Core-shell Samples Research Articles

Magneto-fluorescent core–shell Sr0.8La0.2Fe11CuO19 @ CQDs for the detection of metal ions

The fabrication of a sensor based on a core–shell structure of Sr0.8La0.2Fe11CuO19 @ CQDs was effectively achieved through the combination of high quantum yield carbon quantum dots (CQDs) with La-Cu doped M−type strontium hexaferrites (SLFCO HF). The structural, morphological, and spectroscopic information of the as-synthesized samples were characterized through X-ray diffraction (XRD), Raman spectroscopy (RS), Fourier transform infrared (FT-IR), energy dispersive X-ray (EDX), high-resolution transmission electron microscopy (HR-TEM), and UV–Vis-NIR spectroscopy. The magnetic properties were tested using a vibrating sample magnetometer (VSM) and Mössbauer spectroscopy. HR-TEM confirmed the formation of a hexagonal core–shell sample at the nanoscale. Based on photoluminescence (PL) spectra and the CIE chromaticity map, the parent sample and core–shell structure of SLFCO/CQDs were found to have color coordinates corresponding to yellow-green emission. It was found that the core–shell sample has an increased light-absorption capacity, low photogenerated electron-hole recombination, high coercivity, small crystallite size, and showed good sensitivity towards the detection of Zn2+, Cd2+, and K+ ions. A high efficiency in detecting potassium (K+) ions with a limit of detection (LOD) of 15 ppm was observed. Moreover, the distinctive magnetism of CQDs @ SLFCO aided in the collection and recycling of the sensor.

Formation of core-shell structure MnCo2O4 microspheres and as a bifunctional catalyst for zinc-air batteries

Efficient and stable bifunctional catalysts, facilitating oxygen reduction and oxygen evolution, play a pivotal role in energy conversion and storage fields. In this paper, four core-shell MnCo2O4 catalyst samples are prepared by controlling different solvent heating time, which are 0.5 h, 2 h, 6 h, and 12 h, respectively. The subsequent tests indicate that the sample with a 6 h not only has an ideal core-shell structure, but also exhibits favorable performance. The unique core-shell structure and favorable electrochemical performance are mainly attributed to the prepared precursor spheres. The microspheres have an inherent core-shell structure. Detailed studies of the morphological variations of MnCo2O4 catalysts with the different solvent heating time are performed using transmission electron microscopy and field emission scanning electron microscopy. Furthermore, we analyze the potential formation mechanism of the core-shell structure MnCo2O4 catalyst. The obtained core-shell structured MnCo2O4 catalysts provide a new way for the preparation of cathode catalyst for zinc-air batteries.

Highly Bright and Stable CsPbX3@Cs4PbX6 Hexagonal Nanoarchitectonics Created by Controlling Dissolution-Recrystallization of CsPbX3 Nanomaterials.

CsPbBr3@Cs4PbBr6 hexagonal NCs with a bright photoluminescence (PL) peak of 456nm are created through the dissolution-recrystallization of CsPbBr3 nanoplatelets. Small CsPbBr3 nanocrystals are encapsulated in hexagonal Cs4PbBr6 during recrystallization to form a core-shell structure and keep high brightness and stability. The recrystallization kinetics is systematically investigated to explore the roles of methyl acetate, oleylamine, and n-hexane. Result further indicates that core/shell NCs remained high PL under a variety of harsh conditions (e.g., light irradiation and heat treatment) because of Cs4PbX6 shell and the controlling of recrystallization. Their initial PL intensity is remained after 4 months of storage under ambient conditions and continuous exposure to UV lamp for 180min. The bright PL is also maintained even treatment at 120°C. To indicate the universality of this synthesis method, CsPbX3@Cs4PbX6 hexagonal NCs with different emission colors are fabricated by changing temperature, solvent viscosity, and precursors (e,g, oleylamine and halogens). These core-shell samples reveal bright and stable green, orange, and red PL. Because of its high stability, the core/shell NCs are dispersed in flexible films to create diverse patterns. The films also exhibit high brightness and excellent stability. This strategy opens a novel avenue for the application of perovskite nanomaterials in the display field.

Fabrication of Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell and improvement of its photocatalyst properties

Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell structures were made by a two-step method, first, bismuth ferrite nanoparticles by hydrothermal method and then, aniline core-shell by co-precipitation method. The bismuth ferrite (BFO) XRD pattern showed no impurities of Sm, Cr, or their compounds in the samples, indicating that Sm+3 and Cr+3 had been replaced in the BFO structure. The XRD pattern of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell shows all peaks of Bi0.90Sm0.1Fe0.97Cr0.03O3 composition with lower intensity, as a result, the Bi0.90Sm0.1Fe0.97Cr0.03O3 composition is phase single. This lower intensity is attributed to the presence of amorphous polyaniline in the core-shell structure. Since there is in the FT-IR spectrum of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell, characteristic peaks of both polyaniline and bismuth ferrite simultaneously so, the FT-IR spectrum of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell is a perovskite structure. The synthesized samples exhibit weak magnetic properties and behave as a paramagnetic material. The absorption capability of core-shell compared to core nanoparticles has increased in the visible region, and this enhancement is attributed to the influence of the presence of polyaniline. All the peaks in the UV–visible absorption spectrum characterize the nano-sized bismuth ferrite and polyaniline in the UV–visible spectrum of the core-shell. The intensity of the photoluminescence spectrum in the doped sample is significantly higher compared to the core-shell sample. This indicates a much faster recombination rate in the doped nanoparticles compared to the core-shell nanocomposite. The doping of the core with Cr and Sm elements, as well as the coating of the core with a polymeric shell, has led to an increase in the degradation rate of the red dye. We also found that shell thickness plays a vital role in dye degradation efficiency and photocatalytic performance. The Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell exhibits significant photocatalytic activity under visible light. The photocatalytic studies show that the best sample is Bi0.9Sm0.1Fe0.97Cr0.03O3@PANI core-shell with aniline concentration of 0.2 mL and a pH = 2 which was able to destroy 100 % of Congo red dye molecules.

Advancing highly selective low-temperature ammonia oxidation: Hydrophobic silicalite-1 shell confining silver nanoparticles on Cu/ZSM-5 core

A judiciously devised core–shell NH3-SCO catalyst featuring a Cu/ZSM-5 core enveloped by an Ag/silicalite-1 shell (Cu/ZSM-5@Ag/S-1) was rationally constructed. Integrating the silicalite-1 shell effectively suppresses the migration of Ag into Cu/ZSM-5 core, conserving the active Cu2+ sites for the catalytical conversion of byproducts NOx. Concurrently, the shell averts the formation of positively charged Ag species, facilitating the generation of abundant Ag0 nanoparticles encapsulated in the S-1 shell. Comprehensive characterizations reveal abundant Ag0 species within the core–shell Cu/ZSM-5@Ag/S-1 catalyst, boosting O2 activation and NH3 dehydrogenation and thereby contributing to superior low-temperature activity in NH3-SCO reactions. Furthermore, the hydrophobic S-1 shell effectively reinforces the hydrothermal stability of the core–shell Cu/ZSM-5@Ag/S-1. DRIFTS coupled with DFT studies elucidate that the core–shell sample follows the imide mechanism, while the shell-free sample adheres to the hydrazine mechanism. This work advances our understanding of catalyst design and presents a promising solution with practical implications for ammonia oxidation processes.

Photocatalysis and antimicrobial activity of ZnO@TiO2 core-shell nanoparticles

Wet chemical synthesis was used in this instance to create ZnO@TiO2 core-shell nanoparticles. By examining X-ray diffraction and Selected Area Electron Diffraction patterns, it was determined that the phase formation of prepared nanoparticles was a hexagonal primitive structure of ZnO and Tetragonal bcc structure of anatase phase of TiO2 devoid of impurity peaks. It was discovered that crystallites were 25 nm in size on average. The results of a surface morphology analysis utilizing High-Resolution Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy show that all of the particles are spherical. The energy dispersive X-ray spectroscopy study provided proof for the existence of core-shell elemental compositions. Fourier-Transform Infrared spectrum revealed the presence of characteristics of metal bonding with oxygen of ZnO and TiO2. UV-visible absorption analysis exhibited absorption peak in the UV region and the band gap energy of ZnO@TiO2 core-shell nanoparticles. The thermal behavior of ZnO@TiO2 core-shell nanoparticles was analyzed by using Thermogravimetric Analysis, Differential scanning calorimetry, and Differential Thermal Analysis techniques. The X-ray photoelectron spectroscopy analysis exhibited the coating of TiO2 (shell) on the surface of ZnO (core) for the formation of a core-shell nanostructure. Due to its extremely small crystallite size, wide surface area, and reduced band gap, the ZnO@TiO2 core-shell sample demonstrated outstanding photocatalytic activity when rhodamine-B dye was photocatalytically degraded in the presence of UV light irradiation. Finally, the antibacterial and antifungal activities of ZnO@TiO2 core-shell nanoparticles were investigated, and it was shown that antifungal activity was superior to antibacterial activity. A suitable material for environmental and biological applications that produced core-shell nanoparticles displayed regulated grain size, outstanding photocatalytic performance, and high antifungal activity.

Nanoarchitectonics toward Full Coverage of CdZnS Nanospheres by Layered Double Hydroxides for Enhanced Visible-Light-Driven H2 Evolution.

Nanoarchitectonics of semiconductors shed light on efficient photocatalytic hydrogen evolution by precisely controlling the surface microenvironment of cocatalysts. Taking cadmium zinc sulfide (CZS) nanoparticles as a target, the spontaneous modifications are conducted by interactions between surface Cd2+/Zn2+ atoms and thiol groups in thioglycolic acid. The capping ligand impacts the semiconductor surface with a negative electronic environment, contributing to the full coverage of CZS by nickel-cobalt hydroxides (NiCo-LDHs) cocatalysts. The obtained core-shell CZS@NiCo-LDHs, possessing a shell thickness of ≈20nm, exhibits a distinguished topology (SBET=87.65m2g-1), long surface carrier lifetime, and efficient charge-hole separation. Further photocatalytic hydrogen evaluation demonstrates an enhanced H2 evolution rate of 18.75mmolg-1h-1 with an apparent quantum efficiency of 16.3% at 420nm. The recorded catalytic performance of the core-shell sample is 44.6 times higher than that of pure CZS nanospheres under visible light irradiation. Further density functional theory simulations indicate that sulfur atoms play the role of charge acceptor and surface Ni/Co atoms are electron donors, as well as a built-in electric field effect can be established. Altogether, this work takes advantage of strong S affinity from surface metal atoms, revealing the interfacial engineering toward improved visible-light-driven photocatalytic hydrogen evolution (PHE)activity.

Tuning the optical properties of Ln3+-doped-Y2O3@ZnO@Au core-shell heterostructures for visible-to-NIR photon harvesting

Here, compact Yb3+-Er3+-Tm3+ doped Y2O3 phosphor microspheres were synthesized by solvothermal method which gave emission in the entire visible region under 980 nm excitation. The effect of doping alkali ions like lithium on the upconversion emission of YYET phosphors is investigated. An epitaxial layer of ZnO is grown around the YYETL (Li+ doped YYET) microspheres by hydrothermal technique. An analysis of the influence of the ZnO shell thickness on the upconversion emission of core microspheres is done. Initial growth of a thin layer of ZnO on the YYETL microspheres causes enhancement in upconversion emission due to passivation of surface defects of core microspheres. Quenching of anti-Stokes emission occurs for thicker ZnO shell coating. Further, it is decorated with AuNPs to study the effect of plasmonics on the optical property of the developed heterostructure. The overlap between the upconversion emission spectra of core microspheres and the LSPR peak of AuNPs modulates the property of the entire structure. The optimized samples were checked for photocatalytic application by degradation of Rh6G dye under solar irradiation. YYETL@ZnO@Au core-shell samples exhibited highest rate constant of 0.00395 min−1, which is attributed to better exploitation of the UV–Vis-NIR region of the solar spectrum by all three components of the heterostructure.

Synthesis of core-shell magnetic mesoporous silica nanoparticles to disperse amine functionalities for post-combustion carbon dioxide capture

BackgroundPost-combustion capture technology appears a suitable approach to reduce the emission of CO2 by power plants. The use of solid sorbents would permit to overcome the limitations of the well-established liquid amine-based absorption process. In particular, mesoporous silica materials have been proposed as suitable sorbents especially if functionalized with amines. MethodsThe properties of as-synthesized (by using dodecylamine as synthesis amine) and calcined hexagonal mesoporous silica (HMS), impregnated or not with tetraethylenepentamine (TEPA), were studied. Magnetite (Fe3O4) nanoparticles were specifically used to obtain HMS core-shell nanoparticles in order to investigate the effect of the magnetite core on CO2 uptake capability. CO2 uptake measurements were carried out on all HMS and core-shell particles. Furthermore, Transmission Electron Microscopy (TEM) images, Fourier Transform Infrared (FTIR) spectra and N2 adsorption/desorption measurements allowed analyzing some important properties of the sorbent particles, such as particle aggregation, incorporation and dispersion of amines, surface area, pore volume and pore size distribution. Significant FindingsThe best performance in terms of chemical CO2 uptake was obtained on core-shell material, calcined and impregnated with TEPA (about 89 mg/g), but also the as prepared core-shell sample impregnated with TEPA seems promising since the synthesis dodecylamine sites can be activated during the impregnation process.

Tuning the plasmon resonance of Au-Ag core-shell nanoparticles: The influence on the visible light emission for inorganic fluorophores application

In this study, the gold and gold-silver (Au-Ag) core-shell nanoparticles were synthesized via chemical reduction method at different types and quantities of precursor materials. Initially, the gold nanoparticles were prepared with different reducing agents (i.e., sodium borohydride, sodium citrate, and ascorbic acid) and their composites. The optical absorbance, morphology, and size distribution of gold nanoparticles were analyzed to observe the best deposition conditions, used for the Au-Ag core-shell synthesis. Then, the Au-Ag core-shell nanoparticles were grown at four different quantities (i.e., 175 µL, 200 µL, 225 µL, and 250 µL) of silver nitrate precursor to study their effects on the fluorescence property. Optical absorbance, transmission electron microscopy, and laser scanning confocal microscopy were used to characterize the as-synthesized Au-Ag core-shell nanoparticles. From the results of optical absorbance, a single peak is seen for gold nanoparticles while two peaks (major and minor peaks) are observed for Au-Ag core-shell nanoparticles. The sizes of gold and core-shell particles observed from TEM measurement are less than 10 nm, which is typically used in fluorescence applications. The CoSh-2 sample showed a better fluorescence property compared to other core-shell samples. With a rise in exposure time in a laser with a specific wavelength of 405 nm, the intensity of fluorescence declined more for the filter having shorter wavelengths than larger wavelengths. Analyzing these results can be useful to understand the perspective applications of Au-Ag core-shell nanoparticles like synthetic fluorophores application.

An exhaustive scrutiny to amplify the heating prospects by devising a core@shell nanostructure for constructive magnetic hyperthermia applications

An interfacial integration at the nanoscale domain through a core@shell (CS) nanostructure has constructively unbarred a wide dimension to researchers on biomedical applications, especially for magnetic fluid hyperthermia. Lately, the interconnection of the exchange bias effect (EBE) through the interface coupling to the magnetic heating efficiency has uttered its utmost prominence for researchers. Here, we delineate the ascendency of the heating ability through a coalescing assembly of mixed ferrite Co0.5Zn0.5 Fe2O4 (CZ) and soft magnetic material Fe3O4 (F), by devising a network of CoZnFe2O4@Fe3O4 (CZF) CS nanostructure. A hefty interface activity with validation of the EBE phenomenon is divulged through magnetic scrutiny for the CS sample. The magnetic nanoparticles heating response to applied magnetic field and frequency is discerned at three distinct fields, where the outcome prevailed to inflated specific loss power for CS CZF in distinction to bare F and CZ samples for all the assessments. Remarkably; a lofty intrinsic loss parameter is also perceived for the CS sample recorded to about 5.36 nHm2 g−1; which is another eccentric outcome that significantly labels the CS CZF sample as a potentially high heating competence agent. This comprehension accords to a finer perspective to meliorate the theranostic environment for hyperthermia applications.

Influence of Ligands on Physicochemical Characteristics of Magnetic Nanoparticles

Magnetic-bead separation or purification serves as a technique for effective isolation of biomolecules. In presented work we prepared and characterized core-shell magnetic nanoparticle samples consisted of Fe 3 O 4 core coated with SiO 2 shell. Samples were subsequently coated with ligands MPTMS (3-(mercaptopropyl)trimethoxysilane), CPTMS (3-(chloropropyl)trimethoxysilane) and MMSP (3-(trimethoxysilyl)propyl methacrylate) with aim to increase the number of active centers for specific binding with RNA. Such samples were further investigated for their magnetic properties, size, and morphology. Magnetic properties were studied in DC field up to 5 T in temperature range 5 – 300 K. Size and morphology were determined from SEM micrographs and elemental compositions of the samples were investigated using EDX analysis. Modification of nanoparticle surface with different ligands leads to modification of active centers on the SiO 2 surface on which the DNA and RNA molecules can be bounded. It also causes the change in magnetic and structural properties of nanoparticles.

Polymeric nanocomposite multifunctional core-shell membrane for periodontal repair and regeneration applications

Periodontal inflammation injuries affect more than 50% of adults in the society and if left untreated it can result in tooth loss. Here, core-shell nano-fibrous membrane of polycaprolactone/gelatin core and poly (vinyl alcohol)/polyvinylidene fluoride shell is fabricated through electrospining. To facilitate tissue regeneration, bioactive glass nanoparticle (BG) is incorporated within the core and the effect of concentration (10, 25 and 50 wt%) on physical, mechanical and biological properties is thoroughly studied. The diameter of the fibrous structures was 270 ± 25 nm to 510 ± 39 nm. The tensile strength was greatly influenced by the addition of BG such that ultimate tensile stress increased from 2.7 MPa to 3.4 MPa in 0 and 10 wt% BG containing group, respectively. By investigating the piezoelectricity of the membranes, core-shell sample with 25% BG showed the highest output voltage of 39 ± 4 kV m−3. The core-shell sample with 25% BG sample was shown great hemocompatibility with a low hemolysis ratio of 0.5% and platelets attachment test confirmed that the attached platelets were not activated and aggregated or pseudopodium. Drug loaded membrane revealed an antibacterial activity against Staphylococcus aureus bacteria. The cell proliferation was positively influenced by the presence of BG, further confirming the suitability of the resultant structure for periodontal applications.

Concurrent achievement of giant energy density and ultrahigh efficiency in antiferroelectric ceramics via core–shell structure design

The boom in high-power-density electronics and advanced pulsed power systems has led to a requirement for high-energy-density dielectric capacitors, for which the key enabler is the availability of dielectric materials with high energy densities and high efficiencies. Although antiferroelectric ceramics are promising dielectric materials with high energy densities, they have low efficiencies. In this study, we address this problem through the core–shell structure design. A phase-field model is developed by considering the core as antiferroelectric and the shell as linear dielectric, and the polarization hysteresis loops are determined. The results show that the polarization–electric field loop of the core–shell sample is slanted, with a delayed saturation polarization, decreased maximum polarization, and declined hysteresis loss compared with the pure sample. This phenomenon becomes more distinct with increasing shell fraction and decreasing shell permittivity, and vanished hysteresis is achieved in samples with a high shell fraction and a low shell permittivity. Through deconvolution, it is determined that the underlying mechanism of energy storage is the difference in the antiferroelectric polarization contribution of various shell parameters. It is found that a giant energy density of 15.5 J/cm3 and an ultrahigh efficiency of 99.7% at the saturation polarization can be achieved concurrently for a certain core–shell sample; these values considerably exceed the corresponding values (5.0 J/cm3 and 52.8%) for the pure sample. The findings of this study can serve as guidance for engineering core–shell structures, thus paving the way for enhancing the energy-storage performance of antiferroelectric ceramics.

Bimetallic Cu–Zn Catalysts for Electrochemical CO2 Reduction: Phase-Separated versus Core–Shell Distribution

Electrochemical CO2 reduction to fuels and chemicals is considered as one of the most important technologies to reach carbon neutrality. Bimetallic Cu–Zn materials have been proved as effective catalysts for electrochemical CO2 reduction. However, their structure–activity relation remains indistinct. Herein, we prepared two types of Cu–Zn bimetallic catalysts with core–shell and phase-separated structure distributions and studied their electrochemical CO2 reduction performance in detail. Interestingly, the phase-separated sample exhibited much higher activity and stability than the core–shell sample for reducing CO2 to CO, with a faradic efficiency up to 94% and stability beyond 15 h. The density functional theory calculation revealed that the phase-separated sample exhibited a lower energy barrier to form the *COOH intermediate and a more thermodynamically stable state than the core–shell sample. Our work paves an alternative way to design highly active and stable catalyst for electrochemical CO2 reduction by tuning the element spatial distribution.

Effective regulation of upconversion luminescence in NaErF4 and NaErF4@SiO2 core-shell particles

Upconversion luminescence materials have gained extensive attentions owing to their unique luminescence characteristics of converting near-infrared excitation to visible light emission. However, how to improve the doping concentration of activator (usually <3 mol%) in traditional sensitizer-activator system is still a great challenge due to the luminescence quenching effect. In this work, NaErF4 crystals with diverse crystal phases and morphologies were prepared by simple hydrothermal method, constructing a 100% doping concentration system of activator (Er3+). With the increase of F− content, the phase of NaErF4 transfers from cubic to hexagonal, and the morphology changes from nanospheres to hexagonal microflakes, meanwhile, the upconversion luminescence intensity also increases gradually. In addition, in order to further inhibit the luminescence quenching effect of NaErF4 bare core, a series of NaErF4@SiO2 core-shell samples with different SiO2 shell thickness were successfully prepared. Compared with NaErF4 bare core, the morphology and structure of the NaErF4@SiO2 core-shell samples have no obvious change, but the UC luminescence intensity is significantly enhanced. Interestingly, the change of NaErF4 crystal phase and SiO2 shell thickness can both bring about multicolor luminescence. In addition, different from the traditional NaYF4:Yb, Er co-doping system, the as-prepared hydrophilic NaErF4 and NaErF4@SiO2 samples showed a greater red to green ratio (R/G > 1), which may expand their potential applications in biological imaging and sensing fields.

Tailoring Interfacial Exchange Anisotropy in Hard-Soft Core-Shell Ferrite Nanoparticles for Magnetic Hyperthermia Applications.

Magnetically hard–soft core-shell ferrite nanoparticles are synthesized using an organometallic decomposition method through seed-mediated growth. Two sets of core-shell nanoparticles (S1 and S2) with different shell (Fe3O4) thicknesses and similar core (CoFe2O4) sizes are obtained by varying the initial quantities of seed nanoparticles of size 6.0 ± 1.0 nm. The nanoparticles synthesized have average sizes of 9.5 ± 1.1 (S1) and 12.2 ± 1.7 (S2) nm with corresponding shell thicknesses of 3.5 and 6.1 nm. Magnetic properties are investigated under field-cooled and zero-field-cooled conditions at several temperatures and field cooling values. Magnetic heating efficiency for magnetic hyperthermia applications is investigated by measuring the specific absorption rate (SAR) in alternating magnetic fields at several field strengths and frequencies. The exchange bias is found to have a nonmonotonic and oscillatory relationship with temperature at all fields. SAR values of both core-shell samples are found to be considerably larger than that of the single-phase bare core particles. The effective anisotropy and SAR values are found to be larger in S2 than those in S1. However, the saturation magnetization displays the opposite behavior. These results are attributed to the occurrence of spin-glass regions at the core-shell interface of different amounts in the two samples. The novel outcome is that the interfacial exchange anisotropy of core-shell nanoparticles can be tailored to produce large effective magnetic anisotropy and thus large SAR values.

Out-of-equilibrium supported Pt-Co core-shell nanoparticles stabilized by kinetic trapping at room temperature

The chemical stability of supported CoPt nanoparticles in out-of-equilibrium core-shell configurations was investigated mainly by anomalous grazing incidence small angle X-ray scattering (AGISAXS) in association with combined transmission electron microscopy and X-ray absorption spectroscopy. CoPt nanoparticles were prepared at room temperature by ultrahigh vacuum atom beam deposition using two different routes: simultaneous deposition of the two metals (CoPt) or sequential deposition. In this last case, Co deposition on a Pt-core (Pt@Co) and the reverse configuration (Co@Pt) are explored. In the Pt@Co case, our experimental analysis of 2.5 nm particles shows the stability of a Pt rich-core (80% Pt) surrounded by a two-monolayers-thick Co shell. In the reverse case, the core-shell structure is also stabilized, while the codeposited sample leads to an alloyed structure. These results suggest that the growth kinetics can trap the thermodynamically non-favorable core-shell structure even for this system which has a high alloying tendency. Besides the lack of atom mobility at room temperature, this stabilization can also be associated with core strain effects. Post thermal treatment of core-shell samples induces a structural transition from the core-shell configuration to the equilibrium alloyed configuration. This study demonstrates that the element-selective scattering technique, AGISAXS is highly efficient for the extraction of chemical segregation information from multi-component supported nanoparticles, such as core-shell structures, up to ultimate small sizes.

Fabrication and characterization of chitosan-polycaprolactone core-shell nanofibers containing tetracycline hydrochloride

Chitosan-polycaprolactone (CS-PCL) core-shell structured nanofibers, in which CS and PCL respectively form the core and shell layers, were electrospun by coaxial electrospinning method. In this regard, three sets of core-shell nanofiber samples were prepared and the best one with desirable morphology, smooth surface, and without beads was characterized. Then tetracycline hydrochloride (TCH) is embedded in the CS core. An attempt has been made to prove the formation of the core-shell structure and encapsulation of the drug by water contact angle (WCA) measurements and attenuated total reflectance Fourier transform spectroscopy (ATR-FTIR). Transmission electron microscopy (TEM) was also used for the validation of the core-shell structure. Morphological investigations were conducted using scanning electron microscopy (SEM) which showed smooth CS-PCL nanofibers without any beads and with an average diameter of 285 ± 75 nm. Compositional analysis was carried out by differential scanning calorimetry (DSC) which indicated that about 64.3% of the prepared CS-PCL core-shell nanofibers were composed of PCL constituent. Also, In-vitro degradation of the nanofibers in the Phosphate Buffered Saline (PBS) solution was evaluated. In comparison to the blend nanofibers, TCH-loaded CS-PCL core-shell nanofibers showed a two-stage release of the drug, an initial burst release stage followed by a sustained release. Moreover, the antibacterial activity of CS-PCL core-shell nanofibers loaded with TCH was confirmed; hence, it has some potential applications in biomedical areas such as in wound dressing and drug delivery systems.

Shell thickness-controlled synthesis of Au@Ag core–shell nanorods structure for contaminants sensing by SERS

The accessibility of contaminants detection methods is urgently required for environmental and food safety control. In this report, we developed the Au@Ag core–shell nanorod structures for contaminants sensing by surface-enhanced Raman spectroscopy (SERS). The silver shell thickness and the corresponding plasmon wavelength of Au@Ag core–shell nanorods were tuned by changing the coating time and the silver precursor amount. Moreover, these structures exhibit ultra-sensitive detection ability for Nile blue A dye and Fenobucarb pesticide sensing by SERS. Interestingly, the highest Raman enhancement factor is obtained for the Au@Ag core–shell sample with a minimal silver shell thickness leaded by the optimal enhancement of the electromagnetic field of bimetallic structures. Hence, our report demonstrates that the combination of unique features of two plasmonic metals into core–shell structures promises potential applicability in SERS-based analysis.