Formation Of Core-shell Structures Research Articles

Resistive Gas Sensors Based on 2D TMDs and MXenes.

ConspectusGas sensors are used in various applications to sense toxic gases, mainly for enhanced safety. Resistive sensors are particularly popular owing to their ability to detect trace amounts of gases, high stability, fast response times, and affordability. Semiconducting metal oxides are commonly employed in the fabrication of resistive gas sensors. However, these sensors often require high working temperatures, bringing about increased energy consumption and reduced selectivity. Furthermore, they do not have enough flexibility, and their performance is significantly decreased under bending, stretching, or twisting. To address these challenges, alternative materials capable of operating at lower temperatures with high flexibility are needed. Two-dimensional (2D) materials such as MXenes and transition-metal dichalcogenides (TMDs) offer high surface area and conductivity owing to their unique 2D structure, making them promising candidates for realization of resistive gas sensors. Nevertheless, their sensing performance in pristine form is typically weak and unacceptable, particularly in terms of response, selectivity, and recovery time (trec). To overcome these drawbacks, several strategies can be employed to enhance their sensing properties. Noble-metal decoration such as (Au, Pt, Pd, Rh, Ag) is a highly promising method, in which the catalytic effects of noble metals as well as formation of potential barriers with MXenes or TMDs eventually contribute to boosted response. Additionally, bimetallic noble metals such as Pt-Pd and Au/Pd with their synergistic properties can further improve sensor performance. Ion implantation is another feasible approach, involving doping of sensing materials with the desired concentration of dopants through control over the energy and dosage of the irradiation ions as well as creation of structural defects such as oxygen vacancies through high-energy ion-beam irradiation, contributing to enhanced sensing capabilities. The formation of core-shell structures is also effective, creating numerous interfaces between core and shell materials that optimize the sensing characteristics. However, the shell thickness needs to be carefully optimized to achieve the best sensing output. To reduce energy consumption, sensors can operate in a self-heating condition where an external voltage is applied to the electrodes, significantly lowering the power requirements. This enables sensors to function in energy-constrained environments, such as remote or low-energy areas. An important advantage of 2D MXenes and TMDs is their high mechanical flexibility. Unlike semiconducting metal oxides that lack mechanical flexibility, MXenes and TMDs can maintain their sensing performance even when integrated onto flexible substrates and subjected to bending, tilting, or stretching. This flexibility makes them ideal for fabricating flexible and portable gas sensors that rigid sensors cannot achieve.

A Method for Determining Incorporation Depth in Core-Shell UiO-66 Nanoparticles Synthesized Via Postsynthetic Exchange.

Postsynthetic exchange (PSE) is a key technique for integrating sensitive linkers into metal-organic frameworks (MOFs). Despite its importance, investigations into linker distributions have primarily focused on micrometer-sized crystals due to the analytical limitations, leaving nanoparticles less explored, although they are commonly synthesized and used in applications. In particular, the emergence of core-shell nanostructures via PSE has shown potential for applications in CO2 adsorption and selective catalysis. This study addresses this gap by investigating the formation of core-shell structures on nanoparticles under diffusion-controlled PSE conditions. By analyzing volume-to-surface ratios and conducting time-dependent experiments, we confirmed that these conditions facilitate the development of core-shell architectures. We also developed a straightforward method to calculate the minimum incorporation depth using basic parameters such as particle size and the total amount of incorporated linker. The accuracy of our approach was validated against data obtained from transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. These findings enhance the understanding of PSE in MOF nanoparticles and open up promising avenues for developing advanced MOF core-shell structures for various applications.

Construction of blackberry polysaccharide nano-selenium particles: Structure features and regulation effects of glucose/lipid metabolism in HepG2 cells

In this study, blackberry polysaccharide-selenium nanoparticles (BBP-24-3Se) were first prepared via Na2SeO3/Vc redox reaction, followed by coating with red blood cell membrane (RBC) to form core–shell structure polysaccharide-selenium nanoparticles (RBC@BBP-24-3Se). The particle size of BBP-24-3Se (167.1 nm) was increased to 239.8 nm (RBC@BBP-24-3Se) with an obvious core–shell structure after coating with RBC. FT-IR and XPS results indicated that the interaction between BBP-24-3 and SeNPs formed a new C-O···Se bond with valence state of Se0. Bioassays indicated that RBC coating markedly enhanced both the biocompatibility and bioabsorbability of RBC@BBP-24-3Se, and the absorption rate of RBC@BBP-24-3Se in HepG2 cells was 4.99 times higher than that of BBP-24-3Se at a concentration of 10 μg/mL. Compared with BBP-24-3Se, RBC@BBP-24-3Se possessed significantly heightened protective efficacy against oxidative damage and better regulation of glucose/lipid metabolism disorder induced by palmitic acid in HepG2 cells. Mechanistic studies demonstrated that RBC@BBP-24-3Se could effectively improve PI3K/AKT signaling pathway to promote glucose metabolism, inhibit the expression of lipid synthesis genes and up-regulate the expression of lipid-decomposing genes through AMPK signaling pathway to improve lipid metabolism. These results provided a theoretical basis for developing a new type of selenium supplement for the treatment of insulin resistance.

Effect of shell-dependent variation on the photocatalytic activity of flower-like core-shell SnSe@SnO2

Flower-like core-shell SnSe@SnO2 was prepared by low-temperature in situ oxidation. The relationship between different oxidation times and the formation of core-shell structures of the samples was explored. The results showed that SnSe was obtained by thermal oxidation of SnO2 in close contact with air. The size range of the flower-like core-shell structure SnSe@SnO2 was 15–20 μm. The flower-like structure was self-assembled from nanoplates with a thickness of about 200 nm. This flower-like core-shell structured SnSe@SnO2 has a band gap of about ∼1.4 eV. The electrochemical characterization of the samples was analyzed for charge transfer phenomena at the junctions as well as at the interface between the shell layer and the aqueous solution. The effect of different SnO2 shell layers on the photocatalytic degradation activity of the composites for methylene blue was evaluated. The samples with SnSe oxidized in air for 8 h showed optimal photocatalytic performance and displayed excellent photostability and reusability. In addition, O2− was the main active species for the degradation of the organic dye methylene blue.

CoFe@[CoFe2O4/Fe(Co)Nx-C] nanoparticles prepared via an ultrasonic atomization coupling pyrolysis process and their magnetic and optical properties

Due to their special qualities, core-shell nanomaterials with two or more functionalities have drawn a lot of attention. Core-shell materials exhibit stronger combined electrical, optical, magnetic, and electronic characteristics than single-component nanomaterials thanks to the creation of the core-shell structure and the synergistic interaction between components. However, the formation of core-shell structures is often difficult due to the incompatibility between components, especially for lattice-mismatched core-shell structures. In this study, CoFe@CoFe2O4-N-C nanoparticles (∼150 nm) were successfully prepared via an ultrasonic atomization coupling pyrolysis process. This exhibits higher coercivity (108 Oe), saturation magnetization (52.3 emu/g) and Curie temperature (>400 K) than CoFe nanoparticles. At the same time, it exhibits high UV–Vis and infrared absorption characteristics and has good electronic properties as a direct band gap semiconductor material (bandgap of 2.87 eV). These characteristics suggest that CoFe@CoFe2O4-N-C NPs have a lot of potential in sectors like magneto-optics and absorbent materials.

An integrated in silico-in vitro approach for bioprinting core-shell bioarchitectures.

Biological tissues possess a high degree of structural complexity characterized by curvature and stratification of different tissue layers. Despite recent advances in in vitro technology, current engineering solutions do not comprise both of these features. In this paper, we present an integrated in silico-in vitro strategy for the design and fabrication of biological barriers with controlled curvature and architecture. Analytical and computational tools combined with advanced bioprinting methods are employed to optimize living inks for bioprinting-structured core-shell constructs based on alginate. A finite element model is used to compute the hindered diffusion and crosslinking phenomena involved in the formation of core-shell structures and to predict the width of the shell as a function of material parameters. Constructs with a solid alginate-based shell and a solid, liquid, or air core can be reproducibly printed using the workflow. As a proof of concept, epithelial cells and fibroblasts were bioprinted respectively in a liquid core (10 mg/mL Pluronic) and in a solid shell (20 mg/mL alginate plus 20 mg/mL gelatin, used for providing the cells with adhesive moieties). These constructs had a roundness of 97.6% and an average diameter of 1500 ±136 μm. Moreover, their viability was close to monolayer controls (74.12% ± 22.07%) after a week in culture, and the paracellular transport was twice that of cell-free constructs, indicating cell polarization.

Electronic Structure Engineered Heteroatom Doped All Transition Metal Sulfide Carbon Confined Heterostructure for Extrinsic Pseudocapacitor.

Ultra-high energy density battery-type materials are promising candidates for supercapacitors (SCs); however, slow ion kinetics and significant volume expansion remain major barriers to their practical applications. To address these issues, hierarchical lattice distorted α-/γ-MnS@Cox Sy core-shell heterostructure constrained in the sulphur (S), nitrogen (N) co-doped carbon (C) metal-organic frameworks (MOFs) derived nanosheets (α-/γ-MnS@Cox Sy @N, SC) have been developed. The coordination bonding among Cox Sy , and α-/γ-MnS nanoparticles at the interfaces and the π-π stacking interactions developed across α-/γ-MnS@Cox Sy and N, SC restrict volume expansion during cycling. Furthermore, the porous lattice distorted heteroatom-enriched nanosheets contain a sufficient number of active sites to allow for efficient electron transportation. Density functional theory (DFT) confirms the significant change in electronic states caused by heteroatom doping and the formation of core-shell structures, which provide more accessible species with excellent interlayer and interparticle conductivity, resulting in increased electrical conductivity. . The α-/γ-MnS@Cox Sy @N, SC electrode exhibits an excellent specific capacity of 277 mA hg-1 and cycling stability over 23600 cycles. A quasi-solid-state flexible extrinsic pseudocapacitor (QFEPs) assembled using layer-by-layer deposited multi-walled carbon nanotube/Ti3 C2 TX nanocomposite negative electrode. QFEPs deliver specific energy of 64.8 Wh kg-1 (1.62 mWh cm-3 ) at a power of 933 W kg-1 and 92% capacitance retention over 5000 cycles.

Numberous fullerenes form core–shell structures via graphdiyne-like chain condensation

Numberous fullerenes form core–shell structures via graphdiyne-like chain condensation

Synthesis of ((CeO2)0.8(Sm2O3)0.2)@NiO Core-Shell Type Nanostructures and Microextrusion Printing of a Composite Anode Based on Them.

The process of the hydrothermal synthesis of hierarchically organized nanomaterials with the core-shell structure with the composition ((CeO2)0.8(Sm2O3)0.2)@NiO was studied, and the prospects for their application in the formation of planar composite structures using microextrusion printing were shown. The hydrothermal synthesis conditions of the (CeO2)0.8(Sm2O3)0.2 nanospheres were determined, and the approach to their surface modification by growing the NiO shell with the formation of core-shell structures equally distributed between the larger nickel(II) oxide nanosheets was developed. The resulting nanopowder was used as a functional ink component in the microextrusion printing of the corresponding composite coating. The microstructure of the powders and the oxide coating was studied by scanning (SEM) and transmission electron microscopy (TEM), the crystal structure was explored by X-ray diffraction analysis (XRD), the set of functional groups in the powders was studied by Fourier-transform infrared spectroscopy (FTIR) spectroscopy, and their thermal behavior in an air flow by synchronous thermal analysis (TGA/DSC). The electronic state of the chemical elements in the resulting coating was studied using X-ray photoelectron spectroscopy (XPS). The surface topography and local electrophysical properties of the composite coating were studied using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Using impedance spectroscopy, the temperature dependence of the specific electrical conductivity of the obtained composite coating was estimated.

Трансформация изопропанола с использованием гибридных цеолитсодержащих систем типа H-ZSM-5 и H-Beta

The continuous depletion of hydrocarbon sources contributes to a wide study of the use of biorenewable raw materials to obtain synthetic hydrocarbons from them. Isopropyl alcohol is traditionally produced by chemical hydration of propylene, however, with the development of biotechnology, broad prospects have opened for its production by fermentation of glucose-containing substrates obtained from agricultural and forestry waste. This way, isopropyl alcohol can also be considered as a bio-renewable raw material and it can be widely used for the production of chemical synthesis products, including hydrocarbons. One of the possible ways of processing isopropyl alcohol is the catalytic transformation of alcohols on zeolites and zeotypes of various natures with the formation of hydrocarbons. Currently, zeolite H-ZSM-5 and zeotype SAPO-34 are the most frequently used catalysts for the transformation of alcohols into hydrocarbons, however, their rapid deactivation due to the formation of a carbon residue remains an unresolved problem. The formation of core-shell structures with H-ZSM-5 zeolite in center and an outer shell consist of H-Beta zeolite with large pores can reduce the deactivation of zeolite because of increase in reagents diffusion rate. In this article is devoted to synthesis of ZSM-5/Beta sample with a core-shell structure, as well as a study of its catalytic and physicochemical properties. To form the H-ZSM-5 zeolite, a colloidal solution of tetrapropylammonium hydroxide, a colloidal solution of silicon oxide, aluminum oxide, sodium hydroxide of distilled water was used. The colloidal solution was placed in an autoclave, heated to 140 °C and kept at this temperature for 48 hours, after which the crystals formed were centrifuged, washed with distilled water and kept in a 1M solution of ammonium nitrate for a day. Then, to form the H-Beta layer, H-ZSM-5 was suspended in a colloidal solution consisting of tetraethylammonium hydroxide, tetraethylammonium chloride, a colloidal solution of silicon oxide, sodium hydroxide, sodium chloride and distilled water. The suspension was placed in an autoclave and kept at a temperature of 140 °C for 48 hours, followed by centrifugation, washing in distilled water, suspended in a 1M solution of ammonium nitrate, with repeated washing with distilled water, drying and calcining at 600 °C. Testing of the synthesized of H-ZSM-5/Beta zeolite sample showed a significant decrease in the rate of deactivation compared to the synthesized sample of H-ZSM-5; it is also necessary to note a slight increase in the fraction of liquid hydrocarbons for the sample H-ZSM-5/Beta.

Regulation of magnetic and electrical performances in core-shell-structured FeSiCr@BaTiO3 soft magnetic composites

Soft magnetic composites (SMCs) are extensively used for designing and manufacturing high-performance electronic devices, such as inductors, filters, mutual inductors and chokes, owing to their high effective permeability (μe) and stable magnetic properties. However, the production of SMCs that meet the demands of high resistivity, high effective permeability (μe), and low core losses (Pcv), which are required for high-frequency miniaturized electronic systems, is challenging. In this study, we improve the electromagnetic performance of SMCs by coating FeSiCr metal particles with BaTiO3 dielectric ceramic powder at various concentrations (0.00–3.75 wt%). The micro-morphological, static magnetic, resistivity (ρ), and core loss (Pcv) properties of FeSiCr@BaTiO3 SMCs are comprehensively investigated. Energy dispersive spectroscopy elemental distribution mapping is used to confirm the formation of core-shell structures with excellent coating quality. With an increase in the BaTiO3 dielectric powder content, the core losses, Pcv (at 800 kHz, 10 mT and 25 °C), initially decrease and subsequently increase, and comprise hysteresis losses (Ph) and eddy current losses (Pe). Moreover, owing to the introduction of the non-magnetic-phase BaTiO3 powder, hysteresis losses increase monotonically, whereas eddy current losses exhibit the opposite trend. The FeSiCr@BaTiO3 SMCs with 2.25 wt% BaTiO3 dielectric ceramic powder exhibit outstanding comprehensive electromagnetic properties with an effective permeability of μe = 48, saturated magnetization of Ms = 115 emu/g, core losses of Pcv = 42 mW/cm3 (at 800 kHz, 10 mT and 25 °C), and resistivity of ρ = 2.74 × 105 Ω∙m. These state-of-the-art FeSiCr@BaTiO3 SMCs present considerable potential for application in high-performance power devices and components.

The microstructures of the TiN–Ti5Si3 hybrid reinforced Cu matrix composites fabricated by the Ti–Si3N4 reaction and its preparation mechanism

An innovative method for the preparation of TiN–Ti 5 Si 3 hybrid reinforced copper matrix composites by the reaction and spontaneous dispersion of Ti–Si 3 N 4 mixture in Cu melts is proposed in this study. The microstructures of the composites and the reaction process of Ti and Si 3 N 4 with different sizes in Cu melts were analyzed. It is found that the Si 3 N 4 with small size, such as 2 μm, can easily react completely with Ti to form TiN and Ti 5 Si 3 . The formed TiN are particle-like and their size ranges from 0.5 μm to 3 μm, while Ti 5 Si 3 are rod-like with a certain length to diameter ratio. In addition, many Ti 5 Si 3 rods are combined with Cu cores to form core–shell structure. It is considered that these microstructure characteristics are helpful for TiN and Ti 5 Si 3 to form a good hybrid enhancement effect. Although the Si 3 N 4 with large size, such as 50 μm, can also be effectively added into Cu melts by Ti–Si 3 N 4 reaction. However, unlike the composite prepared by 2 μm Si 3 N 4 , besides the forming TiN and Ti 5 Si 3 , there are other kinds of core–shell particles present in the matrix, including Si 3 N 4 @TiN, Cu@TiN and Si 3 N 4 @TiN@Cu@TiN.

Surface Engineering and Controlled Ripening for Seed-Mediated Growth of Au Islands on Au Nanocrystals.

Engineering the nucleation and growth of plasmonic metals (Ag and Au) on their pre-existing seeds is expected to produce nanostructures with unconventional morphologies and plasmonic properties that may find unique applications in sensing, catalysis, and broadband energy harvesting. Typical seed-mediated growth processes take advantage of the perfect lattice match between the deposited metal and seeds to induce conformal coating, leading to either simple size increases (e.g., Au on Au) or the formation of core-shell structures (e.g., Ag on Au) with limited morphology change. In this work, we show that the introduction of a thin layer of metal with considerable lattice mismatch can effectively induce the nucleation of well-defined Au islands on Au nanocrystal seeds. By controlling the interfacial energy between the seed and the deposited material, the oxidative ripening, and the surface diffusion of metal precursors, we can regulate the number of islands on the seeds and produce complex Au nanostructures with morphologies tunable from core-satellites to tetramers, trimers, and dimers.

Degradable Spirocyclic Polyacetal-Based Core-Amphiphilic Assemblies for Encapsulation and Release of Hydrophobic Cargo.

Polymeric nanomaterials that degrade in acidic environments have gained considerable attention in nanomedicine for intracellular drug delivery and cancer therapy. Among various acid-degradable linkages, spirocyclic acetals have rarely been used to fabricate such vehicles. In addition to acid sensitivity, they benefit from conformational rigidity that is otherwise not attainable by their non-spirocyclic analogs. Herein, amphiphilic spirocyclic polyacetals are synthesized by Cu-catalyzed alkyne–azide “click” polymerization. Unlike conventional block copolymers, which often form core–shell structures, these polymers self-assemble to form core amphiphilic assemblies capable of encapsulating Nile red as a hydrophobic model drug. In vitro experiments show that while release from these materials can occur at neutral pH with preservation of their integrity, acidic pH accelerates efficient cargo release and leads to the complete degradation of assemblies. Moreover, cellular assays reveal that these materials are fully cytocompatible, interact with the plasma membrane, and can be internalized by cells, rendering them as potential candidates for cancer therapy and/or drug delivery.

Anisotropic MOF-on-MOF Growth of Isostructural Multilayer Metal-Organic Framework Heterostructures.

Isostructural MOFs with similar crystallographic parameter are easily available for MOF-on-MOF growth and possible to form core–shell structure by isotropic growth. However, due to well-matched cell lattice, selective growth in isostructural MOF heterostructures remains a great challenge for engineering atypical MOF heterostructures. Herein, an anisotropic MOF-on-MOF growth strategy was developed to structure a range of multilayer sandwich-like ZIF-L heterostructures via stacking isostructural ZIF-L-Zn and ZIF-L-Co alternately with three-, five-, seven-, and more layer structures. Moreover, these heterostructures with highly designable feature were fantastic precursors for fabricating derivatives with tunable magnetic and catalytic properties. Such strategy explores a novel way of achieving anisotropic MOF-on-MOF growth between isostructural MOFs and opens up new horizons for regulating the properties by MOF modular assembly in versatile functional nanocomposites.

Silver doped glasses from the system BaO/SrO/ZnO/SiO2 – The influence of Sb, Sn, and Ta on the formation of core-shell structures

Three glasses from the base system BaO/SrO/ZnO/SiO2 have been synthesized using conventional melt quenching technique and different concentrations of Ag, Sn, Sb, and Ta. After two-step heat treatments, two glasses showed volume crystallization, while the third glass crystallized solely from the surface. The different crystallization mechanisms were studied by differential scanning calorimetry and both scanning and transmission electron microscopy. It was found that the formation of LEAZit (Low Expansion Alkaline Earth Zinc Silicates) volume crystals runs parallel to the formation of core-shell structures inside the glassy matrix. Such a core-shell structure consists of a metallic Ag core, which is surrounded by a shell composed of Zn2SiO4. Into this crystalline phase, Sb, Sn, as well as Ta can be incorporated. Glasses without Sb show the formation of metallic and spherically shaped Ag particles without any shell, being unsuitable to trigger volume crystallization in the studied glasses. Hence, the presence of Ag, Sn, Sb, or Ta in a suitable ratio is decisive for the nucleation and crystallization mechanism of the studied glasses.

Green synthesis and optical properties of ZnSe:Cu@ZnS core/shell nanocrystals fabricated by new photochemical microwave-assisted colloidal method

Abstract Growth of a secondary material-shell on a core of another material and so, formation of a core-shell system has been a successful route in the surface modification of nanostructured samples. In this research, ZnSe:Cu and ZnSe:Cu@ZnS core-shell nanocrystals (NCs) with different contents of Cu-dopant under microwave irradiation times (MWIRTs) = 0 & 6 min were synthesized by a new and rapid photochemical microwave-assisted method at home temperature. Crystal structure, crystallite size (by XRD analysis), morphology and elemental analysis (by TEM, FESEM, EDX and Map), strain, dislocation density, absorption edge, energy band gap (by exact method of DASF), the exact nature of charge carrier optical transition (m), Urbach energy ( E tail ), Refractive index (n), dielectric constant (e) at the absorption edge and third order non-linear optical susceptibility (χ(3)) were determined. The influences of various experimental variables, including formation of ZnS shell on ZnSe:Cu core, Cu content and MWIRT on their opto-structural features were systematically investigated. The obtained NCs present high degree of crystallinity and have a cubic zinc blende structure which their diameters varies from 1.81 to 2.26 nm. The formation of core-shell structures was confirmed TEM. For ZnSe:Cu@ZnS core-shell NCs, XRD diffraction peaks shifted slightly to higher angles. Band gap of ZnSe NCs was obtained about 3.45 eV, which was tunable by formation of ZnS shell on ZnSe:Cu NCs core and also by altering the synthesis conditions. However, the band gap values of ZnSe:Cu@ZnS systems were generally smaller than that of ZnSe:Cu NCs; also, in each cases of bare ZnSe:Cu NCs and ZnSe:Cu@ZnScore/shell NCs, increase in MWIRT results to the red shift in band gap. For all samples, optical charge carrier transition index of m were found to be nearly around 3/2 (correspond to the direct non-allowed transition gap type), except for ZnSe:Cu(1.5%)@ZnS with MWIRT = 6 min with m-index nearly around 1/2 (correspond to the direct allowed transition gap type); the recent exception may be due to its different structure, which has been caused to its different structure certified by TEM. Upon the all opto-structural performed analysis, ZnSe:Cu(0.75%)@ZnS and ZnSe:Cu(0.1%)@ZnS NCs synthesized photochemically under MWIR = 6 min, have the highest (χ(3)), lowest band gap and lowest lattice suggesting them as promising and potentially materials in nano-optoelectronic applications such as solar cells, fibers or even in strong coating materials.

Phase transformations and changes in the dielectric properties of nanostructured perovskite-like LBZ composites as a result of thermal annealing

The paper presents the results of a study of changes in the phase composition and dielectric properties of perovskite-like composites of the LiBaZrOx type depending on the temperature of the heat treatment. According to the data obtained, the initial samples obtained by the solid-state synthesis method are a three-phase system with the dominance of the orthorhombic phase ZrO2, the average nanoparticle size of which consists of composites, does not exceed 90–110 nm. As a result of thermal annealing, the dependences of phase transformations, as well as the dynamics of structural ordering with the formation of core-shell structures at an annealing temperature of 1000 °C, were established. The reduction of distortions and deformations of the crystal structure as a result of thermal annealing leads to an improvement in ferroelectric properties, as well as a decrease in the Curie temperature characteristic of the maximum dielectric constant. The weak dependence of the change in the dielectric constant with increasing frequency in the temperature range exceeding the Curie temperature indicates the relaxor nature of the properties of composites.

Cleaning synthesis of core–shell structured Ni@PPy composite as excellent lightweight electromagnetic wave absorber

A novel electromagnetic functionalized Ni@PPy composite was synthesized with a cleaning method. XRD and FTIR analyses showed that the Ni@PPy composite was successfully prepared. SEM, TEM, and HRTEM results proved that Ni nanoparticles, produced by the γ-irradiation-induced reduction method, were wrapped with polypyrrole (PPy) shell to form core–shell structure. There existed many Ni cores in a PPy shell, which could induce more interfacial and dipolar polarization than the structure with one core in a shell. With an increase in Ni content, the dielectric loss was obviously decreased and the magnetic loss had little change. Attenuation constant decreased gradually, which was influenced jointly by conductivity loss and dipolar and interfacial polarization loss. When nPy/nNi/nAPS was 1.75:1:1.75, the as-prepared Ni@PPy composite exhibited the highest microwave absorption (RLmax of − 48 dB at 7 GHz and EAB of 3.8 GHz) owing to suitable impedance matching as well as attenuation ability. Therefore, such core–shell structured Ni@PPy composite would be a promising microwave absorber.

Self‒assembled core‒shell structured Si@CuO energetic materials for enhanced exothermic performance

Si is considered as a promising fuel for energetic materials and has received increasing attention. In this study, a novel core‒shell structure Si@CuO energetic material was successfully synthesized by self‒assembly method. Poly(4‒vinylpyridine) was used as cross linker to coat nano‒CuO on the surface of nano‒Si to form core‒shell structure Si@CuO energetic material. The morphology and composition of the nano‒Si, nano‒CuO and Si@CuO energetic materials were investigated in detail by scanning electron microscopy, transmission electron microscopy and X‒ray diffraction. The results demonstrate that the maximum actual heat release of Si@CuO with core‒shell structure is 1061.4 J/g when the equivalent ratio is 1.0, which is greater than 532.8 J/g of Si/CuO energetic materials prepared by ultrasonic mixing method. These results provide a helpful and practical strategy for the preparation of energetic materials with long‒term storage stability.