This thesis details the chemical synthesis and nanocharacterisation of magnetic nanoparticles (MNPs). Throughout this thesis, solution-based synthesis methods are used to fabricate MNPs with a variety of shapes, from spheres and cubes to wires and octapods.
Chapter 3 assesses the role of polyol solvent in autoclave-based magnetite NP synthesis. It was found that solvents containing functional groups (especially primary alcohols) afforded the greatest control over final MNP morphology and that the presence of additional alkyl substituents could disrupt the packing of surfactant molecules around a particle surface, giving rise to more complex ‘compound’ MNPs. Magnetic measurements show the particles to be superparamagnetic, with saturation magnetisation values close to that of the bulk.
In Chapter 4 It was found that by replacing the polyol solvents used in Chapter 3 with a large excess of bulky surfactant molecules it was possible to form high aspect ratio lanthanide oxide (LnOx) nanowires and ribbons. It was found that the nanowires formed via an intriguing 3-stage ‘oriented assembly’ mechanism, in which individual NPs form, before aligning anisotropically and recrystallising into a more crystallographically homogeneous product. The magnetic properties of Gd2O3 nanowires and Dy2O3 nanoribbons are very similar to those of discrete particles, implying that no long-range ordering exists in the nanowires. Optical characterisation of the Eu2O3 nanowires showed that there is an increase in fluorescence lifetime going from bulk Eu2O3 to the nanoscale.
In Chapter 5 the high temperature reflux approach is used in the synthesis of manganese oxide (as MnO) particles, using manganese-containing polynuclear carboxylate complexes as precursors. It was found that control over MnO NP size and shape is dependent on many factors, such as the carboxylate ligand present in the precursor (which can disrupt particle stabilisation by surfactant molecules) and the heating regime, which ii determines if the particles grow under thermodynamic or kinetic growth regimes. The magnetic behaviour of MnO MNPs was found to be dependent on the relative number of surface spins present in the particles.
In Chapter 6 new routes to gadolinium-doped magnetite particles are discussed. It was found that decomposition of a single-source precursor yielded doped magnetite particles which had a gadolinium content of 2–4%. Magnetic characterisation of these particles showed them to be superparamagnetic, with a reduced saturation magnetisation compared to bulk magnetite. Preliminary investigations showed that the gadolinium doped particles (after being rendered water soluble by a ligand exchange reaction) were readily taken up by human fibroblast cells and exhibited low toxicities
