Mechanisms of Nanoparticle Synthesis for the Production of Well-Defined Models of Heterogeneous Catalysts

Abstract

The synthesis of metal nanoparticles (NPs) by hot-injection/heating-up chemical reduction methods is a widely used method for generating size-controlled nanoparticles with narrow dispersity. These are important in a number of fields, for instance, their use in studies to understand structure-activity relationships in catalysis (the focus of our research group). These methods generate capping agent-controlled metal NPs. This thesis focuses mainly on methods using an organic solvent with long-chain amines and acids, along with a reducing agent, to carry out nanoparticle synthesis by chemical reduction.
Chapter 4 starts to build on a procedure reported (but not thoroughly investigated) in the literature that has shown it was possible to synthesize 3.2 nm Ni NPs by using oleic acid (OA), oleylamine (Oly) and borane tributylamine (BTB). This chapter studies the changes in the colour of the solution over time before the reducing agent is added (including with UV-vis-NIR spectroscopy) and develops the method further to produce smaller 1.3 nm Ni NPs.
Chapter 5 continues the work done by previous group members to develop a method to synthesise size-controlled Cu NPs. This chapter shows the ability to manipulate the reaction temperature to yield a uniform size of 4.3 nm Cu NPs. Then, the study of the solvent system over time before the reduction reaction shows the ability to produce monodispersed 1.8 nm Cu NPs.
Chapter 6 reports studies to investigate the amine-borane type reducing agent used in the previous chapters. Amine-borane (AB) compounds are used without understanding how the reduction process is happening. This chapter uses several approaches to suggest that the amine-borane is releasing H2 that supersaturates the solution, and then the H2 reduces the M(acac)2 directly.
Finally, Chapter 7 presents a way to couple two metals NPs of different metals (i.e. unsymmetrical pairs) with covalent tethers. Cu, Pd, and Ni NPs were used with a series of more complex amide linkage coupling systems more commonly used in biological applications. While early attempts were unsuccessful when more complex combinations of coupling reagents were used, it was shown that it was possible to get around 60% of nanoparticles in pairs.
In summary, the thesis examines the synthesis of metal nanoparticles in detail, both the formation of in situ precursors and the impact of this on the resultant nanoparticles and the behaviour of the now widely used amine-borane class of reducing agents. It then goes on to demonstrate their use in developing nanostructures with the long-term goal of exploring mechanisms in catalysis using materials that cannot be prepared without recourse to nanoparticle synthesis.