Nitric acid-mediated shape-controlled synthesis and catalytic activity of silver hierarchical microcrystals
Effective efforts have promoted the development of the shape-controlled synthesis of silver nanoparticles in past decades. However, there has been limited success in the morphology-controlled synthesis of silver microcrystals, especially large-scale synthesis in aqueous solutions. Here, a series of mono-dispersed silver hierarchical microcrystals (AgHMCs) with high yield has been prepared through reducing silver nitrate with L-ascorbic acid in nitric acid-mediated systems. Characterization revealed that the (111) face was a dominant crystal plane exposed on the surface of nano- or submicro- Ag plates, which then assembled to form AgHMCs. It is suggested that the oxidative etching effect of nitric acid and selective deposition of Ag atoms on different crystal facets mainly had an effect on the formation of AgHMCs. A survey on the AgHMCs-driven catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH4 revealed that the silver microcrystals with high surface areas or more spotless surfaces showed high vitality. Our work provides a deeper understanding of the shape-controlled synthesis of silver microcrystals for applications.