Characterisation under static and dynamic conditions of commercial activated carbons for their use in wastewater plants E. Sabio * , F. Zamora, J.F. Gonza ´lez, C.M. Gonza ´lez Garcı ´a, S. Roma ´n, A. Al-Kassir Department of Chemical and Energy Engineering, University of Extremadura, Avda. de Elvas s/n, 06071 Badajoz, Spain Available online 15 December 2005 Abstract The use of activated carbon for removing organic contaminants in fixed beds is increasing. This is a dynamic process in which the kinetics plays an important role. The aim of this paper is to get more insight into adsorption of p-nitrophenol (PNP) in activated carbon under equilibrium and dynamic conditions. Five commercial activated carbons were studied. The analysis carried out were PNP adsorption isotherms in aqueous solution at 20 8C, N 2 at 77 K isotherms, FT-IR and PNP adsorption under dynamic conditions. The results indicate that the external porous affinity toward the organic contaminants determines in large extent the adsorbents behaviour under dynamic conditions. # 2005 Elsevier B.V. All rights reserved. PACS: 81.05.Uw; 81.05.Rm; 82.20.-w Keywords: Activated carbon; Adsorption; Equilibrium 1. Introduction Activated carbons are widely used as adsorbent for removing a broad range of contaminants due to their high capacity and velocity of adsorption [1]. Other advantage of these adsorbents is that they can be regenerated in several ways, such as thermal treatment [2], wet oxidation [3], supercritical fluid [4] and classical solvent regeneration [5]. The most common general procedure for removing organic contaminants from waters involves the use of activated carbon fixed-beds [6]. The adsorption in a fixed-bed is a dynamic, non- steady process, which involves the accumulation of solute molecules from a solvent crossing the column onto an adsorbent. For a sound engineering design of water treatment plants are required both equilibrium and kinetic data [7]. However, these data are difficult to obtain because activated carbons are complex and heterogeneous materials with an adsorption capacity affected by their porous structure and surface chemical nature [2]. Moreover, most of the scientific work published on organic contaminants removal from water solutions has been carried out only in equilibrium conditions. There are several reasons for that, such as: (1) the dynamic experiments are more expensive and time-consuming than the equilibrium ones, (2) the results are more difficult to interpret, and (3) the process depends on several variables that can interact among them. The aim of this paper is to get more insight into the adsorption of p-nitrophenol (PNP) in activated carbon under equilibrium and dynamic conditions. PNP is frequently used as a model molecule for studying the organic-contaminant removal capacity of adsorbents. The PNP belong to the family of phenolic compounds that are widely used as solvent, cleaning agents and in the insecticides synthesis. This family of organic compounds represents an environ- mental problem due to its high toxicity, low biodegradability and high potential of accumulation in animal and plant tissues [8]. 2. Experimental 2.1. Materials Five commercial activated carbons were analyzed: Darco activated carbon 20–40 mesh (Aldrich), granulated activated carbon (Scharlau), no. 3 QP activated carbon (Panreac), 2.5 mm granular activated carbon Merck (Albus), and coconut shell activated carbon. The samples were codified as DA, SC, PA, AL and CN, respectively. www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 6058–6063 * Corresponding author. Tel.: +34 924 289 600; fax: +34 924 289 601. E-mail address: esabio@unex.es (E. Sabio). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.11.026