In Situ Crystallization of Al-Containing Silicate Nanosheets on Monodisperse Amorphous Silica Microspheres

Monolayer Modification of Spherical Amorphous Silica by Clay Nanosheets

Clay-silica nanocomposite materials (CSiN) were prepared by an electrostatic interaction between negatively charged clay nanosheets and positively charged spherical silica, which was modified with an alkyl ammonium group by silane coupling. By optimization of the preparation conditions, 84% coverage of the silica surface by the clay nanosheets was achieved. Adsorption experiments using cationic porphyrin dyes on the CSiN revealed that the clay nanosheet covers the spherical silica as a single layer and does not detach from the silica surface under aqueous conditions. In addition, it turned out that the cationic porphyrin dye did not penetrate the space between the silica surface and the clay nanosheet. Porphyrin molecules were adsorbed only at the outer surface of the clay nanosheet without molecular aggregation even under the high-density adsorption conditions. By combining spherical silica and clay nanosheets, it is possible to prepare novel hybrid materials where the surface can act as a unique adsorption field for dyes.

Formation of moth-eye-like structures on silicon through in situ crystallization of layered Mg silicate

Coating subwavelength-scale pinnacles/thorns on surfaces usually results in antireflection, known as "moth-eye effect". However, fabrication of such coatings is often complicated and expensive. Herein, we present a bottom-up approach for forming a moth-eye-like structure on Si by directly growing layered Mg silicate using a one-step process. When an aqueous solution containing LiF, MgCl2, and urea is heated at 150 °C in the presence of Si, fine crystals of the layered silicate completely cover the Si surface. The resulting thorn-like structures reduce the reflectance of Si in the visible-wavelength range, exhibiting a graded-refractive index profile from air to the Si substrate. The antireflection feature is observed when the height of the thorns is 0.1 μm, which is equivalent to the crystal size of Mg silicate and is influenced by the heating temperature. The heating period is optimized to be 48 h to avoid coprecipitation of light-scattering fine particles, such as amorphous silica and Mg silicate, in excess quantities.

Hydrated Silicate Layer Formation on Mica-Type Crystals

This study aims to investigate the growth of a cation-exchangeable hydrated layer on the surface of mica-type silicates based on a synthetic fluorophlogopite and a natural muscovite. Through the reaction of a synthetic fluorophlogopite using LiF, MgCl₂, and a silica sol in water at 373 K for 48 h in the presence of urea, a hydrated phyllosilicate was formed on the fluoromica. As a result of examining the reaction in the alkali solution in the absence of Mg²⁺, the uptake of the silica sol would be included as a chemical process to begin the crystallization on fluorophlogopite because the lithium and ammonium ions (generated by urea hydrolysis) are known to contribute to enhanced adsorption. We found that the urea hydrolysis increased the pH, which, in turn, assisted the formation of magnesium hydroxide after the isomorphic substitution of Li⁺ for Mg²⁺. Bridging tetrahedral SiO₄ with a magnesium-lithium double hydroxide afforded a 1 nm silicate layer. This facilitated the hectorite-like hydrated silicate layer to adhere closely to both the crystal edge and the cleaved face of the synthetic mica, which was found to coat the surface homogeneously. Only surface crystals were found to form through this process. The layered silicates included exchangeable hydrated cations for the cation-exchange reactions to expand the interlayer space by a cationic surfactant, dimethyldistearylammonium. The layered silicate also adsorbed methylene blue as a cationic dye in the aqueous phase. Apart from fluoromica, the natural muscovite also provided the surface to grow hydrated silicate layers, as a crystal turned dense blue when reacted with methylene blue.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

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

Cation-exchangeable layered silicate nanosheet fine crystals covered thoroughly a commercially available silica fiber filter paper through hydrothermal reactions with LiF, MgCl₂ and urea.