The unique and remarkably diverse electronic and optical properties of single-wall carbon
nanotubes (SWCNTs), which depend critically on their exact chiral structure, have proven to be both a blessing and a curse, as synthesis methods generally produce inhomogeneous mixtures, while applications demand more uniform properties. To realize the numerous potential applications, there is a high need for post-synthesis separation and purification, as well as specialized characterization methods to distinguish SWCNTs based on their structure-dependent electronic and optical properties.
In 2015 I received an ERC Starting Grant under Horizon 2020 with the title: Order in One Dimension: Functional Hybrids of Chirality-Sorted Carbon Nanotubes (ORDERin1D). The project started in May 2016 and exploits the hollow structure of SWCNTs to investigate restricted diameter-dependent molecular stacking and one-dimensional transport as well as the structure sorting of SWCNTs by various techniques, in particular density gradient ultracentrifugation and aqeuous two-phase extraction.
Most important contributions:
When opened and dispersed in aqueous solution, SWCNTs immedeately get filled with water. Therefore aqeuous dispersions of SWCNTs always contain a mixture of empty (closed) and water-filled (opened) SWCNTs (cover Advanced Materials). Even the thinnest SWCNTs can be filled with water, providing the first experimental proof of single-file water-filling inside SWCNTs (Phys. Rev. Lett., editorial in physics). Using density gradient ultracentrifugation, the empty and water-filled SWCNTs can be macroscopically separated based on their differences in buoyant density, with the empty SWCNTs showing enhanced optical properties (cover Angewandte Chemie).
In collaboration with Los Alamos National Laboratory, we have used aqueous two-phase separation to obtain single-chirality SWCNT dispersions and demonstrated the versatility of this new method and the role of surfactants in the sorting mechanism. Furthermore the method can be easily adapted for the isolation of individual SWCNTs from bundles and other impurities in a bulk sample.
We were able to align dipolar molecules inside SWCNTs to yield a large second-order nonlinear optics (published in Nature Nanotechnology and highlighted in a News and Views article - Nonlinear optics: dipoles align inside a nanotube).
Finally, we were able to detect a structural phase transition occuring in a single-file of water molecules encapsulated inside a (6,5) SWCNTs.