Synthesis of Silver Nanoprisms with Variable Size and Investigation of Their Optical Properties: A First-Year Undergraduate Experiment Exploring Plasmonic Nanoparticles

Abstract

A robust and reasonably simple experiment is described that introduces students to the visualization of nanoscale properties and is intended for a first-year laboratory. Silver nanoprisms (NPs) that display different colors due to variation of their plasmonic absorption with respect to size are prepared. Control over the size of the silver nanoprisms is achieved using a novel approach, where bromide is added to the reaction as a size-determining agent, and silver ions are reduced by borohydride in the presence of citrate and peroxide as stabilizing and shape-directing agents, respectively. In a typical experiment, four dispersions of silver nanoprisms with different sizes are produced that are colored from blue (largest) to yellow (smallest). The colors attainable in between are violet, purple, red, and orange. The synthesis of these colored silver NPs is described for the first time as an undergraduate experiment. Once synthesized, the nanoprisms are characterized using UV−vis spectroscopy, and a Beer’s law experiment can be performed. Furthermore, concepts of redox chemistry and visible spectroscopy can be reinforced in this experiment, and it can be further adapted for upper-level laboratories focused on the investigation of nanoparticle properties by more advanced techniques.