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

Fundamental studies on the gas and liquid phase uptake of the chlorinated p esticide lindane (gamma-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 treat ed timbers. As competing water vapour from the environment could reduce the effective uptake of lindane, wet (non-activated) materials with preadsorbe d water were compared with activated and silinised materials. Commercial pe sticide formulations often use toluene as solvent, so this work also invest igated the extent to which toluene affected lindane sorption. Liquid phase uptake measurements were analysed by FTIR spectroscopy. Both lindane and to luene were sorbed by the activated, wet and silinised forms of the NaY zeol ite, with lindane able to displace approximately two-thirds and toluene app roximately half of the preadsorbed water of wet NaY. Silination significant ly reduced the uptake of both lindane and toluene, and this was more pronou nced for the larger lindane molecule. It was found from liquid phase compet itive studies that activated NaY always preferred lindane to toluene, but t hat selectivity for lindane on wet NaY depended on its concentration in the original solution. Gas chromatography showed that lindane was strongly ret ained 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 whethe r 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.