Formation of a kaolinite-serine intercalation compound via exchange of the pre-intercalated transition molecules in kaolinite with serine

Abstract A kaolinite-serine intercalation compound was synthesized via the guest displacement method. Serine molecules were intercalated into kaolinite to form kaolinite-serine through exchange between serine and the guest molecules ethylene glycol or water, which was inserted into the interlayer space of kaolinite beforehand. The thickness of kaolinite-serine particles decreased to 14 nm from 30 nm of raw kaolinite after intercalation. The interlayer distance of kaolinite reached approximately 1.13 nm after the intercalation of serine molecules. The serine molecules inserted in the interlayer space of kaolinite molecules were arranged in a flattened monolayer configuration and partially compressed into the tetragonal holes in the silicate layer. The activation energy Ea for releasing the pre-intercalated molecule before ultimate exchanging with serine determines the intercalation degree of serine into kaolinite. Higher Ea makes the expansion of kaolinite with pre-intercalated molecules more stable, which will facilitate the final intercalation of serine. The activation energy is 6.95 kJ/mol for ethylene glycol and 21.2 kJ/mol for water, respectively, resulting in serine intercalation degree of 45%, and 85% correspondingly. The kaolinite-serine intercalation compound is expected to be applied in the pharmaceutical and cosmetics fields.