表面修饰强化铁基纳米颗粒的分散性及催化还原性研究

Zero-valent iron (ZVI) technology, which has been successfully applied for removal of halogenated organic compounds in water pollution control, has gained wide acceptance as a promising remediation technology. Compared with microscale iron particles,iron-based nanoscale bimetallic particles that are post-coated with the second metal as a catalyst have obvious advantages, such as large specific surface areas, more active sites, and higher dehalogenation efficiency. Therefore, numerous attentions have been focused on catalytic dehalogenation of halogenated organic compounds (HOCs) by iron-based nanoscale bimetallic particles. However, the catalytic dehalogenation efficiency is inevitablly decreased due to aggregation of nanoparticles,especially in aqueous medium. At present, further research on effective dispersion of iron-based nanoscale bimetallic particles is of great concern. In this research project, several kinds of polymers，surfactants, or their combination systems, including poly- methylmethacrylate (PMMA), cetyltrimethylammoniumbromide (CTAB), poly(acrylic acid) (PAA), and composite polymer system are used as dispersants for surface modification of nanoscale Pd/Fe bimetallic particles based on electrostatic effect, stero hindrance effect, and electrostatic/steric hindrance effect. Iron-base bimetallic nanoparticles are prepared by liquid phase method, and modified by depositing the dispersants onto the surface. The objectives of this research are to decrease hard aggregation and to enhance stability of nanoscale Pd/Fe bimetallic particles. The dechlorination efficiency of chlorinated organic compounds (COCs) could be significantly increased by using the surface modified nanoscale Pd/Fe bimetallic particles with lower aggregation degree and more reactive sites.Chlorophenols are chosen as the target pollutants in this research. Some essential parameters of COC dechlorination by surface modified nanoscale Pd/Fe bimetallic particles, including the amount of polymer addtion,the concentration of modification solution, will also be investigated and optimized. The reaction kinetics and mechanisms of COC dechlorination are to be discussed. The results of this research are expected to provide useful theoretical information for application of Pd/Fe bimetallic nanoparticle system in decontamination of water polluted by COCs.

针对强化铁基纳米双金属颗粒对水中氯代有机物催化还原脱氯性能开展研究。旨在解决纳米双金属颗粒因硬团聚所引起的失活问题，研究目的是增强铁基纳米材料的分散性和稳定性，从而提高其对氯代有机物的反应活性，延长其有效使用寿命。研究方法为：以高分子聚合物或离子型表面活性剂等化合物(如聚甲基丙烯酸甲酯(PMMA)、 十六烷基三甲基溴化铵(CTAB)、瓜尔胶 和聚丙烯酸(PAA))对纳米颗粒进行表面修饰改性，分别利用表面修饰剂产生的静电稳定应用、空间位阻作用及静电位阻作用，减少纳米颗粒间的团聚度。 本项目研究有助于强化纳米材料在水性介质中的分散性，研发高效表面修饰剂复合体系，增加对表面修饰改性纳米颗粒脱氯机理的了解。同时探讨铁基纳米双金属颗粒分散改性的最优条件，并进一步揭示水中氯代有机物的催化还原脱氯动力学规律，为纳米零价铁技术去除水中氯代有机物理论的发展和实际工程应用提供科学依据。

本项目围绕克服铁基纳米颗粒在水中严重团聚问题及强化纳米铁还原性能方面展开深入研究。本项目的重要研究成果包括五方面内容：（1）分别以聚电解质、高分子聚合物、阴离子型表面活性剂等为分散剂，对铁基纳米颗粒进行表面化学修饰与功能化，有效提高纳米颗粒在液相中的分散性及稳定性，显著提高铁基纳米颗粒对水中难降解污染物的去除效率；（2）实现纳米铁绿色合成。在纳米铁合成过程中选择同时具有还原剂、分散剂、稳定剂和抗氧化物剂等多重作用的反应物，并辅以声纳化学，提高纳米铁制备的原子经济性；（3）以新型纳米铁基有机-无机复合材料实现纳米铁的负载固定，解决纳米铁的回收及再生循环利用问题，进而延长载铁复合材料的使用周期，降低因纳米颗粒流失进水体而导致的生态风险，并实现聚多巴胺自聚-附着行为对纳米NZVI-PVDF∙Al2O3功能化仿生修饰，为水中污染物去除提供环境友好型材料；（4）构建基于多组分协同效应的NZVI-KMnO4复合技术，可有效克服单独使用零价铁技术易造成铁离子或亚铁离子流失的弊端，同时防止对纳米铁表面形成钝化层而失活，从而有效保持纳米铁的反应活性；（5）探讨纳米铁还原性能受水环境条件的动态变化及随机的地球化学组分影响情况，从而促进零价铁技术在处理实际废水或受污染地下水治理方面的应用。