Date of Award

December 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Mathew M. Maye

Keywords

Diffusometry, ILT, NMR, Relaxometry

Subject Categories

Physical Sciences and Mathematics

Abstract

Colloidal nanomaterials like semiconductor quantum dots (QDs) have size-, shape-, and composition-dependent optoelectronic properties with applications ranging from photovoltaics, to sensing, to medical diagnostics and treatment. These materials also have very high surfaceto- volume ratios, with intricate surface chemistries which control nearly every aspect of their chemical, physical, and colloidal properties. The interaction of the surface with the environment is limited via capping the surface of the nanomaterials with a shell of organic capping molecules. The environment-dependent binding of this organic shell is thus an extremely important aspect of nanomaterial design, however the methodologies to probe these interactions in-situ are limited. In my thesis research, I developed solution-state nuclear magnetic resonance (NMR) methodologies to probe the interactions between this inorganic core and the organic capping layer. I investigated the dynamic surface binding of perovskite QDs via utilization of DOSY NMR to quantify changes to their surface dynamics as a function of QD composition. These results showed that by increasing the concentration of iodide ions in the CsPbBr3xIx lattice yielded a concurrent drop-off in surface coverage of ligands, suggesting a difference in surface energy between the Br-rich and I-rich end members of the family of QDs. I then extended the use of DOSY NMR as well as intergation of ROSY NMR to study in-situ the interactions of capping ligands and organohalide molecules with a CsPbBr3_xIx perovskite lattice. These materials undergo a chemical reaction with the organohalide molecules, whereas the QD lattice composition shifts throughout incorporation of ions from the organohalide molecule. This work foremost demonstrated a new method for quantifying and monitoring changes in surface interactions during reactions at nanomaterial interfaces. Secondly, this work showed that the incoming organohalide molecule orients itself head-group first at the QD interface before reacting with the nanomaterial; indicating that the surface stabilized the occurance of the reaction instead of the molecule just reacting with free ions in solution. Lastly, this thesis introduces a new multidimensional technique T1-T2 correlation spectroscopy. This methodology was extended from previous use in the oil field industry to investigate intricate changes in chemical environment of molecules at nanomaterial interfaces. Using this technique, this work showed slight variations in interactions at the organic-inorganic interface as a function of variable purication technique.

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