Adsorption of methylene blue from aqueous solutions by ZSM-5-type zeolites and related silica polymorphs

Abstract

The silica polymorphs, silicalite 1, silica sodalite, dodecasil 3C and dodecasil 1H, share an inability to adsorb the cationic dye methylene blue from aqueous solution owing to an absence of surface acid sites on their silica framework structure. The uptake of the dye by zeolite ZSM-5 is linearly proportional to its aluminium content. The mechanism of the adsorption process involves replacement of the hydrogen ions from the outside surface of the zeolite crystal upon which the dye exists in monomeric form. Samples of ZSM-5 type material with a relatively low aluminium ion content contain significant quantities of silicalite 1.