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

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 crystal domain (the shell part) tended to be thin (fine crystals) when added LiF amount was small, resulting that the core‐shell samples had quite uniform size distributions . For example, the mean size of the of the hybrid prepared at the molar ratio of LiF : MgCl 2 : SiO 2 =0.21 : 0.8 : 8.0 was 1.16±0.02 μm, and this was larger than the initial silica particles (1.00±0.02 μm) without any change in the deviation.…”

“…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 ).…”

“…When powder silica is used as a starting material, mechanical mixing (∼1 day) has been employed at room temperature before the hydrothermal reaction (hydrolysis of urea and dissolution of silica gel do not occur below 70 °C). The hydrothermal reaction is often performed in a rotating Teflon‐lined autoclave, otherwise the size distribution of the hybrids became broad due to nonuniform coverage with Hect …”

“…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.…”