During the last three decades, great scientific efforts led to the discovery and development of new carbon nanomaterials (e.g. carbon nanotubes or CNTs, carbon nanohorns or CNHs, and graphene or G). In the first chapter of this thesis, a general introduction on carbon nanostructures (CNS) and relevant characterisation techniques is provided (Chapter 1).
Despite their superior electrical, thermal, and mechanical properties, CNS inherent tendency to aggregate initially limited their applications. This issue can be addressed by various chemical functionalisation routes to improve their dispersibility in water and in polar solvents, thus allowing their handling in liquid phase, and their combination with other chemical entities. Assembly of such multicomponent nanomaterials considerably expands CNS use in fields ranging from biology to energy. In this work, CNS were functionalised to be combined with components of different nature into hybrids or composites for diverse applications.
In particular, Chapter 2 discusses the modification of CNTs and G via acid-mediated oxidation or diazo coupling routes to add hydrophilic appendages that favour in situ growth of metal oxide nanostructures (e.g. TiO2). The resulting nanohybrids were tested for photocatalytic hydrogen production. Oxidation of CNT fibres (CNF) was also achieved, first through wet methods, and then by treatment with UV-generated ozone, with only the latter allowing preservation of their macroscopic integrity. The resulting hydrophilic CNF displayed enhanced performance for supercapacitors.
Chapter 3 focusses on in situ polymerisation of dopamine on the surface of CNTs and CNHs. The synthetic protocol was optimised to achieve homogeneous coatings that, after graphitisation through high temperature treatment under argon, became conductive. This two-step sequence resulted in the isolation of N-doped CNHs that catalysed the electrochemical reduction of O2 into H2O2 with superior performance relative to current state-of-the-art catalysts.
Finally, hydrogel composites were prepared from either CNTs, CNHs, or G and a self-assembling tripeptide (Chapter 4). After an oxidative pre-treatment, each CNS was combined with the peptide and formed supramolecular hydrogels of improved rheological properties (i.e. increased stiffness and resistance to applied stress). Interestingly, hydrogels containing CNTs showed self-healing capacity, thus opening a new window of application for these materials
