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Synthesis and reactivity of membrane-supported bimetallic nanoparticles for PCB and trichloroethylene dechlorination.

机译：用于PCB和三氯乙烯脱氯的膜负载双金属纳米颗粒的合成和反应性。

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摘要

Nanosized metal particles have become an important class of materials in the field of catalysis, optical, electronic, magnetic and biological devices due to the unique physical and chemical properties. This research deals with the synthesis of structured bimetallic nanoparticles for the dechlorination of toxic organics. Nanoparticle synthesis in aqueous phase for dechlorination studies has been reported. However, in the absence of polymers or surfactants particles can easily aggregate into large particles with wide size distribution. In this study, we report a novel in-situ synthesis method of bimetallic nanoparticles embedded in polyacrylic acid (PAA) functionalized microfiltration membranes by chemical reduction of metal ions bound to the carboxylic acid groups. Membrane-based nanoparticle synthesis offers many advantages: reduction of particle loss, prevention of particle agglomeration, application of convective flow, and recapture of dissolved metal ions.;The objective of this research is to synthesize and characterize nanostructured bimetallic particles in membranes, understand and quantify the catalytic hydrodechlorination mechanism, and develop a membrane reactor model to predict and simulate reactions under various conditions. In this study, the PAA functionalization was achieved by filling the porous PVDF membranes with acrylic acid and subsequent in-situ free radical polymerization. Target metal cations (iron in this case) were then introduced into the membranes by ion exchange process. Subsequent reduction resulted in the formation of metal nanoparticles (around 30 nm). Bimetallic nanoparticles can be formed by post deposition of secondary appropriate metal such as Pd or Ni. The membranes and bimetallic nanoparticles were characterized by: SEM, TEM, TGA, and FTIR. A specimen-drift-free X-ray energy dispersive spectroscopy (EDS) mapping system was used to determine the two-dimensional element distribution inside the membrane matrix at the nano scale. This high resolution mapping allows for the correlation and understanding the nanoparticle structure, second metal composition in terms of nanoparticle reactivity. Chlorinated aliphatics such as trichloroethylene and conjugated aromatics such as polychlorinated biphenyls (PCBs) were chosen as the model compounds to investigate the catalytic properties of bimetallic nanoparticles and the reaction mechanism and kinetics. Effects of second metal coating, particle size and structure and temperature were studied on the performance of bimetallic system. In order to predict reaction at different conditions, a two-dimensional steady state model was developed to correlate and simulate mass transfer and reaction in the membrane pores under convective flow mode. The 2-D equations were solved by COMSOL (Femlab). The influence of changing parameters such as reactor geometry (i.e. membrane pore size) and Pd coating composition were evaluated by the model and compared well with the experimental data.;KEYWORDS: Bimetallic nanoparticles, dechlorination, membrane reactor, polyacrylic acid, chlorinated organics
机译：由于独特的物理和化学性质，纳米尺寸的金属颗粒已成为催化，光学，电子，磁性和生物装置领域中的重要材料类别。这项研究涉及用于有毒有机物脱氯的结构化双金属纳米颗粒的合成。已经报道了用于脱氯研究的水相中的纳米颗粒合成。然而，在不存在聚合物或表面活性剂的情况下，颗粒可以容易地聚集成具有宽尺寸分布的大颗粒。在这项研究中，我们报告了通过化学还原结合到羧酸基团上的金属离子，在聚丙烯酸（PAA）功能化微滤膜中嵌入双金属纳米颗粒的新型原位合成方法。基于膜的纳米颗粒合成具有许多优势：减少颗粒损失，防止颗粒附聚，应用对流流动和重新捕获溶解的金属离子。本研究的目的是合成和表征膜中的纳米结构双金属颗粒，了解并了解量化催化加氢脱氯机理，并开发膜反应器模型以预测和模拟在各种条件下的反应。在这项研究中，通过用丙烯酸填充多孔PVDF膜并随后进行原位自由基聚合来实现PAA官能化。然后通过离子交换过程将目标金属阳离子（在这种情况下为铁）引入膜中。随后的还原导致形成金属纳米颗粒（约30nm）。双金属纳米粒子可以通过二次沉积适当的金属（例如Pd或Ni）形成。膜和双金属纳米颗粒的特征在于：SEM，TEM，TGA和FTIR。使用无标本漂移的X射线能量色散光谱（EDS）映射系统确定纳米尺度下膜基质内部的二维元素分布。该高分辨率映射允许相关性和理解纳米颗粒结构，就纳米颗粒反应性而言是第二金属成分。选择氯化脂肪族化合物（如三氯乙烯）和共轭芳族化合物（如多氯联苯）作为模型化合物，以研究双金属纳米粒子的催化性能以及反应机理和动力学。研究了第二金属涂层，粒径，结构和温度对双金属体系性能的影响。为了预测在不同条件下的反应，建立了二维稳态模型以关联和模拟在对流流动模式下膜孔中的传质和反应。二维方程由COMSOL（Femlab）求解。通过模型评估了反应器几何形状（即膜孔径）和Pd涂层组成等变化参数的影响，并将其与实验数据进行了比较;关键词：双金属纳米粒子脱氯膜反应器聚丙烯酸氯化有机物

著录项

  • 作者

    Xu, Jian.;

  • 作者单位

    University of Kentucky.;

  • 授予单位 University of Kentucky.;
  • 学科 Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 215 p.
  • 总页数 215
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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