One-Step Synthesis of Carbon-Supported Metal Nanoparticles via Laser Reduction in Liquid

Carbon-supported metal nanoparticles (NPs) are an important class of nanomaterials due to their wide ranging applications in energy storage, catalysis and potential biomedical devices. Extensive efforts are underway to design and produce these metal-carbon hybrid materials with better functionalities and improved application performances. An emerging method to synthesize these materials is the laser synthesis in liquids method. The advantages of employing these methods over chemical synthesis protocols include: control over individual NP characteristics, rapid synthesis times, facile generation of metastable phases and avoidance of surfactants or capping ligands. The absence of these ligands in laser-synthesized NPs often results in higher catalytic activities than their traditionally-synthesized counterparts as ligands block some of the active sites on the surface of the NPs. Amongst the different laser synthesis in liquid techniques, laser ablation in liquid (LAL) is the most popular. It involves focusing of laser beam at the solid-liquid interface of solid target immersed in a solvent, resulting in the ejection of material from the target surface, followed by coalescence into colloidal NPs. However, typically large (\u3e5 nm) NPs with bimodal size distributions are commonly obtained by the LAL method. While additional steps have been employed to narrow down the size distribution, it remains challenging to produce NPs with narrow size-distributions in one step. An alternative to this is the laser reduction in liquid (LRL) has received lesser attention as compared to other techniques. LRL is a bottom-up technique, which involves focusing picosecond (ps) or femtosecond (fs) laser pulses into a solution containing molecular precursors to generate a dense plasma containing electrons which reduce metal ions to metal NPs. While the synthesis of noble metal NPs in water has received significant attention using the LRL method, non-noble metals and the use of organic solvents remain poorly explored. The research presented in this thesis works towards expanding the scope of LRL for synthesis of non-noble metal NPs in organic solvents. First, we discuss the synthesis and characterization of nickel NPs from the LRL of nickelocene in hexane. Ultrasmall NPs were obtained by varying precursor concentrations and laser-focusing conditions. The obtained NPs were also metastable phases of Ni and the carbon support generated during the synthesis possessed very high surface area. The NPs were tested as electrocatalysts for oxygen reduction reaction (ORR) applications. Second, the Ni NP synthesis was modified by including pyrrole to introduce nitrogen-doping in the carbon support. These nitrogen-doped carbon-supported Ni NPs were then characterized and tested for applications in electrochemical glucose sensing. Third, copper NPs (Cu NPs) were synthesized from copper acetylacetonate in a mixture of isopropyl alcohol (IPA) and methanol (MeOH). The precursors were purged with nitrogen and the laser irradiation was also carried out under nitrogen. These conditions led to the synthesis of pure Cu NPs, otherwise usually obtained as oxides. The synthesized NPs were tested for catalytic activities towards reduction of organic molecules. Finally, Cu NP synthesis was extended to include silver acetylacetonate and CuAg alloy NPs were obtained with different bimetallic structures with increasing precursor concentrations. Additionally, compositional variance was also observedin line with variation in Cu:Ag ratios