine (NH₂-CH₂-CH₂-NH₂ or p-EDA) in this intercalation compound, another new intercalated compound-In_1.2Ga_0.8S₃·0.5(NH₂-CH₂-CH₂-NH₂) was synthesized. It was found that the single crystallinity of the initial In_1.2Ga_0.8S₃ samples was retained after their intercalation despite a strong deterioration in quality. The thermal peculiarities of both the intercalation and deintercalation of the title crystal were determined. Furthermore, the unit cell parameters of the intercalation compounds were determined from X-ray diffraction data (XRD). It was found that increasing the c parameter corresponded to the dimension of the intercalated molecule. In addition to the intercalation phases' experimental characterization, the lattice dynamical properties and the electronic and bonding features of the stoichiometric GaInS₃ were calculated using the Density Functional Theory within the Generalized Gradient Approximations (DFT-GGA). Nine Raman-active modes were observed and identified for this compound. The electronic gap was found to be an indirect one and the topological analysis of the electron density revealed that the interlayer bonding is rather weak, thus enabling the intercalation of organic molecules.

Regulated dielectric loss based on core-sheath carbon-carbon hierarchical nanofibers toward the high-performance microwave absorption

As a response to stealth technology and electromagnetic pollution, microwave absorbing materials have attracted the attention of many research scholars. However, achieving effective absorption with a low filling level is still a challenge in the harsh environment. Here, an emerging carbon-carbon composite fiber with a core-sheath structure is cleverly tailored for high-performance microwave absorber by tuning the dielectric loss. Reasonable engineering heterogeneous interfaces and conductive paths give rise to a synergistic effect of the impedance matching, conductive loss, polarization loss and multiple scattering. The obtained CR-800 achieves the maximum reflection loss of -51.91 dB, effective absorbing bandwidth of 4.82 GHz, and radar cross section (RCS) reduction value of 41.5 dBm². Furthermore, the composites own superior environmental adaptation with stable absorbing properties in the harsh environment benefited from great environmental resistance of carbon materials. Given this, the core-sheath carbon-carbon composite fibers are expected to be a candidate for radar stealth technology and electromagnetic pollution.

Mechanism for the Intercalation of Aniline Cations into the Interlayers of Graphite

The dynamic behaviors of aniline cation (ANI⁺) intercalating into graphite interlayers are systematically studied by experimental studies and multiscale simulations. The in situ intercalation polymerization designed by response surface methods implies the importance of ultrasonication for achieving the intercalation of ANI⁺. Molecular dynamics and quantum chemical simulations prove the adsorption of ANI⁺ onto graphite surfaces by cation–π electrostatic interactions, weakening the π–π interactions between graphene layers. The ultrasonication that follows breaks the hydrated ANI⁺ clusters into individual ANI⁺. Thus, the released positive charges of these dissociative cations and reduced steric hindrance significantly improve their intercalation ability. With the initial kinetic energy provided by ultrasonic field, the activated ANI⁺ are able to intercalate into the interlayer of graphite. This work demonstrates the intercalation behaviors of ANI⁺, which provides an opportunity for investigations regarding organic-molecule-intercalated graphite compounds.

Polypyrrole Decorated Flower-like and Rod-like ZnO Composites with Improved Microwave Absorption Performance

In this study, zinc oxide (ZnO)/polypyrrole (PPy) composites with flower- and rod-like structures were successfully fabricated by in situ polymerization and the hydrothermal method and used as microwave absorption (MWA) materials. The surface morphologies, crystal structures, and electromagnetic features of the as-prepared samples were measured by field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and vector network analyzer (VNA). The results show that the conductive polymer PPy was successfully decorated on the surface of ZnO substrates. The MWA ability of flower- and rod-like ZnO/PPy composites is significantly enhanced after introduction of PPy. Rod-like ZnO/PPy composites exhibited superior MWA properties than those of flower-like ZnO/PPy. The former achieved a minimum reflection loss (RLmin) of −59.7 dB at 15.8 GHz with a thickness of 2.7 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covered 6.4 GHz. PPy addition and stacked structure of rod-like ZnO/PPy composites can effectively improve the dielectric properties, form multiple reflections of incident electromagnetic waves, and generate an interfacial polarization effect, resulting in improved MWA properties of composite materials.

Heterointerface Engineering of β-Chitin/Carbon Nano-Onions/Ni-P Composites with Boosted Maxwell-Wagner-Sillars Effect for Highly Efficient Electromagnetic Wave Response and Thermal Management

The rational construction of microstructure and composition with enhanced Maxwell-Wagner-Sillars effect (MWSE) is still a challenging direction for reinforcing electromagnetic wave (EMW) absorption performance, and the related EMW attenuation mechanism has rarely been elucidated. Herein, MWSE boosted β-chitin/carbon nano-onions/Ni-P composites is prepared according to the heterointerface engineering strategy via facile layer-by-layer electrostatic assembly and electroless plating techniques. The heterogeneous interface is reinforced from the aspect of porous skeleton, nanomaterials and multilayer construction. The composites exhibit competitive EMW response mechanism between the conductive loss and the polarization/magnetic loss, as describing like the story of "The Hare and the Tortoise". As a result, the composites not only achieve a minimum reflection loss (RL_min) of - 50.83 dB and an effective bandwidth of 6.8 GHz, but also present remarkable EMW interference shielding effectiveness of 66.66 dB. In addition, diverse functions such as good thermal insulation, infrared shielding and photothermal performance were also achieved in the hybrid composites as a result of intrinsic morphology and chemicophysics properties. Therefore, we believe that the boosted MWSE open up a novel orientation toward developing multifunctional composites with high-efficient EMW response and thermal management.

Heterointerface Engineering in Electromagnetic Absorbers: New Insights and Opportunities

Electromagnetic (EM) absorbers play an increasingly essential role in the electronic information age, even toward the coming "intelligent era". The remarkable merits of heterointerface engineering and its peculiar EM characteristics inject a fresh and infinite vitality for designing high-efficiency and stimuli-responsive EM absorbers. However, there still exist huge challenges in understanding and reinforcing these interface effects from the micro and macro perspectives. Herein, EM response mechanisms of interfacial effects are dissected in depth, and with a focus on advanced characterization as well as theoretical techniques. Then, the representative optimization strategies are systematically discussed with emphasis on component selection and structural design. More importantly, the most cutting-edge smart EM functional devices based on heterointerface engineering are reported. Finally, current challenges and concrete suggestions are proposed, and future perspectives on this promising field are also predicted.

Multiple reflection and scattering effects of the lotus seedpod-based activated carbon decorated with Co3O4 microwave absorbent

The lotus seedpod-based activated carbon (LSAC) is derived from pyrolysis of lotus seedpod as biomass carbon precursor, and Co₃O₄ is then deposited to LSAC by oxidation-precipitation and crystallization process of Co ions from Co(NO₃)₂ solution. The Co₃O₄ particles uniformly decorate on the surface and/or the inner channels of LSAC. The optimal reflection loss (RL) value of LSAC/Co₃O₄-paraffin wax (PW) composite reaches -39.8 dB, and the bandwidth for RL below -10 dB and -20 dB are 10.3 and 3.0 GHz, respectively, much better than that of LSAC-PW composite for the higher magnetic loss. The addition of Co₃O₄ particles in LSAC-PW composite significantly enhance the RL values in various thicknesses. The channels of the LSAC and decorated Co₃O₄ can improve the abilities of multiple scattering, dipole polarization, interface polarization and magnetic loss. This composite provides a promising method to construct high performance absorbers by using biomass carbon to tune the dielectric properties of the ferromagnetic materials.

Design and Synthesis Strategies: 2D Materials for Electromagnetic Shielding/Absorbing

Two-dimensional (2D) materials possess special physical and chemical properties. They have been proved to have potential application advantage in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Particularly, they exhibit positive shielding and absorbing response to EMI. Here, the research progress of preparation, electromagnetic performance and microwave shielding/absorbing mechanisms of 2D composite materials are introduced. Effective preparation routes including introducing heteroatoms, constructing unique structures and 2D composite materials are described. Furthermore, the application prospects and challenges for the development of novel EMI materials are expatiated.

An Electromagnetic Microwave Stealth Photothermal Soft Actuator with Lightweight and Hydrophobic Properties

Electromagnetic (EM) microwave stealth soft robots are in urgent need in military application. Photothermal soft actuators with photomechanical energy conversion have attracted significant interest owing to their remote control, flexibility, and contactless operation. The innovative combination of an electromagnetic microwave absorption (EMA) function with a photothermal actuator paves the way for this aspect. Here, a composite with unique dual three-dimensional foam is fabricated based on graphene and hollow carbon spheres (HCSs). When exposed to 1 sun illumination, the temperature could increase to 50 °C within 1 min and plateaus at 80 °C for hollow carbon spheres-graphene foam-polydimethylsiloxane (HCSs-GF-PDMS), which shows great photothermal performance. A wormlike crawling robot has been constructed based on this composite material, which could move forward under only 1 sun illumination. Remarkably, the EM stealth could be successfully realized because the composite material exhibits great EMA performance with a minimum reflection loss of -56.99 dB at a thickness of 2.5 mm, and the maximum effective absorption bandwidth is 8.65 GHz. In addition, the HCSs-GF exhibits hydrophobic and lightweight functions as well, which lighten the weight of soft robots and lead to self-cleaning and energy saving. This work provides a promising direction of multifunctional EM stealth soft robots.

Three-Dimensional Ordered Mesoporous Carbon Spheres Modified with Ultrafine Zinc Oxide Nanoparticles for Enhanced Microwave Absorption Properties

Currently, electromagnetic radiation and interference have a significant effect on the operation of electronic devices and human health systems. Thus, developing excellent microwave absorbers have a huge significance in the material research field. Herein, a kind of ultrafine zinc oxide (ZnO) nanoparticles (NPs) supported on three-dimensional (3D) ordered mesoporous carbon spheres (ZnO/OMCS) is prepared from silica inverse opal by using phenolic resol precursor as carbon source. The prepared lightweight ZnO/OMCS nanocomposites exhibit 3D ordered carbon sphere array and highly dispersed ultrafine ZnO NPs on the mesoporous cell walls of carbon spheres. ZnO/OMCS-30 shows microwave absorbing ability with a strong absorption (- 39.3 dB at 10.4 GHz with a small thickness of 2 mm) and a broad effective absorption bandwidth (9.1 GHz). The outstanding microwave absorbing ability benefits to the well-dispersed ultrafine ZnO NPs and the 3D ordered mesoporous carbon spheres structure. This work opened up a unique way for developing lightweight and high-efficient carbon-based microwave absorbing materials.

Constructing Ni12P5/Ni2P Heterostructures to Boost Interfacial Polarization for Enhanced Microwave Absorption Performance

Heterostructures with a rich phase boundary are attractive for surface-mediated microwave absorption (MA) materials. However, understanding the MA mechanisms behind the heterogeneous interface remains a challenge. Herein, a phosphine (PH₃) vapor-assisted phase and structure engineering strategy was proposed to construct three-dimensional (3D) porous Ni₁₂P₅/Ni₂P heterostructures as microwave absorbers and explore the role of the heterointerface in MA performance. The results indicated that the heterogeneous interface between Ni₁₂P₅ and Ni₂P not only creates sufficient lattice defects for inducing dipolar polarization but also triggers uneven spatial charge distribution for enhancing interface polarization. Furthermore, the porous structure and proper component could provide an abundant heterogeneous interface to strengthen the above polarization relaxation process, thereby greatly optimizing the electromagnetic parameters and improving the MA performance. Profited by 3D porous heterostructure design, P400 could achieve the maximum reflection loss of -50.06 dB and an absorption bandwidth of 3.30 GHz with an ultrathin thickness of 1.20 mm. Furthermore, simulation results confirmed its superior ability (14.97 dB m² at 90°) to reduce the radar cross section in practical applications. This finding may shed light on the understanding and design of advanced heterogeneous MA materials.

A Facile Synthesis of Novel Amorphous TiO2 Nanorods Decorated rGO Hybrid Composites with Wide Band Microwave Absorption

Amorphous structures may play important roles in achieving highly efficient microwave absorption performance due to the polarization losses induced by the disorders, vacancies and other functional groups existed in them. Herein, a kind of amorphous TiO2/rGO composite (a-TiO2/rGO) was successfully fabricated via a facile one-step solvothermal method. The complex permittivity of the composites can be regulated by adjusting the addition of precursor solution. The minimum reflection loss of a-TiO2/rGO composites reached -42.8 dB at 8.72 GHz with a thickness of 3.25 mm, and the widest efficient absorption bandwidth (EAB) was up to 6.2 GHz (11.8 to 18 GHz) with a thickness of only 2.15 mm, which achieved the full absorption in Ku band (12 to 18 GHz). Furthermore, the EAB was achieved ranging from 3.97 to 18 GHz by adjusting the thickness of the absorber, covering 87.7% of the whole radar frequency band. It is considered that the well-matched impedance, various polarization processes, capacitor-like structure and conductive networks all contributed to the excellent microwave absorption of a-TiO2/rGO. This study provides reference on constructing amorphous structures for future microwave absorber researches and the as-prepared a-TiO2/rGO composites also have great potential owing to its facile synthesis and highly efficient microwave absorption.

Constructing and optimizing hollow ZnxFe3-xO4@polyaniline composites as high-performance microwave absorbers

In this study, a series of hollow Zn_xFe_3-xO₄@polyaniline composites (ZFO@PANI) were synthesized by a facile solvothermal process and followed by in-situ chemical oxidation polymerization method, and then evaluated as microwave absorption (MA) absorbers. The effect of ZFO content on the electrical conductivity, electromagnetic parameters and MA performance of the ZFO@PANI composites was also elaborately investigated. As anticipated, the optimized composites of S2 exhibits the minimum reflection loss (RL_min) of -59.44 dB at 11.04 GHz with a matching thickness of 2.31 mm, and the broadest effective absorption bandwidth (EAB, RL < -10 dB, >90% absorption) of up to 4.65 GHz (13.35-18.0 GHz) at 1.72 mm. Noticeably, by adjusting the thickness from 1.5 to 5.0 mm, it can be observed that its RL_min values are all much lower than -10 dB and the qualified EAB can cover the entire C, X and Ku bands. The enhanced MA performance of S2 is mainly due to the efficient synergistic effect between dielectric loss (PANI) and magnetic loss (ZFO nanosphere), and thus achieving the relative balance of impedance matching (appropriate ZFO content) and attenuation capability. Therefore, it has great prospect to be explored as attractive candidate in practical application.

Design of MOF-derived hierarchical Co@C@RGO composite with controllable heterogeneous interfaces as a high-efficiency microwave absorbent

Carbon-based composites have triggered tremendous attention in the development of high-efficiency microwave absorbers, due to their compatibility, light weight, and high microwave absorption. However, fabricating carbon-based absorbers with a strong absorption ability in a broad frequency range is challenging. Hence, a facile strategy was used to produce Co@C derived from a zeolitic imidazolate framework (ZIF)@ graphene. The Co@C@RGO composite was obtained by annealing the ZIF67/GO nanocomposite precursor at 650 °C in a nitrogen atmosphere. Due to the magnetic loss induced by the Co particles, the dielectric loss generated by the carbon skeletons and graphene, and the interfacial polarization between the components, the hierarchical composite exhibits superior electromagnetic (EM) wave absorption properties. The optimal reflection loss (R_L) of the Co@C@ RGO composite can be up to -67.5 dB at 2.6 mm, and the effective bandwidth (≥-10 dB) is 5.4 GHz (10-15.4 GHz) with a thickness of 2 mm at 20 wt% loading. The dipolar polarization caused by graphene, as well as enhanced impedance matching, synergistic effect and interfacial effect among the components, increase the microwave absorption performance of the composite. This work may open a new path to use the Co@C@RGO composite with its high-efficiency EM wave properties as an absorber.

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.

Enhanced Electromagnetic Wave-Absorbing Performance of Magnetic Nanoparticles-Anchored 2D Ti3C2Tx MXene

Two-dimensional Ti₃C₂T_x MXene-based hybrids-anchored magnetic metal nanoparticles show a huge potential application as effective wave absorbers due to the synergistic electromagnetic (EM) loss effect. In this work, uniform and size-controllable nickel, cobalt, or nickel-cobalt alloy nanoparticles were in situ grown on the surface of MXene via a facile and moderate co-solvothermal method for the first time. As an example, a nickel nanoparticles-anchored MXene (Ni@MXene) hybrid was homodispersed into dielectric polyvinylidene fluoride to develop its EM wave-absorbing capacity to a great extent. As expected, the results showed strong reflection loss (RL_min = -52.6 dB at 8.4 GHz), broad effective absorption bandwidth (EAB = 3.7 GHz including 71% of X-band), low loading (10 wt % Ni@MXene), and thin thickness (3.0 mm). By adjusting the sample thickness, EAB can cover completely the whole X-band with a maximum of 6.1 GHz, showing a huge potential of Ni@MXene hybrid applying as aircraft stealth coating. The mechanism analyses revealed that the excellent impedance matching, magnetocoupling effect, conductance, magnetic loss, and multiple scatterings contribute to the splendid EM wave-absorbing performance of the Ni@MXene hybrid. Considering the excellent overall performance, the Ni@MXene hybrid was identified as a promising candidate for EM wave absorption.