The Role of Iodide in the Formation of Gold Nanotriangles

Abstract

Gold nanotriangles, one of a family of nanoprisms, have attracted a great deal of interest due to their promising applications in catalysis, electronics, imaging, diagnostics, and photothermal therapy. The crucial role of iodide in the formation of anisotropic gold nanotriangle (AuNT) has been assigned to the inhibition of Au(111) facet growth and as a digestion agent (as I₃^–) of non-nanotriangle impurities. However, neither I^– nor I^3– are detectable in the reaction conditions of the growth solution. Instead, an Au(I) complex, [AuI_yCl_2–y]^-, has been identified for the first time as a synthetic precursor of Au nanotriangles. This complex forms in solution on mixing AuCl₄^–, I^–, and ascorbic acid. [AuI_yCl_2–y] is readily reduced by ascorbic acid to form in situ AuNP seeds. Preferential adsorption of in situ generated I^– on the Au(111) facets of the Au(0)NP seeds, relative to the Au(100) edges of a developing plate, results in the selective growth of the latter compared to the former. Control of the formation and reaction conditions of this precursor complex provides an entry point to the sought-after reproducible, one-pot synthesis of AuNT. This refinement of the role of iodide introduces approaches to control the outcomes of the metal nanoparticle synthesis.