Characterization of Methyl Viologen in the Channels of Zeolite L

The degree of exchange of methyl viologen (MV 2+ ) within the channels of zeolite L microcrystals was determined as a function of the amount of MV 2+ added to an aqueous zeolite L suspension. Care was taken to remove molecules that have been adsorbed on the outer zeolite surface. Thus, the obtained values for the maximum occupation probability per unit cell are 0.78 for the commercial and 0.85 MV 2+ for the self-synthesized potassium zeolite L for which the equilibrium constant was found to be in the order of 10 4 at room temperature. Adsorption isotherms and BET results show that the self-synthesized zeolite has a larger specific surface area as well as a larger and, thus, more accessible pore volume for the MV 2+ than the commercial sample. IR spectra of very thin layers on ZnSe in high vacuum and Raman spectra at ambient conditions of MV 2+ −L zeolite at different loading levels are presented. They are compared with a MVCl 2 −KBr pellet and MV 2+ −Y zeolite spectra. The MV 2+ −L zeolite spectra indicate weak interactions between the MV 2+ and the zeolite framework. They also indicate that the two pyridyl rings of the intercalated MV 2+ are twisted. It was found that framework vibrations of the zeolite can be used as an internal standard for fast and nondestructive determinations of the MV 2+ loading. Raman spectra are better suited for this purpose than IR. The reason for this is that the IR intensities of the zeolite framework vibrations at about 1050 cm -1 are much higher than those for all MV 2+ modes, while the only strong zeolite framework Raman band at about 500 cm -1 is narrow and well-isolated and of similar intensity to the relevant MV 2+ signals at high loading. On the basis of Rietveld refinement of X-ray data and molecular modeling, a model of the MV 2+ location in the channels of zeolite L is proposed. The MV 2+ lies along the channel wall, and the angle between the main MV 2+ axis and the c -axis of the zeolite is 27°.