【作者】 夏凌燕；

【导师】 孟明；

【作者基本信息】 天津大学 ， 工业催化， 2007， 硕士

【摘要】 采用水溶液吸附法,在不同pH值和不同初始浓度条件下制备了一系列甘氨酸/高岭土（Gly/Kao）和甘氨酸/蒙脱土（Gly/MMT）样品,考察了甘氨酸在高岭土及蒙脱土上的吸附行为及浓度和pH值对吸附行为的影响。通过TG/DTA、XRD、透射红外（FT-IR）、漫反射红外（DRIFT）及原位漫反射红外（in-situ DRIFT）等多种表征手段,探讨了甘氨酸与不同载体的相互作用模式以及在加热条件下的热缩合反应历程。（1）甘氨酸在高岭土上的吸附结果表明,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110¹60oC温区,有明显的线式二肽形成;随着温度升高至210oC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明显降低。（2）甘氨酸在蒙脱土上的吸附曲线不符合Langmuir模型。pH值越低,甘氨酸在蒙脱土上的吸附量越大。在强酸性溶液中,整个甘氨酸阳离子与蒙脱土中的Na⁺发生阳离子交换,进入蒙脱土的层间,使得吸附量增大;而在弱酸或碱性溶液中,甘氨酸以两性离子或阴离子形式存在,使得阳离子交换性能下降,并且-COO-与蒙脱土表面的≡S-O-（S为Si或Al）基团产生静电排斥,在此情况下,甘氨酸在蒙脱土上的吸附量大大下降。高吸附量时,甘氨酸发生了多层吸附,由于蒙脱土的诱导作用使氢键重构,使α-甘氨酸转化为γ-甘氨酸;TG/DTA显示蒙脱土能够明显降低甘氨酸热缩合反应温度,负载量越低,反应温度越低,蒙脱土的催化作用越明显。In-situ DRIFT结果表明,温度在160℃左右时,两个甘氨酸分子脱水生成哌嗪二酮（DKP）,整个反应中没有检测到线式的二聚体。也没有检测到硅酯类或铝酯类中间体的特征峰。更多还原

【Abstract】 A series of adsorption experiments of glycine on kaolinite and montmorillonite were performed in aqueous solution at different initial concentrations and pH values (acidic/netural/basic). The samples were dried at room temperture, and then characterized by several techniques of XRD、TG/DTA、FT-IR、DRIFT and in-siu DRIFT.(1) The results of the adsorption experiments of glycine on kaolinite indicate that the weakly acidic solution favors the adsorption most, and gives the largest adsorption amount; however, the adsorption isotherm does not meet the Langmuir model. FT-IR results show 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 are the main reason for the decrease of adsorption amount. The in-situ DRIFT results reveal that the linear dimer of glycine is formed during 110~160oC region. Up to 210 oC, the dimer undergos 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 is 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.(2) The adsorption isotherm of glycine on montmorillonite does not meet the Langmuir model. The lower pH value is, the more adsorption amount adsorbed on the support; In the strongly acidic solutions, the glycine exists in the form of cation, which can exchange with Na+ in montmorillonite, and enter into the inter-layer of montmorillonite. This should be the main reason for the high adsorption amout; in weakly acidic and basic solutions, the glycine exists in the form of zwitterion and anion respectively, and the capability of cation exchange decreases. The static repulsion between -COO- and≡S-O- groups is the main reason for the decrease of adsorption amount. At high adsorption amount, the multi-layer adsorption phenomena are observed, which leads to the precipitation and crystallization ofγ-glycine on montmorillonite. The results of TG/DTA indicate that the presence of montmorillonite could decrease the temperature of condensation reactions. The lower the adsorption amount is, the lower the reaction temperature is. The in-situ DRIFT results reveal that the cyclodimer diketopiperazine is formed at about 160oC. During the reaction, no any evidence for the formation of R-CO-O-S (S=Si or Al) intermediates from the esterification reaction and the linear dimer of glycine are found.更多还原