Area Activated Carbon Research Articles

Heterogeneous catalytic reduction of anthropogenic pollutant, 4-nitrophenol by Au/AC nanocatalysts

Activated carbon-supported gold nanocatalysts (Au/AC) were synthesized by the homogeneous deposition–precipitation (HDP) method by adding drop-wise of NaBH4 into the aqueous solution of HAuCl4. Catalytic activity of these nanocatalysts was investigated for the reduction of the anthropogenic pollutant, 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The physico-chemical properties of the nanocatalysts were characterized by XRD, TEM, BET surface area, pore size distribution, XPS and UV–Vis spectroscopy techniques. Gold nanoparticles (Au NPs) with high percentage of dispersion on a high surface area activated carbon (AC) support, show excellent catalytic performance in terms of activity and selectivity for 4-NP reduction. The reaction rate was measured to be pseudo-first-order with respect to 4-NP. The pseudo-first-order rate constant and the activation energy were estimated to be 1.2–4.2 × 10−3 s−1 at 25 °C and 26.38 kJ mol−1, respectively. Moreover, the catalytic activity was found to increase with increase in Au content of the catalyst. The reusability of the nanocatalyst showed a better reduction of 4-NP to 4-AP even after 5 successive re-cycles. The foregoing study clearly suggests that synthesis of Au/AC nanocatalysts by HDP method is efficient towards the development of a newer and a novel catalyst.

Mangosteen peel waste as a sustainable precursor for high surface area mesoporous activated carbon: Characterization and application for methylene blue removal

The aim of this study was the production of high surface area activated carbon (AC) under optimized synthesis conditions from Mangosteen Peels (MP) waste using a single step ZnCl2 activation process. The influence of the various activation parameters such as impregnation ratio, impregnation time, carbonization time, and carbonization temperature on surface area and pore characteristics of synthesized AC was investigated. The AC prepared under optimized conditions showed BET surface area, average pore diameter, and total pore volume of 1621.8 m2/g, 4.4 nm, and 1.805 cm3/g, respectively. The optimized synthesis conditions were as follows: 1:4 impregnation ratio, 600 °C calcination temperature, and 30 min calcination time. The characteristics of the optimized AC were analyzed using nitrogen adsorption-desorption isotherm, scanning electron microscopy, pore structural analysis, Fourier transformed infrared spectroscopy and X-Ray diffraction analysis. The adsorption capacity of activated carbon prepared under optimized conditions for methylene blue was 1193 mg/g. Equilibrium data was best fitted to the Langmuir isotherm, while adsorption kinetics was favorably described by the pseudo-second-order kinetic model. The findings reveal the feasibility of mangosteen peel waste to be used as a potential and cheap precursor for the preparation of high surface area mesoporous AC.

Development of Sulfur Cathode Comprising of Biomass Derived Activated Carbon As Host for Improved Lithium-Sulfur Battery Performance

In the recent years, the intercalation based lithium-ion batteries (LIBs) are considered as the potential candidate for portable electronic devices. However, development of low cost electrode materials with improved energy density and long cycle stability are the great challenges to meet the increasing demands of upcoming electric vehicle technology [1]. Among the rechargeable LIB electrode materials, sulfur cathode offers high theoretical specific capacity of 1672 mAh g-1 (energy density of 2600 Wh kg-1), which is ~ 3-5 times higher than the conventionally used LIB cathode materials. Moreover, the elemental sulfur is abundantly available in nature, eco-friendly and hence the fabricated cells using sulfur cathode is expected to deliver high electrochemical performance with low cost. However, the commercialization of this system is hampered largely owing to low electrical conductivity of elemental sulfur, polysulfide dissolution into the electrolyte and large volume expansion during charge/discharge process resulted in poor electrochemical performance of the cell [2,3]. To mitigate these issues, various strategies including designing of unique cathode structure comprising of carbon based materials (micro & mesoporous carbons, MWCNTs, graphene and graphene oxide), metal oxide composites, conductive polymers, etc have been tried so far. Particularly carbon materials are of interest, because micro and mesoporous carbon materials are known for efficient trapping of dissolved polysulfides during redox process to enhance the performance of lithium-sulfur (Li-S) battery [2]. In the present study, we synthesized a biomass derived high surface area activated carbon (AC) with narrow pore size distribution and high graphitic content and used it as host for sulfur cathode in Li-S battery. FE-SEM and HR-TEM images (Figure 1a and 1b) of as prepared AC reveals the presence of carbon with graphene sheet like structure (inset of Figure 1a and 1b). The elemental mapping of sulfur infused AC confirms homogenous distribution of elemental sulfur throughout the carbon matrix indicating uniform dispersion after melt diffusion process (155 ºC). The schematic representation of Li-S cell with modified separator is shown in Figure 1c. The use of modified separator is expected to inhibit the migration of dissolved polysulfide into electrolyte solution to the anode surface during redox process. The AC/S composite with modified separator displays impressive electrochemical performance in terms of specific capacity, rate capability and cyclic stability due to efficient trapping of polysulfide species and improved ionic and electronic conductivities. Figure 1d shows the long term cycle performance curve measured at 1 C rate with in-set of CV profile for the initial 10 cycles. The detailed physico-chemical and electrochemical measurements will be discussed during the presentation. Figure 1 (a) FE-SEM and (b) TEM images of as prepared AC sample, (c) schematic representation of Li-S cell with modified separator and (d) Electrochemical cyclic stability data’s of AC/S cathode (in-set CV curve) measured in the voltage range of 1.5-2.8 V at current rate of 1C with pristine separator and modified separator.

Tetracycline removal with activated carbons produced by hydrothermal carbonisation of Agave americana fibres and mimosa tannin

Two series of carbons were prepared from Agave americana fibres (A) mixed with mimosa Tannin (T) at different T to A weight ratios W = 0/4; 1/3; 2/2; 3/1 and 4/0. The first series, CTAW, was produced by direct pyrolysis of the precursors (T, A, or blends) and the second one, CHTAW, was produced in two steps, hydrothermal carbonisation (HTC) and then pyrolysis. Materials from the CHTAW series presented higher surface areas, H/C atomic ratios and carbon yields than those of the CTAW series. CHTA2/2 was next activated with CO2 during 1, 2 or 3 h. The appropriate selection of the synthesis conditions allowed obtaining high-surface area activated carbons (ACs) with similar carbon yields and average pore diameters as non-activated, low-surface area, carbon materials. CHTA2/2 activated for 2 h was tested for tetracycline (TC) adsorption, and the equilibrium was reached much faster than for a reference commercial AC due to the presence of macropores and mesopores provided by carbonised A. TC adsorption was spontaneous, and adsorption kinetics was adequately fitted by a pseudo-second-order model. TC adsorption essentially depends on surface area, and the results reported herein are in the range of those reported in the open literature.

High surface area nanostructured activated carbons derived from sustainable sorghum stalk

The Durra (Sorghum) stalk was employed as a novel precursor for the formation of high surface area activated carbons (ACs) by utilizing ZnCl2 as activating agent followed by pyrolysis in a flow of N2 gas. The formation of ACs has been investigated at different pyrolysis temperatures (400, 500 and 600°C) and different ZnCl2 impregnation concentrations. The results indicated that, the AC could be formed with high carbon contents, good thermal stability, large specific surface areas in the range of 1200–1817m2/g and nanostructured in graphene-like layers of 5–6nm in thickness. In addition, textural flexibility (in terms of supermicro/meso porosity) of the produced ACs can be fine-tuned by pyrolysis conditions. The potential application of ACs was tested towards the removal of hazardous cationic dye, methylene blue (MB), in aqueous media. The adsorption isotherms and kinetics of MB on ACs were examined at 25°C. The ACs showed a high adsorption capacity, as high as 386mg2/g. The adsorption of MB was better described by the Langmuir isotherm model and followed the pseudo-second-order equation. In light of the vast availability of durra stalks, as a sustainable residual, non-food/non-feed biomass material and quality of the produced AC materials. The presented ACs are very promising materials for application in many adsorption and purification processes.

Simultaneous Removal of Hg(II) and Phenol Using Functionalized Activated Carbon Derived from Areca Nut Waste

Areca nut waste was utilized to obtain high surface area activated carbon (AC), and it was further functionalized with succinic anhydride under microwave irradiation. The surface morphology and surface functional groups of the materials were discussed with the help of scanning electron microscope(SEM) images and fourier transform infra-red (FT-IR) analysis. The specific surface area of the AC and functionalized-AC was obtained by the Brunauer-Emmett-Teller (BET) method, and found to be 367.303 and 308.032 m2/g, respectively. Batch experiments showed that higher pH favoured the removal of Hg(II), whereas the phenol removal was slightly affected by the changes in the solution pH. The kinetic data followed pseudo-first order kinetic model, and intra-particle diffusion played a significant role in the removal of both pollutants. The maximum sorption capacity of Hg(II) and phenol were evaluated using Langmuir adsorption isotherms, and found to be 11.23 and 5.37 mg/g, respectively. The removal of Hg(II) was significantly suppressed in the presence of chloride ions due to the formation of a HgCl2 species. The phenol was specifically adsorbed, forming the donor–acceptor complexes or π–π electron interactions at the surface of the solid. Further, a fixed-bed column study was conducted for both Hg(II) and phenol. The loading capacity of the column was estimated using the nonlinear Thomas equation, and found to be 2.49 and 2.70 mg/g, respectively. Therefore, the study showed that functionalized AC obtained from areca nut waste could be employed as a sustainable adsorbent for the simultaneous removal of Hg(II) and phenol from polluted water.

Production of high surface area-activated carbons from waste bamboo scaffolding

Bamboo, indigenous to Hong Kong and China, is widely used as scaffolding in construction and building projects. Over 50,000 tonnes of bamboo scaffolding waste is disposed as landfill waste each yea...

A Study of Mediators As Ion Providers in Supercapactors

Doping mediators (soluble redox compounds) in polymer electrolyte contained in the porous electrodes is an effective method to increase the capacitance of supercapacitors. Mediators not only provide additional capacitance but also ions to electrolyte. The total capacity of a supercapacitor is dominated by the minor of the electrode capacity and the number of ions in electrolyte. In this research, we focused on revealing the effect of on the extra ions provided by the mediators during the charge/discharge processes. Two types of supercapacitors were fabricated. For the first type, the active electrode material consisted of 50 wt% mediators (in solid state) and 50 wt% high specific surface area active carbon (AC). For the other type of supercapacitor, the active electrode material consisted of AC only. Acetonitrile was used as liquid phase for both types. Under this circumstance, ions are provided by mediator only. The calculation of specific current was based on total weight of two electrodes and cyclic voltammetry (CV) curves. As shown in Figure 1, supercapacitor (a) (AC only) is unable to store any charges and energy without the ions in the solution. However, supercapacitor (b) can store ten times more energy with the mediator enhancement. In this situation, we can consider mediators as ‘charge harbor’. They can release ions into the liquid phase. These ions then participate in formation of electric double layers (EDLs) on AC. This capability of providing ions into the liquid phase can increase capacity of supercapacitor. CVs (b) and (c) also indicate that different mediators are different in the kinetics of providing ions. Taking supercapacitor (b) as an example, when we charge the supercapacitor, the K2CuFe(CN)6 can release K+ cation into the liquid phase and [CuFe(CN)6]- will still be hold on the solid phase because of the electrostatic force. On the other hand, we can use VOSO4 as a mediator too. V4+ can be reduced and releases SO4 2- anion. Thus, it is preferred to use K2CuFe(CN)6 in the positive electrode while use VOSO4 in the negative electrode. An series of mediators were evaluated using the same method. Figure 1

Effect of Metal Complex Mediators on the Performance of Mediator Supercapacitor

Demand of electrical energy storages is increasing quickly with market expansion of cell phones, electrical vehicles, and stationary energy storage. Supercapacitor is an alternative choice of rechargeable batteries because of their low cost for fabrication and maintenance, high cycle life, high charge rate, and high specific power. Using mediators to enhance the performance of the carbon materials based supercapacitors is more effective than using conductive polymer or metal oxide materials. In this study, we improved the performance using metal complex mediators. Several different mediators were synthesized and compared in this work. The active electrode material consisted of 10% mediator, 90% high specific surface area active carbon (AC). An EDLC made by AC only was also fabricated as a reference. To qualify the industrial requirements, current collector, electrolyte and separator are all commercial. The prototypes were fabricated in the glove box and sealed under vacuum. The calculation of specific energy (SE) was based on total mass of both electrodes and cyclic voltammetry (CV) curves and glvanostatic charge/discharge curves (GCDs). Typical CVs were shown in Figure 1. The mediator supercapacitor exhibited high energy densities (˃40 Wh kg-1), high charge/discharge efficiency (˃99%) and high reversibility (˃90% after 10000 cycles). The effect of the rare earth and transition metals on the effectiveness of the mediators is investigated. As shown in Table 1, for mediators containing rare earth metals, Pr, La, Y are more effective than Ho. For mediators containing transition metals, Mn, Fe, and Co are more effective than Zn. The authors explain the phenomenon with the notions of molecular configurations, electronic structures, and interactions between charged mediators. Figure 1

Characterization, preparation, and reaction mechanism of hemp stem based activated carbon

In this study, hemp stem was used to prepare high surface area activated carbon (AC) by KOH activation. The structure, characterization, thermal and structure analysis on reaction mechanisms of AC were investigated via N2 adsorption–desorption isotherm, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric-mass (TG-MS) spectrometry. Results show that when the impregnation ratio is 4.5:1 (KOH/char), the activation temperature is 800°C, and the activation time is 1.5h, AC has the highest specific surface area of 2388m2·g−1 and exhibits narrow pore size distributions with maxima in the micropore areas. The reaction mechanism of AC from hemp stems by KOH activation is as follows: In the first carbonization stage, it is primarily because of the substitution, scission, and oxidization reactions of methylene. Then in the second activation stage, it is mainly related to polycyclic reactions, reactions between carbon and KOH, and reactions between intermediate potassium oxide species and carbon.

Porous high specific surface area-activated carbon with co-doping N, S and P for high-performance supercapacitors

Porous high specific surface area activated carbon with co-doping N, S and P for high-performance supercapacitors.

More sustainable energy storage: lignin based electrodes with glyoxal crosslinking

Crosslinking lignin on high surface area active carbon using glyoxal as a green crosslinker leads to truly sustainable electrodes with improved performance.

Carbon electrode materials for supercapacitors obtained by co-carbonization of coal-tar pitch and sawdust

High-surface area-activated carbons (ACs) are successfully prepared by coal-tar pitch (CTP)/sawdust (SD) co-carbonization followed by simple KOH activation. The ACs inherit the tubular morphology of the biomass and possess a hierarchical porous structure, a high specific surface area of 2224 m2/g, and a considerable amount of oxygen-containing species on the surface. The AC obtained from the co-carbonization of 67 % CTP and 33 % SD has a 25 wt% higher oxygen content than the AC (0.17 wt%) from 100 % CTP, and has a 27.50 wt% higher carbon yield than the AC (14.42 wt%) from SD. As an electrode material for supercapacitors, the prepared electrode from 67 % CTP and 33 % SD exhibits a favorable specific capacitance of 251 F/g at a current density of 0.5 A/g in 6 mol/L KOH electrolyte. The electrode also demonstrates excellent cycling stability with a retention rate of 93 % over 7000 cycles at 2 A/g and a favorable rate capability with a retention rate of 74 % when the current density increases from 0.5 to 5 A/g. Therefore, the ACs obtained by co-carbonizing CTP and SD have high potential as electrode materials. This route not only enhances the benefit from agricultural wastes, but also reduces the cost of producing electrode materials for supercapacitors.

Synthesis and characterization of nanostructured iron compounds prepared from the decomposition of iron pentacarbonyl dispersed into carbon materials with varying porosities

This work describes the production and characterization of carbon-iron nanocomposites obtained from the decomposition of iron pentacarbonyl (Fe(CO)5) mixed with different carbon materials: a high surface area activated carbon (AC), powdered graphite (G), milled graphite (MG), and carbon black (CB). The nanocomposites were prepared either under argon or in ambient atmosphere, with a fixed ratio of Fe(CO)5 (4.0 mL) to carbon precursor (2.0 g). The images of scanning electron microscopy and the analysis of textural properties indicated the presence of nanostructured Fe compounds homogeneously dispersed into the different classes of pores of the carbon matrices. The elemental Fe content was always larger for samples prepared in ambient atmosphere, reaching values in the range of 20–32 wt%. On the other hand, samples prepared under argon showed reduced Fe content, with values in the range 5–10 wt% for samples prepared from precursors with low surface area (G, MG, and CB) and a much higher value (~19 wt%) for samples prepared from the precursor of high surface area (AC). Mossbauer spectroscopy and X-ray diffractometry showed that the nanoparticles were mostly composed of iron oxides in the case of the samples prepared in oxygen-rich ambient atmosphere and also for the AC-derived nanocomposite prepared under argon, which is consistent with the large oxygen content of this precursor. For the other precursors, with reduced or no oxygen content, metallic iron and iron carbides were found to be the dominant phases in samples prepared under oxygen-free atmosphere. The samples prepared in ambient atmosphere and the AC-derived sample prepared under argon exhibited superparamagnetic behavior at room temperature, as revealed by temperature-dependent magnetization curves and Mossbauer spectroscopy.

Effects of Temperature and Pore Structure on High Surface Area-Activated Carbon Obtained from Peanut Shells

Activated carbon was synthesized from peanut shells by treating with H3PO4 with an intention to enhance the surface area and to find its electrochemical performance in EDLC as electrode material. The powdered peanut shells were pyrolyzed at three different temperatures namely 300 degrees C, 600 degrees C and 800 degrees C respectively. The structural and surface properties of the pyrolyzed carbon materials were studied using N2 adsorption/desorption, Raman, TEM and SEM analysis. There has been remarkable increase in the surface area of the carbon pyrolyzed at 600 degrees C due to the effect of pore generations. The surface area of the 600 degrees C pyrolyzed sample was found to be 1629 m2/g. The electrochemical properties of all the samples were evaluated by cyclic voltammetry, impedance spectroscopy, and galvanostatic charge-discharge tests. The system showed excellent cycleability and a maximum specific capacitance of 291 Fg(-1) was obtained in a 0.1 M H2SO4 electrolyte solution. The effects of the various properties of the activated carbon on the EDLC performance are discussed.

High surface area activated carbon from rice husk as a high performance supercapacitor electrode

In this study, we report on the application of high surface area activated carbon (AC) derived from rice husks as a supercapacitor electrode. The prepared AC was free from Brønsted or Lewis acid sites, thus making the electrical double layer capacitance as the main charge storage mechanism. Three samples of AC with different surface areas were prepared at different activation temperatures and studied electrochemically using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. All AC samples exhibited good electrochemical performance as supercapacitor electrode. The maximum specific capacitance (147Fg−1) was obtained by the AC sample (surface area of 2696m2g−1) which was prepared at an activation temperature of 850°C. Detailed impedance studies revealed the low resistivity (0.23Ω) of AC sample and the fast frequency response (0.11s) of the supercapacitor electrode.

Diesel Fuel Desulfurization via Adsorption with the Aid of Activated Carbon: Laboratory- and Pilot-Scale Studies

The present work is an experimental investigation of commercial diesel fuel liquid desulfurization via adsorption under mild conditions. The sorbent employed was a commercial high surface area activated carbon (AC), and studies involved both laboratory- and pilot-scale experiments performed in dedicated fixed-bed setups. Under laboratory-scale conditions, maximum sulfur removal measured exceeded 90%, while according to breakthrough curves the total sulfur content remained below 2 ppmw for up to 20–22 mL of processed diesel per gram of sorbent. Process scaling-up by a factor of 15 showed a moderate negative effect, with the respective breakthrough fuel amount (total sulfur ≤2 ppmw) being ∼15–17 mL processed fuel/g sorbent. Several sorbent regeneration strategies were studied under laboratory-scale conditions. The one with the highest restoration of initial (i.e., fresh state) AC performance involved heating under vacuum (200 mbara) up to 200 °C and subsequent washing of the material with a binary organic s...

(Invited) Conducting Polymer Transistors Making Use of Activated Carbon Gate Electrodes

The characteristics of the gate electrode have significant effects on the behaviour of organic electrochemical transistors (OECTs), which are intensively investigated for applications in the booming field of organic bioelectronics. In this work, high specific surface area activated carbon (AC) was used as gate electrode material in OECTs based on the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrene sulfonate) (PSS).1 We found that the high specific capacitance of the AC gate electrodes leads to high drain-source current modulation in OECTs. Cyclic voltammetry studies, where PEDOT:PSS is used as the working electrode (WE) and AC is used as the reference electrode (RE) and counter electrode (CE), show that high double-layer capacitance and absence of Faradaic processes permit the development of stable OECTs where the channel potential is uniquely determined by the applied gate bias. The intrinsic quasi-reference characteristics of AC electrodes make unnecessary the presence of an additional reference electrode to monitor the OECT channel potential. The ease of process of AC electrodes for in plane, flexible device architectures constitutes a step forward in the search of new electrode materials for OECTs to be used in iontronics, printed electronics, bio analytical sensing, and other organic bioelectronic devices.

Electrochemical performances of hydrothermal tannin-based carbons doped with nitrogen

Six porous carbon materials, produced by hydrothermal treatment of flavonoid tannin and subsequent carbonization at 1173K, were tested as electrodes of supercapacitors. Four of these carbons were doped with nitrogen by putting tannin in contact with ammonia before or during the hydrothermal treatment. The pyrolyzed hydrothermal carbons had moderate surface areas, within the range 442–684m2g−1, and nitrogen contents ranging from 0.7 to 8.0wt.%. Specific capacitances as high as 320Fg−1 and normalized capacitances as high as 58μFcm−2 were measured at 2mVs−1. These performances are comparable with those obtained with high surface area-activated carbons, whereas, normalized capacitances values are among the highest ever reported. Mesostructuration, within the range 3–13nm, of these materials appears to be a good strategy to improve their electrochemical performances at higher scan rates. We confirmed the beneficial role of oxygen up to 18wt.%, while an optimum in nitrogen content exists from 3 to 6wt.%.

Hydrothermally treated aminated tannin as precursor of N-doped carbon gels for supercapacitors

Aminated tannin submitted to hydrothermal treatment led to nitrogen-doped gels in the absence of any cross-linker. Such gels were subcritically dried, freeze-dried or supercritically dried to obtain organic xerogels, cryogels and aerogels, respectively, having nitrogen contents between 3.0 and 3.7wt.%. After pyrolysis at 900°C, the materials presented nitrogen contents ranging from 1.9 to 3.0wt.%, and surface areas as high as 860, 754 and 585m2g−1 for carbon aerogels, cryogels and xerogels, respectively. All of them displayed micropores associated with different mesopore volumes, depending on both the drying method and initial dilution of the precursor. When tested as supercapacitor electrodes, these carbon gels presented outstanding specific and normalised capacitances, up to 387.6Fg−1 and 69.5μFcm−2, respectively, at a scan rate of 2mVs−1 in 4molL−1 H2SO4 aqueous solution. These performances are higher than those obtained with high apparent surface area-activated carbons, as the measured capacitances are indeed among the highest ever reported. The influence of nitrogen- and oxygen-based moieties was investigated, and optimal N and O contents of 2–3 and 17–18wt.%, respectively, were observed.