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.     

Effect of biocompatible glutathione capping on core–shell ZnS quantum dots

Glutathione capped quantum dots are a potential candidate for different applications like ligand exchange in living cells, cell imaging and detection of glucose levels. Keeping these in mind, glutathione capped ZnS quantum dots were synthesized by using the thiol group of the capping agent by chemical precipitation method. Morphological characterizations were done by XRD and TEM. X-ray diffraction (XRD) measurements showed that the nanocrystals have Zinc Blende structure. Grain size and particle size shows a little variation with glutathione capping. Optical characterizations were done by UV–visible absorption, FTIR and energy resolved photoluminescence. UV–visible studies shows that the band gap also shows a small variation with glutathione capping. FTIR studies confirm glutathione capping on the surface of ZnS quantum dots. Room temperature energy resolved photoluminescence spectrum of samples exhibited a defect-related blue emission band. However, the PL properties seem to start tunability at higher concentration of glutathione which is a very good sign for extending this research further.     

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.     

Dynamic morphology instability in epitaxial ZnO/AZO (aluminum-doped ZnO) core–shell nanowires

Misfit strain relaxation-induced morphology instability is usually observed in epitaxial heterostructures at high temperatures. In this paper, we report that this morphology instability can occur even at room temperature in epitaxial ZnO/AZO (Al-doped ZnO) core–shell nanowires (NWs). As a result, densely distributed ZnO nanodots (NDs) were self-assembled on the NWs. The growth of NDs was slowed down during aging owing to the gradually reduced misfit strain. The final size and shape of the NDs were highly depended on the shell thickness and the doping ratio. It was proved that the morphology stability could be improved by surface passivation, thinning the shell thickness, or lowering the doping ratio. The results may provide instructive suggestions for the reliable design in strain and surface engineering of nanomaterials.     

Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.     

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.     

Effect of core–shell structured modifier ACR on ASA/SAN/ACR ternary blends

In this study, acrylonitrile–styrene–acrylic terpolymer/styrene–acrylonitrile copolymer/acrylic resin (ASA/SAN/ACR) ternary blends with different compositions were prepared by melting blending. Properties of the ternary blends were studied by differential scanning calorimetry, heat distortion temperature (HDT), Fourier transform infrared (FTIR) spectra, melt flow rate (MFR), mechanical properties, and scanning electron microscopy (SEM). The blends showed two T _gs at about −48 and 109 °C. FTIR analyses showed no strong interactions between the characteristic groups existed in the prepared blends. No obvious phase separation observed in SEM images indicated good compatibility in the blend system. With respect to mechanical properties and processability, the addition of ACR not only led to the improvement of impact strength and elongation at break, but also the decline of tensile strength, flexural properties, hardness, and MFR. Furthermore, heat resistance of ASA/SAN (70/30) binary blends decreased with the addition of ACR, but the HDT of ASA/SAN (30/70) almost remain unchanged.     

Effective electron emitters by molybdenum oxide-coated carbon nanotubes core–shell nanostructures

In this article, we showed that simple metal oxide coatings such as MoO₃ can be an effective enhancer for carbon nanotubes (CNTs) in field emission (FE) performance. For comparison, the FE properties of the pristine vertically aligned multi-walled CNTs with the metal oxide-coated CNTs were investigated. The metal oxide coating of the pristine CNTs was carried out by metal–organic chemical vapor deposition (MOCVD) method at 400 °C using Mo(CO)₆ as the precursor. The core–shell structure of the nanocomposite was studied by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) results showed that the surface of the coating material was mainly MoO₃. FE test indicated that the MoO₃-coated CNTs film exhibited an enhanced performance than the pristine CNTs with a turn-on field of 1.33 V μm⁻¹ and a field enhancement factor β estimated to be ~7000. Ultraviolet photoelectron spectroscopy (UPS) results confirmed a lower electron emission barrier height for MoO₃-coated CNTs than for the pristine CNTs. The mechanism of the enhanced FE performance is discussed based on Schottky barrier effect.     

Controllable synthesis of CdSe/ZnS core–shell quantum dots by one-step thermal injection and application in light-emitting diodes

Journal of Materials Science: Materials in Electronics - Quantum dots (QDs) attract extensive attention because of their excellent optoelectronic performance. However, few research has been done on...     

Wedge disclinations in the shell of a core–shell nanowire within the surface/interface elasticity

The elastic behaviors of a two-axes dipole of wedge disclinations and an individual wedge disclination located inside the shell of a free standing core–shell nanowire is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved using complex potential functions, defined through modeling the disclination dipole by two finite walls of infinitesimal edge dislocations. The stress field, disclination strain energies and image forces acting on the disclinations, are calculated and studied in detail. It is shown that the stresses are rather inhomogeneous across the nanowire cross section, change their signs and reach local maxima and minima far from the disclination lines in the bulk or on the surface of the nanowire. For negative values of the surface/interface modulus and relatively small values of the ratio of the shell and core shear moduli, the surface/interface effect manifests itself through non-classical stress oscillations along the shell free surface in the case of a disclination dipole and core–shell interface in both the cases of a disclination dipole and an individual disclination. The non-classical solution for the strain energy deviates from the classical solution with different effects caused by the surface/interface moduli on the wedge disclination dipole and an individual disclination. When the core is softer than the shell, the dipole with radial orientation of its arm has an unstable equilibrium position in the shell. In general, if the surface/interface modulus is positive, the surface/interface effects are rather weak; however, if it is negative, the effect can be very strong, especially near the shell surface.     

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.     

Characterization of solvent-filled polyurethane/urea–formaldehyde core–shell composites

Encapsulation of liquid phases is a crucial step in many self-healing material systems where a healing agent has to be protected during processing and then released during a damage event. In this work, the mechanical properties of polyurethane (PU) reinforced urea–formaldehyde (UF) shells are characterized. It was found that shell thickness is both a function of PU content in the core phase and of the microcapsule diameter. Furthermore, a saturation thickness was found for high PU contents or high capsule diameters and this phenomenon had direct implications on the bursting force under compression of single microcapsules. With help of an analytical model, the Young's modulus of the hybrid PU/UF was determined and in general, PU-reinforced shells had a lower modulus but higher ductility in terms of elongation at break, leading to more resistant microcapsules overall.     

Structural characterization of CdSe/ZnS core–shell quantum dots (QDs) using TEM/STEM observation

CdSe/ZnS core–shell structured nano-crystal quantum dots (QDs) are ideal candidates for light-emission applications due to their high quantum efficiency, narrow-band, and particle-size-tunable photoluminescence. In particular, their small size results in the quantum confinement of semiconductor nano-crystals, which widens their energy gaps. In general, structural analyses of QDs using a transmission electron microscope (TEM) are very important due to the significantly small size of QDs. We were able to obtain structural information of CdSe/ZnS core–shell QDs using nano-beam diffraction by controlling the nano-probe of the dark field scanning TEM (DF-STEM) mode and strain analysis with high-resolution TEM (HRTEM)/STEM images. Furthermore, we could clearly distinguish the interface between the CdSe core and the ZnS shell from the strain analysis with the HRTEM/STEM images.     

Toughening of epoxy using core–shell particles

An epoxy resin, cured using an anhydride hardener, has been modified by the addition of preformed core–shell rubber (CSR) particles which were approximately 100 or 300 nm in diameter. The glass transition temperature, T _g, of the cured epoxy polymer was 145 °C. Microscopy showed that the CSR particles were well dispersed through the epoxy matrix. The Young’s modulus and tensile strength were reduced, and the glass transition temperature of the epoxy was unchanged by the addition of the CSR particles. The fracture energy increased from 77 J/m² for the unmodified epoxy to 840 J/m² for the epoxy with 15 wt% of 100-nm diameter CSR particles. The measured fracture energies were compared to those using a similar amount of carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber. The CTBN particles provided a larger toughening effect when compared to CSR particles, but reduced the glass transition temperature of the epoxy. For the CSR-modified epoxies, the toughening mechanisms were identified using scanning electron microscopy of the fracture surfaces. Debonding of the cores of the CSR particles from the shells was observed, accompanied by plastic void growth of the epoxy and shell. The observed mechanisms of shear band yielding and plastic void growth were modelled using the Hsieh et al. approach (J Mater Sci 45:1193–1210). Excellent agreement between the experimental and the predicted fracture energies was found. This analysis showed that the major toughening mechanism, responsible for 80–90% of the increase in fracture energy, was the plastic void growth.     

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.     

Nanoforests composed of ZnO/C core–shell hexagonal nanosheets: fabrication and growth in a sealed thermolysis reactor and optical properties

An efficient method was developed for fabricating a highly porous nanoforest structure composed of ZnO/C core–shell hexagonal nanosheets (HNSs). Compact thermolysis of zinc acetate dihydrate in a sealed bath reactor at 400 °C over 20 h yielded the nanoforest structures. A carbon shell layer coating was applied in situ during the growth of the ZnO nanosheet core. The structures, morphologies, growth processes, compositions, and binding characteristics of the ZnO/C core–shell HNS nanoforests were analyzed using multi-purpose high-performance X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS) techniques. XRD and XPS results suggest the existence of oxygen vacancy defects in the core surface of ZnO/C core–shell. The ZnO/C core–shell HNS nanoforests exhibited strong absorption features from the visible to the near-IR region (400–1670 nm), and the nanoforest films showed high electrical conductivity.     

Controllable synthesis of hexagonal ZnO–carbon core–shell microrods and the removal of ZnO to form hexagonal carbon microtubes

A simple and efficient approach was developed to produce regular and uniform shaped hexagonal ZnO–C core–shell micro-rods and carbon micro-tubes. A single-source raw material, zinc acetate dihydrate, has been used for the in situ generation of the hexagonal ZnO–C micro-rods in a sealed autoclave system at 500 °C for 12 h without a catalyst. The resulting products were characterized by X-ray powder diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray analysis and room-temperature photoluminescence spectroscopy (PL). The partial or complete carbon coating on the ZnO surfaces plays an important role in modifying the PL properties. Impacting factors including thermolysis temperature, time and dose of the reactant on the evolution of the hexagonal shape were investigated. A possible formation diagram for the materials has been proposed and discussed based on the features of the reaction system.     

Effect of Zn source concentration on structural,optical and electrical properties of zinc sulphide–polyaniline (ZnS–PANI) nanocomposite thin films

Zinc sulphide–polyaniline (ZnS–PANI) nanocomposites are prepared by preparing ZnS nanoparticles in the same reaction bath for synthesis of PANI. Three different composites have been prepared by varying the concentration of zinc source. The films obtained from the colloidal dispersion are characterized by Scanning electron microscopy, energy dispersive analysis of X-rays, transmission electron microscopy, X-ray diffraction studies, Fourier transform infrared spectroscopy, UV–visible optical absorption, photoluminescence and current–voltage studies. Broadening of X-ray diffraction peaks suggest change in crystallite size and this is in agreement with the results from transmission electron microscopy. Fourier transform infrared spectra indicate crosslinking in the composite film. UV–visible absorption spectra of the film exhibit enhancement of doping level which is assigned to the existence of greater number of charges on the polymer backbone. Optical properties of the films are studied by measuring photoluminescence spectra. This shows decrease in intensity and blue shift with the increase in zinc source concentration. The blue shift indicates strong quantum confinement. Current–voltage characteristics exhibit excellent light response indicating tunneling type of conduction.