Understanding phenol adsorption mechanisms on activated carbons
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Understanding phenol adsorption mechanisms on activated carbons Leticia F. Velasco · Conchi O. Ania
Received: 20 April 2010 / Accepted: 6 January 2011 / Published online: 14 January 2011 © Springer Science+Business Media, LLC 2011
Abstract The interactions between phenol molecules and activated carbons were investigated in order to understand the adsorption mechanism of this aromatic compound. A series of activated carbons with varied chemical composition but similar porous features were synthesized and submitted to phenol exposure from aqueous phase, followed by thermogravimetric analysis and identification of the desorbed species by temperature programmed desorption coupled with mass spectrometry. Based on these experiments, both physi- and chemisorption sites for phenol were identified on the activated carbons. Our results demonstrate that physisorption of phenol depends strictly on the porosity of the activated carbons, whereas chemisorption depends on the availability of the basal planes in the activated carbons. Thus, oxidation of the carbon can suppress the fraction of chemisorbed phenol since the surface functionalities incorporate to the edges of the basal planes; notwithstanding, hydrophilic carbons may present a small but not negligible contribution of chemisorbed phenol depending on the extent of the functionalization. Moreover, these adsorption sites (chemi-) are recovered by simply removal of the surface functionalities after thermal annealing. Keywords Activated carbon · Phenol · Physisorption · Chemisorption
1 Introduction Faced with an increasing contamination of water resources, adsorption has become a well-established technique to reL.F. Velasco · C.O. Ania () Instituto Nacional del Carbón, CSIC, P.O. 73, 33080 Oviedo, Spain e-mail: [email protected]
move pollutants, activated carbon being the prevailing adsorbent for the purification of water with low pollutant concentration. Currently, the loaded carbon is regenerated offsite by heating or steaming in large industrial facilities. Although thermal reactivation is a highly skilled process that ensures that spent carbon is returned to a reusable quality, there is a major issue concerning the economic costs of the reactivation of the spent material. The efficiency of the different regeneration processes of activated carbons largely depends on the following factors: the porous structure of the carbon and the chemical condition of its surface, the physico-chemical properties of the adsorbent, the methods applied for regeneration, and the conditions under which the regeneration process is conducted (Dranca et al. 2001; Alvarez et al. 2004; Ania et al. 2005a; Salvador and SanchezJimenez 1996). Phenol is a widespread persistent organic pollutant commonly present in industrial effluents that has been the subject of a number of investigations, since it is a relatively simple and well characterized molecule. Despite the works devoted to the adsorption, desorption and regeneration of phenol using activated carbons, the interactions between activated c
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