【摘要】 本文利用原位液体室透射电子显微镜实时观察了液态下金纳米棒/石墨烯复合物的动态自组装行为。结果表明,由于电荷吸引力,金纳米棒倾向于通过尖端接近方式靠近石墨烯的边缘。组装结构形成以后,金纳米棒与石墨烯边缘可以发生相对旋转,其中金纳米棒边缘贴合石墨烯边缘的结构更稳定,并且没有显示金纳米棒与石墨烯边缘之间的相对角度随时间的变化。观察到了自组装结构的漂移运动,与较小尺寸的自组装结构相比,较大尺寸的结构显得更难以通过液体流动推动运动,并且其运动更容易因为来自液体室窗口基底的阻力而慢下来。利用液体室透射电镜进一步观察石墨烯折叠结构,观察结果表明折叠结构可随时间在液体中打开和闭合,导致固定在石墨烯层上的金纳米棒表现出与石墨烯之间的明显相对位置变化。总体上,自组装结构非常稳定,并且在液体中没有表现出任何的分离行为。进一步,将金纳米棒/石墨烯复合物用作催化剂,在4-硝基苯酚催化还原实验中显示出比单纯金纳米棒更好的催化性能。投料质量比为1:5的金纳米棒/石墨烯复合物表现出最佳性能,表观速率常数值为0.5570min^-1,是单纯金纳米棒的8倍。这一显著改善与优化稳定的金纳米棒/石墨烯复合物结构密切相关。原位液体室透射电镜为分析液体中复杂的自组装行为,及未来的高性能复合催化剂材料的开发,提供了一种强有力的表征方法。更多还原

【Abstract】 In situ liquid cell transmission electron microscopy（LCTEM） was used to observe the dynamic self-assembly behavior of gold nanorod（Au NR）/graphene（G） composites in real-time. Many important reactions in chemistry, physics, and biology occur in solution and real-time imaging of the reaction objects in a liquid medium can further our understanding of the reaction at the nanoscale. Observations of liquid samples using transmission electron microscopy（TEM） have historically been challenging due to issues with evaporation and difficulty in forming thin liquid layers that are suitable for election beam transmission. In situ LCTEM, as an emerging technology, provides novel opportunities for the real-time and high-resolution observation of dynamic processes in solution. In this communication, we report the use of in situ LCTEM to study the assembly behavior of graphene and AuN Rs. By tracking and recording the changes in the positions and shapes of the AuN Rs and graphene over time, novel composite formation mechanisms between AuN Rs and graphene were observed. The AuN Rs tended to approach the graphene edges tip-first due to charge attraction. After the assembled structures were formed, the Au NRs could rotate with the graphene edges, among which the edge-to-edge structure was more stable, without angle changes between the AuN R and graphene edge. Drifting motions of the self-assembled structures were observed. And compared with smaller self-assembled structures, the larger structures seem more effectively resisted pushing by liquid flow. In addition, the motions of the larger structure were more easily slowed due to the drag from the liquid cell window substrate. Graphene folding structures were also observed with LCTEM, suggesting that the folding structure can open and close in the liquid, causing apparent relative position changes between Au and graphene for a fixed AuN R on the graphene layer. Overall, the self-assembled structures are very stable and did not show any disassembly behavior in the liquid. Moreover, the AuN R/graphene composites were used as catalysts and showed improved catalytic performance compared to that of bare AuN Rs in 4-nitrophenol reduction experiments. The self-assembled catalyst with a mass composite 1 : 5 Au NRs/G ratio exhibited the best performance with a kapp value of 0.5570 min^-1, 8 times that of the bare AuN Rs. This significant improvement is closely related to the optimized and stable structure of the AuN R/graphene composites. In situ LCTEM provided a powerful characterization method for analyzing the complex self-assembly behavior of the composites in a liquid and will be useful for the development of high performance composite catalyst materials.更多还原