Abstract:
Intercalation of amino acids into 10.0-A hydrated kaolinite was studied by powder X-ray diffraction (XRD), differential thermal analysis-thermal gravimetry (DTA-TG), and infrared (IR) spec-troscopy. 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 13-alanine ({3-Ala), and 12 M for both ",/-aminobutyric acid ('y-Aba) and g-aminovaleric acid (g-Ava). e-aminocaproic acid (e-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 H20 content. The compositions of the intercalates of the Gly and [3-Ala are AlzSi2Os(OH)4-(Gly)0.67.0.24H20 and AIzSi2Os(OH)4.([~-Ala)0.63.0.25H20, respec-tively, based on TG data. From IR data, Gly and [3-Ala molecules are found intercalated as zwitterions and these molecules form hydrogen bonds with both the A1-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 concen-tration and conditions.