Influence of natural zeolitic tuff and organozeolites surface charge on sorption of ionizable fumonisin B1

Natural zeolitic tuff was modified with 2, 5 and 10 mmol M+/100 g 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 (pHpzc) and by thermal analysis. In vitro sorption of fumonisin B1 (FB1) was studied for all sorbents at pH 3, 7 and 9. pzc for the zeolitic tuff was 6.8 ± 0.1, while the pHpzc for OZ-2, OZ-5 and OZ-10 pHpzc was 7.0 ± 0.1. The curves pHfinal = f(pHinitial) suggest that the surfaces of all sorbents are positively charged at pH 3 and uncharged at pH 7 and 9. High sorption of FB1 by the zeolitic tuff in acidic solution suggests electrostatic interactions between the anionic FB1 and the positively charged surface. At pH 7 and 9, adsorption of FB1 is prevented because anionic FB1 cannot be adsorbed at the uncharged surface. From the pHpzc 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 FB1, electrostatic interactions between positive uncovered surface and anionic FB1 contribute to the sorption, while at pH 7 and 9 there is only the possibility for interactions between FB1 and ODMBA. When the zeolitic surface was completely covered with ODMBA (OZ-10), FB1 sorption was independent of the form of FB1 suggesting only interactions between ODMBA and FB1.