Polymer-based Graphene Oxide Derivatives as a tunable multi-purpose platform

Carbon-based nanomaterials represent a conspicuous slice of potential commodities suitable for nanotechnology. Despite their peculiar features, in a view to improving the environmental sustainability of the advanced technology devices, the growing interest in these materials is supported by the need to switch from finite and expensive commodities towards sustainable and/or widespread ones. Among the available carbon-based nanomaterials, Graphene has gained the role of keystone of this research field. Due to its unique structure based on a single layer carbon atoms honeycomb, it is classified as the thinnest material on earth and is characterized by incredible electric properties, mechanical flexibility and optical transparency. The high conjugate surface area makes it also able to bind aromatic molecules through supramolecular interactions, exploitable in drug delivery. Graphene could be synthesised employing top-down and bottom-up approaches. These last start from molecular carbon precursors, are expensive and not suitable for large scale production. Moreover, Graphene itself is not water-soluble and tends to aggregate in solution driven by Van der Waals forces, thus making difficult any further functionalization of the carbon platform. Instead, the top-down approaches involve Graphite as raw material. Among the available synthesis methods, the most diffused ones employ oxidation and exfoliation procedures of Graphite to obtain Graphene Oxide (GO), which could be considered a Graphene precursor. The synthetic pathways to obtain GO are cheaper and easier affordable than that of Graphene. Moreover, the oxidation degree of the GO provides several functional groups which are useful to stabilize the GO water suspension and serves as binding sites for further derivatizations. These features made the Graphene Oxide even more diffused than Graphene. Among all the functionalization possibilities, polymers represent an interesting moiety to be matched with GO. As a nanofiller, GO improves the mechanical properties of the polymer matrix, but the potentiality of the GO goes beyond this simple application. Indeed, the features of GO could be synergistically matched with the ones of the polymer, producing advanced materials suitable for several application fields. In particular, it has been shown that the features of GO could be tuned and/or implemented by the polymer functionalization, producing devices such as dye-sensitized solar cells, photocatalysts, drug-carrier, membranes, sensors, flexible electronics, and many other. In this framework, this PhD thesis reports the development of different polymer-based GO derivatives, designing the multi-functionality of the GO platform and the polymers to obtain advanced nanomaterials having on-demand functionalities. With the aim to cover different application fields, different polymers have been employed to bind with the GO platform through covalent and non-covalent approaches. Particular care was taken to develop easy, quick and cheap methods to obtain the final nanosystems. To develop an optical sensor suitable for water cationic pollutants, a supramolecular synthesis of GO-based nanosystems was investigated (Chapter 2). A PEGylated Porphyrin derivative was used to produce a stable supramolecular adduct with GO. The resulting adduct was characterized through spectroscopy techniques. The sensing capability as a turn-on fluorescent sensor was investigated employing 1,1’-dimethyl-4,4’-bipyridinium dichloride as a cationic pollutant model. In the field of nanomedicine, PEGylation of GO is a usual approach to improve the biocompatibility of the GO platform. The esterification reaction to bind PEG chains onto the GO platform involves different reactants and solvents, resulting in possible contamination of the products. To solve this issue, a solvent-free method to produce PEGylated GO was developed (Chapter 3). The structural characterization of the products was performed, and the effects of the PEGylation on the chemical-physical properties were investigated. In order to replace common semiconductor-based photocatalysts employed in water remediation with a more sustainable organic-based one, a novel Porphyrin-GO photocatalytic covalent adduct was synthesised (Chapter 4). The structural and functional characterization was performed, and its photocatalytic properties were verified. The covalent adduct, named GOxhyrin, was embedded within a Poly-Vynil Acetate matrix through an in-situ polymerization and its thin-film was employed for photocatalytic water remediation. An important issue regards the antimicrobial agents usually applied on biomedical devices to ensure antibacterial properties. Indeed, there is the need to find an alternative to commonly used antimicrobial agents, because the low adhesiveness coupled with their ubiquitous use have induced the subsequential release into the environment, where they manifest toxicity and act as endocrine disruptors. To overtake these issues, the development of an on-demand tunable antimicrobial nanohybrid system, composed of Graphene-Polymer and Silver Nanoparticles, is here reported (Chapter 5). The synthetic approach was deeply discussed, focusing on single aspects: the reduction of the GO moiety through a microwave-assisted approach; the covalent functionalization of the GO platform employing a reaction suitable for polymers having different nature; finally, the one-pot reaction to reduce AgNPs within the PVA@GO nanosystem. Structural and quali- quantitative characterizations of the so-obtained PVA@GO-Ag nanosystem were performed. Moreover, a preliminary antibacterial assay was conducted to verify the antimicrobial activity.