Preparation of kaolinite-amino acid intercalates derived from hydrated kaolinite

Intercalation of amino acids into 10.0-Angstrom hydrated kaolinite was studied by powder X-ray diffraction (XRD), differential thermal analysis-thermal gravimetry (DTA-TG), and infrared (IR) spectroscopy. Intercalation was found to be dependent on the chain-length, pH, and the concentration of the amino acid zwitterion. Near the isoelectric point, fully intercalated phases were obtained in solutions of concentration >0.5-1 M for glycine (Gly), 2-3 M for beta-alanine (beta-Ala), and 12 M for both gamma-aminobutyric acid (gamma-Aba) and delta-aminovaleric acid (delta-Ava). epsilon-aminocaproic acid (epsilon-Aca) with a long chain (C = 6) was only partially intercalated. Intercalated amino acid formed a mono-molecular arrangement with the alkyl chain tilting toward the layer at an angle related to H2O content. The compositions of the intercalates of the Gly and beta-Ala are Al2Si2O5(OH)(4).(Gly)(0.67).0.24H2O and Al2Si2O5(OH)(4).(beta-Ala)(0.63).0.25H2O, respectively, based on TG data. From IR data, Gly and P-Ala molecules are found intercalated as zwitterions and these molecules form hydrogen bonds with both the AI-OH and Si-O surfaces of kaolinite. Washing the intercalate with water produced a hydrated kaolinite, which may form a second amino-acid intercalate of high order. Thus, hydrated kaolinite intercalates or deintercalates amino acids depending on concentration and conditions.