Monitoring of Galvanic Replacement Reaction between Silver Nanowires and HAuCl4 by In Situ Transmission X-ray Microscopy

Galvanic replacement reaction between silver nanowires and an aqueous solution of HAuCl4 has been successfully monitored in real time by using in situ transmission X-ray microscopy (TXM) in combination with a flow cell reactor. The in situ observations clearly show the morphological evolution of the solid silver nanowires to hollow gold nanotubes in the course of the reaction. Careful analysis of the images reveals that the galvanic replacement reaction on the silver nanowires involves multiple steps: (i) local initiation of pitting process; (ii) anisotropic etching of the silver nanowires and uniform deposition of the resulting gold atoms on the surfaces of the nanowires; and (iii) reconstruction of the nanotube walls via an Ostwald ripening process. The in situ TXM represents a promising approach for studying dynamic processes involved in the growth and chemical transformation of nanomaterials in solutions, in particular for nanostructures with dimensions larger than 50 nm.

通过结合原位透射X射线显微镜（TXM）与流动细胞反应器，成功实现了银纳米线与HAuCl4水溶液之间电化学置换反应的实时监测。原位观察清晰地揭示了固态银纳米线在反应过程中向空心金纳米管形态的演变。对图像的细致分析揭示了银纳米线上的电化学置换反应涉及多个步骤：（i）局部坑蚀过程的启动；（ii）银纳米线的各向异性腐蚀及其结果金原子的均匀沉积在纳米线表面；（iii）通过奥斯瓦尔德成熟过程重构纳米管壁。原位TXM为研究溶液中纳米材料的生长和化学转化过程中的动态过程提供了一种有前景的方法，尤其是对于尺寸大于50 nm的纳米结构。