Core-shell Synthesis Research Articles

Efficient Photocatalytic Core–Shell Synthesis of Titanate Nanowire/rGO

Wide bandgap semiconductor-based photocatalysts are usually limited by their low solar energy conversion efficiency due to their limited absorption solar wavelength, their rapid surface recombination of the photogenerated electron–hole pairs, and their low charge-carrier mobility. Here, we report a novel stepwise solution synthesis for achieving a new photocatalytic core–shell consisting of a titanate nanowire/reduced graphene oxide shell (or titanate/rGO) 1D-nanocomposite. The new core–shell nanocomposite maximized the specific surface area, largely reduced the charge transfer resistance and reaction energy barrier, and significantly improved the absorption of visible light. The core–shell nanocomposites’ large on/off current ratio and rapid photo-responses boosted the photocurrent by 30.0%, the photocatalysis rate by 50.0%, and the specific surface area by 16.4% when compared with the results for the pure titanate nanowire core. Our numerical simulations support the effective charge separation on the new core–shell nanostructure, which can help further advance the novel photocatalysis.

SYNTHESIS AND CHARACTERIZATION ANALYSIS OF FE3O4/SiO2 CORE SHELL

Fe3O4/SiO2 core shell synthesis has been carried out, and its characteristics has been analyzed to be used as a photocatalyst using co-precipitation and sol-gel method. Fe3O4 is used as the core material to eliminate the difficulty of separating the photocatalyst powder from the solution medium, SiO2 is used to avoid oxidation by preventing the Fe3O4 core from coming into direct contact with the solution. The samples were then characterized using X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR), and Vibrating Sample Magnetometer (VSM). The XRD and FTIR results showed that the crystal structure and movement of the sample molecules matched the standard characteristics from previous studies. The VSM characterization results show that SiO2 succeeded in reducing the value of the magnetization of Fe3O4, which proves that Fe3O4 has been successfully coated by SiO2.

Electrochemical Synthesis of Core-Shell Nanoparticles by Seed-Mediated Selective Deposition

Conventional solvothermal synthesis of core–shell nanoparticles results in them being covered with surfactant molecules for size control and stabilization, undermining their practicality as electrocatalysts. Here, we report an electrochemical method for the synthesis of core–shell nanoparticles directly on electrodes, free of surfactants. By implementation of selective electrodeposition on gold cores, 1st-row transition metal shells were constructed with facile and precise thickness control. This type of metal-on-metal core–shell synthesis by purely electrochemical means is the first of its kind. The applicability of the nanoparticle decorated electrodes was demonstrated by alkaline oxygen evolution catalysis, during which the Au–Ni example displayed stable catalysis with low overpotential.

Green synthesis and luminescence characteristics of ZnSe-ZnS core-shell quantum dots

The core-shell quantum dots of ZnSe-ZnS were synthesized in aqueous solution using glutathione (GSH) in an environmentally friendly way. The effects of the concentration of GSH, the synthesis temperature and the NaOH concentration (pH) on the microstructural and optical properties of the prepared core-shell systematically were investigated. Analysis of the XRD patterns and TEM particle images confirmed that the round-typed ZnSe-ZnS quantum dots of size 3 to 5 nm were formed. Comparing to the single core ZnSe, the core-shell ZnSe-ZnS showed an increase in photoluminescence (PL) emission intensity up to 130%. In addition, the core-shell quantum dots showed a good long-term stability maintaining their high PL intensity for at least 84 days. The synthesis process optimization was discussed in detail. The light emission intensities of the quantum dots were dependent on the GSH concentration. The optimum GSH concentration for the core-shell synthesis was found to be around 0.1 mmol. High temperature above 70 C for the core-shell synthesis generally improved the optical properties. However, light discharge characteristics were correlated with the core-shell synthesis temperature and the pH in solution. At the high temperatures of 70 °C and 90 °C, the emission intensities were degraded with high pH of 13 due to the dissociation of the ligand were accelerated. The optimized ZnSe-ZnS quantum dots showed high color purity emitting blue fluorescence light of 378 nm with the narrow full width at half maximum (FWHM) less than 20 nm. Optimization of synthesis parameters showed the possibilities of the simple and eco-friendly manufacture of long term stable and efficient ZnSe-ZnS core-shell quantum dots in aqueous solutions for display applications.

Constructing multiple heterogeneous shell on the CaCu3Ti4O12 core for better dielectric performances

A core-shell synthesis is proposed in this study to improve the dielectric loss and the resistivity of CaCu3Ti4O12 (CCTO), which exhibits a colossal permittivity, make it very interesting for capacitor applications. However, the grain boundaries of this ceramic material play a key role for the good dielectric properties. To control these boundaries can be performed by producing shells around the CCTO grains with different oxide mixtures. The design of core-shell structure is a possible approach to control the thickness and homogeneity of the shell, which will improve the properties of this material. In this work, as-prepared CCTO particles, synthetized by solid-state reaction, were successful coated with double or triple shell (SiO2, Al2O3, TiO2) using conventional sol–gel processing derivative from Stöber method. This coating with several binary oxides is made for the first time and has an innovative character in the improvement of properties for an application The CCTO coated with shell composed of SiO2 + Al2O3 + TiO2 mixture showed the best improvement with a colossal permittivity about 7.104, low loss tangent close to 0.05 and high resistivity equal to 109 Ω cm at 1 kHz. Indeed, a clear increasing of resistivity and decreasing of dielectric loss were observed for these samples compared with the resistivity of CCTO (≈105 Ω cm). Moreover, simulations of impedance curves give the capacitance and resistivity of the grain boundaries, which confirm by their linear behavior that the global properties of this material depend on the behavior of the grain boundaries in agreement with the Internal Bayer Layer Capacitors model.

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.

Review of the Scalable Core-Shell Synthesis Methods: The Improvements of Li-Ion Battery Electrochemistry and Cycling Stability.

The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks.

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Epitaxial growth of surface-passivated core-shell ferrierite

Ferrierite (FER) is both a natural and synthetic zeolite that is commonly utilized as a catalyst in commercial processes that take advantage of its two-dimensional network of micropores. The external surfaces of zeolite crystals often impose deleterious effects on catalyst performance, such as external coking or unselective reactions as a result of unconfined acid sites. One technique that can improve the efficiency of zeolite catalysts is surface passivation wherein the aluminosilicate crystal is encapsulated within a shell of its siliceous isostructure. These core–shell configurations eliminate surface acidity, forcing reactions to occur within interior (confined) pores for improved shape-selectivity while simultaneously reducing rates of deactivation, which extends catalyst lifetime. In this study, we examine whether a Si-rich shell can be epitaxially grown on the surface of an aluminosilicate FER crystal in fluoride-free media. Epitaxial growth of an ultra-thin Si-rich shell was confirmed by multiple characterization techniques showing no evidence of pore blockage or misoriented shell growth during core–shell synthesis. The passivation of external acid sites was confirmed using Friedel-Crafts alkylation of mesitylene and benzyl alcohol as a benchmark reaction for probing surface acidity. Overall, these findings confirm that it is possible to synthesize core–shell ferrierite with an aluminosilicate core and a silicon-rich shell via a facile seed-assisted growth procedure.

Magnetic styrene polymers obtained via coordination polymerization of styrene by Ni and Cu nanoparticles

Magnetic nanocatalysts have attracted attention due to their recyclability, affordability and stability in a broad pH range. Immobilization of transition metals onto the iron oxide surface is of great interest as it allows for increased activity to the magnetic core and serve as stable supports for sensitive Cu and Ni nano-systems. In this work, Cu and Ni coated Fe3O4 nanocomposites were designed using different core-shell synthesis methods and coating salts, respectively. The nanoparticle (NP) formation was monitored using ultraviolet–visible (UV–Vis) spectrophotometry and Fourier-Transform Infrared spectrometry (FTIR), with the size distribution visualized by high-resolution transmission electron microscopy (HR-TEM). The metal content was determined prior to catalysis via Inductively-coupled plasma-optical emission spectrometry (ICP-OES). As Cu and Ni complexes are known pre-catalysts for polymerization reactions, this study focuses on polymerization on the surface of these synthesized nano-catalysts to produce polystyrene (PS) encapsulated magnetic nanosystems. Polymer formation was confirmed by FT-IR and molecular weight determined by gel permeation chromatography (GPC). The obtained polymeric materials were evaluated as adsorbents for oil spills, after which the polymer was easily separated from the effluent, and then recycled after desorption of the oil.

Structural Control over Bimetallic Core-Shell Nanorods for Surface-Enhanced Raman Spectroscopy.

Bimetallic nanorods are important colloidal nanoparticles for optical applications, sensing, and light-enhanced catalysis due to their versatile plasmonic properties. However, tuning the plasmonic resonances is challenging as it requires a simultaneous control over the particle shape, shell thickness, and morphology. Here, we show that we have full control over these parameters by performing metal overgrowth on gold nanorods within a mesoporous silica shell, resulting in Au–Ag, Au–Pd, and Au–Pt core–shell nanorods with precisely tunable plasmonic properties. The metal shell thickness was regulated via the precursor concentration and reaction time in the metal overgrowth. Control over the shell morphology was achieved via a thermal annealing, enabling a transition from rough nonepitaxial to smooth epitaxial Pd shells while retaining the anisotropic rod shape. The core–shell synthesis was successfully scaled up from micro- to milligrams, by controlling the kinetics of the metal overgrowth via the pH. By carefully tuning the structure, we optimized the plasmonic properties of the bimetallic core–shell nanorods for surface-enhanced Raman spectroscopy. The Raman signal was the most strongly enhanced by the Au core–Ag shell nanorods, which we explain using finite-difference time-domain calculations.

Room temperature synthesized solid solution AuFe nanoparticles and their transformation into Au/Fe Janus nanocrystals.

Solid solution AuFe nanoparticles were synthesized for the first time under ambient conditions by an adapted method previously established for the Fe3O4-Au core-shell morphology. These AuFe particles preserved the fcc structure of Au incorporated with paramagnetic Fe atoms. The metastable AuFe can be segregated by transformation into Janus Au/Fe particles with bcc Fe and fcc Au upon annealing. The ferromagnetic Fe was epitaxially grown on low index fcc Au planes. This preparation route delivers new perspective materials for magnetoplasmonics and biomedical applications and suggests the reconsideration of existing protocols for magnetite-gold core-shell synthesis.

A core-shell synthesis of CaCu3Ti4O12 (CCTO) ceramics showing colossal permittivity and low electric losses for application in capacitors

A core-shell synthesis is applied to CaCu3Ti4O12, a material that shows colossal permittivity. The objective was to test several bulk permittivity of the shell material in order to reach a large capacity of the grain boundaries after sintering. The permittivity is improved with certain shells while the bulk resistivity reaches levels approaching that of commercial grain boundary barrier layer (GBBL) ceramic capacitors. The highest permittivity is confirmed to be related to the highest capacity of grain boundaries. The bulk resistivity is related to that of grain boundaries. If one attaches the more important weight to a high bulk resistivity without need of permittivity larger than 15,000, as in commercial GBBL ceramic capacitors, several samples appear convenient. On the other hand, much higher permittivity can be reached like in CCTO with a shell of TiO2 but at the expense of dielectric losses, possibly due to oxygen departure from stoichiometry. Thermal post-treatment under various controlled atmosphere have been applied to reduce dielectric losses.

Oxide-Free Three-Dimensional Germanium/Silicon Core-Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition.

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. Here, we explore the synthesis and properties of a germanium metalattice in which the ∼70 nm periodicity of a silica colloidal crystal template is close to the ∼24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a core-shell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

Metal Oxide (ZnO and TiO2) and Fe-Based Metal–Organic-Framework Nanoparticles on 3D-Printed Fractal Polymer Surfaces for Photocatalytic Degradation of Organic Pollutants

Hybrid nanomaterials have been produced using a combination of core–shell synthesis, 3D printing, and plasma grafting. Metal oxides, that is, ZnO and TiO2, as well as iron-based metal organic frame...

Comparison of colossal permittivity of CaCu3Ti4O12 with commercial grain boundary barrier layer capacitor

The properties of a commercial grain boundary barrier layer (GBBL) SrTiO3-based capacitor are analyzed in terms of capacitance C and resistivity R of two RC elements, one for grains and one for grain boundaries. Results are compared with those of CaCu3Ti4O12 (CCTO) samples showing giant permittivity, measured in the same conditions and analyzed with the same method. All CCTO samples investigated here show higher permittivity than GBBL. This is shown to be related to a higher capacitance of the grain boundaries. However, the electric losses of CCTO measured via conventional tan(δ) are found significantly higher. They are related to a resistivity of the grain boundaries lower than in GBBL capacitor. A better control of the grain boundaries in CCTO possibly via a core-shell synthesis described here, followed by thermal post treatments under a controlled atmosphere as it is performed for GBBL capacitors, is suggested to improve the resistance of CCTO dielectrics.

Photoactive Hybrid Materials with Fractal Designs Produced via 3D Printing and Plasma Grafting Technologies.

The present paper partly aims at exploring the potential of fractal geometry for concrete applications in the field of materials science. It is more specifically a study about the conception of hybrid polymer-based materials with photocatalytic activity. The concept behind this work is to investigate the use of polymer fractal structures manufactured by 3D-printing technology, as a highly ordered substrate with an important surface area to immobilize catalyst nanoparticles, by means of plasma grafting technology. Two types of fractal units, fractal pyramids (fracmids) and fractal cones (fracones), have been described and the former has been extensively characterized on a geometrical aspect. Various complex superstructures have also been described using fractal units as building blocks. 3D structures based on the aforementioned theoretical models have been designed using computer-aided design (CAD). On the basis of CAD models, several structures have been 3D-printed with PLA using fused deposition modeling. PLA substrates have been successfully coated with nanoparticles of ZnO using a combination of core-shell synthesis and plasma grafting. Finally, the photocatalytic activity of a hybrid material has been assessed with a positive outcome, showing the relevance of the concept developed in this study.

Role of N-methyl-2-pyrrolidone for preparation of Fe3O4@SiO2 controlled the shell thickness

We developed a simple and novel approach for the synthesis of Fe3O4@SiO2 nanoparticles with controlled shell thickness, and studied the mechanism. The introduction of N-methyl-2-pyrrolidone (NMP) led to trapping of monomer nuclei in single shell and controlled the shell thickness. Fe3O4@SiO2 controlled the shell thickness, showing a high magnetization value (64.47 emu/g). Our results reveal the role and change in the chemical structure of NMP during the core-shell synthesis process. NMP decomposed to 4-aminobutanoic acid in alkaline condition and decreased the hydrolysis rate of the silica coating process.

Catalytic cracking of 1-butene to propylene using modified H-ZSM-5 catalyst: A comparative study of surface modification and core-shell synthesis

Surface modification of ZSM-5 catalyst was carried out by silica deposition using chemical liquid deposition (CLD) method as well as core-shell silicalite composite material by hydrothermal method. The modified ZSM-5 catalyst was characterized using various physiochemical methods such as XRD, TPD, N2 adsorption-desorption and SEM analysis. Catalytic cracking of 1-butene was carried out using modified ZSM-5 catalysts. The propylene yield was higher for core-shell silicalite composite as compared to silica deposition through CLD method. Silica deposited using CLD method showed propylene-to-ethylene (P/E) ratio of 1.7, whereas core-shell silicalite composite resulted in P/E ratio of 3.0. The higher selectivity to light olefins using core-shell silicalite composite to be attributed to weak acid sites and effective control of external acid sites, which reduces the hydrogen transfer reactions that form alkanes and aromatics. The effective external surface passivation was verified using catalytic cracking of triisopropyl benzene. The core-shell silicalite composite showed excellent stability over 50h for the cracking of 1-butene stream.

Morphology conserving aminopropyl functionalization of hollow silica nanospheres in toluene

Inorganic nanostructures containing cavities of monodisperse diameter distribution find applications in e.g. catalysis, adsorption and drug delivery. One of their possible synthesis routes is the template assisted core-shell synthesis. We synthesized hollow silica spheres around polystyrene cores by the sol-gel method. The polystyrene template was removed by heat treatment leaving behind a hollow spherical shell structure. The surface of the spheres was then modified by adding aminopropyl groups. Here we present the first experimental evidence that toluene is a suitable alternative functionalization medium for the resulting thin shells, and report the comprehensive characterization of the amino-functionalized hollow silica spheres based on scanning electron microscopy, transmission electron microscopy, N2 adsorption, FT-IR spectroscopy, Raman spectroscopy and electrokinetic potential measurement. Both the presence of the amino groups and the preservation of the hollow spherical morphology were unambiguously proven. The introduction of the amine functionality adds amphoteric character to the shell as shown by the zeta potential vs. pH function. Unlike pristine silica particles, amino-functionalized nanosphere aqueous sols can be stable at both acidic and basic conditions.