Adsorption characteristics of activated carbons obtained from corncobs

Dried, crushed, corncobs were carbonized at 500°C and steam activated (in one- or two-step schemes), or activated with H₃PO₄. The products were characterized by N₂ adsorption at 77 K, using the BET, _s and DR methods. Adsorption capacity was demonstrated by the iodine and phenol numbers, and the isotherms of methylene blue and Pb²⁺ ions, from aqueous solutions. A distribution of porosity in the carbons was estimated within the various ranges (ultra-, super-, meso- and macropores). Simple carbonization yields a poor adsorbing carbon; only its uptake for iodine was high and proposed to be due to an addition reaction on residual unsaturation of the parent lignocellulosic structures. Enhanced porosity was best associated with chemical activation and/or steam pyrolysis at 700°C. These activated carbons proved highly porous and rich in mesopores, and showed high adsorption capacity for methylene blue and Pb²⁺ ions. Phenol uptake was found to depend on surface chemical nature of the carbon rather than its porous properties. Corncobs were postulated to be feasible as feedstock to produce good adsorbing carbons, under the one-step activation schemes outlined here.     

Effects of vacuum pyrolysis conditions on the characteristics of activated carbons derived from pistachio-nut shells

Preparation of effective adsorbents from pistachio-nut shells was carried out. Optimization of the vacuum pyrolysis parameters prior to activation was carried out to study the effects of vacuum pyrolysis temperature, hold time, and heating rate on the properties of chars and activated carbons, while CO2 activation conditions were fixed at a temperature of 900 degrees C, an activation time of 30 min, a heating rate of 10 degrees C/min, a CO2 flow rate of 100 cm3/min, and a nitrogen flow rate of 150 cm3/min. The optimum vacuum pyrolysis conditions for preparing activated carbons with high surface area and pore volume were identified. The microstructure and microcrystallinity of the activated carbons prepared were examined by scanning electron microscopy and powder X-ray diffraction techniques respectively while the Fourier transform infrared spectra determined any changes in the surface functional groups produced during different preparation stages. Experimental results show that it is feasible to prepare activated carbons with high BET surface area from pistachio-nut shells.     

Surface morphology of nanostructured polymer-based activated carbons

Complementary techniques, including nitrogen adsorption, small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM), have been utilized to characterize the surface features of highly microporous carbon materials prepared from highly aromatic polymers. Nitrogen adsorption measurement interpreted by BET, DR, HK, and NLDFT methods reveals these nanostructured activated carbons exhibit a high surface area of up to 4000 m2/g, a micropore volume up to approximately 1.75 mL/g, and an average pore size of approximately 10-20 angstroms. A modified equation, based on Porod's law, the Debye-Bueche equation, and fractal dimension theories, has been proposed and successfully applied to analyze the SAXS spectra and to extract the porous texture of these unique activated carbons. AFM 3D imaging combined with the Fourier transform technique has been applied to statistically quantify pore sizes on the carbon surface.     

Surface functionalization of mesoporous and microporous activated carbons by immobilization of diamine

The introduction of amino groups on HNO3-treated microporous (AC(micro)-At) and mesoporous (AC(meso)-At) activated carbon, which was followed by thionyl chloride (SOCl2) treatment, by immobilization of diamine compounds was investigated in terms of change in pore characteristics. The immobilization was improved by treatment with SOCl2. The BET surface area of AC(micro)-At largely decreased by immobilization of ethylenediamine (EDA) and hexamethylenediamine (HMDA). Decreases in BET surface area and pore volume of AC(meso)-At by immobilization of EDA and HMDA were scarcely observed. These results suggest that amino groups introduced to mesoporous activated carbon are effective as functional groups for additional reactions.     

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.     

Effects of pyrolysis conditions on the physical characteristics of oil-palm-shell activated carbons used in aqueous phase phenol adsorption

Oil-palm shells, a biomass by-product from palm-oil mills, were converted into activated carbons by vacuum or nitrogen pyrolysis, followed by steam activation. The effects of pyrolysis environment, temperature and hold time on the physical characteristics of the activated carbons were studied. The optimum pyrolysis conditions for preparing activated carbons for obtaining high pore surface area are vacuum pyrolysis at a pyrolysis temperature of 675 °C and 2 h hold time. The activation conditions were fixed at a temperature of 900 °C and 1 h hold time. The activated carbons thus obtained possessed well-developed porosities, predominantly microporosities. For the pyrolysis atmosphere, it was found that significant improvement in the surface characteristics of the activated carbons was obtained for those pyrolysed under vacuum. Adsorption capacities of activated carbons were determined using phenol solution. For the activated carbons pyrolysed under optimum vacuum conditions, a maximum phenol adsorption capacity of 166 mg/g of carbon was obtained. A linear relationship between the BET surface area and the adsorptive capacity was shown.     

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.     

Structural characteristics of activated carbons and ibuprofen adsorption affected by bovine serum albumin

Structural characteristics of a series of MAST carbons were studied using scanning electron microscopy images and the nitrogen adsorption isotherms analyzed with several models of pores and different adsorption equations. A developed model of pores as a mixture of gaps between spherical nanoparticles and slitlike pores was found appropriate for MAST carbons. Adsorption of ibuprofen [2-(4-isobutylphenyl)propionic acid] on activated carbons possessing different pore size distributions in protein-free and bovine serum albumin (BSA)-containing aqueous solutions reveals the importance of the contribution of mesopores to the total porosity of adsorbents. The influence of the mesoporosity increases when considering the removal of the drug from the protein-containing solution. Cellulose-coated microporous carbon Norit RBX adsorbs significantly smaller amounts of ibuprofen than uncoated micro/mesoporous MAST carbons whose adsorption capability increases with increasing mesoporosity and specific surface area, burnoff dependent variable. A similar effect of broad pores is observed on adsorption of fibrinogen on the same carbons. Analysis of the ibuprofen adsorption data using Langmuir and D'Arcy-Watt equations as the kernel of the Fredholm integral equation shows that the nonuniformity of ibuprofen adsorption complexes diminishes with the presence of BSA. This effect may be explained by a partial adsorption of ibuprofen onto protein molecules immobilized on carbon particles and blocking of a portion of narrow pores.     

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.     

Effect of pore characteristics on electrochemical capacitance of activated carbons

Activated carbons (ACs) for electric double layer capacitors (EDLCs) were fabricated from waste tea leaves, activated with the pore-forming substances ZnCl₂ then, carbonized at high-temperature in N₂ atmosphere. The surface texture and porosity of the ACs were determined using transmission electron micros-copy and N₂ adsorption/desorption studies. The surface area of the 20 wt % ZnCl₂ treated sample was found to be 1029 m²g^?1 and had a distribution of micropores and mesopores. The electrochemical properties of the ACs were evaluated by using cyclic voltammetry and galvanostatic charge-discharge studies. ACs from waste tea leaves exhibited excellent specific capacitance as high as 196 F g^?1 in the 0.1 M Na₂SO₄ neutral electrolyte, with rectangular-like cyclic voltammetry curves at a cell potential of 1.5 V and good cyclability with a capacitance retention of 95% at a high current density of 100 mA g^?1 for 2000 cycles. The results show that the pore texture properties and specific surface area of ACs are dominated by changing carbonization temperature and the amount of activating agent ZnCl₂. The electrochemical performance is influenced mainly by surface area, but the pore size distribution becomes a dominating factor for specific capacitance of a carbon electrode material when the pore structure is in range of micropores/mesopores.     

Structural characteristics of modified activated carbons and adsorption of explosives

Several series of activated carbons prepared by catalytic and noncatalytic gasification and subsequent deposition of pyrocarbon by pyrolysis of methylene chloride or n-amyl alcohol were studied by FTIR, chromatography, and adsorption methods using nitrogen and probe organics (explosives). The relationships between the textural characteristics of carbon samples and the recovery rates (eta) of explosives on solid-phase extraction (SPE) using different solvents for their elution after adsorption were analyzed using experimental and quantum chemical calculation results. The eta values for nitrate esters, cyclic nitroamines, and nitroaromatics only partially correlate with different adsorbent parameters (characterizing microporosity, mesoporosity, pore size distributions, etc.), polarity of eluting solvents, or characteristics of probe molecules, since there are many factors strongly affecting the recovery rates. Some of the synthesized carbons provide higher eta values than those for such commercial adsorbents as Hypercarb and Envicarb.     

Adsorption of phenol by oil-palm-shell activated carbons

Steam activated carbons from oil-palm shells were prepared and used in the adsorption of phenol. The activated carbon had a well-developed mesopore structure which accounted for 45% of the total pore volume. The BET surface area of the activated carbon was 1183 m²/g and a total pore volume of 0.69 cm³/g using N₂ adsorption at 77 K. The adsorption capacity of the activated carbon for phenol was 319 mg/g of adsorbent at 298 K. The adsorption isotherms could be described by both the Langmuir-Freundlich and the Langmuir equations. The adsorption kinetics consisted of a rapid initial uptake phase, followed by a slow approach to equilibrium. A new multipore model is proposed that takes into account of a concentration dependent surface diffusion coefficient within the particle. This model is an improvement to the traditional branched pore model. The theoretical concentration versus time curve generated by the proposed model fitted the experimental data for phenol adsorption reasonably well. Phenol adsorption tests were also carried out on a commercial activated carbon known as Calgon OLC Plus 12×30 and the agreement between these adsorption data and the proposed model was equally good.     

CO2 adsorption by activated templated carbons

Highly porous carbons have been prepared by the chemical activation of two mesoporous carbons obtained by using hexagonal- (SBA-15) and cubic (KIT-6)-ordered mesostructured silica as hard templates. These materials were investigated as sorbents for CO(2) capture. The activation process was carried out with KOH at different temperatures in the 600-800°C range. Textural characterization of these activated carbons shows that they have a dual porosity made up of mesopores derived from the templated carbons and micropores generated during the chemical activation step. As a result of the activation process, there is an increase in the surface area and pore volume from 1020 m(2)g(-1) and 0.91 cm(3)g(-1) for the CMK-8 carbon to a maximum of 2660 m(2)g(-1) and 1.38 cm(3)g(-1) for a sample activated at 800°C (KOH/CMK-8 mass ratio of 4). Irrespective of the type of templated carbon used as precursor or the operational conditions used for the synthesis, the activated samples exhibit similar CO(2) uptake capacities, of around 3.2 mmol CO(2)g(-1) at 25°C. The CO(2) capture capacity seems to depend on the presence of narrow micropores (<1 nm) rather than on the surface area or pore volume of activated carbons. Furthermore, it was found that these porous carbons exhibit a high CO(2) adsorption rate, a good selectivity for CO(2)-N(2) separation and they can be easily regenerated.     

Nanoporous carbons obtained by carbonization of copolymers impregnated by salts

This paper demonstrates the results of research on influence of types of polymer and kinds of salts used for impregnation of the polymer on porous structure formation in the final carbonaceous product. The studies were performed in two stages. In the first stage, the role of polymer structure were mainly studied. To achieve the aim, three different porous copolymers (polyimide and two types of polyester) were impregnated with the same salts (NiSO₄, and the mixture of AgNO₃ and Gd(NO₃)₃). In the second part of the study, only one polymer (polyimide) was impregnated by three mixtures of salts (chlorides, nitrates and sulphates of K, Cu(II) and Fe(III)). This approach allowed to evaluate the impact of the mixture of salts on porosity of the carbons, which were to be prepared. The obtained results revealed that when the impregnation was applied as a method for activation and moulding of porosity of carbonaceous materials prepared from polymers, several factors should be taken into account. First of all, initial decomposition temperatures of the polymers and the salts should be compared to find out if carbonization and activation processes proceed simultaneously or not. If the copolymer was carbonized and gases were released from decomposing salts, they reacted each other and synergic effect of polymer and salts properties were observed. Such conditions favored the development of microporous structure of the obtained carbon. On the contrary, if the processes were separated in time because of high temperature of melting point of the salts more mesopores were retained.     

Catalytic decomposition of peroxides by medicinal activated carbons

The catalytic properties of carbon hemosorbents were investigated in reactions of the decomposition of peroxide compounds simulating the peroxides of lipids. It was shown that SKN carbons have much higher catalytic activity than SKS or VAS-MU. A mechanism of the catalytic action of the carbons during hemocarboperfusion is proposed on the basis of theories of radical-chain degenerate branched processes. It is concluded that catalytic reactions must be taken into account in extracorporal detoxification. The mechanism that is given is in agreement with the experimental data according to the intensity of the EPR signal in the blood during ischemic heart disease and other pathologies.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 366–370, May–June, 1989.     

吡啶预处理抑制煤热解过程中交联反应的研究

采用吡啶蒸气、吡啶溶液两种溶胀方式对伊泰褐煤进行了预处理,用热重结合在线质谱仪考察了两种处理方式对煤热解过程中交联反应的抑制效果。结果表明,两种预处理方法对煤热解过程的交联反应都有不同程度的抑制,但其作用温度和机理不同。吡啶蒸气预处理可能通过与煤形成N—OH氢键、断开煤本身含氧官能团之间的氢键,从而在400℃以前抑制煤本身含氧官能团之间的氢键交联反应;吡啶溶液预处理主要是通过改变煤的结构,减少煤小分子同大分子网络结构之间缔合,提高氢的传递效率等因素来抑制小分子同煤大分子网络结构及其热解过程中间碎片之间的交联反应。     

The effect of chemical activation method on properties of activated carbons obtained from pine cones

A method for obtaining carbonaceous adsorbents from pine cones by chemical activation with NaOH is described. Activated carbons were obtained by two methods of activation (physical mixing and impregnation) and two variants of thermal treatment. It has been shown that pine cones can be successfully used as cheap precursor of carbonaceous adsorbents of well-developed surface area, large pore volume and good sorption properties. All activated carbon samples obtained show strongly microporous structure and surface of acidic character. The best physicochemical properties and greatest sorption capacity towards iodine were found for the carbon samples obtained by physical mixing of the precursor with the activating agent and then subjected to thermal activation at 600°C.     

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.     

Fire hazard evaluation of activated carbons

Journal of Thermal Analysis and Calorimetry - Activated carbons are widely used in the iodine adsorbers in nuclear plants, but little information about their combustibility is available for fire...     

Chemisorption of o-xylene on activated carbons

It was determined volumetrically that at temperature of gas-phase oxidative catalysis (473–573 K) o-xylene is chemisorbed on SKN and oxidized AG-3 carbons. The chemisorption is weak and reversible and is not accompanied by dissociation of o-xylene molecules, The active chemisorption centers are surface heteroatoms of nitrogen (in SKN carbon) or oxygen (in oxidized AG-3 carbon), promoting polarization of the C-H bond of the methyl group of o-xylene.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 370–374, May–June, 1986.