Gas and liquid phase sorption studies of lindane on NaY and MCM-41 molecular sieves

Abstract

Fundamental studies on the gas and liquid phase uptake of the chlorinated pesticide lindane (γ-hexachlorocyclohexane) on aluminosilicate molecular sieves NaY and MCM-41 (d-spacing=1.26 nm, Si/Al=2.6/1) were undertaken in an effort to evaluate their ability to act as barrier coatings on treated timbers. As competing water vapour from the environment could reduce the effective uptake of lindane, wet (non-activated) materials with preadsorbed water were compared with activated and silinised materials. Commercial pesticide formulations often use toluene as solvent, so this work also investigated the extent to which toluene affected lindane sorption. Liquid phase uptake measurements were analysed by FTIR spectroscopy. Both lindane and toluene were sorbed by the activated, wet and silinised forms of the NaY zeolite, with lindane able to displace approximately two-thirds and toluene approximately half of the preadsorbed water of wet NaY. Silination significantly reduced the uptake of both lindane and toluene, and this was more pronounced for the larger lindane molecule. It was found from liquid phase competitive studies that activated NaY always preferred lindane to toluene, but that selectivity for lindane on wet NaY depended on its concentration in the original solution. Gas chromatography showed that lindane was strongly retained on both NaY and MCM-41, but that even at the lowest temperatures MCM-41 was not able to retain toluene. Thermal gravimetric analysis of the gas phase uptakes of toluene and lindane were similar and independent of whether the zeolite was in its activated or wet form, with silination giving only a slight reduction in uptake. Uptake of lindane and toluene on NaY zeolite was more than twice that on MCM-41.