Magnetic polyacrylonitrile-Fe@FeO nanocomposite fibers - Electrospinning, stabilization and carbonization

Microstructure, Physical and Biological Properties, and BSA Binding Investigation of Electrospun Nanofibers Made of Poly(AA-co-ACMO) Copolymer and Polyurethane

In this study, poly(AA-co-ACMO) and polyurethane-based nanofibers were prepared in a ratio of 1:1 (NF11) and 2:1 (NF21) as antimicrobial carriers for chronic wound management. Different techniques were used to characterize the nanofibers, and poly(AA-co-ACMO) was mostly found on the surface of PU. With an increase in poly(AA-co-ACMO) dose from 0 (PU) and 1:1 (NF11) to 2:1 (NF21) in the casting solution, the contact angle (CA) was reduced from 137 and 95 to 24, respectively, and hydrophilicity was significantly increased. As most medications inhibit biological processes by binding to a specific protein, in vitro protein binding was investigated mechanistically using a stopped-flow technique. Both NF11 and NF21 bind to BSA via two reversible steps: a fast second-order binding followed by a slow first-order one. The overall parameters for NF11 (K_a = 1.1 × 10⁴ M^-1, K_d = 89.0 × 10^-6, ΔG⁰ = -23.1 kJ mol^-1) and NF21 (K_a = 189.0 × 10⁴ M^-1, K_d = 5.3 × 10^-6 M, ΔG⁰ = -27.5 kJ mol^-1) were determined and showed that the affinity for BSA is approximately (NF11)/(NF21) = 1/180. This indicates that NF21 has much higher BSA affinity than NF11, although BSA interacts with NF11 much faster. NF21 with higher hydrophilicity showed effective antibacterial properties compared to NF11, in agreement with kinetic data. The study provided an approach to manage chronic wounds and treating protein-containing wastewater.

PCN-224 Nanoparticle/Polyacrylonitrile Nanofiber Membrane for Light-Driven Bacterial Inactivation

Increasing issues of pathogen drug resistance and spreading pose a serious threat to the ability to treat common infectious diseases, which encourages people to explore effective technology to meet the challenge. Photodynamic antibacterial inactivation (aPDI) is being explored for inactivating pathogens, which could be used as a novel approach to prevent this threat. Here, porphyrin-embedded MOF material (PCN-224) with photodynamic effect was synthesized, then the PCN-224 nanoparticles (NPs) were embedded into PAN nanofibers with an electrospinning process (PAN-PCN nanofiber membrane). On the one hand, polyacrylonitrile (PAN) nanofibers help to improve the stability of PCN-224 NPs, which could avoid their leakage. On the other, the PAN nanofibers are used as a support material to load bactericidal PCN-224 NPs, realizing recycling after bacterial elimination. An antibacterial photodynamic inactivation (aPDI) study demonstrated that the PAN-PCN 0.6% nanofiber membrane processed 3.00 log unit elimination towards a E. coli bacterial strain and 4.70 log unit towards a S. aureus strain under illumination. A mechanism study revealed that this efficient bacterial elimination was due to singlet oxygen (¹O₂). Although the materials are highly phototoxic, an MTT assay showed that the as fabricated nanofiber membranes had good biocompatibility in the dark, and the cell survival rates were all above 85%. Taken together, this work provided an application prospect of nanofibers with an aPDI effect to deal with the issues of pathogen drug resistance and spreading.

Silver-loaded carbon nanofibers for ammonia sensing

Carbon nanofibers (CNFs) were prepared by electrospinning, and silver (Ag) ions were grown on the surface of the CNFs by in situ solution synthesis. The structure and morphology of obtained Ag-doped CNFs (Ag-CNFs) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The gas sensibility of the composite fiber was investigated by ammonia (NH3) obtained by natural volatilization from 1 to 4 mL of NH3 solution at room temperature. It was found that the fibers exhibited a sensitive current corresponding to different NH3 concentrations and a greater response at high concentrations. The sensing mechanism was discussed, and the good absorptivity was demonstrated. The results show that Ag-CNF is a promising material for the detection of toxic NH3.

Chemical and Morphological Transition of Poly(acrylonitrile)/Poly(vinylidene Fluoride) Blend Nanofibers during Oxidative Stabilization and Incipient Carbonization

Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.

Multifunctional Gas and pH Fluorescent Sensors Based on Cellulose Acetate Electrospun Fibers Decorated with Rhodamine B-Functionalised Core-Shell Ferrous Nanoparticles

Ferrous core-shell nanoparticles consisting of a magnetic γ-Fe₂O₃ multi-nanoparticle core and an outer silica shell have been synthesized and covalently functionalized with Rhodamine B (RhB) fluorescent molecules (γ-Fe₂O₃/SiO₂/RhB NPs). The resulting γ-Fe₂O₃/SiO₂/RhB NPs were integrated with a renewable and naturally-abundant cellulose derivative (i.e. cellulose acetate, CA) that was processed in the form of electrospun fibers to yield multifunctional fluorescent fibrous nanocomposites. The encapsulation of the nanoparticles within the fibers and the covalent anchoring of the RhB fluorophore onto the nanoparticle surfaces prevented the fluorophore's leakage from the fibrous mat, enabling thus stable fluorescence-based operation of the developed materials. These materials were further evaluated as dual fluorescent sensors (i.e. ammonia gas and pH sensors), demonstrating consistent response for very high ammonia concentrations (up to 12000 ppm) and fast and linear response in both alkaline and acidic environments. The superparamagnetic nature of embedded nanoparticles provides means of electrospun fibers morphology control by magnetic field-assisted processes and additional means of electromagnetic-based manipulation making possible their use in a wide range of sensing applications.

Innovative nanofiber technology to improve carbon dioxide biofixation in microalgae cultivation

The aim of this study was to develop nanofibers containing nanoparticles with potential for the biological fixation of CO₂ together with the microalgae Chlorella fusca LEB 111. An electrospinning technique was used for the production of polymeric nanofibers with different concentrations of iron oxide nanoparticles: 0, 2, 4, 6, 8, and 10% (w v^-1). Nanofibers with a nanoparticle concentration of 4% (w v^-1) were selected for use in the microalgal cultivation due to their smaller diameter (434 nm), high specific surface area (13.8 m² g^-1) and higher CO₂ adsorption capacity (164.2 mg g^-1). The microalgae C. fusca LEB 111 presented a higher CO₂ biofixation rate of 216.2 mg L^-1 d^-1 when cultivated with these nanofibers. The results demonstrated the potential of electrospun nanofibers as physical adsorbents of CO₂ since they can increase the contact time between the gas and the microorganism and consequently increase the CO₂ biofixation by the microalgae.

Electrocatalytic N-Doped Graphitic Nanofiber - Metal/Metal Oxide Nanoparticle Composites

Carbon-based nanocomposites have shown promising results in replacing commercial Pt/C as high-performance, low cost, nonprecious metal-based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal-air batteries. Herein, a general approach for the production of 1D porous nitrogen-doped graphitic carbon fibers embedded with active ORR components, (M/MO_x , i.e., metal or metal oxide nanoparticles) using a facile two-step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite-metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N-doped graphitic carbon fibers, especially Co₃ O₄ , exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co₃ O₄ and robust 1D porous structures composed of interconnected N-doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.

Controllable synthesis of mesoporous carbon nanoparticles based on PAN-b-PMMA diblock copolymer micelles generated via RAFT polymerization as electrode materials for supercapacitors

PAN-b-PMMA micelles were synthesized via RAFT emulsion polymerization, followed by carbonization to form mesoporous carbon nanoparticles (MCNs). The as-prepared MCNs were exploited as electrode material for supercapacitors.

Effects of oxygen content in the atmosphere on thermal oxidative stabilization of polyacrylonitrile fibers

The effects of oxygen content in the atmosphere on thermal oxidative stabilization of polyacrylonitrile fibers have been studied based on the evolution of the interaction between cyclization and oxidation reactions.

Radiotherapeutic bandage based on electrospun polyacrylonitrile containing holmium-166 iron garnet nanoparticles for the treatment of skin cancer

Radiation therapy is used as a primary treatment for inoperable tumors and in patients that cannot or will not undergo surgery. Radioactive holmium-166 ((166)Ho) is a viable candidate for use against skin cancer. Nonradioactive holmium-165 ((165)Ho) iron garnet nanoparticles have been incorporated into a bandage, which, after neutron-activation to (166)Ho, can be applied to a tumor lesion. The (165)Ho iron garnet nanoparticles ((165)HoIG) were synthesized and introduced into polyacrylonitrile (PAN) polymer solutions. The polymer solutions were then electrospun to produce flexible nonwoven bandages, which are stable to neutron-activation. The fiber mats were characterized using scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and inductively coupled plasma mass spectrometry. The bandages are stable after neutron-activation at a thermal neutron-flux of approximately 3.5 × 10(12) neutrons/cm(2)·s for at least 4 h and 100 °C. Different amounts of radioactivity can be produced by changing the amount of the (165)HoIG nanoparticles inside the bandage and the duration of neutron-activation, which is important for different stages of skin cancer. Furthermore, the radioactive bandage can be easily manipulated to irradiate only the tumor site by cutting the bandage into specific shapes and sizes that cover the tumor prior to neutron-activation. Thus, exposure of healthy cells to high energy β-particles can be avoided. Moreover, there is no leakage of radioactive material after neutron activation, which is critical for safe handling by healthcare professionals treating skin cancer patients.

Synthesis and Thermal Properties of Acrylonitrile/Butyl Acrylate/Fumaronitrile and Acrylonitrile/Ethyl Hexyl Acrylate/Fumaronitrile Terpolymers as a Potential Precursor for Carbon Fiber

A synthesis of acrylonitrile (AN)/butyl acrylate (BA)/fumaronitrile (FN) and AN/EHA (ethyl hexyl acrylate)/FN terpolymers was carried out by redox polymerization using sodium bisulfite (SBS) and potassium persulphate (KPS) as initiator at 40 °C. The effect of comonomers, BA and EHA and termonomer, FN on the glass transition temperature (T_g) and stabilization temperature was studied using Differential Scanning Calorimetry (DSC). The degradation behavior and char yield were obtained by Thermogravimetric Analysis. The conversions of AN, comonomers (BA and EHA) and FN were 55%-71%, 85%-91% and 76%-79%, respectively. It was found that with the same comonomer feed (10%), the T_g of AN/EHA copolymer was lower at 63 °C compared to AN/BA copolymer (70 °C). AN/EHA/FN terpolymer also exhibited a lower T_g at 63 °C when compared to that of the AN/BA/FN terpolymer (67 °C). By incorporating BA and EHA into a PAN system, the char yield was reduced to ~38.0% compared to that of AN (~47.7%). It was found that FN reduced the initial cyclization temperature of AN/BA/FN and AN/EHA/FN terpolymers to 228 and 221 °C, respectively, in comparison to that of AN/BA and AN/EHA copolymers (~260 °C). In addition, FN reduced the heat liberation per unit time during the stabilization process that consequently reduced the emission of volatile group during this process. As a result, the char yields of AN/BA/FN and AN/EHA/FN terpolymers are higher at ~45.1% and ~43.9%, respectively, as compared to those of AN/BA copolymer (37.1%) and AN/EHA copolymer (38.0%).

Cell behaviors on magnetic electrospun poly-D, L-lactide nanofibers

It is widely accepted that magnetic fields have an influence on cell behaviors, but the effects are still not very clear since the magnetic field's type, intensity and exposure time are different. In this study, a static magnetic field (SMF) in moderate intensity (10mT) was employed to investigate its effect on osteoblast and 3T3 fibroblast cell behaviors cultured respectively with magnetic polymer nanofiber mats. The magnetic mats composed of random oriented or aligned polymer nanofibers were fabricated by electrospinning the mixed solution of poly-d, l-lactide (PLA) and iron oxide nanoparticles. The fiber morphology was characterized by scanning electron microscopy (SEM), the nanoparticle distribution in fiber matrix was measured with transmission electron microscope (TEM). Mechanical properties of nanofiber mats are studied by uniaxial tensile test. The results showed the nanofibers loaded with magnetic nanoparticles displayed excellent magnetic responsibility and biodegradability. In vitro cytotoxicity analysis demonstrated that the osteoblast proliferation of all fiber mats stimulated with or without SMF was increased with the increase of the culturing days. Furthermore, in the horizontal SMFs, cell orientation tended to deviate from nanofiber orientation to field direction while the nanofiber orientation is perpendicular to the field direction, while the horizonal direction of SMFs could also direct the cell growth orientation. The magnetic nanofiber mats provide a potential platform to explore the cell behaviors under the stimulation of external magnetic field.

Electrospinning of calixarene-functionalized polyacrylonitrile nanofiber membranes and application as an adsorbent and catalyst support

Polyacrylonitrile (PAN) nanofiber membranes functionalized with calix[8]arenes (C[8]) were successfully prepared by electrospinning of PAN solutions with addition of various calixarenes. Uniform electrospun C[8]/PAN nanofibers were obtained by incorporating three types of calix[8]arenes into the PAN matrix and characterized by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR), thermal gravimetric analysis (TGA), and X-ray powder diffraction (XRD). The SEM results showed that the addition of calix[8]arenes resulted in a decrease in the diameter of PAN nanofibers. Static adsorption behavior was studied by using C[8]/PAN nanofibers as an adsorbent and Congo red and Neutral red as model dye molecules. The adsorption of Congo red onto Amide-Cal[8]-15/PAN nanofibers fitted the second-order kinetic model, and the apparent adsorption rate constant was 1.1 × 10(-3) g·mg(-1)·min(-1) at 25 °C. Then, by virtue of electrostatic attraction, as-prepared Au nanoparticles were immobilized on Amide-Cal[8]/PAN nanofibers to form Au/Amide-Cal[8]/PAN composite nanofibers. The catalytic activity of the as-prepared Au/Amide-Cal[8]/PAN composite nanofibers was investigated by monitoring the reduction of Congo red in the presence of NaBH4. The reduction kinetics was explained by the assumption of a pseudo-first-order reaction with regard to Congo red. Au/Amide-Cal[8]/PAN composite nanofibers exhibited high catalytic activity, excellent stability, and convenient recycling.

Electrospun poly(vinyl alcohol)/α-zirconium phosphate nanocomposite fibers

Poly(vinyl alcohol) (PVA)/α-zirconium phosphate (ZrP) polymer nanocomposite (PNC) fibers were successfully prepared by a simple and low-cost electrospinning process. ZrP nanoparticles with two different dimensions, that is, ZrP-500 with a lateral dimension of ∼320 nm and an aspect ratio of ∼500 and ZrP-1500 with a lateral dimension of ∼950 nm and an aspect ratio of ∼1500, were utilized to illustrate the size effect on the electrospun nanofibers. In order to obtain defect-free, uniform PNC fibers, a number of parameters including polymer concentration, feed rate, applied voltage and working distance between the needle tip and the fiber collecting substrate were investigated. Scanning electron microscopic morphological analysis showed smooth and nonwoven electrospun nanofiber mat. Strong intermolecular interactions between the PVA matrix and the included ZrP nanofillers were revealed by the attenuated total reflectance Fourier transform infrared spectroscopy. The incorporation of ZrP nanofillers drastically improved the thermal stability of the PNC fibers. Results of thermogravimetric analysis demonstrated a clear thermal stability dependence on the aspect ratio of the crystalline ZrP nanofillers. The degradation temperature was increased by 90°C for the ZrP-1500 and 60°C for ZrP-500, when the loading level was increased from 1 wt% to 5 wt%. Furthermore, the viscoelastic properties of the PNC solutions were studied by the rheometer. The solutions with higher loading of the nanofiller exhibited higher viscosity and demonstrated different fluid nature when compared with the solutions at lower loading level.

Fe2O3/TiO2 tube-like nanostructures: synthesis, structural transformation and the enhanced sensing properties

The paper describes for the first time the successful synthesis of Fe(2)O(3)/TiO(2) tube-like nanostructures, in which TiO(2) shell is of quasi-single crystalline characteristic and its thickness can be controlled through adjusting the added amount of aqueous Ti(SO(4))(2) solution. The characterization of samples obtained at different stages using transmission electron microscope indicates that the outer TiO(2) shell is changed gradually from amorphous and polycrystalline phase into quasi-single crystal under thermal actions through the Ostwald ripening process, accompanying the corrosion of the central parts of Fe(2)O(3) nanorods, and the formation of small particles separating each other, leading to the special core/shell nanorods. Furthermore, Fe(2)O(3)/TiO(2) tube-like nanostructures can be transformed into Fe(2)TiO(5) nanostructures after they are thermally treated at higher temperatures. Those nanostructures exhibit enhanced ethanol sensing properties with respect to the monocomponent. Our results imply that not only hollow nanostructures, but also a novel type of nanostructures can be fabricated by the present method for nanodevices.

Multifunctional composite core-shell nanoparticles

In this review paper, the state-of-the-art knowledge of the core-shell multifunctional nanoparticles (MNPs), especially with unique physiochemical properties, is presented. The synthesis methods were summarized from the aspects of both the advantages and the demerits. The core includes the inexpensive and easily oxidized metals and the noble shells include the relatively noble metals, carbon, silica, other oxides, and polymers. The properties including magnetic, optical, anti-corrosion and the surface chemistry of the NPs are thoroughly reviewed. The current status of the applications is reviewed with the detailed examples including the catalysis, giant magnetoresistance (GMR) sensing, electromagnetic interface shielding or microwave absorption, biomedical drug delivery, and the environmental remediation.