Characteristics of activated carbons prepared from pistachio-nut shells by physical activation

Activated carbons were prepared from pistachio-nut shells, which are one type of lignocellulosic material, by a two-step physical method. The effects of the preparation variables on the activated carbon pore structure were studied, followed by the optimization of these operating parameters. It was found that the activation temperature and dwell time are the important parameters that affect the characteristics of the activated carbons obtained. The effects of CO(2) flow rate and heating rate during activation were also studied. Under the experimental conditions used, the optimum conditions to prepare activated carbons with high surface area and pore volume were identified. The microstructure of the activated carbons prepared was examined by scanning electron microscopy while the Fourier transform infrared spectra showed the changes in the surface functional groups produced during the different preparation stages.     

Effects of activation conditions on the structural and adsorption characteristics of pinecones derived activated carbons

This study was conducted to understand and optimize the activation process for the production of a low-cost activated carbon (AC) using a renewable and plentiful biomass waste, pinecones. This was achieved by tracking the changes in porous structure, surface chemistry and adsorption properties of the AC produced using different activating agents, activation temperatures, holding times and heating rates. Generally, produced ACs were predominantly microporous with small external surface area and were different in terms of H/C and O/C ratios. Study of Pb²⁺ cations adsorption on these samples proved the high affinity of the pinecones derived ACs to this cation. The best adsorption behaviour was recognized in sample prepared by impregnation with H₃PO₄ at weight ratio of 2, then heating at 400?°C for 2?h at 5?°C/min heating rate. This sample possessed the highest BET surface area (1335 m²/g). The adsorption process obeyed the pseudo-first-order and Freundlich model slightly better than the pseudo-second-order kinetics and Langmuir model. The high Langmuir maximum adsorption capacity of 418?mg/g supports the applicability of the produced AC for the removal of Pb²⁺ cations from wastewater.     

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.     

Characteristics of activated carbon prepared from pistachio-nut shell by zinc chloride activation under nitrogen and vacuum conditions

Activated carbons with well-developed pore structures were prepared from pistachio-nut shells by chemical activation using zinc chloride under both nitrogen atmosphere and vacuum conditions. The effects of preparation parameters on the carbon pore structure were studied in order to optimize these parameters. It was found that under vacuum conditions, the characteristics of the activated carbons produced are better than those under nitrogen atmosphere. The impregnation ratio, the activation temperature, and the activation hold time are the important parameters that influence the characteristics of the activated carbons. The optimum experimental conditions for preparing predominantly microporous activated carbons with high pore surface area and micropore volume are an impregnation ratio of 0.75, an activation temperature of 400 degrees C, and a hold time of 1 h. Under these conditions, the BET surface areas of the carbons activated under nitrogen atmosphere and vacuum conditions were 1635.37 and 1647.16 m2/g, respectively. However, at a ZnCl2 impregnation ratio of 1.5, a furnace temperature of 500 degrees C, and a hold time of 2 h, the predominantly mesoporous activated carbon prepared under vacuum condition had a BET surface area of 2527 m2/g. Fourier transform infrared spectra were used to detect changes in the surface functional groups of the samples during the different preparation stages.     

Surface characteristics of activated carbons obtained by pyrolysis of plasma pretreated PET

Activated carbon materials have been prepared by pyrolysis of plasma pretreated recycled PET. The obtained carbon materials have been texturally characterized by N2 (77 K) and CO2 (273 K) adsorption. Atomic force microscopy (AFM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) have been used to analyze the surface of the treated precursors. Carbon materials obtained by He, N2, and CO2 plasma pretreatments (4 min) of the precursor and subsequent pyrolysis have shown a higher adsorption capacity than the corresponding chars (untreated pyrolised PET). This effect seems to be related to the elimination by the plasma treatments of low-molecular-weight products in the precursor, which are responsible for the formation of amorphous carbon deposits during the carbonization that blocks the porosity. Longer periods of treatment (15 min) do not favor the opening of the microporosity because cross-linking reactions in the precursor producing high molecular weight deposits prevail. The development of porosity is less relevant if oxygen plasma is used, as a considerable amount of oxygen functionalities are also formed. These groups can decompose during pyrolysation producing the above-mentioned amorphous carbon deposits. The textural characteristics of the carbon materials obtained after 4 min of plasma treatment on the precursor are very similar to those obtained after 4 h of CO2 (1073 K) activation of the same char. Therefore, this method can be an alternative to avoid the burnoff and high energy cost of the activation step.     

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.     

Multicomponent adsorption on activated carbons under supercritical conditions

Adsorption of binary mixtures onto activated carbon Norit R1 for the system nitrogen-methane-carbon dioxide was investigated over the pressure range up to 15 MPa. A new model is proposed to describe the experimental data. It is based on the assumption that an activated carbon can be characterized by the distribution function of elements of adsorption volume (EAV) over the solid-fluid potential. This function may be evaluated from pure component isotherms using the equality of the chemical potentials in the adsorbed phase and in the bulk phase for each EAV. In the case of mixture adsorption a simple combining rule is proposed, which allows determining the adsorbed phase density and its composition in the EAV at given pressure and compositions of the bulk phase. The adsorbed concentration of each adsorbate is the integral of its density over the set of EAV. The comparison with experimental data on binary mixtures has shown that the approach works reasonably well. In the case of high-pressure binary mixture adsorption, when only total amount adsorbed was measured, the proposed model allows reliably determining partial amounts of the adsorbed components.     

Thermal properties of pitch-polymer compositions and derived activated carbons

The evaluation of the possibilities to use coal-tar pitch modified with waste poly(ethylene terephthalate) or phenol?Cformaldehyde resin for the preparation of activated carbons was carried out. The measurement of thermal analysis (DSC), softening point, coking value, content of components insoluble in toluene and quinoline of pitch-polymer compositions were carried out. Coal-tar pitch and pitch-polymer compositions were carbonized and activated with steam at 800?°C to 50?% burn-off. For the obtained activated carbons the determination of thermal analysis (DSC), BET surface area on the basis of volumetric low-temperature adsorption of nitrogen, mesopore, and micropore volume from benzene adsorption/desorption isotherms (gravimetric McBain-Bakr method) were carried out.     

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.     

A comparative study on characterizations of biomass derived activated carbons prepared by both normal and inert atmospheric heating conditions

In the present study, cost effective activated carbon from wasteland biomass of Calotropis gigantea stem was prepared at 400 °C, 600 °C, 750 °C and 900 °C carbonization temperatures in normal atmosphere (NA) and at 600 °C, 750 °C in inert atmosphere (IA) of nitrogen by using Potassium Carbonate (K₂CO₃) as chemical activating agent in the impregnation ratios of 0.5, 1 and 2. Activated carbons prepared under NA and IA were characterized and compared. Field Emission Scanning Electron Microscopy (FESEM) study confirmed presence of micropores and mesopores. While Xray Diffraction (XRD) analysis confirmed presence of both disordered amorphous carbon humps and graphitic crystallite peaks. Presences of functional groups were more prominent in NAC; found from Fourier Transform Infra-Red Spectroscopy (FTIR) analysis. BET surface area at 750 °C at chemical impregnation ratio 1 under NA was recorded highest containing both micropores and mesopores. Disordered carbon structure was confirmed from RAMAN spectroscopic analysis and nanoporous structure of activated carbon was confirmed from HRTEM analysis. NA activated carbons processed from wasteland weed can be preferred for different adsorption related applications as they are reasonable with improved properties.     

Pre-formed activated carbon matting derived from the pyrolysis of biomass natural fibre textile waste

Low grade biomass fibre produced as a by-product from the flax and hemp industry was manufactured into a non-woven, pre-formed matting material via entanglement, layering and needling. The advantage of such a structure is that textile technology is used to form a self supporting fibre matrix, utilising the ease with which fibre can be worked. The non-woven matting was then pyrolysed and gasified with steam to produce activated carbon. The influence of pyrolysis process conditions on the production of chars and activated carbon from the pre-formed, non-woven textile matting were investigated.     

Adsorption kinetic and isotherm studies of Azure A on various activated carbons derived from agricultural wastes

The present study narrates the eminent role of agricultural wastes as adsorbents viz., Indian almond shell carbon (IASC), ground nut shell carbon (GSC), areca nut shell carbon (ASC), tamarind shell carbon (TSC) and cashew nut shell carbon (CSC) for the removal of Azure A (AA) dye from waste water. Different experimental parameters such as effect of initial concentration, contact time, dose, pH and particle size have been studied. The experimental results were analysed using Freundlich, Langmuir, Temkin, Redlich–Peterson and Dubinin–Radushkevich isotherm models. Different kinetic equations (first order, pseudo first order and pseudo second order) were applied to study the adsorption kinetics of AA on various activated carbons. Surface morphology of the adsorbents before and after adsorption is studied by Scanning Electron Microscopy (SEM). FT-IR studies revealed the presence of functional groups of dye on the adsorbents. It is inferred from the experimental result that the activated carbons (IASC, GSC, ASC, TSC and CSC) from agricultural wastes can be applied as an adsorbent substitute to commercial activated carbon (CAC) in the removal of AA dye from waste water.     

Promising activated carbons derived from cabbage leaves and their application in high-performance supercapacitors electrodes

In this paper, cabbage leaves (CLs) were used to synthesize porous activated carbon by the carbonization and activation processes. The material for CLs were carbonized at 600 °C and activated at 800 °C with the KOH/C-600 mass ratio 4 (denoted as AC-800) show typical amorphous character and display porous structures with high specific surface areas 3102 m²/g via XRD and BET measurements. As the electro-active material, AC-800 electrode exhibit ideal capacitive behaviors in aqueous electrolytes and the maximal specific capacitance is as high as 336 F/g at the current density of 1 A/g. Furthermore, AC-800 electrode shows excellent electrochemical cycle stability with ～95 % initial capacitance being retained after 2000 cycles. The desirable capacitive performances enable the CLs to act as a new biomass source of carbonaceous materials for high-performance supercapacitors and low-cost electrical energy storage devices.     

Production of activated carbons from pine nutshells

Optimal conditions for obtaining activated carbons from pine nutshells were determined. Their sorption properties were studied.     

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.     

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.     

Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers

The composition, structure, and adsorption behavior of activated carbons (ACs) derived from three different types of waste polymers, i.e., tire rubber (TR), polyvinyl chloride (PVC), and polyethyleneterephtalate (PET), by KOH activation were compared. The AC derived from PET exhibited the largest surface area (2831 m(2)/g) and pore volume (1.68 cm(3)/g) due to the homogenous aromatic composition of PET. The AC derived from PVC exhibited relatively lower surface area (2666 m(2)/g) but more narrowed pore size distribution (2-3 nm). The complex composition and high ash content of tire particles resulted in AC product with significantly lower surface area (398.5 m(2)/g) and heterogeneous pore width. Adsorption data of methylene blue (MB) were fitted well by Langmuir equation, indicating monolayer coverage on the ACs. The high oxygen content of PET-derived AC heavily affected its adsorption to MB and iodine. Due to the remarkable surface area and highly mesoporous structures, ACs based on both PET and PVC exhibited much higher adsorption capacities than that of TR and commercial coal-based AC (F400). This study demonstrates that the properties of ACs are highly dependent on their starting polymers and the potential of converting synthetic polymer waste into effective adsorbents for environmental remediation and cleanup.     

The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater

Adsorption of a basic dye, methylene blue, from aqueous solutions onto as-received activated carbons and acid-treated carbons was investigated. The physical and surface chemical properties of the activated carbons were characterized using BET-N(2) adsorption, X-ray photoelectron spectroscopy (XPS), and mass titration. It was found that acid treatment had little effect on carbon textural characteristics but significantly changed the surface chemical properties, resulting in an adverse effect on dye adsorption. The physical properties of activated carbon, such as surface area and pore volume, have little effect on dye adsorption, while the pore size distribution and the surface chemical characteristics play important roles in dye adsorption. The pH value of the solution also influences the adsorption capacity significantly. For methylene blue, a higher pH of solution favors the adsorption capacity. The kinetic adsorption of methylene blue on all carbons follows a pseudo-second-order equation.     

Effect of activation temperature on the textural and chemical properties of potassium hydroxide activated carbon prepared from pistachio-nut shell

The effect of activation temperature on the textural and chemical properties of activated carbons prepared from pistachio-nut shells by potassium hydroxide activation was studied. Relatively high activation temperature was required to develop high porosities. However, too high an activation temperature resulted in the burn-off of the carbon structures and the widening of micropores to meso- and macropores. The microstructures and microcrystallinities of the carbons prepared were examined using a scanning electron microscope and a powder X-ray diffraction analyzer, respectively, while the Fourier transform infrared spectra indicated the changes in the surface functional groups that were formed during the different preparation stages.     

钾对松木热解特性影响实验研究

采用管式炉热解实验装置对浸渍K2CO3松木进行直接热解,并将松木热解气通过含钾石英砂层、含钾焦层以模拟钾对热解气体反应的影响。结果表明,松木中浸渍K后会促进热解固体焦生成,提高H2/CO比,低温下K会降低液相产率、提高气相产率,而热解温度较高时则使气体产率下降、液体产率提高。松木热解气经过含K石英砂后发生催化裂解,液体产率降低,CO、CO2和H2产量上升。松木焦也可以催化裂解焦油,使气体产物增加,H2和CO2产量提高,CO、CH4和C2产量降低。K与松木焦共同作用,不仅使焦油发生裂解而且促进更多焦参与气固反应。钾对松木热解作用是通过对松木的直接热解、对气体中间产物再反应的均相催化及对固体焦气化的非均相催化等复杂过程实现的。