Pt-au nanoparticle heterodimers as seeds for pt-au-metal sulfide heterotrimers: Thermal stability and chemoselective growth characteristics

Three-component colloidal hybrid nanoparticles are important multifunctional nanoscale constructs that present interesting and complex features. Their synthesis typically requires a third nanoscale material to nucleate and grow on a two-component heterodimer seed that has two distinct surfaces exposed and accessible. Identifying and understanding chemoselective growth behavior is therefore important for predicting the most favorable product in systems where multiple three-component configurations could be anticipated. Here, we studied Pt-Au heterodimers as seeds for the formation of several Pt-Au-M_xS_y (metal sulfide) heterotrimers. Pt and Au have similar lattice constants but different chemical preferences and metal-sulfur bond strengths, and the chosen metal sulfides included both crystalline and amorphous nanoparticles that span a range of threshold synthetic conditions required for them to form. These systems therefore allowed us to study the key factors that would be anticipated to contribute to chemoselective growth preferences. We first evaluated the thermal stability of the Pt-Au heterodimer seeds in solution and determined that they transform to Pt@Au core-shell particles by 210 °C, which sets an upper limit on the temperatures that permit seeded growth reactions to generate Pt-Au-M_xS_y and other heterotrimers. We then studied the growth of PbS, CdS, and Cu_xS_y on the Pt-Au seeds and observed that the metal sulfide domain grew exclusively on the exposed Au surfaces, despite control studies where heterostructures of platinum and all of the metal sulfides were also accessible. We therefore concluded that the relative strengths of the interfacial Au-S bonds served as a key driving force behind the observed chemoselective growth behavior.