Abstract

Intercalation of amino acids into 10.0-Aa 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 H 2 O content. The compositions of the intercalates of the Gly and beta -Ala are Al 2 Si 2 O 5 (OH) 4 . (Gly) (sub 0.67) . 0.24H 2 O and Al 2 Si 2 O 5 (OH) 4 . (beta -Ala) (sub 0.63) . 0.25H 2 O, respectively, based on TG data. From IR data, Gly and beta -Ala molecules are found intercalated as zwitterions and these molecules form hydrogen bonds with both the Al-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.

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