物理化学学报 >> 2007, Vol. 23 >> Issue (01): 32-36.doi: 10.3866/PKU.WHXB20070107

研究论文 上一篇    下一篇

甘氨酸在高岭土表面的吸附和热缩合反应

孟明;夏凌燕;郭丽红   

  1. 天津大学化工学院催化科学与工程系, 天津300072
  • 收稿日期:2006-07-17 修回日期:2006-08-04 发布日期:2007-01-08
  • 通讯作者: 孟明 E-mail:mengm@tju.edu.cn

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

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摘要： 采用TG/DTA、FT-IR和in situ DRIFT等技术对甘氨酸在高岭土表面的吸附和热缩合反应进行了表征, 考察了甘氨酸平衡浓度和溶液pH值对吸附行为的影响, 同时探讨了原位条件下甘氨酸的缩合反应历程. 结果表明, 溶液呈弱酸性时, 甘氨酸在高岭土上的吸附量最大, 但吸附等温线不符合Langmuir模型. 在强酸性、弱酸性和碱性溶液中, 吸附态的甘氨酸分别主要以阳离子、两性离子和阴离子形式存在. 弱酸性溶液中, 甘氨酸的—NH3+基团与高岭土表面的≡S—O−(S为Si或Al)基团之间的氢键作用是吸附的主要驱动力, 而强酸性溶液中, ≡S—O−基团的质子化, 以及碱性溶液中—NH3+向—NH2的转化, 是导致吸附量下降的主要原因. In situ DRIFT结果表明, 在110−160 ℃温区, 有明显的线式二肽形成; 随着温度升高至210 ℃时, 二肽进一步脱水, 形成环化缩合产物哌嗪二酮(DKP). 没有检测到硅酯类或铝酯类中间体的特征峰, 反应可能按氢键促进下的自缩合机理进行, 高岭土的存在使缩合反应温度有明显降低.

关键词: 甘氨酸, 高岭土, 吸附, 热缩合, 甘氨酸二肽, 哌嗪二酮

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