Interaction between guest AgI and host zeolite FAU studied by optical spectra and EXAFS

AgI molecules were dilutely adsorbed into nano- cages of Na+, K+ and Cs+ type FAU zeolites in order to understand the interaction between host zeolite and guest AgI. This interaction was investigated using optical absorption spectroscopy and extended X-ray absorption fine structure (EXAFS). The optical spectra strongly depend on the type of the alkali cations. Compared with the lowest absorption band of AgI molecules in gas phase, the spectra of AgI molecules adsorbed in the zeolite cages shifts to higher energy in the order of Cs+, K+, and Na+. On the contrary, Ag-I bond lengths of adsorbed AgI molecules obtained from EXAFS were independent of the type of the alkali-cations. The bond length was very close to gas phase AgI molecules. Therefore, the interaction between AgI molecules and the zeolite, whose magnitude is Na+ > K+ > Cs+, is important in the photo-excited electronic state.