Interconnected Nanofibers Research Articles

Surface adsorption and self-assembly of Cu(II) ions on TEMPO-oxidized cellulose nanofibers in aqueous media

TEMPO-mediated oxidized cellulose nanofibers (TOCNFs) have shown potential in the bioremediation of metal ions from contaminated water due to their interaction with positively charged metal ions via electrostatic interactions involving surface carboxyl groups. Copper is one of the most common pollutants in industrial effluents and is thus the target metal in the current study. The specific surface adsorption of Cu(II) was similar for TOCNFs with different degrees of functionalization and directly impacted the zeta potential. SEM imaging of the TOCNF after Cu(II) adsorption revealed interesting nanostructured clusters that were attributable to Cu(II) ions first being adsorbed by carboxylate groups on the TOCNF and subsequently being reduced and self-assembled to Cu(0) nanoparticles (NPs) or copper oxide NPs by microprecipitation. TOCNF turned superhydrophilic and resulted in faster water filtration after copper adsorption due to the stronger polarity of the copper ions or the self-assembled Cu(0) NPs creating voids or highly water-permeable channels at the interface between the interconnected TEMPO-oxidized nanofibers. Thus, the adsorption of Cu(II) ions and self-assembly into the Cu NPs on TOCNF favors a faster water purification process and provides a viable route to reuse/recycle TOCNFs studded with Cu nanoparticles as biocidal materials.

Dopant-Enabled Supramolecular Approach for Controlled Synthesis of Nanostructured Conductive Polymer Hydrogels.

Conducting polymer hydrogels emerge as a novel class of polymeric materials that show great potential in many energy, environmental, and biomedical devices. We describe here for the first time a general supramolecular approach toward controlled in situ synthesis of one-dimensional nanostructured conductive hydrogels (polypyrrole (PPy) as a model system) using a rational dopant counterion, which is a disc-shaped liquid crystal molecular copper phthalocyanine-3,4',4″,4‴-tetrasulfonic acid tetrasodium salt (CuPcTs). The dopant molecule CuPcTs cross-linked the PPy chains to form a three-dimensional network that gelated into a hydrogel. The PPy hydrogel could be synthesized in bulk quantities with uniform morphology of self-assembled interconnected nanofibers. The tetra-functional dopant favors a supramolecular self-assembly mechanism to form one-dimensional PPy nanostructures. Furthermore, the enhanced interchain charge transport of CuPcTs doped PPy resulted in greatly enhanced conductivity and pseudocapacitance compared with pristine PPy.

Poly(3-butylthiophene) Inducing Crystallization of Small Molecule Donor for Enhanced Photovoltaic Performance

Morphological control over the bulk heterojunction (BHJ) microstructure of 7′-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl)bis(6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5](thiadiazole) (p-DTS(FBTTh2)2) and [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) system was demonstrated by introducing a small amount of poly(3-butylthiophene) (P3BT) into the active layer. The P3BT could serve as a heterogeneous nucleating agent, inducing the crystallization of p-DTS(FBTTh2)2 to form interconnected nanofibers throughout the whole film. Moreover, the phase separation sizes of the active layer increased after incorporation of P3BT, accompanied by the enhanced surface roughness of the films. Therefore, the power conversion efficiency of the devices increased from 3.4% to 5.0% as the P3BT content reached 10 wt %, due to the enhanced light absorption of the active layer, as well as the higher and more balanced hole and electron mobility.

Detailed mechanism of aniline nucleation into more conductive nanofibers

A large number of studies have been focused on synthesis optimization of conductive hydrogels for medical and sensor approaches. Heterogeneous nucleation of aniline monomers is resulted from secondary nucleation that not only depends on number of reaction groups but also system temperature. In this study, 4°C was examined as a critical temperature applying limited mode of heterogeneous nucleation. Our observations showed this undercooling condition can behave in a cooperative manner with the number of carboxylate groups. Herein, polyacrylic acid-based hydrogel was obtained by different ratios of acrylic acid (AA)/N,N′-methylenebisacrylamide (MBAA) as 18.77 and 14.03. The based hydrogels exposed carboxylate terminates as nucleation centers for aniline cations. The smaller ratio of AA/MBAA produced the based-hydrogels with the higher number of reaction points for aniline monomers. Accordingly, the higher nucleation number of corresponding monomers leads to larger ratio of aniline/Ammonium persulfate (APS) at growth phase. Therefore, secondary nucleation of aniline monomers was limited by undercooling condition at 4°C and 3D interconnected nanofibers resulted by limited heterogeneous nucleation. The corresponding nanofibers showed higher conductivity value compared to 1D nanofibers which was resulted as a function of homogeneous nucleation.

Sulfonic Acid- and Lithium Sulfonate-Grafted Poly(Vinylidene Fluoride) Electrospun Mats As Ionic Liquid Host for Electrochromic Device and Lithium-Ion Battery.

Electrospun polymer nanofibrous mats loaded with ionic liquids (ILs) are promising nonvolatile electrolytes with high ionic conductivity. The large cations of ILs are, however, difficult to diffuse into solid electrodes, making them unappealing for application in some electrochemical devices. To address this issue, a new strategy is used to introduce proton conduction into an IL-based electrolyte. Poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) copolymer is functionalized with sulfonic acid through covalent attachment of taurine. The sulfonic acid-grafted P(VDF-HFP) electrospun mats consist of interconnected nanofibers, leading to remarkable improvement in dimensional stability of the mats. IL-based polymer electrolytes are prepared by immersing the modified mats in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM(+)BF4(-)). It is found that the SO3(-) groups can have Lewis acid-base interactions with the cations (BMIM(+)) of IL to promote the dissociation of ILs, and provide additional proton conduction, resulting in significantly improved ionic conductivity. Using this novel electrolyte, polyaniline-based electrochromic devices show higher transmittance contrast and faster switching behavior. Furthermore, the sulfonic acid-grafted P(VDF-HFP) electrospun mats can also be lithiated, giving additional lithium ion conduction for the IL-based electrolyte, with which Li/LiCoO2 batteries display enhanced C-rate performance.

Nanofibrous spongy microspheres enhance odontogenic differentiation of human dental pulp stem cells.

Dentin regeneration is challenging due to its complicated anatomical structure and the shortage of odontoblasts. In this study, a novel injectable cell carrier, nanofibrous spongy microspheres (NF-SMS), is developed for dentin regeneration. Biodegradable and biocompatible poly(l-lactic acid)-block-poly(l-lysine) are synthesized and fabricated into NF-SMS using self-assembly and thermally induced phase separation techniques. It is hypothesized that NF-SMS with interconnected pores and nanofibers can enhance the proliferation and odontogenic differentiation of human dental pulp stem cells (hDPSCs), compared to nanofibrous microspheres (NF-MS) without pore structure and conventional solid microspheres (S-MS) with neither nanofibers nor pore structure. During the first 9 d in culture, hDPSCs proliferate significantly faster on NF-SMS than on NF-MS or S-MS (p < 0.05). Following in vitro odontogenic induction, all the examined odontogenic genes (alkaline phosphatase content, osteocalcin, bone sialoprotein, collagen 1, dentin sialophosphoprotein (DSPP)), calcium content, and DSPP protein content are found significantly higher in the NF-SMS group than in the control groups. Furthermore, 6 weeks after subcutaneous injection of hDPSCs and microspheres into nude mice, histological analysis shows that NF-SMS support superior dentin-like tissue formation compared to NF-MS or S-MS. Taken together, NF-SMS have great potential as an injectable cell carrier for dentin regeneration.

Novel, Facile, Single-Step Technique of Polymer/TiO₂ Nanofiber Composites Membrane for Photodegradation of Methylene Blue.

Novel photocatalyst membrane materials were successfully fabricated by an air jet spinning (AJS) technique from polyvinyl acetate (PVAc) solutions containing nanoparticles (NPs) of titanium dioxide (TiO2). Our innovative strategy for the production of composite nanofibers is based on stretching a solution of polymer with a high-speed compressed air jet. This enabled us to rapidly cover different substrates with TiO2/PVAc interconnected nanofibers. Surprisingly, the diameters of the as-spun fibers were found to decrease with increasing amount of NPs. Our results showed that AJS PVAc-based fibrous membranes with average fiber diameters of 505-901 nm have an apparent porosity of about 79-93% and a mean pore size of 1.58-5.12 μm. Embedding NPs onto the as-spun fibers resulted in increasing the tensile strength of the obtained composite fiber mats. The photodegradation property of TiO2 membrane mats proved a high efficiency in the decomposition of methylene blue dye. The novel fiber spinning technique discussed in this paper can provide the capacity to lace together a variety of types of polymers, fibers and particles to produce interconnected fibers layer. Our approach, therefore, opens the door for the innovation in nanocomposite mat that has great potential as efficient and economic water filter media and as reusable photocatalyst.

Visible light photocatalytic activity of rutile TiO2 fiber clusters in the degradation of terephthalic acid

Rutile TiO2 nanoparticles, in different structural and morphological properties, were produced by the hydrolysis of titanium tetrachloride in a highly acidic reaction media at moderate temperatures without calcination. Their photocatalytic activities were investigated in the liquid-phase degradation of terephthalic acid under visible light illumination. The parameters, which are the concentration of the titanium tetrachloride solution (0.1–1 M) and reaction temperature (60–95 °C), effective on the properties of the particles, and their photocatalytic performances, were investigated. The XRD patterns indicated a pure rutile crystal structure at moderate temperatures without need of calcination. The FEGSEM images showed the formation of flower-, pinecone-, and sphere-like clusters consisting of interconnected nanofibers. The N2 adsorption–desorption isotherms pointed out the microporous structure of the clusters. Band gap energies were found to be varying between 3.02 and 3.08 eV due to the well-developed rutile crystallite structure. Systematic studies elucidated that the optimum reactant concentration and reaction temperature are 0.5 M TiCl4 and 95 °C, respectively. The rutile clusters synthesized at the optimum reaction conditions exhibited 99 % of the photocatalytic degradation of TPA under visible light illumination at shorter irradiation times compared with commercial P25 TiO2.

Green Electrospinning and Crosslinking of Polyvinyl Alcohol/Citric Acid

The present study reports green electrospinning of polyvinyl alcohol (PVA) / citric acid nanofiber membranes, and the membranes were then crosslinked by heat treatment. The electric conductivity of the PVA aqueous solution increases rapidly and the growth slows down along with the increase of citric acid content. The viscosity of 13 wt% PVA aqueous solutions with citric acid had a small increase and remained stable in one week, which was suitable for electrospinning fibers. Porous, interconnected nonwoven nanofiber membranes were electrospun from a thoroughly mixing of PVA/ citric acid aqueous solution. The membranes were then heat treated at 140 °C for 2 h. The postelectrospinning crosslinked nanofiber membranes were insoluble in water, while the non-crosslinked electrospun nanofiber membranes dissolved instantaneously. FT-IR spectrum, X-ray diffraction, and DSC thermograms reveal that crosslinking of PVA nanofiber membranes occurred through esterfication reaction during heat treatment.

High-transparent and Flexible Au Nanofiber Films†

High-transparent and flexible Au nanofiber films were successfully fabricated by a combination of electrospinning technique and ion sputtering technology, in the presence of polyvinylpyrrolidone(PVP) nanofiber films as template. The as-prepared Au nanofiber films show typical interconnected nonwoven nanofiber networks, and the average diameters of Au nanofibers range from 291 nm to 322 nm. When sputtering time is 75 s, the average transmittance of the as-prepared Au nanofiber film in visible region is 92%, the reflectance in near infrared region is about 7%, and the resistivity is 2. 9x10(-3) Omega . cm. Importantly, after 500 cycles of bending, the as-prepared Au nanofiber films show no obvious electrical degradation. The Au nanofiber films with transparent and near-IR reflective properties may provide promising applications for flexible liquid crystal displays, solar cells and flexible and transparent functional electronics.

Cellulose nanocrystal isolation from tomato peels and assembled nanofibers

Pure cellulose has been successfully isolated from tomato peels by either acidified sodium chlorite or chlorine-free alkaline peroxide routes, at 10.2–13.1% yields. Negatively charged (ζ=−52.4mV, 0.48at% S content) and flat spindle shaped (41:2:1 length:width:thickness) cellulose nanocrystals (CNCs) were isolated at a 15.7% yield via sulfuric acid hydrolysis (64% H2SO4, 8.75mL/g, 45°C, 30min). CNCs could be facilely assembled from dilute aqueous suspensions into highly crystalline (80.8%) cellulose Iβ fibrous mass containing mostly sub-micron fibers (ϕ=260nm) and few interconnected nanofibers (ϕ=38nm), with 21.7m2/g specific surface and 0.049m3/g pore volume. More uniformly nanofibers with average 42nm width and significantly improved specific surface area (101.8m2/g), mesoporosity and pore volume (0.4m3/g) could be assembled from CNCs in 1:1 v/v tert-butanol/water mixture.

Theoretical analysis of flexible strain-gauge sensor with nanofibrillar mechanical interlocking

A flexible, and skin-attachable strain gauge sensor based on interconnected nanofibers was recently reported with discernible gauge factor for a flexible and highly sensitive pressure sensor. Here, we present a simple theory that can explain the observed electrical responses by employing the well-established friction law and electrical circuit analysis. The results are in good agreement with the experimental data obtained under physical loads.

Farbrication and Characterization of Flexible, Transparent and Self-standing Sb Doped SnO2 Electrospun Nanofiber Films†

Flexible,transparent and self-standing Sb doped SnO2(ATO) nanofiber films were successfully fabricated by means of a low-cost and scalable electrospinning process,with tin tetrachloride and antimony trichloride as precursors. The as-prepared ATO nanofiber films are typical interconnected nanofiber networks and show a single SnO2 rutile crystal structures. With increasing the calcination temperature from 520 ℃ to 700℃,the average diameter of ATO nanofibers decrease from 200 nm to 150 nm,but accompanied by an increase in the average diameter of ATO nanoparticles. Meanwhile,the transmittance of the ATO nanofiber film increases from 72% to 80%,while their resistance decreases from 5. 23 Ω·cm to 2. 20 Ω·cm. Importantly,after500 cycles of bending,the self-standing ATO nanofibers show no obvious electrical degradation. The ATO nanofiber films show promise for application in many fields,such as flexible liquid crystal displays,solar cells and flexible and transparent functional electronics.

60 keV Ar+-ion induced modification of microstructural, compositional, and vibrational properties of InSb

Room temperature irradiation of InSb(111) by 60 keV Ar+-ions at normal (0°) and oblique (60°) angles of incidence led to the formation of nanoporous structure in the high fluence regime of 1 × 1017 to 3 × 1018 ions cm−2. While a porous layer comprising of a network of interconnected nanofibers was generated by normal ion incidence, evolution of plate-like structures was observed for obliquely incident ions. Systematic studies of composition and structure using energy dispersive x-ray spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Raman mapping, grazing incidence x-ray diffraction, and cross-sectional transmission electron microscopy revealed a high degree of oxidation of the ion-induced microstructures with the presence of In2O3 and Sb2O3 phases and presence of nanocrystallites within the nanoporous structures. The observed structural evolution was understood in terms of processes driven by ion-induced defect accumulation within InSb.

Hierarchical porous polyaniline–silsesquioxane conjugated hybrids with enhanced electrochemical capacitance

We prepared multi-armed polyaniline–silsesquioxane conjugates (PANI–SQ) with hierarchical porous structure by introducing various amounts of octa-aminophenylsilsesquioxane (OASQ). A rapid-mixing-dilute polymerization reaction was used to synthesize PANI–SQ. PANI–SQ conjugates were characterized by a set of methods, including FTIR, UV-vis, N2 adsorption measurement, wide-angle X-ray diffraction (WXRD), TEM and field-emission scanning electron microscopy (FE-SEM). These conjugates exhibited a high surface area (122.69 m2 g−1) and an average pore width of 1.6 nm, which was significantly lower than that of the pure PANI (29.1 nm). By increasing the mass of OASQ, a decrease in crystallinity and in electrical conductivity can be observed. For PANI–SQ conjugates, FE-SEM and TEM images revealed that interconnected porous nanofiber networks have been formed with a nanofiber diameter of 10–30 nm because of the incorporation of OASQ onto the skeleton. The as-synthesized PANI–SQ conjugate exhibited excellent specific capacitance and stability, suggesting its potential use as electrode material.

Chitosan/polyaniline nanofibers coating on the quartz crystal microbalance electrode for gas sensing

In situ polymerization of aniline using ammonium peroxydisulphate (APS) as an oxidizing agent in the presence of chitosan (Cs) was used to synthesize Cs/polyaniline (PANI) nanofibers. The structure and morphology of the Cs/PANI nanofibers powder were characterized by using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–visible spectroscopy and scanning electron microscope (SEM). The surface of the Cs/PANI seems like interconnected nanofibers with diameters of approximately 50nm. A film of the Cs/PANI nanofibers was built onto a quartz crystal microbalance (QCM) electrode by drop casting and this film was used to develop a sensor to measure the concentration of volatile organic vapors such as amines and alcohols in air. The frequency shifts (Δf) of the QCM, due to the vapor adsorption onto the Cs/PANI nanofibers film, were measured and related to the vapors’ concentrations. Linear relationships existed between the Δf (Hz) and the analytes’ concentrations. The sensor showed a good sensitivity, reproducibility and reversibility. The influence of different temperatures on the vapor adsorption onto the Cs/PANI nanofibers film was studied. The kinetics of diffusion of the gases and the diffusion coefficients (D), were discussed.

Composite nanofibers prepared from metallic iron nanoparticles and polyaniline: High performance for water treatment applications

Presented here is a simple preparation of metallic iron nanoparticles, supported on polyaniline nanofibers at room temperature. The preparation is based on polymerization of interconnected nanofibers by rapid mixing of the aniline monomer with Fe(III) chloride as the oxidant, followed by reductive deposition of Fe0 nanoparticles, using the polymerization by-products as the Fe precursor. The morphology and other physico-chemical properties of the resulting composite were characterized by scanning and transmission electron microscopy, Brunauer–Emmett–Teller method, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and vibrating-sample magnetometry. The composite fibers were 80–150nm in diameter and exhibited the expected ferromagnetic behavior. The composite rapidly and efficiently removed As(V), Cr(VI), and also Congo red dye, from aqueous solutions suggesting their usefulness for removal of toxic materials from wastewater. The composite fibers have high capacity for toxin removal: 42.37mg/g of As(V), 434.78mg/g of Cr(VI), and 243.9mg/g of Congo red. The fibers are easily recovered from fluids by exploiting their ferromagnetic properties.

Evolution of porous network in GaSb under normally incident 60 keV Ar+-ion irradiation

• We show the evolution of a nanoporous layer in GaSb under Ar + -ion bombardment at normal incidence in the hitherto unexplored high fluence regime, namely 7 × 10 16 –3 × 10 18 ions cm −2 . • Fluence dependent formation and growth of patches on top of the nanoporous layer is demonstrated by scanning electron microscopy. • We also show high amount of oxidation of such ion-beam-generated nanoporous structures, with formation of Ga 2 O 3 and Sb 2 O 3 . • Our study reveals the presence of nanocrystallites within the porous layer even at the highest fluence used in the experiment. • We interpret the experimental observations through a qualitative model where we take into account the effect of re-deposition of atoms sputtered from the nanoporous layer during Ar + -ion irradiation of GaSb. GaSb(1 0 0) samples were irradiated with 60 keV Ar + -ions at normal incidence for fluences in the range of 7 × 10 16 to 3 × 10 18 ions cm −2 at room temperature, showing gradual evolution of a porous surface layer containing interconnected nanofibers. In particular, fluence dependent formation of patches on the nanoporous layer is observed by scanning electron microscopy. Combined results of grazing incidence x-ray diffraction and transmission electron microscopy reveal the presence of nanocrystallites in the porous structures. Compositional analysis by x-ray photoelectron spectroscopy indicates the development of oxide phases, mainly Ga 2 O 3 and Sb 2 O 3 where the former increases with fluence. We have proposed a model addressing a competition between ion-induced-defect driven growth of the nanoporous layer and redeposition of sputtered target atoms on the growing layer.

Preparation of interconnected carbon nanofibers as electrodes for supercapacitors

The interconnected carbon nanofibers were prepared by an electrospinning technique using a polymer solution composed of polyacrylonitrile (PAN), poly(acrylonitrile-co-butadiene (PAN-co-PB) copolymer, and N,N-dimethylformamide. Post-treatment including stabilization at 250°C and carbonization at 800°C converted electrospun fibers to bonded carbon nanofibers. The formation of interconnected carbon nanofibers was attributed to the decomposition of PB, which reduced the viscosity of nanofibers and caused the fusion of connecting points. As a result, the conductive pathways developed, leading to an increase in both the electrical conductivity and microcrystallite size. Electrochemical measurements revealed that the specific capacitance of the 90:10 PAN/PAN-co-PB derived carbon nanofibers was 170.2 F/g, which was about 24% higher than that of the neat PAN-derived carbon nanofibers. Furthermore, the fibers showed good cycling stability of energy storage with the retention ratio of 100% after 2000 cycles. Our results corroborated the advantage of these interconnected nanofibers.

Templateless electrogeneration of polypyrrole nanostructures: impact of the anionic composition and pH of the monomer solution

Different superhydrophilic polypyrrole nanostructures can be electrosynthezised in the presence of anions of weak acid (monohydrogenophosphate) and non-acidic anions (perchlorate) without the need for templates. Actually the type of nanostructures formed depends both on the concentration of anions at the electrode and on the interfacial pH. Depending on the anion composition of the pyrrole aqueous solution the film electrogenerated under a given applied potential is either a very thin membrane (10–20 nm) consisting of overoxidized polypyrrole or a tridimensional film with oriented nanowire array or a network of more or less interconnected nanofibers. The formation of such nanostructures is explained by a side reaction which is water oxidation. Since this reaction is pH-dependent, the pH of the pyrrole solution is one of the key parameter for the synthesis of such nanostructures. The reaction mechanism is discussed and compared to those proposed in the literature for nanofiber network electrosynthesis. Actually in the monomer solution, the role of the anions of weak acid is twofold. On the one hand they allow to limit the decrease of the interfacial pH during pyrrole oxidation and on the other hand to decrease the interfacial anion concentration, so that water oxidation takes place with formation of hydroxyl radicals and dioxygen nanobubbles.