Preparation and Characterization of Activated Carbon from Sesame Seed Shells by Microwave and Conventional Heating with Zinc Chloride Activation

The preparation of activated carbon from sesame shells as raw precursor was investigated in the study by sequentially applying microwave and conventional heating methods assisted by zinc chloride activation. The optimizisation of experimental parameters including microwave power, microwave treatment time, conventional activation time, conventional activation temperature and zinc chloride concentration ratio for the microwave and conventional heating method was performed. The characterization of the prepared activated carbon was done by thermogravimetric and differential thermal measurements, infrared spectroscopy, scanning electron microscopy and specific surface area analyses. The maximum surface area of 1254?m²/g for the prepared activated carbon was obtained at a microwave power of 750?W, a microwave treatment time of 20?min, an activation time of 45?min, an activation temperature of 500°C and zinc chloride concentration ratio of 1:1. Methylene blue and iodine adsorption capacities for the prepared activated carbon were 103 and 1199?mg/g, respectively.     

Preparation of activated carbon from cotton stalk and its application in supercapacitor

High specific capacitance and low cost are the critical requirements for a practical supercapacitor. In this paper, a new activated carbon with high specific capacitance and low cost was prepared, employing cotton stalk as the raw material, by using the phosphoric acid (H₃PO₄) chemical activation method. The optimized conditions were as follows: the cotton stalk and activating agent with a mass ratio of 1:4 at an activation temperature of 800 °C for 2 h. The samples were characterized by nitrogen adsorption isotherms at 77 K. The specific surface area and pore volume of activated carbon were calculated by Brunauer–Emmett–Teller (BET) and t-plot methods. With these experimental conditions, an activated carbon with a BET surface area of 1,481 cm²?g^?1 and micropore volume of 0.0377 cm³?g^?1 was obtained. The capacitance of the prepared activated carbon was as high as 114 F?g^?1.The results indicate that cotton stalk can produce activated carbon electrode materials with low cost and high performance for electric double-layer capacitor.     

Adsorption of Dyes from Aqueous Textile By-Products on Activated Carbon from Scenedesmus obliquus

The adsorption of activated carbon prepared from Scenedesmus obliquus (algae) was evaluated through adsorption of Astrazon red. The adsorption efficiency of activated carbon was determined based on the specific surface area and pore size distribution. These results were compared with the results obtained with untreated algae. Approximately a 3-fold increase in the percentage of dye removal was observed for activated carbon compared to the untreated material. The primary reason for this observation may be the increase in specific surface area and total pore volume by chemical activation from 0.0136 to 423.7001?m²?g^?1 and from 0.0012 to 0.1643?cm³?g^?1, respectively. A pseudo-second-order model was fit with the kinetic data and the results indicate chemical adsorption. The maximum adsorption capacity of activated carbon was 181.82?mg?g^?1 at 25°C according to Langmuir isotherm model.     

Highly stable performance of supercapacitors using microporous carbon derived from phenol–melamine–formaldehyde resin

A series of microporous carbons were prepared by simple carbonization and activation of phenol–melamine–formaldehyde resin. The morphology, surface area, and elemental composition of the samples were investigated by scanning electron microscope, Brunauer–Emmett–Teller measurement, Raman spectra, and elemental analysis, respectively. Electrochemical characteristics were evaluated by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6.0?mol?L^?1 KOH. The microporous carbon activated by KOH presented a high specific capacitance of 202?F?g^?1 at a scan rate of 2?mV?s^?1. Furthermore, the KOH-activated microporous carbon electrode exhibited durable operation, the total loss of capacitance after 20,000 cycles is 2% at a current density of 500?mA?g^?1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, larger pore volume as well as oxygen groups.     

Preparation and Characterization of Activated Carbon from Microwave and Conventional Heated Almond Shells Using Phosphoric Acid Activation

Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m²/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon.     

The effect of activation technology on the electrochemical performance of calcium carbide skeleton carbon

Porous CaC₂-derived carbon (CCDC) was synthesized by one-step route from CaC₂ in a freshly prepared chlorine environment at lower temperature. As-prepared CCDC was activated by H₃PO₄, ZnCl₂, and KOH, respectively. The effects of the activation technology on the structure and morphology of CCDC were studied by X-ray diffraction, physical N₂ adsorption/desorption, and transmission electron microscopy. It has been found that the pore structure and specific surface area of CCDC are apparently improved after activation; the CCDC activated by KOH especially showed an excellent specific surface area of 1,100?m²?g^?1. The electrochemical performance of supercapacitors using activated CCDC as electrode active material was studied by cyclic voltammery, galvanostatic charge/discharge, and cycle life measurements. The results indicated that the CCDCs activated by H₃PO₄, ZnCl₂, and KOH revealed enhanced capacitances of 172.6, 198.1, and 250.1?F?g^?1 in 6?M KOH electrolyte, which were increased by 11.4, 27.8, and 61.2?% compared with the pristine CCDC (155?F?g^?1), respectively. Furthermore, the supercapacitors using all activated CCDCs as electrode active material exhibited excellent cycle stability, and the specific capacitance for all activated CCDC samples had nearly no change after 5,000 cycles.     

Activated carbon prepared from polyaniline base by K2CO3 activation for application in supercapacitor electrodes

An activated carbon was prepared from a polyaniline base using K₂CO₃ as an activating agent. The morphology, surface chemical composition, and surface area of the as-prepared carbon materials were investigated by scanning electron microscope, X-ray photoelectron spectroscopy, and Brunauer?CEmmett?CTeller measurement, respectively. Electrochemical properties of the as-prepared sample were studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6?mol?L^?1 KOH aqueous solution. Compared with the non-activated carbon, activated carbon showed superior capacitive performance. The activation carbon presented a high specific gravimetric capacitance of 210?F?g^?1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, the presence of nitrogen and oxygen functional groups, and larger pore volume.     

Preparation and performance of polyvinyl alcohol-based activated carbon as electrode material in both aqueous and organic electrolytes

Porous carbon materials with high surface area and different pore structure have been successfully prepared by phenolic resin combined with polyvinyl alcohol (PVA) and KOH as activation agents. The surface morphology, structure, and specific surface area of the carbon materials were studied by scanning electron microscopy, X-ray diffraction, and nitrogen sorption measurement, respectively. Furthermore, the effects of specific surface area, pore structure, and electrolyte on electrochemical properties were investigated by galvanostatic charge–discharge measurement. The results show that KOH–PVA-activated carbon materials display specific capacitance as high as 218 F?g^?1 in 30 wt.% KOH aqueous electrolyte, 147 F?g^?1 in 1 M LiPF₆/(ethylene carbonate (EC) + dimethyl carbonate) (1:1?v/v), and 115 F?g^?1 in 1 M Et₃MeNBF₄/propylene carbonate organic electrolyte, respectively. In addition, the carbon materials demonstrate long-term cycle stability, especially the AK3P-0.30 in aqueous electrolyte and the AK2P-0.30 with excellent rate capability in organic electrolyte. These reveal that the existence of a micro-mesoporous structure of activated carbon is beneficial to store energy in an aqueous supercapacitor and broad pore size distribution of activated carbon is favorable to energy storage in an organic supercapacitor. The carbon materials with pore size distribution in different ranges improve the electrochemical performance of supercapacitor in different electrolytes. A new pore-expand agent (PVA combining with KOH) was used to obtain porous carbons with enhanced properties for supercapacitor.     

The production of activated carbon from cation exchange resin for high-performance supercapacitor

High-performance activated carbon for electrochemical double-layer capacitors (EDLC) has been prepared from cation exchange resin by carbonization and subsequent activation with KOH. The activation temperature has a key role in the determination of porous carbon possessing high surface areas, and large pore structures. The porous carbon activated at 700 °C (carbon-700-1:4) has high surface area (2236 m²?g^?1) and large total pore volume (1.15 cm³?g^?1), which also displays best capacitive performances due to its well-balanced micro- or mesoporosity distribution. In details, specific capacitances of the carbon-700-1:4 sample are 336.5 F?g^?1 at a current density of 1 A?g^?1 and 331.8 F?g^?1 at 2 A?g^?1. At high current density as 20 A?g^?1, the retention of its specific capacitance is 68.4 %. The carbon-700-1:4 sample also exhibits high performance of energy density (46.7 Wh?kg^?1) and long cycle stability (～8.9 % loss after 3,000 cycles). More importantly, due to the amount of waste ion-exchange resins increasing all over the world, the present synthetic method might be adopted to dispose them, producing high-performance porous carbons for EDLC electrode materials.     

Supercapacitor performance of activated carbon derived from rotten carrot in aqueous,organic and ionic liquid based electrolytes

In this work, we report the synthesis of porous activated carbon (AC). AC was derived from rotten carrot, at different values of activating temperature under inert atmosphere, employing chemical activation method and ZnCl₂ as activation agent. On the basis of results observed by surface area and pore size analysis, effect of activation temperature on synthesized AC was determined. Other material properties such as morphology, thermal stability, vibrational response, and crystal structure of prepared AC were studied using standard techniques of material characterization. Further, the electrochemical performance of synthesized AC was studied as an electrode, in aqueous, organic and ionic liquid based electrolyte. It was found that the synthesized AC based electrode exhibits highest specific capacitance (135.5?F?g^?1 at 10?mHz) in aqueous electrolyte and highest specific energy (29.1?Wh?kg^?1 at 2.2?A?g^?1) and specific power (142.5?kW?kg^?1 at 2.2?A?g^?1) in ionic liquid based electrolyte. This shows the suitability of synthesized material for use in energy storage applications.     

Enthalpic characterisation of activated carbon monoliths obtained from lignocellulosic materials

In this study, energetic interactions between activated carbon monoliths and various liquids were evaluated by determining immersion enthalpies in C₆H₆, H₂O and aqueous solutions of NaOH and HCl. Immersion enthalpies depend on both the surface chemistry and the interactions between specific groups, and were compared with results from volumetric titrations. Immersion enthalpies of activated carbon monoliths were between ?95.85 and ?176.5 J g^?1 for C₆H₆ and between ?11.19 and ?68.31 J g^?1 for H₂O; whereas immersion enthalpies in NaOH and HCl solutions were between ?20.36 and ?82.25 J g^?1 and ?18.81 and ?96.16 J g^?1, respectively. In support of these results, a high level of acidic groups was found on the surface of the activated carbon monoliths by Boehm volumetric titrations, with values between 719 and 1,290 g mol^?1, in agreement with the higher immersion enthalpies observed in NaOH. Correlations were established between immersion enthalpies in the liquids and the surface chemistry properties of the activated carbon monoliths determined by volumetric titrations, demonstrating that immersion enthalpy is a useful parameter for characterisation of these materials in specific liquids.     

Preparation of activated carbon from waste Camellia oleifera shell for supercapacitor application

The cost-effective activated carbons derived from waste Camellia oleifera shell (COS) by ZnCl₂ activation method are investigated as the active electrode material in electric double-layer capacitors (EDLCs) for the first time. The activation temperature and ZnCl₂/COS impregnation ratio are two key factors affecting the surface area and pore structure of the prepared activated carbons, which accordingly affect their capacitive performances. Electrochemical investigations indicate that the activated carbon (AC-3-600) obtained at the activation temperature of 600 °C and impregnation ratio of 3 shows the maximum specific capacitance of 374 and 266 F?g^?1 in 1 mol L^?1 H₂SO₄ and 6 mol L^?1 KOH electrolytes at 0.2 A g^?1, respectively. The high capacitance of the AC-3-600 is attributed to its high surface area (1,935 m² g^?1), high total pore volume (1.02 cm³ g^?1), and especially the large percentage of micropores (735 m² g^?1). Meanwhile, the activated carbon presents good cycle stability in both acid and alkaline electrolytes during 5,000 cycles at a fair current density of 4 A g^?1. So, we had reasons to believe that the activated carbons from waste COS by ZnCl₂ activation might be one of the innovative carbon electrode materials for EDLCs application.     

Accessible area and hydrophobicity of activated carbons obtained from the enthalpy characterization

Were determined the immersion enthalpy in benzene and water for 24 carbonaceous materials, granular activated carbon and activated carbon monoliths prepared from African palm stone by chemical activation with H₃PO₄, ZnCl₂ and CaCl₂ solutions. The immersion enthalpies in benzene and water were exothermic, in accordance with a surface process that takes place between the solid and liquid. Benzene enthalpies for this set of solids were ?20.26 and ?181.1 J g^?1 and water enthalpies were between ?7.42 and ?67.01 J g^?1. The textural and chemical surface properties of the activated carbons were related to the immersion enthalpies. Since the evaluation of the porous structure was made with non-polar liquids with which the solid does not have a specific interaction, immersion enthalpy was proportional to the surface area accessible to liquid molecules, which was calculated from the enthalpic determinations based on the assumption of the existence of a direct relationship between the immersion enthalpy and the total area of the solid accessible to liquid molecules. The hydrophobic factor was calculated by dividing the immersion enthalpy in benzene and the immersion enthalpy in water; this is related to the acidity, basicity and hydrophobicity of the activated carbons.     

Hierarchical Activated Mesoporous Phenolic‐Resin‐Based Carbons for Supercapacitors

A series of hierarchical activated mesoporous carbons (AMCs) were prepared by the activation of highly ordered, body‐centered cubic mesoporous phenolic‐resin‐based carbon with KOH. The effect of the KOH/carbon‐weight ratio on the textural properties and capacitive performance of the AMCs was investigated in detail. An AMC prepared with a KOH/carbon‐weight ratio of 6:1 possessed the largest specific surface area (1118 m² g^?1), with retention of the ordered mesoporous structure, and exhibited the highest specific capacitance of 260 F g^?1 at a current density of 0.1 A g^?1 in 1 M H₂SO₄ aqueous electrolyte. This material also showed excellent rate capability (163 F g^?1 retained at 20 A g^?1) and good long‐term electrochemical stability. This superior capacitive performance could be attributed to a large specific surface area and an optimized micro‐mesopore structure, which not only increased the effective specific surface area for charge storage but also provided a favorable pathway for efficient ion transport.     

Modified surface chemistry of activated carbons

In this study, immersion calorimetry was used to characterise different samples of commercial granular activated carbon (GAC) which undergo oxidation with HNO₃ (GACOxN) and thermal treatments to modify its superficial group contents, as well as to determine the textural characteristics of the materials through nitrogen adsorption at 77 K and its superficial chemistry by Boehm titration and zero point of charge. Correlations between the immersion enthalpies and the results of the other techniques of characterisation were established. The immersion enthalpies in dichloromethane obtained were greater, which were found to be between ?88.36 and ?155.6 J g^?1, in contrast to those in carbon tetrachloride, which were found to be between ?50.21 and ?94.29 J g^?1. The dependence of the immersion enthalpies in water on the contents of total acidity and basicity surface groups was also established, and a good correlation between the accessible surface area determined by calorimetric technique and the BET area was found.     

Contribution enthalpic in the interaction of activated carbon with polar and apolar solvents

A method is presented for calculating the contribution that enthalpies make for every component of mixtures of activated carbon–water and activated carbon–hexane to the immersion enthalpy using the concepts that are used in the solution enthalpies. The immersion enthalpies of microporous activated carbon in water and in hexane have values from ?18.97 to ?27.21 and ?25.23 to ?47.89 J g^?1, respectively. From the immersion enthalpies and mass relation of the activated carbon in each of the solvents, the differential enthalpies are calculated for the activated carbon in water, Hw_DIFac, with values between ?15.95 and ?26.81 J g^?1, as are the differential enthalpies for the activated carbon in hexane, ΔHh_DIFac, with values between ?6.86 and ?46.97 J g^?1. For a low mass relation of the mixture components the contributions to the immersion enthalpy of the activated carbon and water differ by 3.20 J g^?1, while the difference between the contributions of the activated carbon and hexane is 19.41 J g^?1.     

Hierarchical mesoporous carbon materials: preparation by direct tri-constituent co-assembly and the electrochemical performance

Hierarchical mesoporous carbon materials with large microporosity were prepared by direct tri-constituent co-assembly with the use of resols as the carbon precursor, tetraethyl orthosilicate as the inorganic precursor, and triblock copolymer F127 as the soft template. Bimodal pore size distributions in the range of 1.5–4 and 7.5–12 nm were obtained in the synthesized hierarchical mesoporous carbon materials after etching of silica by HF acid, showing a high surface area of 1,675 m²?g^?1 with a large pore volume of 2.06 cm³?g^?1. The electrochemical performance of the hierarchical mesoporous carbons was evaluated as an electrode material for electrochemical supercapacitor, showing a specific capacitance as high as 152 F?g^?1 at a scan rate of 5 mV?s^?1 in 6 M KOH aqueous solution and a good cycling stability with capacitance retention of 99 % over 500 cycles.     

Investigation of porous carbon fabricated by polymer blending of phenolic resin and suberic acid

Porous carbons used for electric double-layer capacitors were fabricated by chemical blending and carbonization of phenolic resin (PF) and suberic acid (SA). The reaction of PF with diacid was confirmed by longer wavelength shift of carbonyl stretching peak of diacid in FTIR spectra and higher decomposition temperature of suberic acid in TG curves. The decomposition of suberic acid at high temperature contributed to the formation of micropores in PF resin during carbonization process. The influence of the ratio of PF to SA on pore structure, adsorption behavior and capacity performance was investigated. The specific surface area and total pore volume increase with decrease of ratio of PF to SA at first and then decrease. The maximum specific surface area and total pore volume were obtained at ratio 3, which corresponds to 511 m² g^?1and 0.26?cm³?g^?1, respectively. Electrochemical investigation indicates that a satisfactory specific capacitance of 145?Farad?g^?1 in 30 wt% KOH aqueous electrolytes is obtained. The capacitance maintenance achieves 72% as the current density increases 50 times. Porous carbon with reasonable pore structure was produced by chemical blending of diacid and phenolic resin, which offers a new development direction for preparation of porous carbon materials.     

Relation between immersion enthalpies of activated carbons in different liquids,textural properties,and phenol adsorption

The immersion enthalpies in benzene, cyclohexane, water, and phenol aqueous solution with a concentration of 100 mg L^?1 are determined for eight activated carbons obtained from peach seeds (Prunus persica) by thermal activation with CO₂ at different temperatures and times of activation. The results obtained for the immersion enthalpy show values between ?4.0 and ?63.9 J g^?1 for benzene, ?3.0 and ?47.9 J g^?1 for cyclohexane, ?10.1 and ?43.6 J g^?1 for water, and ?11.1 and ?45.8 J g^?1 for phenol solution. From nitrogen adsorption isotherms, the surface area, micropore volume, and average pore diameter of the activated carbons were obtained. These parameters are related with the immersion enthalpies, and the obtained trends are directly proportional with two first parameters in the nonpolar solvents, which is a behavior of microporous activated carbons with hydrophobic character. Phenol adsorption from aqueous solution on activated carbons is proportional to their surface area and their immersion enthalpy in the solution.     

Nitrogen-containing nanoporous carbons by a rational template carbonization method evinced in the cases of 1, 10-phenanthroline and benzimidazole

We demonstrate a rational template carbonization method to produce nitrogen-containing nanoporous carbons at 800 °C, using 1, 10-phenanthroline (or benzimidazole) as carbon/nitrogen source and magnesium citrate as template. The mass ratio of 1, 10-phenanthroline (or benzimidazole) and magnesium citrate has exerted the vital role in the determination of pore structures and the resulting electrochemical performances. It reveals that the carbon-P:Mg-1:1 (obtained by heating 1, 10-phenanthroline and magnesium citrate at 800 °C with the mass ratio of 1:1) and carbon-B:Mg-1:1 (obtained by heating benzimidazole and magnesium citrate at 800 °C with the mass ratio of 1:1) samples both are amorphous, nitrogen-containing, and highly nanoporous in nature. The carbon-P:Mg-1:1 sample has a large BET surface area of 1,657.4 m² g^?1 and high pore volume of 1.83 cm³ g^?1, and those of carbon-B:Mg-1:1 sample are of 1,105.4 m² g^?1 and 1.67 cm³ g^?1, respectively. Based on a three-electrode system using a 6-mol L^?1 KOH aqueous solution as electrolyte, the carbon-P:Mg-1:1 and carbon-B:Mg-1:1 samples can deliver large specific capacitances of 289.0 and 255.6 F g^?1 at a current density of 0.5 A g^?1. They can also exhibit high energy densities of 40.1 and 35.5 Wh kg^?1 when designated the power density as 0.25 kW kg^?1 as well as highly long-term cycling durabilities.