Chao Yan

Continuously prepared highly conductive and stretchable SWNT/MWNT synergistically composited electrospun thermoplastic polyurethane yarns for wearable sensing

Highly conductive and stretchable yarns have attracted increasing attention due to their potential applications in wearable electronics. The integration of conductive yarns with large stretching capability renders the composite yarns with new intriguing functions, such as monitoring human body motion and health. However, simultaneously endowing the yarns with high conductivity and stretchability using an easily scalable approach is still a challenge. Here, highly conductive and stretchable yarns based on electrospun thermoplastic polyurethane (TPU) fiber yarns successively decorated with multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) were prepared by a combined electrospinning, ultrasonication adsorbing, and bobbin winder technique. The improved thermal stability of the SWNT/MWNT/TPU yarn (SMTY) indicated strong interfacial interactions between the CNTs and electrospun TPU fibers. The synergism between the successively decorated SWNTs and MWNTs significantly enhanced the conductivity of the TPU yarns (up to 13 S cm−1). The as-fabricated yarns can be easily integrated into strain sensors and exhibit high stretchability with large workable strain range (100%) and good cyclic stability (2000 cycles). Moreover, such yarn can be attached to the human body or knitted into textiles to monitor joint motion, showing promising potential for wearable electronics, such as wearable strain sensors.

Two-dimensional nanosheets for electrocatalysis in energy generation and conversion

The 2D structures and tunable properties of nanosheets make them intriguing catalytic materials. This research area is being driven by a need to replace scarce noble metal-based catalysts in energy technologies. We describe recent advances in nanosheet electrocatalysis of oxygen reduction, oxygen evolution, hydrogen evolution, and CO2 reduction reactions. We find at this early stage of development that nanosheet catalysis has surpassed classical noble metal catalysts in several of these applications and is showing high potential in others. CO2 reduction to methane is now catalyzed best by metal-free carbon nanosheets. These trends will likely transform heterogeneous catalysis.

Melt crystallization and crystal transition of poly(butylene adipate) revealed by infrared spectroscopy.

The structure evolution of poly(butylene adipate) (PBA) during isothermal melt crystallization and phase transition processes is investigated by Fourier transform infrared spectroscopy (FTIR). Detailed IR spectra analysis and band assignment are performed to disclose the bands sensitive to the alpha-form crystalline order of PBA. It is revealed from the in situ IR study that the functionalities within PBA chains alter simultaneously during the melt crystallization process. From the analysis of the spectral changes, it is found that band shifts take place during the phase transition process of PBA from its metastable beta-form crystal to the stable alpha-form. Notable band shifts in the 1300-1100 cm(-1) region indicate that the twist of polymer chains in the alpha-form is located in the C-O-C and C-O linkages. Moreover, the results elucidated that the different segments of molecular chains tune up their conformations synchronously during the beta to alpha crystal transition process of PBA. It is suggested that the betaalpha phase transition process proceeds randomly throughout the solid at a constant rate.

Mechanical and environmental stability of polymer thin-film-coated graphene.

A uniform polymer thin layer of controllable thickness was bar-coated onto a chemical vapor deposition (CVD) grown monolayer graphene surface. The effects of this coating layer on the optical, electric, and tribological properties were then investigated. The thin polymer coating layer did not reduce the optical transmittance of the graphene films. The variation in the sheet resistance of the graphene films after the coating depended on the interaction between polymer and graphene. The top coating layer can maintain the high conductivity of chemical doped graphene films under long-term ambient conditions compared with uncovered doped samples. Friction tests demonstrated that the polymer coating layer can enhance both the friction force and the coefficient of friction of the graphene films and protect the graphene against damage in the repeated sliding processes.

An overview of metamaterials and their achievements in wireless power transfer

Metamaterials have been deployed for a wide range of fields including invisible cloak, superlens, electromagnetic wave absorption and magnetic resonance imaging, owing to their peculiar electromagnetic properties. However, few investigations on metamaterials were focused on wireless power transfer (WPT). WPT is the transmission of electrical energy from a power source to an electrical load without conductors like wires or cables. Metamaterials can enhance the transfer efficiency and enlarge the transfer distance due to their ability of focusing magnetic flux, which opens up a novel approach to promoting the development and application of WPT. This review paper aims to provide an overview of the fabrications, exotic properties, and their applications especially in the WPT field. Meanwhile, the perspective and future challenges of metamaterials and WPT are proposed.

Novel TiO₂-Pt@SiO₂ nanocomposites with high photocatalytic activity.

This article reports a facile and controllable two-step method to construct TiO(2)-Pt@SiO(2) nanocomposites. TiO(2) nanoparticles (NPs), with small size and high surface energy, were synthesized by a solvothermal reaction process. The TiO(2)-Pt@SiO(2) nanocomposites were fabricated by a reverse micro-emulsion method. SiO(2) shell coated NPs were adopted for further photocatalytic reaction. Because of their small size and high surface energy, TiO(2)@SiO(2) and TiO(2)-Pt@SiO(2) nanocomposites show higher photocatalytic activity than commercial Degussa P25. Compared with TiO(2)@SiO(2), TiO(2)-Pt@SiO(2)nanocomposites have improved photocatalytic activity due to the Pt induced spatial separation of electrons and holes. The silica shells not only maintain the structure of the nanocomposites but also prevent their aggregation during the photocatalytic reactions, which is highly important for the good durability of the photocatalyst. This strategy is simple, albeit efficient, and can be extended to the synthesis of other composites of noble metals. It has opened a new window for the construction of hetero-nanocomposites with high activity and durability, which would serve as excellent models in catalytic systems of both theoretical and practical interest.

Synthesis and applications of graphene electrodes

The near explosion of attention given to graphene has attracted many to its research field. As new studies and findings about graphene synthesis, properties, electronic quality control, and pos sible applications simultaneous burgeon in the scientific community, it is quite hard to grasp the breadth of graphene history. At this stage, graphene’s many fascinating qualities have been amply reported and its potential for various electronic applications are increasing, pulling in ever more newcomers to the field of graphene. Thus it has become important as a community to have an equal understanding of how this material was discovered, why it is stirring up the scientific com munity and what sort of progress has been made and for what purposes. Since the first discovery, the hype has expediently led to near accomplishment of industrial-sized production of graphene. This review covers the progress and development of synthesis and transfer techniques with an emphasis on the most recent technique of chemical vapor deposition, and explores the potential applications of graphene that are made possible with the improved synthesis and transfer.

Silica microsphere templated self-assembly of a three-dimensional carbon network with stable radio-frequency negative permittivity and low dielectric loss

Percolative composites always suffer from their unstable and filler-loading dependent microstructures and negative electromagnetic parameters. Here, stable negative permittivity is achieved by in situ constructing a three-dimensional carbon network in the silica spherical matrix after a self-assembly and pyrolysis process. An electrical percolation phenomenon appears with the formation of a carbon network. Once the carbon network is formed, further increasing carbon loadings will only influence the porosity rather than the connectivity due to the nature of the porous carbon itself. Hence, the microstructure and plasma-like negative permittivity are not sensitive to carbon loading, leading to a negligible carbon loading dependent permittivity behavior. Moreover, negative permittivity with small values (−100 < e′ < 0), beneficial for matching with permeability, was effectively adjusted by changing the carbonization temperature. The carbon composites with negative permittivity showed an extremely low dielectric loss (tanu2006δ = 1–7) compared with metal composites (usually tanu2006δ = 10–100). This work provides a convenient means to obtain stable negative permittivity properties. The carbon composites can be regarded as a promising candidate for metamaterials and will facilitate the applications of materials with negative electromagnetic parameters.

Controlled pyrolysis of MIL-88A to Fe2O3@C nanocomposites with varied morphologies and phases for advanced lithium storage

Carbon-coated α-Fe2O3 hollow nanospindles and varied-phase Fe2O3@C (γ-Fe2O3@C, αγ-Fe2O3@C, and α-Fe2O3@C) nanobipyramids were prepared by controlling pyrolysis of MIL-88A nanobipyramids at different temperatures and time in air or in nitrogen. The corresponding pyrolysis stage in air, followed by a self-oxidation/reduction-like mechanism in nitrogen was proposed for the first time. When used as anodes for lithium-ion batteries (LIBs), the α-Fe2O3 hollow nanospindles with carbon-coated shells can not only facilitate the contact between the electrode and electrolyte and accommodate mechanical stress and volume change over multiple cycles but also enhance the electronic conductivity of the electrode materials. Benefiting from the unique carbon-coated hollow structure, the α-Fe2O3 nanospindle electrode delivered an over-theoretical capacity of about 1207 mA h g−1 after 200 cycles at 0.2C and reversible lithium storage capacity as high as 961.5 mA h g−1 after 500 cycles at 1C. Moreover, αγ-Fe2O3@C nanobipyramid electrode exhibits a superior specific capacity of 631.6 mA h g−1 at 1C after 150 cycles due to its derived unique nanoflake structure.

A graphene–melamine-sponge for efficient and recyclable dye adsorption

Graphene sponges have attracted extensive interest as adsorbents. However, the hydrophobic nature of graphene hinders the submergence of graphene sponge into the water solution. In the present study, we developed a graphene–melamine-sponge (GMS) that can readily submerge into water solution with the help of a superhydrophilic melamine skeleton and investigated its adsorption behaviors for methylene blue (MB) and orange G (OG). The obtained GMS efficiently adsorbed methylene blue with competitive capacity. Isotherm analysis indicated that the adsorption corresponded to the Langmuir isotherm model in a monolayer manner. The maximum adsorption capacities for MB and OG obtained from the Langmuir isotherm equation are 286.5 mg g−1 and 80.51 mg g−1, respectively. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetics model. The as-prepared GMS could be easily regenerated and maintained 95% adsorption capacity after 10 cycles.