BiOI基@磁载体可见光催化剂湿法光催化氧化脱除Hg0的机理研究

The key to the technique of controlling mercury pollution is an efficient oxidation of elemental mercury (Hg0), thus, the oxidation of Hg0 using wet photocatalytic technique under visible light is important for both theoretical research and future application. However, the mechanism of this technique is unclear. In this project, the experimental and mechanism study on wet photocatalytic oxidation of Hg0 using BiOI-based@magnetic carrier photocatalyst was investigated in detail. By adding a small amount of Cl or Br or Ag, the efficient BiOI-based heterogeneous photocatalysts were synthesized. The effects of preparation method, solvent, and the coupling mode between BiOI-based photocatalyst and magnetic carrier on Hg0 oxidation were investigated and optimized. To establish the essential relationship between structural characteristics and Hg0 oxidation activity, the physical and chemical structure of the photocatalyst and the evolution of active compositions before and after the reaction, as well as the complex compound of mercury and its speciation were explored by using a variety of characterization methods. The transfer rules of photogenerated electron-hole pairs over BiOI-based@magnetic carrier photocatalyst were clarified. The reactive species and the mechanism of wet photocatalytic oxidation of Hg0 under visible light were also elucidated, and then the macro-kinetics model on BiOI-based@magnetic carrier photocatalyst for higher Hg0 removal was established. The performances of desulfurization and Hg0 removal, as well as magnetic separation recovery of the photocatalyst were also investigated when a small amount of Ca(OH)2 was added. Through the above research, a reliable scientific basis for achieving the integrated removal of SO2 and Hg0 from coal-fired flue gas using sunlight can be provided.

燃煤烟气中单质汞的高效氧化是治理汞污染技术的关键，利用可见光湿法光催化技术氧化单质汞具有重要的研究价值和潜在的应用前景，但该技术的作用机理尚不清楚。本项目拟深入开展BiOI基@磁载体可见光催化剂湿法光催化氧化单质汞的机理研究。拟通过添加少量的Cl或Br或Ag构筑高效的异质结BiOI基光催化剂，研究制备方法、溶剂、BiOI基与磁载体耦合方式等对单质汞氧化的影响并进行优化；采用多种表征手段研究光催化剂的物化结构及反应前后活性成分的演变规律，明确汞的络合产物及其形态，构建结构特征与氧化活性之间的本质联系，揭示可见光下BiOI基@磁载体光催化剂光生电子-空穴对的转移规律；阐明湿法光催化氧化单质汞的活性物种及其作用机理，建立其高效脱汞的宏观反应动力学模型；研究氢氧化钙协同催化剂的脱硫脱汞性能及磁性光催化剂的磁回收特性，为利用洁净的太阳光进行燃煤烟气中SO2和汞的一体化脱除提供可靠的科学理论依据。

单质汞（Hg0）的有效脱除是当今燃煤烟气污染物控制领域的一大难题，研究高效、经济和环境友好的燃煤烟气汞污染物控制技术是能源与环境领域的热点。燃煤烟气中单质汞的高效氧化是治理汞污染技术的关键，利用可见光湿法光催化技术氧化单质汞具有重要的研究价值和潜在的应用前景，但该技术的作用机理尚不清楚。基于此，本项目采用沉淀法、研磨法和水热合成法制备出三种BiOI可见光催化剂，研究了制备方法对BiOI光催化剂脱汞性能的影响，研究了EDTA、EG、I/Bi摩尔比和碱液改性对BiOI光催化剂脱汞性能的影响，研究了Ag、Cl或Br等物质掺杂对BiOI基光催化剂脱汞性能的影响，对Ag、AgCl等负载量进行了优化；深入研究了银基（Ag、AgI、Ag2WO4、Ag2CO3和Ag2CrO4）改性磁性BiOI基可见光催化剂的脱汞性能；采用N2吸附-脱附、XRD、SEM、TEM、DRS、XPS、光电流、TGA、PL和ESR等技术对光催化剂进行了物理化学结构表征。研究结果阐明了制备方法、溶剂、BiOI基与磁载体耦合方式等对单质汞氧化的影响，获得了反应温度、溶液pH、烟气成分和可溶性无机阴离子等对系列光催化剂脱汞性能的影响及其作用机制，揭示了可见光辐照下磁性BiOI基光催化剂光生电子-空穴对在催化氧化反应中的流向和转移规律，明确了湿法光催化氧化脱除Hg0的活性物种、作用机制和汞的络合产物及其赋存形态，建立了可见光催化氧化Hg0的宏观反应动力学模型。铋基光催化剂可见光催化氧化单质汞过程中，最主要的活性物质是阴离子超氧自由基（•O2−）和空穴（h+），羟基自由基（•OH）的脱汞作用较小。开发出两种可见光下脱汞活性高、成分稳定的BiOI基光催化材料，它们具有广阔的商业应用前景。研究成果丰富了能源化工、环境科学、催化化学等理论知识，为燃煤烟气脱汞技术的发展提供了重要理论与科学基础。