Optical properties of core–shell structured Ag/SiO2 nanocomposites

Silver nanoclusters coated by SiO₂ were synthesized by a reverse micelle technique to obtain a core–shell microstructure with tunable particle size less than 50 nm. The refractive indices of the Ag/SiO₂ nanocomposites were calculated based on a theoretical model for binary composite materials which illustrated a strong correlation to the size of the metallic core and the dielectric shell. Dynamic light scattering analysis of the Ag/SiO₂ nanocomposites revealed that the refractive index of the nanocomposites was about 2.40, which was well in the range predicted by theoretical modeling. Optical absorption spectra and silver quantum dot size induced color change of the Ag/SiO₂ nanocomposites suspension were also investigated.     

Fabrication,physiochemical and optoelectronic characterization of SiO2/CdS core–shell nanostructures

Silica/CdS core–shell nanostructures have been developed using a simple wet chemical route. This method utilizes silica spheres formation followed by successive ionic layer adsorption and reaction method assisted CdS shell layer formation. The morphological studies revealed the uniformity in size distribution with core size of 250 nm and shell thickness of 9 nm. The electron microscopic images also indicate the irregular morphology of CdS shell layer. The structural studies indicate the simple cubic system of CdS shell with no other trace for impurities in the crystal structure. This CdS layer exhibit the band gap energy of 2.66 eV, due to weak quantum confinement and numerous defects presence. The studies on room temperature photoluminescence measurement indicate the emission properties and the corresponding electronic energy levels of defect states. Further, the physiochemical understanding of core–shell formation mechanism clearly matches with the motive behind the defects present in the CdS shell layer.     

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.     

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.     

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.     

Room temperature single electron transistor with two-dimensional array of Au–SiO2 core–shell nanoparticles

The composite nanoparticles of gold core coated with SiO₂ shell have been fabricated into 2-dimensional array on a silicon surface by a simple self-assembly method combined with the technique of AFM (atomic force microscopy) nanolithography. The double-barrier-tunneling junction with AFM tip was also fabricated for the room-temperature single-electron tunneling study, by which the AFM tip was orientated on the surface of the SiO₂ coated gold composite nanoparticles. The 2D array shows well-pronounced Coulomb staircases with a period of 200 mV at room temperature, demonstrating single electron transistor behavior.     

Structural and optical properties of individual GaP/ZnO core–shell nanowires

Structural and optical properties of ZnO–GaP core–shell nanowires were studied by means of electron microscopy and microphotoluminescence. A thin ZnO shell layer was deposited by RF sputtering on GaP nanowires, which were grown on GaP (111)B substrates under vapour–liquid–solid mode by MOVPE. The SEM and TEM characterization showed that the ZnO shells fully covered the surface of the NWs from top to bottom. Each GaP NW core is composed of many well-defined twinned segments with the planes of twinning oriented in perpendicular to the growth direction. This was contradicted in kinked GaP NWs: their growth direction was initially perpendicular to the twinning planes, but once the NW had kinked, it changed to lie within the twinning planes. The ZnO shell deposited on the GaP core has a columnar morphology. The columns are inclined at a positive angle close to 70° with respect to the GaP growth axis. All observed columns were tilted at this angle to the growth direction. Micro-photoluminescence study showed that thermal annealing improved the quality of the ZnO crystallographic structure; the annealing made observable the photoluminescence peak related to the band-to-band transition in ZnO.     

Influence of different nucleating agent additives on phase structure and ferroelectric properties of SrO–BaO–Nb2O5–CaO–SiO2–B2O3 glass-ceramics

Ferroelectric glass-ceramics of the SrO–BaO–Nb₂O₅–CaO–SiO₂–B₂O₃ system with different nucleating agents Cr₂O₃, BaF₂, ZrO₂, CaF₂ and CeO₂, have been prepared by conventional melt casting followed by controlled crystallization processing. The effect of different nucleating agent additions on crystallization mechanism, crystallization behaviors, microstructures and dielectric properties of the glass-ceramics are studied using DTA, XRD techniques, SEM and LCR analyzer. The results show that the addition of different nucleating to the glass-ceramics decreases the crystallization temperatures, accelerates the secondary phase elimination and promotes the uniform distribution of grain size. The well development of microstructure promoted by the nucleating agents can result in the improvement of the dielectric constant as well as energy storage density remarkably. The sample with CeO₂ as the optimum nucleating agent achieves the dielectric constant of 301, breakdown strength of 622 kV/cm and the highest energy storage density of 5.15 J/cm³.     

Maximum SiO2 layer thickness by utilizing polyethylene glycol as the surfactant in synthesis of core/shell structured TiO2–SiO2 nano-composites

TiO₂–SiO₂ nano-composites with the core/shell structure have been prepared by means of a technique based on an extension of well-known Stöber process. In this way, the silica coating of TiO₂ nano-particles in the presence of various commercially available surfactants of cationic, anionic and nonionic has been conducted with the aim to increase barrier properties against UV (UV blocking) radiation, in order to optimize photo-killing ability of the TiO₂ nano-particles and decline of the high photo-catalytic property of titania. The influences of varying coating parameters such as time and temperature on the silica content of nano-composites have been studied and optimum conditions for attaining a thick layer of SiO₂ have been determined. Electro-phoretic mobility measurements indicated that the silica coating shifted the iso-electric point of titania toward that of a typical pure colloidal silica. Surface elemental composition of core/shell structured TiO₂–SiO₂ nano-composites was verified by using energy dispersive X-ray analysis. It was found that maximum silica shell thickness can be obtained in the presence of polyethylene glycol as a nonionic surfactant at 80 °C for 360 min. The photo-catalytic activities were evaluated by the degradation of an aqueous solution of methylene blue under UV light irradiation. In addition, the resultant optimum nano-composites have been characterized by FESEM, TEM, BET, FTIR and UV–Vis spectroscopy.     

Fabrication of multilayered Au/silica/gadolinium compound core–shell particles and their imaging properties

The present work proposes a preparation method for multilayered Au nanoparticle/silica/gadolinium compound core–shell (Au/SiO₂/GdC) particles. Silica-coated Au core–shell (Au/SiO₂) particles with a size of 38.0?nm were prepared by a sol-gel reaction in the presence of the Au nanoparticles with a size of 15.5?nm. Multilayered Au/SiO₂/GdC particles with sizes of ca. 35–52?nm were prepared by a homogeneous precipitation reaction in the presence of Au/SiO₂ particles. The computed tomography (CT) value of the Au/SiO₂/GdC colloid solution containing 4.3?×?10^?2?M Au was 344.1?HU: Its converted CT value (CT divided by Au concentration) was as large as 8.0?×?10³?HU/M. The r₁ value of the Au/SiO₂/GdC colloid solution was as large as 3.5?mM^?1?s^?1.     

Structural and dielectric properties of Li2O–ZnO–BaO–B2O3–CuO glasses

Glass samples of the system (15Li₂O–30ZnO–10BaO–(45 − x)B₂O₃–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant εφ, loss tan δ, a.c. conductivity, σ_ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration. The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content indicates structural changes of the glass matrix. The glass transition temperature, T _g, and crystallization temperature, T _c, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter (T _c − T _g) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BO₃, BO₄, and ZnO₄. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction.     

Effect of zinc oxide concentration in fluorescent ZnS:Mn/ZnO core–shell nanostructures

In the present work, we have prepared zinc sulphide (ZnS:Mn)/zinc oxide (ZnO) core–shell nanostructures by a chemical precipitation method and observed the effect of ZnO concentration on the fluorescent nanoparticles. Change in the morphological and optical properties of core–shell nanoparticles have been observed by changing the concentration of ZnO in a core–shell combination with optimum value of Mn to be 1 % in ZnS. The morphological studies have been carried out using X-ray diffraction (XRD) and transmission electron microscopy. It was found that diameter of ZnS:Mn nanoparticles was around 4–7 nm, each containing primary crystallites of size 2.4 nm which was estimated from the XRD patterns. The particle size increases with the increase in ZnO concentration leading to the well-known ZnO wurtzite phase which was coated on the FCC phase of ZnS:Mn. Band gap studies were performed by UV–visible spectroscopy and a red shift in absorption spectra have been observed with the addition of Mn as well as with the capping of ZnO on ZnS:Mn. The formation of core–shell nanostructures have been also confirmed by FTIR analysis. Photoluminescence studies show that emission wavelength is red shifted with the addition of ZnO layer on ZnS:Mn(1 %). These core–shell ZnS:Mn/ZnO nano-composites will be a very suitable material for specific kind of tunable optoelectronic devices.     

A review of noble metal (Pd,Ag, Pt,Au)–zinc oxide nanocomposites: synthesis,structures and applications

As a promising candidate for future catalytic applications, the noble metal–ZnO nanocomposites are gaining increasing interest due its high catalytic property, and super stability. In this review, the noble metal–ZnO nanocomposites with various composites and structures for catalytic applications will be discussed. We introduce the multi-catalytic properties and design concept of the noble metal–ZnO nanocomposites, and then particular highlight key finding of synthesis method for various noble metal–ZnO nanocomposites. The catalytic activity of noble metal–ZnO nanostructures has been found to rely on not only the species of noble metal but also the architecture of the catalyst material. Moreover, the typical works of modification on noble metal–ZnO nanostructures have been introduced. Critically, the challenges for future research development and our future perspectives are presented.     

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,growth mechanism,photoluminescence and field emission properties of metal–semiconductor Zn–ZnO core–shell microcactuses

Metal–semiconductor Zn–ZnO core–shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH₃ as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65–75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor–liquid–solid (VLS) based growth mechanism was proposed for the formation of Zn–ZnO core–shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn–ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn–ZnO core–shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices.     

Investigating the surface reactivity of SiO2–TiO2–CaO–Na2O/SrO bioceramics as a function of structure and incubation time in simulated body fluid

This study focuses on evaluating the biocompatibility of a SiO₂–TiO₂–CaO–Na₂O/SrO glass and glass–ceramic series. Glass and ceramic samples were synthesized and characterized using X-ray diffraction. Each material was subject to maturation in simulated body fluid over 1, 7 and 30 days to describe any changes in surface morphology. Calcium phosphate (CaP) deposition was observed predominantly on the Na⁺ containing amorphous and crystalline materials, with plate-like morphology. The precipitated surface layer was also observed to crystallize with respect to maturation, which was most evident in the amorphous Na⁺ containing glasses, Ly-N and Ly-C. The addition of Sr²⁺ greatly reduced the solubility of all samples, with limited CaP precipitation on the amorphous samples and no deposition on the crystalline materials. The morphology of the samples was also different, presenting irregular plate-like structures (Ly-N), needle-like deposits (Ly-C) and globular-like structures (Ly-S). Cell culture analysis presented a significant increase in cell viability with the Na⁺ materials, 134 %, while the Sr²⁺ containing glasses, 60–80 % and ceramics, 60–85 % presented a general reduction in cell viability, however these reductions were not significant.     

Preparation, characterization, and fluorescence properties of well-dispersed core–shell CdS/carbon nanoparticles

The core–shell CdS-carbon (CdS/C) nanoparticles were synthesized for the first time via a facile pyrolysis approach of bis(β-mercaptoethanol)-cadmium(II) as a single-source precursor. After using acid treatment method, well-dispersed and homogeneous core–shell CdS/C nanoparticles were obtained. The morphology, structure, and properties of CdS/C nanoparticles were investigated by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. Most of the prepared nanoparticles presented core–shell structures with core diameter of ~10 nm and shell thickness of ~4 nm. The CdS core belonged to hexagonal crystal system. The carbon shell was employed as a good dispersion medium to form well-dispersed small sized CdS particles. XRD and XPS results revealed that there is an interaction between CdS core and carbon shell. Fluorescence measurement showed that the monodispersed CdS-carbon nanoparticles exhibit remarkable fluorescence enhancement effect compared with that of the pristine CdS nanoparticles, which indicates the prepared nanoparticles are a promising photoresponsive material.