Mesopore-dominant porous carbon derived from bio-tars as an electrode material for high-performance supercapacitors

For the first time, toxic bio-tars collected from the gasification of pine sawdust are used as the precursor for activated carbons. Various types of activation agents including KOH, K₂CO₃, H₃PO₄ and ZnCl₂ were screened for obtaining superior activated carbons. When KOH was used as an activation agent, the obtained activated carbons exhibited high specific surface area and large mesopore volume. The activated carbons were further employed to be the electrode material of supercapacitors, and its specific capacitance reached up to 260 F g^?1 at 0.25 A g^?1 current density. Also, it showed an excellent rate performance from preserving a relatively high specific capacitance of 151 F g^?1 at 50 A g^?1. The assembled device also exhibited the good electrochemical stability with the capacity retention of 90% after 5000 cycles. Furthermore, the maximum energy density of the activated carbons in organic electrolyte reached 17.8 Wh kg^?1.     

Synthesis of spherically shaped granulated carbon sorbent

New technological procedure for obtaining spherical carbon sorbents was considered. The method is based on oil granulation in the technology of coal benefication. The coal dust of 2SS brand and coal tar were used to obtain spherical activated carbons with high sorption and strength characteristics. The influence exerted by the introduction of surfactants in the course of molding on the quality parameters of activated carbons was examined. The basic physicochemical and sorption characteristics of the carbons being developed were analyzed and it was shown that spherical carbon adsorbents with micropore volume of up to 0.31 cm³ g^–1 and abrasion strength of up to 91% can be obtained.     

NO2 removal on adsorbents prepared from coffee industry waste materials

A technology for obtaining carbonaceous adsorbents by physical and chemical activation of waste materials from coffee industry is described. The effect of pyrolysis temperature and type of activation procedure on the textural parameters, acid–base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterized by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by evaluation of nitrogen dioxide adsorption in dry and wet conditions. The final products were adsorbents of specific surface area ranging from 5 to 2,076 m²/g and pore volume from 0.03 to 1.25 cm³/g, showing very diverse acidic–basic character of the surface. The results obtained in our study have proved that a suitable choice of the pyrolysis and activation procedure for coffee industry wastes permits production of adsorbents with high sorption capacity of nitrogen dioxide, reaching to 44.5 and 84.1 mg NO₂/g in dry and wet conditions, respectively.     

The use of microwave radiation for obtaining carbonaceous adsorbents from biomass and their use in elimination of inorganic pollutants

A new technology of obtaining activated carbons by physical and direct activation of biomass with the use of microwave radiation is described. The effect of activation temperature (700 and 800 °C) and two periods of time (15 and 30 min) on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was tested. The resulting carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions as well as by iodine removal from aqueous solution. The final products were adsorbents of surface area ranging from 291 to 368 m²/g and pore volume from 0.20 to 0.26 cm³/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permit producing adsorbents with good capacity toward toxic gases of acidic character as well as inorganic pollutants of molecules of size similar to that of iodine molecules.     

Structural and sorption characteristics of carbon adsorbents from waste formed in wood processing

The structural and sorption characteristics of microporous sorbents from industrial lignin with respect to some toxic substances, Pb²⁺, Cd²⁺, Cu²⁺, and NH⁺ ₄ ions, and also the possibility of accumulation of methane on these carbons were studied. Simple procedures for modification of the carbon surface to improve the sorption power of the carbons were suggested.     

New carbon from low cost vegetal precursors: acorn and cypress cone

Thermal-treated carbons from acorn and cypress cone were prepared and characterized. The uptakes of heavy metal ions (Ag⁺, Cd²⁺ and Cr⁺³) and organics (phenol, methylene blue and sodium dodecylbenzenesulfonate) from aqueous solution have been studied. Effects of activation by HCl and HNO₃ acids on the sorption properties of these carbons were investigated by mass titration, sorption isotherms, IRS, SEM and XRS. The models of Langmuir and Freundlich do not represent our sorption data very well. An earlier proposed empirical correlation is applied successfully to carry out a parameter of comparison between the studied carbons. The acidic treatment changes the surface chemical properties of the two thermal-treated carbons lowering their sorption performances. The carbons show good capacities to uptake metals, phenol and methylene blue, but sodium dodecylbenzenesulfonate is removed from its solutions to minor extent. The up-taking properties are found similar to those of two worldwide used commercial grade carbons.      

Specific features of the absorption of divalent manganese ions from aqueous solutions by zeolites

Sorption properties of natural zeolites from various Russia’s deposits for the Mn²⁺ ion were studied in comparison with various industrial adsorbents and some minerals. It was demonstrated that the equilibrium sorption capacity of these materials can be raised by their Na⁺-modification. The natural zeolites are advantageous at low Mn²⁺ ion concentrations over synthetic cation exchangers and activated carbons. The sorption capacity of the natural zeolites grows with increasing temperature.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Removal of NO<Subscript>2</Subscript> by carbonaceous adsorbents obtained from residue after supercritical extraction of marigold

Carbonaceous adsorbents were obtained from the residue after supercritical extraction of marigold subjected to physical activation and used as nitrogen dioxide and iodine adsorbents. The effect of carbonisation and activation temperature on the textural parameters, acid–base character of the surface and sorption properties of the activated carbons was tested. The materials obtained were activated carbons of low-developed surface area varying from 2 to 206 m²/g, showing clearly basic character of the surface. The results proved that proper selection of the carbonisation and activation procedure of the residue after supercritical extraction of marigold permitted obtaining carbonaceous adsorbents with good capacity toward liquid as well as gas inorganic pollutants. The effectiveness of NO₂ removal was found to depend to large extent on the conditions of adsorption. The preliminary wetting of the adsorbent bed was shown to significantly increase the amount of pollutants removed.     

Physical and electrochemical characterization of activated carbons with high mesoporous ratio for supercapacitors based on ionic liquid as the electrolyte

A series of activated carbons with high mesoporous ratio were prepared by KOH reactivation based on activated carbon as the precursor. As the KOH/AC mass ratio was increased to 4:1, the mesoporous ratio increases from 60% to 76%, and the average pore size from 2.23 to 3.14?nm. Moreover, the specific capacitance for the activated carbon in ionic liquid 1-ethyl-3-methylmidazolium tetrafluoroborate ([EMIm]BF₄) can reach the maximum value of 189?F?g^?1 (8.0???F?cm^?2). In addition, the decrease of specific capacitance for activated carbons by KOH reactivation with current density increase shows two regimes, suggesting that activated carbons with high mesoporous ratio are much fit for charge?Cdischarge at larger current density.     

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.     

Sorption of heavy metal ions with activated carbons obtained from polyethylene terephthalate waste

The sorption capacity of activated carbons obtained from polyethylene terephthalate containers and packages with respect to heavy metal ions was examined. Based on the sorption capacities for Co²⁺, Mn²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, the selectivity series were established for the samples prepared by conventional steam and gas activation and by the procedure involving pretreatment with sulfuric acid.     

Calorimetric evaluation of activated carbons modified for phenol and 2,4-dinitrophenol adsorption

Two commercial activated carbons with differences in their superficial chemistry, one granular and the other pelletised, were modified for use in phenol and 2,4-dinitrophenol adsorption. In this paper, changes to the activated carbon surface will be evaluated from their immersion calorimetry in water and benzene, and they will then be compared with Area BET, chemical parameters, micropore size distributions and hydrophobicity factors of the modified activated carbons. The activated carbons were modified using 60 % solutions of phosphoric acid (H₃PO₄), nitric acid (HNO₃), zinc chloride (ZnCl₂) and potassium hydroxide (KOH); the activated carbon/solution ratio was 1:3 and impregnation was conducted 291 K for a period of 72 h before samples were washed until a constant pH was obtained. Water immersion calorimetry showed that the best results were obtained from activated carbons modified with nitric acid, which increased from ?10.6 to ?29.8 J g^?1 for modified granular activated carbon, and ?30.9 to ?129.3 J g^?1 for pelletised activated carbon. Additionally, they showed the best results in phenol and 2.4-dititrophenol adsorption. Those results indicate that impregnation with nitric acid under the employed conditions could generate a greater presence of oxygenated groups on their surface, which favours hydrogen bond formation and the increased adsorption of polar compounds. It should also be noted that immersion enthalpy in benzene for modified activated carbon with nitric acid is the method with the lowest value, which is consistent with the increased presence of polar groups on its surface. Regarding hydrophobicity factors, it was observed that granular carbons modified with nitric acid and potassium hydroxide have the lowest ratios, indicating greater interaction with water.     

Production of activated carbons from biodegradable waste materials as an alternative way of their utilisation

New carbonaceous adsorbents were prepared by means of direct, physical and chemical activation of corn cobs and cherry stones as well as coffee and tobacco industry waste materials. The effect of activation method on the textural parameters, acid-base character of the surface and sorption properties toward toxic gases of the materials obtained was tested. Depending on the precursor as well as method of preparation, the final products were micro/mesoporous activated carbons of surface area reaching to 1426 m²/g, showing largely different acid-base properties of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for industrial and agricultural biodegradable waste materials permits production of cheap carbonaceous adsorbents with very high sorption capacity towards nitrogen dioxide and hydrogen sulphide reaching to 83 mg NO₂/g_ads and 215 mg H₂S/g_ads, respectively.     

Electric conductivity of active carbons from phenol-formaldehyde oligomers and its relationship with the sorption of noble metals

The electric resistance of samples of active carbons, obtained from phenolformaldehyde oligomers of different nature and activated at different conditions, has been investigated. A clear relationship has been found to exist between the specific electric resistance of the carbons and the temperature of their thermal treatment. The structure of the polymer, from which the carbon had been obtained, as well as the nature of the activator affect its electric conductivity. A relationship has been established between the sorption characteristics of carbon sorbents towards substances, absorbed by the carbon, based on a donor-acceptor mechanism, and the electric conductivity of these samples. A symbatic relationship exists between the sorption of [Au(CN)₂]^– and the electric resistance.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 508–511, July–August, 1989.     

Calorimetric determination of activated carbons in aqueous solutions

The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the determination of immersion enthalpies. It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of zero charge, pH_PZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity. The immersion heat of the activated carbons in CCl₄ and water is determined obtaining values which are higher for CCl₄ immersion and vary from 31.4 to 48.6 J g⁻¹. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl₄ and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values obtained in CCl₄ when compared to the values obtained in water. Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g⁻¹ and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g⁻¹; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol.     

Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation

The paper presents results of a study on obtaining activated carbon from common corn cobs and on its use as adsorbent for removal of pollution from liquid and gas phases. The crushed precursor was subjected to pyrolysis at 500 and 800?°C in argon atmosphere and next to physical or chemical activation by CO₂ and KOH respectively. The effect of pyrolysis conditions and activation method on the physicochemical properties of the materials obtained was tested. The sorption properties of the carbonaceous adsorbents obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide sorption from gas stream in dry and wet conditions as well as by iodine and methylene blue removal from aqueous solution. The final products were microporous activated carbons of well-developed surface area varying from 337 to 1213 m²/g and showing diverse acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for corn cobs permits production of cheap adsorbents with high sorption capacity toward toxic gases of acidic character as well as different pollutants from liquid phase.     

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.     

活性炭孔隙结构对催化氧化脱除单质汞的影响

研究活性炭在硫化氢存在条件下催化氧化脱除煤气中单质汞的吸附机理和探讨提高其吸附能力的方法,在模拟煤气气氛下对3种活性炭和一种活性焦进行汞的吸附性能实验,并进一步分析活性炭(焦)的孔隙结构。用BET方程处理N₂等温吸附数据,计算比表面积;用HK法进行微孔分析;用BJH法计算中孔孔径分布。结果表明,硫化氢被催化氧化后,生成吸附在活性炭孔壁上的活性硫促进了对汞的吸附;随着活性炭微孔和中孔体积的增大,活性炭对汞的吸附能力得到提高。     

<Superscript>129</Superscript>Xe NMR spectroscopy of adsorbed xenon: Possibilites for exploration of microporous carbon materials

Despite the extensive use of ¹²⁹Xe NMR for characterization of high surface-to-volume porous solids, particularly zeolites, this method has not been widely used to explore the properties of microporous carbon materials. In this study, commercial amorphous carbons of different origin (produced from different precursors) and a series of activated carbons obtained by successive cyclic air oxidation/pyrolysis treatments of a single precursor were examined. Models of ¹²⁹Xe chemical shift as a function of local Xe density, mean pore size, and temperature are discussed. The virial coefficient arising from binary xenon collisions, σ_Xe-Xe, varied linearly with the mean pore size given by N₂ adsorption analysis; σ_Xe-Xe appeared to be a better probe of the mean pore size than the chemical shift extrapolated to zero pressure, σ_S.