Weimin Kang

A review of recent developments in rechargeable lithium–sulfur batteries

The research and development of advanced energy-storage systems must meet a large number of requirements, including high energy density, natural abundance of the raw material, low cost and environmental friendliness, and particularly reasonable safety. As the demands of high-performance batteries are continuously increasing, with large-scale energy storage systems and electric mobility equipment, lithium-sulfur batteries have become an attractive candidate for the new generation of high-performance batteries due to their high theoretical capacity (1675 mA h g-1) and energy density (2600 Wh kg-1). However, rapid capacity attenuation with poor cycle and rate performances make the batteries far from ideal with respect to real commercial applications. Outstanding breakthroughs and achievements have been made to alleviate these problems in the past ten years. This paper presents an overview of recent advances in lithium-sulfur battery research. We cover the research and development to date on various components of lithium-sulfur batteries, including cathodes, binders, separators, electrolytes, anodes, collectors, and some novel cell configurations. The current trends in materials selection for batteries are reviewed and various choices of cathode, binder, electrolyte, separator, anode, and collector materials are discussed. The current challenges associated with the use of batteries and their materials selection are listed and future perspectives for this class of battery are also discussed.

Solution blowing of submicron-scale cellulose fibers.

Solution blowing is an innovative process for spinning micro-/nano-fibers from polymer solutions using high-velocity gas flow as fiber forming driving force. Submicron-scale cellulose fibers were successfully solution blown by two improvement measures. First, cellulose solution was directly blown to fibers of 260-1900 nm in diameter by raising the air temperature along the spinning line which was proved to accelerate the evaporation of solvent and fiber forming. Second, coaxial solution blowing technique was established with cellulose solution and polyethylene oxide (PEO) solution used as core and shell liquids, respectively. The core-shell structures of the fibers were examined by SEM and TEM. Cellulose fibers with diameter between 160 nm and 960 nm were further obtained after removing PEO shell. X-ray diffraction studies showed that the two kinds of submicron-scale cellulose fibers are mostly amorphous.

Solution blowing nylon 6 nanofiber mats for air filtration

Solution blowing process is a new nanofiber fabricating method with high productivity. In the present study, nylon 6 nanofiber mats were solution blown and the effects of spinning conditions on nanofibers morphology were investigated. The fiber diameter ranged from 150 to 750 nm which was affected by solution concentration, gas pressure and solution feeding rate. The solution blown fibers were three-dimensional curly which made loose construction in bulk. The filtration performance of solution blown mats was evaluated. The tested solution blown nanofiber mats showed high filtration efficiency of 83.10 % to 93.45 % for 0.3 µm particles filtration and extremely low pressure drop of 15.37 to 30.35 Pa. The results indicate the solution blown nanofiber mats will find potential application of high efficiency and low resistance filter.

A new method for preparing alumina nanofibers by electrospinning technology

A new method for synthesizing alumina (Al2O3) nanofibers through the electrospinning method was reported. The spinning solutions of anhydrous aluminium chloride/polyvinylpyrrolidone (AlCl3/PVP), wh...A new method for synthesizing alumina (Al2O3) nanofibers through the electrospinning method was reported. The spinning solutions of anhydrous aluminium chloride/polyvinylpyrrolidone (AlCl3/PVP), which were prepared by the sol-gel process of the mixture of AlCl3, PVP, ethanol and redistilled water, were electrospun to form AlCl3/PVP organic-inorganic hybrid fibers. Alumina nanofibers with average diameters of 100—800 nm were obtained by calcinations of the as-prepared fibers. The fibers were characterized by SEM, TG-DTA, FTIR, XPS and XRD. The results showed that with the increase of the concentration of spinning solution, the diameter of fibers also increased, and that the diameter of fibers decreased with the increase of the applied voltage and calcination temperature. The uncrystalline Al2O3, γ-Al 2O3 and α-Al2O3 were obtained after calcinations of about 5 h at 450, 900 and 1100°C, respectively.

Flexible hollow CeO2/Al2O3 fibers: preparation, characterization and dye adsorption efficiency

Flexible hollow CeO2/Al2O3 fibers were successfully prepared, for the first time, by a coaxial electro-blowing spinning technique. The diameter of these fibers could be controlled by adjusting spinning parameters. Upon sintering the as-spun fibers at 600 °C, flexible hollow CeO2/Al2O3 fibers were obtained with continuous morphologies. Their microstructure was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and specific surface area (BET). A dye removal experiment was evaluated from the adsorption efficiency of Methyl Orange (MO) in aqueous solution. They exhibited strong adsorption capacity for MO molecules in dark conditions and were easily separated by simple filtration, thus showing promise for application in wastewater treatment and environmental purification.

Coaxial solution blown core-shell structure nanofibers for drug delivery

Abstract

Removal of Textile Dyes from Aqueous Solution by Heterogeneous Photo-Fenton Reaction Using Modified PAN Nanofiber Fe Complex as Catalyst

The modified PAN nanofiber Fe complex was prepared by the amidoximation and Fe coordination of PAN nanofiber was obtained using electrospinning technique and then used for the heterogeneous Fenton degradation of textile dyes as a novel catalyst. Some main factors affecting dye degradation such as Fe content of catalyst, irradiation intensity, H2O2 initial concentration, the solution pH as well as dye structure, and initial concentration were investigated. UV-Vis spectrum analysis and TOC measurement were also used to evaluate the dye degradation process. The results indicated that the modified PAN nanofiber Fe complex exhibited a much better catalytic activity for the heterogeneous Fenton degradation of textile dyes than the Fe complex prepared with conventional PAN yarns in the dark or under light irradiation. Increasing Fe content of catalyst or irradiation intensity would accelerate the dye degradation. And the highest degradation efficiency was obtained with 3.0 mmol L−1 H2O2 at pH 6. Moreover, this complex was proved to be a universal and efficient catalyst for degradation of three classes of textile dyes including azo dye, anthraquinone dye, and triphenylmethane dye. Additionally, the dye mineralization was also significantly enhanced in the presence of this complex.

Fabrication of a polyvinylidene fluoride tree-like nanofiber web for ultra high performance air filtration

A novel polyvinylidene fluoride (PVDF) tree-like nanofiber web was successfully fabricated via one-step electrospinning. The effect of the tree-like structure on the pore size distribution and specific surface area were measured, and the filtration properties of the tree-like nanofiber webs with different basis weights were investigated. The results showed that the tree-like structure significantly decreased the pore size and narrowed the range of pore size distribution, and dramatically enhanced the specific surface area. In comparison with common PVDF nanofiber webs, the tree-like nanofiber webs exhibited excellent filtration performance. The filtration efficiency of the tree-like nanofiber webs with the basis weight of 1 g m−2 to 0.26 μm NaCl particles was 99.999% and the pressure drop was only 124.2 Pa which was comparable to ultra low penetration air filters (ULPA). The tree-like nanofiber webs will be widely used in the field of high efficiency and precision filter materials and medical protective materials.

Chitin nanowhisker-supported sulfonated poly(ether sulfone) proton exchange for fuel cell applications

To balance the relationship among proton conductivity and mechanic strength of sulfonated poly(ether sulfone) (SPES) membrane, chitin nanowhisker-supported nanocomposite membranes were prepared by incorporating whiskers into SPES. The as-prepared chitin whiskers were prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated oxidation of α-chitin from crab shells. The structure and properties of the composite membranes were examined as proton exchange membrane (PEM). Results showed that chitin nanowhiskers were dispersed incompactly in the SPES matrix. Thermal stability, mechanical properties, water uptake and proton conductivity of the nanocomposite films were improved from those of the pure SPES film with increasing whisker content, which ascribed to strong interactions between whiskers and between SPES molecules and chitin whiskers via hydrogen bonding. These indicated that composition of filler and matrix got good properties and whisker-supported membranes are promising materials for PEM.

Preparation of a polyvinylidene fluoride tree-like nanofiber mat loaded with manganese dioxide for highly efficient lead adsorption

A novel polyvinylidene fluoride/tetrabutylammonium chloride (PVDF/TBAC) tree-like nanofiber mat loaded with manganese dioxide (MnO2) as a highly efficient lead adsorbent was successfully fabricated. The adsorbent was prepared by in situ polymerization of pyrrole monomer on the surface of the PVDF/TBAC tree-like nanofiber mat, and subsequently reacted with KMnO4 solution to deposit MnO2. The morphology and structure of the as-prepared adsorbent were measured by field emission scanning electron microscopy (FE-SEM) and the tree-like structures can be clearly seen from the FE-SEM images. Fourier transform infrared spectroscopy (FT-IR) results confirmed the presence of PPy and MnO2 layers on the surface of PVDF/TBAC tree-like nanofibers. Thermo-gravimetric analysis (TGA) results exhibited that MnO2 accounted for about 43.27% in the PVDF/TBAC–polypyrrole–MnO2 (PVDF/TBAC–PPy–MnO2) nanofiber mat. The kinetics of Pb2+ adsorption was found to follow a pseudo-second-order rate model. The adsorption isotherms were fitted best with the Langmuir isotherm model. The thermodynamic analysis confirmed that the adsorption process was endothermic and spontaneous. The regeneration experiments showed that the obtained tree-like PVDF/TBAC–PPy–MnO2 nanofiber mat also exhibited high recyclable removal efficiency. XPS analysis showed that ion exchange was the main mechanism for Pb2+ adsorption.