Anisotropic growth of gold nanocrystals induced by concerted adsorption using a photochemical approach

Abstract

Photochemical reduction of noble metal ions in the presence of stabilizers that selectively adsorb on different crystal planes is a fascinating method for synthesizing shape-controlled metal nanocrystals (NCs). In this study, we demonstrate the photoreduction of Au3+ ions in the presence of polyvinylpyrrolidone (PVP) and Br− ions, that are classified into different categories of protective agents. Au nanoplates with atomically flat surfaces are obtained by the photoirradiation of an aqueous solution containing Au3+, PVP and Br−. Notably, PVP preferentially adsorbs along the perimeter, while Br− ions tend to adsorb on the flat top and bottom (111) faces. The selective adsorption of these structurally distinct stabilizers promotes two-dimensional growth of the Au nanoplates. PVP serves not only as a protective agent but also as a reduction agent in the photoreduction process. At high concentrations of Br− ions, the adsorption of the Br− ions also occurs at the perimeter, which kinetically traps the side growth of the nanoplates and leads to the formation of polygonal Au nanoplates. In other words, competitive adsorption of PVP and Br− at the facets and their density kinetically affect the shape of the formed Au NCs. This concept was successfully applied to control the photoreduction of Au3+ ions into icosahedral Au nanoparticles.