CHARACTERIZATION OF CDS-NAX COMPOSITE-MATERIAL SYNTHESIZED IN ALKALINE-SOLUTION

The composite material consisting of CdS in a NaX zeolite host was syn thesized in an alkaline aqueous solution at temperatures ranging from 25 to 70 degrees C, using cadmium chloride and thiourea as reactive su bstances. We found that CdS loading in the zeolite is controlled by th e reaction temperature. This method allows the room temperature synthe sis of CdS clusters and superclusters in the zeolite, stable at ambien t conditions. X-ray diffraction patterns, scanning and transmission el ectron microscopy images and diffuse reflectance spectra of the sample s were measured as a function of the reaction temperature. The evoluti on in the formation of CdS superclusters and the transition to CdS agg regates in the zeolite matrix was studied. The absorption spectrum of the samples prepared at the lowest temperature (25 and 30 degrees C) s hows the transitions due to CdS clusters and superclusters in the zeol ite matrix. In the samples prepared at higher temperatures CdS synthes izes in the zeolite matrix asa polycrystalline material with crystalli te size depending on reaction temperature. A blue shift in the absorpt ion edge of CdS is observed as a consequence of particle size effects. (C) 1997 Elsevier Science Ltd. All rights reserved.