Rosillo-Lopez, Martin; (2018) Preparation, chemistry and applications of novel carbon nanomaterials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The isolation of graphene in 2004, and subsequent Nobel Prize for Physics being awarded to Andre Geim and Konstantin Novoselov in 2010, has sparked a renewed interest in graphene around the world due to graphene’s remarkable physical properties such as mechanical stability, optical transparency, impermeability and electrical and thermal conductivity. Graphene Oxide (GO), the oxidised analogue of graphene, has also received much attention owing to its hydrophilic nature. This has made GO a very promising material for aqueous processing, giving it a significant advantage over graphene. In this way, GO has been used in many composite materials, involving biological molecules, metal-organic-frameworks (MOFs) and other hybrid systems. Unfortunately, much uncertainty surrounds the chemical nature of GO, and therefore its chemistry, thus creating a lot of controversy in the literature. Similarly, the preparation of GO also results in lengthy procedures and toxic by-products. To address these issues, this thesis describes the preparation of alternative carbon nanomaterials, as a potential substitute to GO, which have well-defined structures and chemistry and/or reduce the toxic waste produced. The chemistry and applications of these new materials are explored and benchmarked against conventional GO, which is prepared via permanganate oxidation (PM-GO). The preparation of three novel carbon materials, carboxylated graphene nanoflakes (cx-GNFs), nano-graphene oxide (nGO) and GO prepared via dichromate oxidation (DC-GO) are initially reported, along with extensive characterisations. The cx-GNFs are a highly soluble (~100 mg mL-1) and well-defined material consisting of carboxyl groups and unoxidised sp2 carbon only. nGO is prepared via an eco-friendly procedure producing nano-sized GO and DC-GO was prepared in order to elucidate its chemical structure which remains uncertain in the literature. The thermal annealing behaviour of the materials are reported next and the cx-GNFs and the nGO are shown to form carboxylic anhydrides in yields up to 81%, which is the first experimental evidence for this functional group at the graphene edge. The existence of carboxylic anhydrides in dynamic equilibrium with carboxylic acids in water was demonstrated at room temperature for the cx-GNFs, and was consequently exploited for room temperature chemical functionalisations with well-known amines such as ethylenediamine and cysteamine. These functionalised materials were then explored in the context of tagging gold nanoparticles and changing the zeta potential of the native cx-GNFs. The application of these novel materials in heavy-metal extraction is also presented and found to greatly exceed the capacity of PM-GO - by up to six times. Collaborations with other research groups in the field of nano-sensors, ice-nucleation and electrochemistry, revealed the cx-GNFs to be a particularly promising material.

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