Nano-Gold Desert Roses: An Engaging Dive into Nanostructure Wonders for Undergraduate and Graduate Students

We present an accessible and practical demonstration platform for undergraduate and graduate chemistry students, designed to facilitate the synthesis of gold nanoparticles with various shapes and to explore their remarkable structural, optical, and catalytic properties. Specifically, we demonstrate the rapid and straightforward creation of diverse supported and unsupported gold nanostructures, such as nanoflowers, nanoroses, nanocauliflowers, nanopillars, and even fractal formations, achieved simply by adding halides and/or a carbon paper support to an aqueous solution of gold(III). The fractal morphologies can be observed with the naked eye and under a standard microscope, while detailed examinations of the different nanostructures are accomplished using a Scanning Electron Microscope (SEM). The synthesized free nanostructures form colloidal solutions that display classical nanoparticle properties, including plasmonic colors, and also exhibit remarkable dichroic properties. When these nanostructures are dispersed in a polymer, they create a dichroic glass material with properties akin to the renowned Lycurgus Cup, with a distinctive blue-to-brown color change with light orientation. Additionally, the supported gold nanoroses serve to demonstrate electrochemical setups, such as lead underpotential deposition (UPD), which reveals surface types on the nanostructures, or glucose electrocatalysis: these gold nanostructures are shown to be efficient electrocatalysts for glucose electrochemical oxidation.