PH dependence of chlordecone adsorption on activated carbons and role of adsorbent physico-chemical properties

Abstract

From the 1960s to the 1990s, the large-scale production of banana in the French West Indies required an intensive use of chlorinated pesticides, such as chlordecone (Kepone), resulting in the diffuse contamination of soil and surface waters in the banana-producing areas. For this reason, drinking water plants were equipped with filters containing commercial activated carbons, being one of the challenges to find local adsorbents for the sustainable management of water treatment plants. In this paper, the adsorption of chlordecone (CLD) on activated carbons (ACs) prepared from sugar cane bagasse is studied, aiming to understand the mechanism of CLD adsorption on the AC surface. First, textural, acido-basic and chemical characteristics of the ACs were determined by thermal desorption, X-ray photoelectron and Boëhm studies. Adsorption isotherms of CLD show that the adsorption capacity increases with the amount of carbon and acidic groups at the AC surface whereas basic groups, hydroxyl and ether groups are detrimental to adsorption. The adsorption capacity is maximized at a solution pH level equal to the pHpzc of the considered AC. From temperature programmed desorption studies, it is proposed that chlordecone adsorption mechanism onto ACs is mainly governed by interaction with carboxylic groups. These results were correlated to molecular modeling studies of CLD interactions with surface functional groups of AC. The models of preferential positions, corresponding to minimal value of association energy, of interactions between CLD and AC functional groups were obtained.