Development of Multifunctional Magnetic Core Nanoparticles

Abstract

Multifunctional magnetic materials have a great importance in various fields of application, e.g., material science, chemistry, physics, environmental chemistry and biomedicine. Although a large number of scientific papers already describe the synthesis of multifunctional materials by various methods and technologies, a simple, fast and economically feasible synthesis procedure to combine all the materials in one system is still of interest.

This thesis contributes to the development of multifunctional magnetic-core materials scientifically in three parts. Firstly, the synthesis of magnetic core, i.e., magnetite nanoparticles, was attempted using only ferrous ions (Fe2+) of various concentrations as a magnetite precursor under ambient atmosphere. It was found that the synthesized magnetite was in a non-stoichiometric state, i.e., oxidation occurs. The introduction of Stöber silica (SiO2) layer in the form of a coreshell structure prevented the oxidation of the synthesized particles, as suggested by the low temperature magnetic measurement and Mössbauer study. Secondly, this thesis introduces a simple, room temperature synthesis method for further functionalization of the magnetite-silica coreshell powders with silver (Ag) and silver/silver chloride (Ag/AgCl) nanoparticles. Based on the proposed approaches, the Ag deposition on the silica shells can take place by three possible mechanisms: a) absorption of Ag+ on the silica surface by ionic bonding between the silver ions and hydroxyl groups (OH) of silica followed by the reduction of Ag+ by polyvinylpyrrolidone (PVP), b) hydrogen bonding between the PVP-coated Ag and the SiO2 shells, and c) electrostatic attraction between PVP-coated Ag and SiO2 shells. The silver chloride particles are formed when a certain amount of hydrochloric acid (HCl) is introduced. The particle morphology is controlled by the concentration of HCl. Thirdly, the thesis makes a scientific contribution by introducing novel properties by compacting the magnetite-silica coreshell powders into bulk material by pulsed electric current sintering (PECS). By adjusting the amount of magnetite-core inside the silica structure, it is possible to produce a transparent magnetic compact. In addition, the effects of the sintering atmosphere and temperature on the final properties of the compacts were also studied.