Zero-dimensional carbon nanomaterials: synthesis, characterisations and applications

Abstract

Reduction in the size of materials in all three dimensions to nanoscale results in zero-dimensional (0-D) nanomaterials which exhibit novel and tunable properties. 0-D carbon nanomaterials include many interesting materials such as fullerenes, graphene quantum dots,carbon dots, carbon nano onions and nanodiamonds. Graphene quantum dots (GQDs) are nanometre-sized fragments of graphene which have attracted considerable interest recently because of their band gap tunability, strong photoluminescence, higher water solubility, better chemical stability,low toxicity, excellent biocompatibility. The doping of nitrogen into GQDs (NGQDs) gives rise to much more attractive properties, such as electrocatalytic activity,photocatalyticactivity,broad tunable photoluminescence. The exciting future of GQDs and N-GQDs as green sensitizers in various titanium dioxide based photocatalytic systems are investigated here by means of an important reaction, the photocatalytic generation of hydrogen via water splitting. The splitting water using solar energy for hydrogen generation have attracted much attention because of its cost-effectiveness, simplicity and the massive potential for further development. In addition, the hydrothermal synthesis, characterisation and biological applications of small-sized GQDs including anti-cancer, anti-oxidant, cell imaging are also presented here. The prepared GQDs exhibited concentration-dependent cytotoxicity towards MCF-7 cells.On the other hand, negligible toxicity was shown towards normal breast cells.The unique excitation-dependent emission property of GQDs was utilised in cellular labelling. Fluorination is an efficient method to modify the properties of carbon materials. F doping can intensively modulate the chemical, structural, and electronic features of GQDs due to the electronegativitydifference between carbon and fluorine. The investigations leading to the development of fluorine-rich graphene quantum dots (FGQDs) from hydroxy fluorographene and its application for fluorescence sensing of ferric ions are discussed here. Carbon nano onions (CNOs) or multi-layered fullerenes are fascinating carbon nano-allotropes consisting of multiple shells of sp 2 hybridised carbon with spherical or polyhedral shape, possessing high surface to volume ratio, thermal stability and electrical conductivity. This Ph.D dissertation focus on the facile and cost-effective synthesis of spherical and dense CNOs as well as hollow, polyhedral CNOs. The biological applications of hollow, polyhedral CNOs are demonstrated here - including anti-cancer, anti-oxidant, cell imaging applications.