The Adsorption Mechanism of Modified Activated Carbon on Phenol

Abstract

Abstract. Modified activated carbon was prepared by thermal treatment at high temperature under nitrogen flow. The surface properties of the activated carbon were characterized by Boehm titration, BET and point of zero charge determination. The adsorption mechanism of phenol on modified activated carbon was explained and the adsorption capacity of modified activated carbon for phenol when compared to plain activated carbon was evaluated through the analysis of adsorption isotherms, thermodynamic and kinetic properties. Results shows that after modification the surface alkaline property and pHpzc value of the activated carbon increase and the surface oxygen-containing functional groups decrease. The adsorption processes of the plain and modified carbon fit with Langmuir isotherm equation well, and the maximum adsorption capacity increase from 123. 46, 111.11, 103.09mg/g to 192.31, 178.57, 163,93mg/g under 15, 25 and 35°C after modification, respectively. Thermodynamic parameters show that the adsorption of phenol on activated carbon is a spontaneously exothermic process of entropy reduction, implying that the adsorption is a physical adsorption. The adsorption of phenol on activated carbon follows the pseudo-second-order kinetics (R2>0.99). The optimum pH of adsorption is 6~8.

An Insight into the Separation of 1,2-Propanediol, Ethylene Glycol, Acetol and Glycerol from an Aqueous Solution by Adsorption on Activated Carbon

“…Lin et al, found that the pH of a solution close to pH pzc increases adsorption due to the fact that surface electrostatic interactions on activated carbon were zero, and phenol remained in molecular forms making π-π dispersion interaction stronger. A decrease in the pH leads to a more positive charge of the activated carbon surface, decreasing the adsorption capacity [20]. In this case, as compound's pH is far from pH pzc , electrostatic interactions does not seem to have an influence in the process.…”

“…Some parameters are summarized in Table 1. The pH pzc of activated carbon was 10.08, from which it can be seen that for a pH lower than 10.08 the activated carbon surface has a positive charge and if the pH is higher the surface charge is negative [20]. These results are compared with the solution and solute properties in order to provide some explanations about the adsorption mechanisms.…”

“…Some authors, who studied different compounds, consider that these oxidized groups could be the sites of adsorption and that the mechanism of adsorption is based on π-π interaction, hydrogen bonding and dispersion interaction between the solute and the surface [16][17][18]. In addition, compounds with shorter length chains are expected to be less adsorbed due to their lower interaction with the surface, and it has been postulated that micropore volume provides most of the active sites [17,19,20]. Yu et al [17] proposed that micropores might be the crucial factor for acetone adsorption over activated carbons.…”

“…Peereboom et al [19] concluded that the quantities of 1,2-propanediol and glycerol adsorbed on activated carbons are related to the carbon micropore volume. Lin et al [20] review some works and reported that micropores were the major provider of adsorption sites and played a relevant role in the phenol adsorption on activated carbon.…”

“…Surface area is an important parameter because large surface areas can lead to a high adsorption capacity, regardless of whether the pore size increases [20] or decreases [21]. Furthermore, the molecule size of each adsorbate compound has a significant effect because of the possibility of being adsorbed in the smallest pores and its influence on the diffusion inside the pores [22].…”