Abstract
This thesis focuses on the design and delivery of new carbon-based nanohybrid dyes of relevance to the search for affordable solar energy harvesting solutions. New hybrid nanomaterials incorporating covalently and non-covalently linked porphyrins graphted onto carbon nanomaterials such as single-walled carbon nanotubes (SWNTs), graphene oxide (GO) and thermally reduced graphene oxide (TRGO) were synthesised and characterised using a range of spectroscopy methods and microscopies. The synthesis of aryl-substituted porphyrins, achieved on a laboratory scale suitable for further modification with carbon nanomaterials and functional materials development is also discussed.Chapter one is a literature review, which constitutes the thesis introduction and background to this research, with a view towards highlighting the potential of porphyrins and related nanomaterials in the quest for sustainable chemistry applications and solar cells technologies.
Chapter two reports on the synthesis of the carbon nanomaterials used hereby and includes discussions on the modified protocols for graphene oxide synthesis and advanced purification of single-walled carbon nanotubes as well as the surface modification of single-walled carbon nanotubes. In chapter two, the strategy applied here for the reduction of graphene oxide is discussed and the achievement of the desired material demonstrated on the basis of the spectroscopic measurements performed, i.e. the synthesised materials were characterised by TEM/HRTEM and SEM whereas Raman spectroscopy was applied to bulk materials aiming to study the inner structure and purity on the nanoscale.
Chapter three describes the lab scale synthesis and characterisation of a free base porphyrin and Zn(II)-porphyrin. These were specifically selected for this study to have two aryl thioacetate-functionalised side groups at meso-position, which can be employed as reaction sites in further transformations aimed to covalently link this to nano particulate supports. The porphyrins chosen also incorporate four hexyl chains at the β-position, which was found to be necessary in order to increase the solubility of these porphyrins in common solvents which in turns was found to facilitate their purification on a lab scale with respect to the starting materials. The design was chosen aiming to prevent self-aggregation, minimise self-stacking on a carbon support and facilitate their binding to other materials in a supramolecular fashion chemistry is discussed for both the free base porphyrin and after the converted to Zn(II) metalloporphyrin. Attempts to incorporate Ga(III)Cl and In(III)Cl at the core of the ligand are also discussed. The spectroscopic measurements of light absorption and emission properties of the porphyrins, carried out by UV-vis and fluorescence microscopy are discussed and DFT calculations (gas phase) were included to investigate the electronic structure and HOMO-LUMO energy levels of the Zn(II)-porphyrin.
Chapter four presents a new strategy for the supramolecular complex formation at the exposure of single-walled carbon nanotubes (purified as described in Chapter 2) to the Zn(II)-porphyrin discussed in Chapter 3 above. Furthermore, in this chapter, the formation of a non-covalently linked Zn(II)-porphyrin@SWNTs hybrid and that of a new covalently linked Zn(II)-porphyrin@SWNTs nanomaterial was analysed and discussed. The surface morphology information of those complexes compared and contrasted using information obtained on the nanoscale by TEM and AFM techniques. Raman spectroscopy was carried out to study the inner structure of the complex materials. Upon its attachment onto the SWNTs surface, Zn(II)-porphyrin showed efficient fluorescence quenching and a strong red-shift of the Soret bands. Lifetime measurements using single-photon laser confocal fluorescence measurements on these materials deposited onto a thin fil support were carried out to explore their potential application in photovoltaic devices.
Chapter five described the formation of a new nano-dimensional hybrid material, denoted Zn(II)-porphyrin@GO, formed at the non-covalent binding of Zn(II) porphyrins onto graphene oxides. This section describes the novel synthetic approach to a three dimensionally structured material, denoted porphyrin@TRGO (where thermally reduced graphene oxides were used to form the new supramolecular complex). This chapter aims to describe the steps taken towards the modification (or ‘decoration’) of graphene oxide surface with the Zn(II)-porphyrin though π-π stacking. A three-dimensional scaffold material based on RGO was achieved by a one-step hydrothermal reaction. Imaging using TEM, SEM and AFM techniques were applied to analyse the surface morphology modifications in the presence and absence of porphyrin layers.
Chapter six describes conclusions and proposes future works.
Chapter seven contains full experimental details for the work described in this thesis.
| Date of Award | 28 Oct 2015 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Sofia Pascu (Supervisor) |
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