Effect of Precursor Ligands and Oxidation State in the Synthesis of Bimetallic Nano-Alloys

The characteristics of bimetallic nanomaterials are dictated by their size, shape, and elemental distribution. Solution synthesis is widely utilized to form nanomaterials, such as nanoparticles, with controlled size and shape. However, the effects of variables on the characteristics of bimetallic nanomaterials are not completely understood. In this study, we used a continuous-flow synthetic strategy to explore the effects of the precursor ligands and the precursor oxidation state in the shape-controlled synthesis of platinum alloy nano-octahedra and show their effect on the nanoparticle size and the elemental distribution within the alloy nanoparticle. We demonstrate that this strategy can tune the size of monodisperse PtM (M = Ni or Cu) alloy nanocrystals ranging from 3 to 16 nm with an octahedral shape using acetylacetonate or halide precursors of Pt­(II), Pt­(IV), and Ni­(II) or Cu­(II). The nanoparticles formed from halide precursors showed an enrichment of platinum on their surfaces, and the use bromide ligands in the presence of air showed the formation of concave and uneven surface facets. The two nanocrystal precursors can be utilized independently and can control the size with a trend of Pt­(acac)2 < PtCl2 < PtCl4 < PtBr2 < PtBr4 and M­(acac)2 < MCl2 < MBr2 for the secondary metal (copper or nickel). These results open up avenues to understand the effect of the ligand shell of a precursor during the synthesis of alloy nanoparticles as well as to control, in a scalable manner, the nanomaterial size and surface chemistry.