Preparation, magnetic and electromagnetic properties of polyaniline/strontium ferrite/multiwalled carbon nanotubes composite

Strontium ferrite particles were firstly prepared by sol-gel method and self-propagating synthesis, and then the polyaniline/strontium ferrite/multiwalled carbon nanotubes composites were synthesized through in situ polymerization approach. Structure, morphology and properties of the composite were characterized by various instruments. XRD analysis shows that the output of PANI increases with the increase of the content of MWCNTs, due to the large surface area of MWCNTs. Because of the coating of PANI, the outer diameter of MWCNTs increases from 10 nm to 20-40 nm. The electrical conductivity of the composites increases with the amount increase of MWCNTs and reaches 7.2196 S/cm in the presence of 2 g MWCNTs. The coercive force of the composites prepared with 2 g MWCNTs is 7457.17 Oe, which is much bigger than that of SrFe₁₂O₁₉ particles 6145.6 Oe, however, both the saturation magnetization and the remanent magnetization of the composite become much smaller than those of SrFe₁₂O₁₉ particles. The electromagnetic properties of the composite are excellent in the frequency range of 2-18 GHz, which mainly depend on the dielectric loss in the range of 2-9 GHz, and mainly on the magnetic loss in the range of 9-18 GHz.     

Electrospinning of complex oxide nanofibers

Electrospinning is a versatile process for drawing fibers of diverse materials including polymers, ceramics, and composites. We demonstrate here its application in the synthesis of complex ceramic oxide materials. The phase formation and morphology of BaTiO₃ nanofibers synthesized via electrospinning is investigated as a function of heat treatment conditions. Fully crystallized BaTiO₃ nanofibers with the perovskite structure are obtained after annealing at 750 °C and show an average grain size of about 30 nm. Tetragonal crystal structure of the fibers is indicated by XRD peak splitting (calculated c/a ratio=1.007), and confirmed by Raman spectroscopy. Furthermore, the advancement in heat treatment of the electrospun fibers yields single crystalline BaTiO₃ nanofibers with 50 nm in diameter and lengths up to 1 μm.     

Two-nozzle electrospinning of (MWNT/PU)/PU nanofibrous composite mat with improved mechanical and thermal properties

Composite nanofibrous mat composed of neat polyurethane (PU) and multiwalled carbon nanotubes/polyurethane (MWNT/PU) nanofibers have been fabricated by one-step angled two-nozzle electrospinning. The morphological, thermal, and mechanical properties of the electrospun nanofibers were evaluated. The diameters of electrospun neat PU and composite nanofibers ranged from 239 to 1058 nm. The two-nozzle electrospun (MWNT/PU)/PU composite nanofibers showed curly, and randomly-oriented fibers with interfiber bonding, and were generally bigger in size than single-nozzle electrospun nanofibers. The tensile strength of the neat PU composite nanofiber mat obtained from two-nozzle electrospinning was 25% higher than that obtained from neat PU single-nozzle electrospinning. The incorporation of MWNTs in the composite nanofiber increased the tensile strength by as much as 64% without reducing elongation, made the composite nanofiber more thermally stable, and improved the melting zone. The present results showed that side-by-side angled two-nozzle electrospinning can improve the quality of the electrospun nanofibers that could have potential application in different fields such as filtration, protective clothing and tissue engineering.     

静电纺丝法制备聚丙烯腈/银纳米粒子复合纳米纤维及其SERS特性

利用静电纺丝技术制备了一种聚丙烯腈/银纳米粒子复合纳米纤维的表面增强拉曼光谱基底。通过调节聚丙烯腈溶液的浓度可得到不同直径、不同厚度的纤维薄膜,将聚丙烯腈的N,N-二甲基甲酰胺溶液与硝酸银溶液混合得到聚丙烯腈/Ag种子溶液,然后利用静电纺丝技术制备聚丙烯腈/Ag种子/AgNO₃复合纳米纤维;加入AgNO₃并利用水合肼二次还原后可制备适合拉曼检测的聚丙烯腈/Ag纳米粒子复合纤维膜,聚合物纤维表面和内部的金属纳米粒子的密度可调节。通过调节不同的纳米粒子的密集程度,可构筑出具有较高的电磁场增强效果的特殊的“热”结构(高局域强电磁场的亚波长区域)。而聚合物纤维内部的银纳米粒子可通过溶胀作用吸附更多的探针分子,提高拉曼检测的灵敏度。该基底有很好的SERS信号,并且可大规模制备。     

Enhanced photocatalytic degradation of organic dyes by ultrasonic-assisted electrospray TiO2/graphene oxide on polyacrylonitrile/β-cyclodextrin nanofibrous membranes

Polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) composite nanofibrous membranes immobilized with nano-titanium dioxide (TiO₂) and graphene oxide (GO) were prepared by electrospinning and ultrasonic-assisted electrospinning. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) confirmed that TiO₂ and GO were more evenly dispersed on the surface and inside of the nanofibers after 45 min of ultrasonic treatment. Adding TiO₂ and GO reduced the fiber diameter; the minimum fiber diameter was 84.66 ± 40.58 nm when the mass ratio of TiO₂-to-GO was 8:2 (PAN/β-CD nanofibrous membranes was 191.10 ± 45.66 nm). Using the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB) as pollutant models, the photocatalytic activity of the nanofibrous membrane under natural sunlight was evaluated. It was found that PAN/β-CD/TiO₂/GO composite nanofibrous membrane with an 8:2 mass ratio of TiO₂-to-GO exhibited the best degradation efficiency for the dyes. The degradation efficiency for MB and MO were 93.52 ± 1.83% and 90.92 ± 1.52%, respectively. Meanwhile, the PAN/β-CD/TiO₂/GO composite nanofibrous membrane also displayed good antibacterial properties and the degradation efficiency for MB and MO remained above 80% after 3 cycles. In general, the PAN/β-CD/TiO₂/GO nanofibrous membrane is eco-friendly, reusable, and has great potential for the removal of dyes from industrial wastewaters.     

UV-protection properties of electrospun polyacrylonitrile nanofibrous mats embedded with MgO and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

This article describes the ultraviolet (UV) protection of MgO and Al₂O₃ nanoparticles embedded electrospun polyacrylonitrile (PAN) nanofibrous mats. UV radiation is a harmful part of sunlight and prolonged exposure to it can cause serious skin damages. In this research, nanofibrous mats consisting of nanofibers with different diameters containing different amounts of MgO, Al₂O₃, MgO Plus, and Al₂O₃ Plus nanoparticles were produced, and their UV-protection was measured. The specific surface area of MgO, MgO Plus, Al₂O₃, and Al₂O₃ Plus nanoparticles was 230, 600, 275, and 550 m²/g, respectively. The mean diameter of electrospun PAN nanofibers embedded with metal oxide nanoparticles was in the range of 665–337 nm. The results showed that the UV-protection (shielding) capability of the mats strongly depends on fiber diameter; in fact a thin mat of nanofibers has a much stronger UV-protection in comparison to a thicker mat composed of regular fibers. UV transmission is reduced as a result of embedding MgO and Al₂O₃ nanoparticles in the electrospun PAN nanofibrous mats. MgO Plus and Al₂O₃ Plus show higher UV-protection than MgO and Al₂O₃.     

Directional conductivity in layered alumina

Here we report a novel strategy to consolidate layered alumina demonstrating the directional electrical and thermal conductivity. The material was produced via incorporation of alumina nanofibers (20 ± 2 nm in diameter) decorated by several layers of graphene wrapped around longitudinal axes of the fibers. The graphenated fibers, obtained with the help of one-step catalyst-free CVD process, offered inhibition of grain growth combined with electrical conductivity to the sandwiched composites, which were consolidated by spark plasma sintering. Impact of the concentration of the fillers together with thickness of the conductive graphene-containing layer on thermal properties was studied. A graphene-containing interlayer with 50 μm thickness, sandwiched between two monolithic 10 mm layers of alumina shows ~30% enhancement in isotropic thermal conductivity of monolithic alumina.     

Development of high efficiency nanofilters made of nanofibers

Electrospinning is a fabrication process that uses an electric field to control the deposition of polymer fibers onto a target substrate. This electrostatic processing strategy can be used to fabricate fibrous polymer mats composed of fiber diameters ranging from several microns down to 100 nm or less. In this study, optimized conditions to produce nanofibers using Nylon 6 are investigated and the Nylon 6 nanofilters using nanofibers of 80–200 nm in diameter are designed and evaluated the filtration efficiency and pressure drop across the filter. When the Nylon 6 concentration is 15 wt.%, electrospun fibers have an average diameter of 80 nm, but there are many beads, and the concentration increases to 24 wt.%, the fiber diameter gradually thickens to 200 nm, but there are not any beads. When the spinning distance is small, the thinner nanofibers are produced and the more fibers are collected on the grounded electrode. The filtration efficiency of Nylon 6 nanofilters is 99.993% superior to the commercialized HEPA filter at the face velocity of 5 cm/s using 0.3 μm test particles. Even though the high pressure drops across the nanofilter, they show the potential to have the application of HEPA and ULPA grade high efficiency filter.     

Electrospun precursor carbon nanofibers optimization by using response surface methodology

Ultrafine fibers were electrospun from Polyacrylonitrile and N,N-dimethylformamide solution to be used as a precursor for carbon nanofibers. An electrospinning set-up was used to collect fibers with diameter ranging from 104 nm to 434 nm. Morphology of fibers and its distribution were investigated by varying Berry's number, charge density, spinning angle, spinneret diameter and collector area. A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by using response surface methodology. It was concluded that; Berry's number, charge density and spinneret diameters played an important role to the diameter of nanofibers and its standard deviation. Spinning angle and collector area had no significant impact. Based on response surface methodology the optimum Polyacrylonitrile average fiber diameter of 280 nm and 28 nm standard deviation, were collected at 1.6 kV/cm charge density, 8 Berry's number and 0.9 mm spinneret diameter.     

Nanocomposite fabric formation by electrospinning and electrospraying technologies

Electrospraying and electrospinning processes were employed for the production of nanocomposite material of polymer nanofibers blended with nanoparticles. The diameter of polymer nanofibers made of PVC, PSU or nylon was smaller than 500 nm. Metal oxide nanoparticles of TiO₂, MgO, and Al₂O₃ of the size 20–100 nm suspended in methanol were deposited on the polymer nanofibers. Three configurations of electrospray/electrospun nozzles used for the nanocomposite production were tested: 1. simultaneous electrospraying during the electrospinning process, 2. electrospraying onto the same rotating drum after the electrospinning is completed, and 3. electrospraying onto the electrospun mat removed from the drum and placed onto a heated table.     

Poly(Butylene Terephthalate)/Single Wall Carbon Nanotubes Composite Nanofibers by Electrospinning

Poly(buthylene terephthalate)(PBT)/single wall carbon nanotubes (SWCNTs) composite nanofibers were prepared by electrospinning. The effect of carbon nanotubes on the morphology, crystallization, and mechanical properties of the electrospun composite nanofibers were investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of SWCNTs resulted in finer nanofibers for lower loading; however, a broader distribution, especially for the higher diameter ranges was found for nanofibers with higher amounts of carbon nanotubes. SWCNTs accelerated crystallization and acted as a nucleating agent; the degree of crystallinity increased with increasing content of SWCNTs, followed by a moderate decrease at higher content. Specific tensile strength and modulus of the PBT/SWCNTs composite nanofibers mats were higher than that of neat PBT nanofibers mat. However, the elongation at break of composite nanofibers mats was lower than that of the neat PBT nanofibers mat.     

Preparation of carbon nanotubes-incorporated polymeric microspheres for electrorheological fluids

Electrically conducting polymeric microspheres having an average diameter of 92 μm were prepared from composites of multiwalled carbon nanotubes (MWCNTs) and suspension-polymerized poly(vinyl chloride) (PVC) particles. Cetyl trimethylammonium bromide and sodium dodecylbenzene sulfonate were selected as the surfactants to stably disperse the MWCNTs in water. Strong adhesion of MWCNTs on the surfaces of the PVC microspheres was observed from the images obtained by field emission scanning electron microscopy. The amount of MWCNTs adsorbed on the microspheres was approximately 2 wt.%, determined by thermogravimetric analysis. The electrical conductivity of these composite-microspheres was remarkably increased upto 1.5 × 10⁻⁴ S/cm compared with that of the pure PVC microspheres (less than 10⁻¹⁴ S/cm), because of the electrically conducting MWCNTs on their surfaces. These microspheres also showed an electrorheological (ER) effect under an electric field (1.8 kV/mm) owing to the interfacial polarization of the MWCNTs-adsorbed microspheres, when they were dispersed in silicone oil (20 wt.%). The MWCNT-adsorbed PVC microspheres formed linear structures by electric force; i.e. the individual microspheres were connected to neighboring microspheres.     

Influence of carbon nanofibers on electrochemical properties of carbon nanofibers/glass fibers composites

Conducting glass fiber fabrics (GFs) with double-scale roughness were fabricated by growing carbon nanofibers (CNFs) on its surfaces. The homogeneous growth of CNFs was achieved by the decomposition of C₂H₂ on glass fibers surfaces coated with Fe-doped mesoporous silica films at different C₂H₂ flow rates. The chemical composition and surface structure of the GFs before and after CNFs growth were examined by electron dispersive X-ray spectrometry (EDX), N₂ full isotherms, and scanning electron microscopy (SEM). The electrical properties of the GFs were examined using a four-probe volume resistivity tester. The CNFs with a mean diameter of 50 nm grew uniformly and densely on the glass fiber surfaces. The CNFs/GFs fabrics surface exhibited excellent electrochemical properties due to the CNFs. The specific capacitance of the GFs ranged from 0.2 to 4 F/g at 1 A/g in a 1 M H₂SO₄ aqueous solution.     

Room-temperature power factor of CuAlO2 composite tablets enhanced by MWCNTs

CuAlO₂ with high theoretical thermoelectric performance has potential applications in thermal energy conversion. Herein, multi-wall carbon nanotubes (MWCNTs)/CuAlO₂ composite tablets are prepared by using different amounts of MWCNTs and solid paraffin binder, where MWCNTs served as a conductive agent and rendered three orders of magnitude increase in electrical conductivity. Seebeck coefficient of the composites was reduced with increasing MWCNTs content. Consequently, an optimal room-temperature thermoelectric power factor (PF) of 1.31 μW m⁻¹K⁻² has been rendered by MWCNTs/CuAlO₂ composite tablet with 1 wt % MWCNTs. Moreover, PF value increased with increasing temperature after a slight decrease at 333 K, which can be ascribed to the modulation of electrical conductivity. Current work provides an effective strategy to improve thermoelectric performance of CuAlO₂ materials.     

High Adsorption Pearl‐Necklace‐Like Composite Membrane Based on Metal–Organic Framework for Heavy Metal Ion Removal

The zeolitic imidazolate framework‐67 (ZIF‐67)‐based “pearl‐necklace‐like” composite membranes are prepared by in situ intergrown on the surface of 2‐methylimidazole/cellulose acetate (MIM/CA) electrospun nanofibers for the first time. With the aid of MIM, the ZIF‐67 nanocrystals successfully grow throughout the composites and attach to the fibers just like the pearls in necklace. The incubation time of ZIF‐67 has a significant influence on the structures and properties of the composites. And with an approximate saturation of ZIF‐67 nanocrystals, the integrated composites achieve a much higher surface area of 463.1 m2 g⁻¹, which is as dozens of times as that of pure MIM/CA electrospun nanofibers (6.9 m2 g⁻¹). In addition, the composites performed a high Cu(II) and Cr(VI) adsorption of 18.9 mg g⁻¹ and 14.5 mg g⁻¹, respectively. The adsorption data are well fitted with the pseudo‐second‐order kinetics. Moreover, adsorption mechanism is also discussed, and the electrostatic adsorption and ions exchange contribute to the high adsorption of Cu(II) and Cr(VI), and the existence of Cr(III) indicates that the Cr(VI) ions are partially reduced to Cr(III) during the adsorption. Therefore, the fabricated metal organic framework‐composite membrane with special “pearl‐necklace‐like” is a promising environmental material for removing heavy metal ions from water.     

Fabrication and characterization of bismuth oxide–holmia nanofibers and nanoceramics

In this article, a novel and simple method to produce both boron doped and undoped holmia stabilized bismuth oxide nanoceramic materials has been put forward. Boron doped and undoped poly (vinyl alcohol)/bismuth–holmia acetate nanofibers were produced using the electrospinning technique and were calcined at 850 °C afterward in order to obtain nanopowder. The characteristics of the nanofibers were investigated with FT-IR, XRD, and SEM. XRD analyses showed that boron undoped holmia stabilized bismuth oxide nanopowders have the face-centered cubic structure (δ-phase), and that the incorporation of boron atoms into the composite prevents the nucleus formation and turns the structure into a more amorphous glassy form. The SEM micrographs of the fibers showed that the addition of boron results in the formation of cross-linked bright-surfaced fibers. The average fiber diameters for electrospun boron doped and undoped PVA/Bi–Ho acetate nanofibers were calculated using the ImageJ software as 102 nm and 171 nm, respectively.     

Investigation of Effect of Electrospinning Parameters on the Morphology of Polyacrylonitrile/Polymethylmethacrylate Nanofibers: A Box–Behnken-Based Study

Polyacrylonitrile (PAN)- and polymethylmethacrylate (PMMA)-blended nanofibers produced using electrospinning and mat morphology were studied. The response surface method was exploited to optimize the diameter and its standard deviation of electrospun PAN/PMMA non-woven membranes. The diameter and its standard deviation were related to the solution concentration, applied voltage, and PMMA composition. The morphology of nanofibers was studied by means of field emission scanning electron microscopy. The importance of parameters and their interactions was investigated through the analysis of variance. The nanofibers' diameter increased with solution concentration and decreased with applied voltage. The data showed that the diameter of nanofibers decreased up to 50% with PMMA composition, and then increased with further increase of PMMA composition. Some important interactions between the parameters were detected.     

Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning

In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25 kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75-110 nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.     

Thermal and electrical conductivity of poly(l-lactide)/multiwalled carbon nanotube nanocomposites

Multiwalled carbon nanotubes (MWCNTs) are considered to be the ideal reinforcing agent for high-strength polymer composites, because of their fantastic mechanical strength, high electrical and thermal conductivity and high aspect ratio. Polymer/MWCNTs composites are easily molded, and the resulting shaped plastic articles have a perfect surface appearance compared with polymer composites made using usual carbon or glass fibers. Good interfacial adhesion between the MWCNTs and the polymer matrix is essential for efficient load transfer in the composite. The ultrahigh strength polymer composites demand the uniform dispersion of the MWCNTs in the polymer matrix without their aggregation and the good miscibility between MWCNT and polymer matrix. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt-compounded with MWCNTs. A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The electrical conductivity of the composites was determined by measuring the volume resistivity, which is a value of the resistance expressed in a unit volume by two-probe method. The thermal diffusivity and heat capacity of composites was measured by laser flash method, and the effects of modification of the MWCNT in PLLA matrix are discussed.     

Preparation and Characterization of Polyacrylonitrile and Polyacrylonitrile/β-cyclodextrins Microspheres

Polyacrylonitrile (PAN) and PAN/β-cyclodextrin (β-CD) microspheres were prepared via an electrospinning method. The PAN microspheres could be successfully obtained in a suitable range of concentrations of electrospun PAN solutions. When β-CD was added to the PAN solutions, electrospun PAN/β-CD composite spheres were prepared. The morphology of the spheres was characterized by scanning electron microscopy (SEM); it showed that the spheres had uniform diameter and a smooth surface. The composition of the composite microspheres was studied by Fourier transform infrared spectroscopy (FTIR). The results showed that the β-CD was incorporated in the polymer microspheres.