Seed-mediated synthesis of Pd nanocrystals: Factors influencing a kinetic- or thermodynamic-controlled growth regime

Palladium nanoparticles with defined morphologies were synthesized using a seed-mediated approach in the presence of cetyltrimethylammonium bromide (CTAB). This seeding technique, already applied to Ag and Au nanostructures, was successfully extended here to Pd, a noble metal with important applications in catalysis. Various types of morphologies were obtained going from 0-D nanocrystals (cubes, icosahedral multiply twinned particles) to 1-D (nanorods) and 2-D nanocrystals (triangular nanosheets). Palladium nanorods were obtained in a relatively high yield and present a well-defined 5-fold symmetry similar to that reported previously for Ag and Au. Embedding the PdCl42- precursor inside CTAB micelles was found to be a key parameter to decrease the rate of reduction of palladium and to allow a better kinetic-controlled growth regime, favoring the formation of nanorods. Shifting the experimental conditions to a thermodynamic-controlled growth regime also selectively led to the formation of cubic (similar to 80%) or icosahedral (similar to 100%) particles.