Date of Award
Doctor of Philosophy (PhD)
As the production of fullerenes and fullerene-based materials approaches industrial scale, there are increasing interests/concerns regarding their (potential) environmental impact(s) upon release. To date, a number of critical, aqueous-based fullerene transformation pathways under environmentally relevant conditions remain poorly understood. Comprehensive, fundamental, and quantitative understanding of the potential (major) reaction pathways and resulting products of fullerene materials, particularly in aquatic systems, is now crucial for their accurate fate, transport, life cycle, risk assessment(s), and thus ultimate material sustainability.
Herein, this dissertation is focused on identifying and elucidating aqueous transformation pathways of fullerene materials, focused on C60 as a model fullerene, under a variety of relevant environmental scenarios. First, we elucidate the mechanisms by which hydrophobic, solid fullerene and hydrogenated C60 derivatives become water available/stable through extended mixing, without transferring solvents, in the presence of light and electron acceptors (e.g. oxygen). Resulting products exist as stable nano-scale C60 aggregates (termed as aqu/nC60) or, depending on the reaction, as oxidized fullerenes (termed as fullerol), respectively. Additionally, water stable/soluble fullerenes (nC60 and fullerol) can undergo further oxidation by common oxidants such as free chlorine, which is dramatically enhanced via photo-irradiation (under sunlight mimicked conditions). Finally, under environmentally relevant reducing scenarios, oxidized fullerene derivatives (fullerol) were also observed to be susceptible to reduction reactions by effective electron donors (e.g. zero-valent zinc). For all, reactions were explored and described via kinetic analyses with resulting products completely characterized via a battery of analytical techniques (e.g.13C-NMR, FTIR, Raman Spectroscopy, XPS, TEM, UV-vis, QCM-D, etc.) as well as comparative (physical) partitioning behaviors. Overall, these new findings highlight the likely potential for fullerene aqueous-based transformations within a variety of common environmental scenarios. It is demonstrated that such reactions will also generate products with significantly altered physicochemical properties, which correspondingly result in relatively different partitioning/transport behavior(s) in natural systems. This body of work also underscores the clear and present need to consider and fundamentally understand other advanced (nano)material(s) aqueous reactivities, in both natural and engineered treatment systems if a sustainable nanomaterial industry is to be eventually realized.
John D. Fortner
Parag Banerjee, Daniel Giammar, Young-Shin Jun, Jaehong Kim,