The Role of Iodide\nin the Formation of Gold Nanotriangles

Gold nanotriangles, one of a family of nanoprisms, have\nattracted\na great deal of interest due to their promising applications in catalysis,\nelectronics, imaging, diagnostics, and photothermal therapy. The crucial\nrole of iodide in the formation of anisotropic gold nanotriangle (AuNT)\nhas been assigned to the inhibition of Au(111) facet growth and as\na digestion agent (as I<sub>3</sub><sup>–</sup>) of non-nanotriangle\nimpurities. However, neither I<sup>–</sup> nor I<sup>3–</sup> are detectable in the reaction conditions of the growth solution.\nInstead, an Au(I) complex, [AuI<sub><i>y</i></sub>Cl<sub>2–<i>y</i></sub>]<sup>-</sup>, has been identified\nfor the first time as a synthetic precursor of Au nanotriangles. This\ncomplex forms in solution on mixing AuCl<sub>4</sub><sup>–</sup>, I<sup>–</sup>, and ascorbic acid. [AuI<sub><i>y</i></sub>Cl<sub>2–<i>y</i></sub>] is readily reduced\nby ascorbic acid to form <i>in situ</i> AuNP seeds. Preferential\nadsorption of <i>in situ</i> generated I<sup>–</sup> on the Au(111) facets of the Au(0)NP seeds, relative to the Au(100)\nedges of a developing plate, results in the selective growth of the\nlatter compared to the former. Control of the formation and reaction\nconditions of this precursor complex provides an entry point to the\nsought-after reproducible, one-pot synthesis of AuNT. This refinement\nof the role of iodide introduces approaches to control the outcomes\nof the metal nanoparticle synthesis.