Fabrication of MWNTs/nylon conductive composite nanofibers by electrospinning

MWNT/nylon 6, 6 composite nanofibers were fabricated using an electrospinning method, and the electrical properties were examined as a function of the filler concentration. Initially, the pristine, purified MWNTs were treated with a 3:1 mixture of concentrated H₂SO₄/HNO₃ to introduce carboxyl groups onto the MWNT surface. The carboxylated MWNTs were then treated with thionyl chloride and an ethylenediamine solution for amide functionalization. FT-IR spectroscopy was used to examine the functionalization of the MWNTs. Nylon 6, 6 is readily soluble in formic acid. Therefore, the amide functionalized MWNTs were dispersed in formic acid. The solution remained stable and uniform for more than 40 h. –NH₂ termination of the MWNTs improved the dispersion stability of the MWNTs in formic acid. The MWNTs-suspended in a solution of nylon 6, 6 in formic acid was electrospun to obtain the nanofibers. The electrical properties of the nanofibers were examined as a function of the filler concentration. The results showed that the I–V properties of the nanofiber sheet improved with increasing filler concentration.     

Synthesis of TiO2 scaffold by a 2 step bi-layer process using a molten salt synthesis technique

TiO₂ scaffolds of anisotropic rutile particles were grown from rutile seeds by using molten salt synthesis techniques. The rutile seeds were either in the form of a separate layer applied on a substrate or a sintered bulk pellet. Mixtures of amorphous titanium hydroxide and salt applied as coatings on the rutile seeds were heat treated. Depending on the morphology of the seed layer, heat treatment temperature, time and salt medium, rutile was grown with different morphologies and microstructures. For NaCl-KCl eutectic salt mixture and heat treatment at 700 °C for 5 h, nano-whiskers of 20-50 nm diameter and 0.5-1 μm length were obtained. For the NaCl salt sample treated at 850 ºC for 20 h, rutile platelets of 2-5 μm thick, 2-10 μm wide and 5-25 μm in length were produced. X-ray diffraction and Raman scattering were used to identify and characterize the rutile phase of the nanowhiskers.     

Electrochemical properties of polypyrrole/sulfonted SEBS composite nanofibers prepared by electrospinning

The electrochemical behavior of electrospun polypyrrole (PPy)/sulfonated-poly(styrene-ethylene-butylenes-styrene) (S-SEBS) composite nanofibers was investigated, compared to PPy/poly(styrene-ethylene-butylenes-styrene) (SEBS) fibers prepared by a casting method. The electrospun PPy/S-SEBS (E-PSS) fibers were about 300 nm in average diameter, while PPy/SEBS composite (C-PS) prepared by a casting method showed the granular macroporous structure. The effect by both electrospinning and sulfonation results in higher electrochemical capacity due to the increase of doping level, high electrical conductivity, low interfacial resistance, and high reversibility by easy intercalation of Li ion. In addition, sulfonated SEBS induces higher elongation force to jet in the processing of electrospinning due to the role of dopant.     

Synthesis and characterization of calcium zirconate nanofibers produced by electrospinning

Calcium zirconate fibers were produced by electrospinning and characterized in this work. The solution was prepared from zirconium and calcium salts, using polyvinyl-pyrrolidone (PVP) as processing aid. The decomposition of the organic fraction and crystallization of calcium zirconate were followed by thermogravimetry and differential scanning calorimetry (TG/DSC). Raman Spectroscopy was used to measure the vibrational modes in the green as well as in the calcined fibers. The final phase composition was studied by means of X-ray diffraction (XRD). The fiber morphology was investigated by confocal laser scanning microscopy (CLS) and scanning electron microscopy (SEM). The formation reaction of calcium zirconate was observed at about 740 °C. Highly crystalline fibers were obtained already at 800 °C, but the crystallinity and calcium zirconate yield improved when the temperature was increased to 1000 °C.     

Synthesis and characterization of PVB/silica nanofibers by electrospinning process

This paper describes PVB/silica nanofibers which were fabricated by electrospinning. Although electrospinning has developed rapidly over the past few years, electrospinning nanofibers are still at a premature research stage which is a process by which polymer nanofibers can be formed when a droplet of viscoelastic polymer solution is subjected to high voltage electrostatic field. PVB/silica nanofibers were obtained when the PVB/silica precursor ratio was 15% and the average diameters ranged from 100 to 200 nm and increased with increasing solution concentration and electrospinning synthesized at 12 kV of the applied voltage. The morphologies and structures of PVB/silica nanofibers were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analyzer (TGA), Fourier transform infrared spectrometer (FTIR), energy dispersive spectrometer (EDS).     

Growth of Zn2GeO4 thin film by thermal evaporation on ITO substrate for thermoelectric power generation applications

In this paper, we have reported the growth of Zn₂GeO₄ thin film and investigated its potential for thermoelectric power generation applications. Zn₂GeO₄ alloy thin film was grown on Indium coated glass substrate by the evaporation of Zn and Ge metals with constant oxygen gas flow rate of 100 sccm in tube furnace. The grown film was cut into pieces and annealed at various temperatures from 500° to 700°C with a step of 100?°C in a programmable furnace for one hour. The structure of as grown and annealed thin films was verified by XRD and Raman spectroscopy measurements. The XRD data evident that Zn₂GeO₄ alloy hexagonal structure along with GeO₂ and ZnO phases were observed at annealing temperatures 600 and 700?°C but below this temperature no alloy phase was detected by XRD and Raman Spectroscopy. To calculate the thermoelectric properties, temperature dependent Seebeck measurements were performed in the temperature range of 25–100?°C. It was observed that the value of Seebeck coefficient was increased from 91 to 847?μV/K as the annealing temperature increases from 500° to 700°C. This behavior was explained as; high temperature causes stress and cracks in the grown films which may induce electric and thermal discontinues at tips of cracks which cause high thermoelectric concentration. Scanning electron microscope images verified the development of cracks in the samples as annealing temperature increases. The behavior of Seebeck coefficient with the measurement temperature was also observed and explained in detail. The high value of Seebeck coefficient suggested that this material can be a potential candidate for thermoelectric power generation applications in near future.     

Effect of reaction temperature on CVD-made TiO2 primary particle diameter

The effect of chemical reaction rate on the generation of titania nanoparticles by chemical vapor deposition using two different precursors was investigated by FTIR, XRD, and microscopy. The size of the primary particle exhibited a minimum with increasing reactor temperature. At lower reaction temperatures, the continuous and gradual formation of titania monomers occurred followed by coagulation and/or surface reaction on the existing particles. In addition, unreacted precursor condensed at the reactor exit. As the reaction temperature increased, the rate of monomer production increased, the dominant characteristics of particle growth were coagulation and sintering. The reactor temperature where the minimum primary particle diameter was produced was different for the two precursors due to differences in chemical reaction rates. Phase composition as well as the primary particle diameter of product titania were affected by the chemical reaction rate. Particle-laden reactor wall enhanced the precursor conversion at low reactor temperatures, where surface reactions compete effectively with gas-phase precursor conversion.     

Preparation of ordered TiO2 nanofibers/nanotubes by magnetic field assisted electrospinning and the study of their photocatalytic properties

Ordered-and-oriented TiO₂ nanofibers and nanotubes were prepared by magnetic field-assisted electrospinning, and photocatalytic properties of all samples were analyzed under UV–Vis shine. TiO₂ nanofibers/nanotubes prepared by magnetic field-assisted electrospinning showed better degradation effect on rhodamine B, reduced the band gap, increased the contact area of organic pollutants with the sample and higher photocatalytic activity than TiO₂ nanofibers/nanotubes prepared by classical electrospinning. The product obtained after high temperature annealing was a mixed phase of rutile phase and anatase phase and could be advantageous to the segregate of photogenic electron hole pairs and enhance the high dye absorption capacity; Surface roughness could increase more active sites and accelerate the reaction rate of photocatalytic activity; the addition of magnetic field regulated the morphology of TiO₂, and narrowed the band gap to favor photocatalytic performance. The magnetic field-assisted electrospinning study prepared in this paper was an easy-to-use and versatile method for the preparation of ordered TiO₂ nanomaterials, which could be easily extended to practical applications or other materials for photocatalysis and water cleavage.     

Characterization of SrWO4-PVA and SrWO4 spiders’ webs synthesized by electrospinning

Mixtures of strontium acetate, ammonium metatungstate hydrate, and different contents of poly (vinyl alcohol) (PVA, 125,000 MW) were electrospun by a +15 kV direct voltage to synthesize SrWO₄-PVA spiders’ webs. The spider's web, synthesized from the solution containing 1.3 g PVA, was further calcined in air at 300-600 °C for 3 h. The SrWO₄-PVA spider's web was analyzed by thermogravimetric analyzer (TGA) to specify the evaporation and decomposition of PVA and volatile components. In addition, the SrWO₄-PVA and SrWO₄ spiders’ webs were characterized by X-ray diffractometer (XRD), selected area electron diffraction (SAED), scanning and transmission electron microscopes (SEM, TEM), and ultraviolet (UV)-visible and photoluminescence (PL) spectrometers, including the vibration modes by Fourier transform infrared (FTIR) and Raman spectrometers. A possible formation mechanism of SrWO₄-PVA and SrWO₄ spiders’ webs was also proposed according to the experimental results.     

The effects of atmosphere and calcined temperature on photocatalytic activity of TiO2 nanofibers prepared by electrospinning

TiO₂-based nanofibers were synthesized using a sol–gel method and electrospinning technique. The as-spun composite fibers were heat-treated at different temperatures (500°C, 550°C, 600°C, and 650°C) and atmospheres (ammonia and nitrogen) for 4 h. The fibers had diameters of 50 to 200 nm and mainly featured anatase and rutile phases. The anatase phase decreased and the rutile phase increased with increasing temperature. Different nitrogen conditions exerted minimal effects on the TiO₂ crystalline phase. Different nitriding atmospheres during preservation heating yielded various effects on fibers. The effect of nitrogen in ammonia atmosphere is better than that in nitrogen atmosphere. The fibers heat-treated at 600°C and subjected to preservation heating in NH₃ showed high photocatalytic activity.     

Effect of tethering chemistry of cationic surfactants on clay exfoliation, electrospinning and diameter of PMMA/clay nanocomposite fibers

We examine the influence of tethering chemistry of cationic surfactants on exfoliation of montmorillonite (MMT) clay dispersed in methyl methacrylate (MMA) followed by in-situ polymerization to form poly(methyl methacrylate) (PMMA) nanocomposites, the effect of exfoliation and clay loading on the rheology of polymer/clay dispersions in dimethyl formamide, and the diameters of nanocomposite fibers formed from these dispersions by electrospinning. Incorporation of an additional reactive tethering group of methacryl functionality significantly improves the intercalation and exfoliation of clays in both in-situ polymerized PMMA nanocomposites and the corresponding electrospun fibers. The proper surfactant chemistry also increases the dispersion stability, extensional viscosity, extent of strain hardening and thus the electrospinnablity of the nanocomposite dispersions, especially at low nanocomposite concentrations. The degree of the enhancement in electrospinnability by clays with proper tethering chemistry is at least the same as or greater than that obtained with three times higher loading level of clay particles without proper tethering chemistry in the nanocomposites. These results suggest a new strategy to produce smaller diameter fibers from very dilute polymer solutions, which are otherwise not electrospinnable, by incorporating a small amount of well-exfoliated clays.     

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 − x)SiO₂-(x)ZrO₂ (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO₂ were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO₂ in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.     

Polyvinylbutyral assisted synthesis and characterization of chalcopyrite quaternary semiconductor Cu(InxGa1−x)Se2 nanofibers by electrospinning route

Chalcopyrite quaternary semiconductor Cu (In_xGa_1−x) Se₂ nanocrystals were successfully prepared via a relatively simple electrospinning route and characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Semiconductor Cu(In_xGa_1−x)Se₂ nanofibers were obtained for PVB/Cu(In_xGa_1−x)Se₂ precursor at an applied voltage of 20 kV after annealing treatment at 400 °C for 6 h. The optical property of Cu (In_xGa_1−x) Se₂ nanocrystals was also recorded by means of UV-vis absorption spectroscopy. We also report the first electrospinning synthesis of uniform chalcopyrite crystals Cu (In_xGa_1−x)Se₂ nanofibers and demonstrate can be used to create simple thin film solar cells, with our first cells exhibiting an efficiency of 1.96% under AM1.5 illumination.     

Structural,morphological, optical,and thermal properties of electrospun PbS/PVP-PEO nanofibers

This study describes the preparation and characterization of PVP-PEO nanofibers filled with PbS nanoparticles. The effect of polymer concentrations, surface morphology, and diameter distribution studies of the nanofibers was evaluated by Scanning Electron Microscopy (SEM). The SEM images revealed that smooth and homogeneous nanofibers could be achieved at 12% PVP-PEO (50:50 wt%) concentration. The XRD and TEM analysis confirmed the formation of PbS nanoparticles in the PVP-PEO blend matrix, which also revealed the high crystalline behaviour of the PbS nanoparticles. The XRD data showed that the intensity and average crystallite size increase with PbS concentration. The FTIR and TGA studies revealed the interaction between PbS nanoparticles and the PVP-PEO blend matrix. UV–Vis diffuse reflectance studies have shown that the reflectance onset shifted toward a blue shift than bulk PbS. The optical bandgap determined using the Kubelka-Munk function lies 1.08–1.56 eV range by varying PbS concentration.     

Microstructure and elastic modulus of electrospun Al2O3-SiO2-B2O3 composite nanofibers with mullite-type structure prepared at elevated temperatures

In the present work, Al₂O₃-SiO₂-B₂O₃ composite nanofibers with mullite-type structure were prepared using electrospinning technique. The microstructure and elastic modulus of the composite nanofibers obtained at elevated temperatures were studied. The results showed that Al₄B₂O₉ phase formed at 900 °C and then transformed to Al₁₈B₄O₃₃ at 1100 °C. Mullite was also detected in the nanofibers prepared at 1100 °C. Amorphous SiO₂ existed in all samples even the calcination temperature reached up to 1400 °C. The continuous and uniform structure of the composite nanofibers was kept after calcining at different temperatures, while rougher surface was evident due to the growth of the grain caused by the elevated temperature. An increase of elastic modulus of the samples from 9.47 ± 1.91 GPa to 27.30 ± 2.61 GPa was observed when calcination temperatures increased from 800 °C to 1400 °C.     

Highly sensitive acetone-sensing properties of Pt-decorated CuFe2O4 nanotubes prepared by electrospinning

Pristine and Pt-decorated copper ferrite nanotubes (Pt-CuFe₂O₄ NTs, 0.1%, 0.5%, and 1.0%, mole percent) were prepared by a simple electrospinning method. The samples were characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscope. Their gas-sensing properties were evaluated by a commercial CGS-4TPs system. Microscopic images showed that all samples consisted of well-defined nanotubes with diameter of 70?100 nm. Gas-sensing measurements revealed that the Pt-CuFe₂O₄ NTs had an improved acetone-sensing properties compared with pristine CuFe₂O₄ NTs. In particular, 0.5% Pt-CuFe₂O₄ NT-based sensor showed a high response (16.5 at 100 ppm), good selectivity, and long-term stability for acetone at 300 °C. In addition, more Pt dopants would have a greater effect on promoting the sensing properties of the CuFe₂O₄ NTs at high acetone concentrations. A gas-sensing enhancement mechanism of Pt-CuFe₂O₄ NT-based sensors was proposed, according to the catalytic oxidation process of acetone molecules, which could be due to the kinetic competition between Pt dopants and CuFe₂O₄ NTs.     

Structural,magnetic and photocatalytic properties of Sr2+ doped BiFeO3 nanofibres fabricated by electrospinning

Sr²⁺ doped BiFeO₃ (Bi_1-xSr_xFeO₃, 0?≤x?≤?0.35) nanofibres were fabricated by a sol-gel based electrospinning method. The as-spun BiFeO₃ (BFO) nanofibres consist of fine grained particles with high crystallinity. With Sr²⁺ doping, both the magnetic and photocatalytic properties of BFO are effectively improved. The best photocatalytic property for degradation of the methylene blue (MB) is obtained in Bi_0.75Sr_0.25FeO₃ nanofibres due to their weakest photoluminescence (PL) intensity. Meanwhile, the photocatalytic property of Bi_0.75Sr_0.25FeO₃ nanofibres is much higher than that of nanoparticles with the same constituent, which is attributed to the unique one-dimension fibrous structure benefiting the separation and decreased recombination of e^-/h⁺ pairs. This work proposes an effective approach for the degradation of organic pollutes.     

Improved performance of dense TiO2/CdSe coupled thin films by low temperature process

Dense TiO₂ and TiO₂/CdSe coupled nanocrystalline thin films were synthesized onto ITO coated glass substrate by chemical route at relatively low temperature (≤100 °C). TiO₂ films were nanocrystalline and crystallinity disappears after CdSe deposition as evidenced by X-ray powder diffraction. Surface morphology and physical appearance of films were studied from SEM and actual photo-images, reveals dense nature of TiO₂ (10-12 nm spherical grains, faint violet) and CdSe (80-90 nm spherical grains, deep brown), respectively. Presence of two absorption edges in UV spectra implies existence of separate phases rather than composite formation. TiO₂ film was found to have higher water contact angle (71°) than TiO₂/CdSe (61°) and CdSe (56°). I-V and stability tests of photo-electrochemical cells were performed with TiO₂ and TiO₂/CdSe film electrodes (under light of illumination intensity 80 mW/cm²) in lithium iodide as an electrolyte using two-electrode system.     

Effect of LiCl on electrospinning of PAN polymer solution: theoretical analysis and experimental verification

Polyacrylonitrile(PAN) is used to study the effect of surface charge on electrospinning by adding LiCl. The theoretical analysis shows that the relationship between radius r of jet and the axial distance z from nozzle follows an allometric law in the form r∼z^−0.5 in case of full surface charge, and the scaling exponent becomes larger for partly charged fibers in electrospinning.     

Growth of Mg2GeO4 nano-crystals on Si substrate and modulation of Seebeck coefficient by post growth annealing technique

We have reported the successful growth of Mg₂GeO₄ nano-crystals by simple thermal evaporation technique. The Mg and Ge metal powders were evaporated on the Si substrate and kept the oxygen flow rate of 100 sccm. The modulation of structural, morphological, thermoelectric and electrical properties was performed by controlling the thermal energy of carriers using different annealing temperatures. XRD data showed a peak at 61.8⁰ which was related to (212) plane of Mg₂GeO₄. XRD data further suggested that sample annealed at 700 °C has stable crystal structure while sample annealed at 800 °C posses degraded structure because the presence of highest density of donors defects. This defect concentration causes an increase in the conductivity of annealed samples as evident by the Hall data. This argument was also supported by Raman spectroscopy which showed that sample annealed at 700 °C has strongest Mg₂GeO₄ Raman peak. SEM images also verified the smooth surface of the sample annealed at 700 °C. The temperature dependent (25–100 °C) Seebeck effect measurements were performed to calculate the Seebeck coefficient of Mg₂GeO₄ nano-crystals at different measurement temperatures. The highest value of room temperature Seebeck coefficient (397 μV/⁰C) for the sample annealed at 800 °C is due the high density of carrier concentration.