Influence of organic cations sorption on the point of zero charge of natural zeolite

Abstract

In this paper, the results of the surface modification of natural zeolite with different amounts (2, 5 and 10 mmol M+/100g) of octadecyldimethylbenzyl ammonium ions (ODMBA) are presented. The obtained organozeolites were denoted as OZ-2, OZ-5 and OZ-10. The degree of ion exchange was followed by determination of amounts of inorganic cations released from zeolite. Results confirmed that reaction between ODMBA and starting zeolite has occurred via ion exchange mechanism. The obtained value for point of zero charge, pHpzc, of natural zeolite was 6.8?0.1, while for OZ-2, OZ-5 and OZ-10 pHpzc was 7.0?0.1. Below the pHpzc, the surfaces of materials are positive while at pH values higher than pHpzc their surfaces are negative. Compared to the pHpzc of natural zeolite, no significant differences in pHpzc was observed for all three organozeolites indicating that obtained products have similar functional groups with similar acid and basic characteristics as starting zeolite. The pHpzc was not dependent on the amount of ODMBA ions at the zeolitic surface and the value of pHpzc for all investigated sorbents is the same for all three electrolyte concentrations indicating that the pHpzc of each material is independent of the ionic strength of KNO3.U radu su prikazani rezultati modifikovanja povrsine prirodnog zeolita razlicitim kolicinama (2, 5 i 10 mmol M+/100 g) oktadecildimetil benzil amonijum jona (ODMBA). Dobijeni organozeoliti su oznaceni kao OZ-2, OZ-5 i OZ-10. Stepen jonske izmene pracen je odredjivanjem sadrzaja oslobodjenih neorganskih katjona iz zeolita. Rezultati su potvrdili da se reakcija izmedju ODMBA i polaznog zeolita odvija mehanizmom katjonske izmene i da je izmena kvantitativna. Dobijena vrednost za tacku nultog naelektrisanja, pHpzc, za prirodni zeolit iznosi 6,8?0,1, dok pHpzc za organozeolite OZ-2, OZ-5 i OZ-10 iznosi 7,0?0,1. Znacajna razlika u pHpzc nije zapazena ni kod jednog organozeolita u odnosu na polazni mineral, sto ukazuje da dobijeni organozeoliti imaju slicne povrsinske funkcionalne grupe sa slicnim kiselo-baznim karakteristikama kao i polazni zeolit.