Heterogeneous adsorption of activated carbon nanofibers synthesized by electrospinning polyacrylonitrile solution

This study focuses on the adsorption properties of activated carbon nanofibers (CNFs) fabricated by electrospinning polyacrylonitrile solutions dissolved in dimethylformamide, followed by heat treatment at high activation temperatures (700, 750, 800 degrees C). The samples were characterized by BET, SEM, and XRD. In addition, the adsorption energy distribution functions of CNFs were analyzed by using the generalized nonlinear regularization method. Comparative analysis of energy distribution functions provided significant information on the energetic and structural heterogeneities of CNFs. Furthermore, an investigation of adsorption equilibrium and kinetics of methylene blue (MB) and congo red (CR) revealed that the adsorption capacity and kinetics of MB are much higher and faster than that of CR on a given sample. Our experimental and theoretical results suggest that the CNFs used in this work may be widely used as an adsorbent.     

Composite nanofibers produced by modified needleless electrospinning

A needleless electrospinning method was used to prepare poly(vinyl alcohol) nanofibers with a content of single walled (SWCNTs) and multi walled carbon nanotubes (MWCNTs). The needleless process of electrospinning from free surface of polymeric solution requires perfect solutions of polymers and additives (carbon nanotubes in the case). The solutions were prepared by sonication method and by usage of surface modified carbon nanotubes. The presence of carbon nanotubes inside the electrospun nanofibrous materials were proved by means of Raman spectroscopy. This process example can be modified for other polymer solutions to produce nanocomposite fibrous structures by electrospinning in mass scale.     

静电纺丝法制备多孔纳米炭纤维及其电化学性能研究

分别以聚乙烯醇(PVA)/热固性酚醛树脂(PF)/碳酸钾(K2CO3)和PVA/PF的水溶液为纺丝原液,通过静电纺丝、固化和炭化处理制得多孔纳米炭纤维。利用扫描电子显微镜(SEM)、低温氮气吸脱附等对所制多孔炭纳米纤维进行表征,并将所制多孔炭纤维作为模拟电容器电极材料,利用循环伏安和恒电流充放电进行了电化学性能测试。结果表明:纺丝原液中加入K2CO3后所制多孔纳米炭纤维的比表面积增大(从564 m.2g-1提高到668 m.2g-1),电化学性能提高(在电流密度为0.2 A.g-1的情况下,比电容由165 F.g-1提高到178 F.g-1)。     

Titania nanofibers prepared by electrospinning

TiO₂ nanofibers with a diameter of 54-78 nm have been successfully prepared by electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and Ti(IV)-isopropoxide. The effect of viscosity and applied electric field on the morphology of the electrospun titania fibers was investigated. It has been observed that the increase in electric field causes bead formation and discontinuity in nanofiber morphology.     

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.     

Characterization of carbon thin films prepared by the thermal decomposition of spin coated polyacrylonitrile layers containing metal acetates

Polyacrylonitrile (PAN) layers were cast from dimethyl-formamide solutions onto quartz substrates by spin coating and subsequently annealed at up to 1000 °C in N₂ atmosphere. Carbonization was catalyzed by nickel or cobalt added to the solution as acetate salts. The synthesized films were approx. 970 nm thick and were characterized by Raman and infrared spectroscopy as well as thermogravimetric and electrical conductance measurements. We discuss the effects of carbonization temperature and metal concentration on the morphology, composition and electrical properties of the formed carbon layer. Increasing the amount of catalyst and the pyrolysis temperature was beneficial for the process and resulted in carbonaceous films with a higher degree of structural order as evidenced by the decreasing Raman I_D/I_G ratio and the increasing electrical conductivity of the films. Cobalt is a better catalyst for PAN carbonization than nickel as far as the structure of the product film is concerned.     

Electrically conducting thin films obtained by ion implantation in pyrolyzed polyacrylonitrile

Heat treatment of polyacrylonitrile (PAN) leads to products with semiconductor-to-metal range of conductivities. The electrical properties of these materials are further modified by ion implantation. The conductivity, 1×10^–7 (Ω cm)^–1, of heat treated PAN at 435°C (PAN435) increases upon ion implantation with As⁺, Kr⁺, Cl⁺ or F⁺, reaching the maximum value of 8.9×10^–1 (Ω cm)^–1 at a dose of 5×10¹⁶ ion/cm² and an energy of 200 KeV for the case of F⁺ implantation. On the other hand, ion implantation in the more conducting heat-treated PAN at 750 °C (PAN750) leads to a decrease in the electrical conductivity. It is shown that the conductivity modifications are primarily due to structural rearrangements induced by the energetic ions. Specific chemical doping contribution to conductivity is noted for halogen implantation in PAN435. The temperature dependence of conductivity of PAN heat treated at 750°C suggests a two path conduction, namely a three dimensional variable range hopping conduction and a metallic conduction. After ion implantation, the conductivity-temperature dependence is interpreted in terms of a variable range hopping conduction mechanism. Received: 25 August 2000 / Reviewed and accepted: 28 August 2000     

Preparation of hierarchical porous carbon by post activation

A series of hierarchical porous carbons (HPCs) have been prepared by a combination of soft-templating and post activation. As evidenced by N₂ sorption tests, the pristine mesopores were basically preserved and micropores were generated on the mesopore wall of mesoporous carbon (MC). The micropore generation on the mesoporous skeleton can be controlled by simply adjusting the KOH ratio and activation temperature. The BET surface area, mesopore surface area and total pore volume of the HPCs increase monotonously with increasing activation temperature and KOH/MC ratio. In contrast, the micropore surface area reaches the maximum at the ratio of KOH/MC of 4. Further increase of KOH/MC ratio and activation temperature reduces the micropore surface area. Structural characterizations confirm that the main mesopore channel was preserved during activation.     

Effect of plasma treatment on surface chemical-bonding states and electrical properties of polyacrylonitrile nanofibers

Electrospun polyacrylonitrile (PAN) nanofibers were subjected to surface modification by atmospheric pressure (AP) plasma treatment with reactive gases. There was no damage to the surfaces after this plasma treatment, and no significant changes were observed in the morphologies of the nanofibers. The surface energies of O₂- and N₂-plasma-treated PAN (abbreviated as OPP and NPP, respectively) nanofibers increased by almost 138.7% and 190.6%, respectively, in comparison with that of an untreated nanofiber (256.6 mJ/m²). The binding energies of both OPP and NPP samples increased through the formation of many hydrophilic bonds involving oxygen. The current-voltage (I-V) characteristics of the nanofibers were determined for the different reactive gases, and the plasma-treated nanofibers showed higher protein immobilization compared to the untreated ones. This result indicates that electrospun PAN nanofibers have the potential to be used in protein biosensor systems.     

HCHO sensing properties of Ag-doped In2O3 nanofibers synthesized by electrospinning

Ag-doped In₂O₃ nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In₂O₃ nanofibers could be used to fabricate high performance HCHO sensors in practice.     

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).     

Fabrication of multi-walled carbon nanotube reinforced polyelectrolyte hollow nanofibers by electrospinning

Hybrid hollow multi-walled carbon nanotubes (MWCNTs)/polyelectrolytes (PE) nanofibers were prepared by a combination of the electrospinning method and layer-by-layer (LbL) technique. The mixed polystyrene (PS)/MWCNTs nanofibers were obtained by electrospinning method, which were employed as templates to self-assembly multilayered polyelectrolytes by LbL technique. Hollow MWCNTs/PE nanofibers were obtained by selectively removed part of the template: PS, which is confirmed by Raman spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Preparation of poly (vinyl alcohol)/silica composite nanofibers membrane functionalized with mercapto groups by electrospinning

Membranes of poly vinyl alcohol (PVA)/silica functionalized with mercapto groups are synthesized by electrospinning. Scanning electron microscopy (SEM) studies showed that the fiber diameters are in the range of 200-300 nm. The thickness of nanofiber decreases with an increase in calcination temperature. The results of Fourier transform infrared (FTIR) indicated that PVA/silica nanofibers are functionalized by mercapto groups via the hydrolysis poly-condensation method. N₂ adsorption-desorption showed that organic molecules can be removed completely when the PVA/silica composite fibers are calcinated at 800 °C. The fibers calcinated at 800 °C were pure inorganic silica species with a mesoporous structure. These mercapto groups functionalized PVA/silica nanofibers have a great potential application in the field of adsorption of heavy metal ions.     

Novel carbon fiber/epoxy composite toughened by electrospun polysulfone nanofibers

Novel carbon fiber/epoxy composite toughened by electrospun polysulfone (PSF) nanofibers was prepared to enhance fracture toughness of the composite, and compared the morphology and toughness to those of composite toughened by PSF films prepared by solvent method. Polysulfone nanofibers with the average diameter of 230 nm were directly electrospun onto carbon fiber/epoxy prepregs to toughen the composite. SEM observations of the polysulfone nanofibers toughened composite revealed that polysulfone spheres with uneven sizes presented uniform dispersion through interleaves of the composite, which was different from those of composite toughened by PSF films. Mode I fracture toughness (G_IC) of the nanofibers toughened composite was 0.869 kJ/m² for 5.0 wt.% polysulfone nanofibers content, which was 140% and 280% higher than those of PSF films toughened and untoughened composite due to the uniform distribution of polysulfone spheres.     

Conductive composite films composed of polyaniline thin layers on microporous polyacrylonitrile surfaces

A facile approach for preparing flexible and conductive composite films by chemical polymerization of aniline monomers on the microporous polyacrylonitrile (PAN) surfaces was reported. A good adherence between polyaniline thin layer and PAN substrate was ascribed to the formation of a continuous conductive network in the film thickness along the capillary channel within PAN matrix. The electronic properties of the resulting composite films were tuned easily with the mass fraction of aniline monomer in the PAN solution or through chemical process. It is also found that the thermal stabilities of the composite films were significantly enhanced, while good mechanical properties were maintained.     

静电纺丝法制备聚丙烯腈基纳米炭纤维及其表面结构表征

通过稳定化、炭化静电纺制的聚丙烯腈(PAN)前驱体纤维制备了直径为100nm～300nm的纳米炭纤维.用扫描电镜(SEM)、场发射扫描电镜(FESEM)、扫描隧道显微镜(STM)及扫描量热分析法(DSC)研究了纳米炭纤维及其前驱体纤维的形貌及结构.结果表明:纳米炭纤维及其前驱体纤维的直径表现为对数正态分布.静电纺制纤维的环化放热峰移向低温,表明静电纺制纤维可在较低的温度下引发环化.由于静电纺制纤维的粗糙表面及在热处理过程中的收缩行为,在纳米炭纤维表面形成了长度为10nm宽度为5nm的凹坑.     

Enhancement of electrochemical properties on TiO2/carbon nanofibers by electrospinning process

In the present work, we report the preparation of TiO₂–carbon/carbon dual nanofibers using an electrospinning technique. The dual nanofibers were synthesized using a modified side-by-side spinneret, which allowed the fabrication of the desired dual nanofiber architecture in a one-step process. A subsequent heat treatment permitted the control on the crystal structure of the synthesized dual nanofibers. Scanning electron microscopy and transmission electron microscopy results confirmed the continuity and duality of the obtained nanofibers. The difference in composition between the fibers composing the dual fibers was clearly observed by energy dispersive X-ray spectroscopy. The effect of heat treatment on crystallinity was evident on the results obtained from the X-ray diffraction and selected area electron diffraction studies; where, depending on the heat treatment conditions, clear signals for anatase and rutile phases of TiO₂ were observed. Electrochemical studies suggest an improvement on the conduction properties of TiO₂–carbon/carbon dual nanofibers compared to single TiO₂–carbon nanofibers, attributed to the carbon nanofiber contribution attached to the TiO₂ nanofibers. Based on the morphological and structural features of this novel nanostructured material, and to the electrochemical performance observed, it has a wide range of potential applications.     

A novel kind of porous carbon nitride using H-magadiite as the template

A novel kind of porous carbon nitride was prepared by pyrolysis of polymerized ethylenediamine using H-magadiite as the template. This material was characterized by XRD, FT-IR, XPS, and nitrogen sorption at 77 K. The BET surface area, pore volume and the median pore width are 436 m²/g, 0.69 cm³/g and 0.84 nm, respectively, based on the N₂ sorption. Using glass carbon electrodes modified by this material, an excellent linear determination range (0.05-0.99 μM) with a low detected concentration limit of 6.9 × 10^− 3 μM could be obtained on the determination of differential pulse voltammetries of dopamine in the presence of 400-fold excess of ascorbic acid.