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.
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