Construction of Self-Assembly Based Tunable Absorber: Lightweight, Hydrophobic and Self-Cleaning Properties

Engineering Porosity and Functionality in a Robust Twofold Interpenetrated Bismuth-Based MOF: Toward a Porous, Stable, and Photoactive Material

Defect engineering in metal-organic frameworks (MOFs) has gained worldwide research traction, as it offers tools to tune the properties of MOFs. Herein, we report a novel 2-fold interpenetrated Bi-based MOF made of a tritopic flexible organic linker, followed by missing-linker defect engineering. This procedure creates a gradually augmented micro- and mesoporosity in the parent (originally nonporous) network. The resulting MOFs can tolerate a remarkable extent of linker vacancy (with absence of up to 60% of linkers per Bi node) created by altering the crystal-growth rate as a function of synthesis temperature and duration. Owing to the enhanced porosity and availability of the uncoordinated Lewis acidic Bi sites, the defect-engineered MOFs manifested improved surface areas, augmented CO2 and water vapor uptake, and catalytic activity. Parallel to this, the impact of defect engineering on the optoelectronic properties of these MOFs has also been studied, offering avenues for new applications.

Interface Engineering of Titanium Nitride Nanotube Composites for Excellent Microwave Absorption at Elevated Temperature

Currently, the microwave absorbers usually suffer dreadful electromagnetic wave absorption (EMWA) performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss. Consequently, the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority. Herein, due to the high melting point, good electrical conductivity, excellent environmental stability, EM coupling effect, and abundant interfaces of titanium nitride (TiN) nanotubes, they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process. Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane (PDMS), enhanced polarization loss relaxations were created, which could not only improve the depletion efficiency of EMWA, but also contribute to the optimized impedance matching at elevated temperature. Therefore, the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature (298-573 K), while achieved an effective absorption bandwidth (EAB) value of 3.23 GHz and a minimum reflection loss (RLmin) value of - 44.15 dB at 423 K. This study not only clarifies the relationship between dielectric loss capacity (conduction loss and polarization loss) and temperature, but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.

Hierarchical-Bioinspired MOFs Enhanced Electromagnetic Wave Absorption

Proteins exhibit complex and diverse multi-dimensional structures, along with a wide range of functional groups capable of binding metal ions. By harnessing the unique characteristics of proteins, it is possible to enhance the synthesis of metal-organic frameworks (MOFs) and modify their morphology. Here, the utilization of biomineralized bovine serum albumin (BSA) protein as a template for synthesizing Mil-100 with superior microwave absorption (MA) properties is investigated. The multi-dimensional structure and abundant functional groups of biomineralized BSA protein make it an ideal candidate for guiding the synthesis of Mil-100 with intricate network structures. The BSA@Mil-100 synthesized using this method exhibits exceptional uniformity and monodispersity of nanocrystals. The findings suggest that the BSA protein template significantly influences the regulation of nanocrystal and microstructure formation of Mil-100, resulting in a highly uniform and monodisperse structure. Notably, the synthesized 2-BSA@Mil-100 demonstrates a high reflection loss value of -58 dB at 8.85 GHz, along with a maximum effective absorption bandwidth value of 6.79 GHz, spanning from 6.01 to 12.8 GHz. Overall, this study highlights the potential of utilizing BSA protein as a template for MOF synthesis, offering an effective strategy for the design and development of high-performance MA materials.

Modulation Engineering of Electromagnetic Wave Absorption Performance of Layered Double Hydroxides Derived Hollow Metal Carbides Integrating Corrosion Protection

Layered double hydroxides (LDHs) with unique layered structure and atomic composition are limited in the field of electromagnetic wave absorption (EMA) due to their poor electrical conductivity and lack of dielectric properties. In this study, the EMA performance and anticorrosion of hollow derived LDH composites are improved by temperature control and composition design using ZIF-8 as a sacrifice template. Diverse regulation modes result in different mechanisms for EMA. In the temperature control process, chemical reactions tune the composition of the products and construct a refined structure to optimize the LDHs conductivity loss. Additionally, the different phase interfaces generated by the control components optimize the impedance matching and enhance the interfacial polarization. The results show that the prepared NCZ (Ni3ZnC0.7/Co3ZnC@C) has a minimum reflection loss (RLmin ) of -58.92 dB with a thickness of 2.4 mm and a maximum effective absorption bandwidth (EABmax ) of 7.36 GHz with a thickness of 2.4 mm. Finally, due to its special structure and composition, the sample exhibits excellent anticorrosion properties. This work offers essential knowledge for designing engineering materials derived from metal organic framework (MOF) with cutting-edge components and nanostructures.

Self-Assembly of Binderless MXene Aerogel for Multiple-Scenario and Responsive Phase Change Composites with Ultrahigh Thermal Energy Storage Density and Exceptional Electromagnetic Interference Shielding

The severe dependence of traditional phase change materials (PCMs) on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios. Here, we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing. Subsequently, a series of MXene/ K+/paraffin wax (PW) phase change composites (PCCs) were obtained via vacuum impregnation in molten PW. The prepared MXene-based PCCs showed versatile applications from macroscale technologies, successfully transforming solar, electric, and magnetic energy into thermal energy stored as latent heat in the PCCs. Moreover, due to the absence of binder in the MXene-based aerogel, MK3@PW exhibits a prime solar-thermal conversion efficiency (98.4%). Notably, MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion (producing 206 mV of voltage with light radiation intensity of 200 mw cm-2). An excellent Joule heat performance (reaching 105 °C with an input voltage of 2.5 V) and responsive magnetic-thermal conversion behavior (a charging time of 11.8 s can achieve a thermal insulation effect of 285 s) for contactless thermotherapy were also demonstrated by the MK3@PW. Specifically, as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions, MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value (57.7 dB) than pure MXene aerogel/PW PCC (29.8 dB) with the same MXene mass. This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.

Preparation of NiS/Ti3C2Tx co-doped with N and P at the covalent interface and its electromagnetic wave absorption properties

The harm of electromagnetic waves on human daily life has gradually received attention, and electromagnetic waves absorption materials have been used to address this issue. MXene, as a new type of 2D material, is a very promising electromagnetic wave absorption material. In this study, NiS nanoparticles were grown on the surface of S terminated Ti3C2Tx, and -S group acted as sulfur sources to construct Ti-S-Ni covalent interface directly in NiS/Ti3C2Tx composites. To further regulate the interface structure and electromagnetic properties, -P and -NH2 groups were also introduced onto the surface of MXene to achieve the N, P co-doping NiS/Ti3C2Tx composites with covalent interface. By investigating the electromagnetic wave absorption performance of the composites, it was found that N and P doping could effectively enhance the electron transfer rate at the interface and optimize the conduction loss, resulting in a significant improvement in performance. The minimum reflection loss was -50.6 dB at a frequency of 15.6 GHz, and the matching thickness was only 1.14 mm with an effective absorption bandwidth of 3.6 GHz. These results provide an important references and guidance for further research and development of high-performance electromagnetic wave absorption materials.

Impact mechanisms of aggregation state regulation strategies on the microwave absorption properties of flexible polyaniline

In the field of electromagnetic (EM) wave absorption, intrinsic conductive polymers with conjugated long-chain structures, such as polyaniline (PANI) and polypyrrole (PPy), have gained widespread use due to their remarkable electrical conductivity and loss ability. However, current research in this area is limited to macroscopic descriptions of the absorption properties of these materials and the contribution of various components to the absorption effect. There has been insufficient exploration of the impact mechanisms of polymer aggregation states on the material's absorption performance and mechanism. To address this, a series of flexible PANI sponge absorbers with different molecular weights and aggregation states were prepared. By carefully controlling the crystallinity and other aggregation characteristics of PANI through the adjustment of its preparation conditions, we were able to influence its electrical conductivity and electromagnetic parameters, thereby achieving control over the material's absorption properties. The resulting PANI sponge absorbers exhibited an effective absorption bandwidth (EAB) that covered the entire X-band at a thickness of 3.2 mm. This study comprehensively explores the absorption mechanisms of conductive polymer absorbers, starting from the microstructure of PANI, and providing a more complete theoretical support for the research and promotion of polymer absorbers.

Efficient Electromagnetic Wave Absorption and Thermal Infrared Stealth in PVTMS@MWCNT Nano-Aerogel via Abundant Nano-Sized Cavities and Attenuation Interfaces

Pre-polymerized vinyl trimethoxy silane (PVTMS)@MWCNT nano-aerogel system was constructed via radical polymerization, sol-gel transition and supercritical CO2 drying. The fabricated organic-inorganic hybrid PVTMS@MWCNT aerogel structure shows nano-pore size (30-40 nm), high specific surface area (559 m2 g-1), high void fraction (91.7%) and enhanced mechanical property: (1) the nano-pore size is beneficial for efficiently blocking thermal conduction and thermal convection via Knudsen effect (beneficial for infrared (IR) stealth); (2) the heterogeneous interface was beneficial for IR reflection (beneficial for IR stealth) and MWCNT polarization loss (beneficial for electromagnetic wave (EMW) attenuation); (3) the high void fraction was beneficial for enhancing thermal insulation (beneficial for IR stealth) and EMW impedance match (beneficial for EMW attenuation). Guided by the above theoretical design strategy, PVTMS@MWCNT nano-aerogel shows superior EMW absorption property (cover all Ku-band) and thermal IR stealth property (ΔT reached 60.7 °C). Followed by a facial combination of the above nano-aerogel with graphene film of high electrical conductivity, an extremely high electromagnetic interference shielding material (66.5 dB, 2.06 mm thickness) with superior absorption performance of an average absorption-to-reflection (A/R) coefficient ratio of 25.4 and a low reflection bandwidth of 4.1 GHz (A/R ratio more than 10) was experimentally obtained in this work.

Multiphase Interfacial Regulation Based on Hierarchical Porous Molybdenum Selenide to Build Anticorrosive and Multiband Tailorable Absorbers

Electromagnetic wave (EMW) absorbing materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. And in order to cope with the complex electromagnetic environment, the design of multifunctional and multiband high efficiency EMW absorbers remains a tremendous challenge. In this work, we designed a three-dimensional porous structure via the salt melt synthesis strategy to optimize the impedance matching of the absorber. Also, through interfacial engineering, a molybdenum carbide transition layer was introduced between the molybdenum selenide nanoparticles and the three-dimensional porous carbon matrix to improve the absorption behavior of the absorber. The analysis indicates that the number and components of the heterogeneous interfaces have a significant impact on the EMW absorption performance of the absorber due to mechanisms such as interfacial polarization and conduction loss introduced by interfacial engineering. Wherein, the prepared MoSe2/MoC/PNC composites showed excellent EMW absorption performance in C, X, and Ku bands, especially exhibiting a reflection loss of - 59.09 dB and an effective absorption bandwidth of 6.96 GHz at 1.9 mm. The coordination between structure and components endows the absorber with strong absorption, broad bandwidth, thin thickness, and multi-frequency absorption characteristics. Remarkably, it can effectively reinforce the marine anticorrosion property of the epoxy resin coating on Q235 steel substrate. This study contributes to a deeper understanding of the relationship between interfacial engineering and the performance of EMW absorbers, and provides a reference for the design of multifunctional, multiband EMW absorption materials.

Construction of MoS2-ReS2 Hybrid on Ti3C2Tx MXene for Enhanced Microwave Absorption

Utilizing interface engineering to construct abundant heterogeneous interfaces is an important means to improve the absorbing performance of microwave absorbers. Here, we have prepared the MXene/MoS2-ReS2 (MMR) composite with rich heterogeneous interfaces composed of two-dimensional Ti3C2Tx MXene and two-dimensional transition metal disulfides through a facile hydrothermal process. The surface of MXene is completely covered by nanosheets of MoS2 and ReS2, forming a hybrid structure. MRR exhibits excellent absorption performance, with its strongest reflection loss reaching -51.15 dB at 2.0 mm when the filling ratio is only 10 wt%. Meanwhile, the effective absorption bandwidth covers the range of 5.5-18 GHz. Compared to MXene/MoS2 composites, MRR with a MoS2-ReS2 heterogeneous interface exhibits stronger polarization loss ability and superior absorption efficiency at the same thickness. This study provides a reference for the design of transition metal disulfides-based absorbing materials.

Anion Exchange of Metal Particles on Carbon-Based Skeletons for Promoting Dielectric Equilibrium and High-Efficiency Electromagnetic Wave Absorption

The combination of carbon materials and magnetic elements is considered as an effective strategy to obtain high-performance electromagnetic wave (EMW) absorption materials. However, using nanoscale regulation to the optimization of composite material dielectric properties and enhanced magnetic loss properties is facing significant challenges. Here, the dielectric constant and magnetic loss capability of the carbon skeleton loaded with Cr compound particles are further tuned to enhance the EMW absorption performance. After 700 °C thermal resuscitation of the Cr3-polyvinyl pyrrolidone composite material, the chromium compound is represented as a needle-shaped structure of nanoparticles, which is fixed on the carbon skeleton derived from the polymer. The size-optimized CrN@PC composites are obtained after the substitution of more electronegative nitrogen elements using an anion-exchange strategy. The minimum reflection loss value of the composite is -105.9 dB at a CrN particle size of 5 nm, and the effective absorption bandwidth is 7.68 GHz (complete Ku-band coverage) at 3.0 mm. This work overcomes the limitations of impedance matching imbalance and magnetic loss deficiency in carbon-based materials through size tuning, and opens a new way to obtain carbon-based composites with ultra-high attenuation capability.

Integration of Multiple Heterointerfaces in a Hierarchical 0D@2D@1D Structure for Lightweight, Flexible, and Hydrophobic Multifunctional Electromagnetic Protective Fabrics

The development of wearable multifunctional electromagnetic protective fabrics with multifunctional, low cost, and high efficiency remains a challenge. Here, inspired by the unique flower branch shape of "Thunberg's meadowsweet" in nature, a nanofibrous composite membrane with hierarchical structure was constructed. Integrating sophisticated 0D@2D@1D hierarchical structures with multiple heterointerfaces can fully unleash the multifunctional application potential of composite membrane. The targeted induction method was used to precisely regulate the formation site and morphology of the metal-organic framework precursor, and intelligently integrate multiple heterostructures to enhance dielectric polarization, which improves the impedance matching and loss mechanisms of the electromagnetic wave absorbing materials. Due to the synergistic enhancement of electrospinning-derived carbon nanofiber "stems", MOF-derived carbon nanosheet "petals" and transition metal selenide nano-particle "stamens", the CoxSey/NiSe@CNSs@CNFs (CNCC) composite membrane obtains a minimum reflection loss value (RLmin) of -68.40 dB at 2.6 mm and a maximum effective absorption bandwidth (EAB) of 8.88 GHz at a thin thickness of 2.0 mm with a filling amount of only 5 wt%. In addition, the multi-component and hierarchical heterostructure endow the fibrous membrane with excellent flexibility, water resistance, thermal management, and other multifunctional properties. This work provides unique perspectives for the precise design and rational application of multifunctional fabrics.

Assessment of Electromagnetic Field Exposure on European Roads: A Comprehensive In Situ Measurement Campaign

The rapid evolution of wireless communication technologies (such as fifth-generation (5G) cellular networks) in the last years has allowed connecting different objects (from wearable electronics to vehicles) and people through communication networks, and at the same time, has led to widespread deployment of base stations. Along with this growth, questions about the potential adverse effects on human health due to electromagnetic fields (EMFs) from base station antennas have also been raised. In this paper, we focus on the assessment of EMFs in automobiles during short (between cities) and long (between countries) trips on several European roads. Comprehensive measurement campaigns were carried out in several European countries: Austria, Bulgaria, Croatia, Hungary, Italy, Slovenia, and the Republic of Serbia. The results show that the median total electric field is 0.23-0.24 V/m in Bulgaria, Croatia, Hungary, Italy, and the Republic of Serbia. In Austria and Slovenia, the median is 0.28-0.31 V/m. Austria demonstrated the highest value for the total electric field, at 17.4 V/m.

Controlled formation of multiple core-shell structures in metal-organic frame materials for efficient microwave absorption

The design of metal-organic frameworks (MOF) derived composites with multiple loss mechanisms and multi-scale micro/nano structures is an important research direction of microwave absorbing materials. Herein, multi-scale bayberry-like Ni-MOF@N-doped carbon composites (Ni-MOF@NC) are obtained by a MOF assisted strategy. By utilizing the special structure of MOF and regulating its composition, the effective improvement of Ni-MOF@NC's microwave absorption performance has been achieved. The nanostructure on the surface of core-shell Ni-MOF@NC can be regulated and N doping on carbon skeleton by adjusting the annealing temperature. The optimal reflection loss of Ni-MOF@NC is -69.6 dB at 3 mm, and the widest effective absorption bandwidth is 6.8 GHz. This excellent performance can be attributed to the strong interface polarization caused by multiple core-shell structures, the defect and dipole polarization caused by N doping, and the magnetic loss caused by Ni. Meanwhile, the coupling of magnetic and dielectric properties enhances the impedance matching of Ni-MOF@NC. The work proposes a particular idea of designing and synthesizing an applicable microwave absorption material that possesses excellent microwave absorption performance and promising application potential.