Colloidal synthesis of metal nanoparticles

Abstract: Metal nanoparticles (NPs) are central in a wide range of industrial areas including catalytic and biomedical applications. Due to their interesting physical properties, the demand of these precious materials is steadily increasing, which has created a need for the development of effective and high-performing NPs. Because the properties are closely correlated to NP size, shape, and crystal structure, the development of controlled synthesis of metal NPs has emerged. However, the challenge of understanding how reaction parameters influence the outcome of the synthesis currently limits the production of precisely designed metal NPs. Additionally, low reproducibility and control during scale-up has often restricted the production to small scale which limits the use in industrial applications.   The studies presented in this thesis focus on the controlled synthesis of uniform metal NPs using solution-based colloidal methods. Firstly, the multiple roles of the NP stabilizers were investigated. In the synthesis of Cu NPs, alkanethiol stabilizers only provided temporary stabilization of the Cu NPs and decomposed under heating in inert atmosphere, forming Cu2S NPs. In another study, uniform Pd NPs stabilized with a binary surfactant combination were synthesized without using traditional reductants. The fatty acid stabilizer contributed to the reduction of Pd-precursors, and the reduction kinetics follow a pseudo-first order kinetics. The specific stabilizers investigated influence reduction kinetics, NP sizes and shapes. Secondly, to address scale-up challenges in NP synthesis, the development of flow synthesis routes were explored. Uniform Pd nanocubes (NCs) and PdPt core-shell NPs were produced in a single-phase flow reactor, and a segmented flow reactor was developed to produce uniform Au NPs. The flow production was scaled-up, and the uniformity of Au NPs was confirmed by inline optical spectroscopy quality control. Catalytic evaluation of the function of PdPt core-shell NPs in a model NO2 reduction reaction showed improved catalytic activity, selectivity and temperature stability compared to Pd NCs.