INTRAZEOLITE SEMICONDUCTORS - NA-23 MAS NMR, TL+ LUMINESCENCE QUENCHING, AND FAR-IR STUDIES OF ACID-BASE PRECURSOR CHEMISTRY IN ZEOLITE-Y


MCMURRAY L., HOLMES A., KUPERMAN A., OZIN G., ÖZKAR S.

JOURNAL OF PHYSICAL CHEMISTRY, vol.95, no.23, pp.9448-9456, 1991 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 95 Issue: 23
  • Publication Date: 1991
  • Doi Number: 10.1021/j100176a077
  • Title of Journal : JOURNAL OF PHYSICAL CHEMISTRY
  • Page Numbers: pp.9448-9456

Abstract

Proton-loaded zeolites, prepared from fully dehydrated zeolites and gaseous, anhydrous Bronsted acids, represent an important step in the synthesis of intrazeolite semiconductor quantum supralattices. Adsorption-induced Na-23 MAS NMR chemical shifts, far-IR Na+ and Tl+ translatory mode frequency shifts, and Tl+ luminescence quenching effects were chosen as probes of cation-anion interaction in these materials. Samples of zeolite Y with various loadings of Tl+ were prepared via aqueous ion-exchange techniques. The samples were characterized by powder X-ray diffraction and far-IR spectroscopy. Luminescence measurements revealed Tl+ excitation and emission bands in the UV spectral region. Exposure of thallium Tl(I) zeolite Y to anhydrous HBr quenched the luminescence intensity. The intensity quenching followed Stern-Volmer quenching kinetics. Preliminary luminescence lifetime studies of this system supported a static ion pair quenching model. Compelling additional evidence in favor of cation-anion pair formation comes from the observation of alpha-cage site-specific Na-23 MAS NMR chemical shifts in HBr/Na56Y compared to virgin Na56Y. The relevance of these observations for proton-loaded zeolite Y to the acid-base precursor chemistry involved in the synthesis of semiconductor nanostructures encapsulated in zeolite Y is critically discussed.