Core-shell Structure Composites Research Articles

Solvethermal synthesis and thermochromic properties of CaF2@VO2-based core-shell structure composites

Vanadium oxide (VO2)-based core-shell structures exhibit unique properties due to their reversible metal–insulator transition (MIT). As a result, numerous applications on the device level have been reported in the literature. However, since VO2 are multivalent compounds, the controllable preparation of VO2 core-shell-based particles is quite challenging. Along these lines, in this work, to overcome these limitations, the growth mechanism of VO2 shells on spherical substrates was systematically investigated. More specifically, the CaF2@VO2 core-shell microspheres were fabricated successfully by applying the solvent/hydrothermal-calcination method for the first time, while the phase evolution and morphological characteristics of the preparation process were studied in detail. From the obtained results, it was demonstrated that the composite particle's morphology and phase structure strongly depend on the activator, solvent, annealing atmosphere, and the annealing temperature. In addition, the infrared transmittance of the prepared CaF2@VO2(M) coating exhibited a decrease of 34.08 % during the metal–semiconductor phase transition in the 4–12 μm wavelength. Compared with the VO2 coatings and the uncoated CaF2/VO2 coatings, the transmittance conversion performance (ΔT) of the CaF2@VO2(M) coating was also increased by 22.62 % and 21.22 %, respectively.

Construction of boron-based double-layer core-shell structure composites and their combustion energy release characteristics

Although boron (B) powder has a high energy density, the high boiling point oxide layer (B2O3) on the surface seriously hinders the combustion of internal B particles, which further limits the use of B powder. In order to solve this issue, polydopamine (PDA) was used as a sandwich layer (sandwich layer used to connect solid-liquid interface) between the original B powder and liquid perfluoropolyether (PFPE), and then a double-layer core-shell structure B@PDA@PFPE was prepared through the electrostatic self-assembly method. Herein, PDA not only helps remove naturally occurring B2O3, but also provides more active sites and improves the reactivity of B and PFPE. The results indicate that the B@PDA@PFPE has excellent combustion flame and energy release characteristics due to the superior dispersion and reactivity of PFPE. Compared to that of the original B powder, the results of thermal decomposition and combustion heat of B@PDA@PFPE with 30%PFPE discloses that the oxidation temperature drops by about 19.5 ℃, the combustion efficiency rises by about 22.3 %, and the flame expansion rate and flame temperature rise by approximately 40 times and 95.6 ℃, respectively. Therefore, the construction of double-layer core-shell structure effectively promotes the combustion of B powder. This work provides a new strategy for the application of B powder.

Progress and Challenges of Ferrite Matrix Microwave Absorption Materials.

Intelligent devices, when subjected to multiple interactions, tend to generate electromagnetic pollution, which can disrupt the normal functioning of electronic components. Ferrite, which acts as a microwave-absorbing material (MAM), offers a promising strategy to overcome this issue. To further enhance the microwave absorption properties of ferrite MAM, numerous works have been conducted, including ion doping and combining with other materials. Notably, the microstructure is also key factor that affects the microwave absorption properties of ferrite-based MAM. Thus, this article provides a comprehensive overview of research progress on the influence of the microstructure on ferrite-based MAM. MAMs with sheet and layered structures are also current important research directions. For core-shell structure composites, the solid core-shell structure, hollow core-shell structure, yolk-eggshell structure, and non-spherical core-shell structure are introduced. For porous composites, the biomass porous structure and other porous structures are presented. Finally, the development trends are summarized, and prospects for the structure design and preparation of high-performance MAMs are predicted.

Core-shell structured α-AlH3/Fe2O3 thermite with improved heat-release and combustion performance

Thermites are widely used in propellants, explosives and ignition materials because of their high heat release rate and good combustion efficiency. Structural control over thermites to achieve improved performance leads to a promising research area. Among these, core-shell structured composites have attracted wide attention due to their excellent properties and close contact among components. Herein, core-shell structured α-AlH3/Fe2O3 thermites were prepared, which exhibit high heat-release and excellent combustion performance. At an equivalence ratio of 2.0, the core-shell structured α-AlH3/Fe2O3 has the most heat release (1213.8 J/g) and the lowest reaction activation energy (147.5 kJ/mol). The ignited combustion performance of α-AlH3/Fe2O3 was notably strengthened by the shorter ignition delay period (11 ms). Interestingly, the core-shell structured α-AlH3/Fe2O3 was less sensitive to electrostatic discharge, which suggests that the core-shell structured α-AlH3/Fe2O3 reaches the goal of high energy release and electrostatic safety. The core-shell thermite system with α-AlH3 as metal fuel could provide an efficient alternative to hunt for thermites with high reactivity.

Cold sintering preparation of B4C@SiO2/20BP ceramic matrix composite and its dry tribological properties

To achieve low-temperature sintering of B4C ceramic, 'sol-gel' method is employed to create a B4C@SiO2 core-shell structure composite. Black phosphorus (BP) is exfoliated through 3 methods to obtain few-layer black phosphorene (FLBP) with sizes ranging from 100 µm to 1 µm. B4C@SiO2/20BP composite is successfully prepared through cold sintering process at 3 GPa and 90 °C, using NaOH solution as the transient liquid phase. The dry friction properties of B4C@SiO2/20BP composites with different sizes of FLBP are investigated in a ball-on-disc contact form. The findings reveal that as the FLBP size decreases, the friction coefficient gradually increases, inversely correlating with the wear rate. The wear mechanism shifts from adhesive wear to fatigue wear, leading to a diminishing anti-friction effect of FLBP.

In situ growth of ZIF-67 to construct core-shell mosaic structural composites for efficient extraction of benzoylurea insecticides.

A novel mosaic structure Silica@C/Co@ZIF-67 composite was synthesized by successfully embedding Co nanoparticles on the surface of silica spheres with the help of thermoplastic polyethyleneimine by carbon-reduction. The ZIF-67 half-shell layer structure was synthesized by the in-situ growth of ZIF-67 on the surface of silica spheres through the coordination of 2-methylimidazole with Co metal nodes. The composite was used as a magnetic solid-phase extraction adsorbent combined with high performance liquid chromatography-ultraviolet detector (HPLC-UV) for the extraction and determination of benzoylurea insecticides (BUs) in vegetables and tea. Based on the presence of π-π, hydrophobic and hydrogen bonding interactions between Silica@C/Co@ZIF-67 and BUs, the BUs were rapidly captured by the composites resulting in high adsorption performance. Under the optimal extraction parameters, the linear ranges were 0.3-200µg L-1 for diflubenzuron, 0.6-200µg L-1 for chlorbenzuron, and 1.0-200µg L-1 for triflumuron, teflubenzuron, and flufenoxuron, with correlation coefficients (R2) greater than 0.9991. The limits of detection (LODs) of the method were 0.1-0.3μg L-1, and the relative standard deviations (RSDs) were 1.2-3.0% for intra-day and 2.6-4.6% for inter-day. In the spiked recovery experiments of vegetables and tea, the recoveries of the five kinds of BUs ranged from 75.8 to 112.9%. In addition, after 10 repetitions using Silica@C/Co@ZIF-67, the recoveries of the five kinds of BUs were still as high as 78.4 to 83.9%.

SnO2/Sn with core-shell structure Schottky heterojunctions loaded in graphene to promote electrochemical reaction kinetics and enable efficient lithium-ion storage.

The stannic oxide (SnO2) anode expands in volume during cycling causing a decrease in reversible capacity. In this work, we generated a spherical SnO2/Sn heterojunction with core-shell structure composites encapsulated by graphene (SnO2/Sn/G) in situ using a simple one-step hydrothermal and subsequent annealing process. SnO2/Sn heterojunction nanospheres dispersed in a porous graphene framework accelerate the diffusion kinetics of electrons and ions. In addition, the structure plays a key role in mitigating large volume changes and nanostructure agglomeration. As a result, SnO2/Sn/G exhibits excellent performance as an anode material for lithium-ion batteries (LIBs), maintaining a reversible specific capacity of 720.6 mA h g-1 even after 600 cycles at a current density of 0.5 A g-1.

Ambient synthesis of one-dimensional core-shell nanocomposites by encapsulating SiC nanowires with layered double hydroxide nanosheets for high-performance microwave absorption application

The optimization design of micro/nanostructure and composition is an effective strategy for preparing high-performance electromagnetic wave absorption (EMA) material. Here, we provide a single-step in-situ electrostatic self-assembly growth approach at room temperature for the efficient construction of core-shell structural composites, consisting of bimetallic layered double hydroxides (LDH) nanosheets tightly wrapped around SiC nanowires. The formation of the bimetallic LDH nanosheets shell is caused by the binding of the bimetallic cations to OH−, which mainly arises from the hydrolysis of water induced by the 2-methylimidazole molecule, while the protonated 2-methylimidazole acts as an interlayer equilibrium anion. Through a heat-treatment process under air, the resulting derivatives of Co, Ni-LMc@SiC, and Zn, Ni-LMc@SiC generate excellent EMA properties due to the intrinsic and synergistic properties of the dielectric/magnetic components and the core-shell structure that provides numerous physical contacts and endows the composite with enhanced interfacial polarization and electron transport. As a result, Zn, Ni-LMc@SiC displays the highest RLmin value of −55.59 dB at 2.8 mm and EABmax of 6.28 at 2.4 mm, while Co, Ni-LMc@SiC has the widest EAB of 6.32 GHz at a thinner thickness of 2.2 mm. The successful construction of core-shell structures for LDH and SiC nanowires in such a facile strategy will broaden the application and development of high-performance EMA materials.

Polyarylene ether nitrile dielectric films modified by HNTs@PDA hybrids for high-temperature resistant organic electronics field

Abstract In this work, mussel-inspired surface functionalization of halloysite nanotubes (HNTs) were coated by in situ self-polymerization of polydopamine (PDA) to synthesize core-shell structural composites (HNTs@PDA), and then incorporated into polyarylene ether nitrile (PEN) matrix. Due to the strong adhesion of the PDA modification layer and the formation of hydrogen bonds between the polar nitrile group of PEN and the catechol group of PDA, the dispersion and interfacial compatibility of HNTs@PDA in the PEN matrix are improved. The results show that the dielectric constant of PEN/HNTs@PDA 20 nanocomposites reaches 11.56 (1 kHz), which is 3.2 times that of pure PEN. In addition, after heat treatment, a chemical cross-linking reaction occurred between the PEN matrix to form a cross-linked PEN (CPEN) based nanocomposites, which further improved the thermal stability of the nanocomposites. The results show that the T g of CPEN/HNTs@PDA 20 nanocomposites reaches 215.5°C, which is 47.7°C higher than that of PEN/HNTs@PDA 20. Moreover, the dielectric constant-temperature coefficient of all CPEN nanocomposites is less than 7 × 10−4°C−1 at the temperature range of 25–180°C. All in all, this work provides a simple and environmentally friendly strategy to adjust the dielectric properties of polymer-based ceramic nanocomposites, which provides a pathway for its application as a dielectric material in the film capacitors field.

Core-Shell Structured Silica-Coated Iron Nanowires Composites for Enhanced Electromagnetic Wave Absorption Properties.

In this study, we successfully prepared core-shell heterostructured nanocomposites (Fe NWs@SiO2), with ferromagnetic nanowires (Fe NWs) as the core and silica (SiO2) as the shell. The composites exhibited enhanced electromagnetic wave absorption and oxidation resistance and were synthesized using a simple liquid-phase hydrolysis reaction. We tested and analyzed the microwave absorption properties of Fe NWs@SiO2 composites with varied filling rates (mass fractions of 10 wt%, 30 wt%, and 50 wt% after mixing with paraffin). The results showed that the sample filled with 50 wt% had the best comprehensive performance. At the matching thickness of 7.25 mm, the minimum reflection loss (RLmin) could reach -54.88 dB at 13.52 GHz and the effective absorption bandwidth (EAB, RL < -10 dB) could reach 2.88 GHz in the range of 8.96-17.12 GHz. Enhanced microwave absorption performance of the core-shell structured Fe NWs@SiO2 composites could be attributed to the magnetic loss of the composite, the core-shell heterogeneous interface polarization effect, and the small-scale effect induced by the one-dimensional structure. Theoretically, this research provided Fe NWs@SiO2 composites with highly absorbent and antioxidant core-shell structures for future practical applications.

Microstructure and Mechanical Properties of Core-Shell B4C-Reinforced Ti Matrix Composites.

Composite material uses ceramic reinforcement to add to the metal matrix to obtain higher material properties. Structural design is an important direction of composite research. The reinforcement distribution of the core-shell structure has the unique advantages of strong continuity and uniform stress distribution. In this paper, a method of preparing boron carbide (B4C)-coated titanium (Ti) powder particles by ball milling and preparing core-shell B4C-reinforced Ti matrix composites by Spark Plasma Sintering was proposed. It can be seen that B4C coated on the surface of the spherical Ti powder to form a shell structure, and B4C had a certain continuity. Through X-ray diffraction characterization, it was found that B4C reacted with Ti to form layered phases of titanium boride (TiB) and titanium carbide (TiC). The compressive strength of the composite reached 1529.1 MPa, while maintaining a compressive strain rate of 5%. At the same time, conductivity and thermal conductivity were also characterized. The preparation process of the core-shell structure composites proposed in this paper has high feasibility and universality, and it is expected to be applied to other ceramic reinforcements. This result provides a reference for the design, preparation and performance research of core-shell composite materials.

Synthesis and electromagnetic wave absorption properties of Gd-Co ferrite@carbon core–shell structure composites

Synthesis and electromagnetic wave absorption properties of Gd-Co ferrite@carbon core–shell structure composites

Fabrication of silicon nanoparticles/porous carbon@porous carbon nanofibers core-shell structured composites as high-performance anodes for lithium-ion batteries

Silicon-based electrodes hold a great potential application in lithium-ion batteries (LIBs) due to the high-energy-density. However, huge volume expansion and poor electric conductivity hinder the commercial application of silicon-based materials. To alleviate these problems, two different hierarchical core-shell composites, silicon/carbon@porous carbon nanofibers (Si/C@PCNF) and silicon@hollow porous carbon nanofiber (Si@HPCNF) are designed and prepared through coaxial electrospinning. The shell layer prevents silicon contacting with electrolyte directly, and the porous carbon nanofibers shorten Li+ diffusion distance and facilitate ion transport. Compared with Si@HPCNF composites, Si/C@PCNF composites achieve a better electrochemical performance owing to the high surface area (68.05 m2/g) and the fact that silicon nanoparticles are connected to each other by porous carbon in the core. The Si/C@PCNF electrodes deliver a large reversible capacity (842.1 mAh∙g−1 after 500 cycles at 0.5 A∙g−1), a good rate capability (1366.6 mAh∙g−1 at 0.5 A∙g−1) and an excellent cycle stability (420.3 mAh∙g−1 at 2.0 A∙g−1 after 1000 cycles), indicating that it can be served as a promising anode for high-performance LIBs.

Synthesis of carbon-coated cobalt ferrite core–shell structure composite: A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density, which results in unsatisfactory electromagnetic wave (EMW) absorption performance. In this study, the CoFe 2 O 4 @C core–shell structure composite was synthesized by a two-step hydrothermal method. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and vector network analysis et al . were used to test the structure and EMW absorption properties of CoFe 2 O 4 @C composite. The results show that the reflection loss (RL) of the CoFe 2 O 4 @C composite reaches the maximum value of −25.66 dB at 13.92 GHz, and the effective absorbing band (EAB) is 4.59 GHz (11.20–15.79 GHz) when the carbon mass content is 6.01%. The RL and EAB of CoFe 2 O 4 @C composite are increased by 219.55% and 4.59 GHz respectively, and the density is decreased by 20.78% compared with the cobalt ferrite. Such enhanced EMW absorption properties of CoFe 2 O 4 @C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite, moreover, the carbon coating layer adjusts the impedance matching of the composite, and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.

Self-supported Co-Ni-S@CoNi-LDH electrode with a nanosheet-assembled core-shell structure for a high-performance supercapacitor

In this work, a nanosheet-assembled core-shell structure composite of Co-Ni-S@CoNi-LDH was prepared on Ni foam via hydrothermal synthesis, in which Co-Ni-S nanowires as cores were assembled with the shell of CoNi-LDH nanosheets. The combination of the high conductivity of Co-Ni-S, the high specific surface area of CoNi-LDH and the multivalent state of Ni and Co provided more active sites, short and effective ion transport paths, and great synergy, which played significant roles in the excellent performance of Co-Ni-S@CoNi-LDH. Meanwhile, the nanosheet-assembled core-shell structure improved the overall stability. Based on the characterisation and the performance measurements, the Co-Ni-S@CoNi-LDH electrode showed an excellent electrochemical performance. The Co-Ni-S@CoNi-LDH electrode acquired a specific capacitance of 2414 F/g at a 1 A/g current density and a high cycle stability with an 89.7% retention after 3000 cycles. The assembled hybrid supercapacitor Co-Ni-S@CoNi-LDH//AC delivered a high energy density of 59.11 Wh kg −1 at an 855.43 W kg −1 power density, as well as an excellent rate performance of 81% after 5000 cycles at a 5 A/g current density, showing good potential for practical applications. • Nanosheets are assembled oriented on the nanowires by hydrothermal synthesis. • The effects of the reactants ratio on the structure were investigated. • The Co-Ni-S@CoNi-LDH delivers a high gravimetric specific capacity of 2414 F/g. • Co-Ni-S@CoNi-LDH//AC device was assembled with excellent electrochemical performance.

Preparation and microwave absorption properties of Gd–Co ferrite@silica@carbon multilayer core–shell structure composites

Developing microwave absorbing materials having a low reflection loss (RL) and wide effective absorption band (EAB) is important. In this study, spherical Gd–Co ferrite nanoparticles were synthesized by using a co-precipitation method. Silica and carbon shells were coated on the surface of Gd–Co ferrite particles by polymerizing tetraethyl orthosilicate and glucose. Three composites were prepared: Gd–Co ferrite@silica, Gd–Co ferrite@carbon, and Gd–Co ferrite@silica@carbon. The results showed that Gd–Co ferrite@silica@carbon exhibited the best absorbing performance, with its RL reaching the minimum value of –46.85 dB and its EAB was 3.14 GHz (8.74–11.88 GHz) at an absorption layer thickness of 2.5 mm and a frequency of 9.93 GHz. This excellent microwave absorption performance is attributed to two factors: the magnetic loss caused by the natural resonance and eddy current loss of Gd–Co ferrite and the dielectric loss enhanced by the interfacial polarization and dipole polarization caused by the multilayer core–shell structure such that the composite has excellent impedance matching. Thus, Gd–Co ferrite@silica@carbon composites can be used as high-performance microwave absorption material.

Growth of magnetic metals on carbon microspheres with synergetic dissipation abilities to broaden microwave absorption

• Facile electrostatic assembly approach for preparation of core-shell C/magnetic metal composite microspheres. • Excellent microwave absorption performance including a maximum reflection loss value of −54.1 dB and a broad effective absorption bandwidth of 6.7 GHz. • Profound magnetic coupling effect and magnetic-dielectric synergy mechanism for enhancing microwave absorption performance. Microwave absorption (MA) materials have been captured extensive attentions due to the serious electromagnetic (EM) pollution. Numerous interests focus on the MA performances of core-shell structural composites with magnetic constituents as cores and dielectric constituents as shells, which inevitably suppressed the magnetic coupling causing the decrease of magnetic loss to some extent. Herein, the core-shell structural carbon (C) microsphere/magnetic metal composites were fabricated through the combination of an electrostatic assembly approach and subsequent in-situ reduction reaction. The complex permittivity and permeability of core-shell C@magnetic metal composite system can be effective adjusted by the constituent and microstructure of shells. Thanks to the distinct magnetic coupling from the subtle designed structures and the promotion of the magnetic-dielectric synergy, the C@magnetic metal composite exhibited enhanced MA properties. The optimal reflection loss (RL) of C@Ni composite was -54.1 dB with a thickness of 3.4 mm, meanwhile the effective absorbing band could reach over 5.5 GHz at only a 1.8 mm thickness. Broad absorption bandwidth with RL below -10 dB could achieve 6.0 GHz and 6.7 GHz for C@Co and C@NiCo composites with a thin 2.1 mm thickness, respectively. Our exciting findings might lead a guide on the novel structure design for the functional core-shell structural composites used for microwave absorption. Graphical Abstract .

Novel Z-scheme In2S3/Bi2WO6 core-shell heterojunctions with synergistic enhanced photocatalytic degradation of tetracycline hydrochloride

Semiconductor photocatalytic technology is an effective strategy to cope with the current environmental issues. Therefore, the development of low-cost and environment-friendly catalysts with high efficacy has become a research focus and emphasis. Herein, novel Z-scheme In2S3/Bi2WO6 core-shell structure composites were controllably prepared by template and hydrothermal route. Highly improved photocatalytic degradation of tetracycline hydrochloride (TCH) over In2S3/Bi2WO6 core-shell composites was observed under visible-light (VL) irradiation (∼96.0%), which was 2.4 and 2.1 folds higher than that of In2S3 and Bi2WO6, respectively. The excellent oxygen activation and catalytic performance was ascribed to the synergistic effects of built-in electric field to ensure easy charge exchange at the interface of In2S3 and Bi2WO6, Z-scheme charge transfer path and the extended range of VL absorption. Superoxide radical (·O- 2) and hydroxyl (·OH) radicals were verified to be involved in the photocatalytic reaction by the active species capture experiment and the electron spin response (ESR) detection. The recycling experiments demonstrate the excellent stability and reusability of the In2S3/Bi2WO6. In addition, in accordance with the experimental results, the highly efficient Z-scheme photocatalytic mechanism and degradation paths were proposed. This work provided a new way for preparation of Z-scheme core-shell composites which had broad applications prospect in environmental remediation.

MOF as the rigid shell to improve the mechanical sensitivity of nitramine explosives

Metal-organic Framework (MOF) was selected to fabricate three typical nitramine explosives (RDX, HMX and CL-20) based core–shell structure composites. The results showed that the decomposition peak temperature of the three typical energetic materials after being wrapped by the MOF material had advanced, while the activation energy value has increased significantly. The impact sensitivity and the friction sensitivity have decreased a lot, indicating that the stability has been further enhanced after wrapped with MOF. In addition, software simulation proves that the addition of MOF material will not affect the detonation performance of the original energetic material, which means these composites can still maintain a better energy performance.

Enhanced dielectric properties of poly(arylene ether nitrile) composite films employing MoS2-based semiconductors for organic film capacitor applications

Polymer-based dielectric composites are potential substitute dielectrics for organic thin film capacitors. In this work, the exfoliated molybdenum disulfide (MoS2) was functionalized by mussel-inspired poly(dopamine) (PDA) to form core-shell structured composites (MoS2@PDA) under easy-handling and eco-friendly conditions, and then as filler incorporated into poly(arylene ether nitrile) (PEN) matrix. The interfacial interaction and dispersion of MoS2@PDA in PEN matrix were improved by the strong adhesion of PDA interlayer to exfoliated MoS2, π-π conjugation and hydrogen bond interactions, which formed by the polar nitrile group of PEN and catechol groups of PDA. Therefore, the PEN/MoS2@PDA composite films exhibited enhanced dielectric constant, synchronously maintaining better flexibility, thermal stability and the same level of dielectric loss with PEN. Particularly, the addition of 20 wt% MoS2@PDA into PEN matrix leaded to substantial growth of dielectric constant up to 12.9 at 1 kHz, while the PEN matrix was just 4.2. Meanwhile, the dielectric composites maintained relatively low dielectric loss of 0.022 at 1 kHz, which was ascribed to the improved compatibility and interfacial interaction between filler and PEN. All in all, a eco-friendly and easy-handling strategy was provided to tune the dielectric constant and dielectric loss of semiconductor/polymer composites, which has great potential to promote the development of dielectric in the fields of organic thin film capacitors.