Controlled release of paraquat from surface-modified zeolite Y

The surface hydroxyl groups of zeolite Y were reacted with 1,1,3,3-tetramethyldisilazane, HN(SiHMe2)2 under ambient conditions and the grafting of siloxy functionality on the zeolite was confirmed by infrared, NMR spectroscopy and elemental analysis. Paraquat (methyl viologen) was ion-exchanged into the zeolite, followed by treatment with the disilazane reagent. Surface modification of paraquat-loaded zeolites encapsulates the guest molecules in the zeolite cages and release of paraquat by ion-exchange with sodium ions was studied. The total amount of paraquat released was dependent on the concentration of Na+ in solution, and was similar for the derivatized and underivatized samples. In the absence of surface modification, equilibration occurred within 20 min, whereas with surface modification, the equilibration time was extended to 7 days. These kinetics are reflected in the effective diffusion coefficients (D) of paraquat, with D = 1.2 × 10−15 cm2 s−1 for derivatized zeolite Y and D = 0.2–1.1 × 10−7 cm2 s−1 for the underivatized sample. Paraquat was chosen as the guest molecule, since it is widely used as an herbicide and its controlled release is of interest in agricultural applications.