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A flexible felt consisting of electrospun anatase TiO 2 and amorphous SiO 2 nanofibers together with anatase TiO 2 nanoparticles was explored as an innovative anode material for lithium ion battery. The electrochemical characterization of the half-cell of the composite felt ( vs. Li metal) showed that the felt had a high initial discharge capacity of 170 mAh/g and an excellent rate capability; furthermore, the capacity was retained at 84% of initial value after 100 cycles at fast charge/discharge rate of 1 A/g. The binder-free composite felt maintained superior flexibility/robustness and good electrochemical performance after 5,000 continuous bending cycles. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid mat consisting of anatase-phase TiO2 nanofibers (~75wt.%) and structurally amorphous SiO2 nanofibers (~25wt.%) was prepared for the first time by electrospinning with dual spinnerets followed by pyrolysis in air at 500°C. Unlike many other TiO2 nanostructures, the TiO2/SiO2 hybrid mat was mechanically flexible; after being sensitized with N719 dye, the dye-sensitized mat was then assembled as a photo-detector for visible light. The fabricated photo-detector was also flexible; it exhibited excellent sensitivity and reproducibility/reversibility under varied light intensities, and it also showed high performance under the bending condition. Additionally, it is envisioned that the reported method could be a general approach for the preparation of flexible hybrid mats with different electrospun nanofibers of semiconducting metal oxides (e.g., TiO2 and ZnO) for various applications. [Copyright &y& Elsevier]

Abstract: Two types of electrospun TiO2 nanotubes were prepared by the technique of co-axial electrospinning followed by pyrolysis of electrospun core–shell nanofibers at 500°C. The SEM/TEM images showed that both types of TiO2 nanotubes were polycrystalline with diameters of ~400–500nm and crystallite/grain sizes of ~10nm. The XRD results indicated that the TiO2 nanotubes possessed the anatase crystalline phase/structure. Upon sonication, both types of TiO2 nanotubes could be shortened; whereas the average lengths were different (i.e., shorter and longer TiO2 nanotubes). The dye-sensitized solar cell (DSSC) with photoanode based on the shorter TiO2 nanotubes had higher short-circuit current density and device efficiency while lower open-circuit voltage than the DSSC with photoanode based on the longer TiO2 nanotubes. The results are discussed in terms of dye loading amount and electron recombination lifetime. [Copyright &y& Elsevier]

Abstract: Carbon nanofibrous mat (nano-felt) surface-attached with Pd nanoparticles was prepared from electrospun polyacrylonitrile nano-felt surface-functionalized with amidoxime groups, and its application for hydrogen sensing was explored. The material consisted of relatively uniform and randomly overlaid carbon nanofibers with diameters of ~300nm, while the attached Pd nanoparticles had sizes in the range from a few to tens of nanometers. The electrospun carbon nano-felt was mechanically flexible/resilient, and the resistance of the material varied upon exposure to H2 at room temperature. The study suggested that electrospun carbon nano-felts surface-attached with metal nanoparticles could be a material of choice for the fabrication of gas- and/or bio-sensors, and the amidoxime-functionalization of electrospun polyacrylonitrile nano-felt could be a general approach for the development of various carbon nano-felts surface-attached with different metal nanoparticles. [Copyright &y& Elsevier]

The ultimate goal of this study was to further improve tensile properties of continuous bundles of highly aligned carbon nanofibers. The hypothesis was that adopting moderate tension during carbonization could improve the formation and orientation of graphite crystallites, leading to increased tensile properties of carbon nanofibers. In this study, bundles consisting of highly aligned PAN copolymer nanofibers were first prepared by electrospinning and collected via a flowing water bath, followed by 3-time stretching and oxidative stabilization. The stabilized PAN nanofibers were then carbonized under tensions of 10–50 cN which corresponding to 254.7–1273.5 MPa, respectively. The effects of carbonization tension on structural and tensile properties of carbon nanofibers were investigated by WAXD, Raman spectroscopy and filament specimen methods. The results indicated that the orientation of graphite crystallites in carbon nanofibers could be improved by increasing carbonization tensions from 254.7 MPa to 509.4 MPa; and the highest tensile strength and modulus of carbon nanofibers could reach 1115 MPa and 194.5 GPa, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Mechanically flexible mats consisting of electrospun carbon nanofibers (ECNFs) were prepared by first electrospinning aqueous mixtures containing a natural product of alkali lignin together with polyvinyl alcohol (PVA) into composite nanofiber mats followed by stabilization in air and carbonization in an inert environment. Morphological and structural properties, as well as specific surface area, total pore volume, average pore size, and pore size distribution, of the lignin-based ECNF mats were characterized; and their electrochemical performances (i.e., capacitive behaviors) were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The lignin-based ECNF mats exhibited outstanding performance as free-standing and/or binder-free electrodes of supercapacitors. For example, the ECNFs made from the composite nanofibers with mass ratio of lignin/PVA being 70/30 (i.e., ECNFs (70/30)) had the average diameter of ∼100 nm and the Brunauer–Emmett–Teller (BET) specific surface area of ∼583 m2 g−1. The gravimetric capacitance of ECNFs (70/30) electrode in 6 M KOH aqueous electrolyte exhibited 64 F g−1 at current density of 400 mA g−1 and 50 F g−1 at 2000 mA g−1. The ECNFs (70/30) electrode also exhibited excellent cycling durability/stability, and the gravimetric capacitance merely reduced by ∼10% after 6000 cycles of charge/discharge. [Copyright &y& Elsevier]

Abstract: Electrospun anatase-phase TiO2 nanofibers with desired morphological structure and relatively high specific surface area are expected to outperform other nanostructures (e.g., powder and film) of TiO2 for various applications (particularly dye-sensitized solar cell and photo-catalysis). In this study, systematic investigations were carried out to prepare and characterize electrospun anatase-phase TiO2 nanofibers with different morphological structures (e.g., solid, hollow/tubular, and porous) and specific surface areas. The TiO2 nanofibers were generally prepared via electrospinning of precursor nanofibers followed by pyrolysis at 500°C. For making hollow/tubular TiO2 nanofibers, the technique of co-axial electrospinning was utilized; while for making porous TiO2 nanofibers, the etching treatment in NaOH aqueous solution was adopted. The results indicated that the hollow/tubular TiO2 nanofibers (with diameters of ∼300–500nm and wall-thickness in the range from tens of nanometers to ∼200nm) had the BET specific surface area of ∼27.3m2/g, which was approximately twice as that of the solid TiO2 nanofibers (∼15.2m2/g) with diameters of ∼200–300nm and lengths of at least tens of microns. Porous TiO2 nanofibers made from the precursor of Al2O3/TiO2 composite nanofibers had the BET specific surface area of ∼106.5m2/g, whereas porous TiO2 nanofibers made from the precursor of ZnO/TiO2 composite nanofibers had the highest BET specific surface area of ∼148.6m2/g. [Copyright &y& Elsevier]

Abstract: The form-stable phase change materials (PCMs) with fatty acid eutectics absorbed in and/or supported by the overlaid mats of electrospun polyacrylonitrile (PAN) nanofibers or the derived carbon nanofibers were explored for storage and retrieval of thermal energy. The carbon mats were made from the PAN mats through stabilization in air followed by carbonization in nitrogen. Three fatty acid eutectics of capric acid–lauric acid, capric acid–palmitic acid, and capric acid–stearic acid were studied as model PCMs; for comparison, the individual fatty acid of capric acid was also studied. The results indicated that electrospun nanofibrous mats were highly porous and capable of absorbing a large amount of PCMs, and the maximum absorption capacities of PAN and carbon mats were ∼99wt% and ∼81wt%, respectively. The composite materials (i.e., the form-stable PCMs) could well-retain their overall shapes when the PCMs were in the molten stage; i.e., they would not flow/leak from the mats. The conversion of PAN mats into carbon mats increased the thermal energy storage/retrieval rates of the resulting composite PCMs; nonetheless, the thermal treatments of stabilization and carbonization also made the mats to be less fluffy, leading to the reduction of absorption amount. Morphological structures, as well as the properties of thermal energy storage, absorption capacity, and thermal energy storage/retrieval rates, of electrospun nanofibrous mats and the resulting composite PCMs were studied by scanning electron microscopy, differential scanning calorimetry, and measurement of melting/freezing times. The results indicated that the melting temperatures and enthalpies of the prepared composite PCMs were in the range of 19.8–31.4°C and 120.1–165.4kJ/kg for PAN mats, and 18.8–30.7°C and 92.1–128.0kJ/kg for carbon mats, respectively. In comparison with melting times of CA–PA/PAN and freezing times of CA–SA/PAN, the melting times of CA–PA/carbon and freezing times of CA–SA/carbon were shortened by about 49.5% and 41.0%, respectively. It is envisioned that this innovative type of form-stable PCMs could be utilized for potential applications in building energy conservation. [Copyright &y& Elsevier]

• Mechanical properties of carbon nanofibrous mats were studied upon carbonization temperature. • The highest tensile strength and modulus of carbon nanofibrous mats are 130.2 MPa and 17.53 GPa, respectively. • The graphite microstructure was mostly formed at 1100 °C. Electrospun carbon nanofibrous mat (CNFM) is prepared by the carbonization of stabilized PAN nanofibers under temperatures between 900 °C and 1300 °C. The effects of carbonization temperatures on the structure and mechanical strength of the CNFMs are investigated via Scanning-electron-microscopy, X-ray-diffraction, Raman spectroscopy, and mechanical strength characterizations. Results show that the majority of non-carbon elements are removed from the fibers and that the graphite microstructures are mostly formed below 1100 °C, which led to quickly enhanced conductivity and mechanical strength of CNFMs. When the carbonization temperature further increase to 1300 °C, the graphite crystallite continues to grow and the mechanical strength continues to increase, but at a slower rate. The highest tensile strength of 130.2 ± 16.7 MPa and modulus of 17.53 ± 1.53 GPa were achieved at a carbonization temperature of 1300 °C. [ABSTRACT FROM AUTHOR]