Systematic Shape Evolution of Gold Nanocrystals Achieved through Adjustment in the Amount of HAuCl4 Solution Used

Past work on the synthesis of gold nanocrystals has revealed that changing the reaction cell potential enables particle shape evolution. Although various parameters in the Nernst equation has been used to achieve this, adjusting the metal precursor concentration has not been demonstrated before. Using the reported synthetic conditions with cetyltrimethylammonium chloride (CTAC) surfactants to grow gold nanocubes, rhombic dodecahedra, and octahedra as the starting points, fixing the ascorbic acid volume, and tuning the volume of HAuCl4 solution introduced allow the formation of the same series of crystal shape evolution from rhombic dodecahedral to trisoctahedral and cubic structures in the presence of a tiny amount of NaBr. In another series, by gradually increasing the HAuCl4 solution volume but fixing potassium iodide and ascorbic acid volumes, gold nanocrystals with tunable morphologies from octahedra to corner-truncated octahedra, edge- and corner-truncated octahedra, and rhombic dodecahedra can be synthesized. These results demonstrate that adjustment of the metal precursor concentration is also effective in metal particle shape control. Using spectral analysis, the formation of CTA–AuCl4 and CTA–AuCl2 complexes has been confirmed, so CTAC acts as a coordinating species to the metal source and provides halide ions to influence the overall cell potential. Thus, all species in the reaction mixture are noninnocent and are involved in redox chemistry. The strategy has been applied to the synthesis of small Cu nanocubes with tunable sizes and nanowires.