SURFACE AND INTERGALLERY CATALYTIC PROPERTIES OF CU(II)-EXCHANGED HECTORITE - A SCANNING FORCE MICROSCOPE STUDY

Many layered silicate clay minerals such as hectorite readily adsorb o r intercalate organic species. Surface or intergallery structural effe cts, electric fields, or charged particles may then facilitate polymer ization or other reactions, resulting in novel inorganic/organic host- guest composite systems. We have studied the interaction of Cu(II)-exc hanged hectorite with the polar monomer aniline, nonpolar styrene, and the amino acid glycine. Hectorite is known to readily intercalate ani line into its intergallery regions, where spontaneous polymerization o ccurs, resulting in nearly two-dimensional sheets of the conducting po lymer polyaniline. In addition, aniline vapor is spontaneously polymer ized on the surface of Cu(II)-exchanged hectorite, due to the presence of micro-pore sites on the silicate surface where oxidizing CU2+ cati ons are available. For the nonpolar styrene molecule, little or no int ercalation occurs. Surface polymerization of styrene is observed for l ong, intense exposures to the monomer in solution. Cu(II)-exchanged he ctorite was also exposed to the amino acid glycine and subjected to al ternate cycles of heating and wetting. Concentration and condensation of the amino acid into short glycine oligomers was observed. These rea ctions were seen to occur only at surface step edges and micro-pore si tes. Polymerization of biological molecules on the surface of clay min erals under simulated prebiotic conditions may help to explain the eme rgence of these more complex molecules on the early Earth. (C) 1998 Am erican Vacuum Society.