Structure and Thermal Behavior of a Layered Silver Carboxylate

Abstract

We have investigated the structure and thermal behavior of nonmolecularly layered silver stearate by using various analytical tools, i.e., X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal analysis, UV/VIS spectroscopy, and transmission electron microscopy (TEM). The XRD pattern was composed of a series of peaks that could be indexed to (0k0) reflections of a layered structure. The alkyl chains in silver stearate as prepared were in an all-trans conformational state with little or no significant gauche population. Upon heating the sample, structural changes took place particularly at two temperatures. The binding state of carboxylate group changed from bridging to unidentate along with the disordering of alkyl chains at ∼380 K. The layered structural motif was, however, sustained in that temperature region, indicative of the overall structural change to be partially irreversible. A second dramatic structural change that must be associated with the decomposition of silver stearate, and thus a totally irreversible process, took place at ∼500 K. The major decomposition products appeared to be metallic silver and stearic acid, but surprisingly, both species seemed finally to produce stearate-derivatized silver nanoparticles with a size of ∼4 nm.