Spherical Core-shell Particles Research Articles

Synthesis and Characterization of a Thermoresponsive Copolymer with an LCST-UCST-like Behavior and Exhibiting Crystallization.

In this work, the diblock copolymer methoxy-poly(ethylene glycol)-block-poly(ε-caprolactone) (MPEG-b-PCL) was synthesized with a block composition that allows this polymer in aqueous media to possess both an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST) over a limited temperature interval. The value of the UCST, associated with crystallization of the PCL-block, depended on heating (H) or cooling (C) of the sample and was found to be CPUCSTH = 32 °C and CPUCSTC = 23 °C, respectively. The LCST was not affected by the heating or cooling scans; assumed a value of 52 °C (CPLCSTH = CPLCSTC). At intermediate temperatures (e.g., 45 °C), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM) showed that the solution consisted of a large population of spherical core-shell particles and some self-assembled rodlike objects. At low temperatures (below 32 °C), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) in combination with SAXS disclosed the formation of crystals with a cylindrical core-shell structure. Cryo-TEM supported a thread-like appearance of the self-assembled polymer chains. At temperatures above 52 °C, incipient phase separation took place and large aggregation complexes of amorphous morphology were formed. This work provides insight into the intricate interplay between UCST and LCST and the type of structures formed at these conditions in aqueous solutions of MPEG-b-PCL diblock copolymers.

Upper critical solution temperature polymer assemblies via variable temperature liquid phase transmission electron microscopy and liquid resonant soft X-ray scattering

Here, we study the upper critical solution temperature triggered phase transition of thermally responsive poly(ethylene glycol)-block-poly(ethylene glycol) methyl ether acrylate-co-poly(ethylene glycol) phenyl ether acrylate-block-polystyrene nanoassemblies in isopropanol. To gain mechanistic insight into the organic solution-phase dynamics of the upper critical solution temperature polymer, we leverage variable temperature liquid-cell transmission electron microscopy correlated with variable temperature liquid resonant soft X-ray scattering. Heating above the upper critical solution temperature triggers a reduction in particle size and a morphological transition from a spherical core shell particle with a complex, multiphase core to a micelle with a uniform core and Gaussian polymer chains attached to the surface. These correlated solution phase methods, coupled with mass spectral validation and modeling, provide unique insight into these thermoresponsive materials. Moreover, we detail a generalizable workflow for studying complex, solution-phase nanomaterials via correlative methods.

Brochosome-Inspired Metal-Containing Particles as Biomimetic Building Blocks for Nanoplasmonics: Conceptual Generalizations.

Recently, biological nanostructures became an important source of inspiration for plasmonics, with many described implementations and proposed applications. Among them are brochosome-inspired plasmonic microstructures—roughly spherical core-shell particles with submicrometer diameters and with indented surfaces. Our intention was to start from the nanoplasmonic point of view and to systematically classify possible alternative forms of brochosome-inspired metal-containing particles producible by the state-of-the-art nanofabrication. A wealth of novel structures arises from this systematization of bioinspired metal-containing nanocomposites. Besides various surface nanoapertures, we consider structures closely related to them in electromagnetic sense like surface nano-protrusions, shell reliefs obtained by nano-sculpting, and various combinations of these. This approach helped us build a new design toolbox for brochosome-inspired structures. Additionally, we used the finite elements method to simulate the optical properties of simple brochosome-inspired structures. We encountered a plethora of advantageous optical traits, including enhanced absorption, antireflective properties, and metamaterial behavior (effective refractive index close to zero or negative). We conclude that the presented approach offers a wealth of traits useful for practical applications. The described research represents our attempt to outline a possible roadmap for further development of bioinspired nanoplasmonic particles and to offer a source of ideas and directions for future research.

Synthesis of nanoparticles composed of a poly(methylmethacrylate-co-laurylmethacrylate) core and a polysiloxane shell as vehicles for limonene

In this study, hybrid nanoparticles composed of poly(methylmethacrylate-co-laurylmethacrylate) (PMMA-co-LMA) and poly(3-(trimethoxysilyl)propyl methacrylate) (PMS) obtained via seeded emulsion polymerisation were synthesised. A series of copolymers of LMA and MMA was obtained via emulsion polymerisation in the presence of β-cyclodextrin as a phase transport catalyst. The resulting spherical particles of approximately 50 nm were used as seeds for MPS polymerisation, resulting in spherical core-shell particles. These materials were evaluated as vehicles for limonene. Initially, it was observed that the extent of particle swelling by limonene was enhanced at the highest fractions of LMA. The same trend was obtained when the loading capacity and encapsulation efficiency were determined. Although when the core contained PLMA only, the particles exhibited the highest encapsulation capacity, these nanoparticles presented the poorest control on the release of limonene. The cytotoxicity evaluation of the core-shell nanoparticles revealed that they are slightly cytotoxic with cell viabilities higher than 70% at all the concentrations. Our results indicated that core-shell nanoparticles containing a core composed of P(MMA-co-LMA) and a siloxane shell were promising vehicles for nonpolar and volatile compounds, such as limonene, and they showed potential for applications in various fields, such as pest control, food and pharmaceutical industries.

Emulsifier‐free reversible addition–fragmentation chain transfer emulsion polymerization of alkyl acrylates mediated by symmetrical trithiocarbonates based on poly(acrylic acid)

AbstractEmulsifier‐free batch emulsion polymerization of n‐butyl acrylate and its semi‐batch copolymerization with 2,2,3,3,4,4,5,5‐octafluoropentyl acrylate and 2,2,3,4,4,4‐hexafluorobutyl acrylate both mediated by poly(acrylic acid) containing the trithiocarbonate group in the chain was employed to produce amphiphilic triblock copolymers. The polymerization‐induced self‐assembly of these copolymers in aqueous media gave rise to spherical core–shell particles. Irrespective of the experimental conditions, the polymeric product was characterized by a bimodal molecular weight distribution. The apparent violation of the reversible addition–fragmentation chain transfer polymerization mechanism may be attributed to restricted accessibility of the trithiocarbonate group in the self‐assembled block copolymers for propagating radicals that enter into the particle. Mean‐field theoretical arguments were employed to explain the exclusively spherical morphology of the particles observed in the experiment. © 2019 Society of Chemical Industry

Cloud droplet activation properties and scavenged fraction of black carbon in liquid-phase clouds at the high-alpine research station Jungfraujoch (3580 m a.s.l.)

Abstract. Liquid clouds form by condensation of water vapour on aerosol particles in the atmosphere. Even black carbon (BC) particles, which are known to be slightly hygroscopic, have been shown to readily form cloud droplets once they have acquired water-soluble coatings by atmospheric aging processes. Accurately simulating the life cycle of BC in the atmosphere, which strongly depends on the wet removal following droplet activation, has recently been identified as a key element for accurate prediction of the climate forcing of BC. Here, to assess BC activation in detail, we performed in situ measurements during cloud events at the Jungfraujoch high-altitude station in Switzerland in summer 2010 and 2016. Cloud droplet residual and interstitial (unactivated) particles as well as the total aerosol were selectively sampled using different inlets, followed by their physical characterization using scanning mobility particle sizers (SMPSs), multi-angle absorption photometers (MAAPs) and a single-particle soot photometer (SP2). By calculating cloud droplet activated fractions with these measurements, we determined the roles of various parameters on the droplet activation of BC. The half-rise threshold diameter for droplet activation (Dhalfcloud), i.e. the size above which aerosol particles formed cloud droplets, was inferred from the aerosol size distributions measured behind the different inlets. The effective peak supersaturation (SSpeak) of a cloud was derived from Dhalfcloud by comparing it to the supersaturation dependence of the threshold diameter for cloud condensation nuclei (CCN) activation measured by a CCN counter (CCNC). In this way, we showed that the mass-based scavenged fraction of BC strongly correlates with that of the entire aerosol population because SSpeak modulates the critical size for activation of either particle type. A total of 50 % of the BC-containing particles with a BC mass equivalent core diameter of 90 nm was activated in clouds with SSpeak≈0.21 %, increasing up to ∼80 % activated fraction at SSpeak≈0.50 %. On a single-particle basis, BC activation at a certain SSpeak is controlled by the BC core size and internally mixed coating, which increases overall particle size and hygroscopicity. However, the resulting effect on the population averaged and on the size-integrated BC scavenged fraction by mass is small for two reasons: first, acquisition of coatings only matters for small cores in clouds with low SSpeak; and, second, variations in BC core size distribution and mean coating thickness are limited in the lower free troposphere in summer. Finally, we tested the ability of a simplified theoretical model, which combines the κ-Köhler theory with the Zdanovskii–Stokes–Robinson (ZSR) mixing rule under the assumptions of spherical core–shell particle geometry and surface tension of pure water, to predict the droplet activation behaviour of BC-containing particles in real clouds. Predictions of BC activation constrained with SSpeak and measured BC-containing particle size and mixing state were compared with direct cloud observations. These predictions achieved closure with the measurements for the particle size ranges accessible to our instrumentation, that is, BC core diameters and total particle diameters of approximately 50 and 180 nm, respectively. This clearly indicates that such simplified theoretical models provide a sufficient description of BC activation in clouds, as previously shown for activation occurring in fog at lower supersaturation and also shown in laboratory experiments under controlled conditions. This further justifies application of such simplified theoretical approaches in regional and global simulations of BC activation in clouds, which include aerosol modules that explicitly simulate BC-containing particle size and mixing state.

Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state

Abstract. Among the variety of particle types present in the atmosphere, black carbon (BC), emitted by combustion processes, is uniquely associated with harmful effects to the human body and substantial radiative forcing of the Earth. Pure BC is known to be non-hygroscopic, but its ability to acquire a coating of hygroscopic organic and inorganic material leads to increased diameter and hygroscopicity, facilitating droplet activation. This affects BC radiative forcing through aerosol–cloud interactions (ACIs) and BC life cycle. To gain insights into these processes, we performed a field campaign in winter 2015–2016 in a residential area of Zurich which aimed at establishing relations between the size and mixing state of BC particles and their activation to form droplets in fog. This was achieved by operating a CCN counter (CCNC), a scanning mobility particle sizer (SMPS), a single-particle soot photometer (SP2) and an aerosol chemical speciation monitor (ACSM) behind a combination of a total- and an interstitial-aerosol inlet. Our results indicate that in the morning hours of weekdays, the enhanced traffic emissions caused peaks in the number fraction of externally mixed BC particles, which do not act as CCN within the CCNC. The very low effective peak supersaturations (SSpeak) occurring in fog (between approximately 0.03 % and 0.06 % during this campaign) restrict droplet activation to a minor fraction of the aerosol burden (around 0.5 % to 1 % of total particle number concentration between 20 and 593 nm) leading to very selective criteria on diameter and chemical composition. We show that bare BC cores are unable to activate to fog droplets at such low SSpeak, while BC particles surrounded by thick coating have very similar activation behaviour to BC-free particles. Using simplified κ-Köhler theory combined with the ZSR mixing rule assuming spherical core–shell particle geometry constrained with single-particle measurements of respective volumes, we found good agreement between the predicted and the directly observed size- and mixing-state-resolved droplet activation behaviour of BC-containing particles in fog. This successful closure demonstrates the predictability of their droplet activation in fog with a simplified theoretical model only requiring size and mixing state information, which can also be applied in a consistent manner in model simulations.

Fluorescently Labelled Silica Coated Gold Nanoparticles as Fiducial Markers for Correlative Light and Electron Microscopy

In this work, gold nanoparticles coated with a fluorescently labelled (rhodamine B) silica shell are presented as fiducial markers for correlative light and electron microscopy (CLEM). The synthesis of the particles is optimized to obtain homogeneous, spherical core-shell particles of arbitrary size. Next, particles labelled with different fluorophore densities are characterized to determine under which conditions bright and (photo)stable particles can be obtained. 2 and 3D CLEM examples are presented where optimized particles are used for correlation. In the 2D example, fiducials are added to a cryosection of cells whereas in the 3D example cells are imaged after endocytosis of the fiducials. Both examples demonstrate that the particles are clearly visible in both modalities and can be used for correlation. Additionally, the recognizable core-shell structure of the fiducials proves to be very powerful in electron microscopy: it makes it possible to irrefutably identify the particles and makes it easy to accurately determine the center of the fiducials.

On the Elastic Description of a Spherical Janus Particle

Abstract The elastic problem of a spherical core-shell particle with a truncated core is solved within the isotropic classical theory of elasticity. A transition to a Janus particle consisting of two unequal spherical segments with lattice mismatch is demonstrated. Elastic fields in the Janus particle are found and described in detail. The strain energy of the Janus particle in dependence on the interface coordinate is discussed.

A novel synthetic strategy of Fe@Cu core-shell microsphere particles by integration of solid-state immiscible metal system and low wettability

Herein, a novel preparation route of bimetallic spherical core-shell particles of immiscible metal system was developed and demonstrated through the synthesis of Fe@Cu core–shell microsphere particles. Copper ferrite (CuFe2O4) was used as precursor for the preparation of the Core–shell structured Fe@Cu microsphere using the solid-state immiscibility of Fe and Cu and the low wettability strategy of the liquid-solid interface of graphite at 1403 K. The results showed that phase separation occurred between Cu and Fe, where Cu tended to move towards the surface of the particles and Fe was more concentrated in the center of the particles, due to the lower surface energy of liquid Cu with respect to solid Fe. This was followed by formation of metal droplets located on loose graphite flakes on the spherical Fe@Cu due to the solid-liquid interfacial tension. The as-prepared Fe@Cu microsphere exhibited good spherical shapes and smooth surfaces. The cross-sectional micrographics and element mapping of the spherical particles confirmed the evenly distributions of the Fe-rich core and Cu-rich shell. This strategy is promising for the fabrication of core–shell structured spherical particles for immiscible alloys.

Tracking Water Sorption in Glassy Aerosol Particles using Morphology-Dependent Resonances.

Morphology-dependent resonances (MDRs) can serve as a sensitive probe of the size and composition of microspheres. While the utilization of MDRs to characterize homogeneous spheres is now routine, analysis of spherical particles with more complicated refractive index profiles can be extremely difficult and time consuming. In ultraviscous and glassy aerosol particles, the concentration profile of water during sorption often contains a sharp front that propagates from the particle surface to the particle center over time. Here we show that the MDR positions associated with this type of concentration profile closely match those of a spherical core-shell profile. Due to the similarities, a core-shell model can be used to simplify the analysis of MDR positions that are observed during water uptake by high-viscosity aerosol particles. We examined the applicability and limitations of this core-shell model in the tracking of water sorption by single particles. Overall, the core-shell model allows for the radial position of a sharp diffusion front to be readily found using MDR positions observed during water sorption, making the analysis of light-scattering measurements much faster and less error prone than previously used fitting schemes. Additionally, methods for calculating MDRs in spherical core-shell particles are also discussed.

Synthesis of Core–Shell Particles of Nickel–Manganese–Cobalt Hydroxides in a Continuous Couette-Taylor Crystallizer

A Taylor vortex flow was used as an effective continuous process for synthesizing uniform and spherical core–shell particles of nickel–manganese-cobalt hydroxides, consisting of a (Ni0.90Mn0.05Co0.05)(OH)2 (Ni-rich hydroxide) core and (Ni0.475Co0.05Mn0.475)(OH)2 (half–half hydroxide) shell. Tiny half–half hydroxide particles (primary particles) were initially precipitated and then adhered to core particles of the Ni-rich hydroxide to form core–shell particles via collision and agglomeration between the primary particles and the core particles. pH 10 was determined as the optimum condition for maximizing the interaction between the primary particles and the core particles. The shell-layer formation depended strongly on the operating parameters of the Couette-Taylor (CT) crystallizer, including the inner cylinder rotation speed, reactant concentration, and mean residence time. Using those parameters, the shell-layer thickness was controlled from 0.4 mm to 2.0 mm. Plus, a narrow size distribution (coefficien...

A general method for retrieving thermal deformation properties of microencapsulated phase change materials or other particulate inclusions in cementitious composites

This study examined the effects of spherical core-shell particle inclusions, such as microencapsulated phase change materials (PCMs), on the thermal deformation behavior of cement-based composites. First, simulations of volumetric thermal deformation in representative microstructures were carried out, based on the finite element method (FEM), to predict the effective thermal deformation coefficient of the composites. Excellent agreement was found between the effective thermal deformation coefficient predicted by FEM and by the effective medium approximation (EMA) developed by Schapery (1968). Furthermore, the effective thermal deformation coefficient of cementitious composites with either microencapsulated PCM or quartz particulates was measured. The measured effective thermal deformation coefficients together with Schapery's model were used to retrieve the thermal deformation coefficients of the inclusions themselves. The thermal deformation coefficient of PCM microcapsules was estimated to be similar to that of the shell component due to partial filling of the microcapsules. The results show a means for (i) retrieving the thermal deformation properties of functional core-shell inclusions and (ii) for designing cementitious composites with PCMs which find use in the built environment and high-performance composites.

In-situ assembly of diblock copolymers onto submicron-sized particles for preparation of core-shell and ellipsoidal particles

We describe a facile and simple method to prepare colloidal architectures by the in situ assembly of amphiphilic diblock copolymers onto submicron-sized core particles. Polystyrene-b-poly(acrylic acid) diblock copolymers (PStmPAAn) were directly assembled onto hydrophobic silica (SiO2) core particles, forming spherical core-shell particles. By varying the surface hydrophobicity of the core particles and the compositions of the diblock copolymers, core-shell particles with tailored shell thickness were observed. Furthermore, we demonstrated the preparation of ellipsoidal particles, which containing two core particles, based on this strategy.

The Effect of Shell Thickness, Sintering Temperature and Interdiffusion on the Electrochemical Properties of Lithium-Rich Core-Shell Cathodes

Core-shell (CS) structured positive electrode materials based on layered Li-Ni-Mn-Co oxide could be the next generation of positive electrode materials for high energy density lithium-ion batteries. This is because a high energy core material with poor stability against the electrolyte can be protected by a thin layer of a stable shell material. In our previous report1–2, Li and Mn-rich materials were used as the protecting shell, and Ni-rich materials were used as the core. It was shown that the Mn-rich shell can effectively protect the Ni-rich core from reactions with the electrolyte while the Ni-rich core renders a high and stable average voltage.1 However, diffusion of the cations between the core and shell phases occurs during sintering 2. In this work, the effect of the initial shell thickness, sintering temperature and the interdiffusion in a ternary system on the electrochemical performance of CS cathodes was studied. CS precursors with (Ni0.6Mn0.2Co0.2)(OH)2 as the core and 10 mol% (CS10), 20 mol% (CS20) or 33 mol% (CS33) (Ni0.2Mn0.6Co0.2)(OH)2 shell were first synthesized. Lithiated samples were then prepared by sintering the precursor and LiOH with three different lithium contents (average Li/TM of 1.02, 1.04 and 1.06) for each shell content at 850 or 900oC for 10 h. The samples were labeled as CS10 (20, 33) - 850 (900) - 1 (2,3), which indicate the initial shell content, sintering temperature and lithium content, respectively. For example, CS20-900-3 indicates a sample with 20 mol.% shell, sintered at 900oC with a Li/TM ratio of 1.06. Figure 1 shows a SEM image and energy dispersive spectroscopy (EDS) mapping results of CS33-850-2. Figures 1c, 1d and 1e show that the Mn-rich shell was maintained, while the Ni and Co content at the surface is lower than that in the core (less bright) after sintering. Figures 1a and 1b clearly show that the core and shell have two different morphologies where the core was sintered to a polycrystalline monolith nearly free of interior voids (besides some big pores), whereas the shell was composed of spiky flakes with pores in between. This could be improved by adjusting the synthesis approach in the future. In order to further examine the interdiffusion phenomena in spherical CS particles, a focused ion-beam (FIB) was used to cut a thin slice (~100 nm) through the center of a randomly selected particle. Figure 2a shows a scanning transimission electron microscope (STEM) image of the prepared slice. The yellow line shows the path where EDS point analysis was performed. Figure 2b shows the measured concentration profiles with symbols, calculated profiles with solid lines and simulated initial concentration profiles with dashed lines respectively. Ni moved from the core to the shell and the Ni content on the surface changed from ~21% to ~30% during sintering, while Mn moved from the shell into the bulk, and the Mn content on the surface changed from ~57% to ~55%. Surprisingly, Co moved into the core from the shell, even though the initial Co content in the core and shell was the same, in order to compensate for the increase of Ni content in the surface. This is because the interdiffusion between Ni/Co is much faster than Ni/Mn as discussed in Ref. 2. This suggests that the present of Co in the shell can accelerate the diffusion of Ni from the core to the shell. Samples CS20-850-3 and CS33-900-3 were selected from 24 synthesized samples for testing in full cell coin cells with graphite as the counter electrode using two different electrolytes, in comparison to a commercial material (Umicore coated NMC622) designed for high voltages. The control electrolyte was 1M LiPF6in 3:7 v:v ethylene carbonate (EC): diethylcarbonate (DEC). PES211 electrolyte is the control electrolyte plus 2% prop-1-ene-1,3-sultone + 1% Methylene methane disulfonate + 1% tri(trimethylsilyl) phosphite (PES). The cells were tested between 2.8 and 4.6 V with a rate of C/5 followed by one cycle of C/20 in every 20 cycles. Figure 3 shows the capacity of the cells as a function of cycle number. It is seen that cells with PES 211 have slightly higher capacity than the control cells. Figure 3a shows that the cells have similar capacity retention with control electrolyte, while Figure 3b shows that CS20-850-3 has slightly better capacity retention (~90% after 100 cycles ) comparing to CS33-900-3 and coated NMC622, References (1) Li, J.; Camardese, J.; Shunmugasundaram, R.; Glazier, S.; Lu, Z.; Dahn, J. R. Chem. Mater. 2015, 27, 3366–3377. (2) Li, J.; Doig, R.; Camardese, J.; Plucknett, K.; Dahn, J. R.;Chem. Mater. 2015, 27 (22), 7765–7773. . Figure 1

Surface mode hybridization in the optical response of core-shell particles

We present an exact rewriting of the Mie coefficients describing the scattering of light by a spherical core-shell particle which enables their interpretation in terms of an hybridization of the two surface modes arising, respectively, at the core-shell and the shell-medium interface. For this particular case we thus obtain from the Mie theory--analytically for all multipole orders and hence for arbitrarily sized particles--the hybridization scenario, which so far has been employed primarily for small particles in the electrostatic approximation. To demonstrate the strength of the rewriting approach we also extract the hybridization scenario for a stratified sphere directly from the expansion coefficients for the electromagnetic fields.

Sliver spherical nanoshells coated gain-assisted ellipsoidal silica core for low-threshold surface plasmon amplification

Abstract We have proposed an ellipsoidal gain-assisted silica core coated with a spherical Ag nanoshell for the stable low-threshold spaser generation. The results show that the surface plasmon can be amplified greatly by increasing the optical gain to a critical value (gain threshold). By varying the ellipticities of the ellipsoidal dielectric core nanoparticles (NPs), the gain threshold of the silica can drop 32.7% compared to that of a spherical core–shell particle. The physical mechanism of the lower gain threshold has been explained and discussed in detail by investigating the quality factor (QF) and the localized field distributions associated with the laser mode. Furthermore, we have also investigated the influence of the ellipticities of the gain-assist silica core on the level of gain threshold. With increasing the ellipticities of the silica core, the level of gain threshold decreases accordingly, and the corresponding super-resonance wavelength also shows a red shift.

Metal-enhanced fluorescence of dye-doped silica nano particles.

Recent advancements in metal-enhanced fluorescence (MEF) suggest that it can be a promising tool for detecting molecules at very low concentrations when a fluorophore is fixed near the surface of metal nanoparticles. We report a simple method for aggregating multiple gold nanoparticles (GNPs) on Rhodamine B (RhB)-doped silica nanoparticles (SiNPs) utilizing dithiocarbamate (DTC) chemistry to produce MEF in solution. Dye was covalently incorporated into the growing silica framework via co-condensation of a 3-aminopropyltriethoxysilane (APTES) coupled RhB precursor using the Stöber method. Electron microscopy imaging revealed that these mainly non-spherical particles were relatively large (80nm on average) and not well defined. Spherical core-shell particles were prepared by physisorbing a layer of RhB around a small spherical silica particle (13nm) before condensing an outer layer of silica onto the surface. The core-shell method produced nanospheres (~30nm) that were well defined and monodispersed. Both dye-doped SiNPs were functionalized with pendant amines that readily reacted with carbon disulfide (CS2) under basic conditions to produce DTC ligands that have exhibited a high affinity for gold surfaces. GNPs were produced via citrate reduction method and the resulting 13nm gold nanospheres were then recoated with an ether-terminated alkanethiol to provide stability in ethanol. Fluorescent enhancement was observed when excess GNPs were added to DTC coated dye-doped SiNPs to form nanoparticle aggregates. Optimization of this system gave a fluorescence brightness enhancement of over 200 fold. Samples that gave fluorescence enhancement were characterized through Transmission Emission Micrograph (TEM) to reveal a pattern of multiple aggregation of GNPs on the dye-doped SiNPs.

Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes.

The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.

Plasmonic detection of Cd2+ ions using surface-enhanced Raman scattering active core–shell nanocomposite

The present study was structured to address development of an efficient devise for sensing of toxic Cd2+ ions at trace level in aqueous media. In order to achieve this objective, the speckled core–shell nanocomposites (NCs) of silica-gold (SiO2@Au) using ~30nm diameter of spherical gold nanoparticles (Au NPs) with 420nm diameter of silica cores was synthesized. Au NPs showed the surface plasmon resonance (SPR) peak at 522nm and spherical core–shell particles at 541nm. Both Au NPs and SiO2@Au solutions were found to be sensitive to Cd2+ ions in aqueous sample. The colour change occurred in presence of SiO2@Au at 0.1ppm (100ppb) of Cd2+ ions whereas 2ppm (2000ppb) concentration of Cd2+ ions was necessary for the colour change in Au NPs solution confirmed that SERS active SiO2@Au core–shell NCs 20 times more sensitive compared to Au NPs. The technique using SiO2@Au NCs is quantitative between 100 and 2000ppb (0.1 to 2ppm) while effective but non-quantitative above upto 10ppm, the maximum concentration studied in present investigation. The detection limit using SiO2@Au NCs is 100ppb (0.1ppm) while Au NPs is able to detect Cd2+ as low as 2000ppb (2ppm). The scanning electron microscopy (SEM) of Au NPs and SiO2@Au particles showed aggregation of Au NPs and SiO2@Au NCs in the presence of Cd2+ ions. The surface enhanced Raman spectroscopy (SERS) was used to compare sensitivities of Au NPs and SiO2@Au towards Cd2+ ions and confirmed that SiO2@Au core–shell NCs is 20 times more sensitive than Au NPs.