An IGC Study of the Role of Washing Procedures on the Adsorption Properties of Activated Carbons (original) (raw)
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Adsorption properties of two different activated carbons, steam and chemically activated, respectively, were examined by inverse gas chromatography (IGC). The influence of acid, basic and combined washings, carried out in order to remove ashes, on the adsorption properties of these materials was also tested using this technique. Chemical and textural characterization was carried out by nitrogen adsorption, ICP-MS and temperature programmed desorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined by IGC. Washing procedures (specially those involving acid washing) removes almost completely the mineral ashes of the carbons. Concerning to the effect on porous structure, this procedures only affect significantly to the properties of chemically activated carbon, with increases of micropore volume of up to 43%. The steam activated carbon shows the best adsorptive behaviour, with an enthalpy of adsorption up to 16% higher than the corresponding to chemically activated one, as well as a large amount of micropores. The removal of these ashes enhances the adsorption of studied compounds, especially for alkanes and chlorinated ones. Washing procedures also modify the chemical structure of the organic functionalities, but this effect does not seem to be very important on the adsorption properties of these materials.
Carbon, 2001
The general mechanisms for the adsorption of organic molecules on the surface of solids are well known for flat / smooth non-porous materials. They depend on low energy dispersive interactions (London-Van der Waals) responsible for reversible physical adsorption and specific forces of greater energy associated with dipolar or acid / base interactions. However in the case of activated carbons (ACs) the study of these mechanisms is considerably hindered by their microporosity. The pores increase the surface area considerably but impede the study of the surface itself. The comparative study of inverse gas chromatography (IGC) at infinite dilution and a capillary wetting method shows that the dispersive component of the surface energy is greatly influenced by the porosity. The specific adsorption forces liable to intervene in the adsorption of alkenes do not appear due to steric hindrance. However alcohols are better adsorbed than alkanes, even more so as the surface overlap increases. A method for estimating adsorption energy based on capillary wetting shows clearly that porosity is responsible for an increase in the dispersive adsorption energies and that the non-specific hydrophobic component is much more important than acid / base interactions susceptible to intervene with the surface functional groups of ACs.
Environmental Science & Technology, 1999
Uptake of two synthetic organic contaminants (SOCs), trichloroethylene and trichlorobenzene, by one coal-based and one wood-based granular activated carbon (GAC), modified using liquid-phase oxidation (HNO 3) and heat treatment in an inert atmosphere (N 2), and by several different as-received GACs was compared. Carbons were characterized by elemental analysis, surface area and pore size distribution, water vapor adsorption, acid-base adsorption characteristics measured using the Boehm technique, and a mass titration/pH equilibration method to determine the pH pzc. The results of isotherm experiments with the surface-treated coal-and wood-based carbons indicated that carbon surface acidity played an important role on the adsorption of hydrophobic SOCs. It was found that increasing surface acidity increased the polarity of the surface and reduced adsorption of hydrophobic SOCs by GAC. However, no significant trend was evident for as-received carbons; their behavior differed significantly from surface-treated carbons. The Boehm characterization technique did not appear to be a robust predictor of surface reactivity of as-received carbons toward lowmolecular weight hydrophobic target compounds. However, the Boehm method was useful for correlating the reactivity of carbon surfaces precleaned by acid-washing and heat treatment, and subsequently modified with a single oxidant, as done in this study.
Analysis of some adsorption experiments with activated carbon
Chemical Engineering Science, 1976
A simple method is proposed whereby the film transfer coefficient and coefficient of diffusion in the particles may be determined from finite bath adsorption experiments. The method also makes it possible to separate pore and surface diffusion. Under certain conditions it is also possible to determine the influence of particle phase concentration on the surface diffusivity. The method is based on models describing the instationary diffusion in the solids. Data from six different adsorption systems were analysed using this method. The adsorbed components were: phenol, paranitrophenol, parachlorophenol, bensoic acid, phenylacetic acid and 24dichlorophenoxyacetic acid. In all systems surface diffusion was the determining transport mechanism in the particles. In the system phenol and phenylacetic acid the surface diffusion coefficient increased by about a factor 3 with an increase in surface concentration of about 40%. For parachlorophenol the increase was somewhat less. For the other systems there was no significant increase. The increase in diffusivity is explained by a decrease in bonding forces with increasing concentration.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2008
The commercial activated carbon Norit ROW 0,8 Supra was modified in various conditions (heating under vacuum, in ammonia, in ammonia-oxygen atmosphere, oxidation with moist air, and with concentrated nitric acid) in order to differentiate its surface properties. The surface and structure characteristics of the carbon samples were obtained on the basis of different techniques: low-temperature nitrogen adsorption/desorption (77.5 K), Boehm method, decomposition of hydrogen peroxide, and thermogravimetry. The effect of adsorbent and adsorbate properties on adsorption from liquid phase was studied for the chosen organic substances of aromatic character. The isotherms of phenol, 4-nitrophenol and 4-chlorophenol adsorption were measured from aqueous solutions on all carbons. The possible mechanisms of adsorption process and solute interactions with carbon surface were analyzed. The effect of substituent in aromatic ring of adsorbate molecule on the adsorption affinity toward carbon surface was regarded.
Chemical engineering transactions, 2021
Activated carbons (AC) are widely used in a variety of applications because of their controllable porosity and surface functionalities. In this work, AC were prepared from different hard woods through one- and two-step pyrolysis/activation for the adsorption of organic pollutants in water. Water vapor was used as the activating agent. The influence of the precursor and preparation methods on the properties of the resulting AC was evaluated through multiple techniques. Temperature-programmed oxidation (TPO) measured the reactivity toward oxygen of chars and AC, while temperature-programmed desorption coupled with mass spectrometry (TPD/MS) revealed functional groups on AC surface. Methylene blue adsorption tests evaluated the adsorption capacity of the prepared AC and the presence of mesopores. Depending on the oxidation reactivity of the char produced by pyrolysis, the resulting AC show different surface composition and adsorption performance. With the increasing char oxidation reac...
Study of Multielemental Adsorption on Activated Carbon
International Journal of Modern Physics: Conference Series, 2012
In this study, multielemental adsorption on activated carbon (AC) was investigated. The treatment parameters (pH, AC concentration, metal concentration and contact time) in the adsorption process of multiple metals such as Bi , Cd , Co , Ga , Mn , Mo , Ni , In , Pb , Pd , Sn , Rh , Ru and W were experimented. Three types of characteristic behaviors of analyte elements were observed when the pH was varied. The adsorption rate of Bi , Co , Ga , Ni , In , Pb , Sn , Ru and W were over 80% within 30 min.
Study of adsorption from binary liquid mixtures on thermally treated activated carbon
Applied Surface Science, 2004
Activated carbon Norit R3ex after ash removal was thermally treated at various temperatures (950, 1500, 1800 and 2100 °C) in an inert gas atmosphere (Ar). Characterization of porosity of obtained samples was performed by applying the gas adsorption/desorption technique and SAXS method. The substantial decrease of the porosity is observed in the case of carbons prepared within the range of higher temperatures. Heats of wetting for the carbon samples were measured. The specific excess adsorption isotherms from binary and ternary liquid mixtures of benzene, n-heptane and 2-propanol were measured on the carbon samples by a static immersion method. Adsorption parameters were calculated for all investigated gas and liquid systems. The influence of the degree of graphitization of investigated carbons on the adsorption from liquid phase is discussed.
Carbon, 1999
The effects of treatment with inorganic salts exemplified by Mg (NO) or Ba (NO) on the physical-chemical 3 2 3 2 characteristics of activated carbon were studied. Results indicate that the pore volume remains relatively unchanged upon saltt reatment when the pore diameter ranges between 7 A and 20 A. Significant variation in pore volume was observed when pore diameter is less than 7 A; generally, the pore volume of AC is greater than AC-Ba and AC-Mg. Major oxygen functional groups such as hydroxyl group for AC, carboxyl group for AC-Ba, and hydroxyl and carbonyl groups for AC-Mg were created. Regenerated at a temperature of 4008C, creates more pore volume especially when treated with Mg(NO) with an increase of 13.0%. The regenerated AC-Mg exhibits the greatest acetic acid adsorption capacity among 3 2 all activated carbons studies.
Adsorption from binary liquid mixtures on commercial activated carbons
Carbon, 1995
Adsorption from binary liquid mixtures of completely miscible components of different polarity was studied, in order to characterize the adsorption properties of commercial activated carbons. The excess adsorption isotherms were measured for three binary liquid systems: acetone + n-heptane, acetone + benzene, and benzene + n-heptane on four activated carbons of various ash content. Textural characteristics of the adsorbents were determined on the basis of the adsorption/desorption isotherms of argon at 77.5 K. The relationship between the extent of adsorption from the liquid phase as well as the shape of the adsorption isotherms and various parameters characterizing the investigated activated carbons are discussed. A good agreement is found as far as the actual surface area of the materials is concerned.