Facile Synthesis of Silver Nanocubes with Sharp Corners and Edges in an Aqueous Solution

It remains a challenge to synthesize Ag nanocubes in an aqueous system, although the polyol process was successfully adopted more than one decade ago. Here, we report an aqueous method for the synthesis of Ag nanocubes with an average edge length of 35-95 nm. It involves the formation of AgCl octahedra by mixing CF₃COOAg with cetyltrimethylammonium chloride, followed by the nucleation and growth of Ag nanocrystals in the presence of ascorbic acid (AA) and FeCl₃. The Fe³⁺/Fe²⁺ redox pair is responsible for the removal of multiply twinned seeds through oxidative etching. The Cl^- ions play two critical roles in the nucleation and growth of Ag nanocubes with a single-crystal structure. First, the Cl^- ions react with Ag⁺ ions to generate nanometer-sized AgCl octahedra in the initial stage of a synthesis. In the presence of room light and a proper reducing agent such as AA, the AgCl can be reduced to generate Ag_n nuclei followed by their evolution into single-crystal seeds and then Ag nanocrystals. Second, the Cl^- ions can act as a specific capping agent toward the Ag(100) surface, enabling the formation of Ag nanocubes with sharp corners and edges. Based on the results from a set of time-lapse studies and control experiments, we formulate a plausible mechanism to account for the formation of Ag nanocubes that resembles the formation and development of latent image centers in silver halide grains in the photographic process.