光催化和表面增强拉曼双活性AgX/Ag复合纳米结构的构建及原位光催化过程研究

Due to its good stability and high solar-energy utilization, AgX/Ag nanocomposite-based visible-light photocatalyst has been given widespread research in recent years, especially in applications like environmental decontamination, and may become an important supplement to traditional photocatalysts like TiO2. However, the following concerns must be issued before using this new photocatalyst in real environment conditions: (i) devoloping an effective way to control the size of synthesized AgX/Ag nanocomposite, as the reported procedures only give birth to AgX/Ag nanocomposite with diameter larger than 100 nm; (ii) understanding the mechanism of typical environment pollutants degradation on AgX/Ag nanocomposite; and (iii) uncovering the environmental behaviors of AgX/Ag nanocomposite in real environment conditions, including their migration, transformation and fate. The aim of this study is to combining the photocatalytic activity of AgX/Ag nanocomposite, the surface enhanced Raman scattering (SERS) activity of Ag nanostructure, and the structural characteristics of Ag nanoporous film to fabricate AgX/Ag hybrid nanoporous films with both high photocatalytic activity and high SERS activity. The constructed AgX/Ag nanostructure will function as a research platform for in-situ SERS study of the photocatalytic degradation process of typical persistent organic pollutants, such as polybrominated diphenyl ethers and chlorophenols. The key reaction intermediates and possible reaction pathway will be identified based on the Raman spectrum and quantum chemical calculations (DFT), and the toxicity of the identified intermediates will be predicted by Quantitative structure-activity relationship (QSAR) model. To assess the feasibility of applicating the fabricated nanostrcuture under real environmental conditions, the effects of some key environment factors such as temperature, ionic strength, pH and dissolved organic matters on the photocatalytic process will be evaluated, and the fate of the synthesized AgX/Ag nanocomposite will be also studied. The completion of this project will provide theoretical support for the safe and efficient utilization of the fabricated nanostructures for the degradation of environmental pollutants.

银半导体/银（AgX/Ag）催化体系因其高稳定性和高可见光利用率而受到了研究者广泛的关注，有望成为传统光催化剂如TiO2的重要补充，但目前尚无制备高活性的小粒径AgX/Ag纳米颗粒的有效方法，且AgX/Ag对典型污染物的光降解过程及其本身在实际环境中的迁移转化过程尚不清楚。本项目拟利用Ag纳孔膜的结构特性和光学活性，构建具有高催化活性和高表面增强拉曼散射(SERS)活性的AgX/Ag复合纳孔膜；以此纳米结构作为研究平台，利用SERS技术原位研究多溴联苯醚和氯酚等典型持久性污染物的可见光催化降解行为，并结合DFT计算识别出反应中间产物，揭示降解途径，利用QSAR评估上述中间产物的毒性；考察主要环境因素对降解过程的影响，研究AgX/Ag纳米结构在环境条件下的迁移转化行为。项目的实施，可为安全、高效地将AgX/Ag纳米结构用于去除实际环境中的污染提供理论依据和数据积累。

现有催化体系性能的改进和新型催化剂的设计依赖于人们对催化过程的认识， 因此深入研究环境污染物的催化降解过程，特别是利用各种原位技术监控环境催化过程以获得反应动力学和机理信息具有重要意义。因其具有高灵敏度、高分辨率、不受水分子干扰、样品制备简单、分析时间短和对样品损伤可控等优点， 表面增强拉曼光谱成为理想的化学反应过程监控/研究手段。本项目立足于构建（光）催化/表面增强拉曼双活性纳米结构，原位研究环境污染物的光催化降解过程。.项目在以下方面取得一定进展：. 发展了Ag纳米线自沉降成Ag纳孔膜作为SERS基底的新方法。构建的基底具有高表面均一性，低背景干扰等优点，其高SERS活性能够满足单分子检测的需要。进一步利用溶液合成和自沉降过程对材料的兼容性，提出了构建任务专一型SERS基底的概念，实现了砷的SERS检测和催化反应的SERS监控，证明了其可行性和应用前景。 . 利用Cl-对Ag NPF的氯化作用，构建了具有光催化/SERS双活性Ag@AgCl 结构，并据此完成了染料分子等污染物的光催化过程原位SERS研究，揭示了偶氮键的断裂时偶氮染料光降解的首要步骤。. 设计了Au纳米线表面包裹Pt亚原子层的新型SERS—催化双活性纳米结构。利用该体系，我们首次实现了苯硝基的催化还原过程的亚毫秒水平原位监控，并给出不依赖于偶氮中间体的反应机理。. 通过引入Ag原子单层，实现了壳层Pd原子构象由连续原子到高分散原子的调控，这一结果得到了SERS和EXAFS的支持。基于该材料，首次从实验上将催化剂的原子构象与催化 活性进行关联：高分散Pd原子是催化还原苯硝基的主要活性位点，而至少需要两个以上连续的Pd原子才能构成电催化氧化乙醇的活性中心。. 利用Au@Pd 和Ag@Pd为代表性催化剂，以4-NPT还原反应为模型反应，原位研究Au和Ag的SPR过程生成热电子促进该还原反应的可行性。揭示了SERS监测反应过程中可能存在的光促进反应效应，以及Ag基共振催化剂中可能因为Ag针孔的存在导致热电子被浪费，解释了长期以来Ag未用于共振催化的原因。. 设计了以Cu2O/N-掺杂石墨烯和N-掺杂TiO2/N-掺杂石墨烯为代表的新型肖特结型光催化剂，提高了光催化剂对可见光的利用效率和电子-空穴的分离效率，实现了高效可见光催化。