XPS INVESTIGATION OF METHYLENE-BLUE INCORPORATED INTO FAUJASITES AND AIPO FAMILY MOLECULAR-SIEVES

The distribution of methylene blue (MB) between shell and core domains of molecular sieve crystals and the extent of aggregation of the molecules in the molecular sieve hosts is studied using X-ray photoelectron spectroscopy. It follows (i) from differences of the binding energies of the N1s electrons of solid MB and of molecular sieve-supported MB and (ii) from N/Si atomic ratios that MB is encapsulated inside molecular sieve cages and channels as isolated singular species or small aggregate if added as dissolved dye to the batch composition for the hydrothermal crystallization of molecular sieves (faujasite Y, SAPO-5, SAPO-34, AIPO-5). Ion-exchange of the MB cation into zeolites results also in high dispersions of the dye, but can produce a local destruction of the zeolite framework at the crystal surface. The structure-directing role of the dye was recognized for MB-loaded SAPO-5 and SAPO-34, exhibiting an improved phase purity.