Shape Evolution of Octahedral and Triangular Platelike Silver Nanocrystals from Cubic and Right Bipyramidal Seeds in DMF

Octahedral and triangular platelike silver (Ag) nanocrystals were synthesized using cubic and right bipyramidal nanocrystals as seeds using a two-step preparation method. First, cubic and right-triangular bipyramidal Ag nanocrystals with {100} facets were prepared by reducing AgNO3 in ethylene glycol (EG) in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant under oil-bath heating. Subsequently, the obtained Ag seeds were added to N,N-dimethylformamide (DMF) solution containing Ag+ ions for overgrowth of Ag crystals with {111} facets. Transmission electron microscope (TEM) observations show that Ag octahedra and triangular plates were formed, respectively, from Ag cubic and bipyramidal seeds. It is found that the average size of Ag octahedra is about 14% smaller than that expected from original sizes of the Ag cubes, although that of Ag triangular plates agreed with that expected from that of the Ag bipyramids. This is explainable by oxidative etching of the corner at the second step. Results show that it is possible to prepare Ag nanocrystal structures with {111} facets in DMF that is generally difficult to prepare using conventional methods.