AZO DYES ENCAPSULATED WITHIN ALUMINOSILICATE MICROPOROUS MATERIALS

A novel synthetic method is presented for the encapsulation of azo dye s within a range of zeolites by in situ diazotisation and coupling rea ctions. The pH changes of methyl red, methyl orange and dimethyl yello w indicator dyes encapsulated in zeolites HY, NaY, ZSM5, mordenite and ultrastable Y were investigated by visual inspection and UV/visible s pectroscopy. Changes depended on the concentration of hydrogen ions wi thin the zeolite and, with ageing, equilibration with the external buf fer solution produced colour change in the zeolite dye residue. Since the dye molecules were small enough to pass out of the pores of the ze olite, leaching was anticipated but was found to depend on the dye's p olarity and nature of the solvent. The industrial application of these solid phase indicators is currently under investigation as is their p otential to act as bleed-resistant pigments. There is some evidence th at methyl;violet is formed in situ from the sorbed coupling component N,N-dimethylaniline.