Use of Graphene Oxide for Sorption of Radionuclides and Other Cations and Synthesis of Graphene-Based Nanoribbons
Slesarev, Alexander Sergeyevich
Tour, James M.
Doctor of Philosophy
This dissertation describes the application of graphene oxide to radionuclides and other ions separation from various media and synthesis of some graphene-based nanoribbons. Fundamental phenomena underlying these effects are studied and discussed. Chapter 1 presents the first observation of graphene oxide efficiency for sorption of radionuclides from aqueous solutions. Sorption capacity and pH-dependency of sorption are shown and outstandingly fast kinetics is demonstrated. Sorptive properties in simulated environmental water are studied and compared to other commonly used sorbents. In chapter 2, study of sorptive properties of graphene oxide is extended to sorption of low valence ions present in nuclear disaster sites – Cs(I) and Sr(II) – in water of significant salinity. Sorption capacity and pH-dependency of sorption properties of lab-scale synthesized and commercial nuclear grade graphene oxide are determined. In chapter 3, the mechanism behind outstanding sorption properties of graphene oxide is discussed using Eu sorption as a model system. Lack of chemical change in carbon and europium states upon sorption is shown by NMR and fluorescence spectroscopy, which agrees with reversibility of sorption but disagrees with the sorption mechanisms proposed in literature. Adsorption mechanism based on morphological change and phase transition (formation of coacervate) upon sorption is proposed and supported with experimental data. In chapter 4, the mechanism of meniscus mask lithography for planar graphene nanoribbon synthesis is proposed and experimentally supported. Formation of the meniscus mask is based on condensation of water in the wedge of the lithography pattern. The macroscopic models are not applicable to this system, and a simple molecular model is proposed. In chapter 5, oxidative unzipping of multi-walled carbon nanotubes with potassium chlorate is demonstrated. The proposed oxidative unzipping method is mild and leads to formation of graphene nanoribbons with much less structural damage compared to other oxidative unzipping methods, but the resulting ribbons are not exfoliated and are attached to the core nanotube that is not unzipped, which should make this product promising material for energy storage, carbon fiber synthesis or other applications. In chapter 6, the mechanism of oxidative unzipping of multi-walled carbon nanotubes is proposed. The driving force for the unzipping is the oxidation of CNT layers, whereas the process directionality arises from mechanical stress in the nanotube layers developed due to increase of interlayer distances upon oxidation of CNT layer basal planes. This hypothesis is supported by a time-resolved study of interlayer distance evolution compared to kinetics of unzipping directly and by observations of CNT and graphene oxide nanoribbon morphology by SEM. Overall, the work accomplished in this dissertation opens a route for environmentally friendly remediation of nuclear waste and nuclear disaster sites and provides deeper understanding for graphene nanoribbon formation processes.
graphene oxide; radiochemistry; physical chemistry; nanofabrication; graphene nanoribbons