Sorption of aromatic hydrocarbons onto montmorillonite as affected by norfloxacin

Abstract

Effect of norfloxacin (Nor) on the sorption of 1,3-dinitrobenzene (1,3-DNB), and PAHs (naphthalene (NAPH), phenanthrene (PHEN) and pyrene (PYR)) to K +-montmorillonite was studied. Nor suppressed 1,3-DNB sorption due to their competition for the same sorption sites. 1,3-DNB was sorbed on K +-montmorillonite surface via cation–polar interaction and n–π electron donor–acceptor interaction. Nor also was sorbed on these sites through cation exchange, cation bridging and/or surface complexation. Nor increased three PAHs sorption on montmorillonite and the enhanced magnitude was positively correlated with the π-donor strength of three PAHs. The enhanced sorption of PAHs by Nor was primarily attributed to π–π interaction between π-electron-depleted quinoline ring of Nor and π-electron-rich PAHs. Compared with cation (Nor +) and anion (Nor −), zwitterion (Nor ±) of Nor increased PHEN and PYR sorption more pronounced due to additional cation–π interaction between the sorbed Nor ± and PAHs. 1H NMR spectrum provided direct evidence for π–π and cation–π complexation between PAHs and Nor + in solution by ring-current-induced upfield chemical shifts of amino group and methylene group of Nor +.