Pitch-based Activated Carbon Fibers Research Articles

Optimization of pore structure and surface chemical properties of activated carbon fiber via liquid-phase stabilization for enhanced supercapacitor performance

Stabilization is a crucial factor influencing both the structure and properties of pitch-based activated carbon fiber (PACF). The traditional air stabilization not only requires a high softening point of precursor but also consumes a considerable amount of time and energy. In this study, liquid-phase stabilization was employed to streamline the preparation process, and its influence on resultant PACF was investigated. The oxidation stabilization process is fully conducted in just 1 h through liquid-phase stabilization. The obtained N-doped pitch-based activated carbon fiber (NPACF) possessed higher specific surface area and higher nitrogen content (3.77 wt%) compared to PACF obtained by air oxidization. The specific capacitance of NPACF electrode attained 325 F/g at 0.5 A/g. The device based on two equal NPACF electrodes exhibited a specific capacitance of 222 F/g at 0.5 A/g, an energy density of 7.6 Wh/kg at 248 W/kg, and excellent cycle stability of 92.0 % after 10,000 cycles.

Exploring oxygen migration and capacitive mechanisms: Crafting oxygen-enriched activated carbon fiber from low softening point pitch

A green pitch fiber from coal tar distillation residue, with a softening point of 190 °C, was used to make activated carbon fiber through an in-situ oxygen-doped method. Oxygen-rich pitch-based activated carbon fibers (OPACFs) were successfully created with a three-stage stabilization process using this low softening point pitch fiber. The OPACFs exhibit a moderate pore size distribution and high surface oxygen content (20.83 at%). The migration and transformation of oxygen during this process were studied. Due to the formation of stable oxygen-containing functional groups (CO), the resulting material shows excellent electrochemical performance. It achieved a specific capacitance of 334 F/g at 0.5 A/g and maintained good rate capacity (73.7 %, 0.5–50 A/g) in a 6 M KOH electrolyte. The assembled supercapacitor displayed exceptional cycle stability, retaining 91.4 % capacitance at 1 A/g after 10,000 cycles. Further investigation revealed that the specific capacitance includes both surface-controlled and diffusion-controlled capacitance, with oxygen doping significantly enhancing the latter.

Nitrogen-Doped Pitch-Based Activated Carbon Fibers with Multi-Dimensional Metal Nanoparticle Distribution for the Effective Removal of NO

The design of catalytic materials for NOX removal by the selective catalytic reduction with NH3 (NH3-SCR) has been a focus of research in the field of waste gas treatment. In this work, pitch-based activated carbon fibers (ACFs) were impregnated with copper nitrate and cerium nitrate, and then the ACFs that were loaded with bimetallic nanoparticles (ACF@Cu/Ce) were obtained after the pyrolyzation and reduction were performed. Moreover, the ACF@Cu/Ce were furtherly treated through the chemical vapor deposition and NH3 activation, through which the N-doped carbon nanofibers (N-CNFs) were grown on the surface of the ACFs. Thus, the catalytic material with a multi-dimensional metal nanoparticle distribution and nitrogen-rich network structure, namely the N-CNF/ACF@Cu/Ce, was constructed. In the NH3-SCR reaction, the NO conversion of the N-CNF/ACF@Cu/Ce could be maintained at about 72~81% in a wide temperature window of 295~495 °C, which enabled the N-CNF/ACF@Cu/Ce to meet the requirements of the practical applications.

Effect of anion species on preparation and properties of pitch-based activated carbon fibers by in-situ catalytic activation of metal nanoparticles

Effect of anion species on preparation and properties of pitch-based activated carbon fibers by in-situ catalytic activation of metal nanoparticles

Optimization of ethanol-extracted lignin from palm fiber by response surface methodology and preparation of activated carbon fiber for dehumidification

Lignin is a renewable bioresource that can be used for a variety of value-added applications. However, the effective separation of lignin from lignocellulosic biomass remains an ongoing challenge. In this study, lignin was extracted from waste palm fiber and successfully converted into a dehumidifying material. The following four process parameters of lignin extraction from palm fiber were optimized systematically and comprehensively using the response surface methodology: reaction time, extraction temperature, ethanol concentration and solid/liquid ratio. The results revealed that under the optimum processing conditions (111 min of extraction at 174 °C using 73% ethanol at 1/16 g/mL solid/liquid ratio), the extraction yield of lignin was 56.2%. The recovery of ethanol solvent was as high as 91.8%. Further, the lignin could be directly used without purification to produce lignin-based activated carbon fibers (LACFs) with specific surface area and total pore volume of 1375 m2/g and 0.881 cm3/g, respectively. Compared with the commercial pitch-based activated carbon fiber, the LACF has a higher specific area and superior pore structure parameters. This work provides a feasible route for extracting lignin from natural palm fiber and demonstrates its use in the preparation of activated carbon fiber with a remarkable performance as a solid dehumidification agent.Graphical

Preparation of pitch-based activated carbon fibers with high specific surface area and excellent adsorption properties

Preparation of pitch-based activated carbon fibers with high specific surface area and excellent adsorption properties

A Superior Potassium-Ion Anode Material from Pitch-based Activated Carbon Fibers with Hierarchical Pore Structure Prepared by Metal Catalytic Activation.

The pitch-based activated carbon fibers with nickel sulfide nanoparticles (ACF/NiS) were designed by in situ polymerization of ethylene tar with the addition of nickel nitrate followed by melt spinning, stabilization, carbonization, steam activation, and vulcanization processes. The ACF/NiS with hierarchical pore structure and abundant active sites was used as an anode material to improve Coulombic efficiency and increase capacity of potassium-ion batteries (PIBs). The results showed the obtained ACF/NiS with excellent specific surface area of 1552 m2 g-1 and high mesopore volume contribution of 38%, which delivered a high initial Coulombic efficiency of 84.22%, a high capacity of 292.5 mAh g-1, and retained 95.7% capacity retention after 200 cycles at 0.5 A g-1 current density. The NiS provided abundant active sites for the adsorption of potassium-ion, and the rich hierarchical structure shortened the electrolyte penetration path and expanded the storage space of potassium-ion, making it easier to store potassium-ion inside the ACF/NiS anode to obtain a better performance. This work presented one strategy for designing the hierarchical pore structure of pitch-based ACF to boost the capacity storage of PIBs and revealed that ACF-based carbon materials served as potential anodes for high-performance PIBs.

Highly oxidation-resistant graphene-based porous carbon as a metal catalyst support

Porous graphene (PG) prepared from reduction and KOH activation of graphene oxide was heat-treated under argon atmosphere to obtain a partially graphitized porous carbon with high oxidation resistance. Transmission electron microscopy, Raman spectroscopy, synchrotron X-ray diffraction, and N2 adsorption isotherms (77 K) clearly illustrate the structural ordering and porosity change of PG under heat treatment. Pitch-based activated carbon fiber (ACF) was studied for comparison. PG is more graphitizable than ACF under heat treatment because it consists of highly flexible graphene units of larger size than those in ACF. Thermogravimetric studies indicate that heat treatment enhances more the thermal stability of PG than ACF, and metal-loading has a less detrimental effect on the thermal stability of heat-treated PG than heat-treated ACF and other reported carbon supports. Heat-treated PG shows great superiority to other carbon supports due to its both splendid oxidation resistance and high surface area. This study provides a promising route for the preparation of carbon-based catalyst supports for mild oxidative environments.

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics.

The characterization of fluorinated carbon fibers by water sorption has been broadly investigated in this work. In brief, a pitch-based activated carbon fiber (ACF) was submitted to a fluorination process under different conditions of partial pressure (F2:N2 ratio) and temperature. This led to samples with varied fluorine content and C-F type bonding. The effect of the fluorination treatment on the textural properties of the ACF was studied by means of nitrogen and carbon dioxide adsorption at −196 and 0°C, respectively, while the changes induced in the surface chemistry of the materials were analyzed by XPS. Also, the affinity and stability of the materials toward water was evaluated by single and cycling isotherms. The obtained results show that a mild fluorination not only can preserve most of the textural properties of the parent ACF, but enhance the water uptake at the first stages of the water sorption process, together with a shift in the upswing of the water isotherms toward lower relative humidities. This indicates that fluorination under certain conditions can actually enhance the surface hydrophilicity of carbon materials with specific properties. On the contrary, higher partial pressures led to highly fluorinated fibers with lower porosity and more hydrophobic character. Moreover, they presented a lower chemical stability as demonstrated by a change in the shape of the water isotherms after two consecutive measurements. The kinetics of water sorption in the ACFs provided further insights into the different sorption phenomena involved. Hence, water sorption can definitely help to tailor the water affinity, stability and performance of fluorinated porous carbon materials under humid conditions.

Feasibility of regenerative adsorption of a hydrofluorocarbon (HFC-134a) using activated carbon fiber studied by the gaseous flow method

The adsorption and desorption behavior of the refrigerant HFC-134a on pitch-based activated carbon fibers (ACFs) with various Brunauer–Emmett–Teller surface areas was investigated by the flow method. Fixed-bed adsorption experiments performed at 20, 5, –15, –20, and −25 °C showed that the use of lower temperatures resulted in an increase in the adsorption capacity of the ACF. In particular, the complete adsorption time was dramatically increased at −25 °C. Crucially, even after five cycles of adsorption at –20 °C and desorption at 30 °C of HFC-134a in a electrothermal swing adsorption apparatus, significant decreases in the adsorption capability were not observed. The desorption of HFC-134a from saturated ACF was carried out using electric power directly applied to the ACF itself. The electric heating increased the ACF temperature, causing desorption within several minutes. The results of this study show that the regenerative adsorption of HFC-134a by ACF coupled with electric power is possible.

Selective and enhanced CO2 adsorption on fluorinated activated carbon fibers

Pitch-based activated carbon fibers (ACFs) were fluorinated in temperatures from 298 to 473 K using diluted fluorine gas. The N2 adsorption and desorption isotherms at 77 K for the ACFs fluorinated at 298 K (F298) showed a decrease in the amount of adsorbed N2 mainly because of diffusional problems of the N2 molecule. Enhanced CO2 adsorption was also observed on the F298. The CO2 absorptivity for the F298 is probably caused by the development of microporosity and enhanced interactions between the weakened CF bonds and CO2 molecules.

Preparation and electrochemical performance of the N-doped hollow pitch-based activated carbon fibers as supercapacitor electrodes

Mixtures of polyethyleneimine (PEI) and ethylene tar pitch (0, 15, 20, 30 wt% of PEI) were melt-spun, stabilized, carbonized and activated to prepare nitrogen-doped (N-doped) activated carbon fibers (ACFs). The morphology, porous structure and surface chemistry of the N-doped ACFs were characterized by N2 adsorption, XPS and SEM. Their electrochemical performance as supercapacitor electrode materials was investigated. Results indicate that the specific surface area, pore volume and number of nitrogen-containing functional groups of the N-doped ACFs are much increased compared to undoped ACFs. PEI pyrolysis during the carbonization of the fibers leads to the formation of hollow N-doped ACFs that increases the utilization% of the surface area, resulting in a significant increase of the specific capacitance. When 20 wt% PEI was added, the specific surface area of the N-doped ACF reached 2 756 m2/g, its pore sizes ranged from 0.7 to 2 nm, and its specific capacitance reached 314 F/g at 0.5 A/g, which is much higher than that (194 F/g) of the undoped ACF.

Structural mechanism of reactivation with steam of pitch-based activated carbon fibers

Customized micro- and mesoporous carbons are in high demand for ecofriendly technologies. Reactivation of the well-characterized pitch-based activated carbon fiber (ACF) can provide a clear understanding of the structural mechanism of steam activation, which would be helpful for designing better micro- and mesoporous carbons. ACFs were reactivated with steam at 973–1173 K. X-ray diffraction and Raman spectroscopy indicated that the stacking number of graphene-like layers of the pore wall decreased with an increase in the reactivation temperature. The average fiber diameter of the ACFs, which was measured via scanning electron microscopy, decreased with the increase in the reactivation temperature. The relationship between the decrease in the fiber diameter and the burn-off suggested that reactivation above 1023 K produced micropores inside the fiber. A deconvolution analysis of the pore-size distribution revealed the variation of the distribution. The peak difference was approximately 0.3 nm, depending on the reactivation temperature. These results indicate that reactivation with steam proceeds via the preferential one-by-one gasification of less-crystalline graphene-like units.

Pitch-Derived Activated Carbon Fibers for Emission Control of Low-Concentration Hydrocarbon.

The unburned hydrocarbon (HC) emissions of automobiles are subject to strong regulations because they are known to be converted into fine dust, ozone, and photochemical smog. Pitch-based activated carbon fibers (ACF) prepared by steam activation can be a good solution for HC removal. The structural characteristics of ACF were observed using X-ray diffraction. The pore characteristics were investigated using N2/77K adsorption isotherms. The butane working capacity (BWC) was determined according to ASTM D5228. From the results, the specific surface area and total pore volume of the ACF were determined to be 840–2630 m2/g and 0.33–1.34 cm3/g, respectively. The butane activity and butane retentivity of the ACF increased with increasing activation time and were observed to range between 15.78–57.33% and 4.19–11.47%, respectively. This indicates that n-butane adsorption capacity could be a function not only of the specific surface area or total pore volume but also of the sub-mesopore volume fraction in the range of 2.0–2.5 nm of adsorbents. The ACF exhibit enhanced BWC, and especially adsorption velocity, compared to commercial products (granules and pellets), with lower concentrations of n-butane due to a uniformly well-developed pore structure open directly to the outer surface.

Urea/nitric acid co-impregnated pitch-based activated carbon fiber for the effective removal of formaldehyde

Urea/nitric acid co-impregnated pitch-based activated carbon fibers (ACFs) were examined as adsorbents for the removal of low-concentration formaldehyde gas from dry and humid atmospheres. Urea, which is a harmless and environmentally friendly primary amine, was selected as an effective reagent to capture formaldehyde and nitric acid was used to promote the oxidation of formaldehyde into formic acid, which inhibits the liberation of formaldehyde even under humid atmospheres. The optimized urea/nitric acid co-impregnated ACF showed a 110-fold (0.72mg/g to 79.28mg/g) improvement in its formaldehyde removal capability as compared to that of pristine ACF at 40% humidity. The formaldehyde removal mechanism is proposed based on careful analysis and quantification of the inlet and outlet gases. Further, the optimized sample facilitates complete removal of formaldehyde from ambient air at humidity of 11–88% and temperatures of 3–26.9°C over 24h, whereas only 81.5% formaldehyde removal is achieved with pristine ACF under the same conditions.

Effects of oxygen content of pitch precursors on the porous texture and surface chemistry of pitch-based activated carbon fibers

Oxidized pitches with different oxygen content were prepared using ethylene tar as a raw material by air-blowing method, then the resultant pitch-based activated carbon fibers (ACFs) were prepared through spinning, stabilization, carbonization, and CO2 activation processes. The results showed that the oxygen content of prepared oxidized pitch was up to 4.44% when the basic pitch was air-blown at 250 °C, and the BET surface area of the corresponding ACF was up to 1047 m2/g with 0.536 mmol/g carboxylic group, 0.043 mmol/g lactonic group and 0.193 mmol/g phenolic hydroxyl group on the surface after 900 °C CO2 activation. It revealed that the spinnability of oxidized pitch became poor as increasing its oxygen content, while the obtained carbon fiber was easy to be activated and the prepared ACF was equipped with large specific surface area and rich surface functional groups. However, the pore structure was easy to collapse and the surface area was seriously decreased when the oxygen content of pitch precursor was too high. Therefore, the property regulation of pitch precursor could effectively improve the porous texture and surface chemistry of the resultant ACF.

Synthesization and Characterization of Pitch-based Activated Carbon Fiber for Indoor Radon Removal

In this study, pitch-based activated carbon fibers (ACFs) were modified with pyrolysis fuel oil (PFO). Carbonized ACF samples were activated at 850℃, 880℃ and 900℃. A scanning electron microscope (SEM) and a BET surface area apparatus were employed to evaluate the indoor radon removal of each sample. Among three samples, the BET surface area and micropore area of ACF880 recorded the highest value with 1,420 m2∙g-1 and 1,270 m2∙g-1. Moreover, ACF880 had the lowest external surface area and BJH adsorption cumulative surface area of pores with 151 m2∙g-1 and 35.5 m2∙g-1. This indicates that satisfactory surface area depends on the appropriate temperature. With the above scope, ACF880 also achieved the highest radon absorption rate and speed in comparison to other samples. Therefore, we suggest that the optimum activation temperature for PFO containing ACFs is 880℃ for effective indoor radon adsorption.

Isotope effect on water adsorption on hydrophobic carbons of different nanoporosities

The adsorption isotherms of H2O and D2O on pitch-based activated carbon fibers (ACFs) of different pore widths from 0.6 to 1.5 nm were measured at 298 K. Briefly speaking, the D2O adsorption isotherms are close to the H2O adsorption isotherms. However, we observed an evident difference in the rising and desorption relative pressures for the H2O and D2O adsorption isotherms. The D2O adsorption rises at a higher relative pressure than the H2O adsorption. Correspondingly the D2O desorption occurs at a higher relative pressure than the H2O desorption. Detailed comparison of the H2O and D2O adsorption isotherms confirmed a reproducible difference over the whole relative pressure range. The different adsorption behavior of H2O and D2O in the hydrophobic micropores is discussed with the relevance to the difference in the hydrogen bonding of H2O and D2O.

피치계 활성탄소섬유를 이용한 페이퍼 제조 및 흡착특성

피치계 활성탄소섬유를 이용한 페이퍼 제조 및 흡착특성

Electrochemical Performance of Pitch-Based Activated Carbon Fibers for Anode Electrode in Supercapacitors

Electrochemical Performance of Pitch-Based Activated Carbon Fibers for Anode Electrode in Supercapacitors