Junhe Yang

In Situ Formed Lithium Sulfide/Microporous Carbon Cathodes for Lithium-Ion Batteries

Highly stable sulfur/microporous carbon (S/MC) composites are prepared by vacuum infusion of sulfur vapor into microporous carbon at 600 °C, and lithium sulfide/microporous carbon (Li2S/MC) cathodes are fabricated via a novel and facile in situ lithiation strategy, i.e., spraying commercial stabilized lithium metal powder (SLMP) onto a prepared S/MC film cathode prior to the routine compressing process in cell assembly. The in situ formed Li2S/MC film cathode shows high Coulombic efficiency and long cycling stability in a conventional commercial Li-ion battery electrolyte (1.0 M LiPF6 + EC/DEC (1:1 v/v)). The reversible capacities of Li2S/MC cathodes remain about 650 mAh/g even after 900 charge/discharge cycles, and the Coulombic efficiency is close to 100% at a current density of 0.1C, which demonstrates the best electrochemical performance of Li2S/MC cathodes reported to date. Furthermore, this Li2S/MC film cathode fabricated via our in situ lithiation strategy can be coupled with a Li-free anode, such as graphite, carbon/tin alloys, or Si nanowires to form a rechargeable Li-ion cell. As the Li2S/MC cathode is paired with a commercial graphite anode, the full cell of Li2S/MC-graphite (Li2S-G) shows a stable capacity of around 600 mAh/g in 150 cycles. The Li2S/MC cathodes prepared by high-temperate sulfur infusion and SLMP prelithiation before cell assembly are ready to fit into current Li-ion batteries manufacturing processes and will pave the way to commercialize low-cost Li2S-G Li-ion batteries.

Nanofibers Fabricated Using Triaxial Electrospinning as Zero Order Drug Delivery Systems

A new strategy for creating functional trilayer nanofibers through triaxial electrospinning is demonstrated. Ethyl cellulose (EC) was used as the filament-forming matrix in the outer, middle, and inner working solutions and was combined with varied contents of the model active ingredient ketoprofen (KET) in the three fluids. Triaxial electrospinning was successfully carried out to generate medicated nanofibers. The resultant nanofibers had diameters of 0.74 ± 0.06 μm, linear morphologies, smooth surfaces, and clear trilayer nanostructures. The KET concentration in each layer gradually increased from the outer to the inner layer. In vitro dissolution tests demonstrated that the nanofibers could provide linear release of KET over 20 h. The protocol reported in this study thus provides a facile approach to creating functional nanofibers with sophisticated structural features.

High Performance C/S Composite Cathodes with Conventional Carbonate-Based Electrolytes in Li-S Battery

High stable C/S composites are fabricated by a novel high-temperature sulfur infusion into micro-mesoporous carbon method following with solvent cleaning treatment. The C/S composite cathodes show high Coulombic efficiency, long cycling stability and good rate capability in the electrolyte of 1.0 M LiPF6 + EC/DEC (1:1 v/v), for instance, the reversible capacity of the treated C/S-50 (50% S) cathode retains around 860 mAh/g even after 500 cycles and the Coulombic efficiency is close to 100%, which demonstrates the best electrochemical performance of carbon-sulfur composite cathodes using the carbonate-based electrolyte reported to date. It is believed that the chemical bond of C-S is responsible for the superior electrochemical properties in Li-S battery, that is, the strong interaction between S and carbon matrix significantly improves the conductivity of S, effectively buffers the structural strain/stress caused by the large volume change during lithiation/delithiation, completely eliminates the formation of high-order polysulfide intermediates, and substantially avoids the shuttle reaction and the side reaction between polysulfide anions and carbonate solvent, and thus enables the C/S cathode to use conventional carbonate-based electrolytes and achieve outstanding electrochemical properties in Li-S battery. The results may substantially contribute to the progress of the Li-S battery technology.

Nanosized sustained-release drug depots fabricated using modified tri-axial electrospinning

Nanoscale drug depots, comprising a drug reservoir surrounded by a carrier membrane, are much sought after in contemporary pharmaceutical research. Using cellulose acetate (CA) as a filament-forming polymeric matrix and ferulic acid (FA) as a model drug, nanoscale drug depots in the form of core-shell fibers were designed and fabricated using a modified tri-axial electrospinning process. This employed a solvent mixture as the outer working fluid, as a result of which a robust and continuous preparation process could be achieved. The fiber-based depots had a linear morphology, smooth surfaces, and an average diameter of 0.62±0.07μm. Electron microscopy data showed them to have clear core-shell structures, with the FA encapsulated inside a CA shell. X-ray diffraction and IR spectroscopy results verified that FA was present in the crystalline physical form. In vitro dissolution tests revealed that the fibers were able to provide close to zero-order release over 36h, with no initial burst release and minimal tailing-off. The release properties of the depot systems were much improved over monolithic CA/FA fibers, which exhibited a significant burst release and also considerable tailing-off at the end of the release experiment. Here we thus demonstrate the concept of using modified tri-axial electrospinning to design and develop new types of heterogeneous nanoscale biomaterials. STATEMENT OF SIGNIFICANCE Nanoscale drug depots with a drug reservoir surrounded by a carrier are highly attractive in biomedicine. A cellulose acetate based drug depot was investigated in detail, starting with the design of the nanostructure, and moving through its fabrication using a modified tri-axial electrospinning process and a series of characterizations. The core-shell fiber-based drug depots can provide a more sustained release profile with no initial burst effect and less tailing-off than equivalent monolithic drug-loaded fibers. The drug release mechanisms are also distinct in the two systems. This proof-of-concept work can be further expanded to conceive a series of new structural biomaterials with improved or new functional performance.

Self-aligned graphene as anticorrosive barrier in waterborne polyurethane composite coatings

Graphene reinforced waterborne polyurethane (PU) composite coatings were fabricated on steel surfaces. When the filler content was 0.4 wt%, self-alignment of graphene was driven by the reduction of the total excluded volume. The superior anticorrosion properties were proven by electrochemical impedance spectroscopy (EIS) analysis for the PU matrix composite coating reinforced by 0.4 wt% of aligned graphene. The interaction mechanism between electrolyte and graphene layers was discussed for the three-dimensional randomly distributed graphene and the in-plane aligned graphene, respectively, to better understand their effects as anticorrosive barriers.

Influence of the drug distribution in electrospun gliadin fibers on drug-release behavior

Abstract Drug distribution within its carrier in a solid dosage form often generates a profound influence on its release profile, particularly when the physicochemical properties of the carrier are exploited to manipulate drug release behavior. In this job, two different types of distributions of a model drug ibuprofen (IBU) within a protein gliadin in their electrospun nanofibers were intentionally created. One was homogeneous distribution in the monolithic fibers fabricated using a modified coaxial process, and the other one was heterogeneous distribution in the core/shell fibers prepared through a traditional coaxial process. SEM observations clearly demonstrated the different distributions of IBU within gliadin in the two kinds of nanofibers although both of them had smooth surfaces and linear morphology. XRD results showed that IBU was amorphously distributed in the monolithic fibers, but that some IBU crystalline lattices presented in the core/shell fibers. FTIR and RM spectra suggested that gliadin had good compatibility with IBU. In vitro dissolution tests verified that the gliadin nanofibers with a heterogeneous drug distribution could provide a better sustained release profile than its counterpart in terms of initial burst release and sustained release time period. Both the fiber formation and drug‐controlled release mechanisms are suggested. The present study demonstrated a concept that drug distribution with the medicated nanomaterials can be exploited as a tool to optimize the drug sustained release profile.

Strengthening of Graphene Aerogels with Tunable Density and High Adsorption Capacity towards Pb2

Graphene aerogels (GAs) with high mechanical strength, tunable density and volume have been prepared only via soaking graphene hydrogels (GHs) in ammonia solution. The density and volume of the obtained GAs are controlled by adjusting the concentration of ammonia solution. Although volume of the GAs decreases with increasing the concentration of ammonia solution, its specific surface area maintains at about 350 m2 g−1, and the inner structure changes to radial after ammonia solution treatment. Thus, GAs are particularly suitable for the adsorption and energy storage applications owing to their high specific surface area and unique porous structure. The adsorption capacity of GAs for Pb2+ from aqueous solution maintains at about 80 mg g−1, which could reach as high as 5000 g m−3 per unit volume and they can be separated easily from water after adsorption.

Solid lipid nanoparticles self-assembled from electrosprayed polymer-based microparticles

A new strategy for manipulating molecular self-assembly to produce solid lipid nanoparticles (SLNs) in situ is reported. Microparticulate composites (consisting of the polymer PVP, naproxen and tristearin as a lipophilic carrier) were prepared using an elevated temperature electrospraying process. Tristearin/naproxen SLNs formed spontaneously when the composite microparticles were placed into water, as a result of the PVP polymer matrix dissolving. The self-assembled SLNs had average diameter of 376 ± 20 nm, a drug entrapment efficiency of 86.2% and provided sustained drug release over 24 h, with 87.6% of the total NAP freed into the dissolution medium in this time. These findings open a new route for developing novel biomaterials and nanoparticulate drug delivery systems, and for resolving problems associated with the formulation of poorly water-soluble drugs.

Synthesis, optical and electrochemical properties of ZnO nanowires/graphene oxide heterostructures.

Large-scale vertically aligned ZnO nanowires with high crystal qualities were fabricated on thin graphene oxide films via a low temperature hydrothermal method. Room temperature photoluminescence results show that the ultraviolet emission of nanowires grown on graphene oxide films was greatly enhanced and the defect-related visible emission was suppressed, which can be attributed to the improved crystal quality and possible electron transfer between ZnO and graphene oxide. Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising for application in supercapacitors.

Facile Synthesis of Zn0.5Cd0.5S Ultrathin Nanorods on Reduced Graphene Oxide for Enhanced Photocatalytic Hydrogen Evolution under Visible Light

A new contact model between ZnxCd1−xS nanorods and reduced graphene oxide (RGO) was obtained by rational formation of ultrathin Zn0.5Cd0.5S (ZCS) nanorods on RGO through a facile oleylamine–DMSO mediated synthesis approach. The 1 D/2 D model of ZCS/RGO provides a strong contact line‐to‐line interface, which is not only conducive for the fast collection and transfer of photogenerated electrons but also stabilizes the ultrathin nanorod structure of ZCS. The photocatalytic test results indicated that the ZCS/RGO nanocomposites exhibit significantly enhanced photocatalytic H2 evolution rate and cycling stability under visible light compared with free ZCS and the physical mixture of ZCS and RGO.