Activated Carbon Fibers Research Articles

Modification of polyacrylonitrile-based activated carbon fibers and their p-nitrophenol adsorption and degradation properties

Activated carbon fibers (ACFs) are widely used adsorbent materials for wastewater treatment. In this study, polyacrylonitrile-based ACFs (PAN–ACF) were modified with oxalic acid to promote their adsorption of p-nitrophenol (PNP) in wastewater. The obtained results revealed that the adsorption efficiency of the modified ACFs amounted to 98.05%. The photocatalytic degradation of PNP by ACFs loaded with nano-TiO2 and nano-ZnO photocatalysts was examined as well; under ultraviolet (UV) light irradiation, their PNP removal rates reached 99.85% and 98.31%, respectively. Moreover, the effects of pH, PNP concentration, and catalyst concentration on the PNP adsorption efficiency were systematically investigated. By conducting kinetic studies, it was found that the PNP adsorption on the PAN–ACF surface followed a pseudo-first-order model, while the PAN–ACF/TiO2 and PAN–ACF/ZnO obeyed a pseudo-second-order model, and all samples followed the Langmuir adsorption isotherm. Additionally, an integrated high-pressure microwave reactor was designed and fabricated, and the possibility of degrading PNP through the microwave-assisted catalytic oxidation by PAN–ACF/TiO2 was considered. The results of this work suggest that the novel modified PAN–ACF, PAN–ACF/TiO2 and PAN–ACF/ZnO adsorbents are promising materials for the removal of PNP-based pollutants from wastewater due to their facile application procedure, low fabrication costs, and good scale-up abilities.

Surface modification of activated carbon fiber by low-temperature oxygen plasma: Textural property, surface chemistry, and the effect of water vapor adsorption

The effects of adsorbent characteristics on its water adsorption performance were investigated using low-temperature oxygen plasma technology (LTOP) as a surface modification method. A series of activated carbon fiber (ACF)-based adsorbents was prepared to get further insight into the functions of water vapor adsorption behavior with textural property and surface chemistry. The result shows that LTOP treatment does not alter drastically the physical surface properties and simultaneously functionalize oxygen-containing functional groups (OFGs) especially carboxyl groups on the ACF surface when the treatment time and effective output voltage are 15 min and 8–9 kV, respectively. Meanwhile, the carbon atoms with unpaired electrons are found to be increased during the process of plasma treatment and used as active sites for chemical adsorption. Both OFGs and carbon atoms with unpaired electrons on the carbon surface play a vitally important role for water vapor adsorption. The surface functionalities and chemical adsorption may govern the adsorption–desorption behavior of water vapor at low relative humidity (RH less than 40%). Adsorption mechanism of water vapor on the carbon surface before and after LTOP treatment is proposed. After several adsorption and desorption cycles, the adsorption capacity of LTOP-treated ACFs is still higher than that of ACF-raw. Therefore, this technology may shed light on the potential application of LTOP-treated ACFs in harvesting water from air at low relative humidity.

Adsorption of acetaldehyde from air by activated carbon and carbon fibers

The adsorption of acetaldehyde from air using various activated carbon and carbon fibers was investigated in this study. These adsorbents included activated carbon (AC), carbon fibers (CFs), activated carbon fibers (ACFs), and metal-coated carbon fibers (MCCFs) supplied by different manufacturers. AC was categorized as AC1, AC2, AC3, and AC4, CFs were denoted as ACF1, while ACFs and MCCFs were expressed as ACF2 and ACF3, respectively. Five composite materials were prepared using the AC and ACFs in different ratios, and experiments were conducted to assess their acetaldehyde adsorption efficiency under dry and wet conditions. The results showed that the acetaldehyde adsorption efficiency of an impregnated AC4 was higher (95.9%) than that of both non-impregnated AC1 and AC3 and an impregnated AC2 after 1 min of operation. ACF2 showed a higher acetaldehyde adsorption efficiency (50.9%) as compared to ACF1 and ACF3 because of its larger surface area and selective absorption capability after 1 min of operation. A composite material comprising 6.3 g of AC4 and 1 g of ACF2 showed the highest adsorption efficiency of 97.9% under dry conditions. However, this adsorption efficiency significantly decreased under wet conditions.

Preparation of well-developed mesoporous activated carbon fibers from plant pulp fibers and its adsorption of methylene blue from solution

Well-developed mesoporous plant-based activated carbon fibers (ACFs) with paper structure were prepared from plant pulp fibers (cotton, sisal hemp, manila hemp, softwood and bleached softwood) using phosphoric acid activation at 450°C. The structure and performance of ACFs were studied. Results show that ACFs exhibit high mesoporous rate of 72.8%-82.7%, large specific surface area of 1688–1825 m2/g and average pore size of 2.53–3.31 nm. ACFs show relatively high methylene blue (MB) adsorption capacity with 367.5–490.9 mg/g. SHP-ACFs have the largest MB adsorption capacity, the adsorption equilibrium data follows the Langmuir model and the kinetic data could be described by the pseudo-second-order model.

Dual-defects induced band edge reconstruction of tin dioxide via cobalt and nitrogen Co-Doping for wearable supercapacitor application

Dual-defects induced band edge reconstruction of tin dioxide (SnO2) via metal and non-metal ions co-doping strategy is applied to synthesize cobalt and nitrogen co-doped tin dioxide (Co, N-SnO2) on activated carbon fiber (ACF) for supercapacitor. N-doping contributes to upward shift of valence band edge through the hybridization of N-2p and O-2p and Co-doping contributes to downward shift of conduction band edge through the hybridization of Co-3d and O-2p. The bandgap is highly narrowed from 2.29 eV for SnO2 to 0.68 eV for Co, N-SnO2. The Co, N-SnO2/ACF electrode achieves specific capacitance of 361.2 F g−1 at 1 A g−1, rate capability of 61.1% from 1 to 10 A g−1 and cycling stability of 103.3% for 10,000 cycles. The density functional theory proves that Co-doping mainly promotes the capacity due to its easier deprotonation process in acid electrolyte, whereas N-doping mainly promotes the rate capability due to its narrower bandgap and thus facile electron transport. The wearable bracelet-supercapacitor based on Co, N-SnO2/ACF electrode delivers an energy density of 70.7 Wh Kg−1 under a wide potential window of 2.0 V. This finding provides a feasible route to regulate the band edge of metal oxide electrode for the promising energy storage.

Experimental study of desalination and ion selection performance using electro-sorption technology with an activated carbon fiber electrode

ABSTRACT The realization of high-efficiency desalination technologies is the key to the reuse of circulating cooling sewage in power plants. Desalination experiments were carried out on an electro-sorption device with an activated carbon fiber (ACF) plate as an electrode, using the mixed salt solution to simulate actual circulating cooling sewage. The effects of flow rate and voltage on desalination and ion selection performance were investigated in the paper. Experimental results show that different ions can be effectively removed using activated carbon fiber electrodes. Under the same adsorption conditions, the adsorption rate of ions is inversely proportional to the mass-to-charge ratio; the smaller the hydration radius of ions, the larger the ion removal rate; the ion selection performance is related to the pore size distribution of the selected electrode material. The experimental results can provide basic data and reference for the treatment of circulating cooling water using electro-sorption technology.

Precise control of ultramicropore structure of activated carbon fiber for the application of Cu(II) adsorption/electro-adsorption

To enhance the Cu(II) electro-adsorptivity of activated carbon fiber felt (ACFF), the ultramicropore volume at 0.56 nm is precisely enhanced by the process of sonication-assisted hydrochloric acid reactivation. The surface elemental composition of ACFF-H5 changes slightly and the chemical structure contains more carboxyl groups after the reactivation process. By the precise control of ultramicropore volume at 0.56 nm, Cu(II) adsorptivity of ACFF is increased by 267% in the process of 50 mg/L Cu(II) static adsorption. For the Cu(II) electro-adsorption process, the Cu(II) electro-adsorptivity of ACFF cathode are 49.94 mg/g and 85.16 mg/g for 50 mg/L and 130 mg/L Cu(II) solution respectively. By the low-temperature pickling regeneration process, this cathode can basically achieve 100% recovery of Cu(II) electro-adsorptivity in five cycles. SummarizationBy using ACFF with precise control of ultramicropore at 0.56 nm as a soft cathode, the Cu(II) electro-adsorptivity reaches 85.16 mg/g for 130 mg/L Cu(II) solution.

Electromechanical properties of embedded multifunctional energy storage composite with activated carbon fiber/PVDF gel electrolyte

ABSTRACT This paper presents a standardized process for fabricating multifunctional energy storage composites that involves using activated carbon fiber (CF) electrodes and a poly(vinylene fluoride) (PVDF)-based gel polymer electrolyte (GPE) as building materials for embedded supercapacitors. A two-step packaging method was used to fabricate composites that can simultaneously bear mechanical loads and store energy. CF electrodes were subjected to three activation procedures, and the optimal composition of the PVDF-based GPE was determined by comparing the performance of PVDF-based GPEs of various compositions through electrochemical tests. The specific capacitance and energy density of a supercapacitor embedded with a glass-fiber-reinforced composite was 168 mF/g and 140 J/kg, respectively. The aforementioned values were 15.3% and 21.9% higher, respectively, than the corresponding values obtained for a bare cell. Mechanical tests indicated that the average tensile strength of the aforementioned composite was 350.1 MPa. With a gradual increase in the tensile load, the supercapacitor energy density increased by approximately 10% and then plateaued until fracture. Under cyclic tensile loads, the fabricated supercapacitors functioned normally until the composite failed.

APPLICATIONS OF ACTIVATED CARBON IN WASTE WATER TREATMENT AS A LOW COST MEDIA

Environmental pollution caused by the anthropogenic activities is a global challenge. Pollution due to discharge of untreated wastewater, contributes to it considerably. High expenditures for the treatment technologies can be considered as one of the major reason for improper wastewater discharge. Activated carbon provides an excellent solution for this issue as it can be used as a low cost wastewater treatment adsorbent. This paper review, types of activated carbon, their applications and recovery methods in wastewater treatment. Activated carbon from conventional waste such as agricultural waste, woody waste and non conventional waste such as municipal waste can be used as a low cost media for waste water purifications. Physical and chemical processes are used to improve the adsorption property of the activated carbon. H3PO4, KOH and ZnCl2 are the most frequently used chemicals for the activation process. Granular activated carbon, powdered activated carbon, activated carbon fibers and carbon clothes are the major physical forms of the activated carbon. These physical forms are important to maximize the adsorption process according to the purpose of usage. Activated carbon is used to remove heavy metals, dyes, COD, BOD, organic contaminants and volatile organic compounds in the waste water. Various recovery methods are applied to regenerate activated carbons. Among them, chemical, thermal, and bio regeneration methods are examined. Strengths, weaknesses, opportunities, threats related to use of activated carbon and future research priority areas are also discussed

Quantitative evaluation of carbon materials for humidity buffering in a novel dehumidification shutter system powered by solar energy

Recently, solid dehumidification systems have been widely used in various industries and are effective in buffering the humidity in the environment. The dehumidification materials and structure of the system have a significant influence on the over system performance. This study aims to quantitatively evaluate dehumidification materials produced from activated carbon fibre cloth (ACFC) and coconut-shell activated carbon (CAC) for suitability in a dehumidification shutter system. First, the physical and chemical properties of ACFC and CAC were characterised via N2 adsorption–desorption isotherms, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Second, the adsorption of water vapour was experimentally investigated, including adsorption kinetics, adsorption isotherms, and thermodynamics, and fitted by various models. The results show that the specific surface areas of ACFC and CAC were 1425 m2/g and 986 m2/g, respectively, while the total pore volume were 0.748 cm3/g and 0.554 cm3/g, respectively. At a relative humidity of 98% and an adsorption temperature of 298 K, the maximum water vapour adsorption capacities of ACFC and CAC were 395.6 mg/g and 277.6 mg/g, respectively. More importantly, ACFC retained a high adsorption capacity after five adsorption/regeneration cycles, indicating that it is an effective and renewable adsorbent for dehumidification. Third, a novel dehumidification shutter system was designed and constructed. The dehumidification performance and thermal comfort indices of the system were then analysed. In conclusion, the dehumidification shutter system fabricated using ACFC is a feasible and effective way to buffer the indoor humidity when solar energy is chosen as the renewable regeneration heat source.

Air-cooled adsorption-based device for harvesting water from island air

Adsorption-based, atmospheric water harvesting is a promising method for addressing water scarcity, which is a common issue in island areas, which often contain a large amount of fresh water in the air. Most existing adsorption-based atmospheric water harvesting systems usually require an additional cooling source, e.g., water-cooling, to cool the released humid high-temperature air below its dew point to harvest liquid water. To date, large-scale atmospheric water harvesting devices that use air cooling in such conditions have not yet been developed. Herein, we report a forced air-cooled proof-of-concept device for harvesting water from island air. Fabricated using 21 kg activated carbon fibre felt (ACFF)–silica sol–LiCl30, this device generated up to 7.7 kg of water (adsorption at 31 °C with 63% relative humidity) per day-and-night cycle, with a thermal efficiency (ratio of thermal energy to water conversion) of 0.37, using air cooling alone in laboratory-simulated island conditions. This study verifies the possibility of using air cooling to condense released humid air. It provides a flexible water generation solution for island regions with limited supplies of fresh water and power.

Efficacy of treated sodium alginate and activated carbon fibre for Pb(II) adsorption

Efficacy of treated sodium alginate (TSA) and activated carbon fibre (ACF) for aqueous Pb(II) uptake was comparatively investigated. By employing FTIR, SEM, EDX, XRD, point of zero charges and surface area measurements, the available functional groups, morphology, crystallinity, surface charge and surface areas of both adsorbents were respectively elucidated. The Pb(II) uptake performance of both adsorbents was also studied via batch mode at varied process conditions. The experimental isotherm and kinetic data for both adsorbents were best fitted to nonlinear forms of Langmuir and pseudo-first-order models, respectively. Similarly, intraparticle diffusion was the sole controlling mechanism. Despite the huge variation in the surface area, TSA (7.8 m2/g) with high carboxyl content (395.6 meq-COOH/100 g of sample) performed better by all standards than the ACF (975 m2/g). This finding showed that although the surface area of a given adsorbent is a key indicator of its adsorptive performance, the inherent surface functional groups play a superior role. The experimentally derived maximum adsorption capacities of 221.25 mg/g (for TSA) and 183.34 mg/g (for ACF) were recorded at an equilibrium time of 30 min and 45 min, respectively. Therefore, TSA and ACF demonstrated effectiveness for aqueous Pb (II) sequestration.

Preparation and characterization of ACF/carbon composite membranes for efficient oil/water separation

The development of high-performance membrane materials is a key issue for membrane technology to effectively treat oily wastewater. Here, a new kind of activated carbon fiber (ACF)/carbon composite membranes was fabricated by compressive shaping and carbonization of a mixed powder from phenolic resin and activated carbon fiber. The thermal stability, functional groups, mechanical strength, microstructure and morphology of the membranes were characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy, Tension Tester, X-ray diffraction and scanning electron microscopy, respectively. The effects of ACF dosage, trans-membrane pressure and feed flowrate on the separation performance of the composite membranes for emulsified oil-water solution were investigated. The results have shown that the ACF incorporation is beneficial for the enhancement of separation performance of the derived membranes for oily wastewater. The highest oil rejection reaches to 96.7%, along with the water permeation flux of 198.7 kg /m2h for the membranes formed by a proportion of 10 wt% ACF in starting materials under the operation condition of feed concentration of 200 mg/L, trans-membrane pressure of 0.02 MPa and feed flowrate of 6 mL/min. In summary, the developed composite membrane material is great promising for theoretical study and practical application in the oily wastewater treatment.

Pore-scale study on heat and mass transfer of electrothermal swing adsorption process into X-ray tomography reconstructed activated carbon fibre felt

Activated carbon fibre (ACF) absorbent is a promising material for capturing volatile organic compounds from gas streams. Electrothermal swing adsorption (ESA) technology was proposed to achieve the regeneration of adsorption-saturated ACF materials. A numerical study on the adsorption and electrothermal desorption processes in ACF felt at the pore scale was conducted. A 3D pore-scale lattice Boltzmann model was used to describe the momentum/heat/mass transfers coupled with the adsorption/desorption effect. Using this model, a numerical simulation was performed to investigate the heat and mass behaviours of ESA in the pore structure of ACF felt, which was reconstructed using X-ray micro-tomography technology. The simulation results reveal the effects of key operation parameters on the process properties of ESA in the adsorption step and the electrothermal regeneration step. Moreover, the pore-scale study illustrates the influence of carrier gas velocity on the distribution homogeneity of the adsorbate concentration and desorption temperature.

Activated carbon fiber-supported nano zero-valent iron on Cr(VI) removal

Nanoscale zero valent iron (nZVI) was adsorbed on activated carbon fiber (ACF) for efficient removal of hexavalent chromium. The composite materials were characterized by XRD, SEM, FTIR, BET and XPS. Fe2+ was adsorbed by ACF and then restored by NaBH4. This sample was named ACF-nZVI-a. While Fe2+ was restored by NaBH4 and nZVI was adsorbed by ACF. That sample was named ACF-nZVI-b. BET analysis indicated that ACF-nZVI-a had a high specific surface area of 1087 m2/g, while ACF-nZVI-b had a low specific surface area of 928 m2/g, which indicated that it was easier for nZVI to go into the ACF pores than ionic condition Fe2+. Batch experiments showed that Cr (VI) removal rate was 98.9% for ACF-nZVI-b, which was higher than that for both ACF (33.7%) and ACF-nZVI-a (50.7%). Furthermore, the removal rate of Cr (VI) by ACF-nZVI-b showed strong dependence on initial solution pH. Low pH and initial Cr (VI) concentration favored both removal efficiency and rate constants. The reaction followed a pseudo first-order model under different initial Cr (VI) concentrations. The Cr (VI) removal was attributed to both the adsorption of ACF and the reducibility of nZVI, but the main cause was the reduction of nZVI. This study demonstrated that the ACF-nZVI-b had the potential to become an effective agent for the removal of Cr (VI) from polluted water.

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.

Viscose\u2010based porous carbon fibers: improving yield and porosity through optimization of the carbonization process by design of experiment

In this study, the production of porous carbon fibers from viscose fibers was investigated. The effects of final carbonization temperature (600–1000 °C) and heating rate (6–600 °C h−1), which determine the carbonization process, on carbon yield, and specific surface area were investigated using a central composite design. The statistical models found were then used to optimize both the yield and the porosity of the carbonized fibers, which are the most important factors for further use as precursors for activated carbon fibers. Despite the contrary effects, porous carbon fibers with a yield of 21.2% could be produced, which at the same time have a specific surface area of 175 m2 g−1. The fibers produced were also characterized by SEM, FTIR and Raman spectroscopy, XRD and CHNS analysis.

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.

Amino‐Decorated Activated Carbon Fibers with Efficient Static Adsorptivity for Low‐Concentration Formaldehyde Gas in a Confined Space

AbstractTo develop an absorbent with high removal rate and adsorptivity for low‐concentration formaldehyde (FA) gas, amino‐decorated viscose‐based activated carbon fiber (VACF‐N) was synthesized by ethylenediamine (EDA) grafting process on the surface of viscose‐based activated carbon fiber (VACF). A simulated static adsorption of low‐concentration FA gas in a confined space was used as research target. For 2.45 and 8.15 ppm of FA gas, both the FA removal rate and the adsorptivity of VACF‐N were enhanced significantly after the EDA grafting process. The maximum of FA adsorptivity was 0.59 mg/g (1.92 times that of pristine VACF) for 2.45 ppm FA gases and 1.17 mg/g for 8.15 ppm FA gases. In particular, FA removal rate reached 100 % in only 28 minutes under the static adsorption of 2.45 ppm of FA gas. Predictably, VACF‐N has wide application prospects in the field of low‐concentration FA gas purification in a confined space.