Abstract
In the past decades, fullerene (C60) has attracted significant scientific and technological attention since being discovered in 1985. Among various C60-related nanomaterials, wire-like C60 nanocrystals, also known as C60 nanowires, as 1-dimensional nanostructure of C60, are of particular interest due to their unique properties and great potential in diverse application areas. As the C60 nanowires are mostly composed of carbon with only a very tiny amount of hydrogen, they are expected to exhibit excellent biocompatibility, which renders them more promising in applications in biological areas.
Over the years, effort has been devoted to exploring the growth methods, structural and compositional characterizations, and application-related investigations of this novel carbon nanomaterial. However, the growth mechanism and the possible biochemical applications of this material have not been studied in depth and fully understood, and the lack of efficient large-scale synthesis method remains a big problem which limits the exploration of application-oriented studies on this material. To solve these problems, the research and achievements which have been made in this PhD project are summarized as follows:
Firstly, a novel solid–liquid two-phase precipitation method utilizing a good solvent and a counter-solvent of C60 to form a solid–liquid two-phase interface is proposed for the synthesis of C60 nanowires. The obtained C60 nanowires possessed high crystallinity, a length-to-diameter ratio of up to several thousand with a diameter as small as ~85 nm.
To assess the viability and scalability of the process, synthesis was also carried out at a larger solution volume of 40 ml. The overall consistency of the growth results of different scales indicated that the SLTPP method is promising for large-scale preparation of C60 nanowires.
To improve the synthesis efficiency and to control the shape and size of C60 nanowires, experimental conditions have been studied by investigating the dependence of C60 nanowire growth on solvent volume ratio and C60 concentration. It was observed that the optimal growth conditions for C60 nanowire growth were 2–3 mg/ml of C60-m-xylene and m-xylene to IPA volume ratio of 1:2, respectively. Moreover, a comparison study to the LLIP method has been performed under identical experimental conditions. Compared with LLIP method, the new SLTPP method not only has higher efficiency, but also is more controllable in the formation of C60 nanowires.
The morphology, chemical composition and the structure of the as-obtained C60 nanowires have been studied in detail through a variety of characterization techniques.
The optical and fluorescence properties of C60 nanowires, which is expected to be significantly useful in exploration of their potential bio-applications, have also been studied. A clear enhancement in fluorescence emission was found in C60 nanowires than pristine C60 powder, and a unique optical phenomenon of C60 nanowires was observed, where the fluorescence emission of a C60 nanowire was much stronger at both wire-tips than that of the wire-body, which has never been reported in previous studies. Studies were also carried out to understand their fluorescence mechanism and the cause of the difference in fluorescence intensity of a single nanowire. The solvent molecules trapped in the nanowire structure were found to play an important role in fluorescence of C60 nanowires.
In conclusion, this work gave insights to not only large-scale synthesis of C60 nanocrystals, but also the properties and the relevant mechanism of this 1D C60 nanomaterial. The reliable synthesis route of 1D C60 related carbon nanomaterial developed here showed novelty, validity and superiority as compared to the current widely used method. Furthermore, by fully understanding the properties of this material, this work went a step further for the exploration of the potential applications of C60 nanowires.