The solvent matters: kinetic versus thermodynamic shape control in the polyol synthesis of rhodium nanoparticles

The polyol process is one of the most common methods for synthesizing metal nanoparticles with controlled shapes and sizes due to its wide applicability and ease of use. These nanostructures often have unique morphology-dependent properties that are useful in a range of applications, including catalysis, plasmonics, and medical diagnostics and therapeutics. While many variations of the polyol process have been developed to produce shape-controlled nanoparticles, there has been no systematic investigation that defines the influence of the solvent on the shape and uniformity of the product. Here we show that proper selection of the polyol solvent can be used to manipulate the metal nanoparticle morphology. Each polyol has a different oxidation potential which, along with the metal reagent, defines the temperature at which particle formation takes place. For a given system, particle growth will vary between a kinetic and thermodynamic regime depending on the thermal conditions, which can be modulated through selection of the appropriate solvent. This strategy, which is demonstrated for the catalytically relevant rhodium system, facilitates the high-yield synthesis of monodisperse rhodium nanoparticles with shapes that include icosahedra, cubes, triangular plates, and octahedra.