Materials World Network: Novel Catalyst Systems for Carbon Nanotube (CNT) Synthesis and their Underlying Mechanisms

Chemical vapor deposition (CVD) techniques employing nano-particulate catalysts and catalyst films have proven to be versatile and effective methods for synthesizing carbon nanostructures, such as nanotubes (CNTs) and graphene. CVD enabled extensive investigation of these structures as well as opened routes towards their application in integrated circuits, energy storage, transparent conductors, thermal management surfaces, hierarchical composites, sensors, drug delivery and biomimetics. Despite these successes, the detailed mechanisms of catalytic CVD remain poorly understood and the CVD process lacks deterministic control, in particular regarding CNT chirality. Common catalysts, such as Ni and Fe, are active in their metallic state and hence are prone to coarsening and support interactions at the elevated temperatures required for CVD. We recently demonstrated that nano-particulate zirconia catalyses CNT growth at moderate temperatures, whereby it neither reduces to a metal nor forms a carbide. The low reactivity and limited restructuring of oxides promise a high level of control for the CVD process. We propose to study a range of oxides as CVD catalysts. We plan to use in-situ X-ray photoemission spectroscopy and environmental transmission electron microscopy to explore the mechanism(s) of graphene formation and nanotube nucleation on pre-treated oxide films and size-selected oxide nanoparticles. We will analyse the chiral selectivity of oxide-assisted CNT CVD and explore the possibility of large area graphene CVD on oxide films.

We anticipate that our research will enable the controlled, scalable synthesis of carbon nanostructures. Such nanostructures and their handling are seen as key to future technological developments in the International Technology Roadmap for Semiconductors. Our research impacts the use of nanotechnologies in widely diverse industries, such as energy storage, pharmaceuticals, advanced structures and aero- and astronautics. In particular, the U.S. project partner of this proposal is leading an industry-funded Consortium including Airbus and Lockheed Martin, and we infer that our results and collaboration could progress advanced materials applications in the UK and secure employment in this area. Our research offers several advantages beyond synthesis control and efficiency: (1) a greater-than-50% reduction in energy requirements, (2) reduced input of feedstock precursor molecules, (3) orders-of-magnitude reductions in the emission of regulated toxicants. Recent reports have highlighted the need for improved understanding of the environmental, health, and safety risks associated with nanomaterials and their fabrication. This is an important point for policy makers and regulators to consider. Our proposed research can mitigate the environmental impact of the production of nanostructures at industrial level. Environmentally benign manufacturing is an important requirement to the advancement of industrial development in this area. Our proposed work overlaps with the field of catalysis and our results can of significant benefit to the bulk chemical synthesis, and green-fuel industries.