Date of Award
Chemistry and Biochemistry
Gold nanoparticles, Iron oxide nanoparticles, nitroxide, Stable radical, TEMPO
The topic of this dissertation is the surface modification and functionalization of inorganic nanoparticles with free radicals. These particles have a diameter up to ca. 15 nm and consist of an inorganic core with an organic surface coating comprising open shell organic TEMPO radicals. Chapter 1 describes synthetic methods for the preparation of gold nanoparticles (AuNPs) and introduces the range of analytical methods for nanoparticle characterization. A survey of previous work on radical-coated nanoparticles is presented and the objectives of the current studies are outlined, highlighting the range of different bonding strategies for attaching the TEMPO radical to the AuNP surface. Chapter 2 describes the synthesis and characterization of citrate-coated AuNPs of 18 nm diameter. Treatment of these citrate-stabilized AuNPs with a water-soluble TEMPO radical [WS-TEMPO]Br led to aggregation at high [WS-TEMPO]Br concentrations identified by a long wavelength absorption but is suppressed at low concentration (10-4 M). Treatment with [WS-TEMPO]Br unexpectedly led to bromide/citrate exchange on the AuNP surface which was determined by IR spectroscopy and EDS. EPR studies on the resultant 14 nm nanoparticles reveal low concentrations of WS-TEMPO on the surface and these particles appear stable up to 345 K. Chapter 3 describes a one-pot reaction to covalently bond TEMPO radicals to the AuNP surface via an Au-S bond generated from TEMPO-thioacetate precursors or via a TEMPO-disulfide derivative. IR spectroscopy was used to identify cleavage of the thioacetate bond to generate a thiolate-bound TEMPO radical. TEM images reveal spherical AuNPs of ca. 3 nm diameter with EPR studies revealing high coverage of TEMPO radicals on the nanoparticle surface. Variable temperature UV/vis and EPR spectroscopies show that the effect of heat on these radical-coated AuNPs appears sensitive to the length of the alkyl chain. Thus, heat can variously lead to either an increase or decrease in AuNP size on heating. Chapter 4 examines the use of non-covalent, hydrophobic, dispersion driven interactions to tether TEMPO radicals to the AuNP. N-Octyl thiolate-coated AuNPs were prepared and treated with n-C8H17-O-TEMPO to afford 18 nm diameter nanoparticles. EPR studies reveal only low coverage of TEMPO radical on the surface. Preliminary studies showed that these radical-coated AuNPs could be used in the thermal polymerization of styrene, suggesting that free-radical moderation of the polymerization process is operative. Chapter 5 examines the synthesis of a more complex core topology, comprising a superparamagnetic iron core and gold outer shell of 9 nm diameter. This was then coated using a covalent S-bound thiolate-TEMPO surface. Unlike the S-bonded AuNPs described in Chapter 3, surface coating with TEMPO radicals is low. This system was confirmed by IR, EDX, PXRD, UV-vis and EPR spectroscopy. Chapter 6 summarises the findings of the current studies and reviews potential areas for future exploitation.
Alsaleh, Aisha Abdulwahab, "Preparation and characterization of radical-coated nanoparticles" (2018). Electronic Theses and Dissertations. 7598.