Strategies for electromagnetic wave absorbers derived from zeolite imidazole framework (ZIF-67) with ferrocene containing polymers

Fabrication of flower-like CoFe/C composites derived from ferrocene-based metal-organic frameworks: an in situ growth strategy toward high-efficiency electromagnetic wave absorption

Magnetic/dielectric composites can achieve high-efficiency electromagnetic wave (EMW) absorption performance by integrating multiple mechanisms such as dielectric loss and magnetic loss. The bimetallic metal-organic frameworks (MOFs) assembled from ferrocene (Fc) derivative-based bridging ligands are considered ideal precursors for the preparation of magnetic/dielectric composites due to tailored alloy components with magnetic losses. Herein, a novel CoFe/C composite with nanoflower structures is successfully obtained via an in situ growth strategy to decompose an Fc-based bimetallic MOF assembled from 1,1'-ferrocene dicarboxylic acid as bridging ligands and Co2+ ions. Notably, the nanoflower structures of the obtained composites provide an effective path for the scattering and reflection of the EMW, thereby improving the impedance matching by combining dielectric and magnetic loss. The CoFe/C composite exhibits excellent EMW absorption performance and has a minimum reflection loss of -61.6 dB at 3.7 mm and an effective absorption bandwidth of 6.24 GHz at a corresponding thickness of 2.2 mm. Moreover, the obtained composite exhibits lightweight characteristics and a low radar cross-section. This work presents a novel method through Fc-based bimetallic MOF derivatives to design and develop novel magnetic/dielectric composites with efficient EMW absorption properties for comprehensive applications.

Mechanical Properties and Electromagnetic Interference Shielding of Carbon Composites with Polycarbonate and Acrylonitrile Butadiene Styrene Resins

As environmental pollution becomes a serious concern, considerable effort has been undertaken to develop power devices with minimal production of carbon dioxide (CO₂) and exhaust gases. Owing to this effort, interest in technologies related to hybrid and electric products that use fuel cells has been increasing. The risk of human injuries owing to electromagnetic waves generated by electrical and electronic devices has been also rising, prompting the development of mitigating technologies. In addition, antistatic devices for protecting operators from static electricity have also been considered. Therefore, in this study, we investigated the development of thermoplastic carbon composites containing carbon fibers (CFs) and carbon nanotubes (CNTs). Ultimately, materials with improved mechanical properties (e.g., flexural, impact, and tensile strength properties of about +61.09%, +21.44%, +63.56%, respectively), electromagnetic interference (EMI) shielding (+70.73 dB), and surface resistivity (nearly zero) can be developed by impregnating CFs and CNTs with polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) resins, respectively. The total average mechanical properties of PC and ABS composites increased by 24.35% compared with that of ABS composites, while that of PC composites increased by 32.86% with that of PC and ABS composites. Therefore, in this study, we aimed to develop carbon composites, to take advantage of these thermoplastic resins.

A versatile platform for colorimetric, fluorescence and photothermal multi-mode glyphosate sensing by carbon dots anchoring ferrocene metal-organic framework nanosheet

Concerns regarding pesticide residues have driven attempts to exploit accurate, prompt and straightforward approaches for food safety pre-warning. Herein, a nanozyme-mediated versatile platform with multiplex signal response (colorimetric, fluorescence and temperature) was proposed for visual, sensitive and portable detection of glyphosate (GLP). The platform was constructed based on a N-CDs/FMOF-Zr nanosensor that prepared by in situ anchoring nitrogen-doped carbon dots onto zirconium-based ferrocene metal-organic framework nanosheets. The N-CDs/FMOF-Zr possessed excellent peroxidase (POD)-like activity and thus could oxide colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue oxidized TMB (oxTMB) in presence of H₂O₂. Intriguingly, owing to the blocking effect triggered by multiple interaction between GLP and N-CDs/FMOF-Zr, its POD-like activity of the latter was remarkably suppressed, which can modulate the transformation of TMB into oxTMB, generating tri-signal responses of fluorescence enhancement, absorbance and temperature decrease. More significantly, the temperature mode can be facilely realized by a portable home-made mini-photothermal device and handheld thermometers. The proposed multimodal sensing was capable of providing sensitive results by fluorescence mode and simultaneously realized visual/portable testing by colorimetric and photothermal channels. Consequently, it exhibited more adaptability for practical applications, which can satisfy different testing requirements according to sensitivity and available instruments/meters, presenting a new horizon for exploiting multifunctional sensors.

Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Texture regulation of metal-organic frameworks (MOFs) is essential for controlling their electromagnetic wave (EMW) absorption properties. This review systematically summarizes the recent advancements in texture regulation strategies for MOFs, including etching and exchange of central ions, etching and exchange of ligands, chemically induced self-assembly, and MOF-on-MOF heterostructure design. Additionally, the EMW absorption mechanisms in approaches based on structure-function dependencies, including nano-micro topological engineering, defect engineering, interface engineering, and hybrid engineering, are comprehensively explored. Finally, current challenges and future research orientation are proposed. This review aims to provide new perspectives for designing MOF-derived EMW-absorption materials to achieve essential breakthroughs in mechanistic investigations in this promising field.

Construction of heterointerfaces and honeycomb-like structure for ultrabroad microwave absorption

Heterointerface design is an effective strategy to improve the effective absorption bandwidth in electromagnetic wave EMW absorbing materials. In this paper, honeycomb-like Fe-doped tremella carbide composites (FCT) with a large number of heterogeneous interfaces were obtained by in-situ construction of multiphase composite particles (Fe₃C, Fe₃O₄, and a-Fe) during the carbonization process. The effects of Fe doping on the phase, structure, morphology, and absorption properties of FCT were investigated. The results show that the porous structure and the heterogeneous interface can significantly improve the electromagnetic wave absorption performance of FCT. Iron doping introduces a heterogeneous multiphase structure into FCT, which increases the interfacial loss and magnetic loss of the material, thereby improving the overall impedance matching of the material. FCT-4 composite exhibited excellent microwave attenuation capability with a reflection loss of -34.6 dB. Simultaneously, the widest effective absorption bandwidth is up to 8.84 GHz (9.16-18 GHz) with a matching thickness of 2.8 mm, which covers almost the entire X (8-12 GHz) and Ku (12-18 GHz) bands. Thus, this paper provides an effective strategy for the preparation of excellent electromagnetic wave absorbing materials by in situ construction of heterointerfaces.

A hollow CuS@Mn(OH)2 particle with double-shell structure for Ultra-wide band electromagnetic absorption

Hollow materials have many advantages when acting as electromagnetic wave (EMW) absorber, such as excellent impedance matching properties, rich micro-interfaces and light weight. In this work, a novel hollow particle with double-shell composed with CuS and Mn(OH)₂ is synthesized by coordination etching, precipitation and sulfuration using tetrakaidecahedral Cu₂O as template. These hollow particles are expected to be used as improved EMW absorption property at an ultra-wide band. In this hollow particle, tetrakaidecaheral CuS acts as inner shell and Mn(OH)₂ acted as outer shell, thus having rich heterogeneous interfaces which induce strong interfacial polarization. Moreover, the lower electrical conductivity and loose structure of the Mn(OH)₂ shell facilitates the entry of EMW into the absorbers, and the hollow structure in this particle is beneficial to improve the impedance matching according to Maxwell-Garnett (MG) theory. Therefore, hollow CuS@Mn(OH)₂ particles with double-shell exhibit excellent EMW absorption performance. The effective absorption bandwidth (reflection loss (RL) ≤ -10 dB) is 6.88 GHz (from 11.12 GHz to 18 GHz) at 2.3 mm thickness of sample.

High Performance Microwave Absorption of Lightweight and Porous Non-carbon-based Polymeric Monoliths via Gel Emulsion Template

A special porous non-carbon-based microwave-absorbing materials are designed and synthesized by bonding di(prop-1-en-2-yl) ferrocene into porous polymeric monoliths made by gel-emulsions as templates. In this study, a sequence of porous...

ZIF-based boronic acid functionalized metal-organic frameworks for the enrichment of cis-diol-containing luteolin from food samples prior to HPLC

Zeolite imidazole framework-based boronic acid-functionalized metal-organic frameworks (ZIF-67@PDA@BA-Zr-MOFs) were developed as an adsorbent for solid phase extraction (SPE) of luteolin (LTL) from peanut shell samples. Herein, ZIF-67 as a support matrix, polydopamine (PDA) as a coating to introduce amino and hydroxyl groups on the matrix surface to fix metal-organic frameworks (MOFs), zirconium tetrachloride (ZrCl₄) as a precursor, terephthalic acid (TPA), and 3-carboxyphenylboronic acid (3-CPBA) as the mutual organic building blocks, and 3-CPBA was also a boronate affinity functional monomer. The effects of synthesis conditions, SPE conditions, selectivity, competitivity, reproducibility, and reusability were evaluated in detail. Under the optimal conditions, the maximum adsorption capacity is 71.4 mg g^-1. The utility of ZIF-67@PDA@BA-Zr-MOFs as an adsorbent for SPE of LTL is supported by the presence of the abundant pore structure, as well as the boronate affinity sites facilitated the rapid binding of the adsorbent to the template. The concentration of the extracted LTL was determined by the high-performance liquid chromatography-ultraviolet (HPLC-UV), with calibration plots being linear in the concentration range 0.05-100 mg L^-1 and a limit of detection (LOD) of 0.035 mg L^-1. The method was applied to determine the LTL in peanut shell samples and recovered the target analyte in the range 85.6% to 99.2% (the standard deviations are less than 3.3%, n = 3). In addition, we incorporated boronate affinity and MOFs material into an SPE system to provide a promising strategy to detect other cis-diol-containing analytes in the complex matrix.

Electromagnetic absorbers with Schottky contacts derived from interfacial ligand exchanging metal-organic frameworks

Various types of polycrystals have been regarded as excellent electromagnetic (EM) microwave absorbents, while differentiated heterointerfaces among grains usually manipulate conductive loss and polarization relaxation, especially interfacial polarization. Herein, polar facets that dominated the optimization of EM attenuation were clarified by carefully designing polycrystalline Schottky junctions with metal-semiconductor contacts for the first time. An ingenious ligand exchange technique was utilized to construct Zn-MOF (ZIF-L) precursors for Fe-ZnO polycrystals, in which Fe-containing Fe(CN)₆^3- etching ligand acted as metallic source in Schottky junctions. By adjusting the Schottky contacts in polycrystals, the enhanced grain boundaries mainly induced stronger interfacial polarization and affected the microcurrent lightly. This is because Schottky barriers can cause local charge accumulation on heterointerfaces for polarization relaxation. Additionally, the coexistence of Zn and O vacancies brought a lot of lattice defects and distortions for dipole polarization. Thus, optimal EM wave absorbability was obtained by polycrystals with 8 h ligand exchange and an effective absorption band reaching 4.88 GHz. This work can provide guidance for designing advanced polycrystalline EM absorption materials and also highlight the mechanism and requirement of Schottky junctions dominating polarization.

Recent progress of MOF-derived porous carbon materials for microwave absorption

Microwave absorbing materials (MAM) have attracted considerable attention over the years in stealth and information technologies. Metal–organic framework (MOF) with a unique microstructure and electronic state has become an attractive focus as self-sacrificing precursors of microwave absorbers. The MOF-derived porous carbon (PC) materials exhibit a high absorbing performance due to the stable three-dimensional structure and homogeneous distribution of metal particles. MOF-derived PC materials are promising for ideal MAM via tuning of the structure and composition, resulting in appropriate impedance matching and the synergistic effect between magnetic and dielectric loss. In this review, the MOF-derived PC materials and their basic absorption mechanisms (dielectric loss, magnetic loss and impedance matching) are introduced, as well as the characters of various MOF-derived PC materials. In addition, this review provides a comprehensive introduction and tabulates the recent progress based on the classification of the MOF-derived metallic state, such as pure PC (without reduced metals), mono-metal/PC, multi-metal/PC, metal oxides/PC and other derived PC composites. Finally, the challenges faced by MOF-derived PC materials are overviewed, and their further development is mentioned.

MOF-derived PC materials with unique characteristic have been widely concerned as microwave absorbers over the years.

Synthesis of 3D flower-like ZnO/ZnCo2O4 composites with the heterogeneous interface for excellent electromagnetic wave absorption properties

Reasonable structure and composition are essential for electromagnetic wave absorption (EMW). Herein, ZnO hollow spheres were prepared with carbon spheres as templates and then synthesized ZnO/ZnCo₂O₄ composites by the solvothermal method and annealing treatment. The flower-like ZnCo₂O₄ material was produced by self-assembly of ZnCo₂O₄ nanosheets. The absorbing material with the complex structure has multiple scattering and reflection, conduction loss, resonance, and eddy current loss characteristics. Furthermore, the addition of ZnO hollow spheres has a significant impact on electromagnetic parameters and absorption properties. As a result, the addition of ZnO hollow spheres can greatly enhance the complex permittivity of the ZnO/ZnCo₂O₄ composites and obtain excellent EMW absorbing properties. It is worth noting that ZnO/ZnCo₂O₄ composites show the best EMW absorption properties when the ZnO hollow spheres were added up to 5 mg. The minimum reflection loss is -55.42 dB and a matching thickness of 1.99 mm while the maximum effective absorption bandwidth can also reach 7.44 GHz with a matching thickness of 2.4 mm. Our research can prove that the structure and composition have a significant influence on the properties of the absorbing material, which provides ideas for the development of absorbing materials with high-performance.

Design of Ti3C2Tx/TiO2/PANI multi-layer composites for excellent electromagnetic wave absorption performance

Ti₃C₂T_x MXene is an excellent electromagnetic wave (EMW) absorber with excellent electrical conductivity and abundant surface functional groups. In this research, Ti₃C₂T_x/TiO₂/PANI multi-layer composites were successfully synthesized by HCl and LiF etching, one-step hydrothermal method and in-situ polymerization. Ti₃C₂T_x can provide more electron transfer paths due to its unique multilayer structure and high specific surface area. The growth of TiO₂ particles on the surface of Ti₃C₂T_x through hydrothermal reaction enhances the interface polarization, and then polyaniline (PANI) is doped on the surface of Ti₃C₂T_x where TiO₂ particles are grown by in-situ polymerization. Due to the excellent dielectric properties and synergistic effects of the material itself, Ti₃C₂T_x/TiO₂/PANI composites have excellent EMW absorption property. In this study, the Ti₃C₂T_x/TiO₂/PANI composites showed the strong reflection loss (RL) of at 13.92 GHz, which was -65.61 dB, and the thickness was only 2.18 mm. Moreover, the composites also exhibit a wide absorption band, with an effective absorption bandwidth (RL < -10 dB) of 5.92 GHz (11.84 GHz to 17.76 GHz) at 2.10 mm. The results show that the Ti₃C₂T_x/TiO₂/PANI composites are expected to become EMW absorber with thin thickness and high absorption strength.