Development of Multifunctional Magnetic Core Nanoparticles

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Norsuria Mahmed Name of the doctoral dissertation Development of multifunctional magnetic core nanoparticles Publisher School of Chemical Technology Unit Department of Materials Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 58/2013 Field of research Materials Science Manuscript submitted 4 February 2013 Date of the defence 26 April 2013 Permission to publish granted (date) 19 March 2013 Language English Monograph Article dissertation (summary + original articles) 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.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 PVPcoated 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.