具吸附位硅烷在磁性纳米颗粒表面的单分子层自组装及其除磷性能研究

This project attempts to investigate a new method to self-assemble silanes holding adsorption sites, in the form of monolayer and perpendicular orientation, onto the surface of magnetite in water. Based on this method, the project will develop novel magnetic nanoparticle adsorbents. In silane-water-magnetite system, there exist two parallel reactions: the Si-O-Si coupling reaction between SiOH groups of monomer silanes and the Si-O-Fe coupling reaction between the SiOH group of monomer silane and FeOH group of magnetite. The former results in the formation of undesirable polymer, while the latter gives rise to the production of silane monolayer coated magnetite nanoparticles which are desirable. This project will probe into the characteristics of the kinetics of the two coupling reactions, such as the reaction order and the activation energy. Meanwhile, the present project will study the effect of dynamic conditions (silane concentration, temperature, pH, ionic strength etc) on the rate of the two reactions, so as to pursue the method to facilitate Si-O-Fe reaction while retard the Si-O-Si reaction in water. In addition, this project will explore the ways by which the monolayer silanes will adopt a perpendicular orientation on magnetite surface. Based on these studies, the current project will develop several kinds of self-assembled silane (having adsorption sites for phosphate) monolayer loaded magnetic nanoparticle adsorbents, followed by the investigation of the properties of the materials for phosphate removal..We believe that the implementation of this project will provide theoretical support for the fabrication of self-assembled monolayer on magnetic nanoparticles in water, to create new adsorbents.

本项目试图研究在水中将具吸附位的硅烷按单分子层和垂直取向方式自组装于磁铁矿表面的方法，研制出新型磁性纳米颗粒吸附剂。在硅烷—水—磁铁矿三组分体系中存在着两个平行反应：水中硅烷分子SiOH基团之间的Si-O-Si交联反应和硅烷分子SiOH基团与磁铁矿表面FeOH基团之间的Si-O-Fe交联反应。前者生成项目不需要的聚合物；后者产生所需要的单分子层硅烷包被的磁铁矿纳米颗粒。本项目将研究两个交联反应的的动力学特征（反应级数、活化能等），以及它们的反应速率对不同反应条件（硅烷浓度、温度、pH、溶液离子强度等）的响应，探索抑制水中Si-O-Si交联反应和促进Si-O-Fe交联反应的化学动力学调控方法。此外还将研究硅烷分子形成垂直取向的调控方法。通过研制具除磷吸附位的硅烷单分子层包被的磁性纳米颗粒吸附剂数种，验证其除磷性能。本项目的实施将为在水中构建自组装单分子层包被磁性纳米颗粒吸附剂提供理论支撑。

本项目以易于从水中分离和反复使用的、用于污水除磷的新型磁性纳米颗粒吸附剂的构建为目标，针对有机硅烷—水—磁铁矿三组分体系，研究了如何不让硅烷分子在水中发生Si-OH基团之间的Si-O-Si交联反应生成聚合物，而是以单分子层的形式在磁铁矿表面发生Si-OH基团与Fe-OH基团之间的Si-O-Fe交联反应这一关键科学问题，探索了有机硅烷在磁铁矿纳米颗粒表面的单分子层自组装有机改性调控技术。通过研究交联反应对外界条件（硅烷浓度、温度、溶剂、pH、离子强度等）的不同响应，发现保持低硅烷浓度、提高温度和离子强度是促进Si-O-Fe交联反应的有效手段。通过调控硅烷负载条件，成功获得了单层覆盖度达到~100%的动力学控制产物—自组装单分子层硅烷负载的磁性纳米颗粒吸附剂。研究表明，由于所有吸附位都位于吸附剂最外面，单层硅烷负载的磁性纳米颗粒吸附剂对磷，铬（六价）等含氧阴离子具有良好的吸附去除效果，特别是动力学过程极快：1分钟（六价铬）或1小时（磷）内达到吸附平衡。这与前人需要数小时甚至数天才达到吸附平衡的吸附剂相比，优越性突出。项目还研究了在磁性纳米颗粒硅烷改性后进一步负载水合金属氧化物，获得了除磷效果良好的新型磁性磷吸附剂。针对磁铁矿中Fe2+可被氧化、稳定性差的问题，研究了结构中不含变价中心原子的磁性纳米颗粒及内部掺稀土制备锌铁氧体和掺铈锌铁氧体磁性材料，为将来更好地制备结构稳定、除磷性能优良的硅烷负载磁性纳米颗粒创造了条件。项目研究揭示了以上数种磁性磷吸附剂的除磷机理，阐明了pH、离子强度、时间、竞争离子等各种溶液化学条件的影响、吸附剂的脱附再生与反复使用性能。本项目为在水中构建自组装单分子层包被磁性纳米颗粒吸附剂提供了理论依据和调控方法，对进一步研制可反复多次使用的其它磁性除磷材料具有重要参考意义。