Ascorbic acid-mediated synthesis and characterisation of iron oxide/gold core–shell nanoparticles.

The current article reports on providing surface modification of magnetic nanoparticles with gold to provide stability against aggregation. Gold-coated magnetite nanoparticles were synthesised to combine both magnetic as well as surface plasma resonance (SPR) properties in a single moiety. The nanocomposites were produced by reduction (using ascorbic acid) of gold chloride on to the surface of iron oxide nanoparticles. Ascorbic acid not only acts as a reducing agent, but also the oxidised form of ascorbic acid i.e. Dehydro-ascorbic acid acts as a capping agent to impart stability to as synthesised gold-coated iron oxide nanocomposites. The synthesised nanocomposite was monodispersed with a mean particle size of around 16 nm and polydispersity index of 0.190. X-ray diffraction analysis confirms presence of gold on the surface of magnetite nanoparticles. The synthesised nanocomposites had a total organic content of around 3.2% w/w and also showed a shifted SPR peak at 546 nm as compared to gold nanoparticles (528 nm). Both uncoated and gold-coated magnetite exhibited superparamagnetic behaviour at room temperature. Upon coating with gold shell, saturation magnetisation of iron oxide nanoparticles decreases from 42.806 to 3.54 emu/gram.     

Development of electrosprayed artesunate-loaded core–shell nanoparticles

Objective: Artesunate (ART) is proven to have potential anti-proliferative activities, but its instability and poor aqueous solubility limit its application as an anti-cancer drug. The present study was undertaken to develop coaxial electrospraying as a novel technique for fabricating nanoscale drug delivery systems of ART as the core–shell nanostructures.

Methods: The core–shell nanoparticles (NPs) were fabricated with coaxial electrospraying and the formation mechanisms of NPs were examined. The physical solid state and drug–polymer interactions of NPs were characterized by X-ray powder diffraction (XRPD) and Fourier transform infrared (FTIR) spectroscopy. The effects of materials and electrospraying process on the particle size and surface morphology of NPs were investigated by scanning electron microscopy (SEM). The drug release from NPs was determined in vitro by a dialysis method.

Results: The ART/poly(lactic-co-glycolic) acid (PLGA) chitosan (CS) NPs exhibited the mean particle size of 303?±?93?nm and relatively high entrapment efficiency (80.5%). The release pattern showed an initial rapid release within two hours followed by very slow extended release. The release pattern approached the Korsmeyer–Peppas model.

Conclusions: The present results suggest that the core–shell NPs containing PLGA and CS have a potential as carriers in the anticancer drug therapy of ART.     

General synthesis of high-performing magneto-conjugated polymer core–shell nanoparticles for multifunctional theranostics

Recently,increasing attention has been paid to magneto-conjugated polymer core-shell nanopartides (NPs) as theranostic platforms.However,the utilization of surfactants and extra oxidizing agents with potential toxidty in synthesis,the lack of general methods for the controlled synthesis of various kinds of magnetic NP (MNP)@conjugated polymer NPs,and the difficulty of obtaining balanced magneto-optical properties have greatly limited the applications of magneto-conjugated polymers in theranostics.We developed an in situ surface polymerization method free of extra surfactants and oxidizing agents to synthesize MNP@polypyrrole (PPy) NPs with balanced,prominent magneto-optical properties.MNP@PPy NPs with an adjustable size,different shapes,and a controlled shell thickness were obtained using this method.The method was extended to synthesize other MNP-conjugated polymer core-shell NPs,such as MNP@polyaniline and MNP@poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS).We discuss the formation mechanism of the proposed method according to our experimental results.Finally,using the optical and magnetic properties of the obtained MNP@PEDOT:PSS NPs,in vivo multimodal imaging-guided hyperthermia was induced in mice,achieving an excellent tumor-ablation therapeutic effect.Our work is beneficial for extending the application of MNP-conjugated polymer core-shell NPs in the biomedical field.     

Facile synthesis of FeCo@NC core–shell nanospheres supported on graphene as an efficient bifunctional oxygen electrocatalyst

Electrocatalytic conversion of oxygen holds great potential for clean energy technologies,including water electrolysis,regenerative fuel cells,and rechargeable metal-air batteries.The development of highly efficient and inexpensive oxygen electrocatalysts as replacements for precious metal-based catalysts is vitally important for large-scale practical application in the future.A bifunctional oxygen electrocatalyst based on FeCo nanoparticles/N-doped carbon core-shell spheres supported on N-doped graphene sheets was prepared via one-step pyrolysis of graphitic carbon nitride and acetylacetonates.The optimized product exhibited an oxygen electrode activity of 0.87 V and excellent durability.The remarkable performance is mainly attributed to the synergetic effect arising from the FeCo nanoparticles and N-doped carbon shell.This study introduces an inexpensive and simple way to develop highly active bifunctional oxygen electrocatalysts.     

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.     

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.     

Effect of zinc oxide concentration on the core–shell ZnS/ZnO nanocomposites

In this work, synthesis and characterization of core–shell zinc sulphide (ZnS)/zinc oxide (ZnO) nanocomposites has been reported to see the effect of ZnO concentration in core–shell combination. The nascent as well as core–shell nanostructures were prepared by a chemical precipitation method starting with the synthesis of nascent ZnS nanoparticles. The change in morphological and optical properties of core–shell nanoparticles was studied by changing the concentration of ZnO for a fixed amount of ZnS. The nascent ZnS nanoparticles were of 4–6 nm in diameter as seen from TEM, each containing primary crystallites of size 1.8 nm which was estimated from the X-ray diffraction patterns. However, the particle size increases appreciably with the increase in ZnO concentration leading to the well known ZnO wurtzite phase coated with FCC phase of ZnS. Band gap studies were done by UV–visible spectroscopy and it shows that band gap tunability can be achieved appreciably in case of ZnS/ZnO core–shell nanostructures by varying the concentration of ZnO. Fourier transform infrared analysis also proves the formation of core–shell nanostructures. Photoluminescence studies show that emission wavelength blue shifts with the increase in ZnO concentration. These core–shell ZnS/ZnO nanocomposites will be a very suitable material for any type of optoelectronic application as we can control various parameters in this case in comparison to the nascent nanostructures.     

Controllable synthesis and characterization of Ag@AgBr core–shell nanowires

Ag@AgBr core–shell nanowires have been synthesized in large quantities via a redox reaction between Ag nanowires and FeBr₃ in solution at room temperature. The effect of the molar ratio of Fe:Ag on the formation and optical absorption of the Ag@AgBr core–shell nanowires was systematically studied. The results showed that Ag nanowires were converted into Ag@AgBr core–shell nanowires and finally into AgBr nanorods with the increase of the molar ratio of Fe:Ag. At the same time, the optical absorption of Ag nanowires decreased gradually and disappeared finally. In addition, the growth mechanism of the Ag@AgBr core–shell nanowires was also discussed in detail.     

Modeling the solar absorption performance of Copper@Carbon core–shell nanoparticles

Journal of Materials Science - The working fluid is a critical component in direct absorption solar collectors. Nanoparticle (NP) suspensions can be used as efficient solar absorption media. In...     

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.     

In situ monitoring of NiO–Al2O3 nanoparticles synthesis by thermo-Raman spectroscopy

Simultaneous thermogravimetric analysis and thermo-Raman spectroscopy (TRS) measurements for in situ monitoring of wet chemical reaction of Ni(OH)₂·4H₂O and Al(OH)₃ forming NiO–Al₂O₃ nanoparticles is studied and compared with the solid-state reaction. Herein, a different approach of synthesis and monitoring of NiO–Al₂O₃ by TRS is presented, in which, in situ thermo-Raman spectra are recorded at every degree interval from 25 to 800 °C to understand the structural and compositional changes in NiO–Al₂O₃ as a function of temperature. Slow controlled heating of the sample as in TRS, enables better control over morphology and particle size distribution (～10–20 nm diameter). The X-ray diffraction (XRD) shows that smaller particle size is obtained using wet chemical reaction than the solid-state reaction (～25 nm diameter). TRS studies also reveal that, the bulk NiAl₂O₄ forms at temperatures above 800 °C, although, the onset of formation is around 600 °C. Condensation of Al(OH)₃ forming Al₂O₃ is also monitored, wherein, presence of hydrocarbon is found to contribute to the observed fluorescence background. Based on the TRS and complementary characterizations using XRD, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis, the formation of supported NiO–Al₂O₃ is discussed.     

Fabrication of hollow core–shell conductive nanoparticles based on nanocrystalline cellulose for conductive adhesive

A novel environmentally friendly method was developed to fabricate hollow core–shell conductive nanoparticles using a natural and nontoxic material, nanocrystalline cellulose (NCC), as the template. The NCC used in this study has nano-scale rod-like structure. After the oxidization to dialdehyde cellulose, the insulated NCC was functionalized by poly(dopamine) (PDA) in weakly alkaline conditions through Schiff base reaction and self-polymerization. The Schiff base can be hydrolyzed in an aqueous acetone solution via ultraviolet radiation so that the hollow structure constructed. This structure not only strengthened the mechanical properties but also provided more active sites for silver deposition. Utilizing the chelating ability of the catechol groups in PDA, electroless plating method was used to form the silver coating layer. Scanning electron microscope and Dynamic Light Scattering measurements indicated that these nanoparticles (NPs) had well-defined morphology and a mean diameter of 100–120 nm. Moreover, these prepared Ag–DA–NCC₀ NPs exhibited excellent conductivity. Their electrical resistivity reached 0.2 mΩ·cm, which is much higher than that of many other conductive particles used in conductive adhesive.     

In situ fabricated metal-carbide with core–shell structure for high impact-toughness iron-matrix composite

A series of metal-carbide (Ta–TaC, Nb–NbC and W–WC) with core–shell structure for iron-matrix composites are fabricated by in situ solid-phase diffusion. Results show that the formation of metal-carbide with a rod-shaped core–shell structure, in which the metal-rod surface was covered with a carbide shell layer, in the iron- matrix after in situ solid-phase diffusion. The TaC, NbC, and WC shell layers are in situ synthesised by the diffusion of carbon atoms from the iron-matrix onto the surface of the Ta, Nb, and W rods, respectively. Metallurgical integration occurs between metal-carbide and iron-matrix. The metal-carbide-reinforced iron-matrix composites show excellent impact resistance, and the shell-layer hardness is extremely high.     

The effect of zinc oxide–phosphate core–shell pigments on the properties of blend rubber composites

In this work the rheological, physico-mechanical, thermal and morphology studies were performed on a blend of EPDM/SBR (ethylene propylene diene monomer/styrene butadiene rubber) (50/50) loaded with a new prepared core–shell pigment based on a core of zinc oxide which presents the major component of the prepared pigment (≈90%) covered with a shell of phosphate, this shell comprises only about (≈10%). The new pigments were added in different concentration to the rubber blend and were compared to blends pigmented with commercial zinc oxide and zinc phosphate. The results showed that the new pigments exhibited better rheometric, and physico-mechanical properties. In addition, these prepared pigments showed decrease of equilibrium swelling in toluene solvent and increase in crosslink density for EPDM/SBR blend. The efficiency of prepared core–shell pigments were also evaluated by studying the surface morphology (SEM) and thermal properties TGA (thermal gravimetric analysis). The prepared pigments loading of 10 phr (parts per hundred parts of rubber) showed the optimum properties of EPDM/SBR blend than rubber loaded with higher concentration of the commercial pigments, which indicated that the new core–shell pigment is more economic with better performance than commercial zinc oxide and phosphates individually.     

Thermal stress dependence of magnetic hysteretic processes in core–shell nanoparticles

The control of thermal stresses in the core–shell structures is an important task in order to understand their temperature dependent magnetization processes. This paper is dedicated to a theoretical and micromagnetic study of the thermal stresses on the hysteretic processes in core–shell nanoparticles. The analytical model can predict the thermal and elastic behavior of the core–shell nanoparticle supposed to a forced cooling process. The temperature and thermal stresses values obtained by direct computation from the analytical model were used to evaluate the magneto-elastic energy of the core–shell system. A micromagnetic model was used to compute the equilibrium positions of the particle magnetization as function of the applied field. The model allows an evaluation of the increase of the particle coercive field and of the blocking temperature as an effect of the thermal stress.     

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.     

Fast synthesis,formation mechanism,and control of shell thickness of CuS–polystyrene core–shell microspheres

The silanol-modified polystyrene microspheres were prepared through dispersion polymerization. Then copper sulfide particles were grown on silanol-modified polystyrene through sonochemical deposition in an aqueous bath containing copper acetate and sulfide, released through the hydrolysis of thioacetamide. The resulting particles were continuous and uniform as characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fourier transform infrared, thermogravimetric analysis and UV–vis absorption spectroscopy were used to characterize the structure and properties of core–shell particles. The results showed the coating thickness of CuS shell can be controlled by the amount of silanol and the UV–vis absorption intensity of PSt/CuS composite also changed with the coating thickness of CuS.