Core-shell Strategy Research Articles

Polymer nanocomposites for energy applications

energy production, energy transportation, and storage, has grown rapidly in recent years due to the increase in fossil fuel consumption, environmental issue and global warming. Nanomaterials with different morphologies, properties and structures (e.g. barium titanate nanoparticles, carbon nanotubes, ZnO nanowires) offer superior chemical, mechanical or physical properties compared to their micro meter-scale counterparts. Accordingly, they are potential candidate materials for clean energy applications such as the energy storage, fuel cells, and solar cells (ISBN: 978-0-12-407796-6). The nanomaterials can be incorporated into polymers at low loading levels to form nanocomposites with greater mechanical flexibility, tailored properties and functionalities. These include bipolar plates of fuel cells (DOI: 10.1039/c0ee00689k), high-energy density capacitors, solid polymer electrolytes, and hybrid polymer/nanoparticle solar cells (DOI: 10.1016/ j.jcis.2011.12.016). Nanofillers offer larger interfacial area that allows better interaction with the polymer matrix. Polymers provide structural support and protection for nanomaterials during their industrial service lives. A wide variety of polymers can be selected for making nanocomposites for various fields of energy applications depending on the designed chemical, physical and mechanical properties. The major challenges of achieving high-performance polymer nanocomposites are the attainment of uniform dispersion of nanofillers in the polymer matrix and the manipulation of nanofiller/polymer interfaces. Typical approaches include surface modification of nanofillers via covalent and noncovalent functionalization. Significant research efforts have been devoted by chemists and materials scientist for developing polymer nanocomposites with novel functionalities using improved fabrication techniques recently. For instance, polymeric materials with high dielectric constant (k) and low loss find useful application for making supercapacitors. The !-phase of polyvinylidene fluoride is known to exhibit excellent ferroelectric and piezoelectric effects. This phase can be increased to ~46% by adding 0.5 wt% carbon nanotubes and processed through electrospinning. The process stretches polymer solution uniaxially under an electric potential. It can be further increased over 90% by mechanical drawing (DOI: 10.1021/jp4011026). To reduce dielectric loss, core-shell nanoparticle strategy emerges as a powerful method for preparing high-k nanocomposites especially filled with conducting nanomaterials (DOI: 10.1002/adma.201401310). To fully realize widespread commercial applications of polymer nanocomposites, it is necessary to develop cost-effective processes for the mass production of these materials in large quantities.

Fabrication of Ag/γ-Fe2O3@TiO2hollow magnetic core–shell nanospheres as highly efficient catalysts for the synthesis of β-enaminones

Herein, we describe a method to prepare hollow magnetic mesoporous sphere catalysts (Ag/γ-Fe2O3@meso-TiO2).

Programmed synthesis of Pd@hTiO2hollow core–shell nanospheres as an efficient and reusable catalyst for the reduction of p-nitrophenol

Here, we report a facile synthesis approach to obtain a Pd@hTiO2 hollow mesoporous nanocomposite composed of tiny Pd nanoparticles cores encapsulated within hollow TiO2 mesoporous shells. The core–shell strategy efficiently prevents the aggregation of Pd NPs (Pd nanoparticles) in the high temperature calcination process and the leaching of Pd NPs for the catalytic reaction in a liquid phase. The catalyst was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption, elemental analysis and inductively coupled plasma atomic emission spectrometry (ICP-AES). The synthesized catalyst exhibited high catalytic activity in the reduction of p-nitrophenol with NaBH4 aqueous solution at room temperature. Furthermore, Pd@hTiO2 had an excellent recyclability, evidenced by being extensively reused for eight times without any substantial loss of activity.

Aggregation- and Leaching-Resistant, Reusable, and Multifunctional Pd@CeO2 as a Robust Nanocatalyst Achieved by a Hollow Core–Shell Strategy

To develop various strategies to prevent the aggregation, sintering, or leaching of noble metal nanoparticles (NPs) represents a crucial issue for efficient synthesis and utilization of supported noble metal NPs with highly active and stable catalytic performance. Here, we report a facile synthesis approach to obtain a Pd@hCeO2 hollow core–shell nanocomposite that is composed of tiny Pd nanoparticles cores encapsulated within CeO2 hollow shells. The core–shell strategy efficiently prevents the aggregation of Pd NPs in the high temperature calcination process and the leaching of Pd NPs for the catalytic reaction in a liquid phase. This anti-aggregation and anti-leaching behavior is not able to be achieved for traditional supported Pd/CeO2 catalyst. Such a Pd@hCeO2 composite can serve as an efficient multifunctional nanocatalyst in both heterogeneous thermocatalytic and photocatalytic selective reduction of aromatic nitro compounds in water under ambient conditions. Each component, namely Pd metal core or s...

Core–shell conjugated microporous polymers: a new strategy for exploring color-tunable and -controllable light emissions

A core-shell strategy is demonstrated for designing a conjugated microporous polymer that allows the tuning of light emission over a wide wavelength range in a controlled manner. The polymers not only emit efficiently with an eight-fold enhanced luminescence but also sustain light emissions, irrespective of solvent and state.

Iodine‐Doped‐Poly(3,4‐Ethylenedioxythiophene)‐Modified Si Nanowire 1D Core‐Shell Arrays as an Efficient Photocatalyst for Solar Hydrogen Generation

A new 1D core-shell strategy is demonstrated for a hydrogen-generation photo-electrochemical cell (PEC). This Si/iodine-doped poly(3,4-ethylenedioxythiophene) (PEDOT) 1D nanocable array shows an encouraging solar-to-chemical energy-conversion efficiency. Coating with iodine-doped PEDOT can effectively enhance the photocatalytic efficiency and stability of SiNW arrays. The PEC model proposed shows a potentially promising structure for H(2) production using solar energy.

Core–Shell Strategy Leading to High Reversible Hydrogen Storage Capacity for NaBH4

Owing to its high storage capacity (10.8 mass %), sodium borohydride (NaBH(4)) is a promising hydrogen storage material. However, the temperature for hydrogen release is high (>500 °C), and reversibility of the release is unachievable under reasonable conditions. Herein, we demonstrate the potential of a novel strategy leading to high and stable hydrogen absorption/desorption cycling for NaBH(4) under mild pressure conditions (4 MPa). By an antisolvent precipitation method, the size of NaBH(4) particles was restricted to a few nanometers (<30 nm), resulting in a decrease of the melting point and an initial release of hydrogen at 400 °C. Further encapsulation of these nanoparticles upon reaction of nickel chloride at their surface allowed the synthesis of a core--shell nanostructure, NaBH(4)@Ni, and this provided a route for (a) the effective nanoconfinement of the melted NaBH(4) core and its dehydrogenation products, and (b) reversibility and fast kinetics owing to short diffusion lengths, the unstable nature of nickel borohydride, and possible modification of reaction paths. Hence at 350 °C, a reversible and steady hydrogen capacity of 5 mass % was achieved for NaBH(4)@Ni; 80% of the hydrogen could be desorbed or absorbed in less than 60 min, and full capacity was reached within 5 h. To the best of our knowledge, this is the first time that such performances have been achieved with NaBH(4). This demonstrates the potential of the strategy in leading to major advancements in the design of effective hydrogen storage materials from pristine borohydrides.

Hydration forces as a tool for the optimization of core–shell nanoparticle vectors for cancer gene therapy

The high cationic charge density of the polymers used in synthetic gene therapy vectors makes these systems toxic and induces non-specific interactions with blood components. Covalent modification of the positively charged terminal amines with hydroxyl, acetyl, poly(ethylene glycol) or methyl groups reduces not only the toxicity but also the condensation capacity, leading to lower transfection efficiency and changes in nanoparticle biodistribution. The colloidal properties of such nanoparticulate systems can be optimised based on the hydration forces active on their surface. Specifically, a core–shell strategy was used to optimise hydration forces and stabilise the vector system by separating vector functions into those provided by the core, where polypropylenimine dendrimers (DAB-Am16) mediate complexation and transfection functionality, and those linked to the shell, where a hyaluronic acid (HA) coat affords colloidal stability and systemic targeting. This core–shell vector allows a 6-fold reduction in the amount of cationic polymer used to form the nucleic acid core complex, compared to conventional nanoparticles. The HA shell was optimised in terms of thickness and density by maximising short-range hydration forces under physiological conditions. The resulting vector particles also allow specific targeting and transfection of CD44 positive cancer cells. The HA coated particles show reduced toxicity (2.5-fold) and increased transfection (8-fold) compared to the conventional dendriplex. In conclusion, we demonstrate a strategy for independent optimisation of vector core and shell functionality which allows specific targeting and increases the therapeutic index of the non-viral vector system 20-fold.

Propellant-based inhalers for the non-invasive delivery of genes via oral inhalation

In this work we describe the development of a propellant-based, portable oral inhalation platform for the pulmonary delivery of genes. A core–shell strategy is utilized to efficiently disperse cationic-polymer-DNA nanoparticles in hydrofluoroalkane propellants, and to generate aerosols from the corresponding pressurized metered-dose inhaler formulations (pMDIs) that have excellent aerosol characteristics, suitable for deep lung deposition. The engineered polyplexes and core–shell structures were fully characterized, and their ability to transfect model lung alveolar epithelium cells in vitro was demonstrated. We also show that the propellant does not affect the biological activity of the plasmid DNA, and that the core–shell formulations have no in vitro cytotoxicity. The relevance of this work stems from the fact that pMDIs are the least expensive and most widely used portable oral inhalation devices, and are thus promising platforms for targeting genes to the lungs for the treatment of medically relevant diseases including asthma, cystic fibrosis, chronic obstructive pulmonary disease, and lung cancer.

A Core-Shell Strategy for Constructing a Single-Molecule Junction

Understanding the effects of intermolecular interactions on the charge-transport properties of metal/molecule/metal junctions is an important step towards using individual molecules as building blocks for electronic devices. This work reports a systematic electron-transport investigation on a series of "core-shell"-structured oligo(phenylene ethynylene) (Gn-OPE) molecular wires. By using dendrimers of different generations as insulating "shells", the intermolecular π-π interactions between the OPE "cores" can be precisely controlled in single-component monolayers. Three techniques are used to evaluate the electron-transport properties of the Au/Gn-OPE/Au molecular junctions, including crossed-wire junction, scanning tunneling spectroscopy (STS), and scanning tunneling microscope (STM) break-junction techniques. The STM break-junction measurement reveals that the electron-transport pathways are strongly affected by the size of the side groups. When the side groups are small, electron transport could occur through three pathways, including through single-molecule junctions, double-molecule junctions, and molecular bridges between adjacent molecules formed by aromatic π-π coupling. The dendrimer shells effectively prohibit the π-π coupling effect, but at the same time, very large dendrimer side groups may hinder the formation of Au-S bonds. A first-generation dendrimer acts as an optimal shell that only allows electron transport through the single-molecule junction pathway, and forbids the other undesired pathways. It is demonstrated that the dendrimer-based core-shell strategy allows the single-molecule conductance to be probed in a homogenous monolayer without the influence of intermolecular π-π interactions.

Monodisperse crystalline semiconducting ZnS hollow microspheres by a new versatile core-shell strategy

Monodisperse crystalline ZnS hollow microspheres have been synthesized by employing an ethylenediamino-functionalized ordered mesoporous material which acts as a synthesis-directing agent. This new strategy implies the use of surface-modified ordered mesoporous silica spheres that chelate zinc ions and precisely orientate the ZnS shell formation at the entry to the mesochannels of the silica spheres. The silica spherical cores can be removed by chemical etching, leading to the fabrication of homogeneous crystalline ZnS hollow microspheres of around 1–2 µm in diameter. This versatile method for the preparation of crystalline hollow microspheres can be applied to the fabrication of any shape and any chemical composition of hollow structures. These new advanced materials were characterized by (FE-)SEM, TEM, HRTEM and SAED.

Conductive Polymer/Transition Metal Oxide Hybrid Materials for Lithium Batteries

AbstractOrganic-inorganic hybrid materials were synthesized for use of lithium battery electrode by two strategies: 1) core-shell strategy for tri-dimensional transition metal oxide and 2) intercalation strategy for bi-dimensional (lamellar) transition metal oxide. We choose conductive polymers as an organic component for high electric conductivity and 3d-transition metal oxides as an inorganic counterpart for large capacity and processibility. Polypyrrole/maghemite and poly(3,4-ethylenedioxythiophene) (PEDOT)/vanadium pentoxide hybrids will be presented and compared with their pristine materials for core-shell and intercalation strategies, respectively. Polypyrrole/maghemite showed an enhanced electrochemical reversibility and capacity up to ∼270 mAh/g in the potential range between 1.3 and 4.3 V vs. Li at 8 mA/g. PEDOT/vanadium pentoxide also exhibited improved reversibility and capacity up to ∼330 mAh/g at 15 mA/g between 2.0 ∼ 4.4 V vs. Li on the second discharge. XRD, IR, electron microscopy, XPS and Xray absorption spectroscopy were used to characterize the samples, and to examine oxidation state of the transition metals, doping character of the polymer and the nature of interaction between the polymer and the transition metal oxides.

Designing studies to investigate client-treatment matching.

The process of designing studies of client-treatment matching involves a number of methodological complexities. Besides the large number of potential client characteristics and a range of possible outcome variables, a variety of treatment attributes can be matched including modality, intensity, duration, format, setting, therapist and goal. Hindsight matching designs (which can include hypothesis testing) examine interactions between client characteristics and treatments to which they were not intentionally matched. Foresight matching designs involve a prospective experimental test of a matching hypothesis, comparing the outcomes of cases matched by specific decision rules with other cases not so matched. Under certain conditions, these hindsight and foresight matching designs are logically equivalent. Mathematical modeling of clinical judgment offers yet another promising avenue for future studies of matching schemas. Glaser's core-shell strategy provides a practical model for implementing clinical systems and research on matching within ongoing services.