In situ formed core–shell structured particle reinforced aluminum matrix composites

Particulate reinforced metal matrix composites (PRMMCs) have high strength but their plasticity and toughness are usually low. Here in this paper a new PRMMC with both high strength and plasticity was successfully developed. The composite is composed of three distinct phases, including ductile matrix, ductile core phase and in situ formed hard intermetallic shell. The strength can be substantially improved by transferring the applied stress from the soft matrix to the hard shell. The propagation of the cracks in the shell during deformation can be inhibited since both tips of each crack become blunt due to the high ductility of the matrix and core phases. The designed structure provides guidance for developing new PRMMCs with high strength and plasticity.     

Synthesis of water-compatible surface-imprinted composite microspheres with core–shell structure for selective recognition of thymopentin from aqueous solution

A novel water-compatible surface-imprinted core–shell microsphere, which had multiple non–covalent interactions with template molecule, was successfully prepared by the surface grafting polymerization method in acetonitrile–water systems with thymopentin as template through ionic liquid-functionalized polyethyleneglycolmethacrylate-co-vinylimidazole microsphere as the matrix. The average diameter of matrix was 1 μm ± 20 nm and the thickness of imprinted layer was about 50 nm. The results of static adsorption experiments indicated that ionic liquid-functionalized molecularly imprinted microspheres showed the good adsorption capacity and specific recognition for template peptide. The binding-isotherm analysis showed that Langmuir isotherm models gave a good fit in the range of concentrations, suggesting that there was only one kind of binding site in imprinted layer. Measurements of the binding kinetics revealed that surface-imprinted composite microspheres reached peptide-adsorption equilibrium in 60 min and the maximum adsorption capacity for TP5 was 38.4 mg g^?1. The effects of pH, salt concentration, and temperature on the adsorption capacities were investigated. The microspheres were found to have a high specificity for TP5 with little affinity for BSA and Hb. Finally, the core–shell microspheres can be reused with only 15.6 % decrease in TP5 adsorption capacity after six times.     

In situ preparation and protein delivery of silicate–alginate composite microspheres with core-shell structure

The efficient loading and sustained release of proteins from bioactive microspheres remain a significant challenge. In this study, we have developed bioactive microspheres which can be loaded with protein and then have a controlled rate of protein release into a surrounding medium. This was achieved by preparing a bioactive microsphere system with core-shell structure, combining a calcium silicate (CS) shell with an alginate (A) core by a one-step in situ method. The result was to improve the microspheres'' protein adsorption and release, which yielded a highly bioactive material with potential uses in bone repair applications. The composition and the core-shell structure, as well as the formation mechanism of the obtained CS–A microspheres, were investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, energy dispersive spectrometer dot and line-scanning analysis. The protein loading efficiency reached 75 per cent in CS–A microspheres with a core-shell structure by the in situ method. This is significantly higher than that of pure A or CS–A microspheres prepared by non-in situ method, which lack a core-shell structure. CS–A microspheres with a core-shell structure showed a significant decrease in the burst release of proteins, maintaining sustained release profile in phosphate-buffered saline (PBS) at both pH 7.4 and 4.3, compared with the controls. The protein release from CS–A microspheres is predominantly controlled by a Fickian diffusion mechanism. The CS–A microspheres with a core-shell structure were shown to have improved apatite-mineralization in simulated body fluids compared with the controls, most probably owing to the existence of bioactive CS shell on the surface of the microspheres. Our results indicate that the core-shell structure of CS–A microspheres play an important role in enhancing protein delivery and mineralization, which makes these composite materials promising candidates for application in bone tissue regeneration.     

In situ controllable synthesis of Ag@AgCl core–shell nanoparticles on graphene oxide sheets

Graphene oxide-supported uniform Ag@AgCl core–shell nanoparticle composites have been successfully prepared by a facile two-step synthetic process. First, graphene oxide sheets were used as carriers to anchor and disperse Ag nanoparticles on their surface. Then these fixed Ag nanoparticles on carbon sheets are utilized as precursors, around which AgCl nanocrystals form in situ using FeCl₃ as oxidant, forming graphene oxide-supported Ag@AgCl core–shell nanoparticle composites. The composition of these attached Ag@AgCl core–shell nanoparticles can be easily controlled by adjusting the usage of FeCl₃, resulting in the formation of controllable core–shell nanostructures. Furthermore, these as-prepared graphene oxide–Ag@AgCl nanoparticle composites display effective photodegradation of methylene orange dye under visible light irradiation, which indicates their potential applications in environmental areas.     

N-GQDs modified core–shell structure ZnCdS/N-GQDs@ZnS for enhancing photoelectric properties

Journal of Materials Science: Materials in Electronics - In this paper, core–shell quantum dots were successfully synthesized by condensation reflux at low temperatures using reduced...     

Facile method to synthesise polystyrene/silver composite nanoparticles with core–shell structures

We report a facile method for the fabrication of polystyrene/silver composite nanoparticles with core–shell nanostructures. First, polystyrene (PS) nanoparticles with carboxyl acid groups on their surfaces were prepared via the dispersion polymerisation of styrene in water with the assistance of acrylic acid. Second, with the addition of [Ag(NH₃)₂]⁺ to the PS dispersion, [Ag(NH₃)₂]⁺ was absorbed onto the surfaces of the modified PS nanoparticles. Finally, the [Ag(NH₃)₂]⁺ complex ions were reduced to Ag to form the PS/Ag nanocomposites upon heating. The resulting PS/Ag composite nanoparticles were characterized via scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and dynamic light scattering.     

Nanofibres of CA/PAN with high amount of carbon nanotubes by core–shell electrospinning

We prepared polyacrylonitrile (PAN) and cellulose acetate (CA) based nanofibres with high amount of carbon nanotubes (CNTs) by core–shell electrospinning. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to evaluate the morphology and structure of the electrospun nanofibres. Raman spectroscopy (Raman) and TEM indicate alignment of CNTs in the polymer fibres. Core–shell electrospinning improved the distribution and uniformity of the fibres. The loading of carbon nanotubes showed better thermal stability.     

In situ preparation of a SiC–TiB2 composite and its wear fracture mechanism at high temperatures

Journal of Materials Science - The unsatisfactory high-temperature performance of commonly used silicon carbide (SiC)-based ceramics calls for a novel approach for their reinforcement. We present...     

In situ synthesis of concentric C@MoS<Subscript>2</Subscript> core–shell nanospheres as anode for lithium ion battery

Molybdenum disulfide (MoS₂) is a promising anode material for lithium ion batteries (LIBs) due to its high theoretical capacity, but it is suffered from intrinsically poor electronic/ionic conductivity and vast volume expansion/contraction during repeated charge–discharge process. In the present work, we report a spherical C@MoS₂ nanocomposite as a high-performance anode for LIBs. The C@MoS₂ nanocomposite with carbon nanosphere cores and ultrathin MoS₂ nanosheet shells was prepared through an in situ solvothermal reaction, where carbon and MoS₂ were simultaneously formed in one pot. The basal plane of MoS₂ layer is highly parallel to the surface of carbon sphere, constructing a concentric nanostructure. This unique architecture can provide strong and stable interfacial contact between the MoS₂ nanosheets and carbon and thus improve its structural stability and maximize the electrical contact. Owing to the effective combination and synergistic interaction of the two nanoscale phases, the C@MoS₂ nanocomposite exhibited markedly enhanced performance with high rate capability and cycle stability for reversible Li⁺ storage.     

Preparation and properties of antibacterial TiO2@C/Ag core–shell composite

Abstract

An environment-friendly hydrothermal method was used to prepare TiO₂@C core–shell composite using TiO₂ as core and sucrose as carbon source. TiO₂@C served as a support for the immobilization of Ag by impregnation in silver nitrate aqueous solution. The chemical structures and morphologies of TiO₂@C and TiO₂@C/Ag composite were characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive x-ray spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The antibacterial properties of the TiO₂@C/Ag core–shell composite against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were examined by the viable cell counting method. The results indicate that silver supported on the surface of TiO₂@C shows excellent antibacterial activity.     

CeNi nanoparticles with shell structure for hydrogen storage

A new kind of Ce-Ni nanoparticle was prepared by hydrogen arc plasma method. The nanoparticles consist of a large Ni core and a thin outer shell of CeNi alloy and CeO₂. A large quantity of hydrogen was stored in the particles, which was released at about 400 °C. The particles possess a lot of defects, dislocations and twin faults, which increase the number of surface active centers of the particles. The mechanism of shell structure formation of the nanoparticles is discussed in terms of the low solubility of Ce in Ni, and surface segregation under non-equilibrium cooling conditions.     

Fabrication of Cu@Ag core–shell nanoparticles for nonlinear optical applications

We report the preparation of the core–shell structured Cu@Ag nanoparticles by a simple wet chemical route at room temperature. The surface plasmon resonance band at 405 nm is indicative of the formation of Cu@Ag nanoparticles. The powder X-ray diffraction and energy dispersive X-ray analyses were carried out to elucidate the structure and chemical composition respectively. The morphological investigations made by electron microscopes revealed that the particles are spherical in shape with core–shell structures having size of about 50 nm. The X-ray photoelectron spectroscopy was performed to elucidate surface state composition of the core–shell structured nanoparticles based on the binding energies and confirmed the formation of Cu@Ag core–shell nanoparticles. The enhanced non-linear optical response of the Cu@Ag core–shell nanoparticles was demonstrated by z-scan experiment using He–Ne laser. This report provides a simple, economical and practical technology to fabricate Cu@Ag core–shell nanoparticles with enhanced nonlinear optical properties.     

Preparation of polystyrene–polyisoprene core–shell nanoparticles for reinforcement of elastomers

Latex-formed core–shell nanoparticles composed of cross-linked polystyrene (PS) core and polyisoprene (PI) shell were successfully synthesized by means of a two-stage emulsion polymerization. The PS core possessed a Z-average diameter of 50.3 nm, and the PS–PI particles took a spherical shape with a Z-average size of 50–70 nm in diameter. Shell thickness was controlled by varying isoprene loading. Necessary interphase interactions between the core and shell domains were also achieved by grafting and swelling polymerization. Latex compounding method was employed to prepare the filled elastomer compounds. As expected, the PS–PI core–shell nanoparticles exhibited excellent reinforcement to elastomeric matrix, enhancing the tensile strength of the styrene–butadiene rubber by approximately 400%. The lower density, better interfacial interactions, and latex compounding process would benefit the PS–PI nanoparticles reinforced elastomer nanocomposites in energy saving.     

Red@Black phosphorus core–shell heterostructure with superior air stability for high-rate and durable sodium-ion battery

Heterostructured electrodes have gained increasing attentions owing to the synergistic effects from individual building components and the unique interfaces. However, rational design and controllable fabrication of high areal capacity and durable phosphorus-based heterostructure anode for industry remains a critical challenge. Herein, a new red@black phosphorus core–shell heterostructure anchored on three-dimensional N-doped graphene (RP@BP/3DNG) has been prepared via a facile one-step solvothermal strategy. As demonstrated by experimental data and theoretical calculations, RP@BP/3DNG shows a superior high electronic conductivity and an extremely low Na⁺ diffusion barrier due to the build-in filed at the RP@BP heterointerface, thus RP@BP/3DNG delivers an ultra-high areal capacity of 3.46 mAh cm⁻² (1440.2 mAh/g at 0.05 A/g), impressive rate performance (521.3 mAh/g at 10.0 A/g) as well as unprecedented capacity retention rate of 89.3% after 1200 cycles at 10.0 A/g when evaluated as an anode for sodium ion batteries (SIBs). Furthermore, the internal electric field at the interfaces of RP@BP leads to the shift of electron cloud from BP to RP, which greatly suppresses the reaction activity of lone-pair electrons of BP atoms, and therefore RP@BP/3DNG shows much enhanced air stability. This work heralds a new insight for designing high-performance and stable P-based anodes for rechargeable batteries.     

Study on the structure and properties of core–shell Fe/Al composite powder synthesized by MOCVD in fluidized bed

Core–shell Fe/Al composite powder with different thicknesses of Fe layer has been prepared by MOCVD in a fluidized bed reactor. The products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX) and simultaneous thermogravimetry–differential scanning calorimetry (TG–DSC). The results show that a compact nano-Fe layer is covered on the surface of Al to form core–shell Fe/Al composite powder. Nano-Fe layer thickness can be controlled by adjusting deposition time. The Fe layer thickness is evaluated by weight increase in TG curve at the temperature range of 350–550 °C in air atmosphere. Combustion properties of Fe/Al composite powder have great improvement compared with raw Al.     

In situ synthesis of gold–polyaniline composite in nanopores of polycarbonate membrane

In situ one-step chemical synthesis route for the preparation of a gold–polyaniline composite in nanopores of polycarbonate (PC) membrane is reported. PC membrane, which was placed in a specially designed two-compartment cell, separated the aqueous solution of aniline from HAuCl₄ solution. Concentration gradient across the membrane caused movement of AuCl₄ ⁻ and anilinium ions in the pores of polycarbonate membrane. Nanopores in PC membrane acted as reaction vessels where aniline and HAuCl₄ were allowed to mix together, and the redox reaction between aniline and HAuCl₄ led to the formation of gold–polyaniline composite. The gold–polyaniline composite in PC membrane was characterised by EDXRF, XRD, UV–Vis spectroscopy, FTIR and TEM. Peak broadening in XRD suggests that Au particles formed in the membrane are nanocrystallites and average crystallite size is (24 ± 4) nm. TEM studies show that gold nanoparticles are randomly dispersed in polyaniline clusters formed in the nanopores of PC membrane. Characterisation results show that the surfaces of the PC membrane exposed to HAuCl₄ and aniline have significantly higher concentrations of Au nanoparticles and polyaniline, respectively.     

Using layer-by-layer assembly to fabricate NaLa(MoO4)2@CdTe core–shell microspheres with high fluorescence

The development of fluorescent materials with low energy consumption, low cost and desirable optical properties is needed for the perspective of practical application. Here, functional NaLa(MoO₄)₂@CdTe core–shell microspheres with high fluorescence were prepared by layer-by-layer self-assembly technique. Through the consecutive electrostatic adsorption of charged cetyltrimethyl ammonium bromide and CdTe quantum dots (QDs), the uniform and regular multilayer shell of CdTe QDs was synthesized. The NaLa(MoO₄)₂@CdTe microspheres exhibited improved photoluminescence intensity and stability of red emission, compared with that of the CdTe QDs powder, and the fluorescence enhancement mechanism were investigated. The CdTe QDs multilayer shell is expected to supersede the Eu³⁺ ion for producing a novel red phosphor.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.