Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study

This paper deals with the removal of alpha-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of alpha-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that alpha-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of alpha-endosulfan molecules on BrOnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of alpha-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of alpha-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of alpha-endosulfan. The HY(40) sample was the most efficient for the removal of alpha-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for alpha-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g. (C) 2011 Elsevier B.V. All rights reserved.