Photoluminescent electrospun polymeric nanofibers incorporating germanium nanocrystals

The photoluminescent germanium nanocrystals (Ge-NCs) were successfully incorporated into electrospun polymeric nanofiber matrix in order to develop photoluminescent nanofibrous composite web. In the first step, the synthesis of Ge-NCs was achieved by nanosecond pulsed laser ablation of bulk germanium wafer immersed in organic liquid. The size, the structural and the chemical characteristics of Ge-NCs investigated by TEM, XPS, XRD and Raman spectroscopy revealed that the Ge-NCs were highly pure and highly crystalline having spherical shape within 3–20 nm particle size distribution. In the second step, Ge-NCs were mixed with polyvinyl alcohol (PVA) polymer solution, and then, Ge-NC/PVA nanofibers were obtained via electrospinning technique. The electrospinning of Ge-NCs/PVA nanoweb composite structure was successful and bead-free Ge-NCs/PVA nanofibers having average fiber diameter of 185 ± 40 nm were obtained. The STEM analysis of the electrospun Ge-NCs/PVA nanofibers elucidated that the Ge-NCs were distributed homogeneously in the polymeric nanofiber matrix. The UV–Vis absorption and photoluminescence spectroscopy studies indicated the quantum confinement effect of Ge-NCs on the optical properties of the electrospun Ge-NCs/PVA nanoweb.     

Fabrication of cadmium titanate nanofibers via electrospinning technique

Here we present an electrospinning technique for the fabrication of cadmium titanate/polyvinyl-pyrrolidone composite nanofibers. The composite nanofibers are then annealed at 600 °C to obtain ilmenite rhombohedral phase cadmium titanate nanofibers. The structure, composition, thermal stability and optical properties of as synthesized and annealed cadmium titanate nanofibers are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. The average diameter and length of the nanofibers are found to be ～150–200 nm and ～100 μm, respectively.     

Photocatalytic degradation of dairy effluent using AgTiO2 nanostructures/polyurethane nanofiber membrane

Dairy effluent (DE) is environmentally toxic and needs special attention. Photocatalytic degradation of DE was studied using novel polyurethane (PU)-based membranes. Typically, silver–titanium dioxide nanofibers (AgTiO₂ NFs) and silver–titanium dioxide nanoparticles (AgTiO₂ NPs) were individually incorporated in PU electrospun nanofibers to overcome the mandatory sophisticated separation of the nanocatalysts, which can create a secondary pollution, after the treatment process. These nanomembranes were characterized in SEM, TEM, XRD and UV studies. The polymeric electrospun nanofibers were smooth and continuous, with an average diameter of about 550 nm, and held their nanofibrous morphology even after more than 2 h of photocatalytic degradation of DE, due to the good stability of PU in the aqueous solutions, which indicates good imprisoning of the functional photocatalysts. The PU–AgTiO₂ NPs and PU–AgTiO₂ NFs were effective materials for degradation of DE, even after two successive cycles. PU–AgTiO₂ NPs and PU–AgTiO₂ NFs showed a maximum degradation of 75% and 95%, respectively after 2 h. The significant enhancement of degradation in the PU–Ag–TiO₂ NPs and PU–Ag–TiO₂ NFs is attributed to the photoactivity of Ag–TiO₂ material under visible light irradiation.     

Graphene oxide/hydroxyapatite composite coatings fabricated by electrophoretic nanotechnology for biological applications

Graphene oxide (GO) was firstly employed as nanoscale reinforcement fillers in hydroxyapatite (HA) coatings by a cathodic electrophoretic deposition process, and GO/HA coatings were fabricated on pure Ti substrate. The transmission electron microscopy observation and particle size analysis of the suspensions indicated that HA nanoparticles were uniformly decorated on GO sheets, forming a large GO/HA particle group. The addition of GO into HA coatings could reduce the surface cracks and increase the coating adhesion strength from 1.55 ± 0.39 MPa (pure HA) to 2.75 ± 0.38 MPa (2 wt.% GO/HA) and 3.3 ± 0.25 MPa (5 wt.% GO/HA), respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy studies indicated that the GO/HA composite coatings exhibited higher corrosion resistance in comparison with pure HA coatings in simulated body fluid. In addition, superior (around 95% cell viability for 2 wt.% GO/HA) or comparable (80–90% cell viability for 5 wt.% GO/HA) in vitro biocompatibility were observed in comparison with HA coated and uncoated Ti substrate.     

Improved graphitization and electrical conductivity of suspended carbon nanofibers derived from carbon nanotube/polyacrylonitrile composites by directed electrospinning

Single suspended carbon nanofibers on carbon micro-structures were fabricated by directed electrospinning and subsequent pyrolysis at 900 °C of carbon nanotube/polyacrylonitrile (CNT/PAN) composite material. The electrical conductivity of the nanofibers was measured at different weight fractions of CNTs. It was found that the conductivity increased almost two orders of magnitude upon adding 0.5 wt.% CNTs. The correlation between the extent of graphitization and electrical properties of the composite nanofiber was examined by various structural characterization techniques, and the presence of graphitic regions in pyrolyzed CNT/PAN nanofibers was observed that were not present in pure PAN-derived carbon. The influence of fabrication technique on the ordering of carbon sheets in electrospun nanofibers was examined and a templating effect by CNTs that leads to enhanced graphitization is suggested.     

Composite chitosan/poly(ethylene oxide) electrospun nanofibrous mats as novel wound dressing matrixes for the controlled release of drugs

The aim of this study was to develop novel biomedical electrospun nanofiber mats for controlled drug release, in particular to release a drug directly to an injury site to accelerate wound healing. Here, nanofibers of chitosan (CS), poly(ethylene oxide) (PEO), and a 90 : 10 composite blend, loaded with a fluoroquinolone antibiotic, such as ciprofloxacin hydrochloride (CipHCl) or moxifloxacin hydrochloride (Moxi), were successfully prepared by an electrospinning technique. The morphology of the electrospun nanofibers was investigated by scanning electron microscopy. The functional groups of the electrospun nanofibers before and after crosslinking were characterized by Fourier transform infrared spectroscopy. X‐ray diffraction results indicated an amorphous distribution of the drug inside the nanofiber blend. In vitro drug‐release evaluations showed that the crosslinking could control the rate and period of drug release in wound‐healing applications. The inhibition of bacterial growth for both Escherichia coli and Staphylococcus aureus were achieved on the CipHCl‐ and Moxi‐loaded nanofibers. In addition, both types of CS/PEO and drug‐containing CS/PEO nanofibers showed excellent cytocompatibility in the cytotoxicity assays. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42060.     

Self-assembly of silver–graphene hybrid on electrospun polyurethane nanofibers as flexible transparent conductive thin films

A method of integrating hybrid thin films of graphene nanosheets (GNSs) and silver nanoparticles (AgNps) by in situ chemical reduction to prepare transparent conductive films (TCFs) is studied. The surface functional groups of graphite oxide (GO) serve as nucleation sites of silver ions for adsorption of AgNps. To fabricate conductive films with high transmittance, polyurethane (PU) nanofibers are introduced to help construct two-dimensional conductive networks consisting of AgNps and GNSs (AgNps–GNSs). This method requires only a low percentage of conducting AgNps–GNSs covering the transparent substrate, thereby improving the transmittance. The flexible GNSs serve as nanoscale bridges between conductive AgNps and PU nanofibers, resulting in a highly flexible TCF. The optical transmittance can be further increased after melting the PU nanofibers at 100 °C. A fused film obtained after electrospinning (ES) a PU solution for 120 s and immersion in 0.05 wt.% AgNp–GNS (5:1) solution has a surface resistance of 150 Ω/sq and 85% light transmittance. Mechanical testing shows that AgNps–GNSs on flexible substrates yield excellent robustness. Thus, TCFs with a 3:1 ratio of AgNps:GNSs have high conductivity, good mechanical durability, and barely one order of magnitude increase of surface resistance when bent to an angle of 90°.     

Preparation and characterization of antimicrobial electrospun poly(vinyl alcohol) nanofibers containing benzyl triethylammonium chloride

The aim of this study was to characterize antimicrobial electrospun poly(vinyl alcohol) (PVA) nanofibers containing benzyl triethylammonium chloride (BTEAC) as an antimicrobial agent. The antimicrobial BTEAC-PVA nanofibers were prepared through electrospinning at the optimal conditions of 15 kV voltage and a 1.0 mL h^− 1 flow rate. Based on the minimum inhibitory concentration (MIC) test results against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumonia, BTEAC-PVA nanofibers containing 2.6% BTEAC were fabricated to test the antibacterial and antiviral activities. The average diameter of the BTEAC-PVA nanofibers increased from 175.7 to 464.7 nm with increasing BTEAC concentration from 0 to 2.6%. The antimicrobial activities of the BTEAC-PVA nanofibers were tested against bacteria. The antibacterial tests with 2.6% BTEAC-PVA nanofibers demonstrated that bacterial reduction in PVA nanofibers was similar to the control value, indicating that PVA had a minimal effect on bacteria death. For the BTEAC-PVA nanofibers, the bacterial reduction ratio increased with increasing contact time, demonstrating that BTEAC-PVA nanofibers successfully inhibited the growth of bacteria. In addition, the antiviral tests against viruses (bacteriophages MS2 and PhiX174) showed that the BTEAC-PVA nanofibers inactivated both MS2 and PhiX174.     

Facile preparation and characterization of poly(vinyl alcohol)/chitosan/graphene oxide biocomposite nanofibers

Poly(vinyl alcohol) (PVA)/chitosan (CS)/graphene oxide (GO) biocomposite nanofibers have been successfully prepared using aqueous solution by electrospinning. CS colloidal gel in 1% acetic acid can be changed to homogeneous solution by using electron beam irradiation (EBI). The uniform distributions of GO sheets in the nanofibers were investigated by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. FESEM images illustrated that the spread single GO sheet embedding into nanofibers was formed via self-assembly of GO sheet and PVA/CS chains. And the average diameters of the biocomposite nanofibers decreased (200, 173, 160 and 123 nm) with increasing the contents of GO (0.05, 0.2, 0.4 and 0.6 wt%). Raman spectra verified the presence of GO in the biocomposite nanofibrous mats. The mechanical properties of as-prepared materials related with GO contents. It revealed that the highest tensile strength was 2.78 MPa, which was 25% higher than that of neat PVA/CS nanofibers. Antibacterial test demonstrated that the addition of GO to PVA/CS nanofiber had great ability to increase inhibition zone till 8.6 mm. Overall, these features of PVA/CS/GO nanofibers which were prepared by eco-friendly solvent can be a promising candidate material in tissue engineering, wound healing and drug delivery system.     

Preparation and characterization of barium titanate nanofibers by electrospinning

PVP–BaTiO₃ composite nanofibers were successfully prepared by electrospinning and pure BaTiO₃ fibers were produced after calcination at 1000 °C. A homogeneous viscous solution of barium acetate + titanium acetate/titanium isopropoxide in poly vinyl pyrrolidone (PVP) was prepared by varying PVP concentration in the range of 8–12%. The above sols were electrospun at 9 kV DC by maintaining tip to collector distance (TCD) of 7 cm. The electrospun fibers were calcined at 1000 °C for 2 h. Thermo gravimetric analysis (TGA) of the fibers indicates the complete decomposition of organics below 700 °C with 45% weight loss. Scanning electron microscopy (SEM) study shows the fibers cylindrical, smooth with diameters in the range of 50–400 nm and the aspect ratio >1000. The average diameter of the fibers increases with the increase in PVP concentration. The calcined BaTiO₃ nanofibers were found to be coarse, brittle and diameter reduced by 12%. FT-IR study confirms the formation of metal oxide bond at higher temperature.     

Preparation of graphene/carbon hybrid nanofibers and their performance for NO oxidation

A series of novel microdomain-graphitized polyacrylonitrile (PAN)-based nanofibers were prepared by adding varied amounts of graphene oxide into the precursor via the electrospinning method. These hybrid electrospun nanofibers with were stabilized in ambient atmosphere, carbonized in nitrogen atmosphere and treated in NH₃ atmosphere for NO oxidation with low concentration (50 ppm) at room temperature. The samples were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and nitrogen adsorption at 77 K. Oxidation of NO into NO₂ at room temperature was investigated in a fiber fixed-bed. The results demonstrated that the reduced graphene oxide sheets provide catalytic active sites embedded in the PAN-based nanofibers. In addition it was determined that nitrogen-containing functional groups played important roles in the enhancement of the catalytic oxidation of NO to NO₂. The samples with 5 wt.% GO exhibit the most catalytic oxidation of NO into NO₂.     

Characterization of Mg doped ZnO nanocrystallites prepared via electrospinning

Undoped and Mg doped ZnO nanofibers with different doping concentrations were successfully synthesized using the electrospinning technique. The nanofiber structures were calcined at 300 °C, 400 °C, 500 °C, and 600 °C respectively. It was observed that the nanofibers turned into a nanoparticular structure at the calcining temperature of 400 °C. The nanoceramic mats were characterized by the Fourier transform infrared-attenuated total reflectance spectroscopy and by the scanning electron microscopy. The electronic band transitions of as-deposited and calcined films were identified by the evaluation of the photoluminescence measurements at room temperature. It was observed that the exitonic transition energy of the ZnO nanostructure blue-shifted to a high energy value with an increasing Mg doping ratio. In order to estimate the decomposition temperature of the nanofibers turning into a nanoparticular structure, the nanofiber structure was calcined at temperatures between 300 °C and 400 °C, the temperature ramp being 20 °C. The evaluation of the emission spectra of the calcined structures show that the decomposition of electrospun nanofibers started at 320 °C. In addition, band gap energies of the samples were determined by the transmittance measurement of the samples and by the UV–VIS spectrophotometer at the room temperature.     

EELS characterisation of β-tricalcium phosphate and hydroxyapatite

Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are of great interest due to their potential application as bone-replacement materials. In particular, composites made of a mixture of these Ca-phosphates revealed improved mechanical properties; however, the reason for this improvement is unknown. Future development and properties enhancement of such bioceramics is linked to the possibility to characterise their particular microstructure. In this context, the ability to quickly identify individual grains of HA and β-TCP within these composites will allow acquiring information about the phase distributions and the phase-boundary microstructure. The aim of the present study is, therefore, to demonstrate that electron energy-loss spectroscopy (EELS) can be successfully employed to differentiate between individual grains of HA and β-TCP. In particular, the analysis of the near-edge structure of the oxygen K-ionisation edge allows detection of a characteristic signal at ca. 536 eV that can be employed as an identification tool for HA. EELS investigations were performed first on as-received and calcined (1000 °C) HA and β-TCP powders and subsequently on pure bulk HA and β-TCP samples sintered at 1250 °C. Finally, this method was successfully applied to a HA/β-TCP (50/50 wt.%) composite sintered at 1250 °C.     

Effect of carbon nanotube addition on friction coefficient of nanotubes/hydroxyapatite composites

Carbon nanotubes/hydroxyapatite (CNTs/HA) composites with different CNTs contents were synthesized by in situ method and were characterized by XRD, TEM and Raman spectroscopy. Friction coefficients of the composites were tested using UMT-2 friction tester. Effect of various factors including CNTs content, testing time and applied load on friction coefficient was carried out. Results show that the CNTs/HA composites exhibited lower friction coefficient than pure HA and their friction coefficients decreased with increase of CNTs content from 0 to 20 wt.%. Addition of CNTs in composite is beneficial to increase wear resistance of the CNTs/HA composite and to decrease its friction coefficient.     

Synthesis and electrochemical properties of nickel oxide/carbon nanofiber composites

The electrospinning of polyacrylonitrile (PAN) with a polyaniline and graphene sol–gel mixture produced uniform, smooth fibers with an average diameter of 0.3 μm. These electrospun fibers were stabilized for 2 h at 200 °C and then carbonized at 800 °C for 5 h. Composites were prepared by depositing Ni(OH)₂ on the carbon nanofibers (CNFs) and calcining them at different temperatures. The composites were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The effect of the calcination temperatures on the electrochemical properties was studied using cyclic voltammetry and electrochemical impedance spectroscopy. The specific capacitance (SC) was found to be highest (738 F g⁻¹) at a calcination temperature of 400 °C. The charge transfer resistance (R_p) decreased as the calcination temperature was increased. However, the electrical double layer capacitance (EDLC) increased with an increase in the calcination temperature. The EDLC increased from 0.144 F g⁻¹ at a calcination temperature of 100 °C to 485 F g⁻¹ at a calcination temperature of 500 °C.     

Highly sensitive acetone sensor based on Eu-doped SnO2 electrospun nanofibers

In this study, a series of undoped and Eu-doped SnO₂ nanofibers were synthesized via a simple electrospinning technique and subsequent calcination treatment. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were carefully used to characterize the morphologies, structures and chemical compositions of these samples. The results reveal that the as-prepared nanofibers are composed of crystallite grains with an average size of about 10 nm and Eu³⁺ ions are successfully doped into the SnO₂ lattice. Compared with pure SnO₂ nanofibers, Eu-doped SnO₂ nanofibers demonstrate significantly enhanced sensing characteristics (e.g., large response value, short response/recovery time and outstanding selectivity) toward acetone vapor, especially, the optimal sensor based on 2 mol% Eu-doped SnO₂ nanofibers shows the highest response (32.2 for 100 ppm), which is two times higher than that of the pure SnO₂ sensor at an operating temperature of 280 °C. In addition, the sensor exhibits a good sensitivity to acetone in sub-ppm concentrations and the detection limit could extend down to 0.3 ppm, making it a potential candidate for the breath diagnosis of diabetes.     

Sono-synthesis of nanohydroxyapatite: Effects of process parameters

Hydroxyapatite (HA) [Ca₁₀(PO₄)₆(OH)₂] is a bioactive ceramic with excellent osteoconductive properties. This characteristic helps HA to be integrated into the bone without provoking an immune reaction, thus making it a useful biocompatible material for load bearing bone implant. In this study, nanohydroxyapatite (NHA) was synthesised using a precipitation method assisted with ultrasonication. The process parameters such as ultrasonic time (t) (10–30 min), ultrasonic amplitude (A) (50–70%), solution temperature (T) (50–90 °C), and solution pH (7–9) were varied on the basis of single factor and their effects on NHA synthesis was investigated. Besides that, the effect of calcination on the NHA powder morphology was also studied by varying the calcination time (2, 4 and 6 h) and temperature (400, 800 and 1200 °C). The characterisations of the synthesised NHA powder were conducted using thermogravimetric analysis (TGA), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM), zeta-sizer and Fourier transform infrared spectroscopy (FTIR). It was found that nano-sized HA particles can be produced at optimum set of process parameters of t=25 min, T=90 °C, A=65%, and pH=8. Results revealed that the thermal stability, morphology and crystallinity of the NHA powder was further improved by calcinating the powder at optimum temperature and time of 800 °C and 2 h, respectively.     

The adsorptive extraction of oxidized sulfur-containing compounds from fuels by using molecularly imprinted chitosan materials

An innovative approach for desulfurisation of fuels is proposed. It relies on the formation of recognition sites, complementary to oxidized sulfur-containing compounds, on cross-linked chitosan microspheres and electrospun chitosan nanofibers using the molecularly imprinted polymer technique. Benzothiophene sulfone (BTO₂), dibenzothiophene sulfone (DBTO₂) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO₂) were used as templates for the preparation of molecularly imprinted polymers (MIPs). The possible molecular interactions between imprinted chitosan adsorbent and oxidized sulfur-containing compounds were investigated by molecular modeling using density functional theory (DFT) and results indicated that interactions took place via hydrogen bonding. The molecularly imprinted polymer adsorbents (cross-linked microspheres and electrospun nanofibers) gave better selectivity for the target sulfonated compounds and the adsorption isothermal studies followed the Freundlich model. Maximum adsorption capacities of 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g were observed for model BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively at 1 mL/h when imprinted nanofibers were employed, and the imprinted microspheres gave maximum adsorption capacity of 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g for BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively. Application of the nanofibers to oxidized hydro-treated fuel under continuous flow adsorption system at 1 mL/h indicated that 84% of sulfur was adsorbed, with adsorption capacity of 2.2 ± 0.2 mg/g.     

Synthesis and microwave absorption properties of Fe–C nanofibers by electrospinning with disperse Fe nanoparticles parceled by carbon

The Fe–C nanofibers were achieved using electrospinning technique. The microstructure was characterized by field emission scanning electron microscope and high resolution transmission electron microscopy equipped with energy-dispersive X-ray analysis. The results indicated that magnetic Fe nanoparticles uniformly dispersed along nanofibers and were parceled by carbon matrix. For the Fe–C nanofibers/paraffin composite, a minimum reflection loss (RL) value of −44 dB was observed at 4.2 GHz. Moreover, the frequency range with RL peak value below −10 dB was achieved in a wide frequency range from 2.2 to 13.2 GHz. The excellent microwave absorption properties were due to the combination of complex permeability and permittivity resulting from magnetic Fe particles and lightweight carbon.     

Effect of polymer concentration,needle diameter and annealing temperature on TiO2-PVP composite nanofibers synthesized by electrospinning technique

In this study, TiO₂-PVP nanofibers were successfully synthesized on an aluminium collector by using cost-effective electrospinning technique. The nanofibers were prepared at different polymer concentrations, needle diameters and annealing temperatures and properties were studied by various characterizations. The structural properties were studied by X-ray diffraction (XRD) and Raman spectroscopy techniques. Surface morphology and elemental analysis of the samples were investigated by scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS). The optical properties were carried out by UV–Visible absorption spectroscopy (UV–Vis). By varying the polymer concentration and needle diameter, the effect of viscosity and surface tension on the formation of TiO₂-PVP nanofibers was clearly observed by SEM micro images. EDS spectrum shows effective composition of pure TiO₂ nanofibers. XRD peaks observed at temperatures 500 °C, 700 °C and 900 °C confirmed the anatase, mixed and rutile phases of TiO₂ nanofibers respectively. Raman studies also confirmed these phases of TiO₂ nanofibers. The optical band-gap values calculated using Kubelka-Munk function lies in the range of 3.02–3.22 eV.