Extended gold nano-morphology diagram: synthesis of rhombic dodecahedra using CTAB and ascorbic acid

The shape control of gold nanoparticles is still one of the most important challenges remaining to achieve geometry-dependent properties. Thus far, several strategies have been developed to control the shape of nanoparticles, such as adding capping agents and diverse additives or adjusting the temperature and pH. Here, we used an already established seed-mediated method which allowed us to focus on controlling the growth stage. Cetyltrimethylammonium bromide (CTAB) and ascorbic acid (AA) were used as the ligand and the reducing agent, respectively, without using any additional additives during the growth stage. We investigated how the relative ratio of CTAB and AA concentrations can be a major determinant of the nanoparticle shape over wide concentration ranges of CTAB (15 mM to 45 mM) and AA (3 mM to 71 mM). As a result, a morphology diagram was constructed experimentally which covers the growth conditions of rods, cuboctahedra, cubes and rhombic dodecahedra. The trends in the morphology diagram emphasize the importance of the interplay between CTAB and AA and can provide useful guidelines for designing various faceted geometries. Furthermore, we demonstrated the synthesis of rhombic dodecahedral gold nanocrystals in a CTAB and AA system for the first time.