Synthesis of Fe-oxide nanoparticles using microreactors

Simmons, Matthew David

Abstract

The work described in this thesis focuses upon the development of a novel adaptable continuous flow technique for the synthesis of iron oxide nanoparticles using commercially available microreactor system, to allow for easy scaling up towards a larger industrial scale. The development of the technique focussed around the conversion of commonly used research techniques, which require the use of specifically designed microreactors, for use upon commercially available microreactors in which the design is fixed. A 2D continuous flow focussed technique was developed based upon the attempted conversion of the droplet coalescence and co-axial flow technique which has been previously used for nanoparticle synthesis by other research groups.

The nanoparticles produced using this technique were extensively characterised, in terms of physical and magnetic properties, and seen to be comparable, to those produced by other groups and those currently used as magnetic cores for MRI contrast applications. A critical evaluation of the effect of reaction parameters, e.g. reagent concentration, flow rate, and temperature upon nanoparticle size was made, however little quantifiable conclusions could be drawn. The structure of the nanoparticles was further investigated using a previously developed powder X-ray diffraction calibration technique which relied upon the asymmetry of peaks relating to specific reflections in the γ-Fe₂O₃ and Fe₃O₄ phases present in the nanoparticles. The structures were determined to contain higher quantities of γ-Fe₂O₃ which is more chemically stable but less magnetically favourable of the two phases. Further analysis using Mössbauer and solid state Infra-red analysis confirmed these findings, and as such attempts were made to control the amount of these phases within the nanoparticles. The synthesis technique was therefore adapted to allow for control of the amount of these phases within the nanoparticles by addition of oxidation and reducing agents into the synthesis. By doing this it proved able to synthesise nanoparticles which using the above powder X-ray diffraction technique were seen to be almost completely formed of γ-Fe₂O₃, synthesis of nanoparticles with higher weight percentages of Fe₃O₄, however proved not to be possible.

Further work upon attempting to alter the magnetic properties of the nanoparticles has involved developing cation substitution reactions performed using microreactors. In batch these reactions are common place, however to the best of the author’s knowledge however no attempt has yet been made at cation substitution using microreactors. Partial replacement of Fe with another metal cation in the spinel structure was attempted to create a series of MxFe₃₋ₓO₄ compounds, this has been seen to alter the cation distribution and magnetic properties of the nanoparticles by other research groups. Several attempts at substituting Co, Mn, Zn, V, and Sn into the structure in batch. Zn substitution appeared the most successful in batch, and the synthesis was adapted to form ZnxFe₃₋ₓO₄ nanoparticles, with greater amounts of substitution into the nanoparticles seen when performing the synthesis in microreactors rather than batch.

The 2D continuous flow focussed technique would therefore prove a useful tool for the synthesis of biomedical nanoparticles. Not only those it produce nanoparticles with the correct physical and magnetic properties, but also allows for their adaptation and manipulation of these properties to be tailored for specific applications.

Thesis Type	Thesis
Deposit Date	Sep 9, 2015
Publicly Available Date	Feb 23, 2023
Keywords	Chemistry
Public URL	https://hull-repository.worktribe.com/output/4217046
Additional Information	Department of Chemistry, The University of Hull
Award Date	Oct 1, 2014

Synthesis of Fe-oxide nanoparticles using microreactors

Simmons, Matthew David

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