Free standing thin webs of porous carbon nanofibers of polyacrylonitrile containing iron-oxide by electrospinning

We present for the first time a novel strategy of producing carbon nanofibers (CNFs) using polyacrylonitrile (PAN)-incorporated with iron oxide particles using electrospinning method. The successfully electrospun iron oxide-incorporated PAN thin white web was stabilized in air. Formation of iron oxide nanoparticles resulted in the formation of porous structure on the web. Following heat treatment to the stabilized fibers to about 1000 °C in an N₂ atmosphere resulted in CNFs with specific surface areas, which ranged from 310, 420, and 550 m² g^− 1, for PAN containing 1, 2 and 3 wt.% iron oxide, respectively.     

Plasma modification of polyacrylonitrile ultrafiltration membrane

Polyacrylonitrile (PAN) ultrafiltration (UF) membranes were modified by plasma treatments and plasma polymerization. Influences of plasma modifications on membrane characteristics were investigated. The obtained results indicated that plasma treatments using non-polymer-forming plasma gases such as Ar, He and O₂ led to the increase of membrane surface hydrophilicity and membrane permeability. By using O₂ plasma treatment, UF property of PAN membranes could be improved with the enhancement of membrane flux meanwhile its albumin rejection was almost maintained. The experimental results also showed that plasma polymerization using acrylic acid vapor as monomer and PAN UF membrane as a substrate led to the formation of reverse osmosis membrane due to the deposition of plasma polymer layer onto substrate membrane surfaces. Plasma techniques can control membrane pore size and have a potential to improve the membrane characteristics by using their advantages.     

Preparation of porous polyacrylonitrile fibers by electrospinning a ternary system of PAN/DMF/H2O

Polyacrylonitrile (PAN) porous fibers were prepared in one step by electrospinning a ternary system of PAN/N, N-dimethylformamide (DMF)/water at ambient environment. The formation of porous structures was mainly due to the spinodal decomposition phase separation occurred during the electrospinning process. The concentration of PAN varied from 3 to 10 wt.% with the water content changing from 2 to 8 wt.%. When PAN concentration was above 5 wt.%, the composition of the ternary system was close to the “cloud point” and fibers with porous structures were obtained. In addition, the surface tension and viscosity of PAN solutions increased with water which may lead to the diameter increase of the fibers. The Brunauer-Emmett-Teller (BET) surface area of porous PAN nanofibers obtained from 8 wt.% PAN solution containing 7 wt.% of water was 46.4 m² g⁻¹, which was 3 times higher than that of nonporous PAN nanofibers prepared under the same conditions from a solution without water.     

Electrospinning of PAN/DMF/H2O containing TiO2 and photocatalytic activity of their webs

Polyacrylonitrile (PAN) nanofiber webs containing titanium dioxide (TiO₂) were prepared via electrospinning. Either dimethyl formamide (DMF) or its mixture with small amount of water (3 and 5%w/w.) was employed to prepare 5%w/w.PAN/DMF or PAN/DMF/H₂O solution, respectively. Introducing non-solvent water in PAN/DMF/H₂O solution was attempted to induce phase separation, which may lead to formation of porous structure on nanofibers surface. Different amounts of TiO₂ (1 to 3 wt.%) were added into PAN/DMF/(H₂O) solutions and then electrospun into nanofiber webs. From SEM, nanofibers possessed rough surfaces and had averaged diameters in ranges of 170–430 nm., showing tendency to increase with amount of TiO₂ and water. Porous structure on fiber surfaces was not clearly observed, which was suspected to be due to insufficient amount of water employed. Less homogeneity in polymer solution due to presence of TiO₂ disfavored increasing water content higher than 5%w/w. EDS data confirmed presence of TiO₂ in electrospun webs. From photocatalysis evaluation, webs containing 2 and 3 wt.% TiO₂ showed good photocatalytic activity such that 80 percent of 10 ppm. methylene blue degraded in 24 hours. Slight increase in photocatalytic activity was observed in webs obtained from PAN/DMF/H₂O solutions.     

Synthesis and Characterization of Cu Nanoparticles Embedded in PAN/β-Cyclodextrin (β-CD) Composite Nanofiber Films

In the study, PAN/β-cyclodextrin (β-CD) one dimensional composite nanofibers were synthesized with sol-gel method and electrospinning, and then, we dipped the composite nanofibers into NaBH₄ aqueous solution acted as reducing agent to fabricate PAN/β-CD/Cu composite nanofibers. We got the PAN/β-CD/Cu composite nanofibers with different concentration of β-CD, and Cu nanoparticles formed on its surface. The final products were characterized using scanning electronic microscope (SEM), fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). The results of characterization showed that the Cu nanoparticles with small size were well-distributed on the composite nanofibers.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

Room temperature plasma oxidation: A new process for preparation of ultrathin layers of silicon oxide, and high dielectric constant materials

In this paper we present basic features and oxidation law of the room temperature plasma oxidation, (RTPO), as a new process for preparation of less than 2 nm thick layers of SiO₂, and high-k layers of TiO₂. We show that oxidation rate follows a potential law dependence on oxidation time. The proportionality constant is function of pressure, plasma power, reagent gas and plasma density, while the exponent depends only on the reactive gas. These parameters are related to the physical phenomena occurring inside the plasma, during oxidation. Metal-Oxide-Semiconductor (MOS) capacitors fabricated with these layers are characterized by capacitance-voltage, current-voltage and current-voltage-temperature measurements. Less than 2.5 nm SiO₂ layers with surface roughness similar to thermal oxide films, surface state density below 3 × 10¹¹ cm^− 2 and current density in the expected range for each corresponding thickness, were obtained by RTPO in a parallel-plate reactor, at 180 mW/cm² and pressure range between 9.33 and 66.5 Pa (0.07 and 0.5 Torr) using O₂ and N₂O as reactive gases. MOS capacitors with TiO₂ layers formed by RTPO of sputtered Ti layers are also characterized. Finally, MOS capacitors with stacked layers of TiO₂ over SiO₂, both layers obtained by RTPO, were prepared and evaluated to determine the feasibility of the use of TiO₂ as a candidate for next technology nodes.     

Catalytic graphitization and formation of macroporous-activated carbon nanofibers from salt-induced and H2S-treated polyacrylonitrile

We present here a facile method to produce macroporous-activated carbon nanofibers (AMP-CNFs) by post-treating electrospun cobalt(II) chloride (CoCl₂) containing polyacrylonitrile (PAN/CoCl₂) nanofibers with hydrogen sulfide (H₂S) followed by carbonization. A range of techniques including scanning and transmission electron microscopy, FTIR and Raman spectroscopy is used to examine and characterize the process. Because of the phase behavior between carbon and cobalt, cobalt particles are formed in the nanofibers, some of which leave the fibers during the heat treatment process leading to macroporous fibrous structures. The number of the macroporous increase significantly with increasing CoCl₂ concentration in the precursor H₂S-treated PAN/CoCl₂ nanofibers. The cobalt phase in the fibers also leads to catalytic graphitization of the carbon nanofibers. The produced AMP-CNFs may be a promising candidates in many applications including anode layer in lithium ion batteries, air and liquid purifiers in filters, as well as in biomedical applications.     

In-situ analyses on the reactive sputtering process to deposit Al-doped ZnO films using an Al-Zn alloy target

The kinetic energies of generated ions were investigated during the reactive sputtering process to deposit Al-doped ZnO (AZO) films using an Al-Zn alloy target. The sputtering system was equipped with specially designed double feedback system to stabilise the reactive sputtering processes and analysis was performed with a quadrupole mass spectrometer combined with an energy analyser. Negative ions O⁻, O₂⁻, AlO⁻ and AlO₂⁻ with high kinetic energies corresponding to cathode voltage are generated at the partially oxidised target surface, after which some of the ions undergo subsequent charge exchange and/or dissociation. Positive ions O⁺, Ar⁺, Zn⁺ and Al⁺ with lower kinetic energies (around 10 eV) are generated by charge exchange of sputtered neutral O, Ar, Zn and Al atoms, respectively. As the target surface oxidises, cathode voltage decrease, the flux of high-energy negative ions increases and the electrical properties of the AZO degrade by ion bombardment as well as the AZO films that are deposited by conventional magnetron sputtering using an AZO target.     

Electrospun polymeric nanofibrous composites containing TiO2 short nanofibers

In this study, polymeric nanofibrous composites containing anatase TiO₂ short nanofibers (TiO₂-SNF) were successfully produced via electrospinning. The fabrication of the nanofibrous composite structure includes two steps. First, anatase TiO₂ nanofibers were obtained by calcination of electrospun PVP/TiO₂ nanofibers and then crushed into short nanofibers ranging from few microns in length. Second, these TiO₂-SNF were dispersed into polymer solutions and then electrospun into nanofibrous composites. We obtained nanofibers containing TiO₂-SNF from different polymer types including PMMA, PAN, PET and PC. The SEM and TEM imaging indicated that some of the TiO₂-SNF were fully covered by the polymeric matrix whereas some TiO₂-SNF were partially covered and/or stick on the surface of the fibers. The photocatalytic activity of nanofibrous composites containing TiO₂-SNF was evaluated by monitoring the photocatalytic decomposition of a model dye (rhodamine-6G) under UV irradiation.     

In Situ Synthesis of Cuprous Oxide/Cellulose Nanofibers Gel and Antibacterial Properties

Cellulose nanofibers were synthesized by acetobacter xylinum (xylinum 1.1812). The cellulose nanofibers with 30-90 nm width constructed three-dimension network gel, which could be used as a wound dressing since it can provide moist environment to a wound. However, cellulose nanofibers have no antimicrobial activity to prevent wound infection. To achieve antimicrobial activity, the cellulose nanofibers can load cuprous oxide (Cu₂O) particles on the surface. The cuprous oxide is a kind of safe antibacterial material. The copper ions can be reduced into cuprous oxides by reducing agents such as glucose, N₂H₄ and sodium hypophosphite. The cellulose nanofibers network gel was soaked in CuSO₄ solution and filled with copper ions. The cuprous oxide nanoparticles were in situ synthesized by glucose and embedded in cellulose nanofibers network. The morphologies and structure of the composite gel were analyzed by FESEM, FTIR, WAXRD and inductively coupled plasma (ICP). The sizes of Cu₂O embedded in cellulose nanofibers network are 200-500 nm wide. The peak at 605 cm⁻¹ attributed to Cu(I)-O vibration of Cu₂O shits to 611 cm⁻¹ in the Cu₂O/ cellulose composite. The Cu₂O/ cellulose nanofibers composite reveals the obvious characteristic XRD pattern of Cu₂O and the results of ICP show that the content of Cu₂O in the composite is 13.1%. The antibacterial tests prove that the Cu₂O/ cellulose nanofibers composite has the high antibacterial activities which is higher against S. aureus than against E. coli.     

Catalytic and antibacterial activities of green-synthesized silver nanoparticles on electrospun polystyrene nanofiber membranes using tea polyphenols

An efficient and environmentally friendly method has been developed to prepare Ag nanoparticles (AgNPs) coated tea polyphenols/polystyrene (Ag-TP/PS) nanofiber membrane, which combines electrospinning and in situ reduction of [Ag(NH₃)₂]⁺ using TP as the reductant and stabilizer. In this method, TP/Pluronic/PS nanofiber membranes are fabricated by electrospinning and then immersed in the aqueous solution of [Ag(NH₃)₂]⁺. While TP is being released from TP/Pluronic/PS nanofibers, the surface of TP/Pluronic/PS nanofibers could function as reactive sites for reduction of [Ag(NH₃)₂]⁺ without any extra reagents. XRD results indicate that AgNPs thus formed are in metallic form of Ag⁰. SEM images show that AgNPs can be densely and uniformly coated on the surface of TP/Pluronic/PS nanofibers. The as-prepared Ag-TP/PS nanofiber membranes exhibit excellent catalytic properties for the degradation of methylene blue. Furthermore, the effect of [Ag(NH₃)₂]⁺ concentration on the morphology and catalytic activity of the membrane is investigated. In addition, the antibacterial assays reveal that Ag-TP/PS nanofiber membrane possesses extraordinary antibacterial activity against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli microorganisms. The free-standing membrane is flexible and easy to handle, which is promising for potential applications in catalysis, antibacterial agents and water remediation fields.     

Preparation of silver nanoparticles dispersed in polyacrylonitrile nanofiber film spun by electrospinning

Ag nanoparticles dispersed in polyacrylonitrile (PAN) nanofiber film spun by electrospinning were in situ prepared by reduction of silver ions in N₂H₅OH aqueous solution. The Ag/PAN nanocomposite film was characterized by UV absorption spectroscopy, transmission electron microscopy (TEM) and surface-enhanced Raman scattering (SERS) spectroscopy. UV spectrum and TEM image show that silver nanoparticles with average diameter of 10 nm were obtained and dispersed homogeneously in PAN nanofibers. SERS spectrum indicates that the structure of PAN has been changed after Ag nanoparticles are dispersed in PAN.     

Influence of graphene oxide sheets on the pore structure and filtration performance of a novel graphene oxide/silica/polyacrylonitrile mixed matrix membrane

The novel graphene oxide (GO)/silica (SiO₂)/polyacrylonitrile (PAN) mixed matrix membranes (MMMs) with high filtration flux and excellent antifouling performance were designed and fabricated in situ by the method of non-solvent induced phase separation (NIPS) from the precursor of PAN hybridized with GO, tetraethoxysilane and 3-aminopropyltriethoxysilane. The influences of GO sheets on the pore and chemical structure, hydrophilic nature and filtration performance of derived GO/SiO₂/PAN MMMs were investigated by the scanning electron microscopy, field emission scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray, Fourier transform infrared spectrometer, pure water contact angles and filtration performance. Results indicated that in situ incorporation of GO sheets and SiO₂ molecules into PAN matrix via NIPS reconstructs the porous structure of derived GO/SiO₂/PAN MMMs with the upright finger-like holes, porous bottom, thinner top layer and high porosity. The spontaneous surface migration or segregation of hydrophilic GO sheets and SiO₂ molecules as well as their synergistic interaction occurred during NIPS greatly ameliorate the top surface structure and property of derived membranes with smoother surface, uniform pore structure and good hydrophilicity. The derived GO/SiO₂/PAN MMMs exhibit a high water filtration flux of 387 L m^?2 h^?1 with the bull serum albumin rejection rate up to 99% and significant enhancement of antifouling performance.     

Preparation of amorphous cobalt/carbon nanofibers composite as binder-free and conductive-free electrode materials for high supercapacitor

One dimensional carbon nanofibers embedded amorphous cobalt oxide with high electrochemical performances were successfully prepared by electrospinning Co(NO₃)₂ in PAN/DMF solution followed by a high-temperature heat treatment process. The different molar ratio of AN/Co(NO₃)₂ were synthesis. The optimized Co/CNFs(30), in which the molar ratio of AN/Co(NO₃)₂ was 30/1, exhibited a specific capacitance of 1096 F g^?1 at 1 A g^?1 and almost no decay in specific capacitance after cycling 2500 times at 5 A g^?1. The Co/CNFs were characterized by scanning electron microscopy, X-ray diffraction, Raman, transmission electron microscopy, X-ray photoelectron spectroscopy, thermal-gravity-analysis and the N₂ adsorption–desorption. The result showed that cobalt element was successfully dispersed in the carbon nanofibers with an amorphous state.     

Electrical properties of Al2O3 and AlPxOy dielectric layers on InP

Al₂O₃ and AlP_xO_y dielectric layers have been deposited on n-type InP substrates and the electrical properties of the interfaces have been evaluated by current-voltage and capacitance-voltage (C-V) measurements on metal- insulator-semiconductor diodes. Layers were deposited by combining trimethyl- aluminum, oxygen and phosphine in a low pressure chemical vapor deposition reactor in which the oxygen was excited in an r.f. plasma prior to mixing with the reactive gases in the deposition zone. The Al₂O₃ layers were invariably too conductive for meaningful C-V measurements; however, the AlP_xO_y layers not only were of high resistivity (? > 10¹⁶ Ω cm) but also exhibited interfacial properties superior to those of SiO₂ layers on InP. The surface potential could be modulated over the full band gap of InP since the surface density was less than 10¹¹ cm^-2 eV^-1 over much of the band gap.     

Flexible Janus nanofiber to acquire tuned and enhanced simultaneous magnetism-luminescence bifunctionality

A novel nanostructure of [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] magnetic-luminescent bifunctional Janus nanofibers has been successfully fabricated via electrospinning technology using a homemade parallel spinneret. Electrospun YAG:7 % Tb³⁺ luminescent nanofibers and CoFe₂O₄ magnetic nanofibers were respectively incorporated into polyvinyl pyrrolidone (PVP) matrix and electrospun into Janus nanofibers with CoFe₂O₄ magnetic nanofibers/PVP as one strand nanofiber and YAG:7 % Tb³⁺ luminescent nanofibers/PVP as another strand nanofiber. [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] magnetic-luminescent bifunctional Janus nanofibers possess superior magnetic and luminescent properties due to their peculiar nanostructure, and the luminescent characteristics and saturation magnetizations of the Janus nanofibers can be tuned by adding various amounts of YAG:7 % Tb³⁺ luminescent nanofibers and CoFe₂O₄ magnetic nanofibers. Compared with CoFe₂O₄/YAG:7 % Tb³⁺/PVP composite nanofibers, the magnetic-luminescent bifunctional Janus nanofibers provide higher performances due to isolating YAG:7 %Tb³⁺ luminescent nanofibers from CoFe₂O₄ magnetic nanofibers. Formation mechanism of [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] Janus nanofibers is also presented. The design conception and construction technology are of universal significance to fabricate other bifunctional Janus nanofibers.     

Fabrication of TiO2 hollow fibers with surface nanostructure

Polyvinyl alcohol-TiO₂ (PVA-TiO₂) core sheath nanofibers were fabricated by electrospinning an aqueous solution of PVA and introducing the thread-like droplets directly into a titanium tetraisopropoxide (TTIP)/hexane solution. Rod-like and sheet-like structures of lepidocrocite-type layered titanate formed on the surface of the TiO₂ sheath of the nanofibers by alkaline treatment in 1 mol L⁻¹ aqueous NaOH solution at 363 K. The nanofibers were converted to hollow TiO₂ nanofibers with surface nanostructure and anatase crystallinity by acid treatment to remove sodium ions and heat treatment at 773 K. The surface nanostructures enhanced the crystallinity and external surface area of the nanofiber and contributed to the improvement of photocatalytic oxidation activity.     

Thermally induced porous carbon nanofibers for electrochemical capacitor electrodes from phenylsilane and polyacrylonitrile blend solutions

This work focuses on preparations of porous carbon composite nanofibers (CCNFs) with silicon-containing compounds and the introduction of a high specific surface area through the creation of pores by a simple thermal treatment. Blends of phenylsilane (PS) solutions at various concentrations and polyacrylonitrile (PAN) were electrospun into nanofibers. This process was followed by carbonization at 800 °C to create CCNFs with diameters of 60–200 nm and a high specific surface area of over 800 m²/g. The specific capacitance of the electrode in 6 M KOH solution was extraordinarily high (180 F/g).     

Li+‐Containing,Continuous Silica Nanofibers for High Li+ Conductivity in Composite Polymer Electrolyte

Solid‐state electrolytes have recently attracted significant attention toward safe and high‐energy lithium chemistries. In particular, polyethylene oxide (PEO)‐based composite polymer electrolytes (CPEs) have shown outstanding mechanical flexibility and manufacturing feasibility. However, their limited ionic conductivity, poor electrochemical stability, and insufficient mechanical strength are yet to be addressed. In this work, a novel CPE supported by Li⁺‐containing SiO₂ nanofibers is developed. The nanofibers are obtained via sol–gel electrospinning, during which lithium sulfate is in situ introduced into the nanofibers. The uniform doping of Li₂SO₄ in SiO₂ nanofibers increases the Li⁺ conductivity of SiO₂, generates mesopores on the surface of SiO₂ nanofibers, and improves the wettability between SiO₂ and PEO. As a result, the obtained SiO₂/Li₂SO₄/PEO CPE yields high Li⁺ conductivity (1.3 × 10^?4 S cm^?1 at 60 °C, ≈4.9 times the Li₂SO₄‐free CPE) and electrochemical stability. Furthermore, the all‐solid‐state LiFePO₄‐Li full cell demonstrates stable cycling with high capacities (over 80 mAh g^?1, 50 cycles at C/2 at 60 °C). The Li⁺‐containing mesoporous SiO₂ nanofibers show great potential as the filler for CPEs. Similar methods can be used to incorporate Li salts into other filler materials for CPEs.