Encapsulation mechanism of N2 molecules into the central hollow of carbon nitride multiwalled nanofibers

Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C₂H₂, NH₃, and N₂ gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules.     

Formulation development and optimization of alpha ketoglutarate nanoparticles for cyanide poisoning

The purpose of this research work was to formulate and evaluate alpha ketoglutarate nanoparticles as dry powder inhaler for treatment of cyanide poisoning. Non-polymeric particles were prepared by nano-precipitation technique using various stabilizers. Selection of co-solvent and stabilizer was a key to produce stabilized particles. A combination of lutrol F68 and PVA as a crystal growth inhibitor seems to be best in achieving minimum particle size of 110.2 nm. On the basis of preliminary trials a Box-Behnken statistical design was employed to study the effect of independent variables, drug concentration (X₁), stirring speed (X₂), stirring time (X₃), PVA concentration (X₄), poloxomer concentration (X₅) and volume of co-solvent (X₆) on average particle size. Particle size varied from 110 to 875 nm depending upon the significant terms. Optimized formulation was predicted at drug concentration (50 μg/ml), stirring speed (640 rpm), stirring time (1 min), PVA concentration (1%), poloxomer concentration (1.69%) and volume of co-solvent (30 ml) with 104.6% experimental validity. The nanosized particles were further characterized by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FT-IR) analysis. The results of particle characterization indicate that there was no physical disparity when compared with the commercial α-KG sample.     

Growth mechanism of single-crystal α-Al2O3 nanofibers fabricated by electrospinning techniques

Crystal-growth-related microstructures and the length-to-diameter ratio of a single-crystal-type α-Al₂O₃ nanofiber were examined using HR-TEM techniques. The fibers exhibited diameters ranging from 50 to 100 nm and lengths of several tens of micrometers. During thermal treatments, the alumina fiber went through phase transformations similar to boehmite. Therefore, the phase evolution, especially the final θ- to α-Al₂O₃ stage of the phase transformation, may be the determining factor in the microstructural evolution of the nanofibers. HR-TEM techniques were utilized to demonstrate that the single crystals were formed by the coalescence of well-elongated α-Al₂O₃ colonies. The fibers grew in the [1 1 0] or [1 1 2] direction instead of [0 0 1]. A thermodynamic analysis revealed that if the α-Al₂O₃ nanofiber that transformed from θ-Al₂O₃ behaved in a stable manner, there could be a size ratio limit for the length and diameter of each α-Al₂O₃ colony. The smallest potential diameter was calculated to be around 17 nm.     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

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.     

Control of catalyst particle crystallographic orientation in vertically aligned carbon nanofiber synthesis

Vertically aligned carbon nanofibers (VACNF) have been synthesized where the crystallographic orientation of the initial catalyst film was preserved in the nanoparticle that remained at the nanofiber tip after growth. A substantial percentage of catalyst particles (75%), amounting to approximately 200 million nanofibers over a 100 mm Si wafer substrate, exhibited a sixfold symmetry attributed to a cubic Ni(1 1 1)∥Si(0 0 1) orientation relationship which was verified by X-ray diffraction studies. The Ni catalyst films were prepared by rf-magnetron sputtering under substrate bias conditions to yield a single (1 1 1) film texture. The total energy of the Ni thin film was estimated by calculating the sum of the surface free energy and strain energy. The total film energy was minimized by the evolution of the plane of lowest surface free energy, the (1 1 1) texture. This result was in agreement with X-ray diffraction measurements. The preferred orientation present in the Ni catalyst film prior to nanofiber growth was preserved in the Ni catalyst particles throughout the VACNF growth process. The Ni catalyst particles at the nanofiber tips were not pure single crystals but rather consisted of a mosaic structure of Ni nanocrystallites embedded within Ni catalyst nanoparticles (200-400 nm). The tip-located nanoparticles exhibited a faceted, crystal morphology with the faceting transferred to the underlying carbon nanofiber during the growth process. The possibility of precisely and accurately controlling VACNF growth velocity over macroscopic wafer dimensions with uniformly aligned catalyst particles is discussed.     

Electrospinning of poly(styrene-co-maleic anhydride) (SMA) and water-swelling behavior of crosslinked/hydrolyzed SMA hydrogel nanofibers

Random and alternating poly(styrene-co-maleic anhydrides) (SMAs) with respective maleic anhydride (MAh) content of 32 and 48% were synthesized through radical polymerization. SMA nanofibers with diameter down to 180 nm were generated by electrospinning from solvents acetone, dimethylformamide (DMF), and their mixtures. Fiber diameter increased dramatically when the SMA concentration in the spinning solution reached to a critical point where the SMA chains are extensively entangled. The diameter of SMA nanofiber decreased with increasing DMF content in the mixture, but beads are often accompanied as DMF content is over 50%. The optimum acetone/DMF ratio was found to be 2:1, in which continuous electrospinning was achieved and bead-free nanofibers were obtained. SMA nanofibers with MAh content of 32 and 48% were crosslinked with diethyleneglycol and subsequently hydrolyzed in NaOH/EtOH to turn SMA into crosslinked sodium form SMA (SMA-Na) hydrogel nanofiber. These hydrogel nanofibers were able to retain fiber form after immersing in water for 24 h. Their water absorption ratio was up to 37.6 and 8.2 g/g in distilled water and 0.25 N NaCl aq. solution, respectively.     

Cone-stacked carbon nanofibers with cone angle increasing along the longitudinal axis

Using porous anodic aluminum oxide as template and petroleum pitch as precursor, a massive amount of uniform carbon nanofibers was obtained after thermal treatment. The diameter and length were 300 nm and 60 μm, respectively. The difference between these and the classic herringbone structure is that the angle between the graphenes and the fiber axis increases regularly along the axis instead of being fixed. TEM observations show that the nanofiber consists of stacked conical graphenes with cone angles that steadily increase from 60° to 180° along the fiber axis. This structure is the first to be produced without using catalytic CVD, and has not been reported using template procedures. The large deformation of the graphene planes at the tip of the nanofiber may produce interesting electronic applications.     

Palladium nanoparticles embedded chitosan/poly(vinyl alcohol) composite nanofibers as an efficient and stable heterogeneous catalyst for Heck reaction

In this study, palladium nanoparticles were successfully embedded into modified chitosan/poly(vinyl alcohol) composite nanofibers (Pd-CS/PVA nanofibers) by electrospinning. Then, the Pd-CS/PVA nanofibers were treated at evaluated temperature to improve its solvent resistance and in situ reduce Pd²⁺ cations into Pd⁰ active species. The incorporated palladium nanoparticles with ultra small mean diameter of 3.73 ± 1.04 nm are evenly distributed inside the Pd-CS/PVA nanofiber. The resulting Pd-CS/PVA nanofiber mat exhibits high catalytic activity for Heck reaction of aromatic iodides with alkenes and can be recycled for 18 times without loss of initial activity. The high catalytic activity and stability of Pd-CS/PVA nanofiber mat can be attributed to the ultra small diameter nanofibers, strong chelating ability of chitosan, and fine embedment of palladium species inside the nanofiber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48026.     

Functionalization of carbon nanofibers through electron beam irradiation

Carbon nanofibers were oxidized in air at 350 °C under the influence of a 3 MeV electron beam at doses of 1000 and 3500 kGy. XPS analysis showed that oxygen was readily incorporated on the surface: the ratio O 1s/C 1s increased approximately by a factor of three when the carbon nanofibers were irradiated at 3500 kGy. The oxidized nanofibers exhibited better dispersion than as-received nanofibers when mixed with water/methanol (50% v/v). Raman spectroscopy revealed that the ID/IG ratios were statistically unchanged for all samples because the damage on the nanofiber surface was highly localized and did not lead to modifications on the bulk carbon nanofiber structure. On the other hand, SEM, TEM, and AFM images illustrated that cutting, welding, and collapse may occur on the structure of irradiated nanofibers. BET analysis showed that the surface area of irradiated samples did not significantly increase, probably because the radiation process may lead to micro-porosity formation. The temperature during irradiation had no effect on the nanofibers’ surface and the thermal stability of the irradiated samples was determined to be lower.     

Bis-GMA/TEGDMA Dental Composites Reinforced with Electrospun Nylon 6 Nanocomposite Nanofibers Containing Highly Aligned Fibrillar Silicate Single Crystals

The objective of this research was to study the reinforcement of electrospun nylon 6/fibrillar silicate nanocomposite nanofibers on Bis-GMA/TEGDMA dental composites. The hypothesis was that the uniform distribution of nano-scaled and highly aligned fibrillar silicate single crystals into electrospun nylon 6 nanofibers would improve the mechanical properties of the resulting nanocomposite nanofibers, and would lead to the effective reinforcement of dental composites. The nylon 6/fibrillar silicate nanocomposite nanofibers were crystalline, structurally oriented and had an average diameter of approximately 250 nm. To relatively well distribute nanofibers in dental composites, the nanofiber containing composite powders with a particle structure similar to that in interpenetration networks were prepared first, and then used to make the dental composites. The results indicated that small mass fractions (1% and 2%) of nanofiber impregnation improved the mechanical properties substantially, while larger mass factions (4% and 8%) of nanofiber impregnation resulted in less desired mechanical properties.     

Electrocatalytic properties of Pt/carbon composite nanofibers

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H₂SO₄ and 5.0 mM K₄[Fe(CN)₆] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm⁻² has the highest activity.     

Poly(ethylene terephthalate) nanofibers prepared by CO2 laser supersonic drawing

Poly(ethylene terephthalate) (PET) nanofibers were prepared by irradiating a PET fiber with radiation from a carbon dioxide (CO₂) laser while drawing it at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The flow velocity from the orifice was estimated by computer simulation; the fastest flow velocity was calculated to be 401 m s⁻¹ at a chamber pressure of 6 kPa. A nanofiber obtained using a laser power of 8 W and a chamber pressure of 6 kPa had an average diameter of 193 nm and a draw ratio of about 900,000. This technique is a novel method for producing nanofibers.     

The effect of graphitization temperature on the structure of helical-ribbon carbon nanofibers

Structural rearrangement of helical-ribbon carbon nanofibers (CNFs) was studied as a function of graphitization temperature. The as-produced nanofibers are composed of a helical ribbon of graphene spiralled about and angled to the fiber axis. The discrete layers of graphene ribbon overlap each other forming the helical-ribbon in contrast to the discontinuous cones of the more common stacked-cup CNF morphology. After heat treatment to 2400 °C and above, the CNFs were completely free of residual metal catalyst inclusions, principally nickel used in their synthesis, and other functionalities. The formation of loops at the graphene edges was also observed. Heat treatment through the temperature range 1500-2800 °C resulted in a relatively minor contraction in interlayer spacing d₀₀₂ from 0.3381 to 0.3363 nm. This was attributed to the highly graphitic character of the as-produced CNFs. However, there were significant increases in the crystallite thickness L_c through this temperature range. In addition, heat treatment above 2400 °C induced a marked change of the nanofiber morphology from circular to faceted polygonal cross-section resulting from the re-ordering of the turbostratic, curved graphene layers to regions of planar graphene layers with 3-dimensional graphitic structure (AB stacking).     

Development of carbon nanofibers from aligned electrospun polyacrylonitrile nanofiber bundles and characterization of their microstructural, electrical, and mechanical properties

Carbon nanofibers with diameters of 200-300 nm were developed through stabilization and carbonization of aligned electrospun polyacrylonitrile (PAN) nanofiber bundles. Prior to the oxidative stabilization in air, the electrospun PAN nanofiber bundle was tightly wrapped onto a glass rod, so that tension existed during the stabilization. We also investigated several carbonization procedures by varying final carbonization temperatures in the range from 1000 to 2200 °C. The study revealed that: (1) with increase of the final carbonization temperature, the carbon nanofibers became more graphitic and structurally ordered; (2) the carbon nanofiber bundles possessed anisotropic electrical conductivities, and the differences between the parallel and perpendicular directions to the bundle axes were over 20 times; and (3) the tensile strengths and Young's moduli of the prepared carbon nanofiber bundles were in the ranges of 300-600 MPa and 40-60 GPa, respectively.     

Evidence for growth mechanism and helix-spiral cone structure of stacked-cup carbon nanofibers

New evidence for the structure of Ni-catalyzed stacked-cup carbon nanofibers (CNFs) has been found. This type of carbon nanofiber exhibits a wide hollow core as well as a large diameter (between 40 and 140 nm). The fibers have been produced by the floating catalyst method using natural gas as carbon feedstock, a sulfur compound, and a nickel catalyst. It was found that the catalytic particles are heterogeneous with two different parts: one composed of metallic Ni, which is the catalytically active portion of the particle, and another composed of NiS, which allows for the hollow nanofiber structure. The hollow core of the fibers has similar dimensions to the NiS volume of the particle and the graphitic layers grow from the rear nickel region of the particle. Nevertheless, the NiS component seems to be indispensable in producing the helix-spiral formation of the graphitic structure, as clearly shown by the TEM studies.     

小麦蛋白/聚乙烯醇复合纳米纤维的制备及其表征

以小麦蛋白、聚乙烯醇(PVA)为原料,采用静电纺丝法制备小麦蛋白/PVA共混复合纳米纤维,重点研究纺丝液质量分数、电压、接收距离对纤维形态的影响,利用扫描电镜、傅里叶变换红外光谱、X-射线衍射光谱对纤维的形态与结构进行表征。结果表明:在纺丝液质量分数10%、小麦蛋白与PVA质量比8∶2、电压12 kV、接收距离10 cm的条件下,可以制备平均直径为280 nm左右的均一、表面光滑的纳米纤维。小麦蛋白与PVA复合后,分子间以氢键结合。     

Preparation of polyaniline nanofibers and their use as a cathode of aqueous rechargeable batteries

Normal pulse voltammetric method was used to synthesize nanofibers of polyaniline (PANi) in HCl solution on a platinum electrode. The influences of the synthesis parameters, such as potential increment, pulse duration and monomer concentration on the electrochemical properties of the PANi films were investigated. Scanning electron microscopic micrographs clearly revealed the formation a nanofiber structure with average diameter in range 70-100 nm under optimum experimental conditions. The electrochemical properties of PANi films were studied with the impedance analysis, cyclic voltammetry and charge/discharge capacities. FT-IR results revealed that the PANi nanofibers were in emeraldine salt form. The film was employed as a positive electrode (cathode) for a PANi-Zn secondary battery containing 1.0 M ZnCl₂ and 0.5 M NH₄Cl as electrolyte. The cells were charged and discharged under a pulse current of 0.31 mA cm⁻². It was found that the maximum capacity of the PANi-Zn battery is 235.60 Ah kg⁻¹ with a columbic efficiency of 97-100% over a wide range of current density of 0.3-5.6 mA cm⁻². The specific energy was 287.43 Wh kg⁻¹ and the PANi cathode exhibited good recycleability.