An Examination of the Effects of Ionic Additives on Au Nanoparticle Synthesis

In this thesis, an introduction to nanoparticle synthesis, and specifically to the seed-mediated syntheses is offered, with the importance of the seeds detailed. Several common shape- and facet-controlling mechanisms are explained. In Chapter 2, a complex bimetallic system is introduced, with two growth mechanisms identified. Additionally, the role of chloride vs bromide is introduced. In Chapter 3, the effect of two anionic additives, sodium hydroxide and sodium bromide, on a similar Au system to that in Chapter 2 was analyzed, and a mechanistic pathway proposed. Specifically, this work examined the intricate reaction mechanisms by which bimetallic Au-Cu particles may be grown, and a synthesis using the superior seed-mediated method was found, with greater monodispersity and yield of THH over the existing method found in literature. Furthermore, a high presence of DTBP was also found, with very few syntheses known for this unique shape, despite the relationship between THH and DTBP. Kinetic studies showed two distinct regions of growth for this bimetallic system: the first was for approximately twenty minutes, with UPD being the dominant mechanism. After twenty minutes, galvanic exchange appeared to be the guiding factor for further particle growth; it was noted that this resulted in a relatively uneven surface, when compared to particles whose growth was halted after the UPD stage had subsided. A cursory examination of the impact halides had on the system was performed. However, further studies were deemed necessary to draw conclusions beyond the type of facets formed. Additionally, this work proposes two new synthetic pathways to obtain the high-index faceted HOH shapes, which see applications in a variety of areas. The application of existing principles was used to guide the anionic additions in order to increase the reaction rate. This was accomplished using NaOH, wherein a small adjustment to the pH, undetectable through pH paper, allowed for an increase in reaction. This was also accomplished using incredibly dilute concentrations of NaI, wherein a potential mechanism for the particle formation was proposed. Through this mechanism, and in alignment with the other two (NaOH and literature), the concept of iodide increasing reaction rate was formulated, which lead to an addendum of the common guiding principles involving iodides in nanoparticle formation.