Activated Carbon Fiber Cloth Research Articles

Adsorption of pharmaceuticals onto activated carbon fiber cloths – Modeling and extrapolation of adsorption isotherms at very low concentrations

Activated carbon fiber cloths (ACFC) have shown promising results when applied to water treatment, especially for removing organic micropollutants such as pharmaceutical compounds. Nevertheless, further investigations are required, especially considering trace concentrations, which are found in current water treatment. Until now, most studies have been carried out at relatively high concentrations (mg L−1), since the experimental and analytical methodologies are more difficult and more expensive when dealing with lower concentrations (ng L−1). Therefore, the objective of this study was to validate an extrapolation procedure from high to low concentrations, for four compounds (Carbamazepine, Diclofenac, Caffeine and Acetaminophen). For this purpose, the reliability of the usual adsorption isotherm models, when extrapolated from high (mg L−1) to low concentrations (ng L−1), was assessed as well as the influence of numerous error functions. Some isotherm models (Freundlich, Toth) and error functions (RSS, ARE) show weaknesses to be used as an adsorption isotherms at low concentrations. However, from these results, the pairing of the Langmuir-Freundlich isotherm model with Marquardt's percent standard of deviation was evidenced as the best combination model, enabling the extrapolation of adsorption capacities by orders of magnitude.

Heel formation during volatile organic compound desorption from activated carbon fiber cloth

Heel formation on three activated carbon fiber cloths (ACFC10, ACFC15, and ACFC20, with increasing pore widths and volumes) was assessed after cyclic adsorption/resistive heating regeneration using 1,2,4-trimethylbenzene (TMB). Following regeneration at 288 °C, cumulative heel for ACFC10, ACFC15, and ACFC20 was 3.5 wt%, 4.1 wt%, and 4.2 wt%, respectively. Adsorption capacity of ACFC10; however, dropped by 83% compared to only 9% and 5% for ACFC15 and ACFC20, respectively. To prevent these capacity losses, regeneration temperature was increased to 400 °C. However, this increased cumulative heel and adsorption capacity losses to 3.7 wt% and 93% (ACFC10), 10.4 wt% and 51% (ACFC15), and 18.9 wt% and 50% (ACFC20), respectively. It is proposed that these observations results from carbon deposition due to thermal degradation of TMB during regeneration and rapid adsorbent heating. Increasing regeneration temperature enhances the endothermic decomposition processes, increasing heel buildup. Because the pores in ACFC10 are narrower than in ACFC15 and ACFC20, even small amounts of heel obstruct ACFC10's pores, explaining its notably larger decrease in adsorption capacity. These results suggest that rapid heating could be associated with reduced adsorbent performance. Regeneration conditions could be optimized to allow fast desorption with minimal adsorbate decomposition.

Electrothermal adsorption and desorption of volatile organic compounds on activated carbon fiber cloth

Adsorption is an effective means to selectively remove volatile organic compounds (VOCs) from industrial gas streams and is particularly of use for gas streams that exhibit highly variable daily concentrations of VOCs. Adsorption of such gas streams by activated carbon fiber cloths (ACFCs) and subsequent controlled desorption can provide gas streams of well-defined concentration that can then be more efficiently treated by biofiltration than streams exhibiting large variability in concentration. In this study, we passed VOC-containing gas through an ACFC vessel for adsorption and then desorption in a concentration-controlled manner via electrothermal heating. Set-point concentrations (40–900ppmv) and superficial gas velocity (6.3–9.9m/s) were controlled by a data acquisition and control system. The results of the average VOC desorption, desorption factor and VOC in-and-out ratio were calculated and compared for various gas set-point concentrations and superficial gas velocities. Our results reveal that desorption is strongly dependent on the set-point concentration and that the VOC desorption rate can be successfully equalized and controlled via an electrothermal adsorption system.

Removal of ozone by activated carbons modified by oxidation treatments

Granular Activated Carbon and Activated Carbon Fiber Cloth were oxidized by nitric acid treatment or by bleaching treatment (NaOCl). The raw and oxidized materials were exposed to an ozone flow (concentration of 10 ppmv in air with controlled 50% relative humidity) until saturation. The breakthrough curves and removal efficiencies were determined and discussed in relation with the materials characteristics (surface chemistry and texture) prior and after their exposure to ozone.

Oxidative dehydrogenation of isobutane catalyzed by an activated carbon fiber cloth exposed to supercritical fluids

Modifications that supercritical fluids promote in the surface chemistry of carbon materials are scarcely investigated. Due to this lack of knowledge, carbon materials exposed to supercritical fluids have not been tested in any catalytic application. Here, we present the oxidative dehydrogenation of isobutane catalyzed by an activated carbon fiber cloth previously exposed to supercritical carbon dioxide, supercritical water and nitric acid. The role of carbonyl–quinone groups as active sites is confirmed by their direct correlation with catalytic activity. The ability of the active sites to produce isobutene is hindered by the presence of acidic groups. Supercritical treatments develop microporosity, while removing acidic oxygen surface groups and incorporating carbonyl–quinone groups, so they are appropriate methods to develop efficient carbon catalysts for this reaction. Coke deposits formed during reaction modify the surface chemistry and porosity of the catalysts. Samples presenting high surface areas are deactivated by coke deposition more slowly. Thanks to it, fibers exposed to supercritical water showed the best performance.

Novel activated carbon fiber cloth filter with functionalized silica nanoparticles for adsorption of toxic industrial chemicals

Toxic industrial chemicals (TICs) are used for various civilian and military operations but can be hazardous to humans. There is interest in developing filters that can remove a wide range of airborne TICs (e.g., basic, acidic, organophosphate, and aromatic compounds) to reduce exposure in the work place and from terrorist attacks. A regenerable TIC air filter is particularly desirable because it removes the need for costly filter disposal and replacement. This study evaluates commercially available activated carbon fiber cloth (ACFC) and ACFC that has been modified with functionalized nanoparticles for their abilities to adsorb select TICs and for the regenerability of the adsorbents. The unmodified and modified ACFC samples were tested here for their ability to adsorb anhydrous ammonia (NH3), hydrogen cyanide (HCN), and dimethyl methylphosphonate (DMMP) in dry and humid gas streams as representative basic, acidic, and organophosphate compounds, respectively. The unmodified ACFC was not an effective adsorbent for NH3 (i.e., 2 and 3.1 mg NH3/g ACFC at 1000 ppmv NH3 in dry and humid air respectively) or HCN (no detectable adsorption), but successfully adsorbed 840 mg DMMP/g ACFC at 100 ppmv DMMP. The modified ACFC showed significant improvements for NH3 and HCN adsorption in dried air (i.e., 19.5 mg NH3/g ACFC at 1000 ppmv NH3 and 4.7 mg HCN/g ACFC at 150 ppmv HCN, respectively) and in humid air (i.e., 41.4 mg NH3/g ACFC at 1000 ppmv NH3 and 1.6 mg HCN/g ACFC at 50 ppmv HCN, respectively) when compared to the unmodified sample. The modified ACFC also showed 2–5 % degradation of its initial dry mass after regeneration and then showed no detectable degradation. The modified ACFC also had similar electrical resistance to that of unmodified ACFC (i.e., within 1 %), indicating that it can be regenerated using electrothermal heating.

Pulse-Reversal Deposition of Nickel Sulfide Thin Film as an Efficient Cathode Material for Hybrid Supercapacitors

In this study, nickel sulfide (Ni3S2) thin film was electrodeposited on Ni foam substrate by using a facile potentiodynamic (PD) and pulse-reversal (PR) method, respectively. After optimization of deposition parameters, the optimized Ni3S2 electrode was prepared by using PR mode under −1 V pulse-on potential, 0 V pulse-reversal potential, duty cycle of 0.5 and pulse frequency of 0.1 Hz. It delivered an impressive specific capacity up to 179.5 mAh g−1 at current density of 2 A g−1.The hybrid supercapacitor (SC) was assembled by using the optimized Ni3S2 electrode as cathode and activated carbon fiber cloth (ACFC) as anode, respectively. The Ni3S2//ACFC hybrid SC exhibited a high specific capacity of 26.7 mAh g−1 at charge-discharge current density of 2 A g−1 and displayed a maximum energy density of 26.4 Wh kg−1 at 1978 W kg−1 based on the total mass of active material of 9.2 mg. Furthermore, the Ni3S2//ACFC hybrid SC showed an impressive excellent cycling performance in 1 M KOH aqueous electrolyte at current density of 2 A g−1, with 97% specific capacitance retained after cycling of 400–5000 consecutive charge/discharge tests.

Evaluation of Degradation and Adsorption of Activated Carbon Fiber Cloth Loaded with Titanium Dioxide

This study combines active carbon fiber cloth (ACFC) with the photocatalyst of titanium dioxide (TiO2). The proposed method mainly depends on the adsorption effect to effectively catch the adsorbent and then further decompose the surface of the photocatalyst so that the original adsorption site of the active carbon can be emptied. In this way, the absorption site can regain the capability of catching the adsorbent and prevent saturation of the ACFC, hence, extending the service life. The findings of this study show that TiO2/ACFC possesses good photocatalytic adsorption capability. The same results are observed after several rounds of testing.

Adsorption and Electrothermal Desorption of Volatile Organic Compounds and Siloxanes onto an Activated Carbon Fiber Cloth for Biogas Purification

Although biogases mainly consist of a mixture of carbon dioxide and methane, traces of volatile organic compounds are present, and these undesirable compounds must be removed during the purification process. Adsorption onto an activated carbon fiber cloth (ACFC) was investigated and, in particular, the feasibility of electrothermal desorption. Five compounds were chosen, and their desorption was assessed by monitoring the electric resistance of the material as a function of the temperature. The results were confirmed by thermogravimetric analysis. Toluene, dichloromethane, and isopropanol were entirely desorbed at 420 K, whereas siloxane D4 and ethyl mercaptan (ethanethiol) were partially removed. These conclusions were confirmed by dynamic adsorption measurements. Cycles of adsorption followed by electrothermal desorption were first carried out for a single component (toluene). Although there was a loss of adsorption capacity between the first and second cycles, a steady performance was reached, shedding...

Effect of isobutane adsorption on the electrical resistivity of activated carbon fiber cloth with select physical and chemical properties

It is important to develop new materials to improve our ability to purify gas streams. This study characterizes activated carbon fiber cloth’s (ACFC’s) electrical resistivity and the change in resistivity from isobutane adsorption. Results are presented for ACFC samples with select ranges of micropore volumes (0.35–0.92cm3/g) and surface oxygen contents (2.2–7.7at.%). The resistivity of all samples decreased with increasing temperature, which is attributed to the additional energy for electron hopping between nanographite domains. Increasing micropore volume resulted in a larger decrease in resistivity after an isobutane adsorption cycle, which is attributed to increased adsorption capacity with increasing micropore volume. However, increasing surface oxygen increased the change in resistivity/unit mass of isobutane adsorbed. Increasing oxygen for lower oxygen content samples increased the percent change in resistivity due to isobutane adsorption, while increasing oxygen for moderate oxygenated samples had no effect on this value. Thus, increasing surface oxygen improves ACFC’s ability to sense adsorbed mass based on resistivity up to a threshold oxygen value. These results provide valuable insight into the factors affecting ACFC resistivity due to adsorption, which can be used to detect the amount of adsorbed mass and to determine the remaining adsorption capacity of the adsorbent.

Electrochemical Energy Storage Device with a Lewis Acidic AlBr3−1-Ethyl-3-methylimidazolioum Bromide Room-Temperature Ionic Liquid

Now room-temperature ionic liquid (RTIL) is becoming a general term in the fields of science and technology owing to its useful physicochemical properties. A great number of applications with RTIL are proposed to date. Here we report an original electrochemical energy storage device with a Lewis acidic 60.0–40.0 mol% AlBr3−1-ethyl-3-methylimidazolioum bromide ([C2mim]Br) RTIL. The unique electrochemical reactions related to [AlBr4]− anion on the positive electrode have a crucial role in the energy storage device. The charge-discharge ratio for the beaker cell prepared in this investigation was almost 100% at 2.0 ∼ 5.0 mA (150 ∼ 370 mA g−1 for activated carbon fiber cloth) if the cutoff voltage for the charging process was less than 1.70 V. The clear self-discharge behavior was not observed and the cell capacity after 100 cycles was identical to the maximum value.

Nitric oxide oxidation catalyzed by microporous activated carbon fiber cloth: An updated reaction mechanism

New catalysts, in particular activated carbons, are being developed to improve NO oxidation kinetics and to minimize the negative impacts of water vapor and SO2 as an alternative NOx control strategy for flue gases. However, the literature is inconclusive about the pathway to achieve a stable downstream NO2 concentration, creating discrepancies in the NO oxidation mechanism. In this paper, a simple two-step mechanism is proposed and justified for NO oxidation catalyzed by microporous activated carbon. In the first mechanistic step, NO is rapidly oxidized to NO2 in activated carbon's micropores with constant NO conversion efficiency, prior to the formation of adsorbed intermediates (e.g., C*NO2, C*NO3 or C*NONO3). This conclusion challenges the idea that NO oxidation to NO2 requires decomposition of the C*NONO3 intermediate. Instead, we show that the physical properties of the catalyst (i.e., micropore width and volume) control steady-state NO oxidation kinetics, with carbon's chemical properties having no apparent impact for the conditions tested here. In the second mechanistic step, newly formed NO2 is chemically adsorbed on the carbon surface, resulting in formation of NO and CN or CO complexes. Chemical disproportion of NO2 proceeds until the carbon surface is saturated with these complexes. It follows that the first step of the mechanism (NO oxidation in micropores) controls steady state NO oxidation kinetics while the second step (NO/carbon surface reactions) controls transient NO oxidation kinetics. This two-step mechanism is confirmed via in situ cyclic experiments and NO2 pre-adsorption tests. Pre-saturation of the carbon surface with functional groups decreases the impact of the second mechanistic step, affecting transient NO oxidation kinetics but having no impact on steady-state oxidation kinetics. A more complete understanding of the reaction mechanism allows us to better prepare tailored carbonaceous NO oxidation catalysts.

Activated carbon fiber cloth and CaCl2 composite sorbents for a water vapor sorption cooling system

In this work, we investigated activated carbon fiber cloth (ACFC) and CaCl2 composite sorbent (CS) prepared using impregnation method. Formation mechanism of the composite was investigated. During the impregnation process, a solution of CaCl2 is concentrated inside the pores of the ACFC. The solution concentration process is described using the Polanyi potential theory and the Dubinin–Radushkevich equation while ignoring Ca2+ adsorption by the surface functional groups. If the CaCl2 content of the CS is less than 38.2%, all the CaCl2 locates inside the pores of the ACFC. The water sorption performances of the CS of different CaCl2 contents were measured using an ASAP2020M Accelerated Surface Area and Porosimetry analyzer. The CSs with a CaCl2 content of 15.2 and 22.8% exhibit a greater amount of absorbed water than the equivalent CaCl2. This is because the CaCl2 dispersed inside within pores exhibits a lower hydration pressure than the bulk CaCl2, and the ACFC contributes to the amount of water that is absorbed. However, it is likely that the hydration pressure of the dispersed CaCl2 in the CS containing the maximum possible amount of CaCl2 does not change. Water sorption in this kind of CS can reach as high as 90% of the equilibrium water sorption amount within 2 min. The coefficient of performance for the air conditioning cycles calculated from the isosters of the CS containing the maximum CaCl2 content may reach 0.7, which is considered promising for sorption cooling.

Performance of an Electrothermal Swing Adsorption System with Postdesorption Liquefaction for Organic Gas Capture and Recovery

The use of adsorption on activated carbon fiber cloth (ACFC) followed by electrothermal swing adsorption (ESA) and postdesorption pressure and temperature control allows organic gases with boiling points below 0 °C to be captured from air streams and recovered as liquids. This technology has the potential to be a more sustainable abatement technique when compared to thermal oxidation. In this paper, we determine the process performance and energy requirements of a gas recovery system (GRS) using ACFC-ESA for three adsorbates with relative pressures between 8.3 × 10(-5) and 3.4 × 10(-3) and boiling points as low as -26.3 °C. The GRS is able to capture > 99% of the organic gas from the feed air stream, which is comparable to destruction efficiencies for thermal oxidizers. The energy used per liquid mole recovered ranges from 920 to 52,000 kJ/mol and is a function of relative pressure of the adsorbate in the feed gas. Quantifying the performance of the bench-scale gas recovery system in terms of its ability to remove organic gases from the adsorption stream and the energy required to liquefy the recovered organic gases is a critical step in developing new technologies to allow manufacturing to occur in a more sustainable manner. To our knowledge, this is the first time an ACFC-ESA system has been used to capture, recover, and liquefy organic compounds with vapor pressures as low as 8.3 × 10(-5) and the first time such a system has been analyzed for process performance and energy consumption.

Electrochemical Properties of Electrochemical Capacitors Using NiO Electrode

The NiO positive electrode active material was prepared on Ni foam and Ni mesh substrates by chemical bath deposition, and a hybrid capacitor (HC) composed of the NiO-loaded Ni foam or Ni mesh positive electrode and the activated carbon fiber cloth negative electrode was assembled. Both HCs had the maximum operating voltage of 1.6 V. The HC using the Ni foam substrate with heavier weight had higher surface area, lower charge-transfer resistance and higher rate capability, while the HC using the Ni mesh with lighter weight had higher specific energy and power density. The discharge capacitance at 100 mA (700 C-rate) for the HC with the Ni foam was ca. 30 F g-1 and was maintained even at 105th cycle.

Application of Chitosan-based Gel Electrolytes with Ionic Liquids for High-Performance and Safe Electric Double Layer Capacitors

Chitosan-based gel electrolytes with ionic liquids (Chi/IL) were prepared and investigated for use in electric double-layer capacitors (EDLCs). The voltage drop for the test cell with Chi/EMImBF4 (EMImBF4 = 1-ethyl-3-methylimidazolium tetrafluoroborate) or Chi/DEMEBF4 (DEMEBF4 = N,N-diethyl-N-methyl-N-2-methoxyethylammonium tetrafluoroborate) and activated carbon fiber cloth electrodes (ACFCs) was smaller than that with the corresponding ionic liquid electrolyte. To clarify the effect of the presence of Chi in contact with the carbon electrode, we also prepared the Chi-containing ACFC electrode (Chi+ACFC) and evaluated its charge-discharge characteristics in EMImBF4. The results proved that the presence of Chi on the active materials reduces the internal resistances of the cell and plays an important role in the improvement of the EDLC performance. In addition, the high-voltage operation of the test cells with Chi-based gel electrolytes was investigated. These results suggest that the Chi is suitable for use in practical high-performance and safe EDLCs.

Evolution and impact of acidic oxygen functional groups on activated carbon fiber cloth during NO oxidation

Fundamental studies describing the impact of carbon’s physical and chemical properties on NO oxidation allow for the development of catalysts tailored specifically for abating emissions of nitrogen oxides. Here, we show that acidic oxygen functional groups are developed on activated carbon fiber cloth during carbon-catalyzed NO oxidation. Reaction and thermal desorption cycle experiments demonstrate the continuous addition of oxygen to carbon as carbonyl and carboxyl functional groups. After four cycles, the oxygen content of carbon increased by 280%. There is also a 65% reduction in the time required to release NO2 from the carbon surface, allowing the reaction to achieve steady-state NO conversion 45% faster. The steady-state NO oxidation rate remains constant during the four cycles (48.5±1.6μmol/h), which is attributed to stable physical properties of carbon during the cycles. Oxygen groups added during the cycles, therefore, have no detectable impact on the overall conversion of NO over carbon, but control the pathway to achieving stable conditions. Carbon catalysts prepared with acidic oxygen functionalities are promising as NO oxidation catalysts, as confirmed with NO2 and nitric acid treatments. It is proposed that carbon’s chemical properties impact NO oxidation kinetics while carbon’s physical properties impact the steady-state NO oxidation rate.

Temperature Control during Regeneration of Activated Carbon Fiber Cloth with Resistance-Feedback

Electrothermal swing adsorption (ESA) of organic compounds from gas streams with activated carbon fiber cloth (ACFC) reduces emissions to the atmosphere and recovers feedstock for reuse. Local temperature measurement (e.g., with a thermocouple) is typically used to monitor/control adsorbent regeneration cycles. Remote electrical resistance measurement is evaluated here as an alternative to local temperature measurement. ACFC resistance that was modeled based on its physical properties was within 10.5% of the measured resistance values during electrothermal heating. Resistance control was developed based on this measured relationship and used to control temperature to within 2.3% of regeneration set-point temperatures. Isobutane-laden adsorbent was then heated with resistance control. After 2 min of heating, the temperature of the adsorbent with isobutane was 13% less than the adsorbent without isobutane. This difference decreased to 2.1% after 9 min of heating, showing desorption of isobutane. An ACFC cartridge was also heated to 175 °C for 900 cycles with its resistance and adsorption capacity values remaining within 3% and 2%, respectively. This new method to control regeneration power application based on rapid sensing of the adsorbent's resistance removes the need for direct-contact temperature sensors providing a simple, cost-efficient, and long-term regeneration technique for ESA systems.

Effect of ACF Properties on the Electric Adsorption Performance of the ACF Electrode

The properties of four different activated carbon fiber cloth (ACF), such as specific surface area, pore volumes and pore size distribution, were evaluated. The relationship between ACF properties and its electrosorption performance was analyzed. The experimental results show that pore structure has more influence on the performance of ACF electrode than that of specific surface area for ACF material. More abundant mesopores and shallower pore channels for ACF is favorable to improve the specific capacitance and electrosorption capacity of ions.

Physical and chemical properties of PAN-derived electrospun activated carbon nanofibers and their potential for use as an adsorbent for toxic industrial chemicals

A recently developed carbon material, electrospun Activated Carbon nanoFiber (ACnF), exhibits strong potential for use as an adsorbent for toxic industrial chemicals (TICs). As-prepared ACnF contains as much as 9.6 wt% nitrogen, creating a basic surface that enhances acid-gas adsorption. ACnF shows 4–20 times greater HCN adsorption capacities and 2–5 times greater SO2 adsorption capacities in dry nitrogen, compared to commercially available activated carbon fiber cloth (ACFC) and Calgon BPL™ granular activated carbon, which are considered here as reference adsorbents. ACnF has 50 % of the micropore volume (0.30 cm3/g) of these reference adsorbents, which limits its adsorption capacity at high concentrations for volatile organic compounds (>500 ppmv). However, at low concentrations (<500 ppmv), ACnF has a similar capacity to ACFC and about three times the VOC adsorption capacity of Calgon BPL™. ACnF’s small fiber diameters (0.2–1.5 μm) allow for higher mass transfer coefficients, resulting in adsorption kinetics nearly twice as fast as ACFC and eight times as fast as Calgon BPL™. ACnF drawbacks include hydrophilicity and reduced structural strength. The rapid adsorption kinetics and high capacity for acidic TICs warrant further investigation of ACnF as an adsorbent in respiratory protection and indoor air quality applications.