Polyoxometalate-assisted synthesis of metal/metal oxide nanoparticles and studies on their catalytic properties and toxicity

Abstract

Nanoparticles have attracted considerable interest owing to their unique physical and chemical properties different from those of the bulk counterparts, which have great potential applications in biomedicine, optics, electronics, and catalysis. With increasingly attention, nanoparticle with various shapes and components were intensively reported. Most of them were synthesized in the presence of organic surfactants as stabilizing and capping agents, but it has often interrupting the enhancement of properties by block the surface of nanoparticles. Polyoxometalates (POMs) are a class of anionic metal oxygen clusters with remarkable properties and functions Recently, a new synthetic strategy of nanoparticles has been developed using polyoxometalates as inorganic stabilizing and capping agents. Nevertheless, studies on synthesis method of nanoparticle with a variety of shape and composition remain insufficient. Therefore, the main objective of this thesis focuses on the synthesis of various nanoparticles using polyoxometalates and the investigation of their catalytic properties. In chapter 2, we report polyoxometalate-assisted synthesis of Pd@Pt bimetallic NPs and their application in methanol oxidation reaction. The core-shell NPs are synthesized under aqueous system in present of polyoxometalate. Three different types of surface morphology of Pt shell are formed on the octahedral-Pd core via control of growth rate. The prepared polyoxometalate-stabilized Pd@Pt nanoparticle (POM-Pd@Pt NPs) with octa-hedral morphology showed enhanced catalytic activity and stability toward methanol oxidation reaction. In chapter 3, we report the transition-metal-substituted polyoxometalate-mediated synthesis of ZnO nanoaggregates (m =Co, Fe, Zn) and their catalytic activity in cycloaddition reaction of carbon dioxide to epoxides. The catalytic activity of the m-POM-ZnO nanoaggregates is higher than the ZnO NPs without POM in the presence of dimethylaminopyridine (DMAP) as a co-catalyst because of the synergy effect with POM and ZnO nanoaggregates. In addition, the catalyst can be reused without significant loss of activity In chapter 4, we report the effects of ultrahigh concentration cationic silica nanoparticles on cell with human breast cancer cell line (MCF-7). High concentrations of cationic colloidal silica nanoparticles have been widely used for the enrichment of plasma membrane proteins. However the interaction between the nanoparticles and cells under the required concentration for the isolation of plasma membrane are rarely investigated. We evaluated the internalization and toxicity of the 15 nm cationic colloidal silica nanoparticles which were exposed at high concentrations with short time in human breast cancer cells with transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and colorimetric assays.