Monoalcohol-Directed Shape Control in a Surfactant-Free Gold Nanoplate Synthesis

Incorporating shape-directing additives in colloidal syntheses has proved critical in exerting architectural control over noble metal nanostructures, but these same additives can prove problematic in downstream processing and applications. This deficiency has led to the emergence of a class of synthetic protocols, referred to as surfactant-free syntheses, that mitigate these issues by using reagents that realize nanoparticle surfaces that are unencumbered by persistent shape-directing agents. Polyol- and monoalcohol-based growth solutions have proven highly effective in this regard; however, shape-control in the absence of additives has proved elusive. Herein, a seed-mediated photochemical synthesis is demonstrated that can form arrays of highly faceted gold nanoplates in a room-temperature growth solution of HAuCl₄, water, and a monoalcohol. Wavelength-dependent characterization and first-principles density functional theory (DFT) calculations provide insights into the photoredox and shape-control mechanisms responsible for the unexpected emergence of nanoplates. It is demonstrated that the illumination of the growth solution is the key driver of nanoplate growth. DFT calculations indicate that two-dimensional growth stems from the {111} surface-selective co-adsorption of the monoalcohols and chlorine. Taken together, this work establishes the viability of a shape-controlled monoalcohol-based synthesis and advances the mechanistic framework needed to direct nanometal growth trajectories along pathways yielding planar geometries.