Crystal architectures of a layered silicate on monodisperse spherical silica particles cause the topochemical expansion of the core-shell particles

Anisotropic structural changes in an expandable layered silicate (directed towards the c-axis) occurring on isotropic and monodisperse microspheres were detected by measurable increases in the grain size. The hierarchical changes were observed through pursing the sophisticated growth of expandable layered silicate crystals on monodisperse spherical silica particles with diameters of 1.0 mu m; the core-shell hybrids with a quite uniform grain size were successfully produced using a rotating Teflon-lined autoclave by reacting spherical silica particles in a colloidal suspension with lithium and magnesium ions under alkaline conditions at 373 K. The size distribution of the core-shell particles tended to be uniform when the amount of lithium ions in the initial mixture decreased. The intercalation of dioctadecyldimethylammonium ions into the small crystals through cation-exchange reactions expanded the interlayer space, topochemically increasing the grain size without any change occurring in the shapes of the core-shell particles. (C) 2015 Elsevier Inc. All rights reserved.ArticleMICROPOROUS AND MESOPOROUS MATERIALS. 215:168-174 (2015)journal articl

Swellable Microsphere of a Layered Silicate Produced by Using Monodispersed Silica Particles

Monodispersed spherical particles are potentially available for various applications as building blocks for photonic crystals, chromatography stationary phase, and drug support for controlled release. Immobilization of a molecular recognizable unit to the surface of the spherical particles is important in such applications. Here we report that silica spheres of submicrometer size were covered by a swellable layered silicate, which plays a role in accommodating cationic species. The coverage was conduced by using colloidal monodispersed silica spheres as a sacrificial template in the presence of urea and layered silicate sources (LiF and MgCl₂) at 373 K. X-ray diffraction peaks ascribed to hectorite (smectite group of layered clay) were observed in the resulting solid. The zeta potential distribution of the resulting solid had a single peak and shifted from that of the original silica. Transmission electron microscopy (TEM) observations revealed that stacks of the silicate layers lay on the surface of the silica core. Quantitative ion exchange reactions of the interlayer cations with a cationic surfactant were shown. The layered silicate was firmly glued onto the silica particles because the silicate with a cationic dye did not flake off from the product