EFFECT OF SURFACE MODIFICATION ON THE INTERLAYER CHEMISTRY OF IRON INA SMECTITE CLAY

A hydrophobic nanostructured composite has been created through the ad dition of an organic monolayer to the external surface of a smectite c lay. This film inhibits the free exchange of water in to and out of th e interlayer located between the aluminosilicate of the clay. The effe ct of the presence of such a monolayer, which is formed from octadecyl trimethoxysilane, on iron(III) cations exchanged into the clay interla yer has been examined using X-ray absorption spectroscopy. Mild hydrot hermal conditions have been used to increase the rate of potential rea ctions involving the ferric ions. The addition of the organic coating results in partial reduction of the iron to the ferrous state, a proce ss that is furthered by hydrothermal treatment of the hydrophobic clay . In contrast, the iron in the simple ion-exchanged clay aggregates in to small iron-oxygen clusters but is not reduced. These results are di scussed in the context of the reduction potential of iron(III) and the susceptibility of that iron to hydrolysis in aqueous solution.