Activated Carbon Nanofibers Research Articles

Hydrogen sorption kinetics, hydrogen permeability, and thermal properties of compacted 2LiBH4[sbnd]MgH2 doped with activated carbon nanofibers

To improve the packing efficiency in tank scale, hydrides have been compacted into pellet form; however, poor hydrogen permeability through the pellets results in sluggish kinetics. In this work, the hydrogen sorption properties of compacted 2LiBH4MgH2 doped with 30 wt % activated carbon nanofibers (ACNF) are investigated. After doping with ACNF, onset dehydrogenation temperature of compacted 2LiBH4MgH2 decreases from 350 to 300 °C and hydrogen released content enhances from 55 to 87% of the theoretical capacity. The sample containing ACNF releases hydrogen following a two-step mechanism with reversible hydrogen storage capacities up to 4.5 wt % H2 and 41.8 gH2/L, whereas the sample without ACNF shows a single-step decomposition mainly from MgH2 with only 1.8 wt % H2 and 15.4 gH2/L. Significant kinetic improvement observed in the doped system is due to the enhancement of both hydrogen permeability and heat transfer through the pellet.

Influence of the Formulation on the Microstructure and Thus Performance of Li-Ion Batteries

The research in the field of Li-ion batteries is stronger than ever, with a common aim of increasing the energy and power density. More and more studies pinpoint the limitation of power-related performance for Li-ion batteries to the microstructure of each electrode. This random arrangement of the active material and carbon filling particles bound by the binder is typically characterized through physical values such as tortuosity, porosity and MacMullin Number. To investigate the relationship between microstructure and performance in details, we used a design of experiment to evaluate close to seventy different formulations with LiFePO4 and Li4Ti5O12 as the active materials (AM), carbon black (CB) and carbon nanofibers (CNF) as the conductive fillers, and two different binders: polyvinylidene fluoride and a thermoplastic elastomer. By keeping the loading and porosity constant throughout the study, all formulations are homogenously dispersed in a regular tetrahedron of coordinates (AM, CB, CNF, Binder). First, the microstructure was characterized in order to extract data related to the tortuosity, porosity and electrical conductivity. Then, galvanostatic measurements, in charge and discharge, from C/25 to 30C allowed to gather information such as the low- and high-rate capacity, energy and power and the Peukert constant for intermediate rates. The statistical analysis of all these results showed some clear correlation between the formulation and the microstructure and performance of the cells. Thus, it was made possible to draw the optimal formulation to get the best compromise depending on the application requirements (energy, rate or power). Finally, trends between the physical properties and performance were deciphered. This could be used to fine-tune the best possible electrode. Figure 1

Electrospun melamine‐blended activated carbon nanofibers for enhanced control of indoor CO2

ABSTRACTElectrospun carbon nanofibers were activated with melamine–polyacrylonitrile [melamine‐blended carbon nanofibers (MACNFs)] for use as a fibrous adsorbent for indoor CO2 removal. Although, melamine doping was intended solely to incorporate basic nitrogen functionalities on the nanofibers, it also shortened fabrication time, conserving time, and energy cost. The specific surface area and microporosity of the fibers were enhanced from 412 m2 g−1 and 0.1646 cm3 g−1 to 547 m2 g−1 and 0.220 cm3 g−1, respectively, upon final CO2 activation of the nanofibers. With the chemical properties, we observed significant tethering of pyridine functionality. The sample, MACNF‐7 (10 mL of polymer solution doped with 0.7 g of melamine), provided the optimum melamine doping condition to achieve the highest CO2 adsorption capacity of 3.15 mmol g−1. The adsorption performance was based on simultaneous improvement in microporosity (physical) and surface basicity (chemical) properties of the adsorbent. However, in a binary mixture with nitrogen, the selective adsorption of CO2 showed the predominance of the improved surface basicity over microporosity. The highest CO2 selective capture (1.22 mmol g−1) was occurred for a CO2:N2 ratio of 0.15:0.85, with a selectivity of 58.19 at 273 K. In a regeneration test, stable and robust performance was achieved more than five cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47747.

Zno/Carbon nanofibers for efficient adsorption of lead from aqueous solutions

ABSTRACT Hybrid nanofibers based on ZnO loaded activated carbon nanofibers (ZnO-ACNFs) are proposed here for the elimination of hazardous lead from aqueous solutions. The prepared ZnO nanoscale material was loaded into the polyacrylonitrile nanofibers (PAN NFs) which were later carbonized by using a novel method named as a plate-sandwich method. The Synthesized nanofibrous composite was characterized by SEM, TEM, EDX, FTIR and XRD techniques to analyze its chemical and morphological properties. Moreover, the nanocomposite was efficaciously applied for the lead (Pb2+) ions removal from wastewater and simulated water through continuous filtration and batch filtration. The ZnO-ACNFs membrane showed outstanding results in adsorptive removal, giving adsorption capacity of 92.59 mg/g within the contact time of 45 min. Compared to their counterparts (ZnO and CNFs), the hybrid ZnO-ACNFs showed excellent performance in removing toxic lead.

Activated Carbon Nanofiber Nonwovens: Improving Strength and Surface Area by Tuning Fabrication Procedure

Electrospun-based activated carbon nanofiber nonwovens (ACNFN) are interesting candidate materials for adsorption processes due to their high surface area and low flow-through resistance. However, the mechanical properties of these materials must be sufficient to withstand the conditions for use and to prevent breakage and fiber shedding. Improvements in the mechanical properties of the ACNFNs should not be accompanied by deterioration of other beneficial properties, however. In this research, improving the mechanical properties of ACNFN based on 14 wt % PAN/DMF was done by tuning the fabrication conditions. Carbonization occured at 600 °C for 2 h followed by steam activation at 750 °C for 1 h. We demonstrated the capability to generate ACNFN with high accessible surface area that reached 520 m 2 /g and acceptable mechanical strength (break strength, 0.9; 75 MPa, Young's modulus) for improved handling and use in different applications.

The preparation of liquefied bio-stalk carbon nanofibers and their application in supercapacitors.

Carbon nanofibers (CNFs) have been widely used in electrochemical energy storage devices because of their excellent conductivity, extremely large surface area and structural stability. Herein, we obtained a viscous, liquefied bio-stalk carbon via the simple chemical treatment of biomass, and mixed it with polyacrylonitrile to prepare a spinning solution. Subsequent electrospinning and high temperature activation resulted in the successful preparation of liquefied lignin-based activated carbon nanofibers. The as-prepared liquefied bio-stalk carbon nanofibers exhibited an outstanding electrochemical performance (specific capacitance of 273 F g−1 at 0.5 A g−1 current density), and a capacitance retention of 210 F g−1 even under a large current density of 10 A g−1. Besides its high specific capacitance and outstanding rate capability, the symmetrical supercapacitor cell based on the liquefied carbon-based nanofiber electrodes also exhibited an excellent cycling performance with 92.76% capacitance retention after 5000 charge–discharge cycles. This study provides a new strategy for the future development of supercapacitor electrode materials and enhances the development of biomass energy.

Transient, in situ synthesis of ultrafine ruthenium nanoparticles for a high-rate Li–CO2 battery

Ultrafine Ru nanoparticles anchored on freestanding activated carbon nanofibers with porous structure are synthesized as a high performing cathode for Li–CO2 batteries via a transient, in situ thermal shock method.

Synergistic effects of transition metal halides and activated carbon nanofibers on kinetics and reversibility of MgH2

MgH2 doped with transition metal halides (TiF4, NbF5, and ZrCl4) and activated carbon nanofibers (ACNF) for reversible hydrogen storage is prepared by ball milling technique. Transition metal halides provide catalytic effects for de/rehydrogenation kinetics, while ACNF benefits thermal conductivity and hydrogen permeability as well as prevents particle agglomeration during cycling. Significant reduction of onset and main dehydrogenation temperatures of MgH2 (ΔT = 243 and 158 °C, respectively) are achieved by doping with 5–10 wt % of NbF5, ACNF-TiF4 and ACNF-NbF5. During the 1st cycle, the latter samples liberate 4.7–5.0 wt % H2 within 1 h 30 min, whereas MgH2 doped with ACNF reaches only 1.5 wt % H2. The reaction between MgF2 and NbHx (x < 1) (MgH2-NbF5 and MgH2-ACNF-NbF5) during dehydrogenation results in the formation of new catalytic active species of Nb-F-Mg favoring kinetics. Upon four hydrogen release and uptake cycles, kinetics and reversibility within 1 h 30 min of MgH2-ACNF-NbF5 are preserved at 5.0 wt % H2, while those of MgH2-NbF5 and MgH2-ACNF-TiF4 decay to 4.4 wt % H2. Activation energy (EA) for dehydrogenation of MgH2 considerably decreases from 140.0 ± 10.2 to 37.8 ± 1.5 kJ/mol after doing with ACNF-NbF5. Superior performance of MgH2-ACNF-NbF5 to MgH2-NbF5 is due to synergistic effects of NbF5 and ACNF. In the case of MH2-ACNF-TiF4, the disappearance of active species benefiting kinetic properties and the formation of thermally stable TiH2 account for inferior hydrogen content reversible.

Preparation and electrochemical performance of electrospun biomass-based activated carbon nanofibers

Biomass-based nanofibers were prepared by electrospinning a mixture of polyacrylonitrile and acid-treated biomass from industrial hemp straw. The as-prepared biomass-based nanofibers were then carbonized and activated by high-temperature carbonization and KOH to obtain the activated biomass-based carbon nanofibers. The scanning electron microscopy images show that the precursors and carbon nanofibers are composed of fibers 179 nm in diameter, and the nitrogen adsorption/desorption measurements indicate that the carbon nanofibers possess a high-specific surface area of 2348.73 m2·g−1. The carbon nanofibers exhibit excellent electrical performance. The specific capacitance is as high as 244.8 F·g−1 at a current density of 1 A·g−1. The specific capacitance remains at 96% after 3000 cycles of charge and discharge at a current density of 2 A·g−1, showing excellent cycle stability. This work provides new ideas for the future development of supercapacitors electrode materials and enhances the development of biomass energy.

A flexible supercapacitor consisting of activated carbon nanofiber and carbon nanofiber/potassium-pre-intercalated manganese oxide

Potassium-pre-intercalated δ-phase MnO2 is uniformly grown on carbon nanofibers for the positive electrode of asymmetric supercapacitors. An electrospun CNF is chemically activated with KOH at 800 °C for the negative electrode, showing ideal capacitive behavior. The crystallinity of MnO2 is significantly reduced by the pre-intercalation of K ions into its layered structure. This textural characteristic is beneficial to the K+ diffusion into/out the interlayer structure, leading to effective utilization of the electroactive material of KxMnO2. This unique composite electrode provides both ideal pseudo-capacitive behavior from KxMnO2 and excellent electric conductivity from the CNF network, exhibiting a fairly high specific capacitance value of 279 F g-1 at 1 A g−1 with ca. 82.3% capacitance retention from 1 to 32 A g−1. A flexible ASC consisting of the positive KxMnO2@CNF electrode, a paper separator, and the negative ACNF electrode is successfully assembled. This cell shows superior ASC performances: a high cell voltage between 0 and 2 V, excellent capacitance retention (10,000 cycles with 10% decay), and simultaneously reaching high specific energy and power of 21.1 Wh kg−1 and 9.5 kW kg−1. The charge storage behavior of this cell without bending and with a bending angle of 90° shows no apparent difference, demonstrating its potential in the next-generation flexible energy storage devices.

Uniform Coating of Polyaniline on Porous Carbon Nanofibers as Efficient Electrodes for Supercapacitors

Porous activated carbon nanofibers (A-CNFs) are fabricated and considered as promising electrode materials for electrochemical double layer capacitors (EDLCs) due to their free-standing and hierarchical pore structure. They exhibit high specific capacitances in 1 M H2SO4 without any significant loss at high scan rates. To further enhance charge storage, we incorporated polyaniline onto A-CNFs with the aim to combine the benefits of both EDLCs (high power density) and pseudocapacitors (high energy density). By using a simple galvanostatic deposition, we achieve a uniform coating of polyaniline on A-CNFs. Combination of two different storage mechanisms results in an excellent specific capacitance of 290 F g−1. Cyclic voltammetric measurements show no significant change at scan rates up to 100 mV s−1.

Preparation of Filtration Sorptive Materials from Nanofibers, Bicofibers, and Textile Adsorbents without Binders Employment.

The article deals with the preparation and possibilities of using combined filtration sorption systems usable for the construction of folded filters or respirators. The studied materials are made of several structural layers—a filter membrane made of polymeric nanofibers, an adsorbent containing active carbon or porous silicon dioxide nanofibers, and a supporting or cover nonwoven bicomponent fabric. The layers are connected only by pressure at an elevated temperature without the use of binders, according to utility model PUV 31 375. The result is a compact fabric material of textile character with a high permeability, good mechanical resistance, which effectively catches the submicron particles and the gases of the organic substances. The prepared samples of the filter sorptive material have been evaluated not only from the point of view of morphology and microstructure, but also from the point of view of the capture of pollutants.

Controlling the Surface Oxygen Groups of Polyacrylonitrile-Based Carbon Nanofiber Membranes While Limiting Fiber Degradation

Enhancing the performance of nanofibrous carbons requires the specific chemical functionalization of the surface, while limiting material degradation or causing other detrimental changes in the surface area and pore structures. We compare traditional oxidation protocols using HNO3, HNO3/H2SO4, and KMnO4 with the much less used oxidants RuO4 and OsO4, in tandem with secondary oxidants (such as KMnO4 or Oxone®), for their ability to form carboxylic acids on the surface of polyacrylonitrile-based activated carbon nanofiber membrane (ACNF) materials. While the traditional methods increased the carboxylic acid contents, they also destroyed the macrostructure of the ACNF, concomitant with the loss of up to 17 wt.% of the material. RuO4-mediated oxidations proved also to be too harsh. On the contrary, some of the OsO4-based protocols were characterized by very high mass yields; significant increase in carboxylic acid functionalization (6.3 µmol/mg) compared with the unmodified ACNF (1.7 µmol/mg), but with no concomitant loss of macrostructure, as measured by the retention of the Brunauer-Emmett-Teller (BET) surface area; and average pore width. While there was some reduction in micropore volume, the microporosity of the material remained high. The temperature-programmed desorption mass spectrometry (up to 1000 °C) indicated the presence of both single and adjacent carboxylic acid groups. We thus identified mild and highly effective reaction conditions for the functionalization of carbon nanomaterials without undue degradation of their physical properties.

Reusable carbon nanofibers for efficient removal of methylene blue from aqueous solution

This work demonstrates the preparation of polyacrylonitrile (PAN) based activated carbon nanofibers (ACNFs) through electrospinning followed by thermal treatment. Resulted activated carbon nanofibers having diameters in the range of 240–280nm were then examined for the adsorption capability for methylene blue dye from aqueous solution. Batch mode experiments were carried out at room temperature to study the effect of amount of nanofiber, contact time and pH on dye adsorption. It was found that activated carbon nanofibers showed remarkable adsorption efficiency while completely decolorizing the dye solution within 60min of contact. Results revealed that the adsorption data followed Langmuir isotherm giving maximum adsorption capacity of 72.46mg/g and pseudo second order kinetic model. Furthermore, the reusability of activated carbon nanofibers had shown removal efficiency more than 80% up to 3 cycles. Morphology and structure of PAN nanofibers and ACNFs were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR).

Electrospun N‐Doped Hierarchical Porous Carbon Nanofiber with Improved Degree of Graphitization for High‐Performance Lithium Ion Capacitor

The lithium-ion capacitor (LIC) has been regarded as a promising device that combines the merits of lithium-ion batteries and supercapacitors, and that meets the requirements for both high energy and high power density. The development of advanced electrode materials is the key requirement. Herein, we report the bottom-up synthesis of activated carbon nanofiber (a-PANF) with a hierarchical porous structure and a high degree of graphitization. Electrospinning has been employed to prepare an interconnected fiber network with macropores, and ferric acetylacetonate has been introduced as both a mesopore-creating agent and a graphitic catalyst to increase the degree of graphitization. Furthermore, chemical activation enlarges the specific surface area by producing abundant micropores. Half-cell evaluation of the as-prepared a-PANF gave a discharge capacity of 80 mA h g-1 at 0.1 A g-1 within 2-4.5 V and no capacity fading after 1000 cycles at 2 A g-1 , which represents a significant improvement compared to conventional activated carbon (AC). Furthermore, an as-assembled LIC with a-PANF cathode and Fe3 O4 anode showed a superior energy density of 124.6 W h kg-1 at a specific power of 93.8 W kg-1 , which remained at 103.7 W h kg-1 at 4687.5 W kg-1 . This indicates promising application potential of a-PANF as an electrode material for efficient energy storage systems.

Development of Polysulfone/Activated Carbon Nanofibers Mixed Matrix Membrane for CO2/CH4 Separation

This study was performed primarily to investigate the effect of activated carbon nanofiber (ACNF) on carbon dioxide and methane separation performance of mixed matrix membrane (MMM). In this study, polysulfone (PSf)/ACNF mixed matrix membranes was fabricated using dry/wet inversion technique. The effect of PSf concentration and ACNF loading on the performance of mixed matrix membrane in terms of permeability and selectivity of CO2/CH4 gas separation was observed. The fabricated flat sheet mixed matrix membranes were characterized using Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) analysis. From the SEM observations, it shows that sponge like structures images were observed upon the addition of ACNFs in the PSf/ACNF membranes was slowly decreased due to increasing weight percentage of ACNF. FT-IR result indicating the presence of carboxyl group in MMM at wavelength 1750 cm-1. Meanwhile, the MMMs were further tested to pure permeation test using pure CO2 and CH4 gas, the CO2 permeance improved and the selectivity of CO2/CH4 increased after the addition of ACNFs.

Effects of manganese(VI) oxide on polyacrylonitrile-based activated carbon nanofibers (ACNFs) and its preliminary study for adsorption of lead(II) ions

In this work, the effect of adding manganese oxide towards polyacrylonitrile-based activated carbon nanofibers (ACNFs) was evaluated. The properties of PAN-based ACNFs/MnO2 were analyzed by using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and Fourier transform infrared (FTIR). The sorption study of the electrospun ACNFs/MnO2 in comparison to neat ACNFs and commercial granular AC towards lead (Pb) was also conducted. SEM micrograph analysis displays more compact nanofibers with dispersion of beads that were observed in the ACNF/MnO2 with the diameter of 437.2 nm while aligned nanofibers with the diameter of 575.5 nm were observed in the neat ACNFs. The FTIR analysis showed the peak of Mn–O, which indicates the presence of MnO2 in the ACNFs/MnO2. In comparison to the neat ACNFs, surface area of the prepared ACNFs/MnO2 is lower. It was found out that the removal of Pb(II) using ACNFs and ACNFs/MnO2 is higher than commercial granular activated carbon with a removal rate of 100% at initial concentration of 3.5 ppm. The promising results of ACNFs/MnO2 contributed by their satisfactory specific surface area and vast presence of surface functional groups.

Fabrication and electrochemical properties of activated CNF/Cu x Mn1−xFe2O4 composite nanostructures

This work reports the fabrication and electrochemical properties of activated carbon nanofibers composited with copper manganese ferrite (ACNF/Cu x Mn1−xFe2O4: x = 0.0, 0.2, 0.4, 0.6, 0.8) nanostructures. The obtained samples were characterized by means of X-ray diffraction, field emission scanning electron microscopy, Brunauer–Emmett–Teller analyzer, thermal gravimetric analysis, X-ray photoemission spectroscopy, and X-ray absorption spectroscopy. The supercapacitive behavior of the electrodes is tested using cyclic voltammetery, galvanostatic charge–discharge and electrochemical impedance spectroscopy. By varying ‘x’, the highest specific capacitance of 384 F/g at 2 mV/s using CV and 314 F/g at 2 A/g using GCD are obtained for the x = 0.2 electrode. The second one of 235 F/g at 2 mV/s using CV and 172 F/g at 2 A/g using GCD are observed for x = 0.8 electrode. The corresponding energy densities are 74 and 41 Wh/kg, respectively. It is observed that the cyclic stability of the prepared samples strongly depend on the amount of carbon, while the specific capacitance was enhanced by the sample with nearly proportional amount between carbon and CuMnFe2O4. Such results may arise from the synergetic effect between CuMnFe2O4 and ACNF.

Investigation of optical and dispersion parameters of electrospinning grown activated carbon nanofiber (ACNF) layer

Activated carbon nanofiber (ACNF) layers are prepared by electrospinning method. We have investigated the optical properties of ACNF layer using UV–vis-NIR spectrophotometer. The optical constants such as refractive index, extinction coefficient and dielectric constants were evaluated using reflectance and transmittance spectra for ACNF layer. The optical energy gap of ACNF layer was determined as 1.07 eV. The refractive index dispersion of ACNF layer was analyzed by using the single oscillator model proposed by Wemple and DiDomenico. The dispersion parameters such as oscillator energy and dispersion energy values of ACNF layer were determined. Several dispersion parameters such as optical dielectric constant at higher frequency, lattice dielectric constant, oscillator average wavelength, oscillator average strength and the ratio of carrier concentration to the effective mass were also determined by analysis of refractive index dispersion. Furthermore, the optical conductivity of ACNF layer was evaluated from the analysis of optical dielectric constants.

Preparation of Ni-Al layered double hydroxide hollow microspheres for supercapacitor electrode

In this study, Ni-Al layered double hydroxide (NiAl-LDH) hollow microspheres with a high surface area and large pore volume were prepared using Al2O3 hollow microspheres composed of Al2O3 nanosheets as templates. During a mild microwave-assisted hydrothermal process, the Al2O3 nanosheets transformed to NiAl-LDH nanosheets without any damage to the assembled hollow spherical structure. The as-prepared NiAl-LDH hollow microspheres exhibited a high specific capacitance (1578F g−1 at a current density of 1 A g−1) and good cycling performance (capacitance retention of 93.75% after 10,000 cycles). Moreover, an asymmetric supercapacitor was successfully assembled using the synthesized hollow microspheres as the positive electrode and activated carbon nanofibers as the negative electrode. The supercapacitor device achieved a relatively high energy density and power density (energy densities of 20 Wh kg−1 and 6.6 Wh kg−1 at power densities of 0.75 kW kg−1 and 11.25 kW kg−1, respectively).