Date of Award
Doctor of Philosophy (PhD)
Recently discovered, graphene and graphene oxide materials have drawn considerable research attention due to outstanding and novel properties, which underpin wide material potential for a number of advanced applications including supercapacitors, solar cells, sensors, catalysts, semiconductors, sorbents, and membranes, among others. Graphene oxides (GO), which are considered as a family of oxidized graphene materials (derivatives), is a key precursor to the synthesis of free-standing graphene via oxidation-exfoliation-reduction pathways. GO properties depend on the synthesis routes/conditions (i.e. derivatization), including partially maintaining graphene (i.e. sp2) properties. Further, oxygen-containing functionalities (epoxy, hydroxyl, carbonyl, and carboxyl groups) render GO hydrophilic – and correspondingly stability in water, thus underpinning (aqueous-based) transport and even reactivity. Juxtaposed with aforementioned application potential, the inadvertent implications of GO, and corresponding daughter products, in environmental systems remain largely unknown. For successful aqueous applications, it is necessary to overcome two fundamental challenges: 1) control of the functional group quantity/type via synthesis process, and 2) understand the behavior (e.g. fate and transport, application) of the material(s) as a function of surface chemistry and reactivity.
In this work, classic graphene oxide synthesis is systematically explored and evaluated, including synthesis temperature, reaction time, oxidant ratios, and sonication time, with resulting material properties described, For this matrix, materials are characterized with regard to aqueous stability and spectral analyses including transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermogravimetric analysis (TGA), total organic carbon analysis (TOC), and Fourier transform infrared spectroscopy (FTIR). Additionally, the reactivity and transformation of these materials in the presence of free chlorine, a common oxidant, under light irradiation is also described. Specifically, reaction kinetics and mechanism(s) are systematically evaluated as a function of pH, dissolved oxygen, and initial size of graphene oxide (coupons). For these reactions, partially mineralization is confirmed via direct CO2 detection and carbon mass balance. Final product(s) are described via TEM, FTIR, XPS, Raman spectroscopy, and mass spectrometry (MS). Further, we evaluated and describe graphene oxide applications, including as a platform sorbent for rare earth metals, focusing on cerium(III) and lanthanum(III). For these, graphene oxide functionality (both function group type and quantity), solution pH, and ionic strength are systematically evaluated and described towards sorption optimization. Lastly, graphene oxide membranes are explored with regard to surface reactivity (i.e. exposure to free chlorine), under both dark and light irradiation conditions, as it relates membrane stability and (separation) performance for related water treatment processes.
John Gleaves, Marcus Foston, Young-Shin Jun, Erik Henriksen,