New procedures for the preparation of CdS and heterogeneous Cr/CdS phases in hybrid xerogel matrixes. Pore structure analysis and characterization

Abstract

A CdS phase dispersed in a porous poly( 1,4-~henylene)-bridged silsesquioxane (PPS) xerogel was prepared from a sol-gel solution containing Cd2+ ions. Both wet and dried Cd2+-doped gels and xerogels were exposed to a sulfide source to produce “low-dimensional” microcrystalline CdS phases dispersed in the polysilsesquioxane xerogel. The CdS phase was characterized by EDAX, electron diffraction, UV, XPS, and fluorescence analyses. The doping procedure produces xerogels with surface areas and average pore sizes that were somewhat lower and smaller that the undoped materials, but in all cases an open cell porous xerogel structure was retained. Related technology has been used to prepare dispersed heterogeneous phases consisting of intimate mixtures of CdS and chromium metal in a porous polysilsesquioxane xerogel. In this case, the chromium metal precursor, a sol-gel processable aryl tricarbonyl chromium(0) complex, is homogeneously incorporated into the xerogel matrix. A microcrystalline CdS phase was independently prepared by successive diffusion of Cd2+ and S2ions in the dried xerogel. This was followed by heat treatment under vacuum (120 “C, < 1 mmHg) to liberate chromium atoms, which produced the mixed Cr/CdS phase in the xerogel matrix. TEM images show domains rich in microcrystalline CdS and Cr/CdS clusters in the xerogel. The Cr and CdS crystalline phases in these xerogels were identified by both electron diffraction and EDAX experiments.