Acta Phys. -Chim. Sin. ›› 2007, Vol. 23 ›› Issue (01): 32-36.doi: 10.3866/PKU.WHXB20070107

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Adsorption and Thermal Condensation of Glycine on Kaolinite

MENG Ming;XIA Ling-Yan;GUO Li-Hong   

  1. Department of Catalysis Science and Technology, School of Chemical Engineering and Technology, Tianjin University , Tianjin 300072, P. R. China
  • Received:2006-07-17 Revised:2006-08-04 Published:2007-01-08
  • Contact: MENG Ming E-mail:mengm@tju.edu.cn

Abstract: Glycine was adsorbed on the surface of kaolinite from aqueous solution with variable concentrations and pH values. The TG/DTA, FT-IR and in situ DRIFT techniques were employed to characterize the adsorption and thermal condensation performances of glycine on kaolinite. The results of the adsorption experiment indicated that the weakly acidic solution favored the adsorption greatly, and gave the largest adsorption amount, however, the adsorption isotherm did not meet the Langmuir model. FT-IR results showed that in the strongly acidic, weakly acidic, and basic solutions, the glycine exists in the form of cation, zwitterion, and anion, respectively. In the weakly acidic solution, the hydrogen bond interaction between —NH3+ and ≡S—O− groups should be the driving force of the adsorption, the hydroxylation of ≡S—O− group in strongly acidic solution and the conversion of —NH3+ to —NH2 in the basic solution were the main reasons for the decrease of adsorption amount. The in situ DRIFT results revealed that linear dimer of glycine was formed during 110−160 ℃ region. Up to 210 ℃, the dimer underwent further intra-molecular condensation to form the cyclodimer diketopiperazine (DKP). During the reaction, no any evidence of the formation of R—CO—O—S(S=Si or Al) intermediates from the esterification reaction was found. The reaction should proceed by the self-condensation mechanism promoted by the hydrogen bond interaction between glycine and kaolinite. The presence of the kaolinite has remarkably decreased the temperature of the condensation reaction.

Key words: Glycine, Kaolinite, Adsorption, Thermal condensation, Glycylglycine, Diketopiperazine