Natural zeolitic tuff was modified with 2, 5 and 10mmol M + /100g of octadecyldimethylbenzyl ammonium (ODMBA) ions and the products were denoted as OZ-2, OZ-5 and OZ-10. The starting material and organozeolites were characterized by determination of the point of zero charge (pH pzc ) and by thermal analysis. In vitro sorption of fumonisin B 1 (FB 1 ) was studied for all sorbents at pH 3, 7 and 9.The pH pzc for the zeolitic tuff was 6.8±0.1, while the pH pzc for OZ-2, OZ-5 and OZ-10 pH pzc was 7.0±0.1. The curves pH final =f(pH initial ) suggest that the surfaces of all sorbents are positively charged at pH 3 and uncharged at pH 7 and 9. High sorption of FB 1 by the zeolitic tuff in acidic solution suggests electrostatic interactions between the anionic FB 1 and the positively charged surface. At pH 7 and 9, adsorption of FB 1 is prevented because anionic FB 1 cannot be adsorbed at the uncharged surface. From the pH pzc for the organozeolites, it is possible that with lower amounts of ODMBA (OZ-2 and OZ-5), at pH 3, beside interactions between head groups of ODMBA and its alkyl chains and anionic FB 1 , electrostatic interactions between positive uncovered surface and anionic FB 1 contribute to the sorption, while at pH 7 and 9 there is only the possibility for interactions between FB 1 and ODMBA. When the zeolitic surface was completely covered with ODMBA (OZ-10), FB 1 sorption was independent of the form of FB 1 suggesting only interactions between ODMBA and FB 1 .
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