CHEMISTRY ON THE EDGE - A MICROSCOPIC ANALYSIS OF THE INTERCALATION, EXFOLIATION, EDGE FUNCTIONALIZATION, AND MONOLAYER SURFACE TILING REACTIONS OF ALPHA-ZIRCONIUM PHOSPHATE

The intercalation and exfoliation reactions of alpha-zirconium phospha te, Zr(HPO4)(2). H2O (alpha-ZrP), were studied microscopically by atom ic force microscopy (AFM) and transmission electron microscopy (TEM). The reaction of alpha-ZrP with tetra(n-butylammonium) hydroxide (TBA()OH(-)) initially produces intercalation compounds, which then transfo rm to unilamellar colloids. The rate-determining step in intercalation is the opening of the interlamellar galleries. Subsequent diffusion o f TBA(+) ions into the opened galleries is rapid. The hydrolysis react ion of alpha-ZrP colloids proceeds from the edges inward, forming simi lar to 4-nm hydrated zirconia particles that decorate the edges of the sheets. The reaction does not go to completion, as it is limited by e quilibrium associated with the release of phosphate into the solution. The hydrolysis reaction is negligible at 0 degrees C, which permits t he synthesis of hydrolysis-free unilamellar colloids. Remarkably, thes e colloids form monolayer films on amine-derivatized silicon surfaces with a high density that suggests significant surface mobility during the adsorption process. Addition of appropriate phosphonic acids to co lloidal alpha-ZrP suspensions enables modification of the sheet edges, illustrated here by the anchoring of osmium oxide particles to the sh eet edges by a vinylphosphonate linker.