Facile fabrication of metal-organic framework derived Fe/Fe3O4/FeN/N-doped carbon composites coated with PPy for superior microwave absorption

MOF-Derived Hollow Fe/FeN/C Heterogeneous Composites for Broad-Band and Efficient Microwave Absorption

The construction of hollow structures and the incorporation of metal nanoparticles have been shown to be two potential approaches to achieving high-performance microwave absorption. In this study, a hollow polyhedron material featuring an FeN/Fe-doped carbon matrix was synthesized by an acidification corrosion and pyrolysis strategy. The formation of heterojunctions, coupled with the design of hollow structures, significantly improved the dielectric loss capacity of the material. Furthermore, the incorporation of magnetic metal nanoparticles not only increased the magnetic loss but also enriched the loss mechanisms of the material, leading to an overall improvement in the magnetic loss. Under the synergistic effects of these factors, the material exhibited exceptional microwave absorption properties. In particular, at a material thickness of only 2.3 mm, the minimum reflection loss value of the FeN/Fe@HC nanocomposite reached -64.5 dB with an effective absorption bandwidth of 5.1 GHz. These results further highlight the importance of a hollow structure design and metal atom doping in improving microwave absorption performance.

State-of-the-Art, Insights, and Perspectives for MOFs-Nanocomposites and MOF-Derived (Nano)Materials

Composite structures created from metal‒organic framework (MOF) matrices are reviewed in this work. Depending on the nature of the second component apart from the MOF platform, several synergistic properties may arise; at the same time, the initial features of the single constituent materials are usually maintained, and individual shortcomings are mitigated. Currently, timely energy and environmental challenges necessitate the quest for more advanced materials and technologies. Significant developments in MOF-nanocomposites have enabled their application across a wide range of modern and traditional fields. This review demonstrates in an exhaustive and critical way a broad range of MOF-based nanocomposites, namely, MOF/perovskite nanoparticles (NPs), MOF/metal (non-iron) oxide NPs, MOF/Fe3O4 NPs, MOF/metal chalcogenide NPs, MOF/metal NPs, and MOF/carbon-based materials, as well as nanocomposites of MOFs with other semiconductor NPs. Key points related to the synthesis, characterization, and applications of these materials are provided. Depending on their configuration, the composites under discussion can be applied in domains such as photoelectrochemical sensing, antibiotic/dye degradation, optoelectronics, photovoltaics, catalysis, solar cells, supercapacitors, batteries, water remediation, and drug loading. Sometimes, MOFs can undergo certain processes (e.g. pyrolysis) and act as precursors for composite materials with appealing characteristics. Therefore, a special section in the manuscript is devoted to MOF-derived NP composites. Toward the end of the text, we conclude while also describing the challenges and possibilities for further investigations in the umbrella of material categories analyzed herein. Despite the progress achieved, key questions remain to be answered regarding the relationships among the morphology, properties, and polyvalent activity of these materials. The present work aims to shed light on most of their aspects and innovative prospects, facilitating a deeper comprehension of the underlying phenomena, functionality, and mechanistic insights governing their behavior.

Multi-metallic MOF based composites for environmental applications: synergizing metal centers and interactions

The escalating threat of environmental issues to both nature and humanity over the past two decades underscores the urgency of addressing environmental pollutants. Metal-organic frameworks (MOFs) have emerged as highly promising materials for tackling these challenges. Since their rise in popularity, extensive research has been conducted on MOFs, spanning from design and synthesis to a wide array of applications, such as environmental remediation, gas storage and separation, catalysis, sensors, biomedical and drug delivery systems, energy storage and conversion, and optoelectronic devices, etc. MOFs possess a multitude of advantageous properties such as large specific surface area, tunable porosity, diverse pore structures, multi-channel design, and molecular sieve capabilities, etc., making them particularly attractive for environmental applications. MOF-based composites inherit the excellent properties of MOFs and also exhibit unique physicochemical properties and structures. The tailoring of central coordinated metal ions in MOFs is critical for their adaptability in environmental applications. Although many reviews on monometallic, bimetallic, and polymetallic MOFs have been published, few reviews focusing on MOF-based composites with monometallic, bimetallic, and multi-metallic centers in the context of environmental pollutant treatment have been reported. This review addresses this gap by providing an in-depth overview of the recent progress in MOF-based composites, emphasizing their applications in hazardous gas sensing, electromagnetic wave absorption (EMWA), and pollutant degradation in both aqueous and atmospheric environments and highlighting the importance of the number and type of metal centers present. Additionally, the various categories of MOFs are summarized. MOF-based composites demonstrate significant promise in addressing environmental challenges, and this review provides a clear and valuable perspective on their potential in environmental applications.

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.

MOF-derived Co-C composites with 3D star structure for enhanced microwave absorption

The demand of microwave absorption materials (MAMs) with unique morphologies and electromagnetic (EM) balance has become necessary in recent years. Due to the ease of synthesis and tunable structure, metal-organic frameworks (MOFs) are widely used for this special MAMs. In this study, a new three-dimensional hybrid MOF is proposed that is co-doped with six equally branched star morphologies. The Co-C composite has the same six-branched morphology as that of the precursor. When the EM wave is incident, this special structure makes it easier for the EM wave to enter the material vertically due to the expansion of the incident surface, which is effective in adjusting the transmission path of the electron and the reflection and distribution of the EM wave. Because of the special morphology and magneto-dielectric synergy, the Co-C composite shows a minimum reflection loss (RLmin) of -48.5 dB at 11.0 GHz at an absorption thickness of 3.0 mm, with a microwave absorption bandwidth (EAB) of 6.1 GHz. This research provides a practical guidance for preparing the MAMs of special star structure.

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.

A review on composite strategy of MOF derivatives for improving electromagnetic wave absorption

To address the electromagnetic wave (EMW) pollution issues caused by the development of electronics and wireless communication technology, it is urgent to develop efficient EMW-absorbing materials. With controllable composition, diverse structure, high porosity, and large specific surface area, metal-organic framework (MOF) derivatives have sparked the infinite passion and creativity of researchers in the electromagnetic field. Against the challenges of poor inherent impedance matching and insufficient attenuation capability of pure MOF derivative, designing and developing MOF derivative-based composites by compounding MOF with other materials, such as graphene, CNTs, MXene, and so on, has been an effective strategy for constructing high-efficiency EMW absorbing materials. This review systematically expounds the research progress of MOF derivative-based composite strategies, and discusses the challenges and opportunities faced by MOF derivatives in the field of EMW absorption. This work can provide some good ideas for researchers to design and prepare high-efficiency MOF-based EMW absorbing materials in applications of next-generation electronics and aerospace.

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.

Heterostructured Ni3B/Ni nanosheets for excellent microwave absorption and supercapacitive application

The development of electronic information technology has placed higher demands on microwave absorption materials (MAMs), especially the exploration of novel MAMs to broaden their application. At present, little attention has been given the wave absorption properties of transition metal borides (TMBs). In this work, a simple and economical method is developed to prepare Ni₃B/Ni heterostructure nanosheets and their possible applications for microwave absorption (MA) and supercapacitor are evaluated. It is worth noting that Ni₃B/Ni nanosheets exhibit excellent MA properties due to the aggregated nanosheet-like morphology of Ni₃B/Ni with enhancing interfacial polarization, as well as the synergistic effect of dielectric and magnetic losses. It is observed in experiments that the minimum reflection loss value of Ni₃B/Ni is -41.60 dB at 16.8 GHz. Moreover, the maximum effective absorption bandwidth can reach 3.28 GHz. Furthermore, Ni₃B/Ni has good energy storage characteristics and is able to provide a specific capacity of 1150.6F g^-1 at a current density of 1 A g^-1. Meanwhile, it has the ability to maintain an initial capacity of 74.4 % after 1000 cycles at a current density of 10 A g^-1. Therefore, this study provides an idea to explore TMBs as high-performance MA and supercapacitor materials.

Single-step fabrication of surface morphology tuned iron oxide anchored highly porous carbon nanotube hybrid foam for a highly stable supercapacitor electrode

The pseudocapacitive metal oxide anchored nanocarbon-based three-dimensional (3D) materials are considered attractive electrode materials for high-performance supercapacitor applications. However, the complex multistep synthesis approaches raise production costs and act as a major barrier to the practical real-world field. To overcome this limitation, in this study, an easily scalable and effective fabrication approach for the development of iron oxide (Fe₃O₄) anchored highly porous carbon nanotube hybrid foam (f-Fe₃O₄/O-CNTF) with micro/mesoporous structure was suggested to improve the durability and energy storage performance. The surface morphology-tuned f-Fe₃O₄/O-CNTF (f-Fe₃O₄/O-CNTF(M)) was fabricated through electromagnetic interaction between the anchored magnetic Fe₃O₄ on the CNT surface and the applied magnetic field. The obtained results clearly demonstrated that the changed surface morphology of the f-Fe₃O₄/O-CNTF(M) strongly affected the meso- and micropore structure, electrochemical performance, and durability. Consequently, the f-Fe₃O₄/O-CNTF(M) showed an almost 120% enhanced specific surface area and nearly 1.9 times increased specific capacitance compared to that of the f-Fe₃O₄/O-CNTF. Furthermore, the changed surface morphology successfully prevented the re-aggregation of the initial structure and significantly improved durability. As a result, f-Fe₃O₄/O-CNTF(M) showed outstanding cycling stability, maintaining almost 100% capacitance retention after 14,000 cycles. Consequently, the assembled symmetric supercapacitor device delivered an energy density of 20.1 Wh·kg^-1 at a power density of 0.37 kW·kg^-1 with good cycling stability. These results suggest that the f-Fe₃O₄/O-CNTF(M) can potentially be used as an electrode for supercapacitors with good durability.

Conductive PPy@cellulosic Paper Hybrid Electrodes with a Redox Active Dopant for High Capacitance and Cycling Stability

Polypyrrole@cellulose fibers (PPy@CFs) electrode materials are promising candidates in the energy storage. Various strategies have been pursued to improve their electrochemical performance. However, the poor conductivity, specific capacitance, and cyclic stability still hindered its application. Compared with the previous studies, we selected AQS with electrochemical activity as a dopant to improve these defects. It exhibits a high capacitance of 829.8 F g⁻¹ at a current density of 0.2 A g⁻¹, which is much higher than that of PPy@CFs electrode material (261.9 F g⁻¹). Moreover, the capacitance retention of PPy:AQS/p-PTSA@CFs reaches up to 96.01% after 1000 cycles, indicating superior cyclic stability. Therefore, this work provides an efficient strategy for constructing high-performance electrode materials for energy storage.

Hydrophobic, flexible electromagnetic interference shielding films derived from hydrolysate of waste leather scraps

With the rapid development of wireless telecommunication technologies, it is of fundamental and technological significance to design and engineer high-performance shielding materials against electromagnetic interference (EMI). Herein, a three-step procedure is developed to produce hydrophobic, flexible nanofiber films for EMI shielding and pressure sensing based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of HWLS/polyacrylonitrile (PAN) nanofiber films, (ii) adsorption of silver nanowires (AgNWs) onto HWLS/PAN nanofiber films, and (iii) coating of HWLS/PAN/AgNWs nanofiber films with polydimethylsiloxane (PDMS). Scanning electron microscopy studies show that AgNWs are interweaved with HWLS/PAN nanofibers to form a conductive network, exhibiting an electrical conductivity of 10⁵ S m^-1 and shielding efficiency of 65 dB for a 150 μm-thick HWLS/PAN/AgNWs film. The HWLS/PAN/AgNWs/PDMS film displays an even better electromagnetic shielding efficiency of 80 dB and a water contact angle of 132.5°. Results from this study highlight the unique potential of leather solid wastes for the production of high-performance, environmentally friendly, and low-cost EMI shielding materials.

Enhanced Electromagnetic Wave Absorption Properties of Ultrathin MnO2 Nanosheet-Decorated Spherical Flower-Shaped Carbonyl Iron Powder

In this work, spherical flower-shaped composite carbonyl iron powder@MnO₂ (CIP@MnO₂) with CIP as the core and ultrathin MnO₂ nanosheets as the shell was successfully prepared by a simple redox reaction to improve oxidation resistance and electromagnetic wave absorption properties. The microwave-absorbing properties of CIP@MnO₂ composites with different filling ratios (mass fractions of 20%, 40%, and 60% after mixing with paraffin) were tested and analyzed. The experimental results show that compared with pure CIP, the CIP@MnO₂ composites have smaller minimum reflection loss and a wider effective absorption bandwidth than CIP (RL < -20 dB). The sample filled with 40 wt% has the best comprehensive performance, the minimum reflection loss is -63.87 dB at 6.32 GHz, and the effective absorption bandwidth (RL < -20 dB) reaches 7.28 GHz in the range of 5.92 GHz-9.28 GHz and 11.2 GHz-15.12 GHz, which covers most C and X bands. Such excellent microwave absorption performance of the spherical flower-like CIP@MnO₂ composites is attributed to the combined effect of multiple beneficial components and the electromagnetic attenuation ability generated by the special spherical flower-like structure. Furthermore, this spherical flower-like core-shell shape aids in the creation of discontinuous networks, which improve microwave incidence dispersion, polarize more interfacial charges, and allow electromagnetic wave absorption. In theory, this research could lead to a simple and efficient process for producing spherical flower-shaped CIP@MnO₂ composites with high absorption, a wide band, and oxidation resistance for a wide range of applications.