Facile synthesis of rhodium icosahedra with controlled sizes up to 12 nm

We report a facile synthesis of Rh icosahedra with average sizes up to 12.0±0.8 nm through the use of a relatively slow reduction process. By using Rh(acac)₃ as a precursor to Rh and poly(vinyl pyrrolidone) (PVP) as a reducing agent, the reduction kinetics can be manipulated such to promote the formation of twin defects in the Rh nanocrystals. When Rh(acac)₃ is replaced by other precursors containing mono-dentate ligands, single-crystal Rh nanocrystals are obtained due to the acceleration of reduction rate. By increasing the molecular weight of PVP from 10000 to 1300 000, the resulting Rh nanocrystals are transformed from single-crystal octahedra to multiply twinned icosahedra and stacking-fault-lined plates. These results suggest that the successful preparation of Rh icosahedra could be facilitated by varying the binding strength of a ligand to Rh in the precursor and/or the molecular weight of PVP to optimize the reduction kinetics.