PVP nanofibers prepared using co-axial electrospinning with salt solution as sheath fluid

A modified co-axial electrospinning process using salt solutions as sheath fluids for preparing polymer nanofibers was investigated. A series of polyvinylpyrrolidone (PVP) fibers were prepared with NaCl aqueous solutions at varying concentrations as sheath fluids. The sheath fluid had a significant influence on the formation of the compound Taylor cone. Scanning electron microscopy results demonstrated that the diameters of PVP nanofibers could be manipulated through the concentration of NaCl solutions within an appropriate range. With 2 mg ml^− 1 NaCl solution as sheath fluid, the smallest PVP nanofibers, with a diameter of 120 ± 40 nm, were obtained. Co-axial electrospinning with salt solutions as sheath fluids is a facile method for achieving finer, homogeneous polymer nanofibers.     

Preparation of poly (vinyl alcohol)/silica composite nanofibers membrane functionalized with mercapto groups by electrospinning

Membranes of poly vinyl alcohol (PVA)/silica functionalized with mercapto groups are synthesized by electrospinning. Scanning electron microscopy (SEM) studies showed that the fiber diameters are in the range of 200-300 nm. The thickness of nanofiber decreases with an increase in calcination temperature. The results of Fourier transform infrared (FTIR) indicated that PVA/silica nanofibers are functionalized by mercapto groups via the hydrolysis poly-condensation method. N₂ adsorption-desorption showed that organic molecules can be removed completely when the PVA/silica composite fibers are calcinated at 800 °C. The fibers calcinated at 800 °C were pure inorganic silica species with a mesoporous structure. These mercapto groups functionalized PVA/silica nanofibers have a great potential application in the field of adsorption of heavy metal ions.     

CO gas sensing of Pd-doped ZnO nanofibers synthesized by electrospinning method

Pure and Pd-doped ZnO nanofibers were synthesized by electrospinning method, and characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The diameters of the fibers annealed at 600 °C range from 70 to 160 nm. Compared with pure ZnO nanofiber sensor, the Pd-doped ZnO nanofiber sensor exhibits improved sensing properties to CO at 220 °C. Moreover, this sensor processes considerable sensitivity to low concentration CO in the range of 1-20 ppm with good selectivity. The response and recovery times are in the range of 25-29 s and 12-17 s, respectively. The sensing mechanism is also discussed.     

Fabrication and texture evolution of hexagonal YMnO3 nanofibers by electrospinning

Hexagonal YMnO₃ nanofibers were successfully fabricated by sol-gel preparation based on electrospinning. The as-spun fibers dried at 125 °C were round and had a rather uniform diameter around 0.7 μm-2 μm over its length. In order to get pure hexagonal YMnO₃ nanofibers, crystalline structures and microstructures of fibers at various temperatures for 6 h were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reasonable evaluations for the change of morphology with the increasing temperature were proposed. After being heated at 1100 °C for 6 h, the pure hexagonal YMnO₃ nanofibers were obtained with a reduced diameter ranging from 200 nm to 800 nm and the fibers were homogenous in chemical constitution over its length.     

Synthesis of high-performance one-dimensional polyaniline nanostructures using dodecylbenzene sulfonic acid as soft template

High-performance one-dimensional polyaniline (PANI) nanostructures, i.e. nanotubes and nanofibers were synthesized in the presence of dodecylbenzene sulfonic acid (DBSA) and hydrochloric acid (HCl) aqueous solution, with ammonium peroxydisulfate (APS) as oxidant. And the resulting PANI nanotubes possessed the diameters of 350-650 nm and length up to tens of micrometers and PANI nanofibers with diameters of 120-160 nm, respectively. Especially, the PANI nanotubes had a very uniform structure (nearly 100% in nanotubes) and the reaction yield was about 110% (compared to the quantity of aniline in the reaction). The formation mechanism of 1D PANI nanostructures was also proposed. The guide effect of the initial “soft-template” formed by aniline and DBSA was greatly controlled by its content and chemical structures.     

Study of Structural Morphology of Hemp Fiber from the Micro to the Nanoscale

The focus of this work has been to study how high pressure defibrillation and chemical purification affect the hemp fiber morphology from micro to nanoscale. Microscopy techniques, chemical analysis and X-ray diffraction were used to study the structure and properties of the prepared micro and nanofibers. Microscopy studies showed that the used individualization processes lead to a unique morphology of interconnected web-like structure of hemp fibers. The nanofibers are bundles of cellulose fibers of widths ranging between 30 and 100 nm and estimated lengths of several micrometers. The chemical analysis showed that selective chemical treatments increased the α-cellulose content of hemp nanofibers from 75 to 94%. Fourier transform infrared spectroscopy (FTIR) study showed that the pectins were partially removed during the individualization treatments. X-ray analysis showed that the relative crystallinity of the studied fibers increased after each stage of chemical and mechanical treatments. It was also observed that the hemp nanofibers had an increased crystallinity of 71 from 57% of untreated hemp fibers.     

Synthesis of ultrafine lanthanum ferrite (LaFeO3) fibers via electrospinning

Ultrafine one-dimensional LaFeO₃ nanofibers were synthesized by electrospinning utilizing sol-gel precursors. The surface morphology, microstructure and crystal structure were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The nanofibers with smaller diameter were continuous and uniformly distributed. Typical fiber diameter was between 180 nm and 220 nm and the average diameter was 200 nm. The fibers consisted of many single-crystal LaFeO₃ grains and the grain size was about 20-50 nm. The relationship between the diameter of as-synthesized fibers and the PVP concentration of the precursor was investigated. The experimental results indicated that the PVP concentration had a great impact on the fiber size and 5.89 wt.% PVP concentration in sol-gel precursors was advantageous to the formation of more uniform electrospun composite fibers with smaller diameter.     

Structure and properties of novel electrospun tussah silk fibroin/poly(lactic acid) composite nanofibers

The tussah silk fibroin (TSF)/poly(lactic acid) (PLA) composite nanofibers with different composition ratios were prepared by electrospinning with 1,1,1,3,3,3-Hexafluoro-2-propanol as the solvent. The morphology and secondary structure of the fibers were characterized by Scanning electronic microscope, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The thermal and mechanical tests were also performed. The spinnability of TSF solution was improved significantly through adding 10% PLA, and the average diameter of the fibers decreased from 583 nm to 178 nm with an obvious improvement in fiber diameter uniformity. In addition, the mechanical properties of electrospun nanofibers increased evidently after blending 10% PLA, whereas the thermal properties kept stable. FTIR and XRD analysis indicated the addition of 5% PLA could induce a conformation transformation of TSF from random coil and α-helix to β-sheet, however, when PLA content was more than 10%, the β-sheet structure of TSF in composite nanofibers decreased, and the phase separation of two compositions occurred. Therefore, when PLA content exceeded 15%, the average diameters of TSF/PLA composite nanofibers increased and appeared to be polarized, moreover, the mechanical properties of the fibers decreased with the increase of PLA content, and the fibers displayed the mechanical behavior of PLA component more.     

Synthesis of vanadium oxide nanofibers and tubes using polylactide fibers as template

A new method to produce vanadium oxide nanofibers with dimensions <140 nm and tubes is reported. Vanadium oxide was coated on polylactide fibers by a sol-gel method using a reaction mix of ammonium vanadate and acetic acid as starting materials and water as solvent. Vanadium oxide tubes, of about 1 μm in diameter, were formed when this coated fiber was heated in nitrogen and oxygen at 300 and 250 °C for 1 h. Hydrothermal treatment of the polylactide fibers with the reaction mix at 160 °C for 12 h followed by heating in oxygen at 300 °C for 1 h formed vanadium oxide nanofibers, 60-140 nm in width and several microns in length. Electrochemical studies reveal that these vanadium oxide nanofibers are redox active and readily undergo reversible reactions with lithium in non-aqueous cells.     

LaOCl nanofibers derived from electrospun PVA/Lanthanum chloride composite fibers

Electrospun nanofibers of poly (vinyl alcohol) (PVA)/Lanthanum (Ш) chloride (LaCl₃) composite were employed to prepare the LaOCl nanofibers by calcination. TG-DSC was used to investigate the thermal property of precursor, while FT-IR, XRD, FESEM and TPD were employed to characterize the derived LaOCl nanofibers. Results indicate that the addition of LaCl₃ leads to the formation of fork segments in the structure of electrospun PVA/LaCl₃ composite nanofibers, therefore, changing the decomposition behavior of the fibers. Pure LaOCl fibers with a diameter range of 90-220 nm can be obtained by calcination of electrospun PVA/LaCl₃ composite nanofibers at 700 °C for 7 h. The resultant LaOCl nanofibers show a good sensing behavior for CO₂ gas.     

Templated synthesis of polyaniline nanotubes with Pd nanoparticles attached onto their inner walls and its catalytic activity on the reduction of p-nitroanilinum

In this paper, polyaniline (PANI) nanotubes with palladium nanoparticles (NPs) attached onto their inner walls were synthesized via a templating method which contains three steps. First, electrospun polystyrene (PS) nanofibers were coated with nearly monodispersed Pd NPs (d = 3.411 nm, σ = 0.687 nm, d is the average diameter of Pd NPs and σ is the standard deviation of their diameters) through in situ reduction of Pd²⁺ ions on the surface of sulfonated PS nanofibers. Then we used a self-assembly method to coat the composite with a PANI layer. The final product was obtained after the removal of PS nanofibers by diluting them in tetrahydrofuran. The morphology of samples was analyzed by scanning electron microscopy and transmission electron microscopy and the structure was characterized by Fourier transform infrared, ultraviolet–visible spectra, X-ray diffraction patterns and X-ray photoelectron spectroscopic patterns. Inductively coupled plasma atomic spectra were used to show the weight percentage of Pd nanoparticles. Its catalytic activity on the reduction of p-nitroanilinum was also investigated and compared to Pd/C catalyst and Pd/MWNTs.     

Fabrication of TiO2/ZnO composite nanofibers by electrospinning and their photocatalytic property

TiO₂/ZnO composite nanofibers with diameters in the range of 85–200 nm were fabricated via the electrospinning technique using zinc acetate and titanium tetra-isopropoxide as precursors, cellulose acetate as the fiber template, and N,N-dimethylformamide/acetone 1:2 (v/v) mixtures as the co-solvent. After treated with 0.1 mol/L NaOH aqueous solution, TiO₂/zinc acetate/cellulose acetate composite nanofibers were transformed into TiO₂/Zn(OH)₂/cellulose composite nanofibers. TiO₂/ZnO composite nanofibers were obtained by calcinating the hydrolyzed composite fibers at 500 and 700 °C for 5 h. The structure and morphology of composite nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. With the blending of ZnO into TiO₂, a new crystallite ZnTiO₃ was formed in addition to the ZnO and TiO₂ crystallites, and the ultraviolet light absorption efficiency was enhanced according to the UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of TiO₂/ZnO composite nanofibers toward the decomposition of Rhodamine B and phenol was investigated. Almost 100% Rhodamine B and 85% phenol were decomposed in the presence of TiO₂/ZnO composite nanofibers under mild conditions. The results demonstrated that the blending of ZnO in the TiO₂/ZnO composite nanofibers increased the photocatalytic efficiency. The optimum ZnO content in the TiO₂/ZnO composite nanofibers was 15.76 wt% to reach the most efficient photocatalytic activity. A schematic diagram of photocatalytic mechanism of TiO₂/ZnO composite nanofibers was also presented.     

Effects of the size of nano-copper catalysts and reaction temperature on the morphology of carbon fibers

In this study, carbon fibers with different morphologies, including coiled carbon nanofibers and straight carbon fibers, were obtained by the chemical vapor deposition using a Cu-catalytic pyrolysis of acetylene at 250 °C. The influences of nano-copper catalyst particle size and the reaction temperature on the morphology of carbon fibers were investigated. Under the same reaction condition, coiled carbon nanofibers generally were synthesized using nano-copper catalyst with smaller particles size, and bigger copper particles are apt to produce straight carbon fibers. With decreasing of reaction temperature to 200 °C, straight carbon fibers were obtained, instead of coiled carbon nanofibers at 250 °C. The product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

Preparation and humidity sensing properties of Ba0.8Sr0.2TiO3 nanofibers via electrospinning

Ba_0.8Sr_0.2TiO₃/Poly (vinylpyrrolidone) (BST/PVP) composite fibers were successfully synthesized via electrospinning. The ceramic nanofibers were obtained after calcining the composite at 800 °C for 2 h. The morphology and structure of the BST fibers were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that the as-synthesized BST nanofibers show a diameter of 50-150 nm with the length over 0.1 mm, and a well-defined perovskite crystal structure. The electrical properties of the as-synthesized BST nanofibers were investigated through an impedance-type humidity sensor. The nanofibers exhibited excellent humidity sensing properties at room temperature. The possible sensing mechanism was proposed.     

Synthesis and characterization of nanofiber-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite oxide used as a cathode material for low-temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) was synthesized in two forms: as a powder (by the sol-gel combined citrate-EDTA complexing (CC-EDTA) method) and as nanofibers (by electrospinning). Both forms were sintered at 950 °C for 5 h in air before their morphology and structure were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and specific surface area analysis based on the BET theory. Moreover, the mass loss and heat flow of as-electrospun BSCF nanofibers were analyzed by differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results showed that these materials had a perovskite oxide crystal structure. The CC-EDTA method yielded BSCF in powder form, with a particle size of 1-10 μm and a specific surface area of 1.0 m²/g. On the other hand, BSCF obtained by the electrospinning technique was in the form of highly porous nanofibers with diameters in the range of 100-200 nm and a specific surface area of 2.4 m²/g. To demonstrate the potential applications of BSCF as a cathode material in low-temperature solid oxide fuel cells (LT-SOFCs), the electrochemical properties of the samples were determined using electrochemical impedance spectroscopy (EIS). The area specific resistance (ASR) of the BSCF nanofiber cathode was determined to be 0.094 Ω cm² at 600 °C, whereas that of the BSCF powder cathode was 0.468 Ω cm² under similar conditions.     

Preparation of Fe3O4/PVA nanofibers via combining in-situ composite with electrospinning

A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe₃O₄/poly(vinyl alcohol) (PVA) composite nanofibers. Fe₃O₄ magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe₃O₄/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe₃O₄ nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (M_s = 2.42 emµ·g^-1) although only 4 wt.% content.     

Structure and magnetic property of CoFe2−xSmxO4 (x = 0–0.2) nanofibers prepared by sol–gel route

CoFe_2−xSm_xO₄ (x = 0–0.2) nanofibers with diameters about 100–300 nm have been prepared using the organic gel-thermal decomposition method. The composition, structure and magnetic properties of the CoFe_2−xSm_xO₄ nanofibers were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductive coupling plasma mass analyzer and vibrating sample magnetometer. The CoFe_2−xSm_xO₄ (x = 0–0.2) nanofibers obtained at 500–700 °C are of a single spinel structure. But, at 800 °C with a relatively high Sm content of 0.15–0.2 the spinel CoFe_2−xSm_xO₄ ferrite is unstable and the second phase of perovskite SmFeO₃ occurs. The crystalline grain sizes of the CoFe_2−xSm_xO₄ nanofibers decrease with Sm contents, while increase with the calcination temperature. This grain reduction effect of the Sm³⁺ ions doping is largely owing to the lattice strain and stress induced by the substitution of Fe³⁺ ions with larger Sm³⁺ ions in the ferrite. The saturation magnetization and coercivity increase with the crystallite size in the range of 8.8–57.3 nm, while decrease with the Sm content from 0 to 0.2 owing to a smaller magnetic moment of Sm³⁺ ions. The perovskite SmFeO₃ in the composite nanofibers may contribute to a high coercivity due to the interface pinning, lattice distortion and stress in the ferrite grain boundary fixing and hindering the domain wall motion.     

Oxolane-2,5-dione modified electrospun cellulose nanofibers for heavy metals adsorption

Functionalized cellulose nanofibers have been obtained through electrospinning and modification with oxolane-2,5-dione. The application of the nanofibers for adsorption of cadmium and lead ions from model wastewater samples is presented for the first time. Physical and chemical properties of the nanofibers were characterized. Surface chemistry during preparation and functionalization was monitored using Fourier transform-infrared spectroscopy, scanning electron microscopy, carbon-13 solid state nuclear magnetic resonance spectroscopy and Brunauer Emmett and Teller. Enhanced surface area of 13.68 m² g⁻¹ was recorded for the nanofibers as compared to the cellulose fibers with a surface area of 3.22 m² g⁻¹. Freundlich isotherm was found to describe the interactions better than Langmuir: K_f = 1.0 and 2.91 mmol g⁻¹ (r² = 0.997 and 0.988) for lead and cadmium, respectively. Regenerability of the fiber mats was investigated and the results obtained indicate sustainability in adsorption efficacy of the material.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Synthesis of single-crystalline α-MnO2 nanotubes and structural characterization by HRTEM

Single-crystalline α-MnO₂ nanotubes were synthesized by hydrothermal method. The growth of α-MnO₂ nanotubes is through the formation of the core (γ-MnO₂)-shell (α-MnO₂) nanofibers, and then through the formation of the cavity by the dissolution of the core. The outer and the inner diameters of as-synthesized nanotubes are in the range from 13.3 to 39.2 nm, and from 2.0 to 10.8 nm, respectively. The lattice images on the wall and in the center correspond to the (2 2 0), and the (2 1 1) interplanar spacing of the tetragonal-structure α-MnO₂.