Self-assembly of saponite nanoparticles originated from nano-layered structure

Department of Environmental Sciences, Tokyo Gakugei University, 4-1-1 Koganei, Tokyo 184-8501, Japan

Abstract

The mechanism of self-assembly induced by H₂O molecules is studied for layered saponite nanoparticles and zeolite with the cage structure by means of positronium (Ps) annihilation spectroscopy together with thermogravimetry and differential thermal analysis (TG-DTA). Prior to hydration the saponite exhibits two kinds of open spaces with their sizes of ∼3 Å and ∼9 Å, whereas open spaces with their sizes of ∼3 Å and ∼5 Å corresponding to β and α cages are obtained for the zeolite. The occupation of both α and β cages by H₂O molecules proceeds along with hydration up to 2.5 h, which well synchronizes with the weight gain in TG data. On the contrary, the angstrom-scale open spaces for the saponite vary with hydration in the time scale with ∼100 h much longer than that of TG-DTA with ∼8 h. The present results suggest that the long-term self assembly originates from not the cage but the nanolayered structures.