Crystal engineering and process optimization in the preparation of magnetic iron oxide nanoparticle suspensions

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Title: Crystal engineering and process optimization in the preparation of magnetic iron oxide nanoparticle suspensions
Authors: Shingte, Sameer Dinesh
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Date: 2022
Online since: 2022-06-30T13:51:34Z
Abstract: Iron oxide magnetic nanoparticles (MNPs) are key components in responsive materials for many biomedical applications, due to their characteristic responses to applied magnetic fields coupled with their biocompatibility and biodegradability. Size and shape control enables tuning of the magnetic properties for magnetic hyperthermia, MRI applications. MNPs are often synthesized by thermal decomposition of iron precursors such as iron oleate (FeOl) or iron acetylacetonate (Fe(acac)3), which provide MNPs with good crystallinity, however, they raise challenges in reproducibility of MNP properties. Major focus was on synthesis of cubic MNPs, which provide superior AC-field (hyperthermic) heating ability than nanospheres. The effect of ligand to precursor ratio (L/P) on MNP size for nanocubes synthesized through thermal decomposition of FeOl was attempted for the first time. In the L/P range of 0.5 to 3.0, the MNP size decreased with increasing L/P for all freshly prepared iron oleate batches. However, specific absorption rate (SAR) values measured for the nanocubes were inconsistent and predominantly low, despite having well morphology and colloidal properties. An elaborate investigation of the probable cause for such anomalous behaviour highlighted that the magneto-crystalline characteristics of the MNPs are closely associated with their heating efficiency. The work on cubic MNPs suggested that thermal gradients and inconsistent mixing could be critical limitations contributing to SAR non-reproducibility. An optimized reaction setup, called as Multiple Reaction Setup (MRS) was developed as an alternative to conventional reaction setup that can provide uniform reaction conditions to improve the reproducibility of MNP properties. Additionally, a Continuous Flow Reactor (CFR) was developed to synthesize MNPs in flow. Preliminary experimentation in these setups validated their versatility to synthesize variety of MNPs by using thermal decomposition as well as coprecipitation processes. The apparent success of these modifications using engineering principles could be beneficial in addressing the issues of non-reproducibility and scaling across nanomaterials science. The MNP properties can be enhanced by separation based on their magnetocrystalline characteristics under the influence of magnetic field, known as Magnetic Field-Flow Fractionation (MFFF). A MFFF model was developed to understand the effect of factors like magnetic field strength and its gradient, channel geometry, solvent viscosity on the transport of MNPs. This provided the framework for the development of the MFFF device which enabled separation of MNPs with distinct morphologies. Moreover, their heating abilities were improved compared to their feed suspensions using multiple passes through the device. his MFFF device presented is an effective tool to evaluate the distribution of magnetic hyperthermic responses experimentally for real MNP suspensions for the first time. Continuing the pursuit of MNP suspensions with superior magnetic properties, the focus was shifted to the polyol process, which provides multicore nanoflowers that are stable in aqueous suspension. With a view of developing a reproducible process to synthesize MNPs with tailored magnetic properties, the polyol route showed promising potential. Multiple MNF syntheses at a standard scale (55 mL) were carried out to acquire the critical understanding of the polyol process for determining design specifications of the scaled-up setup. The setup was designed to perform the synthesis involving 1100 mL of reaction volume that enabled production of 20 times higher amount of MNFs, having similar magnetic properties to those prepared at a standard scale. The achieved capability to prepare a large quantities of iron oxide MNPs having monodisperse morphology, excellent colloidal stability and optimum hyperthermic responses (SAR>200 W/g) will be ideal for biomedical applications.
Type of material: Doctoral Thesis
Publisher: University College Dublin. School of Chemistry
Qualification Name: Ph.D.
Copyright (published version): 2022 the Author
Keywords: Iron oxide nanoparticle synthesisColloidal stabilisationMagnetic propertiesHyperthermia
Language: en
Status of Item: Peer reviewed
This item is made available under a Creative Commons License:
Appears in Collections:Chemistry Theses

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