Characterization of CdS-NaX composite material synthesized in alkaline solution

The composite material consisting of CdS in a NaX zeolite host was synthesized in an alkaline aqueous solution at temperatures ranging from 25 to 70°C, using cadmium chloride and thiourea as reactive substances. We found that CdS loading in the zeolite is controlled by the reaction temperature. This method allows the room temperature synthesis of CdS clusters and superclusters in the zeolite, stable at ambient conditions. X-ray diffraction patterns, scanning and transmission electron microscopy images and diffuse reflectance spectra of the samples were measured as a function of the reaction temperature. The evolution in the formation of CdS superclusters and the transition to CdS aggregates in the zeolite matrix was studied. The absorption spectrum of the samples prepared at the lowest temperature (25 and 30°C) shows the transitions due to CdS clusters and superclusters in the zeolite matrix. In the samples prepared at higher temperatures CdS synthesizes in the zeolite matrix as a polycrystalline material with crystallite size depending on reaction temperature. A blue shift in the absorption edge of CdS is observed as a consequence of particle size effects.