Interactions of imidacloprid with organic-and inorganic-exchanged smectites

Sorption of the polar insecticide imidacloprid on organic-saturated octadecylammonium (C18) and dioctadecyldimethylammonium (DOD) and inorganic- (Fe-) saturated Wyoming (W) and Arizona (A) montmorillonites has been investigated. Sorption isotherms were fitted to the Freundlich equation. Imidacloprid-montmorillonite complexes were studied by X-ray diffraction and FT-IR techniques. Imidacloprid sorption coefficients, Kf, decreased in the order WC18 > AC18 > WFe > WDOD greater than or equal to ADOD. The low layer charge and saturation by primary alkylammonium cation facilitates sorption of imidacloprid in the interlayer of the smectite, corroborated by the increase in basal spacing observed in X-ray diffraction patterns and by the presence of absorption band shifts in FT-IR spectra. Imidacloprid sorbs in the interlayer space of smectite mainly by hydrophobic interactions with the alkyl chains in organic smectites and with the uncharged siloxane surface in Fe(III)-smectite. Further polar bonds between the NO2 group of imidacloprid and the NH of the primary alkyl cations and protonation of imidacloprid in Fe-smectites enhanced sorption in these cases.