Andrzej Swiatkowski

On surface of micropores and fractal dimension of activated carbon determined on the basis of adsorption and SAXS investigations

Abstract Granulated commercial activated carbon obtained from hardcoal was separated for fractions, by elutriation, in an air stream of constant flow-rate. Three samples of different fall down distances from the outlet tube were demineralized. Benzene adsorption isotherms were determined at 293 K and SAXS measurements were performed for each one. The Dubinin–Izotova and Dubinin–Stoeckli equations were used for evaluation of micropore structural parameters of examined carbon samples. On the basis of these equations different methods of calculation of geometric surface area were discussed. Obtained results were compared with values evaluated by using the method proposed here. This method comprises results of SAXS and adsorption measurements. Changes of geometric surface area were confirmed by analysis of surface roughness measured by fractal dimension. The values of fractal dimension were obtained by method of calculation on the basis of adsorption data proposed previously by Ehrburger–Dolle and were compared with modification proposed here. This modification is based on well known correlation given by McEnaney. Obtained values of fractal dimension were compared with values determined on the basis of SAXS data.

Investigations of the electrochemical properties of activated carbon and carbon black

Abstract Potentiometric studies have been carried out on activated carbon and carbon black immersed in aqueous solutions of electrolytes. The samples studied were subjected to various modifying treatments: demineralization, oxidation in liquid and gaseous phases, saturation with hydrogen, and degassing. It was found that the potential of carbon increases during contact with the electrolyte solution; the amount of anions in the solution decreases with a simultaneous rise of the solution pH. Measurements of the potentials of the carbon samples of large specific surface area immersed in buffer solutions or solutions of established pH have shown that in the range 2.0

Interdependence of different parameters characterizing the chemistry of an activated carbon surface

The chemistry of the surface of activated carbon has been analysed. Five activated carbons obtained by a modification of raw carbon were investigated. The following techniques were employed: elemental analysis, acid—base reactions, thermal decomposition, IR spectroscopy, calorimetric heat determination, wetting with water and benzene, water vapour adsorption. The methods yield similar results. The correlations of pH, ψ, a0, ΔE vs. total oxygen content and the number of oxygen functional groups were found.

Adsorption of phenol from aqueous solutions on activated carbons with different oxygen contents

The effect of the chemical character of the surface of an activated carbon on phenol adsorption from aqueous solutions is described. The adsorbents used consisted of five types of activated carbon obtained by modification of the raw material. The results obtained indicate that the principal factor influencing adsorption is the oxygen contained in those surface functional groups which exhibit an acidic character. Moderately and slightly acidic groups are the most important in this context.

Sorption equilibrium prediction of competitive adsorption of herbicides 2,4-D and MCPA from aqueous solution on activated carbon using ANN

The simultaneous adsorption of two herbicides—2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)—from their aqueous binary mixtures onto granular activated carbon was studied. The quantities adsorbed were determined by HPLC with UV detection. The experimental data were analysed using the Freundlich adsorption isotherm. The high correlation coefficients indicated that the adsorption equilibrium fitted the Freundlich isotherm well. A multilayer perceptron (MLP) (an artificial neural network model—ANN) was applied to describe the adsorption equilibrium in multicomponent systems. This enabled sorption isotherms to be predicted for all possible combinations of the two herbicides. The experimental results and the calculated data obtained from MLP for the solutions of the individual components and their mixtures suggest that MCPA is better adsorbed onto activated carbon than 2,4-D.

Changes in the Surface Chemistry and Adsorptive Properties of Active Carbon Previously Oxidized and Heat-Treated at Various Temperatures. III. Studies of the Adsorption of Organic Solutes from Aqueous Solutions

The dependence between the surface chemistry characteristics of thermally modified active carbon samples with previously oxidized surfaces and their ability to adsorb organic solutes from aqueous solutions was investigated. The characteristics of the surface functional groups and the porous structure of the samples obtained were estimated using various experimental methods. The adsorption isotherms of nitrobenzene and 4-nitrophenol from dilute aqueous solutions onto all the carbon samples obtained were measured. The experimental systems were analyzed in terms of the theory of adsorption onto energetically heterogeneous solids. The relationships between the optimized isotherm parameters, i.e. equilibrium constants and heterogeneity parameters, and the characteristics of the active carbons were discussed.

Non-carcinogenic carbon sorbents for respiratory protection

Activated carbons impregnated with compounds of chromium, copper and silver (Cr-Cu-Ag) are widely used for removing toxic substances from air, mainly in respiratory protection for industrial and military applications. Toxicological and epidemiological studies have shown chromium (especially hexavalent Cr) to have carcinogenic properties. Hence, research has been launched to develop a new adsorption-catalytic complex without chromium, which is intended to replace the activated carbon-catalyst (Cr-Cu-Ag) system. In this work activated carbon obtained from plum stones as carrier and molybdenum, copper and silver salts as impregnates were studied. The porous structure of the carbon carrier was investigated using low temperature nitrogen adsorption. Cyanogen chloride breakthrough dynamics was analyzed in order to characterize the protection properties. Studies on the substitution of chromium by non-carcinogenic metals will be continued.

Adsorption of water vapor on modified activated carbons

SummaryThe adsorption isotherms of water vapor on modified activated carbons are measured in order to study the role of various surface groups in the primary adsorption of water molecules on these adsorbents. These adsorption isotherms are analysed by means of the Dubinin-Serpinsky and Jovanovic equations, which take into account the special features of water vapor adsorption on microporous activated carbons. Numerical analysis of the measured adsorption isotherms by means of the above mentioned equations showed their limited applicability for interpreting adsorption mechanism of water molecules on activated carbons.ZusammenfassungDie Adsorptionsisothermen von Wasserdampf auf modifizierter Aktivkohle wurden gemessen, um die Rolle verschiedener Oberflächentypen auf die Primäradsorption von Wassermolekülen auf diesen Adsorbenzien zu untersuchen. Die Adsorptionsisothermen wurden mittels der Dubinin-Serpinsky- und Jovanovic-Gleichungen analysiert, welche die speziellen Eigenheiten von Wasser auf mikroporöser Aktivkohle berücksichtigen. Die numerische Analyse der gemessenen Adsorptionsisothermen mittles der genannten Gleichungen zeigte ihre limitierte Anwendbarkeit zur Interpretation von Adsorptionsmechanismen von Wassermolekülen auf modifizierter Aktivkohle.

Application of isotherm equation associated with gamma micropore-size distribution for characterizing activated carbons

Abstract The isotherm equation associated with the gamma-type micropore-size distribution is applied for studying the benzene adsorption on various activated carbons. It is shown that this isotherm gives a good representation of the experimental adsorption isotherms on microporous activated carbons. Parameters of the above isotherm equation are useful for calculating the micropore-size distribution and the adsorption potential distribution, which characterize heterogeneity of microporous structure of activated carbons.

Validation of the Reliability of the Porous Structure Parameters for Activated Carbons as Evaluated on the Basis of Adsorption Isotherms from the Gaseous Phase

Adsorption/desorption isotherms from the gaseous phase (benzene vapour, nitrogen) have been determined consecutively a number of times on the same activated carbon sample. The porous structure parameters were evaluated on the basis of the experimental data using the Dubinin-Radushkevich, Dubinin-Astakhov, Finger-Büllow, Dubinin-Stoeckli and Horvath-Kawazoe equations for the calculations. Analyses of the mean values and relative errors of particular structural parameters were made as well as comparisons of the stability of the adsorption models used. It was found that the reliability of the results obtained was better for the benzene vapour adsorption isotherms determined by a gravimetric method than for those determined by a volumetric method using nitrogen as the adsorbate.