Synthesis, Characterisation and Applications of Iron Oxide Nanoparticles

This thesis deals with the synthesis, characterisation, and some applications of ferrimagnetic iron oxide nanoparticles. The iron oxide systems presented in this work are Fe3O4, γ-Fe2O3, NixFe3−xO4, CoxFe3−xO4. Iron oxide nanoparticles were prepared using chemical synthesis methods. Nanoparticles with a narrow size distribution were synthesised using zone confinement methods such as nanoemulsions and the novel flow injection synthesis. The flow injection method consisted of the precipitation of iron oxide nanoparticles in a continuous or segmented flow in a capillary reactor under laminar flow. Also, the preparation of particles in a ∼ 40 g/batch scale was carried out in a computer controlled stirred reactor which allowed reproducible synthesis conditions such a ∆pH ∼ 0.1 and ∆T ∼ 1 ◦C. Several chemical and hydrodynamic parameters were optimised to achieve high phase purity and magnetisation. These methods allowed the preparation of particles with tailored mean particle size from 3 up to 12 nm. Spinel iron oxide nanoparticles were also doped with Ni and Co. The influence of the synthesis parameters on the morphological and magnetic properties of nickeland cobalt-doped magnetite (NixFe3−xO4 and CoxFe3−xO4) was studied. Particle size, morphology, and composition of the materials are strongly dependent on reaction conditions, e.g., metal to hydroxide ratio and temperature. Cubic, spherical, and particles of CoxFe3−xO4 with varying morphology could be obtained by varying the metal to hydroxide ratio. Mössbauer studies indicated a disordered structure with a relatively low degree of inversion in the spinel structure. The coercivity of the particles increased with the cobalt content. High resolution microscopy and electron diffraction studies showed that cubic particles are monocrystalline. Iron oxide nanoparticles (Fe3O4 and γ-Fe2O3) with a particle size of about 10 nm were coated with layers of inorganic materials such as silica and gold to render the particles higher functionality and vary the surface properties. Iron oxide nanoparticles were coated with silica in a controlled manner producing either single coated particles, with a mean particle size varying from 12 to 60 nm, or multiparticle-beads with mean particle size in the range of 50-250 nm. The use of iron oxide nanoparticles in two applications was studied, i.e., for DNA purification and as optical power limiting agents. Silica-coated iron oxide particles were investigated for use in magnetic purification of plasmid DNA of the size range 0.1–1.7 kbp. The prepared nanoparticles have shown higher DNA recovery yields when compared to commercial particles. Single silica-coated nanoparticles have DNA recovery yield of about 70%, while the beads of multiple particles showed a recovery of approximately 50%. The optical power limiting application of coated and non-coated iron oxide nanoparticles was investigated. Both aqueous suspensions of pristine iron oxide nanoparticles consisting mainly of γ-Fe2O3 and silica-coated iron oxide nanoparticles had a clamping level of about 3 μJ. The photoinduced nonlinear light scattering is the dominating nonlinear mechanism. Silica-coated nanoparticles have shown a better performance as a result of their higher colloidal stability.