Fabrication of CuS/Fe(3)O(4)@polypyrrole flower-like composites for excellent electromagnetic wave absorption

Regulation of PPy Growth States by Employing Porous Organic Polymers to Obtain Excellent Microwave Absorption Performance

Regulating the different growth states of polypyrrole (PPy) is a key strategy for obtaining PPy composites with high electromagnetic wave (EMW) absorption properties. This work finds that the growth states of PPy is regulated by controlling the amount of pyrrole added during the preparation of composites, so as to regulate the development of conductive networks to obtain excellent EMW absorption performance. The POP/PPy-200 composite achieves an effective absorption bandwidth (EAB) of 6.24 GHz (11.76-18.00 GHz) at a thickness of only 2.34 mm, covering 100% of the Ku band. The minimum reflection loss of -73.05 dB can be demonstrated at a thickness of only 2.29 mm, while at the same time showing an EAB of 5.96 GHz to meet the requirements of "thin", "light", "wide", and "strong". Such excellent EMW absorption performance is attributed to the conductive loss caused by the regulation of the growth states of PPy and the polarization loss caused by the heterostructure. This work also addresses the key challenge that porous organic polymers (POPs) cannot be applied to EMW absorption due to poor conductivity and providing new insights into the candidates for EMW absorbing materials.

Carboxymethyl cellulose-based photothermal film: A sustainable packaging with high barrier and tensile strength for food long-term antibacterial protection

Traditional packaging materials feed the growing global food protection. However, these packaging materials are not conducive to environment and have not the ability to kill bacteria. Herein, a green and simple strategy is reported for food packaging protection and long-term antibacterial using carboxymethylcellulose-based photothermal film (CMC@CuS NPs/PVA) that consists of carboxymethyl cellulose (CMC) immobilized copper sulfide nanoparticles (CuS NPs) and polyvinyl alcohol (PVA). With satisfied oxygen transmittance (0.03 cc/m2/day) and water vapor transmittance (163.3 g/m2/day), the tensile strength, tear strength and burst strength reached to 3401.2 N/m, 845.7 mN and 363.6 kPa, respectively, which could lift 4.5 L of water. The composite film had excellent photothermal conversion efficiency and photothermal stability. Under the irradiation of near infrared (NIR), it can rapidly heated up to 197 °C within 25 s. The antibacterial analysis showed that the inhibition rate of composite film against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) could all reach >99 %. Furthermore, the synthesized CuS NPs was well immobilized and the residual rate of copper kept 98.7 % after 10 days. Noticeably, the composite film can preserve freshness of strawberries for up to 6 days. Therefore, the composite film has potential application for food antibacterial protection.

Hierarchical etching-assembly engineering of Fe-based composite microspheres with balanced magnetic-dielectric synergy towards ultrahigh electromagnetic wave absorption

Hierarchical engineering of magnetic-dielectric composite microspheres has attracted increasing attention owing to its potential to enhance electromagnetic wave absorption (EMA) through magnetic-dielectric synergy. However, optimizing magnetic-dielectric balance in composite microspheres at the nanoscale remains a formidable task due to their limited component optimization and microstructural regulation. Herein, a novel approach is proposed to modify conventional carbonyl iron powder (CIP) microspheres via synergistic etching-assembly strategy. By applying a polydopamine coating, successive tannic acid (TA) etching-assembly, and pyrolysis, hierarchical iron@carbon-1/N-doped carbon (Fe@C-1/NC) composite microspheres are obtained. This overcomes the drawbacks of CIP microspheres, including their high density and poor impedance matching, which hinder EMA performance. Hierarchical carbon layer engineering can introduce abundant dipole centers, heterogeneous interfaces, and conductive networks to induce dielectric loss, while magnetic components contribute to magnetic resonance and eddy current loss, as demonstrated by the results. Accordingly, Fe@C-1/NC composite microspheres demonstrate a minimum reflection loss (RLmin) of -70.7 dB and an effective absorption bandwidth of 3.75 GHz at a matching thickness of 2.3 mm. Generally, this work paves the way towards CIP engineering to provide guidance to the future exploration of hierarchical magnetic-dielectric EMA materials.

The Utilization of Metal-Organic Frameworks and Their Derivatives Composite in Supercapacitor Electrodes

Up to now, the mainstream adoption of renewable energy has brought about substantial transformations in the electricity and energy sector. This shift has garnered considerable attention within the scientific community. Supercapacitors, known for their exceptional performance metrics like good charge/discharge capability, strong power density, as well as extended cycle longevity, have gained widespread traction across various sectors, including transportation and aviation. Metal-organic frameworks (MOFs) with unique traits including adaptable structure, highly customizable synthetic methods, and high specific surface area, have emerged as strong candidates for electrode materials. For enhancing the performance, MOFs are commonly compounded with other conducting materials to increase capacitance. This paper provides a detailed analysis of various common preparation strategies and characteristics of MOFs. It summarizes the recent application of MOFs and their derivatives as supercapacitor electrodes alongside other carbon materials, metal compounds, and conductive polymers. Additionally, the challenges encountered by MOFs in the realm of supercapacitor applications are thoroughly discussed. Compared to previous reviews, the content of this paper is more comprehensive, offering readers a deeper understanding of the diverse applications of MOFs. Furthermore, it provides valuable suggestions and guidance for future progress and development in the field of MOFs.

Fabrication of hollow core-shell NiCo2O4@polypyrrole nanofibers/reduced graphene oxide ternary composites with excellent microwave absorption performances

In contemporary times, electromagnetic radiation poses a significant threat to both human health and the normal functioning of electronic devices. Developing composites as adsorption materials possess exceptional electromagnetic wave absorption performances can efficient address this critical issue. Herein, hollow core-shell NiCo2O4@polypyrrole nanofibers/reduced graphene oxide (NiCo-HFPR) composites are fabricated by the combination of electrostatic spinning, air calcination, in-situ polymerization, freeze-drying and hydrazine vapor reduction. As anticipated, NiCo-HFPR-0.2 exhibits noteworthy properties, with the minimum reflection loss (RLmin) of -61.20 dB at 14.26 GHz and 1.56 mm, as well as the effective absorption bandwidth (EAB) of 4.90 GHz at 1.57 mm. Additionally, the simulation procedure is employed to determine the radar cross-section (RCS) attenuation. In comparison to a singular perfect electrically conductive (PEC) layer, the PEC layer coated with NiCo-HFPR-0.2 consistently yields an RCS value below -10 dB m2 within the range of -60° < θ < 60°. The RCS attenuation value of the NiCo-HFPR-0.2 coating achieves an outstanding 31.0 dB m2 at θ = 0°, strongly affirming the ability to effectively attenuate electromagnetic wave in real-world applications. The employed experimental methodology, the meticulously crafted composite, and the simulation outcomes presented in this study bear great promise for the progressive advancement of both theoretical investigations and practical applications within the domain of electromagnetic wave absorption.

Fabrication of the hollow dodecahedral NiCoZn layered double hydroxide for high-performance flexible asymmetric supercapacitor

Layered double hydroxides (LDHs) with unique layered structure have excellent theoretical capacitance. Nevertheless, the constrained availability of electrically active sites and cationic species curtails their feasibility for practical implementation within supercapacitors. Most of the reported materials are bimetallic hydroxides, and fewer studies are on trimetallic hydroxides. In here, the hollow dodecahedron NiCoZn-LDH is synthesized using CoZn metal-organic frameworks (CoZn-MOFs) as template. Its morphology and composition are studied in detail. Concurrently, the effect of the amount of third component on the resulting structure of NiCoZn-LDH is also researched. Benefiting from its favorable structural and compositional attributes to efficient transfer of ions and electrons, NiCoZn-LDH-200 demonstrates outstanding specific capacitance of 1003.3F g-1 at 0.5 A/g. Furthermore, flexible asymmetric supercapacitor utilizing NiCoZn-LDH-200 as the positive electrode and activated carbon (AC) as the negative electrode reveals favorable electrochemical performances, including a notable specific capacitance of 184.7F g-1 at 0.5 A/g, a power density of 368.21 W kg-1 at a high energy density of 65.66 Wh kg-1, an energy density of 31.78 Wh kg-1 at a high power density of 3985.97 W kg-1, a capacitance retention of 92 % after 8000 cycles at 5 A/g, and a good capacitance retention of 90 % after 500 cycles of bending. The template method presented herein can effectively solve the problem of easy accumulation and improve the electrochemical properties of the materials, which exhibits a broad research prospect.

Data-Driven oriented diatomic doping strategy to customize frequency dispersion for considerable microwave absorption

The electromagnetic (EM) parameters are the key factors to decode the complex microwave absorption properties, including matching thickness, absorption bandwidth and intensity. Numerous works hence have been focused on optimizing EM parameters to reinforce the comprehensive absorption performance, while most of the adopted experimental means still remain in sporadic and random attempts. In this work, the data-driven approach is first employed to forecast that a fierce frequency-dispersion of permittivity is necessary for the broad absorption, and the appropriate magnetic component can mitigate this elusive trend of required permittivity. Oriented by the simulated results, the B/N diatomic doped C/Fe3C magnetoelectric composites are successfully constructed, aiming at the precise regulation of electronic properties to achieve these specially customized EM parameters by forming multi-polarization resonances. The results demonstrate that the introduction of N defects and B defects could enrich the types of dipole pairs (CN, C-B, CNB, vacancy, etc.) and thus activate multi-polarization behavior. The charge density differences calculated by the first-principle further demonstrate that the occupation of B for C bonded with Pyridinic-N and Pyrrolic-N contributes to intense polarization behaviors over the lower frequency range. As a result, excellent microwave absorption properties can be finally achieved with an effective absorbing bandwidth reaching 7.2 GHz at 2.1 mm, implying that the joint use of data-driven and doping engineering strategies to customize frequency dispersion characteristics provides precious guidelines for boosting microwave absorption performance.

Fabrication of 1D Ni nanochains@Zn2+ doping polypyrrole/reduced graphene oxide composites for high-performance electromagnetic wave absorption

Nowadays, electromagnetic radiation significantly impacts the normal operation of electronic devices and poses risks to human health. To effectively address this problem, the development of composites that exhibit exceptional electrochemical wave absorption through the combination of different components holds great promise. In this study, we have successfully prepared 1D Ni nanochains@Zn2+ doping polypyrrole/reduced graphene oxide (Ni NCs@Z-P/RGO, denoted as R-x) composites using a combination of hydrothermal, solvothermal, in situ polymerization, and physical blending methods. Notably, the R-2 composite demonstrates a remarkable minimum reflection loss (RLmin) of -63.58 dB at 14.3 GHz, with a thickness of 1.61 mm. Furthermore, the R-2 composite exhibits an impressive effective absorption bandwidth (EAB) of 5.08 GHz (11.92 GHz-17 GHz) at a thickness of 1.67 mm. These outstanding performances can be attributed to the synergistic effect of the different components and a well-thought-out structural design. Moreover, to showcase the practical applicability of the material, we have conducted additional investigations on the reduction of the radar cross-sectional area (RCS). The results strongly demonstrate that the prepared composite material, when used as a coating, effectively reduces the RCS value by up to 26.6 dB m2 for R-2 at θ = 0°. The experimental methods and simulations presented in this study hold significant potential for application in wave absorption research and practical implementations. Additionally, the prepared Ni NCs@Z-P/RGO composites demonstrate feasibility as wave-absorbing materials for future utilization.

Fabrication of cobalt-zinc bimetallic oxides@polypyrrole composites for high-performance electromagnetic wave absorption

Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co3O4/ZnCo2O4 and ZnCo2O4/ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal-organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core-shell structures known as Co3O4/ZnCo2O4@PPy (CZCP) and ZnCo2O4/ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RLmin) of -71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials.

Design and synthesis of one-dimensional magnetic composites with Co nanoparticles encapsulated in carbon nanofibers for enhanced microwave absorption

With the increased usage of electromagnetic microwaves (EM) in wireless communication technology, the problem of electromagnetic radiation pollution has grown dramatically. This study successfully prepared novel Co/C magnetic nanocomposite fibers for EM absorption using the electrospinning and carbonization methods. The morphology, composition, magnetic properties, and EM absorption performance were extensively characterized. This material shows exceptional EM absorption performance, achieving -72.01 dB (at 2.08 mm) for minimum reflection loss (RLmin) and 5.4 GHz (at 1.68 mm) for effective absorption bandwidth (EAB). The performance surpasses not only any single precursor but also stands as the best in similar investigations. It can be attributed to the microstructure of magnetic Co nanoparticles encapsulated in carbon nanofibers and the macrostructure of cross-linked three-dimensional (3D) conductive networks. The combination of these structures resulted in excellent dielectric loss, magnetic loss, and impedance matching. This research offers new insights into the production of one-dimensional (1D) carbon-based absorbers, while also establishing a theoretical foundation for exploring the application potential of this material. These findings may contribute to the development of more efficient and practical EM absorption materials in the future.

Simple fabrication of cobalt-nickel alloy/carbon nanocomposite fibers for tunable microwave absorption

A series of CoNi/C nanocomposite fibers with different Co and Ni ratios were successfully prepared by electrospinning and carbonization techniques for the study of electromagnetic microwave (EMW) absorbing materials. We systematically studied the influence of Co and Ni content on the microstructure, chemical composition, magnetic properties, and EMW absorption characteristics of the samples. The results showed that CoNi/C nanocomposite fibers obtained excellent EMW absorption ability through the reasonable design of the composition, and the Co/Ni ratio significantly affected the microstructure and EMW absorption performance. When the Co/Ni ratio was 1/3, the minimum reflection loss (RLmin) is -71.2 dB (2.4 mm, 13.4 GHz), and the maximum effective absorption bandwidth (EAB, RL＜-10 dB) is up to 5.9 GHz (2.2 mm, 12.1-18 GHz), covering almost the entire Ku band. This study demonstrated the enormous potential of one-dimensional structure in the field of EMW absorption. In addition, the CoNi/C nanocomposite fiber synthesized using a straightforward and low-cost method not only has excellent EMW absorption performance but also has the potential for practical application. The results of this study provide a simple and effective approach for designing high-performance EMW absorbing materials.

Nitrogen-Doped Magnetic-Dielectric-Carbon Aerogel for High-Efficiency Electromagnetic Wave Absorption

Carbon-based aerogels derived from biomass chitosan are encountering a flourishing moment in electromagnetic protection on account of lightweight, controllable fabrication and versatility. Nevertheless, developing a facile construction method of component design with carbon-based aerogels for high-efficiency electromagnetic wave absorption (EWA) materials with a broad effective absorption bandwidth (EAB) and strong absorption yet hits some snags. Herein, the nitrogen-doped magnetic-dielectric-carbon aerogel was obtained via ice template method followed by carbonization treatment, homogeneous and abundant nickel (Ni) and manganese oxide (MnO) particles in situ grew on the carbon aerogels. Thanks to the optimization of impedance matching of dielectric/magnetic components to carbon aerogels, the nitrogen-doped magnetic-dielectric-carbon aerogel (Ni/MnO-CA) suggests a praiseworthy EWA performance, with an ultra-wide EAB of 7.36 GHz and a minimum reflection loss (RLmin) of - 64.09 dB, while achieving a specific reflection loss of - 253.32 dB mm-1. Furthermore, the aerogel reveals excellent radar stealth, infrared stealth, and thermal management capabilities. Hence, the high-performance, easy fabricated and multifunctional nickel/manganese oxide/carbon aerogels have broad application aspects for electromagnetic protection, electronic devices and aerospace.

One-dimensional core-shell CoC@CoFe/C@PPy composites for high-efficiency microwave absorption

In recent years, electromagnetic pollution has become more and more serious, and there is an urgent need for microwave absorbing materials with superior performance. Prussian blue analogue (PBA) is a metal organic framework material with the advantages of diverse morphology and tunable composition. Therefore, PBA has attracted a lot of attention in the field of microwave absorption. In this work, PBA was coated on the surface of carbon composites by hydrothermal method, and then PPy was compounded on its surface after carbonization treatment to construct hierarchical core-shell CoC@CoFe/C@PPy fibers. The fibers have Co-doped C composites as the core and CoFe/C decorated with PPy as the shell. This unique hierarchical structure and various microwave absorption mechanisms are described in detail. The microwave absorption performance is optimized by adjusting the filling of the sample. The best microwave absorption performances are achieved at 25 wt% filling of CoC@CoFe/C@PPy. At a thickness of just 1.69 mm, CoC@CoFe/C@PPy fiebrs have a minimum reflection loss (RLmin) of -64.32 dB. When the thickness is 1.88 mm, CoC@CoFe/C@PPy achieves a maximum effective absorption bandwidth (EABmax) of 5.38 GHz. The results indicate that the CoC@CoFe/C@PPy composite fibers have a great potential in the field of microwave absorption.

Magnetic Core@Shell Fe3O4@Polypyrrole@Sodium Dodecyl Sulfate Composite for Enhanced Selective Removal of Dyestuffs and Heavy Metal Ions from Complex Wastewater

Adsorption materials have demonstrated huge potential in treating sewage; however, it is a great challenge to fabricate an adsorbent effectively adsorbing multiple dyestuffs and heavy metal ions simultaneously. Here, a magnetic core@shell Fe3O4@polypyrrole@sodium dodecyl sulfate (Fe3O4@PPy@SDS) composite is prepared through the combination of a hydrothermal method, an in situ polymerization method, and modification, exhibiting enhanced selective removal of five dyestuffs (methylene blue (MB), malachite green (MG), rhodamine B (RhB), Congo red (CR), acid red 1 (AR1)), and heavy metal ions (Mn(VII)). The effects of adsorbent type, time, initial concentration of the adsorbate, and temperature on adsorption performances are investigated in detail. Kinetics and isotherm studies indicate that all adsorption processes are more in line with the pseudo-second-order kinetic model and the Langmuir model, the diffusion behavior is controlled by intraparticle diffusion and liquid film diffusion, and research of thermodynamics reveals a spontaneous endothermic behavior. The removal efficiency after five desorption-adsorption cycles can still reach more than 90%. The prepared Fe3O4@PPy@SDS composite is an efficient and promising renewable adsorbent for the treatment of dyestuffs and Mn(VII), exhibiting a wide range of applications in the field of adsorption.

Fabrication of hierarchical reduced graphene oxide decorated with core-shell Fe3O4@polypyrrole heterostructures for excellent electromagnetic wave absorption

The design of heterostructures with reasonable chemical composition and spatial structure is one of the effective strategies to achieve high performances electromagnetic wave (EMW) absorption. Herein, reduced graphene oxide (rGO) nanosheets decorated with hollow core-shell Fe₃O₄@PPy (FP) microspheres have been prepared by the combination of hydrothermal method, in situ polymerization method, directional freeze-drying and hydrazine vapor reduction. FP acting as traps can consume EMW trapped into their interior through the magnetic and dielectric losses. RGO nanosheets forming the conductive network are served as multi-reflected layers. Moreover, the impedance matching is optimized by the synergistic effect between FP and rGO. As expected, the synthetic Fe₃O₄@PPy/rGO (FPG) composite shows excellent EMW absorption performances with the minimum reflect loss (RL_min) of -61.20 dB at 1.89 mm and the effective absorption bandwidth (EAB) of 5.26 GHz at 1.71 mm. The excellent performances for the heterostructure are attributed to the synergistic effect of conductive loss, dielectric loss, magnetic loss, multiple reflection loss, and optimized impedance matching. This work provides a simple and effective strategy for the fabrication of lightweight, thin and high-performances EMW absorbing materials.

Urchin-like Fe3O4@C hollow spheres with core-shell structure: Controllable synthesis and microwave absorption

The steadily increasing use of microwave stealth materials in aerospace flying vehicles needs the development of lightweight absorbers with low density and high thermal stability for printing or spraying. In that regard, the structural designability of typical microwave absorbers made of Fe₃O₄ seems to be a significant roadmap. In this work, a hollow spherical structure with a uniform carbon shell around the urchin-like Fe₃O₄ core (Fe₃O₄@C) was produced via a two-step hydrothermal method and annealing. The Fe₃O₄@C absorber exhibited a strong minimum reflection loss (RL_min) of -73.5 dB at the matching thickness of 3.23 mm. The maximum effective absorption bandwidth (EAB_max) was 4.78 GHz at 4.55 mm. The proposed urchin-like core-shell structure was shown to provide good impedance matching and electromagnetic loss ability due to the synergistic effect of Fe₃O₄ and C. In particular, the urchin-like structure increases the heterogeneous interfaces and effectively improves their polarization and relaxation. On the other hand, it reduces the density of the absorber and enhances multiple scattering attenuations of electromagnetic waves (EMWs). Therefore, the findings of the present study open up prospects for the design of high-efficiency lightweight microwave absorbers with specialized structures.

A crosslinked coral-like Co@CoO/RGO nanohybrid structure with good electromagnetic wave absorption performance

The combination of magnetic and dielectric materials followed by appropriate structure design is an effective approach to achieve high electromagnetic wave absorption properties. Here, crosslinked Co@CoO/reduced graphene oxide nanohybrids (CCRGO) were fabricated via a simple three-step method. The experimental results show that compared with previous works, the as-prepared CCRGO nanohybrids achieve higher electromagnetic wave absorption and broader effective bandwidth at a lower filler loading. The electromagnetic parameters and electromagnetic wave absorption performance could be apparently adjusted by controlling the adding content of graphene oxide (GO) and the reduction temperature. Among a series of samples, CCRGO3-650 nanohybrid yields the best electromagnetic wave absorption performance benefiting from the proper GO addition and reduction temperature. At a filler loading of 20 wt%, the maximal reflection loss reaches to -64.67 dB at a thickness of 2.53 mm and the effective bandwidth below -10 dB covers the whole X band at a thickness of 2.51 mm. The good performance may be ascribed to the advantages of the dielectric and magnetic component as well as the special crosslinked structure, which triggers a synergistic absorption mechanism including multiple reflection/scattering, interface polarization, dipole polarization, conductive loss, eddy current loss, exchange resonance in the electromagnetic wave dissipation process. The good electromagnetic wave absorption performance affirms the potential application of CCRGO nanohybrids in the field of stealth materials.