41 KJEMI 6 2025 Zeeshan Ali Date: 20th of June PhD thesis: Investigating Influence of Reaction Conditions in Formation of Silica Coated Iron Oxide Nanoparticles Trial lecture: Is it possible to model and predict by simulation the thickness of the silica shell with various core size? Assessment Committee • First opponent: Professor Nguyen TK Thanh, University College London, England • Second opponent: Professor Rajdip Bandyopadhyaya, IIT Bombay, India • Chair of the committee: Professor Gisle Øye, Department Chemical Engineering, NTNU Supervisors • Main supervisor: Associate Professor Sulalit Bandyopadhyay, Department of Chemical Engineering, NTNU • Co-supervisors: Professor Jens-Petter Andreassen, Department of Chemical Engineering, NTNU and Professor Magnar Bjørås, Department of Clinical and Molecular Medicine, NTNU Summary of thesis Iron oxide nanoparticles (IONPs), owing to their unique magnetic properties, have emerged as a valuable tool in the field of diagnostics. The physicochemical attributes of IONPs, i.e. particle size, particle size distribution (PSD), morphology, magnetic properties and surface chemistry, are crucial for their target applications. However, the inherent tendency of IONPs to aggregate presents significant challenges in achieving precise control over their properties. Hence, surface modification of IONPs through coating with inorganic material, particularly silica, is widely employed to tune their particle size, PSD, morphology and magnetic saturation. In addition, silica coating provides possibilities for further functionalization with specific surface ligands by providing binding sites through surface silanol groups, to prepare them for specific diagnostic applications. Modified Stöber’s method is usually employed for such functionalization due to its low processing temperature, but experimental conditions play a decisive role in shaping the properties of resulting silanized IONPs. This thesis primarily focuses on the effect of various reaction conditions of modified Stöber’s method on the properties of resultant silica coated IONPs (SIONPs) and on their possible formation mechanism. A full factorial design of experiments (DoE) was conducted to study the effects of nature of solvent, IONPs- to-silica precursor mass ratio, ammonium hydroxide concentration, and the surface chemistry of IONPs on outcomes such as particle size, particle size distribution, morphology, and magnetic saturation of SIONPs. Furthermore, electrostatic stability of IONPs and reaction volume are factors that are usually overlooked in previously reported studies. Hence, two types of IONPs, with different isoelectric points, were employed during silanization that demonstrated the significance of maintaining the pH of IONPs dispersion higher or lower than their isoelectric point to synthesize smaller and spherical SIONPs. Moreover, this study also explored how the structure of silica precursors affects particle morphology and surface functional groups of SIONPs, which are crucial for their diagnostic applications. Finally, the synthesis process was studied in-depth to gain insights into the formation mechanism of SIONPs via modified Stöber’s method by investigating the changes in the mass, morphology and size of the particles during the reaction time. Hence, the reported findings contribute to understanding the effect of various reaction conditions on the resultant properties and formation mechanism of SIONPs synthesized via modified Stöber’s method. This will assist researchers not only in tailoring SIONPs with the desired particle size, particle morphology and magnetic saturation but also in controlling their surface groups, which are desirable for their downstream applications.
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