Microporous Active Carbons Research Articles

Adsorption of ionic liquids onto activated carbons: Effect of pH and temperature

Adsorption isotherms and kinetics of three ionic liquids (1-methyl-3-octylimidazolium chloride, 1-butyl-3-methylimidazolium chloride and N-octylpyridinium bromide) were studied on several types of activated carbon (AC) – a microporous granular AC (from China), a microporous–mesoporous AC fabric (Zorflex from Calgon) and an AC prepared from Artichoke leaves using phosphoric acid activation. ACs were characterized by N2 adsorption measurement at 77K (DFT pore size distribution), acido-basic titrations (Boehm method) and point of zero charge measurement. Isotherms were studied, using UV–visible spectrometry, in buffer solutions at pH=2, 7 and 9, in the temperature range 20–50°C. Kinetics models were found to be dependent on adsorbent type. Adsorption uptakes were correlated to the AC porous structures. The kind of interactions between organic cations and the carbon surface were found to be related to the amount of oxygenated groups and to the ionic liquid type. Presence of oxygen groups promoted electrostatic interactions which were stronger for the more hydrophilic cation (1-butyl-3-methylimidazolium). The calculated thermodynamic parameters showed that as compared to methylimidazolium, the adsorption of longer chain cations and pyridinium like cations was more favorable.

Equilibrium and intra-particle diffusion of stabilized landfill leachate onto micro- and meso-porous activated carbon

Stabilized landfill leachate has previously been treated with activated carbon (AC); however, information on the selectivity of AC depending upon the pore size is minimal. Isotherm and kinetic experiments were conducted using three commercially available AC products, one micro-porous and two meso-porous. Equilibrium adsorption and intra-particle diffusion of organic matter from stabilized leachate was studied. Isotherm experimental data were fitted to Langmuir, Freundlich, and Redlich–Peterson isotherm models in non-linear forms. Of the three isotherm models, the Redlich–Peterson model provided the best fit to the experimental data and showed a similar organic matter adsorption capacity (approximately 0.2 g total organic carbon (TOC) g −1 AC) for both micro-porous and meso-porous AC. The organic matter effective intra-particle diffusion coefficients ( D e ) in both AC types were on the order of 10 −10 m 2 s −1 for AC particle sizes greater than 0.5 mm. Meso-porous ACs showed slightly higher D e compared to micro-porous AC. Rapid small-scale tests showed a maximum of 80% TOC removal from leachate by each AC investigated. Fluorescence spectroscopy showed a preferential adsorption of fulvic-type organic matter with an increase in empty bed contact time by each AC.

Long-term performance of activated carbon air cathodes with different diffusion layer porosities in microbial fuel cells

Activated carbon (AC) air-cathodes are inexpensive and useful alternatives to Pt-catalyzed electrodes in microbial fuel cells (MFCs), but information is needed on their long-term stability for oxygen reduction. AC cathodes were constructed with diffusion layers (DLs) with two different porosities (30% and 70%) to evaluate the effects of increased oxygen transfer on power. The 70% DL cathode initially produced a maximum power density of 1214 ± 123 mW/m 2 (cathode projected surface area; 35 ± 4 W/m 3 based on liquid volume), but it decreased by 40% after 1 year to 734 ± 18 mW/m 2. The 30% DL cathode initially produced less power than the 70% DL cathode, but it only decreased by 22% after 1 year (from 1014 ± 2 mW/m 2 to 789 ± 68 mW/m 2). Electrochemical tests were used to examine the reasons for the degraded performance. Diffusion resistance in the cathode was found to be the primary component of the internal resistance, and it increased over time. Replacing the cathode after 1 year completely restored the original power densities. These results suggest that the degradation in cathode performance was due to clogging of the AC micropores. These findings show that AC is a cost-effective material for oxygen reduction that can still produce ∼750 mW/m 2 after 1 year.

Using a New Finite Slit Pore Model for NLDFT Analysis of Carbon Pore Structure

In this work, we present a model for analyzing activated carbon micropore structures based on graphene sheet walls of finite thickness and extent. This is a two-dimensional modification of the widely used infinite slit pore model that assumes graphite-like infinitely extended pore walls. The proposed model has two versions: (1) a strip pore constructed with graphene strip walls that have a finite length L in the x-direction and are infinite in the y-direction. Strip pores are open on both sides in the x-direction; (2) a channel pore, i.e. a strip pore partially closed along one edge by a perpendicularly orientated graphene wall. This more realistic model allows pore termination via both physical pore entrances and pore blockage. The model consequently introduces heterogeneity of the adsorption potential that is reduced near pore entrances and enhanced near the corners of pore walls. These energetically heterogeneous structures fill with adsorbate more gradually than homogeneous pores of the same width. As...

Supercritical adsorption of nitrogen on EcoSorb-activated carbon at temperatures up to 383 K and pressures up to 2 MPa

Abstract Single adsorption isotherms and differential enthalpies of adsorption of nitrogen were measured on a microporous-activated carbon at various temperatures. A new way for calculating the differential enthalpies of adsorption is presented, and the results obtained were compared to those obtained by the isosteric method derived from the equilibrium data using the Clausius–Clapeyron equation. The measurements were made thanks to a coupled thermostated calorimetric–manometric apparatus which can be operated for pressures up to 2.5 MPa and temperatures from 303 to 423 K. This article provides experimental data which can be used for the adjustment of interaction potential in computational simulations for supercritical adsorption.

Purification of aqueous alcohol solutions in two-bed adsorber filters

The possibility of replacing imported carbon-fiber filters, which are used for the purification of aqueous alcohol solutions in the manufacture of vodka at a number of domestic distilleries, by the developed adsorber filters was studied. These adsorber filters combine the filtration of a solution on a macroporous ceramic filter element with adsorption on microporous active carbon; in this case, the filter bed is responsible for the selective chemisorption of metal ions, whereas the adsorbing bed is responsible for the total extraction of organic pollutants. A comparative study of the adsorption characteristics of the competing purification systems was performed, and the advantage of the proposed two-step system for the purification of aqueous alcohol solutions was demonstrated.

Activated carbon obtained by pyrolysis of potato peel for the removal of heavy metal copper (II) from aqueous solutions

Activated carbons (ACs) were prepared by pyrolysis of potato peel in presence of zinc chloride (chemical activities). Potato peel from Colombian cultives were impregnated with aqueous solutions of ZnCl 2 following a variant of the incipient wetness method. Different concentrations were used to produce impregnation ratios of 40, 70, 110 and 160 wt.%. Activation was carried out under argon flow by heating to 823 K with 4 h soaking time. The porous texture of the obtained ACs was characterized by physical adsorptions of N 2 at 77 K and CO 2 at 273 K. The impregnation ratio had a strong influence on the pore structure of these ACs, which could be easily controlled by simply varying the proportion of ZnCl 2 used in the activation. Thus, low impregnation ratio led to essentially microporous ACs. At intermediate impregnation ratios, ACs with wider pore size distribution (from micropores to mesopores) were obtained. Finally, high impregnation ratios yielded essentially mesoporous carbons with high surface area and pore volume. The four best-fit three-parameter isotherms Sips, Toth, Radke–Prausnitz and Vieth–Sladek suggest that the sorption capacity of activated carbon of potato peel to uptake copper ions to be 74 mg/g.

Influence of reactor material and activated carbon on the thermocatalytic decomposition of methane for hydrogen production

A series of experiments was conducted to study the catalytic effects of the stainless-steel reactor material and activated carbon (AC) on the decomposition of methane for production of hydrogen. Additionally, the effects of the methane flow rate, amount of AC, decomposition temperature, and particle size on methane conversion, initial decomposition rate and deactivation time were determined in a fixed bed reactor. The reactor wall seriously affected the methane decomposition when the temperature was higher than 850 °C. The activity of the AC increased with the increase in methane decomposition temperature (775–850 °C), and changing the particle size (135–1095 μm) did not have a significant effect. The initial rate of methane decomposition showed an inverse and non-linear relationship with increasing weight of AC due to the dilution of methane by the produced hydrogen. However, the method of changing the volume hourly space velocity, i.e., by changing either the AC weight at a constant methane flow rate or the methane flow rate at a constant AC weight, did not cause differences in the measured AC initial activity. Various measurements on the AC at the beginning and end of the experiment revealed that methane decomposition occurs mainly within AC micropores.

Effect of activation method on the physicochemical properties and NO 2 removal abilities of sorbents obtained from plum stones ( Prunus domestica)

Carbonaceous adsorbents from plum stones were obtained by physical and chemical activation and used as nitrogen dioxide adsorbents. The effect of activation procedure on the physicochemical and sorption properties of active carbons was tested. The materials obtained were microporous active carbons of well-developed surface area varying from 373 to 2570 m 2/g and pore volume from 0.18 to 1.35 cm 3/g, showing different acid–base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for plum stones can produce activated carbons with high sorption capacity of nitrogen dioxide, reaching to 65.0 and 37.5 mg NO 2/g in dry and wet conditions, respectively. The sorption capacity towards NO 2 of the adsorbents obtained was proved to be determined mainly by the surface chemistry and the reactions taking place on the surface rather than by the specific surface area development.

Energy characteristics of adsorbed water in active carbons according to the NMR relaxation data

Nuclear magnetic relaxation measurements were used to determine activation energy E act of the motion of water molecules adsorbed in active carbons. The E act value was found to depend on the filling of active carbon pores due to changes in the state of water molecules under adsorption. It was established that the E act = f(p/p s) plots, where p/p s is the relative pressure of water vapor observed for microporous active carbons (FAS-1, 2, N-15, SKT-6A), are similar in form to the corresponding plots of changes in water adsorption heats. In particular, we concluded that the plateau in the E act = f(p/p s) dependences, as in the case of adsorption heats, reflects the volumetric filling of active carbon micropores with water. We show that a linear function describes the increase in E act values for water upon the complete filling of micropores with an increase in the volume of adsorbed water clusters per one primary adsorption center (W 0/a m ). We establish that, for water in the FAS-3 sample, the deviation of E act values from this linear function was due to the contribution from the vapor phase in the mesopores (x 0 = 0.7−1.2 nm) that make up a considerable part of the active carbon’s porous system.

Sorption properties of active carbons obtained from walnut shells by chemical and physical activation

A technology of obtaining active carbon from common walnut shells is described. The effect of activation methods, temperature and heating mode on the surface properties has been tested. The resulting carbons were characterised by elemental analysis, low-temperature nitrogen sorption and determination of the number of surface oxygen groups. The sorption properties of the active carbons obtained were characterised by determination of nitrogen dioxide adsorption in dry conditions and the number of iodine adsorption. The final products were microporous active carbons of well-developed surface area reaching to 2305 m 2/g and pore volume to 1.15 cm 3/g, showing diverse acid–base character of the surface. The results have shown that the important effect on the content and type of surface oxides generated on the active carbons surface have both the temperature and the method of activation. The results obtained in our study have proved that a suitable choice of the activation procedure for walnut shells can produce activated carbons with high capacity of nitrogen dioxide, reaching to 66 mg NO 2/g. The results of our study have also shown that the adsorption ability of carbonaceous sorbents depends on the method and procedure of activation as well as on their textural parameters and acid–base properties of their surface.

Adsorption of copper from aqueous solution by activated carbons obtained by pyrolysis of cassava peel

Activated carbons (ACs) were prepared by pyrolysis of cassava peel in presence of chloride zinc (chemical activities). Cassava peel from Colombian cassava cultives were impregnated with aqueous solutions of ZnCl 2 following a variant of the incipient wetness method. Different concentrations were used to produce impregnation ratios of 40, 70, 110 and 160 wt.%. Activation was carried out under argon flow by heating to 823 K with 1 h soaking time. The porous texture of the obtained ACs was characterized by physical adsorptions of N 2 at 77 K and CO 2 at 273 K. The impregnation ration had a strong influence on the pore structure of these ACs, which could be easily controlled by simply varying the proportion of ZnCl 2 used in the activation. Thus, low impregnation ratio led to essentially microporous ACs. At intermediate impregnation ratios, ACs with wider pore size distribution (from micropores to mesopores) were obtained. Finally, high impregnation ratios yielded essentially mesoporous carbons with high surface area and pore volume. The four best-fit three-parameter isotherms Sips, Toth, Radke–Prausnitz and Vieth–Sladek suggests that the sorption capacity of activated carbon of cassava peel to uptake copper ions to be 55 mg/g.

Study of activated carbons by pyrolysis of cassava peel in the presence of chloride zinc

Activated carbons (ACs) were prepared by pyrolysis of cassava peel in the presence of chloride zinc (chemical activities). Cassava peel from Colombian Cassava cultives was impregnated with aqueous solutions of ZnCl 2 following a variant of the incipient wetness method. Different concentrations were used to produce impregnation ratios of 40, 70, 110 and 160 wt.%. Activation was carried out under argon flow by heating to 823 K with 1 h soaking time. The porous texture of the obtained ACs was characterized by physical adsorptions of N 2 at 77 K and CO 2 at 273 K. The impregnation ration had a strong influence on the pore structure of these ACs, which could be easily controlled by simply varying the proportion of ZnCl 2 used in the activation. Thus, low impregnation ratio led to essentially microporous ACs. At intermediate impregnation ratios, ACs with wider pore size distribution (from micropores to mesopores) were obtained. Finally, high impregnation ratios yielded essentially mesoporous carbons with high surface area and pore volume.

XPS study and physico-chemical properties of nitrogen-enriched microporous activated carbon from high volatile bituminous coal

N-enriched microporous active carbons of different physico-chemical parameters have been obtained from high volatile bituminous coal subjected to the processes of ammoxidation, carbonisation and activation in different sequences. Ammoxidation was performed by a mixture of ammonia and air at the ratio 1:3 (flow ratio 250 ml/min:750 ml/min) at 350 °C, at each stage of production i.e. that of precursor, carbonisate and active carbon. Ammoxidation performed at the stage of demineralised coal or carbonisate has been shown to lead to a significant nitrogen enrichment and to have beneficial effect on the porous structure of the carbon during activation, allowing obtaining samples of the surface area of 2600–2800 m 2/g and pore volume 1.29–1.60 cm 3/g to be obtained with the yield of about 50%. The amount of nitrogen introduced into the carbon structure was found to depend on the sequence of the processes applied. The greatest amount of nitrogen was introduced for the processes in the sequence carbonisation → activation → ammoxidation. The introduction of nitrogen at the stage of active carbon leads to a reduction in the surface area and lowering of its sorption capacity. From the XPS study, ammoxidation introduces nitrogen mainly in the form of imines, amines, amides, N-5 and N-6, irrespective of the processing stage at which it is applied.

Comparison of Physicochemical Properties of Nitrogen-enriched Activated Carbons Prepared by Physical and Chemical Activation of Brown Coal

Nitrogen-enriched active carbon has been obtained from Polish brown coal from the “Konin” colliery. The process of ammoxidation by a mixture of ammonia and air at the ratio of 1:3 has been performed at two temperatures (300 and 350 °C) at different stages of the production, that is, at that of precursor, char, and active carbon. It has been shown that the stage at which the process of ammoxidation is conducted has profound effect on the amount of nitrogen introduced into the carbon structure. The carbonization and activation (by steam or KOH) of nitrogen-enriched samples leads to significant reduction of the nitrogen content. The final products were microporous active carbons of well-developed surface area varying from 604 to 3181 m2/g and having nitrogen content from 0.4 to 6.5 wt%, showing different acid−base character of the surface.

Simulating of alcohol adsorption in slitlike micropores of active carbon by the molecular dynamics method

Benzene, methanol, ethanol, and 1,3-propanediol adsorption in model pores of active carbon is studied by the molecular dynamics method using the OPLSAA universal force field with allowance for the microheterogeneous structure of the carbon. It is shown that, in a slitlike pore with a width and a diameter of 0.7 and 3 nm, respectively, adsorbate molecules are, on average, located in parallel with pore walls and have a constant deviation from this position. When few molecules are contained in a limited pore space, they are located independently of one another in two different layers; however, as their concentration increases, initially, aggregates bonded (in the case of alcohols) through hydrogen bonds and, subsequently, dense layers are formed that strongly affect one another.

Polyethyleneimine impregnation on activated carbon: Effects of impregnation amount and molecular number on textural characteristics and metal adsorption capacities

This paper presents findings on polyethyleneimine (PEI) impregnation on palm shell activated carbon (AC) with regards to effects of impregnation amount and types of PEI used on surface characteristics as well as metal ions adsorption capacities of the AC. Fundamental interactions between PEI molecules and metal ions on textural surface (micro- and mesopores) of the AC are elucidated. Three types of low molecular weight PEI distinguished by their molecular numbers, Mn (423, 600 and 1200) are used for the impregnation process. Impregnation at 8.41 wt% 423-PEI/AC provides optimum increases for nickel and copper adsorption capacities by factors of 2.6 and 1.5 respectively at 49% reduction of Brunauer–Emmett–Teller (BET) surface area as compared to virgin AC. Only 423-PEI molecules are shown to have considerably filled the micropores of AC whereas the 600- and 1200-PEI molecules are too large (in terms of molecular sizes) to infiltrate the micropores.

Influence of high temperature treatment of porous carbon on the electrochemical performance in supercapacitor

Mesoporous carbon (MoC), prepared by the template method from phenol resin, commercial mesoporous carbon fiber (ACF) and microporous activated carbon (MiC) were heat-treated under 1200 °C in nitrogen. The samples before and after high temperature heat treatment (HTT) were used as electrodes in 30% KOH electrolyte for supercapacitor. The structure and electrochemical properties of these samples were characterized by X-ray diffraction (XRD), galvanotactic charge–discharge, cyclic voltammetry (CV) and electrochemical impedance spectra, respectively. Results showed that HTT caused a remarkable increase of mesoporous ratio in texture accompanied with a significant reduction of surface area. After HTT, the layer–layer space among graphite crystallite decreased and the degree of graphitization was improved. The capacitance values of mesoporous carbons increased and a more stable tendency for specific capacitance was obtained compared with the contrary performance of MiC-1200. The cyclic voltammetry of the samples at different sweep rates was close to the rectangular shape, which represented the lower ESR and higher power density. It was also found that high temperature treatment could improve the electrical conductivity and decrease the impedance of the electrode remarkably. The improved specific capacitance and the better conductivity of mesoporous carbons could be ascribed to the expanding and reorganization of crystallite structure as well as increase of mesopore ratio.

Siberian anthracite as a precursor material for microporous activated carbons

The technology of obtaining active carbon from anthracite mined in Siberia is described. The effect of the activating agent, anthracite/activator ratio and activation temperature has been tested. The activation either with KOH or NaOH has been found to lead to microporous active carbon samples of well-developed surface area reaching from 588 to 2260m2/g and pore volume from 0.29 to 1.12m3/g. The structural properties of the active carbons obtained have been found to depend first of all on the anthracite/activating agent ratio, on the kind of activating agent and finally on the temperature of activation.

Electrochemical regeneration of activated carbon loaded with p-nitrophenol in a fluidized electrochemical reactor

This paper described a novel electrochemical process for the regeneration of activated carbon (AC) loaded with p-nitrophenol (PNP), aiming to reduce regeneration time and improve cost-effectiveness of the process by adoption of a novel non-active anode of modified lead dioxide and operation of AC in a fluidized mode. The regeneration parameters such as current density, liquid flow rate, NaCl concentration, pH of the solution and regeneration time were systematically investigated. Under the optimum conditions, the regeneration efficiency of AC could reach 90% in 1.5 h, and no significant declination was observed after five-times continuous adsorption–regeneration cycles, confirming the reuse feasibility of the regenerated AC. The adsorption of organic pollutants was confirmed occurring in the micropore of AC, and AC regeneration was mainly due to the decomposition of organics by the attack of active species such as hydroxyl radical that were generated by electrochemical oxidation. The time-space production for AC regeneration has been greatly improved in the present modified process, indicating this regeneration process is much more potentially cost-effective for application.