Inert Shell Research Articles

In Situ Confined Synthesis of Ti4O7 Supported Platinum Electrocatalysts with Enhanced Activity and Stability for the Oxygen Reduction Reaction

AbstractHerein, an in situ confined synthesis of highly conductive titanium oxide supported Pt catalysts is successfully employed. The method involves crystallization and formation of TiO2 particles inside the inert silica shell introduced by using hexamethyldisilazane (HMDS). The conductivity of titania is found to be greatly enhanced by increased annealing temperature, whereas the inevitable decrease in the specific surface area was effectively inhibited by the confining silica shell derived from HMDS. The optimal catalyst (20Pt 850 FHST), exhibited better oxygen reduction reaction (ORR) activity with a maximum current density of 0.049 mA cm−2 at 0.9 V (vs. normal hydrogen electrode (NHE)) and an onset potential of 0.86 V (vs. NHE). The prolonged cycling test demonstrated superior stability compared with Pt/C (JM 20). Moreover, X‐ray absorption spectroscopy asserts that the increased electron population in the Pt 5d orbital, emanating from the strong metal–support interaction, improves the electrochemical performance in the ORR. The in situ HMDS‐assisted synthesis can also be extended to other oxide‐supported catalytic systems.

Effect of Surface Functionalization on Structural and Optical Properties of Luminescent LaF₃:Sm Nanoparticles.

Samarium (Sm3+)-doped LaF3 nanoparticles (NPs) subsequently encapsulated with inert crystalline LaF3 and amorphous silica layers were prepared by polyol and sol-gel chemical process, respectively. These surface modified core/shell/SiO2-nanostructured were characterized by X-ray diffraction (XRD), FE-transmission electron microscopy (TEM), thermal analysis, FTIR, UV/Vis absorption, bang gap energy and photoluminescence spectroscopy. The FETEM, EDX and FTIR spectral studies clearly revealed that the silica layer has been formed surrounding the core-NPs. Comparative spectral analysis indicated that core/shell/SiO2-NPs revealed high solubility in aqueous and non-aqueous solvents. The decrease in band gap energy after surface growth of an inert LaF3 and silica shells is directly correlated to the increase in grain size. On comparing the emission intensity, a significant enhancement was observed after inert layer coating, whereas, it suppress after silica encapsulation due to the non-radiative transitions. The increase luminescent intensity after inert shell growth indicates that a significant amount of non-radiative centers existing on the surface of core/shell nanoparticles can be eliminated by the shielding effect of LaF3 shells. These observed results indicate that the as-prepared core/shell/SiO2-NPs could be highly useful in broad photonic based applications such as optical sensor/optical bio-probe and light emitting diode.

Preparation and upconversion properties of rare earth doped core-shell Y(OH)3 and β-NaYF4 hybrid nanorods

Er3+/Yb3+-doped Y(OH)3@β-NaYF4 core-shell nanorods are synthesized through in situ ion exchange reaction using Y(OH)3 nanorods as templates. Further, inert shells of β-NaYF4 without activated dopants are coated by a facile hydrothermal method. Upconversion intensity increases dramatically by ion exchange reaction, and it can be further enhanced through coating inert shells. The maximal enhanced factor of inert coating reaches 6.58. On the basis of the structural tests and spectral data, formation mechanisms of the core-shell nanorods are discussed, as well as their upconversion properties.

Inhibition of CdS photocorrosion by Al2O3 shell for highly stable photocatalytic overall water splitting under visible light irradiation

Efficiency and stability are the two key points for CdS photocatalyst because its application has been seriously restricted owing to serious photocorrosion issue and the recombination of photo-induced charge pairs. In this paper, CdS nanoparticles (NPs) were surface-modified by chemical inert Al2O3 shell. This modification could prevent nascent formed oxygen induced photo-corrosion and enhance the photo-stability of CdS during water splitting significantly. In addition, it was found that such a shell could enhance efficient separation of photo-induced charge pairs. Besides, with the assistance of artificial gill of removing nascent formed O2 from water, Pt/CdS@Al2O3 photocatalyst can achieve overall water splitting under visible light irradiation. The rate of H2 evolution increased 126 times over Pt/CdS@Al2O3 composite compared with pure CdS NPs, and the stability was maintained in several cycles of reaction without any decrease. The measurement of concentration of Cd2+ in solution after long cycles by ICP method confirmed this anti-photo-corrosion property of Al2O3 shell on CdS. This work provides a new potential way to design and fabricate more stable and efficient CdS-based nanocomposite photocatalysts for versatile solar energy conversion.

Preserving the inflated structure of lyophilized sporopollenin exine capsules with polyethylene glycol osmolyte

Extracted from natural pollen grains, sporopollenin exine capsules (SECs) are robust, chemically inert biopolymer shells that posess highly uniform size and shape characteristics and that can be utilized as hollow microcapsules for drug delivery applications. However, it is challenging to extract fully functional SECs from many pollen species because pollen grains often collapse, causing the loss of architectural features, loading volume, and bulk uniformity. Herein, we demonstrate that polyethylene glycol (PEG) osmolyte solutions can help preserve the native architectural features of extracted SECs, yielding inflated microcapsules of high uniformity that persist even after subsequent lyophilization. Optimal conditions were first identified to extract SECs from cattail (Typhae angustfolia) pollen via phosphoric acid processing after which successful protein removal was confirmed by elemental (CHN), mass spectrometry (MALDI-TOF), and confocal laser canning microscopy (CLSM) analyses. The shape of SECs was then assessed by scanning electron microscopy (SEM) and dynamic image particle analysis (DIPA). While acid-processed SECs experienced high degrees of structural collapse, incubation in 2.5% or higher PEG solutions significantly improved preservation of spherical SEC shape by inducing inflation within the microcapsules. A theoretical model of PEG-induced osmotic pressure effects was used to interpret the experimental data, and the results show excellent agreement with the known mechanical properties of pollen exine walls. Taken together, these findings demonstrate that PEG osmolyte is a useful additive for preserving particle shape in lyophilized SEC formulations, opening the door to broadly applicable strategies for stabilizing the structure of hollow microcapsules.

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

Core@shell design represents an important class of architectures because of its capability not only to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend toward the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDXS) and X-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe the local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth c...

Boosting the down-shifting luminescence of rare-earth nanocrystals for biological imaging beyond 1500\u2009nm

In vivo fluorescence imaging in the near-infrared region between 1500–1700 nm (NIR-IIb window) affords high spatial resolution, deep-tissue penetration, and diminished auto-fluorescence due to the suppressed scattering of long-wavelength photons and large fluorophore Stokes shifts. However, very few NIR-IIb fluorescent probes exist currently. Here, we report the synthesis of a down-conversion luminescent rare-earth nanocrystal with cerium doping (Er/Ce co-doped NaYbF4 nanocrystal core with an inert NaYF4 shell). Ce doping is found to suppress the up-conversion pathway while boosting down-conversion by ~9-fold to produce bright 1550 nm luminescence under 980 nm excitation. Optimization of the inert shell coating surrounding the core and hydrophilic surface functionalization minimize the luminescence quenching effect by water. The resulting biocompatible, bright 1550 nm emitting nanoparticles enable fast in vivo imaging of blood vasculature in the mouse brain and hindlimb in the NIR-IIb window with short exposure time of 20 ms for rare-earth based probes.

Controlled Isotropic and Anisotropic Shell Growth in β-NaLnF4 Nanocrystals Induced by Precursor Injection Rate

Precise morphology and composition control is vital for designing multifunctional lanthanide-doped core/shell nanocrystals. Herein, we report controlled isotropic and anisotropic shell growth techniques in hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals by exploiting the kinetics of the shell growth. A drastic change of the shell morphology was observed by changing the injection rate of the shell precursors while keeping all other reaction conditions constant. We obtained isotropic shell growth for fast sequential injection and a preferred growth of the shell layers along the crystal's c-axis [001] for slow dropwise injection. Using this slow shell growth technique, we have grown rod-like shells around different almost spherical core nanocrystals. Bright and efficient upconversion was measured for both isotropic and rod-like shells around β-NaYF4 nanocrystals doped with Yb3+/Er3+ and Yb3+/Tm3+. Photoluminescence upconversion quantum yield and lifetime measurements reveal the high quality of the core/shell nanocrystal. Furthermore, multishell rod-like nanostructures have been prepared with optically active cores and tips separated by an inert intermediate shell layer. The controlled anisotropic shell growth allows the design of new core/multishell nanostructures and enables independent investigations of the chemistry and physics of different nanocrystal facets.

Features of the terahertz spectra of iron oxide nanoparticles in a silicon dioxide shell and of iron oxide and hydroxide nanoparticles

New methods have been developed for noninvasive monitoring of pathological processes in a living organism by means of terahertz spectroscopy and visualization using contrast agents based on magnetic nanoparticles. The nanoparticles must possess good magnetic characteristics, must be nontoxic and stable against aggregation, and must exhibit chemical stability; therefore, they are enclosed in a biologically inert shell. This paper discusses the spectral features of iron oxide nanoparticles in a biologically inert shell consisting of silicon dioxide and nanoparticles of iron oxide and hydroxide in the terahertz frequency range. It is shown that the crystalline phase of iron oxide can be identified for both types of nanoparticles by means of terahertz spectroscopy.

Structural synergy in a core-shell spin crossover nanoparticle investigated by an electroelastic model

Understanding how surrounding environments act on the functional properties of switchable nano-objects across extended and multiple length scales is of growing interest in many areas of material science. Here, we examine in details, using a microscopic model, the interplay between the structural properties of an inert shell and a spin-active spin-crossover (SCO) core, composed of atoms which can switch thermally between the low-spin (LS) and high-spin (HS) states, a transition which is accompanied with a volume expansion. To come closer to realistic experimental data, we considered a shell having the lattice parameter of the HS state. Intensive Monte Carlo simulations, running on the spin states and atomic positions, are performed on the core-shell spin-crossover nanoparticle using an electroelastic model based on a compressible 2D lattice. A detailed analysis of the effect of the shell's size and rigidity on the magnetostructural properties of the core allows us to address the following issues: (i) the heteroelastic properties of the lattice induce a spatially inhomogeneous pressure (negative in the shell and positive in the core) which strongly distorts the lattice when the core is in the LS state, creating a visible spatial deflection of the shell/core interface; (ii) the thermally-induced first-order SCO transition of the core is significantly affected by the increase of the shell size, which lowers the transition temperature and reduces the thermal hysteresis width; (iii) the shell's rigidity dependence of the thermal hysteresis of the nanoparticle exhibited a resonance behavior when the shell's rigidity equals that of the core, a feature that is analyzed on the basis of acoustic impedance mismatch between the core and the shell. All these outcomes reflect the crucial influence of the surrounding environment on the structural properties of the nanoparticle and provide potentialities in the control of the bistability and cooperativity of the SCO nanoparticles by acting on their shell's rigidity.

Osmotic Pressure Triggered Rapid Release of Encapsulated Enzymes with Enhanced Activity

In this study, a single‐step microfluidic approach is reported for encapsulation of enzymes within microcapsules with ultrathin polymeric shell for controlled release triggered by an osmotic shock. Using a glass capillary microfluidic device, monodisperse water‐in‐oil‐in‐water double emulsion droplets are fabricated with enzymes in the core and an ultrathin middle oil layer that solidifies to produce a consolidated inert polymeric shell with a thickness of a few tens to hundreds of nanometers. Through careful design of microcapsule membranes, a high percentage of cargo release, over 90%, is achieved, which is triggered by osmotic shock when using poly(methyl methacrylate) as the shell material. Moreover, it is demonstrated that compared to free enzymes, the encapsulated enzyme activity is maintained well for as long as 47 days at room temperature. This study not only extends industrial applications of enzymes, but also offers new opportunities for encapsulation of a wide range of sensitive molecules and biomolecules that can be controllably released upon applying osmotic shock.

Optimal Sensitizer Concentration in Single Upconversion Nanocrystals.

Each single upconversion nanocrystal (UCNC) usually contains thousands of photon sensitizers and hundreds of photon activators to up-convert near-infrared photons into visible and ultraviolet emissions. Though in principle further increasing the sensitizers' concentration will enhance the absorption efficiency to produce brighter nanocrystals, typically 20% of Yb3+ ions has been used to avoid the so-called "concentration quenching" effect. Here we report that the concentration quenching effect does not limit the sensitizer concentration and NaYbF4 is the most bright host matrix. Surface quenching and the large size of NaYbF4 nanocrystals are the only factors limiting this optimal concentration. Therefore, we further designed sandwich nanostructures of NaYbF4 between a small template core to allow an epitaxial growth of the size-tunable NaYbF4 shell enclosed by an inert shell to minimize surface quenching. As a result, the suspension containing 25.2 nm sandwich structure UCNCs is 1.85 times brighter than the homogeneously doped ones, and the brightness of each single 25.2 nm heterogeneous UCNC is enhanced by nearly 3 times compared to the NaYF4: 20% Yb3+, 4% Tm3+ UCNCs in similar sizes. Particularly, the blue emission intensities of the UCNCs with the sandwich structure in the size of 13.6 and 25.2 nm are 1.36 times and 3.78 times higher than that of the monolithic UCNCs in the similar sizes. Maximizing the sensitizer concentration will accelerate the development of brighter and smaller UCNCs as more efficient biomolecule probes or photon energy converters.

Preparation of concave magnetoplasmonic core-shell supraparticles of gold-coated iron oxide via ion-reducible layer-by-layer method for surface enhanced Raman scattering

Preparation of suprastructure assemblies with unique colloidal and optical properties remains challenging. Non-uniform covering of magnetic nanoparticles (NPs) with an external inert Au shell has been attempted to protect the magnetic core against oxidation as well as to produce multifunctional supraparticles (SPs) possessing respective optical and magnetic properties. In this study, a concave Au NP coating was deposited on magnetic nanoparticles (MNPs) with precise control of the shell thickness and roughness through a layer-by-layer (LbL) assisted ionic reduction method termed ion-reducible LbL (IR-LbL) method. Surface enhanced Raman spectra were obtained using graphene quantum dots (GQDs) on the magnetically aligned structure of the prepared core-shell SPs. It is probable that this synthesis method and the generated SPs are essential for characterizing the merge of electronics and magnetism in the nano-regime and may be applicable for further electronics, magnetic storage, and biomedical applications.

Size Control of Silver-Core/Silica-Shell Nanoparticles Fabricated by Laser-Ablation-Assisted Chemical Reduction.

Aqueous colloidal silver nanoparticles have substantial potential in biological application as markers and antibacterial agents and in surface-enhanced Raman spectroscopy applications. A simple method of fabrication and encapsulation into an inert shell is of great importance today to make their use ubiquitous. Here we show that colloids of silver-core/silica-shell nanoparticles can be easily fabricated by a laser-ablation-assisted chemical reduction method and their sizes can be tuned in the range of 2.5 to 6.3 nm by simply choosing a proper water-ethanol proportion. The produced silver nanoparticles possess a porous amorphous silica shell that increases the inertness and stability of colloids, which decreases their toxicity compared with those without silica. The presence of a thin 2 to 3 nm silica shell was proved by EDX mapping. The small sizes of nanoparticles achieved by this method were analyzed using optical techniques, and they show typical photoluminescence in the UV-vis range that shifts toward higher energies with decreasing size.

Direct Evidence for Coupled Surface and Concentration Quenching Dynamics in Lanthanide-Doped Nanocrystals

Luminescence quenching at high dopant concentrations generally limits the dopant concentration to less than 1-5 mol% in lanthanide-doped materials, and this remains a major obstacle in designing materials with enhanced efficiency/brightness. In this work, we provide direct evidence that the major quenching process at high dopant concentrations is the energy migration to the surface (i.e., surface quenching) as opposed to the common misconception of cross-relaxation between dopant ions. We show that after an inert epitaxial shell growth, erbium (Er3+) concentrations as high as 100 mol% in NaY(Er)F4/NaLuF4 core/shell nanocrystals enhance the emission intensity of both upconversion and downshifted luminescence across different excitation wavelengths (980, 800, and 658 nm), with negligible concentration quenching effects. Our results highlight the strong coupling of concentration and surface quenching effects in colloidal lanthanide-doped nanocrystals, and that inert epitaxial shell growth can overcome concentration quenching. These fundamental insights into the photophysical processes in heavily doped nanocrystals will give rise to enhanced properties not previously thought possible with compositions optimized in bulk.

Alleviating the emitter concentration effect on upconversion nanoparticles via an inert shell

An inert shell has been proved to alleviate the concentration effect by not only considerably improving the upconversion intensity, but also greatly preserving the integrity of the upconversion profile, when the emitter concentration was enhanced from 2 mol% to 20 mol%.

Heterogeneously Nd3+ doped single nanoparticles for NIR-induced heat conversion, luminescence, and thermometry.

The current frontier in nanomaterials engineering is to intentionally design and fabricate heterogeneous nanoparticles with desirable morphology and composition, and to integrate multiple functionalities through highly controlled epitaxial growth. Here we show that heterogeneous doping of Nd3+ ions following a core-shell design already allows three optical functions, namely efficient (η > 72%) light-to-heat conversion, bright NIR emission, and sensitive (SR > 0.1% K-1) localized temperature quantification, to be built within a single ca. 25 nm nanoparticle. Importantly, all these optical functions operate within the transparent biological window of the NIR spectral region (λexc ∼ 800 nm, λemi ∼ 860 nm), in which light scattering and absorption by tissues and water are minimal. We find NaNdF4 as a core is efficient in absorbing and converting 808 nm light to heat, while NaYF4:1%Nd3+ as a shell is a temperature sensor based on the ratio-metric luminescence reading but an intermediate inert spacer shell, e.g. NaYF4, is necessary to insulate the heat convertor and thermometer by preventing the possible Nd-Nd energy relaxation. Moreover, we notice that while temperature sensitivity and luminescence intensity are optically stable, increased excitation intensity to generate heat above room temperature may saturate the sensing capacity of temperature feedback. We therefore propose a dual beam photoexcitation scheme as a solution for possible light-induced hyperthermia treatment.

Definition of ingredient composition of caramel mass in order to increase shelf life

According to the Principles of State Policy of the Russian Federation in the field of healthy nutrition for the period up to 2020 we set the task of expanding the range of specialized food for various population groups, in particular, enriched with vitamins and minerals. The range of sugar confectionery is constantly updated and expanded, increasing the scale of production. Note particularly the increase in consumer demand for bakery products with improved organoleptic properties, increased food and reduced energy value. Given the popularity of sugary confectionery products to the public, subject to foodstuffs enrichment of biologically active components can serve as caramel. Of particular interest are sugar confectionery suckable characterized pleasant taste and increased comfort of use, combined with the speed and completeness of release of active substances absorption. Earlier studies have shown that the molecule biologically active substances surrounded by sugar “glass”, as it were covered by an inert gas-tight shell, and are resistant chemical changes. Important advantages of this group of products are relatively large periods of storage and good portability, which expands the geographical possibilities of its use. However, the use of sucrose as a main flavor component and preservative, is an unfavorable factor for a healthy diet as a whole, and particularly for certain groups of the population for health. Therefore, when designing articles of caramel syrup containing as a sugar substitute, the authors suggested the use of polyols in combination with a sweetener vegetable isomalt and stevioside.

Impact of LaF3 and silica shell formation on the crystal, optical and photo-luminescence properties of LaF3:Ce/Tb nanoparticles

A new LaF3:Ce/Tb nanoparticle designed via a polyol process shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of an inert LaF3 shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable in luminescence biolabeling, optical bio-probes, etc.

Employing shells to eliminate concentration quenching in photonic upconversion nanostructure.

It is generally accepted that a lanthanide ions based upconversion material follows an activator low doping strategy (normally <3 mol%), because of the restriction of the harmful concentration quenching effect. Here, we demonstrate that this limitation can be broken in nanostructures. Simply by using an inert shell coating strategy, the concentration quenching effect for the activator (Er3+) could be eliminated and highly efficient upconversion luminescence realized in the activator fully doped nanostructure, e.g. NaErF4@NaYF4. More importantly, this novel nanostructure achieves some long-cherished desires, such as multiple-band co-excitation (∼800 nm, ∼980 nm and ∼1530 nm) and monochromic red emission. Proof-of-concept experiments are presented of the potential benefit of this structure in solar cells and anti-counterfeiting. This nanostructure offers new possibilities in realizing high upconversion emission and novel functionalities of lanthanide based nanomaterials.