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几种离子和纳米粒子在水油界面吸附过程的二次谐波研究
吴畏
学位类型博士
导师干为
2016-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理化学
关键词水-油界面 二次谐波 Zeta电位 表面活性剂 氢氧根离子 氢离子 纳米粒子
摘要

研究离子、分子和纳米粒子与水-油界面的相互作用,对理解含油污水处理过程中涉及的水-油稳定机制至关重要。本论文主要使用具有界面选择特性的二次谐波(SHG)技术,结合Zeta电位表征,研究离子、表面活性剂分子及纳米粒子在水-油界面的吸附动力学过程。第一部分为全内反射构型SHG实验样品池对测量精度的影响。通过理论分析和实验测量,发现当水-油界面高度发生微小变化时,用文献中常用的圆形样品池在全内反射构型下研究物质对界面SHG信号的影响时会产生误差,应选用方形样品池进行实验。本实验对于设计合理的样品池,准确测量界面SHG信号具有重要的意义。第二部分为常见表面活性剂在水-油界面吸附过程的研究。通过SHG方法和Zeta电位表征研究了两种水溶性表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)在十六烷-水界面的吸附过程,观测到了以疏水长链离子为主的初始吸附过程,之后为对离子和疏水长链离子共同吸附的过程。根据对离子影响较小的初始吸附过程合理地估算了表面活性剂在界面的吸附自由能。此外,利用SHG方法分析了两种油溶性表面活性剂油酸和油胺在十六烷-水界面的吸附过程,并计算了相应的吸附自由能。最后通过离子强度实验分析了界面SHG信号来源于界面电场存在下水分子的取向。本实验证明SHG方法研究表面活性剂在水-油界面的吸附十分灵敏,为进一步深入研究其对水-油界面的作用奠定了理论基础。第三部分内容研究了OH-离子和H+离子在水-油界面的吸附性能。SHG方法结合Zeta电位表征发现界面对OH-离子具有特性吸附,而对H+离子则无特性吸附,并通过理论分析得到了二者吸附性能差异的原因。本工作澄清了长期以来水-油界面负电位来源的争议,并理清了OH-离子和H+离子在界面的吸附性能。第四部分在以上表面活性剂和离子对界面SHG信号影响的基础上,研究了纳米粒子在水-油界面的吸附过程。运用SHG方法初步考察了带不同电荷的聚乙烯乳胶粒子、四氧化三铁纳米粒子和蒙脱土在水-油界面的吸附动力学过程,为今后研究纳米粒子与水-油界面的作用找到了新的方法,同时为纳米粒子用于稳定水-油界面的机理探测奠定了理论基础。 综上所述,通过SHG方法结合Zeta电位表征分析了常用表面活性剂分子、离子和纳米粒子在水-油界面的吸附动力学过程、界面电位和界面分子结构,为从分子层次理解其他界面过程的机理提供了一种切实有效的方法,为含油污水处理奠定了理论基础。

其他摘要

Studying the effect of ions, molecules and nanoparticles on the properties of water-oil interfaces is crucial for understanding the stability of water-oil mixtures which significantly influences the water-oil separation process. This thesis mainly focuses on investigating the adsorption dynamics of ions, surfactants molecules and nanoparticles at water-oil interfaces utilizing surface-sensitive Second Harmonic Generation (SHG) technique and Zeta potential measurements.In the first part, the influence of sample cell on the accuracy of total internal reflection-SHG (TIR-SHG) measurement was studied. Through theory analysis and experiment measurements, it was found that with a commonly circle cell, a small height change of the water-oil interface would cause a big deviation of SHG signal. If a square cell was used, such deviation would be avoided. Therefore, square cell is a more appropriate choice for accurate TIR-SHG measurements.In the second part, the adsorption of several common surfactants at the hexadecane-water interface was presented. Through SHG and Zeta potential measurements, it was revealed that the adsorption of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) at the hexadecane-water interface was initialed by a step dominated by the adsorption of the hydrophobic part of the surfactant, and a latter step involved comparable contributions from both the hydrophobic part and the counter ion. The adsorption free energies involved in the initial step can be quantitatively analyzed. In addition, the adsorption of two oil soluble amphiphiles at the hexadecane-water interface was also studied. Analysis of the ionic strength dependent SHG signal at the hexadecane-water interface reveals that the origin of the SHG emission is mainly the water molecules at the interfacial layer. This study verifies the sensitivity of SHG technique for exploring the adsorption processes of surfactants at the water-oil interfaces.In the third part, by probing the SHG signal radiated from the reoriented water molecules at the hexadecane-water interface and Zeta potential at the surface of oil droplets in hexadecane-water emulsions, we investigated the adsorption of ions at this oil-water interface. It revealed that hydronium ions don't have specific affinities to the oil-water interface although hydroxide ions do. The difference in adsorption properties of hydroxide ions and hydronium ions were explained by theoretical study. A long-running debate about the source of negative potential at oil-water interfaces was clarified and the adsorption properties of hydroxide ions and hydronium ions were also revealed.In the last part, based on the effect of surfactants and ions on the SHG emission from oil-water interface, the adsorption of polystyrene, Fe3O4 and montmorillonite nanoparticles with different charges on the hexadecane-water interface was investigated. This method provides a new way for investigating the interaction between nanoparticles and oil-water interfaces. In conclusion, this thesis not only presents the adsorption dynamics of common surfactants, ions and nanoparticles at oil-water interfaces, but also analyzes the electric charge and molecular structure of the oil-water interfaces. The approaches in this work are ready to be applied in understanding the molecular level mechanisms of many other interfacial processes. This study lays a foundation for water-oil separation process.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4571
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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吴畏. 几种离子和纳米粒子在水油界面吸附过程的二次谐波研究[D]. 北京. 中国科学院大学,2016.
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