Highly monodisperse cubic and octahedral rhodium nanocrystals: Their evolutions from sharp polyhedrons into branched nanostructures and surface-enhanced Raman scattering

We report the preparation of poly(vinylpyrrolidone) (PVP)-protected Rh nanoparticles by modified polyol method with the reduction of RhCl₃ in ethylene glycol at 160 °C using AgNO₃. This method is used to synthesize highly cubic and octahedral Rh nanoparticles with their well-controlled size ∼714 nm characterized by transmission electron microscopy (TEM). At a low AgNO₃ concentration, the appearance of the sharply good morphology of Rh nanoparticles due to their controlled growth of {1 0 0} and {1 1 1} selective surfaces for ∼1015 min is observed. Their morphology between cubic and octahedral shape exhibits their competitive growth along the [1 1 1] and [1 0 0] directions. Interestingly, sharply and highly branched Rh nanoparticles with their shapes of very sharp corners or sharp-tip arms growing in the [1 1 1] directions are synthesized for ∼30 min at the same concentration of RhCl₃ and AgNO₃ precursors. However, at a higher concentration of AgNO₃, the assemblies of Rh multipods leading to large porous Rh nanoparticles are observed. The problems of reaction time and temperature are discussed to clarify the nucleation and growth of Rh nanoparticles. In addition, monolayers of Rh nanoparticles on SERS substrates using a probe as malachite green (MG) molecule exhibit the high sensitivity for their potential applications in chemical and biochemical sensing.