MgAl-Layered Double Hydroxide Films on Muscovite Mica: Epitaxial Growth and Catalytic Activity in Acetone Self-Condensation

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.

Flame-retardant and smoke-suppressing wood obtained by the in situ growth of a hydrotalcite-like compound on the inner surfaces of vessels

MgAl-CO₃²⁻-LDH was directly grown on the inner surfaces of wood vessels via a one-step hydrothermal process, which greatly enhanced the flame retardant and smoke suppression properties of the wood.

Preparation of Nickel-Aluminum-Containing Layered Double Hydroxide Films by Secondary (Seeded) Growth Method and Their Electrochemical Properties

Thin films of nickel-aluminum-containing layered double hydroxide (NiAl-LDH) have been prepared on nickel foil and nickel foam substrates by secondary (seeded) growth of NiAl-LDH seed layer. The preparation procedure consists of deposition of LDH seeds from a colloidal suspension on the substrate by dip coating, followed by hydrothermal treatment of the nanocrystals to form the LDH film. The secondary grown film is found to provide a higher crystallinity and more uniform composition of metal cations in the film layer than the in situ grown film on seed-free substrate under identical hydrothermal conditions. A systematic investigation of the film evolution process reveals that the crystallite growth rate is relatively fast for the secondary grown film because of the presence of LDH nanocrystal seeds. Electrochemical performance of the resulting NiAl-LDH films as positive electrode material was further assessed as an example of their practical applications. The secondary grown film electrode delivers improved recharge-discharge capacity and cycling stability compared with that of the in situ grown film, which can be explained by the existence of a unique microstructure of the former. Our findings show an example for the effective fabrication of LDH film with controllable microstructure and enhanced application performance through a secondary (seeded) growth procedure.