Synthesis,characterization and bactericidal activity of silica/silver core–shell nanoparticles

Silica/silver core–shell nanoparticles (NPs) were synthesized by coating silver NPs on silica core particles (size ~300 ± 10 nm) via electro less reduction method. The core–shell NPs were characterized for their structural, morphological, compositional and optical behavior using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–Visible spectroscopy, respectively. The size (16–35 nm) and loaded amount of silver NPs on the silica core were found to be dependent upon reaction time and activation method of silica. The bactericidal activity of the NPs was tested by broth micro dilution method against both Bacillus subtilis (gram positive) and Escherichia coli ATCC25922 (gram negative) bacterium. The bactericidal activity of silica/silver core–shell NPS is more against E. coli ATCC25922, when compared to B. subtilis. The minimal inhibitory concentration of the core–shell NPs ranged from 7.8 to 250 μg/mL and is found to be dependent upon the amount of silver on silica, the core. These results suggest that silica/silver core–shell NPs can be utilized as a strong substitutional candidate to control pathogenic bacterium, which are otherwise resistant to antibiotics, making them applicable in diverse medical devices.     

Synthesis of nanoparticles composed of silver and copper for metal–metal bonding

A metal–metal bonding technique is described that uses nanoparticles composed of silver and copper. Colloid solutions of nanoparticles with an Ag content of 0–100?mol% were prepared by simultaneous reduction of Ag⁺ and Cu²⁺ using hydrazine with polyvinylpyrrolidone and citric acid as stabilisers. The nanoparticles ranged in size from 34 to 149?nm depending on the Ag content. Copper discs were strongly bonded at 400°C for 5?min under 1.2?MPa pressure in hydrogen gas; the maximum shear strength was as high as 23.9?MPa. The dependence of shear strength on the Ag content was explained by a mismatch between the d-spacings of Cu metal and Ag metal.     

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.     

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.     

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.     

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.     

Synthesis of Au@CdS core–shell nanoparticles and their photocatalytic capacity researched by SERS

High-quality Au@CdS core–shell nanoparticles (CSNs) have been synthesized to improve photo-conversion efficiency in photocatalysis. They demonstrate higher photocatalytic activity in the experiment of photocatalytic degradation of rhodamine 6G (R6G) solution than that of CdS counterparts. Au@CdS CSNs can broaden the absorption range in visible region compared to CdS counterparts. The heterojunction interface between Au and CdS facilitates the separation of photo-generated electron–hole pairs, and transfers electrons from CdS region to Au core. The two advantages are crucial to improve the photocatalytic activity of Au@CdS CSNs. Charge transfer mechanism between metal and semiconductor is efficient that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices to effectively utilize the solar power. In this paper, we research the photocatalytic process by surface-enhanced Raman scattering (SERS). The combination of photocatalysis and SERS not only can show the change in concentration of R6G solution, but also can provide the information of the change of R6G molecular structure in photocatalytic process.     

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 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.     

Synthesis and characterization of core–shell magnetic molecularly imprinted polymer nanoparticles for selective extraction of tizanidine in human plasma

In this study, simple, effective and general processes were used for the synthesis of a new nano-molecularly imprinted polymers (MIPs) layer on magnetic Fe₃O₄ nanoparticles (NPs) with uniform core–shell structure by combining surface imprinting and nanotechniques. The first step for the synthesis of magnetic NPs was co-precipitation of Fe²⁺ and Fe³⁺ in an ammonia solution. Then, an SiO₂ shell was coated on the magnetic core with the Stöber method. Subsequently, the C=C groups were grafted onto the silica-modified Fe₃O₄ surface by 3-(trimethoxysilyl) propyl methacrylate. Finally, MIPs films were formed on the surface of Fe₃O₄@SiO₂ by the copolymerization of C=C end groups with methacrylic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker), 2,2-azobisisobutyronitrile (initiator) and tizanidine (template molecule). The products were characterized using techniques that included Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), UV spectrophotometry, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Measurement of tizanidine through use of the core–shell magnetic molecularly imprinted polymers nanoparticles (MMIPs-NPs) in human plasma samples compared to the paracetamol showed that the synthesized nanosized MMIP for tizanidine has acted selectively.     

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 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.     

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.     

Synthesis of Al/Fe3Al core–shell intermetallic nanoparticles by chemical liquid deposition method

In this work, an Al/Fe₃Al core–shell nanoparticle was obtained by heat treatment of a precursor in high purity of argon. The precursor, with Fe(CO)₅ and nano Al as raw materials, was synthesized simply by a chemical liquid deposition method. The evolution of the phase and morphology during the heat-treatment has been carefully studied by XRD and TEM. The results indicate that the precursor transformed to core–shell structure of Fe₃Al intermetallic nanoparticle. The formation of the Fe₃Al intermetallic nanoparticle was explored by DSC test, which reveals that the formation temperature of the nanoparticle is around 587 °C. Moreover, the TG–DSC measurements from 50 °C to 1000 °C in compressed air (20% O₂ and 80% N₂) reveal that the heat-treated powder of the precursor remains thermal stability in relatively low temperature but becomes concentrated combustion in elevated temperature.     

Synthesis and characterization of quaternized carboxymethyl chitosan/poly(amidoamine) dendrimer core–shell nanoparticles

With the aim to develop a novel water-soluble modified chitosan nanoparticle with tuned size and improved antibacterial activity, quaternized carboxymethyl chitosan/poly(amidoamine) dendrimers (CM-HTCC/PAMAM) were synthesized. Firstly low-generation amino-terminated poly(amidoamine) (PAMAM) dendrimers were prepared via repetitive reactions between Michael addition and amidation, which were then employed for modifying quaternized carboxymethyl chitosan (CM-HTCC). Prior to the reaction of CM-HTCC with PAMAM, carboxylic groups in CM-HTCC were activated with EDC/NHS in order to enhance the reaction efficiency. FT-IR, ¹H NMR, elemental analysis and XRD were performed to characterize CM-HTCC/PAMAM dendrimers. Turbidity measurements showed that CM-HTCC/PAMAM dendrimers had good water-solubility. TEM images indicated that CM-HTCC/PAMAM dendrimers existed as smooth and spherical nanoparticles in aqueous solution. The results of antibacterial activity explored that CM-HTCC/PAMAM dendrimer nanoparticles displayed higher antibacterial activity against Gram-negative bacteria Escherichia coli (E. coli), whereas they showed much less efficiency against Gram-positive bacteria Staphylococcus aureus (S. aureus) compared to quaternized chitosan (HTCC).     

Synthesis and characterization of core–shell nanoparticles and their influence on the mechanical behavior of acrylic bone cements

Core–shell nanoparticles consisting of polybutyl acrylate (PBA) rubbery core and a polymethyl methacrylate (PMMA) shell, with different core–shell ratios, were synthesized in order to enhance the fracture toughness of the acrylic bone cements prepared with them. It was observed by TEM and SEM that the core–shell nanoparticles exhibited a spherical morphology with ca. 120 nm in diameter and that both modulus and tensile strength decreased by increasing the PBA content; the desired structuring pattern in the synthesized particles was confirmed by DMA. Also, experimental bone cements were prepared with variable amounts (0, 5, 10 and 20 wt.%) of nanoparticles with a core–shell ratio of 30/70 in order to study the influence of these nanostructured particles on the physicochemical, mechanical and fracture properties of bone cements. It was found that the addition of nanostructured particles to bone cements caused a significant reduction in the peak temperature and setting time while the glass transition temperature (T_g) of cements increased with increasing particles content. On the other hand, modulus and strength of bone cements decreased when particles were incorporated but fracture toughness was increased.     

Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO₂ nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.

     

Synthesis,structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO₂) and Zinc oxide (ZnO) as well as Silica (SiO₂) coated ZrO₂ core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO₂ on ZrO₂@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO₂) and the shell materials (ZnO and SiO₂) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.     

Theoretical study of the optical absorption behavior of Au/Ag core–shell nanoparticles

The dependence of linear optical response properties of bimetallic core–shell spherical nanoparticles is investigated as a function of size and relative composition. Two kinds of schematic models have been tested for describing the dielectric behavior of bimetallic particles and the related linear electromagnetic response: (i) Drude model, in conjunction with bulk dielectric data relative to the pure metals, in the assumption of a simple combination law; (ii) DFT-based approach to the dynamic polarizability of a binary particle, with the nature of the metals involved taken into account through their Wigner–Seitz radius.     

Synthesis and luminescence properties of highly uniform SiO2@LaPO4:Eu3+ core–shell phosphors

SiO₂@LaPO₄:Eu³⁺ core–shell phosphors have been successfully synthesized by a one-step and economical wet-chemical route at low temperature. The as-obtained products were characterized by means of photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The SEM, EDS and XPS analysis indicate that SiO₂@LaPO₄:Eu³⁺ core–shell phosphors can only be synthesized in a pH range of 8–11 and the possible mechanism has been proposed. The XRD results demonstrate that the structure of LaPO₄:Eu³⁺ layers is transferred into monoclinic phase from hexagonal phase after annealing at 800 °C for 2 h. The SiO₂@LaPO₄:Eu³⁺ phosphors show strong orange–red luminescence under ultraviolet excitation. The relative emission intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles, and the optimum concentration for Eu³⁺ was determined to be 5 mol% of La³⁺ in SiO₂@LaPO₄ phosphors.