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考察了甘氨酸水溶液平衡浓度和pH值对其在SiO2 表面吸附行为的影响,采用DTG ,XRD和FT IR等手段对甘氨酸在SiO2 表面的吸附量及晶相结构等进行了表征.结果表明,甘氨酸在SiO2 上的吸附不符合Langmuir吸附模型,当甘氨酸水溶液平衡浓度小于0 0 73mol/L时,主要为特定位置吸附,此时SiO2 对甘氨酸的吸附源于其表面≡Si-O-基团与甘氨酸离子的-NH+3 端的相互作用;当平衡浓度大于0 0 73mol/L时,呈多层吸附,形成α和β两种晶型的甘氨酸.用TPD MS对甘氨酸的热缩合行为进行了考察,结合FT IR结果表明,产物为环状二聚体哌嗪二酮(DKP) ,没有检测到线式二聚体以及表面硅酯类物种形成.SiO2 对表面吸附的甘氨酸分子产生了诱导活化,使其热缩合温度与体相α甘氨酸相比降低了5 0℃左右.
The effects of equilibrium concentration and pH value of glycine aqueous solution on the adsorption behavior on SiO2 were investigated, and the adsorption capacity and crystal structure of glycine on SiO2 were characterized by DTG, XRD and FT IR. The results showed that When the equilibrium concentration of glycine aqueous solution is less than 0 0 73mol / L, the adsorption on SiO2 is not suitable for the adsorption of glycine. At this time, the adsorption of glycine on SiO2 originates from the surface of the ≡Si-O- group and glycine ion -NH + 3-terminal interaction.When the equilibrium concentration is more than 0 0 73mol / L, it is multi-layer adsorption to form glycine in both α and β forms.The thermal condensation behavior of glycine was investigated by TPD MS, FT IR results showed that the product was cyclic dimer piperazine diketone (DKP), no linear dimer was detected and the formation of surface silicon ester species.SiO2 induced activation of glycine adsorbed on the surface, making it The thermal condensation temperature is about 50 ℃ lower than the bulk α-glycine.