FORMATION OF NEW MATERIALS WITH THIN METAL LAYERS THROUGH DIRECTED REDUCTION OF IONS AT SURFACE-IMMOBILIZED SILYL HYDRIDE FUNCTIONAL-GROUPS, SILVER ON SILICA

A novel two-step method is described for the controlled deposition of ultrathin layers of metals on surfaces originally having pendant hydro xy groups. The method is described here using silver on silica. ''Redu cing'' silica was prepared easily by the reaction of trichlorosilane w ith silica gel. The product, characterized with Si-29 CP/MAS NMR and I R (DRIFT) techniques, displayed chemical reactivity expected of materi als with covalently anchored SiH functional groups. This material was reactive toward aqueous and methanolic KF, methanolic KCl, and aqueous solutions of certain metal ions, Each SiH group was shown to function as an one-electron reducing site. Quantitative estimation of the surf ace-immobilized silyl hydrides was achieved using a gravimetric aqueou s AgNO3 method. Study by SEM X-ray dot mapping techniques of the mater ial consisting of silver deposited by this manner on silica indicated uniform distribution of the silver across the surface, as defined by t he original distribution of covalently attached SiH functions. In the presence of excess aqueous silver ions there was no increase in the to tal mass of silver deposited on the silica, but a slow redistribution of the silver into aggregates occurred, The silver was recovered quant itatively from the surface upon treatment with nitric acid.