Developing New Synthetic Methods for Colloidal Hybrid Nanoparticles: Conversion Chemistry and Chemoselectivity

Open Access
Author:
Bradley, Matthew Joseph
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 26, 2015
Committee Members:
  • Raymond Edward Schaak, Dissertation Advisor
  • Tom Mallouk, Committee Member
  • Benjamin James Lear, Committee Member
  • Robert Martin Rioux Jr., Committee Member
Keywords:
  • Hybrid Nanoparticles
  • Conversion Chemistry
  • Chemoselectivity
  • Nanoparticle Synthesis
  • Heterodimers
Abstract:
Colloidal hybrid nanoparticles contain multiple domains, and through their solid-solid interfaces, can facilitate synergistic relationships between domains, resulting in the incorporation of multiple functionalities as well as modification of the intrinsic properties of each domain. Although there is a growing number of materials and applications associated with these unique types of particles, new synthetic methods must be investigated in order to realize the full potential of this new class of particles. To address this need, we demonstrate that the concepts used in total synthesis of complex organic molecules, can be applied to the synthesis of colloidal hybrid nanoparticles. Site selective growth, conversion chemistry, condensation chemistry, and protection/deprotection reactions are examined as ways to add complexity to colloidal hybrid nanoparticles. First, we will discuss the synthesis of PtPb-Fe3O4 and Pt3Sn-Fe3O4 heterodimer particles via a solution mediated conversion chemistry process. These types of reactions are known to be useful for nanoparticle systems but had not been explored as a method for adding complexity to colloidal heterodimers. Pt−Fe3O4 heterodimers react with Pb(acac)2 and Sn(acac)2 at 180−200 °C in a mixture of benzyl ether, oleylamine, oleic acid, and tert-butylamine borane to form PtPb−Fe3O4 and Pt3Sn−Fe3O4 heterodimers, respectively. This chemical transformation reaction introduces intermetallic and alloy components into the heterodimers, proceeds with morphological retention, and preserves the solid−solid interface that characterizes these hybrid nanoparticle systems. In addition, the PtPb−Fe3O4 heterodimers spontaneously aggregate to form colloidally stable (PtPb−Fe3O4)n nanoflowers via a process that is conceptually analogous to a molecular condensation reaction. Next, we will discuss the methanol oxidation activity of PtPb-Fe3O4 and Pt3Sn-Fe3O4 heterodimers as well as examine the role of ligand exchange in this process. Before ligand exchange was performed, surfactant molecules on the surface of the colloidal hybrid nanoparticles inhibited catalytic activity. We therefore used NOBF4 to remove the surfactant molecules and found that once removed, Pt nanoparticles showed much higher activity than before the exchange took place. It was also observed that the solvent the ligand exchange reaction takes place in has an impact on the catalytic activity. Unfortunately, the colloidal hybrid nanoparticles did not show any catalytic activity after the exchange reaction. Finally, in an attempt to determine the driving forces behind site selective growth, we grew PbS, CuxSy, and CdS off of Pt-Au heterodimers. Pt-Au heterodimers are an interesting model system for studying chemoselectivity because Pt and Au have very similar lattice constants but different chemical preferences. First, we studied the thermal stability of Pt-Au heterodimers and determined that they begin to thermally degrade in solution around 210 °C. We then grew the three metal sulfide domains off the Pt-Au heterodimers and synthesized Pt-Au-PbS heterotrimers, Pt-Au-CuxSy heterotrimers, and (Pt@Au)-CdS heterostructures. We concluded that the strong nature of the Au-S bond was the primary driving force for chemoselectvity in these systems. We also studied the growth of Fe3O4 off of Pt-Au heterodimers, and Au off of Pt-CdS heterodimers, as well as developed a method for SnS based heterodimers with Au and Pt domains.