Solvatochromatic indicator study of silicalite and zeolite ZSM-5

Abstract

Reflectance spectrophotometric measurements on the solvatochromic indicator 4-nitroanisole adsorbed from cyclohexane solution by silicalite and ZSM-5 zeolites containing various amounts of aluminium ion have been made and used to calculate the parameter Π^*, which is a single-value measure of polarity and polarizability properties for each solid material. Adsorption isotherms concerned with the uptake of the dye by the solid materials have been determined. The values of Π^* for silicate are less than half of those determined from similar measurements on amorphous silica. Compared with silicalite, the values of Π^* for the zeolites ZSM-5 are somewhat greater, showing a levelling-off with increasing content of aluminium ion, in keeping with the conservation of hydrophobicity with increasing acidity of the zeolite surface.