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

Abstract

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.

An inorganic anionic polymer filter disc: direct crystallization of a layered silicate nanosheet on a glass fiber filter

“…We have discovered that a hectoritelike layered silicate fine crystal (abbreviated as Hect, with the ideal formula Mx(Mg6-xLixSi8O20(OH)4•nH2O, where M represents interlayer exchangeable cations), an anionic 2D inorganic polymer, crystallizes directly on spherical, monodisperse amorphous silica particles through hydrothermal reactions. 23,24 Hect layered silicates [34][35][36][37][38] including Laponite®, supplied by conventional homogeneous nucleation reactions, have been widely investigated for their application as adsorbents, 39 dye-supports, 40 sensors, 41,42 photonics, 33,43 column packing materials, 44 and polymer-clay hybrid gels. 45,46 In addition to spherical substrates, silica substrates (e.g., plate, fiber, and monolith) are versatile in shape and morphology; hence, they are expected to exhibit greater applicability for hybrid systems.…”

Direct Crystallization of Layered Silicates on the Surface of Amorphous Silica

“…The layered silicate was firmly glued onto the silica particles because the Hect with MB did not flake off from the product . Firm immobilization of Hect on the fiber silica was also confirmed by immersing in aqueous LiCl solution for a long period .…”

“…We thereby initiated studies using monodisperse spherical silica particles for the direct crystallization of hectolite‐like layered silicate (abbreviated as Hect) to provide core‐shell type particles (abbreviated as silica@Hect) . This reaction has been performed by mixing the spherical silica particles (diameter of 0.6 μm) and an aqueous solution of LiF, MgCl 2 , and urea, followed by heating at 373 K for 48 h. Basically, the molar ratio of LiF : MgCl 2 : SiO 2 in the starting mixture was 0.21(or 0.28):0.8(or 1.1):8.0, where the added amounts of Li and Mg, relative to the amount of SiO 2 , were decreased to 15 % (or 20 %) from the Li : Mg : Si ratio of 1.4 : 5.6 : 8.0 that was reported to formation of individual Hect crystals for remaining silica sphere as the core parts ,. Because urea decomposes to NH 3 and CO 2 upon being heated in aqueous solution, a precursor of Hect as soluble silicate was supplied from the spherical silica particles by increasing the solution pH (Figure ).…”

“…We estimated the portion of Hect in silica@Hect hybrids using the exchange reactions of interlayer exchangeable cations in Hect with a cationic surfactant (2C 18 : di(octadecyl)‐dimethylammonium) ,. When the molar ratio of LiF : MgCl 2 :SiO 2 in the starting mixture was 0.21 : 0.8 : 8.0, the adsorbed amount of 2C 18 was 0.11 mmol/g.…”

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

“…In that process the silica particles were found to be consumed through hydrothermal reactions without losing the silica morphology, and the silica that was consumed was found to be used as the source of the smectite. [56] allowed the size of the Hect on the silica to be the negative-layer charge density of the Hect on the silica to be varied, from 0.5 to 0.9 mEq/g of Hect. The topochemical expansion of the Silica@Hect core-shell particles occurred when cationic surfactants were intercalated into the Hect via ion-exchange reactions.…”