Claudia Leiggener

The electronic structure of Cu + , Ag + , and Au + zeolites

A variety of procedures have been used to prepare d10-zeolite materials. The electronic structure of these materials can be regarded to a first approximation as a superposition of the framework, of the charge compensating ions, of solvent molecules and of guest species. Zeolite oxygen to d10-ion charge transfer transitions dominate the electronic spectra if the ions coordinate to the zeolite oxygens. Specific coordination sites can influence the energy and the intensity of these transitions remarkably. Intra guest transitions dominate in quantum dot materials, as discussed in detail for luminescent Ag2S zeolite A. The zeolite is not needed for the photocatalytic water oxidation on Ag+/AgCl photo anodes with visible light. It can, however, be used to increase the active surface area substantially.

Luminescence properties of Ag2S and Ag4S2 in zeolite A

Silver sulfide particles of different size are synthesized in the cavities of zeolites A and ZK-4 by exposing the Ag+-exchanged dehydrated zeolites to H2S. The two smallest stable particles synthesized by this method are the Ag2S molecule and the Ag4S2 cluster. Both show photoluminescence in the visible region. The luminescence properties of the samples are studied as a function of temperature, of the silver sulfide content, and of the co-cations. By using the Ca2+-exchanged form of zeolite A it is possible to synthesize silver sulfide–zeolite systems which contain Ag2S and Ag4S2 in the same zeolite crystal. After excitation with UV light energy transfer from the excited Ag2S to Ag4S2 most probably occurs. These systems are potential materials for thermometry because their luminescence properties strongly depend on the temperature.

Zeolite A and ZK-4

The synthesis of zeolite A and ZK-4 crystals of high purity and well-defined morphology is described. Three procedures are detailed, leading to cubic crystals of zeolite A with chamfered edges (average size 3–5 µm), cubic crystals of ZK-4 with sharp edges (average size 1–2 µm), and nano-sized cubic crystals of zeolite A with slightly rounded edges (size ≤ 1 µm).

14-O-04-Silver ions and quantum-sized silver sulfide clusters in zeolite A

Publisher Summary This chapter presents silver ions and quantum-sized silver sulfide clusters in zeolite A. Ultraviolet/visible (UV/vis) spectroscopic studies of Ag + x Na + 12-x A, Ag + x Ca 2 6-0.5x A Ag + 9.5 A in conjunction with molecular orbital calculations lead to the result that four-ring coordinated Ag + is responsible for the deep yellow color observed in silver-loaded zeolite A activated at room temperature. Electronic transitions can be interpreted as charge transfer from zeolite oxygen lone pair to Ag + . The reaction of hydrogen sulfide (H 2 S) with activated Ag + -loaded zeolite A leads to the formation of quantum-sized, luminescent silver sulfide clusters inside the zeolite cavities. The cluster size can be varied by adjusting silver loading.