Graphene-based nanomaterials, particularly graphene quantum dots (GQDs), have attracted attention because of their unique electronic, optical, and mechanical properties, making them promising materials for applications in energy storage and optoelectronics. Understanding their structure-property relationship is essential for the rational design of improved graphene-based materials.
This thesis employs density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to investigate how structural modifications influence the stability, electronic structure, optical properties, and mechanical behaviour of graphene-based nanomaterials. The work focuses on three aspects: (i) the role of sp3 carbon defects in hydrogenated GQDs, (ii) nitrogen and sulphur doping and co-doping of GQDs, (iii) the mechanical deformation of graphene mesosponges.
The results show that sp2 carbons preferentially form stable arrangements as dimers and continuous chains along the edges of GQDs. Their incorporation modifies the HOMO-LUMO gap depending on the defect location and generally reduces the absorption intensity, producing a blue shift of the main absorption peak and extending absorption into the red and near-infrared region (600-900 nm).
Nitrogen and sulphur doping effectively tunes the electronic and optical properties of GQDs, with edge doping, particularly amino nitrogen and thiol sulphur, being the most stable configurations. The optical response depends strongly on the dopant configuration, while nitrogen-sulphur co-doping exhibits a synergistic effect in improving light-harvesting performance.
Mechanical deformation investigations of porous graphene mesosponges under strain show that the mechanical response depends strongly on the location and type of the applied strain. The deformation mechanisms range from elastic bond distortion to structural rearrangements, including the formation of Stone-Wales defects. These findings reveal a non-uniform yet resilient mechanical behaviour. The sp3 junctions act as stress-distribution centres while the surrounding sp2 graphene domains provide structural flexibility. Overall, the results demonstrate that controlled mechanical strain can serve as an additional strategy for tailoring the properties of three-dimensional graphene-based materials.
