Directed and random self-assembly of Pt-Au nanoparticles

The results and findings of the controlled synthesis of poly-vinyl-pyrrolidone (PVP)-protected Pt and Pt-Au nanoparticles of sharp and polyhedral morphology using the modified polyol method are reported. The highly sharp cubic, octahedral, and tetrahedral Pt nanoparticles are prepared by the reduction of H2PtCl6 using ethylene glycol (EG) at 160 °C with the assistance of AgNO3. Here, PVP and H2PtCl6 are added gradually. In order to make the synthesis of Pt-Au bimetal nanoparticles, these polyhedral Pt nanoparticles have been used as seeds for the reduction of HAuCl4 by EG at an appropriate time. The reduction of HAuCl4 modifies the sharp morphology of Pt nanoparticles into the cubic Pt-Au nanoparticles. It is important to note that the cubic Pt-Au alloy nanoparticles appear after a short reduction time namely, approximately 15 min. The reported findings of the spherical and irregular Pt-Au alloy nanoparticles in their oriented as well as random self-assembled form are interesting and useful. The results show that single and bimetal nanoparticles with their sharp corners arrange themselves regularly and directly, where as nanoparticles with less sharp corners arrange irregularly.